One-step hydrothermal synthesis of MoO3/MoO2 composite for efficient removal of methylene blue from aqueous solutions

Abstract

In this study, the MoO3/MoO2 composite nanoparticles were fabricated for the first time using a simple one-step hydrothermal method with the aid of polyvinyl alcohol (PVA) as a reducing agent. The samples were characterized using different techniques, including X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, field-emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA) and the Brunauer–Emmett–Teller (BET) method. Under dark conditions and within 30 min, the MoO3/MoO2 composite adsorbed 95 % of methylene blue (MB) from aqueous solutions on a stirrer, whereas the adsorption rate of pure MoO3 sample was 25 % and that of MoO2 10 %, which showed the significantly-higher performance of the composite nanoparticles. The pseudo second-order and Langmuir models were respectively found to better explain the adsorption kinetics and isotherms of MB on the composite nanoparticles. The Langmuir model showed the maximum capacity of MoO3/MoO2 for adsorbing MB to be 1250 mg/g, which is significantly higher than the values reported for other substances. The high adsorption capacity of this sample can be attributed to its fairly large specific surface area and formation of a composite adsorbent between MoO3 with semiconducting properties and MoO2 with metallic properties, which can improve adsorption by facilitating electron transfer to organic molecules. It is expected the composite sample has the required capability for practical applications in water treatment.