The mechanism of the hydrothermal synthesis of nanostructured alumina shows that the NaOH : Al molar ratio affects not only the resulting morphology but also the yield. Successful reusability of the reaction medium opens the door to large scale manufacturing.

This paper reports for the first time the size control of well-defined and morphologically pure alumina (gAl 2 O 3 ) nanorods, presenting an economic and reproducible route for the manufacture of these materials with tuneable sizes for useful applications, for example serving as adsorbents, catalysts and catalyst supports. A detailed understanding of the different steps taking place during the hydrothermal synthesis has been deduced herein. Understanding the effect of temperature on the relative rates of these steps is essential for achieving size and morphology selectivity, but has often been overlooked in the literature.This systematic study identifies six distinct steps taking place during the synthesis: (1)

Hydrogen production from ammonia decomposition using Co/-Al 2 O 3 catalysts -Insights into the effect of synthetic method.

This paper presents a high aluminum yield route for the large-scale production of nanostructured alumina with high morphological purity. Morphologically selective hydrothermal formation of alumina nanorods can be achieved at low pH values (<3.5), with a low NaOH:Al ratio (0.77:1); however, it presents a low aluminum yield (35 wt %) with a significant proportion of aluminum remaining unreacted in the solution. Higher yields can be achieved at higher pH levels but at a price of leading to mixed, uncontrolled morphologies. In this work, we demonstrate a semicontinuous system where the synthesis supernatant solution is recycled while maintaining the initial NaOH:Al ratio constant, leading to >95 wt % aluminum yield. The γ-Al 2 O 3 materials produced by the recycle procedure possess the same crystallinity, surface area and morphology as the γ-Al 2 O 3 nanorods obtained from the batch hydrothermal route. We have explored the potential accumulation of spectator ions from recycling the supernatant and no effect on the recycled product quality has been determined. As such, we demonstrate herein the economic feasibility of hydrothermal methods for manufacturing of nanostructured γ-Al 2 O 3 nanorods, which could be applied to other industrially relevant metal oxides, as the recycle assays validate the shift from a conventional batch to a semicontinuous process, simultaneously reducing waste streams and improving atom efficiency.