Abstract
In the present work, a temperature and pH-responsive hybrid catalytic system using copolymer-capped mesoporous silica particles with metal nanoparticles is proposed. The poly(2-(dimethylamino)ethyl methacrylate)(DMAEMA)-co-N-tert-butyl acrylamide) (TBA)) shell on mesoporous silica SBA-15 was obtained through free radical polymerization. Then, copper nanoparticles (CuNPs) decorated SBA-15/copolymer hybrid materials were synthesized using the NaBH4 reduction method. SBA-15 was functionalized with trimethoxylsilylpropyl methacrylate (TMSPM) and named TSBA. It was found that the CuNPs were uniformly dispersed in the mesoporous channels of SBA-15, and the hybrid catalyst exhibited excellent catalytic performance for the selective oxidation of different substituted benzyl alcohols in water using H2O2 as an oxidant at room temperature. The dual (temperature and pH-) responsive behaviors of the CuNPs/p(DMAEMA-co-TBA)/TSBA catalyst were investigated using the dynamic light scattering technique. The conversion of catalytic products and selectivity were calculated using gas chromatographic techniques, whereas the molecular structure of the products was identified using 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. The catalyst showed excellent catalytic activity toward the oxidation of alcohol to aldehyde in an aqueous medium below the lower critical solution temperature (LCST) and pKa values (7–7.5) of the copolymer. The main advantages of the hybrid catalyst, as compared to the existing catalysts, are outstanding alcohol conversion (up to 99%) for a short reaction time (1 h), small amount of the catalyst (5 mg), and good recyclability equal to at least five times.
Highlights
Selective oxidation of benzyl alcohol to benzaldehyde is essential in perfumery and food industries
0.2 g of modified SBA-15 (named TSBA, which is SBA-15 functionalized with trimethoxyl silyl propyl methacrylate (TMSPM); the detailed experimental procedure is provided in the Supplementary Data) was added to the reaction mixture
CuNPs were successfully immobilized on a temperature- and pH-responsive copolymer with mesoporous silica SBA-15, which was found to be a highly active, eco-friendly, and recyclable catalyst for the selective oxidation of alcohols in water at room temperature
Summary
Selective oxidation of benzyl alcohol to benzaldehyde is essential in perfumery and food industries. Precious metals used for the catalysts are usually not so cheap. In this sense, copper-supported catalysts may be an alternative [8,9,10,11,12]. Few works on the use of copper or copper oxide nanoparticles-based catalysts were, reported in benzyl alcohol oxidation [8,9,10,11,12,13]. The use of copper nanoparticles (CuNPs) is restricted by Cu’s inherent instability under atmospheric conditions, which makes it prone to oxidation. Some supporting materials increase the stability of CuNPs by altering their sensitivity to oxygen, water, and other chemical entities, which has encouraged the exploration of alternative Cu-based NPs with more complex structures [12,14]
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