Unsaturated NiII Centers Mediated the Coordination Activation of Benzylamine for Enhancing Photocatalytic Activity over Ultrathin Ni MOF-74 Nanosheets

CO driven tunable syngas synthesis via CO2 photoreduction using a novel NiCo bimetallic metal-organic frameworks

Syngas has important industrial applications, and converting CO2 to CO is critical for syngas production. Metal-organic frameworks (MOFs) have demonstrated significant potential in photocatalytic syngas conversion, although the impact of catalytic reactions on tunable H2/CO ratios remains unclear. Herein, we present a novel bimetallic NiCo-MOF catalyst, Ni0.4Co0.6, exhibiting high catalytic activity in syngas conversion due to the CO product self-driven effect. Our investigation, integrating experimental data with density functional theory (DFT) analysis, uncovers a high photocurrent response and a low charge-transfer resistance. Furthermore, the introduction of cobalt into Ni-MOF caused an upshift of the d-band center, which facilitated the conversion efficiency of *COOH intermediates, which has been identified as the rate-determining step in CO2 conversion, resulting in increased CO yield. Additionally, the concentration of undesorbed CO rises, while CO co-adsorption diminishes the catalyst's binding energy for *H, thereby enhancing H2 generation. These combined effects contribute to a self-driven enhancement in the catalytic production of syngas. By adjusting the Ni/Co ratio, a tunable H2/CO ratio (0.21-0.85) was achieved, with Ni0.4Co0.6 exhibiting optimal catalytic performance, yielding 17.6 mmol·g-1·h-1 gas products. This study provides a novel insight into the correlation between reaction products and catalyst design, offering a perspective on perspective on modulating syngas composition.

Tailoring Electrocatalytic Ov-NiOOH by Regulating the Reconstruction in Ni-Based Metal-Organic Frameworks with Highly Asymmetric Ni-O Coordination

Metal-organic frameworks have aroused growing interest in the research of energy conversion and storage. However, their specific configuration, especially the coordination environment of metal active sites, has not been well designed. Their role in regulating the structural reconstruction of pre-electrocatalysts remains ambiguous. Herein, this work reports a dual-ligand strategy to design a Ni-MOF with asymmetric Ni-O coordination, named Ni-BDC-DOBDC, which occupies unsaturated Ni sites and strengthens Ni-O bonds. As inspected by X-ray absorption near edge structure as well as a series of in situ and ex situ characterizations, this special Ni-O coordination contributes to Ov-NiOOH with rich oxygen vacancies during fast self-reconstruction at a lower potential. Moreover, theoretical results reveal that Ni sites in Ov-NiOOH occupy a higher d-band center, a lower adsorption energy barrier, and a more electronic negative surface in the oxygen evolution reaction, leading to good electrocatalytic performance. Overall, Ni-BDC-DOBDC catalysts exhibit a low overpotential of 202 mV at 10 mA cm-2 and outstanding stability within 240 h. The insights in this work pave the way for high-performance MOF-based catalysts by regulating their self-reconstruction kinetics through a new aspect of asymmetric ligand engineering.

Preparation of a Nanosheeted Uranyl-Organic Framework for Enhanced Photocatalytic Oxidation of Toluene

Preparation of ultrathin metal-organic framework (MOF) nanosheets is an effective way to improve the catalytic efficiency of MOF photocatalysts owing to their superiority in reducing the recombination rate of photogenerated electrons and holes and enhancing charge transfer. Herein, a light-sensitive two-dimensional uranyl-organic framework named HNU-68 was synthesized. Due to its interlayer stacking structure, the corresponding ultrathin nanosheets with a thickness of 4.4 nm (HNU-68-N) can be obtained through ultrasonic exfoliation. HNU-68-N exhibited an enhanced ability to selectively oxidize toluene to benzaldehyde, with the value of turnover frequency being approximately three times higher than that of the bulk HNU-68. This enhancement is attributed to the smaller size and interface resistance of the layered HNU-68-N nanosheets, which facilitate more thorough substrate contact and faster charge transfer, leading to an improvement in the photocatalytic efficiency. This work provides a potential candidate for the application of ultrathin uranyl-based nanosheets.

Ligand Defect-Induced Active Sites in Ni-MOF-74 for Efficient Photocatalytic CO2 Reduction to CO

The conversion of CO2 into valuable carbon-based products using clean and renewable solar energy has been a significant challenge in photocatalysis. It is of paramount importance to develop efficient photocatalysts for the catalytic conversion of CO2 using visible light. In this study, the Ni-MOF-74 material is successfully modified to achieve a highly porous structure (Ni-74-Am) through temperature and solvent modulation. Compared to the original Ni-MOF-74, Ni-74-Am contains more unsaturated Ni active sites resulting from defects, thereby enhancing the performance of CO2 photocatalytic conversion. Remarkably, Ni-74-Am exhibits outstanding photocatalytic performance, with a CO generation rate of 1380 µmol g-1 h-1 and 94% CO selectivity under visible light, significantly surpassing the majority of MOF-based photocatalysts reported to date. Furthermore, experimental characterizations reveal that Ni-74-Am has significantly higher efficiency of photogenerated electron-hole separation and faster carrier migration rate for photocatalytic CO2 reduction. This work enriches the design and application of defective MOFs and provides new insights into the design of MOF-based photocatalysts for renewable energy and environmental sustainability. The findings of this study hold significant promise for developing efficient photocatalysts for CO2 reduction under visible-light conditions.

Hollow structured CdS@ZnIn2S4 Z-scheme heterojunction for bifunctional photocatalytic hydrogen evolution and selective benzylamine oxidation

Photocatalytic hydrogen evolution (PHE) is frequently constrained by inadequate light utilization and the rapid combination rate of the photogenerated electron-hole pairs. Additionally, conventional PHE processes are often facilitated by the addition of sacrificial reagents to consume photo-induced holes, which makes this approach economically unfavorable. Herein, we designed a spatially separated bifunctional cocatalyst decorated Z-scheme heterojunction of hollow structured CdS (HCdS) @ZnIn2S4 (ZIS), which was prepared by a sacrificial hard template method followed by photo-deposition. Consequently, PdOx@HCdS@ZIS@Pt exhibited efficient PHE (86.38 mmol·g-1·h-1) and benzylamine (BA) oxidation coupling (164.75 mmol·g-1·h-1) with high selectivity (97.34 %). The unique hollow core-shelled morphology and bifunctional cocatalyst loading in this work hold great potential for the design and synthesis of bifunctional Z-scheme photocatalysts.

Synergistic Interplay of Dual-Active-Sites on Metallic Ni-MOFs Loaded with Pt for Thermal-Photocatalytic Conversion of Atmospheric CO2 under Infrared Light Irradiation

Infrared light driven photocatalytic reduction of atmospheric CO2 is challenging due to the ultralow concentration of CO2 (0.04 %) and the low energy of infrared light. Herein, we develop a metallic nickel-based metal-organic framework loaded with Pt (Pt/Ni-MOF), which shows excellent activity for thermal-photocatalytic conversion of atmospheric CO2 with H2 even under infrared light irradiation. The open Ni sites are beneficial to capture and activate atmospheric CO2 , while the photogenerated electrons dominate H2 dissociation on the Pt sites. Simultaneously, thermal energy results in spilling of the dissociated H2 to Ni sites, where the adsorbed CO2 is thermally reduced to CO and CH4 . The synergistic interplay of dual-active-sites renders Pt/Ni-MOF a record efficiency of 9.57 % at 940 nm for converting atmospheric CO2 , enables the procurement of CO2 to be independent of the emission sources, and improves the energy efficiency for trace CO2 conversion by eliminating the capture media regeneration and molecular CO2 release.

Amino-functionalized MIL-125(Ti) for photodenitrification of pyridine in fuels via coordination activation by unsaturated Ti4+ centers

Due to their explicit structure, metal-organic frameworks (MOFs) have been supposed to be credible platforms to research the micro-mechanism of heterogeneous photocatalysis. In this study, amino-functionalized MOFs (MIL-125(Ti)-NH₂ (denoted as MTi), UiO-66(Zr)-NH₂ (denoted as UZr) and MIL-68(In)-NH₂ (denoted as MIn)) with three different metal centers were synthesized and applied for the denitrification of simulated fuels under visible light irradiation, during which pyridine was used as a typical nitrogen-containing compound. The results showed that MTi had the best activity among the above three MOFs, and the denitrogenation rate increased to 80% after 4 h of visible light irradiation. On the grounds of the theoretical calculation of pyridine adsorption and actual activity experiments, it can be presumed that the unsaturated Ti⁴⁺ metal centers should be the key active sites. Meanwhile, the XPS and in situ infrared results verified that the coordinatively unsaturated Ti⁴⁺ sites facilitate the activation of pyridine molecules through the surface -N⋯Ti- coordination species. The coordination-photocatalysis synergism promotes the efficiency of photocatalytic performance and the corresponding mechanism is proposed.