Min W. Lee

ADSORPTION OF CONGO RED BY CHITOSAN HYDROGEL BEADS IMPREGNATED WITH CARBON NANOTUBES

The adsorption performance of chitosan (CS) hydrogel beads was investigated after multiwalled carbon nanotubes (MWCNTs) impregnation for the removal of congo red (CR) as an anionic dye. The study of the adsorption capacity of CS/CNT beads as a function of the CNT concentration indicated that 0.01% CNT impregnation was the most useful for enhancing the adsorption capacity. The sulfur (%) in the CS/CNT beads measured by energy dispersive X-ray (EDX) was 2.5 times higher than that of normal CS beads after CR adsorption. Equilibrium adsorption isotherm data of the CS/CNT beads exhibited better fit to the Langmuir isotherm model than to the Freundlich isotherm model, and the heterogeneity factor (n) value of the CS/CNT beads calculated from the Sips isotherm model was close to unity (0.98). The maximum adsorption capacity of CS/CNT beads obtained from the Langmuir model was 450.4 mg g(-1).

Enhanced adsorption of congo red from aqueous solutions by chitosan hydrogel beads impregnated with cetyl trimethyl ammonium bromide

The adsorption of congo red (CR) onto chitosan (CS) beads impregnated by a cationic surfactant (CTAB, cetyl trimethyl ammonium bromide) was investigated. Chitosan beads impregnated at a ratio of 1/20 of CTAB to CS (0.05% of CTAB and 1% of CS) increased the CR adsorption capacity by 2.2 times from 162.3 mg/g (0% CTAB) to 352.5 mg/g (0.05% CTAB). The CR adsorption decreased with an increase in pH of the CR solution from 4.0 to 9.0. The Sips isotherm model showed a good fit with the equilibrium experimental data and the values of the heterogeneity factor (n) indicated heterogeneous adsorption of CR onto CS/CTAB beads, as well as CS beads. The kinetic data showed better fit to the pseudo second-order rate model than to the pseudo first-order rate model. The impregnation of CS beads by cationic surfactants showed the highest adsorption capacities of CR compared to any other adsorbents and would be a good method to increase adsorption efficiency for the removal of anionic dyes in a wastewater treatment process.

Congo red adsorption from aqueous solutions by using chitosan hydrogel beads impregnated with nonionic or anionic surfactant

The adsorption performance of CS beads impregnated with triton X-100 (TX-100) as a nonionic surfactant and sodium dodecyl sulfate (SDS) as an anionic surfactant was investigated for the removal of anionic dye (congo red) from aqueous solution. While the adsorption capacity of CS/TX-100 beads was enhanced at all concentrations of TX-100 (0.005-0.1%), the increase in the concentration of SDS above 0.01% in the CS/SDS beads gradually reduced the adsorption capacity of the beads. Equilibrium adsorption isotherm data indicated a good fit to the Sips isotherm model and a heterogeneous adsorption process. The Sips maximum adsorption capacity in dry weight of the CS/TX-100 beads was 378.79 mg/g and 318.47 mg/g for the CS/SDS beads, higher than the 223.25mg/g of the CS beads. Modification of CS beads by impregnation with nonionic surfactant, or even anionic surfactant, at low concentrations is a possible way to enhance adsorption of anionic dye.

Nitrate removal from aqueous solutions by cross-linked chitosan beads conditioned with sodium bisulfate.

The investigation of adsorption of nitrate onto chitosan beads modified by cross-linking with epichlorohydrin (ECH) and surface conditioning with sodium bisulfate was performed. The results indicated that both cross-linking and conditioning increased adsorption capacity compared to normal chitosan beads. The maximum adsorption capacity was found at a cross-linking ratio of 0.4 and conditioning concentration of 0.1mM NaHSO(4). The maximum adsorption capacity was 104.0 mg g(-1) for the conditioned cross-linked chitosan beads at pH 5, while it was 90.7 mg g(-1) for normal chitosan beads. The Langmuir isotherm model fit the equilibrium data better than the Freundlich model. The mean adsorption energies obtained from the Dubinin-Radushkevich isotherm model for all adsorption systems were in the range of 9.55-9.71 kJ mol(-1), indicating that physical electrostatic force was potentially involved in the adsorption process.

Coagulation of soil suspensions containing nonionic or anionic surfactants using chitosan, polyacrylamide, and polyaluminium chloride.

Effective coagulation and separation of particles in a soil-washed solution is required for a successful soil washing process. The effectiveness of chitosan (CS), a polycationic biodegradable polymer, as a coagulant was compared to polyacrylamide (PAA) and polyaluminium chloride (PAC) for the coagulation of a soil suspension (5 gL(-1)). The effect of surfactants in the coagulation process was investigated using Triton X-100 (TX-100), a nonionic surfactant, and sodium dodecyl sulfate (SDS), an anionic surfactant. CS (5 mgL(-1)) removed 86% and 63% of the suspended soil in the presence of TX-100 (5 gL(-1)) and SDS (5 gL(-1)), respectively, after 30 min at a pH of 6. The results prove that coagulation in the presence of TX-100 is more effective than with SDS. CS was found to be more efficient compared to PAA and PAC under all coagulation conditions. The optimum concentration of CS required for maximum coagulation of soil suspension was 5 mgL(-1). PAA and PAC could not achieve the same degree soil removal as CS even after increasing their concentrations up to 50 mgL(-1). Maximum levels of 50% and 60% soil removal were achieved using PAA (50 mgL(-1)) and PAC (50 mgL(-1)), respectively, after 30 min from a 5 gL(-1) suspension containing TX-100 (5 gL(-1)). The soil coagulation process was found to decrease with an increase in the pH of the suspension, and maximum coagulation was achieved with an acidic pH.

Mathematical evaluation of activated carbon adsorption for surfactant recovery in a soil washing process.

The performances of various soil washing processes, including surfactant recovery by selective adsorption, were evaluated using a mathematical model for partitioning a target compound and surfactant in water/sorbent system. Phenanthrene was selected as a representative hazardous organic compound and Triton X-100 as a surfactant. Two activated carbons that differed in size (Darco 20-40 mesh and >100 mesh sizes) were used in adsorption experiments. The adsorption isotherms of the chemicals were used in model simulations for various washing scenarios. The optimal process conditions were suggested to minimize the dosage of activated carbon and surfactant and the number of washings. We estimated that the requirement of surfactant could be reduced to 33% of surfactant requirements (from 265 to 86.6g) with a reuse step using 9.1g activated carbon (>100 mesh) to achieve 90% removal of phenanthrene (initially 100mg kg-soil(-1)) with a water/soil ratio of 10.