By adding drop wise addition of sodium hydroxide to zinc chloride in ethanol medium stirring vigorously, will zinc oxide nanoparticles be formed? If so what is the mechanism of formation?
Sodium hydroxide is a reducing agent which causes formation of ZnO according to the following equation:
ZnCl2+2NaOH=ZnO+H2O+2NaCl(aq)
ZnO is more stable than ZnCl2, thermodynamically. However, kinetic of the reaction is other important parameter. In reactions with high kinetic rate, time is so vital for reaching nanometer size. If reaction proceeds for long time particles become bigger than nano size.
The general mechanism for this reaction is nuclear & growth. It means nucleations create in system then by adding more Zn2+ and O2- ions, they become larger.
Sodium hydroxide is a base and not a reducing agent! It is a metathesis reaction leading to Zinc hydroxide which loses water to give zinc oxide!which would be precipitated! Try the reaction in a microemulsion medium!
Narasimhan
Generally the synthesis of ZnO nanoparticles starts by reaction between Zn+2 (from zinc precursor) and hydroxide ions (LiOH, NH4OH, NaOH etc) which is followed by an aggregation process. The attached paper may help you……….
You dont tell about the pH value? Its very important in this reaction
If you do the synthesis of ZnO nanoparticles in NaOH, they will aggregate a lot after the synthesis is done and it is almost impossible to break the aggregates and they do not go through a 0.2 um filter. I have observed this multiple times. However, if you do the reaction with KOH, the final ZnO NP are much more stable. All this may be due to a pH effect as Ismail suggested. But I have not checked the pH of my solutions.
Prakash Sista, How you know what amount of KOH or NaOh to complete the reaction? It depends on pH. you must measure it.
pH is important. if you use NaOH more it can react with nucleus and decrease ZnO particles. you should find optimum pH by adding acid.
ZnCl2+2NaOH=Zn(OH)2+2NaCl(aq)
Zn(OH)2 ======Sintering===== ZnO
what thing said the peoples in earlier was correct, but you can try with ammonia i.e liq ammonia to maintain the pH about more than 10 you will get Zn hydroxide, then you filter it and ignite around 500 degrees. but you cannot get direct ZnO precipitate in the any methods.
Mukhlis Ismail, I have done this reaction a few years back and do not have my notes with me. I zoned in on one reference which seemed the most reasonable synthetic method that time. I used Zinc acetate as the reactant. Also, there was a specific molar ratio of Zn/KOH which was more like 7:1 or 1:7. But this is very clearly specified in many reference papers for synthesis of ZnO NP.
You prepare sample depends on pH but not in direct measurements, when you use a definite molar ratio of Zn/KOH.
yes... that is true. What I meant to say was, I did not measure the pH. But, there was a definite pH where the reaction worked. It depends on the concentration of acetate ion in solution and KOH in solution. Both determine the pH together. However, the first step in this reaction is for Zn(CH3COO)2 to break down to form Zn(OH)2. Which would then give ZnO NP. So, the pH of the reaction keeps changing based on the intermediates formed.
Dear all: you may also consider running the reaction at elevated temperature. One statement above seemed to claim that ZnO cannot form from solution directly but needs calcination. This is incorrect, there are countless examples where people have made ZnO from aqueos or alcoholic solution between RT and 100 C. Higher temperatures will sped up the hydroxide - oxide transition.
The pH is of course important, and obe thing we should not ignore is the fact that the pH will change over the course of the reaction. We did - a while ago - perform detailed studies on ZnO formation from solution, so maybe these papers are of use to you.
Article Kinetics and Particle Formation Mechanism of Zinc Oxide Part...
Here comes the second mechanistic study and pH measurement
Article Room Temperature ZnO Mesocrystal Formation in the Hydrated I...
by adding more NaOH in solution or by making solution more alkaline you may get good ZnO nanoparticles
But I want to make ina acids. Is there any special condition for ZnCl when heating... I mean maybe from the thermodynamic site , there is such as important to do when we synthesized a ZnO nanoparticles
Dear all and dear Melanie, indeed the addition of an alcaline medium is not necessary. All Zn precursors salts contain water molecules and in proper conditions of temperature it is possible to get the ZnO by a simple de-hydration reaction. In this case the source of O for ZnO is water. Here I can suggest a paper from my self:, where no alkaline additive was used, and the synthesis performed at temperature higher than 100°C.
Distaso, M.; Klupp Taylor, R.; Taccardi, N.; Wasserscheid, P.; Peukert, W. Chem. Eur. J. 2011, 17, 2923-2930.
The synthesis of ZnO in acidic environment cannot be performed as ZnO is soluble at low pH. At very high pH, Zn(OH)2 is the main species in solution. According to some authors (and to my personal experience as well) the de-hydration of Zn(OH)2 is a very fast process even at low temperatures (which makes very complicated the isolation of Zn(OH)2! See these references:
1. V. K. Ivanov, A. S. Shaporev, F. Y. Sharikov, A. Y. Baranchikov Superlatt. Microstr. 2007, 42, 421-424.
2. A. S. Shaporev, V. K. Ivanov, A. E. Baranchikov, Yu. D. Tretyakov Inorg. Mater. 2007, 43, 38-43.
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nanostructured Materials
- Nanoparticles