Synthesis, characterization and exploitation of nano-TiO2/feldspar-embedded chitosan beads towards UV-assisted adsorptive abatement of aqueous arsenic (As)

Abstract

This study aimed to develop an ecofriendly bio-photocatalyst for arsenic abatement in the aqueous phase. Nano-TiO2/feldspar embedded chitosan composite was developed by immobilizing nano-sized TiO2 and feldspar fine particles in the matrix of chitosan, which was then characterized via Fourier Transform Infrared Spectrometry (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDX), and Brunauer, Emmett and Teller (BET) surface area analyses. Batch adsorption experiments equipped with UV-illumination set-up were conducted to study operational parameters, e.g. solution pH, UV light and co-existing ions, along with the kinetics, isotherm and thermodynamics of the process. Unlike other TiO2-based remediation techniques, the synthesized composite effectively removed arsenic in a wide range of pH, with a slight removal drop with increasing pH for arsenate and negligible pH influence on arsenite removal. It showed selective removal for arsenate in the presence of co-existing ions including fluoride and sulfate, yet, phosphate indicated somewhat competing effect when existed in higher concentrations. The isotherm and kinetics of adsorption were investigated through linear and nonlinear modeling. Sips isotherm and pseudo-second order kinetic models best fitted with the experimental data. Langmuir’s maximum adsorption capacities via linear and nonlinear modeling were found to be 2000 and 2025μg/g, respectively. The adsorption-photocatalysis system under UV exposure resulted in higher removal of both arsenate and arsenite. UV irradiation enhanced removal efficiencies from 33% to 73% and from 23% to 84% for arsenate and arsenite (4800μg/L), respectively. Temperature studies revealed a thermodynamically spontaneous and favorable process. Identified through characterization analyses, functional groups on chitosan structure including –NH2 and –OH along with the metal oxide contents of the bio-photocatalyst are introduced as the adsorptive-photoactive sites.