Photocatalytic Reduction of CO2 to CO over Quinacridone/BiVO4 Nanocomposites

Pivotal Impact Factors in Photocatalytic Reduction of CO2 to Value-Added C1 and C2 Products

Over the past decades, CO2 greenhouse emission has been considerably increased, causing global warming and climate change. Indeed, converting CO2 into valuable chemicals and fuels is a desired option to resolve issues caused by its continuous emission into the atmosphere. Nevertheless, CO2 conversion has been hampered by the ultrahigh dissociation energy of C=O bonds, which makes it thermodynamically and kinetically challenging. From this prospect, photocatalytic approaches appear promising for CO2 reduction in terms of their efficiency compared to other traditional technologies. Thus, many efforts have been made in the designing of photocatalysts with asymmetric sites and oxygen vacancies, which can break the charge distribution balance of CO2 molecule, reduce hydrogenation energy barrier and accelerate CO2 conversion into chemicals and fuels. Here, we review the recent advances in CO2 hydrogenation to C1 and C2 products utilizing photocatalysis processes. We also pin down the key factors or parameters influencing the generation of C2 products during CO2 hydrogenation. In addition, the current status of CO2 reduction is summarized, projecting the future direction for CO2 conversion by photocatalysis processes.

Photoelectrochemical C-H Activation Through a Quinacridone Dye Enabling Proton-Coupled Electron Transfer

Dye-sensitized photoanodes for C-H activation in organic substrates are assembled by vacuum sublimation of a commercially available quinacridone (QNC) dye in the form of nanosized rods onto fluorine-doped tin oxide (FTO), TiO₂ , and SnO₂ slides. The photoanodes display extended absorption in the visible range (450-600 nm) and ultrafast photoinduced electron injection (<1 ps, as revealed by transient absorption spectroscopy) of the QNC dye into the semiconductor. The proton-coupled electron-transfer reactivity of QNC is exploited for generating a nitrogen-based radical as its oxidized form, which is competent in C-H bond activation. The key reactivity parameter is the bond-dissociation free energy (BDFE) associated with the N⋅/N-H couple in QNC of 80.5±2.3 kcal mol^-1 , which enables hydrogen atom abstraction from allylic or benzylic C-H moieties. A photoelectrochemical response is indeed observed for organic substrates characterized by C-H bonds with BDFE below the 80.5 kcal mol^-1 threshold, such as γ-terpinene, xanthene, or dihydroanthracene. This work provides a rational, mechanistically oriented route to the design of dye-sensitized photoelectrodes for selective organic transformations.

Recent review of BixMOy (M=V, Mo, W) for photocatalytic CO2 reduction into solar fuels

The utilization of solar energy for CO₂ conversion not only enables a green and low-carbon recycling of CO₂ with renewable energy, but also solves ecological problems. Bi_xMO_y (M = V, Mo, W) materials have typical layered structures and unique electronic properties that provide suitable band gaps and potential to meet the basic conditions for CO₂ reduction. However, pristine Bi_xMO_y faces with problems such as small specific surface area, insufficient active sites, low charge carriers' separation and utilization efficiency. This review comprehensively described the basic principles and reaction pathways of photocatalytic CO₂ reduction, and further presented the research progress of Bi_xMO_y catalysts in CO₂ conversion reactions. In this perspective, we further focus on the design concepts and modification strategies to improve the photocatalytic CO₂ reduction activity of Bi_xMO_y, such as morphology control, constructing surface vacancies and heterojunction fabrication. Finally, based on representative researches, the present review will be expected to provide updated information and insights for developing advanced Bi_xMO_y materials to further improve CO₂ reduction activity and selectivity.

Carbazolic Conjugated Organic Polymers for Visible-Light-Driven CO2 Photoreduction with H2 O to CO with High Efficiency and Selectivity

Visible-light-driven CO₂ photoreduction with H₂ O to value-added chemicals in high efficiency and selectivity is significant but challenging. Herein, a series of carbazolic conjugated organic polymers (CB-COPs) with electron donor-acceptor (D-A) structures were prepared, which showed high efficiency for visible-light-driven photocatalytic reduction of CO₂ with H₂ O in a solid-gas mode, affording CO as the exclusive carbonaceous product. Especially, CB-COP-mpd derived from 3,5-di(9H-carbazol-9-yl)pyridine exhibited the highest CO evolution rate up to 191.46 μmol g^-1  h^-1 with a selectivity of 100 %. Mechanism studies showed that carbazolyl is a promising electron donor candidate for constructing CB-COPs with D-A structures, capable of improving the catalytic efficiency and suppressing H₂ generation. The acceptor building block with excessive electron withdrawing capability was favorable to H₂ O adsorption, thus resulting in the generation of H₂ . This work provides new insights for designing COPs photocatalysts for CO₂ photocatalytic reduction.

Ni-Co Bimetallic Hydroxide Nanosheet Arrays Anchored on Graphene for Adsorption-Induced Enhanced Photocatalytic CO2 Reduction

Photocatalytic CO₂ reduction can be implemented to use CO₂ , a greenhouse gas, as a resource in an energy-saving and environmentally friendly way, in which suitable catalytic materials are required to achieve high-efficiency catalysis. Insufficient accessible active sites on the catalyst surface and inhibited electron transfer severely limit the photocatalytic performance. Therefore, porous aerogels are constructed from composites comprising different ratios of Ni-Co bimetallic hydroxide (Ni_x Co_y ) grown on reduced graphene oxide (GR) into a hierarchical nanosheet-array structure using a facile in situ growth method. Detailed characterization shows that this structure exposes numerous active sites for enhanced adsorption-induced photocatalytic CO₂ reduction. Moreover, under the synergistic effect of Ni-Co bimetallic hydroxide, the CO₂ adsorption capacity as well as charge-carrier separation and transfer are excellent. As a result, the Ni₇ Co₃ -GR catalyst exhibits highly improved catalytic performance when compared with recently reported values, with a high CO release rate of 941.5 µmol h^-1  g^-1 and a selectivity of 96.3% during the photocatalytic reduction of CO₂ . This work demonstrates a new strategy for designing nanocomposites with abundant active sites structures.

A Critical Review on Black Phosphorus-Based Photocatalytic CO2 Reduction Application

Energy shortages and greenhouse effects are two unavoidable problems that need to be solved. Photocatalytically converting CO₂ into a series of valuable chemicals is considered to be an effective means of solving the above dilemmas. Among these photocatalysts, the utilization of black phosphorus for CO₂ photocatalytic reduction deserves a lightspot not only for its excellent catalytic activity through different reaction routes, but also on account of the great preponderance of this relatively cheap catalyst. Herein, this review offers a summary of the recent advances in synthesis, structure, properties, and application for CO₂ photocatalytic reduction. In detail, the review starts from the basic principle of CO₂ photocatalytic reduction. In the following section, the synthesis, structure, and properties, as well as CO₂ photocatalytic reduction process of black phosphorus-based photocatalyst are discussed. In addition, some possible influencing factors and reaction mechanism are also summarized. Finally, a summary and the possible future perspectives of black phosphorus-based photocatalyst for CO₂ reduction are established.

Plasmon-assisted photocatalytic CO2 reduction on Au decorated ZrO2 catalysts

ZrO₂ is one of the most stable metal oxides which is applicable to various chemical reactions in harsh environments. However, the photocatalytic performance of ZrO₂ is relatively poor due to the negligible use of the solar spectrum caused by the wide bandgap (E_g = 5.3 eV). Here, we report plasmon enhanced Au nanoparticles decorated onto ZrO₂ through a facile tannic acid-reduction method. The Au/ZrO₂ heterojunctions exhibited efficient and stable photocatalytic activity of reducing CO₂ into main CO and CH₄, at the rates of 25.6 μmol g^-1 h^-1 and 5.1 μmol g^-1 h^-1 at most, respectively, approximately 6-fold enhanced compared to the pristine ZrO₂, under simulated solar light. The reduction rates could also be improved over 10-fold under visible light when Au nanoparticles were loaded onto ZrO₂. UV-Vis diffuse reflectance spectra confirmed the enhanced visible-light absorption of Au/ZrO₂ caused by localized surface plasmon resonance (LSPR). Electrochemical impedance spectra (EIS) and photocurrent tests proved the more efficient charge transport and electron-hole separation of Au/ZrO₂ heterojunctions. This study demonstrates an effective strategy of LSPR effects to improve the photocatalytic performances of semiconductors.