We present a potential solution to
the problem of extraction of
photogenerated holes from CdS nanocrystals and nanowires. The nanosheet
form of C3N5 is a low-band-gap (E
g = 2.03 eV), azo-linked graphenic carbon nitride framework
formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods
(NRs) following the synthesis of pristine chalcogenide or intercalated
among them by an in situ synthesis protocol to form
two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively.
CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol
by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP
also enhanced the sunlight-driven photocatalytic activity of bare
CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable
300% through the improved extraction and utilization of photogenerated
holes due to surface passivation. More interestingly, CdS-MHP provided
reaction pathway control over RhB degradation. In the absence of scavengers,
CdS-MHP degraded RhB through the N-deethylation pathway. When either
hole scavenger or electron scavenger was added to the RhB solution,
the photocatalytic activity of CdS-MHP remained mostly unchanged,
while the degradation mechanism shifted to the chromophore cleavage
(cycloreversion) pathway. We investigated the optoelectronic properties
of CdS-C3N5 heterojunctions using density functional
theory (DFT) simulations, finite difference time domain (FDTD) simulations,
time-resolved terahertz spectroscopy (TRTS), and photoconductivity
measurements. TRTS indicated high carrier mobilities >450 cm2 V–1 s–1 and carrier relaxation
times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower
mobilities
<150 cm2 V–1 s–1 and short carrier relaxation times <20 ps. Hysteresis in the
photoconductive J–V characteristics of CdS
NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected
DFT simulations indicated a delocalized HOMO and a LUMO localized
on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low band gap, can function
as a shuttle to extract carriers and excitons in nanostructured heterojunctions,
and enhance performance in optoelectronic devices. Our results demonstrate
how carrier dynamics in core–shell heterostructures can be
manipulated to achieve control over the reaction mechanism in photocatalysis.
Preliminary studies established methods for obtaining maximum yields of viable cells. Liquid shaken cultures of Histoplasma capsulatum provided a maximum of 4 x 108 to 5 X 108 cells/ml regardless of the inoculum size. Under optimum condi
Octacarboxylated cobalt phthalocyanine (CoPc) was covalently
conjugated
to cellulose nanocrystals (CNCs) by employing an esterification protocol.
Solid-state NMR, X-ray photoelectron spectroscopy (XPS), Raman, and
infrared spectra were used to verify and study the nature of covalent
attachment responsible for the immobilization of CoPc on the CNC surface.
The covalent attachment was investigated from a theoretical simulation
perspective using dispersion-corrected density functional theory (DFT)
calculations, which verified the stable bond formation between CNC
and CoPc. CoPc is an organic semiconductor with a high exciton binding
energy, and CNCs are known to be insulating. Yet, Kelvin probe force
microscopy (KPFM) indicated charge carrier generation and long-lived
charge separation in the CNC–CoPc conjugate compared to pristine
CoPc under visible light illumination. Such behavior is more typical
of a semiconductor nanocomposite. The CNC–CoPc conjugate exhibited
superior performance in the visible-light-driven surface photocatalytic
reduction of 4-nitrobenzenethiol (4-NBT) to p,p′-dimercaptoazobenzene (DMAB) and photodegradation
of rhodamine B.
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