The uptake performance and microscopic mechanism of inorganic-organic phosphorus hybrid amorphous hydroxyapatite for multiple heavy metal ions

Abstract

Our previous studies have shown that the modification of hydroxyapatite with organic phosphonates can greatly improve the adsorption effect of hydroxyapatite on heavy metal ion pollutants. Hydroxyethylydene-1,1-diphosphonate (HEDP) is a widely used multi-purpose chemical agent with the advantage of lower-cost, but the preparation and application of hydroxyapatite composites doped by HEDP have not been reported. Therefore, in the present work, calcium nitrate and diammonium hydrogen phosphate were used as the calcium source and inorganic phosphorus source, respectively. 5%, 10%, 20% and 25% HEDP was added as an organophosphine source in the process of preparing hydroxyapatite （HAP）to obtain inorganic-organic phosphorus hybrid HAP composite materials with different HEDP doping amounts, respectively. XRD characterization showed that when HEDP doping was 20% of total phosphorus, the crystallinity of the resulting composite material was greatly reduced and became amorphous HAP, and the maximum adsorption capacity of the obtained amorphous HAP was 1893.7 mg/g, 239.3 mg/g, 285.4 mg/g, and 339.7 mg/g for Pb2+, Cu2+, Zn2+ and Cd2+, respectively, which was 8.47, 4.25, 3.29, 3.41 times that of the commercial HAP, respectively. Furthermore, Hirshfeld surface analysis specially including fingerprint plot was applied to investigate the interaction between HEDP and HAP, and reduced density gradient (RDG) method was carried out to explore the interaction mechanism of HEDP doping amorphous HAP composite and heavy metal ions. Because of the low price of HEDP, the simple and low-consumption preparation method and the excellent removal effect to various heavy metal pollutants, the inorganic-organic phosphorus hybrid amorphous HEDP-HAP composite material will have broad application prospects in the field of heavy metal pollution control.