Ultrasonically prepared poly(acrylamide)-kaolin composite hydrogel for removal of crystal violet dye from wastewater

• Synthesis of PAAm-K hydrogel performed via ultrasound assisted in situ emulsion polymerization.
• Uniform dispersion of kaolin nanoparticles in PAAm hydrogel is achieved using ultrasound.
• This uniform dispersion of kaolin improves the adsorption of CV dye.

In the present study, synthesis of poly(acrylamide)-kaolin (PAAm-K) hydrogel nanocomposite has been carried out via ultrasound assisted in situ emulsion polymerization. Kaolin was used as a cross-linker and use of ultrasound during synthesis helps in uniform dispersion of kaolin in the hydrogel matrix increasing the strength and stability of hydrogel leading to improved adsorption of an organic pollutant. The viability of the synthesized PAAm-K hydrogel nanocomposite was studied for the removal of crystal violet (CV) dye. The adsorption studies were performed under different pH, temperature, initial dye concentration, kaolin clay content and cavitation conditions. The % dye removal efficiency is higher for higher pH and temperature. Also the adsorption process is highly favorable at the lower dye concentration and higher quantity of hydrogel where the maximum removal efficiency of dye was obtained. The obtained data are processed using adsorption kinetics, isotherm models and the thermodynamic behavior of the cationic dye adsorption is studied. It is found that the formation of network of cross-linked polymer hydrogel shows a good swelling behavior due to the presence of kaolin. The combined effect of hydrogel and ultrasound demonstrate a higher percent removal of the dye as compared to hydrogel alone. Pseudo-second-order kinetic model provided a better correlation for the experimental data in comparison to the pseudo-first-order kinetic model. The experimental error observed is less than 5%. The negative value of ΔG° indicates the feasibility and spontaneity of the adsorption process. The positive ΔH° suggests the endothermic nature of the adsorption.