Transition metal ion doped TiO2 as well as preparation method and application thereof

Abstract

The invention provides transition metal ion doped TiO2 as well as a preparation method and application thereof, and relates to the technical field of photocatalysis. The invention provides a preparation method of transition metal ion doped TiO2, which comprises the following steps: mixing a soluble transition metal salt solution with layered titanic acid for ion exchange to obtain transition metal ion intercalated layered titanic acid; the interlayer spacing of the layered titanic acid before mixing is 0.91 to 0.97 nm; the concentration of transition metal ions in the soluble transition metal salt solution is 0.1-2M; the ion exchange temperature is 20-50 DEG C, and the ion exchange time is 2-24 hours; and carrying out heat treatment on the transition metal ion intercalated layered titanic acid to obtain the transition metal ion doped TiO2. The photocatalytic activity of the metal ion doped TiO2 is improved by controlling the interlayer spacing of the layered titanic acid, the concentration of the transition metal ions in the soluble transition metal salt solution, the ion exchange temperature and the ion exchange time.

Description

Technical Field

[0001] The present invention relates to the field of photocatalysis technology, and in particular to transition metal ion-doped TiO2 and a preparation method and application thereof. Background Art

[0002] Synthesis gas is mainly composed of CO and H2, which is an important raw material for the production of hydrocarbons or high-value-added fine chemicals by the Fischer-Tropsch synthesis process. At present, synthesis gas is mainly produced by high-temperature vaporization or cracking of fossil fuels such as coal, coke, and natural gas. This reaction is usually accompanied by high carbon emissions and high energy consumption. The co-reduction of CO2 and H2O to produce adjustable ratio synthesis gas (H2 / CO) through photocatalytic reaction is considered to be a mild and green way to produce synthesis gas on an industrial scale with high economic benefits. It is also an effective way to solve the greenhouse effect and global energy demand.

[0003] The process of photocatalytic CO2 reduction to produce synthesis gas involves the adsorption and activation of H2O and CO2. In the process of photocatalytic reaction, the positions with low Ti ion coordination number on the TiO2 surface can usually serve as the active center of the catalytic reaction. Due to the high bonding strength of Ti-O on the TiO2 surface, the Ti ion coordination number on the TiO2 surface is mainly six-coordinated, resulting in fewer active sites on the TiO2 surface. Secondly, there are a small number of oxygen vacancies on the TiO2 surface, which leads to the Ti 3+ The formation of TiO2 causes uncoordinated electrons to exist on the surface of TiO2. When two substances come into contact, electrons usually flow from the substance with weaker electronegativity to the substance with stronger electronegativity. Since the electronegativity of the TiO2 surface is lower than that of CO2 but higher than that of H2O, after CO2 is adsorbed on the TiO2 surface, the uncoordinated electrons on the TiO2 surface can be transferred to the CO2 surface, while after H2O is adsorbed on the TiO2 surface, the electrons on the TiO2 surface cannot be transferred to the H2O surface. When CO2 and H2O are adsorbed on the TiO2 surface, the electrons transferred to the CO2 surface can activate CO2. The above reasons lead to the fact that when TiO2 photocatalytically reduces CO2 in water, it is usually easier to reduce CO2 to produce CO, etc., while it is difficult to reduce H2O to produce hydrogen at the same time.

[0004] Therefore, it is expected to achieve the co-reduction of CO2 and H2O by enriching the catalytic active sites on the TiO2 surface and regulating the surface electronegativity of TiO2. By regulating the defect composition of TiO2, the concentration of uncoordinated electrons on the TiO2 surface can be changed, thereby regulating the electronegativity of the TiO2 surface. Common methods for regulating the defect composition of TiO2 include surface hydrogenation treatment and ion doping. Among them, doping TiO2 with transition metal ions can not only regulate the defect composition of TiO2 surface, but also reduce the coordination number of Ti ions on the TiO2 surface and increase the concentration of uncoordinated electrons on the TiO2 surface, since the coordination number of metal ions on the surface of transition metal oxides is easy to change. Moreover, the introduced metal ions can serve as active sites for photocatalytic reactions, enriching the types of reaction active sites of TiO2 to achieve the co-reduction of CO2 and H2O.

[0005] The existing process generally achieves transition metal ion doping through a sol-gel method, but it is difficult to control defect locations using the sol-gel method, and the photocatalytic activity of transition metal ion-doped TiO2 prepared by the method still needs to be improved. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a transition metal ion doped TiO2 and a preparation method and application thereof. The transition metal ion doped TiO2 prepared by the present invention has high photocatalytic activity.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing transition metal ion-doped TiO2, comprising the following steps:

[0009] A soluble transition metal salt solution is mixed with layered titanic acid for ion exchange to obtain layered titanic acid intercalated with transition metal ions; the interlayer spacing of the layered titanic acid before mixing is 0.91 to 0.97 nm; the concentration of transition metal ions in the soluble transition metal salt solution is 0.1 to 2 M; the temperature of the ion exchange is 20 to 50° C., and the time is 2 to 24 hours;

[0010] The layered titanic acid intercalated with the transition metal ions is heat treated to obtain the transition metal ion-doped TiO2.

[0011] Preferably, the ratio of the volume of the soluble transition metal salt solution to the mass of the layered titanic acid is 50-100 mL:1 g.

[0012] Preferably, the transition metal ion includes Co 2+ 、Ni 2+ and Mn 2+ One or more of .

[0013] Preferably, the soluble transition metal salt solution contains two transition metal ions.

[0014] Preferably, the soluble transition metal salt in the soluble transition metal salt solution comprises nitrate and / or hydrochloride.

[0015] Preferably, the method for preparing the layered titanic acid comprises the following steps:

[0016] Alkali metal hydroxide and / or alkaline earth metal hydroxide are mixed with TiO2 and subjected to a low temperature eutectic reaction to obtain titanate; the temperature of the low temperature eutectic reaction is 150 to 250° C. and the time is 12 to 24 hours;

[0017] The titanate is mixed with an acid solution and subjected to an acidification treatment to obtain layered titanic acid.

[0018] Preferably, the ratio of the total mass of the alkali metal hydroxide and / or alkaline earth metal hydroxide to the mass of TiO2 is 1:1.

[0019] Preferably, the heat treatment temperature is 200-800° C. and the time is 1-24 hours.

[0020] The present invention also provides transition metal ion-doped TiO2 prepared by the preparation method described in the above technical solution.

[0021] The present invention also provides the application of the transition metal ion-doped TiO2 described in the above technical solution in the field of photocatalytic production of synthesis gas.

[0022] The present invention provides a method for preparing transition metal ion-doped TiO2, comprising the following steps:

[0023] A soluble transition metal salt solution is mixed with layered titanic acid for ion exchange to obtain layered titanic acid intercalated with transition metal ions; the interlayer spacing of the layered titanic acid before mixing is 0.91 to 0.97 nm; the concentration of transition metal ions in the soluble transition metal salt solution is 0.1 to 1 M; the temperature of the ion exchange is 20 to 50° C., and the time is 2 to 24 hours;

[0024] The layered titanic acid intercalated with the transition metal ions is heat treated to obtain the transition metal ion-doped TiO2.

[0025] The present invention realizes effective control of the doping position and uniformity of the doped metal ions in the TiO2 lattice by controlling the interlayer spacing of layered titanate, the concentration of transition metal ions in the soluble transition metal salt solution, and the temperature and time of ion exchange, thereby realizing effective regulation of the TiO2 energy band structure, defect composition, degree of lattice distortion, work function, coordination number of surface Ti ions and type of reaction active sites, thereby improving the photocatalytic activity of TiO2 doped with transition metal ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 XRD diagram of TiO2 co-doped with metal ions in Examples 1 to 3;

[0027] Figure 2 TEM image of Ni-Co metal ion co-doped TiO2 in Example 1;

[0028] Figure 3 This is an activity test diagram of metal ion co-doped TiO2 and TiO2 in water to produce synthesis gas by photocatalytic CO2 reduction. DETAILED DESCRIPTION

[0029] The present invention provides a method for preparing transition metal ion-doped TiO2, comprising the following steps:

[0030] A soluble transition metal salt solution is mixed with layered titanic acid for ion exchange to obtain layered titanic acid intercalated with transition metal ions; the interlayer spacing of the layered titanic acid before mixing is 0.91 to 0.97 nm; the concentration of transition metal ions in the soluble transition metal salt solution is 0.1 to 2 M; the temperature of the ion exchange is 20 to 50° C., and the time is 2 to 24 hours;

[0031] The layered titanic acid intercalated with the transition metal ions is heat treated to obtain the transition metal ion-doped TiO2.

[0032] The invention mixes a soluble transition metal salt solution with layered titanic acid to carry out ion exchange, thereby obtaining layered titanic acid with transition metal ions intercalated therein.

[0033] In the present invention, the method for preparing the layered titanic acid preferably comprises the following steps:

[0034] Alkali metal hydroxide and / or alkaline earth metal hydroxide are mixed with TiO2 and subjected to a low temperature eutectic reaction to obtain titanate; the temperature of the low temperature eutectic reaction is 150 to 250° C. and the time is 12 to 24 hours;

[0035] The titanate is mixed with an acid solution and subjected to an acidification treatment to obtain layered titanic acid.

[0036] The present invention mixes alkali metal hydroxide and / or alkaline earth metal hydroxide with TiO2 and then performs a low temperature eutectic reaction to obtain titanate.

[0037] In the present invention, the ratio of the total mass of the alkali metal hydroxide and / or alkaline earth metal hydroxide to the mass of TiO2 is preferably 1:1; the alkali metal hydroxide preferably includes potassium hydroxide and / or lithium hydroxide; and the alkaline earth metal hydroxide preferably includes magnesium hydroxide.

[0038] In the present invention, the temperature of the low-temperature eutectic reaction is 150-250°C. In a specific embodiment of the present invention, the temperature of the low-temperature eutectic reaction may be 150°C, 180°C, 200°C, 220°C or 250°C; the time is 12-24h. In a specific embodiment of the present invention, the time of the low-temperature eutectic reaction may be 12h, 15h, 18h, 20h or 24h.

[0039] After obtaining the titanate, the present invention mixes the titanate with an acid solution for acidification treatment to obtain layered titanic acid.

[0040] In the present invention, the volume ratio of the mass of the titanate to the acid solution is preferably 1g:50-100mL. In a specific embodiment of the present invention, the volume ratio of the mass of the titanate to the acid solution can be 1g:50mL, 1g:60mL, 1g:70mL, 1g:80mL, 1g:90mL or 1g:100mL.

[0041] The acid solution preferably includes hydrochloric acid or sulfuric acid; the concentration of the acid solution is preferably 0.5-1M. In a specific embodiment of the present invention, the concentration of the acid solution can be 0.5M, 0.6M, 0.7M, 0.8M, 0.9M or 1M.

[0042] In the present invention, the temperature of the acid treatment is preferably room temperature, and the time is preferably 12 to 24 hours. In a specific embodiment of the present invention, the time of the acid treatment can be 12 hours, 16 hours, 20 hours or 24 hours.

[0043] After the acid treatment, the present invention preferably includes: washing and drying the obtained acid-treated product after solid-liquid separation to obtain the layered titanic acid.

[0044] The present invention has no particular limitation on the washing, and washing can be performed using a scheme well known to those skilled in the art until the pH value reaches 6.8 to 7.0.

[0045] In the present invention, the interlayer spacing of the layered titanic acid before mixing is 0.91-0.97 nm. In a specific embodiment of the present invention, the interlayer spacing of the layered titanic acid before mixing can be 0.91 nm, 0.92 nm, 0.93 nm, 0.94 nm, 0.95 nm, 0.96 nm or 0.97 nm.

[0046] In the present invention, the volume ratio of the soluble transition metal salt solution to the mass ratio of the layered titanic acid is preferably 50 to 100 mL: 1 g. In the present invention, the volume ratio of the soluble transition metal salt solution to the mass ratio of the layered titanic acid is 50 mL: 1 g, 60 mL: 1 g, 70 mL: 1 g, 80 mL: 1 g, 90 mL: 1 g or 100 mL: 1 g. The transition metal ions in the soluble transition metal salt solution preferably include Co 2+ 、Ni 2+ and Mn 2+ One or more of; the soluble transition metal salt solution preferably contains two transition metal ions; the transition metal salt in the soluble transition metal salt solution preferably includes nitrate and / or hydrochloride.

[0047] In the present invention, the temperature of the ion exchange is 20-50°C. In a specific embodiment of the present invention, the temperature of the ion exchange can be 20-50°C, 30°C, 40°C or 50°C; the time is 2-24h. In a specific embodiment of the present invention, the time of the ion exchange can be 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h.

[0048] After the ion exchange reaction, the present invention preferably includes: washing and drying the obtained ion exchange reaction product after solid-liquid separation to obtain the transition metal ion intercalated layered titanic acid.

[0049] After obtaining the transition metal ion intercalated layered titanic acid, the present invention heat treats the transition metal ion intercalated layered titanic acid to obtain the transition metal ion-doped TiO2.

[0050] In the present invention, the heat treatment temperature is preferably 200-800°C. In a specific embodiment of the present invention, the heat treatment temperature can be 200°C, 300°C, 400°C, 500°C, 600°C, 700°C or 800°C. The time is preferably 1-24h. In a specific embodiment of the present invention, the heat treatment time can be 1h, 3h, 5h, 8h, 12h, 15h, 18h, 20h or 24h. After the heat treatment, the layered titanic acid is dehydrated to generate TiO2.

[0051] The present invention also provides transition metal ion-doped TiO2 prepared by the preparation method described in the above technical solution.

[0052] The present invention also provides the application of the transition metal ion-doped TiO2 described in the above technical solution in the field of photocatalytic production of synthesis gas.

[0053] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] Example 1

[0055] 1) 10 g of TiO2, 5.8 g of potassium hydroxide and 4.2 g of lithium hydroxide were uniformly mixed, and reacted at 150° C. for 24 h by a low temperature eutectic method to prepare potassium lithium titanate with an open structure;

[0056] 2) 10 g of potassium lithium titanate was then treated with 1000 mL of 0.5 M hydrochloric acid at room temperature for 12 h, and the sample was then washed with water to a pH of 6.8, filtered and dried, thereby preparing layered titanic acid with an interlayer spacing of 0.91 nm;

[0057] 3) ion exchange reaction was carried out between 100 mL of a solution containing 0.1 M cobalt chloride and 0.1 M nickel chloride and 2 g of layered titanic acid (the temperature of the ion exchange reaction was 20° C. and the time was 24 h), and Ni-Co ion-intercalated layered titanic acid was obtained after solid-liquid separation, washing and drying;

[0058] 4) Ni-Co metal ion co-doped TiO2 was prepared by heat treatment of Ni-Co ion intercalated layered titanate at 300℃ for 5h.

[0059] Example 2

[0060] 1) After 10 g of TiO2 and 10 g of potassium hydroxide were uniformly mixed, the mixture was reacted at 180° C. for 16 h by a low temperature eutectic method to prepare potassium titanate with an open structure;

[0061] 2) Then, 10 g of potassium titanate was treated with 500 mL of 1 M sulfuric acid at room temperature for 24 h, and then the sample was washed with water to a pH of 6.8, filtered and dried, thereby preparing layered titanic acid with an interlayer spacing of 0.93 nm;

[0062] 3) ion exchange reaction was carried out between 100 mL of a solution containing 0.5 M nickel nitrate and 0.5 M manganese nitrate and 1 g of layered titanic acid (the temperature of the ion exchange reaction was 50° C. and the time was 2 h), and Ni-Mn ion intercalated layered titanic acid was obtained after solid-liquid separation, washing and drying;

[0063] 4) Ni-Mn ion co-doped TiO2 was prepared by heat treatment of Ni-Mn ion intercalated layered titanate at 500℃ for 3h.

[0064] Example 3

[0065] 1) 10 g of TiO2 and 10 g of magnesium hydroxide were mixed uniformly as raw materials, and reacted at 250° C. for 12 h by a low temperature eutectic method to prepare magnesium titanate with an open structure;

[0066] 2) 10 g of magnesium titanate was then treated with 750 mL of 0.5 M hydrochloric acid at room temperature for 16 h, and the sample was then washed with water to a pH of 6.8, filtered and dried, thereby preparing layered titanate with an interlayer spacing of 0.97 nm;

[0067] 3) 100 mL of a solution containing 1 M cobalt nitrate and 1 M manganese chloride was subjected to an ion exchange reaction with 1.5 g of layered titanic acid (the temperature of the ion exchange reaction was 30° C. and the time was 12 h), and Co-Mn ion-intercalated layered titanic acid was obtained after solid-liquid separation, washing and drying;

[0068] 4) Co-Mn ion co-doped TiO2 was prepared by heat treatment of Co-Mn ion intercalated layered titanate at 800℃ for 1h.

[0069] Figure 1 The XRD diagram of metal ion co-doped TiO2 in Examples 1 to 3 is shown in FIG. Figure 1 It can be seen that the prepared products are all anatase phase.

[0070] Figure 2 TEM image of Ni-Co metal ion co-doped TiO2 in Example 1. Figure 2 It can be seen that the prepared samples are nanosheets with a large number of pore structures on the surface.

[0071] Figure 3 This is an activity test chart of metal ion co-doped TiO2 and TiO2 in Examples 1 to 3 for photocatalytic CO2 reduction in water to produce synthesis gas (using CO2 continuous gas phase flow method: 50 mg of metal ion co-doped TiO2 and TiO2 in Examples 1 to 3 are dispersed in 100 mL of water and their photocatalytic activity is tested in a 1 L reactor. The illumination condition is a 300 W xenon lamp simulating sunlight with a light intensity of 1 sun; the flow rate of CO2 is 20 mL / min). Figure 3 It can be seen that the product of pure phase TiO2 photocatalytic CO2 reduction in water is CO, and its yield is 15.67μmol / g / h. 2+ 、Co 2+ and Mn 2+The combination of the three elements was doped into TiO2 to obtain Ni-Co-TiO2, Co-Mn-TiO2 and Ni-Mn-TiO2, which photocatalytically reduced CO2 in water to CO and H2, and could directly produce synthesis gas. The H2 yields of Ni-Mn-TiO2, Co-Mn-TiO2 and Ni-Co-TiO2 were 181.91μmol / g / h, 174.99μmol / g / h and 107.82μmol / g / h, respectively; the CO yields were 14.39μmol / g / h, 7.94μmol / g / h and 34.84μmol / g / h, respectively.

[0072] The above results indicate that by regulating the type of TiO2 doping elements, the active sites of the TiO2 photocatalytic CO2 reduction reaction can be changed, and the type of CO2 reduction products in water can be regulated, thereby producing synthesis gas with adjustable composition ratio.

[0073] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing transition metal ion-doped TiO2, characterized in that: The following steps are involved: A soluble transition metal salt solution is mixed with layered titanic acid for ion exchange to obtain layered titanic acid intercalated with transition metal ions; the interlayer spacing of the layered titanic acid before mixing is 0.91 to 0.97 nm; the concentration of transition metal ions in the soluble transition metal salt solution is 0.1 to 2 M; the temperature of the ion exchange is 20 to 50° C., and the time is 2 to 24 hours; The layered titanic acid intercalated with the transition metal ions is heat treated to obtain the transition metal ion-doped TiO2.

2. The preparation method according to claim 1, characterized in that: The volume ratio of the soluble transition metal salt solution to the mass ratio of the layered titanic acid is 50-100 mL:1 g.

3. The preparation method according to claim 1 or 2, characterized in that: The transition metal ions include Co 2+ 、Ni 2+ and Mn 2+ One or more of .

4. The preparation method according to claim 3, characterized in that: The soluble transition metal salt solution contains two transition metal ions.

5. The preparation method according to claim 1, characterized in that: The soluble transition metal salt in the soluble transition metal salt solution includes nitrate and / or hydrochloride.

6. The preparation method according to claim 1, characterized in that: The preparation method of the layered titanic acid comprises the following steps: Alkali metal hydroxide and / or alkaline earth metal hydroxide are mixed with TiO2 and subjected to a low temperature eutectic reaction to obtain titanate; the temperature of the low temperature eutectic reaction is 150 to 250° C. and the time is 12 to 24 hours; The titanate is mixed with an acid solution and subjected to an acidification treatment to obtain layered titanic acid.

7. The preparation method according to claim 6, characterized in that: The ratio of the total mass of the alkali metal hydroxide and / or alkaline earth metal hydroxide to the mass of TiO2 is 1:

1.

8. The preparation method according to claim 1, characterized in that: The heat treatment temperature is 200-800° C. and the time is 1-24 hours.

9. Transition metal ion-doped TiO2 prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the transition metal ion-doped TiO2 as claimed in claim 9 in the field of photocatalytic production of synthesis gas.

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