Showing papers by "Congjie Gao published in 2018"

Fluoride Removal from Water by Membrane Capacitive Deionization with a Monovalent Anion Selective Membrane

Abstract: Contamination of groundwater by monovalent anions, for instance, fluoride (F–) and nitrite (NO2–), leaves an adverse impact on human health. This study aims at investigating the feasibility of the application of membrane capacitive deionization (MCDI) combined with a monovalent anion permselective exchange membrane (PSM) for the removal of fluoride from water. In this study, various parameters (anion composition and concentration, pH, operating voltage, flow rate, and time) were studied for the purpose of attaining the maximum selectivity. Evaluation of the selectivity for monovalent anions was performed with the help of a lab-made MCDI with a model aqueous system (F–/SO42–). As revealed by the empirical findings, the removal of both F– and SO42– anions increased with the increase in anion concentration and pH, in addition to the increase in the selectivity for monovalent anions (F–). The removal of anions and selectivity also exhibited an increase with flow rate and operating time. Contrarily, the select...

Formation of morphologically confined nanospaces via self-assembly of graphene and nanospheres for selective separation of lithium

Abstract: Selective separation of lithium ions is crucial to recycle lithium from saline lakes Here, a novel multilayer framework membrane was constructed based on graphene oxide and sulfonated amino-polystyrene nanospheres (rGO@SAPS) via amide condensation reaction and self-assembly With the large specific surface area of these nanospheres and the anchored multitudinous sulfonate groups and amino groups, the synthesized rGO@SAPS formed unique membranes with morphologically confined nanospaces, and are applicable for the selective separation of Li+ under an electric field It was estimated that in an electrodialysis system (solution velocity 250 mL min−1, current density 1273 mA cm−2 and membrane thickness 10 μm), the selective separation efficiency parameter (retention or separation parameter between two different ions) of Mg2+/Li+ and K+/Li+ of rGO@SAPS-2 in 20 min is 4613% and 990%, respectively

Engineering of thermo-/pH-responsive membranes with enhanced gating coefficients, reversible behaviors and self-cleaning performance through acetic acid boosted microgel assembly

Abstract: Inspired by stomata, a series of single or dual thermo-/pH-responsive smart gating membranes (SGMs) were prepared with in situ assembled stimuli-responsive microgels as gates. Highly cross-linked poly(N-isopropylacrylamide-co-methylacrylic acid) P(NIPAM-co-MAA) microgels underwent in situ surface segregation during the acetic acid-assisted phase inversion process, and they were uniformly decorated on the surface of the membranes and the channels. The hydraulic permeability performance of SGMs was studied within the temperature range of 25–70 °C and a wide pH range (spanning pH 3–11). Investigations revealed that microgels based on different NIPAM/MAA ratios provided different thermo/pH-responsive properties to SGMs. Higher NIPAM/MAA ratios determined the thermo-responsive performance, and higher MAA/NIPAM ratios determined the pH-responsive performance. Moreover, the SGMs with in situ assembled microgels on the surface and channel surface have enhanced gating coefficients, stimuli-reversible behaviours and self-cleaning performance.

High-Performance Membrane Capacitive Deionization Based on Metal-Organic Framework-Derived Hierarchical Carbon Structures.

Abstract: Membrane capacitive deionization (MCDI) is a simple and highly energy efficient method to convert brackish water to clean water. In this work, a high-performance MCDI electrode architecture, which is composed of three-dimensional graphene networks and metal-organic frameworks (MOFs)-derived porous carbon rods, was prepared by a facile method. The obtained electrode material possesses not only the conducting networks for rapid electron transport but also the short diffusion length of ions, which exhibits excellent desalination performance with a high salt removal capacity, i.e., 37.6 mg g-1 at 1.2 V in 1000 mg L-1 NaCl solution. This strategy can be extended to other MOF-derived MCDI electrodes.

Surface layer modification of AEMs by infiltration and photo-cross-linking to induce monovalent selectivity

Abstract: Surface modification of anion exchange membranes (AEMs) by attaching a negatively charged layer is the main method for preparing monovalent anion selective membranes However, tremendous increase of membrane resistance and poor long term stability of the modified membranes face great challenges In this work, a photosensitive molecule (4,4-diazostilbene-2,2-disulfonic acid disodium salt (DAS)) was infiltrated into the membrane surface and immobilized in the structure by cross-linking under UV irradiation This method introduced negative charge to the surface layer of the AEMs without increasing membrane thickness, leading to high performance membrane with high monovalent anion selectivity The optimized membrane (D-5) shows the highest perm-selectivity of 1121, which is superior to the commercial selective membrane Selemion® ASV and previously reported monovalent anion selective AEMs Furthermore, the newly developed membrane exhibits excellent long-term stability, which can maintain constant selectivity during the 80 h ED experiment This article is protected by copyright All rights reserved

Preparation and characterization of an amphiphilic polyamide nanofiltration membrane with improved antifouling properties by two-step surface modification method

Abstract: Membrane fouling is an urgent problem needing to be solved for practical application of nanofiltration membranes. In this study, an amphiphilic nanofiltration membrane with hydrophilic domains as well as low surface energy domains was developed, to integrate a fouling-resistant defense mechanism and a fouling-release defense mechanism. A simple and effective two-step surface modification of a polyamide NF membrane was applied. Firstly, triethanolamine (TEOA) with abundant hydrophilic functional groups was grafted to the membrane surface via reacting with the residual acyl chloride group of the nanofiltration membrane, making the nanofiltration membranes more hydrophilic; secondly, the 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTS), well-known as a low surface energy material, was covalently grafted on the hydroxyl functional groups through hydrogen bonding. Filtration experiments with model foulants (bovine serum albumin (BSA) protein solution, humic acid solution (HA) and sodium alginate solution (SA)) were performed to estimate the antifouling properties of the newly developed nanofiltration membranes. As a result of surface modification proposed in this study the antifouling properties of an amphiphilic modified F-PA/PSF membrane were enhanced more than 10% compared to the PA/PSF specimen in terms of flux recovery ratio.