Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C₃N₅ Core–Shell Nanowires

Abstract

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.

Internal Electric-Field-Driven CoAl-LDH Coupled N-Rich Carbon Nitride of C3N5 for Improved Photocatalytic Performance

“…To further elaborate the chemical structure of C 3 N 5 , we used solid-state NMR spectroscopy for the analysis. 13 C NMR spectral results of C 3 N 5 are shown in Figure S1, with two NMR signals at 164 ppm and 156 ppm that belonged to the N 2 C–NN– and CN 3 carbons in the C 3 N 5 structure, respectively, which coincided with the results previously reported in the literature …”

“…13 C NMR spectral results of C 3 N 5 are shown in Figure S1, with two NMR signals at 164 ppm and 156 ppm that belonged to the N 2 C−N� N− and CN 3 carbons in the C 3 N 5 structure, respectively, which coincided with the results previously reported in the literature. 40 3.1.2. Morphological Analysis of the Prepared Materials.…”

Colloidal-ALD-Grown Hybrid Shells Nucleate via a Ligand–Precursor Complex

“…Solution nuclear magnetic resonance (NMR) spectroscopy is among the most common tools to study NP–ligand interactions. − This technique focuses mainly on the organic species, since the resolution is often limited by the slow overall tumbling of the NPs. On the other hand, solid-state NMR can provide rich structural and dynamic information for both the core and the capping groups. − However, NMR experiments are often limited by low sensitivity, especially in the case of NPs with thin shell layers. In recent years, dynamic nuclear polarization surface-enhanced NMR spectroscopy (DNP SENS) has been developed to overcome these limitations. − In these experiments, the system is wetted with a solution containing a stable radical, and the greater polarization of the unpaired electrons is transferred to enhance the NMR signal of nuclei at the surface of the material.…”

Unusual Electronic Properties of Cellulose Nanocrystals Conjugated to Cobalt Phthalocyanine: Long-Lived Charge Separation and Visible-Light-Driven Photocatalytic Activity

“…In the second route, namely, N -deethylation, a dye cation radical is formed through oxidation of the dye in the presence of a strong electron acceptor. The photogenerated holes in the semiconductor valence band react with such an RhB cation radical by eliminating one alkyl group in this N -deethylation mechanism. , To get more insight into the RhB degradation mechanisms, we performed a scavenger test. Figures S9a and S10d,e (Supporting Information) show the scavenger test results with electron and hole scavengers AgNO 3 and ethylenediaminetetraacetic acid (EDTA), respectively.…”