Ravishankar Harish, Christy Jens, Jegatheesan Veeriah
School of Engineering, RMIT University, Melbourne, VIC 3000, Australia.
Membranes (Basel). 2018 Sep 6;8(3):77. doi: 10.3390/membranes8030077.
Graphene oxide (GO) has been widely reported and used for treatment of heavy metals from different waste streams. Although their use as additives for membranes has greatly enhanced membrane properties, there is still a bottleneck in obtaining membranes with high heavy-metal rejection efficiencies while maintaining high flux, mechanical strength, and porosity. In the present study, different compositions of GO (0⁻1 wt %)-blended membranes were prepared using 1-methyl-2-pyrrolidone (NMP) as solvent and water with 5% ethanol as non-solvent, and studied for the rejection of the chosen model heavy-metal lead. The prepared membranes were characterized for hydrophilicity, membrane porosity, flux, permeability, pore-size, mechanical strength, and membrane morphology. From the results, it was inferred that membranes having maximum GO in their blend (1 wt %) showed better hydrophilicity (water contact angle 34.2°), porosity (82.2%), permeability (52.1 L/m² h bar), and pure water flux (163.71 L/m² h) at 3-bar pressure as opposed to other compositions. The pore sizes of the membranes ranged between 18 to 24 nm. Tensile strength tests showed the role of GO as a positive reinforcement on the mechanical properties of membranes through Young's modulus (188.13 ± 15.36 MPa) for the membrane having 0.25 wt % GO composition. Environmental Scanning Electron Microscopy (ESEM) images displayed the dense top layer supported by a porous, finger-like structure, obtained from instantaneous de-mixing favored by NMP and GO. The observed reduction in flux of lead solution for GO-blended membranes was due to osmotic pressure build-up caused by the retained nitrate salt by GO on the retentate side of the membrane. A maximum rejection of 98% was achieved with 1 wt % GO membrane at 1-bar pressure with flux of 43.62 L/m² h, which decreased to 94% at 3-bar pressure with flux of 142.95 L/m² h. These results showed how the application of NMP as solvent and GO as an additive could facilitate in obtaining high-flux and high-rejection membranes.
氧化石墨烯（GO）已被广泛报道并用于处理来自不同废物流的重金属。尽管将其用作膜添加剂极大地提高了膜的性能，但在获得具有高重金属截留效率同时保持高通量、机械强度和孔隙率的膜方面仍存在瓶颈。在本研究中，使用1-甲基-2-吡咯烷酮（NMP）作为溶剂，以5%乙醇的水作为非溶剂，制备了不同组成（0⁻1 wt%）的GO共混膜，并研究了其对选定的模型重金属铅的截留情况。对制备的膜进行了亲水性、膜孔隙率、通量、渗透率、孔径、机械强度和膜形态的表征。结果表明，共混物中GO含量最高（1 wt%）的膜在3巴压力下表现出更好的亲水性（水接触角34.2°）、孔隙率（82.2%）、渗透率（52.1 L/m² h bar）和纯水通量（163.71 L/m² h），与其他组成的膜相比。膜的孔径范围在18至24纳米之间。拉伸强度测试表明，对于GO组成含量为0.25 wt%的膜，GO通过杨氏模量（188.13 ± 15.36 MPa）对膜的机械性能起到了积极的增强作用。环境扫描电子显微镜（ESEM）图像显示，由NMP和GO促进的瞬间相分离形成了致密的顶层，其下方是多孔的指状结构。观察到GO共混膜对铅溶液通量的降低是由于GO在膜截留侧截留的硝酸盐导致渗透压升高所致。1 wt% GO膜在1巴压力下通量为43.62 L/m² h时，最大截留率达到98%，在3巴压力下通量为142.95 L/m² h时，截留率降至94%。这些结果表明，使用NMP作为溶剂和GO作为添加剂如何有助于获得高通量和高截留率的膜
