1, 3, * 1, * 1,3
Volume 10, Issue 3, 2020, 5648 - 5655ISSN 2069-5837Biointerface Research in Applied rg/10.33263/BRIAC103.648655Original Research ArticleOpen Access JournalReceived: 14.02.2020 / Revised: 20.03.2020 / Accepted: 21.03.2020 / Published on-line: 29.03.2020Synthesis and characterization of single phase ZnO nanostructures via solvothermalmethod: influence of alkaline sourceEric Kwabena Droepenu 1, 3, *Aquisman Asare 1,3, Boon Siong Wee 1, *, Suk Fun Chin1, Kuan Ying Kok 2, Ebenezer1Resource Chemistry Program, Faculty of Resource Science and Technology, Universiti Malaysia Sarawak 94300, Kota Samarahan, Sarawak, MalaysiaMalaysian Nuclear Agency, Bangi, Kajang, 43000 Selangor, Malaysia3Graduate School of Nuclear and Allied Sciences, University of Ghana, AE1, Kwabenya-Accra, Ghana*corresponding author e-mail address: kobladodzie01@yahoo.com; swboon@unimas.my Scopus ID 571945060962ABSTRACTSingle phase ZnO nanostructures were synthesized by simple and low temperature solvothermal process from two different alkalinesources; Potassium hydroxide (KOH) and Sodium hydroxide (NaOH) with zinc acetate dihydrate (Zn(CH 3COO)2 2H2O) as precursor.This facile and rapid synthesis technique achieve high purity of Zinc oxide (ZnO) nanostructures on large scale negating the use ofcomplex and high temperature routes. The synthesized particles were characterized by X-Ray Diffraction (XRD), Field EmissionScanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDX),Fourier Transform Infrared (FT-IR) Spectroscopy, Ultraviolet Visible (UV-Vis) spectroscopy and Brunauer-Emmett-Teller (BET)analysis. ZnO synthesized using KOH and NaOH exhibit wurtzite hexagonal and flake-like nanostructures with average crystallite sizeof 11.0 nm and 14.9 nm respectively. Surface area of 59.50 m2/g and 31.43 m2/g were determined for KOH and NaOH sourcesrespectively. The optical absorption spectra of the two samples showed absorption bands of 367.70 and 365.30 nm. The results showedthe effect of alkaline sources on the surface morphology, structural and optical properties of ZnO.Keywords: Nanostructures; Solvothermal synthesis; Alkaline source; Precursor; Microscopy; Spectroscopies.1. INTRODUCTIONTechnology today endeavor the use of crystalline particlesin nanometric scale with uniform size and shape due to theirnumerous fascinating properties including catalytic, electrical andoptical; which are desired in many promising applications. Amongthese, ZnO has attracted much attention because of its wideversatility in various fields such as pharmaceutical, electronics,cosmetics, optical and electrical devices, drug delivery andenvironmental remediation [1-6].ZnO has many interesting properties including its wideband gap (3.37 eV), high bond strength, high thermal stability andlarge exciton binding energy (60 meV), which are required inelectronics, optoelectronics and laser technologies [7-13]. Besides,ZnO also possesses good electrical, optical and antibacterialproperties which are pre-requisite in the photoconductors,integrated sensors, electrodes and biomedicine industries [14-18].Different routes have been used in synthesizingnanocrystalline ZnO powders as well as other nanostructures suchas hydrothermal, spray pyrolysis, sol-gel, precipitation, microwaveassisted, thermos-decomposition processes, micro-emulsion,electrodeposition, ultrasonic, microwave-assisted technique andchemical vapour deposition [19-27]. All these methods producesimilar nanocrystalline structures based on different conditions.These conditions may arise from the precursor and alkalinesources used, temperature variation, reaction time for nucleationof the nanoparticles as well as the calcination temperatures [2830]. It should be noted that some of the methods employed infabricating these nano-sized particles require complex processesand sophisticated equipment. Solvothermal technique, however,offers many great advantages over other techniques mentionedabove. This technique requires simple setup, less expensiveequipment, relatively low synthesis temperature to yield a largearea of deposition. Also, it allows the microstructural control ofthe particles produced by altering experimental parameters such astemperature, reaction time, type of solvent, surfactant andprecursor. Qualities of nanostructures in the manufacture ofdevices such as sensors, photo diodes, transistors are based on theshape, size and purity of the synthesized nanoparticles. Theseproperties can also be achieved using simple experimental set-upswith minimum reaction conditions not necessarily using highlycomplex equipment under very high reaction conditions. It isagainst this backdrop that the current study employed two alkalinesources (KOH and NaOH) in synthesizing ZnO NPs with Zincacetate dihydrate precursor in a solvothermal method at relativelylower reaction conditions to achieve high quality ZnOnanostructures. The quality of the ZnO produced was investigatedusing a series of physiochemical characterization tools.2. MATERIALS AND METHODS2.1. Materials.Zinc acetate dihydrate [Zn(CH3COO)2 2H2O], Potassiumhydroxide (KOH), Sodium hydroxide (NaOH), 95% AbsoluteEthanol (C2H5OH). All chemicals were of analytical reagent gradefrom Sigma-Aldrich without further purification.Page 5648
Synthesis and characterization of single phase ZnO nanostructures via solvothermal method: influence of alkaline source2.2. Synthesis of Zinc oxide (ZnO) Nanoparticles (NPs).Synthesis of ZnO NPs was based on the solvothermaltechnique reported by [31] with slight modification. A weighedmass of 1.83 0.1 g (0.01 mol) of [Zn(CH3COO)2 2H2O], [SigmaAldrich, India] was dissolved in 100 mL of absolute ethanol in a250 mL Schott bottle and heated to a temperature of 60 C withconstant stirring using electrical stirring hotplate (Favorit).Subsequently, 5.60 0.1 g (0.01 mol) of KOH (VWR Amresco,US) was also weighed and dissolved in 100 mL of absoluteethanol in 250 mL Schott bottle under the same condition as theZinc acetate. After complete dissolution, the alkaline solution(KOH) was slowly drained dropwise from a burette into theZn(CH3COO)2 2H2O solution, maintaining the temperature at 60 C with vigorous stirring for 60 minutes until white precipitatewas formed. The mixture was allowed to cool at room temperaturefor 180 minutes before centrifuging with FLETA 5 Multi-PurposeCentrifuge at 4000 rpm for 30 minutes. The precipitate wasfiltered using 0.45 μm Whatman filter membrane, washed twicewith acetone and then with deionized water, dried at roomtemperature and finally ground in a powdery form forcharacterization. The same process was repeated for the NaOH(VWR Amresco, US) where 4.0 0.1 g (0.01 mol) was weighedinto 100 mL of 95% absolute ethanol under the same reactionconditions.2.3. Characterization of synthesized ZnO.The synthesized samples were characterized using X-rayDiffraction, XRD, (Xpert Pro MPD PW3040/60) for their crystalstructure and crystallite size. Diffraction patterns from the XRDanalysis in Figure 1 (a & b) were obtained using X-raydiffractometer with Cu-Kα radiation of 40 kV and 30 mA withstep size of 0.017 . The morphology of ZnO NPs was determinedusing Field Emission Scanning Electron Microscopy (Carl ZeissGeminiSEM 500) with acceleration voltage of 10.0 kV, theworking distance of 11.6 mm and a chamber pressure of 40 Pa.Sample preparation for FE-SEM, TEM, EDX, FT-IR and UV-visanalysis was carried out using the method outlined by [32]. Thepowdered solid ZnO NPs were coated on a silicon wafer with thehelp of a carbon tape. Before the FE-SEM imaging, the drypowders were mounted on a stub followed by coating withPlatinum (Pt) for 1 minute using a sputter coater. TEM analysiswas done using TEM (JEOL 1230, Japan). Powdered ZnO NPswere first diluted with absolute ethanol (95%) and sonicated withultrasonic cleaner (Elma, Germany) for 30 minutes. A 4 µl of thesolution sample was loaded onto a Foamvar film Copper grid(FF300-Cu) before being observed under TEM. The purity of theZnO NPs was determined with EDX (JEOL 6390LA, Japan). TheZnO NPs were diluted with 95% Absolute ethanol and sonicatedwith ultrasonic cleaner (Elma, Germany) for 30 minutes. A 4 µl ofZnO NPs sample was loaded onto an aluminium plate beforebeing analyzed.FT-IR (Thermo Scientific Nicolet iS10, US) and UV-Vis(UV-1800 SHIMADZU UV Spectrophotometer) was used todetermine the surface functional groups and the optical property ofthe sample. The FT-IR sample preparation involved mixing thepowdered ZnO with Potassium bromide (KBr) in the ratio of 1: 19[33]. The sample was then placed in the metal hole, pressed untilthe sample compressed inside the hole, and analyzed using FT-IR.In the case of UV-Vis, the spectral range of 4000–400 cm-1 withresolution of 4 cm-1 was used. The optical property of the sampleswas determined by measuring their maximum absorbance usingUV–vis spectrophotometry. The ZnO-NPs were dispersed inethanol and sonicated for 10 minutes before it was used for ET)(Quantachrome, US Autosorb iQ,version 2.01) was used for thesurface area determination. Approximately, 0.3 g of ZnO NPspowder was degassed at 175 C for 2 hours [34] in a flowing N2gas. The N2 absorption-desorption isotherms of the samples werethen be measured.3. RESULTS3.1. Structural Properties.3.1.1. XRD Results.The XRD pattern of the ZnO prepared by the solvothermalprocess at 60 C for 180 minutes from KOH and NaOH alkalinesource is shown in Figure 1 (a & b). All detectable peaks can beindexed to ZnO wurtzite structure with ICSD Number (ICSD: 98000-9346) and PDF Number (Experimental and calculated powderdiffraction data) of 36-1451 and 01-074-0534 respectively. Thepatterns are broadened due to the nanosize of the ZnO crystals[35,31,36]. Based on the XRD diffraction patterns, all synthesizedZnO NPs were identified as being 100 % pure ZnO. The averagecrystallite size of the samples was calculated using Scherer’sformula [37].(1)where;K shape factor 0.89 (2)the peak broadening after removing the instrumental broadening.β(FWHM) is the full width half maximum of the diffraction peak andβ0 is the correction factor for instrumental broadening (0.07o2θ).The average crystallite size of ZnO prepared using KOHdetermined from the Panalytical X’Pert Pro MPD, diffraction peakwas found to be 11.0 1.3 nm whereas the sample synthesizedusing NaOH was 14.9 1.2 nm. When these results werecompared to a study by Ramachandra et al., the crystallite sizedetermined in their study was 43 nm and 45 nm usinghydrothermal method at a reaction temperature of 150 oC andcalcination temperature of 600 oC [38]. This is evident that,despite the simplicity and moderate conditions employed in thisstudy, smaller crystallite sizes could be produced. According to[39], a crystallite size of 21.59 nm and 36.89 nm can be obtainedfor ZnO from KOH and NaOH, respectively in a sol-gel method.Their reaction time and drying temperature were maintained at 2hours and 70 oC. In another study by [24], an average crystallitesize of 33 nm was recorded in a solvothermal method using Zincacetate and Triethanolamine (TEA) media. In their study, theTEA/Zn2 solution was autoclaved at 150 oC for 18 hours.3.1.2. FE-SEM and TEM Results.The FE-SEM and TEM images of ZnO nanoparticlesprepared from KOH and NaOH alkaline sources are shown inFigure 2 (a & b) and Figure 2 (c & d) respectively. The FE-SEMPage 5649
Eric Kwabena Droepenu, Boon Siong Wee, Suk Fun Chin, Kuan Ying Kok, Ebenezer Aquisman aggregation of the particles. FE-SEM and TEMimages of ZnO NPs synthesized from KOH source (Figure 2 a &c) confirm the formation of homogeneous hexagonal wurtzitestructures.Figure 1. XRD diffractogram of ZnO nanoparticles synthesized using (a)KOH and (b) NaOH.The sample synthesized using KOH displayed morphologysimilar to the nanostructures obtained by [24], when zinc acetateand Triethanolamine (TEA) were used in a solvothermal methodautoclaved at a temperature of 150 oC for 18 hours. Samplesshown in Figure 2a have a high surface area due to their smallparticle size, rendering them appropriate for catalytic applications[40].When NaOH was used under the same experimentalconditions, the morphology changed to flake-like nanostructuresas depicted in Figure 2 (b). Its corresponding TEM image, Figure2 (d) also shows flake-like nanostructures. For nanocrystallineZnO powder synthesized by sol-gel method, flake-likenanostructures were fabricated at a lower concentration asPolyvinylpyrrolidone (PVP) was used as a capping agent whenZn(ZnCH3COO)2 2H2O was reacted with NaOH and calcined at atemperature of 600 oC [41]. In other study by Gopal and Kamila,ZnO flake-like nanostructures were obtained from a reaction ofzinc nitrate and NaOH using precipitation technique at acalcination temperature of between 400-600 oC [42]. Apart fromGopal and Kamila, other studies that fabricated flake-likenanostructures using different synthesis techniques include [4346]. In all these studies, complicated methods, expensiveequipment with very critical reaction conditions were used ascompared to this study. Table 1 below gives a summary of theconditions and the particle size synthesized by the differentstudies.Figure 2. FE-SEM images of synthesized ZnO NPs with (a) KOH and (b)NaOH, alkaline source and TEM images of synthesized ZnO NPs with (c)KOH and (d) NaOH alkaline source.3.1.3. FT-IR Results.The FT-IR spectra of ZnO NPs synthesized from KOH andNaOH are shown in Figure 3. The characteristic band of wurtziteZnO in the two samples occurred at peaks of 420 cm-1 and 422 cm1respectively. This agrees with [51-53,33], who estimated therange to be between 400-500 cm-1.Figure 3. FT-IR spectra of ZnO NPs synthesized from KOH and NaOHalkaline source.Both samples show broad absorption bands in the peakrange of 3500-3700 and 1400-1600 cm-1 (in the case of ZnO fromNaOH) corresponding to O-H stretching and bending of hydroxylPage 5650
Synthesis and characterization of single phase ZnO nanostructures via solvothermal method: influence of alkaline sourcegroup [54-56]. But in the case of ZnO synthesized from KOH,peaks within the 1400-1600 cm-1 range diminishes. It can also beobserved that asymmetric and symmetric C O stretching of zincacetate is intense in ZnO synthesized from NaOH than that ofKOH at peak range of 1640 and 1500 cm-1 [41]. This might be theeffect of difference in pH which results in low rate oftransformation thereby introducing some carboxylate (-COO-)functional group [57]. The –C – H bending in alkane is much moreintense in the ZnO synthesized from NaOH than the one fromKOH which occurs at 1400 cm-1.3.1.4. UV-Vis ResultsThe UV-Vis absorption spectra of ZnO NPs synthesizedusing NaOH and KOH respectively are illustrated in Figure 4 (a &b). The absorption spectra of the synthesized samples wereacquired using UV-Vis spectrophotometer in the wavelengthregion of 300-400 nm. The spectrum reveals a strongcharacteristic absorption band of ZnO at wavelength of 367.70 nmand 365.30 nm for the KOH and NaOH alkaline sourcerespectively. The absorption depends on factors such as band gap,oxygen deficiency, size and structure of the nanoparticles, surfaceroughness and impurity centers [58]. The good absorptioncharacteristics of the ZnO-NPs in the UV region proves itssuitability in applications such as sunscreen protectors orantiseptic ointments [59-60].were of high purity. Similar findings were also reported inprevious studies by [62,49,31].Figure 5. EDX spectra of ZnO NPs synthesized using (a) KOH and (b)NaOH.3.1.6. BET ResultsFigure 6 (A and B) shows the BET analysis isotherms ofZnO NPs synthesized using KOH and NaOH.Figure 4. Optical absorption Spectra of ZnO NPs synthesized using (a)KOH and (b) NaOH.3.1.5. EDX Results.EDX spectroscopy was used to provide elemental analysisof the particles and is displayed in the spectra in Figure 5 (a & b).The spectra show the presence of two main elements,namely Zn and O in the proportion of 75.2%: 24.8% and73.9%:26.1% for samples A and B respectively. When these datawere compared to the theoretical value of Zn and O (80.3:19.7) by[61], it can be concluded that the synthesized ZnO nanostructuresFigure 6. Nitrogen (N2) adsorption- desorption isotherms of ZnO NPssynthesized using (A) KOH and (B) NaOH alkaline sources.The specific surface area was also determined to be 59.50m2/g and 31.43 m2/g for the zinc oxide NPs synthesized fromKOH and NaOH respectively. This suggests that sample A showsa large surface area as compared to sample B. Furthermore, thePage 5651
Eric Kwabena Droepenu, Boon Siong Wee, Suk Fun Chin, Kuan Ying Kok, Ebenezer Aquisman Asareaverage particle size calculated from BET data for sample A dueto its spherical shape was 16.5 nm based on the equation;(3)where;is the average particle size determined by BET, ρ isthe theoretical density of the sample which was 6.11 g cm–3, andSABET is the obtained surface area [34,63].Table 1. Characteristics of ZnO nanostructures synthesized by different studies.Precursor Zinc and Alkali saltSynthesis conditionPropertiesReferenceZn(CH3COO)2 2H2O KOHReaction temp: 60 oCReaction time: 3 hDrying temp: room temp.Ave. crystallite size: 11.0Current studyZn(CH3COO)2 2H2O NaOHSame conditions as above.Ave. crystallite size: 14.9Zn(CH3COO)2 NaOHReaction temp: 25 oCDrying: 100 oC 4 hCalcined: 400 oC 2 hReaction time: 7 hSynthesis time: 8 hParticle size: 97-174 nmAve. crystallite size: 23.04 nmZn(NO3)2 NaOHSynthesis condition same as the aboveParticle size: 52-93 nmAve. crystallite size: 19 nm[42]Synthesis condition same as the aboveZn(SO4)2 NaOHZn(CH3COO)2 (TEA) NaOHZn(NO3)2 6H2O NaOHZn(CH3COO)2 2H2O Polyvinylpyrrolidone (PVP) NaOHZn(CH3COO)2 2H2O N2H4Zn(NO3)2 6H2O NaOH NH3Zn(CH3COO)2 2H2O CTAB NaOHZn(CH3COO)2 2H2O NaOHZn(CH3COO)2 2H2O (CTAB) NaOHZn(CH3COO)2 2H2O KOHReaction temp: 60 oCDrying: 60 oC overnightCalcined: 150 oC 18 hReaction temp: 150 oCReaction time: 7 hCalcined: 600 oC 1 hReaction time: 1 hDrying: 60 oCCalcined: 600 oC 1 hIrradiation: 15 min 510W10 min 680 WDrying: 100 oC 2 hIrradiation: 15 min 150 WDrying: 100 oC 2 hCalcination: 600 oC 3 hReaction temp: 25, 35, 55 & 75 oCReaction temp: 90 oCReaction time: 2 hReaction time: 50 minReaction temp: 25 oCDrying: 60 oC 2hReaction time: 3 hReaction temp: 60 oCDrying: room temp.Zn(CH3COO)2 2H2O NaOHConc. ratio (1:1, 1:2, 1:4, 1:8)Reaction time: 1-3 hReaction temp: 120 oCDrying: 100 oCZn(CH3COO)2 2H2O NaOHReaction temp: room tempDrying temp: 100 oC 5 hCalcination: 250 oC 3 hZn(NO3)2 NaOHReaction time: 2 h 24 hDrying: 70 oC for several hoursZn(NO3)2 KOHZn(CH3COO)2 2H2O NaOHZn(NO3)2 NaOHZn(SO4)2 NaOHZn(CH3COO)2 2H2O C2H4(OH)2Reaction Temp: 25 oCReaction time: 7 hDrying: 100 oC for 4 HCalcination: 400 oC for 2 hSynthesis time: 8 hReaction temp: 70 oCMicrowave radiation: 600 W, 2.45 GHzReaction time: 25 min 220 oCDrying: freeze dryingParticle size: 49-179 nmAve. crystallite size: 37 nmParticle size: 48 7 nmAve. crystallite size: 23 2 nm[22]Pore diameter size: 9-12 nmAve. crystallite size: 45 & 43 nm[38]Ave. crystallite size: 45, 48, 49, & 56 nmfor different conc. of PVPParticle size: 150 nm[41][43]Needle shaped structureFlower shaped structuresParticle diameter: 50-150 nmParticle size: 23.7-88.8 nmCrystallite size: 23.7, 82.5, 69.6 & 88.8nmCrystallite size: 75 & 54 nmParticle diameter: 10-30 nmParticle length: 150-250 nmParticle size: 7.4 1.2 nmCrystallite size: 10.08 nm[45][46][47][31][48]Crystallite size: 300 nm to 10 μmCrystallite size: 20-36 nmParticle size: 18-36 nm[49]Crystallite size: 36.89 and 21.59 nmParticle size: 17-25 nm[39]Crystallite size: 21.59 nmParticle size: 30-50 nmCrystallite/Particle size: 23.04 nm/97174 nmCrystallite/Particle size: 19.00 nm/52-93nmCrystallite/Particle size: 37.00 nm/49179 nmParticle size: 25-50 nmCrystallite size: 23-48 nm[28][50]Page 5652
Synthesis and characterization of single phase ZnO nanostructures via solvothermal method: influence of alkaline source4. CONCLUSIONSSingle phase ZnO nanostructures were successfullysynthesized by a simple and low temperature solvothermal processfrom two different alkaline sources (KOH and NaOH) with zincacetate dehydrate (Zn(CH3COO)2 2H2O) as the precursor. Thesynthesis technique achieved a high purity ZnO nanostructureswith wurtzite hexagonal and flake-like nanostructures of averagecrystallite size of 11.0 nm and 14.9 nm for the two alkaline sourcerespectively. The average surface area of 59.50 m2/g and 31.43m2/g was determined for ZnO NPs obtained from KOH and NaOHsources respectively. The optical absorption spectra of the twosamples showed absorption bands of 367.70 and 365.30 nm as anindication for a pure ZnO NPs. EDX has also proven the purity ofsynthesized samples to contain high Zn and O elementcomposition. 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3.1. Structural Properties. 3.1.1. XRD Results. The XRD pattern of the ZnO prepared by the solvothermal process at 60 C for 180 minutes from KOH and NaOH alkaline source is shown in Figure 1 (a & b). All detectable peaks can be indexed to ZnO wurtzite structure with ICSD Number (ICSD: 98-000
the use of counselling skills. 2. To present basic attending and responding skills to the participants. 3. To provide participants with the opportunity to practise these skills in a safe and supportive environment. 4. To set these skills within the essential ethical framework of a counselling approach. 5. To introduce participants to the concept and experience of self-awareness and personal .
2 BETH REVIS helped her lie down in the clear cryo box. It would have looked like a cof-fin, but coffins have pillows and look a lot more comfortable. This looked more like a shoebox. “It’s cold,” Mom said. Her pale white skin pressed flat against the bot-tom of the box. “You won’t feel it,” the first worker grunted. His nametag said dE. I looked away as the other worker, Hassan .
beverages so that we can decrease our reliance on imports from outside the province, and the country. This local food and beverages strategy was created, and will be implemented and measured, in a collaborative manner through a multi-departmental committee that includes government, representatives from the food and beverages sector and Indigenous community representatives. This will ensure .
20172018 Brown Samuel Special Education Teacher Inclusion KILMER 89,815.00 20172018 Brown Deirdre MATHEMATICS TEACHER TCHS (Chambers) STEM Academy 89,015.00 20172018 Brown Elaine Special Education Teacher Resource WILSON 58,315.00 20172018 Brown Elizabeth PRE-KINDERGARTEN TEACHER WILSON 96,315.00
Stock, J. H. and Watson, M. W. (2014) Introduction to Econometrics, 3rd Edition, Pearson Material such as lecture slides, examples, and tutorial questions will be available on the unit home page. The lecture notes, together with the lectures and additional references will provide students with a clear indication of the basic content of the unit. It is recommended that students listen to all .
the expected effects of climate change on water resources and water programs. This knowledge will help us to prepare for and adapt to the effects of climate change. The information in this module is organized by the following questions: 1. Climate Change 101: How is the global climate changing and what are the causes?
the Cold War progressed and the United States sought to contain the spread of communism, large numbers of refugees made their way from Asia, Latin America, and the Middle East. Students will analyze a set of primary and secondary sources to determine how Cold War foreign policies shifted the demographics of the immigrant population. OBJECTIVES
“Electrical Safety in the Workplace” 2 Course Goal – The aim of this program is to provide comprehensive on-site training to high-risk workers (i.e. skilled trades and maintenance workers) and management on the requirements of Sub Part S, and the prevention
