CN117563618A

CN117563618A - A kind of magnetic nanocomposite photocatalyst and its preparation method and application

Info

Publication number: CN117563618A
Application number: CN202311472142.3A
Authority: CN
Inventors: 于海辉; 许晶; 赵明玉; 黄巨擘
Original assignee: Northeast Dianli University
Current assignee: Northeast Electric Power University
Priority date: 2023-11-07
Filing date: 2023-11-07
Publication date: 2024-02-20
Anticipated expiration: 2043-11-07
Also published as: CN117563618B

Abstract

The invention discloses a magnetic nano composite photocatalyst, a preparation method and application thereof, comprising the following steps: preparation of heteropolyacid precursor alpha-SiW ₉ The method comprises the steps of carrying out a first treatment on the surface of the alpha-SiW using heteropolyacid precursors ₉ Preparation of SiW ₉ Mo ₃ The method comprises the steps of carrying out a first treatment on the surface of the Preparation of Co ₃ O ₄ The method comprises the steps of carrying out a first treatment on the surface of the Preparation of Co ₃ O ₄ /SiW ₉ Mo ₃ . And at presentCompared with the prior art, the magnetic nano composite photocatalyst has good photocatalytic activity, under the experimental condition that the concentration of the organic dye is 20mg/L, the magnetic nano composite photocatalyst is added into a reaction system, the pH value of the reaction system is regulated to 7, and an externally applied magnetic field is 200Gs, so that the magnetic nano composite photocatalyst has optimal photocatalytic degradation activity and efficiency, has good stability and can be repeatedly used, and is a magnetic auxiliary photocatalyst with excellent performance.

Description

Magnetic nano composite photocatalyst and preparation method and application thereof

Technical Field

The invention relates to the technical field of photocatalysts, in particular to a magnetic nano composite photocatalyst, a preparation method and application thereof.

Background

With the development of industry and the improvement of the living standard of people, the demand of people for resources is obviously increased, and a series of negative effects, particularly water pollution, are generated. Prolonged exposure of humans to wastewater causes a series of hazards such as anemia, neurological diseases, carcinogenesis, etc. Therefore, efficient treatment of domestic sewage and industrial wastewater is becoming important. Various water remediation technologies such as biological, precipitation, coagulation, flocculation, ion exchange, membrane filtration and reverse osmosis have been developed to purify sewage, however, some organic contaminants are difficult to remove.

Polyoxometalates (POMs) are considered ideal photocatalysts in solar light conversion processes because of their thermal and chemical stability as a non-metallic semiconductor photocatalyst. POMs are easily dissolved in water when used alone as photocatalysts, so that the POMs are not easy to separate after reaction and are difficult to reuse, thus the application of the POMs is greatly limited ^[12] . At present, a large number of POMs are used to synthesize novel composite materials by compounding with nanomaterials. SiW is prepared by sol-gel method ₁₂ And PW (pseudo wire) ₁₂ Uniformly dispersing into silicon dioxide bulk phase to synthesize microporous silicon dioxide immobilized POMs photocatalyst, and preparing POMs/SiO ₂ The photocatalyst has high water-insoluble property and high stability ^[13] . In addition, the formed micropore structure has higher specific surface area and higher practicability for removing hexachlorocyclohexane. By stepwise coating with magnetite Fe ₃ O ₄ Is core and then covered with Ag and H in turn ₃ PW ₁₂ O ₄₀ A magnetic POMs-based photocatalyst having a core-shell structure was prepared. Under the irradiation of visible light, compared with pure POMs, the double-coating photocatalyst has obvious photocatalytic degradation capability on rhodamine B (RhB)And (3) the enhancement is remarkable.

The promotion of catalytic performance by magnetic fields has attracted a great deal of attention and has made great progress in some catalytic fields, and external magnetic field regulation has been widely discussed as a non-contact, environmentally friendly method and has effectively promoted sustainable development, in the sense that the use of external magnetic fields to enhance performance in photocatalytic processes is an attractive behavior. While most of it relates to Fe ₃ O ₄ The photocatalysis is studied by compounding the catalyst with a catalyst main body, so that the excellent recycling effect is achieved, and a large amount of Fe is avoided ₃ O ₄ The addition of the (C) can cause shading effect and surface defect, and the core-shell structure can keep better photocatalysis performance.

Therefore, there is a need to develop a magnetic nanocomposite photocatalyst.

Disclosure of Invention

In order to solve the technical problems, the invention provides a magnetic nano composite photocatalyst, and a preparation method and application thereof.

In order to achieve the above purpose, the invention is implemented according to the following technical scheme:

a first object of the present invention is to provide a method for preparing a magnetic nanocomposite photocatalyst, comprising the steps of:

s1, preparing heteropolyacid precursor alpha-SiW ₉ ；

S2, utilizing heteropolyacid precursor alpha-SiW ₉ Preparation of SiW ₉ Mo ₃ ；

S3, preparing Co ₃ O ₄ ；

S4, preparing Co ₃ O ₄ /SiW ₉ Mo ₃ : 1g SiW was taken ₉ Mo ₃ Dissolving in 10mL of water, adding SiW ₉ Mo ₃ Co 1-9 wt% ₃ O ₄ Stirring for 30min to completely mix; dropwise adding 10mL of 0.1mol/L tetrabutylammonium bromide aqueous solution; stirring for 5-6 hr, centrifuging to separate sample, washing with deionized water and ethanol for several times, and drying at 60deg.C for 6 hr to obtainMagnetic nano composite photocatalyst Co ₃ O ₄ /SiW ₉ Mo ₃ 。

Further, the step S1 specifically includes:

weighing 18.20g of sodium tungstate and 1.10g of sodium silicate, dissolving in 20mL of 80-100 ℃ hot water, and stirring and mixing; then 13mL of hydrochloric acid solution with the concentration of 6M is added dropwise, when the solution is boiled to the volume of 30mL, the solution is filtered and centrifuged to remove unreacted Si, and the filtrate is collected; dissolving 5.00g of anhydrous sodium carbonate in 15mL of water, slowly adding the solution into the filtrate, slowly forming a precipitate, completely precipitating, filtering to separate out solid, mixing and stirring the separated solid with 100mL of sodium chloride solution with the concentration of 4M, and then filtering again; finally, washing with absolute ethyl alcohol to remove impurities, accelerating crystallization and vacuum drying to obtain heteropolyacid precursor alpha-SiW ₉ 。

Further, the step S2 specifically includes:

2.50g of heteropoly acid precursor alpha-SiW is taken ₉ 、0.70gNa ₂ MoO ₄ Mixing and dissolving in 10mL of water, stirring thoroughly, adding 3M hydrochloric acid solution dropwise until the solid is completely dissolved, adjusting pH to 1, heating in water bath at 80deg.C for 15min, cooling to room temperature, filtering, and drying to obtain yellowish green solid, i.e. SiW ₉ Mo ₃ 。

Further, the step S3 specifically includes:

0.8g of Co (CH 3 COO) 2.6H was taken ₂ O is added into a mixed solution of 16mL of water and 24mL of ethanol, stirred for 1h, then 4mL of ammonia water with mass fraction of 25% is added, the mixture is stirred in the air for 20min, then the liquid is transferred into a 100mL high-pressure reaction kettle, the reaction is carried out for 3h at 150 ℃, after the high-pressure kettle is naturally cooled, the obtained liquid is washed with deionized water for multiple times, and is dried for 4h at 60 ℃ to obtain black solid Co ₃ O ₄ 。

Preferably, siW is added in the step S4 ₉ Mo ₃ 7% by mass of Co ₃ O ₄ 。

A second object of the present invention is to provide a magnetic nanocomposite photocatalyst produced by the above method.

The third object of the invention is to provide an application of the magnetic nano composite photocatalyst in photocatalytic degradation of organic dye, wherein under the experimental condition that the concentration of the organic dye is 20mg/L, 0.6g/L of the magnetic nano composite photocatalyst is respectively added into a reaction system, the pH of the reaction system is regulated to 7, and a magnetic field of 100Gs-300Gs is additionally applied to perform photocatalytic degradation of the organic dye.

Preferably, the externally applied magnetic field is 200Gs.

Compared with the prior art, the magnetic nano composite photocatalyst has good photocatalytic activity, under the experimental condition that the concentration of the organic dye is 20mg/L, the magnetic nano composite photocatalyst is added into a reaction system, the pH value of the reaction system is regulated to 7, and an externally applied magnetic field is 200Gs, so that the magnetic nano composite photocatalyst has optimal photocatalytic degradation activity and efficiency, has good stability and can be repeatedly used, and is a magnetic auxiliary photocatalyst with excellent performance.

Drawings

FIG. 1 is a diagram of a-SiW ₉ -infrared spectrogram of POM.

FIG. 2SiW ₉ Mo ₃ -infrared spectrogram of POM.

FIG. 3 is SiW ₉ Mo ₃ X-ray powder diffraction (XRD) patterns of (a).

FIG. 4 is SiW ₉ Mo ₃ An ultraviolet-visible spectrum diagram (a) and a band gap energy diagram (b).

FIG. 5 is SiW ₉ Mo ₃ Scanning electron microscopy of POM.

FIG. 6 is Co ₃ O ₄ Is an X-ray powder diffraction pattern of (c).

FIG. 7 is Co ₃ O ₄ Electron microscopy images (a) and Co ₃ O ₄ Sample surface EDS elemental mapping (b).

FIG. 8 is Co ₃ O ₄ An ultraviolet-visible spectrum diagram (a) and a band gap energy diagram (b).

FIG. 9 shows Co of different proportions ₃ O ₄ /SiW ₉ Mo ₃ Infrared spectrogram of the composite material.

FIG. 10 is a composite Co ₃ O ₄ /SiW ₉ Mo ₃ Is an X-ray powder diffraction pattern of (c).

FIG. 11 is Co ₃ O ₄ /SiW ₉ Mo ₃ The XPS measurement spectrum (a) of (b) Si 2p, (c) W4f, (d) Mo3d, (e) Co 2p, and (f) O1s XPS spectrum.

FIG. 12 shows Co at different ratios ₃ O ₄ /SiW ₉ Mo ₃ Ultraviolet spectrogram of the composite material.

FIG. 13 shows CoMo at different ratios ₆ /Fe ₃ O ₄ @ C composite Nyquist plot (a) and Bode plot (b).

FIG. 14 shows Co at different ratios ₃ O ₄ /SiW ₉ Mo ₃ Fluorescent spectrum diagram of composite material.

FIG. 15 shows Co ratios under the action of magnetic field ₃ O ₄ /SiW ₉ Mo ₃ Electrochemical alternating current impedance spectrum (a) and Bode graph (b) of the composite material.

FIG. 16 is a methylene blue solution standard curve.

FIG. 17 is a direct photolytic curve for methylene blue.

FIG. 18 is a composite Co ₃ O ₄ /SiW ₉ Mo ₃ Photocatalytic data plot (a) and rate plot (b) at different dye concentrations.

FIG. 19 is a composite Co ₃ O ₄ /SiW ₉ Mo ₃ Photocatalytic data plot (a) and rate plot (b) at different dye concentrations.

FIG. 20 is a composite Co ₃ O ₄ /SiW ₉ Mo ₃ Photocatalytic data plot (a) and rate plot (b) at different dosing ratios.

FIG. 21 is a composite Co ₃ O ₄ /SiW ₉ Mo ₃ Data plot (a) and rate plot (b) at different concentrations of inorganic ions.

FIG. 22 is a composite Co ₃ O ₄ /SiW ₉ Mo ₃ Degradation data plot (a) and rate plot (b) at different pH.

FIG. 23 is a composite Co ₃ O ₄ /SiW ₉ Mo ₃ Photocatalytic data plot (a) and velocity plot (b) at different magnetic field strengths.

FIG. 24 is a composite cycle experiment C/C ₀ Time-dependent plot (a) and cycle test-like comparative plot (b) outside magenta.

FIG. 25 is a composite Co ₃ O ₄ /SiW ₉ Mo ₃ Is a masking agent test chart of (2).

FIG. 26 is SiW ₉ Mo ₃ Mott-Schottky graph (a) and Co of POM ₃ O ₄ Mott-Schottky graph (b).

FIG. 27 is a photocatalytic mechanical drawing of a composite material.

Detailed Description

The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. The specific embodiments described herein are for purposes of illustration only and are not intended to limit the invention.

Example 1

S1, preparing a heteropoly acid precursor alpha-SiW:

weighing 18.20g of sodium tungstate and 1.10g of sodium silicate, dissolving in 20mL of 80-100 ℃ hot water, and stirring and mixing; then 13mL of hydrochloric acid solution with the concentration of 6M is added dropwise, when the solution is boiled to the volume of 30mL, the solution is filtered and centrifuged to remove unreacted Si, and the filtrate is collected; dissolving 5.00g of anhydrous sodium carbonate in 15mL of water, slowly adding the solution into the filtrate, slowly forming a precipitate, completely precipitating, filtering to separate out solid, mixing and stirring the separated solid with 100mL of sodium chloride solution with the concentration of 4M, and then filtering again; finally, washing with absolute ethyl alcohol to remove impurities, accelerating crystallization and vacuum drying to obtain heteropolyacid precursor alpha-SiW ₉ ；

To determine molecular structure and chemical composition, the samples tested were characterized by infrared spectroscopy (FI-IR), as shown in fig. 1. The characteristic absorption peak of the infrared spectrum mainly appears at 981cm ^-1 、930cm ^-1 、864cm ^-1 And 807cm ^-1 . Wherein 981cm ^-1 Attributing to w=o _d Characteristic absorption peak of bond, 930cm ^-1 Due to Si-O _a Characteristic absorption peak of bond, 864cm ^-1 And 807cm ^-1 Characteristic absorption peaks ascribed to W-O-W bonds. This is basically the polyacid precursor α -SiW as determined by comparison with the literature ₉ 。

S2, utilizing heteropolyacid precursor alpha-SiW ₉ Preparation of SiW ₉ Mo ₃ ：

2.50g of heteropoly acid precursor alpha-SiW is taken ₉ 、0.70gNa ₂ MoO ₄ Mixing and dissolving in 10mL of water, stirring thoroughly, adding 3M hydrochloric acid solution dropwise until the solid is completely dissolved, adjusting pH to 1, heating in water bath at 80deg.C for 15min, cooling to room temperature, filtering, and drying to obtain yellowish green solid, i.e. SiW ₉ Mo ₃ ；

FIG. 2 is SiW ₉ Mo ₃ Is characterized by having an absorption peak of 978cm ^-1 ，922cm ^-1 ，879cm ^-1 And 777cm ^-1 W=o respectively _d Characteristic absorption peak of bond, si-O _a Characteristic absorption peak of bond, W-O _b W bond and W-O _c Telescopic vibration absorption peak of-W bond, and alpha-SiW ₉ The absorption peaks of the infrared spectrogram are offset to some extent because mo=o formed when Mo element is introduced _d Bond, si-O _a Bond, mo-O _b -Mo bond and Mo-O _c Characteristic absorption peaks of Mo bonds such that the characteristic absorption peaks in the infrared plot are shifted.

SiW as shown in fig. 3 ₉ Mo ₃ As can be seen from the X-ray powder diffraction (XRD) pattern of POM, the synthesized SiW ₉ Mo ₃ The characteristic diffraction peaks of the POM can be observed at the 2 theta angles of 16-22 DEG and 25-30 DEG, which correspond to the characteristic diffraction peaks reported in the literature for Keggin type POMs one by one. The synthesized substance can be proved to have a stable Keggin structure.

The band structure of POMs is an important factor in determining its photocatalytic activity, and is used for synthesizing SiW through ultraviolet-visible spectrum (UV-vis) ₉ Mo ₃ The POM was optically analysed. As shown in FIG. 4 (a), we can observe SiW ₉ Mo ₃ The light absorption range of POM is 200-480nm, whereasSiW ₁₂ The light absorption range of (2) is 200-400nm, and the mixed heteropoly acid SiW ₉ Mo ₃ POM can significantly extend the light absorption range. The measured ultraviolet spectrogram data is calculated by a Kubelka-Munk equation to obtain SiW ₉ Mo ₃ The band gap width of POM is 2.61eV, see FIG. 4 (b).

The morphological characteristics of the material have a great impact on its properties. As shown in FIG. 5 as SiW ₉ Mo ₃ Scanning electron microscopy of POM, as can be seen clearly in fig. 5, the POM is a short rod-like structure, with dimensions of about 600nm.

S3, preparing Co ₃ O ₄ ：

0.8g of Co (CH 3 COO) 2.6H was taken ₂ O is added into a mixed solution of 16mL of water and 24mL of ethanol, stirred for 1h, then 4mL of ammonia water with mass fraction of 25% is added, the mixture is stirred in the air for 20min, then the liquid is transferred into a 100mL high-pressure reaction kettle, the reaction is carried out for 3h at 150 ℃, after the high-pressure kettle is naturally cooled, the obtained liquid is washed with deionized water for multiple times, and is dried for 4h at 60 ℃ to obtain black solid Co ₃ O ₄ ；

The resulting samples were analyzed for crystal phase structure and composition changes by x-ray diffraction (XRD), and the results are shown in fig. 6. For pure Co ₃ O ₄ Diffraction peaks of the sample, 19.0 °, 31.3 °, 36.8 °, 44.8 °, 59.3 °, and 65.2 °, respectively, correspond to Co ₃ O ₄ The (111), (220), (311), (400), (511) and (440) crystal planes are identical (PDF 74-2120), and no other impurity peaks appear.

SEM was used to observe Co ₃ O ₄ The shape and surface shape of the sample are shown in fig. 7 (a). The sample is nano-particle, and agglomeration phenomena with different degrees exist. Co (Co) ₃ O ₄ As shown in FIG. 7 (b), the sample EDS element mapping test chart shows that Co and O elements can be clearly observed in the sample and are uniformly distributed.

Co synthesized by ultraviolet visible spectrum (UV-vis) pair ₃ O ₄ Optical analysis was performed. As shown in FIG. 8, we can observe the absorption of ultraviolet and visible light at 200-400nm and 600-800nm, and the measured ultraviolet spectrum data is calculated by the Kubelka-Munk equationTo Co ₃ O ₄ The band gap width of (a) is 1.58eV, see fig. 8 (b).

S4, preparing Co ₃ O ₄ /SiW ₉ Mo ₃ : 1g SiW was taken ₉ Mo ₃ Dissolving in 10mL of water, adding SiW ₉ Mo ₃ Co 1 mass% ₃ O ₄ Stirring for 30min to completely mix; dropwise adding 10mL of 0.1mol/L tetrabutylammonium bromide aqueous solution; stirring for 5-6 hr, centrifuging to separate sample, washing with deionized water and ethanol for several times, and drying at 60deg.C for 6 hr to obtain magnetic nanometer composite photocatalyst Co ₃ O ₄ /SiW ₉ Mo ₃ Is denoted as Co ₃ O ₄ /SiW ₉ Mo ₃ -1％。

Example 2

Unlike example 1, siW was added in step S4 ₉ Mo ₃ 3% by mass of Co ₃ O ₄ The obtained magnetic nano composite photocatalyst is denoted as Co ₃ O ₄ /SiW ₉ Mo ₃ -3％。

Example 3

Unlike example 1, siW was added in step S4 ₉ Mo ₃ Co 5% by mass ₃ O ₄ The obtained magnetic nano composite photocatalyst is denoted as Co ₃ O ₄ /SiW ₉ Mo ₃ -5％。

Example 4

Unlike example 1, siW was added in step S4 ₉ Mo ₃ 7% by mass of Co ₃ O ₄ The obtained magnetic nano composite photocatalyst is denoted as Co ₃ O ₄ /SiW ₉ Mo ₃ -7％。

Example 5

Unlike example 1, siW was added in step S4 ₉ Mo ₃ Co 9% by mass ₃ O ₄ The obtained magnetic nano composite photocatalyst is denoted as Co ₃ O ₄ /SiW ₉ Mo ₃ -9％。

Examples 1-5 different ratios of ingredientsThe FI-IR spectrum of the prepared magnetic nano composite photocatalyst is shown in figure 9, wherein Co ₃ O ₄ The proportion is 1%,3%,5%,7%,9% respectively. 978cm ^-1 ，922cm ^-1 ，879cm ^-1 And 777cm ^-1 W=o respectively _d Characteristic absorption peak of bond, si-O _a Characteristic absorption peak of bond, W-O _b W bond and W-O _c -a telescopic vibration absorption peak of the W bond. Confirm Co ₃ O ₄ /SiW ₉ Mo ₃ Structural integrity of the Keggin units.

Co was characterized by XRD testing ₃ O ₄ /SiW ₉ Mo ₃ The crystal structure and chemical composition of (a) are shown in fig. 10. And by combining SiW ₉ Mo ₃ POM and Co ₃ O ₄ Compounding, the SiW can be found in the XRD pattern of the loaded composite material ₉ Mo ₃ POM and Co ₃ O ₄ Is indicative of Co ₃ O ₄ Is not affected by SiW ₉ Mo ₃ The Keggin unit structure is complete. And different proportioning ratio composite materials Co ₃ O ₄ /SiW ₉ Mo ₃ The diffraction peak positions of the XRD of the (B) are the same, and the peak types are consistent.

Co prepared by X-ray photoelectron spectroscopy (XPS) analysis ₃ O ₄ /SiW ₉ Mo ₃ The surface chemical state of the composite sample is taken as a reference by C1s (283.4 eV). FIG. 11 (a) shows the overall spectrum, co ₃ O ₄ /SiW ₉ Mo ₃ Co, O, N, C, mo, si and W elements were present in the composite sample, indicating Co ₃ O ₄ And SiW ₉ Mo ₃ Successful compounding. As can be seen from fig. 11 (b), one XPS peak of Si at 2p is shown at 102.09 eV. FIG. 11 (c) shows the nuclear energy spectrum of the W4f spin orbit. Characteristic peaks centered at 35.7eV and 37.9eV correspond to W, respectively ⁶⁺ W4f of (2) _5/2 And 4f _7/2 . FIG. 11 (d) is a nuclear energy spectrum of the Mo3d spin orbit. Characteristic peaks centered at 232.8eV and 235.9eV correspond to Mo, respectively ⁶⁺ Mo3d of (2) _5/2 And 3d _3/2 . FIG. 11 (e) shows the nuclear energy spectrum of Co 2p spin orbitals. Due to Co ₃ O ₄ Co 2p in (C) _3/2 And Co 2p _1/2 Two strong signals were detected in the Co 2p spectra of 780.7eV and 795.9 eV. FIG. 11 (f) is a nuclear energy spectrum of O1s spin orbitals ^[34] . Two peaks at 530.4 and 532.4eV, respectively, are attributed to lattice oxygen (O) _latt ) And H ₂ And O molecules.

FIG. 12 Co ₃ O ₄ /SiW ₉ Mo ₃ Composite material (Co) ₃ O ₄ Different loadings). Co (Co) ₃ O ₄ /SiW ₉ Mo ₃ Generates strong characteristic absorption peak at 300nm and 700nm, and the absorption peak at 250nm can be attributed to O _t The absorption peak at 340nm generated by p pi-d pi charge transfer of W can be attributed to O _b,c The p pi-d pi charge transfer of W results from the absorption peak at 700nm due to Co ₃ O ₄ Co in (C) ³⁺ -Co ²⁺ Caused by the d-d metal transition of (2). Can prove SiW ₉ Mo ₃ With Co ₃ O ₄ Compounding is successful.

To verify the relationship between the separation rate of photogenerated charge carriers and photocatalytic performance, we tested electrochemical alternating current impedance (EIS) and fluorescence spectroscopy (PL).

The separation efficiency of the photo-generated carriers in the prepared catalyst can be examined by EIS, and FIG. 13 (a) is Co ₃ O ₄ 1%,3%,5%,7% and 9% of the mass ratio of the Nyquist diagram of the electrode of the composite material. It is generally considered that the Nyquist diagram is divided into a high frequency region and a low frequency region, the high frequency region usually representing a semicircle, and the low frequency region representing a linear variation curve. The radius of the circular arc of the high frequency region of the Nyquist plot is positively correlated with the charge transfer impedance (Rct) of the sample, with a smaller radius of the circular arc representing a smaller charge transfer impedance. The low frequency region of the Nyquist plot and the slope of the curve are positively correlated, the greater the slope, the faster the electron diffusion rate. As can be seen from the figure, when Co ₃ O ₄ When the proportions are different, the arc radius of the composite material in a high-frequency area and the slope of the composite material in a low-frequency area are different to a certain extent, and the minimum arc radius and the maximum slope are both composite samples with the load proportion of 7%. I.e. with minimum charge transfer impedance and maximumElectron diffusion rate of (a). The photo-generated carriers are shown to have higher separation efficiency and are efficiently transferred at the electrode/electrolyte interface, so that the photo-catalytic reaction is facilitated. As shown in fig. 13 (b), the lower the mode value in the Bode plot, the faster the photogenerated carrier generation. From the graph X, it can be judged that the composite material Co ₃ O ₄ /SiW ₉ Mo ₃ 7% of the electron-hole pairs are generated most rapidly, which is favorable for the photocatalytic reaction, and the theoretical photocatalytic activity is highest.

The investigation of the recombination rate and transfer efficiency of the photogenerated electron-hole pairs in the prepared catalyst by fluorescence spectroscopy (PL) is also considered to be a major key factor for improving the photocatalytic efficiency. When the catalyst is irradiated by light, the catalyst is excited to generate electron-hole pairs, electrons are transited from a valence band to a conduction band, and the same number of holes are generated in the conduction band. Only when the electron holes recombine and are released in the form of light, a luminescence phenomenon occurs. The higher the fluorescence intensity, the easier the electron-hole pair of the material is compounded, and the lower the photocatalytic activity. At an excitation wavelength of 397 nm. Obtaining Co ₃ O ₄ /SiW ₉ Mo ₃ As shown in fig. 14. All samples showed similar fluorescence emission peaks at 592 nm. The fluorescent intensity of the composite materials with different proportions is different, so that the separation degree and the transfer effect of the photo-generated electron-hole pairs are also different. Compared with the composite material with the proportion of 1%,3%,5% and 9%, co ₃ O ₄ /SiW ₉ Mo ₃ 7% has a lower fluorescence peak intensity, i.e. the lowest carrier recombination rate and higher photocatalytic activity.

Co is mixed with 1%,3%,5%,7% and 9% of the total weight of the alloy ₃ O ₄ Is of composite Co of (C) ₃ O ₄ /SiW ₉ Mo ₃ And (3) carrying out complete magnetization and carrying out electrochemical alternating current impedance test (EIS) under a magnetic field, and discussing the separation efficiency of photo-generated carriers of the prepared catalyst after magnetization. As shown in FIG. 15, co is the smallest in the arc under the magnetic field ₃ O ₄ /SiW ₉ Mo ₃ -7%, indicating Co ₃ O ₄ The composite material with 7% ratio has the smallest radius of circular arc, i.e. the smallest impedance.The modulus in the Bode plot can also prove Co ₃ O ₄ /SiW ₉ Mo ₃ 7% of the composite material is theoretically more photocatalytic. Thus, co is adopted successively ₃ O ₄ /SiW ₉ Mo ₃ 7% to perform the following externally applied magnetic field experiments.

Application examples

By Co ₃ O ₄ /SiW ₉ Mo ₃ The nanocomposite is a photocatalyst, a photocatalytic degradation experiment is carried out on the methylene blue solution by simulating sunlight, and the system analyzes the influence of different experimental factors (catalyst dosage, concentration of pollutant solution and the batching ratio of the catalyst) on the photocatalytic degradation. And taking a certain amount of photocatalyst and dye solution with a certain concentration to perform a photocatalysis experiment to evaluate the photocatalysis activity of the composite material. Meanwhile, the photocatalytic activity and stability of the composite photocatalyst are evaluated through degradation methylene blue cycle performance research.

By adding methanol (h) to the methylene blue dye solution ⁺ Quenching agent), isopropanol (OH capture agent) and p-benzoquinone (O) ₂ ^- Quencher), combined with photocatalytic data, explore Co ₃ O ₄ /SiW ₉ Mo ₃ The composite material is used for photocatalytic degradation of main active species in methylene blue experiments.

(1) Standard curve

100mg of methylene blue is weighed and dissolved in 500mL of deionized water to prepare a methylene blue standard solution with the concentration of 200 mg/L. The standard solutions were removed by pipetting gun in different volumes and placed in 15mL cuvettes and diluted to 10mL with deionized water to give methylene blue solutions of each concentration (25, 20, 15, 10, 5 and 2 mg/L). The absorbance was measured at a wavelength of 664nm to give a linear relationship between absorbance and concentration.

A plurality of methylene blue standard solutions of different concentrations were prepared, their absorbance at wavelength 664nm was measured using an ultraviolet-visible spectrophotometer, and the absorbance (a) was plotted as a standard curve with the concentration (C) as the ordinate and the absorbance (a) as the abscissa, as shown in fig. 16. The standard curve equation generated after fitting is y=0.1173x+0.1912,correlation coefficient: r is R ² = 0.9981. The results show that the absorbance and the concentration have good linear relation in a certain wavelength range.

(2) Direct photolysis experiments on methylene blue dyes

In the direct photocatalytic experiment process of the methylene blue dye, no photocatalyst is added into a reaction system, direct entry illumination is performed, sampling is performed at certain intervals, and the results are shown in fig. 17. The concentration of methylene blue solution does not substantially change after a certain period of illumination. The results show that under the condition that no photocatalyst exists, methylene blue can generate direct photolysis to a certain extent, but the photolysis degree is smaller, and the decolorization rate only reaches about 10.1 percent.

(3) Effect of different initial concentrations on photocatalysis

As shown in FIG. 18, the concentrations of methylene blue solutions were 15mg/L,20mg/L,25mg/L, and 30mg/L, respectively, co ₃ O ₄ /SiW ₉ Mo ₃ Photocatalytic decomposition of methylene blue solutions presents a degradation trend.

As can be seen from FIG. 18, the catalyst has a strong degradation ability to the dye at the dye concentrations of 15mg/L and 20 mg/L. When the dye concentration is 15mg/L, the degradation effect is very high, but the degradation is almost completed in 30min, and more than 80% can be achieved in the dark light adsorption, the photocatalysis effect is not obvious, and when the dye concentration is 20mg/L, the degradation rate of 88.96% can be achieved in the dark light adsorption stage at about 50% after photocatalysis, and the photocatalysis effect is very obvious. However, with the increase of the initial concentration of methylene blue, the photocatalytic degradation efficiency gradually decreases, and when the dye concentration is 25mg/L and 30mg/L, the overall effect of photocatalysis is not very good, and the degradation rate is slow, wherein the overall effect is about 55.99% and 28.10% respectively. This is because the amount of catalyst added is relatively reduced with increasing concentration, and the active sites on the catalyst surface are also relatively reduced, which affects the progress of the photocatalytic reaction. Thus a dye concentration of 20mg/L can be selected for subsequent experiments.

(4) Effect of different catalyst addition levels on photocatalysis

Under the experimental condition that the methylene blue concentration is 20mg/L, catalysts of 0.4g/L,0.5g/L,0.6g/L and 0.7g/L are respectively added into a reaction system to explore the influence of different addition amounts of the catalysts on the photocatalytic reaction. The experimental results are shown in FIG. 19.

As can be seen from FIG. 19 (a), the degradation rate of methylene blue increased from 53.62% to 88.33% with increasing catalyst amount. This is because as the catalyst particles increase, more active species are produced under illumination, accelerating the degradation of the dye. When the catalyst amount reached 0.6g/L, the degradation rate did not rise any more, and it can be seen in FIG. 19 (b) that the reaction rate was lowered. The reason for the analysis is that when the catalyst is used in an excessive amount, the turbidity of the suspension system formed is large, and at this time, visible light is reflected and scattered, so that the catalytic rate is affected.

(5) Effect of different ratios of ingredients on photocatalysis

Under the condition that the catalyst addition amount is 0.6g/L and the methylene blue concentration is 20mg/L, different mixing ratios (Co ₃ O ₄ /SiW ₉ Mo ₃ Middle Co ₃ O ₄ The results of the photocatalytic degradation of the dye by the catalyst with the ratios of 1%,3%,5%,7% and 9%, respectively, are shown in fig. 20.

As can be seen from FIG. 20 (a), co ₃ O ₄ /SiW ₉ Mo ₃ 7% of the composite material has the best photocatalytic degradation effect on methylene blue, which shows that 7% of wt-Co ₃ O ₄ The amount of the composite material is the optimal point of degradation and reaches 89.37 percent. When the proportion is 1%,3%,5% and 9%, the final degradation rate of photocatalysis is 59.1%, 57.13%, 72.31% and 66.72%, respectively, and the degradation efficiency is reduced. Co is also evident by comparing the rate plot of the degraded methylene blue solution of FIG. 20 (b) ₃ O ₄ /SiW ₉ Mo ₃ The decomposition rate of 7% for 20mg/L methylene blue is highest and the catalytic activity is best.

(1) Effect of different chloride ion concentrations on photocatalysis

The effect of different chloride ion concentrations on the photocatalysis was investigated under the conditions that the catalyst addition amount was 0.6g/L, the methylene blue concentration was 20mg/L and the recombination ratio was 7%, wherein the chloride ion concentrations were 100mg/L, 300mg/L, 500mg/L and 700mg/L.

As can be seen from FIG. 21 (a), the photocatalytic degradation rate was significantly higher than that in pure water with the addition of chloride ions at the first 20min, because of the fact that with Cl ^- The concentration increases and will occur (. O) ₂ ^- +Cl ^- →OCl ^- +O ₂ ) (OCl) ^- +H ₂ O→HOCl+OH ^- ) The HOCl produced has strong oxidizing property, thereby increasing degradation efficiency. After 20min, the amount of HOCl produced increased with the reaction, and (HOCl+. O) was produced ₂ ^- →O ₂ +Cl ^- ) Superoxide radicals and HOCl are consumed, resulting in reduced photocatalytic degradation efficiency. Co is also evident by comparing the rate plot of the degraded methylene blue solution of FIG. 21 (b) ₃ O ₄ /SiW ₉ Mo ₃ 7% of the catalyst has the highest decomposition rate of methylene blue without chloride ions and the best catalytic activity.

(2) Effect of different pH on photocatalysis

In order to investigate the chemical stability of the photocatalyst in an acidic environment and the effect of different pH on the photocatalysis at a catalyst addition of 0.6g/L, a methylene blue concentration of 20mg/L and a recombination ratio of 7% were investigated, wherein the pH was 1, 3, 5, 7.

As shown in fig. 22 (a), the photocatalytic rate of methylene blue showed different trends at different pH values. It can be clearly seen that the dim light adsorption data is relatively stable in all adsorption data, mainly concentrated in the interval of 10% -20%. This indicates that the composite material has stability, and the presence of hydrogen ions does not continue to change the stability of the composite material, so that the adsorption of the composite material tends to be stable. As can be seen from the figure, the highest photocatalytic efficiency can be reached up to 89.37% at ph=7. As is evident from FIG. 22 (b), the remaining group of photocatalytic degradation rates at pH 7 are much higher because as the H+ concentration increases, (. O) occurs ₂ ^- +2H ⁺ →H ₂ O ₂ ) And H is ₂ O ₂ Has strong oxidizing property, can accelerate the degradation of pollutants, and H as the reaction proceeds ₂ O ₂ The production of H is continuously increased ₂ O ₂ Will occur (2H) ₂ O ₂ →2H ₂ O+O ₂ ) Thereby consuming O ₂ ^- Resulting in a decrease in photocatalytic degradation efficiency. Finally, it was concluded that the photocatalytic effect was optimal at pH 7.

(6) Influence of the magnetic field on the photocatalytic Properties

In Co ₃ O ₄ /SiW ₉ Mo ₃ Under the conditions of the optimal dye initial concentration corresponding to 7% of the catalyst and the optimal catalyst addition amount, different magnetic field strength experiments are carried out to photo-catalytically degrade methylene blue, and the influence of the magnetic field on the photo-catalyst efficiency is considered. As shown in FIG. 23, the photocatalytic reaction performance and rate were compared with those of the photocatalytic reaction in the absence of a magnetic field applied to the catalytic device at a magnetic field of 100Gs to 300Gs, respectively. When the magnetic field strength is 200Gs, the degradation rate is optimal and can reach 85.97%, the degradation rate is faster, and under the magnetic field strength of 500Gs, as can be seen from a right graph rate chart, the catalysis rate reaches 0.0281, and the experiment level proves that the certain magnetic field strength is favorable for the photocatalytic reaction.

The addition of an external magnetic field causes Co to be formed ₃ O ₄ /SiW ₉ Mo ₃ The photocatalytic activity of 7% is further enhanced, providing a suitable magnetic field for the separation and migration of the photocarriers under the action of lorentz force. The improvement of the carrier separation efficiency can lead more electrons and holes to reach the surface of the catalyst and then participate in the subsequent oxidation-reduction reaction, so that the catalytic capacity and the catalytic efficiency are improved.

(7) Composite Co ₃ O ₄ /SiW ₉ Mo ₃ Photocatalytic cycle experiments

The ideal photocatalytic performance of the photocatalyst plays an extremely important role in practical application, and the stability of the photocatalyst occupies the same position. The photocatalytic cycle test is a continuous cycle test for degrading eosin B to judge whether the photocatalyst is stable and reusable. FIG. 24 (a) shows that, after two cycling experiments, Co ₃ O ₄ /SiW ₉ Mo ₃ The photocatalytic activity of (a) was slightly decreased from 89.37% at the first time to 85.69% at the third cycle. The secondary cycle experiment shows that Co ₃ O ₄ /SiW ₉ Mo ₃ Has enough stable photocatalytic degradation activity. And the structure is unchanged before and after the cyclic experiment, the complete Keggin structure is still maintained, and the activity loss is small, as shown in an infrared spectrogram in fig. 24 (b). This further confirms Co ₃ O ₄ /SiW ₉ Mo ₃ 7% has good stability.

(8) Kinetic and photocatalytic mechanism testing

To better understand Co ₃ O ₄ /SiW ₉ Mo ₃ The mechanism of catalytic degradation of methylene blue we performed radical and hole trapping experiments. In this study, we selected methanol, isopropanol and ascorbic acid as photogenerated holes (h ⁺ ) Hydroxyl radicals (. OH) and superoxide radicals (. O) ₂ ^- ) A capture agent for a species. As shown in the results of FIG. 25, under the condition of ascorbic acid, & O ₂ ^- Masked, the photocatalytic result of the composite was reduced to about 77.83%, proving O ₂ ^- Is an important factor of the photocatalytic decomposition of methylene blue. Under the condition of methanol and isopropanol, the photocatalytic decomposition rate and the final catalytic result are almost unchanged, which proves that h ⁺ OH is not a major factor limiting photocatalytic activity. In summary, we speculate that in experiments with photocatalytic decomposition of methylene blue, the photocatalytic process is completed by the action of superoxide radicals.

To further clarify SiW ₉ Mo ₃ And Co ₃ O ₄ We performed Mott-Schottky (M-S) to analyze and determine the flat-band potential (E _cb ) ^[37] As shown in FIG. 26, siW was measured according to the M-S equation ₉ Mo ₃ And Co ₃ O ₄ The conduction band positions of (2) are 0.37eV and-0.37 eV. Then converting SiW by K-M equation ₉ Mo ₃ And Co ₃ O ₄ The ultraviolet-visible spectrum of (a) gives a gap width between the conduction band and the valence band of 2.61eV and 1.58eV, and then calculates the position (E) _{(HOMO)(2.98V)} ＝E _{(LUMO)(0.37V)} +Eg _(2.61V) ) And (E) _(VB)(1.21V) ＝E _(CB)(-0.37V) +Eg _(1.58V) ). And drawing a photocatalysis mechanical drawing of the composite material according to the conduction band, the valence band and the band gap width, and the photocatalysis mechanical drawing is shown in fig. 27.

The technical scheme of the invention is not limited to the specific embodiment, and all technical modifications made according to the technical scheme of the invention fall within the protection scope of the invention.

Claims

1. The preparation method of the magnetic nano composite photocatalyst is characterized by comprising the following steps of:

s1, preparing heteropolyacid precursor alpha-SiW ₉ ；

S3, preparing Co ₃ O ₄ ；

S4, preparing Co ₃ O ₄ /SiW ₉ Mo ₃ : 1g SiW was taken ₉ Mo ₃ Dissolving in 10mL of water, adding SiW ₉ Mo ₃ Co 1-9 wt% ₃ O ₄ Stirring for 30min to completely mix; dropwise adding 10mL of 0.1mol/L tetrabutylammonium bromide aqueous solution; stirring for 5-6 hr, centrifuging to separate sample, washing with deionized water and ethanol for several times, and drying at 60deg.C for 6 hr to obtain magnetic nanometer composite photocatalyst Co ₃ O ₄ /SiW ₉ Mo ₃ 。

2. The method for preparing a magnetic nanocomposite photocatalyst according to claim 1, wherein the step S1 specifically comprises:

weighing 18.20g of sodium tungstate and 1.10g of sodium silicate, dissolving in 20mL of 80-100 ℃ hot water, and stirring and mixing; then 13mL of hydrochloric acid solution with the concentration of 6M is added dropwise, when the solution is boiled to the volume of 30mL, the solution is filtered and centrifuged to remove unreacted Si, and the filtrate is collected; then 5.00g of anhydrous sodium carbonate was dissolved in 15mL of water, andslowly adding into the filtrate, slowly forming precipitate, filtering to separate solid, mixing the separated solid with 100mL sodium chloride solution with concentration of 4M, stirring, and filtering again; finally, washing with absolute ethyl alcohol to remove impurities, accelerating crystallization and vacuum drying to obtain heteropolyacid precursor alpha-SiW ₉ 。

3. The method for preparing a magnetic nanocomposite photocatalyst according to claim 1, wherein the step S2 specifically comprises:

4. The method for preparing a magnetic nanocomposite photocatalyst according to claim 1, wherein the step S3 specifically comprises:

5. The method for preparing a magnetic nanocomposite photocatalyst according to claim 1, wherein SiW is added in step S4 ₉ Mo ₃ 7% by mass of Co ₃ O ₄ 。

6. A magnetic nanocomposite photocatalyst produced by the method of any one of claims 1-5.

7. Use of the magnetic nanocomposite photocatalyst according to claim 6 for photocatalytic degradation of organic dyes.

8. The application of the magnetic nano composite photocatalyst in photocatalytic degradation of organic dye according to claim 7, wherein under the experimental condition that the concentration of the organic dye is 20mg/L, the magnetic nano composite photocatalyst is added into a reaction system respectively, the pH of the reaction system is regulated to 7, and a magnetic field of 100Gs-300Gs is added to perform photocatalytic degradation of the organic dye.

9. The use of a magnetic nanocomposite photocatalyst according to claim 8 for photocatalytic degradation of organic dyes, wherein the externally applied magnetic field is 200Gs.