Highly Dispersive Ni@C and Co@C Nanoparticles Derived from Metal-Organic Monolayers for Enhanced Photocatalytic CO2 Reduction

Integrating carbon quantum dots with oxygen vacancy modified nickel-based metal organic frameworks for photocatalytic CO2 reduction to CH4 with approximately 100 % selectivity

Solar-light-driven reduction of CO2 into renewable fuels has great potential in the production of sustainable energy, addressing the energy crisis and environmental problems simultaneously. However, it is a significant challenge to achieve high selectivity for the conversion of CO2 into CH4, which is a type of fuel with a high calorific value. Herein, carbon quantum dots (CQDs) were integrated with an oxygen vacancy modified nickel-based metal organic frameworks (NiMOFs) to form the CQDs-X/NiMOFV series, which exhibited superior performance for CO2 photoreduction into CH4 compared with pure NiMOFs in the presence of hole scavengers under visible light irradiation. The highest yielding rate of CH4 (1 mmol g-1 h-1) and selectivity (97.58 %) were obtained using a CQDs-25/NiMOFV catalyst. Most importantly, in diluted CO2 atmosphere, the yield of CH4 was almost unchanged and the selectivity of CH4 over CQDs-25/NiMOFV was higher than that in pure CO2. The superior performance of CQDs-25/NiMOFV may be attributed to the following two factors: (i) both CQDs and oxygen vacancies facilitate the transmission of electrons to promote the eight-electron reaction producing CH4, and (ii) oxygen vacancies can act as the electron trap to capture the photogenerated electrons to react with adsorbed CO2 on Ni2+. This study offers a valuable strategy for designing efficient photocatalysts to convert CO2 into CH4 with superior selectivity.

Guest-Induced Multilevel Charge Transport Strategy for Developing Metal-Organic Frameworks to Boost Photocatalytic CO2 Reduction

Encapsulating photogenerated charge-hopping nodes and space transport bridges within metal-organic frameworks (MOFs) is a promising method of boosting the photocatalytic performance. Herein, this work embeds electron transfer media (9,10-bis(4-pyridyl)anthracene (BPAN)) in MOF cavities to build multi-level electron transfer paths. The MOF cavities are accurately regulated to investigate the significance of the multi-level electron transfer paths in the process of CO2 photoreduction by evaluating the difference in the number of guest media. The prepared MOFs, {[Co(BPAN)(1,4-dicarboxybenzene)(H2 O)2 ]·BPAN·2H2 O} and {[Co(BPAN)2 (4,4'-biphenyldicarboxylic acid)2 (H2 O)2 ]·2BPAN·2H2 O} (denoted as BPAN-Co-1 and BPAN-Co-2), exhibit efficient visible-light-driven CO2 conversion properties. The CO photoreduction efficacy of BPAN-Co-2 (5598 µmol g-1  h-1 ) is superior to that of most reported MOF-based catalysts. In addition, the enhanced CO2 photoreduction ability is supported by density functional theory (DFT). This work illustrates the feasibility of realizing charge separation characteristics in MOF catalysts at the molecular level, and provides new insight for designing high-performance MOFs for artificial photosynthesis.

Regulating Activity and Selectivity of Photocatalytic CO2 Reduction on Cobalt by Rare Earth Compounds

Cobalt-based catalysts are ideal for CO₂ reduction reaction (CO₂RR) due to the strong binding and efficient activation of CO₂ molecules on cobalt. However, cobalt-based catalysts also show low free energy of hydrogen evolution reaction (HER), making HER competitive with CO₂RR. Therefore, how to improve the product selectivity of CO₂RR while maintaining the catalytic efficiency is a great challenge. Here, this work demonstrates the critical roles of the rare earth (RE) compounds (Er₂O₃ and ErF₃) in regulating the activity and selectivity of CO₂RR on cobalt. It is found that the RE compounds not only promote charge transfer but also mediate the reaction paths of CO₂RR and HER. Density functional theory calculations verify that the RE compounds lower the energy barrier of *CO → CO conversion. On the other hand, the RE compounds increase the free energy of HER, which leads to the suppression of HER. As a result, the RE compounds (Er₂O₃ and ErF₃) improve the CO selectivity of cobalt from 48.8 to 69.6%, as well as significantly increase the turnover number by a factor of over 10.

3D/2D Heterojunction Fabricated from RuS2 Nanospheres Encapsulated in Polymeric Carbon Nitride Nanosheets for Selective Photocatalytic CO2 Reduction to CO

Micro/nanostructure control of heterostructures is still a challenge for achieving high efficiency and selectivity of photocatalytic CO₂ conversion. In this work, a new three-dimensiona/two-dimensional (3D/2D) heterostructure is fabricated by encapsulating RuS₂ nanospheres in the interlayer of mesoporous polymeric carbon nitride (PCN) nanosheets based on an in situ growth and polymerization strategy. The unique microstructure of the obtained 3D/2D RuS₂/PCN heterojunction can effectively improve the transfer and separation efficiency of photogenerated charge carriers, reduce the mass transfer resistance of CO₂ toward active sites, and provide a confined reaction space, thus propelling the photocatalytic CO₂ reduction to CO with high selectivity. The CO yield over the optimal 5%-RuS₂/PCN sample reaches 4.2 and 2.8 times as high as that of single PCN and RuS₂ within 4 h, respectively. Furthermore, the plausible charge transfer mechanism and CO₂ reduction path are revealed by time-dependent in situ Fourier transform infrared (FT-IR) spectra combined with photophysical, electrochemical, and photoelectrochemical techniques and density functional theory (DFT) calculations. This work develops the microstructural engineering design strategy of PCN-based heterojunctions for selective photocatalytic CO₂ fuel conversion.

Facile Insights into Hydrothermal Synthesis of Ultrathin Bi4NbO8Cl Nanosheets for Efficient CO2 Photoreduction

Developing novel two-dimensional photocatalysis is an excellent strategy for high-efficiency CO₂ photoreduction. Herein, for the first time, we demonstrate a facile hydrothermal synthesis method to construct ultrathin Bi₄NbO₈Cl nanosheets using tartaric acid as a complexing agent, which can restrain the speed of nucleation. The ultrathin Bi₄NbO₈Cl nanosheets exhibit excellent catalytic activity of CO and CH₄ production (10.84 and 4.45 μmol g^-1 h^-1), which are up to 1.9 and 1.4 times higher than those of the bulk Bi₄NbO₈Cl, respectively. Photoelectric experiments and mechanism analysis systematically show that the as-obtained enhanced performance should be attributed to the formation of ultrathin Bi₄NbO₈Cl nanosheets, and charge separation and migration are significantly boosted. Therefore, this ultrathin Bi₄NbO₈Cl structure has provided new insights into the controllable preparation of ultrathin nanosheet photocatalysts to effectively improve the catalytic performance.

Designed assembly of heterometallic zeolite-like framework materials from two different supertetrahedral metal clusters

This work demonstrates a feasible strategy for the synthesis of new zeolite-like framework materials. With the strategy of using two different supertetrahedral clusters as secondary building units, two new heterometallic zeolite-like frameworks with isomeric structures but tunable topologies were first made. Besides, the porous nature and the proton conduction performance of the new materials were further studied.