Photocatalytic reduction of CO2 to solar fuels and/or fine chemicals is a promising way to increase the energy supply and reduce greenhouse gas emissions. However, the conventional reaction system ...for CO2 photoreduction with pure H2O or sacrificial agents usually suffers from low catalytic efficiency, poor stability, or cost‐ineffective atom economy. A recent surge of developments, in which photocatalytic CO2 valorization is integrated with selective organic synthesis into one reaction system, indicates an efficient modus operandi that enables sufficient utilization of photogenerated electrons and holes to achieve the goals for sustainable economic and social development. In this Review we discuss current advances in cooperative photoredox reaction systems that integrate CO2 valorization with organics upgrading based on heterogeneous photocatalysis. The applications and virtues of this strategy and the underlying reaction mechanisms are discussed. The ongoing challenges and prospects in this area are critically discussed.
The photoredox‐catalyzed win–win coupling strategy, in which CO2 valorization is integrated with organic synthesis in one reaction system, provides a promising approach that enables sufficient utilization of excited electrons and holes to achieve feasible and sustainable light‐mediated artificial photosynthesis.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Merging hydrogen (H
) evolution with oxidative organic synthesis in a semiconductor-mediated photoredox reaction is extremely attractive because the clean H
fuel and high-value chemicals can be ...coproduced under mild conditions using light as the sole energy input. Following this dual-functional photocatalytic strategy, a dreamlike reaction pathway for constructing C-C/C-X (X = C, N, O, S) bonds from abundant and readily available X-H bond-containing compounds with concomitant release of H
can be readily fulfilled without the need of external chemical reagents, thus offering a green and fascinating organic synthetic strategy. In this review, we begin by presenting a concise overview on the general background of traditional photocatalytic H
production and then focus on the fundamental principles of cooperative photoredox coupling of selective organic synthesis and H
production by simultaneous utilization of photoexcited electrons and holes over semiconductor-based catalysts to meet the economic and sustainability goal. Thereafter, we put dedicated emphasis on recent key progress of cooperative photoredox coupling of H
production and various selective organic transformations, including selective alcohol oxidation, selective methane conversion, amines oxidative coupling, oxidative cross-coupling, cyclic alkanes dehydrogenation, reforming of lignocellulosic biomass, and so on. Finally, the remaining challenges and future perspectives in this flourishing area have been critically discussed. It is anticipated that this review will provide enlightening guidance on the rational design of such dual-functional photoredox reaction system, thereby stimulating the development of economical and environmentally benign solar fuel generation and organic synthesis of value-added fine chemicals.
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Solar‐driven syngas production by CO2 reduction provides a sustainable strategy to produce renewable feedstocks. However, this promising reaction often suffers from tough CO2 activation, sluggish ...oxidative half‐reaction kinetics and undesired by‐products. Herein, we report a function‐oriented strategy of deliberately constructing black phosphorus quantum dots‐ZnIn2S4 (BP/ZIS) heterostructures for solar‐driven CO2 reduction to syngas, paired with selectively oxidative C−N bond formation, in one redox cycle. The optimal BP/ZIS heterostructure features the enhanced charge‐carrier separation and enriched active sites for cooperatively photocatalytic syngas production with a tunable ratio of CO/H2 and efficient oxidation of amines to imines with high conversion and selectivity. This prominent catalytic performance arises from the efficient electronic coupling between black phosphorus quantum dots and ZnIn2S4, as well as the optimized adsorption strength for key reaction intermediates, as supported by both experimental and theoretical investigations. We also demonstrate a synergistic interplay between CO2 reduction and amine dehydrogenation oxidation, rather than simply collecting these two single half‐reactions in this dual‐functional photoredox system.
A function‐oriented strategy of engineering black phosphorus quantum dots‐ZnIn2S4 heterostructures for solar‐driven CO2 reduction to syngas, paired with selectively oxidative C−N bond formation, in one redox cycle is reported. The promoted charge‐carrier separation, enriched active sites and optimized adsorption strength of key reaction intermediates for CO2 reduction, as well as the cooperative photoredox manner, jointly contribute to the enhanced photoactivity and selectivity.
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Heterogeneous photocatalysis is a promising strategy for addressing the worldwide environmental pollution and energy shortage issues. However, unlike TiO2 with good photostability, the intrinsic ...drawback of photoinduced decomposition, i.e., photocorrosion, of semiconductors significantly challenges durable photocatalysis. In this review, the photocorrosion mechanisms of typical semiconductors and different characterization methods proposed for monitoring the photocorrosion process of semiconductor-based composite photocatalysts are elaborated. Dedicated emphasis is put on the strategies for improving the anti-photocorrosion property of semiconductor-based photocatalysts, including modifying the crystal structure or morphology of semiconductors, doping with heteroatoms, hybridizing with various semiconductors and/or cocatalysts, and regulating the photocatalytic reaction conditions. Finally, we cast a personal prospect on the future development of the rational design of corrosion-controlled semiconductor-based photocatalysts toward versatile photoredox applications.
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Carbon quantum dots (CQDs) as a rising star of carbon nanomaterials, by virtue of their unique physicochemical, optical and electronic properties, have displayed tremendous momentum in numerous ...fields such as biosensing, bioimaging, drug delivery, optoelectronics, photovoltaics and photocatalysis. In particular, the rich optical and electronic properties of CQDs including efficient light harvesting, tunable photoluminescence (PL), extraordinary up-converted photoluminescence (UCPL) and outstanding photoinduced electron transfer have attracted considerable interest in different photocatalytic applications for the sake of full utilization of the solar spectrum. This review aims to demonstrate the recent progress in the synthesis, properties and photocatalytic applications of CQDs, particularly highlighting the fundamental multifaceted roles of CQDs in photoredox processes. Furthermore, we discuss the challenges and future direction of CQD-based materials in this booming research field, with a perspective toward the ultimate achievement of highly efficient and long-term stable CQD-based photocatalysts.
The recent progress in the synthesis, properties and photocatalytic applications of carbon quantum dots (CQDs) has been elaborately demonstrated, and some perspectives on the challenges and opportunities for future exploration in this arena are discussed.
The efficiency of solar hydrogen evolution closely depends on the multiple electrons accumulation on the catalytic center for two‐electron‐involved water reduction. Herein, we report an effective ...approach to enable broadband light absorption and unidirectional electron flow for efficiently accumulating electrons at active sites for hydrogen evolution by rationally engineering the nanostructure of Pt nanoparticles (NPs), TiO2, and SiO2 support. In addition to Schottky‐junction‐driven electron transfer from TiO2 to Pt, Pt NPs also produce hot electrons by recycling the scattered visible and near‐infrared (vis‐NIR) light of the support. Unidirectional electron flow to active sites is realized by tuning the components spatial distribution. These features collectively accumulate multiple electrons at catalytic Pt sites, thereby affording enhanced activity toward hydrogen evolution under simulated sunlight.
Broadband light harvesting and unidirectional electron flow are integrated by rationally engineering a nanostructure of Pt nanoparticles, TiO2, and SiO2 support. The composite nanostructure efficiently accumulates electrons at active sites for enhanced solar hydrogen generation.
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We report the assembly of nanosized ZnS particles on the 2D platform of a graphene oxide (GO) sheet by a facile two-step wet chemistry process, during which the reduced graphene oxide (RGO, also ...called GR) and the intimate interfacial contact between ZnS nanoparticles and the GR sheet are achieved simultaneously. The ZnS–GR nanocomposites exhibit visible light photoactivity toward aerobic selective oxidation of alcohols and epoxidation of alkenes under ambient conditions. In terms of structure–photoactivity correlation analysis, we for the first time propose a new photocatalytic mechanism where the role of GR in the ZnS–GR nanocomposites acts as an organic dye-like macromolecular “photosensitizer” for ZnS instead of an electron reservoir. This novel photocatalytic mechanism is distinctly different from all previous research on GR–semiconductor photocatalysts, for which GR is claimed to behave as an electron reservoir to capture/shuttle the electrons photogenerated from the semiconductor. This new concept of the reaction mechanism in graphene–semiconductor photocatalysts could provide a new train of thought on designing GR-based composite photocatalysts for targeting applications in solar energy conversion, promoting our in-depth thinking on the microscopic charge carrier transfer pathway connected to the interface between the GR and the semiconductor.
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Photocatalytic epoxide alcoholysis through C−O bond cleavage and formation has emerged as an alternative to synthesizing anti‐tumoral pharmaceuticals and fine chemicals. However, the lack of crucial ...evidence to interpret the interaction between reactants and photocatalyst surface makes it challenging for photocatalytic epoxide alcoholysis with both high activity and regioselectivity. In this work, we report the hierarchical ZnIn2S4@CdS photocatalyst for epoxide alcoholysis with high regioselectivity nearly 100 %. Mechanistic studies unveil that the precise activation switch on exposed Zn acid sites for C−O bond polarization and cleavage has a critical significance for achieving efficient photocatalytic performance. Furthermore, the establishment of Z‐scheme heterojunction facilitates the interface charge separation and transfer. Remarkably, the underlying regioselective photocatalytic reaction pathway has been distinctly revealed.
Hollow CdS nanocages wrapped in ultrathin ZnIn2S4 nanosheets were synthesized to form the hierarchical photocatalyst ZnIn2S4@CdS. Surface‐exposed Zn acid centers and the Z‐Scheme pathway between ZnIn2S4 and CdS promote the polarization of epoxide molecules and interfacial charge transfer, leading to photoredox‐catalyzed regioselective alcoholysis of epoxides.
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The nanocomposites of TiO2−graphene (TiO2−GR) have been prepared via a facile hydrothermal reaction of graphene oxide and TiO2 in an ethanol−water solvent. We show that such a TiO2−GR nanocomposite ...exhibits much higher photocatalytic activity and stability than bare TiO2 toward the gas-phase degradation of benzene, a volatile aromatic pollutant in air. By investigating the effect of different addition ratios of graphene on the photocatalytic activity of TiO2−GR systematically, we find that the higher weight ratio in TiO2−GR will decrease the photocatalytic activity. Analogous phenomenon is also observed for the liquid-phase degradation of dyes over TiO2−GR. In addition, the key features for TiO2−GR including enhancement of adsorptivity of pollutants, light absorption intensity, electron−hole pairs lifetime, and extended light absorption range have also been found in the composite of TiO2 and carbon nanotubes (TiO2−CNT). These strongly manifest that TiO2−GR is in essence the same as other TiO2−carbon (carbon nanotubes, fullerenes, and activated carbon) composite materials on enhancement of photocatalytic activity of TiO2, although graphene by itself has unique structural and electronic properties. Notably, this key fundamental question remains completely unaddressed in a recent report ( ACS Nano 2010, 4, 380 ) regarding liquid-phase degradation of dyes over the TiO2−GR photocatalyst. Thus, we propose that TiO2−GR cannot provide truly new insights into the fabrication of TiO2−carbon composite as high-performance photocatalysts. It is hoped that our work could avert the misleading message to the readership, hence offering a valuable source of reference on fabricating TiO2−carbon composites for their application as a photocatalyst in the environment cleanup.
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Probing the dynamic evolution of catalyst structure and chemical state under operating conditions is highly important for investigating the reaction mechanism of catalysis more in depth, which in ...turn advances the rational design of redox catalysis in using renewable energy to produce fuels. Herein, the evolution of atomically dispersed Cu species supported by mesoporous TiO2 (mTiO2) during the in situ photocatalytic reduction of CO2 with H2O to valuable solar fuels has been reported. The results unveil that the initial atomically dispersed Cu(II) undergoes reduction to Cu(I) and ultimately to Cu(0); the Cu(I)/Cu(0) mixture is proposed to be more effective for CH4 formation. In addition, the enhanced CO2 adsorption ability benefited from the structural advantage of mTiO2 and the elevated charge carrier transfer synergistically contributes to the CO2 photoreduction. It is anticipated that this work would guide the rational design of Cu-based light-harvesting catalysts for artificial CO2 reduction to value-added feedstocks and inspire further interest in using in situ techniques to study the structure–activity interplay of photocatalysts under operating reaction conditions.
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