Journal of Science: Advanced Materials and Devices (2018) 303e309 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article E tirucalli plant latex mediated green combustion synthesis of ZnO nanoparticles: Structure, photoluminescence and photo-catalytic activities K.H Sudheer Kumar a, **, N Dhananjaya b, *, L.S Reddy Yadav a a b Department of Chemistry, BMS Institute of Technology and Management, Bengaluru 560064, India Department of Physics, BMS Institute of Technology and Management, Bengaluru 560064, India a r t i c l e i n f o a b s t r a c t Article history: Received 16 February 2018 Received in revised form 20 June 2018 Accepted 13 July 2018 Available online 20 July 2018 ZnO nanoparticles were synthesized using esterases contained E tirucalli plant latex as a fuel The structural, morphological and spectroscopic studies of the as-synthesized ZnO nanoparticles were analyzed using powder X-ray Diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), UVeVisible absorption and photoluminescence (PL) spectroscopy The structural parameters were refined by the Rietveld refinement method using PXRD data and confirmed that the prepared compound is pure hexagonal wurtzite structure with space group P63mc (No 186) The average crystallite size was estimated by Scherrer's and WeH plots and found to be in the range 17e23 and 20e26 nm respectively The band gap of ZnO nanoparticles was estimated using WoodeTauc relation and found to be in the range of 3.10e3.25 eV PL studies revealed that a broad yellow emission peak appeared at 570 nm upon 380 nm excitation peaks Photocatalytic degradation of Methylene blue (MB) dye was studied under UV irradiations 5.5 ml of 5% esterases contained E tirucalli plant latex used for the synthesis of ZnO shows 96% of degradation (5  10À5 M MB at pH 12) The prepared ZnO nanoparticles find application in optical and photo-catalytic degradations © 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: E tirucalli Green synthesis ZnO nanoparticles FTIR SEM Photocatalytic degradation Introduction In recent years, the synthesis of oxide nanoparticles using green products such as leaves, roots, latex, stem and bark has received much attention by the researchers [1,2] It is clean, non-toxic, ecofriendly, free from unwanted by-products and non-hazardous [3] Recently, great efforts have been made to the synthesis of size and shape controlled phosphor by different techniques [4,5] Among them, aqueous combustion synthesis technique has been used to prepare cost-effective and cheap phosphors [6,7] On the other hand, the production of eco-friendly, low cost ZnO nanoparticles in large scale by the existing routes remains difficult [8] Therefore, it was expected to be an important host material for several applications such as light emitting diodes (LEDs), X-ray imaging, scintillations, sensors, optical communication, fluorescence imaging [8e10] Further, ZnO was non-toxic, compatible with skin and was highly useful as UV-blocker in sun-screen and biomedical applications [11] Various techniques have been employed to prepare ZnO nanoparticles such as solvothermal, hydrothermal, solegel, microwaveassisted hydrothermal, co-precipitation, MetaleOrganic Chemical Vapour Deposition [12e17] Most of these techniques need sophisticated equipment's, timeconsuming experimental procedure and special precautions of experimental conditions [18] Green combustion synthesis (GCS) is an alternative of a simple, versatile and informal synthesis technique with time and energy saving prospect Green combustion methodology has been extended to other oxides, such as LnCaAlO4, Sm2O3, ZnO, CuO, PdO, Co3O4, NiO with natural plant extract [19e24] In this study, ZnO nanoparticles were prepared by green combustion technique with esterases contained E tirucalli plant latex as a fuel The structural, spectroscopic and photo-catalytic studies were discussed in detail for environmental applications Experimental * Corresponding author ** Corresponding author E-mail addresses: sudheerkh.158@gmail.com (K.H Sudheer Kumar), ndhananjayas@bmsit.in (N Dhananjaya) Peer review under responsibility of Vietnam National University, Hanoi 2.1 Synthesis of ZnO nanoparticles In a typical synthesis of ZnO nanoparticles, ml of 5% esterases contained E tirucalli plant latex was added in a borosil glass dish https://doi.org/10.1016/j.jsamd.2018.07.005 2468-2179/© 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) 304 K.H Sudheer Kumar et al / Journal of Science: Advanced Materials and Devices (2018) 303e309 containing g of Zn(NO3)3 6H2O already dissolved in 10 ml of double distilled water This reaction mixture was mixed well using magnetic stirrer for ~5e10 and then placed in a preheated muffle furnace maintained at 350 ± 10 C The liquids of E tirucalli plant latex containing fats, unsaturated oils containing double bonds, flavonoids and tannins are inclined to spontaneous ignition of the mixture The reaction mixture boils froths and thermally dehydrates forming a foam The entire process was completed in a few minutes A similar procedure was repeated by taking the different volume of 5% esterases contained E tirucalli plant latex (4e8 ml) [4,25] 2.2 Characterization The crystal structure of ZnO nanoparticles was determined using Shimadzu powder X-ray diffractometer using Cu Ka radiation The Fourier transform infrared (FTIR) spectra of the sample were recorded using Perkin Elmer Spectrometer (Spectrum 1000) with KBr pellets The UVeVisible absorption spectra of the samples were measured with SL 159 ELICO UVeVIS Spectrophotometer Photoluminescence (PL) spectra were measured using Horiba Delta Flex TCSPC system Photocatalytic studies under UV light are carried out in-house fabricated photochemical reactor 2.3 Photocatalytic degradation of dye Photocatalytic experiments were carried out using 250 W high-pressure mercury lamps as the UV radiation source An aqueous suspension was prepared by dispersing 20 mg of ZnO nanoparticles in 30 ml of  10À5 M methylene blue dye solution During the photocatalytic experiments, the slurry composed of dye solution and catalyst was placed in the reactor and stirred magnetically for agitation with simultaneous exposure to UV light A known volume (5 ml) of the exposed solution was withdrawn at a specific interval of time (initially 20 and then 30 min) Then, ZnO nanoparticles were removed from the solution by centrifugation to assess the extent of degradation The rate of degradation of dye was measured using spectrophotometer at 664 nm The % degradation of dye can be determined using the following formula % degradation ¼ Ci À Cf  100 Ci where Ci and Cf are the initial and final dye concentrations respectively Results and discussions 3.1 Structural characterization (PXRD and Rietveld refinement) Fig 1(a) shows the PXRD patterns of ZnO nanoparticles prepared by different volume of esterases contained E tirucalli plant latex (3e8 ml; 5% latex) It was evident from the Fig that, for all the plant latex content, a broadening was observed, which indicates that the particle sizes were in the nanoscale range All the diffraction peaks were well indexed to pure hexagonal wurtzite ZnO (JCPDS card no 36-1451) having the lattice parameters a ¼ 3.2537 (Å), c ¼ 5.2063 (Å) No other impurity peaks are detected The average crystallite size for hexagonal ZnO nanoparticles for a different volume of esterases contained E tirucalli plant latex were estimated by Scherer's (d) and Williamson and Hall (WeH) plots (d0 ) using following relations [26,27]: d¼ kl b cos q b cos q ¼ ð4 sin qị ỵ (1) kl d0 (2) where l is the wavelength of the X-ray radiation (1.5418 Å), k is the shape factor (0.9), q is scattering angle, b is (full width at half maximum, FWHM in radian) measured for different XRD lines corresponding to different planes and is the strain The equation represents a straight line bcosq (Y-axis) versus sinq (X-axis), the slope of the line gives the strain (3 ) and intercept (kl/d0 ) of this line on the Y-axis gives average crystallite size (d0 ) (Fig 1(b)) It was observed that d0 is slightly larger than d (Table 1), because the strain component is assumed to be zero for calculating d and observed broadening of the diffraction peak In this case, the finding is considered as a result of reducing crystallite size The structural parameters were refined by the Rietveld method using powder PXRD data The optimized parameters were scale factor, background, global thermal factor, asymmetric factor, profile half-width parameters (u, v, w), lattice parameters (a, c) and site occupancy factors (Wyckoff) were used to obtain a structural refinement with better quality and reliability Fig 2(a) shows the Rietveld refinement performed on the green combustion synthesized ZnO nanoparticles The refined parameters are displayed in Table The crystal structure of ZnO was modeled using Rietveld refined structural parameters by Diamond program (Fig 2(b)) In this structure, Zn is connected to oxygen atoms in a tetrahedral configuration 3.2 Spectroscopic studies (FTIR, UVeVisible and PL) Fig 3(aec) shows the FTIR spectra of 5% esterases contained E tirucalli plant latex and ZnO nanoparticles prepared with and 5.5 ml, 5% esterases contained E tirucalli plant latex respectively The absorption band near 3398 cmÀ1 was due to OeH mode and 1400e1649 cmÀ1 were attributed to C]O stretching mode As the volume of 5% latex increases the band at 1400e1649 cmÀ1 peak decreases The peak at ~ 2340 cmÀ1 arises due to absorption of atmospheric CO2 on the metallic cations The bands at 431 cmÀ1 correspond to the bonding between ZneO [28] The UVeVisible absorption spectra of ZnO nanoparticles (3, 5.5 and ml of 5% esterases contained E tirucalli plant latex) were shown in Fig 4(aec) respectively The abrupt change at ~380 nm is due to lamp change over from UV to visible region in UV Visible spectrophotometer The direct energy band gap for the ZnO nanoparticles was estimated by Wood and Tauc relation [29]: À Á ðahyÞ2 ¼ A hn À Eg (3) where a is the optical absorption coefficient, hn is the photon energy, Eg is the direct bandgap and A is a constant The plots of (ahn)1/2 vs photon energy of ZnO nanoparticles were shown in Fig It was found to be in the range 3.10e3.25 eV These Eg values were smaller than that of bulk ZnO (3.37 eV) [30] The excitation spectrum of ZnO nanoparticles (5.5 ml; 5% latex) recorded at room temperature (RT) and was shown in Fig The near-band-edge (NBE) excitation peak at 380 nm was recorded at an emission wavelength of 270 nm (inset of Fig 6) The defect emission in the visible region is attributed to ZnO surface detects, in which oxygen deficiencies are the most suggested defects Further, the emission spectrum of pure ZnO showed a broad yellow emission at 570 nm along with sharp peaks at ~ 430 nm and ~ 460 nm, which indicates the existence of a large number of surface defects K.H Sudheer Kumar et al / Journal of Science: Advanced Materials and Devices (2018) 303e309 305 Fig (a) PXRD patterns and (b) WeH plots of ZnO nanoparticles for different volume of esterases contained E tirucalli plant latex (3e8 ml; 5% latex) Table Various parameters of ZnO nanoparticles prepared with different volume of esterases contained E tirucalli plant latex Plant latex (ml) Average crystallite size (nm) Scherrer's equation (d) WeH plots (d ) 5.5 17 18 19 20 21 22 23 20 21 22 23 24 25 26 Strain, (10À3) 0.74 0.84 1.08 1.10 1.15 1.19 1.21 Band gap (eV) 3.28 e e 3.26 e e 3.10 The broad ~ 570 nm peak may be due to the transition between single charged oxygen vacancy and the photoexcited holes in the valence band of the ZnO nanoparticles [31] Fig shows the SEM image of ZnO nanoparticles (5.5 ml; 5% latex) The image clearly shows the presence of almost spherically shaped particles with agglomeration The porous nature was observed in SEM images This is due to the liberation of a large amount of gases during green combustion process 3.3 Photo-catalytic activity The photocatalytic activities of ZnO nanoparticles (5.5 ml; 5% latex) were estimated by monitoring the degradation of Methylene Blue (MB) as a model pollutant in a self-assembled apparatus with a 250 W high-pressure mercury lamps as the UV radiation source Typically, for the photocatalytic experiment, 20 mg of photocatalysts (ZnO nanoparticles) were suspended in 30 ml of MB aqueous solution with a concentration of  10À5 M in a beaker The suspension was magnetically stirred for 30 to reach the adsorption/desorption equilibration without light exposure Following this, the photocatalytic reaction was started by exposure to UV light (20e120 min) After that, the ml sample was centrifuged and collected for UVeVisible absorption measurement The Fig (a) Rietveld refinement and (b) wurtzite hexagonal crystal structure of ZnO nanoparticles prepared using 5.5 ml of 5% esterases contained E tirucalli plant latex 306 K.H Sudheer Kumar et al / Journal of Science: Advanced Materials and Devices (2018) 303e309 Table Rietveld refined structural parameters for ZnO nanoparticles prepared with 5.5 ml of 5% plant latex (c) Absorbance (a.u.) Compound Crystal system Space group Lattice parameter a (Å) b (Å) Cell volume (Å)3 Zn1 (2) x y z O1 (À2) x y z R-factors RP RWP Rexp ZnO Hexagonal P63-mc (186) 3.2537(1) 5.2063(2) 47.73(4) (2b) 0.3330 0.6667 0.0000 (2b) 0.3330 0.6667 0.3828(2) RBragg RF (b) (a) 8.08 8.85 8.14 1.18 4.17 3.85 c2 Lamp change over 200 300 400 500 600 700 800 900 1000 1100 Wavelength (nm) 431 1400 2340 3398 Transmittance (a.u.) Fig UVeVisible spectra of ZnO nanoparticles prepared by (a) ml (b) 5.5 ml and (c) ml of 5% esterases contained E tirucalli plant latex (c) (b) (a) 4000 3500 3000 2500 2000 1500 1000 500 -1 Wavenumber (cm ) Fig FTIR spectra of (a) 5% esterases contained E tirucalli plant latex and ZnO nanoparticles prepared by (b) ml and (c) 5.5 ml of 5% esterases contained E tirucalli plant latex intensity of the main absorption peak (664 nm) of the MB dye was referred to as a measure of the residual dye concentration [31] Fig 8(a) shows the degradation of MB in the presence of 20 mg of ZnO (5.5 ml; 5% plant latex) nanoparticles with 20e120 UV irradiation It was found that 120 irradiation degrade 40% of  10À5 M MB Photocatalytic activity of ZnO was attributed to both of the donor states caused by a large number of defect sites such as oxygen vacancies and interstitial zinc atom and to the acceptor states which arise from zinc vacancies and interstitial oxygen atoms Oxygen vacancies located at energy positions 2.35e2.50 eV were responsible for green luminescence upon illumination with UV light Here, we assume that the interfacial electron transfer takes place predominantly between these donor states (oxygen vacancies and interstitial Zn atom) Being a cationic dye, MB acquires electron from excited donor states and decomposes The kinetic behaviour of ZnO nanoparticles is shown in Fig 8(b) It is observed that the nanoparticles exhibit first-order Fig Bandgap of ZnO nanoparticles prepared by (a) ml (b) 5.5 ml and (c) ml of 5% esterases contained E tirucalli plant latex kinetics in agreement with a general LangmuireHinshelwood mechanism [32]: R ẳ dC=dt ẳ kKC=1 ỵ KC (4) where r is the degradation rate of reactant (mg/l min), C is the concentration of reactant (mg/l), t the illumination time, K is the absorption coefficient of reactant (l/mg) and k is the reaction rate K.H Sudheer Kumar et al / Journal of Science: Advanced Materials and Devices (2018) 303e309 Fig Excitation and emission spectra of ZnO nanoparticles prepared using 5.5 ml of 5% esterases contained E tirucalli plant latex 307 Fig Degradation of MB in the presence of photocatalysts (ZnO nanoparticles prepared using 5.5 ml of 5% esterases contained E tirucalli plant latex) with different pH (5e12 pH) constant (mg/l min) If C is very small then the above equation could be simplied to: lnC0 =Cị ẳ kKt ¼ kapp t Fig (a) SEM Image of ZnO nanoparticles prepared using 5.5 ml of 5% esterases contained E tirucalli plant latex (5) where C0 is the initial concentration of the MB aqueous solution and C is the concentration of the MB aqueous solution for different times of UV illuminations From the plot of ln(C0/C) vs the irradiation time (t) (Fig 10), the reaction rate constant (k) value are calculated and found to be 0.0038 minÀ1 UV irradiation for different pH was recorded and shown in Fig The 96% degradation of  10À5 M MB (20 mg ZnO) was observed for pH 12 This compound may be useful for catalytic applications Fig 10 shows the mechanism of photocatalysis in ZnO nanoparticles under UV light When a photon incident on ZnO nanoparticles, it will generate photoelectron (eÀcb) and photoinduced holes (hỵvb) The photoelectrons are trapped by adsorbed O2 as electron acceptors and the photo-induced holes are accepted by the negative species like OHÀ or organic pollutants, to oxidize organic dyes such as MB The oxygen vacancies are beneficial to the degradation of the MB It will restrain the combination of eÀcb and Fig (a) Degradation of MB in the presence of photocatalysts (ZnO nanoparticles prepared using 5.5 ml of 5% esterases contained E tirucalli plant latex) with different UV irradiation time and (b) First order kinetic reactions for ZnO nanoparticles 308 K.H Sudheer Kumar et al / Journal of Science: Advanced Materials and Devices (2018) 303e309 Fig 10 Mechanism of photo catalysis in ZnO nanoparticles under UV light hỵvb The corresponding photocatalytic reaction process is as follows: ZnO ỵ hy / ecb ỵ hỵvb ecb ỵ O2 / O2 hỵvb ỵ OH / OH O2 ỵ C16H18N3SCl / Oxidation products OH ỵ C16H18N3SCl / Oxidation products Conclusion We have successfully synthesized ZnO nanoparticles via the green synthesis technique using E tirucalli plant latex as a fuel Pure hexagonal wurtzite structure was observed from PXRD studies The particle size was estimated from Scherer's and WeH plots and found to be in the range 17e26 nm The emission peaks at 570 nm were observed under the excitations of 380 nm The synthesized nanoparticles were employed to study the catalytic activity of Methylene blue dye degradation UVeVisible spectra of Methylene blue (5  10À5 M) dye degradation as a function of different UV irradiation time and pH were performed ZnO nanoparticles prepared with 5.5 ml of 5% esterases contained E tirucalli plant latex show 96% dye degradation at pH ¼ 12 Further, the green combustion synthesized ZnO nanoparticles may be useful in display and catalytic applications Acknowledgements One of the 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and the photoexcited holes in the valence band of the ZnO nanoparticles [31] Fig shows the SEM image of ZnO nanoparticles (5.5 ml; 5% latex) The image clearly... Spectrometer (Spectrum 1000) with KBr pellets The UVeVisible absorption spectra of the samples were measured with SL 159 ELICO UVeVIS Spectrophotometer Photoluminescence (PL) spectra were measured... 6) The defect emission in the visible region is attributed to ZnO surface detects, in which oxygen deficiencies are the most suggested defects Further, the emission spectrum of pure ZnO showed a