Template free hydrothermal synthesis and gas sensing application of lanthanum cuprate (La2CuO4): Effect of precursors on phase formation and morphology

Highlights: • Template free hydrothermal synthesis of electrically conducting lanthanum cuprate. • The types of precursors affect the morphologies of the products. • The product formation has been elucidated by XRD and TG analysis. • Lanthanum cuprate shows positive response for toxic (CO and NO) gases. -- Abstract: Orthorhombic lanthanum cuprate (La2CuO4) has been obtained with various morphologies when synthesized in presence of different precursors (nitrate, acetate and chloride) by hydrothermal method at 140 °C. Influence of various parameters such as molar ratio of precursors (1:1, 2:1 and 1:2) and precursors to hydrolyzing agent (from 1:5 to 1:17) has been investigated. The metal–oxygen (M–O), M–OH and other bond frequencies along with the probable products formed at every stage of calcination (200–900 °C) have been assigned using fourier transform infrared spectroscopy. A suitable reaction mechanism involved in the product formation has been proposed with the help of X-ray diffraction and thermogravimetric analysis of the samples. Pure phase lanthanum cuprate were obtained after calcining the hydrothermally activated products at 800 °C for 6 h. Cubic, spherical and porous rod like structures were revealed from the scanning electron microscopic analysis of the samples. The La:Cu atomic ratio of 2:1 for the pure phase product was confirmed by inductively coupled plasma atomic emission spectroscopy. High surface areas (23.6 and 20.9 m2 g−1) of products were revealed from the Brunauer–Emmett–Teller surface area analysis. The samples bear good electrical conductivity at room temperature and exhibit response to carbon monoxide and nitric oxide gases