The Synthesis And High Pressure Study Of Aluminium Oxyhydroxide Nanotubes

One-dimensional nanostructured inorganic materials,such as nanotubes and nanowires,are important building materials for nanoscience and engineering.This material can achieve ideal properties that are difficult to achieve with traditional three-dimensional materials,such as rapid charge/mass/heat transfer,an adjustable electronic structure,a confinement effect,and a high surface area.Although considerable progress has been made in controlling the synthesis of inorganic materials,the difficulty will increase significantly when the length of one or more dimensions of an object is reduced to less than 10 nanometers while maintaining the uniformity of morphology and composition.Therefore,the research of synthesizing one-dimensional nanostructured materials with controllable morphology and achieving wide application in the fields of thermodynamics,electricity,magnetism,etc.has always been the enthusiasm of scientists.In this study,one-dimensionalγ-AlOOH nanotubes with controllable morphology were prepared by alcoholysis in one step,and the element composition,microstructure,structural changes under high pressure and other properties were deeply explored.The research results are as follows:（1）One-dimensionalγ-AlOOH nanotubes were prepared by alcoholysis.Conduct multiple sets of comparative experiments to explore the best preparation conditions for crystallinity.The product has good crystallinity and high purity.Through XRD and EDS analysis,it can be determined that it is aγ-AlOOH crystal material with a good element ratio.Space group Amam is an orthorhombic crystal material.After Rietveld refinement,the lattice parameter ofγ-AlOOH nanotubes a=0.368 nm,b=1.203 nm,c=0.288 nm,which matches the standard XRD diffraction pattern Boehmite（JCPDS card No.21-1307）.The samples were analyzed by SEM and TEM and found that the preparedγ-AlOOH crystals were formed by weaving and stacking tubular structures with uniform shape,hollow inside and average aspect ratio,and the surface of the sample was smooth and flawless.After physical experimentation,a singleγ-AlOOH one-dimensional nanotube was obtained,which was vertical and flat,the tube wall was smooth,and basically no impurity adhesion was observed.It has a regular external morphology and good crystallinity.The longitudinal size of the nanotube is approximately in the range of 100-300 nm,its diameter is approximately in the range of 10-20 nm,and the tube wall thickness is approximately in the range of 2-5 nm.（2）Using in-situ high-pressure synchrotron radiation X-ray diffraction（ADXRD）to analyze the mechanical properties of theγ-AlOOH nanotube materials obtained in the experiment and explore the compression behavior at different pressure points,the maximum pressure of the experiment can reach 22.3 GPa.Through data analysis,the following conclusions can be received:During the entire compression process,no additional peaks appeared in the XRD spectrum of the sample.As the pressure increased,the diffraction peaks tended to shift to higher angles,and the diffraction peaks were broadened and the intensity decreased.Under the pressure up to 22.3 GPa,theγ-AlOOH structure of the orthorhombic system remains stable without phase change.The compression of the system has obvious anisotropy,and the compression rate of the lattice in b direction is significantly higher than other directions,which is also derived from the structural characteristics of theγ-AlOOH（The Al-O framework forms a two-dimensional layer connected by hydrogen bonds in boehmite,the hydrogen bonds were perpendicular to the ac plane,due to the structure has strong anisotropy.Therefore,they were most easily compressed in b direction）.This also shows that the compression of the crystal structure is mainly carried out by the contraction and deformation of hydrogen bonds.However,the compression rate of the c-axis of the lattice is different from the previous reports on the compression behavior ofγ-AlOOH nanosheets.There has a new phenomenon which is the change rate of c/c₀is not linear decrease and shows a curvature at 10.6 GPa.We speculate that this feature is depend on their own structural characteristics of the one-dimensionalγ-AlOOH nanotube material.In addition,we did not found that the structure of bulkγ-AlOOH materials mentioned in the previous reports exhibited a pressure-induced superimposed disordered layer displacement along the a-axis during the high pressure research process.We think that this is also caused by the different structure between the one-dimensionalγ-AlOOH nanotube material and the bulkγ-AlOOH material.This study is important for exploring the mechanical properties and compression behaviors of aluminum oxyhydroxide nanocrystals with different structures（compounds containing hydrogen bonds）under high pressure.