The effect of pH in the synthesis of carbon quantum dots from rice husk on their photoluminescence properties

The dependence of photoluminescence properties to pH solution of carbon quantum dots (CQDs) has been widely investigated. However, the influence of pH condition in synthesis process of CQDs was rarely explored, especially in synthesis by using natural precursor. Herein, this report established the synthesis of CQDs from rice husk by using hydrothermal method in varying pH condition (pH 0-14). The oxidation treatment during synthesis process leads to the initiation of surface defect on carbon precursor. Since surface defect plays crucial role in tuning photoluminescence properties, controlling the amount of oxidant agents was suggested to tune distinct photoluminescence properties. According to High-Resolution Transmission Electron Microscope (HRTEM), pH condition during synthesis affects the size of CQDs which has diameter in the range of 3-20 nm. X-ray Diffractometer (XRD) spectra revealed that the obtained CQDs were amorphous with (002) plane of graphite, while the presence of silica on CQDs was revealed by Energy Dispersive X-ray Spectroscopy (EDX) and Fourier Transform Infrared Spectroscopy (FTIR) findings. Photoluminescence spectroscopy showed that the variation of pH in synthesis process broadens the photoluminescence properties of CQDs from green region wavelength to cyan – orange region wavelength (510-632 nm). Therefore, this study suggests that the variation of pH is able to tune photoluminescence properties of CQDs that will be beneficial for its application. (paper)