| In recent years,the forward osmosis membrane separation technology has received extensive attention due to its advantages of low energy consumption,low pollution and high water recovery rate.However,the problem of internal concentration polarization?ICP?in the use of traditional forward osmosis membranes with a supporting layer structure limits the popularization and application of this technology.Therefore,a new type of membrane material is used to prepare a self-standing forward osmosis membrane to alleviate the internal concentration polarization phenomenon,which is crucial to improve the performance of the forward osmosis membrane.In this paper,polyoxadiazole?POD?with excellent mechanical and thermal stability was used as the membrane matrix material,and MOFs with a porous structure and good hydrophilicity?NH2-MIL-125?were used as the membrane modification materials.The POD forward osmosis membrane was modified by physical blending and chemical bonding to prepare a self-standing forward osmosis membrane with excellent performance.The specific research content was as follows:?1?NH2-MIL-125 was introduced into the POD-COOH forward osmosis membrane by physical blending.A series of self-standing NH2-MIL-125/POD-COOH composite forward osmosis membranes with different contents of NH2-MIL-125 were prepared by solution casting.The water contact angle?CA?,zeta potential,and mechanical performance test results showed that the hydrophilic properties and electronegativity of the surface of composite positive osmosis membranes were improved,and the mechanical properties were reduced slightly and kept within a controllable range.The results of the forward osmosis experiment showed that when the content of NH2-MIL-125 was 3%,the composite osmosis membrane had the best permeability and selection permeability.Its water flux?Jw?,reverse salt flux?Js?,and selective permeability?Jw/Js?were 27.4 L/m2·h,74.0 mmol/m2·h and 370.3 L/mol,respectively.?2?NH2-MIL-125 was grafted firmly on the side chain of the POD-COOH polymer matrix by chemical bonding to synthesize NH2-MIL-125/POD-COOH hybrid material to prepare a new type of self-standing NH2-MIL-125/POD-COOH hybrid forward osmosis membrane.The strong chemical bond between the filler and the polymer matrix allowed the functional filler to maintain a uniform distribution on the nanometer scale in the hybrid forward osmosis membrane,which was beneficial to its efficient water penetration and salt retention function.The test results showed that NH2-MIL-125 was introduced successfully and dispersed evenly in the hybrid forward osmosis membrane.As the content of NH2-MIL-125 increased,the hydrophilicity and electronegativity of the surface of the hybrid positive osmosis membranes were improved significantly,and the mechanical properties were maintained at a high level.The results of forward osmosis experiment showed that as the content of NH2-MIL-125 increased,the water flux?Jw?of the hybrid forward osmosis membrane increased,while the reverse salt flux?Js?decreased,which improved greatly the forward osmosis membrane penetration performance.And when the amount of NH2-MIL-125 was 10%,the permeability of the membrane was the best.Its water flux?Jw?,reverse salt flux?Js?and selective permeability?Jw/Js?were 34.2 L/m2·h,28.3 mmol/m2·h and 1208.4 L/mol,respectively.Furthermore,performance parameters such as water permeability coefficient?A?,salt permeability coefficient?B?,and salt rejection rate?R?of the 10%NH2-MIL-125/POD-COOH hybrid forward osmosis membrane were evaluated by reverse osmosis experiment.The structural parameter?S?of the membrane was calculated finally.The study found that when the thickness of 10%NH2-MIL-125/POD-COOH hybrid forward osmosis membrane was 5 ?m,it had an extremely low structural parameter?S?value of 2.3 ?m.It showed that the hybrid forward osmosis membrane with self-standing homogeneous structure overcomed the concentration polarization phenomenon in the process of forward osmosis. |
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