Adjustable optical transmittance of superhydrophobic carbon soot coatings by in-situ single-step control of their physicochemical profile

Soot aerosol formation in the ambient atmosphere, due to inappropriate and incomplete incineration of various fossil fuels or waste materials, has been considered as one of the major anthropogenic contributions to the global warming. However, despite of their adverse environmental impact, the soot nanoparticles are extremely useful in many practical applications if deposited as coatings, since they impart superhydrophobicity of the hosting solid substrate. Here, we unveil novel experimental results on the optical transmittance of superhydrophobic soot coatings with three different physicochemical profiles, synthesized by controlling the atmospheric air flow rate during the combustion of rapeseed oil. The in-depth morphological, chemical and optical analyses using scanning electron microscopy, X-ray photoelectron spectroscopy and spectrophotometry, show relation among the thickness, chemical bonds, morphology and light transmission coefficient (T %) of the soot. In turn, at equal film thicknesses, the gradual decrease of pi bonds in the material leads to enhanced light transmittance in the NIR range, while the soot morphology regulates the width of the spectral region with T > 0 %. Our findings demonstrate interconnection between the combustion conditions and the derivative physicochemical properties of the soot coatings, allowing single-step adjustment of their optical behavior, possibly for future underwater optical applications.