Phosphate functionalized activated carbon sachet filters for drinking water purification

Abstract

This study reports the synthesis and characterization of a phosphate functionalized porous activated carbon filter material suitable for sachet filters to remove fluoride, hardness and bacterial pathogens in drinking water. Phosphate functionalized activated carbon is prepared by treating waste coconut coir dust with phosphoric acid/water vapor followed by pyrolysis under an inert environment at 500 °C for 1 h. Unlike other reported chemical functionalization methods, the current approach allows controlling the amount of surface functional groups, thus facilitating the maintenance of pH and conductivity of treated water. Morphological studies and BET surface area analysis of phosphoric acid vapor activated carbon (FAC) suggest the presence of a highly porous network structure with pore sizes ranging from the micro to nano-range (2.2 μm–3.23 nm). Fourier transform infrared and X-ray photoelectron spectroscopy and the shifts in the D and G bands in Raman spectroscopy analysis confirm the functionalization of the activated carbon matrix with phosphate and hydroxyl groups. The isoelectric point of the filter material is 5.9. The hardness and fluoride removal efficiencies of 1.0 g of FAC in a sachet for a contact time of 20 min under static conditions are found to be approximately 45–60% and 45–50%, respectively, for natural water samples. Adsorption complies with the Freundlich isotherm model, and the adsorption kinetics is well described by the pseudo-second-order model. The laboratory scale method has been scaled up and the process parameters have been optimized.