Regulating Lewis Acidic Sites of 1T-2H MoS2 Catalysts for Solar-Driven Photothermal Catalytic H2 Production from Lignocellulosic Biomass.

Solar-driven photothermal catalytic H2 production from lignocellulosic biomass was achieved by using 1T-2H MoS2 with tunable Lewis acidic sites as catalysts in an alkaline aqueous solution, in which the number of Lewis acidic sites derived from the exposed Mo edges of MoS2 was successfully regulated by both the formation of an edge-terminated 1T-2H phase structure and tunable layer number. Owing to the abundant Lewis acidic sites for the oxygenolysis of lignocellulosic biomass, the 1T-2H MoS2 catalyst shows high photothermal catalytic lignocellulosic biomass-to-H2 transformation performance in polar wood chips, bamboo, rice straw corncobs, and rice hull aqueous solutions, and the highest H2 generation rate and solar-to-H2 (STH) efficiency respectively achieves 3661 µmol·h-1·g-1 and 0.18% in the polar wood chip system under 300 W Xe lamp illumination. This study provides a sustainable and cost-effective method for the direct transformation of renewable lignocellulosic biomass to H2 fuel driven by solar energy.

Tailored Metal-Organic Frameworks for Water Purification: Perfluorinated Fe-MOFs for Enhanced Heterogeneous Catalytic Ozonation.

An industrially viable catalyst for heterogeneous catalytic ozonation (HCO) in water purification requires the characteristics of good dispersion of active species on its surface, efficient electron transfer for ozone decay, and maximum active species utilization. While metal-organic frameworks (MOFs) represent an attractive platform for HCO, the metal nodes in the unmodified MOFs exhibit low catalytic activity. Herein, we present a perfluorinated Fe-MOF catalyst by substituting H atoms on the metalated ligands with F atoms (termed 4F-MIL-88B) to induce structure evolution. The Lewis acidity of 4F-MIL-88B was enhanced via the formation of Fe nodes, tailoring the electron distribution on the catalyst surface. As a result of catalyst modification, the rate constant for degradation of the target compounds examined increased by ∼700% compared with that observed for the unmodified catalyst. Experimental evidence and theoretical calculations showed that the modulated polarity and the enhanced electron transfer between the catalyst and ozone molecules contributed to the adsorption and transformation of O3 to •OH on the catalyst surface. Overall, the results of this study highlight the significance of tailoring the metalated ligands to develop highly efficient and stable MOF catalysts for HCO and provide an in-depth mechanistic understanding of their structure-function evolution, which is expected to facilitate the applications of nanomaterial-based processes in water purification.

Tighter Confinement Increases Selectivity of d-Glucose Isomerization Toward l-Sorbose in Titanium Zeolites.

Aqueous-phase isomerization of d-glucose to d-fructose and l-sorbose is catalyzed in parallel by Lewis acidic Ti sites in siliceous frameworks. Glucose isomerization rates (per Ti, 373 K) are undetectable when Ti sites are confined within mesoporous voids (Ti-MCM-41, TiO2 -SiO2 ) and increase to detectable values when Ti sites are confined within the smaller 12-membered ring (12-MR) micropores of Ti-Beta. Isomerization rates decrease to lower values (by ≈20×) with further decreases in micropore size as Ti sites are confined within 10-MR pores (Ti-MFI, Ti-CON), likely because of intrapore reactant diffusion restrictions, and reach undetectable values within the 8-MR pores of Ti-CHA as size exclusion prevents glucose from accessing active sites. Remarkably, the selectivity toward l-sorbose over d-fructose increases systematically as spatial constraints around Ti sites become tighter, and is >10 on Ti-MFI. These findings demonstrate the marked influence of confinement around Ti active sites on the selectivity between parallel stereoselective sugar isomerization pathways.

Lewis acid-rich SrFexTi1-xO3/TiO2 to enhance the photocatalytic reduction of nitrate to N2.

The photocatalytic reduction of nitrate has received considerable attention due to its high efficiency and environmentally friendly nature. The excessive addition of hole scavengers is the most commonly used method to increase the nitrate reduction efficiency. However, achieving high selectivity in the photocatalytic reduction of nitrate to N2 with low concentration of hole scavengers remains challenging. In this study, the SrFexTi1-xO3/TiO2 S-scheme heterojunction photocatalysts with many Lewis acidic adsorption sites have been developed. The experimental results demonstrated that the incorporation of 6% Fe into SrFe0.06Ti0.94O3/TiO2 (SFTO6) resulted in the nitrate conversion rate of 97.68% and the N2 selectivity reached 96.35% with 25 mmol/L formic acid. Moreover, it also exhibited excellent stability and recycle ability. After 5 cycles, SFTO6 still exhibited a stable photocatalytic denitration efficiency of 92.94%, highlighting its potential for practical application. Through comprehensive mechanistic investigations, enhancing direct reduction process is considered the key to its high reduction efficiency with low formic acid. And the Lewis acidic adsorption sites enhance N2 selectivity by enriching NOx- on the surface of the material. Overall, this study provides a novel approach for achieving efficient photocatalytic reduction of nitrate to N2 under conditions with low concentration of hole scavengers.

Mixed-Metal-Organic Framework with Effective Lewis Acidic Sites for Sulfur Confinement in High-Performance Lithium-Sulfur Batteries.

The mixed-metal-organic framework approach and a representative zirconium-metalloporphyrin framework (MOF-525) have been developed to create novel sulfur hosts and Li-S batteries. The different local environments at the centers of the porphyrin moieties in a series of MMOFs-MOF-525(2H), MOF-525(FeCl), and MOF-525(Cu)-have led to their different behaviors for the confinement of sulfur and thus Li-S batteries. The unique structure of MOF-525(Cu) has enabled each Cu(2+) site to offer two Lewis acidic sites, featuring it as a very powerful MOF host for the inclusion of sulfur and polysulfides. The S@MOF-525(Cu) cathode has demonstrated the best performance among all reported sulfur/MOFs composite cathode materials, with a reversible capacity of about 700 mAh/g at 0.5 C after 200 cycles.