Succinylated Salvia spinosa hydrogel: Modification, characterization, cadmium-uptake from spiked high-hardness groundwater and statistical analysis of sorption data

Herein, we synthesized sodium salt of succinylated Salvia spinosa hydrogel (NaS-SSH), a novel and green polysaccharide-based ion-exchanger for cadmium uptake from deionized water (DW) and spiked high -hard ground water (HGW). The S. spinosa hydrogel (SSH), succinylated SSH (S-SSH) and its sodic form (NaS-SSH) were characterized through Fourier transform infrared spectroscopy, solid-state CP/MAS 13C-NMR spectroscopy, scanning electron microscopy-energy dispersive spectroscopy, and thermogravi-metric analysis. The surface charge on NaS-SSH was calculated by performing point of zero charge pH, i.e., pHZPC analysis and it was found to be 4.77 +/- 0.35. Cd(II) uptake efficiency of NaS-SSH was accessed on pH (1-7), sorbent dosage (10-90 mg/100 mL), initial concentration of Cd(II) ions (10-250 mg L-1), contact time (5-150 min), and temperature (298-338 K). Sorption data fitted well to Langmuir isothermal model and sorption maxima (Qmax) was calculated as 344.83 mg g-1 for DW and 312.5 mg g-1 for HGW and found comparable with the experimental sorption capacities. The sorption kinetics followed the pseudo-second-order kinetic model and occurred through the exchange of ions via chemisorption. Thermodynamics of the sorption process was judged through negative values of thermodynamic triplets (DG degrees, DH degrees, and DS degrees) and revealed spontaneous and exothermic in nature. Competitive studies indicated the potential of NaS-SSH for metal removal from a binary mixture of Ni(II)-Cd(II). Moreover, NaS-SSH was regenerated and could be used over several repetitive cycles. Comparing the sorption efficiency of NaS-SSH with already reported succinylated biosorbents having similar structural features, it was noted that our developed biosorpbent is more effective for Cd(II) uptake. (c) 2023 Elsevier B.V. All rights reserved.