Semiconductor photocatalysis is a trustworthy approach to harvest clean solar light for energy conversions, while state‐of‐the‐art catalytic efficiencies are unsatisfactory because of the finite ...light response and/or recombination of robust charge carriers. Along with the development of modern material characterization techniques and electronic‐structure computations, oxygen vacancies (OVs) on the surface of real photocatalysts, even in infinitesimal concentration, are found to play a more decisive role in determining the kinetics, energetics, and mechanisms of photocatalytic reactions. This Review endeavors to clarify the inherent functionality of OVs in photocatalysis at the surface molecular level using 2D BiOCl as the platform. Structure sensitivity of OVs on reactivity and selectivity of photocatalytic reactions is intensely discussed via confining OVs onto prototypical BiOCl surfaces of different structures. The critical understanding of OVs chemistry can help consolidate and advance the fundamental theories of photocatalysis, and also offer new perspectives and guidelines for the rational design of catalysts with satisfactory performance.
Tiny concentrations of oxygen vacancies on the surface of real photocatalysts can influence the kinetics and energetics and the mechanisms of photocatalytic reactions decisively. Oxygen vacancies on BiOCl surfaces are described at the molecular level, and their structure correlated with reactivity and selectivity in photocatalytic reactions.
Although photocatalytic hydrogen evolution (PHE) is ideal for solar-to-fuel conversion, it remains challenging to construct a highly efficient PHE system by steering the charge flow in a precise ...manner. Here we tackle this challenge by assembling 1T MoS2 monolayers selectively and chemically onto (Bi12O17) end-faces of Bi12O17Cl2 monolayers to craft two-dimensional (2D) Janus (Cl2)-(Bi12O17)-(MoS2) bilayer junctions, a new 2D motif different from van der Waals heterostructure. Electrons and holes from visible light-irradiated Bi12O17Cl2 are directionally separated by the internal electric field to (Bi12O17) and (Cl2) end-faces, respectively. The separated electrons can further migrate to MoS2 via Bi-S bonds formed between (Bi12O17) and MoS2 monolayers. This atomic-level directional charge separation endows the Janus bilayers with ultralong carrier lifetime of 3,446 ns and hence a superior visible-light PHE rate of 33 mmol h(-1) g(-1). Our delineated Janus bilayer junctions on the basis of the oriented assembly of monolayers presents a new design concept to effectively steer the charge flow for PHE.
BiOCl single-crystalline nanosheets with exposed {001} and {010} facets were selectively synthesized via a facile hydrothermal route. The resulting BiOCl single-crystalline nanosheets with exposed ...{001} facets exhibited higher activity for direct semiconductor photoexcitation pollutant degradation under UV light, but the counterpart with exposed {010} facets possessed superior activity for indirect dye photosensitization degradation under visible light.
Incorporating carbon into Bi3O4Cl enhances its internal electric field by 126 times, which induces a bulk charge separation efficiency (ηbulk) of 80%. This ultrahigh ηbulk value presents a ...state‐of‐the‐art result in tuning the bulk charge separation. The generated C‐doped Bi3O4Cl has a noble‐metal‐ and electron‐scavenger‐free water‐oxidation ability under visible light, which is difficult to achieve with most existing photocatalysts.
In this study, ZnO/BiOI heterostructures were synthesized by a facile chemical bath method at low temperature. Control of the morphology and constituents of the ZnO/BiOI heterostructures was realized ...by simply tuning the Bi/Zn molar ratios. The resulting ZnO/BiOI heterostructures exhibited high photocatalytic activity in the degradation of methyl orange under visible-light irradiation. The high photocatalytic activity of the ZnO/BiOI heterostructures was first attributed to their high surface area. Surface photovoltage spectroscopy and transient photovoltage measurements revealed that the photoinduced charge-transfer property of p-type BiOI could be improved greatly by coupling with n-type ZnO. The heterojunction at the interface between the BiOI and ZnO could efficiently reduce the recombination of photoinduced electron–hole pairs to increase the lifetime of charge carriers by 15 times and thus enhance the photocatalytic activity of the ZnO/BiOI heterostructures, in addition to the high surface area. This study reveals that the heterostructure construction between two different semiconductors plays a very important role in determining the dynamic properties of their photogenerated charge carriers and their photocatalytic properties.
We theoretically and experimentally demonstrate that carbon self-doping could induce intrinsic electronic and band structure change of g-C(3)N(4)via the formation of delocalized big π bonds to ...increase visible light absorption and electrical conductivity as well as surface area and thus enhance both photooxidation and photoreduction activities.
Selective organic transformation under mild conditions constitutes a challenge in green chemistry, especially for alcohol oxidation, which typically requires environmentally unfriendly oxidants. ...Here, we report a new plasmonic catalyst of Au supported on BiOCl containing oxygen vacancies. It photocatalyzes selective benzyl alcohol oxidation with O2 under visible light through synergistic action of plasmonic hot electrons and holes. Oxygen vacancies on BiOCl facilitate the trapping and transfer of plasmonic hot electrons to adsorbed O2, producing •O2 – radicals, while plasmonic hot holes remaining on the Au surface mildly oxidize benzyl alcohol to corresponding carbon-centered radicals. The hypothesized concerted ring addition between these two radical species on the BiOCl surface highly favors the production of benzaldehyde along with an unexpected oxygen atom transfer from O2 to the product. The results and understanding acquired in this study, based on the full utilization of hot charge carriers in a plasmonic metal deposited on a rationally designed support, will contribute to the development of more active and/or selective plasmonic catalysts for a wide variety of organic transformations.
In this study, we demonstrate that protocatechuic acid (PCA) can significantly promote the alachlor degradation in the Fe(III)/H2O2 Fenton oxidation system. It was found that the addition of ...protocatechuic acid could increase the alachlor degradation rate by 10 000 times in this Fenton oxidation system at pH = 3.6. This dramatic enhancement of alachlor degradation was attributed to the complexing and reduction abilities of protocatechuic ligand, which could form stable complexes with ferric ions to prevent their precipitation and also accelerate the Fe(III)/Fe(II) cycle to enhance the ·OH generation. Meanwhile, the Fe(III)/PCA/H2O2 system could also work well at near natural pH even in the case of PCA concentration as low as 0.1 mmol/L. More importantly, both alachlor and PCA could be effectively mineralized in this Fenton system, suggesting the environmental benignity of PCA/Fe(III)/H2O2 Fenton system. We employed gas chromatography–mass spectrometry to identify the degradation intermediates of alachlor and then proposed a possible alachlor degradation mechanism in this novel Fenton oxidation system. This study provides an efficient way to remove chloroacetanilide herbicides, and also shed new insight into the possible roles of widely existed phenolic acids in the conversion and the mineralization of organic contaminants in natural aquatic environment.
In this study, we demonstrate that the photocatalytic sodium pentachlorophenate removal efficiency of Bi2WO6 under visible light can be greatly enhanced by bismuth self-doping through a simple ...soft-chemical method. Density functional theory calculations and systematical characterization results revealed that bismuth self-doping did not change the redox power of photogenerated carriers but promoted the separation and transfer of photogenerated electron-hole pairs of Bi2WO6 to produce more superoxide ions, which were confirmed by photocurrent generation and electron spin resonance spectra as well as superoxide ion measurement results. We employed gas chromatography-mass spectrometry and total organic carbon analysis to probe the degradation and the mineralization processes. It was found that more superoxide ions promoted the dechlorination process to favor the subsequent benzene ring cleavage and the final mineralization of sodium pentachlorophenate during bismuth self-doped Bi2WO6 photocatalysis by producing easily decomposable quinone intermediates. This study provides new insight into the effects of photogenerated reactive species on the degradation of sodium pentachlorophenate and also sheds light on the design of highly efficient visible-light-driven photocatalysts for chlorophenol pollutant removal.
In this study we demonstrate Fe@Fe2O3 core–shell nanowires can improve Fenton oxidation efficiency by two times with rhodamine B as a model pollutant at pH > 4. Active species trapping experiments ...revealed that the rhodamine B oxidation enhancement was attributed to molecular oxygen activation induced by Fe@Fe2O3 core–shell nanowires. The molecular oxygen activation process could generate superoxide radicals to assist iron core for the reduction of ferric ions to accelerate the Fe(III)/Fe(II) cycles, which favored the H2O2 decomposition to produce more hydroxyl radicals for the rhodamine B oxidation. The combination of Fe@Fe2O3 core–shell nanowires and ferrous ions (Fe@Fe2O3/Fe2+) offered a superior Fenton catalyst to decompose H2O2 for producing OH. We employed benzoic acid as a probe reagent to check the generation of OH and found the OH generation rate of Fe@Fe2O3/Fe2+ was 2–4 orders of magnitude larger than those of commonly used iron based Fenton catalysts and 38 times that of Fe2+. The reusability and the stability of Fe@Fe2O3 core–shell nanowires were studied. Total organic carbon and ion chromatography analyses revealed the mineralization of rhodamine B and the releasing of nitrate ions. Gas chromatograph-mass spectrometry was used to investigate the degradation intermediates to propose the possible rhodamine B Fenton oxidation pathway in the presence of Fe@Fe2O3 nanowires. This study not only provides a new Fenton oxidation system for pollutant control, but also widen the application of molecular oxygen activation induced by nanoscale zero valent iron.
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•Fe@Fe2O3 core–shell nanowires can accelerate the Fe(III)/Fe(II) cycles during Fenton oxidation.•Fe(III)/Fe(II) cycles are accelerated by superoxide radicals generated by Fe@Fe2O3 core–shell nanowires at pH > 4.•Fe@Fe2O3 core–shell nanowires and ferrous ions decompose H2O2 to produce more hydroxyl radicals.
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