How Size Determines the Value of Gold: Economic Aspects of Wet Chemical and Laser‐Based Metal Colloid Synthesis

Abstract

Gold is one of the most valuable materials, and its monetary value is enhanced by size reduction from bullions to colloidal nanoparticles by a factor of 450. Wet-chemical reduction with subsequent centrifugation and pulsed laser ablation in liquids are frequently used for pure colloidal gold synthesis. Both methods provide similar physicochemical nanoparticle properties, but are very different synthesis techniques. However, the costs inherent to these methods are surprisingly seldom discussed. Both methods have in common that the labor effort poses the majority of synthesis costs. Besides an increase in batch size and mass concentration, especially an increase of the nanoparticle productivity via higher laser power and centrifugation capacity reduces synthesis costs if pilot- or industrial-scale applications are intended. In this case, laser-based synthesis is more economical if its productivity exceeds a break-even value of 550 mg h , where the costs arising are limited by the metal costs. In contrast to industrial scale production, wet-chemical synthesis is more feasible for laboratory-scale applications, especially if the advantageous nanoparticle properties provided by laser ablation in liquids are not needed.

Perspective of Surfactant‐Free Colloidal Nanoparticles in Heterogeneous Catalysis

“…hereby corresponding to 16 kg of a catalyst containing 1 wt% of nanoparticles per 40 h week production . Note that regarding characteristic economic indicators, laser‐based catalyst production may even be cheaper than chemical synthesis, as has been calculated in detail at the example of gold nanoparticles (Au NPs) . Following the previous statements, the laser‐generated catalysts do not require any sophisticated purification steps and are therefore obtained directly or after centrifugation and rinsing with pure water without further high temperature (≫100 °C) calcination, as shown, amongst others, by Dong et al .…”

“…Regarding the economic feasibility, a benchmark productivity of ∼550 mg nanoparticles per hour has been determined by Jendrzej et al. with laser ablation becoming economically favored when exceeding the given productivity threshold …”

Recent Advances in Surfactant‐Free, Surface‐Charged, and Defect‐Rich Catalysts Developed by Laser Ablation and Processing in Liquids

“…Surface chemistry plays an important role in the activity of a catalyst . LAL‐synthesized catalysts are different from Chem catalysts (Figure ) . The M−O − and M−OH − bonds endow the metal (e.g., Au) NPs with surface charges upon implementing LAL in water (Figure a) .…”

“…Because the synthetic conditions for LAL are completely different from the “mild” conditions of chemical methods, novel nanomaterials with unique physical and chemical properties may form . The innate surfactant‐free feature of LAL‐generated nanomaterials is very attractive for high‐performance catalytic applications because 1) it frees researchers from time‐consuming cleaning procedures, such as centrifugation, solvent extraction, calcination, or ozonolysis; 2) continuous processes are also more cost‐efficient owing to a lower staff workload during the continuously running process, whereas batch processes require regular removal of target compounds, fresh liquids, and cleaning steps; and 3) without the blocking effect of surfactants, LAL‐generated catalysts are highly active . However, LAL‐synthesized surfactant‐free NPs often suffer from polydispersity; thus hindering the investigation of the size effects of LAL‐synthesized NPs on catalytic applications.…”

“…We started with the properties of the materials because of the importance of surface chemistry and particle evolution for particle characterization and catalytic applications. Dangling bonds at NP surfaces are often terminated by small functional groups, such as hydroxy, methoxy, and ethoxy, during the implementation of LAL/LPL in water, methanol, and ethanol, respectively . Hence, surfactant‐free is a more accurate way to describe the surface chemistry of LAL‐/LPL‐synthesized nanomaterials, rather than the widely used ligand‐free and naked terms.…”