Sustainable catalysis: Transforming spent diatomaceous earth into Fenton-like catalysts for emerging pollutant mineralization

Abstract

This study examines the transformation of spent diatomaceous earth (SD), an abundant waste material from the brewing industry, into catalysts for the Fenton-like oxidation of bisphenol-A (BPA), a concerning emerging water pollutant. The material modification process included thermal treatment to remove organic matter, alkaline etching to enhance surface area and iron impregnation to introduce active sites. The catalysts were thoroughly characterized using N2 Physisorption technique, Scanning Electron Microscopy, X-ray Diffraction, Energy Dispersive Spectroscopy, Fourier Transform Infrared Spectroscopy, and Mössbauer Spectroscopy. The catalysts were tested in batch Fenton-like processes to evaluate their performance in BPA degradation and mineralization. Alkaline etching markedly improved the textural properties and increased the relative iron content of SD, boosting its catalytic activity. Iron-impregnated samples demonstrated decreased iron leaching and higher oxidant efficiency compared to non-impregnated ones. Among the samples, the catalyst containing 10 wt% added iron exhibited excellent activity, stability and reusability over multiple Fenton-like reaction cycles, proving its suitability for long-term applications. The highest mineralization level (85 %) was achieved with this catalyst at 70 °C and pH 3, using a catalyst load of 2 g/L and a single oxidant dose (36:1 H2O2/BPA molar ratio). This research offers a sustainable approach for the valorization of spent diatomaceous earth, converting this industrial waste into an efficient catalyst, thereby addressing critical environmental challenges in water treatment by advanced oxidation processes.