Fluorescent Properties of Carbon Quantum Dots (CQDs) Synthesized from Lemon Juice Using Hydrothermal Techniques for Adsorption Application

Abstract

In this research, the optical properties of CQDs synthesis from lemon juice via hydrothermal techniques under different temperatures and their applications for the adsorption of MB dyes in an aqueous solution were investigated. The synthesized CQDs were characterized by XRD, UV-Vis, UV lamp, PL, FT-IR spectroscopic, and zeta potential techniques. An XRD analysis indicated maximum peaks at a 2θ value of 20.1° , 18.07° , and 14.57° were observed at the temperature of 160, 180, and 200 °C respectively, and had an amorphous structure. Similarly, UV-Vis spectrophotometric confirmed the presence of two absorption peaks at 217.5 and 282 nm at 160 °C. While CQDs synthesized at 180, and 200 °C display shoulders peaks at 222 and 219.5 nm respectively. The synthesized CQDs were illuminated by UV light with different excitation wavelengths, (254 nm, 365 nm, and visible regions) and green, blue, and dark brownish colors respectively. Photoluminescence (PL) spectral analysis of synthesized CQDs confirmed excitation-dependent emission peaks at different excitation wavelength from 360 to 520 nm with the 20 nm interval. The obtained quantum yield (Φ) of CQDs ranges from 14 to 41 % for synthesized at 160, 180, and 200 °C the difference is attributed to functional groups of CQDs. Also, the FT-IR spectrum of CQDs confirmed the presence of different functional groups such as N-H/OH(3270.23 cm−1), COOH(2360.48 cm−1), C=O(1635 cm−1), and C-O(1228 cm−1) for CQDs synthesized at 160°C, N-H/OH (3315.08 cm−1), C=O (1637.29 cm−1), and C-O (1222.66 cm−1) for CQDs synthesized at 180°C, and N-H/OH (3282.3 cm−1), and C=O (1637.3 cm) for CQDs synthesized at 200°C. Zeta potential result shows that CQDs are ~1.55 mV. After confirmation and characterization, the synthesized CQDs were further evaluated for their effectiveness in the adsorption of MB dyes. The result shows that synthesized CQDs are excellent adsorbents for effective adsorption of MB with a removal efficiency of 60 - 82 % in an aqueous solution and an extremely fast adsorption rate of 5.525x10-2 min -1 for MB dye in a short contact time. CQDs synthesized via hydrothermal techniques may be useful for resolving the critical problems in the drinking water the world facing due to MB dye contaminations.