Photocatalytic reactor for carbon oxide reduction comprising plasmonically active metallic nanoparticles, and process for producing such photocatalytic reactor

Abstract

Photocatalytic reactor for carbon oxide reduction, comprising a plurality of lateral light diffusion waveguides. Each lateral light diffusion waveguide comprises a core covered with a cladding having at least one microstructured and / or nanostructured outer lateral surface, which is in turn coated with a layer of photocatalytic material decorated with nanoparticles of plasmonically active metallic material.

Description

[0001] Photocatalytic reactor for carbon oxide reduction comprising plasmonically active metallic nanoparticles, and process for producing such photocatalytic reactor

[0002] DESCRIPTION

[0003] Field of the invention

[0004] The present invention relates to a photocatalytic reactor for carbon oxide reduction. The reactor of the present invention comprises a plurality of lateral light diffusion waveguides, each one of which comprises a layer of photocatalytic material decorated with plasmonically active metallic particles. The present invention further concerns a process for producing a photocatalytic reactor as described above, as well as the use of such a photocatalytic reactor for reducing carbon dioxide (CO2) and / or carbon monoxide (CO).

[0005] Background art

[0006] In the field of photocatalytic reactors for carbon oxide reduction, several solutions are known which are based on the use of optical fibers.

[0007] For example, patent document US 2011 / 0122646 A1 shows optical fibers containing nanostructured voids that deflect the light outwards, resulting in quasi constant diffusion of the optical radiation along the fiber.

[0008] Patent document WO 2016 / 064940 A1 shows a fiber made up of two concentric cores surrounded by a cladding. The cores have different internal voids, resulting in the light being scattered out.

[0009] US 5,875,384 illustrates a photochemical reactor employing optical fibers coated with a TiO2 layer. Light is scattered through the fiber up to the TiO2 layer, which uses such energy to oxidize 4-chlorophenol. Publication by Logunov et al., “Light diffusing optical fiber for Illumination", Renewable Energy and the Environment Congress, 2013, describes a light diffusing fiber containing scattering centers within the core.

[0010] Article by Tugaoen et al., “Compact light-emitting diode optical fiber immobilized T1O2 reactor for photocatalytic water treatment’ , Science of the Total Environment, 2018, describes a photocatalytic reactor made by coating optical fibers with TiO2 and coupling them with an LED. The scattered light allows for degradation of organic pollutants in solution into organic compounds with a lower molecular weight.

[0011] Article by Infante et al., “Durable, superhydrophobic, antireflection, and low haze glass surfaces using scalable metal dewetting nanostructuring" , Nano Research, 2013, proposes a nanostructured surface made on glass to obtain superhydrophobic, antireflection, low-haze and high-transmission glass through a scalable nanostructuring process.

[0012] In Collado et al., “Effect of Au surface plasmon nanoparticles on the selective CO2 photoreduction to CH4", Applied Catalysis B: Environmental, 2015, gold nanoparticles were deposited onto TiCh catalysts in order to study the effect of nanoparticles on photocatalytic activity. According to the authors, nanoparticles promote CO2 reduction to methane and hydrogen, as opposed to CO and hydrogen. An optimal quantity of nanoparticles is also proposed which ensures high photocatalytic activity.

[0013] Publication by Nguyen et al., “Photoreduction ofCC>2 in an optical-fiber photoreactor: Effects of metals addition and catalyst carried’, Applied Catalysis A: General 2008, shows a photocatalytic reactor made by using optical fibers coated with a Cu- Fe / TiO2 catalyst under irradiation of UVA and UVC radiations. The goal was to reduce CO2 to methane and ethylene. Adding Fe onto the catalysts helped reduce methane formation, resulting in the production of more ethylene.

[0014] Wu, “Photocatalytic Reduction of Greenhouse Gas CO2 to Fuef’, Catalysis Surveys from Asia, 2009, illustrates an optical-fiber reactor using fibers coated with different photocatalysts for converting CO2 to methanol, methane, and ethylene. The goal of this study was to monitor the reaction resulting from the different catalysts employed.

[0015] Article by Khalid et al., “Highly visible light responsive metal loaded N / T1O2 nanoparticles for photocatalytic conversion of CO2 into methane", Ceramics International, 2017, describes the photocatalytic reduction of CO2 obtained by using H2O as a reducing agent and N / TiO2-based photocatalysts loaded with different metals. The photocatalytic activity of the various catalysts was then monitored under a source of visible radiation, and it was discovered that Ag-N / TiO2 offers promising performance for developing the CO2 reduction reaction.

[0016] De Sun et al., “TiO2-coated optical fiber bundles used as a photocatalytic filter for decomposition of gaseous organic compounds", Journal of Photochemistry and Photobiology A: Chemistry, 2000, proposes a photocatalytic reactor designed as a filter for decomposing gaseous isopropanol. Efficiency and capacity results were better than those obtained from a TiC -coated glass surface or from a honeycomb monolith. According to the authors, this was possible due to high input light intensities and to the large number of fibers employed. Furthermore, each fiber was considered as a single microreactor, with the whole bundle making up the complete reactor.

[0017] Notwithstanding some promising results, the photocatalytic reactors according to the current state of the art, employed for reducing carbon oxides and based on optical fibers, still have relatively low yields.

[0018] Object of the invention

[0019] The present invention aims at overcoming the problems suffered by the prior art.

[0020] In particular, it is one object of the present invention to provide a photocatalytic reactor for carbon oxide reduction, which offers high yields of conversion of carbon oxides into hydrocarbons and / or alcohols.

[0021] It is a further object of the present invention to provide a catalytic reactor for carbon oxide reduction which ensures a high level of abatement of CO2 emissions from low- concentration (less than 30% of CO2) gaseous streams, e.g. coming from industrial or domestic boilers.

[0022] It is a further object of the present invention to provide a photocatalytic reactor for carbon oxide reduction which can supply small amounts of hydrocarbons wherever access to fossil fuels is not guaranteed.

[0023] It is another object of the present invention to provide a photocatalytic reactor for carbon oxide reduction which allows removing carbon dioxide produced by human or animal breathing in indoor or poorly ventilated environments. It is another object of the present invention to provide a photocatalytic reactor for carbon oxide reduction which operates by exploiting solar radiation.

[0024] It is another object of the present invention to provide a photocatalytic reactor for carbon oxide reduction which can be highly optimized as a function of the geometry and dimensions required in a specific application.

[0025] It is another object of the present invention to provide a photocatalytic reactor for carbon oxide reduction which ensures good adhesion between the waveguide and the layer of photocatalytic material.

[0026] It is a further object of the present invention to provide a photocatalytic reactor for carbon oxide reduction which allows delaying catalyst poisoning phenomena.

[0027] It is another object of the present invention to provide a photocatalytic reactor for carbon oxide reduction which is strong, economical, and easy to manufacture.

[0028] The objects of the present invention also include a process for producing said photocatalytic reactor, as well as the use of said photocatalytic reactor for reducing carbon monoxide and / or carbon dioxide.

[0029] These and other objects will become apparent to those skilled in the art in light of the following detailed description of the present invention and of the accompanying drawings.

[0030] Summary of the invention

[0031] The following will describe, by way of non-limiting example, some preferred embodiments of the present invention. Other embodiments, although not described herein but conceivable by a person skilled in the art, are included as well.

[0032] The photocatalytic reactor for carbon oxide reduction according to the present invention comprises a plurality of lateral light diffusion waveguides, i.e. light diffusing or light scattering waveguides. This type of waveguides makes it possible to diffuse, through scattering phenomena, most of the luminous radiation within a specific wavelength suitably chosen according to the reactor’s dimensions and geometry. Each lateral light diffusion waveguide comprises a core having at least one first lateral outer surface and a cladding having at least one second lateral outer surface. The cladding covers the at least one first lateral outer surface. According to the invention, the at least one second lateral outer surface is microstructured and / or nanostructured, and is coated with a layer of photocatalytic material. According to the invention, the layer of photocatalytic material is decorated with nanoparticles of plasmonically active metallic material.

[0033] According to one embodiment, the microstructuring and / or nanostructuring of the at least one second lateral outer surface, i.e. the lateral outer surface of the cladding, may alternatively or additionally be present also on the at least one first lateral outer surface, i.e. the lateral outer surface of the waveguide core.

[0034] According to one aspect, the at least one microstructured and / or nanostructured second lateral outer surface has microstructures and / or nanostructures having a height ranging between 10 nm and 2 pm.

[0035] According to one aspect, such microstructures and / or nanostructures have a conical, frustoconical, or cylindrical pillar-like shape.

[0036] According to one aspect, such microstructures and / or nanostructures comprise metals, e.g. Ti, Ag, Cu.

[0037] According to one aspect, the layer of photocatalytic material has a thickness ranging between 10 nm and 100 pm, preferably between 20 nm and 50 pm, even more preferably between 100 nm and 10 pm.

[0038] According to one aspect, the layer of photocatalytic material has semiconducting properties and comprises, for example, materials such as ZnO, TiO2, CU2O, etc.

[0039] According to one embodiment, the photocatalytic reactor for carbon oxide reduction according to the invention comprises a layer of protective oxide coating the layer of photocatalytic material.

[0040] According to one aspect, said layer of protective oxide has a thickness of 20 nm or less.

[0041] According to one aspect, said layer of protective oxide comprises, for example, TiO2, SiC>2, AI2O3, etc.

[0042] According to one embodiment, the nanoparticles of plasmonically active metallic material used for decorating the layer of photocatalytic material comprise, for example, Cu, Ag, Au.

[0043] According to one embodiment, the plurality of lateral light diffusion waveguides of the photocatalytic reactor of the invention are a plurality of optical fibers.

[0044] According to one aspect, the optical fibers are glass fibers or fibers of polymeric material (e.g. PMMA). According to one aspect, the optical fibers are arranged in a parallel and / or concentric pattern inside the reactor.

[0045] According to an aspect which is alternative to the preceding one, the optical fibers are wound along supports (e.g. poles or tubes) inside the reactor.

[0046] According to an embodiment which is alternative to the preceding one, the plurality of lateral light diffusion waveguides are a plurality of planar waveguides.

[0047] According to one aspect, the planar waveguides are arranged in a parallel configuration inside the reactor.

[0048] The present invention further relates to a process for producing a photocatalytic reactor for carbon oxide reduction comprising a plurality of lateral light diffusion waveguides. Each lateral light diffusion waveguide comprises a core having at least one first lateral outer surface and a cladding having at least one second lateral outer surface, the cladding covering the at least one first lateral outer surface, i.e. the lateral outer surface of the core. Each lateral light diffusion waveguide is subjected to the steps of depositing a shadow mask comprising metallic nanoparticles and / or nanostructures onto the at least one second lateral outer surface, and nanostructuring the at least one second lateral outer surface by plasma treatment in fluorinated atmosphere.

[0049] The process of the present invention further comprises the steps of coating the at least one second outer lateral surface with a layer of photocatalytic material, and decorating the layer of photocatalytic material with nanoparticles of plasmonically active metallic material.

[0050] According to one embodiment, the shadow mask comprises metals such as, for example, Ti, Ag, Cu, and / or, in general, any metal which will be able to withstand the subsequent nanostructuring treatments.

[0051] According to one aspect, the step of depositing a shadow mask comprising metallic nanoparticles and / or nanostructures comprises depositing a thin film, i.e. a film having a thickness ranging between 1 and 100 nm, onto the at least one second lateral outer surface by, for example, sputtering, thermal evaporation or e-beam evaporation, followed by dewetting by thermal treatment or laser treatment.

[0052] According to an aspect which is alternative to the preceding one, the step of depositing a shadow mask comprising metallic nanoparticles and / or nanostructures comprises depositing the nanoparticles, previously synthesized, onto the at least one second lateral outer surface, previously functionalized with a bifunctional molecule capable of binding to both the waveguide material and the metallic nanoparticles.

[0053] According to one embodiment, the step of nanostructuring the at least one second lateral outer surface comprises a dry-etching treatment in fluorinated atmosphere.

[0054] According to one possible embodiment, the dry-etching treatment may be followed by a step of removing any mask residues, e.g. by means of a suitable wet etching agent (Kl / H- or aqua regia for Ag and Au, FeCh for Cu, cerium and ammonium salts and acetic or nitric acid for Cr, etc.).

[0055] According to one embodiment, the step of coating the at least one second lateral outer surface with a layer of photocatalytic material comprises using physical vapor deposition techniques (RF sputtering, e-beam evaporator) or chemical vapor deposition techniques.

[0056] According to an embodiment which is alternative to the preceding one, the step of coating the at least one second lateral outer surface with a layer of photocatalytic material comprises depositing a paste containing a semiconductor material, e.g. ZnO, TiO2, CU2O, followed by debinding thermal treatment and sintering.

[0057] According to one embodiment, the step of decorating the layer of photocatalytic material with nanoparticles of plasmonically active metallic material comprises a substep of functionalizing the layer of photocatalytic material by means of bifunctional molecules having a silane group capable of reacting with and binding to oxides and an amine or mercaptan group capable of binding to metals.

[0058] According to a preferred variant of the preceding embodiment, the substep of functionalizing the layer of photocatalytic material is preceded by a substep of treating said layer of photocatalytic material with O2 plasma.

[0059] According to one embodiment, the step of decorating the layer of photocatalytic material with nanoparticles of plasmonically active metallic material comprises a substep of immersing the waveguides in a suspension containing such nanoparticles.

[0060] According to an embodiment which is alternative to the preceding one, the step of decorating the layer of photocatalytic material with nanoparticles of plasmonically active metallic material comprises a substep of using drop casting techniques. According to one embodiment, the process for producing a photocatalytic reactor for carbon oxide reduction of the present invention further comprises a step of coating the layer of photocatalytic material with a layer of protective oxide.

[0061] According to one embodiment, if the waveguides comprise a coating, it will be necessary to execute a step of removing the coating prior to executing any other step of the process of the present invention.

[0062] According to one aspect, the coating can be removed by mechanical means, e.g. knives, scissors, or other bladed tools, without damaging the cladding and the core of the waveguide.

[0063] According to an aspect which is alternative to the preceding one, the coating can be removed by exposing the waveguides to an aggressive chemical, e.g. an acid or an organic solvent, which can decompose, degrade, bring in solution, and / or promote the detachment of the coating from the cladding of the waveguide. For example, for a PMMA coating one may use, as a solvent, dichloromethane (CH2CI2), which causes dissolution and swelling of the polymeric material, which can then be easily removed without leaving any residue.

[0064] The present invention further relates to the use of a photocatalytic reactor for carbon oxide reduction as described above for converting carbon monoxide and / or carbon dioxide into hydrocarbons and / or alcohols.

[0065] Brief description of the drawings

[0066] The following description will refer to the accompanying drawings, provided merely by way of non-limiting example, wherein:

[0067] - Figures 1 a), 1 b), 1 c), 1 d), 1 e), 1 f) schematize the various steps of a process for producing one waveguide of a plurality of waveguides to be inserted in a photocatalytic reactor of the present invention, in accordance with one possible embodiment thereof, when the waveguide is an optical fiber;

[0068] - Figure 2 is a flow chart of the various steps of a process for producing one waveguide of a plurality of waveguides to be inserted in a photocatalytic reactor of the present invention, in accordance with one possible embodiment thereof; Figures 3a), 3b), 3c) schematize some possible embodiments implementing three different configurations of the photocatalytic reactor according to the present invention.

[0069] Detailed description of some preferred embodiments of the invention

[0070] In the following description, expressions such as “right”, “left”, “over”, “under”, “upper”, “lower”, “horizontal”, “vertical”, and the like, may be used merely for illustration purposes to refer to particular arrangements of elements shown in the annexed drawings, without however any limiting meaning.

[0071] The present invention concerns a photocatalytic reactor for carbon oxide reduction. The reactor of the present invention comprises a plurality of lateral light diffusion waveguides, also known as light diffusing waveguides.

[0072] Figures 1 a) to 1f) schematically illustrate the structure of a waveguide according to the present invention, in the case wherein said waveguide is a waveguide of the light diffusing type, through the various steps of the process of preparing them for manufacturing the photocatalytic reactor.

[0073] The process for producing a waveguide to be inserted in the photocatalytic reactor of the invention is also summarized in the flow chart of Figure 2.

[0074] Figure 1 a) shows a lateral light diffusion waveguide 1 , e.g. an optical fiber, comprising a core 2 having at least one first lateral outer surface 20. The lateral outer surface of the core, or first lateral outer surface 20, is covered by a cladding 3. In turn, the cladding 3 has at least one lateral outer surface, or second lateral outer surface 30, which is generally coated with a coating 4.

[0075] Figure 1 b) illustrates a lateral light diffusion waveguide without the coating.

[0076] For the purposes of the present invention, the optical fiber must have no coating. Therefore, it is necessary to use uncoated optical fibers, as shown in Figure 1 b), or, if a coating is present, as shown in Figure 1 a), it will have to be removed, e.g. by mechanical and / or chemical means, before the fiber is subjected to any further treatment.

[0077] Figure 1 c) shows a light diffusing optical fiber 1 , wherein, on the lateral outer surface of the cladding 3, or second lateral outer surface 30, a shadow mask has been applied which comprises metallic nanoparticles, e.g. copper, silver, gold, chrome, etc. The shadow mask can be applied in several ways, some of which have been previously described herein and are summarized in the flow chart of Figure 2, e.g. through the use of sputtering techniques, preferably followed by (thermal or e-beam) evaporation processes and subsequent dewetting by thermal treatment or laser treatment. Alternatively, the nanoparticle-containing shadow mask can be applied by using bifunctional molecules capable of binding to both the metallic particle and the outer surface of the cladding. In this latter case, the second lateral outer surface 30 of the cladding 3 should first be subjected to a functionalization treatment.

[0078] The nanostructuring of the second lateral outer surface 30 of the cladding 3 is obtained by means of a dry-etching treatment in fluorinated atmosphere: the optical fiber 1 is treated in Reactive Ion Etching (RIE) equipment with an Inductive Coupled Plasma (RIE-ICP) generator, using plasma based on fluorinated gases such as, for example, CHFs, CF4, C2F6 in variable compositions, and optionally using also Ar or O2. The composition of the process atmosphere is selected on the basis of the composition of the material, e.g. glassy material, of the optical fiber. This treatment lasts as long as necessary to obtain structures having a height ranging between 10 nm and 2 pm.

[0079] Inert gases, such as argon, may also be added to the process atmosphere, which can speed up the removal of any non-volatile compounds that may be present in the glass (e.g. oxides of alkali or alkaline earth metals). After the dry-etching step, a cleaning treatment may also be carried out through the use of aggressive solutions (Acid and Basic Piranha) or air-based or 02-based plasma at high power (at least 100W) in order to remove any residues that may have formed due to polymerization of the fluorine-based gases during the etching treatment.

[0080] As previously described herein, wet-etching treatments may also be performed. The optical fiber shown in Figure 1d) will then have a nanostructured outer surface with a pillar-like structure.

[0081] The nanostructuring of the outer surface of the cladding 3, i.e. the second lateral outer surface 30, provides a number of advantages: in the first place, a large active specific area is obtained, resulting in a higher specific yield of the reactor. Secondly, the nanostructuring of the second lateral outer surface 30 ensures a larger interface area between the cladding and the next layer of photocatalytic material 5, resulting in better adhesion between the two and preventing any delamination phenomena. Figure 1e) shows a nanostructured optical fiber as described above, wherein the cladding 3 is coated with a layer of photocatalytic material 5.

[0082] The photocatalytic material is generally a semiconductor material, e.g. zinc oxide, titanium dioxide, copper oxide, etc., or mixtures thereof. The layer of photocatalytic material 5 that coats the cladding 3 generally has a thickness ranging between 10 nm and 100 pm, preferably between 20 nm and 50 pm, even more preferably between 100 nm and 10 pm.

[0083] The cladding can be coated with the photocatalytic material by using different techniques, as summarized in Figure 2.

[0084] For example, as previously described herein, it is possible to use physical vapor deposition techniques (RF sputtering, e-beam evaporator) or chemical vapor deposition techniques.

[0085] Alternatively, it is possible to deposit a paste based on photocatalytic material onto the second lateral outer surface 30 of the cladding, and then perform suitable debinding and sintering thermal treatments.

[0086] Lastly, as shown in Figure 1 f), the layer of photocatalytic material is decorated with nanoparticles of plasmonically active metallic material, e.g. copper, silver, gold, etc., or mixtures thereof.

[0087] Several application techniques may be used during the process of decoration with nanoparticles of plasmonically active metallic material.

[0088] For example, the layer of photocatalytic material may be functionalized by means of bifunctional molecules having a silane group capable of reacting with and binding to oxides and an amine or mercaptan group capable of binding to plasmonically active metals. Some examples of such molecules are aminopropyltrimethoxysilane (APTMS), aminopropyltriethoxysilane (APTES), and 3- mercaptopropyltrimethoxysilane. Such functionalization may occur either by exposure of the optical fiber to vapor containing the functionalizing molecule or by immersion in solution. A preliminary treatment with O2 plasma may improve the bond between the oxide surface and the silane groups. In any case, the optical fiber thus functionalized will then be immersed in a suspension containing the metallic nanoparticles.

[0089] Alternatively, the decoration with nanoparticles of plasmonically active metallic material may also be achieved by using drop casting techniques. The metallic nanoparticles may have different geometries to maximize optical absorption within a given wavelength range.

[0090] Optionally, it is possible to coat the layer of photocatalytic material with a layer of protective oxide (not shown in the drawing) in order to protect the metallic nanoparticles from degradation phenomena. The layer of protective oxide generally has a thickness of 20 nm or less, and may comprise, for example, titanium oxide, zinc oxide, copper oxide, silicon oxide, aluminum oxide, etc.

[0091] Figures 3a) and 3b) schematically show two different configurations of a photocatalytic reactor 100 according to the present invention.

[0092] In the reactor shown in Figure 3a), the optical fibers are arranged in parallel planes that are perpendicular to the longitudinal axis of the reactor, and are wound concentrically to a cylindrical lateral surface of the reactor 100. In the reactor shown in Figure 3b), on the other hand, the optical fibers are wound around poles or vertical supports disposed parallel to the longitudinal axis of the reactor 100, which in this example is also cylindrical in shape.

[0093] Lastly, the reactor shown in Figure 3c) uses planar waveguides. Such waveguides can be disposed parallel to the longitudinal axis of the reactor 100, which will generally have a parallelepiped shape.

[0094] The photocatalytic reactor thus conceived can be used for reducing carbon monoxide and / or carbon dioxide. For example, it may be installed downstream of exhaust systems of furnaces, engines, chemical reactors, boilers or stoves, or it may be used for removing carbon dioxide produced by human or animal breathing in indoor or poorly ventilated environments.

[0095] In particular, the photocatalytic reactor of the present invention is especially effective in treating fumes having a carbon dioxide concentration equal to or lower than 30%, e.g. 20% or less.

[0096] The products of carbon dioxide conversion obtained from the photocatalytic reactor of the present invention - which, by the way, can be powered simply by natural light radiation - include methane, ethanol, methanol, etc.

[0097] List of references

[0098] 1 lateral light diffusion waveguide

[0099] 2 core 3 cladding

[0100] 4 coating

[0101] 5 layer of photocatalytic material

[0102] 20 first lateral outer surface

[0103] 30 second lateral outer surface

[0104] 100 photocatalytic reactor

Claims

CLAIMS1 . Photocatalytic reactor (100) for carbon oxide reduction, comprising a plurality of lateral light diffusion waveguides, wherein each waveguide (1 ) comprises a core (2) having at least one first outer lateral surface (20); a cladding (3) having at least one second outer lateral surface (30), the cladding (3) covering the at least one first outer lateral surface (20), wherein the at least one second outer lateral surface (30) is microstructured and / or nanostructured, and wherein the at least one second outer lateral surface (30) is coated with a layer of photocatalytic material (5), the layer of photocatalytic material (5) being decorated with nanoparticles of plasmonically active metallic material.

2. Photocatalytic reactor (100) for carbon oxide reduction according to claim 1 , comprising a layer of protective oxide coating the layer of photocatalytic material (5).

3. Photocatalytic reactor (100) for carbon oxide reduction according to any one of claims 1 or 2, wherein the layer of photocatalytic material (5) has a thickness ranging between 10 nm and 100 pm, preferably between 20 nm and 50 pm, even more preferably between 100 nm and 10 pm.

4. Photocatalytic reactor (100) for carbon oxide reduction according to any one of claims 1 , 2 or 3, wherein the plurality of lateral light diffusion waveguides are a plurality of optical fibers.

5. Photocatalytic reactor (100) for carbon oxide reduction according to any one of claims 1 , 2 or 3, wherein the plurality of lateral light diffusion waveguides are a plurality of planar waveguides.

6. Process for producing a photocatalytic reactor (100) for carbon oxide reduction comprising a plurality of lateral light diffusion waveguides according to any one of claims 1 to 5, wherein each lateral light diffusion waveguide (1 )comprises a core (2) having at least one first outer lateral surface (20) and a cladding (3) having at least one second outer lateral surface (30), the cladding (3) covering the at least one first outer lateral surface (20), and wherein each lateral light diffusion waveguide is subjected to the steps of depositing a shadow mask comprising metallic nanoparticles and / or nanostructures onto the at least one second outer lateral surface (30); nanostructuring the at least one second outer lateral surface (30) by plasma treatment in fluorinated atmosphere; coating the at least one second outer lateral surface (30) with a layer of photocatalytic material (5), and decorating the layer of photocatalytic material (5) with nanoparticles of plasmonically active metallic material.

7. Process for producing a photocatalytic reactor (100) for carbon oxide reduction according to claim 6, wherein the step of coating the at least one second outer lateral surface (30) with a layer of photocatalytic material (5) makes use of techniques of vapor deposition or techniques of deposition of a paste containing semiconductor materials.

8. Process for producing a photocatalytic reactor (100) for carbon oxide reduction according to any one of claims 6 or 7, wherein the step of decorating the layer of photocatalytic material (5) with nanoparticles of plasmonically active metallic material comprises the substeps of functionalizing the layer of photocatalytic material and immersing the plurality of waveguides in a suspension containing the nanoparticles of plasmonically active metallic material.

9. Process for producing a photocatalytic reactor (100) for carbon oxide reduction according to any one of claims 6 or 7, wherein the step of decorating the layer of photocatalytic material (5) with nanoparticles of plasmonically active metallic material makes use of drop casting techniques.

0. Use of a photocatalytic reactor (100) for carbon oxide reduction according to any one of claims 1 to 5 for converting carbon monoxide and / or carbon dioxide into hydrocarbons and / or alcohols.

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