A bimetallic photocatalyst with titanium dioxide as carrier doped with Fe loaded with Pd, and a preparation method and application thereof

Abstract

The application discloses a bimetallic photocatalyst with titanium dioxide as a carrier, doping Fe and loading Pd, and a preparation method and application thereof. The bimetallic photocatalyst is prepared by the following steps: preparing a Fe-TiO2 modified carrier through a sol-gel method, and loading Pd through a sodium borohydride reduction method. The Pd / Fe-TiO2 photocatalyst obtained in the application has high degradation rate, high mineralization rate and high stability in the process of photocatalytic degradation of toluene, and the preparation method is simple and easy to implement, so the application has a good application prospect in the terminal treatment process of photocatalytic VOCs oxidation and degradation.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of atmospheric governance, the field of organized emission VOCs waste gas governance, the field of unorganized emission VOCs waste gas governance, and specifically relates to a bimetallic photocatalyst with titanium dioxide as a carrier doped with Fe loaded Pd, a preparation method and application thereof. The bimetallic modified catalyst can realize photocatalytic degradation of VOCs, has good degradation rate, mineralization rate and stability, and provides a new idea for photocatalytic oxidation and degradation of VOCs. BACKGROUND

[0002] Volatile organic compounds (VOCs) are considered to be a key factor leading to many environmental problems such as haze, global warming, etc. In addition to the governance at the source, tail gas treatment technologies such as physical adsorption, thermal catalysis, photocatalysis and plasma catalysis should be strengthened. Among them, photocatalysis is considered to be an innovative and low-energy process due to its relatively strong oxidation ability and low-temperature reaction conditions. The mechanism of photocatalytic degradation of volatile organic pollutants is worth further studying to provide theoretical support for the design of efficient catalysts. In the past few decades, photocatalysts have been applied to the degradation of VOCs, but there has always been a problem of poor stability. For example, P25 has commercial application value because it is low-cost, non-toxic, chemically stable, and has strong oxidation ability, but it also has the problem of poor stability, which limits its application in practical environments. It is worth noting that many toxic intermediates and by-products can be detected during the degradation of volatile organic pollutants. Recent studies have shown that the formation of intermediates can be one of the reasons for the deactivation of photocatalysts. Many works have explored new photocatalysts by developing more active catalysts, such as by constructing heterojunctions, metal loading, and doping. These methods can improve the performance of the catalyst, but the intrinsic relationship between intermediates and photocatalyst deactivation still needs to be further explored.

[0003] Based on the specific active oxygen species (ROS) activated in semiconductor photocatalysts, it has unique advantages in oxidizing various pollutants. Therefore, analyzing and studying the generation and reaction mechanism of ROS is crucial for better understanding the principles of photocatalytic elimination of pollutants. Generally speaking, in a photocatalytic system, the generation mechanism of several ROS is as follows: when a semiconductor is irradiated with ultraviolet-visible light with energy greater than its band gap, an oxidation-reduction reaction occurs. The excited electrons quickly migrate from the valence band VB to the conduction band CB, leaving h + in VB. In addition, H2O adsorbed on the surface of the photocatalyst is oxidized by h + in VB to form hydroxyl radicals •OH and protons hydrogen, and O2 adsorbed on the surface of the photocatalyst is reduced by e - to superoxide radicals •O2 -Therefore, it can be seen that in the process of photocatalytic degradation reaction, the photo-generated electrons and holes formed under light excitation adsorb and activate O2 and H2O respectively to generate superoxide radicals and hydroxyl radicals, which are two important active radicals in the reaction. Therefore, in the process of catalyst design, by inhibiting the recombination of photo-generated electrons and holes, forming a suitable electron transfer mode, constructing a system that can activate a suitable proportion of radicals, and providing adsorption sites for toluene degradation intermediates in the entire electron cycle process, the activated radicals are realized under photo-thermal conditions, and the adsorption and oxidation of toluene, the adsorption and mineralization of intermediate species, and the synergistic process of the three steps. If the process in this electron cycle does not achieve a synergistic effect, the phenomenon of low catalyst efficiency or deactivation will occur. In the face of the above challenges, the present application uses a catalyst modification method to realize the above-mentioned synergistic mode through the interaction rules of different metals in the bimetallic catalyst. SUMMARY

[0004] In view of the problems of low degradation rate and mineralization rate and poor stability in the existing application of VOCs photocatalytic oxidation degradation, the application provides a preparation method and application of a bimetallic photocatalyst doped with Fe and loaded with Pd on a titanium dioxide carrier. The method is simple and fast, and the prepared Pd / Fe-TiO2 catalyst has high photocatalytic VOCs oxidation degradation rate and mineralization rate and stability, provides a thought for subsequent catalyst design, and has good application prospect.

[0005] To achieve the above object, the application adopts the following technical scheme:

[0006] A bimetallic photocatalyst doped with Fe and loaded with Pd on a titanium dioxide carrier, which is a highly dispersed bimetallic photocatalyst composed of a titanium dioxide carrier and iron and palladium as main active components; wherein the content of Pd is 0.1-1.0 wt%, the content of Fe is 0.1-0.8 wt%, and the rest is the titanium dioxide carrier.

[0007] As described above, the photocatalyst is used for photocatalytic oxidation degradation evaluation by using a 300w xenon lamp to control the wavelength (lambda) range of 320-780nm, and the reaction temperature is controlled at 165℃. Under the condition that the air speed is 30000mL⋅g −1 ⋅h −1 , the degradation rate is 95%, the mineralization rate is 86%, and the catalytic activity is stable for 6h.

[0008] The preparation method of the bimetallic photocatalyst doped with Fe and loaded with Pd on a titanium dioxide carrier as described above uses a tetrabutyl titanate and iron nitrate solution as raw material to prepare a Fe-TiO2 carrier by a sol-gel method and then loads active component palladium on the obtained Fe-TiO2 carrier by a sodium borohydride reduction method. The specific preparation steps are as follows:

[0009] (1) First, 20 mL glacial acetic acid was added to 10 mL tetrabutyl titanate in an ice bath under vigorous magnetic stirring, then deionized H2O was added dropwise until a clear solution was obtained, then 0.1M Fe(NO3)3·9H2O solution was added dropwise to the above transparent solution, the amount of addition was 0 ml, 1.68 ml, 3.36 ml respectively. After stirring for 6 h, the formed sol was aged at room temperature for 12 h, then heated in a 80 ℃ silicon oil bath to obtain a solid precursor. Finally, calcination was carried out in a muffle furnace at a heating rate of 2 ℃ per minute to 500 ℃ for 1 h to obtain Fe-doped TiO2, 0wt% Fe-TiO2, 0.4wt% Fe-TiO2, 0.8wt% Fe-TiO2 respectively;

[0010] (2) 2 g Fe-TiO2 carrier prepared above was added to 100 ml deionized water, 1M NaOH solution and 2.33ml PdCl2 solution, the volume ratio of deionized water and 1M NaOH solution was 50:1, stirring for 1 h, then 0.25M NaBH4 solution was added, the volume ratio of deionized water and 0.25M NaBH4 solution was 25:1, continue stirring for 1 h, centrifugation, deionized water washing to obtain the precipitate, 80℃ drying, to obtain a bimetallic photocatalyst of Fe-doped Pd supported on TiO2 carrier. The concentration of PdCl2 solution is 6 mg·mL -1 .

[0011] The bimetallic photocatalyst of Fe-doped Pd supported on TiO2 carrier is applied to VOCs photocatalytic oxidation degradation. The Pd / Fe-TiO2 bimetallic modified catalyst can realize photocatalytic degradation of VOCs, and has good degradation rate, mineralization rate and stability, which provides a new idea for photocatalytic VOCs oxidation degradation.

[0012] The significant advantages of the present application are:

[0013] The present application modifies TiO2 by introducing appropriate proportions of Fe and Pd two metals, and the modified catalyst has good photo-generated carrier transfer efficiency and good photo-thermal catalytic oxidation activity. Due to the synergistic effect of the bimetallic based on TiO2, the two different active sites realize the activation of free radicals in the process of photoexcited electron transfer, the adsorption and ring-opening oxidation reaction of toluene, and the adsorption and mineralization reaction of intermediate species, so that the stability and high mineralization rate are maintained in the process of toluene oxidation degradation. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1XRD patterns of 0.7wt% Pd / TiO2, 0.7wt% Pd / 0.4wt% Fe-TiO2, 0.7wt% Pd / 0.8wt% Fe-TiO2 obtained from Example 1;

[0015] Figure 2 UV-Vis diffuse reflectance spectra of 0.7wt% Pd / TiO2, 0.7wt% Pd / 0.4wt% Fe-TiO2, 0.7wt% Pd / 0.8wt% Fe-TiO2 obtained from Example 1;

[0016] Figure 3 TEM images of 0.7wt% Pd / 0.4wt% Fe-TiO2 obtained from Example 1;

[0017] Figure 4 Impedance plots of 0.7wt% Pd / TiO2, 0.7wt% Pd / 0.4wt% Fe-TiO2, 0.7wt% Pd / 0.8wt% Fe-TiO2 obtained from Example 1;

[0018] Figure 5 Photocatalytic oxidation degradation of toluene evaluation plots of 0.7wt% Pd / TiO2, 0.7wt% Pd / 0.4wt% Fe-TiO2, 0.7wt% Pd / 0.8wt% Fe-TiO2 obtained from Example 1. DETAILED DESCRIPTION

[0019] In order that the above features and advantages of the present application can be more clearly understood, the following examples are given with reference to the accompanying drawings, in which:

[0020] Example 1

[0021] Preparation of 0.7wt% Pd / TiO2, 0.7wt% Pd / 0.4wt% Fe-TiO2, 0.7wt% Pd / 0.8wt% Fe-TiO2 catalysts

[0022] (1) First, 20 mL of glacial acetic acid was added to 10 mL of tetrabutyl titanate in an ice bath under vigorous magnetic stirring, then deionized H2O was added dropwise until a clear solution was obtained, then 0.1M Fe(NO3)3·9H2O solution was added dropwise to the above transparent solution, the amount of addition was 0 ml, 1.68 ml, 3.36 ml, respectively. After stirring for 6 h, the sol formed was aged at room temperature for 12 h, then heated in a silicon oil bath at 80 ℃ to obtain a solid precursor. Finally, calcination was carried out in a muffle furnace at a heating rate of 2 ℃ per minute to 500 ℃ for 1 h to obtain iron-doped TiO2, 0wt% Fe-TiO2, 0.4wt% Fe-TiO2, 0.8wt% Fe-TiO2, respectively;

[0023] (2) The 2 g Fe-TiO2 support prepared above with different doping amounts were respectively added with 100 ml deionized water, 1 M NaOH solution and 2.33 ml PdCl2 solution, the volume ratio of deionized water and 1 M NaOH solution was 50:1, stirring for 1 h, then 0.25 M NaBH4 solution was added, the volume ratio of deionized water and 0.25 M NaBH4 solution was 25:1, continue stirring for 1 h, centrifugation, deionized water washing to obtain the precipitate, drying at 80℃, obtaining the bimetallic photocatalyst of Fe doped Pd supported on titanium dioxide carrier, finally obtaining 0.7wt%Pd / TiO2, 0.7wt%Pd / 0.4wt%Fe-TiO2, 0.7wt%Pd / 0.8wt%Fe-TiO2. The concentration of PdCl2 solution was 6 mg·mL -1 .

[0024] Example 2

[0025] Performance evaluation of catalyst

[0026] In the process of evaluating the photocatalytic degradation of toluene, 200 ppm of toluene mixed gas was used under normal pressure, the oxygen content was 6%, the relative humidity was 70%, the flow rate was 100 ml / min, the catalyst dosage was 200 mg loaded in a quartz reactor (20×20×1 mm 3 ), the space velocity was 30000 mL⋅g −1 ⋅h −1 , the photocatalytic degradation of catalyst was evaluated by controlling the wavelength (λ) range of 320−780 nm by 300 w xenon lamp, and the reaction temperature was controlled at 165℃. The concentrations of toluene and CO2 were detected by gas chromatography FID detector. The toluene degradation rate and mineralization rate calculation formula (1) (2) are as follows.

[0027] Toluene degradation rate (%) = ([C7H8] in − [C7H8] out ) / [C7H8] in ×100% (1)

[0028] Toluene mineralization rate (%) = [CO2] out / ([C7H8] in ×7)×100% (2)

[0029] Figure 1 XRD patterns of the obtained 0.7wt%Pd / TiO2, 0.7wt%Pd / 0.4wt%Fe-TiO2, 0.7wt%Pd / 0.8wt%Fe-TiO2 catalysts. From Figure 1It can be seen from the figure that there is no X-ray diffraction peak of metal or metal oxide of Pd and Fe, which indicates that the amount of the two metals introduced is small, and they are uniformly distributed in the anatase crystal phase without destroying its inherent crystal structure.

[0030] Figure 2 The UV-Vis diffuse reflectance spectra of the obtained 0.7wt%Pd / TiO2, 0.7wt%Pd / 0.4wt%Fe-TiO2, 0.7wt%Pd / 0.8wt%Fe-TiO2 catalysts are shown in the figure. Figure 2 It can be seen from the figure that the synergistic effect of Fe and Pd shows a significant red shift of the absorption edge and a significant enhancement of the visible light capture ability, which reduces the band gap and significantly improves the transport efficiency of photo-generated carriers.

[0031] Figure 3 The transmission electron microscope image of the obtained 0.7wt%Pd / 0.4wt%Fe-TiO2 catalyst is shown in the figure. Figure 3 It can be seen from the figure that the catalyst has a cubic shape, and the Pd metal nanoparticles are uniformly distributed and closely combined with the catalyst carrier.

[0032] Figure 4 The impedance diagrams of the obtained 0.7wt%Pd / TiO2, 0.7wt%Pd / 0.4wt%Fe-TiO2, 0.7wt%Pd / 0.8wt%Fe-TiO2 are shown in the figure. Figure 4 It can be seen from the figure that a smaller impedance radius indicates a better electron transfer ability, which will accelerate electron transfer and inhibit the recombination of photo-generated electron-hole pairs. When the Pd / Fe ratio is 7:8, the impedance is large, which hinders the transfer of electrons. When the Pd / Fe ratio is 7:4, the impedance becomes smaller, and the synergistic effect of the bimetallic reaches the optimal efficiency, thereby improving the reaction activity.

[0033] Figure 5 The photocatalytic oxidation degradation of toluene evaluation diagram of the obtained 0.7wt%Pd / TiO2, 0.7wt%Pd / 0.4wt%Fe-TiO2, 0.7wt%Pd / 0.8wt%Fe-TiO2 catalysts is shown in the figure. Figure 5 It can be seen from the figure that 0.7wt%Pd / 0.4wt%Fe-TiO2 can achieve 200ppm toluene gas at a space velocity of 30000mL⋅g −1 ⋅h −1Under the condition of 6h, the degradation rate of 0.7wt%Pd / TiO2 is 95%, the mineralization rate is 86%, and the catalytic activity is stable. In the same 6h catalytic degradation evaluation, the degradation rate of 0.7wt%Pd / TiO2 is reduced to 71%, the mineralization rate is 74%; the degradation rate of 0.7wt%Pd / 0.8wt%Fe-TiO2 is reduced to 80%, and the mineralization rate is 70%. 0.7wt%Pd / TiO2, 0.7wt%Pd / 0.8wt%Fe-TiO2, both catalysts have low degradation rate, low mineralization rate, and low stability.

[0034] The above merely describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the present application should be included in the scope of the present application.

Claims

1. The application of a bimetallic photocatalyst with titanium dioxide as a support and Fe-supported Pd in ​​VOCs degradation, characterized in that: The bimetallic photocatalyst with titanium dioxide as a support and Fe-supported Pd is applied to the end-of-pipe treatment system for VOCs oxidation and degradation under ultraviolet-visible light photocatalysis, ultraviolet photocatalysis, ultraviolet-visible light photothermal catalysis, or ultraviolet photothermal catalysis. The photocatalyst described is a highly dispersed supported catalyst with TiO2 as the support and Fe and Pd bimetallic modification, in which the two active components work synergistically. The photocatalyst contains 0.7 wt% Pd, 0.4 wt% Fe, and the remainder is a TiO2 support. The method for preparing the bimetallic photocatalyst with titanium dioxide as a support and Fe-supported Pd involves using tetrabutyl titanate as a precursor, adding ferric nitrate nonahydrate to synthesize an iron-modified Fe-TiO2 support, and then using a simple sodium borohydride reduction method to load the second active component Pd onto the obtained Fe-TiO2 support with PdCl2 solution.

2. The application according to claim 1, characterized in that: The preparation method of the bimetallic photocatalyst with titanium dioxide as a support and Fe-supported Pd includes the following steps: (1) Fe-TiO2 sample was synthesized by sol-gel method: First, glacial acetic acid was added to tetrabutyl titanate in an ice bath under vigorous magnetic stirring, with a volume ratio of 2:

1. Then, deionized water was added dropwise until a clear solution was obtained. A certain amount of 0.1M Fe(NO3)3·9H2O solution was added and stirred for 6 h. The formed sol was aged at room temperature for 12 h. Then, it was heated in an 80 ℃ silicone oil bath to obtain a solid precursor. Finally, it was calcined in a muffle furnace at 500℃ for 1 h at a heating rate of 2℃ per minute to obtain iron-doped TiO2. (2) Deionized water, 1M NaOH solution and PdCl2 solution were added to the Fe-TiO2 support obtained in step (1). The volume ratio of deionized water to 1M NaOH solution was 50:

1. The mixture was stirred for 1 h. Then 0.25M NaBH4 solution was added. The volume ratio of deionized water to 0.25M NaBH4 solution was 25:

1. The mixture was stirred for another 1 h. The mixture was centrifuged, washed with deionized water to obtain a precipitate, and dried at 80 °C to obtain a bimetallic photocatalyst with Fe-supported Pd doped with titanium dioxide.

3. The application according to claim 2, characterized in that: In step (1), the amount of tetrabutyl titanate used is 10 ml, and the amount of glacial acetic acid used is 20 mL.

4. The application according to claim 2, characterized in that: In step (2), the concentration of the PdCl2 solution is 6 mg·mL. -1 .

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