CN110639559A

CN110639559A - Composite photocatalyst

Info

Publication number: CN110639559A
Application number: CN201910843551.7A
Authority: CN
Inventors: 崔春娜; 黄继涛; 颜桂炀
Original assignee: Ningde Normal University
Current assignee: Ningde Normal University
Priority date: 2019-09-06
Filing date: 2019-09-06
Publication date: 2020-01-03

Abstract

The invention provides a composite photocatalyst, which comprises Bi dissolved in a polar solvent₁₀O₂₅Br₁₂And reduced graphene oxide, said Bi₁₀O₂₅Br₁₂And the reduced graphene oxide adsorption/desorption equilibrium, wherein the Bi₁₀O₂₅Br₁₂And the mass ratio of the reduced graphene oxide to the reduced graphene oxide is 150: 8-12.

Description

Composite photocatalyst

Technical Field

The invention relates to a composite photocatalyst, in particular to a bismuth-series composite photocatalyst.

Background

With the development of the social political economy, environmental problems are more and more concerned by people. The photocatalytic technology is characterized by low energy consumption, high reaction speed, complete catalytic degradation and no selectivity, so the photocatalytic technology is applied to pollution treatment and environmental protection. The research shows that most semiconductor materials belong to the category of photocatalytic materials, and the semiconductor photocatalytic materials have good application prospects in the aspects of treating air pollution, water pollution, soil pollution and the like by utilizing the principle that the semiconductor photocatalytic materials can be activated by stimulation under the condition of illumination. The technology is a green environmental management technology and has wide application prospect.

Referring to fig. 1, a semiconductor crystal band structure has a low-level Valence Band (VB) containing a large number of electrons and a high-level Conduction Band (CB) having a relatively large number of empty-space valence bands and filled with filled electrons. There is a difference between the conduction band energy and the valence band energy, which we refer to as the forbidden bandwidth. When a semiconductor is exposed to light energy greater than or equal to the forbidden band width, the original electrons in the valence band change to an excited state, and then jump to the conduction band, and a reduction-active electron (e) is formed in the conduction band^-) And also leaves a positively charged hole (h) in the valence band⁺) This hole tends to have high oxidation activity.

Photocatalysts are the main core of photocatalytic technology. According to the report, the published photocatalytic article in recent years shows an exponential growth trend. The literature relating to titanium dioxide as a photocatalyst occupies almost a large part, and TiO currently occupies the majority₂Photocatalysts have been widely used in environmental remediation, although TiO s have been used₂No toxicity, high efficiency, good environmental protection and chemical inertia, but because of TiO₂The band gap of (a) is large, so that it can only respond to absorption of ultraviolet light, and quantum efficiency is low, and it is difficult to uniformly and firmly load on a carrier. These significant drawbacks greatly limit its further participation in practical applications. To compensate TiO₂Due to the defects of the photocatalyst, a novel visible light responding photocatalyst is needed to be prepared. Therefore, the recent discovery of bismuth-based photocatalysts has made up for the lack of titanium dioxide. The bismuth-based photocatalytic material has very good visible light absorption capability and very strong organic matter degradation effect due to the very characteristic electronic structure of the bismuth-based photocatalytic material.

Therefore, it is necessary to provide a bismuth-based photocatalytic material having a good photocatalytic performance.

Disclosure of Invention

Further, the reduced graphene oxide is a small-particle-size reduced graphene oxide with a particle size of less than 4 microns or a large-particle-size reduced graphene oxide with a particle size of more than 4 microns.

Further, said Bi₁₀O₂₅Br₁₂The mass ratio of the small-particle-size reduced graphene oxide to the large-particle-size reduced graphene oxide is 150: 8-10: 8 to 10.

Within 45min of xenon lamp irradiation, the degradation rates of the three photocatalysts are gradually improved, and Bi is added₁₀O₂₅Br₁₂The small-particle-size RGO composite material has the fastest promotion amplitude, and Bi₁₀O₂₅Br₁₂The photodegradation rate of small-particle RGO is 96% relative to Bi alone₁₀O₂₅Br₁₂Photocatalyst, degradation rate of which is improved by 38%, Bi₁₀O₂₅Br₁₂Photocatalytic performance of/RGO compared with single Bi₁₀O₂₅Br₁₂And the method has good promotion. Addition of RGO can increase Bi₁₀O₂₅Br₁₂The catalytic performance of (2).

Drawings

Fig. 1 shows the photocatalytic principle.

FIG. 2 shows the molecular formula of RGO.

FIG. 3 shows the molecular formula of rhodamine B.

FIG. 4 shows Bi₁₀O₂₅Br₁₂X-ray energy spectrum of the catalyst.

FIG. 5 shows Bi₁₀O₂₅Br₁₂And Bi thereof₁₀O₂₅Br₁₂And XRD diffractometry results of the composite of RGO.

FIG. 6 shows Bi₁₀O₂₅Br₁₂、Bi₁₀O₂₅Br₁₂Large particle size RGO and Bi₁₀O₂₅Br₁₂The effect graph of rhodamine B degradation of small-particle-size RGO samples in an ultraviolet visible spectrophotometer is shown.

FIG. 7 shows Bi₁₀O₂₅Br₁₂、Bi₁₀O₂₅Br₁₂Large particle size RGO and Bi₁₀O₂₅Br₁₂A fit line of small-particle-size RGO for degrading rhodamine B.

FIG. 8 shows Bi₁₀O₂₅Br₁₂、Bi₁₀O₂₅Br₁₂Large particle size RGO and Bi₁₀O₂₅Br₁₂Graph showing the effect of photodegradation rate of small-particle-diameter RGO.

Detailed Description

The invention provides a preparation method of a composite photocatalyst, which comprises the following steps:

step S1: preparation of Bi₁₀O₂₅Br₁₂；

Step S2: preparing reduced graphene oxide; and

step S3: the Bi is added₁₀O₂₅Br₁₂And adding the reduced graphene oxide into a polar solvent, and stirring to establish an adsorption/desorption equilibrium.

In step S1, preparing Bi₁₀O₂₅Br₁₂The preparation method specifically comprises the following substeps:

step S11: 3.5mol of Bi (NO) are weighed₃)₃Putting the mixture into a 250mL beaker, adding 100mL of glycol solution into the beaker, and uniformly stirring the mixture by using a glass rod to obtain a solution A;

step S12: weighing 3.5mol of KBr, putting the KBr into a 100mL beaker, slowly adding 50mL of ethylene glycol into the beaker, and fully stirring the resulting solution by using a glass rod to obtain a solution B;

step S13: slowly dropwise adding the solution B into the solution A by using a rubber head dropper, stirring for one hour by using a magnetic stirrer to obtain a solution called as a mixed solution C, heating and stirring the solution for 5 hours, cooling to room temperature, and continuing stirring for 0.5 hour;

step S14: slowly and dropwise adding the mixed solution C into a solution of 100mL to 200mL of ethanol and distilled water with the volume ratio of 10:1 by using a rubber head dropper to obtain a white precipitate D;

step S15: washing the white precipitate for multiple times, preferably three times, by using distilled water and absolute ethyl alcohol, and drying the white precipitate obtained by suction filtration in an oven at the temperature of 80 ℃ for two hours to obtain BiOBr;

step S16: uniformly dispersing the white precipitate D in proper amount of glycol in ultrasound, cooling and refluxing for 2h at 100 ℃, cleaning the white precipitate D with distilled water and absolute ethyl alcohol for a small amount of times, drying the filtered precipitate in an oven at 80 ℃ for 1h, transferring the obtained white powdery substance D into a muffle furnace, heating to 600 ℃ at a heating rate of 2 ℃/min, and keeping the temperature for 3h to obtain yellow Bi₁₀O₂₅Br₁₂Yellow nanosheets.

Understandably, the Bi₁₀O₂₅Br₁₂The preparation method can be a solvothermal method, high temperature and high pressure are provided by adopting the solvothermal method, and reaction parameters are controlled, so that a proper reaction environment can be created, and insoluble or insoluble substances can be dissolved and recrystallized. The reaction not only controls the particle size and the shape of the product, so that the prepared powder material has small crystal particles, uniform distribution and less agglomeration, but also the obtained compound is very complex. Solvothermally reacting Bi (NO)₃)₃·5H₂Preparing Bi by taking O and CTAB as raw materials and ethylene glycol as solution₁₀O₂₅Br₁₂。

Understandably, the Bi₁₀O₂₅Br₁₂The preparation method of (1) can also be prepared by a microwave method. Microwaves are electromagnetic waves with a frequency between 300MHz and 300 GHz. The microwave method is prepared by taking bismuth nitrate and CTAB as raw materials. Microwave method improves Bi₁₀O₂₅Br₁₂The quality of (c).

In step S2, the method for preparing reduced graphene oxide RGO includes the following specific steps:

step S21: 2.5g of graphite powder and 1.25g of sodium nitrate were weighed and poured into a three-necked flask, to which 60mL of 95% concentrated H was added₂SO₄Stirred in an ice bath for 30min, during which 7.5g KMnO was slowly added₄Adding into a flask, keeping the temperature below 20 ℃, and then stirring at room temperature for 12 h;

step S22: after adding 75mL of distilled water to the flask and oil bathing at 98 deg.C, the mixture turned a yellowish brown color and was incubated for 24 h. Finally, 25mL of 30% H was added to the flask₂O₂Centrifuging, washing the obtained product with a 5% hydrochloric acid solution and distilled water for a few times, and drying at 60 ℃ to obtain brown Graphene Oxide (GO);

step S23: accurately weighing 100mg GO powder by using an analytical balance, pouring the GO powder into a 250mL beaker, adding 100mL distilled water, carrying out ultrasonic treatment for 1h by using an ultrasonic cleaning instrument to form brownish yellow stable suspension, heating the suspension in a water bath, dropwise adding 2mL hydrazine hydrate solution into the suspension, carrying out full reaction for one day, continuously stirring until the suspension is slowly changed into a black solution, filtering the solution until black solids are found, filtering the black solids, washing the black solids for a plurality of times by using a small amount of methanol and distilled water, and drying the black solids in an oven to obtain the GO powder.

RGO can be prepared by chemical vapor deposition. The chemical vapor deposition method is a reaction of reactants in a gaseous state, and then graphene is formed on the surface of a substrate after being formed into a solid. The method is an important method for preparing high-polymerized graphene. The chemical vapor deposition method mainly decomposes organic gas or liquid at high temperature to decompose carbon atoms by high temperature reaction, and graphene is formed and deposited on a metal substrate. And then removing the metal matrix through chemical corrosion to finally obtain the graphene sheet.

RGO can also be prepared by mechanical exfoliation. The earliest preparation method of graphene was a mechanical exfoliation method, specifically isolating graphite from a graphite sheet, and adhering two faces of the graphite sheet to an adhesive tape. Repeating the steps, the graphite sheet isolated by the stripping method becomes thinner and thinner, and finally, the graphene is successfully prepared when the graphite sheet is thin to a certain degree, namely, the graphite sheet is constructed by only one layer of carbon atoms.

In step S3, the aqueous solution may be distilled water. In step S3, Bi is preferably Bi₁₀O₂₅Br₁₂And the mass ratio of the reduced graphene oxide to the reduced graphene oxide is 150: 8-12. More preferably, the Bi₁₀O₂₅Br₁₂And the mass ratio of the reduced graphene oxide to the reduced graphene oxide is 150: 9-10. It can be understood that by controlling the Bi₁₀O₂₅Br₁₂And the mass ratio of the reduced graphene oxide, whereby the Bi can be made to be₁₀O₂₅Br₁₂And the reduced graphene oxide can rapidly reach an adsorption/desorption equilibrium.

The invention also provides a composite photocatalyst which comprises Bi dissolved in a polar solvent₁₀O₂₅Br₁₂And RGO. The polar solvent is water. RGO can be small particle size RGO or large particle size RGO. Size or granule of small particle size RGOThe diameter is less than 4 microns with a minimum dimension of 0.1 microns. In contrast, the large-particle-diameter RGO is larger than 4 micrometers in size, and the average size thereof is in the range of 5 micrometers to 7 micrometers, and the maximum size of the large-particle-diameter RGO is 13 micrometers. The thickness of RGO ranges from 0.68 nm to 1.6 nm. The small particle size RGO is less than 1 nanometer thick.

The composite photocatalyst has the beneficial effects that:

first, Bi₁₀O₂₅Br₁₂Is a derivative of bismuth oxyhalide photocatalyst, which is a novel visible light photocatalyst because Bi₁₀O₂₅Br₁₂The band gap between the optics of this material is narrower than that of BiOBr, and the photocatalytic activity will therefore also become higher. Bi₁₀O₂₅Br₁₂The conduction band potential of the BiOBr is much higher than that of the BiOBr and even larger than the potential energy of decomposing hydrogen, and Bi₁₀O₂₅Br₁₂The semiconductor material is in transition with direct band gap, the optical forbidden band width of the semiconductor material is 3.24eV, the semiconductor material not only can show very strong ultraviolet light emission performance, but also has very good photocatalytic activity under the irradiation of ultraviolet light.

Second, all carbon atoms of the Reduced Graphene Oxide (RGO) two-dimensional planar honeycomb structure are sp2 hybridized carbon atoms, with an in-plane C ═ C bond length of 0.142 nm. RGO has a specific structure of a single atomic layer so that it has unique physicochemical properties including a high surface area, a good adsorption capacity, a strong mechanical strength, and excellent stability and conductivity, and an ideal catalyst carrier must have these properties. RGO is removed from the oxidized group of graphene oxide by a series of chemical methods, and thus the structure of RGO is stable. Please refer to fig. 2, which shows the molecular formula of RGO.

Thirdly, as the composite photocatalyst comprises Bi₁₀O₂₅Br₁₂And RGO, the catalytic effects of the two are mutually enhanced, so that the composite photocatalyst has a good catalytic effect.

Hereinafter, rhodamine B is taken as an example to verify the purification effect of the composite photocatalyst, and the following experiment is performed to prove the good catalytic effect.

1. Performance test of composite photocatalyst

The following performance tests were conducted with rhodamine B as the contaminant. Rhodamine B is a toxic red carcinogen with the molecular formula C₂₃H₃₁ClN₂O₃The molecular weight is 479.029, rhodamine B is easily soluble in water and ethanol, and the maximum absorption wavelength of the rhodamine B is 552 nm. The molecular formula of rhodamine B is shown in figure 3.

The specific performance testing steps are as follows: four 250mL beakers and stirrers were washed for use, 5mg of rhodamine B was weighed on an analytical balance, and diluted to 1L with distilled water to prepare 5mgL^-1Then four portions of 150mg Bi weighed by an analytical balance₁₀O₂₅Br₁₂The catalyst was dispersed in 100mL of four cups of RhB (5 mgL)^-1) In the solution, one cup was used as a reference, and 10mg of large-particle-size RGO and small-particle-size RGO were added to the other two cups, respectively, and agitated for one hour in the dark to establish adsorption/desorption equilibrium. Then, a 500W xenon lamp (400nm) was used as a light source to illuminate the sample for 45min, 10mL of the solution was taken out every 5min, and 8000r.min was used^-1Centrifuging for 15min to remove catalyst, and collecting supernatant.

2. Structural testing and performance characterization

2.1X-ray Spectroscopy (EDS) analysis

The composition of the chemical elements of the catalyst was semi-quantitatively analyzed by EDS. The prepared sample is subjected to point taking analysis under the conditions that the working voltage is 15kV, the amplification factor is 10um, and the working distance is 10 mm.

2.2XRD diffraction method

The obtained RGO and Bi₁₀O₂₅Br₁₂、Bi₁₀O₂₅Br₁₂Large particle size RGO, and Bi₁₀O₂₅Br₁₂The/small-particle-diameter RGO sample is put into an X-ray powder diffractometer for detection, and data obtained by scanning the sample in a 2 theta-5-80 DEG range are analyzed by using a software originPro8.0.

2.3 ultraviolet Spectroscopy

The supernatant solutions obtained in the experiment were measured for absorbance at a wavelength of 554nm using a UV-vis spectrophotometer with distilled water as a reference solution and a base line. The obtained data are mapped by using the originPro8.0 software for analysis and comparison.

2.4 photocatalytic efficiency

The photocatalytic effect of the sample is evaluated by analyzing the concentration change of rhodamine B under the condition of visible light, the decomposition rate of the rhodamine B is calculated by measuring the absorbance change of the solution before and after reaction, and the calculation formula is

Wherein A0 is the absorbance of the initial dye solution; a is the absorbance of the dye solution at time t.

3. Experimental results and discussion

3.1X-ray Spectroscopy (EDS) analysis

Please refer to fig. 4, which shows Bi₁₀O₂₅Br₁₂The X-ray energy spectrum of the catalyst shows that the catalyst only contains three elements of O, Br and Bi, the atomic percentages are obtained according to an EDS spectrum, wherein the relative atomic mass of O atoms accounts for 11.58 percent of the molecular mass, the relative atomic mass of Br atoms accounts for 27.8 percent of the molecular mass, and the relative atomic mass of Bi atoms accounts for 60.61 percent of the molecular mass, and the molecular formula of the molecule is Bi according to calculation₁₀O₂₅Br₁₂。

3.2 analysis of the results of XRD diffraction

Referring to FIG. 5, Bi is clearly seen₁₀O₂₅Br₁₂And Bi thereof₁₀O₂₅Br₁₂And RGO, it is noted that the unique peaks at 28.9 °, 29.7 °, 30.9 °, 31.7 °, and 39.7 ° can be indexed to Bi₁₀O₂₅Br₁₂Respective characteristic crystal planes of (040), (208), (214), (17) and (06), however, for Bi₁₀O₂₅Br₁₂And RGO, there is no characteristic peak of RGO, which is probably due to the small amount of RGO,no peak of the typical RGO is detected.

3.3 analysis of photocatalytic Performance results

3.3.1 analysis of the ultraviolet Spectroscopy results

Please refer to fig. 6, which shows Bi₁₀O₂₅Br₁₂、Bi₁₀O₂₅Br₁₂Large particle size RGO and Bi₁₀O₂₅Br₁₂The effect graph of rhodamine B degradation of small-particle-size RGO samples in an ultraviolet visible spectrophotometer is shown. Please refer to fig. 7, which shows Bi₁₀O₂₅Br₁₂、Bi₁₀O₂₅Br₁₂Large particle size RGO and Bi₁₀O₂₅Br₁₂A fit line of small-particle-size RGO for degrading rhodamine B.

As can be seen from FIG. 6, Bi was observed after 45min of xenon lamp irradiation₁₀O₂₅Br₁₂The degradation rate of degrading rhodamine B is about 58%. The composite photocatalyst has obvious improvement on the rate of degrading rhodamine B, and Bi₁₀O₂₅Br₁₂The degradation rate of large-particle-size RGO to rhodamine B is about 89 percent, and Bi is₁₀O₂₅Br₁₂The degradation rate of small-particle-size RGO to rhodamine B is about 96 percent, and further proves that Bi₁₀O₂₅Br₁₂Bi complex with RGO₁₀O₂₅Br₁₂The photocatalytic activity of (A) has a significant influence. As shown in FIG. 7, Bi is calculated from the fit line₁₀O₂₅Br₁₂、Bi₁₀O₂₅Br₁₂Large particle size RGO and Bi₁₀O₂₅Br₁₂Reaction kinetic constants of small-particle-size RGO for degrading rhodamine B are respectively 0.0177min^-1、0.0446min^-1、0.0753min^-1The numerical values are increased in sequence, and Bi is observed₁₀O₂₅Br₁₂The efficiency of degrading rhodamine B by using RGO with small particle size is highest.

3.3.2 analysis of photodegradation Rate results

As can be seen from FIG. 8, the degradation effect of the photocatalyst in the degradation process of rhodamine B under visible light conditions has a certain effect, and the degradation rates of the three photocatalysts are within 45min of xenon lamp irradiationThe amplitude is gradually increased, wherein Bi₁₀O₂₅Br₁₂Maximum degradation amplitude of the/RGO photocatalyst is 94.74%, Bi₁₀O₂₅Br₁₂The decomposition rate of large-particle-size RGO is 89.7%, wherein Bi₁₀O₂₅Br₁₂The degradation amplitude of (A) is less than 70.38%, thus showing that Bi₁₀O₂₅Br₁₂The efficiency of degrading rhodamine B by using RGO with small particle size is highest. The compound photocatalyst Bi can be found by the analysis₁₀O₂₅Br₁₂The catalytic performance of/RGO is optimal.

The present invention provides RGO and Bi₁₀O₂₅Br₁₂Experiments show that the degradation rate of the synthesized composite material under the condition of visible light can be concluded as follows:

first, semi-quantitative analysis of X-ray energy spectrum (EDS) shows that the molecular formula of the catalyst is Bi₁₀O₂₅Br₁₂；

Second, XRD test results show that Bi is present in₁₀O₂₅Br₁₂The XRD pattern of the/RGO composite material does not show RGO characteristic peak, which is probably because the RGO composite quantity is less; and

thirdly, the analysis of the result of the photocatalytic performance shows that the degradation rate of the three photocatalysts is gradually increased within 45min of xenon lamp irradiation, and Bi is added₁₀O₂₅Br₁₂The small-particle-size RGO composite material has the fastest promotion amplitude, and Bi₁₀O₂₅Br₁₂The photodegradation rate of small-particle RGO is 96% relative to Bi alone₁₀O₂₅Br₁₂Photocatalyst, degradation rate of which is improved by 38%, Bi₁₀O₂₅Br₁₂Photocatalytic performance of/RGO compared with single Bi₁₀O₂₅Br₁₂The improvement is good, and it is concluded that the addition of RGO can increase Bi₁₀O₂₅Br₁₂The catalytic performance of (2).

The composite photocatalyst has the following practical applications: (1) purifying air: the gaseous pollutants mainly comprise volatile organic compounds (low-carbon organic solvents, benzene, halogenated hydrocarbons and the like), oxynitride compounds, sulfur oxide compounds and the like in the environment of daily life. The photocatalyst can play a role in excellent air purification; (2) and (3) antibacterial sterilization: the photocatalytic material can kill pathogenic bacteria such as escherichia coli, MRSA and the like, has good inhibition effect, and can decompose viruses; (3) hydrogen production by photolysis of water: the hydrogen energy source is the most ideal clean energy source to date for human, has high thermal efficiency and does not produce any pollution after being used. Although hydrogen is the most abundant element in the universe, there is no hydrogen resource directly available on earth. Hydrogen resources become accessible by photocatalysis; (4) wastewater treatment: the organic pollutants in the polluted water are various and most of the pollutants are difficult to degrade, and can be successfully degraded by using a photocatalyst. The rhodamine B is one of the components which pollute water resources and are discharged from the dye industry. Rhodamine B, also known as basic rose essence, has been widely used as a food additive, but is prohibited from the food industry because of its carcinogenic properties proved by experiments. For degradation and treatment of rhodamine B, a physical treatment method, a biological method and a chemical treatment method are available at present.

Claims

1. A composite photocatalyst is characterized by comprising Bi dissolved in a polar solvent₁₀O₂₅Br₁₂And reduced graphene oxide, said Bi₁₀O₂₅Br₁₂And the reduced graphene oxide adsorption/desorption equilibrium, wherein the Bi₁₀O₂₅Br₁₂And the mass ratio of the reduced graphene oxide to the reduced graphene oxide is 150: 8-12.

2. The composite photocatalyst of claim 1, wherein the polar solvent is water.

3. The composite photocatalyst of claim 1, wherein the reduced graphene oxide is a small-particle-size reduced graphene oxide having a particle size of less than 4 microns or a large-particle-size reduced graphene oxide having a particle size of greater than 4 microns.

4. The composite photocatalyst of claim 3, wherein the reduced graphene oxide has a thickness in the range of 0.68 nm to 1.6 nm.

5. The composite photocatalyst of claim 4, wherein the small-particle size reduced graphene oxide is less than 1 nm thick.