- Email: [email protected]
Bi-doped ZnO yellow nanopigments: Synthesis, characterization, and antibacterial application for painting humid places
Ceramics International xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Bi-doped ZnO yellow nanopigments: Synthesis, characterization, and antibacterial application for painting humid places R. Mastana, A. Khorsand Zakb,∗, R. Pilevar Shahria a b
Department of Physics, Payame Noor University (PNU), P.O. Box 19395-3697, Tehran, Iran Nanotechnology Lab., Esfarayen University of Technology, Esfarayen, North Khorasan, Iran
A R T I C LE I N FO
A B S T R A C T
Keywords: Nanopigments ZnO nanoparticles Yellow pigment Bi-doped Zno
The main objective of the present study is the synthesis of yellow nanopigments with antibacterial properties that are suitable to paint humid places. Bismuth doped zinc oxide nanopigments were prepared through a gelatin based sol gel root. The nanopigment powders were obtained through the calcination of the prepared gels at 600 °C for 2 h. The synthesized samples were analyzed by x-ray diffraction (XRD), UV–visible spectroscopy (UV–vis), and transition electron microscopy (TEM). The powder XRD investigations and TEM observations revealed wurtzite hexagonal structure with particle and crystalline sizes lower than 100 nm. The colorimetric properties were indicated by color space method. The achievements showed yellow color for the Bi-doped samples. The antibacterial effects of the prepared samples were observed by disk diffusion method against the gram positive (G+) bacteria Bacillus Subtilis (PTCC 1420) staphylococcus aurous (PTCC 1431) and gram negative (G-) pseudomonas aeruginosa (PTCC 1074) and Escherichia Coli (PTCC 1399) bacteria that grow normally in humid places. The results showed that the prepared yellow nanopigments are suitable candidate for painting humid places.
1. Introduction Inorganic pigments are supported by a long history. These pigments are widely used to cover and color tools and materials that work in with range of temperature [1,2]. Many kinds of the pigment have heavy or transitional materials in the component which is not environmentally friendly and can endanger human health [3,4]. There are numerous researchers that one cried out to synthesis environmentally friendly pigments [5–7]. Today, nanopigments play an important role in industry [8,9]. Bacterial and antibacterial pigments are special class of pigment, used for medical, biological purposes [10,11]. According to literature, different kinds of inorganic pigments have been prepared from the combination of the nano-sized metal oxides. For example, TiO2, ZnO, CeO2, and SnO2 nanoparticles have been synthesized to be used as white pigments [12–15]. Also, some complex compounds are used as pigments including Y2BaCuO5 as green and NiTiO3 as yellow pigment [16]. Some pigments have complex compositions which are not easy for the preparation (e.g. the synthesis of (Ca1-xyEuxZny)2Al2SiO7+δ pigments reported by Bao et al.) Nowadays, many studies have been conducted to find simply-prepared pigments. Also, several materials have been examined, among which ZnO with wide energy band gap (about 3.2 eV) and numerously great properties is
∗
known to be an important material for painting. The synthesis of ZnObased nanopigments is simple and low cost. Besides, it is an antibacterial material with low toxicity which makes it the right candidate for some biological use. ZnO powder is originally white but it can change colors when doped with other elements [17]. For instance, green pigment is obtained by doping cobalt into ZnO and red pigments by adding Mn element to ZnO matrix [18,19]. Also, some other ZnObased pigments have been presented in the literature [20,21]. In this work, Bi-doped ZnO nanopigments were synthesized via a gelatin based sol-gel method. Yellow nanopigments were obtained by doping different quantities of bismuth element into the white ZnO nanopigment during the synthesis process. The prepared nanopigments were then analyzed. 2. Experimental 2.1. Materials To prepare Bi-doped ZnO nanopigments, analytical grade bismuth nitrate hexahydrate [Bi(NO3)2.6H2O, Merck %99], Zinc nitrate hexahydrate [Zn(NO3)2.H2O, Merck %99.8] and gelatin [(NHCOCH-R1)n, R1=amino acid] were selected as precursor materials and distilled
Corresponding author. E-mail addresses: [email protected], [email protected] (A. Khorsand Zak).
https://doi.org/10.1016/j.ceramint.2019.12.090 Received 26 November 2019; Received in revised form 8 December 2019; Accepted 8 December 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: R. Mastan, A. Khorsand Zak and R. Pilevar Shahri, Ceramics International, https://doi.org/10.1016/j.ceramint.2019.12.090
Ceramics International xxx (xxxx) xxx–xxx
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Fig. 1. Structure of gelatin molecule. Bi cations are attracted by the negative sites.
water as solvent. 2.2. Synthesis of the Bi-doped nanopigment samples The specific amount of zinc and bismuth nitrate were dissolved in the minimum amount of distilled water. Zn1-xBixO chemical formula was considered to measure the precursor materials quantities to prepare 10 g of the final products, where x = 0, 0.01, 0.03, and 0.05. A gelatin solution was prepared by dissolving 8 g gelatin in 120 ml distilled water. The temperature of the water was kept at 80 °C in the oil bath, meanwhile, the gelatin powder was gradually added to the water and stirred to achieve a clear gelatin solution. After that, the cation solutions were added to the gelatin solution. The stirring speed was reduced about 50 from 120 rpm and the temperature of the solution checked to be fixed at 80 °C. The solution was left in this process for about 3 h to evaporate the initial water and obtain a viscose gel. The simple reactions occurs during the gelation of the sol. Fig. 1, shows that gelatin has a complex structure with long chains of amino acids. There are O=C ̶ O ̶ sites that have negative charge. The Bi+n and Zn+2 cations are attracted by these negative sites and attached to gelation chains. Therefore, they cannot easily reach each other when the gel burning process, thereby terminating the growth of Bi-doped ZnO nanoparticles. Gelatin affects as capping agent and eliminates the growth of crystals. The obtained gel was then calcined at 600 °C for 2 h by a box furnace. The calcination temperature was chosen based on the TGA results obtained in our earlier research [22]. The same processes were conducted to prepare pure and Bi-doped samples.
Fig. 2. Images of the used bacteria in this research.
measuring the inhibition zone around the sample discs. Gentamicin antibiotic and sterptomain (Hi-Media) were used as the positive controls and strilled water as the negative control to compare the efficacy of the test sample. 2.3.2. The colorimetric studies The color space CIE L*a*b* (CIELAB), known as a color space, has been specified by the international commission on humanities. This model is used as a reference device independent model which describes all the color in the visible range for the human eye. Thus, it is presented by most of the industries and companies to evaluate the color of the days. There are three coordinations in CIELAB indicated by L*, a*, and b*. The lightness of the color represents L* from zero (yield black) to 100 (diffuse white, specular white may be higher). The symbol a* shows green while positive values show magenta. The position between yellow (positive value) and blue (negative value) is shown by b*. In addition, there are two cylindrical coordinates c* and hͦ that shows Chroma, relative saturation hue angle, hue angle in CIELab color wheel, respectively. Color-coded coordinates, data were obtained in D65/10° conditions by Konica Minulta spectrophotometer CS2000 (CS-Slow) in the wavelength rage of 300–780 nm (D65 is the simulation of day light and 10° is the detector angle). The spectrophotometer is placed in front of the sample and the light sources in both sides with direction angle of 45° in relation to them. All the destinations were 75 C < superscript > < / superscript > m < superscript > < /superscript > , Fig. 3. The measurements were applied on sample in powder form.
2.3. Characterization techniques The structural and phase evaluations of the prepared samples were studied by x-ray diffraction method using (Philips, Xpert, CuKα). A Hitachi H-7100 electron microscope was used for the TEM observation. The UV–vis reflectance spectra of the samples were recorded in the range of 300–800 nm using PerkinElmer UV–vis spectrophotometer (Lambda 25, PerkinElmer). 2.3.1. The antibacterial evaluations Disk diffusion method against the test bacteria on Muller-Hinton agar was used for the antibacterial test. The test were performed on gram positive (G+) bacteria Bacillus Subtilis (PTCC 1420) staphylococcus aurous (PTCC 1431) and gram negative (G-) pseudomonas aeruginosa (PTCC 1074) and Escherichia Coli (PTCC 1399), Fig. 2. These bacteria grow in humid and moisture condition and therefore they were chosen for the test process. Accordingly, the bacteria suspension growth was performed on tryplic soy broth (TSB) with 0.5 Mc Farland that is equal to 1.5 × 108 unit of bacteria per milliliter (CFU/mL). The media plates (MHA) were streaked with bacteria for 3 times to have a homogenous distribution. The prepared plates were incubated at 37 °C for 24 h. The antibacterial property of the sample were analyzed by
3. Results and discussion 3.1. Structure analysis Fig. 4 presents the XRD patterns of Zn1-xBixO (x = 0.0, 0.02, 0.04, 2
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Fig. 3. Scheme of the used system for colorimetric measurements. Fig. 5. XRD pattern of the prepared pure and Bi–ZnO nanopigments between 27 and 38°.
Fig. 4. XRD pattern of the prepared pure and Bi–ZnO nanopigments. Fig. 6. Absorbance spectra of the prepared pure and Bi–ZnO nanopigments.
0.06, and 0.08). There are some extra diffraction peaks in Bi–ZnO nanopigments. As indexed in pattern, the stared peaks are related to hexagonal structure of the ZnO nanopigments, JCPDS: 36-1451. The other peaks are attributed to monoclinic phase of α-Bi2O3, JCPDS: 0010709. The crystalline sizes of the synthesized pure and Bi–ZnO nanopigments were calculated by size strain plot (SSP) method that detected under the consideration of all the diffraction peaks to obtain more reliable value for crystallite sizes of Bi–ZnO nanopigments. If we consider d as the plane distance, β as the FWHM, θ as the angle value of the maximum of the detected diffraction peaks, and ε as the lattice strain. The term (dβcosθ)2 is plotted against to d2βcosθ based on the SSP equation:
(dhkl βhkl cos θ )2 =
Bi2O3, grow by the Bi increases. It is indicated that Bi2O3 crystals grow independently beside the ZnO nanostructures.
3.2. Optical analysis Fig. 6 present absorbance spectra of the obtained pure and doped samples in the wavelength range of 300–600 nm. The absorbance increased after 365 nm that attributed to the electron transition from valence band to conduction band (O2p-Zn3d) [ ]. It is seen that the absorbance edge is blue-shifted by adding Bi into ZnO. The optical band gaps of the prepared samples were obtained by Kubelka-Munck calculations for direct band gap we have
K 2 ε 2 (dhkl βhkl cos θ) + ⎛ ⎞ D ⎝2⎠
(αhν )2 = (hν − Eg )
The crystallite size is calculated from the slop of the linear fitted data and obtained between 30 and 15 nm for pure to 8% Bi-doped ZnO nanopigments. A specific observation was conducted by focusing at the XRD pattern of the pure and Bi–ZnO nanopigments in the range of 27–38°, Fig. 5. It is observed that the diffraction peaks related to the
The term (αhν)2 is drown in respect to hν. The band gap is estimated from the sloop of the curve Fig. 7. The obtained band gap of the pure and Bi-doped samples were obtained to be between 3.23 and 3.28 eV. 3
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3.3. Morphological study Fig. 8 shows the typical micrograph TEM images of synthesized ZnO and Bi–ZnO nanoparticles. To measure the particle size of the pure and doped samples, the diameter of the particles were measured based on the scale by Image Tools 3 software and the results were analyzed by SPSS software and then their obtained size histograms are presented beside the TEM images. The average particles sizes of the pure and 4% of Bi–ZnO nanoparticles were measured to be 39 ± 11 and 30 ± 18 nm, respectively. It is indicated that size of the Bi–ZnO particles is smaller than that of the pure ZnO nanoparticles. In the other words, Bi atoms affect as impurity to and terminate the growth of the ZnO nanopigments. Also, some small particles are detected beside the ZnO nanopigments which may be attributed to the Bismuth oxide nanocrystals which means that the Bi2O nanoparticles grew independently beside the ZnO nanoparticles. The obtained results are supported by the XRD results verified by the presence of the Bi2O nanoparticles.
3.4. Colorimetric properties Fig. 7. The results obtained by Kubelka-Munck method and the estimated bandgaps for the prepared pure and Bi–ZnO nanopigments.
The obtained results of coordinates for the prepare samples were reported in Table 1. The two dimensional coordination's (a*-b*) for the nanopigments were shown in Fig. 9. Also, it is indicated that the samples color is a component of yellow and green color; however, the yellow color intensity is higher in comparison with the green one. As a
Fig. 8. Typical TEM micrographs of the pure and Zn0.96Bi0.04O nanopigments. 4
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Table 1 Results of coordinates for the prepare samples. Name
L*
a*
b*
C*
h°
ZnO ZnO0.98Bi0.02O ZnO0.96Bi0.04O ZnO0.94Bi0.06O ZnO0.92Bi0.08O
91.59 93.44 93.23 92.77 90.65
−0.63 −1.34 −1.46 −1.57 −2.06
8.37 8.69 6.32 9.53 10.16
8.4 8.79 6.49 9.65 10.37
94.31 98.74 103.04 99.33 101.47
Fig. 11. The disc diffusion results obtained for antibacterial properties of the samples against the selected bacterial.
visible for S. Aureus and the results are insignificantly visible for B. Subtilis. In this research, the synthesized nanopigments were checked on the same petri-dish of (G-) P. Aeruginosa and E. coli. For E. Coli the results were the same as that observed for B. Subtilis. When the prepared pure and Bi–ZnO nanopigments were tested on P. Aerugiosa, no zones of inhibition were observed. In short, the synthesized nanopigments could kill S. Aureus bacteria, thus the zones of inhibitions were obviously visible (i.e. the antibacterial effect of the pure and Bi–ZnO nanopigments on B. Subtilis and E. Coli is weak compared to that for A. Aureus). In the case of P. Aeruginosa, the prepared nanopigments do not show any antibacterial effects for the selected concentrations. The results showed in Fig. 11. In brief, the synthesized pure and Bi-doped ZnO nanopigments are able to terminate the growth of (PTCC 1431) and with lower effect (PT 1420 and PT 1399). Therefore, are suitable for painting humid places.
Fig. 9. Two dimentional coordinations (a*-b*) diagram for the prepared pure and Bi–ZnO nanopigments.
4. Conclusions Pure and Bi-doped ZnO nanopigments were synthesized via a modified sol-gel method. XRD and UV–vis spectroscopy were used to study of the structure and optical properties of the ZnO and Bi–ZnO nanopigments, respectively. It was found that both ZnO and Bi2O3 nanocrystals exist in the doped pigment powders. The XRD patterns were then analyzed by SSP method and the average crystalline size were obtained to be between 30 and 15 nm for Zn1-xBixO when x increases from 0.0 to 0.08. The UV–vis spectroscopy results showed that the band gap of the pure and Bi–ZnO nanopigments increases from 3.23 to 3.28 eV as the Bi content increases. The typical TEM observations were conducted on the pure and Zn0.96Bi0.04O samples. The achievements indicated that the particle size is decreased by adding Bi impurity to the pure sample. The colorimetric observations indicated that the color of the samples is a combination of yellow and green but the yellow intensity is higher than the green one. Therefore, it can be said that the prepared pigment are yellow. The antibacterial test proved that the synthesized nanopigments could control the S. Aureus, B. Subtilis, and E. Coli bacteria growth. By summarizing the obtained results, it is indicated that the prepared nanopigments are proper candidates for painting humid places.
Fig. 10. The intensity of green and yellow colors in respect to the amount of Bi content for the prepared samples. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
result, the color of the doped samples seems to be yellow. All the prepared nanopigments show brightness (L*) more than 90. Also, the results confirmed that the color of the pigments is the main component of green and yellow colors, whose intensity was increased by the Bi content. This increase, however, is faster for yellow compared to green, meaning that the detected visible color of the Bi doped ZnO nanopigments is yellow for the human eyes (see Fig. 10).
3.5. Antibacterial results The prepared purity and Bi-doped ZnO nanopigments were qualitatively examined for antibacterial properties by the disk diffusion root. The pure and Bi-doped ZnO nanopigments were applied to (G+) B. Subtilis and S. Aureus. The zones of inhibition were found around the tablet of the nanopigments dipped disk. The zone inhibitions are clearly 5
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Declaration of competing interest
review of current status and future opportunities, 3 Biotech 8 (2018) 207. [11] M.D. Vukic, N.L. Vukovic, G.T. Djelic, S.L. Popovic, M.M. Zaric, D.D. Baskic, G.B. Krstic, V.V. Tesevic, M.M. Kacaniova, Antibacterial and cytotoxic activities of naphthoquinone pigments from Onosma visianii Clem, EXCLI journal 16 (2017) 73. [12] G. Duerr, M. Kern, R. Mertsch, J. Meyer, G. Michael, J. Tschernjaew, Paint System Containing Anti-fouling Metal Oxide and Fumed Silica, Google Patents, 2018. [13] V. Heydari, Z. Bahreini, Synthesis of silica-supported ZnO pigments for thermal control coatings and analysis of their reflection model, J. Coat. Technol. Res. 15 (2018) 223–230. [14] F.H. Pierre, S. Bettini, J. Dupuy, N. Naud, S. Taché, C. Cartier, C. Comera, E. Gaultier, J.-P. Cravedi, E. Boutet, Food-grade TIO2 pigment initiates preneoplastic lesions and promotes aberrant crypt development in the rat colon, Gastroenterology 152 (2017) S418. [15] K.Y. Jung, J.C. Lee, D.S. Kim, B.-K. Choi, W.-J. Kang, Co-doping effect of monovalent alkali metals on optical properties of CeO2: Eu nanophosphor prepared by spray pyrolysis and application for preparing pearlescent pigments with red emission, J. Lumin. 192 (2017) 1313–1321. [16] A. Moghtada, A. Shahrouzianfar, R. Ashiri, Facile synthesis of NiTiO 3 yellow nanopigments with enhanced solar radiation reflection efficiency by an innovative onestep method at low temperature, Dyes Pigments 139 (2017) 388–396. [17] H. Kazemi, S. Mollazadeh Beidokhti, J. Vahdati Khaki, Solution Combustion Synthesis of Cobalt-Doped Zinc Oxide Nano Pigments, The 7th International Color and Coating Congress, 2017. [18] M. Rostami, S. Rasouli, B. Ramezanzadeh, A. Askari, Electrochemical investigation of the properties of Co doped ZnO nanoparticle as a corrosion inhibitive pigment for modifying corrosion resistance of the epoxy coating, Corros. Sci. 88 (2014) 387–399. [19] H. Saal, M. Binnewies, M. Schrader, A. Börger, K.D. Becker, V.A. Tikhomirov, K. Jug, Unusual optical properties of Mn‐doped ZnO: the search for a new red pigment—a combined experimental and theoretical study, Chem. Eur J. 15 (2009) 6408–6414. [20] G. Buxbaum, Industrial Inorganic Pigments, John Wiley & Sons, 2008. [21] S. Ekambaram, Combustion synthesis and characterization of new class of ZnObased ceramic pigments, J. Alloy. Comp. 390 (2005) L4–L6. [22] A.K. Zak, W.A. Majid, M. Darroudi, R. Yousefi, Synthesis and characterization of ZnO nanoparticles prepared in gelatin media, Mater. Lett. 65 (2011) 70–73.
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. References [1] L. Ghezzi, C. Duce, L. Bernazzani, E. Bramanti, M.P. Colombini, M.R. Tiné, I. Bonaduce, Interactions between inorganic pigments and rabbit skin glue in reference paint reconstructions, J. Therm. Anal. Calorim. 122 (2015) 315–322. [2] L. Liu, A. Han, M. Ye, M. Zhao, Synthesis and characterization of Al3+ doped LaFeO3 compounds: a novel inorganic pigments with high near-infrared reflectance, Sol. Energy Mater. Sol. Cells 132 (2015) 377–384. [3] P. Rainbow, Heavy Metal Levels in Marine Invertebrates, Heavy Metals in the Marine Environment, CRC press, 2017, pp. 67–79. [4] Y.J. Kim, M.G. Choi, H.J. Kim, H.S. Kim, J.H. Yang, Y.R. Seo, Safety assessment of red-colored iron oxide as heavy metal lead pigment substitute in terms of genotoxicity in rat liver tissue, Toxicol. Environ. Health Sci. 9 (2017) 36–40. [5] B. Huang, Y. Xiao, C. Huang, J. Chen, X. Sun, Environment-friendly pigments based on praseodymium and terbium doped La2Ce2O7 with high near-infrared reflectance: synthesis and characterization, Dyes Pigments 147 (2017) 225–233. [6] B. Bae, S. Tamura, N. Imanaka, Novel environment-friendly yellow pigments based on praseodymium (III) tungstate, Ceram. Int. 43 (2017) 7366–7368. [7] R. Oka, Y. Shobu, F. Aoyama, T. Tsukimori, T. Masui, Synthesis and characterisation of SrY 2− x Ce x O 4 as environmentally friendly reddish-brown pigments, RSC Adv. 7 (2017) 55081–55087. [8] R. Cortez, D.A. Luna‐Vital, D. Margulis, E. Gonzalez de Mejia, Natural pigments: stabilization methods of anthocyanins for food applications, Compr. Rev. Food Sci. Food Saf. 16 (2017) 180–198. [9] J.M. Calatayud, P. Pardo, J. Alarcón, Hydrothermal-mediated synthesis of orange Cr, Sb-containing TiO2 nano-pigments with improved microstructure, Dyes Pigments 139 (2017) 33–41. [10] M. Numan, S. Bashir, R. Mumtaz, S. Tayyab, N.U. Rehman, A.L. Khan, Z.K. Shinwari, A. Al-Harrasi, Therapeutic applications of bacterial pigments: a
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Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Bi-doped ZnO yellow nanopigments: Synthesis, characterization, and antibacterial application for painting humid places R. Mastana, A. Khorsand Zakb,∗, R. Pilevar Shahria a b
Department of Physics, Payame Noor University (PNU), P.O. Box 19395-3697, Tehran, Iran Nanotechnology Lab., Esfarayen University of Technology, Esfarayen, North Khorasan, Iran
A R T I C LE I N FO
A B S T R A C T
Keywords: Nanopigments ZnO nanoparticles Yellow pigment Bi-doped Zno
The main objective of the present study is the synthesis of yellow nanopigments with antibacterial properties that are suitable to paint humid places. Bismuth doped zinc oxide nanopigments were prepared through a gelatin based sol gel root. The nanopigment powders were obtained through the calcination of the prepared gels at 600 °C for 2 h. The synthesized samples were analyzed by x-ray diffraction (XRD), UV–visible spectroscopy (UV–vis), and transition electron microscopy (TEM). The powder XRD investigations and TEM observations revealed wurtzite hexagonal structure with particle and crystalline sizes lower than 100 nm. The colorimetric properties were indicated by color space method. The achievements showed yellow color for the Bi-doped samples. The antibacterial effects of the prepared samples were observed by disk diffusion method against the gram positive (G+) bacteria Bacillus Subtilis (PTCC 1420) staphylococcus aurous (PTCC 1431) and gram negative (G-) pseudomonas aeruginosa (PTCC 1074) and Escherichia Coli (PTCC 1399) bacteria that grow normally in humid places. The results showed that the prepared yellow nanopigments are suitable candidate for painting humid places.
1. Introduction Inorganic pigments are supported by a long history. These pigments are widely used to cover and color tools and materials that work in with range of temperature [1,2]. Many kinds of the pigment have heavy or transitional materials in the component which is not environmentally friendly and can endanger human health [3,4]. There are numerous researchers that one cried out to synthesis environmentally friendly pigments [5–7]. Today, nanopigments play an important role in industry [8,9]. Bacterial and antibacterial pigments are special class of pigment, used for medical, biological purposes [10,11]. According to literature, different kinds of inorganic pigments have been prepared from the combination of the nano-sized metal oxides. For example, TiO2, ZnO, CeO2, and SnO2 nanoparticles have been synthesized to be used as white pigments [12–15]. Also, some complex compounds are used as pigments including Y2BaCuO5 as green and NiTiO3 as yellow pigment [16]. Some pigments have complex compositions which are not easy for the preparation (e.g. the synthesis of (Ca1-xyEuxZny)2Al2SiO7+δ pigments reported by Bao et al.) Nowadays, many studies have been conducted to find simply-prepared pigments. Also, several materials have been examined, among which ZnO with wide energy band gap (about 3.2 eV) and numerously great properties is
∗
known to be an important material for painting. The synthesis of ZnObased nanopigments is simple and low cost. Besides, it is an antibacterial material with low toxicity which makes it the right candidate for some biological use. ZnO powder is originally white but it can change colors when doped with other elements [17]. For instance, green pigment is obtained by doping cobalt into ZnO and red pigments by adding Mn element to ZnO matrix [18,19]. Also, some other ZnObased pigments have been presented in the literature [20,21]. In this work, Bi-doped ZnO nanopigments were synthesized via a gelatin based sol-gel method. Yellow nanopigments were obtained by doping different quantities of bismuth element into the white ZnO nanopigment during the synthesis process. The prepared nanopigments were then analyzed. 2. Experimental 2.1. Materials To prepare Bi-doped ZnO nanopigments, analytical grade bismuth nitrate hexahydrate [Bi(NO3)2.6H2O, Merck %99], Zinc nitrate hexahydrate [Zn(NO3)2.H2O, Merck %99.8] and gelatin [(NHCOCH-R1)n, R1=amino acid] were selected as precursor materials and distilled
Corresponding author. E-mail addresses: [email protected], [email protected] (A. Khorsand Zak).
https://doi.org/10.1016/j.ceramint.2019.12.090 Received 26 November 2019; Received in revised form 8 December 2019; Accepted 8 December 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: R. Mastan, A. Khorsand Zak and R. Pilevar Shahri, Ceramics International, https://doi.org/10.1016/j.ceramint.2019.12.090
Ceramics International xxx (xxxx) xxx–xxx
R. Mastan, et al.
Fig. 1. Structure of gelatin molecule. Bi cations are attracted by the negative sites.
water as solvent. 2.2. Synthesis of the Bi-doped nanopigment samples The specific amount of zinc and bismuth nitrate were dissolved in the minimum amount of distilled water. Zn1-xBixO chemical formula was considered to measure the precursor materials quantities to prepare 10 g of the final products, where x = 0, 0.01, 0.03, and 0.05. A gelatin solution was prepared by dissolving 8 g gelatin in 120 ml distilled water. The temperature of the water was kept at 80 °C in the oil bath, meanwhile, the gelatin powder was gradually added to the water and stirred to achieve a clear gelatin solution. After that, the cation solutions were added to the gelatin solution. The stirring speed was reduced about 50 from 120 rpm and the temperature of the solution checked to be fixed at 80 °C. The solution was left in this process for about 3 h to evaporate the initial water and obtain a viscose gel. The simple reactions occurs during the gelation of the sol. Fig. 1, shows that gelatin has a complex structure with long chains of amino acids. There are O=C ̶ O ̶ sites that have negative charge. The Bi+n and Zn+2 cations are attracted by these negative sites and attached to gelation chains. Therefore, they cannot easily reach each other when the gel burning process, thereby terminating the growth of Bi-doped ZnO nanoparticles. Gelatin affects as capping agent and eliminates the growth of crystals. The obtained gel was then calcined at 600 °C for 2 h by a box furnace. The calcination temperature was chosen based on the TGA results obtained in our earlier research [22]. The same processes were conducted to prepare pure and Bi-doped samples.
Fig. 2. Images of the used bacteria in this research.
measuring the inhibition zone around the sample discs. Gentamicin antibiotic and sterptomain (Hi-Media) were used as the positive controls and strilled water as the negative control to compare the efficacy of the test sample. 2.3.2. The colorimetric studies The color space CIE L*a*b* (CIELAB), known as a color space, has been specified by the international commission on humanities. This model is used as a reference device independent model which describes all the color in the visible range for the human eye. Thus, it is presented by most of the industries and companies to evaluate the color of the days. There are three coordinations in CIELAB indicated by L*, a*, and b*. The lightness of the color represents L* from zero (yield black) to 100 (diffuse white, specular white may be higher). The symbol a* shows green while positive values show magenta. The position between yellow (positive value) and blue (negative value) is shown by b*. In addition, there are two cylindrical coordinates c* and hͦ that shows Chroma, relative saturation hue angle, hue angle in CIELab color wheel, respectively. Color-coded coordinates, data were obtained in D65/10° conditions by Konica Minulta spectrophotometer CS2000 (CS-Slow) in the wavelength rage of 300–780 nm (D65 is the simulation of day light and 10° is the detector angle). The spectrophotometer is placed in front of the sample and the light sources in both sides with direction angle of 45° in relation to them. All the destinations were 75 C < superscript > < / superscript > m < superscript > < /superscript > , Fig. 3. The measurements were applied on sample in powder form.
2.3. Characterization techniques The structural and phase evaluations of the prepared samples were studied by x-ray diffraction method using (Philips, Xpert, CuKα). A Hitachi H-7100 electron microscope was used for the TEM observation. The UV–vis reflectance spectra of the samples were recorded in the range of 300–800 nm using PerkinElmer UV–vis spectrophotometer (Lambda 25, PerkinElmer). 2.3.1. The antibacterial evaluations Disk diffusion method against the test bacteria on Muller-Hinton agar was used for the antibacterial test. The test were performed on gram positive (G+) bacteria Bacillus Subtilis (PTCC 1420) staphylococcus aurous (PTCC 1431) and gram negative (G-) pseudomonas aeruginosa (PTCC 1074) and Escherichia Coli (PTCC 1399), Fig. 2. These bacteria grow in humid and moisture condition and therefore they were chosen for the test process. Accordingly, the bacteria suspension growth was performed on tryplic soy broth (TSB) with 0.5 Mc Farland that is equal to 1.5 × 108 unit of bacteria per milliliter (CFU/mL). The media plates (MHA) were streaked with bacteria for 3 times to have a homogenous distribution. The prepared plates were incubated at 37 °C for 24 h. The antibacterial property of the sample were analyzed by
3. Results and discussion 3.1. Structure analysis Fig. 4 presents the XRD patterns of Zn1-xBixO (x = 0.0, 0.02, 0.04, 2
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Fig. 3. Scheme of the used system for colorimetric measurements. Fig. 5. XRD pattern of the prepared pure and Bi–ZnO nanopigments between 27 and 38°.
Fig. 4. XRD pattern of the prepared pure and Bi–ZnO nanopigments. Fig. 6. Absorbance spectra of the prepared pure and Bi–ZnO nanopigments.
0.06, and 0.08). There are some extra diffraction peaks in Bi–ZnO nanopigments. As indexed in pattern, the stared peaks are related to hexagonal structure of the ZnO nanopigments, JCPDS: 36-1451. The other peaks are attributed to monoclinic phase of α-Bi2O3, JCPDS: 0010709. The crystalline sizes of the synthesized pure and Bi–ZnO nanopigments were calculated by size strain plot (SSP) method that detected under the consideration of all the diffraction peaks to obtain more reliable value for crystallite sizes of Bi–ZnO nanopigments. If we consider d as the plane distance, β as the FWHM, θ as the angle value of the maximum of the detected diffraction peaks, and ε as the lattice strain. The term (dβcosθ)2 is plotted against to d2βcosθ based on the SSP equation:
(dhkl βhkl cos θ )2 =
Bi2O3, grow by the Bi increases. It is indicated that Bi2O3 crystals grow independently beside the ZnO nanostructures.
3.2. Optical analysis Fig. 6 present absorbance spectra of the obtained pure and doped samples in the wavelength range of 300–600 nm. The absorbance increased after 365 nm that attributed to the electron transition from valence band to conduction band (O2p-Zn3d) [ ]. It is seen that the absorbance edge is blue-shifted by adding Bi into ZnO. The optical band gaps of the prepared samples were obtained by Kubelka-Munck calculations for direct band gap we have
K 2 ε 2 (dhkl βhkl cos θ) + ⎛ ⎞ D ⎝2⎠
(αhν )2 = (hν − Eg )
The crystallite size is calculated from the slop of the linear fitted data and obtained between 30 and 15 nm for pure to 8% Bi-doped ZnO nanopigments. A specific observation was conducted by focusing at the XRD pattern of the pure and Bi–ZnO nanopigments in the range of 27–38°, Fig. 5. It is observed that the diffraction peaks related to the
The term (αhν)2 is drown in respect to hν. The band gap is estimated from the sloop of the curve Fig. 7. The obtained band gap of the pure and Bi-doped samples were obtained to be between 3.23 and 3.28 eV. 3
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3.3. Morphological study Fig. 8 shows the typical micrograph TEM images of synthesized ZnO and Bi–ZnO nanoparticles. To measure the particle size of the pure and doped samples, the diameter of the particles were measured based on the scale by Image Tools 3 software and the results were analyzed by SPSS software and then their obtained size histograms are presented beside the TEM images. The average particles sizes of the pure and 4% of Bi–ZnO nanoparticles were measured to be 39 ± 11 and 30 ± 18 nm, respectively. It is indicated that size of the Bi–ZnO particles is smaller than that of the pure ZnO nanoparticles. In the other words, Bi atoms affect as impurity to and terminate the growth of the ZnO nanopigments. Also, some small particles are detected beside the ZnO nanopigments which may be attributed to the Bismuth oxide nanocrystals which means that the Bi2O nanoparticles grew independently beside the ZnO nanoparticles. The obtained results are supported by the XRD results verified by the presence of the Bi2O nanoparticles.
3.4. Colorimetric properties Fig. 7. The results obtained by Kubelka-Munck method and the estimated bandgaps for the prepared pure and Bi–ZnO nanopigments.
The obtained results of coordinates for the prepare samples were reported in Table 1. The two dimensional coordination's (a*-b*) for the nanopigments were shown in Fig. 9. Also, it is indicated that the samples color is a component of yellow and green color; however, the yellow color intensity is higher in comparison with the green one. As a
Fig. 8. Typical TEM micrographs of the pure and Zn0.96Bi0.04O nanopigments. 4
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Table 1 Results of coordinates for the prepare samples. Name
L*
a*
b*
C*
h°
ZnO ZnO0.98Bi0.02O ZnO0.96Bi0.04O ZnO0.94Bi0.06O ZnO0.92Bi0.08O
91.59 93.44 93.23 92.77 90.65
−0.63 −1.34 −1.46 −1.57 −2.06
8.37 8.69 6.32 9.53 10.16
8.4 8.79 6.49 9.65 10.37
94.31 98.74 103.04 99.33 101.47
Fig. 11. The disc diffusion results obtained for antibacterial properties of the samples against the selected bacterial.
visible for S. Aureus and the results are insignificantly visible for B. Subtilis. In this research, the synthesized nanopigments were checked on the same petri-dish of (G-) P. Aeruginosa and E. coli. For E. Coli the results were the same as that observed for B. Subtilis. When the prepared pure and Bi–ZnO nanopigments were tested on P. Aerugiosa, no zones of inhibition were observed. In short, the synthesized nanopigments could kill S. Aureus bacteria, thus the zones of inhibitions were obviously visible (i.e. the antibacterial effect of the pure and Bi–ZnO nanopigments on B. Subtilis and E. Coli is weak compared to that for A. Aureus). In the case of P. Aeruginosa, the prepared nanopigments do not show any antibacterial effects for the selected concentrations. The results showed in Fig. 11. In brief, the synthesized pure and Bi-doped ZnO nanopigments are able to terminate the growth of (PTCC 1431) and with lower effect (PT 1420 and PT 1399). Therefore, are suitable for painting humid places.
Fig. 9. Two dimentional coordinations (a*-b*) diagram for the prepared pure and Bi–ZnO nanopigments.
4. Conclusions Pure and Bi-doped ZnO nanopigments were synthesized via a modified sol-gel method. XRD and UV–vis spectroscopy were used to study of the structure and optical properties of the ZnO and Bi–ZnO nanopigments, respectively. It was found that both ZnO and Bi2O3 nanocrystals exist in the doped pigment powders. The XRD patterns were then analyzed by SSP method and the average crystalline size were obtained to be between 30 and 15 nm for Zn1-xBixO when x increases from 0.0 to 0.08. The UV–vis spectroscopy results showed that the band gap of the pure and Bi–ZnO nanopigments increases from 3.23 to 3.28 eV as the Bi content increases. The typical TEM observations were conducted on the pure and Zn0.96Bi0.04O samples. The achievements indicated that the particle size is decreased by adding Bi impurity to the pure sample. The colorimetric observations indicated that the color of the samples is a combination of yellow and green but the yellow intensity is higher than the green one. Therefore, it can be said that the prepared pigment are yellow. The antibacterial test proved that the synthesized nanopigments could control the S. Aureus, B. Subtilis, and E. Coli bacteria growth. By summarizing the obtained results, it is indicated that the prepared nanopigments are proper candidates for painting humid places.
Fig. 10. The intensity of green and yellow colors in respect to the amount of Bi content for the prepared samples. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
result, the color of the doped samples seems to be yellow. All the prepared nanopigments show brightness (L*) more than 90. Also, the results confirmed that the color of the pigments is the main component of green and yellow colors, whose intensity was increased by the Bi content. This increase, however, is faster for yellow compared to green, meaning that the detected visible color of the Bi doped ZnO nanopigments is yellow for the human eyes (see Fig. 10).
3.5. Antibacterial results The prepared purity and Bi-doped ZnO nanopigments were qualitatively examined for antibacterial properties by the disk diffusion root. The pure and Bi-doped ZnO nanopigments were applied to (G+) B. Subtilis and S. Aureus. The zones of inhibition were found around the tablet of the nanopigments dipped disk. The zone inhibitions are clearly 5
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Declaration of competing interest
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