Synthesis of triangular lignin photonic crystal nanoparticles: Investigating solvent effects and dialysis...

Synthesizing nanoparticles with controlled shapes has been highly desirable for nanoparticle assembly research but is fraught with challenges. While the production of traditional spherical lignin nanoparticles (LNPs) has evolved as a solution to address the highly changeable and complex chemical structure of lignin, more complicated geometries with photonic nature are still needed for optical applications. This work represents the first study to fabricate a novel triangular lignin photonic crystal nanoparticle via a green technique that combines solvent shifting and acid precipitation. This new model system has successfully produced LNPs with different structural architectures, ranging from spherical shapes to triangular plates. The structural transformation and formation mechanism of LNPs were investigated through various techniques. The nanotriangles grow depending on the employed solvents with dialysis, which involve controlled nucleation, Ostwald ripening-driven growth, particle coalescence, and geometric optimization. The isolated LNPs displayed excellent hydrophobic properties and remarkable UV-blocking efficiency. Furthermore, they preserved nearly the same zeta potential in aqueous suspensions over 6 months of storage, which is considered highly stable for colloidal systems. Thus, this simple method provides a sustainable and straightforward route for producing triangular LNPs with a wide range of potential applications in sunscreen products.