Magnetic Metal-Organic Framework(MOF) And MOF-Based Magnetic Derivatives For The Removal Of Organic Pollutants

Anthropogenic activities such as industrialization,farming,advances in drug discovery,etc.have resulted in significant destabilization of the ecosystem due to the release of toxic substances into the environment.Although some of these pollutants including dyes,pharmaceutical residues,and herbicides are inadvertently introduced into the environment,their consequential effects on human health and other organisms cannot be overemphasized.The elimination of organic pollutants from the environment has therefore received significant attention in recent times.The present work focuses on the removal of organic pollutants from aqueous media.The catalytic reduction of various organic pollutants was extensively explored.The possibility of harnessing the magnetic property of the synthesized MOF composites and MOF-based composites to enhance the kinetics of pollutant reduction was investigated.Findings from this research will open new frontiers for enhanced elimination of organic pollutants from the environment and also offer a new route for the prospective adaptation of magnetic nanocomposites as stirrers for small-scale reaction systems where conventional stir bars are not applicable due to size limitations.The removal of the organic pollutants 4-nitrophenol(4-NP),methylene blue(MB),and rhodamine B(Rh B)was explored using a magnetic-rod metal-organic framework metal composite for the catalytic reduction of the pollutants.Magnetic Fe3O4 nanorods were synthesized via a hydrothermal method and used as templates for the in-situ depositing of MIL-100(Fe)and gold nanoparticles.The obtained triad composite,Fe3O4@MIL-100(Fe)-Au does not only possess the properties that enable it to function as a catalyst but also has the propensity to enhance the kinetics of catalysis on a magnetic field and conveniently separate the catalyst from the reaction with an external magnet.As a proof-of-concept,both magnetic field-assisted and non-magnetic fieldassisted catalytic reduction of 4-NP,MB,and Rh B was extensively explored using the assynthesized Fe3O4@MIL-100(Fe)-Au catalyst.The results show that the rates of the catalysis of the organic pollutants on the magnetic field-assisted system were tremendously expedited.Despite the fascinating properties and the potential applications of MOFs and MOF-based composites in various fields,their relative lack of stability and difficulty in separation after use remains a major drawback to their applications.To circumvent this challenge,ZIF-8@ZIF-67 coreshell,a typical ZIF-on-ZIF MOF was synthesized via a seed-mediated strategy using ZIF-8 seeds to grow ZIF-67 shells to obtain the core-shell structure.Upon carbonization at 600 ℃ in N2 environment,a stable magnetic derivative,Zn/Co@CN was obtained from the ZIF-8@ZIF-67 intermediate.Informed by the excellent properties exhibited by the material after characterization by X-ray diffraction(XRD),transmission electron microscopy(TEM),nitrogen adsorptiondesorption isotherm analysis(BET),vibrating sample magnetometer(VSM)analysis,thermogravimetric analysis(TGA),high-angular annular dark-field scanning transmission electron microscopy(HAADF-STEM),energy-dispersive X-ray spectroscopy(EDX)elemental mapping among others,which confirm the formation of the magnetic derivative,the removal of ciprofloxacin was explored.Since natural attenuation mechanisms and conventional treatment methodologies have not sufficed for the abatement of such pharmaceutical pollutants,their presence in the environment can lead to dire repercussions on public health delivery.The prepared composite proved effective for the catalytic reduction of ciprofloxacin.The kinetics of magnetic field-assisted catalytic reduction of ciprofloxacin using the Zn/Co@CN was significantly higher than the non-magnetic field-assisted catalytic reduction.The versatility of the composite for the elimination of antibiotic pollutants was further explored by applying the composite as an adsorbent for the elimination of ciprofloxacin.Similarly,magnetic field-assisted adsorption resulted in enhanced elimination of the pollutant as compared to the non-magnetic field-assisted adsorption.Population growth and the quest for food sufficiency have resulted in the use of herbicides in agricultural activities to control weeds.Although pendimethalin is approved for use in many jurisdictions including the European Union for agricultural purposes,its persistence in the environment exerts toxic effects on aquatic organisms and ultimately affects the food chain.For the remediation of pendimethalin pollution,a simple but cost-effective non-noble metal catalytic reduction approach was used.MXene@ZIF-67 derived magnetic composite,Ti3C2@Co CN was obtained after the carbonization of MXene@ZIF-67 composite at 600 ℃ in N2 environment.Characterization by TEM,HAADF-STEM,EDX elemental mapping,XRD,and VSM analysis confirm the formation of magnetic Ti3C2@Co CN.The synergistic effect between the components of the composite was utilized for the catalytic reduction of the herbicide using Na BH4 as reductant.Detailed comparative analysis of both magnetic field-assisted catalytic reduction and nonmagnetic field-assisted reduction of pendimethalin reveals a four-fold increase in the efficiency of the former.Not only was the magnetic property of the resultant composite utilized to enhance the catalysis but also to conveniently separate the catalyst from the solution using an external magnet.Furthermore,the catalyst is relatively stable and can be used for four successive runs.This research work has highlighted the importance of the synergistic effect between the individual components of magnetic MOFs and magnetic derivatives of MOF-based composites.The magnetic property of such materials can be effectively used to enhance the kinetics of the catalytic reduction of organic pollutants.In addition,the magnetic property can be exploited to conveniently separate catalyst from solution after application thereby avoiding laborious filtration and the energy-intensive centrifugation processes of separation.