5 research outputs found
Photon Reabsorption and Nonradiative Energy-Transfer-Induced Quenching of Blue Photoluminescence from Aggregated Graphene Quantum Dots
A deep
understanding of the photoluminescence (PL) from aggregated graphene
quantum dots (GQDs) is very important for their practical applications.
Here the PL spectra from GQDs solutions at different concentrations
are studied. We find that the intensity of the green emission (ca.
530–560 nm) linearly relies on the concentration of GQDs, whereas
the blue PL (ca. 425 nm) intensity is below the linear relationship,
indicating a concentration-induced partial quenching of blue PL. Confocal
fluorescence images explicitly demonstrate the aggregation of GQDs
at high concentration. The concentration-induced PL quenching is successfully
interpreted by a model of photon reabsorption and nonradiative energy
transfer, indicating that, at the aggregated states, the excited electrons
of GQDs may nonradiatively relax to ground states through couplings
with neighboring ones. Simulated fluorescence decay results show that
the energy transfer between neighboring GQDs results in a prolonged
dwell time of electron on high-energy state and thus increases the
decay time of 425 nm emission, while 550 nm emission remains unaffected,
which is consistent with the experimental results. This work will
contribute to a deep understanding on PL of GQDs and is also of huge
importance to extend GQDs’ applications
Photothermal Contribution to Enhanced Photocatalytic Performance of Graphene-Based Nanocomposites
Photocatalysts possessing high efficiency in degrading aquatic organic pollutants are highly desirable. Although graphene-based nanocomposites exhibit excellent photocatalytic properties, the role of graphene has been largely underestimated. Herein, the photothermal effect of graphene-based nanocomposites is demonstrated to play an important role in the enhanced photocatalytic performance, which has not been considered previously. In our study on degradation of organic pollutants (methylene blue), the contribution of the photothermal effect caused by a nanocomposite consisting of P25 and reduced graphene oxide can be as high as ∼38% in addition to trapping and shuttling photogenerated electrons and increasing both light absorption and pollutant adsorptivity. The result reveals that the photothermal characteristic of graphene-based nanocomposite is vital to photocatalysis. It implies that designing graphene-based nanocomposites with the improved photothermal performance is a promising strategy to acquire highly efficient photocatalytic activity
Emission from Trions in Carbon Quantum Dots
The photoluminescence (PL) spectra
acquired from 1 to 6 nm large
carbon quantum dots (CQDs) prepared by refluxing activated carbon
in HNO<sub>3</sub> show blue emission independent of the excitation
wavelength as well as long-wavelength emission depending on the excitation
wavelength. The dependence of the two emissions on pH is investigated,
and the experimental results show that the peak position of the long-wavelength
emission does not change with pH; however, the blue emission becomes
more asymmetrical, and obvious shoulder peaks emerge as the pH increases.
A model based on defect-bound trions in the CQDs is proposed to explain
the shoulder peaks in the blue emission at high pH, and the calculated
results agree well with experimental data concerning the integral
intensity ratio of the trion to exciton emissions versus pH. Our experimental
and theoretical results demonstrate for the first time emission from
trions in CQDs
Ultrasensitive Detection of Matrix Metalloproteinase 2 Activity Using a Ratiometric Surface-Enhanced Raman Scattering Nanosensor with a Core–Satellite Structure
Matrix
metalloproteinase 2 (MMP-2) has been considered a promising
molecular biomarker for cancer diagnosis due to its related dysregulation.
In this work, a core–satellite structure-powered ratiometric
surface-enhanced Raman scattering (SERS) nanosensor with high sensitivity
and specificity to MMP-2 was developed. The SERS nanosensor was composed
of a magnetic bead encapsulated within a 5,5′-dithiobis(2-nitrobenzoic
acid) (DTNB)-labeled gold shell as the capture core and a 4-mercaptobenzonitrile
(MBN)-encoded silver nanoparticle as the signal satellite, which were
connected through a peptide substrate of MMP-2. MMP-2-triggered cleavage
of peptides from the core surface resulted in a decrease of the SERS
intensity of MBN. Since the SERS intensity of DTNB was used as an
internal standard, the reliable and sensitive quantification of MMP-2
activity would be realized by the ratiometric SERS signal, with a
limit of detection as low as 2.067 ng/mL and a dynamic range from
5 to 100 ng/mL. Importantly, the nanosensor enabled a precise determination
of MMP-2 activity in tumor cell secretions, which may provide an avenue
for early diagnosis and classification of malignant tumors
Cubic In<sub>2</sub>O<sub>3</sub> Microparticles for Efficient Photoelectrochemical Oxygen Evolution
Cubic In<sub>2</sub>O<sub>3</sub> microparticles with exposed {001}
facets as well as single morphology and size are produced on a large
scale on silicon with a high yield. The morphological evolution during
chemical vapor deposition is investigated and the new knowledge enables
precise facet cutting. The synthesized Cubic In<sub>2</sub>O<sub>3</sub> microparticles possess superior photoelectrocatalytic activity and
excellent chemical and structural stability in oxygen evolution reaction
on account of the unique surface structure and electronic band structure
of the {001} facets. Our results reveal that it is feasible to promote
the photolectrochemical water splitting efficiency of photoanode materials
by controlling the growth on specific crystal facets. The technique
and concept can be extended to other facet-specific materials in applications
such as sensors, solar cells, and lithium batteries