Synthesis and characterization of zinc oxide nanocomposite for fluoride ion removal from aqueous solution

In India, the problem of fluorosis has arisen in semi-urban and rural areas due to the intake of groundwater. The development and application of zinc oxide nanocomposite recently received a lot of attention for fluoride ion removal. Nanotechnology and nanocomposites are widely used by researchers to treat wastewater and control water pollution. Rice husk is extensively found in rice-producing countries such as India that contributes about twenty-two percent of worldwide rice production. Rice husk is used to synthesize nanocellulose using chemical and mechanical approaches. To increase the effectiveness, nanocellulose was modified and coated with a zinc oxide layer to form nanocomposite by chemical precipitation method. Functional groups and morphological, structural, and surface area analysis were characterized by FTIR, FESEM, XRD, and BET. Results revealed that zinc oxide modification on nanocellulose was observed at 440.29 cm^-1 and 616.94 cm^-1. Maximum fluoride ion removal was achieved at varied initial ion concentrations 2 ppm (86%), 5 ppm (84%), 8 ppm (82%), 10 ppm (80%), 13 ppm (76%), and 15 ppm (75%) at pH 5 using 0.8 g/50 ml at 30°C in 60 min using zinc oxide nanocomposite in the batch study. The isotherm model's best-fitted order was Langmuir (R²=0.999) > Sips (R²=0.996) > Baudu (R²=0.993) > Fritz-Schluender (R²=0.992) > Freundlich (R²=0.986). A pseudo-second-order kinetic model (R²=0.989) fitted well with fluoride ion adsorption data showed chemical adsorption. The thermodynamic study showed the adsorption of fluoride ions due to physical adsorption.