Strategies to Design Efficient Silica-Supported Photocatalysts for Reduction of CO2

Direct Conversion of CO2 into Hydrocarbon Solar Fuels by a Synergistic Photothermal Catalysis

Photothermal coupling catalysis technology has been widely studied in recent years and may be a promising method for CO2 reduction. Photothermal coupling catalysis can improve chemical reaction rates and realize the controllability of reaction pathways and products, even in a relatively moderate reaction condition. It has inestimable value in the current energy and global environmental crisis. This review describes the application of photothermal catalysis in CO2 reduction from different aspects. Firstly, the definition and advantages of photothermal catalysis are briefly described. Then, different photothermal catalytic reductions of CO2 products and catalysts are introduced. Finally, several strategies to improve the activity of photothermal catalytic reduction of CO2 are described and we present our views on the future development and challenges of photothermal coupling. Ultimately, the purpose of this review is to bring more researchers’ attention to this promising technology and promote this technology in solar fuels and chemicals production, to realize the value of the technology and provide a better path for its development.

Critical Aspects of Metal-Organic Framework-Based Materials for Solar-Driven CO2 Reduction into Valuable Fuels

Photoreduction of CO2 into value-added fuels is one of the most promising strategies for tackling the energy crisis and mitigating the "greenhouse effect." Recently, metal-organic frameworks (MOFs) have been widely investigated in the field of CO2 photoreduction owing to their high CO2 uptake and adjustable functional groups. The fundamental factors and state-of-the-art advancements in MOFs for photocatalytic CO2 reduction are summarized from the critical perspectives of light absorption, carrier dynamics, adsorption/activation, and reaction on the surface of photocatalysts, which are the three main critical aspects for CO2 photoreduction and determine the overall photocatalytic efficiency. In view of the merits of porous materials, recent progress of three other types of porous materials are also briefly summarized, namely zeolite-based, covalent-organic frameworks based (COFs-based), and porous semiconductor or organic polymer based photocatalysts. The remarkable performance of these porous materials for solar-driven CO2 reduction systems is highlighted. Finally, challenges and opportunities of porous materials for photocatalytic CO2 reduction are presented, aiming to provide a new viewpoint for improving the overall photocatalytic CO2 reduction efficiency with porous materials.

All-inorganic perovskite/graphitic carbon nitride composites for CO2 photoreduction into C1 compounds under low concentrations of CO2

CsPbBr₃ is widely used in solar cells and LEDs for its excellent photoelectric properties that are also attractive for CO₂ photoreduction, but it is less used in the photocatalytic reduction of CO₂ mainly owing to its limited charge separation efficiency. To alleviate this issue, herein, all-inorganic orthorhombic CsPbBr₃ was combined with graphitic carbon nitride (g-C₃N₄) and the resultant composite (CsPbBr₃@g-C₃N₄) showed enhanced activity in CO₂ photoreduction. Under the irradiation of AM1.5 filter for 12 h, CO₂ was converted into CH₄ and CO with high selectivity to methane (91%) and the total amount of gaseous products up to ∼300 μmol g^-1. This reactivity is 6-fold and 4-fold higher than that of pure g-C₃N₄ and CsPbBr₃, respectively. CsPbBr₃@g-C₃N₄ also shows excellent catalytic activity at low concentrations of CO₂. Studies of energy band level and steady-state and transient photoluminescence spectroscopy indicated that the incorporation of CsPbBr₃ and g-C₃N₄ increases charge separation, which may result in sharply enhanced catalytic efficiency. This study has provided opportunities for the combination of CsPbBr₃ and other semiconductor catalysts for the photocatalytic reduction of CO₂.

Reduced graphene oxide supported C3N4 nanoflakes and quantum dots as metal-free catalysts for visible light assisted CO2 reduction

The visible light photocatalytic reduction of CO₂ to fuel is crucial for the sustainable development of energy resources. In our present work, we report the synthesis of novel reduced graphene oxide (rGO)-supported C₃N₄ nanoflake (NF) and quantum dot (QD) hybrid materials (GCN) for visible light induced reduction of CO₂. The C₃N₄ NFs and QDs are prepared by acid treatment of C₃N₄ nanosheets followed by ultrasonication and hydrothermal heating at 130-190 °C for 5-20 h. It is observed that hydrothermal exposure of acid-treated graphitic carbon nitride (g-C₃N₄) nanosheets at low temperature generated larger NFs, whereas QDs are formed at higher temperatures. The formation of GCN hybrid materials was confirmed by powder X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy (TEM), and UV-vis spectroscopy. High-resolution TEM images clearly show that C₃N₄ QDs (average diameter of 2-3 nm) and NFs (≈20-45 nm) are distributed on the rGO surface within the GCN hybrid material. Among the as-prepared GCN hybrid materials, GCN-5 QDs exhibit excellent CO₂ reductive activity for the generation of formaldehyde, HCHO (10.3 mmol h^-1 g^-1). Therefore, utilization of metal-free carbon-based GCN hybrid materials could be very promising for CO₂ photoreduction because of their excellent activity and environmental sustainability.

Porous Graphene-Confined Fe-K as Highly Efficient Catalyst for CO2 Direct Hydrogenation to Light Olefins

We devised iron-based catalysts with honeycomb-structured graphene (HSG) as the support and potassium as the promoter for CO₂ direct hydrogenation to light olefins (CO₂-FTO). Over the optimal FeK1.5/HSG catalyst, the iron time yield of light olefins amounted to 73 μmol_CO2 g_Fe^-1 s^-1 with high selectivity of 59%. No obvious deactivation occurred within 120 h on stream. The excellent catalytic performance is attributed to the confinement effect of the porous HSG on the sintering of the active sites and the promotion effect of potassium on the activation of inert CO₂ and the formation of iron carbide active for CO₂-FTO.

Insight into the role of UV-irradiation in photothermal catalytic Fischer–Tropsch synthesis over TiO2 nanotube-supported cobalt nanoparticles

To explore an efficient catalytic system with high activity and selectivity is the key to improve Fischer–Tropsch synthesis (FTS) technology and the main focus in the academic field.

Water Oxidation Mechanisms of Metal Oxide Catalysts by Vibrational Spectroscopy of Transient Intermediates

Water oxidation is an essential reaction of an artificial photosystem for solar fuel generation because it provides electrons needed to reduce carbon dioxide or protons to a fuel. Earth-abundant metal oxides are among the most attractive catalytic materials for this reaction because of their robustness and scalability, but their efficiency poses a challenge. Knowledge of catalytic surface intermediates gained by vibrational spectroscopy under reaction conditions plays a key role in uncovering kinetic bottlenecks and provides a basis for catalyst design improvements. Recent dynamic infrared and Raman studies reveal the molecular identity of transient surface intermediates of water oxidation on metal oxides. Combined with ultrafast infrared observations of how charges are delivered to active sites of the metal oxide catalyst and drive the multielectron reaction, spectroscopic advances are poised to play a key role in accelerating progress toward improved catalysts for artificial photosynthesis.

HZSM-5 zeolites containing impurity iron species for the photocatalytic reduction of CO2 with H2O

The impurity [Fe³⁺–O²⁻] species in HZSM-5 zeolite is predominantly tetrahedrally coordinated and is the photoactive centre for photocatalytic CO₂ conversion.

Coupling carbon dioxide reduction with water oxidation in nanoscale photocatalytic assemblies

Closing the photosynthetic cycle on the nanometer scale under membrane separation of the half reactions for developing scalable artificial photosystems.

One-pot multicomponent synthesis of tetrahydropyridines promoted by luminescent ZnO nanoparticles supported by the aggregates of 6,6-dicyanopentafulvene

Pot-shaped fluorescent aggregates of 6,6-dicyanopentafulvene derivative serve as reactors and stabilizers for the preparation of luminescent ZnO nanoparticles, which exhibit high catalytic efficiency in one-pot multicomponent synthesis of tetrahydropyridines.