Size And Shape Dependence Of Photocatalysis Properties And Gas Phase Adsorption/Desorption Properties Of Nano-SnO₂

Compared with bulk materials,nanomaterials have excellent photocatalytic properties and absorption/desorption properties,and are now widely used in many fields,and these properties are affected by size and shape.However,the effects of size and shape on photocatalytic properties,the relationship between the size-dependent photocatalytic properties and size-dependent adsorption properties are unclear;the influence mechanisms of size and shape on gas desorption kinetics and adsorption/desorption are not reported.In this paper,taking the nano-SnO₂ as the research system,spherical and octahedral nano-SnO₂ with different particle sizes were prepared,and the effects of size and shape on photocatalytic properties and gas phase adsorption/desorption properties were studied.In the preparation of nano-SnO₂,the effects of different experimental conditions on particle size and shape were obtained by changing different experimental conditions.In the photocatalytic properties of nano-SnO₂,the photocatalytic selectivity and selectivity mechanism of nano-SnO₂ for different dyes were studied.Secondly,taking the malachite green as the photocatalytic object,the photocatalytic properties of spherical and octahedral nano-SnO₂ with different sizes,and the relationship between the size-dependent photocatalytic properties and size-dependent adsorption properties were studied.In the gas phase adsorption/desorption of nano-SnO₂,the total adsorption amounts of spherical nano-SnO₂ with different adsorption temperatures for NH₃ were determined,and the influences of temperature and particle size on the total adsorption amount were obtained.In addition,the desorption curves of NH₃ on the spherical and octahedral nano-SnO₂ with different particle sizes were determined by temperature-programmed desorption method?TPD?,and then the desorption kinetic parameters?desorption activation energy E_a and the logarithm of the desorption preexponential factor lnA?were obtained according to the desorption equation,the influences of size and shape on the desorption kinetic parameters were discussed.In addition,according to the range and area of the desorption peak,the intensities and amounts of the surface acid sites of spherical and octahedral nano-SnO₂ with different particle sizes were obtained.The relationship between the size-dependent desorption kinetic parameters and size-dependent surface acid sites was discussed,and the influence mechanism of size and shape on the desorption kinetic parameters were explained.The conclusions are as follows,?1?Preparation regularities of nano-SnO₂:The preparation of spherical nano-SnO₂ adopts two schemes.The hydrothermal temperature is the main factor affecting the particle size.With the hydrothermal temperature increasing,the particle size of spherical nano-SnO₂ prepared by the two schemes increases.In addition,for spherical nano-SnO₂?d>20 nm?,with the hydrothermal time increasing,the particle size increases gradually and the morphology is more regular,with the amount of oxalic acid and PVP-K30 increasing,the particle size decreases.For spherical nano-SnO₂?d<20 nm?,the particle size increases with the increase of the concentration of Sn⁴⁺.For the preparation of octahedral nano-SnO₂,the volume of HCl,the volume of water and ethanol are the main factors affecting the particle size and morphology,with the volume of HCl,the volume of water and ethanol increasing,the particle size decreases.According to these rules,the controllable synthesis of spherical and octahedral nano-SnO₂with different particle size can be realized.?2?Effect of size and shape on photocatalytic property:The photocatalytic selectivity of spherical nano-SnO₂ is consistent with its adsorption selectivity.Spherical nano-SnO₂ does not adsorb anionic dyes methyl orange and congo red,and has no photocatalytic effect on these two dyes;however,for the cationic dye base magenta and malachite green,the adsorption rate constant,adsorption rate,photocatalytic rate constant and degradation rate of nano-SnO₂ on malachite green are larger than that of the basic magenta.In addition,the photocatalytic properties of spherical and octahedral nano-SnO₂ for malachite green solution increase with the particle size decreasing;When the equivalent particle diameters of octahedral and spherical nano-SnO₂ are equal,the photocatalytic degradation rate and degradation rate constant of nano-octahedral nano-SnO₂ are higher than that of spherical nano-SnO₂,and the smaller the particle size,the more obvious the effect of shape.Therefore,the particle size and shape have significant effect on the photocatalytic properties of nano-SnO₂.?3?Effects of size and shape on gas phase adsorption/desorption:The total adsorption amount of spherical nano-SnO₂ to NH₃ is affected by the adsorption temperature and particle size.As the adsorption temperature and particle size decrease,the total adsorption amount increases.In addition,the total adsorption amount of NH₃ on spherical nano-SnO₂ is affected by the adsorption temperature and particle size.As the adsorption temperature and particle size decrease,the total adsorption amount increases.Size and shape dependence of desorption kinetics and adsorption/desorption amount are attributed to size and shape dependence of the strength and amount of surface acid sites.The smaller the particle size of spherical and octahedral nano-SnO₂,the stronger the intensity of the surface acid sites and the more the acid sites,which leads to the enhanced adsorption of basic gas NH₃ on nano-SnO₂ and provides more adsorption activity,therefore,both the desorption kinetic parameters and the adsorption/desorption amount increase.As for shape-effect,the intensity of the acid sites on the surface of the octahedral nano-SnO₂ with the same equivalent particle size is stronger than that of the spherical nano-SnO₂,and the acid sites are more.Therefore,Ea_octahedron>Ea_sphere,ln A_octahedron>lnA_sphere.The regulrities of preparation of nano-SnO₂ obtained in this paper can provide guidance for the preparation of nano-SnO₂ with different morphology and particle size;The influence of size and shape on the photocatalytic performance can provide important reference for the adsorption and photocatalysis of nano-SnO₂ and other photocatalysts;The influence of size and shape on gas phase adsorption/desorption provides guidance and reference for the research and application of nano-SnO₂ adsorption,catalysis and desorption processes.