Aqueous Synthesis And Application Of Monodisperse CdS Nanospheres

Three-dimensional photonic crystal（PC）assembled by nanospheres has shown great potential in the structural color field.However,limited by building blocks,the structural color based on the PC with both high brightness and low angle dependence was difficult to achieve.Increasing the refractive index（RI）of the blocks is a potential strategy to solve the above problems.In particular,the PC composed of Cd S spheres has obvious advantages in the field of optical anti-counterfeiting due to their high refractive index（n=2.51）.However,there have certain defects in the synthesis of Cd S nanospheres.In this thesis,monodisperse Cd S nanospheres were synthesized in the aqueous phase by a simple and green method.Meanwhile,the three-dimensional PC was constructed with Cd S spheres as the basic unit.The stability of the Cd S PC was also improved by integrating UV-curable polymers.Furthermore,the Cd S PC with high brightness and low angle-dependent structural color was introduced to the field of anti-counterfeiting.A structural color label of double-sided anti-counterfeiting was designed,which can be decoded/encoded by alcohol wiping.A synthesis strategy was designed to prepare uniform Cd S spheres in an aqueous solution,which was carried out in acidic aqueous using cadmium nitrate as Cd source,thioacetamide as S source,and polyvinylpyrrolidone（PVP）as ligand respectively.In the traditional synthesis process of Cd S nanospheres,the too-fast hydrolysis rate of the metal salt precursor leads to the unbalanced growth of nanospheres and thereby low uniformity.In this work,the Cd²⁺precursor solution was added to the system by the controlled injection at an appropriate rate.The optimal reaction conditions for synthesizing uniform Cd S nanospheres were determined through conditional experiments:The reaction temperature was 70^oC,the amount of PVP was 20 g/L,and the amount of Cd and S source was 133 mmol/L.Meanwhile,controlled injection of Cd²⁺precursor makes it possible to tune the diameter of spheres.Monodisperse Cd S nanospheres with particle sizes ranging from 180 to 410 nm were synthesized.The results of diffraction of X-rays,infrared spectroscopy,and electron microscopy indicated that the cubic phase polycrystalline Cd S nanospheres coated with the PVP were synthesized successfully.A multilayer anti-counterfeiting label based on Cd S PC was designed and fabricated.The Cd S PC with bright and low angle-dependent structural colors was fabricated by the dip-coating method using the glass slide as the substrate.Then,the freestanding Cd S/ETPTA PC films were prepared by integrating UV-curable ethoxylated trimethylolpropane triacrylate（ETPTA）polymer with the Cd S PC.Compared with the PC constructed with low RI spheres,the self-supporting film with high brightness and low angle-dependent structural color ensured the stability of information expression,which has great application prospects in the fields of display and anti-counterfeiting.Subsequently,an anti-counterfeiting label based on a multilayer PC was constructed.The patterned Cd S/ETPTA PC worked as an information layer and a polymer porous structure worked as a shielding layer.The transparency of the shielding layer can be tuned by the wiping of alcohol.Before decoding,the multiple scattering effects caused by the shielding layer could effectively hide the information of the inside information layer.After wiping the label with alcohol tissue,the shielding layer of the label became transparent and the information layer with patterns was displayed.The stable information expression capability and simple decoding method endow the self-supporting label with the potential for application in fields of daily anti-counterfeiting.