Construction of ternary rGO/1D TiO2 nanotubes/3D ZnIn2S4 microsphere heterostructure and mutually-reinforcing synergy for high-efficiency H2 production photoactivity under visible light

The novel ternary reduced graphene oxide/1D TiO₂ nanotubes/3D ZnIn₂S₄ microspheres (rGO/TiO₂/ZIS) heterostructured photocatalyst with high-efficiency H₂ production capacity under visible light illumination is designed and prepared in this work. In rGO/TiO₂/ZIS system, the 1D TiO₂ nanotubes are tightly inserted in the interspace of flower-like ZnIn₂S₄ microspheres, which are further covered by rGO, leading to an intimate contact among ZnIn₂S₄, TiO₂ and rGO. The exquisite design of rGO/TiO₂/ZIS makes it possess remarkable superiority in photocatalysis. Firstly, the unique 3D microsphere structure of ZIS increases the surface area and visible light absorption ability caused by their unique hollow structure. More importantly, the matched CB and VB positions between ZIS and TiO₂ contribute to separate photogenerated holes and electrons of ZIS efficiently under visible light; then, the separated electrons on TiO₂ are further transferred to rGO due to the superior-strong electron-attracting ability of rGO. At last, the thoroughly suppressing recombination of photogenerated holes and electrons is achieved by the mutually-reinforcing synergy among ZIS, TiO₂ and rGO, and thus the hydrogen generation capacity of ZIS is significantly enhanced. The H₂ production amount and rate of rGO/TiO₂/ZIS (2.0 wt% rGO and 50 wt% ZIS) after 10 h are 4623 μmol/g and 462.3 μmol/g/h, respectively, which is 71.1 times of pristine TiO₂ and 1.6 times of ZIS under the same condition. The apparent quantum yield of rGO/TiO₂/ZIS (2.0 wt% rGO and 50 wt% ZIS) in 10 h is about 0.6888%. This excellent photocatalytic performance is ascribed to the mutually-reinforcing synergy among ZIS, TiO₂ and rGO, which can be confirmed by X-ray photoelectron spectroscopy, photoelectrochemical measurements and photoluminescence spectrum. Based on the photocatalytic and characterization results, the corresponding mechanism is proposed.     

Electrostatic self-assembly of 2D-2D CoP/ZnIn2S4 nanosheets for efficient photocatalytic hydrogen evolution

Constructing efficient and cost-effective photocatalysts are highly desirable for photocatalytic hydrogen evolution. Herein, we prepare a unique 2D-2D architecture photocatalyst composed of CoP and ZnIn₂S₄ (ZIS) nanosheets through electrostatic self-assembly method. The constructed 2D-2D CoP/ZIS exhibit a remarkably enhanced photocatalytic performance with hydrogen production rate of 8.775 mmol g⁻¹ h⁻¹, and this value is much higher than ZIS and most of other ZIS-based nanohybrids. Additionally, the nanohybrids possess excellent stability with 96.3% of initial activity remaining after 24 hours of testing. These satisfactory results are attributed to the large/intimate contact interface and the photo/electro-chemical properties of ZIS and CoP, which improves light absorption, facilitates photoelectron transport and suppresses charge recombination. This work not only demonstrates ZIS nanosheet can serve as a versatile and effective platform supporting non-noble metal nanosheets to boost their photocatalytic performance, but also offers a general and simple electrostatic self-assembly method to design 2D-2D-based heterostructures for hydrogen conversion from water splitting.     

Bismuth oxide cocatalyst and copper oxide sensitizer in Cu2O/TiO2/Bi2O3 ternary photocatalyst for efficient hydrogen production under solar light irradiation

A novel Cu₂O/TiO₂/Bi₂O₃ ternary nanocomposite was prepared, in which copper oxide improves the visible light absorption of TiO₂ and bismuth oxide improves electron–hole separation. The ternary composite exhibited extended absorption in the visible region, as determined by UV–Vis diffuse reflectance spectroscopy. High-resolution transmission electron microscopy images showed close contact among the individual semiconductor oxides in the ternary Cu₂O/TiO₂/Bi₂O₃ nanocomposite. Improved charge carrier separation and transport were observed in the Cu₂O/TiO₂/Bi₂O₃ ternary composite using electrochemical impedance spectroscopy and photocurrent analysis. TiO₂ modified with bismuth and copper oxides showed exceptional photocatalytic activity for hydrogen production under natural solar light. With optimum bismuth and copper oxide loadings, the Cu₂O/TiO₂/Bi₂O₃ ternary nanocomposite exhibited an H₂ production (3678 μmol/h) 35 times higher than that of bare TiO₂ (105?μmol/h). The synergistic effect of improved visible absorption and minimal recombination was responsible for the enhanced performance of the as-synthesized ternary nanocomposite.     

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.     

Rational design of MoS2/g-C3N4/ZnIn2S4 hierarchical heterostructures with efficient charge transfer for significantly enhanced photocatalytic H2 production

The rational design of hierarchical heterojunction photocatalysts with efficient spatial charge separation remains an intense challenge in hydrogen generation from photocatalytic water splitting. Herein, a noble-metal-free MoS₂/g-C₃N₄/ZnIn₂S₄ ternary heterostructure with a hierarchical flower-like architecture was developed by in situ growth of 3D flower-like ZnIn₂S₄ nanospheres on 2D MoS₂ and 2D g-C₃N₄ nanosheets. Benefiting from the favorable 2D-2D-3D hierarchical heterojunction structure, the resultant MoS₂/g-C₃N₄/ZnIn₂S₄ nanocomposite loaded with 3 wt% g-C₃N₄ and 1.5 wt% MoS₂ displayed the optimal hydrogen evolution activity (6291 μmol g^?1 h^?1), which was a 6.96-fold and 2.54-fold enhancement compared to bare ZnIn₂S₄ and binary g-C₃N₄/ZnIn₂S₄, respectively. Structural characterizations reveal that the significantly boosted photoactivity is closely associated with the multichannel charge transfer among ZnIn₂S₄, MoS₂, and g-C₃N₄ components with suitable band-edge alignments in the composites, where the photogenerated electrons migrate from g-C₃N₄ to ZnIn₂S₄ and MoS₂ through the intimate heterojunction interfaces, thus enabling efficient electron-hole separation and high photoactivity for hydrogen evolution. In addition, the introduction of MoS₂ nanosheets highly benefits the improved light-harvesting capacity and the reduced H₂-evolution overpotential, further promoting the photocatalytic H₂-evolution performance. Moreover, the MoS₂/g-C₃N₄/ZnIn₂S₄ ternary heterostructure possesses prominent stability during the photoreaction process owing to the migration of photoinduced holes from ZnIn₂S₄ to g-C₃N₄, which is deemed to be central to practical applications in solar hydrogen production.     

Preparation of ZnIn2S4/K2La2Ti3O10 composites and their photocatalytic H2 evolution from aqueous Na2S/Na2SO3 under visible light irradiation

ZnIn₂S₄/K₂La₂Ti₃O₁₀ composite photocatalysts were synthesized via a hydrothermal route. The photocatalysts were characterized by the X-ray diffraction, scanning electron microscopy, ultraviolet–visible (UV–vis) diffuse reflection spectra and photoluminescence measurements. The UV–vis results indicated that ZnIn₂S₄/K₂La₂Ti₃O₁₀ has a strong absorption in the visible light region. The compositions of ZnIn₂S₄/K₂La₂Ti₃O₁₀ composite photocatalysts were optimized according to the photocatalytic activity for hydrogen production from aqueous Na₂S/Na₂SO₃. The composite photocatalyst loading 25 wt.% ZnIn₂S₄ exhibited the highest photocatalytic activity, the amount of H₂ production was 6.29 mmol/g after 3 h irradiation under visible light irradiation.     

Well-designed ZnIn2S4/TiO2 Z-type heterojunction for efficient photocatalytic reduction of Cr(VI)

ZnIn₂S₄/TiO₂ photocatalyst was obtained by a facile hydrothermal method. Various techniques were used to characterize the ZnIn₂S₄/TiO₂, crystal structure and optical properties of ZnIn₂S₄/TiO₂. Cr (Ⅵ) as highly-toxic pollutant was used as the target reduction product to evaluate the catalytic performance of ZnIn₂S₄/TiO₂ under visible light irradiation. According to the experiment results, the reduction rate of Cr(VI) in the presence of ZnIn₂S₄/TiO₂ reaches 99% within 60 min, which is much better than ZnIn₂S₄ and TiO₂, respectively. At the same time, ZnIn₂S₄/TiO₂ also performs good stability for reduction rate hardly changes after 5 recycling experiments.     

Novel CdIn2S4 nano-octahedra/TiO2 hollow hybrid heterostructure: In-situ synthesis,synergistic effect and enhanced dual-functional photocatalytic activities

The development of highly efficient and multifunctional composite photocatalysts for both energy conversion and environmental governance has obtained great concerns. Here, a novel CdIn₂S₄/TiO₂ (CIS/THS) hollow composite photocatalyst was firstly designed and synthesized via a facile in-situ growth process, where the CdIn₂S₄ nano-octahedra densely attached on the surface of TiO₂ hollow spheres to form the unique hybrid heterostructure. The as-synthesized CIS/THS heterojunctions exhibit much superior photocatalytic activities for hydrogen evolution and Methyl Orange (MO) decomposition in comparison to pure CdIn₂S₄ and TiO₂ hollow spheres. The experimental results display that the CIS/THS-3 sample with the 30 wt% of TiO₂ presents the optimal photocatalytic H₂ production efficiency and its generation rate is 3.38 and 2.56 times as high as those of pure TiO₂ and CdIn₂S₄. Besides, the as-synthesized CIS/THS-3 hybrid also possesses the best MO photodegradation performance and its rate constant is 11.43 and 8.34 times higher than those of pure TiO₂ and CdIn₂S₄. The enhanced photocatalytic activities can be assigned to the synergistic effect, optimized light-harvesting capacity and the formation of hybrid heterostructure for boosting interfacial charge transfer and separation. Furthermore, based on the trapping experiments and ESR analysis, the possible type-Ⅱ interface charge transport mechanism was also proposed. Our study may provide the direct guidance for constructing other hollow TiO₂-based composite photocatalysts with superior photocatalytic water splitting and degradation performances.     

Synthesis of carbon quantum dots/TiO2 nanocomposite for photo-degradation of Rhodamine B and cefradine

Pure TiO₂ and carbon quantum dots (CQDs)-doped TiO₂ nanocomposite (CQDs/TiO₂ nanocomposite) were prepared by a sol-gel approach for photocatalytic removal of Rhodamine B and cefradine. Analyses by Transmission electronmicroscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), UV–visible spectroscopy and X-ray powder diffraction (XRD) confirmed the successful formation of CQDs/TiO₂ heterostructure. The as-prepared TiO₂ and CQDs/TiO₂ composite possessed small particles, spherical-like shape, and anatase crystal form. Meanwhile, Rhodamine B and cefradine were chosen to evaluate the photocatalytic activity of TiO₂ and CQDs/TiO₂ composite. Results revealed that with the facile decoration of CQDs, the absorption of photocatalyst was extended into visible light region and photocatalytic activity was improved in comparison with pure TiO₂. Furthermore, the mechanism for the improvement of the photocatalytic performance of the composites was discussed on the basis of the results. CQDs play an important role in the photocatalytic process, due to their superior ability to extend the visible absorption and produce more electrons and electron–hole pairs for the degradation of pollutants. In all, the paper offers further insights into the development of CQDs/TiO₂ nanocomposite as photocatalyst for the degradation of antibiotics.     

Efficient decomposition of organic compounds with FeTiO3/TiO2 heterojunction under visible light irradiation

FeTiO₃/TiO₂, a new heterojunction-type photocatalyst working at visible light, was prepared by a simple sol–gel method. Not only did FeTiO₃/TiO₂ exhibit greatly enhanced photocatalytic activity in decomposing 2-propanol in gas phase and 4-chlorophenol in aqueous solution, but also it induced efficient mineralization of 2-propanol under visible light irradiation (λ ≥ 420 nm). Furthermore, it showed a good photochemical stability in repeated photocatalytic applications. FeTiO₃ showed a profound absorption over the entire visible range, and its valence band (VB) position is close to that of TiO₂. The unusually high photocatalytic efficiency of the FeTiO₃/TiO₂ composite was therefore deduced to be caused by hole transfer between the VB of FeTiO₃ and TiO₂.     

TiO2, TiO2/Ag and TiO2/Au photocatalysts prepared by spray pyrolysis

TiO₂, TiO₂/Ag and TiO₂/Au photocatalysts exhibiting a hollow spherical morphology were prepared by spray pyrolysis of aqueous solutions of titanium citrate complex and titanium oxalate precursors in one-step. Effects of precursor concentration and spray pyrolysis temperature were investigated. By subsequent heat treatment, photocatalysts with phase compositions from 10 to 100% rutile and crystallite sizes from 12 to 120 nm were obtained. A correlation between precursor concentration and size of the hollow spherical agglomerates obtained during spray pyrolysis was established. The anatase to rutile transformation was enhanced with metal incorporations and increased precursor concentration. The photocatalytic activity was evaluated by oxidation of methylene blue under UV-irradiation. As-prepared TiO₂ particles with large amounts of amorphous phase and organic residuals showed similar photocatalytic activity as the commercial Degussa P25. The metal incorporated samples showed comparable photocatalytic activity to the pure TiO₂ photocatalysts.     

Photocatalytic properties of TiO2 sol-gel modified nanocomposite films

TiO₂ nanocomposite films with different concentrations of TiO₂ MT-150A nanoparticles were immobilized on glass substrates using a dip coating process. The crystalline structure and surface chemical state of nanocomposite film properties were examined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The specific surface area and morphology of TiO₂ MT-150A nanoparticles were evaluated by the BET method and Field Emission Scanning Electron Microscopy (FE-SEM). The photocatalytic activities of films were evaluated by the methyl orange decoloring rate. XPS measurements showed that the oxygen amount (%) was related to the film composition. The composite film with 10 g/L MT-150A loading yielded the highest amount of surface oxygen (26.82%) and TiO₂ rutile showed the lowest amount of surface oxygen (13.67%) in the form of surface hydroxyl groups. The remaining oxygen was identified as lattice oxygen. In addition, the nanocomposite film with 10 g/L MT-150A loading yielded the highest photocatalytic activity.     

TiO2/SnO2 double-shelled hollow spheres-highly efficient photocatalyst for the degradation of rhodamine B

TiO₂/SnO₂ double-shelled hollow spheres are successfully synthesized by two-step liquid-phase deposition method using carbon sphere templates. The formation process of TiO₂/SnO₂ hollow spheres is discussed. The samples are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and UV–vis absorption spectroscopy. The behavior of photogenerated charges in the TiO₂/SnO₂ heterojunction structures has been investigated through surface photovoltage spectroscopy. The TiO₂/SnO₂ hollow spheres which are realized show significantly enhanced photocatalytic activities, with respect to the cases of SnO₂ and TiO₂ hollow spheres. Furthermore, TiO₂/SnO₂ hollow spheres show good recyclable photocatalytic activities.     

A unique Cu2O/TiO2 nanocomposite with enhanced photocatalytic performance under visible light irradiation

A unique Cu₂O/TiO₂ nanocomposite with high photocatalytic activity was synthesized via a two-step chemical solution method and used for the photocatalytic degradation of organic dye. The structure, morphology, composition, optical and photocatalytic properties of the as-prepared samples were investigated in detail. The results suggested that the Cu₂O/TiO₂ nanocomposite is composed of hierarchical TiO₂ hollow microstructure coated by a great many Cu₂O nanoparticles. The photocatalytic performance of Cu₂O/TiO₂ nanocomposite was evaluated by the photodegradation of methylene blue (MB) under visible light, and compared with those of the pure TiO₂ and Cu₂O photocatalysts synthesized by the identical synthetic route. Within 120 min of reaction time, nearly 100% decolorization efficiency of MB was achieved by Cu₂O/TiO₂ photocatalyst, which is much higher than that of pure TiO₂ (26%) or Cu₂O (32%). The outstanding photocatalytic efficiency was mainly ascribed to the unique architecture, the extended photoresponse range and efficient separation of the electron-hole pairs in the Cu₂O/TiO₂ heterojunction. In addition, the Cu₂O/TiO₂ nanocomposite also retains good cycling stability in the photodegradation of MB.     

Ag nanoparticles loaded TiO2/MWCNT ternary nanocomposite: A visible-light-driven photocatalyst with enhanced photocatalytic performance and stability

A visible light active photocatalyst, Ag/TiO₂/MWCNT was synthesized by loading of Ag nanoparticles onto TiO₂/MWCNT nanocomposite. The photocatalytic activity of Ag/TiO₂/MWCNT ternary nanocomposite was evaluated for the degradation of methylene blue dye under UV and visible light irradiation. Ag/TiO₂/MWCNT ternary nanocomposite exhibits (~9 times) higher photocatalytic activity than TiO₂/MWCNT and (~2 times) higher than Ag/TiO₂ binary nanocomposites under visible light irradiation. The enhancement in the photocatalytic activity is attributed to the synergistic effect between Ag nanoparticles and MWCNT, which enhance the charge separation efficiency by Schottky barrier formation at Ag/TiO₂ interface and role of MWCNT as an electron reservoir. Effect of different scavengers on the degradation of methylene blue dye in the presence of catalyst has been investigated to find the role of photogenerated electrons and holes. Simultaneously, the Ag/TiO₂/MWCNT shows excellent photocatalytic stability. This work highlights the importance of Ag/TiO₂/MWCNT ternary nanocomposite as highly efficient and stable visible-light-driven photocatalyst for the degradation of organic dyes.     

Photocatalytic activity of TiO2 supported on multi-walled carbon nanotubes under simulated solar irradiation

TiO₂ particles supported on multi-walled carbon nanotubes (MWCNTs) were prepared using a sol–gel method to investigate their photocatalytic activity under simulated solar irradiation for the degradation of methyl orange (MO) in aqueous solution. The prepared composites were analyzed using XRD, SEM, EDS and UV–vis absorption spectroscopy. The results of this study indicated that there was little difference in the shape and structure of MWCNTs/TiO₂ composite and pure TiO₂ particles. The composite exhibited enhanced absorption properties in the visible light range compared to pure TiO₂. The degradation of MO by MWCNTs/TiO₂ composite photocatalysts was investigated under irradiation with simulated solar light. The results of this study indicated that MWCNTs played a significant role in improving photocatalytic performance. Different amounts of MWCNTs had different effects on photodegradation efficiency, and the most efficient MO photodegradation was observed for a 2% MWCNT/TiO₂ mass ratio. Photocatalytic reaction kinetics were described using the Langmuir–Hinshelwood (L–H) model. The photocatalyst was reused for eight cycles, and it retained over 95.2% photocatalytic degradation efficiency. Possible decomposition mechanisms were also discussed. The results of this study indicated that photocatalytic reactions with TiO₂ particles supported on MWCNTs under simulated solar light irradiation are feasible and effective for degrading organic dye pollutants.     

3D/2D ZnIn2S4/BiFeO3 as S-scheme heterojunction photocatalyst for boosted visible-light hydrogen evolution

Photocatalytic H₂ evolution technique has been proved to be one of the promising approaches to overcome the present energy and environmental issues caused by the combustion of fossil fuel. Constructing heterojunction can realize the efficient separation and migration of charges and thus achieve enhanced H₂ evolution performance. Herein, we designed and prepared a ZnIn₂S₄/BiFeO₃ heterojunction photocatalyst with a 3D/2D structure via an ultrasonic self-assembly process. The typical 3D/2D structure with intimate interface was obtained, which not only provided more active sites but also boosted the migration of photogenerated charges. The optimal mass ratio of BiFeO₃ in ZnIn₂S₄/BiFeO₃ was determined to be 10%, and a 10.5-fold increase in H₂ evolution rate in comparison with of pure ZnIn₂S₄ was achieved. Furthermore, the ZnIn₂S₄/BiFeO₃ composite exhibited excellent recyclability and structural stability based on cycling experiment. A S-scheme heterojunction mechanism was revealed according to the experimental results of photocatalytic H₂ evolution and electrochemical tests.     

Alkali-free synthesis of a novel heterostructured CeO2-TiO2 nanocomposite with high performance to reduce Cr(VI) under visible light

In this study, a novel CeO₂-TiO₂ nanocomposite denoted as CeO₂-3TiO₂ was successfully synthesized via a facile one pot hydro-thermal method without alkali. It exhibits high photocatalytic reduction reactivity toward Cr(VI) under visible light. The photocatalytic reactivity of CeO₂-3TiO₂ is 18 times higher than that of pure CeO₂, 28 times higher than pure TiO₂, 15 times higher than the sample of simply mixed CeO₂ and TiO₂. The solution with Cr(VI) initial concentration of 2780 ppb can be fast photoreduced by CeO₂-3TiO₂ in 60 min under visible light to meet the criterion of U.S. Environmental protection Agency. Characterization results indicate CeO₂-3TiO₂ has the good crystal form of heterojunction structure, narrow pore size distribution, narrow energy gap and high photogenerated electron-hole separation efficiency. Based on the experimental results, a speculated photocatalytic mechanism was proposed.     

Preparation and characterization of Cu2O/TiO2 nano–nano heterostructure photocatalysts

Cu₂O/TiO₂ nano–nano heterostructures with different concentrations of Cu₂O were prepared by an alcohol-aqueous based chemical precipitation method, and were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and UV–vis diffuse reflection absorption spectra. The photocatalytic efficiency of the Cu₂O/TiO₂ heterostructures was evaluated by degradation of Acid Orange II in water under UV–vis light and visible light irradiation. The results show that the heterostructures have dramatically improved photocatalytic activity comparing with pure TiO₂ (P25). The prepared Cu₂O/TiO₂ heterostructures with the Cu₂O concentrations of 30% and 70% have the best photocatalytic efficiencies, which are 6 times and 27 times higher than that of pure TiO₂ (P25) under UV–vis light and visible light irradiation, respectively.     

Enhancement of the visible light photocatalytic performance of C-doped TiO2 by loading with V2O5

V₂O₅ was loaded on the surface of C-doped TiO₂ (C-TiO₂) by incipient wetness impregnation in order to enhance the visible light photocatalytic performance. The physicochemical properties of the C-TiO₂/V₂O₅ composite were characterized by XRD, Raman, TEM, XPS, UV–vis diffuse reflectance spectra, and PL in detail. The result indicated that a heterojunction between C-TiO₂ and V₂O₅ was formed and the separation of excited electron–hole pairs on C-TiO₂/V₂O₅ is greatly promoted. Thus, this composite photocatalyst exhibited enhanced visible light photocatalytic activity in degradation of gas-phase toluene compared with the pristine C-TiO₂.