CN103007913A - Preparation method of Ti3+ doped TiO2 composite graphene photocatalyst - Google Patents

Abstract

The invention relates to a preparation method of a Ti<3+>-doped TiO2 composite graphene photocatalyst. Graphene oxide and gas-phase titanium dioxide (P25) are used as precursors to prepare the novel Ti<3+>-doped TiO2 composite graphene photocatalyst by a low-temperature vacuum activation method. Compared with the prior art, the invention can simultaneously implement Ti<3+> autodoping modification of TiO2 by one step, so that the photocatalyst has strong visible light response range; by carrying out reduction modification on the graphene oxide, the photocatalyst has higher electron transmission capacity; and the supporting modification is carried out on the graphene surface by using the TiO2 nanoparticles to generate a Ti-O-C chemical bond, thereby promoting the transfer of photoproduced electrons from TiO2 to the graphene surface. The prepared graphene-supported TiO2 photocatalyst has high ultraviolet and visible light activity, and also has high capacity for hydrogen production by composing water under visible light.

Description

Preparation method of Ti3+ doped TiO2 composite graphene photocatalyst

technical field

The present invention relates to the field of nanometer photocatalytic materials, in particular to using cheap and easy-to-obtain P25 as a raw material, which can realize Ti3 ⁺ self-doping modification of _TiO2 , reduction modification of graphene oxide, and TiO2 and _TiO2 in one step. Composite modification of graphene to obtain a novel Ti ³⁺ doped TiO ₂ composite graphene photocatalyst preparation method.

Background technique

As we all know, TiO ₂ photocatalytic technology can only effectively utilize the ultraviolet light energy that is less than 6% of the sunlight incident on the earth's surface, and does not fully have the potential for sustainable development. In order to overcome this shortcoming of TiO ₂ , research on compound modification of TiO ₂ with carbon materials to improve its response to visible light has gradually attracted people's attention. Graphene is a rising star in materials science and condensed matter physics. Graphene, an absolute two-dimensional material, has excellent mechanical, thermal, optical and electrical properties, which has greatly inspired people to design graphene-based materials, which can be applied to nanoelectronics, biosensing, polymer composites, Interest in novel materials in technological fields such as hydrogen production and storage, drug delivery and photocatalytic technologies. Graphene is considered to be a multifunctional material that can transport electrons or holes better than carbon nanotubes due to its superior electrical properties, good electrical conductivity and chemical stability. In recent years, using the unique electrical properties of graphene to modify some materials and prepare new composite materials with better performance is a current research hotspot. The application of graphene to modify the electrochemical properties of _TiO2 is a research hotspot in the field of photocatalysis recently. As a carrier, graphene can not only play the role of electron transfer channel, but also improve the optical, electrical and photoelectric conversion properties of TiO ₂ . The recombination between graphene and titania will greatly improve the transfer efficiency of photogenerated carriers. Therefore, designing and preparing a new type of high-efficiency TiO ₂ composite graphene photocatalyst is a research hotspot and focus in the field of TiO ₂ photocatalysis.

Although graphene-supported _TiO2 has become a new type of high-performance photocatalyst, there are still many questions about the reduction of graphene oxide. For example, hydrazine hydrate is widely used as a reducing agent in the reduction of graphene oxide, but it is highly toxic and causes environmental pollution. Alcohol has low reducibility and can only reduce epoxy groups in graphene oxide, but not hydroxyl and carboxyl groups. The resulting graphene is actually an intermediate transition form, with properties and structures between graphene oxide and "fully" reduced graphene. Therefore, it is necessary to find a new green and environment-friendly reducing agent and to explore a new one-step reduction method, which has gradually become a research hotspot of graphene composite photocatalysts.

Contents of the invention

The purpose of the present invention is exactly to provide a kind of realization to TiO ₂ and the reduction modification of graphene oxide in order to overcome the defective that above-mentioned prior art exists, strengthens the Ti ³⁺ doped TiO ₂ composite graphene photocatalysts of the response of visible light Preparation.

The purpose of the present invention can be achieved through the following technical solutions:

The preparation method of Ti ³⁺ doped TiO ₂ composite graphene photocatalyst, this method uses graphene oxide, fumed titanium dioxide (P25) as precursor, adopts low-temperature vacuum activation method to prepare novel Ti ³⁺ doped TiO ₂ composite graphene photocatalyst Catalyst, specifically comprises the following steps:

Disperse the graphene oxide aqueous solution in ultrapure water, ultrasonically disperse for 1 hour, then add gas-phase titanium dioxide, stir magnetically for 1 hour, then ultrasonically disperse for 1 hour, dry at 100°C, and vacuum activate at 300°C for 3 hours to prepare Ti ^{3 +} Doped _TiO2 composite graphene photocatalyst.

The concentration of the graphene oxide aqueous solution is 2-3mg/ml.

The addition ratio of the gas-phase titanium dioxide to the graphene oxide aqueous solution is 0.5g gas-phase titanium dioxide/0.05-4.0ml graphene oxide aqueous solution.

The graphene oxide aqueous solution is prepared by the Hummer method.

The prepared negative Ti ³⁺ doped TiO ₂ composite graphene photocatalyst has a very strong absorption of visible light.

Taking methyl orange organic compound as the target degradation product, the Ti ³⁺ doped TiO ₂ composite graphene photocatalyst showed better UV, Visible light degradation ability.

Under visible light irradiation, the Ti3 ⁺ -doped _TiO2 composite graphene photocatalyst has a stronger performance of photo-splitting water to produce hydrogen than the blank P25.

Compared with the prior art, the invention adopts a low-temperature vacuum activation method to prepare a series of novel _TiO2 composite graphene photocatalysts. The one-step vacuum activation method can not only realize the reductive modification of _TiO2 , but also realize the reductive modification of graphene oxide at the same time. During the vacuum activation process, the surface and bulk phase of TiO ₂ will generate a large number of active Ti ³⁺ and oxygen vacancies. The impurity energy levels formed by Ti ³⁺ and oxygen vacancies effectively reduce the band gap of TiO ₂ , enhance its response to visible light, and greatly improve the visible light catalytic activity of TiO ₂ . The vacuum activation process can also effectively remove the hydroxyl groups on the surface of the catalyst, thereby increasing the degree of reduction of graphene oxide and making its conductivity closer to that of fully reduced graphene. In addition, the vacuum activation process can also promote the detachment of lattice oxygen and surface hydroxyl groups on the surface of _TiO2 , which is beneficial to the combination of C atoms in graphene and Ti on the surface of _TiO2 , and enhances the transmission efficiency of photogenerated electrons from _TiO2 to graphene. More importantly, the synergy between Ti ³⁺ self-doping and Ti-OC chemical bonds is the main reason for the photocatalytic activity of graphene composite TiO ₂ photocatalysts. The unique method, the vacuum activation method has simple equipment, greatly reduces the production cost, and is conducive to industrialization. In order to further enhance the photocatalytic activity of the composite photocatalyst, we will also perform a series of doping modifications on graphene and its surface-loaded _TiO2 . The number of photogenerated electrons generated by doped modified graphene and _TiO2 will be greatly increased, and the transfer efficiency of photogenerated electrons will be further improved, including the following advantages:

1) Compared with traditional modification methods such as doping and compounding, the vacuum activation method has simple equipment, greatly reduces production costs, and is conducive to industrialization.

2) The one-step vacuum activation method can not only realize the reductive modification of _TiO2 , but also realize the reductive modification of graphene oxide at the same time.

3) The surface and bulk phase of TiO ₂ will generate a large number of active Ti ³⁺ and oxygen vacancies. The impurity energy level formed by Ti ³⁺ and oxygen vacancies effectively reduces the forbidden band width of TiO ₂ and enhances its response to visible light.

4) The vacuum activation process can also effectively remove the hydroxyl groups on the surface of the catalyst, thereby increasing the degree of reduction of graphene oxide and making its conductivity closer to that of graphene in a completely reduced state.

5) The vacuum activation process can also promote the detachment of lattice oxygen and surface hydroxyl groups on the surface of TiO ₂ , which is beneficial to the combination of C atoms in graphene and Ti on the surface of TiO ₂ , and enhances the transmission efficiency of photogenerated electrons from TiO ₂ to graphene.

6) The prepared graphene-supported TiO ₂ photocatalyst not only has high ultraviolet and visible light activity, but also has high visible light water splitting ability to produce hydrogen.

Description of drawings

Fig. 1 is the TEM photo of the graphene oxide prepared by embodiment 2;

Fig. 2 is the XRD spectrogram of graphene oxide and the reduced graphene prepared by embodiment 2;

Fig. 3 is the Raman spectrum before and after catalyst reduction prepared by embodiment 8;

Fig. 4 is the UV-DRS spectrogram of prepared catalyst and comparative sample;

Fig. 5 is the adsorption column diagram (A) of prepared catalyst and comparative sample to MO (10mg/L) and its MO degradation curve (B) degraded under visible light;

Figure 6 is a graph of the photocatalytic activity of the prepared catalyst and comparative samples degrading MO under ultraviolet light;

Fig. 7 is the visible light activity figure of prepared catalyst and comparative sample;

Fig. 8 is a graph showing the activity of the prepared catalyst and the comparative sample for hydrogen production by photolysis of water under visible light.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1

Preparation of Graphene Oxide (GO)

The "Hummer" method was used to prepare GO, and the specific method was as follows: 3 g of graphite was dispersed in 12 ml of concentrated sulfuric acid containing 2.5 g of potassium persulfate and 2.5 g of phosphorus pentoxide, stirred at 80 °C for 4.5 h, then cooled to room temperature and placed at room temperature for 12 h . The resulting mixture was filtered, washed and naturally dried for 12 h. The pretreated graphite was added to 120ml of concentrated sulfuric acid, and 15g of potassium permanganate was added while stirring while keeping the temperature below 20°C, and stirred at 35°C for 2h. The mixture was diluted with 250 mL of deionized water, and the temperature was kept below 50°C in an ice-water bath. After stirring for 2 h, 0.7 L of deionized water was added, followed by the slow addition of 20 ml of 30% hydrogen peroxide. The mixed solution was bright yellow and bubbling. Stand still, remove the supernatant, add 10% hydrochloric acid to wash several times, wash several times with deionized water until it is not easy to settle, and dialyze for 10-15 days. The obtained sample was ultrasonically dispersed to obtain a uniformly dispersed graphene oxide aqueous solution.

Example 2

Preparation of Graphene (GR) Composite P25 Photocatalyst

The graduated cylinder measures the graphene oxide (GO) 0.02ml of 2.1mg/ml concentration prepared in Example 1, and is dispersed in 40ml ultrapure water. After ultrasonic dispersion for 1h, 0.5g P25 is added, and after magnetic stirring for 1h, then After ultrasonication for 1h, drying at 100°C, and vacuum activation at 300°C for 3h, a P25 supported graphene (GR) catalyst was obtained, marked as: V-P25-0.02GR.

Example 3

The graduated cylinder measures 0.05ml of graphene oxide (GO) with a concentration of 2.1mg/ml prepared in Example 1, and is dispersed in 40ml of ultrapure water. After ultrasonic dispersion for 1h, 0.5g of P25 is added, and after magnetic stirring for 1h, then After ultrasonication for 1h, drying at 100°C, and vacuum activation at 300°C for 3h, a P25 supported graphene (GR) catalyst was obtained, marked as: V-P25-0.05GR.

Example 4

Measure the graphene oxide (GO) 0.10ml that the concentration that embodiment 1 prepares is 2.1mg/ml by measuring cylinder, be dispersed in 40ml ultrapure water, after ultrasonic dispersion 1h, add 0.5g P25 again, after magnetic stirring 1h, again After ultrasonication for 1h, drying at 100°C, and vacuum activation at 300°C for 3h, a P25 supported graphene (GR) catalyst was obtained, marked as: V-P25-0.10GR.

Example 5

Measure the graphene oxide (GO) 0.20ml that the concentration that embodiment 1 prepares is 2.1mg/ml by measuring cylinder, be dispersed in 40ml ultrapure water, after ultrasonic dispersion 1h, add 0.5g P25 again, after magnetic stirring 1h, again After ultrasonication for 1h, drying at 100°C, and vacuum activation at 300°C for 3h, a P25 supported graphene (GR) catalyst was obtained, marked as: V-P25-0.20GR.

Example 6

The graduated cylinder measures the graphene oxide (GO) 0.50ml of 2.1mg/ml concentration prepared in Example 1, disperses it in 40ml ultrapure water, after ultrasonic dispersion for 1h, then adds 0.5g P25, after magnetic stirring for 1h, then After ultrasonication for 1h, drying at 100°C, and vacuum activation at 300°C for 3h, a P25 supported graphene (GR) catalyst was obtained, marked as: V-P25-0.50GR.

Example 7

Measure the graphene oxide (GO) 1.0ml that the concentration that embodiment 1 prepares is 2.1mg/ml by measuring cylinder, be dispersed in 40ml ultrapure water, after ultrasonic dispersion 1h, add 0.5g P25 again, after magnetic stirring 1h, again After ultrasonication for 1h, drying at 100°C, and vacuum activation at 300°C for 3h, a P25 supported graphene (GR) catalyst was obtained, marked as: V-P25-1.0GR.

Example 8

Measure the graphene oxide (GO) 2.0ml that the concentration that embodiment 1 prepares is 2.1mg/ml by measuring cylinder, be dispersed in 40ml ultrapure water, after ultrasonic dispersion 1h, add 0.5g P25 again, after magnetic stirring 1h, again After ultrasonication for 1h, drying at 100°C, and vacuum activation at 300°C for 3h, a P25-loaded graphene (GR) catalyst was obtained, marked as: V-P25-2.0GR.

Example 9

Measure the graphene oxide (GO) 4.0ml that the concentration that embodiment 1 prepares is 2.1mg/ml by measuring cylinder, be dispersed in 40ml ultrapure water, after ultrasonic dispersion 1h, add 0.5g P25 again, after magnetic stirring 1h, again After ultrasonication for 1h, drying at 100°C, and vacuum activation at 300°C for 3h, a P25 supported graphene (GR) catalyst was obtained, marked as: V-P25-4.0GR.

comparative example

After mechanically mixing P25 after vacuum activation at 300°C with GO after vacuum activation at 300°C, the resulting sample is labeled: mixture of V-P25 and GR.

The photocatalytic activity evaluation method provided by the invention is as follows:

The visible light catalytic activity of the prepared catalyst was evaluated by degrading methyl orange (MO, 10 mg/L) under visible light. The photocatalytic degradation experiment was carried out on a self-made device. Weigh 0.0700g catalyst sample into a quartz reaction tube, add 70mL of MO solution. Stir magnetically for 30min under the condition of no light, so that the MO molecules reach the adsorption-desorption equilibrium on the surface of the catalyst; Stirring was continued during the process, and the distance between the light source and the center of the quartz tube was 10 cm.

The ultraviolet photocatalytic activity of the prepared catalyst was evaluated by degrading methyl orange (MO, 20 mg/L) under ultraviolet light. In addition to the light source, the photocatalytic activity of the sample under ultraviolet light is tested in the same steps as the visible light activity test. Use a 300W high-pressure mercury lamp as the ultraviolet light source (the maximum emission wavelength of the light source is 365nm), the distance from the lamp to the center of the quartz tube is 24cm, and use an ultraviolet radiation meter UV-A (365nm single-channel probe, measuring range: 320-400nm ) measured that the average light intensity irradiated on the surface of the catalyst was 1230 μW/cm ^-2 .

During the above-mentioned visible and ultraviolet photocatalytic activity test process, a certain amount of reaction solution was taken out at regular intervals, centrifuged, and then the catalyst was filtered out with a filter head, and the clear liquid was injected into a cuvette, and the Cary100 ultraviolet light was used to - Determination of the absorbance value (A) of the degradant solution at the maximum absorption wavelength by a visible spectrophotometer. Lambert-Beer law is compounded between absorbance A and concentration of degradant molecules, so the degradation rate can be calculated by formula (1).

The experiment of hydrogen production by photolysis of water is carried out in a closed circulation system. The specific process is as follows: Weigh 0.05g of the catalyst and disperse it in 60ml of 25% methanol aqueous solution, then add 0.5ml of H ₂ PtCl ₆ (1g/L), and stir magnetically for 5min. Then the solution was irradiated under a 300W high-pressure mercury lamp for 120min to load Pt on the surface of the catalyst. After the whole circulation system is evacuated, the visible light of the xenon lamp is still used as the light source (the ultraviolet light <420nm is filtered out with a 420nm filter). H2 produced by photolysis of water was analyzed by gas chromatography (TechompGC-7890II, thermal conductivity detector (TCD)).

Instructions in the accompanying drawings: V-P25-0.02GR, V-P25-0.05GR, V-P25-0.10GR, V-P25-0.20GR, V-P25-0.50GR, V-P25-1.0GR, V -P25-2.0GR, V-P25-4.0GR correspond to the catalyst products prepared in Examples 2-9 respectively, mixture of V-P25 and GR is the comparative sample prepared in the comparative example, P25 is blank titanium dioxide, V-P25 GO is graphene oxide, and GR is graphene after vacuum reduction.

Fig. 1 is the TEM photo of the graphene oxide prepared in embodiment 2. Figure 1 shows that although the surface of graphene oxide prepared by the "Hummers" method has wrinkles, it is still relatively smooth.

Figure 2 is the XRD spectrum of graphene oxide and the reduced graphene prepared in Example 2, and Figure 3 is the Raman spectrum of V-P25/2.0GR before and after reduction. Figure 2 shows that, compared with the blank P25, the crystal form and crystallinity of the catalyst V-P25, which has only been vacuum activated at 300°C without graphene, have basically not changed. This shows that the vacuum activation method we adopt is not only simple to operate, but also has a relatively low calcination temperature, and can better maintain the crystal form of TiO ₂ . After loading graphene, the crystal form and crystallinity of the catalyst did not change significantly, and both before and after loading showed good mixed crystals of anatase and rutile. In addition, in the XRD spectrum of the graphene-loaded photocatalyst, a characteristic peak of reduced graphene appeared at around 2θ=18.0°. Compared with the blank graphene oxide (GO), the XRD peaks of the vacuum-reduced graphene (GR) changed significantly. The characteristic peak of GO at 10.2° increased to 16.6° after vacuum reduction treatment, which indicated that graphene oxide was reduced to graphene. The XRD peak at 18.0° of the graphene-loaded P25 also indicates that the vacuum activation process successfully reduced graphene oxide to graphene. In Figure 3, a represents before reduction; b represents after reduction. After 300°C vacuum reduction of GO loaded with P25, the peak position of the G band shifts from 1610.7 cm ^-1 to 1598.7 cm ^-1 , while the G band characteristic of graphene The peak is at 1598cm ^-1 , which indicates that vacuum reduction can partially reduce graphene oxide to graphene. At the same time, the ratio of D/G increases significantly after reduction, indicating that the surface defect content of graphene oxide after vacuum activation increases, and indirectly proves that graphene oxide does undergo a reduction reaction during vacuum activation.

Fig. 4 is the UV-DRS spectrogram of the catalyst prepared in Example 1. Figure 4 shows that with the increase of GO addition, the absorption of the catalyst in the visible region is gradually enhanced. It is worth noting that the absorption of the samples prepared by the vacuum activation method and the samples prepared by the mechanical grinding method is obviously different in the visible light region. Compared with P25, the absorption band in the visible light region of the sample treated by vacuum activation has a significant red shift, especially when the loading amount of graphene is greater than 0.50mL, its absorption in the visible light region is significantly enhanced.

Fig. 5 is the adsorption histogram (A) of the prepared catalyst and comparative sample to MO (10mg/L) and its degradation curve (B) of MO under visible light degradation. Figure 5(A) shows that the catalyst prepared after loading graphene on P25 has a good adsorption effect on MO. Figure 5(B) shows that with the increase of GO addition, the adsorption of MO by the catalyst is gradually enhanced, and its visible light activity is also gradually increased.

Fig. 6 is a diagram of the photocatalytic activity of the prepared catalyst and the comparative sample for degrading MO under ultraviolet light. Figure 6 shows that the catalyst prepared by loading graphene on P25 also has a good adsorption effect on 20 mg/L MO, and with the increase of GR loading, the ultraviolet light activity of the catalyst also gradually increases.

Fig. 7 is the visible light activity diagram of the prepared catalyst and comparative samples. Figure 7 shows that although the catalyst prepared by the mechanical mixing method also has a good adsorption effect on MO, its ultraviolet light activity is much worse than that of the catalyst prepared by the vacuum activation method, which shows that P25 and There is an interaction between GR, which is mainly manifested in the formation of Ti-OC bonds, while the catalyst prepared by the mechanical mixing method is only a simple physical mixing, and there is no chemical bond formation between P25 and GR. The low-temperature vacuum activation method can not only realize the reduction of GO to GR in one step, but also realize the true recombination of P25 on the surface of GR. The formation of Ti-OC bonds between _TiO2 and GR will facilitate the transfer of photogenerated electrons, thereby promoting the separation of photogenerated electrons and holes, and finally enhancing the UV photoactivity of graphene-supported _TiO2 photocatalysts.

Fig. 8 is a graph showing the activity of the prepared catalyst and the comparative sample for hydrogen production by photolysis of water under visible light. Figure 8 shows that after P25 and graphene are combined, the hydrogen production ability under visible light is significantly stronger than that of the blank P25, indicating that the catalyst prepared by the vacuum activation method has a good ability to photolyze water to produce hydrogen.

Claims (4)

1.Ti ³⁺Doped Ti O ₂The preparation method of composite graphite alkene photochemical catalyst is characterized in that, the method adopts the cryogenic vacuum activation method to prepare new Ti take graphene oxide, gas phase titanium dioxide (P25) as presoma ³⁺Doped Ti O ₂Composite graphite alkene photochemical catalyst specifically may further comprise the steps:

The graphite oxide aqueous solution is scattered in the ultra-pure water, behind the ultrasonic dispersion 1h, adds gas phase titanium dioxide again, behind the magnetic agitation 1h, ultrasonic dispersion 1h after 100 ℃ of dryings, in 300 ℃ of lower vacuum activating 3h, namely prepares Ti again ³⁺Doped Ti O ₂Composite graphite alkene photochemical catalyst.

2. Ti according to claim 1 ³⁺Doped Ti O ₂The preparation method of composite graphite alkene photochemical catalyst is characterized in that, the concentration of described graphite oxide aqueous solution is 2-3mg/ml.

3. Ti according to claim 1 ³⁺Doped Ti O ₂The preparation method of composite graphite alkene photochemical catalyst is characterized in that, described gas phase titanium dioxide is 0.5g gas phase titanium dioxide/0.05-4.0ml graphite oxide aqueous solution with the addition ratio of graphite oxide aqueous solution.

4. Ti according to claim 1 ³⁺Doped Ti O ₂The preparation method of composite graphite alkene photochemical catalyst is characterized in that, described graphite oxide aqueous solution adopts the Hummer method to prepare.

Images