Description:FIELD OF THE INVENTION
The present invention relates to the field of photocatalytic reduction of CO2 to liquid solar fuel. More specifically, the present invention relates to a mixed metal oxide heterocomposite material comprising a transition metal oxide as nanorod arrays partially coated with a lanthanide metal oxide, as a heterogeneous photocatalyst for CO2 photoreduction and processes thereof.

BACKGROUND OF THE INVENTION
Burning of fossil fuel has accounted for over 80 % of global CO2 emission which is causing severe climate change. One of the very effective way to tackle this situation is to convert the emitted CO2 into fuel. Since, CO2 is a thermally stable molecule; energy must be supplied to drive the desired transformation. Generally, high temperatures, extremely reactive reagents, electricity, or the energy from photons needs to be employed to carry out carbon dioxide reactions. Among the various methods available for CO2 reduction to fuel, photochemical has attained immense significance because of some key benefits like economic feasibility and environmental compatibility along with the use of renewable solar energy. The vast development in the field of semiconductor composite materials with tunable band gap properties to improve product selectivity, extended absorption spectrum and enhanced light harvesting efficiency have elevated the efficacy of this method for CO2 reduction.

Although, various types of semiconductor materials have previously been explored for photocatalytic CO2 reduction but the challenge of addressing the specific product selectivity, prolonged separation of charges after photoexcitation and enhanced light harvesting efficiency has not been accomplished yet. Recently, metal oxide based semiconductor photocatalysts with interfaces and heterojunctions have emerged as promising photoactive materials to be used for such conversions meeting all the requirements. Several transition metal oxides have been reported to be a quintessential catalyst for photo catalytic reactions because it exhibits excellent properties like non-toxicity, a high quantum yield and cheapness. However, the material suffers intrinsic drawbacks that severely limit its applications in the photocatalytic field like having a wide band gap (Eg = approximately 3.37 eV) and absorption spectrum in the range of 350-370 nm making it suitable only for UV region and a high exciton binding energy of nearly 60 meV. These limitations can easily be overcome by synthesizing semiconductor composites with intrinsic heterojunction within the system or by controlling the morphology in order to provide exposed active facets having directional flow of charge carriers. So, the constitution of a heterojunction at the interfaces of two or more semiconductors can both help in the improvement of visible light harvesting and in the reduction of the photo excited charge carriers’ recombination rate since they are stabilized on the two different materials.

WO2016058862A1 discloses a photocatalytic carbon dioxide reduction method carried out in liquid and/or gas phase under irradiation, using a photocatalyst containing a first semiconductor SC1, particles comprising one or more metallic-state elements M, and a second semiconductor SC2. The first semiconductor can be ZnO and second semiconductor can be Ce2O3. However, the use of Pt as metallic-state elements M make the photocatalyst expensive.

CN117427627A discloses about a photocatalyst for preparing ethanol by coupling carbon dioxide with methane wherein the catalyst is based on cerium oxide composite zinc oxide nano particles. It is also disclosed that the products such as methanol can also be obtained apart from main product, i.e., ethanol.

Vali et al discloses a Cu/ZnO/CeO2 based catalyst supported on MOF-5 which resulted in high methanol yield and selectivity. It is also disclosed that the catalyst performed well in terms of stability, showing an insignificant activity loss after 5 h of continuous reaction [Seyed Alireza Vali, Javier Moral-Vico, Xavier Font & Antoni Sánchez; Cu/ZnO/CeO2 Supported on MOF-5 as a Novel Catalyst for the CO2 Hydrogenation to Methanol: A Mechanistic Study on the Effect of CeO2 and MOF-5 on Active Sites. Catal Lett (2024)].

Singh et al discloses about the effect of incorporating CeO2 to the precursor chemistry of Cu/ZnO catalytic system. It is also disclosed that the incorporation of CeO2 into the Cu/ZnO catalytic system improved methanol selectivity. This catalytic conversion of captured CO2 to MeOH is a possible solution to mitigate the rising CO2 emissions [Rajan Singh, Kaushik Kundu, Kamal K. Pant; CO2 hydrogenation to methanol over Cu-ZnO-CeO2 catalyst: Reaction structure–activity relationship, optimizing Ce and Zn ratio, and kinetic study, 2024, 479, 147783].

Guo et al discloses about solar-driven catalytic CO2 reduction to produce usable fuels and value-added chemicals, wherein photocatalytic CO2 reduction using semiconductor QDs are performed in the presence of sacrificial reagent (triethylamine; TEA) in organic solvent of dimethylformamide (DMF) [Efficient and Selective CO2 Reduction Integrated with Organic Synthesis by Solar Energy
Qing Guo, Fei Liang, Xu-Bing Li, Yu-Ji Gao, Mao Yong Huang, Yang Wang, Shu-Guang Xia, Xiao-Ya Gao, Qi-Chao Gan, Zhe-Shuai Lin, Chen-Ho Tung, Li-Zhu Wu, 2019, 5(10), 2605-2616].

However, it is clear from the prior arts that attempts have been made to provide an efficient photocatalyst for the photocatalytic reduction of CO2. But none of the prior art discloses specifically designed morphology of the photocatalyst with heterojunction interface having an extended absorption spectrum and facile electron transport system for enhanced photocatalytic CO2 reduction to alcohols in good yields at mild reaction conditions i.e., at room temperature and atmospheric pressure. Also, none of the prior art discloses the optimized parameters such as solvent ratio that could further enhance the CO2 reduction in the presence of photocatalyst.

Therefore, there exists a requirement of economic and efficient photocatalyst for the photocatalytic reduction of CO2 into valuable products in good yields.
OBJECTIVES OF THE INVENTION
The main objective of the present invention is to provide a mixed metal oxide heterocomposite material as heterogeneous photocatalyst for enhanced photocatalytic reduction of CO2 to alcohols.

Another objective of the present invention is to provide a process for preparing mixed metal oxide heterocomposite material.

Another objective of the present invention is to provide a process for the photocatalytic reduction of CO2 to alcohols using the mixed metal oxide heterocomposite material as heterogeneous photocatalyst.

SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention and nor is it intended to determine the scope of the invention.

The present invention provides a mixed metal oxide heterocomposite material as heterogeneous photocatalyst for CO2 photoreduction, wherein the mixed metal oxide heterocomposite material comprises a transition metal oxide selected from NiO, ZnO, CuO, TiO2, and Fe3O4 and a lanthanide metal oxide selected from ceria (CeO2), lanthanum oxide, and ytterbium oxide, wherein the transition metal oxide has a specific nanorod array arranged in a 3D flower like morphology coated with the lanthanide metal oxide; and wherein the lanthanide metal oxide has a percentage loading of 1 % to 3%.

The mixed metal oxide heterocomposite material is ZnO-CeO2 consisting of ZnO nanorods coated with CeO2; wherein ZnO-CeO2 has a bandgap of 2.62 eV. The ZnO nanorods in ZnO-CeO2 have an average length of 2 to 3 micron and diameter of 100 nm to 150 nm. The ZnO-CeO2 has a surface area of 327.51 m2/g, and an average pore diameter of 2.02 nm.

The present invention also provides a process for the preparation of a mixed metal oxide heterocomposite material as defined above, comprises:
i. mixing and agitating a transition metal precursor solution and a lanthanide metal precursor solution;
ii. adding a cross linking agent to the solution of step i) and stirring; wherein pH of the solution is maintained between 6 to 8;
iii. heating the solution in an autoclave to obtain a precipitate;
iv. washing the precipitate, followed by drying the precipitate to obtain the mixed metal oxide heterocomposite material.

The solution is agitated for 4 to 6 hours. The stirring is done for 15 to 30 minutes. The transition metal precursor and the lanthanide metal precursor has a molar ratio of 10:1. The cross linking agent is added in a molar concentration of 0.10 M to 0.16 M. The pH of the solution is maintained by adding ammonium hydroxide. The solution is heated at a temperature of 150 to 190 ? for 7 to 10 hours. The precipitate is washed with ethanol and DI water.

The transition metal precursor is selected from a group comprising zinc acetate, zinc nitrate, zinc sulphate, and zinc chloride. The lanthanide metal precursor is selected from a group comprising cerium nitrate, cerium chloride, lanthanum chloride, lanthanum nitrate, ytterbium nitrate, and ytterbium chloride. The cross linking agent is selected from a group comprising triallylamine, allyl methacrylate (AMA), tetraallyloxyethane and hexamethylenetetramine (HMTA).

The present invention also provides a process for CO2 photoreduction using a mixed metal oxide heterocomposite material as heterogeneous photocatalyst in the presence of visible light, the process comprises:
i. adding the mixed metal oxide heterocomposite material as heterogenous photocatalyst into a reaction mixture comprising dimethyl formamide (DMF), water and triethyl amine (TEA), followed by stirring;
ii. degassing the reaction mixture;
iii. purging the reaction mixture with CO2; and
iv. irradiating the reaction mixture with the visible light.

The reaction mixture comprises water (H2O), trimethylamine (TEA), and dimethyl formamide (DMF) having DMF:TEA:H2O in a ratio of 60:20:20. The reaction is carried out for 5 hours under visible light irradiation.

The mixed metal oxide heterocomposite material has a selectivity of 68 % for methanol, and 31.9 % for ethanol.

BRIEF DESCRIPTION OF THE DRAWINGS:
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 depicts SEM images of (a) ZnO nanocubes, (b) CeO2 nanoclusters (c) ZnO-CeO2 heterocomposite and EDAX spectrum of (d) ZnO nanocubes, (e) CeO2 nanoclusters (f) ZnO-CeO2 nanocomposite.
Figure 2 depicts the plot for yield of ethanol and ethanol obtained from the photoreduction of CO2 with respect to photocatalyst concentration.

DETAILED DESCRIPTION OF THE INVENTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments in the specific language to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated process, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The composition, methods, and examples provided herein are illustrative only and not intended to be limiting.

The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

The term “some” as used herein is defined as “none, or one, or more than one, or all”. Accordingly, the terms “none”, “one”, “more than one”, “more than one, but not all” or “all” would all fall under the definition of “some”. The term “some embodiments” may refer to no embodiments or to one embodiment or to several embodiments or to all embodiments. Accordingly, the term “some embodiments” is defined as meaning “no embodiment, or one embodiment, or more than one embodiment, or all embodiments”.

More specifically, any terms used herein such as but not limited to “includes”, “comprises”, “has”, “consists” and grammatical variants thereof is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. The specification will be understood to also include embodiments which have the transitional phrase “consisting of” or “consisting essentially of” in place of the transitional phrase “comprising”. The transitional phrase “consisting of” excludes any element, step, or ingredient not specified in the claim, except for impurities associated therewith. The transitional phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps “and those that do not materially affect the basic and novel characteristic(s)” of the claimed invention.

Whether or not a certain feature or element was limited to being used only once, either way it may still be referred to as “one or more features” or “one or more elements” or “at least one feature” or “at least one element”. Furthermore, the use of the terms “one or more” or “at least one” feature or element do NOT preclude there being none of that feature or element, unless otherwise specified by limiting language such as “there NEEDS to be one or more” or “one or more element is REQUIRED”.

Use of the phrases and/or terms such as but not limited to “a first embodiment”, “a further embodiment”, “an alternate embodiment”, “one embodiment”, “an embodiment”, “multiple embodiments”, “some embodiments”, “other embodiments”, “further embodiment”, “furthermore embodiment”, “additional embodiment” or variants thereof do NOT necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and/or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and/or elements may be described herein in the context of only a single embodiment, or alternatively in the context of more than one embodiment, or further alternatively in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

The terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and does not limit, restrict, or reduce the spirit and scope of the invention.

In order to overcome the limitations as described above, the present invention provides a mixed metal oxide heterocomposite material as heterogeneous photocatalyst for CO2 photoreduction. The mixed metal oxide heterocomposite material is a semiconductor material that is designed in a way so as to have a suitable band edge position to selectively promote the formation of methanol and ethanol. The photocatalytic material comprises of metal oxides as nanorod arrays partially coated with lanthanide metal oxide. The synthesized nanocatalyst has a co-catalyst or secondary semiconductor that provides a heterojunction interface allowing the spatial separation of photo generated charge carriers at the interface which leads to their effective utilization to carry out the multi-step electronic reduction of the CO2 molecule to thermodynamically feasible product.

The mixed metal oxide heterocomposite material comprises hierarchically designed nanorod arrays of a transition metal oxide partially coated with lanthanide metal oxide nanoparticle. The photocatalyst follows a Z-scheme pathway to facilitate the electron transport chain to achieve enhanced absorption spectrum for photocatalytic reduction of CO2 to alcohol. Lanthanide metal oxides have an expanded absorption spectrum of 300-800 nm covering the UV and visible region and has excellent redox property as well as large specific surface area providing numerous active sites.

The present invention also provides a process for the production of alcohols by photocatalytic reduction of CO2. The photocatalyst used is a novel 3D flower like transition metal oxide nanorod array providing a Z-scheme electron transport chain (ETC) which is loaded partially with oxide of lanthanide metal which is ceria. Wherein, the 3D flower like structure comprises of transition metal oxide nanorods arranged in the form of an array which are partially coated with lanthanide metal oxide. The partial ceria loading is providing an expanded solar absorption spectrum and also enabling enough exposure to the nanorod facets for photoexcitation hence, minimizing the recombination rate of photogenerated charge carriers which significantly enhances the efficiency of the catalyst.

The present invention provides a mixed metal oxide heterocomposite material as heterogeneous photocatalyst for CO2 photoreduction, wherein the mixed metal oxide heterocomposite material comprises a transition metal oxide selected from NiO, ZnO, CuO, TiO2, and Fe3O4 and a lanthanide metal oxide selected from ceria (CeO2), lanthanum oxide, and ytterbium oxide, wherein the transition metal oxide has a specific nanorod array morphology with 3D flower like morphology coated with lanthanide metal oxide.

In an embodiment the percentage loading of lanthanide metal oxide is 1 % to 3%.

In an embodiment of the present invention, the mixed metal oxide heterocomposite material is ZnO-CeO2 consisting of ZnO nanorods coated with CeO2. The ZnO-CeO2 has a bandgap of 2.62 eV. ZnO-CeO2 heterocomposite material has a surface area of 327.51 m2/g, and an average pore diameter of 2.02 nm.

In an embodiment of the present invention, the ZnO nanorods in ZnO-CeO2 have an average length of 2 to 3 micron and diameter of 100 nm to 150 nm.

The present invention also provides a process for the preparation of a mixed metal oxide heterocomposite material as defined above, comprises:
i. mixing and agitating a transition metal precursor solution and a lanthanide metal precursor solution;
ii. adding a cross linking agent to the solution of step i) and stirring; wherein pH of the solution is maintained between 6 to 8;
iii. heating the solution in an autoclave to obtain a precipitate;
iv. washing the precipitate, followed by drying the precipitate to obtain the mixed metal oxide heterocomposite material.

In an embodiment the solution is agitated for 4 to 6 hours. In a preferred embodiment, the solution is agitated for 4 hours. The stirring is done for 15 to 30 minutes. The transition metal precursor solution and the lanthanide metal precursor has a molar ratio of 10:1 The cross linking agent is added in a molar concentration of 0.10 M to 0.16 M.

In an embodiment, the pH of the solution is maintained between 6 to 8 by adding ammonium hydroxide.

In an embodiment, the solution is heated at a temperature of 150 to 190 ? for 7 to 10 hours. In a preferred embodiment, the solution is heated at a temperature of 150 to 190 ? for 7 to 10 hours.

The precipitate is washed with ethanol and DI water.

The transition metal precursor is selected from a group comprising zinc acetate, zinc nitrate, zinc sulphate, and zinc chloride.

In an embodiment, the transition metal precursor is zinc acetate.

The lanthanide metal precursor is selected from a group comprising cerium nitrate, cerium chloride, lanthanum chloride, lanthanum nitrate, ytterbium nitrate, and ytterbium chloride.

In an embodiment, the lanthanide metal precursor is cerium nitrate.

The cross linking agent is selected from a group comprising triallylamine, allyl methacrylate (AMA), tetraallyloxyethane and hexamethylenetetramine (HMTA).

In a preferred embodiment, the cross linking agent is hexamethylenetetramine (HMTA).

The present invention also provides a process for CO2 photoreduction using a mixed metal oxide heterocomposite material as heterogenous photocatalyst in the presence of visible light, the process comprises:
i. adding the mixed metal oxide heterocomposite material as heterogenous photocatalyst into a reaction mixture comprising dimethyl formamide (DMF), water and triethyl amine (TEA), followed by stirring;
ii. degassing the reaction mixture;
iii. purging the reaction mixture with CO2; and
iv. irradiating the reaction mixture with the visible light.

Water (H2O) is used as reductant and trimethylamine (TEA) is used as hole scavenger, along with dimethyl formamide (DMF) to increase the absorption of CO2.

In an embodiment of the present invention, DMF:TEA:H2O has a ratio of 60:20:20. The reaction is carried out for 5 h under visible light irradiation.

The ZnO-CeO2 heterocomposite material has a selectivity of 68 % for methanol, and 31.9 % for ethanol.

In an embodiment of the present invention, the photocatalytic activity of the heterocomposite material is also compared with pristine transition metal oxide and lanthanide metal oxide. The mixed metal oxide heterocomposite material provides highest methanol yield under reported reaction conditions. The heterocomposite material also yields ethanol in good quantity which is not reported elsewhere under mentioned reaction conditions.

The mixed metal oxide heterocomposite material is used as heterogeneous photocatalyst for photocatalytic CO2 reduction under visible light irradiation for 5 hours in batch mode yielding methanol in the range of 4500 to 5000 micromoles/g and ethanol in the range of 2000 to 3000 micromoles/g.

EXAMPLES:
The present disclosure with reference to the accompanying examples describes the present invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. It is understood that the examples are provided for the purpose of illustrating the invention only and are not intended to limit the scope of the invention in any way.

EXAMPLE 1: Synthesis of ZnO-CeO2
The mixed metal oxide heterocomposite material ZnO-CeO2 with CeO2 loading of 3 % was synthesized using hydrothermal method. Firstly, solutions of 0.1 M to 0.5 M zinc acetate and 0.01 M to 0.05 M cerium nitrate were prepared in DI water and were mixed and agitated constantly for 4 h. Defined molar concentration of cross linking agent HMTA was added dropwise and kept on stirring, wherein the molar concentration of the of cross linking agent is 0.10 M to 0.16 M. After 15-30 minutes, ammonium hydroxide was added dropwise to maintain the pH. The mixture was stirred for another half an hour and then whole solution was poured in an autoclave and was heated for 7-10 h at 150 ?. The precipitate was washed several times with ethanol and DI water and kept for drying.

Characterization:
The band gap energy of the synthesize ZnO-CeO2 was calculated using Kubelka-Munk function. Visible light covers the range of approximately 390-700 nm, or 1.8-3.1 eV. The metal oxide heterocomposite semiconductors (ZnO-CeO2) are having band gap in the range of visible light favouring alcohol formation. The band gap values of ZnO, CeO2 and ZnO-CeO2 heterocomposite material is given in table 1 below:
Table 1
S.No. Catalyst Absorbance [nm] *Band gap [ev]
1 ZnO 355 3.4
2 CeO2 320-670 2.9
3 ZnO-CeO2 450 2.62

SEM image in Figure 1 compares the morphologies of bare ZnO and CeO2 with that of the ZnO-CeO2 heterocomposite material. When the zinc and flower shaped zinc oxide nanorod arrays were obtained as shown in the SEM image.

From the surface area analysis, the ZnO-CeO2 heterocomposite material has the lowest average pore diameter of 2 nm which favoured the formation of C2 alcohol (ethanol). The surface properties of the ZnO-CeO2 photocatalyst are given below in table 2.
Table 2
S.No. Catalyst Surface area
[m2 g-1] Total pore volume
[cm3 g-1] Average pore diameter
[nm]
1 ZnO 17.93 0.04 10.97
2 CeO2 174.8 0.25 5.88
3 ZnO-CeO2 327.51 0.16 2.02

PHOTOCATALYTIC REDUCTION REACTION:
Experiments were conducted to carry out the CO2 photoreduction reaction in the batch reactor. The synthesized photocatalyst consisted of mixed metal oxides heterocomposite containing NiO or ZnO or CuO or TiO2 or Fe3O4 in the form of nanorod array which was partially coated with a lanthanide metal oxide. The specific examples are listed below:

EXAMPLE 2: Photoreduction of CO2 using ZnO-CeO2
The photocatalytic reduction reaction was carried out in a batch reactor of 500 ml using a 450 W visible lamp with calculated amount of catalyst dispersed in the reaction mixture. Dimethyl formamide was used as the reaction solvent and water was used as a reductant. Triethyl amine was also added as a hole scavenger and the mixture was poured and placed in the reactor with suspended catalyst. All of the openings of the reactor were closed tightly and CO2 purging valve was also connected. Before starting the reaction, 15 minutes degassing was done to remove any air present in the reactor with constant stirring at 250 rpm followed by half an hour of CO2 purging. The reaction was performed at 25 ? and 1 atmospheric pressure. After completion of the process, the reactor was connected with the chiller and water circulation was started and kept for 15 minutes. Then, the lamp was switched on and the reaction was continued for 5 h. After the reaction, samples were collected and analysed using GC.

1 g of ZnO-CeO2 photocatalyst was suspended in 50 ml of solution and 15 minutes of degassing followed by 30 minutes CO2 purging was done. The reaction was irradiated with visible light for 5 h. The product was collected and filtered and analysed using GC.
The efficiency of the photocatalyst was calculate using the formula:

In the reaction of photochemical reduction of CO2 to alcohol, water is used as reductant and trimethylamine (TEA) is used as hole scavenger, along with dimethyl formamide (DMF) to increase the absorption of CO2. The yields are shown in Figure 2.

EXAMPLE 3:
The procedure was essentially the same as in Example 2, except the reaction was continuously stirred at 100 rpm.
The yield of methanol obtained in example 3 was in the range of 3000-4000 micromoles/g.
The yield of ethanol obtained in example 3 was in the range of 900-1050 micromoles/g.

EXAMPLE 4:
The procedure was essentially the same as in Example 2, except the reaction was carried out for 8 h at 25 ?.
The yield of methanol obtained in example 4 was in the range of 3000-4000 micromoles/g.
The yield of ethanol obtained in example 4 was in the range of 900-1050 micromoles/g.

EXAMPLE 5:
The procedure was essentially the same as in Example 2, except the reaction was done without trimethylamine (TEA).
The yield of methanol obtained in example 5 was in the range of 3000-4000 micromoles/g.
The yield of ethanol obtained in example 5 was in the range of 900-1050 micromoles/g.

EXAMPLE 6:
The procedure was essentially the same as in Example 2, except the dosage amount of catalyst was 0.8 g.
The yield of methanol obtained in example 6 was in the range of 3000-4000 micromoles/g.
The yield of ethanol obtained in example 6 was in the range of 900-1050 micromoles/g.

EXAMPLE 7:
The procedure was essentially same as in Example 2, except the total reaction mixture taken was 80 ml.
The yield of methanol obtained in example 7 was in the range of 3000-4000 micromoles/g.
The yield of ethanol obtained in example 7 was in the range of 900-1050 micromoles/g.

Advantages of the present invention:
• CO2 reduction in the milder reaction conditions to lower alcohols (Methanol and Ethanol) has direct application in industries.
• The alcohols thus obtained can be used as fuel additives or can be upgraded for producing olefins, gasoline, and aviation fuels
• Photocatalytic conversion of CO2 to fuels (hydrocarbons) is an attractive route that avoid significant energy inputs and H2 requirement as in the case of thermolytic routes , Claims:1. A mixed metal oxide heterocomposite material as heterogeneous photocatalyst for CO2 photoreduction, wherein the mixed metal oxide heterocomposite material comprises:
a transition metal oxide selected from NiO, ZnO, CuO, TiO2, and Fe3O4; and
a lanthanide metal oxide selected from ceria (CeO2), lanthanum oxide, and ytterbium oxide, wherein the transition metal oxide has a specific nanorod array arranged in a 3D flower like morphology coated with the lanthanide metal oxide oxide; and wherein the lanthanide metal oxide has a percentage loading of 1 % to 3 %.

2. The mixed metal oxide heterocomposite material as claimed in claim 1, wherein the mixed metal oxide heterocomposite material is ZnO-CeO2 consisting of ZnO nanorods coated with CeO2; wherein ZnO-CeO2 has a bandgap of 2.62 eV.

3. The mixed metal oxide heterocomposite material as claimed in claim 2, wherein the ZnO nanorods in ZnO-CeO2 have an average length of 2 to 3 micron and diameter of 100 nm to 150 nm; wherein ZnO-CeO2 has a surface area of 327.51 m2/g, and an average pore diameter of 2.02 nm.

4. A process for the preparation of a mixed metal oxide heterocomposite material as claimed in claims 1-3, wherein the process comprises:
i. mixing and agitating a transition metal precursor solution and a lanthanide metal precursor solution;
ii. adding a cross linking agent to the solution of step i) and stirring; wherein pH of the solution is maintained between 6 to 8;
iii. heating the solution in an autoclave to obtain a precipitate; and
iv. washing the precipitate, followed by drying the precipitate to obtain the mixed metal oxide heterocomposite material.

5. The process as claimed in claim 4, wherein the solution is agitated for 4 to 6 hours; wherein the stirring is done for 15 to 30 minutes; wherein the transition metal precursor and the lanthanide metal precursor has a molar ratio of 10:1; wherein the cross linking agent is added in a molar concentration of 0.10 M to 0.16 M; wherein the pH of the solution is maintained by adding ammonium hydroxide; and wherein the solution is heated at a temperature of 150 to 190 ? for 7 to 10 hours; wherein the precipitate is washed with ethanol and DI water.

6. The process as claimed in claim 4, wherein the transition metal precursor is selected from zinc acetate, zinc nitrate, zinc sulphate, and zinc chloride; wherein the lanthanide metal precursor is selected from cerium nitrate, cerium chloride, lanthanum chloride, lanthanum nitrate, ytterbium nitrate, and ytterbium chloride ; wherein the cross linking agent is selected from a group comprising triallylamine, allyl methacrylate (AMA), tetraallyloxyethane and hexamethylenetetramine (HMTA), preferably the cross linking agent is hexamethylenetetramine (HMTA).

7. A process for CO2 photoreduction using a mixed metal oxide heterocomposite material as heterogenous photocatalyst in the presence of visible light, the process comprises:
i. adding the mixed metal oxide heterocomposite material as heterogenous photocatalyst into a reaction mixture comprising dimethyl formamide (DMF), water and triethyl amine (TEA), followed by stirring;
ii. degassing the reaction mixture;
iii. purging the reaction mixture with CO2; and
iv. irradiating the reaction mixture with the visible light.

8. The process as claimed in claim 7, wherein the reaction mixture comprises water (H2O), trimethylamine (TEA), and dimethyl formamide (DMF); wherein DMF:TEA:H2O has a ratio of 60:20:20.

9. The process as claimed in claim 7, wherein the reaction is carried out for 5 hours under visible light irradiation.

10. The process as claimed in claim 7, wherein the mixed metal oxide heterocomposite material has a selectivity of 68 % for methanol, and 31.9 % for ethanol.