Preparation And Properties Of Wood Nanofibers Embedded Molybdenum Disulfide Catalyst

Biomass is a green material which is abundant,renewable and degradable on earth.Wood nanofibers(CNF)prepared from wood fibers have good characteristics such as large aspect ratio,high surface chemical activity,excellent mechanical strength and small nanometer size.Integrating the advantages of wood nanofibers to prepare catalysts can not only make wood fibers efficiently utilized and improve their quality and efficiency,but also provide directions for highly stable catalytic materials.Among the current catalysts for hydrogen evolution,there are still two problems affecting the catalytic activity of molybdenum disulfide based powder catalyst,including low conductivity and agglomeration.Carboxylated multi-walled carbon nanotubes(cMWCNT)can effectively improve the conductivity of catalysts,but the strong van der Waals forces between carbon nanotubes lead to partial agglomeration,which is not conducive to the construction of stable catalysts.Therefore,in this study,wood nanofibers were used to construct efficient hydrogen evolution catalysts with a cross-linked three-dimensional network structure through regulating wettability and improving dispersion.The stabilization mechanism of wood nanofibers on high stability and good dispersion of hydrogen evolution catalysts is deeply investigated.The main research contents and results are as follows:(1)Based on the wood nanofibers obtained by different preparation methods,the catalytic substrate materials constructed by these three wood nanofibers and carboxylated multi-walled carbon nanotubes were prepared,and the effects of wood nanofibers obtained by different treatment methods on the catalytic substrate were investigated.The morphologies of mechanical wood nanofibers(M-CNF),strong acid hydrolyzed wood nanofibers(S-CNF)and TEMPO wood nanofibers(T-CNF)were compared.CNF had a uniform distribution in aqueous solution,a higher degree of nanometer,a more uniform diameter,and a cross-linked network structure.Three kinds of wood nanofibers and carboxylated multi-walled carbon nanotubes were synthesized as catalytic substrates.After comparative analysis,it is found that T-CNF/cMWCNT has smooth and uniform morphology,good mechanical strength,abundant pore volume of appropriate size(0.4478 cm3 g-1),large specific surface area(80.85 m2 g-1),abundant oxygen-containing groups,good hydrophilicity,and most importantly,the best electrical conductivity.(2)The optimum preparation conditions of wood nanofibers immobilized molybdenum disulfide hydrogen evolution catalyst were investigated.Firstly,T-CNF/cMWCNT/MoS2 catalysts were constructed with different additions of metal and wood nanofibers,and the influence of the two additions on the catalyst was studied.When the addition amount of MoS2 is 10 wt%,and the concentration of T-CNF is 0.8%,the catalyst exhibits the best conductivity and hydrogen evolution performance.The electrochemical performance of the optimal T-CNF0.8/cMWCNT/MoS2-2 was further compared with that of the control sample,and it was found that the T-CNF-immobilized molybdenum disulfide catalyst exhibited good hydrogen evolution performance.It only needs 154 mV overpotential to reach the current density of 10mA cm-2,and the corresponding Tafel slope is 46.19mV dec-1.Starting from the dispersion characteristics of the catalyst,the macromorphology,micromorphology and pore structure of the T-CNF embed MoS2 catalyst were studied,and its structural composition was also explored.It was found that the three-dimensional network structure of T-CNF0.8/cMWCNT/MoS2-2 effectively embedd MoS2,and the cross-linked structure increased the specific surface area,enhanced the electrical conductivity,and exposed more active sites.(3)In order to further explore the stability of the catalyst,stability tests of TCNF0.8/cMWCNT/MoS2-2 in different environments were carried out.After high-power ultrasonic testing,the cMWCNT/MoS2 was pulverized in solution,while the TCNF0.8/cMWCNT/MoS2-2 was intact.Various stability tests have been carried out in acids,and the decay rate of cMWCNT/MoS2 catalyst is as high as 35.83%after 100 hours chronopotentiometric measurement,while the decay rate of T-CNF0.8/cMWCNT/MoS2-2 catalyst is only 6.99%.In addition,the properties and morphology of catalyst were not significantly different before and after the stability test at different temperatures in acid.After 8 hours chronopotentiometry test in seawater,the decay rate of cMWCNT/MoS2 increased sharply and fractured in the solution,while the decay rate of TCNF0.8/cMWCNT/MoS2-2 was 15.88%after 18 h test.It can be seen from the above that the presence of T-CNF improves the binding strength of catalyst and greatly improves its stability.(4)In order to clarify the stabilizing mechanism of wood nanofibers on the catalysts with high stability,from the analysis of wettability and mechanism,the hydrophilic sites(hydroxyl and carboxyl groups)on the surface of the wood nanofibers significantly improved the hydrophilic/aerophobic properties of the catalyst,effectively realizing the excellent gas-liquid mass transfer and the stability of the catalytic reaction.Meanwhile,the internal steric hindrance and strong hydrogen bonding interaction between T-CNF and cMWCNTs improve the structural dispersion and bonding strength of the catalysts,which is beneficial to the long-term hydrogen evolution catalytic reaction.The excellent hydrogen evolution stability of wood nanofiber-embedded MoS2 catalysts in different catalytic environments was achieved.In summary,based on the unique one-dimensional nanostructure,abundant oxygencontaining functional groups and large specific surface area of wood nanofibers,this paper uses it as a dispersant to construct a hydrogen evolution catalyst with carboxylated multiwalled carbon nanotubes and molybdenum disulfide.The catalyst has a conductive crosslinked network structure and can effectively embed metal particles,thereby solving the problems of low conductivity and agglomeration of the molybdenum disulfide powder type catalyst.Owing to the stabilizing mechanism of wood nanofibers on the catalyst,the hydrogen evolution catalyst showed excellent stability in different environments.In this study,the efficient utilization of wood fibers was realized,and this research also provides a new direction for the development of new biomass composite electrocatalytic materials.