We report on a single-step thermolysis strategy to prepare highly luminescent nitrogen-doped and amino acidfunctionalized graphene quantum dots (NA-GQDs) by using glycine as both carbon and nitrogen source. The NA-GQDs display an excitation wavelength-dependent fluorescence with maximum excitation and emission wavelengths of 380 and 450 nm, respectively, and a quantum yield of~16 %. Fluorescence is quenched by Fe(III) and Hg(II), and the effect was used to develop a method for the determination of Fe(III). Quenching by Fe(III) is attributed to its higher thermodynamic affinity (compared to other transition-metal ions) for the ligands on the GQDs in which nitrogen atoms mainly act as the chelating atoms. A linear relationship was observed between fluorescence intensity and the concentration of Fe(III) over the 0.5 μM to 0.5 mM range. The detection limit is 0.1 μM.
Persistent free radicals (PFRs) may cause negative impacts to human health and the environment because of the induced reactive oxygen species. We expect that PFRs could be generated in the condensable volatiles formed during lignocellulose biomass pyrolysis. Elucidating the structural origin and the formation mechanism of PFRs is important for an in-depth understanding of air pollutants from the pyrolysis or combustion of lignocellulose biomass. This work selected rice straw and pine sawdust to represent agricultural and forest biomass residues. The pyrolysis mechanism, volatile components, and PFR generation were discussed based on the analysis of thermogravimetry−Fourier transform infrared spectroscopy−mass spectrometry (MS), pyrolysis−gas chromatography/MS, and electron spin resonance (ESR). Levoglucosan, furans, and 2-methoxyphenols were the main pyrolytic compounds for cellulose (CL), hemicellulose (HC), and lignin (LG), respectively. Obvious ESR signals were detected in the condensable volatiles of LG, while no ESR signals were detected for those of CL and HC. Higher ESR signals were detected in lignocellulose with a higher content of LG. Therefore, LG was the main structural basis to generate PFRs in lignocellulose condensable volatiles, mostly attributed to the methoxyphenol components. This study provides useful information regarding the generation mechanisms of and the structures related to PFRs, which is essential to understand the risks of lignocellulose pyrolytic volatiles.
With
a combination of outstanding properties and a wide spectrum
of applications, graphene has emerged as a significant nanomaterial.
However, to realize its full potential for practical applications,
a number of obstacles have to be overcome, such as low-temperature,
transfer-free growth on desired substrates. In most of the reports,
direct graphene growth is confined to either a small area or high
sheet resistance. Here, an attempt has been made to grow large-area
graphene directly on insulating substrates, such as quartz and glass,
using magnetron-generated microwave plasma chemical vapor deposition
at a substrate temperature of 300 °C with a sheet resistance
of 1.3k Ω/□ and transmittance of 80%. Graphene is characterized
using Raman microscopy, atomic force microscopy, scanning electron
microscopy, optical imaging, UV–vis spectroscopy, and X-ray
photoelectron spectroscopy. Four-probe resistivity and Hall effect
measurements were performed to investigate electronic properties.
Key to this report is the use of 0.3 sccm CO
2
during growth
to put a control over vertical graphene growth, generally forming
carbon walls, and 15–20 min of O
3
treatment on as-synthesized
graphene to improve sheet carrier mobility and transmittance. This
report can be helpful in growing large-area graphene directly on insulating
transparent substrates at low temperatures with advanced electronic
properties for applications in transparent conducting electrodes and
optoelectronics.
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