Photochemical Activity Modulation And Analytical Application Of 2D Lanthanide Porphyrin Metal Organic Frameworks

Metal-organic frameworks(MOFs),as a new class of porous crystalline materials,possess super high specific surface area,versatile structures and functionalizable porosity and unsaturated coordination metal active sites,as well as flexible and adjustable structure,composition,and functional characteristics,making them different from traditional porous materials.Recent years,MOFs have been widely used in gas storage and separation,energy storage and conversion,biomedical,chemical sensing,and catalysis,etc.Among the various functional organic bridging ligands used in the synthesis of MOFs,porphyrin-based bridging ligands have attracted much attention due to their unique geometry and functions.Porphyrins and metalized porphyrin derivatives widely exist in organisms,such as cytochrome,heme,and chlorophyll,which are essential components of life activities and play an important role in physiological function,as well as have high potential application value in luminescence,bionics,and catalysis.While,porphyrins are usually used in homogeneous systems as functional molecules,but the heterogenization of these functional molecules in the crystal frameworks with long range ordered structure is not only conducive to recycling,but also is helpful to understand its structure-property relationship at the molecular or atomic level.Porphyrin-based MOFs(Por-MOFs)are novel periodic network framework materials constructed by porphyrins or metalloporphyrins as structural units.As a fascinating subclass of MOFs,Por-MOFs not only have the porosity and other excellent properties of MOFs material,but also possesse the good physiological and chemical activities of porphyrin functional ligands.It has a broad application prospect in adsorption,photoelectric converter,medicine,bionics,sensing,catalysis,and other fields.In the past few years,although the number of new Por-MOFs structures is increasing,the structure-activity relationship has not been systematically studied.It is still necessary to further explore the structural design and synthesis methods of Por-MOFs to study the structure-activity relationship.Por-MOFs show excellent light absorption and chemical activity due to the special conjugated aromatic macrocyclic structure of porphyrin units,and have became a kind of catalysts with excellent photocatalytic performance.However,the research and application of the photochemical activity of Por-MOFs are far from being fully developed.The photochemical activity of the existing Por-MOFs is still poor,which needs to be further improved to meet different application requirements.In order to improve the photochemical activity of Por-MOFs to the maximum extent,further exploration and optimization of the photochemical behavior of Por-MOFs are needed.Therefore,a series of 2D lanthanide porphyrin MOFs(2D Ln-TCPP)and their composites were designed and prepared by controllable preparation and functionalization strategy in this thesis,and their photochemical activity were regulated by means of thickness and metal nodes,functional molecular synergy and plasma coupling.And the applications in biochemical analysis were further investigated.The main contents of this thesis include the following three parts:Part 1.Photochemical activity of 2D Ln-TCPP nanosheets regulated by thickness and metal nodes.As well known,structure determines performance.When the external conditions are fixed,the performance of the material depends on the internal structure of the material.This structure is the type and component of atoms that make up the material,as well as their arrangement and spatial distribution.In this part of work,a series of 2D lanthanide porphyrin MOFs with different thickness(namely 2D Ln-TCPP)were synthesized by using a good photosensitive porphyrin molecule(meso-tetra(4-carboxyphenyl)porphyrin,H₂TCPP)and lanthanide metal ions(Ce³⁺,Sm³⁺,Eu³⁺,Tb³⁺,Yb³⁺)with similar electronic structure via microwave-assisted method combining with controlling the concentration of acetic acid.The effects of thickness and metal node on photochemical activity were discussed in detail.The results showed that the nanosheets with thinner thickness demostrated higher BET surface areas,carrier density,light harvesting ability,and e-h separation efficiency,endowing the high photochemical performance.In addition,compared to other Ln³⁺,theoretical calculations and control experiments showed that the effective energy transfer(Dexter energy transfer)between TCPP and Yb³⁺may facilitate the intersystem crossing from ¹TCPP to ³TCPP through spin–orbit coupling.Meanwhile,because of the small energy gap between the ³TCPP and ²F_5/2 of Yb³⁺,thermally activated back energy transfer(BEn T)from ²F_5/2 of Yb³⁺to³TCPP may occur,which could extend the ³TCPP lifetime.Therefore,the efficient intersystem crossing and prolonged triplet state lifetime of TCPP facilitated the generation of singlet oxygen(¹O₂)through ?-type photodynamic mechanism,thus boosting the photocatalytic activity effectively.In addition,because of the ²F_5/2 energy level of Yb³⁺matched well with that of TCPP,the photogenerated electrons can be effectively transferred to Yb³⁺center,which can effectively promote the e-h separation,and thus promoting the formation of superoxide anion(·O₂^-)through I-type photodynamic mechanism.This work not only lighted a new beacon for the controllable synthesis of 2D MOFs,but also offered novel perspectives for photochemical activity tailoring.Part 2.Artificial light-harvesting system with synergistically regulated ?-type photodynamic activity by functional molecule for hydroxynitrobenzene compounds detection.Light-harvesting system is an important way to capture,transmit and utilize light energy.It is still a serious challenge for researchers to develop an efficient artificial light-harvesting system.In the previous work,we successfully screened out 2D Yb-TCPP nanosheets with good photochemical activity.To further improve the photochemical activity of 2D Yb-TCPP nanosheets,in this part of work,we have successfully constructed 2D MB/Yb-TCPP-SO₄ artificial light-harvesting system by modifying the photosensitizer methylene blue(MB)onto the surface of 2D Yb-TCPP nanosheets by electrostatic self-assembly strategy.On the one hand,the loaded MB on the surface of 2D Yb-TCPP nanosheets broadened the absorption range of the solar spectrum,making it have 100%spectral efficiency in the visible region;on the other hand,because the emission spectrum of 2D Yb-TCPP nanosheets overlaped well with the absorption spectrum of MB,and the closely distance between MB and exposed porphyrin pigment molecules on the outer surface,making 2D Yb-TCPP nanosheets and MB have an effective fluorescence resonance energy transfer(FRET).The energy transfer efficiency was as high as 78.6%,which effectively improves the energy utilization rate.Experimental results showed that the synergistic effect between MB and 2D Yb-TCPP nanosheets promoted ?-type photodynamic activity,promoting the formation of ¹O₂.The¹O₂ quantum yield of 2D MB/Yb-TCPP-SO₄ was higher than that of MB,Yb-TCPP and MB+Yb-TCPP.The as-prepared 2D MB/Yb-TCPP-SO₄ artificial light-harvesting system could catalyze the fluorescence reaction of thiochrome.Based on the fluorescence quenching effect of hydroxynitrobenzene compounds on the reaction system,an analytical method for hydroxynitrobenzene compounds detection(such as picric acid(PA))was successfully established.This work not only developed a new type of artificial light-harvesting system,but also provided a new idea to explore the synergy between different functional materials to regulate the photochemical activity.Part 3.Photoelectrochemical sensor with regulated electron-hole separation efficiency by plasmon coupling for SARS-Co V-2 spike glycoprotein detection.Photoelectrochemical(PEC)detection technology is widely used in food safety analysis,biological detection,drug detection,environmental monitoring and other fields because of its high sensitivity,fast detection speed and low cost.It is worth noting that the performance of photoactive materials is particularly important for the sensitivity of PEC sensors.In this part of work,to improve the separation efficiency of e-h in 2D Yb-TCPP nanosheets,we have successfully constructed Au NPs/Yb-TCPP Schottky junction photoelectrochemical sensor by growing Au NPs on the surface of 2D Yb-TCPP nanosheets through in-situ growth strategy.On the one hand,the plasmon resonance effect of Au NPs can increase the optical absorption cross section of 2D Yb-TCPP nanosheets.On the other hand,it can improve the e-h formation rate and separation efficiency through the plasmon-induced resonance energy transfer(PIRET),thereby improving the photoelectrochemical response.At the same time,the thermal electron transfer between Au NPs and 2D Yb-TCPP nanosheets also helps to improve the photoelectrochemical response of Au NPs/Yb-TCPP.Therefore,Au NPs/Yb-TCPP showed high photoelectrochemical activity,and its photocurrent intensity was approximately 16 times higher than that of Au NPs and 2D Yb-TCPP nanosheets.The modified aptamer on the surface of Au NPs/Yb-TCPP can effectively capture SARS-Co V?2 spike glycoprotein(S protein).Due to the large steric hindrance and low electrical conductivity of S protein,the electron transfer between Au NPs/Yb-TCPP nanosheets and electrolyte was hindered,thus reducing the photocurrent signal.Based on this,a photoelectrochemical aptamer sensor for highly sensitive detection of coronavirus S protein was constructed.This work not only realized the plasma coupling regulation of the e-h separation efficiency of 2D Yb-TCPP nanosheets,and developed a new PEC sensor with high photoelectrochemical performance,but also provided a potential biosensing strategy for the detection of SARS-Co V-2.To sum up,the 2D Ln-TCPP nanosheets were taken as the research object in this thesis.Firstly,structure-photochemical activity modulation was realized by adjusting thickness and metal nodes.Then,2D Yb-TCPP nanosheets with better photochemical activity were screened out for further optimizing and modulating by external functionalization strategy.On the one hand,the photosensitizer MB was successfully loaded onto 2D Yb-TCPP nanosheets surface to construct 2D MB/Yb-TCPP-SO₄ artificial light-harvesting system.The synergistic effect between the functional molecules effectively improved the light-harvesting ability and energy utilization of 2D Yb-TCPP nanosheets,thus improving the?-type photodynamic activity.Based on the photocatalytic oxidation properties of the artificial light-harvesting system,a fluorescence analytical method for hydroxynitrobenzene compounds(such as picric acid(PA),etc.)was constructed by using vitamin B₁(VB₁)as catalytic chromogenic substrate.On the other hand,Au NPs were successfully grown on the surface of 2D Yb-TCPP nanosheets by in-situ growth strategy,and the plasmon-enhanced photoelectrochemical sensor Au NPs/Yb-TCPP was constructed.The localized surface plasmon resonance effect of Au NPs effectively improved e-h separation efficiency of 2D Yb-TCPP nanosheets,endowing excellent photoelectrochemical response activity of Au NPs/Yb-TCPP.Furthermore,based on aptamer sensing technology,high-sensitivity detection of S protein was realized.This thesis not only provides a new strategy for the regulation of the photochemical activity of Por-MOFs,but also paves a new way for the application of photochemical activity of Por-MOFs in analysis and sensing.