摘要
以甲醇为溶剂,静置沉淀法合成Co掺杂的ZIF(zeolitic imidazolate framework)-8,将其在管式炉中空气氛围下退火得到多面体双壳层Co_(3)O_(4)-ZnO.通过X射线衍射仪(Xray diffraction,XRD)、扫描电子显微镜(scanning electron microscope,SEM)、透射电子显微镜(transmission electron microscope,TEM)、热重分析仪(thermal gravimetric analyzer,TGA)手段对合成材料的组成、形貌和热稳定性进行了表征.结果表明,纯ZIF-8在较低的退火温度下保持稳定,更高温度的退火使ZIF-8生成结构坍塌的ZnO.4%Co掺杂的ZIF-8在较低温度下退火后得到多面体双壳结构的Co_(3)O_(4)-ZnO(CZO-4),表明Co在ZIF-8的氧化过程中提供了催化氧化的活性位点,降低了2-甲基咪唑的氧化反应能垒.同时,较低的退火温度给予ZnO充分的成型时间,使其保持菱形十二面体结构而不坍塌.由Co元素催化由外而内的氧化生长过程,最终使ZnO生长为双壳层结构.而将Co的载量提高到8%,得到的双壳层则变得不明显(CZO-8).在对CO气敏测试结果分析中发现,相对于CZO-8和ZnO,CZO-4具有更优异的CO传感性能,具有高灵敏度(R_(a)/R_(g)=21.8@100×10^(-6)CO)、高选择性(达到H_(2)灵敏度的8.7倍)和长期稳定性(在42 d测试中信号平稳).这是由于CZO-4具有较大的比表面积和气体传输通道,以及Co作为活性位点对CO催化氧化作用带来的气敏性能的提升.
Herein,Co-doped ZIF(zeolitic imidazolate framework)-8 was synthesised via static precipitation method using methanol as solvent.The synthesised ZIF-8 was subsequently annealed under air atmosphere in a tubular furnace,yielding polyhedral bi-shell Co_(3)O_(4)-ZnO.The composition,morphology,and thermal stability of the synthesised materials were characterised via X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),and thermal gravimetric analyzer(TGA).Results show that the pure ZIF-8 remained stable at relatively low annealing temperature,whereas at higher annealing temperature,ZIF-8 transformed to a collapsed ZnO structure.The polyhedral bi-shell Co_(3)O_(4)-ZnO(CZO-4)was obtained by annealing 4%Co-doped ZIF-8 at a low temperature,suggesting that Co provides an active site for catalytic oxidation during the oxidation of ZIF-8 and reduces the oxidation barrier of 2-methylimidazole.Meanwhile,the low annealing temperature can provide sufficient forming process for ZnO to retain the rhombic dodecahedron structure.The oxidation growth process,catalysed by Co element,from outside to inside eventually results in the growth of ZnO into the bi-shell structure.When the Co loading is increased to 8%,the formation of bi-shell layer is not obvious(CZO-8).Compared with CZO-8 and ZnO,CZO-4 has better CO sensing performance,high sensitivity(R_(a)/R_(g)=21.8@100×10^(-6)CO),high selectivity(up to 8.7 times of H_(2)response),and long-term stability(stable signal in 42-day tests).This is because CZO-4 has a large specific surface area,gas transport channels,and Co as an active site for CO catalytic oxidation,resulting in an enhancement in gas sensing performance.
作者
袁同伟
张文爽
马志恒
徐甲强
YUAN Tongwei;ZHANG Wenshuang;MA Zhiheng;XU Jiaqiang(College of Sciences,Shanghai University,Shanghai 200444,China)
出处
《上海大学学报(自然科学版)》
CAS
CSCD
北大核心
2021年第5期866-878,共13页
Journal of Shanghai University:Natural Science Edition
基金
上海市科委重大专项计划项目(U1704255)
关键词
ZIF-8
CO掺杂
催化氧化
双壳层结构
气敏性质
CO传感
ZIF(zeolitic imidazolate framework)-8
Co doping
catalytic oxidation
bishell structure
gas sensing properties
CO sensing