Pure and doped γ-Al 2 O 3 by metal oxides including SnO 2 , ZrO 2 , CeO 2 and MgO were used as the supports of the combustion catalysts. The Al 2 O 3 based supports doped with the metal oxides were prepared by coprecipitation method. The noble metal Pd with 15 wt% loading amount was then loaded on the as-prepared supports using isometric impregnation. The measuring results of Brunauer-Emmett-Teller-specific surface areas revealed that the specific surface areas of supports have been improved to a certain extent by doping of metal oxides. The measurement of gas sensing properties showed that the metal oxides have great influences on the sensitivity to CH 4 . The sensing performance of catalytic combustion methane sensors had been improved by doping SnO 2 , ZrO 2 , CeO 2 or MgO in Al 2 O 3 .
Abstract Immobilization of fragile enzymes in a suitable support material provides new opportunities to improve the performance of immunosensor, but construction remains challenging due to the dimensional limitation or denaturation during the process. Herein, an enzyme‐engineered assembly strategy that enables the in situ fusion of enzymes into the framework structure during the crystal formation process via the covalent‐polymerization‐permeation mechanism is demonstrated, utilizing the dynamic covalent chemistry property of covalent organic frameworks (COFs‐PB). By finely regulating the assembling order of building blocks, enzyme‐COFs composite with the spatial distribution structure of the enzyme (such as uniform, sub‐surfaces, or interface) can be evolved, featuring controllable activity and structural stability. Impressively, the apparent enzymatic kinetics of the enzyme can be well maintained after encapsulation in COFs‐PB, and enzyme@COFs‐PB composite has shown outstanding stability in strongly acidic environments. Benefiting from structural integration, a robust enzyme@COFs‐PB‐based immunosensor is built for the sensitive detection of isocarbophos pesticide, which performed a 56‐fold enhancement in sensitivity compared with that of the standard immunosensor. This study gives valuable insight into a comprehensive understanding of the interfacial interactions between enzymes and COFs in designing ideal biocatalytic nanosystems, providing important guidance for the development of advanced immunosensors in on‐site application.
Metal-organic framework (MOF)-derived metal oxide semiconductors have received significant attention for gas sensing applications. Herein, we reported core-shell In2O3@ZnO n-n heterostructures by depositing ZIF-8 derivative onto wrinkled In2O3 sphere, realizing the control of ZnO shell thickness (12.6-72.4 nm) through controlling MOF growth time. Due to the formation of n-n heterojunction at the core-shell interface, the tuning of shell thickness can lead to the radial modulation of the electron-accumulation layer in ZnO, and realizing the control of free charge carrier concentration that participated in gas sensing reaction. What’s more, the MOF-derived ZnO shell with rich oxygen vacancies is beneficial for oxygen chemisorption. Accordingly, compared with the In2O3 based sensor, the In2O3@ZnO based sensor exhibited higher sensitivity to trace-level acetone (100 ppb), faster response time (2 s vs. 100 ppm), better selectivity, and stronger anti-humidity capacity at operating temperature 300 °C, while the thickness of ZnO shell is 55.3 nm. In addition, the increase of ZnO shell thickness can lead to the selectivity change from ethanol to acetone of In2O3@ZnO owing to the inherent catalytic oxidation activity. Thus, the remarkable performance of the In2O3@ZnO sensor mainly relies on ZnO shell layer.
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