Fluoride removal from living entities is the foremost task as it is a non-biodegradable and harmful pollutant mostly found in groundwater. Nowadays, the application of nanoparticles as an adsorbent of fluoride is becoming an intense research due to its high surface area. In the present study, zeolitic imidazolate framework-8 (ZIF-8) nanoparticles adsorption behavior and its efficiency in fluoride removal from an aqueous phase were studied. Various structures, sizes and morphologies of nanoparticles were investigated by Fourier-transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscope, transmission electron microscopy, Raman spectroscopy and zeta seizer. By varying process parameters such as contact time, adsorbent dosage, stirring rate, temperature, and pH, batch adsorption was carried out. The optimum conditions for fluoride removal by ZIF-8 nanoparticles were found as contact time 15 min, adsorbent dosage 0.06 g/L, agitation rate 400 rpm, temperature 20 °C, pH 8. Pseudo-second order in kinetic study showcases that the regression coefficient was found to be 0.99. The experimental data of Langmuir isotherm model of adsorption system reveal the adsorption capacity of 90 mg/g which has better adsorption capacity than other adsorbents. The isothermal multistage adsorption was also studied to understand the mechanism of adsorption of ZIF-8 nanoparticles for fluoride removal. The result in the present work gives a promising adsorbent for the fluoride removal.

The study of behaviour of propagation of ultrasonic waves in liquid system and solids is now rather well established as an effective means for examining certain physical properties of the materials. It is particularly well adapted to examine changes in such physical properties while they occur. The data obtained from ultrasonic propagation parameters such as ultrasonic velocity, adiabatic compressibility, molar volume, free length etc; and their variation with concentration of one of the component of the medium are useful in understanding the nature of molecular interaction in terms of physical parameters owing to the sensitivity to very low population densities at high energy states ultrasonic methods have been preferred and are reported to be complementary to other techniques like dielectric relaxation, I.R spectroscopy, N.M.R etc. Hence the author preferred to study the ultrasonic velocity and density measurement of aqueous solutions for NaCl and KCl of various concentrations. One of the important intermolecular properties of a liquid is the free length L f between the surfaces of two neighbouring molecules and in the distance covered by the propagating acoustic waves between the surfaces of the two neighbouring molecules. The non-linear variations are observed in acoustic parameters of NaCl and KCl solutions indicating the formation of complex ions. Molecular interactions can be studied through Rao's constants and Wada's constants which are constants in non interacting systems. The abrupt change observed in Rao's constant and Wada's constant shows existence of molecular interaction.