Optical characteristics and photothermal conversion of natural iron oxide colloid

Abstract

Background: Chemical compositions and spectroscopic characteristics of the natural floating colloids in brine mineral water were investigated in this study. Methods: The natural colloidal materials were investigated using electron microscopy, X-ray crystallography, elemental analysis, and absorption and emission spectroscopies. Results: The natural colloidal particles have a spherical shape, with average diameter of 200 nm, and amorphous crystalline structure. The colloids are mostly composed of iron and oxygen atoms; they also contained small amounts of trace elements and rare earth minerals. In particular, the colloids show remarkable absorption and emission characteristics in the wide spectral region from ultraviolet (UV) to near infrared (NIR), which could make it useful in photoconversion and hyperthermal applications. Conclusion: From the photothermal conversion efficiency measurement using an infrared thermography under irradiation of visible and NIR light, interestingly, it was found that the natural colloids have higher photothermal conversion efficiency, as compared with those of several different-typed minerals.