Preparation And Photocatalytic Performance Of Amorphous SiO₂ Nanoparticles Catalyzed By Buffer Solution

Amorphous Si O₂ nanoparticles are widely used in environmental adsorption and purification,biomedicine and engineering materials due to their small particle size,high specific surface area and large surface energy.Among the methods for the preparation of amorphous Si O₂ nanoparticles,the sol-gel method is the most widely used,however,the hydrolysis polycondensation reaction rate of silicon source is difficult to control,resulting in a wide particle size distribution.At the same time,with the decrease of particle size,the dispersion of the sample becomes worse.The size,distribution range and dispersion of amorphous Si O₂ nanoparticles affect their performance and application.It is of great significance to prepare amorphous Si O₂nanoparticles with small particle size and narrow distribution range.The main factors affecting the relative rate of hydrolysis and condensation of silicon source are catalyst type,silicon source addition and solvent system.In this paper,buffer solution is used instead of catalyst,on the one hand,it acts as a catalyst to catalyze the hydrolysis and polycondensation reaction of silicon source,at the same time,the relative rate of hydrolysis and polycondensation of silicon source can be effectively controlled by buffering and keeping the p H value constant during the reaction,and amorphous Si O₂nanoparticles with small size,narrow distribution range and good dispersion were prepared.The photocatalytic applications of amorphous Si O₂ nanoparticles are further explored to verify the correlation between the particle size and dispersion of amorphous Si O₂ nanoparticles and their performance.（1）Under the condition of acidic buffer catalysis,the effects of buffer type and p H value,silicon source addition amount and solvent system on the size,distribution range,dispersion and morphology of the samples were systematically studied.The optimum experimental conditions were as follows:in CH₃COOH-CH₃COONa buffer solution with p H=6,water was used as solvent,and 0.125 mol/L ethyl orthosilicate was added,amorphous Si O₂ nanoparticles with an average particle size of 5.3 nm,a size distribution of 3-9 nm and a specific surface area of 418 m²/g were prepared,it has small size,narrow distribution and good dispersion.（2）Under the condition of alkaline buffer catalysis,the effects of the type of buffer solution and its p H value,the amount of silicon source and the solvent system on the size and distribution range,dispersibility and morphology of the samples were systematically studied.The optimum experimental conditions were as follows:in NH₄Cl-NH₃·H₂O buffer solution with p H=11,methanol/water with a volume ratio of1:1 was used as solvent（total volume 200 m L）,and 0.125 mol/L ethyl orthosilicate was added,amorphous Si O₂ nanoparticles with an average particle size of 4.3 nm,a size distribution of 3-7 nm,and a specific surface area of 548 m²/g were successfully prepared,it has small size,narrow distribution range and good dispersion.（3）The g-C₃N₄/Si O₂ composites were prepared by using amorphous Si O₂nanoparticles and dicyandiamide as raw materials.The effects of the addition amount,particle size and dispersion of Si O₂ nanoparticles on the photocatalytic performance of g-C₃N₄/Si O₂ composites were investigated by using rhodamine B solution（50 m L10 mg/L）as the target pollutant.The results showed that the photocatalytic degradation ability of g-C₃N₄/Si O₂ was enhanced with the increase of the amount of Si O₂ nanoparticles,the decrease of particle size and the increase of dispersion.Among them,the g-C₃N₄/Si O₂ composite material prepared from amorphous Si O₂nanoparticles with an average particle size of 4.3 nm has the best photocatalytic degradation effect on rhodamine B solution,and the degradation rate reaches 98.9%in 30 min,the degradation rate was 3.2 times higher than that of g-C₃N₄.