Preparation And Properties Of Nitrogen-containing Carbon Quantum Dots/indium Niobate Nanocomposites

At present,environmental pollution is serious,and photocatalysts have received widespread attention due to their non-toxicity and high stability.A scheelite-type indium niobate photocatalyst having visible light response and two octahedrons(NbO6 and InO6)in a unit cell,which is generally considered to facilitate separation of photogenerated electron/hole pairs.It has a narrow forbidden band width(～2.5 eV),good photoinduced hydrophilicity and stable property.At present,the preparation of InNbO4 is mainly based on conventional methods,and it is necessary to develop a new synthesis method.In this paper,the indium niobate material with exposed(002)crystal plane was successfully synthesized by solvothermal method,and the InNbO4 material was composited with nitrogen-containing carbon quantum dots to improve the up-conversion and electron storage characteristics of nitrogen-containing carbon quantum dots.Its use of visible light improves the photocatalytic performance of InNbO4 materials.The main research contents of this paper are as follows:(1)Preparation of InNbO4 material and its photocatalytic properties.InNbO4 cubes with exposed(002)crystal planes were prepared by solvothermal method using In(NO3)3·4.5H2O and NbCl5 as raw materials.The solvothermal temperature and solution synthesis pH were studied for the crystal structure and morphology,light absorption performance and specific surface of InNbO4.The photocatalytic performance of InNbO4 prepared under different pH conditions was studied by using the quinolone antibiotic pefloxacin as the degradation target.The experimental results show that the morphology and properties of InNbO4 materials synthesized under different temperature and pH conditions are quite different.The reaction system has a forbidden band width of 2.51 eV and a specific surface area of 34.20 m2/g at 250℃ and pH5.The synthesized InNbO4 material having a(002)crystal plane has a higher photocatalytic effect.The initial loading of the catalyst,the initial concentration of the contaminant and the initial pH of the solution were studied by using the InNbO4 material with(002)crystal plane synthesized under the optimal conditions.The results showed that the catalyst dosage was 1.5 g/L,and the initial concentration of pefloxacin was 15 mg/L and the initial pH of the solution was 7.04.Cyclic experiments show that the sample is stable.Mechanism experiments show that ·O2-and holes are the main active species in the degradation process.The photocurrent experiment results show that the light response intensity of InNbO4-pH5 is the highest.(2)Preparation of nitrogen-containing carbon quantum dots(N-CQDs).The fresh ecuadorian shrimp shell was used as raw material,and the nitrogen-containing carbon quantum dots were obtained by one-step hydrothermal method at 180℃ for 12 hours.The N-CQDs were characterized by XRD,TEM and PL.The XRD results show that the broad peak near 22°is the peak of N-CQDs.The TEM results show that the size of the obtained nitrogen-containing carbon quantum dots ranges from 1 to 5 nm.From HRTEM,the lattice spacing is 0.3 nm.This is the(002)crystal plane of N-CQDs.And its photoluminescence performance is very good,it is light yellow under sunlight,blue fluorescence under ultraviolet light;elemental analysis results show that the sample has nitrogen content of 9.89%,carbon content of 40.77%,and hydrogen content is 5.71%.XPS results show that the nitrogen-containing carbon quantum dot samples contain O,N and C elements,which are further proved to be N-CQDs materials.The above results show that the photoluminescence properties of nitrogen-containing carbon quantum dots can be used to improve the visible light response,thereby improving its photocatalytic performance.(3)Preparation of nitrogen-containing carbon quantum dots/indium niobate nanocomposites and their photocatalytic properties.InNbO4 and N-CQDs were used as raw materials,and the synthesis ratios of N-CQDs/InNbO4 composite were 1 wt%,3 wt%,5 wt%and 7 wt%,respectively.XRD results showed that the crystal faces of the N-CQDs/InNbO4 materials in the respective proportions were consistent with the standard cards.The high-resolution XPS spectra showed that the materials contained In,Nb,O and N elements,indicating two substances were combined successfully;TEM(HRTEM)analysis showed that the composite material contained both the(002)crystal plane of N-CQDs and the(120)crystal plane of InNbO4 material,which further proved that the two materials were successfully combined.UV-vis DRS results showed that the forbidden band width of InNbO4 is 2.70 eV,and the N-CQDs/InNbO4 bandgap reduction at the 3 wt%composite amount is the most,which is 2.20 eV,which proves that the nitrogen-containing C quantum dots have the effect of broadening the light absorption range.By combining with N-CQDs,the photocurrent intensity is improved,indicating that the 3 wt%N-CQDs/InNbO4 composite can effectively absorb photons and delay the recombination of photogenerated carriers.Repeated experiments show that the composite has good stability and can be reused.The photocatalytic degradation properties of N-CQDs/InNbO4 composites were evaluated by using ipronidazole as the degradation target.The experimental results showed that when the concentration of propidazole is 10 mg/L,the amount of catalyst is 1.5 g/L,and the irradiation time is 3 h,the photocatalytic degradation performance of 3 wt%N-CQDs/InNbO4 composites is the highest,which can reach 97.19%.