High Yield Manufacturing of γ-Al2O3 Nanorods

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-Al2O3 materials produced by the recycle procedure possess the same crystallinity, surface area and morphology as the γ-Al2O3 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-Al2O3 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.