Highly efficient phosphate adsorption using calcium silicate hydrate-embedded calcium crosslinked polyvinyl alcohol thin film.

The removal of phosphate from water is necessary to avoid eutrophication. In this work, a novel composite film of calcium silicate hydrate (CSH) immobilized within calcium cross-linked polyvinyl alcohol (CSH-PVA) was developed for efficient phosphate removal from water using a simple and environmentally friendly preparation method. The characterization showed that flake crystal-like CSH nanoparticles were immobilized on a PVA film (86-106 μm). Amorphous calcium phosphate and hydroxyapatite were observed after phosphate adsorption. The adsorption efficiency and capability of phosphate were examined under various conditions using batch experiments. The phosphate removal data fitted well to the pseudo-second-order kinetic model (R = 0.9903-0.9999) and the Langmuir isotherm model (R = 0.9958), which estimated a maximum removal capacity (99.01 mg g). Phosphate adsorption was found to be endothermic with spontaneous adsorption via chemisorption with strong affinity (ΔG° = -3.96 to -8.62 kJ mol, ΔH° = 65.4 kJ mol, and ΔS° = 232.94 J mol K). Additionally, significant amounts of fluoride and carbonate ions affected phosphate adsorption at levels exceeding 5-fold and 20-fold that of phosphate, respectively. An excellent removal efficiency was achieved in the range of 72.06%-97.87% using phosphate-containing real samples. Therefore, the proposed CSH-PVA film showed great potential for effective phosphate removal from water, with potential for further use as a fertilizer.