Hexagonal-like Nb₂O₅ nanoplates-based photodetectors and photocatalyst with high performances

Niobium: The Focus on Catalytic Application in the Conversion of Biomass and Biomass Derivatives

The world scenario regarding consumption and demand for products based on fossil fuels has demonstrated the imperative need to develop new technologies capable of using renewable resources. In this context, the use of biomass to obtain chemical intermediates and fuels has emerged as an important area of research in recent years, since it is a renewable source of carbon in great abundance. It has the benefit of not contributing to the additional emission of greenhouse gases since the CO2 released during the energy conversion process is consumed by it through photosynthesis. In the presented review, the authors provide an update of the literature in the field of biomass transformation with the use of niobium-containing catalysts, emphasizing the versatility of niobium compounds for the conversion of different types of biomass.

Heterojunction formation between AgNbO3 and Co3O4 for full solar light utilization with improved charge-carrier separation

In the present study, the charge-carrier recombination of visible light active perovskite silver niobate (AgNbO₃) was reduced by forming heterojunction with Co₃O₄ through simple impregnation and calcination route. The loading percentage of Co₃O₄ was varied as 2, 5, and 10 wt.%. The XRD study revealed reduced interlayer spacing in the composite due to the replacement of the bigger Ag⁺ ions by the smaller Co²⁺ and Co³⁺ ions of Co₃O₄. It was observed that the light harvesting efficiency of the materials was increased with increased loading of Co₃O₄. The TEM and XPS analysis confirmed the presence of Ag nanoparticles over the perovskite in the composite. The electrochemical analysis revealed enhanced charge-carrier number density and increased charge-carrier lifetime in the composite as a result of the presence of both silver and cobalt ions in the lattice. Further this enhanced charge-carrier separation of the composites was established through photocatalysis of Bisphenol-A under both solar and LED light. Charge-trapping study indicated *O₂^- and *OH as the major radicals involved and Z-scheme as the predominant charge transfer pathway for generation of these reactive oxygen species.

Enhanced adsorption and degradation of methylene blue over mixed niobium-cerium oxide - Unraveling the synergy between Nb and Ce in advanced oxidation processes

Formation of reactive oxygen species (ROS) via H₂O₂ activation is of vital importance in catalytic environmental chemistry, especially in degradation of organic pollutants. A new mixed niobium-cerium oxide (NbCeO_x) was tailored for this purpose. A thorough structural and chemical characterization of NbCeO_x along with CeO₂ and Nb₂O₅ reference materials was carried out using TEM/STEM/EDS, SEM, XRD, XPS, EPR, UV-vis and N₂ physisorption. The ability of the catalysts to activate H₂O₂ towards ROS formation was assessed on the basis of EPR and Raman measurements. Catalytic activity of the oxides was evaluated in degradation of methylene blue (MB) as a model pollutant. Very high activity of NbCeO_x was attributed to the mixed redox-acidic nature of its surface, which originated from the synergy between Nb and Ce species. These two properties (redox activity and acidity) ensured convenient conditions for efficient activation of H₂O₂ and degradation of MB. The activity of NbCeO_x in MB degradation was found 3 times higher than that of the commercial Nb₂O₅ CBMM catalyst and 240 times higher than that of CeO₂. The mechanism of the degradation reaction was found to be an adsorption-triggered process initiated by hydroxyl radicals, generated on the surface via the transformation of O₂^-•/O₂^2-.

Facile Synthesis of Uniform Mesoporous Nb2O5 Micro-Flowers for Enhancing Photodegradation of Methyl Orange

The removal of organic pollutants using green environmental photocatalytic degradation techniques urgently need high-performance catalysts. In this work, a facile one-step hydrothermal technique has been successfully applied to synthesize a Nb₂O₅ photocatalyst with uniform micro-flower structure for the degradation of methyl orange (MO) under UV irradiation. These nanocatalysts are characterized by transmission and scanning electron microscopies (TEM and SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) method, and UV-Vis diffuse reflectance spectroscopy (DRS). It is found that the prepared Nb₂O₅ micro-flowers presents a good crystal phases and consist of 3D hierarchical nanosheets with 400–500 nm in diameter. The surface area is as large as 48.6 m² g⁻¹. Importantly, the Nb₂O₅ micro-flowers exhibit superior catalytic activity up to 99.9% for the photodegradation of MO within 20 mins, which is about 60-fold and 4-fold larger than that of without catalysts (W/O) and commercial TiO₂ (P25) sample, respectively. This excellent performance may be attributed to 3D porous structure with abundant catalytic active sites.

Unraveling the Origin of Photocatalytic Deactivation in CeO2/Nb2O5 Heterostructure Systems during Methanol Oxidation: Insight into the Role of Cerium Species

The study provides deep insight into the origin of photocatalytic deactivation of Nb₂O₅ after modification with ceria. Of particular interest was to fully understand the role of ceria species in diminishing the photocatalytic performance of CeO₂/Nb₂O₅ heterostructures. For this purpose, ceria was loaded on niobia surfaces by wet impregnation. The as-prepared materials were characterized by powder X-ray diffraction, nitrogen physisorption, UV-visible spectroscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and photoluminescence measurements. Photocatalytic activity of parent metal oxides (i.e., Nb₂O₅ and CeO₂) and as-prepared CeO₂/Nb₂O₅ heterostructures with different ceria loadings were tested in methanol photooxidation, a model gas-phase reaction. Deep insight into the photocatalytic process provided by operando-IR techniques combined with results of photoluminescence studies revealed that deactivation of CeO₂/Nb₂O₅ heterostructures resulted from increased recombination of photo-excited electrons and holes. The main factor contributing to more efficient recombination of the charge carriers in the heterostructures was the ultrafine size of the ceria species. The presence of such highly dispersed ceria species on the niobia surface provided a strong interface between these two semiconductors, enabling efficient charge transfer from Nb₂O₅ to CeO₂. However, the ceria species supported on niobia exhibited a high defect site concentration, which acted as highly active recombination centers for the photo-induced charge carriers.

Design of highly sensitive and selective ethanol sensor based on α-Fe2O3/Nb2O5 heterostructure

The introduction of heterostructures is a new approach in gas sensing due to their easy and quick transport of charges. Herein, facile hydrothermal and solid-state techniques are employed to synthesize an α-Fe₂O₃/Nb₂O₅ heterostructure. The morphology, microstructure, crystallinity and surface composition of the synthesized heterostructures are investigated by scanning electron microscope, transmission electron microscope, x-ray diffraction, x-ray photoelectron spectroscopy and Brunauer-Emmett-Teller analyses. The successful fabrication of the heterostructures was achieved via the mutual incorporation of α-Fe₂O₃ nanorods with Nb₂O₅ interconnected nanoparticles (INPs). A sensor based on the α-Fe₂O₃(0.09)/Nb₂O₅ heterostructure with a high surface area exhibited enhanced gas-sensing features, maintaining high selectivity and sensitivity, and a considerable recovery percentage towards ethanol gas. The sensing response of the α-Fe₂O₃(0.09)/Nb₂O₅ heterostructure at lower operating temperature (160 °C) is around nine times higher than a pure Nb₂O₅ (INP) sensor at 180 °C with the flow of 100 ppm ethanol gas. The sensors also show excellent selectivity, good long-term stability and a rapid response/recovery time (8s/2s, respectively) to ethanol. The superior electronic conductivity and upgraded sensitivity performance of gas sensors based on the α-Fe₂O₃(0.09)/Nb₂O₅ heterostructure are attributed due to its unique structural features, high specific surface area and the synergic effect of the n-n heterojunction. The promising results demonstrate the potential application of the α-Fe₂O₃(0.09)/Nb₂O₅ heterostructure as a good sensing material for the fabrication of ethanol sensors.

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.

High-Performance Two-Dimensional Perovskite Ca2Nb3O10 UV Photodetectors

We first report two-dimensional (2D) perovskite Ca₂Nb₃O₁₀ ultraviolet photodetectors (UV PDs), which are prepared via a facile calcination-exfoliation method. The 2D Ca₂Nb₃O₁₀ PDs demonstrate high performance at 3 V at 280 nm, high responsivity (14.94 A W^-1), high detectivity (8.7 × 10¹³ Jones), high spectral selectivity (R₂₈₀/R₄₀₀ = 8.84 × 10³), fast speed (0.08/5.6 ms), and long-term stability, exceeding those of most reported UV PDs. Furthermore, the Ca₂Nb₃O₁₀ PDs integrated with poly(ethylene terephthalate) (PET) show excellent flexibility and have high linear dynamic range (96 dB). Our work provides a general strategy for searching new UV PDs based on numerous layered niobates. The Ca₂Nb₃O₁₀ nanosheets may be one of the optimum semiconductor materials for next-generation high-performance UV PDs.

A GeSe micro air brick crystal-based film for the sunlight photodegradation of dye-polluted waters

Pinkish purple rhodamine B polluted water was efficiently photodegraded into colorless by the GeSe MAB crystal-based film under sunlight irradiation.

Designed growth of porous 2D Nb2O5 with Ag nano-particles for differential detection of UV-A and UV-C

We demonstrate the differential detection of UV-A (ultra-violet 320-400 nm region) and UV-C (100-280 nm) using porous two-dimensional (2D) Nb₂O₅ and additional Ag nano-particle decoration. The 2D Nb₂O₅, which has band-absorption edge near the UV-A zone, was synthesized by thermodynamic conversion of 2D material NbSe₂ (Nb₂O₅ has lower Gibbs formation energy than NbSe₂). For the differential detection (to distinguish with UV-C absorption), we decorated the Ag nano-particles on the Nb₂O₅ surface. By coating Ag nano-particles, we can expect (i) a decrease in the area of light absorption by the Ag-coated area, and (ii) an increase of surface plasmon absorption by Ag nano-particles, especially the UV-A region, resulting in strong intensity ratio change UV-A/UV-C.

Asymmetric electrode incorporated 2D GeSe for self-biased and efficient photodetection

2D layered germanium selenide (GeSe) with p-type conductivity is incorporated with asymmetric contact electrode of chromium/Gold (Cr/Au) and Palladium/Gold (Pd/Au) to design a self-biased, high speed and an efficient photodetector. The photoresponse under photovoltaic effect is investigated for the wavelengths of light (i.e. ~220, ~530 and ~850 nm). The device exhibited promising figures of merit required for efficient photodetection, specifically the Schottky barrier diode is highly sensitive to NIR light irradiation at zero voltage with good reproducibility, which is promising for the emergency application of fire detection and night vision. The high responsivity, detectivity, normalized photocurrent to dark current ratio (NPDR), noise equivalent power (NEP) and response time for illumination of light (~850 nm) are calculated to be 280 mA/W, 4.1 × 10⁹ Jones, 3 × 10⁷ W⁻¹, 9.1 × 10⁻¹² WHz^−1/2 and 69 ms respectively. The obtained results suggested that p-GeSe is a novel candidate for SBD optoelectronics-based technologies.

The recent progress of triboelectric nanogenerator-assisted photodetectors

Since 2012, triboelectric nanogenerator (TENG) has attracted significant interest from researchers in the field of energy conversion due to its unique output characteristics of high voltage, pulse and low current. In addition, recent advancements have demonstrated that photodetection platforms based on TENG exhibit great advantages such as being simple, low-cost, portable, with high sensitivity, high response, etc, and are environment friendly. Here, this article provides a comprehensive review on the state-of-the-art photodetectors based on TENG in recent years, and a detailed introduction to the structural design and potential mechanisms. It mainly focuses on self-powered photodetectors (including photodetectors as a load resistance of a TENG and photosensitive materials such as tribo-layer of TENG) and the modulation of photodetectors based on TENG (including utilizing the voltage of TENG as well as triboelectric microplasma). Finally, we put forward some perspectives and outlook, including structure engineering and mechanism guidance, for the future development of simple, high-performance and portable photodetectors based on TENG.

Porous niobia spheres with large surface area: alcothermal synthesis and controlling of their composition and phase transition behaviour

Submicron-sized niobia (Nb2O5) porous spheres with a high specific surface area (300 m2 g-1) and nano concave-convex surfaces were synthesized via a rapid one-pot single-step alcothermal reaction. Prolonged reaction time or high reaction temperatures resulted in a morphology change of Nb2O5 from amorphous sphere to rod crystals with hexagonal crystal phase. A similar alcothermal reaction yielded TiO2-Nb2O5 composite porous spheres, whose Ti : Nb molar ratio was controlled by changing the precursor solution component ratios. A simple thermal treatment of amorphous TiO2-Nb2O5 porous spheres consisting of 1 : 2 (molar ratio) Ti : Nb at 600 °C for 2 h induced crystal phase transfer from amorphous to a monoclinic crystal phase of submicron-sized TiNb2O7 porous spheres with a specific surface area of 50 m2 g-1.

Recent advances in solution-processed photodetectors based on inorganic and hybrid photo-active materials

Due to their excellent and tailorable optoelectronic performance, low cost, facile fabrication, and compatibility with flexible substrates, solution-processed inorganic and hybrid photo-active materials have attracted extensive interest for next-generation photodetector applications. This review gives a comprehensive compilation of solution-processed photodetectors. The basic structures of the device and important parameters of photodetectors will be firstly summarized. Then the development of various solution processing technologies containing solution synthesis and liquid phase film-forming processes for the preparation of semiconductor films is described. From the materials science point of view, we give a comprehensive overview about the current status of solution processed semiconductor materials including inorganic and hybrid photo-active materials for the application of photodetectors. Moreover, challenges and future trends in the field of solution-processed photodetectors are proposed.

Fabrication of a novel BiOI/KTaO3 p–n heterostructure with enhanced photocatalytic performance under visible-light irradiation

In this study, a series of BiOI/KTaO₃ p–n heterojunctions were prepared via a facile in situ chemical bath strategy. The photocatalytic properties of the catalysts was tested by the degradation of Rhodamine B (RhB) and phenol under visible light irradiation. The BiOI/KTaO₃ composites exhibited improved photocatalytic efficiency compared to the individual catalysts. In particular, 54 wt% BiOI/KTaO₃ displayed the highest photocatalytic activity since it degraded 98.6% RhB within 30 minutes, while only 68.1% RhB was degraded over pure BiOI under identical conditions. In addition, the reaction kinetic constant of RhB degradation over 54 wt% BiOI/KTaO₃ was approximately 2.56 and 115-fold larger than those of pure BiOI and KTaO_3, respectively. The results of PL, photocurrent and EIS indicated that the improved photocatalytic efficiency could root in the p–n junction formed between BiOI and KTaO₃, which was conducive to the separation and migration of photo-generated carriers. Furthermore, a free-radical capture experiment illustrated that h⁺ and ˙O₂⁻ were the key factors in the photodegradation of RhB.

Schematic diagram of the formation of p–n junction and the charge transfer and separation process under visible light irradiation.

Characterization of electron beam deposited Nb2O5 coatings for biomedical applications

Niobium oxide coatings deposited on Ti₆Al₄V substrates by electron beam deposition and annealed in air at 600 °C and 800 °C were evaluated for their suitability towards dental, maxillofacial or orthopaedic implant applications. A detailed physico-chemical properties investigation was carried out in order to determine their elemental and phase composition, surface morphology and roughness, mechanical properties, wettability, and corrosion resistance in simulated body fluid solution (pH = 7.4) at room temperature. The biocompatibility of the bare Ti₆Al₄V substrate and coated surfaces was evaluated by testing the cellular adhesion and viability/proliferation of human osteosarcoma cells (MG-63) after 72 h of incubation. The coatings annealed at 800 °C exhibit more phase pure nanocrystalline Nb₂O₅ surfaces with enhanced wettability, reduced porosity and enhanced corrosion resistance properties making them good candidate for dental, maxillofacial or orthopaedic implant applications.

Facile route for C–N/Nb2O5 nanonet synthesis based on 2-methylimidazole for visible-light driven photocatalytic degradation of Rhodamine B

Herein, we fabricated a C and N co-modified Nb₂O₅ nanonet structure (C–N/Nb₂O₅NNs) from niobium oxalate using 2-methylimidazole (Hmim) as a source for C and N via a simple hydrothermal route. The obtained nanonets are robust and cost-effective with excellent recycling stability. Compared with N-doped TiO₂ (N-TiO₂) and a Nb₂O₅ control sample (Nb₂O₅-CS), the resulting nanonets exhibited the highest performance toward the photocatalytic degradation of Rhodamine B (RhB) upon visible light irradiation (λ > 420 nm). Through this study, we revealed that the synergetic effects of C and N on the nanonet surface, which were effectively incorporated into the surface of the Nb₂O₅ nanonet structure, not only remarkably enhanced the visible light response by decreasing the bandgap to 2.9 eV but also improved the light utilization efficiency and photo-induced electron–hole pair separation efficiency of our nanonet structure. We also proposed that the presence of carbonate species (CO_x) and nitrogen species (NO_x) increased the population of generated holes (h⁺) that had the key role in the photodegradation mechanism of RhB, suggesting reasonable importance for the modification of Nb₂O₅ with C and N. This synergism offers a new view to reveal the origin of photodegradation processes, introducing h⁺ as a key intermediate. Our approach provides a new insight to design 2D nanostructures with potential applications in catalysis, solar energy conversion, and environmental protection.

Solar energy utilization: facile synthesis route of C–N/Nb₂O₅NNs using 2-methylimidazole to enhance its photocatalytic degradation towards RhB under visible irradiation.

Good practices for reporting the photocatalytic evaluation of a visible-light active semiconductor: Bi2O3, a case study

The use of dyes to evaluate visible-light photocatalysts requires a proper determination of the contribution from the competing processes: adsorption, sensitization, photobleaching and degradation.

Triangular radial Nb2O5 nanorod growth on c-plane sapphire for ultraviolet-radiation detection

Nb2O5 nanostructures with excellent crystallinities were grown on c-plane sapphire and employed for ultraviolet-(UV)-radiation detection. The triangular radial Nb2O5 grown on the c-sapphire substrate had a 6-fold symmetry with domain matching epitaxy on the substrate. Owing to the radial growth, the nanorods naturally connected when the deposition time increased. This structure can be used as a UV-detector directly by depositing macroscale electrodes without separation of a single nanorod and e-beam lithography process. It was confirmed that electric reactions occur at different UV irradiation wavelengths (254 nm and 365 nm).

Construction of g-C₃N₄-mNb₂O₅ Composites with Enhanced Visible Light Photocatalytic Activity

A series of composites consisting of g-C₃N₄ sheet and mesoporous Nb₂O₅ (mNb₂O₅) microsphere were fabricated by in situ hydrolysis deposition of NbCl₅ onto g-C₃N₄ sheet followed by solvothermal treatment. The samples were characterized using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), N₂ adsorption-desorption, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectroscopy (PL). The photocatalytic activity of the composites was studied by degradation of rhodamine B (RhB) and tetracycline hydrochloride (TC-HCl) in aqueous solution under visible light irradiation (λ > 420 nm). Compared with g-C₃N₄ and mNb₂O₅, g-C₃N₄-mNb₂O₅ composites have higher photocatalytic activity due to synergistic effect between g-C₃N₄ and mNb₂O₅. Among these composites, 4% g-C₃N₄-mNb₂O₅ has the highest efficiency and good recyclability for degradation of both RhB and TC-HCl.

Transparent, Flexible Silicon Nanostructured Wire Networks with Seamless Junctions for High-Performance Photodetector Applications

Optically transparent photodetectors are crucial in next-generation optoelectronic applications including smart windows and transparent image sensors. Designing photodetectors with high transparency, photoresponsivity, and robust mechanical flexibility remains a significant challenge, as is managing the inevitable trade-off between high transparency and strong photoresponse. Here we report a scalable method to produce flexible crystalline Si nanostructured wire (NW) networks fabricated from silicon-on-insulator (SOI) with seamless junctions and highly responsive porous Si segments that combine to deliver exceptional performance. These networks show high transparency (∼92% at 550 nm), broadband photodetection (350 to 950 nm) with excellent responsivity (25 A/W), optical response time (0.58 ms), and mechanical flexibility (1000 cycles). Temperature-dependent photocurrent measurements indicate the presence of localized electronic states in the porous Si segments, which play a crucial role in light harvesting and photocarrier generation. The scalable low-cost approach based on SOI has the potential to deliver new classes of flexible optoelectronic devices, including next-generation photodetectors and solar cells.

Photochromism in oxalatoniobates

Addition of 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen) or 2-aminopyridine (2-NH₂-py) to aqueous solutions of (NH₄)[NbO(C₂O₄)₂(H₂O)₂]·3H₂O (Nb-Ox) yields tris-oxalate complexes (bpyH₂)(bpyH)[NbO(C₂O₄)₃]·2H₂O (1), (phenH)₃[NbO(C₂O₄)₃]·3H₂O (2), and (2-NH₂-pyH)₃[NbO(C₂O₄)₃]·2H₂O (3), which were characterised by XRD, IR and EA. Bipyridinium salt 1 demonstrates remarkable photoactivity even under irradiation by daylight. The nature of the photoactivity was studied by diffuse reflectance (DR) spectroscopy, ESR and quantum-chemical calculations.

Facile fabrication of alveolate Cu2−xSe microsheets as a new visible-light photocatalyst for discoloration of Rhodamine B

A new photocatalyst, alveolate Cu_2−xSe microsheets, is developed, which reveals superior photocatalytic discoloration of Rhodamine B.

Transport Across Heterointerfaces of Amorphous Niobium Oxide and Crystallographically Oriented Epitaxial Germanium

Because of the high carrier mobility of germanium (Ge) and high dielectric permittivity of amorphous niobium pentoxide (a-Nb₂O₅), Ge/a-Nb₂O₅ heterostructures offer several advantages for the rapidly developing field of oxide-semiconductor-based multifunctional devices. To this end, we investigate the growth, structural, band alignment, and metal-insulator-semiconductor (MIS) electrical properties of physical vapor-deposited Nb₂O₅ on crystallographically oriented (100), (110), and (111)Ge epilayers. The as-deposited Nb₂O₅ dielectrics were found to be in the amorphous state, demonstrating an abrupt oxide/semiconductor heterointerface with respect to Ge, when examined via low- and high-magnification cross-sectional transmission electron microscopy. Additionally, variable-angle spectroscopic ellipsometry and X-ray photoelectron spectroscopy (XPS) were used to independently determine the a-Nb₂O₅ band gap, yielding a direct gap value of 4.30 eV. Moreover, analysis of the heterointerfacial energy band alignment between a-Nb₂O₅ and epitaxial Ge revealed valance band offsets (ΔE_V) greater than 2.5 eV, following the relation ΔE_V⁽¹¹¹⁾ > ΔE_V⁽¹¹⁰⁾ > ΔE_V⁽¹⁰⁰⁾. Similarly, utilizing the empirically determined a-Nb₂O₅ band gap, conduction band offsets (ΔE_C) greater than 0.75 eV were found, likewise following the relation ΔE_C⁽¹¹⁰⁾ > ΔE_C⁽¹⁰⁰⁾ > ΔE_C⁽¹¹¹⁾. Leveraging the reduced ΔE_C observed at the a-Nb₂O₅/Ge heterointerface, we also perform the first experimental investigation into Schottky barrier height reduction on n-Ge using a 2 nm a-Nb₂O₅ interlayer, resulting in a 20× increase in reverse-bias current density and improved Ohmic behavior.

Novel UV-Visible Photodetector in Photovoltaic Mode with Fast Response and Ultrahigh Photosensitivity Employing Se/TiO2 Nanotubes Heterojunction

A feasible strategy for hybrid photodetector by integrating an array of self-ordered TiO₂ nanotubes (NTs) and selenium is demonstrated to break the compromise between the responsivity and response speed. Novel heterojunction between the TiO₂ NTs and Se in combination with the surface trap states at TiO₂ help regulate the electron transport and facilitate the separation of photogenerated electron-hole pairs under photovoltaic mode (at zero bias), leading to a high responsivity of ≈100 mA W^-1 at 620 nm light illumination and the ultrashort rise/decay time (1.4/7.8 ms). The implanting of intrinsic p-type Se into TiO₂ NTs broadens the detection range to UV-visible (280-700 nm) with a large detectivity of over 10¹² Jones and a high linear dynamic range of over 80 dB. In addition, a maximum photocurrent of ≈10⁷ A is achieved at 450 nm light illumination and an ultrahigh photosensitivity (on/off ratio up to 10⁴ ) under zero bias upon UV and visible light illumination is readily achieved. The concept of employing novel heterojunction geometry holds great potential to pave a new way to realize high performance and energy-efficient optoelectronic devices for practical applications.

Scalable-Production, Self-Powered TiO2 Nanowell-Organic Hybrid UV Photodetectors with Tunable Performances

Hybrid inorganic-organic photoelectric devices draw considerable attention because of their unique features by combining the tunable functionality of organic molecules and the superior intrinsic carrier mobilities of inorganic semiconductors. An ordered thin layer of TiO₂ nanowells is formed in situ with shallow nanoconcave patterns without cracking with scalable production by a facile and economic strategy, and these layers are used as building blocks to construct hybrid UV photodetectors (PDs). Organic conducting polymers (polyaniline (PANI) with various morphologies) have been exploited as p-type materials, enabling tunable photodetection performances at zero bias. The thin layer of n-type TiO₂ nanowells is favorable for electron transport and light absorption with respect to their conventional nanotubular counterparts, while PANI acts as a hopping state or bridge to largely enhance the transition probability of the valence electrons in TiO₂ to its conduction band, resulting in an increase in photocurrent in a self-powered mode. In particular, the lowest polyaniline loading sample (TP1) exhibits the highest responsivity (3.6 mA·W^-1), largest on-off switching ratio (∼10³), excellent wavelength selectivity, fast response speed (3.8/30.7 ms), and good stability under 320 nm light illumination (0.56 mW·cm^-2) without an external energy supply. This work might be of great value in developing tunable UV photoresponse materials with respect to low cost and a large area for future energy-efficient optoelectronic devices.

A novel hybrid blend based on phenoxy-substituted boron subphthalocyanine for organic photodetectors

Phenoxy-substituted boron subphthalocyanine, blended with a conductive polymer MEH-PPV, is presented as a photoresistive organic material. Using an easily accessible drop casting technique, the blend produces a thin-layer organic photoresistor with a photoresistive ratio of ~2–12. Variations in the blend composition and morphology are shown to change the transport properties of the material. The photoelectrochemical characteristics of the photoresistor are discussed in terms of impedance spectroscopy and the morphology of the material is analyzed using confocal fluorescent microscopy. The device developed is a daylight detector.

Photonics and optoelectronics of two-dimensional materials beyond graphene

Apart from conventional materials, the study of two-dimensional (2D) materials has emerged as a significant field of study for a variety of applications. Graphene-like 2D materials are important elements of potential optoelectronics applications due to their exceptional electronic and optical properties. The processing of these materials towards the realization of devices has been one of the main motivations for the recent development of photonics and optoelectronics. The recent progress in photonic devices based on graphene-like 2D materials, especially topological insulators (TIs) and transition metal dichalcogenides (TMDs) with the methodology level discussions from the viewpoint of state-of-the-art designs in device geometry and materials are detailed in this review. We have started the article with an overview of the electronic properties and continued by highlighting their linear and nonlinear optical properties. The production of TIs and TMDs by different methods is detailed. The following main applications focused towards device fabrication are elaborated: (1) photodetectors, (2) photovoltaic devices, (3) light-emitting devices, (4) flexible devices and (5) laser applications. The possibility of employing these 2D materials in different fields is also suggested based on their properties in the prospective part. This review will not only greatly complement the detailed knowledge of the device physics of these materials, but also provide contemporary perception for the researchers who wish to consider these materials for various applications by following the path of graphene.

The Large Scale Synthesis of Aligned Plate Nanostructures

We propose a novel technique for the large-scale synthesis of aligned-plate nanostructures that are self-assembled and self-supporting. The synthesis technique involves developing nanoscale two-phase microstructures through discontinuous precipitation followed by selective etching to remove one of the phases. The method may be applied to any alloy system in which the discontinuous precipitation transformation goes to completion. The resulting structure may have many applications in catalysis, filtering and thermal management depending on the phase selection and added functionality through chemical reaction with the retained phase. The synthesis technique is demonstrated using the discontinuous precipitation of a γ' phase, (Ni, Co)3Al, followed by selective dissolution of the γ matrix phase. The production of the nanostructure requires heat treatments on the order of minutes and can be performed on a large scale making this synthesis technique of great economic potential.

Magnetoelectric Coupling, Ferroelectricity, and Magnetic Memory Effect in Double Perovskite La3Ni2NbO9

We observe ferroelectricity in an almost unexplored double perovskite La3Ni2NbO9. Ferroelectricity appears below ∼60 K, which is found to be correlated with the significant magnetostriction. A reasonably large value of spontaneous electric polarization is recorded to be ∼260 μC/m(2) at 10 K for E = 5 kV/cm, which decreases signifi- cantly upon application of a magnetic field (H), suggesting considerable magnetoelectric coupling. The dielectric permittivity is also influenced by H below the ferroelectric transition. The magnetodielectric response scales linearly to the squared magnetization, as described by the Ginzburg-Landau theory. Meticulous studies of static and dynamic features of dc magnetization and frequency dependent ac susceptibility results suggest spin-glass state below 29 K. Intrinsic magnetic memory effect is observed from zero-field cooled magnetization and isothermal remanent magnetization studies, also pointing spin-glass state below 29 K. Appearance of ferroelectricity together with a significant magnetoelectric coupling in absence of conventional long-range magnetic order is promising for searching new magnetoelectric materials.

New architecture of a petal-shaped Nb2O5 nanosheet film on FTO glass for high photocatalytic activity

A petal-shaped Nb₂O₅ nanosheet thin film was grown directly on FTO glass substrate via a facile hydrothermal method. The petal-shaped Nb₂O₅ nanosheet array film without annealing showed excellent photocatalytic activity for degrading aqueous rhodamine B.

Fabrication of WO3 nanorods on graphene nanosheets for improved visible light-induced photocapacitive and photocatalytic performance

Visible light-induced photocatalytic degradation of organic pollutants using WO₃ nanorods–graphene nanocomposite.

Elucidating the promotional effects of niobia on SnO2 for CO oxidation: developing an XRD extrapolation method to measure the lattice capacity of solid solutions

Using an XRD extrapolation method, the SnO₂ lattice capacity for Nb₂O₅ is quantified. A Sn–Nb solid solution without excess Nb₂O₅ is promising for CO oxidation.