Adsorption of methyl orange from aqueous solution by composite magnetic microspheres of chitosan and quaternary ammonium chitosan derivative

Novel composite magnetic microspheres containing chitosan and quaternary ammonium chitosan derivative(CHMMs) were prepared by inverse suspension method,and used for the methyl orange(MO) removal from aqueous solutions.The CHMMs were characterized by a scanning electron microscope,a transmission electron microscope,and Fourier transform infrared spectroscopy,respectively.Compared with the chitosan beads,the incorporation of quaternary ammonium chitosan derivative significantly reduced the particle size.The MO adsorption by CHMMs was investigated by batch adsorption experiments.The adsorption kinetics was conformed to the pseudo second-order kinetics equation.The adsorption isotherm followed the Langmuir model better than the Freundlich model and the calculated maximum MO adsorption capacity was 266.6 mg·g^-1 at 293 K.Thermodynamic studies indicated that the MO adsorption was endothermic in nature with the enthalpy change(△H°) of 99.44 kJ·mol^-1.The CHMMs had a stable performance for MO adsorption in the pH range of 4-10,but high ionic strength deteriorated the MO removal due to the shielding of the ion exchange interaction.A 1 mol·L^-1 NaCl solution could be used to regenerate the exhausted CHMMs.The proposed CHMMs can be used as an effective adsorbent for dye removal or recovery from the dye wastewater.

17α-Ethinylestradiol removal from water by magnetic ion exchange resin

Magnetic ion exchange(MIEX) resins have received considerable attention in drinking water treatment due to their fast and efficient removal of dissolved organic carbon(DOC). Two types of mechanisms, i.e., ion exchange,reversible and irreversible adsorption, may occur during pollutants removal by MIEX. This work examined the removal mechanism of 17α-Ethinylestradiol(EE2) by MIEX. As one of typical estrogen micro-pollutants,EE2 existed as neutral molecule in natural water, and its charge density was close to zero [(0.00000219 ±0.00000015) meq·(μg EE2)^(-1)] based on the potentiometric titration method. However, the removal of EE2 by MIEX was much higher than that of other micro-pollutants previously reported. Multi-cycle adsorptionregeneration experiments and ion exchange stoichiometry analysis were conducted to elucidate the removal mechanism of EE2 by MIEX resin. The results suggested that the main removal mechanism of EE2 by MIEX was ion exchange instead of reversible micro-pore adsorption. The experimental analysis based on Donnan theory indicated that the internal micro-environment of resin beads was alkaline, in the alkaline environment EE2 would be ionized into negatively charged groups. As a result, ion exchange reaction occurred inside the pore of MIEX resin, and the removal process of EE2 by MIEX was dominated by the ion exchange reaction.

Bifunctional copper modified graphitic carbon nitride catalysts for efficient tetracycline removal:Synergy of adsorption and photocatalytic degradation

In order to efficiently re move tetracycline in wastewater through the synergistic effect of adsorption and photocatalytic degradatio n,a series of novel composite materials(Cu doped g-C_(3)N_(4))were synthesized by two-pot hydrothermal method.It was found that the composite materials with optimized ratio(Cu/CN-1)displayed outstanding adsorption and photocatalytic performance as compared with pure g-C_(3)N_(4) photocatalyst.The removal efficiency of tetracycline(TC,50 mg/L)reached almost 99%within 30 min by Cu/CN-1 through the synergy of adsorption and photocatalysis under visible-light irradiation,which was the highest re moval efficiency ever reported.The adsorption kinetics and isotherms of TC on the Cu/CN-1 were well fitted with the pseudo-second-order kinetic model and Langmuir model,respectively.Moreover,it was confirmed that the main effective reactive groups were O_(2)^·and h^(+) in photocatalytic process.The Cu/CN-1 exhibited high stability and excellent reusability after five cycle experiments.Finally,the mechanism of synergy between Cu and g-C_(3)N_(4) was proposed:on the one hand,the decoration of Cu particles significantly increased the adsorption sites of Cu/CN-1 to tetracycline,on the other hand,the modification of Cu particles effectively inhibits charge recombination and broadens the visible light absorption range of the photocatalyst.This study provided a promising photocatalyst to be used for TC removal in the actual wastewater.

Tracing the impact of stack configuration on interface resistances in reverse electrodialysis by in situ electrochemical impedance spectroscopy

Reverse electrodialysis(RED)is an emerging membrane-based technology for the production of renewable energy from mixing waters with different salinities.Herein,the impact of the stack configuration on the Ohmic and non-Ohmic resistances as well as the performance of RED were systematically studied by using in situ electrochemical impedance spectroscopy(EIS).Three different parameters(membrane type,number of cell pairs and spacer design)were controlled.The Ohmic and non-Ohmic resistances were evaluated for RED stacks equipped with two types of commercial membranes(Type I and Type II)supplied by Fujifilm Manufacturing Europe B.V:Type I Fuji membranes displayed higher Ohmic and non-Ohmic resistances than Type II membranes,which was mainly attributed to the difference in fixed charge density.The output power of the stack was observed to decrease with the increasing number of cell pairs mainly due to the increase in ionic shortcut currents.With the reduction in spacer thickness from 750 to 200μm,the permselectivity of membranes in the stack decreased from 0.86 to 0.79 whereas the energy efificiency losses increased from 31%to 49%.Overall,the output of the present study provides a basis for understanding the impact of stack design on internal losses during the scaling-up of RED.