Hollow hybrid titanate/Au@TiO2 hierarchical architecture for highly efficient photocatalytic application

Hollow hybrid titanate/Au@TiO₂ hierarchical architecture consisting of titanate and anatase titanium dioxide (TiO₂) loaded with Au nanoparticles was prepared via a sol-impregnation method combined with a hydrothermal etching process. The titanate/Au@TiO₂ architecture possesses unique hollow spherical configuration with Au nanoparticles loaded in the middle of titanate and TiO₂ shells and allows to be used as a microreactor for photocatalytic application. The hybrid titanate/Au@TiO₂ photocatalyst shows significantly enhanced photocatalytic activity on degradation of methylorange (MO) under UV light irradiation due to the lower electron–hole pairs recombination rate arisen from the synergistic effect of titanate-Au-TiO₂ in hybrid hierarchical architecture.     

Fabrication of graphene films on TiO2 nanotube arrays for photocatalytic application

Graphene film was formed on the surface of titanium dioxide nanotube (TiO₂ NT) arrays through in situ electrochemical reduction of a graphene oxide dispersion by cyclic voltammetry. The residual oxygen-containing groups and other structural defects such as sp³-hybridized carbons in the electrodeposited graphene were further removed by photo-assisted reduction of the underlying TiO₂ NTs, thus achieving the maximum restoration of π-conjugation in the graphene planes. Spectroscopic, electrochemical, and photoelectrochemical techniques were used to characterize the graphene films, and the use of the resulting graphene–TiO₂ NT material in photocatalysis was investigated. The results showed that the graphene–TiO₂ NT material exhibited a greatly improved photocatalytic activity compared with unmodified TiO₂ NTs.     

A multifunctional Ag/TiO2/reduced graphene oxide with optimal surface-enhanced Raman scattering and photocatalysis

A multifunctional Ag/TiO₂/reduced graphene oxide (rGO) ternary nanocomposite was prepared by a one-step photochemical reaction with TiO₂ and Ag nanoparticles successively deposited on reduced graphene oxide. The structure, morphology, composition, optical, and photoelectrochemical properties of Ag/TiO₂/rGO were investigated in detail. Meanwhile, the ternary nanocomposite possessed much higher adsorption capacity to organic dyes compared with bare TiO₂ and binary Ag/TiO₂, which would help to its use for surface-enhanced Raman scattering detection and photocatalytic degradation. Due to the charge transfer between rGO and organic dyes and enhanced electromagnetic mechanism of Ag, Ag/TiO₂/rGO nanocomposites as surface-enhanced Raman scattering substrates demonstrated dramatically improved sensitivity and good uniformity. The detection limit of rhodamine 6G (R6G) was as low as 10⁻⁹ mol/L, and the relative standard deviation values of the intensities remained below 5%. Most importantly, the synergistic coupling effect of three components extended the photoresponse range and accelerated separation of the electron-hole pairs, leading to greatly improved photocatalytic activity under simulated sunlight. The maximum rate constant (k, 0.06243 min⁻¹) of Ag/TiO₂/rGO was 50 and four times higher than that of TiO₂ and Ag/TiO₂, respectively.     

Synthesis and photocatalytic performance of PVA/TiO2/graphene‐MWCNT nanocomposites for dye removal

TiO₂/graphene‐MWCNT nanocomposite was prepared using solvothermal reaction for the effective distribution of TiO₂ nanoparticles on carbonaceous materials. TiO₂/graphene‐MWCNT nanocomposite was immobilized in poly(vinyl alcohol) (PVA) matrix for a convenient recovery after wastewater purification. MWCNT was incorporated in a nanocomposite not only to prevent the restacking of graphene but also to increase the electron transfer from TiO₂. The detailed characterization of the nanocomposite was performed using SEM, EDX, XRD, XPS, and FTIR. The photocatalytic performance of PVA/TiO₂/graphene‐MWCNT nanocomposite was investigated by UV spectroscopy on the basis of degradation of organic pollutants. PVA/TiO₂/graphene‐MWCNT nanocomposite showed improved photocatalytic decomposition of more than 70% of residual dye left in case of using PVA/TiO₂/graphene nanocomposite due to the improved electron transfer and the higher adsorption of organic pollutants. PVA/TiO₂/graphene‐MWCNT nanocomposite was suitable as a promising material for the recyclable photocatalytic wastewater purification system. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40715.     

P123 assisted morphology-engineered and hierarchical TiO<Subscript>2</Subscript> microspheres for enhanced photocatalytic activity

In this study, hierarchical titanium dioxide (TiO₂) microspheres with controlled morphology derived from calcination treatment of hierarchical titanate microspheres were fabricated. The obtained hierarchical TiO₂ microspheres with diameters of 1 to 2 µm were composed of polycrystalline anatase nanosheets with thickness of 10 nm. The morphology was manipulated by simply adjusting the molar ratio of tetrabutyl titanate/P123. At a low molar ratio of 17.04, TiO₂ microspheres composed of a large number of nanosheets closely packed together were obtained. At a high molar ratio of 34.08, TiO₂ hybrid architectures with polycrystalline anatase hierarchical microspheres and single-crystal anatase mesoporous (approximately 5 nm) nanospheres were obtained. Investigations on evolution formation revealed that P123 played a key role in the formation of a well-defined hierarchical structure. The photocatalytic performances of the obtained samples were investigated by the degradation of methylene blue and papermaking wastewater. When compared with commercial P25, the obtained hierarchical TiO₂ microspheres exhibit superior photocatalytic activity, high degradation efficiency, and good reproducibility. The product with hybrid architectures exhibited the highest photocatalytic activity. The chemical oxygen demand and the chroma removal rate of papermaking wastewater achieved 85.5 and 100%, respectively, after 12 h of photodegradation.     

Ternary Pt@TiO2/rGO Nanocomposite to Boost Photocatalytic Activity for Environmental and Energy Use

This work explores the effect of ternary nanostructure for the enhanced photocatalytic degradation of pollutants and dyes. One-pot solvothermal-assisted approach was used for producing nanosized Pt@TiO₂ hybrid nanoparticles (NPs) decorated on reduced graphene oxide (rGO) layers. The microstructure, morphology, chemical composition, and optical absorption of the designed photocatalyst was successfully characterized (using XRD, TEM, Raman, UV–visible absorption spectra, and XPS techniques). The ternary Pt@TiO₂-rGO photocatalyst consist of monodisperse quasi-spherical Pt@TiO₂ NPs with an average size of 11 nm deposited on the rGO nanosheets. Furthermore, Pt@TiO₂-rGO was further investigated for the photodegradation of pesticide and dyes under UV and visible light. The ternary Pt@TiO₂-rGO photocatalyst proved a significant improvement on the photodecomposition of pollutants compared to hybrid Pt@TiO₂. The Pt@TiO₂-rGO photocatalyst was found to show seven- and threefold increase in the photocatalytic activity compared to TiO₂ and Pt@TiO₂ NPs, respectively which resulted from the high surface area of rGO and as well as the strong Pt/TiO₂/rGO interactions which ensured excellent properties of charge separation. On the other hand, the ternary photocatalyst exhibited very good recycle and reuse capacity up to five cycles.

     

Graphene–Titania Hybrid Photoanodes by Supersonic Kinetic Spraying for Solar Water Splitting

We report the synthesis of graphene–TiO₂ (G–TiO₂) composite films that exhibit significantly enhanced photoelectrochemical water‐splitting performance relative to pure TiO₂. Supersonic kinetic spraying was used to produce strongly adhered, electrically and mechanically robust G–TiO₂ composite films containing 0.1, 0.5, 1.0, and 5.0 wt.% graphene. Films with an intermediate graphene content of 1.0 wt.% demonstrated the best water‐splitting performance. G–TiO₂ composite films with 1.0 wt.% graphene exhibited photocurrent density ten times that of pure TiO₂ films. The electron transfer between TiO₂ and graphene suppresses the recombination of photoinduced charge carriers and prolongs the electron excited‐state lifetime, which contributes to the enhanced photoelectrochemical water‐splitting performance.     

Innovative synthesis of a novel ZnO/ZnBi2O4/graphene ternary heterojunction nanocomposite photocatalyst in the presence of tragacanth mucilage as natural surfactant

Developing interfacial connections is one of the breakthrough strategies to improve the photocatalytic activity of graphene/p-n heterojunction systems. Herein, natural tragacanth mucilage, for the first time, was employed as cost-effective and ecofriendly surfactant to prepare highly efficient ZnO–ZnBi₂O₄/graphene hybrid photocatalyst. The results indicated that the methylene blue (MB) photocatalytic degradation efficiency of ZnO–ZnBi₂O₄/graphene-mucilage heterojunction, containing 10 wt% ZnBi₂O₄ and 1 wt% graphene, was ～1.2, 1.4, 3.1 and 8.3 times higher than that of ZnO–ZnBi₂O₄/graphene, ZnO–ZnBi₂O₄, ZnBi₂O₄ and ZnO samples, respectively. This significant improvement in the photocatalytic performance could be mainly ascribed to the desirable advantages of using natural mucilage as surfactant, including uniform distribution of ZnO–ZnBi₂O₄ nanoparticles on the surface of graphene sheets, increasing of the effective surface area, and improving of the charge carriers separation. Based on the trapping experiments, electron spin resonance and photoelectrochemical Mott-Schottky tests, direct Z-Scheme charge transfer mechanism with hydroxyl radicals as main active species was suggested for photocatalytic degradation of MB on the ZnO–ZnBi₂O₄/graphene-mucilage nanocomposite. This study provides a new insight to fabricate more homogeneous and close contact interfaces in graphene-based hybrid photocatalytic systems for environmental remediation.     

Structural and photoelectrochemical characterization of TiO2 nanowire/nanotube electrodes by electrochemical etching

TiO₂ nanowire/nanotube electrodes were synthesized by anodization of titanium foils in ethylene glycol solution containing 0.5 wt% NH₄F and 1 wt% water at 60 V for 6 h. The microstructure and morphology of the asprepared electrodes were investigated by XRD and SEM. A possible formation mechanism and oxidation parameters of nanocomposite structure were discussed. The relationship between structural characteristics of TiO₂ nanowire/nanotube electrodes and its photoelectrochemical characterization were evaluated by electrochemical analyzer and photocatalytic degradation of methylene blue (MB) solution. Furthermore, these TiO₂ nanowire/nanotube electrodes promoted the photoelectrochemical characterization due to the larger surface areas, enhanced light harvesting and electron transport rate. The results show that photocurrent density of 1.44mA/cm² and photocatalytic degradation of 95.51% was achieved for TiO₂ nanowire/nanotube electrodes, which were 0.55mA/cm² and 20.52% higher than the TiO₂ nanotube electrodes under a similar condition, respectively.     

Fabrication of CdO–graphene embedded mesoporous TiO2 composite for the visible-light response and its organic dye remediation

ABSTRACT

In this study, mesoporous CdO–graphene and mesoporous TiO₂ were successfully synthesized using a facile method. The results indicated that photocatalytic activity can be enhanced with the combination of mesoporous CdO–graphene and mesoporous TiO₂. The photocatalytic performance of the mesoporous CdO–graphene–TiO₂ photocatalyst presents significantly improved photocatalytic activity of safranine O, reactive black B, and GA due to the improvement of the surface area and the small average pore size distribution of the as-prepared mesoporous CdO–graphene–TiO₂. The photodegradation rate was optimized by safranine O at a pH solution of 11 and by GA at the dosage amount of 0.07 g photocatalyst.     

Microwave-assisted synthesis of Ag–TiO2/graphene composite for hydrogen production under visible light irradiation

Novel photocatalysts based on silver (Ag), TiO₂, and graphene were successfully synthesized by microwave-assisted hydrothermal method. The prepared photocatalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) specific surface area analysis, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The influence of silver loading and graphene incorporation on photocatalytic hydrogen (H₂) production of as-prepared samples was investigated in methanolic aqueous solution under visible light irradiation (λ≥420 nm). The results showed that Ag–TiO₂/graphene composite had appreciably enhanced photocatalytic H₂ production performance under visible light illumination compared to pure TiO₂, Ag–TiO₂ and TiO₂/graphene samples. The enhanced photocatalytic hydrogen production activity of Ag–TiO₂/graphene composite under visible light irradiation could be attributed to increased visible light absorption, reduced recombination of photogenerated charge carriers and high specific surface area. This novel study provides more insight for the development of novel visible light responsive TiO²⁻ graphene based photocatalysts for energy applications.     

TiO2 nanoparticles assembled on graphene oxide nanosheets with high photocatalytic activity for removal of pollutants

A novel method was developed to synthesize graphite oxide/TiO₂ composites as a highly efficient photocatalyst by in situ depositing TiO₂ nanoparticles on graphene oxide nano-sheets by a liquid phase deposition, followed by a calcination treatment at 200 °C. The two-dimensional porous graphene oxide/TiO₂ composites had specific surface area of 80 m² g⁻¹ being considerably larger than that of P25 and the similarly prepared neat TiO₂ particles without using graphene oxide. The composites exhibited excellent photocatalytic activity, being influenced by post-calcination temperature, graphene oxide content and solution pH. Under optimal conditions, the photo-oxidative degradation rate of methyl orange and the photo-reductive conversion rate of Cr(VI) over the composites were as high as 7.4 and 5.4 times that over P25, respectively. The excellent enhancing effect of graphene oxide nano-sheets on the photocatalytic properties of TiO₂ was attributed to a thin two-dimensional sheet support, a large surface area and much increased adsorption capacity, and the strong electron transfer ability of the thermally reduced graphene oxide in the composite.     

One-pot self-assembled TiO2/graphene/poly(acrylamide) superporous hybrid for photocatalytic degradation of organic pollutants

We report the development of TiO₂/graphene/poly(acrylamide) superporous hybrid by a radical polymerization reaction and explore its environmental application as photocatalyst of organic pollutants. During the polymerization reaction, graphene nanosheets and TiO₂ nanoparticles homogeneously distribute on the hydrogel, in which TiO₂ nanoparticles with a uniform size are densely anchored onto graphene and self-assembled into different structures with various graphene contents. The resultant TiO₂/graphene/poly(acrylamide) superporous hybrid experiences tremendous adsorption toward dye pollution before photodegradation, and it also displays similar photodecomposition efficiency with pristine TiO₂. Moreover, the TiO₂/graphene/poly(acrylamide) superporous hybrid is recyclable, which demonstrates the potential of hybrid as an attractive photocatalyst for wastewater treatment. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47033.     

Graphene modified Nd/TiO2 photocatalyst for methyl orange degradation under visible light irradiation

A novel nanoscale GR–Nd/TiO₂ composite photocatalyst was synthesized by the hydrothermal method. Its crystal structure, surface morphology, chemical composition and optical properties were studied using XRD, TEM, and XPS, DRS and PL spectroscopy. It was found that graphene and neodymium modification shifts the absorption edge of TiO₂ to visible-light region. The results of photoluminescence (PL) emission spectra show that GR–Nd/TiO₂ composites possess better charge separation capability than do Nd/TiO₂ and pure TiO₂. The photocatalytic activity of prepared samples was investigated by degradation of methyl orange (MO) dye under visible light irradiation. The results show that the GR–Nd/TiO₂ composite can effectively photodegrade MO, showing an impressive photocatalytic activity enhancement over that of pure TiO₂. The enhanced photocatalytic activity of the composite catalyst might be attributed to the large adsorptivity of dyes, extended light absorption range and efficient charge separation due to Nd doping and graphene incorporation.     

Photocatalytic Decomposition of Lactic Acid in Water on a Photoelectrochemical Circuit System Consisting of a Rod-type TiO2 Electrode and Silicon Solar Cell

Lactic acid, a well-known substance causing dental caries, was dissolved in water and completely oxidized into CO₂ and H₂O on a powdered TiO₂ photocatalyst under UV light irradiation. Furthermore, a unique photoelectrochemical circuit system consisting of a rod-type TiO₂ electrode and counter electrode connected through a silicon solar cell was constructed and its photocatalytic activity for the decomposition of lactic acid was investigated. The photoelectrochemical circuit system was found to effectively mineralize the lactic acid in water into CO₂ while the negative bias applied on the rod-type TiO₂ electrode enhanced the photocatalytic decomposition rate of the lactic acid.     

Anticorrosion reinforcement of waterborne polyacrylate coating with nano-TiO2 loaded graphene

Photocathodic protection coatings have been widely applied in various areas such as ship and architectural protection, or chemical industry. In this work, a composite of titanium dioxide loaded with reduced graphene oxide (RGO/TiO₂) was prepared and used as filler on waterborne polyacrylate (PA) coating to reinforce the metal protection against corrosion. Compared with the current filler of zinc phosphate used for anticorrosive coating, the photoelectrochemical properties of RGO/TiO₂-PA coating exhibit improved photocathodic protection under visible light illumination since RGO/TiO₂ composite has significant superiority in enhancing metal protection due to its dispersion, micropore blocking ability, and photoelectrochemical conversion performance. The mechanism of anticorrosion reinforcement of RGO/TiO₂-PA coating was hypothesized that graphene provides an extrabarrier layer to obstruct corrosive in dark condition and photocathodic protection under lighting. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48733.     

One-pot synthesis of CdS sensitized TiO2 decorated reduced graphene oxide nanosheets for the hydrolysis of ammonia-borane and the effective removal of organic pollutant from water

A hybrid material of reduced graphene oxide (RGO) sheets decorated with CdS-TiO₂ NPs was prepared through a facile one-pot hydrothermal method. The assembly of CdS-TiO₂ nanoparticles (NPs) on RGO sheets was in-situ produced. As-synthesized nanocomposites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy disperse X-ray spectrum (EDS), fourier transform infrared spectroscopy (FTIR), and photoluminescence spectroscopy (PL). The obtained nanocomposites exhibited a good photocatalytic activity for the visible-light-induced decomposition of methylene blue (MB) dye and hydrolysis of ammonia borane. The results showed that by incorporation of CdS and TiO₂ NPs on graphene oxide sheets the photocatalytic efficiency was enhanced. The significant enhancement in the photocatalytic activity of CdS-TiO₂/RGO nanocomposites under visible light irradiation can be ascribed to the effect of CdS by acting as electron traps in TiO₂ band gap. Reduced graphene oxide worked as the adsorbent, electron acceptor and a photo-sensitizer to efficiently enhance the dye photo decomposition. Such nanocomposite photocatalyst might find potential application in a wide range of fields, including hydrogen energy generation, air purification, and wastewater treatment.     

Preparation, characterization and visible-light-driven photocatalytic activity of Fe-doped titania nanorods and first-principles study for electronic structures

Fe-doped TiO₂ (Fe-TiO₂) nanorods were prepared by an impregnating-calcination method using the hydrothermally prepared titanate nanotubes as precursors and Fe(NO₃)₃ as dopant. The as-prepared samples were characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, N₂ adsorption–desorption isotherms and UV–vis spectroscopy. The photocatalytic activity was evaluated by the photocatalytic oxidation of acetone in air under visible-light irradiation. The results show that Fe-doping greatly enhance the visible-light photocatalytic activity of mesoporous TiO₂ nanorods, and when the atomic ratio of Fe/Ti (R_Fe) is in the range of 0.1–1.0%, the photocatalytic activity of the samples is higher than that of Degussa P25 and pure TiO₂ nanorods. At R_Fe = 0.5%, the photocatalytic activity of Fe-TiO₂ nanorods exceeds that of Degussa P25 by a factor of more than two times. This is ascribed to the fact that the one-dimensional nanostructure can enhance the transfer and transport of charge carrier, the Fe-doping induces the shift of the absorption edge into the visible-light range with the narrowing of the band gap and reduces the recombination of photo-generated electrons and holes. Furthermore, the first-principle density functional theory (DFT) calculation further confirms the red shift of absorption edges and the narrowing of band gap of Fe-TiO₂ nanorods.     

Immobilization of TiO2 on an ITO substrate to facilitate the photoelectrochemical degradation of an organic dye pollutant

In this study, we developed an immobilized TiO₂ semiconductor on an ITO glass substrate (TiO₂/ITO) and investigated its photocatalytic and electrochemical performance. The TiO₂/ITO samples were prepared via a spin-coating process followed by calcination and were used for the photocatalytic or electrochemical degradation of an organic dye pollutant. The measured photocatalytic performance was comparable to that reported in previous publications; however, a remarkable result was obtained in our electrochemical system. The formation of hydroxyl radicals (OH) strongly dominated the electrochemical system, which resulted in outstanding degradation performance. Therefore, we propose a commercializable photoelectrochemical system that can maximize the degradation of pollutants in wastewater treatment plants.     

Combination of sonochemical and freeze-drying methods for synthesis of graphene/Ag-doped TiO2 nanocomposite: A strategy to boost the photocatalytic performance via well distribution of nanoparticles between graphene sheets

Preparation of visible-light active photocatalysts for efficient degradation of pollutants from the industrial wastewater has received considerable attention in recent decades. The present study introduces a new sonochemical route for the preparation of graphene/TiO₂/Ag nanocomposite for visible-light photocatalytic degradation of X6G (C.I. Reactive Yellow 2), a commonly used textile azo-dye. The obtained graphene/TiO₂/Ag nanocomposite is extracted from the reaction solution by two drying methods: (1) conventional centrifuging and drying, and (2) freeze drying. Both of the dried samples are calcinated at 500 °C. The TEM images reveal that distribution of TiO₂/Ag nanoparticles within the graphene sheets in the freeze dried nanocomposite is better than the conventional dried sample. Furthermore, the freeze dried nanocomposite has higher photocatalytic activity than the other nanocomposite. In conventional centrifuging and drying method, some of the TiO₂/Ag nanoparticles are gradually pushed out from the graphene sheets during the drying process and graphene layers are stacked, therefore the dispersion effect of sonication is destroyed. However, in the freeze dried nanocomposite, because of the fast freezing of the sonicated sample by liquid N₂, the TiO₂/Ag nanoparticles are kept between the graphene sheets and calcination process attached and fixed them to the graphene, preserving the dispersion effect of sonication.