Synthesis Of Zr-MOFs Composite Membrane Loaded On Polyurethane Foam For Removal Of Organic Dyes In Wastewater

Because of its potential carcinogenic,teratogenic,mutagenic hazards and enormous biological toxicity,dye wastewater poses a serious threat to the environment and human health.It is particularly important to treat dye wastewater by appropriate methods.Treating dye wastewater by membrane filtration technology has received much attention from researchers all over the world,however,current studies mainly focused on the removal of singly charged dyes but actual wastewater usually contains dyes with different charges.In this study,the removal of neutral,cationic and anionic dyes in binary or ternary systems was conducted by using zirconium-based metal organic frameworks loaded on pretreated polyurethane foam membrane（Zr-MOFs-PUF membrane and PUF/PDA/UNG membrane）with in-situ hydrothermal synthesis approach or soaking method.Neutrally charged Rhodamine B（RB）,positively charged Methylene blue（MB）,and negatively charged Congo red（CR）were chosen as model pollutants for investigating filtration performance of the membrane.The results of filtration experiments showed that the Zr-MOFs-PUF membrane could simultaneously remove RB,MB,and CR not only from their binary system including RB/MB,RB/CR,and MB/CR mixtures,but also from RB/MB/CR ternary system.The removal of dyes by Zr-MOFs-PUF membrane was mainly attributed to the electrostatic interactions,hydrogen bond interaction,and Lewis acid-base interactions between the membrane and dye molecules.The maximum removal efficiencies by Zr-MOFs-PUF membrane were 98.80%for RB at pH≈7,97.57%for MB at pH≈9,and 87.39%for CR at pH≈3.Additionally,the removal efficiencies of RB,MB and CR by Zr-MOFs-PUF membrane were 93.08%,79.52%,and 97.82%,respectively,when the NaCl concentration reached 0.5 mol/L in single dye solutions.In the filtration experiments of PUF/PDA/UNG membrane,the pH of solution has a greater effect on the removal efficiency of MB and CR than on the removal of RB.When the dye solution was co-existed with salt ions,the removal efficiency of MB by PUF/PDA/UNG membrane was affected to varying degrees with the valence state of salt ion.When NaCl,KCl,CaCl₂ and Na₂SO₄ coexisted in dye solution,the removal efficiency of MB by PUF/PDA/UNG membrane were 96.62%,98.17%,86.39%and99.34%,respectively.The higher valence of cations in salt ions would have the stronger competitive adsorption with MB,which resulted in the weaker electrostatic interaction between dye molecules and the membrane surface,thus reducing the removal efficiency of MB.The introduction of organic humic acid has a slight inhibitory effect on the removal of MB by PUF/PDA/UNG membrane（71.93%）.The main reason might be the formation of hydrogen bonds between the carboxyl group of humic acid and MB,which formed a barrier between MB and the PUF/PDA/UNG membrane and reduced the contact between MB and the membrane surface,thus reducing the removal efficiency of MB.The experimental results for mixed dyes filtration were shown that PUF/PDA/UNG membrane could effectively remove MB,RB and CR in MB/RB,RB/CR and MB/RB/CR mixed dye systems through secondary filtration.And PUF/PDA/UNG membrane could remove MB and CR simultaneously through one-time filtration in MB/CR binary system.The removal mechanism was mainly attributed to the aggregation of mixed dyes,the electrostatic interaction between dye molecules and membrane surface,and hydrogen bonding s.All the results suggested that the as-prepared Zr-MOFs-PUF membrane and PUF/PDA/UNG membrane have great potential in practical treatment of dye wastewater.