Sodium modified polyheptazine imine photocatalyst as well as preparation method and application thereof

Abstract

The invention provides a sodium modified polyheptazine imine photocatalyst as well as a preparation method and application thereof, and relates to the technical field of photocatalytic materials. The preparation method of the sodium-modified polyheptazine imine photocatalyst comprises the following steps: performing thermal polymerization reaction in an oxygen atmosphere to obtain pyriller-type carbon nitride, and heating the pyriller-type carbon nitride and a sodium-containing alkali metal mixed salt together for modification. According to the preparation method disclosed by the invention, the crystal structure of carbon nitride is regulated and controlled, the performance of the carbon nitride photocatalyst is improved, and sodium modification is combined, so that the polyheptazine imine photocatalyst disclosed by the invention has relatively high visible light absorption performance and relatively low photon-generated carrier recombination efficiency, and has better gold dissolving performance compared with a traditional TiO2 catalyst; and the preparation method is simple and convenient, and is easy for industrial popularization and application.

Description

Technical Field

[0001] The invention relates to the technical field of photocatalytic materials, and in particular to a sodium-modified polyheptazine imine photocatalyst and a preparation method and application thereof. Background Art

[0002] At present, the commonly used chemical method for gold leaching in the industrial recovery process is hydrometallurgy, which requires the use of a large amount of corrosive or toxic reagents, and the process is cumbersome, the cost is high, and serious secondary pollution problems will occur. Therefore, the development of green and environmentally friendly precious metal dissolution technology has important environmental significance, among which photocatalysis is a relatively energy-saving and environmentally friendly method. Precious metals, especially gold, have high standard redox potential values ​​and are not easily oxidized. Therefore, the photocatalyst needs to have high oxidation performance to achieve photocatalytic technology dissolution and recovery.

[0003] Carbon nitride, as a polymer semiconductor, is an environmentally friendly photocatalytic material. The graphite phase carbon nitride prepared by traditional methods has problems such as rapid recombination of photogenerated electron-hole pairs and low visible light absorption capacity, which inhibits its photocatalytic activity and limits its application in the field of photocatalysis. Crystal structure regulation is one of the common methods to improve the photocatalytic performance of carbon nitride. There are large differences in the crystal phase type and degree of polymerization of carbon nitride obtained by different preparation methods. By developing a new carbon nitride preparation strategy, it is possible to construct and optimize the carbon nitride crystal phase structure and improve the performance of carbon nitride photocatalysts. Summary of the invention

[0004] In view of this, the present invention provides a method for preparing a sodium-modified polyhepta-azine imine photocatalyst and its application in visible light photocatalytic dissolution and recovery of precious metals. The present invention improves the performance of the carbon nitride photocatalyst by preparing pyrimidine-type carbon nitride and performing sodium doping modification, so that the prepared sodium-modified polyhepta-azine imine photocatalyst has higher visible light absorption performance and lower photogenerated carrier recombination efficiency, and can be used for the recovery of precious metals, especially gold, in waste circuit boards under visible light conditions.

[0005] The present invention provides a method for preparing a sodium-modified polyheptazine imine photocatalyst, which specifically comprises the following steps:

[0006] The method comprises preparing a pyrimidine-type carbon nitride, and then performing sodium doping modification on the pyrimidine-type carbon nitride to obtain a sodium-modified polyheptazine imine photocatalyst.

[0007] Preferably, the preparation method of the pyrimidine-type carbon nitride is as follows:

[0008] The precursor is heated to 450°C to 600°C at a heating rate of 2 to 4°C / min under an oxygen atmosphere and then subjected to a thermal polymerization reaction for 4 to 6 hours to obtain pyrimidine-type carbon nitride.

[0009] Preferably, the precursor is a precursor rich in carbon and nitrogen. More preferably, the precursor is at least one of dicyandiamide, cyanamide, and urea.

[0010] Preferably, the sodium doping modification method is as follows:

[0011] The pyrimidine-type carbon nitride and the sodium-containing alkali metal mixed salt are evenly mixed, and then heated to 550°C to 600°C at a heating rate of 2 to 4°C / min in an oxygen atmosphere, and a second thermal polymerization reaction is carried out. The reaction time is 3 to 5 hours. After the reaction is completed, a sodium-modified polyheptazine imine photocatalyst is obtained.

[0012] Preferably, the sodium-containing alkali metal mixed salt is a mixture of sodium chloride and lithium chloride and / or potassium chloride. More preferably, the mass ratio of sodium chloride to lithium chloride and / or potassium chloride is 1:(1.5-3).

[0013] Preferably, the mass ratio of the pyrimidine-type carbon nitride to the sodium-containing alkali metal mixed salt is 1:(5-15).

[0014] The present invention also provides a sodium-modified polyheptazine imine photocatalyst prepared according to the above method.

[0015] The present invention provides an application of a sodium-modified polyheptadiamine photocatalyst in visible light photocatalytic dissolution and recovery of precious metals. The sodium-modified polyheptadiamine photocatalyst is the sodium-modified polyheptadiamine photocatalyst described in the above technical solution.

[0016] Preferably, the noble metal is gold.

[0017] Preferably, the application method of the sodium-modified polyheptazine imine photocatalyst in the visible light photocatalytic dissolution and recovery of gold is as follows:

[0018] The sodium-modified polyheptazine imine photocatalyst is dispersed in a solvent, and a visible light photocatalytic dissolution and recovery reaction of gold in waste circuit boards is carried out under oxygen and light conditions. After the reaction is completed, centrifugation and filtration are performed to achieve the recovery of gold in the waste circuit boards.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are:

[0020] The sodium-modified polyheptazine imine of the present invention has improved mass transfer efficiency, effectively inhibits the recombination efficiency of photogenerated carriers, and enhances the absorption and utilization rate of visible light.

[0021] The sodium-modified polyheptadienimine photocatalyst of the present invention has heptadienimine as a structural unit and is suitable for the visible light photocatalytic dissolution and recovery of precious metals in secondary resources, especially gold. Compared with the traditional TiO2 catalyst, it has outstanding visible light photocatalytic gold dissolution performance.

[0022] The preparation method of the sodium-modified polyheptazine imine photocatalyst provided by the invention is simple, easy to control, and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below in conjunction with the accompanying drawings.

[0024] Figure 1 This is a SEM image of the sodium-modified polyheptazoline imine photocatalyst prepared in Example 1;

[0025] Figure 2 The X-ray diffraction pattern of the sodium-modified polyheptazoline imine photocatalyst prepared in Example 1;

[0026] Figure 3 The X-ray photoelectron spectrum of the sodium-modified polyheptazoline imine photocatalyst prepared in Example 1;

[0027] Figure 4 The room temperature electron paramagnetic resonance spectra of the pyrimidine-type carbon nitride and sodium-modified polyheptazine imine prepared in Example 1 without illumination and under visible light irradiation;

[0028] Figure 5 The solubility of gold recovered by photocatalytic dissolution of the sodium-modified polyheptazine imine photocatalyst prepared in Example 1-4;

[0029] Figure 6 The solubility of gold recovered by visible light photocatalytic dissolution of the sodium-modified polyheptazine imine photocatalyst prepared in Example 1 and the P25 photocatalyst. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0031] The present invention provides a method for preparing a sodium-modified polyheptazine imine photocatalyst, which specifically comprises the following steps:

[0032] The method comprises preparing a pyrimidine-type carbon nitride, and then performing sodium doping modification on the pyrimidine-type carbon nitride to obtain a sodium-modified polyheptazine imine photocatalyst.

[0033] The present invention adjusts the electronic structure and photocatalytic performance of the polyheptazoline imine photocatalyst by sodium doping modification, so that the polyheptazoline imine photocatalyst can generate solvated electrons during the visible light photocatalytic reaction, and react with oxygen to form superoxide free radicals [·O 2- ], which has a stronger driving force for oxidation than holes.

[0034] The first step of the present invention is to synthesize the pyrimidine-type carbon nitride, specifically: the precursor is heated to 450°C to 600°C at a heating rate of 2 to 4°C / min under an oxygen atmosphere, and then thermally polymerized for 4 to 6 hours to obtain the pyrimidine-type carbon nitride. In some specific embodiments of the present invention, the precursor is a precursor rich in carbon and nitrogen elements. In some preferred embodiments of the present invention, the precursor is at least one of dicyandiamide, cyanamide, and urea.

[0035] The second step of the present invention is to perform sodium doping modification on the pyrimidine-type carbon nitride to obtain a sodium-modified polyseptazine imine photocatalyst, specifically: the pyrimidine-type carbon nitride is evenly mixed with a sodium-containing alkali metal mixed salt, and then heated to 550°C to 600°C at a heating rate of 2 to 4°C / min under an oxygen atmosphere, and then a second thermal polymerization reaction is carried out. The reaction time is 3 to 5 hours. After the reaction is completed, a sodium-modified polyseptazine imine photocatalyst is obtained. In some specific embodiments of the present invention, the sodium-containing alkali metal mixed salt is a mixture of sodium chloride and lithium chloride and / or potassium chloride. In some preferred embodiments of the present invention, the mass ratio of sodium chloride to lithium chloride and / or potassium chloride is 1: (1.5 to 3). In some specific embodiments of the present invention, the mass ratio of the pyrimidine-type carbon nitride to the sodium-containing alkali metal mixed salt is 1: (5 to 15).

[0036] In some specific embodiments of the present invention, after the second thermal polymerization reaction is completed, the obtained solid powder is boiled and washed with deionized water to remove residual medium salt, and then centrifuged and dried at 70° C. to 80° C. to obtain a sodium-modified polyheptazine imine photocatalyst.

[0037] The present invention also provides a sodium-modified polyheptazine imine photocatalyst prepared according to the above method.

[0038] The present invention also provides an application of a sodium-modified polyheptaazirine imine photocatalyst in visible light photocatalytic dissolution and recovery of precious metals, wherein the sodium-modified polyheptaazirine imine photocatalyst is the sodium-modified polyheptaazirine imine photocatalyst described in the above technical solution. In some specific embodiments of the present invention, the precious metal is gold.

[0039] The application method of the sodium-modified polyheptazine imine photocatalyst of the present invention in the visible light photocatalytic dissolution and recovery of gold is as follows:

[0040] The sodium-modified polyheptazine imine photocatalyst is dispersed in a solvent, and a visible light photocatalytic dissolution and recovery reaction of gold in waste circuit boards is carried out under oxygen and light conditions. After the reaction is completed, centrifugation and filtration are performed to achieve the recovery of gold in the waste circuit boards.

[0041] In some specific embodiments of the present invention, the solvent is a mixture of acetonitrile and dichloroethane, wherein the volume ratio of acetonitrile to dichloroethane is 3:1, the dosage of the sodium-modified polyheptazine imine photocatalyst is 1 mg / mL, the oxygen flow rate is 1 L / min, and the illumination conditions are 300W xenon lamp irradiation for 12 h.

[0042] In order to further illustrate the present invention, the following examples are provided for detailed description. The raw materials used in the following examples of the present invention are all commercially available.

[0043] Example 1 A method for preparing a sodium-modified polyheptazine imine photocatalyst, comprising the following steps:

[0044] (1) 3 g of dicyandiamide was placed in a muffle furnace, and the temperature was raised to 500° C. at a heating rate of 2° C. / min under an oxygen atmosphere and calcined for 4 h to obtain pyrimidine-type carbon nitride;

[0045] (2) Take 1 g of the obtained pyrimidine-type carbon nitride, 3.5 g of NaCl, and 6.5 g of LiCl, grind and mix them thoroughly, then put them into a muffle furnace, and heat them to 550° C. at a heating rate of 4° C. / min under an oxygen atmosphere and calcine for 4 h. Then, the obtained solid powder is boiled and washed with deionized water to remove residual medium salt, and then centrifuged and dried at 70° C. to obtain a sodium-modified polyheptadienimine photocatalyst, which is recorded as Na-PHI 1.

[0046] Depend on Figure 1 It can be seen that the microscopic morphology of the sodium-modified poly(heptazine imine) photocatalyst prepared in this embodiment is a hierarchical structure formed by closely arranged nanorods.

[0047] Depend on Figure 2 It can be seen that the two significant diffraction peaks of the sodium-modified polyheptazine imine photocatalyst prepared in this embodiment at 8.23° and 14.44° correspond to the (100) crystal plane and (110) crystal plane of the structure, indicating the formation of polyheptazine imine.

[0048] Depend on Figure 3 It can be seen that the Na 1s peak indicates the presence of Na element, and no Cl element is found, indicating that when the NaCl / LiCl mixed salt is used as the salt melt medium, Na doped modified polyheptazine imine is produced during ion thermal polymerization.

[0049] Depend on Figure 4 It can be seen that the sodium-modified polyheptazine imine prepared in this example shows an obvious characteristic EPR signal of solvated electrons when the g signal value is 2.002, indicating that free solvated electrons will be generated under the irradiation of visible light.

[0050] Example 2

[0051] Same as Example 1, except that 3 g of cyanamide is used to replace dicyandiamide, recorded as Na-PHI 2.

[0052] Example 3

[0053] Same as Example 1, except that 3 g of urea was used to replace dicyandiamide, recorded as Na-PHI 3.

[0054] Example 4

[0055] Same as Example 1, except that 3.5 g NaCl and 6.5 g KCl are used instead of 3.5 g NaCl and 6.5 g LiCl as a mixed salt, which is recorded as Na-PHI 4.

[0056] Comparative Example 1

[0057] The same as Example 1, except that the pyrimidine-type carbon nitride is not modified by sodium doping to obtain the pyrimidine-type carbon nitride photocatalyst.

[0058] Comparative Example 2

[0059] The same as Example 1, except that 3.5 g of NaCl and 6.5 g of LiCl were replaced by 3.5 g of LiCl and 6.5 g of KCl to obtain a polyheptazine imine photocatalyst.

[0060] Test Example 1

[0061] As a photocatalyst, the photocatalytic dissolution and recovery reaction of gold in waste circuit boards is carried out, and the specific steps are as follows:

[0062] 50 mg of the sodium-modified polyhepta-azine imine photocatalyst prepared in Examples 1-4, the pyrimidine-type carbon nitride photocatalyst prepared in Comparative Example 1, the polyhepta-azine imine photocatalyst prepared in Comparative Example 2 and 3 mg of the gold foil peeled off from the waste circuit board were added to the quartz reactor respectively, and then 50 mL of the mixed solvent (V 乙腈 :V 二氯乙烷 =3:1), oxygen was introduced (the oxygen flow rate was 1 L / min), and a photocatalytic reaction was carried out under 300W xenon lamp irradiation for 12 h under the condition of 400r / min magnetic stirring. After the reaction was completed, centrifugation and filtration were performed, and the absorbance of the gold dissolving reaction solution was measured, and the solubility of the gold foil was calculated based on the absorbance.

[0063] The experimental results show that the pyrimidine-type carbon nitride photocatalyst prepared in Comparative Example 1 and the polyhepta-azine imine photocatalyst prepared in Comparative Example 2 do not have the performance of photocatalytically dissolving gold. The gold solubility of the sodium-modified polyhepta-azine imine photocatalysts of Examples 1-4 is as follows: Figure 5 shown.

[0064] Depend on Figure 5It can be seen that under full spectrum conditions, after 12 hours of photocatalytic reaction, the gold foil solubility of Na-PHI 1 photocatalyst is 37.6 mg / L, while the gold foil solubility of Na-PHI 2, Na-PHI 3, and Na-PHI 4 are 32.4 mg / L, 32.0 mg / L, and 36.2 mg / L, respectively. It can be seen that the performance of Na-PHI 1 in dissolving gold is slightly better than that of other Na-PHIs.

[0065] Test Example 2

[0066] The sodium-modified polyheptazoline imine prepared in Example 1 and commercial TiO2 (Macklin, P25, 20 nm, product code P25) were used as photocatalysts to carry out visible light photocatalytic dissolution and recovery reaction of gold in waste circuit boards. The specific steps are as follows:

[0067] 50 mg of sodium-modified polyheptazoline imine photocatalyst or P25 and 3 mg of gold foil peeled off from waste circuit boards were added to a quartz reactor, and then 50 mL of mixed solvent (V 乙腈 :V 二氯乙烷 =3:1), oxygen was introduced (the oxygen flow rate was 1 L / min), and a 300 W xenon lamp with a >400 nm cutoff filter was irradiated for 12 h under 400 r / min magnetic stirring conditions for photocatalytic reaction. After the reaction was completed, the mixture was centrifuged and filtered, and the absorbance of the gold dissolving reaction solution was determined, and the solubility of the gold foil was calculated based on the absorbance.

[0068] Depend on Figure 6 It can be seen that under visible light conditions, the photocatalytic reaction lasted for 12 hours, and the solubility of the sodium-modified polyheptazine imine photocatalyst gold foil was 22.7 mg / L, while the solubility of the P25 gold foil was 0.29 mg / L. This shows that the sodium-modified polyheptazine imine photocatalyst has outstanding visible light response performance compared to the traditional TiO2 photocatalyst.

[0069] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a sodium-modified polyheptazine imine photocatalyst, characterized in that: The following steps are involved: preparing a pyrimidine-type carbon nitride, and then performing sodium doping modification on the pyrimidine-type carbon nitride to obtain a sodium-modified polyheptazine imine photocatalyst; The preparation method of the pyrimidine type carbon nitride is as follows: The precursor is heated to 450°C to 600°C at a heating rate of 2 to 4°C / min under an oxygen atmosphere and then subjected to a thermal polymerization reaction for 4 to 6 hours to obtain pyrimidine-type carbon nitride.

2. The preparation method according to claim 1, characterized in that: The precursor is a precursor rich in carbon and nitrogen elements.

3. The preparation method according to claim 2, characterized in that: The precursor rich in carbon and nitrogen elements is at least one of dicyandiamide, cyanamide and urea.

4. The preparation method according to claim 1, characterized in that: The sodium doping modification method is as follows: The pyrimidine-type carbon nitride and the sodium-containing alkali metal mixed salt are evenly mixed, and then heated to 550°C to 600°C at a heating rate of 2 to 4°C / min in an oxygen atmosphere, and a second thermal polymerization reaction is carried out. The reaction time is 3 to 5 hours. After the reaction is completed, a sodium-modified polyheptazine imine photocatalyst is obtained.

5. The preparation method according to claim 4, characterized in that: The sodium-containing alkali metal mixed salt is a mixture of sodium chloride and lithium chloride and / or potassium chloride.

6. The preparation method according to claim 5, characterized in that: The mass ratio of the sodium chloride to the lithium chloride and / or potassium chloride is 1:(1.5-3).

7. The preparation method according to claim 4, characterized in that: The mass ratio of the pyrimidine-type carbon nitride to the sodium-containing alkali metal mixed salt is 1:(5-15).

8. A sodium-modified polyheptazine imine photocatalyst, characterized in that: Prepared by the method according to any one of claims 1 to 7.

9. Application of a sodium-modified polyheptazine imine photocatalyst in visible light photocatalytic dissolution and recovery of precious metals, characterized in that: The sodium-modified polyheptadiamine photocatalyst is a sodium-modified polyheptadiamine photocatalyst prepared by the method described in any one of claims 1 to 7 or a sodium-modified polyheptadiamine photocatalyst described in claim 8.

10. The use according to claim 9, characterized in that: The precious metal is gold.

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