TiO2 Sheets Research Articles

Hierarchical heterojunction comprising of in-situ derived TiO2 and salicylaldimine-supported Co catalysts in metal-organic frameworks for enhancing photocatalytic hydrogen generation

We present the design of a novel functional metal-organic framework here, denoted as Co-sal–NH2–MOF@TiO2, featuring the comprise of controllably in-situ grown TiO2 sheets from NH2-MOF(Ti) and [Co] catalytic sites stabilized by salicylaldimine moiety via site isolation for visible-light-driven hydrogen evolution from water. The hierarchical organization of TiO2 and Co catalyst within NH2-MOF (Ti) leads to outstanding photocatalytic performance, as evidenced by a H2 yield of 15,584 μmolg−1h−1 and turnover numbers (TON) reaching 5844 over 24 h. This catalyst also signifies distinctly enhanced activities of approximately 105-fold, 354-fold, 15-fold, and 100-fold, compared to the pristine NH2-MOF(Ti), MOF-derived TiO2, NH2-MOF(Ti)@TiO2 and the combination of [Co catalyst + NH2-MOF(Ti) + TiO2], respectively. EXAFs and XPS etc. analyses revealed a stable coordination environment for salicylaldimine-supported Co(II) catalytic unit, which integrated with in-situ grown TiO2 sheets can not only guarantee catalyst stability, but also generate much more densely packed light-harvesting heterojunction units and thus promote separation and transfer of photogenerated carriers between TiO2 and Co catalyst in NH2-MOF(Ti) under light through optimized band gap structure. This work outlines the in-situ construction of organic and inorganic hybrid heterojunction for H2 production from water.

Synergistic effect of Ru single atom and nanoparticle on photothermal methane dry reforming reaction

Dry reforming of methane is indeed an attractive pathway for converting greenhouse gases into syngas. However, owing to the strong-endothermic nature of this reaction, high reaction temperature is commonly involved which causes high energy consumption, catalytic deactivation by sintering of active species, and/or coke formation. Herein, a RuSA+NP/TiO2 composite catalyst consisting of uniformly dispersed Ru nanoparticles (RuNP) and Ru single atoms (RuSA) on TiO2 sheet is fabricated. This catalyst demonstrates remarkable syngas generation rates of 1380 mmol g-1h−1 for CO and 933 mmol g-1h−1 for H2 at 500 °C under light irradiation. It is concluded that the presence of Ru single atoms modulates the electronic structure of catalyst, reducing energy barrier in the DRM process. Additionally, the electron-deficient Ru nanoparticles provide effective sites for CH4 dissociation. Light irradiation is found to reduce the apparent activation energy (Ea) of DRM and enhance durability of catalyst by retarding coking process.

Air-gap-assisted solvothermal process to synthesize unprecedented graphene-like two-dimensional TiO2 nanosheets for Na+ electrosorption/desalination

Designing a high-performance capacitive deionization setup is limited due to the slow salt removal and charge storage capacities. Efforts are being made to replace traditional electrodes with advanced 2D materials. We introduce a simple method for synthesizing two-dimensional titanium dioxide graphene-like nanosheets via a unique air-gap-assisted solvothermal method. Crystalline 2D graphene-like anatase-TiO2 sheets of unprecedented quality were obtained by tuning the air gap in the solvothermal reactor. The 2D TiO2 synthesized by air-gap-assisted solvothermal process has shown an exceptionally high surface area of 934.5 m2/g compared to the pristine TiO2 (249.5 m2/g). The sheets were used as Faradaic electrodes in ion-electrosorption and their capacitive deionization capabilities were evaluated. The electrochemical conductivity was examined via an in situ investigation of Na+-ion migration and storage. The adsorption capacity of 2D TiO2 sheets increased with higher applied potential while keeping the adsorption time constant at 15 min. At adsorption potentials of –0.8 V, –1.0 V, and –1.2 V, desalting rates of 2.09, 2.18, and 2.20 mg g−1 min−1 resulted in adsorption capacities of 31.33, 32.73, and 33.023 mg g–1, respectively. The 2D TiO2 electrode demonstrated high electron-transfer rates, a large desalination capacity, and a rapid average desalting rate. The specific capacity of the 2D-layered TiO2 electrode was found to be about 45.68 F g−1. These results can be attributed to the large specific surface area, short ionic diffusion paths, numerous active adsorption sites, surface defects, and pseudocapacitance. This air-gap-assisted solvothermal method is expected to open new avenues for the synthesis of high-quality 2D materials.

Theoretical Modeling of Surface Plasmon Resonance Biosensor Using Titanium Dioxide and Graphene Nanomaterial for Refractive Index Sensing

The most popular method to determine the sensitivity of surface plasmon resonance (SPR) sensors in the last couple of decades has been angular interrogation. The silver layer (Ag), a 2D layer of TiO2, and dielectric material layer such as silicon (Si) with heterostructure material graphene are all stacked in the proposed SPR sensor. To increase sensitivity of SPR sensor in the visible area, the device structure focuses on the Kretschmann configuration, by which a TiO2 sheet is sandwiched between silver and silicon sheets. The proposed device structure makes use of the operational wavelength of 633 nm. The numerical simulation has been performed in MATLAB software in this device structure. The simulation results show that an analyte of refractive indices ranges 1.345–1.350. A single layer of silicon 3 nm and TiO2 10 nm makes up the suggested SPR configuration, which increases the sensitivity to 281° RIU−1. Herein, it has also been computed the figure of merit, detection accuracy, limit of detection, full width at half maximum, and transverse magnetic electric field intensity. The biomedical and chemical fields have benefited from the proposed SPR sensor structure design.

Ag-Doped Free-Standing 2D TiO2 Sheets: Electronic, Optical, Magnetic, and Self-Healing Behaviour.

Beyond a critical doping level, Ag - 2D TiO2 sheets (ATO) are deemed to be a flexible transparent conductor, useful for visible-range functional photonic/optoelectronic devices/sensors, sunlight-sensitive catalysis, and light-activated resistive switching. Due to the lack of control of surface energy which often leads to the formation of structural defects and even dimensionality crossover (2D to 0D) of materials during doping reaction, it is challenging to obtain ATO with a controlled doping level. Gauging the urgency, therefore we report the surface energy-controlled synthesis of ATO employing liquid phase exfoliation of TiO2 and subsequent hydrothermal Ag-doping in the presence of Hexamethylenetetramine (HMTA). Electron microscopy and atomic force microscopy reveal ATO sheets with large lateral dimensions. 6-fold, 4-fold, and strain-mediated crystallographic phases of 2D ATO have been revealed by high-resolution electron imaging. Successful tuning of the band gap down to ~ 2 eV with Ag doping up to ~ 10% is obtained. Synthesized 2D ATO have been investigated for their electrical, optical, optoelectronic, photoluminescence, and ferromagnetic behaviour. Visible light-sensitive thermally/structurally robust semiconductor/conductor via tuneable doping will pave the way for their flexible as well as wearable device applications. Self-healing effect of AFM tip-generated mechanical stress has also been demonstrated.

Enhanced Cr(VI) Photocatalysis Reduction by Layered N‐doped TiO2 Sheets from Template Free Solvothermal Method

AbstractLayered TiO2 sheets with high Cr(VI) photoreduction ability were prepared by template free solvothermal method using ethylene glycol (EG) as structure directing agent. EG linking function in the layered TiO2 structure were confirmed by SEM, TEM, FTIR, XPS and so on. Moreover, the obtained large sized TiO2 (20~50 μm in length, about 5~10 μm in width) were assembled by N‐doped TiO2 thin sheets with about 1.2 nm gap in between, resulting in very high surface area (327.5 m2/g) and abundant Ti3+ sites for Cr(VI) adsorption and reduction. This structure can not only have good performance during Cr(VI) photocatalysis reduction application (Cr(VI) removal rate: 0.84 mg*g−1*min−1), but also endow the material with good cycle ability.

Synergy of Surface Phosphates and Oxygen Vacancies Enables Efficient Photocatalytic Methane Conversion at Room Temperature.

Room-temperature photocatalytic conversion of CH4 into liquid oxygenates with O2/H2O provides an appealing route for sustainable chemical industry, which, however, suffers from poor efficiency due to the undesired carrier kinetics and low yield of reactive oxygen species of the currently available photocatalysts. Here, we report an effective surface engineering strategy where concurrent constructions of oxygen vacancies and phosphate sites on TiO2 nanosheets address the above challenge. The surface oxygen vacancies and phosphates are respective acceptors of photogenerated electrons and holes for promoted separation and migration of charge carriers. Moreover, in addition to the facilitated activation of O2 to •OH by electrons at oxygen vacancies, the surface phosphates also facilely adsorb H2O via hydrogen bonds and thus effectively transfer holes to H2O for enhanced •OH production, thereby boosting CH4 conversion. As a result, compared with TiO2 sheets with only oxygen vacancies, a 2.8 times improvement in liquid oxygenate production with near-unity selectivity is achieved by virtue of the synergy of surface oxygen vacancies and phosphate sites, together with an unprecedent quantum efficiency of 19.8% under 365 nm irradiation.

Construction of TiO2/TiOF2 heterojunction as a cathode material for high-performance Mg2+/Li+ hybrid-ion batteries

Anatase TiO2 has attracted significant interest as a cathode material for Mg-ion batteries or Mg2+/Li+ hybrid-ion batteries. However, owing to the semiconductor property and slower Mg2+ diffusion kinetics it still suffers from poor electrochemical performance. Herein, a TiO2/TiOF2 heterojunction consisting of in situ formed TiO2 sheets and TiOF2 rods, was prepared by adjusting the amount of HF in the hydrothermal process, and used as cathode of Mg2+/Li+ hybrid-ion battery. The TiO2/TiOF2 heterojunction prepared by adding 2 mL HF (TiO2/TiOF2-2) exhibits high electrochemical performance, with a high initial discharge capacity (378 mAh/g at 50 mA/g), an outstanding rate performance (128.8 mAh/g at 2000 mA/g), and good cycle stability (capacity retention of 54 % after 500 cycles), which is much superior to that of Pure TiO2 and Pure TiOF2. The reactions of Li+ intercalation/detercalation in the TiO2/TiOF2 heterojunction are revealed by investigating the evolution of the hybrids during different electrochemical states. Moreover, theoretical calculations prove that the Li+ formation energy in the TiO2/TiOF2 heterostructure is much lower than that of TiO2 and TiOF2, demonstrating that the heterostructure plays a crucial role in the enhanced electrochemical performance. This work provides a novel method to design cathode materials with high performance by constructing heterostructure.

CeO2–TiO2 Nanoparticle-Grafted gC3N4 Sheets as an Efficient Catalyst for the Oxidation of Cyclohexane to KA oil

Here, we report a sustainable catalytic process operating on CeO2–TiO2 nanoparticle-grafted gC3N4 sheets (gC3N4/CeO2–TiO2) in the presence of a H2O2 green oxidant for the liquid phase oxidation of cyclohexane to produce KA oil (cyclohexanone + cyclohexanol). The process achieved enhanced cyclohexane conversion (62%) toward 95% KA oil (cyclohexanone 83% + cyclohexanol 12%), which is the highest ever reported to the best of our knowledge. The excellent catalytic behavior of gC3N4/CeO2–TiO2 in the present study due to its enhanced active sites, that is, Ce3+ and Ti3+, is facilitated by the redox reaction between CeO2–TiO2 and gC3N4 sheets. The high stability of gC3N4/CeO2–TiO2 catalyst in the liquid phase reaction study indicates the robust nature of this catalyst facilitated by strong interactions between CeO2–TiO2 species and electron-rich sites (N and π) of gC3N4 sheets. The overall study suggests that the gC3N4/CeO2–TiO2 material can be a promising catalyst for the sustainable production of KA oil from cyclohexane oxidation in the presence of the H2O2 oxidant.

Flexible Nano-TiO2 Sheets Exhibiting Excellent Photocatalytic and Photovoltaic Properties by Controlled Silane Functionalization-Exploring the New Prospects of Wastewater Treatment and Flexible DSSCs.

TiO2 nanoparticles surface-modified with silane moieties, which can be directly coated on a flexible substrate without the requirement of any binder materials and postsintering processes, are synthesized and characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, Brunauer–Emmett–Teller, X-ray photoelectron spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, time-correlated single-photon counting, and transmission electron microscopy. The viability of the prepared surface-modified TiO2 (M-TiO2) sheets as a catalyst for the photo-induced degradation of a model dye, methylene blue, was checked using UV–visible absorption spectroscopy. The data suggest that, compared to unmodified TiO2, M-TiO2 sheets facilitate better dye-degradation, which leads to a remarkable photocatalytic activity that results in more than 95% degradation of the dye in the first 10 min and more than 99% of the degradation in the first 50 min of the photocatalytic experiments. We also demonstrate that M-TiO2 can be recycled with negligible reduction in photocatalytic activity. Further, the photovoltaic properties of the developed M-TiO2 sheets were assessed using UV–visible absorption spectroscopy, electrochemical impedance spectroscopy (EIS), and photochronoamperometry. Dye-sensitized solar cells (DSSC) fabricated using M-TiO2 as the photoanode exhibited a photoconversion efficiency of 4.1% under direct sunlight. These experiments suggested that M-TiO2 sheets show enhanced photovoltaic properties compared to unmodified TiO2 sheets, and that, when N-719 dye is incorporated, the dye–TiO2 interaction is more favorable for M-TiO2 than bare TiO2. The simple solution processing method demonstrated in this paper rendered a highly flexible photoanode made of M-TiO2 with superior charge-separation efficiency to an electrode made of bare TiO2. We propose that our findings on the photovoltaic properties of M-TiO2 open up arenas of further improvement and a wide scope for the large-scale production of flexible DSSCs on plastic substrates at room temperature in a cost-effective way.

Construction of carbon dots-deposited TiO2 Photocatalysts with visible-light-induced photocatalytic activity for the elimination of pollutants

Element decomposition is a promising modification technique for enhancing the photocatalytic activity of TiO2. Firstly, (i) It may accelerate photogenerated electron–hole separation as electron traps, (ii) broaden the sunlight absorption region into the visible range and promote surface electron excitation by plasmon resonances excited under visible light and (iii) modify the surface performance of semiconductors. Herein, we describe the introduction of carbon dots (CDs) as solid-state electron mediator on TiO2 sheets (TNs) via a highly effective hydrothermal process. The as-prepared CDs/TNs nanocomposites was measured by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, UV–visible diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy analysis. The results proved that CDs were firmly scattered in the TNs interface. Furthermore, the resultant CDs/TNs nanocomposites exhibited remarkable photocatalytic activity for the degradation of different model pollutants under visible light, which is considerably superior to that of bare TNs. The enhanced photocatalytic activity highlights that CDs can promote the separation and migration efficiency of photoexcited electron–hole pairs. The striking stability of CDs/TNs was investigated by performing five successive cycles of degradation of Congo red. Moreover, the degradation intermediates of three pollutants were monitored by liquid chromatography-tandem mass spectrometry, and potential removal pathways are proposed. We firmly believe that this work may inspire new insights and approaches for the design of highly efficient photocatalysts.

Heterostructured Ceria-Titania-Supported Platinum Catalysts for the Water Gas Shift Reaction.

The water gas shift (WGS) reaction is a key process in the industrial hydrogen production and the development and application of the proton exchange membrane fuel cell. Metal oxide-supported highly dispersed Pt has been proved as an efficient catalyst for the WGS reaction. In this work, a series of supported 0.5Pt/xCe-10Ti (x = 1, 3, or 5) catalysts with different Ce/Ti molar ratios were prepared by a simple deposition-precipitation method. Compared with single TiO2- or CeO2-supported Pt catalysts, it was found that the 0.5Pt/3Ce-10Ti catalyst showed an obvious advantage in activity for the WGS reaction. In this catalyst, dispersed CeO2 nanoparticles were supported on the TiO2 sheets, and Pt single atoms and nanoparticles were located on CeO2 and at the boundary of TiO2 and CeO2, respectively. It found that the reduction ability of the supported Pt catalyst was remarkably improved; meanwhile, the adsorption strength of CO on the surface of 0.5Pt/3Ce-10Ti was moderate. The heterostructured CeO2-TiO2 support gave an effective regulation on the Pt status and further influenced the CO adsorption ability, inducing excellent WGS reaction activity. This work provides a reference for the development and application of heterostructured materials in heterogeneous catalysis.

Photocatalytic TiO2 incorporated PVDF-co-HFP UV-cleaning mixed matrix membranes for effective removal of dyes from synthetic wastewater system via membrane distillation

We report membranes with UV-cleaning properties by incorporating photocatalytic porous TiO2 sheets (PTS) (0–5 wt%) in the PVDF-co-HFP matrix. PTS were synthesized using controllable large-scale synthesis protocols by spray drying followed by calcination. These membranes were assessed for the removal of Congo red (CR) and methylene blue (MB) from synthetic textile industry wastewater system (CR: 100 mg l−1 + MB: 100 mg l−1 + 4% NaCl) via direct contact membrane distillation (DCMD) configuration and their UV-cleaning properties. The PTS were characterized by FE-SEM, TEM and different spectral techniques, while membranes were assessed by surface morphology (FE-SEM, AFM), thermal stability, hydrophobicity, permeate flux, and dye rejection performance. The surface morphology study of PTS revealed its micro-sized sheet with the porous surface. With increased PTS concentration in the membrane matrix, the flux and dye rejection of mixed matrix membranes improved. Suitably optimized PT3 (3 wt% PTS in PVDF-co-HFP matrix) membrane showed ~100% dye removal efficiency (MB and CR) and 6.1 kg m−2 h−1 vapour flux. Long run (5 days) DCMD experiments showed >91% flux recovery ratio (FRR) after UV-cleaning. This study suggests the suitability of the prepared membranes to treat textile wastewater and their UV-cleaning properties.

Antibacterial coating of titanium-doped hydroxyapatite nanoparticles on a polymer substrate

Calcined and dispersible titanium-doped hydroxyapatite (Ti-HAp) nanoparticles at different [Ti/(Ca+Ti)] atomic ratios (0.3, 0.4, and 0.5) were prepared using an anti-sintering method. The Ti substitution ratios of the HAp structures in the feed of Ti-HAp preparation were approximately 80%. Ti-HAp nanoparticles were coated on polyethylene terephthalate (PET) sheets through polyacrylic acid graft-polymers. The PET substrate was almost completely covered with monolayer nanoparticles (over 95%). Antibacterial activity of coated Ti-HAp was calculated from the survival ratio of the bacteria, Staphylococcus aureus, after ultraviolet (UV) irradiation at 312 nm and 6.4 mW/cm2 for 30 s. The number of S. aureus on the Ti-HAp coated substrate decreased by 43% compared to those on the original PET and normal HAp coatings as negative controls. The antibacterial activity of Ti-HAp coated substrate was, furthermore, no statistically difference with TiO2 sheet as a positive control.

The enhanced performance of Cr(VI) photoreduction and antibiotic removal on 2D/3D TiO2/ZnIn2S4 nanostructures

In this study, 2D/3D TiO2/ZnIn2S4 nanostructures with TiO2 sheet cluster embedded into ZnIn2S4 micro flowers were fabricated via hydrothermal method. The matched band structure, the enlarged surface area and the efficient photo-induced charge transfer offered by effective heterostructures formed between the two components endowed the TiO2/ZnIn2S4 nanoarchitecture with excellent photocatalytic Cr(VI) reduction and tetracycline hydrochloride (TC) degradation performance. Especially, the Cr(VI) photoreduction efficiency of 50% TiO2/ZnIn2S4 was 8.8 times higher compared to pure ZnIn2S4. The enhanced separation efficiency of photo-excited charge carriers was induced by the matched band structure, the enlarged surface area and the strong interaction between TiO2 and ZnIn2S4. The key roles of ·O2− was confirmed via trapping experiments. Otherwise, the pathway of TC degradation was investigated. The proposed mechanism during photocatalysis process was also discussed according to the photocatalytic and characterization results.

Unravelling the favorable photocatalytic effect of hydrogenation process on the novel g-C3N4-TiO2 catalysts for water purification

Exploring desirable and photostable homostructured catalysts is an explosive scientific hotspot for energy crisis and wastewater treatment. Efficient pollutants removal from wastewater is an attractive route to sustainable development. We here present an ideal photocatalyst that incorporates both g-C3N4 and TiO2 sheets (TNs), creating a novel nanomaterial of the type g-C3N4/TNs catalyst. The obtained photocatalyst can accelerate the interfacial charge transfer rate. Subsequently, we prepared 2:1O−-g-C3N4/TNs photocatalysts by H2 treatment, which not only generated more active defects on 2:1O−-g-C3N4/TNs surface, but also produced oxygen vacancies. As measured by the degradation of CR (CR), the as-prepared g-C3N4/TNs samples perform outstanding removal properties due to high photocurrent response under visible light irradiation, which are transcend than bulk g-C3N4 or pure TNs separately. Specially, the obtained 2:1O−-g-C3N4/TNs catalysts exhibit the highest photocatalytic rate for decomposition of CR (86.7%, 2 h), which was 107.5, 7.167, and 1.43 times higher than that of TNs, g-C3N4, and 2:1 g-C3N4/TNs. The decisive factor in enhancing the photocatalytic ability of this optimal sample is the richly available reaction sites exposed by hydrogenation process.

MXene-based porous and robust 2D/2D hybrid architectures with dispersed Li3Ti2(PO4)3 as superior anodes for lithium-ion battery

Two-dimensional (2D) MXenes become the predominant choice of lithium-ion battery electrode materials owing to large surface-area-to-volume ratio and metallic conductivity, but severe restacking still remains the main obstruct. Herein, a new strategy of avoiding restacking and assuring structural stability is proposed. We demonstrate the fabrication of novel hierarchically porous and robust 2D/2D hybrid architectures consisting of a large thin Ti3C2 flake with many standing intersecting TiO2 nanosheets, followed by generation of well-dispersed Li3Ti2(PO4)3 nanocrystals. The resulting TiO2 sheets of 4 ~ 5 nm thick inherit specific layered atomic structures of 2D MXene through in-situ ultrafast reactions in molten-salt, and thus are composed of few layers with ~ 0.8 nm layer spacing. The MXene-based composite as an anode delivers high discharge capacity of 204 mAh g−1 at 50 mA g−1, rate capability (115 mAh g−1 at 1000 mA g−1) and remarkable cycling stability with 193 mAh g−1 after 500 cycles at 100 mA g−1. This are attributed to high surface capacitive contributions of the unique 2D/2D robust hybrid architecture that provides enough spaces to accelerate ionic transfer and favorable tolerance to volume variation. This work provides an effective route to rapid generation of MXene-based 2D/2D hierarchical composites for many applications.

Preparation, Characteristics, and Application of Bifunctional TiO2 Sheets.

TiO2 is a high-reflectance material for preparing sheets during dry reagent chemical tests in detail. In this study, bifunctional TiO2 sheets with diffusive and reflective properties were prepared using TiO2 microspheres (particle size 2–3 µm) and cellulose acetate (CA). Factors such as the CA dosage, water content, mixing time, and the choice of surfactant were investigated. The structure and properties of the bifunctional TiO2 sheets were characterized by thermogravimetry and differential thermal analysis (TG-DAT), scanning electron microscopy (SEM), dynamic contact angle test and reflectance spectroscopy. By studying the above experimental results, it was concluded that the most optimal preparation conditions for preparing the bi-functional TiO2 sheets under natural drying conditions were as follows: the mass ratio of CA to TiO2 microspheres was 0.05:1; Triton-100 was used to improve the diffusion performance of the bifunctional sheets, after mixing for 5 h and coating. The light reflectivity of the bifunctional TiO2 sheets in the 420 to 800 nm range was higher than 90%. Serum diffused in the bifunctional TiO2 sheets reacted in the reagent sheets and formed uniform colorful spots. Considering the repeatability of spot proportion and light reflectivity, the sheet offered a uniform serum diffusion and good repeatability. So, the bifunctional TiO2 sheets are nominated as a promising material for dry chemical diagnostic reagents.

Visible active TiO2-CdS-rGO ternary nanocomposite for enhanced photodecomposition of methylene blue

TiO2-CdS-rGO ternary nanocomposite was prepared hydrothermally. Anatase phase TiO2 was confirmed by XRD analysis. Spherical CdS nanoparticles are present uniformly on anatase TiO2 and rGO sheets. TiO2-CdS-rGO nanocomposite has extended visible absorption than TiO2-CdS and TiO2. Band gap of TiO2 is reduced by CdS and rGO from 3.2 to 2.4 eV. Photodegradation efficiency of TiO2-CdS-rGO is very high as revealed by 96.4% methylene blue decomposition in 50 min.

Enhanced photocatalytic H2-production activity of WO3/TiO2 step-scheme heterojunction by graphene modification

Sunlight-driven photocatalytic water-splitting for hydrogen (H2) evolution is a desirable strategy to utilize solar energy. However, this strategy is restricted by insufficient light harvesting and high photogenerated electron–hole recombination rates of TiO2-based photocatalysts. Here, a graphene-modified WO3/TiO2 step-scheme heterojunction (S-scheme heterojunction) composite photocatalyst was fabricated by a facile one-step hydrothermal method. In the ternary composite, TiO2 and WO3 nanoparticles adhered closely to reduced graphene oxide (rGO) and formed a novel S-scheme heterojunction. Moreover, rGO in the composite not only supplied abundant adsorption and catalytically active sites as an ideal support but also promoted electron separation and transfer from the conduction band of TiO2 by forming a Schottky junction between TiO2 and rGO. The positive cooperative effect of the S-scheme heterojunction formed between WO3 and TiO2 and the Schottky heterojunction formed between TiO2 and graphene sheets suppressed the recombination of relatively useful electrons and holes. This effect also enhanced the light harvesting and promoted the reduction reaction at the active sites. Thus, the novel ternary WO3/TiO2/rGO composite demonstrated a remarkably enhanced photocatalytic H2 evolution rate of 245.8 μmol g−1h−1, which was approximately 3.5-fold that of pure TiO2. This work not only presents a low-cost graphene-based S-scheme heterojunction photocatalyst that was obtained via a feasible one-step hydrothermal approach to realize highly efficient H2 generation without using noble metals, but also provides new insights into the design of novel heterojunction photocatalysts.