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., FeOx ) 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 /WO3-x framework, and meanwhile FeOx nanolayers are in situ partially deposited on the supported Pt NPs due to the strong metal-support interaction between FeOx and Pt. The selective modification of Pt NPs with FeOx makes the Pt NPs present an electron-deficient state, which promotes the mobility of CO and activates the oxidation of CO. Therefore, mesoporous SiO2 /WO3-x -FeOx /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).

Ultrasensitive sensing performances of amphiphilic block copolymer induced gyrus-like In2O3 thick films to low-concentration acetone

In the present work, an inducible assembly of di-block polymer compounds approach was employed for the synthesis of mesoscopic gyrus-like In₂O₃ by using lab-made high-molecular-weight amphiphilic di-block copolymer poly(ethylene oxide)-b-polystyrene (PEO-b-PS) as a revulsive, with indium chloride as an indium source and THF/ethanol as the solvent. The obtained mesoscopic gyrus-like In₂O₃ indium oxide materials exhibit a large surface area and a highly crystalline In₂O₃ nanostructure framework, and the gyrus distance is about 40 nm, which can facilitate the diffusion and transport of acetone vapor molecules. By using this material as a chemoresistance sensor, the obtained gyrus-like indium oxides were used as sensing materials, showing an excellent performance to acetone at a low operating temperature (150 °C) due to their high porosity and unique crystalline framework. The limit of detection of the thick-film sensor based on indium oxides is appropriate for diabetes exhaled breath acetone concentration detection. Moreover, the thick-film sensor shows a very fast response-recovery dynamics upon contacting acetone vapor due to its abundant open folds mesoscopic structure, and also to the large surface area of the nanocrystalline gyrus-like In₂O₃.

Rare-earth-doped indium oxide nanosphere-based gas sensor for highly sensitive formaldehyde detection at a low temperature

Formaldehyde (HCHO) is widely viewed as a carcinogenic volatile organic compound in indoor air pollution that can seriously threaten human health and life. Thus, there is a critical need to develop gas sensors with improved sensing performance, including outstanding selectivity, low operating temperature, high responsiveness, and short recovery time, for HCHO detection. Currently, doping is considered an effective strategy to raise the sensing performance of gas sensors. Herein, various rare earth elements-doped indium oxide (RE-In₂O₃) nanospheres were fabricated as gas sensors for improved HCHO detection via a facile and environmentally solvothermal method. Such RE-In₂O₃ nanosphere-based sensors exhibited remarkable gas-sensing performance, including a high selectivity and stability in air. Compared with pure, Yb-, Dy-doped In₂O₃ and different La ratios doped into In₂O₃, 6% La-doped In₂O₃ (La-In₂O₃) nanosphere-based sensors demonstrated a high response value of 210 to 100 ppm at 170 °C, which was around 16 times higher than that of the pure In₂O₃ sensor, and also exhibited a detection limit of 10.9 ppb, and a response time of 30 s to 100 ppm HCHO with a recovery time of 160 s. Finally, such superior sensing performance of the 6% La-In₂O₃ sensors was proposed to be attributed to the synergistic effect of the large specific surface area and enhanced surface oxygen vacancies on the surface of In₂O₃ nanospheres, which produced chemisorbed oxygen species to release electrons and provided abundant reaction sites for HCHO gas. This study sheds new light on designing nanomaterials to build gas sensors for HCHO detection.

NIR-regulated dual-functional silica nanoplatform for infected-wound therapy via synergistic sterilization and anti-oxidation

Nature-derived bioactive components and photothermal synergistic therapy bring potential strategies for fighting bacterial infection and accelerating would healing by virtue of their excellent therapeutic efficiencies and ignorable side effects, where photothermal property not only acts as sterilization energy but also as a doorkeeper to control the natural component release. Herein, by integrating the excellent antibacterial property of cinnamaldehyde (CA) and the outstanding photothermal performance of copper sulfide nanoparticles (CuS NPs), a multifunctional nanoplatform of SiO₂ @CA@CuS nanospheres (NSs) is constructed with silica nanosphere (SiO₂ NSs) as carrier. SiO₂ @CA@CuS NSs exhibit photothermal property, bacterial absorption capacity, extraordinary antibacterial activity and antioxidant property. Mechanism characteriazation and antibacterial experiment indicate that positive charged SiO₂ @CA@CuS can adhere to the negative charged surface of bacteria, and quickly kill bacteria through the synergistic action of the released CA and heat produced under near infrared light (NIR) irradiation at 980 nm. The sterilization efficiencies for Escherichia coli (E. coli) and S. aureus reach 99.86% and 99.84%, respectively. Furthermore, NIR-regulated SiO₂ @CA@CuS perform great biocompatibility, as well as effective effects for accelerating S. aureus-infected wound healing at a low photothermal temperature (45 °C) relying on synergistic sterilization and anti-oxidation.

Synthesis, mechanism and characterization of Urchin-like Ga2O3 microspheres

An effective method without catalyst and template was developed to synthesize a novel micro-/nanostructures of gallium oxide (Ga2O3) for the first time. The urchin-like microspheres with uniformly distributed nanowires were...

Self-Hybrid Transition Metal Oxide Nanosheets Synthesized by a Facile Programmable and Scalable Carbonate-Template Method

2D transition metal oxides (TMO) nanosheets have attracted considerable attention in both fundamental research and practical applications. Herein, a convenient programmable and scalable carbonate crystals templating synthesis is developed to produce high-quality self-hybrid TMO nanosheets (Si-WO_{3- x} , Ta_x O_y , Mn_x O_y ) and their respective polymetallic oxide hybrid nanosheets with tunable composition, low-cost and high-yield. Taking tungsten oxide nanosheets as example, silicotungstic acid precursor is in situ converted into tungsten oxide nanosheets like scales on the surface of calcium carbonate crystals through the simple soaking-drying-calcination process, and after selectively dissolving calcium carbonate by etching, the dispersive tungsten oxide nanosheets with unique self-hybrid Si-doped h-WO₃ /ε-WO₃ /WO₂ compositions are obtained, which show excellent acetone gas-sensing performances at low temperatures. This carbonate-template method opens up the possibility to economically produce various functional TMO nanosheets with specific compositions for diverse applications.

Printable Single-Unit-Cell-Thick Transparent Zinc-Doped Indium Oxides with Efficient Electron Transport Properties

Ultrathin transparent conductive oxides (TCOs) are emerging candidates for next-generation transparent electronics. Indium oxide (In₂O₃) incorporated with post-transition-metal ions (e.g., Sn) has been widely studied due to their excellent optical transparency and electrical conductivity. However, their electron transport properties are deteriorated at the ultrathin two-dimensional (2D) morphology compared to that of intrinsic In₂O₃. Here, we explore the domain of transition-metal dopants in ultrathin In₂O₃ with the thicknesses down to the single-unit-cell limit, which is realized in a large area using a low-temperature liquid metal printing technique. Zn dopant is selected as a representative to incorporate into the In₂O₃ rhombohedral crystal framework, which results in the gradual transition of the host to quasimetallic. While the optical transmittance is maintained above 98%, an electron field-effect mobility of up to 87 cm² V^-1 s^-1 and a considerable sub-kΩ^-1 cm^-1 ranged electrical conductivity are achieved when the Zn doping level is optimized, which are in a combination significantly improved compared to those of reported ultrathin TCOs. This work presents various opportunities for developing high-performance flexible transparent electronics based on emerging ultrathin TCO candidates.

Mesoporous WO3 modified by Au nanoparticles for enhanced trimethylamine gas sensing properties

Au-Doped mesoporous WO₃ is prepared and it exhibited higher response to TMA gas.

Au Nanoparticles Decorated Mesoporous SiO2 -WO3 Hybrid Materials with Improved Pore Connectivity for Ultratrace Ethanol Detection at Low Operating Temperature

Semiconducting metal oxides-based gas sensors with the capability to detect trace gases at low operating temperatures are highly desired in applications such as wearable devices, trace pollutant detection, and exhaled breath analysis, but it still remains a great challenge to realize this goal. Herein, a multi-component co-assembly method in combination with pore engineering strategy is proposed. By using bi-functional (3-mercaptopropyl) trimethoxysilane (MPTMS) that can co-hydrolyze with transition metal salt and meanwhile coordinate with gold precursor during their co-assembly with PEO-b-PS copolymers, ordered mesoporous SiO₂ -WO₃ composites with highly dispersed Au nanoparticles of 5 nm (mesoporous SiO₂ -WO₃ /Au) are straightforward synthesized. This multi-component co-assembly process avoids the aggregation of Au nanoparticles and pore blocking in conventional post-loading method. Furthermore, through controlled etching treatment, a small portion of silica can be removed from the pore wall, resulting in mesoporous SiO₂ -WO₃ /Au with increased specific surface area (129 m²  g^-1 ), significantly improved pore connectivity, and enlarged pore window (>4.3 nm). Thanks to the presence of well-confined Au nanoparticles and ε-WO₃ , the mesoporous SiO₂ -WO₃ /Au based gas sensors exhibit excellent sensing performance toward ethanol with high sensitivity (R_a /R_g = 2-14 to 50-250 ppb) at low operating temperature (150 °C).

Bimetallic PtCu Nanocrystal Sensitization WO3 Hollow Spheres for Highly Efficient 3-Hydroxy-2-butanone Biomarker Detection

As a foodborne bacterium, Listeria monocytogenes (LM) can cause serious diseases and even death to weak people. 3-Hydroxy-2-butanone (3H-2B) has been proven to be a biomarker for exhalation of LM. Detection of 3H-2B is a fast and effective method for determining whether the food is infected. Herein, we present an excellent 3H-2B gas sensor based on bimetallic PtCu nanocrystal modified WO₃ hollow spheres. The structure and morphology of the PtCu/WO₃ were characterized, and their gas sensitivities were measured by a static testing method. The results showed that the sensor response of WO₃ hollow spheres was enhanced by about 15 times after modification with bimetallic PtCu nanocrystal. The maximum response value of the PtCu/WO₃ sensor to 10 ppm 3H-2B is as high as 221.2 at 110 °C. In addition, the PtCu/WO₃ sensor also exhibited good selectivity to 3H-2B, fast response/recovery time (9 s/28 s), and low limit of detection (LOD < 0.5 ppm). Furthermore, the sensitivity mechanism was studied by monitoring the reaction products by gas chromatography-mass spectrometry. The excellent gas-sensing performance can be attributed to the synergy between PtCu and WO₃, including the unique spillover effect of O₂ on PtCu nanoparticles, the regulated depletion layer by p-type Cu_xO to n-type WO₃, and their selective catalysis to 3H-2B. Hence, this work offers the rational design and synthesis of highly efficient sensitive materials for the detection of LM for food security.

Fabrication of LaFeO3 and rGO-LaFeO3 microspheres based gas sensors for detection of NO2 and CO

In the present report, gas sensing devices based on LaFeO₃ and rGO-LaFeO₃ were fabricated by a photolithography technique. The X-ray diffraction, Raman spectra and FT-IR results confirm the formation of a perovskite phase and composite. XPS and TEM give the chemical compositions for both products. The higher roughness, greater surface area (62.1 m² g⁻¹), larger pore size (16.4 nm) and lower band gap (1.94 eV) of rGO-LaFeO₃ make it a suitable candidate to obtain high sensitivity. The gas sensing performance of the devices was investigated for various concentrations of NO₂ and CO gases at temperatures of 200 and 250 °C. It was observed that the rGO-LaFeO₃ based device exhibited a high relative response (183.4%) for a 3 ppm concentration of NO₂ at a 250 °C operating temperature. This higher response is attributed to the large surface area, greater surface roughness, and numerous active sites of rGO-LaFeO₃. The gas sensing properties investigated show that rGO-LaFeO₃ is an excellent candidate for an NO₂ sensor.

In the present report, gas sensing devices based on LaFeO₃ and rGO-LaFeO₃ were fabricated by a photolithography technique.

Growth of faceted pores in a multi-component crystal by applying mechanical stress

The theory for controllable growth of pores in a multicomponent crystal using mechanical stress is proposed.

Ag Nanoparticles Sensitized In2O3 Nanograin for the Ultrasensitive HCHO Detection at Room Temperature

Formaldehyde (HCHO) is the main source of indoor air pollutant. HCHO sensors are therefore of paramount importance for timely detection in daily life. However, existing sensors do not meet the stringent performance targets, while deactivation due to sensing detection at room temperature, for example, at extremely low concentration of formaldehyde (especially lower than 0.08 ppm), is a widely unsolved problem. Herein, we present the Ag nanoparticles (Ag NPs) sensitized dispersed In₂O₃ nanograin via a low-fabrication-cost hydrothermal strategy, where the Ag NPs reduces the apparent activation energy for HCHO transporting into and out of the In₂O₃ nanoparticles, while low concentrations detection at low working temperature is realized. The pristine In₂O₃ exhibits a sluggish response (R_a/R_g = 4.14 to 10 ppm) with incomplete recovery to HCHO gas. After Ag functionalization, the 5%Ag-In₂O₃ sensor shows a dramatically enhanced response (135) with a short response time (102 s) and recovery time (157 s) to 1 ppm HCHO gas at 30 °C, which benefits from the Ag NPs that electronically and chemically sensitize the crystal In₂O₃ nanograin, greatly enhancing the selectivity and sensitivity.

A General and Straightforward Route to Noble Metal-Decorated Mesoporous Transition-Metal Oxides with Enhanced Gas Sensing Performance

Controllable and efficient synthesis of noble metal/transition-metal oxide (TMO) composites with tailored nanostructures and precise components is essential for their application. Herein, a general mercaptosilane-assisted one-pot coassembly approach is developed to synthesize ordered mesoporous TMOs with agglomerated-free noble metal nanoparticles, including Au/WO₃ , Au/TiO₂ , Au/NbO_x , and Pt/WO₃ . 3-mercaptopropyl trimethoxysilane is applied as a bridge agent to cohydrolyze with metal oxide precursors by alkoxysilane moieties and interact with the noble metal source (e.g., HAuCl₄ and H₂ PtCl₄ ) by mercapto (SH) groups, resulting in coassembly with poly(ethylene oxide)-b-polystyrene. The noble metal decorated TMO materials exhibit highly ordered mesoporous structure, large pore size (≈14-20 nm), high specific surface area (61-138 m² g^-1 ), and highly dispersed noble metal (e.g., Au and Pt) nanoparticles. In the system of Au/WO₃ , in situ generated SiO₂ incorporation not only enhances their thermal stability but also induces the formation of ε-phase WO₃ promoting gas sensing performance. Owning to its specific compositions and structure, the gas sensor based on Au/WO₃ materials possess enhanced ethanol sensing performance with a good response (R_air /R_gas = 36-50 ppm of ethanol), high selectivity, and excellent low-concentration detection capability (down to 50 ppb) at low working temperature (200 °C).

Highly sensitive ethanol gas sensor based on ultrathin nanosheets assembled Bi2WO6 with composite phase

Bismuth tungstate (Bi₂WO₆) has many intriguing properties and has been the focus of studies in a variety of fields, especially photocatalysis. However, its application in gas-sensing has been seldom reported. Here, we successfully synthesized assembled hierarchical Bi₂WO₆ which consists of ultrathin nanosheets with crystalline-amorphous composite phase by a one-step hydrothermal method. X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM) techniques were employed to characterize its composition, morphology, and microstructure. By taking advantage of its unique microstructure, phase composition, and large surface area, we show that the resulting Bi₂WO₆ is capable of detecting ethanol gas with quick response (7 s) and recovery dynamic (14 s), extremely high sensitivity (R_a/R_g = 60.8@50 ppm ethanol) and selectivity. Additionally, it has excellent reproducibility and long-term stability (more than 50 d). The Bi₂WO₆ outperform the existing Bi₂WO₆-based and most of the other state-of-the-art sensing platforms. We not only provided one new member to the field of gas sensor, but also offered several strategies to reconstruct nanomaterials.

Crystal-Defect-Dependent Gas-Sensing Mechanism of the Single ZnO Nanowire Sensors

Though the chemical origin of a metal oxide gas sensor is widely accepted to be the surface reaction of detectants with ionsorbed oxygen, how the sensing material transduces the chemical reaction into an electrical signal (i.e., resistance change) is still not well-recognized. Herein, the single ZnO NW is used as a model to investigate the relationship between the microstructure and sensing performance. It is found that the acetone responses arrive at the maximum at the NW diameter ( D) of ∼110 nm at the D range of 80 to 400 nm, which is temperature independent in the temperature region of 200 °C-375 °C. The electrical properties of the single NW field effect transistors illustrate that the electron mobility decreases but electron concentration increases with the D ranging from ∼60 nm to ∼150 nm, inferring the good crystal quality of thinner ZnO NWs and the abundant crystal defects in thicker NWs. Subsequently, the surface charge layer ( L) is calculated to be a constant of 43.6 ± 3.7 nm at this D range, which cannot be explained by the conventional D- L model in which the gas-sensing maximum appears when D approximates 2 L. Furthermore, the crystal defects in the single ZnO NW are probed by employing the microphotoluminescence technique. The mechanism is proposed to be the compromise of the two kinds of crystal defects in ZnO (i.e., more donors and fewer acceptors favor the gas-sensing performance), which is again verified by the gas sensors based on the NW contacts.

Ultrathin In2O3 Nanosheets with Uniform Mesopores for Highly Sensitive Nitric Oxide Detection

Nitric oxide (NO_x, including NO and NO₂) is one of the most dangerous environmental toxins and pollutants, which mainly originates from vehicle exhaust and industrial emission. The development of sensitive NO_x gas sensors is quite urgent for human health and the environment. Up to now, it still remains a great challenge to develop a NO_x gas sensor, which can satisfy multiple application demands for sensing performance (such as high response, low detection temperature, and limit). In this work, ultrathin In₂O₃ nanosheets with uniform mesopores were successfully synthesized through a facile two-step synthetic method. This is a success due to not only the formation of two-dimensional (2D) nanosheets with an ultrathin thickness of 3.7 nm based on a nonlayered compound but also the template-free construction of uniform mesopores in ultrathin nanosheets. The sensors based on the as-obtained mesoporous In₂O₃ ultrathin nanosheets exhibit an ultrahigh response (R_g/R_a = 213) and a short response time (ca. 4 s) toward 10 ppm NO_x, and a quite low detection limit (10 ppb NO_x) under a relatively low operating temperature (120 °C), which well satisfies multiple application demands. The excellent sensing performance should be mainly attributed to the unique structural advantages of mesopores and 2D ultrathin nanosheets.

Facile synthesis of nanoparticle packed In2O3 nanospheres for highly sensitive NO2 sensing

Nanoparticle packed In₂O₃ nanospheres are successfully synthesized via a facile one-step solvothermal method followed by annealing.

Surface chemistry and stability of metastable corundum-type In2O3

Highly correlated surface- and electrochemical characterization is linked to the metastability of rh-In₂O₃ for explanation of sensing and catalytic properties.

Assembly of 3D flower-like NiO hierarchical architectures by 2D nanosheets: synthesis and their sensing properties to formaldehyde

NiO flower-like hierarchical architectures were synthesized by a solvothermal route, which exhibited good formaldehyde gas sensing performance. The effect of reaction time and ethanol/water volume ratio on morphologies was investigated and a synthesis mechanism was proposed.

Designed Synthesis of In₂O₃ Beads@TiO₂-In₂O₃ Composite Nanofibers for High Performance NO₂ Sensor at Room Temperature

Porous single crystal In2O3 beads@TiO2-In2O3 composite nanofibers (TINFs) have been prepared via a facile electrospinning method. The beads were formed because of the existence of hemimicelles in pecursor solution. The formation of hemimicelles was attributed to the synergy of tetrabutyl titanate (TBT) and polyvinylpyrrolidone (PVP). Abundant In(3+) ions were drawn toward the ketonic oxygen of PVP resulting in In(3+) ions aggregation. Compared with pristine In2O3 nanofibers (INFs), the as-prepared TINFs exhibited excellent properties for sensing NO2 gas at room temperature (25 °C). The enhanced sensing property was due to much absorbed oxygen and Schottky junctions between the porous single crystal In2O3 beads and the Au electrode of the sensor. The strategy for combining the unique In2O3 beads@TiO2-In2O3 nanofibers structure which possessed superior conductivity and sufficient electrons with the addition of TiO2 offered an innovation to enhance the gas sensing performance.