Carbon nanotube / cadmium selenide quantum dot heterojunction photoelectric catalyst as well as preparation method and application thereof

Abstract

The invention discloses a carbon nanotube / cadmium selenide quantum dot heterojunction photoelectric catalyst as well as a preparation method and application thereof. The method comprises the following steps: activating single-wall and / or multi-wall carbon nanotubes by aqua regia at room temperature, dispersing the single-wall and / or multi-wall carbon nanotubes in an aqueous solution containing CdCl2. 5H2O, adding a Na2SeSO3 selenium source and 3-mercaptopropionic acid, and reacting at 110-150 DEG C, so that CdSe quantum dots with the particle size of 1-5 nm are subjected to in-situ nucleation growth on the surfaces and / or the interiors of the carbon nanotubes and form a heterojunction interface. The obtained catalyst and Nafion are prepared into ink drops, the ink drops are coated on conductive glass to construct a photocathode, in an H-type electrolytic tank with a light path, a high-purity CO2 saturated bicarbonate aqueous solution is used as an electrolyte, Ag / AgCl is used as a reference electrode, and under irradiation of an LED light source with the maximum wavelength being 450 nm and bias voltage ranging from-0.1 V (vs. RHE) to-1.0 V (vs. RHE), CO is generated through water-phase photoelectrocatalysis CO2 reduction. The photoelectrocatalyst has the characteristics of simple synthesis method and excellent photoelectrocatalytic reduction effect of carbon dioxide.

Description

Technical Field

[0001] This invention belongs to the field of artificial photosynthesis and photoelectrocatalytic materials technology, specifically relating to a composite photoelectrocatalyst with carbon nanotubes (CNTs, including single-walled carbon nanotubes and multi-walled carbon nanotubes) as the conductive framework, cadmium selenide quantum dots (CdSe QDs) being nucleated and grown in situ on their surface and / or inside through an in-situ aqueous reaction to form a heterojunction interface, and its preparation method. It also relates to the application of this catalyst in the photoelectrocatalytic reduction of carbon dioxide to carbon monoxide (CO) in an aqueous system. Background Technology

[0002] The photoelectrochemical reduction of carbon dioxide (CO2) can couple light and electrical energy into chemical energy, with CO serving as an important platform chemical that can be used in syngas and subsequent chemical processes. However, common quantum dot photocatalysts in existing technologies (such as CdSe) suffer from problems such as easy aggregation, limited interfacial charge extraction efficiency, and insufficient stability. Although carbon nanotubes have excellent conductivity and large specific surface area, their light response to CO2 reduction is insufficient and their activity / selectivity is limited when used alone as a catalyst.

[0003] In addition, some existing technical routes focus on "CdSe quantum dot bulk" technology, exposing metal sites by adjusting pH and acid stripping surface ligands, and then using photocatalytic systems (such as organic solvents / amine sacrificial agents) for CO2 reduction. This route differs from aqueous photoelectrocatalytic (PEC) electrode systems in terms of material morphology, reaction system, and mechanism of action.

[0004] Therefore, there is an urgent need for a composite photoelectrocatalyst that can be constructed and stably operated in an aqueous electrolyte to improve the separation and transport efficiency of photogenerated carriers by forming a heterojunction interface, so as to achieve high efficiency and durability of CO2→CO. Summary of the Invention

[0005] In view of the above shortcomings, the present invention provides a carbon nanotube / cadmium selenide quantum dot heterojunction photoelectrocatalyst, its preparation method and application, which enables CdSe quantum dots to nucleate and grow in situ on / inside activated CNTs and form a heterojunction interface, thereby achieving efficient reduction of CO2 to CO in an aqueous bicarbonate electrolyte under the synergistic conditions of applied bias voltage and visible light; the system can operate stably for 100 hours.

[0006] To achieve the above-mentioned technical effects, the present invention employs the following technical means:

[0007] This invention first discloses a carbon nanotube / cadmium selenide quantum dot heterojunction composite photocatalyst, comprising:

[0008] Carbon nanotubes and cadmium selenide quantum dots loaded on the surface and / or inside the carbon nanotubes; wherein:

[0009] The carbon nanotubes are single-walled carbon nanotubes, multi-walled carbon nanotubes, or mixtures thereof;

[0010] The cadmium selenide quantum dots are nucleated and grown in situ on carbon nanotubes activated by aqua regia through an in situ aqueous reaction and form a heterojunction interface with the carbon nanotubes.

[0011] The particle size of the cadmium selenide quantum dots is 1~5 nm.

[0012] Furthermore, the carbon nanotubes are activated with aqua regia at room temperature for 6-12 hours.

[0013] Furthermore, the mass ratio of the carbon nanotubes to cadmium selenide quantum dots is 0.5:1 to 2:1.

[0014] Furthermore, the average particle size of the cadmium selenide quantum dots is 2 nm.

[0015] This invention also discloses a method for preparing any of the above-mentioned carbon nanotube / cadmium selenide quantum dot heterojunction composite photocatalysts, comprising:

[0016] (1) Add carbon nanotubes to aqua regia and treat at room temperature for 6 to 12 hours, wash until neutral and dry to obtain activated carbon nanotubes;

[0017] (2) Disperse activated carbon nanotubes in deionized water containing CdCl2·2.5H2O and stir for 10-60 minutes to obtain a mixed system;

[0018] (3) Add Na2SeSO3 and 3-mercaptopropionic acid to the mixed system and react at 110~150 °C for 1~6 hours to generate and load cadmium selenide quantum dots in situ on the surface and / or inside of carbon nanotubes;

[0019] (4) Centrifuge, wash and dry to obtain composite photocatalyst.

[0020] Further, the room temperature treatment described in step (1) lasts for 8 hours.

[0021] Further, the stirring in step (2) lasts for 30 minutes.

[0022] Further, in step (3), the molar ratio of Cd source to Se source is 4:1, and the molar ratio of 3-mercaptopropionic acid to Cd source is 6:5.

[0023] Further, the reaction described in step (3) is: react at 130 °C for 3 hours.

[0024] The present invention also discloses a carbon nanotube / cadmium selenide quantum dot heterojunction composite photocatalyst prepared according to the above method.

[0025] The key technical point of this invention is that it uses carbon nanotubes as a conductive framework, and induces CdSe quantum dots to grow in situ on / inside the carbon nanotubes through activation treatment to form a heterojunction interface, which is then used as a photocathode for the reduction of PEC CO2 in aqueous phase. This invention does not require "acid exfoliation and cadmium enrichment of the CdSe quantum dot matrix surface" as a necessary technical feature, nor does it require pH adjustment to 9-11, acid exfoliation pH to 2-5, or an organic solvent / amine sacrificial photocatalytic system as necessary conditions. Therefore, it differs substantially from the technical route of CN110314701A in terms of materials and reaction system.

[0026] The present invention also discloses the application of the carbon nanotube / cadmium selenide quantum dot heterojunction composite photocatalyst according to any of the above in the aqueous phase photocatalytic reduction of carbon dioxide to carbon monoxide.

[0027] Furthermore, the application includes:

[0028] (1) The composite catalyst is dispersed in a solution containing Nafion to form a catalyst ink;

[0029] (2) Apply ink droplets to conductive glass to form a working electrode;

[0030] (3) An H-type electrolytic cell with a light path is used (its schematic diagram is shown in Figure 1). Figure 5 As shown in the figure, the electrolyte is an aqueous solution of bicarbonate saturated with high-purity CO2 gas, and the reference electrode is an Ag / AgCl electrode;

[0031] (4) Photoelectrocatalytic CO2 reduction was performed under LED illumination with a maximum wavelength of 450 nm by applying a bias voltage of -0.1 to -1.0 V (vs. RHE);

[0032] (5) The product CO is quantitatively analyzed by gas chromatography (GC), using manual injection and calibrated with high-purity CO standard gas; it can operate stably for 100 hours under the above conditions.

[0033] Further, the drop loading in step (2) is 0.1~2 mg·cm³. -2 The conductive glass is fluorine-doped tin oxide conductive glass (FTO) or tin oxide conductive glass (ITO).

[0034] Further, the concentration of the bicarbonate aqueous solution in step (3) is 0.1 mol·L⁻¹. -1 ~saturation.

[0035] Furthermore, the concentration of the bicarbonate aqueous solution is 0.2 mol·L⁻¹. -1 .

[0036] Furthermore, the LED light intensity in step (4) is 40~70 mW·cm. -2 .

[0037] Furthermore, the bicarbonate includes: Na salt, K salt, and ammonium salt.

[0038] The beneficial effects of this invention are as follows:

[0039] Compared with the simple physical mixture system of carbon nanotubes and CdSe quantum dots, the present invention has at least the following beneficial effects:

[0040] (1) In-situ nucleation growth enables CdSe QDs to form a heterojunction interface with CNTs, which is conducive to the directional injection of photogenerated electrons into the CNT conductive network and their participation in CO2 reduction, thereby increasing the CO generation rate;

[0041] (2) Confined nucleation can obtain quantum dots of 1~5 nm and improve dispersion, reduce agglomeration and enhance stability;

[0042] (3) Under the specified PEC conditions, the highest CO generation efficiency is 1.5 mmol·g. -1 It can run stably for 100 hours. Attached Figure Description

[0043] Figure 1 This is a flowchart illustrating the preparation process of the carbon nanotube / cadmium selenide quantum dot heterojunction composite photocatalyst of the present invention.

[0044] Figure 2 This is a transmission electron microscope (TEM) image of CdSe QDs.

[0045] Figure 3 TEM image of CNT / CdSe QDs.

[0046] Figure 4 TEM image of HAADF mode for CNT / CdSe QDs.

[0047] Figure 5 This is a schematic diagram of an H-type photoelectrolysis cell.

[0048] Figure 6 The photoelectrocatalytic efficiency of CNT / CdSe QDs under different bias voltages (photoelectrocatalysis for 20 hours).

[0049] Figure 7 The long-term photoelectrocatalytic curves of CNT / CdSe QDs are shown.

[0050] Figure 8 This is a comparison chart of the photoelectrocatalytic efficiency of the present invention with that of physical mixing and quantum dot photoelectrocatalysis (photoelectrocatalysis for 20 hours). Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, and are therefore only examples, and should not be used to limit the scope of protection of the present invention.

[0052] Example 1

[0053] Preparation of CNT / CdSe QDs heterojunction photocatalysts

[0054] (1) Add single-walled and / or multi-walled carbon nanotubes to aqua regia and activate at room temperature for 8 hours; wash with deionized water until near neutral and then dry to obtain activated carbon nanotubes.

[0055] (2) Disperse activated carbon nanotubes in a deionized aqueous solution containing CdCl2·2.5H2O and stir for 30 minutes.

[0056] (3) The Na2SeSO3 solution generated by the reaction of selenium powder and sodium sulfite was added as the selenium source, and the molar ratio of Cd source to Se source was controlled to be 4:1.

[0057] (4) Add 3-mercaptopropionic acid and control the molar ratio of 3-mercaptopropionic acid to Cd source to be 6:5; heat to 130 °C and react for 3 hours.

[0058] (5) After the reaction is completed, centrifuge, wash and dry to obtain CNT / CdSe QDs composite catalyst.

[0059] (6) TEM characterization showed that CdSe quantum dots grew and were uniformly distributed on the surface and / or inside CNTs, with a particle size of 1-5 nm and an average of about 2 nm (see Figure 3 and Figure 4 and with Figure 2 (Compare the CdSe QDs shown).

[0060] Example 2

[0061] Electrode construction

[0062] (1) The catalyst obtained in Example 1 was added to a solution containing Nafion to prepare a homogeneous catalyst ink.

[0063] (2) The catalyst ink is drop-coated onto FTO or ITO conductive glass and allowed to air dry to form the working electrode; the drop-coating loading is controlled at 0.1~2 mg·cm⁻¹. -2 .

[0064] Example 3

[0065] Aqueous PEC CO2 Reduction to CO Production and Quantitative Analysis

[0066] (1) Use an H-type electrolytic cell with a light path; add KHCO3 aqueous solution to the cathode chamber and pass high-purity CO2 gas through for at least 30 minutes, and keep the chamber sealed and saturated during the test.

[0067] (2) The reference electrode is Ag / AgCl, and the potential is converted to RHE; the counter electrode is an inert electrode.

[0068] (3) Irradiate with an LED light source with a maximum wavelength of 450 nm; apply a bias voltage of -0.1~-1.0 V (vs. RHE) to the working electrode for photoelectrocatalysis for 20 hours.

[0069] (4) Quantitative analysis of CO by GC: manual injection was used; a calibration curve was established and quantified using high-purity CO standard gas.

[0070] (5) Under the above conditions, the CO generation efficiency can reach up to 0.8 mmol·g. -1 (See Figure 6 ).

[0071] Experimental Example 1

[0072] Stability test

[0073] Under constant bias and illumination conditions, the CO generation rate or photocurrent was recorded over time. The results showed that the system could operate stably for 100 hours, and the CO generation efficiency could reach 1.5 mmol·g⁻¹. -1 (See Figure 7 ).

[0074] Comparative Example 1

[0075] CNT and CdSe QDs physical mixing

[0076] Electrodes were prepared by physically mixing CNTs and CdSe QDs at the same feed ratio as in the example. Under the same conditions, the CO generation efficiency of PEC after 20 hours was 0.53 mmol·g. -1 The Faraday efficiency is 61%; under the same conditions, the CO generation efficiency and Faraday efficiency are 66.2% and 71.8% of those of this invention, respectively (see [reference]). Figure 8 This indicates that the in-situ growth of CdSe QDs to form heterojunctions in CNTs effectively enhances their photoelectrocatalytic performance.

[0077] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A carbon nanotube / cadmium selenide quantum dot heterojunction composite photocatalyst, comprising: Carbon nanotubes and cadmium selenide quantum dots loaded on the surface and / or inside the carbon nanotubes; wherein: The carbon nanotubes are single-walled carbon nanotubes, multi-walled carbon nanotubes, or mixtures thereof; The cadmium selenide quantum dots are nucleated and grown in situ on carbon nanotubes activated by aqua regia through an in situ aqueous reaction and form a heterojunction interface with the carbon nanotubes. The particle size of the cadmium selenide quantum dots is 1~5 nm.

2. The composite photocatalyst according to claim 1, wherein: The carbon nanotubes were activated with aqua regia at room temperature for 6-12 hours.

3. The composite photocatalyst according to claim 1, wherein: The mass ratio of carbon nanotubes to cadmium selenide quantum dots is 0.5:1 to 2:

1.

4. A method for preparing a carbon nanotube / cadmium selenide quantum dot heterojunction composite photocatalyst as described in any one of claims 1-3, comprising: (1) Add carbon nanotubes to aqua regia and treat at room temperature for 6 to 12 hours, wash until neutral and dry to obtain activated carbon nanotubes; (2) Disperse activated carbon nanotubes in deionized water containing CdCl2·2.5H2O and stir for 10-60 minutes to obtain a mixed system; (3) Add Na2SeSO3 and 3-mercaptopropionic acid to the mixed system and react at 110~150 °C for 1~6 hours to generate and load cadmium selenide quantum dots in situ on the surface and / or inside of carbon nanotubes; (4) Centrifuge, wash and dry to obtain composite photocatalyst.

5. The method according to claim 4, wherein: In step (3), the molar ratio of Cd source to Se source is 4:1, and the molar ratio of 3-mercaptopropionic acid to Cd source is 6:

5.

6. A carbon nanotube / cadmium selenide quantum dot heterojunction composite photocatalyst prepared by the method according to claim 4 or 5.

7. The application of a carbon nanotube / cadmium selenide quantum dot heterojunction composite photoelectrocatalyst according to any one of claims 1 to 3 or 6 in the aqueous phase photoelectrocatalytic reduction of carbon dioxide to carbon monoxide.

8. The application according to claim 7, wherein: (1) The composite catalyst is dispersed in a solution containing Nafion to form a catalyst ink; (2) Apply ink droplets onto conductive glass to form a working electrode; (3) An H-type electrolytic cell with optical path is used, the electrolyte is an aqueous solution of bicarbonate saturated with high-purity CO2 gas, and the reference electrode is an Ag / AgCl electrode. (4) Photoelectrocatalytic CO2 reduction is performed under LED illumination with a maximum wavelength of 450 nm; (5) The product CO is quantitatively analyzed by gas chromatography, using manual injection and calibrated with high-purity CO standard gas; it can operate stably for 100 hours under the above conditions.

9. The application according to claim 8, wherein: The drop loading in step (2) is 0.1~2 mg·cm³. -2 The conductive glass is FTO or ITO; The concentration of the bicarbonate aqueous solution in step (3) is 0.1 mol·L⁻¹. -1 ~saturation; The luminous intensity of the LED light in step (4) is 40~70 mW·cm. -2 .

10. The application according to claim 8 or 9, wherein: The bicarbonates include: Na salts, K salts, and ammonium salts.

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