Agrochemical method

Abstract

A method of increasing growth of a plant, the method comprising applying a titanium dioxide photocatalyst to a surface of the plant and converting nitrogen monoxide or nitrogen dioxide to nitrate on the surface of the plant. The titanium dioxide may be particulate with a mean diameter greater than 1 micron, preferably greater than 10 microns. The titanium dioxide photocatalyst may be doped with manganese, calcium, magnesium, zinc, nitrogen, or potassium. Also claimed is the use of titanium dioxide to improve plant physiology, crop yields or characteristics, to increase the nitrogen content of plants and for removing nitrogen monoxide or dioxide from the atmosphere.

Description

The present invention relates to a method of improving plant growth using a titanium dioxide photocatalyst, a titanium dioxide photocatalyst, an agrochemical composition 5 comprising a titanium dioxide photocatalyst, a process for preparing a titanium dioxide photocatalyst and / or an agrochemical composition comprising a titanium dioxide photocatalyst, and the use of a titanium dioxide photocatalyst. Background to the Invention 10 Managing nitrogen pollution is a significant focus of governments and companies across the world at least because (i) source nitrogen pollution is known to damage the natural environment, for example via eutrophication (as is the case with over fertilisation in agriculture); and (ii) because atmospheric nitrogen pollution is a known 15 contributor to global warming, acid rain, and human and animal conditions / diseases (as is the case with nitrous oxides formed in combustion). However, nitrogen pollution is a constant product of industry and agriculture and has traditionally been difficult to address using market forces alone. As such, governments have enacted legal instruments that are directed at encouraging technologies that limit the amount of 20 nitrogen pollution. In industry, efforts have traditionally focused on reducing the total amount of nitrous oxides emitted. For example, technologies have been developed that lead to cleaner combustion and / or reduce nitrous oxides from the waste gases of combustion 25 chambers. Cleaner energy sources are also being heavily invested in for the same reasons. However, these technologies and energy sources are currently not effective enough to reduce the nitrous oxide output of industry to acceptable levels. In agriculture, efforts have focused on reducing fertiliser application, developing less 30 harmful fertilisers, growing perennial crops instead of annual crops, growing winter cover crops, developing expertise regarding the timing of fertiliser application, and introducing buffer zones near know pollution areas. These measures have all been shown to have some impact on reducing the effect of nitrogen pollution in the natural environment. However, they are expensive to implement and often have drawbacks 35 associated with them (such as reduced crop yield and / or crop quality). As the population of the world is estimated to increase to approximately 9.8 billion people by the year 2050, such drawbacks are often not economically feasible. In an emerging field, catalysts have been investigated with the aim of reducing 5 atmospheric nitrogen content. For example, catalysts are known that can convert nitrous oxides to nitrate. These catalysts have been used in paints to coat walls and allegedly reduce nitrous oxide in some conditions (for example, many of these catalyst only work in specific lighting conditions). However, these kinds of products are merely changing one problem for another, i.e. converting atmospheric nitrogen pollution 10 (atmospheric nitrous oxide) into a source nitrogen pollution (nitrate fixed to wall which is then washed off into the local water system). As such, these types of technologies are interesting but cannot significantly address the environmental problems associated with nitrogen pollution. It is coincidental that some catalysts have also been used in agriculture, for example for their antimicrobial properties when applied to the roots or 15 seeds of a plant. Description of the Invention The present invention relates to a method of improving plant growth using a titanium 20 dioxide photocatalyst, a titanium dioxide photocatalyst, an agrochemical composition comprising a titanium dioxide photocatalyst, a process for preparing a titanium dioxide photocatalyst and / or an agrochemical composition comprising a titanium dioxide photocatalyst, and the use of a titanium dioxide photocatalyst. 25 The present invention is a complete and entirely sustainable approach that both reduces atmospheric nitrogen pollution and improves the growth of a plant (thereby reducing the amount of fertiliser that is required and reducing the deleterious effects associated with such fertiliser application). 30 Figure 1 shows the Raman spectra of pure titanium dioxide and of titanium dioxide photocatalysts according to some embodiments of the present invention. Figures 2A-D show the efficacy of a titanium dioxide photocatalyst according to some embodiments of the present invention under visible light and under UV light. Figure 3 shows the irradiance spectrum of the fluorescent light source. Figures 4-9 show the efficacy of titanium dioxide photocatalysts according to some embodiments of the present invention. 5 In one aspect, the invention provides a method of improving plant growth. The method comprises applying a titanium dioxide photocatalyst to a surface of a plant, and converting nitrogen monoxide or nitrogen dioxide to nitrate on the surface of the plant. 10 In one aspect, the invention provides a method of increasing growth of a plant, the method comprising applying a titanium dioxide photocatalyst to a surface of the plant, and converting nitrogen monoxide or nitrogen dioxide to nitrate on the surface of the plant. 15 In one aspect, the invention provides a method of improving crop yield / growth comprising applying a titanium dioxide photocatalyst to a surface of a plant, contacting the titanium dioxide photocatalyst with nitrogen monoxide or nitrogen dioxide so as to convert nitrogen monoxide or nitrogen dioxide to nitrate, and the nitrate being absorbed by the surface of the plant. 20 In one aspect, the invention provides the use of a titanium dioxide photocatalyst for improving crop yield / growth by applying a titanium dioxide photocatalyst to a surface of a plant. 25 In one aspect, the invention provides an agrochemical composition comprising a particulate titanium dioxide photocatalyst, wherein the particulate titanium photocatalyst has a mean diameter of greater than about 2 pm, preferably greater than about 5 pm, more preferably greater than about 8 pm. 30 In one aspect, the invention provides a method of supplying nitrate to the surface of a plant using a doped photocatalyst. In one aspect, the invention provides the use of a doped photocatalyst to produce nitrate on the surface of plants. In one aspect, the invention provides a method of converting NOx to nitrate on the surface of a plant to improve growth. In one aspect, the invention provides a method to produce nitrate on a plant surface by 5 depositing a doped photocatalyst which converts atmospheric nitrous oxides (NOx) to nitrate. In one aspect, the invention provides the use of a double doped photocatalyst deposited on the surface of plants to convert atmospheric NOx into nitrate available for plant 10 uptake. In one aspect, the invention provides the use of a double doped photocatalyst deposited on the surface of plants to convert atmospheric NOx into nitrate available / absorbed as plant feed. 15 In one aspect, the invention provides a method to generate nitrate from atmospheric NOx using a double doped photocatalyst comprising of titanium dioxide and the deposition of the nitrate on the plant’s surface to utilise it as building block / feed / for growth. 20 In one aspect, the invention provides a method to provide a continuous supply of nitrate to plants by spraying a double doped photocatalytic material comprising of Ti02 to increase plant growth. 25 Plant growth encompasses (i) the amount of plant growth and (ii) the quality of plant growth. For example, plant growth may encompass plant yield (e.g. natural plant weight or dry plant weight) and / or the content of the plant (e.g. elemental composition, protein content, moisture content, and / or Hagberg content). 30 In one embodiment, the method comprises, contacting the titanium dioxide photocatalyst with nitrogen monoxide or nitrogen dioxide to convert nitrogen monoxide or nitrogen dioxide to nitrate. In one embodiment, the nitrate is absorbed by the plant, preferably by the surface of 35   the plant. The method of the invention therefore provides the plant with a usable source of nitrogen. In one embodiment, the method comprises spraying the titanium dioxide photocatalyst onto a surface of a plant, e.g. by means of an electrostatic or other conventional sprayer. In other embodiments, the method comprises applying the titanium dioxide 5   photocatalyst onto a surface of a plant, e.g. by fumigation or by dusting. In some embodiments, the surface of the plant includes the foliage and / or leaves and / or stems of the plant. The surface of the plant does not include the roots and or seeds of a plant. 10 In one embodiment, the nitrogen monoxide or nitrogen dioxide is atmospheric nitrogen monoxide or nitrogen dioxide. The invention therefore provides a method of reducing the concentration of atmospheric nitrogen monoxide or nitrogen dioxide in an environment, preferably an environment with a high concentration of nitrogen 15 monoxide or nitrogen dioxide. Such an environment may be near a source of nitrogen monoxide or nitrogen dioxide production, such as a road, port, or factory. In one embodiment, the method comprises contacting the titanium dioxide photocatalyst with rainwater / water / dewthat is present on the surface of the plant. 20   Without wishing to be bound by theory, it is understood that the rainwater / water / dew that collects on the surface of the plant contributes to efficient nitrate production / conversion. It is also understood that the rainwater / water / dew solubilises the nitrate so that it enhances its availability for uptake by the plant. 25 In one embodiment, the nitrate is washed from the titanium dioxide photocatalyst by application of a water source to the surface of the plant. The water source may be naturally applied (i.e. rain) or artificially applied (i.e. involving human influence such as irrigation or other watering techniques). Washing of the nitrate from the titanium dioxide photocatalyst allows for the titanium dioxide photocatalyst to be partially or 30 fully reactivated. The method of the invention therefore provides a time and cost effective way of improving crop yield / crop growth because few (preferably only one or two) applications to the plant is required. In one embodiment, the method comprises providing the plant with nitrate for a period 35 of at least about 30 days, preferably at least about 45 days, more preferably at least about 60 days. The method of the invention therefore provides a method of improving crop yield / crop growth over an extended period of time, preferably over multiple growth stages. In one embodiment, the method comprises applying the titanium photocatalyst once 5 per 10 days / growing cycle, preferably once per 30 days / growing cycle, more preferably once per 60 days / growing cycle. When applied to the plant, the titanium dioxide photocatalyst may be applied in amount from about 50 g / ha (hectare) to about 80 g / ha, from about 100 g / ha to about 10   250 g / ha, or from about 200 g / ha to about 500 g / ha. For example, the titanium dioxide photocatalyst maybe applied in an amount of about 400 g / ha or about 500 g / ha. In some embodiments, plant growth includes plant weight, ear weight, flag leaf weight, 15 total yield or a mixture thereof. In some embodiments, the method comprises improving plant growth by between about 0.1 % and about 20 %, or between about 1 % and about 15 %, or between about 5 % and about 10 %. 20 Photocatalyst In one embodiment, the titanium dioxide photocatalyst is a particulate titanium dioxide photocatalyst. In one embodiment, the particulate titanium dioxide photocatalyst has a 25 mean diameter greater than about 1 pm, about 2 pm, about 5 pm, about 8 pm or about 10 pm. Preferably, the particulate titanium dioxide photocatalyst has a mean diameter greater than about 8 pm or about 10 pm. In some embodiments, the titanium dioxide photocatalyst of the invention will not be absorbed by the plant. 30 In some embodiments, the particulate titanium dioxide photocatalyst has a mean diameter of no more than about 25 pm, about 20 pm, about 15 pm, or about 10 pm. In some embodiments, the titanium dioxide photocatalyst of the invention will not easily be washed off the plant. 35 In some embodiments, the particulate titanium dioxide photocatalyst has a mean diameter from about 2 pm or about 5 pm to about 10 pm or about 15 pm. Preferably, the particulate titanium dioxide photocatalyst has a mean diameter from about 2 pm to about 20 pm. Preferably, the particulate titanium dioxide photocatalyst has a mean diameter from about 2 pm to about 15 pm. More preferably, the particulate titanium dioxide photocatalyst has a mean diameter from about 2 pm to about 10 pm. More 5 preferably, the particulate titanium dioxide photocatalyst has a mean diameter from about 2 pm to about 8 pm In some embodiments, the titanium dioxide photocatalyst of the invention will not be absorbed by the plant and will not easily be washed off the plant. 10 In one embodiment, at least about 90 vol. % of the particulate titanium dioxide photocatalyst has a diameter of less than about 35 pm, about 30 pm, about 25 pm, about 20 pm, about 15 pm, about 10 pm, or about 8 pm. Preferably, at least about 90 vol. % of the particulate titanium dioxide photocatalyst has a diameter of less than about 10 pm, more preferably less than about 8 pm. 15 In one embodiment, at least about 90 vol. % of the particulate titanium dioxide photocatalyst has a diameter of greater than about 0.1 pm, about 0.5 pm, about 1 pm, or about 2 pm. Preferably, at least about 90 vol. % of the particulate titanium dioxide photocatalyst has a diameter of greater than about 1 pm, more preferably greater than 20 about 2 pm. In one embodiment, at least about 90 vol. % of the particulate titanium dioxide photocatalyst has a diameter of less than about 30 pm and at least about 90 vol. % of the particulate titanium dioxide photocatalyst has a diameter of greater than about 0.1 25 pm. In one embodiment, at least about 90 vol. % of the particulate titanium dioxide photocatalyst has a diameter of less than about 25 pm and at least about 90 vol. % of the particulate titanium dioxide photocatalyst has a diameter of greater than about 0.5 pm. Preferably, at least about 90 vol. % of the particulate titanium dioxide photocatalyst has a diameter of less than about 20 pm and at least about 90 vol. % of 30 the particulate titanium dioxide photocatalyst has a diameter of greater than about 1 pm. Preferably, at least about 90 vol. % of the particulate titanium dioxide photocatalyst has a diameter of less than about 15 pm and at least about 90 vol. % of the particulate titanium dioxide photocatalyst has a diameter of greater than about 2 pm. Preferably, at least about 90 vol. % of the particulate titanium dioxide 35   photocatalyst has a diameter of less than about 10 pm and at least about 90 vol. % of the particulate titanium dioxide photocatalyst has a diameter of greater than about 2 |um. Preferably, at least about 90 vol. % of the particulate titanium dioxide photocatalyst has a diameter of less than about 8 pm and at least about 90 vol. % of the particulate titanium dioxide photocatalyst has a diameter of greater than about 2 pm. 5 According to some embodiments, it is possible to prepare a preferred suspension for spraying onto a plant, the suspension provides a titanium dioxide photocatalyst with a maximum surface area (to provide a highest photocatalytic activity) without being absorbed by the plant or being easily washed off. 10 In one embodiment, the titanium dioxide photocatalyst is a powder. In one embodiment, at least about 70 vol. % of the particulate titanium dioxide photocatalyst has a diameter of about 1 pm, about 2 pm, about 5 pm, about 8 pm, or about 10 pm. Preferably, at least about 80 vol. %, about 90 vol. %, about 95 vol. % or 15 about 98 vol. % of the particulate titanium dioxide photocatalyst has a diameter of about 1 pm, about 2 pm, about 5 pm, about 8 pm, or about 10 pm. In one embodiment, at least about 95 vol. % of the particulate titanium dioxide photocatalyst has a diameter of about 10 pm. In one embodiment, at least about 98 vol. % of the particulate titanium dioxide photocatalyst has a diameter of about 10 pm. 20 In one embodiment, at least about 70 vol. % of the particulate titanium dioxide has a diameter between about 2 pm and about 10 pm. In one embodiment, at least about 80 vol. % of the particulate titanium dioxide has a diameter between about 2 pm and about 10 pm. In one embodiment, at least about 90 vol. % of the particulate titanium dioxide 25 has a diameter between about 2 pm and about 10 pm. In one embodiment, at least about 95 vol. % of the particulate titanium dioxide has a diameter between about 2 pm and about 10 pm. In one embodiment, at least about 98 vol. % of the particulate titanium dioxide has a diameter between about 2 pm and about 10 pm. 30 In one embodiment, the titanium dioxide photocatalyst has a specific surface area of greater than about 3000 m2, about 5000 m2, about 7000 m2, or about 10,000 m2 per 500 g. In one embodiment, the titanium dioxide photocatalyst comprises a crystalline phase 35   and / or a non-crystalline phase. Preferably, the titanium dioxide photocatalyst comprises a crystalline phase, i.e. the titanium dioxide photocatalyst comprises crystalline titanium dioxide. For example, the titanium dioxide photocatalyst comprises anatase titanium dioxide and / or rutile titanium dioxide. Preferably, the titanium dioxide photocatalyst comprises anatase titanium dioxide and rutile titanium dioxide. 5 In one embodiment, the ratio of rutile titanium dioxide to anatase titanium dioxide in the titanium dioxide photocatalyst is between about 1:3 and about 1:5. Preferably, the ratio of rutile titanium dioxide to anatase titanium dioxide in the titanium dioxide photocatalyst is about 1:3, about 1:4 or about 1:5, more preferably about 1:3. 10 In one embodiment, the titanium dioxide photocatalyst is a doped titanium dioxide photocatalyst. For example, the titanium dioxide photocatalyst is doped with at least one dopant selected from the group consisting of alkali metals, alkaline earth metals, and transition metals. When the titanium dioxide photocatalyst is doped with two or more dopants, each dopant may be individually selected from the group consisting of 15 alkali metals, alkaline earth metals, and transition metals, preferably from the group consisting of alkaline earth metals and transition metals. When the titanium dioxide photocatalyst is doped with two dopants, one dopant maybe an alkaline earth metal and the other dopant may be a transition metal. The titanium dioxide photocatalyst of the invention has been shown to be particularly effective conversion of nitrogen 20 monoxide or nitrogen dioxide to nitrate in sunlight. For example, the titanium dioxide photocatalyst is doped with at least one of the following dopants Mn, Ca, Mg, Zn, N, Mg and K, preferably Mn, Ca, Mg, Zn, and K. In one embodiment, the titanium dioxide photocatalyst is doped with at least two of the 25 following dopants Mn, Ca, Mg, Zn, N, Mg and K, preferably Mn, Ca, Mg, Zn, and K. Preferably, the titanium dioxide photocatalyst is doped with Mn and Ca. When the titanium dioxide photocatalyst is a doped with two dopants, the ratio of a first of the two dopants to a second of the two dopants is between about 10:1 and about 30   1:10, preferably between about 7:1 and about 1:7, preferably between about 5:1 and about 1:5, preferably between about 2:1 and about 1:2. In one embodiment, the ratio of a first of the two dopants to a second of the two dopants is between about 7:1 and about 1:1. In one embodiment, the ratio of a first of 35 the two dopants to a second of the two dopants is between about 5:1 and about 1:1. In one embodiment, the ratio of a first of the two dopants to a second of the two dopants is between about 3:1 and about 1:1. Preferably, the ratio of a first of the two dopants to a second of the two dopants is about 5:1, about 3:1, or about 1:1, more preferably about 3:1- 5 In one embodiment, the titanium dioxide photocatalyst comprises the dopant in an amount between about 0.01 wt.% and about 1 wt.%, or between about 0.05 wt.% and about 0.5 wt.%, or between about 0.075 wt.% to about 0.25 wt.% relative to the total weight of the titanium dioxide photocatalyst. Preferably, the titanium dioxide photocatalyst comprises the dopant in an amount between about 0.075 wt. % to about 10   0.25 wt.% relative to the total weight of the titanium dioxide photocatalyst. In one embodiment, the titanium dioxide photocatalyst comprises the dopant in an amount about 0.075 wt.%, about 0.1 wt.% or about 0.25 wt.% relative to the total weight of the titanium dioxide photocatalyst. Preferably, the titanium dioxide 15 photocatalyst comprises the dopant in an amount about 0.1 wt.% relative to the total weight of the titanium dioxide photocatalyst. In one embodiment, the titanium dioxide photocatalyst is catalytically active when exposed to light with a wavelength between about 300 and about 800 nm, preferably 20 between about 300 and about 700 nm, about 300 and about 600 nm, about 300 and about 550 nm, about 300 and about 520 nm, or about 350 and about 500 nm. Preferably, the titanium dioxide photocatalyst is catalytically active when exposed to light with a wavelength between about 430 and about 550 nm. 25 In one embodiment, the titanium dioxide photocatalyst has a maximum absorbance at about 400 nm, about 450 nm or about 500 nm. Preferably, the titanium dioxide photocatalyst has a maximum absorbance at about at about 450 nm. When the titanium dioxide photocatalyst is catalytically active or has a maximum 30 absorbance as defined in relation to some embodiments, the titanium dioxide photocatalyst is particularly effective at supplying the plant with nitrate. Without wishing to be bound by theory, it is believed that this is because the catalytic activity corresponds to daytime environmental conditions (when the ambient outdoor light and NOx concentrations are most suitable for efficient nitrate production). 35 In one embodiment, the titanium dioxide photocatalyst is not comprised in a separate physical body or a porous body. For example, the titanium dioxide photocatalyst is not comprised in a zeolite or other porous body. The titanium dioxide photocatalyst of the invention may therefore be in direct contact with the plant surface. As such, the nitrate 5 produced is in close proximity (e.g. in direct contact) with the plant surface which aids in uptake of the nitrate. Agrochemical Composition 10 In one embodiment, the titanium dioxide photocatalyst is part of an agrochemical composition. For example, an agrochemical composition comprising the titanium dioxide photocatalyst dissolved in or suspended in an aqueous or non-aqueous medium. Preferably, the medium is water based. More preferably, the medium is water. 15 In some embodiments, the composition comprises an active ingredient selected from the group consisting of harpin, systemin, oligouronides, chitosan, carbanilide, calreticulin, flagellin and P-glucan-containing elicitors. In some embodiments, the composition comprises other conventional agrochemical 20 ingredients such as agrochemical nutrients (such as macro and micro nutrients), and agro-chemically acceptable excipients. Suitable macro nutrients include but are not limited to sources of nitrogen, phosphorous, potassium, sulphur and calcium. Suitable micro nutrients include but are not limited to sources of manganese, boron and zinc. Others include cobalt, chromium, fluoride, iodine, molybdenum, zinc, manganese, 25 selenium and others. Preferably, the composition comprises manganese, zinc and / or molybdenum. In some embodiments, the composition comprises micronutrients, each micronutrient being comprised in amount from 0.01 % to about 5 % w / w, preferably in an mount 30 between about 0.05 % and about 2.5 % w / w. In some preferred embodiments, the composition comprises micronutrients, each micronutrient being comprised in an amount of about 0.07 %, about 1.3 %, or about 2.4 % w / w. In some embodiments, the composition comprises one or more agrochemically 35 acceptable excipients. Examples of such components include water, amino acids, vitamins, seaweed and other plants extracts, weak acids, plant oils, essential oils, metabolic stimulating agents, emulsifiers, thickeners, colouring agents, suspension agents, dispersion agents, carriers or excipients and wetting agents. As used herein, the expression "weak acid" refers to a weak organic acid such as acetic 5 acid, citric acid, humic acid, fulvic acid or propanoic acid; preferably the weak acid is citric acid. In a further aspect, the invention provides an agrochemical composition comprising a combination of (i) and (ii) as defined herein, and optionally one or more agrochemical 10 excipients. If required, an emulsifier may be employed in the composition. An emulsifier may be employed to improve the dissolvability of a component. Suitable emulsifiers for use in the compositions of the present invention include any known agriculturally acceptable 15 emulsifier. In particular, the emulsifier may comprise a surfactant such as: fatty alcohol polyethylene glykol ether, typically alkylaryl sulphonates, ethoxylated alcohols, polyalkoxylated butyl ethers, calcium alkyl benzene sulphonates, polyalkylene glycol ethers and butyl polyalkylene oxide block copolymers as are known in the art. Nonyl phenol emulsifiers such as Triton N57(TM) are particular examples of emulsifiers, 20   which may be used in the compositions of the invention, as are polyoxyethylene sorbitan esters such as polyoxyethylene sorbitan monolaurate (sold by ICI under the trade name "Tween(TM)"). In some instances, natural organic emulsifiers maybe preferred, particularly for organic farming applications. Coconut oils such as coconut diethanolamide is an example of such an compound. Palm oil products such as lauryl 25 stearate may also be used. Suitable emulsifiers include commercially available sorbitol products such as Tween® 20, 40, and 60. In some embodiments, the composition comprises a growth regulator. In one embodiment, the growth regulator, or plant growth regulator, is chosen from the group 30   of plant hormones, or chemical compounds with analogous activity. Suitable examples of such compounds are auxins, cytokines, gibberlins, ethylene precursors (like ethephon), or abscisic acid. In another embodiment, the growth regulator, or plant growth regulator, is a growth inhibitor, like for example chlormequat or mepiquat chloride, certain triazole or triazole like compounds, or prohexadione, daminozide, 35 trinexapac ethyl type compounds, or ethylene inhibitors. Suitable auxins include natural or synthetic chemicals that behave like the naturally occurring auxins produced by plant enzyme systems, and the term "auxin" and "auxins" as used herein refers to such compounds in natural and synthetic form. Indoleacetic acids, indol- 3 -butyric acid (3-BA); naphthaleneacetamide; 2 methyl-1- 5 naphthaleneacetic acid and 2-methyl-l-naphthylacetamide have hormonal activity and may be substituted for the naturally occurring auxins. It may be useful to have metal ions present with the auxins, such as for example zinc or manganese. In preferred embodiments, the auxin employed is selected from the group consisting of 3-indolebutyric acid, 3-indoleacetic acid, i-naphthylacetic acid, 3-indolebutyric acid, and 10 salts and esters thereof. Preferably, the metal ions required for a good activity are supplied together with the auxin. Suitable cytokinins are a class of plant regulation substances (phytohormones) that promote cell division, or cytokinesis, in plant roots and shoots. There are two types of 15 cytokinins: adenine-type cytokinins represented by kinetin, zeatin, and 6-benzylaminopurine (also referred to as BAP, 6-BAP, or 6-benzyladenine), and phenylurea-type cytokinins like diphenylurea (DPU), diphenylthiourea (DPTU) and thidiazuron (TDZ). In preferred embodiments the cytokinin is selected from the group consisting of kinetin (synthetic or derived from seaweed), 6-BAP, l-(2-chloropyridin-4-20 yl)-3-phenylurea (CPPU), and TDZ. In some embodiments, the composition comprises sodium naphthalene sulphonate formaldehyde condensate, a silicon based antifoaming agent, ethoxylated alcohol, a cocoyl hydroxyethyl imidazoline based amphoteric surfactant, xanthan gum or a 25 mixture thereof. The formulations according to the invention can be applied either as such or after prior dilution with water, or other diluents, i.e. for example, as emulsions, suspensions, solutions, or aerosols. 30 In a particular preferred embodiment, the formulation is in the form of a concentrate which is diluted with solvent, e.g. water, prior to the actual application. In another embodiment, the formulation is in the form of a diluted formulation containing additional solvent, e.g. water, but retaining the same ratio / proportion of active 35 ingredients found in the concentrate. In some embodiments, the concentrate is a suspension. The concentration of the titanium dioxide photocatalyst may be from about i g / litre (g / 1) to about 1000 g / 1, from about 100 g / 1 to about 700 g / 1, from about 200 g / 1 to about 500 g / 1. For example, the concentration of the titanium dioxide photocatalyst 5 maybe about 100 g / 1, about 200 g / 1, about 300 g / 1, about 400 g / 1, or about 500 g / 1. When applied to the plant, the composition may be applied in amount from about 0.1 1 / ha (hectare) to about 1001 / ha, from about 0.51 / ha to about 101 / ha, or from about 1 1 / ha to about 51 / ha. For example, the titanium dioxide photocatalyst maybe applied in 10 an amount of about 11 / ha or about 21 / ha. In one embodiment, the agrochemical composition is a foliar agrochemical composition. 15  Photocatalyst per se In a second aspect, the invention provides a titanium dioxide photocatalyst as described herein. 20 Agrochemical Composition per se In a third aspect, the invention provides an agrochemical composition as described herein. 25 Process In a fourth aspect, the invention provides a process of preparing a titanium dioxide photocatalyst according to the second aspect and / or an agrochemical composition according to the third aspect. 30 In one embodiment, the process comprises providing a raw material comprising or consisting of titanium dioxide; and processing the raw material to provide a titanium dioxide photocatalyst. 35 In one embodiment, processing the raw material to provide a titanium dioxide photocatalyst comprises: Adding a source of dopant to the raw material to form a first processed material; Blending and / or grinding the first processed material to form a second processed material; Heating the second processed material to form the titanium dioxide catalyst. 5 In one embodiment, the raw material is processed before a source of dopant is added thereto, for example by grinding, milling or sieving. In one embodiment, this processing results in the desired particle size, for example the desired mean diameter. 10 In one embodiment, the titanium dioxide photocatalyst is further processed, for example by grinding, milling or sieving. In one embodiment, this processing results in the desired particle size, for example the desired mean diameter. In one embodiment, the raw material comprises or consists of anatase and / or rutile 15 titanium dioxide. Preferably, the raw material comprises between about 65% and about 95% anatase titanium dioxide, or between about 70% and about 90% anatase titanium dioxide, or between about 80% and about 85% anatase titanium dioxide. Preferably, the raw material comprises between about 1% and about 35% rutile titanium dioxide, or between about 10% and about 30% rutile titanium dioxide, or between about 15% and 20   20% rutile titanium dioxide. In one embodiment, the raw material is particulate and has mean diameter of about 2 pm or about 10 pm. Preferably, about 70, 80, 90, 95 or 98 vol. % of the raw material has a mean diameter of about 2 pm or about 10 pm. 25 In one embodiment, the source of dopant is a source of one or more selected from the group consisting of alkali metals, alkaline earth metals, and transition metals, preferably from the group consisting of alkaline earth metals and transition metals. More preferably, the source of dopant is a source of an alkaline earth metal and a 30 transition metal. In one embodiment, the source of dopant is a source of at least one of the following dopants Mn, Ca, Mg, Zn, N, Mg and K, preferably Mn, Ca, Mg, Zn, and K. In one embodiment, the source of dopant is a source of at least two of the following 35 dopants Mn, Ca, Mg, Zn, N, Mg and K, preferably Mn, Ca, Mg, Zn, and K. Preferably, the source of dopant is a source of Mn and Ca. When the source of dopant is a source of at least two of the following dopants Mn, Ca, Mg, Zn, N, Mg and K, the ratio of a first dopant to a second dopant is between about 1:1 and about 9:1, preferably between about 1:1 and about 7:1, or between about 1:1 and 5:1, 5 or between about 1:1 and 3:1. For example, the ratio of a first dopant to a second dopant is about 5:1, about 3:1, or about 1:1, more preferably about 3:1. In one embodiment, the source of dopant comprises a salt of an alkali metal, alkaline earth metal, a transition metal, or a mixture thereof. For example, the source dopant 10 may comprise a nitrate salt, carbonate salt, sulphate salt, a chloride salt, or a mixture thereof. Preferably, the source of dopant comprises a carbonate salt and / or a sulphate salt. For example, the source of dopant may comprise calcium carbonate and / or manganese sulphate. Preferably, the source of dopant comprises calcium carbonate and manganese sulphate. 15 In one embodiment, source of dopant is a particulate source of dopant. Preferably, the mean particle size of the source of dopant is between about 0.01 pm and about 25 pm, or about 0.1 pm and about 10 pm. 20 The source of dopant may be added to the raw material in an amount of about 0.01 wt.% to about 5 wt.% relative to the raw material. Preferably, the dopant is added to the raw material in an amount of about 0.01 wt.% to about 2 wt.%, or about 0.2 wt.% to about 1 wt.%, or about 0.5 wt.% to about 1 wt.% relative to the raw material. 25 In one embodiment, one or more solvents is added to the first processed material, before or during the blending and / or grinding. For example, hydrogen peroxide, potassium hydroxide and / or sulphuric acid maybe added to the first processed material. 30 In one embodiment, blending and / or grinding the first processed material to form a second processed material is carried out using a ball mill, high shear mixer, a pin mill or a mix thereof. Preferably, the blending and / or grinding is first carried out using a ball mill and secondly by a pin mill. Without wishing to be bound by theory, it is understood that ball milling allows the dopant to infuse into the titanium dioxide 35 structure. Preferably, the blending and / or grinding is carried out for between about 5 minutes and about 90 minutes, preferably between about 30 minutes and about 90 minutes, more preferably between about 60 minutes and about 90 minutes. 5 In some embodiments, the first processed material is checked for content uniformity during the blending and / or grinding. In some embodiments, the blending and / or grinding is performed until the mixture has a content uniformity of about 90%. In one embodiment, heating the second processed material to form the titanium 10 dioxide catalyst comprises heating the second processed material at a temperature of about 400 °C to about 1000 °C, preferably at a temperature of about 400 °C to about 800 °C or about 500 °C to about 700 °C. Preferably, heating the second processed material to form the titanium dioxide catalyst comprises heating the second processed material at a temperature of about 400 °C, about 500 °C, about 600 °C, about 700 °C, 15 or about 800 °C. In one embodiment, the second processed material is heated for between about 1 hour and about 6 hours, preferably between about 2 hours and about 5 hours, or between about 3 hours and about 4 hours. In one embodiment, the second processed material is 20 heated in a kiln (e.g. a rotary or non-rotatory kiln). In one embodiment, the titanium dioxide photocatalyst is further processed, for example by grinding or milling, to reduce the particle size of the titanium dioxide photocatalyst. This may, for example, be carried out using a ball mill, high shear mixer, 25 or a pin mill. In one embodiment, the particulate titanium dioxide photocatalyst has a mean diameter greater than about 1 pm, about 2 pm, about 5 pm, about 8 pm or about 10 pm. Preferably, the particulate titanium dioxide photocatalyst has a mean diameter greater 30 than about 2 pm or about 5 pm. Preferably, the particulate titanium dioxide photocatalyst has a mean diameter greater than about 8 pm or about 10 pm. In some embodiments, the titanium dioxide photocatalyst of the invention will not be absorbed by the plant. 35 In some embodiments, the particulate titanium dioxide photocatalyst has a mean diameter of no more than about 25 pm, about 20 pm, about 15 pm, about 10 pm, or about 8 Jim. In some embodiments, the titanium dioxide photocatalyst of the invention will not easily be washed off the plant. In one embodiment, the titanium dioxide photocatalyst is added to a liquid to form a 5 suspension so that the concentration of the photocatalyst is between about 200 g / 1 and about 700 g / 1 (preferably about 500 g / 1). The suspension can therefore be sprayed on a plant surface. Product by Process 10 In a fifth aspect, the invention provides a titanium dioxide photocatalyst according to the second aspect and / or an agrochemical composition according to the third aspect produced by a process according to the fourth aspect. 15  Use of Photocatalyst and / or Agrochemical Composition In a sixth aspect, the invention provides the use of a titanium dioxide photocatalyst according to the second aspect and / or an agrochemical composition according to the third aspect for improving plant physiology. 20 The present invention has been shown to be useful in improving plant physiology in vegetable, fruit and flowering plants. For example, the present invention has been shown to be useful in improving plant physiology in ivy and typical greenwall species, cereals (such as wheat and barley) and pea plants. The plants that the present invention 25 can be used with include any that can be benefited from nitrogen. In a further aspect, the invention provides the use of a titanium dioxide photocatalyst according to the second aspect and / or an agrochemical composition according to the third aspect for improving crop growth / crop yield / crop characteristics. For example, 30 the present invention has been shown to be useful in improving crop yield / crop characteristics in cereals, vegetables, fruit and flowering plants. For example, the present invention has been shown to be useful in improving crop yield / crop characteristics in ivy, wheat and pea plants. 35 In a further aspect, the invention provides the use of a titanium dioxide photocatalyst according to the second aspect and / or an agrochemical composition according to the third aspect for increasing the nitrogen content of a plant. For example, the present invention has been shown to increase the nitrogen content of cereals, vegetables, fruit and flowering plants. For example, the present invention has been shown to be useful in increasing the nitrogen content of ivy, wheat and pea plants. 5 In a further aspect, the invention provides the use of a titanium dioxide photocatalyst according to the second aspect and / or an agrochemical composition according to the third aspect for removing nitrogen monoxide or nitrogen dioxide from the atmosphere. 10 Definitions A photocatalyst is a material that catalyses a chemical reaction. A titanium dioxide photocatalyst is a photocatalyst that comprises titanium dioxide. Dopant: an atom / element that is intentionally incorporated in the catalyst’s elemental 15 structure or crystal lattice. Mg / 1 or mg / lt: milligrams per litre. NOx: Gaseous nitrous oxides (including nitrogen monoxide and nitrogen dioxide) ha = hectare 20 t = tiller Particle Size Distribution Throughout the present disclosure, the mean diameter is the volume weighted mean 25 diameter measured using a laser diffractometer. Throughout the present disclosure, the % of particles having a specific diameter is the volume weighted % measured using a laser diffractometer. 30 The particle size distribution of the photocatalyst of the invention can be measured using the laser diffractometer: Mastersizer 2000, produced by Malvern Instruments Ltd. (software version 5.60). To determine the particle size distribution, a sample of the particles to be measured is dispersed in water and the particle size distribution is measured. The particle size distribution obtained is volume weighted. Therefore, the 35 mean diameter of the particles is the volume weighted mean diameter (D[4,3]); and the % of particles having a specific diameter refers to the volume % of particles having the specific diameter. Unless otherwise stated, the mean diameter is the volume weighted mean diameter. 5 Examples The most effective titanium dioxide photocatalysts were prepared and tested in accordance with the following examples. 10 Preparation of Titanium Dioxide Photocatalyst Manganese sulphate (0.75 g) and calcium carbonate (0.25 g) were added to particulate titanium dioxide (1000 g; having at least 95 vol.% of the particles with a diameter of 15 between 2 pm and 10 pm). The resulting mixture was ball rolled for between 30 and 60 minutes and then pin milled for a further 30 minutes. The process was repeated if the mixture had a uniformity of less than 90%. The mixture was then heated at 6oo°C for 3 hours to form the titanium dioxide photocatalyst. After the resulting product cooled, the product was pin milled and sieved until at least 95 vol. % of the particles had 20 diameter of between 2 pm and 10 pm. Preparation of Composition 500g of the prepared titanium dioxide photocatalyst was suspended in a composition 25 comprising 750 mL water, 30g of sodium naphthalene sulphonate formaldehyde condensate, 5g of silicon based antifoaming agent, 10g of ethoxylated alcohol, 10g of cocoyl hydroxyethyl imidazoline based amphoteric surfactant, and 6g xanthan gum. The formulation referred to herein additionally contained 2.4 %w / w Mn, 1.3 % w / w Zn, 30 and 0.07 % w / w Mo. The composition had a specific gravity of about 1.5 (i.5kg / lt). Characterisation of Titanium Dioxide Photocatalyst Raman spectra of samples 1-9 of the titanium dioxide photocatalyst were recorded using 35 a LABRAM 300 (Horiba Jobin Yvon) with an excitation line of 532 nm (Figure 1). The instrument was equipped with an Olympus microscope BX41, which was used to collect Raman spectra from the powder using a 50 x, 0.50 NA Leica objective with a long working distance that focused the laser onto the surface of the powder. A sample was placed on microscopic slide and tested by focusing the laser and an output power of 50mW, 5 s of exposure time, and 2 accumulations were used. The method was used to 5 demonstrate the changes in structure of the produced material and to characterise them. Figure 1 shows the Raman spectra of pure titanium dioxide and of titanium dioxide photocatalysts of the present invention (S1-S9 were prepared in accordance with the example above). 10 Further, XRD analysis was used to characterise and compare the doped titanium dioxide photocatalyst with the raw titanium dioxide using a Bruker make diffractometer, Cu-Ka X-rays of wavelength (X)=i.54o6 A. 15 Photocatalytic Activity The photocatalytic activity of a titanium dioxide photocatalyst was tested using an acetone degradation experiment, ig of particulate titanium dioxide and ig of a photocatalyst prepared according to the present example were each placed in a separate 20 reaction cell with 3 ml of acetone. The reaction cells were kept in the dark for 30 minutes to reach equilibrium. The reactions cells were then irradiated with UV light (2 15W 352 nm lamps) for 3 hours. CO2 generation was measured over time. See Figure 2A (particulate titanium dioxide) and Figure 2B (photocatalyst of the example). 25 The same experiments was conducted but using a different light source (fluorescent / visible spectrum light source). CO2 generation was measured over time (see Figure 2C and 2D). The spectrum of the fluorescent light source is shown in Figure 3)- 30 As shown in Figure 2A and 2B, the titanium dioxide photocatalyst as prepared in accordance with the example (Figure 2B) above showed a tenfold increase in its ability to photocatalyse under UV irradiation relative to the raw titanium dioxide (Figure 2A). This significant increase shows that the photocatalyst of the invention have significant activity and therefore use in industry / agriculture. Not only do the photocatalysts of the invention show improved activity when irradiated with UV light, they also show a significant improvement when irradiated with the visible spectrum light. Figure 2D shows that the photocatalyst of the invention are particularly appropriate for application where daylight available, for example on the 5 surface of plants. Example 1 The formulation of the invention was applied to a first section of green screen of ivy 10 positioned near to a road in Hammersmith, London. The formulation was applied at 31t / ha. A second section of the same green screen was left untreated. This was replicated in three areas. The nitrogen dioxide content in the vicinity of the treated and untreated sections of the 15 green screen was measured using a NOx diffusion tube over a period of 8 weeks. As shown in Figure 4, the total nitrogen dioxide content in the vicinity of the treated section of the green screen was 8.3% lower than the untreated section of the green screen (total of 7.25 pg and 6.65 pg respectively). 20   A sample of the ivy from each of the treated and untreated sections of the green screen were sent for tissue content analysis. As it can be seen from table 1, total nitrogen content of the ivy from the treated section was 21.3% greater than the ivy from the untreated section. This significant increase is consistent with the understanding that the photocatalyst in the formulation of the invention provides an increase in nitrate to 25 the plant over the 8 week period. Table 1 Content Analysis Treated Ivy Untreated Ivy Nitrogen (%) 2.16 1.78 Phosphorous (%) 0.13 0.10 Potassium (%) 1-52 1.01 Sulphur (%) O.27 0.25 Copper (mg / Kg) 9.8 8.9 Zinc (mg / Kg) 153-8 135-4 Boron (mg / Kg) 28.4 25-1 Example 2 5 The formulation of the invention was applied to sections of grass at three locations (location 1, location 2 and location 3). The formulation was applied at 1 It / ha at a first subsection and 5 It / ha at second subsection of grass at each location. A control formulation was applied to different sections of grass at location 1, location 2 10 and location 3. The control formulation was the same as the formulation of the invention except that it did not contain the titanium dioxide photocatalyst. After a period of 4 weeks, samples of the grass were sent for sap content analysis. As can be seen in table 2, the formulation of the invention significantly increased the 15 nitrogen content of the grass. A dose response is also seen. This is explained as more titanium dioxide photocatalyst enables more N to be produced. Table 2 Nitrogen Content (mg / Kg): Location 1 Nitrogen Content (mg / Kg): Location 2 Nitrogen Content (mg / Kg): Location 3 Control 56 71 71 Formulation of Invention (ilt / ha) 76 132 91 Formulation of Invention (51t / ha) 101 No data 122 20 Example 3 The formulation of the invention was applied to sections of a field of wheat (durum) plants and sections of a field of grain pea plants. The formulation was applied three times at 1 It / ha. The applications were spaced 4-6 weeks apart. Sections of the field of wheat (durum) plants and the field of grain pea plants were left untreated with the formulation of the invention (but were otherwise treated identically in respect of watering, fertiliser application and herbicide application) to act as a control. 5 After a period of 12 weeks, samples of the plants were harvested and analysed. As can be seen in table 3, the formulation of the invention significantly increased the total yield of both the wheat plants and grain pea plants. The formulation of the invention also significantly increased the protein content of the grain pea plants. 10 Table 3 Wheat (treated) Wheat (untreated) Grain Peas (treated) Grain Peas (untreated) Yield (Kg / ha) 5270 4400 6170 5100 Protein (%) No data No data 16.5 16.1 Example 4 15 The formulation of the invention was applied to a 25 metre x 25 metre plot of wheat plants. The formulation was applied twice at 1 It / ha: (i) when the plants reached three tillers; and (ii) 6 weeks following the first treatment. A corresponding plot of wheat plants was left untreated with the formulation of the invention (but was otherwise treated identically) to act as a control. 20 The plants were harvested and analysed by an external laboratory. As can be seen in table 4, the formulation of the invention significantly increased yield (tillers per hectare: t / ha), protein content, natural weight and Hagberg content. 25 Table 4 Yield (t / ha) Protein Moisture Natural Weight Hagberg Untreated 10.3 10-44 17-1 64-3 179 Treated 12.3 11.05 16.5 65-6 191 Example 5 A control formulation and formulations containing the photocatalyst of the example in water (1 It / ha and 2 It / ha) were applied to individual plots of wheat 5 crop. The control formulation was water. The formulations were applied at 3 tillers and 6 weeks after the first application. Measurements were taken from 10 plants randomly selected from each plot. The weight of plants, the weight of the ears (heads) only, and the length of the flag leaf were 10 measured. The results (shown in Figures 5, 6 and 7) clearly demonstrate that the photocatalyst of the invention improves crop growth. Example 6 15 Plots of a wheat field were treated with a control formulation, a formulation comprising 6g of titanium dioxide, a formulation comprising 3g of a Mn doped titanium dioxide, a formulation comprising 6g of a Mn doped titanium dioxide, or a formulation comprising 6g of the titanium dioxide photocatalyst according to the present example. The medium of the formulations was water, with the control formulation comprising 20   only water. Five NOx diffusion tubes were placed in each of the plots of the wheat field. Four of the five NOx diffusion tubes from each plot were sent for analysis before harvest (at regular intervals from application of the formulations until harvest). The fifth NOx tube was 25 sent for analysis at harvest. In this example, the wheat plants were harvested when the seed moisture level was 17 %. The yield was then calculated. Figure 8 shows the yield of each plot. Figure 9 shows the total NO2 measured at each plot. As shown in Figure 8, the formulation comprising titanium dioxide, the formulation 30 comprising 3g of a Mn doped titanium dioxide, or the formulation comprising 6g of a Mn doped titanium dioxide did not significantly increase yield relative to the control formulation. In contrast, the formulation comprising 6g of the titanium dioxide photocatalyst according to the present example increased yield significantly. As shown in Figure 9, the formulation comprising 6g of the titanium dioxide photocatalyst according to the present example reduced the concentration of nitrogen dioxide significantly more than any other formulation. 5 It is also noted that whilst the formulation comprising titanium dioxide, the formulation comprising 3g of a Mn doped titanium dioxide, and the formulation comprising 6g of a Mn doped titanium dioxide slightly reduced the nitrogen dioxide concentration relative to the control, this reduction did not result in a significant increase in yield. In contrast, the formulation comprising 6g of the titanium dioxide 10 photocatalyst according to the present example reduced the concentration of nitrogen dioxide and increased the yield. As such, it is clear that the photocatalyst of the invention converts nitrogen dioxide to nitrate and makes the nitrate available for the plant to uptake and utilise which increases plant growth / yield. 15

Claims

1. A method of increasing growth of a plant, the method comprising applying a titanium dioxide photocatalyst to a surface of the plant, and converting5              nitrogen monoxide or nitrogen dioxide to nitrate on the surface of the plant;wherein the titanium dioxide photocatalyst is a particulate titanium dioxide photocatalyst which has a mean diameter greater than about i pm.

2. The method according to claim 1, wherein the nitrate is absorbed by theio15CM CMLO 20CMplant, preferably by the surface of the plant.

3. A method according to claim 1 or claim 2, wherein the titanium dioxidephotocatalyst is doped with at least Mn and Ca; and the titanium dioxide photocatalyst is a particulate titanium dioxide photocatalyst which has a mean diameter from about 2 pm to about 8 pm.

4. The method according to claim 1 or claim 2, wherein the method comprises spraying the titanium dioxide photocatalyst onto a surface of a plant.

5. The method according to any one of the preceding claims, wherein the nitrogen monoxide or nitrogen dioxide is atmospheric nitrogen monoxide or nitrogen dioxide.

6. The method according to any one of the preceding claims, wherein the 25              nitrate is washed from the titanium dioxide photocatalyst by application of awater source to the surface of the plant.

7. The method according to any one of the preceding claims, wherein the particulate titanium dioxide photocatalyst has a mean diameter greater than 30             about 2 pm, about 5 pm, about 8 pm or about 10 pm.

8. The method according to any one of the preceding claims, wherein at least about 70 vol. % of the particulate titanium dioxide has a diameter between about 2 pm and about 10 pm, preferably wherein at least about 80 vol. %, 35              about 90 vol. %, about 95 vol. %, or about 98 vol. % of the particulatetitanium dioxide has a diameter between about 2 pm and about 10 pm9- The method according to any one of the preceding claims, wherein the titanium dioxide photocatalyst has a surface area of greater than about 5000 m2 per 500 g, about 7000 m2 per 500 g, or about 10,000 m2 per 500 g.

510. The method according to any one of the preceding claims, wherein the titanium dioxide photocatalyst is a doped titanium dioxide photocatalyst.

11. The method according to any one of claims 1-2, or 4-10, wherein the10              titanium dioxide photocatalyst is doped with at least one of the followingdopants Mn, Ca, Mg, Zn, N, Mg and K.

12. The method according to claim 3,10 or 11, wherein the titanium dioxide photocatalyst is a doped with two dopants and the ratio of a first of the two 15             dopants to a second of the two dopants is between about 10:1 and about1:10.

Images