Sustainable waste mitigation: biotemplated nanostructured ZnO for photocatalytic water treatment via extraction of biofuels from hydrothermal carbonization of banana stalk

Working at the food-energy-water nexus, we identified an abundant agricultural waste with little intrinsic value - banana stalk - that can be converted to biofuels via hydrothermal carbonization. However, to make biomass to biofuel conversions economically viable, we must identify value-added products to add to the biorefinery, such as materials for water treatment. Both the resulting hydrochar and raw biomass were biotemplated with zinc acetate to yield ZnO nanostructures with surface areas similar to 20 m(2) g(-1). The zincite particles were able to degrade a model organic dye (methylene blue) from aqueous solution. Though both the raw biomass and hydrochar yielded particles with similar surface areas, the photocatalytic activity of the raw templated particles was superior. We believe this is due to a higher concentration of calcium (naturally present in the banana biomass) in the hydrochar relative to the raw biomass. The calcium produced calcite crystals in the biotemplated materials, which may hinder the ZnO photocatalytic activity. However, the CaO may be useful for removing heavy metals from water and catalyzing biofuel production.