Photocatalytic properties of Bi₂MoO₆ nanoparticles prepared by an amorphous complex precursor

Abstract

Nanoparticles of Bi₂MoO₆ have been synthesized using an amorphous complex precursor. The evolution of the oxide was followed by TGA/DTA, XRD and TEM in order to investigate the formation process, crystal structure and morphology of synthesized samples. The effects of calcination temperature on the morphology, surface area and properties of Bi₂MoO₆ nanoparticles have been investigated in detail. The photocatalytic activity of Bi₂MoO₆ nanoparticles was evaluated by degradation of rhodamine B molecules in water under visible light irradiation. The photocatalyst evaluation criteria involved the photocatalytic properties of samples at different calcination temperatures. The kinetic degradation of rhodamine B followed a first order reaction with k = 2.2 × 10⁻² min⁻¹ and t_1/2 = 31.6 min for the best material obtained.

Introduction

Throughout last decades, heterogeneous photocatalysis has been positioned as a promissory efficient technology to resolve environmental and energy problems. Since the discovery of photocatalytic activity of TiO₂ by UV irradiation [1], many works have been written describing novel methods to synthesized photocatalysts with special characteristics to achieve a high catalytic activity in red–ox reactions. The major applications investigated for this technology are the colour removal and dyes destruction, reduction of chemical oxygen demand (COD), mineralization of hazardous organics and purification and disinfection of water [2]. Within the overall category of dyestuffs rhodamine B dye (RhB), see Fig. 1, is famous for the stability as dye laser material. It has become a common organic pollutant, so the photodegradation of RhB is important to the purification of dye effluents to avoid damage in aquatic organisms [3].

Recently, some binary oxides with perovskite and related structures have shown photocatalytic activity under irradiation with visible light [4], [5], [6]. In this sense, oxides with Aurivillius structure type have received special attention. Some authors have reported Bi₂WO₆ as an interesting photocatalyst for water splitting and photodegradation of organic compounds under visible light irradiation [7], [8]. Moreover photocatalytic activity for O₂ evolution has been observed in the analogous phase Bi₂MoO₆ [9], [10]. Particularly, the binary system Bi₂O₃–MoO₃ have received special attention due the capacity of several oxides belonging the system to act as catalysts in the partial oxidation of olefins to produce unsaturated aldehydes, unsaturated nitrides or dienes [11]. Bi₂MoO₆ is the most studied compound within this family due to its interesting properties such as ion conductive, dielectric capacity, and luminescent and catalytic properties.

Frequently the solid-state reaction method employed to obtain the photocatalyst leads to materials with poor photocatalytic activity due to the small surface area developed. The so-called soft chemistry methods have shown to be efficient to prepare better catalysts than those synthesized by classical methods. In this sense, Kudo and Hijii [8] have reported the synthesis of Bi₂MoO₆ by hydrothermal synthesis, additionally the mechanosynthesis has been also employed for this purpose [12]. Recently Zhang et al. [13] have reported the formation of Bi₂WO₆ nanoparticles through a complex organic precursor. In the present work, the procedure described by Zhang has been followed in order to obtain the analogous oxide Bi₂MoO₆ with small particle size. The successful synthesis of nanoparticles of Bi₂MoO₆ will be providing an interesting candidate for photocatalytic applications.