Hydrothermal Synthesis of Fluorescent Carbon Dots By Microwave-Assisted Autoclave Treatment

Abstract

Fluorescent carbon nanoparticles (carbon dots) can be synthesized through hydrothermal treatment of carbon materials in an autoclave. Carbon dots are expected to possess homogeneous properties by using a microwave heating system instead of an electric heating system. Here, we reports particulate and photoluminescent (PL) properties of the carbon dots synthesized by microwave-assisted autoclave treatment. D(+)-glucose and potassium dihydrogen phosphate were dissolved in ultrapure water. The solution was purged with Ar gas and transferred into a Teflon vessel. The sealed Teflon vessel was heated at 200 °C using a microwave-assisted autoclave. The heating duration was changed from 5 to 60 min. The resulting dispersion was purified by centrifuging, dialyzing, and filtrating to yield a dispersion of carbon dots. The powder of carbon dots was obtained by freeze drying. According to the TEM observation, the mean particle size of carbon dots increased proportionally to hydrothermal treatment duration. According to the XRD pattern, carbon dots were mainly amorphous. Raman spectra revealed that carbon dots had a framework of graphite. A broad band with its maximum at ~360 nm was observed in PL excitation spectra of dispersions. The PL peak shifted to longer wavelength with increasing excitation wavelength. Thus, the PL spectra contained broad bands with maxima at ~400–700 nm. Maximum PL intensity and absorbance at optimum excitation wavelength increased with increasing hydrothermal treatment duration. This is attributed to an increase in fluorescence-related sites inside grown carbon dots.