Preparation method and application of quasi-homogeneous-phase titanium citrate photocatalyst for eliminating hexavalent chromium

Abstract

The invention relates to a preparation method and application of a quasi-homogeneous titanium citrate photocatalyst for eliminating hexavalent chromium, and the application method comprises the following steps: adding a water-soluble photocatalyst titanium citrate into hexavalent chromium sewage, firstly stirring in a dark place to enable the photocatalyst and a hexavalent chromium aqueous solution to reach a quasi-homogeneous state balance, and then carrying out a photocatalytic reaction under ultraviolet irradiation. The method has the characteristics of environmental protection, high efficiency and low cost, is convenient to operate, and can efficiently degrade hexavalent chromium without other excessive treatment.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, in particular to a preparation method and application of a titanium citrate photocatalyst for quasi-homogeneous elimination of hexavalent chromium. Background Art

[0002] Industrial production such as electroplating and leather making will generate a large amount of wastewater containing hexavalent chromium, which is highly toxic and easy to migrate. Traditional treatment methods have problems such as high cost and easy to cause secondary pollution. Hexavalent chromium is generally non-biodegradable in nature, which means that it will stay in the environment for a long time, pollute the soil and water, and pose a major health risk to humans and wildlife. Common treatment and disposal of hexavalent chromium wastewater generally includes ion exchange, electrocoagulation (EC), adsorption and bioremediation methods, but these technical methods often have disadvantages such as high energy consumption, high cost, complex operation, incomplete treatment and poor effect, and harm to the environment.

[0003] Photocatalysis, as an advanced oxidation technology that uses light energy as energy, has the advantages of high efficiency, greenness, economy, and simple operation, and has great application prospects in eliminating pollutants. Commonly used catalysts for photocatalytic reduction of hexavalent chromium include graphene, g-C3N4, and metal oxides such as titanium dioxide, zinc oxide, and WO3. However, these catalysts usually use heterogeneous catalysis to degrade hexavalent chromium, so they face disadvantages such as long reaction time and low efficiency. Summary of the invention

[0004] The present invention aims to provide a preparation method and application of a titanium citrate photocatalyst for quasi-homogeneous elimination of hexavalent chromium, so as to improve the removal efficiency of hexavalent chromium in sewage.

[0005] In order to solve the above technical problems, the specific scheme adopted by the present invention is: a method for preparing a titanium citrate photocatalyst for quasi-homogeneous elimination of hexavalent chromium, wherein a titanium source is dissolved in hydrochloric acid and then citric acid is added, and after stirring evenly, deionized water is added, and then crystals are precipitated by controlling low temperature, and the precipitated crystals are washed and dried to obtain a titanium citrate photocatalyst.

[0006] Preferably, the titanium source is titanium tetrachloride.

[0007] Preferably, the concentration of hydrochloric acid is 10-12 mol / L, and the volume ratio of the titanium source to the hydrochloric acid is 1:(1-4).

[0008] Preferably, the molar ratio of the titanium source to the citric acid is 1:(1-3).

[0009] Application of any of the above-mentioned titanium citrate photocatalysts for quasi-homogeneous elimination of hexavalent chromium in the degradation of hexavalent chromium.

[0010] A water treatment method for efficiently degrading hexavalent chromium in sewage comprises adding a titanium citrate photocatalyst to sewage containing hexavalent chromium and stirring the sewage, and then irradiating the sewage with ultraviolet light.

[0011] Preferably, the dosage of the titanium citrate photocatalyst is 10-80 mg of the titanium citrate photocatalyst per 50 mL of sewage.

[0012] Preferably, the ultraviolet light irradiation time is 35-45 min.

[0013] Preferably, a xenon lamp is used for ultraviolet irradiation with a power of 280-350W.

[0014] Preferably, the hexavalent chromium ion content in the sewage is 20-150 mg / L.

[0015] The titanium citrate prepared in the present application can be dissolved in water, so that it can be in the same phase as the catalyst and the reactant, the contact between the two is more complete, and the electrons and holes are more easily transferred to the reactant after light excitation, thus having excellent photocatalytic performance.

[0016] The photocatalyst titanium citrate has a double-layer structure with two layers corresponding to each other, and is composed of a centrosymmetric neutral octamer, in which there are two planar Ti4 (four Ti atoms) layers, each containing four Ti atoms connected by four linear oxygen bridges. Figure 1 From the SC-XRD pattern of the photocatalyst titanium citrate, it can be found that the periphery of titanium citrate is wrapped by citric acid, that is, 4 citric acids are distributed on the periphery of the photocatalyst. The water solubility of citric acid will drive the overall water solubility of titanium citrate. At the same time, this also lays the foundation for the subsequent quasi-homogeneous photocatalytic degradation of hexavalent chromium.

[0017] In addition, we also conducted a detailed discussion on the mechanism of photocatalytic degradation of hexavalent chromium by photocatalyst titanium citrate. On the one hand, by adding tert-butyl alcohol, triethanolamine, potassium persulfate and p-benzoquinone to the reaction system, the photocatalytic activity of titanium citrate on hexavalent chromium was measured to explore the active species in the photocatalytic reaction process. The results showed that when potassium persulfate (K2S2O8) was added as an electron capture agent, the photocatalytic activity was significantly reduced, indicating that electrons play an important role in the reduction process of hexavalent chromium; when p-benzoquinone was added as ·O2 - When studying the effect of scavengers on the reduction of hexavalent chromium, unlike many previous studies, this work unexpectedly found that in the presence of p-benzoquinone, the reduction efficiency of hexavalent chromium increased rapidly in a short period of time. This may be because O2 -It will oxidize trivalent chromium, resulting in a decrease in the reduction efficiency of hexavalent chromium. On the other hand, aqueous titanium citrate solution will undergo photochromic behavior. Under ultraviolet irradiation, the color of the solution changes from colorless to blue-black as the illumination progresses. This phenomenon may be caused by the reduction of Ti ions from a tetravalent (colorless) oxidation state to a trivalent (black) reduction state. After the irradiation is stopped, the solution gradually returns to colorless in the air over time, indicating that Ti ions gradually change from trivalent to tetravalent. Therefore, in the presence of trivalent titanium, it can also react with hexavalent chromium to reduce the hexavalent chromium.

[0018] In summary, due to the unique structure of titanium citrate, it can degrade hexavalent chromium through multiple pathways, so its degradation efficiency of hexavalent chromium is extremely high. In addition, the photocatalyst titanium citrate preparation method of the present invention also has the advantages of simple operation and low production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 SC-XRD diagram of the photocatalyst titanium citrate prepared in the present invention;

[0020] Figure 2 H, C NMR and Raman spectra of the photocatalyst titanium citrate prepared by the present invention;

[0021] Figure 3 This is a graph showing the degradation results of hexavalent chromium by the photocatalyst titanium citrate prepared in the present invention under different conditions in different embodiments. DETAILED DESCRIPTION

[0022] The preparation method of a titanium citrate photocatalyst for quasi-homogeneous elimination of hexavalent chromium of the present invention comprises the following steps:

[0023] Step 1: Use a pipette to quickly transfer 5 mL of titanium tetrachloride into a beaker containing concentrated hydrochloric acid (10-12 mol / L), weigh citric acid in a ratio of 1:1-1:3 and add it to the beaker, then place the beaker on a heated magnetic stirrer (control the temperature at 80°C, average 500 r / min), and continue heating and stirring for 60 minutes until the solution turns light orange.

[0024] Step 2: dilute the solution into a 100 ml volumetric flask, place it in a refrigerator, and refrigerate it at a low temperature (5-10°C) for 48 hours until the solution crystallizes. Take out the crystals, wash them repeatedly with deionized water for several times, and then dry them to obtain the photocatalyst titanium citrate.

[0025] The degradation effect of the above-mentioned photocatalyst titanium citrate on hexavalent chromium is verified by 5 examples below:

[0026] Example 1

[0027] Step 1: Add 20 mg of photocatalyst titanium citrate to the wastewater containing hexavalent chromium, and stir for 30 minutes under dark conditions to allow the photocatalyst and the hexavalent chromium aqueous solution to reach a quasi-homogeneous state equilibrium. The dosage ratio of photocatalyst titanium citrate to hexavalent chromium aqueous solution is: 20 mg of photocatalyst photocatalyst titanium citrate, 50 mL of 100 mg / L hexavalent chromium wastewater, and the pH value of the control system is 1-6.

[0028] Step 2: The wastewater containing hexavalent chromium after the dark reaction in step 1 is irradiated with ultraviolet light to perform a photocatalytic reaction to reduce the hexavalent chromium in the wastewater. After 50 minutes, at pH = 5, the degradation rate of the hexavalent chromium can reach 80%.

[0029] Example 2

[0030] Step 1: Add 20 mg of photocatalyst titanium citrate to the wastewater containing hexavalent chromium, and stir for 30 minutes under dark conditions to allow the photocatalyst titanium citrate and the hexavalent chromium aqueous solution to reach a quasi-homogeneous state equilibrium. The dosage ratio of the photocatalyst titanium citrate and the hexavalent chromium aqueous solution is: 20 mg of photocatalyst, 50 mL of 100 mg / L hexavalent chromium wastewater, and the pH value of the control system is 2.

[0031] Step 2: The wastewater containing hexavalent chromium after the dark reaction in step 1 is irradiated with ultraviolet light to perform a photocatalytic reaction to reduce the hexavalent chromium in the wastewater. After 50 minutes, at pH = 2, the degradation rate of the hexavalent chromium can reach 90%.

[0032] Example 3

[0033] Step 1: Add 50 mg of photocatalyst titanium citrate to the wastewater containing hexavalent chromium, and stir for 30 minutes under dark conditions to allow the photocatalyst titanium citrate and the hexavalent chromium aqueous solution to reach a quasi-homogeneous state equilibrium. The dosage ratio of the photocatalyst titanium citrate and the hexavalent chromium aqueous solution is: 50 mg of photocatalyst, 50 mL of 100 mg / L hexavalent chromium wastewater, and the pH value of the control system is 5.

[0034] Step 2: The wastewater containing hexavalent chromium after the dark reaction in step 1 is irradiated with ultraviolet light to perform a photocatalytic reaction to reduce the hexavalent chromium in the wastewater. After 20 minutes, at pH = 5, the degradation rate of the hexavalent chromium can reach 99.9%.

[0035] Example 4

[0036] Step 1: Add 20 mg of catalyst to the wastewater containing hexavalent chromium, and stir for 30 minutes under dark conditions to allow the photocatalyst and the hexavalent chromium aqueous solution to reach a quasi-homogeneous state equilibrium, wherein the photocatalyst is titanium citrate, and the dosage ratio of the photocatalyst to the hexavalent chromium aqueous solution is: 20 mg of photocatalyst, 50 mL of 50 mg / L hexavalent chromium wastewater, and the pH value of the control system is 5.

[0037] Step 2: The wastewater containing hexavalent chromium after the dark reaction in step 1 is irradiated with ultraviolet light to perform a photocatalytic reaction to reduce the hexavalent chromium in the wastewater. After 20 minutes, at pH = 5, the degradation rate of the hexavalent chromium can reach 99.9%.

[0038] Example 5

[0039] Step 1: Add 20 mg of photocatalyst titanium citrate to the wastewater containing hexavalent chromium, and stir for 30 minutes under dark conditions to allow the photocatalyst titanium citrate and the hexavalent chromium aqueous solution to reach a quasi-homogeneous state equilibrium. The dosage ratio of the photocatalyst titanium citrate and the hexavalent chromium aqueous solution is: 20 mg of photocatalyst, 50 mL of 20 mg / L hexavalent chromium wastewater, and the pH value of the control system is 5.

[0040] Step 2: The wastewater containing hexavalent chromium after the dark reaction in step 1 is irradiated with ultraviolet light to perform a photocatalytic reaction to reduce the hexavalent chromium in the wastewater. After 10 minutes, at pH = 5, the degradation rate of the hexavalent chromium can reach 99.9%.

Claims

1. A method for preparing a titanium citrate photocatalyst for quasi-homogeneous elimination of hexavalent chromium, characterized in that: The titanium source is dissolved in hydrochloric acid, and then citric acid is added. After stirring evenly, deionized water is added, and then crystals are precipitated by low temperature control. The precipitated crystals are washed and dried to obtain the titanium citrate photocatalyst.

2. The method for preparing a titanium citrate photocatalyst for quasi-homogeneous elimination of hexavalent chromium as claimed in claim 1, characterized in that: The titanium source is titanium tetrachloride.

3. The method for preparing a titanium citrate photocatalyst for quasi-homogeneous elimination of hexavalent chromium as claimed in claim 2, characterized in that: The concentration of hydrochloric acid is 10-12 mol / L, and the volume ratio of the titanium source to the hydrochloric acid is 1:(1-4).

4. The method for preparing a titanium citrate photocatalyst for quasi-homogeneous elimination of hexavalent chromium as claimed in claim 2, characterized in that: The molar ratio of the titanium source to the citric acid is 1:(1-3).

5. Use of any one of the titanium citrate photocatalysts for quasi-homogeneous elimination of hexavalent chromium as claimed in claims 1 to 4 in the degradation of hexavalent chromium.

6. A water treatment method for efficiently degrading hexavalent chromium in sewage, characterized by: Titanium citrate photocatalyst is added to wastewater containing hexavalent chromium and stirred, and then irradiated with ultraviolet light.

7. A water treatment method for efficiently degrading hexavalent chromium in sewage as claimed in claim 6, characterized in that: The dosage of the titanium citrate photocatalyst is 10-80 mg of the titanium citrate photocatalyst per 50 mL of sewage.

8. A water treatment method for efficiently degrading hexavalent chromium in sewage as claimed in claim 6, characterized in that: The UV irradiation time is 35-45 minutes.

9. A water treatment method for efficiently degrading hexavalent chromium in sewage as claimed in claim 6, characterized in that: A xenon lamp was used for ultraviolet irradiation with a power of 280-350W.

10. A water treatment method for efficiently degrading hexavalent chromium in sewage as claimed in claim 6, characterized in that: The hexavalent chromium ion content in sewage is 20-150 mg / L.

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