International Journal of Cosmetic Science, 2015, 37, 123–128
doi: 10.1111/ics.12179
Temperature dependence and P/Ti ratio in phosphoric acid treatment of titanium dioxide and powder properties H. Onoda and A. Matsukura Department of Informatics and Environmental Sciences, Kyoto Prefectural University, 1-5, Shimogamo Nakaragi-cyo, Sakyo-ku Kyoto 606-8522, Japan
Received 17 July 2014, Accepted 11 September 2014
Keywords: chemical synthesis, skin barrier, spectroscopy
Synopsis OBJECTIVE: Titanium dioxide has photocatalytic activity and is used as a white pigment for cosmetics. A certain degree of sebum on the skin is decomposed by the ultraviolet radiation in sunlight. In this work, titanium dioxide was shaken with phosphoric acid to synthesize a white pigment for cosmetics. METHODS: Titanium dioxide was treated with 0.1 mol/L of phosphoric acid at various P/Ti molar ratios, and then shaken in hot water for 1 h. The chemical composition, powder properties, photocatalytic activity, colour phase, and smoothness of the obtained powder were studied. RESULTS: The obtained materials indicated XRD peaks of titanium dioxide, however the peaks diminished subsequent to phosphoric acid treatment. The samples included small particles with submicrometer size. The photocatalytic activity of the obtained powders decreased, decomposing less sebum on the skin. Samples prepared at high P/Ti ratio with high shaking temperature indicated low whiteness in in L*a*b* colour space. The shaking and heating temperature and P/Ti ratio had influence on the smoothness of the obtained materials. CONCLUSION: Phosphoric acid treatment of titanium dioxide is an effective method to inhibit photocatalytic activity for a white pigment. sume Re OBJECTIF: Le dioxyde de titane qui possede une activite photocatalytique est utilise en tant que pigment blanc pour les produits cosmetiques. Un certain degre de sebum sur la peau est decompose par le rayonnement ultraviolet de la lumiere solaire. Dans ce travail, le dioxyde de titane a ete traite avec de l’acide phosphorique pour synthetiser un pigment blanc pour les produits cosmetiques. l’acide phosphoriMETHODES: Le dioxyde de titane a ete traite a divers rapports molaires P/Ti, et ensuite a l’eau que 0.1 mol/L a chaude en agitant pendant 1 heure. La composition chimique, les proprietes de poudre, une activite photocatalytique, la phase de couleur, et la fluidite de la poudre obtenue ont ete etudiees. RESULTATS: Les materiaux obtenus indiquent des pics de diffraction des rayons X du dioxyde de titane, cependant, les pics devien l’acide phosphorique. Les nent plus faibles suite au traitement a Correspondence: Hiroaki Onoda, Department of Informatics and Environmental Sciences, Kyoto Prefectural University, 1-5, Shimogamo Nakaragi-cyo, Sakyo-ku, Kyoto 606-8522, Japan. Tel.: 81-75-7035653; fax: 81 75 703 5653; e-mail; [email protected]
echantillons comprenaient de petites particules de taille submicrometrique. L’activite photocatalytique des poudres obtenues a diminue, ainsi decomposant moins de sebum sur la peau. Les echantillons prepares a ratio P/Ti et a temperature eleves donnent une blancheur plut^ot faible dans l’espace de couleur L*a*b*. La temperature lors de l’agitation et le ratio P/Ti ont eu une influence sur la finesse des materiaux obtenus. l’acide phosCONCLUSION: Le traitement du dioxyde de titane a phorique est une methode efficace pour inhiber l’activite photocatalytique d’un pigment blanc.
Introduction As a white pigment, titanium dioxide is used for cosmetic applications [1]. This dioxide is well known to have photocatalytic activity. Therefore, a certain degree of sebum on the skin is decomposed by the ultraviolet radiation in sunlight. To repress this effect, technical processes of several kinds have been investigated and used. For example, as one such technique, composite particles with silicon dioxide have been used [2]. However, these particle materials are too hard for use on a human face. Mild materials are required for use as a white pigment on a human face. In addition, one report has described that microfine titanium dioxide is adsorbed through the skin [3]. A white pigment that is not adsorbed must be used. Phosphates have been used for ceramic materials, catalysts, adsorbent, fluorescent materials, dielectric substances, biomaterials, for metal surface treatment, as fertilizer, detergents, food additives, in fuel cells, pigments and in other applications [4, 5]. Phosphate materials are well known to have high affinity for living organisms. Therefore, as a white pigment, phosphates are expected to be useful as cosmetics. In earlier studies [6, 7], we prepared a titanium phosphate pigment with titanium chloride and phosphoric acid that had no catalytic activity. This compound had a weak point that the titanium chloride is difficult to treat because of the formation of smoke and undesirable precipitate. Generally, raw materials have influence on the formation and properties of materials. In the group of titanium compounds, titanium sulphate is also important compound to obtain titanium dioxide as well as titanium chloride. In previous work, titanium phosphate was prepared with titanium sulphate and phosphoric acid [8]. The obtained phosphates also indicated no photocatalytic activity. Small and homogeneous particles are suitable for cosmetic applications. However, overly small particles have a major shortcoming
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie
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in that they enter the pores of the skin [3]. Generally, pigments with submicrometre size are used. The standard size of white pigment particles used in cosmetics is difficult to determine because the pore sizes of the skin are affected by such factors as age, gender and climate. Furthermore, overly large particles are inappropriate owing to a cracking of their coating on the skin. It is therefore important to control the particle sizes of the pigment. In the previous works [6–8], the titanium phosphates prepared from titanium chloride and phosphoric acid, from titanium sulphate and phosphoric acid had larger particles than 10 lm. Because these particles were too large, the novel process was required to produce the smaller particles as a white pigment. The titanium phosphate without photocatalytic activity had too much large particles; on the other hand, titanium dioxide in small particle size had a photocatalytic activity. In this work, we suggest the titanium dioxide particles with titanium phosphate coating. Our purpose in this work was to obtain the white pigment in submicrometre size without photocatalytic activity. In this work, titanium dioxide was shaken with phosphoric acid under various conditions. The respective chemical compositions, powder properties, photocatalytic activity, colour phases, and smoothness of the obtained samples and their thermal products were studied for application to cosmetics. Materials and methods Titanium dioxide was set with 0.1 mol L 1 of phosphoric acid (50 mL) at molar ratios of P/Ti = 2/1, 1/1, 1/2 and 1/4 in a glass tube (4–16 tubes, total amount of sample; about 0.8 g), and then, this glass tube was shaking in hot water at 60, 70 and 80°C for 1 h (rate of shaking; 100 times min 1). The solutions were decantated off, and the powder samples were washed with water and then dried at 50°C over 3 days. All chemicals were of commercial purity from Wako Chemical Industries Ltd. (Osaka, Japan) and used without further purification. The chemical compositions of these materials were analysed using X-ray diffraction (XRD). The XRD patterns were recorded on an X-ray diffractometer (MiniFlex; Rigaku Corp., Akishima, Japan) using monochromated CuKa radiation. Samples were heated at 100, 200 and 400°C for 1 h in air conditions (MMF1; AS ONE corp., Osaka, Japan). These thermal products were also analysed according to their XRD patterns. The particle shapes and sizes of the precipitates, as well as their thermal products at 100, 200 and 400°C, were estimated based on scanning electron microscopy (SEM) images and particle-size distributions. The SEM images of the sample powders were observed (JGM5510LV; JEOL, Akishima, Japan). The particle-size distributions of these materials were measured using a centrifugal precipitation particle-size distribution (SA-CP3L, Shimadzu Corp., Kyoto, Japan). The cosmetic properties were estimated according to the photocatalytic activity, the colour phase and the smoothness. The photocatalytic activity of samples was estimated with the decomposition of methylene blue by 365 nm radiation [9, 10]. The 0.01 g of sample was placed in 4 mL of methylene blue solution (1.0 9 10 5 mol L 1), and then, this solution was radiated. The decrease of the absorption at about 660 nm was estimated for 120 min (number of replicates; three times). The colour of phosphate pigments was estimated using ultraviolet–visible (UV–Vis) reflectance spectra with a spectrometer (UV2100; Shimadzu Corp., Kyoto, Japan) (reference compound; BaSO4). The whiteness was also estimated with TES135 plus colour
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analyser (TES Electrical Electronic Corp, Taipei, Taiwan) (average of five times). The particle smoothness was measured on artificial leather with KES-SE objective evaluation of surface friction property (Kato Tech Co. Ltd., Kyoto, Japan) (average of five times). The values of MIU and MMD, respectively, represent the slipping resistance (coefficient of kinetic friction) and roughness of powders (dispersion on coefficient of kinetic friction). Sample powders were spread on the leather. Then a sensor was run over these powders. The values of MIU and MMD were calculated, respectively, from the power to move a sensor and the pitching of a sensor. The values of MIU and MMD have no unit because these values are related with coefficient of friction and scattering, respectively. Results and discussion Chemical composition and powder properties Figure 1 presents XRD patterns of samples prepared in P/Ti = 1/1 at various shaking temperature and then heated at 100°C for 1 h in air condition. All samples treated with phosphoric acid indicated the same peak pattern with original titanium dioxide. However, the peak intensity became weak by the phosphoric acid treatment. A part of titanium dioxide was considered to react with phosphoric acid. Table I shows the ratios of XRD peak intensities of samples prepared under various conditions. These ratios were calculated from the peak intensities of samples and original titanium dioxide. The value ‘100%’ meant the same intensity with original titanium dioxide, namely titanium dioxide had no change by the phosphoric acid treatment. The lower ratio was corresponding with the reaction between titanium dioxide and phosphoric acid. Samples prepared with shaking at 80°C had the lower ratio than samples prepared with shaking at 60 and 70°C. Titanium dioxide reacted with phosphoric acid at high temperature in the shaking process.
Figure 1 XRD patterns of samples prepared in P/Ti = 1/1 at various shaking temperatures and then heated at 100°C for 1 h in air condition: (a) original TiO2, (b) 60°C, (c) 70°C and (d) 80°C.
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 123–128
H. Onoda and A. Matsukura
Phosphoric acid treatment of titanium dioxide Table I Ratios of XRD peak intensities of samples prepared under various conditions
Heating temperature/°C
a b c d e f g h
P/Ti
Shaking temp. /°C
R.T.
100
200
400
2/1 1/1 1/1 1/1 1/2 1/2 1/2 1/4
80 80 70 60 80 70 60 80
43.1 57.9 1a 1a 47.9 60.8 49.8 88.2
30.7 49.1 71.3 88.7 69.5 78.8 71.2 82.4
54.7 51.8 81.8 93.8 71.7 81.9 84.9 83.6
52.3 53.9 86.5 76.0 77.3 73.4 83.4 83.6
a
1, could not estimate because of the aggregation with water.
The high heating temperature had the weak tendency to indicate the higher ratio of XRD peak intensity. Samples prepared at high P/Ti ratio indicated lower ratio of XRD peak intensity, because the large amount of phosphoric acid reacted with titanium dioxide easily. XRD peak intensity in the most reacted material decreased by 70%. Therefore, as an image of particles, the core part of sample particles was titanium dioxide and the surface of particles was considered to be titanium phosphate. Because titanium phosphate was easy to form amorphous state in previous works [6–8], no novel peaks were observed in XRD patterns. From the viewpoint of particle shape, spherical particles are suitable for cosmetic applications. Figure 2 portrays SEM images of samples prepared in P/Ti = 1/1 with various shaking temperatures and then heated at 100°C. Titanium dioxide assembled to larger
particles than 10 lm (Fig. 2a). All samples prepared with shaking in phosphoric acid also had large particles. The small particles were observed in large particles with shaking at 60 and 70°C (Fig. 2b,c). On the other hand, sample prepared with shaking at 80°C had less particle boundary in large particles. By shaking at 80°C, the aggregation of particles was considered to take place. Figure 3 presents the particle-size distribution of samples prepared in P/Ti = 1/1 with shaking at 80°C and then heated at various temperatures. Because sample without heating had smaller particles than 1 lm, the large particles dispersed by stirring before the measurement of particle-size distribution. By shaking at 80°C, sample particles aggregated imperfectly. Sample heated at 400°C had a certain degree of larger particles than 1 lm (Fig. 3e). The sample particles aggregated by shaking at 80°C and then heating at 400°C. Generally, the pigments with submicrometre size are used for cosmetics. Some samples had the particles with the suitable submicrometre size, except for the samples prepared with heating at 200 and 400°C. Samples with shaking at 60 and 70°C had large particles by heating at 200 and 400°C (not shown). Totally, the dispersion process was important to use as a white pigment, because the major part of samples obtained in this work had the suitable particle size. Cosmetic properties Figure 4 shows the photocatalytic activity of samples prepared in various P/Ti ratios with shaking at 80°C and then heated at 100°C. Methylene blue was decomposed with titanium dioxide using UV radiation (Fig. 4b). The photocatalytic activity of titanium dioxide was inhibited by the phosphoric acid treatment (Fig. 4c–f). Sample prepared at P/Ti = 1/4 indicated the weakest photocatalytic activity. From XRD results, sample prepared at high P/Ti ratio reacted with phosphoric acid easily. Titanium phosphate, expected as a product on the surface of particles, had no photocatalytic activity
(a)
(b)
(c)
(d)
Figure 2 SEM images of samples prepared in P/Ti = 1/1 at various shaking temperatures and then heated at 100°C: (a) original TiO2, (b) 60°C, (c) 70°C and (d) 80°C.
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 123–128
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Figure 3 Particle-size distribution of samples prepared in P/Ti = 1/1 with shaking at 80°C and then heated at several temperatures: (a) original TiO2, (b) without heating, (c) heated at 100°C, (d) 200°C and (e) 400°C.
Figure 5 Photocatalytic activity of samples prepared in P/Ti = 1/1 at various shaking temperatures and then heated at 100°C: (a) blank, (b) original TiO2, (c) 60°C, (d) 70°C and (e) 80°C.
Figure 4 Photocatalytic activity of samples prepared in various P/Ti ratios with shaking at 80°C and then heated at 100°C: (a) blank, (b) original TiO2, (c) P/Ti = 2/1, (d) 1/1, (e) 1/2 and (f) 1/4.
Figure 6 Photocatalytic activity of samples prepared in P/Ti = 1/1 with shaking at 80°C and then heated at several temperatures: (a) blank, (b) original TiO2, (c) R.T., (d) 100°C, (e) 200°C and (f) 400°C.
[6–8]. The inhibition of photocatalytic activity was corresponding with the reaction between titanium dioxide and phosphoric acid. Sample powders prepared at P/Ti = 1/4 were considered to be coated on the whole by titanium phosphate. Because sample prepared at P/Ti = 2/1 reacted with phosphoric acid easily, the formed titanium phosphate on the particle increased. The cracking was formed at surface on particles; therefore, the internal part of particles worked as a photocatalyst. To suppress the photocatalytic activity, the titanium dioxide was treated in the mild condition, low P/Ti ratio.
Figure 5 shows the photocatalytic activities of samples prepared in P/Ti = 1/1 at various shaking temperature and then heated at 100°C. In spite of the shaking temperature, the photocatalytic activity of titanium dioxide became weak by the phosphoric acid treatment. Sample treated at 60°C indicated the weakest photocatalytic activity (Fig. 5c). From XRD analysis, the reaction between titanium dioxide and phosphoric acid took place much more at sample treated at 80°C. The condition to react easily was not suitable to suppress the photocatalytic activity. These results had same tendency with the results about P/Ti ratios.
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© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 123–128
H. Onoda and A. Matsukura
Phosphoric acid treatment of titanium dioxide
Table II Whiteness of samples prepared under various conditions
Heating temperature/°C
a b c d e f g h
P/Ti
Shaking temp. /°C
R.T.
100
200
400
2/1 1/1 1/1 1/1 1/2 1/2 1/2 1/4
80 80 70 60 80 70 60 80
1a 96.6 97.6 1a 96.3 98.8 1a 1a
1a 93.8 97.8 96.4 94.4 97.1 96.1 99.2
96.0 92.9 94.9 92.3 93.4 96.5 96.0 97.2
92.9 96.3 97.7 94.5 97.0 99.6 97.5 98.9
a Could not estimate because of the aggregation with water. Original TiO2: 98.0.
Figure 7 UV–Vis. reflectance spectra of samples prepared at various shaking temperatures and then heated at 100°C: (a) original TiO2, (b) 60°C, (c) 70°C and (d) 80°C.
Figure 6 shows the photocatalytic activities of samples prepared in P/Ti = 1/1 with shaking at 80°C and then heated at various temperatures. Samples without heating and sample heated at 200°C had stronger photocatalytic activity than titanium dioxide. Because the influence of heating temperature was difficult to clear, further experimental results about the heating temperature were required to clear this influence. Figure 7 shows UV–Vis reflectance spectra of samples prepared in P/Ti = 1/1 at various shaking temperature and then heated at 100°C. Samples treated with phosphoric acid indicated lower reflectance than titanium dioxide. In particular, sample prepared with shaking at 80°C had low reflectance in the range of visible light. The decrease of reflectance was related with the reaction between titanium dioxide and phosphoric acid. The absorption near 400 nm had little change by the phosphoric acid treatment. Samples prepared at high P/Ti ratio indicated a little lower reflectance (not shown). This was caused from the reaction between titanium dioxide and phosphoric acid. The colour of sample powder was also estimated by L*a*b* colour space. Table II shows the whiteness of samples prepared in various conditions. These values were L* value in L*a*b* colour space. Because all samples indicated over 90, the obtained samples were suitable as a white pigment. There was a tendency that samples prepared at high P/Ti ratio with high shaking temperature had low whiteness. The heating temperature had little influence on the whiteness of samples. As described above, pigment with high smoothness spreads well on the skin. The powder smoothness is also important for cosmetics [11]. Table III shows the smoothness of samples prepared under various conditions. Generally, for a cosmetic application, the suitable MIU and MMD values are smaller than 0.6 and smaller than 0.04, respectively. Titanium dioxide and samples prepared at P/Ti = 1/4 indicated high MIU values and a little high MMD values. These results were related with the reaction between titanium dioxide and phosphoric acid. Samples prepared at high P/Ti ratio and high shaking temperature indicated the lower MIU and
Table III Smoothness of samples prepared under various conditions
a b c d e f g h i j
P/Ti
Shaking Temp. /°C
Heating Temp. /°C
MIU /
MMD /
TiO2 2/1 1/1 1/2 1/4 1/2 1/2 1/4 1/4 1/4
– 80 80 80 80 60 70 80 80 80
– 400 400 400 400 400 400 200 100 R.T.
1.278 0.416 0.652 0.420 0.766 0.564 0.820 1.152 1.202 1.278
0.019 0.010 0.011 0.009 0.009 0.008 0.008 0.019 0.021 0.018
MMD values. The smoothness of samples improved by the phosphoric acid treatment at high P/Ti ratio, high shaking temperature and high heating temperature. Conclusion Titanium dioxide was shaken in phosphoric acid under various conditions. The obtained materials indicated XRD peaks of titanium dioxide; however, these peaks became weak by phosphoric acid treatment. These samples had small particles with submicrometre size. The photocatalytic activity of titanium dioxide was inhibited by the phosphoric acid treatment. Samples prepared at high P/Ti ratio with high shaking temperature indicated a little low whiteness in L*a*b* colour space. The smoothness of samples was affected by P/Ti ratio, shaking and heating temperatures in the phosphoric acid treatment. The phosphoric acid treatment of titanium dioxide is an effective method to inhibit their photocatalytic activity for a white pigment. Acknowledgement The authors are grateful to Dr. Takeshi Toyama, Nihon University, Japan, for smoothness measurements.
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 123–128
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References 1. Diebold, U. The surface science of titanium dioxide. Surf. Sci. Rep. 48, 53–229 (2003). 2. Senzuki, M., Tamura, T., Miura, K., Ikarashi, Y., Watanabe, Y. and Fujii, M. Study on penetration of titanium dioxide (TiO2) nanoparticles into intact and damaged skin in vitro. J. Toxicol. Sci. 35, 107–113 (2010). 3. Gamer, A.O., Leibold, E. and Van Ravenzwaay, B. The in vitro absorption of microfine zinc oxide and titanium dioxide through porcine skin. Toxicol. In Vitro 20, 301–307 (2006). 4. Jones, D.J., Aptel, G., Brandhorst, M. et al. High surface area mesoporous titanium phosphate: synthesis and surface acidity determination. J. Mater. Chem. 10, 1957–1963 (2000).
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5. Bhaumik, A. and Inagaki, S. Titanium phosphate molecular sieves with ion-exchange capacity. J. Am. Chem. Soc. 123, 691–696 (2001). 6. Onoda, H. and Yamaguchi, T. Influence of ultrasonic treatment on preparation and powder properties of titanium phosphates. J. Mater. Chem. 22, 19826–19830 (2012). 7. Onoda, H., Yamaguchi, T. and Takenaka, A. Synthesis and pigmental properties of titanium phosphates with the addition of urea. Int. J. Cosmet. Sci. 34, 86–90 (2012). 8. Onoda, H., Fujikado, S. and Toyama, T. Preparation of titanium phosphates with titanium sulfate and their powder properties. J. Adv. Ceram. 3, 132–136 (2014).
9. Ramaswamy, V., Jagtap, N.B., Vijayanand, S., Bhange, D.S. and Awati, P.S. Photocatalytic decomposition of methylene blue on nanocrystalline titania prepared by different methods. Mater. Res. Bull. 43, 1145–1152 (2008). 10. Du, P., Bueno-Lopez, A., Verbaas, M., Almeida, A.R., Makkee, M., Moulijn, J.A. and Mui, G. The effect of surface OH-population on the photocatalytic activity of rare earthdoped P25-TiO2 in methylene blue degradation. J. Catal. 260, 75–80 (2008). 11. Cheng, S.Y., Yuen, C.W.M., Kan, C.W., Cheuk, K.K.L., Tang, J.C.O. and Li, S.Y. A comprehensive study of silicone-based cosmetic textile agent. Fib. Polym. 10, 132– 140 (2009).
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 123–128
doi: 10.1111/ics.12179
Temperature dependence and P/Ti ratio in phosphoric acid treatment of titanium dioxide and powder properties H. Onoda and A. Matsukura Department of Informatics and Environmental Sciences, Kyoto Prefectural University, 1-5, Shimogamo Nakaragi-cyo, Sakyo-ku Kyoto 606-8522, Japan
Received 17 July 2014, Accepted 11 September 2014
Keywords: chemical synthesis, skin barrier, spectroscopy
Synopsis OBJECTIVE: Titanium dioxide has photocatalytic activity and is used as a white pigment for cosmetics. A certain degree of sebum on the skin is decomposed by the ultraviolet radiation in sunlight. In this work, titanium dioxide was shaken with phosphoric acid to synthesize a white pigment for cosmetics. METHODS: Titanium dioxide was treated with 0.1 mol/L of phosphoric acid at various P/Ti molar ratios, and then shaken in hot water for 1 h. The chemical composition, powder properties, photocatalytic activity, colour phase, and smoothness of the obtained powder were studied. RESULTS: The obtained materials indicated XRD peaks of titanium dioxide, however the peaks diminished subsequent to phosphoric acid treatment. The samples included small particles with submicrometer size. The photocatalytic activity of the obtained powders decreased, decomposing less sebum on the skin. Samples prepared at high P/Ti ratio with high shaking temperature indicated low whiteness in in L*a*b* colour space. The shaking and heating temperature and P/Ti ratio had influence on the smoothness of the obtained materials. CONCLUSION: Phosphoric acid treatment of titanium dioxide is an effective method to inhibit photocatalytic activity for a white pigment. sume Re OBJECTIF: Le dioxyde de titane qui possede une activite photocatalytique est utilise en tant que pigment blanc pour les produits cosmetiques. Un certain degre de sebum sur la peau est decompose par le rayonnement ultraviolet de la lumiere solaire. Dans ce travail, le dioxyde de titane a ete traite avec de l’acide phosphorique pour synthetiser un pigment blanc pour les produits cosmetiques. l’acide phosphoriMETHODES: Le dioxyde de titane a ete traite a divers rapports molaires P/Ti, et ensuite a l’eau que 0.1 mol/L a chaude en agitant pendant 1 heure. La composition chimique, les proprietes de poudre, une activite photocatalytique, la phase de couleur, et la fluidite de la poudre obtenue ont ete etudiees. RESULTATS: Les materiaux obtenus indiquent des pics de diffraction des rayons X du dioxyde de titane, cependant, les pics devien l’acide phosphorique. Les nent plus faibles suite au traitement a Correspondence: Hiroaki Onoda, Department of Informatics and Environmental Sciences, Kyoto Prefectural University, 1-5, Shimogamo Nakaragi-cyo, Sakyo-ku, Kyoto 606-8522, Japan. Tel.: 81-75-7035653; fax: 81 75 703 5653; e-mail; [email protected]
echantillons comprenaient de petites particules de taille submicrometrique. L’activite photocatalytique des poudres obtenues a diminue, ainsi decomposant moins de sebum sur la peau. Les echantillons prepares a ratio P/Ti et a temperature eleves donnent une blancheur plut^ot faible dans l’espace de couleur L*a*b*. La temperature lors de l’agitation et le ratio P/Ti ont eu une influence sur la finesse des materiaux obtenus. l’acide phosCONCLUSION: Le traitement du dioxyde de titane a phorique est une methode efficace pour inhiber l’activite photocatalytique d’un pigment blanc.
Introduction As a white pigment, titanium dioxide is used for cosmetic applications [1]. This dioxide is well known to have photocatalytic activity. Therefore, a certain degree of sebum on the skin is decomposed by the ultraviolet radiation in sunlight. To repress this effect, technical processes of several kinds have been investigated and used. For example, as one such technique, composite particles with silicon dioxide have been used [2]. However, these particle materials are too hard for use on a human face. Mild materials are required for use as a white pigment on a human face. In addition, one report has described that microfine titanium dioxide is adsorbed through the skin [3]. A white pigment that is not adsorbed must be used. Phosphates have been used for ceramic materials, catalysts, adsorbent, fluorescent materials, dielectric substances, biomaterials, for metal surface treatment, as fertilizer, detergents, food additives, in fuel cells, pigments and in other applications [4, 5]. Phosphate materials are well known to have high affinity for living organisms. Therefore, as a white pigment, phosphates are expected to be useful as cosmetics. In earlier studies [6, 7], we prepared a titanium phosphate pigment with titanium chloride and phosphoric acid that had no catalytic activity. This compound had a weak point that the titanium chloride is difficult to treat because of the formation of smoke and undesirable precipitate. Generally, raw materials have influence on the formation and properties of materials. In the group of titanium compounds, titanium sulphate is also important compound to obtain titanium dioxide as well as titanium chloride. In previous work, titanium phosphate was prepared with titanium sulphate and phosphoric acid [8]. The obtained phosphates also indicated no photocatalytic activity. Small and homogeneous particles are suitable for cosmetic applications. However, overly small particles have a major shortcoming
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie
123
H. Onoda and A. Matsukura
Phosphoric acid treatment of titanium dioxide
in that they enter the pores of the skin [3]. Generally, pigments with submicrometre size are used. The standard size of white pigment particles used in cosmetics is difficult to determine because the pore sizes of the skin are affected by such factors as age, gender and climate. Furthermore, overly large particles are inappropriate owing to a cracking of their coating on the skin. It is therefore important to control the particle sizes of the pigment. In the previous works [6–8], the titanium phosphates prepared from titanium chloride and phosphoric acid, from titanium sulphate and phosphoric acid had larger particles than 10 lm. Because these particles were too large, the novel process was required to produce the smaller particles as a white pigment. The titanium phosphate without photocatalytic activity had too much large particles; on the other hand, titanium dioxide in small particle size had a photocatalytic activity. In this work, we suggest the titanium dioxide particles with titanium phosphate coating. Our purpose in this work was to obtain the white pigment in submicrometre size without photocatalytic activity. In this work, titanium dioxide was shaken with phosphoric acid under various conditions. The respective chemical compositions, powder properties, photocatalytic activity, colour phases, and smoothness of the obtained samples and their thermal products were studied for application to cosmetics. Materials and methods Titanium dioxide was set with 0.1 mol L 1 of phosphoric acid (50 mL) at molar ratios of P/Ti = 2/1, 1/1, 1/2 and 1/4 in a glass tube (4–16 tubes, total amount of sample; about 0.8 g), and then, this glass tube was shaking in hot water at 60, 70 and 80°C for 1 h (rate of shaking; 100 times min 1). The solutions were decantated off, and the powder samples were washed with water and then dried at 50°C over 3 days. All chemicals were of commercial purity from Wako Chemical Industries Ltd. (Osaka, Japan) and used without further purification. The chemical compositions of these materials were analysed using X-ray diffraction (XRD). The XRD patterns were recorded on an X-ray diffractometer (MiniFlex; Rigaku Corp., Akishima, Japan) using monochromated CuKa radiation. Samples were heated at 100, 200 and 400°C for 1 h in air conditions (MMF1; AS ONE corp., Osaka, Japan). These thermal products were also analysed according to their XRD patterns. The particle shapes and sizes of the precipitates, as well as their thermal products at 100, 200 and 400°C, were estimated based on scanning electron microscopy (SEM) images and particle-size distributions. The SEM images of the sample powders were observed (JGM5510LV; JEOL, Akishima, Japan). The particle-size distributions of these materials were measured using a centrifugal precipitation particle-size distribution (SA-CP3L, Shimadzu Corp., Kyoto, Japan). The cosmetic properties were estimated according to the photocatalytic activity, the colour phase and the smoothness. The photocatalytic activity of samples was estimated with the decomposition of methylene blue by 365 nm radiation [9, 10]. The 0.01 g of sample was placed in 4 mL of methylene blue solution (1.0 9 10 5 mol L 1), and then, this solution was radiated. The decrease of the absorption at about 660 nm was estimated for 120 min (number of replicates; three times). The colour of phosphate pigments was estimated using ultraviolet–visible (UV–Vis) reflectance spectra with a spectrometer (UV2100; Shimadzu Corp., Kyoto, Japan) (reference compound; BaSO4). The whiteness was also estimated with TES135 plus colour
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analyser (TES Electrical Electronic Corp, Taipei, Taiwan) (average of five times). The particle smoothness was measured on artificial leather with KES-SE objective evaluation of surface friction property (Kato Tech Co. Ltd., Kyoto, Japan) (average of five times). The values of MIU and MMD, respectively, represent the slipping resistance (coefficient of kinetic friction) and roughness of powders (dispersion on coefficient of kinetic friction). Sample powders were spread on the leather. Then a sensor was run over these powders. The values of MIU and MMD were calculated, respectively, from the power to move a sensor and the pitching of a sensor. The values of MIU and MMD have no unit because these values are related with coefficient of friction and scattering, respectively. Results and discussion Chemical composition and powder properties Figure 1 presents XRD patterns of samples prepared in P/Ti = 1/1 at various shaking temperature and then heated at 100°C for 1 h in air condition. All samples treated with phosphoric acid indicated the same peak pattern with original titanium dioxide. However, the peak intensity became weak by the phosphoric acid treatment. A part of titanium dioxide was considered to react with phosphoric acid. Table I shows the ratios of XRD peak intensities of samples prepared under various conditions. These ratios were calculated from the peak intensities of samples and original titanium dioxide. The value ‘100%’ meant the same intensity with original titanium dioxide, namely titanium dioxide had no change by the phosphoric acid treatment. The lower ratio was corresponding with the reaction between titanium dioxide and phosphoric acid. Samples prepared with shaking at 80°C had the lower ratio than samples prepared with shaking at 60 and 70°C. Titanium dioxide reacted with phosphoric acid at high temperature in the shaking process.
Figure 1 XRD patterns of samples prepared in P/Ti = 1/1 at various shaking temperatures and then heated at 100°C for 1 h in air condition: (a) original TiO2, (b) 60°C, (c) 70°C and (d) 80°C.
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 123–128
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Phosphoric acid treatment of titanium dioxide Table I Ratios of XRD peak intensities of samples prepared under various conditions
Heating temperature/°C
a b c d e f g h
P/Ti
Shaking temp. /°C
R.T.
100
200
400
2/1 1/1 1/1 1/1 1/2 1/2 1/2 1/4
80 80 70 60 80 70 60 80
43.1 57.9 1a 1a 47.9 60.8 49.8 88.2
30.7 49.1 71.3 88.7 69.5 78.8 71.2 82.4
54.7 51.8 81.8 93.8 71.7 81.9 84.9 83.6
52.3 53.9 86.5 76.0 77.3 73.4 83.4 83.6
a
1, could not estimate because of the aggregation with water.
The high heating temperature had the weak tendency to indicate the higher ratio of XRD peak intensity. Samples prepared at high P/Ti ratio indicated lower ratio of XRD peak intensity, because the large amount of phosphoric acid reacted with titanium dioxide easily. XRD peak intensity in the most reacted material decreased by 70%. Therefore, as an image of particles, the core part of sample particles was titanium dioxide and the surface of particles was considered to be titanium phosphate. Because titanium phosphate was easy to form amorphous state in previous works [6–8], no novel peaks were observed in XRD patterns. From the viewpoint of particle shape, spherical particles are suitable for cosmetic applications. Figure 2 portrays SEM images of samples prepared in P/Ti = 1/1 with various shaking temperatures and then heated at 100°C. Titanium dioxide assembled to larger
particles than 10 lm (Fig. 2a). All samples prepared with shaking in phosphoric acid also had large particles. The small particles were observed in large particles with shaking at 60 and 70°C (Fig. 2b,c). On the other hand, sample prepared with shaking at 80°C had less particle boundary in large particles. By shaking at 80°C, the aggregation of particles was considered to take place. Figure 3 presents the particle-size distribution of samples prepared in P/Ti = 1/1 with shaking at 80°C and then heated at various temperatures. Because sample without heating had smaller particles than 1 lm, the large particles dispersed by stirring before the measurement of particle-size distribution. By shaking at 80°C, sample particles aggregated imperfectly. Sample heated at 400°C had a certain degree of larger particles than 1 lm (Fig. 3e). The sample particles aggregated by shaking at 80°C and then heating at 400°C. Generally, the pigments with submicrometre size are used for cosmetics. Some samples had the particles with the suitable submicrometre size, except for the samples prepared with heating at 200 and 400°C. Samples with shaking at 60 and 70°C had large particles by heating at 200 and 400°C (not shown). Totally, the dispersion process was important to use as a white pigment, because the major part of samples obtained in this work had the suitable particle size. Cosmetic properties Figure 4 shows the photocatalytic activity of samples prepared in various P/Ti ratios with shaking at 80°C and then heated at 100°C. Methylene blue was decomposed with titanium dioxide using UV radiation (Fig. 4b). The photocatalytic activity of titanium dioxide was inhibited by the phosphoric acid treatment (Fig. 4c–f). Sample prepared at P/Ti = 1/4 indicated the weakest photocatalytic activity. From XRD results, sample prepared at high P/Ti ratio reacted with phosphoric acid easily. Titanium phosphate, expected as a product on the surface of particles, had no photocatalytic activity
(a)
(b)
(c)
(d)
Figure 2 SEM images of samples prepared in P/Ti = 1/1 at various shaking temperatures and then heated at 100°C: (a) original TiO2, (b) 60°C, (c) 70°C and (d) 80°C.
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 123–128
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Figure 3 Particle-size distribution of samples prepared in P/Ti = 1/1 with shaking at 80°C and then heated at several temperatures: (a) original TiO2, (b) without heating, (c) heated at 100°C, (d) 200°C and (e) 400°C.
Figure 5 Photocatalytic activity of samples prepared in P/Ti = 1/1 at various shaking temperatures and then heated at 100°C: (a) blank, (b) original TiO2, (c) 60°C, (d) 70°C and (e) 80°C.
Figure 4 Photocatalytic activity of samples prepared in various P/Ti ratios with shaking at 80°C and then heated at 100°C: (a) blank, (b) original TiO2, (c) P/Ti = 2/1, (d) 1/1, (e) 1/2 and (f) 1/4.
Figure 6 Photocatalytic activity of samples prepared in P/Ti = 1/1 with shaking at 80°C and then heated at several temperatures: (a) blank, (b) original TiO2, (c) R.T., (d) 100°C, (e) 200°C and (f) 400°C.
[6–8]. The inhibition of photocatalytic activity was corresponding with the reaction between titanium dioxide and phosphoric acid. Sample powders prepared at P/Ti = 1/4 were considered to be coated on the whole by titanium phosphate. Because sample prepared at P/Ti = 2/1 reacted with phosphoric acid easily, the formed titanium phosphate on the particle increased. The cracking was formed at surface on particles; therefore, the internal part of particles worked as a photocatalyst. To suppress the photocatalytic activity, the titanium dioxide was treated in the mild condition, low P/Ti ratio.
Figure 5 shows the photocatalytic activities of samples prepared in P/Ti = 1/1 at various shaking temperature and then heated at 100°C. In spite of the shaking temperature, the photocatalytic activity of titanium dioxide became weak by the phosphoric acid treatment. Sample treated at 60°C indicated the weakest photocatalytic activity (Fig. 5c). From XRD analysis, the reaction between titanium dioxide and phosphoric acid took place much more at sample treated at 80°C. The condition to react easily was not suitable to suppress the photocatalytic activity. These results had same tendency with the results about P/Ti ratios.
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© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 123–128
H. Onoda and A. Matsukura
Phosphoric acid treatment of titanium dioxide
Table II Whiteness of samples prepared under various conditions
Heating temperature/°C
a b c d e f g h
P/Ti
Shaking temp. /°C
R.T.
100
200
400
2/1 1/1 1/1 1/1 1/2 1/2 1/2 1/4
80 80 70 60 80 70 60 80
1a 96.6 97.6 1a 96.3 98.8 1a 1a
1a 93.8 97.8 96.4 94.4 97.1 96.1 99.2
96.0 92.9 94.9 92.3 93.4 96.5 96.0 97.2
92.9 96.3 97.7 94.5 97.0 99.6 97.5 98.9
a Could not estimate because of the aggregation with water. Original TiO2: 98.0.
Figure 7 UV–Vis. reflectance spectra of samples prepared at various shaking temperatures and then heated at 100°C: (a) original TiO2, (b) 60°C, (c) 70°C and (d) 80°C.
Figure 6 shows the photocatalytic activities of samples prepared in P/Ti = 1/1 with shaking at 80°C and then heated at various temperatures. Samples without heating and sample heated at 200°C had stronger photocatalytic activity than titanium dioxide. Because the influence of heating temperature was difficult to clear, further experimental results about the heating temperature were required to clear this influence. Figure 7 shows UV–Vis reflectance spectra of samples prepared in P/Ti = 1/1 at various shaking temperature and then heated at 100°C. Samples treated with phosphoric acid indicated lower reflectance than titanium dioxide. In particular, sample prepared with shaking at 80°C had low reflectance in the range of visible light. The decrease of reflectance was related with the reaction between titanium dioxide and phosphoric acid. The absorption near 400 nm had little change by the phosphoric acid treatment. Samples prepared at high P/Ti ratio indicated a little lower reflectance (not shown). This was caused from the reaction between titanium dioxide and phosphoric acid. The colour of sample powder was also estimated by L*a*b* colour space. Table II shows the whiteness of samples prepared in various conditions. These values were L* value in L*a*b* colour space. Because all samples indicated over 90, the obtained samples were suitable as a white pigment. There was a tendency that samples prepared at high P/Ti ratio with high shaking temperature had low whiteness. The heating temperature had little influence on the whiteness of samples. As described above, pigment with high smoothness spreads well on the skin. The powder smoothness is also important for cosmetics [11]. Table III shows the smoothness of samples prepared under various conditions. Generally, for a cosmetic application, the suitable MIU and MMD values are smaller than 0.6 and smaller than 0.04, respectively. Titanium dioxide and samples prepared at P/Ti = 1/4 indicated high MIU values and a little high MMD values. These results were related with the reaction between titanium dioxide and phosphoric acid. Samples prepared at high P/Ti ratio and high shaking temperature indicated the lower MIU and
Table III Smoothness of samples prepared under various conditions
a b c d e f g h i j
P/Ti
Shaking Temp. /°C
Heating Temp. /°C
MIU /
MMD /
TiO2 2/1 1/1 1/2 1/4 1/2 1/2 1/4 1/4 1/4
– 80 80 80 80 60 70 80 80 80
– 400 400 400 400 400 400 200 100 R.T.
1.278 0.416 0.652 0.420 0.766 0.564 0.820 1.152 1.202 1.278
0.019 0.010 0.011 0.009 0.009 0.008 0.008 0.019 0.021 0.018
MMD values. The smoothness of samples improved by the phosphoric acid treatment at high P/Ti ratio, high shaking temperature and high heating temperature. Conclusion Titanium dioxide was shaken in phosphoric acid under various conditions. The obtained materials indicated XRD peaks of titanium dioxide; however, these peaks became weak by phosphoric acid treatment. These samples had small particles with submicrometre size. The photocatalytic activity of titanium dioxide was inhibited by the phosphoric acid treatment. Samples prepared at high P/Ti ratio with high shaking temperature indicated a little low whiteness in L*a*b* colour space. The smoothness of samples was affected by P/Ti ratio, shaking and heating temperatures in the phosphoric acid treatment. The phosphoric acid treatment of titanium dioxide is an effective method to inhibit their photocatalytic activity for a white pigment. Acknowledgement The authors are grateful to Dr. Takeshi Toyama, Nihon University, Japan, for smoothness measurements.
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 123–128
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