| It is one of the important safety measures to eliminate and control hydrogen isotope gas produced by surroundings with organic molecules containing alkynyl,which have the ability to react with H2 in the existence of catalyst.The hydrogenation of organic molecules usually occurs at high temperature and pressure in solution or gaseous system.However,as for hydrogen getters,especially those used in closed environment are in solid state form and the catalytic hydrogenation is required at room temperature and low hydrogen partial pressure.Improving hydrogen absorption efficiency includes two factors: one is sufficient contact between the solid reactant and the solid catalyst,the other is effective dispersion of metal catalyst particles.In this study,alkynyl-modified polyvinyl alcohol(a-PVA)was prepared and used to stabilize Pd nanoparticles(Pd NPs).It is hoped that the integration of a-PVA with Pd nanoparticles can improve the factors mentioned above,to a certain extent,and support in development of getters with hydrogen elimination performance at room temperature and normal pressure.In this paper,a novel functionalized PVA with pendant acetylene groups was prepared by etherification and carbamate esterification respectively.The structure and grafting degrees of the resulting alkynyl-modified PVA(a-PVA)were characterized by means of fourier transform infrared spectroscopy(FT-IR)and nuclear magnetic resonance hydrogen spectroscopy(1H-NMR).a-PVA /Pd NPs composites were synthesized via chemical reduction reaction in N,N-dimethyl formamide(DMF)solvent.The microstructure and the particle size of Pd NPs were analyzed by means of transmission electron microscopy(TEM)and dynamic light scattering(DLS).Results show that the grafting degree of propargyl bromide-modified PVA is only up to 22%.Furthermore,phenomena of the low solubility for propargyl bromide-modified PVA in common used solvents and poor dispersion of Pd NPs beacuse the agglomeration of the Pd particles were observed.While different grafting degrees of propargylaminemodified PVA polymers,ranging from 20 to 67 percent,could be produced by modifying dosages of N,N'-carbonyldiimidazole and propargylamine.With the increase of the grafting degree,the solubility of a-PVA will fall down in DMF solvent,which results in poor dispersion and large average particle size of Pd NPsIn order to test hydrogen absorption performance of a-PVA/Pd NPs,hydrogen absorption materials were prepared by two methods,one was by direct evaporation solvent or diatomite loading a-PVA/Pd NPs and then removing solvent.The other was to mix a-PVA with Pd/C catalyst and then mechanical grinding uniformly.And the hydrogen uptake capability of the hydrogen getter was characterized by PVT method.Results show that the hydrogen absorption performance of the sample prepared by direct evaporation solvent was the worst.Because of the agglomeration of Pd NPs during the process of solvent concentration and leading to a poor catalytic ability.While the hydrogen absorption performance of the samples prepared by diatomite loading with a-PVA/Pd NPs composite is much better.Comparing the hydrogen absorption capacities of the samples with different grafting degrees,can we find that it should have a compromise for the solubility of a-PVA polymer in solvents and the alkynyl contents in a-PVA for a good hydrogen getter.For the samples preparedby mixing a-PVA with Pd/C catalyst,a good hydrogen absorption performance was demonstrated and its hydrogen absorption capacity shows a linear relationship with grafting degree of alkynyl.In other words,the more alkynyl content hydrogen getter has,the better hydrogen absorption performan ce will be. |
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