鉑與四氧化三鈷修飾氧化銦奈米結構於室溫一氧化碳感測之增益效應

Abstract

本研究設計並成功以多步驟化學法合成一系列新穎之Co3O4與Pt奈米粒子雙重修飾In2O3階層式奈米結構，用以發展低能耗室溫型CO氣體感測器。作為氣體感測之In2O3基材，是由無數In2O3奈米粒子自組裝而成之花狀三維奈米組裝體，具有極高之表體比，除可大幅增加氣體分子吸附位置外，更可加速氣體之擴散。Pt奈米粒子則可產生接面電子效應與化學催化效應促進氣體分子吸附與脫附反應，進而大幅降低氣感材料之工作溫度。而Co3O4為一P型氧化物，與N型氧化物In2O3接合後會產生P-N接面，形成空乏區，進而提升感測靈敏度，再加上其具有低Co-O鍵能、高氧氣解離能力、及高CO氣體分子吸附效率等特性，可進一步強化感測效能。結果發現，Pt奈米粒子修飾之花狀In2O3奈米結構在室溫下感測100 ppm CO靈敏度高達12，響應時間為100秒。而Co3O4/Pt奈米粒子雙重修飾之In2O3奈米結構於室溫下所有CO濃度之感測靈敏度皆高於Pt奈米粒子單一修飾In2O3奈米結構，且靈敏度之增益效應於極低濃度之CO氣氛下更為明顯，於5 ppm之CO氣氛下仍可維持靈敏度高達3，遠高於Pt奈米粒子修飾之花狀In2O3奈米結構近於1之靈敏度。充份証明Co3O4與Pt奈米粒子之雙重修飾確實能有效增益室溫下之CO氣體感測能力。

In this study, we newly design and successfully synthesized a serious of innovative Co3O4 and Pt nanoparticles co-decorated In2O3 hierarchical nanostructures via multi-step facile chemical approaches for developing low-energy-consumption room-temperature CO gas nanosensors. The synthesized flower-like In2O3 nanoassembles, as the base oxide material of the present gas sensors comprising numerous self-assembled In2O3 nanoparticles, exhibit a very high surface-to-volume ratio and are expected provide not only to a great amount of reaction sites for the targeting gas molecules, but cross-linked open channels for inward and outward gas diffusion. Pt nanoparticles could significantly lower the operating temperature required via the two key mechanisms, namely the catalytic effects raised from the tiny Pt nanoparticles themselves, and the electric effect induced by the direct contact between Pt and In2O3. The decoration of p-type Co3O4 on the n-type In2O3 nanoassembly could form functional P-N junctions which are theoretically and experimentally proven to form depletion regions and thus to enhance the sensitivity. In addition, the relatively lower Co-O bonding energy, the high capability to activate oxygen, and the higher adsorption efficiency of CO molecules would be beneficial for further improving the CO sensing performance. A very high sensitivity up to 12 is found at 100 ppm CO at room temperature for the optimized Pt nanoparticles decorated flower-like In2O3 nanostructures and the response time is about 100 s. It is worthy emphasizing that the sensitivity for the Pt-Co3O4 co-decorated In2O3 nanostructures is always higher than that for the Pt nanoparticles decorated ones under the same sensing conditions. In addition, the enhancement in sensitivity increases with the decreasing of CO concentration and the sensitivity at 5 ppm CO approximates to 3 which is much higher than that of close to 1 for Pt decorated In2O3 nanostructures. The present results evidently indicate that the co-decoration of Pt and Co3O4 nanoparticles on In2O3 nanostructures indeed an effective strategy for advance gas nanosensor in the next generation.