Kinetic Ultrafine Control Of Aluminum Nanosheets And Properties

As the most abundant metal element in the earth's crust,aluminum has a higher plasma density than precious metals such as gold and silver,so its plasma response spans the ultraviolet and visible regions of the spectrum.At present,aluminum nanostructures have shown some promising application prospects,such as photocatalysis,photoelectric detection,sensing and surface enhanced spectroscopy.In the past 20 years,although the controlled synthesis of metal nanomaterials has gradually matured,the synthesis of aluminum nano-materials is very limited.Up to now,the main synthesis methods are top-down methods,such as physical milling,laser etching,electric spark and plane printing,etc.,but these methods still have problems in morphology control or crystallinity,while in liquid phase synthesis,there are more possibilities for morphology control.However,the slow progress in controllable liquid phase synthesis of aluminum is due to its higher reduction potential than precious metals such as gold and silver.Therefore,the precursor and capping agent of aluminum need to be further explored.At present,there are two methods used in liquid phase synthesis.One is the synthesis of aluminum nanoparticles by oxidation-reduction reaction of Al(acac)3 and LiAlH4.Up to now,there are few reports on this method.The other is to obtain aluminum nanoparticles through slow release or thermal decomposition of alumoxane or alumoxane compounds,and the commonly used capping agent is an organic polymer containing N,O and P,but due to the high electropositivity of aluminum,the binding energy with the capping agent is high,which is not conducive to morphology control.Of all the above methods,the most convenient and inexpensive method for synthesis is undoubtedly that the precursor containing Al ions directly reacts with LiAlH4,and the whole reaction can be carried out in one step in solvent.However,this method is undoubtedly the most difficult in regulation,because LiAlH4 reacts with water very quickly,so the reaction must be carried out in organic solvent.However,LiAlH4 as an ionic compound has very low solubility in organic solvents,so the reaction involves solid-liquid two phases,which brings great difficulties to the control of the reaction,which is also the main reason why no regular aluminum nano-materials have been synthesized by this method so far.In the previous work,we determined the synthesis method of aluminum nanosheets with AlCl3 and LiAlH4 as precursors and dissolved oxygen as capping agents.In this work,we established the kinetic model of the reaction according to the synthesis mechanism of aluminum nanosheets,analyzed the process of solid-liquid reaction,and determined the influencing factors that can control the morphology of the products according to the model are oxygen concentration,stirring rate and precursors' activity.The two influencing factors of oxygen concentration and stirring rate in the reaction process are regulated,and the limit of oxygen concentration is determined to be 15%-40%.In addition,stirring rate has regulating effect on atmosphere.We also adjusted the precursor,proving that the introduction of Al(acac)3 can make the morphology of the product more uniform.According to the regulation method,we have prepared samples with different thicknesses to test the 3PL properties of the aluminum nanosheets.The results show that the aluminum nanosheets has 3PL properties,and the nanosheets with a thickness of 2 nm has the best 3PL properties.This work enriched the synthetic methods of aluminum nanomaterials and proveded the potential application prospect in optics.