Preparation of activated carbon-metal nanoparticle composite materials for the catalytic reduction of organic pollutants

This work focuses on the preparation of inexpensive composite materials based on activated carbon-containing metallic nanoparticles MNPs (M = Cu, Ag, Fe). The metal nanoparticles supported on the activated carbon were prepared by ultrasound followed by chemical treatment using a reducing agent NaBH4. The obtained materials were characterized by XRD, XRF, FTIR, XPS, TGA, SEM, and TEM analysis. The different samples were tested as catalysts for the catalytic reduction of organic pollutants (MB, MO, 4-NP) in a simple and binary system in the presence of NaBH4. The results confirmed that the content of metal nanoparticles was in the following sequence 2.12%, 11.15%, and 12.13% for the materials AC-Ag, AC-Cu, and AC-Fe, respectively. According to TEM analysis, the size and dispersion of nanoparticles differ from one catalyst to another, hence the AC-Cu material exhibited good dispersion of CuNPs having ultrafine particles in the range of 4-14 nm. In order to optimize the best conditions for the reduction reaction, the effect of the nature of the catalyst, the initial concentration of NaBH4, the concentration of the pollutant, the mass of the catalyst and the nature of the pollutant were studied, and discussed. In terms of efficiency, the AC-Cu sample was the most efficient catalyst compared to AC-Fe, and AC-Ag, mainly due to the good dispersion of CuNPs on the surface of activated carbon. The recorded rate constant for the MB, MO, and 4-NP in the single system using the same operating conditions was 0.0259 s-1, 0.0218 s-1, and 0.0074 s-1, respectively. In the binary system containing MB + MO or MB + 4-NP, the AC-Cu catalyst was more selective towards the MB dye in both systems. The reuse of the AC-Cu catalyst towards the reduction of the MB dye showed good performance during five consecutive cycles without losing its efficiency.