Breathable Lignin Nanoparticles as Reversible Gas Swellable Nanoreactors

The design of stimuli-responsive lignin nanoparticles (LNPs) for advanced applications has hitherto been limited to the preparation of lignin-grafted polymers in which usually the lignin content is low (<25 wt.%) and its role is debatable. Here, the preparation of O-2-responsive LNPs exceeding 75 wt.% in lignin content is shown. Softwood Kraft lignin (SKL) is coprecipitated with a modified SKL fluorinated oleic acid ester (SKL-OlF) to form colloidal stable hybrid LNPs (hy-LNPs). The hy-LNPs with a SKL-OlF content ranging from 10 to 50 wt.% demonstrated a reversible swelling behavior upon O-2/N-2 bubbling, increasing their size - approximate to 35% by volume - and changing their morphology from spherical to core-shell. Exposition of hy-LNPs to O-2 bubbling promotes a polarity change on lignin-fluorinated oleic chains, and consequently their migration from the inner part to the surface of the particle, which not only increases the particle size but also endows hy-LNPs with enhanced stability under harsh conditions (pH < 2.5) by the hydration barrier effect. Furthermore, it is also demonstrated that these new stimuli-responsive particles as gas tunable nanoreactors for the synthesis of gold nanoparticles. Combining a straightforward preparation with their enhanced stability and responsiveness to O-2 gas these new LNPs pave the way for the next generation of smart lignin-based nanomaterials.

Automated summary

In this study, stimuli-responsive lignin nanoparticles (LNPs) with high lignin content (>75 wt.%) were successfully prepared. These LNPs exhibited reversible swelling behavior and changed their morphology from spherical to core-shell upon alternating O2/N2 bubbling. The introduction of oxygen gas promoted a polarity change on lignin-fluorinated oleic chains, resulting in their migration to the particle surface and enhancing the stability of hy-LNPs under harsh conditions. Additionally, these LNPs were demonstrated to be gas tunable nanoreactors for the synthesis of gold nanoparticles.