Study On The Lignin-Assisted Synthesis And Properties Of Micro/nano ZnO

Due to their small size and large specific surface area, ZnO of microstructure shows much better performance than bulk ZnO. The properties of microstructure ZnO are greatly influenced by its structure and morphology. Along with the environmental pollution and energy crisis, the use of renewable bioresources becomes very important. Our work is based on the utilization of lignin based bioresources, which are the by-product of pulp and paper industries. We aim to prepare micro/nano ZnO crystals with different morphologies by the assistance of the lignin based bioresources and study their properties.Firstly, prepare micro/nano ZnO crystals with the assistance of alkali lignin. In order to increase its surface activity, we modified the alkali lignin by amination and then prepared ZnO crystals using direct precipitation method with the surfactant (the modified alkali lignin). XRD results show that the prepared ZnO samples are wurzite hexagonal structure and of good purity and high crystallinity. The addition amount of lignin amine can influence the shape and BET surface area of the prepared ZnO. By addition of10mL lignin amine, ZnO is of flower structure composed of conical petals and the BET surface area reach to21.5m2·g-1. The influence of alkali concentration on the morphologies of ZnO is also discussed. When the dosage of lignin amine is decided, both the alkali concentration and the total ion concentration will influence the final morphology of ZnO grains. ZnO presents fragment morphology with increase of alkali concentration. The photoluminescence spectra show that the prepared ZnO present ultraviolet light emission at389nm and visible light emission centerd at550nm. Alkali concentration and the amount of lignin amine can influence the intensity of both ultraviolet light and visible light emission.Secondly, we prepared micro/nano ZnO in hydrosolvent system with the assistance of sodium lignosulphonate. Results show that the dosage of sodium lignosulphonate can influence the morphology of ZnO. ZnO particle-bar, mesh-lamina and quasi-sphere structures have been successfully synthesized by changing the amount of sodium lignosulphonate. TEM analysis shows that the prepared mesh-lamina ZnO synthesized with10g sodium lignosulphonate is of abundant mesopores and macropores, which can greatly promote the mass transfer in the photocatalytic process. Photocatalytic experiments prove that the prepared mesh-lamina ZnO can reach a high degradation efficiency (above95%) when the UV irradiation power is equal or greater than8W. Meanwhile, photoluminescence test shows that the addition of sodium lignosulphonate can improve the intensity ratio of UV and visible light.Finally, Three-dimensional (3D) multi-level structure of ZnO crystals were prepared by the assistance of sodium lignosulphonate in water and alcohol mixed solvent system. SEM results show that the ZnO is composed by parallel or vertical stacked sub-structural disks. The amount of sodium lignosulphonate and the presence of ethanol have important effects on the formation of the special morphology. TEM and N2absorption and desorption experiments show that the prepared ZnO has a porous structure and a high BET surface area (82.9m2·g-1), which is much higher than ZnO prepared without adding the surfactant (16.7m2·g-1). Photocatalytic experiments show that3D flowerlike ZnO exhibits excellent photocatalytic degradation efficiency to methylene blue, which is comparative to degussa P25TiO2. Meanwhile, the cyclic tests also give the evidence that this3D flowerlike ZnO has a good recycle performance.