| Nowadays,water pollution become more and more serious.Dyestuff pollution is one of the most serious water pollution problems in the world.Congo red,one of the benzidine-based anionic disazo dyes,is easy to run off and enter the natural water during the fabrication and application,resulting in large damages to environment.Traditional methods for dye removal from wastewater,such as physical,chemical and biochemical technologies,generally have some disadvantages,such as high cost,the secondary pollution,limiting their application.Adsorption is a widely used technique because of its low cost,high efficiency,environmentally friendliness,simplicity of operation and regeneration.Hence,it is urgent to develop a simple and efficient adsorbent for researchers.Zeolite imidazole frameworks-8?ZIF-8?is one of the most widely used metal organic frameworks?MOFs?.It not only contains the advantages of MOFs,such as high specific surface area,large pore volume,adjustable hole size,but also overcome the shortcomings of general MOFs,such as poor thermal stability and chemical stability,complex synthesis process,low production rate and high production cost.Providing so many advantages,ZIF-8 has attracted widespread attention in adsorption field.Electrostatic spinning is a kind of preparation method for nanometer fiber.The simple operation,low cost,large production and easy recycle make electrostatic spinning technology more and more wildly used.But now,it is rare reported for the use of electrostatic spinning technology to prepare nanofiber membrane as an adsorbent applied in dye wastewater treatment.In this study,ZIF-8 was synthesized and characterized by BET,XRD,FTIR,SEM and XPS.The results indicated that the sample structure was in accordance with those reported in literatures else.The prepared ZIF-8 was then used for the adsorption removal of CR.From adsorption experiment,it was found that the Langmuir model and the pseudo-second-order model were better fitted to the adsorption of CR solution process,the maximum equilibrium adsorption capacity up to 775 mg·g-1.The outstanding adsorption characteristics towards CR were achieved at neutral pH value?6.0-8.0?.Increasing the ionic strength(Na+ or Ca2+)could slightly improve the adsorption capacity of CR.Thermodynamic analysis results showed that the sorption process was spontaneous and exothermic.The possible mechanisms of CR adsorption onto ZIF-8 was attributed to electrostatic attraction,pore-filling effect,?–? interaction and hydrogen bonding interaction.Furthermore,to solve the running off problem of ZIF-8 powders,electrostatic spinning technique was used to produce ZIF-8/PVA fiber membrane adsorbent.The ratio of ZIF-8 and PVA and the electrostatic spinning parameters were studied to explore their influence for the synthetic membrane morphology.The preparation condition was optimized to get the best spinnability.When the concentration of ZIF-8 was 10%?wt%?,the surface was smooth and the diameter was uniform of the nanofiber membrane.Characterize techniques,such as FTIR,EDS and TEM were used to analyze the structure of ZIF-8/PVA composite fibers.In the performance tests,ZIF-8/PVA composite fibers revealed superior mechanical capacity.After being immerged in water for 12 h,only 7.94% weight of the fibers was lost,showing a good water stability.In the adsorption experiment of CR,the qe of ZIF-8/PVA was 160 mg·g-1 when the initial CR was 40 ppm.After recycle for 3times,95% of the fibers was maintained,higher than that of ZIF-8.Therfore,ZIF-8/PVA not only maintained the efficient adsorption characteristics of ZIF-8,but also showed good mechanical properties,water stability and regeneration performance at the same time.These results showed that ZIF-8/PVA membrane had good application prospect in the field of wastewater treatment. |
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