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Core-shell Nano-structures For Light-energy Conversion In Photocatalysis And Photothermal Therapy

Posted on:2018-04-01Degree:MasterType:Thesis
Country:ChinaCandidate:B B ChenFull Text:PDF
GTID:2334330512490110Subject:Inorganic Chemistry
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In recent years,energy consumption and environmental contamination has become the most serious issue,which brings about various diseases,such as cancer,that threatens the human survival.Instead,the sun and solar energy,as a renewable and clean energy,has attracted wide attention.Solar energy conversion,including photocatalysis and photothermal therapy are the effective ways to resolve the problems from the environmental deterioration and tumor diseases.Photocatalysis uses the photo-induced electrons or holes to generate new substances by redox reaction,where light is converted into chemical energy.Photocatalysts with high activity and selectivity are necessary for effective light energy conversion,therefore design and fabrication of the photocatalysts is fundamentally important for improving the efficiency of the light energy conversion.Cerium dioxide,as an n-type semiconductor,has the capacity of Ce(?)-Ce(?)redox cycle as well as the storage and release of O,and therefore it has been widely used in photocatalytic reactions.However,due to theband gap ofCeO2is 3.2?eV and it only responds to ultraviolet light.The carrier mobility in CeO2 is low and the electrons cannot be transferred to the surface to participate in chemical reactions.These defects limit its usage in the actual production and application.The light is focused on the surface of the precious metal nanoparticles due to the local surface plasmon resonance,and the utilization of the sunlight is greatly improved.In addition,adding another kind of metal with low cost will be helpfulfor enhancingconduction in CeO2.Photothermal therapy(PTT)is a recent developed method of tumor theory.PTT transforms light energy into heat to kill the tumor tissue and cancer cell,which is targeted therapy with high cure rates and low toxic and side effect.The most developed PTT including the noble metals or the carbon materials have demonstrated high light-to-heat conversion,but have potential seriousconcern for the nonbiodegradablity,which severely restricts their further application in photothermal treatment.Organic molecules have structures that are facilelytailored and easily degradable,providing the potential near-IR(NIR)responsive PPTs.However,the reported organic molecular PPs are generally unstable toward light irradiation or heating,which showed serious attenuation of photothermal conversion.Moreover,the organic molecules bearing the hydrophobic structure,which hindered the adsorption and function in vivo.Perylene imides(PDIs)are molecules with highly conjugated structure,which have high light and heat stability.PDIs are developed as photoelectric materials,such as luminescent materials and fluorescence probe,on account of their high absorbance in the visible region and the uniquefluorescence quantum efficiency.Quite recently,PDIs have also beenexploredfor bioimaging.Silica is a non-toxic biocompatible material with high transparence that is widely used in biomedical applications such as biologic imaging,drug release and nanotherapy.Fabrication of SiO2coated PDIs may provide novel PTT agents with water solubility and high NIR photo-conversion efficiency.Focusing on the light energy conversion and utilization,in this paper,two series of core-shell nanocomposites are designed and fabricated to investigate the photocatalytic oxidation of the benzyl alcohol,as well as the NIR photothermal therapy,respectively.1.Supported bimetallic nanomaterials are promising in photocatalysis due to the multi-component interaction between metals and between metals and carriers.Au and Cu nanoparticles were deposited respectively or together on CeO2nanorods by an in-situ reduction method to make monometallic catalysts(AuCeO2 and CuCeO2)and a series of bimetallic catalysts(Au8Cu2CeO2,Au5Cu5CeO2 and Au1Cu9CeO2),respectively.Photo-assisted oxidation of benzyl alcohol to benzaldehyde was performed over the above samples,and the reactivity presented a parabolic plot with the increase of Cu content,reaching the summit at Au1Cu9CeO2.Inpouring of Cu enlarged the specific surface area and generated more oxygen vacancies,which are significant for improving the photocatalytic performance.The intimate correlation between the reactivity and the concentration of the oxygen vacancies provides that surface of the CeO2 support with large number of oxygen vacancies serve as the active sites for the aerobic oxidation.Accordingly,a mechanism is proposed for the photocatalytic efficiency enhancement as the function of the Cu concentration.Particularly,the catalyst Au1Cu9@CeO2 containing quite low amount of Au species,demonstrated the best catalytic activity,high selectivity and stability,which is strongly desired for the cost-effective catalysts.The advantages of in-situ reduction synthetic method to obtain supported multi-component nanomaterials were one-step strategy.No toxic organic reagents and dispersing agents were employed and reaction occurred at low temperature in our system,simplifying the synthesis procedures greatly and being fully in line with the conditions of green chemical synthesis.2.Despite tremendous effort to explore organic photothermal agents with high near-infrared(NIR)absorbance and good biocompatibility,the photo-stability remains a serious concern.In this work,a new photothermal therapy agent based on perylene diimide(PDI)-encapsulated PEGylated silica nanocapsules(SNCs)is developed.The spatial confinement of PDI in the SNCs induces aggregation of PDI molecules associated with a strong NIR absorption band and negligible fluorescence emission.Unprecedented photo-stability is achieved for the PDI-encapsulated SNCs owing to the robust molecular skeleton of PDI.Furthermore,the PDI-encapsulated SNCs with low cellular cytotoxicity demonstrates excellent in vivo imaging and photothennal efficacy in tumor ablation in a tumor-bearing zebrafish model,and thus provide a new photothermal agent potentially useful in clinical applications.
Keywords/Search Tags:light energy conversion, photocatalysis, photothermal therapy, CeO2, AuCu alloy, PDI, silica nanocapsules
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