Preparation of Amorphous Calcium Phosphate (ACP) by Precipitation Method at Low Temperature and Its Application in the Removal of Congo Red (CR)

Abstract To tackle Congo red contamination in dye wastewater, this study undertook the modification of ACP by adding β‐cyclodextrin (β‐CD), citric acid (CA), and polyethylene glycol (PEG), with the objective of augmenting its adsorption efficiency for Congo red (CR). Adsorption experiments were performed based on various factors, such as initial Congo red concentration, solution pH, temperature, and contact time. The results demonstrated that β‐CD‐ACP had excellent adsorption properties and could quantitatively remove Congo red from wastewater with a wide pH value (3 − 10). When the initial concentration is 2000 mg L −1 , the maximum adsorption capacity of β‐CD‐ACP for CR has reached 662.47 mg g −1 . The experimental data for CR adsorption were more consistent with the pseudo‐second‐order kinetic model and the Langmuir isotherm model. The thermodynamic parameters indicated that the adsorption of CR by β‐CD‐ACP was a spontaneous and endothermic process. Moreover, the internal diffusion model revealed a linear relationship, suggesting that internal diffusion played a role in the adsorption process. The adsorption of β‐CD‐ACP onto CR involves hydrogen bonding, the ion‐exchange mechanism of PO 4 3− and the chelation effect of Ca 2+ . The β‐CD‐ACP we prepared exhibits excellent adsorption performance and recyclability, demonstrating great potential for removing CR from wastewater.