CN115475648B - Preparation method of a mesoporous P-doped carbon nitride hollow sphere catalyst with Ni2P supported on both inner and outer surfaces - Google Patents

Abstract

The invention discloses a preparation method of a mesoporous P-doped carbon nitride hollow sphere catalyst with Ni ₂ P loaded on both inner and outer surfaces. The catalyst uses carbon nitride hollow spheres as a carrier and Ni ₂ P as a cocatalyst. The impregnation-phosphating method, in the process of synthesizing carbon nitride hollow spheres, by adjusting the synthesis sequence of the template SiO ₂ and Ni ₂ P for synthesizing carbon nitride hollow spheres, Ni ₂ P is loaded on the mesoporous P-doped The inner and outer surfaces of carbon nitride hollow nanospheres provide sufficient active sites on the inner and outer surfaces, and the heterojunction formed by the two simultaneously promotes the migration and separation of photogenerated charges on the inner and outer surfaces. The catalyst improves the atom utilization and realizes the internal and external synergy, thus significantly improving the photocatalytic water splitting performance. The method of the invention is generally applicable to other hollow structure semiconductors, and provides guidance for better utilization of hollow structure semiconductor photocatalysis.

Description

A mesoporous P-doped carbon nitride hollow sphere catalyst with Ni2P supported on both inner and outer surfaces preparation method

technical field

The invention belongs to the technical field of preparation of photocatalysts for water splitting driven by solar energy, and in particular relates to a preparation method of photocatalysts that use the inner and outer surfaces of nano hollow spheres to simultaneously load nanoparticles.

Background technique

Hydrogen energy is one of the most ideal alternative energy sources for fossil fuels. Photocatalytic water splitting technology is considered as one of the ideal methods for producing hydrogen due to its low cost, no pollution, mild reaction conditions, and high stability. Hollow nanostructured photocatalytic materials have special physical and chemical properties and have great application potential in the field of photocatalysis. For example: the light scattering inside the hollow nanomaterial is beneficial to light harvesting, light absorption and utilization; the internal space can also be used as a microreactor to promote the conversion of reactants; the hollow nanostructure provides a high specific surface area for surface reactions; the nanoscale A thin shell can reduce the migration distance of photogenerated carriers to the surface, thereby reducing the probability of recombination. Among many photocatalytic semiconductor materials, graphite-like carbon nitride (gC ₃ N ₄ ) has the advantages of absorption in the visible light region, acid and alkali resistance, cheap and easy to obtain, and the design and synthesis of carbon nitride with hollow nanostructures (such as Hollow carbon nitride nanospheres) have the potential to improve photocatalytic efficiency. However, the inherent characteristics of gC ₃ N ₄ still have problems such as low photogenerated charge separation efficiency and lack of surface active sites that affect the efficiency of photocatalytic water splitting.

Generally, in order to improve the photocatalytic activity, supporting co-catalysts and element doping are good modification methods. Doping with non-metallic elements such as P, C, S, and B can change the electronic structure and promote light absorption and charge separation. The supported co-catalyst can promote the transfer of photogenerated charge carriers, reduce the overpotential of photocatalyst water splitting, and significantly improve the water splitting activity. However, previous studies usually supported the cocatalyst on the outer surface of hollow nanospheres. For example, Cui et al. (ACSAppl. ₂ nanosheets were assembled in situ on the outer surface of N, P co-doped hollow carbon nanospheres (MoSe ₂ /NP-HCNSs), and the resulting nanoengineered materials could be well used as anodes for KIBs; Sun et al. ( International journal of hydrogen energy 2020,45,2840-2851) prepared hollow gC ₃ N ₄ @α-Fe ₂ O ₃ /Co-Pi composite heterojunction sphere photocatalyst, in which α-Fe ₂ O ₃ and spherical gC ₃ N ₄ contacts on the outer surface of the ball to form a z-type heterojunction, and Co-Pi as a hole storage agent can further reduce the recombination of photogenerated electrons and holes. Metal phosphides such as Ni ₂ P have been proven to be good cocatalysts for photocatalytic hydrogen production due to their low overpotential and stability. After loading Ni ₂ P co-catalyst, carbon nitride absorbs sunlight to generate photogenerated carriers. The electrons are transferred to the Ni ₂ P nanoparticles, which improves the charge separation efficiency and facilitates the reduction of H ⁺ on Ni ₂ P. But this fails to take full advantage of the advantages of the hollow structure, resulting in the ineffective use of the inner surface and inner space. Due to the lack of co-catalysts inside, there will still be high-frequency recombination of electron holes on the inner surface and close to the inner surface, and the photocatalytic activity is not ideal.

Contents of the invention

The purpose of the present invention is to provide a method for preparing a mesoporous P-doped carbon nitride hollow sphere catalyst with Ni ₂ P loaded on both inner and outer surfaces.

For above-mentioned purpose, the preparation method that the present invention adopts comprises the following steps:

1. Reflux _SiO2 microspheres, γ-aminopropyltriethoxysilane and isopropanol at 70-80°C for 2-3 hours, centrifuge and dry, and mix and stir the dried product with nickel chloride aqueous solution for 6-10 hours , centrifuged and dried, then ground and mixed with excess sodium phosphite, and calcined at 350-400°C for 1.5-2.5 hours under flowing argon to obtain non-porous SiO ₂ microspheres loaded with Ni ₂ P;

2. Add ammonia water to the mixed solution of ethanol and deionized water. After stirring evenly, add non-porous SiO ₂ microspheres loaded with Ni ₂ P. After stirring evenly, add tetraethyl orthosilicate and Octadecyltrimethoxysilane, the resulting mixed solution is allowed to stand at room temperature for 2 to 4 hours. After the reaction, it is centrifuged, dried and calcined at 500 to 600°C in the air for 5 to 6 hours, soaked in hydrochloric acid, deionized and washed. Dry to obtain Ni ₂ P-SiO ₂ templates;

3. Add the Ni ₂ P-SiO ₂ template into the cyanamide aqueous solution, rotate and mix under vacuum for 2-4 hours, then in turn ultrasonicate at 50-60°C for 2-3 hours, and stir at 50-60°C for 6-10 hours , the obtained mixture was transferred to a porcelain boat after centrifugal separation and drying, and calcined at 500-600°C for 3-5 hours under flowing argon to obtain unetched carbon nitride nanospheres wrapped with Ni ₂ P inside;

4. Disperse the unetched carbon nitride nanospheres wrapped with Ni ₂ P in deionized water, add nickel chloride under stirring condition, after stirring for 8-10 hours, dry at 80-100°C, dry the product with excess phosphorous acid Sodium is mixed and transferred to a magnetic boat, calcined at 350-400°C for 2-3 hours under flowing argon, cooled naturally to room temperature, etched with 4mol/L NH ₄ HF ₂ aqueous solution to remove the SiO ₂ template, centrifuged to collect the powdery product, and used Washing with deionized water and drying to obtain mesoporous P-doped carbon nitride hollow nanospheres with Ni ₂ P loaded on both inner and outer surfaces.

In the above step 1, it is preferred that the _SiO2 microspheres, γ-aminopropyltriethoxysilane and isopropanol are added in a ratio of 1g: 2-3mL: 50-60mL, and the _SiO2 microspheres and chlorinated The mass ratio of nickel and sodium phosphite is 1:0.015-0.030:0.025-0.06.

In the above step 1, it is further preferred that the SiO ₂ microspheres have a particle size of 300-500 nm.

In the above step 2, preferably the volume ratio of the ammonia water to ethanol, tetraethyl orthosilicate deionized water, and octadecyltrimethoxysilane is 1: 15～20: 2～2.5: 1～1.1: 0.4～0.6 , the feeding ratio of the non-porous SiO ₂ microspheres loaded with Ni ₂ P and tetraethyl orthosilicate is 1g: 3-4mL.

In the above step 3, preferably, the mass ratio of the Ni ₂ P-SiO ₂ template to cyanamide is 1:2-4.

In the above step 3, preferably, the vacuum degree of the vacuum is 10-80 Pa, and the rotation speed is 30-100 rpm.

In the above step 4, preferably, the mass ratio of the unetched carbon nitride nanospheres wrapped with Ni ₂ P to nickel chloride and sodium phosphite is 1:0.1-0.3:0.4-0.5.

The beneficial effects of the present invention are as follows:

1. The present invention successfully synthesizes mesoporous P-doped carbon nitride hollow nanospheres (PCNHS) by impregnation-phosphating method, and simultaneously supports Ni ₂ P co-catalysts on its inner and outer surfaces. This approach is of great significance for better utilization of hollow nanostructured semiconductors for photocatalytic reactions.

2. In the present invention, triethanolamine is used as a hole sacrificial agent, and Ni ₂ P@PCNHS@Ni ₂ P is used as a photocatalyst to test the photocatalytic hydrogen production performance under the irradiation of visible light. Ni ₂ P@PCNHS@Ni ₂ P provides sufficient active sites for proton reduction on both the inner and outer surfaces, and at the same time promotes the migration and separation of photogenerated carriers on the inner and outer surfaces, improving the utilization of atoms and realizing The internal and external synergistic photocatalytic water splitting, its efficiency is significantly improved.

Description of drawings

Fig. 1 is Ni ₂ P@PCNHS@Ni ₂ P (Ni content is 3.80wt.%) in embodiment 1 and CNHS in comparative example 1, Ni ₂ P/CNHS in comparative example 2, PCNHS in comparative example 3, comparative example XRD patterns of PCNHS@Ni ₂ P (Ni content: 0.05 wt.%) in 5 and Ni ₂ P@PCNHS (Ni content: 3.19 wt.%) in Comparative Example 6.

Fig. 2 is a SEM image of Ni ₂ P@PCNHS@Ni ₂ P (Ni content: 3.80wt.%) in Example 1.

Fig. 3 is a TEM image of Ni ₂ P@PCNHS@Ni ₂ P (Ni content: 3.80wt.%) in Example 1.

Fig _. 4 is a lattice fringe HRTEM image of Ni ₂ P@PCNHS@Ni ₂ P (with a Ni content of 3.80wt.%) in Example 1.

Fig. 5 is a lattice fringe HRTEM diagram of Ni ₂ P inside Ni 2 P@PCNHS@Ni ₂ P ₍ Ni content is 3.80wt.%) in Example 1.

Fig. 6 is a dark-field STEM map of Ni ₂ P@PCNHS@Ni ₂ P (with a Ni content of 3.80wt.%) in Example 1 and a map of C, N, Ni, and P elements.

Fig. 7 is Ni ₂ P@PCNHS@Ni ₂ P (Ni content is 3.80wt.%) in Example 1 and CNHS in Comparative Example 1, Ni ₂ P/CNHS in Comparative Example 2, PCNHS in Comparative Example 3, and Comparative Example Comparison of photocatalytic hydrogen production activity of Pt@PCNHS in 4.

Figure 8 shows Ni ₂ P@PCNHS@Ni ₂ P (Ni content is 3.80wt.%) in Example 1 and PCNHS@Ni ₂ P (Ni content is 0.05wt.%) in Comparative Example 5, Ni in Comparative Example 6 Comparison of photocatalytic hydrogen production activity of ₂ P@PCNHS (Ni content 3.19wt.%).

Figure 9 shows Ni ₂ P@PCNHS@Ni ₂ P (Ni content is 3.80wt.%) in Example 1 and PCNHS@Ni ₂ P (Ni content is 0.05wt.%) in Comparative Example 5, Ni in Comparative Example 6 _2P @PCNHS (Ni content 3.19wt.%) photocatalytic hydrogen production mass normalized activity comparison chart.

Figure 10 shows Ni ₂ P@PCNHS@Ni ₂ P (Ni content is 3.80wt.%) in Example 1 and PCNHS@Ni ₂ P (Ni content is 0.05wt.%) in Comparative Example 5, Ni in Comparative Example 6 ₂ Comparison of photocatalytic water splitting activity of P@PCNHS (Ni content 3.19wt.%) without sacrificial agent triethanolamine.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

Example 1

硅溶胶。将/>

硅溶胶直接离心、干燥、研磨，得到粒径约300nm的SiO₂微球。将1.2g SiO₂微球与3mLγ-氨丙基三乙氧基硅烷和63mL异丙醇在80℃下回流2h，离心、干燥，再将干燥产物与50mL含28mg NiCl₂·6H₂O的水溶液搅拌8h，离心、干燥后与47mg NaH₂PO₂·H₂O研磨混合，在流动的氩气下以5℃/min的升温速率升温至350℃，煅烧2h，自然冷却后研磨，得到负载Ni₂P的无孔SiO₂微球。1. Add 4.35mL of ammonia water (32wt.%) to the mixture of 75mL of ethanol and 10mL of deionized water, stir at 30°C for 30min, then add 5.6mL of tetraethyl orthosilicate (TEOS), and continue to stir for 1h. get even

Silica sol. will />

The silica sol is directly centrifuged, dried, and ground to obtain SiO ₂ microspheres with a particle size of about 300 nm. Reflux 1.2g of SiO ₂ microspheres with 3mL of γ-aminopropyltriethoxysilane and 63mL of isopropanol at 80°C for 2h, centrifuge and dry, then mix the dried product with 50mL of an aqueous solution containing 28mg of NiCl ₂ ·6H ₂ O Stir for 8 hours, centrifuge and dry, grind and mix with 47mg NaH ₂ PO ₂ ·H ₂ O, heat up to 350°C at a rate of 5°C/min under flowing argon, calcinate for 2h, cool naturally and then grind to obtain loaded Ni ₂ P nonporous SiO ₂ microspheres.

2. Add 4.35mL of ammonia water (32wt.%) to the mixture of 75mL of ethanol and 10mL of deionized water, stir at 30°C for 30min, then add 1.2g of Ni ₂ P-loaded non-porous SiO ₂ microspheres, and continue stirring After 30 min, 4.5 mL (4.17 g) of TEOS and 2.15 mL (1.87 g) of octadecyltrimethoxysilane (C ₁₈ TMOS) were added dropwise with stirring, and then the mixed solution was allowed to stand at room temperature for 3 h. After the reaction, it was centrifuged, dried at 70°C and calcined at 550°C in air for 6h, and finally soaked in 1mol/L HCl aqueous solution, washed, and dried at 80°C for 10h to obtain a Ni ₂ P-SiO ₂ template. The process involves the cohydrolysis and condensation of TEOS and _C18 TMOS on _Ni2P -loaded nonporous _SiO2 microspheres to form a mesoporous _SiO2 shell on its surface.

3. Add 2g of Ni ₂ P-SiO ₂ template to 10g of cyanamide aqueous solution with a mass concentration of 50%, rotate and mix at 50ppm for 3h under a vacuum of 90Pa, then ultrasonicate at 60°C for 2h, then at 60°C The resulting mixture was separated by centrifugation and dried at 80°C in the air for 24h. Finally, the obtained solid was transferred to a porcelain boat and heated to 550°C at a rate of 4.4°C/min under flowing argon. After calcination for 4 hours and natural cooling to room temperature, unetched carbon nitride nanospheres (CNHS@Ni ₂ P) wrapped with Ni ₂ P inside were obtained, wherein the content of Ni was 0.05wt.%.

4. Disperse 1.12g CNHS@Ni ₂ P into 50mL deionized water, then add 168mgNiCl ₂ ·6H ₂ O under vigorous stirring, after stirring for 10h, dry at 100°C, dry the product with 500mg NaH ₂ PO ₂ ·H ₂ O After mixing, transfer to a magnetic boat, raise the temperature to 350°C at a heating rate of 5°C/min under flowing argon, and calcinate for 2h. Then cool naturally to room temperature, etch with 4mol/L NH ₄ HF ₂ aqueous solution for 12 hours to remove the SiO ₂ template, centrifuge to collect the powder product, wash with deionized water, and dry in an oven at 60°C to obtain Ni ₂ P loaded on the inner and outer surfaces. The mesoporous P-doped carbon nitride hollow nanospheres are denoted as Ni ₂ P@PCNHS@Ni ₂ P, where the content of Ni is 3.80%.

Comparative example 1

硅溶胶。在搅拌条件下将4.5mL(4.17g)TEOS和2.15mL(1.87g)十八烷基三甲氧基硅烷(C₁₈TMOS)滴加到/>

硅溶胶中，然后将混合溶液在室温下静置反应3h。反应结束后，离心，将其在70℃下干燥并在空气中550℃煅烧6小时，最后用1mol/L HCl水溶液浸泡、洗涤、80℃下干燥10h，得到SiO₂模板。1. Add 4.35mL of ammonia water (32wt.%) to the mixture of 75mL of ethanol and 10mL of deionized water, stir at 30°C for 30min, then add 5.6mL of tetraethyl orthosilicate (TEOS), and continue to stir for 1h. get even

Silica sol. Add 4.5mL (4.17g) TEOS and 2.15mL (1.87g) octadecyltrimethoxysilane (C ₁₈ TMOS) dropwise to

Silica sol, and then the mixed solution was allowed to stand at room temperature for 3 h. After the reaction, it was centrifuged, dried at 70°C and calcined at 550°C in air for 6 hours, and finally soaked with 1mol/L HCl aqueous solution, washed, and dried at 80°C for 10h to obtain a SiO ₂ template.

2. Add 2g of _SiO2 template to 10g of cyanamide aqueous solution with a mass concentration of 50%, rotate and mix at 50ppm for 3h under a vacuum of 90Pa, then sonicate at 60°C for 2h and stir at 60°C for 8h, The obtained mixture was separated by centrifugation and dried in air at 80°C for 24h. Finally, the obtained solid was transferred to a porcelain boat, and the temperature was raised to 550°C at a rate of 4.4°C/min under flowing argon, and calcined for 4h. After cooling to room temperature, etched with 4mol/L NH ₄ HF ₂ aqueous solution for 12h to remove the SiO ₂ template, centrifuged to collect the powder product, washed with deionized water, and dried in an oven at 60°C to obtain carbon nitride hollow nanospheres (CNHS) .

Comparative example 2

Grind 50mg NiCl ₂ ·6H ₂ O and 84mg NaH ₂ PO ₂ ·H ₂ O, transfer to a magnetic boat after grinding, raise the temperature to 400°C at a rate of 2°C/min under flowing Ar, and calcinate for 2h. After naturally cooling to room temperature, it was washed three times with deionized water and ethanol, and dried at 60° C. for 10 h to obtain pure Ni ₂ P crystal powder. Disperse 100mg of CNHS (preparation method as in Comparative Example 1) in 30mL of deionized water, add 3mg of pure _Ni2P crystals and stir for 10h, then wash with deionized water, and finally dry at 60°C for 10h to obtain _Ni2P / Carbon Nitride Hollow Nanosphere Composite Catalyst (Ni ₂ P/CNHS).

Comparative example 3

2g SiO _template (preparation method is the same as step 1 of Comparative Example 1) was added to 10g of cyanamide aqueous solution with a mass concentration of 50%, rotated and mixed at 50ppm for 3h under a vacuum of 90Pa, and then ultrasonicated at 60°C for 2h , stirred at 60°C for 8h, the obtained mixture was separated by centrifugation, and dried at 80°C in air for 24h, and finally the obtained solid was transferred to a porcelain boat, and the temperature was raised at a rate of 4.4°C/min under flowing argon to 550°C, calcined for 4 hours, cooled naturally to room temperature, ground with 500mg NaH ₂ PO ₂ ·H ₂ O, transferred to a magnetic boat, and heated to 350°C at a rate of 5°C/min under flowing argon. Calcined for 2 h, cooled to room temperature naturally, etched with 4mol/L NH ₄ HF ₂ aqueous solution for 12 h to remove SiO ₂ template, centrifuged to collect the powder product, washed with deionized water, dried in an oven at 60°C to obtain phosphorus-doped nitrogen carbonized hollow nanospheres (PCNHS).

Comparative example 4

Disperse 100mg PCNHS (preparation method is the same as Comparative Example 3) in 30mL deionized water, add 150μL 6.59mgPt/mL H ₂ PtCl ₆ aqueous solution, stir evenly, add 200mg NaBH ₄ , continue stirring for 10h, then use deionized water and After washing with ethanol three times, and finally drying at 80 °C for 10 h, the Pt-doped carbon nitride hollow nanospheres loaded with Pt (Pt@PCNHS) were obtained.

Comparative example 5

硅溶胶。将/>

硅溶胶直接离心、干燥、研磨，得到的SiO₂微球与3mLγ-氨丙基三乙氧基硅烷和63mL异丙醇在80℃下回流2h，离心、干燥，得到的SiO₂微球与3mLγ-氨丙基三乙氧基硅烷和63mL异丙醇在80℃下回流2h，离心、干燥，再将干燥产物分别与50mL含不同质量(28mg、84mg、168mg、252mg、336mg)NiCl₂·6H₂O的水溶液搅拌8h，离心、干燥后与500mg NaH₂PO₂·H₂O研磨混合，在流动的氩气下以5℃/min的升温速率升温至350℃，煅烧2h，自然冷却后研磨，分别得到不同Ni含量的负载Ni₂P的无孔SiO₂微球。1. Add 4.35mL of ammonia water (32wt.%) to the mixture of 75mL of ethanol and 10mL of deionized water, stir at 30°C for 30min, then add 5.6mL of tetraethyl orthosilicate (TEOS), and continue to stir for 1h. get even

Silica sol. will />

The silica sol was directly centrifuged, dried and ground, and the obtained SiO ₂ microspheres were refluxed with 3 mL γ-aminopropyltriethoxysilane and 63 mL isopropanol at 80 ° C for 2 h, centrifuged and dried, and the obtained SiO ₂ microspheres were mixed with 3 mL γ -Aminopropyltriethoxysilane and 63 mL of isopropanol were refluxed at 80°C for 2 hours, centrifuged and dried, and then the dried product was mixed with 50 mL of NiCl ₂ ·6H Stir _{the 2} O aqueous solution for 8 hours, centrifuge and dry, grind and mix with 500mg NaH ₂ PO ₂ ·H ₂ O, heat up to 350°C at a rate of 5°C/min under flowing argon, calcinate for 2h, cool naturally and then grind , to obtain Ni ₂ P-loaded non-porous SiO ₂ microspheres with different Ni contents.

2. 2g _Ni2P - _SiO2 template (preparation method is the same as step 2 of Example 1) was added to 10g mass concentration of 50% cyanamide aqueous solution, and the vacuum degree was 90Pa with 50ppm rotary mixing for 3h, and then Sonicate at 60°C for 2h and stir at 60°C for 8h in turn. The resulting mixture is separated by centrifugation and dried at 80°C in air for 24h. The heating rate of ℃/min is raised to 550 ℃, calcined for 4 hours, cooled to room temperature naturally, ground with 500mg NaH ₂ PO ₂ ·H ₂ O and transferred to a magnetic boat, under flowing argon at a rate of 5 ℃/min The heating rate was raised to 350°C, and calcined for 2 hours. Then cool to room temperature, etch with 4mol/L NH ₄ HF ₂ aqueous solution for 12h to remove the SiO ₂ template, centrifuge to collect the powder product, wash with deionized water, and dry in an oven at 60°C to obtain mesoporous phosphorus coated with Ni ₂ P Doped carbon nitride hollow nanospheres (PCNHS@Ni ₂ P). According to the mass of NiCl ₂ ·6H ₂ O added in step 1, PCNHS@Ni ₂ P with Ni contents of 0.05%, 0.15%, 0.03%, 0.45%, and 0.60% were respectively obtained.

Comparative example 6

2g SiO _template (preparation method is the same as step 1 of Comparative Example 1) was added to 10g of cyanamide aqueous solution with a mass concentration of 50%, rotated and mixed at 50ppm for 3h under a vacuum of 90Pa, and then ultrasonicated at 60°C for 2h , stirred at 60°C for 8h, the obtained mixture was separated by centrifugation, and dried at 80°C in air for 24h, and finally the obtained solid was transferred to a porcelain boat, and the temperature was raised at a rate of 4.4°C/min under flowing argon to 550° C., calcined for 4 hours, and naturally cooled to room temperature to obtain unetched carbon nitride nanospheres. Disperse 1.12 g of unetched carbon nitride nanospheres into 50 mL of deionized water, then add 56 mg, 112 mg, 168 mg, 224 mg, and 280 mg of NiCl ₂ 6H ₂ O under vigorous stirring, stir for 10 h, and dry at 100°C. The product was mixed with 500mg NaH ₂ PO ₂ ·H ₂ O and then transferred to a magnetic boat, heated to 350°C at a rate of 5°C/min under flowing argon, calcined for 2 hours, cooled naturally to room temperature, and then heated with 4mol/ L NH ₄ HF ₂ aqueous solution etched for 12 h to remove the SiO ₂ template, the powder product was collected by centrifugation, washed with deionized water, and dried in an oven at 60 °C to obtain mesoporous phosphorus-doped carbon nitride hollow nanospheres with external Ni ₂ P loading (Ni ₂ P@PCNHS). According to the mass of NiCl ₂ ·6H ₂ O added, Ni ₂ P@PCNHS with Ni contents of 1.86%, 3.19%, 4.63%, 5.98%, and 7.31% were respectively obtained.

Structural characterization was performed on the samples prepared in the above-mentioned Example 1 and Comparative Examples 1-6, and the results are shown in Figures 1-6. As shown in Fig. 1, pure CNHS and all composites have two distinct diffraction peaks at 13.1° and 27.6°, the peak at 13.1° is due to the periodicity of the continuous triazine ring network in the carbon nitride plane Stacking, the peak at 27.6° is related to the stacking of the graphitic layered structure ( _{002 ) plane} of the conjugated arene system. There are obvious diffraction peaks at 47.3° and 54.3°, which point to the (111), (201), (210), and (300) planes of hexagonal Ni ₂ P (JCPDS 03-0953), respectively, indicating that the Ni ₂ P cocatalyst Successful loading; no reflection related to Ni ₂ P was observed on the XRD pattern of PCNHS@Ni ₂ P, which was due to the fact that the Ni ₂ P loaded inside was covered by carbon nitride and the content of Ni ₂ P was low. Sincerely. It can be observed from Figure 2 and Figure 3 that Ni _{2 P nanoparticles in Ni 2} P@PCNHS@Ni ₂ P are loaded on the inner and outer surfaces respectively, _and the lattice stripes of the nanoparticles loaded on the outside can still be observed through HRTEM. The interplanar distance d=0.22nm (see Figure 4), but the inner nanoparticles are hindered by carbon nitride so that the lattice stripes are not obvious (see Figure 5), but they can still match the lattice distance of Ni ₂ P. Furthermore, we tested the energy-dispersive X-ray (EDX) and elemental mapping of Ni ₂ P@PCNHS@Ni ₂ P (see Figure 6), and the results showed that C, N, Ni, and P were distributed inside and outside the hollow nanospheres , the outer light spot is more obvious, while the inner light spot is relatively weak due to the blocking of PCNHS, which further proves that the inside and outside of PCNHS are successfully loaded with Ni ₂ P.

In order to prove the beneficial effects of the present invention, the samples prepared in Example 1 and Comparative Examples 1-6 were respectively used as catalysts to conduct photocatalytic water splitting hydrogen production activity tests. Under the irradiation of visible light, use a heat-resistant glass reactor equipped with a top quartz glass plate and a closed glass gas renewable circulation system for testing. The specific operation steps are: add 90mL deionized water and 10mL triethanolamine to the reactor, After stirring and dissolving, 20 mg of catalyst was added, stirred and vacuumed for 30 minutes to remove air in the device and the reaction solution, and then reacted under visible light irradiation (light intensity: 1.12 W/cm ² ), and the reaction temperature was 20°C. The finally produced hydrogen was tested by the thermal conductivity detector (TCD) of the gas chromatograph (Shiweipx GC7806) through the air pump and within a certain time interval (1h). The results are shown in Figures 7-10.

It can be seen from Figure 7 that with triethanolamine as the hole sacrificial agent, under the irradiation of visible light, it can be found that the catalysts corresponding to Comparative Examples 1, 2, and 3: CNHS, Ni ₂ P/CNHS, and PCNHS have hydrogen production rates of 0.1, 1.65, 1.86 μmol·g ^-1 ·h ^-1 . It shows that after Ni ₂ P is loaded, the hydrogen production rate is increased, which can reach 1.65 μmol·g ^-1 ·h ^-1 , and element doping can also effectively improve the photocatalytic activity. Therefore, in the preparation process, we loaded Ni ₂ P At the same time, the P element was doped into CNHS, and the two also produced a synergistic effect. The photocatalytic hydrogen evolution rate of PCNHS was 1.86μmol·g ^-1 ·h ^-1 , but when the two existed simultaneously, the Ni ₂ The hydrogen evolution rate of P@PCNHS@Ni ₂ P can reach 817.90μmol·g ^-1 ·h ^-1 , which is even higher than that of Pt supported on PCNHS (Pt@PCNHS) at 339.22μmol·g ^-1 ·h ^-1 (2.4 times ). It can be clearly seen from Fig. 8 that PCNHS@Ni ₂ P (W _Ni ＝0.05～0.60wt.%) with different Ni content and Ni ₂ P@PCNHS (W _Ni ＝1.86～7.50wt.%) photocatalytically produced The performance of hydrogen is far inferior to that of Ni ₂ P@PCNHS@Ni ₂ P. In order to further confirm the activity of internal and external synergy, PCNHS@Ni ₂ P (W _Ni =0.60wt.%) in Comparative Example 5 and Ni ₂ P@PCNHS (W _Ni =3.19wt.%) in Comparative Example 6 were selected, and the content of Ni The photocatalytic hydrogen evolution activity of the same catalyst as that of Ni ₂ P@PCNHS@Ni ₂ P (W _Ni =3.80wt.%) in Example 1 was compared. As shown in Figure 9, the hydrogen evolution activity of Ni ₂ P@PCNHS@Ni ₂ P (W _Ni =3.80wt.%) is greater than that of PCNHS@Ni ₂ P (W _Ni =0.60wt.%) in Comparative Example 5 and Ni in Comparative Example 6 ₂ P@PCNHS (W _Ni =3.19wt.%), and much larger than the sum of the two, showing synergy. The hydrogen evolution rate of Ni ₂ P@PCNHS@Ni ₂ P(W _Ni ＝3.80wt.%) calculated by unit Ni content can reach 21.52mmol·g _Ni ^-1 ·h ^-1 , which are respectively PCNHS@Ni ₂ P(3.00 mmol·g _Ni ^-1 ·h ^-1 ) and Ni ₂ P@PCNHS (16.67mmol·g _Ni ^-1 ·h ^-1 ) 7 times and 1.3 times. As shown in Figure 10, the photocatalytic water splitting activity of the three catalysts with the same content as above was further tested. Under visible light irradiation, the hydrogen evolution rate of PCNHS@Ni ₂ P can reach 2.02 μmol g ^-1 h ^-1 , Ni ₂ P The hydrogen evolution rate of @PCNHS can reach 3.35μmol·g ^-1 ·h ^-1 , and the hydrogen evolution rate of Ni ₂ P@PCNHS@Ni ₂ P can reach 12.70μmol·g ^-1 ·h ^-1 , realizing "1+1>2" internal and external synergies.

Claims (7)

1. a kind of preparation method of the _mesoporous P-doped carbon nitride hollow sphere catalyst that supports Ni at the same time inside and outside the P, it is characterized in that described preparation method comprises the following steps: (1) Reflux _SiO2 microspheres with γ-aminopropyltriethoxysilane and isopropanol at 70-80°C for 2-3 h, centrifuge and dry, and mix and stir the dried product with nickel chloride aqueous solution for 6 ~10 h, after centrifugation and drying, grind and mix with excess sodium phosphite, and calcinate at 350~400°C for 1.5~2.5 h under flowing argon to obtain non-porous SiO ₂ microspheres loaded with Ni ₂ P; (2) Add ammonia water to the mixture of ethanol and deionized water, stir well, add non-porous SiO ₂ microspheres loaded with Ni ₂ P, stir well, add tetraethyl orthosilicate dropwise under stirring condition and octadecyltrimethoxysilane, and the resulting mixed solution was allowed to stand at room temperature for 2 to 4 hours. After the reaction, it was centrifuged, dried and calcined at 500 to 600°C in the air for 5 to 6 hours, soaked in hydrochloric acid, and removed. Ion washing and drying to obtain a Ni ₂ P-SiO ₂ template; (3) Add the Ni ₂ P-SiO ₂ template into the cyanamide aqueous solution, rotate and mix under vacuum for 2-4 h, then in turn sonicate at 50-60°C for 2-3 h, and stir at 50-60°C After 6-10 h, the obtained mixture was centrifuged and dried, then transferred to a porcelain boat, and calcined at 500-600 ° C for 3-5 h under flowing argon to obtain unetched carbon nitride nanometers with Ni ₂ P inside. ball; (4) Disperse the unetched carbon nitride nanospheres wrapped with Ni ₂ P in deionized water, add nickel chloride under stirring conditions, and after stirring for 8-10 h, dry at 80-100 °C, and dry the product with excess Sodium phosphite was mixed and transferred to a magnetic boat, calcined at 350-400°C for 2-3 h under flowing argon, cooled naturally to room temperature, etched with 4 mol/L NH ₄ HF ₂ aqueous solution to remove the SiO ₂ template, and collected by centrifugation The powdery product is washed with deionized water and dried to obtain mesoporous P-doped carbon nitride hollow nanospheres with Ni ₂ P loaded on the inner and outer surfaces. 2. The preparation method of the mesoporous P-doped carbon nitride hollow sphere catalyst with Ni ₂ P loaded on the inner and outer surfaces according to claim 1, characterized in that: in step (1), the SiO ₂ microspheres and γ -Aminopropyltriethoxysilane and isopropanol are added in a ratio of 1 g: 2 to 3 mL: 50 to 60 mL; the mass ratio of SiO _microspheres to nickel chloride and sodium phosphite is 1: 0.015～0.030: 0.025～0.06. 3. The preparation method of the mesoporous P-doped carbon nitride hollow sphere catalyst with Ni ₂ P loaded on the inner and outer surfaces according to claim 1 or 2, characterized in that: in step (1), the SiO ₂ microspheres The particle size is 300-500 nm. 4. The preparation method of the mesoporous P-doped carbon nitride hollow sphere catalyst with Ni ₂ P loaded on the inner and outer surfaces according to claim 1, characterized in that: in step (2), the ammonia water, ethanol, deionized The volume ratio of water, tetraethyl orthosilicate, and octadecyltrimethoxysilane is 1:15~20:2~2.5:1~1.1:0.4~0.6, and the non-porous SiO ₂ loaded with Ni ₂ P The feeding ratio of microspheres and tetraethyl orthosilicate is 1 g: 3-4 mL. 5. The preparation method of the mesoporous P-doped carbon nitride hollow sphere catalyst with Ni ₂ P loaded on the inner and outer surfaces according to claim 1, characterized in that: in step (3), the Ni ₂ P-SiO ₂ The mass ratio of template to cyanamide is 1:2-4. 6. The preparation method of the mesoporous P-doped carbon nitride hollow sphere catalyst with Ni ₂ P loaded on the inner and outer surfaces according to claim 1, characterized in that: in step (3), the vacuum degree of the vacuum is 10 ～80 Pa, the rotation speed is 30～100rpm. 7. The preparation method of the mesoporous P-doped carbon nitride hollow sphere catalyst with Ni ₂ P loaded on the inner and outer surfaces according to claim 1, characterized in that: in step (4), the inner wrapped Ni ₂ P The mass ratio of unetched carbon nitride nanospheres to nickel chloride and sodium phosphite is 1:0.1-0.3:0.4-0.5.

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