Water-Content Dependence of ZnO Crystallite Size in Single-Step Microwave Solvothermal Co-Synthesis of ZnO/Ag Nanocomposites

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Abstract
In microwave solvothermal synthesis (MSS), ZnO particle size increases with precursor water content. This study tested whether that dependence changes when metallic silver forms in the same step. ZnO/Ag nanocomposites with nominally 2 mol% Ag were obtained by single-step MSS from zinc and silver acetates in ethylene glycol, without a separately added reducing agent, at measured precursor water contents of 1.47–3.97 wt%. XRD detected wurtzite ZnO and metallic Ag0 but no crystalline silver oxides. As the water content increased, the apparent ZnO crystallite size grew monotonically from 15 to 25 nm in the a–b basal plane and from 18 to 40 nm along the c axis. The BET specific surface area fell from 50.7 to 29.0 m2/g and the equivalent diameter d(BET) rose from 22 to 38 nm. Standardless EDS gave similar area-averaged Ag estimates for all samples, and AsB imaging of one sample revealed high-Z features consistent with an Ag-rich phase. An Ag-free ZnO reference series synthesised in the same reactor under identical conditions showed a similar dependence on water content. For three pairs of samples with nearly matched water contents, the series differed in specific surface area and d(BET) by at most about 7%, much less than the changes with water content. The separate preparation of the two series and the lack of replicate syntheses limit the ability to attribute the observed differences unambiguously to the presence of silver. Antimicrobial and photocatalytic activity was not investigated.
Funding Information
  • European Commission (No. POIR.01.02.00-00-0064/16)

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