Chemical modification of Aloe vera leaf hydrogel for efficient cadmium-removal from spiked high-hardness groundwater

Abstract

Herein, the hydrogel from the leaf of the Aloe vera plant (ALH) was succinylated (SALH) and saponified (NaSALH). The FTIR, solid-state CP/MAS ¹³C NMR, and SEM-EDX spectroscopic analyses witnessed the formation of SALH and NaSALH from ALH. The pH_ZPC for NaSALH was found to be 4.90, indicating the presence of -ve charge on its surface. The Cd²⁺ sorption efficiency of NaSALH was found to be dependent on pH, NaALH dose, Cd²⁺ concentration, contact time, and temperature. The maximum Cd²⁺ removal from DW and HGW was found to be 227.27 and 212.77 mg g^-1 according to the Langmuir isothermal model (>0.99) at pH of 6, NaSALH dose of 40 mg g^-1, Cd²⁺ concentration of 90 mg L^-1, contact time of 30 min, and temperature of 298 K. The kinetic analysis of Cd²⁺ sorption data witnessed that the Cd²⁺ removal by chemisorption mechanism and followed pseudo-second-order kinetics (>0.99). The -ve values of ΔG° and ΔH° assessed the spontaneous and exothermic nature of sorption of Cd²⁺ by NaSALH. The regeneration and sorption/desorption studies indicated that the sorbent NaSALH is regenerable.

Keywords: Aloe vera hydrogel; Cadmium uptake; Chemisorption; Esterification; Langmuir isotherm; Regeneration.