Abstract
Low-cost and earth-abundant coal has been considered to have a unique structural superiority as carbon sources of carbon quantum dots (CQDs). However, it is still difficult to obtain CQDs from raw coal due to its compactibility and lower reactivity, and the majority of the current coal-based CQDs usually emit green or blue fluorescence. Herein, a facile two-step oxidation approach (K2FeO4 pre-oxidation and H2O2 oxidation) was proposed to fabricate bandgap tunable CQDs from anthracite. The K2FeO4 pre-oxidation can not only weaken the non-bonding forces among coal molecules which cause the expansion of coal particles, but also form a large number of active sites on the surface of coal particles. The above effects make the bandgap tunable CQDs (blue, green, or yellow fluorescence) can be quickly obtained from anthracite within 1 h in the following H2O2 oxidation by simply adjusting the concentration of H2O2. All the as-prepared CQDs contain more than 30 at% oxygen, and the average diameters of which are <10 nm. The results also indicate that the high oxygen content only can create new energy states inside the band gap of CQDs with average diameter more than 3.2 ± 0.9 nm, which make the as-prepared CQDs emit green or yellow fluorescence.
Highlights
Carbon quantum dots (CQDs), new zero-dimensional carbon nanomaterials whose size are similar with conventional semiconductor quantum dots but the skeleton is based on carbon, have attracted tremendous research interest after been found (Jaleel and Pramod, 2018; Kaur et al, 2018; Riyanto et al, 2019; Wang et al, 2019; Zhou et al, 2019)
Pulverized coal could be very well-moistened with water and the volume of raw coal expanded significantly after the pre-oxidation, indicating that the pre-oxidation has the powerful influence on the structure and properties of anthracite
To obtain more information about the structure change of anthracite after the pre-oxidation, original and oxidized samples were analyzed by the X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR)
Summary
Carbon quantum dots (CQDs), new zero-dimensional carbon nanomaterials whose size are similar with conventional semiconductor quantum dots but the skeleton is based on carbon, have attracted tremendous research interest after been found (Jaleel and Pramod, 2018; Kaur et al, 2018; Riyanto et al, 2019; Wang et al, 2019; Zhou et al, 2019). Different nanometer-sized CQDs can be prepared solely from anthracite in concentrated H2SO4 and HNO3, and the size control of CQDs was achieved through cross-flow ultrafiltration, controlling the reaction temperature of the oxidation process or conjugating pristine CQDs with poly aromatic rings (Ye et al, 2015; Yan et al, 2018). Another approach for narrowing the bandgap is forming intramolecular Z-schemes structure via functionalization of pristine CQDs with electron-donating chemical groups (Yan et al, 2018).
Sign-in/Register to view highlights & summary 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 callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
