Continuous and Ultrafast Preparation of In(OH)3, InOOH, and In2O3 Series in a Microreactor for Gas Sensors

Polyoxometalate-Complexed Indium Hydroxide: Atomically Homogeneous Impregnation via Countercation Exchange

Metal hydroxides catalyze organic transformations and photochemical processes and serve as precursors for the oxide layers of functional multicomponent devices. However, no general methods are available for the preparation of stable water-soluble complexes of metal hydroxide nanocrystals (NCs) that might be more effective in catalysis and serve as versatile precursors for the reproducible fabrication of multicomponent devices. We now report that In^III-substituted monodefect Wells-Dawson (WD) polyoxometalate (POM) cluster anions, [α₂-P₂W₁₇O₆₁In^IIIOH)]^8-, serve as ligands for stable, water-soluble complexes, 1, of platelike, predominantly cubic-phase (dzhalindite) In(OH)₃ NCs that after optimization contain ca. 10% InOOH. Images from cryogenic tranmsission electron microscopy reveal numerous WD ligands at the surfaces of platelike NCs, with average dimensions of 17 × 28 × 2 nm, each complexed by an average of ca. 450 In^III-substituted WD cluster anions and charge-balanced by 3600 Na⁺ countercations. Facilitated by the water solubility of 1, countercation exchange is used to stoichiometrically disperse ca. 1800 Cu²⁺ ions in an atomically homogeneous fashion around the surfaces of each NC core. The utility of this impregnation method is illustrated by using the ion-exchanged material as an electrocatalyst that reduces CO₂ to CO 15 times faster per milligram of Cu than does K₆Cu[P₂Cu^II(H₂O)W₁₇O₆₁] (control) alone. More generally, the findings point to POM complexation as a promising method for stabilizing and solubilizing reactive d-, p-, and f-block metal hydroxide NCs and for enabling their utilization as versatile components in the fabrication of functional multicomponent materials.

Monolithically Integrated Diffused Silicon Two-Zone Heaters for Silicon-Pyrex Glass Microreactors for Production of Nanoparticles: Heat Exchange Aspects

We present the design, simulation, fabrication and characterization of monolithically integrated high resistivity p-type boron-diffused silicon two-zone heaters in a model high temperature microreactor intended for nanoparticle fabrication. We used a finite element method for simulations of the heaters’ operation and performance. Our experimental model reactor structure consisted of a silicon wafer anodically bonded to a Pyrex glass wafer with an isotropically etched serpentine microchannels network. We fabricated two separate spiral heaters with different temperatures, mutually thermally isolated by barrier apertures etched throughout the silicon wafer. The heaters were characterized by electric measurements and by infrared thermal vision. The obtained results show that our proposed procedure for the heater fabrication is robust, stable and controllable, with a decreased sensitivity to random variations of fabrication process parameters. Compared to metallic or polysilicon heaters typically integrated into microreactors, our approach offers improved control over heater characteristics through adjustment of the Boron doping level and profile. Our microreactor is intended to produce titanium dioxide nanoparticles, but it could be also used to fabricate nanoparticles in different materials as well, with various parameters and geometries. Our method can be generally applied to other high-temperature microsystems.

ZnO-Decorated In/Ga Oxide Nanotubes Derived from Bimetallic In/Ga MOFs for Fast Acetone Detection with High Sensitivity and Selectivity

The development of acetone gas sensors is desirable but challenging for both air quality monitoring and medical diagnosis. Herein, starting from bimetallic In/Ga metal-organic frameworks (MOFs) (MIL-68 (In/Ga)), a facile strategy is proposed to couple with zinc ions to design In/Ga oxide (IGO)@ZnO core-shell nanotubes for efficient acetone detection. In such a heterostructure, tiny ZnO nanoparticles are closely decorated on IGO nanotubes, which is beneficial to enlarge the specific surface area and create rich oxygen vacancies and heterojunction interfaces. Benefiting from the structural merits and synergetic effects, the IGO@ZnO-based gas sensor exhibits a low detection limitation (200 ppb), a high response, good linearity relationship between the sensing responses and wide testing acetone concentrations, and fast response and recovery time (6.8/6.1 s) with good selectivity and stability. These sensing performances strongly indicate the practical application to quantitatively detect acetone.