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Biomass, a naturally abundant, sustainable and clean resource has great potential as an alternative to replace the limited fossil feedstock for value‐added chemicals and fuels. Biomass with abundant reductive functional groups could theoretically act as electron donor to consume photogenerated holes and/or active free radicals. Biomass photoreforming over semiconductor photocatalysts using solar light as energy input attracts much attention in this context. However, biomass photoreforming still suffers low conversion efficiency and product selectivity due to its structural complexity, poor solubility and unclear reaction mechanism. Owing to the advanced features of mass diffusion of biomass derivatives and adjustable surface properties, hierarchically porous photocatalysts with desired active sites at each length scale of porosity have shown their superiority in boosting the conversion efficiency and selectivity of biomass photoreforming. Herein, a critical review is presented on selective biomass photoreforming for simultaneous H2 and value‐added chemicals co‐production on hierarchically porous photocatalysts. The fundamentals of biomass photoreforming and current bottleneck of biomass valorization by photocatalytic process are presented and analyzed. The rational photocatalyst design with hierarchically porous structure to improve the biomass conversion and product selectivity by boosting mass transfer is highlighted. Finally the challenges and opportunities for photocatalytic biomass valorization are presented in the perspective ssection. [ABSTRACT FROM AUTHOR]

Photorefining of biomass and its derivatives to value-added chemicals is an alternative solution to address the global energy shortage and environmental issues. Herein, efficient and selective oxidation of 5-hydroxymethylfurfural (HMF, 91.1% conversion) to 2,5-diformylfuran (DFF, 99.4% selectivity) is demonstrated by visible light-driven photocatalysis over cocatalyst-free ZnIn2S4 nanosheets with crystal facet engineering. The spatial accumulation of photogenerated electrons and holes on the (110) and (102) crystal facets triggers a two-electron oxygen reduction reaction (2e-ORR) for H2O2 generation and HMF oxidation into DFF, respectively. The severe attenuation of photostability is caused by the irreversible photocorrosion of Zn–S with the formation of Zn–O chemical bonds by the formation of ˙OH from the in situ decomposition of H2O2. Spontaneous substitution of oxygen with sulfur has been proven to efficiently improve the photostability of ZnIn2S4. This present work provides insights into improving the durability of ZnIn2S4 and sheds new light on biomass valorization via photorefinery. [ABSTRACT FROM AUTHOR]

The electrochemical transformation of biomass to high value‐added products is attractive. Herein, Cu sulfide‐mediated in‐situ synthesis of Cu oxide was achieved for efficient electro‐oxidation of biomass derived 5‐hydroxymethylfurfural (HMF) to 2,5‐furandicarboxylic acid (FDCA). The copper foam‐supported Cu sulfide (Cu−S/CF) was in‐situ converted to Cu oxide during the electro‐oxidation process. The in‐situ formed Cu oxide presented high HMF conversion, FDCA yield, and faradaic efficiency in 1 m KOH with HMF concentration up to 100 mm. The oxidation of HMF on Cu oxide started with the formation of high‐valence Cu species with the assistance of OH−, which then oxidized HMF spontaneously. An anion exchange membrane (AEM) electrolyzer with Cu−S/CF as the anode was assembled to continuously produce FDCA with H2 generation at the cathode. The AEM electrolyzer ran stably for 60 h with FDCA content higher than 85 % at a cell voltage between 1.50 and 1.60 V. [ABSTRACT FROM AUTHOR]

Photocatalytic hydrogen production is a promising route to the provision of sustainable and green energy. However, the excess addition of traditional electron donors as the sacrificial agents to consume photogenerated holes greatly reduces the feasibility of this approach for commercialization. Herein, considering the abundant hydroxyl groups in cellulose, the major component of biomass, we adopted glucose (a component unit of cellulose), cellobiose (a structure unit of cellulose) and dissolving pulp (a pretreated cellulose) as electron donors for photocatalytic hydrogen production over a TiO2-Au-CdS material. The well-designed ternary TiO2-Au-CdS possesses a hierarchical three-dimensional ordered macroporous (3DOM) structure, which not only benefits light harvesting but can also facilitate mass diffusion to boost the reaction kinetics. As expected, the fabricated photocatalyst exhibits considerable hydrogen production from glucose (645.1 μmol·h−1·g−1), while the hydrogen production rates gradually decrease with the increased complexity in structure from cellobiose (273.9 μmol·h−1·g−1) to dissolving pulp (79.7 μmol·h−1·g−1). Other gaseous components such as CO and CH4 are also produced, indicating the partial conversion of biomass during the photoreforming process. This work demonstrates the feasibility of sustainable hydrogen production from biomass by photoreforming with a rational photocatalyst design. [ABSTRACT FROM AUTHOR]

Photoreforming of biomass to value-added chemicals and fuels is a chemical approach to extract photosynthetically-trapped energy in complex biomolecules which otherwise disintegrate naturally in the environment. Designing precise photocatalytic materials that can selectively break the sturdy, nature-designed biomass with multiplex chemical composition/bonding and inaccessible sites is central to deploying this technology. Polymeric carbon nitride (CN) comprised of a 2D network of condensed heptazine/triazine (C6N7/C3N3) core has shown great promise for photoreforming of biomass derivatives due to intriguing physicochemical and optical properties. This review comprehensively summarizes the state-of-the-art applications of CN-based photocatalysts for the conversion of lignocellulosic biomass derivatives. Various chemical and structural modifications in CN structure such as doping, surface functionalization, hybridization entailing to higher selectivity and conversion have been discussed aiming at providing valuable guidance for future CN-based materials design. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass valorization is regarded as a promising approach to alleviate energy crisis and achieve carbon neutrality. Bioactive enzymes have attracted great attention and been commonly applied for biomass valorization owing to their high selectivity and catalytic efficiency under environmentally benign reaction conditions. Same as biocatalysis, photo−/electro-catalysis also happens at mild conditions (i.e., near ambient temperature and pressure). Therefore, the combination of these different catalytic approaches to benefit from their resulting synergy is appealing. In such hybrid systems, harness of renewable energy from the photo−/electro-catalytic compartment can be combined with the unique selectivity of biocatalysts, therefore providing a more sustainable and greener approach to obtain fuels and value-added chemicals from biomass. In this review, we firstly introduce the pros/cons, classifications, and the applications of photo−/electro-enzyme coupled systems. Then we focus on the fundamentals and comprehensive applications of the most representative biomass-active enzymes including lytic polysaccharide monooxygenases (LPMOs), glucose oxidase (GOD)/dehydrogenase (GDH) and lignin peroxidase (LiP), together with other biomass-active enzymes in the photo−/electro- enzyme coupled systems. Finally, we propose current deficiencies and future perspectives of biomass-active enzymes to be applied in the hybrid catalytic systems for global biomass valorization. • Lignocellulosic biomass valorization is an effective approach to alleviate energy crisis and achieve carbon neutrality. • The photo−/electro-enzyme coupled systems are more sustainable and greener to obtain fuels and value-added chemicals. • The state-of-the-art research progress of biomass-active enzymes in bio-photo/electro hybrid systems have been discussed. • Biomass-active enzymes hold great potentials in bio-photo/electro hybrid catalytic systems for global biomass valorization. [ABSTRACT FROM AUTHOR]

Herein, we report on a 3D MoS x /Zn 3 In 2 S 6 nanoflower for efficient photocatalytic selective oxidation of benzyl alcohol (BA) to benzaldehyde (BAD) (100 % conversion and 96.18 % selectivity in 1 h) with simultaneous H 2 coproduction. The experimental results, in combination with DFT calculations, reveal that MoS x not only endows photothermal properties of the composite but also acts as an electron transport bridge promoting photogenerated charge transfer, which in turn promotes the extraction of C α -H to produce H 2. MoS x /Zn 3 In 2 S 6 also demonstrated strong ability to selectively oxidize a lignin model compound, 2-phenoxy-1-phenylethanol (PP-ol), to 2-phenoxyacetophenone (PP-one) with H 2 coproduction. When incorporated with peroxydisulfate (PDS) for organic pollutant degradation, the MoS x /Zn 3 In 2 S 6 showed exceptional efficiency with 99.51 % removal of 2-mercaptobenzothiazole (MBT) in 20 min. This is attributed to Mo4+/Mo5+/Mo6+ redox interactions that activate PDS and promote generation of reactive oxygen radicals. This work provides a feasible strategy to design photocatalyst for biomass valorization and organic pollutants degradation. [Display omitted] • MoS x endows the photothermal properties of 3D MoS x /Zn 3 In 2 S 6 nanoflower. • DFT provides evidence and guidance for the electrons transfer pathway of MoS x. • MoS x promotes the extraction of C α -H to produce H 2. • 3D MoS x /Zn 3 In 2 S 6 nanoflower acts efficiently for real biomass photoreforming. • The Mo4+/Mo5+/Mo6+ redox interactions enhance the degradation of MBT. [ABSTRACT FROM AUTHOR]

Biomass photoreforming represents an attractive and promising approach to produce renewable and sustainable chemicals and fuels. A growing number of investigations aim to selectively attain valuable chemicals and high-quality fuels from the abundant biomass via UV/visible-light-driven photocatalysis. However, a cost-effective conversion process for biomass valorization to selective production of valuable chemicals and fuels is still difficult to achieve. This review mainly focuses on photocatalyst development and the effect of experimental conditions for selectivity enhancement of heterogeneous photocatalytic transformations. Photocatalyst development with high selectivity aims to avoid the formation of highly oxidative radicals such as •OH that are widely regarded as nonselective species. Electronic band structure and photochemical properties can be tailored to regulate the reaction pathway and selectively produce the desired chemicals via morphology modification, doping, co-catalyst metal loading, and the formation of special crystal facets and phase. The reaction conditions, such as solvent, pH, atmosphere, influence the interaction between photocatalyst and substrate, reaction kinetics, and the solubility of reactive species. The optimization of external factors can improve the reactivity and selectivity. In addition, the utilization of protection chemicals could effectively prevent the formation of destructive radical species and the mineralization of preferred products, thus enhancing the selectivity and productivity. This review provides insights into the photocatalytic upgrading of various biomass substrates to fine chemicals and fuels with an attempt to elucidate the mechanisms involved in the process of biomass photoconversion. Future perspectives and challenges for selective production of valuable chemicals and fuels from biomass photo-upgrading are discussed. [Display omitted] • Insights into photocatalyst and reaction conditions for selectivity enhancement. • Photocatalyst modifications to regulate photochemical properties and the pathway. • Discussion on the effects of external conditions on the reactivity and selectivity. • The selective photocatalytic conversion of biomass and its various derivatives. • Biomass photoreforming as a meaningful approach to valuable products and fuels. [ABSTRACT FROM AUTHOR]