Insights into Catalytic Reduction of Organic Pollutants Catalyzed by Nanoparticles Supported on Zeolite Clinoptilolite

In this study, the clinoptilolite zeolite was used as a support for the stabilization of several metallic nanoparticles MNPs (M: Ag, Cu and Ni) through ion exchange and chemical treatment. The modified samples were used as a catalyst for the degradation of various organic pollutants (three nitrophenol isomers (2-NP, 3-NP and 4-NP), methylene blue (MB) and congo red (CR)). In order to study the selectivity of the catalyst, the reduction of different pollutants was carried out in a simple and binary system. All materials were characterized by XRD, XPS, FTIR, XRF and SEM to get more information on their properties. Several parameters affecting the reaction were investigated and optimized such as the nature of the catalyst, the catalyst mass, the concentration of NaBH4, and the initial concentration of the pollutants. The results showed that the nanoparticles were well formed on the surface of the zeolite clinoptilolite. According to XRF analysis, the content of nanoparticles in each catalyst differs in the following order: 2.3%, 1.1% and 0.9% for ZC-Ag, ZC-Cu and ZC-Ni, respectively. The catalytic reduction showed that all prepared catalysts have the power to reduce organic pollutants, but the catalyst ZC-Cu containing CuNPs was the best in terms of efficiency. The greatest rate constant recorded by this catalyst was 0.0078 s(-1) for the reduction of MB dye. The application of this catalyst in a binary system between MB dye and 4-NP showed that the catalyst ZC-Cu was selective with the MB dye. This selectivity towards the MB dye was explained by electrostatic interactions between the cationic dye and the negative charge of ZC-Cu. The reuse of the catalyst ZC-Cu for the reduction of 4-NP during five cycles has shown encouraging results with a higher conversion of 4-NP to 4-AP. The catalyst ZC-Cu after its reuse for five cycles does not show any Cu leaching confirming its stability.