Facile synthesis of luminescent carbon dots from mangosteen peel by pyrolysis method
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Carbon dots (C-Dots) from mangosteen peel has been synthesized by pyrolysis method. Synthesis of C-Dots is done using precursor solution which is prepared from extract of mangosteen peel as carbon source and urea as passivation agent. C-Dots is successfully formed with absorbance spectra at wavelength 350–550 nm. Urea affects to the formed C-Dots, while the absorbance and the luminescent spectra are independent toward urea. C-Dots from extract of mangosteen peel has size in range ~2–15 nm. The absorbance peaks of C-Dots shows significant wavelength shift at visible region as the increasing of synthesized temperature. Shift of wavelength absorbance indicates the change of electronic transition of C-Dots. Meanwhile, the luminescent of C-Dots can be controlled by synthesized temperature as well. C-Dots luminescent were increasing as higher synthesized temperature. It was shown by the shift of wavelength emission into shorter wavelength, 465 nm at 200 °C, 450 nm at 250 °C, and 423 nm at 300 °C. Synthesized temperature also affects size of C-Dots. It has size ~10–15 nm at 200 °C, ~7–11 nm at 250 °C and ~2–4 nm at 300 °C. In addition, temperature corresponds to the structure of carbon chains and C–N configuration of formed C-Dots from mangosteen peel extract.
KeywordsCarbon dots Mangosteen peel Luminescent Pyrolysis
Carbon dots (C-Dots) have been attracted many researchers during last decade because of their fascinating luminescent properties, low toxicity, stability and chemical inertness [1, 2]. C-Dots are new carbon nanomaterials with size below 10 nm, first obtain during purification of single wall carbon nanotubes (SWNCTs) through electrophoresis in 2004 . Small size and strong photoluminescent properties of C-Dots have shown great impact in various applications such as optoelectronic devices, photocatalyst, electrocatalyst and bioimaging [1, 4, 5, 6, 7, 8, 9, 10]. Moreover, C-Dots can be synthesized from natural carbon sources in low temperature that shows green, cheap and facile synthesis process.
Generally, synthesized processes of C-Dots can be classified into top-down and bottom-up process. Top-down method is based on cutting from a carbon source to form C-Dots particle, such as arch discharge, laser ablation and electrochemical oxidation [11, 12, 13]. Bottom-up method is using molecule precursors that are including polymerization of monomer, dehydration, and carbonization, as well as hydrothermal, pyrolysis, microwave, and supported synthesized [14, 15, 16]. Pyrolysis method is widely used as an effective one-step bottom-up method.
Nature provides unlimited carbon sources to engineer it as C-Dots materials. Several natural carbon sources that have been reported were orange, soybean, ginger, etc. [14, 15, 17, 18]. Generally, carbon sources with abundant of carbon compound can be fabricated as C-Dots. One of interesting natural carbon source for C-Dots is mangosteen peel. Mangosteen (Garcinia mangostana L.) is a native fruit of Southeast Asia and widely grown in there . The Mangosteen peel is known as source of anthocyanin pigment that commonly use as natural colorant and absorber material [19, 20, 21]. The pigment shows light absorption that corresponds to the electronic transition, but it cannot produce electron and hole since the absence of photoluminescent in the pigment. Therefore, synthesis of C-Dots from mangosteen peel gives a chance to reveal luminescent mechanism of C-Dots while it’s mechanism still lacking.
Synthesis of C-Dots from mangosteen peel was used pyrolysis method. Five-teen gram of mangosteen peel was heated in 100 ml distilled water at 70 °C. The result solution showed yellow–brown color and then 20 ml of the solution added by urea as precursor solution. The precursor solution is heated in the furnace along 30 min for forming C-Dots. The Influence of urea and heating temperature were proposed to study the properties of C-Dots. The urea, 1–6 g was used in precursor solution while the synthesized temperature was 200 °C. To study the influence of temperature on C-Dots properties, the synthesized temperature was conducted in 200, 250 and 300 °C.
Result and discussion
Electronic transition of C-Dots occurred in HOMO as minimum level energy to LUMO as the higher level energy . To electron transition is occurred, the minimum energy must be provided. Hence, structure of C-Dots energy gap probably to be controlled by heating temperature. Energy gap of C-Dots has been determined by Tauc plot method.
According to the FTIR result, synthesized C-Dots from mangosteen peel at 200 °C shows band peaks at 3459, 3362 cm−1 that assign stretching OH (hydroxyl and carboxylate group), stretching N–H (amine group) [25, 26]. The FTIR result also display sharp peaks at 1670, 1624, and 1456 cm−1 which correspond to stretching C=O (ketone group), stretching C=C, and deformation C–H (methyl group) for synthesized C-Dots at 200 °C [13, 27]. Synthesized C-Dots at 250 °C shows stretching OH (3454 cm−1), stretching N–H (3362 cm−1), stretching C=O (1670 cm−1), deformation C–H (1456 cm−1), that confirms carboxylate, hydroxyl, amine, ketone and methyl group in surface ligands of C-Dots [1, 3, 12]. The appearance of stretching C=C peak at 1624 cm−1 corresponds to ring structure of C-Dots core for graphite structure since C-Dots is consist of core and ligand molecule [3, 28]. C-N configuration was appears at 1334 cm−1 in synthesized C-Dots at 250 °C shows nitrogen containing from urea successfully modify C-Dots structure [25, 27, 29]. As the results in synthesized C-Dots at 200 and 250 °C, synthesized C-Dots at 300 °C the detection peaks at 3208, 1721, 1456 cm−1 are relate to OH stretching (hydroxyl group) and C=O stretching (carboxyl group) and deformation C–H (methyl group) which indicate surface ligands of C-Dots, while aromatic structure of C–H stretching (3034 cm−1) indicate graphitic structure in C-Dots core.
C-N configuration also appears in the synthesized C-Dots at 300 °C. The peak detection is sharper than the synthesized C-Dots at 250 °C which is shown at 1339 cm−1. The C–N configuration plays an important role on PL of C-Dots. Nitrogen dopes graphitic structure in the core of C-Dots that presence C–N bonding. The presence of C–N bounding creates emission energy trap that increase radiative recombination induced by the electron–hole pairs . Due to the increasing radiative recombination in C-Dots, the numbers of photons emission are increasing as well. So that it leads to the higher of PL intensity.
C-Dots from mangosteen peel have been synthesized using pyrolysis method. The result shows number of formed C-Dots can be controlled by the urea concentration. However, the synthesized temperature affects to the electronic transition and PL properties of C-Dots. Luminescent of C-Dots increases as the higher of synthesized temperature, which corresponds to the shift of wavelength emission into shorter wavelength. Furthermore, the synthesized temperature leads to form C–N configuration of C-Dots that plays an important role on the structure and luminescent energy as well.
We are very thankful to Jotti Karunawan, Annisa Lidia Wati, Aan Priyanto, Ita Rahmawati, and Nila Fitriya for helping in discussion, sample preparation and TEM analysis.
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