Patent ID: 12234150

The foregoing and other objects, features and advantages of the present invention, as well as the invention itself, will be more fully understood from the following description of preferred embodiments, when read together with the accompanying drawings.

DETAILED DESCRIPTION

The present disclosure relates to the field of photothermal synthesis gas production, and more particularly to photothermal synthesis gas production using MOF derived nanocomposite oxide catalyst being grown on titanium dioxide (TiO2).

The principles of the present invention and their advantages are best understood by referring toFIG.1atoFIG.7b. In the following detailed description of illustrative or exemplary embodiments of the disclosure, specific embodiments in which the disclosure may be practiced are described in sufficient detail to enable those skilled in the art to practice the disclosed embodiments. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims and equivalents thereof. References within the specification to “one embodiment,” “an embodiment,” “embodiments,” or “one or more embodiments” are intended to indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure.

FIG.1ashows a method of synthesizing MOF derived cobalt oxide according to an embodiment of the present disclosure.

A co-precipitation technique is used to create the cobalt-based ZIF-67 MOF. First, 75 mL of methanol112is used to dissolve 5.46 g of Cobalt (II) nitrate hexahydrate (Co(NO3)2·6H2O)103, which is then stirred magnetically for 30 minutes.

Next, another 75 mL of methanol112is used to dissolve 6.16 g of 2-methylimidazole101. After adding the 2-methylimidazole combination to the cobalt mixture dropwise105, the mixture was vigorously stirred with a magnetic stirrer for a further six hours at room temperature. ZIF-67 MOF crystals109were obtained by drying107the purple suspension in an oven at 80° C. for an entire night following three rounds of methanol washing.

The ZIF-67 MOF109then undergoes thermal treatment111to become Co3O4114. To produce the final product of Co3O4114powders, ZIF-67 crystals are first placed in a crucible and then calcined for 4 hours at 350° C. in a muffle furnace.

FIG.1bshows a method of synthesizing MOF derived nanocomposite cobalt oxide catalyst according to an embodiment of the present disclosure.

Graphitic carbon nitride104is produced using a melamine100precursor. The melamine100precursor is thermally decomposed102at 500° C. for 2 hours to arrive at graphitic carbon nitride104.

In embodiments, the graphitic carbon nitride is two dimensional graphitic carbon nitride nanosheets (2D g-C3N4).

For the synthesis of exfoliated graphitic carbon nitride (ECN)110, a mixture of melamine and urea106is used. Melamine and urea106in equal amounts are mixed and placed in a ceramic crucible before being heated108to 550° C. for the duration of 2 hours.

The gas produced by the decomposition of urea is used to exfoliate graphitic carbon nitride layers and produce defective graphitic carbon nitride with oxygen vacancies. The product obtained is grinded to a fine powder and is given the name exfoliated graphitic carbon nitride (ECN)110.

It has been found that synthesizing exfoliated 2D nanosheets of graphitic carbon nitrides with the use of the method using melamine/urea with controlled thermal decomposition conditions results in a larger surface area and higher charge separation efficiency.

The Co3O4/g-C3N4composites122were synthesized using a self-assembly approach. For this purpose, Co3O4114and g-C3N4104were used as discussed previously. First, g-C3N4104of specific quantity (0.2 to 1 g) was dispersed in methanol112(5 to 20 mL) and stirred148for a specific time (1 to 4 hours) to get good dispersion in suspension116. In the next step, specific amount of Co3O4114(1 to 10 wt. %) is dispersed in methanol and is added 118 to the above suspension116under stirring and the solution was stirred for another 4 hours in addition to ultrasonic to get well-dispersed Co3O4-loaded g-C3N4. The solution was finally dried120in an oven at 100° C. overnight to get a Co3O3/g-C3N4composite122.

In embodiments, the Co3O3/g-C3N4composite is a binary composite.

FIG.1cshows a method of synthesizing MOF derived nanocomposite cobalt oxide catalyst according to an embodiment of the present disclosure.

The Co3O4/TiO2composites123are synthesized using a self-assembly approach. For this purpose, titanium dioxide (TiO2)115is used, which is synthesized using the sol-gel method. The sol-gel method results in TiO2quantum dots. First, TiO2115of specific quantity (0.2 to 1 g) is dispersed in methanol112(5 to 20 mL) and stirred117for a specific time (1 to 4 hours) to get good dispersion.

In the next step, a specific amount of Co3O4114(1 to 10 wt. %) dispersed in methanol is added to the above suspension under stirring119and the solution is then stirred for another 4 hours in addition to ultrasonic application to get well-dispersed Co3O4-loaded TiO2. The solution is finally dried121in an oven at 100° C. overnight to get a Co3O4/TiO2composite123.

In embodiments, the Co3O4/TiO2composite is a binary composite.

In embodiments, Co3O4/0D TiO2 binary composite is synthesized using an in-situ growing method of ZIF-derived 3D Co3O4 over titania (TiO2) quantum dots. This method is termed a solvothermal synthesis method and is designed to achieve easy morphological regulation of MOF derivatives in the final binary composites.

In embodiments, the method of synthesizing MOF derived nanocomposite cobalt oxide catalyst is a method of synthesizing MOF derived nanocomposite cobalt oxide catalyst, wherein the composite is a ternary composite. In embodiments, the ternary composite comprises titanium dioxide, cobalt oxide, and graphitic carbon nitride.

In embodiments, The ternary oxides/nitrides composites of three dimensional cobalt oxide coupled with two dimensional exfoliated graphitic carbon nitride and titanium dioxide nano dots (3DCo3O4/2D E-gC3N4/0D TiO2) with hierarchical nanotexture were synthesized using an ultrasonic approach with good interface interaction, Schottky formation, maximum band structure position and good stability under photothermal conditions at low-temperature range.

The ultrasonic approach may comprise a combination of the steps ofFIG.1bandFIG.1c. The ultrasonic approach for synthesizing the ternary composite may comprise dispersing TiO2of specific quantity (0.2 to 1 g) in methanol (5 to 20 mL) and stirring for a specific time (1 to 4 hours) to get good dispersion. The method may also comprise dispersing g-C3N4of specific quantity (0.2 to 1 g) in methanol (5 to 20 mL) and stirring for a specific time (1 to 4 hours) to get good dispersion in suspension. The method may also comprise mixing the g-C3N4dispersion with the TiO2dispersion. The method may comprise mixing Co3O4with methanol and adding it to the g-C3N4— TiO2mixture. In embodiments, the Co3O4mixed with methanol is added to either the g-C3N4dispersion or the TiO2dispersion first, and then mixed. The method may then comprise drying the final mixture to arrive at the ternary composite.

It has been found that the ternary composite exhibits a higher oxidation potential.

FIG.2shows a photoreactor according to an embodiment of the present disclosure.

A continuous flow stainless steel fixed bed photothermal reactor300is used to carry out the photocatalytic, thermochemical and photothermal driven CO2reforming of methane (CH4) reaction. The reactor comprises a main reactor chamber307, a glass window305to pass the light and a heating jacket309to control the reactor temperature. The catalyst350is placed inside the reactor's bottom surface with a loading amount of 150 mg and it can be varied from 50 to 250 mg. The feed mixture311comprises CO2and CH4with a feed ratio of 1:1. The gas311is flowed through the reactor at a flow rate of 15 mL/min and is kept constant in at steady state.

In embodiments, depending on the size of the photoreactor, the flowrates and quantities of catalyst may be different as required by the scale.

In embodiments, the temperature of the reactor is greater than 25° C. In embodiments, the temperature of the reactor is greater than 100° C. In embodiments, the temperature of the reactor is greater than 150° C.

Transmitted light303passes into the photoreactor to initiate the reaction process.

Typically, some light301is reflected off the reactor surface. The intensity of the sunlight is typically in the region of 100 mW/cm2.

EXPERIMENTS

The photothermal reactor ofFIG.2was used to conduct experiments on the efficacy of the catalysts.

The following experiments were conducted:CO2reforming with CH4over Co3O4/g-C3N4(Co3O4loading: 1 to 5 wt. %) at 100° C. and with light;CO2reforming with CH4over 3% Co3O4/g-C3N4at different temperatures from 25 to 200° C. and with light;CO2reforming with CH4over 3% Co3O4/g-C3N4at different temperatures from 100 to 200° C. and without light;CO2reforming with CH4over Co3O4/TiO2(Co3O4loading: 1 to 5 wt. %) at 100° C. and with light;CO2reforming with CH4over 3% Co3O4/TiO2at different temperatures from 25 to 200° C. and with light; andCO2reforming with CH4over 3% Co3O4/TiO2at different temperatures from 100 to 200° C. and without light.

FIG.3shows x-ray diffraction (XRD) analysis of g-C3N4, ZIF-67, MOF-derived Co3O4and their Co3O4-based composites.

The peaks observed at 2-theta (2θ) of 12.85° were related (100) crystal planes of g-C3N4, whereas, a strong peak at 20 of 27.47° reflects the (002) crystal plane of g-C3N4having a typical aromatic ring with interlayers. The anatase phase of TiO2is represented by the diffraction peaks in the XRD patterns of pure TiO2that belong to the lattice plans of (101), (004), (200), (220), and (215). On the other hand, a different lattice design at (110) verifies the existence of a smaller-sized rutile phase of TiO2. The as-prepared ZIF-67 showed peaks at 10.36°, 12.71°, 14.68°, 16.41°, 17.96°, 22.06°, 24.47°, 26.56° and 29.61° corresponding to (002), (112), (022), (013), (222), (114), (233), (134) and (044), respectively, with the highest peak at 7.33° showing the (011) plane. Co3O4is successfully generated by thermally heating ZIF-67 at 350° C. for 4 hours, as evidenced by the characteristic peaks at 20=19.09°, 31.3°, 36.9°, 45.0°, 59.47°, and 65.31°. For the composite Co3O4/TiO2and Co3O4/g-C3N4, all the peaks related to Co3O4, g-C3N4and TiO2were present, which confirms the successful synthesis of these composites.

Field emission scanning electron microscopy (FESEM) was conducted to understand the dimensionality, morphology, and structure of the prepared samples. ZIF-67 exhibited uniform three-dimensional (3D) dodecahedral particles with smooth surfaces. The morphology of Co3O4was similar to ZIF-67 with a 3D dodecahedron structure. However, Co3O4surfaces were relatively rough without obvious edges when it was compared to ZIF-67. Uniform size and shape of TiO2particles was also observed. The morphology of g-C3N4had a 2D layered structure. When Co3O4was added to g-C3N4, there was no change in morphology, however, Co3O4was uniformly spread over the g-C3N surface to provide a heterojunction among the two materials. This shows that self-assembly is a promising approach to produce 3D/2D heterojunction composites.

It was also seen that Co3O4with large sizes and clear edges are distributed within the TiO2particles. With high magnification a 3D Co3O4dodecahedron structure can be observed. All these results further support the successful synthesis of single materials and binary composites with controlled structure and morphology.

FIG.4ashows the yield of H2of pure g-C3N4and various Co3O4(1 to 5 wt. %) loaded g-C3N4samples at different reaction times.

It can be seen that the production of H2is fairly consistent across the entire reaction time, evidenced by the steady increase in the total yield over time.

The production of H2was very small with pure g-C3N4411and there was no significant impact on the yield of H2with 1% Co3O4413loading. However, when Co3O4loading was increased to 3 wt. % 415 and 5 wt. %417, a significant amount of H2was produced.

FIG.4bshows the yield of carbon monoxide (CO) of pure g-C3N4and various Co3O4(1 to 5 wt. %) loaded g-C3N4samples at different reaction times.

The production of CO was very small with pure g-C3N4411, however, CO yield was significantly increased with 1% Co3O4413loading. The highest yield of CO was obtained with 3 wt. % Co3O4415loading into g-C3N4. However, when Co3O4loading was increased to 5 wt. %417, the production of CO was decreased.

The trends for CO and H2production over Co3O4/g-C3N4composites were different during CO2reforming of CH4reactions. The production of H2was increased with Co3O4loading, which shows it is beneficial to maximize hydrogen production. On the other hand, production of CO was decreased with higher Co3O4loading, which was possibly due to the photocatalytic effect. The increasing Co3O4may increase the charge recombination centres and also more active sites to active sides reactions. Overall, Co3O4/g-C3N4composite was more selective to produce CO during dry reforming of methane reaction.

FIG.5ashows the yield of H2of pure TiO2and various Co3O4(1 to 5 wt. %) loaded TiO2samples at different reaction times.

Again, it is clear that the production rate of H2is fairly continuous over the entire reaction time.

The production of H2was lower with pure TiO2511and there was no significant impact on the yield of H2with 1% Co3O4513loading. However, when Co3O4loading was increased to 3 wt. % 515 and 5 wt. %517, a significant amount of H2was produced.

In embodiments, the Co3O4loading is between 3 wt. % and 5 wt. %.

FIG.5bshows the yield of CO of pure TiO2and various Co3O4(1 to 5 wt. %) loaded TiO2samples at different reaction times.

The production of CO was very small with pure TiO2511; however, CO yield was significantly increased with 1% Co3O4513loading. The highest yield of CO was obtained with 3 wt. % Co3O4515loading into g-C3N4. However, when Co3O4loading was increased to 5 wt. %517, the production of CO was decreased.

The trends for CO and H2production over Co3O4/TiO2composites were different during CO2reforming of CH4reactions. The production of H2was increased with Co3O4loading, which shows it is beneficial to maximize hydrogen production. On the other hand, production of CO was decreased with higher Co3O4loading, which was possibly due to the photocatalytic effect. The increasing Co3O4may increase the charge recombination centres and also more active sites to active site reactions. Overall, the Co3O4/TiO2composite was more selective in producing CO during dry reforming of the methane reaction.

FIG.6ashows the production of H2at different reaction temperatures with light and without light using 3% Co3O4/g-C3N4composite catalyst. It was observed that the production of hydrogen was increased with the increase of temperature, and its yield was higher when both the light and the temperature were used through the photothermal process. This was evidently due to the higher stability of methane and its need for higher activation energy, which can be minimized using a hybrid system.

There are seven bars represented in the chart for each time period, with the bars representing, from left to right: 25° C.+light; 100° C.+light; 150° C.+light; 200° C.+light; 100° C. (no light); 150° C. (no light); and 200° C. (no light) respectively.

FIG.6bshows the production of CO over 3% Co3O4/g-C3N4composite at different temperatures and photothermal conditions. The sequence of conditions represented by the bars are in the same order and arrangement as that ofFIG.6a.

Interestingly, it is observed that without light and using only thermal conditions, the yield of CO was very small, however, when both the light and the temperature were employed, the yield of CO was significantly increased. These results confirm that photothermal with the use of light and heat over Co3O4/g-C3N4is a promising approach to convert CO2and CH4through dry reforming process to produce CO and H2.

FIG.7ashows the production of H2at different reaction temperatures with light and without light using 3% Co3O4/TiO2. The sequence of conditions represented by the bars are in the same order and arrangement as that ofFIG.6a.

It was observed that the production of hydrogen was increased with the increase of temperature, and its yield was higher when both the light and the temperature were used through the photothermal process. This was due to the higher stability of methane and it need higher activation energy, which can be minimized using a hybrid system.

FIG.7bshows the production of CO over 3% Co3O4/TiO2composite at different temperatures and photothermal conditions. The sequence of conditions represented by the bars are in the same order and arrangement as that ofFIG.6a.

Interestingly, it can be observed that without light and using only thermal conditions, the yield of CO was very small, however, when both the light and the temperature were employed, the yield of CO was significantly increased. These results confirm that photothermal with the use of light and heat over Co3O4/TiO2is a promising approach to convert CO2and CH4through a dry reforming process to produce CO and H2.

It has been found that both the Co3O4/g-C3N4and Co3O4/TiO2composites increased the production of H2and CO, with a loading of about 3% CO3O4yielding good results.

3D CO3O4according to the present disclosure can be an efficient sensitizer, and can be used as a catalyst/cocatalyst with semiconductors to increase charge separation efficiency, electrical conductivity, and solar energy harvesting efficiency.

Synthesizing TiO2 nanoparticles with the sol-gel method with suitable operating conditions has been found to be beneficial to adjusting surface area, light harvesting efficiency and charge separation productivity under solar energy irradiation.

Furthermore, the highest yield of CO was obtained when the reaction temperature of 100° C. was used with the light energy. When the temperature was increased to 150 and 200° C., the production of CO was decreased. These results can be explained based on the adsorption-desorption process. Using a higher temperature of more than 100° C., there is possible desorption of reactants over the catalyst surface, which lowers the catalytic activity. When the reaction was conducted without light, there was very small amount of CO formation, which shows at lower temperatures, reaction with Co3O4/TiO2composite is more dependent on the light energy than using heat energy. This can be further confirmed by the results of 200° C., in which the yield of CO was increased without light, the yield of CO was increased.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. The disclosures and the description herein are intended to be illustrative and are not in any sense limiting the present disclosure, defined in scope by the following claims.

Many changes, modifications, variations and other uses and applications of the present disclosure will become apparent to those skilled in the art after considering this specification and the accompanying drawings, which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications, which do not depart from the spirit and scope of the present disclosure, are deemed to be covered by the invention, which is to be limited only by the claims which follow.