Photocatalytic titanium dioxide with multi-element impurities and production method

Abstract

A photocatalyst consists of TiO.sub.2 with impurities of metal elements from the d-block and the p-block of the periodic table. The method of production of the photocatalyst includes a) preparation of a mixture including titanium and elements or compounds, comprising at least one metal element or compound of a metal element of d-block, preferably manganese and a metal element or a compound of a metal element of the p-block, preferably aluminum, b) processing of the mixture and c) obtaining the photocatalyst containing TiO.sub.2 with impurities of at least one metal element from the d-block and at least one metal element from the p-block. When the photocatalyst is activated in the presence of solar radiation and inactivate bacteria resistant to antibiotics and microorganisms with different levels of resistance to stressful disinfection conditions, it removes degrading residual water resistance genes and decompose antibiotics from waste-water, effluent and other liquid wastes.

Claims

1. Method of production of a photocatalyst that includes (a) preparation of a mixture including titanium and elements or compounds, whereby the elements or compounds include i) at least one metal element of d-block of the periodic table or a compound of a metal element of d-block of the periodic table and ii) at least one metal element of p-block of the periodic table or a compound of a metal element of p-block of the periodic table, (b) treatment of the mixture after the addition of said elements or compounds and (c) obtaining the photocatalyst containing titanium dioxide and at least one metal element of d-block of the periodic table and at least one metal element of p-block of the periodic table.

2. Method according to claim 1, whereby the mixture is prepared from a titanium solution, a solution of an element of d-block of the periodic table and/or a solution of an element of p-block of the periodic table.

3. Method according to claim 1, whereby the mixture is prepared from a titanium solution, a solution of a metal element of d-block of the periodic table, the element of d-block within the solution of the metal element of d-block having a concentration within a range of 0.01 M to 0.1 M, and/or a solution of metal element of p-block of the periodic table, the element of p-block within the solution of the metal element of p-block the having a concentration within a range of 0.01 M to 0.1 M.

4. Method according to claim 1, whereby the mixture includes a solution of an aluminum salt solution and a manganese salt solution.

5. Method according to claim 4, whereby the mixture includes a solution of aluminum nitrate or/and a solution of acetic manganese, preferably a solution of aluminum nitrate and a solution of acetic manganese.

6. Method according to claim 1, whereby the treatment of the mixture includes production of powder and annealing of the powder in a temperature within a range.

7. Method according to claim 1, whereby the treatment of the mixture includes production of powder, and its subsequent drying and pulverization.

8. Method according to claim 1, whereby the mixture is a homogenous solution and the method includes the following steps: stirring of the homogeneous solution, adding an alkaline medium to obtain a gel with a pH higher than the pH of the homogeneous solution, maturation of the gel, separation of the gel to obtain powder, washing the powder, drying the powder, pulverizing of powder by milling or grinding, heat treatment of the powder.

9. Photocatalyst in the form of granules, which have titanium dioxide formations with impurities of a metal element of d-block of the periodic table and impurities of a metal element of the p-block of the periodic table.

10. Photocatalyst according to claim 9, consisting of granules with a granule size less or equal than about 20 .Math.m.

11. Photocatalyst according to claim 9 with impurities of at least one of the following elements: manganese, cobalt, iron, chromium, preferably manganese or cobalt.

12. Photocatalyst according to claim 9 with impurities of at least one of the following elements: indium, aluminum.

13. Photocatalyst according to claim 9, whereby the sum of the atomic ratio of the element of d-block of the periodic table and titanium and the atomic ratio of the element of p-block of the periodic table and titanium is equal or less than 10:100 or about 10:100.

14. Photocatalyst according to claim 13, whereby the sum of the atomic ratio of manganese and titanium and the atomic ratio of aluminium and titanium is equal or less than 4:100 or about 4:100.

15. Photocatalyst according to claim 9, whereby the impurity of the element of d-block of the periodic table is in the form of pure element and/or the impurity of the element of p-block of the periodic table is in the form of pure element.

16. Photocatalyst according to claim 9, whereby the impurity of the element of d-block of the periodic table is in the form of an oxide and/or the impurity of the element of p-block of the periodic table is in the form of an oxide.

17. Photocatalyst according to claim 9, which absorbs 20 % - 25 % of incident radiation with a wavelength between 450 and 500 nm.

18. Photocatalyst according to claim 9 embodied in a substrate or applied on a surface of a solid.

19. Method to activate a photocatalyst according to claim 18 with solar or artificial ultraviolet or visible radiation.

Description

[0034] Examples of invention are described with reference to FIGS. 1 to 17, whereby:

[0035] FIG. 1 shows the method of preparing a photocatalytic material according to the invention

[0036] FIG. 2 shows the discoloration of methylene blue in an aqueous solution in the presence of a photocatalyst that has been heat treated at 700° C., when exposed to ultraviolet (UV) radiation

[0037] FIG. 3 shows the discoloration of methylene blue in aqueous solution in the presence of the photocatalyst that has been heat treated at 400° C., when exposed to ultraviolet (UV) radiation

[0038] FIG. 4 shows the discoloration of methylene blue in an aqueous solution in the presence of the photocatalyst undergoing heat treatment at 700° C., when exposed to visible radiation.

[0039] FIG. 5 shows the discoloration of methylene blue in aqueous solution in the presence of the photocatalyst that has been heat treated at 400° C., when exposed to visible radiation.

[0040] FIG. 6 presents comparatively the activity of a photocatalyst according to the invention of a well-known photocatalyst under ultraviolet (UV) radiation

[0041] FIG. 7 presents comparatively the activity of a photocatalyst according to the invention of well-known photocatalysts under visible radiation

[0042] FIG. 8 shows an example of photocatalyst activity in disinfecting the Escherichia coli bacterium under sunlight

[0043] FIG. 9 shows an example of the activity of the photocatalyst in comparison with the commercial material P25 in the disinfection of the bacterium Enterococcus under sunlight

[0044] FIG. 10 shows an example of the structural characterization of a multi-element catalyst according to the invention at different concentrations and proportions of impurities that have undergone heat treatment at 700° C.

[0045] FIG. 11 shows an example of the structural characterization of a multi-element catalyst, according to the invention at different concentrations and proportions of impurities that have been heat treated at 400° C.

[0046] FIG. 12 shows the optical characterization - absorption of light - of a multi-element catalyst according to the invention at different concentrations and proportions of impurities that have been heat treated at 700° C.

[0047] FIG. 13 shows the optical characterization - absorption of light - of a multi-element catalyst according to the invention at different concentrations and proportions of impurities undergone heat treatment at 400° C.

[0048] FIG. 14 shows images of Scanning Electron Microscopy (SEM- scanning electron microscope) of multi-element catalysts in different concentrations and proportions of impurities undergone heat treatment at 700° C.

[0049] FIG. 15 presents an example of an Energy-Dispersive X-ray Spectroscopy (EDS) analysis of a multi-element catalyst, according to the invention under 700° C. heat treatment

[0050] FIG. 16 shows the reaction rate constant k for photocatalytic degradation under ultraviolet radiation for a number of different multi-element catalysts and different concentrations

[0051] FIG. 17 shows the reaction rate constant k for photocatalytic degradation under visible radiation for a number of different multi-element catalysts and different concentrations

[0052] In the Figures and description, when reference is made to a ratio of one or more elements to TiO.sub.2, the number indicates the ratio of the atoms or the numerator to the titanium atoms, e.g. 0.04 Al/TiO.sub.2 indicates an atomic ratio of Al to Ti atoms equal to 0.04 and 0.04 (Al-Mn)/TiO.sub.2 indicates an atomic ratio of Al and Mn atoms to Ti atoms equal to 0.04. Also, the ratio of atoms to the impurities, i.e. the admixtures, is indicated by the ratio of the atomic ratio of each admixture to the titanium, e.g. Al/Mn 0.1:0.1, denotes an Al ratio of atoms with respect to Ti atoms equal to 0.1 and a ratio of Mn atoms relative to Ti atoms equal to 0.1. The atomic ratio is referred to as a decimal number or % (concentration).

[0053] An embodiment of the invention, i.e. a photocatalytic material, which is titanium dioxide with a mixture of manganese and aluminum, was prepared from a mixture produced by the concatenation, i.e. co-precipitation, of manganese and aluminum in a titanium solution. An illustrative example of a method of invention using titanium sulphate includes the following steps (reference signs in bold refer to FIG. 1): [0054] providing a titanium sulphate solution, Titanium (II) Sulfate (TiSO.sub.4) [0055] adding manganese and aluminum solutions to the titanium sulphate solution, so as to obtain a mixture 1, [0056] stirring 2 of the mixture at room temperature for a period of between 2 and 24 hours, preferably for 3 hours [0057] adding 3 an alkaline solution, e.g. ammonia NH.sub.4OH, NH.sub.3, NaOH, to obtain a gel with a pH between 6 and 10, preferably between 6 and 8 [0058] stirring 4 the gel for a period of 12 to 48 hours, preferably about 24 hours to mature [0059] separation 5 of the gel using a centrifuge or by filtering to obtain powder [0060] rinsing 6 the powder with distilled water until the sulfur and ammonium ions are completely or almost completely removed [0061] drying 7 the powder [0062] pulverizing 8 the powder for example by crushing, ball-milling grinding etc., until fine-grained granules are obtained, e.g. with granule size less or equal than 20 .Math.m, and [0063] heat treatment, annealing 9 of the powder at a temperature ranging from 400° C. to 800° C., indicative about 700° C.

[0064] The process mentioned above is just one example of the invention. For example, other titanium sources can be used, e.g. titanium isopropoxide, titanium butoxide, or any other titanium solution. Also, instead of an aluminum solution and a manganese solution, other solutions can be used, a solution of a metal element of d-block and a solution of a metal element of p-block of the periodic table. In the example above, the concentration of aluminum in the aluminum solution is from about 0.01 M to about 10 M, preferably less than about 0.1 M. and the concentration of manganese in the manganese solution is from about 0.01 M to about 10 M, preferably less than about 0.1 M or about 0.1 M. Indicative only, the value of the concentration of nitric aluminum solution and the solution of acetic manganese solution is 0.1 M or about 0.1 M.

[0065] The above example of the invention method is presented schematically in FIG. 1.

[0066] The final product is in the form of powder or granules and is prepared by a method based on concatenation. Photocatalytic material, according to the invention, is a multi-element catalyst with transition metals from d-block of the periodic table, e.g. manganese, cobalt, iron, chromium, and a metal element of p-block of the periodic table, e.g. indium, aluminum at different concentrations and mixing ratios in the titanium oxide (titania). The impurities may be pure metals, in particular, when the concentration is less than 1%, that replace titanium and at higher concentrations the minerals or oxides, e.g. manganese oxide, in particular, when the concentration is higher than 1%.

[0067] In some examples of the invention the transition metal of d-block is manganese. In some other examples of the invention the element of the p-block of the periodic table is aluminum. Preferably the d-block transition metal is manganese and the p-block element of the periodic table is aluminum.

[0068] FIG. 10 and FIG. 11 show the structural characterization of a sample of multi-element catalysts according to the invention in different concentrations and proportions of impurities, which have undergone heat treatment at 400° C. (FIG. 11) and at 700° C. (FIG. 10). FIG. 10 shows that at low concentrations, the anatase structure is favored, while at high concentrations we have a mixture of anatase / rutile without the presence of peaks that correspond to oxides of aluminum or manganese respectively. FIG. 11 shows that heat treatment at low temperatures leads to the presence of materials with anatase structure which show wide peaks that indicate that the material has not crystallized at that temperature.

[0069] Respectively, FIG. 12 and FIG. 13 show the optical characterization - light absorption - of an example of multi-element catalysts according to the invention in different concentrations and proportions of impurities, which underwent annealling / heat treatment during their production at 400° C. (FIG. 13) and at 700° C. (FIG. 12). In both cases it is easy to see that we have an increase in absorption in the area of visible 400 nm - 800 nm, which indicates an introduction of the admixtures in the structure of titania.

[0070] FIG. 14 shows indicative images of SEM multi-element catalysts, granules and aggregates, at different concentrations and proportions of impurities under heat treatment at 700° C., before pulverizing.

[0071] FIG. 15 presents an EDS (Energy Dispersive Spectroscopy) elemental analysis of a multi-element catalyst, according to the invention for an indicative material with a 1% mixing concentration.

[0072] The photocatalyst produced according to the invention, is a material that may have various oxidative states, since aluminum has an oxidative state of 3.sup.+, manganese 2.sup.+ and titanium 4.sup.+.

[0073] FIG. 16 and FIG. 17 show the reaction rate constant k of photocatalytic reactions under ultraviolet radiation (FIG. 16) and under visible radiation (FIG. 17) for a number of different multi-element catalysts and different mixing concentrations. For each catalyst, the constant k is presented for atomic ratios of 0.04, 0.1, 0.2 and 1 in this order. The first bar to left shows the reaction rate constant k for the undoped catalyst. As can be seen from FIG. 16 and FIG. 17, the effectiveness of photocatalytic reactions depends on both the impurities and their concentrations on the photocatalyst, with the most effective combination for the examples of these Figures being the combination of manganese and aluminum impurities with atomic ratio Mn/AI:Ti equal to 0.04. Other combinations that have very good efficiency in ultraviolet and visible light are by mixing Al and Co with atomic ratios to titanium equal with 0.1 or In and Co with atomic ratios to titanium equal to 0.04. Combinations are also presented with excellent performance in ultraviolet or visible light, such as In with Fe or In with Cr.

[0074] An example of photocatalyst according to the invention contains titanium, manganese and aluminum. Manganese acts equally as an impurity and as a photosensitizer.

[0075] The photocatalyst is activated in the presence of sunlight or artificial light and is capable of breaking down organic and inorganic pollutants. For example, the photocatalyst can be used to decompose volatile organic compounds (VOCs) such as acetaldehyde (CH.sub.3CHO), formaldehyde (CH.sub.2O), benzene, toluene, etc. and volatile inorganic compounds such as NO.sub.x, CO.sub.2 in the presence of UV, visible and sunlight. In general, the photocatalyst can be used as received or incorporated into a structural material matrix (e.g. concrete, cement, mortar, putty, paint, etc.) or immobilized on or inside a solid surface (e.g. metal, wood, plastic, glass, cloth, fabric,paper, etc. The photocatalyst can be further used for air, water or liquid waste decontamination.

[0076] FIG. 2 to FIG. 5 show the results of methylene blue discoloration experiments in aqueous solution in the presence of a photocatalyst based on ISO - ISO 10678: 2010 - Determination of photocatalytic activity of surfaces in an aqueous medium by degradation of methylene blue (MB) - subjected to heat treatment at 700° C. (FIG. 2 and FIG. 4), or 400° C. (FIG. 3 and FIG. 5), when exposed to ultraviolet (UV) or visible radiation. The photocatalyst used was titanium dioxide with a mixture of manganese and aluminium with atomic ratio - Al-Mn:Ti between 0.01 and 1. FIG. 2 shows the photocatalytic activity of photocatalysts that have been heat treated at 700° C. during UV exposure, with the material showing the best photocatalytic activity of > 90% MB degradation by those with atomic ratio of 0.04. Correspondingly, FIG. 4 shows the photocatalytic activity of photocatalysts that have been heat treated at 700° C., during exposure to visible (Vis) radiation, with the material showing the best photocatalytic activity of > 90% MB degradation by those with atomic ratio of 0.04.

[0077] FIG. 8 shows the decomposition time of the bacterium E. coli inactivation after exposure to sunlight in the presence of a multi-element photocatalyst with an atomic ratio of aluminum to manganese of 1:1. FIG. 9 shows the time of degradation of Enterococci inactivation after exposure to sunlight in the presence of the same multi-element photocatalyst shown in FIG. 8, compared to the known commercial photocatalyst P25. As it is easily understood, the multi-element photocatalyst is much more active than the corresponding commercial one.

[0078] The application of examples of photocatalysts of the invention based on titania - multi-element co-doped titanium dioxide - show a catalyst high activity, e.g. decomposing a number of pollutants in water (azo dyes, phenols, pesticides), in the air (nitrogen oxides, aromatic hydrocarbons) and has significant activity in disinfecting and destroying bacteria (e-coli, Enterococci, etc.) and other microorganisms.

[0079] The presence of manganese and aluminum leads to a drastic improvement in the photocatalytic activity of the final multi-element catalyst under solar radiation in relation to materials containing only manganese or only aluminum impurity, i.e. admixture, as shown in FIG. 6 and FIG. 7. In these Figures, all three catalysts have the same atomic ratio, equal to 0.04, of impurities to titania. Their activity under sunlight makes them particularly suitable for outdoor applications. They can be used e.g. for water purification and in powder form in surface coatings for external use.