Impact of long-term storage of various redox-sensitive supported nanocomposites on their application in removal of dyes from wastewater: Mechanisms delineation through spectroscopic investigations

For the prevention of freshwater reservoirs from contamination through industrial effluents, eco-friendly adsorbents with minimal aging impact are required. Here, redox-sensitive nanoscale zero-valent iron(nZVI) particles were supported on four different surfaces with varying bentonite(B)/charcoal(C) ratio to mimic layered and porous surfaces. Different dyes, i.e. rhodamine-B(RB) and methylene blue(MB) were reacted with redox-sensitive supported nZVI composites, and degradation mechanisms were delineated using FT-IR spectroscopic analysis of reaction precipitates. A 300-day exposure to open-air was provided to the composites to comparatively evaluate the impact of aging on their reactivity for dyes in wastewater. Results interpret that dyes removal was a combination of different interfacial chemical processes, i.e., reduction or organic degradation probably through Fenton like processes, along with sorption. These mechanisms were found to be surface dependent, i.e., nZVI on charcoal enriched porous surfaces, degrade dyes through organic degradation while on layered clay surfaces, MB gets removed through reduction with limited and slower RB removal. Nanocomposites show a minimal impact of aging with removal capacities >100 mg/g for BC-1/3-nZVI and C-nZVI for MB and 50-75 mg/g for RB with significant removal in wastewater. Overall, the study concludes C-nZVI and novel BC-1/3-nZVI as two efficient dye adsorbents with minimal aging impact.