A method for preparing a photocatalyst and application of the catalyst

Abstract

The invention discloses a method for preparing a photocatalyst, wherein biochar is prepared first, and then 10 mL of TBOT is added dropwise into 100 mL of ultrapure water and stirred for 12 h, and then a certain amount of biochar is added, and the stirring is continued for 12 h, and the prepared suspension is placed in a blast drying oven at 80°C for 24 h, and the sample is dried and ground and placed in a tube furnace, and heated to 500°C for calcination for 1 h in an NH3 atmosphere, wherein the heating rate is 2°C / min, and the sample obtained by calcination is a nitrogen-doped TiO2 / nitrogen-doped biochar composite catalyst, named NCNT, and the biochar and TiO2 in the NCNT are both nitrogen-doped. The invention uses HN3 as a nitrogen source for nitrogen doping, and studies have found that nitrogen-doped TiO2 and nitrogen-doped biochar have a synergistic effect on the photocatalytic degradation of methyl orange.

Description

Technical Field

[0001] The invention belongs to the field of photocatalysts, and in particular relates to a method for preparing a photocatalyst. Background Art

[0002] Doping with non-metallic elements is an effective method for modifying TiO2, which can change the valence band potential structure of the semiconductor, which is beneficial to reducing the band gap energy and broadening the light absorption range.

[0003] Commonly used non-metallic elements include N, S, I, and F, and nitrogen doping is the most common and has a good effect. The doped nitrogen element will form a new impurity energy level above the TiO2 valence band, which is beneficial to reduce the bandgap width and promote the absorption edge to shift to a higher wavelength, that is, the doped TiO2 can obtain significant photocatalytic activity under visible light irradiation.

[0004] Recent studies have reported that nitrogen-doped biochar can improve electron transfer efficiency and enhance photoelectrochemical properties. Matos et al. prepared nitrogen-doped biochar using NH3 as the nitrogen source, and further prepared TiO2 / nitrogen-doped biochar composite catalysts. The study found that the activity of the composite catalyst was significantly improved compared with TiO2, and the nitrogen functional groups in nitrogen-doped biochar can play a photo-assisted role.

[0005] However, there are few reports on the photocatalytic effect of TiO2 and biochar composite catalysts doped with nitrogen.

[0006] In view of this, the inventor of this case conducted in-depth research. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing a photocatalyst with better catalytic effect.

[0008] Another object of the present invention is to provide an application of a photocatalyst in the degradation of methyl orange.

[0009] In order to achieve the above object, the technical solution of the present invention is:

[0010] A method for preparing a photocatalyst comprises the following steps:

[0011] 10 mL of TBOT was added dropwise into 100 mL of ultrapure water and stirred for 12 h. Then a certain amount of biochar was added and stirred for another 12 h. The prepared suspension was placed in a forced air drying oven and dried at 80 °C for 24 h. After the sample was dried and ground, it was placed in a tubular furnace and heated to 500 °C for calcination for 1 h in an NH3 atmosphere, with a heating rate of 2 °C / min. The sample obtained by calcination was a nitrogen-doped TiO2 / nitrogen-doped biochar composite catalyst, named NCNT. Both the biochar and TiO2 in NCNT were doped with nitrogen.

[0012] Furthermore, the mass ratio of the added biochar to titanium ranges from 0.1:1 to 1:1.

[0013] Furthermore, the preparation method of biochar is as follows: the dried walnut shells are crushed with a grinder and then sieved to select particles with a diameter of less than 0.25 mm. The screened walnut shell powder is placed in a tubular furnace and heated to 700°C for pyrolysis under a N2 atmosphere, wherein the heating rate is 10°C / min and the constant temperature time is 2h. The prepared walnut shell biochar is named WB700.

[0014] Furthermore, the NCNT is used for the degradation of methyl orange, and the decolorization efficiency of methyl orange reaches 97%.

[0015] After adopting the above technical scheme, the preparation method of a photocatalyst of the present invention has the following beneficial effects: the present invention uses HN3 as a nitrogen source for nitrogen doping, and the research finds that the composite catalyst of nitrogen-doped TiO2 and nitrogen-doped biochar has a synergistic effect on the degradation of methyl orange. NCNT is applied to the degradation of methyl orange, and the photocatalytic decolorization efficiency of methyl orange can reach up to 97%. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a graph showing the photocatalytic degradation efficiency of methyl orange by different composite catalysts of the present invention;

[0017] Figure 2 This is a graph showing the photocatalytic degradation efficiency of methyl orange by different catalysts of the present invention;

[0018] Figure 3 This is the SEM-EDS mapping diagram of N-WB700, N-TiO2 and NCNT0.2 / 1 of the present invention. DETAILED DESCRIPTION

[0019] In order to further explain the technical solution of the present invention, the present invention is described in detail below through specific embodiments.

[0020] 1. Catalyst preparation

[0021] The present invention provides a method for preparing a photocatalyst, comprising the following steps:

[0022] (1) Preparation of biochar

[0023] The walnut shells were washed several times with deionized water and dried in a forced air drying oven at 80°C. After drying, the walnut shells were crushed with a grinder and then passed through a 60-mesh sieve to select particles with a diameter of less than 0.25 mm. The screened walnut shell powder was placed in a tubular furnace and heated to 700°C for pyrolysis under a N2 atmosphere (purity 99.99%), with a heating rate of 10°C / min and a constant temperature time of 2h. The prepared walnut shell biochar was named WB700.

[0024] (2) Preparation of nitrogen-doped TiO2 / nitrogen-doped biochar composite catalyst

[0025] 10mL TBOT was added dropwise into 100mL ultrapure water and stirred for 12h, then a certain amount of biochar was added (the mass ratio of biochar to titanium was 0.1 / 1, 0.2 / 1, 0.5 / 1, 0.8 / 1 and 1 / 1, respectively), and stirring was continued for 12h. The prepared suspension was placed in a blast drying oven and dried at 80℃ for 24h. After the sample was dried and ground, it was placed in a tube furnace and heated to 500℃ for calcination for 1h in an NH3 atmosphere, where the heating rate was 2℃ / min. The calcined samples were nitrogen-doped composite catalysts, and the catalysts were named NCNT0.1 / 1, NCNT0.2 / 1, NCNT0.5 / 1, NCNT0.8 / 1 and NCNT1 / 1.

[0026] 2. Catalyst Activity Study

[0027] 1. In the present invention, the catalyst activity is evaluated and analyzed by the photocatalytic degradation (decolorization rate and mineralization rate) of methyl orange.

[0028] The photocatalytic degradation experiment was carried out on a multi-position photocatalytic reactor with an annular reaction platform and a high-transmittance quartz cold trap, and a 500W long-arc mercury lamp was used as the ultraviolet light source, and a stabilized power supply was used to maintain the intensity of the light source, with a main wavelength of 360nm. In the experiment, 10mg of the catalyst was added to 40mL of a 20mg / L methyl orange solution and stirred continuously for 1 hour in the dark to reach adsorption equilibrium, and then the mercury lamp was turned on for irradiation and kept stirring. For subsequent analysis, an appropriate amount of solution was taken from the test tube and filtered with a 0.22μm filter membrane (PES, JINTENG) to remove the catalyst. The experiment was repeated under the same conditions.

[0029] The photocatalytic activity of the catalyst was evaluated by the decolorization rate and mineralization rate of methyl orange. The absorbance of methyl orange was measured by a spectrophotometer (Lambda 750, Perkinelmer) at a maximum absorption wavelength of 464 nm to determine the real-time concentration and thus the decolorization rate. The mineralization rate of methyl orange was determined by the total organic carbon measured by a total organic carbon analyzer (Vario TOC, Elementar).

[0030] The decolorization rate is calculated by formula 2-2:

[0031] decolorization efficiency(%)=100×([MO] o -[MO] t ) / [MO]0 (2-2)

[0032] where [MO] initial concentration of 0-methyl orange (mg / L);

[0033] [MO] t -Real-time concentration of methyl orange (mg / L).

[0034] The mineralization rate is calculated by formula 2-3:

[0035] mineralization efficiency(%)=100×([TOC] o -[TOC] t ) / [TOC]0 (2-3)

[0036] Where, [TOC] 0-initial total organic carbon of methyl orange (mg / L);

[0037] [TOC] t - Real-time total organic carbon (mg / L) of methyl orange.

[0038] 2. Decolorization rate

[0039] (1) Preparation of other composite catalysts

[0040] Preparation of TiO2 / biochar composite catalyst (hereinafter referred to as CT);

[0041] Nitrogen-doped TiO2 / biochar composite catalyst (hereinafter referred to as NTC);

[0042] TiO2 / nitrogen-doped biochar composite catalyst (hereinafter referred to as NCT);

[0043] Nitrogen-doped TiO2 / nitrogen-doped biochar composite catalyst (hereinafter referred to as NCNT)

[0044] The specific preparation method can be referred to as follows:

[0045] Preparation of CT: TiO2 / biochar composites were prepared by direct hydrolysis and subsequent high-temperature calcination: 10 mL TBOT was added dropwise to 100 mL ultrapure water and stirred for 12 h, then a certain amount of biochar was added (the mass ratio of biochar to titanium can be 0.2 / 1), and stirring was continued for 12 h. The prepared suspension was placed in a forced air drying oven at 80 ° C for 24 h, and the sample was dried and ground and placed in a tube furnace, heated to 500 ° C in a N2 atmosphere and calcined for 1 h, with a heating rate of 2 ° C / min. The sample obtained by calcination is the composite catalyst, and the catalyst is named CT 0.2 / 1.

[0046] Preparation of NCT: The preparation steps of TiO2 / nitrogen-doped biochar composite material are the same as those of the above-mentioned CT. The main difference is that the added biochar is nitrogen-doped biochar. The obtained catalyst is named NCT 0.2 / 1. The preparation method of nitrogen-doped biochar is as follows: the walnut shell biochar (WB700) prepared above is heated to 500℃ and calcined for 1h under NH3 atmosphere, wherein the heating rate is 2℃ / min. The calcined product is nitrogen-doped biochar, and the sample is named N-WB700.

[0047] Preparation of NTC: First, 10 mL of TBOT was added dropwise into 100 mL of ultrapure water and stirred for 12 h, then placed in a forced air drying oven at 80 °C for 24 h. After the sample was dried, it was placed in a tube furnace and heated to 500 °C for calcination for 1 h in an NH3 atmosphere, with a heating rate of 2 °C / min. The sample obtained by calcination is nitrogen-doped TiO2, named N-TiO2.

[0048] Then, the biochar was mixed with N-TiO2 (the mass ratio of biochar to titanium can be 0.2 / 1) to make a suspension, which was placed in a forced air drying oven at 80°C for 24 hours. After the sample was dried and ground, it was placed in a tube furnace and heated to 500°C in a N2 atmosphere for calcination for 1 hour, with a heating rate of 2°C / min. The sample obtained by calcination is the nitrogen-doped TiO2 / biochar composite catalyst, and the catalyst is named NTC.

[0049] It should be noted that in each composite catalyst, the mass ratio of (nitrogen-doped) biochar to titanium is 0.1 / 1, 0.2 / 1, 0.5 / 1, 0.8 / 1 and 1 / 1 respectively.

[0050] CT is named CT0.1 / 1, CT0.2 / 1, CT0.5 / 1, CT0.8 / 1 and CT1 / 1 accordingly.

[0051] NTC is named NTC0.1 / 1, NTC0.2 / 1, NTC0.5 / 1, NTC0.8 / 1 and NTC1 / 1 accordingly.

[0052] NCTs were named NCT0.1 / 1, NCT0.2 / 1, NCT0.5 / 1, NCT0.8 / 1, and NCT1 / 1, respectively.

[0053] NCNT0.1 / 1, NCNT0.2 / 1, NCNT0.5 / 1, NCNT0.8 / 1 and NCNT1 / 1

[0054] (2) Comparison of photocatalytic degradation efficiency of methyl orange between CT and NCNT

[0055] The photocatalytic degradation efficiency of methyl orange of each catalyst of CT and NCNT (CT0.1 / 1, CT0.2 / 1, CT0.5 / 1, CT0.8 / 1 and CT1 / 1 and NCNT0.1 / 1, NCNT0.2 / 1, NCNT0.5 / 1, NCNT0.8 / 1 and NCNT1 / 1) is shown in the figure Figure 1 shown.

[0056] Depend on Figure 1 It can be seen that the decolorization efficiency of composite catalysts CT0.1 / 1, CT0.2 / 1, CT0.5 / 1, CT0.8 / 1 and CT1 / 1 for methyl orange are 65.69%, 76.37%, 62.61%, 46.57% and 42.89% respectively, while the decolorization efficiency of a series of composite catalysts doped with nitrogen in the same proportion are 89.3%, 97.56%, 90.38%, 74.22% and 66.66% respectively, which are 35.94%, 27.75%, 44.35%, 58.76% and 55.42% higher than the same period last year. Therefore, after a series of TiO2 / biochar composite catalysts are doped with nitrogen, the degradation rate of methyl orange is improved. The reason for the improvement of the catalyst performance is the synergistic effect of nitrogen-doped TiO2 and nitrogen-doped biochar. At the same time, it can be observed that NCNT0.2 / 1 has the highest photocatalytic activity, which is mainly due to the existence of an optimal value for the biochar content. Excessive biochar forms a filtering effect on light, hindering light from reaching the catalyst surface and inhibiting the absorption of photons on the TiO2 surface, thereby reducing the catalyst performance.

[0057] (3) Comparison of photocatalytic degradation efficiency of methyl orange by NCT, NTC and NCNT

[0058] The photocatalytic degradation efficiency of NCT, NTC and NCNT catalysts for methyl orange is shown in the figure below. Figure 2 As shown, Figure 2 In the figure, the abscissa represents the mass ratio of biochar to titanium.

[0059] Depend on Figure 2 As shown, the decolorization efficiency of methyl orange by composite catalysts CT0.1 / 1, CT0.2 / 1, CT0.5 / 1, CT0.8 / 1 and CT1 / 1 were 65.69%, 76.37%, 62.61%, 46.57% and 42.89%, respectively. The decolorization efficiency of methyl orange by biochar nitrogen-doped composite catalysts (i.e. NCT) of CT, NCT0.1 / 1, NCT0.2 / 1, NCT0.5 / 1, NCT0.8 / 1 and NCT1 / 1 were 71.51%, 83.24%, 70.43%, 55.37% and 50.26%, respectively, which were increased by 8.86%, 9.00%, 12.97%, 18.90% and 17.18%, respectively.

[0060] The decolorization efficiency of CT's TiO2 nitrogen-doped composite catalyst (NTC), NTC0.1 / 1, NTC 0.2 / 1, NTC 0.5 / 1, NTC 0.8 / 1 and NTC 1 / 1 for methyl orange were 80.77%, 87.91%, 81.25%, 63.43% and 55.31%, respectively. The decolorization efficiency of CT's biochar and TiO2 nitrogen-doped composite catalyst (NCNT) for methyl orange were 89.3%, 97.56%, 90.38%, 74.22% and 66.66%, respectively. They were increased by 22.97%, 15.11%, 29.77%, 36.20% and 28.96%, respectively.

[0061] The improvement of methyl orange decolorization efficiency of NCNT compared with CT is greater than the sum of the improvement of decolorization efficiency of NCT compared with CT and the improvement of decolorization efficiency of NTC compared with CT. Specifically, the improvement of methyl orange decolorization efficiency of NCNT compared with CT is 12.91%, 15.09%, 4.38%, 6.64% and 20.11% higher than the sum of the improvement of decolorization efficiency of NCT compared with CT and the improvement of decolorization efficiency of NTC compared with CT, respectively.

[0062] It can be seen that nitrogen-doped TiO2 and nitrogen-doped biochar have a synergistic effect on the photocatalytic degradation of methyl orange, and the catalytic effect of NCNT is unpredictable.

[0063] 3. Catalyst energy spectrum

[0064] (1) Preparation of nitrogen-doped biochar

[0065] The walnut shells were washed several times with deionized water and dried in a forced air drying oven at 80°C. After drying, the walnut shells were crushed with a grinder and then passed through a 60-mesh sieve to select particles with a diameter of less than 0.25 mm. The screened walnut shell powder was placed in a tubular furnace and heated to 700°C for pyrolysis under a N2 atmosphere (purity 99.99%), with a heating rate of 10°C / min and a constant temperature time of 2h. The prepared walnut shell biochar was named WB700.

[0066] The prepared walnut shell biochar was heated to 500℃ in an NH3 atmosphere and calcined for 1h at a heating rate of 2℃ / min. The calcined biochar was nitrogen-doped and the sample was named N-WB700.

[0067] (2) Preparation of nitrogen-doped TiO2

[0068] 10 mL of TBOT was added dropwise into 100 mL of ultrapure water and stirred for 12 h, then placed in a forced air drying oven at 80 °C for 24 h. After the sample was dried, it was placed in a tube furnace and heated to 500 °C for calcination for 1 h in an NH3 atmosphere, with a heating rate of 2 °C / min. The sample obtained by calcination was nitrogen-doped TiO2, named N-TiO2.

[0069] In the present invention, the SEM-EDS mapping of N-WB700, N-TiO2 and NCNT0.2 / 1 is as follows: Figure 3 As shown in (a)(b)(c), (a) corresponds to N-WB700, (b) corresponds to N-TiO2, and (c) corresponds to NCNT0.2 / 1.

[0070] Depend on Figure 3 The presence of nitrogen in the three catalysts can be observed. The EDS-mapping diagram of N-WB700 shows that nitrogen is doped into the walnut shell biochar prepared by pyrolysis after calcination with NH3. The EDS-mapping diagram of N-TiO2 shows that nitrogen is doped into TiO2 after calcination with NH3. Therefore, the EDS-mapping diagram of NCNT0.2 / 1 can be inferred that the nitrogen in its sample exists in both biochar and TiO2.

[0071] The above embodiments and drawings do not limit the product form and style of the present invention. Any appropriate changes or modifications made thereto by ordinary technicians in the relevant technical field should be deemed to be within the patent scope of the present invention.

Claims

1. A method for preparing a photocatalyst, characterized in that: The method comprises the following steps: 10 mL TBOT is added dropwise into 100 mL ultrapure water and stirred for 12 h, then a certain amount of biochar is added and stirred for 12 h, the suspension is placed in a forced air drying oven at 80 °C for 24 h, the sample is dried and ground and placed in a tube furnace, and the temperature is raised to 500 °C for calcination for 1 h in an NH3 atmosphere, wherein the heating rate is 2 °C / min, and the sample obtained by calcination is a nitrogen-doped TiO2 / nitrogen-doped biochar composite catalyst, named NCNT, wherein the biochar and TiO2 in the NCNT are both nitrogen-doped; The mass ratio of added biochar to titanium was 0.2:1; The NCNT is used for the degradation of methyl orange, and the synergistic effect of nitrogen-doped TiO2 and nitrogen-doped biochar on the decolorization efficiency of methyl orange reaches 97%.

2. The method for preparing a photocatalyst according to claim 1, wherein: The preparation method of biochar is as follows: the dried walnut shells are crushed with a grinder and then sieved to select particles with a diameter less than 0.25 mm. The screened walnut shell powder is placed in a tubular furnace and heated to 700 °C for pyrolysis under a N2 atmosphere. The heating rate is 10 °C / min and the constant temperature time is 2 h. The prepared walnut shell biochar is named WB700.

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