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A novel zinc oxide–zirconium (IV) phosphate nanocomposite as antibacterial material with enhanced ion exchange properties
Colloids and Interface Science Communications 7 (2015) 1–6
Contents lists available at ScienceDirect
Colloids and Interface Science Communications journal homepage: www.elsevier.com/locate/colcom
Rapid Communication
A novel zinc oxide–zirconium (IV) phosphate nanocomposite as antibacterial material with enhanced ion exchange properties Sandeep Kaushal a, Pushpender K. Sharma b, Susheel K. Mittal c, Pritpal Singh a,⁎ a b c
Department of Chemistry, Sri Guru Granth Sahib World University, Fatehgarh Sahib, (Pb), India Department of Biotechnology, Sri Guru Granth Sahib World University, Fatehgarh Sahib, (Pb), India School of Chemistry & Biochemistry, Thapar University, Patiala 147004, India
a r t i c l e
i n f o
Article history: Received 15 August 2015 Accepted 22 November 2015 Available online 4 January 2016 Keywords: Nanocomposite ZnO\ \ZrP ion exchanger Electrochemical studies Antibacterial activity
a b s t r a c t Zinc oxide–zirconium (IV) phosphate (ZnO\\ZrP) nanocomposite was synthesized by sol gel method at pH ≈ 2. It was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermal analysis (TGA/DTA/DSC). The nanocomposite was also explored for different properties such as ion exchange capacity, membrane potential, transport number, permselectivity, and fixed charge density. The nanocomposite ion exchanger showed an ion-exchange capacity of 0.60 meq/g for Na+ ions. The effect of addition of ZnO nanoparticles on the properties of zirconium (IV) phosphate ion-exchange membrane has been studied. The membrane was characterized at different electrolyte concentrations. Interestingly, the nanocomposite also displayed some antibacterial activity towards the Gram negative E. coli culture. © 2015 Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
The ion-exchange membranes (IEMs) play an important role in biochemical and chemical industry [1–3]. The IEMs have also been employed for treatment of industrial and biological effluents [2,4–8]. The IEMs with special physio-chemical characteristics like good permeability, high ionic conductivity, and suitable thermal and mechanical resistances have been employed for advanced applications [9,10]. Due to chemical and electrochemical properties of ion exchangers, the IEMs act as separation wall between the two solutions. The membrane contains a large number of counter ions but relatively few co-ions due to Donnan exclusion, when electrolyte of low or moderate concentration is in contact with the membrane. ZnO nanoparticles are the new class of advanced materials with very interesting features in material science such as high thermal and chemical stability, high catalytic activity, intensive radiation absorption, and effective antibacterial activity [11]. The inorganic nanoparticles or fillers have been incorporated in polymeric materials to enhance the properties like mechanical, thermal, and chemical stability of ion exchanger in severe conditions like high temperature, and to improve the separation properties of the membrane [12,13]. Different groups have investigated the antimicrobial activities of nanocomposite by diverse methodologies [14,15]. Zirconium phosphate is an excellent inorganic ion exchanger of the class of tetravalent metal acid salts. It has recently been confirmed as a
⁎ Corresponding author. E-mail address: [email protected] (P. Singh).
very good sorbent for heavy metals due to its high selectivity, thermal stability, and insolubility in water. In the present investigation, a heterogonous ion exchange membrane of zirconium phosphate has been prepared by incorporation of ZnO nanoparticles. The behavior of nanocomposite inorganic ion-exchange membrane was studied at different concentrations of alkali and alkaline earth metal chlorides and compared with that of pristine membrane. In addition, the nanocomposite ion exchanger acted as inhibitor for the growth of E. coli bacteria. Scanning electron microscope (SEM) images were taken to observe the topography of synthesized nanoparticles. The SEM image of synthesized particles (in the powder form) taken at a magnification of 2500× (Fig. 1a) revealed the formation of a large number of overlapped distorted spherical particles with composite structure. The composite structure showed two distinct phases. The dark phase in background that formed the matrix indicated the presence of an element with high atomic weight which may be zirconium, and the light phase may be due to presence of zinc. The light phase particles of irregular shapes are reinforced in the matrix. The inset picture in Fig. 1(a) shows the SEM image of zirconium phosphate exchanger, which indicated enormous range of particle sizes with irregular shapes. More detailed study of the composite structure has been carried out using transmission electron microscope and is discussed in later part. The EDX spectrum of ZnO\\ZrP (Fig. 1b) confirmed the presence of Zr, P, Zn, and O in the nanocomposite (Table 1). An investigation of the synthesized product on atomic scale was carried out by high-resolution transmission electron microscope (TEM). Fig. 2 shows that the TEM micrograph of ZnO\\ZrP with selected area
http://dx.doi.org/10.1016/j.colcom.2015.11.003 2215-0382/© 2015 Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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Fig. 1. (a) SEM of ZnO\ \ZrP nanocomposite (inset image of ZrP), 1(b) EDX images of ZnO\ \ZrP nanocomposite, 1(c) FTIR spectra ZrP and ZnO\ \ZrP nanocomposite, 1(d) XRD spectra of ZrP and ZnO\ \ZrP nanocomposite 1 (e) TGA and DTA curves of ZnO\ \ZrP nanocomposite
energy diffraction (SAED) pattern. It was observed from the TEM micrograph (Fig. 2a) that the synthesized particles consist of core-shell type structure with varying particle sizes. These particles are found to be distorted in spherical shape. Regardless of their overlapping, they are not agglomerated as their grain boundary is clearly visible and distinctive. It was observed from TEM micrograph (Fig. 2a) at 30,000× magnification that the domain boundaries of core and shell have different density of particles. The TEM was recorded at 200,000× magnification to get more clarity of the core-shell structures, and the focus was done
Table 1 Percentage elemental composition of ZnO\ \ZrP nanocomposite. Element PK Zn K Zr L O
Weight (%)
Atomic (%)
16.43 1.59 44.69 37.28
15.72 0.72 14.52 69.05
on a single particle (Fig. 2c). This TEM micrograph clearly showed the density difference between the core-shell particles. Dark region showed the higher density or higher atomic number element regions (ZrP, as confirmed from EDX), and bright region showed the low atomic density or lighter atomic number element regions (ZnO, as confirmed from EDX). A full magnification of 1,000,000 × was carried out at core part (Fig. 2d) and core-shell boundary (Fig. 2e), to observe the crystallite nature of core-shell particles. The inset (Fig. 2d) showed the single crystallite nature of the particles of core, and the inset (Fig. 2e) showed the crystallite nature of core as well as shell (as confirmed by XRD). The single crystallite nature of particles was further confirmed from the SAED pattern (Fig. 2b). There is an amorphous region between the core and shell boundary. This region is due to diffusion of oxygen particles into the core. The core and shell were found to have a diameter of 70 ± 10 nm and 10 ± 3 nm, respectively. The d-spacing for ZnO and ZrP was found to be approximately 2.3 Å and 1.9 Å, respectively. FTIR spectroscopic studies were carried out on pure zirconium phosphate and zinc oxide–zirconium phosphate nanocomposite (Fig. 1c). The FTIR spectrum of pure zirconium phosphate showed a broad band in the region ≈ 3420 cm− 1 due to symmetric and asymmetric \\OH
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Fig. 2. TEM micrographs of ZnO\ \ZrP nanocomposite at different magnifications.
stretching, whereas the bands at ≈1615 cm−1 and 1020 cm−1 are attributed to H\\O\\H bending and PO stretching, respectively. A broad band observed at 3383 cm−1 in ZnO\\ZrP nanocomposite may be due to \\OH stretching. The band at 1645 cm− 1 is attributed to the presence of moisture in sample, and the band in the vicinity of 500– 600 cm−1 is due to Zn\\O stretching in ZnO [16]. Fig. 1(d) presents X-ray diffraction (XRD) patterns of synthesized ZrP and ZnO\\ZrP nanocomposite. ZrP is amorphous in nature, but the matrix assumes crystalline nature with the addition of ZnO nanoparticles. The JCPDS 00-053-0958 has confirmed the formation of monoclinic crystalline phase of zinc-zirconium phosphate, with the empirical formula Zn0.5Zr2P3O12. Thermal studies (TGA/DTA) of ZnO\\ZrP nanocomposite are shown in Fig. 1(e). The nanocomposite exchanger was heated from room temperature to 700 °C, with an increment of 10 °C/min in air. The weight loss by TGA in temperature range 60–125 °C corresponds to exothermic hump in the same region in DTA curve, and this weight loss (16.7%) may be due to evaporation of water molecules from sample [17]. Similarly, there is an exothermic hump in the region 210–310 °C, which corresponds to weight loss (11.7%) shown by TGA curve in the same region. This may be due to conversion of some phosphate into pyrophosphate [18]. The last and final exothermic hump is observed in the temperature range 390–420 °C which also corresponds to weight loss (3.3%) in TGA curve in the same region. This may be attributed to condensation of exchangeable hydroxyl groups which is usual behavior of inorganic ion exchangers [19]. ZnO\\ZrP nanocomposite showed enhanced ion-exchange capacity for Na+ ions (0.60 meq/g) as compared to ZrP, its inorganic counterpart (0.50 meq/g). The higher Na+ ion-exchange capacity of ZnO\\ZrP may be due to better adsorption properties of ZnO nanoparticles.
The membrane potential of nanocomposite membrane has been observed to be more than that of pristine ZrP membrane for different 1:1 and 1:2 electrolytes at all the mean concentrations (Fig. 3 a, b). This may be due to the fact that charge density of nanocomposite ion-exchange membrane increases due to better adsorption properties of ZnO nanoparticles. Thus, the ion transport across the membrane is facilitated due to enhanced interactions between the electrolyte ions and the membrane surface. This resulted in increase of membrane potential due to enhanced Donnan exclusion. The transport numbers (Fig. 3 c, d) and permselectivity (Fig. 4a) of different 1:1 and 1:2 electrolytes in the ZnO\\ZrP nanocomposite membrane are higher than those in the pristine ZrP membrane. This may be due to higher fixed ion concentration in the nanocomposite membrane as compared to that in the pristine membrane. The increased fixed ionic concentration provides suitable ionic pathways in the membrane for movement of ions. The fixed charge density (Fig. 4b) of ions on ZnO\\ZrP nanocomposite ion-exchanger is higher than that in the corresponding ZrP ionexchanger. It may be due to the fact that a larger portion of internal fixed charge density remains inactive in ZrP ion-exchanger, but the concentration of active fixed charges on the surface of nanocomposite increases due to better adsorption characteristics of ZnO nanoparticles. The fixed charge density of Li+ ion on the nanocomposite was enhanced to a greater extent as compared to that of other 1:1 and 1:2 electrolyte ions. Antibacterial studies of ZnO, ZrP, and ZnO\\ZrP nanocomposite demonstrated interesting results. It is evident from Fig. 5 that ZnO and ZrP alone at various concentrations do not inhibit the bacterial growth to a marked level under the experimental conditions, whereas ZnO\\ZrP nanocomposite exhibited noticeable inhibition.
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Fig. 3. Effect of concentration on membrane potential for (a) alkali (b) alkaline earth metal ions, (c) Effect of concentration on transport number for (c) alkali (d) alkaline earth metal ions.
Interestingly, the inhibition increases with increase in concentration from 0.05 to 0.1 mg/mL, and it was observed to be inhibitory at all time points at higher concentration. It can be hypothesized here that the nanoparticles may readily pass through the cell wall having
thickness of ~5–7 nm and may attach with the cytoplasmic organelles. This may result in oxidative and cellular damages that can readily interfere with the metabolism and replication, leading to bacterial growth inhibition.
Fig. 4. Variation of permselectivity with mean concentration of (a) alkali metal ions, (b) Fixed charge density of ZnO\ \ZrP and ZrP for different electrolytes.
S. Kaushal et al. / Colloids and Interface Science Communications 7 (2015) 1–6
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of electrolyte solution. When not in use, the electrode chambers were filled with demineralized water. Membrane potential measurements were made using saturated calomel electrodes as reference electrodes in a water thermostat maintained at 27 ± 0.1 °C. Hg/Hg2Cl2, Cl−//soln. C1/Membrane/Soln. C2//Cl−, Hg2Cl2 (s)/Hg
Fig. 5. Growth inhibition curve of E coli for ZnO, ZrP, and ZrP–ZnO. nanocomposite.
Zirconyl oxychloride (Loba Chemie, India), boric acid (S.D. Fine Chem., India), phosphoric acid (Loba Chemie, India) and zinc oxide were used for synthesis. All other chemicals used were of AR grade. Standard solutions were prepared by direct weighing of AR grade reagents using double distilled water. The characterization of ZnO\\ZrP nanocomposite was performed on thermo gravimetric analyzer (Hitachi, STA-7300), X-ray diffractometer (PAN analytical, System No. DY 3190), surface scanning electron microscope (SEM JEOl, JSM-6510LV), transmission electron microscope (TEM, MIC JEM 2100), FTIR spectrometer (Perkin Spectrum-400), and Digital potentiometer (Systronic 318). Zinc oxide based nanocomposite was synthesized by sol gel method. Solutions of orthophosphoric acid (0.1 M) and zirconium (IV) oxychloride (0.1 M) were gradually mixed with continuous stirring at pH 2. The mixture was stirred for 1 h to obtain zirconium (IV) phosphate (ZrP) gel. Zinc oxide nanoparticles were then added to zirconium (IV) phosphate gel. The resulting gel was continuously stirred for 5 h and then allowed to stand for 24 h in contact with the mother liquor. The gel was filtered through Whatmann No.1 filter paper using Buchner funnel and suction pump. The gel was washed repeatedly with distilled water to remove excess chloride ions. The gel was then transferred from Buchner funnel to petri dish and dried in air oven at 40 °C. Precipitates of ZnO\\ZrP were converted to H+ form by equilibration with 0.1 M HCl solution for 24 h. The precipitates were then washed repeatedly with demineralized water to remove any excess acid, and finally dried in air oven at 40 °C. Ion-exchange capacity of ZnO\\ZrP nanocomposite was determined by column operation, using sodium nitrate solution (0.1 M) as an eluent. The ion-exchange capacity was calculated from the amount of H+ ions eluted. Equal quantities (w/w) of finely ground zinc oxide–zirconium (IV) phosphate and polystyrene were mixed thoroughly. The mixture was then kept in membrane press for 2 h, under a pressure of about 100 t at a temperature of 60 °C, to get a membrane of ≅1mm thickness. The sheet of membrane thus obtained was cut with a sharp knife, into circular disks of about 18 mm diameter. The membrane disks with good surface qualities were selected for further investigations. The membrane was pasted between the two parts of electrode assembly, using araldite. The electrode chambers were filled with 1.0 M solution of each of the concerned electrolytes for 16 h, to convert the membrane into appropriate ionic form. After equilibration, the membrane was washed and kept immersed in DMW for 2 h to remove excess
Potential measurements were made for different concentrations of the same electrolyte on two sides of membrane in such a way that the concentration ratio δ (C2/C1) = 10. The electrode chambers were rinsed with electrolyte solution of next higher concentration and then filled with same solution. The membrane was allowed to equilibrate for 2 h and the new potential difference was then noted. The membrane potentials across zirconium phosphate–zinc oxide nanocomposite membrane were determined using some 1:1 and 1:2 electrolytes, in overall concentration range of 0.01–0.1 M. The antibacterial properties of ZrP\\ZnO nanocomposite were investigated by carrying out a set of experiments to measure the bacterial growth (E. coli), in presence and absence of ZnO, ZrP, and ZnO\\ZrP, as a function of time. The E. coli strain was initially cultured in 5 mL LB medium aseptically in laminar air-flow, followed by its sub-culturing into 50 ml LB of two sets, each having ZnO, ZrP, and ZnO–ZrP at a concentration of 0.1 and 0.05 mg/ml, respectively. Simultaneously, a control experiment having no nanoparticles was also carried out. The bacterial growth was monitored after intervals of 1 h, by recording OD600 nm in UV–Visible spectrophotometer for the control and test samples. Most of the bacterial cultures develop dark orange color as their culture grows more and more dense. The OD 600 nm corresponds to orange light and hence optical density of bacterial growth is measured at 600 nm. The final OD600 nm was recorded after 24 h of growth. A graph of OD600nm versus time was plotted to check the inhibitory action of nanocomposite on bacterial growth. In summary, ZnO\\ZrP nanocomposite ion-exchanger has been prepared with higher ion-exchanger capacity than its inorganic counterpart ZrP. The incorporation of ZnO nanoparticles modified the nature of ion exchanger from amorphous to microcrystalline as confirmed by XRD. The SEM image revealed the compact structure of ZnO\\ZrP nanocomposite. The TEM images indicated that the particle size of ZnO\\ZrP was in nano-range. EDX and FTIR studies confirmed the formation of composite ion exchanger. ZnO\\ZrP nanocomposite illustrated better electrochemical properties such as permselectivity, membrane potential, and fixed charge density than its inorganic counterpart, ZrP. The nanocomposite material has been successfully used as an effective antimicrobial agent against E. coli bacteria. Acknowledgments SK, PKS, and PPS gratefully acknowledge Vice Chancellor Sri Guru Granth Sahib World University, Fatehgarh Sahib, Punjab (India), for support and lab facilities. SKM is thankful to Director, Thapar University, Patiala, for support. References [1] T. Sata, W. Yang, J. Membr. Sci. 206 (2002) 31. [2] R.K. Nagarale, G.S. Gohil, V.K. Shahi, G.S. Trivedi, R. Rangarajan, J. Colloid Interface Sci. 277 (2004) 162. [3] J.P.G. Villaluenga, V.M. Barragan, M.A. Izquierdo-Gil, M.P. Godino, B. Seoane, C. RuizBauza, J. Membr. Sci. 323 (2008) 421. [4] M.Y. Kariduraganavar, R.K. Nagarale, A.A. Kittur, S.S. Kulkarni, Desalination 197 (2006) 225. [5] E. Volodina, N. Pismenskaya, V. Nikonenko, C. Larchet, G. Pourcelly, J. Colloid Interface Sci. 285 (2005) 247. [6] C.O. M' Bareck, Q.T. Nguyen, S. Alexandre, I. Zimmerlin, J. Membr. Sci., 278 (2006) 1018. [7] T. Xu, J. Membr. Sci. 263 (2005) 1. [8] J. Schauer, L. Brozova J. Membr. Sci., 250 (2005)151. [9] S.M. Hosseini, S.S. Madaeni, A.R. Khodabakhshi, Sep. Sci. Technol. 45 (2010) 2308. [10] G. Saracco, Ann. Chim. 93 (2003) 817. [11] P. Nagaranjan, V. Rajgopalan, Sci. Technol. Adv. Mater. 9 (3) (2008) 1468. [12] S.M. Hosseini, S.S. Madaeni, A.R. Khodabakhshi, J. Membr. Sci. 362 (2010) 550.
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[13] Y. Mansourpanah, S.S. Madaeni, A. Rahimpour, A. Farhadian, A.H. Taheri, J. Membr. Sci. 330 (2009) 297. [14] B.S. Rathore, G. Sharma, D. Pathania, V.K. Gupta, J. Carb. Poly. 103 (2014) 221. [15] M. Zarrinkhameh, A. Zendehnam, S.S. Hosseini, Korean J. Chem. Eng. 31 (7) (2014) 1187. [16] F. Parvizian, S.M. Hosseini, A.R. Hamidi, S.S. Madaeni, A.R. Moghadassi, J. Taiwan Inst. Chem. Eng. 45 (2014) 2878.
[17] C. Duval, Inorganic Thermogravimetric Analysis, Elsevier, Amsterdam, 1963. [18] S.A. Innamuddin, W.A. Khan, A.A. Siddiqui, A.A. Khan, Talanta 71 (2007) 841. [19] K. Moosavi, S. Setayeshi, M.G. Maragheh, S. Javadahmdi, M.R. Kardan, J. Appl. Sci. 9 (11) (2009) 2180.
Contents lists available at ScienceDirect
Colloids and Interface Science Communications journal homepage: www.elsevier.com/locate/colcom
Rapid Communication
A novel zinc oxide–zirconium (IV) phosphate nanocomposite as antibacterial material with enhanced ion exchange properties Sandeep Kaushal a, Pushpender K. Sharma b, Susheel K. Mittal c, Pritpal Singh a,⁎ a b c
Department of Chemistry, Sri Guru Granth Sahib World University, Fatehgarh Sahib, (Pb), India Department of Biotechnology, Sri Guru Granth Sahib World University, Fatehgarh Sahib, (Pb), India School of Chemistry & Biochemistry, Thapar University, Patiala 147004, India
a r t i c l e
i n f o
Article history: Received 15 August 2015 Accepted 22 November 2015 Available online 4 January 2016 Keywords: Nanocomposite ZnO\ \ZrP ion exchanger Electrochemical studies Antibacterial activity
a b s t r a c t Zinc oxide–zirconium (IV) phosphate (ZnO\\ZrP) nanocomposite was synthesized by sol gel method at pH ≈ 2. It was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermal analysis (TGA/DTA/DSC). The nanocomposite was also explored for different properties such as ion exchange capacity, membrane potential, transport number, permselectivity, and fixed charge density. The nanocomposite ion exchanger showed an ion-exchange capacity of 0.60 meq/g for Na+ ions. The effect of addition of ZnO nanoparticles on the properties of zirconium (IV) phosphate ion-exchange membrane has been studied. The membrane was characterized at different electrolyte concentrations. Interestingly, the nanocomposite also displayed some antibacterial activity towards the Gram negative E. coli culture. © 2015 Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
The ion-exchange membranes (IEMs) play an important role in biochemical and chemical industry [1–3]. The IEMs have also been employed for treatment of industrial and biological effluents [2,4–8]. The IEMs with special physio-chemical characteristics like good permeability, high ionic conductivity, and suitable thermal and mechanical resistances have been employed for advanced applications [9,10]. Due to chemical and electrochemical properties of ion exchangers, the IEMs act as separation wall between the two solutions. The membrane contains a large number of counter ions but relatively few co-ions due to Donnan exclusion, when electrolyte of low or moderate concentration is in contact with the membrane. ZnO nanoparticles are the new class of advanced materials with very interesting features in material science such as high thermal and chemical stability, high catalytic activity, intensive radiation absorption, and effective antibacterial activity [11]. The inorganic nanoparticles or fillers have been incorporated in polymeric materials to enhance the properties like mechanical, thermal, and chemical stability of ion exchanger in severe conditions like high temperature, and to improve the separation properties of the membrane [12,13]. Different groups have investigated the antimicrobial activities of nanocomposite by diverse methodologies [14,15]. Zirconium phosphate is an excellent inorganic ion exchanger of the class of tetravalent metal acid salts. It has recently been confirmed as a
⁎ Corresponding author. E-mail address: [email protected] (P. Singh).
very good sorbent for heavy metals due to its high selectivity, thermal stability, and insolubility in water. In the present investigation, a heterogonous ion exchange membrane of zirconium phosphate has been prepared by incorporation of ZnO nanoparticles. The behavior of nanocomposite inorganic ion-exchange membrane was studied at different concentrations of alkali and alkaline earth metal chlorides and compared with that of pristine membrane. In addition, the nanocomposite ion exchanger acted as inhibitor for the growth of E. coli bacteria. Scanning electron microscope (SEM) images were taken to observe the topography of synthesized nanoparticles. The SEM image of synthesized particles (in the powder form) taken at a magnification of 2500× (Fig. 1a) revealed the formation of a large number of overlapped distorted spherical particles with composite structure. The composite structure showed two distinct phases. The dark phase in background that formed the matrix indicated the presence of an element with high atomic weight which may be zirconium, and the light phase may be due to presence of zinc. The light phase particles of irregular shapes are reinforced in the matrix. The inset picture in Fig. 1(a) shows the SEM image of zirconium phosphate exchanger, which indicated enormous range of particle sizes with irregular shapes. More detailed study of the composite structure has been carried out using transmission electron microscope and is discussed in later part. The EDX spectrum of ZnO\\ZrP (Fig. 1b) confirmed the presence of Zr, P, Zn, and O in the nanocomposite (Table 1). An investigation of the synthesized product on atomic scale was carried out by high-resolution transmission electron microscope (TEM). Fig. 2 shows that the TEM micrograph of ZnO\\ZrP with selected area
http://dx.doi.org/10.1016/j.colcom.2015.11.003 2215-0382/© 2015 Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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Fig. 1. (a) SEM of ZnO\ \ZrP nanocomposite (inset image of ZrP), 1(b) EDX images of ZnO\ \ZrP nanocomposite, 1(c) FTIR spectra ZrP and ZnO\ \ZrP nanocomposite, 1(d) XRD spectra of ZrP and ZnO\ \ZrP nanocomposite 1 (e) TGA and DTA curves of ZnO\ \ZrP nanocomposite
energy diffraction (SAED) pattern. It was observed from the TEM micrograph (Fig. 2a) that the synthesized particles consist of core-shell type structure with varying particle sizes. These particles are found to be distorted in spherical shape. Regardless of their overlapping, they are not agglomerated as their grain boundary is clearly visible and distinctive. It was observed from TEM micrograph (Fig. 2a) at 30,000× magnification that the domain boundaries of core and shell have different density of particles. The TEM was recorded at 200,000× magnification to get more clarity of the core-shell structures, and the focus was done
Table 1 Percentage elemental composition of ZnO\ \ZrP nanocomposite. Element PK Zn K Zr L O
Weight (%)
Atomic (%)
16.43 1.59 44.69 37.28
15.72 0.72 14.52 69.05
on a single particle (Fig. 2c). This TEM micrograph clearly showed the density difference between the core-shell particles. Dark region showed the higher density or higher atomic number element regions (ZrP, as confirmed from EDX), and bright region showed the low atomic density or lighter atomic number element regions (ZnO, as confirmed from EDX). A full magnification of 1,000,000 × was carried out at core part (Fig. 2d) and core-shell boundary (Fig. 2e), to observe the crystallite nature of core-shell particles. The inset (Fig. 2d) showed the single crystallite nature of the particles of core, and the inset (Fig. 2e) showed the crystallite nature of core as well as shell (as confirmed by XRD). The single crystallite nature of particles was further confirmed from the SAED pattern (Fig. 2b). There is an amorphous region between the core and shell boundary. This region is due to diffusion of oxygen particles into the core. The core and shell were found to have a diameter of 70 ± 10 nm and 10 ± 3 nm, respectively. The d-spacing for ZnO and ZrP was found to be approximately 2.3 Å and 1.9 Å, respectively. FTIR spectroscopic studies were carried out on pure zirconium phosphate and zinc oxide–zirconium phosphate nanocomposite (Fig. 1c). The FTIR spectrum of pure zirconium phosphate showed a broad band in the region ≈ 3420 cm− 1 due to symmetric and asymmetric \\OH
S. Kaushal et al. / Colloids and Interface Science Communications 7 (2015) 1–6
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Fig. 2. TEM micrographs of ZnO\ \ZrP nanocomposite at different magnifications.
stretching, whereas the bands at ≈1615 cm−1 and 1020 cm−1 are attributed to H\\O\\H bending and PO stretching, respectively. A broad band observed at 3383 cm−1 in ZnO\\ZrP nanocomposite may be due to \\OH stretching. The band at 1645 cm− 1 is attributed to the presence of moisture in sample, and the band in the vicinity of 500– 600 cm−1 is due to Zn\\O stretching in ZnO [16]. Fig. 1(d) presents X-ray diffraction (XRD) patterns of synthesized ZrP and ZnO\\ZrP nanocomposite. ZrP is amorphous in nature, but the matrix assumes crystalline nature with the addition of ZnO nanoparticles. The JCPDS 00-053-0958 has confirmed the formation of monoclinic crystalline phase of zinc-zirconium phosphate, with the empirical formula Zn0.5Zr2P3O12. Thermal studies (TGA/DTA) of ZnO\\ZrP nanocomposite are shown in Fig. 1(e). The nanocomposite exchanger was heated from room temperature to 700 °C, with an increment of 10 °C/min in air. The weight loss by TGA in temperature range 60–125 °C corresponds to exothermic hump in the same region in DTA curve, and this weight loss (16.7%) may be due to evaporation of water molecules from sample [17]. Similarly, there is an exothermic hump in the region 210–310 °C, which corresponds to weight loss (11.7%) shown by TGA curve in the same region. This may be due to conversion of some phosphate into pyrophosphate [18]. The last and final exothermic hump is observed in the temperature range 390–420 °C which also corresponds to weight loss (3.3%) in TGA curve in the same region. This may be attributed to condensation of exchangeable hydroxyl groups which is usual behavior of inorganic ion exchangers [19]. ZnO\\ZrP nanocomposite showed enhanced ion-exchange capacity for Na+ ions (0.60 meq/g) as compared to ZrP, its inorganic counterpart (0.50 meq/g). The higher Na+ ion-exchange capacity of ZnO\\ZrP may be due to better adsorption properties of ZnO nanoparticles.
The membrane potential of nanocomposite membrane has been observed to be more than that of pristine ZrP membrane for different 1:1 and 1:2 electrolytes at all the mean concentrations (Fig. 3 a, b). This may be due to the fact that charge density of nanocomposite ion-exchange membrane increases due to better adsorption properties of ZnO nanoparticles. Thus, the ion transport across the membrane is facilitated due to enhanced interactions between the electrolyte ions and the membrane surface. This resulted in increase of membrane potential due to enhanced Donnan exclusion. The transport numbers (Fig. 3 c, d) and permselectivity (Fig. 4a) of different 1:1 and 1:2 electrolytes in the ZnO\\ZrP nanocomposite membrane are higher than those in the pristine ZrP membrane. This may be due to higher fixed ion concentration in the nanocomposite membrane as compared to that in the pristine membrane. The increased fixed ionic concentration provides suitable ionic pathways in the membrane for movement of ions. The fixed charge density (Fig. 4b) of ions on ZnO\\ZrP nanocomposite ion-exchanger is higher than that in the corresponding ZrP ionexchanger. It may be due to the fact that a larger portion of internal fixed charge density remains inactive in ZrP ion-exchanger, but the concentration of active fixed charges on the surface of nanocomposite increases due to better adsorption characteristics of ZnO nanoparticles. The fixed charge density of Li+ ion on the nanocomposite was enhanced to a greater extent as compared to that of other 1:1 and 1:2 electrolyte ions. Antibacterial studies of ZnO, ZrP, and ZnO\\ZrP nanocomposite demonstrated interesting results. It is evident from Fig. 5 that ZnO and ZrP alone at various concentrations do not inhibit the bacterial growth to a marked level under the experimental conditions, whereas ZnO\\ZrP nanocomposite exhibited noticeable inhibition.
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Fig. 3. Effect of concentration on membrane potential for (a) alkali (b) alkaline earth metal ions, (c) Effect of concentration on transport number for (c) alkali (d) alkaline earth metal ions.
Interestingly, the inhibition increases with increase in concentration from 0.05 to 0.1 mg/mL, and it was observed to be inhibitory at all time points at higher concentration. It can be hypothesized here that the nanoparticles may readily pass through the cell wall having
thickness of ~5–7 nm and may attach with the cytoplasmic organelles. This may result in oxidative and cellular damages that can readily interfere with the metabolism and replication, leading to bacterial growth inhibition.
Fig. 4. Variation of permselectivity with mean concentration of (a) alkali metal ions, (b) Fixed charge density of ZnO\ \ZrP and ZrP for different electrolytes.
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of electrolyte solution. When not in use, the electrode chambers were filled with demineralized water. Membrane potential measurements were made using saturated calomel electrodes as reference electrodes in a water thermostat maintained at 27 ± 0.1 °C. Hg/Hg2Cl2, Cl−//soln. C1/Membrane/Soln. C2//Cl−, Hg2Cl2 (s)/Hg
Fig. 5. Growth inhibition curve of E coli for ZnO, ZrP, and ZrP–ZnO. nanocomposite.
Zirconyl oxychloride (Loba Chemie, India), boric acid (S.D. Fine Chem., India), phosphoric acid (Loba Chemie, India) and zinc oxide were used for synthesis. All other chemicals used were of AR grade. Standard solutions were prepared by direct weighing of AR grade reagents using double distilled water. The characterization of ZnO\\ZrP nanocomposite was performed on thermo gravimetric analyzer (Hitachi, STA-7300), X-ray diffractometer (PAN analytical, System No. DY 3190), surface scanning electron microscope (SEM JEOl, JSM-6510LV), transmission electron microscope (TEM, MIC JEM 2100), FTIR spectrometer (Perkin Spectrum-400), and Digital potentiometer (Systronic 318). Zinc oxide based nanocomposite was synthesized by sol gel method. Solutions of orthophosphoric acid (0.1 M) and zirconium (IV) oxychloride (0.1 M) were gradually mixed with continuous stirring at pH 2. The mixture was stirred for 1 h to obtain zirconium (IV) phosphate (ZrP) gel. Zinc oxide nanoparticles were then added to zirconium (IV) phosphate gel. The resulting gel was continuously stirred for 5 h and then allowed to stand for 24 h in contact with the mother liquor. The gel was filtered through Whatmann No.1 filter paper using Buchner funnel and suction pump. The gel was washed repeatedly with distilled water to remove excess chloride ions. The gel was then transferred from Buchner funnel to petri dish and dried in air oven at 40 °C. Precipitates of ZnO\\ZrP were converted to H+ form by equilibration with 0.1 M HCl solution for 24 h. The precipitates were then washed repeatedly with demineralized water to remove any excess acid, and finally dried in air oven at 40 °C. Ion-exchange capacity of ZnO\\ZrP nanocomposite was determined by column operation, using sodium nitrate solution (0.1 M) as an eluent. The ion-exchange capacity was calculated from the amount of H+ ions eluted. Equal quantities (w/w) of finely ground zinc oxide–zirconium (IV) phosphate and polystyrene were mixed thoroughly. The mixture was then kept in membrane press for 2 h, under a pressure of about 100 t at a temperature of 60 °C, to get a membrane of ≅1mm thickness. The sheet of membrane thus obtained was cut with a sharp knife, into circular disks of about 18 mm diameter. The membrane disks with good surface qualities were selected for further investigations. The membrane was pasted between the two parts of electrode assembly, using araldite. The electrode chambers were filled with 1.0 M solution of each of the concerned electrolytes for 16 h, to convert the membrane into appropriate ionic form. After equilibration, the membrane was washed and kept immersed in DMW for 2 h to remove excess
Potential measurements were made for different concentrations of the same electrolyte on two sides of membrane in such a way that the concentration ratio δ (C2/C1) = 10. The electrode chambers were rinsed with electrolyte solution of next higher concentration and then filled with same solution. The membrane was allowed to equilibrate for 2 h and the new potential difference was then noted. The membrane potentials across zirconium phosphate–zinc oxide nanocomposite membrane were determined using some 1:1 and 1:2 electrolytes, in overall concentration range of 0.01–0.1 M. The antibacterial properties of ZrP\\ZnO nanocomposite were investigated by carrying out a set of experiments to measure the bacterial growth (E. coli), in presence and absence of ZnO, ZrP, and ZnO\\ZrP, as a function of time. The E. coli strain was initially cultured in 5 mL LB medium aseptically in laminar air-flow, followed by its sub-culturing into 50 ml LB of two sets, each having ZnO, ZrP, and ZnO–ZrP at a concentration of 0.1 and 0.05 mg/ml, respectively. Simultaneously, a control experiment having no nanoparticles was also carried out. The bacterial growth was monitored after intervals of 1 h, by recording OD600 nm in UV–Visible spectrophotometer for the control and test samples. Most of the bacterial cultures develop dark orange color as their culture grows more and more dense. The OD 600 nm corresponds to orange light and hence optical density of bacterial growth is measured at 600 nm. The final OD600 nm was recorded after 24 h of growth. A graph of OD600nm versus time was plotted to check the inhibitory action of nanocomposite on bacterial growth. In summary, ZnO\\ZrP nanocomposite ion-exchanger has been prepared with higher ion-exchanger capacity than its inorganic counterpart ZrP. The incorporation of ZnO nanoparticles modified the nature of ion exchanger from amorphous to microcrystalline as confirmed by XRD. The SEM image revealed the compact structure of ZnO\\ZrP nanocomposite. The TEM images indicated that the particle size of ZnO\\ZrP was in nano-range. EDX and FTIR studies confirmed the formation of composite ion exchanger. ZnO\\ZrP nanocomposite illustrated better electrochemical properties such as permselectivity, membrane potential, and fixed charge density than its inorganic counterpart, ZrP. The nanocomposite material has been successfully used as an effective antimicrobial agent against E. coli bacteria. Acknowledgments SK, PKS, and PPS gratefully acknowledge Vice Chancellor Sri Guru Granth Sahib World University, Fatehgarh Sahib, Punjab (India), for support and lab facilities. SKM is thankful to Director, Thapar University, Patiala, for support. References [1] T. Sata, W. Yang, J. Membr. Sci. 206 (2002) 31. [2] R.K. Nagarale, G.S. Gohil, V.K. Shahi, G.S. Trivedi, R. Rangarajan, J. Colloid Interface Sci. 277 (2004) 162. [3] J.P.G. Villaluenga, V.M. Barragan, M.A. Izquierdo-Gil, M.P. Godino, B. Seoane, C. RuizBauza, J. Membr. Sci. 323 (2008) 421. [4] M.Y. Kariduraganavar, R.K. Nagarale, A.A. Kittur, S.S. Kulkarni, Desalination 197 (2006) 225. [5] E. Volodina, N. Pismenskaya, V. Nikonenko, C. Larchet, G. Pourcelly, J. Colloid Interface Sci. 285 (2005) 247. [6] C.O. M' Bareck, Q.T. Nguyen, S. Alexandre, I. Zimmerlin, J. Membr. Sci., 278 (2006) 1018. [7] T. Xu, J. Membr. Sci. 263 (2005) 1. [8] J. Schauer, L. Brozova J. Membr. Sci., 250 (2005)151. [9] S.M. Hosseini, S.S. Madaeni, A.R. Khodabakhshi, Sep. Sci. Technol. 45 (2010) 2308. [10] G. Saracco, Ann. Chim. 93 (2003) 817. [11] P. Nagaranjan, V. Rajgopalan, Sci. Technol. Adv. Mater. 9 (3) (2008) 1468. [12] S.M. Hosseini, S.S. Madaeni, A.R. Khodabakhshi, J. Membr. Sci. 362 (2010) 550.
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