Fig. 2

Characterizations of metal-gallate nanoparticles. a Schematic structure of coordination between gallic acid and metal ions (M represent metal ions). b–d TEM images of CaGA, MnGA and FeGA nanoparticles. e XRD patterns of FeGA, MnGA and CaGA nanoparticles. f FTIR curves of gallic acid, FeGA, MnGA and CaGA nanoparticles. g Specific surface area of FeGA, MnGA and CaGA nanoparticles. h Degradations of FeGA, MnGA and CaGA nanoparticles in PBS at pH 7.4. i Vis–NIR spectra of GA, FeGA, MnGA and CaGA nanoparticles. j–l Temperature changes of CaGA, MnGA and FeGA nanoparticles at various concentrations (0.05, 0.1, 0.2, 0.4 mg/L) after 808 nm NIR laser irradiation. m–o Photographs of CaGA, MnGA and FeGA in PBS with pH 7.4, 6.5 and 5.0