Hydrothermal in situ synthesis of high-crystallinity layered double hydroxide on electrospun polyacrylonitrile non-woven membrane: Application as anion capture filter

Layered double hydroxide (LDH) crystals were grown in the presence of polyacrylonitrile (PAN) nanofibers to develop a three-dimensionally-structured hybrid filter with high anion adsorption performance. The tensile strength and chemical resistance of the PAN nanofibers manufactured by electrospinning were improved upon heat treatment at 250 °C for 60 min. The growth of LDH on PAN was conducted by hydrolysis using urea or hexamethylenetetramine (HMT), and optimum conditions for this “in situ synthesis” were investigated. As a result, LDH plate-like crystals with a lateral size of ~20 μm were obtained by hydrothermal treatment at 140 °C for 24 h using HMT. The crystals grew densely perpendicular to the surface of the PAN fibers. After converting the LDH grown on the fiber fabric to LDH contain Cl− in the interlayer, the resulting fabric was set in a filter holder and a phosphoric acid adsorption test was conducted. The results showed that the hybrid filter prepared by this in situ hydrothermal synthesis had good phosphate adsorption characteristics, and that small amounts of phosphate ions were adsorbed selectively from water containing competing sulfate ions.