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.

Bathurst Burr (Xanthium spinosum) Powder—A New Natural Effective Adsorbent for Crystal Violet Dye Removal from Synthetic Wastewaters

“…The decrease of adsorption capacity as the ionic strength increases is based on the competitive effect between the dye and sodium ions in occupying the available adsorption sites on the adsorbent surface [ 45 , 46 ]. A similar influence of ionic strength on the crystal violet adsorption process has been reported in other previous scientific articles [ 43 , 48 , 49 ].…”

“…After 30 min, the equilibrium is reached and the value of this parameter remains practically constant. In the first 15 min the increase is more pronounced because at the beginning of the process many free adsorption sites on the surface of the adsorbent are available to retain the dye, [ 8 , 9 , 24 , 42 , 49 ]. After 15 min the adsorption capacity increases more slowly, because more and more free sites on the adsorbent surface are occupied by dye molecules and repulsive forces between adsorbed and liquid phase molecules may occur [ 8 , 9 , 45 , 50 ].…”

“…The physisorption is involved in the process (ΔH 0 < 40 kJ mol −1 ) [ 25 , 44 ] and van der Waals interaction plays an important role in the physical adsorption (ΔH 0 < 20 kJ mol −1 ) [ 63 ]. When standard Gibbs free energy change (ΔG 0 ) ranges from −20 to −80 (kJ mol −1 ) the process is physisorption, intensified by the chemical effect [ 49 ].…”

The Use of Bilberry Leaves (Vaccinium myrtillus L.) as an Efficient Adsorbent for Cationic Dye Removal from Aqueous Solutions

“…The value of ΔH 0 lower than 20 (kJ mol −1 ) reveals the physical adsorption presence [ 89 ] with van der Waals interaction implied in the process mechanism [ 84 , 90 ]. The physisorption is involved in the process when ΔG 0 ranges from −20 to 0 (kJ mol −1 ) and the physisorption together with chemisorption is involved when ΔG 0 ranges from −20 to −80 (kJ mol −1 ) [ 29 , 91 , 92 ]. The ΔG 0 value ( Table 5 ) indicates the involvement of physisorption, but a small chemical effect may enhance the process.…”

Adsorption Behavior of Acid-Treated Brazilian Palygorskite for Cationic and Anionic Dyes Removal from the Water

“…The Pal-2M presented a high adsorption capacity (82.1 mg/g). CV adsorption studies accomplished with others adsorbents presented the following CV adsorption capacities (Figure 16): chitosan-graphite oxide-modified polyurethane (1.98 mg/g) [113], titanate nanotubes (8.36 mg/g) [114], nano mesocellular foam silica (6.64 mg/g) [115], Moroccan clay (17.05 mg/g) [116], magnetically modified ac-tivated carbon (67.1 mg/g) [117], Chinese palygorskite treated with HCl [33] (180.24 mg/g) and Oman palygorskite (70 mg/g) [41]. Palygorskites from different regions showed better CV adsorption performances when compared to synthetic adsorbents.…”