Amphiphilic Nanocatalysts:Design,Synthesis And Applications In Catalysis

With the ever-increasing awareness of environmental problems,the use of water as the reaction medium has become an urgent research topic for green and sustainable chemistry due to its appealing advantages including low toxicity,non-inflammability,low volatility,high heat capacity and ease of separation from organic products.Despite the significant progress made and the appealing potential,most aqueous catalytic reactions still suffer from low reaction efficiency due to the extremely high mass transfer resistance that is caused by the immiscibility of water with organics.To overcome this problem,co-solvents and phase-transfer regents are usually added to accelerate aqueous reactions.However,extra procedures are required to remove these additives from the final product at the end of the reaction.In this context,a general strategy to design efficient solid catalysts toward aqueous reactions is still highly desired.It has been demonstrated that the introduction of hydrophobic moieties onto a solid catalyst surface is beneficial to improve the aqueous reaction rate because the hydrophobic surface can facilitate the adsorption of organic reactants from water.However,the enhanced hydrophobicity inevitably leads to the poor dispersibility of catalyst nanoparticles in water(often floating on the surface of the aqueous phase),which in turn limits their catalytic efficiencies.In this paper,a series of multifunctional multiphase interfacial catalysts are constructed by designing the structure of amphiphilic nanocatalysts.Based on organic-inorganic mesoporous organosilica,Janus carbon/silica composites via structural design and multicompartmentalized mesoporous organosilica,multi-functionalize amphiphilic materials in magnetic response function,adsorption of organic compounds and desorption of water molucules mass transport function,spatial compartmentalization function for multiple active centers.And explore catalytic rate and selectivity of oxidation of alcohols,one-pot oxidation-condensation cascade reaction for synthesis of imines from alcohols and amines,sequential hydrogenation of nitrobenzene in water.In the chapter ?,we reported an amphiphilic magnetic nanocomposite with a well-defined yolk-shell structure and a unique hydrophilicity/hydrophobicity through our previous growth-induced etching strategy,which is composed of a Fe3O4 core and an amphiphilic PMO(periodic mesoporous organosilica)shell as well as a protective layer SiO2.To the best of our knowledge,this is the first time that amphiphilic magnetic nanocomposite is proposed.When another functional group thiol was introduced on the surface of PMO mesochannels,the obtained nanocomposite Fe3O4@SiO2@HS-PMO can be used as a multicomponent adsorbent with high efficiency and recyclability for organic and inorganic contaminants in water.The unique amphiphilic nanocomposites enabled selective oxidation of alcohols to proceed efficiently in water under aerobic condition.Moreover,this nanocomposite catalyst could be completely recovered using an external magnet due to the superparamagnetic behavior of Fe3O4 and can be recycled with sustained selectivity and activity.In the chapter ?,we prepared a Janus nitrogen-doped carbon@silica hollow nanostructure via confined pyrolysis to construct a novel multifunctional amphiphilic nanoreactor.The nitrogen-doped carbon partly embedded into the mesoporous silica shell,leading to the formation of external silica surface and internal carbon surface as well as buffered carbon/silica interface.Such a unique Janus structure endowed the material superior hydrophobicity/hydrophilicity,and then presenting extreme affinity towards organics in water.Additionally,the doped nitrogen atoms in carbon matrix can not only provide anchoring sites for stabilizing ultrasmall metal nanoparticles but also serve as basic active sites.On the basis of these merits,our amphiphilic nanoreactor showed significantly enhanced activity and selectivity for base-free aerobic oxidation of various alcohols in water using air as the oxidant.Moreover,one-pot synthesis of imines from alcohols and amines could be achieved with good yields via oxidation-condensation tandem catalysis.Furthermore,owing to the high stability of framework for silica and carbon,the nanoreactor possessed extremely stable amphiphilicity,thus leading to an excellent catalytic stability.In the chapter ?,we report a novel multicompartmentalized mesoporous organosilica(MCPMO)for loading spatially separated Ru and Pd nanoparticles to explore sequential hydrogenation reactions.Our material contains two separated nanocavities that are connected by a uniform mesoporous structure,ensuring spatially isolating two different metal nanocatalysts and their catalytic cycles yet keeping them in communication.As a proof of this concept,the obtained catalyst Ru/Pd/MCPMO exhibits a remarkable catalytic activity in one-pot sequential hydrogenation of nitroarenes to cyclohexylamines.To our knowledge,this is the first example that spatially separated bimetallic nanocatalyst was applied in sequential hydrogenation reactions.Importantly,we find a fascinating spatiotemporal coupling effect,a key factor to complex cellular reactions,in which the reaction rates of Ru and Pd nanoparticles are significantly enhanced via reciprocally transfering intermediates,contributing to the excellent catalytic performance.