Open Access

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

SpringerPlus20165:369

https://doi.org/10.1186/s40064-016-1805-5

Received: 12 December 2015

Accepted: 12 February 2016

Published: 24 March 2016

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, ​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.

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):
$$2{\text{AgNO}}_{3} + {\text{Na}}_{2} {\text{CO}}_{3} \to {\text{Ag}}_{2} {\text{CO}}_{3} \downarrow + \,2{\text{NaNO}}_{3}$$
(1)
$${\text{Ag}}_{2} {\text{CO}}_{3} \to {\text{Ag}}_{2} {\text{O}} + {\text{CO}}_{2} \uparrow$$
(2)
$$2{\text{Ag}}_{2} {\text{O}} \to 4{\text{Ag}} + {\text{O}}_{2} \uparrow$$
(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.

Experimental section

Materials

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.

Characterization

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.).

Results and discussion

The XRD patterns of the as-prepared Ag–Ag2O, g-C3N4 and Ag–Ag2O/g-C3N4 composites were shown in Fig. 1. All diffraction peaks could be indexed as “” of Ag, “” of Ag2O, “” of g-C3N4. The results indicated that the diffraction peak at 13.1° and 27.8° could be indexed as (100) and (002) diffraction planes (JCPDS 87-1526) (Wang et al. 2009). And the (100) diffraction peak is weakening with the decreasing content of g-C3N4. With the increasing Ag–Ag2O content, the diffraction peaks at 32.8° and 54.9° gradually appeared while the intensity increased, and the peaks were assigned to the (111) and (220) planes (JCPD 41-1104) (Wang et al. 2011) of Ag2O crystal, respectively. Four diffraction peaks at 32.8°, 44.3°, 64.4° and 77.5° in Ag were indexed to the (111), (200), (220) and (311) planes of Ag (JCPDS 04-0783) (Liu et al. 2015), respectively. As discussed above, the Ag–Ag2O/g-C3N4 nanocomposites were successfully prepared via a simple liquid phase synthesis path and a facile calcination method.
Fig. 1

XRD patterns of Ag–Ag2O, g-C3N4 and Ag–Ag2O/g-C3N4 composite

Figure 2 showed the FTIR spectra of the Ag–Ag2O, g-C3N4 and a series of Ag–Ag2O/g-C3N4 composite photocatalysts, respectively. The broad peak at 3000–3500 cm−1 was ascribed to the stretching vibration of N–H and that of O–H of the physically adsorbed water (Xu et al. 2013; Yan et al. 2014). In the case of g-C3N4, the strong band of 1200–1700 cm−1, with the characteristic peaks at 1242, 1322, 1412, 1563 and 1634 cm−1 were attributed to the typical stretching vibration of CN heterocycles (Xu et al. 2013; Yan et al. 2014). In addition, the peak at 807 cm−1 is associated with the breathing mode of triazine units (Min and Lu 2012; Lotsch and Schnick 2006). Moreover, for the Ag–Ag2O, the observed broad peak around 600 cm−1 belongs to Ag–O bond vibration (Xu et al. 2013). The FT-IR spectra of the Ag–Ag2O/g-C3N4 composites represented the spectra of both g-C3N4 and Ag–Ag2O. It should be noted that the intensity of the peak at 807 cm−1 decreased with the reduction of the g-C3N4 content.
Fig. 2

FT-IR of the as synthesized Ag–Ag2O, g-C3N4 and Ag–Ag2O/g-C3N4 composite

XPS was further made use of to analyze the chemical status and compositions of the 50 wt% Ag–Ag2O/g-C3N4 composite. Figure 3a showed the XPS analysis spectrum of the as-prepared composites, from which only Ag, O, C and N elements could be observed. In order to investigate the detailed chemical states of 50 wt% Ag–Ag2O/g-C3N4 nanoparticles, the peaks of Ag 3d, O 1s, C 1s and N 1s had been conducted and given in Fig. 3b–e. There were two peaks located at 374.2 and 368.2 eV could attach to the binding energies of Ag3d5/2 and Ag 3d3/2 (Melian et al. 2012), which belonged to Ag+ in Ag–Ag2O (Fig. 3b). Besides, the peak at 368.2 eV could be further divided into two bands of 368.1 eV and 369.0 eV for the binding energy of Ag(I) 3d5/2 and Ag(0) 3d3/2, respectively. And the peak at 374.2 eV could be also de-convoluted into two different peaks at 374.1 eV and 374.9 eV for Ag(I) 3d5/2 and Ag(0) 3d3/2, respectively. The peak centered at 530.9 eV could be attributed to the lattice oxygen atoms of Ag–Ag2O (Huang et al. 2013) (Fig. 3c). Figure 3d showed that the peaks located at 288.2 and 284.7 eV correspond to the sp3-bonded C in C–N of g-C3N4 and C–C coordination of the surface adventitious carbon (Li et al. 2013; Yan et al. 2012; Yan et al. 2010). Compared with the intensity of g-C3N4, the peak at 288.2 eV was strengthened and the peak at 284.7 eV was weakened. In the N 1s spectrum (Fig. 3e), the peak at 398.8 eV was assigned to C=N–C coordination (Wang et al. 2014), the intensity of which was stronger than that of g-C3N4. In the N 1s spectrum (Fig. 3e), the peak at 398.8 eV was assigned to C=N–C coordination (Wang et al. 2014). In the end, results from XRD, FT-IR and XPS indicated that the as-prepared samples contained Ag–Ag2O and g-C3N4.
Fig. 3

XPS spectra a profiles of survey, b Ag 3d, c O 1s, d C 1s and e N 1s

The morphological characterization of as-synthesized products was investigated by using SEM and TEM. SEM images were shown in Fig. 4a, b, which clearly depicted layer structure of g-C3N4 (Xu et al. 2013). From SEM images, it was obvious that these Ag–Ag2O nanoparticles were well dispersed on the surface of the g-C3N4. To further observe the combination of Ag–Ag2O and g-C3N4, EDS mapping images were shown in Additional file 1: Fig. S1, which indicated that Ag and O element were well distributed in the samples. TEM was used to investigate the morphology and microstructure of the sample. The TEM and HR-TEM images of 50 wt% Ag–Ag2O/g-C3N4 were shown in Fig. 4c–e. It can be seen that Ag–Ag2O particles were uniformly deposited on the surface of g-C3N4. The existence of heterojunction between Ag and Ag2O could be seen in the HR-TEM. Two different kinds of lattice fringes were clearly observed. The d = 0.236 of the first fringe matches the (111) crystallographic plane of Ag (Liu et al. 2015), and another of d = 0.273 and 0.167 nm are attached to the (111) and (220) crystallographic plane of Ag2O (Wang et al. 2011) respectively. What’s more, an integration interface between g-C3N4 and Ag–Ag2O is possibly formed, which was contributed to the transport of photoexcited carriers. At last, from the EDS, we could see that there were only Ag, O, C, N and Si elements, which consistent with the XRD in Fig. 4f. The corresponding EDS spectrum of the sample 50 wt% Ag–Ag2O/g-C3N4 confirmed that there were C, N, O, Si and Ag elements in the sample as shown in Fig. 4f. Also from the Additional file 1: Table S1, the actual data of the content of Ag–Ag2O in the sample were close to the theoretical data of that. Even though there were some differences between the theoretical data and the actual data, these might be due to the loss of g-C3N4 in the calcination process. In addition, the observed Si peaks in the above EDS spectrum arose from the silicon grids was used for SEM analysis.
Fig. 4

SEM morphologies of g-C3N4 (a), 50 wt% Ag–Ag2O/g-C3N4 (b), TEM morphologies of g-C3N4 (c), 50 wt% Ag–Ag2O/g-C3N4 (d), HR-TEM morphologies of 50 wt% Ag–Ag2O/g-C3N4 (e) and EDS of the 50 wt% Ag–Ag2O/g-C3N4 composite (f)

The DRS of Ag–Ag2O/g-C3N4, Ag–Ag2O and g-C3N4 were shown in Fig. 5. The absorption edges were varied by changing the amount of Ag–Ag2O. As shown in Fig. 5a, the g-C3N4 had the absorption edge of around 460 nm. When the ratio of Ag–Ag2O/g-C3N4 was increased from 5 to 50 wt%, the absorption edge of the composites shifted to the larger wavelength region and the composites exhibited stronger absorbance in the visible region due to the surface plasmon resonance (SPR) absorption of metal Ag nanocrystal. Compared with the 30 wt% and 50 wt% Ag–Ag2O/g-C3N4 composites, the 30 wt% Ag–Ag2O/g-C3N4 showed more obvious SPR than 50 wt% Ag–Ag2O/g-C3N4 which had more content of Ag–Ag2O attached to the surface of g-C3N4, that leaded to the absorption peak widen and then changed the SPR (Xu et al. 2011). The band gap values (Eg) of Ag–Ag2O and g-C3N4 were calculated by plots of (αhυ)1/2 versus photon energy, which were shown in Fig. 5b. From the Fig. 5b, the band gap energy of g-C3N4 was 2.7 eV. At the same time, the band energy of Ag–Ag2O was 1.3 eV, which would be used in the possible mechanism at the end. To give a direct analysis, the potentials of the conduction band (CB) and valence band (VB) edges of g-C3N4 and Ag2O were evaluated by Mulliken electronegativity theory:
$${\text{E}}_{\text{CB}} = {\text{X}} - {\text{E}}_{\text{C}} - 1/2{\text{E}}_{\text{g}}$$
$${\text{E}}_{\text{CB}} = {\text{E}}_{\text{VB}} - {\text{E}}_{\text{g}}$$
where X was the absolute electronegativity of the atom semiconductor [(XAg2O = 4.44 * 4.44 * 7.54)1/3 = 5.29], defined as the geometric mean of the absolute electronegativity of the constituent atoms, and expressed as the arithmetic mean of the atomic electro affinity and the first ionization energy; EC was the energy of free electrons with the hydrogen scale (4.5 eV); Eg was the band gap of the semiconductor (Xu et al. 2013). Based on the band gap positions, the CB and VB edge potentials of Ag2O were at +0.14 eV and +1.44 eV, respectively. The CB and VB edge potentials of g-C3N4 were at −1.13 eV and +1.57 eV, which were consistent with the previous literature, respectively (Xu et al. 2013).
Fig. 5

DRS (a), versus photon energy of the Ag–Ag2O/g-C3N4 treated for different proportions and plots of (αhυ)1/2 (b) versus photon energy of the Ag2O and g-C3N4

Commonly, a high value of the photocurrent demonstrates that the composite holds strong ability in generating and transferring the photoexcited charge carrier under irradiation. As shown in Fig. 6, the g-C3N4 and different ratios of Ag–Ag2O/g-C3N4 composite were characterized by transient photocurrent. The 50 wt% Ag–Ag2O/g-C3N4 had a higher photocurrent than g-C3N4, which indicates that Ag–Ag2O/g-C3N4 composite exhibits stronger ability than g-C3N4 in the separation of electron–hole pairs. While under visible-light irradiation, the pure g-C3N4 showed lower photocurrent response, because of its lower efficiency of the charge carriers’ separation. The results in Fig. 6 could well correspond to those from the MO degradation experiments which were shown as the following.
Fig. 6

Transient photocurrent response for g-C3N4 and 50 wt% Ag–Ag2O/g-C3N4 composite

Figure 7 showed the MO degradation curves of the photocatalysts of g-C3N4 and Ag–Ag2O/g-C3N4 with different Ag–Ag2O modifying amount under visible light irradiation. As shown in Fig. 7, the g-C3N4 showed poor activity, on which ~12 % of MO was decomposed after visible light irradiation for 3.5 h. After combining Ag–Ag2O with g-C3N4, the experiments clearly demonstrated that the Ag–Ag2O/g-C3N4 composite was determined as an efficient visible light photocatalyst, which was higher than the g-C3N4. Above all, the photoactivity of 50 wt% Ag–Ag2O/g-C3N4 composite was about 7.5 times higher compared to g-C3N4 and had the best photoactivity of all. The results may according to that there is a heterojunction between the Ag–Ag2O and g-C3N4, which can improve separation of electron–holes pairs and therefore enhance the photocatalytic activity of the g-C3N4.
Fig. 7

MO dye degradation curves of the g-C3N4 and Ag–Ag2O/g-C3N4 with different Ag–Ag2O modifying amount under visible light irradiation

Hydroxyl radicals and photogenerated holes are two main species for the oxidization of organic molecular in aqueous solution. In order to understand the photocatalysis profoundly, the effects of holes and hydroxyl radicals on the photocatalytic evaluation were investigated. As shown in Fig. 8, due to the tert-Butyl alcohol (TBA) could efficiently entrap the ·OH radicals, which was selected as ·OH scavenger. The change for the photodegradation of MO was small of the TBA, revealing that the hydroxyl radicals were not the main active species. However, after introducing EDTA-2Na as a hole scavenger, the photodegradation efficiency of MO over Ag–Ag2O/g-C3N4 greatly reduced from 95 to 11 % after irradiation for 4.5 h. These results indicated that the holes played an important role in the degradation of MO over Ag–Ag2O/g-C3N4.
Fig. 8

Effect of different scavengers on the degradation of methyl orange in the presence of 50 wt% Ag–Ag2O/g-C3N4 composites under visible light irradiation

The Fig. 9 showed the possible mechanism of photodegradation of MO over Ag–Ag2O/g-C3N4 photocatalyst under visible-light irradiation as follows. When under the visible-light exposure, both of the Ag2O and g-C3N4 generate valence band holes (h+) and conduction band electrons (e). In order to give a direct analysis, the potentials of the conduction band (CB) and valence band (VB) edges of Ag2O and g-C3N4 were evaluated by Mulliken electronegativity theory (Xu et al. 2013). Due to the valence band potential of Ag2O was more negative than that of g-C3N4 and the conduction band potential of Ag2O was more positive than that of g-C3N4, the photoinduced holes on the valence band and the electrons on the conduction band of g-C3N4 could move to Ag2O.
Fig. 9

Proposed mechanism for the promotion of the photocatalytic MO degradation performance of Ag–Ag2O/g-C3N4 composites

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.

Conclusion

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.

Declarations

Authors’ contributions

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.

Acknowledgements

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).

Competing interests

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.

Authors’ Affiliations

(1)
School of Chemistry and Chemical Engineering, Institute for Energy Research, Jiangsu University
(2)
Hainan Provincial Key Lab of Fine Chemistry, Hainan University
(3)
School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology

References

  1. 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
  2. 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
  3. 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
  4. 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
  5. 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
  6. 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
  7. 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
  8. 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
  9. 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
  10. 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
  11. 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
  12. Liu A, Cohen M (1989) Prediction of New low compressibility solids. Science 245(4920):841–842View ArticleGoogle Scholar
  13. 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
  14. 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
  15. 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
  16. 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
  17. 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
  18. 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
  19. 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
  20. 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
  21. 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
  22. 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
  23. 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
  24. 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
  25. 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
  26. 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
  27. 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
  28. 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
  29. 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
  30. 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
  31. 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
  32. 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
  33. 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
  34. 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
  35. 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
  36. 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
  37. 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
  38. 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
  39. 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
  40. 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
  41. 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
  42. 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
  43. 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
  44. 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
  45. 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
  46. 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
  47. 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

Copyright

© Wang et al. 2016