TiO2 is an efficient sorbent for arsenic removal due to its high affinity and stability. Although researchers have focused on the crystalline TiO2 for arsenic removal, some studies reveal that amorphous metal (hydr)oxides show a better promise in adsorbing arsenic. Also, utilizing metal (hydr)oxide adsorbents in the fine powder form causes severe operational problems. So, in this study, activated carbon blocks (CB), as point-of-use (POU) filters with high surface area and appropriate pore size, were impregnated with TiO2 through different methods to obtain an amorphous metal oxide impregnation. All impregnated CBs were characterized and analyzed for arsenic removal effectiveness. Sol-gel-derived TTIP-EtOH CB, impregnated with the most amorphous TiO2, showed the most promising performance with an arsenic adsorption capacity of 31 mg/g Ti at pH 6.3 ± 0.1 and initial arsenate concentration of 1.35 µM. On the other side, the CBs impregnated with semi-crystalline titania showed poorer performance at the same conditions that proved the effectiveness of amorphous metal (hydr)oxides in arsenic adsorption. Also, the most and least amorphous adsorbents were analyzed for arsenic removal from tap water matrices with different conductivities, where the amorphous adsorbent was still more promising than the semi-crystalline one. The efficiency of TTIP-EtOH CB in removing para-chlorobenzoic acid (p-CBA), as a chlorinated organic compound, was not only maintained but also was improved after impregnation with amorphous titania. Freundlich isotherm evaluation of TTIP-EtOH showed 1/n and K values of 0.23 and 10.7 (µg/mg)(L/µg)1/n, respectively, confirming the super-favorable adsorption of arsenic on amorphous TTIP-EtOH with a high capacity. Also, the pore surface diffusion model (PSDM) was utilized to support justifying the better performance of amorphous TTIP-EtOH. Finally, long-term column tests were run to compare the performance of TTIP-EtOH CB in both continuous and intermittent modes as a POU filter.

Amorphous TiO2-impregnated activated carbon block filter as an efficient adsorbent for mitigation of arsenic from water

ACS Spring 2022

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