Effects of organic acids of different molecular size on phosphate removal by HZO-201 nanocomposite

- Three diverse-sized organic acids have distinct effect on P-PO43− uptake by HZO-201.
- The small-sized GA reduce capacity of P-PO43− by competing for sites directly.
- The middle-large TA inhibit P-PO43− adsorption rate due to pore blockage.
- The largest HA pose little impact on P-PO43− removal because of size exclusion.
- The organic acids compete for R-N+(CH3)3 of HZO-201 instead of the nano-HZO sites.

Various organic acids in wastewater effluent could significantly influence the performance of phosphate adsorbent. This study focused on the effects of organic acids of different-molecular-size on phosphate adsorption by a novel nanocomposite HZO-201. Three organic acids (gallic acid (GA), tannic acid (TA) and humic acid (HA)) with distinct molecular size (HA > TA > GA) were chosen for this purpose. Both isotherm and kinetic tests of phosphate adsorption were conducted in the single-phosphate and binary system, and a series of microscopic techniques (i.e., XPS, FT-IR and SEM-EDX) and N2 adsorption-desorption test were employed to explore the underlying mechanism. It was found that GA could greatly weaken phosphate adsorption capability of HZO-201 by directly competing for ammonium group on the nanocomposite, TA exhibited significant inhibition on phosphate adsorption rate mainly through pore constriction/blockage, while HA posed negligible impact on phosphate adsorption because of the size exclusion effect. It was also observed that although GA, TA and HA showed substantial influence on bulky HZO due to complexation, their impact on the nano-HZO loaded inside HZO-201 was little. The covalently bounded ammonium group and the networking pore structure of HZO-201 may play important roles in it.