Field of the invention

The present invention relates to a highly porous amorphous Mesoporous Magnesium

Carbonate (MMC) and a sunscreen composition comprising such MMC. In particular, the invention relates to a highly porous amorphous mesoporous magnesium carbonate comprising incorporated UV-absorbing semiconductor particles, such as titanium dioxide (TiC ) and/or zinc oxide (ZnO) nanoparticles.

Background of the invention

UV radiation comprises approximately 5% of the solar spectrum which reaches the surface of the earth, with the rest of the spectrum being visible light and infrared radiation. UV radiation (UVR) can further be divided into three subtypes; UVA (320 - 400 nm), UVB (280 - 320 nm) and UVC (200 - 280 nm). While UVC is mainly absorbed by the ozone layer, most UVA and UVB rays are able to penetrate the stratosphere. Despite being a minor constituent of the electromagnetic spectrum, a strong correlation between UVR and premature skin aging and damage as well as skin cancer has been proven. Sunscreens have commonly been employed to prevent photo-induced skin damage by absorbing, scattering and reflecting UVA and UVB rays.

Modem sunscreens are traditionally divided into two main groups: Organic/chemical sunscreen filters, which absorb UVR and; Inorganic/physical sunscreen filters, which mainly scatter and reflect UVR. Inorganic filters (e.g. TiCk and ZnO) have advantages over organic filters as they generally do not induce skin irritation, have limited skin penetration and can block UVA and UVB rays. Sunscreens available today can use special grades of inorganic filters. Larger particles (non-nano) are considered safe to use but will leave a white layer on the skin, which is not esthetically desirable. Inorganic filters in nanoparticle form protect the skin by absorbing UV radiation, but unlike larger particles they are transparent rather than white.

Thus, in order to reduce the whitening effect and increase the translucency of the sunscreen, many of the sunscreen formulations in use today contain inorganic UV filters particles in the nanometer size range (20 - 50 nm). The inclusion of crystalline TiCk and ZnO nanoparticles in formulations that can lead to the formation of airborne nanoparticles is not considered as safe however, as these nanoparticle agglomerates could have adverse health effects if inhaled. A material that can be used to encapsulate such nanoparticle aggregates and impart other functional properties without greatly affecting the UV blocking properties of the

semiconductors or reduce the translucency would be highly sought for. A prerequisite for the use of TiCk/ZnO nanoparticles in sunscreen is that they are coated with materials such as silica, alumina, polymethyl methacrylate or dimethicone to reduce their photocatalytic effect. TiCk and ZnO belong to a class of materials denoted as semiconductors and can reflect as well absorb UVR. The absorption of UVR leads to the formation of electron-hole-pairs in the material that can react with adsorbed molecules on the surface of the particles. This in turn can lead to the generation of free radicals and reactive oxygen species.

Amorphous mesoporous magnesium carbonate (MMC) has attracted attention as an absorbent of lipids and moisture as well as a carrier of substances for cosmetic or therapeutic applications, among other applications. MMC is a highly porous material composed of amorphous magnesium carbonate and magnesium oxide. The specific surface area of MMC can be varied from 100 m ² /g up to 800 m ² /g (BET), the total pore volume larger than 0.1 cm ³ /g and the average pore size can be varied from 2 to 20 nm, by tuning the synthesis conditions. MMC particles are irregularly shaped and the particle sizes can be controlled by various sieving or milling techniques known in the art, both large particles (several mm) or small particles (pm) can be produced. The material has also been shown in vitro to be non- cytotoxic, showing no toxicity to human dermal fibroblast cells at concentrations of 1000 pg/ml and below and does not induce any skin irritation or skin sensitization when dermatology tested on human subjects. US 9,580,330 relates to an X-ray amorphous mesoporous magnesium carbonate with large specific surface area and extraordinary moisture sorption capacity. The material is suggested for various uses, including but not limited to delivery and carrier systems for therapeutic and cosmetic or volatile agents. US 9,580,330 is hereby incorporated by reference.

WO2017/174458 discloses a method of controlling several characteristic parameters of an X- ray amorphous mesoporous magnesium carbonate including the pore size. The mesopores are in the range from 10 nm to 30 nm. A surface area larger than 120 m ² /g and a total pore volume larger than 0.5 cm ³ /g is reported. WO2017/174458 is hereby incorporated by reference.

WO2017/174457 relates to a getter material suitable for incorporation in transparent layers, comprising composite nanoparticles comprising one or more cores of crystalline magnesium oxide surrounded by amorphous magnesium carbonate. WO2017/174457 is hereby incorporated by reference.

US 2005/0031655 describes an emulsion for skin application which provides improvements in skin feel and which comprises an aqueous component, one or more water-insoluble organic components and a solid component consisting of porous silica having an average particle size of 5-20 um, such as MSS-500W (Kobo Products, Inc.). The silica may be pre-treated with water or an aqueous solution before being included in the emulsion in order to fill the pores with the aqueous material and prevent significant oil adsorption. The oil component may be selected from a group including among others avobenzone. Titanium dioxide is listed as one out of a large number of typical sunscreen activities approved in the USA.

'Functionalization of Upsalite® with TiC for UV-blocking applications', Uppsala University, Department of Engineering Sciences, Nanotechnology and Functional Materials, 2016, UPTEC Q 16 012, ISSN 1401-5773, discloses a material comprising MMC and TiCh. During the described synthesis TiCh is introduced in a manner that results in that the TiCh is in an amorphous form which makes it unsuitable for UV-absorbing purposes.

Summary of the invention

The object of the invention is to provide a product with UV-absorbing properties typically associated with semiconductor nanoparticles, such as crystalline TiC and/or ZnO

nanoparticles, minimizing the exposure of nanoparticles to a user of the product.

This is achieved by the composite material of highly porous amorphous mesoporous magnesium carbonate and crystalline semiconductor particles as defined by claim 1, a sunscreen composition as defined in claim 9, a cosmetic composition as defined in claim 10, a cosmetic powder as defined in claim 11, and the method of producing the composite material as defined in claim 12.

The composite material according to the invention comprises a matrix of highly porous amorphous mesoporous magnesium carbonate (MMC) and crystalline UV-absorbing semiconductor particles. The UV-absorbing semiconductor particles are incorporated within the matrix of highly porous amorphous mesoporous magnesium carbonate. The composite material has similar properties with regards to the morphology and the mesoporous structure as a corresponding highly porous amorphous mesoporous magnesium carbonate without incorporated UV-absorbing semiconductor particles.

The composite material has an average pore size between 2 and 20 nm, and a total pore volume of above 0.2 cm ³ /g, preferably above 0.3 cm ³ /g, and even more preferably above 0.4 cm ³ /g.

According to one aspect of the invention the UV-absorbing semiconductor particles of the composite material are crystalline UV-absorbing semiconductor nanoparticles.

According to one aspect of the invention the UV-absorbing semiconductor particles are crystalline TiCh and/or ZnO nanoparticles.

The composite material can be used in sunscreen applications, for example in cosmetic powders, in cosmetic compositions or sunscreen compositions.

According to one aspect of the invention the crystalline UV-absorbing semiconductor particles constitute up to 50 weight % of the composite material. The amount of TiCh nanoparticles and ZnO nanoparticles may be equal.

According to one aspect of the invention the composite material is provided with different amounts of crystalline T1O2 nanoparticles and ZnO nanoparticles Thanks to the invention a composite material can be providedwhich has the structure of an MMC and the UV-absorbing and non-whitening properties associated with crystalline semiconductor nanoparticles and which minimizes the risk of a user being exposed to nanoparticles.

One advantage is that the composite material can be used in a wide range of products such as sunscreen compositions, cosmetic powders and sprays.

A further advantage is that, unlike T1O2 and ZnO nanoparticles, the composite material comprising MMC with incorporated T1O2 and ZnO nanoparticles showed no photocatalytic activity in an amaranth degradation study.

A further advantage is that the MMC matrix does not impair the UV-blocking properties of the semiconductor particles.

A further advantage is that the composite material can be used as carrier of, or an

adsorber/absorber of other substances, due to the mesoporous properties being similar to that of non-composite MMC.

The method according to the invention of producing a composite material, which comprises a matrix of highly porous amorphous mesoporous magnesium carbonate and crystalline UV- absorbing semiconductor particles, comprises the steps of

- dispersing MgO in methanol in a pressure reaction vessel;

- subjecting the dispersion subjected to a pressure of 1-5 bar CO2 for 1-30 hours during stirring or similar mixing to obtain a reaction mixture;

- adding and mixing the UV-absorbing semiconductor particles with the reaction mixture;

- drying the reaction mixture with the added UV-absorbing semiconductor particles to obtain wet granulates; and

- heat treatment to form a dry powder of the composite material.

According to one aspect of the method the step of adding and mixing UV-absorbing semiconductor particles comprises adding crystalline T1O2 and/or ZnO nanoparticles.

According to one aspect of the invention the method comprises an additional step of milling, or by other means pulverize, the dry powder in order to achieve a desired particle size distribution.

According to the method of the invention crystalline nanoparticles of T1O2 and ZnO are added to the MMC synthesis liquid prior to gelling and forming the solid compound. This enables incorporation of crystalline oxide nanoparticles in the MMC matrix while the pore formation typical to the pure MMC material still occurs. The metal oxides are and remain crystalline after inclusion into the matrix. The pore structure is intact due to that the metal oxide nanoparticles reside in the MMC matrix and not in the pores of MMC. The light absorbance in the UV-region of the crystalline nanoparticles incorporated in MMC is comparable to that of the pure crystalline nanoparticle powders but the encapsulation in the MMC matrix diminishes their photocatalytic activity. Such a material can be useful in cosmetic formulations, where protection towards UV-irradiation is desired but where exposure to nanoparticles is to be avoided.

In the following, the invention will be described in more detail, by way of example only, with regard to non-limiting embodiments thereof, reference being made to the accompanying drawings.

Brief description of the drawings

Figure 1. XRPD patterns of a) MMC-TiCk-ZnO, b) MMC, c) T1O2 (rutile) and d) ZnO (wurtzite);

Figure 2. IR spectra of a) MMC-Ti0 ₂ -ZnO, b) MMC and c) T1O2 (rutile);

Figure 3. Raman spectrum of MMC-Ti0 ₂ -ZnO showing (a) the full spectrum, (b) bands from ZnO (wurtzite) and T1O2 (rutile) and (c) band from MMC;

Figure 4. (a) nitrogen sorption isotherms for synthesized MMC-Ti0 ₂ -ZnO (■) and MMC (·) material, (b) differential pore volume distribution (■) and cumulative pore volume (·) of MMC and (c) differential pore volume distribution (■) and cumulative pore volume (·) of MMC-Ti0 ₂ -ZnO;

Figure 5. SEM images of (a) MMC-Ti0 ₂ -ZnO, (b) MMC and (c) a TEM-image of MMC- Ti0 ₂ -ZnO, (d) SEM (SE) image of MMC-Ti0 ₂ -ZnO, (e-i) SEM (BSE) images showing the elemental distribution of (e) Carbon (C), (f) Magnesium (Mg), (g) Oxygen (O), (h) Titanium (Ti), (i) Zink (Zn).

Figure 6. UV-Vis transmittance of 20 wt.% cream formulations of (a) MMC, (b) MMC-Ti0 ₂ - ZnO and (c) T1O2 (rutile)/ZnO mixture;

Figure 7. The effect of MMC-Ti0 ₂ -ZnO ( _■ ), MMC (►), T1O2 + ZnO (◄) and T1O2 + ZnO + MgC0 ₃ (A) and T1O2 + ZnO + MMC (¨) on the adsorption and photocatalytic degradation of the anionic azo dye amaranth;

Figure 8. Particle size distribution (volume density) of MMC- 25 TΪ0 ₂ -25 ZnO powder (solid line) along with T1O2 (dashed-dotted line) and ZnO (dashed) nano-powders

Detailed description

The term“UV-absorbing semiconductor particles” used herein should be understood as particles of a compound that absorbs UV-rays through a physical process, the most well- known examples being the crystalline forms of T1O2 and ZnO.

MMC refers herein to a highly porous amorphous mesoporous magnesium carbonate with a total pore volume larger than 0.2 cm ³ /g. The material typically has a specific surface area of between 200 and 800 m ² /g (BET), a and an average pore size between 2 and 10 nm. The terms“non-composite MMC” and“composite MMC” is used herein to distinguish between MMC with no added substances or particles (“non-composite MMC”) and a composite material of MMC with crystalline UV semiconductor particles incorporated within the amorphous matrix of MMC (’’composite MMC”).

The term“particles incorporated within” as in“nanoparticles incorporated within MMC” used herein should be understood as the majority of particles being surrounded by MMC and together with the MMC forming a continuous material or agglomerations orders of magnitudes larger than the individual particles. An alternative way of describing the composite material is a matrix of MMC with particles evenly dispersed in the MMC matrix wherein the MMC maintain its fundamental properties such as total pore volume, average pore size and surface area. This is in contrast to prior art MMC loaded with an additional substance, for example as described in US 9,580,330, wherein substances are loaded into the pores of the MMC.

The term“nanoparticles” refer to a distribution of particles having an average size of 1-100 nm. TiC and ZnO, which are sold as non-nano can have an average particles size around 130 nm whereas the commercially available nanoparticle TiC and ZnO typically have sizes around 20-30 nm.

“Crystalline particles” and“crystalline nanoparticles” should herein be understood as particles which are to their major part crystalline and appear as crystalline in commonly applied methods of establishing crystallinity such as X-ray diffraction measurements. As well known by the skilled person a crystalline particle or nanoparticles may have minor portions with defects in the crystal structure or non-crystalline structure.

The composite material according to the invention comprises MMC and UV-absorbing semiconductor particles incorporated within the MMC. The amount of UV-absorbing semiconductor particles may be up to 50 weight %. Preferably, the UV-absorbing

semiconductor particles are nanoparticles. The composite material has an average pore size between 2 and 10 nm, and a total pore volume of above 0.2 cm ³ /g, preferably above 0.3 cm ³ /g, and even more preferably at or above 0.4 cm ³ /g. This indicates that the structure of the composite MMC is essentially the same as the structure of a non-composite MMC. Preferably UV-absorbing semiconductor particles are nanoparticles of T1O2 and/or ZnO. This composite material will be referred to as MMC-Ti0 ₂ -ZnO. An embodiment of the composite material comprises 25 wt.% TiCh and 25 wt.% ZnO incorporated within MMC. According to one embodiment the composite material comprises 20 wt% crystalline T1O2 nanoparticles.

The method according to the invention of preparing a composite material of MMC and UV- absorbing semiconductor particles comprises initial steps known in the art, for example from WO2017/174458 of preparing an MMC. These initial steps comprise:

- Dispersing MgO in methanol in a pressure reaction vessel.

- Subjecting the dispersion subjected to a pressure of 1-5 bar CO2 for 1-30 hours during stirring, or with other mixing methods, to obtain an off white cloudy liquid, referred to as MMC reaction mixture.

- Optionally, remove the large solid MgO particles from the MMC reaction mixture, by, for instance, centrifugation of the MMC reaction mixture.

The method according to the invention comprises the further steps of:

-Adding and mixing the UV-absorbing semiconductor particles with the MMC reaction mixture.

The MMC reaction mixture with the added UV-absorbing semiconductor particles is then dried to obtain wet granulates. The wet granulates were subsequently heat treated to obtain the dry powder of the composite material according to the invention. The drying and heat treatment are known from the art. The dry powder of the composite material may be further treated or processed to optimize the material for the intended use. This includes, but is not limited to, to provide particles in a predetermined size range, for example by milling or other forms of pulverization. Examples of further processing includes loading the composite MMC as has been described for non-composite MMC, in for example US 9,580,330,

WO2017/174458 and WO2017/174457, and to mix the composite MMC with other substances to form products such as sunscreen compositions, cosmetic compositions and cosmetic powders.

Experimental

Materials

Magnesium Oxide (>99% trace metal basis -325 mesh), Rutile Titanium (IV) dioxide (Ti02, rutile) (<100 nm 99.5% trace metal basis), Zinc oxide (ZnO wurtzite) (<100 nm -80% Zn basis), Polydimethylsiloxane (PDMS) and Amaranth dye were purchased from Sigma- Aldrich. Methanol (HPLC HiPerSolv Chromanorm) was purchased from VWR. All chemicals were used as purchased without further purification.

Amorphous mesoporous magnesium carbonate (MMC) synthesis

MMC was synthesized according to Cheung et al.; 10 g MgO was dispersed in 150 ml methanol in a pressure reaction vessel (Andrew Glass Company, Vineland, USA). The vessel was sealed, and the dispersion subjected to 4 bar CO2 for 24 hours at 500 rpm. The obtained off-white cloudy liquid (referred to as MMC reaction mixture) was centrifuged at 3,800 rpm for 30 min in order to remove larger solid MgO particles. The step of removing residual MgO-particles is optional and may be omitted in an industrial process. The MMC liquid was then dried in a warm water bath and the obtained wet granulates were subsequently heat treated at 150°C for 24 hours. The heat treatment can also be performed at higher

temperatures but below the decomposition temperature of MMC at 350 °C, depending on the desired properties of the powder.

Ti0 ₂ /ZnO in a matrix of MMC (MMC-Ti0 ₂ -ZnO)

The MMC-TiCk-ZnO sample was prepared by mixing approximately 6.43 g of T1O2 (Rutile, <100 nm particle size) and 6.43 g of ZnO (<100nm particle size)with 100 ml of MMC reaction mixture (MMC content -12.9 g) after centrifugation, corresponding to a composite material of MMC with 25wt% T1O2 and 25 wt% ZnO. The mixture was then dried in a warm water bath and the obtained wet granulates were subsequently heat treated at 150°C for 24 hours.

A sample comprising only T1O2, MMC-T1O2, was prepared in the same manner as described above with 20 wt% crystalline T1O2 nanoparticles.

Analysis Methods

X-ray powder diffraction (XRPD)

XRPD patterns were recorded using a Bruker TwinTwin (Bruker, Bremen, Germany) instrument using Cu ka radiation (l = 1.5418 A), an acceleration voltage of 40 kV and a current of 40 mA. Data was collected from 5° to 80° with a step-size of 0.02044° and a step time of 38.4 seconds. Samples were finely grounded and mounted on silicon zero background sample holders for all measurements. Infrared spectroscopy (IR)

IR spectra were recorded using a Bruker Tensor 27 (Bruker, Billerica, USA) with a Platinum attenuated total reflectance (ATR) multiple crystals diamond accessory. The resolution was set to 4 cm ¹ , background and sample scan time to 32 scans.

Raman spectroscopy

Raman spectra were recorded using a Horiba (Kyoto, Japan) Labram HR spectrometer with a Nd: YAG laser with a wavelength of 532 nm (50 mW).

Surface area and porosity

The surface area and porosity of the synthesized materials were determined using a

Micromeritics ASAP 2020 porosity analyzer (Micromeritics, Norcross, USA). The experiments were carried out at liquid nitrogen (77 K) in a liquid nitrogen bath. Prior to the analysis the materials were degassed for 6 hours at 100°C using dynamic vacuum with a Micromeritics Smart VacPrep instrument (Micromeritics Instrument Corporation, Norcross, USA). The density of MMC and MMC-TiCk-ZnO was measured using Helium pycnometry utilizing a Micromeritics AccuPyc 1340 gas pycnometer (Micromeritics, Norcross, USA).

Electron microscopy imaging

Scanning electron microscopy (SEM) images were obtained by using a Zeiss LEO 1550 (Carl Zeiss Microscopy, Oberkochen, Germany). Grounded samples were mounted on aluminum stubs using double sided carbon tape and coated with Pd/Au by a Polaron SC7640 sputter coater (Thermo VG Scientific, Waltham, USA) prior to being imaged. The sputter coater was set to 2000 kV and the samples were coated for 40 seconds using a plasma current of 20 mA. Energy-dispersive X-ray spectroscopy (EDS) was used to obtain elemental maps were performed using the Back-scattered Electron Detector (BSE). Prior to EDS analysis the EDS was calibrated at 10 kV with titanium as a reference.

Transmission electron microscopy (TEM) images were recorded using a JEOL JEM-2100 microscope (Tokyo, Japan) equipped with a Schottky field-emission gun and operated at 200 kV at room temperature.

UV-Vis transmittance of cream formulations

The UV-Vis transmittance spectra of MMC, MMC-TiCh-ZnO, TiCh and ZnO were recorded on a PerkinElmer Lambda 900 UV/VIS/NIR Spectrometer (PerkinElmer, Waltham,

Massachusetts, USA). The materials were finely grounded in a mortar and dispersed in Polydimethylsiloxane (PDMS) to a final concentration of 20 wt%. 32.5 mg of this mixture was subsequently spread onto HD6 poly(methyl methacrylate) Helioplates (purchased from HelioScreen Laboratories, Creil, France) in accordance with the COLIPA in vitro UVA test method ¹⁹ . Three plates were prepared per material and the UV/VIS transmittance spectrum of each plate was recorded once. The obtained transmittance data was used to calculate the in vitro sun protection factors (SPF) for MMC-TiCh-ZnO as well as the TiCh and ZnO mixture.

Photocatalytic degradation of the azo dye amaranth

MMC-TiCh-ZnO was tested for its photocatalytic ability by monitoring the degradation of an anionic azo dye amaranth. 120 mg of MMC-TiCh-ZnO was mixed with 30 ml of 50 mM amaranth solution in on open glass test tube at 500 rpm. The mixture was placed in a homemade chamber with no external light penetration and left to equilibrate for 30 min in the dark. After equilibration for 30 minutes the sample was exposed to a UV source built-in to the chamber for 90 minutes. Aliquots were taken every 15 min during the equilibration and irradiation period. The aliquots were centrifuged at 10,000 rpm for 5 minutes and then analyzed using a UV-1800 UV-VIS Spectrophotometer (Shimadzu Corporation, Kyoto,

Japan). The dye degradation experiments were performed in triplicates for all

materials/mixtures.

Particle size distribution

Particle size distributions were measured for MMC- 25 TΪ02-25 ZnO and nanopowders of T1O2 and ZnO (as purchased) by laser diffraction. Size refers to the mean equivalent spherical diameter of particles and measurements were performed in a Malvern - Mastersizer 3000 using dry mode.

RESULTS AND DISCUSSION

Semiconductor nanoparticles incorporated within MMC matrix

T1O2 and ZnO nanoparticles were incorporated within MMC to produce MMC-Ti0 ₂ -ZnO using the procedures detailed in the experimental section. The XRPD pattern of the MMC- Ti0 ₂ -ZnO, MMC, T1O2 and ZnO are shown in Figure 1 for comparison; XRPD patterns of a) MMC-Ti0 ₂ -ZnO, b) MMC, c) T1O2 (rutile) and d) ZnO (wurtzite). It was clear from the XRPD pattern of MMC-Ti0 ₂ -ZnO that T1O2 and ZnO were successfully dispersed in MMC, as diffraction peaks corresponding to crystalline T1O2 (rutile) and crystalline ZnO (wirtzite) were distinctively observed showing that the nanoparticles of T1O2 and ZnO are crystalline when incorporated into the MMC. The amorphousness of MMC was unaffected by the addition of TiC and ZnO. Hence the composite material MMC-TiCh-ZnO comprises of crystalline nanoparticles of TiCh and ZnO in an amorphous matrix of MMC.

The IR spectra of the MMC-Ti0 ₂ -ZnO, MMC and T1O2 are shown in Figure 2a; a) MMC- Ti0 ₂ -ZnO, b) MMC and c) T1O2 (rutile). The characteristic bands of MMC were observed at 1413, 1095 and 852, 700 cm ¹ , these bands corresponded to the asymmetric (V3) and symmetric (vi) stretching as well as in and out of plate bending (V2) vibration mode, respectively. Apart from the IR bands related to MMC, a broad band related to the presence of T1O2 was detected at around 500 cm ¹ . This band corresponded to the Ti-0 stretching of T1O2. No shifts of the carbonate bands were observed for MMC-TiCh-ZnO when compared with MMC. The lack of band shift indicated that there were no strong covalent interactions between the carbonate surface of MMC and the T1O2 or ZnO nanoparticles.

The Raman spectrum of MMC-Ti0 ₂ -ZnO is shown in Figure 3; (a) the full spectrum, (b) bands from ZnO (wurtzite) and T1O2 (rutile) and (c) band from MMC. The Raman spectrum ofMMC-Ti0 ₂ -ZnO displays the characteristic bands shown in the Raman spectra of MMC. The Raman bands related to MMC could be identified by the vi carbonate symmetric stretching band (for MgC0 ₃ ) centered at around 1104 cm ¹ . This band was slightly shifted when compared with crystalline MgC0 ₃ , most probably due to the amorphous nature of MMC. The Raman bands related to T1O2 dominated the Raman spectrum of MMC-Ti0 ₂ -ZnO. The most intense bands were the E _g and Ai _g modes of T1O2 which were centered at around 447 cm ¹ and 608 cm ¹ . A low intensity band related to the Bi _g vibration mode of T1O2 was observed at around 142 cm ¹ and an additional broad band centered at around 237 cm ¹ . The broad band was related to the second-order effect (SOE) or combination bands, respectively. The Raman bands related to ZnO were less intense than those for T1O2, and only one low intensity band related to ZnO was observed at around 98 cm ¹ . This band was assigned to the E2° ^W vibration mode. The other ZnO bands (Figure 3a) could not be observed clearly due to overlapping with the high intensity T1O2 bands. It is important to note that the intensity of the bands was not related to the chemical compositions of MMC-Ti0 ₂ -ZnO. The Raman spectrum of MMC-Ti0 ₂ -ZnO confirmed the presence of both T1O2 and ZnO within the MMC structure. No band shifts were observed when comparing the Raman spectra of T1O2, ZnO and MMC with MMC-Ti0 ₂ -ZnO, confirming that there was no chemical interaction between the semiconductor and the MMC. The N2 adsorption and desorption isotherm of MMC-TiCh-ZnO is shown in Figure 4a; MMC- TiCh-ZnO (■) and MMC (·). Figure 4b shows differential pore volume distribution (■) and cumulative pore volume (·) of MMC and Figure 4c shows differential pore volume distribution (■) and cumulative pore volume (·) of MMC-TiCh-ZnO. The figures show that the MMC-TiCh-ZnO is a highly porous material. The specific BET surface area of MMC- TiCh-ZnO was 398 nrig ¹ and the total pore volume was 0.41cm ³ g ¹ . The specific BET surface area and pore volume was lower than that for MMC (619 nrig ¹ and 0.58 cnrig ¹ , see Table 1), due to the presence of 50 wt. % of the heavier T1O2 and ZnO particles within the structure of MMC. The incorporation of T1O2 and ZnO nanoparticles within MMC increased the solid density from 2.05 g cm ³ to 2.91 g cm ³ as determined by Helium pycnometry. It is important to note that the average pore size of MMC-Ti0 ₂ -ZnO was comparable to non-composite MMC (Figure 4b-4c), meaning that T1O2 and ZnO nanoparticles were dispersed into the MMC matrix without blocking the pores. The preserved porosity of the MMC could be utilized for hosting another compound. The high porosity of MMC-Ti0 ₂ -ZnO means that MMC-Ti0 ₂ -ZnO could also be employed in various cosmetic related applications where porosity is important, such as the sorption of excess moisture or oil from the skin.

BET Surface Total Volume in Sample Density

Area (m ² /g) Pores (cm ³ /g) (g/cm ³ )

MMC-TiCh-ZnO 398 0.41268 9Ϊ

MMC 619 0.58273 2.05

Table 1. BET surface area and total pore volume of MMC-TiCh-ZnO and MMC.

Figures 7a-i are electron microscopy images of the composite materials according to the invention and of the reference material MMC, wherein (a) is a SEM image of MMC-TiCh- ZnO, (b) is a SEM image of MMC, (c) a TEM-image of MMC-TiCE-ZnO, (d) a SEM (SE) image of MMC-TiCh-ZnO, and (e, f, g, h, i) are Energy Dispersive X-ray Spectroscopy maps of carbon, magnesium, oxygen, titanium and zinc, respectively, for the same analysed spot as depicted in (d).The SEM image of the MMC-TiCh-ZnO, Figure 5a shows MMC-TiCh-ZnO as irregularly shaped particles with very similar morphology as MMC, Figure 5b. The TEM image shown in Figure 5c reveals that the Ti0 ₂ and ZnO clusters (dark areas) are dispersed throughout the MMC-Ti0 ₂ -ZnO sample. According to the Energy Dispersive Spectroscopy analysis, Figure 5e-i and summarized in Table 2, Ti and Zn appears to be evenly distributed in the material, with some micron sized aggregates present.

It is clear from these SEM and TEM images that Ti0 ₂ and ZnO nanoparticles are incorporated within individual MMC particles, and that there was no obvious chemical interactions or reactions between the MMC and Ti0 ₂ or ZnO as previously discussed with reference to the Raman spectra of Figures 3a-c.

Element MMC (at. %) MMC-Ti02-Zn0 (at.

%)

Oxygen 64.6 ± 8.0 60.9 ±5.6

Carbon 18.7 ± 2.0 17.5 ± 1.4

Magnesium 16.8 ± 1.6 13.5 ± 1.0

Titanium — 4.1 ± 0.3

Zinc — 4.0 ± 0.5

Table 2. Elemental analysis of MMC and MMC-Ti02-ZnO obtained from SEM-EDX mappings of the area shown in Figure S4.

UV blocking properties of MMC-TiC -ZnO

The lack of chemical interaction between MMC and the semiconductor particles suggested that the UV-blocking properties of Ti0 ₂ and ZnO would be preserved. Therefore, the UV blocking properties of MMC-TiCk-ZnO (25 wt% Ti0 ₂ , 25 wt% ZnO) were examined. Figure 6 shows the UV/VIS transmittance curve for a PDMS formulation containing i) 20 wt.% MMC (PDMS/MMC, Fig. 6a), ii) 20 wt.% of MMC-Ti0 ₂ -ZnO (PDMS/MMC-25 wt% Ti0 ₂ - 25 wt% ZnO, Fig. 6b) and iii) 5 wt.% Ti0 ₂ and 5 wt.% ZnO (PDMS/Ti0 ₂ , ZnO nanoparticle powders, Fig. 6c). Note that the Ti0 ₂ and ZnO contents were kept constant in all formulations containing semiconductor particles.

The data presented in Figure 6 demonstrated that the PDMS/MMC-Ti0 ₂ -ZnO formulation had a similar transmittance curve to the PDMS/Ti0 ₂ -ZnO formulation; the UV transmission through these two samples was blocked by the semiconductor particles within the formulations. The UVA and UVB blocking properties of T1O2 and ZnO were retained in MMC-Ti0 ₂ -ZnO (note that UVC was not considered in this study, as light rays with wavelength less than 280 nm are typically absorbed by the ozone layer ).In vitro SPF values were calculated for 20 wt. % PDMS/MMC-Ti0 ₂ -ZnO and 20 wt. % PDMS/Ti0 ₂ -ZnO formulations to be 5.26±0.35 and 5.42±0.42, respectively (a 50 wt.% PDMS/MMC-Ti0 ₂ -ZnO formulation was also tested by Abich Sri, Verbania, Italy, according to ISO 24443:2010 in vitro SFP standard, to a value of 8.9). The PDMS/MMC formulation had high transparency in the visible light spectrum.

Photocatalytic activity of MMC-TiC -ZnO

Most T1O2 and ZnO particles used in cosmetics are coated with silica, alumina, polymethyl methacrylate or dimethicone in order to reduce their photocatalytic activity. Particles with high photocatalytic activity are not desirable for cosmetic applications due to their ability to facilitate the production of free radicals. The effect of the MMC on the photocatalytic activity of T1O2 and ZnO was therefore investigated by monitoring the degradation of the anionic azo dye amaranth in the presence of UV-radiation. Figure 7. shows the effect of MMC-Ti0 ₂ -Zn0 ( _■ ), MMC (►), T1O2 + ZnO (◄) and T1O2 + ZnO + MgC0 ₃ (A) and T1O2 + ZnO + MMC (¨) on the adsorption and photocatalytic degradation of the anionic azo dye amaranth. All materials/mixtures were measured in triplicates. Note that during the first hour, the mixtures were isolated from any light sources (including UV lights) to allow the dye adsorption process to reach equilibrium. As shown in Figure 7, adsorption of amaranth occurred on all of the tested materials. The T1O2 + ZnO mixture and the T1O2 + ZnO + crystalline MgC0 ₃ mixture both adsorbed approximately 15% of the amaranth in solution. The other three mixtures (MMC-Ti0 ₂ -Zn0, MMC and T1O2 + ZnO + MMC) adsorbed -90% of the dye. The high surface area and porosity of MMC-Ti0 ₂ -ZnO and MMC in conjunction with possible electrostatic interactions between the anionic dye and magnesium ions in MMC-Ti0 ₂ -ZnO and MMC could have led to the rapid and high adsorption of amaranth.

The mixtures were exposed to UV irradiation after 1 hour when equilibrium adsorption of the dye was reached, and the dye concentrations were continued to be monitored as shown in Figure 7. The amaranth concentration was found to decrease rapidly with exposure to UV light for the T1O2 + ZnO as well as the T1O2 + ZnO + crystalline MgC0 ₃ mixtures. On the other hand, the amaranth concentration did not decrease upon UV exposure of the MMC- Ti0 ₂ -ZnO, MMC (due to the lack of semiconductors) and T1O2 + ZnO + MMC mixtures. This observation demonstrated that the catalytic activity of T1O2 and ZnO was inhibited by the presence of MMC and that MMC could hinder the photocatalytic activities of T1O2 and ZnO. This property of MMC is likely related to its amorphous nature, as the T1O2 and ZnO mixture with crystalline MgC0 ₃ showed significant photocatalytic activity as shown in Figure 7.

Particle size distribution

MMC- 25 TΪ02-25 ZnO and nanopowders of T1O2 and ZnO were characterized in a Malvern - Mastersizer 3000 using dry mode. Figure 8 is a graph illustrating the measured volume density of the MMC- 25 TΪ02-25 ZnO powder (solid line) along with the volume density of the T1O2 (dashed-dotted line) and ZnO (dotted line) nano-powders. The nanoparticle powders form micrometer sized agglomerates as can be observe in Figure 8. The main peak of the particle size distribution of the MMC- 25 TΪ02-25 ZnO powder is well separated from the main peaks of the separate nanoparticle powders.

T1O2 and ZnO nanoparticles were incorporated within the structure of amorphous mesoporous magnesium carbonate (MMC). The particle morphology and porous structure of the resulting MMC-TiC -ZnO (50 wt. % MMC, 25 wt.% T1O2 and 25 wt.% ZnO) material was unchanged as compared to MMC without T1O2 and ZnO. The porosity of MMC-Ti0 ₂ -ZnO remained high with a BET surface area of -400 nrg ' The UV blocking ability of T1O2 and ZnO nanoparticles was retained when incorporated in MMC. Thus, MMC-Ti0 ₂ -ZnO gave a calculated in vitro SPF value of 5.3 in a 20 wt.% formulation with dimethicone (i.e. 5 wt% of each filter in the final formulation), which is comparable to the in vitro SPF of 5.4 for the same amount free T1O2 and ZnO nanoparticles in dimethicone without MMC. Unlike T1O2 and ZnO nanoparticles, the MMC-Ti0 ₂ -ZnO showed no photocatalytic activity in the amaranth degradation study _. The MMC-Ti0 ₂ -ZnO materials hence show interesting properties for potential application as filler materials in cosmetics with UV-protecting properties.

Incorporating T1O2 and ZnO nanoparticles into the pm sized MMC particles will reduce the risk of nanoparticle exposure. The MMC matrix does not affect the overall SPF values of the semiconductors but drastically decrease their photocatalytic activities, which will lower the risk of harmful free radical production. Furthermore, MMC-Ti0 ₂ -ZnO showed high porosity which can be utilized in cosmetic applications e.g. for sebum absorption REFERENCES

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