Lignosulfonate (LS), one type of industrial lignin and natural macromolecular sun blocker, was applied to modify TiO 2 via one-pot hydrothermal esterification. The reaction mechanism and composite structure of LS@TiO 2 were investigated by DLS, TEM, AFM, TG, UV, FTIR, XPS, XRD, ESR, and contact angle measurements. The results show that the esterification modification occurred between the carboxyl groups of lignin and the hydroxyl groups on the surface of TiO 2 . Lignosulfonate of 3.4 wt % with a thickness of 13 nm effectively coated the normal TiO 2 , and the LS@TiO 2 composites were nanoscale with an average size of 119 nm. Hydroxylated TiO 2 particles were more reactive, and the contents of LS on TiO 2 were processed by 0.1 and 1 M HCl and increased to 5.0 wt % (LS@TiO 2 -0.1M) and 6.0 wt % (LS@TiO 2 -1M), respectively. Chemically coated LS not only improved the dispersibility of TiO 2 in the substrates, but also significantly boosted its UV-blocking ability. Therefore, TiO 2 @LS nanocomposites were applied as the sole active in the pure cream and the sunscreen performance was compared with that of TiO 2 . The sun protection factor (SPF) values of creams containing 5, 10, and 20 wt % LS@TiO 2 were 16, 26, and 48, respectively. They were 30−60% higher than those of the creams containing the same amount of TiO 2 . The sunscreen performance of LS@TiO 2 improved with LS content. The SPF value of pure cream containing 10 wt % LS@TiO 2 -1M reached 50+. The possible UV-blocking enhancement mechanism of LS@TiO 2 was also revealed. Preparation of LS@TiO 2 nanocomposites provides a facile and green way for value-added utilization of lignin biomass and highly efficient UV-blocking of nano-TiO 2 materials.
Lignin nanospheres with broad-spectrum UV adsorption and excellent antioxidant properties were obtained by demethoxylation of alkali lignin (AL) and grafting the benzophenone moiety (UV-0) followed by a reverse selfassembly. The critical wavelength (λ c ) of the optimal AL-UV0 3 sample was ∼375 nm, while the UVA/UVB ratio reached 0.84. When it was applied as a unique active in sun cream, the sun protection factor value of the cream containing 10 wt % AL-UV0 3 was 22.81, which could further increase to 56.14 when it formed reverse colloidal spheres (LRCS) with a size of ∼130 nm. The self-assembly process and the UVabsorbing enhancement mechanism of LRCS were monitored and revealed by fluorescence, UV, and light scattering analysis. In addition, AL-UV0 3 exhibited superior photostability due to the three-dimensional network structure of lignin. The antioxidant activities of AL-UV0 3 and LRCS were better than that of AL and could increase continuously with the dosage. Both AL-UV0 3 and LRCS exhibited good biocompatibility. HaCaT cell activity remained 72−78% when their concentration was as high as 1.0 mg/mL. The novel lignin broad-spectrum UV blocker and antioxidant show good potential in skincare products and polymeric materials.
Lignin colloidal spheres (LCSs) are promising biomaterials for application in drug storage and delivery, pollutant adsorption, and ultraviolet protection due to their biocompatibility, amphiphilicity, and conjugated structure. However, wide size distribution of LCSs greatly limits their performances, especially in many precise and advanced applications. Herein, the fabrication of monodispersed LCSs with tailorable sizes ranging from the nanoscale to microscale is reported. Lignin raw materials are first fractionated by solvent extraction, and then the lignin fraction is used to fabricate monodispersed LCSs by solvent/antisolvent self‐assembly. The underlying mechanism for the formation of monodispersed LCS is primarily ascribed to the improved homogeneity of long‐range intermolecular forces, especially the electrostatic forces and hydrophobic forces, between lignin molecules. Moreover, by manipulating the short‐range order of LCSs, an innovative application of lignin as bio‐photonic materials with tunable structural colorations (e.g., red, green, or blue) is demonstrated. This work not only provides deep insight and an effective strategy to eliminate the serious inhomogeneity of LCSs, but also makes lignin resources have great potential as biodegradable and biocompatible photonic materials in diverse advanced optical application fields such as photonic devices, anti‐counterfeiting labels, and structural color pigments.
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