Ultrasonically accelerated synthesis of silver nanocomposite hydrogel based on salep biopolymer: application in Rhodamine dye adsorption

Silver nanocomposite hydrogel (SNH) based on poly(acrylic acid) grafted onto salep was prepared without initiator and under just 2 min ultrasonic irradiation for the first time. The SNH was then applied as an adsorbent for Rhodamine removal from aqueous solution. The SNH adsorbent was characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy images and X-ray photoelectron spectroscopy. A 2⁴ full factorial central composite design, a linear mathematical model representing the influence of different variables and their interactions, was successfully employed for experimental design and analysis of the results. Analysis of variance demonstrated that Rhodamine adsorption significantly increased with increases in the amount of adsorbent, extraction time, stirring rate of the solution and Rhodamine volume as donor phase volume, but slightly decreased with an increase in temperature and pH of Rhodamine solution. The adsorption behaviors showed that the adsorption kinetics were in good agreement with a pseudo-second-order model for Rhodamine removal from aqueous solution. Thermodynamic studies revealed the feasibility and exothermic nature of the system. Adsorption mechanism was studied through two important adsorption isotherm models (Langmuir and Freundlich models). Under the optimal experimental conditions, the detection limit was found to be 0.94 µg mL^?1 for Rhodamine adsorption. The limit of quantification and the linear range of calibration curve were 3.14 µg mL^?1 and 1.00–10.98 µg mL^?1, respectively.