Synthesis and characterization of a broad-spectrum TiO2@lignin UV-protection agent with high antioxidant and emulsifying activity

Recent Advances of Sustainable UV Shielding Materials: Mechanisms and Applications

The escalating global threat of ultraviolet (UV) radiation is manifested through multifaceted damage pathways including cutaneous carcinogenesis, photodegradation of organic substrates, marine ecosystem destabilization, and infrastructure weathering. These urgent challenges have catalyzed sustained interdisciplinary efforts toward advanced UV-shielding technologies spanning biomedical, environmental, and industrial domains. Current material arsenals include melanin, lignin, tannin, polydopamine, zinc oxide and titanium dioxide, etc. These materials can be applied to diverse fields such as food packaging, sunscreen fabrics, sunscreen creams, eyeglasses, and sunscreen films through tailored processing techniques and employing distinct photoprotective mechanisms. Notwithstanding significant progress, the development of an integrated selection framework that reconciles efficiency, durability, and environmental compatibility persists as a critical knowledge gap. In this context, the main mechanisms of various types of UV shielding materials and their applications in different fields are described systematically. Subsequently, a comparative analysis of the advantages and shortcomings of different materials is presented, focusing on their UV shielding efficiency and stability impact. Moreover, the review delves into their unique value in specific scenarios. Finally, building on these analyses, current challenges and future development prospects of UV shielding materials are further discussed, with emphasis on scalability, eco-friendly alternatives, and multifunctional integration, providing valuable insights and guidance for advancing research and promoting sustainable and functional innovations in this field.

Hyaluronic acid-grafted titanium dioxide nanoparticles for moisture-retentive and non-cytotoxic sunscreen creams

The escalating UV exposure has emerged as a significant threat to human health, manifesting in both acute and chronic health impairments. To mitigate these risks, a biosafety sunscreen cream was prepared for UV protection and moisturization. TiO2 nanoparticles (NPs) were sequentially coated with Al(OH)3 and chemically grafted with hyaluronic acid (HA) to produce TiO2-g-HA NPs. The optimized TiO2-g-HA0.1 NPs achieved a grafting efficiency of 6.2 %, enhancing its sun protection factor (SPF) from 13.3 ± 1.4 (TiO2 NPs) to 19.1 ± 0.7. In the contrast, the TiO2-g-HA0.1 NPs exhibited a low photocatalytic activity to avoid the generation of hydroxyl radicals in a sunscreen formation. The TiO2-g-HA NPs under a state of aqueous slurries were then incorporated into a commercial sunscreen formulation. The TiO2-g-HA0.1 Cream demonstrated exceptional stability, retaining >95 % of its initial SPF (24.5 ± 0.3) after 10 heating-cooling cycles, with no phase separation observed. In addition, the TiO2-g-HA0.1 Cream sustained an enhanced moisturization performance (>80.0 % hydration retention under thermal and convective stress). Biocompatibility assessments on HaCaT keratinocytes revealed minimal cytotoxicity, with 88.5 ± 0.9 % cell viability for the TiO2-g-HA0.1 Cream. Moreover, in vitro penetration profiles were possessed with the BALB/c mouse skin, confirming most nanoparticles retained on the epidermal surface for the TiO2-g-HA0.1 Cream.

3D structure-functional design of a biomass-derived photocatalyst for antimicrobial efficacy and chemical degradation under ambient conditions

Surface sterilization and hazardous chemical degradation under ambient conditions can provide significant benefits for public and environmental health. Materials with sterilization and chemical degradation capacity under sunlight can efficiently reduce infectious disease incidence rates and toxic chemical exposure. Utilizing renewable energy for sustainable sterilization and degradation is more desirable as it reduces the potential secondary contamination. Herein, we report functional structure design using lignin, a renewable carbon heterogeneous polymer, to synthesize a highly efficient and stable photocatalyst that degrades environmentally hazardous organic compounds rapidly. Through a hydrolysis reaction between Ti-OH and the hydroxyl groups of lignin, Ti-O-C and Ti-O-Ti bonds were established and a lignin based photocatalyst with a hollow sphere structure (Clignin@H-TiO2) was formed. The presence of a homozygous carbon modified TiO2 structure contributes to the enhanced photodegradation activity with solar light. The close hetero-interfacial contact between carbonized lignin and TiO2 further improves the photocatalytic efficiency by facilitating effective charge carrier separation. After synthesis optimization, the resulting Clignin@H-TiO2 photocatalyst exhibits excellent performance in the degradation of atenolol under solar light irradiation with 100% degradation within five minutes. Additionally, it efficiently removes approximately 50% of PFOA and kills about 90% of bacteria within three hours. The uniform distribution of lignin within the crosslinking structures ensures a durable carbon modified TiO2 framework, which remains stable after 10 cycles of usage. The robustness of the lignin-based photocatalyst enables incorporating the catalyst into diversified material formats and various usages. Coating of the photocatalyst onto device surfaces shows bacterial killing efficacy under sunlight. The photocatalysts based on lignin valorization present a green chemistry approach for environmental remediation and surface sterilization, which has long-term environmental protection benefits, with broad applications in toxin treatment and health protection against pathogen infection.

Design of a hybrid nanoscaled skin photoprotector by boosting the antioxidant properties of food waste-derived lignin through molecular combination with TiO2 nanoparticles

TiO2 nanoparticles loaded with pistachio shell lignin (8 % and 29 % w/w) were prepared by a hydrothermal wet chemistry approach. The efficient interaction at the molecular level of the biomacromolecule and inorganic component was demonstrated by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-Visible (UV-Vis), Fourier transform infrared (FT-IR), dynamic light scattering (DLS), and electron paramagnetic resonance (EPR) analysis. The synergistic combination of lignin and TiO2 nanoparticles played a key role in the functional properties of the hybrid material, which exhibited boosted features compared to the separate organic and inorganic phase. In particular, the hybrid TiO2-lignin nanoparticles showed a broader UV-Vis protection range and remarkable antioxidant performance in aqueous media. They could also better protect human skin explants from the DNA damaging effect of UV radiations compared to TiO2 as indicated by lower levels of p-H2A.X, a marker of DNA damage, at 6 h from exposure. In addition, the samples could protect the skin against the structural damage occurring 24 h post UV radiations by preventing the loss of keratin 10. These results open new perspectives in the exploitation of food-waste derived phenolic polymers for the design of efficient antioxidant materials for skin photoprotection in a circular economy perspective.

Electrospun Photodynamic Antibacterial Konjac Glucomannan/Polyvinylpyrrolidone Nanofibers Incorporated with Lignin-Zinc Oxide Nanoparticles and Curcumin for Food Packaging

Due to the growing concerns surrounding microbial contamination and food safety, there has been a surge of interest in fabricating novel food packaging with highly efficient antibacterial activity. Herein, we describe novel photodynamic antibacterial konjac glucomannan (KGM)/polyvinylpyrrolidone (PVP) nanofibers incorporated with lignin-zinc oxide composite nanoparticles (L-ZnONPs) and curcumin (Cur) via electrospinning technology. The resulting KGM/PVP/Cur/L-ZnONPs nanofibers exhibited favorable hydrophobic properties (water contact angle: 118.1°), thermal stability, and flexibility (elongation at break: 241.9%). Notably, the inclusion of L-ZnONPs and Cur endowed the nanofibers with remarkable antioxidant (ABTS radical scavenging activity: 98.1%) and photodynamic antimicrobial properties, demonstrating enhanced inhibitory effect against both Staphylococcus aureus (inhibition: 12.4 mm) and Escherichia coli (12.1 mm). As a proof-of-concept study, we evaluated the feasibility of applying nanofibers to fresh strawberries, and the findings demonstrated that our nanofibers could delay strawberry spoilage and inhibit microbial growth. This photodynamic antimicrobial approach holds promise for design of highly efficient antibacterial food packaging, thereby contributing to enhanced food safety and quality assurance.

Preparation of uniform lignin/titanium dioxide nanoparticles by confined assembly: A multifunctional nanofiller for a waterborne polyurethane wood coating

We report a facile synthesis for lignin/titanium dioxide (TiO2) nanoparticles (LT NPs) at room temperature by confining assembly of lignin macromolecules. The LT NPs had a uniform nanosize distribution (average diameter ∼ 68 nm) and were directly employed as multifunctional nanofillers to reinforce a waterborne polyurethane wood coating (WBC). X-ray diffraction, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy revealed the mechanism by which formed TiO2 confined lignin assembly. The LT NPs considerably increased the tensile strength of a WBC film from 16.3 MPa to 28.1 MPa. The WBC-LT NPs exhibited excellent ultraviolet (UV) A and UVB blocking performances of 87 % and 98 %, respectively, while maintaining 94 % transmittance in the visible region. Incorporating LT NPs into the WBC enhanced the coating performance (the hardness, adhesion, and abrasion resistance) on wood substrates. A quantitative color and texture analysis revealed that the LT NPs increased the decorativeness of actual wooden products. After nearly 1800 h of UV irradiation, wood coated with the WBC-LT NPs exhibited good color stability, where the original color remained unchanged or even became brighter. In this study, value-added valorization of lignin is enabled by using organic-inorganic nanofillers and insights are gained into developing multifunctional WBCs.

Construction of photo-responsive lignin as a broad-spectrum sunscreen agent

Lignin has potential to serve as promising sunscreen agents as it has good ultraviolet (UV) absorption and antioxidant properties. However, the weak absorption capacity of lignin in the long-wave UV region (UVA, 320-400 nm) limits its further development. In this work, a spiropyran-modified lignin (DLSP) with photo-responsive property was prepared by in-situ construction of spiropyran (SP) structure in the demethylated lignin (DL). Due to the presence of SP moiety, the absorption of DLSP in the UVA region was significantly improved. Under UV irradiation, its absorption peak was redshifted as unconjugated SP form isomerized to conjugated merocyanine (MC) form, and the UVA/UVB ratio increased from 0.62 to 0.74. The free-radical scavenging ability of lignin could protect SP from photodegradation, which provided DLSP excellent fatigue resistance. DLSP were blended into creams to investigate its sunscreen performance. Results indicated that DLSP exhibited radiation-enhanced sunscreen performance, the sun protection factor (SPF) of cream containing 10 wt% of DLSP improved from 20 to 67 after 8 h of UV irradiation. Moreover, DLSP showed low skin penetration and good biocompatibility. These results provide a useful guideline for the rational design of sunscreens with special functionalities.

Recent advances in lignin antioxidant: Antioxidant mechanism, evaluation methods, influence factors and various applications

Lignin, a by-product of processing lignocellulosic materials, has a polyphenolic structure and can be used as an antioxidant directly or synergistically with synthetic types of antioxidants, leading to different applications. Its antioxidant mechanism is mainly related to the production of ROS, but the details need to be further investigated. The antioxidant property of lignin is mainly related to the content of phenolic hydroxyl group, but methoxy, purity will also have an effect on it. In addition, different methods to detect the antioxidant properties of lignin have different advantages and disadvantages. In this paper, the antioxidant mechanism of lignin, the methods to determine the antioxidant activity and the progress of its application in various fields are reviewed. In addition, the current research on the antioxidant properties of lignin and the hot directions are provided, and an outlook on the research into the antioxidant properties of lignin is provided to broaden its potential application areas.

Design of Proanthocyanidins and TiO2 Nanoparticles-Based Novel Emulsions as a Platform for UV Protection

A white oil-in-water novel emulsion stabilized by TiO2 nanoparticles with UVB shielding properties and proanthocyanidins with antioxidant activity was prepared, where the proanthocyanidins aggregated at the oil-water interface to reduce interfacial tension while TiO2 nanoparticles were dispersed in the continuous water phase to hinder droplet coalescence. It was found that the average oil droplet size was less than 10 μm and decreased with the increase of proanthocyanidins concentration, but the increase of the content of TiO2 nanoparticles had little effect on it. The combination of TiO2 nanoparticles and proanthocyanidins was versatile for oil phases with different polarities, and the resulting emulsion exhibited high stability in the face of centrifugation, heating and prolonging storage time. After encapsulating the UVA filter avobenzone in white oil, the emulsion was endowed with the ability to resist UVB and UVA. Further, the emulsion showed great free radical scavenging ability for superoxide anion radical (⋅O2 - ), hydroxyl radical (⋅OH) with the clearance rate of over 70 %, indicating the good antioxidant activity. The ingenious combination of UVB, UVA filter and antioxidant with emulsion as carrier provides a new idea for the preparation of full-band sunscreen emulsion.

Revealing the relationship between molecular weight of lignin and its color, UV-protecting property

Lignin has great potential as a natural, green, and sustainable broad-spectrum sunscreen active ingredient. However, the coexistence of dark color and sunscreen properties hinders its application in cosmetics. In this study, we focus on the effects of the molecular weight of lignin on tis UV-protecting property and color in order to prepare lignin-based sunscreen with high performance. A prepared sunscreen containing low molecular weight lignin (F5, <1000 g/mol) exhibits good UV-protecting property (sun protection factor (SPF) = 7.14) and light color advantages (ΔE = 46.2). Moreover, a strong synergistic effect on UV-protecting property exists between low molecular weight lignin and ethylhexyl methoxycinnamate (EHMC), resulting in high SPF of F5@EHMC-based sunscreen (55.56). Additionally, added TiO2 can efficiently mitigate the dark color of lignin-based sunscreens due to prominent covering power of TiO2. Moreover, lignin-based sunscreens have good biocompatibility with HaCaT cells. This work is useful for understanding the mechanism of the UV-protecting property and dark color of lignin, and for designing an efficient and safe lignin-based sunscreen.