Adsorption mechanism of phosphate by polyaniline/TiO2 composite from wastewater

Abstract The adsorption behavior of polyaniline/TiO2 (PANI/TiO2) for phosphate from wastewater was investigated, and the mechanism was interpreted in details in this study. PANI/TiO2 exhibited enhanced adsorption efficiency and high stability for phosphate removal in wide pH range (1–6) compared with PANI and TiO2. The equilibrium time was much shorter than other similar sorbents reported, like HFO-201 and La-201, and 60 min was enough for the adsorption of 98% phosphate (10 mg P/L). After 5 times reuse of the NaOH (0.5 mol L−1) for desorption, phosphate solution was concentrated from 10 mg P/L to 180 mg P/L without obvious loss of adsorption and desorption efficiency. The mechanism of the phosphate adsorption onto PANI/TiO2 was revealed with the aid of SEM, XRD, EDS, FTIR and XPS. Two adsorption sites of protonated imino groups in PANI chains and the Ti(OH)n(4-n)+ from TiO2 part were verified, and the binding force of Ti-P was the main pathway for the removal of phosphate. Generally, electrostatic interaction, ion-exchange and hydrogen bond were demonstrated to be involved during the adsorption. The synergistic effect of the PANI and TiO2 make the organic/inorganic composite a promising sorbent for phosphate removal from wastewater.