Titanium dioxide incorporated in cellulose nanofibers with enhanced UV blocking performance by eliminating ROS generation

Abstract

The preparation of sunblocks with dispersion stability, ultraviolet blocking, and photocompatibility remains a considerable challenge. Plant-derived natural polymers, such as cellulose nanofibers (CNF), show versatile traits, including long aspect ratio, hydrophilic nature, resource abundance, and low material cost. In the present study, a facile and cost-effective strategy is reported for the fabrication of nanostructured inorganic materials by incorporating natural polymers as interspersed, systematically nanosized titanium dioxide (TiO₂) particles onto CNF. Among all experiments, the optimized TiO₂@CNF3 showed higher ultraviolet blocking performance and less whitening effect. The outstanding performance is attributed to the engineering of equally dispersed nano-sized TiO₂ particles on the CNF surface and stable dispersion. Significantly, TiO₂@CNF3 exhibited excellent compatibility with avobenzone (80%), an oil-soluble ingredient used in sunblock products, illustrating the photoprotection enhancement under ultraviolet A (UVA) and ultraviolet B (UVB). Moreover, only 14.8% rhodamine B (Rho-B) dye degraded through photocatalytic oxidation process with the TiO₂@CNF3, which is negligible photocatalytic activity compared to that of TiO₂ (95% dye degraded). Furthermore, commercial inorganic and organic sunblock products with SPF lifetimes of 35⁺ and 50⁺ were modified using CNF, significantly enhancing the transmittance performance compared to that of the pure sunblock. However, it was also observed that hydrophilic CNF tended to demulsify the creams due to electrostatic disequilibrium. This CNF-based modified TiO₂ system is a new window to replace effective sunblock products in high-value-added applications, such as cosmetics.

Scheme 1. Graphical illustration for the TiO₂@CNF hybrid synthesis process with derived structure.

Fig. 1. Microscopic analysis of TiO₂@CNF hybrids at the various concentrations of TiO₂ NPs and pristine TiO₂ NPs: (a–c) TiO₂@CNF1 (TBT : CNF = 5 : 1), (d–f) TiO₂@CNF2 (TBT : CNF = 10 : 1), (g–i) TiO₂@CNF3 (TBT : CNF = 15 : 1).

Fig. 2. EDX analysis for TiO₂@CNF hybrids at the various concentrations of TiO₂ NPs and pristine TiO₂ NPs: (a) TiO₂@CNF1, (b) TiO₂@CNF2, (c) TiO₂@CNF3 and (d) the yield (%) of TiO₂ in terms of TBT concentration.

Fig. 3. (a) XPS survey spectrum of the pristine TiO₂ and optimized TiO₂@CNF3 hybrid, (b) high-resolution XPS spectrum of the Ti 2p for pristine TiO₂ (c) high-resolution XPS spectrum of the O 1s for pristine TiO₂, (d) high-resolution XPS spectrum of the Ti 2p for TiO₂@CNF3, (e) high-resolution XPS spectrum of the O 1s for TiO₂@CNF3 and (f) high-resolution XPS spectrum of C 1s for TiO₂@CNF3.

Fig. 4. UV shielding performance for the (a) pristine TiO₂ NPs, TiO₂@CNF4, TiO₂@CNF3, TiO₂@CNF2, TiO₂@CNF1 hybrids and pristine CNF, and (b) summary of the UV absorption at the 220 nm and 800 nm of wavelength. (c) Dispersion effect at the 0.1 wt% and 0.5 wt% of concentrations after 0 h and 24 h such as (i) pristine TiO₂ NPs, (ii) pristine CNF, (iii) TiO₂@CNF1, (iv) TiO₂@CNF2, (v) TiO₂@CNF3 and (vi) TiO₂@CNF4. (d) Photo digital images for all samples to assess the whitening effect.

Fig. 5. Avobenzone (Avb) compatibility with TiO₂@CNF hybrid at the low and high concentrations under UVA and UVB illuminations for 300 min, respectively, (a–c) TiO₂@CNF1, TiO₂@CNF2 and TiO₂@CNF3 hybrid with Avb (0.2 μg L⁻¹) under UVA, respectively. (d–f) TiO₂@CNF1, TiO₂@CNF2 and TiO₂@CNF3 hybrid with Avb (0.2 μg L⁻¹) under UVB, respectively. (g and h) Degradation efficiency (%) with respect to the UVA and UVB illuminations, respectively. Notice: LTiO₂, HTiO₂ means the lower and higher concentration of the TiO₂ NPs.

Fig. 6. Transmittance performance of the commercial inorganic and organic sunblock's with SPF life 35⁺ and 50⁺ containing different CNF amounts in the 200–800 nm of wavelength ranging. The corresponding SPF 35⁺ and 50⁺ sunblocks (ioSB1 and ioSB2 are inorganic while oSB1 and oSB2 are organic sunblocks) were purchased by the multiple companies and used as a reference. (a) HERA sun mate daily cream; modified by the CNF (ioSB1(35⁺) + 3 and 5 g CNF gel), (b) the face shop natural sun block eco super perfect with SPF life 50⁺; modified by CNF i.e., ioSB2(50⁺) + CNF gel with 3 and 5 g (c) MediFlower brand sunblock; modified by CNF (oSB1(50⁺) + CNF with 3 and 5 g) (d) V10 UV shield; modified by CNF (oSB2(50⁺) + CNF with 3 and 5 g). Solid and dotted lines indicate 0.1 and 0.2 mg mL⁻¹, respectively.

Fig. 7. Photocatalysis activity of the TiO₂@CNF1–3 hybrids and pristine TiO₂ NPs. (a and b) Change of Rho-B concentration against UVA and UVB illumination time, respectively and (c and d) change of Rho-B concentration against UVA and UVB illumination time using various scavengers such as FFA, IPA, AO and BQ, respectively.