A novel chitosan sorbent enriched with nickel ions: An effective approach for eliminating excess phosphate(V) anions in water

Abstract

Phosphorus is an essential nutrient for living beings. Unfortunately, high phosphate(V) levels can lead to eutrophication in aquatic ecosystems. One promising technique for removing phosphate(V) contamination is sorption, which uses various sorbents. In particular, chitosan, a natural polysaccharide, has gained special attention due to its excellent sorption properties, biocompatibility, and ease of modification. This study proposes a new sorbent, a chitosan-based hydrogel modified with nickel ions (Cs-Ni), for effectively sorbing phosphate(V) anions from both model and natural waters. The maximum sorption capacity of phosphates(V) by the Cs-Ni hydrogel calculated by the Langmuir model was 62.5 mg/g, which was much higher compared to the unmodified chitosan-based hydrogel. The phosphates(V) sorption rate by Cs-Ni hydrogel was best explained by the pseudo-second-order kinetic model, which established the time to reach equilibrium as 24 h. Phosphates(V) desorption to 95 % efficiency was achieved using a 0.1 M NaOH solution. Multi-cycle sorption and desorption studies showed that the Cs-Ni hydrogel can be reused at least five times without any loss of nickel(II) ions from the structure of the sorbent. Most coexisting anions in natural waters had a minor impact on phosphate(V) removal by the Cs-Ni hydrogel, with the exception of sulfate(VI), which reduced the phosphorus removal efficiency by ∼50 %. Modification of chitosan with nickel(II) significantly enhanced its properties for both physical and chemical sorption of phosphate(V) anions. The hydrogel beads’ design allows for easy solid-phase separation from the purified water, making the Cs-Ni hydrogel advantageous for removing phosphates(V) from real aqueous systems.