Modification of Au nanoparticles electronic state by MOFs defect engineering to realize highly active photocatalytic oxidative esterification of benzyl alcohol with methanol

Photocatalyzed Oxidative Tandem Reaction Mediated by Bipyridinium for Multifunctional Derivatization of Alcohols

The multifunctional derivatization of alcohols has been achieved by the bipyridinium-based conjugated small molecule photocatalysts with redox center and Lewis acid site. Besides exhibiting high activity in the selective generation of aldehydes/ketones, acids from alcohols through solvent modulation, this system renders the first selective synthesis of esters via an attractive cross-coupling pattern, whose reaction route is significantly different from the traditional condensation of alcohols and acids or esterification from hemiacetals. Following the oxidization of alcohol to aldehyde via bipyridinium-mediated electron and energy transfer, the Lewis acid site of bipyridinium then activates the aldehyde and methanol to obtain the acetal, which further reacts with methanol to generate ester. This method not only demonstrates a clear advantage of bipyridinium in diverse catalytic activities, but also paves the way for designing efficient multifunctional small molecule photocatalysts. This metal- and additive-free photocatalytic esterification reaction marks a significant advancement towards a more environmentally friendly, cost-effective and green sustainable approach, attributed to the utilization of renewable substrate alcohol and the abundant, low-cost air as the oxidant. The mildness of this esterification reaction condition provides a more suitable alternative for large-scale industrial production of esters.

Highly Dispersive Gold Nanoclusters Confined within Micropores of Defective UiO-66 for Highly Efficient Aldehyde Oxidation at Mild Conditions

The oxidative esterification of aldehydes under mild conditions remains a significant challenge. This study introduces a unique defective UiO-66 to achieve gold nanoclusters (AuNCs) for efficient aldehyde oxidation under mild conditions. The construction and characterization of these materials are thoroughly investigated by techniques of XRD, SEM and TEM images, FT-IR, Raman, and XPS spectrum, emphasizing the unique microporous in defective UiO-66 are conducive to the fabrication of AuNCs. The catalytic performance of the prepared materials in aldehyde oxidation reactions is systematically evaluated, demonstrating the remarkable efficiency of dispersed Au@UiO-66-25 with high-content (9.09 wt%) Au-loading and ultra-small size (~2.7 nm). Moreover, mechanistic insights into the catalytic process under mild conditions (70 °C for 1 h) are provided, elucidating the determination of defective UiO-66 in the confined fabrication of AuNCs and subsequent furfural adsorption, which underlie the principles governing the observed enhancements. This study establishes the groundwork for the synthesis of highly dispersed and catalytically active metal nanoparticles using defective MOFs as a platform, advancing the catalytic esterification reaction of furfural to the next level.

One-pot synthesis of oxygen-vacancy-rich Cu-doped UiO-66 for collaborative adsorption and photocatalytic degradation of ciprofloxacin

UiO-66, as one of the most stable metal-organic frameworks (MOFs), has attracted a lot of attention in the field of adsorption and photocatalysis. However, this application of UiO-66 is still limited due to either the low accessibility of micropores or the poor electron-hole charge separation capability. This study aims to promote UiO-66 accessibility of micropores and charge separation through the construction of oxygen vacancies (OVs) and mesopore defects as well as copper incorporation. Herein, mesopore Cu doped UiO-66 with rich OVs was synthesized by a one-pot method and demonstrated high efficiency for the removal of ciprofloxacin (CIP) from the aquatic system. First of all, denatured mesopore defects were produced in Cu doped UiO-66 which possessed a 58% increase in specific surface area compared to UiO-66, facilitating the adsorption of molecular oxygen. Secondly, e^- was preferentially trapped by OVs under light irradiation. Electron (e^-) reacted rapidly with the surface adsorbed oxygen to generate superoxide radical (O₂^-). Meanwhile, copper incorporation increased the photocurrent and reduced the interfacial charge transfer resistance, thereby improving the charge separation efficiency. As a result, the adsorption efficiency and photocatalytic performance of mesopore Cu doped UiO-66 with OVs were 8.1 and 3.7 times higher than those of UiO-66, respectively. This study paved a way for the one-step synthesis of MOFs containing OVs and broadened the possibilities of practical applications for photo-induced removal of antibiotics from effluent.

Generating Catalytic Sites in UiO-66 through Defect Engineering

UiO-66 is regarded as an epitome of metal-organic frameworks (MOFs) because of its stability. Defect engineering has been used as a toolbox to alter the performance of MOFs. UiO-66 is among the most widely explored MOFs because of its capability to bear a high number of defects without undergoing structural collapse. Several representative works in the field of MOF-based defect engineering are available based on UiO-66. In this review, more emphasis is given toward the construction of catalytic sites by engineering defects in UiO-66 as a representative including all the detailed synthesis procedures for inducing defects, and the characterization techniques used to analyze these defects in UiO-66 are discussed. Furthermore, a comprehensive review for the defects themselves and the support using defects in catalysis is provided to accentuate the importance of defect engineering.

Investigation of Au/Co3O4 nanocomposites in glycol oxidation by tailoring Co3O4 morphology

The interfacial perimeter of nanogold and supports is often deemed as the catalytically active site for multiple reactions while the geometrical configuration of the interfacial perimeter at atomic scale is less studied. Herein, gold nanoparticles (NPs) of ca. 2.0 nm are dispersed on Co3O4 support in the shape of nanocubes (dominant Co3O4(001) facet) and nanoplates (Co3O4(111)), which forms different Au-Co3O4 interfaces with respect to the specific facet of the oxide support. A comparison is made on the basis of the interfacial structures and catalytic behavior of ethylene glycol oxidation. STEM analysis identifies that these metallic Au NPs interact with Co3O4 with an orientation relationship of Au/Co3O4(001) and Au/Co3O4(111). XPS and Raman spectroscopy investigations reveal the important variations in the reactivity of surface oxygen, surface Oads/OL ratio, and evolution of surface oxygen vacancies upon variation of the Co3O4 shape. Au/Co3O4-P exhibits much better catalytic activity than the Au/Co3O4-C counterpart in the aerobic oxidation of ethylene glycol, which is promoted by surface oxygen vacancies and intrinsic defects. It has been revealed that the surface oxygen vacancies participate in activating O2, thus making Co3O4-P a superior support for Au NPs in the catalysis of ethylene glycol oxidation.

Active metal single-sites based on metal–organic frameworks: construction and chemical prospects

Metal single-point is a novel and potential design strategy that has been applied for the development of metal organic frameworks.