Effect of PH Variation on Particle Size and Purity of

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Effect of PH Variation on Particle Size and Purity of Nano Zinc Oxide Synthesized by Sol-Gel. Method. Radyum Ikono, Putri Riskia Akwalia, Siswanto, Wahyu ...
International Journal of Engineering & Technology IJET-IJENS Vol:12 No:06

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Effect of PH Variation on Particle Size and Purity of Nano Zinc Oxide Synthesized by Sol-Gel Method Radyum Ikono, Putri Riskia Akwalia, Siswanto, Wahyu Bambang W, Agus Sukarto, Nurul Taufiqu Rochman* Abstract -- In recent years, there have been many methods developed to synthesize Zinc Oxide (ZnO) nanoparticles. Nevertheless, a simple yet cheap method to prepare single crystal with high purity nano ZnO was still yet to be established. In this research, nano Zinc oxide (ZnO) was prepared by sol-gel method. The pH variation effect to the resulting ZnO product was also observed. (CH3COOH)2Zn.2H2O powder and NaOH solution were used as precursors. NaOH solution was added to (CH3COOH)2Zn.2H2O solution by titration until colloids with different pH were obtained, then precipitates of nano ZnO were formed. From the precipitation profile, it can be observed that increasing pH led to shortened precipitation time, which also means increasing particle size. It was also further confirmed that particle size at pH 7 and pH 12 was 1.3 nm an d 73.8 nm, respectively. XRD profile showed that increasing pH led to increasing purity of nano ZnO: 42.9%, 62.2%, 64.7%, and 100% at pH 7, pH 8, pH 10, an d pH 12, respectively. To conclude, nano ZnO synthesized by S ol-Gel method was highly affected by pH of the working solution. Increasing pH led to increasing particle size, however led to higher purity of nano ZnO produced.

Index Term-- Nano ZnO; sol-gel; pH variation I. INTRODUCTION Zinc Oxide (Zn O) ceramics have gained much attention due to their d istinct properties and characteristics. ZnO ceramics in various forms are used extensively in electronic applications, such as LED, sensor, or solar cells [1]. In recent years, it has also been found that ZnO can be used in other potential applications like photocatalysis and antibacterial substance, thus ma king them excit ing co mmodities for industries [2]. Radyum Ikono is with Nanotechnology Research and Business Center, T angerang Selatan, Indonesia, and with Department of Metallurgy, School of Engineering and T echnology Sumbawa (ST T S), Sumbawa, Indonesia (email: [email protected]) Putri Riskia Amalia is with Department of Physics, Airlangga University, Surabaya, Indonesia Siwanto is with Department of Physics, Airlangga University, Surabaya, Indonesia ([email protected]) Wahyu Bambang is with Research Center for Physics, Indonesian Institute of Science (LIPI), T angerang Selatan, Indonesia (email: [email protected]) Agus Sukarto is with Research Center for Physics, Indonesian Institute of Science (LIPI), T angerang Selatan, Indonesia (email: [email protected]) *Nurul T aufiqu Rochman is with Research Center for Metallurgy, Indonesian Institute of Science (LIPI), T angerang Selatan, Indonesia (Corresponding Author. Ph: +62 21 7587 0479 fax: +62 21 7560553 email: [email protected])

At the same t ime, nanotechnology becomes much more popular nowadays. Scientists believe that by engineering material size into nanoscale, there will be an enhancement on properties of the material. In many literatures, it can also be learned that nano ZnO offers better performance compared to that of in bulk size [3]. There have been many methods to synthesize nano ZnO. Some of the widely used methods are, for instance, Chemical vapor deposition (CVD), d ip coating, o r mechanical alloy ing [4,5,6]. Those methods have their own advantages and disadvantages. For example, CVD and dip coating, they can produce nano ZnO with high purity, however high growth temperature is needed in their system. Also, the preparation scheme is quite co mplex and can be very expensive [7]. Mechanical alloying is another interesting method where it can synthesize nano Zn O in relatively simple manner [8]. Nevertheless, to date, there has been no reports on mechanical alloying method that can yield pure nano ZnO. Another possible method is sol-gel method. The good thing about this method is that, it is relatively simple and cheap in process, and it does not need to be treated in high growth temperature [9]. Ho wever, to date, there is still a little knowledge on the effect of pH variation on sol-gel wo rking solution, also whether high purity of nano ZnO can be achieved by this method. In this research, nano ZnO was synthesized by sol-gel method, in an attempt to find the optimu m condition to produce single crystal ZnO with relatively s mall size. The pH condition would be varied for this optimization process. II. EXPERIM ENTAL PROCEDURE 4.39 gram (CH3 COOH)2 Zn.2H2 0 (Merck) powder was dissolved in 100 mL methanol. It was then sonicated at 750 Watt for 30 minutes to obtain homogenous solution of 0.2 M. Separately, 1.0 M NaOH was dissolved in 500 mL distilled water. After that, optimizat ion for t itration was conducted to find the optimu m condition of the time, temperature, and stirring speed. The optimized condition was used for titration of NaOH solution dropped to (CH3 COOH)2 Zn.2H2 0 solution. Titration was continued until 5 p H variations were obtained: pH 7, pH 8, p H 9, pH 10, pH 11, and pH 12. After the colo r of the solution become milky wh ite, the solution was sonicated for another 30 minutes. It was then idled fo r several days to observe the precipitation of nano ZnO in the solution.

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International Journal of Engineering & Technology IJET-IJENS Vol:12 No:06 After the precipitation could be clearly seen through, solution was centrifuged at 3000 rp m for 30 minutes. The supernatant was then removed, and the precip itation which contains nano ZnO was obtained. Nano ZnO precipitates was first treated in 800 C oven to remove the remaining water. Finally, nano ZnO was grinded with mortar to be shaped into powder. To find out the particle size, Particle Size Analy zer ( DelsaTM Nano C Beckman Coulter) was used. Briefly, nano ZnO was dissolved in distilled water in 1:10 concentration. It was then stirred until ZnO suspension in water was formed. 1 mL of the suspension was then tested to obtain the average particle size. The solution was then centrifuged, and the supernatant was removed to obtain the nano ZnO. Finally, nano Zn O powder was achieved after heat treatment at 800 C. The Xray diffract ion (XRD) pattern of the final Zn O nanoparticles was obtained with Cu Kα radiation (Shimad zu, Japan). The peak positions and relative intensities were characterized by comparison with the Joint Co mmittee for Po wder Diffraction Standards (JCPDS). Williamson-Hall plot was used to analyze the crystal size at different pH. The preparation scheme was shown in Fig. 1. III. RESULTS AND DISCUSSIONS The time for nano ZnO to precipitate fro m solution was observed. It can be seen from Fig. 2 that time to precipitate decreased over increasing pH. The range fro m p H 7 condition which needed 72 hours to pH 12 condition which needed only 120 minutes to precipitate showed that pH plays a very significant role in sol-gel experiment. One of the pro minent charactristics of nanoparticles are that they tend to float in solution and they need much longer time to be precipitated inasmuch as the gravitation force exerting them is very small, or even almost negligib le [10]. It was hypothesized that by varying the pH condition, the size of the particle obtained would also be varied, and this would affect the p recipitat ion profile of the Zn O nanoparticles. To test above hypotheses, size of the particles at lower and upper pH (pH 7 and pH 12) were measured by PSA mach ine. Results showed that the size of nanoparticles at pH 7 and pH 12 were 1,3 n m and 73,8 n m, respectively. It is in agreement with hypotheses above that as pH of the solution increased, the size of the nanoparticle increased as well. Finally, XRD graph in Fig. 4 gave us information about the elements of the particles fo rmed at p H 7, 8, 10 and 12. Fro m the graph, it can be inferred that the purity of nano ZnO produced increased as pH increased. On ly at p H 12 the 100% ZnO without any contamintants or mixture with other compounds were obtained. The quantitative data of Zn O purity at pH 7, 8, 10, and 12 was as follows: 42.9%, 62.2%, 64.7%, and 100%, respectively. This phenomenon was well explained by Sunandan, et al. that the growth of Zn O is normally enhanced in basic med iu m. The final gro wth of ZnO depends upon the competition between gro wth and etching [10]. The size became significantly bigger at basic condition maybe

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because high purity ZnO nanoparticles tend to bind each other and agglomaerate. In lower p H, although the particle was much smaller in size, the ZnO obtained was still in mixtu re with other co mpounds, such as CH3 COONa and Zn(OH)2 , therefore they tend to be separated, hence each has small size. Interestingly, at p H 7 there was almost no ZnO part icles could be observed. It can be understood that at pH 7, the growth of ZnO was suppressed. It can be predicted that at pH lower than 7, there might be no ZnO produced by sol-gel method using protocol implemented in this research. Another interesting finding was observed fro m measurement of crystal size using Williamson-Hall plot analysis as shown in Table I. Fro m those data, it can be seen by comparing the particle size (before heat treatment) and crystal size (after heat treat ment), there was a tendency for the particle to grow in size. This might be due to recrystallizat ion happened due to heat treatment effect. Nevertheless, it can be deduced that the size increment was not significant. IV. CONCLUSIONS Nano ZnO was synthesized succesfully fro m precursor (CH 3 COOH) 2Zn.2H 2O and NaOH. pH of the working solution was varied to see the different resulting nano ZnO produced. Nano ZnO precipitation time increased over increasing pH, wh ile the size of the nanoparticle also increased over increasing pH. The XRD data showed that fro m pH 7 to pH 12, there was significant imp rovement of the nano ZnO purity. Interestingly, 100% purity of nano ZnO could be obtained at pH 12. This research showed that pH condition in sol-gel reaction plays a very significant ro le to control the characteristics of nano ZnO produced. Further modification and characterizat ion works are needed before this nano ZnO used in several applicat ions, such as tooth cements, or cosmetics. REFERENCES [1] Shen L., Bao N., Yanagisawa K., Do men K., Gupta A., Grimes C.A. “Direct synthesis of ZnO nanoparticles by a solution-free mechanochemical reaction”, Nanotechnology 17 (2006) 5117-5123. [2] Puckett S.D., Taylor E., Raimondo T., et al. “The relationship between the nanostructure of titanium surfaces and bacterial attachment”, Biomaterials 31 (2010) 706–713. [3] Salah N., Habib S.S., Khan Z.H., Memic A., Azam A., Alarfaj E., Zahed N., Al-Hamedi S. “ High-energy ball milling technique for ZnO nanoparticles as antibacterial material”, Intl. J. Nanomed. 6 (2011) 863-869. [4] Wang J.R., Ye Z.Z., Huang J.Y., et al. “ ZnMgO nanorod arrays grown by metal-organic chemical vapor deposition”, Mater. Lett. 62 (2008) 1263–1266. [5] Sasani G.M., Vafaee M . “Sol–gel derived zinc oxide buffer layer for use in random laser media”, Mater. Lett. 62 (2008) 1754–1756. [6] Ye X.Y., Zhou Y.M., Chen J., Sun Y.Q., Wang Z.Q., et al. “Coating of ZnO nanorods with nanosized silver

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International Journal of Engineering & Technology IJET-IJENS Vol:12 No:06 particles by electroless plating process”, Mater. Lett. 62 (2008) 666–669. [7] Damonte L.C., Mendoza Z.L.A., Mari S.B., Fenollosa H.M.A. “Nanoparticles of ZnO obtained by mechanical milling”, Powder Technol. 148 (2004) 15–19. [8] Yan J., Liu Y., Peng A., Lu Q. “Fabrication of nanocrystalline W-Ni-Fe pre -alloyed powders by mechanical alloying technique”, Trans. Nonferrous. Met. Soc. Ch ina 19 (2009) s711-s717.

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[9] Ansari A.A., Singh R., Su mana G., Malhotra B.D., “Solgel derived nano-structured zinc oxide film for sexually transmitted disease sensor”, Royal Soc. Chem. 134 (2009) 997-1002. [10] Sunandan B., Joydeep D. “pH dependent growth oxide nanorods”, J. Crystal Growth 318 (2009) 8 2549-2554

Fig. and Tables

Zn(CH3 COO)2 + CH3 OH Sonicate 750 watt, 30 menit

1 M NaOH dissolved in distilled water

Optimization of titration (time)

Optimization of titration NaOH + water with magnetic stirrer

Optimization of titration (temperature)

Optimization result of titration for getting pH variation (7,8,9,10,11,12)

Observation of precipitation time

Optimization of titration (stirring speed)

Particle size analysis by PSA

Centrifuge (3000 rpm)

Heat treatment (800 C)

Nano ZnO powder

XRD analysis (pH 7, 8, 10, 12) Fig. 1. Experiment scheme

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Time to Precipitate (hours)

80 70 60 50 40 30

20 10

0 6

7

8

9

10

11

12

13

pH Fig. 2. T he graph of precipitation time over pH of working solution

Fig. 3. Size distribution of ZnO nanoparticle at pH 7 (top) and pH 12 (bottom)

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Fig. 4. XRD graph of nano ZnO at pH 7, pH 8, pH 10, and pH 12 T ABLE I CRYSTAL SIZE ANALYZED BY WILLIAMSON - HALL P LOT

pH

Crystal size (nm)

7

10,94±0,99

8

17,44±5,36

10

38,27±2,14

12

74,04±41,77

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