Preparation And Adsorption Properties Of Lignin-silica Nano Composite Particles

Lignin nanoparticles were firstly prepared by nanoprecipitation method from acetic acid lignin. The optimal preparation conditions, morphology, chemical structure, crystal structure and surface and interface properties of lignin nanoparticles were characterized by dynamic light scattering, electronic microscope, infrared spectroscopy, X-ray diffractometry, elemental analysis, X-ray photoelectron spectroscopy and contact angle measurements, respectively. Then, the covalent bonding lignin-silica nanoparticles!LS-NPs$were prepared by grafting biodegradable lignin onto silica nanoparticles surface via the click reaction. The preparation process, morphology, particle size, the dispersibility and thermostability of LS-NPs were systematically investigated. Finally, the adsorption properties of acetic acid lignin, lignin nanoparticles, silica nanoparticles and LS-NPs on various heavy metal ion were studied, and the effect of adsorption conditions on theadsorptivity of LS-NPson Cu!,$and Pb!,$were investigated.The main contents and conclusions of this paper were listed as follows:1.The diameter of lignin nanoparticels were controlled by changing fabrication conditions, the experimental results indicated that stirring rate, dropping rate, ratio of THF to H2O!v/v$ and concentration of lignin solution were critical factors of the preparation conditions of lignin NPs, and the most suitable conditions for the preparation of the lignin NPs were as follow: stirring rate was above 300 r/min, dropping rate of lignin solution was 5 ~ 40 m L/h, ratio of THF to H2O!v/v$ was 5D100 ~ 10D100 and the initial concentration of lignin was 10 ~ 20 g/L. Under the optimal conditions, the obtained lignin nanoparticles were mostly spherical with diameters of about 150 nm. The tests further confirmed that the morphology of obtained lignin NPs by nanoprecipitation method was dispersed evenly as regular nanoparticles. Lignin nanoparticles did not chemically change on their structures but kept amorphous polymers form and formed a hydrophobic surface in a hydrophilic aggregation process which enhanced their stability.2.LS-NPs were prepared by grafting lignin onto silica nanoparticles surface via the copper!I$ catalyzed azide-alkyne cycloaddition reaction. Azido group was firstly grafted onto the surface of silica nanoparticles by silanization reaction, then the azido silica nanoparticles were modified with propargylated lignin obtained from acetic acid lignin to yield LS-NPs through triazole units via click reaction catalyzed by copper!I$. The chemical structure of products produced in every step were characterized by fourier transform infrared reflection spectra, elemental analysis and X-ray photoelectron spectroscopy. The morphology and physicochemical properties of LS-NPs were investigated by scanning electron microscopy transmission electron microscopy, Zeta potential and thermal gravimetric analysis. Experimental results indicated that the lignin was successfully grafted onto silica nanoparticles surface through triazole units via the copper!I$ catalyzed azide-alkyne cycloaddition reaction, which provided a novel way to fabricate lignin based nanocomposites. The diameter of LS-NPs was measured from 50 to 100 nm, particllarly, the dispersibility and thermostability of LS-NPs improved significantly.3.The adsorption properties of LS-NPs for different heavy metal ion were investigated in different condition, and the optimum adsorption conditions were determined. The results showed that LS-NPs had selective adsorption for various heavy metal ion, particularly, a relatively strong adsorption capacity for Cu!!$and Pb!!$. In addition, LS-NPs had better adsorption than the acetic acid lignin, lignin NPs, silica nanoparticles as expected. When it came to the adsorption of LS-NPs for Pb!!$, the adsorption effect was best when the pH value was 5.5. With the increase of Pb!!$initial concentration, adsorption capacity of adsorbent increased and the removal effciency decreased, which indicated that the adsorption property of LS-NPs associated with the limited adsorption sites. The Langmuir and Freundlich adsorption isotherm model were applied to describle the process of adsortption of LS-NPs for Pb!!$ and their isotherm coefficients R2 were 0.9904 and 0.8637, respectively. It indicated that the adsortption process accorded with Langmuir adsorption isotherm model and a monolayer adsorption behavior.