A Study On Super Hydrophilic PVDF Microfiltration Membrane And Its Oil-water Separation Property Based On Tannic Acid Interface Modification

Oily wastewater has certain characteristics of toxicity,bioaccumulation and hindering plant growth,which seriously endangers human health and ecological security.Based on the ultra-wetting microfiltration membrane separation technology developed by the microfiltration membrane,it synchronizes high flux with high efficiency,which is an environmentally friendly separation method and has a good application prospect in the treatment of oily wastewater.The super hydrophilic microfiltration membrane surface can enhance the oil-water separation performance of the microfiltration membrane.Therefore,this paper discusses the separation properties of oil-water mixtures based on the preparation technology of super hydrophilic microfiltration membranes based on the tannic acid surface under the biomimetic principle of mussels.The main research contents are as follows:（1）Using potassium permanganate as oxidant,tannic acid adhered on the surface of the commercial PVDF microfiltration membrane was oxidized to prepare the PVDF@C-TA membrane.With the aid of infrared spectroscopy（ATR-FTIR）and scanning electron microscopy（SEM）,the hydrophilic contact angle and pure water flux were used to optimize the adhesion of TA and the oxidation conditions of potassium permanganate.The separation performance of the PVDF@C-TA membrane on the emulsified oil-water mixture was evaluated.The results showed that with the increase of TA solution concentration,the adhesion time increased,the surface contact angle of the PVDF@TA membrane decreased,the pure water flux increased first and then decreased,and the TA concentration was 10 mg/m L,and the pure water flux of the PVDF@TA membrane was the highest when the adhesion time was 15 min.When the concentration of potassium permanganate was 4 mg/m L,the oxidation time is 5 min,the PVDF@C-TA membrane performance was optimal.The oil-water separation experiments show that the PVDF@C-TA membrane has a good oil-water separation efficiency（greater than 90%）,and good recycling and chemical stability.（2）The STA-K-PVDF and STA-T-PVDF membranes were prepared by using the unique adhesion of phenolic hydroxyl groups rich in tannic acid（TA）.We used the silane coupling agent KH560 and ethyl orthosilicate TEOS as the composite modifiers in weak alkaline solutions and co-deposited with TA through ring-opening reaction and hydrogen bonding on the surface of commercial PVDF microfiltration membranes.The deposition conditions such as the concentration of KH560 and TEOS,deposition time and so on were investigated to influence the surface properties of STA-K-PVDF and STA-T-PVDF membranes.The results showed that when the concentration of fixed TA was 2 mg/m L,the hydrophilicity and pure water flux of STA-K-PVDF and STA-T-PVDF membranes increased first and then decreased with the increase of the amount of KH560 and the reaction time.The reaction time was 6 h,STA-K-PVDF and the WCA of the STA-T-PVDF membrane reached 10°to 15°at the concentration of 9 and 12 mg/m L,respectively.The oil-water separation experiments show that both STA-K-PVDF and STA-T-PVDF membranes have good oil-water separation performance.（3）The super hydrophilic PVDF@C-TA@CaCO₃ membrane was obtained CaCO₃,in situ mineralization on the surface of the PVDF@C-TA membrane by alternating impregnation（ASP）using calcium chloride and sodium carbonate as the mineralizing solution.SEM CaCO₃ particles with uniform surface distribution were observed in the figure.Based on the static water contact angle and underwater oil contact angle,it is confirmed that the PVDF@C-TA@CaCO₃ membrane has super hydrophobicity and underwater superoleophobicity.Oil-water separation results show that the PVDF@C-TA@CaCO₃ membrane can separate the emulsified oil-water mixture.