This invention relates to a method for the preparation of a silica dioxide-polyethersulfone conductive ultrafiltration membrane, the obtained ultrafiltration membrane and guidance on membrane applications.
Antibiotics are among the most frequently used chemicals worldwide and this excessive use has resulted in antibiotic substances being detected in aquatic environments and drinking water at relatively high concentrations. Refractory antibiotics may persist in aquatic environments for a long period of time, posing a serious risk to drinking water quality, public health and the whole ecosystem. High concentrations of antibiotics existing in the environment cause body malformation, microbiota dysfunction, suppress immunity and further affect antioxidant capacity, and trigger DNA damage. Therefore, it is essential that technologies and methods are developed for the removal of antibiotics from water.
Membrane separation technologies are widely used in the field of water treatment, due to their advantages of simple modes of operation, no secondary pollutants, and good separation effects. However, despite continual membrane technology development, membrane fouling remains a major problem that inhibits its widespread application. In addition, due to the characteristics of membrane separation processes, pollutants are often trapped on the membrane surface and cannot be removed.
Electrocatalytic membrane filtration technology is a new membrane separation technology which combines membrane separation with electrocatalytic oxidation. The combination of electrocatalysis and membrane filtration technologies allows pollutants to be intercepted and degraded, effectively removing them from water and alleviating membrane fouling. A conductive porous material with stable physical and chemical properties is utilized as the base membrane, which is modified by coating with nano-materials exhibiting electrocatalytic properties. Under the conditions of a low-voltage electric field, organic pollutants are decomposed by oxidation, using oxidants generated by direct or indirect oxidation of the electrocatalytic membrane, such as hydrogen peroxide (H2O2), hydroxyl (.OH) and superoxide (.O2−) radicals.
The polymer film material, such as polyvinylidenefluoride (PVDF) and Polyethersulfone (PES), commonly used in membrane separation achieve stable performance and good separation effects, although they cannot usually be used in electrocatalytic processes as the polymers are often not conductive. In addition, due to the electrochemical process, active substances gradually separate from the currently used electrocatalytic membranes, resulting in a reduction in stability with continual membrane use and poor antibiotics treatment effects.
In order to overcome the shortcomings of existing technologies, the present invention presents a silicon dioxide—polyether sulfone conductive ultrafiltration membrane and its preparation method, with guidance for its practical application. Long-term stability of the ultrafiltration membrane has been verified after 8 cycles of reuse under constant circulating water flux and antibiotics pollution conditions, with the membrane exhibiting good recycling performance and maintaining a high antibiotics removal rate.
The technical scheme for this invention is as follows:
The invention discloses the preparation method for the silicon dioxide-polyethersulfone conductive ultrafiltration membrane, which includes the following steps:
The invention method was optimized to establish the optimal hydrophilic CFCF pretreatment steps (step 1 above). Immerse the hydrophilic CF cloth in a mixed solution of acetone, deionized water and anhydrous ethanol (1:1:1 volume ratio) and subject the solution to ultrasonication for 20-40 min, then dry the solution at 50-70° C. Hydrophilic CF CFcloths are an existing technology that are available for purchase commercially.
The invention was optimized to establish the ideal molar ratio of tetraethyl orthosilicate, anhydrous ethanol, deionized water and concentrated hydrochloric acid as 1:3-4:6-7:0.88-0.09 (step 2 above).
The invention was optimized to establish the suitable silica film thickness to be 100-200 μm, with a preferred thickness of 200 μm (step 3 above). Furthermore, the invention was optimized to ensure effective bonding of the silica solution to the pretreated hydrophilic CF cloth, requiring the use of 2-4 layers of film scraping (step 3 above).CF
The invention was optimized to establish the method for polymerization of polyethersulfone (PES) onto the film (step 4 above). Dissolve PES powder in NMP/DMF mixture (weight ratio is 1:1) and stir at 1000 rpm for 20-28 hr, then let the mixture stand for 24 hr to obtain the PES casting solution. The PES casting solution is then scraped on to the film, ensuring even coverage. After the film has been scraped, the membrane should be left to evaporate at room temperature for 15-25 s, then slowly immersed in deionized water for 10-14 h at room temperature, before being dried at 40-60° C. to obtain the final silica dioxide-polyethersulfone conductive ultrafiltration membrane.
The invention was optimized to establish the optimal PES film thickness after scraping to be 180-220 μm, with a preferred value of 200 μm (step 4 above). The invention was also optimized to establish the suitable average molecular weight of PES to be 45000-55000 (step 4 above). Furthermore, the mixed solvent solution was optimized to establish the optimal mass ratio of N,N-dimethyl acetamide and N-methyl pyrrolidone to be 1:1, while the PES casting film solution was optimized to establish an ideal PES mass concentration of 10-20% (step 4 above).
Following optimization, the silica dioxide-polyethersulfone conductive ultrafiltration membrane was obtained using the described method and stored in deionized water prior to further use.
The silicon dioxide-polyethersulfone conductive ultrafiltration membrane was applied to remove antibiotics from wastewater on the basis of an applied voltage using an external DC power supply, with the voltage is controlled between 1-3 V. When the voltage exceeds 3 V, the antibiotic wastewater treatment effect exhibits no further increase.
The technical characteristics and beneficial effects of the invention are as follows:
The invention is further described below in combination with the attached drawings and implementations, although the scope of protection of the invention is not limited to these examples.
Furthermore, the experimental methods described in the following examples are conventional methods unless otherwise specified. The reagents, materials and equipment used are commercially available unless otherwise specified.
The preparation method for the silicon dioxide-polyethersulfone conductive ultrafiltration membrane was as follows:
The SEM and XPS images of the prepared SiO2-ployethersulfone conductive ultrafiltration membrane are shown in
Application of silica dioxide-polyethersulfone conductive ultrafiltration membrane:
The SiO2-ployethersulfone conductive ultrafiltration membrane was placed in membrane filtration system, with a 1 V direct current applied. Samples were taken at the outlet to determine the antibiotic content of the treated wastewater.
The same conditions were maintained for 8 cycles of reuse, with the treatment cycle including antibiotic wastewater treatment with ultrafiltration membrane for 30 minutes, then followed by cleaning ultrafiltration membrane with deionized water before repeat use for wastewater treatment. The results are shown in
The preparation method for the SiO2-ployethersulfone conducting ultrafiltration membrane was the same as described in example 1, with the exception that the thickness of the silica film was 100 μm and the concentration of PES in the casting solution was 20 wt. %.
The preparation method of the SiO2-ployethersulfone conducting ultrafiltration membrane was as described in example 1, with the exception that the thickness of the silica film was 200 μm and the concentration of PES in the casting solution was 10 wt. %.
The preparation method of the SiO2-ployethersulfone conducting ultrafiltration membrane was as described in example 1, with the exception that the thickness of the silica film was 200 μm and the PES concentration in the casting solution was 20 wt. %.
The preparation method of the SiO2-ployethersulfone conducting ultrafiltration membrane was as described in example 1, with the exception that the SiO2-ployethersulfone membrane was applied to an existing wastewater treatment system with a 3 V direct current applied to the membrane.
Experimental Cases:
Removal rate of antibiotics: To establish whether the silica dioxide-polyethersulfone conductive ultrafiltration membrane is applicable under existing wastewater treatment system conditions, the membrane was applied with simulated antibiotic wastewater containing 5 mg/L tetracycline (pH 6.5), with a 1 V direct current applied. Ultrafiltration membrane outlet sampling was performed for determination of the antibiotics content of wastewater, allowing the antibiotics removal rate to be calculated. The water flux results for different membranes are shown in
Number | Date | Country | Kind |
---|---|---|---|
201910799727.3 | Aug 2019 | CN | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/CN2020/109981 | 8/19/2020 | WO |