Modification of Recovered Silicon from End-of-Life Photovoltaic Panels for Catalytic Reduction of Cr(VI)

Abstract

As installed photovoltaic panels (PVPs) approach their End of Life (EoL), the need for a sustainable recovery plan becomes imperative. This work aims to reuse silicon from EoL PVPs as a potential catalyst/photocatalyst for wastewater treatment. PVPs were pretreated thermally. The resulting mixture was separated into different fractions using a trommel screen. Recovered silicon flakes were cleaned with HΝO3 and HF in order to obtain pure Si, which was then etched through a single stage Ag-assisted Chemical Etching process and decorated with Ag/Cu. Photocatalytic reduction of Cr(VI) in the presence of 5 mM citric acid was carried out in a 600 mL batch reactor irradiated by a Xenon 150 W arc lamp as well as under dark conditions. It was found that, in the presence of 1.2 g/L of Si catalyst, Cr(VI) at an initial concentration of 15 mg/L can be reduced below the detection limit (>99%), even under dark conditions, in 30–180 min, depending on the pH of the solution and the citric acid concentration. Citric acid was proved to assist the reaction in three ways: lowering the pH, increasing the solubility of the precipitate, preventing inhibition, and as sacrificial agent in photocatalysis. Irradiation, however, was shown to possibly inhibit the process if the citric acid concentration is low.