- Open Access
MO degradation by Ag–Ag2O/g-C3N4 composites under visible-light irradation
© Wang et al. 2016
- Received: 12 December 2015
- Accepted: 12 February 2016
- Published: 24 March 2016
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.
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, Graphitic 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 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.
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.
All reagents in this work were AR grade and used without further purification.
Preparation of g-C3N4
The g-C3N4 was synthesized by calcination method. In a typical process, 6 g dicyandiamide was put into three crucibles with three covers, sealed in a quartz tube partially backfilled with pure nitrogen, annealed at 350 °C for 2 h and annealed at 600 °C for 2 h again. Then the crucibles were cooled to room temperature.
Preparation of Ag–Ag2O/g-C3N4 nanoparticles
The Ag–Ag2O/g-C3N4 was also synthesized via a simple liquid phase synthesis path and a facile calcination method. The method was as follow: 0.2 g of g-C3N4 was added into 20 ml of deionized water. Then they were magetic stirred for 5 min and sonicated for 15 min. Further, 0.2932 g of silver nitrate (AgNO3) was added into the solution and sonicated for 15 min. Next, 0.5 ml hydrated ammonia (NH3·H2O) was also added into the solution, which was still magetic stirred for 15 min. In addition, 0.1829 g of sodium carbonate (Na2CO3) was added drop by drop under stirring in 15 min. Moreover, the pH of the solution was adjusted to 7 and heated in water bath at 25 °C for 1 h. Next, the product was obtained by centrifugation, washed with ethanol and deionized water for several times and dried at 60 °C for 8 h. At last, the sample was annealed at 220 °C for 90 min. The 50 wt% Ag–Ag2O/g-C3N4 could be obtained. All the experiments were carried out at room temperature. The Ag–Ag2O/g-C3N4 composites with different mass ratios were synthesized using the same method through changing the amount of g-C3N4, AgNO3 and Na2CO3, such as 5, 10, 30 and 40 wt%, respectively.
The crystal phase of Ag–Ag2O, g-C3N4 and Ag–Ag2O/g-C3N4 powders were analyzed by X-ray diffraction (XRD) analysis using a Bruker D8 diffractometer with Cu-Kα radiation (λ = 1.5418 Å) in the 2θ range of 20°–80°. Scanning electron microscopy (SEM) image and transmission electron microscopy (TEM) micrographs were taken with a JEOL-JEM-2010 (JEOL, Japan) operating at 200 kV. High resolution transmission electron microscopy (HR-TEM) micrographs were taken with a FEI F20. Energy Dispersive spectrum (EDS) measurements were performed by a JEM-2100F electron microscope. The UV–Vis diffuse-reflectance spectra (DRS) of the samples were obtained on a UV–Vis spectrophotometer (UV-2450, Shimadzu Corporation, Japan). They were measured in solid state, and BaSO4 powder was used as the substrate. Fourier transform infrared (FT-IR) spectra of all the catalysts (KBr pellets) were recorded on Nicolet Model Nexus 470 IR equipment. X-ray photoemission spectroscopy (XPS) was measured on a PHI5300 with a monochromatic Mg Kα source to explore the elements on the surface. The photocurrents were measured with an electrochemical analyzer (CHI660B, CHI Shanghai, Inc.).
In addition, the metallic Ag can further complete efficient electron migration process to efficiently inhibit the recombination of the photoexcited pairs (Xu et al. 2013). So it can be seen that even the VB and CB of g-C3N4 are higher than that of Ag2O, the Ag can be worked as the charge transmission bridge, which transfers the photogenerated electrons from the CB of Ag2O to Ag0 and then the photogenerated electrons were trapped by O2 to produce ·O2 −. At last, the ·O2 − transformed into ·OH. As a result, with the assistance of Ag–Ag2O, the Ag–Ag2O/g-C3N4 photocatalysts could effectively enhance the separation of photoexcited electron-hole pairs and reduced the recombination of electrons and holes. Thus, the Ag–Ag2O nanoparticles loaded on the surface of the g-C3N4 could form the heterojunction structure, which contributed to the promotion of the photocatalytic activity.
In summary, we have demonstrated that Ag–Ag2O nanophases were active catalysts for degrading MO. The results revealed that the optimal activity of Ag–Ag2O/g-C3N4 is 7.5 times as high as that of g-C3N4 and even better than that of Ag–Ag2O. In this investigation the as-synthesized samples were characterized by a collection of techniques, such as XRD, SEM, TEM, HR-TEM, DRS, EDS, XPS and FT-IR. Based on structural analysis, we concluded that the Ag–Ag2O nanoparticles are dispersed on the surface of the g-C3N4. The modified g-C3N4 samples were robust and able to show better photocatalytic activities than Ag–Ag2O and g-C3N4. In addition, the photocatalysis mechanism was also investigated by entrapping active species. These results indicated that the holes played important roles in the degradation of MO over sample Ag–Ag2O/g-C3N4.
XW prepared the sample, had done the experiment of the XRD, FT-IR, XPS, TEM, SEM, HR-TEM, DRS, transient photocurrent and MO dye degradation and drafted the manuscript. JY provided with design ideas and teaching methods to improve the article. HYJ, ZGC, YGX, LYH, QZ, YHS checked and improved the manuscript. HX conceived of the study, and participated in its design and coordination and helped to draft the manuscript. HML conceived of the study, and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.
The authors genuinely appreciate the financial support of this work from the National Nature Science Foundation of China. The authors genuinely appreciate the financial support of this work by the National Nature Science Foundation of China (21476097, 21476098,21407065 and 21406094), the Natural Science Foundation of Jiangsu Province (BK20131207 and BK2012717, BK20140533).
All authors declare that they have no competing interests.
Open AccessThis 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.
- Cao SW, Yuan YP, Barber J, Loo SCJ, Xue C (2014) Noble-metal-free g-C3N4/Ni(dmgH)2 composite for efficient photocatalytic hydrogen evolution under visible light irradiation. Appl Surf Sci 319:344–349View ArticleGoogle Scholar
- Chang F, Xie YC, Li CL, Chen J, Luo JR, Hu XF, Shen JW (2013) A facile modification of g-C3N4 with enhanced photocatalytic activity for degradation of methylene blue. Appl Surf Sci 280:967–974View ArticleGoogle Scholar
- Chang F, Zhang J, Xie YC, Chen J, Li CL, Wang J, Luo JR, Deng BQ, Hu XF (2014) Fabrication, characterization, and photocatalytic performance of exfoliated g-C3N4–TiO2 hybrids. Appl Surf Sci 311:574–581View ArticleGoogle Scholar
- Chen W, Liu TY, Huang T, Liu XH, Zhu JW, Duan GR, Yang XJ (2015) In situ fabrication of novel Z-scheme Bi2WO6 quantum dots/g-C3N4 ultrathin nanosheets heterostructures with improved photocatalytic activity. Appl Surf Sci 355:379–387View ArticleGoogle Scholar
- Cho IS, Chen ZB, Forman AJ, Kim DR, Rao PM, Jaramillo TF, Zheng X (2011) Branched TiO2 nanorods for photoelectrochemical hydrogen production. Nano Lett 11(11):4978–4984View ArticleGoogle Scholar
- Dong F, Li YH, Wang ZY, Ho WK (2015) Enhanced visible light photocatalytic activity and oxidation ability of porous graphene-like g-C3N4 nanosheets via thermal exfoliation. Appl Surf Sci 358:393–403View ArticleGoogle Scholar
- Huang LY, Xu H, Zhang RX, Cheng XN, Xia JX, Xu YG, Li HM (2013a) Synthesis and characterization of g-C3N4/MoO3 photocatalyst with improved visible-light photoactivity. Appl Surf Sci 283:25–32View ArticleGoogle Scholar
- Huang LY, Xu H, Li YP, Li HM, Cheng XN, Xia JX, Xu YG, Cai GB (2013b) Visible-light-induced WO3/g-C3N4 composites with enhanced photocatalytic activity. Dalton Trans 42(24):8606–8616View ArticleGoogle Scholar
- Li YB, Zhang HM, Liu PR, Wang D, Li Y, Zhao HJ (2013) Cross-linked g-C3N4/rGO nanocomposites with tunable band structure and enhanced visible light photocatalytic activity. Small 9(19):3336–3344Google Scholar
- Li YF, Zhao Y, Fang L, Jin RX, Yang Y, Xing Y (2014) Highly efficient composite visible light-driven Ag–AgBr/g-C3N4 plasmonic photocatalyst for degrading organic pollutants. Mater Lett 126:5–8View ArticleGoogle Scholar
- Li ZJ, Wang JH, Zhu KX, Ma FL, Meng A (2015) Ag/g-C3N4 composite nanosheets: synthesis and enhanced visible photocatalytic activities. Nat Mater 145:167–170Google Scholar
- Liu A, Cohen M (1989) Prediction of New low compressibility solids. Science 245(4920):841–842View ArticleGoogle Scholar
- Liu ZY, Zhang XT, Nishimoto S, Murakami T, Fujishima A (2008) Efficient photocatalytic degradation of gaseous acetaldehyde by highly ordered TiO2 nanotube arrays. Environ Sci Technol 42(22):8547–8551View ArticleGoogle Scholar
- Liu CB, Cao CH, Luo XB, Luo SL (2015) Ag-bridged Ag2O nanowire network/TiO2 nanotube array p–n heterojunction as a highly efficient and stable visible light photocatalyst. J Hazard Mater 285:319–324View ArticleGoogle Scholar
- Lotsch BV, Schnick W (2006) From triazines to heptazines: novel nonmetal tricyanomelaminates as precursors for graphitic carbon nitride materials. Chem Mater 18(7):1891–1900View ArticleGoogle Scholar
- Melian EP, Díaza OG, Rodrigueza JMD, Colon G, Naviob JA, Macias M, Pena JP (2012) Effect of deposition of silver on structural characteristics and photoactivity of TiO2-based Photocatalysts. Appl Catal B Environ 127:112–120View ArticleGoogle Scholar
- Min SX, Lu GX (2012) Enhanced electron transfer from the excited eosin Y to mpg-C3N4 for highly efficient hydrogen evolution under 550 nm irradiation. J Phys Chem C 116(37):19644–19652View ArticleGoogle Scholar
- Park JH, Kim S, Bard AJ (2006) Novel carbon-doped TiO2 nanotube arrays with high aspect ratios for efficient solar water splitting. Nano Lett 6(1):24–28View ArticleGoogle Scholar
- Peng Y, Qin SC, Wang WS, Xu AW (2013) Fabrication of porous Cd-doped ZnO nanorods with enhanced photocatalytic activity and stability. CrystEngComm 15(33):6518–6525View ArticleGoogle Scholar
- Ren HT, Jia SY, Wu Y, Wu SH, Zhang TH, Han X (2014) Improved photochemical reactivities of Ag2O/g-C3N4 in phenol degradation under UV and visible light. Ind Eng Chem Res 53(45):17645–17653View ArticleGoogle Scholar
- Su FZ, Mathew SC, Lipner G, Fu XZ, Antonietti M, Blechert S, Wang XC (2010) mpg-C3N4-catalyzed selective oxidation of alcohols using O-2 and visible light. J Am Chem Soc 132(46):16299–16301View ArticleGoogle Scholar
- Subramanian V, Wolf E, Kamat PV (2001) Semiconductor-metal composite nanostructures. To what extent do metal nanoparticles improve the photocatalytic activity of TiO2 films. J Phys Chem B 105(46):11439–11446View ArticleGoogle Scholar
- Tian N, Huang HW, Guo YX, He Y, Zhang YH (2014) A g-C3N4/Bi2O2CO3 composite with high visible-light-driven photocatalytic activity for rhodamine B degradation. Appl Surf Sci 322:249–254View ArticleGoogle Scholar
- Vignesh K, Kang M (2015) Facile synthesis, characterization and recyclable photocatalytic activity of Ag2WO4@g-C3N4. Mater Sci Eng B 199:30–36View ArticleGoogle Scholar
- Wang J, Zhang WD (2012) Modification of TiO2 nanorod arrays by graphite-like C3N4 with high visible light photoelectrochemical activity. Electrochim Acta 71:10–16View ArticleGoogle Scholar
- Wang XC, Maeda K, Thomas A, Takanabe K, Xin G, Carlsson JM, Domen K, Antonietti M (2009a) A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nat Mater 8(1):76–80View ArticleGoogle Scholar
- Wang XC, Maeda K, Chen XF, Takanabe K, Domen K, Hou YD, Fu XZ, Antonietti M (2009b) Polymer semiconductors for artificial photosynthesis: hydrogen evolution by mesoporous graphitic carbon nitride with visible light. J Am Chem Soc 131(5):1680View ArticleGoogle Scholar
- Wang XF, Li SF, Yu HG, Yu JG, Liu SW (2011) Ag2O as a new visible-light photocatalyst: self-stability and high photocatalytic activity. Chem Eur J 17(28):7777–7780View ArticleGoogle Scholar
- Wang SM, Li DL, Sun C, Yang SG, Guan Y, He H (2014) Synthesis and characterization of g-C3N4/Ag3VO4 composites with significantly enhanced visible-light photocatalytic activity for triphenylmethane dye degradation. Appl Catal B Environ 144:885–892View ArticleGoogle Scholar
- Xie Y, Kum J, Zhao XJ, Cho SO (2011) Enhanced photocatalytic activity of mesoporous S–N-codoped TiO2 loaded with Ag nanoparticles. Semicond Sci Technol 26(8):085037View ArticleGoogle Scholar
- Xiu ZL, Bo H, Wu YZ, Hao XP (2014) Graphite-like C3N4 modified Ag3PO4 nanoparticles with highly enhanced photocatalytic activities under visible light irradiation. Appl Surf Sci 289:394–399View ArticleGoogle Scholar
- Xu H, Li HM, Xia JX, Yin S, Luo ZJ, Liu L, Xu L (2011) One-pot synthesis of visible-light-driven plasmonic photocatalyst Ag/AgCl in ionic liquid. ACS Appl Mater Interfaces 3(1):22–29View ArticleGoogle Scholar
- Xu M, Han L, Dong SJ (2013a) Facile fabrication of highly efficient g-C3N4/Ag2O heterostructured photocatalysts with enhanced visible-light photocatalytic activity. ACS Appl Mater Interfaces 5(23):12533–12540View ArticleGoogle Scholar
- Xu H, Yan J, Xu YG, Song YH, Li HM, Xia JX, Huang CJ, Wan HL (2013b) Novel visible-light-driven AgX/graphite-like C3N4 (X=Br, I) hybrid materials with synergistic photocatalytic activity. Appl Catal B Environ 129:182–193View ArticleGoogle Scholar
- Yan SC, Li ZS, Zou ZG (2010) Photodegradation of rhodamine B and methyl orange over boron-doped g-C3N4 under visible light irradiation. Langmuir 26(6):3894–3901View ArticleGoogle Scholar
- Yan HJ, Chen Y, Xu SM (2012) Synthesis of graphitic carbon nitride by directly heating sulfuric acid treated melamine for enhanced photocatalytic H-2 production from water under visible light. Int J Hydrogen Energy 37(1):125–133View ArticleGoogle Scholar
- Yan J, Xu H, Xu YG, Wang C, Song YH, Xia JX, Li HM (2014) Synthesis, characterization and photocatalytic activity of Ag/AgCl/Graphite-Like C3N4 under visible light irradiation. J Nanosci Nanotechnol 14(9):6809–6815View ArticleGoogle Scholar
- Yang XY, Wolcott A, Wang GM, Sobo A, Fitzmorris RC, Qian F, Zhang JZ, Li Y (2009) Nitrogen-doped ZnO nanowire arrays for photoelectrochemical water splitting. Nano Lett 9(6):2331–2336View ArticleGoogle Scholar
- Yao XX, Liu XH, Hu XL (2014) Synthesis of the Ag/AgCl/g-C3N4 composite with high photocatalytic activity under visible light irradiation. Chemcatchem 6(12):3409–3418Google Scholar
- Yu JG, Xiong JF, Cheng B, Liu SW (2005) Fabrication and characterization of Ag–TiO2 multiphase nanocomposite thin films with enhanced photocatalytic activity. Appl Catal B Environ 60(3–4):211–221View ArticleGoogle Scholar
- Yu HG, Liu R, Wang XF, Wang P, Yu JG (2012) Enhanced visible-light photocatalytic activity of Bi2WO6 nanoparticles by Ag2O cocatalyst. Appl Catal B Environ 111:326–333View ArticleGoogle Scholar
- Yu CL, Li G, Kumar S, Yang K, Jin RC (2014) Phase transformation synthesis of novel Ag2O/Ag2CO3 heterostructures with high visible light efficiency in photocatalytic degradation of pollutants. Adv Mater 26(6):892–898View ArticleGoogle Scholar
- Yu HG, Chen FY, Chen F, Wang XF (2015) In situ self-transformation synthesis of g-C3N4-modified CdS heterostructure with enhanced photocatalytic activity. Appl Surf Sci 358:385–392View ArticleGoogle Scholar
- Zhao SS, Chen S, Yu HT, Quan X (2012) g-C3N4/TiO2 hybrid photocatalyst with wide absorption wavelength range and effective photogenerated charge separation. Sep Purif Technol 99:50–54View ArticleGoogle Scholar
- Zhao W, Guo Y, Wang SM, He H, Sun C, Yang SG (2015) A novel ternary plasmonic photocatalyst: ultrathin g-C3N4 nanosheet hybrided by Ag/AgVO3 nanoribbons with enhanced visible-light photocatalytic performance. Appl Catal B Environ 165:335–343View ArticleGoogle Scholar
- Zhou WJ, Liu H, Wang JY, Liu D, Du GJ, Cui JJ (2010) Ag2O/TiO2 nanobelts heterostructure with enhanced ultraviolet and visible photocatalytic activity. ACS Appl Mater Interfaces 2(8):2385–2392View ArticleGoogle Scholar
- Zong X, Sun CH, Yu H, Chen ZG, Xing Z, Ye DL, Lu GQ, Li XY, Wang LZ (2013) Activation of photocatalytic water oxidation on N-doped ZnO bundle-like nanoparticles under visible light. J Phys Chem C 117(10):4937–4942View ArticleGoogle Scholar