Design,Synthesis And Catalytic Applications Of Porous Composite Materials

With the quick development of social economy,the energy crisis,environmental pollution,and global warming are serious problems with great concerns throughout the world.A diverse range of researchers are driven to find ecofriendly and cost-effective routes with the aim of resolving these problems.Catalytic system with porous composited materials has been developed as ideal candidates for resolving many of the practical issues encountered,such as environmental pollution and global warming.Porous composite materials are an important category of catalysts,which has found their practical applications in many chemical reactions because of various reasons.On the one hand,the active catalytic sites of the composite catalyst are well dispersed,which could effectively prevent their agglomeration during the catalytic process and thus improve their stability.The porous structure of the composite materials may create more unsaturated coordination environment during reactions,making the catalytic active site more exposed,and improving the catalytic activity of the composite materials.On the other hand,the specific components and spatial structure of the porous support could provide additional catalytic activity of loading active species,producing a synergistic or template effect to improve catalytic performance of composite materials.Therefore,based on these advantages,this dissertation designed and prepared a series of porous composite catalysts by combining metal organic framework(MOFs)and porous biochar with active catalytic sites.We investigated the applications of these porous composite catalysts in several energy and environmental fields,including electrocatalytic energy storage and conversion,as well as catalytic pollutants removal.The details of this dissertation are summarized briefly as follows:1.A core-shell nanostructured composite material,in which the metallic Pd nanoparticles cores were encapsulated by the MOF(ZIF-67)shells,was facilely synthesized through an impregnation-reduction process.The as-synthesized Pd@ZIF-67 material,with highly dispersed Pd nanoparticles encapsulated in the porous ZIF-67 structure,exhibited favorable catalytic performance towards the formic acid(HCOOH)-induced reduction of highly toxic hexavalent chromium(Cr(VI)).The transmission electron microscope clearly confirms that Pd nanoparticles and metal-organic framework indeed form a core-shell structure material.Dynamic Light Scattering reveals that Pd@ZIF-67 has highly hydrophilic and swellable nature.Benefiting from these properties,the composite catalyst has favorable catalytic activity,which could efficiently convert Cr(VI)into Cr(III)within 5 min,and could be reused 10 times without significant loss of its catalytic activity.The highly hydrophilic and swellable nature of the ZIF-67 was proposed to be responsible mainly for the favorable durability of the Pd@ZIF-67.2.Heterogeneous electro-Fenton is an efficient advanced oxidation process for the degradation of refractory organic contaminants in wastewater,and its efficiency is governed by cathodic catalysts.In this dissertation,the Fe,N doped biochar materials(Fe/N/biochar)were synthesized via a simple ionothermal carbonization of biomass and used as a cathodic catalyst for heterogeneous electro-Fenton.The as-synthesized biochar materials with uniform doping of N and Fe significantly improved the performance of the electro-Fenton process via promoting the two-electron transfer oxygen reduction reaction for H2O2 production,and subsequent H2O2 activation for reactive oxygen species(e.g.,·OH and ·O2-)generation.The Fe,N doped biochar catalyst showed excellent recyclability in the cycle runs of the electro-Fenton process,in which its catalytic activity did not fade but continuously increased.Based on the ex-situ high resolution transmission electron microscopy and electron paramagnetic resonance results,more active catalytic site exposure was induced by the interfacial crystalline-phase transformation and contributed to the excellent recyclability of the catalyst.This work would provide new insights into the rational design and synthesis of efficient electro-Fenton catalysts with a prominent activity and recyclability.3.The development of high-efficiency bifunctional electrocatalyst for oxygen reduction and evolution reactions(ORR/OER)is critical for rechargeable metal-air batteries,a typical electrochemical energy storage and conversion technology.This work reported a general approach for the synthesis of Pd@PdO-Co3O4 nanocubes using the zeolite-type metal-organic framework(MOF)as a template.The as-synthesized materials exhibited a high electrocatalytic activity toward OER and ORR,which is comparable to those of commercial RuO2 and Pt/C electrocatalysts,while its cycle performance and stability are much higher than those of commercial RuO2 and Pt/C electrocatalysts.Various physicochemical characterizations and Density functional theory(DFT)calculations indicated that the favorable electrochemical performance of the Pd@PdO-Co3O4 nanocubes is mainly attributed to the synergistic effect between PdO and the robust hollow structure composed of interconnected crystalline Co3O4 nanocubes.This work establishes an efficient approach for the controlled design and synthesis of MOF-templated hybrid nanomaterials,and provides a great potential for developing high-performance electrocatalysts in energy storage and conversion..