Patent Application
20250223163
The present invention generally relates to carbon nitrides with highly crystalline framework, and in particular to heteroatom functionalised mesoporous and non-porous carbon nitrides with highly crystalline framework which find application for hydrogen generation from seawater. The present invention relates to a process for producing such carbon nitrides with highly crystalline framework.
Global energy consumption has grown at a rapid rate of 2.3% since the year 2000 and is expected to reach 22TW in 2030. The ongoing major source of this energy is fossil fuels which account for more than 80% of global energy consumption. Energy derived from fossil fuels involves the emission of a large amount of CO2 and other toxic air contaminants to the earth's atmosphere, which have been shown to cause global warming as well as adverse effects on human health. The release of CO2 into the atmosphere is predicted to increase over the next several decades through the large-scale consumption of fossil fuels and is also predicted to cause catastrophic environmental damage posing a significant threat to society.
New technologies that can produce clean energy from renewable energy sources seek to address the above environmental challenges and to meet the growing energy demand.
Carbon nitrides (CN) are excellent candidates to complement nanocarbons and have the advantages of unique electronic structure, the intrinsic bandgap of ˜2.7 eV, Lewis basic functionalities, hydrogen bonding motifs, high chemical and thermal stabilities, and excellent chemical resistance. To date, five different carbon nitrides have been identified, which include α-C3N4, β-C3N4, cubic-C3N4, pseudo-cubic C3N4, and g-C3N4. Among these carbon nitride, g-C3N4, whose structure is similar to graphitic nanostructure, can be prepared by molecular or chemical precursors at low temperature or pressure conditions. This carbon nitride has unique semiconducting and Lewis basic properties and offers a wide range of application possibilities in energy storage and conversion. Although this material exhibits unique properties, it suffers from poor specific surface area, pore volume and ordered porous structure.
In recent times, there has been some success in introducing mesoporosity into the carbon nitride, g-C3N4 nanostructure resulting in mesoporous carbon nitride (MCN-1) with an ordered porous structure, high specific surface area and large pore volume. However, the performance of the MCN in semiconducting applications is limited to the MCN framework with a small bandgap.
By varying the nitrogen contents and the chemistry and the structure of the carbon nitride precursors, a series of non-porous and mesoporous carbon nitride with C3N5, C3N6, C3N7 and C3N8 stoichiometries with different chemical structures have been successfully produced. These materials have been found to have a variety of potential uses including for photocatalytic seawater splitting, energy storage and conversion, heterogeneous catalysis and carbon capture and conversion. However, one of the major issues in these materials is their amorphous carbon nitride framework. The poor crystallinity significantly affected the performance of these materials in various applications, including the photocatalytic splitting of seawater.
Photocatalytic water splitting is one of the most efficient techniques for converting water molecules into hydrogen and oxygen fuels by photoexcited electron-hole pairs generated on the surface of semiconducting photocatalysts using sunlight and water. Several photocatalysts including semiconducting metal oxides such as titanium dioxide, metal phosphides, metal oxides, metal nitrides and metal oxynitrides have been used as photocatalysts for the generation of hydrogen through photocatalytic water splitting.
The water-splitting potential of non-porous carbon nitride with amorphous wall structure under visible light was realized as early as 2009. Unfortunately, the activity of these materials was found to be low owing to their amorphous wall structure and the lack of the number of active sites due to low specific surface area.
The preferred embodiments of the present invention seek to provide highly crystalline carbon nitride nanostructures to address one or more of these disadvantages, and/or to at least provide the public with a useful alternative.
The reference in this specification to any prior publication (or information derived from the prior publication), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from the prior publication) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
According to one aspect, there is provided a process for the preparation of a crystalline carbon nitride including the steps of:
In certain embodiments, the carbon nitride precursor is selected from: thiourea, urea, aminoguanidine hydrochloride, diaminotriazine, diaminotriazole, 5,5-Dithiobis(1-Phenyl-1H-Tetrazole), dithiooxamide, and 3-amino-1,2,4-triazole. In one form, the carbon nitride precursor is thiourea.
In certain embodiments, the metal salt is selected from: potassium chloride, sodium chloride, magnesium chloride, lithium chloride or a mixture thereof.
In certain embodiments, the carbon nitride precursor is mixed with the metal salt to form the first mixture in a weight ratio of about 4:0.5 to about 4:10. In one form, the carbon nitride precursor is mixed with the metal salt to form the first mixture in a weight ratio of about 4:2 to about 4:5. In a further form, the carbon nitride precursor is mixed with the metal salt to form the first mixture in a weight ratio of about 4:3.
In certain embodiments, the first mixture is thermally treated during step c. at a temperature ranging from about 450° C. to about 700° C. In one form, the first mixture is thermally treated during step c. at a temperature ranging from about 500° C. to about 600° C. In a further form, the first mixture is thermally treated during step c. at a temperature of about 550° C.
In certain embodiments, the first mixture is thermally treated during step c. for a period of time ranging from 1 hour to about 8 hours. In one form, the first mixture is thermally treated during step c. for a period of time ranging from 3 hours to about 5 hours. In a further form, the first mixture is thermally treated during step c. for about 4 hours.
In certain embodiments, the crystalline carbon nitride produced in step c. is washed with an acidic solution to remove alkaline salts and by-products. In one form, the acidic solution includes hydrochloric acid.
In certain embodiments, mixing the carbon nitride precursor material with a metal salt to form a first mixture is in a dry form in step b.
In certain embodiments, a soft templating technique or a hard templating technique is used to increase the mesoporosity of the crystalline carbon nitride. In one form, the soft templating technique or the hard templating technique is employed during step b.
In certain embodiments, the hard templating technique utilises mesoporous silica nanoparticles. In one form, the mesoporous silica is added to the mixture including the carbon nitride precursor material with the metal salt in a colloidal solution at step b. In one form, the colloidal solution includes water. In a further form, the colloidal solution is evaporated resulting in the first mixture in the form of a dry powder prior to step c.
In certain embodiments, the step of thermally treating the first mixture is conducted in an atmosphere selected from nitrogen, argon, helium or is conducted under vacuum.
According to another aspect, there is provided a highly crystalline mesoporous sulphur functionalized carbon nitride with SBET (m2/g) of between about 40 and about 70 m2/g. In one form, the highly crystalline mesoporous sulphur functionalized carbon nitride with SBET of about 60 m2/g.
According to another aspect, there is provided a crystalline carbon nitride produced from the process as herein described.
According to another aspect, there is provided a use of the carbon nitride as herein described as a photocatalyst for the production of hydrogen. In one form, the production of hydrogen is from saline water including from seawater.
Example embodiments are apparent from the following description, which is given by way of example only, of at least one non-limiting embodiment, described in connection with the accompanying figures, in which:
The following modes, given by way of example only, are described in order to provide a more precise understanding of one or more embodiments.
It was found that by introducing the crystallinity in the semiconducting framework of a functionalized carbon nitride nanostructure with different nitrogen contents, chemical structures and morphologies, a new family of carbon nitride nanostructures with unique semiconducting and electronic properties was identified. In addition, this new family of carbon nitride nanostructures was found to enhanced performance in photocatalytic hydrogen generation and other energy storage and conversion applications.
In accordance with embodiments described herein, the highly crystalline and functionalized carbon nitride framework was produced via a “salt moulding approach” in which metal salts are used. Without wishing to be bound by theory, it is thought the metals salts not only help to enhance the polymerization of carbon nitride precursors by connecting the molecules and assisting cross-linking, but also prevent the decomposition of carbon nitride precursors at high temperatures. In addition, it is also understood the ions of the metal salts may assist to increase the surface area and thereby increase the crystallinity of the final carbon nitride materials.
The highly crystalline carbon nitride materials produced in accordance with embodiments described herein when utilised in photocatalytic hydrogen generation from saline water including seawater include vacant sites that are created by the alkali metal salts and which then capture the alkali metal ions from the saline water. It is thought these ions assist to increase the charge transfer kinetics and also suppress the electron-hole recombination to enhance the photocatalytic activity of saline water splitting.
The highly crystalline carbon nitride materials produced in accordance with embodiments described herein may also include heteroatoms such as sulphur into the carbon nitride framework which is understood to create intra-band-gap states close to the conduction band edges for enhancing the visible light splitting of saline water. The performance may be further increased by creating mesoporosity in these unique crystalline functionalized carbon nitride materials as the mesoporosity provides more active sites.
Splitting of saline water such as sea water with visible sunlight is considered a challenging process owing to the large concentration of alkali salts in the water, which suppress the activity of photocatalysts. By using the highly crystalline CN materials produced in accordance with embodiments described herein, these issues may be overcome as the proposed materials appear to offer vacant sites together with the porosity which may capture these alkali ions and activate the catalysts.
In accordance with certain embodiments, there is provided a process for the preparation of a crystalline carbon nitride including the steps of: providing a carbon nitride precursor material; mixing the carbon nitride precursor material with a metal salt to form a first mixture; and, thermally treating the first mixture to produce the crystalline carbon nitride.
The carbon nitride precursor may be selected from any suitable precursor material which includes significant quantities of carbon and nitrogen. In a preferred form the carbon nitride precursor further includes a significant quantity of a heteroatom such as sulphur. In preferred forms, the carbon nitride precursor may be selected from: thiourea, urea, aminoguanidine hydrochloride, diaminotriazine, diaminotriazole, 5,5-dithiobis(1-phenyl-1H-tetrazole), dithiooxamide, and 3-amino-1,2,4-triazole.
The metal salt may be selected from any suitable metal salt. In a preferred form, the metal salt is selected from: potassium chloride sodium chloride, lithium chloride, magnesium chloride and the mixture of these chlorides. The mixtures of the different metal chlorides may be made with different molar ratios.
In certain embodiments, the first mixture including the carbon nitride precursor material with a metal salt may be thermally treated at a temperature ranging from about 450° C. to about 700° C. In a preferred form, the temperature may range from about 500° C. to about 600° C. In a further preferred form, the temperature is about 550° C.
The thermal treatment may be for a period of time ranging from 1 hour to about 8 hours. In a preferred form, the thermal treatment may be for a period of time ranging from 3 hours to about 5 hours. More preferably, the thermal treatment may be for about 4 hours.
In certain embodiments, the crystalline carbon nitride produced by thermally treating the first mixture of carbon nitride precursor material with a metal salt may be washed with an acidic solution to remove alkaline salts and by-products. The acidic solution may be selected from any suitable acidic solution such as for example a solution of hydrochloric acid.
In certain embodiments, the process as herein described may include a soft templating technique or a hard templating technique to increase the mesoporosity of the crystalline carbon nitride so produced.
As herein described the term “soft templating” refers to a direct synthesis of the porous carbon nitride materials, with block copolymers or surfactants being employed as structure-directing agents leading to the construction of the desired mesoporosity of the crystalline carbon nitrides so produced.
As herein described the term “hard templating” refers to the fabrication of porous materials with a stable porous structure by depositing the targeted materials into the confined spaces of the template, resulting in a reverse replica of the template. The structure replication may utilise porous “hard templates” including mesoporous silica or carbon.
In certain embodiments, the soft templating technique or the hard templating technique is employed during the mixing of the carbon nitride precursor material with the metal salt to form the first mixture. For example a hard templating technique includes mesoporous silica added to the mixture including the carbon nitride precursor material the metal salt in a colloidal solution including water. The colloidal solution may then be evaporated resulting in the first mixture in the form of a dry powder prior to step c.
In another example, colloidal silica nanoparticles of different sizes with different structures and pore diameters may be used as a structure-directing agent in a hard templating technique.
After the formation of the carbon nitrides using a hard and/or soft templating technique, the templates may be removed by 5 wt % of Hydrofluoric acid (HF) or NaOH solution.
In certain embodiments, the soft templating technique may include the use of polystyrene particles with different sizes or other polymeric surfactants with different molecular weights as structure-directing agents. These structure-directing agents are mixed with carbon nitride precursor and the metal salt to form an aqueous homogeneous solution, and the water is slowly evaporated. Then, the mixture may be thermally treated at 550° C. to form the mesoporous new crystalline carbon nitride structure.
In certain embodiments, sulphur containing highly crystalline carbon nitride with a new crystal structure may be synthesized from thiourea (TU) and potassium chloride. Thiourea is a organosulphur compound which is single molecular precursor and offers a large amount of C, N, and S for the direct synthesis of sulphur-containing highly crystalline carbon nitride.
In certain embodiments, urea may be used as a carbon nitride precursor containing C, N and O. By using this precursor, new carbon nitride with novel crystal structure may be synthesized by using salt moulding technique.
The present invention will become better understood from the following examples of preferred but non-limiting embodiments thereof.
The present invention will become better understood from the following examples of preferred but non-limiting embodiments thereof.
Materials: Synthesis of Carbon Nitride with a Novel Crystal Structure SCCN from Thiourea (SCCN-TU)
6.0 g of thiourea (TU) as carbon nitride precursor was mixed and ground with 4.47 g (60 mmol) of potassium chloride (KCl). Different samples were prepared by varying the carbonization time from 1 to 6 h. The mixture of TU and KCl was calcined at 550° C. for different times (1, 2, 3, 4 and 6 h). Then, the obtained yellowish powder was washed with 2 M HCl and deionized hot water together with ethanol to remove the alkaline salt and by-products. The filtered particles were re-dispersed in 300 mL of deionized water at around 60° C. under stirring for 20 min, and then filtered and washed with water and ethanol. The final materials were denoted as SCCN-TU-xh, where x denotes the thermal-polymerization time in hours. For the comparison with SCCN-TU synthesized via alkaline salt moulding method, bulk graphitic carbon nitride was synthesized without any KCl and calcined at 550° C. for 4 h. The prepared sample is denoted as gCN-TU.
Silica nanoparticles with uniform size were used in line with a hard templating technique to make mesoporous carbon nitrides with a new crystal structure. 6.0 g of TU was dissolved in 30 mL of deionized water at 60° C. 5 g of Ludox HS-40 (40% SiO2 nanoparticle with 12 nm size) colloidal solution and 4.47 g (60 mmol) of KCl were added to this solution under stirring at 60° C. till the clear solution is formed. Subsequently, the water was slowly evaporated, resulting in the white powder. The resulting white powder was ground and calcined at 550° C. in a muffle furnace under the nitrogen atmosphere for 3 h. The obtained yellowish product was washed with 2 M HCl and deionized hot water together with ethanol to remove the alkaline salt and by-products. The filtered yellowish power was re-dispersed and stirred in 300 mL of 5 wt % HF (aq) for removing the silica template. The resulting suspension was then filtered and washed with water and ethanol. The filtered powders were dried at 100° C. for 12 h. The final materials are denoted as MSCCN-TU.
CCN from Urea (CCN-U)
8.0 g of urea as carbon nitride precursor is mixed and grounded with and 4.47 g (60 mmol) of KCl. The mixture of urea and KCl is calcined at 550° C. for 1 h. The obtained yellowish powder is washed with 2 M HCl and deionized hot water together with ethanol to remove the alkaline salt and by-products. The filtered particles were re-dispersed in 300 mL of deionized water at around 60° C. under stirring for 20 min, and then filtered and washed with water and ethanol. In order to completely remove the alkaline salt, the washing process was carried out one more time. The final materials are denoted as CCN-U-1h. The effect of the thermal-polymerization time was not studied as the samples decomposed when the thermal-polymerization time was more than 1 h. For the comparison with CCN-U synthesized via alkaline salt molding method, bulk graphitic carbon nitride was synthesized prepared by calcining 8 g of urea at 550° C. for 4 h without any KCl and the prepared sample is denoted as gCN-U.
CCN from 3-Amino-1,2,4-Triazole (CCN-AT)
3.0 g of 3-amino-1,2,4-triazole (AT) as carbon nitride precursor was mixed and ground with 5.96 g (80 mmol) of potassium chloride (KCl). The mixture was calcined at 550° C. for 3 h, 4 h and 6 h. The obtained yellowish powder is washed with 2 M HCl and deionized hot water together with ethanol to remove the alkaline salt and by-products. The filtered particles were re-dispersed in 300 mL of deionized water at around 60° C. under stirring for 20 min, and then filtered and washed with water and ethanol. In order to completely remove the alkaline salt, this washing process was carried out one more time. The final materials are denoted as CCN-AT-xh where x denotes the thermal-polymerization time in hour. For the comparison with CCN-AT synthesized via alkaline salt moulding method, bulk graphitic carbon nitride was synthesized prepared by calcining 3 g of 3-aminotriazole at 550° C. for 4 h, which is denoted as gCN-AT.
Mesoporous carbon nitride with a new crystal structure was synthesized via a hard template method. 3.0 g of 3-aminotriazole as carbon nitride precursor was dissolved in 35 mL of deionized water at 60° C. 3.75 g or 7.00 g of Ludox HS-40 (40% SiO2 nanoparticle with 12 nm size) colloidal solution and 5.96 g (80 mmol) of KCl are added to this solution under stirring at 60° C., to a clear solution. Then the water was slowly evaporated under stirring, resulting in the white powder. The resulting white powder was ground and calcined at 550° C. in a muffle furnace under the nitrogen atmosphere for 4 h. The obtained yellowish product is washed with 2 M HCl and deionized hot water together with ethanol to remove the alkaline salt and by-products. The filtered yellowish power is re-dispersed and stirred in 150 mL of 5 wt % HF (aq) for removing the silica template. The resulting suspension is then filtered and washed with water and ethanol. The filtered powders are dried at 100° C. for 12 h. The final materials are denoted as MCCN-AT-1 for 3.75 g of Ludox and MCCN-AT-2 for 7.00 g of Ludox.
CCN from Aminoguanidine Hydrochloride (CCN-AG)
Aminoguanidine hydrochloride (AG) is a non-aromatic and non-cyclic CN precursor with a low amount of C and a high nitrogen content and was used to make a carbon nitride with a crystal structure. 9.0 g of aminoguanidine hydrochloride (AG) was mixed and ground with and 4.47 g (60 mmol) of potassium chloride (KCl). The mixture of urea and KCl is calcined at 550° C. for 4 h. The obtained yellowish powder was washed with 2 M HCl and deionized hot water together with ethanol to remove the alkaline salt and by-products. The filtered particles were re-dispersed in 300 mL of deionized water at around 60° C. under stirring for 20 min, and then filtered and washed with water and ethanol. In order to completely remove the alkaline salt, the washing process was carried out one more time. The final materials are denoted as CCN-AG-4h. For the comparison with CCN-AG synthesized via alkaline salt molding method, bulk graphitic carbon nitride was synthesized by calcining 9 g of aminoguanidine hydrochloride at 550° C. for 4 h, which is denoted as gCN-AG.
Mesoporous carbon nitride with a new crystal structure may be also synthesized via a hard template method. 9.0 g of AG as carbon nitride precursor was dissolved in 35 mL of deionized water at 60° C. 5 g of Ludox HS-40 (40% SiO2 nanoparticle with 12 nm size) colloidal solution and 4.47 g (60 mmol) of KCl were added to this solution under stirring at 60° C. till a clear solution was formed. The water was then slowly evaporated, resulting in the white powder. The resulting white powder is ground and calcined at 550° C. in a muffle furnace under the nitrogen atmosphere for 4 h. The obtained yellowish product is washed with 2 M HCl and deionized hot water together with ethanol to remove the alkaline salt and by-products. The filtered yellowish power is re-dispersed and stirred in 200 mL of 5 wt % HF (aq) for removing the silica template. The resulting suspension was then filtered and washed with water and ethanol. The filtered powders were dried at 100° C. for 12 h. The final materials are denoted as MCCN-AG.
The crystal structure of the various synthesized carbon nitrides was characterized by using Powder X-ray diffraction (PXRD). PXRD patterns of all the samples were recorded with Panalytical Empyrean X-ray diffractometer equipped with Cu-Kα radiation (λ=1.5418 Å) and with Galipix Detector at 40 kV and 40 mA. A continuous scan mode was employed in a wide angle range (2θ=5-60°). The optical property of the carbon nitride was evaluated from the UV-Vis diffuse reflectance spectroscopic method. Fourier transform infrared (FT-IR) spectra were obtained with a Perkin Elmer Frontier FTIR/NIR spectrometer by the KBr disk method. The spectra were recorded with Perkin Elmer Lambda 1050+. Quantification of C and N of the samples was carried out with a Perkin Elmer EA 2400 Elemental Analyzer. The porous textures such as specific surface area and total pore volume were investigated by N2 adsorption-desorption isotherm analysis at liquid nitrogen temperature by using ASAP 2040. The samples were degassed under vacuum (10−5 torr) at 200° C. for 24 h before the measurement.
The photocatalytic reactions were carried out in a top-irradiation Pyrex reactor connected to a closed gas circulation and evacuation system. 0.1 g of the sample was dispersed in 100 mL of 10 Vol % triethanolamine aqueous solution as a hole scavenger under stirring in a reactor. The Pt cocatalyst (Pt/catalyst=3 wt %) was in-situ photo deposited on the functionalized carbonitride photocatalyst in the suspension during the photocatalytic reaction. In order to completely remove the air in the suspension, the reaction vessel was evacuated several times, and Ar gas was introduced to the reactor up to ˜50 torr. The suspension was irradiated with the solar simulated light with 1 sun power using a Newport Class ABB solar simulator equipped with 450 W Xe lamp and 1.5 G air mass filter through a water filter to cut the infrared light. The reaction temperature was maintained at 25° C. by keeping the reactor in the water jacket controlled by a circulating chiller system. The evolved gas was periodically analysed through the in-situ auto-injection system of a gas chromatograph (PerkinElmer Clarus 580 GC) equipped with TCD detector and stainless-steel column packed with Molecular Sieve 5 A, where Ar gas was used as a carrier gas.
SCCN from Thiourea (SCCN-TU)
Sulphur functionalized crystalline carbon nitride with a new crystal structure can be successfully synthesized from thiourea and KCl via controlling the reaction time at 550° C.
As can be seen in the
The optical property of SCN-TU was analysed by the UV-Vis spectrophotometer and the spectra are shown in
Functional groups of SCCN with a new crystal structure were analyzed by Fourier transform infrared spectroscopy (FT-IR) and the data are shown in
In addition, the local structure of the SCCN-TU samples was also analysed by using near edge absorption fine structure spectroscopy (NEXAFS). C K-edge, N K-edge and S L-edge NEXAFS spectra for SCCN-TU samples together with the reference samples such gCN and gCN-TU are plotted in
The textural properties such as the specific surface area and the total pore volumes of the synthesized samples are analysed from the N2 adsorption-desorption isotherm analysis. The values are summarized in Table 1. The BET (Brunauer-Emmett-Teller) specific surface area and pore volume of SCCN-TU-4h are 11 m2/g and 0.03 mL/g, which is almost the same as those of gCN-TU (11 m2/g and 0.07 mL/g). The specific surface area (22 m2/g) and the specific pore volume (0.09 mL/g) are slightly increased when the reaction time is increased from 4 h to 6 h.
The photocatalytic activity of carbon nitride for H2 evolution is strongly dependent on its crystal structure and reaction time. The photocatalytic H2 evaluation of the synthesized catalyst loaded with 3 wt % Pt as a cocatalyst is carried out in 100 mL of 10 Vol % triethanolamine aqueous solution under the solar simulated light with 1 sun power. The result is plotted in
Sulfur functionalized mesoporous carbon nitrides with a new crystal structure can be synthesized from thiourea with KCl via a hard template method by using silica nanoparticles. The XRD patterns are plotted in
UV-Vis spectroscopic analysis was carried out to analyse the optical property of MSCCN-TU with a new crystal structure synthesized from thiourea and KCl via the hard template method, and the spectra are plotted in
The specific surface area, the specific pore volume and the photocatalytic hydrogen evolution activity are given in Table 2. The BET (Brunauer-Emmett-Teller) specific surface area and pore volume of MSCCN-TU are 61 m2/g and 0.09 mL/g, which is larger than those of SCCN-TU-4h (11 m2/g and 0.03 mL/g) and gCN-TU (13 m2/g and 0.07 mL/g). As can be seen in the adsorption isotherm, the amount of nitrogen adsorbed at the lower and higher relative pressure for MSCCN-TU is much higher than that of the SCCN-TU-4h and gCN-TU, revealing a significant enhancement in the specific surface area and the specific pore volume. The specific surface area of MSCCN-TU is 5.5 times larger than that of SCCN-TU-4h, indicating that the porous texture is successfully formed via a hard template method. This is also clearly reflected by the fact the nitrogen adsorption isotherm of the MSCCN-TU is well-defined type IV with a sharp capillary condensation step. This also confirms the presence of mesoporosity in the MSCCN-TU sample. This is the first report on the highly crystalline mesoporous sulphur functionalized carbon nitride. It should be noted that the size of the mesopores can be tuned by adjusting the size of the silica nanoparticles used as the templates. In this case, the size of the pores is almost similar to the size of the silica nanoparticles used. Similarly, various other mesostructured CCN-TU can be prepared by varying the nature of the silica templates. For example, mesoporous silica templates such as SBA-15, KIT-6, SBA-1, SBA-16, KIT-5, and MCM-48 can be used to make MCCN-TU with different mesoporous structures and pore diameters.
The photocatalytic activity of carbon nitride for H2 evolution strongly depends on their porous texture and crystal structure. The photocatalytic H2 evaluation of the synthesized catalyst loaded with 3 wt % Pt as a cocatalyst is carried out in 100 mL of 10 Vol % triethanolamine aqueous solution under the solar simulated light with 0.1 W/cm2. As displayed in
SCCN from Urea (SCCN-U)
Urea can form the carbon nitride with a new crystal structure by the calcination with KCl at 550° C. for 1 h. According to the X-ray diffraction analysis (
The optical property of SCCN-U-1h with a new crystal structure is analysed by the UV-Vis spectrophotometer and its UV-Vis spectrum is plotted with that of gCN-U, and the results are shown in
The porous textures such as the specific surface area and the total pore volumes of CCN-Us together with gCN-U are summarized in Table 3. The BET specific surface area and pore volume of CCNU-1h are 31 m2/g and 0.14 mL/g, which are smaller than those of gCN-U (64 m2/g and 0.26 mL/g) but higher than that of SCCN-TU samples (Table 2).
The photocatalytic H2 evaluation of the synthesized CCN-Us and gCN-U loaded with 3 wt % Pt as a cocatalyst is carried out in 100 mL of 10 Vol % triethanolamine aqueous solution under the solar simulated light with 0.1 W/cm2. The time course of photocatalytically evolved H2 for the samples is displayed in
CCN from 3-Amino-1,2,4-Triazole (CCN-AT)
3-amino-1,2,4-triazole (AT) with heterocyclic ring and a high N content was also used as the carbon nitride precursor. This precursor was mixed with the KCl and thermally polymerized at 550° C. for 4 h. The X-ray diffraction patterns for the samples are displayed in
The optical property of MCCN-ATs together with CCN-AT-4h and gCN-AT were analysed by the UV-Vis spectrophotometer and their spectra are plotted in
The specific surface area and the total pore volumes of MCCN-ATs synthesized from 3-amino-1,2,4-triazole and KCl via a hard template method and CCN-AT-4h and gCN-AT are analysed from the N2 adsorption isotherm analysis and the evaluated values are summarized in Table 4. N2 adsorption isotherms and BJH pore-size distribution curves are displayed in
The photocatalytic activity of carbon nitride for H2 evolution is strongly dependent on their crystal structure, crystallinity and surface area. The photocatalytic H2 evaluation of the synthesized catalyst loaded with 3 wt % Pt as a cocatalyst is carried out in 100 mL of 10 Vol % triethanolamine aqueous solution under the solar simulated light with 0.1 W/cm2. The time-course curves of photocatalytic H2 evolution are displayed in
CCN from Aminoguanidine Hydrochloride (CCN-AG)
Non-cyclic and non-aromatic precursor with a high nitrogen content, such as aminoguanidine hydrochloride (AG) was also used for the preparation of novel crystalline carbon nitride through the salt moulding technique. Novel carbon nitride with a new crystal structure by the thermal polymerization with KCl and with and without SiO2 nanoparticles as a hard template was prepared. Their crystal structures were analyzed by the X-ray diffraction analysis and the XRD patterns are plotted in
The optical property of CCN-AG-4h and MCCN-AG with a new crystal structure synthesized from AG and KCl with and without SiO2 nanoparticles was analysed by the UV-Vis spectrophotometer. Their UV-Vis spectra are plotted in
The porous textures such as the specific surface area and the total pore volumes of the carbon nitride samples synthesized from AG and KCl with and without silica nanoparticles are analysed from the N2 adsorption-desorption isotherm analysis. The values are summarized in Table 5, and their N2 adsorption isotherms and BJH pore-size distribution curves are plotted in
The time-course curves of photocatalytic H2 evolution for the samples are displayed in
Among the samples prepared, MCCN-TU and SCCN-TU were found to be the best photocatalysts that are active in the visible region. The photocatalytic H2 evolution reaction was tested in different salt water conditions such as 0.5M NaCl(aq), 0.25M K2HPO4(aq) and 0.5M KI(aq) over SCCN-TU. The photocatalytic reactions are carried out in a top-irradiation Pyrex reactor connected to a closed gas circulation and evacuation system. 0.1 g of SCCN-TU-4h sample was dispersed in 100 mL of 10 Vol % triethanolamine aqueous salt solution as a hole scavenger under stirring in a reactor. Pt cocatalyst (Pt/catalyst=3 wt %) is in-situ photodeposited on the carbonitride photocatalyst in the suspension during the photocatalytic reaction. In order to completely remove the air in the suspension, the reaction vessel was evacuated several times, and Ar gas was introduced to the reactor up to ˜50 torr. Then, solar simulated light with 1 sun power is irradiated on the suspension by using a Newport Class ABB solar simulator equipped with 450 W Xe lamp and 1.5 G air mass filter through a water filter to cut the infrared light with 0.1 W/cm2. The reaction temperature is maintained at 25° C. by keeping the reactor in the water jacket controlled by a circulating chiller system. The evolved gas is periodically analyzed through the in-situ auto-injection system of gas chromatograph (PerkinElmer Clarus 580 GC) equipped with TCD detector and stainless steel column packed with Molecular Sieve 5 A, where Ar gas is used as a carrier gas.
The time-course curves of photocatalytic H2 evolution for SCCN-TU-4h in the different salt waters together with pure water are displayed in
Comparison of Photocatalytic H2 Evolution Activity of SCCN-TU-4h and Commercial TiO2 Photocatalyst (P25).
The high activity of photocatalytic H2 production of SCCN-TU-4h can be revealed by comparing the activity with commercial TiO2 photocatalyst (P25, Degussa) and gCN-Bulk in the pure water and 0.5M NaCl(aq) as simulated sea water condition under visible light. The photocatalytic H2 evolution curves are displayed in
In order to optimize the loading amount of Pt used as cocatalyst, 2˜5 wt % Pt were in-situ photodeposited on SCCN-TU-4h in 10 vol % TEA in 0.5M NaCl(aq) under the solar simulated light. As can be shown in
In order to optimize the concentration of triethanolamine (TEA) concentration in 0.5M NaCl(aq) for photocatalytic H2 production of SCCN-TU-4h, the photocatalytic reaction was carried out in 0˜25 vol % TEA in 0.5M NaCl(aq). As shown in
To understand the potential of the prepared catalysts for real world application, we investigated the photocatalytic H2 production of SCCN-TU-4h in the seawater collected in a different area near Newcastle. The seawater is collected at Caves Beach, Swansea Entrance, Redhead Beach, Merewether Beach, Nobys Beach, Anna Bay Birubi Beach, Nelson Bay Little Beach Reserve and Salamander Bay Soldiers Point. The seawater was used after the filtering process with a nylon membrane filter with 0.4 μm pore size for removing particles and some algae in the water. The results are displayed in
The photocatalytic H2 production activity of SCCN-TU-4h can be enhanced by modifying the porous texture as shown in Table 2 in 10 vol % TEA (aq) with 3 wt % Pt as a cocatalyst. This phenomenon is also observed in the salt water condition. As shown in
AQY (%)=(Number of evolved H2 molecules×2)/(Number of incident photons)×100
The number of incident photons irradiated to the reactor (55.4 cm2) were evaluated to be 1.56×1021 at 400-420 nm by using a Si photodiode power meter and 2 long-pass filters (λ>400 nm and λ>420 nm). The H2 evolution rate of MSCCN-TU calculated with 3 wt % Pt under the irradiation of 400 nm<λ<420 nm (average 410 nm) is 2800 μmol·g−1h−1 in 0.5M NaCl(aq). The QY of MSCCN-TU is calculated to be 22.6% under 400 nm<λ<420 nm. AQY of other carbon nitride materials are summarized in Table 7. MSCCN-TU shows very high AQY which could be related with its large surface area and high crystallinity together with enhanced light absorption property compared with other carbon nitride materials even though the reaction conditions are different.
10Bulk gCN
13Mesoporous
14S-doped
15CNNS
In the foregoing description of preferred embodiments, specific terminology has been resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar technical purpose.
Optional embodiments may also be said to broadly include the parts, elements, steps and/or features referred to or indicated herein, individually or in any combination of two or more of the parts, elements, steps and/or features, and wherein specific integers are mentioned which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.
Although a preferred embodiment has been described in detail, it should be understood that modifications, changes, substitutions or alterations will be apparent to those skilled in the art without departing from the scope of the present invention.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprised”, “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.
As used herein, a, an, the, at least one, and one or more are used interchangeably, and refer to one or to more than one (i.e. at least one) of the grammatical object. By way of example, “an element” means one element, at least one element, or one or more elements.
In the context of this specification, the term “about” is understood to refer to a range of numbers that a person of skill in the art would consider equivalent to the recited value in the context of achieving the same function or result.
This application is a continuation of, and claims priority to and the benefit of, PCT International Application No. PCT/AU2022/050842, filed Aug. 4, 2022 and entitled “CARBON NITRIDES WITH HIGHLY CRYSTALLINE FRAMEWORK AND PROCESS FOR PRODUCING SAME,” which is hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/AU2022/050842 | Aug 2022 | WO |
| Child | 19044426 | US |
