Ag₂WO₄ polymorph with enhanced photocatalytic performance

Full text: The Ag₂WO₄ is an important semiconductor with interesting electronic, electrochemical, gas sensoring, and photocatalytic properties. Ag₂WO₄ can exist in the thermodynamically stable phase orthorhombic α-Ag₂WO₄ and the less stable phases: hexagonal β- Ag₂WO₄ and cubic γ- Ag₂WO₄. Due to (i) difficulties in the effective synthesis of pure material and (ii) their unique physical/chemical properties which are different from those of the more stable phase, it is a great challenge to explore the behavior of new metastable materials with novel and fascinating technological applications. This work present a comparative study on the photocatalytic degradation properties of the three Ag₂WO₄ polymorphs on two organics: Rhodamine B (RhB) and Amirolide (AML) from experimental and theoretical points of view. The Ag₂WO₄ polymorphs have been prepared by precipitation method and characterized by the X-ray diffraction, scanning electronic microscope, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance spectra. For the both organics, the more efficient photodegradation process is founded when β-Ag₂WO₄ is the catalytic (~100% photodegration occurs within 20 min for AML and 110 min for RhB). In order to quantify photoactivity, the kinetics of the degradation was analyzed in terms of Langmuir-Hinshelwood kinetic model. The results show that the pseudo-first-order equation is the model that gives the best fit to the experimental data. Some physical-chemistry aspects were considered in the elucidation and better understanding the degradation properties in addition to the simulation of faceted Ag₂WO₄ polymorphs, using the Wulff construction approach, in order to obtain a complete surface-properties relationship picture. Thus, the present work can provide some new insight into the smart design, preparation and potential applications of metastable materials taking a promising potential for the remediation and purification fields. (author)