The Synthesis,Self-assembled Structure And Catalytic Applications Of Supramolecular Gels Derived From Dicarboxylic Acid Derivatives

Supramolecular gels,a category of the―smart‖soft materials,have attracted significant attention owning to their broad potential applications in catalysis,biomedicine,environmental remediation,material syntheses,sensors,soft-optics,art conservation,molecular recognition etc.Catalysis is one of the key fields in material science due to the widely application in modern chemistry.In the field of industrial applications,heterogeneous catalysts have aroused more tremendous attention than the homogeneous because of the convenience of separation and recycling.Functional carbon-based materials are the most interesting catalysts,which not only exhibit excellent chemical activity and selectivity,but also have other advantages,including long durability,low costs and environmental friendliness.The transition metal-coordinated N/C material is one of the most promising non-precious metal catalysts.The traditional method for preparing metal-N-C involves the direct pyrolysis of mixture（nitrogen,carbon,and transition metal precursors）.However,the distribution uniformity of various components in physical mixing process is usually unsatisfactory owing to the bad compatibility,leading to the agglomeration of metal particles.Therefore,a homogeneous organic compounds/metal system is very crucial to obtain high-performance metal-N-C catalysts or metal oxide/carbon composite materials.In this dissertation,a novel strategy to construct the homogeneous metal/N/C-containing composite is demonstrated based on the sol-gel method of dicarboxylic acids/dicarboxylic acid derivatives and Fe³⁺.The uniform distribution of metal particles in carbon precursor is solved by the high compatibility and coordinating capability of carboxyl,pyridyl and amide groups in dicarboxylic acids/dicarboxylic acid derivatives with metal ions during the sol-gel process.A magnetically recyclable,low-cost and highly efficient Fe-N-C nanocatalyst used for the hydrogenation of nitro compounds was developed via a facile pyrolysis of N-doped supramolecular metallogel.Firstly,a series of dicarboxylic acids/dicarboxylic acid derivatives-based supramolecular gels were explored.Secondly,Fe-N-C nanocatalysts were prepared via a pyrolysis of N-doped supramolecular gel.Finally,the chemical activity and selectivity of the as-prepared nanocatalysts were evaluated.The results are as follows:1.A novel two-component organogel system based on dicarboxylic acids and primary alkyl amines（R-NH₂）,in which the aggregation morphology of gelators can be efficiently adjusted by solvent polarity and tail alkyl chain length,was designed and synthesized.Interestingly,flower-like self-assemblies could be obtained in organic solvents with medium polarity,such as tetrahydrofuran,aminobenzene and dichloromethane,when the gelators possess a suitable length of carbon chain(R₁₄,R₁₆ and R₁₈).Moreover,further instrumental analyses reveal that the intermolecular acid–base interaction and van der Waals interaction are critical driving forces in the process of gelation.In addition,this kind of supramolecular organogel system with controllable self-assembled structures displays excellent mechanical properties and thermo-reversibility,and the relevant self-assembly mechanism is also proposed.This work can provide a novel strategy for constructing tunable supramolecular nano-architectures with potential applications in functional soft materials.2.A novel 3,5-pyridinedicarboxylic acid derivative（PDA-N4）-based supramolecular hydrogels were designed and constructed via a solvent-mediated strategy under mild conditions.It was found that the self-assembled aggregates of PDA-N4 could be efficiently modulated via water content in mixed solvents.Moreover,the PDA-N4 gels not only displayed solid-like behavior,pH-and thermo-reversible characteristics,but also showed a solution–gel–crystal transition upon extending the aging time.Further instrumental analyses revealed that the intermolecular hydrogen bonding andπ-πstacking interactions were critical driving forces in gelation process.In addition,the human umbilical venous endothelial cell culture results showed that the PDA-N4 exhibited good cytocompatibility,and the corresponding gels presented controllable drug release for VB₁₂.This research is expected to provide a new material for the cell culture and controlled drug release.3.A simple gelator（thiodiglycolic acid）that can congeal an alcohol-water mixture to obtain a transparent,strong,and self-supporting gel with multiple-stimulus responsive properties was investigated.When combined with FeCl₃/Fe（NO₃）₃ and water,thiodiglycolic acid in alcohol aggregates to a strong supramolecular metallogel.The metallogel is highly selective towards Fe³⁺and does not need any sonication or heating-cooling,and exhibited sharp phase transitions in response to a series of disparate stimuli,including temperature,pH changes,oxidation reduction reactions（redox）,and light.The non-explosive metallogel can be packaged in a polyethylene tube and used as a safe fuel for indoor and outdoor heating.4.A novel self-assembled metallogel was synthesized from a ligand of thiophene-2,5-didicarboxylic acid derivative（TPA-N3）.TPA-N3 can be dissolved easily in aqueous solution containing Fe³⁺/Al³⁺/Cr³⁺upon heating,and subsequently self-assembled into metallogels after cooling.The as-prepared metallogels were characterized by SEM,FT-IR,¹H NMR,DSC and rheological measurements.The results suggest that TPA-N3 can self-assemble into fibrous aggregate through the intermolecular hydrogen bonding and metal-ligand interactions.5.Three types of multi-responsive and self-sustaining metallogels were synthesized by the reaction of the ligand 1,4-Naphthalenedicarboxylic acid derivative（NDC-N4）with Fe（Ⅲ）,Al（Ⅲ）or Cr（Ⅲ）.These metallogel systems display excellent mechanical properties and thermo-reversibility.Moreover,further analyses of ¹H nuclear magnetic resonance spectroscopy and FT-IR reveal that the intermolecular hydrogen bond,π–πstacking and metal-ligand interactions are critical driving forces in the process of gelation.Additionally,the GO-doped supramolecular metallogel（NDC-N4/Fe₂（SO₄）₃/GO）was obtained.6.Heterogeneous,magnetically recyclable,low-cost and highly efficientγ-Fe₂O₃-based NPs encapsulated with a N-doping porous carbon nanocatalyst used for the hydrogenation of nitro compounds were developed via the pyrolysis of supermolecule metallogel（TPA-N3/Fe₂（SO₄）₃）.The smallγ-Fe₂O₃ NPs are well dispersed inside the N-doping porous carbon,which effectively limits the aggregation and growth of the high-density NPs.Notably,this non-noble metal oxide-based nanocomposite behaves as stable and efficient catalyst for the hydrogenation of substituted aromatic into their corresponding amines.In addition to the tolerance to general groups,the catalyst exhibits high chemoselectivity to the reducible groups,including halogen,alkyne,olefin,etc.The nanocatalyst is readily recycled with an external magnet and could be reused for at least 7 times without distinct loss of activity.This study provides a versatile platform based on supermolecule metallogel to introduce active metal oxide species highly dispersed inside heteroatom-doping porous carbon matrix with improved performance toward hydrogenation of nitro compounds.7.A novel strategy to construct the homogeneous metal/N/GO-containing composite is demonstrated based on the sol-gel method of 1,4-naphthalene-dicarboxylic acid derivative（NDC-N4）,Fe₂（SO₄）₃ and GO.The magnetically recyclable,low-cost and highly efficient Fe-N-GO-C nanocatalyst for the hydrogenation of nitro compounds were developed via the facile pyrolysis of GO-doped supramolecular metallogel NDC-N4/Fe₂（SO₄）₃/GO.After oxidision of air,most of Fe³⁺converted into activeγ-Fe₂O₃ species.Notably,this non-noble metal oxide-based nanocomposite behaves as efficient and stable catalyst for the hydrogenation of various substituted aromatic,into their corresponding amines.This catalyst exhibits high chemoselectivity to the reducible groups,including halogen,ester,aldehyde,ketone,etc.In addition to benchmark substrates,marketed nitro-substituted drugs（nilutamide,niclosamide and nimodipine）were hydrogenated to the corresponding amines with high selectivity.Moreover,The Fe-N-GO-C nanocatalyst is readily recycled with an external magnet and can be reused for at least5 times without any loss of activity.This Fe-N-GO-C nanocatalyst is expected to be used in catalytic reductive aminations with molecular hydrogen.