Ti3C2 MXene coupled with CdS nanoflowers as 2D/3D heterostructures for enhanced photocatalytic hydrogen production activity

As a novel co-catalyst, Ti₃C₂ MXene has an excellent prospect in the field of photocatalysis. Herein, the 2D/3D Ti₃C₂ MXene@CdS nanoflower (Ti₃C₂@CdS) composite was successfully synthesized by a hydrothermal method. The combination of 2D Ti₃C₂ MXene and 3D CdS nanoflowers can promote carrier transfer and separation, which can improve the performance of CdS. Compared to pure CdS nanoflowers, Ti₃C₂@CdS composite presents lower photoluminescence intensity, longer fluorescence lifetime, higher photocurrent density and smaller electrochemical impedance. The Ti₃C₂@CdS composite with 15 wt% Ti₃C₂ adding amount presents high photocatalytic hydrogen evolution activity (88.162 μmol g^?1 h^?1), 91.57 times of pure CdS. The improved photocatalytic activity of Ti₃C₂@CdS composite is ascribed to the addition of lamellar Ti₃C₂ MXene, which improves the electrical conductivity of the photocatalytic system and effectively accelerates the excited electrons transfer from CdS to Ti₃C₂ MXene.     

Facile preparation of ZnS/CdS core/shell nanotubes and their enhanced photocatalytic performance

In this paper, ZnS/CdS core/shell nanotubes were successfully synthesized by combining hydrothermal treatment and ion exchange conversion, and the significant influence of CdS content in the shell on photo absorption and photocatalytic activity was also investigated. The core/shell nanotubes structure of CdS deposition on both sides of ZnS nanotube was confirmed by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The room temperature PL spectra of ZnS/CdS core/shell nanotubes indicated that CdS on the shell can reduce the recombination of photon-generated electron and hole. The photocatalytic activity tests prove that ZnS/CdS nanotubes have much higher photocatalytic hydrogen production activity than ZnS nanotube and CdS nanotube. Under the irradiation of visible light, the highest photocatalytic hydrogen production rate of 110 μmol h⁻¹ g⁻¹ is observed over the ZnS/CdS core/shell nanotubes with CdS/ZnS molar ratio of 1:4, which is about 11.02 and 5.56 times more active than ZnS nanotube and CdS nanotube, respectively. The improved performance of ZnS/CdS samples can be due to the strong photo response in the visible light region and the efficient separation of electron–hole pairs.     

Sonochemistry synthesis of Bi2S3/CdS heterostructure with enhanced performance for photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution from water splitting is an efficient, eco-friendly method for the conversion of solar energy to chemical energy. A great number of photocatalysts have been reported but only a few of them can respond to visible-light. Metal sulfides, a class of visible-light response semiconductor photocatalysts for hydrogen evolution and organic pollutant degradation, receive a lot of attention due to their narrow band gaps. Herein, we report the sonochemical synthesis of Bi₂S₃/CdS nanocrystal composites with microsphere structure at mild temperature. The phases of Bi₂S₃ and CdS can be observed obviously in HRTEM image. The heterostructure consisting of the two species of nanocrystals plays a key role in separating photo-generated charge carriers. Photocatalytic activities for water splitting are investigated under visible-light irradiation (λ > 400 nm) and an enhanced photocatalytic activity is achieved. The initial rate of H₂ evolution is up to 5.5 mmol h⁻¹ g⁻¹ without resorting to any cocatalysts.     

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.     

Fabrication of 1D/2D CdS/CoSx direct Z-scheme photocatalyst with enhanced photocatalytic hydrogen evolution performance

In this work, we fabricate a 1D/2D heterojunction photocatalyst composed of n-type CdS nanorods and p-type CoS_x nanoflake. This photocatalyst achieves a hydrogen evolution rate of 9.47 mmol g^?1 h^?1, which is 13.7 times higher than that of pure CdS nanorods. Scanning Kelvin Probe, Mott-Schottky plots, UV–Vis absorption spectra and surface photocarrier orienting reaction results indicate that the enhanced photocatalytic performance of CdS/CoS_x is owing to the fabrication of direct Z-Scheme heterojunction system which greatly improves the utilization, migration and separation rate of photo-generated carriers. To the best of our knowledge, this work is the first time to describe a CdS/CoS_x direct Z-scheme system with 1D/2D nanostructure, which can expedite the transfer process of photogenerated carriers with strong redox energy to participate in photocatalytic reactions.     

Hierarchical porous TS-1/Pd/CdS catalysts for enhanced photocatalytic hydrogen evolution

The conversion of water to hydrogen through solar energy is considered as a promising solution to the energy shortage and environmental problems. In this work, the alkali-treated titanium silicalite-1 (TS-1) with a hierarchical porous structure was used as a carrier to prepare the TS-1/Pd/CdS catalysts with large specific surface area and wide photoresponse range. The hydrogen evolution rate of the 0.3NaOH-TS-1/Pd/CdS can reach 2556.0 μmol/h under visible light, which is about 3.5 times that of the Untreated TS-1/Pd/CdS. Herein, the catalysts with a composite structure are beneficial to the uniform dispersion of palladium and CdS quantum dots, the increase of the relative concentration of the active phase tetracoordinated titanium in the framework, and the enhancement of the reflecting and scattering of light in the multi-level pores, thus promoting the photocatalytic hydrogen production reaction.     

In-situ constructing cobalt incorporated nitrogen-doped carbon/CdS heterojunction with efficient interfacial charge transfer for photocatalytic hydrogen evolution

Designing an efficient heterojunction interface is an effective way to promote the electrons' transfer and improve the photocatalytic H₂ evolution performance. In this work, a novel hollow hybrid system of Co@NC/CdS has been fabricated and constructed. CdS nanospheres are anchored on the hollow-structured cobalt incorporated nitrogen-doped carbon (Co@NC) through a one-pot in-situ chemical deposition approach, forming an intimate interface and establishing an excellent channel to improve the electrons transfer and charge carriers separation between CdS and Co@NC cocatalyst, which immensely promotes the photocatalytic activity. The rate of photocatalytic H₂ evolution over hollow structured Co@NC/CdS heterojunction can be achieved 8.2 mmol g^?1 h^?1, which is about 45 times of pristine CdS nanospheres. The photocatalytic H₂ evolution mechanism has been investigated by the techniques of photoluminescence (PL) spectra, photocurrent-time (i-t) curves, electrochemical impedance spectroscopy (EIS) etc. This work aims to provide a new way in developing of high-performance advanced 3D heterojunction for photocatalytic hydrogen evolution.     

Greatly enhanced photocatalytic hydrogen production on CdS/(Pt/g-C3N4) via dual functions of Pt on semiconductors interface

CdS and g-C₃N₄ are famous semiconductors in photocatalytic hydrogen evolution, however, their low efficiencies limit their further application. Here, a highly efficient ternary catalyst CdS/(Pt/g-C₃N₄) was reported and its photocatalytic hydrogen production activity reached up to 1465.9 μmol/h/g, which is 5.3 times of Pt/CdS and 4.0 times of Pt/g-C₃N₄, respectively. TEM and HRTEM images demonstrate the Pt nanoparticles exists on the interface of between CdS and g-C₃N₄ acting as a cocatalyst for hydrogen evolution. SPV spectra and electrochemical tests demonstrate that Pt as bridge between CdS and g-C₃N₄ also accelerates the electrons transforming which benefits for the inhibition of the recombination of photoexcited electrons and holes. This study demonstrated the dual roles of interface Pt and provides a new method to design a highly efficient photocatalyst.     

Cu2ZnSnS4 decorated CdS nanorods for enhanced visible-light-driven photocatalytic hydrogen production

Design and preparation of high performance photocatalysts are always the keys for photocatalytic hydrogen production by using green and unlimited solar energy. In this work, we present the synthesis of Cu₂ZnSnS₄ (CZTS) decorated CdS nanorods and their use for visible-light-driven photocatalytic hydrogen production. The as-synthesized CZTS decorated CdS nanorods exhibit much higher visible-light-driven photocatalytic hydrogen production performance than that of individual CdS nanorods and individual CZTS nanoparticles. Specifically, the hydrogen production rate of representative CZTS decorated CdS nanorods was 48-times and 165-times higher than that of individual CdS nanorods and individual CZTS nanoparticles. The enhanced photocatalytic hydrogen production performance may be contributed by the p-n heterojunction as well as the synergistic effect between CdS nanorods and CZTS particles. The present work not only reported new low-cost and highly efficient photocatalysts for visible-light-driven photocatalytic hydrogen production, but also provided new method for the design and preparation of high performance visible-light-driven heterostructured photocatalysts for photocatalytic hydrogen production.     

Efficient interfacial charge transfer of 2D/2D CoP/CdS heterojunction for extremely boosted photocatalytic H2 evolution performance

Constructing 2D/2D heterojunction photocatalysts has attracted great attentions due to their inherent advantages such as larger interfacial contact areas, short transfer distance of charges and abundant reaction active sites. Herein, 2D/2D CoP/CdS heterojunctions were successfully fabricated and employed in photocatalytic H₂ evolution using lactic acid as sacrificial reagents. The multiple characteristic techniques were adopted to investigate the crystalline phases, morphologies, optical properties and textual structures of heterojunctions. It was found that integrating 2D CoP nanosheets as cocatalysts with 2D CdS nanosheets by Co–S chemical bonds would significantly boost the photocatalytic H₂ evolution performances, and the 7 wt% 2D/2D CoP/CdS heterojunction possessed the maximal H₂ evolution rate of 92.54 mmol g^?1 h^?1, approximately 31 times higher than that of bare 2D CdS nanosheets. Photoelectrochemical, steady photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements indicated that there existed an effective charge separation and migration over 2D/2D CoP/CdS heterojunction, which then markedly lengthened the photoinduced electrons average lifetimes, retarded the recombination of charge carriers, and caused the dramatically boosted photocatalytic H₂ evolution activity. Moreover, the density functional theory (DFT) calculation further corroborated that the efficient charge transfer occurred at the interfaces of CoP/CdS heterojunction. This present research puts forward a promising strategy to engineer the 2D/2D heterojunction photocatalysts endowed with an appealing photocatalytic H₂ evolution performance.     

V2O5 nanoribbons/N-deficient g-C3N4 heterostructure for enhanced visible-light photocatalytic performance

Visible-light-induced heterostructure photocatalysts have been regarded as promising candidates in clean energy production and environmental treatment of organic pollutants. In this study, we have prepared nanocomposites of V₂O₅/N-deficient g-C₃N₄ (VO/Ndef-CN), which have been characterized by a variety of techniques. The as-synthesized nanocomposites show efficient bifunctional photocatalytic properties toward hydrogen generation and pollutants degradation (dye and antibiotic). The optimized 5VO/Ndef-CN photocatalyst exhibits improved photoactivity for H₂ production (5892 μmol g^?1 h^?1), with a high quantum yield of 6.5%, and fast degradation of organic pollutants, as well as high photocatalytic stability under visible light irradiation. The high photocatalytic efficiency is due to the presence of N defects and S-scheme heterojunction formation, which leads to rapid charge separation, enhanced visible-light absorption, and increased active sites. Furthermore, the possible activity-enhanced mechanism and the photodegradation pathway are proposed based on the experimental and density functional theory (DFT) investigations.     

Vanadium diboride as an efficient cocatalyst coupled with CdS for enhanced visible light photocatalytic H2 evolution

Exploiting active, stable, and cost-efficient cocatalysts is crucial to enhance the photocatalytic performance of semiconductor-based photocatalysts for H₂ evolution from water splitting. Herein, we report on using vanadium diboride (VB₂) as an efficient cocatalyst to enhance the photocatalytic H₂ evolution performance of CdS nanoparticles under visible light irradiation (λ ≥ 420 nm). The CdS/VB₂ composites prepared by a facile solution-mixing method exhibit much improved H₂ evolution activities in 10 vol% lactic acid (LA) solution relative to pristine CdS. The most efficient CdS/VB₂ composite with 20 wt% VB₂ (CB20) exhibits a H₂ evolution rate as high as 12.1 mmol h⁻¹ g⁻¹, which is about 11 times higher than that of CdS alone (1.1 mmol h⁻¹ g⁻¹). Moreover, the highest apparent quantum efficiency (AQE) of 4.4% is recorded on CB20 at 420 nm. The improved photocatalytic activity of CdS/VB₂ composite can be attributed to the excellent cocatalytic effect of VB₂, which can not only enhance the charge separation on CdS but also accelerate the H₂ evolution kinetics. This work demonstrates the great potential of using transition metal brodies (TMBs) as efficient cocatalysts for developing noble-metal-free and stable photocatalysts for solar photocatalytic H₂ evolution.     

Improved photocatalytic efficiency and stability of CdS/ZnO shell/core nanoarrays with high coverage and enhanced interface combination

Photocatalytic hydrogen production of CdS/ZnO shell/core nanoarrays were investigated by combining the sensitization and calcining techniques. Long single crystal ZnO nanoarrays hydrothermally grown on FTO were fully covered with CdS using an optimized chemical bath deposition method. Heating treatment not only improved the interface connection and CdS crystallinity but also formed a (Cd_0.8Zn_0.2)S buffer layer between ZnO and CdS. The CdS/ZnO shell/core arrays showed gradually enhanced photocatalytic activity with raising the calcining temperature. This is predominantly attributed to the improved CdS crystallinity and the resultant (Cd_0.8Zn_0.2)S. The (Cd_0.8Zn_0.2)S buffer layer formed by calcining shows dramatic effect on the photocatalytic activity and stability. The CdS/ZnO shell/core arrays calcined at 550 °C exhibits the optimized photocurrent density of 5.1 mA cm^?2 and a photocatalytic stability over 12 h under visible-light irradiation.     

A Z-scheme g-C3N4/Ag3PO4 nanocomposite: Its photocatalytic activity and capability for water splitting

Photodegradation of Rifampin (Rf) was evaluated by g-C₃N₄/Ag₃PO₄ nanocomposite (NC) under the visible-light irradiation. The samples were characterized by XRD, SEM-EDX, and X-Ray mapping, FTIR, and DRS. The XRD patterns showed the body-centered cubic phase for Ag₃PO₄ with an average size of 21.4 ± 3.8 nm and 20 nm for the NC by the Scherrer and Williamson-Hall equations, respectively. The pHpzc values about 10.7, 9.7, and 6.9 and the bandgap energies of 2.39, 2.97, and 2.90 eV were respectively for the as-synthesized Ag₃PO₄, g-C₃N₄, and g-C₃N₄/Ag₃PO₄ samples. The absorbencies of Rf solutions at maximum wavelengths of 330 and 470 nm were used to estimate the Rf photodegradation extent. Greater degradation extents were obtained by the absorbencies recorded at 470 nm. The percentage of the composite components varied the photodegradation efficiency, and the composite containing 60% g-C₃N₄ (G60) showed the highest activity. The best photodegradation results obtained at C_Rf: 2 ppm, solution pH: 5.5, catalyst dose: 1 g/L, irradiation time: 10 min. The solutions with degradation extents of 96 and 97% showed the mineralization extents of 96.4 and 98.2%, calculated from the COD results. The photodegradation pathway obeyed the direct Z-Scheme mechanism. This mechanism pathway was theoretically evaluated for the probable ability of the composite for the hydrogen production and water splitting. The potential of the CB positions (Ag₃PO₄: −1.08 V, g-C₃N₄: 0.21 V) confirms that the accumulated electrons in CB-Ag₃PO₄ position are stronger reducing agent than that of g-C₃N₄ for the reduction of dissolved oxygen to the superoxide radicals and they are also capable of reducing water molecules or protons to hydrogen molecules.     

Well-defined Z-scheme Na2Ti3O7/Ag/CdS multidimensional heterojunctions with enhanced H2 production from seawater under visible light

Production of H₂ from photocatalytic seawater splitting is a more promising but more difficult way than from pure water due to the high salinity of seawater. Efficient and stable photocatalyst is crucial and desired. In this work, well-defined Z-scheme Na₂Ti₃O₇/Ag/CdS (N₁₀A₁C₅) multidimensional heterojunctions composed of zero-dimensional Ag nanoclusters, one-dimensional Na₂Ti₃O₇ (NTO) nanotubes, and two-dimensional CdS nanoplates were constructed. Zero-dimensional Ag nanoclusters decorated on the surface of NTO nanotubes not only act as electron mediator for the formation of Z-scheme between NTO and CdS, but also provide hot electrons due to their plasma effect. CdS nanoplates cooperated with Ag nanoclusters act as visible light absorber, which improve both the visible light absorption range and intensity. With Na₂S·9H₂O (0.25 M) and Na₂SO₃ (0.35 M) as the sacrificial agent, the resultant Z-scheme N₁₀A₁C₅ heterojunctions show a H₂ production of 1793 μmol/(g·h) from visible-light-driven photocatalytic seawater splitting, which is 9.7 times that of NTO/CdS type II heterojunctions. Notably, the Z-scheme N₁₀A₁C₅ also exhibit stability of structure in the high salinity environment due to the interlayer structure of NTO, which can accommodate metal cations in seawater. After four 3-h cycles, the catalytic activity can still maintain 96.6%. This Z-scheme heterojunction is expected to provide a strategy for the design of efficient and stable photocatalysts for the solar energy driven seawater splitting.     

Hollow heterostructure CoS/CdS photocatalysts with enhanced charge transfer for photocatalytic hydrogen production from seawater

In recent years, there have been many studies on photocatalytic water splitting, but there are still few high-efficiency photocatalysts for photocatalytic seawater splitting. In this study, a series of hollow Co sulphide-supported CdS catalyst (H–CoS/CdS) composite photocatalysts were prepared by loading CdS onto the surface of H–CoS, which can be used for efficient H₂ production in pure water and simulated seawater. The heterojunction H–CoS/CdS exhibited H₂ production of 572.4 μmol g^?1 (4 h) from simulated seawater, which is 97.7 and 2.96 times those of H–CoS and CdS, respectively. The h-CoS cocatalyst extended the light absorption range of CdS, improved the chemical stability, and significantly enhances the charge separation efficiency. This study provides guidance for the reasonable design of a photocatalytic seawater-based H₂ production catalyst with high efficiency and low cost.     

Crystallinity and phase controlling of g-C3N4 /CdS hetrostructures towards high efficient photocatalytic H2 generation

The heterostructures of graphitic carbon nitride (g-C₃N₄) and CdS were synthesized by controlling the crystalline degree of g-C₃N₄ and the phase composition of CdS. A thermal polycondensation process of N precursors was adjusted to get amorphous and crystalline g-C₃N₄. A multistep adsorption method was used to deposit CdS nanoparticles on g-C₃N₄. An annealed process was used to adjust the phase composition of CdS from cubic to hexagonal. The morphology of CdS was changed to rod. Amorphous g-C₃N₄/CdS heterostructures revealed enhanced photocatalytic activity because the amorphous g-C₃N₄ has a lower crystallinity, it is easier to form a heterojunction with the CdS. Further, an annealing process resulted in the phase transfer and morphology change of CdS. The high stability and rod morphology of CdS make the heterostructures with high H₂ generation rate to 5440 μmol h-1 g-1 which is ~5 times high compared with g-C₃N₄.     

In-situ synthesis of well dispersed CoP nanoparticles modified CdS nanorods composite with boosted performance for photocatalytic hydrogen evolution

Development of photocatalysts with characters of low-cost, environment friendliness, visible light response and good performance is vital for the transformation of solar energy into hydrogen fuel. Here, we constructed CoPCdS nanorods hybrid composites via a novel two-step in-situ growth method for the first time. The obtained CoPCdS composites exhibited remarkably enhanced photocatalytic performance and excellent stability in comparison with bare CdS nanorods. Notably, the optimum H₂ evolution rate of 1 wt%CoPCdS was 9.11 times higher than that of pristine CdS. The apparent quantum efficiency of the photocatalyst was calculated to be 11.6%. The superior activity of this material could be attributed to the role of well dispersed CoP nanoparticles and the intimate interface between CoP cocatalysts and CdS nanorods, which efficiently accelerated the separation and transfer of photogenerated electrons. This work provided a new in-situ growth method for the preparation of transition metal phosphides coated photocatalysts with boosted photocatalytic activity of hydrogen evolution.     

Design and preparation of CdS/H-3D-TiO2/Pt-wire photocatalysis system with enhanced visible-light driven H2 evolution

In recent years, tremendous efforts have been devoted to develop new photocatalyst with wide spectrum response for H₂ generation from water or aqueous solution. In this work, CdS nanoparticles (NPs) have been immobilized on hydrogenated three-dimensional (3D) branched TiO₂ nanorod arrays, resulting in a highly efficient photocatalyst, i.e, CdS/H-3D-TiO₂. In addition, electrochemical reduction of H⁺ ion is identified as a limiting step in the photocatalytic generation of H₂ at this catalyst, while here a Pt wired photocatalysis system (CdS/H-3D-TiO₂/Pt-wire) is designed to overcome this barrier. Without the application of potential bias, visible light photocatalytic hydrogen production rate of CdS/H-3D-TiO₂/Pt-wire is 18.42 μmol cm^?2 h^?1, which is 11.2 times that of CdS/H-3D-TiO₂ without Pt (1.64 μmol cm^?2 h^?1). The Pt wire acts as an electron super highway between the FTO substrate and H⁺ ions to evacuate the generated electrons to H⁺ ions and catalyze the reduction reaction and consequently generate H₂ gas. This work successfully offers a novel direction for dramatic improvement in H₂ generation efficiency in photocatalysis field.     

Construction of chlorine doped graphitic carbon nitride nanodisc for enhanced photocatalytic activity and mechanism insight

The development of high-performance doped graphite carbon nitride (g-C₃N₄) by one-step method has always been potential and yet demanding. Here, we designed a novel Cl doped nanodisc structure g-C₃N₄ (Cl(CN)) by one step HCl treatment, without calcination and adding any precursors during the preparation procedure. The photocatalytic activities of samples were assessed toward the hydrogen (H₂) generation and degradation of rhodamine B (RhB) under simulated solar irradiation, of which the hydrogen production efficiency and degradation efficiency of Cl(CN) were 4 folds and 2.18 folds that of g-C₃N₄ (CN), respectively. The overwhelming photocatalytic performance of Cl(CN) was attributed to the synergy effect between the unique nanodisc morphology with high surface area and the regulation of the band structure by the Cl element. To exclude the effect of protonation, the CH₃COOH, H₂SO₄, HNO₃, KCl, NaCl and NH₄Cl treatments were introduced to compare with HCl treatment. The position of doped Cl and its influence on the band gap as well as electronic structure over g-C₃N₄ were investigated by the density functional theory (DFT). In addition, the photocatalytic mechanism of as-prepared samples was further investigated and discussed in detail. This work provided a green and facile protocol for highly active and reusable g-C₃N₄ that can address the environmental issuers and energy challenges.