Interfacial\nInteraction between Zn<sup>2+</sup> and\nSurface Functional Groups Impacting Self-Assembly of ZnO on Cellulose\nNanofibrils

The mechanism underlying the interfacial interaction\nbetween ZnO\nand surface functional groups, which drives the self-assembly of ZnO\nnanoflowers on the cellulose nanofibril (CNF) surface, remains inadequately\nunderstood. Moreover, the ideal sites for the loading and growth of\nZnO nanoflowers on the oxygen atoms (O<sub>s</sub>) of various surface\nfunctional groups on the CNF surface are not well-defined. This work\naddressed these gaps by systematically regulating the size and surface\ncharge density of CNF templates through minor surface modifications\nand adjustments in processing cycles by using an ultrafine grinder.\nPhysicochemical analyses demonstrated that the ZnO nanoflowers exhibited\nsizes (μm)/pieces/thickness (nm) of 0.86/16/20.1 for ZnO/TOCNFs,\n0.88/17/20.4 for ZnO/ACNFs, and 0.89/16/20.5 for ZnO/ECNFs, respectively.\nSimulation calculations revealed that the interaction between Zn<sup>2+</sup> ions and the O<sub>s</sub> of hydroxyl (−OH) groups\nexhibited the most favorable binding energy of −31.7 kcal/mol.\nThese findings suggested that the surface charge density rather than\nspecific surface functional groups primarily governs the loading and\ngrowth of ZnO nanoflowers on the CNF surface. The O<sub>S</sub> from\n−OH groups on the surface of CNF templates were optimal for\nboth the loading and growth of ZnO nanoflowers. Overall, this study\nprovides crucial theoretical insights into the design and optimization\nof the ZnO/CNF composites.