Electroless Dealloying of Thin-Film Nanocrystalline Au-Ag Alloys: Mechanisms of Ligament Nucleation and Sources of Its Synthesis Variability.

Control of ligament size in nanoporous gold through process inputs in chemical dealloying holds the potential to exploit its size dependent properties in applications in energy and biomedicine. While its morphology evolution is regulated by the kinetics of coarsening, recent studies are focused on the early stage of dealloying (e.g., ∼ 5-42 at. % in residual alloy content) to understand mechanisms of ligament nucleation and its role in altering process-structure relationships. This paper examines this stage in chemical dealloying of nanocrystalline Au49Ag51 thin films and finds that ligaments are nucleated uniformly through its thickness due to the dealloying front rapidly propagating through the thickness of the film. Further, through the establishment of process-structure relationships with large data sets (i.e., 80 samples), this paper quantifies sources of variability that alter the kinetics of ligament growth such as aging of the precursor (e.g., grain growth) and solution evaporation. It is found that ligament diameter is better predicted by the residual silver content rather than by the dealloying time even amidst both effects and independent control of ligament diameter and solid area fraction is demonstrated within a limited window.

Comparison of Land, Water, and Energy Requirements of Lettuce Grown Using Hydroponic vs. Conventional Agricultural Methods.

The land, water, and energy requirements of hydroponics were compared to those of conventional agriculture by example of lettuce production in Yuma, Arizona, USA. Data were obtained from crop budgets and governmental agricultural statistics, and contrasted with theoretical data for hydroponic lettuce production derived by using engineering equations populated with literature values. Yields of lettuce per greenhouse unit (815 m2) of 41 ± 6.1 kg/m2/y had water and energy demands of 20 ± 3.8 L/kg/y and 90,000 ± 11,000 kJ/kg/y (±standard deviation), respectively. In comparison, conventional production yielded 3.9 ± 0.21 kg/m2/y of produce, with water and energy demands of 250 ± 25 L/kg/y and 1100 ± 75 kJ/kg/y, respectively. Hydroponics offered 11 ± 1.7 times higher yields but required 82 ± 11 times more energy compared to conventionally produced lettuce. To the authors' knowledge, this is the first quantitative comparison of conventional and hydroponic produce production by example of lettuce grown in the southwestern United States. It identified energy availability as a major factor in assessing the sustainability of hydroponics, and it points to water-scarce settings offering an abundance of renewable energy (e.g., from solar, geothermal, or wind power) as particularly attractive regions for hydroponic agriculture.