Synthesis, characterization and adsorption studies of hydroxy ethyl cellulose grafted polyacrylic acid hydrogels; using basic yellow-28 as model dye

Abstract

Novel hydrogels of hydroxy ethyl cellulose and polyacrylic acid (HEC-G-pAAc) were created by varying the ratio of hydroxy ethyl cellulose to acrylic acid and were characterized using analytical techniques. The synthesized hydrogels were characterized through SEM, TGA, FTIR, pH studies and Fick’s law. The SEM images revealed that the fabricated hydrogels have different adsorption sites for the dyes. According to the TGA results the decomposition of the hydrogels occurs in three successive stages (22–200 °C, 200–310 °C, 310–500 °C). The optimum pH for the adsorption of basic yellow-28 is on the HEC-G-pAAc is pH-8 as it was observed in the pH studies. The optimum temperature for the adsorption of basic yellow-28 is on the HEC-G-pAAc was found to be 293 K.The Basic Yellow-28 dye was successfully removed from wastewater with a 98% effectiveness using synthetic hydrogels as an adsorbent. The adsorption parameters were calculated using a number of different kinetic models like pseudo-second order, Elovich, intraparticle-diffusion and Bangham kinetic models. The pseudo-2nd order kinetics model was found to best fit the kinetics data, while the Langmuir isotherm offered the most thorough explanation of the adsorption process. Basic Yellow-28 dye was removed to the greatest extent by the synthesized hydrogels (pAAc = 156 mg/g, 10%HEC-G-pAAc =166.3 mg/g, 20%HEC-G-pAAc =176.2 mg/g) after 90 min of contact at 293 K. The process was exothermic because the values of ΔH were found to be negative (ΔH = −4.93, −6.49 and −5.741 kJ/mol for pAAc, 10%HEC-G-pAAc and 20%HEC-G-pAAc respectively). The adsorption process in this study is spontaneous, as clear from the negative values of ΔG, (ΔG = −4.81, −5.34 and −5.40 kJ/mol for pAAc, 10%HEC-G-pAAc and 20%HEC-G-pAAc at 293 K respectively). The adsorption process on synthesized hydrogels showed decrease in dis-orderness that was clear from its negative values.