Abstract
Caesalpinia sappan L., known as sappan wood, has been extensively explored by many researchers because it contains various structural types of phenolic compounds. This study objectives are to investigate the effect of pH on the flourescent color of carbon dots (CDs) from sappan wood and its application as an acid-base indicator under UV light for the first time. CDs were synthesized through the hydrothermal route in ethanol solvents. The synthesized CDs were further characterized by UV-Vis spectrophotometry, fluorescence and Fourier Transform Infrared (FT-IR) spectroscopy. Based on the results, CD solutions performed multiple flourescent colors (yellow, orange and green) under UV light at 365 nm when the pH was adjusted to be 1, 3, 5, 7, 9 and 11. These multiple colors were produced because of the instability of phenolic compounds in the sample, especially brazilin which was easily oxidized to brazilein in alkaline condition. According to the FT-IR spectra, the most prominent differences of the sample before and after the treatment process was observed in the peak region ranging from 1500-1700 cm-1. The characteristic band of carbonyl groups was identified at 1697 cm-1 in the treated sample (pH 9), but it was unobserved in the spectrum of sappan wood and the treated sample (pH 5). The presence of carbonyl group can be assumed that brazilin has been oxidized to brazilein after the alkaline treatment process and making the flourescent color was gradually shifted from yellow to green. Under normal light, the sappan wood�s extract and CD solution produced yellow and red colors in acidic and alkaline conditions, respectively. However, only CD solutions which have yellow, orange and green emissions in different pH conditions under UV light. Therefore, the synthesized CDs can be used as an acid-base indicator in both different light conditions.
Highlights
Nowadays, carbon dots (CDs) have attracted widespread attention as one of the most important material for a variety of applications because of its low toxicity, good water soluble, chemical inertness and more environmentally friendly [1]
Brazilin has been reported as the major component in sappan wood, which produced yellow color in solution and more stable under the acidic pH [7]
The multi-color fluorescent CDs were successfully synthesized through simple hydrothermal method using ethanol solvent under various pH condition
Summary
Carbon dots (CDs) have attracted widespread attention as one of the most important material for a variety of applications because of its low toxicity, good water soluble, chemical inertness and more environmentally friendly [1]. They exhibit different optical properties depending on their size, such as chemiluminescence, photoluminescence and photoinduced electron transfer. Several synthetic processes used to convert the precursor to be CDs are ultrasonication, solvothermal, chemical oxidation and hydrothermal [3] Among of these conventional method, hydrothermal is the most frequently method used because of its simple process, environmentally friendly and higher yield with a good CD surface in fluorescence properties. The use of natural sources for preparing CDs are investigated by experts [5]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call