Facile
synthesis of cost-effective carbon-supported Co single atoms
(Co-SAs) exhibits huge potential applications in energy storage and
conversion devices. We here report the implantation of Co-SAs into
hollow carbon spheres (Co-SAs-HCS) via a facile wet-chemistry strategy
followed by controlled pyrolysis. Electron-rich histidine acted as
a Lewis base effectively immobilizing Co2+ (Lewis acid)
via the electrostatic effect and hydrogen bonds, thus achieving the
scalable synthesis of Co-SAs-HCS. We constructed a series of histidine-Co2+ structure models to elucidate the formation of histidine-Co2+ complexes by analyzing their binding energy. X-ray absorption
fine-structure results verify that central Co atoms with four N coordination
atoms possess a non-planar Co-N4 structure. Electrochemical
results indicate that the as-prepared Co-SAs-HCS catalyst shows a
low potential difference (0.809 V) between the oxygen evolution reaction
potential at 10 mA cm–2 and the oxygen reduction
reaction half-wave potential, outperforming the commercial Pt/C catalysts
(0.996 V). Moreover, an assembled Zn-air battery based on Co-SAs-HCS
exhibits an unexpected long-term durability. We have demonstrated
that non-planar Co-N4-1-O2 sites are the source
for highly efficient adsorption and dissociation of O2 molecules
and then reduction of the free energy of desorption of the intermediates
by density functional theory. Our findings provide a new design insight
into the exploration of advanced electrocatalysts, which will be applied
in the design of green energy devices in the future.
In this work, a protonated graphitic carbon nitride (P-g-C3N4)-coated graphene oxide (GO) composite (GO/P-g-C3N4) was prepared via wet-chemistry exfoliation,
followed by a freeze-drying process. The GO/P-g-C3N4 composite was found to have an outstanding photodegradation
performance effect on the reactive red 195 (RR195) dye and very strong
antibacterial properties. Both the GO structure and the dispersed
state of P-g-C3N4 were found to play a significant
role in enhancing the photocatalytic activity of GO/P-g-C3N4. The GO/P-g-C3N4 obtained via
freeze-drying retained a large number of oxygen-containing groups
and showed higher catalytic activity and reusability than the reduced
GO (rGO)/g-C3N4 obtained via thermal reduction.
Characterization of the samples indicates that GO/P-g-C3N4 has a higher specific surface area and photocurrent
density than rGO/g-C3N4; it is likely that these
properties lead to the superior photocatalytic activity observed in
GO/P-g-C3N4. Adsorption energy calculations
indicate that O2 can be readily adsorbed onto the GO surface,
which results in stronger oxidizing superoxide anion radicals (•O2
–) and holes (h+); these active radicals can rapidly degrade RR195 dyes. Moreover,
broad-spectrum antibacterial activity (demonstrated against Staphylococcus aureus and Escherichia
coli) was observed in the case of the GO/P-g-C3N4 composite irradiated with visible light. This
work offers new insights into the design of cost-effective g-C3N4-based photocatalysts for environmental remediation.
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