Highly stable and antifouling graphene oxide membranes prepared by bio-inspired modification for water purification

Graphene oxide (GO) membranes show great potential in molecular separation for water treatment. However, the inferior stability of GO membranes is a major bottleneck for practical applications. In this study, bio-inspired polydopamine (PDA) deposition is reported for enhancing the stability of GO membranes. Through simple and mild immersion, PDA is self-polymerized on GO membranes. The blocking of PDA chains to membrane defects improves the rejections for various molecules. Because the inherently strong adhesion and crosslinking of PDA greatly strengthen the interactions of substrates to GO layers and the binding force of GO nanosheets, the prepared PDA-GO membranes exhibit impressive long-term stability in cross-flow filtration, and maintain good nanofiltration performance at various feed pressures, tangential velocities, and even after external scratching. Moreover, because the deposited PDA layers obstruct the direct contact between GO and contaminants, the antifouling property of the PDA-GO membranes increases substantially, with recovery ratio about 98%.     

Greener approach for process intensification of iron haematinics by membrane nanofiltration

Iron haematinics are high-volume, low-cost drug products used to treat anaemia. For the preparation of iron haematinics, the manufacturers depend heavily on multipurpose-batch or semi-batch reactors. Here, process intensification of haematinics was carried out using membrane nanofiltration as a major operation. A total of three haematinics namely, iron (III) hydroxide polymaltose, iron gluconate, and iron sucrose complex were prepared, and the process intensified on dead-end filtration set up by using a polymeric membrane. Iron (III) hydroxide polymaltose experimental results were compared with commercially available standard. The membrane performance was characterized by various parameters such as flux, permeability, flux decline ratio, flux recovery ratio, percentage retention, fouling, etc., at different transmembrane pressures. The membrane surface was analysed by Scanning Electron Microscopy (SEM) to understand its morphology and fouling. The iron concentration was detected in the permeate stream using inductively coupled plasma optical emission (ICP-OES) spectroscopy to detect %retention (>99.99%) under all experimental conditions tested. The study led to optimized conditions for haematinics concentration by a membrane at a 10-bar trans-membrane pressure, which was applied for the preparation of iron gluconate salt. Overall, the study resulted in a green process with increased productivity.     

超支化聚酯低压纳滤膜的制备与表征

通过超支化聚酯(HPE)末端的羟基与戊二醛(GA)之间的羟醛缩合反应,采用简单的浸涂-交联方法,制备了一种以聚砜超滤膜为支撑层,交联的HPE为活性分离层的复合纳滤膜.采用衰减全反射红外光谱(ATR-FTIR)、接触角测定、扫描电子显微镜(SEM)对纳滤膜的表面化学组成、亲水性和膜形貌进行了表征.考察了HPE溶液浓度、GA溶液浓度对膜分离和渗透性能的影响,优化的HPE和GA溶液浓度分别为9.8 g/L和7.4 g/L,此时在0.4 MPa下膜的水通量达69.6 L/(m2.h),对Na2SO4脱除率为93.2%,表现出低操作压力、高通量、高脱盐率的优异性能.纳滤膜对无机盐的截留顺序为Na2SO4>NaCl>MgSO4>MgCl2,呈现明显的荷负电特征.     

Nanofiltration and ultrafiltration of endocrine disrupting compounds, pharmaceuticals and personal care products

Reports of endocrine disrupting compounds (EDCs) and pharmaceuticals and personal care products (PPCPs) have raised substantial concern among important potable drinking water and reclaimed wastewater quality issues. Our study investigates the removal of EDC/PPCPs of 52 compounds having different physico-chemical properties (e.g., size, hydrophobicity, and polarity) by nanofiltration (NF) and ultrafiltration (UF) membranes using a dead-end stirred-cell filtration system. EDC/PPCPs were applied to the membrane in one model water and three natural waters. Experiments were performed at environmentally relevant initial EDC/PPCP concentrations ranging typically from 2 to <250 ng/L. EDC/PPCP retention was quantified by liquid and gas chromatography with mass spectroscopy–mass spectroscopy. A general separation trend due to hydrophobic adsorption as a function of octanol–water partition coefficient was observed between the hydrophobic compounds and porous hydrophobic membrane during the membrane filtration in unequilibrium conditions. The results showed that the NF membrane retained many EDC/PPCPs due to both hydrophobic adsorption and size exclusion, while the UF membrane retained typically hydrophobic EDC/PPCPs due mainly to hydrophobic adsorption. However, the transport phenomenon associated with adsorption may depend on water chemistry conditions and membrane material.     

纳滤膜分离技术的应用进展

纳滤膜是一崭新的分离膜,本文综述了纳滤膜技术在食品、化工、饮用水、废水处理等领域的应用进展.并简单介绍了纳滤膜在有机溶剂中的应用研究.     

纳滤膜分离技术分离纯化多肽和氨基酸

综述了近十年来纳滤膜技术在氨基酸和多肽分离与纯化方面的研究进展。多肽和氨基酸的纳滤分离过程受溶液物化性质、氨基酸和多肽分子尺寸、所带电荷以及膜孔径、膜带电状态等多种因素的影响,建立该过程的分离机理模型、组合并优化分离条件是当前研究的热点。     

Controlling Pore Size and its Distribution of γ-Al2O3 Nanofiltration Membranes

The preparation process of γ-A12O3 nanofiltration membranes were studied by N2 absorption and desorption test and retention rate vs thickness gradient curve method. It was found that template and thermal treatment were key factors for controlling pore size and its distribution.Under the optimized experimental conditions, the BJH (Barret-Jovner-Halenda) desorotion average pore diameter, BJH desorption cumulative volume of pores and BET (Brunauer-Emmett-Teller)surface area of obtained membranes were about 3.9 nm, 0.33 cm3/g and 245 m2/g respectively, the pore size distribution was very narrow. Pore size decreased with the increasing of thickness and no evident change after the dense top layer was formed. The optimum thickness can be controlled by retention rate vs thickness gradient curve method.     

Preparation and characterization of nanofiltration membranes by coating polyethersulfone hollow fibers with sulfonated poly(ether ether ketone) (SPEEK)

A new type of nanofiltration membrane is reported based on coating a sulfonated poly(ether ether ketone) (SPEEK) layer on top of a polyethersulfone support. The membranes were characterized by dextran mixtures, salt solutions as well as negatively charged dyes. The SPEEK coated nanofiltration membranes showed molecular weight cutoff for dextran in the range of ultrafiltration, however, rather high rejection for sodium sulfate; retention for salts in the order of RNa₂SO₄>RNaCl>RMgCl₂$R_{\text{N}{\text{a}}_2\text{S}{\text{O}}_4}>R_{\text{NaCl}}>R_{\text{MgC}{\text{l}}_2}$; in addition, the membranes showed a 97–100% retention to the organic dyes. The rejection rates were improved by an increase in the coating thickness and the polymer concentration in the coating solution at the penalty of permeability decrease. Furthermore, it was found that pore penetration of SPEEK into the support membrane effectively constrained the swelling rate of SPEEK and increased the retention. The Donnan–Steric Pore Model was used to describe the transport properties of the membrane. Modeling identified a very tortuous passage within the active separation layer.     

Nanofiltration of biogenic amines in acidic conditions: Influence of operation variables and modeling

Biogenic amines are present in some fermented and non-fermented beverages and can cause diseases. This study analyzes the feasibility of separating biogenic amines by nanofiltration in acidic medium. Solutions of chloride salts of three biogenic amines: putrescine, histamine and tyramine were filtered through a nanofiltration membrane with a 1000 Da molecular weight cut-off (MWCO) and a positive electrical charge at pH 3. Increasing the transmembrane pressure or cross flow velocity led to an increase in solute rejection and permeate flow. Moreover, a higher electrical charge or lower concentration of amine cations caused a larger rejection indicating that membrane-solutes repulsion governs the filtration process. Finally, the experimental results were analyzed using the classic Donnan–Steric pore model. Values of 0.83 nm and 5.4 μm were estimated for pore radius and membrane effective ratio thickness-porosity from the filtration of neutral solutes. Membrane volumetric charge density and the proton diffusivity inside the pores were estimated from the experimental results.