| Ammonia borane(NH3BH3),as a new type of hydrogen storage compound,has the highest hydrogen content(19.59%)so far,and exists in stable solid state at room environment.It can controllably release hydrogen under mild conditions,and thus has attracted more and more attention in the field of new energy.However,the cost of its comprehensive preparation is excessively high due to scarcely applicative synthesizing approach,expensive raw material and complicated process.Since there is still not an accurate,reliable and convenient method,the quantitative analysis of ammonia borane mainly depends on the indirect determination of the released hydrogen gas volume.Up to now,the comprehensive and systematical research about spectral properties of ammonia borane has not been reported.Here,in order to further improve the theoretical level for structure-function relationship of ammonia borane and to promote its applications,the preparation method,separation and purification,quality evaluation and spectral properties of ammonia borane were systematically studied,which is of great theoretical significance and application value.As a main part of the program of the National Natural Science Foundation of China(No.21576073),this paper focuses on the systematic analysis and research on the synthesis method,quantitative analysis and spectroscopic properties of ammonia borane.1.Synthesis of ammonia borane by liquid-phase reduction method based on sodium borohydride:(1)Using ammonium sulfate and sodium borohydride as raw materials,ammonia borane was prepared through reflux reaction in liquid phase at 40 ? for 6 h.The product was purified by repeated recrystallization from ether,and the product was analyzed and characterized by elemental analysis and X-ray diffraction(XRD).The effects of different ammonium salts,reaction solvents and reaction temperatures on the yield of ammonia borane were investigated.The results showed that the high yield of ammonia borane(78.32%)could be achieved under the reaction of ammonium sulfate and sodium borohydride in the water bath and 40 ?;The solvent should use organic solvents polar and easy to separation,such as tetrahydrofuran and dioxane.(2)Synthesised and separated copper sulfate-ammonia complex.Cu(NH3)4SO4 and Ni(NH3)6Cl2 were obtained throw separation,purification and vacuum drying by thereaction of copper salt,nickel salt and concentrated ammonia.Ammonia borane and the nanoparticles was prepared throw reflux reaction in liquid phase at 25 ? for 5 h,copper sulfate-ammonia complex and sodium borohydride used as raw materials.The effects of different metal amines,different solvents(ethanol,n-butanol,n-heptane,acetone,ether and tetrahydrofuran)and different reaction temperatures(15,25 and35 ?)on the yield were also studied.The product was purified by repeated recrystallization from ether,and the product was analyzed and characterized by elemental analysis and X-ray diffraction(XRD).The results showed that the reaction of copper sulfate-ammonia complex and sodium borohydride in the water bath at25 ? can achieved high yield(72.36%)and high purity(more than 95%)ammonia borane;the water bath temperature has little effect on the reaction rate and yield.The reaction system of Cu(I),Cu(II)chloride as an oxidizing agent or ethanol,acetone and n-heptane as solvent can not achieved ammonia borane.The simultaneous addition of metal nano-Cu,Ni,can be used to catalyze the release of ammonia borane.2.Quantitative analysis of ammonia borane by chemical analysis:(1)Analysis of boron(B)in solution by mannitol titration: Ammonia borane hydrolyzate contains borate,which can be converted to boric acid by acidification.Mannitol binds to boric acid can form strong acid complex C6H8(OH)2?(BO3H)2,then the amount of ammonia borane can be determined reversibly by acid-base titration.The solution system of borax,sodium metaborate and ammonium borate and ammonium pentaborate was used as the research object.The contents of boron were determined by mannitol method.And the corresponding relative purity of borate is deduced.The maximum relative deviation is less than 0.36%.At the same time,in order to avoid the influence of NH4+ in the solution,the ammonia was removed before titration,which effectively eliminated the adverse effect caused by the ammonium,and avoided the positive deviation of the ammonium borate titration.The hydrolyzate of the ammonia borane was titrated by the mannitol method,and the content of the ammonia borane was estimated indirectly.The accuracy was high and the results were reliable.(2)Determination of nitrogen(N)in solution by formaldehyde titration.ammonia borane hydrolysis to produce quantitative ammonium metaborate,ammonia borane content can be indirectly obtained by measuring the solution of ammonium(NH4+).The solution system of ammonium borate and ammonium pentaborate was used as the research object,the content of nitrogen(N)was determined by formaldehyde method,and the corresponding purity of ammonium borate was deduced.The maximum relative deviation of the titration results was 1.36%.The results show that the accuracy of the obtained results is relatively low.The ammonia borane hydrolyzate is analyzed by formaldehyde method,and the content of ammonia borane is measured indirectly.The error is relatively high.(3)Determination of ammonia borane in water by hydrogen release.Ammonia borane fully hydrolyzed after the quantitative release of hydrogen,by measuring the amount of hydrogen,we can calculate the content of ammonia borane.The amorphous alloy Co-P-B powder was prepared by hydrothermal method,and it was proved that it could catalyze the complete hydrolysis of ammonia borane efficiently.Then,the amount of hydrogen released from the three different methods was tested by a selfdesigned hydrolysis device.The experimental data were processed by ideal gas and van der waals gas equation.The results show that the hydrogenation method can be used to determine the content of ammonia boron,the accuracy is higher than the general chemical analysis method,and the calculation result obtained by van der Waals true gas equation is more reliable.The results are in good agreement with the nominal content,hydrogenation method can meet the quantitative requirements of quantitative analysis of ammonia borane.3.Study on the basic spectroscopic properties of ammonia boraneTG,DTA,DSC,XRD,FT-IR,Raman spectroscopy,1H NMR and11 B NMR were used to analyze the typical spectroscopy of ammonia borane obtained by the three different methods.(1)The results of comprehensive thermal analysis show that the ammonia borane can be directly pyrolyzed without catalyst.The decomposition process is composed of several complicated steps,and the heating rate will also affect the pyrolysis rate and the product type to a great extent.(2)The XRD characteristics of the ammonia borane crystals are consistent with the NH3BH3 phase indicated by PDF No.74-0894.No impurity peaks are observed.The products of ammonia borane have good crystallinity and high purity.(3)Through the FT-IR and Raman test results,the main bonding properties of the ammonia borane molecules were analyzed,and the absorption peaks were scientifically assigned.(4)The solid-state NMR spectra of ammonia boron were analyzed by 1H NMR and 11 B NMR.The four characteristic peaks of the H spectra were axial-NH,HB-,BH2 and-NH2 from the low field to the right high field.In the B spectra,the quartet of ammonia borane appears at a chemicalshift of-27.37 ppm. |
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