Nanozymes,
the enzyme-mimicking nanomaterials, have been developed
to overcome the low stability and high cost of natural enzymes. Unlike
highly active and specific enzymes, however, the catalytic activities
of nanozymes are moderate and lack specificity. To address these issues,
herein we demonstrated an effective and general strategy to specifically
enhance the peroxidase-mimicking activities of carbon nanozymes. By
doping heteroatom nitrogen (N) into reduced graphene oxide (rGO) and
mesoporous carbon (MC), their peroxidase-mimicking activities were
enhanced by over 100- and 60-fold, respectively. Moreover, N-doping
did not significantly affect the oxidase-, superoxide dismutase (SOD)-,
or catalase-mimicking activities of rGO and MC, demonstrating a specific
enhancement of the peroxidase-mimicking activities. To understand
the origin of the specific enhancement, we performed density functional
theory calculations to examine the catalytic reaction mechanisms responsible
for the peroxidase-, catalase-, oxidase-, and SOD-mimicking activities
of N-doped rGO (N-rGO). We revealed that N-rGO selectively activated
H2O2 rather than O2 and •O2
– by forming and stabilizing radical
oxygen species adjacent to the N sites of N-rGO. The radical oxygen
species then oxidized peroxidase substrates, endowing N-rGO with peroxidase-mimicking
activity. This study will aid in the rational design of highly active
and specific peroxidase mimics and help elucidate the catalytic mechanisms
of nanozymes.
Graphene is often regarded as one of the most promising candidates for future nanoelectronics. As an indispensable component in graphene-based electronics, the formation of junctions with other materials not only provides utility functions and reliable connexions, but can also improve or alter the properties of pristine graphene, opening up possibilities for new applications. Here we demonstrate an intramolecular junction produced by the controllable unzipping of single-walled carbon nanotubes, which combines a graphene nanoribbon and single-walled carbon nanotube in a one-dimensional nanostructure. This junction shows a strong gate-dependent rectifying behaviour. As applications, we demonstrate the use of the junction in prototype directionally dependent field-effect transistors, logic gates and highperformance photodetectors, indicating its potential in future graphene-based electronics and optoelectronics.
The discovery of short-range order, associated with diffuse bands in electron diffraction patterns, provides new insights into defective half-Heusler thermoelectric crystals.
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