Multi-nitrogen Organic Molecule TPPE Modulates The Visible Photocatalytic Performance Of Iron-based MOF For The Removal Of Pollutants From Water

The accelerated development of industrialization has led to serious pollution of water resources,which poses a threat to humans and other living organisms.Therefore,it is urgent to find efficient and green methods to remove water pollutants.Iron-based organic framework materials are widely used for the adsorption and photocatalytic degradation of water pollutants due to their unsaturated metal sites and good response to visible light.However,the low separation rate of electron-hole pairs in iron-based organic frameworks often limits their more efficient applications.Based on the above,finding suitable methods to regulate the adsorption and visible light catalytic performance of iron-based organic framework materials for the removal of residual pollutants in water is of great significance.In this study,TPPE(1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethane),a conjugated organic molecule with pyridine nitrogen,was used to regulate the adsorption and catalytic properties of iron-based MOF.From the perspective of post-synthesis modification,a novel nitrogen containing core shell MIL-101(Fe)-based nanocomposite material(MIL101(Fe)@TPPE)was prepared by using TPPE as a surface modification agent for MIL-101(Fe)by alcohol-thermal method.Compared to MIL-101(Fe),this hybrid material shows faster and stronger visible light response,lower band gap energy,and higher electron hole separation efficiency.Batch removal studies of the model pollutant(tetracycline hydrochloride(TC))have shown that the optimized nanocomposite material(MT-5)can effectively photocatalytic degrade TC under visible light,and the total removal rate can reach about 95%at pH=6.In addition,MT-5 has a high adsorption capacity for tetracycline hydrochloride(TC)with a maximum adsorption capacity of 576.13 mg·g-1 at pH=8.The mechanism study shows that h+and·O2-play a major role in the photodegradation process.Besides,the degradation intermediates were analyzed by HPLC-MS,and the toxicity of TC and its intermediates were evaluated by QSAR.Recycling experiments have shown that MT-5 has good cycle stability and practicality.The above results indicate that the method of modifying the surface of TPPE organic molecules with MIL-101(Fe)can effectively regulate their visible light catalytic and adsorption abilities.Secondly,to explore the feasibility of internal regulation of organic molecule TPPE to enhance the visible light catalytic performance of iron-based MOF,a novel iron-based MOF(Fe-TPPE)was successfully prepared by solvothermal method using TPPE as an organic ligand and directly coordinating with Fe(Ⅲ).The structure and size of Fe-TPPE were controlled by changing the synthesis temperature and time,and a rectangular crystal was obtained at 150 ℃ for 24 h.Single crystal diffraction analysis and XPS characterization confirmed that Fe-TPPE is a metal organic framework structure formed by coordination of Fe(Ⅲ)with two pyridine nitrogen in two molecules of TPPE.The photoelectric performance characterization results show that Fe-TPPE has stronger and wider visible light absorption ability compared to MIL-101(Fe)@TPPE.By studying the removal performance of model pollutants TC,Rhodamine B(Rh-B),Methylene blue(MB),and Cr(Ⅵ),it was confirmed that Fe-TPPE has a good visible light utilization efficiency.However,the removal rate of TC by Fe-TPPE has decreased by about 35.53%after three cycles of use,indicating the poor stability of the photocatalyst.Therefore,it is necessary to find suitable methods to enhance its stability and recoverability.Finally,in order to enhance the stability of Fe-TPPE and its recyclability in practical applications,a new type of magnetic separation Fe3O4@Fe-TPPE composites was synthesized by combining with the magnetic carrier Fe3O4.The structure and composition of the composite were characterized by XRD,FT-IR.and other analytical methods.Furthermore,the photoelectric performance tests showed that Fe3O4@Fe-TPPE has stronger visible light utilization efficiency than Fe-TPPE.The adsorption and photocatalytic degradation capabilities of Fe3O4@Fe-TPPE,and its versatility as a photocatalyst for water pollutants were evaluated through research on the removal of model pollutants TC,Rh-B,MB,and Cr(Ⅵ).Besides,the results of the removal of simulated wastewater containing multiple pollutants showed that,Fe3O4@Fe-TPPE has higher photocatalytic degradation efficiency of organic pollutants under the coexistence of Cr(Ⅵ).This may be attributed to the rapid reaction of Cr(Ⅵ)with electrons,hindering the recombination of electron hole pairs,improving the charge separation efficiency,and thus improving the photocatalytic degradation rate of organic pollutants.Moreover,Fe3O4@Fe-TPPE shows fast magnetic separation performance and good cycle stability,indicating its great application potential as a water pollutant treatment agent.