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Nanosensor Arrays
Published in Suresh Kaushik, Vijay Soni, Efstathia Skotti, Nanosensors for Futuristic Smart and Intelligent Healthcare Systems, 2022
Naumih M. Noah, Peter M. Ndangili
Precipitation synthesis processes involve ion exchange reactions in which one of the products formed is insoluble. These reactions are not complex and mostly proceed spontaneously since one species in the reaction is strong enough to displace the other from its compound. For instance, the reaction between sodium hydroxide (NaOH) and zinc sulfate (ZnSO4) forms insoluble zinc hydroxide (Zn(OH)2), which can further be heated to give zinc oxide (ZnO) nanoparticles. This method has been used to prepare both doped and undoped ZnO nanoparticles such ZnO (Sani et al. 2017), ZnWO4 (Hosseinpour-Mashkani et al. 2016), Ce-doped ZnO (Lang et al. 2016), and many other different types of metal oxide nanoparticles. Magnetic metal particles are known to aggregate to form bulk materials, which are thermodynamically stable (Ma et al. 2013). This aggregation decreases their surface area and hence the adsorption sites. Synthesis procedures for these particles therefore should include steps that ensure post-synthesis non-aggregation. This can be done using surface modification techniques such as coating the nanoparticle with a more stable shell; for instance, a metal oxide layer. This is because metal oxide particles once hydrated form hydroxyl groups. These hydroxyl groups can undergo protonation and deprotonation reactions depending on the pH to form negative charges or positive charges on the surface of the nanoparticle. A positive charge density is developed at pH values less than the point of zero charges (PZC) pH whereas a negative charge density develops at pH values higher than PZC pH (Ma et al. 2013). A dense negative charge on a nanomaterial surface creates electrostatic repulsive forces on the individual particles, hence keeping them apart. The same principle applies for a dense positive charge on nanoparticle surface.
Effects of aging conditions on the morphologies of ZnO particles synthesized under hydrothermal conditions from layered zinc hydroxide as a precursor derivered from zinc acetate
Published in Journal of Asian Ceramic Societies, 2020
Layered zinc compounds (formula: Zn5(OH)10-x(Am-)x/m•nH2O[A:Anion]) belong to the family of metal hydroxide salts (MHS) with the general formula Ma(OH)b(Ac-)(2a-b)/c•nH2O[A:Anion], whereM = Zn2+, Co2+, Ni2+, Mn2+, etc. MHS consists of positively charged brucite-like layers of metal hydroxides that require the presence of interlayer anions to maintain their overall charge neutrality. These interlayer anions can be Cl−, CO32-, CH3COO−, or SO42- [17]. Layered zinc hydroxide acetate (ZHA) is synthesized by direct precipitation by adding sodium hydroxide solution to Zn(OCOCH3)2 solution, or by stirring ZnO powder with zinc acetate in solution [18–20], etc. Besides being studied as an ion-exchange application in catalysis [18], layered zinc hydroxide is often studied as a precursor of ZnO. Layered zinc hydroxides can provide ZnO powders through dissolution/reprecipitation processes under wet conditions [21].