Terbium-doped anatase type titanium dioxide photocatalytic material and application thereof in arsenic polluted water treatment

Abstract

The invention belongs to the technical field of photocatalysis and water pollution treatment, and particularly relates to a terbium-doped anatase type titanium dioxide photocatalytic material and application thereof in arsenic polluted water treatment. The preparation method comprises the following steps: dissolving titanium dioxide in an alkali solution, uniformly dispersing, and carrying out hydrothermal reaction to obtain a potassium titanate nanowire precursor; and then mixing the precursor, hexamethylenetetramine and a TbCl3 solution, and carrying out secondary hydrothermal reaction and calcination treatment to obtain the terbium-doped TiO2 material. The material is mainly based on a crystal face (101), and the visible light absorption and carrier separation efficiency is remarkably improved through terbium doping. Under visible light, the oxidation rate of As (III) is increased by 3.5-4 times or above compared with pure TiO2 and commercial P25, and the photocatalyst is suitable for treatment of arsenic-polluted water with the pH value of 1-13 and has the advantages of being efficient, environmentally friendly and low in cost.

Description

Technical Field

[0001] The present invention belongs to the technical fields of photocatalysis and water pollution treatment, and particularly relates to a terbium-doped anatase titanium dioxide photocatalytic material and its application in the treatment of arsenic-polluted water. Background Art

[0002] Arsenic is a toxic element widely present in the environment, and its presence in water seriously threatens human health. Compared with As(V), As(III) is more toxic and more difficult to be removed by conventional adsorbents. In the prior art, the photocatalytic oxidation method has become an important method for treating arsenic pollution due to its high efficiency and environmental friendliness. However, traditional titanium dioxide (such as commercial P25) has a relatively large band gap (about 3.0 - 3.2 eV), can only utilize ultraviolet light, and has a high recombination rate of photo-generated electrons and holes, resulting in low catalytic efficiency under visible light. In recent years, regulating the energy band structure of TiO 2 by element doping (such as rare earth elements) has become a research hotspot, but there has been no report in the prior art on synthesizing a terbium-doped anatase TiO 2 material mainly with (101) crystal plane by hydrothermal method and systematically applying it to the visible-light photocatalytic oxidation of As(III). Summary of the Invention

[0003] In order to overcome the above deficiencies of the prior art, the present invention provides a preparation method of a terbium (Tb)-doped anatase titanium dioxide (TiO 2 ) photocatalytic material, and the prepared terbium-doped anatase TiO 2 material can efficiently catalyze the oxidation of trivalent arsenic (As(III)) in water to pentavalent arsenic (As(V)) under visible light.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] The first aspect of the present invention provides a preparation method of a terbium-doped anatase titanium dioxide photocatalytic material, and the method includes the following steps:

[0006] S1. Dissolve titanium dioxide in an alkali solution, disperse it evenly, and obtain a potassium titanate nanowire precursor through hydrothermal reaction;

[0007] S2. Mix the potassium titanate nanowire precursor, hexamethylenetetramine and TbCl 3 solution, carry out a secondary hydrothermal reaction, and after pickling and drying, then carry out calcination treatment to obtain the terbium-doped anatase titanium dioxide photocatalytic material.

[0008] Preferably, calculated by atomic percentage, the doping concentration of terbium is 4.8% - 13.2%.

[0009] Preferably, the alkali solution is an 8-12M KOH solution.

[0010] Preferably, the conditions of the two hydrothermal reactions are the same, both being a reaction at 190-250 °C for 20-30 hours.

[0011] Preferably, in S2, the concentration of hexamethylenetetramine is 0.03-0.08M, and the mass concentration of the TbCl 3 solution is 4%-7%.

[0012] Preferably, the temperature of the calcination treatment is 300-400 °C, and the time is 2-5 hours.

[0013] The second aspect of the present invention provides a terbium-doped anatase titanium dioxide photocatalytic material prepared by the preparation method described in the first aspect.

[0014] The third aspect of the present invention provides the application of the terbium-doped anatase titanium dioxide photocatalytic material described in the second aspect in the treatment of arsenic-polluted water.

[0015] The terbium-doped anatase TiO 2 material prepared by the present invention has an oxidation rate of As(III) under visible light that is 3.5-4 times higher than that of pure TiO 2 and commercial P25, and is applicable to the treatment of arsenic pollution in water bodies within a wide pH range (pH 1-13).

[0016] Preferably, the terbium-doped anatase titanium dioxide photocatalytic material described in the second aspect is added to the As(III)-containing water body, and catalytic oxidation is carried out for not less than 90 minutes under visible light and oxygen conditions.

[0017] More preferably, the dosage of the terbium-doped anatase titanium dioxide photocatalytic material is 0.1-0.3 g / L, and the pH range of the water body is 1-13.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] The present invention discloses a preparation method of a terbium-doped anatase titanium dioxide photocatalytic material. This terbium-doped TiO 2 material is synthesized by a hydrothermal method. Specifically, titanium dioxide is first dissolved in an alkali solution, and after being dispersed evenly, a potassium titanate nanowire precursor is prepared through a hydrothermal reaction; then the precursor, hexamethylenetetramine and TbCl 3 solution are mixed, and after a secondary hydrothermal reaction and a calcination treatment, it is obtained. The prepared terbium-doped TiO 2 material is mainly based on the (101) crystal plane, and terbium doping significantly improves the visible light absorption and carrier separation efficiency. Under visible light, its oxidation rate of As(III) is higher than that of pure TiO 2It is 3.5 - 4 times or more higher than commercial P25 and is applicable to the treatment of arsenic - contaminated water bodies with pH ranging from 1 to 13, having the advantages of high efficiency, environmental protection, and low cost. Specifically, the present invention has the following advantages:

[0020] (1) Through terbium doping and (101) crystal plane regulation, the visible - light absorption ability and carrier separation efficiency of TiO2 are significantly improved;

[0021] (2) The hydrothermal method has a simple process and low energy consumption, being suitable for large - scale production;

[0022] (3) It can efficiently oxidize As(III) within a wide pH range, providing an efficient and environmentally - friendly solution for the treatment of arsenic - contaminated water bodies. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 : XRD pattern and XPS spectrum of terbium - doped TiO 2 ;

[0024] Figure 2 : Raman test pattern of terbium - doped TiO 2 ;

[0025] Figure 3 : SEM, HRTEM and EDS element distribution maps of terbium - doped TiO 2 ;

[0026] Figure 4 : Photochemical performance tests (PL, UV - Vis, EIS, M - S curves) of terbium - doped TiO 2 ;

[0027] Figure 5 : Photocatalytic oxidation experiment of terbium - doped TiO 2 ;

[0028] Figure 6 : Comparative photocatalytic oxidation experiment and kinetic fitting of terbium - doped TiO 2 with pure TiO 2 and commercial P25;

[0029] Figure 7 : Free radical oxidation capture experiment;

[0030] Figure 8 : Adsorption kinetics and isotherm fitting of terbium - doped TiO2 for As(V); DETAILED DESCRIPTION OF THE INVENTION

[0031] The following further describes the specific embodiments of the present invention. It should be noted here that the description of these embodiments is used to help understand the present invention, but does not limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] In the following experimental methods of the examples, unless otherwise specified, they are all conventional methods. The test materials used in the following examples, unless otherwise specified, can all be obtained through conventional commercial channels.

[0033] All the following experiments were repeated three times, and the data error was less than 5%.

[0034] Example: Terbium-doped anatase TiO 2 Preparation and characterization of materials

[0035] (1) Take 22.4 g of solid KOH, dissolve it in 40 mL of deionized water to make a 10 M KOH solution. Then add 1 g of commercial titanium dioxide (P25) to the KOH solution. After ultrasonic and stirring to make the dispersion sufficient, transfer it to a polytetrafluoroethylene reaction kettle and carry out a hydrothermal reaction at 200 °C for 24 hours to obtain a potassium titanate nanowire precursor;

[0036] (2) Mix 0.2 g of the dried precursor with 0.28 g of 0.05 M hexamethylenetetramine and 0.0526 g of 5% TbCl 3 solution, carry out a secondary hydrothermal reaction at 200 °C for 24 hours. After pickling (2.5 mol / L dilute sulfuric acid) and drying, then calcine it at 350 °C for 3 hours to obtain terbium-doped TiO 2 . By mass concentration, the doping concentration of terbium is 3.00%.

[0037] XRD( Figure 1 a) shows that the prepared terbium-doped TiO 2 is a pure anatase phase. The Raman spectrum ( Figure 2 ) is consistent with the characteristic peak of the (101) crystal plane, indicating substitutional doping. The instrument used for Raman testing is Renishaw inVia produced by Renishaw in the UK, laser: 532 nm, wavenumber range 100 - 800 cm -1 . Figure 1 b is the full spectrum of XPS, and no other oxidation state peaks appear, suggesting a high chemical purity of the surface titanium species, and the content of the secondary oxidation state is lower than the detection limit of XPS. Figure 1 c is Ti 4+ The Ti 2p 3 / 2 and Ti 2p 1 / 2 , indicating that there is spin-orbit splitting of titanium elements, which is a normal phenomenon. Ti 4+Corresponding to a relatively high binding energy, consistent with the standard value, and the peak shape is symmetric, which may indicate that titanium is in a single chemical environment, that is, uniform Ti 4+ state, indicating that titanium mainly exists in the form of Ti 4+ and there are no other oxidation states. XPS( Figure 1 d) further confirmed the successful doping of Tb 3+ .

[0038] SEM( Figure 3 a) shows that the material has an octahedral structure; HRTEM( Figure 3 b) shows that the interplanar spacing of the (101) crystal plane is 0.343 nm; Figure 3 c is the total EDS spectrum of terbium-doped titanium dioxide. It can be seen that the doping distribution is uniform and there is no aggregation or segregation of Figure 3 ; d is the spectrum of titanium. The signal uniformity of titanium reflects the chemical stability of the matrix (such as TiO 2 ), indicating that the local structure is not damaged due to Tb doping; Figure 3 e is the spectrum of oxygen. The uniform distribution of oxygen is related to the formation of the matrix oxide (such as TiO 2 ). It can be seen that the signal intensity is stable, indicating that the oxidation state of the material is consistent; Figure 3 f is the spectrum of Tb. The signal is obvious, indicating successful doping and uniform distribution, and no enrichment region is formed.

[0039] PL spectrum( Figure 4 a) shows that terbium doping significantly inhibits electron-hole recombination; UV-visible spectrum( Figure 4 b) shows enhanced visible light absorption and the band gap is reduced to 3.19 eV; Figure 4 c is obtained from the original data test of Figure 4 b and is the intuitive band gap result calculated by the diffuse reflection law (Kubelka-Munk equation), Figure 4 d is the test result of EIS, that is, alternating current impedance. The smaller the radius, the smaller the resistance value, indicating better conductivity. The results show that Tb doping can effectively improve the conductivity and the mobility of photo-generated electron-hole pairs of titanium dioxide, and the oxidation effect is better; Figure 4 e is to further study the transfer ability of photo-generated carriers using the Nyquist plot. It can obtain the flat band potential (E FB ). Generally, the flat band potential of an n-type semiconductor is about 0.1 eV more positive than the conduction band potential (E CB ). For an n-type semiconductor, the approximate relationship between the flat band potential (E FB ) and the bottom of the conduction band (E CB ) is: E FB ≈E CB +0.1 eV; accordingly, the bottom of the conduction band of pure TiO 2 isCB ≈ -0.55 - 0.1 = -0.65 eV, the bottom of the conduction band E doped with Tb CB ≈ -0.41 - 0.1 = -0.51 eV. Combining Figure 4 c with the measured band gap, and then according to the formula E VB = E g + E CB it can be calculated that the valence band potential (E VB ) of Tb-doped is +2.78 eV, which is larger than the valence band potential (E VB ) +2.71 eV of pure titanium dioxide; the above results show that the more positive the valence band potential, the stronger the photocatalytic ability.

[0040] From the above results, it can be seen that the terbium-doped anatase TiO 2 prepared in this example has the (101) plane as the main crystal plane. At the same time, it can be seen from Table 1 that the doping concentration of terbium is 4.8% (atomic percentage), and the lattice constant is The specific surface area (SBET) is 26.29 m 2 / g, and the average pore diameter is 17.17 nm.

[0041] Table 1 XPS data of terbium-doped anatase TiO 2

[0042]

[0043] Experimental example: Photocatalytic performance of terbium-doped anatase TiO 2 material

[0044] Add the terbium-doped TiO 2 (0.1 g / L) prepared in the example to the water body containing As(III) (initial concentration 1 mg / L), and carry out catalytic oxidation under visible light (35 W xenon lamp) and oxygen conditions, adjust the pH range to 1 - 13, and sample every 15 minutes to measure its arsenic content. The results are as Figure 5 shown. The highest oxidation rate of As(III) can reach 82.88% (pH 10) within 90 minutes; within the wide pH range of pH 1 - 13, the lowest oxidation rate of As(III) has reached 40%, indicating that the terbium-doped TiO 2 of the present invention is suitable for the treatment of arsenic pollution in water bodies with a wide pH range (pH 1 - 13).

[0045] At the same time, under the conditions of pH = 7 or 10, a photocatalytic oxidation comparative experiment was carried out on the terbium-doped TiO 2 and pure TiO 2 and commercial P25 as three different adsorbents. The experimental concentration conditions and experimental environment are the same as above. The results are as Figure 6 ​As shown, at pH 7, the oxidation rate constant (k 2 ) of As(III) doped with terbium in TiO 1 is 0.01008 min -1 , which is 3.5 times that of pure TiO 2 (0.00286 min -1 ) and 4 times that of commercial P25 (0.00252 min -1 ) ( Figure 6 b); at pH 10, the As(III) concentration decreases from 1000 μg / L to 197 μg / L (removal rate is 82.88%) ( Figure 6 a);

[0046] In addition, a radical trapping experiment was carried out under the condition of pH = 7. First, nitrogen was passed through to remove oxygen to exclude the interference of oxygen radicals on the experiment. A blank control group and an experimental group were set up (the experimental concentration conditions and experimental environment were the same as above). A radical scavenger was used to explore the active species of photocatalytic oxidation. If the catalytic oxidation effect was not greatly affected, it indicated that it was not the main active species. Among them, the radical scavenger benzoquinone (BQ) was used for O2· - , disodium ethylenediaminetetraacetate (ENTA-2Na) was used for H + , and tert-butanol (BA) was used as the photogenerated hydroxyl radical (·OH); the concentration of the scavenger used was 1:1 with the concentration of arsenic.

[0047] The radical trapping experiment ( Figure 7 ) showed that the hydroxyl radical (·OH) was the main active species.

[0048] Furthermore, the capture ability of the material for As(V) was verified through an adsorption experiment, indicating that Tb-TiO 2 could not only oxidize As(III), but also adsorb and fix As(V) through adsorption, realizing a closed-loop process of oxidation-adsorption collaborative treatment. The adsorption experiment was measured under dark and light-free conditions. The concentration of pentavalent arsenic was 1 mg / L, the dosage of Tb-TiO 2 was 0.1 g / L, and it was adsorbed in the dark for 180 minutes. Samples were taken every 15 minutes to check the remaining concentration of pentavalent arsenic ions. Figure 8 a shows the adsorption effect of Tb-TiO 2 on As(V) under different pH conditions, Figure 8 b conforms to the second-order kinetic model, indicating that the adsorption rate is controlled by chemical adsorption (such as the chemical bonding between surface active sites and As(V)), indicating that the adsorption process is efficient and controllable. Figure 8c conforms to the Langmuir model, indicating monolayer adsorption dominance and the existence of a saturated adsorption capacity, suggesting that the material surface has uniform active sites. The maximum adsorption capacity can be used to evaluate the potential for practical engineering applications (such as the arsenic load that can be treated by a unit mass of the material). At the same time, it can be seen that Tb-TiO 2 exhibits better catalytic oxidation effect of As(III) in an alkaline environment, while better adsorption effect of As(V) in an acidic environment. This is related to the species of As(V) at different pH values. At low pH, As(V) mainly exists in the forms of H 2 AsO4 - and HAsO 4 2- and is easily adsorbed by the positively charged adsorbent surface. As the pH increases, the surface of the adsorbent may become negatively charged, resulting in repulsion with the anionic species of As(V) and a decrease in adsorption capacity. The surface charge of Tb-TiO 2 may be affected by pH, thus influencing the adsorption effect. Alkaline conditions promote the generation of ·OH (such as enhanced hydroxylation of the TiO 2 surface), and As(V) has the best adsorption at pH = 4 because it exists in the forms of H 2 AsO 4 - / HAsO 4 2- and has electrostatic attraction with the positive surface charge (protonated at low pH) of Tb-TiO 2 .

[0049] In summary, the terbium-doped anatase TiO 2 material prepared by the method of the present invention has an oxidation rate of As(III) under visible light that is 3.5 - 4 times or more higher than that of pure TiO 2 and commercial P25, and is applicable to the treatment of arsenic pollution in water bodies within a wide pH range (pH 1 - 13), having important application prospects in the treatment of arsenic-polluted water.

[0050] The above has described the embodiments of the present invention in detail, but the present invention is not limited to the described embodiments. For those skilled in the art, without departing from the principles and spirit of the present invention, various changes, modifications, substitutions, and variations made to these embodiments still fall within the protection scope of the present invention.

Claims

1. A method for preparing a terbium-doped anatase-type titanium dioxide photocatalytic material, characterized in that: The following steps are involved: S1, dissolving titanium dioxide in an alkaline solution, dispersing it evenly, and then subjecting it to a hydrothermal reaction to obtain a potassium titanate nanowire precursor; S2. Mixing potassium titanate nanowire precursor, hexamethylenetetramine and TbCl3 solution, subjecting to secondary hydrothermal reaction, acid washing, drying, and then calcining, terbium-doped anatase titanium dioxide photocatalytic material is obtained.

2. The method for preparing a terbium-doped anatase-type titanium dioxide photocatalytic material according to claim 1, characterized in that: The doping concentration of terbium is 4.8%-13.2% by atomic percentage.

3. The method for preparing a terbium-doped anatase-type titanium dioxide photocatalytic material according to claim 1, characterized in that: The alkali solution is 8-12M KOH solution.

4. The method for preparing a terbium-doped anatase-type titanium dioxide photocatalytic material according to claim 1, characterized in that: The conditions of the two hydrothermal reactions were the same, both at 190-250° C. for 20-30 hours.

5. The method for preparing a terbium-doped anatase-type titanium dioxide photocatalytic material according to claim 1, characterized in that: In S2, the concentration of hexamethylenetetramine is 0.03-0.08M, and the mass concentration of TbCl3 solution is 4%-7%.

6. The method for preparing a terbium-doped anatase-type titanium dioxide photocatalytic material according to claim 1, characterized in that: The calcination temperature is 300-400°C and the calcination time is 2-5 hours.

7. A terbium-doped anatase-type titanium dioxide photocatalytic material prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the terbium-doped anatase-type titanium dioxide photocatalytic material according to claim 7 in the treatment of arsenic-contaminated water.

9. The use according to claim 8, characterized in that: The terbium-doped anatase-type titanium dioxide photocatalytic material according to claim 7 is added to an As(III)-containing water body and catalytically oxidized under visible light and oxygen conditions for not less than 90 minutes.

10. The use according to claim 8, characterized in that: The dosage of the terbium-doped anatase-type titanium dioxide photocatalytic material is 0.1-0.3 g / L, and the pH range of the water body is 1-13.

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