Device for capturing co 2 from the atmosphere, and method for manufacturing it

Abstract

The present invention relates to a method for preparing a CO2 capture device in which olivine nanoparticles are deposited on a substrate by magnetron sputtering technique. A CO2 capture device obtained by the above method is also presented.

Description

[0001] DEVICE FOR CAPTURING CO2FROM THE ATMOSPHERE, AND METHOD FOR MANUFACTURING IT

[0002] DESCRIPTION

[0003] TECHNICAL FIELD

[0004] The present invention relates to the field of carbon dioxide, CO2, capture and storage.

[0005] BACKGROUND

[0006] To mitigate climate change, CO2 capture from the atmosphere is considered an effective method to reduce the greenhouse effect and consequently lower the earth's temperature.

[0007] Capturing and storing CO2 means removing CO2 from the atmosphere, possibly in such a way that the CO2 combines with other substances so that it cannot escape again, except under controlled conditions.

[0008] One solution, known since the 1970s, for CO2 capture and storage, consists of trapping CO2 emitted by power plants and other localized sources, compressing it to a liquid state, and transporting it to a storage site where it is injected deep into a rocky soil, typically basalt rock.

[0009] This solution, however, is very energy consuming and does not give certainty that the CO2 can be released back into the atmosphere or groundwaters.

[0010] More recently, researchers have verified the ability of olivine, a naturally occurring mineral, to absorb CO2 directly from the atmosphere. The use of olivine is a particularly promising solution for CO2 storage since 1000 kg of olivine can capture approximately 5-600 kg of CO2 from the air.

[0011] The ability to absorb CO2 occurs with the formation of carbonates in mineral compounds, e.g., rocks. Carbonation of olivine rock, also known as "olivine carbonation reaction", is a geological process that occurs over a long period of time. It involves the reaction of olivine minerals (typically forsterite, Mg2SiO4 or fayalite Fe2SiO4 but also rarely tephroite Mn2SiC>4 and glaucorite CaMnSiO4) with carbon dioxide (CO2) to form magnesium and iron carbonates (MgCCh and FeCCh) and hydrated carbonate species (such as, for example, Mgs(CO3)4(OH)2- 4-8H2O, MgCO3-3H2O, or Mgs(CO3)4(OH)2-5H2O) if the reaction takes place in the presence of water. This process plays a role in the terrestrial carbon cycle by sequestering carbon dioxide from the atmosphere. The limited carbonation rate of olivine due to passivation is the main problem that does not allow, to date, a realistic industrial use of this mineral for CO2 sequestration.

[0012] The rate at which olivine carbonation occurs can vary depending on environmental conditions such as temperature, pressure and availability of water and CO2. In natural geological settings, the carbonation of olivine under atmospheric conditions is generally a very slow process and can take thousands of years to complete, depending on the specific conditions. The weathering of the Olivine is required to expose fresh Olivine surface to react with CO2. The rate of carbonation can also be influenced by factors such as the presence of catalytic agents and the availability of reactive surface area on the olivine grains. Several studies over the last ten years have shown promising results in CO2 capture by exploiting mineral carbonation with olivine microparticles at high temperatures (100-200 °C) using supercritical CO2 (i.e. with pressure Pco2 > 100 Bar) since olivine carbonation reaches its maximum yield at 185 °C and a CO2 partial pressure of 150 Bar. [1-4]

[0013] To increase the rate of CO2 storage in olivine, it has been proposed to grind olivine to nanoscale size.

[0014] Although the preparation of olivine at the nanoscale by ball milling is known, this process is energy-intensive and time-consuming.

[0015] For example, in [5] a complicated process is reported for the reaction with CO2, which involves grinding at high intensity to mechanically remove the carbonate layer that is formed. However, the formation of a passivation layer on the olivine surface with a thickness much smaller than that of the microparticle size is observed, which makes the fact that these larger nanoparticles have formed, almost useless.

[0016] In [6], mechanical grinding is used to activate olivine, i.e. to remove in a continuous way carbonate layers being present on the olivine surface. In this case, water must also be used, which introduces more complex chemical reactions.

[0017] In any case, in all these studies, no dimensions below 20 nm could be achieved. Nanoparticles (~27 nm) of Forsterite, were synthesized using a sol-gel process which involves very high temperatures (800°C) and is, therefore, industrially unprofitable. [7]

[0018] There is therefore a need for an effective method for CO2 capture and storage using olivine. References

[0019] [1] O. Rahmani, J. Highfield, R. Junin, M. Tyrer, and A. B. Pour, 'Experimental Investigation and Simplistic Geochemical Modeling of CO2 Mineral Carbonation Using the Mount Tawai Peridotite', Molecules, vol. 21, no. 3, 2016, doi: 10.3390 / molecules21030353.

[0020] [2] P. B. Kelemen and J. Matter, 'In situ carbonation of peridotite for CO2 storage', Proceedings of the National Academy of Sciences, vol. 105, no. 45, pp. 17295-17300, Nov. 2008, doi: 10.1073 / pnas.0805794105.

[0021] [3] F. Wang, D. Dreisinger, M. Jarvis, and T. Hitchins, 'Kinetics and mechanism of mineral carbonation of olivine for CO2 sequestration', Minerals Engineering, vol. 131, pp. 185-197, Jan. 2019, doi: 10.1016 / j.mineng.2018.11.024.

[0022] [4] L. Turri et al., 'CO2 sequestration by carbonation of olivine: a new process for optimal separation of the solids produced', Green Processing and Synthesis, vol. 8, no. 1, pp. 480-487, 2019, doi: doi:10.1515 / gps-2019-0016.

[0023] [5] A. Dufourny, C. Julcour, J. Esvan, L. Cassayre, P. Laniesse, and F. Bourgeois, 'Observation of the depassivation effect of attrition on magnesium silicates' direct aqueous carbonation products', Frontiers in Climate, vol. 4, 2022, doi: 10.3389 / fclim.2022.946735.

[0024] [6] V. Farina et al., 'CO2 Hydrogenation Induced by Mechanochemical Activation of Olivine With Water Under CO2 Atmosphere', Frontiers in Energy Research, vol. 7, 2019, doi: 10.3389 / fenrg.2019.00107.

[0025] [7] K. P. Sanosh, A. Balakrishnan, L. Francis, and T. N. Kim, 'Sol-gel synthesis of forsterite nanopowders with narrow particle size distribution', Journal of Alloys and Compounds, vol. 495, no. 1, pp. 113-115, Apr. 2010, doi: 10.1016 / j.jallcom.2010.01.097.

[0026] [8] M. Andreani, L. Luquot, P. Gouze, M. Godard, E. Hoise, and B. Gibert, 'Experimental Study of Carbon Sequestration Reactions Controlled by the Percolation of CO2-Rich Brine through Peridotites', Environ. Sci. Technol., vol. 43, no. 4, pp. 1226-1231, Feb. 2009, doi: 10.1021 / es8018429.

[0027] OBJECTS AND SUMMARY OF THE INVENTION

[0028] The object of the present invention is to overcome the problems of the prior art outlined above.

[0029] In particular, it is an object of the present invention to present a method for efficiently manufacturing a device adapted to capture CO2 capturing and storing CO2 from the atmosphere. These and other objects are achieved by means of a method and a device incorporating the features of the appended claims.

[0030] According to a first aspect, the invention relates to a method for preparing a device for capturing CO2, in which olivine nanoparticles are deposited on a substrate by means of a sputtering technique, and in particular magnetron sputtering.

[0031] In particular, the method according to an embodiment of the invention preferably comprises the following steps: a) Placing an olivine disc (target) on a magnetron cathode positioned inside a sputtering zone of a sputter and aggregation chamber. b) Placing a substrate element in a deposition chamber which is in fluid communication with the sputtering and aggregation chamber through an orifice; alternatively, the substrate is placed in a deposition zone of the same chamber and is in direct fluid communication with an aggregation zone of the sputter and aggregation chamber. c) Injecting a stream of an inert gas, particularly argon, in the sputtering and aggregation chamber; preferably, at a flow rate comprised between 0.8x10- 7 and lOxlO'7m3 / s. d) Creating a plasma by ionizing the inert gas; preferably, by applying a DC or AC Voltage between an anode and the cathode on which the olivine is placed. Preferably in case AC voltage is applied, this alternating voltage has frequencies in the RF range, even more preferably comprised between 400 Hz and 900MHz, but more preferably in the range between 10 and 100 MHz. e) Bombarding the olivine disc with plasma ions in order to sputter atoms of elements constituting the olivine disc (e.g., Mg, Fe, Si, O in their neutral state or anionic / cationic state). f) Obtaining olivine nanometric particles by aggregation of sputtered atoms in the aggregation zone. Preferably, the olivine nanometric particles have an average diameter comprised between about 2 nm to about 20 nm. g) Transferring the olivine nanometric particles in the deposition chamber / zone by means of a flow of the inert gas. h) Depositing the olivine nanometric particles on the substrate for a predetermined time period. i) Extracting from the deposition chamber the product obtained by depositing olivine nanoparticles onto the substrate. Preferably before start to inject the inert gas into the aggregation chamber, air is pumped out from the aggregation and deposition chambers in order to clean the inside from impurities and create a vacuum. More preferably air can be pumped out creating vacuum in the sputter and aggregation chamber until the pressure in the sputter and aggregation chamber reaches or is below 1-mbar, i.e. 100-10 Pa. Preferably, in industrial application, especially for mass production, the pressure in the sputter and aggregation chamber is maintained at about 1 mbar (10 Pa). In case high purity of the final product is required, the pressure inside the chamber can be lowered between 10-6and IO-8mbar (i.e., 0,1 - 0,001 Pa) or lower.

[0032] According to different embodiments, the substrate can be made of any vacuum compatible material, i.e. a material that will not evaporate because of the vacuum inside the deposition chamber. Examples of vacuum compatible material are plastic or metal foil (roll-to-roll), paper.

[0033] According to another aspect, the invention is directed to a device comprising a bottom substrate and a top layer of olivine, wherein the top layer of olivine is obtained by depositing olivine nanoparticles on the bottom substrate by sputtering technique, and in particular by magnetron sputtering.

[0034] A further aspect of the present invention relates to a method for capturing and storing CO2 in the atmosphere at room temperature by means of the device of the invention.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The invention will be described below with reference to some examples, provided for explanatory and non-limiting purposes, illustrated in the accompanying figures.

[0037] Figure 1 schematically shows a magnetron for producing a CO2 capture and storage device according to the invention.

[0038] Figure 2 is a flow chart of a method for producing a CO2 capture and storage device according to the invention.

[0039] Figure 3 schematically represents a device according to the invention obtained by the method of figure 2.

[0040] Figure 4a is a photograph of a sample of a device obtained by the method of figure 2 and analyzed within 15 minutes of exposure to air with a TEM microscope after extraction from the magnetron aggregation chamber. Figure 4b is a photograph of a sample of a device obtained by the method of figure 2 and analyzed by TEM microscope after exposure to a pressure of 1 bar (100 KPa) of pure CO2 in a special container for 48 hours.

[0041] Figure 4c is a photograph of a sample of a device obtained by the method of figure 2 and analyzed under a TEM microscope after being exposed for one week to air.

[0042] Figure 5 is a micrograph of a sample of a device by the method of figure 2 and analyzed under an AFM microscope comprising a structure made of olivine nanoparticles.

[0043] Figure 6 shows several spectra, obtained by X-ray photoelectron spectroscopy (XPS), of some CO2 capture devices exposed to air at different time periods.

[0044] Figure 7 shows some spectra, obtained by X-ray photoelectron spectroscopy (XPS), of some CO2 capture devices exposed to air and / or CO2 for different time periods.

[0045] DETAILED DESCRIPTION OF THE INVENTION

[0046] While the invention is susceptible to various alternative modifications, certain preferred embodiments will be described in detail below. It should be understood, however, that there is no intention to limit the invention to the specific embodiment illustrated, but, on the contrary, the invention is intended to cover all modifications, and equivalents falling within the scope of the invention as defined by the claims.

[0047] With reference to Figures 1 and 2, a method for producing a device for capturing and storing CO2 from the atmosphere is described herein.

[0048] In an embodiment, the method according to the invention comprises depositing nanometric particles of olivine on a substrate using a "magnetron sputtering" technique.

[0049] As is well known, 'sputtering' is a process wherein atoms of the elements constituting a 'target', solid, material are emitted due to bombarding of the target material by high-energy particles. The target material is placed inside a sputter and aggregation chamber in which there is a rarefied inert gas (e.g. argon) and an electric field originating from a (alternating or continuous) potential difference between a cathode, on which the target material is placed, and an anode, typically constituted of a metal cup surrounding the cathode and guiding the sputter gas flow. The potential difference ionizes the gas, creating a plasma with high-energy positive ions that are attracted to the cathode and strike the target material, resulting in the emission of target material atoms. The atoms are aggregating to form particles inside the aggregation zone / area and flow, due to the difference in pressure between the aggregation chamber and the deposition chamber, through an orifice until they deposit on a substrate being placed in a deposition chamber in fluid communication with the aggregation chamber.

[0050] In the case of magnetron sputtering, a magnetic field is created in at the back of the olivine sputter target to direct the plasma ions towards the center of the sputter target.

[0051] In the embodiments described below, the magnetron 1 is a device as described in H. Haberland et at., "Filling of micron-sized contact holes with copper by energetic cluster impact", p. 2925, J. Vac. Sci. Technol. A 12(5), Sept / Oct 1994. The invention is not limited to the use of this device and other magnetrons can be used to implement the method described here below.

[0052] The magnetron 1, shown in figure 1, comprises two deposition related chambers: a sputtering and aggregation chamber 10 for cluster and nanoparticle generation and a deposition chamber 20 containing a substrate holder. Preferably but not limitatively, a security arrangement, e.g. a load lock chamber 30 for substrate extraction / insertion is provided to ensure technicians safety. In figure 1 the sputtering and aggregation chamber 10 is a liquid nitrogen (LN2) cooled chamber, nevertheless the chamber can be water cooled or cooled with other means. In different embodiments, the load lock chamber 30 can be omitted and the deposition chamber is provided with a closable opening for accessing the substrate holder.

[0053] The method for producing a device for capturing and storing CO2 from the atmosphere involves placing (step 101) a piece of olivine 2 (hereinafter also referred to as a target material) in a sputtering zone 10A of the sputtering and aggregation chamber 10. More in detail, the piece of olivine is placed on the cathode 3 of a magnetron discharge unit 4.

[0054] The magnetron discharge unit 4 comprises a water cooled cathode 3 surrounded by a cup shaped anode 5, magnets 6 placed in the cathode behind the sputtering target 1 holding element, and one or more conduits 11 for conveying an inert gas (e.g. Argon) in front of the sputtering target material.

[0055] The olivine target preferably has a slab-like shape, and more preferably a discoidal or rectangular shape.

[0056] The size of the olivine target depends on the size of the magnetron cathode and the operating conditions of the magnetron itself. In particular, the olivine target has a surface area substantially equal to that of the cathode. Since some magnetrons are usually equipped with systems for fixing the target to the cathode, in these cases the olivine target will have to be of a size that fits on the cathode and that can be fixed to the cathode by the available fixing systems. - shaped targets may preferably be between 2.5 cm and 100 cm in diameter to suit magnetrons currently on the market; however, the use of larger targets is not excluded.

[0057] As far as thickness is concerned, the olivine target is thick enough for the target to effectively dissipate the heat produced during sputtering. Preferably, the thickness is greater than 5 mm.

[0058] The tests conducted by the applicant and described below were carried out using an olivine disc with a diameter of 2.56 cm and a thickness of 6 mm as a target, placed inside an NC200U-B device from Oxford Applied Research Ltd.

[0059] As is known, olivine is an isomorphic mixture of forsterite (Mg2SiO4) and fayalite (Fe2SiO4). For the purposes of the present invention, olivine may comprise forsterite (Mg2SiO4) and fayalite (Fe2SiO4) in any ratio, as well as intermediate terms of the series obtained by substitution of iron and magnesium for manganese and / or calcium, for example olivine may contain one or more of: tephroite (M SiQi), glauchocroite (CaMnSiO4), monticellite (CaMgSiO4) and kirschteinite (CaFeSiCh).

[0060] The method (step 102) then provides for placing a substrate 7 on a substrate holder 8 in the deposition chamber 20.

[0061] The substrate 7 may be made of any material that does not evaporate in the deposition chamber at the temperature and pressure conditions at which the magnetron is operated. As an example, silicon, germanium, plastic or metallic materials can be used as substrates, but also some oils (particularly, vacuum compatible oils and greases, such as mineral oils or synthetic oils - e.g., Polyalphaolefins (PAO), Polyether (PEs), Perfluoropolyethers (PFPEs), Silicone Oils) can be used as substrates. Further the substrate can assume various shapes such as one among a flat or bent slab, a flat or bent foil, a plate, a disc, a cup, a cone, a cylinder shape.

[0062] Preferably, but not mandatory, after placing the target 2 on the cathode 3 and the substrate 7 in the deposition chamber 20, a vacuum is created in the sputtering and aggregation chamber 10 (step 103) to remove air and impurities present in the sputtering and aggregation chamber 10. The vacuum is created by means of a vacuum pump (not showed in figure 1) in fluid communication with the sputtering and aggregation chamber 10 via a valve. Preferably the pump creates the vacuum by bringing the pressure in the sputtering and aggregation chamber 10 below 1 mbar (100 Pa), for experimental and / or small batches productions, nevertheless higher pressures are allowed depending on the destination of use of the device for capturing CO2. In an industrial process, in fact, a certain percentage of impurities is allowed and use of a simple, and cheap, pump to remove most of the air from the inside of the sputtering and aggregation chamber 10 (e.g. to bring pressure between IO-3and 1 mbar, i.e. 0,1 - 100 Pa) can be used.

[0063] Additionally, vacuum is created also in the deposition chamber 20 (step 104). Preferably, the pressure in the deposition chamber 20 is at least ten times lower than the pressure in the sputtering and aggregation chamber 10, force a suitable flow of fluids from the sputtering and aggregation chamber 10 to the deposition chamber 20 that ensure a fast and reliable deposition process.

[0064] After placing the olivine in the sputtering zone of the sputtering and aggregation chamber 10 and the substrate in the deposition chamber 20, and, if necessary, creating the vacuum in the sputtering and aggregation chamber, a stream of inert gas 9, Argon in this example, is injected (step 105) into the aggregation chamber with flow rates, or velocities, comprised between 0.8xl0'7and 10xl0'7m3 / s, and more preferably between 5xl0'7and 6.7xl0'7m3 / s. With reference to figure 1, Argon is injected in front of olivine 2 by means of the conduits 11 internal to the magnetron discharge unit 4.

[0065] Argon gas can be used both as a sputter plasma, aggregation medium and as a carrier gas carrying the olivine particles from an aggregation zone 10B of the sputtering and aggregation chamber 10 to the deposition chamber 20 through an orifice 12. For example, in a magnetron 1 for tests and / or small batches production, the orifice 12 has substantially circular shape with a diameter ranging from about 5 mm to about 10 mm. Alternatively, as shown in figure 1, Helium, Xenon or another inert gas 13 can be used as sputter and carrier and aggregation gas. Particularly, the Applicant has found that Xenon can outperform Argon as a carrier and aggregation gas. Carrier and aggregation gas 13 is injected in the sputtering and aggregation chamber 10 via a dedicated inlet 14.

[0066] While the inert gas (both plasma sputter gas 9 and carrier gas 13) is inserted into the sputtering and aggregation chamber 10, or after the inert gas is inserted into the sputtering and aggregation chamber 10, a potential difference is applied (step 106) between the anode 5 and cathode 3 sufficient to create a plasma in the sputtering zone 10 A of the sputtering and aggregation chamber 10. The application of this potential difference creates free electrons which, when colliding with the inert gas, generate energetic ions that strike the target material 2.

[0067] The ions hit the target material and cause the emission of atoms that constitute the target material made of olivine (step 107) that then aggregate in the aggregation zone 10B of the sputtering and aggregation chamber 10 to form nanoparticles (step 108), which move from this region to the deposition chamber 20 (step 109), where they, finally, deposit on the substrate 7 (step 110).

[0068] Particularly, the free atoms emitted from the olivine target comprise Mg, Fe, Si and O in any between a neutral, cationic or anionic state as they might be generated by the interaction between the material target and the plasma particles. Possibly, dimers or clusters (i.e., polymers made by two or more atoms) may be also generated during the sputtering process at particular conditions.

[0069] Single atoms recombine in olivine nanoparticles while suspended in the Argon gas in the aggregation zone. Then, in the considered embodiment, the difference in pressure between the aggregation zone 10B and the deposition chamber 20 generates a flow of inert gas and olivine nanoparticles flowing from the aggregation zone 10B to the deposition chamber 20 through the orifice 12. Particularly, the flow rate of the inert gas and olivine nanoparticles is adjustable by leveraging the difference between the pressure in the aggregation zone and in the deposition chamber and / or by selecting an appropriate orifice size (e.g., diameter).

[0070] In one embodiment, during deposition, the substrate is moved perpendicular to the particle beam, back and forward to obtain a more uniform deposition layer. More preferably, the substrate is moved in a plane on which the substrate rests; movement can be made back and forward along one or more directions, or along a closed path (e.g. a circular path) or an open path (e.g. a spiral path).

[0071] The potential difference between anode and cathode of the magnetron can be a DC voltage or an AC voltage. Preferably, in case AC voltage is applied, this voltage has a frequency in the RF range, preferably comprised between 400 Hz and 900 MHz, but more preferably in the range between 10 and 100 MHz.

[0072] In the applicant's experiments, the magnetron was supplied with a power of -170 W (0.45 A and 375 V), injecting argon (both from conduits 11 and inlet 14) into the aggregation chamber at a rate of 5.8xl0'7m3 / s. The experiment was conducted at room temperature (20°C) with a pressure in the aggregation chamber of IO-3mbar, or 0,1 Pa. Under these conditions, the deposition rate 0 o varied between ~8 A / s and 30 A / s measured with a quartz microbalance; the deposition process then ended after about ten minutes.

[0073] Once the deposition of olivine nanoparticles on the substrate is finished, a product 300, illustrated schematically in Figure 3, consisting of the substrate 7 coated with olivine nanoparticles 303 can be extracted from the deposition chamber (step 111). In the example of figure 3, the substrate 7 comprises a layer 301 of n-doped silicon coated with a layer 302 of SiO2 silicon oxide, nevertheless other materials can be used for the substrate, which can also be made of one single material, e.g. a plastic material. Product 300 is, or may be part of, a CO2 capture device.

[0074] Although in the above description the method for manufacturing the CO2 capture and storage device makes use of a magnetron sputtering technique, it is also possible to use other sputtering techniques. For example, either the RF sputtering technique (a technique involving vaporization induced by a radio frequency - Radio Frequency) or the DC sputtering technique (a variant of conventional sputtering in which a high DC voltage (Direct Current) is maintained between the target to be sputtered and the substrate to be coated) can be used indifferently. In other embodiments, the sputtering technique known as High-Power Impulse Magnetron Sputtering (HiPIMS) is used in order to achieve an efficient sputtering of the target material.

[0075] Additionally, in different embodiments, it is provided a deposition zone in fluid communication with the aggregation zone to the sputtering and aggregation chamber rather than a distinct deposition chamber. In this case the deposition zone is positioned adjacent to the aggregation zone and in direct contact (fluid communication) with the latter.

[0076] Moreover, it is clear that steps 101 and 102 of the method above described can be inverted, i.e. it is possible to place first the substrate and then the olivine target.

[0077] Examples

[0078] Several CO2 capture devices were manufactured using the NC200U-B device from Oxford Applied Research Ltd in the same process conditions as illustrated below.

[0079] Inside the aggregation chamber, a 2.56 cm disc of olivine was attached to the cathode, while a substrate consisting of a bottom layer of n-doped silicon and a top layer of silicon oxide was placed on the deposition holder in the deposition chamber. Tests were conducted at room temperature (~20°C).

[0080] After creating a vacuum in the aggregation chamber, a flow of argon was injected at a rate of 5.8xl0-7m3 / s and a magnetron sputtering process was initiated by powering the magnetron with a power of -170 W (0.45 A and 375 V).

[0081] The sputtering process lasted 10 minutes and resulted in the deposition of an approximately 50 nm layer of olivine in nanoparticle form after a deposition phase that lasted 10 minutes.

[0082] Some samples of devices produced in this way have been characterized using transmission electron microscopy (TEM), which is an analytical technique used to visualize the smallest structures of matter. Unlike optical microscopes, which rely on light in the visible spectrum, TEM can reveal details on an atomic scale by magnifying nanometric structures up to 50 million times.

[0083] In the conducted tests, TEM images were recorded with an FEI Tecnai F20, which is a transmission electron microscope (Field Emission Gun -FEG) with an accelerating voltage of 200 kV. The microscope was equipped with an S-Twin lens that provides a point resolution of 0.24 nm. An energy-dispersive X-ray spectrometer (EDS) with an ultra-thin window (Xplore-Oxford Instruments) was used for elemental analysis, which confirmed the presence of all constituents of the sputter target.

[0084] Some images, obtained in this way, are shown in Figures 4a, 4b and 4c. These figures show different morphologies with which the olivine 403 nanoparticles deposited on the substrate appear; in particular, on the silicon oxide layer 402. Figure 4a refers to a sample 400 extracted from the deposition chamber and immediately analyzed under a TEM microscope, thus a sample that came into contact with air for a short time. Figure 4b refers to a 410 sample that was put into a container saturated with CO2 for 2 days before being analyzed, while Figure 4c refers to a 420 sample that was left in air for one week before being analyzed.

[0085] All samples contained irregularly shaped nanoparticles and clusters formed by the aggregation of two or more nanoparticles. In an embodiment, the prevailing morphology is spherical or semi-spherical, evident in all samples and indicated with reference 4030. Another common morphology, indicated by reference 4031, has the shape of a cauliflower, characterized by its complex fractal structure resembling the head of a cauliflower, which arises from the aggregation or assembly of smaller nanoparticles into interconnected branches. Square structures, 4032, characterized by well-defined edges and corners, are predominantly visible in samples exposed to air (Figure 4c) and CO2 (Figure 4b).

[0086] The size distributions of the nanoparticles, obtained by measuring the size of about 200 particles from TEM micrographs, show clear log-normal behavior.

[0087] Fitting with a log-normal function provided the average particle size for each deposition and treatment.

[0088] The sample that was exposed to air for the shortest time (Figure 4a) had an average diameter of the olivine nanoparticles of 12±3 nm, while the nanoparticles exposed to air (Figure 4b) and CO2 (Figure 4c) for one week had diameters of 14±4 nm and 23±6 nm, respectively. This increase in time of the average diameter indicates the capacity to capture CO2 from the environment.

[0089] Further, Figure 5 shows an atomic force microscopy (AFM) micrograph of a sample of a structure of deposited olivine nanoparticles wherein smaller nanoparticles of about 15 nm in diameter are aggregated into larger cauliflowerlike nanoparticle structures of about 150 nm of diameter.

[0090] In order to quantify the CO2 absorption capacity of the device produced by the method of the present invention, some samples were then analyzed by X-ray photoelectron spectroscopy (XPS). XPS technology can measure the elemental composition and the chemical and electronic state of atoms within a material. XPS spectra are obtained by irradiating a solid surface with an X-ray beam and measuring the kinetic energy of electrons emitted from the top 1-10 nm of the analyzed material.

[0091] The penetration depth of XPS is typically <10 nm and provided information on the reactions within the bulk volume of the olivine nanoparticles. Figures 5 and 6 show the Cis spectra of a plurality of samples exposed to air and CO2 for different time periods.

[0092] The main result is the detection of the carbonate peak (501) at 289.2 eV, which confirms that olivine carbonation has indeed occurred.

[0093] The largest signal at 284.8 eV (502) indicates the presence of so-called 'adventitious carbon', originating from organic contaminants through exposure to air, and is displaced by the carbonate peak with values ranging from 4.4 to 4.7 eV in good agreement with literature values of 4.5±0.6 eV.

[0094] Both figures 6 and 7 show that the carbonate peak value remains almost constant for samples being exposed to air or CO2 for 30 minutes or many hours; this indicates that most of the carbonation reaction took place in the first few minutes after exposure of the samples.

[0095] The Cis XPS spectra of olivine nanoparticles were deconvoluted using three Gaussian-Lorentian GL(30) peaks (which means 30% of Lorentzian and 70% of Gaussian) placed at 284.8eV, 289.2eV, and 292.7eV respectively for the contribution of adventitious carbon, carbonate, and CCI4 to obtain the net area of the carbonate peaks.

[0096] Using the area of the Mg 2p and Fe 2ps / 2 peaks, the relative concentration of these elements (a) was calculated, resulting in a=CMg / CFe=3.5±0.1 which corresponds to a composition of 78% Forsterite and 22% Fayalite.

[0097] From the area of the carbonate peaks and the relative concentrations of magnesium and iron (a), the carbonation yield § was calculated constantly higher than 14% conversion, typically varying between 44 and 76% conversion, which progressed by a further 6% after subsequent exposure to CO2. This is a very important result.

[0098] Consider, in fact, that in previous literature studies, e.g. the article [8], on sintered Olivine aggregates with an average grain diameter of ~84 gm and a porosity of 17%, a carbonation of 3% was achieved in 7.5 hours in a supercritical CO2 atmosphere at 120 bar (12 MPa) and 150°.

[0099] In [6], a carbonation yield of 50% was obtained after 2.5 hours. The convenient preparation of olivine nanoparticles according to the process of the invention and the subsequent rapid carbonation under ambient conditions as described in the above examples clearly exceed what has been reported in previous studies.

[0100] Finally, it should be noted that the parameters values and / or ranges provided in the embodiment and examples above should not be considered limiting. Particularly, the parameters values / ranges of above are selected to obtain an effective production of small batches of the CO2 capturing product - comprising small numbers (e.g., 1 to 5 pieces) of the CO2 capturing product and / or smallsized CO2 capturing products (e.g., magnetrons designed to receive an olivine sputter target in the order of square meters). Differently, for larger productions - i.e., industrial / mass manufacturing of the product - i.e., larger number of pieces manufactured or larger sizes of the product (e.g., able to have a throughput of 1 ton per 15 minutes or l,lKg / s) -, parameters values and ranges significantly increase. Particularly, inert gas injection velocity may be increased by an order of magnitude 100 or 1000 with respect to the ones used for small batch production, e.g. injection velocities can range between 0.8xl0'5and 10xl0'3m3 / s. Similarly, power and electric currents / voltages can be increased up to 100 times with respect to the values used for small batch production, e.g. up to about 17 KW (e.g., 45 A and 375 V). Nonetheless, also current and voltage values can be increased; e.g., with currents in the order of hundreds of Amperes and / or voltages in the order of thousands of Volts. Furthermore, also the operating temperatures can be incremented up to 200°C.

Claims

CLAIMS1. Method for manufacturing a CO2 capture device, wherein olivine nanoparticles are deposited on a substrate using a magnetron sputtering technique, comprising the steps of:- positioning (101) a solid piece of olivine in a sputter zone of a sputter and aggregation chamber (10),- positioning (102) a substrate in a deposition zone of the sputter and aggregation chamber (10) or in a deposition chamber (20), generating (106) a plasma by ionizing an inert gas in the sputter zone, and- bombarding (107) the olivine piece with plasma ions, thus sputtering atoms from the olivine piece into an aggregation zone of the sputter and aggregation chamber (10), the sputtered atoms are atoms of elements constituting the olivine, and wherein the sputtered atoms aggregate (108) into olivine nanoparticles in the aggregation zone containing inert gas , the olivine nanoparticles having an average diameter comprised between 2 and 20 nm,- transferring (109) the olivine nanoparticles to the deposition zone or chamber (20) in fluid communication with the aggregation chamber by means of a flow of the inert gas, wherein the olivine nanoparticles deposit (110) on a substrate positioned in the deposition chamber (20).

2. Method according to claim 1, wherein the substrate is made of metal, plastics or other polymers, doped / undoped semiconductors or a combination thereof.

3. Method according to claim 1 or 2, wherein the substrate is shaped as one among a flat or bent slab, a flat or bent foil, a plate, a disc, a cup, a cone, a cylinder.

4. Method according to claim 1, wherein the substrate is made of a mineral or synthetic oil or grease.

5. Method according to any one of the preceding claims, wherein the inert gas is Argon or Xenon.

6. Method according to any one of the previous claims, wherein the inert gas is injected into the aggregation chamber at a flow rate comprised between 0.8x10’7and 10xl0’7m3 / s, for small batches and comprised between 0.8xl0’5and 10x10’4m3 / s for large batches.

7. Method according to any one of the preceding claims, comprising the step of creating (103) vacuum in the sputter, aggregation chamber and in thedeposition chamber or zone before injecting the inert gas into the sputter and aggregation chamber, bringing the pressure in the sputter and aggregation chamber equal to or lower than 100 Pa (1 mbar), preferably comprised between 10 Pa (0,1 mbar) and 100 Pa (1 mbar).

8. Method according to claim 7, further comprising the step of creating (104) vacuum in the deposition chamber or zone, wherein the pressure in the deposition chamber / zone is lower than the pressure in the sputter and aggregation chamber, during operation, by at least a factor of ten.

9. Method according to claim 8, wherein the step of transferring (109) the olivine nanoparticles to the deposition zone or chamber (20) comprises having a flow of inert gas and olivine nanoparticles flowing from the aggregation zone to the deposition chamber through an orifice in a wall separating the aggregation zone and the deposition chamber, wherein the flow rate of the flow inert gas and olivine nanoparticles is defined by the difference between the pressure in the aggregation zone and in the deposition chamber.

10. Method according to any one of the preceding claims , wherein generating a plasma comprises supplying a power of about 170 W for small batches production or up to about 17 KW for large batches to a magnetron provided in the aggregation chamber (10).

11. Method according to any one of the preceding claims, wherein the magnetron is supplied with an electric current of about 0.45 A and / or a voltage of about 375 V for small batches production or up to 45 A and / or a voltage of about 1000 V for large batches.

12. Method according to claim 10 or 11, wherein the magnetron comprises an anode and a cathode between which an AC or DC voltage is applied, and wherein the applied AC voltage has a frequency in the RF range, preferably comprised in between 400 Hz and 900MHz, but more preferably in the range comprised between 10 and 100 MHz.

13. Method according to any one of the preceding claims, wherein generating a plasma comprises controlling the magnetron to preform High-Power Impulse Magnetron Sputtering (HiPIMS).

14. Method according to any one of the preceding claims, being performed at a temperature of about 20°C for small batches and up to 200°C for large batches.

15. A CO2 capturing device comprising a substrate (7) and an upper layer of olivine in nanoparticle form (303, 403), wherein the upper layer of olivine innanoparticle form is a structure comprising irregularly shaped nanoparticles formed by the aggregation of two or more atoms obtained by the method according to any one of claims 1 to 14.

16. The CO2 capturing device of claim 15, wherein the upper layer of olivine in nanoparticle form (303, 403) comprises nanoparticles with a semi-spherical morphology before exposition to CO2.

17. The CO2 capturing device of claim 15 or 16, wherein the upper layer of olivine has a composition of about 78% Forsterite and about 22% Fayalite.

18. A method for capturing and storing CO2 characterized by the use of the device according to claim 15 to 17 having at least a carbonation yield of 14%.

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