Carbon-based nanomaterials (CNPs) have attracted considerable interest because of their unique electronic, optical and mechanical properties. Among them, CNPs have become increasingly popular mainly due to their photoluminescence (PL) properties which make them ideal for bio-medical imaging or drug-delivery in addition to light-emitting devices because of their low toxicity, environmental friendliness, low cost and relatively simple synthesis processes. There are many routes for the synthesis of CNPs divided into top-down nano-cutting methods and bottom-up organic approaches. The first one includes laser ablation, arc discharge, chemical and electrochemical oxidation of large carbon structures; recently, starting from the pioneering work of Liu et al. [1], also the so called "candle soot" turned out to be an excellent precursor for the synthesis of CNPs for a variety of applications [2]. A wide set of studies indicates that the constituents of CNPs in flames are mainly PAHs of moderately size [3, 4]. Furthermore, there is a large body of evidence indicating a change in the electronic and optical properties of CNPs during their early stages of nucleation and growth [5] and recently, Liu et al. [6] demonstrated quantum dots behavior of the CNPs, in the particle range 4-23 nm, directly produced and collected from flames. Therefore, carbon particle nucleation and growth in flames can be exploited as a bottom up process for CNPs through direct sampling CNPs from a well-controlled flame reactor. In this work particle size has been measured on-line in aerosol phase by a differential mobility analyzer. Particles with different average sizes have been sampled and characterized for the first time by scanning tunneling microscopy/spectroscopy (STM/STS). The electronic properties, i.e., density of states and energy band gap, of flame-formed nanoparticles measured by STS have been correlated to nanostructure determined by Raman spectroscopy and the UV-visible absorption spectra and optical band gap determined by Tauc analysis. [1] H. Liu et al., Fluorescent Carbon Nanoparticles Derived from Candle Soot, Angew. Chem. Int. Ed. 46 (2007) 6473 -6475. [2] M.R. Mulay et al., Candle soot: Journey from a pollutant to a functional material, Carbon 144 (2019) 684-712. [3] F. Schulzet al., Insights into incipient soot formation by atomic force microscopy, Proc. Combust. Inst. 37, 2019, 885-892. [4] M. Commodo et al., On the early stages of soot formation: Molecular structure elucidation by high-resolution atomic force microscopy, Combust. Flame 205 (2019) 154-164. [5] M. Commodo et al., Physicochemical evolution of nascent soot particles in a laminar premixed flame: from nucleation to early growth, Combust. Flame 162 (2015) 3854-3863. [6] C. Liu et al., Flame-Formed Carbon Nanoparticles Exhibit Quantum, Proc. Natl. Acad. Sci. U.S.A. 2019, DOI: 10.1073/pnas.1900205116.
TUNING THE OPTICAL PROPERTIES OF FLAME-SYNTHESIZED CARBON NANOPARTICLES
Mario Commodo;Patrizia Minutolo;Gianluigi De Falco;
2019
Abstract
Carbon-based nanomaterials (CNPs) have attracted considerable interest because of their unique electronic, optical and mechanical properties. Among them, CNPs have become increasingly popular mainly due to their photoluminescence (PL) properties which make them ideal for bio-medical imaging or drug-delivery in addition to light-emitting devices because of their low toxicity, environmental friendliness, low cost and relatively simple synthesis processes. There are many routes for the synthesis of CNPs divided into top-down nano-cutting methods and bottom-up organic approaches. The first one includes laser ablation, arc discharge, chemical and electrochemical oxidation of large carbon structures; recently, starting from the pioneering work of Liu et al. [1], also the so called "candle soot" turned out to be an excellent precursor for the synthesis of CNPs for a variety of applications [2]. A wide set of studies indicates that the constituents of CNPs in flames are mainly PAHs of moderately size [3, 4]. Furthermore, there is a large body of evidence indicating a change in the electronic and optical properties of CNPs during their early stages of nucleation and growth [5] and recently, Liu et al. [6] demonstrated quantum dots behavior of the CNPs, in the particle range 4-23 nm, directly produced and collected from flames. Therefore, carbon particle nucleation and growth in flames can be exploited as a bottom up process for CNPs through direct sampling CNPs from a well-controlled flame reactor. In this work particle size has been measured on-line in aerosol phase by a differential mobility analyzer. Particles with different average sizes have been sampled and characterized for the first time by scanning tunneling microscopy/spectroscopy (STM/STS). The electronic properties, i.e., density of states and energy band gap, of flame-formed nanoparticles measured by STS have been correlated to nanostructure determined by Raman spectroscopy and the UV-visible absorption spectra and optical band gap determined by Tauc analysis. [1] H. Liu et al., Fluorescent Carbon Nanoparticles Derived from Candle Soot, Angew. Chem. Int. Ed. 46 (2007) 6473 -6475. [2] M.R. Mulay et al., Candle soot: Journey from a pollutant to a functional material, Carbon 144 (2019) 684-712. [3] F. Schulzet al., Insights into incipient soot formation by atomic force microscopy, Proc. Combust. Inst. 37, 2019, 885-892. [4] M. Commodo et al., On the early stages of soot formation: Molecular structure elucidation by high-resolution atomic force microscopy, Combust. Flame 205 (2019) 154-164. [5] M. Commodo et al., Physicochemical evolution of nascent soot particles in a laminar premixed flame: from nucleation to early growth, Combust. Flame 162 (2015) 3854-3863. [6] C. Liu et al., Flame-Formed Carbon Nanoparticles Exhibit Quantum, Proc. Natl. Acad. Sci. U.S.A. 2019, DOI: 10.1073/pnas.1900205116.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
