Lu2O3 / g-C3N4 composite material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of inorganic material synthesis, in particular to a Lu2O3 / g-C3N4 composite material as well as a preparation method and application thereof.The Lu2O3 / g-C3N4 composite material is prepared by firstly preparing faint yellow g-C3N4 powder through medium-temperature calcination, then ultrasonically dispersing the faint yellow g-C3N4 powder and Lu (NO3) 3.6 H2O together in deionized water, heating in an oil bath and then performing medium-temperature calcination. Lu2O3 black particles with the diameter of about 5nm are successfully and uniformly dispersed on the surface of the ultrathin g-C3N4 nanosheet with curved surface wrinkles, high thermal stability and strong biocompatibility, so that the active region exposure area and the light absorption and utilization rate of the single g-C3N4 material are remarkably increased, the carrier mass transfer and conduction speed is accelerated, and the light absorption and utilization rate of the single g-C3N4 material is increased. The doping of the rare earth Lu element with a 4f electronic structure additionally inhibits electron-hole recombination, so that the catalytic activity of the Lu2O3 / g-C3N4 composite material in the photodegradation reaction of bromophenol blue is remarkably improved, and the Lu2O3 / g-C3N4 composite material has the advantages of small dosage, short time, high speed and low energy consumption in the catalytic process, good stability and recyclability of the catalyst, and high environmental protection degree of the degraded solution.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic material synthesis, and in particular to a Lu2O3 / g-C3N4 composite material, a preparation method and application thereof. Background Art

[0002] In recent years, with the development of science and technology, natural water resources have been polluted by industrial products including pesticides, metal materials, organic solvents, paints, household chemicals, medicines and domestic sewage. Statistical analysis shows that by 2025, more than 1 billion people in the world will lack clean water, and pollutants in water can also cause various diseases such as respiratory system, intestinal system, nervous system and even cancer. Therefore, water pollution has become one of the urgent problems to be solved in the world today. In the past, wastewater treatment used chemical, biological and physical means applicable to a certain type of pollutants, including filtration, coagulation, reverse osmosis, precipitation, flotation, oxidation, precipitation, evaporation and adsorption. For industrial wastewater containing diverse pollutants such as difficult-to-degrade dyes, pesticides and heavy metal ions, photocatalytic technology, which can alleviate energy shortages, effectively convert solar energy into chemical energy, does not produce secondary pollutants during the treatment process, is simple to operate and has mild reaction conditions, has obvious application advantages.

[0003] Polymer graphite carbon nitride (g-C3N4) is a non-metallic semiconductor material that is non-toxic, low-cost, stable, has a large specific surface area, a bandgap width of less than 3eV, and can respond to visible light. It has attracted widespread attention from scholars in the fields of solar energy conversion, catalysis, and environmental pollution control. It is well known that the high catalytic activity (PCA) of catalysts in photocatalytic technology strongly depends on the visible light response range, photogenerated electrons (e - )-hole (h + ) has an important influence on the separation mobility, charge transfer rate, exposed reactive area, and the formation of hydroxyl radicals (·OH), superoxide radicals (·O2 - ), which are precisely the bottlenecks for the large-scale application of g-C3N4. Therefore, fine-tuning, modification, modification and performance optimization of materials are important ways to improve the photocatalytic activity of g-C3N4. For example, studies have shown that the photocatalytic efficiency of the g-C3N4 / BiVO4 heterojunction formed by the composite of wide-bandgap and narrow-bandgap semiconductors is almost 6.2 times that of a single g-C3N4 sample. In addition, WO3 / g-C3N4 nanocomposites exhibit excellent photocatalytic activity for methyl orange (MO) and tetracycline (TC) under visible light irradiation.

[0004] As a typical rare earth oxide, Lu2O3 has special optical properties. The Lu element has a relatively large radius, an unsaturated 4f and 5d electron configuration, and is easily polarized by adjacent atoms. Its energy band structure can be conveniently adjusted, and various sub-energy levels can be formed on the energy band through Vis-UV or NIR-UV upconversion effects, expanding the utilization of light energy. In addition, it has good stability, small thermal expansion, good mechanical strength and thermal conductivity. In particular, the conduction band position may match that of g-C3N4, and it can enable the photo-generated electron-hole pairs to be transmitted along a fixed direction, promising to form an effective heterojunction structure with g-C3N4 to enhance the catalytic activity and thus play a stronger application potential in the field of photocatalysis.

[0005] In view of the above defects, the inventors of the present invention have finally obtained the present invention through long-term research and practice. Summary of the Invention

[0006] The purpose of the present invention is to solve the problems in the use of existing photocatalysts, such as expensive raw materials, complex preparation processes, narrow light absorption range, inability to fully utilize visible light, slow carrier mass transfer and conduction speed, high electron-hole recombination rate, small exposed active site area, poor material stability and reusability, etc. A Lu2O3 / g-C3N4 composite material, a preparation method thereof and an application thereof are provided.

[0007] In order to achieve the above purpose, the present invention discloses a preparation method of a Lu2O3 / g-C3N4 composite material, which includes the following steps:

[0008] S1, Weigh urea and place it in a muffle furnace, set the heating rate and temperature for calcination to obtain light yellow g-C3N4. After naturally cooling to room temperature, take out the calcined powder solid and grind it fine with an agate mortar for later use;

[0009] S2, Add the g-C3N4 powder prepared in step S1, Lu(NO3)3·6H2O and deionized water into a flask respectively, disperse them by ultrasonic wave, then place them in an oil bath, heat and stir to react, and evaporate the solvent to obtain a light yellow solid powder;

[0010] S3, Pour the powder obtained in step S1 into a crucible and wrap it with tin foil on the outside, place it in a muffle furnace, set the heating rate and calcination temperature, and obtain the light yellow target product Lu2O3 / g-C3N4 composite material after calcination and annealing.

[0011] In the above step S1, the heating rate is 4-6 °C / min, the calcination temperature is 450-650 °C, and the calcination time is 2-5 h.

[0012] In the above step S2, the dosage of the g-C3N4 powder is 200 mg, the dosage of Lu(NO3)3·6H2O is 2-20 mg, and the dosage of deionized water is 20-40 mL.

[0013] In step S2, the ultrasonic dispersion time is 3 - 6 min.

[0014] In step S2, the oil bath heating temperature is 50 - 80 °C, and the heating time is 4 - 8 h.

[0015] In step S3, the heating rate is 4 - 6 °C / min, the calcination temperature is 450 - 650 °C, and the calcination time is 2 - 5 h.

[0016] The present invention also discloses the Lu2O3 / g-C3N4 composite material prepared by the above preparation method, and the application of this Lu2O3 / g-C3N4 composite material as a catalyst in the photocatalytic degradation process of organic dye bromophenol blue.

[0017] The present invention uses the non-metallic semiconductor material graphitic carbon nitride g-C3N4, which is inexpensive, highly stable, biocompatible, and can respond to visible light, as a support material. By a simple impregnation and calcination coupling method, rare earth oxide Lu2O3 nanomaterials with unsaturated 4f and 5d electron configurations and special optical characteristics are loaded to construct a heterojunction, regulating the light absorption range of the narrow-band semiconductor, changing its energy band structure. At the same time, using the better light absorption coefficient of the rigid structure g-C3N4, the energy is transferred to Lu2O3, promoting electron transfer and inhibiting carrier recombination, exposing a larger catalytic active area, so that the Lu2O3 / g-C3N4 composite material plays a synergistic role and exhibits stronger photocatalytic degradation activity for bromophenol blue dye (BPB) than single materials, and can be popularized for the research fields of water treatment and environmental remediation.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. The raw materials for making the composite material in the present invention are inexpensive, the preparation method is simple, and no complex instrument equipment is required;

[0020] 2. The dosage of each reagent in the present invention is small, the main reaction is carried out in the aqueous phase, and it is environmentally friendly;

[0021] 3. During the photocatalytic reaction process, the dosage of the composite material catalyst is small;

[0022] 4. It has strong photocatalytic activity, short time, fast speed, and low energy consumption during the catalytic process;

[0023] 5. The stability and recyclability of the composite material catalyst are good.

[0024] 6. Using the Lu2O3 / g-C3N4 composite material in the present invention as a catalyst to degrade organic dye bromophenol blue, the environmental protection degree of the degraded solution is high. Description of the Drawings

[0025] Figure 1 Schematic diagram of the preparation of the Lu2O3 / g-C3N4 composite material of the present invention and the mechanism of photocatalytic degradation of bromophenol blue;

[0026] Figure 2 TEM images (a), HRTEM image (c), SEM image (d), elemental mapping images (e - h) and EDS spectrum (i) of the 5% Lu2O3 / g-C3N4 composite material prepared by the method of Example 3;

[0027] Figure 3 XPS survey spectrum (a), XPS spectra of C 1s (b), N 1s (c), O 1s (d) and Lu 4d (e) of the 5% Lu2O3 / g-C3N4 composite material prepared by the method of Example 3;

[0028] Figure 4 Comparison chart of the degradation efficiency of bromophenol blue by Lu2O3 material, g-C3N4 material and 5% Lu2O3 / g-C3N4 composite materials prepared by the methods of Examples 1 - 9 under visible light irradiation for 30 min;

[0029] Figure 5 UV - Vis spectra (a - e) of the photocatalytic degradation of bromophenol blue by 1% Lu2O3 / g-C3N4, 3% Lu2O3 / g-C3N4, 7% Lu2O3 / g-C3N4, 10% Lu2O3 / g-C3N4 and 5% Lu2O3 / g-C3N4 composite materials prepared by the method of Example 3 under visible light;

[0030] Figure 6 Degradation efficiency diagram (a) and kinetic linear fitting curve (b) of the photocatalytic degradation of bromophenol blue by 1% Lu2O3 / g-C3N4, 3% Lu2O3 / g-C3N4, 7% Lu2O3 / g-C3N4, 10% Lu2O3 / g-C3N4 and 5% Lu2O3 / g-C3N4 prepared by the method of Example 3;

[0031] Figure 7 Effect of solution pH (a) and catalyst dosage (b) on the photocatalytic activity of the photocatalytic degradation system of bromophenol blue by the 5% Lu2O3 / g-C3N4 composite material prepared by the method of Example 3, cyclic stability test (c) of the 5% Lu2O3 / g-C3N4 composite material prepared by Example 3 and XRD comparison chart (d) of the material before and after the photocatalytic degradation reaction;

[0032] Figure 8Impedance diagrams (a), transient photocurrent response diagrams (b), ultraviolet-visible diffuse reflection spectra diagrams (c), and band gap diagrams (d) of Lu2O3, g-C3N4 prepared by the method of Example 3, and 5% Lu2O3 / g-C3N4;

[0033] Figure 9 N2 adsorption-desorption isotherms (a) and corresponding pore size distributions (b) of the 5% Lu2O3 / g-C3N4 composite material prepared by the method of Example 3. Detailed implementation manners

[0034] The following further elaborates on the above and additional technical features and advantages of the present invention in conjunction with the accompanying drawings.

[0035] I. Preparation of Lu2O3 / g-C3N4 composite material

[0036] Example 1

[0037] The preparation method is as Figure 1 shown:

[0038] (1) Add 10 g of weighed urea into a crucible, cover the crucible lid, wrap it with tin foil outside, place it in a muffle furnace, and calcine it from room temperature to 450 °C at a heating rate of 4 °C / min for 5 h. After naturally cooling to room temperature, take out the calcined pale yellow g-C3N4 solid and grind it fine with an agate mortar for later use;

[0039] (2) Add 200 mg of g-C3N4 powder, different amounts of Lu(NO3)3·6H2O (2 mg, 6 mg, 10 mg, 14 mg, and 20 mg), and 20 mL of deionized water into a 100 mL flask, ultrasonically disperse for 3 min, then place it in an oil bath and set to stir at 50 °C for 8 h, and then evaporate the solvent to obtain a pale yellow solid powder;

[0040] (3) Then place the solid powder obtained by the above method in a crucible and wrap it with tin foil outside, put it into a muffle furnace, and heat it to 450 °C at a heating rate of 4 °C / min for 5 h to finally obtain light yellow Lu2O3 / g-C3N4 composite materials with doping ratios of 1%, 3%, 5%, 7%, and 10% respectively.

[0041] Example 2

[0042] The preparation method is as Figure 1 shown:

[0043] (1) Add 10 g of weighed urea into a crucible, cover the crucible lid, wrap it with tin foil outside, place it in a muffle furnace, and calcine it from room temperature to 500 °C at a heating rate of 5 °C / min for 4 h. After naturally cooling to room temperature, take out the calcined pale yellow g-C3N4 solid and grind it fine with an agate mortar for later use;

[0044] (2) Add 200 mg of g-C3N4 powder, different amounts of Lu(NO3)3·6H2O (2 mg, 6 mg, 10 mg, 14 mg, and 20 mg), and 25 mL of deionized water into a 100 mL flask, ultrasonically disperse for 3 min, then place it in an oil bath, set the temperature at 60 °C, stir and react for 7 h, and then evaporate the solvent to obtain a pale yellow solid powder;

[0045] (3) Then place the solid powder obtained by the above method in a crucible, wrap it with tin foil on the outside, put it into a muffle furnace, and heat it to 600 °C at a heating rate of 6 °C / min and calcine for 4 h to finally obtain light yellow Lu2O3 / g-C3N4 composites with doping ratios of 1%, 3%, 5%, 7%, and 10% respectively.

[0046] Example 3

[0047] The preparation method is as Figure 1 shown:

[0048] (1) Add 10 g of weighed urea into a crucible, cover the crucible lid, wrap it with tin foil on the outside, place it in a muffle furnace, and heat it from room temperature to 550 °C at a heating rate of 5 °C / min and calcine for 3 h. After naturally cooling to room temperature, take out the calcined pale yellow g-C3N4 solid and grind it finely with an agate mortar for later use;

[0049] (2) Add 200 mg of g-C3N4 powder, different amounts of Lu(NO3)3·6H2O (2 mg, 6 mg, 10 mg, 14 mg, and 20 mg), and 30 mL of deionized water into a 100 mL flask, ultrasonically disperse for 5 min, then place it in an oil bath, set the temperature at 70 °C, stir and react for 6 h, and then evaporate the solvent to obtain a pale yellow solid powder;

[0050] (3) Then place the solid powder obtained by the above method in a crucible, wrap it with tin foil on the outside, put it into a muffle furnace, and heat it to 550 °C at a heating rate of 5 °C / min and calcine for 3 h to finally obtain light yellow Lu2O3 / g-C3N4 composites with doping ratios of 1%, 3%, 5%, 7%, and 10% respectively.

[0051] Example 4

[0052] The preparation method is as Figure 1 shown:

[0053] (1) Add 10 g of weighed urea into a crucible, cover the crucible lid, wrap it with tin foil on the outside, place it in a muffle furnace, and heat it from room temperature to 600 °C at a heating rate of 5 °C / min and calcine for 3 h. After naturally cooling to room temperature, take out the calcined pale yellow g-C3N4 solid and grind it finely with an agate mortar for later use;

[0054] (2) Add 200 mg of g-C3N4 powder, different amounts of Lu(NO3)3·6H2O (2 mg, 6 mg, 10 mg, 14 mg, and 20 mg), and 40 mL of deionized water into a 100 mL flask, ultrasonically disperse for 6 min, then place it in an oil bath, set the temperature to 80 °C, stir and react for 3 h, and then evaporate the solvent to obtain a pale yellow solid powder;

[0055] (3) Then place the solid powder obtained by the above method in a crucible, wrap it with tin foil on the outside, put it into a muffle furnace, and heat it to 500 °C at a heating rate of 4 °C / min and calcine for 5 h to finally obtain light yellow Lu2O3 / g-C3N4 composites with doping ratios of 1%, 3%, 5%, 7%, and 10% respectively.

[0056] Example 5

[0057] The preparation method is as Figure 1 shown:

[0058] (1) Add 10 g of weighed urea into a crucible, cover the crucible lid, wrap it with tin foil on the outside, place it in a muffle furnace, and heat it from room temperature to 650 °C at a heating rate of 6 °C / min and calcine for 2 h. After naturally cooling to room temperature, take out the calcined pale yellow g-C3N4 solid and grind it finely with an agate mortar for later use;

[0059] (2) Add 200 mg of g-C3N4 powder, different amounts of Lu(NO3)3·6H2O (2 mg, 6 mg, 10 mg, 14 mg, and 20 mg), and 35 mL of deionized water into a 100 mL flask, ultrasonically disperse for 5 min, then place it in an oil bath, set the temperature to 75 °C, stir and react for 5 h, and then evaporate the solvent to obtain a pale yellow solid powder;

[0060] (3) Then place the solid powder obtained by the above method in a crucible, wrap it with tin foil on the outside, put it into a muffle furnace, and heat it to 650 °C at a heating rate of 6 °C / min and calcine for 2 h to finally obtain light yellow Lu2O3 / g-C3N4 composites with doping ratios of 1%, 3%, 5%, 7%, and 10% respectively.

[0061] Example 6

[0062] The preparation method is as Figure 1 shown:

[0063] (1) Add 10 g of weighed urea into a crucible, cover the crucible lid, wrap it with tin foil on the outside, place it in a muffle furnace, and heat it from room temperature to 600 °C at a heating rate of 5 °C / min and calcine for 4 h. After naturally cooling to room temperature, take out the calcined pale yellow g-C3N4 solid and grind it finely with an agate mortar for later use;

[0064] (2) Add 200 mg of g-C3N4 powder, different amounts of Lu(NO3)3·6H2O (2 mg, 6 mg, 10 mg, 14 mg, and 20 mg), and 40 mL of deionized water into a 100 mL flask, ultrasonically disperse for 6 min, then place it in an oil bath, set the temperature at 80 °C, stir and react for 4 h, and then evaporate the solvent to obtain a pale yellow solid powder;

[0065] (3) Then place the solid powder obtained by the above method in a crucible, wrap it with tin foil on the outside, put it into a muffle furnace, and heat it to 600 °C at a heating rate of 5 °C / min for calcination for 4 h, and finally obtain light yellow Lu2O3 / g-C3N4 composites with doping ratios of 1%, 3%, 5%, 7%, and 10% respectively.

[0066] Example 7

[0067] The preparation method is as Figure 1 shown:

[0068] (1) Add 10 g of weighed urea into a crucible, cover the crucible lid, wrap it with tin foil on the outside, place it in a muffle furnace, and heat it from room temperature to 500 °C at a heating rate of 4 °C / min for calcination for 5 h. After naturally cooling to room temperature, take out the calcined pale yellow g-C3N4 solid and grind it fine with an agate mortar for later use;

[0069] (2) Add 200 mg of g-C3N4 powder, different amounts of Lu(NO3)3·6H2O (2 mg, 6 mg, 10 mg, 14 mg, and 20 mg), and 35 mL of deionized water into a 100 mL flask, ultrasonically disperse for 5 min, then place it in an oil bath, set the temperature at 60 °C, stir and react for 7 h, and then evaporate the solvent to obtain a pale yellow solid powder;

[0070] (3) Then place the solid powder obtained by the above method in a crucible, wrap it with tin foil on the outside, put it into a muffle furnace, and heat it to 500 °C at a heating rate of 5 °C / min for calcination for 5 h, and finally obtain light yellow Lu2O3 / g-C3N4 composites with doping ratios of 1%, 3%, 5%, 7%, and 10% respectively.

[0071] Example 8

[0072] The preparation method is as Figure 1 shown:

[0073] (1) Add 10 g of weighed urea into a crucible, cover the crucible lid, wrap it with tin foil on the outside, place it in a muffle furnace, and heat it from room temperature to 550 °C at a heating rate of 5 °C / min for calcination for 5 h. After naturally cooling to room temperature, take out the calcined pale yellow g-C3N4 solid and grind it fine with an agate mortar for later use;

[0074] (2) Add 200 mg of g-C3N4 powder, different amounts of Lu(NO3)3·6H2O (2 mg, 6 mg, 10 mg, 14 mg, and 20 mg), and 30 mL of deionized water into a 100 mL flask, ultrasonically disperse for 4 min, then place it in an oil bath, set the temperature at 75 °C, stir and react for 5 h, and then evaporate the solvent to obtain a pale yellow solid powder;

[0075] (3) Then place the solid powder obtained by the above method in a crucible, wrap it with tinfoil on the outside, put it into a muffle furnace, heat it to 600 °C at a heating rate of 6 °C / min, and calcine for 3 h. Finally, obtain light yellow Lu2O3 / g-C3N4 composites with doping ratios of 1%, 3%, 5%, 7%, and 10% respectively.

[0076] Example 9

[0077] The preparation method is as Figure 1 shown:

[0078] (1) Add 10 g of weighed urea into a crucible, cover the crucible lid, wrap it with tinfoil on the outside, place it in a muffle furnace, heat it from room temperature to 600 °C at a heating rate of 6 °C / min, and calcine for 3 h. After naturally cooling to room temperature, take out the calcined pale yellow g-C3N4 solid and grind it finely with an agate mortar for later use;

[0079] (2) Add 200 mg of g-C3N4 powder, different amounts of Lu(NO3)3·6H2O (2 mg, 6 mg, 10 mg, 14 mg, and 20 mg), and 20 mL of deionized water into a 100 mL flask, ultrasonically disperse for 3 min, then place it in an oil bath, set the temperature at 65 °C, stir and react for 7 h, and then evaporate the solvent to obtain a pale yellow solid powder;

[0080] (3) Then place the solid powder obtained by the above method in a crucible, wrap it with tinfoil on the outside, put it into a muffle furnace, heat it to 450 °C at a heating rate of 4 °C / min, and calcine for 5 h. Finally, obtain light yellow Lu2O3 / g-C3N4 composites with doping ratios of 1%, 3%, 5%, 7%, and 10% respectively.

[0081] According to the addition amounts of Lu(NO3)3·6H2O in Examples 1 - 9 being 2 mg, 6 mg, 10 mg, 14 mg, and 20 mg, the final products are respectively labeled as 1% Lu2O3 / g-C3N4, 3% Lu2O3 / g-C3N4, 5% Lu2O3 / g-C3N4, 7% Lu2O3 / g-C3N4, and 10% Lu2O3 / g-C3N4.

[0082] II. Performance Characterization of Lu2O3 / g-C3N4 Composites

[0083] Figure 2a is the TEM image of g-C3N4, showing it as an ultrathin nanosheet structure with curved folds, having a relatively large specific surface area, which means a large reactive area and is expected to promote the adsorption of reactants and the diffusion of products. After loading Lu2O3, many black spherical particles were observed to be uniformly dispersed and deposited on the surface of g-C3N4 with a graphite-like phase characteristic ( Figure 2 b), and the diameter of the Lu2O3 particles is about 5 nm. Through the high-resolution transmission electron microscopy image (HRTEM) of the composite material ( Figure 2 c), the lattice fringes of Lu2O3 on the surface of g-C3N4 can be observed, and the lattice spacing is 0.19 nm, corresponding to the (4 0 0) crystal plane of Lu2O3. The SEM image of the 5% Lu2O3 / g-C3N4 composite material ( Figure 2 d) faintly shows that black Lu2O3 is dispersed in the pores of the g-C3N4 material. Combining the elemental surface scan analysis ( Figure 2 e-h) and the EDS image ( Figure 2 I) further confirms the uniform distribution of C, N, O, and Lu elements in the composite material, verifying that Lu2O3 is successfully loaded on the surface of g-C3N4. The chemical composition and morphology of the 5% Lu2O3 / g-C3N4 composite material prepared by the method of Example 3 were characterized by X-ray electron energy spectrometer and electron microscope. As Figure 3 shown in a, the high-resolution XPS total spectrum shows that the peak shapes at binding energies of 287.8, 398.6, 528.8 eV, and 198 eV confirm the presence of C, N, O, and Lu elements in the 5% Lu2O3 / g-C3N4 composite sample. In Figure 3 b, the high-resolution C1s spectrum of the 5% Lu2O3 / g-C3N4 composite material is fitted into two peaks centered at 284.9 eV and 288.2 eV, corresponding to C=C bonds and N=C-N coordination respectively. The spectral peaks of the N 1s spectrum at 398.4 eV and 400.2 eV correspond to N-(C3) and C-N=C ( Figure 3 c). From Figure 3 d, it can be found that two peaks appear in the O 1s spectrum at 531.5 eV and 532.6 eV. The former may be due to surface adsorbed oxygen, and the latter may correspond to the lattice oxygen in Lu2O3. Figure 3 e shows that before the combination of Lu2O3 and g-C3N4, Lu4d 3 / 2 and Lu 4d 5 / 2 appear at 206.3 eV and 196.4 eV respectively. After it is anchored on the surface of g-C3N4, the positions of these two peaks show a slight shift, proving the existence of an interaction between Lu2O3 and g-C3N4.

[0084] III. Evaluation of the photocatalytic degradation effect of Lu2O3 / g-C3N4 composite material on bromophenol blue

[0085] Figure 4 Shows the degradation efficiency (C t / C0) of a single Lu2O3 material, a g-C3N4 material, and Lu2O3 / g-C3N4 composites with a Lu2O3 doping amount of 5% prepared according to the methods of Examples 1-9, respectively, after 30 min of visible light irradiation for the catalytic degradation of the target bromophenol blue.

[0086] To explore the changes in the UV-visible absorption spectra of the composites with different Lu2O3 doping amounts prepared in Example 3 before and after the catalytic degradation of bromophenol blue under visible light irradiation, as Figure 5 shown in a-E, and then calculate the catalytic activity comparison diagram of each material based on the spectrogram ( Figure 6 a). It is observed that when 1% of Lu2O3 is loaded on the surface of g-C3N4 according to the preparation method of Example 3, the degradation rate slightly increases to 42.14% within the same degradation time. When 3% of Lu2O3 is loaded on the surface of g-C3N4, the degradation rate further increases to 71.11%. As the Lu2O3 loading amount increases to 5%, the degradation rate of bromophenol blue reaches the highest ( Figure 6 b). However, when the Lu2O3 loading amount continues to increase to 7% and 10%, the degradation rate decreases to 79.03% and 87.33%, respectively, probably because the excessive loading amount affects the absorption of visible light by g-C3N4, resulting in a decrease in the photocatalytic activity of the composite material. Therefore, the order of photocatalytic activity of all materials is summarized as: 5% Lu2O3 / g-C3N4 > 10% Lu2O3 / g-C3N4 > 7% Lu2O3 / g-C3N4 > 3% Lu2O3 / g-C3N4 > 1% Lu2O3 / g-C3N4 > g-C3N4 > Lu2O3. By fitting the degradation data, it is found that the kinetic curves of all materials conform to the pseudo-first-order reaction kinetics, and the slope k of each straight line can represent the apparent photocatalytic activity. After calculation, it is found that the k value of the 5% Lu2O3 / g-C3N4 composite material prepared by the method of Example 3 is 0.09193 min -1 for single g-C3N4 (k = 0.0144 min -1) It is 6.384 times that of (), and is the largest among all composite materials, which is consistent with the degradation rate order. Therefore, selecting 5% Lu2O3 / g-C3N4 prepared by the method of Example 3 in this system as the best photocatalyst can exhibit excellent characteristics such as less dosage, fast speed, and high removal completeness during the degradation process of bromophenol blue dye.

[0087] Furthermore, various determination conditions including the pH value of the system and the dosage of the catalyst were further optimized for the photocatalytic degradation of bromophenol blue by 5% Lu2O3 / g-C3N4 prepared by the method of Example 3. The results show that the photocatalytic activity of the composite material under acidic conditions is higher than that under alkaline conditions ( Figure 7 a). The possible reason is that more ·OH is generated under acidic conditions, which promotes the progress of the photocatalytic reaction. On the other hand, when the input amount of the catalyst is relatively low, the photocatalytic activity of the composite material is relatively low. With the increase of the catalyst input amount, its photocatalytic activity increases because an appropriate amount of catalyst can effectively increase the solid-liquid contact area during the photocatalytic reaction process, thereby generating more active species and higher photon utilization energy. However, when the catalyst dosage increases to a certain extent, the catalyst particles will cause shielding and scattering effects on light, thereby reducing the absorbed light energy, and the photocatalytic activity will instead show a weakening phenomenon. Therefore, during the photocatalytic reaction process, the optimal input amount of the 5% Lu2O3 / g-C3N4 composite material of the catalyst is 20 mg ( Figure 7 b). Subsequently, the repeated stability of the 5% Lu2O3 / g-C3N4 composite photocatalytic material prepared by the method of Example 3 was studied ( Figure 7 c). The research found that with the increase of the number of repetitions, the adsorption capacity of the composite photocatalytic material did not change, while the photocatalytic activity decreased, which may be caused by a small amount of loss of the catalyst during the recycling process. According to the experimental results, the second, third, fourth, and fifth degradation experiments were calculated to be 2.12%, 6.47%, 9.44%, and 14.08% lower than the first time respectively, indicating that after five cyclic experiments, the degradation ability of the composite material for BPB is still good. Further, the XRD pattern ( Figure 7 d) was used to explore the changes of the catalyst before and after the bromophenol blue degradation reaction, and it was found that the crystal phase structure of the composite photocatalyst had no obvious change compared with the original sample, only the peak intensity decreased slightly, confirming that the 5% Lu2O3 / g-C3N4 composite photocatalytic material prepared by the method of Example 3 indeed shows a potential application prospect for water remediation.

[0088] IV. Analysis of the mechanism of photocatalytic degradation of bromophenol blue by Lu2O3 / g-C3N4 composite materials

[0089] By studying the electrochemical impedance curves and transient photocurrent signals of the g-C3N4, Lu2O3, and the 5% Lu2O3 / g-C3N4 composite material modified electrode prepared in Example 3, the separation and migration of photo-generated carriers were analyzed. Figure 8 a). The results show that the impedance of the 5% Lu2O3 / g-C3N4 composite material prepared according to the method of Example 3 is significantly smaller than that of the g-C3N4 and Lu2O3 single materials, and the 5% Lu2O3 / g-C3N4 composite material calculated by the equivalent circuit diagram fitted by Zview software has the smallest charge transfer resistance, fully confirming that the carrier transfer rate in the bulk phase of this composite material and at the interface with the electrolyte is the fastest, thus enhancing its photocatalytic activity. Transient photocurrent response curve Figure 8 b) shows that in the repeated on-off cycle experiment, the photocurrent density of the 5% Lu2O3 / g-C3N4 composite material is almost always about twice that of the single g-C3N4 material, indicating its effective separation rate of photo-generated electrons and holes. The ultraviolet-visible diffuse reflection spectra data of Lu2O3, g-C3N4, and composite materials with different Lu2O3 doping ratios show Figure 8 c) that Lu2O3 has no absorption in the visible light region, g-C3N4 and Lu2O3 / g-C3N4 composite materials have an absorption edge in the visible light region, and when Lu2O3 is combined with g-C3N4, a slight red shift appears in the optical absorption edge band, broadening the visible light response range of the sample, that is, the composite material has a higher utilization rate of visible light, which helps to generate more photo-generated electron-hole pairs. By calculation, the band gap of g-C3N4 is 2.98 eV, while the band gap of 5% Lu2O3 / g-C3N4 prepared according to the method of Example 3 is 2.86 eV Figure 8 d), and the band gap is significantly narrowed, indicating that the loading of Lu2O3 changes the original electronic structure of g-C3N4 to form a heterojunction, increasing the light absorption range, and thus showing stronger photocatalytic performance.

[0090] The specific surface area and pore size structure of g-C3N4 and the 5% Lu2O3 / g-C3N4 composite material prepared by the method of Example 3 were analyzed by the N2 adsorption-desorption method. Figure 9 a and 9b), it can be observed that both materials show a typical H3 hysteresis loop type IV isotherm at a relative pressure (P / P0>0.7). The pores of the samples are in the mesoporous region (2-50 nm) and are widely distributed. The wide distribution of pores is beneficial to reducing the mass transfer resistance of pollutants entering and leaving the catalyst surface and increasing the potential for the catalyst to be reused. In addition, the specific surface area of g-C3N4 calculated by the BET isotherm is 62 m 2 / g, and the specific surface area reaches 67 m after loading Lu2O3 2 / g, and the average pore size also increases from 20 nm to 29 nm. The possible reason is that during the high-temperature thermal exfoliation process in the preparation reaction, the hydrogen bonds and van der Waals forces between the g-C3N4 layers are weakened, resulting in the splitting of the thick stacked layers of g-C3N4 into thinner stacked layers, which increases by forming new surfaces. The increase in the specific surface area and pore size of the composite material is beneficial to increasing the area of the reaction active region and effectively improving the conduction rate of the photocatalytic reaction.

[0091] Sodium oxalate, p-benzoquinone, and isopropanol were respectively added to the system as hole (h + ), superoxide anion radical (·O2 - ), and hydroxyl radical (·OH) scavengers to systematically analyze the influence of free radicals in the reaction. The experimental results show that when there is no scavenger, after irradiation with visible light for 30 min, the dye degradation rate is 93.8%. When sodium oxalate and p-benzoquinone are respectively added to the photocatalytic system, their degradation rates decrease significantly, about 43.25% and 44.3%, while when isopropanol is added to the system, although the degradation rate decreases, it is not as obvious as that of the former two, and it still reaches 81.19%, confirming that h + and ·O2 - play a key role in the photocatalytic degradation of bromophenol blue by the Lu2O3 / g-C3N4 composite material, while ·OH plays an auxiliary role.

[0092] The above description is only a preferred embodiment of the present invention, which is illustrative rather than restrictive to the present invention. Those skilled in the art understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, but all will fall within the protection scope of the present invention.

Claims

1. A method for preparing a Lu2O3 / g-C3N4 composite material, characterized in that: The following steps are involved: S1, weigh urea and place it in a muffle furnace, set the heating rate and temperature to heat and calcine to obtain light yellow g-C3N4, and after naturally cooling to room temperature, take out the powder solid obtained by calcination and grind it with an agate mortar for later use; S2, respectively add the g-C3N4 powder, Lu(NO3)3·6H2O and deionized water prepared in step S1 into a flask, ultrasonically disperse, place in an oil bath, heat and stir to react, evaporate the solvent to obtain a light yellow solid powder; S3, pouring the powder obtained in step S1 into a crucible and wrapping it with tin foil, placing it in a muffle furnace, setting the heating rate and calcination temperature, and obtaining a light yellow target product Lu2O3 / g-C3N4 composite material after calcination and annealing.

2. The method for preparing a Lu2O3 / g-C3N4 composite material according to claim 1, characterized in that: In the step S1, the heating rate is 4-6°C / min, the calcination temperature is 450-650°C, and the calcination time is 2-5h.

3. The method for preparing a Lu2O3 / g-C3N4 composite material according to claim 1, characterized in that: In the step S2, the amount of g-C3N4 powder used is 200 mg, the amount of Lu(NO3)3·6H2O used is 2 to 20 mg, and the amount of deionized water used is 20 to 40 mL.

4. The method for preparing a Lu2O3 / g-C3N4 composite material according to claim 1, characterized in that: In the step S2, the ultrasonic dispersion time is 3 to 6 minutes.

5. The method for preparing a Lu2O3 / g-C3N4 composite material according to claim 1, characterized in that: In step S2, the oil bath heating temperature is 50-80° C., and the heating time is 4-8 hours.

6. The method for preparing a Lu2O3 / g-C3N4 composite material according to claim 1, characterized in that: In the step S3, the heating rate is 4-6°C / min, the calcination temperature is 450-650°C, and the calcination time is 2-5h.

7. A Lu2O3 / g-C3N4 composite material prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the Lu2O3 / g-C3N4 composite material as claimed in claim 7 as a catalyst in the photodegradation process of the organic dye bromophenol blue.

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