g-C3N4 nanocomposite with high photocatalytic and antibacterial activity

Materials Letters 257 (2019) 126708

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Novel AgCl/CNTs/g-C3N4 nanocomposite with high photocatalytic and antibacterial activity Chun Liu a, Yu-bin Tang a,⇑, Peng-wei Huo b,⇑, Fang-yan Chen a a b

School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang, Jiangsu 212005, PR China Institute of Green Chemistry and Chemical Technology, School of Chemistry & Chemical Engineering, Jiangsu University, Zhenjiang 212013, PR China

a r t i c l e

i n f o

Article history: Received 30 July 2019 Received in revised form 15 September 2019 Accepted 17 September 2019 Available online 18 September 2019 Keywords: g-C3N4 AgCl Carbon nanotubes Photocatalytic activity

a b s t r a c t In this study, we were constructed a photocatalytic and antibacterial material AgCl/Carbon nanotubes (CNTs)/graphitic carbon nitride (g-C3N4) by deposition–precipitation method. A series of characterizations indicate that AgCl nanoparticles are deposited on CNTs and then dispersed together on g-C3N4 (CN). The photocatalytic properties of the composites were investigated by photodegrading tetracycline under visible light. The AgCl/CNTs/CN nanocomposites exhibit excellent photocatalytic efficiency of 86.44%, which is three times the photocatalytic degradation efficiency of pure CN and AgCl/CN. In addition, the catalytic activity of AgCl/CNTs/CN composites against Escherichia coli (E. coli) was also investigated. The inhibition zone experiment showed that the composite had a strong inhibitory effect on E. coli. Ó 2019 Elsevier B.V. All rights reserved.

1. Introduction In the past decade or so, with the rapid development of industry, human beings have released a large number of antibiotics and pathogens into the environment, which seriously threatens human health [1,2]. In recent years, AgCl has a good potential for degrading antibiotics under visible light as a photosensitive material with a wide band gap [3,4]. Zhang et al. [5] reports that the catalytic efficiency of photocatalytic reduction of hexavalent chromium can be significantly improved by constructing Ag/AgCl/NH2-UiO-66 heterojunction ternary hybrid system. Wang’s team reports that the prepared convex polyhedral AgCl has a good degradation effect on organic dyes and antibiotics [6]. Nowadays, it has been reported that Ag+ can sterilize by destroying biological molecules with biological functions [7]. Xia et al. [8] team finds that Ag/AgX/rGO composites release Ag+ to destroy microbial cell membranes and disrupt normal bacterial metabolism. Therefore, AgCl has potential applications in the field of photocatalysis and antibacterial. However, AgCl nanoparticles are prone to agglomeration and instability during the preparation process. Graphene carbon nitride is a promising carrier material because of its unique two-dimensional layered structure. The selfassembled carbonitride prepared by molecular doping copolymer-

⇑ Corresponding authors. E-mail addresses: [email protected] (Y.-b. Tang), [email protected] (P.-w. Huo). https://doi.org/10.1016/j.matlet.2019.126708 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.

ization of urea and 2-thiobarbituric acid has excellent degradation efficiency to sulfamethazine [9]. Sun et al. [10] reports that the dispersion of AgCl particles by poly-o-phenylenediamine on g-C3N4 has a good degradation efficiency for tetracycline. However, the poor separation efficiency of photo-generated carriers and holes of g-C3N4 limits its application in photocatalysis [11,12]. Carbon nanotubes are widely used as catalyst carriers due to their excellent chemical and electrochemical properties. Carbon nanotubes can effectively improve the dispersion and stability of nanoparticles [13]. At the same time, carbon nanotubes can promote the transfer of electrons, increase the mobility of photogenerated electrons and enhance the separation of electron-hole pairs. Shi’s group reports that AgX nanoparticles loaded on CNTs have high catalytic activity for organic pollutants [14]. In this study, AgCl/CNTs/CN composites were synthesized by simple deposition. The CNTs in the composite material act as an electron medium, which is beneficial to accelerate the transfer of photogenerated electrons and improve the photocatalytic performance of the composite materials. The composite material has high catalytic activity the antibiotic tetracycline and against excellent inhibition of E. coli.

2. Experimental The synthetic route of AgCl/CNTs/CN nanocomposites is shown in Fig. 1. The specific synthesis scheme can be found in the support information. The experimental test procedures and the

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Fig. 1. Experimental flow chart for preparing composite AgCl/CNTs/CN.

instruments and equipment required for the experiment are specifically described in electronic supplementary material. 3. Results and discussion The XRD pattern of the nanocomposite is shown in Fig. 2a. The prepared CN has an inter-planar packing peak of a typical conjugated aromatic system. It can be clearly observed that CN has characteristic peaks at 2h = 27.4 and 13.2 , which is related to the (0 0 2) and (1 0 0) diffraction layers of g-C3N4 [15]. The CNTs has a peak at 2h = 26.2 , which is attributed to the (0 0 2) diffraction planes (JCPDS No. 41-1487). The angles of diffraction peaks of AgCl/CN, AgCl/CNTs and AgCl/CNTs/CN nanocomposites are at

2h = 27.8 , 32.3 , 46.3 , 54.9 , 57.6 , 67.5 and 76.8 assigned to Bragg’s reflections from the (1 1 1), (2 0 0), (2 2 0), (3 1 1), (2 2 2), (4 0 0) and (4 2 0) planes of AgCl (JCPDS No. 31-1238) [16]. In summary, AgCl/CNTs/CN nanocomposites were successfully prepared. Fig. 2b shows the FT-IR spectra of nanocomposites. The peaks appearing at 810 cm 1 can be attributed to breathing pattern of the tri-s-triazine units [17]. The bands at 1230 cm 1 to 1640 cm 1 are related to the representative skeletal vibrations of g-C3N4 heterocycles [10]. The absorption characteristics of nanocomposites were investigated by UV-vis. As shown in Fig. 2c, the absorption edges of CN and AgCl/CN are 450 nm and 435 nm. The absorption edge of the ternary composite AgCl/CNTs/CN gets red-shifted to 500 nm. Com-

Fig. 2. (a) XRD patterns, (b) FT-IR spectra and (c) UV-vis absorption spectra of prepared samples. (d) XPS survey spectra for AgCl/CNTs/CN.

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Fig. 3. The SEM images (a,b) and the TEM images (c,d) of AgCl/CNTs/CN.

pared with CN and AgCl/CN, the addition of CNTs significantly improves the absorption capacity of the composite in the visible region. This facilitates the migration of photogenerated carriers and the generation of electron-hole pairs. XPS was used to investigate the chemical state of AgCl/CNTs/CN nanocomposite. The XPS spectra clearly reveal that the existence of N, C, O, Cl and Ag in AgCl/CNTs/CN nanocomposite (Fig. 2d). The morphologies of the AgCl/CNTs/CN nanocomposite were studied by FESEM and TEM analysis (See Fig. 3). Fig. 3a and b show the FESEM image of AgCl/CNTs/CN nanocomposite obtained by deposition-precipitation method. The AgCl nanoparticles are cubically uniformly dispersed on the CNTs. The size of AgCl is approximately in the range of 100–250 nm. It can be seen more clearly from Fig. 3c and d that AgCl/CN is uniformly distributed on the CN nanosheets. This indicates that the AgCl/CNTs/CN composite is successfully prepared. The photocatalytic activities of the as-prepared photocatalysts were evaluated by the removal of TC under visible-light irradiation to assess their potential capability in water purification (Fig. 4a). The adsorption desorption equilibrium between the mixture liquid and the sample is achieved prior to the start of the reaction. In these experiments, the photodegradation of TC on the AgCl/CN and AgCl/CNTs nanocomposite are only 16.78% and 25.81%, while the TC removal ratios of AgCl/CNTs/CN is 86.44%, respectively, which is attributed to the those CNTs promote the separation of photogenerated electron-hole pairs. The antibacterial activity of AgCl/CNTs/CN composites against Escherichia coli was tested using agar diffusion method. As shown in Fig. 4b, no inhibition zone for pure CNTs was observed. For AgCl/CN and AgCl/CNTs/CN, the radial diameters of the zone of inhibition are 30 ± 0.5 mm and

26 ± 0.3 mm, respectively. This indicates that the nanocomposite exhibits a high antibacterial activity. The transient photocurrent response (Fig. 4c) is used to manifest the exciton separation rates of the as-prepared samples [18]. The photocurrent intensity is significantly enhanced from CN to AgCl/CNTs/CN, which verifies the most efficient separation of excitons in AgCl/CNTs/CN. Electrochemical impedance spectra (EIS) (Fig. 4d) are also collected to disclose the charge carriers transfer resistance of the as-prepared samples [19]. It is well-known that the smaller radius of EIS plot suggests the lower resistance in charge transport or, in other words, the higher charge transfer rate on the interfaces [20]. AgCl/CNTs/CN shows the highest the transport ability of photoinduced charge carriers from inside to surface, which is consistent with the photocurrent result. This further indicates that CNTs can improve the migration efficiency of photogenerated carriers and promote efficient separation of photogenerated electron-hole pairs.

4. Conclusions The AgCl/CNTs/CN nanocomposites were successfully prepared by simple chemical deposition. The AgCl/CNTs/CN nanocomposites have excellent degradation activity for tetracycline, which is three times more efficient than those of pure CN and AgCl/CN degradation. Because CNTs are added as electron mediators, the transmission rate of photogenerated electrons is greatly improved, and the recombination of photogenerated electrons and holes is effectively suppressed. At the same time, the prepared nanocomposites were subjected to antibacterial experiments. Experiments show that

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Fig. 4. (a) Photocatalytic activities of nanocomposites for TC under visible-light irradiation. (b) The images of inhibition zones for different samples against E. coli. (c) Photocurrent transient response and (d) EIS Nyquist plots of samples.

AgCl/CNTs/CN nanocomposites have a strong inhibitory effect on E. coli. Therefore, AgCl/CNTs/CN nanocomposites have a good development prospect in photocatalytic degradation of antibiotics and antibacterial. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgment This work was supported by Zhangjiagang Science and Technology Support Program (Social Development) of Jiangsu Province, China (grant number:ZKS1510). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.126708. References [1] V.J. Jones, N.L. Rose, A.E. Self, N. Solovieva, H. Yang, Global. Planet Change 134 (2015) 82–90. [2] Y. Yang, C. Zhang, C. Lai, G.M. Zeng, D.L. Huang, M. Cheng, J.J. Wang, F. Chen, Adv. Colloid Interface Sci. 254 (2018) 76–93.

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