Fabrication and Characterization of Hydroxyapatite Water Purification Filter with Continuous Pore Structure Using Polysaccharide as Pore-forming Agent

Securing safe water remains an important global issue. PoU (Point of Use) water purification technology using filter media is promising for treating contaminated water in areas where infrastructure development is difficult. In this study, fabrication of a porous hydroxyapatite (HAp) bulk body with a connected pore structure was attempted as a filter that has the function of purifying water contaminated with microorganisms. HAp exhibits high adsorption properties for various substances such as proteins, bacteria, and viruses. In order to introduce a continuous pore structure into the porous body, corn starch, a polysaccharide, was used as a pore-forming agent. Three-dimensional observation of the internal structure of the porous body using a confocal laser fluorescent microscope and liquid immersion technique revealed a shell-like pore structure derived from the starch and the continuous pore structure inside the porous material. A filtration test of a buffer solution containing Escherichia coli (E. coli) was conducted and the filtrate did not contain detectable concentrations of E. coli. A high virus removal rate was demonstrated in a filtration test of a buffer solution containing human coronavirus. It was demonstrated that hydroxyapatite porous materials have excellent properties for filter applications to purify water contaminated with bacteria and viruses.