Highly functional bio-based micro- and nano-structured materials for neodymium recovery

One of the main pillars of sustainable development is the preparation of functional materials derived from renewable resources. Nevertheless, facile methods to convert lignocellulosic biomass into value-added, highly functional materials remain limited. Here, we evaluate the potential of an acid-free method to convert a variety of lignocellulosic biomass into highly charged micro- and nano-structured materials. We show how the sequential oxidation of delignified (e.g., softwood pulp and cotton) or untreated (e.g., corncob and tomato peel) lignocellulosic sources yield three distinct products, including biopolymeric nanoparticles (BNP), solubilized biopolymers (SB), and microproducts (MP), bearing up to 6 mmol of carboxylate groups per gram, which is up to ∼ 500 % beyond the theoretical charge content of conventional cellulose nanocrystals (CNC). The main difference among the products was the type of nanoparticles: delignified sources yielded hairy cellulose nanocrystals, whereas lignin nanoparticles were formed from the untreated sources. As a proof-of-concept for the applications of these materials, we show that carboxylated cotton microproducts remove ∼ 92.5 mg of neodymium ions per gram from a dilute solution in less than 5 min and recover approximately 64 % of it via pH adjustment. This work may provide new opportunities for the conversion of a wide array of lignocellulosic biomass to highly functional biocolloids with extremely high charge density for advanced sustainable applications.