Enhancing corrosion stability and shelf life of nanoscale zero-valent iron via encapsulation in porous Ze-TiO2 matrix: An interface for simultaneous oxidation and adsorption of As(III)

The potential of Nanoscale zero-valent iron (nZVI) for arsenic removal is immense, however its stability is still a concern, as it forms aggregates and is quickly oxidized in groundwater. The focus of the present work is to enhance the shelf life of nZVI and simultaneously using it to develop a material with high rate of adsorption (i.e. 10 mg g−1 in 60 min) for As(III) in ultra-low concentrations (100−1000 μg L−1). The composite was prepared by growing nano-titania on zeolite (Ze) surface in multilayers, and doping it with nZVI. Characterization of the composite was done using SEM, TEM, FT-IR, BET and XPS studies. The porous titania layer imparts a hydrophilic character to an otherwise hydrophobic substrate of zeolite, enhancing rate of As(III) adsorption. Nano TiO2 in the composite plays an important role by preventing nZVI against corrosion, besides oxidizing As(III) to less toxic As(V) which is then removed by adsorption and subsequent complexation with nZVI. The design of the proposed composite structure resulted in a remarkable increase in the shelf life of nZVI upto six months and showed corrosion stability even after numerous adsorption-desorption cycles. The As(III) adsorption mechanism has been proposed using kinetics and isotherm study. Additionally, the ease of magnetic separation and recyclability substantiates the potential utilization of the composite for treatment of As(III) contaminated drinking water.