Fig. 1. (a) Natural leaves with stomatal and chloroplast structures produce oxygen under light. (b) Free radical leaves with porous structure produce and release free radicals. Liquid and solid functional components are combined to form a flexible film, which is a novel solid-liquid two-phase integrated structure.

Fig. 2. Characterization and photoactivity of plasma prepared N-TiO2 samples. (a) Schematic diagram of experimental device for synthesis of N-doped TiO2. (b) EDS elemental mapping, (c) XRD pattern and (d) UV-Vis-NIR reflectance spectrum for N-TiO2. These results confirmed the N-doping, crystallization and enhancement of visible light absorption of plasma prepared N-TiO2 samples. (e) MB photodegradation performance of the N-TiO2 and the pure TiO2 sample under visible light irradiation. An Enhanced visible light photocatalytic activity of plasma N-TiO2 was observed.

Fig. 3. Characterization of TP-GEL samples. (a) SEM image of PAAm hydrogels. (b) SEM image of TP-GEL. (c) XRD patterns of PAAm hydrogels and TP-GEL. (d) Raman spectra of PAAm hydrogels and TP-GEL. N-TiO2 was successfully coupled to the hydrogel network. ESR spectra of (e) PAW and (f) TP-GEL, using the aqueous solution of 5,5-Dimethyl-1-pyrroline N-oxide (DMPO) as the trapping agent. •OH radicals were stored and released from PAW and TP-GEL.

Fig. 4. Evaluation of tooth whitening effect and safety. (a) The illustration of tooth whitening process of TP-GEL. TP-GEL can work well with or without light irradiation. (b) Comparison the change of tooth color treated with different bleaching method. TP-GEL presents significantly higher performance than 30% H2O2. The overall color change (ΔE) of the samples were calculated using the following expression: ${\rm{\Delta }}E = {\left[ {{{\left( {{\rm{\Delta }}{L^*}} \right)}^2} + {{\left( {{\rm{\Delta }}{a^*}} \right)}^2} + {{\left( {{\rm{\Delta }}{b^*}} \right)}^2}} \right]^{1/2}}.$ (c) Tooth images after treatment by control and TP-GEL group. (d) Elemental analysis and (e) enamel morphology of teeth treated by different agents. The satisfactory security of TP-GEL for tooth whitening was observed. Significant differences between groups are marked with different letters (p < 0.05).

Fig. 5. Evolution tendency of (a) intermediate radicals, (b) H2O and •OH, (c) C29 and C7 molecules obtained via ReaxFF. (d) Distribution of the products at the end of simulation. (e) Proposed tooth bleaching mechanism of TP-GEL and the removal of dental stains by TP-GEL in detail.