Controlled synthesis of ZnO particles on the surface of natural cellulosic fibers: effect of concentration, heating and sonication

We report on the use of fique natural fibers as solid matrices for the deposition of zinc oxide (ZnO). Fique fibers, native to Colombia, are composed of cellulose (63–70 %) and have a heterogeneous surface morphology with high oxygen density that facilitates metal oxide nanoparticle growth and stabilization. Fique fiber–ZnO biocomposites were synthesized by a co-precipitation method using ZnSO₄ as precursor, NaOH for hydroxide formation and thermal/ultrasound energy to promote Zn(OH)₂/Zn(OH) ₄ ²⁻ decomposition and ZnO formation. The biocomposite was characterized using X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy with attenuated total reflectance, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The synthesis of ZnO nanoparticles has been widely reported on inorganic substrates and soft natural fibers; however studies on how experimental parameters affect ZnO features on heterogeneous phase reactions are scarce, as well as the use of hard complex cellulosic fibers as solid supports for its growth. We observed that [OH⁻]/[Zn²⁺] ratios, heating or sonication time wield a strong influence on the amount, shape, size and distribution of ZnO crystals on the fique fibers; hence confirming the potential of hard natural fibers as surface active materials for novel biocomposites synthesis. We believe these materials, where the hard fiber robustness and the transition metal oxide catalytic properties are synergistically combined, could be promising functional alternatives that will favor a widespread nanoparticle usage for environmental applications such as wastewater treatment processes.