Enhancement Of Heterogeneous Catalytic Performance Of Transition Metal-Based Nanomaterials By Surface And Interface Regulation

With the expansion of population and the rapid development of industrial economy,energy crisis and environmental pollution are becoming more and more serious.Heterogeneous catalytic reactions occurring at different phase interfaces are of great practical significance for solving these two problems.For example,the development and utilization of green hydrogen energy can be realized through the electrocatalytic water decomposition reaction at the solid-liquid interface.The effective monitoring of toxic and harmful gases in the environment can be realized through the gas sensing reaction at the solid-gas interface.The oxidation or reduction degradation of trace environmental pollutants in water can be realized through the photocatalytic reaction at the solid-liquid interface.For various heterogeneous catalytic reactions,catalyst is the core factor.In order to meet the practical needs of large-scale applications,the development of efficient and cheap catalysts to speed up the heterogeneous catalytic reactions has become one of the research hotspots in the field of chemical engineering and materials science in recent years.The heterogeneous catalytic reaction mainly occurs on the surface or interface of the catalyst.Therefore,the controlling of surface and interface is the key to improve the heterogeneous catalytic performance.In this paper,the surface and interface characteristics of several typical transition metal based compounds(including Ni S₂,Mn O₂,Co₃O₄)were effectively controlled using the strategies of highly active crystal facets design,highly efficient heterogeneous interface construction,one-dimensional and porous structure construction,and the related heterogeneous catalytic reaction performance(including electrocatalytic decomposition of water,gas sensing,photocatalytic degradation of trace water pollution)were significantly improved.On this basis,the structure-activity relationship between the surface/interface properties and the performance of the catalyst was systematically studied by first principles calculation and experimental characterization,and the catalytic mechanism was elucidated.The main research results are as follows:1.Two kinds of pyrite type transition metal sulfide Ni S₂nanocrystals with different crystal facets({111}and{100})were prepared by a simple surfactant assisted hydrothermal method.Based on these two kinds of nanocrystals,the facets effect of HER was systematically studied.The results showed that Ni S₂nanocrystals with{111}facets exhibited significantly enhanced HER activity compared with Ni S₂nanocrystals with{100}facets.Based on the first principles calculation of density functional theory,the mechanism of the facet-dependent electrocatalytic activity was further studied.The results showed that{111}facets had higher surface energy and more ideal hydrogen atom adsorption capacity compared with{100}facets,which were the key to enhance HER activity.This study enriches the research on facet-dependent HER activity,which is of great significance for further understanding the HER mechanism and accurate designing of highly efficient HER electrocatalysts;2.Novel one-dimensional shish-kebab structures composed of active(110)-faceted?-Mn O₂nanowires as backbones and(111)-faceted Co₃O₄nanocrystals as shells were prepared by a hydrothermal method followed by an in-situ epitaxial attachment growth strategy.The gas sensing performance of the Co₃O₄@Mn O₂heterostructures was studied.It was shown that the Co₃O₄@Mn O₂heterostructures exhibited obvious enhanced triethylamine sensing performance compared with bare Mn O₂nanowires and Co₃O₄nanocrystals,suggesting a strong synergistic effect.The study of gas sensitivity mechanism showed that the unique one-dimensional shish-kebab structures,increased surface active oxygen species and closely-attached hetero-interface which can achieve efficient charge transfer were the key factors to improve the triethylamine sensing performance.This work provides an in-situ growth method of one-dimensional heterostructure,which realizes the comprehensive control of morphology,surface crystal plane and heterogeneous interface,and provides a new idea for improving the gas sensing performance of transition metal oxides;3.On the basis of the first work mentioned above,the in-situ growth of active{111}facets of Ni S₂nanocrystals on the surface of reduced graphene oxide nanosheets was realized by adding graphene oxide nanosheets into the growth process of Ni S₂nanocrystals.The results of photocatalytic activity test showed that the degradation of Cr(VI)and organic dyes(including methyl orange and methylene blue)in water could be achieved through the synergistic effect of active crystal facets exposure and graphene recombination.Through the first principles theoretical calculation,dark adsorption and photo-current experiments,it is found that the reasons for enhancing the photocatalytic activity are as follows:Firstly,{111}crystal facets have higher surface energy,which can effectively achieve the adsorption and capture of pollutant molecules;Secondly,graphene nanosheets can not only effectively prevent the agglomeration of nanocrystals,but also act as an ideal electron transport channel,which can realize the effective separation of photogenerated electrons and holes.The research results have important guiding significance for the development of efficient semiconductor photocatalysts based on the co-regulation strategy of surface and interface;4.One dimensional Ni S₂nanotube arrays and Ni S₂nanorod arrays were successfully grown on the surface of nickel foam by one-step hydrothermal technology.Electrocatalytic experiments showed that the overpotential of the Ni S₂nanotube arrays for HER and OER was 209 m V and 367 m V,respectively(at a current density of 50 m A/cm²),which was much lower than that of the synthesized Ni S₂nanorod arrays and other Ni S₂nanostructures reported previously.In addition,the Ni S₂nanotube arrays can also be used as efficient bifunctional electrocatalysts for overall splitting of water,which can provide a current density of 10 m A/cm²at a low overpotential of 1.58 V.The excellent electrocatalytic properties of Ni S₂nanotubes are attributed to the high specific surface area and abundant active sites of one-dimensional hollow porous structure,and the in-situ growth strategy can greatly increase the charge transfer efficiency.This study not only enriches the morphology of Ni S₂nanostructures,but also provides a practical way for the synthesis of one-dimensional nanotube structures.In a word,the research of this paper provide a new idea for enhancing heterogeneous catalytic performance by surface and interface control,and deepen the understanding of relevant catalytic mechanism,which also have important practical significance for solving energy and environmental problems.