Photocatalytic Hydrogen Generation Rate Research Articles

Black ZrO2 synthesized by molten lithium reduction strategy for photocatalytic hydrogen generation

AbstractTo promote the performance of metal oxides, introducing oxygen vacancies is an effective strategy. Oxygen vacancies can tailor the atomic arrangement and band structure, thus optimizing the physical and chemical properties of metal oxides. Herein, we prepared oxygen‐deficient black ZrO2 nanoparticles via molten lithium (Li) reduction. Massive oxygen vacancies were introduced into ZrO2 nanoparticles as well as defective disorder domains formed in ZrO2 lattice during the molten lithium treatment process. Benefitting from the defective structure, black ZrO2 with enhanced light absorption demonstrated increased photocatalytic hydrogen generation rate, which was ~5 times higher than that of pristine ZrO2. Moreover, molten lithium reduction provides a powerful way to not only implant oxygen vacancies to metal oxides but also extend their applications.

Highly exposed (001) facets Ni(OH)2 induced formation of nickle phosphide over cadmium sulfide nanorods for efficient photocatalytic hydrogen evolution

An efficient Ni2P–CdS photocatalyst for photocatalytic hydrogen evolution was synthesized by phosphorizing β-Ni(OH)2 nanosheet with exposed (001) facets on CdS nanorods. The obtained Ni2P–CdS composite displays an outstanding and stable photocatalytic hydrogen generation rate of 68.47 mmol g−1 h−1 in 10 vol% lactic acid under visible light irradiation, more than 17 times higher than that for pure CdS nanorods. The transient photocurrent response, EIS measurement, Mott-Schottky plots, acidic LSV measurement, and PL spectra have proved that Ni2P loading can significantly improve the separation of photo-excited electron-hole pairs in CdS nanorods and enhance the hydrogen evolution capability for CdS. These improvements are achieved by features of Ni2P such as the high capability of trapping photo-generated electrons from CdS, lifting the total Fermi level and lowering the hydrogen evolution overpotential of the composite. The results show that β-Ni(OH)2 precursor with a high exposure degree of (001) facet is contributed to the epitaxial formation of (001)-facet-exposed Ni2P co-catalyst on CdS nanorods, resulting in that the Fermi level and the hydrogen evolution overpotential of the composite can be further lifted and lowered. This study has provided a novel precursor-derived route to fabricate high-performance co-catalysts with highly exposed active facets on CdS nanorods for effective photocatalytic hydrogen evolution.

Cd0.5Zn0.5S/Ni2P noble-metal-free photocatalyst for high-efficient photocatalytic hydrogen production: Ni2P boosting separation of photocarriers

Establishing efficient co-catalytic loaded semiconductors for efficient charge separation is a hopeful way for enhance photocatalytic water splitting hydrogen evolution. Herein, we successfully constructed the Cd0.5Zn0.5S/Ni2P (CZS/Ni2P) nanocomposites via two-step hydrothermal method. The CZS/Ni2P composites show much improved activity than the origin CZS for photocatalytic H2 generation. When the content of Ni2P loaded on the Cd0.5Zn0.5S (CZS) is 0.3 mol%, the photocatalyst achieves the highest photocatalytic hydrogen generation rate of 41.26 mmol g−1 h−1 under visible light. The Ni–S bonds on the close contact interface between CZS and Ni2P can be act as electron-bridge to provide a channel for electron transfer. During the photocatalysis processing, Ni2P can be used as electron traps to attract electrons from CZS, resulting in the improvement of the photocatalytic performance.

Defect-rich and electron-rich mesoporous Ti-MOFs based NH2-MIL-125(Ti)@ZnIn2S4/CdS hierarchical tandem heterojunctions with improved charge separation and enhanced solar-driven photocatalytic performance

Defective-rich and electron-rich mesoporous NH2-MIL-125(Ti)@ZnIn2S4/CdS hierarchical tandem heterojunctions were fabricated through two-step solvothermal and one-step hydrothermal strategies. The interface with electron enrichment can cause active interface reaction, fast transfer and separation of charge carriers and restrain the photocorrosion of CdS. ZnIn2S4, as a bridge to connect Ti-MOFs and CdS, favors the separation of charge carriers and forms tandem heterojunctions. The as-prepared photocatalyst has a relative large surface area of ∼877.0 m2 g−1 and a narrow band gap of ∼1.84 eV, which could absorb visible light efficiently. Furthermore, it exhibits a high photocatalytic hydrogen generation rate which was increased to 2.367 mmol g−1 h−1 and the high photocatalytic degradation efficiency for 2,6-dichlorophen and 2,4,5-trichlorophenol which were 98.6% and 97.5%, respectively. Additionally, recycling text for several cycles indicates the high stability. This novel Ti-MOFs based core@shell hierarchical tandem heterojunctions may offer a new insight for fabricating high-performance heterojunctions for multi-channel charges transfer.

In-situ synthesis of PdAg/g-C3N4 composite photocatalyst for highly efficient photocatalytic H2 generation under visible light irradiation

Novel PdAg bimetallic alloy nanoparticle modified graphitic carbon nitride (g-C3N4) nanosheet was designed and prepared by an in situ chemical reduction procedure. By optimizing the loading content of the PdAg alloy NPs, the PdAg/g-C3N4 composite photocatalyst showed a champion photocatalytic hydrogen generation rate of 3.43 mmol h−1 g−1, and the apparent quantum yield (AQY) was determined to be 8.43% at 420 nm. Moreover, the photoluminescence and photoelectrochemical experimental results suggest that a higher separation efficiency of photo-induced charge carriers (e-and h+) was obtained after loading PdAg alloy NPs on g-C3N4. The experimental outcomes indicate that there is a synergistic effect formed between PdAg and g-C3N4, which could significantly promote the charge transfer photo-induced charge carriers in the hybrid sample. A reasonable catalytic mechanism for the enhanced photocatalytic performance of the composite photocatalyst was proposed and verified by TRPL measurement, which could be taken as a guidance for the development of novel high performance catalytic system.

Ultrasmall MoOx Clusters as a Novel Cocatalyst for Photocatalytic Hydrogen Evolution.

To enhance the performance of semiconductor photocatalysts, cocatalysts are used to accelerate surface reactions. Herein, ultrasmall molybdenum-oxygen (MoOx ) clusters are developed as a novel non-noble cocatalyst, which significantly promotes the photocatalytic hydrogen generation rate of CdS nanowires (NWs). As indicated by extended X-ray absorption fine structure analysis, direct bonds are formed between CdS NWs and MoOx clusters, which guarantee the migration of photo-generated charge carriers. Moreover, the MoOx clusters induce deep electron trap states owing to the unique atomic arrangement and configuration with the generation of long-lived electrons to enhance the activity. These findings may guide the design of efficient cocatalytic materials for solar water splitting and open a new avenue toward practical applications of ultrasmall clusters.

Cooperative effect between BaTiO3 and CaFe2O4 in a cocatalyst-free heterojunction composite for improved photochemical H2 generation

A series of novel BaTiO3/CaFe2O4 heterojunction composites with different weight ratios of CaFe2O4 vs BaTiO3 was successfully fabricated by sonication-calcination method using the pre-prepared BaTiO3 and CaFe2O4 powders synthesized in hydrothermal and sol-gel methods, respectively. The composites were well characterized using XRD, UV–vis DRS, SEM, TEM, EDS and XPS to substantiate that BaTiO3 and CaFe2O4 coexist in the heterojunction composite. The highest photocatalytic hydrogen generation rate was obtained for BaTiO3/CaFe2O4 (40 wt%) compared to either of its individual counterparts and this improvement indicated the existence of a cooperative effect between BaTiO3 and CaFe2O4 in the heterojunction. Based on UV-vis-DRS, photoluminescence and time-resolved fluorescence lifetime measurements, the cooperative effect between BaTiO3 and CaFe2O4 originated from the improved photoresponse in the visible light region and efficient separation of the photogenerated electron–hole pairs augmenting their availability for the photocatalytic reaction. A plausible photocatalytic mechanism was also deduced using electrochemical impedance spectroscopy measurements, describing the migration direction of the separated charge carriers. Moreover, the best composite BaTiO3/CaFe2O4 (40 wt%) exhibited fairly stable photoactivity for H2 production using the sacrificial agent (Na2S and Na2SO3) without the assistance of any noble metals as cocatalysts.

Enhanced Photocatalytic Hydrogen Evolution by Integrating Dual Co-Catalysts on Heterophase CdS Nano-Junctions

Development of novel low price porous nanostructures with robust photocatalytic hydrogen generation rate and high durability is critical to help to meet the future energy demand. A prominent number of sunlight active semiconductor photocatalyst nanostructures have been formulated for the aforementioned photocatalytic reactions. However, their practical application has been limited by low efficiency and unstability induced by the rapid recombination of charge carriers. To effectively reduce the recombination rate, the addition of electron-transporting cocatalysts is a promising strategy. However, the rate of photogenerated holes is generally slower than that of photogenerated electrons, extending the recombination. To overcome this difficulty in this study for the first time, coloading of both photogenerated electrons and hole-transporting cocatalysts (C@CoS2 and TFA) on light-harvesting semiconductor heterophase homojunction CdS (OD-2D CdS) is established as a productive way to ameliorate the photocatalyt...

Nickel Boride Cocatalyst Boosting Efficient Photocatalytic Hydrogen Evolution Reaction

Noble metals have been extensively used as catalyst promoters to driven highly efficient photocatalytic hydrogen evolution reaction (HER). However, noble-metal-based promoters are limited by their expensive costs and scarcities. Recently, massive efforts have been focused on metal phosphides, metal sulfides, and metal carbides as cocatalysts to achieve high HER performance. Currently, metal borides were reported as promoters for hydrogen evolution. Here, we demonstrate amorphous nickel boride (NiB) with a suitable band gap prepared by the chemical reduction of nickel nitrate hexahydrate using sodium borohydride as a cocatalyst over graphite carbon nitride (C3N4), thus achieving higher hydrogen evolution performance than C3N4. With the B(δ−)–Ni(δ+)–N(δ−) bonds between NiB and C3N4, the as-prepared C3N4/NiB7.5 shows a dramatically enhanced photocatalytic hydrogen generation rate (464.4 μmol h–1 g–1), and reaches a quantum efficiency of 10.92% with 365 nm light irradiation.

Enhanced visible light activated hydrogen evolution activity over cadmium sulfide nanorods by the synergetic effect of a thin carbon layer and noble metal-free nickel phosphide cocatalyst

Photocatalytic water splitting is considered to be a promising strategy for addressing the global energy crisis through the expanded use of solar energy. Herein, cadmium sulfide (CdS) nanorods modified with a thin conductive carbon layer and a nickel phosphide co-catalyst, referred to as cadmium sulfide coated with a carbon layer and nickel phosphide (CdS@C/Ni2P, where @ indicates a core–shell structure), were synthesized and applied as a novel composite photocatalyst for water splitting. The optimized CdS@C/Ni2P composite showed a high photocatalytic hydrogen generation rate of 32030 μmol h−1 g−1, which was approximately 19 times as high as that of pure CdS. We believed that the thin carbon layer acted as an electron acceptor to promote charge transfer and protect the CdS nanorods from photocorrosion. In addition, the surface loading of the nickel phosphide (Ni2P) cocatalyst was able to further draw photogenerated electrons from the cadmium sulfide coated with a carbon layer (CdS@C) heterojunction and provide active sites for hydrogen evolution. Thus, greatly enhanced hydrogen generation was achieved through a combination of carbon coating and surface cocatalyst loading. This development provides a new way to design composite photocatalysts with multiple junctions for efficient water splitting performance.

Heterogeneous p-n Junction CdS/Cu2O Nanorod Arrays: Synthesis and Superior Visible-Light-Driven Photoelectrochemical Performance for Hydrogen Evolution.

Heterogeneous p-n junction CdS/Cu2O nanorod arrays have been fabricated by using a facile successive ionic-layer adsorption and reaction process to grow Cu2O nanoparticles on the surface of ordered CdS nanorod arrays. The heterogeneous p-n junction nanorod arrays exhibit superior photoelectrochemical performance for hydrogen (H2) generation and high stability under visible-light irradiation. The highest photocurrent density achieved by heterogeneous nanorod array photoelectrode is 4.2 mA cm-2 in a sacrificial Na2S and Na2SO3 mixture electrolyte solution at 0 V versus Ag/AgCl, which is 4 times higher than that of a pure CdS nanorod array photoelectrode. In addition, the heterogeneous nanorod array photoelectrode achieves an incident photon conversion efficiency value of 40.5% at 470 nm. The photocatalytic hydrogen generation rate of the heterogeneous nanorod array photoelectrode reaches up to 161.2 μmol h-1, around 3-fold increase compared to that of a bare CdS photoelectrode. Furthermore, the heterogeneous p-n junction CdS/Cu2O nanorod arrays show an excellent stability under long light illumination of 7200 s. The improved photoelectrochemical performance, photocatalytic activity, and excellent stability of the heterogeneous nanorod array photoelectrode resulted from the efficient separation of photoinduced electron-hole pairs, which is achieved by the synergistic effects of CdS, Cu2O, p-n junction, and an inner electric field in the photoelectrode. The present work provides a new strategy to fabricate a heterogeneous photoelectrode. This facile strategy is expected to be utilized to fabricate electrodes of other materials for highly efficient solar-driven water splitting application.

Engaging the flux-grown La1−xSrxFe1−yTiyO3 crystals in visible-light-driven photocatalytic hydrogen generation

Perovskite LaFeO3 is regarded as one of the promising photocatalysts for solar splitting of water to hydrogen and oxygen due to its suitable band edge positions, visible light absorbance, and high chemical stability. To further improve its photocatalytic performance of LaFeO3, the effects of solute concentration in the KCl-flux growth and partial A– and B–site substitution are investigated in this work. Controlling the solute concentration in the range of 1–20 mol% is crucial to grow phase-pure LaFeO3 crystals with idiomorphic shape. With increasing the solute concentration, the flux-based growth route gradually changes to a solid state-based growth route because of a decrease in solubility and an increase in the crystallization core number. The La1−xSrxFe1−yTiyO3 (x,y = 0,0; 0,0.15; 0.15,0; 0.1125,0.0375; 0.0375,0.1125; and 0.075,0.075) crystals were also synthesized by a KCl-flux method to explore the effect of partial Sr2+-to-La3+ and/or Ti4+-to-Fe2−4+ substitution on photocatalytic performance of LaFeO3. The Sr2+–Ti4+ co-substitution is found to enhance the photocatalytic performance of LaFeO3 as compared with the corresponding individual substitution (Sr2+ or Ti4+). The highest photocatalytic hydrogen generation rate (83.2 μmol h−1) was observed for Pt-photodeposited La0.925Sr0.075Fe0.925Ti0.075O3 crystals in 5-h reaction due to the improvement of both bulk properties and photoactivity and the reduction in both grain boundaries and lattice defects stemmed from the Sr2+–Ti4+ co-substitution and KCl flux growth.

Photocatalytic hydrogen evolution of palladium nanoparticles decorated black TiO2 calcined in argon atmosphere

Black TiO2 nanoparticles (BTN) was prepared by sol-gel derived precursor calcined in an argon atmosphere. The synthesized BTN with trivalent titanium ion, structural defect, and oxygen vacancy shows a remarkably high absorbance in the visible light spectrum. BTN thus behaves a higher visible-active nanoreactor than white TiO2 nanoparticles (WTN) in the aqueous solution for organic pollutant degradation. Moreover, palladium decoration on the BTN surface (Pd-BTN) demonstrates a fascinating clean energy application. The obtained Pd-BTN fulfills a satisfied green material demand in the photocatalytic hydrogen production application. Pd-BTN calcined at 400°C (Pd-BTN-400) shows the high photocatalytic hydrogen generation rate of 5200μmol/gh under UV-A irradiation and 9300μmol/gh under UV-B irradiation, respectively. The well-developed material, Pd-BTN-400, could be one of the best solutions in the concern of clean energy and water-purification with regard to the continuous environmental issue.

Preparation, characterization and photocatalytic activity of novel CeO2 loaded porous alkali-activated steel slag-based binding material

In the present study, CeO2 loaded porous alkali-activated steel slag-based photocatalyst (CeO2-PASSP) as a new catalyst for photocatalytic water-splitting of hydrogen production was prepared via impregnation method. The BET result showed that adding pore-forming agent changed the pore structure of the alkali-activated steel slag-based binding material and the mesoporous volume of photocatalyst carrier increased by 70%. The XRD, TEM and HRTEM results indicated that calcium silicate hydrate was mainly mineral phase in the alkali-activated steel slag-based binding material. CeO2 nanoparticles with particle size about 10 nm were highly dispersed on the surface of photocatalyst carrier. The photocatalyst loaded 8 wt% CeO2 showed the weakest photoluminescence intensity. 8CeO2-PASSP sample exhibited the highest photocatalytic hydrogen production activity (68.64 mmol/g) and hydrogen generation rate (13.73 mmol/(g⋅h)) in the simulated solar light irradiation for 5 h, and was quite stable after exposure to photocatalytic hydrogen production for a long time. The excellent activity of hydrogen production for 8CeO2-PASSP specimen was ascribed to the co-action of the high SBET, large mesoporous volume and the active components of the CeO2 and FeO existed in photocatalyst carrier.

Carrier Step-by-Step Transport Initiated by Precise Defect Distribution Engineering for Efficient Photocatalytic Hydrogen Generation.

Semiconductor photocatalysts have been widely used for solar-to-hydrogen conversion; however, efficient photocatalytic hydrogen generation still remains a challenge. To improve the photocatalytic activity, the critical step is the transport of photogenerated carriers from bulk to surface. Here, we report the carrier step-by-step transport (CST) for semiconductor photocatalysts through precise defect engineering. In CST, carriers can fast transport from bulk to shallow traps in the defective subsurface first, and then transfer to the surface active acceptors. The key challenge of initiating CST lies in fine controlling defect distribution in semiconductor photocatalysts to introduce the special band matching between the crystalline bulk and defect-controllable surface, moderate bridgelike shallow traps induced by subsurface defects, and abundant surface active sites induced by surface defects. In our proof-of-concept demonstration, the CST was introduced into typical semiconductor TiO2 assisted by the fluorine-assisted kinetic hydrolysis method, and the designed TiO2 can exhibit the state-of-the-art photocatalytic hydrogen generation rate among anatase TiO2 up to 13.21 mmol h-1 g-1, which is 120 times enhanced compared with crystalline anatase TiO2 under sunlight. The CST initiated by precise defect distribution engineering provides a new sight on greatly improving photocatalytic hydrogen generation performance of semiconductor catalysts.

Synthesis of nano-fibrillated cellulose/magnetite/titanium dioxide (NFC@Fe3O4@TNP) nanocomposites and their application in the photocatalytic hydrogen generation

Nano-fibrillated cellulose (NFC), an abundant renewable bio-macromolecule, has received much attention in the research community. The study detailed herein is related to the preparation of photocatalytic nanocomposites consisting of nano-fibrillated cellulose/magnetite/titanium dioxide nanoparticles (NFC@Fe3O4@TNP). The aim of this study is to improve the photocatalytic efficiency of NFC-TNP composites and to improve their recyclability during the photocatalytic hydrogen generation. The NFC@Fe3O4@TNP nanocomposites were characterized by TEM, EDX, SAED, XRD, XPS, FTIR, Raman spectra and VSM techniques. The results showed that Fe3O4 NP and TNP were well-distributed on the surface of NFC. The photocatalytic efficiency study showed that NFC@Fe3O4@TNP nanocomposites represented a higher photocatalytic hydrogen generation rate in comparison with that of NFC-TNP sample. In addition, the NFC@Fe3O4@TNP nanocomposites can be readily recovered from the system using a magnet due to their stable superparamagnetic properties, and they had only a marginal loss of TNP and photocatalytic efficiency after fifteen cycles.

Fabricating efficient CdSe–CdS photocatalyst systems by spatially resetting water splitting sites

Modulating reaction sites and charge transfer can speed up the photocatalytic hydrogen generation rate from 1.0 to 1270 mmol g−1 h−1.

The impact of nitrogen doping and reduced-niobium self-doping on the photocatalytic activity of ultra-thin Nb3O8- nanosheets.

Nitrogen doping via high-temperature ammonization is a frequently used strategy to extend the light harvesting capacity of wide-bandgap catalysts in the visible region. Under such a reductive atmosphere, the reduction of transition metals is supposed to occur, however, this has not been thoroughly studied yet. Here, by combining chemically-controlled doping and subsequent liquid exfoliation, ultra-thin [Nb3O8]- nanosheets with separate N doping, reduced-Nb doping and N/reduced-Nb codoping were fabricated for comparative studies on the doping effect for photocatalytic hydrogen evolution. Layered KNb3O8 was used as the starting material and the above-mentioned three doping conditions were achieved by high-temperature treatment with urea, hydrogen and ammonia, respectively. The morphology, crystal and electronic structures, and the catalytic activity of the products were characterized thoroughly by means of TEM, AFM, XRD, XPS, EPR, absorption spectroscopy and photocatalytic hydrogen evolution. Significantly, the black N/reduced-Nb co-doped monolayer [Nb3O8]- nanosheets exhibit the mostly enhanced photocatalytic hydrogen generation rate, indicating a synergistic doping effect of the multiple chemical-design strategy. The modified electronic structure of [Nb3O8]- nanosheets and the role of exotic dopants in bandgap narrowing are put forward for the rational design of better photocatalysts with reduced-metal self-doping.

Structure-controlled CdS(0D, 1D, 2D) embedded onto 2D ZnS porous nanosheets for highly efficient photocatalytic hydrogen generation

Modulating the CdS morphology with a 1D structure with high conduction band energy can speed up the electron transfer to Pt sites and increase the photocatalytic hydrogen generation rate from 7.7 to 26 mmol g−1 h−1.

“One-Pot” Synthesis and Photocatalytic Hydrogen Generation with Nanocrystalline Ag(0)/CaTiO3 and in Situ Mechanistic Studies

We describe a previously not reported “one-pot” synthesis of nanocrystalline Ag(0)/CaTiO3 in aqueous suspension and the following in situ photocatalytic testing in the same suspension to generate hydrogen. The Ag(0)/CaTiO3 showed an enhancement of photocatalytic hydrogen generation rate vs CaTiO3 precursor. The obtained Ag(0)/CaTiO3 photocatalyst was ex situ characterized by XPS, XRD, UV–vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy, and concluded to have metallic silver nanoparticles on the surface of calcium titanate nanocrystals. The three photocatalytic mechanisms in Ag(0)/CaTiO3 were considered: (a) bandgap narrowing in CaTiO3, (b) enhanced electron–hole separation in CaTiO3, and (c) excitation of surface plasmon resonance (SPR) in metallic Ag nanoparticles. In mechanistic studies, photocatalytic suspensions with CaTiO3 precursor, with silver precursor, and with both CaTiO3 and Ag precursors to form Ag(0)/CaTiO3 were illuminated, flash-frozen to 77 K, and charact...