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.     

2D-2D heterostructured CdS–CoP photocatalysts for efficient H2 evolution under visible light irradiation

Visible-light photocatalytic water splitting for hydrogen evolution has attracted tremendous attention in past decades, but it still suffers from low solar-hydrogen conversion efficiency. In this paper, two-dimensional (2D) CdS was synthesized by the hydrothermal method, and 2D CoP nanosheets were synthesized by successive hydrothermal, oxidation and phosphodation process. Then 2D-2D CdS–CoP photocatalysts were formed by ultrasonically dispersing the mixed solution of CdS and CoP, and their heterostructure was confirmed by transmission electron microscopy, X-ray photoelectron spectroscopy, fluorescence spectrometer and so on. CdS–CoP with 2% CoP loading amounts exhibits a maximum photocatalytic performance of 56.3 mmolg⁻¹h⁻¹ under visible light irradiation, which is 11.3 times as high as bare CdS. The enhanced photocatalytic performance of CdS–CoP should be due to the following two points: (1) high catalytic activity of CoP; (2) highly efficient separation and transfer of electron-hole pairs photogenerated in CdS due to the synthesized 2D-2D heterostructure.     

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.     

Decoration of nicale phosphide nanoparticles on CdS nanorods for enhanced photocatalytic hydrogen evolution

Manipulation of the co-catalyst plays an important role in charge separation and reactant activation to enhance the activity of CdS based photocatalysts. Transition-metal phosphides have aroused widespread interest in catalysis owing to their special structure and catalytic behavior. Herein, Ni₂P as a cocatalyst coupled with CdS for efficient photocatalytic hydrogen evolution with a rate of 483.25 mmol g^?1.h^?1, which was nearly 525 and 1.92 times higher than that of CdS (0.92 mmol g^?1.h^?1) and 1 wt% noble metal Pt modified CdS (251.29 mmol g^?1.h^?1), respectively. Its apparent quantum yield reaches 70% at 420 nm. Based on data analysis, Schottky heterostructure was constructed by combining Ni₂P with CdS. The Schottky junction provides a convenient way for photoinduced electrons to transfer and promotes the effective separation of photoinduced carriers.     

Inserting MOF into flaky CdS photocatalyst forming special structure and active sites for efficient hydrogen production

Due to unique structure and properties of MOFs, a well-designed functional CdS/ZIF-67 composite photocatalyst was successfully synthesized by hydrothermal synthesis to achieve efficient hydrogen evolution. The obtained composite photocatalyst can not only make use of the specific surface area of ZIF-67 to provide a larger reaction place, but also can positively promote the reaction by binding sites between CdS and ZIF-67. Under visible light (5 W LED white light) irradiation, the maximum amount of hydrogen evolution reached 308 μmol in 5 h which was about 50 times higher than that of pure ZIF-67. The composite photocatalyst exhibited a significantly stronger stability than single component. The in-depth study of binding sites by electrochemical experiments showed that the photocurrent of the photocatalyst has increased to 1.8 μA cm⁻³, which showed that the existence of binding sites could effectively improve the electron transfer rate. And the synergy between them also can promote the separation of electron-holes and reduce the recombination rate. Therefore, reaction mechanism was proposed from the view of electron transfer for deep understanding.     

Highly active FexCo1-xP cocatalysts modified CdS for photocatalytic hydrogen production

In this paper, we report a ternary Fe_xCo_1−xP co-catalyst, which can greatly improve the photocatalytic performance of CdS photocatalyst for hydrogen production under visible light irradiation. The high efficiency of ternary Fe_xCo_1-xP loaded CdS is mainly due to the high electrochemical activity and efficient charge transfer between Fe_xCo_1-xP cocatalyst and CdS. Experimental results have shown that the substitution of Fe ions for some Co ions in CoP can change the electrochemical properties of Fe_xCo_1-xP. The electrocatalytic performance of Fe_xCo_1-xP and the photocatalytic activity of Fe_xCo_1-xP/CdS are both dependent on the molar concentration x of Fe. When x = 0.4 the hydrogen generation rate (18.27 mmol h⁻¹ g⁻¹) and the quantum efficiency (50.6% at 420 nm) for 0.5 wt% Fe_0.4Co_0.6P/CdS photocatalyst is 5.85 times higher than that of pure CdS and 1.35 times higher than that of 0.5 wt% CoP/CdS. This new noble-metal-free Fe_xCo_1-xP cocatalyst is beneficial for the solar hydrogen economy.     

Well-designed NiS/CdS nanoparticles heterojunction for efficient visible-light photocatalytic H2 evolution

Heterojunction photocatalysts based on semiconducting nanoparticles show excellent performance in many photocatalytic reactions. In this study, 0D/0D heterojunction photocatalysts containing CdS and NiS nanoparticles (NPs) were successfully synthesized by a chemical precipitation method. The NiS NPs were grown in situ on CdS NPs, ensuring intimate contact between the semiconductors and improving the separation efficiency of hole-electron pairs. The obtained NiS/CdS composite delivered a photocatalytic H₂ evolution rate (7.49 mmol h^?1 g^?1), which was 39.42 times as high as that of pure CdS (0.19 mmol h^?1 g^?1). This study demonstrates the advantages of 0D/0D heterojunction photocatalysts for visible light-driven photocatalytic hydrogen production.     

One-pot hydrothermal synthesis of CdS/NiS photocatalysts for high H2 evolution from water under visible light

The development of efficient and stable noble-metal-free photocatalysts is crucial for hydrogen evolution from water splitting as clean energy. This study reports uniform CdS/NiS spherical nanoparticles through a simple one-pot hydrothermal method with the aid of KOH. The prepared CdS/NiS composites show superior photocatalytic activities toward the water splitting under visible light. A suitable amount of KOH in the synthesis benefits to form CdS/NiS photocatalysts with the improved activity. The CdS/NiS composite including 10 mol% metal percentage of Ni exhibits the highest photocatalytic activity. The high hydrogen evolution rate of 24.37 mmol h^?1 g^?1 is achieved over the CdS/NiS composite photocatalyst. The CdS/NiS photocatalyst has good photocatalytic stability in the recycling uses. The present CdS/NiS as a noble-metal-free photocatalyst provides the superior visible-light driven catalytic activity for hydrogen evolution.     

Efficient photocatalytic hydrogen evolution on amorphous MoSx-modified CdS/KTaO3 heterojunctions under visible light irradiation

Constructing heterostructures with efficient charge separation is a promising route to improve photocatalytic hydrogen production. In this paper, MoS_x/CdS/KTaO₃ ternary heterojunction photocatalysts were successfully prepared by a two-step method (hydrothermal method and photo deposition method), which improved the photocatalytic hydrogen evolution activity. The results show that the rate of hydrogen evolution for the optimized photocatalyst is 2.697 mmol g^?1·h^?1under visible light, which is 17 times and 2.6 times of the original CdS (0.159 mmol g^?1 h^?1) and the optimal CdS/KTaO₃(1.033 mmol g^?1 h^?1), respectively, and the ternary photocatalyst also shows good stability. The improvement on photocatalytic hydrogen evolution performance can be attributed to the formation of heterojunction between the prepared composite materials, which effectively promotes the separation and migration of photo-generated carriers. Amorphous MoS_x acts as an electron trap to capture photogenerated electrons, providing active sites for proton reduction. This provides beneficial enlightenment for hydrogen production by efficiently utilizing sunlight to decompose water.     

In2Se3/CdS nanocomposites as high efficiency photocatalysts for hydrogen production under visible light irradiation

Hydrogen energy is an important clean energy. Using visible light to produce hydrogen by semiconductor photocatalysts is one of the current research hotspots. In this work, In₂Se₃/CdS nanocomposite photocatalysts with different mass content of CdS are prepared. The In₂Se₃/CdS photocatalyst with 85.25% CdS mass content exhibits the optimal photocatalytic hydrogen evolution activity (1.632 mmol g^?1 h^?1), which is much higher than that of CdS (0.715 mmol g^?1 h^?1) and In₂Se₃ (trace). Moreover, the In₂Se₃/CdS photocatalyst still maintains a high hydrogen evolution rate after five cycles. The high photocatalytic activity and stability of the In₂Se₃/CdS nanocomposite is due to the formation of heterojunction between In₂Se₃ and CdS. The existence of heterojunction is confirmed by high resolution transmission electron microscopy image and X-ray photoelectron spectra. Theoretical calculations and experimental results indicate that the electron transfer route at the heterojunction is step-scheme. The step-scheme helps the separation of photogenerated electrons and holes, and maximize the hydrogen evolution activity. This work provides a high efficiency step-scheme photocatalyst for hydrogen production.     

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.     

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.     

Enhanced photocatalytic hydrogen evolution over semi-crystalline tungsten phosphide

Increasing the separation efficiency and transfer rate of photogenerated charges is the dominant factor for improving photocatalytic activity. Herein, we successfully prepared semi-crystalline WP (SC-WP) with good optical properties and as a cocatalyst to modify CdS nanorods (CdS NRs) to construct SC-WP/CdS (PD) composite catalyst by simple electrostatic self-assembly method for photocatalytic hydrogen evolution. Two high-efficiency and stable photocatalytic hydrogen evolution systems were constructed with 1.0 M ammonium sulfite solution and 10 vol% lactic acid solution as sacrificial agents, respectively. Surprisingly, the maximum photocatalytic H₂ production rate of 15446.21 μmol h⁻¹ g⁻¹ is obtained over 10PD composite, which is 10.58 times greater than that of pure CdS. The improved photocatalytic activity can be attributed to the fact that the SC-WP nanoparticles provides a large number of exposed active sites on the surface of CdS for hydrogen evolution reaction, which can efficiently capture photogenerated electrons from CdS nanorods and promotes the transport and separation of light-induced charges. And the introduction of SC-WP nanoparticles with excellent optical properties can efficiently improve the visible light absorption range and the utilization rate of the absorbed light of the PD composite. In addition, the SC-WP nanoparticles show semi-crystalline state, which is also conducive to enhancing the photocatalytic activity.     

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.     

Amorphous sulfur-rich CoSx nanodots as highly efficient cocatalyst to promote photocatalytic hydrogen evolution over TiO2

In this work, amorphous cobalt sulfide with a sulfur-rich structure (sr-CoS_x) is developed as the cocatalyst for photocatalytic hydrogen evolution. Through a facile hydrothermal reaction, sr-CoS_x nanodots are in situ grown on TiO₂ to obtain a heterojunction photocatalyst (sr-CoS_x/TiO₂). The as-prepared photocatalyst exhibits remarkable improved hydrogen evolution performance compared with TiO₂. Under the irradiation of xenon lamp, the hydrogen evolution rate of sr-CoS_x/TiO₂ can reach 507 μmol h^?1 g^?1, which is about 121 times that of pristine TiO₂, indicating that sr-CoS_x is a highly efficient cocatalyst to promote hydrogen evolution on TiO₂. Moreover, sr-CoS_x/TiO₂ exhibits better performance than crystalline CoS₂ or amorphous CoS modified TiO₂, suggesting the important role of sulfur-rich structure and amorphous state in promoting the cocatalytic effect. Electrochemical and photoluminescence measurements show the most efficient carrier separation between sr-CoS_x and TiO₂, which also contributes to its high photocatalytic hydrogen evolution performance.     

The construction of 3D hierarchical CdS/NiAl-LDH photocatalyst for efficient hydrogen evolution

The development of excellent photocatalysts for hydrogen evolution is of great significance to solving the global energy crisis. In this work, a novel 3D hierarchical CdS/NiAl-LDH photocatalyst was fabricated by a facile electrostatic assembly strategy, which was composed of 1D CdS nanorods and 3D flower-like NiAl-LDH microspheres. Under the visible irradiation, the CNA-20 hierarchical photocatalyst presents the optimum hydrogen evolution rate achieved to 3.24 mmol g^?1 h^?1, which is improved 6.23-fold in comparison with the pure CdS. Through the analysis of energy band structures and first-principles calculation, the type-Ⅱ charge transfer mechanism was proposed. Driven by the built-in electric field, as well as the effect of intimate interface contact of CdS and NiAl-LDH, the photogenerated charge could be achieved rapidly separate and migrate, which effectively promotes the H₂ evolution. This well-designed synergistic 1D/3D interface interaction and provides an economic approach to rationally developing metal-free photocatalysts for hydrogen production.     

Facile preparation of Pt/CdS photocatalyst by a modified photoreduction method with efficient hydrogen production

A series of 0.75 wt% Pt/CdS photocatalysts were successfully synthesized via a modified photoreduction process, with the assistance of a protective agent (polyvinylpyrrolidone, PVP) and/or structural inducer (NaI, NaBr, and NaCl). The physicochemical properties of the obtained 0.75 wt% Pt/CdS photocatalysts were characterized in more detailed. Their photocatalytic efficiencies were evaluated by visible-light photocatalytic hydrogen production. The results show that the photocatalytic activities of 0.75 wt% Pt/CdS photocatalysts for H₂ production mainly depend on the type of structural inducer. Furthermore, a suitable ratio of PVP/NaI is necessary to optimize the photocatalytic performance of Pt/CdS composites. Notably, 0.75 wt% Pt/CdS (PVP/NaI = 4:1) gains the highest hydrogen production activity with a rate of 1155.8 μmol h^?1, which is 1.8 times higher than that of 0.75 wt% Pt/CdS obtained from the traditional photoreduction method (640.9 μmol h^?1) and 17.3 times higher than that of the bare CdS sample (66.9 μmol h^?1). The as-prepared 0.75 wt% Pt/CdS photocatalyst (PVP/NaI = 4:1) also exhibits a good stability. An optimum ratio of PVP/NaI not only causes a decrease in particle size of Pt nanoparticles but also leads to an increase in BET specific surface area of Pt/CdS and an enhanced electron transfer capability of Pt nanoparticles, which should be responsible for the enhanced photocatalytic performance.     

Adenine-functionalized conjugated polymer as an efficient photocatalyst for hydrogen evolution from water

Conjugated polymers have emerged as a promising class of organic photocatalysts for photocatalytic hydrogen evolution from water splitting due to their adjustable chemical structures and electronic properties. However, developing highly efficient organic polymer photocatalysts with high photocatalytic activity for hydrogen evolution remains a significant challenge. Herein, we present an efficient approach to enhance the photocatalytic performance of linear conjugated polymers by modifying the surface chemistry via introducing a hydrophilic adenine group into the side chain. The adenine unit with five nitrogen atoms could enhance the interaction between the surface of polymer photocatalyst and water molecules through the formation of hydrogen bonding, which improves the hydrophilicity and dispersity of the resulting polymer photocatalyst in the photocatalytic reaction solution. In addition, the strong electron-donating ability of adenine group with plentiful nitrogen atoms could promote the separation of light-induced electrons and holes. As a result, the adenine-functionalized conjugated polymer PF6A-DBTO2 shows a high photocatalytic activity with a hydrogen evolution rate (HER) of 25.21 mmol g^?1 h^?1 under UV-Vis light irradiation, which is much higher than that of its counterpart polymer PF6-DBTO2 without the adenine group (6.53 mmol g^?1 h^?1). More importantly, PF6A-DBTO2 without addition of a Pt co-catalyst also exhibits an impressive HER of 21.93 mmol g^?1 h^?1 under visible light (λ > 420 nm). This work highlights that it is an efficient strategy to improve the photocatalytic activity of conjugated polymer photocatalysts by the modification of surface chemistry.     

Synthesis and photocatalytic performance of MoS2/Polycrystalline black phosphorus heterojunction composite

As a promising catalyst for solar hydrogen production, black phosphorus (BP) has received widespread attention due to variable band gaps, high carrier mobility, and strong light absorption performance. Herein, we use MoS₂ as a cocatalyst to synthesize BP/MoS₂ catalyst with polycrystalline BP to improve photocatalytic performance under visible light irradiation. A small amount of MoS₂ can reduce the recombination of electron-hole pairs in the composite, increase carrier transport efficiency, and then improve photocatalytic performance. As expected, the 10/0.5 ratio of BP/MoS₂ catalyst exhibits the highest photocatalytic hydrogen evolution performance with a hydrogen evolution rate of 575.4 μmol h^?1 g^?1, which is 2.5 times of pure BP. Based on the results above, a simple method is provided to synthesize low-cost black phosphorus-based photocatalysts.     

Fabricating NixCo1−xO@C cocatalysts sensitized by CdS through electrostatic interaction for efficient photocatalytic H2 evolution

Exploiting efficient and stable noble metal-free hydrogen evolution catalysts for water splitting is of great importance. In this work, Ni_xCo_1-xO@C/CdS hybrid is successfully fabricated through an electrostatic interaction of oppositely charged nanoparticles on their surfaces. The resulting Ni_xCo_1-xO@C nanoboxes cocatalysts which were derived from NiCo-LDH@ZIF-67 with Ni–Co layered double hydroxides (LDH) decorated with ZIF-67 precursor exhibited improved hydrogen production rate compared with bare CdS semiconductor from 0.7 mmol g⁻¹ h⁻¹ to 56 mmol g⁻¹ h⁻¹. It is demonstrated that the electrostatic interaction between the two surface charged nanoparticles of Ni_xCo_1-xO@C and CdS play an important role in migrating and separating of photogenerated charge carriers. The synthesized Ni_xCo_1-xO@C as excellent candidates for cost-effective cocatalysts is aimed to substitute for noble metals in photocatalytic H₂ evolution.