Carboxymethyl β-cyclodextrin immobilized on hydrated lanthanum oxide for simultaneous adsorption of nitrate and phosphate

Background: Excessive nitrate and phosphate in water is a major cause for eutrophication. Methods: Carboxymethyl β-cyclodextrin immobilized on hydrated lanthanum oxide (LaCD) composite was fabricated, using carboxymethyl β-cyclodextrin (CM-β-CD) to immobilize hydrated lanthanum oxide (HLO). LaCD can efficiently and simultaneously adsorb nitrate and phosphate. Significant findings: Results disclosed that the adsorption capacity in sole system reached 37.50 mg N/g and 66.98 mg P/g, whereas the adsorption capacity in binary system reached 31.62 mg N/g and 64.05 mg P/g. LaCD can also maintain high and stable adsorption efficiency within a wide pH range (4–11). Characterizations indicated excellent adsorption efficiency of LaCD for nitrate and phosphate. This finding may be due to electrostatic interaction, hydrogen bonding of abundant oxygen-containing groups on CM-β-CD surface and host-guest interaction in β-cyclodextrin (β-CD) cavity. HLO on LaCD had specific adsorption to phosphate through Lewis acid-base interaction and ligand exchange. Ten cycles verified LaCD had excellent reusability in adsorption-desorption experiments. This study may provide a supplementary method for synchronous and efficient removal for nitrate and phosphate to solve water eutrophication problem.