Preparation And Performance Study Of Amorphous SiO₂ Nanoparticles Under Different Catalytic Conditions

SiO₂ nanoparticles have stable chemical properties.They have high hardness,friction resistance and corrosion resistance,also show good optical properties and biocompatibility,widely used in catalysis,architecture,medicine and other fields.The performance of SiO₂ nanoparticles is strongly correlated with their size and dispersity.SiO₂ nanoparticles are also the prerequisite for the preparation of SiO₂ nanoglass.Nanoglass is composed of high-density glass regions at the nanoscale and glass/glass interface with more free volume,which provides the possibility for the toughening of quartz glass.The size,morphology and dispersity of amorphous SiO₂ nanoparticles have an important influence on the preparation of nanoglass.Therefore,it is hoped to synthesize ultrafine,disperse,and amorphous SiO₂ nanoparticles with high purity.It is very difficult to prepare amorphous SiO₂ nanoparticles with ultrafine size and good dispersity by the traditional sol-gel method,and agglomeration becomes more serious with the decrease of particle size.This paper aims to synthesize amorphous SiO₂nanoparticles with small particle size and good dispersity by improving and adjusting the process and parameters of sol-gel method under different catalytic conditions.Under the condition of acidic catalysis,the influence of the type and p H value of catalyst,the type and concentration of surfactant,and the calcination temperature on particle size,morphology and dispersity of SiO₂ particles were explored.In the solvent with a 3:1 volume ratio of methanol/water,using 1.9 mol/L tetraethyl orthosilicate as a silicon source,1 m L hydrochloric acid solution with p H=6 as a catalyst,0.15 g/L polyethylene glycol 1000 as a surfactant,reaction at 30℃for 1 h,calcination at 700℃for 4 h,ultrafine,disperse,well-spherical,and amorphous SiO₂nanoparticles with an average diameter of 5.1 nm,size distribution of 2-10 nm and specific surface area up to 560 m²/g were successfully synthesized.The maximum adsorption capacity of amorphous SiO₂ nanoparticles for Rhodamine B is 28.9 mg/g,and the adsorption model is more consistent with the Langmuir model.Under the condition of alkaline catalysis,the optimum alkaline catalyst for the preparation of small and amorphous SiO₂ nanoparticles was explored.Amorphous SiO₂ nanoparticles with average particle sizes of 7.4 nm,6.8 nm,9.3 nm and 11.5 nm were synthesized by using trimethylamine,triethylamine,tripropylamine and tributylamine as catalysts,but partial agglomeration was found in these particles.Based on triethylamine as a catalyst,the influence of catalyst concentration,surfactant concentration,reaction time,alcohol/water solvent system types,and other factors on the morphology of SiO₂ nanoparticles were explored.In the ethanol/water solvent with a volume ratio of 1:3,0.44 mol/L tetraethyl orthosilicate as a silicon source,0.1 mol/L triethylamine as a catalyst,0.15 g/L hexadecyl trimethyl ammonium bromide as a surfactant,reaction at 60℃for 20 h and the calcination condition was600℃for 4 h,the spherical and amorphous SiO₂ nanoparticles with high purity,good dispersity,and fine size were prepared.The average particle size was 5.8 nm,the size distribution was 2-11 nm and the specific surface area was 386 m²/g.Amorphous SiO₂nanoparticles with an average particle size of 6.4 nm and size distribution of 3-10 nm were prepared in the n-propanol/water solvent,which showed good dispersity and sphericity.With the increase of alcohol chain in alcohol/water solvent system,the characteristic peak position of Si-O-Si bond shifts to higher wave number,and the full width at half maximum decreases gradually,reflecting the increase of Si-O-Si bond angle.The adsorption capacity of SiO₂ nanoparticles with average particle sizes of 5.8nm,7.5 nm,9.3 nm and 11.5 nm for Rhodamine B solution（50 m L 10 mg/L）was84%,82%,80%and 77%,respectively.The result shows that the adsorbability of amorphous SiO₂ nanoparticles increases with the decrease of particle size.In this paper,the amorphous SiO₂ nanoparticles with ultrafine particle size,narrow size distribution and specific surface area up to 560 m²/g were prepared for the first time.The size of SiO₂ nanoparticles was adjusted by changing the chain length of organic amine and alcohol,and the correlation between particle size and performance was verified.This lays a good foundation for the preparation of SiO₂ nanoglass,and also provides an important idea for expanding the application of SiO₂ nanoparticles.