Effect of Zinc Oxide Modification by Indium Oxide on Microstructure, Adsorbed Surface Species, and Sensitivity to COстатья
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Дата последнего поиска статьи во внешних источниках: 21 мая 2019 г.
Аннотация:Additives in semiconductor metal oxides are commonly used to improve sensing
behavior of gas sensors. Due to complicated effects of additives on the materials
microstructure, adsorption sites and reactivity to target gases the sensing mechanism
with modified metal oxides is a matter of thorough research. Herein, we establish the
promoting effect of nanocrystalline zinc oxide modification by 1–7 at.% of indium on
the sensitivity to CO gas due to improved nanostructure dispersion and concentration
of active sites. The sensing materials were synthesized via an aqueous coprecipitation
route. Materials composition, particle size and BET area were evaluated using
X-ray diffraction, nitrogen adsorption isotherms, high-resolution electron microscopy
techniques and EDX-mapping. Surface species of chemisorbed oxygen, OH-groups, and
acid sites were characterized by probe molecule techniques and infrared spectroscopy.
It was found that particle size of zinc oxide decreased and the BET area increased
with the amount of indium oxide. The additive was observed as amorphous indium
oxide segregated on agglomerated ZnO nanocrystals. The measured concentration of
surface species was higher on In2O3-modified zinc oxide. With the increase of indium
oxide content, the sensor response of ZnO/In2O3 to CO was improved. Using in situ
infrared spectroscopy, it was shown that oxidation of CO molecules was enhanced on
the modified zinc oxide surface. The effect of modifier was attributed to promotion of
surface OH-groups and enhancement of CO oxidation on the segregated indium ions,
as suggested by DFT in previous work.