Sustainable industrial wastewater via photocatalysis using green-synthesised MnO <sub>2</sub> nanoparticles
A. G. Bharathi Dileepan, S. Jeyaram
Abstract
In this study, manganese dioxide (MnO2) nanoparticles (NPs) were synthesised using a green method that employed Shuteria involucrata (S. involucrata) leaf extract as a natural reducing and stabilising agent. The resulting nanoparticles were thoroughly characterised to evaluate their structural, optical, and catalytic properties. X-ray diffraction confirmed that the nanoparticles have a tetragonal rutile phase, with an average crystallite size of 47.99 nm. UV–vis spectroscopy indicated a reduced bandgap of 1.53 eV, suggesting their potential for visible-light-driven photocatalysis. Fluorescence and infrared spectroscopy revealed the presence of surface defects and organic functional groups, indicating improved stability and surface modification. Morphological analysis showed the formation of nanoclusters ranging from 100 to 200 nm, while BET analysis confirmed a mesoporous structure with a surface area of 9.706 m2/g. The photocatalytic efficiency was assessed through the degradation of industrial wastewater (black liquor), which demonstrated significant reductions in COD by 75%, TOC by 76%, and BOD by 58%. GC–MS analysis confirmed the breakdown of complex organic compounds into simpler intermediates. Furthermore, NLO studies using the Z-scan technique revealed reverse saturable absorption and negative nonlinearity, with a third-order susceptibility (χ3) value of 2.64 × 10−7 esu. These findings underscore the multifunctional potential of green-synthesised MnO2 NPs for environmental remediation and photonic applications, highlighting their significant role in sustainable and eco-friendly technologies.