Microwave-Assisted Au and Ag Nanoparticle Synthesis: An Energy Phase-Space Projection Analysis

Abstract

Microwave-assisted synthesis of gold and silver nanoparticles, as a function of Green Chemistry, non Green Chemistry, and four applicator types are reported. The applicator types are Domestic microwave ovens, commercial temperature controlled microwave chemistry ovens (TCMC), digesters, and axial field helical antennae. For each of these microwave applicators the process energy budget where estimated (Watts multiplied by process time = kJ) and energy density (applied energy divided by suspension volume = kJ⋅ml −1 ) range between 180 ± 176.8 kJ, and 79.5 ± 79 kJ⋅ml −1 , respectively. The axial field helical field antenna applicator is found to be the most energy efficient (0.253 kJ⋅m −1 per kJ, at 36 W). Followed by microwave ovens (4.47 ± 3.9 kJ⋅ml −1 per 76.83 ± 39 kJ), and TCMC ovens (2.86 ± 2.3 kJ⋅m −1 per 343 ± 321.5 kJ). The digester applicators have the least energy efficiency (36.2 ± 50.7 kJ⋅m −1 per 1010 ± 620 kJ). A comparison with reconstructed 'non-thermal' microwave oven inactivation microorganism experiments yields a power-law signature of n = 0.846 (R 2 = 0.7923) four orders of magnitude. The paper provides a discussion on the Au and Ag nanoparticle chemistry and bio-chemistry synthesis aspects of the microwave applicator energy datasets and variation within each dataset. The visual and analytical approach within the energy phase-space projection enables a nanoparticle synthesis route to be systematically characterized, and where changes to the synthesis are to be mapped and compared directly with historical datasets. In order to help identify lower cost nanoparticle synthesis, in addition to potentially reduce synthesis energy to routes informed changes to potentially reduce synthesis energy budget, along with nanoparticle morphology and yield.

Green Chemistry Allometry Test of Microwave-Assisted Synthesis of Transition Metal Nanostructures

“…In these papers, a log-linear energy phase-space projection was used; where the process energy budget (cavity-magnetron power multiplied by process time (J•s −1 × s = kJ) is plotted on the x-axes and the process energy density (process energy budget divided by suspension volume, measured in ml, (kJ•mol −1 ). American Journal of Analytical Chemistry Using the same energy phase-space projection technique, but using a log-log transformation of both x-axes and y-axes, historical microwave-assisted synthesis of transition metal nanostructures (monometallic, bimetallic structures, and metal decorated sheets) has also been examined: for silver (Ag), and gold (Au) (Law and Denis (2023) [7]), and for palladium (Pd), Ag, platinum (Pt), Au, and zinc oxide (ZnO) (Law and Denis (2023) [8]). Typically the synthesis operated within a multimode cavity the microwave power source operated at a free running frequency of f o = 2.45 ± 0.05 GHz (free wavelength, λ ~ 12.2 cm).…”

“…Finally, combining the outcome for the Ag and Au (here referred to as Database A, n = 30) study [7], and the Pd, Ag, Pt, Au, ZnO (here referred to Database B, n = 50) study [8] a global power-law signature (y = 0.7172x 0.791 , or an approximate 3/4 fraction is obtained. Using a log-linear plot of the linear regression residual data 3-sigma and non-parametric cluster, the power-law was verified over four orders of magnitude with outliers identified and associated with a microwave Digestion application-type and a phase-transition between microwave oven-type and microwave Digestion applicator-type.…”

Microwave-Assisted Transition Metal Nanostructure Synthesis: Power-Law Signature Verification

“…In the following year (2023), the energy mapping technique was applied to historical "non-thermal" microwave-assisted microorganism inactivation experiments and their reconstruction using pseudo microorganism suspension, in this case, the eco-friendly and benign solvent "water" (H 2 O) (Law and Dowling (2023) [7]). More recently it has been shown that using log-log coordinates, historical microwave-assisted synthesis of gold (Au), and silver (Ag) nanostructure data (n = 30) may be visualized [8]) with the addition of fitting in a general power-law function (Equation ( 1)) where small and large events are common over four orders of magnitude in both x-and y-axes.…”

“…Figure 1. Log-log energy phase-space projection of Au and Ag claimed Green Chemistry and non Green Chemistry for the axial field helical antenna system (star), TCMC systems (black square), turntable loaded digestion systems (black circle), and microwave oven (black diamond), and "non thermal" inactivation of microorganisms within microwave ovens (plus sign, star and open circles [8]).…”

“…From a statistics and probability perspective the power-law signature is a 0-dimensional (0-D) representation of the underlying microwave synthesis processes. However, the power-law signature encompasses different microwave applicators-types used (domestic microwave oven, temperature controlled microwave chemistry (TCMC) applicator, digestion applicator, and the axial field helical antenna applicator (Discover2), metal precursors, and synthesis chemistries [8]. Therefore it is reasonable to postulate that the power-law signature may contain phase-transitions (PT) arising from the applicator-type and the mode that it is used (batch, or, continuous flow) or the way the microwave power is applied.…”