| Membrane distillation process has attracted more and more attention in recent years because of its unique advantages in high brine desalination and wastewater recovery.Membrane distillation(MD)is a highly efficient and low energy consumption membrane separation process driven by temperature and vapor pressure gradients on a microporous hydrophobic membrane,usually allowing only steam to enter the cold side.However,in the treatment of wastewater containing hydrophobic(such as oily)and amphiphilic(such as surfactant)pollutants,the problems of wetting and fouling of traditional hydrophobic membrane seriously hinder the wide application of membrane distillation process.Therefore,it is very important to develop new anti-fouling and anti-wetting membrane for membrane distillation.In this paper to solve the problem of membrane fouling and wetting membrane distillation as a starting point,choose to use palygorskite material itself the characteristics of the physical characteristics and easy to be modified fluoride,get omniphobic functional palygorskite,combined with spraying technology,biological inspired further prepared wetting resistance,resistance to pollution at the same time new Janus membrane has good stability.Specific research contents are as follows:Due to the asymmetric properties of Janus membrane on both sides of the membrane or at the membrane interface,it can be combined with the different characteristics of both sides at the same time with anti-fouling and wettability.The research focus is to find low-cost and easy to omniphobic modified materials to prepare the omniphobic layer.The low cost palygorskite(PAL)can be used to prepare the membrane total phobic layer of membrane distillation because of its natural rod shape,large specific surface area,excellent pore volume and abundant free nano channels.First,palygorskite was modified with dopamine to construct spherical bulges on the rod-like structure,thus forming two layers of micro-nano structure.Then,the material was modified by fluorination to make the fluoroalkyl silane coating adhere to the surface of palygorskite,and omniphobic palygorskite material was prepared.The modified material was characterized by transmission electron microscopy(TEM),and a new spherical bulge was found on the surface.X-ray photoelectron spectroscopy(XPS)and energy dispersive X-ray spectroscopy(EDX)were used to analyze the surface of modified nanomaterials containing F and Si elements.Fourier transform infrared spectroscopy(ATR-FTIR)indicated that the surface of palygorskite contained characteristic peaks of Si-O,C-F and N-H groups,which proved that palygorskite nanomaterials were successfully modified.The novel Janus membrane was prepared by deposition of dopamine(DA)on the surface of PTFE/PET commercial membrane,and coating of functional attapulgite on one side to construct an omniphobic layer.Janus film has excellent asymmetrical wettability.By analyzing the wettability of the surface of the film through contact angle(CA),it can be found that the upper layer is omniphobic,and the water contact angle is 163.9°.The bottom layer is hydrophilic in air and superhydrophobic under water,and the contact angle of underwater mineral oil is 157.2°.In the direct contact membrane distillation(DCMD)process,the Janus membrane can treat different types of surfactant stabilized mineral oil-water emulsion,including sodium dodecyl sulfate(SDS)stabilized mineral oil-water emulsion,Tween 80 stabilized mineral oil-water emulsion.In the test,the Janus membrane showed high salt rejection performance(salt removal rate is approximately 100%)and excellent stability(stable operation for more than 50 hours),which proved that the membrane has good wetting and fouling resistance.The results showed that a simple,rapid and effective method for membrane preparation was proposed to solve the problems of membrane wetting and fouling in membrane distillation.In the research and development of membrane distillation membrane,a multilayer reentrant layer was prepared for the first time using fluorinated palygorskite.The new Janus membrane with significant asymmetric wettability has good stability,moisture resistance and pollution resistance in the direct contact membrane distillation experiment,even if the water-in-oil emulsions stabilized by different surfactants are used as the feed solution.It provides a feasible membrane solution for the treatment of oily and high-salt wastewater. |
