Sustainable synthesis of reusable nitrogen-doped hydrochar from cassava pulp for simultaneous dye removal in environmental water

Cassava is an agricultural plant produced for the consumption of its roots. Leftovers from the processing step result in excessive amounts of agricultural waste, most of which is made up of cassava pulp. Advantageously, over 55% of dried cassava pulp is starch, making it rich in carbon and a suitable precursor for synthesizing carbon-based materials. In this work, cassava pulp was utilized as a precursor for synthesizing nitrogen-doped hydrochar (HC) via a hydrothermal carbonization method. The synthesized HC was studied as an adsorbent for removing organic dyes from aqueous solutions. HC showed great adsorption abilities towards methylene blue, methyl violet, and crystal violet, with the maximum adsorption capacities being 96.5%, 99.7%, and 99.8%, respectively, obtaining equilibrium within 10 min. The HC showed was reusable exceeding 90% after 4 cycles of adsorption/desorption, being able to maintain an adsorption capacity of greater than 50% for up to 9 rounds of reuse. Furthermore, HC was demonstrated as an adsorbent for commercial textile dyes.