The conversion and storage of solar energy to chemical energy via artificial photosynthesis holds significant potential for optimizing the energy situation and mitigating the global warming effect. Photocatalytic water splitting utilizing particulate semiconductors offers great potential for the production of renewable hydrogen, while this cross-road among biology, chemistry, and physics features a topic with fascinating interdisciplinary challenges. Progress in photocatalytic water splitting has been achieved in recent years, ranging from fundamental scientific research to pioneering scalable practical applications. In this review, we focus mainly on the recent advancements in terms of the development of new light-absorption materials, insights and strategies for photogenerated charge separation, and studies towards surface catalytic reactions and mechanisms. In particular, we emphasize several efficient charge separation strategies such as surface-phase junction, spatial charge separation between facets, and polarity-induced charge separation, and also discuss their unique properties including ferroelectric and photo-Dember effects on spatial charge separation. By integrating time- and space-resolved characterization techniques, critical issues in photocatalytic water splitting including photoinduced charge generation, separation and transfer, and catalytic reactions are analyzed and reviewed. In addition, photocatalysts with state-of-art efficiencies in the laboratory stage and pioneering scalable solar water splitting systems for hydrogen production using particulate photocatalysts are presented. Finally, some perspectives and outlooks on the future development of photocatalytic water splitting using particulate photocatalysts are proposed.

Recent advances and perspectives for solar-driven water splitting using particulate photocatalysts.

Metallosphaera sedula (Sulfolobales, Crenarchaeota) uses the 3-hydroxypropionate/4-hydroxybutyrate cycle for autotrophic carbon fixation. In this pathway, acetyl-coenzyme A (CoA) and succinyl-CoA are the only intermediates that can be considered common to the central carbon metabolism. We addressed the question of which intermediate of the cycle most biosynthetic routes branch off. We labeled autotrophically growing cells by using 4-hydroxy[1-14C]butyrate and [1,4-13C1]succinate, respectively, as precursors for biosynthesis. The labeling patterns of protein-derived amino acids verified the operation of the proposed carbon fixation cycle, in which 4-hydroxybutyrate is converted to two molecules of acetyl-CoA. The results also showed that major biosynthetic flux does not occur via acetyl-CoA, except for the formation of building blocks that are directly derived from acetyl-CoA. Notably, acetyl-CoA is not assimilated via reductive carboxylation to pyruvate. Rather, our data suggest that the majority of anabolic precursors are derived from succinyl-CoA, which is removed from the cycle via oxidation to malate and oxaloacetate. These C4 intermediates yield pyruvate and phosphoenolpyruvate (PEP). Enzyme activities that are required for forming intermediates from succinyl-CoA were detected, including enzymes catalyzing gluconeogenesis from PEP. This study completes the picture of the central carbon metabolism in autotrophic Sulfolobales by connecting the autotrophic carbon fixation cycle to the formation of central carbon precursor metabolites.

Labeling and Enzyme Studies of the Central Carbon Metabolism in Metallosphaera sedula

Plastic waste remains a global challenge due to the massive amounts being produced without satisfactory treatment technologies for recycling and upcycling. Photocatalytic processes are emerging as green and promising approaches to upcycle plastics into value‐added products under mild conditions using sunlight as the energy source. In this review, the recent advances in plastic conversion through photocatalysis have been comprehensively summarized. Special emphasis is placed on the photocatalytic mechanism and the selective CC and CH bond transformations of plastics to access fuels, chemicals, and materials. Finally, the challenges and the perspectives on establishing a new paradigm toward a sustainable and circular plastic economy are also put forward.

Photocatalytic Conversion of Plastic Waste: From Photodegradation to Photosynthesis

Paired electroreduction and electrooxidation of organics with water as a feedstock to produce value-added chemicals is meaningful. A comprehensive understanding of reaction mechanism is critical for the catalyst design and relative area development. Here, we have systematically studied the mechanism of the paired electroreduction and electrooxidation of organics on Fe-Mo-based phosphide heterojunctions. It is shown that active H* species for organic electroreduction originate from water. As for organic electrooxidation, among various oxygen species (OH*, OOH*, and O*), OH* free radicals derived from the first step of water dissociation are identified as active species. Furthermore, explicit reaction pathways and their paired advantages are proposed based on theoretical calculations. The paired electrolyzer powered by a solar cell shows a low voltage of 1.594 V at 100 mA cm-2, faradaic efficiency of ≥99%, and remarkable cycle stability. This work provides a guide for sustainable synthesis of various value-added chemicals via paired electrocatalysis. 

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Unraveling the mechanism for paired electrocatalysis of organics with water as a feedstock

Solid state synthesis and characterization of a triple chain calcium(II) coordination polymer showing two different bridging 4-nitrobenzoate coordination modes

Due to the depletion of fossil sources, it is imperative to develop a sustainable and carbon-neutral biorefinery for supporting the fuel and chemical supply in modern society. Lignin, the only renewable aromatic source, is still an underutilized component in lignocellulose. Very recently, it has been found that hydrogenolysis is a promising technology for lignin valorization. However, high-pressure H2 is necessary during lignin hydrogenolysis, resulting in safety problems. Furthermore, H2 is mainly produced from steam reforming of fossil sources in industry, which makes the conversion of renewable lignin unsustainable and costly. Plentiful aliphatic hydroxyl and methoxy groups exist in native lignin and offer a renewable alternative to H2, and can be hydrogen sources for the depolymerization and upgradation of lignin via the intramolecular catalytic transfer hydrogenation. The hydrogen source in situ generated from lignin is a type of green hydrogen, decreasing the carbon footprint. The purpose of this review is to provide a summary and perspective of lignin valorization via self-transfer hydrogenolysis, mainly focusing on a comprehensive understanding of the mechanism of catalytic self-transfer hydrogenolysis at the molecular level and developing highly effective catalytic systems. Moreover, some opportunities and challenges within this attractive field are given to discuss future research directions.

Catalytic self-transfer hydrogenolysis of lignin with endogenous hydrogen: road to the carbon-neutral future.

Radical generation and fate control for photocatalytic biomass conversion

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Photocatalytic conversion of waste plastics to low carbon number organic products

In the title coordination polymer, [Ca(C7H2N2O7)(H2O)]n, the CaII atom is seven-coordinate by six O atoms from four 3,5-dinitro­salicylatate ligands and one water mol­ecule, and displays a distorted penta­gonal–bipyramidal geometry. Centrosymmetrically related dinuclear calcium units with a Ca⋯Ca separation of 3.8665 (8)A form layers which are self-assembled into a three-dimensional network by inter­molecular O—H⋯O hydrogen bonds.

Chao-Hua Zhang

Papers

Catalytic self-transfer hydrogenolysis of lignin with endogenous hydrogen: road to the carbon-neutral future.

Radical generation and fate control for photocatalytic biomass conversion

Photocatalytic conversion of waste plastics to low carbon number organic products

Poly[aqua(μ3-3,5-dinitrosalicylato)calcium(II)]

Single site Ni(II) anchored tetraethylene pentamine for enhancing CO2 kinetic adsorption rate and long-term cyclic stability

Chao-Hua Zhang

Papers

Catalytic self-transfer hydrogenolysis of lignin with endogenous hydrogen: road to the carbon-neutral future.

Radical generation and fate control for photocatalytic biomass conversion

Photocatalytic conversion of waste plastics to low carbon number organic products

Poly[aqua­(μ3-3,5-dinitro­salicylato)calcium(II)]

Single site Ni(II) anchored tetraethylene pentamine for enhancing CO2 kinetic adsorption rate and long-term cyclic stability

Poly[aqua(μ3-3,5-dinitrosalicylato)calcium(II)]