Ultra-sensitive room-temperature H<Subscript>2</Subscript>S sensor using Ag–In<Subscript>2</Subscript>O<Subscript>3</Subscript> nanorod composites

Ultra-sensitive H₂S sensors operated at room temperature were fabricated using Ag–In₂O₃ nanorod composites synthesized using sol–hydrothermal method followed by NaBH₄ reduction process. TEM proved that the In₂O₃ was nanorod structures of?~?110 nm in length and?~?35 nm in diameter. Ag nanoparticles with diameters from 10 to 15 nm homogeneously decorated on the surfaces of the In₂O₃ naonorods. XRD and XPS analysis proved that the Ag elements existed as zero-valent metallic silver on the surface of the In₂O₃ nanorods. Ag nanoparticles could enhance the formation of chemisorbed oxygen species and interactions between H₂S molecules and oxygen species due to spillover effect, and the electron transfer between Ag and In₂O₃ nanorods also enhanced the sensing properties. Therefore, the H₂S sensors based on the Ag–In₂O₃ nanorod composites showed significantly improved sensing performance than those based on the pure In₂O₃ nanorods. The optimized content of Ag nanoparticles is 13.6 wt%. Operated at room temperature, the H₂S sensors made of 13.6 wt% Ag–In₂O₃ nanorod composites exhibited an ultra-high response of 93719 to 20 ppm H₂S and a superior detection limit of 0.005 ppm. The sensor also showed good reversibility, good selectivity, excellent reproducibility and stability for detection of H₂S gas.     

Ultrathin In2O3 Nanosheets toward High Responsivity and Rejection Ratio Visible-Blind UV Photodetection

Photoelectrochemical-type visible-blind ultraviolet photodetectors (PEC VBUV PDs) have gained ever-growing attention due to their simple fabrication processes, uncomplicated packaging technology, and high sensitivity. However, it is still challenging to achieve high-performance PEC VBUV PDs based on a single material with good spectral selectivity. Here, it is demonstrated that individual ultrathin indium oxide (In₂O₃) nanosheets (NSs) are suitable for designing high-performance PEC VBUV PDs with high responsivity and UV/visible rejection ratio for the first time. In₂O₃ NSs PEC PDs show excellent UV photodetection capability with an ultrahigh photoresponsivity of 172.36 mA W⁻¹ and a high specific detectivity of 4.43 × 10¹¹ Jones under 254 nm irradiation, which originates from the smaller charge transfer resistance (R_ct) at the In₂O₃ NSs/electrolyte interface. The light absorption of In₂O₃ NSs takes a blueshift due to the quantum confinement effect, granting good spectral selectivity for visible-blind detection. The UV/visible rejection ratio of In₂O₃ NSs PEC PDs is 1567, which is 30 times higher than that of In₂O₃ nanoparticles (NPs) and exceeds all recently reported PEC VBUV PDs. Moreover, In₂O₃ NSs PEC PDs show good stability and good underwater imaging capability. The results verify that ultrathin In₂O₃ NSs have potential in underwater optoelectronic devices.     

Au@Ag Nanopencil with Au Tip and Au@Ag Rod: Multimodality Plasmonic Nanoprobe based on Asymmetric Etching for the Detection of SCN− and ClO−

In this paper, Au@Ag nanopencil is designed as a multimodality plasmonic nanoprobe based on asymmetric etching for the detection of SCN⁻ and ClO⁻. Au@Ag nanopencil with Au tip and Au@Ag rod is prepared by asymmetric tailoring of uniformly grown silver-covered gold nanopyramids under the combined effect of partial galvanic replacement and redox reaction. By asymmetric etching in different systems, Au@Ag nanopencil exhibits diversified changes in the plasmonic absorption band: O₂^•− facilitated by SCN⁻ etches Au@Ag rod from the end to the tip, causing a blue shift of the localized surface plasmon resonance (LSPR) peak as the aspect ratio decreases; while the ClO⁻ can retain Au@Ag shell and etch Ag within rod from the tip to the end, causing a redshift of the LSPR peak as the coupling resonance weakens. Based on peak shifts in different directions, a multimodality detection of SCN⁻ and ClO⁻ has been established. The results demonstrate the detection limits of SCN⁻ and ClO⁻ are 160 and 6.7 nm , and the linear ranges are 1–600 µm and 0.05–13 µm , respectively. The finely designed Au@Ag nanopencil not only broadens the horizon of designing heterogeneous structures, but also enriches the strategy of constructing multimodality sensing platform.     

TiO2-SnO2 system for gas sensing—Photodegradation of organic contaminants

Catalytic photodegradation of organic contaminants by means of UV light has been demonstrated for gas sensors based on composites of TiO₂-SnO₂. Thin film resistive-type gas sensors of TiO₂-SnO₂ have been deposited at 350 °C by RF sputtering from a Ti-SnO₂ target with varying surface ratio of SnO₂/Ti. Photodegradation experiments of bromothymol blue by UV light have been performed by means of the optical spectrophotometry over the wavelength range extending from 300 nm to 600 nm. The influence of the UV illumination on the sensor response to 100-20,000 ppm of H₂ has been investigated in situ on motor oil contaminated sensors. It has been found that sequential exposures to UV light lead to a partial recovery of the sensor signal to hydrogen.     

Luminous properties of color tunable strontium thio-selenide phosphors for LEDs application

In this study, alkali earth thio-selenide phosphor, SrS_xSe_1 ? x:Eu²⁺_, was prepared using the conventional solid state reaction method. The synthesized phosphor displayed a broad excitation band that was suitable for blue or near UV LED applications and emitted light at various wavelengths (563–605 nm) with different chemical compositions. Like the case of other alkali phosphors, Zn²⁺ substitution for Sr²⁺ greatly enhanced the emission of this thio-selenide phosphor. The LED fabricated with the synthesized phosphor produced white light using a blue LED with a CIE-1931 coordinate, T_c and R_a of (0.3199, 0.3107), 6577 K and 51.6, respectively.     

Polymer-Grafted,Gold Nanoparticle-Based Nano-Capsules as Reversible Colorimetric Tensile Strain Sensors

Colloidal colorimetric microsensors enable the in-situ detection of mechanical strains within materials. Enhancing the sensitivity of these sensors to small scale deformation while enabling reversibility of the sensing capability would expand their utility in applications including biosensing and chemical sensing. In this study, we introduce the synthesis of colloidal colorimetric nano-sensors using a simple and readily scalable fabrication method. Colloidal nano sensors are prepared by emulsion-templated assembly of polymer-grafted gold nanoparticles (AuNP). To direct the adsorption of AuNP to the oil-water interface of emulsion droplets, AuNP (≈11nm) are functionalized with thiol-terminated polystyrene (PS, M_n = 11k). These PS-grafted gold nanoparticles are suspended in toluene and subsequently emulsified to form droplets with a diameter of ≈30µm. By evaporating the solvent of the oil-inwater emulsion, we form nanocapsules (AuNC) (diameter < 1µm) decorated by PS-grafted AuNP. To test mechanical sensing, the AuNC are embedded in an elastomer matrix. The addition of a plasticizer reduces the glass transition temperature of the PS brushes, and in turn imparts reversible deformability to the AuNC. The plasmonic peak of the AuNC shifts towards lower wavelengths upon application of uniaxial tensile tension, indicating increased inter-nanoparticle distance, and reverts back as the tension is released.     

Photo-sensing properties of Cd-doped In2S3 thin films fabricated via low-cost nebulizer spray pyrolysis technique

In this study, we report the fabrication of cadmium-doped indium sulfide thin films (In₂S₃:Cd) using a low-cost nebulizer-aided spray pyrolysis process at 350 °C on glass substrates for photo-sensing applications. The impact of 0, 2, 4, and 8 wt% cadmium concentrations on the structure, morphology, optical properties, and photo-sensing capabilities of In₂S₃ thin films were examined systematically. From X-ray diffraction (XRD) analysis, the major peak is located in the (103) plane for all Cd-doped In₂S₃ thin film samples, and the maximum crystallite size for the 4 wt% sample is 59 nm. The field emission scanning electron microscope (FESEM) image revealed a homogenous large-grained surface of Cd-doped In₂S₃ film that completely covered the substrate. UV–Vis absorption analysis demonstrated good absorption for all thin film samples in the visible and ultraviolet regions of the electromagnetic spectrum, particularly, the 4% Cd-doped concentration showed excellent absorption as is observed from Tauc relation. The highest PL intensity at 680 nm was observed for the sample coated with 4 wt% of Cd. Under UV light, the I–V behavior depicts a light current of 1.06?×?10^–6 A for a 5 V bias voltage. The In₂S₃: Cd (4%) sample had the highest responsivity of 2.12?×?10^?1A/W and a detectivity of 1.84?×?10¹¹ Jones, with a high EQE of 50%. The study manifests that the developed Cd (4%)-doped In₂S₃ thin film sample might be better suited for the application of photodetectors.

     

Luminescent properties of Ca2BO3Cl:Eu yellow-emitting phosphor for white light-emitting diodes

The Ca₂BO₃Cl:Eu²⁺ phosphor was synthesized by the general high temperature solid-state reaction and an efficient yellow emission under near-ultraviolet and blue excitation was observed. The emission spectrum shows a single intense broad emission band centered at 573 nm, which corresponds to the allowed f-d transition of Eu²⁺. The excitation spectrum is very broad extending from 350 to 500 nm, which is coupled well with the emission of UV LED (350-410 nm) and blue LED (450-470 nm). The measured emission of In-GaN-based Ca₂BO₃Cl:Eu²⁺ LED shows white light to the naked eye with a chromatic coordinate of (0.33, 0.36). The Ca₂BO₃Cl:Eu²⁺ is a very appropriate yellow-emitting phosphor for white LEDs.     

Luminescence properties of monodispersed spherical BaWO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> microphosphors for white light-emitting diodes

Monodispersed spheres (1–4 μm in diameter) of BaWO₄:Eu³⁺ (hereafter BWO:Eu) red-phosphor exhibiting intense emission at 615 nm were synthesized via a mild hydrothermal method. X-ray diffraction, scanning electron microscope, photoluminescence excitation and emission spectra, and decay curve were used to characterize the properties of BWO:Eu phosphors. An intense red emission was obtained by exciting either into the ⁵L₆ state with 394 nm or the ⁵D₂ state with 465 nm, that correspond to two popular emission lines from near-UV and blue LED chips, respectively. The values of Ω _2,4 experimental intensity parameters (13.8 × 10⁻²⁰ and 8.2 × 10⁻²⁰ cm²) are determined. The high-emission quantum efficiency of the BWO:Eu phosphor suggests this material could be promising red phosphors for generating white light in phosphor-converted white light-emitting diodes.     

Nanogap Engineered Plasmon‐Enhancement in Photocatalytic Solar Hydrogen Conversion

Graphitic carbon nitride modified with plasmonic Ag@SiO₂ core–shell nanoparticles (g‐C₃N₄/Ag@SiO₂) are proposed for enhanced photocatalytic solar hydrogen evolution under visible light. Nanosized gaps between the plasmonic Ag nanoparticles (NPs) and g‐C₃N₄ are created and precisely modulated to be 8, 12, 17, and 21 nm by coating SiO₂ shells on the Ag NPs. The optimized photocatalytic hydrogen production activity for g‐C₃N₄/Ag@SiO₂ is achieved with a nanogap of 12 nm (11.4 μmol h⁻¹) to be more than twice as high as that of pure g‐C₃N₄ (5.6 μmol h⁻¹). The plasmon resonance energy transfer (PRET) effect of Ag NPs is innovatively proved from a physical view on polymer semiconductors for photoredox catalysis. The PRET effect favors the charge carrier separation by inducing electron–hole pairs efficiently formed in the near‐surface region of g‐C₃N₄. Furthermore, via engineering the width of the nanogap, the PRET and energy‐loss Förster resonance energy transfer processes are perfectly balanced, resulting in considerable enhancement of photocatalytic hydrogen production activity over the g‐C₃N₄/Ag@SiO₂ plasmonic photocatalyst.     

Micellar Nanoreactors Enabled Site-Selective Decoration of Pt Nanoparticles Functionalized Mesoporous SiO2/WO3-x Composites for Improved CO Sensing

Site-selective and partial decoration of supported metal nanoparticles (NPs) with transition metal oxides (e.g., FeO_x) can remarkably improve its catalytic performance and maintain the functions of the carrier. However, it is challenging to selectively deposit transition metal oxides on the metal NPs embedded in the mesopores of supporting matrix through conventional deposition method. Herein, a restricted in situ site-selective modification strategy utilizing poly(ethylene oxide)-block-polystyrene (PEO-b-PS) micellar nanoreactors is proposed to overcome such an obstacle. The PEO shell of PEO-b-PS micelles interacts with the hydrolyzed tungsten salts and silica precursors, while the hydrophobic organoplatinum complex and ferrocene are confined in the hydrophobic PS core. The thermal treatment leads to mesoporous SiO₂/WO_3-x framework, and meanwhile FeO_x nanolayers are in situ partially deposited on the supported Pt NPs due to the strong metal-support interaction between FeO_x and Pt. The selective modification of Pt NPs with FeO_x makes the Pt NPs present an electron-deficient state, which promotes the mobility of CO and activates the oxidation of CO. Therefore, mesoporous SiO₂/WO_3-x-FeO_x/Pt based gas sensors show a high sensitivity (31 ± 2 in 50 ppm of CO), excellent selectivity, and fast response time (3.6 s to 25 ppm) to CO gas at low operating temperature (66 °C, 74% relative humidity).     

WO3 Nanofiber‐Based Biomarker Detectors Enabled by Protein‐Encapsulated Catalyst Self‐Assembled on Polystyrene Colloid Templates

A novel catalyst functionalization method, based on protein‐encapsulated metallic nanoparticles (NPs) and their self‐assembly on polystyrene (PS) colloid templates, is used to form catalyst‐loaded porous WO₃ nanofibers (NFs). The metallic NPs, composed of Au, Pd, or Pt, are encapsulated within a protein cage, i.e., apoferritin, to form unagglomerated monodispersed particles with diameters of less than 5 nm. The catalytic NPs maintain their nanoscale size, even following high‐temperature heat‐treatment during synthesis, which is attributed to the discrete self‐assembly of NPs on PS colloid templates. In addition, the PS templates generate open pores on the electrospun WO₃ NFs, facilitating gas molecule transport into the sensing layers and promoting active surface reactions. As a result, the Au and Pd NP‐loaded porous WO₃ NFs show superior sensitivity toward hydrogen sulfide, as evidenced by responses (R_air/R_gas) of 11.1 and 43.5 at 350 °C, respectively. These responses represent 1.8‐ and 7.1‐fold improvements compared to that of dense WO₃ NFs (R_air/R_gas = 6.1). Moreover, Pt NP‐loaded porous WO₃ NFs exhibit high acetone sensitivity with response of 28.9. These results demonstrate a novel catalyst loading method, in which small NPs are well‐dispersed within the pores of WO₃ NFs, that is applicable to high sensitivity breath sensors.     

Ag nanoparticles enhanced near-IR emission from Er3+ ions doped glasses

Vitreous materials containing rare-earth (RE) ions and metallic nanoparticles (NPs) attract considerable interest because the presence of the NPs may lead to an intensification of luminescence. In this work, the characteristics of 1.54 μm luminescence for the Er³⁺ ions doped bismuthate glasses containing Ag NPs were studied under 980 nm excitation. The surface plasmon resonance (SPR) band of Ag NPs appears from 500 to 1500 nm. Transmission electron microscopic (TEM) image reveals that the Ag NPs are dispersed homogeneously with the size from 2 to 7 nm. The strength parameters Ω_t(t = 2, 4, 6), spontaneous emission probability (A), radiative lifetime (τ) and stimulated emission section (σ_em) of Er³⁺ ions were calculated by the Judd–Ofelt theory. When the glass contains 0.2 wt% AgCl, the 1.54 μm fluorescence intensity of Er³⁺ reaches a maximum value, which is 7.2 times higher than that of glass without Ag NPs. The Ag NPs embedded glasses show significantly fluorescence enhancement of Er³⁺ ions by local field enhancement from SPR.     

Surface-enhanced Raman spectroscopy studies of orderly arranged silica nanospheres-synthesis,characterization and dye detection

Silica nanospheres have been explored much for drug delivery, photocatalysis, sensors and energy storage applications. It also acts as a template for Surface-Enhanced Raman Spectroscopy (SERS) substrates. Uniform nanostructures at low cost with high reproducibility are the major challenges in SERS substrate fabrication. In the present work, silica nanospheres were synthesized using stober method and deposited on to glass slides using Vertical deposition techniques. Different size/thickness of Silver (Ag) nanoparticles were deposited onto silica thin films using sputter deposition technique. The monodispersity of silica nanospheres and size of silver nanoparticles (10 nm, 20 nm and 30 nm) were confirmed by FESEM analysis. The structural properties were confirmed through XRD. UV–Vis analysis revealed that the plasmonic properties of Ag@SiO₂ give high surface plasmons for 30 nm thickness of silver. The binding energy of Ag@SiO₂ confirmed through XPS spectrum. The fabricated SERS substrates were used to detect Rhodamine 6G (R6G), Methylene blue (MB), Methylene violet (MV) and Methyl orange dyes as an analyte molecule with a limit of detection at about 10^?11 mol/L. The addition of SiO₂ nanospheres decreases the Ag oxidation rate and increases their stability. The maximum enhancement factor (1.5?×?10⁷) achieved for 30nm thickness of Ag@SiO₂. The results and technique establish the potential applications and reproducible SERS substrate.

     

HCHO sensing properties of Ag-doped In2O3 nanofibers synthesized by electrospinning

Ag-doped In₂O₃ nanofibers with diameters ranging from 60 to 130 nm and lengths of several tens of micrometers were synthesized by an electrospinning method. The XRD results indicated that the dopant in the nanofibers was metal Ag. The sensor fabricated from these fibers exhibited excellent HCHO sensing properties at 115 °C. The sensitivity was up to 3 when the sensor was exposed to 5 ppm HCHO, and the response and recovery time were about 5 and 10 s, respectively. Good selectivity was also observed in our investigations. These results indicated that the Ag-doped In₂O₃ nanofibers could be used to fabricate high performance HCHO sensors in practice.     

Nickle-ion-substituted ceria nanoparticles-based electrochemical sensor for sensitive detection of thiourea

Nickel-substituted ceria nanoparticles (CeO₂:Ni NPs) were prepared by the co-precipitation process under environmental conditions. X-ray diffraction (XRD), field emission-transmission electron microscopy, UV/visible, X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy techniques were successfully used to investigate the crystallographic structure, phase purity, morphology, optical properties, chemical composition, and electrocatalytic properties of the as-prepared ceria NPs. XRD pattern shows the formation of single-phase, highly crystalline, and cubic phase nanostructure with an average of 10 nm crystalline size. As observed from TEM micrographs, particles were highly aggregated may be due to the synthesis in aqueous media. The electrochemical properties and sensing performance of the CeO₂:Ni NPs pasted on glassy carbon electrode were measured against different thiourea concentrations. The fabricated electrode revealed excellent electrocatalytic activity against thiourea concentrations as well as characterization in comparison to the bare electrode. The electrode exhibited a linear detection range between 3.56 and 1000 µM, detection limit 3.56 µM, and sensitivity 2.52 µA mL µM^?1 cm^?2 with regression coefficient 0.995. The electrochemical stability, chemical kinetic, and reproducibility were also examined in the presence of thiourea in phosphate buffer solution.

     

Formation and textural characterization of size-controlled LaFeO3 perovskite nanoparticles for efficient photocatalytic degradation of organic pollutants

A series of LaFeO₃ perovskite nanoparticles (NPs) were successfully formed by a direct sol-gel method involving different citric acid to metal ratios of x (where x  = 2–16). The resulted precursors were treated via auto-combustion, followed by calcination at different temperatures (300–700 °C). Size-controlled LaFeO₃ NPs were getting smaller down to 18.8 nm at high citric acid ratio, showing relatively high surface area up to 27.6 m²/g . Photocatalytic activity of the formed LaFeO₃ NPs was explored for methylene blue (MB) degradation in the absence and presence of 0.5 mM H₂O₂ under light irradiation. Results showed that variation of citric acid to metal ratio alter the band gap and reduce the photo-generated charge carriers recombination of LaFeO₃ NPs. Moreover, the LFC4-500 material (LaFeO₃ synthesized using ×  = 4, and calcined at 500 °C) was the most active photocatalyst in solution at pH = 3 and 0.5 mM H₂O₂, with the highest efficiency > 99% within 30 min and showed excellent reusability without etching even after several cycles. Significantly, the LaFeO₃ NPs characteristics were correlated with their synthesis conditions and the type of interaction with citric acid during initial stages of crystal formation.     

A facile synthesis of monodisperse Au nanoparticles and their catalysis of CO oxidation

Monodisperse Au nanoparticles (NPs) have been synthesized at room temperature via a burst nucleation of Au upon injection of the reducing agent t-butylamine-borane complex into a 1, 2, 3, 4-tetrahydronaphthalene solution of HAuCl₄·3H₂O in the presence of oleylamine. The as-synthesized Au NPs show size-dependent surface plasmonic properties between 520 and 530 nm. They adopt an icosahedral shape and are polycrystalline with multiple-twinned structures. When deposited on a graphitized porous carbon support, the NPs are highly active for CO oxidation, showing 100% CO conversion at −45 °C. This article is published with open access at Springerlink.com     

Ag nanoparticle-decorated SiO2@TiO2 hierarchical microspheres improve the efficiency of dye-sensitized solar cells

SiO₂@TiO₂-Ag (STA) microspheres decorated with Ag nanoparticles (Ag NPs) were prepared and assembled into the photoanode. The photoanode composed of STA microspheres and TiO₂ nanoparticles (P25) was prepared by doctor blade method. UV–vis measurement indicates that the introduction of a few STA microspheres observably enhances the light scattering and capturing ability of the photoanode. The photoelectric conversion efficiency of the DSSCs with 2wt% STA photoanode increased to 7.4% from 4.3% comparing with pure P25 TiO₂ nanoparticles. The configuration DSSCs have the maximum short circuit current density (J_sc) of 16.0 mA cm^?2 and open-circuit voltage (V_oc) of 0.780 V, which are significantly higher than the pure TiO₂ DSSCs. The significant improvement of the DSSCs performance can be due to the synergistic effect of the superior light scattering of STA and the localized surface plasma resonance (LSPR) effect of Ag NPs modified on the microspheres surface.

     

Luminescent properties of Eu doped α-Gd2(MoO4)3 phosphor for white light emitting diodes

A novel red emitting phosphor α-Gd₂(MoO₄)₃:Eu³⁺ was developed for white light emitting diodes (LEDs). The phosphor was prepared by solid-state reaction. The effects of the flux content and the activator concentration on the crystal structure, morphology and luminescent properties were investigated by using XRD, SEM, and fluorescent spectra. These results showed that this phosphor can be effectively excited by ultraviolet (UV) (395 nm) and blue (465 nm) light, matching the output wavelengths of ultraviolet or blue LED chips. The α-Gd₂ (MoO₄)₃ phosphor may be a better candidate for solid state lighting application.