COF Supported Zirconium Oxyhydroxide Nanoparticles as Heterogeneous Catalyst for Knoevenagel Condensation and Nerve Agent Simulant Detoxification

Abstract

Covalent Organic Frameworks are crystalline polymers with intrinsic porosity and covalent linkages connecting their building blocks. They have been utilised extensively in gas storage, sensing, charge storage, catalysis, and other applications due to their great chemical stability, surface area, and tunability. Encapsulating COFs with small-sized metal, metal oxide, or oxyhydroxide nanoparticles enables them to serve as heterogeneous catalysts with recyclability, high selectivity, yield, and ease of handling. Lewis acidic zirconium, surface hydroxyl groups, and the equilibrium between oxide and hydroxide ions make zirconium oxyhydroxide a potential multifunctional catalyst, and loading of zirconium oxyhydroxide nanoparticle inside COF makes it a potential multifunctional heterogeneous catalyst. Herein, we report the successful loading of zirconium oxyhydroxide inside COF with precise control on the amount of loading. We achieved a zirconium loading of nearly 7.8 wt% and found that the loaded zirconium oxyhydroxide is converted to zirconium oxide at higher temperatures by burning the loaded COF under air at 600°C. The saturation N2 uptake of the pristine COF was 10 mmol/g, while the saturation N2 uptake of the zirconium oxyhydroxide-loaded COF was 6 mmol/g. Zirconium oxyhydroxide loaded COF was employed as a catalyst for the Knoevenagel condensation reaction. Our catalyst exhibits significant activity at room temperature with a catalyst loading of 0.8 mol% and a turnover number of 103-120, and a turnover frequency of 2.78 - 6 /min using water as a solvent. The catalyst has been proven to be recyclable for up to ten cycles. After catalysis, the crystallinity of COF has been slightly compromised, but the chemical linkages have remained intact. Additionally, 2.2 mol% of zirconium oxyhydroxide loaded COF can efficiently catalyze the hydrolysis of Dimethyl nitrophenyl phosphate (DMNP), a mimetic of nerve agent Soman, with a conversion rate of 37% in just over 180 minutes while the precursors COF and zirconium oxyhydroxides showed minimal-low activity.