Monoclinic bismuth oxide α-Bi2O3 nanoparticles were synthesized starting from a mixture of oxalate complexes of bismuth Bi(C2O4)OH and Bi2(C2O4)3·xH2O obtained by a direct solid-state reaction between a nitrate salt of bismuth and oxalic acid. The starting oxalate mixture precursors were studied by thermal gravimetric analysis (TGA) and characterized by Fourier transform infrared spectroscopy (FTIR). After heat treatment of the oxalate precursors, the obtained oxide α-Bi2O3 was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). These α-Bi2O3 nanoparticles show low efficiency in photodegradation under UV light irradiation of the dye rhodamine B

Nickel molybdate (NiMoO₄) nanoparticles were synthesized via calcination of an oxalate complex in static air at 500 °C. The oxalate complex was analyzed by thermal gravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). The as-synthesized nickel molybdate was characterized by Brunauer–Emmett–Teller technique (BET), X-ray diffraction (XRD), and transmission electron microscopy (TEM) and its catalytic efficiency was tested in the reduction reaction of the three-nitrophenol isomers. The nickel molybdate displays a very high activity in the catalytic reduction of the nitro functional group to an amino. The reduction progress was controlled using Ultraviolet-Visible (UV-Vis) absorption.

Zinc molybdate (ZnMoO₄) was prepared by thermal decomposition of an oxalate complex under a controlled temperature of 500 °C. Analyses of the oxalate complex were carried out using Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). On the other hand, analyses of the synthesized zinc molybdate were carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller technique (BET). The efficiency of the synthesized catalyst was tested with the reduction reaction of 3-nitrophenol (3-NP), and was also applied as a sorbent for methylene blue dye (MB) in aqueous solutions. The catalytic test of zinc molybdate shows a very high activity. The concentration reduction progress and adsorption of the dye were followed by an ultraviolet-visible (UV-vis) spectrophotometer.

Nano Molybdenum trioxide (α-MoO₃) was synthesized in an easy and efficient approach. The removal of methylene blue (MB) in aqueous solutions was studied using this material. The effects of various experimental parameters, for example contact time, pH, temperature and initial MB concentration on removal capacity were explored. The removal of MB was significantly affected by pH and temperature and higher values resulted in increase of removal capacity of MB. The removal efficiency of Methylene blue was 100% at pH = 11 for initial dye concentrations lower than 150 ppm, with a maximum removal capacity of 152 mg/g of MB as gathered from Langmuir model. By comparing the kinetic models (pseudo first-order, pseudo second-order and intraparticle diffusion model) at various conditions, it has been found that the pseudo second-order kinetic model correlates with the experimental data well. The thermodynamic study indicated that the removal was endothermic, spontaneous and favorable. The thermal regeneration studies indicated that the removal efficiency (99%) was maintained after four cycles of use. Fourier Transform Infrared (FTIR) and Scanning Electron Microscopy (SEM) confirmed the presence of the MB dye on the α-MoO₃ nanoparticles after adsorption and regeneration. The α-MoO₃ nanosorbent showed excellent removal efficiency before and after regeneration, suggesting that it can be used as a promising adsorbent for removing Methylene blue dye from wastewater.