Mantel Tomi, Benne Paul, Parsin Stanislav, Ernst Mathias
Institute for Water Resources and Water Supply, Hamburg University of Technology, Am Schwarzenberg-Campus 3, 20173 Hamburg, Germany.
Membranes (Basel). 2018 Aug 16;8(3):64. doi: 10.3390/membranes8030064.
Next to the pore size distribution, surface charge is considered to be one main factor in the separation performance of ultrafiltration (UF) membranes. By applying an external surface potential onto an electro-conductive UF membrane, electrostatic induced rejection was investigated. This study introduces in a first part a relatively simple but yet not reported technology of membrane modification with direct current sputter deposition of ultrathin (15 nm) highly conductive gold layers. In a second part, characterization of the gold-coated UF flat sheet membrane with a molecular weight cut-off (MWCO) of 150 kDa is presented. Membrane parameters as contact angle (hydrophobicity), pure water permeability, MWCO, scanning electron microscopy imaging, zeta potential, surface conductivity and cyclic voltammetry of the virgin and the modified membrane are compared. Due to the coating, a high surface conductivity of 10⁷ S m was realized. Permeability of the modified membrane decreased by 40% but MWCO and contact angle remained almost unchanged. In a third part, cross-flow filtration experiments with negative charged Suwannee River Natural Organic Matter (SRNOM) are conducted at different cathodic and anodic applied potentials, different pH values (pH 4, 7, 10) and ionic strengths (0, 1, 10 mmol L). SRNOM rejection of not externally charged membrane was 28% in cross-flow and 5% in dead-end mode. Externally negative charged membrane (-1.5 V vs. Ag/AgCl) reached rejection of 64% which was close to the performance of commercial UF membrane with MWCO of 5 kDa. High ionic strengths or low pH of feed reduced the effect of electrostatic rejection.
除孔径分布外，表面电荷被认为是超滤（UF）膜分离性能的一个主要因素。通过在导电超滤膜上施加外部表面电位，研究了静电诱导截留。本研究第一部分介绍了一种相对简单但尚未报道的膜改性技术，即通过直流溅射沉积超薄（15 nm）高导电金层。第二部分介绍了截留分子量（MWCO）为150 kDa的金涂层超滤平板膜的表征。比较了原始膜和改性膜的膜参数，如接触角（疏水性）、纯水渗透率、MWCO、扫描电子显微镜成像、zeta电位、表面电导率和循环伏安法。由于涂层作用，实现了10⁷ S m的高表面电导率。改性膜的渗透率下降了40%，但MWCO和接触角几乎保持不变。第三部分，在不同的阴极和阳极施加电位、不同的pH值（pH 4、7、10）和离子强度（0、1、10 mmol L）下，对带负电荷的苏万尼河天然有机物（SRNOM）进行错流过滤实验。未带外部电荷的膜在错流模式下对SRNOM的截留率为28%，在死端模式下为5%。外部带负电荷的膜（相对于Ag/AgCl为-1.5 V）截留率达到64%，接近截留分子量为5 kDa的商业超滤膜的性能。进料的高离子强度或低pH值降低了静电截留的效果。
