MO degradation by Ag–Ag2O/g-C3N4 composites under visible-light irradation

Wang et al. SpringerPlus (2016) 5:369 DOI 10.1186/s40064-016-1805-5 Open Access RESEARCH MO degradation by Ag–Ag2O/g‑C3N4 composites under visible‑light irradation Xin Wang1, Jia Yan1, Haiyan Ji1, Zhigang Chen1, Yuanguo Xu1, Liying Huang1, Qi Zhang2, Yanhua Song3, Hui Xu1* and Huaming Li1* *Correspondence: ; lihm@ujs. edu.cn 1 School of Chemistry and Chemical Engineering, Institute for Energy Research, Jiangsu University, Zhenjiang 212013, People’s Republic of China Full list of author information is available at the end of the article Abstract The paper demonstrated the synthesis of Ag–Ag2O/g-C3N4 nanoparticles via a simple liquid phase synthesis path and a facile calcination method. The synthesized Ag–Ag2O/ g-C3N4 composites were well characterized by various analytical techniques, such as X-ray diffraction, Fourier transform infrared (FT-IR), X-ray photoemission spectroscopy, transmission electron microscopy, scanning electron microscopy, high resolution transmission electron microscopy, the UV–Vis diffuse-reflectance spectra and transient photocurrent. From the structure and surface characterization, it indicated that Ag–Ag2O/g-C3N4 composites were formed by an effective covering of g-C3N4 with Ag– Ag2O. The results revealed that the 50 wt% nanoparticle had a great effection on the degradation of the methyl orange (MO), which was almost 7.5 times as high as that of g-C3N4. Based on the experimental results, the possible photocatalytic mechanism with photogenerated holes as the main active species was presented. Keywords: Ag–Ag2O, g-C3N4, MO, Photocatalytic Background With the development of the society, the environmental pollution has become one of the important problems which aroused more and more focus. It is well known that the TiO2 has been proved to be the most distinguished and widely used in the photocatalytic degradation of dyes (Liu et al. 2008; Chang et al. 2014) and H2 production (Cho et al. 2011; Park et al. 2006; Yang et al. 2009). However, with the increasing demands of the photocatalytic materials searching for more semiconductor photocatalysts is becoming more urgent. Thus, the mental and non-mental composites with g-C3N4 have attracted more attention (Peng et al. 2013; Zong et al. 2013). As a good photocatalyst, G raphitic carbon nitride (g-C3N4) has been widely investigated since the discovery of its excellent properties by Liu and Cohen (1989). To date, it exhibits catalytic activity for extensive reactions, such as water splitting, oxidation reaction, dye photodegradation, nitric oxide (NO) decomposition and so on (Huang et al. 2013; Vignesh and Kang 2015; Chen et al. 2015; Yu et al. 2015; Dong et al. 2015; Chang et al. 2013; Su et al. 2010). This new material also possesses the good capabilities such as environmental friendly, stable, low cost and efficient. The reason why the g-C3N4 has a good photocatalytic activity is that the g-C3N4 possesses special optical characteristics and outstanding chemical stability. But, even with those merits, the g-C3N4 still has © 2016 Wang et al. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http:// creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Wang et al. SpringerPlus (2016) 5:369 Page 2 of 13 some disadvantages which show the limited photocatalytic property, such as the poor dispersion, easy agglomeration, recycling difficulties and so on. Yet combined with other materials such as the g-C3N4/MoO3 (Huang et al. 2013), g-C3N4/Ni(dmgH)2 (Cao et al. 2014), g-C3N4/Bi2O2CO3 (Tian et al. 2014), g-C3N4/Ag3PO4 (Xiu et al. 2014) and so on could enhance the catalytic activity of g-C3N4. For example, in recent years, a g-C3N4 was modified with a composite semiconductor could possess the performance of water splitting and remove organic pollutants, which were reported by Wang et al. (2009) and Zhao et al. (2012). Wang and Zhang (2012) reported a g-C3N4–TiO2 pohotocatalyst fabricated by a simple impregnation method which has good activities for the H2 production. In fact, the approach indicates a synergetic effect of the impregnation preparation which provides a better junction between g-C3N4 and TiO2. It can be seen that the composites may have better photoactivities. However, not only can TiO2 doped possess the properties of degrading the pollutants, but also other mental and non-mental materials doped could have good activities. As we all know, the Ag-based materials have good photocatalytic activity. Thus, enormous efforts have been made to study more photocatalysts which needed Ag-based materials modification, such as Ag/C3N4 (Li et al. 2015), Ag/AgVO3/g-C3N4 (Zhao et al. 2015), Ag/ AgCl/g-C3N4 (Yao et al. 2014), Ag–AgBr/g-C3N4 (Li et al. 2014) and so on. In this paper, the Ag–Ag2O/g-C3N4 composites were successfully fabricated via a simple liquid phase synthesis path and a facile calcination method. The approach is different from the paper that has been reported by Xu et al. (2013) and Ren et al. (2014). The preparation of Ag–Ag2O can be described as following (Yu et al. 2014): 2AgNO3 + Na2 CO3 → Ag2 CO3 ↓ + 2NaNO3 (1) Ag2 CO3 → Ag2 O + CO2 ↑ (2) 2Ag2 O → 4Ag + O2 ↑ (3) Simultaneously, Ag2O nanoparticles were partially reduced to Ag0 as it was calcined at 220 °C for 90 min to prepare the desired Ag–Ag2O photocatalysts. This method is also used the same as the preparation of Ag–Ag2O/g-C3N4 nanocomposites. Then the intimate contacted interfaces between the Ag–Ag2O and g-C3N4 were also developed. In addition, prepared g-C3N4 via Ag–Ag2O doping has been proved to control the migration photon-generated carriers, so that the electrons and holes could be separated selectively at the edges, respectively. The mechanism of this report can explain phenomenon for it which indicates Ag–Ag2O has a great potential to be used as a stable and highly efficient photocatalyst to degrade the pollutants under the visible-light irradiation. MO, a representative of dyestuffs resistant to biodegradation, was selected as a model for the study. From our study, we find that the proportion of Ag–Ag2O loading on g-C3N4 surface has the most enhanced adsorption capacity and the best photocatalytic activity is 50 wt%. Therefore, both Ag and Ag2O maybe act as traps to capture photogenerated electrons which contribute to the separation of electron–hole pairs (Yu et al. 2005, 2012; Zhou et al. 2010; Subramanian et al. 2001; Xie et al. 2011). Based on the experimental results, a possible photocatalytic mechanism for the degradation of MO over Ag–Ag2O doped g-C3N4 nanosheets under visible-light irradiation was proposed. Wang et al. SpringerPlus (2016) 5:369 Experimental section Materials All reagents in this work were AR grade and used without (...truncated)