Optical and photocatalytic properties of undoped and Ca doped NaNbO3

Abstract

The adverse effect of growing industrialization has resulted in many environmental, economical and social problems such as global warming etc. To protect the environment and also to resolve these issues, it is necessary to find some good and highly efficient techniques for the treatment of waste water and harmful substances. In order to address these, some catalytic processes have been developed. Among all the known materials, peroveskite ABO3 type of structures viz. NaNbO3 holds special importance because of its nontoxic nature and high photocatalytic properties which can be used for dye degradation, CO2 conversion and hydrogen generation. It also exhibits ferroelectric and piezoelectric properties. In the present study, undoped and Ca-doped (0.5%2.0%,4.0%,6.0%) sodium niobate nanoparticles have been synthesized through chemical precipitation method using ammonium niobate oxalate hydrate (C4H4NNbO9.xH2O) and sodium sulphide (Na2S) as niobium and sodium source, respectively. Various experiments were performed by varying the molar ratio (1:1,1:2,1:5,1:10,1:15,1:20,1:25) at different temperatures (600,700 and 800˚C) for the holding time of 5h. The phase composition, band gap and morphology are investigated by using X-ray diffraction (XRD), UV-visible spectroscopy, field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) respectively. XRD and electron microscopy confirmed the formation of faceted orthorhombic NaNbO3 at 800˚C with the average crystallite size of 23.43 nm. UV–visible absorption spectroscopy showed the optical band gap 3.44 eV and 3.24 for undoped and Ca doped NaNbO3, respectively. Synthesized nanoparticles were used as a photocatalyst to study the photocatalytic degradation of methylene blue dye under visible radiation. Firstly, the concentration of photocatalyst (undoped NaNbO3) has been optimized to degrade 400 mg/L in solution of MB dye (1 mg/L). Now, the degradation of MB dye has been studied with undoped, Ca doped NaNbO3 nanoparticles. From the results, it has been found that Ca doping concentration of 1.0% is optimal for its higher photo physical and photocatalytic properties. Catalyst shows the maximum photo degradation of MB dye in 6h under visible radiation.