Preparation of hydroxyapatite microspheres by hydrothermal self-assembly of marine shell for effective adsorption of Congo Red

In recent years, numerous dyes have been discharged into rivers and oceans, which causes serious environmental pollution. Hydroxyapatite (HA) may have a wide range of applications as a candidate adsorbent in the adsorption of dyes. In this study, marine shell waste was converted into HA microspheres using a hydrothermal self-assembly method. Phosphoric acid was used as a source of phosphorus while poly-L-aspartic acid (PASP) and sodium citrate (SC) acted as co-chelating agents for self-assembly. Prepared HA microspheres have high specific surface area and negative surface potential. HA microspheres were used to adsorb Congo red (CR) in solution. The effects of solution pH, initial CR concentration and temperature were investigated. The maximum adsorption capacity of abalone HA microspheres for CR could reach 495.5626 mg/g when the initial CR concentration reaches 800 mg/L. The adsorption process of CR by HA microspheres is spontaneous and exothermic. This study may provide a novel method for the preparation of HA microspheres and an excellent adsorbent for the removal of CR.