Na-mediated carbon nitride realizing CO2 photoreduction with selectivity modulation.

The depressed directional separation of photogenerated carriers and weak CO2 adsorption/activation activity are the main factors hampering the development of artificial photosynthesis. Herein, Na ions are embedded in graphitic carbon nitride (g-C3N4) to achieve directional migration of the photogenerated electrons to Na sites, while the electron-rich Na sites enhance CO2 adsorption and activation. Na/g-C3N4 (NaCN) shows improved photocatalytic reduction activity of CO2 to CO and CH4, and under simulated sunlight irradiation, the CO yield of NaCN synthesized by embedding Na at 550°C (NaCN-550) is 371.2 µmol g-1 h-1, which is 58.9 times more than that of the monomer g-C3N4. By means of theoretical calculations and experiments including in situ fourier transform infrared spectroscopy, the mechanism is investigated. This strategy which improves carrier separation and reduces the energy barrier at the same time is important to the development of artificial photosynthesis.

S­scheme heterojunction of thin-layer O-modified graphitic carbon nitride/cobalt porphyrin to promote photocatalytic CO2 conversion.

The emissions of CO2 are increasing year by year, which have led to serious environmental problems. Converting CO2 into valuable fuels through photocatalysis is a promising strategy. In this research, oxygen atoms were successfully innovated into graphitic carbon nitride (CN). Additionally, cobalt porphyrin (CoTPP) was successfully loaded onto the modified carbon nitride (Co/CN). The generation of interfacial electric fields and bending bands between CN and CoTPP was demonstrated experimentally. The electrons in the CN and the holes in the CoTPP were combined to form a unique S-scheme heterojunction structure, and efficient separation of carriers was promoted. As a result, the CO conversion under visible light irradiation reached an impressive 100.70 µmol g-1 h-1. By integrating theoretical and experimental findings, this study underscores the critical role of catalyst design in enabling efficient photocatalytic CO2 reduction.

Piezo-photocatalysis for efficient charge separation to promote CO2 photoreduction in nanoclusters.

The substantial emissions of CO2 greenhouse gases have resulted in severe environmental problems, and research on the implementation of semiconductor materials to minimize CO2 is currently a highly discussed subject. Effective separation of interface charges is a major challenge for efficient piezo-photocatalytic systems. Meanwhile, the ultrasmall-sized metal nanoclusters can shorten the distance of electron transport. Herein, we synthesized Au25(p-MBA)18 nanoclusters (Au25 NCs) modified red graphitic carbon nitride (RCN) nanocatalysts with highly exposed Au active sites by in-situ seed growth method. The loading of Au25 NCs on the RCN surface provides more active sites and creates a long-range ordered electric field. It allows for the direct utilization of the piezoelectric field to separate photogenerated carriers during photo-piezoelectric excitation. Based on the above advantages, the rate of CO2 reduction to CO over Au25 NCs/RCN (111.95 µmol g-1 h-1) was more than triple compared to that of pristine RCN. This paper has positive implication for further application of metal clusters loaded semiconductor for piezo-photocatalytic CO2 reduction.

Porous silver microrods by plasma vulcanization activation for enhanced electrocatalytic carbon dioxide reduction.

Metal electrode is considered as an ideal candidate for electrocatalytic carbon dioxide (CO2) reduction considering its excellent chemical stability, application potential and eco-friendly properties. Optimization process such as morphological control, non-metallic doping, alloying is widely studied to improve the efficiency of metal electrodes. In this work, we successfully improved the CO2 reduction performance of silver using a facile plasma vulcanization treatment. The obtained sulfide derived silver (Ag) porous microrods (SD-AgPMRs) are optimized from both morphology and composition aspects, and demonstrates high Faradaic efficiency and partial current density for carbon monoxide (CO) production at low potentials. The larger specific surface area of porous microrod structure and the improved adsorption energy of important intermediates in comparison with Ag foil are realized by introduction of sulfur (S) atoms after plasma vulcanization activation, as suggested by density functional theory (DFT) calculations. This work presents a novel strategy to optimize metal electrocatalysts for CO2 reduction as well as to improve catalysis in other fields.

Positively charged silver improve carbon dioxide electroreduction reaction performance by introducing phosphate.

For noble metal catalysts such as Au and Ag, the weak adsorption of intermediates is an important factor in limiting the efficiency of CO2 electroreduction. Positively charged metals, which can lower the energy barriers of intermediate reactions, greatly facilitate the rapid conversion of CO2 molecules. In this work, a simple in situ synthesis method was utilized to form an Ag3PO4 oxide layer on the surface of Ag foil, and the oxidation state of silver retained after pre-reduction. The Ag3PO4/Ag catalyst not only increased the electrochemical surface area, but also enhanced the adsorption of intermediates to the active sites, resulting in the catalytic selectivity of 94.4% for the electroreduction of CO2 to CO. DFT calculations show that through internal electron regulation, PO43- can stabilize the positive state of Ag, thus increasing the Ag-O bond energy, which is conducive to the reduction of the reaction energy barrier and the improvement of catalytic stability.

Ultrathin structure of oxygen doped carbon nitride for efficient CO2photocatalytic reduction.

Photocatalytic conversion of carbon dioxide into fuels and valuable chemicals is a promising method for carbon neutralization and solving environmental problems. Through a simple thermal-oxidative exfoliation method, the O element was doped while exfoliated bulk g-C3N4into ultrathin structure g-C3N4. Benefitting from the ultrathin structure of g-C3N4, the larger surface area and shorter electrons migration distance effectively improve the CO2reduction efficiency. In addition, density functional thory computation proves that O element doping introduces new impurity energy levels, which making electrons easier to be excited. The prepared photocatalyst reduction of CO2to CO (116µmol g-1h-1) and CH4(47µmol g-1h-1).

Unique Dual-Sites Boosting Overall CO2 Photoconversion by Hierarchical Electron Harvesters.

Low selectivity and poor activity of photocatalytic CO2 reduction process are usually limiting factors for its applicability. Herein, a hierarchical electron harvesting system is designed on CoNiP hollow nano-millefeuille (CoNiP NH), which enables the charge enrichment on CoNi dual active sites and selective conversion of CO2 to CH4 . The CoNiP serves as an electron harvester and photonic "black hole" accelerating the kinetics for CO2 -catalyzed reactions. Moreover, the dual sites form from highly stable CoONiC intermediates, which thermodynamically not only lower the reaction energy barrier but also transform the reaction pathways, thus enabling the highly selective generation of CH4 from CO2 . As an outcome, the CoNiP NH/black phosphorus with dual sites leads to a tremendously improved photocatalytic CH4 generation with a selectivity of 86.6% and an impressive activity of 38.7 µmol g-1  h-1 .

Accelerated Photoreduction of CO2 to CO over a Stable Heterostructure with a Seamless Interface.

Photocatalytic CO2 reduction is a means of alleviating energy crisis and environmental deterioration. In this work, a rising two-dimensional (2D) material rarely reported in the field of photocatalytic CO2 reduction, black phosphorus (BP) nanosheets, is synthesized, on which Co2P is in situ grown by solvothermal treatment using BP itself as a P source. Co2P on the BP nanosheets (BPs) surface can prevent the destruction of BPs in ambient air and, in the meantime, favor charge separation and CO2 adsorption and activation during the catalytic process. Upon light irradiation, Co2P can extract the photogenerated electrons effectively across the intimate interface and lower the CO2 activation energy barrier, supported by both experimental characterizations and theoretical calculations. Benefitting from integrated advantages of BPs and Co2P, the optimal Co2P/BPs exhibit photocatalytic reduction of CO2 to CO at a rate of 25.5 µmol g-1 h-1 with a selectivity of 91.4%, both of which are higher than those of pristine BPs. This work presents ideas for stabilizing BPs and improving their CO2 reduction performance simultaneously.

Plasma-induced defect engineering: Boosted the reverse water gas shift reaction performance with electron trap.

The reverse water gas shift reaction is a promising approach to solve the problem of excessive CO2 emission and energy shortage. However, insufficient charge separation efficiency of numerous semiconductor photocatalysts hamper their CO2 photoreduction performance. Defect engineering is considered as a desired method to tackle that shortcoming by the boosting the electron capture process. Herein, the sulfur vacancies-rich CdIn2S4 (VS-CdIn2S4) was synthesized by an efficient low-temperature plasma-enhanced technology. The outstanding VS-CdIn2S4 shows a more excellent CO formation rate of 103.6 µmol g-1 h-1 comparing that of traditional CdIn2S4 (31.36 µmol g-1 h-1). The density function theory (DFT) calculation reveals the sulfur vacancy is the center of electron capture. Moreover, the formed defect level after introduce of surface vacancy effectively optimizes the light absorption propertie of the prepared material. Thus, the enhanced photocatalytic CO2 reduction performance can be attributed to the double improvement of light absorption and carrier separation. This work provides a novel and facile strategy to mediate carriers' movement behavior via defect engineering for high-efficient CO2 photoreduction.

Metal-Oxide-Mediated Subtractive Manufacturing of Two-Dimensional Carbon Nitride for High-Efficiency and High-Yield Photocatalytic H2 Evolution.

g-C3N4 is a promising visible-light-driven photocatalyst for H2 evolution reaction; however, the achievement of the high photocatalytic performance is primarily limited by the low separation efficiency of the photogenerated charge carriers and partly restricted by the slow kinetics of charge transfer. 2D g-C3N4 can significantly improve the charge generation, transfer, and separation efficiencies. The 2D g-C3N4-based Z-scheme heterostructure can further enhance the charge-carrier separation and simultaneously increase the redox ability, thereby further boosting the photocatalytic performance. Here we report a transition-metal-oxide (TMO)-mediated subtractive manufacturing process toward the large-scale synthesis of 2D g-C3N4 and the simultaneous formation of a 2D/2D TMO/g-C3N4 Z-scheme heterojunction. The TMOs serve as catalysts to facilitate the hydrolysis reaction of the bulk g-C3N4 in the presence of moist air, forming 2D g-C3N4. The resulting 2D/2D TMO/g-C3N4 catalysts, in particular, 2D/2D Co3O4/g-C3N4, exhibit high-efficiency and high-yield photocatalytic H2 evolution due to the suppression of electron-hole pair recombination and enhanced redox ability. The 2D/2D Co3O4/g-C3N4 photocatalyzes the H2 evolution with a rate of ∼370 µmol h-1 within λ > 400 nm. The external quantum efficiency of 2D/2D Co3O4/g-C3N4 at λ = 405 nm reaches 53.6%, which is among the highest values for g-C3N4-based catalysts.