Microwave-assisted synthesis of MnO2 nanosorbent for adsorptive removal of Cs(I) and Sr(II) from water solutions.

In this study, a flower-like porous δ-MnO2 nanostructure was synthesized by a microwave-assisted hydrothermal process for adsorptive removal of strontium (Sr(II)) and cesium (Cs(I)) from wastewater. The prepared δ-MnO2 nanosorbent exhibited superior affinity for Sr(II) over Cs(I) in the single-solute system, with partition coefficient (PC) values of 10.2 and 2.3 L/g, respectively, at pH 6.0. In the two-solute system, the flower-like δ-MnO2 also adsorbed Sr(II) (PC = 3.81 L/g) more selectively than Cs(I) (PC 1.15 L/g). Further, their adsorption capacities decreased by 12 and 16%, respectively, relative to the single-solute system. In contrast, adsorption of the ions onto δ-MnO2 was affected less sensitively in dual than in single system when changes occurred in environmental variables such as pH (2-8) and ionic strength (1-100 mM). Adsorption kinetics, thermodynamics, and isotherm studies demonstrated the pivotal role of the monolayer surface active sites of endothermic δ-MnO2 (e.g., a complexation interaction with Mn-OH). Furthermore, the δ-MnO2 nanosorbent exhibited good regenerability, retaining more than 80% of its adsorption capacity when tested over four reuse cycles. The overall results of this study are expected to help establish strategies to effectively remove metal contaminants from wastewater using a green and low-cost hierarchical nanosorbent.

Synthesis of DMEA-Grafted Anion Exchange Membrane for Adsorptive Discharge of Methyl Orange from Wastewaters.

This manuscript describes the synthesis of dimethylethanolamine (DMEA)-grafted anion exchange membrane (AEM) by incorporating dimethylethanolamine as ion-exchange content into the polymer matrix via the solution casting method. The synthesis of the DMEA-grafted AEM was demonstrated by Fourier transform infrared (FTIR) spectroscopy. The prepared DMEA-grafted AEM exhibited higher thermal stability, homogeneous morphology, water uptake (WR) of 115%, and an ion exchange capacity (IEC) of 2.70 meq/g. It was used for the adsorptive removal of methyl orange (MO) from an aqueous solution via batch processing. The effect of several operating factors, including contact time, membrane dosage, initial concentration of aqueous dye solution, and temperature on the percentage discharge of MO and adsorption capacity, was evaluated. Experimental data for adsorption of MO onto the DMEA-grafted AEM was analyzed with two parameter and three parameter nonlinear adsorption isotherm models but fitted best using a nonlinear Freundlich isotherm. Adsorption kinetics were studied by using several models, and attained results showed that experimental data fitted well to pseudo-second-order kinetics. A thermodynamic study showed that adsorption of MO onto the prepared DMEA-grafted AEM was an endothermic process. Moreover, it was a feasible and spontaneous process.

BPPO-Based Anion Exchange Membranes for Acid Recovery via Diffusion Dialysis.

To reduce the environmental impact of acids present in various industrial wastes, improved and robust anion exchange membranes (AEMs) are highly desired. Moreover, they should exhibit high retention of salts, fast acid permeation and they should be able to operate with low energy input. In this work, AEMs are prepared using a facile solution-casting from brominated poly-(2,6-dimethyl-1,4-phenylene oxide) (BPPO) and increasing amounts of 2-phenylimidazole (PI). Neither quaternary ammonium salts, nor ionic liquids and silica-containing compounds are involved in the synthesis. The prepared membranes showed an ion exchange capacity of 1.1-1.8 mmol/g, a water uptake of 22%-47%, a linear expansion ratio of 1%-6% and a tensile strength of 0.83-10.20 MPa. These membranes have potential for recovering waste acid via diffusion dialysis, as the acid dialysis coefficient (UH) at room temperature for HCl is in the range of 0.006-0.018 m/h while the separation factor (S) is in the range of 16-28, which are higher than commercial DF-120B membranes (UH = 0.004 m/h, S = 24).

Removal of Congo Red from Aqueous Solution by Anion Exchange Membrane (EBTAC): Adsorption Kinetics and Themodynamics.

The adsorption behavior of anionic dye congo red (CR) from aqueous solutions using an anion exchange membrane (EBTAC) has been investigated at room temperature. The effect of several factors including contact time, membrane dosage, ionic strength and temperature were studied. Kinetic models, namely pseudo-first-order and pseudo-second-order, liquid film diffusion and Elovich models as well as Bangham and modified freundlich Equations, were employed to evaluate the experimental results. Parameters such as adsorption capacities, rate constant and related correlation coefficients for every model were calculated and discussed. The adsorption of CR on anion exchange membranes followed pseudo-second-order Kinetics. Thermodynamic parameters, namely changes in Gibbs free energy (∆G°), enthalpy (∆H°) and entropy (∆S°) were calculated for the adsorption of congo red, indicating an exothermic process.