Hybrid nanoarchitecturing of hierarchical zinc oxide wool-ball-like nanostructures with multi-walled carbon nanotubes for achieving sensitive and selective detection of sulfur dioxide

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>This work reports a facile glycerol-assisted solvothermal method for synthesizing hierarchical three-dimensional (3D) wool-ball-like zinc oxide (ZnO) nanostructures and their subsequent modifications with multi-walled carbon nanotubes (MWCNTs) as modifiers for achieving sensitive and selective detection of toxic sulfur dioxide (SO<SUB>2</SUB>) gas. Structurally, the as-synthesized 3D wool-ball-like ZnO is assembled of two-dimensional (2D) plate-like structures, which themselves are arranged by numerous small nanoparticles. Furthermore, in this work we observed an interesting new phenomenon in which when a high concentration of MWCNTs is introduced, many small nanorods grew on the surface of the plate-like structures which assemble the 3D wool-ball-like ZnO nanostructures. When evaluated for SO<SUB>2</SUB> detection, the ZnO/MWCNTs (10:1) composite (ZnO:MWCNTs = 10:1) shows a high response of 220.8 to 70 ppm of SO<SUB>2</SUB> gas (approximately three times higher than the response of pure wool-ball-like ZnO) at an optimum operating temperature of 300 °C. Additionally, the composite also displays good stability and selectivity to SO<SUB>2</SUB> with the response to 50 ppm of SO<SUB>2</SUB> being 7–14 times higher than the responses to other tested gases at a similar concentration. The excellent sensing performance of the wool-ball-like ZnO/MWCNTs (10:1) composite is mainly attributed to: (i) the formation of <I>p</I>-<I>n</I> heterojunctions at the ZnO/MWCNTs interfaces, which greatly enhance the resistance changes upon exposure to SO<SUB>2</SUB> gas and (ii) the increased amount of adsorption sites for O<SUB>2</SUB> and SO<SUB>2</SUB> gas molecules owing to the larger surface area of the composite and defects sites generated by the functionalization process of MWCNTs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hierarchical 3D wool-ball-like ZnO nanostructures were synthesized via a solvothermal method. </LI> <LI> 3D wool-ball like ZnO/MWCNT composites with different ratios (3:1, 5:1, and 10:1) were prepared. </LI> <LI> The 3D wool-ball like ZnO/MWCNT composite showed high response and good selectivity to SO<SUB>2</SUB> gas. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>