Adsorption and degradation of Congo red on a jarosite-type compound

Abstract

Natrojarosite particles were prepared by forced hydrolysis. X-ray diffraction and field-emission scanning electron microscopy were used to characterize the resulting products. Degradation of the azo dye Congo red (CR) by natrojarosite was investigated under various conditions, such as in the presence or absence of visible-light irradiation, catalyst loading, H₂O₂ concentration, and initial pH. Total organic carbon determination, UV-visible spectroscopy, and direct infusion-electrospray ionization mass spectrometry in the negative ion mode provided insight into the nature of the degradation products. Moreover, a complete degradation mechanism of CR on natrojarosite was presented. The degradation of CR in the current system occurred even at neutral pH, and the total degradation rate was close to 99.1% for a 30 mg L⁻¹ CR solution. Approximately 80% of the samples were completely mineralized and the other 20% were degraded to small-molecule products. The novel natrojarosite catalysts are potentially valuable for industrial applications because of their high activity, low iron leaching, and low cost.