Phosphate removal from actual wastewater via La(OH)3-C3N4 adsorption: Performance, mechanisms and applicability

In this study, La(OH)3 nanoparticles were immobilized on C3N4 to effectively restrict their aggregation and subsequently enhance the La utilization efficiency to promote phosphate adsorption. The prepared La(OH)3-C3N4 nanocomposite was characterized by SEM, XRD, FTIR, XPS, BET and Zeta potential analysis. Batch and continuously-fed (fixed-bed column) experiments to assess the adsorption performance of La(OH)3-C3N4 showed that the composite exhibits superior utilization efficiency, resulting to relatively quick adsorption with a short equilibrium time of 30 min. The theoretical maximum P adsorption capacity reached the 148.35 mg·g-1, efficiency that remained unaffected by the anions and HA present. The adsorption mechanism showed stability in a wide pH range (4.0-11.0) and is considered effective even after extensive use (five-cycles). The dynamics of the adsorption capacity and the half-penetration time values were estimated by 'Thomas' and 'Yoon-Nelson' models showed that are better represented from the experimental values obtained from the fixed-bed column trial. The adsorption mechanisms were attributed to surface precipitation, electrostatic attraction, and inner-sphere complexation via ligand exchange. Furthermore, La(OH)3-C3N4 demonstrated high efficiency in scavenging phosphate from both diluted and concentrated wastewater (natural pond and swine wastewater respectively). The above confirm that La(OH)3-C3N4 is a promising composite material for phosphate management in aqueous environments.