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Liquid phase synthesis of pectin–cadmium sulfide nanocomposite and its photocatalytic and antibacterial activity
Journal of Molecular Liquids 196 (2014) 107–112
Contents lists available at ScienceDirect
Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq
Liquid phase synthesis of pectin–cadmium sulfide nanocomposite and its photocatalytic and antibacterial activity Vinod Kumar Gupta a,⁎, Deepak Pathania b, Mohammad Asif c, Gaurav Sharma b a b c
Department of Chemistry, Indian Institute of Technology Rookree, Roorkee 247667, India Department of Chemistry, Shoolini University, Solan, Himachal Pradesh 173212, India Department of Chemical Engineering, King Saud University, Riyad, Saudi Arabia
a r t i c l e
i n f o
Article history: Received 7 March 2014 Received in revised form 12 March 2014 Accepted 16 March 2014 Available online 27 March 2014 Keywords: Pectin Cadmium sulfide Nanocomposite Photocatalytic activity Antibacterial properties
a b s t r a c t We report the synthesis of pectin–cadmium sulfide nanocomposite (Pc/CSNC) in aqueous phase at 60 °C using pectin as the coupling negotiator. The nanocomposite was characterized by using techniques such as X-ray powdered diffraction (XRD), transmission electron spectroscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). TEM results indicated that the average size of particles in Pc/CSNC was in the range from 4 nm to 10 nm. These results were consistent with the results obtained from XRD data. Pc/CSNC was explored for the photocatalytic degradation of methylene blue (MB) dye from waste water in the presence of sunlight and sodium lamp source. Photocatalytic degradation of methylene blue dye was recorded to be higher under visible light irradiation (95.5%) as compared to that under sodium lamp source (88.9%) after 6 h of irradiation. Pc/CSNC offered excellent antibacterial activity against Escherichia coli bacteria culture. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Interest in nano-sized objects has increased recently due to their unique physical, chemical, electrical and optical properties in comparison to their bulk counterparts. Synthesis of semiconductors of groups II–VI in a nanopowder form is currently an area of intense scientific interest due to their vital applications in optoelectronics, photonics, biomedical and light emitting devices [1–3]. CdS is one such semiconductor with a direct band gap of 2.42 eV at 300 K. It's applications for optoelectronics, being used in photosensitive and photovoltaic devices, solar cells, transistors, light emitting diodes, photo catalysis and photoluminescence sensors are already established by various studies [4–7]. CdS nanomaterials have been used as bioorganic detector of proteins or DNA [8]. CdS nanoparticles with accurate surface modification have recorded enhanced luminescence properties [9,10]. Recently, hybrid organic–inorganic nano-composites have gained much attention due to their credibility to offer synergistic feature of polymeric material with those of inorganic constituents. They offer the dual advantages of the inorganic material like rigidity, thermal stability, etc. and those of organic polymer like flexibility, dielectric, ductility, and processability. In polymer based nano-composites the small size of the fillers results in dramatic increase in interfacial area as compared to their traditional composites. This interfacial area creates a significant
⁎ Corresponding author. Tel.: +91 1332285801; fax: +91 1332273560. E-mail addresses: [email protected], [email protected] (V.K. Gupta).
http://dx.doi.org/10.1016/j.molliq.2014.03.021 0167-7322/© 2014 Elsevier B.V. All rights reserved.
volume fraction of interfacial polymer with properties different from the bulk polymer even at low loadings [11–13]. The surfaces of inorganic particles are usually hydrophilic, while those of polymers are usually hydrophobic. Therefore, the surfaces of inorganic particles need to be modified or pretreated by using some coupling agents in order to promote the compatibility between polymeric phase and inorganic phase and to maintain unique morphology [14]. Polymers are exceptional host materials for nanoparticles of metals and semiconductor [15]. Hybrid materials have high specific stiffness and strength, high toughness, corrosion resistance, low density and thermal insulation [16–18]. Pectin is a natural, non-toxic and amorphous carbohydrate present in cell walls of all plant tissues and functions as an intercellular and intracellular cementing material. Pectin has been commonly used in the food industry on account of its gelling, stabilizing thickening and emulsifying properties and also due to its excellent eco-friendly biodegradable applications [19–21]. Pectin macromolecules are able to bind with some organic or inorganic substances through molecular interactions. Dyes are discharged into water system from the effluents of industries like textile, paper, printing, plastics and leather. Many of these dyes are toxic, non-biodegradable, carcinogenic and mutagenic to aquatic life and human being [22,23]. Thus, the presence of even small amount of dye in water is of high concern. A number of techniques have been used for the removal of dyes from water system [24–28]. Nowadays bio-adsorbent based materials have gained importance due to their low-cost, easy processability, high-volume application, renewable nature and possibility of recycling.
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Although adsorption has been a widely used method for dye treatment, but it results in secondary pollution due to transfers of dye from aqueous to solid phase. On the other hand, advanced oxidation process initiated by photocatalytic degradation can offer a better solution for decolorization, breakdown and mineralization of dyes [29]. Since photocatalytic reaction takes place on the surface of the semiconductors, morphology and surface alteration have a strong influence on the photocatalytic effect [30]. The semiconductor nanoparticles, when irritated with light, produce an electron–hole pair, with an electron in the conduction band and hole in the valence band. Photocatalytic process results in oxidation–reduction and finally the degradation of a wide variety of organic pollutants through their interaction with photo generated holes or reactive oxygen species, such as •OH− and •O2− radicals. The developments of nanoparticles with antimicrobial activity are of considerable interest due to microbial contamination in food industry. Nanoparticles have been reported to have effective antibacterial properties against Gram-positive and Gram-negative bacteria [31]. Our group has been working on the synthesis and application of polymer based nanocomposites. Recently, CuS–pectin, CdO–BSA, CdS– BSA, etc. nanocomposites have been synthesized and are having diverse applications [32]. To the best of our knowledge, no study has been attempted on the synthesis of Pc/CSNC nanocomposite with photocatalytic and antibacterial activity. In the present work, Pc/CSNC nanocomposites were synthesized in aqueous phase at a temperature of 60 °C. Pc/CSNC was characterized by XRD, FTIR, TEM, TGA, etc. The nanocomposites were further evaluated for their photocatalytic degradation ability of methylene blue dye in the presence of sodium lamp source and sunlight radiation. Pc/CSNC was explored for antibacterial activity against Gram-negative Escherichia coli bacteria culture. 2. Experimental 2.1. Chemicals All chemicals used in this study were of analytical grade. Pectin, CdSO4, Na2S and methylene blue (MB) were purchased from SigmaAldrich Company (India) and used as received. All the solutions were prepared in double distilled water. 2.2. Instrumentation The phase composition of the CdS nanocomposite was determined by using X-ray diffractometer (Panalytical S X. Pert Pro) using CuKα radiation. Their morphology was studied with a transmission electron microscope (Hitachi TEM System). Thermal analysis was determined with Mettler Toledo (DSC-851E). Fourier transforms infrared spectroscopy analysis was done by using infrared spectrophotometer (Perkin-Elmer Spectrum 400). The concentration of dye was determined by using UV–visible spectrophotometer (Systronics 117). 2.3. Synthesis of Pectin–CdS nanocomposite (Pc/CSNC) Pectin–cadmium sulfide nanocomposites (Pc/CSNC) were synthesized in aqueous phase at 60 °C using co-precipitation method followed by direct encapsulation with pectin. In a typical synthesis, different solutions of 0.1 M CdSO4, 0.1 M Na2S and pectin (0.20 g in 20 mL water) were prepared. 20 mL of pectin was added in 50 mL of 0.1 M CdSO4 at room temperature with continuous stirring for 20 min. 100 mL of 0.1 M Na2S was added dropwise to the above mixture with continuous stirring. The resulting mixture was stirred at magnetic stirrer for 3 h at 60 °C to obtain orange colored solution. The resulting solution was centrifuged at the rate of 10,000 rpm for 15 min on cooling. The precipitates obtained were cooled followed by washing several times with methanol and distilled water to remove the impurities. Finally the precipitates were dried in oven at 50 °C for 24 h.
2.4. Photocatalytic activity The photocatalytic activity of the Pc/CSNC was evaluated for the degradation of methylene blue dye in the presence of solar light and sodium lamp radiation sources. In this process, 0.25 g Pc/CSNC was dispersed in 100 mL of 1 × 10−4 M methylene blue dye solution and stirred in the dark for 30 min. Then suspensions were exposed to solar light and sodium lamp radiation with constant stirring. 5 mL of solution was withdrawn at regular intervals and centrifuged to remove the catalyst particles. The concentration of MB in the solution was determined at 653 nm by UV–visible spectrophotometer. All the experiments were undertaken in triplicate with errors below 5% and average values were reported. The decolorization efficiency of MB dye was calculated by using the following equation: % degradation ¼
C0 −Ct 100 C0
ð1Þ
where Co is the initial concentration and Ct is the instant concentration of the sample. The kinetics of dye degradation was described by pseudo first-order kinetics. The rate constant (k) was calculated by using Eq. (2). k ¼ 2:303 slope
ð2Þ
where the slope was obtained from the plot of ln(c) versus t. 2.5. Antibacterial properties of Pc/CSNC In this method, a colony was picked from the overnight Nutrient Agar plate culture of E. coli and was inoculated into 10 mL Nutrient Broth (NB) in a universal container and incubated at 37 °C under shaking condition of 100 rpm for 24 h. The culture was diluted to 10−5 CFU/mL (colony forming unit per mL) with NB according to MacFarland standard (Dual, 1963). 10 mL of the dilute culture was added into 190 mL NB in different conical flasks. Nanocomposites of different amounts (50 μg/mL and 100 μg/mL) were added into the above flasks. The flasks were incubated to 100 rpm at 37 °C for 24 h. 3 mL fraction of each sample was analyzed for optical density after every hour using spectrophotometer at 620 nm. A positive control was also analyzed simultaneously. The well diffusion method was also used to investigate the antibacterial activity of Pc/CSNC. The samples were prepared between in dimethyl sulphoxide (DMSO) in the range between 50 and 100 μg/mL. 15–20 mL of molten agar medium was poured into the sterilized petri dish and inoculated with 0.3 mL suspension of E. coli by spread plate method. Using sterile borex, three wells were made. The wells were filled with 100 and 50 μg/mL solution of Pc/CSNC. The petri dish was sealed with paraffin and incubated at 37 °C. The petri dish was examined for zone of inhibition after 48 h. 2.6. Fourier transform infrared spectroscopy (FTIR) FTIR spectrum of Pc/CSNC was recorded by using KBr disk method. 10 mg of Pc/CSNC was thoroughly mixed with 100 mg of KBr, powdered and a disk was formed by applying the pressure. FTIR spectrum of Pc/CSNC was recorded between 400 and 4000°cm−1. 2.7. X-ray studies The X-ray diffraction pattern of Pc/CSNC was recorded by X-ray diffractometer using CuKα radiation. The spectrum was recorded between 10° to 80° at 2θ. 2.8. Scanning electron microscopy (SEM) Scanning electron microphotographs of Pc/CSNC were recorded at different magnifications using scanning electron microscope.
V.K. Gupta et al. / Journal of Molecular Liquids 196 (2014) 107–112
2.9. Transmission electron microscopy (TEM) TEM analysis was performed to determine the size of the particles in a nanocomposite. The particles size and morphology of Pc/CSNC were analyzed by using a high resolution transmission electron microscopy Hitachi, H7500, Germany. 2.10. Thermal analysis The thermal analysis of Pc/CSNC was determined by heating the sample up to 1000 °C at a constant rate of 10 °C/min) in nitrogen atmosphere.
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peaks at 1735.96 cm− 1 and 2925.96 cm− 1 are induced by carboxyl and –CH2 groups of pectin, respectively. The results clearly revealed that the pectin moiety may have been introduced in the Pc/CSNC. Fig. 1b shows the XRD pattern of the synthesized pectin–cadmium sulfide nanocomposite (Pc/CSNC). The result confirmed the good crystallinity and cubic structure of the Pc/CSNC. The XRD peaks are found to be broad which indicates the fine size of grain. The XRD patterns exhibit the prominent broad peaks at 2θ values of 25.91, 44.24 and 52.20° matching the (111), (220) and (311) crystalline planes of cubic CdS, thereby indicating the formation of CdS. The considerable broadening of XRD peaks may be due to quantum size effect of nanocrystallites. The average particle size of Pc/CSNC estimated by Debye–Scherrer formula was found to be 3.2 nm.
3. Results and discussion FTIR spectra of Pc/CSNC was recorded in the range from 400 cm−1 to 4000 cm− 1 and shown in Fig. 1a. The strong absorption peaks at 616.28 cm−1 and 760.75 cm−1 correspond to Cd\S stretching. The absorption peak at 1010.52 cm−1 may be due to C_O and C_C bond of the pectin. The absorption peaks at 1369.94 cm−1 and 1603.51 cm−1 may be due to stretching vibration of COO− groups of the pectin. The
D ¼ 0:9l=β cosθ where λ is the wavelength of the incident X-rays, β is the full width at the half maximum of the line (FWHM), and θ is the diffraction angle. Fig. 2a–b shows the SEM images of Pc/CSNC at different magnifications. The result confirmed the porous irregular shaped particles on the polymeric backbone. TEM images of Pc/CSNC are given in
Fig. 1. (a) FTIR spectra of Pc/CSNC (b) XRD pattern of Pc/CSNC.
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Fig. 2. (a) SEM images of Pc/CSNC at different magnifications. (b) TEM micrographs of Pc/CSNC.
Fig. 2c–d. It is revealed that the average particles size was in the range between 4 nm to 10 nm. Thus the results obtained from the TEM analysis are consistent with the XRD results. The aggregation of the CdS nanoparticles was observed due to cross-linked long chain of the pectin. This indicated the successful encapsulation of the CdS nanoparticles onto pectin matrix and the good uniformity was observed between the two phases. Thermogravimetric analysis curves of Pc/CSNC are shown in Fig. 3. The figure reveals that weight loss of only 6.8% was observed up to 175 °C, which may be due to loss of water molecule [33]. The weight loss of about 28% between 175 and 520 °C may be due to complete
decomposition of the organic part of the nanocomposite material. Further weight loss may be due to formation of metal oxides. The photocatalytic degradation of methylene blue dye onto Pc/CSNC was studied under visible sunlight and sodium lamp radiation and the results are depicted in Fig. 4. In visible sunlight enhanced photochemical degradation of methylene blue dye was observed as compared to that under sodium lamp radiation source. It was recorded that about 92% of MB dye was degraded in visible sunlight as compared to 84% of dye degradation in the presence of sodium lamp radiation source within 6 h of radiation.
Fig. 3. Thermogravimetric analysis (TGA) curve of Pc/CSNC.
Fig. 4. Percentage degradation of methylene blue dye onto Pc/CSNC.
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It has been observed that the nano materials exhibit a strong inhibitory effect towards a broad spectrum of bacterial strains [35]. The results indicated that with the increase in concentration of nanocomposite, the value of optical density decreases which indicates that the antibacterial effect was more prominent at high concentration of nanocomposite [36–38]. The possible mechanisms involved in the interaction of nanomaterials with the biological macromolecules are that the nano-materials release ions which then react with the thiol groups (–SH) of the proteins present on the bacterial cell surface. Thus they deactivate the proteins, decreasing the membrane permeability and eventually causing cellular death [39–65]. 4. Conclusion
Fig. 5. Photocatalytic degradation kinetics of methylene blue dye onto Pc/CSNC.
It was inferred that the rate of photocatalytic degradation of MB dyes followed the pseudo first-order kinetic model [34]. The plot of In Ao/A vs irradiation time showed a linear correlation with good precision as shown in Fig. 5. Hence the photocatalytic degradation of MB dye using Pc/CSNC was fitted in pseudo first-order kinetics. The value of rate constant for visible sunlight and sodium lamp radiation was found to be K = 0.0033 min−1 and 0.00413 min−1 as calculated from the slope of the plots. The value of the R2 for MB dye degradation in the presence of both sunlight and sodium lamp radiation has been absorbed to be 0.9993 and 0.9997 respectively. The antibacterial activity of nanocomposites was determined against Gram-negative E.coli bacteria strain by growth curve method and the results are depicted in Fig. 6. Pc/CSNC has been found to be an effective antibacterial agent against E. coli at 50 μg/mL and 100 μg/mL for 12 h of the incubation. The antimicrobial activity of Pc/CSNC was also studied by using well diffusion method (Fig. 6 Inset). It was revealed that the zone of inhibition was greater at higher Pc/CSNC nanocomposite (14 mm for 50 μg/ml and 27 mm for 100 μg/mL) [36]. It may be that strong binding of nanoparticles to the outer membrane of E. coli caused the inhibition of active transport and retarded the enzyme activity. The reactive species such as free electrons hinders the normal cell functioning. These processes ultimately resulted in the inhibition of RNA, DNA and protein synthesis, which leads to cell lysis.
Fig. 6. Growth curve of E. coli in presence of Pc/CSNC.
The Pc/CSNC has been prepared under environment friendly conditions at 60 °C temperature. The synthesized Pc/CSNC was characterized by techniques such as FTIR, XRD, SEM, TEM and TGA. TEM images confirmed the particle size in the nano dimensions. FTIR results revealed the encapsulation of Pectin in the Pc/CSNC materials. The nanocomposite has been explored for the photocatalytic degradation of methylene blue dye in the presence of sodium lamp and visible sunlight radiations. Photochemical degradation of methylene blue dye was recorded more under visible sunlight compared to that under sodium lamp radiation. Pc/CSNC was studied for the antibacterial activity against E. coli. Acknowledgment The authors are grateful to the Vice Chancellor of Shoolini University of Biotechnology and Management Sciences for providing laboratory facilities and financial support. References [1] M. Tamborra, M. Striccoli, R. Comparelli, M.L. Curri, A. Petrella, A. Agostiano, Nanotechnology 15 (2004) 240–244. [2] N. Tessler, V. Medvedev, M. Kazes, S. Kan, U. Banin, Science 295 (2002) 1506–1508. [3] D. Battaglia, X. Peng, Nano Lett. 2 (2002) 1027–1030. [4] G.S. Wu, X.Y. Yuan, T. Xie, G.C. Xu, L.D. Zhang, Y.L. Zhuang, Mater. Lett. 58 (2004) 794–797. [5] K. Ravichandran, P. Philominathan, Sol. Energy 82 (2008) 1062–1066. [6] A.P. Alivisatos, Science 271 (1996) 933–937. [7] V.L. Colvin, M.C. Schlamp, A.P. Alivisatos, Nature 370 (1994) 354–357. [8] C.M. Niemeyer, Angew. Chem. Int. Ed. 40 (2001) 4128–4158. [9] M. Braun, C. Burda, M.A.E. Sayed, A. Mostafa, J. Phys. Chem. 105 (2001) 5548–5551. [10] A. Mews, A. Eychmüeller, M. Giersig, D. Schooss, H. Weller, J. Phys. Chem. 98 (1994) 934–941. [11] W. Caseri, in: H.S. Nalwa (Ed.), Encyclopedia of Nanoscience and Nanotechnology, vol. 6, American Scientific Publishers, Stevenson Ranch, 2004, pp. 235–247. [12] L.S. Schadler, L.C. Brinson, W.G. Sawyer, JOM 59 (2007) 50–58. [13] D.W. Schaefer, R.S. Justice, Macromolecules 40 (2007) 8501–8517. [14] H.M. Caris, V. Carola, P.M. Elven, V. Louisa, M. Herk, L. Anton Alex, Polymer 21 (1989) 133–140. [15] D. Pathania, P. Singh Sarita, S. Pathania, Desalin. Water Treat. (2013) 1–7. [16] A.P. Mouritz, A.G. Gibson, Fire Properties of Polymer Composite Materials, vol. 143, Springer, Heidelberg, 2006, (Chapter 12). [17] T.R. Hull, B.K. Kandola, Fire Retardancy of Polymers: New Strategies and Mechanisms, Royal Society of Chemistry, Cambridge, 2009. 418. [18] A.R. Horrocks, D. Price, Fire Retardant Materials, Woodhead Publishing Ltd., Cambridge, 2001. [19] W.G.T. Willats, J.P. Knox, J.D. Mikkelsen, Trends Food Sci. Technol. 17 (2006) 97–104. [20] J. Leroux, V. Langendorff, G. Schick, V. Vaishnav, J. Mazoyer, Food Hydrocoll. 17 (2003) 455–462. [21] M. Akhtar, E. Dickinson, J. Mazoyer, V. Langendorff, Food Hydrocoll. 16 (2002) 249–256. [22] V.K. Gupta, D. Pathania, S. Agarwal, P. Singh, J. Hazard. Mater. 243 (2012) 179–186. [23] V.K. Gupta, I. Ali, Sep. Purif. Technol. 18 (2000) 131–140. [24] V.K. Gupta, R. Jain, S. Varshney, J. Hazard. Mater. 142 (2007) 443–448. [25] B.K. Koerbahti, K. Artut, C. Gecgel, A. Ozer, Chem. Eng. J. 173 (2011) 677–688. [26] V.K. Gupta, I. Ali, J. Environ. Sci. Technol. 42 (2008) 766–770. [27] I. Ali, Chem. Rev. 112 (2012) 5073–5091. [28] V.K. Gupta, I. Ali, V.K. Saini, T.V. Gerven, B.V. Bruggen, C. Vandecasteele, Ind. Eng. Chem. Res. 44 (2005) 3655–3664. [29] D. Beydoun, R. Amal, G. Low, S. McEvoy, J. Nanopart. Res. 1 (1999) 439–458. [30] S. Kant, D. Pathania, P. Singh, P. Dhiman, A. Kumar, Appl. Catal. B 147 (2014) 340–352.
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Contents lists available at ScienceDirect
Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq
Liquid phase synthesis of pectin–cadmium sulfide nanocomposite and its photocatalytic and antibacterial activity Vinod Kumar Gupta a,⁎, Deepak Pathania b, Mohammad Asif c, Gaurav Sharma b a b c
Department of Chemistry, Indian Institute of Technology Rookree, Roorkee 247667, India Department of Chemistry, Shoolini University, Solan, Himachal Pradesh 173212, India Department of Chemical Engineering, King Saud University, Riyad, Saudi Arabia
a r t i c l e
i n f o
Article history: Received 7 March 2014 Received in revised form 12 March 2014 Accepted 16 March 2014 Available online 27 March 2014 Keywords: Pectin Cadmium sulfide Nanocomposite Photocatalytic activity Antibacterial properties
a b s t r a c t We report the synthesis of pectin–cadmium sulfide nanocomposite (Pc/CSNC) in aqueous phase at 60 °C using pectin as the coupling negotiator. The nanocomposite was characterized by using techniques such as X-ray powdered diffraction (XRD), transmission electron spectroscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). TEM results indicated that the average size of particles in Pc/CSNC was in the range from 4 nm to 10 nm. These results were consistent with the results obtained from XRD data. Pc/CSNC was explored for the photocatalytic degradation of methylene blue (MB) dye from waste water in the presence of sunlight and sodium lamp source. Photocatalytic degradation of methylene blue dye was recorded to be higher under visible light irradiation (95.5%) as compared to that under sodium lamp source (88.9%) after 6 h of irradiation. Pc/CSNC offered excellent antibacterial activity against Escherichia coli bacteria culture. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Interest in nano-sized objects has increased recently due to their unique physical, chemical, electrical and optical properties in comparison to their bulk counterparts. Synthesis of semiconductors of groups II–VI in a nanopowder form is currently an area of intense scientific interest due to their vital applications in optoelectronics, photonics, biomedical and light emitting devices [1–3]. CdS is one such semiconductor with a direct band gap of 2.42 eV at 300 K. It's applications for optoelectronics, being used in photosensitive and photovoltaic devices, solar cells, transistors, light emitting diodes, photo catalysis and photoluminescence sensors are already established by various studies [4–7]. CdS nanomaterials have been used as bioorganic detector of proteins or DNA [8]. CdS nanoparticles with accurate surface modification have recorded enhanced luminescence properties [9,10]. Recently, hybrid organic–inorganic nano-composites have gained much attention due to their credibility to offer synergistic feature of polymeric material with those of inorganic constituents. They offer the dual advantages of the inorganic material like rigidity, thermal stability, etc. and those of organic polymer like flexibility, dielectric, ductility, and processability. In polymer based nano-composites the small size of the fillers results in dramatic increase in interfacial area as compared to their traditional composites. This interfacial area creates a significant
⁎ Corresponding author. Tel.: +91 1332285801; fax: +91 1332273560. E-mail addresses: [email protected], [email protected] (V.K. Gupta).
http://dx.doi.org/10.1016/j.molliq.2014.03.021 0167-7322/© 2014 Elsevier B.V. All rights reserved.
volume fraction of interfacial polymer with properties different from the bulk polymer even at low loadings [11–13]. The surfaces of inorganic particles are usually hydrophilic, while those of polymers are usually hydrophobic. Therefore, the surfaces of inorganic particles need to be modified or pretreated by using some coupling agents in order to promote the compatibility between polymeric phase and inorganic phase and to maintain unique morphology [14]. Polymers are exceptional host materials for nanoparticles of metals and semiconductor [15]. Hybrid materials have high specific stiffness and strength, high toughness, corrosion resistance, low density and thermal insulation [16–18]. Pectin is a natural, non-toxic and amorphous carbohydrate present in cell walls of all plant tissues and functions as an intercellular and intracellular cementing material. Pectin has been commonly used in the food industry on account of its gelling, stabilizing thickening and emulsifying properties and also due to its excellent eco-friendly biodegradable applications [19–21]. Pectin macromolecules are able to bind with some organic or inorganic substances through molecular interactions. Dyes are discharged into water system from the effluents of industries like textile, paper, printing, plastics and leather. Many of these dyes are toxic, non-biodegradable, carcinogenic and mutagenic to aquatic life and human being [22,23]. Thus, the presence of even small amount of dye in water is of high concern. A number of techniques have been used for the removal of dyes from water system [24–28]. Nowadays bio-adsorbent based materials have gained importance due to their low-cost, easy processability, high-volume application, renewable nature and possibility of recycling.
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Although adsorption has been a widely used method for dye treatment, but it results in secondary pollution due to transfers of dye from aqueous to solid phase. On the other hand, advanced oxidation process initiated by photocatalytic degradation can offer a better solution for decolorization, breakdown and mineralization of dyes [29]. Since photocatalytic reaction takes place on the surface of the semiconductors, morphology and surface alteration have a strong influence on the photocatalytic effect [30]. The semiconductor nanoparticles, when irritated with light, produce an electron–hole pair, with an electron in the conduction band and hole in the valence band. Photocatalytic process results in oxidation–reduction and finally the degradation of a wide variety of organic pollutants through their interaction with photo generated holes or reactive oxygen species, such as •OH− and •O2− radicals. The developments of nanoparticles with antimicrobial activity are of considerable interest due to microbial contamination in food industry. Nanoparticles have been reported to have effective antibacterial properties against Gram-positive and Gram-negative bacteria [31]. Our group has been working on the synthesis and application of polymer based nanocomposites. Recently, CuS–pectin, CdO–BSA, CdS– BSA, etc. nanocomposites have been synthesized and are having diverse applications [32]. To the best of our knowledge, no study has been attempted on the synthesis of Pc/CSNC nanocomposite with photocatalytic and antibacterial activity. In the present work, Pc/CSNC nanocomposites were synthesized in aqueous phase at a temperature of 60 °C. Pc/CSNC was characterized by XRD, FTIR, TEM, TGA, etc. The nanocomposites were further evaluated for their photocatalytic degradation ability of methylene blue dye in the presence of sodium lamp source and sunlight radiation. Pc/CSNC was explored for antibacterial activity against Gram-negative Escherichia coli bacteria culture. 2. Experimental 2.1. Chemicals All chemicals used in this study were of analytical grade. Pectin, CdSO4, Na2S and methylene blue (MB) were purchased from SigmaAldrich Company (India) and used as received. All the solutions were prepared in double distilled water. 2.2. Instrumentation The phase composition of the CdS nanocomposite was determined by using X-ray diffractometer (Panalytical S X. Pert Pro) using CuKα radiation. Their morphology was studied with a transmission electron microscope (Hitachi TEM System). Thermal analysis was determined with Mettler Toledo (DSC-851E). Fourier transforms infrared spectroscopy analysis was done by using infrared spectrophotometer (Perkin-Elmer Spectrum 400). The concentration of dye was determined by using UV–visible spectrophotometer (Systronics 117). 2.3. Synthesis of Pectin–CdS nanocomposite (Pc/CSNC) Pectin–cadmium sulfide nanocomposites (Pc/CSNC) were synthesized in aqueous phase at 60 °C using co-precipitation method followed by direct encapsulation with pectin. In a typical synthesis, different solutions of 0.1 M CdSO4, 0.1 M Na2S and pectin (0.20 g in 20 mL water) were prepared. 20 mL of pectin was added in 50 mL of 0.1 M CdSO4 at room temperature with continuous stirring for 20 min. 100 mL of 0.1 M Na2S was added dropwise to the above mixture with continuous stirring. The resulting mixture was stirred at magnetic stirrer for 3 h at 60 °C to obtain orange colored solution. The resulting solution was centrifuged at the rate of 10,000 rpm for 15 min on cooling. The precipitates obtained were cooled followed by washing several times with methanol and distilled water to remove the impurities. Finally the precipitates were dried in oven at 50 °C for 24 h.
2.4. Photocatalytic activity The photocatalytic activity of the Pc/CSNC was evaluated for the degradation of methylene blue dye in the presence of solar light and sodium lamp radiation sources. In this process, 0.25 g Pc/CSNC was dispersed in 100 mL of 1 × 10−4 M methylene blue dye solution and stirred in the dark for 30 min. Then suspensions were exposed to solar light and sodium lamp radiation with constant stirring. 5 mL of solution was withdrawn at regular intervals and centrifuged to remove the catalyst particles. The concentration of MB in the solution was determined at 653 nm by UV–visible spectrophotometer. All the experiments were undertaken in triplicate with errors below 5% and average values were reported. The decolorization efficiency of MB dye was calculated by using the following equation: % degradation ¼
C0 −Ct 100 C0
ð1Þ
where Co is the initial concentration and Ct is the instant concentration of the sample. The kinetics of dye degradation was described by pseudo first-order kinetics. The rate constant (k) was calculated by using Eq. (2). k ¼ 2:303 slope
ð2Þ
where the slope was obtained from the plot of ln(c) versus t. 2.5. Antibacterial properties of Pc/CSNC In this method, a colony was picked from the overnight Nutrient Agar plate culture of E. coli and was inoculated into 10 mL Nutrient Broth (NB) in a universal container and incubated at 37 °C under shaking condition of 100 rpm for 24 h. The culture was diluted to 10−5 CFU/mL (colony forming unit per mL) with NB according to MacFarland standard (Dual, 1963). 10 mL of the dilute culture was added into 190 mL NB in different conical flasks. Nanocomposites of different amounts (50 μg/mL and 100 μg/mL) were added into the above flasks. The flasks were incubated to 100 rpm at 37 °C for 24 h. 3 mL fraction of each sample was analyzed for optical density after every hour using spectrophotometer at 620 nm. A positive control was also analyzed simultaneously. The well diffusion method was also used to investigate the antibacterial activity of Pc/CSNC. The samples were prepared between in dimethyl sulphoxide (DMSO) in the range between 50 and 100 μg/mL. 15–20 mL of molten agar medium was poured into the sterilized petri dish and inoculated with 0.3 mL suspension of E. coli by spread plate method. Using sterile borex, three wells were made. The wells were filled with 100 and 50 μg/mL solution of Pc/CSNC. The petri dish was sealed with paraffin and incubated at 37 °C. The petri dish was examined for zone of inhibition after 48 h. 2.6. Fourier transform infrared spectroscopy (FTIR) FTIR spectrum of Pc/CSNC was recorded by using KBr disk method. 10 mg of Pc/CSNC was thoroughly mixed with 100 mg of KBr, powdered and a disk was formed by applying the pressure. FTIR spectrum of Pc/CSNC was recorded between 400 and 4000°cm−1. 2.7. X-ray studies The X-ray diffraction pattern of Pc/CSNC was recorded by X-ray diffractometer using CuKα radiation. The spectrum was recorded between 10° to 80° at 2θ. 2.8. Scanning electron microscopy (SEM) Scanning electron microphotographs of Pc/CSNC were recorded at different magnifications using scanning electron microscope.
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2.9. Transmission electron microscopy (TEM) TEM analysis was performed to determine the size of the particles in a nanocomposite. The particles size and morphology of Pc/CSNC were analyzed by using a high resolution transmission electron microscopy Hitachi, H7500, Germany. 2.10. Thermal analysis The thermal analysis of Pc/CSNC was determined by heating the sample up to 1000 °C at a constant rate of 10 °C/min) in nitrogen atmosphere.
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peaks at 1735.96 cm− 1 and 2925.96 cm− 1 are induced by carboxyl and –CH2 groups of pectin, respectively. The results clearly revealed that the pectin moiety may have been introduced in the Pc/CSNC. Fig. 1b shows the XRD pattern of the synthesized pectin–cadmium sulfide nanocomposite (Pc/CSNC). The result confirmed the good crystallinity and cubic structure of the Pc/CSNC. The XRD peaks are found to be broad which indicates the fine size of grain. The XRD patterns exhibit the prominent broad peaks at 2θ values of 25.91, 44.24 and 52.20° matching the (111), (220) and (311) crystalline planes of cubic CdS, thereby indicating the formation of CdS. The considerable broadening of XRD peaks may be due to quantum size effect of nanocrystallites. The average particle size of Pc/CSNC estimated by Debye–Scherrer formula was found to be 3.2 nm.
3. Results and discussion FTIR spectra of Pc/CSNC was recorded in the range from 400 cm−1 to 4000 cm− 1 and shown in Fig. 1a. The strong absorption peaks at 616.28 cm−1 and 760.75 cm−1 correspond to Cd\S stretching. The absorption peak at 1010.52 cm−1 may be due to C_O and C_C bond of the pectin. The absorption peaks at 1369.94 cm−1 and 1603.51 cm−1 may be due to stretching vibration of COO− groups of the pectin. The
D ¼ 0:9l=β cosθ where λ is the wavelength of the incident X-rays, β is the full width at the half maximum of the line (FWHM), and θ is the diffraction angle. Fig. 2a–b shows the SEM images of Pc/CSNC at different magnifications. The result confirmed the porous irregular shaped particles on the polymeric backbone. TEM images of Pc/CSNC are given in
Fig. 1. (a) FTIR spectra of Pc/CSNC (b) XRD pattern of Pc/CSNC.
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Fig. 2. (a) SEM images of Pc/CSNC at different magnifications. (b) TEM micrographs of Pc/CSNC.
Fig. 2c–d. It is revealed that the average particles size was in the range between 4 nm to 10 nm. Thus the results obtained from the TEM analysis are consistent with the XRD results. The aggregation of the CdS nanoparticles was observed due to cross-linked long chain of the pectin. This indicated the successful encapsulation of the CdS nanoparticles onto pectin matrix and the good uniformity was observed between the two phases. Thermogravimetric analysis curves of Pc/CSNC are shown in Fig. 3. The figure reveals that weight loss of only 6.8% was observed up to 175 °C, which may be due to loss of water molecule [33]. The weight loss of about 28% between 175 and 520 °C may be due to complete
decomposition of the organic part of the nanocomposite material. Further weight loss may be due to formation of metal oxides. The photocatalytic degradation of methylene blue dye onto Pc/CSNC was studied under visible sunlight and sodium lamp radiation and the results are depicted in Fig. 4. In visible sunlight enhanced photochemical degradation of methylene blue dye was observed as compared to that under sodium lamp radiation source. It was recorded that about 92% of MB dye was degraded in visible sunlight as compared to 84% of dye degradation in the presence of sodium lamp radiation source within 6 h of radiation.
Fig. 3. Thermogravimetric analysis (TGA) curve of Pc/CSNC.
Fig. 4. Percentage degradation of methylene blue dye onto Pc/CSNC.
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It has been observed that the nano materials exhibit a strong inhibitory effect towards a broad spectrum of bacterial strains [35]. The results indicated that with the increase in concentration of nanocomposite, the value of optical density decreases which indicates that the antibacterial effect was more prominent at high concentration of nanocomposite [36–38]. The possible mechanisms involved in the interaction of nanomaterials with the biological macromolecules are that the nano-materials release ions which then react with the thiol groups (–SH) of the proteins present on the bacterial cell surface. Thus they deactivate the proteins, decreasing the membrane permeability and eventually causing cellular death [39–65]. 4. Conclusion
Fig. 5. Photocatalytic degradation kinetics of methylene blue dye onto Pc/CSNC.
It was inferred that the rate of photocatalytic degradation of MB dyes followed the pseudo first-order kinetic model [34]. The plot of In Ao/A vs irradiation time showed a linear correlation with good precision as shown in Fig. 5. Hence the photocatalytic degradation of MB dye using Pc/CSNC was fitted in pseudo first-order kinetics. The value of rate constant for visible sunlight and sodium lamp radiation was found to be K = 0.0033 min−1 and 0.00413 min−1 as calculated from the slope of the plots. The value of the R2 for MB dye degradation in the presence of both sunlight and sodium lamp radiation has been absorbed to be 0.9993 and 0.9997 respectively. The antibacterial activity of nanocomposites was determined against Gram-negative E.coli bacteria strain by growth curve method and the results are depicted in Fig. 6. Pc/CSNC has been found to be an effective antibacterial agent against E. coli at 50 μg/mL and 100 μg/mL for 12 h of the incubation. The antimicrobial activity of Pc/CSNC was also studied by using well diffusion method (Fig. 6 Inset). It was revealed that the zone of inhibition was greater at higher Pc/CSNC nanocomposite (14 mm for 50 μg/ml and 27 mm for 100 μg/mL) [36]. It may be that strong binding of nanoparticles to the outer membrane of E. coli caused the inhibition of active transport and retarded the enzyme activity. The reactive species such as free electrons hinders the normal cell functioning. These processes ultimately resulted in the inhibition of RNA, DNA and protein synthesis, which leads to cell lysis.
Fig. 6. Growth curve of E. coli in presence of Pc/CSNC.
The Pc/CSNC has been prepared under environment friendly conditions at 60 °C temperature. The synthesized Pc/CSNC was characterized by techniques such as FTIR, XRD, SEM, TEM and TGA. TEM images confirmed the particle size in the nano dimensions. FTIR results revealed the encapsulation of Pectin in the Pc/CSNC materials. The nanocomposite has been explored for the photocatalytic degradation of methylene blue dye in the presence of sodium lamp and visible sunlight radiations. Photochemical degradation of methylene blue dye was recorded more under visible sunlight compared to that under sodium lamp radiation. Pc/CSNC was studied for the antibacterial activity against E. coli. Acknowledgment The authors are grateful to the Vice Chancellor of Shoolini University of Biotechnology and Management Sciences for providing laboratory facilities and financial support. References [1] M. Tamborra, M. Striccoli, R. Comparelli, M.L. Curri, A. Petrella, A. Agostiano, Nanotechnology 15 (2004) 240–244. [2] N. Tessler, V. Medvedev, M. Kazes, S. Kan, U. Banin, Science 295 (2002) 1506–1508. [3] D. Battaglia, X. Peng, Nano Lett. 2 (2002) 1027–1030. [4] G.S. Wu, X.Y. Yuan, T. Xie, G.C. Xu, L.D. Zhang, Y.L. Zhuang, Mater. Lett. 58 (2004) 794–797. [5] K. Ravichandran, P. Philominathan, Sol. Energy 82 (2008) 1062–1066. [6] A.P. Alivisatos, Science 271 (1996) 933–937. [7] V.L. Colvin, M.C. Schlamp, A.P. Alivisatos, Nature 370 (1994) 354–357. [8] C.M. Niemeyer, Angew. Chem. Int. Ed. 40 (2001) 4128–4158. [9] M. Braun, C. Burda, M.A.E. Sayed, A. Mostafa, J. Phys. Chem. 105 (2001) 5548–5551. [10] A. Mews, A. Eychmüeller, M. Giersig, D. Schooss, H. Weller, J. Phys. Chem. 98 (1994) 934–941. [11] W. Caseri, in: H.S. Nalwa (Ed.), Encyclopedia of Nanoscience and Nanotechnology, vol. 6, American Scientific Publishers, Stevenson Ranch, 2004, pp. 235–247. [12] L.S. Schadler, L.C. Brinson, W.G. Sawyer, JOM 59 (2007) 50–58. [13] D.W. Schaefer, R.S. Justice, Macromolecules 40 (2007) 8501–8517. [14] H.M. Caris, V. Carola, P.M. Elven, V. Louisa, M. Herk, L. Anton Alex, Polymer 21 (1989) 133–140. [15] D. Pathania, P. Singh Sarita, S. Pathania, Desalin. Water Treat. (2013) 1–7. [16] A.P. Mouritz, A.G. Gibson, Fire Properties of Polymer Composite Materials, vol. 143, Springer, Heidelberg, 2006, (Chapter 12). [17] T.R. Hull, B.K. Kandola, Fire Retardancy of Polymers: New Strategies and Mechanisms, Royal Society of Chemistry, Cambridge, 2009. 418. [18] A.R. Horrocks, D. Price, Fire Retardant Materials, Woodhead Publishing Ltd., Cambridge, 2001. [19] W.G.T. Willats, J.P. Knox, J.D. Mikkelsen, Trends Food Sci. Technol. 17 (2006) 97–104. [20] J. Leroux, V. Langendorff, G. Schick, V. Vaishnav, J. Mazoyer, Food Hydrocoll. 17 (2003) 455–462. [21] M. Akhtar, E. Dickinson, J. Mazoyer, V. Langendorff, Food Hydrocoll. 16 (2002) 249–256. [22] V.K. Gupta, D. Pathania, S. Agarwal, P. Singh, J. Hazard. Mater. 243 (2012) 179–186. [23] V.K. Gupta, I. Ali, Sep. Purif. Technol. 18 (2000) 131–140. [24] V.K. Gupta, R. Jain, S. Varshney, J. Hazard. Mater. 142 (2007) 443–448. [25] B.K. Koerbahti, K. Artut, C. Gecgel, A. Ozer, Chem. Eng. J. 173 (2011) 677–688. [26] V.K. Gupta, I. Ali, J. Environ. Sci. Technol. 42 (2008) 766–770. [27] I. Ali, Chem. Rev. 112 (2012) 5073–5091. [28] V.K. Gupta, I. Ali, V.K. Saini, T.V. Gerven, B.V. Bruggen, C. Vandecasteele, Ind. Eng. Chem. Res. 44 (2005) 3655–3664. [29] D. Beydoun, R. Amal, G. Low, S. McEvoy, J. Nanopart. Res. 1 (1999) 439–458. [30] S. Kant, D. Pathania, P. Singh, P. Dhiman, A. Kumar, Appl. Catal. B 147 (2014) 340–352.
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