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Parameters affecting synthsis of ZnO nanoparticles

  1. 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
  3. 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
  4. Parameters PH Metal Precursors Stirring Speed Reaction Time Temperatu- re Capping Agent
  5. 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
  6. 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.
  7. 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.
  8. 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
  9. 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.
  10. 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
  11. 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.
  12. 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
  13. 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.
  14.  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
  15. 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.
  16.  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.
  17. 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.
  18. Nature of Capping Agent
  19. 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
  20. 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.
  21. 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.
  22. Future Usage  Future research should focus on the immobilization of ZnO nanoparticles on suitable supports for easy separation after usage.
  23. 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: extraction-and-application-ofbioactive-ingredients-from-plant- materials/