Mechanochemical production of cellulose–metal NP composites requires no capping or reducing agents, and yields antibacterial and catalytically active materials.

In nature, nonequilibrium systems reflect environmental changes, and these changes are often “recorded” in their solid body as they develop. Periodic precipitation patterns, aka Liesegang patterns (LPs), are visual sums of complex events in nonequilibrium reaction–diffusion processes. Here we aim to achieve an artificial system that “records” the temperature changes in the environment with the concurrent LP formation. We first illustrate the differences in 1-D LPs developing at different temperatures in terms of band spacings, which can demonstrate the time, ramp steepness, and extent of a temperature change. These results are discussed and augmented by a mathematical model. Using scanning electron microscopy, we show that the average size of the CuCrO 4 precipitate also reflects the temperature changes. Finally, we show that these changes can also be “recorded” in the 2-D and 3-D LPs, which can have applications in long-term temperature tracking and complex soft material design.

Contact electrification (CE), or the development of surface charges upon contact and separation, is a millennia-old scientific mystery and the source of many problems in the industry. Since the 18th century, efforts to understand CE have involved ranking materials according to their charging propensities. In all these reports, wood, an insulator, turns out to be surprisingly immune to CE. Here, we show that this unique antistatic nature of wood is attributable to its lignin content, i.e., lignin removal from wood ceases the antistatic property, and (re)addition brings it back. The antistatic action of lignin (also an insulator) is proposed to be related to its radical scavenging action and can be explained through the bond-breaking mechanism of CE. Our results also show that lignin, a sustainable, low-cost biopolymer, can be used as an antistatic additive in some representative examples of elastomers and thermoplastics, displaying the universal nature of its antistatic action.

No abstract

The global demand for sustainable and functional fibers and textile materials is increasing with the pressure to limit the synthetic petroleum-based counterparts. In this study, we use ultrasonication for the preparation of eco-friendly cellulose fabrics bearing silver or gold nanoparticles (NPs). The mechanochemistry of cellulose is based on the breakage of glycosidic bonds and the formation of mechanoradicals. These mechanoradicals can reduce Au 3+ and Ag + ions in solution, and the reduced metals can be stabilized by the cellulose chains as nanoparticles. Here, we formed the mechanoradicals in the fabrics by sonication (on the order of 10 18 per gram), which is confirmed by ESR. The sizes and the metallic nature of NPs and the structural and morphological changes in the fabrics upon ultrasonication were studied by SEM, XPS, FTIR-ATR, XRD, and TEM. The displayed preparation method is shown to yield antibacterial AgNP-fabric and catalytically active AuNP-fabric composites, with up to a 14% yield of metal ion reduction. Since the method involves only the sonication of the fabric in aqueous solutions, and uses no hazardous reducing and stabilizing agents, it provides quick and environment-friendly access to fabric nanocomposites, which have applications in medical textiles, catalysis, and materials for energy.