| Poly ether sulfone (PES), which is not only an excellent thermal stability and oxidation resistance, but also have stable mechanical properties, excellent creep resistance and other outstanding characteristics, is a widely used membrane material. However, due to its strong hydrophobic property, the pure PES membrane will cause fouling easily, leading to low flux, low operational efficiency and even shorten membrane life. Therefore, the modification for the pure PES ultrafiltration membrane is urgent. Blending by inorganic/organic material is a simple and efficient modification method, which is widely used in the preparation of high-performance ultrafiltration membranes. Blending one or more additives can effectively improve the properties of pure organic membranes, not only improving the hydrophilic property and resistance, but also can getting some special function. In this study, Co3O4-GO nanocomposites were prepared by supporting cobalt oxide (Co3O4) on graphite oxide (GO), then hybrid membranes were prepared by phase inversion method. In order to improve the properties, three parts, the compatibility between additives and membrane materials, the blending content of Co3O4-GO and the optimal condition of catalytic cleaning, were studied.In this study, flake graphite as raw material, graphite oxide was prepared by Hummers method, and then Co3O4-GO nano-composites were synthesized by by-step thermal solvent. And the nano-composites were characterized by XRD、SEM and HRTEM, the results indicated that the nano-sized particles Co3O4 successfully loaded onto GO sheets, which contains a large amount of hydroxyl, carboxyl and other oxygen-containing functional groups on surface, and the size of Co3O4-GO were less than 100nm. In the experiment of selecting optimal organic solvent, Co3O4-GO were dispersed in DMF, DMAC and NMP, after ultrasound treatment DMAC was optimal, additionally, uniform and stable casting solution were formed successfully after the additive stirring. The characterization results of EDS surface scanning showed that, the nanosheets uniformly dispersed in hybrid membranes, significant agglomeration did not appear, indicating great compatibility was formed between additive and organic matrix.In order to investigate the influence of CO3O4-GO on membrane structure, SEM and AFM was applied to characterize the structure and the surface roughness of membranes, the result was that:compared with the pristine membrane, the finger structure of hybrid membranes become more regular, which indicated the penetration is better and will be helpful for improve water flux. However, when the content of nanosheets were more than 1.5wt.%, some horizontal lamellar structure showed on dense layer which will clog some pores. AFM characterization results showed the surface of hybrid membranes were smoother than the pristine, and the roughness increased as more content of nanosheets embedded.Meanwhile, the measurement of tensile strength, static contact angle, water flux, rejection ratio, antifouling and antibacterial properties were conducted to study the influence of embedding content of CO3O4-GO, the results as followed:the mechanical property of hybrid membranes were improved obviously; Static contact angle of the pristine was 75.2°, and it decreased successively with the increased amount of additive, and it got minimum (54.75 °), which indicated best hydrophilicity, when the embedding content was 2.0 wt.%; the pure water flux of the hybrid membrane was improved from 101.1L·m-2·h-1 to 347.9L·m-2·h-1 comparing with the pristine membrane. Furthermore, antifouling performance was investigated through multicycles of aerobic activated sludge (SV30) filtration tests, where the permeability recovery ratio increased from 55.7% for the pristine membrane to 81.1% for nanosheets modified membrane. Additionally, remarkable improvement was also observed for antibacterial performance (89.8%, against Escherichia coli).The study of membrane catalytic cleaning, which was fouled after the ultrafiltration of leachate, was conducted by taking Oxone as cleaning agent, which produced sulfate free radical catalyzed by CO3O4, the result as below:the flux recovery ratio after the fouling of ultrafiltration process of landfill leachate was promoted with the increase of blending content of CO3O4-GO, the concentration of Oxone and membrane immersion time, the optimal cleaning condition was that membrane with 1.5 wt.% nanocomposites,5 mM Oxone and immersing 30 min.Cobalt ion elution and the stability of hybrid membranes after catalytic cleaning were studied by inductively coupled plasma emission spectrometer (ICP) and BSA rejection ratio, respectively. After numerous ultrafiltration operation cobalt ions were detected by ICP, and BSA rejection ratio of the hybrid membrane still remained above 94%, indicating that the catalytic cleaning did not produce secondary pollution and could maintain stability during the ultrafiltration operation. |
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