P-doped surface coatings and process of preparation thereof

Abstract

A process for the preparation of an antimicrobial P-doped coating solution is described. The process for the preparation of the antimicrobial coating solution uses non-volatile and non-oxidising phosphoric acid. The antimicrobial coatings are active in both the UV and visible light spectrum.

Claims

1. A process for the preparation of an antimicrobial coating composition, the process comprising the steps of: preparing a coating solution by (i) mixing a chelating agent with a titanium alkoxide and a phosphorylating agent; and (ii) adding an aqueous solution to the mixture formed from step (i).

2. The process of claim 1, wherein the aqueous solution is added in step (i) and the phosphorylating agent is added in step (ii).

3. The process of claim 1, wherein the aqueous solution and the phosphorylating agent are added in step (ii).

4. The process of claim 1, wherein the chelating agent is a carboxylic acid selected from the group consisting of formic acid, propionic acid, butanoic acid and acetic acid.

5. (canceled)

6. The process of claim 4, wherein the carboxylic acid is acetic acid in the form of glacial acetic acid, and wherein the amount of glacial acetic acid used is in the range 12 to 18 wt %.

7. (canceled)

8. (canceled)

9. The process of claim 1, wherein the titanium alkoxide is selected from the group consisting of titanium isopropoxide, titanium ethoxide, titanium methoxide and titanium butoxide.

10. The process of claim 9, wherein the titanium alkoxide is titanium isopropoxide, and wherein the amount of titanium isopropoxide used is in the range 4 to 15 wt % of the coating solution.

11. (canceled)

12. The process of claim 1, wherein the phosphorylating agent is selected from the group consisting of orthophosphoric acid, phosphorus pentoxide, ammonium dihydrogen phosphate and diammonium hydrogen phosphate, wherein the phosphorylating agent is orthophosphoric acid, and wherein the amount of orthophosphoric acid used is in the range in the range 0.0002 to 0.005 wt %.

13. (canceled)

14. (canceled)

15. The process of claim 1, wherein the amount of water in the aqueous solution is in the range of 30 wt % to 99.5 wt %.

16. (canceled)

17. The process of claim 15, wherein the aqueous solution comprises an organic solvent in the range of 0-20% by weight of the aqueous solution.

18. (canceled)

19. (canceled)

20. The process of claim 1, comprising the step of, after step (ii), (iii) the addition of a dispersing agent.

21. The process of claim 20, wherein the dispersing agent is selected from one or more of the group comprising: Disperbyk 180, Disperbyk 2060, Disperbyk 2061, Disperbyk 2062, Disperbyk 2080, Disperbyk 2081 and Disperbyk 2205.

22. (canceled)

23. The process of claim 1, further comprising evaporating the solvents from the solution and then annealing the residue at a temperature between 300° C. and 1400° C. to form an antimicrobial powder.

24. The process of claim 23, further comprising the step of mixing the antimicrobial powder with a coating solution prepared by the process of claim 1.

25. An antimicrobial coating composition obtained by the process of claim 24.

26. The antimicrobial coating composition of claim 25, wherein the antimicrobial coating composition exhibits antimicrobial activity under both UV and visible light and in reduced light.

27. (canceled)

28. (canceled)

29. (canceled)

30. (canceled)

31. (canceled)

32. (canceled)

33. (canceled)

34. (canceled)

35. (canceled)

36. (canceled)

37. A coated substrate comprising: a substrate; and an antimicrobial coating prepared by the process of claim 24, wherein the antimicrobial coating is coated on the substrate.

38. The coated substrate of claim 37, wherein the substrate is selected from the group consisting of glass and related composite materials, ceramics, plastic, cement and clay.

39. The coated substrate of claim 38, wherein the substrate further comprises a metal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present application will now be described with reference to the accompanying drawings in which:

[0041] FIG. 1 is a schematic of photocatalytic activity of a TiO.sub.2 surface;

[0042] FIG. 2 is a Raman spectrum of KCS 110 @ 900° C.;

[0043] FIG. 3 is a Raman spectrum of KCS 110 @ 950° C.;

[0044] FIG. 4 is a Raman line-scan spectrum of KCS 110 @1000° C.;

[0045] FIGS. 5a, 5b and 5c are images from Raman imaging of KCS 110 @ 1000° C.;

[0046] FIG. 6 is a Raman spectrum of KCS 111 @ 700° C.;

[0047] FIG. 7 is a Raman spectrum of KCS 111 @ 900° C.;

[0048] FIG. 8 is a Raman spectrum of KCS 111 @ 950° C.;

[0049] FIG. 9 is a Raman spectrum via line-scan mode from KCS111 @ 1000° C.;

[0050] FIGS. 10a and 10b are an Optical micrograph and Raman imaging maps of anatase and rutile phases from the scanned red square area of KCS 111 @ 1000° C. respectively;

[0051] FIGS. 11a, 11b, 11c and 11d are total average spectrum and anatase and rutile maps of KCS 111 @ 1100° C.;

[0052] FIG. 12 is a Raman spectrum of KCS 112 @ 900° C.;

[0053] FIG. 13 is a Raman spectrum of KCS 112 @ 950° C.;

[0054] FIGS. 14a, 14b, 14c, 14d and 14e are an optical micrograph, total average spectrum, and anatase, rutile, TPP phase Raman maps from KCS112 @ 1000° C. respectively;

[0055] FIGS. 15a, 15b, 15c, 15d and 15 are an optical micrograph, total average spectrum, and various phases Raman maps of KCS 112 @1100° C. respectively;

[0056] FIG. 16 is an XRD spectrum of KCS 110 @700° C.;

[0057] FIG. 17 is an XRD spectrum of KCS 100 @ 900° C.;

[0058] FIG. 18 is an XRD spectrum of KCS 110 @ 950° C.;

[0059] FIG. 19 is an XRD spectrum of KCS 110 @ 1000° C.;

[0060] FIG. 20 is an XRD spectrum of KCS 110 @ 1100° C.;

[0061] FIG. 21 is an XRD spectrum of KCS 111 @ 700° C.;

[0062] FIG. 22 is an XRD spectrum of KCS 111 @ 900° C.;

[0063] FIG. 23 is an XRD spectrum of KCS 111 @ 950° C.;

[0064] FIG. 24 is an XRD spectrum of KCS 111 @ 1000° C.;

[0065] FIG. 25 is an XRD spectrum of KCS 111 @ 1100° C.;

[0066] FIG. 26 is an XRD spectrum of KCS 112 @ 700° C.;

[0067] FIG. 27 is an XRD spectrum of KCS 112 @ 900° C.;

[0068] FIG. 28 is an XRD spectrum of KCS 112 @ 950° C.;

[0069] FIG. 29 is an XRD spectrum of KCS 112 @ 1000° C.;

[0070] FIG. 30 is an XRD spectrum of KCS 112 @ 1100° C.;

[0071] FIG. 31 is a UV spectrum of KCS 110 @ 700° C.;

[0072] FIG. 32 is a UV spectrum of KCS 110 @ 900° C.;

[0073] FIG. 33 is a UV spectrum of KCS 111 @ 700° C.;

[0074] FIG. 34 is a UV spectrum of KCS 111 @ 900° C.;

[0075] FIG. 35 is a UV spectrum of KCS 112 @ 700° C.;

[0076] FIG. 36 is a UV spectrum of KCS 112 @ 900° C.;

[0077] FIG. 37 is a UV spectrum of KCS 112 @ 900° C.—extrapolated intercept of the V absorption range into the visible range;

[0078] FIG. 38 is a UV spectrum of KCS 117 @ 700° C.;

[0079] FIG. 39 is a UV spectrum of KCS 118 @ 700° C.;

[0080] FIG. 40 is a UV spectrum of KEF002 @1000° C.;

[0081] FIG. 41 is a UV spectrum of KEF002 @1050° C.;

[0082] FIG. 42 is a UV spectrum of KEF004 @1000° C.; and

[0083] FIG. 43 is a UV spectrum of KEF004 @1000° C.

DETAILED DESCRIPTION OF THE DRAWINGS

[0084] The present application provides an industrially viable water-based environmentally benign, processing technology for the production of antimicrobial coating solutions.

[0085] The P-doped anti-microbial coating solution described herein is eco-friendly which is highly desirable. The solution used is water based and the phosphorus doping agent is more environmentally favourable in comparison to its corrosive trifluoroacetic acid counterpart.

[0086] Orthophosphoric acid was chosen as the preferred phosphorus source as it is readily available in high purity, is non-toxic, non-volatile, relatively inexpensive and as an acid, does not introduce any cations not already present in the sol. in the phosphorus source, such as orthophosphoric acid, is suitable for use in the process and can be used in relatively low concentrations (in the range of 0.0001 to 1 wt %), since losses through evaporation prior to firing will be minimal.

[0087] The present invention will now be described with reference to the following examples which are provided, by way of example only.

TABLE-US-00001 TABLE 1 P-Doping amounts P-Doping amounts Volume OPA Batch added (ml) (x doping) OPA % v/v KCS110 0.057 1 0.0004 KCS111 0.14 2.46 0.0009 KCS112 0.5 8.77 0.0033 KCS117 0.14 2.46 0.0009 KCS118 0.14 2.46 0.0009

[0088] The formulation may optionally include a dispersing agent, to increase the stability of the titanium dioxide dispersion, over and above that achieved by the ionic double layer repulsion resulting from adsorption of the dissociated acids. Such a dispersing agent should ideally be added to the formulation after the hydrolysis is complete. Suitable dispersing agents include organic compounds such as alkanes and alkene oligomers modified with multiple carboxylic acid groups, amine groups or alcohols on side chains. Examples of suitable dispersing agents include Disperbyk 180, Disperbyk 2060, Disperbyk 2061, Disperbyk 2062, Disperbyk 2080, Disperbyk 2081 and Disperbyk 2205. The five samples, logged as KCS110, KCS111,KCS112, KCS 117 and KCS 118 were prepared as follows.

EXAMPLE 1

[0089] Examples 1-3 describe an embodiment of the invention wherein the order of addition is as follows:

[0090] a) tetraisopropoxide

[0091] b) glacial acetic acid

[0092] c) orthophosphoric acid (aqueous) and finally

[0093] d) de-ionised water. [0094] In an alternative embodiment a dispersing agent may be added following the addition of de-ionised water.

[0095] KCS110: [0096] 1. 10 mL titanium tetraisopropoxide (TTIP) was placed in a polypropylene beaker. [0097] 2. 19.2 mL glacial acetic acid was added while stirring. [0098] 3. 0.057 mL 86% orthophosphoric acid (aqueous) was added while stirring. [0099] 4. 120 mL deionised water was added while stirring and the mixture stirred for a further 40 minutes, to form a colourless, slightly hazy sol, which was then bottled.

EXAMPLE 2

[0100] KCS111: [0101] 1. 10 mL TTIP was placed in a polypropylene beaker. [0102] 2. 19.2 mL glacial acetic acid was added while stirring. [0103] 3. 0.14 mL 86% orthophosphoric acid (aqueous) was added while stirring. A small quantity of white precipitate began to form. [0104] 4. 120 mL deionised water was added while stirring and the mixture stirred for a further 40 minutes. A sol with a translucent milky white appearance was formed and the precipitate previously formed re-dispersed, which was then bottled.

EXAMPLE 3

[0105] KCS112: [0106] 1. 10 mL TTIP was placed in a polypropylene beaker. [0107] 2. 19.2 mL glacial acetic acid was added while stirring. [0108] 3. 0.5 mL 86% orthophosphoric acid (aqueous) was added while stirring. A larger quantity of white precipitate began to form than in the case of KCS111. [0109] 4. 120 mL deionised water was added while stirring and the mixture stirred for a further 40 minutes. A sol with a translucent milky white appearance was formed, that was denser in colour than KCS111, which was then bottled.

EXAMPLE 4

[0110] Example 4 describes an alternative embodiment, wherein the order of addition of the reagents is as follows: [0111] a) TTIP [0112] b) Glacial acetic acid [0113] c) De-ionised water [0114] d) Orthophosphoric acid (aqueous) [0115] A dispersing agent may be added following the addition of orthophosphoric acid.

[0116] KCS117: [0117] Orthophosphoric acid can be added after the addition of the deionised water to the glacial acetic acid/TTIP mixture. [0118] 1. 10 mL TTIP was placed in a polypropylene beaker. [0119] 2. 19.2 mL glacial acetic acid was added while stirring. [0120] 3. 120 mL deionised water was added while stirring and the mixture stirred for 20 minutes. A sol with a translucent milky white appearance was formed. [0121] 4. 0.14 mL 86% orthophosphoric acid (aqueous) was added while stirring. A small quantity of white precipitate began to form. The sol was stirred for a further 40 minutes and this precipitate re-dispersed.

EXAMPLE 5

[0122] Example 5 describes an alternative embodiment, wherein the order of addition of the reagents is as follows: [0123] a) TTIP [0124] b) Glacial acetic acid [0125] c) Orthophosphoric acid (aqueous) dissolved in de-ionised water
A dispersing agent may be added following the addition of orthophosphoric acid.

[0126] KCS118: [0127] Orthophosphoric acid can be added at the same time as the addition of the deionised water to the glacial acetic acid/TTIP mixture. [0128] 1. 10 mL TTIP was placed in a polypropylene beaker. [0129] 2. 19.2 mL glacial acetic acid was added while stirring and the mixture stirred for 20 minutes. [0130] 3. 0.14 mL 86% orthophosphoric acid (aqueous) was dissolved in 120 mL deionised water. This solution was added to the mixture of TTIP and glacial acetic acid while stirring and the mixture stirred for 40 minutes. A sol with a translucent milky white appearance was formed.

Antimicrobial Testing Results

[0131] Antimicrobial testing was carried out to determine the antibacterial activity of a photocatalytic material applied to ceramic tiles against Staphylococcus aureus after 6 hours exposure to light as per ISO 27447:2009.

[0132] 18 ceramic tiles coated with KCS116 and 24 uncoated ceramic tiles were submitted to an independent third party, namely, Airmid Healthgroup Ltd., for testing by the Applicant. Six coated and nine uncoated control ceramic tiles were randomly selected for testing.

[0133] The number of viable bacteria recovered from the tiles at t=0 and after 6 hours exposure to UV or dark conditions are expressed as colony forming units per ml (cfu/ml). The photocatalytic antibacterial activity value after irradiation (RL) and the photocatalytic antibacterial activity including any effect in the dark (ΔR) are calculated from the logarithmic values for viable bacteria (cfu/ml) according to the formulae in ISO 27447: 2009. These results are presented in Table 2 below.

TABLE-US-00002 TABLE 2 Antimicrobial testing of coated and uncoated samples Summary of Results for Staphylococcus aureus Log Sample Contact Time Values Sample Exposure 0 Hrs 6 Hrs Log.sub.10 KCS116 UV 3.88E+05 3.33E+01 0.47 coated 0.25 mW/cm.sup.2 KCS116 Dark 3.88E+05 1.69E+05 5.12 coated Uncoated UV 3.88E+05 9.67E+04 4.93 Control 0.25 mW/cm.sup.2 Uncoated Dark 3.88E+05 1.04E+05 5.01 Control
It can be seen from the results outlined in Table 2 that there is a significant reduction in the number of colony forming units following UV exposure observed regarding the formulation coated sample in comparison to the control.
The log values from the Table 2 were used to calculate RL and ΔR, where the Photocatalytic antibacterial activity RL=3.46 and the Photocatalytic antibacterial activity including any effect in the dark ΔR=3.67.

Sample Preparation

[0134] The crystal structure, phase composition, and bandgap of P-doped solution were determined by Raman spectroscopy, X-ray diffraction, and UV-Vis spectroscopy after heating to 700° C., 900° C., 950° C., 1000° C. and 1100° C.

[0135] Powders were prepared from each sol by heating samples of approximately 20 mL to 200° C. on a hotplate. The dried residue was then heated at a rate of 10° C. per minute to the target temperature, held for 1 hour and then allowed to cool naturally to room temperature.

Antibacterial Activity of Photocatalytic Materials According to ISO 27447:2009

Purpose

[0136] The purpose this test was to determine the antibacterial activity of a photocatalytic material applied to ceramic tiles against Staphylococcus aureus after 6 hrs exposure to UV light as per ISO 27447:2009.

Procedure

[0137] The experimental procedure was performed according to ISO 27447: 2009.

[0138] Details of the test-setup are summarised in the following table.

TABLE-US-00003 Test set-up details ISO27447 Method used: Film Adhesion Method Bacteria Staphylococcus aureus (ATCC ® 6538P) Light Source UV 15 W Fluorescent Blacklight Lamp (F15T8/BL) UV intensity 0.25 mW/cm.sup.2 UV Contact Time 6 hrs

Calculations

[0139] Number of viable bacteria recovered from the tiles at t=0 and after 6 hours exposure to UV or dark are expressed as colony forming units per ml (cfu/ml). The photocatalytic antibacterial activity value after irradiation (R.sub.L) and the photocatalytic antibacterial activity including any effect in the dark (ΔR) are calculated from the logarithmic values for viable bacteria (cfu/ml) according to the formulae in ISO 27447: 2009. These results are presented in Table 4.1.

Satisfaction of Criteria for a Valid Test

[0140] Test results obtained were assessed for validity according to the criteria specified in ISO 27447:2009. The criteria are summarised in Table 4.2 below. All four criteria shown in Table 4.2 must be met in order for the test to be valid. If one or more of these criteria are not met, the test is deemed invalid and must be repeated.

Results

[0141] Log values for viable bacterial counts (cfu/ml) recovered from the coated and uncoated ceramic tiles after 6 hrs contact time with UV or in the dark were are shown in Table 4.1.

TABLE-US-00004 TABLE 4.1 Summary of Results for Staphylococcus aureus Log Sample Contact Time Values Sample Exposure 0 Hrs 6 Hrs Log.sub.10 KCS116 UV 3.88E+05 3.33E+01 0.47 coated 0.25 mW/cm.sup.2 KCS116 Dark 3.88E+05 1.69E+05 5.12 coated Uncoated UV 3.88E+05 9.67E+04 4.93 Control 0.25 mW/cm.sup.2 Uncoated Dark 3.88E+05 1.04E+05 5.01 Control

Photocatalytic Antibacterial Activity Results—R.SUB.L .and ΔR

[0142] The log values from the Table 4.1 were used to calculate R.sub.L and ΔR

Summary of Results

Photocatalytic Antibacterial Activity R.SUB.L.=3.46

Photocatalytic Antibacterial Activity Including any Effect in the Dark ΔR=3.67

Validity of Results

[0143]

TABLE-US-00005 TABLE 4.2 Summary of Validity Criteria for ISO 27447 test Criteria Criterion Result Met (✓/x) Log value of No. (Lmax − Lmin)/ 5.60 − 5.58/ ✓ bacteria at 0 hrs (Lmean) < 0.2 5.59 = 0.004 after inoculation No. bacteria at 0 1 × 10.sup.5 to 3.8 × 10.sup.5 to ✓ hrs after inoculation 4 × 10.sup.5 4.0 × 10.sup.5 (cfu/ml) No. bacteria after >1 × 10.sup.3 4.0 × 10.sup.4 to ✓ 6 hrs UV exposure 3.95 × 10.sup.4 for uncoated tiles (cfu/ml) No. bacteria after >1 × 10.sup.3 7.5 × 10.sup.4 to ✓ 6 hrs in dark for 1.2 × 10.sup.5 uncoated tiles (cfu/ml)

Analysis and Results

Raman Spectroscopy

[0144] As stated in the background, in order for a TiO.sub.2 surface to be photocatalytic, it must be in the Anatase or Brookite phase (more commonly Anatase). Therefore, the factor which limits the temperature range for firing of a TiO.sub.2 solution, is the temperature at which it will still have enough Anatase present to be a functional photocatalyst. This transition from Anatase to Rutile is also time dependent, however, if time is kept constant across all quality checks, then a comparison can be built up between the abilities of the F-doped and P-doped solutions to maintain Anatase at high temperatures.

[0145] Samples of the different levels of P-doping were converted to powder form by calcination at various temperatures. These samples were then examined by Raman Spectroscopy to determine the presence of Anatase, Rutile and Brookite in them.

[0146] The Raman measurements were carried out using a laser with excitation wavelength of 532 nm (700-800 nm sampling depth). The spectra were recorded in two modes, namely line scan and image scan. In the line scan mode, 30 points across a line with integration time of 15 s were measured across several areas of the powdered specimen. For Raman imaging, 3600 spectra were averaged in the chosen areas across the sample. This comprehensive Raman sampling ensured the obtained spectra are representative of the powder sample characteristics.

Summary of Raman Results

[0147] For reference, the Raman peak position of three natural TiO.sub.2 polymorphs has been tabulated and shown in Table 3. It is noted that in each crystal phase, there is a strong Raman peak which is indicative of the presence of that TiO.sub.2 crystal phase in the sample. If that peak is observed, then other peaks can be assigned accordingly; otherwise, assigning unknown peaks that appear at the wavenumbers close to the values shown in Table 3 to a particular titania crystal phase is incorrect.

TABLE-US-00006 TABLE 3 TiO.sub.2 natural polymorph Raman peak positions. Anatase Rutile Brookite 127, strong, A.sub.1g 133, weak, B.sub.1g 144, very strong, E.sub.g 143, weak, B.sub.1g 153, very strong, A.sub.1g 159, shoulder, B.sub.1g 172, shoulder, B.sub.3g 197, weak, E.sub.g 194, weak, A.sub.1g 215, weak, B.sub.1g 235, broad medium, combination band 247, medium, A.sub.1g 254, weak, B.sub.2g 273, shoulder 287, weak, B.sub.3g 320, very weak, 320, weak, 320, weak, B.sub.1g combination band 2.sup.nd order band 329, weak, B.sub.2g 357, weak, 2.sup.nd order band 366, weak, B.sub.2g 399, medium, B.sub.1g 395, shoulder, B.sub.2g 412, weak, A.sub.1g 415, weak, B.sub.1g 447, strong, E.sub.g 452, weak, B.sub.3g 463, weak, B.sub.2g 476, weak, B.sub.3g 497, weak, A.sub.1g 502, weak, B.sub.1g 516, medium, A.sub.1g & B.sub.1g 612, strong, A.sub.1g 545, weak, B.sub.3g 584, weak, B.sub.2g 618, weak, B.sub.3g 639, medium, E.sub.g 640, strong, A.sub.1g 695, very weak, combination band 796, weak, B.sub.1g overtone 826, weak, B.sub.2g

[0148] The Raman spectrum of FIG. 2 was recorded from a sample fired at 900° C. The most prominent Raman band is the peak at 143.2 cm.sup.−1 that is confidently assigned to the Anatase E.sub.g Raman mode. The other Raman peak observed in the spectrum are also assigned to various other Raman modes of Anatase which appear with less intensity.

[0149] The spectrum of FIG. 3 was recorded from a sample fired at 950° C. but cooled in a furnace with faster cooling rate in comparison to the previous specimen. The A refers to Anatase and R denoted Rutile phase in the spectrum. One can notice that faster cooling rate results in higher fraction of Rutile which could be due to the fact that Anatase is an elongated structure, so the atoms need more time for diffusion along the c axis of the crystal.

[0150] FIG. 4 shows a line scan spectrum averaged over 30 points of data acquisition, showing similar bands to the previous spectrum. One can note that even at 1000° C. there is still Anatase detectable in the specimen. To further analyse the distribution of anatase and its fraction, Raman imaging was carried out whose results are shown in FIG. 5. The results confirm that Anatase is present in satisfactory quantity over the surface.

[0151] FIG. 6 shows the line scan averaged spectrum of specimen fired at 700° C. As expected, the only detectable Raman peaks are related to Anatase phase, comprising %100 of the specimen.

[0152] FIG. 7 displays the averaged Raman line-scan spectrum of 900° C., clearly showing presence of Anatase phase in the specimen. The very weak almost negligible peaks at ˜796 cm.sup.−1 and cm.sup.−1>1000 are attributed to titanium phosphate phases.

[0153] FIG. 8 shows the Raman spectrum of 950° C. sample averaged over 30 points in a line-scan. The spectrum only consists of Anatase peaks, implying one-phase nature of this sample.

[0154] FIG. 9 shows the average spectrum of 1000° C. specimen, showing a mixed-phase nature. The medium and strong peaks are assigned as (left to right): 143.1 to Anatase, 234.9 to Rutile, 447.7 to Rutile, 611.3 to Rutile. The peaks at 720 and ˜1036 are attributed to titanium phosphate phases.

[0155] FIG. 10 shows the optical microscope image (left) and the scanned area (red square) and the corresponding Raman imaging maps of Anatase and Rutile phases.

[0156] FIG. 11 shows the optical microscope image, total average spectrum, and corresponding Anatase and Rutile maps of the red square marked in the green image. These results suggest that even at a temperature as high as 1100° C., there is still noticeable amount of Anatase present in the specimen.

[0157] FIG. 12 displays the Raman spectrum of sample averaged over 30 points line-scan acquisitions. The spectrum consists of strong representative Anatase peaks and some weak peaks at wavenumbers >1000 cm.sup.−1 which are assigned to Ti phosphate phases. The same behaviour was observed in the case of specimen fired at 950° C. (see FIG. 13).

[0158] FIG. 14 shows the Raman imaging results from the 1000° C. sample. The main point to note is the strong Anatase signal and the titanyl pyrophosphate (TPP) phase. This implies that a higher P content in the sol results in stabilisation of Anatase, while the fraction of TPP phase also increases.

[0159] FIG. 15 shows the Raman imaging results of sample fired at 1100° C. While Rutile makes up the matrix phase of specimen, it is interesting to see that Anatase is still present at such a high temperature. One difference to note is the intensity of TPP phase that has increased in this sample, possibly due to the higher energy input in the system to overcome the energy barrier needed to form TPP phases. Since TPP can act as photocatalyst itself, the overall photocatalytic performance of the system is expected to improve.

X-Ray Diffractometry (XRD) Results

[0160] KCS110

[0161] KCS110 consisted entirely of anatase at 700° C. (FIG. 16) and 900° C. (FIG. 17), while at 950° C. (FIG. 18), the majority phase was rutile. A small minority of anatase was present at 1000° C. (FIG. 19) and at 1100° C. (FIG. 20), the only phase detected was rutile. The peak resolution increased between 700° C. and 900° C. It is not clear whether this was due to the elimination of a small quantity of residual amorphous material, or reduced peak spreading caused by grain growth.

[0162] KCS111

[0163] As was the case with KCS110, KCS111 was composed entirely of anatase at 700° C. (FIG. 21) and 900° C. (FIG. 22), but at 950° C. (FIG. 23), anatase remained the majority component, with only a small proportion of rutile, in approximately the reverse proportion to that seen in KCS110. After heating to 1000° C. (FIG. 24), only a small fraction of anatase remains and at 1100° C. (FIG. 25), the sample is entirely rutile.

[0164] KCS112

[0165] After heating to 700° C. (FIG. 26), KCS112 appears to be composed of anatase, but the spectrum shows substantially more peak spreading than was the case for KCS110 or KCS111. After heating to 900° C. (FIG. 27), associated with the anatase structure are more clearly defined, but a second phase is clearly present. It has not yet been established whether this is a phosphorus oxide, or a titanium phosphate. At 950° C. (FIG. 28), the spectrum continues to evolve, with peaks consistent with a composition containing at least three phases, anatase, rutile and the third phase that was appearing at 900° C.

[0166] At 1000° C. (FIG. 29), the spectrum is overly complex. A multitude of peaks, many of which were not present at 950° C., indicates that as well as rutile and a small fraction of anatase, there are at least two other phases present. Given the composition of the powder, it is reasonable to postulate that these are a mixture of titanium phosphates. After heating to 1100° C. (FIG. 30), the spectrum is simpler again, with peaks indicating that the sample contains only rutile and one or more titanium phosphates, distinct from the phase that formed at 900° C.

UV-Visible Spectroscopy and Band Gap Calculations

[0167] Samples were prepared for UV-visible spectroscopy, by mixing approximately 1% of the powders calcined at 700° C. and 900° C. in dry potassium bromide, grinding to a fine powder and pressing into discs in a 13 mm pellet die. Spectra (FIGS. 31-37) were collected in transmission mode over a range of 600 nm to 250 nm, using a Shimadzu 1800 spectrophotometer. Spectra were plotted as a function of absorbance against wavelength and band gap energies were calculated by fitting tangents to the high transparency part of the spectrum in visible wavelengths and the range over which the material underwent a transition from transparent to opaque. The wavelength A, at the intersection of the two tangents was taken as the onset of the transition from transparent to opaque and the band gap energy calculated from the formula e=λ/1236, where 1236=hc.

Results are given in the Table 4 below.

TABLE-US-00007 TABLE 4 UV-Visible Spectroscopy and band gap calculations KCS110 KCS111 KCS112 KCS117 KCS118 Absorption Band Absorption Band Absorption Band Absorption Band Absorption Band edge gap edge gap edge gap edge gap edge gap Temp. wavelength energy wavelength energy wavelength energy wavelength energy wavelength energy (° C.) nm eV nm eV nm eV nm eV nm eV 700° C. 397.88 3.11 397.03 3.11 396.28 3.12 394.38 3.13 385.01 3.21 900° C. 397.73 3.11 393.05 3.15 364.05 3.40 *428.77 *2.89 *KCS112 showed a spectrum in which the absorbance increased by approximately 0.4 over a range of 20 nm, then continued to increase smoothly and gradually in the UV range. This value is the extrapolated intercept of this UV absorption range into the visible range.
Examples with reduced acetic acid P-doped process with dispersants: [0168] Two formulations were prepared, using a reduced quantity of acetic acid, combined with a polymeric dispersant. The purpose of making these formulations was to determine whether a stable, dispersed sol could be made, which had a pH as close to 7.0 as possible and at least greater than 3.0. This was intended to yield a product which was subject to less stringent transport controls than the known product and which needed less stringent exposure control measures during use. [0169] The two formulations, recorded as KEF002 and KEF004 were prepared according to the following process steps: The relevant spectra are shown in accompanying FIGS. 40 to 43, inclusive, in which: [0170] FIG. 40 is a UV spectrum of KEF002 @1000° C.; [0171] FIG. 41 is a UV spectrum of KEF002 @1050° C.; [0172] FIG. 42 is a UV spectrum of KEF004 @1000° C.; and [0173] FIG. 43 is a UV spectrum of KEF004 @1050° C.

[0174] KEF002: [0175] 5. 5 mL titanium tetraisopropoxide (TTIP) was placed in a polypropylene beaker. [0176] 6. 7.5 mL glacial acetic acid was added while stirring. [0177] 7. 0.085 mL 86% orthophosphoric acid (aqueous) was added while stirring. [0178] 8. 1 mL BYK Disperbyk 180 polymeric dispersant was added while stirring [0179] 9. 90 mL deionised water was added while stirring and the mixture stirred for a further 40 minutes, to form a white, hazy suspension, which was then bottled.

[0180] KEF004: [0181] 1. 5 mL titanium tetraisopropoxide (TTIP) was placed in a polypropylene beaker. [0182] 2. 7.5 mL glacial acetic acid was added while stirring. [0183] 3. 0.085 mL 86% orthophosphoric acid (aqueous) was added while stirring. [0184] 4. 0.2 mL BYK Disperbyk 180 polymeric dispersant was added while stirring [0185] 5. 90 mL deionised water was added while stirring and the mixture stirred for a further 40 minutes, to form a white, hazy suspension, which was then bottled. [0186] Both of these formulations, KEF002 and KEF004, were viscous white suspensions, with a small quantity of residual hard aggregates. These aggregates formed as a precipitate early in the hydrolysis, the majority of which redispersed during stirring, but a small quantity of which remained undispersed. [0187] The dispersant was added to the non-aqueous reagents before hydrolysis to allow it to bond to the titania particles as soon after formation as possible, since performing the hydrolysis in mixtures with low acid concentrations or neutral pH was found to produce a highly aggregated suspension and adding the dispersant after completing the hydrolysis had not produced finely dispersed sols. [0188] The pH of each suspension was measured, the results being: [0189] KEF002 pH3.3 [0190] KEF004 pH2.9 [0191] These results are consistent with the dispersant having amine-terminated functional groups that bond the dispersant's polymeric backbone to the titania surface. [0192] Samples of these formulations, KEF002 and KEF004, were dried in crucibles on hotplates at 200° C. and then calcined at 1000° C. and 1050° C. for 1 hour. The calcined powders were then analysed by XRD. [0193] Both formulations contained a mixture of anatase and rutile after calcination at 1000° C., with the majority of the material being rutile, but a substantial minority, approximately 20 to 30% being retained anatase. After calcination at 1050° C., KEF002 consisted almost entirely of rutile. Small peaks indicated the presence of another phase, but there was no evidence of retained anatase. The spectrum of KEF004 attached in FIG. 43, calcined at the same temperature of 1050° C. showed that it was also predominantly rutile, with small peaks consistent with a minimal amount of retained anatase, near the detection limit and a third phase forming the balance.

[0194] As can be seen and, as is evidenced by the above discussion and attached Figures, the present invention provides a process comprising an anionic dopant source that provides several simultaneous advantages over known formulations.

[0195] Firstly, by using a non-volatile dopant source, phosphoric acid, in place of trifluoroacetic acid, the doping efficiency is much improved, as practically none of the dopant source is lost during the coating process and it is instead incorporated into the titanium dioxide matrix.

[0196] It has surprisingly been found by the inventors that the introduction of phosphorus for fluorine as a dopant increases the anatase to rutile transformation by between 50° C. and 100° C., while still maintaining the reduction in bandgap energy that brings the longest effective light wavelength for photocatalysis into the violet part of the visible spectrum. Equally, there was an increase in pH from 1.1 to over 3.0 which makes the formulation less acidic.

[0197] The level of phosphorus doping provided by the present invention defines the advantageous technical effect that the band gap energy is shifted into the visible part of the spectrum, the anatase to rutile transformation temperature is increased and the formation of titanium phosphates is avoided and the doping method of the present invention has the surprising technical advantage of promoting uniform doping in a stable nanoparticulate sol, suitable for preparing robust, transparent coatings.

[0198] The words comprises/comprising when used in this specification are to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.