Studies of adsorption of crystal violet from aqueous solution by nano mesocellular foam silica: process equilibrium, kinetic, isotherm, and thermodynamic studies

Abstract

Mesocellular foam (MCF) silica molecular sieve material was successfully synthesized using a hydrothermal method. X-ray diffraction, infrared spectroscopy, low nitrogen adsorption–desorption, scanning electron microscopy, and transmission electron microscopy (TEM) characterization techniques were used to characterize the material. Low temperature nitrogen adsorption–desorption method showed that pore size of the synthesized MCF was 12 nm. TEM study showed that the synthesized MCFs had honeycomb structure pores, which can be good for the absorbance of dye organic macromolecule substances. This work studied the adsorption of crystal violet by MCF and the results showed that when the adsorptive conditions were pH = 9.0, MCF:crystal violet = 150:1, and when the contact time was 10 min at room temperature of 25 ± 1 ◦C, the adsorption rate reached 99.71% and adsorption capacity was 6.646 mg/g. This study found that the adsorption is a Freundlich type, it is a multimolecular layer adsorption, and it belongs to the pseudo-second-order kinetic model. According to the ΔG0 obtained from adsorption thermodynamics, when the temperature is 25–40 ◦C, the adsorption enthalpy change ΔH0 = -25.65 kJ/mol, ΔG0 < 0, the adsorption is an exothermic reaction and can spontaneously occur. The adsorption entropy change ΔS0 = 5.54 J/(mol·K) and the entropy of system increased.