Titanium-containing materials

Abstract

The invention relates to a method of preparing a solution containing colloidal particles which contain crystalline titanium dioxide wherein one or more hydrolysable titanium-containing compound(s) is stabilised by oxalic acid in a reaction medium. The reaction further relates to the preparation of titania materials (including particulate materials, coating solutions and films) which comprise or include anatase phase titania, and so are suitable in photocatalytic applications. The invention also deals with a method of preparing B-phase titania.

1 . A method of preparing a solution containing colloidal particles which contain titanium ions comprising or including the step of: 
 A. reacting or otherwise stabilising one or more hydrolysable titanium-containing compound(s) with oxalic acid in a reaction medium.    
     
     
         2 . A method of preparing a solution as claimed in  claim 1  wherein A occurs under conditions such that peptization of the colloidal solution is substantially obtained and substantially maintained.  
     
     
         3 . A method of preparing a solution as claimed in  claim 2  wherein the conditions include stirring or agitation of the one or more hydrolysable titanium-containing compound(s) with oxalic acid in the reaction medium, at a temperature between ambient temperature to near the boiling point of the reaction mixture.  
     
     
         4 . A method of preparing a solution as claimed in  claim 3  wherein the reaction medium comprises water or a water/alcohol mixture and wherein the titanium-containing compound is hydrolysable in water and/or in base.  
     
     
         5 . A method of preparing a solution as claimed in  claim 4  wherein, the titanium containing compound is water-hydrolysable and is of the formula Ti(OR) 4 , where R is a C 2 -C 6  linear or branched chain alkyl group.  
     
     
         6 . A method of preparing a solution as claimed in  claim 5  wherein the titanium-containing compound is titanium tetraisopropoxide and/or titanium tetrabutoxide.  
     
     
         7 . A method of preparing a solution as claimed in  claim 6  wherein the titanium containing compound is: 
 first combined with a solution of oxalic acid in alcohol, followed by addition of water, or  
 added directly to water, or to a mixture of water and an alcohol, to form a slurry, followed by addition of oxalic acid, or  
 added to a solution of oxalic acid in water or in a mixture of water and alcohol.  
 
     
     
         8 . A method of preparing a solution as claimed in  claim 4  wherein the titanium-containing compound is base-hydrolysable and the titanium-containing compound is selected from, but not restricted to, TiCl 4  and/or TiOSO 4 .  
     
     
         9 . A method of preparing a solution as claimed in  claim 8  wherein the base-hydrolysable titanium-containing compound is hydrolysed to a hydrolysis product, using a base prior to reaction with or stabilisation by oxalic acid, the hydrolysis product being filtered and/or washed, to form a slurry before reaction with or stabilisation by, the oxalic acid.  
     
     
         10 . A method of preparing a solution as claimed in any one of the preceding claims wherein the amount of oxalic acid is such as to provide a mole ratio of oxalic acid:titanium in the range of about 0.2:1 to about 1:1.  
     
     
         11 . A method of preparing a solution as claimed in  claim 10  wherein the water content of the reaction medium is such as to provide a mole ratio of water:titanium in the range of from about 400:1 to about 600:1.  
     
     
         12 . A method of preparing a solution as claimed in any one of  claims 4  to  11  wherein, when alcohol is present in the reaction medium the alcohol is a mono hydroxyl aliphatic alcohol having the formula ROH, where R is a C 1  to C 4  linear or branched alkyl group, such as ethanol or t-butanol, and the preferred amount of alcohol present is such as to provide a mole ratio of alcohol:titanium of between 10:1 to 50:1 in the solution.  
     
     
         13 . A method of preparing a solution as claimed in any one of the preceding claims wherein the oxalate concentration of the solution is at any stage reduced by irradiating the solution with UV light.  
     
     
         14 . A solution containing colloidal particles which contain titanium ions prepared substantially according to the method as claimed in anyone of  claims 1  to  13 .  
     
     
         15 . A method of preparing a solution containing colloidal particles which contain crystalline titanium dioxide comprising or including the step of: 
 A. reacting or otherwise stabilising one or more hydrolysable titanium-containing compound(s) with oxalic acid in a reaction medium.    
     
     
         16 . A method of preparing a solution as claimed in  claim 15  wherein A occurs under conditions such that peptization of the colloidal solution is substantially obtained and substantially maintained.  
     
     
         17 . A method of preparing a solution as claimed in  claim 16  wherein the conditions include stirring or agitation of the one or more hydrolysable titanium-containing compound(s) with oxalic acid in the reaction medium, at a temperature between ambient temperature to near the boiling point of the reaction mixture.  
     
     
         18 . A method of preparing a solution as claimed in  claim 17  wherein the reaction medium comprises water or a water/alcohol mixture and wherein the titanium-containing compound is hydrolysable in water and/or in base.  
     
     
         19 . A method of preparing a solution as claimed in  claim 18  wherein, the titanium containing compound is water-hydrolysable and is of the formula Ti(OR) 4 , where R is a C 2 -C 6  linear or branched chain alkyl group.  
     
     
         20 . A method of preparing a solution as claimed in  claim 19  wherein the titanium-containing compound is titanium tetraisopropoxide and/or titanium tetrabutoxide.  
     
     
         21 . A method of preparing a solution as claimed in  claim 20  wherein the titanium containing compound is: 
 first combined with a solution of oxalic acid in alcohol, followed by addition of water, or  
 added directly to water, or to a mixture of water and an alcohol, to form a slurry, followed by addition of oxalic acid, or  
 added to a solution of oxalic acid in water or in a mixture of water and alcohol.  
 
     
     
         22 . A method of preparing a solution as claimed in  claim 18  wherein the titanium-containing compound is base-hydrolysable and the titanium-containing compound is selected from, but not restricted to, TiCl 4  and/or TiOSO 4 .  
     
     
         23 . A method of preparing a solution as claimed in  claim 22  wherein the base-hydrolysable titanium-containing compound is hydrolysed to a hydrolysis product, using a base prior to reaction with or stabilisation by oxalic acid, the hydrolysis product being filtered and/or washed, to form a slurry before reaction with or stabilisation by, the oxalic acid.  
     
     
         24 . A method of preparing a solution as claimed in any one of  claims 15  to  23  wherein the amount of oxalic acid is such as to provide a mole ratio of oxalic acid:titanium in the range of about 0.2:1 to about 1:1.  
     
     
         25 . A method of preparing a solution as claimed in  claim 24  wherein the water content of the reaction medium is such as to provide a mole ratio of water:titanium in the range of from about 400:1 to about 600:1.  
     
     
         26 . A method of preparing a solution as claimed in any one of  claims 15  to  25  wherein, when alcohol is present in the reaction medium the alcohol is a mono hydroxyl aliphatic alcohol having the formula ROH, where R is a C 1  to C 4  linear or branched alkyl group, such as ethanol or t-butanol, and the preferred amount of alcohol present is such as to provide a mole ratio of alcohol:titanium of between 10:1 to 50:1 in the solution.  
     
     
         27 . A method of preparing a solution as claimed in any one of  claims 15  to  26  wherein the oxalate concentration of the solution is at any stage reduced by irradiating the solution with UV light.  
     
     
         28 . A solution containing colloidal particles which contain crystalline titanium dioxide prepared substantially according to the method as claimed in anyone of  claims 15  to  27 .  
     
     
         29 . A solution containing colloidal particles which contain crystalline titanium dioxide prepared substantially as herein described with reference to any one or more of the accompanying examples.  
     
     
         30 . A method of preparing a TiO 2 -Containing Product comprising or including the steps of: 
 1) preparation of a solution containing colloidal particles which contain crystalline titanium dioxide wherein the particles are stabilised by oxalic acid or stabilised by having been reacted with oxalic acid as claimed in any one of  claims 15  to  27 , and    2) preparation of a colloidal mixture by addition of, or mixing with, one or more additives to the solution, and    3) further processing of the solution to obtain the product.    
     
     
         31 . A method of preparing a TiO 2 -Containing Product as claimed in  claim 30  wherein the TiO 2  phase in the product, at least initially, includes, is predominantly or is substantially anatase.  
     
     
         32 . A method of preparing a TiO 2 -Containing Product as claimed in claims  30  or  31  wherein the additives of step 2) include one or more of: 
 a) silica or a silica precursor,  
 b) water, or alcohol, soluble ketone(s),  
 c) metal precursor(s),  
 d) surfactant(s),  
 e) silane(s).  
 
     
     
         33 . A method of preparing a TiO 2 -Containing Product as claimed in  claim 32  wherein when silica is added it is as colloidal silica, it is added in an amount to yield a ratio substantially from 30-60 wt % relative to titanium in the product, and the concentration of the colloidal silica is such as to provide between about 1 and 50% by weight.  
     
     
         34 . A method of preparing a TiO 2 -Containing Product as claimed in  claim 32  wherein when a metal precursor is added, it is a metal salt or metal complex of one or more of Pd, Pt, Ag and Cu.  
     
     
         35 . A method of preparing a TiO 2 -Containing Product as claimed in  claim 34  wherein the metal is Pd or Pt and the precursor is one of the hexachloro-complexes of Pd or Pt.  
     
     
         36 . A method of preparing a TiO 2 -Containing Product as claimed in  claim 35  wherein the Pd or Pt hexachloro-complex is mixed with a low carbon organic compound as a sacrificial compound, such as formaldehyde, formic acid, methanol or ethanol, the sacrificial compound added in excess relative to the precursor metal.  
     
     
         37 . A method of preparing a TiO 2 -Containing Product as claimed in  claim 34  wherein the metal is Ag and the precursor is one or both of silver acetate or silver nitrate.  
     
     
         38 . A method of preparing a TiO 2 -Containing Product as claimed in  claim 34  wherein the metal is Cu and the precursor is one or more of copper acetate, copper sulphate and copper nitrate.  
     
     
         39 . A method of preparing a TiO 2 -Containing Product as claimed in  claim 32  wherein the silane(s) is added neat or as solution in an aqueous or organic solvent that is miscible with water, and is a hydrolysable or partially hydrolysable silane compound of a formula RSiX 3 , R 2 SiX 2  and SiX 4  (where R is a simple or functionalised organic group and X could be a halide or an alkoxide group).  
     
     
         40 . A method of preparing a TiO 2 -Containing Product as claimed in any one of  claims 30  to  39  wherein step 3) includes one or both the steps of: 
 i) causing the solution to gel (a gelling step),  
 ii) curing of the gel (a curing step) to remove or reduce the quantity of the oxalic acid and/or any one or more additives.  
 
     
     
         41 . A method of preparing a TiO 2 -Containing Product as claimed in  claim 40  wherein curing of the gel is effected by exposure to UV radiation and/or by heat, and the wavelength of the UV radiation substantially or partially coincides with the photo catalytically active band gap of the TiO 2  in the anatase phase.  
     
     
         42 . A method of preparing a TiO 2 -Containing Product as claimed in any one of  claims 30  to  41  wherein there is an additional step 4), which includes one or both the steps of: 
 i) impregnation of the titanium containing-product with a metal precursor, (an impregnation step) and/or  
 ii) transformation of any metal precursor to a metal or metal oxide added within step 2) and/or step 4) (a transformation step).  
 
     
     
         43 . A method of preparing a TiO 2 -Containing Product as claimed in  claim 42  wherein the metal of the precursor of step i) is one or more of Pd, Pt, Cu or Ag.  
     
     
         44 . A method of preparing a TiO 2 -Containing Product as claimed in  claim 42  or  43  wherein the transformation step is employed and occurs by one or more of: 
 i) heating at a suitable temperature to transform the metal precursor to the metal or metal oxide, and/or  
 ii) exposing the metal precursor or the TiO 2 -Containing Product containing the metal precursor, to a dilute hydrazine hydrate solution for a sufficient time to allow the complete reduction of the metal to zero valency, and/or  
 iii) UV irradiation to form metal particles and/or metal oxides within the titanium dioxide.  
 
     
     
         45 . A method of preparing a TiO 2 -Containing Product as claimed in  claim 44  wherein the final metal content in the TiO 2  of the TiO 2 -product is between 0.2 to 0.5% by weight.  
     
     
         46 . A method of preparing a TiO 2 -Containing Product as claimed in any one of  claims 30  to  45  wherein sometime prior to step 3) the oxalate concentration of the solution is reduced by irradiating the solution with UV light.  
     
     
         47 . A method as claimed in  claim 46  wherein the product is a particulate product.  
     
     
         48 . A method of preparing a TiO 2  coating solution comprising or including the steps of: 
 1) preparation of a solution containing colloidal particles which contain crystalline titanium dioxide wherein the particles are stabilised by oxalic acid, or are stabilised by having been reacted with oxalic acid as prepared in any one of  claims 15  to  27 , and    2) preparation of a colloidal mixture by addition of one or more additives to the solution.    
     
     
         49 . A method of preparing a coating solution as claimed in  claim 48  wherein step 2) includes any one or more of the following: 
 i) Addition of or mixing with silica, or a silica precursor,  
 ii) Addition of or mixing with any proportion of water-soluble or alcohol-soluble ketone(s),  
 iii) Addition of or mixing with any proportion of surfactant(s),  
 iv) Addition of or mixing with one or more metal precursor(s),  
 v) Addition of or mixing with one or more silane(s).  
 
     
     
         50 . A method of preparing a coating solution as claimed in  claim 49  wherein one or more metal precursor(s) is added or mixed and is a soluble metal salt or complex of the group of Pd, Pt, Ag and Cu.  
     
     
         51 . A method of preparing a TiO 2 -coated substrate comprising or including the steps of: 
 I. preparation of a coating solution as claimed in any one of  claims 48  to  50 , and    II. further processing of the solution to obtain the coated substrate.    
     
     
         52 . A method of preparing a coated substrate as claimed in  claim 51  wherein the TiO 2  phase in the coated substrate, at least initially, includes, is predominantly or is substantially anatase.  
     
     
         53 . A method of preparing a coated substrate as claimed in  claim 52  wherein the substrate is one or more of (but not restricted to) glass, quartz, glass fibre, woven glass fibre, ceramics, silicon wafers, metals, polymer surfaces (such as polyethylene or polyester), wood, or building materials such as mortar, brick, tiles, or concrete.  
     
     
         54 . A method of preparing a coated substrate as claimed in  claim 53  wherein step II includes: 
 i) application of the coating solution to a substrate, and  
 ii) a gelling step, and  
 iii) a curing step.  
 
     
     
         55 . A method of preparing a coated substrate as claimed in  claim 54  wherein prior to application of the coating solution a protective layer of amorphous silica and/or alumina is applied to the substrate, or a precursor of amorphous silica selected from (but not limited to) the series tetraalkoxysilanes, alkoxychlorosilanes; or a precursor of amorphous aluminia selected from (but not limited to) the series aluminium trialkoxides and wherein the precursors may convert to the silica or alumina by hydrolysis in acid solution.  
     
     
         56 . A method of preparing a coated substrate as claimed in any one of  claims 54  to  55  wherein curing of the gel is effected by exposure to UV radiation and/or by heat and the wavelength of the radiation substantially or partially coincides with the photocatalytic band gap of anatase TiO 2 .  
     
     
         57 . A method of preparing a coated substrate as claimed in any one of  claims 51  to  56  wherein there is a further step III which includes one or both the steps of: 
 i) impregnation of the titanium containing-product with a metal precursor, (an impregnation step) and/or  
 ii) transformation to a metal or metal oxide of any metal precursor added within step I) and/or step III) (a transformation step).  
 
     
     
         58 . A method of preparing a coated substrate as claimed in  claim 57  wherein the metal of the precursors of step i) is one or more of Pd, Pt, Cu or Ag.  
     
     
         59 . A method of preparing a patterned TiO 2 -coated substrate comprising or including the steps of: 
 i) preparation of a coated substrate as claimed in any one of  claims 51  to  58 , but prior to any gelling or curing steps (if any),    ii) masking one or more regions of the coating,    iii) curing of the unmasked region(s) of coating by exposing the unmarked region(s) to an ultraviolet light to photocatalytically destroy the oxalic acid and other organic materials present in the titanium oxide of the unmasked region(s),    iv) development of the film.    
     
     
         60 . A method of preparing a patterned TiO 2 -coated substrate as claimed in  claim 59  wherein the coating solution produces a film which contains 50 to 100% by weight titania after curing.  
     
     
         61 . A method of preparing a patterned TiO 2 -coated substrate as claimed in  claim 60  wherein development of the film is by one or more of: 
 i) application of an acid solution wherein the acid solution is any dilute mineral acid such as sulphuric and/or an organic acid solution such as oxalic, lactic, citric, tartaric and/or an acidic salt solution where the salt is, ammonium sulphate or aluminium sulphate, and/or,  
 ii) application of other materials such as hydrogen peroxide, and/or,  
 iii) a radiational or mechanical method including ultrasonication, and/or  
 iv) any other method for redissolution of the UV—unexposed gel.  
 
     
     
         62 . A method of preparing a patterned TiO 2 -coated substrate as claimed in  claim 61  wherein development is at room temperature.  
     
     
         63 . A method of preparing a patterned TiO 2 -coated substrate as claimed in  claim 62  wherein curing of the coating is by exposure to UV radiation, the wavelength of the UV radiation substantially or partially coinciding with the photocatalytically active band gap of the TiO 2  in the anatase phase.  
     
     
         64 . A method of preparing a patterned TiO 2 -coated substrate as claimed in  claim 63  wherein there is a final step of sintering the coating.  
     
     
         65 . A method of increasing the content of rutile and/or TiO 2 —B phases in a TiO 2  product including or comprising: 
 preparing a TiO 2 -containing product as claimed in any one of claims  30 - 47  wherein the TiO 2  phase is predominantly or at least partially anatase, or is predominantly or at least partially TiO 2 —B phase and  
 heating to increase the anatase and/or rutile content.  
 
     
     
         66 . A method as claimed in  claim 65  wherein heating to substantially between 200° C. to 400° causes or initiates phase change of TiO 2 —B to anatase phase to titanium dioxide-B and/or rutile phase in the product.  
     
     
         67 . A method as claimed in  claim 65  wherein further heating to substantially above 400° C. will increase the content of the rutile phase in the product.  
     
     
         68 . A method as claimed in  claim 65  wherein the TiO 2  undergoes a phase change substantially entirely to rutile at temperatures substantially higher than 500° C.  
     
     
         69 . A method as claimed in any one of  claims 65  to  68  wherein addition of substantially up to 50% by weight silica results in stabilisation of the anatase phase and/or TiO 2 —B phase thereby requiring heating to over 600° C. to initiate and/or complete the transformation to rutile phase.  
     
     
         70 . A TiO 2 -containing product substantially prepared according to the method as claimed in any one of claims  30 - 47 .  
     
     
         71 . A TiO 2 -containing product prepared substantially as herein described with reference to any one or more of the accompanying examples.  
     
     
         72 . A TiO 2 -containing coating solution substantially prepared according to the method as claimed in any one of  claims 48  to  50 .  
     
     
         73 . A TiO 2 -containing coating solution prepared substantially as herein described with reference to any one or more of the accompanying examples.  
     
     
         74 . A TiO 2 -containing coated substrate substantially prepared according to the method as claimed in any one of  claims 51  to  64 .  
     
     
         75 . A TiO 2 -containing coated substrate prepared substantially as herein described with reference to any one or more of the accompanying examples.  
     
     
         76 . A method of preparing a TiO 2 -based photocatalyst including or comprising the following steps: 
 1) preparation of a solution containing colloidal particles which contain crystalline titanium dioxide wherein the particles are stabilised by oxalic acid, or stabilised by reaction with oxalic acid as claimed in any one of  claims 15  to  27 ,    2) further processing of the solution to obtain the photocatalyst.    
     
     
         77 . A method of preparing a TiO 2 -based photocatalyst as claimed in  claim 76  wherein the TiO 2 -based photocatalyst is a TiO 2  particulate material, and the further processing includes a gelling and a curing step.  
     
     
         78 . A method of preparing a TiO 2 -based photocatalyst as claimed in  claim 77  wherein the TiO 2 -based photocatalyst is a TiO 2  coating or film on a substrate, and the further processing includes preparation of a coating solution, application of the coating solution to the substrate, and a gelling and a curing step.  
     
     
         79 . A method of preparing a TiO 2 -based photocatalyst as claimed in  claim 77  or  78  wherein the TiO 2  phase in the particulate material, coating or film, at least initially, includes, is predominantly or is substantially anatase and/or TiO 2 —B.  
     
     
         80 . A method of preparing a TiO 2 -based photocatalyst as claimed in  claim 79  wherein the TiO 2 -based photocatalyst acts as a photocatalyst upon irradiation of or exposure to UV light.  
     
     
         81 . A method of preparing a TiO 2 -based photocatalyst as claimed in  claim 80  wherein the TiO 2 -based photocatalyst is metal or metal-oxide doped, and the metal is selected from Pt, Pd, Cu or Ag.  
     
     
         82 . A method of preparing a TiO 2 -based photocatalyst as claimed in  claim 79  or  80  wherein the TiO 2 -based photocatalyst can be used to photocatalytically degrade organic compounds and wherein the degradation occurs via application of or exposure to UV radiation.  
     
     
         83 . A method of preparing a TiO 2 -based photocatalyst as claimed in  claim 79  or  80  wherein the TiO 2 -based photocatalyst can act as a hydrophilic surface when coated on a substrate.  
     
     
         84 . A TiO 2 -based photocatalyst prepared substantially according to the method as claimed in any one of claims  76 - 83 .  
     
     
         85 . A TiO 2 -based photocatalyst prepared substantially as herein described with reference to any one or more of the examples.  
     
     
         86 . A method of preparing B phase TiO 2  including or comprising the following steps: 
 1) preparation of a solution containing colloidal particles which contain crystalline titanium dioxide wherein the particles are stabilised by oxalic acid, or stabilised by reaction with oxalic acid, as claimed in any one of  claims 15  to  27     2) further processing of the solution to obtain TiO 2  predominantly or substantially in the TiO 2 —B phase,    3) heating of the TiO 2  to substantially between 200-300° C.    
     
     
         87 . A method of preparing B phase TiO 2  as claimed in  claim 86  wherein the further processing step 2) includes removal of the solvent and/or a gelling step and/or a curing step.  
     
     
         88 . A method of preparing B phase TiO 2  as claimed in  claim 87  there is a further step 4) of heating beyond 450° C. provide TiO 2  in the rutile phase.  
     
     
         89 . B phase TiO 2 , prepared substantially according to the method of  claims 86  to  89 .  
     
     
         90 . B phase TiO 2 , prepared substantially as herein described with reference to any one or more of the examples.