| Lignin,as a natural biomass resource,is the second most available biopolymer,mainly found in woody biomass,representing an abundant renewable feedstock for bioenergy,chemicals and materials production.However,it is still an underexploited source and has long been regarded as waste and simply discarded from the pulp and paper industry due to its complex structures.The low-value utilization is still the main problem,resulting in extreme waste of resources.In recent years,with the rapid development of nanocomposites,the nanotechnology to prepare lignin-functionalized nanoparticles from industrial lignin can provide a bright way to increase the value of lignin-based products.In this study,a novel and effective green system consisting of deep eutectic solvent(DES)was proposed to prepare lignin nanoparticles(LNPs)without any lignin modification.It is proved for the first time that DES can be used as a "green solvent" to form LNPs.This technology has not only successfully masked the heterogeneity of lignin but also endowed the lignin with nano-character.LNPs initiate many new promising applications in composites,UV protection,wastewater treatment and catalytic carriers.The main research contents of this paper are as follows:(1)The green synthesis method of LNPs was dialysis and dropping nano-precipitation method.Dynamic light scattering(DLS),scanning electron microscopy(SEM),transmission electron microscope(TEM),Zeta potential and gel permeation chromatography(GPC)have been utilized to determine the effect of precipitation on LNPs;Fourier infrared spectroscopy(FTIR)and nuclear magnetic resonance(NMR)have also been used to study the influence of the chemical structure of LNPs.From the result,it was found that the diameters of LNPs varied from 10 to200 nm.The types of DES,initial lignin concentration,and p H strongly affected the size morphology and structure of fabricated particles.Moreover,after 30 days,the average diameter of LNPs did not change significantly.The preparation of LNPs using dialysis showed more uniform and symmetric spherical LNPs.With increasing of initial lignin concentration,the diameter of the nanospheres increased.(2)We assessed the technical feasibility of the multifunctional nanocomposites through casting LNPs/PVA films.The overall performance of the obtained nanocomposites was investigated by UV-Visible spectrophotometer,thermogravimetric analyzer,mechanical testing instrument and static contact angle test.The interactions between LNPs and PVA matrix were established by Fourier transform infrared(FTIR)spectroscopy and SEM.The results show that nanocomposite films prepared by incorporating the LNPs into biodegradable poly(vinyl alcohol)(PVA)matrix display good mechanical properties(tensile strength of 82.5 MPa and breaking strain of103.3%),excellent UV-blocking(100% shielding of the UV spectrum region),strong hydrophobicity(static contact angle of 117.0°)and better thermal stability(the maximum thermal weight loss temperature increased by 40°C).Overall,this study not only facilitates the advancement of lignin-based nanotechnology by DES,but also paves a way for the PVA polymer composites as potential food and medical packaging materials.(3)To further realize the high value utilization of LNPs,we developed a green and low-cost technique by the new LNPs based beads for MB removing.The influence of experimental conditions such as contact time,content of LNPs,temperature,dosage of adsorbent and dye concentration on the adsorption performance was analyzed,and the adsorption kinetics was calculated to determine the adsorption efficiency of the composite beads.The adsorption efficiency and kinetics of MB were also systematically investigated.The results indicated SA composite with LNPs showed better thermal stability and removal efficiency(97.1%)of MB compared to SA/bulk kraft lignin composite(82.9%)and pure SA(77.4%).The adsorption process obeyed pseudo-second-order kinetics and adequate fitting of the adsorption data using Langmuir and Freundlich model,with a maximum adsorption capacity of 258.5 mg/g.Based on this research,the prepared bio-nanocomposite material with better thermal stability may be considered as an effective adsorption platform for water purification. |
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