Photoenzymatic Catalytic Cascade System of a Pyromellitic Diimide/g-C3N4 Heterojunction to Efficiently Regenerate NADH for Highly Selective CO2 Reduction toward Formic Acid

Constructing a CdS QDs/silica gel composite with high photosensitivity and prolonged recyclable operability for enhanced visible-light-driven NADH regeneration

Visible-light-driven nicotinamide adenine dinucleotide (NADH) regeneration is one of the most effective measures, and cadmium sulfide (CdS) materials are typically used as low-cost photocatalysts. The CdS photocatalysts, however, still suffer from low regeneration efficiency and poor cycle stability. In this work, the CdS quantum dots (QDs) less than 10 nm embedded onto silica gel (CdS QDs/Silica gel) were constructed for visible-light-driven NADH regeneration by a successive ionic layer adsorption reaction and ball milling method. Results demonstrate that the photosensitivity of the CdS QDs/Silica gel composite was 31 times higher than that of the bulk CdS. Moreover, the conduction band (CB) edge of the CdS QDs/Silica gel composite is -1.34 eV, which is more negative 0.5 eV than that of the bulk CdS. The obtained CdS QDs/Silica gel composites showed the highest NADH regeneration yields of 68.8% under visible-light (LED, 420 nm) illumination and can be reused for over 40 cycles. Finally, the bioactivity of NADH toward enzyme catalysis is further confirmed by the hydrogenation of benzaldehyde to benzyl alcohol catalyzed with an alcohol dehydrogenase as enzyme catalysis.

Preparation of Structure Vacancy Defect Modified Diatomic-Layered g-C3 N4 Nanosheet with Enhanced Photocatalytic Performance

Structure self-modification of graphitic carbon nitride (g-C3 N4 ) without the assistance of other species has attracted considerable attention. In this study, the structure vacancy defect modified diatomic-layered g-C3 N4 nanosheet (VCN) is synthesized by thermal treatment of bulk g-C3 N4 in a quartz tube with vacuum atmosphere that will generate a pressure-thermal dual driving force to boost the exfoliation and formation of structure vacancy for g-C3 N4 . The as-prepared VCN possesses a large specific surface area with a rich pore structure to provide more active centers for catalytic reactions. Furthermore, the as-formed special defect level in VCN sample can generate a higher exciton density at photoexcitation stage. Meanwhile, the photogenerated charges will rapidly transfer to VCN surface due to the greatly shortened transfer path resulting from the ultrathin structure (≈1.5 nm), which corresponds to two graphite carbon nitride atomic layers. In addition, the defect level alleviates the drawback of enlarged bandgap caused by the quantum size effect of nano-scaled g-C3 N4 , resulting in a well visible-light utilization. As a result, the VCN sample exhibits an excellent photocatalytic performance both in hydrogen production and photodegradation of typical antibiotics.

Development of an Integrated System for Highly Selective Photoenzymatic Synthesis of Formic Acid from CO2

Herein, a Zr-based dual-ligand MOFs with pre-installed Rh complex was employed for NADH regeneration in situ and also used for immobilization of formic acid dehydrogenase (FDH) in order to realize a highly efficient CO₂ fixation system. Then, based on the detailed investigations into the photochemical and electrochemical properties, it is demonstrated that the introduction of the photosensitive meso-tetra(4-carboxyphenyl) porphin (TCPP) ligands increased the catalytic active sites and improved photoelectric properties. Furthermore, the electron mediator Rh complex, anchored on the zirconium-based dual-ligand MOFs, enhanced the efficiency of electron transfer efficiency and facilitated the separation of photogenerated electrons and holes. Compared with UiO-66-NH₂ , Rh-H₂ TCPP-UiO-66-NH₂ exhibits an optimized valence band structure and significantly improved photocatalytic activity for NAD⁺ reduction, resulting the synthesis of formic acid from CO₂ increased from 150 μg mL^-1 (UiO-66-NH₂ ) to 254 μg mL^-1 (Rh-H₂ TCPP-UiO-66-NH₂ ). Moreover, the assembled photocatalyst-enzyme coupled system also allows facile recycling of expensive electron mediator, enzyme, and photocatalyst.

Artificial Photoenzymatic Reduction of Carbon Dioxide to Methanol by Using Electron Mediator and Co-factorAssembled ZnIn2 S4 Nanoflowers

Increased absorption of visible light, low electron-hole recombination, and fast electron transfer are the major objectives for highly effective photocatalysts in biocatalytic artificial photosynthetic systems. In this study, a polydopamine (PDA) layer containing electron mediator, [M], and NAD⁺ cofactor was assembled on the outer surface of ZnIn₂ S₄ nanoflower, and the as-prepared nanoparticle, ZnIn₂ S₄ /PDA@poly/[M]/NAD⁺ , was used for photoenzymatic methanol production from CO₂ . Because of effective capturing of visible light, reduced distance of electron transfer, and elimination of electron-holes recombination, a high NADH regeneration of 80.7±1.43 % could be obtained using the novel ZnIn₂ S₄ /PDA@poly/[M]/NAD⁺ . In the artificial photosynthesis system, a maximum methanol production of 116.7±11.8 μm was obtained. The enzymes and nanoparticles in the hybrid bio-photocatalysis system could be easily recovered using the ultrafiltration membrane at the bottom of the photoreactor. This is due to the successful immobilization of the small blocks including the electron mediator and cofactor on the surface of the photocatalyst. The ZnIn₂ S₄ /PDA@poly/[M]/NAD⁺ photocatalyst exhibited good stability and recyclability for methanol production. The novel concept presented in this study shows great promise for other sustainable chemical productions through artificial photoenzymatic catalysis.

Recent advances in high-crystalline conjugated organic polymeric materials for photocatalytic CO2 conversion

The photocatalytic conversion of carbon dioxide (CO₂) to high-value-added fuels is a meaningful strategy to achieve carbon neutrality and alleviate the energy crisis. However, the low efficiency, poor selectivity, and insufficient product variety greatly limit its practical applications. In this regard, conjugated organic polymeric materials including carbon nitride (g-C₃N₄), covalent organic frameworks (COFs), and covalent triazine frameworks (CTFs) exhibit enormous potential owing to their structural diversity and functional tunability. Nevertheless, their catalytic activities are largely suppressed by the traditional amorphous or weakly crystalline structures. Therefore, constructing relevant high-crystalline materials to ameliorate their inherent drawbacks is an efficient strategy to enhance the photocatalytic performance of conjugated organic polymeric materials. In this review, the advantages of high-crystalline organic polymeric materials including reducing the concentration of defects, enhancing the built-in electric field, reducing the interlayer hydrogen bonding, and crystal plane regulation are highlighted. Furthermore, the strategies for their synthesis such as molten-salt, solid salt template, and microwave-assisted methods are comprehensively summarized, while the modification strategies including defect engineering, element doping, surface loading, and heterojunction construction are elaborated for enhancing their photocatalytic activities. Ultimately, the challenges and opportunities of high-crystalline conjugated organic polymeric materials in photocatalytic CO₂ conversion are prospected to give some inspiration and guidance for researchers.