Size control mechanism of ZnO nanoparticles obtained in microwave solvothermal synthesis

Abstract

The aim of the paper is to explain the mechanism of zinc oxide (ZnO) nanoparticle (NP) size control, which enables the size control of ZnO NPs obtained in microwave solvothermal synthesis (MSS) within the size range between circa 20 and 120 nm through the control of water content in the solution of zinc acetate in ethylene glycol. Heavy water was used in the tests. The mechanism of ZnO NPs size control was explained, discussed and experimentally verified. The discovery and investigation of this mechanism was possible by tracking the fate of water molecules during the whole synthesis process. All the synthesis products were identified. It was indicated that the MSS of ZnO NPs proceeded through the formation and conversion of intermediates such as Zn(OH)(CHCOO) · xHO. Esters and HO were the by-products of the MSS reaction of ZnO NPs. We justified that the esterification reaction is the decisive stage that is a prerequisite of the formation of ZnO NPs. The following parameters of the obtained ZnO NPs and of the intermediate were determined: pycnometric density, specific surface area, phase purity, average particles size, particles size distribution and chemical composition. The ZnO NPs morphology and structure were determined using scanning electron microscopy.

Current Trends in the Development of Microwave Reactors for the Synthesis of Nanomaterials in Laboratories and Industries: A Review

“…An example is zinc oxide, which is usually obtained in the form of a powder with an average grain diameter of above 100 nm [42], while as a result of a solvothermal-microwave process, the average grain diameter can be even less than 60 nm [43]. A similar ZnO synthesis method independently developed at IHPP PAS, involving an MSS2 reactor [44] and zinc acetate as a raw material in an ethylene glycol environment, allows for the very precise planning of the ZnO nanoparticles size in the range of 15-120 nm (specific surface area by the BET method (SSA BET) 74-9 m 2 /g) [45][46][47]. In solvothermal synthesis, it is possible to obtain many NPs (nanoparticles) doped by other elements and displaying different morphologies and different shapes.…”

Zinc Oxide Nanoparticles Obtained by Supercritical Antisolvent Precipitation for the Photocatalytic Degradation of Crystal Violet Dye

“…Traditional synthesis methods, such as precipitation, coprecipitation, colloidal methods, sol-gel processing, water-oil microemulsions method, hydrothermal synthesis, solvothermal, sonochemical, as well as polyol method [24], make it difficult to obtain well-separated nanoparticles with a narrow particle size distribution (PSD). Moreover, a massive use of organic and inorganic solvents, like nitrates, ammonia, diethylene glycol [25], ethylene glycol [26], 2-methoxyethanol with monoethanolamine [27], and hydroxides, are often required to obtain ZnO nanopowders [28][29][30][31].…”

Size Control of Cobalt-Doped ZnO Nanoparticles Obtained in Microwave Solvothermal Synthesis

“…The dynamic development of the broadly understood microwave heating technology and the new design solutions of microwave reactors have contributed to the increased popularity of the microwave solvothermal synthesis (MSS) [60][61][62][63][64] and the microwave hydrothermal synthesis (MHS) methods [65][66][67]. The advantages of microwave heating and microwave syntheses of NMs and organic compounds are described in detail in the relevant literature [63][64][65][66][67][68][69][70][71][72][73][74].…”

“…It must be emphasised that the MSS method also has great potential for obtaining ZnO NPs. The MSS of ZnO NPs developed by us permits controlling the NPs size within the range of 15 nm to 120 nm [60,61].…”