Tailoring Band Gap and Light Absorption in M-TiNT (M= Cu2+, Ni2+, Co2+ and Fe3+) for Water Remediation

Tailoring Band Gap and Light Absorption in M-TiNT (M= Cu2+, Ni2+, Co2+ and Fe3+) for Water Remediation | 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 Tailoring Band Gap and Light Absorption in M-TiNT (M= Cu 2+ , Ni 2+ , Co 2+ and Fe 3+ ) for Water Remediation Melissa Méndez-Galván, César L. Ordoñez-Romero, Hugo A. Lara-García, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7013762/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Oct, 2025 Read the published version in Journal of Nanoparticle Research → Version 1 posted 9 You are reading this latest preprint version Abstract The need for effective wastewater treatment is critical, particularly in light of increasing environmental concerns and the prevalence of persistent organic pollutants. Among the various strategies developed to address this challenge, photocatalysis has emerged as a promising approach due to its potential for sustainable and efficient pollutant degradation. In this context, developing novel photocatalytic materials remains a research priority. In the present study, we explore the simultaneous incorporation of transition metal cations (Cu²⁺, Ni²⁺, Co²⁺, and Fe³⁺) into the crystalline structure of titanate nanotubes (H 2 Ti 3 O 7 , TiNT) via a simple ion-exchange method. This modification also facilitates the formation of an n–p heterostructure between TiNT and the respective metal oxides (CuO, NiO, CoO, and Fe₂O₃). Notably, the incorporation of metal cations results in a significant reduction of the band gap from 3.3 eV to 1.5 eV. At the same time, the formation of n–p heterojunctions contribute to the appearance of a new absorption feature. Together, these modifications effectively extend the light absorption capability of the material into the visible region. The photocatalytic activity of the resulting M-TiNT semiconductors was evaluated for the degradation of ibuprofen and indigo carmine, under UV and visible light irradiation. The observed enhancement in photocatalytic efficiency is directly correlated with improved light absorption and increased charge carrier density, contributing to the generation of reactive redox species. These findings offer valuable insights into the design of nanostructured semiconductors for environmental remediation and highlight the potential of metal-doped TiNTs as efficient and versatile photocatalysts. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Introduction Due to modern human activities, significant quantities of emerging pollutants are continuously discharged into wastewater. These include residues of organic compounds from personal care products, pharmaceuticals, pesticides, and various industrial chemicals.[ 1 , 2 ] Due to the inefficiency of conventional wastewater treatment systems, many of these pollutants are released into natural water bodies, leading to environmental disturbances and adverse effects on aquatic ecosystems.[ 2 – 5 ] Therefore, developing effective wastewater treatment technologies for removing emerging pollutants has become crucial. Among the available strategies, heterogeneous photocatalysis has emerged as one of the most promising approaches for degrading organic contaminants in aqueous environments. This technique offers several advantages: it can target a broad spectrum of pollutants, operates efficiently under solar irradiation, achieves a high degree of pollutant degradation in short times, and allows the complete mineralization of the contaminants.[ 6 – 11 ] The photocatalytic mechanism is triggered when incident light, possessing energy greater than or equal to the semiconductor's bandgap, irradiates the material. This process leads to the excitation of electrons from the valence band to the conduction band, generating electron-hole pairs. These charge carriers can either recombine or migrate to the semiconductor surface, where they participate in redox reactions with adsorbed species.[ 12 ] To enhance the photocatalytic efficiency in the degradation of emerging pollutants, developing and investigating novel materials is an active area of research. Among nanostructured materials based on titanium dioxide (TiO₂), titanate nanotubes (TiNT, H₂Ti₃O₇) have emerged as promising photocatalysts due to their distinctive one-dimensional tubular morphology and lamellar crystalline structure.[ 8 , 13 – 31 ] These structural characteristics provide several advantageous properties, including a high specific surface area, reduced electron-hole recombination rates, preferential pathways for charge carrier transport, and the facility for tuning the optoelectronic properties. Moreover, the photogenerated holes in TiNT exhibit strong oxidizing power, promoting the formation of hydroxyl radicals (•OH), key reactive species in photocatalytic degradation.[ 32 – 34 ] Despite these advantages, the primary limitation of TiNT lies in their wide bandgap energy (3.3 eV), which restricts photoexcitation to the ultraviolet region of the spectrum.[ 34 ] This significantly limits their efficiency under solar irradiation, and focuses on search strategies to extend their light absorption into the visible range. TiNT-based photocatalysts have been extensively studied for environmental remediation, particularly for the degradation of dyes, personal care products, and polycyclic aromatic hydrocarbons (PAHs), including methyl orange, methylene blue, sulfamethazine, amoxicillin, estradiol, and phenanthrene.[ 6 , 7 , 26 , 31 , 35 – 40 ] Per example, Barrocas et al. ,[ 41 ] reported the in-situ hydrothermal synthesis of TiNT doped with cobalt (1% and 5%), demonstrating enhanced photocatalytic activity under UV–vis irradiation for the degradation of phenol, naphthol yellow, and brilliant green. Incorporating cobalt into the TiNT crystalline lattice led to improved degradation efficiencies for individual pollutants and their mixtures. Wen Liu et al .,[ 42 ] reported the synthesis of titanate nanotubes (TiNTs) superficially modified with α-Fe₂O₃ and interstitially doped with Fe³⁺ ions for the simultaneous removal of As(III) and As(V), utilizing the combined effects of photocatalysis and adsorption. In their study, the photocatalytic performance of the Fe-TiNT material was nearly 250 times higher than that of pristine TiNTs. This remarkable enhancement was attributed to the role of interlayer Fe³⁺ ions as temporary electron or hole trapping sites, while the α-Fe₂O₃ acted as a charge carrier, facilitating the transfer of electrons from the TiNT structure. Additionally, Ruey-an Doong et al.,[ 27 ] investigated the UV photocatalytic degradation of bisphenol A (BPA) using a composite system of titanate nanotubes (TiNTs) coupled with TiO₂ and metallic copper nanoparticles. The study found that incorporating 5–10 wt% of copper significantly enhanced the photocatalytic performance, reducing the total reaction time by half compared to the TiNT–TiO₂ system. The improvement in photocatalytic performance was attributed to the addition of copper, which reduces the recombination rate of electron–hole pairs. In this work, we report the photocatalytic performance of TiNT modified with 1 wt.% of various metal cations (Cu²⁺, Ni²⁺, Co²⁺, and Fe³⁺). Physicochemical characterization revealed that a fraction of the metal cations is incorporated into the TiNT lattice, resulting in a bandgap narrowing (ranging from 1.5 eV to 3.1 eV). Concurrently, the remaining metal content is deposited on the TiNT surface as corresponding metal oxides (CuO, NiO, CoO, and Fe₂O₃), forming n-p heterojunctions. These structural and compositional modifications enhance charge carrier density, increase generation of reactive redox species, decrease electron-hole recombination, and improve visible-light absorption. As a result, the modified TiNT exhibits significantly enhanced photocatalytic activity for the degradation of ibuprofen and indigo carmine, underscoring their potential for practical applications in water purification and environmental remediation. Experimental section a) Synthesis of materials Pristine titanate nanotubes (TiNT) were synthesized via a hydrothermal method, following previously reported procedures,[34, 43] 5.0 g of commercial TiO₂ (anatase phase, Sigma-Aldrich) were dispersed in 80 mL of a 10 M NaOH aqueous solution. under continuous magnetic stirring. The resulting suspension was transferred into a Teflon-lined stainless-steel autoclave and heated at 140 °C for 20 h. Afterward, the autoclave was cooled down to room temperature. To achieve the exchange of Na + cations by H + cations, the resulting solid was washed repeatedly with a 0.1 M HCl solution until the pH of the filtrate reached neutral. The final product was dried at 80 °C for 8 h to collect the TiNT material. Metal-modified titanate nanotubes (M–TiNT) were synthesized by the ion-exchange method. In a typical procedure, 0.5 g of previously prepared TiNT was dispersed in 80 mL of distilled water and maintained at 80 °C under continuous stirring. Subsequently, the desired metal nitrate precursor (copper(II) nitrate hemipentahydrate (Cu(NO₃)₂·2.5H₂O), nickel(II) nitrate hexahydrate (Ni(NO₃)₂·6H₂O), cobalt(II) nitrate hexahydrate (Co(NO₃)₂·6H₂O), or iron(III) nitrate nonahydrate (Fe(NO₃)₃·9H₂O), Sigma-Aldrich)) was added to achieve a final metal loading of 1 wt.%. No pH adjustment was made during this process. The final suspension was stirred for 3 h to ensure homogeneous dispersion of the metal species. The resulting solid was filtered, thoroughly washed with distilled water, and dried at 80 °C for 8 h under ambient atmosphere. a) Characterization The crystalline structure of the as-prepared samples was characterized through X-ray diffraction (XRD) using a Bruker D-8 Advance diffractometer equipped with Cu-Kα radiation (λ = 1.5406 Å), a Ni filter (0.5% Cu-Kα) in the secondary beam, and a one-dimensional position-sensitive silicon strip detector (Bruker, Linxeye). Diffraction patterns were collected over a 2θ range of 6° to 60°, with a step size of 0.039° and a counting time of 134.4 seconds per step. Phase identification and quantification were carried out via Rietveld refinement using the BGMN software, with Profex employed as the graphical user interface.[44] High-resolution transmission electron microscopy (HRTEM) was performed using a JEM-2010 FasTem analytical electron microscope to investigate the morphological and structural features of the materials at the nanoscale. Specific surface area and pore size distribution were evaluated using nitrogen adsorption–desorption isotherms at −196 °C, measured with a Quantachrome Autosorb MP-1 instrument. Before analysis, samples were degassed under vacuum at 80 °C for 4 hours. Surface area was determined via the Brunauer–Emmett–Teller (BET) method, while pore size distribution was derived from the desorption branch using the Barrett–Joyner–Halenda (BJH) model. The elemental composition and metal content of the materials were determined by energy-dispersive X-ray spectroscopy (EDS), using a Thermo Noran microanalysis system coupled to a JSM-5600 LV scanning electron microscope (SEM). Micrographs were acquired at an accelerating voltage of 20 kV and a magnification of 500×. X-ray photoelectron spectroscopy (XPS) was employed to assess the chemical composition and oxidation states of surface elements. Measurements were carried out using a SPECS spectrometer equipped with a PHOIBOS 150 WAL hemispherical analyser and an Al Kα X-ray source (hν = 1486.6 eV). Binding energies were calibrated using the C 1s signal at 284.8 eV as an internal reference. Background subtraction was performed using the Shirley method. The optical properties of the samples were analysed by UV–vis diffuse reflectance spectroscopy (DRS) using a Shimadzu UV-2600 spectrophotometer equipped with an integrating sphere (ISR-2600). Spectra were collected in the 200–600 nm wavelength range, with BaSO₄ as the reflectance standard. The absorption spectra were converted using the Kubelka–Munk function, and the optical band gap energy was estimated by plotting (F(R) x hν) 1/2 vs. hν, considering an indirect electronic transition for TiNT.[23, 40, 45, 46] Photoelectrochemical characterization was conducted using an AUTOLAB PGSTAT302N potentiostat-galvanostat, in a conventional three-electrode electrochemical cell configuration. A platinum wire served as the counter electrode, while an Ag/AgCl electrode (0.5 M KCl) was used as the reference. The working electrode was prepared by immobilizing the photocatalyst onto an indium tin oxide (ITO) glass substrate. All measurements were conducted in a 1.0 M NaOH electrolyte solution. Mott-Schottky (MS) analysis was employed to determine the flat band potential (E FB ), calculated from the intercept of the MS plot on the potential axis.[47] The charge carrier density (N D ) was estimated using the equation: N D = 2/𝜀𝜀 0 𝐴 2 • 𝑒 • 𝑚; where e = 1.602 x 10 -19 C; ε = 14,000; 𝜀 0 = 8.8541 x 10 -12 F m -1 ; A 2 = 0.25 cm 2 and m the slope of the C -2 vs V plot. Given that TiNT is an n-type semiconductor,[37, 48, 49] the flat band potential closely approximates the position of the conduction band edge. Quantification of hydroxyl radicals (•OH) was performed using the fluorescence-based terephthalic acid (TA) probe. In this method, the generation of 2-hydroxyterephthalic acid (HTA), which exhibits fluorescence, is used as an indirect indicator of •OH radical formation. A suspension was prepared by dispersing 10 mg of photocatalyst in an aqueous solution containing 0.040 g of terephthalic acid and 0.020 g of NaOH. The mixture was subjected to UV irradiation (254 nm, Pen-Ray lamp) or visible light irradiation (Philips MASTER Colour 70 W, 380–700 nm). Before irradiation, the solution was stirred in the dark for 30 minutes to establish adsorption–desorption equilibrium. Aliquots were collected at 0, 20, 40, and 60 minutes of irradiation, followed by filtration. The fluorescence emission spectra of HTA were recorded using a PerkinElmer LS55 fluorescence spectrophotometer, with an excitation wavelength of 315 nm and emission at 426 nm. a) Photocatalytic tests Photocatalytic activity was evaluated by dispersing 10 mg of the photocatalyst powder in 250 mL of an aqueous solution (0.04 g L -1 ). The temperature of the reactor was constantly maintained at 23° C through recirculating water. The initial concentration of ibuprofen varied depending on the irradiation source: 130 ppm was used for the probes under UV light, while 10 ppm was employed for visible light experimentsTo ensure oxygen saturation in the system, air was continuously bubbled through the suspension at a flow rate of 50 mL · min⁻¹. Before irradiation, the mixture was stirred in the dark for 30 minutes to establish adsorption–desorption equilibrium. The photocatalytic tests were conducted for 5 hours under UV or visible light. UV irradiation was performed using a Pen Ray lamp (254 nm), while visible light irradiation was provided by a PHILIPS MASTER Colour lamp (70 W, 370 – 800 nm). Ibuprofen degradation was monitored by UV–Vis spectroscopy (Thermo Scientific GENESYS 150), measuring the absorbance at 222 nm. Aliquots of 5 mL were collected and filtered at intervals of 0, 1, 2, 3, 4, and 5 hours. Spectral data were acquired over the 200–600 nm range. Kinetic analysis of the degradation process was carried out using a pseudo-first-order kinetic model: ln (C 0 /C i ) = k t.[50]; where C 0 is the initial concentration, C i the concentration at i time and k the reaction constant. Results and discussion The crystalline structure of the as-prepared samples was analyzed by XRD (Figure S1 ). All the samples, including the pristine and the M-TiNT, exhibited identical diffraction patterns corresponding to the H₂Ti₃O₇ phase, as indexed to the JCPDS card No. 75–0393. This phase belongs to the monoclinic crystal system with a C 2/m space group.[ 31 , 51 ] XRD detected no additional crystalline phases. As in our previous research,[ 34 ] Rietveld refinement indicates that after the ion-exchange synthesis, the only parameter that changes is the “a” parameter, which confirms the introduction of the metal cations (Cu²⁺, Ni²⁺, Co²⁺, and Fe³⁺) into the TiNT lamellar structure. High-resolution transmission electron microscopy (HRTEM) was employed to examine the morphology and local crystallinity of the samples. As shown in Fig. 1 a), the TiNT exhibited a multi-walled nanotubular morphology with lengths ranging from 25 nm to 150 nm, outer diameters from 13 nm to 17 nm, and inner diameters of 6 nm to 10 nm. In a previous report the Cu-TiNT sample micrographs have been characterized, and the Fast Fourier Transform (FFT) analysis of the surface nanoparticles revealed lattice fringes characteristic of the monoclinic CuO phase.[ 52 ] Similarly, the HRTEM image of the Fe-TiNT sample (Figure S2c) showed nanoparticles with FFT patterns matching those of Fe₂O₃, which crystallizes in a rhombohedral structure.[ 53 ] In contrast, metal oxide phase identification via HRTEM was inconclusive for the Ni-TiNT and Co-TiNT samples (Figure S2). In the case of Co-TiNT (Figure S2a), a moiré pattern was observed between the nanoparticle and the TiNT support, which hindered FFT indexing. For Ni-TiNT, the interplanar spacings observed in the nanoparticles did not match those of either NiO or metallic Ni, suggesting that the Ni species may be embedded within the nanotube walls. The presence of NiO and CoO was subsequently confirmed by complementary XPS and UV–vis spectroscopy. HRTEM analysis confirmed the presence of metal oxide nanoparticles in close contact with the TiNT matrix, indicating the formation of n–p heterojunctions. This phenomenon has been previously observed in metal oxide-modified TiNT systems prepared via ion-exchange followed by ambient drying.[ 23 , 54 , 55 ] This approach facilitates the intercalation of metal cations into the layered TiNT structure, thereby promoting the formation of metal oxide nanoparticles on the surface.[ 23 , 55 , 56 ] Furthermore, it enables a uniform dispersion of nanoparticles across the nanotube surface.[ 55 – 57 ] In the present study, no additional pH adjustment was made during the ion-exchange process. As a result, the TiNT surface retained a negative charge, which enhanced electrostatic interactions with metal cations in solution. These interactions favoured the adsorption of metal ions and their subsequent incorporation onto or within the TiNT framework The textural properties of the samples were assessed by nitrogen adsorption–desorption isotherms. All materials exhibited type IV isotherms with H3-type hysteresis loops, characteristic of mesoporous structures. The Brunauer–Emmett–Teller (BET) surface areas ranged from 201 to 223 m² · g⁻¹, corresponding to the Ni-TiNT and pristine TiNT samples, respectively.[ 34 ] Pore size distribution analysis, based on the Barrett–Joyner–Halenda (BJH) method, revealed a bimodal distribution, attributed to pores within the nanotube channels as well as interstitial voids between individual nanotubes.[ 57 ] Metal loading in the M-TiNT samples was determined via energy-dispersive X-ray spectroscopy (EDS). The metal contents measured were 0.82, 0.72, 1.06, and 1.32 wt.% for Cu-TiNT, Ni-TiNT, Co-TiNT, and Fe-TiNT, respectively, values close to the nominal target 1.0 wt.%. Additionally, all samples, including the pristine TiNT, retained residual sodium levels below 10 wt.%, indicating that complete Na⁺ exchange was not achieved. The surface chemical composition and bonding structure of the materials were investigated by X-ray photoelectron spectroscopy (XPS). Consistent with energy-dispersive X-ray spectroscopy (EDS) results, the XPS survey spectra (data not shown) confirmed the presence of Ti, O, and Na for the pristine TiNT sample, characteristic peaks were observed at binding energies of 486.6 eV and 530.5 eV, corresponding to Ti 2p and O 1s orbitals, respectively (Figure S3). Deconvolution of the O 1s spectrum revealed three distinct components at 529.4, 529.8, and 531.5 eV, which were assigned to oxygen in Ti–O bonds, surface hydroxyl groups ( – OH), and adsorbed water (H₂O), respectively.[ 57 ] In the modified M-TiNT samples, peaks corresponding to the 2p orbitals of the incorporated metal cations were observed (Figure S4). Specifically, the 2p ₃/₂ peaks appeared at 932.9 eV for Cu²⁺, 855.7 eV for Ni²⁺, and 780.4 eV for Co²⁺, consistent with the presence of divalent metal species.[ 54 , 58 – 64 ] In the case of Fe-TiNT, a prominent peak at 710.7 eV was detected, indicative of trivalent Fe³⁺. 61 In all cases, deconvolution of the 2p ₃/₂ peaks revealed two distinct components along with their corresponding satellite features. One component is attributed to metal cations integrated into the TiNT crystalline lattice, while the other corresponds with surface-deposited metal oxide nanoparticles. These findings are consistent with previous studies,[ 34 , 52 , 65 ] where the metal cations in M-TiNT systems are distributed in two distinct chemical environments. The optical properties of the materials were investigated using UV–vis diffuse reflectance spectroscopy (DRS).[ 34 ] Pristine TiNT displayed an absorption edge near 380 nm and a pronounced absorption peak around 270 nm, in agreement with literature reports, confirming its predominant absorption in the UV region.[ 31 , 36 , 41 , 57 , 66 ] In contrast, M-TiNT samples exhibited a noticeable redshift in the absorption edge, indicating enhanced absorption in the visible range. This redshift varied from approximately 400 nm in Cu-TiNT to around 600 nm in Fe-TiNT. The shift is attributed to the incorporation of 3d transition metal orbitals into the TiNT band structure, which facilitates charge transfer between the TiNT conduction band and the d-electrons of the metal cations.[ 40 , 41 , 67 ] Additional absorption bands associated with the metal oxide nanoparticles were also observed. For example, Cu-TiNT showed a broad absorption band centred near 600 nm, characteristic of CuO nanoparticles, consistent with HRTEM findings.[ 52 , 68 – 71 ] Ni-TiNT presented a distinct absorption peak around 490 nm, attributed to NiO nanoparticles, 68 while Co-TiNT exhibited a signal starting at ~ 500 nm, corresponding to CoO. [ 68 – 71 ] Consistent with the XPS results. In the case of Fe-TiNT, the absorption spectrum of Fe₂O₃ overlapped with that of TiNT, as Fe₂O₃ exhibits absorption from ~ 400 nm up to a maximum near 500 nm.[ 42 , 72 – 75 ] These combined absorption features further support the formation of n–p heterostructures between TiNT and the respective metal oxides (Fig. 2 ). The optical band gaps were determined using Tauc plots based on the equation: (αhν) = A(ν – E g ) ½ [ 76 , 77 ] assuming an indirect electronic transition for TiNT.[ 23 , 40 , 45 , 46 ] Band gap energies were extracted from the linear portions of the (αhν)¹ᐟ² vs. photon energy (E) plots. Pristine TiNT exhibited a band gap of 3.3 eV, consistent with previous studies indicating UV-range excitation. In comparison, the metal-modified TiNTs showed reduced band gaps: 3.1 eV (Cu-TiNT), 2.8 eV (Ni-TiNT), 2.4 eV (Co-TiNT), and 1.5 eV (Fe-TiNT), enabling effective photoactivation under visible light. These findings are in line with prior density functional theory (DFT) calculations,[ 34 ] which suggest that the incorporation of partially oxidized metal cations (M δ+ ) introduces intermediate energy levels into the TiNT band structure, thereby narrowing the band gap. Electrochemical characterization was carried out to estimate the flat band potential E FB of the synthesized semiconductor materials. Mott–Schottky (M–S) analysis (Fig. 3 ) revealed a positive slope typical of an n-type semiconductor in all cases. This behavior is consistent with the TiNT phase,[ 31 ] which constitutes the predominant component of the M-TiNT heterostructures. Consequently, the flat band potential values determined for these systems can be assumed to be close to their respective conduction bands. The flat band potentials (E FB ) of all samples are summarized in Table 1 . For Cu-TiNT, Co-TiNT, and Fe-TiNT, a shift of the E FB toward more negative potentials was observed, with values of − 1.33 V, − 1.33 V, and − 1.50 V (vs. Ag/AgCl), respectively, compared to − 1.17 V (vs. Ag/AgCl) for pristine TiNT. In contrast, the Ni-TiNT sample exhibited a more positive flat band potential of − 1.00 V (vs. Ag/AgCl). These results indicate that no clear trend in E FB shifts can be established across the different metal-modified TiNT samples. Based on the experimentally determined flat band potentials and optical band gap energies, the conduction band (CB) and valence band (VB) edges positions of each material were estimated (Fig. 4 and Table 1 ). The analysis reveals that modifying TiNT with transition metals induces only modest shifts in the conduction band position. Among the M-TiNT materials, Fe-TiNT exhibits the most negative conduction band potential, enhancing its reducing power, whereas Ni-TiNT shows the least negative conduction band potential. In contrast, more pronounced variations were observed in the valence band positions. Notably, Fe-TiNT displays the lowest VB potential, approaching 0.0 V versus Ag/AgCl, which is approximately 2.0 V lower than pristine TiNT. This substantial shift indicates a marked reduction in the oxidative potential of photogenerated holes. Conversely, Ni-TiNT exhibits the most positive VB potential, corresponding to an enhanced oxidative strength of photogenerated holes in this system. These variations in band edge positions reflect the significant influence of transition metal incorporation and the potential formation of n–p heterojunctions on the electronic structure of TiNT. The modified band alignment directly affects the redox potential of photogenerated charge carriers, thereby modulating the photocatalytic activity of the materials by either enhancing or constraining their oxidative and reductive capabilities. In addition, the charge carrier density (N D ) was calculated from the Mott–Schottky plots (Table 1 ). The results indicate that all M-TiNT samples exhibit one to two orders of magnitude higher carrier densities than those of the pristine TiNT. This increase in N D is attributed to the synergistic effects of metal cation incorporation into the TiNT lattice and the formation of heterojunctions, both of which enhance charge carrier mobility and facilitate more efficient electron and hole injection. Furthermore, the n–p heterostructure configuration effectively suppresses electron–hole recombination, as previously evidenced by fluorescence spectroscopy, [ 34 ] thereby improving the efficiency of interfacial charge transfer processes. Table 1 Flat band potential and charge carriers’ density of the as-prepared samples. Sample Flat band potential (V vs Ag/AgCl) Band gap (eV) Charge carriers’ density (cm − 3 ) TiNT -1.17 3.3 4.20 E + 20 Cu- TiNT -1.33 3.1 8.40 E + 21 Ni- TiNT -1.00 2.8 1.30 E + 22 Co- TiNT -1.33 2.4 4.20 E + 21 Fe- TiNT -1.50 1.5 1.26 E + 22 To quantify hydroxyl radical (•OH) generation, photoluminescence (PL) assays using 2-hydroxyterephthalic acid (2-HTA) were conducted under both UV and visible light irradiation (Figs. 5 and S5). Under UV illumination (Fig. 5 ), all materials showed detectable 2-HTA formation as early as 20 minutes, with fluorescence intensity increasing linearly over time, indicating progressive •OH accumulation within the matrix. Among the tested samples, M-TiNT exhibited enhanced •OH generation, with Cu-TiNT showing the highest activity and pristine TiNT the lowest. Under visible light irradiation (Figure S5), 2-HTA formation was detected exclusively in the M-TiNT materials, the pristine TiNT exhibited no measurable fluorescence, indicating negligible •OH radical generation. This enhanced activity is attributed to the narrowed bandgap of M-TiNT, which facilitates the formation of electron–hole pairs under lower-energy visible light, thereby promoting •OH production. Table 2 Formation rate of ⦁OH radicals by the as-prepared samples, under UV and visible light. Sample UV Visible TiNT 7.4 0.0 Cu- TiNT 12.2 9.0 Ni- TiNT 8.9 8.8 Co- TiNT 10.6 8.8 Fe- TiNT 11.1 8.3 The photocatalytic degradation of ibuprofen under UV irradiation was investigated using a 130 ppm aqueous solution at neutral pH. Before the photocatalytic experiments, the adsorption behavior of the photocatalysts was assessed. The absorbance spectra of ibuprofen remained stable for over 5 hours (data not shown), indicating negligible adsorption of the model molecule onto the photocatalyst surfaces in the absence of light. Photolytic degradation reached a maximum of approximately 30% after 5 hours of UV exposure. Figure 6 displays a representative UV–Vis spectrum of ibuprofen degradation using the Co-TiNT photocatalyst. A noticeable decrease in the intensity of the absorption peak at 222 nm, characteristic of ibuprofen, was observed, confirming its degradation. Additionally, a secondary absorption band emerged at approximately 264 nm, attributed to the formation of degradation byproducts, such as 2-(4-isobutylphenyl)acetaldehyde (IBAF).[ 78 – 82 ] This peak increased in intensity during the first 3 hours of reaction and subsequently declined, suggesting concurrent degradation of both ibuprofen and its intermediate byproducts. [ 78 , 81 ] The degradation of ibuprofen under UV irradiation is shown in Fig. 7 . Introducing the pristine photocatalyst (TiNT) led to nearly twice the ibuprofen decomposition compared to photolysis alone. This enhancement is attributed to the ability of TiNT to promote the generation of hydroxyl radicals (•OH), which are known to drive oxidative degradation processes.[ 80 ] Further improvement was observed with M-TiNT semiconductors, achieving a maximum degradation efficiency of 83% with the Co-TiNT sample. This significant enhancement is attributed to a synergistic effect arising from the incorporation of metal cations and the presence of transition metal nanoparticles. These modifications facilitate electron scavenging,[ 83 ] suppressing electron–hole recombination, improving charge carrier separation and availability, and ultimately promoting more efficient •OH radical formation, as previously demonstrated. Figure 8 shows the kinetic analysis of ibuprofen degradation during the first three hours of UV irradiation. A pseudo-first-order kinetic model was applied for this evaluation. The results, summarized in Table 3 , indicate that the Cu-TiNT exhibited the highest degradation rate constant (0.38 h⁻¹), representing a 65% increase compared to the pristine TiNT photocatalyst (0.23 h⁻¹). The Co-TiNT and Fe-TiNT photocatalysts showed similar rate constants of 0.36 h⁻¹, outperforming the unmodified material. As expected, the pristine TiNT displayed the lowest degradation rate among the tested semiconductors. These results demonstrate that the Cu-TiNT photocatalyst exhibits the most rapid reaction kinetics in addition to achieving high ibuprofen removal efficiency. This superior performance is consistent with the enhanced •OH radical generation previously observed for this material under UV light irradiation. In the ibuprofen degradation assessed under visible light irradiation, the concentration of the probe molecule remained unchanged during the adsorption and photolysis tests (data not shown), indicating that neither adsorption nor direct photolysis contributed significantly to its removal. Figure S6 presents a representative UV–Vis spectrum of ibuprofen degradation using the Co-TiNT photocatalyst. A reduction in the absorbance intensity at 222 nm, characteristic of ibuprofen, was observed. Notably, no additional absorption bands associated with degradation byproducts were detected, suggesting limited formation or rapid degradation of intermediates under these conditions. The analysis of the ibuprofen degradation vs. time (Figure S7; Table 3 ) revealed that only the M-TiNT materials could decompose the contaminant molecule, with the Cu-TiNT sample achieving the highest degradation efficiency (37%). Figure S8 shows the pseudo-first-order kinetic fitting of the degradation data during the first three hours under visible light irradiation. Among the tested materials, Cu-TiNT exhibited the highest rate constant (0.13 h⁻¹). This enhanced performance is attributed to the superior ability of Cu-TiNT to generate •OH radicals under visible light irradiation. As observed under UV light, the pristine TiNT photocatalyst exhibited the lowest activity (rate constant = 0.00 h⁻¹), confirming that this material requires UV activation for photocatalytic functionality. Table 3 Ibuprofen degradation (%) and reaction rate constant under UV and visible light. Sample UV (%) R 2 k (h − 1 ) Vis (%) R 2 k (h − 1 ) Photolysis 30 - - 0 - - TiNT 62 0.99 0.23 0 0.96 0.00 Cu- TiNT 80 0.99 0.38 37 0.99 0.13 Ni- TiNT 72 0.99 0.29 16 0.96 0.02 Co- TiNT 83 0.99 0.36 33 0.97 0.12 Fe- TiNT 78 0.99 0.36 30 0.92 0.06 To further evaluate the photocatalytic performance of M-TiNT under visible light, the degradation of indigo carmine (IC), a model organic dye, was investigated. A 5 ppm aqueous solution of IC was prepared, and the experimental conditions were kept consistent with those used for the IB degradation tests under visible light. IC degradation was monitored by measuring the absorbance intensity at 610 nm, corresponding to the characteristic peak of IC. In control experiments with the pristine photocatalyst, no significant change in the absorption spectra was observed during either the adsorption or photolysis stages, confirming the inactivity of this material under visible light. Figure 9 shows a representative spectrum of IC degradation using the Ni-TiNT photocatalyst under visible light. An apparent reduction in the 610 nm peak intensity was observed, indicating successful degradation. Notably, the absence of an isosbestic point at 251 nm suggests direct mineralization of the dye, rather than the accumulation of intermediate degradation products. The time-dependent degradation profile (Figure S9) revealed that only the M-TiNT photocatalysts were effective in decomposing IC. Among them, the Ni-TiNT material showed the highest degradation efficiency, followed closely by Cu-TiNT (Table 4 ). Kinetic analysis using a pseudo-first-order model shows the ibuprofen degradation during the first three hours of UV irradiation. (Fig. 10 ) Kinetic analysis confirmed that Ni-TiNT and Cu-TiNT exhibited the fastest decomposition rates with a rate constant of 0.14 h⁻¹, highlighting their superior activity for IC degradation under visible light. Table 4 Indigo carmine degradation (%) and reaction rate constant under visible light. Sample Degradation IC (%) R 2 k (h − 1 ) Photolysis 0 - - TiNT 0 0.802 0.004 Cu- TiNT 49 0.999 0.140 Ni- TiNT 62 0.998 0.143 Co- TiNT 15 0.987 0.064 Fe- TiNT 10 0.950 0.014 Conclusions The results of the photocatalytic tests under both UV and visible light demonstrate that the dual modification of the pristine TiNT significantly enhances its photocatalytic activity. This improvement is primarily attributed to two key factors: (i) the incorporation of 3d energy states from transition metal cations into the bandgap, effectively narrowing the bandgap energy, and (ii) the formation of n–p heterojunctions. Collectively, these structural modifications enhance the visible-light responsiveness of the semiconductors and facilitate the formation of electron traps, which suppress the direct recombination of electron–hole pairs, thereby increasing charge carrier density and promoting the formation of reactive species involved in redox processes. The Cu-TiNT exhibited the most outstanding performance under UV and visible light among the tested photocatalysts. It achieved the highest degradation efficiencies and fastest reaction rates for ibuprofen and indigo carmine. This superior activity is attributed to the synergistic effect of copper ion incorporation and the formation of a heterojunction with CuO, which collectively results in the most efficient generation of hydroxyl radicals (•OH) among all evaluated materials. In summary, this study offers a first comprehensive insight into the photocatalytic behavior of M-TiNT under dual light conditions for the degradation of two model organic pollutants, ibuprofen and indigo carmine. These findings suggest the promising potential of M-TiNT photocatalysts for developing highly efficient systems for environmental remediation. Future work should optimize the synthesis parameters, evaluate photocatalytic performance under diverse environmental conditions, and explore cost-effective, scalable production methods. Ultimately, using such materials may lead to more sustainable and environmentally friendly solutions for wastewater treatment. Declarations Conflicts of interest There are no conflicts to declare. Author Contribution M. M.G. Investigation, Synthesis, Writing–Original DraftC.L O.R. Investigation, Review and Editing.H.A. L.G Data curation, Supervision, Writing–Review and Editing.G.D Conceptualization, Supervision, Writing–Review and Editing. 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Ordoñez-Romero","email":"","orcid":"","institution":"Universidad Nacional Autónoma de México","correspondingAuthor":false,"prefix":"","firstName":"César","middleName":"L.","lastName":"Ordoñez-Romero","suffix":""},{"id":488743297,"identity":"30e9312a-b002-400d-ba8c-04376de41a4b","order_by":2,"name":"Hugo A. Lara-García","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/UlEQVRIiWNgGAWjYBACAzBZAMTsjQ8OQLnEaAGRPIcNSNUikUyMeiAwl0i/+IDBwC6ff+ZjxoM/CuzkGSRyD366wbAtsQGHFssZOcUGDAbJljNuJzMc5jFINmyQyEuWzmG4bYzTYTdy0iQYDJgNGG7nHzjMYHCAsUEixwCkRY6AlnoD+ZuHGQ7+MDhgD9Ri/BuohQe3lvRjQC2HDQxuMDMc4DE4kAjUYobfljNvmA0SDI4bGJ6B+CW5jeeNmXWOAR6/HE9/+OBDRbWB3PHDzB9//LGz7WfPMb6dU3EbZ4gBo9CAIQGZzwYxCqd6IGB/gE92FIyCUTAKRgEDAwCgLFN7uAOZDgAAAABJRU5ErkJggg==","orcid":"","institution":"Universidad Nacional Autónoma de México","correspondingAuthor":true,"prefix":"","firstName":"Hugo","middleName":"A.","lastName":"Lara-García","suffix":""},{"id":488743298,"identity":"cdb550de-1109-4e03-a52a-57375e230cb5","order_by":3,"name":"Gabriela Díaz","email":"","orcid":"","institution":"Universidad Nacional Autónoma de México","correspondingAuthor":false,"prefix":"","firstName":"Gabriela","middleName":"","lastName":"Díaz","suffix":""}],"badges":[],"createdAt":"2025-06-30 19:38:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7013762/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7013762/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11051-025-06453-5","type":"published","date":"2025-10-06T15:57:45+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":87592019,"identity":"aa6244da-206d-4381-b21f-e273fc58998a","added_by":"auto","created_at":"2025-07-25 15:00:32","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":531081,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative HRTEM image of the TiNT and Fe-TiNT with FFT for the Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e indexation.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7013762/v1/c9f0d85c681049b7458c0081.png"},{"id":87590909,"identity":"b198e768-4626-4ad3-a718-f13e36310a9a","added_by":"auto","created_at":"2025-07-25 14:52:32","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":175739,"visible":true,"origin":"","legend":"\u003cp\u003eAbsorbance spectra and in the inset Tauc analysis of as-prepared M-TiNT materials.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7013762/v1/f34e235202c0aeb360128b87.png"},{"id":87592671,"identity":"80fd5b93-2477-4209-80d6-7d504e0fab25","added_by":"auto","created_at":"2025-07-25 15:08:32","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":230134,"visible":true,"origin":"","legend":"\u003cp\u003eMott–Schottky plots exhibiting a positive slope, characteristic of n-type semiconductors, recorded in a 1.0 M NaOH electrolyte solution.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7013762/v1/90ec36c0c08249bf9171bf9a.png"},{"id":87590913,"identity":"e4543807-1a18-447a-8615-f32c8405906b","added_by":"auto","created_at":"2025-07-25 14:52:32","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":168706,"visible":true,"origin":"","legend":"\u003cp\u003eEstimation of the conduction and valence band positions of the photocatalyst estimated using the bandgap energy derived from Tauc analysis and the flat-band potential obtained from Mott–Schottky analysis.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7013762/v1/b8b8ee8fb3e0c2b2885d8c7f.png"},{"id":87592023,"identity":"f1c342fc-c6e3-4e55-bdb4-9cbfa263d64f","added_by":"auto","created_at":"2025-07-25 15:00:32","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":174268,"visible":true,"origin":"","legend":"\u003cp\u003ePL intensity variation using 2-hydroxyterephthalic acid (2-HTA) to indirectly quantify \u0026nbsp;•OH radical concentration, recorded for pristine and modified TiNT samples under UV irradiation.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7013762/v1/e6c39b000c56a6cfeca9904e.png"},{"id":87590914,"identity":"26eb667e-c2ff-43df-b71a-bc997fae861b","added_by":"auto","created_at":"2025-07-25 14:52:32","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":121837,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative ibuprofen degradation after five hours of UV irradiation using Co-TiNT as the photocatalyst.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7013762/v1/754f5127356343c9cf0b128a.png"},{"id":87590922,"identity":"8fc283ea-2fb7-450d-912f-c32ad9a8cf05","added_by":"auto","created_at":"2025-07-25 14:52:32","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":176165,"visible":true,"origin":"","legend":"\u003cp\u003eTime-dependent ibuprofen degradation under UV light using both pristine and modified TiNT photocatalysts.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-7013762/v1/4c454c26399953d3fc8c9ed1.png"},{"id":87592024,"identity":"5e08323b-66c6-4e3f-b625-63d925377023","added_by":"auto","created_at":"2025-07-25 15:00:32","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":150593,"visible":true,"origin":"","legend":"\u003cp\u003ePseudo first-order kinetics of the ibuprofen degradation under UV-light using both pristine and modified TiNT photocatalysts.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-7013762/v1/d009c0f74c365c78bd9ad9e0.png"},{"id":87590940,"identity":"da71dac2-0bab-4ee0-a4dd-d910b0a2e8d6","added_by":"auto","created_at":"2025-07-25 14:52:33","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":71467,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative IC degradation after five hours of visible irradiation using Ni-TiNT as the photocatalyst.\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-7013762/v1/b16778e5c0f7c1b829d7b57c.png"},{"id":87592028,"identity":"f83ea85e-144a-49cf-9a07-abbdf0ed6382","added_by":"auto","created_at":"2025-07-25 15:00:32","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":147187,"visible":true,"origin":"","legend":"\u003cp\u003ePseudo first-order kinetics of the indigo carmine degradation under visible light using both pristine and modified TiNT photocatalysts.\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-7013762/v1/48ff0855b6e0587c1247f4b0.png"},{"id":93597860,"identity":"a6aed067-dfcf-4641-afe0-f8bbf9b4373d","added_by":"auto","created_at":"2025-10-15 14:24:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2658016,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7013762/v1/0d0d7a86-ac4c-4e0f-ae74-6bcdee9db4d0.pdf"},{"id":87592022,"identity":"6b962bd6-52cf-4281-a687-99543f2c9cb7","added_by":"auto","created_at":"2025-07-25 15:00:32","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":1300558,"visible":true,"origin":"","legend":"","description":"","filename":"InformacionsuppTailoringBandGapandLightAbsorptioninMTiNTMCu2Ni2Co2andFe3forWaterRemediation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7013762/v1/1897f53d86e75e3222401c95.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eTailoring Band Gap and Light Absorption in M-TiNT (M= Cu\u003csup\u003e2+\u003c/sup\u003e, Ni\u003csup\u003e2+\u003c/sup\u003e, Co\u003csup\u003e2+\u003c/sup\u003e and Fe\u003csup\u003e3+\u003c/sup\u003e) for Water Remediation\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eDue to modern human activities, significant quantities of emerging pollutants are continuously discharged into wastewater. These include residues of organic compounds from personal care products, pharmaceuticals, pesticides, and various industrial chemicals.[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] Due to the inefficiency of conventional wastewater treatment systems, many of these pollutants are released into natural water bodies, leading to environmental disturbances and adverse effects on aquatic ecosystems.[\u003cspan additionalcitationids=\"CR3 CR4\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] Therefore, developing effective wastewater treatment technologies for removing emerging pollutants has become crucial. Among the available strategies, heterogeneous photocatalysis has emerged as one of the most promising approaches for degrading organic contaminants in aqueous environments. This technique offers several advantages: it can target a broad spectrum of pollutants, operates efficiently under solar irradiation, achieves a high degree of pollutant degradation in short times, and allows the complete mineralization of the contaminants.[\u003cspan additionalcitationids=\"CR7 CR8 CR9 CR10\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] The photocatalytic mechanism is triggered when incident light, possessing energy greater than or equal to the semiconductor's bandgap, irradiates the material. This process leads to the excitation of electrons from the valence band to the conduction band, generating electron-hole pairs. These charge carriers can either recombine or migrate to the semiconductor surface, where they participate in redox reactions with adsorbed species.[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] To enhance the photocatalytic efficiency in the degradation of emerging pollutants, developing and investigating novel materials is an active area of research. Among nanostructured materials based on titanium dioxide (TiO₂), titanate nanotubes (TiNT, H₂Ti₃O₇) have emerged as promising photocatalysts due to their distinctive one-dimensional tubular morphology and lamellar crystalline structure.[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan additionalcitationids=\"CR14 CR15 CR16 CR17 CR18 CR19 CR20 CR21 CR22 CR23 CR24 CR25 CR26 CR27 CR28 CR29 CR30\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] These structural characteristics provide several advantageous properties, including a high specific surface area, reduced electron-hole recombination rates, preferential pathways for charge carrier transport, and the facility for tuning the optoelectronic properties. Moreover, the photogenerated holes in TiNT exhibit strong oxidizing power, promoting the formation of hydroxyl radicals (\u0026bull;OH), key reactive species in photocatalytic degradation.[\u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] Despite these advantages, the primary limitation of TiNT lies in their wide bandgap energy (3.3 eV), which restricts photoexcitation to the ultraviolet region of the spectrum.[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] This significantly limits their efficiency under solar irradiation, and focuses on search strategies to extend their light absorption into the visible range. TiNT-based photocatalysts have been extensively studied for environmental remediation, particularly for the degradation of dyes, personal care products, and polycyclic aromatic hydrocarbons (PAHs), including methyl orange, methylene blue, sulfamethazine, amoxicillin, estradiol, and phenanthrene.[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan additionalcitationids=\"CR36 CR37 CR38 CR39\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e] Per example, Barrocas \u003cem\u003eet al.\u003c/em\u003e,[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e] reported the \u003cem\u003ein-situ\u003c/em\u003e hydrothermal synthesis of TiNT doped with cobalt (1% and 5%), demonstrating enhanced photocatalytic activity under UV\u0026ndash;vis irradiation for the degradation of phenol, naphthol yellow, and brilliant green. Incorporating cobalt into the TiNT crystalline lattice led to improved degradation efficiencies for individual pollutants and their mixtures. Wen Liu \u003cem\u003eet al\u003c/em\u003e.,[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] reported the synthesis of titanate nanotubes (TiNTs) superficially modified with α-Fe₂O₃ and interstitially doped with Fe\u0026sup3;⁺ ions for the simultaneous removal of As(III) and As(V), utilizing the combined effects of photocatalysis and adsorption. In their study, the photocatalytic performance of the Fe-TiNT material was nearly 250 times higher than that of pristine TiNTs. This remarkable enhancement was attributed to the role of interlayer Fe\u0026sup3;⁺ ions as temporary electron or hole trapping sites, while the α-Fe₂O₃ acted as a charge carrier, facilitating the transfer of electrons from the TiNT structure. Additionally, Ruey-an Doong et al.,[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] investigated the UV photocatalytic degradation of bisphenol A (BPA) using a composite system of titanate nanotubes (TiNTs) coupled with TiO₂ and metallic copper nanoparticles. The study found that incorporating 5\u0026ndash;10 wt% of copper significantly enhanced the photocatalytic performance, reducing the total reaction time by half compared to the TiNT\u0026ndash;TiO₂ system. The improvement in photocatalytic performance was attributed to the addition of copper, which reduces the recombination rate of electron\u0026ndash;hole pairs.\u003c/p\u003e\u003cp\u003eIn this work, we report the photocatalytic performance of TiNT modified with 1 wt.% of various metal cations (Cu\u0026sup2;⁺, Ni\u0026sup2;⁺, Co\u0026sup2;⁺, and Fe\u0026sup3;⁺). Physicochemical characterization revealed that a fraction of the metal cations is incorporated into the TiNT lattice, resulting in a bandgap narrowing (ranging from 1.5 eV to 3.1 eV). Concurrently, the remaining metal content is deposited on the TiNT surface as corresponding metal oxides (CuO, NiO, CoO, and Fe₂O₃), forming n-p heterojunctions. These structural and compositional modifications enhance charge carrier density, increase generation of reactive redox species, decrease electron-hole recombination, and improve visible-light absorption. As a result, the modified TiNT exhibits significantly enhanced photocatalytic activity for the degradation of ibuprofen and indigo carmine, underscoring their potential for practical applications in water purification and environmental remediation.\u003c/p\u003e"},{"header":"Experimental section","content":"\u003cp\u003ea) Synthesis of materials\u003c/p\u003e\n\u003cp\u003ePristine titanate nanotubes (TiNT) were synthesized via a hydrothermal method, following previously reported procedures,[34, 43]\u0026nbsp; 5.0 g of commercial TiO₂ (anatase phase, Sigma-Aldrich) were dispersed in 80 mL of a 10 M NaOH aqueous solution. under continuous magnetic stirring. The resulting suspension was transferred into a Teflon-lined stainless-steel autoclave and heated at 140 \u0026deg;C for 20 h. Afterward, the autoclave was cooled down to room temperature. \u0026nbsp;To achieve the exchange of Na\u003csup\u003e+\u003c/sup\u003e cations by H\u003csup\u003e+\u003c/sup\u003e cations, the resulting solid was washed repeatedly with a 0.1 M HCl solution until the pH of the filtrate reached neutral. The final product was dried at 80 \u0026deg;C for 8 h to collect the TiNT material.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMetal-modified titanate nanotubes (M\u0026ndash;TiNT) were synthesized by the ion-exchange method. In a typical procedure, 0.5 g of previously prepared TiNT was dispersed in 80 mL of distilled water and maintained at 80 \u0026deg;C under continuous stirring. Subsequently, the desired metal nitrate precursor (copper(II) nitrate hemipentahydrate (Cu(NO₃)₂\u0026middot;2.5H₂O), nickel(II) nitrate hexahydrate (Ni(NO₃)₂\u0026middot;6H₂O), cobalt(II) nitrate hexahydrate (Co(NO₃)₂\u0026middot;6H₂O), or iron(III) nitrate nonahydrate (Fe(NO₃)₃\u0026middot;9H₂O), \u0026nbsp;Sigma-Aldrich)) was added to achieve a final metal loading of 1 wt.%. No pH adjustment was made during this process. The final suspension was stirred for 3 h to ensure homogeneous dispersion of the metal species. The resulting solid was filtered, thoroughly washed with distilled water, and dried at 80 \u0026deg;C for 8 h under ambient atmosphere.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea) \u0026nbsp; \u0026nbsp; Characterization\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe crystalline structure of the as-prepared samples was characterized through X-ray diffraction (XRD) using a Bruker D-8 Advance diffractometer equipped with Cu-K\u0026alpha; radiation (\u0026lambda; = 1.5406 \u0026Aring;), a Ni filter (0.5% Cu-K\u0026alpha;) in the secondary beam, and a one-dimensional position-sensitive silicon strip detector (Bruker, Linxeye). Diffraction patterns were collected over a 2\u0026theta; range of 6\u0026deg; to 60\u0026deg;, with a step size of 0.039\u0026deg; and a counting time of 134.4 seconds per step. Phase identification and quantification were carried out via Rietveld refinement using the BGMN software, with Profex employed as the graphical user interface.[44] \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHigh-resolution transmission electron microscopy (HRTEM) was performed using a JEM-2010 FasTem analytical electron microscope to investigate the morphological and structural features of the materials at the nanoscale. Specific surface area and pore size distribution were evaluated using nitrogen adsorption\u0026ndash;desorption isotherms at \u0026minus;196 \u0026deg;C, measured with a Quantachrome Autosorb MP-1 instrument. Before analysis, samples were degassed under vacuum at 80 \u0026deg;C for 4 hours. Surface area was determined via the Brunauer\u0026ndash;Emmett\u0026ndash;Teller (BET) method, while pore size distribution was derived from the desorption branch using the Barrett\u0026ndash;Joyner\u0026ndash;Halenda (BJH) model. The elemental composition and metal content of the materials were determined by energy-dispersive X-ray spectroscopy (EDS), using a Thermo Noran microanalysis system coupled to a JSM-5600 LV scanning electron microscope (SEM). Micrographs were acquired at an accelerating voltage of 20 kV and a magnification of 500\u0026times;. X-ray photoelectron spectroscopy (XPS) was employed to assess the chemical composition and oxidation states of surface elements. Measurements were carried out using a SPECS spectrometer equipped with a PHOIBOS 150 WAL hemispherical analyser and an Al K\u0026alpha; X-ray source (h\u0026nu; = 1486.6 eV). Binding energies were calibrated using the C 1s signal at 284.8 eV as an internal reference. Background subtraction was performed using the Shirley method.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe optical properties of the samples were analysed by UV\u0026ndash;vis diffuse reflectance spectroscopy (DRS) using a Shimadzu UV-2600 spectrophotometer equipped with an integrating sphere (ISR-2600). Spectra were collected in the 200\u0026ndash;600 nm wavelength range, with BaSO₄ as the reflectance standard. The absorption spectra were converted using the Kubelka\u0026ndash;Munk function, and the optical band gap energy was estimated by plotting (F(R) x h\u0026nu;)\u003csup\u003e1/2\u003c/sup\u003e vs. h\u0026nu;, considering an indirect electronic transition for TiNT.[23, 40, 45, 46]\u003c/p\u003e\n\u003cp\u003ePhotoelectrochemical characterization was conducted using an AUTOLAB PGSTAT302N potentiostat-galvanostat, in a conventional three-electrode electrochemical cell configuration. A platinum wire served as the counter electrode, while an Ag/AgCl electrode (0.5 M KCl) was used as the reference. The working electrode was prepared by immobilizing the photocatalyst onto an indium tin oxide (ITO) glass substrate. All measurements were conducted in a 1.0 M NaOH electrolyte solution. Mott-Schottky (MS) analysis was employed to determine the flat band potential (E\u003csub\u003eFB\u003c/sub\u003e), calculated from the intercept of the MS plot on the potential axis.[47] The charge carrier density (N\u003csub\u003eD\u003c/sub\u003e) was estimated using the equation: N\u003csub\u003eD\u003c/sub\u003e = 2/𝜀𝜀\u003csub\u003e0\u003c/sub\u003e𝐴\u003csup\u003e2\u003c/sup\u003e \u0026bull;\u0026nbsp;𝑒\u0026nbsp;\u0026bull;\u0026nbsp;𝑚; where \u003cem\u003ee\u003c/em\u003e = 1.602 x 10\u003csup\u003e-19\u003c/sup\u003e C; \u0026epsilon; = 14,000;\u0026nbsp;𝜀\u003csub\u003e0\u003c/sub\u003e = 8.8541 x 10\u003csup\u003e-12\u003c/sup\u003e F m\u003csup\u003e-1\u003c/sup\u003e; A\u003csup\u003e2\u003c/sup\u003e = 0.25 cm\u003csup\u003e2\u003c/sup\u003e and \u003cem\u003em\u003c/em\u003e the slope of the C\u003csup\u003e-2\u003c/sup\u003e vs V plot. Given that TiNT is an n-type semiconductor,[37, 48, 49] the flat band potential closely approximates the position of the conduction band edge.\u003c/p\u003e\n\u003cp\u003eQuantification of hydroxyl radicals (\u0026bull;OH) was performed using the fluorescence-based terephthalic acid (TA) probe. In this method, the generation of 2-hydroxyterephthalic acid (HTA), which exhibits fluorescence, is used as an indirect indicator of \u0026bull;OH radical formation. A suspension was prepared by dispersing 10 mg of photocatalyst in an aqueous solution containing 0.040 g of terephthalic acid and 0.020 g of NaOH. The mixture was subjected to UV irradiation (254 nm, Pen-Ray lamp) or visible light irradiation (Philips MASTER Colour 70 W, 380\u0026ndash;700 nm). Before irradiation, the solution was stirred in the dark for 30 minutes to establish adsorption\u0026ndash;desorption equilibrium. Aliquots were collected at 0, 20, 40, and 60 minutes of irradiation, followed by filtration. The fluorescence emission spectra of HTA were recorded using a PerkinElmer LS55 fluorescence spectrophotometer, with an excitation wavelength of 315 nm and emission at 426 nm.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea)\u0026nbsp; \u0026nbsp; \u0026nbsp;Photocatalytic tests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePhotocatalytic activity was evaluated by dispersing 10 mg of the photocatalyst powder in 250 mL of an aqueous solution (0.04 g L\u003csup\u003e-1\u003c/sup\u003e). The temperature of the reactor was constantly maintained at 23\u0026deg; C through recirculating water. The initial concentration of ibuprofen varied depending on the irradiation source: 130 ppm was used for the probes under UV light, while 10 ppm was employed for visible light experimentsTo ensure oxygen saturation in the system, air was continuously bubbled through the suspension at a flow rate of 50 mL \u0026middot; min⁻\u0026sup1;. Before irradiation, the mixture was stirred in the dark for 30 minutes to establish adsorption\u0026ndash;desorption equilibrium. The photocatalytic tests were conducted for 5 hours under UV or visible light. UV irradiation was performed using a Pen Ray lamp (254 nm), while visible light irradiation was provided by a PHILIPS MASTER Colour lamp (70 W, 370 \u0026ndash; 800 nm). Ibuprofen degradation was monitored by UV\u0026ndash;Vis spectroscopy (Thermo Scientific GENESYS 150), measuring the absorbance at 222 nm. Aliquots of 5 mL were collected and filtered at intervals of 0, 1, 2, 3, 4, and 5 hours. Spectral data were acquired over the 200\u0026ndash;600 nm range.\u003c/p\u003e\n\u003cp\u003eKinetic analysis of the degradation process was carried out using a pseudo-first-order kinetic model: ln (C\u003csub\u003e0\u003c/sub\u003e/C\u003csub\u003ei\u003c/sub\u003e) = \u003cem\u003ek\u003c/em\u003et.[50]; where C\u003csub\u003e0\u003c/sub\u003e is the initial concentration, C\u003csub\u003ei\u0026nbsp;\u003c/sub\u003ethe concentration at i time and \u003cem\u003ek\u003c/em\u003e the reaction constant.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eThe crystalline structure of the as-prepared samples was analyzed by XRD (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). All the samples, including the pristine and the M-TiNT, exhibited identical diffraction patterns corresponding to the H₂Ti₃O₇ phase, as indexed to the JCPDS card No. 75\u0026ndash;0393. This phase belongs to the monoclinic crystal system with a C\u003csub\u003e2/m\u003c/sub\u003e space group.[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e] XRD detected no additional crystalline phases. As in our previous research,[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] Rietveld refinement indicates that after the ion-exchange synthesis, the only parameter that changes is the \u0026ldquo;a\u0026rdquo; parameter, which confirms the introduction of the metal cations (Cu\u0026sup2;⁺, Ni\u0026sup2;⁺, Co\u0026sup2;⁺, and Fe\u0026sup3;⁺) into the TiNT lamellar structure.\u003c/p\u003e\u003cp\u003eHigh-resolution transmission electron microscopy (HRTEM) was employed to examine the morphology and local crystallinity of the samples. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea), the TiNT exhibited a multi-walled nanotubular morphology with lengths ranging from 25 nm to 150 nm, outer diameters from 13 nm to 17 nm, and inner diameters of 6 nm to 10 nm. In a previous report the Cu-TiNT sample micrographs have been characterized, and the Fast Fourier Transform (FFT) analysis of the surface nanoparticles revealed lattice fringes characteristic of the monoclinic CuO phase.[\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e] Similarly, the HRTEM image of the Fe-TiNT sample (Figure S2c) showed nanoparticles with FFT patterns matching those of Fe₂O₃, which crystallizes in a rhombohedral structure.[\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e] In contrast, metal oxide phase identification via HRTEM was inconclusive for the Ni-TiNT and Co-TiNT samples (Figure S2). In the case of Co-TiNT (Figure S2a), a moir\u0026eacute; pattern was observed between the nanoparticle and the TiNT support, which hindered FFT indexing. For Ni-TiNT, the interplanar spacings observed in the nanoparticles did not match those of either NiO or metallic Ni, suggesting that the Ni species may be embedded within the nanotube walls. The presence of NiO and CoO was subsequently confirmed by complementary XPS and UV\u0026ndash;vis spectroscopy. HRTEM analysis confirmed the presence of metal oxide nanoparticles in close contact with the TiNT matrix, indicating the formation of n\u0026ndash;p heterojunctions. This phenomenon has been previously observed in metal oxide-modified TiNT systems prepared via ion-exchange followed by ambient drying.[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e, \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e] This approach facilitates the intercalation of metal cations into the layered TiNT structure, thereby promoting the formation of metal oxide nanoparticles on the surface.[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e] Furthermore, it enables a uniform dispersion of nanoparticles across the nanotube surface.[\u003cspan additionalcitationids=\"CR56\" citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e] In the present study, no additional pH adjustment was made during the ion-exchange process. As a result, the TiNT surface retained a negative charge, which enhanced electrostatic interactions with metal cations in solution. These interactions favoured the adsorption of metal ions and their subsequent incorporation onto or within the TiNT framework\u003c/p\u003e\u003cp\u003eThe textural properties of the samples were assessed by nitrogen adsorption\u0026ndash;desorption isotherms. All materials exhibited type IV isotherms with H3-type hysteresis loops, characteristic of mesoporous structures. The Brunauer\u0026ndash;Emmett\u0026ndash;Teller (BET) surface areas ranged from 201 to 223 m\u0026sup2; \u0026middot; g⁻\u0026sup1;, corresponding to the Ni-TiNT and pristine TiNT samples, respectively.[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] Pore size distribution analysis, based on the Barrett\u0026ndash;Joyner\u0026ndash;Halenda (BJH) method, revealed a bimodal distribution, attributed to pores within the nanotube channels as well as interstitial voids between individual nanotubes.[\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e]\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eMetal loading in the M-TiNT samples was determined via energy-dispersive X-ray spectroscopy (EDS). The metal contents measured were 0.82, 0.72, 1.06, and 1.32 wt.% for Cu-TiNT, Ni-TiNT, Co-TiNT, and Fe-TiNT, respectively, values close to the nominal target 1.0 wt.%. Additionally, all samples, including the pristine TiNT, retained residual sodium levels below 10 wt.%, indicating that complete Na⁺ exchange was not achieved.\u003c/p\u003e\u003cp\u003eThe surface chemical composition and bonding structure of the materials were investigated by X-ray photoelectron spectroscopy (XPS). Consistent with energy-dispersive X-ray spectroscopy (EDS) results, the XPS survey spectra (data not shown) confirmed the presence of Ti, O, and Na for the pristine TiNT sample, characteristic peaks were observed at binding energies of 486.6 eV and 530.5 eV, corresponding to Ti 2p and O 1s orbitals, respectively (Figure S3). Deconvolution of the O 1s spectrum revealed three distinct components at 529.4, 529.8, and 531.5 eV, which were assigned to oxygen in Ti\u0026ndash;O bonds, surface hydroxyl groups (\u003csup\u003e\u0026ndash;\u003c/sup\u003eOH), and adsorbed water (H₂O), respectively.[\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e] In the modified M-TiNT samples, peaks corresponding to the 2p orbitals of the incorporated metal cations were observed (Figure S4). Specifically, the 2p\u003csub\u003e₃/₂\u003c/sub\u003e peaks appeared at 932.9 eV for Cu\u0026sup2;⁺, 855.7 eV for Ni\u0026sup2;⁺, and 780.4 eV for Co\u0026sup2;⁺, consistent with the presence of divalent metal species.[\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e, \u003cspan additionalcitationids=\"CR59 CR60 CR61 CR62 CR63\" citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e] In the case of Fe-TiNT, a prominent peak at 710.7 eV was detected, indicative of trivalent Fe\u0026sup3;⁺.\u003csup\u003e61\u003c/sup\u003e In all cases, deconvolution of the 2p\u003csub\u003e₃/₂\u003c/sub\u003e peaks revealed two distinct components along with their corresponding satellite features. One component is attributed to metal cations integrated into the TiNT crystalline lattice, while the other corresponds with surface-deposited metal oxide nanoparticles. These findings are consistent with previous studies,[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e, \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e] where the metal cations in M-TiNT systems are distributed in two distinct chemical environments.\u003c/p\u003e\u003cp\u003eThe optical properties of the materials were investigated using UV\u0026ndash;vis diffuse reflectance spectroscopy (DRS).[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] Pristine TiNT displayed an absorption edge near 380 nm and a pronounced absorption peak around 270 nm, in agreement with literature reports, confirming its predominant absorption in the UV region.[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e, \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e]\u003c/p\u003e\u003cp\u003eIn contrast, M-TiNT samples exhibited a noticeable redshift in the absorption edge, indicating enhanced absorption in the visible range. This redshift varied from approximately 400 nm in Cu-TiNT to around 600 nm in Fe-TiNT. The shift is attributed to the incorporation of 3d transition metal orbitals into the TiNT band structure, which facilitates charge transfer between the TiNT conduction band and the d-electrons of the metal cations.[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e] Additional absorption bands associated with the metal oxide nanoparticles were also observed. For example, Cu-TiNT showed a broad absorption band centred near 600 nm, characteristic of CuO nanoparticles, consistent with HRTEM findings.[\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e, \u003cspan additionalcitationids=\"CR69 CR70\" citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e] Ni-TiNT presented a distinct absorption peak around 490 nm, attributed to NiO nanoparticles, \u003csup\u003e68\u003c/sup\u003e while Co-TiNT exhibited a signal starting at ~\u0026thinsp;500 nm, corresponding to CoO. [\u003cspan additionalcitationids=\"CR69 CR70\" citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e] Consistent with the XPS results. In the case of Fe-TiNT, the absorption spectrum of Fe₂O₃ overlapped with that of TiNT, as Fe₂O₃ exhibits absorption from ~\u0026thinsp;400 nm up to a maximum near 500 nm.[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan additionalcitationids=\"CR73 CR74\" citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e] These combined absorption features further support the formation of n\u0026ndash;p heterostructures between TiNT and the respective metal oxides (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The optical band gaps were determined using Tauc plots based on the equation: (αhν)\u0026thinsp;=\u0026thinsp;A(ν \u0026ndash; E\u003csub\u003eg\u003c/sub\u003e)\u003csup\u003e\u0026frac12;\u003c/sup\u003e[\u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e, \u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e77\u003c/span\u003e] assuming an indirect electronic transition for TiNT.[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] Band gap energies were extracted from the linear portions of the (αhν)\u0026sup1;ᐟ\u0026sup2; vs. photon energy (E) plots. Pristine TiNT exhibited a band gap of 3.3 eV, consistent with previous studies indicating UV-range excitation. In comparison, the metal-modified TiNTs showed reduced band gaps: 3.1 eV (Cu-TiNT), 2.8 eV (Ni-TiNT), 2.4 eV (Co-TiNT), and 1.5 eV (Fe-TiNT), enabling effective photoactivation under visible light. These findings are in line with prior density functional theory (DFT) calculations,[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] which suggest that the incorporation of partially oxidized metal cations (M\u003csup\u003eδ+\u003c/sup\u003e) introduces intermediate energy levels into the TiNT band structure, thereby narrowing the band gap.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eElectrochemical characterization was carried out to estimate the flat band potential E\u003csub\u003eFB\u003c/sub\u003e of the synthesized semiconductor materials. Mott\u0026ndash;Schottky (M\u0026ndash;S) analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) revealed a positive slope typical of an n-type semiconductor in all cases. This behavior is consistent with the TiNT phase,[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] which constitutes the predominant component of the M-TiNT heterostructures. Consequently, the flat band potential values determined for these systems can be assumed to be close to their respective conduction bands.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe flat band potentials (E\u003csub\u003eFB\u003c/sub\u003e) of all samples are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. For Cu-TiNT, Co-TiNT, and Fe-TiNT, a shift of the E\u003csub\u003eFB\u003c/sub\u003e toward more negative potentials was observed, with values of \u0026minus;\u0026thinsp;1.33 V, \u0026minus;\u0026thinsp;1.33 V, and \u0026minus;\u0026thinsp;1.50 V (vs. Ag/AgCl), respectively, compared to \u0026minus;\u0026thinsp;1.17 V (vs. Ag/AgCl) for pristine TiNT. In contrast, the Ni-TiNT sample exhibited a more positive flat band potential of \u0026minus;\u0026thinsp;1.00 V (vs. Ag/AgCl). These results indicate that no clear trend in E\u003csub\u003eFB\u003c/sub\u003e shifts can be established across the different metal-modified TiNT samples.\u003c/p\u003e\u003cp\u003eBased on the experimentally determined flat band potentials and optical band gap energies, the conduction band (CB) and valence band (VB) edges positions of each material were estimated (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The analysis reveals that modifying TiNT with transition metals induces only modest shifts in the conduction band position. Among the M-TiNT materials, Fe-TiNT exhibits the most negative conduction band potential, enhancing its reducing power, whereas Ni-TiNT shows the least negative conduction band potential. In contrast, more pronounced variations were observed in the valence band positions. Notably, Fe-TiNT displays the lowest VB potential, approaching 0.0 V versus Ag/AgCl, which is approximately 2.0 V lower than pristine TiNT. This substantial shift indicates a marked reduction in the oxidative potential of photogenerated holes. Conversely, Ni-TiNT exhibits the most positive VB potential, corresponding to an enhanced oxidative strength of photogenerated holes in this system.\u003c/p\u003e\u003cp\u003eThese variations in band edge positions reflect the significant influence of transition metal incorporation and the potential formation of n\u0026ndash;p heterojunctions on the electronic structure of TiNT. The modified band alignment directly affects the redox potential of photogenerated charge carriers, thereby modulating the photocatalytic activity of the materials by either enhancing or constraining their oxidative and reductive capabilities.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn addition, the charge carrier density (N\u003csub\u003eD\u003c/sub\u003e) was calculated from the Mott\u0026ndash;Schottky plots (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The results indicate that all M-TiNT samples exhibit one to two orders of magnitude higher carrier densities than those of the pristine TiNT. This increase in N\u003csub\u003eD\u003c/sub\u003e is attributed to the synergistic effects of metal cation incorporation into the TiNT lattice and the formation of heterojunctions, both of which enhance charge carrier mobility and facilitate more efficient electron and hole injection. Furthermore, the n\u0026ndash;p heterostructure configuration effectively suppresses electron\u0026ndash;hole recombination, as previously evidenced by fluorescence spectroscopy, [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] thereby improving the efficiency of interfacial charge transfer processes.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eFlat band potential and charge carriers\u0026rsquo; density of the as-prepared samples.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFlat band potential\u003c/p\u003e\u003cp\u003e(V vs Ag/AgCl)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eBand gap\u003c/p\u003e\u003cp\u003e(eV)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCharge carriers\u0026rsquo; density (cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-1.17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4.20 E\u0026thinsp;+\u0026thinsp;20\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCu- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-1.33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e8.40 E\u0026thinsp;+\u0026thinsp;21\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNi- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-1.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.30 E\u0026thinsp;+\u0026thinsp;22\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-1.33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4.20 E\u0026thinsp;+\u0026thinsp;21\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFe- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-1.50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.26 E\u0026thinsp;+\u0026thinsp;22\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eTo quantify hydroxyl radical (\u0026bull;OH) generation, photoluminescence (PL) assays using 2-hydroxyterephthalic acid (2-HTA) were conducted under both UV and visible light irradiation (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e and S5). Under UV illumination (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), all materials showed detectable 2-HTA formation as early as 20 minutes, with fluorescence intensity increasing linearly over time, indicating progressive \u0026bull;OH accumulation within the matrix. Among the tested samples, M-TiNT exhibited enhanced \u0026bull;OH generation, with Cu-TiNT showing the highest activity and pristine TiNT the lowest. Under visible light irradiation (Figure S5), 2-HTA formation was detected exclusively in the M-TiNT materials, the pristine TiNT exhibited no measurable fluorescence, indicating negligible \u0026bull;OH radical generation. This enhanced activity is attributed to the narrowed bandgap of M-TiNT, which facilitates the formation of electron\u0026ndash;hole pairs under lower-energy visible light, thereby promoting \u0026bull;OH production.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eFormation rate of ⦁OH radicals by the as-prepared samples, under UV and visible light.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eUV\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eVisible\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e7.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCu- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e12.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e9.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNi- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e8.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e8.8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e10.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e8.8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFe- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e11.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e8.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe photocatalytic degradation of ibuprofen under UV irradiation was investigated using a 130 ppm aqueous solution at neutral pH. Before the photocatalytic experiments, the adsorption behavior of the photocatalysts was assessed. The absorbance spectra of ibuprofen remained stable for over 5 hours (data not shown), indicating negligible adsorption of the model molecule onto the photocatalyst surfaces in the absence of light.\u003c/p\u003e\u003cp\u003ePhotolytic degradation reached a maximum of approximately 30% after 5 hours of UV exposure. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e displays a representative UV\u0026ndash;Vis spectrum of ibuprofen degradation using the Co-TiNT photocatalyst. A noticeable decrease in the intensity of the absorption peak at 222 nm, characteristic of ibuprofen, was observed, confirming its degradation. Additionally, a secondary absorption band emerged at approximately 264 nm, attributed to the formation of degradation byproducts, such as 2-(4-isobutylphenyl)acetaldehyde (IBAF).[\u003cspan additionalcitationids=\"CR79 CR80 CR81\" citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e82\u003c/span\u003e] This peak increased in intensity during the first 3 hours of reaction and subsequently declined, suggesting concurrent degradation of both ibuprofen and its intermediate byproducts. [\u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e, \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e81\u003c/span\u003e]\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe degradation of ibuprofen under UV irradiation is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. Introducing the pristine photocatalyst (TiNT) led to nearly twice the ibuprofen decomposition compared to photolysis alone. This enhancement is attributed to the ability of TiNT to promote the generation of hydroxyl radicals (\u0026bull;OH), which are known to drive oxidative degradation processes.[\u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e80\u003c/span\u003e] Further improvement was observed with M-TiNT semiconductors, achieving a maximum degradation efficiency of 83% with the Co-TiNT sample. This significant enhancement is attributed to a synergistic effect arising from the incorporation of metal cations and the presence of transition metal nanoparticles. These modifications facilitate electron scavenging,[\u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e83\u003c/span\u003e] suppressing electron\u0026ndash;hole recombination, improving charge carrier separation and availability, and ultimately promoting more efficient \u0026bull;OH radical formation, as previously demonstrated.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows the kinetic analysis of ibuprofen degradation during the first three hours of UV irradiation. A pseudo-first-order kinetic model was applied for this evaluation. The results, summarized in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, indicate that the Cu-TiNT exhibited the highest degradation rate constant (0.38 h⁻\u0026sup1;), representing a 65% increase compared to the pristine TiNT photocatalyst (0.23 h⁻\u0026sup1;). The Co-TiNT and Fe-TiNT photocatalysts showed similar rate constants of 0.36 h⁻\u0026sup1;, outperforming the unmodified material. As expected, the pristine TiNT displayed the lowest degradation rate among the tested semiconductors. These results demonstrate that the Cu-TiNT photocatalyst exhibits the most rapid reaction kinetics in addition to achieving high ibuprofen removal efficiency. This superior performance is consistent with the enhanced \u0026bull;OH radical generation previously observed for this material under UV light irradiation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn the ibuprofen degradation assessed under visible light irradiation, the concentration of the probe molecule remained unchanged during the adsorption and photolysis tests (data not shown), indicating that neither adsorption nor direct photolysis contributed significantly to its removal. Figure S6 presents a representative UV\u0026ndash;Vis spectrum of ibuprofen degradation using the Co-TiNT photocatalyst. A reduction in the absorbance intensity at 222 nm, characteristic of ibuprofen, was observed. Notably, no additional absorption bands associated with degradation byproducts were detected, suggesting limited formation or rapid degradation of intermediates under these conditions. The analysis of the ibuprofen degradation vs. time (Figure S7; Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) revealed that only the M-TiNT materials could decompose the contaminant molecule, with the Cu-TiNT sample achieving the highest degradation efficiency (37%). Figure S8 shows the pseudo-first-order kinetic fitting of the degradation data during the first three hours under visible light irradiation. Among the tested materials, Cu-TiNT exhibited the highest rate constant (0.13 h⁻\u0026sup1;). This enhanced performance is attributed to the superior ability of Cu-TiNT to generate \u0026bull;OH radicals under visible light irradiation. As observed under UV light, the pristine TiNT photocatalyst exhibited the lowest activity (rate constant\u0026thinsp;=\u0026thinsp;0.00 h⁻\u0026sup1;), confirming that this material requires UV activation for photocatalytic functionality.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eIbuprofen degradation (%) and reaction rate constant under UV and visible light.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"7\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eUV\u003c/p\u003e\u003cp\u003e(%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003ek (h\u003c/em\u003e\u003csup\u003e\u003cem\u003e\u0026minus;\u0026thinsp;1\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e)\u003c/em\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eVis\u003c/p\u003e\u003cp\u003e(%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cem\u003ek (h\u003c/em\u003e\u003csup\u003e\u003cem\u003e\u0026minus;\u0026thinsp;1\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e)\u003c/em\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePhotolysis\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e62\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.99\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.00\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCu- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.99\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e37\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.99\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.13\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNi- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e72\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.99\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.02\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e83\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.99\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.97\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.12\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFe- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e78\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.99\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.92\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.06\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eTo further evaluate the photocatalytic performance of M-TiNT under visible light, the degradation of indigo carmine (IC), a model organic dye, was investigated. A 5 ppm aqueous solution of IC was prepared, and the experimental conditions were kept consistent with those used for the IB degradation tests under visible light. IC degradation was monitored by measuring the absorbance intensity at 610 nm, corresponding to the characteristic peak of IC. In control experiments with the pristine photocatalyst, no significant change in the absorption spectra was observed during either the adsorption or photolysis stages, confirming the inactivity of this material under visible light. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e shows a representative spectrum of IC degradation using the Ni-TiNT photocatalyst under visible light. An apparent reduction in the 610 nm peak intensity was observed, indicating successful degradation. Notably, the absence of an isosbestic point at 251 nm suggests direct mineralization of the dye, rather than the accumulation of intermediate degradation products. The time-dependent degradation profile (Figure S9) revealed that only the M-TiNT photocatalysts were effective in decomposing IC. Among them, the Ni-TiNT material showed the highest degradation efficiency, followed closely by Cu-TiNT (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Kinetic analysis using a pseudo-first-order model shows the ibuprofen degradation during the first three hours of UV irradiation. (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e) Kinetic analysis confirmed that Ni-TiNT and Cu-TiNT exhibited the fastest decomposition rates with a rate constant of 0.14 h⁻\u0026sup1;, highlighting their superior activity for IC degradation under visible light.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eIndigo carmine degradation (%) and reaction rate constant under visible light.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDegradation IC (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003ek (h\u003c/em\u003e\u003csup\u003e\u003cem\u003e\u0026minus;\u0026thinsp;1\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e)\u003c/em\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePhotolysis\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.802\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.004\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCu- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.999\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.140\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNi- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e62\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.998\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.143\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.987\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.064\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFe- TiNT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.950\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.014\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe results of the photocatalytic tests under both UV and visible light demonstrate that the dual modification of the pristine TiNT significantly enhances its photocatalytic activity. This improvement is primarily attributed to two key factors: (i) the incorporation of 3d energy states from transition metal cations into the bandgap, effectively narrowing the bandgap energy, and (ii) the formation of n\u0026ndash;p heterojunctions. Collectively, these structural modifications enhance the visible-light responsiveness of the semiconductors and facilitate the formation of electron traps, which suppress the direct recombination of electron\u0026ndash;hole pairs, thereby increasing charge carrier density and promoting the formation of reactive species involved in redox processes.\u003c/p\u003e\u003cp\u003eThe Cu-TiNT exhibited the most outstanding performance under UV and visible light among the tested photocatalysts. It achieved the highest degradation efficiencies and fastest reaction rates for ibuprofen and indigo carmine. This superior activity is attributed to the synergistic effect of copper ion incorporation and the formation of a heterojunction with CuO, which collectively results in the most efficient generation of hydroxyl radicals (\u0026bull;OH) among all evaluated materials. In summary, this study offers a first comprehensive insight into the photocatalytic behavior of M-TiNT under dual light conditions for the degradation of two model organic pollutants, ibuprofen and indigo carmine. These findings suggest the promising potential of M-TiNT photocatalysts for developing highly efficient systems for environmental remediation. Future work should optimize the synthesis parameters, evaluate photocatalytic performance under diverse environmental conditions, and explore cost-effective, scalable production methods. Ultimately, using such materials may lead to more sustainable and environmentally friendly solutions for wastewater treatment.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eConflicts of interest\u003c/h2\u003e\u003cp\u003eThere are no conflicts to declare.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eM. M.G. Investigation, Synthesis, Writing\u0026ndash;Original DraftC.L O.R. Investigation, Review and Editing.H.A. L.G Data curation, Supervision, Writing\u0026ndash;Review and Editing.G.D Conceptualization, Supervision, Writing\u0026ndash;Review and Editing.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eA. Gomez- Cort\u0026eacute;s for technical support, A. Morales for XRD diffraction patterns, S. Tehuacanero-Cuapa and R. 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Among the various strategies developed to address this challenge, photocatalysis has emerged as a promising approach due to its potential for sustainable and efficient pollutant degradation. In this context, developing novel photocatalytic materials remains a research priority. In the present study, we explore the simultaneous incorporation of transition metal cations (Cu\u0026sup2;⁺, Ni\u0026sup2;⁺, Co\u0026sup2;⁺, and Fe\u0026sup3;⁺) into the crystalline structure of titanate nanotubes (H\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e, TiNT) via a simple ion-exchange method. This modification also facilitates the formation of an n\u0026ndash;p heterostructure between TiNT and the respective metal oxides (CuO, NiO, CoO, and Fe₂O₃). Notably, the incorporation of metal cations results in a significant reduction of the band gap from 3.3 eV to 1.5 eV. At the same time, the formation of n\u0026ndash;p heterojunctions contribute to the appearance of a new absorption feature. Together, these modifications effectively extend the light absorption capability of the material into the visible region. The photocatalytic activity of the resulting M-TiNT semiconductors was evaluated for the degradation of ibuprofen and indigo carmine, under UV and visible light irradiation. The observed enhancement in photocatalytic efficiency is directly correlated with improved light absorption and increased charge carrier density, contributing to the generation of reactive redox species. These findings offer valuable insights into the design of nanostructured semiconductors for environmental remediation and highlight the potential of metal-doped TiNTs as efficient and versatile photocatalysts.\u003c/p\u003e","manuscriptTitle":"Tailoring Band Gap and Light Absorption in M-TiNT (M= Cu2+, Ni2+, Co2+ and Fe3+) for Water Remediation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-25 14:52:27","doi":"10.21203/rs.3.rs-7013762/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-04T09:46:12+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-02T18:14:58+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-31T19:59:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"27727176912846683498310810622782006245","date":"2025-07-21T17:49:16+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"172267559673286972935339229411454228625","date":"2025-07-21T17:25:09+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-21T17:03:43+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-04T20:42:19+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-01T23:36:03+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Nanoparticle Research","date":"2025-06-30T19:30:03+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-nanoparticle-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"nano","sideBox":"Learn more about [Journal of Nanoparticle Research](http://link.springer.com/journal/11051)","snPcode":"11051","submissionUrl":"https://submission.nature.com/new-submission/11051/3","title":"Journal of Nanoparticle Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"86e3b2bf-2e8f-447f-8434-57975f64f0f6","owner":[],"postedDate":"July 25th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-13T16:04:08+00:00","versionOfRecord":{"articleIdentity":"rs-7013762","link":"https://doi.org/10.1007/s11051-025-06453-5","journal":{"identity":"journal-of-nanoparticle-research","isVorOnly":false,"title":"Journal of Nanoparticle Research"},"publishedOn":"2025-10-06 15:57:45","publishedOnDateReadable":"October 6th, 2025"},"versionCreatedAt":"2025-07-25 14:52:27","video":"","vorDoi":"10.1007/s11051-025-06453-5","vorDoiUrl":"https://doi.org/10.1007/s11051-025-06453-5","workflowStages":[]},"version":"v1","identity":"rs-7013762","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7013762","identity":"rs-7013762","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}