Investigation on structural, morphological and optical properties of 5% Fe-doped TiO2 powder nanostructures synthesized by mechanical alloying

Investigation on structural, morphological and optical properties of 5% Fe-doped TiO2 powder nanostructures synthesized by mechanical alloying | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Investigation on structural, morphological and optical properties of 5% Fe-doped TiO 2 powder nanostructures synthesized by mechanical alloying Hayette Boutarfa, Samah Adjmi, ali hafs, Toufik hafs, Djamel Berdjane, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7059755/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract XRD analysis revealed a gradual anatase-to-rutile transformation with milling, with Fe initially segregated and progressively incorporated into the TiO₂ lattice. Anatase–rutile coexistence was observed between 6 and 12 hours, and a full rutile phase appeared after 24-48 hours. Rietveld refinement showed decreasing crystallite size and increasing microstrain, indicating defect accumulation. SEM confirmed particle refinement and agglomeration, while FTIR identified functional groups typical of the TiO 2 phase. Nanocrystalline TiO 2 powders doped with 5 wt. % Fe were synthesized using the mechanical alloying (MA) technique, with milling durations ranging from 0 to 48 hours. This study aims to investigate the effect of milling time on the structural, morphological, and optical properties of the synthesized materials. A comprehensive characterization was carried out : X-ray diffraction (XRD) combined with Rietveld refinement using MAUD software was employed to examine phase evolution and crystallite size ; scanning electron microscopy (SEM) was used to analyze particle morphology and agglomeration ; and Fourier-transform infrared spectroscopy (FTIR) was performed to identify chemical bonding and functional groups. Fe-doped TiO2 Mechanical alloying X-ray diffraction Rietveld analysis SEM FTIR Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Titanium dioxide (TiO 2 ) has attracted considerable attention in recent decades owing to its remarkable physicochemical properties, including excellent chemical stability, low cost, abundance, non-toxicity, and strong photocatalytic efficiency under ultraviolet (UV) irradiation [ 1 – 3 ]. These properties make TiO₂ a versatile material for a wide range of applications, particularly in environmental purification (e.g., wastewater treatment and air purification), dye-sensitized solar cells (DSSCs), lithium-ion batteries, sensors, and hydrogen production through water splitting [ 4 – 6 ]. However, one of the primary limitations of pure TiO 2 lies in its relatively wide band gap energy (approximately 3.2 eV for anatase and 3.0 eV for rutile), which restricts its photoresponse to the UV region-constituting only about 5% of the solar spectrum [ 7 , 8 ]. This inherent limitation hinders the practical application of TiO₂ in visible-light-driven photocatalysis, thereby motivating efforts to improve its optical response and overall photocatalytic performance. To overcome this drawback, extensive research has focused on modifying the electronic structure of TiO₂ to extend its absorption edge into the visible region. Among the most effective strategies is doping with transition metal ions, which can introduce localized energy states within the band gap, thereby facilitating visible light absorption and reducing electron-hole recombination rates [ 9 – 11 ]. Iron (Fe), in particular, has proven to be a promising dopant due to its comparable ionic radius to that of Ti 4+ and its ability to exist in multiple oxidation states (Fe 2+ /Fe 3+ ), which can introduce beneficial trap states for charge carriers [ 12 , 13 ]. Several studies have demonstrated that the incorporation of Fe into the TiO₂ lattice not only narrows the band gap but also promotes enhanced charge separation and prolongs the lifetime of photogenerated electrons and holes, making Fe-doped TiO 2 a suitable candidate for visible-light photocatalysis [ 14 – 16 ]. In parallel, the synthesis method plays a crucial role in determining the structure, morphology, and doping efficiency of TiO 2 -based materials. While conventional chemical methods such as sol-gel or hydrothermal synthesis are widely used, they often involve complex procedures, costly reagents, and limited scalability. In contrast, mechanical alloying (MA), also known as high-energy ball milling, presents a solid-state route that is simple, cost-effective, and scalable for the synthesis of nanocrystalline materials with controlled composition and microstructure [ 17 – 21 ]. This technique relies on repeated fracturing, cold welding, and mechanical deformation of powder particles, enabling the production of metastable phases, homogeneous dopant dispersion, and grain refinement down to the nanometer scale [ 22 ]. MA has been successfully applied in the preparation of various doped oxides, including TiO 2 , offering the potential to finely tune their structural and functional properties without the use of solvents or complex processing steps. Recently, there has been a growing interest among researchers in the incorporation of TiO 2 powders doped with 5 wt. % Fe as a strategy to enhance the functional properties of TiO 2 -based materials. Iron doping has been shown to influence not only the optical and magnetic behavior of TiO 2 , but also its structural and microstructural characteristics. In a study conducted by Y. Kissoum et al. [ 23 ], the effect of mechanical grinding on TiO 2 powders doped with 5 wt. % Fe was investigated, with a particular focus on milling durations of up to 15 hours. Their results revealed significant modifications in crystallite size, phase composition, and specific surface area, highlighting the crucial role of milling time in tailoring the final properties of the material. Similarly, N. Nasralla et al. [ 24 ] synthesized and characterized TiO 2 nanoparticles doped with 5% Fe (molar ratio) via the sol–gel method, followed by post-annealing in air at 400°C, 600°C, and 800°C. These thermal treatments were found to affect both the structural integrity and the functional behavior of the resulting nanoparticles. Furthermore, J. Poostforooshan et al. [ 25 ] successfully synthesized Fe-doped TiO₂ nanoparticles using the Electrospray-Assisted Flame Spray Pyrolysis (EAFSP) method, with Fe/Ti molar ratios of 1%, 5%, and 10%. Their findings indicated that Fe incorporation into the TiO 2 lattice could effectively reduce crystallite size, promote the formation of the rutile phase, spontaneously generate oxygen vacancies, and lower the optical band gap energy. Collectively, these studies emphasize the strong influence of Fe content, synthesis route, and post-treatment conditions on the structural, microstructural, and optoelectronic properties of Fe-doped TiO 2 -based nanomaterials. In this context, the present study aims to investigate the effect of milling duration on the structural, microstructural, and optical properties of TiO 2 powders doped with 5 wt. % Fe and synthesized via high-energy ball milling. Milling time is a critical processing parameter that directly influences phase formation, crystallite size, lattice strain, and dopant distribution. Therefore, understanding its impact is essential for tailoring material properties and optimizing performance in visible-light-driven applications. The as-milled powders were systematically characterized using X-ray diffraction (XRD) to monitor phase evolution and crystallite refinement, scanning electron microscopy (SEM) to examine morphological features, and Fourier-transform infrared spectroscopy (FTIR) to identify functional groups associated with the TiO 2 structure. The findings from this study contribute to a deeper understanding of structure-property relationships in mechanically synthesized Fe-doped TiO 2 nanomaterials and provide valuable insights into their potential for efficient photocatalytic and optoelectronic applications under visible light irradiation. 2. Experimental details 2.1 Materials and Methods A powder mixture consisting of TiO₂ and Fe with a nominal composition of 5 wt. % Fe was subjected to high-energy mechanical milling for various durations. In this process, elemental TiO₂ powders (Degussa, 99.7% purity, 25 nm) and Fe powders (Alfa Aesar, 99.9% purity, <10 μm) were intensively milled in a controlled environment to promote repeated cold welding, fracturing, and mixing at the nanoscale, ultimately leading to a homogeneous alloyed structure. The mechanical alloying was carried out using a Retsch PM 400 high-energy planetary ball mill. Stainless-steel vials and ten stainless-steel balls (12 mm diameter) were used as the milling media. To avoid oxidation and contamination during the process, the vials were sealed under a high-purity argon atmosphere. Each milling batch consisted of approximately 5 g of powder mixture, and a ball-to-powder weight ratio (BPR) of 15 :1 was maintained. The rotation speed of the disk was set to 350 rpm, ensuring sufficient impact energy to facilitate alloying. To minimize undesirable effects such as excessive heat generation, powder agglomeration, or adhesion to the vial walls and balls, an intermittent milling protocol was adopted. This involved operating the mill for 1 hour followed by a 30-minute rest period. The cycle was repeated as needed to achieve the desired cumulative milling durations of 1, 3, 6, 12, 24, and 48 hours. 2.2 Characterization The structural properties of the as-milled powders were analyzed using X-ray diffraction (XRD) on a Bruker D8 Advance Eco instrument equipped with Cu Kα radiation (λ = 1.5406 Å), operating at 40 kV and 40 mA. Diffraction patterns were collected over the 2θ range of 20°–80° with a step size of 0.02° and a scan speed of 0.5°/min. Phase identification was performed using standard JCPDS files. To evaluate the crystallite size and microstrain, peak broadening was initially analyzed using the Williamson–Hall method, then further refined using the Rietveld method via the MAUD software (version 2.22), a powerful tool for diffraction-based material analysis [26]. This software facilitated a comprehensive structural characterization based on a full-pattern fitting approach. Typically, each individual diffraction peak was modeled using a pseudo-Voigt profile function, which approximates the peak shape as a linear combination of Lorentzian (L) and Gaussian (G) components, as described by Young et al. in 1982 [27]. The peak profile function is expressed as follows : W(2q)=h L (2q, H L )+(1-h) G (2q, H G ) (1) where Ω(2θ) represents the overall peak shape, η is the mixing parameter (0 ≤ η ≤ 1), and H L and H G are the full width at half maximum (FWHM) values of the Lorentzian and Gaussian components, respectively. The total peak broadening β is similarly expressed as: β = ηβ L +(1-η)B G (2) The average crystallite size was then estimated using the Scherrer equation applied to the Lorentzian component : (3) where K is the shape factor (typically 0.9), λ is the X-ray wavelength, and β L is the Lorentzian peak width corrected for instrumental broadening. The root mean square microstrain 1/2 was calculated from the Gaussian contribution using the following relation : (4) This analytical approach allows for the decoupling of size and strain contributions to the peak broadening, thereby offering a more accurate and reliable quantification of the microstructural evolution induced by high-energy ball milling. Morphological and microstructural features of the milled powders were examined using scanning electron microscopy (Quantum 250–FEI). Prior to imaging, the samples were coated with a thin gold layer to enhance electrical conductivity. The particle size distribution and agglomeration state were qualitatively assessed from the acquired micrographs. Fourier-transform infrared (FTIR) spectroscopy was employed to investigate the vibrational modes associated with Ti–O bonds and the presence of surface functional groups. Spectra were recorded in the range of 400–4000 cm⁻¹ using a Bruker Alpha II spectrometer in attenuated total reflectance (ATR) mode. This analysis provided valuable insights into structural modifications, defect states, and surface chemistry induced by Fe doping and the mechanical milling process. 3. Results and Discussion 3.1. Structural and microstructural characteristics Figure.1 presents the X-ray diffraction (XRD) patterns of titanium dioxide (TiO 2 ) powders doped with 5% iron (Fe) for various milling times : 1 h, 3 h, 6 h, 12 h, 24 h, and 48 h. The XRD analysis of the sample milled for 1 hour reveals well-defined diffraction peaks corresponding to the anatase phase, characterized by a tetragonal crystal structure with a space group of I41/amd. The strong intensity of the (011) peak reflects the high crystallinity of the TiO 2 nanoparticles. Additionally, two extra peaks indexed to the (110) and (200) planes of metallic iron indicate partial segregation of the dopant during the mechanosynthesis process. The indexing of the diffraction peaks was performed using the X’Pert HighScore Plus software, which provides access to an extensive database of JCPDS reference cards for various known materials. For the pure anatase phase of TiO 2 , the diffraction peaks observed at 25.42°, 37.78°, 48.24°, 53.84°, and 55.00° were accurately attributed to the (011), (004), (020), (015), and (121) crystallographic planes, respectively. Upon extending the milling time to 3 hours, the diffraction patterns exhibit a pronounced broadening and a significant reduction in the intensity of the anatase peaks. Simultaneously, the fading of the iron-related peaks suggests a progressive incorporation of Fe atoms into the TiO 2 lattice, promoting a more homogeneous distribution of the dopant within the host structure. Afterward, for the powders milled for 6 and 12 hours, the XRD patterns reveal the emergence of a mixed TiO 2 phase, indicating a phase transition from anatase to rutile. This transformation is thermodynamically favored as the mechanical energy input during milling increases, promoting atomic rearrangement and phase stability toward the denser rutile structure. Simultaneously, a distinct iron-rich phase can be observed in the XRD spectra, although its intensity progressively decreases with milling time. This behavior suggests that part of the Fe initially segregated outside the TiO 2 lattice gradually dissolves into the matrix under the effect of prolonged mechanical activation. The decrease in the intensity of the Fe-related peaks may thus be attributed to two concurrent phenomena : the reduction of crystallite size of the segregated Fe phase and the enhanced incorporation of Fe atoms into defect sites or interstitial positions within the TiO 2 structure. The coexistence of anatase and rutile phases, along with partial Fe segregation, reflects a dynamic balance between structural disorder induced by milling and the thermodynamic driving forces leading to phase transformations and dopant diffusion. These structural evolutions are expected to significantly influence the functional properties of the material, such as its optical and electronic behavior, which will be discussed in the following sections. As the milling time extends to 24 and 48 hours, the X-ray diffraction patterns clearly show the complete disappearance of the anatase phase, with only the rutile phase remaining. This transformation is significant because anatase is known to be a metastable phase that can transition into the more thermodynamically stable rutile phase under the influence of external factors such as temperature, pressure, or mechanical stress. In the context of high-energy ball milling, the repeated collisions between the powder particles and the milling media induce substantial lattice strain, generate defects, and locally elevate the temperature, all of which favor the anatase-to-rutile phase transition. The prolonged mechanical action thus promotes atomic rearrangements and enhances the thermodynamic driving force for the stabilization of the rutile structure. Furthermore, the dominance of the rutile phase at extended milling times suggests that the energy input during milling was sufficient not only to initiate but to complete the phase transformation. Meanwhile, faint iron-related signals still persist in the XRD patterns, indicating that a small fraction of iron remains segregated rather than being entirely incorporated into the TiO 2 matrix. Figure.2 illustrates the evolution of the diffraction peaks corresponding to the (110) plane of both anatase and rutile phases of Fe-doped TiO 2 as a function of milling time. For the anatase phase, a slight shift toward higher angles (Δθ) is observed. This phenomenon can be primarily attributed to the partial substitution of Ti⁴⁺ ions (ionic radius ≈ 0.745 Å) by smaller Fe³⁺ ions (ionic radius ≈ 0.645 Å) within the crystalline structure, which alters the interplanar spacing (d). According to Bragg’s law (nλ = 2d·sinθ), this decrease in spacing leads to a shift of the diffraction peaks toward higher 2θ angles. Additionally, high-energy ball milling introduces crystal defects and internal strain, further amplifying this angular shift. The charge imbalance caused by the valence difference between Ti⁴⁺ and Fe³⁺ is compensated by the formation of oxygen vacancies, contributing to lattice distortion and peak broadening. In contrast, for the rutile phase, the (110) diffraction peaks exhibit a slight shift toward lower angles as milling time increases. Although counterintuitive given the smaller size of Fe³⁺ ions, this behavior may result from a local lattice expansion induced by the accumulation of defects, internal strain, and oxygen vacancies generated during mechanical milling. These structural disturbances can increase the interplanar spacing, thus shifting the XRD peaks toward lower 2θ values. These findings confirm not only the effective incorporation of Fe³⁺ dopants into the TiO 2 lattice but also highlight the significant impact of mechanical milling on the crystal structure-through defect generation, lattice distortion, and modification of diffraction parameters. Figure 3 displays the Rietveld refinement results of the X-ray diffraction (XRD) patterns for TiO 2 powders doped with 5% iron (Fe) after different milling durations : 1 h, 3 h, 6 h, 12 h, 24 h, and 48 h. Specifically, Fig. 3 (a) shows the refinement corresponding to the sample milled for 1 hour. The analysis reveals the presence of the tetragonal anatase phase, characterized by lattice parameters a = 0.3781 ± 0.0001 nm and c = 0.9512 ± 0.0001 nm. Additionally, the presence of a body-centered cubic (bcc) iron phase is confirmed, with a lattice parameter a = 0.2863 ± 0.0001 nm. The narrow uncertainties associated with these values indicate a precise fit of the experimental data to the structural model. The consistency and sharpness of the lattice parameters further confirm the presence of a well-ordered and stable crystalline structure, particularly for the anatase phase. Both the anatase and bcc iron phases are also observed in the sample milled for 3 hours, as shown in Fig. 3 (b). The Rietveld refinement reveals slight changes in the lattice parameters, possibly indicating the beginning of dopant incorporation or the development of lattice strain due to prolonged mechanical activation. For the powders milled for 6 h and 12 h (see Fig. 3 (c) and 3(d)), the Rietveld analysis reveals that TiO 2 is no longer present exclusively in the anatase phase, but rather as a mixture of anatase and rutile phases. This phase transformation can be attributed to the progressive incorporation of Fe ions into the TiO 2 lattice, which induces lattice distortions and promotes the anatase-to-rutile transition. This structural evolution is significant, as the rutile phase-although thermodynamically more stable-is generally associated with reduced photocatalytic performance compared to anatase. The appearance of rutile thus reflects a compromise between structural stability and functional properties, directly influenced by the mechanical milling conditions and dopant effects. After 24 h and 48 h of milling (see Fig. 3 (e) and 3(f)), the Rietveld analysis confirms the complete disappearance of the anatase phase, with only the rutile phase and trace amounts of metallic iron remaining. This indicates that prolonged milling facilitates the anatase-to-rutile transition, driven by accumulated lattice strain and localized thermal effects. The presence of residual Fe suggests dopant segregation or partial reduction, likely induced by high-energy impacts during mechanical processing. Although the rutile phase is thermodynamically more stable, its dominance may compromise dopant uniformity and negatively affect photocatalytic performance. Therefore, precise control of the milling duration is essential to achieve an optimal balance between structural stability and functional efficiency. These findings align with previous studies on Fe-doped TiO 2 systems. For instance, research has shown that high-energy mechanical milling of undoped anatase TiO 2 induces the anatase-to-rutile phase transformation via high-pressure srilankite [ 28 ]. Mössbauer spectroscopy analyses revealed that iron atoms are more likely to dissolve in rutile TiO₂, and the composition distribution becomes nonuniform during mechanical alloying, with Fe atoms enriching at the interface or surface of TiO 2 crystallites [ 29 ]. Additionally, studies have indicated that Fe doping can accelerate the anatase-to-rutile transformation process, influenced by crystal defects and the generation of oxygen vacancies [ 30 ]. These structural changes, while favoring the formation of the thermodynamically stable rutile phase, may compromise dopant homogeneity and degrade photocatalytic performance. Therefore, precise control of the milling duration is critical to maintaining a balance between phase stability and functional properties. Figure.4 illustrates the evolution of the lattice parameters for the anatase and rutile phases of 5% Fe-doped TiO 2 powders as a function of milling time, as determined by Rietveld refinement of X-ray diffraction (XRD) data. In Figure.4(a), the lattice parameters a and c of the anatase phase are observed to decrease gradually with increasing milling time. This contraction of the unit cell can be attributed to the incorporation of Fe³⁺ ions into the Ti⁴⁺ sites of the TiO₂ lattice. Since the ionic radius of Fe³⁺ (0.645 Å) is slightly larger than that of Ti⁴⁺ (0.605 Å), such substitution can introduce lattice strain and distortions, resulting in reduced lattice parameters. Additionally, the high-energy impacts during mechanical milling may generate defects and dislocations that further contribute to the lattice contraction. In contrast, Figure.4(b) reveals that the rutile phase, which emerges after 6 h of grinding, exhibits a progressive decrease in both a and c lattice parameters with increasing grinding time. This trend suggests that continued mechanical activation not only stabilizes the rutile structure but also promotes subtle structural distortions, likely due to the incorporation of Fe³⁺ ions and the accumulation of internal stresses and lattice defects. These variations in lattice constants further reflect the dynamic structural evolution induced by prolonged high-energy milling. The observed decrease in lattice parameters for both anatase and rutile phases indicates that Fe³⁺ ions are substituting Ti⁴⁺ sites in the TiO 2 lattice, leading to lattice distortions. This substitution is consistent with previous studies that have reported Fe³⁺ incorporation into TiO 2 structures, resulting in changes in lattice parameters and phase transformations. These structural changes have significant implications for the material's properties, particularly its photocatalytic activity. The incorporation of Fe³⁺ ions and the associated lattice distortions can influence the electronic structure of TiO 2 , potentially affecting its bandgap and charge carrier dynamics. Therefore, understanding the relationship between milling time, lattice parameter evolution, and dopant incorporation is crucial for tailoring the properties of Fe-doped TiO 2 for specific applications. Figure.5 illustrates the variation of the average crystallite size ⟨D⟩ (nm) and the average internal strain ⟨σ²⟩¹ᐟ² (%) for the anatase and rutile phases of 5% Fe-doped TiO₂ powders as a function of milling time, as determined by Rietveld refinement. The average crystallite size decreases systematically with increasing milling time, whereas the microstrain ⟨σ²⟩¹ᐟ² increases progressively. In Figure.5(a), the average crystallite size ⟨D⟩ (nm) of the anatase phase decreases systematically with increasing milling time, while the microstrain ⟨σ²⟩¹ᐟ² (%) increases progressively. This inverse relationship highlights the dual effects of mechanical milling : the fragmentation of crystallites and the accumulation of lattice defects. The reduction in crystallite size is attributed to the repeated fracturing and refinement of powder particles due to high-energy impacts during milling. This process leads to smaller, more refined grains, as observed in similar studies where crystallite size decreased significantly with milling time. Conversely, the increase in microstrain indicates the generation of lattice distortions, dislocations, and point defects induced by mechanical stress. These defects accumulate over time, leading to an overall increase in internal strain energy and a higher degree of disorder in the anatase structure. This behavior reflects the competition between defect generation and structural reorganization under mechanical activation, resulting in a nanostructured anatase phase with altered microstructural properties. In contrast, Figure.5(b) reveals that for the rutile phase, which emerges after 6 h of grinding, the average crystallite size ⟨D⟩ (nm) decreases systematically with increasing milling time, while the microstrain ⟨σ²⟩¹ᐟ² (%) increases progressively. This behavior is consistent with the anatase phase, suggesting that prolonged milling not only promotes the anatase-to-rutile transition but also induces continued fragmentation and accumulation of defects in the newly formed rutile crystallites. The increasing microstrain reflects enhanced lattice distortion and defect density due to the persistent mechanical activation. 3.2. Morphological characteristics Figure.6 presents scanning electron microscopy (SEM) images in backscattered electron (BSE) mode of 5% Fe-doped TiO 2 powders subjected to mechanical milling for (a) 1 h, (b) 3 h, (c) 6 h, (d) 12 h, (e) 24 h, and (f) 48 h. At 1 h of milling (Figure.6(a)), the powders exhibit significant agglomeration and relatively coarse grains. Brighter regions-typically associated with heavier elements such as Fe-are clearly visible, while darker areas correspond primarily to the TiO 2 matrix, where the anatase phase remains dominant. This contrast is characteristic of BSE imaging, which is sensitive to atomic number variations [ 31 ]. After 3 h of milling (Figure.6(b)), noticeable fragmentation is observed along with a more homogeneous particle dispersion. The increasing prevalence of darker regions reflects grain size reduction and enhanced Fe incorporation into the TiO 2 matrix. The reduction in bright agglomerates indicates the early stages of a finer and more uniform Fe distribution [ 32 , 33 ]. At 6 h (Figure.6(c)), the particles become even finer, and darker zones become more prominent. This morphological evolution coincides with the initial appearance of the rutile phase, as confirmed by XRD analysis. These darker regions likely correspond to Fe-enriched rutile nanocrystals, consistent with previous studies showing that Fe-doping facilitates the anatase-to-rutile transformation under mechanical activation [ 34 , 35 ]. The observed contrast is influenced not only by composition but also by local crystallinity and defect density [ 36 ]. At 12 h (Figure.6(d)), the microstructure becomes more uniform, with a marked decrease in grain size. The predominance of darker contrast suggests a further increase in the rutile phase fraction, as also reported in other mechanically alloyed doped- TiO 2 systems [ 35 , 37 ]. The reduced number of bright features supports the progressive homogenization of Fe within the matrix. After 24 h of milling (Figure.6(e)), the powders exhibit a highly fragmented structure with ultrafine particles. The sustained dominance of dark contrast is likely associated with a dense population of rutile nanocrystals and the accumulation of internal strain and defects, typical in high-energy ball-milled oxides [ 38 ]. Finally, at 48 h (Figure.6(f)), the microstructure appears highly compact and homogeneous. The widespread dark contrast is indicative of a well-developed nanostructured rutile phase, extensively doped with Fe. This result reflects the cumulative effects of prolonged mechanical activation, including significant grain refinement, increased microstrain, and defect generation-factors known to stabilize the rutile phase in doped TiO 2 systems [ 35 , 39 ]. 3.3. FTIR Analysis The FTIR spectra of Fe-doped TiO 2 powders milled for various durations (from 1 h to 48 h), as presented in Fig. 7 , provide valuable insights into the evolution of structural features and surface chemistry induced by mechanical alloying. These spectra confirm the successful incorporation of iron impurities into the TiO 2 matrix. A strong absorption band in the range of 400–900 cm⁻¹, attributed to Ti–O and Ti–O–Ti stretching vibrations, is clearly observed in all samples. This confirms the structural integrity of the TiO₂ framework, regardless of milling duration. The progressive broadening of this band with increasing milling time indicates a rise in structural disorder and lattice distortion, likely due to the substitution of Ti⁴⁺ by Fe³⁺ ions and the accumulation of internal strain, as further supported by the Rietveld refinement results. In addition to the fundamental vibrations of the TiO 2 lattice, a weak peak near 1100 cm⁻¹ is detected in all spectra and is assigned to the bending vibrations of molecularly adsorbed water (H–O–H), commonly associated with surface hydroxyl groups. This characteristic band reflects the presence of physisorbed water on the particle surfaces. Its persistence across all milling durations suggests that, despite the mechanical stress imparted by high-energy ball milling, the powders retain a degree of surface hydration-most likely due to post-synthesis exposure to ambient humidity. Notably, the increasing intensity of this band with prolonged milling suggests enhanced water adsorption capacity, which can be attributed to the formation of structural defects such as oxygen vacancies and undercoordinated Ti⁴⁺ cations. These defects increase the hydrophilicity of the surface by providing energetically favorable sites for moisture adsorption. The progressive disorder and elevated surface energy resulting from extended milling thus contribute to this enhanced interaction with water molecules. A weak absorption band around 2400 cm⁻¹ is also observed and is attributed to C–O stretching vibrations [ 40 ]. This feature likely originates from adsorbed atmospheric CO₂ or the formation of surface carbonate species-phenomena commonly observed in metal oxide powders exposed to air. The evolution of this band’s intensity with milling time suggests modifications in surface chemistry and reactivity, possibly driven by an increased density of surface defects and changes in surface area, which facilitate greater interaction with environmental CO₂. Finally, the presence of broad, weak transmittance bands centered around 3000 cm⁻¹ is ascribed to the stretching vibrations of O–H bonds from surface hydroxyl groups or molecularly adsorbed water. These bands, although typically of low intensity due to hydrogen bonding, provide additional evidence of surface hydration and the significant role of surface chemistry in the evolution of the milled powders [ 41 ]. These findings are consistent with previous reports in the literature [ 42 , 43 ], thereby reinforcing the reliability of the present observations regarding the influence of mechanical alloying on structural disorder and surface reactivity. 4. Conclusion This study focused on the structural, microstructural, morphological, and optical properties of TiO 2 powders doped with 5 wt. % Fe, synthesized via high-energy ball milling over durations ranging from 1 to 48 hours. Structural evolution was thoroughly examined by X-ray diffraction (XRD) combined with Rietveld refinement using MAUD software, while morphological changes were analyzed via scanning electron microscopy (SEM). XRD patterns revealed a progressive transformation of the crystalline phases with increasing milling time. After 1 hour of milling, the powders exhibited sharp peaks corresponding to the anatase phase, indicating high crystallinity. Additional reflections attributed to metallic Fe suggested partial segregation of the dopant at this early stage. With 3 hours of milling, broadening and intensity reduction of anatase peaks were observed, along with attenuation of Fe-related signals-indicating the initial stages of Fe incorporation into the TiO 2 lattice. At intermediate durations (6 to 12 hours), the emergence of a biphasic anatase–rutile structure marked the onset of a mechanically induced phase transformation. This transition reflects a competition between mechanically driven disorder and the thermodynamic stability of the rutile phase. Concurrently, the gradual disappearance of Fe-related peaks suggested progressive incorporation of segregated Fe into defect-rich or interstitial sites within the TiO 2 matrix. At prolonged milling times (24 and 48 hours), the XRD patterns confirmed the complete disappearance of anatase peaks, with the rutile phase fully stabilized. This transition indicates that extended milling provided sufficient energy to complete the anatase-to-rutile transformation, facilitated by defect accumulation, lattice strain, and localized thermal effects from repeated impacts. A small amount of Fe remained in a segregated form, though significantly reduced. Rietveld quantitative analysis revealed a continuous decrease in crystallite size and an increase in microstrain with milling duration. These microstructural evolutions were consistent with SEM observations, which showed progressive particle refinement, shape distortion, and agglomeration-attributed to severe plastic deformation, cold welding, and fracture events induced by high-energy impacts. FTIR spectroscopy offered further insights into bonding characteristics and surface chemistry. A pronounced absorption band in the 400–900 cm⁻¹ range, corresponding to Ti–O and Ti–O–Ti stretching vibrations, was consistently present in all samples, confirming the structural integrity of the TiO 2 framework throughout milling. A weak but persistent peak near 1100 cm⁻¹ was attributed to bending vibrations of molecularly adsorbed water (H–O–H), associated with surface hydroxyl groups. Its increasing intensity with milling duration reflected enhanced surface hydration, likely due to the formation of oxygen vacancies and undercoordinated Ti atoms. Additionally, a weak absorption band around 2400 cm⁻¹, assigned to C–O stretching vibrations, was observed and likely originated from adsorbed CO 2 or surface carbonate species. The evolution of this band with milling duration suggests increased surface reactivity caused by defect accumulation and increased surface area. Finally, broad and weak transmittance bands centered around 3000 cm⁻¹ were attributed to O–H stretching vibrations from surface hydroxyl groups or adsorbed water molecules. Although typically of low intensity due to hydrogen bonding, these bands provided further evidence of surface hydration and the crucial role of surface chemistry in the evolution of the milled powders. In summary, high-energy mechanical alloying not only induces substantial changes in the bulk structure and phase composition of Fe-doped TiO 2 powders but also results in pronounced modifications to their surface chemistry. These transformations enhance both hydrophilicity and surface reactivity, which are critical for potential applications in photocatalysis, adsorption, and other surface-driven technologies. Declarations Conflict of interest The authors have no competing interests to declare that are relevant to the content of this article. Funding The authors did not receive support from any organization for the submitted work. Data availability All data generated or analysed during this study are included in this published article. Author contributions HB: synthesis and characterizations, validation, investigation, resources, writing –original draft, writing - review & editing, visualization. SA: conception, methodology, resources, supervision. AH: conception, methodology, resources, review & editing, visualization, supervision, validation. TH: validation, writing - review& editing, visualization.DB: XRD refinement, interpretation of results, manuscript preparation, visualization. RA: validation, writing – review & editing, visualization. Acknowledgments The authors warmly thank the members of the Laboratory for Physico-Chemical Studies of Materials (LEPCM), University of Batna 1, Algeria, for their assistance in acquiring the SEM images. This work was supported by the Algerian Directorate for Scientific Research and Technological Development (DGRSDT). References U. Diebold, The surface science of titanium dioxide, Surf. Sci. Rep, 48(5–8) (2003) 53–229. https://doi.org/10.1016/S0167-5729(02)00100-0 A. Fujishima, X. Zhang, DA. Tryk, TiO 2 photocatalysis and related surface phenomena, Surf. Sci. Rep, 63(12) (2008) 515–582. https://doi.org/10.1016/j.surfrep.2008.10.001 C. Ayappan, R. Xing, X. Zhang, D. Luo, S. Liu, A. Fujishima, TiO 2 -based photocatalysts for emerging gaseous pollutants removal: From photocatalysts to reactors design, Coord. Chem. Rev, 515(2024) 215960. https://doi.org/10.1016/j.ccr.2024.215960 G. Williams, B. Seger, PV. Kamat, TiO 2 -Graphene Nanocomposites. UV-Assisted Photocatalytic Reduction of Graphene Oxide, ACS nano, 2 (7) (2008) 1487-1491. https://doi.org/10.1021/nn800251f H. Tang, K. Prasad, R. Sanjinès, P. E. Schmid, F. Lévy, Electrical and optical properties of TiO 2 anatase thin films, J. Appl. Phys,75(1994) 2042–2047. https://doi.org/10.1063/1.356306 S. Khan, M. Al-Shahry, WB. Ingler Jr, Efficient Photochemical Water Splitting by a Chemically Modified n-TiO 2 , science, 297 (5590) (2002) 2243-2245. https://doi.org/10.1126/science.1075035 M. Wang, X. Xu, L. Lin, D. He, Gd–La codoped TiO 2 nanoparticles as solar photocatalysts, Prog. Nat. Sci. 25(2015) 6-11. https://doi.org/10.1016/j.pnsc.2015.01.002 D.A.H. Hanaor, G. Triani, C.C. Sorrell, Morphology and photocatalytic activity of highly oriented mixed phase titanium dioxide thin films, Surf. Coat. Technol. 205(12) (2011) 3658–3664. https://doi.org/10.1016/j.surfcoat.2011.01.007 R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, Y. Taga, Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides, Science, 293(5528) (2001) 269–271. https://doi.org/10.1126/science.1061051 C. Di Valentin, G. Pacchioni, A. Selloni. Origin of the different photoactivity of N-doped anatase and rutile TiO 2 , Physical Review B, 70(2005) 085116. https://doi.org/10.1103/PhysRevB.70.085116 C. Di Valentin, G. Pacchioni, A. Selloni, S. Livraghi, E. Giamello, Characterization of paramagnetic species in N-doped TiO 2 powders by EPR spectroscopy and DFT calculations, J. Phys. Chem. B, 109(23) (2005) 11414–11419. https://doi.org/10.1021/jp051756t M. Batzill, U. Diebold, The surface and materials science of tin dioxide, Progress in Surface Science, 79(2–4) (2005) 47–154. https://doi.org/10.1016/j.progsurf.2005.09.002 C. Yu Jimmy, Jiaguo Yu, Ho, Jiang, X.Zhang, Effects of F- Doping on the Photocatalytic Activity and Microstructures of Nanocrystalline TiO 2 Powders, American Chemical Society, 14(9) (2002) 3808. https://doi.org/10.1021/cm020027c D. Li, H. Haneda, S. Hishita, N. Ohashia, N.K. Labhsetwar, Fluorine-doped TiO 2 Powders Prepared by Spray Pyrolysis and Their Improved Photocatalytic Activity for Decomposition of Gas-phase Acetaldehyde. Journal of Fluorine Chemistry, 126(2005) 69-77. http://dx.doi.org/10.1016/j.jfluchem.2004.10.044 W. Yang, C. A. Wolden, Plasma-Enhanced Chemical Vapor Deposition of TiO 2 Thin Films for Dielectric Applications, Thin Solid Films, 515(4) (2006) 1708-1713. http://dx.doi.org/10.1016/j.tsf.2006.06.010 W. Avansi Jr, R. Arenal, V. R. de Mendonça, C. Ribeiroe , E. Longo, Vanadium-doped TiO 2 anatase nanostructures: the role of V in solid solution formation and its effect on the optical properties, CrystEngComm, 16(23) (2014) 5021. https://doi.org/10.1039/C3CE42356E C. Suryanarayana, Mechanical alloying and milling. Prog Mater Sci 46(1–2) (2001)1–184. https://doi.org/10.1016/S0079-6425(99)00010-9 J. S. Benjamin, T. E. Volin, The mechanism of mechanical alloying. Metallurgical Transactions, 5(8) (1974) 1929–1934. https://doi.org/10.1007/BF02644161 J. S. Benjamin, Dispersion strengthened superalloys by mechanical alloying, Metall Trans, 1(1970)2943–2951. https://doi.org/10.1007/BF03037835 N. Guemmoud, A. Hafs, T. Hafs, Effect of milling time on the structural, microstructure, and magnetic properties of nanocrystalline Fe 90 Sb 10 powders obtained by high-energy ball milling, Int. J. Adv. Manuf. Technol. 122(2022)2043-2058. https://doi.org/10.1007/s00170-022-10003-x A. Hafs, T. Hafs, D. Berdjane, A. Bendjama, N. Hasnaoui, Magnetic and microstructural properties of thin film Fe‑Sb obtained by thermal evaporation of nanostructured milled powder, Int. J. Adv. Manuf. Technol. 133(2024) 5571–5583. https://doi.org/10.1007/s00170-024-14024-6 T.O. Monastyrska, A.L. Berezina, O.A. Molebny, V. K. Andrii, Effect of alloying with transition metals on the aging of anomalously supersaturated solid solution of Al–Mg alloys, Appl Nanosci,12(2022) 513–521. https://doi.org/10.1007/s13204-021-01705-x Y. Kissoum, D. E. Mekki, M. Bououdina, E. Sakher, S. Bellucci, Dependence of Fe Doping and Milling on TiO 2 Phase Transformation: Optical and Magnetic Studies, J. Supercond. Nov. Magn, 33(2020) 427–440. https://doi.org/10.1007/s10948-019-05169-7 N. Nasralla, M. Yeganeh, Y. Astuti, S. Piticharoenphun, N. Shahtahmasebi, A. Kompanyb, M. Karimipour, B.G. Mendisd, N.R.J. Pooltone, L. Šiller, Structural and spectroscopic study of Fe-doped TiO 2 nanoparticles prepared by sol–gel method, Scientia Iranica F, 20(3) (2013) 1018–1022. https://doi.org/10.1016/j.scient.2013.05.017 J. Poostforooshan, S. Belbekhouche, V. Olszok, M.F.B. Stodt, M. Simmler, M. Bierwirth, H. Nirschl, J. Kiefer, U. Fritsching, A. P. Weber, Synthesis of Pure and Fe-Doped TiO 2 Nanoparticles via Electrospray-Assisted Flame Spray Pyrolysis for Antimicrobial Applications, ACS Applied Nano Materials, 6(24) (2023) 22660–22672. https://doi.org/10.1021/acsanm.3c03107 L. Lutterotti, Laboratorio Scienza e Tecnologia dei Materiali, Universita di Torino, Corso, 2000. R. A. Young, D. B. Wiles, J. Appl. Cryst. 15(1982) 430-438, https://doi.org/10.1107/S002188988201231X L. C. Sánchez, A. M. Calle, J. D. Arboleda, J. J. Beltran, C. A. Barrero, J. Osorio & K. Nomura, Fe-doped TiO 2 prepared by mechanical alloying, Hyperfine Interact, 183(2008) 117–122. https://doi.org/10.1007/s10751-008-9738-1 D. Jiang Dong-mei Ph, Pan Xiao-yan, Shi Wang-zhou, Ma Xue-ming Ph. D., Prof. Mössbauer study on Fe-doped TiO2 by high-energy ball milling. J. of Shanghai Univ, 10(2006) 161–164. https://doi.org/10.1007/s11741-006-0035-4 L. Zhang, X. Luo, J. D. Zhang, Y.F. Long, X. Xue, B.J. Xu, Kinetic Study on the Crystal Transformation of Fe-Doped TiO 2 via In Situ High-Temperature X-ray Diffraction and Transmission Electron Microscopy, ACS Omega, 6(1) (2021) 965–975. https://doi.org/10.1021/acsomega.0c05609 J. I. Goldstein, D. E. Newbury, J. R. Michael, N. W.M. Ritchie, J. H. J. Scott, D.C. Joy, Scanning Electron Microscopy and X-ray Microanalysis, Springer, 2018. https://doi.org/10.1007/978-1-4939-6676-9 H. Zhang, J.F. Banfield, Understanding polymorphic phase transformation behavior during growth of nanocrystalline aggregates : insights from TiO 2 , J. Phys. Chem. B, 104(15) (2000) 481–3487. https://doi.org/10.1021/jp000499j N. R. Mathews, M. A. Corte Jacome, Erik R. Morales, J. A. Toledo Antonio, Structural and spectroscopic study of the Fe doped TiO 2 thin films for applications in photocatalysis, Phys. Status Solidi A, 206(15) (2009) S219-S223. https://doi.org/10.1002/pssc.200881319 M.M. Rashad, E.M. Elsayed, M.S. Al-Kotb, A.E. Shalan, The structural, optical, magnetic and photocatalytic properties of transition metal ions doped TiO 2 nanoparticles, J. Alloys Compd, 581 (2013) 71-78. https://doi.org/10.1016/j.jallcom.2013.07.041 A. Kotta, S.A. Ansari, N. Parveen, H. Fouad, O. Y. Alothman, U. Khaled, H. K. Seo, S. G. Ansari , Z. A. Ansari,Mechanochemical synthesis of melamine doped TiO2 nanoparticles for dye sensitized solar cells application. J Mater Sci : Mater Electron, 29(2018) 9108–9116. https://doi.org/10.1007/s10854-018-8938-y K. Durgam, R. Eppa, M.V. Ramana Reddy, J. Sivakumar, R. Sayanna, Effect of metal ions doping on structural, optical properties and photocatalytic activity of anatase TiO 2 thin films, Surface and Interface Analysis, 53(2) (2020) 194-205. https://doi.org/10.1002/sia.6901 S. Sakthivel, H. Kisch, Daylight Photocatalysis by Carbon-Modified Titanium Dioxide. Angewandte Chemie International Edition, 42(2003) 4908-4911. http://dx.doi.org/10.1002/anie.200351577 Z. Minghua, Y. Jiaguo, C. Bei, Effects of Fe-doping on the photocatalytic activity of mesoporous TiO 2 powders prepared by an ultrasonic method, Journal of Hazardous Materials B137 (2006) 1838–1847. https://doi.org/10.1016/j.jhazmat.2006.05.028 C. Fan , P. Xue , Y. Sun, Preparation of Nano-TiO 2 Doped with Cerium and Its Photocatalytic Activity, Journal of Rare Earths, 24(3) (2006) 309-313. https://doi.org/10.1016/S1002-0721(06)60115-4 C. Deiana, M. Minella, G. Tabacchi, V. Maurino, E. Fois, G. Martra, Shape-controlled TiO 2 nanoparticles and TiO 2 P25interacting with CO and H 2 O 2 molecular probes : a synergic approach for surface structure recognition and physico-chemical understanding. Phys. Chem. Chem. Phys. 15(1) (2013) 307–315. https://doi.org/10.1039/C2CP42381B M. Cernea, C. Valsangiacom, R. Trusca, F. Vasiliu, Synthesis of iron-doped anatase -TiO 2 powders by a particulate sol-gel route, J. Optoelectron. Adv. Mater., 9 (2007) 2648–2652. See https://www.researchgate.net/publication/235351058 I. Ganesh, P.P. Kumar, A.K. Gupta, P.S. Sekhar, K. Radha, G. Padmanabham, G. Sundararajan, Preparation and characterization of Fe-doped TiO 2 powders for solar light response and photocatalytic applications, Processing and Application of Ceramics, 6(1) (2012) 21–36. https://doi.org/10.2298/PAC1201021G H. Khan, I.K. Swati, Fe 3+ -doped anatase TiO 2 with d–d transition, oxygen vacancies and Ti3+ centers : synthesis, characterization, UV–vis photocatalytic and mechanistic studies. Ind. Eng. Chem.Res, 55(23) (2016) 6619–6633. https://doi.org/10.1021/acs.iecr.6b01104 Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7059755","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":483031399,"identity":"2c9895b6-f2b0-48e3-8eb4-31ed08b501fa","order_by":0,"name":"Hayette Boutarfa","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Hayette","middleName":"","lastName":"Boutarfa","suffix":""},{"id":483031400,"identity":"de64b1fd-8abc-4106-a79d-3b5fb68a2da8","order_by":1,"name":"Samah 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20:33:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7059755/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7059755/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":86529663,"identity":"6734cd55-f35f-46c1-ba20-8ff8e5e20746","added_by":"auto","created_at":"2025-07-11 16:46:35","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":48760,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eX-ray diffraction (XRD) patterns of TiO\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e powders doped with 5% iron (Fe) after different milling durations : 1 h, 3 h, 6 h, 12 h, 24 h, and 48 h.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7059755/v1/104198e085fe97495eaddb58.png"},{"id":86529666,"identity":"e7e7b13b-e308-4f08-8614-fb9ec219260c","added_by":"auto","created_at":"2025-07-11 16:46:35","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":27266,"visible":true,"origin":"","legend":"\u003cp\u003eMagnified XRD peaks corresponding to the (011) plane of the anatase phase and the (110) plane of the rutile phase of Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e, showing the angular shift (Δθ) as a function of milling time.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7059755/v1/ae0bdfc6e1a5da45ed31c11f.png"},{"id":86530587,"identity":"306b173c-8052-46f2-b4ba-f5726716dbce","added_by":"auto","created_at":"2025-07-11 16:54:36","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":289792,"visible":true,"origin":"","legend":"\u003cp\u003eRietveld refinement of the XRD patterns of titanium oxide (TiO\u003csub\u003e2\u003c/sub\u003e) powders doped with 5% iron (Fe) after various milling durations : (a) 1 h, (b)3 h, (c)6 h, (d) 12 h, (e) 24 h, and (f) 48 h.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7059755/v1/3a66360f7d69c2eba95a3075.png"},{"id":86530581,"identity":"2c187d80-9542-479b-84f5-b72c29c24f54","added_by":"auto","created_at":"2025-07-11 16:54:35","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":124077,"visible":true,"origin":"","legend":"\u003cp\u003eEvolution of the lattice parameter for the (a) anatase (b) rutile phases of 5% Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e powders as a function of the milling time deduced from the Rietveld refinement.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7059755/v1/8c740cf2c3c4fc02b214db83.png"},{"id":86529668,"identity":"b94a32a3-a663-4340-a3bc-dbafcc1aa05b","added_by":"auto","created_at":"2025-07-11 16:46:35","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":116666,"visible":true,"origin":"","legend":"\u003cp\u003eEvolution of the average crystallite size, \u0026lt;D\u0026gt;(nm), and mean internal strain\u0026lt;σ\u003csup\u003e2\u003c/sup\u003e\u0026gt;\u003csup\u003e1/2\u003c/sup\u003e (%), for the (a) anatase (b) rutile phases of 5% Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e powders as a function of the milling time deduced from the Rietveld refinement.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7059755/v1/0dbfb3aadc85d33671ce9f85.png"},{"id":86530583,"identity":"93b7062f-85e1-4dfc-9031-623e8723b560","added_by":"auto","created_at":"2025-07-11 16:54:35","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":573937,"visible":true,"origin":"","legend":"\u003cp\u003eSEM micrographs of 5% Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e powders as a function of milling time : (a) 1 h, (b) 3 h, (c) 6 h, (d) 12 h, (e) 24 h, and (f) 48 h.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7059755/v1/e8dac14cefdc6db78ec8ef8b.png"},{"id":86531140,"identity":"0955641d-5ec4-4914-a576-043a2119b2e7","added_by":"auto","created_at":"2025-07-11 17:02:35","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":70022,"visible":true,"origin":"","legend":"\u003cp\u003eFourier-transform infrared (FTIR) spectra of 5 wt.% Fe-doped TiO₂ powders milled for various durations, highlighting the evolution of functional groups and surface vibrations as a function of milling time.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7059755/v1/0aa5b9b5b07c5bd55db5011d.png"},{"id":91244768,"identity":"87cb0c6b-d594-447f-94a7-d4de39fd27e4","added_by":"auto","created_at":"2025-09-13 13:31:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1628197,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7059755/v1/e588fef2-379b-48d8-94e5-a193715984c3.pdf"}],"financialInterests":"","formattedTitle":"\u003cp\u003eInvestigation on structural, morphological and optical properties of 5% Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e powder nanostructures synthesized by mechanical alloying\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eTitanium dioxide (TiO\u003csub\u003e2\u003c/sub\u003e) has attracted considerable attention in recent decades owing to its remarkable physicochemical properties, including excellent chemical stability, low cost, abundance, non-toxicity, and strong photocatalytic efficiency under ultraviolet (UV) irradiation [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. These properties make TiO₂ a versatile material for a wide range of applications, particularly in environmental purification (e.g., wastewater treatment and air purification), dye-sensitized solar cells (DSSCs), lithium-ion batteries, sensors, and hydrogen production through water splitting [\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. However, one of the primary limitations of pure TiO\u003csub\u003e2\u003c/sub\u003e lies in its relatively wide band gap energy (approximately 3.2 eV for anatase and 3.0 eV for rutile), which restricts its photoresponse to the UV region-constituting only about 5% of the solar spectrum [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. This inherent limitation hinders the practical application of TiO₂ in visible-light-driven photocatalysis, thereby motivating efforts to improve its optical response and overall photocatalytic performance.\u003c/p\u003e\u003cp\u003eTo overcome this drawback, extensive research has focused on modifying the electronic structure of TiO₂ to extend its absorption edge into the visible region. Among the most effective strategies is doping with transition metal ions, which can introduce localized energy states within the band gap, thereby facilitating visible light absorption and reducing electron-hole recombination rates [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Iron (Fe), in particular, has proven to be a promising dopant due to its comparable ionic radius to that of Ti\u003csup\u003e4+\u003c/sup\u003e and its ability to exist in multiple oxidation states (Fe\u003csup\u003e2+\u003c/sup\u003e/Fe\u003csup\u003e3+\u003c/sup\u003e), which can introduce beneficial trap states for charge carriers [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Several studies have demonstrated that the incorporation of Fe into the TiO₂ lattice not only narrows the band gap but also promotes enhanced charge separation and prolongs the lifetime of photogenerated electrons and holes, making Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e a suitable candidate for visible-light photocatalysis [\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn parallel, the synthesis method plays a crucial role in determining the structure, morphology, and doping efficiency of TiO\u003csub\u003e2\u003c/sub\u003e-based materials. While conventional chemical methods such as sol-gel or hydrothermal synthesis are widely used, they often involve complex procedures, costly reagents, and limited scalability. In contrast, mechanical alloying (MA), also known as high-energy ball milling, presents a solid-state route that is simple, cost-effective, and scalable for the synthesis of nanocrystalline materials with controlled composition and microstructure [\u003cspan additionalcitationids=\"CR18 CR19 CR20\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. This technique relies on repeated fracturing, cold welding, and mechanical deformation of powder particles, enabling the production of metastable phases, homogeneous dopant dispersion, and grain refinement down to the nanometer scale [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. MA has been successfully applied in the preparation of various doped oxides, including TiO\u003csub\u003e2\u003c/sub\u003e, offering the potential to finely tune their structural and functional properties without the use of solvents or complex processing steps.\u003c/p\u003e\u003cp\u003eRecently, there has been a growing interest among researchers in the incorporation of TiO\u003csub\u003e2\u003c/sub\u003e powders doped with 5 wt. % Fe as a strategy to enhance the functional properties of TiO\u003csub\u003e2\u003c/sub\u003e-based materials. Iron doping has been shown to influence not only the optical and magnetic behavior of TiO\u003csub\u003e2\u003c/sub\u003e, but also its structural and microstructural characteristics. In a study conducted by Y. Kissoum et al. [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], the effect of mechanical grinding on TiO\u003csub\u003e2\u003c/sub\u003e powders doped with 5 wt. % Fe was investigated, with a particular focus on milling durations of up to 15 hours. Their results revealed significant modifications in crystallite size, phase composition, and specific surface area, highlighting the crucial role of milling time in tailoring the final properties of the material. Similarly, N. Nasralla et al. [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] synthesized and characterized TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles doped with 5% Fe (molar ratio) via the sol\u0026ndash;gel method, followed by post-annealing in air at 400\u0026deg;C, 600\u0026deg;C, and 800\u0026deg;C. These thermal treatments were found to affect both the structural integrity and the functional behavior of the resulting nanoparticles. Furthermore, J. Poostforooshan et al. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] successfully synthesized Fe-doped TiO₂ nanoparticles using the Electrospray-Assisted Flame Spray Pyrolysis (EAFSP) method, with Fe/Ti molar ratios of 1%, 5%, and 10%. Their findings indicated that Fe incorporation into the TiO\u003csub\u003e2\u003c/sub\u003e lattice could effectively reduce crystallite size, promote the formation of the rutile phase, spontaneously generate oxygen vacancies, and lower the optical band gap energy. Collectively, these studies emphasize the strong influence of Fe content, synthesis route, and post-treatment conditions on the structural, microstructural, and optoelectronic properties of Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e-based nanomaterials.\u003c/p\u003e\u003cp\u003eIn this context, the present study aims to investigate the effect of milling duration on the structural, microstructural, and optical properties of TiO\u003csub\u003e2\u003c/sub\u003e powders doped with 5 wt. % Fe and synthesized via high-energy ball milling. Milling time is a critical processing parameter that directly influences phase formation, crystallite size, lattice strain, and dopant distribution. Therefore, understanding its impact is essential for tailoring material properties and optimizing performance in visible-light-driven applications. The as-milled powders were systematically characterized using X-ray diffraction (XRD) to monitor phase evolution and crystallite refinement, scanning electron microscopy (SEM) to examine morphological features, and Fourier-transform infrared spectroscopy (FTIR) to identify functional groups associated with the TiO\u003csub\u003e2\u003c/sub\u003e structure. The findings from this study contribute to a deeper understanding of structure-property relationships in mechanically synthesized Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e nanomaterials and provide valuable insights into their potential for efficient photocatalytic and optoelectronic applications under visible light irradiation.\u003c/p\u003e"},{"header":"2. Experimental details","content":"\u003cp\u003e\u003cstrong\u003e2.1 Materials and Methods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA powder mixture consisting of TiO₂ and Fe with a nominal composition of 5 wt. % Fe was subjected to high-energy mechanical milling for various durations. In this process, elemental TiO₂ powders (Degussa, 99.7% purity, 25 nm) and Fe powders (Alfa Aesar, 99.9% purity, \u0026lt;10 \u0026mu;m) were intensively milled in a controlled environment to promote repeated cold welding, fracturing, and mixing at the nanoscale, ultimately leading to a homogeneous alloyed structure.\u003c/p\u003e\n\u003cp\u003eThe mechanical alloying was carried out using a Retsch PM 400 high-energy planetary ball mill. Stainless-steel vials and ten stainless-steel balls (12 mm diameter) were used as the milling media. To avoid oxidation and contamination during the process, the vials were sealed under a high-purity argon atmosphere. Each milling batch consisted of approximately 5 g of powder mixture, and a ball-to-powder weight ratio (BPR) of 15 :1 was maintained. The rotation speed of the disk was set to 350 rpm, ensuring sufficient impact energy to facilitate alloying.\u003c/p\u003e\n\u003cp\u003eTo minimize undesirable effects such as excessive heat generation, powder agglomeration, or adhesion to the vial walls and balls, an intermittent milling protocol was adopted. This involved operating the mill for 1 hour followed by a 30-minute rest period. The cycle was repeated as needed to achieve the desired cumulative milling durations of 1, 3, 6, 12, 24, and 48 hours.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2 Characterization\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe structural properties of the as-milled powders were analyzed using X-ray diffraction (XRD) on a Bruker D8 Advance Eco instrument equipped with Cu K\u0026alpha; radiation (\u0026lambda; = 1.5406 \u0026Aring;), operating at 40 kV and 40 mA. Diffraction patterns were collected over the 2\u0026theta; range of 20\u0026deg;\u0026ndash;80\u0026deg; with a step size of 0.02\u0026deg; and a scan speed of 0.5\u0026deg;/min. Phase identification was performed using standard JCPDS files. To evaluate the crystallite size and microstrain, peak broadening was initially analyzed using the Williamson\u0026ndash;Hall method, then further refined using the Rietveld method via the MAUD software (version 2.22), a powerful tool for diffraction-based material analysis [26]. This software facilitated a comprehensive structural characterization based on a full-pattern fitting approach.\u003c/p\u003e\n\u003cp\u003eTypically, each individual diffraction peak was modeled using a pseudo-Voigt profile function, which approximates the peak shape as a linear combination of Lorentzian (L) and Gaussian (G) components, as described by Young et al. in 1982 [27]. The peak profile function is expressed as follows :\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; W(2q)=h \u003cem\u003eL\u003c/em\u003e(2q, \u003cem\u003eH\u003csub\u003eL\u003c/sub\u003e\u003c/em\u003e)+(1-h)\u003cem\u003eG\u003c/em\u003e(2q, \u003cem\u003eH\u003csub\u003eG\u003c/sub\u003e\u003c/em\u003e) \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; (1)\u003c/p\u003e\n\u003cp\u003ewhere\u0026nbsp;\u0026Omega;(2\u0026theta;)\u0026nbsp;represents the overall peak shape,\u0026nbsp;\u0026eta;\u0026nbsp;is the mixing parameter (0 \u0026le;\u0026nbsp;\u0026eta;\u0026nbsp;\u0026le; 1), and H\u003csub\u003eL\u003c/sub\u003e and H\u003csub\u003eG\u003c/sub\u003e are the full width at half maximum (FWHM) values of the Lorentzian and Gaussian components, respectively. The total peak broadening \u0026beta; is similarly expressed as:\u003c/p\u003e\n\u003cp\u003e\u0026beta; = \u0026eta;\u0026beta;\u003cstrong\u003e\u003csub\u003eL\u003c/sub\u003e\u003c/strong\u003e+(1-\u0026eta;)B\u003csub\u003eG\u003c/sub\u003e (2)\u003c/p\u003e\n\u003cp\u003eThe average crystallite size\u0026nbsp;\u0026lt;D\u0026gt;was then estimated using the Scherrer equation applied to the Lorentzian component :\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u003cimg width=\"125\" height=\"32\" src=\"data:image/png;base64,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\" alt=\"image\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(3)\u003c/p\u003e\n\u003cp\u003ewhere\u0026nbsp;K\u0026nbsp;is the shape factor (typically 0.9),\u0026nbsp;\u0026lambda;\u0026nbsp;is the X-ray wavelength, and\u0026nbsp;\u0026beta;\u003csub\u003eL\u003c/sub\u003e\u0026nbsp; is the Lorentzian peak width corrected for instrumental broadening. The root mean square microstrain \u0026lt;\u0026sigma;\u003csup\u003e2\u003c/sup\u003e\u0026gt;\u003csup\u003e1/2\u003c/sup\u003ewas calculated from the Gaussian contribution using the following relation :\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003cimg width=\"154\" height=\"33\" src=\"data:image/png;base64,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\" alt=\"image\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; (4)\u003c/p\u003e\n\u003cp\u003eThis analytical approach allows for the decoupling of size and strain contributions to the peak broadening, thereby offering a more accurate and reliable quantification of the microstructural evolution induced by high-energy ball milling.\u003c/p\u003e\n\u003cp\u003eMorphological and microstructural features of the milled powders were examined using scanning electron microscopy (Quantum 250\u0026ndash;FEI). Prior to imaging, the samples were coated with a thin gold layer to enhance electrical conductivity. The particle size distribution and agglomeration state were qualitatively assessed from the acquired micrographs.\u003c/p\u003e\n\u003cp\u003eFourier-transform infrared (FTIR) spectroscopy was employed to investigate the vibrational modes associated with Ti\u0026ndash;O bonds and the presence of surface functional groups. Spectra were recorded in the range of 400\u0026ndash;4000 cm⁻\u0026sup1; using a Bruker Alpha II spectrometer in attenuated total reflectance (ATR) mode. This analysis provided valuable insights into structural modifications, defect states, and surface chemistry induced by Fe doping and the mechanical milling process.\u003c/p\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e3.1. Structural and microstructural characteristics\u003c/h2\u003e\u003cp\u003eFigure.1 presents the X-ray diffraction (XRD) patterns of titanium dioxide (TiO\u003csub\u003e2\u003c/sub\u003e) powders doped with 5% iron (Fe) for various milling times : 1 h, 3 h, 6 h, 12 h, 24 h, and 48 h.\u003c/p\u003e\u003cp\u003eThe XRD analysis of the sample milled for 1 hour reveals well-defined diffraction peaks corresponding to the anatase phase, characterized by a tetragonal crystal structure with a space group of I41/amd. The strong intensity of the (011) peak reflects the high crystallinity of the TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles.\u003c/p\u003e\u003cp\u003eAdditionally, two extra peaks indexed to the (110) and (200) planes of metallic iron indicate partial segregation of the dopant during the mechanosynthesis process.\u003c/p\u003e\u003cp\u003eThe indexing of the diffraction peaks was performed using the X\u0026rsquo;Pert HighScore Plus software, which provides access to an extensive database of JCPDS reference cards for various known materials.\u003c/p\u003e\u003cp\u003eFor the pure anatase phase of TiO\u003csub\u003e2\u003c/sub\u003e, the diffraction peaks observed at 25.42\u0026deg;, 37.78\u0026deg;, 48.24\u0026deg;, 53.84\u0026deg;, and 55.00\u0026deg; were accurately attributed to the (011), (004), (020), (015), and (121) crystallographic planes, respectively.\u003c/p\u003e\u003cp\u003eUpon extending the milling time to 3 hours, the diffraction patterns exhibit a pronounced broadening and a significant reduction in the intensity of the anatase peaks. Simultaneously, the fading of the iron-related peaks suggests a progressive incorporation of Fe atoms into the TiO\u003csub\u003e2\u003c/sub\u003e lattice, promoting a more homogeneous distribution of the dopant within the host structure.\u003c/p\u003e\u003cp\u003eAfterward, for the powders milled for 6 and 12 hours, the XRD patterns reveal the emergence of a mixed TiO\u003csub\u003e2\u003c/sub\u003e phase, indicating a phase transition from anatase to rutile. This transformation is thermodynamically favored as the mechanical energy input during milling increases, promoting atomic rearrangement and phase stability toward the denser rutile structure.\u003c/p\u003e\u003cp\u003eSimultaneously, a distinct iron-rich phase can be observed in the XRD spectra, although its intensity progressively decreases with milling time. This behavior suggests that part of the Fe initially segregated outside the TiO\u003csub\u003e2\u003c/sub\u003e lattice gradually dissolves into the matrix under the effect of prolonged mechanical activation. The decrease in the intensity of the Fe-related peaks may thus be attributed to two concurrent phenomena : the reduction of crystallite size of the segregated Fe phase and the enhanced incorporation of Fe atoms into defect sites or interstitial positions within the TiO\u003csub\u003e2\u003c/sub\u003e structure.\u003c/p\u003e\u003cp\u003eThe coexistence of anatase and rutile phases, along with partial Fe segregation, reflects a dynamic balance between structural disorder induced by milling and the thermodynamic driving forces leading to phase transformations and dopant diffusion. These structural evolutions are expected to significantly influence the functional properties of the material, such as its optical and electronic behavior, which will be discussed in the following sections.\u003c/p\u003e\u003cp\u003eAs the milling time extends to 24 and 48 hours, the X-ray diffraction patterns clearly show the complete disappearance of the anatase phase, with only the rutile phase remaining. This transformation is significant because anatase is known to be a metastable phase that can transition into the more thermodynamically stable rutile phase under the influence of external factors such as temperature, pressure, or mechanical stress.\u003c/p\u003e\u003cp\u003eIn the context of high-energy ball milling, the repeated collisions between the powder particles and the milling media induce substantial lattice strain, generate defects, and locally elevate the temperature, all of which favor the anatase-to-rutile phase transition.\u003c/p\u003e\u003cp\u003eThe prolonged mechanical action thus promotes atomic rearrangements and enhances the thermodynamic driving force for the stabilization of the rutile structure. Furthermore, the dominance of the rutile phase at extended milling times suggests that the energy input during milling was sufficient not only to initiate but to complete the phase transformation. Meanwhile, faint iron-related signals still persist in the XRD patterns, indicating that a small fraction of iron remains segregated rather than being entirely incorporated into the TiO\u003csub\u003e2\u003c/sub\u003e matrix.\u003c/p\u003e\u003cp\u003eFigure.2 illustrates the evolution of the diffraction peaks corresponding to the (110) plane of both anatase and rutile phases of Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e as a function of milling time. For the anatase phase, a slight shift toward higher angles (Δθ) is observed. This phenomenon can be primarily attributed to the partial substitution of Ti⁴⁺ ions (ionic radius\u0026thinsp;\u0026asymp;\u0026thinsp;0.745 \u0026Aring;) by smaller Fe\u0026sup3;⁺ ions (ionic radius\u0026thinsp;\u0026asymp;\u0026thinsp;0.645 \u0026Aring;) within the crystalline structure, which alters the interplanar spacing (d). According to Bragg\u0026rsquo;s law (nλ\u0026thinsp;=\u0026thinsp;2d\u0026middot;sinθ), this decrease in spacing leads to a shift of the diffraction peaks toward higher 2θ angles. Additionally, high-energy ball milling introduces crystal defects and internal strain, further amplifying this angular shift. The charge imbalance caused by the valence difference between Ti⁴⁺ and Fe\u0026sup3;⁺ is compensated by the formation of oxygen vacancies, contributing to lattice distortion and peak broadening.\u003c/p\u003e\u003cp\u003eIn contrast, for the rutile phase, the (110) diffraction peaks exhibit a slight shift toward lower angles as milling time increases. Although counterintuitive given the smaller size of Fe\u0026sup3;⁺ ions, this behavior may result from a local lattice expansion induced by the accumulation of defects, internal strain, and oxygen vacancies generated during mechanical milling. These structural disturbances can increase the interplanar spacing, thus shifting the XRD peaks toward lower 2θ values.\u003c/p\u003e\u003cp\u003eThese findings confirm not only the effective incorporation of Fe\u0026sup3;⁺ dopants into the TiO\u003csub\u003e2\u003c/sub\u003e lattice but also highlight the significant impact of mechanical milling on the crystal structure-through defect generation, lattice distortion, and modification of diffraction parameters.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e displays the Rietveld refinement results of the X-ray diffraction (XRD) patterns for TiO\u003csub\u003e2\u003c/sub\u003e powders doped with 5% iron (Fe) after different milling durations : 1 h, 3 h, 6 h, 12 h, 24 h, and 48 h.\u003c/p\u003e\u003cp\u003eSpecifically, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a) shows the refinement corresponding to the sample milled for 1 hour. The analysis reveals the presence of the tetragonal anatase phase, characterized by lattice parameters a\u0026thinsp;=\u0026thinsp;0.3781\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0001 nm and c\u0026thinsp;=\u0026thinsp;0.9512\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0001 nm. Additionally, the presence of a body-centered cubic (bcc) iron phase is confirmed, with a lattice parameter a\u0026thinsp;=\u0026thinsp;0.2863\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0001 nm.\u003c/p\u003e\u003cp\u003eThe narrow uncertainties associated with these values indicate a precise fit of the experimental data to the structural model. The consistency and sharpness of the lattice parameters further confirm the presence of a well-ordered and stable crystalline structure, particularly for the anatase phase.\u003c/p\u003e\u003cp\u003eBoth the anatase and bcc iron phases are also observed in the sample milled for 3 hours, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b). The Rietveld refinement reveals slight changes in the lattice parameters, possibly indicating the beginning of dopant incorporation or the development of lattice strain due to prolonged mechanical activation.\u003c/p\u003e\u003cp\u003eFor the powders milled for 6 h and 12 h (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c) and 3(d)), the Rietveld analysis reveals that TiO\u003csub\u003e2\u003c/sub\u003e is no longer present exclusively in the anatase phase, but rather as a mixture of anatase and rutile phases. This phase transformation can be attributed to the progressive incorporation of Fe ions into the TiO\u003csub\u003e2\u003c/sub\u003e lattice, which induces lattice distortions and promotes the anatase-to-rutile transition.\u003c/p\u003e\u003cp\u003eThis structural evolution is significant, as the rutile phase-although thermodynamically more stable-is generally associated with reduced photocatalytic performance compared to anatase. The appearance of rutile thus reflects a compromise between structural stability and functional properties, directly influenced by the mechanical milling conditions and dopant effects.\u003c/p\u003e\u003cp\u003eAfter 24 h and 48 h of milling (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(e) and 3(f)), the Rietveld analysis confirms the complete disappearance of the anatase phase, with only the rutile phase and trace amounts of metallic iron remaining. This indicates that prolonged milling facilitates the anatase-to-rutile transition, driven by accumulated lattice strain and localized thermal effects. The presence of residual Fe suggests dopant segregation or partial reduction, likely induced by high-energy impacts during mechanical processing. Although the rutile phase is thermodynamically more stable, its dominance may compromise dopant uniformity and negatively affect photocatalytic performance. Therefore, precise control of the milling duration is essential to achieve an optimal balance between structural stability and functional efficiency.\u003c/p\u003e\u003cp\u003eThese findings align with previous studies on Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e systems. For instance, research has shown that high-energy mechanical milling of undoped anatase TiO\u003csub\u003e2\u003c/sub\u003e induces the anatase-to-rutile phase transformation via high-pressure srilankite [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. M\u0026ouml;ssbauer spectroscopy analyses revealed that iron atoms are more likely to dissolve in rutile TiO₂, and the composition distribution becomes nonuniform during mechanical alloying, with Fe atoms enriching at the interface or surface of TiO\u003csub\u003e2\u003c/sub\u003e crystallites [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Additionally, studies have indicated that Fe doping can accelerate the anatase-to-rutile transformation process, influenced by crystal defects and the generation of oxygen vacancies [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThese structural changes, while favoring the formation of the thermodynamically stable rutile phase, may compromise dopant homogeneity and degrade photocatalytic performance. Therefore, precise control of the milling duration is critical to maintaining a balance between phase stability and functional properties.\u003c/p\u003e\u003cp\u003eFigure.4 illustrates the evolution of the lattice parameters for the anatase and rutile phases of 5% Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e powders as a function of milling time, as determined by Rietveld refinement of X-ray diffraction (XRD) data.\u003c/p\u003e\u003cp\u003eIn Figure.4(a), the lattice parameters a and c of the anatase phase are observed to decrease gradually with increasing milling time. This contraction of the unit cell can be attributed to the incorporation of Fe\u0026sup3;⁺ ions into the Ti⁴⁺ sites of the TiO₂ lattice. Since the ionic radius of Fe\u0026sup3;⁺ (0.645 \u0026Aring;) is slightly larger than that of Ti⁴⁺ (0.605 \u0026Aring;), such substitution can introduce lattice strain and distortions, resulting in reduced lattice parameters. Additionally, the high-energy impacts during mechanical milling may generate defects and dislocations that further contribute to the lattice contraction.\u003c/p\u003e\u003cp\u003eIn contrast, Figure.4(b) reveals that the rutile phase, which emerges after 6 h of grinding, exhibits a progressive decrease in both a and c lattice parameters with increasing grinding time. This trend suggests that continued mechanical activation not only stabilizes the rutile structure but also promotes subtle structural distortions, likely due to the incorporation of Fe\u0026sup3;⁺ ions and the accumulation of internal stresses and lattice defects. These variations in lattice constants further reflect the dynamic structural evolution induced by prolonged high-energy milling.\u003c/p\u003e\u003cp\u003eThe observed decrease in lattice parameters for both anatase and rutile phases indicates that Fe\u0026sup3;⁺ ions are substituting Ti⁴⁺ sites in the TiO\u003csub\u003e2\u003c/sub\u003e lattice, leading to lattice distortions. This substitution is consistent with previous studies that have reported Fe\u0026sup3;⁺ incorporation into TiO\u003csub\u003e2\u003c/sub\u003e structures, resulting in changes in lattice parameters and phase transformations.\u003c/p\u003e\u003cp\u003eThese structural changes have significant implications for the material's properties, particularly its photocatalytic activity. The incorporation of Fe\u0026sup3;⁺ ions and the associated lattice distortions can influence the electronic structure of TiO\u003csub\u003e2\u003c/sub\u003e, potentially affecting its bandgap and charge carrier dynamics. Therefore, understanding the relationship between milling time, lattice parameter evolution, and dopant incorporation is crucial for tailoring the properties of Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e for specific applications.\u003c/p\u003e\u003cp\u003eFigure.5 illustrates the variation of the average crystallite size ⟨D⟩ (nm) and the average internal strain ⟨σ\u0026sup2;⟩\u0026sup1;ᐟ\u0026sup2; (%) for the anatase and rutile phases of 5% Fe-doped TiO₂ powders as a function of milling time, as determined by Rietveld refinement. The average crystallite size decreases systematically with increasing milling time, whereas the microstrain ⟨σ\u0026sup2;⟩\u0026sup1;ᐟ\u0026sup2; increases progressively.\u003c/p\u003e\u003cp\u003eIn Figure.5(a), the average crystallite size ⟨D⟩ (nm) of the anatase phase decreases systematically with increasing milling time, while the microstrain ⟨σ\u0026sup2;⟩\u0026sup1;ᐟ\u0026sup2; (%) increases progressively. This inverse relationship highlights the dual effects of mechanical milling : the fragmentation of crystallites and the accumulation of lattice defects.\u003c/p\u003e\u003cp\u003eThe reduction in crystallite size is attributed to the repeated fracturing and refinement of powder particles due to high-energy impacts during milling. This process leads to smaller, more refined grains, as observed in similar studies where crystallite size decreased significantly with milling time.\u003c/p\u003e\u003cp\u003eConversely, the increase in microstrain indicates the generation of lattice distortions, dislocations, and point defects induced by mechanical stress. These defects accumulate over time, leading to an overall increase in internal strain energy and a higher degree of disorder in the anatase structure.\u003c/p\u003e\u003cp\u003eThis behavior reflects the competition between defect generation and structural reorganization under mechanical activation, resulting in a nanostructured anatase phase with altered microstructural properties.\u003c/p\u003e\u003cp\u003eIn contrast, Figure.5(b) reveals that for the rutile phase, which emerges after 6 h of grinding, the average crystallite size ⟨D⟩ (nm) decreases systematically with increasing milling time, while the microstrain ⟨σ\u0026sup2;⟩\u0026sup1;ᐟ\u0026sup2; (%) increases progressively.\u003c/p\u003e\u003cp\u003eThis behavior is consistent with the anatase phase, suggesting that prolonged milling not only promotes the anatase-to-rutile transition but also induces continued fragmentation and accumulation of defects in the newly formed rutile crystallites. The increasing microstrain reflects enhanced lattice distortion and defect density due to the persistent mechanical activation.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Morphological characteristics\u003c/h2\u003e\u003cp\u003eFigure.6 presents scanning electron microscopy (SEM) images in backscattered electron (BSE) mode of 5% Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e powders subjected to mechanical milling for (a) 1 h, (b) 3 h, (c) 6 h, (d) 12 h, (e) 24 h, and (f) 48 h.\u003c/p\u003e\u003cp\u003eAt 1 h of milling (Figure.6(a)), the powders exhibit significant agglomeration and relatively coarse grains. Brighter regions-typically associated with heavier elements such as Fe-are clearly visible, while darker areas correspond primarily to the TiO\u003csub\u003e2\u003c/sub\u003e matrix, where the anatase phase remains dominant. This contrast is characteristic of BSE imaging, which is sensitive to atomic number variations [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eAfter 3 h of milling (Figure.6(b)), noticeable fragmentation is observed along with a more homogeneous particle dispersion. The increasing prevalence of darker regions reflects grain size reduction and enhanced Fe incorporation into the TiO\u003csub\u003e2\u003c/sub\u003e matrix. The reduction in bright agglomerates indicates the early stages of a finer and more uniform Fe distribution [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eAt 6 h (Figure.6(c)), the particles become even finer, and darker zones become more prominent. This morphological evolution coincides with the initial appearance of the rutile phase, as confirmed by XRD analysis. These darker regions likely correspond to Fe-enriched rutile nanocrystals, consistent with previous studies showing that Fe-doping facilitates the anatase-to-rutile transformation under mechanical activation [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. The observed contrast is influenced not only by composition but also by local crystallinity and defect density [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eAt 12 h (Figure.6(d)), the microstructure becomes more uniform, with a marked decrease in grain size. The predominance of darker contrast suggests a further increase in the rutile phase fraction, as also reported in other mechanically alloyed doped- TiO\u003csub\u003e2\u003c/sub\u003e systems [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. The reduced number of bright features supports the progressive homogenization of Fe within the matrix.\u003c/p\u003e\u003cp\u003eAfter 24 h of milling (Figure.6(e)), the powders exhibit a highly fragmented structure with ultrafine particles. The sustained dominance of dark contrast is likely associated with a dense population of rutile nanocrystals and the accumulation of internal strain and defects, typical in high-energy ball-milled oxides [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFinally, at 48 h (Figure.6(f)), the microstructure appears highly compact and homogeneous. The widespread dark contrast is indicative of a well-developed nanostructured rutile phase, extensively doped with Fe. This result reflects the cumulative effects of prolonged mechanical activation, including significant grain refinement, increased microstrain, and defect generation-factors known to stabilize the rutile phase in doped TiO\u003csub\u003e2\u003c/sub\u003e systems [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.3. FTIR Analysis\u003c/h2\u003e\u003cp\u003eThe FTIR spectra of Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e powders milled for various durations (from 1 h to 48 h), as presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, provide valuable insights into the evolution of structural features and surface chemistry induced by mechanical alloying. These spectra confirm the successful incorporation of iron impurities into the TiO\u003csub\u003e2\u003c/sub\u003e matrix.\u003c/p\u003e\u003cp\u003eA strong absorption band in the range of 400\u0026ndash;900 cm⁻\u0026sup1;, attributed to Ti\u0026ndash;O and Ti\u0026ndash;O\u0026ndash;Ti stretching vibrations, is clearly observed in all samples. This confirms the structural integrity of the TiO₂ framework, regardless of milling duration. The progressive broadening of this band with increasing milling time indicates a rise in structural disorder and lattice distortion, likely due to the substitution of Ti⁴⁺ by Fe\u0026sup3;⁺ ions and the accumulation of internal strain, as further supported by the Rietveld refinement results.\u003c/p\u003e\u003cp\u003eIn addition to the fundamental vibrations of the TiO\u003csub\u003e2\u003c/sub\u003e lattice, a weak peak near 1100 cm⁻\u0026sup1; is detected in all spectra and is assigned to the bending vibrations of molecularly adsorbed water (H\u0026ndash;O\u0026ndash;H), commonly associated with surface hydroxyl groups. This characteristic band reflects the presence of physisorbed water on the particle surfaces. Its persistence across all milling durations suggests that, despite the mechanical stress imparted by high-energy ball milling, the powders retain a degree of surface hydration-most likely due to post-synthesis exposure to ambient humidity. Notably, the increasing intensity of this band with prolonged milling suggests enhanced water adsorption capacity, which can be attributed to the formation of structural defects such as oxygen vacancies and undercoordinated Ti⁴⁺ cations. These defects increase the hydrophilicity of the surface by providing energetically favorable sites for moisture adsorption. The progressive disorder and elevated surface energy resulting from extended milling thus contribute to this enhanced interaction with water molecules.\u003c/p\u003e\u003cp\u003eA weak absorption band around 2400 cm⁻\u0026sup1; is also observed and is attributed to C\u0026ndash;O stretching vibrations [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. This feature likely originates from adsorbed atmospheric CO₂ or the formation of surface carbonate species-phenomena commonly observed in metal oxide powders exposed to air. The evolution of this band\u0026rsquo;s intensity with milling time suggests modifications in surface chemistry and reactivity, possibly driven by an increased density of surface defects and changes in surface area, which facilitate greater interaction with environmental CO₂.\u003c/p\u003e\u003cp\u003eFinally, the presence of broad, weak transmittance bands centered around 3000 cm⁻\u0026sup1; is ascribed to the stretching vibrations of O\u0026ndash;H bonds from surface hydroxyl groups or molecularly adsorbed water. These bands, although typically of low intensity due to hydrogen bonding, provide additional evidence of surface hydration and the significant role of surface chemistry in the evolution of the milled powders [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThese findings are consistent with previous reports in the literature [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e], thereby reinforcing the reliability of the present observations regarding the influence of mechanical alloying on structural disorder and surface reactivity.\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThis study focused on the structural, microstructural, morphological, and optical properties of TiO\u003csub\u003e2\u003c/sub\u003e powders doped with 5 wt. % Fe, synthesized via high-energy ball milling over durations ranging from 1 to 48 hours. Structural evolution was thoroughly examined by X-ray diffraction (XRD) combined with Rietveld refinement using MAUD software, while morphological changes were analyzed via scanning electron microscopy (SEM).\u003c/p\u003e\u003cp\u003eXRD patterns revealed a progressive transformation of the crystalline phases with increasing milling time. After 1 hour of milling, the powders exhibited sharp peaks corresponding to the anatase phase, indicating high crystallinity. Additional reflections attributed to metallic Fe suggested partial segregation of the dopant at this early stage. With 3 hours of milling, broadening and intensity reduction of anatase peaks were observed, along with attenuation of Fe-related signals-indicating the initial stages of Fe incorporation into the TiO\u003csub\u003e2\u003c/sub\u003e lattice.\u003c/p\u003e\u003cp\u003eAt intermediate durations (6 to 12 hours), the emergence of a biphasic anatase\u0026ndash;rutile structure marked the onset of a mechanically induced phase transformation. This transition reflects a competition between mechanically driven disorder and the thermodynamic stability of the rutile phase. Concurrently, the gradual disappearance of Fe-related peaks suggested progressive incorporation of segregated Fe into defect-rich or interstitial sites within the TiO\u003csub\u003e2\u003c/sub\u003e matrix.\u003c/p\u003e\u003cp\u003eAt prolonged milling times (24 and 48 hours), the XRD patterns confirmed the complete disappearance of anatase peaks, with the rutile phase fully stabilized. This transition indicates that extended milling provided sufficient energy to complete the anatase-to-rutile transformation, facilitated by defect accumulation, lattice strain, and localized thermal effects from repeated impacts. A small amount of Fe remained in a segregated form, though significantly reduced.\u003c/p\u003e\u003cp\u003eRietveld quantitative analysis revealed a continuous decrease in crystallite size and an increase in microstrain with milling duration. These microstructural evolutions were consistent with SEM observations, which showed progressive particle refinement, shape distortion, and agglomeration-attributed to severe plastic deformation, cold welding, and fracture events induced by high-energy impacts.\u003c/p\u003e\u003cp\u003eFTIR spectroscopy offered further insights into bonding characteristics and surface chemistry. A pronounced absorption band in the 400\u0026ndash;900 cm⁻\u0026sup1; range, corresponding to Ti\u0026ndash;O and Ti\u0026ndash;O\u0026ndash;Ti stretching vibrations, was consistently present in all samples, confirming the structural integrity of the TiO\u003csub\u003e2\u003c/sub\u003e framework throughout milling. A weak but persistent peak near 1100 cm⁻\u0026sup1; was attributed to bending vibrations of molecularly adsorbed water (H\u0026ndash;O\u0026ndash;H), associated with surface hydroxyl groups. Its increasing intensity with milling duration reflected enhanced surface hydration, likely due to the formation of oxygen vacancies and undercoordinated Ti atoms. Additionally, a weak absorption band around 2400 cm⁻\u0026sup1;, assigned to C\u0026ndash;O stretching vibrations, was observed and likely originated from adsorbed CO\u003csub\u003e2\u003c/sub\u003e or surface carbonate species. The evolution of this band with milling duration suggests increased surface reactivity caused by defect accumulation and increased surface area. Finally, broad and weak transmittance bands centered around 3000 cm⁻\u0026sup1; were attributed to O\u0026ndash;H stretching vibrations from surface hydroxyl groups or adsorbed water molecules. Although typically of low intensity due to hydrogen bonding, these bands provided further evidence of surface hydration and the crucial role of surface chemistry in the evolution of the milled powders.\u003c/p\u003e\u003cp\u003eIn summary, high-energy mechanical alloying not only induces substantial changes in the bulk structure and phase composition of Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e powders but also results in pronounced modifications to their surface chemistry. These transformations enhance both hydrophilicity and surface reactivity, which are critical for potential applications in photocatalysis, adsorption, and other surface-driven technologies.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003cp\u003eThe authors have no competing interests to declare that are relevant to the content of this article.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThe authors did not receive support from any organization for the submitted work. Data availability All data generated or analysed during this study are included in this published article.\u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e\u003cp\u003eHB: synthesis and characterizations, validation, investigation, resources, writing \u0026ndash;original draft, writing - review \u0026amp; editing, visualization. SA: conception, methodology, resources, supervision. AH: conception, methodology, resources, review \u0026amp; editing, visualization, supervision, validation. TH: validation, writing - review\u0026amp; editing, visualization.DB: XRD refinement, interpretation of results, manuscript preparation, visualization. RA: validation, writing \u0026ndash; review \u0026amp; editing, visualization.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e\u003cp\u003eThe authors warmly thank the members of the Laboratory for Physico-Chemical Studies of Materials (LEPCM), University of Batna 1, Algeria, for their assistance in acquiring the SEM images. This work was supported by the Algerian Directorate for Scientific Research and Technological Development (DGRSDT).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eU. Diebold, The surface science of titanium dioxide, Surf. Sci. Rep, 48(5\u0026ndash;8) (2003) 53\u0026ndash;229. https://doi.org/10.1016/S0167-5729(02)00100-0\u003c/li\u003e\n\u003cli\u003eA. Fujishima, X. Zhang, DA. Tryk, TiO\u003csub\u003e2\u003c/sub\u003e photocatalysis and related surface phenomena, Surf. Sci. Rep, 63(12) (2008) 515\u0026ndash;582. https://doi.org/10.1016/j.surfrep.2008.10.001\u003c/li\u003e\n\u003cli\u003eC. Ayappan, R. Xing, X. Zhang, D. Luo, S. Liu, A. Fujishima, TiO\u003csub\u003e2\u003c/sub\u003e-based photocatalysts for emerging gaseous pollutants removal: From photocatalysts to reactors design, Coord. Chem. Rev, 515(2024) 215960. https://doi.org/10.1016/j.ccr.2024.215960\u003c/li\u003e\n\u003cli\u003eG. Williams, B. Seger, PV. Kamat, TiO\u003csub\u003e2\u003c/sub\u003e-Graphene Nanocomposites. UV-Assisted Photocatalytic Reduction of Graphene Oxide, ACS nano, 2 (7) (2008) 1487-1491. https://doi.org/10.1021/nn800251f\u003c/li\u003e\n\u003cli\u003eH. Tang, K. Prasad, R. Sanjin\u0026egrave;s, P. E. Schmid, F. L\u0026eacute;vy, Electrical and optical properties of TiO\u003csub\u003e2\u003c/sub\u003e anatase thin films, J. Appl. Phys,75(1994) 2042\u0026ndash;2047. https://doi.org/10.1063/1.356306 \u003c/li\u003e\n\u003cli\u003eS. Khan, M. Al-Shahry, WB. Ingler Jr, Efficient Photochemical Water Splitting by a Chemically Modified n-TiO\u003csub\u003e2\u003c/sub\u003e, science, 297 (5590) (2002) 2243-2245. https://doi.org/10.1126/science.1075035\u003c/li\u003e\n\u003cli\u003eM. Wang, X. Xu, L. Lin, D. He, Gd\u0026ndash;La codoped TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles as solar photocatalysts, Prog. Nat. Sci. 25(2015) 6-11. https://doi.org/10.1016/j.pnsc.2015.01.002\u003c/li\u003e\n\u003cli\u003eD.A.H. Hanaor, G. Triani, C.C. Sorrell, Morphology and photocatalytic activity of highly oriented mixed phase titanium dioxide thin films, Surf. Coat. Technol. 205(12) (2011) 3658\u0026ndash;3664. https://doi.org/10.1016/j.surfcoat.2011.01.007\u003c/li\u003e\n\u003cli\u003eR. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, Y. Taga, Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides, Science, 293(5528) (2001) 269\u0026ndash;271. https://doi.org/10.1126/science.1061051\u003c/li\u003e\n\u003cli\u003eC. Di Valentin, G. Pacchioni, A. Selloni. Origin of the different photoactivity of N-doped anatase and rutile TiO\u003csub\u003e2\u003c/sub\u003e, Physical Review B, 70(2005) 085116. https://doi.org/10.1103/PhysRevB.70.085116\u003c/li\u003e\n\u003cli\u003eC. Di Valentin, G. Pacchioni, A. Selloni, S. Livraghi, E. Giamello, Characterization of paramagnetic species in N-doped TiO\u003csub\u003e2\u003c/sub\u003e powders by EPR spectroscopy and DFT calculations, J. Phys. Chem. B, 109(23) (2005) 11414\u0026ndash;11419. https://doi.org/10.1021/jp051756t\u003c/li\u003e\n\u003cli\u003eM. Batzill, U. Diebold, The surface and materials science of tin dioxide, Progress in Surface Science, 79(2\u0026ndash;4) (2005) 47\u0026ndash;154. https://doi.org/10.1016/j.progsurf.2005.09.002\u003c/li\u003e\n\u003cli\u003eC. Yu Jimmy, Jiaguo Yu, Ho, Jiang, X.Zhang, Effects of F- Doping on the Photocatalytic Activity and Microstructures of Nanocrystalline TiO\u003csub\u003e2\u003c/sub\u003e Powders, American Chemical Society, 14(9) (2002) 3808. https://doi.org/10.1021/cm020027c \u003c/li\u003e\n\u003cli\u003eD. Li, H. Haneda, S. Hishita, N. Ohashia, N.K. Labhsetwar, Fluorine-doped TiO\u003csub\u003e2\u003c/sub\u003e Powders Prepared by Spray Pyrolysis and Their Improved Photocatalytic Activity for Decomposition of Gas-phase Acetaldehyde. Journal of Fluorine Chemistry, 126(2005) 69-77. http://dx.doi.org/10.1016/j.jfluchem.2004.10.044\u003c/li\u003e\n\u003cli\u003eW. Yang, C. A. Wolden, Plasma-Enhanced Chemical Vapor Deposition of TiO\u003csub\u003e2\u003c/sub\u003e Thin Films for Dielectric Applications, Thin Solid Films, 515(4) (2006) 1708-1713. http://dx.doi.org/10.1016/j.tsf.2006.06.010\u003c/li\u003e\n\u003cli\u003eW. Avansi Jr, R. Arenal, V. R. de Mendon\u0026ccedil;a, C. Ribeiroe , E. Longo, Vanadium-doped TiO\u003csub\u003e2\u003c/sub\u003e anatase nanostructures: the role of V in solid solution formation and its effect on the optical properties, CrystEngComm, 16(23) (2014) 5021. https://doi.org/10.1039/C3CE42356E\u003c/li\u003e\n\u003cli\u003eC. Suryanarayana, Mechanical alloying and milling. Prog Mater Sci 46(1\u0026ndash;2) (2001)1\u0026ndash;184. https://doi.org/10.1016/S0079-6425(99)00010-9\u003c/li\u003e\n\u003cli\u003eJ. S. Benjamin, T. E. Volin, The mechanism of mechanical alloying. Metallurgical Transactions, 5(8) (1974) 1929\u0026ndash;1934. https://doi.org/10.1007/BF02644161\u003c/li\u003e\n\u003cli\u003eJ. S. Benjamin, Dispersion strengthened superalloys by mechanical alloying, Metall Trans, 1(1970)2943\u0026ndash;2951. https://doi.org/10.1007/BF03037835\u003c/li\u003e\n\u003cli\u003eN. Guemmoud, A. Hafs, T. Hafs, Effect of milling time on the structural, microstructure, and magnetic properties of nanocrystalline Fe\u003csub\u003e90\u003c/sub\u003eSb\u003csub\u003e10\u003c/sub\u003e powders obtained by high-energy ball milling, \u003cem\u003eInt. J. Adv. Manuf. Technol. 122(2022)2043-2058.\u003c/em\u003e https://doi.org/10.1007/s00170-022-10003-x\u003c/li\u003e\n\u003cli\u003eA. Hafs, T. Hafs, D. Berdjane, A. Bendjama, N. Hasnaoui, Magnetic and microstructural properties of thin film Fe‑Sb obtained by thermal evaporation of nanostructured milled powder,\u003cem\u003e \u003cem\u003eInt. J. Adv. Manuf. Technol. 133(2024)\u003c/em\u003e\u003c/em\u003e \u003cem\u003e5571\u0026ndash;5583.\u003c/em\u003e \u003cem\u003ehttps://doi.org/10.1007/s00170-024-14024-6\u003c/em\u003e\u003c/li\u003e\n\u003cli\u003eT.O. Monastyrska, A.L. Berezina, O.A. Molebny, V. K. Andrii, Effect of alloying with transition metals on the aging of anomalously supersaturated solid solution of Al\u0026ndash;Mg alloys, Appl Nanosci,12(2022) 513\u0026ndash;521. https://doi.org/10.1007/s13204-021-01705-x\u003c/li\u003e\n\u003cli\u003eY. Kissoum, D. E. Mekki, M. Bououdina, E. Sakher, S. Bellucci, Dependence of Fe Doping and Milling on TiO\u003csub\u003e2\u003c/sub\u003e Phase Transformation: Optical and Magnetic Studies, J. Supercond. Nov. Magn, 33(2020) 427\u0026ndash;440. https://doi.org/10.1007/s10948-019-05169-7\u003c/li\u003e\n\u003cli\u003eN. Nasralla, M. Yeganeh, Y. Astuti, S. Piticharoenphun, N. Shahtahmasebi, A. Kompanyb, M. Karimipour, B.G. Mendisd, N.R.J. Pooltone, L. \u0026Scaron;iller, Structural and spectroscopic study of Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles prepared by sol\u0026ndash;gel method, Scientia Iranica F, 20(3) (2013) 1018\u0026ndash;1022. https://doi.org/10.1016/j.scient.2013.05.017\u003c/li\u003e\n\u003cli\u003eJ. Poostforooshan, S. Belbekhouche, V. Olszok, M.F.B. Stodt, M. Simmler, M. Bierwirth, H. Nirschl, J. Kiefer, U. Fritsching, A. P. Weber, Synthesis of Pure and Fe-Doped TiO\u003csub\u003e2\u003c/sub\u003e Nanoparticles via Electrospray-Assisted Flame Spray Pyrolysis for Antimicrobial Applications, ACS Applied Nano Materials, 6(24) (2023) 22660\u0026ndash;22672. https://doi.org/10.1021/acsanm.3c03107\u003c/li\u003e\n\u003cli\u003eL. Lutterotti, Laboratorio Scienza e Tecnologia dei Materiali, Universita di Torino, Corso, 2000.\u003c/li\u003e\n\u003cli\u003eR. A. Young, D. B. Wiles, J. Appl. Cryst. 15(1982) 430-438, https://doi.org/10.1107/S002188988201231X\u003c/li\u003e\n\u003cli\u003eL. C. S\u0026aacute;nchez, A. M. Calle, J. D. Arboleda, J. J. Beltran, C. A. Barrero, J. Osorio \u0026amp; K. Nomura, Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e prepared by mechanical alloying, Hyperfine Interact, 183(2008) 117\u0026ndash;122. https://doi.org/10.1007/s10751-008-9738-1\u003c/li\u003e\n\u003cli\u003eD. Jiang Dong-mei Ph, Pan Xiao-yan, Shi Wang-zhou, Ma Xue-ming Ph. D., Prof. M\u0026ouml;ssbauer study on Fe-doped TiO2 by high-energy ball milling. J. of Shanghai Univ, 10(2006) 161\u0026ndash;164. https://doi.org/10.1007/s11741-006-0035-4\u003c/li\u003e\n\u003cli\u003eL. Zhang, X. Luo, J. D. Zhang, Y.F. Long, X. Xue, B.J. Xu, Kinetic Study on the Crystal Transformation of Fe-Doped TiO\u003csub\u003e2\u003c/sub\u003e via In Situ High-Temperature X-ray Diffraction and Transmission Electron Microscopy, ACS Omega, 6(1) (2021) 965\u0026ndash;975. https://doi.org/10.1021/acsomega.0c05609\u003c/li\u003e\n\u003cli\u003eJ. I. Goldstein, D. E. Newbury, J. R. Michael, N. W.M. Ritchie, J. H. J. Scott, D.C. Joy, Scanning Electron Microscopy and X-ray Microanalysis, Springer, 2018. https://doi.org/10.1007/978-1-4939-6676-9\u003c/li\u003e\n\u003cli\u003eH. Zhang, J.F. Banfield, Understanding polymorphic phase transformation behavior during growth of nanocrystalline aggregates : insights from TiO\u003csub\u003e2\u003c/sub\u003e, J. Phys. Chem. B, 104(15) (2000) 481\u0026ndash;3487. https://doi.org/10.1021/jp000499j\u003c/li\u003e\n\u003cli\u003eN. R. Mathews, M. A. Corte Jacome, Erik R. Morales, J. A. Toledo Antonio, Structural and spectroscopic study of the Fe doped TiO\u003csub\u003e2\u003c/sub\u003e thin films for applications in photocatalysis, Phys. Status Solidi A, 206(15) (2009) S219-S223. https://doi.org/10.1002/pssc.200881319\u003c/li\u003e\n\u003cli\u003eM.M. Rashad, E.M. Elsayed, M.S. Al-Kotb, A.E. Shalan, The structural, optical, magnetic and photocatalytic properties of transition metal ions doped TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles, J. Alloys Compd, 581 (2013) 71-78. https://doi.org/10.1016/j.jallcom.2013.07.041 \u003c/li\u003e\n\u003cli\u003eA. Kotta, S.A. Ansari, N. Parveen, H. Fouad, O. Y. Alothman, U. Khaled, H. K. Seo, S. G. Ansari , Z. A. Ansari,Mechanochemical synthesis of melamine doped TiO2 nanoparticles for dye sensitized solar cells application. J Mater Sci : Mater Electron, 29(2018) 9108\u0026ndash;9116. https://doi.org/10.1007/s10854-018-8938-y\u003c/li\u003e\n\u003cli\u003eK. Durgam, R. Eppa, M.V. Ramana Reddy, J. Sivakumar, R. Sayanna, Effect of metal ions doping on structural, optical properties and photocatalytic activity of anatase TiO\u003csub\u003e2\u003c/sub\u003e thin films, Surface and Interface Analysis, 53(2) (2020) 194-205. https://doi.org/10.1002/sia.6901\u003c/li\u003e\n\u003cli\u003eS. Sakthivel, H. Kisch, Daylight Photocatalysis by Carbon-Modified Titanium Dioxide. Angewandte Chemie International Edition, 42(2003) 4908-4911. http://dx.doi.org/10.1002/anie.200351577\u003c/li\u003e\n\u003cli\u003eZ. Minghua, Y. Jiaguo, C. Bei, Effects of Fe-doping on the photocatalytic activity of mesoporous TiO\u003csub\u003e2\u003c/sub\u003epowders prepared by an ultrasonic method, Journal of Hazardous Materials B137 (2006) 1838\u0026ndash;1847. https://doi.org/10.1016/j.jhazmat.2006.05.028\u003c/li\u003e\n\u003cli\u003eC. Fan , P. Xue , Y. Sun, Preparation of Nano-TiO\u003csub\u003e2\u003c/sub\u003e Doped with Cerium and Its Photocatalytic Activity, Journal of Rare Earths, 24(3) (2006) 309-313. https://doi.org/10.1016/S1002-0721(06)60115-4\u003c/li\u003e\n\u003cli\u003eC. Deiana, M. Minella, G. Tabacchi, V. Maurino, E. Fois, G. Martra, Shape-controlled TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles and TiO\u003csub\u003e2\u003c/sub\u003e P25interacting with CO and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e molecular probes : a synergic approach for surface structure recognition and physico-chemical understanding. Phys. Chem. Chem. Phys. 15(1) (2013) 307\u0026ndash;315. https://doi.org/10.1039/C2CP42381B\u003c/li\u003e\n\u003cli\u003eM. Cernea, C. Valsangiacom, R. Trusca, F. Vasiliu, Synthesis of iron-doped anatase -TiO\u003csub\u003e2\u003c/sub\u003e powders by a particulate sol-gel route, J. Optoelectron. Adv. Mater., 9 (2007) 2648\u0026ndash;2652. See https://www.researchgate.net/publication/235351058\u003c/li\u003e\n\u003cli\u003eI. Ganesh, P.P. Kumar, A.K. Gupta, P.S. Sekhar, K. Radha, G. Padmanabham, G. Sundararajan, Preparation and characterization of Fe-doped TiO\u003csub\u003e2\u003c/sub\u003e powders for solar light response and photocatalytic applications, Processing and Application of Ceramics, 6(1) (2012) 21\u0026ndash;36. https://doi.org/10.2298/PAC1201021G\u003c/li\u003e\n\u003cli\u003eH. Khan, I.K. Swati, Fe\u003csup\u003e3+\u003c/sup\u003e-doped anatase TiO\u003csub\u003e2\u003c/sub\u003e with d\u0026ndash;d transition, oxygen vacancies and Ti3+ centers : synthesis, characterization, UV\u0026ndash;vis photocatalytic and mechanistic studies. Ind. Eng. Chem.Res, 55(23) (2016) 6619\u0026ndash;6633. https://doi.org/10.1021/acs.iecr.6b01104\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Fe-doped TiO2, Mechanical alloying, X-ray diffraction, Rietveld analysis, SEM, FTIR","lastPublishedDoi":"10.21203/rs.3.rs-7059755/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7059755/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eXRD analysis revealed a gradual anatase-to-rutile transformation with milling, with Fe initially segregated and progressively incorporated into the TiO₂ lattice. Anatase–rutile coexistence was observed between 6 and 12 hours, and a full rutile phase appeared after 24-48 hours. Rietveld refinement showed decreasing crystallite size and increasing microstrain, indicating defect accumulation. SEM confirmed particle refinement and agglomeration, while FTIR identified functional groups typical of the TiO\u003csub\u003e2\u003c/sub\u003e phase.\u003c/p\u003e\n\u003cp\u003eNanocrystalline TiO\u003csub\u003e2\u003c/sub\u003e powders doped with 5 wt. % Fe were synthesized using the mechanical alloying (MA) technique, with milling durations ranging from 0 to 48 hours. This study aims to investigate the effect of milling time on the structural, morphological, and optical properties of the synthesized materials. A comprehensive characterization was carried out : X-ray diffraction (XRD) combined with Rietveld refinement using MAUD software was employed to examine phase evolution and crystallite size ; scanning electron microscopy (SEM) was used to analyze particle morphology and agglomeration ; and Fourier-transform infrared spectroscopy (FTIR) was performed to identify chemical bonding and functional groups.\u003c/p\u003e","manuscriptTitle":"Investigation on structural, morphological and optical properties of 5% Fe-doped TiO2 powder nanostructures synthesized by mechanical alloying","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-11 16:46:31","doi":"10.21203/rs.3.rs-7059755/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4a41e9e0-afc3-43ce-8612-f1f5775e14b5","owner":[],"postedDate":"July 11th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-09-13T13:23:04+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-11 16:46:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7059755","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7059755","identity":"rs-7059755","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}