Accelerated Water Oxidation Kinetics Triggered by Supramolecular Porphyrin Nanosheet for Robust Visible-Light-Driven CO2 Reduction

Regulating Local Electron Density of Cyano Sites in Graphitic Nitride Carbon by Giant Internal Electric Field for Efficient CO2 Photoreduction to Hydrocarbons

Selective photocatalytic CO2 reduction to high-value hydrocarbons using graphitic carbon nitride (g-C3N4) polymer holds great practical significance. Herein, the cyano-functionalized g-C3N4 (CN-g-C3N4) with a high local electron density site is successfully constructed for selective CO2 photoreduction to CH4 and C2H4. Wherein the potent electron-withdrawing cyano group induces a giant internal electric field in CN-g-C3N4, significantly boosting the directional migration of photogenerated electrons and concentrating them nearby. Thereby, a high local electron density site around its cyano group is created. Moreover, this structure can also effectively promote the adsorption and activation of CO2 while firmly anchoring *CO intermediates, facilitating their subsequent hydrogenation and coupling reactions. Consequently, using H2O as a reducing agent, CN-g-C3N4 achieves efficient and selective photocatalytic CO2 reduction to CH4 and C2H4 activity, with maximum rates of 6.64 and 1.35 µmol g-1 h-1, respectively, 69.3 and 53.8 times higher than bulk g-C3N4 and g-C3N4 nanosheets. In short, this work illustrates the importance of constructing a reduction site with high local electron density for efficient and selective CO2 photoreduction to hydrocarbons.

Matched Redox Kinetics on Triazine-Based Carbon Nitride/Ni(OH)2 for Stoichiometric Overall Photocatalytic CO2 Conversion

Mismatched reaction kinetics of CO2 reduction and H2O oxidation is the main obstacle limiting the overall photocatalytic CO2 conversion. Here, a molten salt strategy is used to construct tubular triazine-based carbon nitride (TCN) with more adsorption sites and stronger activation capability. Ni(OH)2 nanosheets are then grown over the TCN to trigger a proton-coupled electron transfer for a stoichiometric overall photocatalytic CO2 conversion via "3CO2 + 2H2O = CH4 + 2CO + 3O2." TCN reduces the energy barrier of H2O dissociation to promote H2O oxidation to O2 and supply sufficient protons to Ni(OH)2, whereby the CO2 conversion is accelerated due to the enhanced proton-coupled electron transfer process enabled by the sufficient proton supply from TCN. This work highlights the importance of matching the reaction kinetics of CO2 reduction and H2O oxidation by proton-coupled electron transfer on stoichiometric overall photocatalytic CO2 conversion.

Elucidating protonation pathways in CO2 photoreduction using the kinetic isotope effect

The surge in anthropogenic CO2 emissions from fossil fuel dependence demands innovative solutions, such as artificial photosynthesis, to convert CO2 into value-added products. Unraveling the CO2 photoreduction mechanism at the molecular level is vital for developing high-performance photocatalysts. Here we show kinetic isotope effect evidence for the contested protonation pathway for CO2 photoreduction on TiO2 nanoparticles, which challenges the long-held assumption of electron-initiated activation. Employing isotopically labeled H2O/D2O and in-situ diffuse reflectance infrared Fourier transform spectroscopy, we observe H+/D+-protonated intermediates on TiO2 nanoparticles and capture their inverse decay kinetic isotope effect. Our findings significantly broaden our understanding of the CO2 uptake mechanism in semiconductor photocatalysts.

Recent Progress in Porphyrin/g-C3N4 Composite Photocatalysts for Solar Energy Utilization and Conversion

Transforming solar energy into chemical bonds is a promising and viable way to store solar energy. Porphyrins are natural light-capturing antennas, and graphitic carbon nitride (g-C₃N₄) is an effective, artificially synthesized organic semiconductor. Their excellent complementarity has led to a growing number of research papers on porphyrin/g-C₃N₄ hybrids for solar energy utilization. This review highlights the recent progress in porphyrin/g-C₃N₄ composites, including: (1) porphyrin molecules/g-C₃N₄ composite photocatalysts connected via noncovalent or covalent interactions, and (2) porphyrin-based nanomaterials/g-C₃N₄ composite photocatalysts, such as porphyrin-based MOF/g-C₃N₄, porphyrin-based COF/g-C₃N₄, and porphyrin-based assembly/g-C₃N₄ heterojunction nanostructures. Additionally, the review discusses the versatile applications of these composites, including artificial photosynthesis for hydrogen evolution, CO₂ reduction, and pollutant degradation. Lastly, critical summaries and perspectives on the challenges and future directions in this field are also provided.