Over the past few decades, graphitic carbon nitride (g‐C3N4) has arisen much attention as a promising candidate for photocatalytic hydrogen evolution reaction (HER) owing to its low cost and visible ...light response ability. However, the unsatisfied HER performance originated from the strong charge recombination of g‐C3N4 severely inhibits the further large‐scale application of g‐C3N4. In this case, the utilization of cocatalysts is a novel frontline in the g‐C3N4‐based photocatalytic systems due to the positive effects of cocatalysts on supressing charge carrier recombination, reducing the HER overpotential, and improving photocatalytic activity. This review summarizes some recent advances about the high‐performance cocatalysts based on g‐C3N4 toward HER. Specifically, the functions, design principle, classification, modification strategies of cocatalysts, as well as their intrinsic mechanism for the enhanced photocatalytic HER activity are discussed here. Finally, the pivotal challenges and future developments of cocatalysts in the field of HER are further proposed.
Benefitting from the low recombination rate of charge carrier and accelerated surface catalytic reaction induced by cocatalysts, much research has been focused on that how to improve the water reduction reaction efficiency. In this case, the recent advances over the utilization of cocatalysts based on g‐C3N4 are summarized.
TiO2/graphene composites have been well studied as a solar light photocatalysts and electrode materials for lithium-ion batteries (LIBs). Recent reports have shown that ultralight 3D-graphene ...aerogels (GAs) can better adsorb organic pollutants and can provide multidimensional electron transport pathways, implying a significant potential application for photocatalysis and LIBs. Here, we report a simple one-step hydrothermal method toward in situ growth of ultradispersed mesoporous TiO2 nanocrystals with (001) facets on GAs. This method uses glucose as the dispersant and linker owing to its hierarchically porous structure and a high surface area. The TiO2/GAs reported here exhibit a highly recyclable photocatalytic activity for methyl orange pollutant and a high specific capacity in LIBs. The strong interaction between TiO2 and GAs, the facet characteristics, the high electrical conductivity, and the three-dimensional hierarchically porous structure of these composites results in highly active photocatalysis, a high rate capability, and stable cycling.
Hollow structures with an efficient light harvesting and tunable interior component offer great advantages for constructing a Z‐scheme system. Controlled design of hollow cobalt sulfide (Co9S8) cubes ...embedded with cadmium sulfide quantum dots (QDs) is described, using hollow Co(OH)2 as the template and a one‐pot hydrothermal strategy. The hollow CdS/Co9S8 cubes utilize multiple reflections of light in the cubic structure to achieve enhanced photocatalytic activity. Importantly, the photoexcited charge carriers can be effectively separated by the construction of a redox‐mediator‐free Z‐scheme system. The hydrogen evolution rate over hollow CdS/Co9S8 is 134 and 9.1 times higher than that of pure hollow Co9S8 and CdS QDs under simulated solar light irradiation, respectively. Moreover, this is the first report describing construction of a hollow Co9S8 based Z‐scheme system for photocatalytic water splitting, which gives full play to the advantages of light‐harvesting and charges separation.
Fair and square: An efficient light‐ harvesting CdS/Co9S8 catalyst was prepared for direct Z‐scheme photocatalytic water splitting. Hollow Co9S8 cubes eliminate photocorrosion phenomena typical of pure CdS quantum dots and improve harvesting of solar light, thus greatly enhancing photocatalytic H2 evolution.
Although Fenton or Fenton‐like reactions have been widely used in the environment, biology, life science, and other fields, the sharp decrease in their activity under macroneutral conditions is still ...a large problem. This study reports a MoS2 cocatalytic heterogeneous Fenton (CoFe2O4/MoS2) system capable of sustainably degrading organic pollutants, such as phenol, in a macroneutral buffer solution. An acidic microenvironment in the slipping plane of CoFe2O4 is successfully constructed by chemically bonding with MoS2. This microenvironment is not affected by the surrounding pH, which ensures the stable circulation of Fe3+/Fe2+ on the surface of CoFe2O4/MoS2 under neutral or even alkaline conditions. Additionally, CoFe2O4/MoS2 always exposes “fresh” active sites for the decomposition of H2O2 and the generation of 1O2, effectively inhibiting the production of iron sludge and enhancing the remediation of organic pollutants, even in actual wastewater. This work not only experimentally verifies the existence of an acidic microenvironment on the surface of heterogeneous catalysts for the first time, but also eliminates the pH limitation of the Fenton reaction for pollutant remediation, thereby expanding the applicability of Fenton technology.
We have successfully constructed an acidic microenvironment on the surface of CoFe2O4 by chemical bonding MoS2, which ensures the stable circulation of iron ions in the slipping plane and truly overcomes the limitation of pH in pollutant control, thereby expanding the applicability of Fenton technology.
Solar fuels and chemical production using photosynthetic devices by harnessing solar energy remains an attractive prospect owing to its being a potential alternative to fossil feedstocks, though such ...artificial photosynthetic systems for direct solar-to-chemical conversion are still far from industrial applications as a consequence of emergent challenges that may be well addressed by the exploration of integrated photocatalysis devices with enhanced activity, selectivity, and stability. Simultaneously embedding dual cocatalysts onto photocatalysts aims to tackle these limitations of artificial photosynthesis initiated by the bare photocatalyst while offering an opportunity to realize their synergistic operations. In this review, we summarize the essential design principles and emerging configurations of dual cocatalysts, and provide a side-by-side comparison to reveal their strengths and deficiencies. In parallel, we discuss how to choose a pair of redox cocatalysts for a specific photocatalytic redox reaction, and how some key lessons that have emerged from the relevant studies can be applied into further investigations for fuels and chemicals generation. Finally, we outline the remaining challenges and potential advances in the discovery of a robust and renewable artificial photosynthesis system.
This review summarizes the design principle, emerging configurations, and photocatalytic applications of redox cocatalysts, and offers insights and perspectives on this topic.
Platinum nanoparticles (Pt NPs) are one of the most efficient cocatalysts in photocatalysis, and their size determines the activity and the selectivity of the catalytic reaction. Nevertheless, an ...in-depth understanding of the platinum's size effect in the carbon dioxide photocatalytic reduction is still lacking. Through analyses of the geometric features and electronic properties with variable-sized Pt NPs, here we show a prominent size effect of Pt NPs in both the activity and selectivity of carbon dioxide photocatalytic reduction. Decreasing the size of Pt NPs promotes the charge transfer efficiency, and thus enhances both the carbon dioxide photocatalytic reduction and hydrogen evolution reaction (HER) activity, but leads to higher selectivity towards hydrogen over methane. Combining experimental results and theoretical calculations, in Pt NPs, the terrace sites are revealed as the active sites for methane generation; meanwhile, the low-coordinated sites are more favorable in the competing HER.
In this work, we develop an inorganic cocatalyst of commercial MoO2 application in Fenton reaction, which can significantly enhance the Fe(III)/Fe(II) cycling efficiency to improve the oxidation ...activity for the remediation of Lissamine rhodamine B (L-RhB).
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There is a relatively low efficiency of Fe(III)/Fe(II) conversion cycle and H2O2 decomposition (<30%) in conventional Fenton process, which further results in a low production efficiency of OH and seriously restricts the application of Fenton. Herein, we report that the commercial MoO2 can be used as the cocatalyst in Fenton process to dramatically accelerate the oxidation of Lissamine rhodamine B (L-RhB), where the efficiency of Fe(III)/Fe(II) cycling is greatly enhanced in the Fenton reaction meanwhile. And the L-RhB solution could be degraded nearly 100% in 1 min in the MoO2 cocatalytic Fenton system under the optimal reaction condition, which is apparently better than that of the conventional Fenton system (∼50%). Different from the conventional Fenton reaction where the OH plays an important role in the oxidation process, it shows that 1O2 contributes most in the MoO2 cocatalytic Fenton reaction. However, it is found that the exposed Mo4+ active sites on the surface of MoO2 powders can greatly promote the rate-limiting step of Fe3+/Fe2+ cycle conversion, thus minimizing the dosage of H2O2 (0.400 mmol/L) and Fe2+ (0.105 mmol/L). Interestingly, the MoO2 cocatalytic Fenton system also exhibits a good ability for reducing Cr(VI) ions, where the reduction ability for Cr(VI) reaches almost 100% within 2 h. In short, this work shows a new discovery for MoO2 cocatalytic advanced oxidation processes (AOPs), which devotes a lot to the practical water remediation application.
•Graphene based doped TiO2 nanocomposites were prepared.•The intimate contact between doped TiO2 and graphene is achieved simultaneously.•These nanocomposites showed higher photocatalytic activity ...than TiO2 and doped TiO2.•Photocatalytic mechanism was explained thoroughly.
The nanocomposites of reduced graphene oxide based nitrogen doped TiO2 (N–TiO2–RGO) and reduced graphene oxide based nitrogen and vanadium co-doped TiO2 (N, V–TiO2–RGO) were prepared via a facile hydrothermal reaction of graphene oxide and TiO2 in a water solvent. In this hydrothermal treatment, the reduction of graphene oxide and the intimate contact between nitrogen doped TiO2 (N–TiO2) or nitrogen and vanadium co-doped TiO2 (N,V–TiO2) and the RGO sheet is achieved simultaneously. Both N–TiO2–RGO and N,V–TiO2–RGO nanocomposites exhibit much higher visible light photocatalytic activity than N–TiO2 and N,V–TiO2, and the order of visible light photocatalytic activity is N,V–TiO2–RGO>N–TiO2–RGO>N,V–TiO2>N–TiO2>TiO2. According to the characterization, the enhanced photocatalytic activity of the nanocomposites is attributed to reasons, such as enhancement of adsorption of pollutants, light absorption intensity, minimizing the recombination of photoinduced electrons and holes and more excited states of these nanocomposites under visible light irradiation. Overall, this work provides a more marked contrast of graphene based semiconductor nanocomposites and a more comprehensive explanation of the mechanism.
The beneficial co-effects between S doping and Fe(III) doping can largely decrease the band gap energy due to the formation of impurity levels and suppress the recombination of electrons and holes by ...trapping electrons, leading to higher photo activity of FeS codoped TiO2 than that of undoped and S-doped TiO2. Display omitted
► FeS codoped TiO2 photocatalysts were prepared by a facile low-temperature solvothermal method. ► The FeS codoped TiO2 photocatalysts have excellent photocatalytic activity of phenol degradation. ► S and Fe(III) codoping can largely decrease the band gap energy of TiO2, extending the absorption in visible light area. ► The high photocatalytic activity for phenol was caused by the co-effects between S doping and Fe(III) doping.
FeS codoped TiO2 photocatalysts were prepared by a sol–gel process and low-temperature solvothermal method. The obtained samples were characterized by XRD, UV–vis DRS, FT-IR, BET, EPR and XPS. Compared with undoped TiO2 and S doped TiO2 photocatalysts, the FeS codoped TiO2 photocatalysts exhibited much higher photocatalytic activity for phenol degradation under visible light irradiation. The optimal ratio of Fe/Ti is 1.0at%. It was revealed that the band gap of FeS codoped TiO2 was obviously decreased, extending the light response of TiO2 into visible light region, and sulfate ions were absorbed on the surface of the TiO2. The high visible light photocatalytic activity of TiO2 was assigned to the beneficial co-effects between S and Fe. The doped Fe(III) and SO42− anchored on TiO2 surface are favorable for the separation of photo-induced electrons and holes, suppressing the recombination of electrons and holes and consequently promoting the formation of hydroxyl radical.
The research progress and main achievements of graphene-based nanomaterials in the fields of photocatalytic degradation, pollutant adsorption and their mechanism of action are summarized in this ...review.
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Graphene is a two-dimensional nanomaterial with huge surface area, high carrier mobility and high mechanical strength. Because of its great potential in nanotechnology and environmental protection, it has attracted much attention in environmental and energy fields since its discovery in 2004. Although graphene is a star material, many reviews have introduced its use in terms of energy, the research progress in the field of environment, especially water pollution control, has been rarely reported. Here, we review exhaustively the research progress of graphene-based materials in environmental pollution remediation in the past ten years. Firstly, the advantages and classification of graphene were introduced. Secondly, the research progress and main achievements of graphene and its composites in the fields of photocatalytic degradation, pollutant adsorption and water treatment were emphatically described, and the mechanism of action in the above fields was summarized. Finally, we discuss the problems existing in the preparation and summarize the application of graphene in the environment.
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