Abstract

Photocatalyst Bi2O2CO3 modifified by polypyrrole (PPy) was synthesized via a facile hydrothermal method. As-prepared PPy/Bi2O2CO3 composites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV–vis diffuse reflflectance spectroscopy (DRS). Presence of PPy did not affect the crystal structure, but exerted great inflfluence on the photocatalytic activity of Bi2O2CO3 and enhanced absorption band of pure Bi2O2CO3. The photocatalytic activities of the PPy/Bi2O2CO3 samples were determined by photocatalytic degradation of Rhodamine-B (RhB) under ultra violet (UV) irradiation and 0.75 wt.% PPy/Bi2O2CO3 composite showed the highest photocatalytic activity. The enhanced photocatalytic performance could be attributed to the synergistic effect of PPy and Bi2O2CO3. A possible photocatalytic mechanism of the PPy/Bi2O2CO3 photocatalysts was proposed in order to guide the further improvement of its photocatalytic performance.

Introduction

With the development of dyes and dyeing and printing industry, dye wastewater has become one of the main sources of severe pollution problems in recent days. Hence, the production of various dyes has become an urgent problem that needs to be solved quickly [1,2]. At present, most of the dyes are synthetized from aromatic compounds, which may make them stable and difficult to biodegrade. In addition, these dyes are found to be toxic, mutagenic and carcinogenic [3,4], and due to its special properties, such as the high content of organic matter and chroma, complex composition, this kind of wastewater will cause serious pollution and may affect people’s health through food chain directly or indirectly if its emissions are put into the environment. Traditional methods, such as physical methods, biochemical methods or their combinations, are used for decolorization of these dyes [5,6]. Although these methods are verifified valid through long-term and experimental proof and it also has a certain negative factors for the treatment of dye wastewater. Nevertheless, they are usually ineffificient, and costly, and result in secondary pollution. Therefore, they are not the best methods. Thus, it is necessary to develop treatment methods that are more effective in eliminating dyes from wastewaters. In this regard, photocatalysis is regarded as a promising technique to deal with the problems of resources and environment [7–11]. In the photocatalytic process, photocatalysts are regarded as one of the most promising classes of semiconductor materials, due to their well-defined electrochemistry, easy protonation reversibility, excellent redox recyclability [12], good environmental stability [13], and a variety of nanostructured morphologies [14], conforming to the needs of sustainable development. Therefore, we choose the method of photocatalytic degradation to remove dyes from wastewater [15].

   

Ever since Fujishima and Honda reported TiO2 as photochemical electrode for water splitting in 1972 [16], using the technology of photocatalysis to remove environmental pollutants and the utilization of solar energy have attracted increasing attention [17]. Due to broading their photocatalysis applications, the light response range of catalyst was modified by scientists. Composites of conducting polymers and semiconductors have received great attention owing to their recent interests in new catalyst [18–20]. The catalyst Bi2O2CO3 displays a typical Sillen layered structure, with alternating (Bi2O2) 2+ layers [21–23]. The tortile spatial structure of Bi2O2CO3 reveals unique photocatalytic properties under UV–Vis light irradiation. However, Bi2O2CO3 with the forbidden band width of 3.4 eV can only absorb the UV light, which accounts for about 3–6% of the solar spectrum [24–27], and hence the utilization efficiency of solar radiation is very low [28]. Therefore, many scientists paid much attention to how to broaden the photoabsorption region and improve the utilization efficiency of sunlight. A series of Bi2O2CO3/BiOX (X = Cl, Br, I) [29], N-doped (BiO)2CO3 [30,31], comparison of (BiO)2CO3 to CdCO3 [32], flower-like, pinon-like and faceted nanoplates (BiO)2CO3 [33] photocatalysts with largely enhanced visible light photocatalytic activity for degrading methyl orange under visible light and many modification approaches have been adopted to enhance its activity by modifying Bi2O2CO3 with other semiconductors to fabricate new composite photocatalysts. The conjugated polymers, processing p conjugated electron systems such as polypyrrole, polyaniline, polythiophene and their derivatives have shown great promise due to their wide visible range absorption and highly efficient electron transport properties.

Electrochemical measurements

The photoelectrochemical analysis was carried out using an electrochemical workstation (Model CHI 650E) with a three-electrode quartz cell. The prepared samples were employed as the working electrode with an area of 1 * 1 cm2 . A Pt plate and Ag/AgCl electrode were used as the counter and reference electrodes, respectively. The photocatalyst was placed in aqueous solution containing 0.5 mol L 1 Na2SO4. A 300 W Xe arc lamp (CEL-HXF300/CEL-HXUV300) equipped with an ultraviolet fifilter (k < 420 nm) was utilized as the UV light source.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (51262028), Fundamental Research Funds for the Gansu Universities, Gansu Provincial Natural Science Foundation of China (1107RJZA194), Pre-research Foundation of Inchuan Group Co., Ltd and Young Teacher Research Foundation of Northwest Normal University (NWNULKQN-11-17).