A study on the synthesis and characterization of maleate-functionalized Artemisia vulgaris hydrogel for Ni(II) adsorption from groundwater: mechanism, kinetics, and reusability

Life on Earth is at risk due to widespread pollution from industrialization and human activities. The presence of harmful heavy metal ions in drinking water sources is amongst the key pollutants that require immediate remediation. The seeds of the Artemisia vulgaris plant were used to extract the hydrogel, i.e., A. vulgar hydrogel (AVH). Following a base-catalyzed esterification process, the AVH was esterified with maleic anhydride (MAn) to produce maleated-AVH (ML-AVH). After saponification with NaHCO 3 , the ML-AVH was converted to the sodic form of ML-AVH (Na-ML-AVH). The development of ML-AVH and Na-ML-AVH and the loading of nickel (Ni(II)) were verified by the Fourier transform infrared (FTIR) spectroscopic analysis of AVH, ML-AVH, Na-ML-AVH, and Ni(II)-loaded Na-ML-AVH (Ni-ML-AVH). Brunauer-Emmett-Teller (BET) analysis revealed an increased specific surface area of Na-ML-AVH relative to AVH, indicating the generation of additional accessible adsorption sites. The thermogravimetric (TGA) analysis revealed the greater stability of Na-ML-AVH over AVH. The Powder X-ray diffraction (PXRD) patterns showed structural modification of AVH after conversion to Na-ML-AVH. The scanning electron microscopy (SEM) pictures showed the rough and porous characteristics of AVH, ML-AVH, Na-ML-AVH, and Ni-ML-AVH. The point-zero charge pH (pH ZPC ) of Na-ML-AVH was 5.17, indicating that its surface is negatively charged. According to the Langmuir isotherm, the maximum adsorption capacity of Na-ML-AVH to remediate Ni(II) was 200 mg/g for distilled water (DW) and 196.07 mg/g for groundwater (GW). The Ni(II) adsorption on the Na-ML-AVH surface was best explained by the pseudo-second-order kinetic model. Ion-exchange processes were implicated in Ni(II) adsorption, bestowing to the FTIR, Energy Dispersive X-ray spectroscopy (EDX) analysis, and the perfect fitting of Boyd’s model to the Ni(II) adsorption data. The thermodynamic investigations demonstrated that Ni(II) adsorption by Na-ML-AVH is spontaneous and exothermic in nature. Since the Na-ML-AVH was discovered to be regenerable, it can be used several times before needing to be replaced.