TiO2 Nanotube Photocatalyst Research Articles

Enhanced microalgal hydrogen production subsisting on visible light TiO2 nanotubes photocatalyst pre-treated palm kernel expeller

The present study investigated the application of photocatalytic process using TiO2 nanotubes (NTs) photocatalyst as an effective pre-treatment method for palm kernel expeller (PKE) in increasing its biodegradability to enhance the microalgal hydrogen production via dark fermentation. A series of TiO2 NTs photocatalysts were synthesized via employing electrochemical anodization of Ti foil at various voltages each in different types of electrolytes (choline chloride-ethylene glycol (ChCl-EG), choline chloride-urea (ChCl-U), choline chloride-glycerol (ChCl-Gly)). Increasing trend of average NTs diameters at 26.14 ± 1.30, 73.01 ± 1.94 and 122.00 ± 13.32 nm was observed for 25, 30 and 35 V in synthesizing TiO2 NTs using suitable ChCl-EG electrolyte, respectively. The high 35 V had resulted in noticeable pore ruptures within this TiO2 NTs photocatalyst. The PKE pre-treated by TiO2 NTs photocatalyst anodized at optimum 30 V in ChCl-EG electrolyte had demonstrated the highest releases of biochemical oxygen demand (BOD5) and soluble chemical oxygen demand (SCOD) concentrations at 594 and 607 mg/L, respectively. Moreover, the microalgal efficiency of BOD5 conversion and hydrogen yield were also consistently maintained from third cycle of TiO2 NTs photocatalyst's reutilizations, signifying the stability of TiO2 NTs photocatalyst.

Photodegradation of Methyl violet using Ag modified TiO2 nanotubes by UV and UV/ H2O2

Titanium dioxide (TiO2) is a semiconductor material that is frequently utilized in photodegradation applications. Its application in photodegradation is constrained by its broad band gap of 3.2 eV and increased rate of photoelectron recombination. However, by doping TiO2 with metallic nanoparticles, the band gap can be modified and photodegradation can be improved. The present study explores the fabrication of Ag-modified TiO2 nanotube photocatalysts by electrochemical anodization followed by hydrothermal method. The structural, morphological, compositional, optical, and thermal properties of prepared photocatalysts were characterized by X-ray analysis, Field emission scanning electron microscopy, N2 adsorption desorption analysis, X-ray photoelectron spectroscopy, Energy dispersive X-ray spectroscopy, UV–Vis diffuse reflectance analysis and Thermogravimetric-differential thermal analysis. The prepared photocatalyst was utilized to investigate the degradation of methyl violet in the presence of UVA and UVC radiation. The effects of UVA and UVC illumination on the degradation process, the effect of Ag loading in the TiO2 nanotube arrays and the role of H2O2 in the degradation of pollutant were studied. The degradation efficiency of methyl violet in the presence of UVC light was three times that of UVA light. For pristine TiO2 photocatalyst, the maximum degradation of 70% was obtained under UVC illumination in 8 h. When H2O2 was added, complete degradation was observed within 3 h. Reusability studies have shown that photocatalysts are stable and can be used for the degradation of methyl violet.

Biomass-derived carbon deposited TiO2 nanotube photocatalysts for enhanced hydrogen production.

In this study, titanium oxide nanotubes (TiO2NTs) were deposited on the surface of activated carbon (AC) by varying the wt% of AC. The physicochemical properties of synthesized TiO2NTs-AC nanocomposites were analysed by various characterization techniques such as XRD, FT-IR, Raman, DRUV-vis, HR-TEM, XPS, PL, and N2 physisorption. The FT-IR, EDX, and XPS analyses proved the existence of interaction between AC and TiO2NTs. This study found that as the content of AC increases, the surface area and pore volume increase while the energy bandgap decreases. The TiO2NTs-AC nanocomposite with 40% AC exhibited a surface area of 291 m2 g-1, pore volume of 0.045 cm3 g-1 and half pore width = 8.4 Å and had a wide band gap energy (3.15 eV). In addition, the photocatalytic application of the prepared nanocomposites for photocatalytic H2 production was investigated. The H2 was produced via photo-reforming in the presence of a sacrificial agent (methanol) under sunlight irradiation. It was found that the prepared TiO2NTs-AC nanocomposite with 40% AC acted as an efficient photocatalyst for aqueous-methanol reforming under various optimization conditions. Approximately 18 000 μmol-1 hydrogen gas was produced via aqueous-methanol reforming under optimized conditions (catalyst dose = 100 mg, temperature = 25 °C, time = 12 hours, vol. of methanol = 20% (v/v), and pH = 7). The reusability of the TiO2NTs-AC nanocomposite was also investigated for 5 consecutive cycles, and the results suggested only a slight decline in efficiency even after the fifth cycle. This study demonstrates the ability of an activated carbon deposited TiO2NT catalyst to produce hydrogen effectively under sunlight.

Low bandgap carbon nitride nanoparticles incorporated in titania nanotube arrays by in situ electrophoretic anodization for photocatalytic CO2 reduction

We report an in situ electrophoretic anodization process to realize a binary semiconductor heterojunction photocatalyst comprising green-emitting, water-soluble carbon nitride (CN) nanoparticles (NPs) embedded in TiO2 nanotube (TNT) arrays. Embedding CN inside a TiO2 matrix eliminates the possibility of the CNNPs leaching away during photocatalysis or photoelectrochemistry. The synthesized CN exhibits visible light absorption down to 600 nm and an unusually redshifted green emission peak at 527 nm, which are attributed to a carbon rich g-C3N4 composition with a C:N ratio of ∼ 1.9 at the surface. Spectroscopy revealed the excess carbon to be both amorphous and graphitic while the structural features characteristic of g-C3N4 were preserved. Raman spectroscopy, transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) analysis verified the formation of the heterostructure as well as indicated strong interaction between the CN and TiO2 in the hybrid. The CNNP@TNT hybrid demonstrated superior performance in sunlight driven photocatalytic CO2 reduction without the need for a sacrificial agent. The CO yield of photoreduction showed a more than threefold improvement for the CNNP@TNT hybrid compared to the stand-alone TNT photocatalyst. The synergistic enhancement of photocatalytic performance emerged due to the formation of a high-quality interface between the constituent semiconductors (TiO2 and CN) that facilitated efficient charge carrier separation. Density functional theory (DFT) calculations showed the feasibility of efficient photogenerated electron-hole pair separation at the heterointerface. Molecular dynamics (MD) simulations validated the facile dispersibility of CNNPs in water and polar solvents.

A Comprehensive Review on Advances in TiO2 Nanotube (TNT)-Based Photocatalytic CO2 Reduction to Value-Added Products

The photocatalytic reduction of CO2 into solar fuels by using semiconductor photocatalysts is one of the most promising approaches in terms of pollution control as well as renewable energy sources. One of the crucial challenges for the 21st century is the development of potential photocatalysts and techniques to improve CO2 photoreduction efficiency. TiO2 nanotubes (TNTs) have recently attracted a great deal of research attention for their potential to convert CO2 into useful compounds. Researchers are concentrating more on CO2 reduction due to the rising trend in CO2 emissions and are striving to improve the rate of CO2 photoreduction by modifying TNTs with the appropriate configuration. In order to portray the potential applications of TNTs, it is imperative to critically evaluate recent developments in synthesis and modification methodologies and their capability to transform CO2 into value-added chemicals. The current review provides an insightful understanding of TNT production methods, surface modification strategies used to enhance CO2 photoreduction, and major findings from previous research, thereby revealing research gaps and upcoming challenges. Stability, reusability, and the improved performance of TNT photocatalysts under visible light as well as the selection of optimized modification methods are the identified barriers for CO2 photoreduction into valuable products. Higher rates of efficacy and product yield can be attained by synthesizing suitable photocatalysts with addressing the limitations of TNTs and designing an optimized photoreactor in terms of the proper utilization of photocatalysts, incident lights, and the partial pressure of reactants.

Magnetically guidable single TiO2 nanotube photocatalyst: Structure and photocatalytic properties

The influence of annealing temperature, the crystallinity, textural properties of magnetically guidable anodic TiO2 nanotubes in form of single tube powders on the photocatalytic decomposition of model organic dye is investigated for the first time. The powders were prepared from self-organized anodic TiO2 nanotube layers (grown on Ti) by etching in piranha solution, detaching them from the Ti substrate, and annealing in a wide range of temperatures (400–900 °C). The nanotubular shape was preserved up to 800 °C. Powders annealed up to 800 °C did not contain any detectable rutile phase, which is unique among other TiO2 nanomaterials at this temperature. Part of the obtained TiO2 ST-NT powders was decorated with Fe3O4 nanoparticles using an oleic acid-based synthesis. The TiO2 ST-NT and TiO2 ST-NT@Fe3O4NPs powders were characterized in terms of morphology, crystallinity, and specific surface area. Finally, all materials were exploited for the photocatalytic decomposition of a model dye. The best photocatalytic performance of TiO2 ST-NT and TiO2 ST-NT@Fe3O4NPs powders were obtained at annealing temperatures of 600 and 700 °C, respectively. The synergy resulting from annealing, crystallite size, and specific surface area enhances the photocatalytic activity of TiO2 ST-NT and TiO2 ST-NT@Fe3O4NPs powders under UV light. This approach goes beyond the classical Kasuga alkaline hydrothermal approach, enabling the preparation of large quantity of TiO2 nanotubes without any impurities (such as e.g. Na or Ca content resulting from the Kasuga approach).

Enhanced Photoelectrochemical Activity of TiO2 Nanotubes Decorated with Lanthanide Ions for Hydrogen Production

Highly ordered TiO2 nanotubes (TNTs) decorated with a series of lanthanide ions (Ln3+ = Ho3+, Tb3+, Eu3+, Yb3+, and Er3+) were prepared through an electrochemical process and anodization. The composition, structure, and chemical bond of the as-prepared photocatalysts were characterized through scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and ultraviolet diffuse reflectance spectroscopy. Furthermore, the electrochemical characteristics of the catalysts were analyzed and photoelectrochemical properties were investigated through water splitting. All samples were prepared in the anatase phase without changing the crystal structure. The holmium-doped TNT photocatalyst exhibited the best performance with a hydrogen evolution rate of 90.13 μmol cm−2h−1 and photoconversion efficiency of 2.68% (0 V vs. RHE). Photocatalytic efficiency increased because of the expansion of the absorption wavelength range attributed to the appropriate positioning of the band structure and reduced electron/hole pair recombination resulting from the unhindered electron movement. This study demonstrated the preparation of high-potential solar-active photocatalysts through the synergetic effects of the work function, band edge, and bandgap changes caused by the series of lanthanide combinations with TNTs.

Titanium oxide nanotube film decorated with β-Ga2O3 nanoparticles for enhanced water splitting properties

TiO2 is a wide bandgap material with inherent photogenerated charge carrier recombination problems, which reduces its photoelectrochemical (PEC) water splitting efficiency. Considerable efforts have been dedicated to reducing this charge recombination problems by decorating the film’s surface using transition metal nanoparticles (NP) to enhanced device performance. And considerable numbers of literature reports are available to this respect. However, reports are rare for the surface modification of TiO2 nanotubes (TNT) arrays with metal oxide, specially by β-Ga2O3 nanostructures and its potential applications. Herein, the PEC water splitting properties of β-Ga2O3 NP (GNP)-modified TNT arrays is described. The TNT were synthesized by anodization, whereas the GNP were fabricated by chemical vapour deposition method. X-ray diffraction (XRD) results revealed the presence of weak β-Ga2O3 peaks and reduction in crystallite size upon GNP addition. The integration of GNP on the TNT arrays resulted in a slight increase in optical bandgap from 3.4 to 3.6 eV observed by UV–vis measurements. Linear sweep voltammetry measurement for the modified TNT photocatalyst showed a 32.5% enhancement in photocurrent density compared to the bare TNT photoelectrode, measured in 1 M HCl solution. Elemental analysis confirmed the presence of β-Ga2O3, thereby supporting the XRD and UV–vis results. This study demonstrates that GNP-activated TNT arrays could be used as photoanode for enhanced photocatalytic activity in the PEC cell.

Effect of cathode size on the morphology of the anodized TiO2 nanotube photocatalyst

Titanium dioxide nanotubes (TNTs) were synthesized via an electrochemical anodization process. The influence of increasing the cathode surface area on the microstructure and order of the final product was investigated. To study the microstructure of the synthesized nanotubes, field emission scanning electron microscopy (FESEM) was employed. The degree of crystallinity and the characteristic of synthesized nanostructure was evaluated by X-ray diffraction (XRD). The porous initiation layer covering the tube-top became thinner and lost its’ integrity, as a consequence of employing a larger cathode. This is due to the enhanced reaction sites followed by intensifying the electrochemical reaction in the anodic oxidation processes. In contrast, a small surface area of the cathode made it possible to control the obtained nanostructure with no damages to the surface morphology. The average diameter of the surface nanopores increased from 60 to 67 nm by increasing the cathode surface area. Optical characterization demonstrates that the bandgap of the synthesized TiO2 nanotubes is about 3.2 eV. In the process of methylene blue (MB) degradation, the photocatalytic activity of the TNTs with an ordered initiation layer reaches 69% after 480 min irradiation.

Toward efficient photocatalysts for light-driven CO2 reduction: TiO2 nanostructures decorated with perovskite quantum dots

Nanostructured TiO2 is often used for photocatalytic CO2 conversion due to its favorable electronic properties and stability, being coupled with large surface area and unique electrical properties. However, pure TiO2, without any expensive cocatalysts, can not provide highly efficient CO2 conversion because its bandgap and resulted limited numbers of photogenerated electrons and holes limit efficient energy conversion. Here, we demonstrate TiO2 nanotube (TNT) photocatalysts equipped with two different perovskite quantum dots (PQDs) made of CH3NH3PbBr3 and CH3NH3PbI3. The fundamental properties of the PQDs and TNT/PQD photocatalysts are investigated and their potential for more efficient CO2 conversion are discussed, to our best knowledge, for the first time. TNT/CH3NH3PbI3 QD photocatalysts absorb a wider range of light energy and show superior charge transport characteristics due to less sensitivity against surface states at TNT/CH3NH3PbI3 QD interface than the TNT/CH3NH3PbBr3 photocatalysts.

Enhancement of adsorption and photocatalytic activities of alkaline-based TiO2 nanotubes for experimental and theoretical investigation under FeCl3 and H2O2

Industrial and manufacturing processes are major responsible for water pollution, which has many environmental and health consequences. The development of efficient, green, and eco-friendly photocatalysis process to treat wastewater containing organic contaminants is highly desirable to solve significant water pollution problems. Herein, the photoreactivity of alkaline-based TiO2 nanotubes (TNTs) was investigated to catalyze the decomposition of green oxidants namely ferric chloride (FeCl3) and hydrogen peroxide (H2O2) to harvest free hydroxyl radicals (OH) and finally its significance for the remediation of phenol in visible-light irradiation. To our information, this study first reported that alkaline-based TNTs photocatalyst could successfully activate FelC3 and H2O2 and reduced phenol concentration up to 97.63 %. TNTs were prepared via a hydrothermal process in an alkaline environment at 180 °C for 24 h and characterized through XRD, TEM, BET surface area, DRS and FTIR analysis. In adsorption mechanism, pseudo-first-order and Type-1 pseudo-second-order kinetics were proved as best owing to an excellent correlation between experimental and theoretical outcomes and highest R2 up to 0.997. Langmuir and Freundlich isotherms were more appropriate models due to their highest R2 up to 0.994. Several thermodynamic parameters as enthalpy =53.84 kJ/mol, entropy = 173.87 kJ/mol K, Gibbs free energy = −51.76 to −58.71 kJ/mol and activation energy =22.17 kJ/mol were recommended that phenol adsorption method is favourable and spontaneous in nature. The rising temperature was more suitable for phenol removal onto alkaline-based TNTs.

Physicochemical Properties of a Highly Efficient Cu-Ion-Doped TiO₂ Nanotube Photocatalyst for the Degradation of Methyl Orange Under Sunlight.

In this study, a series of copper-ion-doped titanium dioxide (Cu-ion-doped TiO₂) nanotubes (NTs) were synthesized via a hydrothermal method by the concentration variation of doped Cu ions (0.00, 0.50, 1.00, 2.50, and 5.00 mmol). In addition, the samples were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), nitrogen gas adsorption measurements, and ultraviolet-visible (UV-Vis) diffuse-reflectance spectroscopy. The photocatalytic activity of the Cu-iondoped TiO₂ NTs was investigated for the degradation of methyl orange (MO) under sunlight. The results obtained from the structural and morphological studies revealed that, at low concentrations of Cu-doped TiO₂ NTs, Cu is incorporated into the interstitial positions of the TiO₂ lattice, affording a new phase of TiO₂ (hexagonal) instead of the anatase TiO₂ (tetragonal) observed for undoped TiO₂ NTs. EDX analysis confirmed the presence of Cu in the TiO₂-based photocatalyst. All of the investigated samples exhibited a hollow fibrous-like structure, indicative of an NT morphology. The inner and outer diameters of the NTs were 4 nm and 10 nm, respectively. The photocatalysts exhibited a large surface area due to the NT morphology and a type IV isotherm and H3 hysteresis, corresponding to the mesopores and slit-shaped pores. The Cu-ion-doped TiO₂ NTs were excited by sunlight because of their low bandgap energy; and after the incorporation of Cu ions into the interstitial positions of the TiO₂ lattice, the NTs exhibited high visible-light activity owing to the low bandgap.

Photocatalytic Characterization of TiO2 Nanotubes with Pd Particles Synthesized by Photoreduction Process

To decompose dye in aqueous solution, Pd nanoparticle-decorated TiO2 nanotube photocatalysts were fabricated through electrochemical anodization and photoreduction processes. Morphological and surface characterization of the TiO2/Pd heterojunction photocatalyst, as well as photoelectrochemical behaviors, were investigated by X-ray diffraction, UV/Vis diffuse reflectance and photocurrent response. It was found that the precipitated Pd particle size and distribution on TiO2 surface were affected by the photoreduction time. As the photoreduction time increased from 10 min to 180 min, the corresponding average diameter of the precipitated Pd particles on TiO2 photocatalyst increased from 4.35 nm to 9.29 nm. From the Aniline blue degradation results, the Pd decorated TiO2 catalysts enhanced photocatalytic activity compared to bare TiO2 catalyst, and the rate constant for dye degradation was dependent on the Pd particle size on the TiO2 surface. For an average Pd particle size lower than 7.80 nm, the particles were uniformly precipitated on the surface of the TiO2 nanotubes, and the dye degradation rate constants increased with increasing Pd particle size. However, for an average Pd particle size of more than 7.80 nm, the particles were agglomerated on the TiO2 surface, and the dye degradation rate constants gradually decreased. With an optimum Pd particle size of 7.80 nm, the TiO2/Pd photocatalyst showed higher photocatalytic activity and Aniline blue degradation rate, due to high photo absorbance response, and more efficient charge separation through electron transfer from the conduction band of the TiO2 to the Pd particles. Key words: photoreduction, Pd nanoparticles, dye degradation, photocatalytic rate constant

Treatment of Polyaniline Wastewater by Coupling of Photoelectro-Fenton and Heterogeneous Photocatalysis with Black TiO2 Nanotubes

In this study, mineralization of organic pollutants in polyaniline (PANI) wastewater was achieved by a combination of photoelectro-Fenton (PEF) and heterogeneous photocatalysis with black TiO2 nanotubes. Organics were decomposed by the •OH radicals and SO4–• radicals formed on the black TiO2 nanotube photocatalyst and at the IrO2/Ti anode during water oxidation and from the Fenton’s reaction between Fe2+ and generated H2O2. Poor chemical oxygen demand (COD) removal was obtained utilizing visible light/TiO2, anodic oxidation with generated H2O2 (AO-H2O2), visible light/black TiO2/AO-H2O2, and electro-Fenton. The mineralization was strongly increased by the PEF/black TiO2 process because of the photolysis of products under visible light irradiation; it was improved by coupled heterogeneous photocatalysis due to the additional •OH radicals at the black TiO2 nanotube surface. The results demonstrated that about 96.4% COD and 85% total organic carbon of PANI wastewater were removed after 360 min by the PEF/bla...

Super-oleophilicity Co-doping Co2+/F-/TiO2 one-dimensional nanotubes for photocatalytic denitrification of light oil

In this study, a simple hydrothermal synthesis method was adapted for the preparation of Co-doping Co2+/F-/TiO2 nanotubes photocatalyst, and the micro-nano structure of catalysts prepared by biomimetic technology which makes the catalyst have super-oleophilicity property. Co2+/F-/TiO2 revealed improved photocatalytic performance for denitrification of light oil compared to single TiO2 photocatalysts. The enhance of photocatalytic activity can be attributed to narrowing the band gap, increasing the light response wavelength and exposing more highly active crystal surfaces due to synergistic effects of Co2+ and F− in the photocatalyst.

Fabrication and enhanced photocatalytic property of TiO2-ZnO composite photocatalysts

TiO2 nanotube and TiO2-ZnO composite photocatalysts were fabricated by simple hydrothermal method, and the photocatalytic property of as-prepared samples were analyzed by the photo degradation of rhodamine B water solutions under visible light irradiation. The prepared TiO2-ZnO composite photocatalysts exhibited excellent property in photo degradation of rhodamine B water solution, which is better than that of P25. The enhancement photocatalytic property of target photocatalysts could be attributed to the reduced band gap energy, the enhanced-surface physic-chemical properties, the separation of photo induced electron-hole pairs and the decreased recombination rate. In addition, TiO2-ZnO composite photocatalysts showed good stability for rhodamine B photo degradation under visible light.

TiO2 nanotubes co-modified by Ag/AgCl plasmonic photocatalyst and graphene and a comparison of their enhanced photocatalytic performance under ultraviolet and visible light

Ag/AgCl-modified TiO2 nanotube photocatalysts (noted as Ag/AgCl/TiO2 nanotubes) are synthesized by the combine of deposition-precipitation and photoreduction methods firstly, and then reduced graphene oxide (rGO) is deposited on the Ag/AgCl/TiO2 nanotubes via a simple one-pot solvothermal method. TEM, HRTEM, XRD and UV–vis are utilized to characterize the morphology, microstructure, composition and optical property of the obtained samples. The photoactivities of samples are evaluated by the photodegradation of methyl orange under ultraviolet and visible light irradiation, respectively. The effects of contents of AgCl, Ag and rGO on the photocatalytic performance of Ag/AgCl/TiO2 nanotubes and rGO modified Ag/AgCl/TiO2 nanotubes are investigated, respectively, and their optimal contents are obtained. The results reveal that, after Ag/AgCl modification, the samples exhibit an absorption in visible region due to the surface plasmon resonance of metallic Ag nanoparticles. Besides that, the enhanced photocatalytic activities of Ag/AgCl/TiO2 nanotubes and rGO modified Ag/AgCl/TiO2 nanotubes samples are observed during ultraviolet and visible light irradiation. Based on the results, the different photocatalytic mechanisms under ultraviolet and visible light irradiation are proposed.

Fabrication, characterization and photoelectrochemical activity of tungsten-copper co-sensitized TiO2 nanotube composite photoanodes

Tungsten-copper co-sensitized TiO2 nanotube films on titanium substrate, used as photoanodes in photoelectrochemical (PEC) water splitting to produce hydrogen, have been synthesized via anodization and chemical bath deposition (CBD) methods. Field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) were used to study the morphology and elemental composition of the synthetic samples. UV–Vis diffuse reflection spectroscopy (UV–Vis DRS) was sued to investigate the optical features of the samples. The impact of copper and tungsten ratio on the photocatalytic behavior of co-sensitized TiO2 nanotube photoelectrodes in PEC water splitting has been investigated. High photocatalytic activity has been exhibited by the co-sensitized TiO2 nanotube samples due to the synergistic effects of the copper and tungsten. Sample T4 had the highest photoelectrochemical activity compared with other samples. In addition, this sample exhibited outstanding photochemical stability even after four runs in the photocatalytic test. A simple method for the synthesis of high performance co-sensitized TiO2 nanotube photocatalysts for application in solar energy conversion has thus been proposed in this work. The advantages of these new photoanodes for practical applications are low cost, ease of synthesis, high activity in visible light and excellent stability.

Phenol degradation using an anodized graphene-doped TiO2 nanotube composite under visible light

TiO2 nanotubes (TNTs) were doped with reduced graphene oxide (RGO) via anodization. The synthesized catalyst was characterized by FE-SEM, XRD, AES, PL, Raman, and UV–vis DRS. We have synthesized the catalyst with different RGO doping time and RGO concentration. The optimum synthesis conditions for RGO doping were a 0.5gL−1 RGO anodization at 60V for 1min. Compared with un-doped TNTs, the RGO-doped TNT photocatalyst showed a 3.8-fold higher photocatalytic activity, while phenol degradation under visible light irradiation. Optimum phenol degradation was observed at an external bias of 0.5V using a photoelectrocatalytic method, and this degradation rate was 3.5-fold higher than that observed for un-doped TNTs. The intermediate products of phenol were also analyzed using TD-GC-MS method to evaluate the phenol degradation pathways. The RGO-doped TNTs reduced the recombination of photo-induced e- and h+ and thus increased the formation of the OH radicals and superoxides that degrade phenol.

Electrochemical synthesis of co-doped RGO–Bi–TiO2 nanotube composite: Enhanced activity under visible light

Abstract TiO2 nanotube (TNT) photocatalyst with enhanced visible-light activity was synthesized by co-doping with reduced graphene oxide (RGO) and bismuth (Bi). The RGO–Bi–TNTs composite was fabricated using three different approaches: one-step, two-step, and three-step electrochemical anodization. The synthesized catalyst was characterized by FE-SEM, XRD, AES, and PL. Co-doping optimum synthesis using three-step method accomplished 1.5 and 3.8-times higher photocatalytic activity than single-doping and undoped-TNTs, respectively under same conditions. RGO and Bi were favorable for separation of e− and h+, which reduced recombination of charges. This result promoted the formation of OH radicals and increased photocatalytic efficiency of TNTs under visible light.