Zeolitic Imidazolate Framework Coated ZnO Nanorods as Molecular Sieving to Improve Selectivity of Formaldehyde Gas Sensor

Abstract

Zinc oxide (ZnO) and zeolitic imidazolate framework-8 (ZIF–8) core–shell heterostructures were obtained by using the self-template strategy where ZnO nanorods not only act as the template, but also provide Zn2+ ions for the formation of ZIF–8 shell. The ZIF–8 shell was uniformly deposited to form ZnO@ZIF–8 nanorods with core–shell heterostructures at 70 °C for 24 h as the optimum reaction time by the hydrothermal synthesis. Transmission electron microscopy (TEM) images revealed that the ZnO@ZIF–8 heterostructures are composed of ZnO as core and ZIF–8 as shell. Nitrogen (N2) sorption isotherms demonstrated that the as-prepared ZnO@ZIF–8 nanorods are a typical microporous material. Additionally, the ZnO@ZIF–8 nanorods sensor exhibited distinct gas response for reducing gases with different molecule sizes. The selectivity of the ZnO@ZIF–8 nanorods sensor was obviously improved for the detection of formaldehyde owing to the limitation effect of the aperture of ZIF–8 shell. This study demonstrated that semiconductor@MOF core–shell heterostructures may be a novel way to enhance the selectivity of the gas sensing materials.

Surfactant-assisted ZnO processing as a versatile route to ZIF composites and hollow architectures with enhanced dye adsorption

“…By contrast, in a growth dominated process the intergrowth of larger ZIF-8 crystals would eventually mask the shape of the underlying template, and while not apparently a major factor for ZnO microspheres this becomes very important for non-spherical and down-sized oxide templates. In practise, the amount of C 12 Gua surfactant, metal:linker ratio and solvent need to be balanced in order to obtain the desired shape and required level of oxide-to-MOF conversion through fine-tuning of the chemical potential of the framework building blocks relative to the rate of framework growth [18][19][20][21][22] . In the present case we clearly demonstrate that using a C 12 Gua amphiphile that nanoscale ZnO and templates with more complex morphology can also be directly transformed to coreshell ZnO@ZIF-8 composites in water only, whereas all previous studies tend to use alcohol or aqueous-DMF mixtures [18][19][20][21][22] .…”

“…The ZnO@ZIF-8 composites have also been used as sensors where bulk core-shell nanorods can be used for the selective electrochemical detection of volatile organic compounds including formaldehyde 19 , and ZnO@ZIF-8 nanorod arrays for the photoelectrochemical detection of hydrogen peroxide 20 . Pd nanoparticles supported on ZnO it is noted that often only a very narrow range of conditions give rise to only the desired core-shell structures.…”

Green light activated hydrogen sensing of nanocrystalline composite ZnO-In2O3 films at room temperature

“…As early reported, metal oxides composites 11–15 and particularly ZnO-In 2 O 3 composites 16–19 exhibit the enhanced gas sensitivity to reducing gases. However, the effect of visible illumination on the sensitivity of ZnO-In 2 O 3 composites to reducing gases was not investigated.…”

The Effect of Zeolite Composition and Grain Size on Gas Sensing Properties of SnO2/Zeolite Sensor

“…A lot of research has focused on how to improve the selectivity of gas sensors. Various methods including temperature control, doping noble metal and addition of filter layer may be used to improve sensor selectivity [11,12,13,14,15,16]. Among them, the addition of filter layer is the lowest cost and most convenient method.…”