Preparation And Application Of Metal Oxide Nanomaterials By Separate Nucleation And Aging Steps Method(SNAS)

With the development of nanotechnology,metal oxide nanomaterials have been widely applied in various fields,and become one of interdisciplinary strategic technology fields in the 21st century.Precipitation method is one of the most used methods to produce metal oxide nanomaterials in commercial process.However,this method still remains a great challenge such as agglomeration of nanoparticles,large particle size and non-uniform size distribution,and suitable morphology,which not only seriously influences product quality,but also becomes a big problem in commercial product.The Separate Nucleation and Aging Steps method(SNAS)effectively separates the crystalline nucleation and the crystalline growth into two steps,simultaneously realizes nucleation and growth of all primary particles at the same time,and then effectively fix the above two problems:large particle size and nonuniform size distribution.This method has been practically applied in 1000 t/a platform to produce layered double hydroxides and magnisum hydroxides nanomaterials.Up to date,however,the formation process of primary particles in its nucleation stage and the influence of the primary particles on the the morphology and performance of the final product are unclear.In this work,we designed and manufacted primary particles capture device,and carefully investigated the formation process of the primary particles as well as the influence of primary particles on the morphology and properties of the final product using magnesium hydroxide and pseudo-boehmite as the probe.Undoubtedly,this work provides the scientific basis for the large-scale controllable preparation of metal oxide nanomaterials.The main results and conclusions were obtained as follows:(1)Based on the rotating liquid-film reactor currently used in the SNAS method,a real-time capture device of primary particles was designed and manufacted.The main parameters such as the reactor slit width,rotor speed and nucleation mixing time were invesitigated to explore the morphology,size and distribution of the primary particles in the nucleation process of magnesium hydroxide.Here,when the slit width was less than 0.2 mm,the rotor speed in the reactor is the main factor to control the product properties,and the average particle size of magnesium hydroxide decreased following the increase of the rotor speed.When the width of the slit was beyond 0.2mm,the nucleation mixing time played the crucial role,and the average particle size in the same outlet increased following the nucleation mixing time at the beginning.For example,the magnesium hydroxide particle size of No.1 outlet increased from 43.72 nm to 57.48 nm with an increase rate of 31.47%.(2)Using SNAS to prepare MgO product,a series of magnesium hydroxide precursor materials with different sizes in a narrow distribution were prepared by adjusting the different nucleation mixing times when the slit width was fixed at 0.2 mm and then calcined at 500?.Aslo,the adsorption performance towards methyl orange dyes were investigated based on magnesium hydroxides powder and strip-shaped magnesium hydroxides.With the increase of the recycle number in the nucleation process from 1 to 10,the particle size gradually increased from 59.12 nm to 140.60 nm and then reached the growth platform at the fourth time.The change trend of particle size for magnesium oxide was the same with that of the precursor,and the average particle size of magnesium oxide increased from 38.83 nm to 61.03 nm.The BET surface of magnesium oxide powder was 93.9 m2·g-1,and the maximum adsorption quantity of methyl orange dye reached 3971.5 mg·g-1,showing the promising adsorption performance of magnesium oxide due to the particle size effect.Also,the strip-shaped magnesium was prepared using pseudo-boehmite dissolved in nitric acid as a binder in a extruded moulding route,and demonstrated excellent dye adsorption performance,good recycling performance and broad industrial application prospects.(3)The pseudo-boehmite was prepared by SNAS under the optimized conditons:The slit width was 0.2 mm and the recycle number was 6 to produce the series of nano-scale pseudo-boehmite precursors with different alcohol washing times.Also,the series of spherical alumina samples were obtained from calcination of spherical pseudo-boehmite at 500?,which were prepared by dispersing the prepared pseudo-boehmite powder in a self-made aluminum sol and followed a developed oil-column shaping technology and spray shaping technology.The effect of the alcohol washings was investigated on the pore structure of spherical alumina.The alcohol washing was one effective way to improve the pore structure of pseudo-boehmite prepared by the SNAS with an increase of 70%in the BET surface area,and 3.4 times in the pore volume.The particle size of the spherical alumina was regulated,and different particle sizes with a narrow distribution.It provides a scientific basis for the controllable preapartion of novel porous catalyst supports and adsorbent materials.