Multifunctional Aryl Sulfonium Decavanadates: Tuning the Photochromic and Heterogeneous Oxidative Desulfurization Catalytic Properties Using Salicylaldehyde-type Functional Moieties on Counterions

Multifunctional materials based on polyoxovanadates (POVs) have rarely been reported. Herein, we used aryl sulfonium counterions (ASCIs) bearing a salicylaldehyde-type functionality to tune the properties of decavanadate ([V10O28]6-)-based hybrids for their application in photochromism and heterogeneous oxidative desulfurization (ODS) catalysis. The counterions FHPDS ((3-formyl-4-hydroxyphenyl)dimethylsulfonium), DFHPDS ((3,5-diformyl-4-hydroxyphenyl)dimethylsulfonium), and EFPDS ((4-ethoxy-3-formylphenyl)dimethylsulfonium) were clubbed with the decavanadate cluster to generate the hybrids (FHPDS)4[H2V10O28](H2O)4 (HY1), (DFHPDS)4[H2V10O28](H2O)3 (HY2), and (EFPDS)4[H2V10O28](H2O)6 (HY3). The photochromic properties of these hybrids were tested under 365 nm irradiation, which showed a color change from yellow to green. Different hybrids exhibited different photocoloration half-life (t1/2) values in the range of 0.77-28.38 min, suggesting the dependence of the photocoloration properties upon functional groups on the counterions. The hybrid HY2, having a 2,6-diformyl phenol moiety on the ASCI, exhibited an impressive t1/2 of 0.77 min. UP to 70% reversibility of photocoloration was achieved for the best photochromic hybrid HY2 in 48 h at 70 °C under an oxygen atmosphere. Theoretical and experimental data suggested that some of these aryl sulfonium POVs follow a different e--h+ stabilization mechanism than traditional sulfonium POM hybrids. Further, the salicylaldehyde-type ASCIs control the solubility of the decavanadate hybrids, which enables their application as heterogeneous catalysts for the selective oxidation of various sulfides. The nature of the substituents on the ASCIs also affected their catalytic activities; the counterion that facilitates the reversible V4+/V5+ switching enhances the catalytic ODS efficiency of the hybrids. Using HY2 as the catalyst, up to 99% conversion and 96% selectivity toward sulfones were achieved in dibenzothiophene (DBT) oxidation. The present study suggests a new promising approach for controlling POVs' photoresponsive and catalytic properties by using ASCIs bearing salicylaldehyde-type functional moieties.

Polyoxometalates encapsulated into hollow double-shelled nanospheres as amphiphilic nanoreactors for an effective oxidative desulfurization

Although some catalytic hollow nanoreactors have been fabricated in the past, the encapsulated active species focus on metal nanoparticles, and a method for polyoxometalate (POM)-containing hollow nanoreactors has seldom been developed. Herein, we report a synthetic strategy towards POM-based amphiphilic nanoreactors, where the hollow mesoporous double-shelled SiO₂@C nanospheres were used to encapsulate Keggin-type H₃PMo₁₂O₄₀ (PMo₁₂). The outer hydrophobic carbon shell was beneficial for the enrichment of the organic substrate around the nanoreactor and simultaneously prevented the deposition of POMs on the outer surface of the nanoreactor. The inner hydrophilic silica cavity was modified by two types of organosilanes, which not only created an amphiphilic cavity environment but also acted as an anchor to mobilize PMo₁₂. As the POM nanoreactor had the hydrophilic@hydrophobic SiO₂@C shell and an amphiphilic cavity, both dibenzothiophene (DBT) and H₂O₂ could smoothly diffuse into the nanosized cavity, where the DBT was effectively oxidized (conversion: >99%) by the immobilized PMo₁₂ under mild conditions. Importantly, the control experiments indicated that the confined effect of nanoreactor, amphiphilic SiO₂@C double-shell, unique cavity environment, and mesoporous channels accounted for an excellent catalytic performance. Moreover, the nanoreactor was robust and could be reused for five cycles without loss of activity.

Engineering polyoxometalate-intercalated layered double hydroxides for catalytic applications

Polyoxometalate-intercalated layered double hydroxide (POM-LDH) nanocomposites have received considerable attention in recent years because such nanocomposites not only inherit the intrinsic properties of POMs and LDHs but also exert significant synergistic effects during the catalytic process. In this frontier article, we present the latest advances on the POM-LDH nanocomposites ranging from new synthetic methods to catalytic applications. By making use of the host layer modification method and exfoliation assembly method, the as-prepared POM-LDH nanocomposites show a wide range of catalytic applications. The challenges and future opportunities are also discussed by highlighting some creative work on related POM- or LDH-based materials.

Synergistic effects of MOF-76 on layered double hydroxides with superior activity for extractive catalytic oxidative desulfurization

The combination of MOF-76 with an LDH provides a completely new route for the synthesis of MOF–LDH advanced functional materials.

Mono-transition-metal-substituted polyoxometalate intercalated layered double hydroxides for the catalytic decontamination of sulfur mustard simulant

The mono-transition-metal-substituted polyoxometalate intercalated layered double hydroxides Zn₂Cr-LDH-PW₁₁M can effectively catalyze the oxidative decontamination of a sulfur mustard simulant.

Bifunctional Solid Catalyst for Organic Reactions in Water: Simultaneous Anchoring of Acetylacetone Ligands and Amphiphilic Ionic Liquid "Tags" by Using a Dihydropyran Linker

The use of solid catalysts to promote organic reactions in water faces the inherent difficulty of the poor mass-transfer efficiency of organic substances in water, which is often responsible for insufficient reaction and low yields. To solve this problem, the solid surface can be manipulated to become amphiphilic. However, the introduction of surfactant-like moieties onto the surface of silica-based materials is not easy. By using an accessible dihydropyran derivative as a grafting linker, a surfactant-combined bifunctional silica-based solid catalyst that possessed an ionic liquid tail and a metal acetylacetonate moiety was prepared through a mild Lewis-acid-catalyzed ring-opening reaction with a thiol-functionalized silica. The surfactant-combined silica-supported metal acetylacetone catalysts displayed excellent catalytic activity in water for a range of reactions. The solid catalyst was also shown to be recyclable, and was reused several times without significant loss in activity.

Self-Assembly in Polyoxometalate and Metal Coordination-Based Systems: Synthetic Approaches and Developments

Utilizing new experimental approaches and gradual understanding of the underlying chemical processes has led to advances in the self-assembly of inorganic and metal–organic compounds at a very fast pace over the last decades. Exploitation of unveiled information originating from initial experimental observations has sparked the development of new families of compounds with unique structural characteristics and functionalities. The main source of inspiration for numerous research groups originated from the implementation of the design element along with the discovery of new chemical components which can self-assemble into complex structures with wide range of sizes, topologies and functionalities. Not only do self-assembled inorganic and metal–organic chemical systems belong to families of compounds with configurable structures, but also have a vast array of physical properties which reflect the chemical information stored in the various “modular” molecular subunits. The purpose of this short review article is not the exhaustive discussion of the broad field of inorganic and metal–organic chemical systems, but the discussion of some representative examples from each category which demonstrate the implementation of new synthetic approaches and design principles.

One-pot synthesis of polyoxomolybdate anion intercalated layered double hydroxides and their application in ultra-deep desulfurization of fuels under mild conditions

1 mol sulfur-containing compounds can be directly oxidized by 2 mol oxidants into their corresponding sulfones.

A dual-signal sensing system based on organic dyes-LDHs film for fluorescence detection of cysteine

It is of great significance to sense cysteine (Cys) in a simple and fast way because of its potential applications in biological processes.

MoO3 subnanoclusters on ultrasmall mesoporous silica nanoparticles: an efficient catalyst for oxidative desulfurization

MoO₃ subnanoclusters encapsulated in ultrasmall mesoporous silica nanoparticles (ca. 14 nm) exhibited enhanced catalytic activity for oxidative desulfurization.