www.nanoadv.org

Research Article

Nano Adv., 2017, 2, 8−16.

2016, 1, X−X. Nano Advances

http://dx.doi.org/10.22180/na191 Volume 2, Issue 1, 2017

Surface Treatment of Broad-Spectrum Ultraviolet Light Shielding Titania/Zinc Oxide Composites and Their Applications in Sunscreens

Junqian Li, a Chao Yao, abc* Shixiang Zuo, ab Wenjie Liu, a Zhongyu Li, a* Shiping Luo, a and

Aijuan Xie a

a School of Petrochemical Engineering, Changzhou University, Changzhou 213164, P. R. China

b Zhenjiang Nawei New Materials S&T Co. Ltd., Zhenjiang 212009, P. R. China

c R&D Center of Xuyi Attapulgite Applied Technology, Changzhou University, Xuyi 211700, P. R. China

*Corresponding author. Tel./Fax: +86 519 86330227; E-mail: yaochao420 [at] 163.com (C. Yao); zhongyuli [at] mail.tsinghua.edu.cn

(Z. Li).

Received January 12, 2017; Revised February 10, 2017

Citation: J. Li, C. Yao, S. Zuo, W. Liu, Z. Li, S. Luo, and A. Xie, Nano Adv., 2017, 2, 8−16.

Nano-titanium oxide (TiO2) and zinc oxide (ZnO) are widely used in sunscreen products, but many shortcomings for

these both oxides still exist. In this paper, the hydrolysis of tetraethyl orthosilicate (TEOS) in ethanol solution was

used to deposit inorganic silica nano-coating on the surface of TiO2/ZnO composite, followed by grafting by

organosilane. The as-prepared products were characterized by XRD, FTIR, TG and TEM. In addition, Zeta potential,

color difference test, dissolution experiments of zinc ions and water contact angle tests were used to characterize the

effect of inorganic silica coating and organosilane grafting. Subsequently, the modified TiO2/ZnO composites were

applied into the sunscreen formulation and the properties of the as-prepared emulsions were evaluated by the

distribution analysis of the particle size, acceleration test and ultraviolet transmittance analyzer. The results showed

that the sunscreen emulsion prepared by the TiO2/ZnO composite has better sun protection performance and stability

than the emulsion prepared by the mixture of TiO2 and ZnO.

KEYWORDS: TiO2/ZnO composites; Photo-catalytic activity; Surface treatment; Stability; Broad-spectrum

sunscreens

1. Introduction

Ultraviolet light (UV) occupying about 6% of the solar radiation

can reach the Earth’s surface. The ultraviolet spectrum can be

divided into three regions: UVA (320 – 400 nm), UVB (290 –

320 nm) and UVC (200 – 290 nm).1–3 Apart from UVB, which

can cause acute sunburn and direct harm to skin, UVA is

responsible for photosensitivity and photo-aging.4–7 Therefore,

how to effectively shield the UV radiation and prevent the UV

harm is a hot topic. In sunscreen cosmetic industry, sunscreen

can be divided into the two categories: ultraviolet organic

absorber and inorganic shielding agent.8 Regarding the

sunscreen applications, the European Union Normative

(ISO24443)9 established that both UVA and UVB ranges must

be adequately covered against the radiation. Based on this

requirement, the sunscreen products should be a reasonable

blend of organic absorbers and inorganic shielding agents.10

However, compared with inorganic shielding agents, UV

absorbers have some drawbacks such as light degradation and

unfavorable toxicity,10–14 which seriously restrict their

applications.

In order to achieve a broad general sunscreen effect and avoid

the use of UV organic absorbers, some pure inorganic

composites like UV-shielding agents have been developed.

Reinosa and his co-workers have reported a new sunscreen

composite composed of 15 wt% nanoparticles of TiO2 and 85 wt%

of ZnO micro-particles, which can improve the SPF value of ~60%

as compared with the mixture of nano-TiO2 and micro-ZnO.15

Our research results showed that not only the UV shielding

ability of nano-ZnO was much stronger than that of micron ZnO,

but also the transmittance was much higher than that of ZnO in

the visible range. However, nano-TiO2 and ZnO used in

cosmetic formulations have potential toxic health effects when

human excessively contact with them. It has been reported that

the UV-induced reactive oxygen species have initiated

photogenic skin cancer and skin aging.16 These species were

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Research Article Nano Advances

Nano Adv., 2017, 2, 8−16.016, 1, X−X.

doi: 10.22180/na191

transformed into the hydroxyl groups and superoxide radicals

after the photochemical reaction.17 It is a trend that the

nanoparticles coated with one or more layers of different inert

materials on the surface can avoid the generation of free

radicals.18–19 However, for the coating process of ZnO (ZnO

composites), the acidic solution used in the coating process can

dissolve ZnO nanoparticles. Li found that the toxicity of

nano-ZnO to Escherichia coli in aqueous media was identified

mainly due to the free Zn2+ ions.20–21 Therefore, how to coat

uniformly and densely on the surface of nano-ZnO (ZnO

composites) without Zn ions dissolution is a key problem in the

coating process.

In this contribution, TiO2/ZnO composite was first dispersed

in 95% ethanol. Tetraethyl orthosilicate (TEOS) was used as the

silica source and then a nanosized layer of silica was uniformly

deposited on the surface of the composite, which not only

effectively inhibits the Zn ions dissolution and photochemical

activity, but improves the dispersion ability of the composite in

water. Subsequently, the composite material was treated by

N-octyltriethoxysilane (NOTOS), which not only reduces the

agglomeration of the composites due to the adsorption of water,

but also improves the dispersion of the composites in organic

phase. Finally, the UV protection ability of the modified

composites in cosmetic formulation was also investigated.

2. Experimental section

2.01 Materials

All chemical reagents were used without further purification.

Ethanol (95% purity) was purchased from Klamar. Steareth2

(Brij S2), Steareth21 (Brij S21), C12–15 alkyl benzoate

(Crodamol AB), Glycerin (Pricerine 9091) and Glyceryl Stearate

(Cithrol GMS 30) were obtained from CRODA. GTCC (Myritol

318), Panthenol (D-Panthenol USP), EDTA-2Na (Edeta BD) and

Phenoxyethanol (Protectol PE) were purchased from BASF.

Xanthan gum (KELTROL CG) was obtained from CP kelco.

Titanium oxide (TiO2, MT-100TV) was obtained from TAYCA.

Zinc oxide (ZnO, Z-Cote HP1) was purchased from BASF.

Deionized water with a resistivity of 15 μs cm–1 was used for the

emulsions preparation.

2.02 Apparatus

The X-ray diffraction (XRD) analyses of the powered samples

were performed using an X-ray diffractometer with Cu anode

(D/Max 2500 PC, Rigaku Corporation, Japan), running at 60 kV

and 30 mA with a scan range from 10 to 80° at 3° min–1. To

quantify the weight percent of physicochemically immobilized

organic silane on the surface of the composites, the

thermogravimetric measurement (TG 209 F3, NETZSCH,

Germany) was employed. The composites were heated from 25

to 1000 ◦C with a rate of 10 ◦C min–1 under N2 atmosphere. The

morphologies were recorded using transmission electron

microscopy (TEM, JEOL JSM-6360LA, Japan). Fourier

transform infrared spectroscopy (FT–IR) were acquired using

Fourier infrared spectrometer (FTIR-8400S, Shimadzu, Japan).

The color difference (ΔE) of original and modified TiO2/ZnO

composites were conducted before and after UV irradiation was

measured by Automatic color difference meter (SC-80C, China)

with L*a*b* color system. The zinc ions (Zn2+) dissolution of

the original and modified samples were detected by inductively

coupled plasma emission spectrometer (ICP, Varian Vista-AX

America). The surface properties for the original and modified

TiO2/ZnO composites were measured by optical contact Angle

measurement instrument (DSA25, Germany). The viscosity of

emulsion was obtained through viscometer (DV2T,

BROOKFIELD, America). High and low temperature test was

used to test the stability of the emulsions by the high and low

temperature chamber (JYGD-103, China). Droplet size

distribution was performed using dynamic light scattering

(ZEN3600, Malvern, UK). The information of the sun-screening

performance was obtained from Ultraviolet Transmittance

Analyzer (UV-2000S, Labsphere, America).

2.03 TiO2/ZnO dispersion preparation

The dispersion was composed of TiO2/ZnO (TZ) composite and

95% ethanol. The composite was provided by the Changzhou

Nano-materials Co, Ltd. The TiO2/ZnO composites were

dispersed by a horizontal sand mill (Union Process Co., Ltd.), in

which the zirconia ball with a diameter of 0.3 mm were added at

a filling factor of 50% by volume. The frequency of vibration

was 12 s–1. The dispersion time was 90 minutes for all

suspensions. The particle concentration was 20 wt%.

2.04 TEOS hydrolysis

Firstly, 100 g of TiO2/ZnO dispersion was put into a flask which

was maintained at 60–65 ◦C. The pH value was set to 7–8 using

dilute sodium hydroxide solution. Then, a certain amount of

TEOS ethanol solution was dropwise added into the flask. The

slurry was maintained at 60–65 ◦C for 5–7 h with vigorous

agitation. The suspension was collected by filtration and rinsed

with deionized water, then dried at 100 ◦C for 5 h. The products

with different amount of silica were named as TZ-X (X

represents the covering amount of silica on the surface of the

composite materials). For example, TZ-10 indicates 10 wt% of

silica on the surface of TiO2/ZnO composite.

2.05 Organic surface modification process

After the TEOS hydrolysis, the slurry was maintained at 60–65 ◦C with vigorous agitation, then a certain amount of NOTOS

(N-octyltriethoxysilane) ethanol solution was slowly instilled

with continuous stirring for another 3–5 h. The suspension was

collected by filtration and rinsed with deionized water, then

dried at 100 ◦C for 5 h. The products with different amount of

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Research Article Nano Advances

Nano Adv., 2017, 2, 8−16.016, 1, X−X.

doi: 10.22180/na191

coating were named as TZ-X-Y (Y represents the covering

amount of organic silicon on the surface of the composite

materials). For example, TZ-X-10 indicates 10 wt% of organic

silicon on the surface of TiO2/ZnO composite.

2.06 Photo-catalytic activity

The photo-catalytic activity of all the composites was evaluated

by the following method. The paste of samples and 1,

3-butanediol (weight ratio 1:1) were prepared by physical

mixing and placed between glass slides. Each sample was made

three parallel slides (one is the contrast sample) and then the

other two parallel samples were put under high pressure mercury

lamp (250 W) irradiating for 1 h. The color difference (ΔE)

before and after UV irradiation was measured by automatic color

difference meter (SC-80C, China) with L*a*b* color system.

The higher the color difference (ΔE), the greater photo-catalytic

activity of samples. On the contrary, the smaller the color

difference, the better the photo-stability of the samples.

2.07 Zinc ions（Zn2+）dissolution

In order to find an appropriate amount of the coating of

TiO2/ZnO composites, the dissolubility of zinc ions (Zn2+) of

TiO2/ZnO composite with different coating rate in acid solution

was detected by inductively coupled plasma emission

spectrometer (ICP, Varian Vista-AX America). The same

amount of different coating rate of TiO2/ZnO composites was

put into aqueous solution of pH = 3. After stirring for 5 h, the

centrifugal separation for above mixture was performed under

the rotating speed of 10000 rpm min–1 and then Zn ions content

in the supernatants was determined.

2.08 Water contact angle

The change of the water contact angle can be used to evaluate

organic modification on the powder surface and determine the

optimal dosage of the organic modifier. The films containing

different amounts of octyltriethoxysilane were prepared by tablet

machine under the pressure of 10 Mpa. The water contact angles

of all the samples were measured by optical contact angle

measurement instrument (DSA25, Germany).

2.09 Water dispersibility

The same amount of deionized water was added to the

equivalent surface-treated powder, which was treated by

ultrasolication under the same conditions for 5 minutes. Then all

suspensions were transferred into graduated tube and allowed to

stand for 24 h. The dispersions of the powder in water were

observed, which was to evaluate the water dispersibility of all

composites.

2.10 Emulsion preparation

Table 1. Ingredients used in formulations E1 and E2 with their compositions, functions and suppliers.

E1 E2

Content (%w/w) Materials Function Supplier

Phase A 1.5 1.5 Brij S2 Emulsifier CRODA

1 1 Brij S21 Emulsifier CRODA

2 2 Cithrol GMS 30 Emulsifier CRODA

5 5 Myritol 318 Emollient BASF

5 5 CETIOL AB Emollient BASF

15 TZ-10-10 Sunscreen

7.5 MT-100TV Sunscreen TAYCA

7.5 Z-Cote HP1 Sunscreen BASF

Phase B 0.05 0.05 KELTROL CG Thickener CP kelco

5 5 Pricerine 9091 Humectant CRODA

0.1 0.1 Edeta BD Modifier BASF

0.5 0.5 D-Panthenol USP Humectant BASF

Qs Qs Deionised water

Phase C 0.5 0.5 Protectol PE Preservative BASF

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doi: 10.22180/na191

Emulsions were prepared by the following optimized procedures.

Firstly, xanthan gum was sprinkled into deionized water at room

temperature and stirred for 30 min to obtain a 1% stock solution.

The stock solution was then heated with phase B (Table 1) at

80 °C under mechanical stirring to reach homogenization. Phase

A was heated at 80 °C and stirred at 12000 rpm for 5 min to

improve the dispersion of TZ-10-10 in the emulsion with a

rotor-stator type homogenizer (Ultra-Turrax, stator diameter 25

mm, rotor diameter 18 mm, IKA). Then decanting phase B was

poured into phase A with stirring at 15000 rpm for 2 min, the

mixture was natural cooling under mechanical stirring at 500

rpm. Phase C was poured into the mixture when the temperature

is lower than 50 °C. After this, the mixer speed was increased to

1000 rpm for another 15 min and to make the cream more

consistent, then the temperature of cream is cooled to about

30 °C with continuous stirring. Eventually, the cream was then

put under vacuum in order to remove the air bubbles

incorporated during process. For comparison, emulsion E2 was

also prepared in the similar technological conditions.

2.11 Monitoring stability and aging process

The storage stability of the emulsions was measured by an

accelerated centrifuge test. This procedure is a kind of

acceleration test and is widely used in cosmetic industries. The

prepared emulsions were placed in a high and low temperature

chamber from –20 °C to 50 °C for one week. During the high

and low temperature test, three complete cycles were performed

day and night with a heating rate of 2 °C min–1 and cooling rate

of 1 °C min–1. Samplings for analysis were performed at different

test times after emulsification: 1, 3, 5 and 7 days. Centrifugal

sedimentation time T2, defined as the time when emulsions

appeared stratified after centrifugal sedimentation, was obtained

from the test. The storage stability of emulsions is also often

expressed by a gravity sedimentation time T1, which can be

calculated from T1 based on the following equation:22

2

22 1

1 2

4u TRn

u g T

R is the average distance between the sample cuvette and the

rotation axis (m); n is the rotation speed of the centrifuge (rpm)

and g is the gravitational constant (9.8 m2 s–1). In our tests,

centrifugal cuvettes were loaded with emulsions to a height of 10

mm. R and n were 20 mm and 4800 rpm min–1, respectively. In

addition, the droplet size distribution of emulsions is used the

microscopic methods to evaluate the stability of emulsions.

2.12 Sun-screening performance

SPF and PF-UVA, in vitro test method, were used to evaluate

the photo-protection efficiency in the UVB and UVA ranges,

respectively. As following, 32.5 mg of emulsion was spread

across the entire surface of a polymethylmethacrylate (PMMA)

plate (Europlast, Aubervilliers, France) with a single finger and

finger cot using light strokes as quickly as possible. Continue

stroking the surface of the plate in all directions until no puddles

or areas of excess sunscreen exist. The SPF, PF-UVA and λc

(critical wavelength) were displayed in the operation of the

software interface.

3. Results and discussion

In order to prevent the photochemical activity of TiO2/ZnO (TZ)

composites and the dissolution of zinc ions (Zn2+), silica was

coated onto the surface of the composite. The amount of the

coated silica is calculated on the basis of the silica produced by

the hydrolysis of TEOS. The isoelectric points of the different

coated samples are listed in Table 2. The isoelectric point of the

composites decreases sharply with the increase of the coating

amount. When the coating amount reaches 10 wt%, the

isoelectric point of the composites is close to that of silica,23

which indicates that the surface properties of the composites are

consistent with that of silica. It can be considered that the

composite nanoparticles have been completely coated at this

time.

Figure 1 shows the color difference (ΔE) before and after the

UV irradiation of all TZ composites. When the coating amount

is less than 5 wt%, the color difference of the composite

decreases sharply with the increase of the coating amount, and

Table 2. Isoelectric point of TiO2/ZnO composites.

TZ-X Isoelectric point

0 9.2

5 3.8

10 2.1

15 2.1

20 2.1

0 5 10 15 20

5

10

15

20

25

30

35

E

TZ-X

Figure 1. Color difference (ΔE) of TiO2/ZnO composites.

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then the velocity becomes slow. When the coating amount is

more than 10 wt%, the color difference hardly changes, which

implies that the surface of the composite has been completely

covered by the silica nano-coating.

At the same time, we measured the amount of Zn ions

released from the composites in acidic solution. As presented in

Table 3, we can see that the dissolution of Zn ions in the

composites decreases rapidly with the increase of the coating

amount. When the coating amount is larger than 10 wt%, the

dissolution of Zn ions hardly proceeds. Therefore, in

combination with the results from the color difference test and

the isoelectric point experiments, it can be concluded that the

optimal coating amount of the composites is 10 wt%.

In order to determine the amount of the organosilane coating, the

water contact angle values of the composites with different

coating weights were measured. In Figure 2, with the increase of

coating amount, the water contact angle of powder gradually

increase. However, when the coating amount is more than 10

wt%, the water contact angle hardly changes. It may be due to

the fact that the coating reaches the maximum amount.

The XRD patterns of TZ, TZ-10 and TZ-10-10 were shown in

Figure 3. As can be seen from Figure 3a, rutile type TiO2

exhibits strong diffraction peaks at 2θ = 27.41° (JCPDS nos.

88-1175) and the characteristic diffraction peaks of ZnO appear

at 2θ = 31.77°, 34.40° and 36.25° (JCPDS nos. 36-1451).

Moreover, the characteristic peaks of the samples before and

after coating are basically the same. No characteristic peaks of

SiO2 are found due to the amorphous structure of SiO2 coated on

the surface of the composite nanoparticles.

The FT–IR spectra of the samples are provided in Figure 4.

The TZ and TZ-10 have a relatively strong absorption peak at

3459.3 cm–1, corresponding to the –OH stretching vibration and

the peak at 1639.7 cm–1 is ascribed to the H–O–H bending

vibration.24 The strong absorption peak at 1089.7 cm–1 is

attributed to the Si–O–Si bond symmetric stretching vibration in

Figure 4b. In Figure 4c, the peaks at 2973.1, 2925.9, and 2857.3

cm–1 are obviously observed,25 which are attributed to the –C–H

bending stretching vibration and another peak at 1457 cm–1 is

indicated to –C–H bending vibration, proving that silica is

chemically bonded to the surface of the composite nanoparticles.

The thermogravimetric (TG) curves of TZ-10-Y are

intuitively demonstrated in Figure 5. When the temperature

Table 3. Dissolution of zinc ions of TiO2/ZnO composites.

TZ-X Zn2+ (ppm)

0 1793

5 867

10 643

15 640

20 637

Figure 2. Water contact angle of TiO2/ZnO composites.

20 30 40 50 60 70

Z

Z

Inte

nsi

ty (

a.u

.)

2 (degrees)

(a)

(b)

(c)

T

Z

T-TiO2

Z-ZnO

Figure 3. The XRD spectra of (a) TZ, (b) TZ-10 and (c) TZ-10-10.

3200 2400 1600 800

(d)

(c)

(b)

Wavenumber (cm-1

)

(a)

3459.3 1639.7

2973.1

2925.9 2857.31457

1089.7

Inte

nsi

ty (

a.

u.)

Figure 4. FT–IR spectra of (a) TZ, (b) TZ-10, (c) TZ-10-10 and (d)

NOTOS.

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doi: 10.22180/na191

reaches 200 °C, the weight loss ratio of TZ-10 is 6.7% mainly

due to the surface adsorption removal of water. However, the

other samples at this temperature have a less weight loss in the

range of 2.1–3.8%, the obvious decrease of the amount of

adsorbed water indicates that the hydrophobicity of the

composites increases after modification. The weight loss rate of

the composites without organic modification was about 2.1% at

200–600 ℃, which was mainly ascribed to the reduction of

hydroxyl groups on the surface of TZ-10 and the weight loss rate

of the composites TZ-10-5, TZ-10-10, TZ-10-15 and TZ-10-20

are 6.4, 9.8, 9.92 and 9.97%, respectively. This loss mainly

results from the combustion of organic compounds on the

surface of the nanocomposite.

The morphologies of the products are observed by TEM in

Figure 6. As shown in Figure 6a, there is a weak aggregation of

the TZ composite. Figure 6d displays the HRTEM image of TZ.

The interplanar spacing of d = 0.327 nm corresponds to the

interplanar spacing of (110) planes of rutile and the interplanar

spacing of d = 0.264 nm is attributed to the (002) plane spacing

of hexagonal ZnO. Obviously, a uniform thin-layer is found on

the surface of the composites in Figure 6b and Figure 6c.

High-resolution transmission electron microscopy (HRTEM)

was used to determine the film thickness. In the HRTEM images

of Figure 6e and Figure 6f, there are about thin nanolayers of

1.83 and 3.34 nm were observed, indicating that the thickness of

the composite coating increases with the addition of NOTOS.

An equal amount of deionized water was added to the same

amount of samples before and after the modification. After

standing for 24 h, the different phenomena are presented in

Figure 7. The suspension in Figure 7a is severely stratified and

deposited on the bottom, while the dispersion in Figure 7b is

homogeneous, which indicating TZ-10 has better water

dispersibility than TZ. Furthermore TZ-10-10 (Figure 7c) floats

on the surface of water. Therefore, the silica-treated powder not

only suppresses light activity and Zn ions elution, but also

improves the water dispersibility of the powder. The surface of

organosilane-modified powder has increased hydrophobicity.

The storage stability of the emulsions was measured by an

accelerated centrifuge test. Viscosity of the emulsions subjected

to high and low temperature was tested and the results were

presented in Figure 8. It can be seen that viscosity of emulsion

0 200 400 600 800 1000

88

92

96

100

(a)

(b)

(c)

(d)

(e)

Weig

ht

(%)

Temperature (oC)

Figure 5. TG curves of (a) TZ-10, (b) TZ-10-5, (c) TZ-10-10, (d) TZ-10-15

and (e) TZ-10-20.

Figure 6. TEM images of (a) TZ, (b) TZ-10, (c) TZ-10-10 and HRTEM

images of (d) TZ, (e) TZ-10 and (f) TZ-10-10.

Figure 7. Dispersion properties of (a) TZ, (b) TZ-10 and (c) TZ-10-10.

Figure 8. Viscosity of the emulsions subjected to high and low temperature

(0, 1, 3, 5 and 7 days).

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E1 shows hardly change compared with that of emulsion E2.

After cycling test under high and low temperatures for 7 days,

the viscosity of Emulsion E2 varies considerably due to its

demulsification and oil-water separation. This is possibly

attributed to the existence of the heterogeneous nanoparticles

(the mixture of TiO2 and ZnO) in the emulsion caused by mutual

coagulation.

At the same time, the centrifugal acceleration test was carried

out on the emulsions after high and low temperature treatment.

As can be seen from Table 4, the as-prepared emulsions are

stable with a gravity settling time for about two years. However,

compared with the emulsion E1, the stability of emulsion E2

after high and low temperature treatment is more obvious, which

is consistent with the results presented in Figure 8.

Second criterion for characterization of the emulsions quality

is the droplet size distribution. Figure 9 shows the characteristics

of two emulsions (E1 and E2) with different droplet size

distributions after high and low temperature treatment. Droplet

size distribution of Emulsion E1 shows a narrow and high single

peak with the average particle size of ~5 μm. With the increase

of the treatment time, the droplet size distribution of emulsion

E1 is still a unimodal just with broadening and lower peak.

Compared with the emulsion E1, emulsion E2 has a wide droplet

size distribution, and with the increase of high and low

temperature treatment time, droplet size distribution becomes a

bimodal distribution, which shows that Emulsion E1 has a higher

stability than E2.26

Sun-screening performances of Emulsion E1 and E2 were

tested by UV-2000 and shown in Figure 10 and 11, respectively.

From the data of emulsion E1 in Figure 10, three sets of data are

almost coincident, which indicates that emulsion E1 is evenly

daubed on the PMMA. SPF and PA average values are measured

to be 37.60 and 8.50 respectively when the adding amount of

TZ-10-10 is 15 wt%, which implying that emulsionE1 could

achieve SPF30+, PA+++. Emulsion E2 (SPF30+, PA++) has a

similar SPF value but a lower PA value (Figure 11) as compared

to Emulsion E1. This may be attributed to the higher synergistic

effect of the TiO2/ZnO composite in emulsion E1 over the ZnO

and TiO2 mixtures in emulsion E2.

When the dosages of TZ-10-10 and the mixture of TiO2 and

Table 4. Storage stability of emulsions after high and low temperature treatment.

Testing time

(days)

E1 E2

Centrifugal settling time

T1 ( hours )

Gravity settling time

T2 (months)

Centrifugal settling time

T1 ( hours )

Gravity settling time

T2 ( months )

Initial (0) 3.30 23.61 3.29 23.52

1 3.20 22.93 3.13 22.41

3 3.03 21.77 2.89 20.68

5 2.85 20.41 2.72 19.43

7 2.77 19.80 2.42 17.32

100 1000 10000 1000000

10

20

30

40

50

Vo

lum

e (

%)

Emulsion particle size (nm)

(a)

(b)

(c)E1

100 1000 10000 1000000

10

20

30

40

50

Vo

lum

e (

%)

Emulsion particle size (nm)

(a)

(b)

(c)

E2

Figure 9. Droplet size distribution was tested by Melvin particle size

distribution after high and low temperature treatment. Initial (a), 3 days (b)

and 7 days (c).

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ZnO change, the SPF (UVB protection factor), PA (UVA

protection factor), and λc (critical wavelength) of emulsions were

intuitively enumerated in Table 5 and Table 6, respectively.

Table 5 and Table 6 show that regardless of complex or mixed,

sunscreen effects always increases with the increase of the

additive amounts. But the composite sunscreen effect is always

better than that of the mixed because the compound has a higher

synergistic effect. Sun protection parameters of TZ-10-10

emulsion is rapidly increasing when adding amount is more than

6 wt% and the critical wavelength of the emulsion could be more

than 370 nm. Therefore, TZ-10-10 is a broad-spectrum

sunscreen. When the mixture of TiO2 and ZnO is added 15 wt%,

although the SPF value can be consistent with that of the

composite, the PA value is far lower than that of the composite,

which may be due to the fact that the large particles of zinc

oxide in the emulsion E2 can not be well dispersed.

4. Conclusions

In this paper, the hydrolysis of TEOS in ethanol solution was

used to deposit a uniform and dense silica coating on the surface

of broad-spectrum sunscreen (TiO2/ZnO composite

nanoparticles), which not only inhibites the photoactivity and Zn

ions dissolution of the composites, but reduces the toxicity of

nano material and improves the water dispersibility. The results

of Zn ions release tests show that the amount of Zn dissolution

decreased from 1793 to 637 ppm before and after coating. Then,

the surface of the inorganic silica-coated composite is modified

by the organic silicon to make the surface of the composite

become hydrophobic from the hydrophilic, which can improve

its compatibility and dispersibility in the organic system. The

results show that the sunscreen emulsion of the TiO2/ZnO

composite after surface treatment is better in storage stability

and sun protection performance as compared to ZnO and TiO2

mixture sunscreen emulsion.

Acknowledgements

This work was supported by Technology Support Program of

Zhenjiang City (GY2015042), and Technology Support Program

of Huaian City (HAG2015074)

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How to cite this article: J. Li, C. Yao, S. Zuo, W. Liu, Z. Li, S.

Luo, and A. Xie, Nano Adv., 2017, 2, 8−16. doi:

10.22180/na191.

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