Solar-driven Photocatalytic Water Splitting Research Articles

Z-scheme Bi2O3/Bi/ZnIn2S4 photocatalyst for enhancing the removal performance of Cr(VI), 2,4-dinitrophenol and tetracycline

Construction of heterojunctions is conventionally regarded as the prevailing technique to enhance solar-driven photocatalytic water splitting and photodegradation of pollutants. Herein, we report a novel design of a ternary Bi2O3/Bi/ZnIn2S4 system, which was facilely synthesized to satisfy these stringent criteria for sunlight photocatalytic removal of organic and ionic pollutants and hydrogen evolution. Bi2O3/Bi/ZnIn2S4 could degrade 2,4-dinitrophenol (94.6%), tetracycline (96.5%), and Cr6+ (96.3%) effectively under visible light and give a hydrogen production rate of 482.5 μmol·g−1·h−1 under visible light. Based on first-principles calculations and electrochemical results, our system could be identified as a Z-scheme. Photocorrosion of the sulfide is prohibited while the catalytic capabilities are simultaneously benefited due to lowered bandgap in light harvesting, internal electric fields in charge separations, and surface plasmonic resonance enhanced electron boost.

High-efficiency of novel hierarchical 3D macroporous g-C3N4 material on solar-driven photocatalytic water-splitting for hydrogen evolution

The use of multi-pore nanostructured g-C3N4 photocatalysts is an efficient approach to separate photogenerated charge carriers and increase visible light photocatalytic performance. Recent progress has yielded nanostructured material through hard templating, which limits potential applications. Integrating the 2D building block into multidimensional porous structures remains a significant challenge in scalable production. Herein, a novel technique based on P407 bubble clusters templating and fixation by freezing is described for the first time to fabricate a 3D opened-up macroporous g-C3N4 nanostructures for photocatalytic H2 evolution. Three-dimensional hierarchical nanostructures provide more contact active sites and synergistically promote the creation of heterogeneous catalytic interfaces. This feature is very useful for understanding the transfer path of photoinduced charges as well as the origins of the high charge separation efficiency in photocatalytic reactions, thus yielding a remarkable visible light-induced H2 evolution rate of 4213.6 μmol h−1 g−1, which is nearly 5.6 times (716 μmol h−1 g−1) higher than that of lamellar bulk g-C3N4. This newly developed approach offers a promising alternative to synthesize broad-spectral response 3D hierarchal g-C3N4 nanostructures and can be extended to assemble other functional nanomaterials as building blocks into macroscopic configurations coupled with electronic modulation strategy simultaneously.

Non-metal doping induced dual p-n charge properties in a single ZnIn2S4 crystal structure provoking charge transfer behaviors and boosting photocatalytic hydrogen generation

Construction of heterojunction is conventionally regarded as the prevailing technique to render effective solar-driven photocatalytic water splitting. Nonetheless, realization of p-n homojunction emerges to be an appealing scheme attributed to the non-defective layer coupling and minor charge transfer impedance. Herein, nitrogen-doped ZnIn2S4 (N-ZIS) with dual p-n charge properties was facilely synthesized via one-step in-situ solvothermal method. Systematic investigations unveil that the substituting phenomenon of hosting S by extrinsic N atom with dissimilar electronegativity and valence electron, which eventually ameliorates charge transfer rate and inhibits electron-hole pairs recombination. First-principle density functional theory calculations affirm the p-nature induced by N-doping imparting favorable charge redistribution in the ZIS framework and diminishing hydrogen (H2) evolution reaction kinetic barrier at the surface-active sites. Therein, optimal N-ZIS generated 1575.71 μmol∙g−1 of H2 under 6-hour visible-light irradiation (with an apparent quantum yield of 6.59 % at 420 nm monochromatic light irradiation), which is 6.35-fold than the pristine counterpart.

Enhanced solar light-driven hydrogen evolution of activated carbon sphere supported TiO2 hybrid nanocomposites

Solar-driven photocatalytic water splitting has a great promising impact and versatile green approach to producing hydrogen gas from solar energy for future energy storage devices. Furthermore, noble metal free catalysts have significant benefits in photon induced charge carrier transfer and faradic reaction for photocatalytic water splitting. Herein, we successfully synthesized the garlic peel-derived activated carbon sphere (ACS) and nanocomposite with TiO2 nanoparticles (NPs) using a facile hydrothermal technique for photocatalytic water splitting. The surface morphology, optical property and photocatalytic water splitting activity of prepared hybrid nanocomposite are thoroughly investigated with respect to the different ratios of ACS. In photocatalyst water splitting analysis, the optimal hybrid catalyst of ACS (6 % wt) with TiO2 NPs shows enhanced photocatalytic performance with the hydrogen production rate of 203 μmol g−1 h−1 under solar irradiation. The excellent solar driven water splitting performance of optimal hybrid catalyst has been owing to the enhanced photon harvesting ability and formation of the favorable pathway to effective charge separation and migration on TiO2/ACS surface. Thus, the proposed biomass supported nanocomposite scheme as a hybrid photocatalyst represents to develop the effective bio-mass assisted photocatalyst for solar water splitting process.

Photocatalytic water splitting for solving energy crisis: Myth, Fact or Busted?

• Practicality of photocatalytic water splitting is assessed from various aspects. • Employments of unrealistic labscale investigation are pointed out. • Intrinsic limitations of photocatalytic water splitting are summarized. • Energy and economy analysis of photocatalytic water splitting are performed. • H 2 energy generation from photocatalytic water splitting is not industrially viable. Reaping hydrogen energy by utilising eternal sunlight offers a good fit to the theme of popularly-hype sustainable and carbon-free energy future. Contrary to that belief, this review unveils the impracticality of photocatalytic water splitting (solar energy for H 2 energy) to fuel global advancement. Despite some success with idealized laboratory-scale studies, the past research works also mutually evinced an extreme low solar-to-hydrogen efficiency (STH < 1.0%). Hitherto, multifarious endeavours, such as advanced reactor design, facilities to eliminate diffusional restrictions, advanced photocatalyst design and an inclusion of sacrificial reagents, are incapable to raise STH efficiency to the practical threshold of STH > 10%. Regardless of the epitome and modifications of photocatalysts, the intrinsic limitation of charges recombination remains a sturdy obstacle, leading to an appreciable energy losses and low STH. For consequential solar-driven H 2 production, the bandgap energy of photocatalyst employed must stay below 2.36 eV. Meanwhile, most photocatalysts are capped by the theoretical maximum STH of 18%, even with the assumption of 100% quantum yield of corresponding spectrum. Nonetheless, the theoretical maximum STH is unattainable at this juncture due to the inevitable solar energy dissipation associated to the scattering effects of reactor and water. From economy standpoint, H 2 production via photocatalytic water splitting is pricey at 10.36 $/kg with exorbitant upfront costs, which is far beyond the practicable price range of 2 – 4 $/kg. In conclusion, we assert that the H 2 production from solar-driven photocatalytic water splitting is an industrially impractical pathway for solar energy harnessing, despite technically-feasible.

Considerations for a More Accurate Evaluation Method for Photocatalytic Water Splitting.

Over the past decades, various photocatalysts have been developed and great progress has been achieved in the field of solar-driven photocatalytic water splitting. However, the lack of an accurate and comprehensive evaluation method greatly hinders the meaningful comparison between different systems and becomes a serious impediment for the development of photocatalysts. Although many researchers are aware of this, there has been little work in this area. In this Viewpoint, we first analyze the insufficiencies of the existing evaluation methods and then make preliminary suggestions, aiming to stimulate discussion in the research community and hopefully lead to a widely accepted and authoritative evaluation system to assess photocatalyst performance.

Nb2O5–SnS2–CdS heteronanostructures as efficient visible-light-harvesting materials for production of H2 under solar light irradiation

Abstract Solar-driven photocatalytic water splitting is an ideal method to produce clean chemical fuels such as H2 and is promising for reducing the usage of fossil fuels and satisfying the increasing worldwide demand for energy supply. Heteronanostructures (HNSs) are useful for designing sustainable, low-cost, and efficient visible-light photocatalysts. In this study, a high-performance novel Nb2O5–SnS2–CdS HNSs was fabricated using Nb2O5 microspheres, SnS2 nanopetals, and CdS nanoparticles via an ultrasonication method and was employed as an efficient solar-light-driven photocatalyst for the production of H2. These Nb2O5–SnS2–CdS HNSs produced via ultrasonication had desirable properties, with a bandgap of ∼1.96 eV, and were photocatalytically active under visible light. The Nb2O5–SnS2–CdS HNSs exhibited excellent stability of H2 evolution rate under natural solar light irradiation: 55887 μmol/g, which was 2.19 and 2.79 times greater than those for Nb2O5–CdS and SnS2–CdS HNSs, respectively. The enhanced photocatalytic activity of the Nb2O5–SnS2–CdS heterostructure was attributed to the enhanced visible absorption and improved charge separation, which prevented the recombination of electron–hole pairs during the photocatalytic reactions. The present study indicates the vital role of the interactions in the HNS metal sulfides and oxide for improving charge-carrier separation, which is significant for the development of highly efficient Nb2O5–SnS2–CdS HNS photocatalysts for H2 evolution.

Revealing and accelerating interfacial charge carrier dynamics in Z-scheme heterojunctions for highly efficient photocatalytic oxygen evolution

Searching for highly efficient photocatalysts for water oxidation is the footstone for the development of overall water splitting systems and has been actively pursued. The construction of artificial Z-scheme heterojunction photocatalysts has been conclusively proven to be effective in boosting charge transport property and in improving the OER performance. Herein, Ag3PO4 particles anchored on modified crispy g-C3N4 flakes have been successfully fabricated. KOH-assisted surface modification of g-C3N4 flakes and intimate interfacial contact favor the accelerated charge transfer and highly improved OER efficiency. Ultrafast spectroscopy results reveal that modified g-C3N4 with crispy nanostructures possesses more trap-induced long-lived photogenerated holes, which are extremely helpful to combine with photo-generated electrons from the conduction band (CB) position of Ag3PO4 via the specific Z-scheme configuration, leaving more holes in the valence band (VB) of Ag3PO4 for the enhanced OER. Superb oxygen-evolving performance highlight the great promise of Z-scheme Ag3PO4-based heterojunctions in solar-driven photocatalytic water splitting.

Dual Z-scheme g-C3N4/Ag3PO4/Ag2MoO4 ternary composite photocatalyst for solar oxygen evolution from water splitting

Semiconductor-based solar-driven photocatalytic water splitting has been considered as one of the most promising solutions to solve the problem of fossil-based energy crisis, while the development of advanced photocatalytic materials for high-performance oxygen evolution from water splitting is the biggest challenge we are facing. We report the fabrication of novel g-C3N4/Ag3PO4/Ag2MoO4 ternary composite materials and the exploration of heterostructure materials for water oxidation under LED illumination. The hybridization of three semiconductors has been confirmed by microscopic study, chemical and structural analyses. Enhanced oxygen-producing activity over the obtained ternary composite photocatalysts was observed. The reasons responsible for the enhanced oxygen-evolving performance can be ascribed to the improved light absorption toward visible light, faster charge separation and charge transportation, as well as more powerful water oxidation capability originating from the in-situ construction of dual Z-scheme-type channels under visible light irradiation. The key role of in-situ formed metallic Ag as the electron mediator is suggested based on the theoretical and experimental results. The successful synthesis of fascinating ternary water oxidation photocatalysts provides new insights into the development of novel all-solid-state Z-scheme photocatalytic systems for energy and environmental applications.

Fabrication of CdS-Ag3PO4 heteronanostructures for improved visible photocatalytic hydrogen evolution

Solar-driven photocatalytic water splitting is an ideal solution for clean and renewable fuels. The development of sustainable, low-cost, and efficient visible-light photocatalyst continues to be a serious challenge in this field. In this article, CdS−Ag3PO4 heteronanostructures (HNSs) were fabricated for the first time by a solvothermal and subsequent simple chemical reaction method. The as synthesized heterostructured photocatalysts were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–visible spectroscopy. Their photocatalytic hydrogen production rate was evaluated by using an aqueous solution containing 10% methanol under visible light (λ > 420 nm). The resultant CdS-Ag3PO4 HNSs exhibit a higher photocatalytic hydrogen evolution rate than that of CdS NWs under visible light irradiation. The apparent H2 generation rate of CdS-Ag3PO4 HNSs is ∼2 times higher than that of bare CdS nanowires (NWs). The results show that the specially formed heterojunctions between CdS NWs and Ag3PO4 NPs favor the separation of photogenerated electron-hole pairs, which in turn produced the improved photocatalytic hydrogen evolution rate.

Combining photocatalytic hydrogen generation and capsule storage in graphene based sandwich structures

The challenge of safe hydrogen storage has limited the practical application of solar-driven photocatalytic water splitting. It is hard to isolate hydrogen from oxygen products during water splitting to avoid unwanted reverse reaction or explosion. Here we propose a multi-layer structure where a carbon nitride is sandwiched between two graphene sheets modified by different functional groups. First-principles simulations demonstrate that such a system can harvest light and deliver photo-generated holes to the outer graphene-based sheets for water splitting and proton generation. Driven by electrostatic attraction, protons penetrate through graphene to react with electrons on the inner carbon nitride to generate hydrogen molecule. The produced hydrogen is completely isolated and stored with a high-density level within the sandwich, as no molecules could migrate through graphene. The ability of integrating photocatalytic hydrogen generation and safe capsule storage has made the sandwich system an exciting candidate for realistic solar and hydrogen energy utilization.

Pd–MgNix nanospheres/black-TiO2 porous films with highly efficient hydrogen production by near-complete suppression of surface recombination

Hydrogen generated from solar-driven photocatalytic water splitting has the potential to be a clean, sustainable and abundant energy source. Herein, we demonstrate that Pd–MgNix nanospheres/black-TiO2 porous films serve as a highly efficient and convenient catalyst for photogeneration of hydrogen from water. Near-complete suppression of surface recombination ensures the excellent photocatalytic activity of Pd–MgNix nanospheres/black-TiO2 porous films, corresponding to high hydrogen production rates (34.93mmolh−1g−1). The result is promising for overall solar water splitting in a simple system, and is encouraging for application of this surface modification strategy to other candidate semiconductors.

Silicon nanowire array/Cu2O crystalline core–shell nanosystem for solar-driven photocatalytic water splitting

P-type Cu2O nanocrystals were deposited on n-type silicon nanowire arrays (Si NWs) to form core–shell heterojunction arrays structure via a simple electroless deposition technique. Scanning electron microscopy, transmission electron microscope and x-ray diffraction were utilized to characterize the morphology and structure of the core–shell nanosystem. The reflectivity of the obtained core–shell structure measured by UV/vis spectrometry showed a comparatively low reflectivity in the visible-light region, which implied good optical absorption performance. The water splitting performance of the obtained Si NWs, planar Si/Cu2O structure and Si NW/Cu2O core–shell nanosystem were studied. Owing to the large specific surface area, heterojunctions formed between Cu2O nanocrystallites and Si NWs and the light trapping effect of the NW array structure, the photocatalytic performance of the Si NW/Cu2O core–shell nanosystem increased markedly compared with that of pure silicon NWs and a planar Si/Cu2O structure, which means excellent hydrogen production capacity under irradiation with simulated sunlight. In addition, the photocatalytic performance of the core–shell nanosystem was improved obviously after platinum nanoparticles were electrodeposited on it.

Self-regenerated solar-driven photocatalytic water-splitting by urea derived graphitic carbon nitride with platinum nanoparticles

A natural self-regeneration step for urea derived graphitic carbon nitride with platinum nanoparticles is found by simply opening the system to air in the dark under ambient conditions, following its solar-driven hydrogen production. The produced peroxides deactivate the graphitic carbon nitride. Release of weakly bound peroxides on the polymeric semiconductor surface is a crucial process for regeneration.