Adsorption Separation-in Situ Synthesis Of MOF/AC Composite And Its Adsorption Performance

In order to solve the problem of difficult treatment of heavy metals,we separate the adsorbents that have adsorbed heavy metal ions as the metal source for the preparation of metal organic frameworks(MOFs),organically combine the wastewater treatment of heavy metals with the synthesis of MOF to synthesize metal organic frameworks,and then use them for the removal of heavy metals and dyes in wastewater,so as to make the best use of the materials.It was of great practical significance for the removal of heavy metals and dyes in wastewater to recycle the waste.In this paper,based on activated carbon(AC),the adsorption capacity of AC for Cr3+was discussed under different influencing factors,and then the AC adsorbing Cr3+was separated as the chromium source for the preparation of MIL-101(Cr).Finally,MIL-101(Cr)/AC material was prepared.The MIL-101(Cr)/AC material was analyzed by XRD,FT-IR,SEM,bet and other characterization techniques,and was used to adsorb pollutants in simulated wastewater.The main results were as follows:(1)The experiment of adsorption and separation of Cr3+by AC shows that the AC adsorbing Cr3+ can be separated.When the content of AC was different,the adsorption capacity of AC for Cr3+was different;under different pH values and the presence of Ni2+or Co2+,the adsorption capacity of AC for Cr3+was also affected;when the dosage of AC was 0.5 g,pH=3,the adsorption capacity for 24 h was 72.73 mg/g.(2)MIL-101(Cr)/AC was successfully synthesized in situ by using the separated AC adsorbed Cr3+as the chromium source of MIL-101(Cr).XRD results show that MIL-101(Cr))and MIL-101(Cr)/AC were synthesized successfully,and they have complete crystal framework structure.The position of characteristic peak of MIL-101(Cr)/AC composite was basically consistent with that of MIL-101(Cr),but the intensity of characteristic diffraction peak was relatively low.FT-IR analysis showed that there was a characteristic peak of MIL-101(Cr)in the characteristic peak of MIL-101(Cr)/AC composite,and its position was almost the same.SEM characterization results show that MIL-101(Cr)has octahedral morphology and keeps its crystal structure.The particle size is consistent and has a certain regularity and integrity.The morphology and structure of MIL-101(Cr)in MIL-101(Cr)/AC composites change,but keep a certain regularity.The BET characterization results show that the specific surface area of MIL-101(Cr)/AC composites decreases,and the pore volume and pore size also decrease.Zeta potential analysis shows that there was a positive charge on the surface of MIL-101(Cr)/AC.(3)The results of adsorption experiment of MIL-101(Cr)/AC composite for Cr(VI)in simulated wastewater show that:MIL-101(Cr)/AC material shows good adsorption characteristics for Cr(Ⅵ).When the dosage of MIL-101(Cr)/AC was 0.2 g/L,pH was 7,and the adsorption capacity was 47.00 mg/g.From the beginning of adsorption,the adsorption capacity of MIL-101(Cr)/AC adsorbent for Cr(Ⅵ)increased continuously,and reached the adsorption saturation after 180 min.The adsorption of Cr(Ⅵ)on the adsorbent followed the Langmuir adsorption isotherm equation,belonging to the second-order adsorption kinetic model.The adsorption process of Cr(Ⅵ)was spontaneous exothermic.It can be recycled for at least 4 times.(4)The results showed that MIL-101(Cr)/AC showed excellent adsorption characteristics for methyl orange and methylene blue in simulated wastewater.When the dosage of MIL-101(Cr)/AC was 0.2 g/L,pH was 7,and the adsorption capacity was 120.30 mg/g.MIL-101(Cr)/AC showed good adsorption performance for methylene blue When the dosage of MIL-101(Cr)/AC was 0.2 g/L,pH was 7,and the adsorption capacity was 61.34 mg/g.The surface of MIL-101(Cr)/AC material has a certain positive charge,which indicates that it was more conducive to absorb pollutants with negative charge.From the beginning of adsorption,the adsorption capacity of MIL-101(Cr)/AC material for methyl orange and methylene blue increased continuously,and reached the adsorption saturation at 300 min.The adsorption process of MIL-101(Cr)/AC material for methyl orange and methylene blue followed the Langmuir adsorption isotherm equation,which belonged to the second-order adsorption kinetic model and was spontaneous endothermic reaction.