MoS₂ nanoflower-decorated lignin nanoparticles for superior lubricant properties

Lignin has been, for a long time, treated as a low-value waste product. To change this scenario, high-value applications have been recently pursued, e.g., the preparation of hybrid materials with inorganic components. Although hybrid inorganic-based materials can benefit from the reactive lignin phenolic groups at the interface, often responsible for optimizing specific properties, this is still an underexplored field. Here, we present a novel and green material based on the combination of hydroxymethylated lignin nanoparticles (HLNPs) with molybdenum disulfide (MoS₂) nanoflowers grown via a hydrothermal route. By bringing together the lubricant performance of MoS₂ and the structural stability of biomass-based nanoparticles, a MoS₂-HLNPs hybrid is presented as a bio-derived additive for superior tribological performances. While FT-IR analysis confirmed the structural stability of lignin after the hydrothermal growth of MoS₂, TEM and SEM micrographs revealed a homogeneous distribution of MoS₂ nanoflowers (average size of 400 nm) on the HLNPs (average size of 100 nm). Regarding the tribological tests, considering a pure oil as reference, only HLNPs as bio-derived additives led to a reduction in the wear volume of 18%. However, the hybrid of MoS₂-HLNPs led to a considerably higher reduction (71%), pointing out its superior performance. These results open a new window of opportunity for a versatile and yet underexplored field that can pave the way for a new class of biobased lubricants.