Catalytic degradation of organic dyes using eggshell-derived hydroxyapatite coated by silver nanoparticles

Developing chemical remediation techniques has become an increasingly important research topic due to the growth in the use of organic dyes which can be harmful to nature and human health. Catalytic reduction reaction of organic pollutant dyes (OPDs) in the presence of metal nanoparticles (MNPs) such as copper, silver and palladium is an efficient and simple method to treat polluted industrial waters. However, easily agglomeration of the MNPs impacts their efficiency and re-usability. Therefore, we used chicken eggshells as a natural resource to make hydroxyapatite (HAP) as a heterogeneous bed with high contact surface by friendly hydrothermal and environmentally method. The HAP was coated with silver nanoparticles (AgNPs@HAP) and was used as an efficient and recyclable catalyst for the reduction of OPDs (Methylene blue (MB), 4-Nitrophenol (4-NP) and 4-Nitroaniline (4-NA)) in the presence of sodium borohydride. The reduction reaction was performed in less than 10 minutes with excellent efficiency (approximately 100%) and the reaction kinetics were investigated by change of the absorption intensity using a two-beam UV-Vis spectrophotometer. The physical and chemical properties of AgNPs@HAP were evaluated and the prepared solid heterogeneous catalyst was characterized via FTIR, XRD, BET, TEM, FE-SEM/EDS and elemental mapping analysis. This study demonstrates the potential use of HAP derived from biowaste eggshell with high efficiency for the degradation of OPDs under mild reaction conditions at room temperature. In addition, AgNPs@HAP showed high stability and reusability for four cycles with almost constant catalytic performance.