Chitosan supported silver nanoparticles: an active and recyclable heterogenous catalyst for the reduction of organic dyes in waste water

The release of industrial effluent containing organic dyes in main streams of water is a big threat to the ecosystem as well as human beings. In this regards, several physical and chemical methods have been implemented for waste water purification before its discharge back to the natural resources. The aim of this thesis was the synthesis of a heterogenous catalysts containing silver nanoparticles loaded on glutaraldehyde cross-linked chitosan and its catalytic application for the reduction of organic dyes in its aqueous solution. Para-nitroaniline and phenol red are the two organic dyes that have been tested with the synthesized catalysts. The reduction of the dyes was carried out with sodium borohydride as a hydrogen source. FT-IR technique was used for the identification of different functional groups in cross-linked chitosan support and the catalyst. Besides that, the support and the catalyst have been characterized using other techniques, including powder XRD for determining the crystalline phase, SEM analysis for evaluating the sample surface, and ICP-OES for understanding how much silver is loaded onto the chitosan surface. The catalytic activity was tested by varying the catalyst amount, NaBH4 amount, dye concentration, reaction temperature, and silver loading on the catalyst support. The progress of reaction was monitored by using UV-vis spectrophotometry. Kinetic studies of both organic reductions were carried out to identify a rate law, and compute the activation energy, pre-exponential factor using the Arrhenius equation, and partial reaction order. Aging of the catalyst was tested with both dyes, and the results demonstrated that after five recycling cycles, the catalyst was still active. In the case of phenol red dye, besides the reduction with the nanoparticles loaded chitosan and hydrogen source, an adsorption phenomenon on the catalyst surface was also identified. The studies demonstrated that the synthesized catalyst is highly active for the reduction of para-nitroaniline into para-phenylenediamine, and the reduction of phenol red dye.