As(III) removal of aqueous solutions using zerovalent iron nanoparticles: The role of the UVA-Vis irradiation wavelength

PABÓN REYES, DEISY C.; HALAC, EMILIA B.; LITTER, MARTA I.

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY

ELSEVIER SCIENCE SA

Año: 2023 vol. 443

1010-6030

Arsenic contamination in drinking water is dramatic in many countries, particularly in Asia and Latin America.Arsenic removal from water can be achieved through some conventional technologies but some of them havedrawbacks or are very expensive, especially in developing countries, where the population uses groundwater fordrinking purposes. Therefore, the need of searching for new and low-cost methodologies for As removal fromwater is mandatory. Because As(V) is removed more easily than As(III), oxidation of this species, when present, isneeded as the first step. The use of zerovalent iron nanoparticles (nZVI), particularly reactive due to theirextremely small particle size and large surface area can be proposed at a household scale and in isolated regions.The effect of UV–Vis irradiation on the removal of arsenical species using nZVI presents scarce reports in theliterature. In the present work, experiments of As(III) removal with commercial nZVI under UVA-Vis irradiation(λem = 300–800 nm) are described. The effect of the As(III) concentration, the As:nZVI molar ratio (MR = [As(III)]:[FeTOTAL]), and the irradiation wavelength on the As(III) removal were analyzed. Two initial As(III) concentrations,1 and 10 mg L􀀀 1, and different MR in the range 1:10–1:100 were tested at pH 6–6.8. The increase ofthe nZVI amount and the use of UV–Vis irradiation enhanced the As removal under all conditions. The optimalMR for the As(III) removal after 60 min of irradiation at both initial concentrations was 1:30, being 85% for [As(III)]0 = 10 mg L􀀀 1, and 92% for [As(III)]0 = 1 mg L􀀀 1. By the use of chemical optical filters, it was determinedthat the most efficient wavelengths to improve the As(III) removal were those lower than 450 nm. All experimentaldata were adjusted to a biexponential decay suggesting the occurrence of two removal processes, onefaster than the other. It was proposed that the main mechanisms under UVA-Vis irradiation were the action ofoxides and oxyhydroxides already present or formed on the surface of nZVI during the reaction as semiconductorsoriginating oxidative species and a ligand-to-metal charge-transfer reaction on As(III)-Fe(III) complexesformed in the system with simultaneous As(III) oxidation and Fe(III) reduction. It was concluded that theeffect of the light depends on the pollutant and not on the iron material.