Heterostructured SnS2/SnO2 nanotubes with enhanced charge separation and excellent photocatalytic hydrogen production

SnO₂, a promising candidate for photocatalytic water splitting, displays poor activity due to insufficient light utilization and rapid electron-hole recombination of charge carriers. Herein, one-dimensional heterostructures of SnO₂/SnS₂ nanotubes was designed and synthesized through a facile electrospinning followed by vulcanized method. The unique heterostructured SnO₂/SnS₂ could simultaneously promote photocarrier transport and suppress charge recombination through the uniquely coupled SnO₂/SnS₂ heterogeneous interface. Additionally, the optimized type-II heterostructure could also improve light absorption and weak the barrier of photocharge transfer. As a result, the SnO₂/SnS₂ exhibited excellent photocatalytic H₂ evolution performance under simulated light irradiation with high H₂ production rate of 50 μmol h^?1 without the use of any noble metal co-catalyst, which is 4.2 times higher than that of pure SnO₂ under the same condition.     

CuS-modified ZnO rod/reduced graphene oxide/CdS heterostructure for efficient visible-light photocatalytic hydrogen generation

Solar energy utilization is a promising strategy for the photocatalytic generation of H₂ from water. Herein, a CuS-modified ZnO rod/reduced graphene oxide (rGO)/CdS heterostructure was fabricated via Cu-induced electrochemical growth with Zn powder at room temperature. The resulting powder revealed good interfacial bonding and promoted photoexcited carrier transport. The CuS nanoparticles played a pivotal role in enhancing visible-light responses and demonstrated excellent catalytic performance. A high visible-light photocatalytic H₂ generation rate of 1073 μmol h⁻¹ g⁻¹ was obtained from the CuS–ZnO/rGO/CdS heterostructure containing 0.23% CuS and 1.62% CdS. Increased photoexcited electron lifetimes, improved carrier transport rates, and decreased fluorescence intensities confirmed the synergistic effects of each of the components of the heterostructure. This study provides an innovative strategy for constructing multi-component heterostructures to achieve efficient visible-light H₂ evolution.     

Hierarchical nanohybrid of CuS/NiS2/Ti3C2 heterostructure with boosting charge transfer for efficient photocatalytic hydrogen evolution

Fabricating heterostructure photocatalysts with co-catalysts can improve the separation and transfer of photo-induced electrons and holes for photocatalysis reactions. Herein, Ti₃C₂T_x nanosheets are obtained by chemical etching via the hydrothermal route and serve as a template for growing photocatalysts. NiS₂ nanoparticles and CuS nanoneedles are deposited sequentially on the surface of Ti₃C₂T_x nanosheets to form “Type II” CuS/NiS₂/Ti₃C₂T_x hierarchical heterostructure via the solvothermal method. The enormous nanoneedles morphology provides enlarged active sites for the photocatalytic processes. The fabricated CuS/NiS₂/Ti₃C₂T_x heterostructure delivers an increased hydrogen generation rate of 32.66 mmol g⁻¹ h⁻¹, which is higher than that of pure CuS (2.38 folds), NiS₂ (1.93 folds), and NiS₂/Ti₃C₂T_x (1.71 folds). CuS/NiS₂/Ti₃C₂T_x heterostructure also performs a superior hydrogen evolution retention of 97.7% after 4 cycles (one cycle lasts 4 h), implying its decent structural stability and light corrosion resistance. The reasons are ascribed to the constructed “Type II” heterostructure of CuS/NiS₂ with higher active sites, improved conductivity, and efficient separation of electrons and holes. DFT calculation and Mott-Schottky plots results elucidate the formation mechanism of CuS/NiS₂/Ti₃C₂T_x “Type II” structure. CuS/NiS₂/Ti₃C₂T_x heterostructure also obtains a reduced bandgap with increased light absorption. The van der Waals force between 2D materials enhances the transfer of photo-generated electrons. This work demonstrates that designing hierarchical co-catalyst heterostructure without non-noble can effectively promote water splitting in the solar-to-chemical system.     

Direct Z-scheme CoS/g-C3N4 heterojunction with NiS co-catalyst for efficient photocatalytic hydrogen generation

Facilitating the separation of photoexcited electron-hole pairs and enhancing the migration of photogenerated carriers are essential in photocatalytic reaction. CoS/g-C₃N₄/NiS ternary photocatalyst was prepared by hydrothermal and physical stirring methods. The optimized ternary composite achieved a hydrogen yield of 1.93 mmol g^?1 h^?1, 12.8 times that of bare g-C₃N₄, with an AQE of 16.4% at 420 nm. The enhanced photocatalytic activity of CoS/g-C₃N₄/NiS was mainly ascribed to the synergistic interaction between the Z-scheme heterojunction constructed by CoS and g-C₃N₄ and the NiS co-catalyst featuring a large amount of hydrogen precipitation sites, which realized the efficient separation and migration of photogenerated carriers. In addition, the CoS/g-C₃N₄/NiS heterojunction-co-catalyst system exhibited excellent photocatalytic stability and recyclability.     

Morphology-controllable formation of MOF-Derived C/ZrO2@1T-2H MoS2 heterostructure for improved electrocatalytic hydrogen evolution

Though MoS₂ has been regarded a promising alternative to Pt for catalyzing hydrogen evolution reaction (HER), a transition from its natural poorly conductive 2H phase to metastable 1T phase is necessary, which often requires harsh experimental conditions. Herein, using a metal-organic framework (MOF) material (UiO-66) as sacrificing template, we proposed a facile solvothermal strategy to synthesize C/ZrO₂@MoS₂ nanocomposites whose morphology and phase could be effectively engineered simply by controlling reaction time. The optimized double yolk-shell structure allowed a stable hybridization of 1T- and 2H–MoS₂, which exhibited improved HER activity (overpotential of 55 mV at 10 mA/cm² and 58 mV/dec for Tafel slope) and considerable durability. Synergism of ZrO₂–MoS₂ heterointerface induced active sites and energetic favorable phase mixing of MoS₂ is considered responsible for the sufficient electrocatalytic capability of our composite. Our work may offer new scientific insights into a cost-effective method for further enhancing the HER performance of MoS₂-based nanohybrids.     

1T-phase MoS2/holey ultrathin g-C3N4 nanosheets based 2D/2D heterostructure for enhanced photocatalytic hydrogen production

Although graphitic carbon nitride (g-C₃N₄) is widely used for photocatalytic hydrogen production, its practical application is restricted by the high recombination rate of photoinduced electron-hole pairs and limited active sites. In this work, holey ultrathin g-C₃N₄ nanosheets (HCN NSs) with rich active sites are prepared, followed by the growth of 1T-MoS₂ NSs on their surfaces to construct 2D/2D 1T-MoS₂/HCN heterostructure. Due to the high surface area and abundant hydrogen active sites of the hybrid, large and intimate 2D nanointerface between MoS₂ and HCN, hydrogen ion adsorption and charge separation/transport ability are greatly enhanced. As a result, 1T-MoS₂/HCN-4 with the optimal 1T-MoS₂ content of 8 wt% displays the highest H₂ production rate of 2724.2 μmol^?1 h^?1 g^?1 under simulated solar light illumination with apparent quantum efficiency of 8.1% (λ = 370 nm). Moreover, the 1T-MoS₂/HCN-4 hybrid manifests improved stability after a long-time test. This study opens the door to design highly-efficient g-C₃N₄ based 2D/2D heterostructures for photocatalytic H₂ production.     

Enhanced photocatalytic hydrogen evolution and CO2 to CH4 selectivity of Co3O4/Ti3+-TiO2 hollow S-scheme heterojunction via ZIF-67 self-template and Ti3+/Ov

The potential would be an important issue for enhancing photocatalytic HER and CO₂ photoreduction selectivity. Herein, the Co₃O₄/Ti³⁺-TiO₂ hollow S-scheme heterojunction is fabricated via continuous light modification-chemical-annealing-reduction method. Evaluated by photocatalytic performance, the as-prepared Co₃O₄/Ti³⁺-TiO₂ hollow S-scheme heterojunction exhibits remarkable photocatalytic performance enhancement than single TiO₂, including hydrogen evolution (∼396.16 μmol/g·h, ∼15 folds) and CO₂ photoreduction (H₂/CH₄/CO: ∼20.32/80.57/9.85 μmol/g·h, ∼20 folds), and achieves CO₂ photoreduction to CH₄ selectivity enhancement, which can be mainly ascribed to the synergism of Ti³⁺/O_v and S-scheme heterojunction. There, Ti³⁺/O_v can not only increase the solar efficiency, but also decrease the energy barrier of H⁺ and 1CO photoreduction to enhance HER and CO₂ to CH₄ selectivity, including promote the H⁺ diffusion and CO₂ absorption. Additionally, the formed Co₃O₄/Ti³⁺-TiO₂ S-scheme heterojunction can promote the photo-generated carrier separation/transportation. Also, the hollow 3D structure obtained by ZIF-67 self-template can increase solar efficiency and stability.     

Highly efficient white-LED-light-driven photocatalytic hydrogen production using highly crystalline ZnFe2O4/MoS2 nanocomposites

Designing efficient photocatalytic systems for hydrogen evolution is extremely important from the viewpoint of the energy crisis. Highly crystalline heterostructure catalysts have been established, considering their interface electric field effect and structural features, which can help improve their photocatalytic hydrogen-production activity. In this study, we fabricated a highly crystalline heterojunction consisting of ZnFe₂O₄ nanobricks anchored onto 2D molybdenum disulfide (MoS₂) nanosheets (i.e., ZnFe₂O₄/MoS₂) via a hydrothermal approach. The optimized ZnFe₂O₄/MoS₂ photocatalyst, with a ZnFe₂O₄ content of 7.5 wt%, exhibited a high hydrogen-production rate of 142.1 μmol h⁻¹ g⁻¹, which was 10.3 times greater than that for the pristine ZnFe₂O₄ under identical conditions. The photoelectrochemical results revealed that the ZnFe₂O₄/MoS₂ heterojunction considerably diminished the recombination of electrons and holes and promoted efficient charge transfer. Subsequently, the plausible Z-scheme mechanism for photocatalytic hydrogen production under white-LED light irradiation was discussed. Additionally, the influence of cocatalysts on the photocatalytic hydrogen evolution for the ZnFe₂O₄/MoS₂ heterostructure was investigated. This work has demonstrated a simplified coupling of one-dimensional or zero-dimensional structures with 2D nanosheets for improving the photocatalytic hydrogen production activity as well as confirmed that MoS₂ is a viable substitute for precious metal-free photocatalysis.     

Fabrication of CdS/Zn2GeO4 heterojunction with enhanced visible-light photocatalytic H2 evolution activity

CdS/Zn₂GeO₄ (CG) composites were synthesized through the simple hydrothermal process. The crystal structure, morphology and light absorption property of the products were studied in detail. The CG composites showed excellent photocatalytic hydrogen production performance upon visible light illumination. Especially, the CG-3 composite displayed the highest H₂ evolution rate of 1719.8 μmol h⁻¹ g⁻¹, which was about 3.80 and 4.28 times higher than the pure CdS and Zn₂GeO₄. Besides, the cyclic stability of the CG-3 composite was also excellent. The PL, photocurrent response and EIS spectra results testified that the efficient separation and transfer of photoinduced charge carriers achieved between CdS and Zn₂GeO₄, which could result in the promotion of photocatalytic performance. Moreover, a possible mechanism of H₂ generation over CdS/Zn₂GeO₄ heterojunction was discussed. The practicable way to construct heterojunction composites would be helpful for the design of other systems with excellent photocatalytic property.     

Controllable growth of coral-like CuInS2 on one-dimensional SiO2 nanotube with super-hydrophilicity for enhanced photocatalytic hydrogen evolution

Designing a semiconductor photocatalyst with a unique structure is crucial for photocatalytic hydrogen evolution. The adsorption of water molecules is considered to be an important link affecting the photocatalytic activity. Nanoconfined water molecules inside the microporous SiO₂ nanotube adsorbed on the active sites boosting the photocatalytic hydrogen evolution compared with the bulk water system. Herein, hydrophilic porous SiO₂ hollow nanotubes were prepared through electrospinning fiber membranes as templates. CuInS₂ nanoparticles were uniformly deposited on porous SiO₂ hollow nanotubes to form CuInS₂/SiO₂ composites. The unique CuInS₂/SiO₂ hollow nanotube with a coral structure was prepared. A series of characterization results show that CuInS₂ supported on porous SiO₂ hollow nanotubes has two advantages. On the one hand, SiO₂ has excellent hydrophilicity and can be used as a micro water-collecting reactor to reduce mass transfer resistance. On the other hand, SiO₂ reduces the particle size of CuInS₂, thus improving the utilization rate of light, and inhibiting electron-hole recombination. The CuInS₂/SiO₂ with a coral structure exhibited the highest hydrogen production rate of 367.00 μmol g^?1 h^?1 under visible light irradiation (λ ≥ 420 nm), which is 3.1 times than that of CuInS₂ powder. This work points out a novel method to enhance photocatalytic hydrogen evolution.     

Formation of multilayer-Eosin Y-sensitized TiO2 via Fe coupling for efficient visible-light photocatalytic hydrogen evolution

An efficient visible-light active photocatalyst of multilayer-Eosin Y-sensitized TiO₂ is prepared through linkage of Fe³⁺ between not only TiO₂ and Eosin Y but also different Eosin Y molecules to form three-dimensional polymeric dye structure. The multilayer-dye-sensitized photocatalyst is found to have high light harvesting efficiency and photocatalytic activity for hydrogen evolution under visible light irradiation (λ > 420 nm). On the optimum conditions (1:1 initial molar ratio of Eosin Y to Fe(NO₃)₃, initial 10 × 10⁻³ M Eosin Y, and 1.0 wt% Pt deposited by in situ photoreduction), its maximal apparent quantum yield for hydrogen evolution is 19.1% from aqueous triethanolamine solution (TEOA aq). The present study highlights linking between dye molecules via metal ions as a general way to develop efficient visible-light photocatalyst.     

Fabrication of the SnS2/ZnIn2S4 heterojunction for highly efficient visible light photocatalytic H2 evolution

A series of SnS₂/ZnIn₂S₄ (x-SS/ZIS) photocatalysts with different mass ratios of SnS₂ were prepared by a hydrothermal method. The resulted composites were used for photocatalytic hydrogen evolution under visible light excitation. All the SS/ZIS composites exhibited significantly enhanced photocatalytic activity for H₂ evolution. Obviously, the highest H₂ evolution rate of 769 μmol g^?1 h^?1 was observed over 2.5-SS/ZIS, which was approximately 10.5 times that of the ZnIn₂S₄ (73 μmol g^?1 h^?1). The enhanced photocatalytic performance was attributed to the successful construction of SnS₂/ZnIn₂S₄ heterojunctions, leading to rapid charge separation and fast transfer of the photo-generated electrons and holes under light irradiation. On the basis of PL, electrochemical impedance spectroscopy (EIS), photocurrent measurements and the H₂ evolution tests, a plausible photocatalytic mechanism was proposed.     

Sol-gel synthesis of Er3+:Y3Al5O12/TiO2Ta2O5/MoO2 composite membrane for visible-light driving photocatalytic hydrogen generation

By using TiO₂ and Ta₂O₅ colloids, a stable and efficient visible-light driven photocatalyst, Er³⁺:Y₃Al₅O₁₂/TiO₂Ta₂O₅/MoO₂ composite membrane, was successfully prepared via sol–gel dip coating method at room temperature. The XRD, FTIR, SEM, TEM and EDX results confirm that approximately spherical Er³⁺:Y₃Al₅O₁₂ nanoparticles were embedded in TiO₂Ta₂O₅ matrix. UV–vis absorption and PL spectra of Er³⁺:Y₃Al₅O₁₂ were also determined to confirm the visible absorption and ultraviolet emission. The photocatalytic hydrogen generation was carried out by using methanol as sacrificial reagent in aqueous solution under visible-light irradiation. Furthermore, some main influence factors such as heat-treated temperature, heat-treated time and molar ratio of TiO₂ and Ta₂O₅ on visible-light photocatalytic hydrogen generation activity of Er³⁺:Y₃Al₅O₁₂/TiO₂Ta₂O₅/MoO₂ composite membrane were studied in detail. The experimental results showed that the photocatalytic hydrogen generation activity of Er³⁺:Y₃Al₅O₁₂/TiO₂Ta₂O₅/MoO₂ composite membrane heat-treated at 550 °C for 3.0 h was highest when the molar ratio of TiO₂ and Ta₂O₅ was adopted as 1.00:0.50. And that a high level photocatalytic activity can be still maintained after four cycles. In addition, a possible mechanism for the visible-light photocatalytic hydrogen generation of the Er³⁺:Y₃Al₅O₁₂/TiO₂Ta₂O₅/MoO₂ membrane was proposed based on PL spectra.     

Self-assembled CdS@BN core-shell photocatalysts for efficient visible-light-driven photocatalytic hydrogen evolution

CdS@BN NRs core-shell photocatalysts for hydrogen evolution were synthesized by a solvothermal and chemical adsorption method. CdS NRs coated by 5 wt% boron nitride (BN) shell exhibited remarkably visible-light photocatalytic hydrogen evolution activity of up to 30.68 mmol g⁻¹ h⁻¹, nearly 6.79 times higher than that of pure CdS NRs, and the apparent quantum efficiency at 420 nm was 7.5%. Transmission electron microscopy showed the CdS NRs were coated with a thin (~5 nm) BN layer, which together with the hydrogen evolution results proved the photocatalytic ability of CdS NRs was significantly improved. The hydrogen evolution rate of CdS NRs coated by 5 wt% BN remained at 91.4% after four cycles, indicating the photocorrosion of CdS NRs was effectively alleviated. Moreover, the large and close coaxial interfacial contact between the CdS core and the BN shell was beneficial to the separation and transfer of photogenerated electron-hole pairs.     

Non-noble metal ultrathin MoS2 nanosheets modified Mn0.2Cd0.8S heterostructures for efficient photocatalytic H2 evolution with visible light irradiation

A series of non-noble metal ultrathin MoS₂ nanosheets modified Mn_0.2Cd_0.8S heterostructured composites were prepared by an ultrasonic assisted hydrothermal synthesis process. Comparing with the pristine Mn_0.2Cd_0.8S composite, the obtained ultrathin MoS₂/Mn_0.2Cd_0.8S composites exhibited a significantly improved photocatalytic activity for hydrogen evolution from water with visible light response. The optimized photocatalytic activity toward MoS₂/Mn_0.2Cd_0.8S composite is around 8 times of the pristine Mn_0.2Cd_0.8S composite. Moreover, the ultrathin MoS₂/Mn_0.2Cd_0.8S composites displayed good photocatalytic stability in the course of photochemical reaction. The excellent photocatalytic activity of the ultrathin MoS₂/Mn_0.2Cd_0.8S composites might be attributed to the formed heterojunctions in composites itself and the sufficient active edge sites in MoS₂ phase. A possible photocatalytic mechanism was tentatively proposed. Considering its excellent photocatalytic activity and good photochemical stability, the obtained ultrathin MoS₂/Mn_0.2Cd_0.8S composite has potential application in photocatalytic hydrogen evolution from water by using solar energy.     

Design of nanohoneycomb structured Ta3N5/WO3 Z-scheme for enhanced visible light photocatalytic hydrogen evolution

Ta₃N₅ has suitable band positions for visible light photocatalytic hydrogen production from water splitting. However, fast self-recombination of electrons and holes is a drawback for its low efficiency. A Ta₃N₅/WO₃ Z-scheme was therefore considered to solve this problem. Furthermore, a nanohoneycomb (nHC) structure was designed and fabricated based on solution-based nanosphere lithography to offer higher surface area for reaction. The cell size of the nHC was controlled by using 400-, 200-, and 100-nm polystyrene nanospheres as the mask. Under visible light irradiation, the hydrogen generation rates of Ta₃N₅@WO₃ film and Ta₃N₅@100-nm WO₃ nHC were measured to be 4.6 and 8.1 μmol/g·h, respectively, whereas that of pure Ta₃N₅ nHC was negligible. With deposition of Pt cocatalyst, the hydrogen generation rates for Ta₃N₅@WO₃ film and Ta₃N₅@100-nm WO₃ nHC were further raised to 9.9 and 16.6 μmol/g·h, confirming the effectiveness of the structure design.     

3D ordered macroporous Pt/ZnS@ZnO core-shell heterostructure for highly effective photocatalytic hydrogen evolution

ZnO, as a typical n-type semiconductor catalyst with low cost and high electron mobility, is concerned by numerous pursuers in the field of photocatalysis. However, because of its poor photo-reduction ability and high recombination rate, the ZnO in photocatalytic H₂ evolution is greatly limited. To acquire an outstanding photocatalytic H₂ evolution performance, 3D ordered macroporous (3DOM) ZnO is sulfurized in-situ to construct 3DOM ZnS@ZnO heterostructure. The ordered macroporous structure not only accelerates the migration of electrons and ions but also curtails the shift space of electrons and holes. The multi-junction assemblage between ZnO and ZnS effectively decreases the recombination of electron-hole pairs and improves the photo-redox capacity. The 3DOM Pt/ZnS@ZnO heterostructure exhibiting an excellent performance is 87.6 μmol g^?1 h^?1 in pure water. Therefore, our research presents an innovative procedure for designing other porous heterostructure photocatalysts.     

Optimal preparation of molybdenum phosphide cocatalyst for efficient dye-sensitized photocatalytic hydrogen evolution

Searching for non-noble-metal cocatalyst for hydrogen evolution in photocatalytic water–splitting has attracted much attention. Herein, molybdenum phosphide (MoP) as an efficient and stable cocatalyst was prepared in a facile phosphorization process at relatively low temperatures under N₂ atmosphere, and the effect of preparation temperature (300–500 °C) was studied. Using Eosin Y (EY) and the prepared sample as catalyst (sensitizer) and cocatalyst, respectively, the photocatalytic activity for hydrogen evolution was investigated in aqueous trimethylamine (TMA) solution under visible light irradiation (λ ≥ 420 nm). MoP prepared at 400 °C (MoP-400) exhibits the highest sensitization activity and superior stability, and the maximal apparent quantum yield (AQY) for hydrogen evolution is up to 48.0% at 420 nm, much higher than the most reported data for MoP-based photocatalysts. The highest activity can be attributed to the highest P content in MoP-400 and the rapidest electron transfer between photoexcited EY and MoP-400. The possible mechanism was discussed.     

Highly efficient thiomolybdate [Mo2S12]2- nanocluster cocatalyst decorated on TiO2 to boost photocatalytic hydrogen evolution

The exploitation of noble-metal-free photocatalysts with high solar-to-H₂ conversion efficiency is a hot topic in the photocatalysis field. Molybdenum sulfide materials, which have good physicochemical properties and excellent hydrogen evolution activity, have become an effective noble metal cocatalyst substitute and attracted widespread attention. In this work, a highly efficient photocatalyst constructed by decorating thiomolybdate [Mo₂S₁₂]^2- nanoclusters on TiO₂ is reported for the first time. The resultant [Mo₂S₁₂]^2-/TiO₂ photocatalyst shows a remarkable enhanced hydrogen evolution rate under the Xenon light irradiation. At the optimal loading amount of [Mo₂S₁₂]^2-, the photocatalyst exhibits a photocatalytic hydrogen evolution rate of 213.1 μmol h^?1 g^?1, which is about 51 times that of the pure TiO₂. Characterization results show that the intimate contact between [Mo₂S₁₂]^2- and TiO₂ promotes the separation of hole-electron pairs, prolongs the lifetime of carriers, and thereby increases the photocatalytic activity. Furthermore, abundant bridging S in the [Mo₂S₁₂]^2- acts as active sites for hydrogen evolution, which also contributes to the enhanced hydrogen production rate. This work demonstrates an efficient way for the construction of noble-metal-free hydrogen evolution photocatalyst and provides a useful reference for the development of low cost photocatalysts in the future.     

Enhanced photocatalytic hydrogen evolution from aqueous solutions on Ag2S/Ag heteronanostructure

A new approach for synthesis of hybrid Ag₂S/Ag heteronanostructure based on hydrochemical bath deposition with the using of Trilon BD has been suggested. The synthesized Ag₂S/Ag heteronanostructure has shown higher catalytic activity in the hydrogen evolution from the aqueous solution of Na₂S/Na₂SO₃ under irradiation by light with wavelength of 450 nm than nanostructured Ag₂S photocatalyst. The main reason for the enhanced photoactivity of Ag₂S/Ag heterostructure as compared with Ag₂S catalyst is a presence of Ag, and also nonstoichiometry of silver sulfide in this heteronanostructure which leads to the improved charge separation as compared with silver sulfide catalyst.