The Preparation And Photocatalytic Properties Of Carbon Quantum Dots-based Semiconductor Composites

In recent years,the development of nanomaterials and technologies has provided a new direction for the research of high-performance photocatalytic composites.The advantages of the zero-dimensional nanomaterial carbon quantum dots?CQDs?have unique optical properties,excellent water solubility,simple synthetic routes,environmental protection,and good chemical stability,which make it be a good material for developing photocatalysts.In this paper,the titanium dioxide-carbon quantum dots?TiO₂/CQDs?nanocomposites were prepared by sol-gel method.The photocatalytic degradation of rhodamine B?Rh B?was studied for its preparation,performance,and application.Based on the study of metal oxide semiconductor TiO₂/CQDs photocatalytic,non-metallic semiconductor graphite phase carbon nitride?g-C₃N₄?was used as the carrier,and CQDs were loaded to prepare environmentally friendly graphite phase carbon nitride-carbon quantum dots?g-C₃N₄/CQDs?composites and explore composite photocatalytic materials with excellent comprehensive performance.The specific research content is summarized as follows:?1?Using CQDs and tetrabutyl titanate as raw materials,the TiO₂/CQDs composite materials were prepared by sol-gel hydrolysis method.The photocatalytic degradation of Rh B with TiO₂/CQDs experiments were conducted.The results shown that TiO₂/CQDs had the best photocatalytic performance when the calcination temperature was 550?,the calcination time was 120 minutes,and the CQDs content was 5%under the optimum conditions.Characterization of the prepared TiO₂/CQDs composite photocatalyst show that CQDs mainly replace Ti in TiO₂ to form C-O-Ti chemical bonds,promote the formation of TiO₂ crystal defects,improve the use of visible light energy,and broaden the absorption spectrum.Four recycling cycles experiments verified the possibility of practical application of Ti O₂/CQDs in photocatalysis field.In the photocatalytic process,active radicals·O₂^–and h⁺play a key role.?2?Graphite-phase carbon nitride?g-C₃N₄?was prepared by a high-temperature pyrolysis method.And then the non-metallic g-C₃N₄/CQDs composite was obtained by a hydrothermal compound method with CQDs and g-C₃N₄.Using Rh B as model pollutant,the visible light catalytic activity and stability of g-C₃N₄/CQDs were studied.By loading CQDs on the g-C₃N₄,on the one hand,the porosity of g-C₃N₄ was increased,the specific surface area of the catalyst was increased,and so the ability g-C₃N₄/CQDs to adsorb organic pollutants was improved;on the other hand,the spectral absorption side band of g-C₃N₄ exhibited the red-shift and the g-C₃N₄ optical response range was broadened.Studies on the photocatalytic mechanism show that holes?h⁺?,superoxide anion radicals?·O₂^–?,hydrogen peroxide molecules?H₂O₂?,and hydroxyl radicals?·OH?were the main active species in the photocatalytic process.The order of oxidation effect from strong to weak was:h⁺>·O₂^–>H₂O₂>·OH.