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

• 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.

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.