Surfactant-assisted synthesis, characterizations, and room temperature ammonia sensing mechanism of nanocrystalline CuO

CuO nanocrystalline powder has been synthesized by a sol‒gel auto combustion route with cetyltrimethylammonium bromide (CTAB) as cationic surfactant, and sodium dodecyl sulphate (SDS) as anionic surfactant. The powder samples are characterized by TGA/DTA, XRD, FESEM, and TEM techniques. Thermal analysis of the dried gel samples shows that addition of surfactant in the precursor increases the heat of reaction, which is evolved in the decomposition of metal citrate complex. The CTAB and SDS addition in the reaction mixture lowers the average crystallite size to few tens of nanometer. Surfactant doping in precursor causes a variation in lattice strain and changes to its type to compressive. CuO nanoparticles are bound together into facets–like weakly aggregated clusters, as indicated by FESEM images. TEM micrographs indicate the porous, nearly spherical particles having crystallite size around 7 and 18 nm for CTAB and SDS surfactant assisted CuO samples respectively. CuO nanoparticles assembled as thick film have been tested for their response to 100 ppm ammonia gas at room temperature. Cationic surfactant assisted sample shows maximum response to ammonia as compared to anionic surfactant. The CTAB assisted sensor shows almost completes recovery in 500 s whereas SDS assisted sample shows 75% recovery in the same time. The ammonia response of the films obeys the Elovich equation. The response rate of sensor is found to be maximum for CTAB assisted CuO films as compared to other samples. The kinetics of the response reaction shows that the ionic surfactants assisted CuO follows second order reaction kinetics.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis of CuO nanoparticles by a surfactant modified sol-gel auto combustion. ► Comparison of results obtained for cationic (CTAB) and anionic (SDS) surfactants. ► CTAB assisted CuO nanoparticles shows better sensing for ammonia. ► The 2nd order reaction kinetics for ammonia gas adsorption follows Elovich Model.