CN103551150B - A kind of preparation method of the magnetic composite photocatalyst based on carbonaceous material - Google Patents

Abstract

The invention relates to a method for preparing a magnetic composite photocatalyst based on carbonaceous materials, which belongs to the technical field of environmental material preparation. The multi-walled carbon nanotubes were pretreated to obtain acidified multi-walled carbon nanotubes; the activated MWCNTs were sonicated with ethylene glycol, then iron nitrate nonahydrate was sonicated, and finally sodium acetate, polyethylene glycol (1500) and polyethylene glycol were added. Fe ₃ O ₄ /MWCNTs was obtained by ultrasonication of vinylpyrrolidone. Stir anhydrous ethanol and tetra-n-butyl titanate in a sealed manner, add the mixed solution of ethanol, distilled water and concentrated hydrochloric acid drop by drop, and continue to seal and stir; open and stir until it is in the form of a sol, add Fe ₃ O ₄ /MWCNTs and stir at a constant speed until it is in the form of a gel, TiO ₂ /Fe ₃ O ₄ /MWCNTs composite photocatalyst was obtained after aging and calcination. Advantages: The recyclable process of the photocatalyst system can effectively improve the separation efficiency of photogenerated electrons and hole pairs; the magnetic photocatalyst helps to improve the recovery rate of the catalyst, and can better treat mercaptan wastewater.

Description

A kind of preparation method of magnetic composite photocatalyst based on carbonaceous material

technical field

The invention relates to a method for preparing a magnetic titanium dioxide/iron tetroxide/multi-walled carbon nanotube composite photocatalyst by means of hydrothermal synthesis and sol-gel combination, and belongs to the technical field of environmental material preparation.

Background technique

2-Mercapto-1-methylimidazole, as a thiol, in the treatment of hyperthyroidism and non-cyanide silver plating. But its drug resistance and its side effects also seriously affect people's life. Therefore, it is very important to rationally treat 2-mercapto-1-methylimidazole in domestic wastewater. Currently, various techniques such as adsorption, biodegradation, hydrodesulfurization, and electrochemical degradation have been employed to treat mercaptans. Among them, photocatalytic technology has played an important role in the field of energy and environment due to its non-toxic, stable, quick effect and low energy consumption. Due to its good photocatalytic activity, high stability, low cost and low toxicity, semiconductor photocatalyst TiO2 has been widely used in wastewater treatment. The treatment of waste water, waste gas and other pollutants in daily life has achieved good results by modifying titanium dioxide.

Carbon nanotubes have a unique structure, high mechanical strength, good electrical conductivity and thermal stability, and can improve semiconductor photocatalytic activity in terms of environmental treatment. On the other hand, loading magnetic materials such as Fe3O4 nanoparticles onto carbon nanotubes has been introduced into the field of environmental cleaning. Since ferroferric oxide is magnetic, the prepared magnetic composite photocatalyst can be simply separated by an external magnetic field and reused. More importantly, the introduction of ferroferric oxide and carbon nanotubes can effectively improve the photocatalytic activity of titanium dioxide and promote the photocatalytic degradation ability of the system.

Contents of the invention

The invention uses hydrothermal synthesis and sol-gel as preparation means to prepare a carbonaceous material-based magnetic TiO ₂ /Fe ₃ O ₄ /@MWCNTs composite photocatalyst. Its advantage lies in the construction of a cycle process in the system to realize the effective separation of photogenerated electrons and hole pairs; it can effectively use the light source to effectively degrade the mercaptan wastewater in the environment.

The technical scheme adopted in the present invention is:

(1) Preparation of Fe ₃ O ₄ /MWCNTs: The multi-walled carbon nanotubes were stirred with a mixed solution of concentrated nitric acid and concentrated sulfuric acid with a volume ratio of 1:3 at 60 °C for 6 h, washed and dried under vacuum at 50-70 °C overnight. Activated MWCNTs can be obtained by such acidification treatment; the activated MWCNTs and a certain volume of ethylene glycol are added to the reaction kettle for 20 minutes of sonication, and ferric nitrate nonahydrate is ultrasonically dissolved for 20 minutes (wherein the mass ratio of ferric nitrate nonahydrate to MWCNTs is 40 :1), and finally add sodium acetate (the mass ratio of sodium acetate to ferric nitrate nonahydrate is 6:5), a certain amount of polyethylene glycol (1500) and polyvinylpyrrolidone for 20 min of ultrasonication. After hydrothermal synthesis at 200 ℃ for 12 h, washing with water and ethanol respectively, and vacuum drying at 50-70 ℃ overnight, Fe ₃ O ₄ /MWCNTs were obtained.

(2) Preparation of TiO ₂ /Fe ₃ O ₄ /MWCNTs composite photocatalyst: add absolute ethanol and tetra-n-butyl titanate into a three-necked flask at a volume ratio of 18:5, and stir at 40 ℃ for 15 min; A mixed solution of ethanol, distilled water and concentrated hydrochloric acid with a ratio of 180:15:1 was added dropwise to the above solution, the volume ratio of the mixed solution to the above tetra-n-butyl titanate was 196:5, and the sealed stirring was continued for 10 min; Stir non-sealed until it is in the form of a sol, immerse a certain amount of Fe ₃ O ₄ /MWCNTs prepared in the above step (1) into the above TiO ₂ sol, the mass ratio of Fe ₃ O ₄ /MWCNTs and TiO ₂ sol is about 1:70 , stirred at a constant speed to gel, and aged at room temperature for 2 to 4 h; calcined the xerogel at 500 ℃ for 4 h in a nitrogen atmosphere, and cooled naturally to room temperature to obtain TiO ₂ /Fe ₃ O ₄ /MWCNTs composite light catalyst.

The ratio of activated MWCNTs to ethylene glycol in step (1) is 30:25 mg/mL, and the mass ratio of polyethylene glycol (1500) to polyvinylpyrrolidone is 40:1.

The invention adopts hydrothermal synthesis technology to prepare Fe ₃ O ₄ /MWCNTs, and uses sol-gel technology to modify its surface to prepare magnetic TiO ₂ /Fe ₃ O ₄ /MWCNTs composite photocatalyst with high catalytic activity.

Evaluation of photocatalytic activity: carried out in GHX-2 photochemical reaction instrument (purchased from Yangzhou University Teaching Instrument Factory), irradiated by ultraviolet light, adding 50 mL of 2-mercapto-1-methylimidazole simulated wastewater into the reactor and measuring Its initial value, then add the composite photocatalyst, stir magnetically and open the aeration device to let the air in to make the catalyst in a suspended or floating state, take samples and analyze them at intervals of 10 min during the illumination process, and take the liquid after magnetic separation in the ultraviolet spectrophotometer λ _max = Measure the absorbance at 251 nm, and calculate the degradation rate by the formula: Dr=[(C ₀ -C _i )/C ₀ ]×100%, where C ₀ is the concentration of 2-mercapto-1-methylimidazole solution at the beginning of photodegradation Initial concentration, C _i is the concentration of 2-mercapto-1-methylimidazole solution measured by regular sampling.

The technical advantages of the invention: the recyclable process of the photocatalyst system can effectively improve the separation efficiency of photogenerated electrons and hole pairs; the magnetic photocatalyst helps to improve the recovery rate of the catalyst; and can better treat mercaptan wastewater.

Description of drawings

Fig. 1 0.1 g photocatalyst UV photodegradation of 50 mL of 10 mg L ^-1 2-mercapto-1-methylimidazole. The ultraviolet photodegradation rate of TiO ₂ /Fe ₃ O ₄ /MWCNTs composite catalyst to 50 mL of 10 mg/L 2-mercapto-1-methylimidazole reached 82.7%, indicating that the prepared photocatalyst has good photocatalytic activity .

Figure 2 XRD pattern. X-ray diffraction patterns of MWCNTs, Fe ₃ O ₄ /MWCNTs and TiO ₂ /Fe ₃ O ₄ /MWCNTs composite photocatalysts. It can be seen from the figure that the diffraction characteristic peak of _TiO2 in the composite photocatalyst is anatase type.

Fig.3 SEM and EDS: (a) Purified MWCNTs (b) TiO ₂ /Fe ₃ O ₄ /MWCNTs.

TEM: (a) Purified MWCNTs (b) TiO ₂ /Fe ₃ O ₄ /MWCNTs.

SEM, EDS and TEM images of purified MWCNTs and TiO ₂ /Fe ₃ O ₄ /MWCNTs composite catalysts, from which it can be seen that the surface of MWCNTs changes.

Figure 4 UV-vis DRS spectrum. UV-Vis diffuse reflectance of TiO ₂ /Fe ₃ O ₄ /MWCNTs composite catalyst. It can be seen from the figure that the composite photocatalyst has a high absorption intensity in the ultraviolet-visible region.

Figure 5 FT-IR spectrum. FT–IR spectra of pristine MWCNTs and TiO ₂ /Fe ₃ O ₄ /MWCNTs. It shows that the composite photocatalyst has a good modification.

Figure 6 Magnetization curves. Hysteresis loop diagram of TiO ₂ /Fe ₃ O ₄ /MWCNTs composite catalyst. It shows that the sample is ferromagnetic.

Detailed ways

The present invention will be further described below in conjunction with specific implementation examples.

Example: (1) Stir 0.5 g of multi-walled carbon nanotubes with 15 mL of concentrated nitric acid and 45 mL of concentrated sulfuric acid (volume ratio 1:3) at 60 °C for 6 h, wash until neutral and dry in vacuum at 50 °C overnight, Activated MWCNTs were obtained by such acidification treatment; 30 mg of activated MWCNTs and 25 mL of ethylene glycol were added to the reactor for ultrasonication for 20 min, and then 1.239 g of ferric nitrate nonahydrate (the mass ratio of ferric nitrate nonahydrate to MWCNTs was 40 : 1) Sonicate for 20 min, and finally add 1.5 g of sodium acetate (the mass ratio of sodium acetate to ferric nitrate nonahydrate is 6:5), 0.4 g of polyethylene glycol (1500) and 10 mg of polyvinylpyrrolidone for 20 min of sonication. After hydrothermal synthesis at 200 ℃ for 12 h, washing with water and ethanol several times, and vacuum drying at 50 ℃ overnight, Fe ₃ O ₄ /MWCNTs were obtained.

(2) Preparation of TiO ₂ /Fe ₃ O ₄ /MWCNTs composite photocatalyst: Add 36 mL of absolute ethanol and 10 mL of tetra-n-butyl titanate (volume ratio 18:5) into a three-necked flask, and stir at 40 °C 15 min; add 36 mL of ethanol, 3 mL of distilled water and 0.2 mL of concentrated hydrochloric acid mixed solution (the volume ratio of the mixed solution to the above-mentioned tetra-n-butyl titanate is 196:5) into the above solution drop by drop, and continue to seal and stir for 10 min ; Then open and stir until it is in the form of a sol, and immerse 1.0 g of Fe ₃ O ₄ /MWCNTs prepared in the above step (1) into the above TiO ₂ sol (the mass ratio of Fe ₃ O ₄ /MWCNTs to TiO ₂ sol is about 1:70) , stirred at a constant speed until it became gel, aged at room temperature for 2 h; calcined the xerogel at 500 ℃ for 4 h in a nitrogen atmosphere, and naturally cooled to room temperature to obtain the TiO ₂ /Fe ₃ O ₄ /MWCNTs composite photocatalyst .

(3) Take 0.1g of the sample in (2) to conduct a photocatalytic degradation test in an ultraviolet photochemical reaction instrument. It is measured that the degradation rate of the photocatalyst to 2-mercapto-1-methylimidazole reaches 82.7% within 1 h ( As shown in Figure 1), the composite photocatalyst has strong photocatalytic activity.

(4) As shown in Figure 2, from the X-ray diffraction patterns of MWCNTs, Fe ₃ O ₄ /MWCNTs and TiO ₂ /Fe ₃ O ₄ /MWCNTs composite photocatalysts, it can be seen that the diffraction characteristic peak of TiO ₂ in the composite photocatalyst is sharp Titanite type, which corresponds to the characteristic diffraction peaks 2θ=25.3°, 38°, 48.1°, 55.2° and 75.1° of the standard anatase type _TiO2 crystal, which keeps the photocatalytic activity of _TiO2 in the catalyst sample higher Activity; 30.2°, 35.4°, 43.1°, 57.2° and 62.8° are the characteristic diffraction peaks of Fe ₃ O ₄ ; 2θ=25.3° is the diffraction peak of MWCNTs.

(5) As shown in Figure 3, from the SEM, EDS and TEM images of the purified MWCNTs and TiO ₂ /Fe ₃ O ₄ /MWCNTs composite catalysts, it can be seen that the main components of the catalyst sample substrate are Ti, O, Fe and C. The diameter of MWCNT is about 50nm, the surface layer is loaded with Fe ₃ O ₄ , and then covered with TiO ₂ .

(6) As shown in Figure 4, it can be seen from the ultraviolet-visible diffuse reflectance diagram of the TiO ₂ /Fe ₃ O ₄ /MWCNTs composite catalyst that the composite photocatalyst has a high absorption intensity in the ultraviolet-visible region, indicating that it has a good UV and visible light absorption.

(7) As shown in Figure 5, in the FT–IR spectra of pristine MWCNTs and TiO ₂ /Fe ₃ O ₄ /MWCNTs, 3400–3500 cm ⁻¹ belongs to –OH, and 1750 cm ⁻¹ indicates the formation of –C=O groups , 582 cm ⁻¹ belongs to Fe–O, and the other difference between the two figures is due to Ti–O. It shows that the composite photocatalyst has a good modification.

(8) As shown in Figure 6, the hysteresis loop diagram of the TiO ₂ /Fe ₃ O ₄ /MWCNTs composite catalyst, the saturation magnetization is 7.25 emu/g. The coercivity and remanence are 207.68 Oe and 1.59 emu/g, respectively. It shows that the sample is ferromagnetic. Disperse TiO ₂ /Fe ₃ O ₄ /MWCNTs in water, place a magnet outside the beaker, and the solution becomes clear after a few minutes, which also indicates that the sample is magnetic.

Claims (2)

1. A preparation method of a magnetic composite photocatalyst based on carbonaceous material, carried out according to the following steps: (1) Preparation of Fe ₃ O ₄ /MWCNTs: The multi-walled carbon nanotubes were stirred with a mixed solution of concentrated nitric acid and concentrated sulfuric acid with a volume ratio of 1:3 at 60 °C for 6 h, washed and dried under vacuum at 50-70 °C overnight, Activated MWCNTs can be obtained by such acidification treatment; put the activated MWCNTs and a certain volume of ethylene glycol into the reactor for ultrasonication for 20 min, then ferric nitrate nonahydrate for ultrasonic dissolution for 20 min, and finally add sodium acetate, a certain amount of polyethylene glycol Alcohol and polyvinylpyrrolidone were sonicated for 20 min, hydrothermally synthesized at 200 ℃ for 12 h, washed with water and ethanol respectively, and dried in vacuum at 50-70 ℃ overnight to obtain Fe ₃ O ₄ /MWCNTs; (2) Preparation of TiO ₂ /Fe ₃ O ₄ /MWCNTs composite photocatalyst: add absolute ethanol and tetra-n-butyl titanate into a three-necked flask at a volume ratio of 18:5, and stir at 40 ℃ for 15 min; A mixed solution of ethanol, distilled water and concentrated hydrochloric acid with a ratio of 180:15:1 was added dropwise to the above solution, the volume ratio of the mixed solution to the above tetra-n-butyl titanate was 196:5, and the sealed stirring was continued for 10 min; Stir non-sealed until it is in the form of a sol, immerse a certain amount of Fe ₃ O ₄ /MWCNTs prepared in the above step (1) into the above TiO ₂ sol, the mass ratio of Fe ₃ O ₄ /MWCNTs and TiO ₂ sol is 1:70, Stir at a constant speed until it becomes a gel, and age at room temperature for 2-4 h; calcinate the xerogel at 500 °C for 4 h in a nitrogen atmosphere, and cool naturally to room temperature to obtain a TiO ₂ /Fe ₃ O ₄ /MWCNTs composite photocatalyst ; The amount of ferric nitrate nonahydrate added described in the step (1) is: the mass ratio of ferric nitrate nonahydrate to MWCNTs is 40:1; the amount of sodium acetate added is: the mass ratio of sodium acetate to ferric nitrate nonahydrate is 6 :5. 2. According to the preparation method of magnetic composite photocatalyst described in claim 1, it is characterized in that the activated MWCNTs described in step (1) and ethylene glycol ratio are 30:25 mg/mL, polyethylene glycol and polyethylene glycol The mass ratio of vinylpyrrolidone is 40:1.