One-Pot Reduction of Metal Oxides/Salts with Carbohydrate Biomass Under Mild Hydrothermal Conditions

Development of novel strategies to make full use of highly functionalized biomass molecules to expand its application fields is crucial to biomass utilization. Due to possessing diverse reducing functional groups such as hydroxyl and aldehyde, carbohydrate biomass can be employed as reductant for metallic material preparation. Particularly, the reducing ability of carbohydrate biomass is enhanced under hydrothermal conditions. The reported studies focused on reduction of metal ions in acidic solution with the aid of biomass. However, we found alkali hydrothermal conditions are favorable to metal compounds reduction, even direct conversion metal oxides to metals. Meanwhile, low molecular weight organic acids were obtained from biomass oxidation. Based on our previous research on direct reduction of CuO and NiO into the corresponding metals, herein, we investigated metal salts reduction with carbohydrates and compared the reduction performance on glucose and cellulose which are the two most abundant carbohydrates with and without alkali addition. Moreover, conversion of other metal oxides (Fe₂O₃, MnO₂, Co₃O₄, PbO₂) with glucose were studied to illustrate the feasibility to direct reduction of metal oxides with carbohydrates under alkali hydrothermal conditions. The reduction pathway study showed not only carbohydrates but also decomposed intermediates can reduce metal oxides. This study may provide an alternative approach to metal preparation in hydrometallurgy.