Adsorbed Hydroxyl Groups Research Articles

The Effect of Solvents on the Crystal Morphology of Pyriproxyfen

To obtain crystal products with ideal morphology and better quality, it is important to fully understand and grasp the affecting mechanism of solvents on crystal morphology. In this work, the interactions between solvent/solute molecules and different crystal faces of pyriproxyfen are investigated by a combination of experiments and molecular simulations. It is found that pyriproxyfen crystals grow into a lamellar morphology in methanol and ethanol, while the crystal grows into a three-dimensional shuttle morphology in n-butanol and n-heptane. Molecular simulations reveal that the molecular arrangement of crystal faces makes the alcohol hydroxyl adsorption sites exposed in different degrees, and the (002) face is more sensitive to alcohol hydroxyl than other faces. The adsorption of alcohol hydroxyl groups hinders the growth of crystal planes, so (002) and (102) faces become the main crystal planes in methanol and ethanol, and the lamellar crystal is formed. The developed knowledge of the growth mechanism based on the interaction between the solvent and crystal interface can be conducive to the further optimization of the pyriproxyfen crystal products.

Ultrafast short-range catalytic pathway modified peroxymonosulfate activation over CuO with surface oxygen defects for tetracycline hydrochloride degradation

The presence of antibiotics in water bodies seriously threatens the ecosystem and human health. Advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS), an effective method to remove antibiotics, have a bottleneck problem that the low oxidant utilization is attributed to the hindered electron transfer between metal oxides and peroxides. Here, CuO with rich oxygen vacancies (OVs), MSCuO-300, was synthesized to efficiently degrade tetracycline hydrochloride (TTCH) (k = 0.095 min−1). The dominant role of direct adsorption and activation of OVs and its regulated Cu–O, rather than surface hydroxyl adsorption, mediated a short-range catalytic pathway. The shortened catalytic pathway between active sites and PMS accelerated the charge transfer at the interface, which promoted PMS activation. Compared with CuxO-500 and Commercial CuO, the activation rate of PMS was increased by 11.97, and 12.64 times, respectively. OVs contributed to the production of 1O2 and O2•-, the main active species. In addition, MSCuO-300/PMS showed excellent adaptability to real water parameters, such as pH (3–11), anions, and continuous reactor maintained for 168 h. This study provides a successful case for the purification of antibiotic-containing wastewater in the design of efficient catalysts by oxygen defect strategies.

Dissolution mechanism of Fe3O4 scale by 1-hydroxyethane-1,1-diphosphonic acid: an ab initio molecular metadynamics study.

Using the ab initio molecular metadynamics method, the adsorption of the structure of 1-hydroxyethane-1,1-diphosphonic acid (HEDP) on the Fe3O4 surface and subsequent detachment of Fe atoms from the surface were simulated, and the dissolution mechanism by which HEDP dissolves Fe3O4 scale at room temperature while other organic acids cannot was elucidated. The adsorbed hydroxyl groups, water and HEDP on the Fe3O4 surface play a synergistic role in detaching the Fe ions, which increases the coordination number of the Fe atoms and weakens the original Fe-O bond strength. In addition, the strong coordination ability and flexible molecular structure of HEDP also facilitate dissolution of Fe3O4 scale by breaking down the chemical bonds and forming Fe-HEDP complexes. The free energy surface for the dissolution reaction shows a low barrier, and the descaling reaction is easily accomplished.

Enhanced electrochemical glucose sensing of Co/Cu-MOF by hydroxyl adsorption induced reactive oxygen species.

Exploring the factors affecting the electrochemical catalytic signal of an organic-metal material sensor and analyzing the decisive steps of the glucose oxidation behavior are challenging problems. Here, we designed a copper-cobalt-based organic backbone with excellent sensing properties based on the nanostructure of "ultramicroelectrodes", and explored the role of different hydroxyl adsorption capacities in the sensing process of glucose oxidation. Dimethylimidazole was used as a starting substrate, and then copper and cobalt ions were introduced by hydrothermal treatment to prepare a copper-cobalt-based organic backbone (Co/Cu-MOF) with good electrochemical glucose sensing ability. Due to the abundant micro-reaction sites of Co/Cu-MOF and the ability to control the hydroxyl group adsorption by adjusting the Co/Cu ratio, excellent electrocatalytic sensing performance was ensured. Co/Cu-MOF (Co/Cu molar ratio of 20 : 1) showed the best adsorption capacity for hydroxyl groups with a sensitivity of 0.45 mA mM-1 cm-2 and a LOD of 0.82 μM in electrochemical glucose sensing. In summary, the sensing performance was effectively improved by adding adsorbed hydroxyl groups to provide an oxygen source for the glucose oxidation step without changing the specific components.

Ru-doped WO3 enabling efficient hydrogen oxidation reaction in alkaline media.

Developing highly efficient hydrogen oxidation reaction (HOR) electrocatalysts in alkaline media is of great significance for anion exchange membrane fuel cells (AEMFCs). Herein, we report an efficient Ru-doped hexagonal tungsten trioxide (Ru-WO3) HOR electrocatalyst through a hydrothermal strategy. The prepared Ru-WO3 electrocatalyst exhibits enhanced HOR performance with a 6.1 times higher exchange current density and better durability than commercial Pt/C. Structural characterizations and theoretical calculations reveal that the uniformly distributed Ru was modulated by oxygen defects and the electron transfer from O to Ru modulated the H* adsorption of Ru sites. In addition, plenty of W sites can serve as hydroxyl adsorption sites to accelerate the HOR kinetics. This work not only provides an efficient HOR catalyst in alkaline media, but also promotes the fundamental understanding of the effect of modulation on the adsorption of H* and *OH in tungsten oxides with a relatively low oxidation state by Ru doping, broadening the range of HOR catalysts to Ru-doped metal oxides.

Application of a biomimetic wellbore stabilizer with strong adhesion performance for hydrate reservoir exploitation

Natural gas hydrate (NGH) in marine is usually reserved in the pores or cracks of weakly cemented argillaceous siltstones. Moreover, the hydrates are susceptible to variations in temperature and pressure conditions when water-based drilling fluids (WBDFs) are drilled into hydrate reservoirs, leading to the hydrate in-situ decomposition and severe sand production. In this work, an inexpensive and facilely prepared biomimetic wellbore stabilizer with strong adsorption of multiple hydrogen bonds was prepared by fusing catechol-rich tannic acid (TA) and polyvinyl alcohol (PVA) with polyol hydroxyl adsorption function, referred to as TA-PVA complex (TA-PVA). TA-PVA was added to WBDFs to strengthen the NGH reservoir wellbore for ensuring the safety of drilling process in a wide temperature range (2-60℃). The microscopic characterization of TA-PVA and its cohesion mechanism with argillaceous siltstone was investigated by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The mechanical properties of skeleton of the artificial hydrate cores were evaluated by compressive strength test, with maximum compressive strength reaching 0.45 MPa. And the adhesion force of TA-PVA to the probe modified by silica microsphere (PSM) was further studied by AFM. Meanwhile, the adhesion forces between TA-PVA and cyclopentane hydrate particles were measured at 1.5℃. Adhesion test results demonstrate that TA-PVA can bond clay particles, quartz sand and hydrate particles together. In detail, the adhesion force between TA-PVA and PSM reaches more than 164.46 mN/m, the adhesion force between TA-PVA droplet and cyclopentane hydrate particle reaches 43.19 mN/m. The differential scanning calorimetry (DSC)curves demonstrate that TA-PVA releases no heat between 0 and 60 °C, indicating that TA-PVA has no impact on the decomposition of NGH, showing the potential to maintain the integrity of NGH reservoir.

Steering Pt surface via N-doped carbon layer to highly active CO-tolerant hydrogen oxidation reaction catalyst in alkaline media

Improving the CO-tolerant ability of Pt-based electrocatalysts is crucial for fuel cells fed with industrial byproduct hydrogen. Herein, we present a novel core-shell structured Pt@NC/C catalyst consisting of ultrafine Pt nanoparticles (1.63 nm) as the core and ultrathin nitrogen-doped carbon layers (0.36 nm) as the shell. The catalyst exhibits excellent alkaline hydrogen oxidation reaction (HOR) activity with a mass activity of 187 A g−1Pt and a specific activity of 0.20 mA cm−2Pt, which are 1.3 and 2.2-folds to the counterpart Pt/C, respectively. More remarkably, it shows good anti CO-poisoning ability. In presence of H2 with 100 ppm CO, the HOR current degraded by 18.22% on 10% Pt/C versus only 4.81% on 10% Pt@NC/C-400. The combined X-ray photo-electron spectrum (XPS) analysis, COad stripping, CO oxidation and Zeta potential measurements imply that hydroxyl adsorption is enhanced on the NC covered Pt in 10% Pt@NC/C-400 possibly due to electron modulation induced by the strong metal and support interaction, which accelerates HOR kinetics and improvs anti-CO ability. This work provides a facile and feasible strategy to design efficient and CO-resistant Pt-based catalysts.

Nanostructured Gallium Nitride Membrane at Wafer Scale for Photo(Electro)catalytic Polluted Water Remediation.

Photo(electro)catalysis methods have drawn significant attention for efficient, energy-saving, and environmental-friendly organic contaminant degradation in wastewater. However, conventional oxide-based powder photocatalysts are limited to UV-light absorption and are unfavorable in the subsequent postseparation process. In this paper, a large-area crystalline-semiconductor nitride membrane with a distinct nanoporous surface is fabricated, which can be scaled up to a full wafer and easily retrieved after photodegradation. The unique nanoporous surface enhances broadband light absorption, provides abundant reactive sites, and promotes the dye-molecule reaction with adsorbed hydroxyl radicals on the surface. The superior electric contact between the nickel bottom layer and nitride membrane facilitates swift charge carrier transportation. In laboratory tests, the nanostructure membrane can degrade 93% of the dye in 6 h under illumination with a small applied bias (0.5V vs Ag/AgCl). Furthermore, a 2 inch diameter wafer-scale membrane is deployed in a rooftop test under natural sunlight. The membrane operates stably for seven cycles (over 50 h) with an outstanding dye degradation efficiency (>92%) and satisfied average total organic carbon removal rate (≈50%) in each cycle. This demonstration thus opens the pathway toward the production of nanostructured semiconductor layers for large-scale and practical wastewater treatment using natural sunlight.

Impact of TiO2 Reduction and Cu Doping on Bacteria Inactivation under Artificial Solar Light Irradiation.

Preparation of TiO2 using the hydrothermal treatment in NH4OH solution and subsequent thermal heating at 500-700 °C in Ar was performed in order to introduce some titania surface defects. The highest amount of oxygen vacancies and Ti3+ surface defects were observed for a sample heat-treated at 500 °C. The presence of these surface defects enhanced photocatalytic properties of titania towards the deactivation of two bacteria species, E. coli and S. epidermidis, under artificial solar lamp irradiation. Further modification of TiO2 was targeted towards the doping of Cu species. Cu doping was realized through the impregnation of the titania surface by Cu species supplied from various copper salts in an aqueous solution and the subsequent heating at 500 °C in Ar. The following precursors were used as a source of Cu: CuSO4, CuNO3 or Cu(CH3COO)2. Cu doping was performed for raw TiO2 after a hydrothermal process with and without NH4OH addition. The obtained results indicate that Cu species were deposited on the titania surface defects in the case of reduced TiO2, but on the TiO2 without NH4OH modification, Cu species were attached through the titania adsorbed hydroxyl groups. Cu doping on TiO2 increased the absorption of light in the visible range. Rapid inactivation of E. coli within 30 min was obtained for the ammonia-reduced TiO2 heated at 500 °C and TiO2 doped with Cu from CuSO4 solution. Photocatalytic deactivation of S. epidermidis was greatly enhanced through Cu doping on TiO2. Impregnation of TiO2 with CuSO4 was the most effective for inactivation of both E. coli and S. epidermidis.

Hydroxyl-functionalized ZnO monolayers for optoelectronic devices: Atomic structures and electronic properties

Two-dimensional materials have been extensively investigated both experimentally and theoretically due to their appealing physical/chemical properties. Zinc oxide (ZnO) monolayers, as typical two-dimensional materials, have also aroused wide concern. However, the improper bandgap or nonmagnetic limits their applications in optoelectronic or spintronic devices. Herein, based on first-principles calculations, the effects of individual hydroxyl adsorption and hydroxyl group functionalization on the atomic and electronic structures of ZnO monolayers are investigated. The results demonstrated that the most stable structure for individual hydroxyl on the ZnO monolayer is the one in which the hydroxyl is adsorbed on the top of the hollow site with an adsorption energy of −1.448 eV. Furthermore, hydroxyl could easily aggregate on ZnO monolayer with increasing of hydroxyl coverage and form epoxy groups. Upon hydroxyl group functionalization, ZnO monolayers exhibit mechanical and thermal stability. Moreover, OH–ZnO and ZnO–OH monolayers exhibit magnetic semiconductors, while OH–ZnO–OH monolayers are nonmagnetic semiconductor. Additionally, the band gaps of ZnO monolayer with hydroxyl group functionalization could be effectively modulated via applying the strain. This study opens a new avenue for preparing potential high-performance ZnO-based optoelectronic devices.

Synergistic adsorption effect on Co3O4(1 1 0) surface to promote the ethanol sensing properties: Experiment and theory

A deep understanding of the relationship between the properties and structure of transition metal oxide semiconductor gas sensors is essential for optimizing sensor design. Comparing and analyzing the sensing properties of nanomaterials with different morphologies and crystal facets by combining the experiment analysis and the density functional theory (DFT) calculations could identify and understand the corresponding mechanisms at the atomic or ionic level. Here, grown Co3O4 nanosheet (Co3O4-NS) with exposed (111) facets, and Co3O4 nanorods (Co3O4-NR) with exposed (110) facets on alumina ceramic tubes were prepared and studied in sensing ethanol. The adsorption characteristics of ethanol on the sensor surface were analyzed by DFT calculation. The results demonstrated that the sensing performance of Co3O4-NR was superior to Co3O4-NS. The adsorption of hydroxyl groups in ethanol was better than the methyl groups on the surface. The oxygen and hydrogen atoms from the hydroxyl groups in ethanol had the lowest adsorption energies (Eads = −3.44 eV) when they interact with the Co atom and the indirectly adjacent low-coordinate oxygen atoms on the (110) surface, respectively. The synergistic adsorption of target gases by exposed surface atoms induced superior sensing properties of the material.

The role of various components in Ru-NiCo alloys in boosting the performance of overall water splitting

Understanding the synergistic mechanism of multi-component alloys is crucial and challenging for overall water splitting. Herein, Ru-NiCo0.5-600 °C and Ru-Ni0.75Co with excellent electrocatalytic activity are designed and synthesized. The Ru-NiCo0.5-600 °C alloy exhibits remarkable HER activity with an overpotential of 42, 77 and 93 mV at 10 mA cm−2 in alkaline, acidic and neutral conditions, and the Ru-Ni0.75Co electrocatalyst presents outstanding OER activity with an overpotential of 176 mV at 10 mA cm−2 in 1.0 M KOH. The Ru-NiCo0.5-600 °C ||Ru-Ni0.75Co cell requires only 1.48 and 1.69 V to reach 10 and 100 mA cm−2 towards overall water splitting. A series of experiments reveal that the strong electronic coupling among Ru, Ni and Co regulates the electronic structure and enhances the intrinsic catalytic activity and stability of the as-synthesized Ru-NiCo electrocatalysts. Systematic experimental and theoretical results prove that Ni atoms act as the active sites of dissociating water, while Ru and Co are respectively the active centers of proton and hydroxyl adsorption for HER and OER. Our work provides a new perspective for profoundly understanding the synergistic effect of multi-component alloys towards water splitting.

Interface Metal Oxides Regulating Electronic State around Nickel Species for Efficient Alkaline Hydrogen Electrocatalysis.

Heterogeneous electrocatalysis typically depends on the surface electronic states of active sites. Modulating the surface charge state of an electrocatalysts can be employed to improve performance. Among all the investigated materials, nickel (Ni)-based catalysts are the only non-noble-metal-based alternatives for both hydrogen oxidation and evolution reactions (HOR and HER) in alkaline electrolyte, while their activities should be further improved because of the unfavorable hydrogen adsorption behavior. Hereto, Ni with exceptional HOR electrocatalytic performance by changing the d-band center by metal oxides interface coupling formed in situ is endowed. The resultant MoO2 coupled Ni heterostructures exhibit an apparent HOR activity, even approaching to that of commercial 20% Pt/C benchmark, but with better long-term stability in alkaline electrolyte. An exceptional HER performance is also achieved by the Ni-MoO2 heterostructures. The experiment results are rationalized by the theoretical calculations, which indicate that coupling MoO2 with Ni results in the downshift of d-band center of Ni, and thus weakens hydrogen adsorption and benefits for hydroxyl adsorption. This concept is further proved by other metal oxides (e.g., CeO2 , V2 O3 , WO3 , Cr2 O3 )-formed Ni-based heterostructures to engineer efficient hydrogen electrocatalysts.

A selective alkaline etching strategy to prepare hierarchical Beta molecular sieves for the hydrodeoxygenation of phenol

A selective alkaline etching strategy is reported to prepare hierarchical Beta molecular sieves with cetyltrimethyl ammonium bromide (CTAB). The homogeneityof mesopores is tuned by surface modification of Beta molecular sieves. CTAB selectively interacts with crystal defects and protects primary etched small mesopores from continuous destruction to form large mesopores. Under the synergistic effect of NaOH solution and CTAB, the acidity retention of Beta molecular sieves is higher due to the removal of Si(OSi)4 rather than Si(OSi)3 (OAl) species. When employed as the support of Pt/Beta catalysts, hydroxyl adsorption of phenol on Beta molecular sieves and Pt particles are observed. Dispersion of Pt on the surface of Beta molecular sieves is improved due to the uniform distribution of mesopores. A higher dispersion of Pt attributes to a higher deoxygenation conversion of phenol. The unique contribution of the current research is to propose the role of CTAB in alkaline etching process, realizes the controllable porosity regulation, and alleviates the acidity loss of Beta molecular sieves. These results are important to broaden the application fields of aluminum–silicon molecular sieves especially for large molecules engaged reactions and preparation of supported catalysts with a high metal dispersion.

Enhancing hydrogen electrocatalytic oxidation on Ni3N/MoO2 in-plane heterostructures in alkaline solution

AbstractNickel (Ni)-based materials act as one of the most promising candidates as platinum-group-metal-free (PGM-free) electrocatalysts for hydrogen oxidation reaction (HOR) in alkaline solution. Nevertheless, the electrocatalytic activity of pure Ni is significantly limited due to the sluggish kinetics under alkaline condition. To accelerate the kinetics, constructing heterostructures and nitride structures have been developed as two representative strategies. Here, we combined the two methods and presented a facile synthesis of the sheet-like Ni3N/MoO2 in-plane heterostructures for enhanced HOR in alkaline electrolytes. Relative to Ni or Ni3N, the Ni3N/MoO2 in-plane heterostructures exhibited a significantly increased mass activity by 8.6-fold or 4.4-fold, respectively. Mechanistic studies revealed that the enhanced activity of Ni3N/MoO2 could be attributed to the weakened hydrogen adsorption and strengthened hydroxyl adsorption. This work provides a facile approach to design high-efficiency catalysts for hydrogen-oxidation catalysis and beyond.

Hierarchical multiphase (Ni, Co)-Se with adjustable interlayer distance derived from reconstructed ZIF-L for enhanced hybrid-supercapacitors

As attractive electrodes for hybrid-supercapacitors (HSCs), transition-metal selenides (TMSes) demonstrate ideal conductivity and abundant valence states for rapid charge. However, the traditional TMSes are restricted to accumulative or low-correlation active sites and the single phase. Herein, reasonable structures rich in synergistic active sites are solutions to manufacture high-efficiency electrodes. Regular hexagonal NiCo-LDH (layered double hydroxide) is reconstructed on hollow carbon–nitrogen frameworks (CNFs) and a stable hierarchical system is constructed. After systematic gradient selenization (time/temperature), the controllable interlayer spacing with phase transformation of LDH derivatives (multiphase selenides: M-(Ni, Co)-Se (Co9Se8, NiSe2)) is researched. It is found that the hydroxyl adsorption and conductivity can be enhanced due to the synergistic effect between the multiphase TMSes, which can significantly improve the capacity of the electrode. The optimal electrode M-(Ni, Co)-Se@CNFs/CC (carbon cloth) (378.9 mAh g−1, 1 A−1, 6 M KOH) is obtained after systematic research. Furthermore, the HSC (M-(Ni, Co)-Se@CNFs/CC//Activated carbon) exhibits ultrahigh energy density (96.6 Wh kg−1) and excellent stability (10,000 cycles, 133.6 %, 6 M KOH), which is superior to most similar work. The novel path of multiphase synergy is successfully realized through the multiphase system, which has reference significance in the high-efficiency HSC industry.

Influence of temperature, surface composition and electrochemical environment on 2-propanol decomposition at the Co[formula omitted]O[formula omitted] (001)/H[formula omitted]O interface

Ab initio molecular dynamics simulations of a single hydrated 2-propanol molecule were performed to study the role of temperature, surface structure and electrochemical environment for the oxidation of 2-propanol to acetone at the Co3O4 (001)/H2O interface. On the A-terminated and B-terminated surfaces, which differ in the relative number of Co2+ and Co3+ ions at the surface, 2-propanol adsorbs molecularly on the Co2+ and Co3+ sites, respectively. In both cases, no C-H bond cleavage is observed at room temperature. However, under oxidative conditions, which are modeled here by partial dehydrogenation of the mixed hydroxyl/water adsorbate layer, dehydrogenation of the alcoholic OH group is observed on both surface terminations. As a result, adsorbed 2-propanolate is formed. The reaction on the less hydroxylated B-terminated surface further proceeds with C-H bond cleavage at the 2-carbon atom. The oxidation product acetone remains adsorbed on the Co3+ site during the simulation period of approximately 20 ps. Both deprotonation steps are aided by the presence of the adsorbed hydroxyl groups in the vicinity of the adsorbed alcohol molecule, because both hydrogen atoms from the reactand molecule are transferred as protons to form adsorbed water molecules. Different from the case of the partially dehydrogenated environment, raising the system temperature from 300 to 450 K, which can be considered a simple model for high temperature thermal catalysis, does not lead to oxidation via C–H dehydrogenation of the 2-propanol molecule.

Could one non-noble metal surface with non-noble substrate be a good hydrogen evolution catalyst: Performance of transition metal A monolayer on B substrate in theory frame

Could materials only including non-noble metals be good HER catalysts? To deal with this puzzle, computational screening of 132 different non-noble transition metal A/B surfaces for HER (A monolayer on B), are carried out by first-principles calculations systematically. The formation energies and dissolution potentials are calculated to access stabilities of A/B in vacuum and in solution, respectively. The realistic catalytic surfaces with oxygen or hydroxyl (co)adsorption are confirmed by analyzing Surface Pourbaix diagrams. Finally, three A/B surfaces (Cu/Mo, Mo/W, and Ti/Nb) with high stabilities and high HER exchange current densities (8.51, 3.39, 2.83 mA/cm2) are screened out. Further electronic properties analysis reveals that the different interactions between H 1s and d orbital, s orbital of A atoms will determine the feasible application of d and s band centers to uncover water effect and substrate effect on hydrogen adsorption ability, and tune the HER activity of A/B in the end.

Modifying Interface Solvation and Oxygen Reduction Electrocatalysis with Hydrophobic Species

Ionic liquid interlayers improve the oxygen reduction reaction (ORR) kinetics on bulk and nanostructured catalysts for both Pt and alloyed-Pt materials. Despite the demonstrated performance enhancement at the half-cell and membrane electrode assembly level, the mechanism of the improvement is not fully understood. In this work, we combine single-crystal experiments with microkinetic modeling to uncover the origin of the ORR kinetic improvement on Pt(111) in the presence of ionic liquids and hydrophobic cations. With the incorporation of a modified Frumkin isotherm, our model accurately simulates the disorder–order transition observed in hydroxyl and bisulfate adsorption on Pt(111) under acidic conditions. Voltametric analysis shows that ionic liquids impact solvation to break so-called scaling relations between the adsorption strength of OHad and Oad, but these effects have little impact on ORR activity. Instead, destabilized OHad reduces the overall hydroxyl (spectator) coverage, resulting in higher availability of active sites.

Investigation of photocatalytic activity of TiO2 nanotubes synthesized by hydrothermal method

TiO2 nanotubes were synthesized by hydrothermal reaction using commercially available TiO2 powder at 150 °C for 24 h. The transmission electron microscopy, X-ray diffraction, nitrogen adsorption-desorption isotherms and Fourier Transform-Infrared spectroscopy were used to characterize the nanotubes. Anatase phase was not transformed into rutile phase in the range of calcination temperature studied. Increase in calcination temperature result in enhancement of crystallinity and reduction in BET surface area. Photocatalytic removal of Reactive Red 239 (RR239) was investigated using prepared TiO2 nanotubes. Effects of pH, TiO2 nanotube dosage, initial RR239 concentration and calcination temperature were studied. 99%, 97% and 55% of removal efficiency values were attained at pH = 3, 5 and 7, respectively within 60 min or reaction time. With an increase in dosage of TiO2 nanotube in the range of 0.25–0.75 g dm−3, removal rate increased by a steeper slope. Complete removal of RR239 was observed at 20 mg dm−3 RR239 concentrations within 30 min but longer time was required for complete removal at higher concentrations. Langmuir-Hinshelwood kinetic expression was proposed based on nonlinear regression analysis. The removal efficiency of nanotubes calcined at 300 − 450 °C significantly increased but further increase in calcination temperature caused to decrease the efficiency.100% and 85% removal efficiency values were observed using actual solar light within 120 min of reaction time in July and January, respectively. Experiments conducted with scavengers showed that holes and adsorbed hydroxyl radicals were the major species involved in removal of RR239. A pathway for degradation of RR239 was suggested according to detected intermediate compounds.