Eggshell powder as an efficient recyclable catalyst generates H2O2 prompted radicals for selective oxidative mineralization of crystal violet dye at room temperature

Eggshell powder (ESP) was explored as a selective heterogeneous catalyst for oxidative degradation of crystal violet (CV) dye in aqueous media in presence of H2O2 at room temperature. Natural but throw-away material ESP as a carbonate (CO32) source facilitated the formation of carbonate anion radicals in presence of H2O2. Carbonate anion radicals (CO3 (center dot-)), though a weaker oxidant than center dot OH radical, efficiently served as a selective oxidant. Selective degradation of CV dye in aqueous solution was confirmed from the quenching experiments. Synergistic effects of both the radicals (CO3 (center dot-) and center dot OH) in the dye degradation process was experimentally verified. At a dose of 10 g/L of ESP, 91% removal of CV (initial concentration: 10 mg/L) was achieved in 60 min. The reaction kinetics followed first order rate model. Intermediate products formed during CV degradation and the extent of mineralization were confirmed from MALDI-TOF-MS and TOC analysis, respectively. The turnover number (TON) and turnover frequency (TOF) were obtained as 2.45 x 10(-6) mol per g and 6.81 x 10(-10) mol per g per second. A promising reusability was achieved up to seven cycles. The ESP catalyst used in this study was characterized by SEM, FTIR, XRD, XPS, BET surface area analysis, UV-visible DRS, XRF, and pHZPC analyses. The present work offers a novel facile but selective route for CV degradation and opens up newer possibilities for eggshell waste utilization as catalyst.

Automated summary

In this study, eggshell powder (ESP) was used as a selective heterogeneous catalyst for the oxidative degradation of crystal violet (CV) dye in aqueous media. ESP acted as a carbonate (CO32) source, facilitating the formation of carbonate anion radicals (CO3 (center dot-)) in the presence of H2O2. The combination of these radicals and center dot OH radicals led to the selective degradation of CV dye. The use of ESP as a catalyst offers a promising route for CV degradation and the utilization of eggshell waste.