Protocells self-assembled by hydroxyapatite nanoparticles: Highly efficient and selective enrichment of chlorophenols in an aqueous environment

In this paper, amphiphilic hydroxyapatite (HAP) nanoparticles were modified by dibutyl phosphate (DBP) via covalent bonding. The modified HAP particles (m-HAP) were employed as building blocks to construct oil-in-water (O/W) Pickering emulsion, that displayed an excellent performance on the enrichment of organic pollutants dissolved in wastewater by extracting the organic molecules into the oil phase. Environment-friendly organic solvent hexanol was selected as oil phase and three types of monochlorophenol (2-chlorophenol, 3-chlorophenol, 4-chlorophenol) were chosen as model pollutants in simulated wastewater. Two types of natural water were also tested as a proof of principle. The enrichment percentage of chlorophenols was up to 98% in 140 s, following first order kinetics. Thermodynamic study suggested that the enrichment process is spontaneous and exothermic. The external environment of the protocells, such as pH, ionic strength and the natural organic matter have been investigated. This study provides a novel, convenient and environment-friendly approach for enrichment and removal of trace organic pollutants in wastewater.