Method for producing nanoflakes from G-C3N4-metal-composite materials

Abstract

The present invention provides a method for producing g-C3N4 / metal-composite-nanoflakes comprising the steps of: (a) providing a starting material comprising or consisting of FePO4, urea and polyacrylonitrile, the starting material being present as a powder having particles with an average particle size of less than 100 nm; (b) dispersing the starting material in a solvent, the solvent being water; (c) removing the solvent to form a premix comprising the starting material; (d) heating the premix; (e) removing the solvent to form a premix comprising the starting material; (f) removing the solvent to form a premix; (d) heating the premix to form a bulk-g-C3N4 / metal-composite by pyrolysis at a pyrolysis temperature between 200°C and 700°C, preferably between 400°C and 600°C; (e) treating the bulk-g-C3N4 / metal-composite with ultrasound to form g-C3N4 / metal-composite-nanoflakes.

Description

[Technical field]

[0001] The present invention relates to a method for producing nanoflakes from g-C3N4 / metal composites according to the features of independent claim 1. The invention also relates to nanoflakes obtainable by such a method, as well as to hydrogen storage materials and photocatalysts, photoelectrocatalysts and electrocatalysts comprising the nanoflakes according to the invention. [Background technology]

[0002] Graphitic carbon nitride, also known as g-C3N4, is a polymeric material that has been used in various applications in the art, for example in heterogeneous catalytic applications and as a storage material for molecular hydrogen. Pure g-C3N4 is a metal-free compound whose properties can be customized and improved by forming composites with metals or metal compounds.

[0003] gC 3 N 4 Materials based on gC are already known in the art. In the paper "Facile Production of a Fenton-Like Photocatalyst by Two-Step Calcination with a Broad pH Adaptability" by Siyang Ji et al. (nanomaterials, 2020), 3 N 4 Nanoflakes are described, and gC 3 N 4 Iron is incorporated into CN104437643A. 3 N 4 CN110479345A describes a method for impregnating iron with gC supported on iron oxide flakes. 3 N 4 CN110429277A describes sulfur-doped gC quantum dots. 3 N 4 The material is described, but the exact properties of the iron contained are not detailed. The paper "Facile synthesis of graphitic carbon nitride / chitosam / Au nanocomposite: A catalyst for electrochemical hydrogen evolution" by Atefeh Nasri et al. (International Journal of Biological Macromolecules, 2020) states that gC 3 N gold nanocomposites. CN112156662A discloses nanofibers.

[0004] However, the performance characteristics of known g-C3N4 / metal-composites are insufficient, especially for hydrogen storage and photocatalytic production of hydrogen and oxygen from water. In particular, the hydrogen storage capacity and / or achievable hydrogen production rate are issues that require improvement of known C3N4 / metal-composites. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] CN104437643A [Patent Document 2] CN110479345A [Patent Document 3] CN110429277A [Patent Document 4] CN112156662A [Non-patent literature]

[0006] [Non-Patent Document 1] “Facile Production of a Fenton-Like Photocatalyst by Two-Step Calcination with a Broad pH Adaptability”(nanomaterials, 2020) [Non-Patent Document 2] “Facile synthesis of graphitic carbon nitride / chitosam / Au nanocomposite: A catalyst for electrochemical hydrogen evolution” by Atefeh Nasri et al. (International Journal of Biological Macromolecules, 2020) Summary of the Invention [Problem to be solved by the invention]

[0007] It is therefore an object of the present invention to overcome the shortcomings of known g-C3N4 / metal-composite materials, in particular to create g-C3N4 / metal-composite materials improved in at least one of the following performance characteristics: hydrogen storage capacity, hydrogen adsorption capacity, hydrogen production rate, achievable current density in photoelectrocatalysis and water electrolysis. [Means for solving the problem]

[0008] In the context of the present invention, it has surprisingly been found that these and other objectives can be achieved in particular by a composite material produced by the method according to the invention.

[0009] Therefore, the present invention relates to a method for preparing g-C3N4 / metal-composite-nanoflakes, which comprises several steps.

[0010] Optionally, a step (a) may be provided having the following characteristics: providing a starting material comprising or consisting of an iron compound, a g-C3N4-precursor material and a polymer. The iron compound may be iron(III) phosphate. The g-C3N4-precursor material may be urea (CH4N2O). The polymer may be polyacrylonitrile. In particular, the starting material is a powder whose particles have an average particle size of less than 100 nm.

[0011] It has been found that the use of polyacrylonitrile as a starting material results in nanoflakes with particularly favorable properties. Without being bound by theory, it is believed that the polyacrylonitrile forms a template that significantly influences the geometric parameters of the resulting nanoflakes, particularly their length, width, shape and orientation.

[0012] A further advantageous technical effect of polyacrylonitrile, where appropriate, is that cyclization of polyacrylonitrile is carried out as part of the process, thereby forming a conductive polymer, which gives the g-C3N4 material a certain stability, especially with regard to chemical, thermal and mechanical properties. For example, the use of polyacrylonitrile can improve the flame retardancy, fire resistance and heat resistance of the composite material, which is particularly advantageous in applications using hydrogen, since an oxyhydrogen gas mixture may be formed and the burning hydrogen gas cannot ignite the composite material.

[0013] Optionally, a step (b) may be provided having the following characteristics: the starting material is dispersed in a solvent, which is in particular water. In step (b), the water may have a boiling temperature. In some cases, this step leads to incomplete dissolution of the starting material in the solvent.

[0014] Better dispersion, especially achieved by making the particle size of the starting materials as small as possible, is advantageous for the subsequent reaction to g-C3N4, e.g. in terms of yield and kinetics.

[0015] Optionally, there may be a step (c) of removing the solvent to form a premix containing the starting materials.

[0016] Optionally, a step (d) may be provided having the following characteristics: the premix obtained in step (c) is heated and pyrolyzed at a pyrolysis temperature between 200°C and 700°C, preferably between 400°C and 600°C, to form a bulk-g-C3N4 / metal-composite material.

[0017] "Bulk g-C3N4 / metal composite material" in the context of the present invention refers in particular to a material having a coherent layered structure in which multiple layers may be superimposed.

[0018] Optionally, a step (d) may be provided having the following characteristics: the bulk-g-C3N4 / metal-composite is treated with ultrasound to form g-C3N4 / metal-composite nanoflakes.

[0019] In particular, ultrasonic treatment induces exfoliation of the g-C3N4 / metal-composite, forming nanoflakes from the bulk material. Optionally, the layer structure of the bulk material is broken down to form nanoflakes. Another advantage of ultrasonic treatment is a better distribution of metal between the g-C3N4 layers, which then optionally acts as a stabilizing spacer.

[0020] Optionally, the ultrasound used in the treatment of step (d) has a frequency between 20 kHz and 100 kHz. Where appropriate, the energy input by the ultrasound in step (d) is at least 0.25 W per gram of bulk g-C3N4 / metal-composite material.

[0021] In the context of the present invention, "nanoflakes" refers in particular to particles whose external dimensions are precisely in the nanoscale range, ie between 1 nm and 100 nm.

[0022] The nanoflakes produced by the method according to the invention or the nanoflakes according to the invention are in particular nanoporous, i.e. have pores with dimensions in the sub-100 nm range or less. Nanoporosity is achieved in particular by dispersion in step (b) and optional milling and ultrasonication.

[0023] Where appropriate, the amount of iron compound in step (a) is provided between 1.0% and 20% by weight relative to the total amount of starting material.

[0024] Optionally, the dispersion in step (b) can be carried out at a temperature between 80° C. and 100° C., preferably between 90° C. and 100° C., which can partially dissolve the starting materials and improve the completeness of the reaction to g-C3N4.

[0025] Optionally, it is intended to treat the dispersion of step (b) with ultrasound. This treatment can be carried out, for example, by using an ultrasonic rod introduced into the dispersion. Where appropriate, the ultrasound used in the treatment of step (b) has a frequency between 20 kHz and 100 kHz. Optionally, the energy input by the ultrasound of step (d) is at least 0.25 W per mL of dispersion. By ultrasonic treatment, an improvement in the dispersion is achieved, which can improve the completeness of the reaction to g-C3N4.

[0026] Optionally, the dispersion in step (b) takes at least 1 hour, in particular about 2 hours.

[0027] Optionally, the heating rate during heating to the pyrolysis temperature in step (d) may be 5° C. / min or greater.

[0028] Optionally, the pyrolysis temperature in step (d) can be about 450° C. As a result, iron(III) phosphate can be obtained in the layer of the g-C3N4 / metal-composite material produced when iron(III) phosphate is used as the starting material.

[0029] Optionally, the pyrolysis temperature in step (d) can be about 550° C. As a result, iron(III) oxide can be obtained in the layer of the g-C3N4 / metal-composite produced when iron(III) phosphate is used as the starting material.

[0030] Optionally, the pyrolysis in step (d) takes at least 4 hours, in particular about 5 hours.

[0031] Optionally, step (d) is followed by a further step of reducing the iron in the g-C3N4 / metal composite. Optionally, the reduction is carried out by treating the composite with hydrogen. Depending on the extent of reduction, the iron is converted to ferric ions or elemental iron.

[0032] Optionally, it is provided to add a further metal compound in step (a), the further metal compound being selected from an aluminium compound, a lithium compound, a magnesium compound, a titanium compound, a nickel compound, a platinum compound, a palladium compound, a vanadium compound, or any mixture of these compounds.

[0033] The specific properties of the composite material can be tailored by adding further metal compounds.

[0034] Where appropriate, it is provided that the amount of the further metal compound in step (a) is between 0.5% and 5.0% by weight, preferably about 1.0% by weight, relative to the total amount of starting material.

[0035] Optionally, it is contemplated that the pyrolysis of step (d) is carried out under an inert gas atmosphere, in particular under a nitrogen atmosphere, which makes it possible to prevent oxidation of the components.

[0036] To achieve particle sizes of less than 100 nm, it may be necessary to optionally mill the starting material components of step (a) in a ball mill.

[0037] It was found that g-C3N4 / metal composite nanoflakes could also be obtained by another method involving several steps:

[0038] Optionally, a step (a') can be provided having the following characteristics: a mixture of g-C3N4-precursor material and polymer is pyrolyzed at a pyrolysis temperature between 200°C and 700°C, preferably between 400°C and 600°C, to provide g-C3N4; the g-C3N4-precursor material is in particular urea; the polymer is in particular polyacrylonitrile; preferably, the mixture is a powder with particles having an average particle size of less than 100 nm.

[0039] Optionally, the temperature during pyrolysis and step (a') is about 500°. Optionally, the mixture is heated to the pyrolysis temperature of step (a') at a heating rate of about 5° C. / min. Optionally, the pyrolysis of step (a') takes at least 4 hours, in particular about 5 hours.

[0040] Optionally, a step (b') may be provided having the following characteristics: the g-C3N4 obtained in step (a') is mixed with an iron compound, the iron compound being selected from iron oxide, iron sulfide, iron phosphide, iron nitride or mixtures thereof, to obtain a premix. In the context of the present invention, it has been found that the use of iron oxide, iron sulfide, iron phosphide or iron nitride as iron compound gives results similar to those obtained with iron(III) phosphate only if already prepared g-C3N4 is provided. Otherwise, only g-C3N4 clusters are formed around the iron compound, so that the material according to the invention is not obtained.

[0041] Optionally, there may be provided a step (c') having the following characteristics: the premix obtained in step (b') is ground to a particle size of less than 100 nm. Optionally, this can be achieved by ball milling.

[0042] Optionally, a step (d') may be provided having the following characteristics: the ground premix is ​​treated at a temperature between 400°C and 600°C to form g-C3N4 / metal-composite-nanoflakes.

[0043] In particular, the temperature of step (d') is about 550°C, which results in an iron(III) oxide composite material.

[0044] Optionally, the treatment in step (d') can straighten the nanoflakes and repair defects.

[0045] Optionally, step (d') is carried out under an inert gas atmosphere, in particular under a nitrogen atmosphere.

[0046] Both methods provide g-C3N4 / metal-composite-nanoflakes as the final product with comparable properties, therefore, the processes can be considered as alternative processes.

[0047] Where appropriate, the present invention also relates to nanoflakes obtained and / or obtainable by the method according to the invention, the steps of which give the nanoflakes special properties which differ from those of the nanoflakes known in the prior art. In particular, by using the method according to the invention, a composite structure is created which allows a particularly uniform distribution of iron on the surface of the g-C3N4-flakes.

[0048] Optionally, the composite material comprises pores, the pores having an average pore size of less than 100 nm.

[0049] Optionally, g-C3N4 nanoflakes are provided having iron and / or iron compounds supported on the surface thereof, the iron and / or iron compounds being present in particulate form having a particle size of less than 100 nm.

[0050] Optionally, the present invention also relates to a hydrogen storage material comprising or consisting of the g-C3N4 / metal-composite-nanoflakes according to the present invention. Optionally, the present invention relates to the use of the g-C3N4 / metal-composite-nanoflakes according to the present invention as a hydrogen storage material.

[0051] Optionally, the present invention relates to a method for storing hydrogen comprising loading the g-C3N4 / metal-composite-nanoflakes according to the present invention with hydrogen gas, where appropriate the loading is carried out at a pressure of at least 10 bar, preferably at most 25 bar.

[0052] Optionally, desorption of hydrogen can be achieved by heating the loaded composite material, for example to a temperature between 60°C and 100°C.

[0053] The loading is improved by the influence of an electric field. Optionally, the voltage of the electric field is greater than 1000V.

[0054] Optionally, the present invention also relates to a photocatalyst comprising or consisting of the g-C3N4 / metal composite nanoflakes according to the invention. Where appropriate, the present invention relates to the use of the g-C3N4 / metal composite nanoflakes according to the invention as photocatalyst.

[0055] Optionally, the present invention also relates to a photoelectrocatalyst comprising or consisting of the g-C3N4 / metal composite nanoflakes according to the invention. Where appropriate, the present invention relates to the use of the g-C3N4 / metal composite nanoflakes according to the invention as photoelectrocatalyst.

[0056] Optionally, the present invention also relates to an electrocatalyst comprising or consisting of the g-C3N4 / metal composite nanoflakes according to the invention. Where appropriate, the present invention relates to the use of the g-C3N4 / metal composite nanoflakes according to the invention as electrocatalyst.

[0057] The g-C3N4 / metal composite material according to the present invention is a semiconductor whose band gap can be changed by methods such as doping, and therefore has catalytic activity. Therefore, in addition to hydrogen storage, it can also be used as a photocatalyst, electrocatalyst, or photoelectrode catalyst.

[0058] Optionally, the present invention relates to a method for photoelectrocatalysis of water and production of hydrogen, comprising introducing g-C3N4 / metal-composite-nanoflakes according to the present invention into water. Optionally, the g-C3N4 / metal-composite-nanoflakes introduced into water are irradiated with a radiation source, which may be a UV / Vis source. Optionally, the radiation source emits electromagnetic radiation with a wavelength between 200 nm and 1000 nm.

[0059] Further optional features of the invention can be seen from the claims, the figures and the description of embodiments.

[0060] The invention will now be described in detail with reference to exemplary embodiments. [Brief description of the drawings]

[0061] FIG. 1 is the hydrogen storage capacity of the g-C3N4 / metal-composite according to the first embodiment. FIG. 2 is the hydrogen storage capacity of the g-C3N4 / metal-composite according to the second embodiment. FIG. 3 is the hydrogen storage capacity of the g-C3N4 / metal-composite according to the third example embodiment with voltage-assisted loading. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062] Example 1 The first embodiment shows the preparation of a g-C3N4 / iron composite starting material from a mixture of 2% by weight iron(III) phosphate, 95% by weight urea, and 3% by weight polyacrylonitrile. The components are mixed and ball milled at 600 rpm for approximately 45 minutes to form a starting material with an average particle size of less than 100 nm.

[0063] The resulting starting material is dispersed in as little water as possible at a temperature of about 95° C. using a dispersion rod and an ultrasonic bath.

[0064] After dispersion is complete, the water is removed and the remaining material is pyrolyzed in a N2 atmosphere at a pyrolysis temperature of about 550°C for about 5 hours. The heating rate to reach the pyrolysis temperature is about 5°C / min.

[0065] Layered bulk g-C3N4 / metal-composites with iron(III) oxide embedded between the layers were obtained.

[0066] The produced bulk-g-C3N4 / metal-composite was then exfoliated by ultrasonic treatment to form g-C3N4 / metal-composite-nanoflakes.

[0067] This compound can be used as a hydrogen storage material. At up to 25 atm, hydrogen storage capacity is 9.2% by mass at around -20°C and 6.1% by mass at around 25°C. Essentially complete desorption occurs at about 80°C.

[0068] FIG. 1 shows a comparison of hydrogen storage capacity of the g-C3N4 / metal-composite prepared according to the first example embodiment as a function of pressure between about −20° C. (solid circles) and about 25° C. (open circles).

[0069] Example 2 The second example embodiment shows the preparation of a g-C3N4 / iron-titanium composite, where a mixture of 1 wt% iron(III) phosphate, 95 wt% urea and 3 wt% polyacrylonitrile, plus 1 wt% titanium dioxide, is used as the starting material.

[0070] Further steps were carried out similarly to the first embodiment.

[0071] Ti-doped g-C3N4 / Fe composite nanoflakes were obtained that can be used as hydrogen storage materials. Hydrogen storage capacities of 9.6% by mass at around -20°C and 6.3% by mass at around 25°C are obtained for hydrogen storage up to 25 atm. Essentially complete desorption occurs at about 80°C.

[0072] FIG. 2 compares the hydrogen storage capacity of the g-C3N4 / metal-composite prepared according to the second example embodiment as a function of pressure between about −20° C. (solid circles) and about 25° C. (open circles).

[0073] Example 3 The third example embodiment shows the preparation of a g-C3N4 / iron-titanium composite, where a mixture of 3 wt% iron(III) phosphate, 90 wt% urea and 5 wt% polyacrylonitrile was used as the starting material, with 1 wt% titanium dioxide added. The components were mixed and ball milled at 600 rpm for about 45 minutes to form a starting material with an average particle size of 100 nm or less.

[0074] The resulting starting material is dispersed in as little water as possible at a temperature of about 95° C. using a dispersion rod and an ultrasonic bath.

[0075] Once dispersion is complete, the water is removed and the remaining material is pyrolyzed in a N2 atmosphere at a pyrolysis temperature of about 450° C. for about 5 hours. The heating rate to reach the pyrolysis temperature is about 5° C. / min.

[0076] Layered bulk g-C3N4 / metal-composites were obtained with iron(III) phosphate embedded between the layers.

[0077] The produced bulk-g-C3N4 / metal-composite is then exfoliated by ultrasonic treatment to form g-C3N4 / metal-composite-nanoflakes.

[0078] This compound can be used as a hydrogen storage material. A hydrogen storage capacity of 7.4 mass % was obtained at up to 25 bar.

[0079] When an electric field of approximately 1400 V was applied to this composite material, a hydrogen storage capacity of 11.7 mass % was obtained.

[0080] FIG. 3 shows the hydrogen storage capacity of the g-C3N4 / metal-composite fabricated according to the third example embodiment as a function of pressure, comparing the capacity without (closed circles) and with (open circles) voltage-assisted loading.

[0081] Example 4 The g-C3N4 / metal-composite with Ti and Fe prepared according to the third embodiment, as well as other composites according to the present invention, can be used as electrophotocatalysts in the production of hydrogen and oxygen from water.

[0082] When the g-C3N4 / metal-composite dispersion was irradiated in water using a UV / Vis light source, approximately 35.3 mmol / (g * A hydrogen production rate of about 96 mV was measured during hydrogen production. The current density was about 2.67 mA / cm.

Claims

1. g-C, which comprises the steps of: ３ N ４ / Method for producing metal-composite-nanoflakes: a. Iron compounds, g-C ３ N ４ - providing a starting material comprising or consisting of a precursor material and a polymer; i. where the iron compound is FePO ４ and ii. where g-C ３ N ４ - the precursor material is urea, and iii. wherein the polymer is polyacrylonitrile; wherein the starting material is present as a powder having particles with an average particle size of less than 100 nm; b. dispersing the starting material in a solvent, wherein the solvent is water; c. Removing the solvent to form a premix containing the starting materials; d. Heating the premix and pyrolyzing it at a pyrolysis temperature between 200°C and 700°C, preferably between 400°C and 600°C, to obtain bulk-gC. ３ N ４ / forming a metal-composite material, e. Bulk-g-C ３ N ４ / Metal-composite material is treated with ultrasound to form g-C ３ N ４ / Forming metal-composite-nanoflakes.

2. 2. The method according to claim 1, wherein the amount of iron compound in step (a) is 1.0% to 20% by weight based on the total amount of starting materials.

3. 3. The method according to claim 1 or 2, characterized in that the dispersing in step (b) is carried out at a temperature between 80°C and 100°C, preferably between 90°C and 100°C, optionally accompanied by ultrasonic treatment.

4. 3. The method according to claim 1 or 2, characterized in that the heating rate during heating to the pyrolysis temperature in step (d) is 5°C / min or more.

5. 3. The method according to claim 1 or 2, wherein the pyrolysis temperature in step (d) is about 450°C, or the pyrolysis temperature in step (d) is about 550°C.

6. 3. The method according to claim 1 or 2, characterized in that after step (d), the method comprises the further step of: -g-C ３ N ４ / Reducing iron in the metal-composite material.

7. 3. The method according to claim 1 or 2, characterized in that in step (a) a further metal compound is added, the further metal compound being selected from an aluminum compound, a lithium compound, a magnesium compound, a titanium compound, a nickel compound, a platinum compound, a palladium compound, a vanadium compound, or any mixture of these compounds.

8. 8. The method according to claim 7, characterized in that the amount of the further metal compound in step (a) is between 0.5% and 5.0% by weight, preferably about 1.0% by weight, relative to the total amount of starting materials.

9. 3. The method according to claim 1 or 2, characterized in that the pyrolysis in step (d) is carried out under an inert gas atmosphere, in particular under a nitrogen atmosphere.

10. g-C ３ N ４ g-C in the form of nanoflakes, obtainable by the method according to claim 1, characterized in that nanoflakes are provided, on the surface of which iron and / or iron compounds are supported, the iron and / or iron compounds being present in the form of particles with a particle size of less than 100 nm. ３ N ４ / Metal-composite materials.

11. 11. The composite material of claim 10, comprising pores having an average pore size of less than 100 nm.

12. The g-C according to claim 10 or 11 ３ N ４ / Hydrogen storage materials comprising or consisting of metal-composite materials.

13. The g-C according to claim 10 or 11 ３ N ４ / An electrode catalyst for water electrolysis comprising or consisting of a metal-composite material.

14. The g-C according to claim 10 or 11 ３ N ４ / A photocatalyst for water electrolysis comprising or consisting of a metal-composite material.

15. The g-C according to claim 10 or 11 ３ N ４ / A photoelectrode catalyst for water electrolysis comprising or consisting of a metal-composite material.

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