Ag and Cu Nanoparticles Synergistically Enhance Photocatalytic CO2 Reduction Activity of B Phase TiO2

TiO2-Phase-Mediated Size Effect of Rh Nanoparticles on Photothermal Catalytic CO2 Hydrogenation

Photothermal catalytic CO2 hydrogenation on TiO2-based catalysts has drawn extensive attention. However, few reports have focused on the impact of particle size of the active sites by altering TiO2 crystal phase on the CO2 hydrogenation activity. Herein, we successfully regulated Rh nanoparticle size by adjusting the crystal phases of TiO2 at different calcination temperatures and obtained impressive photothermal catalytic CO2 hydrogenation performance. Notably, the anatase-phase TiO2 loaded with Rh nanoparticles achieved a CH4 production rate of 2.7 mmol h-1 with nearly 100 % selectivity and a single-pass CO2 conversion rate of 69.4 %. Given the anatase-phase TiO2 is more favorable for the presence of surface hydroxyl groups and oxygen vacancies, which can facilitate the distribution of Rh cations, Rh nanoparticles on the anatase-phase TiO2 exhibited the smallest sizes. Small Rh particle size further enhanced CO2 adsorption and activation, leading to high photothermal CO2 hydrogenation performance. Furthermore, the optimized Rh nanoparticle-loaded anatase-phase TiO2 catalyst exhibited high structural stability and resistance to coke accumulation, maintaining stability during long-term performance tests. This work investigated the particle size effect of active sites adjusted by crystal phase of light-harvesting materials on the photothermal catalytic performance, providing guidance for the preparation of effective catalysts for CO2 hydrogenation to CH4.

Structurally Asymmetric Ni-O-Mn Node in Metal-Organic Layers on Carbon Nitride Support for CO2 Photoreduction

The Jahn-Teller (J-T) effect-induced lattice distortion presents an advantageous approach to tailor the electronic structure and CO2 adsorption properties of catalytic centers, consequently conferring desirable photocatalytic CO2 reduction activity and selectivity. Nevertheless, achieving precise J-T distortion control over catalytic sites to enhance CO2 adsorption/activation and target-product desorption remains a formidable challenge. In this work, we successfully induced J-T lattice distortion in neighboring Ni sites by exchanging high-spin Mn2+ into Ni-O-Ni nodes. EXAFS results and DFT simulations revealed that the highly asymmetric Ni-O-Mn nodes induced structural contraction (shortened Ni-O bonds) in the adjacent Ni-O lattice. The magnetic hysteresis loop (M-H) confirmed that the introduction of Mn2+ increased the number of spin electrons, thereby increasing the magnetization intensity. The spin mismatch between photogenerated electrons and holes suppressed charge recombination. Significantly, the d orbitals of the Ni sites in the Ni-O-Mn nodes exhibited strong orbital hybridization with the p orbitals of CO2, as evidenced by the enhanced d-p orbital overlap, facilitating rapid CO2 adsorption and activation. Consequently, the sample featuring lattice-mismatched Ni-O-Mn nodes exhibited an 8.79-fold enhancement in CO production rate compared to the Ni-O-Ni nodes, in the absence of cocatalysts and sacrificial reagents.

Plasmon-enhanced photocatalysis: New horizons in carbon dioxide reduction technologies

The urgent need for transition to renewable energy is underscored by a nearly 50 % increase in atmospheric carbon dioxide levels over the past century. The combustion of fossil fuels for energy production, transportation, and industrial activities are the main contributors to carbon dioxide emissions in the anthroposphere. Present approaches to reducing carbon emissions are proving inefficient, thereby accentuating the relevance of carbon dioxide photocatalysis in combating climate change - one of the critical issues of public concern. This process uses sunlight to convert carbon dioxide into valuable products, e.g., clean fuels, effectively reducing the carbon footprint and offering a sustainable use of carbon dioxide. In this context, plasmonic nanoparticles such as gold, silver, and copper play a pivotal role due to their proficiency in absorbing a wide range of light spectra, thereby effectively generating the necessary electrons and holes for the degradation of pollutants and surpassing the capabilities of traditional semiconductor catalysts. This review meticulously examines the latest advancements in plasmon-based carbon dioxide photocatalysis, scrutinizing the methodologies, characterizations, and experimental outcomes. The critical evaluation extends to exploring adjustments in the dimensional and morphological aspects of plasmonic nanoparticles, complemented by the incorporation of stabilizing agents, which may offer additional benefits. Furthermore, the review includes a thorough analysis of production rates and quantum yields based on different plasmonic materials and nanoparticle shapes and sizes, enriching the ongoing discourse on effective solutions in the field. Thus, our work emphasizes the pivotal role of plasmon-based photocatalysts in reducing carbon dioxide, investigating both the merits and challenges associated with integrating this emerging technology into climate change mitigation efforts.

Boosted C-C coupling with Cu-Ag alloy sub-nanoclusters for CO2-to-C2H4 photosynthesis

The selective photocatalytic conversion of CO2 and H2O to high value-added C2H4 remains a great challenge, mainly attributed to the difficulties in C-C coupling of reaction intermediates and desorption of C2H4* intermediates from the catalyst surface. These two key issues can be simultaneously overcome by alloying Ag with Cu which gives enhanced activity to both reactions. Herein, we developed a facile stepwise photodeposition strategy to load Cu-Ag alloy sub-nanoclusters (ASNCs) on TiO2 for CO2 photoreduction to produce C2H4. The optimized catalyst exhibits a record-high C2H4 formation rate (1110.6 ± 82.5 μmol g-1 h-1) with selectivity of 49.1 ± 1.9%, which is an order-of-magnitude enhancement relative to current work for C2H4 photosynthesis. The in situ FT-IR spectra combined with DFT calculations reveal the synergistic effect of Cu and Ag in Cu-Ag ASNCs, which enable an excellent C-C coupling capability like Ag and promoted C2H4* desorption property like Cu, thus advancing the selective and efficient production of C2H4. The present work provides a deeper understanding on cluster chemistry and C-C coupling mechanism for CO2 reduction on ASNCs and develops a feasible strategy for photoreduction CO2 to C2 fuels or industrial feedstocks.

Bimetallic TiO2 Nanoparticles for Lignin-Based Model Compounds Valorization by Integrating an Optocatalytic Flow-Microreactor

The challenge of improving the activity of TiO₂ by modifying it with metals and using it for targeted applications in microreactor environments is an active area of research. Recently, microreactors have emerged as successful candidates for many photocatalytic reactions, especially for the selective oxidation process. The current work introduces ultrasound-assisted catalyst deposition on the inner walls of a perfluoro-alkoxy alkane (PFA) microtube under mild conditions. We report Cu-Au/TiO₂ and Fe-Au/TiO₂ nanoparticles synthesized using the sol-gel method. The obtained photocatalysts were thoroughly characterized by UV-Vis diffuse-reflectance spectroscopy (DRS), high-resolution scanning electron microscopy (HR-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and N₂ physisorption. The photocatalytic activity under UV (375 nm) and visible light (515 nm) was estimated by the oxidation of lignin-based model aromatic alcohols in batch and fluoropolymer-based flow systems. The bimetallic catalyst exhibited improved photocatalytic selective oxidation. Herein, four aromatic alcohols were individually investigated and compared. In our experiments, the alcohols containing hydroxy and methoxy groups (coniferyl and vanillin alcohol) showed high conversion (93% and 52%, respectively) with 8% and 17% selectivity towards their respective aldehydes, with the formation of other side products. The results offer an insight into ligand-to-metal charge transfer (LMCT) complex formation, which was found to be the main reason for the activity of synthesized catalysts under visible light.