Single-Pot Synthesis of ⟨001⟩-Faceted N-Doped Nb2O5/Reduced Graphene Oxide Nanocomposite for Efficient Photoelectrochemical Water Splitting

Biofouling mitigation of Nb2AlC and Mo3AlC2 MXene-precursors doped polyether sulfone mixed matrix membranes for pathogen microorganisms

This study explores the incorporation of Nb2AlC and Mo3AlC2 MAX phases, known for their nano-layered structure, into polyether sulfone (PES) membranes to enhance their antifouling and permeability properties for pathogen microorganism filtration against bovine serum albumin (BSA) and Escherichia coli (E. coli). The composite membranes were characterized for their structural and morphological properties, and their performance in mitigating biofouling was evaluated. The structural characterizations have been performed for all the prepared MAX phases and corresponding composite membranes. The antioxidant ability of Nb2AlC and Mo3AlC2 MAX phases was defined by the DPPH radical scavenging assay, and the highest antioxidant ability was found to be 59.35 %, while 53.69 % scavenging potential was recorded at 100 mg/L. The percentage scavenging ability was raised with an increase in concentrations. The antimicrobial properties of MAX phases, evaluated as the minimum inhibitory concentration, were stated against several pathogen microorganisms. The tested compounds of Nb2AlC and Mo3AlC2 composites containing MAX phases exhibited excellent chemical nuclease activity, and it was determined that Nb2AlC caused double strand DNA cleavage activity while Mo3AlC2 induced the complete fragmentation of the DNA molecule. Biofilm inhibition of Nb2AlC and Mo3AlC2 MAX phases was studied against Staphylococcus aureus, and Pseudomonas aeruginosa and the maximum biofilm inhibition of Nb2AlC and Mo3AlC2 MAX phases was found to be 77.15 % and 69.07 % against S. aureus and also 69.74 % and 65.01 % against P. aeruginosa. Furthermore, Nb2AlC and Mo3AlC2 MAX phases demonstrated excellent E. coli growth inhibition of 100 % at 125 and 250 mg/L.

A systematic review on Nb2O5-based photocatalysts: Crystallography, synthetic methods, design strategies, and photocatalytic mechanisms

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.

Highly [001]-oriented N-doped orthorhombic Nb2O5 microflowers with intercalation pseudocapacitance for lithium-ion storage

Orthorhombic Nb₂O₅ (T-Nb₂O₅), a typical intercalation pseudocapacitor, is favorable for realizing high power and energy density for lithium-ion batteries; furthermore, the 2D layered channels perpendicular to the [001] direction facilitate fast Li⁺ intercalation in T-Nb₂O₅. Herein, N-doped T-Nb₂O₅ microflowers (N-Nb₂O₅) assembled from highly [001]-oriented nanoflakes are rationally synthesized using NH₄F as the nitrogen source and capping agent. It is found that NH₄⁺ can adsorb on the O-terminated (010) plane of T-Nb₂O₅via N-H⋯O hydrogen bonds, which is highly conducive to the generation of 1D nanorods and the subsequent fusion of the nanorods into highly [001]-oriented nanoflakes. The special growth orientation of the T-Nb₂O₅ nanoflakes endows them with abundant available Li⁺ intercalation channels; moreover, the bandgap of N-Nb₂O₅ is narrowed (∼2.91 eV) owing to the doping of N atoms, and the intrinsic electronic conductivity is improved. Accordingly, the intercalation pseudocapacitive behavior of N-Nb₂O₅ is notably promoted and N-Nb₂O₅ exhibits superior Li⁺ storage properties, including large discharge capacity (214.7 mA h g^-1 at 1C), excellent rate capability (203.7 and 174.6 mA h g^-1 at 1 and 20C), and superior cyclic stability (150.7 mA h g^-1 at 10C after 1000 cycles). In addition, the LiNi_0.5Mn_0.3Co_0.2O₂//N-Nb₂O₅ full cell delivers outstanding Li⁺ storage performance, especially in terms of long-term cycling (126.2 mA h g^-1 at 10C after 3500 cycles).

Enhanced Photocatalytic Activity of Nonuniformly Nitrogen-Doped Nb2O5 by Prolonging the Lifetime of Photogenerated Holes

The narrow band gap and significant separation of photogenerated carriers are essential aspects in practical photocatalytic applications. Nitrogen doping usually narrows the band gap of semiconductor oxides, and it enhances photocatalytic activity. Nitrogen-doped Nb₂O₅ was prepared by a multiple hydrothermal method. The non-metal element N inside the nanostructure, working as the trapping sites for the holes, which were effectively incorporated into the crystal lattice of Nb₂O₅ semiconductor oxide, remarkably shorten the band gap (3.1 eV) to enhance the visible light response, effectively reducing the photoinduced electron–hole pair recombination and prolonging carrier lifetime. The multilayer coating structure with a gradient concentration distribution and the type of nitrogen doped is favorable for the migration of photoexcited carriers in the bulk of catalysts. The unique multi-layer coating with the micro-concentration gradient of doped nitrogen provides a fast separation channel and jump steps for the separation of electron–hole pairs.

Polyvinylpyrrolidone regulated synthesis of mesoporous titanium niobium oxide as high-performance anode for lithium-ion batteries

TiNb₂O₇ (TNO) as a promising candidate anode for lithium-ion batteries (LIBs) shows obvious advantages in terms of specific capacity and safety, but which undergoes the intrinsic poor electrical and ionic conductivity. Herein, we propose a simple synthesis strategy of mesoporous TNO via a polymeric surfactant-mediated evaporation-induced sol-gel method, using polyvinylpyrrolidone (PVP) with different molecular weights (average Mw: 10000/58000/1300000) as the regulating agent, which greatly affects the lithium storage performance of the as-prepared TNO. The optimized TNO (i.e., PVP of 58000) delivers a high reversible capacity of 303.1 mAh/g at 1 C, with a retention rate of 73.4% (222.5 mAh/g) after 300 cycles. Even at 5 C, a high reversible capacity of 185.6 mAh/g can be achieved, with a retention rate of 72.3% after 1000 cycles. The superior lithium storage behavior is attributed to the fine mesoporous framework consisting of interconnected TNO nanocrystallites with high specific surface area and high mesoporosity, which greatly increases the active sites, improves the Li⁺ diffusion kinetics and alleviates volume fluctuation induced by the repetitive Li⁺ insertion-extraction processes.

In situ fabrication of niobium pentoxide/graphitic carbon nitride type-II heterojunctions for enhanced photocatalytic hydrogen evolution reaction

The effective conversion of sunlight into H₂ by photocatalytic water splitting has emerged as the most promising strategy to alleviate the energy crisis. In this work, niobium pentoxide (Nb₂O₅)/graphitic carbon nitride (g-C₃N₄) type-II heterojunctions with high photocatalytic H₂ evolution rate under both visible and simulated solar light are fabricated via a novel approach involving in situ 'hydrolysis/calcination' loading of Nb₂O₅ nanoparticles on the g-C₃N₄ surface. After the optimisation, the Nb₂O₅/g-C₃N₄ heterojunctions with 5 wt% Nb₂O₅ content delivers high H₂ evolution rates of 2.07 ± 0.03 and 6.77 ± 0.12 mmol g^-1 h^-1 under visible and simulated solar light exposure, respectively, which are 4.1 and 4.2 times superior to those of pure g-C₃N₄. According to the subsequent characterisations, the effective Nb₂O₅/g-C₃N₄ heterojunction offers sufficient contact interface, which is favourable for the efficient separation of photogenerated charges. In addition, the Nb₂O₅/g-C₃N₄ heterojunction possesses a large surface area, which contributes to the interfacial contact between photocatalyst and water. This work provides insights into the synthesis of novel g-C₃N₄-based hetero-photocatalysts with strong solar energy conversion capabilities.

Synthesis of an Ag3PO4/Nb2O5 Photocatalyst for the Degradation of Dye

In this work, the photocatalytic performance of Ag3PO4, Nb2O5 and Ag3PO4/Nb2O5 hybrid photocatalysts to degrade methyl orange dye, MO, in an aqueous solution under visible light irradiation was evaluated. The Ag3PO4 and Ag3PO4/Nb2O5 photocatalysts, with various Ag to Nb molar ratios, were prepared using a facile precipitation method. The photocatalysts were characterized by X-ray diffraction, UV–Visible, X-ray Photoelectron, and Photoluminescence spectroscopies. Upon the addition of Ag3PO4, the band gap energy of Nb2O5 decreased from 3.0 eV to 2.7 eV, indicating the possible use of the Ag3PO4/Nb2O5 hybrid photocatalysts under visible light irradiation. All of the prepared Ag3PO4/Nb2O5 catalysts exhibited higher photocatalytic performance than Ag3PO4 in degrading methyl orange dye under 23-watt visible light irradiation. The Ag3PO4/Nb2O5 catalyst, with a mole ratio of 2:1, exhibited the fastest MO degradation rate of 7.3 × 10−2 min−1, which is twice faster than that of Ag3PO4. The catalyst also shows better stability, as it is reusable for up to six experimental cycles while maintaining its photocatalytic activity above 60%.

Nb2O5-Based Photocatalysts

Photocatalysis is one potential solution to the energy and environmental crisis and greatly relies on the development of the catalysts. Niobium pentoxide (Nb2O5), a typically nontoxic metal oxide, is eco-friendly and exhibits strong oxidation ability, and has attracted considerable attention from researchers. Furthermore, unique Lewis acid sites (LASs) and Brønsted acid sites (BASs) are observed on Nb2O5 prepared by different methods. Herein, the recent advances in the synthesis and application of Nb2O5-based photocatalysts, including the pure Nb2O5, doped Nb2O5, metal species supported on Nb2O5, and other composited Nb2O5 catalysts, are summarized. An overview is provided for the role of size and crystalline phase, unsaturated Nb sites and oxygen vacancies, LASs and BASs, dopants and surface metal species, and heterojunction structure on the Nb2O5-based catalysts in photocatalysis. Finally, the challenges are also presented, which are possibly overcome by integrating the synthetic methodology, developing novel photoelectric characterization techniques, and a profound understanding of the local structure of Nb2O5.

Facile hydrothermal synthesis of rod-like Nb2O5/Nb2CTx composites for visible-light driven photocatalytic degradation of organic pollutants

The MXene-based transition metal oxide composite is a potential candidate for photocatalysts. Rod-like pseudohexagonal phase Nb₂O₅/Nb₂CT_x composites were synthesized by a simple hydrothermal oxidation of 2D layered Nb₂CT_x. The Nb₂O₅/Nb₂CT_x composites show superior photocatalytic activity for 98.5% of degradation of Rhodamine B (RhB) for 120 min and 91.2% of tetracycline hydrochloride (TC-HCl) for 180 min under visible light irradiation. The Schottky junction is formed between Nb₂O₅ nanorods and Nb₂CT_x and the photo-generated carriers are effectively separated, enhancing the photocatalytic activity of the Nb₂O₅/Nb₂CT_x. High photoactivity and cycle stability of Nb₂O₅/Nb₂CT_x composites indicate that hydrothermal oxidation of 2D layered Nb₂CT_x is an alternative to prepare efficient photocatalyst for degradation of organic pollutants.

Branched Alkylamine-Reduced Graphene Oxide Hybrids as a Dual Proton-Electron Conductor and Organic-Only Water-Splitting Photocatalyst

We report multifunctionalities including the solid electrolytic property, electron conductivity (EnC), and photocatalytic water splitting (PWS) ability of organic-only hybrids obtained by intercalating short and branched-chain alkylamines including methylamine (MA), butylamine (BA), pentylamine (PA), and isomethylbytylamine (IMBA) in reduced graphene oxide (rGO). The alkylamine-rGO hybrids were synthesized by a facile solid-state reduction process. Within the series, IMBA-rGO exhibited high proton conductivity (PrC), EnC, and optimized PWS capacity. The PrC of IMBA-rGO was from 10^-4 to 10^-3 S cm^-1, which is only half an order less than that for pristine GO. The EnC was 1.25 μA/V. Though the PWS performances of MA-rGO, BA-rGO, and PA-rGO were comparatively lower, IMBA-rGO could generate about 1.5 times H₂ compared with that for R-TiO₂. The IR spectra indicate the association of IMBA and GO by chemical bonds. The Raman spectra show the transformation of GO's nonconductive sp³ carbon sites into electron-conductive sp² carbon centers. The thermogravimetric analysis show improved water adsorbing capacity of IMBA-rGO, which resulted in higher PrC. Doping of the nitrogen atom at the graphitic sp² system was confirmed from the presence of pyrrolic N in X-ray photoelectron spectroscopy spectra. The resultant N-type semiconducting behavior is majorly responsible for the PWS process. The powder X-ray diffraction analysis indicates a more flexible interlayer space in IMBA-rGO, which facilitates both the reformation of hydrogen bonds during proton conduction and water dynamics during photocatalysis. The material indicates the possibility of devising graphene-based organic-only multifunctional hybrids.

Facile synthesis of flower-like hierarchical N-doped Nb2O5/C nanostructures with efficient photocatalytic activity under visible light

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 Nb₂O₅ (NBO) nanostructure (denoted N-NBO/C). The as-prepared N-NBO/C possessed a specific surface area of 260.37 m² g⁻¹ and single wire diameter of less than 10 nm. The effect of reaction parameters such as hydrothermal reaction time, temperature and concentration of hexamethylenetetramine (Hmta) on the morphology of NBO was systematically investigated to elucidate the growth mechanism. The carbon on the surface and the nitrogen in the framework of NBO are beneficial for light harvesting, visible light absorption, formation of oxygen vacancies, and electron–hole separation. The photocatalytic performance of the as-fabricated N-NBO/C nanostructures was estimated via the photodegradation of 30 mg L⁻¹ RhB, where greater than 98% of RhB was decomposed within 30 min upon visible-light radiation. Hence, the obtained N-NBO/C nanostructure exhibits much higher photocatalytic activity for the decomposition of RhB upon visible light irradiation than that of pure niobium oxide (NBO), nitrogen-doped titanium oxide (N-TIO), and nitrogen-doped niobium oxide (N-NBO). This work supplies a versatile route for the synthesis of nitrogen-doped and carbon-sensitized metal-oxide nanostructures for possible utilization in solar energy transformation and environmental remediation.

Flower-like hierarchical N-doped Nb₂O₅/C nanostructures with efficient visible light-driven photocatalytic activity synthesized via a facile hexamethylenetetramine-assisted hydrothermal route.

Pd/BiOBr tetragonal platelets with controllable facets by the decoration of La dopant enabling highly efficient photocatalytic activity

Pd particles deposited on BiOBr caused instability of the crystal structure; however, La can stabilize the crystal structure during the deposition of Pd particles.

Effects of different exchanging ions on the band structure and photocatalytic activity of defect pyrochlore oxide: a case study on KNbTeO6

The effects of different exchanging ions including Ag, Cu, and Sn on enhancing the photocatalytic activity of KNbTeO₆ are investigated by means of experiments and calculations.

Crystal Facet Engineering of Photoelectrodes for Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is a promising approach for solar-driven hydrogen production with zero emissions, and it has been intensively studied over the past decades. However, the solar-to-hydrogen (STH) efficiencies of the current PEC systems are still far from the 10% target needed for practical application. The development of efficient photoelectrodes in PEC systems holds the key to achieving high STH efficiencies. In recent years, crystal facet engineering has emerged as an important strategy in designing efficient photoelectrodes for PEC water splitting, which has yet to be comprehensively reviewed and is the main focus of this article. After the Introduction, the second section of this review concisely introduces the mechanisms of crystal facet engineering. The subsequent section provides a snapshot of the unique facet-dependent properties of some semiconductor crystals including surface electronic structures, redox reaction sites, surface built-in electric fields, molecular adsorption, photoreaction activity, photocorrosion resistance, and electrical conductivity. Then, the methods for fabricating photoelectrodes with faceted semiconductor crystals are reviewed, with a focus on the preparation processes. In addition, the notable advantages of the crystal facet engineering of photoelectrodes in terms of light harvesting, charge separation and transfer, and surface reactions are critically discussed. This is followed by a systematic overview of the modification strategies of faceted photoelectrodes to further enhance the PEC performance. The last section summarizes the major challenges and some invigorating perspectives for future research on crystal facet engineered photoelectrodes, which are believed to play a vital role in promoting the development of this important research field.

A hierarchical Nb2O5@NiFe-MMO rod array, fabricated and used as a structured photocatalyst

Recently, using sunlight as a driving force with transitional metal oxides as photocatalysts, due to their unique optical and catalytic properties for organic reactions, has been considered to be a promising strategy in synthetic chemistry. Here, a hierarchically structured photocatalyst, a NiFe mixed metal oxide coated Nb2O5 (denoted as Nb2O5@NiFe-MMO) rod array has been successfully fabricated using Nb foil as a substrate. The Nb2O5 rod array was synthesized by the oxidative etching of Nb metal on the surface of the a substrate. The coating NiFe-MMO was obtained by the calcination of a NiFe layered double hydroxide (NiFe-LDH) precursor via the in situ epitaxial growing technique. The Nb2O5@NiFe-MMO rod array extended the photoresponse light region from ultraviolet light around 400 nm to visible light around 600 nm. With the well-designed architecture and highly dispersed NiO and Fe2O3, the as-prepared photocatalyst exhibited excellent activity and recyclability toward the reaction of aerobic coupling under relatively green conditions, with catalytic efficiency of 228 μmol cm-2 (the area is that of the Ni foil substrate) at 30 °C for 5 h. The present work provides a new strategy for the exploration of excellent structured photocatalysts based on transition metal oxide materials for selective aerobic oxidation of benzylamine to imine.

Structure-retentive synthesis of a highly ordered mesoporous Nb2O5/N-doped graphene nanocomposite with superior interfacial contacts and improved visible-light photocatalysis

A highly ordered mesoporous Nb₂O₅/N-doped graphene nanocomposite was constructed for efficient photocatalytic H₂ evolution under irradiation of visible light.

One-Step Synthesis of Nb2 O5 /C/Nb2 C (MXene) Composites and Their Use as Photocatalysts for Hydrogen Evolution

Hydrogen production through facile photocatalytic water splitting is regarded as a promising strategy to solve global energy problems. Transition-metal carbides (MXenes) have recently drawn attention as potential co-catalyst candidates for photocatalysts. Here, we report niobium pentoxide/carbon/niobium carbide (MXene) hybrid materials (Nb₂ O₅ /C/Nb₂ C) as photocatalysts for hydrogen evolution from water splitting. The Nb₂ O₅ /C/Nb₂ C composites were synthesized by one-step CO₂ oxidation of Nb₂ CT_x . Nb₂ O₅ grew homogeneously on Nb₂ C after mild oxidation, during which some amorphous carbon was also formed. With an optimized oxidation time of 1.0 h, Nb₂ O₅ /C/Nb₂ C showed the highest hydrogen generation rate (7.81 μmol h^-1  g_cat^-1 ), a value that was four times higher than that of pure Nb₂ O₅ . The enhanced performance of Nb₂ O₅ /C/Nb₂ C was attributed to intimate contact between Nb₂ O₅ and conductive Nb₂ C and the separation of photogenerated charge carriers at the Nb₂ O₅ /Nb₂ C interface; the results presented herein show that transition-metal carbide are promising co-catalysts for photocatalytic hydrogen production.

Controlled design of PtPd nanodendrite ornamented niobium oxynitride nanosheets for solar-driven water splitting

A facile road-map is developed for one-pot synthesis of PtPd nanodendrite ornamented niobium oxynitride nanosheets for efficient solar-driven water splitting.

Nanostructured N-doped orthorhombic Nb2O5 as an efficient stable photocatalyst for hydrogen generation under visible light

The synthesis of orthorhombic Nb₂O_5−xN_x nanostructured photocatalyst for excellent hydrogen production via H₂S and water splitting under sunlight has been demonstrated.