Photocatalyst For Hydrogen Generation Research Articles

Integrating configuration, doping and heterojunction into the g-C3N4-based photocatalyst for water splitting

Construction of a highly efficient g-C3N4-based photocatalyst for hydrogen generation is promising but still challenging. In this work, the 1T-phase MoS2 nanosheets are prepared by using supercritical carbon dioxide, which are utilized to build 2D-2D g-C3N4/MoS2 heterojunction for solar H2 generation. In addition, MoS2 is also severed as the precursor of heteroatom to dope into 2D g-C3N4 nanosheets for forming monatomic Mo-doped g-C3N4-based photocatalyst. The obtained single atomic Mo-doped 2D/2D g-C3N4/MoS2 heterojunction exhibits a boosted H2 production of 2222.6 μmol g−1 h−1 with the apparent quantum yield of 9.08%, far exceeding the primitive one. Theoretical calculations and experimental results demonstrate that Mo-PCN/PMS composite possess a Mo-N3 configuration, and the synergy of three promoted strategies, including stripping, doping, and heterojunction plays vital roles in boosting the catalytic activity. This study implies that the integrated g-C3N4-based composite has great potential application in the field of photocatalytic hydrogen evolution.

Synthesis of Graphene Based Graphitic Carbon Nitride Hybrid Nanocomposite Photocatalysts for Hydrogen Generation: A Mini Review

The discovery of visible active photocatalysts for H2 evolution via water splitting is the most awaited and critical goal of many researchers in recent years. Novel polymeric graphitic carbon nitride (GCN/g-CN) has emerged as a versatile material which has attracted the scientific community and industrialist because of its distinctiveness and outstanding electronic properties. g-CN is a metal free semiconductor as well as non-toxic, biodegradable polymeric material with low band gap energy which makes it a promising candidate as a photocatalyst and its efficiency as a catalyst can be modified by forming a hybrid nanocomposite with other semiconducting materials. Reduced graphene oxide, another metal free 2D material is a very good choice for this purpose. This review is an outlook for the synthesis processes and various properties of both g-CN and graphene. Further, it gives the approaches attempted towards the modifications required and done towards the development of a metal-free nano-hybrid material which is cost-effective, eco-friendly, and highly active visible light catalyst for the water- splitting process.

Prediction of Strong Solvatochromism in a Molecular Photocatalyst.

Based on quantum chemical calculations, we predict strong solvatochromism in a light-driven molecular photocatalyst for hydrogen generation, that is we show that the electronic and optical properties of the photocatalyst strongly depend on the solvent it is dissolved in. Our calculations in particular indicate a solvent-dependent relocation of the highest occupied molecular orbital (HOMO). Ground-state density functional theory and linear response time-dependent density functional theory calculations were applied in order to investigate the influence of implicit solvents on the structural, electronic and optical properties of a molecular photocatalyst. Only at high dielectric constants of the solvent, is the HOMO located at the metal center of the photosensitizer, whereas at low dielectric constants the HOMO is centered at the metal atom of the catalytically active complex. We elucidate the electronic origins of this strong solvatochromic effect and sketch the consequences of these insights for the use of photocatalysts in different environments.

Plasmonic Heterojunction Photocatalysts for Hydrogen Generation: A Mini-Review

Plasmonic Heterojunction Photocatalysts for Hydrogen Generation: A Mini-Review

Mesoporous Dual-Semiconductor ZnS/CdS Nanocomposites as Efficient Visible Light Photocatalysts for Hydrogen Generation.

The development of functional catalysts for the photogeneration of hydrogen (H2) via water-splitting is crucial in the pursuit of sustainable energy solutions. To that end, metal-sulfide semiconductors, such as CdS and ZnS, can play a significant role in the process due to their interesting optoelectronic and catalytic properties. However, inefficient charge-carrier dissociation and poor photochemical stability remain significant limitations to photocatalytic efficiency. Herein, dual-semiconductor nanocomposites of ZnS/CdS nanocrystal assemblies (NCAs) are developed as efficient visible light photocatalysts for H2 generation. The resultant materials, synthesized via a polymer-templated self-polymerization method, comprise a unique combination of ~5-7 nm-sized metal-sulfide nanoparticles that are interlinked to form a 3D open-pore structure with large internal surface area (up to 285 m2 g-1) and uniform pores (circa 6-7 nm). By adjusting the ratio of constituent nanoparticles, the optimized ZnS/CdS catalyst with 50 wt.% ZnS content demonstrates a remarkable stability and visible light H2-evolution activity (~29 mmol g-1 h-1 mass activity) with an apparent quantum yield (AQY) of 60% at 420 nm. Photocatalytic evaluation experiments combined with electrochemical and spectroscopic studies suggest that the superior photocatalytic performance of these materials stems from the accessible 3D open-pore structure and the efficient defect-mediated charge transfer mechanism at the ZnS/CdS nanointerfaces. Overall, this work provides a new perspective for designing functional and stable photocatalytic materials for sustainable H2 production.

Effects of metal centers of complexes supported by diiminodiphosphines on catalytic activities for electrochemical and photochemical driven hydrogen production

Two complexes, [Co-tn-P2(NCMe)](ClO4)2 1 and [Ni-tn-P2](ClO4)2 2 (tn-P2: N, N’-bis[o-(diphenylphosphino)benzylidene]-1,3-diaminopropane) have been synthesized and characterized. Both serve as electrocatalysts and photocatalysts for hydrogen generation. With 1 or 2, the electrolysis of a neutral buffer can provide 362 and 708 moles of hydrogen per mole of catalyst per hour under an overpotential of 837.6 mV, respectively. With CdS nanorods as a photosensitizer, and ascorbic acid as a sacrificial electron donor, the photolysis of an aqueous solution (pH 4.5) with 1 or 2 can provide 1755 and 2495 moles H2 per mole of catalyst (mol of H2 (mol of cat)−1) during 30 h blue light irradiation. The average apparent quantum yield is 11.04% ([Co-tn-P2(NCMe)](ClO4)2) and 16.77% ([Ni-tn-P2](ClO4)2), respectively. The results show that [Ni-tn-P2](ClO4)2 exhibits a more efficient activity for hydrogen generation than [Co-tn-P2(NCMe)](ClO4)2.

TiO2 NPs-immobilized silica granules: New insight for nano catalyst fixation for hydrogen generation and sustained wastewater treatment.

In heterogeneous catalytic processes, immobilization of the functional material over a proper support is a vital solution for reusing and/or avoiding a secondary pollution problem. The study introduces a novel approach for immobilizing R25 NPs on the surface of silica granules using hydrothermal treatment followed by calcination process. Due to the privileged characteristics of the subcritical water, during the hydrothermal treatment process, the utilized R25 NPs were partially dissolved and precipitated on the surface of the silica granules. Calcination at high temperature (700°C) resulted in improving the attachment forces. The structure of the newly proposed composite was approved by 2D and 3D optical microscope images, XRD and EDX analyses. The functionalized silica granules were used in the form of a packed bed for continuous removal of methylene blue dye. The results indicated that the TiO2:sand ratio has a considerable effect on the shape of the dye removal breakthrough curve as the exhaustion point, corresponding to ~ 95% removal, was 12.3, 17.4 and 21.3 min for 1:20, 1:10 and 1:5 metal oxides ratio, respectively. Furthermore, the modified silica granules could be exploited as a photocatalyst for hydrogen generation from sewage wastewaters under direct sunlight with a good rate; 75×10-3 mmol/s. Interestingly, after the ease separation of the used granules, the performance was not affected. Based on the obtained results, the 170°C is the optimum hydrothermal treatment temperature. Overall, the study opens a new avenue for immobilization of functional semiconductors on the surface of sand granules.

An Ab Initio Study of Two Dimensional SnX2 and Janus SnXY (X = S, Se) Nanosheets as Potential Photocatalysts for Water Splitting

Discriminating appropriate two-dimensional (2D) photocatalysts for hydrogen generation is among the most prospective schemes to tackle with environmental contaminations. Unfortunately, the inferior capability to harvest solar light together with fast recombination of photoexcited carriers can severely reduce the catalytic ability with consequent limited commercial applications. In this work, a series of single-layer MXY (M = Ge, Sn; X, Y = S, Se, and Te) containing T- and H-phases about photocatalytic capabilities are systematically explored by first-principles calculations. First, the T- and H-MXY monolayers possess transformable band gaps of 0–2.37 and 0–1.49 eV, respectively. Astonishingly, the values of T-GeS2, T-SnS2, T-SnSe2, T-SnSSe, and H-SnS2 monolayers are higher than the threshold of redox potential difference (1.23 eV). Also, importantly, the carrier mobilities of anisotropic T-MXY monolayers can reach ∼1 × 104 cm2 V–1 s–1, which can rapidly transfer and accelerate the separation of the photoexcited carriers during photocatalytic reactions. Inspired by these significant benefits, the T-MXY monolayers have been built for photocatalytic water-splitting. Significantly, the driving force of photoexcited carriers in T-SnX2 and Janus T-SnSSe monolayers can greatly promote during the redox reactions. Furthermore, the hydrogen reduction and water oxidation reactions of T-SnX2 and T-SnXY monolayers can proceed spontaneously under irradiation. In addition, the few-layer and even monolayer T-SnS2 and T-SnSe2 have been experimentally synthesized in the literature. The potential photocatalysts of single-layer T-MXY have the 0.25–0.29 J m–2 cleavage energies, and ab initio molecular dynamics simulations further validate their stability. Our results provide support for 2D group-IV–VI chalcogenides for photocatalytic water splitting.

Novel green synthesis of Ag2S from Diospyros kaki and its application for efficient photocatalytic hydrogen evolution

The development of efficient photocatalysts to produce hydrogen from water is of great interest, both for reducing dependence on fossil fuels and for a clean environment. In this work, we designed and studied an Ag2S photocatalyst for hydrogen generation from water. Ag2S nanoparticles were synthesized from Diospyros kaki fruit by green synthesis method.In addition, three different systems were utilized as sacrificial electron donors which are Na2S/Na2SO3, methanol, and lactic acid solution for the photocatalytic hydrogen production under visible light. The Ag2S nanoparticles demonstrate enhanced hydrogen evolution activity in Na2S/Na2SO3 (2753.3 μmol g−1 h−1) as a sacrificial electron donor compared to the lactic acid (1076.1 μmol g−1 h−1) and methanol (354.12 μmol g−1 h−1) as sacrificial electron donors, respectively. We believe that Ag2S nanoparticles obtained by green synthesis will shed light on different studies in the future as an environmentally friendly photocatalyst.

Nanostructured silicon photocatalysts for solar-driven fuel production.

Solar-driven production of fuels such as hydrogen, hydrocarbons, and ammonia using semiconducting photocatalysts has the potential to be a sustainable alternative to current chemical processes. In recent years, silicon (Si) nanostructures have been recognized as a promising photocatalyst for hydrogen generation and organic oxidation reactions owing to its abundance, biocompatibility, and cost. While bulk Si has been studied extensively, on the nanoscale, plenty of opportunities exist to understand and engineer optimally performing Si photocatalysts. This perspective will highlight key results on the use of Si nanostructures for photocatalytic H2 production, CO2 reduction via light and heat-driven chemical looping, and current challenges in utilizing it for fuel-forming reactions. A brief guide on how these challenges can be addressed in the future and other unexplored questions that remain in the field are also discussed.

Enhanced photocatalytic hydrogen evolution over 0D/3D NiTiO3 nanoparticles/CdIn2S4 microspheres heterostructure photocatalyst

Constructing S-scheme heterojunction is regarded as an effective mode to motivate excellent photocatalytic performance for hydrogen generation. This paper prepares NiTiO3/CdIn2S4 S-scheme heterostructure photocatalyst by hydrothermal method successfully. In the experiments, 20 wt% NiTiO3/CdIn2S4 has the supreme photocatalytic activity with the H2 generation rate of 5168.6 μmol g−1 h−1 and the apparent quantum yield (AQY) of 5.14% at 420 nm, approximately 7.7 times of pure CdIn2S4. Through the phase characterization analyses, NiTiO3 and CdIn2S4 successfully compounded, with NiTiO3 nanoparticles wrapping around CdIn2S4 microspheres to form the irregular clumps. Further analyses of performance reveal the larger specific surface area, wider absorption region, faster charge transfer rate, outstanding photostability and recyclability for 20 wt% NiTiO3/CdIn2S4, all of which play the significant role in photocatalytic hydrogen evolution activity. Finally, a plausible S-scheme photocatalytic mechanism for NiTiO3/CdIn2S4 is proposed. This study provides a novel and effective S-scheme photocatalyst for hydrogen generation from water splitting.

Synthesis and photoelectrochemical catalytic properties of polyoxometalate supported on zeolitic imidazolate Framework, ZIF-9–PMo12

Development of photocatalysts for hydrogen generation is highly imperative in the current scenario for resolving the worldwide energy crisis. Continuous efforts are being made to find low-cost and durable photocatalysts with better light absorption capacity to mitigate energy issues. Herein, a new p-n heterojunction photocatalyst has been synthesized successfully using a polyoxometalate (POM), phosphomolybdic acid (PMo12), and zeolitic imidazolate framework (ZIF-9). Photoelectrochemical studies under visible-light irradiation revealed that ZIF-9–PMo12 exhibits a higher photocurrent density than pure ZIF-9. The support of ZIF-9 prevented the instability of PMo12 in aqueous solutions and improved the photoresponse ability of ZIF-9. The p-n junction formation impedes the recombination of electrons and holes, resulting in the improved photocatalytic property. Photoelectrochemical experiments confirmed the photocatalytic features, and thus this work paves the way for the development of an efficient, stable, and low-cost photocatalyst for green H2 generation.

Synthesis of Zn3V2O8/rGO Nanocomposite for Photocatalytic Hydrogen Production

In this study, zinc vanadate/reduced graphene oxide (Zn3V2O8/rGO) composite has been synthesized via a simple approach. Advanced characterization techniques (powder X-ray, scanning electron microscopy, energy dispersive X-ray spectroscopy and ultraviolet-visible (UV-vis) spectroscopy) have been used to authenticate the formation of Zn3V2O8/rGO composite. Subsequently, Zn3V2O8/rGO was applied as photo-catalyst for hydrogen generation using photo-catalysis. The Zn3V2O8/rGO photo-catalyst exhibited a good hydrogen generation amount of 104.6 µmolg−1. The Zn3V2O8/rGO composite also demonstrates excellent cyclic stability which indicated better reusability of the photo-catalyst (Zn3V2O8/rGO). This work proposes a new photo-catalyst for H2 production application. We believe that the presence of synergistic interactions was responsible for the improved photo-catalytic properties of Zn3V2O8/rGO composite. The Zn3V2O8/rGO composite is an environmentally friendly and cost-effective photo-catalyst and can be used for photo-catalytic applications.

Covalent-Coupled Zn0.4Cd0.6S with g-C3N4 as a Sheet-on-Sheet Z-Scheme Photocatalyst for Water Splitting

Development of heterojunction to improve charge separation efficiency is one of the main strategies to enhance the hydrogen production performance of photocatalysts. Herein, we fabricate a 2D/2D Z-scheme heterojunction-coupled Zn0.4Cd0.6S with g-C3N4 by in situ hydrothermal approach. The sheet-on-sheet architecture provides full contact of heterojunction to accelerate interfacial charge transfer and increase surface-active sites. Additionally, the Zn–N coordination bond acts as a strong interfacial interaction between Zn0.4Cd0.6S and g-C3N4, and photogenerated charges are spatially separated along the Z-scheme mechanism. In particular, under visible-light (λ ≥ 420 nm) irradiation, the optimal photocatalyst exhibits a high hydrogen production (H2 production rates: 7.69 mmol g–1 h–1) without any cocatalysts, 4 times higher than that of the g-C3N4 photocatalyst using Pt as a cocatalyst. The catalyst has a long-term stability of up to 50 h. Therefore, a direct Z-scheme heterojunction with intimate contact and a well-definite bridging chemical bond could be a prospective photocatalyst for hydrogen generation.

Gold supported on graphene oxide/silica photocatalyst for hydrogen generation from formic acid

Hydrogen gas has attracted a great deal of attention as a fuel due to its non-polluting combustion reaction. A wide variety of approaches have been employed to generate this green fuel with a remarkable concentration on photocatalytic pathways, in which a free source of energy is consumed for hydrogen evolution. Accordingly, we focused on construction of a photocatalyst of gold supported on graphene oxide–silicon dioxide (SiO2) for hydrogen generation through photocatalytic degradation of formic acid. It was demonstrated that the modification of SiO2 with graphene oxide and gold surprisingly extended photo-absorption of the semiconductor. The nanocomposite productively consumed photoelectrons for conversion of protons to hydrogen with turnover frequency of 539 h−1 at room temperature. This high activity of the nanocomposite was ascribed to the formation of simultaneous electron-rich and hole-rich centers in interfaces of graphene oxide–gold and graphene oxide–SiO2, respectively, which accelerated the process by both hydrogen generation in electron-doped sites and CO2 evolution in hole-doped platforms.

Co–TiO2 supported on reduced graphene oxide as a highly active and stable photocatalyst for hydrogen generation

We have developed a highly active and stable catalyst based on Co and TiO2 nanoparticles anchored on reduced graphene oxide (rGO) sheets for the photocatalytic hydrogen generation from water splitting. The catalyst was prepared using a novel methodology involving the modified Hummers approach followed by pyrolysis. The crystallinities, morphologies, optical properties, and chemical structures of the synthesized catalysts were investigated using different characterization techniques. The photocatalytic activity was investigated under UV–vis spectroscopy in solutions containing different Na2S + Na2SO3 concentrations and methanol as hole scavengers. The optimized composite that comprises Co: TiO2:rGO (1:6:10) shows a 2.5-fold improvement in the catalyst efficiency under UV–vis compared to bare TiO2, and it was recycled with the same activity for three cycles. This remarkable improvement in the photocatalytic activity of the developed nanocomposites compared to TiO2 can be attributed to the improved capacity of the nanocomposites to absorb visible light and efficiently separate charge carriers at the interface.

The synthesis of Cu-TCPP MOF/g-C3N4 heterojunctions as efficient photocatalysts for hydrogen generation

Semiconductor photocatalysis is a potential solution to meet energy needs with green and inexhaustible solar energy.

Au@CdS Nanocomposites as a Visible-Light Photocatalyst for Hydrogen Generation from Tap Water

The Au@CdS nanocomposites have been synthesized using a combination of wet chemical and hydrothermal approaches at lower reaction temperatures. The concentrations of CdS precursors and reaction temperature can be essential in influencing photocatalytic water splitting under blue-LED light excitation. The optimized Au@CdS nanocomposites (5 mM CdS precursors and 100 °C) exhibited the highest hydrogen evolution rate of 1.041 mmolh−1 g−1, which is 175.3 times higher than CdS nanoparticles for de-ionized water under blue-LED light excitation. This result is ascribed to separate photogenerated charge carriers and increased light absorption by the Au core. The Au@CdS nanocomposites (1.204 mmolh−1 g−1) revealed significant applications in photocatalytic tap water splitting under blue-LED light excitation, which is 512.3 times higher than CdS nanoparticles. In addition, reusability experiments demonstrate that Au@CdS nanocomposites exhibit excellent stability for the long-term photocatalytic tap water splitting process. Furthermore, this research shows that Au nanoparticles decorated with CdS shells effectively achieve high-efficiency conversion from light to hydrogen energy.

Efficient Visible-Light Driven Photocatalytic Hydrogen Production by Z-Scheme ZnWO4/Mn0.5Cd0.5S Nanocomposite without Precious Metal Cocatalyst

How to restrain the recombination of photogenerated electrons and holes is still very important for photocatalytic hydrogen production. Herein, Z-scheme ZnWO4/Mn0.5Cd0.5S (ZWMCS) nanocomposites are prepared and are applied as visible-light driven precious metal cocatalyst free photocatalyst for hydrogen generation. The ZnWO4/Mn0.5Cd0.5S nanocomposites with 30 wt% ZnWO4 (ZWMCS-2) can reach a photocatalytic hydrogen evolution rate of 3.36 mmol g−1 h−1, which is much higher than that of single ZnWO4 (trace) and Mn0.5Cd0.5S (1.96 mmol g−1 h−1). Cycling test reveals that the ZMWCS-2 nanocomposite can maintain stable photocatalytic hydrogen evolution for seven cycles (21 h). The type of heterojunction in the ZWMCS-2 nanocomposite can be identified as Z-scheme heterojunction. The Z-scheme heterojunction can effectively separate the electrons and holes, so that the hydrogen generation activity and stability of the ZWMCS-2 nanocomposite can be enhanced. This work provides a highly efficient and stable Z-scheme heterojunction photocatalyst for hydrogen generation.

Metal Sulfide Photocatalysts for Hydrogen Generation: A Review of Recent Advances

Metal-sulfide nanostructures have piqued the interest of researchers for decades due to their intriguing optoelectronic properties. Indeed, significant advances and improvements have been made in various fundamental aspects for cutting-edge applications, such as water splitting and hydrogen production. Furthermore, rising demand for low-dimensional materials due to lower material consumption and improved performance due to quantum size effects has spurred research on semiconducting metal sulfides. Consequently, size-controllable nanostructures with diverse morphologies have been fabricated and studied for potential applications. However, the photocatalytic hydrogen evolution rate is still limited mainly by fast recombination rate, poor solar energy utilization and lack of surface-active sites for H2 reduction. This review will highlight particularly recent findings in metal-sulfide-based photocatalysts for hydrogen evolution reactions, considering the swift development and excellent research in this field. Following a brief overview of fundamental properties, we will explore state-of-the-art strategies for enhancing H2 generation efficiencies over the pristine, heterostructured and co-catalayzed metal-sulfide photocatalysts.