Fast catalytic degradation of organic dyes in aqueous media using copper sulfate deposited on biowaste-derived hydroxyapatite

Abstract

Conversion of biowastes into valuable products will assist sustainable development and waste management. Eggshell could be used as a bio-template for the synthesis of hydroxyapatite and widely applied in the field of catalytic processes. In this study, copper sulfate supported on hydroxyapatite (CuSO4@HAP) was rationally fabricated using biowaste eggshells (ES) by hydrothermal method and it was used for the fast catalytic degradation of organic pollutant dyes (OPDs) such as methylene blue (MB), 4-nitrophenol (4-NP) and 4-nitroaniline (4-NA) in the presence of sodium borohydride (NaBH4) in aqueous media. The physical and chemical properties of CuSO4@HAP were characterized via FTIR, XRD, BET, TEM, FE-SEM/EDS, and elemental mapping analyses. Results indicated that the synthesized catalyst was crystalline with great purity, homogeneous with fine particles, and mesoporous with a high specific surface area. Besides, the reaction progress was evaluated using a double-beam UV-vis spectrophotometer. The reaction conversion (%) under optimal conditions rapidly increased to an equilibrium state (99% for 4-NP, 96% for 4-NA, and 99.5% for MB) within a short time (t < 10 min). In addition, the catalytic rate constant of MB, 4-NP, and 4-NA in the presence of NaBH4 and CuSO4@HAP was calculated to be about 0.514, 0.492, and 0.317 min− 1, respectively. This study demonstrates the potential use of natural HAP-derived catalyst from biowaste eggshell with high efficiency and stability for degrading OPDs under mild reaction conditions. Additionally, CuSO4@HAP could be effectively separated and reused for four cycles with almost the same catalytic efficacy.