| dc.description.abstract | Alkali-activated municipal waste incineration fly ash (MWFA)-based geopolymers
(GPA, GPB, and GPC) were synthesized under different sodium silicate to sodium
hydroxide (SS/SH) ratios. The geopolymers were applied in the removal of
endosulfan, a persistent and toxic chemical, from water. The adsorbents were
characterized by XRD, SEM-EDX, and FTIR. Variation of SS/SH ratios resulted in
morphologically distinguishable geopolymers with different compositions. The
adsorption equilibrium data were best described by the Langmuir isotherm. The
maximum adsorption capacities increased with an increase in SS/SH ratios in the
order 1.87, 15.89, 16.97, and 20.01 mg/g for MWFA, GPA, GPB, and GPC,
respectively. The kinetic data were best described by the pseudo-first-order
model wherein the adsorption rate (k1) was independent of the SS/SH ratios
and the geopolymer composition. The thermodynamic parameters, that is,
enthalpy (ΔH > 0), Gibbs free energy (ΔG < 0), entropy (ΔS > 0), and activation
energy (Ea > 0), show that the processes were endothermic, spontaneous, physical
(Ea and ΔH < 40 kJ/mol), and entropy-driven. Alkalination was beneficial since the
geopolymers had a higher adsorption capacity (~8–10 times) and affinity for
endosulfan (~30 times) than the precursor material (MWFA). The adsorption
mechanism entailed electrostatic interactions and hydrogen bonding. The
MWFA-based geopolymers are, therefore, potential alternative low-cost
adsorbents for the removal of endosulfan from water and a strategy for the
valorization of MWFA | en_US |
