Abstract
Developing heterogeneous catalyst using chitosan (CS) and magnetic Fe3O4 as support has been remarkably attractive due to their availability, low cost and non-toxicity. In this work, a heterogeneous catalyst (denoted as Fe3O4@CS@MS@Ag) was fabricated by the deposition of silver nanoparticles on magnetic chitosan via an easy and facile modification of its surface with methyl salicylate (MS). The catalyst was characterized using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). To the best of our knowledge, for the first time, CS decorated Fe3O4 (Fe3O4@CS) has shown the catalytic activity for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in presence of NaBH4. Surface modified magnetic chitosan (Fe3O4@CS@MS) also acts as active catalyst towards the reduction of 4-NP. However, catalytic efficiency has increased fourfold when silver-nanoparticles-deposited magnetic chitosan (Fe3O4@CS@MS@Ag) used as our target catalyst. The catalyst was separated with external magnet after each cycle of catalytic reaction and reused effectively five times with almost 90% efficiency.
Highlights
Many researchers are focusing on the development of sustainable materials by minimizing waste and pollution in the chemical synthesis
In the Fourier transform infrared (FTIR) spectrum of the Fe3 O4 (a), the characteristic stretching vibration of Fe-O has been observed at 545 cm−1
Fe3 O4 @CS shows the catalytic efficiency for the reduction of 4-NP to 4-AP in the presence of NaBH4 solution
Summary
Many researchers are focusing on the development of sustainable materials by minimizing waste and pollution in the chemical synthesis. Literature survey reports that the catalyst used at least one step in more than 90% of industrial multi-step synthesis processes [1]. Homogenous catalysts have some advantages such as dissolving in reaction media, active sites of catalysts are radially available for the substrates, monitoring real-life mechanistic study and good selectivity towards desired products [2]. Heterogeneous catalysts are given priority over homogenous catalysts in the industrial application regarding the easy separation of the catalyst from the reaction mixtures and obtaining pure targeted products with minimal involvement of purification steps. Nanomaterials based heterogeneous catalysts have the benefit regarding recovery and reuse in green chemical synthesis processes. Magnetic nanomaterials-based heterogeneous catalysts are superior over the other nanomaterials-based heterogeneous catalysts because of the us of external magnet rather than centrifuge or suction filtration or gravitational filtration for the Catalysts 2019, 9, 839; doi:10.3390/catal9100839 www.mdpi.com/journal/catalysts
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