| Lignocellulose, the world’s most abundant biomass, is widely present in woody and herbaceous plants. Chitin is the second most abundant polysaccharide after cellulose. Most chitin is discarded as industrial waste (mainly shrimp and crab shells) without effective utilization. These renewable biomass resources have been estimated that globally around2×1012t each year, and can be effectively used as the raw materials of biopolymer. Novel biopolymer products can satisfy the demanding of natural materials, such as environmentally friendly and biocompatible. Among the most versatile materials, aerogels are distinguished by their ultra-low densities, synonymous nanoscale pore sizes (1-50nm) and high surface areas of the internal structures. Especially biopolymer aerogels, have high porosity while incorporating good mechanical properties and environmentally friendly degradation, is a kind of biopolymer material with broad prospects of development.The present dissertation will focus on the fabrication of hierarchical structured functional materials based on the controlled assembly biopolymer micro-/nano-building blocks. According to the series experimental studies and analyses, we firstly completely dissolved biomass lignocellulose raw materials with solvent system, and controlled assembled the dissolved lignocellulose molecules as building blocks by use of the’bottom-up’(atoms or molecules self-assembled to complex structures) strategy. Thus, bulk porous aerogels with3D nanofiber network are fabricated. Then, we use the’top-down’(to disassemble larger size material to fabricate nanomaterials) strategy to isolate nanofibrillated cellulose/chitin from plant cell walls/crustacean shell by chemical pretreatments with a combination of high-frequency ultrasonication. The obtained1D nano-building blocks (high-quality NFC/NFCH) can assemble to prepare ultra-transparent films, macroporous foams and mesoporous aerogels with high surface area by different methods. Finally, we assembled inorganic nanomaterials together with micro-/nano-/sub-nano-cellulose matrix by co-dissolved interpenetration, biotemplate mineralization, in situ anchor methods to fabricate several organic/inorganic functional composite materials with hierarchical structures. We also explore all these new materials in the applications of environmental cleaning, such as photocatalytic degradation of organic compounds, and capture radioactive elements. The present dissertation revealed that low-quality wood resources and waste chitin resources are promising to be used as advanced value-added materials. It also provides theoretical bases to exploiting hierarchical structure of biological materials, and reuse assembly technique to build novel functional materials.The main content and innovative results can be summarized as follows: (1) We creatively use’freezing-thawing’(FT) method, to prepare bulk lignocellulose wood cellulose aerogel from lignocellulose/ionic liquid solution in’bottom-up’strategy. The aerogel network structure and porous structure can be controlled adjusted by freezing and thawing process, thus, we successfully prepared full-component lignocellulose aerogel.In this work, Trema orientalis wood flour was firstly dissolved in1-allyl-3-methylimidazolium chloride (AMImCl), an effective ionic liquid, and then repeatedly FT for several times, and regenerated in water. The obtained lignocellulose aerogels dried by ScCO2drying method, and can keep the form of regenerated hydrogel. Solve the problem of that lignocellulose aerogel cannot maintain the morphology during dissolve-regenerate process. The aerogel had the open3D fibrillar network structure. The frequency of FT cycles influenced the intensity, specific surface, crystallinity, and thermal stability of the aerogel. The specific surface area of lignocellulose aerogels can be adjusted in the range of5.～80.7m2·g-1, and the structural properties of the resulting high surface area lignocellulose aerogel are similar to pure cellulose aerogel. This research highlights new opportunities for the development of fully utilize of lignocellulose resources.(2) Clarify the’bottom-up’assembly mechanism of molecular chain from biopolymer/ionic liquid solution during the FT process. We analysis and discuss of the freezing rate, the thawing rate, the frequency of FT cycles, and other factors affecting on the structure and properties of the full-component of lignocellulose aerogels.In this work, we use-20℃and-196℃individually to form different freezing rates, while using room temperature and oven heating to form different thawing rates. And we conclude that the faster freezing rate is favorable toward promoting the assembly of nanofibril network, and intends to promote the preparation of lignocellulose aerogels, while the slower thawing rate of the solution is help to keep the nanofibril network, and is necessary to maintain the network structure. The added FT cycles can enhance the regenerated nanofibril network, the more cycles can lead to the better stability of the nanofibril network. The different freezing rates form different polymer’secondary units’, and the assembly of these’secondary units’are also different in the process of FT cycles.(3) Use high-frequency ultrasound treatment to’top-down’separate1D cellulose/chitin nano-building blocks, and clarify the process mechanism of ultrasound→cavity→nanofibrillate hierarchical biopolymer in polar liquid.In this work, the chemical pretreatment is first to remove other components in matrix from biological organisms, then high frequency ultrasonic wood flour to "top down" fabricate high quality nanofibrillated cellulose NFC (the mean diameter is34.8nm, aspect ratio>280). It is proved that high-frequency ultrasound treatment can effectively break the hydrogen bonds and van der Waals forces between the fibrils, thus gradually break the micro-sized cellulose fibers down to nanofibers. It is the first time using high-frequency ultrasound, as a ’top down’ method to prepare high-quality nanofibrillated a-chitin NFCH (the mean diameter is19.4nm, aspect ratio>500, the crystallinity degree is65%) from shrimp shell. The isolated1D fibrous structural biopolymer, as new green building blocks, can assemble to forming novel functional materials.(4) The nanofibrillated cellulose/chitin can controlled assemble into high-transparent films, macroporous foams, and mesoporous aerogel with different drying methods and preparing processes.In this work, the prepared NFC (nanofibrillated cellulose)/NFCH (nanofibrillated chitin), which have uniform diameter and high aspect ratio, worked as new nanoscale1D building blocks are secondary assembled by room temperature drying, common freeze-drying, and t-BuOH (tert-butanol) freeze-drying, respectively. In the drying process, using the hydrogen bonds and van der Waals between NFCH and NFC, the pure NFC or NFCH formed low porosity (<20%) transparent films, macroporous foams (porosity>99%, specific surface area <5m2·g-1), and aerogels (porosity>99%, the specific surface area up to133m2·g-1), respectively. The structural change during assembly processes was also studied, these new nanostructured materials are expected to be the inorganic functional assembly platforms.(5) Developed several ways to build up organic-inorganic functional composite materials with hierarchical structures based on micro-/nano-/sub-nano-cellulose, including co-dissolve interpenetration, biotemplate mineralization, and in situ anchor, et al. All these composites can be used as environmental purification materials. That provided new opportunities for the development novel applications of cellulose for photosensitized degradation of hazard organic compounds, and efficient capture of radioactive iodide ions/iodine vapor.This part consists of three works:1) During the process of cellulose dissolved in ionic liquid, the manufactured TiO2derived titanate nanotubes (TDTNTs) were uniformly added in cellulose solution. TDTNTs are interpenetrated with cellulose molecules and co-precipitated with cellulose to form composite gel. And TDTNTs/cellulose composite aerogels are prepared after ScCO2drying. The composite aerogel exhibited good photocatalytic degradation activity for Rhodamine B as a photocatalyst. Moreover, the TDTNTs/cellulose composite aerogel had good mechanical properties, which was reusable catalyst in the photodegradation of organic pollutant. The composite photocatalyst was a promising material for wastewater treatment application.2) Sol-gel synthesis titanium oxide nanoparticles on the bamboo cellulose fiber as biotemplates and subsequent removal of the cellulose matrix by calcination. The cellulose-template TiO2inherited the initial millimetric length of the bamboo cellulose. The millimeter-long TiO2was comprised of the spherical nanoparticles with the diameter of about 30nm. Meanwhile, the as-fabricated TiO2presented a superior photocatalytic ability to decompose poison pollution of phenol under ultraviolet irradiation. This approach is facile, and would provide ready access to metallic oxide nanostructures of desired morphology and size with the appropriate templates3) Large-scale NFC derived from lignocellulosic biomass as1D building block can form fine network that are suitable as template of functional materials. The20-80nm thick NFC act as templates in situ anchored Ag2O nanoparticles (diameter,5-15nm) during wet chemistry. This work shows that freeze-dried NFC aerogel can be used as templates for making light-weight open porous silver oxide (Ag2O) nanocrystals anchored aerogels, which were deposited at high loading content～500wt%of the composite material. Ag2O@NFC aerogel of ultrahigh porosity (98%) were prepared using tert-butanol freeze-drying method. These Ag2O nanoparticles efficiently capture I-ions from contaminated water, and can captures significant amount of I2vapor and fixes it effectively. These aerogels are expected to be useful in radioisotopes radioactive waste management, which can not only chemisorb I-ions and I2vapor but efficiently trap them for safe disposal. This new approach was also supplied to research and development of high-effective adsorbents to capturing radioactive ions. |
PDF Full Text Request