Arsenic removal through supercritical carbon dioxide-assisted modified magnetic starch (starch–Fe 3 O 4 ) nanoparticles

Arsenic contamination in groundwater is an alarming issue in Terai region (the low-lying land at the foot of the Himalayas) of Nepal as groundwater serves as chief drinking water source; therefore, it is required to decrease arsenic below the maximum permissible limit (50 ppb). Supercritical carbon dioxide-assisted green chemical technology was used to synthesise starch-modified magnetic nanoparticles (starch-MNPs). Synthesised starch-MNPs were used to remove arsenic from water. Various techniques were used to characterise magnetic nanoparticles (MNPs) and starch modification on MNPs surface, viz. transmission electron microscopy, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and vibrating sample magnetometer. These analyses revealed the crystalline structure of magnetite nanoparticle with size 16 nm and uniform coating of starch onto MNPs with magnetic property. Results showed the highest arsenite [As(III)] removal in a synthetic laboratory solution of 10 ppm with at pH 6 was 99% with 0.01 g starch-MNPs, while complete removal of arsenic from groundwater sample was attained within 15 min using starch-MNPs. Arsenite adsorption agreed well with pseudo-second-order kinetic model and Langmuir isotherm model. Adsorption of arsenite on starch-MNPs reached 124 mg/g of starch-MNPs at pH 6 starch-MNPs could be regenerated in NaOH solutions and could retain more than 50% arsenite removal capacity even in fifth regeneration/reuse cycle.