Solar-enhanced photodegradation of dye and drug mixture and evaluation of phytotoxicity on seed germination and growth by an eggshell HAp/Nb2O5 heterostructure

Abstract

In this work, heterostructures of hydroxyapatite (HAp) and Nb2O5 (NO) were obtained to study their photocatalytic activity under sunlight. The samples were synthesized by the microwave-assisted hydrothermal method, and the calcium precursor used to obtain HAp was obtained from an eggshell. The influence of adding NO at 10, 30 and 50% by mass on the heterostructures was evaluated. The XRD results and the functional groups present in the FTIR spectrum confirmed the presence of the two phases in the heterostructures. UV–vis spectroscopy revealed that activation was promoted by sunlight, while PL and electrochemical analyses indicated minimized recombination of the electron/hole pairs of heterostructures due to improved charge transfer. The TEM micrographs indicated interfacial contact between the two materials. The photocatalytic efficiency of the materials was studied for the degradation of methylene blue (MB), crystal violet (CV) and tetracycline (TC) under sunlight irradiation. The heterostructure with 50% NO showed better efficiency than the other combinations and was also tested for degrading the mixture (MIX) of MB, CV and TC, for which the efficiencies were 100, 98.66 and 67.33%, respectively. Furthermore, the effects of the photocalytic dosage, concentration and pH of the solution were investigated through the MIX degradation efficiency. It was possible to propose the mechanism for the photocatalytic activity of the HAp/NO heterostructure as a direct Z-schema. The reusability of the photocatalyst and the germination tests with treated water indicated that the HAp/NO heterostructure has potential application as an efficient and nontoxic alternative for the degradation of contaminants.