Topotactic Engineering of High-Entropy (Oxy)hydroxide Nanotubes for Enhanced Photocatalysis

Topotactic Engineering of High-Entropy (Oxy)hydroxide Nanotubes for Enhanced Photocatalysis | 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 Article Topotactic Engineering of High-Entropy (Oxy)hydroxide Nanotubes for Enhanced Photocatalysis Sarahi Pacheco-Espinoza, María Ángeles Hernández-Pérez, Alejandro Iván Cuesta-Balderas, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8419535/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 19 Mar, 2026 Read the published version in Scientific Reports → Version 1 posted 12 You are reading this latest preprint version Abstract This study introduces a novel method for synthesizing Ce-Co-Ni-Al-Ga high-entropy (oxy)hydroxide (CeCoNiAlGa HE-OOH) nanotubes via a topotactic transformation using multiwalled carbon nanotubes (MWCNTs) as the parent crystal. CeCoNiAlGa HE-OOHs nanotubes are arranged in concentric cylinders, with high crystalline order, analogous to parent MWCNTs. CeCoNiAlGa HE-OOH nanotubes exhibit a fluorite-like crystalline structure that is supported by a distorted Ce-O framework. A neutral M-OH-M sheet stacking, resembling a partially dehydrated brucite-like layered hydroxide structure, appears to account for the multiwalled configuration of CeCoNiAlGa HE-OOH nanotubes. The fluorite-like structured CeCoNiAlGa HE-OOH (111) planes grow topotactically on the curved C (002) planes. Both the multiwalled arrangement and the stability of the fluorite-like structure are preserved from 80 to 500 ºC. CeCoNiAlGa HE-OOHs exhibit remarkably high concentration of O vacancies. Increasing the heat-treatment temperature leads to gradual dehydroxylation, indicating that HEOOHs are direct structural precursors of HEOs. Notably, the CeCoNiAlGa HE-OOHs obtained at 80 ºC have the highest OH content. They stand out for their remarkable photocatalytic activity under UV light, achieving 96% degradation of ciprofloxacin (CIP) within 45 min. The significant CIP photodegradation is attributed to the synergistic effect of abundant OH species along with O vacancies. Physical sciences/Chemistry Physical sciences/Materials science Physical sciences/Nanoscience and technology High-entropy materials Topotactic transformation Nanostructured catalysts Environmental photocatalysis Ciprofloxacin photodegradation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction In recent years, high-entropy oxides (HEOs) have emerged as promising candidates for advanced energy storage and catalytic applications. [ 1 – 5 ] The synergistic effects arising from their multiple cations enable the tailoring of physicochemical properties to meet the demands of the application. [ 6 ] So far, a considerable number of important studies have shown that HEOs crystallize into a single-phase and highly symmetric crystal structure, for example, rock salt (Co 0.2 Cu 0.2 Mg 0.2 Ni 0.2 Zn 0.2 )O, spinel (Co 0.2 Cr 0.2 Fe 0.2 Mn 0.2 Ni 0.2 ) 3 O 4 , perovskite Ba(Zr 0.2 Sn 0.2 Ti 0.2 Hf 0.2 Nb 0.2 )O 3 , and fluorite (Ce 0.2 La 0.2 Pr 0.2 Sm 0.2 Y 0.2 )O 2−δ types. [ 7 – 10 ] Closely related, HE-OOHs also signify a rapidly advancing area of research with significant potential in electrocatalytic applications. Albeit an evolving area, well-defined structural patterns for HE-OOHs are primarily recognized as orthorhombic, tetragonal, and octahedral layered stacks. [ 11 – 12 ] Additionally, significant efforts have been devoted to developing synthesis methods to expand the functionalities of HEOs, leading to nanostructured HEOs in the form of nanoparticles, nanofibers, and porous structures. [ 13 – 20 ] However, HEO nanotubes have been rarely achieved despite their promising benefits of enhanced surface area and exposure of desirable crystallographic planes. [ 21 , 22 ] Traditional synthesis methods for HEOs and HE-OOHs, although well-established and yielding high-quality results, still restrict the precise control of morphology and nanostructure features. [ 23 ] Furthermore, research delving into technologies that operate beyond the common compositions of HEOs, exploring innovative designs and functionalities, is even scarcer. The topotactic transformation offers an attractive route for achieving highly desirable structures. The topotactic transformation is a solid-state transformation where a parent crystal converts into a pseudomorph, maintaining its crystallographic orientation and morphology. [ 24 ] Inspired by our previous investigations concerning CeO 2−δ nanotubes, the current research explores the feasibility of generating novel CeCoNiAlGa HE-OOH multiwalled nanotube structures. [ 25 ] This is accomplished via topotactic transformation utilizing MWCNTs as the parent crystal. Single-phase HE-OOHs incorporating the unprecedented combination of Ce-Co-Ni-Al-Ga cations have not been previously reported, and their properties remain unexplored. This novel combination is intended to leverage the Ce 3+ /Ce 4+ , Co 2+ /Co 3+ , Ni 2+ /Ni 3+ redox couple activity, Ce ability for fluorite-structure stabilization, synergistic catalytic effects of Co-Ni, and the potential for structural/electronic promotion of Al-Ga. We demonstrate the application of CeCoNiAlGa HE-OOH nanotubes as a catalyst for the CIP photodegradation. The unique characteristics of CeCoNiAlGa HE-OOH nanotubes synthesized via the topotactic method highlight the critical synergistic interaction between OH species and O vacancies, which is highly desirable for photocatalysis. Results and Discussion Figure 1 a depicts typical XRD patterns of f-MWCNTs and topotactically grown products (OHNTs). Table 1 presents a summary of sample identification. The XRD pattern of f -MWCNTs shows distinctive diffraction peaks of the graphite structure at 2θ = 26.06° and 43.60° (JCPDS 041-1487). Besides the small C (002) peak, the XRD patterns of OHNTs exhibit broad peaks close to those of the CeO 2 cubic fluorite structure (JCPDS 34–0394). Although OHNTs do not adopt the ideal cubic fluorite symmetry, the peak proximity suggests a distorted Ce-O framework that is derivative of the fluorite structure. The C (002) and OHNTs (111) peaks were analyzed by deconvolution analysis. Figure 1 b shows that the OHNTs (111) peak was fitted by two Gaussian curves based on CeO 2 and Ce(OH) 3 (JCPDS 019–0284). This confirms the coexistence of dual-phase structures that we interpret as oxy(hydroxides). The fitting analysis reveals, additionally, a temperature-dependent change in the oxide/hydroxide ratio. From 400°C, the oxide phase dominates. Configurational entropy may enable the unusual cationic combination of Ce, Co, Ni, Al, and Ga to form a HE-OOH with a fluorite-like structure that remains stable up to 500°C. The broadening of diffraction peaks may indicate structural disorder and small crystalline regions. A broad and negligible peak corresponding to NiCoxOx emerges at 600°C, which corresponds to a secondary phase. Table 1 Identification of samples. CeCoNiAlGa HE-OOH nanotubes Heat-treatment temperature (ºC) OHNT 80 80 (dried) OHNT 400 400 OHNT 500 500 OHNT 600 600 The minor C (002) peak in the OHNTs diminishes quickly as the temperature rises. The optimal fit for the C (002) peak was achieved using two Gaussian curves, associated with Bernal (π-curve) and non-Bernal (γ-curve) stacking orders commonly found in MWCNTs. [ 26 , 27 ] According to the integrated intensities of π- and γ-curves, the relative intensity of non-Bernal stacking order increased upon forming OHNTs. The increased structural disorder may be attributed to the intercalation of cations (Ce, Co, Ni, Al, Ga) between adjacent graphene layers of parent f -MWCNTs. As previously observed for CeO 2−δ NTs, OHNTs may grow topotactically after an initial stage of cation intercalation into the f -MWCNTs wall spacing. [ 25 , 28 ] A small fraction of intercalated f -MWCNTs may remain unchanged, associated with the small C (002) peak exhibiting a primary γ component. The topotactic synthesis demonstrates its ability to produce single-phase fluorite-like CeCoNiAlGa HE-OOHs at relatively low temperatures (80–500°C). Figures 2 (a-b) show the HR-TEM images of f -MWCNTs and OHNT 400 . These images demonstrate that the main characteristic of OHNT 400 is their well-organized crystalline tubular structure with a concentric cylindrical layer configuration, analogous to parent f -MWCNTs. The fast Fourier transform patterns display spots corresponding to the f -MWCNTs C (002) planes and OHNT 400 (111) planes, respectively. The parent crystal and its pseudomorph share a common tube axis, with the normals to the C (002) or OHNT 400 (111) planes oriented perpendicular to the axis. This strongly suggests that the OHNT 400 has grown topotactically on the MWCNTs, with the OHNT 400 [111] direction oriented normal to the curved C (002) planes. Such a crystallographic relationship should be consistent with favorable lattice matching between the two phases, arising from their compatible hexagonal symmetry. In consequence, the OHNT 400 (111) planes are preferentially aligned parallel to the nanotube surface. The shape and orientation of the parent crystal are effectively inherited despite significant compositional changes during the topotactic transformation. Nevertheless, as shown in Fig. 2 c, local misalignments are noted throughout the multiwalled configuration. These defects may primarily result from variations in composition and/or stress due to the curved shape. Large discontinuity of the tubular morphology is also evident in OHNT 400 . Such a process appears to result in shorter tubes that eventually collapse into irregular particles as heat-treatment temperature increases. In addition, individual randomly oriented crystalline particles are observed on the surface of OHNT 400 nanotubes, suggesting an excess of multicationic precursors during synthesis. Despite the measurement uncertainty, the interlayer spacing of OHNTs is uniform in the radial direction. In OHNT 400 , it is about 0.37 nm, showing that the topotactic transformation occurs throughout the parent f -MWCNTs volume. The interlayer spacing of 0.37 nm is consistent with a partially dehydrated brucite-like layered hydroxide structure composed of neutral M–OH–M sheets. [ 29 ] In such a layered structure the stacking is maintained by weak interlayer interactions. This condition may account for the structural flexibility required to arrange curved HE-OOH (111) layers with progressively larger diameters into a multiwalled nanotube. Figures 2 (c-d) display the HR-TEM image of an individual OHNT 400 along with its corresponding local EELS elemental mapping image. The detection of cerium, cobalt, nickel, aluminum, gallium, and oxygen confirms the presence of a Ce-Co-Ni-Al-Ga-O chemical system in the topotactically grown OHNT 400 . The Raman spectra for f -MWCNTs and OHNTs are depicted in Fig. 3 a. The Raman spectra of OHNTs exhibit the distinctive F 2g band reported for the cubic fluorite structure at ≈ 447 cm-1, which increases in intensity with increasing heat-treatment temperature. The F 2g band shows broadening and a shift to lower frequencies relative to CeO 2 NPs. [ 30 ] The significant shift of ≈ 23 cm⁻¹ and concurrent broadening are ascribed to the distorted structure of OHNTs. The unusual combination of Al, Co, Ni, and Ga cations in a fluorite-like structure leads to significant O vacancies, as indicated by bands in the 500–700 cm⁻¹ range. [ 31 ] The spectra of OHNT 80 and OHNT 400 additionally show distinguishable D, G, and 2D bands of the graphitic structure, indicating the presence of graphitic domains in OHNTs. The G band exhibits a characteristic shoulder associated with lattice distortion caused by intercalated heteroatoms. [ 32 ] This may be attributed to the small, residual fraction of multicationic intercalated f -MWCNTs in OHNTs. OHNT 500 exhibits no graphitic bands, in agreement with previous analyses. [ 25 ] Raman spectra of OHNTs were deconvoluted using a combination of five to six bands (D1-D6), incorporating the model proposed by Sartoretti et al. [ 30 ] Fig. 3 b depicts the curve-fitting analysis of the F 2g band. The D 3 band, assigned to the F 2g first-order symmetric stretching of the fluorite lattice, appears between 441–455 cm − 1 . [ 30 ] This is shifted to a lower wavenumber relative to bulk CeO 2 (≈ 460–465 cm − 1 ), consistent with the defect-induced lattice of OHNTs. The D 1 (≈ 310–330 cm − 1 ) is attributed to the 2TA second-order scattering originating from lattice anharmonicity and disorder. [ 33 ] The D 4 , D 5 , and D 6 bands are characteristic of defect-related local modes. The D 4 has been assigned to O vacancies coupled with reduced Ce 3+ or aliovalent cations. [ 34 ] D 5 is commonly attributed to Frenkel-pair/O-vacancy environments or to aliovalent-containing defect regions. [ 35 , 36 ] The D 6 band is associated with extrinsic defects introduced by aliovalent cations and reflects the formation of MO 8 units in the absence of O vacancies (M = aliovalent cation). [ 36 ] The D 2 band represents the breathing mode of Ce-O framework in OHNTs. [ 37 , 38 ] The progressive upward shifts of several defect bands and the F 2g position in OHNT 600 suggest changes in the local Ce–O bonding and defect density due to the incremental dehydroxylation in OHNTs. Supplementary Table S1 summarizes the identification of first- and second-order Raman bands. Figure 4 a displays the XPS survey spectra of OHNTs, which unequivocally confirm the presence of C, as well as Ce, Co, Ni, Al, and Ga cations. The spectra show a decrease in C 1s peak intensity with increasing temperature, consistent with previous analytical findings. Figure 4 b illustrates a comparison of high-resolution C 1s spectra for f -MWCNTs and OHNTs. OHNTs exhibit a notable broadening of the C 1s peak and an increase in intensity in the C-O (≈ 286.68 eV) and C = C-OH (≈ 288.18 eV) regions, indicative of graphitic phase degradation. The broadening corresponds to a notable increase in sp 3 hybridization, which may be associated with amorphous carbon regions that incorporate oxygen-containing functional groups, particularly in the form of polycyclic aromatic-like structures. [ 25 ] Under these circumstances, the shift of the sp 2 peak may originate from structural and electronic perturbations caused by the intercalation of cations (Ce, Co, Ni, Al, Ga) into f -MWCNTs. Our findings indicate that Ce-O framework supports the formation and stabilization of the fluorite-like structure in OHNTs. Therefore, the Ce 3d core-level spectra of OHNTs were analyzed, as shown in Fig. 4 c. The Ce peaks from 3d5/2 and 3d3/2 levels (V and u) were observed at 880 and 898.7 eV, respectively. Both spin-orbit doublets displayed three corresponding satellite peaks (v′, v″, v‴, u′, u″, and u‴). The high concentration of Ce3 + in OHNTs suggests modulation of the electronic structure driven by aliovalent cation substitution. [ 34 ] The incorporation of smaller cations (Ni 2+ : 0.69 Å, Co 2+ : 0.745 Å, Al 3+ : 0.535 Å, Ga 3+ : 0.62 Å) induces lattice strain because of their size difference from Ce 4+ . [ 39 – 43 ] The high configurational entropy (ΔS = 1.6R) can alleviate the stress, thereby stabilizing the single-phase fluorite-like structure even at relatively low temperatures (80–500 ºC). However, substituting Ce 4+ with considerably smaller cations such as Al 3+ (0.535 Å) restricts phase stability, possibly leading to the secondary phase observed at 600 ºC. Figure 4 d illustrates the high-resolution O 1s spectra for OHNTs. The broad O 1s peak is deconvoluted into four components: lattice O (O L ) at 529.5 eV, O vacancies (O V ) at 531.5 eV, surface-adsorbed oxygen/hydroxyl species (O A ) at 532.0 eV, and chemisorbed water at 533.5 eV. In OHNT 80 , the significant chemisorbed water signal is attributed to a surface passivation mechanism involving water adsorption into O vacancy sites. [ 44 ] As temperature rises, the O V and O A components exhibit an inverse relationship that aligns with the gradual dehydroxylation in OHNTs, along with the formation of O vacancies. [ 45 ] The O V concentration can be calculated by the ratio, O V /(O L +O V +O A ), as shown in Fig. 4 e. The remarkably high concentration of O vacancies likely compensates for the charge imbalance introduced by the presence of aliovalent cations. [ 46 ] The TGA curves of f -MWCNTs and OHNTs in their as-prepared condition are compared in Fig. 5 a. The f -MWCNTs exhibit a single weight-loss event of approximately 93% between 500 and 660°C, typically attributed to combustion, producing CO/CO 2 . [ 47 ] The solid residue (≈ 7%) may arise from the Fe synthesis catalyst. In contrast, the OHNTs exhibit a continuous, multi-step weight loss of ≈ 42% from the onset of heating to 510°C. The corresponding DTA curve ( Fig. 5 b ) shows alternating endothermic and exothermic peaks. The first endothermic event occurring below 100°C is assigned to physisorbed water loss. The subsequent endothermic events at ≈ 182, 263, and 500°C are attributed to stepwise dehydroxylation, which may form complex (oxy)hydroxide intermediates. [ 48 , 49 ] The high-resolution XPS spectra for Co, Ni, Al, and Ga presented in Supplementary Figure S1 illustrate the complexity of the (oxy)hydroxide transformation during the dehydroxylation process. The exothermic events at ≈ 135, 223, and 402 ºC are consistent with the oxidation of residual C within the OHNTs. No significant weight loss occurs above 550°C indicating that OHNTs are a direct structural precursor of HEOs. Figure 6 shows SEM images depicting the morphological evolution of OHNTs as the temperature increases. At 80°C, the OHNTs display a clear 1D morphology; however, their stability gradually deteriorates and, above 600°C, collapses into agglomerated particles. The photocatalytic performance of OHNTs was assessed by photodegradation of ciprofloxacin (CIP) under UV irradiation (λ = 365 nm). The adsorption-desorption equilibrium in dark conditions was reached at 30 min. The UV-vis absorbance spectra shown in Fig. 7 a indicate that the CIP degradation follows a different pathway, varying with the oxide/hydroxide ratio within OHNTs. The OHNT 80 exhibited remarkable photocatalytic activity under UV light, achieving 96% CIP degradation within 45 min. Increasing heat-treatment temperatures, which caused progressive depletion of hydroxides within the OHNTs, resulted in a consistent decrease in their ability to photodegrade CIP. Figure 7 b shows the degradation profile of CIP for the OHNTs. Regardless of the heat-treatment temperature, all OHNTs exhibited similar absorption capacities under dark conditions. Notably, the OHNT 80 showed 90% CIP photodegradation after a brief 15-minute irradiation period. The photodegradation of CIP exhibited pseudo-first-order kinetics, as evidenced by the linear plot generated from -ln(C/C₀) versus irradiation time. Where C₀ denotes the initial CIP concentration, and C is the CIP concentration at time t of the reaction (Fig. 7 c). The reaction rate constant ( k , min − 1 ) was determined from the slope of the linearized pseudo-first-order kinetic plot. The OHNT 80 demonstrates the fastest CIP photodegradation kinetics, achieving a rate of 0.067 min − 1 . The absorption spectra indicate that different photodegradation routes are determined by the ratio of OH species to O vacancies. Specifically, the OHNT 80 is distinguished by its highest OH content. Consequently, the pronounced CIP photodegradation on OHNT 80 is attributed to the synergistic effect of abundant OH species along with O vacancies. Presumably, surface OH species act as precursors for hydroxyl radicals (•OH), which dominate CIP degradation, whereas O vacancies enhance light absorption, facilitate charge separation, and promote ROS generation. [ 50 , 51 ] In summary, topotactic synthesis enables the formation of single-phase fluorite-like CeCoNiAlGa HE-OOHs at relatively low temperatures (80–500°C). The specific properties of CeCoNiAlGa HE-OOHs emphasize the critical synergistic interaction between OH species and O vacancies. Compared with traditional synthesis methods, topotactic transformation offers superior control over the morphology, composition, and functionality of HE-OOHs when favorable crystallographic symmetry alignment exists between the parent and product structures. Methods Synthesis of OHNTs The OHNTs were prepared via an innovative topotactic route in which the entire volume of the parent single-crystalline f -MWCNTs was converted into CeCoNiAlGa HE-OOHs pseudomorphs using the conventional liquid-phase deposition method. As-received commercially available Ce(NO 3 ) 3 ·6H 2 O, Al(NO 3 ) 3 ·9H 2 O, Co(NO 3 ) 2 ·6H 2 O, Ni(NO 3 ) 2 ·6H 2 O, Ga(NO 3 ) 3 ·xH 2 O, and NaOH chemicals were used as metal precursors and an oxidation-promoting reactant, respectively. The MWCNTs were prepared by the thermal decomposition of a toluene/ferrocene solution method, which had been described elsewhere. [ 52 ] First, MWCNTs were functionalized in a 40 vol% HNO 3 solution at 90–110°C for 24 h under reflux. Subsequently, a precursor solution was prepared by mixing an equimolar (0.1 M) mixture of cations in HNO 3 . The resultant functionalized MWCNTs ( f -MWCNTs) were mixed with the precursor solution at a 1:0.6 molar ratio for 1 h in an ultrasonic bath. Then, 0.5 M NaOH solution was added slowly under vigorous stirring until the pH reached 7. The resultant suspension was filtered, and the solid product was repeatedly washed with deionized water and dried in open atmosphere at ≈ 80°C using an infrared lamp. The dried product was heat-treated at 400, 500, and 600°C in air for 30 min using a heating rate of 5°C min − 1 . Structural, morphological, and chemical characterizations The structure of the OHNTs was analyzed by X-ray diffraction (Bruker D8 Advance, with Cu Kα radiation (λ = 1.5405 Å)), in the scanning range (2θ) from 20° to 100 ° with 0.02° step width and constant counting time of 0.6 s/step. The morphology was examined by Field Emission Scanning Electron Microscopy, JEOL JSM6701F, at an accelerating voltage of 5 kV using the secondary electron detector. High-Resolution Transmission Electron Microscopy, JEOL ARM200F, at an accelerating voltage of 200 kV in the bright-field mode coupled with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS), was employed to analyze morphology and element distribution at the nanometer scale. The valence states of OHNTs were investigated by X-ray Photoelectron Spectroscopy using a Thermo Scientific K-Alpha ESCALAB 250Xi equipped with a 180° double-focusing hemispherical analyzer and a monochromatic Al Kα (1486.6 eV) source. The binding energy scale in the XPS spectra was calibrated to 284.8 eV for the C 1s peak of adventitious carbon. Analysis of the XPS spectra was conducted by using the Thermo Scientific Avantage data system. Raman spectroscopy was used to analyze the nature of covalent bonds using a LabRAM HR Evolution Horiba equipment with a wavelength of 532 nm in the range of 200–3000 cm − 1 . The oxidation behavior of f -MWCNTs and OHNTs in their initial condition was studied by thermal gravimetric analysis (TGA/DTA) at 10°C min − 1 in an air flow of 50 mL/min, using alumina crucibles (TGA/DTA; Netzsch Regulus 2500 STA). Photocatalytic evaluation The photocatalytic activity of OHNTs was evaluated by the degradation of CIP (10 m L − 1 ) in aqueous solutions under UV light irradiation. The evaluation was conducted using 50 mg of OHNTs dispersed in 100 mL of the CIP solution. Before the photocatalytic test, the system was maintained in the dark for 30 min to ensure adsorption/desorption equilibrium. The test was performed at room temperature under constant stirring and UV irradiation (λ = 365 nm) for 45 min, with aliquots collected every 15 min. The photodegradation efficiency was monitored using a Perkin Elmer UV–vis Lambda 35 Spectrophotometer by measuring the maximum absorption of CIP at 275 nm. Declarations Competing interests The authors declare no competing interests. Funding The Authors received FUNDING for this work: M.A. H.-P., Instituto Politécnico Nacional, México, IPN-SIP 20250084. J.R. V.-G., Instituto Politécnico Nacional, México, IPN-SIP 20250896. J.R. V.-G., Secretaría de Ciencia, Humanidades, Tecnología e Innovación, México, CBF-2025-I-2873. Author Contribution S.P.-E. wrote the main manuscript text. J.R.V.-G. and M.A.H.-P. supervised the project and contributed to project administration, validation, funding acquisition, and manuscript review and editing. A.I.C.-B., A.V.-P., and R.B.-U. contributed to the methodology, investigation, data curation, and manuscript drafting. All authors reviewed and approved the final manuscript. Acknowledgement S. P.-E. and A.I. C.-B. acknowledge financial support from SECIHTI-Mexico. Data Availability Data is available on request from the corresponding author, Jorge Roberto Vargas-Garcia, through [ [email protected] ](mailto: [email protected] ) References Sham Lal, M. & Sundara, R. High entropy oxides—a cost-effective catalyst for the growth of high yield carbon nanotubes and their energy applications. ACS Appl. Mater. Interfaces . 11 , 30846–30857. 10.1021/acsami.9b08794 (2019). Shi, Y., Li, R. & Lei, Z. Influences of synthetic parameters on morphology and growth of high entropy oxide nanotube arrays. Coatings 13 10.3390/coatings13010046 (2022). Ran, B. et al. High-entropy oxides for rechargeable batteries. Adv. Sci. 11 10.1002/advs.202401034 (2024). Anandkumar, M. & Trofimov, E. Synthesis, properties, and applications of high-entropy oxide ceramics: current progress and future perspectives. J. Alloys Compd. 960 , 170690. 10.1016/j.jallcom.2023.170690 (2023). Sun, Y. & Dai, S. High-entropy materials for catalysis: a new frontier. Sci. Adv. 7 , eabg1600. 10.1126/sciadv.abg1600 (2021). Jia, X. & Li, H. Machine learning enabled exploration of multicomponent metal oxides for catalyzing oxygen reduction in alkaline media-. J. Mater. Chem. A . 12 , 12487–12500. 10.1039/D4TA01884B (2024). Sarkar, A. et al. Nanocrystalline multicomponent entropy stabilised transition metal oxides. J. Eur. Ceram. Soc. 37 , 747–754. 10.1016/j.jeurceramsoc.2016.09.018 (2017). Dąbrowa, J. et al. Synthesis and microstructure of the (Co,Cr,Fe,Mn,Ni) 3 O 4 high entropy oxide characterized by spinel structure. Mater. Lett. 216 , 32–36. 10.1016/j.matlet.2017.12.148 (2018). Sharma, Y. et al. Single-crystal high entropy perovskite oxide epitaxial films. Phys. Rev. Mater. 2 (R). 10.1103/PhysRevMaterials.2.060404 (2018). Cheng, B. et al. Pressure-induced tuning of lattice distortion in a high-entropy oxide. Commun. Chem. 2 10.1038/s42004-019-0216-2 (2019). Abdul Hai, M., Daud, M., Mujtaba, G., Banat, F. & Al-Harthi, M. A. A comprehensive review of two-dimensional high-entropy layered hydroxides: Synthesis, characterization, and applications. Coord. Chem. Rev. 529 , 216435 (2025). Nemani, S. K., Torkamanzadeh, M., Wyatt, B. C., Presser, V. & Anasori, B. Functional two-dimensional high-entropy materials. Commun. Mater. 4 , 16 (2023). Okejiri, F. et al. Ultrasound-mediated synthesis of nanoporous fluorite-structured high-entropy oxides toward noble metal stabilization. iScience 25 , 104214. 10.1016/j.isci.2022.104214 (2022). Patriarchi, A. et al. Evaluation of high-entropy (Cr, Mn, Fe, Co, Ni)-oxide nanofibers and nanoparticles as passive fillers for solid composite electrolytes. Electrochim. Acta . 512 (145425). 10.1016/j.electacta.2024.145425 (2025). Arun, S. R. & Jacob, G. Exploring the charge storage ability of the spinel-type high entropy oxide (MnFeCoNiZn) 3 O 4 nanoparticles for supercapacitor applications. Chem. Eng. J. Adv. 21 , 100708. 10.1016/j.ceja.2025.100708 (2025). Tian, L., Zhang, Z., Liu, S., Li, G. & Gao, X. High-entropy perovskite oxide nanofibers as efficient bidirectional electrocatalyst of liquid-solid conversion processes in lithium-sulfur batteries. Nano Energy . 106 , 108037. 10.1016/j.nanoen.2022.108037 (2023). Asim, M. et al. Microwave synthesis of rock-salt type high entropy oxides immobilized on graphene oxide nanosheets as an efficient catalyst for oxygen evolution reaction. J. Environ. Chem. Eng. 13, 118758;10.1016/j.jece.118758 (2025) (2025). Wang, X. et al. Identification of the reconstruction induced high-entropy spinel oxide nanosheets for boosting alkaline water oxygen evolution. Chem. Eng. J. 503 10.1016/j.cej.2024.158488 (2025). Wang, X. L., Kim, E. M., Senthamaraikannan, T. G., Lim, D. H. & Jeong, S. M. Porous hollow high entropy metal oxides (NiCoCuFeMg) 3 O 4 nanofiber anode for high-performance lithium-ion batteries. Chem. Eng. J. 484, 149509;10.1016/j.cej.149509 (2024) (2024). Liu, X., Tian, F., Sheng, J., Yu, Y. & Yang, W. High-entropy porous spinel ferrite @ amorphous carbon nanocomposites with abundant structural defects for wide-band electromagnetic wave absorption. Chem. Eng. J. 490 , 151848. 10.1016/j.cej.2024.151848 (2024). Zhu, Y. et al. Spinel-type high-entropy oxide nanotubes for efficient oxygen evolution reaction. Colloids Surf. A . 686 , 133315. 10.1016/j.colsurfa.2024.133315 (2024). Lei, Z. et al. Ultrastable metal oxide nanotube arrays achieved by entropy-stabilization engineering. Scr. Mater. 146 , 340–343. 10.1016/j.scriptamat.2017.12.025 (2018). Musicó, B. L. et al. The emergent field of high entropy oxides: design, prospects, challenges, and opportunities for tailoring material properties. APL Mater. 8, 040912; (2020). 10.1063/5.0003149 Müller, U. Symmetry Relationships between Crystal Structures: Applications of Crystallographic Group Theory in Crystal Chemistry 217–226 (Springer, 2013). Pacheco-Espinoza, S. et al. Topotactical route to multiwalled cerium oxide nanotubes from MWCNTs. Part. Part. Syst. Charact. 40 , 2370007. 10.1002/ppsc.202200167 (2023). Cortés-López, A. J., Muñoz-Sandoval, E. & López-Urías, F. Oxygenated surface of carbon nanotube sponges: electroactivity and magnetic studies. AMS Omega . 4 , 18011–18022. 10.1021/acsomega.9b01773 (2019). Dresselhaus, M. S. & Endo, M. Relation of carbon nanotubes to other carbon materials in Carbon nanotubes: synthesis, structure, properties, and applications (Eds (eds Dresselhaus, M. S., Dresselhaus, G. & Avouris, P.) 11–28 (Springer, (2001). Cahen, S., Speyer, L., Lagrange, P. & Hérold, C. Topotactic mechanisms related to the graphene planes: chemical intercalation of electron donors into graphite. Eur. J. Inorg. Chem. 45 , 4798–4806. 10.1002/ejic.201900758 (2019). Wondimu, T. H., Zuo, Y., Shah, A. A. & Leung, P. puiki Leung. The recent progress of high-entropy layered double hydroxides and high-entropy amorphous materials for water electrocatalysis. Decarb 8 , 100110 (2025). Sartoretti, E. et al. In situ Raman analyses of the soot oxidation reaction over nanostructured ceria-based catalysts. Sci. Rep. 9 10.1038/s41598-019-39105-5 (2019). McBride, J. R., Hass, K. C., Poindexter, B. D. & Weber, W. H. Raman and x-ray studies of Ce 1 – x RE x O 2–y , where RE = La, Pr, Nd, Eu, Gd, and Tb. J. Appl. Phys. 76 , 2435–2441. 10.1063/1.357593 (1994). Sadezky, A., Muckenhuber, H., Grothe, H., Niessner, R. & Pöschl, U. Raman microspectroscopy of soot and related carbonaceous materials: Spectral analysis and structural information. Carbon 43 , 1731–1742. 10.1016/j.carbon.2005.02.018 (2005). Loridant, S. Raman spectroscopy as a powerful tool to characterize ceria-based catalysts. Catal. Today . 373 , 98–111. 10.1016/j.cattod.2020.03.044 (2021). Vinodkumar, T., Rao, B. G. & Reddy, B. M. Influence of isovalent and aliovalent dopants on the reactivity of cerium oxide for catalytic applications. Catal. Today . 253 , 57–64. 10.1016/j.cattod.2015.01.044 (2015). Agarwal, S., Zhu, X., Hensen, E. J. M., Lefferts, L. & Mojet, B. L. Defect chemistry of ceria nanorods. J. Phys. Chem. C . 118 , 4131–4142. 10.1021/jp409989y (2014). Li, L., Chen, F., Lu, J. Q. & Luo, M. F. Study of defect sites in Ce 1 – x MxO 2–δ (x = 0.2) solid solutions using Raman spectroscopy. J. Phys. Chem. A . 115 , 7972–7977. 10.1021/jp203921m (2011). Rudolph, W. W. & Irmer, G. Raman spectroscopic characterization of light rare earth ions: La³⁺, Ce³⁺, Pr³⁺, Nd³⁺ and Sm³⁺ – hydration and ion pair formation. Dalton Trans. 46 , 4235–4244 (2017). Schweke, D., Rubin, A., Rabinovitch, L., Kraynis, O. & Livneh, T. Cerium metal oxidation studied by IR reflection-absorption and Raman scattering spectroscopies. J. Phys. : Condens. Matter . 34 , 324002 (2022). Vanpoucke, D. E. P., Bultinck, P., Cottenier, S., Van Speybroeck, V. & Van Driessche, I. Aliovalent doping of CeO 2 : DFT study of oxidation state and vacancy effects. J. Mater. Chem. A . 2 , 13723–13737. 10.1039/C4TA02449D (2014). Matussin, S. N., Khan, F., Harunsani, M. H., Kim, Y. M. & Khan, M. M. Visible-light-induced photocatalytic and photoantibacterial activities of Co-doped CeO 2 . ACS Omega . 8 , 11868–11879. 10.1021/acsomega.2c07058 (2023). Chidaraboyina, S., Nesaraj, A. S. & Arunkumar, M. Aluminium doped cerium oxide as an efficient nanophotocatalyst for the elimination of rhodamine B dye present in water. Asian J. Chem. 35 , 882–886. 10.14233/ajchem.2023.27574 (2023). Ramasamy, V., Mohana, V. & Suresh, G. Study of Ni:CeO 2 nanoparticles for efficient photodegradation of methylene blue by sun light irradiation. Indian J. Phys. 92 , 1601–1612. 10.1007/s12648-018-1246-9 (2018). Wang, F. et al. Ga-doped CeO 2 nanorods as highly active catalysts for the synthesis of dimethyl carbonate from CO 2 and methanol. React. Kinet Mech. Catal. 136 , 2941–2954. 10.1007/s11144-023-02506-9 (2023). Ghobadi, A., Ghobadi, T. G. U., Karadas, F. & Ozbay, E. Angstrom thick ZnO passivation layer to improve the photoelectrochemical water splitting performance of a tio 2 nanowire photoanode: the role of deposition temperature. Sci. Rep. 8 , 16322. 10.1038/s41598-018-34248-3 (2018). Song, X. & Boily, J. F. Surface and Bulk Thermal Dehydroxylation of FeOOH Polymorphs. J Phys. Chem. A . 120 , 6249–6257 (2016). Gager, E. & Nino, J. C. Processing, phase stability, and conductivity of multication-doped ceria. Inorganics 11 , 299. 10.3390/inorganics11070299 (2023). Scheibe, B., Borowiak-Palen, E. & Kalenczuk, R. J. Oxidation and reduction of multiwalled carbon nanotubes — preparation and characterization. Mater. Charact. 61 , 185–191. 10.1016/j.matchar.2009.11.008 (2010). Li, Y. X., Zhou, X. Z., Wang, Y. & You, X. Z. Preparation of nano-sized CeO 2 by mechanochemical reaction of cerium carbonate with sodium hydroxide. Mater. Lett. 58 , 245–249. 10.1016/S0167-577X(03)00454-3 (2004). Ansari, A. A. & Kaushik, A. Synthesis and optical properties of nanostructured Ce(OH) 4 . J. Semicond. 31 10.1088/1674–4926/31/3/033001 (2010). Le Crom, S. & Boily, J. F. Molecular-level insight into ciprofloxacin adsorption on goethite: I. Approach and non-specific binding. Phys. Chem. Chem. Phys. 27 , 4446–4456. 10.1039/d4cp04027a (2025). Queiróz, A. C. B. et al. Ciprofloxacin photodegradation by CeO 2 nanostructures with different morphologies. Water Air Soil. Pollut . 234 10.1007/s11270-023-06424-3 (2023). Andrews, R. et al. Continuous production of aligned carbon nanotubes: a step closer to commercial realization. J. Chen Chem. Phys. Lett. 303 , 467–474. 10.1016/S0009-2614(99)00282-1 (1999). Additional Declarations No competing interests reported. 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16:36:58","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1047007,"visible":true,"origin":"","legend":"\u003cp\u003eHR-TEM images of a) \u003cem\u003ef\u003c/em\u003e-MWCNTs, b-c) OHNT\u003csub\u003e400\u003c/sub\u003e, and d) EELS elemental mapping image.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8419535/v1/5722cc05c60b46eaafdea72e.png"},{"id":99320601,"identity":"4d54002b-8c94-4848-b942-7b44fb9690a0","added_by":"auto","created_at":"2025-12-31 16:38:47","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":365925,"visible":true,"origin":"","legend":"\u003cp\u003ea) Raman spectra of \u003cem\u003ef\u003c/em\u003e-MWCNTs and OHNTs, b) deconvolution analysis of the F\u003csub\u003e2g\u003c/sub\u003e band.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8419535/v1/f84bcda0f9ff488ce1147f1f.png"},{"id":99319265,"identity":"ab582c55-5193-45c6-a0db-85d34e22f704","added_by":"auto","created_at":"2025-12-31 16:36:46","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":706581,"visible":true,"origin":"","legend":"\u003cp\u003ea) Survey spectra for OHNTs, b) high-resolution C 1s spectra for \u003cem\u003ef\u003c/em\u003e-MWCNTs and OHNTs, c) Ce 3d spectra for OHNTs, d) O 1s spectra for OHNTs, and e) O\u003csub\u003eV\u003c/sub\u003e concentration.\u0026nbsp;\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8419535/v1/f93da9b04094725aa2a88ae1.png"},{"id":99319206,"identity":"dccc3948-3403-4941-be07-cadf058b1b39","added_by":"auto","created_at":"2025-12-31 16:36:39","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":164154,"visible":true,"origin":"","legend":"\u003cp\u003ea) TGA curves of \u003cem\u003ef\u003c/em\u003e-MWCNTs and OHNTs in their as-prepared condition, and b) DTA curve of OHNTs\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8419535/v1/72e087b61173c3f61709c6e4.png"},{"id":99320533,"identity":"d111282c-80ec-443d-9d3c-a2588d3186a0","added_by":"auto","created_at":"2025-12-31 16:38:43","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":801790,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of the OHNTs morphological evolution.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8419535/v1/598b9d07d31174be2ace9c03.png"},{"id":99273266,"identity":"c60b708d-c658-4365-893c-4ff17a659bec","added_by":"auto","created_at":"2025-12-31 06:33:50","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":739135,"visible":true,"origin":"","legend":"\u003cp\u003ea) UV-vis absorbance spectra for CIP degradation in the presence of OHNTs, b) rate of CIP photocatalytic removal as a function of time, and c) pseudo-first-order kinetics of OHNTs.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8419535/v1/6faa4db44f0d17662d4a2473.png"},{"id":105223296,"identity":"15875353-6648-4a1d-b00d-15c87aad03f5","added_by":"auto","created_at":"2026-03-23 16:02:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5084536,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8419535/v1/d8920718-4faa-4e9f-ad54-bc299d0eafce.pdf"},{"id":99273250,"identity":"d4cd2507-35d6-4690-9376-3225b4ff1955","added_by":"auto","created_at":"2025-12-31 06:33:48","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":281815,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8419535/v1/095d9761d2cde9f7e9d1d1c1.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Topotactic Engineering of High-Entropy (Oxy)hydroxide Nanotubes for Enhanced Photocatalysis","fulltext":[{"header":"Introduction","content":"\u003cp\u003eIn recent years, high-entropy oxides (HEOs) have emerged as promising candidates for advanced energy storage and catalytic applications.\u003csup\u003e[\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e The synergistic effects arising from their multiple cations enable the tailoring of physicochemical properties to meet the demands of the application.\u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e So far, a considerable number of important studies have shown that HEOs crystallize into a single-phase and highly symmetric crystal structure, for example, rock salt (Co\u003csub\u003e0.2\u003c/sub\u003eCu\u003csub\u003e0.2\u003c/sub\u003eMg\u003csub\u003e0.2\u003c/sub\u003eNi\u003csub\u003e0.2\u003c/sub\u003eZn\u003csub\u003e0.2\u003c/sub\u003e)O, spinel (Co\u003csub\u003e0.2\u003c/sub\u003eCr\u003csub\u003e0.2\u003c/sub\u003eFe\u003csub\u003e0.2\u003c/sub\u003eMn\u003csub\u003e0.2\u003c/sub\u003eNi\u003csub\u003e0.2\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, perovskite Ba(Zr\u003csub\u003e0.2\u003c/sub\u003eSn\u003csub\u003e0.2\u003c/sub\u003eTi\u003csub\u003e0.2\u003c/sub\u003eHf\u003csub\u003e0.2\u003c/sub\u003eNb\u003csub\u003e0.2\u003c/sub\u003e)O\u003csub\u003e3\u003c/sub\u003e, and fluorite (Ce\u003csub\u003e0.2\u003c/sub\u003eLa\u003csub\u003e0.2\u003c/sub\u003ePr\u003csub\u003e0.2\u003c/sub\u003eSm\u003csub\u003e0.2\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003e)O\u003csub\u003e2\u0026minus;δ\u003c/sub\u003e types.\u003csup\u003e[\u003cspan additionalcitationids=\"CR8 CR9\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e Closely related, HE-OOHs also signify a rapidly advancing area of research with significant potential in electrocatalytic applications. Albeit an evolving area, well-defined structural patterns for HE-OOHs are primarily recognized as orthorhombic, tetragonal, and octahedral layered stacks.\u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e Additionally, significant efforts have been devoted to developing synthesis methods to expand the functionalities of HEOs, leading to nanostructured HEOs in the form of nanoparticles, nanofibers, and porous structures.\u003csup\u003e[\u003cspan additionalcitationids=\"CR14 CR15 CR16 CR17 CR18 CR19\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e However, HEO nanotubes have been rarely achieved despite their promising benefits of enhanced surface area and exposure of desirable crystallographic planes. \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e Traditional synthesis methods for HEOs and HE-OOHs, although well-established and yielding high-quality results, still restrict the precise control of morphology and nanostructure features.\u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e Furthermore, research delving into technologies that operate beyond the common compositions of HEOs, exploring innovative designs and functionalities, is even scarcer. The topotactic transformation offers an attractive route for achieving highly desirable structures. The topotactic transformation is a solid-state transformation where a parent crystal converts into a pseudomorph, maintaining its crystallographic orientation and morphology.\u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e Inspired by our previous investigations concerning CeO\u003csub\u003e2\u0026minus;δ\u003c/sub\u003e nanotubes, the current research explores the feasibility of generating novel CeCoNiAlGa HE-OOH multiwalled nanotube structures.\u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e This is accomplished via topotactic transformation utilizing MWCNTs as the parent crystal. Single-phase HE-OOHs incorporating the unprecedented combination of Ce-Co-Ni-Al-Ga cations have not been previously reported, and their properties remain unexplored. This novel combination is intended to leverage the Ce\u003csup\u003e3+\u003c/sup\u003e/Ce\u003csup\u003e4+\u003c/sup\u003e, Co\u003csup\u003e2+\u003c/sup\u003e/Co\u003csup\u003e3+\u003c/sup\u003e, Ni\u003csup\u003e2+\u003c/sup\u003e/Ni\u003csup\u003e3+\u003c/sup\u003e redox couple activity, Ce ability for fluorite-structure stabilization, synergistic catalytic effects of Co-Ni, and the potential for structural/electronic promotion of Al-Ga. We demonstrate the application of CeCoNiAlGa HE-OOH nanotubes as a catalyst for the CIP photodegradation. The unique characteristics of CeCoNiAlGa HE-OOH nanotubes synthesized via the topotactic method highlight the critical synergistic interaction between OH species and O vacancies, which is highly desirable for photocatalysis.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003ea depicts typical XRD patterns of f-MWCNTs and topotactically grown products (OHNTs). Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents a summary of sample identification. The XRD pattern of \u003cem\u003ef\u003c/em\u003e-MWCNTs shows distinctive diffraction peaks of the graphite structure at 2θ = 26.06° and 43.60° (JCPDS 041-1487). Besides the small C (002) peak, the XRD patterns of OHNTs exhibit broad peaks close to those of the CeO\u003csub\u003e2\u003c/sub\u003e cubic fluorite structure (JCPDS 34–0394). Although OHNTs do not adopt the ideal cubic fluorite symmetry, the peak proximity suggests a distorted Ce-O framework that is derivative of the fluorite structure. The C (002) and OHNTs (111) peaks were analyzed by deconvolution analysis. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003eb shows that the OHNTs (111) peak was fitted by two Gaussian curves based on CeO\u003csub\u003e2\u003c/sub\u003e and Ce(OH)\u003csub\u003e3\u003c/sub\u003e (JCPDS 019–0284). This confirms the coexistence of dual-phase structures that we interpret as oxy(hydroxides). The fitting analysis reveals, additionally, a temperature-dependent change in the oxide/hydroxide ratio. From 400°C, the oxide phase dominates. Configurational entropy may enable the unusual cationic combination of Ce, Co, Ni, Al, and Ga to form a HE-OOH with a fluorite-like structure that remains stable up to 500°C. The broadening of diffraction peaks may indicate structural disorder and small crystalline regions. A broad and negligible peak corresponding to NiCoxOx emerges at 600°C, which corresponds to a secondary phase.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e\u003cdiv class=\"gridtable\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\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\u003eIdentification of samples.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCeCoNiAlGa HE-OOH nanotubes\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHeat-treatment temperature (ºC)\u003c/p\u003e \u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOHNT\u003csub\u003e80\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e80 (dried)\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOHNT\u003csub\u003e400\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e400\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOHNT\u003csub\u003e500\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOHNT\u003csub\u003e600\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e600\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003c/div\u003e \u003cp\u003e\u003c/p\u003e \u003cp\u003eThe minor C (002) peak in the OHNTs diminishes quickly as the temperature rises. The optimal fit for the C (002) peak was achieved using two Gaussian curves, associated with Bernal (π-curve) and non-Bernal (γ-curve) stacking orders commonly found in MWCNTs.\u003csup\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e According to the integrated intensities of π- and γ-curves, the relative intensity of non-Bernal stacking order increased upon forming OHNTs. The increased structural disorder may be attributed to the intercalation of cations (Ce, Co, Ni, Al, Ga) between adjacent graphene layers of parent \u003cem\u003ef\u003c/em\u003e-MWCNTs. As previously observed for CeO\u003csub\u003e2−δ\u003c/sub\u003e NTs, OHNTs may grow topotactically after an initial stage of cation intercalation into the \u003cem\u003ef\u003c/em\u003e-MWCNTs wall spacing.\u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e A small fraction of intercalated \u003cem\u003ef\u003c/em\u003e-MWCNTs may remain unchanged, associated with the small C (002) peak exhibiting a primary γ component. The topotactic synthesis demonstrates its ability to produce single-phase fluorite-like CeCoNiAlGa HE-OOHs at relatively low temperatures (80–500°C).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigures \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e \u003cb\u003e(a-b)\u003c/b\u003e show the HR-TEM images of \u003cem\u003ef\u003c/em\u003e-MWCNTs and OHNT\u003csub\u003e400\u003c/sub\u003e. These images demonstrate that the main characteristic of OHNT\u003csub\u003e400\u003c/sub\u003e is their well-organized crystalline tubular structure with a concentric cylindrical layer configuration, analogous to parent \u003cem\u003ef\u003c/em\u003e-MWCNTs. The fast Fourier transform patterns display spots corresponding to the \u003cem\u003ef\u003c/em\u003e-MWCNTs C (002) planes and OHNT\u003csub\u003e400\u003c/sub\u003e (111) planes, respectively. The parent crystal and its pseudomorph share a common tube axis, with the normals to the C (002) or OHNT\u003csub\u003e400\u003c/sub\u003e (111) planes oriented perpendicular to the axis. This strongly suggests that the OHNT\u003csub\u003e400\u003c/sub\u003e has grown topotactically on the MWCNTs, with the OHNT\u003csub\u003e400\u003c/sub\u003e [111] direction oriented normal to the curved C (002) planes. Such a crystallographic relationship should be consistent with favorable lattice matching between the two phases, arising from their compatible hexagonal symmetry. In consequence, the OHNT\u003csub\u003e400\u003c/sub\u003e (111) planes are preferentially aligned parallel to the nanotube surface. The shape and orientation of the parent crystal are effectively inherited despite significant compositional changes during the topotactic transformation. Nevertheless, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, local misalignments are noted throughout the multiwalled configuration. These defects may primarily result from variations in composition and/or stress due to the curved shape. Large discontinuity of the tubular morphology is also evident in OHNT\u003csub\u003e400\u003c/sub\u003e. Such a process appears to result in shorter tubes that eventually collapse into irregular particles as heat-treatment temperature increases. In addition, individual randomly oriented crystalline particles are observed on the surface of OHNT\u003csub\u003e400\u003c/sub\u003e nanotubes, suggesting an excess of multicationic precursors during synthesis. Despite the measurement uncertainty, the interlayer spacing of OHNTs is uniform in the radial direction. In OHNT\u003csub\u003e400\u003c/sub\u003e, it is about 0.37 nm, showing that the topotactic transformation occurs throughout the parent \u003cem\u003ef\u003c/em\u003e-MWCNTs volume. The interlayer spacing of 0.37 nm is consistent with a partially dehydrated brucite-like layered hydroxide structure composed of neutral M–OH–M sheets.\u003csup\u003e[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]\u003c/sup\u003e In such a layered structure the stacking is maintained by weak interlayer interactions. This condition may account for the structural flexibility required to arrange curved HE-OOH (111) layers with progressively larger diameters into a multiwalled nanotube. Figures\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e \u003cb\u003e(c-d)\u003c/b\u003e display the HR-TEM image of an individual OHNT\u003csub\u003e400\u003c/sub\u003e along with its corresponding local EELS elemental mapping image. The detection of cerium, cobalt, nickel, aluminum, gallium, and oxygen confirms the presence of a Ce-Co-Ni-Al-Ga-O chemical system in the topotactically grown OHNT\u003csub\u003e400\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Raman spectra for \u003cem\u003ef\u003c/em\u003e-MWCNTs and OHNTs are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. The Raman spectra of OHNTs exhibit the distinctive F\u003csub\u003e2g\u003c/sub\u003e band reported for the cubic fluorite structure at ≈ 447 cm-1, which increases in intensity with increasing heat-treatment temperature. The F\u003csub\u003e2g\u003c/sub\u003e band shows broadening and a shift to lower frequencies relative to CeO\u003csub\u003e2\u003c/sub\u003e NPs. \u003csup\u003e[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e The significant shift of ≈ 23 cm⁻¹ and concurrent broadening are ascribed to the distorted structure of OHNTs. The unusual combination of Al, Co, Ni, and Ga cations in a fluorite-like structure leads to significant O vacancies, as indicated by bands in the 500–700 cm⁻¹ range.\u003csup\u003e[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]\u003c/sup\u003e The spectra of OHNT\u003csub\u003e80\u003c/sub\u003e and OHNT\u003csub\u003e400\u003c/sub\u003e additionally show distinguishable D, G, and 2D bands of the graphitic structure, indicating the presence of graphitic domains in OHNTs. The G band exhibits a characteristic shoulder associated with lattice distortion caused by intercalated heteroatoms.\u003csup\u003e[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/sup\u003e This may be attributed to the small, residual fraction of multicationic intercalated \u003cem\u003ef\u003c/em\u003e-MWCNTs in OHNTs. OHNT\u003csub\u003e500\u003c/sub\u003e exhibits no graphitic bands, in agreement with previous analyses.\u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eRaman spectra of OHNTs were deconvoluted using a combination of five to six bands (D1-D6), incorporating the model proposed by Sartoretti et al.\u003csup\u003e[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eb depicts the curve-fitting analysis of the F\u003csub\u003e2g\u003c/sub\u003e band. The D\u003csub\u003e3\u003c/sub\u003e band, assigned to the F\u003csub\u003e2g\u003c/sub\u003e first-order symmetric stretching of the fluorite lattice, appears between 441–455 cm\u003csup\u003e− 1\u003c/sup\u003e.\u003csup\u003e[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e This is shifted to a lower wavenumber relative to bulk CeO\u003csub\u003e2\u003c/sub\u003e (≈ 460–465 cm\u003csup\u003e− 1\u003c/sup\u003e), consistent with the defect-induced lattice of OHNTs. The D\u003csub\u003e1\u003c/sub\u003e (≈ 310–330 cm\u003csup\u003e− 1\u003c/sup\u003e) is attributed to the 2TA second-order scattering originating from lattice anharmonicity and disorder.\u003csup\u003e[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003c/sup\u003e The D\u003csub\u003e4\u003c/sub\u003e, D\u003csub\u003e5\u003c/sub\u003e, and D\u003csub\u003e6\u003c/sub\u003e bands are characteristic of defect-related local modes. The D\u003csub\u003e4\u003c/sub\u003e has been assigned to O vacancies coupled with reduced Ce\u003csup\u003e3+\u003c/sup\u003e or aliovalent cations.\u003csup\u003e[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/sup\u003e D\u003csub\u003e5\u003c/sub\u003e is commonly attributed to Frenkel-pair/O-vacancy environments or to aliovalent-containing defect regions.\u003csup\u003e[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/sup\u003e The D\u003csub\u003e6\u003c/sub\u003e band is associated with extrinsic defects introduced by aliovalent cations and reflects the formation of MO\u003csub\u003e8\u003c/sub\u003e units in the absence of O vacancies (M = aliovalent cation).\u003csup\u003e[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/sup\u003e The D\u003csub\u003e2\u003c/sub\u003e band represents the breathing mode of Ce-O framework in OHNTs.\u003csup\u003e[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/sup\u003e The progressive upward shifts of several defect bands and the F\u003csub\u003e2g\u003c/sub\u003e position in OHNT\u003csub\u003e600\u003c/sub\u003e suggest changes in the local Ce–O bonding and defect density due to the incremental dehydroxylation in OHNTs. Supplementary Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e summarizes the identification of first- and second-order Raman bands.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003ea displays the XPS survey spectra of OHNTs, which unequivocally confirm the presence of C, as well as Ce, Co, Ni, Al, and Ga cations. The spectra show a decrease in C 1s peak intensity with increasing temperature, consistent with previous analytical findings. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003eb illustrates a comparison of high-resolution C 1s spectra for \u003cem\u003ef\u003c/em\u003e-MWCNTs and OHNTs. OHNTs exhibit a notable broadening of the C 1s peak and an increase in intensity in the C-O (≈ 286.68 eV) and C = C-OH (≈ 288.18 eV) regions, indicative of graphitic phase degradation. The broadening corresponds to a notable increase in sp\u003csup\u003e3\u003c/sup\u003e hybridization, which may be associated with amorphous carbon regions that incorporate oxygen-containing functional groups, particularly in the form of polycyclic aromatic-like structures.\u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e Under these circumstances, the shift of the sp\u003csup\u003e2\u003c/sup\u003e peak may originate from structural and electronic perturbations caused by the intercalation of cations (Ce, Co, Ni, Al, Ga) into \u003cem\u003ef\u003c/em\u003e-MWCNTs.\u003c/p\u003e \u003cp\u003eOur findings indicate that Ce-O framework supports the formation and stabilization of the fluorite-like structure in OHNTs. Therefore, the Ce 3d core-level spectra of OHNTs were analyzed, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003ec. The Ce peaks from 3d5/2 and 3d3/2 levels (V and u) were observed at 880 and 898.7 eV, respectively. Both spin-orbit doublets displayed three corresponding satellite peaks (v′, v″, v‴, u′, u″, and u‴). The high concentration of Ce3 + in OHNTs suggests modulation of the electronic structure driven by aliovalent cation substitution.\u003csup\u003e[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/sup\u003e The incorporation of smaller cations (Ni\u003csup\u003e2+\u003c/sup\u003e: 0.69 Å, Co\u003csup\u003e2+\u003c/sup\u003e: 0.745 Å, Al\u003csup\u003e3+\u003c/sup\u003e: 0.535 Å, Ga\u003csup\u003e3+\u003c/sup\u003e: 0.62 Å) induces lattice strain because of their size difference from Ce\u003csup\u003e4+\u003c/sup\u003e.\u003csup\u003e[\u003cspan additionalcitationids=\"CR40 CR41 CR42\" citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e–\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]\u003c/sup\u003e The high configurational entropy (ΔS = 1.6R) can alleviate the stress, thereby stabilizing the single-phase fluorite-like structure even at relatively low temperatures (80–500 ºC). However, substituting Ce\u003csup\u003e4+\u003c/sup\u003e with considerably smaller cations such as Al\u003csup\u003e3+\u003c/sup\u003e (0.535 Å) restricts phase stability, possibly leading to the secondary phase observed at 600 ºC.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003ed illustrates the high-resolution O 1s spectra for OHNTs. The broad O 1s peak is deconvoluted into four components: lattice O (O\u003csub\u003eL\u003c/sub\u003e) at 529.5 eV, O vacancies (O\u003csub\u003eV\u003c/sub\u003e) at 531.5 eV, surface-adsorbed oxygen/hydroxyl species (O\u003csub\u003eA\u003c/sub\u003e) at 532.0 eV, and chemisorbed water at 533.5 eV. In OHNT\u003csub\u003e80\u003c/sub\u003e, the significant chemisorbed water signal is attributed to a surface passivation mechanism involving water adsorption into O vacancy sites.\u003csup\u003e[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]\u003c/sup\u003e As temperature rises, the O\u003csub\u003eV\u003c/sub\u003e and O\u003csub\u003eA\u003c/sub\u003e components exhibit an inverse relationship that aligns with the gradual dehydroxylation in OHNTs, along with the formation of O vacancies.\u003csup\u003e[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]\u003c/sup\u003e The O\u003csub\u003eV\u003c/sub\u003e concentration can be calculated by the ratio, O\u003csub\u003eV\u003c/sub\u003e/(O\u003csub\u003eL\u003c/sub\u003e+O\u003csub\u003eV\u003c/sub\u003e+O\u003csub\u003eA\u003c/sub\u003e), as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003ee. The remarkably high concentration of O vacancies likely compensates for the charge imbalance introduced by the presence of aliovalent cations.\u003csup\u003e[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe TGA curves of \u003cem\u003ef\u003c/em\u003e-MWCNTs and OHNTs in their as-prepared condition are compared in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e5\u003c/span\u003ea. The \u003cem\u003ef\u003c/em\u003e-MWCNTs exhibit a single weight-loss event of approximately 93% between 500 and 660°C, typically attributed to combustion, producing CO/CO\u003csub\u003e2\u003c/sub\u003e.\u003csup\u003e[\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]\u003c/sup\u003e The solid residue (≈ 7%) may arise from the Fe synthesis catalyst. In contrast, the OHNTs exhibit a continuous, multi-step weight loss of ≈ 42% from the onset of heating to 510°C. The corresponding DTA curve \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e5\u003c/span\u003eb\u003cb\u003e)\u003c/b\u003e shows alternating endothermic and exothermic peaks. The first endothermic event occurring below 100°C is assigned to physisorbed water loss. The subsequent endothermic events at ≈ 182, 263, and 500°C are attributed to stepwise dehydroxylation, which may form complex (oxy)hydroxide intermediates.\u003csup\u003e[\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]\u003c/sup\u003e The high-resolution XPS spectra for Co, Ni, Al, and Ga presented in Supplementary Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e illustrate the complexity of the (oxy)hydroxide transformation during the dehydroxylation process. The exothermic events at ≈ 135, 223, and 402 ºC are consistent with the oxidation of residual C within the OHNTs. No significant weight loss occurs above 550°C indicating that OHNTs are a direct structural precursor of HEOs.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows SEM images depicting the morphological evolution of OHNTs as the temperature increases. At 80°C, the OHNTs display a clear 1D morphology; however, their stability gradually deteriorates and, above 600°C, collapses into agglomerated particles.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe photocatalytic performance of OHNTs was assessed by photodegradation of ciprofloxacin (CIP) under UV irradiation (λ = 365 nm). The adsorption-desorption equilibrium in dark conditions was reached at 30 min. The UV-vis absorbance spectra shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003ea indicate that the CIP degradation follows a different pathway, varying with the oxide/hydroxide ratio within OHNTs. The OHNT\u003csub\u003e80\u003c/sub\u003e exhibited remarkable photocatalytic activity under UV light, achieving 96% CIP degradation within 45 min. Increasing heat-treatment temperatures, which caused progressive depletion of hydroxides within the OHNTs, resulted in a consistent decrease in their ability to photodegrade CIP.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003eb shows the degradation profile of CIP for the OHNTs. Regardless of the heat-treatment temperature, all OHNTs exhibited similar absorption capacities under dark conditions. Notably, the OHNT\u003csub\u003e80\u003c/sub\u003e showed 90% CIP photodegradation after a brief 15-minute irradiation period. The photodegradation of CIP exhibited pseudo-first-order kinetics, as evidenced by the linear plot generated from -ln(C/C₀) versus irradiation time. Where C₀ denotes the initial CIP concentration, and C is the CIP concentration at time t of the reaction (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003ec). The reaction rate constant (\u003cem\u003ek\u003c/em\u003e, min\u003csup\u003e− 1\u003c/sup\u003e) was determined from the slope of the linearized pseudo-first-order kinetic plot. The OHNT\u003csub\u003e80\u003c/sub\u003e demonstrates the fastest CIP photodegradation kinetics, achieving a rate of 0.067 min\u003csup\u003e− 1\u003c/sup\u003e. The absorption spectra indicate that different photodegradation routes are determined by the ratio of OH species to O vacancies. Specifically, the OHNT\u003csub\u003e80\u003c/sub\u003e is distinguished by its highest OH content. Consequently, the pronounced CIP photodegradation on OHNT\u003csub\u003e80\u003c/sub\u003e is attributed to the synergistic effect of abundant OH species along with O vacancies. Presumably, surface OH species act as precursors for hydroxyl radicals (•OH), which dominate CIP degradation, whereas O vacancies enhance light absorption, facilitate charge separation, and promote ROS generation. \u003csup\u003e[\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eIn summary, topotactic synthesis enables the formation of single-phase fluorite-like CeCoNiAlGa HE-OOHs at relatively low temperatures (80–500°C). The specific properties of CeCoNiAlGa HE-OOHs emphasize the critical synergistic interaction between OH species and O vacancies. Compared with traditional synthesis methods, topotactic transformation offers superior control over the morphology, composition, and functionality of HE-OOHs when favorable crystallographic symmetry alignment exists between the parent and product structures.\u003c/p\u003e"},{"header":"Methods","content":"\u003ch2\u003eSynthesis of OHNTs\u003c/h2\u003e\u003cp\u003eThe OHNTs were prepared via an innovative topotactic route in which the entire volume of the parent single-crystalline \u003cem\u003ef\u003c/em\u003e-MWCNTs was converted into CeCoNiAlGa HE-OOHs pseudomorphs using the conventional liquid-phase deposition method. As-received commercially available Ce(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e·6H\u003csub\u003e2\u003c/sub\u003eO, Al(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e·9H\u003csub\u003e2\u003c/sub\u003eO, Co(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e·6H\u003csub\u003e2\u003c/sub\u003eO, Ni(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e·6H\u003csub\u003e2\u003c/sub\u003eO, Ga(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e·xH\u003csub\u003e2\u003c/sub\u003eO, and NaOH chemicals were used as metal precursors and an oxidation-promoting reactant, respectively. The MWCNTs were prepared by the thermal decomposition of a toluene/ferrocene solution method, which had been described elsewhere.\u003csup\u003e[\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]\u003c/sup\u003e First, MWCNTs were functionalized in a 40 vol% HNO\u003csub\u003e3\u003c/sub\u003e solution at 90–110°C for 24 h under reflux. Subsequently, a precursor solution was prepared by mixing an equimolar (0.1 M) mixture of cations in HNO\u003csub\u003e3\u003c/sub\u003e. The resultant functionalized MWCNTs (\u003cem\u003ef\u003c/em\u003e-MWCNTs) were mixed with the precursor solution at a 1:0.6 molar ratio for 1 h in an ultrasonic bath. Then, 0.5 M NaOH solution was added slowly under vigorous stirring until the pH reached 7. The resultant suspension was filtered, and the solid product was repeatedly washed with deionized water and dried in open atmosphere at ≈ 80°C using an infrared lamp. The dried product was heat-treated at 400, 500, and 600°C in air for 30 min using a heating rate of 5°C min\u003csup\u003e− 1\u003c/sup\u003e.\u003c/p\u003e\u003ch3\u003eStructural, morphological, and chemical characterizations\u003c/h3\u003e\u003cp\u003eThe structure of the OHNTs was analyzed by X-ray diffraction (Bruker D8 Advance, with Cu Kα radiation (λ = 1.5405 Å)), in the scanning range (2θ) from 20° to 100 ° with 0.02° step width and constant counting time of 0.6 s/step. The morphology was examined by Field Emission Scanning Electron Microscopy, JEOL JSM6701F, at an accelerating voltage of 5 kV using the secondary electron detector. High-Resolution Transmission Electron Microscopy, JEOL ARM200F, at an accelerating voltage of 200 kV in the bright-field mode coupled with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS), was employed to analyze morphology and element distribution at the nanometer scale. The valence states of OHNTs were investigated by X-ray Photoelectron Spectroscopy using a Thermo Scientific K-Alpha ESCALAB 250Xi equipped with a 180° double-focusing hemispherical analyzer and a monochromatic Al Kα (1486.6 eV) source. The binding energy scale in the XPS spectra was calibrated to 284.8 eV for the C 1s peak of adventitious carbon. Analysis of the XPS spectra was conducted by using the Thermo Scientific Avantage data system. Raman spectroscopy was used to analyze the nature of covalent bonds using a LabRAM HR Evolution Horiba equipment with a wavelength of 532 nm in the range of 200–3000 cm\u003csup\u003e− 1\u003c/sup\u003e. The oxidation behavior of \u003cem\u003ef\u003c/em\u003e-MWCNTs and OHNTs in their initial condition was studied by thermal gravimetric analysis (TGA/DTA) at 10°C min\u003csup\u003e− 1\u003c/sup\u003e in an air flow of 50 mL/min, using alumina crucibles (TGA/DTA; Netzsch Regulus 2500 STA).\u003c/p\u003e\u003ch3\u003ePhotocatalytic evaluation\u003c/h3\u003e\u003cp\u003eThe photocatalytic activity of OHNTs was evaluated by the degradation of CIP (10 m L\u003csup\u003e− 1\u003c/sup\u003e) in aqueous solutions under UV light irradiation. The evaluation was conducted using 50 mg of OHNTs dispersed in 100 mL of the CIP solution. Before the photocatalytic test, the system was maintained in the dark for 30 min to ensure adsorption/desorption equilibrium. The test was performed at room temperature under constant stirring and UV irradiation (λ = 365 nm) for 45 min, with aliquots collected every 15 min. The photodegradation efficiency was monitored using a Perkin Elmer UV–vis Lambda 35 Spectrophotometer by measuring the maximum absorption of CIP at 275 nm.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThe Authors received FUNDING for this work:\u003c/p\u003e \u003cp\u003eM.A. H.-P., Instituto Polit\u0026eacute;cnico Nacional, M\u0026eacute;xico, IPN-SIP 20250084.\u003c/p\u003e \u003cp\u003eJ.R. V.-G., Instituto Polit\u0026eacute;cnico Nacional, M\u0026eacute;xico, IPN-SIP 20250896.\u003c/p\u003e \u003cp\u003eJ.R. V.-G., Secretar\u0026iacute;a de Ciencia, Humanidades, Tecnolog\u0026iacute;a e Innovaci\u0026oacute;n, M\u0026eacute;xico, CBF-2025-I-2873.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eS.P.-E. wrote the main manuscript text. J.R.V.-G. and M.A.H.-P. supervised the project and contributed to project administration, validation, funding acquisition, and manuscript review and editing. A.I.C.-B., A.V.-P., and R.B.-U. contributed to the methodology, investigation, data curation, and manuscript drafting. All authors reviewed and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eS. P.-E. and A.I. C.-B. acknowledge financial support from SECIHTI-Mexico.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData is available on request from the corresponding author, Jorge Roberto Vargas-Garcia, through [[email protected]](mailto:[email protected])\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eSham Lal, M. \u0026amp; Sundara, R. High entropy oxides\u0026mdash;a cost-effective catalyst for the growth of high yield carbon nanotubes and their energy applications. \u003cem\u003eACS Appl. Mater. Interfaces\u003c/em\u003e. \u003cb\u003e11\u003c/b\u003e, 30846\u0026ndash;30857. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/acsami.9b08794\u003c/span\u003e\u003cspan address=\"10.1021/acsami.9b08794\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShi, Y., Li, R. \u0026amp; Lei, Z. Influences of synthetic parameters on morphology and growth of high entropy oxide nanotube arrays. \u003cem\u003eCoatings\u003c/em\u003e \u003cb\u003e13\u003c/b\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/coatings13010046\u003c/span\u003e\u003cspan address=\"10.3390/coatings13010046\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRan, B. et al. High-entropy oxides for rechargeable batteries. \u003cem\u003eAdv. Sci.\u003c/em\u003e \u003cb\u003e11\u003c/b\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/advs.202401034\u003c/span\u003e\u003cspan address=\"10.1002/advs.202401034\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAnandkumar, M. \u0026amp; Trofimov, E. Synthesis, properties, and applications of high-entropy oxide ceramics: current progress and future perspectives. \u003cem\u003eJ. Alloys Compd.\u003c/em\u003e \u003cb\u003e960\u003c/b\u003e, 170690. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.jallcom.2023.170690\u003c/span\u003e\u003cspan address=\"10.1016/j.jallcom.2023.170690\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSun, Y. \u0026amp; Dai, S. High-entropy materials for catalysis: a new frontier. \u003cem\u003eSci. Adv.\u003c/em\u003e \u003cb\u003e7\u003c/b\u003e, eabg1600. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1126/sciadv.abg1600\u003c/span\u003e\u003cspan address=\"10.1126/sciadv.abg1600\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJia, X. \u0026amp; Li, H. Machine learning enabled exploration of multicomponent metal oxides for catalyzing oxygen reduction in alkaline media-. \u003cem\u003eJ. Mater. Chem. A\u003c/em\u003e. \u003cb\u003e12\u003c/b\u003e, 12487\u0026ndash;12500. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1039/D4TA01884B\u003c/span\u003e\u003cspan address=\"10.1039/D4TA01884B\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSarkar, A. et al. Nanocrystalline multicomponent entropy stabilised transition metal oxides. \u003cem\u003eJ. Eur. Ceram. Soc.\u003c/em\u003e \u003cb\u003e37\u003c/b\u003e, 747\u0026ndash;754. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.jeurceramsoc.2016.09.018\u003c/span\u003e\u003cspan address=\"10.1016/j.jeurceramsoc.2016.09.018\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDąbrowa, J. et al. Synthesis and microstructure of the (Co,Cr,Fe,Mn,Ni)\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e high entropy oxide characterized by spinel structure. \u003cem\u003eMater. Lett.\u003c/em\u003e \u003cb\u003e216\u003c/b\u003e, 32\u0026ndash;36. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.matlet.2017.12.148\u003c/span\u003e\u003cspan address=\"10.1016/j.matlet.2017.12.148\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSharma, Y. et al. Single-crystal high entropy perovskite oxide epitaxial films. \u003cem\u003ePhys. Rev. Mater.\u003c/em\u003e \u003cb\u003e2\u003c/b\u003e (R). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1103/PhysRevMaterials.2.060404\u003c/span\u003e\u003cspan address=\"10.1103/PhysRevMaterials.2.060404\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCheng, B. et al. Pressure-induced tuning of lattice distortion in a high-entropy oxide. \u003cem\u003eCommun. Chem.\u003c/em\u003e \u003cb\u003e2\u003c/b\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1038/s42004-019-0216-2\u003c/span\u003e\u003cspan address=\"10.1038/s42004-019-0216-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAbdul Hai, M., Daud, M., Mujtaba, G., Banat, F. \u0026amp; Al-Harthi, M. A. A comprehensive review of two-dimensional high-entropy layered hydroxides: Synthesis, characterization, and applications. \u003cem\u003eCoord. Chem. Rev.\u003c/em\u003e \u003cb\u003e529\u003c/b\u003e, 216435 (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNemani, S. K., Torkamanzadeh, M., Wyatt, B. C., Presser, V. \u0026amp; Anasori, B. Functional two-dimensional high-entropy materials. \u003cem\u003eCommun. Mater.\u003c/em\u003e \u003cb\u003e4\u003c/b\u003e, 16 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOkejiri, F. et al. Ultrasound-mediated synthesis of nanoporous fluorite-structured high-entropy oxides toward noble metal stabilization. \u003cem\u003eiScience\u003c/em\u003e \u003cb\u003e25\u003c/b\u003e, 104214. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.isci.2022.104214\u003c/span\u003e\u003cspan address=\"10.1016/j.isci.2022.104214\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePatriarchi, A. et al. Evaluation of high-entropy (Cr, Mn, Fe, Co, Ni)-oxide nanofibers and nanoparticles as passive fillers for solid composite electrolytes. \u003cem\u003eElectrochim. Acta\u003c/em\u003e. \u003cb\u003e512\u003c/b\u003e (145425). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.electacta.2024.145425\u003c/span\u003e\u003cspan address=\"10.1016/j.electacta.2024.145425\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eArun, S. R. \u0026amp; Jacob, G. Exploring the charge storage ability of the spinel-type high entropy oxide (MnFeCoNiZn)\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles for supercapacitor applications. \u003cem\u003eChem. Eng. J. Adv.\u003c/em\u003e \u003cb\u003e21\u003c/b\u003e, 100708. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.ceja.2025.100708\u003c/span\u003e\u003cspan address=\"10.1016/j.ceja.2025.100708\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTian, L., Zhang, Z., Liu, S., Li, G. \u0026amp; Gao, X. High-entropy perovskite oxide nanofibers as efficient bidirectional electrocatalyst of liquid-solid conversion processes in lithium-sulfur batteries. \u003cem\u003eNano Energy\u003c/em\u003e. \u003cb\u003e106\u003c/b\u003e, 108037. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.nanoen.2022.108037\u003c/span\u003e\u003cspan address=\"10.1016/j.nanoen.2022.108037\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAsim, M. et al. Microwave synthesis of rock-salt type high entropy oxides immobilized on graphene oxide nanosheets as an efficient catalyst for oxygen evolution reaction. \u003cem\u003eJ. Environ. Chem. Eng.\u003c/em\u003e 13, 118758;10.1016/j.jece.118758 (2025) (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, X. et al. Identification of the reconstruction induced high-entropy spinel oxide nanosheets for boosting alkaline water oxygen evolution. \u003cem\u003eChem. Eng. J.\u003c/em\u003e \u003cb\u003e503\u003c/b\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.cej.2024.158488\u003c/span\u003e\u003cspan address=\"10.1016/j.cej.2024.158488\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, X. L., Kim, E. M., Senthamaraikannan, T. G., Lim, D. H. \u0026amp; Jeong, S. M. Porous hollow high entropy metal oxides (NiCoCuFeMg)\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanofiber anode for high-performance lithium-ion batteries. \u003cem\u003eChem. Eng. J.\u003c/em\u003e 484, 149509;10.1016/j.cej.149509 (2024) (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, X., Tian, F., Sheng, J., Yu, Y. \u0026amp; Yang, W. High-entropy porous spinel ferrite @ amorphous carbon nanocomposites with abundant structural defects for wide-band electromagnetic wave absorption. \u003cem\u003eChem. Eng. J.\u003c/em\u003e \u003cb\u003e490\u003c/b\u003e, 151848. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.cej.2024.151848\u003c/span\u003e\u003cspan address=\"10.1016/j.cej.2024.151848\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhu, Y. et al. Spinel-type high-entropy oxide nanotubes for efficient oxygen evolution reaction. \u003cem\u003eColloids Surf. A\u003c/em\u003e. \u003cb\u003e686\u003c/b\u003e, 133315. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.colsurfa.2024.133315\u003c/span\u003e\u003cspan address=\"10.1016/j.colsurfa.2024.133315\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLei, Z. et al. Ultrastable metal oxide nanotube arrays achieved by entropy-stabilization engineering. \u003cem\u003eScr. Mater.\u003c/em\u003e \u003cb\u003e146\u003c/b\u003e, 340\u0026ndash;343. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.scriptamat.2017.12.025\u003c/span\u003e\u003cspan address=\"10.1016/j.scriptamat.2017.12.025\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMusic\u0026oacute;, B. L. et al. The emergent field of high entropy oxides: design, prospects, challenges, and opportunities for tailoring material properties. \u003cem\u003eAPL Mater.\u003c/em\u003e 8, 040912; (2020). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1063/5.0003149\u003c/span\u003e\u003cspan address=\"10.1063/5.0003149\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eM\u0026uuml;ller, U. \u003cem\u003eSymmetry Relationships between Crystal Structures: Applications of Crystallographic Group Theory in Crystal Chemistry\u003c/em\u003e 217\u0026ndash;226 (Springer, 2013).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePacheco-Espinoza, S. et al. Topotactical route to multiwalled cerium oxide nanotubes from MWCNTs. \u003cem\u003ePart. Part. Syst. Charact.\u003c/em\u003e \u003cb\u003e40\u003c/b\u003e, 2370007. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/ppsc.202200167\u003c/span\u003e\u003cspan address=\"10.1002/ppsc.202200167\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCort\u0026eacute;s-L\u0026oacute;pez, A. J., Mu\u0026ntilde;oz-Sandoval, E. \u0026amp; L\u0026oacute;pez-Ur\u0026iacute;as, F. Oxygenated surface of carbon nanotube sponges: electroactivity and magnetic studies. \u003cem\u003eAMS Omega\u003c/em\u003e. \u003cb\u003e4\u003c/b\u003e, 18011\u0026ndash;18022. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/acsomega.9b01773\u003c/span\u003e\u003cspan address=\"10.1021/acsomega.9b01773\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDresselhaus, M. S. \u0026amp; Endo, M. Relation of carbon nanotubes to other carbon materials in Carbon nanotubes: synthesis, structure, properties, and applications (Eds (eds Dresselhaus, M. S., Dresselhaus, G. \u0026amp; Avouris, P.) 11\u0026ndash;28 (Springer, (2001).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCahen, S., Speyer, L., Lagrange, P. \u0026amp; H\u0026eacute;rold, C. Topotactic mechanisms related to the graphene planes: chemical intercalation of electron donors into graphite. \u003cem\u003eEur. J. Inorg. Chem.\u003c/em\u003e \u003cb\u003e45\u003c/b\u003e, 4798\u0026ndash;4806. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/ejic.201900758\u003c/span\u003e\u003cspan address=\"10.1002/ejic.201900758\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWondimu, T. H., Zuo, Y., Shah, A. A. \u0026amp; Leung, P. puiki Leung. The recent progress of high-entropy layered double hydroxides and high-entropy amorphous materials for water electrocatalysis. \u003cem\u003eDecarb\u003c/em\u003e \u003cb\u003e8\u003c/b\u003e, 100110 (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSartoretti, E. et al. In situ Raman analyses of the soot oxidation reaction over nanostructured ceria-based catalysts. \u003cem\u003eSci. Rep.\u003c/em\u003e \u003cb\u003e9\u003c/b\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1038/s41598-019-39105-5\u003c/span\u003e\u003cspan address=\"10.1038/s41598-019-39105-5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMcBride, J. R., Hass, K. C., Poindexter, B. D. \u0026amp; Weber, W. H. Raman and x-ray studies of Ce\u003csub\u003e1\u0026thinsp;\u0026ndash;\u0026thinsp;x\u003c/sub\u003eRE\u003csub\u003ex\u003c/sub\u003eO\u003csub\u003e2\u0026ndash;y\u003c/sub\u003e, where RE\u0026thinsp;=\u0026thinsp;La, Pr, Nd, Eu, Gd, and Tb. \u003cem\u003eJ. Appl. Phys.\u003c/em\u003e \u003cb\u003e76\u003c/b\u003e, 2435\u0026ndash;2441. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1063/1.357593\u003c/span\u003e\u003cspan address=\"10.1063/1.357593\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (1994).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSadezky, A., Muckenhuber, H., Grothe, H., Niessner, R. \u0026amp; P\u0026ouml;schl, U. Raman microspectroscopy of soot and related carbonaceous materials: Spectral analysis and structural information. \u003cem\u003eCarbon\u003c/em\u003e \u003cb\u003e43\u003c/b\u003e, 1731\u0026ndash;1742. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.carbon.2005.02.018\u003c/span\u003e\u003cspan address=\"10.1016/j.carbon.2005.02.018\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2005).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLoridant, S. Raman spectroscopy as a powerful tool to characterize ceria-based catalysts. \u003cem\u003eCatal. Today\u003c/em\u003e. \u003cb\u003e373\u003c/b\u003e, 98\u0026ndash;111. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.cattod.2020.03.044\u003c/span\u003e\u003cspan address=\"10.1016/j.cattod.2020.03.044\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVinodkumar, T., Rao, B. G. \u0026amp; Reddy, B. M. Influence of isovalent and aliovalent dopants on the reactivity of cerium oxide for catalytic applications. \u003cem\u003eCatal. Today\u003c/em\u003e. \u003cb\u003e253\u003c/b\u003e, 57\u0026ndash;64. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.cattod.2015.01.044\u003c/span\u003e\u003cspan address=\"10.1016/j.cattod.2015.01.044\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2015).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAgarwal, S., Zhu, X., Hensen, E. J. M., Lefferts, L. \u0026amp; Mojet, B. L. Defect chemistry of ceria nanorods. \u003cem\u003eJ. Phys. Chem. C\u003c/em\u003e. \u003cb\u003e118\u003c/b\u003e, 4131\u0026ndash;4142. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/jp409989y\u003c/span\u003e\u003cspan address=\"10.1021/jp409989y\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2014).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, L., Chen, F., Lu, J. Q. \u0026amp; Luo, M. F. Study of defect sites in Ce\u003csub\u003e1\u0026thinsp;\u0026ndash;\u0026thinsp;x\u003c/sub\u003eMxO\u003csub\u003e2\u0026ndash;δ\u003c/sub\u003e (x\u0026thinsp;=\u0026thinsp;0.2) solid solutions using Raman spectroscopy. \u003cem\u003eJ. Phys. Chem. A\u003c/em\u003e. \u003cb\u003e115\u003c/b\u003e, 7972\u0026ndash;7977. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/jp203921m\u003c/span\u003e\u003cspan address=\"10.1021/jp203921m\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2011).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRudolph, W. W. \u0026amp; Irmer, G. Raman spectroscopic characterization of light rare earth ions: La\u0026sup3;⁺, Ce\u0026sup3;⁺, Pr\u0026sup3;⁺, Nd\u0026sup3;⁺ and Sm\u0026sup3;⁺ \u0026ndash; hydration and ion pair formation. \u003cem\u003eDalton Trans.\u003c/em\u003e \u003cb\u003e46\u003c/b\u003e, 4235\u0026ndash;4244 (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSchweke, D., Rubin, A., Rabinovitch, L., Kraynis, O. \u0026amp; Livneh, T. Cerium metal oxidation studied by IR reflection-absorption and Raman scattering spectroscopies. \u003cem\u003eJ. Phys. : Condens. Matter\u003c/em\u003e. \u003cb\u003e34\u003c/b\u003e, 324002 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVanpoucke, D. E. P., Bultinck, P., Cottenier, S., Van Speybroeck, V. \u0026amp; Van Driessche, I. Aliovalent doping of CeO\u003csub\u003e2\u003c/sub\u003e: DFT study of oxidation state and vacancy effects. \u003cem\u003eJ. Mater. Chem. A\u003c/em\u003e. \u003cb\u003e2\u003c/b\u003e, 13723\u0026ndash;13737. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1039/C4TA02449D\u003c/span\u003e\u003cspan address=\"10.1039/C4TA02449D\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2014).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMatussin, S. N., Khan, F., Harunsani, M. H., Kim, Y. M. \u0026amp; Khan, M. M. Visible-light-induced photocatalytic and photoantibacterial activities of Co-doped CeO\u003csub\u003e2\u003c/sub\u003e. \u003cem\u003eACS Omega\u003c/em\u003e. \u003cb\u003e8\u003c/b\u003e, 11868\u0026ndash;11879. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/acsomega.2c07058\u003c/span\u003e\u003cspan address=\"10.1021/acsomega.2c07058\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChidaraboyina, S., Nesaraj, A. S. \u0026amp; Arunkumar, M. Aluminium doped cerium oxide as an efficient nanophotocatalyst for the elimination of rhodamine B dye present in water. \u003cem\u003eAsian J. Chem.\u003c/em\u003e \u003cb\u003e35\u003c/b\u003e, 882\u0026ndash;886. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.14233/ajchem.2023.27574\u003c/span\u003e\u003cspan address=\"10.14233/ajchem.2023.27574\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRamasamy, V., Mohana, V. \u0026amp; Suresh, G. Study of Ni:CeO\u003csub\u003e2\u003c/sub\u003e nanoparticles for efficient photodegradation of methylene blue by sun light irradiation. \u003cem\u003eIndian J. Phys.\u003c/em\u003e \u003cb\u003e92\u003c/b\u003e, 1601\u0026ndash;1612. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s12648-018-1246-9\u003c/span\u003e\u003cspan address=\"10.1007/s12648-018-1246-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, F. et al. Ga-doped CeO\u003csub\u003e2\u003c/sub\u003e nanorods as highly active catalysts for the synthesis of dimethyl carbonate from CO\u003csub\u003e2\u003c/sub\u003e and methanol. \u003cem\u003eReact. Kinet Mech. Catal.\u003c/em\u003e \u003cb\u003e136\u003c/b\u003e, 2941\u0026ndash;2954. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s11144-023-02506-9\u003c/span\u003e\u003cspan address=\"10.1007/s11144-023-02506-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGhobadi, A., Ghobadi, T. G. U., Karadas, F. \u0026amp; Ozbay, E. Angstrom thick ZnO passivation layer to improve the photoelectrochemical water splitting performance of a tio\u003csub\u003e2\u003c/sub\u003e nanowire photoanode: the role of deposition temperature. \u003cem\u003eSci. Rep.\u003c/em\u003e \u003cb\u003e8\u003c/b\u003e, 16322. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1038/s41598-018-34248-3\u003c/span\u003e\u003cspan address=\"10.1038/s41598-018-34248-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSong, X. \u0026amp; Boily, J. F. Surface and Bulk Thermal Dehydroxylation of FeOOH Polymorphs. \u003cem\u003eJ Phys. Chem. A\u003c/em\u003e. \u003cb\u003e120\u003c/b\u003e, 6249\u0026ndash;6257 (2016).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGager, E. \u0026amp; Nino, J. C. Processing, phase stability, and conductivity of multication-doped ceria. \u003cem\u003eInorganics\u003c/em\u003e \u003cb\u003e11\u003c/b\u003e, 299. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/inorganics11070299\u003c/span\u003e\u003cspan address=\"10.3390/inorganics11070299\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eScheibe, B., Borowiak-Palen, E. \u0026amp; Kalenczuk, R. J. Oxidation and reduction of multiwalled carbon nanotubes \u0026mdash; preparation and characterization. \u003cem\u003eMater. Charact.\u003c/em\u003e \u003cb\u003e61\u003c/b\u003e, 185\u0026ndash;191. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.matchar.2009.11.008\u003c/span\u003e\u003cspan address=\"10.1016/j.matchar.2009.11.008\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2010).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, Y. X., Zhou, X. Z., Wang, Y. \u0026amp; You, X. Z. Preparation of nano-sized CeO\u003csub\u003e2\u003c/sub\u003e by mechanochemical reaction of cerium carbonate with sodium hydroxide. \u003cem\u003eMater. Lett.\u003c/em\u003e \u003cb\u003e58\u003c/b\u003e, 245\u0026ndash;249. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/S0167-577X(03)00454-3\u003c/span\u003e\u003cspan address=\"10.1016/S0167-577X(03)00454-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2004).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAnsari, A. A. \u0026amp; Kaushik, A. Synthesis and optical properties of nanostructured Ce(OH)\u003csub\u003e4\u003c/sub\u003e. \u003cem\u003eJ. Semicond.\u003c/em\u003e \u003cb\u003e31\u003c/b\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1088/1674\u0026ndash;4926/31/3/033001\u003c/span\u003e\u003cspan address=\"10.1088/1674\u0026ndash;4926/31/3/033001\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2010).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLe Crom, S. \u0026amp; Boily, J. F. Molecular-level insight into ciprofloxacin adsorption on goethite: I. Approach and non-specific binding. \u003cem\u003ePhys. Chem. Chem. Phys.\u003c/em\u003e \u003cb\u003e27\u003c/b\u003e, 4446\u0026ndash;4456. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1039/d4cp04027a\u003c/span\u003e\u003cspan address=\"10.1039/d4cp04027a\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQueir\u0026oacute;z, A. C. B. et al. Ciprofloxacin photodegradation by CeO\u003csub\u003e2\u003c/sub\u003e nanostructures with different morphologies. \u003cem\u003eWater Air Soil. Pollut\u003c/em\u003e. \u003cb\u003e234\u003c/b\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s11270-023-06424-3\u003c/span\u003e\u003cspan address=\"10.1007/s11270-023-06424-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAndrews, R. et al. Continuous production of aligned carbon nanotubes: a step closer to commercial realization. \u003cem\u003eJ. Chen Chem. Phys. Lett.\u003c/em\u003e \u003cb\u003e303\u003c/b\u003e, 467\u0026ndash;474. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/S0009-2614(99)00282-1\u003c/span\u003e\u003cspan address=\"10.1016/S0009-2614(99)00282-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (1999).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"High-entropy materials, Topotactic transformation, Nanostructured catalysts, Environmental photocatalysis, Ciprofloxacin photodegradation","lastPublishedDoi":"10.21203/rs.3.rs-8419535/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8419535/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study introduces a novel method for synthesizing Ce-Co-Ni-Al-Ga high-entropy (oxy)hydroxide (CeCoNiAlGa HE-OOH) nanotubes via a topotactic transformation using multiwalled carbon nanotubes (MWCNTs) as the parent crystal. CeCoNiAlGa HE-OOHs nanotubes are arranged in concentric cylinders, with high crystalline order, analogous to parent MWCNTs. CeCoNiAlGa HE-OOH nanotubes exhibit a fluorite-like crystalline structure that is supported by a distorted Ce-O framework. A neutral M-OH-M sheet stacking, resembling a partially dehydrated brucite-like layered hydroxide structure, appears to account for the multiwalled configuration of CeCoNiAlGa HE-OOH nanotubes. The fluorite-like structured CeCoNiAlGa HE-OOH (111) planes grow topotactically on the curved C (002) planes. Both the multiwalled arrangement and the stability of the fluorite-like structure are preserved from 80 to 500 \u0026ordm;C. CeCoNiAlGa HE-OOHs exhibit remarkably high concentration of O vacancies. Increasing the heat-treatment temperature leads to gradual dehydroxylation, indicating that HEOOHs are direct structural precursors of HEOs. Notably, the CeCoNiAlGa HE-OOHs obtained at 80 \u0026ordm;C have the highest OH content. They stand out for their remarkable photocatalytic activity under UV light, achieving 96% degradation of ciprofloxacin (CIP) within 45 min. The significant CIP photodegradation is attributed to the synergistic effect of abundant OH species along with O vacancies.\u003c/p\u003e","manuscriptTitle":"Topotactic Engineering of High-Entropy (Oxy)hydroxide Nanotubes for Enhanced Photocatalysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-31 06:33:43","doi":"10.21203/rs.3.rs-8419535/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-01-08T15:11:00+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-06T00:05:40+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-05T07:21:58+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-04T08:05:35+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"187368476497571657736891408661738369609","date":"2026-01-02T02:36:07+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"26872089510847461236911012632152145493","date":"2026-01-01T16:37:08+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"296386399038473689302306354233760573042","date":"2025-12-30T05:26:16+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-30T05:06:47+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-12-26T11:04:57+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-23T07:33:25+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-23T07:32:57+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-12-21T21:22:34+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"1dd69719-c630-456a-8ff9-083b5028a508","owner":[],"postedDate":"December 31st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":60372751,"name":"Physical sciences/Chemistry"},{"id":60372752,"name":"Physical sciences/Materials science"},{"id":60372753,"name":"Physical sciences/Nanoscience and technology"}],"tags":[],"updatedAt":"2026-03-23T16:00:50+00:00","versionOfRecord":{"articleIdentity":"rs-8419535","link":"https://doi.org/10.1038/s41598-026-44418-3","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2026-03-19 15:58:16","publishedOnDateReadable":"March 19th, 2026"},"versionCreatedAt":"2025-12-31 06:33:43","video":"","vorDoi":"10.1038/s41598-026-44418-3","vorDoiUrl":"https://doi.org/10.1038/s41598-026-44418-3","workflowStages":[]},"version":"v1","identity":"rs-8419535","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8419535","identity":"rs-8419535","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}