Structure Optimization Of PDA Hydrophilic Modified Microfiltration Membrane And Its Application In Oil And Water Separation

With the further advancement of the industrialization process,environmental regulatory requirements and pollutant discharge standards have become increasingly stringent,and the demand for oil-water separation and wastewater treatment is also increasing.Traditional mechanical separation and thermal separation equipments are gradually replaced by new separation methods because of their high separation cost and low separation efficiency.The membrane separation method can cover almost all scales of wastewater treatment,and the membrane separation operation process is low in cost and does not produce secondary pollution,and is an ideal separation method for oil-water separation and sewage treatment.Polydopamine?PDA?surface coating hydrophilic modification technology can finish the surface modification of almost all materials and attracts extensive studies,and the PDA modification process has a simple operation process,mild conditions and green pollution-free characteristics in the process of modification.However,at present,the PDA modification technology still has three main defects.?1?The hydrophilicity of a single PDA modification process is not good enough,and the water contact angle is maintained at about 50-60°;?2?The PDA coating is strong.The acid-base solution and the strong polar solvent are not stable and cause secondary pollution to the filtrate.?3?The agglomeration of PDA molecules is serious during the polymerization of dopamine,resulting in certain membrane fouling.This article begins with three chapters from the three major issues of PDA modification technology,analyzes the underlying causes of the problems,and resolves them individually from the PDA polymerization mechanism level,and successfully prepares the underwater super oleophobic/Ultra-hydrophilic PDA modified membranes are used in oil-water separation tests.In the second chapter,L-dopamin was used instead of dopamine to oxidize the terminal amino group of L-dopamine to the carboxyl group under the condition of acidic oxidant catalyst to give more hydrophilicity to polydopamine dopamine?PDOPA?coating and improve the efficiency of single PDOPA modification.A PDOPA-modified polyvinylidene fluoride?PVDF?membrane was prepared by optimizing the conditions under the condition of pH=2 for 6 hours.The membrane exhibited ultra-hydrophilicity and underwater superoleophobicity.The pure water contact angle was obtained.At 28.5±1.2°,the contact angle of underwater oil is 167.6±3.4°.In addition,the oil-water separation of PDOPA-PVDF membrane can reach over 99.9%,and it has good anti-protein adsorption performance.In the third chapter,the introduction of paraformaldehyde?PFA?into a PDA coating to create a stable three-dimensional network structure essentially improves the stability of the PDA coating.Most of the non-polymerized and polymerized parts of the PDA coating are phenols and they will react with paraformaldehyde?PFA?.The non-covalent bonds of dopamine and its oligomers in the PDA coating are chemically bonded.The main structure forms a three-dimensional structure in space to form a whole.The results showed that the cured PDA coating of PFA exhibited good acid stability and solvent stability.It was stable in6M HCl and soaked in DMSO and NMP for 2 months.PDA loss rate was less than 5%.In the fourth chapter of this thesis,Fe³⁺is introduced into the PDA polymerization process.The complexation between metal ions and dopamine breaks the original non-covalent bond,and the oxidation of Fe³⁺is used to catalyze PDA polymerization.The PDA polymerization is essentially changed.Avoid the occurrence of agglomeration during PDA polymerization,and Fe³⁺-catalyzed dopamine polymerization can effectively increase its polymerization rate and PDA deposition rate.In addition,the addition of Fe³⁺enhances the ability of PDA molecules to adhere,resulting in a significant increase in the coating rate of PDA(Fe³⁺).This not only improves the performance of the PDA coating,but also greatly improves the coating efficiency of the PDA coating,reaching at 62 nm h^-1.And the entire reaction and coating process time is greatly shortened,and does not involve strict operation,laying the foundation for the large-scale PDA coating technology.