Iron nanoparticles prepared from South African acid mine drainage for the treatment of methylene blue in wastewater

Abstract

AbstractIn this study, three acid mine drainage (AMD) sources were investigated as potential sources of iron for the synthesis of iron nanoparticles using green tea extract (an environmentally friendly reductant) or sodium borohydride (a chemical reductant). Electrical conductivity (EC), total dissolved solids (TDS), dissolved oxygen (DO), oxidation–reduction potential (ORP), ion chromatography (IC), and inductively coupled plasma-mass spectroscopy (ICP-MS) techniques were used to characterize the AMD, and the most suitable AMD sample was selected based on availability. Additionally, three tea extracts were characterized using ferric-reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picryl-hydrazine-hydrate (DPPH), and the most suitable environmentally friendly reductant was selected based on the highest FRAP (1152 µmol FeII/g) and DPPH (71%) values. The synthesized iron nanoparticles were characterized and compared using XRD, STEM, Image J, EDS, and FTIR analytical techniques. The study shows that the novel iron nanoparticles produced using the selected green tea (57 nm) and AMD were stable under air due to the surface modification by polyphenols contained in green tea extract, whereas the nanoparticles produced using sodium borohydride (67 nm) were unstable under air and produced a toxic supernatant. Both the AMD-based iron nanoparticles can be used as Fenton-like catalysts for the decoloration of methylene blue solution. While 99% decoloration was achieved by the borohydride-synthesized nanoparticles, 81% decoloration was achieved using green tea-synthesized nanoparticles.