Assembly Regulation And Photocatalytic Properties Of Supramolecular Gels

The site of natural photosynthesis is the thylakoid membrane,which is the supramolecular assembly of lipids and other functional components.Among them,chlorophyll and auxiliary pigments in light harvesting complexes(LHCs)act as light collection antennas to absorb solar energy.Meanwhile,porphyrins,as a class of chromophores in chlorophyll,play many key roles during natural photosynthesis process.Therefore,this paper explores the formation of lipid-like bilayer membranes through the assembly of lipid derivatives carrying metal catalytic centers(Co)or chromophores(porphyrins),which are applied to photocatalytic reduction of CO2 or photocatalytic splitting of water for H2 generation.The research content of this paper is mainly divided into the following three parts:1.Metallogels induce hydrophobic microenvironment and binuclear synergistic effect for efficient photocatalytic CO2 reduction.The metallogels were formed by co-assembly of lipid molecules(LG/Nico,LG/Bipy,etc.)and transition metal ions(Co).Electron microscope images show distinct morphological structures of two metallogels after supramolecular assembly.And the contact angle tests also indicate that two metallogels have completely different hydrophilic and hydrophobic properties.Although there is no strong electrical conductivity for initial lipid molecules,the metallogels not only display semiconductor properties,such as conduction band position,valence band position and electrochemical impedance,but also show cyclic voltammetry curves that directly reflect the redox properties of catalyst metals.In the CO2 reduction experiments,the LG/Nico-Co catalyzed stably within 24 hours showing the highest CO production of 208724 μmol g-1 with 90%selectivity for CO/H2;the LG/BipyCo also released 142866 μmol g-1 CO within 15 hours along with 87%selectivity for CO/H2.In addition,the CO generation rate and selectivity of the CO2 reduction for metallogels catalyst can be further adjusted by changing the ratio of H2O and MeCN in the reaction solution.The DFT calculation results show that the LG/NicoCo can construct bilayer nanostructures with closely packed alkyl chains and binuclear Co synergistic metal active sites.Therefore,the formation of hydrophobic microenvironment is helpful to achieve good mass transfer and high catalytic efficiency based on the synergy of two adjacent metal centers.It is worth noting that these lipid-like molecular catalysts can be recycled by simple drying after centrifugation,which can also be dissolved in organic solvents such as chloroform for degradation.This work not only opens a new avenue for the design of new energy appliance based on the assembly of small organic molecules,but also provides some new insights for the application of soft matter in renewable energy.2.Multi-component supramolecular gels induce protonation of porphyrin exciplexes to achieve improved collective optical properties for effective photocatalytic hydrogen generation.Multi-component supramolecular gels were constructed by the lipid molecules and two free-metal porphyrins in diffenert solvent.Electron microscopy images show that the multi-component assemblies formed in different solvents have distinct nanostructures.Unexpectedly,the two kinds of porphyrins were not only protonated in gel under neutral conditions,but also formed exciplexes by using the DMF as solvent.Meanwhile,the protonation and J-aggregation of porphyrins extend absorption spectrum of the supramolecular material to a wider wavelength range(300-750 nm),and its theoretical spectral efficiency is about 50%compared with the wavelength range of solar spectrum(300-1200 nm).In the photocatalytic H2 evolution reaction,the multi-component gel system in DMF exhibits the best photocatalytic performance,which is about 8 times than ethanol system.Therefore,the nanostructure,spectral absorption range and catalytic properties of supramolecular assemblies can be regulated by choosing different solvents.And these interesting characteristics provide the smaller bandgap for photo-induced electron generation,nice charge separation and efficient transportation of photogenerated carriers.The multi-component supramolecular gels represent a new approach for fabrication of photocatalytic systems.3.Multi-chromophore supramolecular gels for photocatalytic hydrogen evolution.By integrating three different types of chromophores(PtTCPP,RuDCBPY and PDI),the multi-chromophore supramolecular gels containing doublephotosensitizers or triple-photosensitizers were constructed.Compared with the solution state of chromophores,both double-photosensitizer gel and triplephotosensitizer gel extend the absorption spectrum to a wider wavelength range,suggesting an effective improvement in light-harvesting performance.Unexpectedly,the UV-Vis spectrum of the triple-photosensitizer gel displayed a new shoulder at 426 nm,indicating the J-aggregation of porphyrins.Meanwhile,the chirality of supramolecular assemblies also gradually disappeared during the transition from the double-photosensitizer to triple-photosensitizer gel,suggesting that different kinds of chromophores have good dispersibility in the supramolecular gels.Both the SEM and AFM images of the triple-photosensitizer gel showed a vortex-like nanostructure,while the double-photosensitizer gel maintained traditional nanoribbon structure on SEM and AFM images.These results display that the introduction of multiple chromophores into supramolecular gels induces a directional change on the alignment orientation.Moreover,the layered and curled formation of triple-photosensitizer gel is favorable for the uniform loading of the cocatalyst Pt nanoparticles,exhibiting more efficient photocatalytic hydrogen evolution efficiency.Therefore,upon integrating different kinds of photosensitizers,the UV-Vis absorption spectra range,charge separation of photogenerated electrons,and carrier transport of supramolecular gels are significantly improved.This research provides insight into the optoelectronic and catalytic properties of multichromophore gel systems.