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The waste products of NdFeB magnets are an attractive resource for the recovery of rare earth elements (REEs), especially for neodymium [Nd]. Conventional methods employed to remove ferric (Fe[II]) from Nd solutions involve high energy consumption and the extensive use of chemicals, including oxidants and pH regulators, leading to substantial wastewater generation. In this work, an environmentally friendly approach utilizing CaMg(CO3)2 was presented to remove Fe(II) from Nd solution. Under optimized conditions, including a reaction temperature of 70°C, a CO32-/Fe2+ ratio of 1.5/1, a reaction time of 240 min, and an initial concentration of 200 mg/L, the heterogeneous precipitation reaction on the surface of CaMg(CO3)2 exhibited an exceptional Fe(II) removal efficiency of 98.6%, with a negligible loss of Nd (only 0.8%). It was observed that the CaMg(CO3)2 not only provide a suitable alkaline environment for the selective precipitation of Fe(II), but also significantly enrich the concentration of dissolved oxygen at a high temperature. In fact, at a CaMg(CO3)2 concentration of 2 g/L, the dissolved oxygen concentration in the solution increased significantly to 15.5 mg/L at 70°C. Consequently, the usage of CaMg(CO3)2 facilitated the rapid conversion of Fe(II) to Fe(III) without the need for additional oxidants, which was perfect for the removal of Fe(II) rather than Nd. [ABSTRACT FROM AUTHOR]

Diffusion dialysis (DD) for acid recovery is significantly restricted by the poor acid dialysis coefficient (UH+) of anion exchange membranes (AEMs). To overcome such problem, porous AEMs with extremely high free space volume have been fabricated herein based on porous membrane substrate, drawing inspiration from the dissolution‐diffusion concept. Specifically, chloromethylated polyethersulfone (CMPES) has been used as the starting material to create the porous substrate via non‐solvent phase inversion, then in‐situ crosslinked and quaternized using ethylenediamine (EDA) and N‐methylimidazole (NMI), respectively. In this study, the degrees of modification of EDA and NMI are controlled to adjust the microstructure and DD performance of the produced porous AEMs. The ideal AEM's UH+ and acid/salt separation factor (S) are 4.3 and 2.6 times greater, respectively, than those of the commercial DF‐120 membrane at the same condition. Additionally, it shows strong organic solvent resistance and thermal stability, and therefore demonstrate the potential for widespread use. [ABSTRACT FROM AUTHOR]

BACKGROUD Organic contaminants in secondary reverse osmosis (SRO) concentrate pose a severe threat to the ecosystem, due to their potential toxicity. In this study, potential of coagulation/granular activated carbon (GAC) adsorption combined with UV/H2O2 and ozonation for removing organic matter from industrial secondary RO concentrate was systematically investigated. RESULTS: Coagulation with 2.0 mmol L−1 FeCl3 yielded 40% removal of dissolved organic carbon (DOC), while adsorption with 5 g L−1 GAC could boost the removal efficiency up to 78.2%. Fractionation results showed that both coagulation and GAC adsorption favored hydrophobic organics. UV/H2O2 oxidation was capable of removing 87.4% of DOC, which outperformed ozonation (58.2%). UV/H2O2 and ozonation showed similar behavior in dissolved organic matter (DOM) degradation: a portion of hydrophobic organics were first transformed into hydrophilic fractions prior to final mineralization. Conclusion: Coupling of GAC as post‐treatment with a UV/H2O2 process yielded 97.9% removal of DOC and the corresponding electrical energy per order (EE/O) was decreased from 66.7 to 35.8 kWh m−3. Consequently, a simple UV/H2O2 and GAC hybrid process was proposed to be a suitable method for removing DOM from SRO concentrate. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

ABSTRACT: Selectivity for monovalent ions is a very important feature of ion exchange membranes in view of a further expansion of the scope of electrodialysis (ED). An efficient one‐step chemical process to graft a thin polyaniline (PANI) layer on the surface and pores of an ultrafiltration (UF) membrane is reported. The existence of a PANI layer on such modified UF membrane was confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy images. These membranes were extensively characterized by studying their properties such as water uptake, ion‐exchange capacity, contact angle, and performance in diffusion dialysis. ED experiments were conducted by comparing desalting of sodium chloride and magnesium chloride solutions. During the desalting procedure, the driving force has two contributions, the electrical field and the salinity‐gradient. Initially, transport of ions by the electrical field is dominant, while at the end of the experiment, diffusion dialysis by the salinity gradient plays a larger role in ion transport. The presence of PANI can hinder Mg2+ transport from the concentrate to the diluate compartment because of the electrostatic effect, while there is no obvious effect on Na+ ions. The ability of such a surface modification layer to improve the membrane selectivity for Na+/Mg2+ was confirmed by means of ED in a mixed solution. The flux of Na+ was slightly increased to 13.21 × 10−8 mol/L/min while the flux of Mg2+ was reduced to 3.32 × 10−8 mol/L/min, so that the permselectivity is almost doubled. The protonation reaction of the PANI layer creates positive charges, thus leading to an electrical repulsion barrier, which may reduce the penetration of divalent cations with respect to monovalent ions. Polyacrylonitrile‐based UF membranes with different molecular cutoff was used to determine the influence of the permselectivity. Results showed that the membrane permselectivity of smaller molecular cutoff UF membranes is higher. It can be concluded that this method is suitable for preparing membranes based on UF membranes for efficient separation of monovalent ions by electro‐driven separation techniques. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45692. [ABSTRACT FROM AUTHOR]

Inspired by the limpet's shell, this study reports an inexpensive and straightforward strategy to create sealed photonic crystals from colloidal hollow microspheres. From the mechanically sealed structure and the periodically isolated air microcavities, the resulting sealed colloidal crystals show enhanced mechanical robustness and an ultrastable photonic band gap. In contrast to the sensitivity and the concomitant tuning capability in conventional opals and inverse opals, the sealed structure repels any liquid, even under high pressure, resulting in ultrastable photonic band gap properties. Moreover, with surface modification, its self-cleaning ability prevents the deterioration of iridescence resulting from surface pollution. This novel photonic structure shows its potential utility in applications requiring an ultrastable photonic band gap in an extreme environment. This study demonstrates this by photonic crystal lasing at a constant wavelength for a sealed crystal, whether dry in air or submerged in water. [ABSTRACT FROM AUTHOR]

Surface functionalization with advanced nanomaterials offers tailored control and targeted design of surface properties, endowing materials with enhanced or new qualities such as high hydrophilicity, excellent selectivity and permeability, and enhanced antimicrobial activity. In this study, we develop two strategies (two-step deposition/co-deposition) that use mussel-inspired polydopamine (PDA) to strongly immobilize copper nanoparticles (CuNPs) onto a porous polymeric membrane, bridging the surface cavities from ultrafiltration (UF) to loose nanofiltration (NF). To confirm the optimization of membrane properties, a series of characterizations were carried out: SEM, EDX analysis, AFM, water contact angle, and zeta potential measurements. The results indicate an overall high performance of surface properties with a homogeneous nanoparticle distribution, low roughness, favorable hydrophilicity, and relatively neutral charge. Co-deposition of PDA and CuNPs exhibits a facile and time-saving process that expedited a higher CuNP loading compared to the two-step strategy, as confirmed by SEM and AFM images. The integration of polyethylenimine (PEI)-modified CuNPs with high density of positive charges plays an important role in fine-tuning the hydrophilicity and compatibility with PDA and in largely neutralizing the negative charge of PDA, thus promoting an outstanding salt permeation (82% Na2SO4, 98% NaCl). In addition, CuNP/PDA-modified membranes show an ultra-high rejection of three types of textile dyes (600–800 Da, ＞99.0%), demonstrating superior NF performance. Furthermore, the functionalized membranes display distinct bactericidal activity with a great reduction of 93.7% in the number of live Escherichia coli (E. coli) bacteria. This study highlights a fast, facile co-deposition strategy to assemble multifunctional coating onto a UF support, which renders a vast potential for the fractionation of dye/salt mixtures. [ABSTRACT FROM AUTHOR]

Surface zwitterionization of graphene oxide (GO) was firstly conducted by grafting poly(sulfobetaine methacrylate) (PSBMA) onto the GO surface via reverse atom transfer radical polymerization (RATRP). Then, a novel type of GO-PSBMA/polyethersulfone (PES) loose nanofiltration membrane (NFM) was constructed by mixing with modified GO composites via phase inversion. FTIR, XRD, TEM, XPS and TGA were applied to analyze the chemical composition and morphology, confirming a favorable synthesis of GO-PSBMA composites. Besides, the effect of the embedded GO-PSBMA nanoplates on the morphology and overall performance of the hybrid membranes was systematically investigated based on the SEM images, water contact angle, zeta potential, and fouling parameters. It was found that the water flux of the hybrid membrane was greatly enhanced from 6.44 L m−2 h−1 bar−1 to 11.98 L m−2 h−1 bar−1 when the GO-PSBMA content increased from 0 to 0.22 wt%. The antifouling tests revealed that the GO-PSBMA embedded membranes had an excellent antifouling performance: a high flux recovery ratio (ca. 94.4%) and a low total flux decline ratio (ca. 0.18). Additionally, the hybrid membranes exhibited a distinct advance in the mechanical strength due to the addition of highly rigid GO. Notably, compared with unmodified membranes, the hybrid membranes had a higher retention of Reactive Black 5 (99.2%) and Reactive Red 49 (97.2%), and a lower rejection of bivalent salts (10% for Na2SO4) at an operational pressure of 0.4 MPa, rendering the membranes promising for dye/salt fractionation. [ABSTRACT FROM AUTHOR]

BACKGROUND Conventional methods for synthesis of quaternary ammonium hydroxides, such as the reaction of quaternary ammonium chloride, ion-exchange and electro-electrodialysis cannot achieve benign production of QAOH without secondary pollution. The objective of the present study was to develop bipolar membrane electrodialysis with a novel stack configuration as an improved method to prepare high purity quaternary ammonium hydroxide from its halide salt. RESULTS To investigate the synthesis of quaternary ammonium hydroxide ( QAOH) with high purity by using electrodialysis with bipolar membranes ( BMED), four different types of quaternary ammonium hydroxides (tetramethylammonium hydroxide, TMAOH; tetrapropylammonium hydroxide, TPAOH; methyltriethylammonium hydroxide, MTAOH; and benzyltrimethylammonium hydroxide, BTAOH) were chosen as the target products. The effect of the molecular structure of four different types of halide salts ( NR4X) on the BMED performance was studied by investigating operating parameters such as current density, feed concentration and feed flow velocity and energy consumption on the basis of ion dimensions and molecular weight, ion electrophoretic mobility and the interaction between ammoniums and membranes. The results indicate that it is feasible to obtain quaternary ammonium hydroxides with high purity (Cl−/Br− content < 500 ppm) by BMED with a novel four-compartment configuration in view of environmental aspects. CONCLUSION For converting higher molecule size halide salts, the process performance was lower, while the energy consumption increased, at similar experimental conditions, which is in line with the theory. © 2014 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]