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(a) XRD patterns of N-NBO/C, and pure NBO, (b) Raman spectra of N-NBO/C, and pure NBO, (c) Fourier transform infrared spectra of NBO-Hmta, and N-NBO/C, and (d) TGA curve of N-NBO/C hybrids
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Significant endeavors have been devoted in the past few years to establish efficient visible light-activated photocatalysts. Herein, we successfully synthesized a flower-like hierarchical nitrogen-doped and carbon-sensitized Nb 2 O 5 (NBO) nanostructure (denoted N-NBO/C). The as-prepared N-NBO/C possessed a specific surface area of 260.37 m 2 g À1...
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Photocatalysis based on semiconductors has recently been receiving considerable research interest because of its extensive applications in environmental remediation and renewable energy generation. Various semiconductor-based materials that are vital to solar energy utilization have been extensively investigated, among which titanium oxide (TiO2) h...
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... Three peaks were identified in the high-resolution O 1s spectrum (Fig. 2e). Two peaks at 529.7 and 530.3 eV are associated with the Nb -O bond, while the broad one centered at 531.3 eV is related to the carboxylate species [56,57]. ...
The metal-organic-frameworks (MOFs) have attracted considerable attention as potential electrode materials for energy storage devices. In the present work, niobium(pyridine-2,6-dicarboxylic acid) MOFs (Nb(PDCA)MOFs) are grown on the surface of electrospun porous carbon nanofiber (CNF) via in-situ solvothermal process. As prepared Nb(PDCA)[email protected] hybrid mats were characterized and used as working electrode for supercapacitor applications. To find out ideal electrolyte, the electrochemical characteristics of the Nb(PDCA)[email protected] electrode were investigated in different electrolytes such as 3 KOH and 1 M LiCl. The hybrid electrode delivered greater specific capacitance in KOH electrolyte, i.e., 1248.8 F/g at 0.5 A/g, compared to LiCl electrolyte (816.8 F/g), while it has a more stable cycling performance in LiCl electrolyte. The asymmetric supercapacitors (ASCs) were constructed with the as-prepared binder-free Nb(PDCA)[email protected] mat as a cathode and the CNF as an anode and investigated their electrochemical properties in both the electrolytes. The higher specific capacitance was achieved for the KOH electrolyte-based ASC. However, the LiCl electrolyte-based ASC delivered superior energy density (64.24 Wh kg⁻¹) and greater cycling stability (98.3 % after 4000 cycles) compared to ASC in KOH electrolyte. The ionic conductivity, chemical nature, and hydrated ionic radius of the electrolyte were found to be important factors to the electrochemical performance of the ASC device.
... Metal oxide-based nanostructures, DNA-based nanostructures, and polymer-based nanostructures fabricated by self-assembly have found widespread applications in diverse fields [83]. For example, a 3D microstructure that contains in situ growth of the Ni(OH) 2 nanowalls at specific locations has been fabricated for use as wafer-scaled miniaturized gas sensors (Fig. 17), and 3D flower-like hierarchical nitrogen-doped and carbonsensitized Nb 2 O 5 (N-NBO/C) nanostructures have been fabricated for solar energy transformation and environmental remediation (Fig. 18) [84,85]. Despite this, the structural control over a larger scale range, mechanical properties of the selfassembly materials, the combination of different molecules into advances have been achieved, as it is still in the early stages, several important issues, such as limited resolution, low throughput, high cost, limited flexibility in material choice, and 3D structure shape, still remain. ...
... CC BY 4.0.). (a) Schematic for the formation of the flower-like hierarchical N-NBO/C nanostructures; (b) mechanism for photodegradation of Rhodamine B by N-NBO/C upon visible-light illumination (Reproduced from[85]. CC BY 4.0.). ...
Among the different nanostructures that have been demonstrated as promising materials for various applications, three–dimensional (3D) nanostructures have attracted significant attention as building blocks for constructing high-performance nanodevices because of their unusual mechanical, electrical, thermal, optical, and magnetic properties arising from their novel size effects and abundant active catalytic/reactive sites due to the high specific surface area. Considerable research efforts have been devoted to designing, fabricating, and evaluating 3D nanostructures for applications, including structural composites, electronics, photonics, biomedical engineering, and energy. This review provides an overview of the nanofabrication strategies that have been developed to fabricate 3D functional architectures with exquisite control over their morphology at the nanoscale. The pros and cons of the typical synthetic methods and experimental protocols are reviewed and outlined. Future challenges of fabrication of 3D nanostructured materials are also discussed to further advance current nanoscience and nanotechnology.
... The nanostructured flower-like hierarchical N-doped Nb 2 O 5 was fabricated through a mild hydrothermal route similar to that reported in our previous work [36]. Initially, 2 mmol of C 10 H 5 NbO 20 ⋅xH 2 O was dissolved in a solution containing 15 mL DW and 10 mL of ethanol and named solution A. Next, 0.5 mmol of Hmta was added to 5 mL DW and named solution B. Subsequently, both solutions were mixed to form solution C. After that, solution C was stirred for 15 min, and then loaded in an autoclave (50 mL) and kept for 12 h at 180 • C followed by the gradual cooling to an ambient temperature. ...
... As displays in Fig. S6(a), the introduction of oxygen heteroatoms into g-C 3 N 4 has changed the XRD peak attributed to (002) plane from 27.4 • for pure g-C 3 N 4 to 27.6 • for O-doped g-C 3 N 4 , leading to the lattice distortions of the graphitic morphology, which is most likely attributable to the pure g-C 3 N 4 stacking distance decreasing after doping with oxygen [42]. [36]. In addition, the shift in the 2theta region corresponding to the nitrogen doping is too hard to be detected in the XRD diffraction peaks due to the small amount of N in the NBO nanostructures. ...
Reasonable construction and engineering of optimal hierarchical photocatalysts have garnered great attention in terms of promoting CO2 photoreduction into fuel production. Herein, we introduce a novel 3D O-doped g-C3N4/N-doped Nb2O5 (OCNNb) S-scheme heterojunction fabricated using control of each material's surface charge-induced heteroaggregation for photocatalytic CO2 reduction (PCR). The optimized sample converts CO2 with substantially greater rates (the sum production rate of CO and CH4) than the blank control, i.e., O-doped g-C3N4 (OCN) and N-doped Nb2O5 (NNBO). The enhanced photocatalytic efficiency can not only be ascribed to the prevention of photogenerated charge carrier recombination mediated by the S-scheme heterojunction but also to the high specific surface areas and abundance of active sites. In the meantime, work function measurement, in situ irradiated, X-ray photoelectron spectroscopy and electron paramagnetic resonance (EPR) studies confirm the S-scheme photogenerated charge transfer mechanism. This study offers a useful approach for fabricating extremely effective heterojunction photocatalysts to convert solar fuels.
... Prior to the light irradiation, adsorption in the dark conditions was carried out for 30 min to ensure equilibrium adsorption. Figure 6a displays the MB photocatalytic degradation behavior of Nb 2 O 5 , Ag 2 S, and Ag 2 S/Nb 2 O 5 composites in the However, the deposition of excessive Ag 2 S on the Nb 2 O 5 surface could not efficiently promote the separation of charges, because excessive Ag 2 S may act as the recombination centers, leading to the decrease in the photocatalytic performance [21,31]. Furthermore, the degradation of MB was used to evaluate the photocatalytic performance of the 10 wt% Ag 2 S/Nb 2 O 5 physically mixed under the same condition. ...
Novel p-Ag2S/n-Nb2O5 heterojunction composites were successfully obtained for the first time by hydrothermal and ion-exchange deposition way. A series of photocatalytic tests and characterization results confirm that the optimized 10 wt% Ag2S/Nb2O5 heterojunction composite exhibits excellent photocatalytic degradation activity for methylene blue (92.8%) under simulated solar light irradiation, which is approximately 2.7 times higher than that of pure Nb2O5 (34.3%) and 2.2 times higher than that of Ag2S (42.0%). The outstanding photocatalytic activity of Ag2S/Nb2O5 heterojunction composites could be ascribed to enhance simulated solar light response and effectively accelerates photo-induced charge separation and migration via a Z-scheme mechanism. Furthermore, the trapping experimental results confirm that both superoxide radicals (·O− 2) and hydroxyl radicals (·OH) play a key role in photocatalytic degradation process.
... As revealed in Fig. 6(d and e), the obtained rate constant (k) values are 0.0277, 0.016 and 0.0551 min − 1 for 1D g-C 3 N 4 , 2D g-C 3 N 4 and 1D/ 2D O-doped g-C 3 N 4 isotype heterojunction. This higher rate in the photocatalytic activity of the 1D/2D O-doped g-C 3 N 4 isotype heterojunction sample than that of 2D g-C 3 N 4 is mainly due to its (1) lower recombination rate, (2) larger specific surface area, which in turn lead to significant adsorption capability and surface reactivity towards RhB [51] and (3) relatively lower bandgap which enhanced the photon absorption and increased the amount of photoinduced e-h pairs during the illumination of visible light [52]. ...
Constructing an isotype 1D/2D O-doped g-C3N4 heterojunction to boost the efficiency of g-C3N4 for the decomposition of organic pollutants under visible light irradiation is a practical approach. It is possible to use such materials to overcomes g-C3N4’s inherent disadvantage of rapid charge recombination. In this work, a straightforward, one-step self-polymerization technique for fabricating 1D/2D O-doped g-C3N4 isotype heterojunctions comprise of O-doped g-C3N4 nanotubes and nanosheets is presented here. A plausible formation mechanism supported by XRD and FT-IR analyses is proposed and investigated. The obtained results show that the fabricated materials exhibit a high surface area (114.4 m2 g−1) while the PL technique confirmed the rapid charge separation. Compared with the as-fabricated 2D g-C3N4 nanosheets, 1D/2D O-doped g-C3N4 isotype heterojunctions possess superior photocatalytic activity for RhB degradation under visible light illumination. The degradation pathway was investigated using LC-MS analysis. The improved photocatalytic degradation ability of 1D/2D O-doped g-C3N4 isotype heterojunctions is attributed to the enhanced absorption capability, high surface area, and separation efficiency of photogenerated charge carriers.
With the increasing popularity of photocatalytic technology and the highly growing issues of energy scarcity and environmental pollution, there is an increasing interest in extremely efficient photocatalytic systems. The widespread immense attention and applicability of Nb2O5 photocatalysts can be attributed to their multiple benefits, including strong redox potentials, non-toxicity, earth abundance, corrosion resistance, and efficient thermal and chemical stability. However, the large-scale application of Nb2O5 is currently impeded by the barriers of rapid recombination loss of photo-activated electron/hole pairs and the inadequacy of visible light absorption. To overcome these constraints, plentiful design strategies have been directed at modulating the morphology, electronic band structure, and optical properties of Nb2O5. The current review offers an extensive analysis of Nb2O5-based photocatalysts, with a particular emphasis on crystallography, synthetic methods, design strategies, and photocatalytic mechanisms. Finally, an outline of future research directions and challenges in developing Nb2O5-based materials with excellent photocatalytic performance is presented.
Semiconductor‐based photocatalytic water splitting is one of the effective ways for future hydrogen (H2) production. However, the wide bandgap of most semiconductors severely limits the solar spectral absorption range, which seriously hinders their practical applications. Herein, porous N‐doped K2Nb2O6 nanocrystals with defective pyrochlore structure are rationally designed to extend the absorption range from ultraviolet to visible region around 550 nm by NH3 heat treatment. The obtained 6N–K2Nb2O6 shows the highest visible‐light activity with an H2 evolution rate of 20.4 μmol h−1 g−1. More detailed exploration demonstrates that NH3 heat treatment can promote the substitutional nitrogen doping in K2Nb2O6 crystals while accompanied by the formation of oxygen vacancies or Nb4+ species. The hybridization of N 2p and O 2p orbitals in the valence band (VB) of the nitrogen‐doped K2Nb2O6 makes the VB maximum move more negatively, whereas the conduction band minimum shifted more positively due to the role of defective Nb4+ species. Such a synergistic effect endows the samples with visible‐light absorption and greatly enhances charge separation and transfer efficiency, resulting in the excellent H2 production performance. This study provides additional insights into the understanding of the effect of nitrogen doping on photocatalysts with excellent visible‐light‐driven photocatalytic activity. N‐doped K2Nb2O6 nanocrystals with excellent visible‐light response and enhanced photocatalytic hydrogen production activity are synthesized by simple NH3 heat treatment of K2Nb2O6 nanocrystals. The higher activity of N‐doped K2Nb2O6 is mainly attributed to its appropriate amount of nitrogen doping, leading to excellent visible‐light response and separation and migration efficiency of photogenerated charge carriers.
Spiky nanoarchitecture composed of numerous nanorods and a spherical core has applications in various fields because of its high performance and durability. However, controlling the spiky structure is challenging because of an unclear formation mechanism. This study investigates the growth mechanism of spiky nanostructure by hydrothermally synthesizing Nb2O5 with various conditions and additives, and we show that adsorption and gradual decomposition of ligands promote the formation of the spiky shape. Disconnected Nb2O5 nanorods form in the presence of acetate ions. Using oxalic acid as an additive and synthesizing at 160 °C, which is below oxalic acid’s decomposition temperature, spherical Nb2O5 with a rough surface that consists of a nanostructure with less than 5 nm size forms, and its surface is protected by oxalate ions. When the synthesis temperature increases to 180°C, oxalate ions are decomposed, and nanorods grow on the spherical particles. The results show that oxalate ions suppress particle growth, promote self‐assembly, and control subsequent particle growth, resulting in complex nanostructures. When used as anode material in lithium‐ion batteries, the spiky Nb2O5 nanoparticles show a higher capacity (143 mAhg−1) than collapsed spiky particles (92 mAhg−1) and nanorods (37 mAhg−1) because of fast lithium‐ion diffusion on the surface nanostructure and high dispersibility. This article is protected by copyright. All rights reserved.
Constructing a suitable heterojunction photocatalytic system from two photocatalytic materials is an efficient approach for designing extremely efficient photocatalysts for a broader range of environmental, medical, and energy applications. Recently, the construction of a step-scheme heterostructure system (hereafter called the S-scheme) has received widespread attention in the photocatalytic field due to its ability to achieve efficient photogenerated carrier separation and obtain strong photo-redox ability. Herein, a novel S-scheme heterojunction system consisting of 2D O-doped g-C3N4 (OCN) nanosheets and 3D N-doped Nb2O5/C (N-NBO/C) nanoflowers is constructed via ultrasonication and vigorous agitation technique followed by heat treatment for the photocatalytic degradation of Rhodamine B (RhB). Detailed characterization and decomposition behaviour of RhB showed that the fabricated material shows excellent photocatalytic efficiency and stability towards RhB photodegradation under visible-light illumination. The enhanced performance could be attributed to the following factors: fast charge transfer, highly-efficient charge separation, extended lifetime of photoinduced charge carriers, and the high redox capability of the photoinduced charges in the S-scheme system. Various trapping experiment conditions and electron paramagnetic resonance (EPR) provide clear evidence of the S-scheme photogenerated charge transfer path, whereas the RhB mineralization degradation pathway was also investigated using LC-MS. For the first time, this study presents a novel approach to constructing Nb2O5-based S-scheme heterojunctions for photocatalytic applications.
