A Z‐scheme heterojunction with spatially separated cocatalysts is proposed for overcoming fundamental issues in photocatalytic water splitting, such as inefficient light absorption, charge ...recombination, and sluggish reaction kinetics. For efficient light absorption and interfacial charge separation, Z‐scheme organic/inorganic heterojunction photocatalysts are synthesized by firmly immobilizing ultrathin g‐C3N4 on the surface of TiO2 hollow spheres via electrostatic interactions. Additionally, two cocatalysts, Pt and IrOx, are spatially separated along the Z‐scheme charge‐transfer pathway to enhance surface charge separation and reaction kinetics. The as‐prepared Pt/g‐C3N4/TiO2/IrOx (PCTI) hollow sphere photocatalyst exhibits an exceptional H2 evolution rate of 8.15 mmol h−1 g−1 and a remarkable apparent quantum yield of 24.3% at 330 nm in the presence of 0.5 wt% Pt and 1.2 wt% IrOx cocatalysts on g‐C3N4 and TiO2, respectively. Photoassisted Kelvin probe force microscopy is used to systematically analyze the Z‐scheme charge‐transfer mechanism within PCTI. Furthermore, the benefits of spatially separating cocatalysts in the PCTI system are methodically investigated in comparison to randomly depositing them. This work adequately demonstrates that the combination of a Z‐scheme heterojunction and spatially separated cocatalysts can be a promising strategy for designing high‐performance photocatalytic platforms for solar fuel production.
A Z‐scheme heterojunction hollow sphere with spatially separated cocatalysts is proposed to overcome the fundamental limitation in photocatalytic water splitting. The Z‐scheme heterojunction effectively stimulates interfacial charge transfer while retaining high redox power, whereas the spatially separated cocatalysts stimulate surface charge separation. Their synergistic effect results in an exceptional photocatalytic H2 evolution performance of 8.15 mmol g−1 h−1.
Due to its low cost, environmentally friendly process, and lack of secondary contamination, the photodegradation of dyes is regarded as a promising technology for industrial wastewater treatment. ...This technology demonstrates the light-enhanced generation of charge carriers and reactive radicals that non-selectively degrade various organic dyes into water, CO2, and other organic compounds via direct photodegradation or a sensitization-mediated degradation process. The overall efficiency of the photocatalysis system is closely dependent upon operational parameters that govern the adsorption and photodegradation of dye molecules, including the initial dye concentration, pH of the solution, temperature of the reaction medium, and light intensity. Additionally, the charge-carrier properties of the photocatalyst strongly affect the generation of reactive species in the heterogeneous photodegradation and thereby dictate the photodegradation efficiency. Herein, this comprehensive review discusses the pseudo kinetics and mechanisms of the photodegradation reactions. The operational factors affecting the photodegradation of either cationic or anionic dye molecules, as well as the charge-carrier properties of the photocatalyst, are also fully explored. By further analyzing past works to clarify key active species for photodegradation reactions and optimal conditions, this review provides helpful guidelines that can be applied to foster the development of efficient photodegradation systems.
With the capability of localizing optical energy via surface plasmon resonance (SPR), plasmonic Au nanostructures hold great promise for enhancing the solar water splitting of semiconductor ...photocatalysts. While the content of Au plays a critical role in mediating interfacial charge transfer, its quantitative influence on the efficiency of plasmon-assisted water splitting is still not fully understood. This work aimed to explore the correlations among plasmonic metal content, SPR-mediated charge transfer and electromagnetic response, and the resultant photoactivity enhancement toward photoelectrochemical (PEC) water splitting. The PEC system was constructed by employing Au particle-decorated ZnO nanocrystals (ZnO–Au) as the plasmonic photoanode. Time-resolved photoluminescence spectroscopy and finite-difference time-domain simulations were utilized to evaluate the optimal Au content which attained effective charge separation and imposed a significant SPR effect for achieving the largest photoactivity enhancement. The charge transfer at the photoanode/electrolyte interface and its dependence on the Au content were examined with electrochemical impedance analysis, which manifested the effectiveness of the optimal Au content in facilitating the hole transfer kinetics. The present study reports a technical advance in the realization of the quantitative effect of Au for designing sophisticated plasmonic PEC systems that enabled efficient solar-to-fuel energy conversion.
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•Strategies to adjust charge dynamics of semiconductor heterostructures are reviewed.•Precise manipulation of charge transfer dynamics is still a grand challenge.•Insights into future ...advancement of photocatalysis technology are summarized.
As a topic of intensive research interest for decades, photocatalysis using semiconductor heterostructures holds the potential to satisfy global energy demand, reduce greenhouse effect and accomplish environmental remediation. This burgeoning technology has quickly become a high-profile emerging scientific and technological field, providing a solution to achieving sustainable development of renewables. However, critical challenges, such as inadequate solar photons absorption, mediocre charge transfer dynamics, poor surface reaction kinetics and lack of long-term stability, have hindered the widespread deployment of semiconductor photocatalysts. Interfacial charge dynamics is particularly relevant to the utility of photocatalysis because it dictates charge transfer and carrier utilization, the two complicated yet key processes involved in the photocatalytic reactions. The means to modulating charge dynamics and even manipulating carrier behavior may pave a new avenue for intelligent design of versatile photocatalysts for advanced applications. This review introduces the recent development on conceptual strategies and experimental approaches that can be exploited to modulating charge dynamics of semiconductor heterostructures for maximizing carrier utilization efficiency. New insights into the future advancement of photocatalysis technology based on the adoption of the proposed tactics are also discussed and summarized.
A vital issue that degrades the entirety of photocatalysis on TiO2 is the requisite of light illumination for performing redox reactions. The ability to maintain the catalytic activity in dark ...environment has been the ultimate goal for the widespread deployment of TiO2 photocatalysts. Here, for the first time we reported the demonstration of an all-day-active photocatalyst model by employing Au@Cu7S4 yolk@shell nanocrystal-decorated TiO2 nanowires. The samples were obtained by depositing a Cu2O layer on the Au surface of Au particle-decorated TiO2 nanowires, followed by the sulfidation treatment on Cu2O layer to grow hollow Cu7S4 shell. By coupling the pronounced charge separation and distinctive peroxidase mimic properties from the constituents, the TiO2-Au@Cu7S4 nanowires were capable of performing efficient methyl orange degradation under light illumination, yet still persisted noticeable activity of decomposing methyl orange after light irradiation was switched off. The present study has embodied a conceptually valuable design of permanently working photocatalysts, which may serve as a versatile platform for the widely distributed environmental and energy applications such as pollutant destruction and organic transformation.
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•TiO2-Au@Cu7S4 nanowire as an all-day-active photocatalyst is demonstrated.•Continuous operation for pollutant degradation in day and night is achieved.•Coupling of photocatalysis and peroxidase mimics enable the permanently working.
Here we demonstrate that the photoactivity of Au-decorated TiO2 electrodes for photoelectrochemical water oxidation can be effectively enhanced in the entire UV–visible region from 300 to 800 nm by ...manipulating the shape of the decorated Au nanostructures. The samples were prepared by carefully depositing Au nanoparticles (NPs), Au nanorods (NRs), and a mixture of Au NPs and NRs on the surface of TiO2 nanowire arrays. As compared with bare TiO2, Au NP-decorated TiO2 nanowire electrodes exhibited significantly enhanced photoactivity in both the UV and visible regions. For Au NR-decorated TiO2 electrodes, the photoactivity enhancement was, however, observed in the visible region only, with the largest photocurrent generation achieved at 710 nm. Significantly, TiO2 nanowires deposited with a mixture of Au NPs and NRs showed enhanced photoactivity in the entire UV–visible region. Monochromatic incident photon-to-electron conversion efficiency measurements indicated that excitation of surface plasmon resonance of Au is responsible for the enhanced photoactivity of Au nanostructure-decorated TiO2 nanowires. Photovoltage experiment showed that the enhanced photoactivity of Au NP-decorated TiO2 in the UV region was attributable to the effective surface passivation of Au NPs. Furthermore, 3D finite-difference time domain simulation was performed to investigate the electrical field amplification at the interface between Au nanostructures and TiO2 upon SPR excitation. The results suggested that the enhanced photoactivity of Au NP-decorated TiO2 in the UV region was partially due to the increased optical absorption of TiO2 associated with SPR electrical field amplification. The current study could provide a new paradigm for designing plasmonic metal/semiconductor composite systems to effectively harvest the entire UV–visible light for solar fuel production.
Z-scheme heterojunctions are fundamentally promising yet practically appealing for photocatalytic hydrogen (H2) production owing to the enhanced redox power, spatial separation of charge carriers, ...and broad-spectrum solar light harvesting. The charge-transfer dynamics at Z-scheme heterojunctions can be accelerated by inserting charge-transfer mediators at the heterojunction interfaces. In this study, we introduce Au nanoparticle mediators in the Z-scheme W18O49/g-C3N4 heterostructure, which enables an improved H2 production rate of 3465 μmol/g·h compared with the direct Z-scheme W18O49/g-C3N4 (1785 μmol/g·h) under 1 sun irradiation. The apparent quantum yields of H2 production with W18O49/Au/g-C3N4 are 3.9% and 9.3% at 420 and 1200 nm, respectively. The improved photocatalytic H2 production activity of W18O49/Au/g-C3N4 is attributable to the triple-channel charge-transfer mechanism: channel IZ-scheme charge transfer facilitates charge separation and increased redox power of the photoexcited electrons; channels II and IIIthe localized surface plasmon resonances from Au (channel II) and W18O49 (channel III) enable light harvesting extension from visible to near-infrared wavelengths.
Understanding of charge transfer processes is determinant to the performance optimization for semiconductor photocatalysts. As a representative model of composite photocatalysts, ...metal-particle-decorated ZnO has been widely employed for a great deal of photocatalytic applications; however, the dependence of charge carrier dynamics on the metal content and metal composition and their correlation with the photocatalytic properties have seldom been reported. Here, the interfacial charge dynamics for metal-decorated ZnO nanocrystals were investigated and their correspondence with the photocatalytic properties was evaluated. The samples were prepared with a delicate antisolvent approach, in which ZnO nanocrystals were grown along with metal particle decoration in a deep eutectic solvent. By modulating the experimental conditions, the metal content (from 0.6 to 2.3 at%) and metal composition (including Ag, Au, and Pd) in the resulting metal-decorated ZnO could be readily controlled. Time-resolved photoluminescence spectra showed that an optimal Au content of 1.3 at% could effectuate the largest electron transfer rate constant for Au-decorated ZnO nanocrystals, in conformity with the highest photocatalytic efficiency observed. The relevance of charge carrier dynamics to the metal composition was also inspected and realized in terms of the energy level difference between ZnO and metal. Among the three metal-decorated ZnO samples tested, ZnO–Pd displayed the highest photocatalytic activity, fundamentally according with the largest electron transfer rate constant deduced in carrier dynamics measurements. The current work was the first study to present the correlations among charge carrier dynamics, metal content, metal composition, and the resultant photocatalytic properties for semiconductor/metal heterostructures. The findings not only helped to resolve the standing issues regarding the mechanistic foundation of photocatalysis but also shed light on the intelligent design of semiconductor/metal composite systems to consolidate their utility in photocatalytic fields.
Using in situ ultrafast laser spectroscopic techniques to monitor the charge dynamics of semiconductor photocatalysts under operating conditions is essential for digging out the veritable ...interactions between charge carriers and the reactive species. This real-time observation is desirable for optimizing individual components and their integration in advanced photoelectrochemical (PEC) and photocatalytic systems, which can achieve the “Holy Grail” of solar energy harvesting and solar fuel generation. This Review summarizes the recent developments of employing transient absorption spectroscopy for in situ measurements of charge dynamics on semiconductor nanostructures. The implications in the PEC and photocatalytic reactions toward hydrogen production and carbon dioxide reduction will be discussed, along with future outlooks and perspectives.
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