Quaternized fenugreek gum grafted poly(acrylamide-co-methacryloxyethyltrimethyl ammonium chloride) novel composite hydrogel for efficient removal of Congo red dye.

To solve the problem of the massive use of Congo red dye in some developing countries and the lack of reasonable solutions. In this study, a novel composite hydrogel consisting of quaternized fenugreek gum (QFG) as a bioskeleton and poly(acrylamide-co-methacryloxyethyltrimethyl ammonium chloride) as a side chain segment was constructed. The hydrogel was used as an adsorbent for removing Congo red with low-cost, reusable, and environmentally friendly efficacy. Fourier Transform Infrared Spectroscopy， Thermogravimetric Analysis， Scanning Electron Microscopy-Energy Dispersive X-ray Analysis, and Brunauer-Emmett-Teller proved the successful synthesis of the adsorbent. Moreover, the adsorbent was shown to have a porous structure and good thermal stability. The experiments indicated that the adsorbent has excellent Swelling capacity (189.1 g/g) and adsorption properties. The optimal adsorption conditions: pH 4-9, initial dye concentration of 400 mg/L, and adsorbent dosage of 12 mg. In addition, the adsorption tests in four different aqueous environments demonstrated the good practical applicability of the adsorbent. The Langmuir model best describes the adsorption behavior with a maximum adsorption capacity of 1828.28 mg/g (298 K). The adsorption process is consistent with the pseudo-second-order kinetic model. Thermodynamic analysis shows that the adsorption process is spontaneously exothermic. Ten regeneration experiments demonstrate excellent reusability. In conclusion, based on the introduction of quaternary ammonium groups in fenugreek gum (FG), by combining with functional organic monomers, the constructed adsorbent with a three-dimensional network structure successfully solved the problems of adsorption performance and cost for the removal of Congo red dye.