MODULAR PHOTOCATALYTIC SYSTEM

Abstract

A fully stand-alone modular system which integrates tandems of photo-anodes and photovoltaic cells in a photo-electrochemical cell configuration.

Such a system consists of devices capable of using only solar energy, in particular by utilizing the visible spectrum, so as to decontaminate the wastewater from emerging pollutants, with the simultaneous production of hydrogen as an added value to the decontamination process, by means of photocatalytic processes.

Claims

1. A photo-electrochemical system for the photo-oxidation of organic substances and the production of hydrogen from aqueous solution, which acts as an electrolyte, using solar radiation, completely stand-alone and modular, consisting of photo-electrochemical devices, each of which mainly comprises: a) a tandem configuration of a cell consisting of the photo-active electrode in contact with the aqueous solution capable of producing hydroxyl radicals from solar radiation so as to oxidize the organic substances present in aqueous solution and a cell consisting of photovoltaic cells capable of generating the voltage required for the reduction of protons generated in hydrogen, developed on a second electrode in contact with the aqueous solution; b) an integrated circuit powered by the photovoltaic cells for the management of the polarization and depolarization cycles of the photo-active electrode.

2. A photo-electrochemical device forming the system according to claim 1, which integrates tandem of a photo-active electrode, referred to as a photo-anode, and photovoltaic cells, electrically connected.

3. The device according to claim 2, wherein the photo-anode consists of a substrate, preferably made of glass, a conductive film and a photo-active material, substantially a semiconductor oxide directly deposited on the conductive film.

4. The device according to claim 3, comprising a conductive film made of fluorine-doped tin oxide, which is transparent to solar radiation, so as to allow such a radiation to reach the photovoltaic cells.

5. The device according to claim 3, wherein the photo-active material comprises colloidal tungsten trioxide generated by means of the sol-gel method.

6. The device according to claim 2, wherein the second cell of the tandem integrated in said device integrates several silicon-based photovoltaic cells.

7. The device according to claim 2, wherein the silicon-based photovoltaic cells have interdigitated contacts and are connected in series.

8. The device according to claim 2, wherein the second electrode consists of a metal cathode placed in contact with the aqueous solution.

9. The device according to claim 6, comprising a printed circuit on which the photovoltaic cells according to claims 6 and 7 arc the second cell of the tandem is welded to the surface facing the photo-anode, and on which the electronic components are welded to the surface facing the cathode.

10. The device according to claim 7, comprising a printed circuit on which the silicon-based photovoltaic cells are welded to the surface facing the photo-anode, and on which the electronic components are welded to the surface facing the cathode.

11. The device according to claim 2, comprising a microcontroller among the electronic components for the management of the polarization and depolarization cycles of the photo-anode.

12. The device according to claim 2, wherein the photovoltaic cells and the printed circuit do not come into contact with the aqueous solution thanks to an encapsulant placed along the edges of the photo-anode and on the side of the printed circuit facing the cathode where the electronic components, also protected by the encapsulant itself, are present.

13. The device according to claim 2, comprising an external structure preferably made of PVC which encloses the tandem device, constructed so as to make the system modular and advantageously combinable.

14. A photo-electrochemical system according to claim 1 enclosed by a structure preferably made of plexiglass or glass which may contain the photo-electrochemical devices described in the preceding claims and the aqueous solution to be treated.

15. The photo-electrochemical system according to claim 1 placed by the side of or directly integrated with inside the structure, by a pumping apparatus for water recirculation.

16. The photo-electrochemical system according to claim 1, provided with a tank containing water to be treated.

17. The photo-electrochemical system according to claim 1, provided with a tank containing water decontaminated by the photo-catalytic action of the device.

18. The photo-electrochemical system according to the preceding claims, provided with a duct for the output of the hydrogen produced by the cathode electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The features and advantages related to the present invention will be better understood from the following detailed description with reference to the accompanying drawings, merely provided by way of explanation and not by way of limitation, in which:

[0046] FIG. 1 diagrammatically shows the photo-anode integrated in the device;

[0047] FIG. 2 is a diagrammatic depiction of the key elements of the photo-electrochemical cell coupled to the photovoltaic cells, viewed in section and placed inside a compartment containing the aqueous solution to be treated;

[0048] FIG. 3 shows the diagram of the single device viewed in section and placed inside the aqueous solution to be treated;

[0049] FIG. 4 shows a depiction of the individual device;

[0050] FIG. 5 shows a depiction of the modular system consisting of the individual devices;

[0051] FIG. 6 shows the graph of the trend of the photocurrent produced by the photo-anode;

[0052] FIG. 7 shows the COD abatement results.

DETAILED DESCRIPTION

[0053] FIG. 1 shows the diagrammatic depiction of the photo-anode 1 integrated in the device of the present invention. Such an anode electrode 1 consists of: [0054] a semiconductor oxide film 2, preferably WO.sub.3, which acts as a catalyst with the function of absorbing the solar radiation by converting it into electron-hole pairs with activation energy such as to allow the demolition of the organic compounds present in the aqueous solution; [0055] a glass substrate 3 made conductive by the presence of a layer of conductive FTO film 4 deposited between the substrate and the semiconductor oxide.

[0056] The key component of a photo-electrochemical system is the photo-electrochemical cell.

[0057] FIG. 2 diagrammatically shows the basic elements of the photo-electrochemical cell (photo-anode 1, cathode 5 and aqueous solution 6) which uses photovoltaic cells 7 and is inserted inside a compartment 8 containing the aqueous solution to be treated 6. The photo-anode 1 is placed in a tandem configuration with the photovoltaic cells 7.

[0058] The radiation 9 enters the system from the left in the Figure passing through the container 8, preferably made of glass or plexiglass, and the aqueous solution 6. Such a radiation then affects the external surface 10 of the photo-anode 1 on which WO.sub.3 (2) and FTO 4 are partially deposited. The photo-anode 1 separates the aqueous solution 6, on the outside of the device, from the internal part where the photovoltaic cells 7 are present.

[0059] The internal part of the device, facing towards the internal surface 11 of the glass substrate, contains the photovoltaic cells 7, preferably made of monocrystalline silicon, with interdigitated rear contacts and connected in series, preferably in a number equal to 4 modules, each with 64 mm.sup.2 of area.

[0060] Such cells are fed by the part of radiation 12 not absorbed by the photo-anode 1 and therefore transmitted towards the internal part of the device. Such modules, with respect to the cathode 5, increase by about 2V the potential of the photo-anode 1, to which they are connected by means of the electrical contact 13, ensuring maximum charge separation efficiency and maximum speed of photo-oxidation, direct or mediated by organic substances.

[0061] Finally, the photovoltaic cells 7 are connected to the metal cathode 5 by means of the electrical contact 14. Thereby, the voltage supplied allows the electrons, accumulated on the cathode contact during the redox processes, to be used for the production of hydrogen.

[0062] FIG. 3 shows the diagram of the cross-section of the device of the present invention. With respect to the photo-electrochemical cell in tandem configuration with the photovoltaic cells 7 described in FIG. 2, the complete device is described.

[0063] On the internal part of the device there is a printed circuit 15, or Printed Circuit Board (PCB). Such an element is in contact with the conductive FTO layer 4 of the photo-anode 1 and with the cathode 5, respectively by means of the contacts 16 and 17. The electronic circuit 15 directly integrates, on the surface 18, facing towards the photo-anode 1, the photovoltaic cells by creating the contacts 19 and 20 with the positive and negative contacts of the photovoltaic cells 7, respectively.

[0064] On the surface of the PCB 21 facing the cathode, the electronic components 22 are, instead, integrated, for driving the anode biasing capable of managing, in particular by means of the microprocessor, polarization and depolarization cycles necessary for restoring the photocatalytic efficiency of the photo-anode 1. Such a microprocessor is directly motorized by the photovoltaic cells 7 and suitably programmed to supply the required voltage in the times required.

[0065] The device is enclosed inside an external shell 23, preferably made of PVC, which encloses the entire tandem cell and the electronic circuit 15, leaving only the external surface 10 of the photo-anode 1 and the cathode 5 exposed to water.

[0066] The photovoltaic cells 7, the printed circuit 15 and the electronic components 22 must not be exposed to the aqueous solution 6, therefore, the device is protected by an encapsulant directly placed on the side 21 of the printed circuit which makes it impermeable to water, resistant to temperature and to corrosion.

[0067] FIG. 4 shows the depiction of the device 24 in the individual components, diagrammatically described in FIG. 3, highlighting the arrangement and connections between the various parts.

[0068] FIG. 5 shows the depiction of the modular system consisting of the individual devices 24, assembled next to one another in a ring configuration 25. Each ring 25 is then stacked with other rings in a cylindrical structure 26. Such a structure is inserted, together with the aqueous solution 6, in the gap of two surfaces, also of a cylindrical shape, one external 27 and one internal 28.

[0069] FIG. 6 shows the graph of the trend of the photocurrent produced by the photo-anode 1. Chrono-amperometry measurements were made, evaluating the photocurrent produced by the photo-anode as a function of time.

[0070] FIG. 7 shows the graph related to the COD abatement results obtained using the device of the present invention on 22.5 ml of a solution of atenolol 10 ppm and Na.sub.2SO.sub.4 0.7 mM in water.

Embodiments

[0071] The convenient aspect concerning the cylindrical shape of the modular system described in FIG. 5 and consisting of the devices of the present invention, is given by the fact that during the day a part of the cylindrical system is always facing the direct radiation from the sun.

[0072] In a particular embodiment, the system described in FIG. 5 may be arranged in an array of devices placed alongside one another, forming a flat surface enclosed between two glass or plexiglass surfaces, inside which the water to be treated 6 may flow, flowing on the front of the device where the photo-anode 1 is present and on the back of the device where the cathode 5 is located.

[0073] In this case, the flat surface may be advantageously inclined, and integrated with a suitable fixed support structure, favoring the exposure to the incident solar radiation of the photo-anode 1.

[0074] Alternatively, the support structure may be mobile and integrated with a solar tracking apparatus so as to keep the radiation exposure of the system of the present invention constant throughout the day.

[0075] If the system structure is cylindrical 26 as described in FIG. 5, the pumping system for the water recirculation may be placed outside the system or integrated inside the cylindrical structure itself, creating a more compact apparatus.

[0076] The pumping system may be powered from the outside, or receive power from a photovoltaic panel, making the entire apparatus, consisting of the system of the present invention and the pumping system for the water recirculation, fully self-powered.

[0077] The flow of the aqueous solution 6 recirculating inside the system may be regulated starting from the pumping system. In the case of laminar flow, the probability that the OH.sup.− radicals come into contact with the polluting substances is greater, making COD abatement faster.

[0078] In a particular embodiment, to allow the system to operate even at nighttime, the latter may be integrated with a LED lighting system arranged so as to irradiate the photo-anodes so as to allow continuous operation. Such a lighting system may be powered from the outside or it may advantageously utilize the energy collected during the day by a photovoltaic system possibly supporting the apparatus.

Industrial Use

[0079] In the light of the new regulations on sustainable water resources management, new techniques for the decontamination of wastewater are increasingly required, especially with regard to emerging pollutants, such as antibiotics, prescription and illegal drugs, and industrial chemicals.

[0080] This invention relates to a fully autonomous, sustainable, and industrially scalable system, capable of utilizing only solar energy and usable in support of current water treatment systems.

[0081] The catalyst used is characterized by a non-selective photocatalytic activity and, therefore, it may be used both for the treatment of water deriving from agricultural and industrial processes, of urban wastewater, and for the purification of groundwater.

[0082] The current passing through the two devices, used for the photocatalytic action and for the electrolysis of water, is a fraction of the current produced by the photovoltaic cells. The remaining current may be advantageously used to power a miniaturized electronic circuit which independently manages the polarization and depolarization cycles of the photo-anode, so as to always ensure an efficient operation and increase the useful life of the device.

[0083] The modular structure of the system makes it expandable according to the volume of water to be treated and adaptable to different types of water treatment plant.

[0084] A device which allows the pronounced photocatalytic action of WO.sub.3 with an integrated biasing system, enabling the generation of H.sub.2, while independently managing the depolarization cycles, is a technological advantage with wide application repercussions.