Removal Of Aqueous Pharmaceuticals By Metal-organic Frameworks: Performance And Mechanism

Pharmaceuticalis a diverse group that belongs to thepharmaceuticals and personal care products(PPCPs).Although most pharmaceuticals are not classified as persistent organic pollutions(POPs)due to significantly shorter half-life.Pharmaceuticals are continuously emitted into the environmental medium at very high amount.Because most pharmaceuticals were designed to affect biological response even at extremely low lose,therefore their environmental and health risks cannot be underestimated.Since conventional methods cannot effectively remove aqueous pharmaceuticals at affordable cost,it is necessary to develop novel materials that can be used to remove aqueous pharmaceuticals.Within our research we have used hydrothermal methods to synthesize a series of metalorganic frameworks(MOFs),and investigated their performance towards aqueous pharmaceuticals adsorption and degradation.Because MOFs were primarily investigated for applications in gas capture and separation,very limited report on their aqueous stability and environmental safety is available.Toward this end,we have synthesized isorecticular MOFs MIL-53(M)(M=Cr,Al,and Fe).We found MIL-53(M)’s structural integrity is retained in the aqueous solution even after prolonged exposure to Xeon lamp irradiation.In addition,we have investigated MIL-53(M)’s environmental safety on both molecular and cellular level.We have found that MIL-53(M)is capable of transforming aqueous pharmaceuticals,and transformation products were hydroxyl adducts.In addition,cytotoxicity of MIL-53(M)on Hep G2 cell line was much lower than conventional materials such as powdered activated carbon and multi-wall carbon nanotubes.We found MIL-53(M)’s cytotoxicity does not increase significantly on elevated concentrations.Therefore due to high aqueous stability and low cytotoxicity,MIL-53(M)can be safety used as environmental functional materials.Comparing to other materials,MOFs can be used at even higher concentration without producing significant biological damage.We can applied different synthetic conditions to the same starting materials to afford MOFs with different topology,MIL-101 and MIL-53.By comparing the pharmaceuticals adsorption ability of these two class of MOFs,we found rigid MOF MIL-101 can efficiently remove pharmaceuticals.Both adsorption capacity and kinetics are superior to those of conventional materials.In addition,MIL-101 adsorbent can be easily regenerated by washing with methanol.We found flexible MOFs MIL-53(M)have excellent selectivity for aqueous pharmaceuticals.By structural determination through XRD,we found pharmaceuticals selectivity in MIL-53(M)is determined by metal nodes present in the structure.We found by tuning metal composition,it is possible to adjust pharmaceuticals selectivity in MIL-53(M),which is of high interest towards developing materials for selective removal of prioritized pharmaceuticals.In order to achieve the ease of regeneration for MOFs adsorbents,we have applied MOFs in photocatalytic degradation and photo-assisted Fenton reaction to degrade aqueous pharmaceuticals.We found MOFs is capable of simultaneously adsorb and degrade aqueous pharmaceuticals.The two-step degradation pathway was probed by radical scanvengers.We found MIL-53(Fe)participates in type II photosensitization while MIL-53(Cr)is dominated by type I photosensitization,the photoreactivity of MIL-53(Al)however is negligible.In addition,the dismutation reaction across MIL-53(Fe)facilitates the production of hydroxyl radicals.In addition,we have used MOFs as precursor for the synthesis of hierarchically porous carbon(HPC).When MOFs HPC was applied as cathodes in E-peroxone process,highly concentratedcarbamazepine in aqueous solutioncan be completely degraded within 10 minutes.