Carbon Quantum Dots from Coconut husk: Green synthesis and evaluation of antioxidant and cytotoxic activity

L A Avinash Chunduri, Aditya Kurdekar, Sandeep Patnaik, Vishnu Dev, Tanu M Rattan, Venkataramaniah K

Department of physics, Sri Sathya Sai Institute of Higher Learning, Prasanthinilyam, 515134, A.P. India

We report for the first time green synthesis of water soluble, monodisperse carbon quantum dots
from coconut husk, anatural biomass as carbon precursor by single step hydrothermal carbonization. Structural and morphological characterization of these carbon quantum dots were carried out using TEM, XRD, Raman, FTIR. As synthesized carbon quantum dots were in the size range of 1 to 8 nm as observed in the TEM, while XRD results confirmed their crystalline nature. Raman spectroscopic measurements exhibited the characterstic D and G bands confirming the formation of low dimentional carbon nanostructures. Optical properties were probed using UV-vis spectrometry and room temperature photoluminiscence measurements. The UV-vis spectrum showed strong absorption band at 278 nm. These carbon quantum dots exhibited fluorescence constantly at 440nm when exited at different wavelengths. The fluorescence of carbon quantum dots was found to be sensitive to pH linearly over the pH range of 4-12 which can be exploited for pH sensor applications. FTIR spectroscopy cpnfirmed the prescence of hydroxyl and carboxyl groups on surface of the carbon quantum dots which play a crucial role in surface passivation leading to more stable nano dispersions. The antioxidant activity of carbon quantum dots was estimated and EC 50 was calculated to be 0.06 mg/ml using DPPH assay. Hemolysis test proved that carbon quantum dots derived from coconut husk, anatural biomass as carbon precursor by single step hydrothermal carbonization. Structural and morphological characterization of these carbon quantum dots were carried out using TEM, XRD, Raman, FTIR. As synthesized carbon quantum dots were in the size range of 1 to 8 nm as observed in the TEM, while XRD results confirmed their crystalline nature. Raman spectroscopic measurements exhibited the characterstic D and G bands confirming the formation of low dimentional carbon nanostructures. Optical properties were probed using UV-vis spectrometry and room temperature photoluminiscence measurements. The UV-vis spectrum showed strong absorption band at 278 nm. These carbon quantum dots exhibited fluorescence constantly at 440nm when exited at different wavelengths. The fluorescence of carbon quantum dots was found to be sensitive to pH linearly over the pH range of 4-12 which can be exploited for pH sensor applications. FTIR spectroscopy cpnfirmed the prescence of hydroxyl and carboxyl groups on surface of the carbon quantum dots which play a crucial role in surface passivation leading to more stable nano dispersions. The antioxidant activity of carbon quantum dots was estimated and EC 50 was calculated to be 0.06 mg/ml using DPPH assay. Hemolysis test proved that carbon quantum dots derived from coconut are biocompatible. The favourable optical properties, anti oxidant and non-cytotoxic properties of these carbon quantum dots can be very well exploited for bio imaging and drug delivery applications.