Aqueous phase synthesis of nanocellulose bound Cu2O crystals with tunable morphologies

Cuprous oxide (Cu 2 O) nano- and microstructures possess unique properties that may find a variety of applications. Environmentally benign synthesis of Cu 2 O with well-controlled morphology is highly desirable. In this study, Cu 2 O crystals with tunable shapes are synthesized using cellulose nanofibrils (CNFs) as a shape regulator and the sole reducing agent in aqueous environment. By simply increasing Cu 2 O precursor concentration, the Cu 2 O crystals evolved from octahedra to cuboctahedra, and finally cubes, accompanied with increasing size from nano- to microscale. The selection of Cu chelating agent (sodium tartrate or potassium sodium tartrate) affected the crystal growth rate. Transition in the relative intensities of the (111) and the (200) crystalline peaks in their XRD patterns was consistent with the morphology change. During the growth of crystals, CNFs were preferably bound to the {111} crystalline facet. The introduction of KBr to the reaction system produced short hexapods. The resultant CNF-Cu 2 O hybrids were incorporated into waterborne polyurethane (WPU) films. Even with 0.5 wt% CNF-Cu 2 O, the WPU film showed significant enhancement in modulus, strength and elongation at break. This work proves the possibility of controlled growth of Cu 2 O particles aided by CNFs and provides a new strategy for improving the performance of eco-friendly WPU films. Graphical Abstract