Acetic Acid Adsorption And Acidic Stability Of Metal-Organic Framework Materials

Metal-organic framework materials(MOFs)with high surface and porous structure have attracted much attention in recent years,which find their applications in catalysis,membrane,sensor and adsorption.On the other hand,volumes of industrial wastewater containing dilute acetic acid are increasing with the development of industry.But,high chemical oxygen demands and strong acidity of dilute acetic acid wastewater make it impossible to discharge directly or process by commonly biochemical method.How to effectively purify the wastewater of dilute acetic acid is urged to be solved.Seven water-stable MOFs including MIL-101(Cr),MIL-100(Cr),MIL-53(Cr),MIL-96(Al),MIL-100(Fe),UiO-66 and ZIF-8 were synthesized and studied on adsorption capacities of acetic acid from water.UiO-66 exhibited the best potential as acetic acid adsorbent than other six materials.So the effects of different contact time,initial acetic acid concentrations and temperature on the adsorption of acetic acid by UiO-66 were studied.The results show that the adsorption would reach equilibrium after eight hours.The adsorption capacities are higher in high initial acetic acid concentrations and at low temperatures.Different kinetic models and adsorption isotherm models were tried to fit the adsorption data of acetic acid on UiO-66,among which pseudo-second-order kinetic model and Freundlich isotherm work well.The calculated thermodynamic parameters including ?G,?H and ?S were all negative,indicating the exothermic spontaneity and decrease of disorder.At last,the regeneration of UiO-66 was conducted by washing with deionized water and ethanol.After three cycles,the adsorption amount of acetic acid on UiO-66 did not decrease remarkably.All of these results demonstrated potential of UiO-66 as an excellent adsorbent for acetic acid removal from water.Furthermore,the stabilities of MIL-101(Cr),UiO-66 and ZIF-8 were studied after immersion at different acetic acid concentrations and temperatures for a period of time.The results show that MIL-101(Cr)is stable at acetic acid solutions.Even soaked in 3% acetic acid at 100?,no obvious changes could be observed on MIL-101(Cr)after 120 hours.UiO-66 is relatively stable at acetic acid solutions.It will decompose and clog together after long time and high temperature in acid solution.ZIF-8 would hydrolyze at acidic conditions absolutely.As time goes by,hexagonal ZIF-8 will transform from ~80 nm particles into a new plate-like product with about 5 ?m larger particle.In a word,MIL-101(Cr)is a highly acid-resistant material,UiO-66 is able to keep structure for a period of time at acidic condition,ZIF-8 is unstable when exposed to acid environment.