Single step hydrothermal synthesis of beyerite, CaBi2O2(CO3)2 for the fabrication of UV-visible light photocatalyst BiOI/CaBi2O2(CO3)2

Abstract

The mineral beyerite (CaBi₂O₂(CO₃)₂), a member of the “sillen” family possessing a layer sequence, (Bi₂O₂)²⁺–CO₃²⁻–Ca²⁺–CO₃²⁻–(Bi₂O₂)²⁺ has successfully been synthesized under hydrothermal conditions in a single step for the first time. Uniform rectangular plates of beyerite crystallites with a surface area of 33 m² g⁻¹ were obtained by heating a solution containing bismuth nitrate and calcium carbonate in ethylene glycol along with the addition of a saturated solution of sodium carbonate at 140 °C. The sample was characterized by powder X-ray diffraction combined with Rietveld refinement, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectra and diffuse reflectance measurements. The band gap estimated for beyerite was found to be 3.97 eV and was utilized subsequently to form heterostructure with BiOI (band gap of 1.76 eV), another member belonging to the sillen family. The formation of the composite BiOI/CaBi₂O₂(CO₃)₂ has been confirmed by a variety of techniques and its photocatalytic properties as a UV-visible photocatalyst has been demonstrated for the degradation of aqueous solutions of rhodamine B and phenol. Photocatalytic experiments in presence of scavengers suggested the possible mechanism occurring through holes and peroxide radicals rather than the hydroxyl radicals.