Preparation Of Triplet-Triplet Annihilation Upconversion Core Shell Materials And Their Enhanced Photocatalytic Properties Of CdS

Photocatalysis is a technology that degrades pollutants through a series of physicochemical reaction against the surface of materials by absorbing and converting sunlight under specific conditions.Photocatalytic technology is clean,efficient,safe and free of secondary pollution.Photocatalytic has received widespread attention research.Photocatalysts are the most important part of the photocatalytic process.As research has progressed and prsctical applications have developed,a number of problems have been revealed in their use.On the one hand,photocatalysts have a wide band gap,resulting in their ability to utilize only less than 5% of the ultraviolet light in the sunlight,and their utilization rate of the sunlight is insufficient.On the other hand,photogenerated electrons and holes are prone to compounding,resulting in reduced photocatalytic efficiency.Therefore,it is necessary to optimise and improve photocatalysts.Triplet-triplet annihilation upconversion materials have an anti stokes effect,converting low energy long waves to high energy short waves.However,the presence of oxygen bursts the triplet excited states of the photosensitizers and the acceptor,preventing the upconversion process from taking place.In this thesis,triplet-tripet annihilation upconversion materials were encapsulated inside silica nanocapsules to prevent oxygen bursts.Finally,CdS was loaded onto the nanocapsules surface by insitu growth method to construct composite photocatalysts.Combining upconversion materials with CdS photocatalysts can substantially extend the absorption range of CdS photocatalysts while maintaining their strong catalytic degradation capability.The specific research contents are as follows:(1)The micellar soft-template method was used to construct silica nanocapsules containing upconversion materials,and their morphology was characterized by TEM and SEM.The effects of various synthesis conditions such as ATES: TEOS molar ratio,stirring times,stirring rate and stirring temperature on the core-shell structure of the nanocapsules and the thickness of the shell layer were investigated to lay the foundation for the rational regulation of the nanocapsule morphology.The test results showed that the synthesized nanocapsules had a spherical core shell structure with a smooth surface and good dispersion.Currently,it was possible to synthesize particles with a particle size of(130-300 nm),shell thickness of nanocapsules was 10 nm,20 nm,24 nm,42 nm,56 nm.(2)An upconversion system based on a triplet-triplet annihilation mechanism was constructed using platinum PtOEP as the photosensitizer and DPA as the acceptor.Characterisation of the optical properties of upconverted materials using(UV-vis)and(PL)techniques in combination with upconversion fluorescence spectroscopy.The experimental results showed that the upconversion material had significant absorption around 532 nm and the upconversion emission spectrum was known to occur at 435 nm.Studies have shown that the highest up-transfer fluorescence intensity was achieved at a molar ratio of the photosensitizer to the receptor of 1: 100,dispersed in oleic acid solvent at a concentration of 5 times.Oleic acid solvents were the most stable,as they contain unsaturated fatty acids,which effectively prevent the sudden inactivation of the photosensitizer as well as the triplet state of the receptor by oxygen.The fluorescence spectrum showed that the upconversion fluorescence intensity increased with increasing excitation power.The upconversion fluorescence intensity of nanocapsules with a shell thickness of 10 nm was twice that of nanocapsules with a thickness of 25 nm.The upconversion material coated with silica nanocapsules maintained 60% of the upconversion fluorescence intensity after 20 days under aerobic conditions.The above data fully demonstrated that the nanocapsule encapsulated upconversion system has achieved good results in isolating oxygen.In this paper,nanocapsules with an upconversion quantum yield of 5.2%,which broadened the application range of triplet-triplet annihilation upconversion materials.(3)The CdS nanoparticles were loaded onto the nanocapsule surface by insitu growth method and the composite photocatalysts were characterized by TEM,SEM,EDS,XRD,FT-IR,UV-vis,PL,etc.The results showed that the surface of CdS loaded nanocapsules were rough.And CdS semiconductors with particle sizes below10 nm could be observed.The loading of CdS semiconductors significantly enhanced the absorption of the upconversion material in the visible region.And the highest upconversion efficiency of the composite photocayalyst was achieved at the CdS loading of 0.03 mmol.Finally,the photocatalytic performance of the organic dyes was investigated by their degradation effect under 532 nm laser irradiation.The results showed that the degradation effect of the composite photocatalyst,under 532 nm laser irradiation,showed an increasing and then decreasing trend.The reason was that excessive CdS loading affected the light transmittance of the nanocapsules.Through investigation,it was known that the optimal CdS loading amount was 0.03 mmol.