Preparation of Cu2O nano-colloid and its application as selective colorimetric sensor for Ag ion

Current work reports a method of preparation of stable yellow copper (I) oxide, nano-colloid by a solution route using Cu (II) salt solution and sodium borohydride. The reduction process was carried out in a controlled manner in air at around 50 °C in the presence of alginate matrix. The nanophase was characterized by techniques such as electronic spectroscopy, infrared spectroscopy, powder X-ray diffraction and transmission electron microscopy. Sensor property of the colloid for the detection of metal ions such as Ag⁺, Na⁺, K⁺, Ca²⁺, Pb²⁺, Cd²⁺, Zn²⁺, Hg²⁺, Mg²⁺ and As⁵⁺ has been studied at room temperature. A distinct color change from yellow to dark brown was noticed in the case of Ag⁺ ion. This is associated with a shift in ‘λ_max’ value from 448 nm to 478 nm. Whereas, no such significant visible color change was noticed on the addition of solutions containing other metal ions. Thus, in the present study Cu₂O nano-colloid was demonstrated as a highly specific and selective liquid colorimetric sensor for Ag⁺ ion.