GROUP # 02
 AISHA HANIF 2022MphilAppChem-202
 BISMA KHALID 2022MphilAppChem-205
 FURQANA BIBI 2022MphilAppChem-207
 MARIAM SOHAIL 2022MphilAppChem-213
 REMSHA RAMZAN 2022MphilAppChem-215
 MEHR-UL-NISA 2022MphilAppChem-221

PARAMETERS EFFECTING
ZINC OXIDE OF NANO
PARTICLES

INTRODUCTION
Zinc oxide is an inorganic compound with the formula ZnO. It is a white
powder that is insoluble in water.
Formula:
ZnO
Molar Mass:
81.38 gram/mole
Density:
5.61 g/cm3
Melting Point:
1.975 ºC
Boiling Point:
2.360 ºC

Parameters
PH
Metal
Precursors
Stirring
Speed
Reaction
Time
Temperatu-
re
Capping
Agent

Parameters Effecting Zinc oxide:
Parameters effecting Zinc oxide of nano particle are given below:
 PH of the reaction mixture
 Calcination Temperature
 Reaction Time
 Stirring Speed
 Nature of Capping Agent
 Concentration of Metal Precursors

Parameters Effecting Zinc oxide:
PH of the Reaction Mixture:
PH of the reaction mixture determines the types of ZnO nanoparticles formed.
The crystallite size, morphology, phases, and surface areas of ZnO nanoparticles
depend largely on the amount of positively and negatively charge ions present
in the medium during the preparation. Solution pH alters the electrical charge of
molecules and such alteration will afect their reduction.

Acidic Medium 7>pH
 Synthesis of ZnO in an acidic medium (pH ˂ 7), the amount of
hydroxyl ions (OH−) is usually low in the solution which hinders
hydrolysis and condensation processes, leading to the smaller
aggregates at the end of poly-condensation process.
 The ZnO nanoparticles synthesized at lower solution pH (acidic
medium) had a smaller crystallite size irrespective of the method and
the reaction conditions compared to the neutral and basic medium
The decrease in the crystallite size of the zinc nanoparticle in an acidic
medium was attributed to the preferential corrosion of the ZnO crystal
structure.

PREPARATION MECHANISM
 The reaction mechanism of growth of ZnO nanoparticles with respect to variation of solution pH from
acidic to basic region.
Zn (1) 2+ + 2OH− ↔ Zn(OH)2
Zn(OH) (2) 2 + 2OH− ↔ [Zn(OH)4]2−
[Zn(OH)4] (3) 2− ↔ ZnO2−2 + 2H2O
ZnO (4) 2−2 + 2H2O ↔ ZnO + 2OH−
ZnO + OH (5) − ↔ ZnOOH−
ZnOH (6) − + Na+ ↔ ZnOOH − Na

Neutral pH=7
 The hydrogen ion (H+) and the hydroxyl ion (OH−) concentrations
are equal, therefore, making the solution having little or no influence
at the interfaces of zinc oxide crystals.

Basic pH<7
 The number of OH− ions is usually high causing strong attraction between
the positively charged Zn+ and OH ion; subsequently, increase
crystallization and formation of a smaller ZnO nanoparticle

Reaction Temperature
 The physical methods mostly employed to synthesize nanoparticles require a
higher temperature above 350∘C, while chemical route used for the synthesis of
nanoparticles can be carried out at room temperature.
 The chemical method is the easiest way to synthesize ZnO nanoparticles. Higher
temperature resulted to increase in reaction rate causing rapid consumption of
metal ion and formation of nanoparticle of a smaller size.
 Low concentration of the precursors often leads to the formation of smaller
crystalline size either at a lower or higher temperature, due to the competition
between nucleation and growth processes.

Reaction Temperature
 A reduction of particle size from 26 to 17 nm when the temperature
of the reaction medium was increased from ambient temperature to
50 °C. The synthesized ZnO nanoparticles were characterized by
SEM, XRD, and UV–visible spectrophotometer.
 Increase in reaction temperature resulted to a quick reduction of Zn+
ions and subsequent formation of ZnO nanoparticles with a smaller
crystallite size.
 Synthesis of ZnO nanoparticles carried out at lower temperature can
also lead to formation of smaller crystallite sizes while at higher
temperature nucleation was more favoured

Calcination Temperature
 Calcination involves heat-treating a material at a controlled temperature and
in a controlled environment.
 During the calcination process, the particles fuse and enlarge its primary
crystallite size. This process is called particle coarsening, a phenomenon in
solid (or liquid) solutions often used for the growth of larger crystals from
those of smaller size and lead to reduction in the number of smaller particles
while larger particles continue to grow.
 The particle coarsening phenomenon occurs due to the fact that the smaller
nanoparticles are less energetic and unstable compared to the well-packed
nanoparticle with a large crystallite size.

 This process can also take place at room temperature and however can
be accelerated during heating process.
 Calcination temperature increases from 200 °C, 400 °C to 500 °C, the
particle size also increases from 30, 41, and 44 nm.
 The higher the calcination temperature, the larger the crystallite size of
the ZnO nanoparticles irrespective of the method, solvent and other
synthesis conditions. Calcination temperatures also afect the
morphology of ZnO nanoparticles and in most cases spherical shape of
ZnO nanoparticles predominate.
Calcination Temperature

Reaction Time
 Reaction time is the time required for completion of all steps during the synthesis
of nanoparticles including the reduction and formation of nanoparticles.
 The formation of nanoparticles starts within minutes after the addition of the metal
salt precursors and increases as the reaction time increases.
 A longer nucleation time leads to the formation of larger crystallite size because the
particles have enough time to fuse and further fusion yielded large ZnO.

 The step by step involved on the variation of reaction time during the
synthesis of ZnO nanoparticles
Step 1:
The nucleation process (the process whereby nuclei (seeds) act as templates
for crystal growth) which is the frst step in the formation of ZnO oxide
nanoparticles. This process takes place within a few seconds of the reaction.
Step 2:
It involves the growth of the nanoparticles up to an average crystallite size of
5.2 nm as the time increases from T1 to T3.

Stirring Speed
 The mean diameter of the nano particles were smaller than the
values obtained by the vigorous magnetic stirring. They also
presented different shapes and morphology form those synthesized
with the stirring velocity of 18000 rpm.
 At stirring speed of 500 rpm, the ZnO-NPs formed are more
agglomerated and thickened with less aspect ratio (L/D fractions),
hence absorb at higher wavelength.

Nature of Capping Agent

Nature of Capping Agent
 Capping agents are often used for controlling the size, aggregation,
and properties of nanoparticles.
 Small-sized ZnO nanoparticles can be prepared using a variety of
organic capping agents, such as 2-mercaptoethanol, octanethiol, and
sodium salicylate. These agents can quench the growth and
agglomeration of nanoparticles.
 These capping agents act as stabilizers or binding molecules that
prevent agglomeration and steric hindrance, alter the biological
activity and surface chemistry, and stabilize the interaction of
nanoparticles within the preparation medium

Concentration of Metal Precursors
 Zinc nitrate (ZnON) and zinc acetate (ZnOA) were used as precursors
for the synthesis of zinc oxide (ZnO) nanoparticles by the sol–gel
method.
 The optimum precursor concentration was 1 g with the smallest
grain size and a high purity level. The increase in annealing
temperature induced an increase in the crystallite size of ZnO
nanoparticles from 24.53 nm (600 °C) to 34.24 nm (800 °C),
however, increasing the level of purity of the nanopowders.

Conclusion
 Acidic medium favoured the formation of smaller size of ZnO nanoparticles compared to
alkaline medium. Several reports indicated a decrease in the crystallite size of ZnO
nanoparticles as the pH increases from 7 to 12. Reaction time, reaction temperature and
calcination temperatures influenced the crystallite size of ZnO nanoparticles.
 Different zinc salts have little effect on the crystallite size but exerted greater influence
on the morphology of the ZnO nanoparticle produced
 Optimization of all these parameters should be carried out to fully understand the
mechanism of the synthesis of ZnO nanoparticles. Regeneration of the ZnO should be
performed to evaluate the cost effectiveness of ZnO as an adsorbent.
 Future research should focus on the immobilization of ZnO nanoparticles on suitable
supports for easy separation after usage.

Future Usage
 Future research should focus on the immobilization of ZnO nanoparticles
on suitable supports for easy separation after usage.

References:
 Andres Moure, H. (2006). Supercritical CO2 Extraction and
Purification of Compounds with Antioxidant Activity. Journal of
Agriculture and food chemistry, 2441-2469.
 E. Ibáñez, M. H. (2014). Supercritical Fluid Extraction. Reference
modules in chemistry, 65-70.
 Swami, N. R. (2016, october 9). Supercritical fluid extraction and
application of bioactive ingredients from plant materials. Retrieved
from newfoodmagzine:
https://www.newfoodmagazine.com/article/74056/supercritical-fluid-
extraction-and-application-ofbioactive-ingredients-from-plant-
materials/

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