| dc.description.abstract | Bio-mass derived materials, such as cellulose nanomaterials (CNs) are naturally abundant, sustainable, and bio-degradable, and they are promising next generation materials to replace petroleum derived systems. The thesis focuses on the management of environmental pollutions caused by the discharge of emulsions and heavy metal ions in wastewater and the use of non-sustainable surfactants and toxic solvents used in conventional pesticide formulation. To achieve this goal, the general approaches adopted in this doctoral study are: 1) development of pesticide emulsion formulation using sustainable cellulose nanocrystals (CNCs) as emulsifiers, 2) development of novel organic solvent- and surfactant- free pesticide nano-dispersion using CNCs as carriers and dispersing agents, 3) development of CNs-based aerogel adsorbents for the treatment of wastewater containing heavy metal ions and emulsion droplets, 4) recovery of water pollutants as nutrients for plant growth.
Firstly, surfactant-like CNC particles were synthesized by grafting aminated polystyrene (PS-NH2) on the end of CNC via reductive amination. The effect of reaction conditions, such as reaction time (1, 3 or 7 days), reaction temperature (room temperature or 70 ℃) and polystyrene chain length (Mn of 5000 or 10000 Da) on the modification degree were investigated. Further, the emulsification capability of the end-modified CNCs was investigated, where the modified CNCs were more effective in emulsifying toluene and hexadecane than pristine CNCs. Various parameters, such as concentration of particles, electrolytes, and polarity of solvents on the characteristics of the emulsions were investigated. Such system, bearing biocompatible and environmentally friendly characteristics, showed excellent encapsulation of a model hydrophobic compound (Nile red) without coalescence over a period of more than 4 months, which offers promise for preparing emulsion formulations for pesticide encapsulation.
Following this, an organic solvent- and surfactant-free pesticide nano-dispersion was developed using pristine CNCs as carriers and dispersing agents, eliminating the use of organic solvents in the final formulation. Such characteristic aligns with one of the key focuses of sustainable agriculture, i.e., development of environmentally friendly nano-sized pesticide formulation. CNC was used as a carrier and dispersing agent for two water-insoluble pesticides (Deltamethrin and Permethrin) to formulate aqueous pesticide formulations. The optimum loading mass ratio between pesticide and CNC was determined as 1:100 from UV-vis spectrophotometer, dynamic light scattering (DLS), zeta potential, and transmission electron microscopy (TEM) analyses. Besides, the possible attractive force between the pesticide molecules and CNC was studied by Fourier transform infrared spectroscopy (FTIR) and Isothermal Titration Calorimetry (ITC). In addition, both laboratory and field trial tests were conducted to evaluate the pest control efficacy of the nano-dispersion, with performance better or equal to existing commercial formulations.
Functionalized cellulose nanofibrils (CNFs) based aerogels were synthesized to remove Cu (II) ions and emulsified emulsion droplets in wastewater streams. Firstly, amine-functionalized CNF was prepared by cross-linking polyethylenimine (PEI) to cellulose nanofibrils (CNF) using 3-glycidyloxypropyl trimethoxysilane (GPTMS). Robust cellulose aerogel beads (CGP, diameter of 3~4 mm) were produced by injecting crosslinked CNF dispersion into liquid nitrogen, followed by freeze drying. The effect of mass ratio between PEI and GPTMS (1:1 or 3:1) on the total amine contents, mechanical strength and morphologies of the aerogel beads were investigated. In addition, the effect of pH, ionic strength, adsorbent dosage, temperature as well as initial concentration on the adsorption performance were studied, where the maximum adsorption capacity, adsorption kinetic were examined. Small CGP beads with desirable characteristics, such as high amine content (5.74 mmol/g for CGP3 beads), large maximum Cu (II) adsorption capacity (163.40 mg/g for CGP3 beads), very fast adsorption rate (< 10 h to reach equilibrium), high shape recovery (2.00 % plastic deformation for CGP3 beads at 50% strain), robust mechanical strength (stress around 10.5 KPa at 50% strain), and possible regeneration were achieved.
As an extension from the previous study, carboxylated CNF aerogel beads were prepared for Cu (II) ions removal. A one step protocol to prepare highly carboxylated and chemically crosslinked cellulose nanofibril (CNF) aerogel beads using maleic anhydride (MA) was developed. The crosslinking was achieved by esterification reaction based on the results from Fourier transform infrared spectroscopy (FTIR) and conductometric-potentiometric titration. The carboxyl groups and ester linkages were produced simultaneously during the ring open reaction of MA, yielding a carboxylic content of up to 2.78 mmol/g. The effect of CNF concentration on the morphology and wet mechanical strength of the crosslinked aerogel beads were also investigated. Results suggested that higher CNF concentration yielded a compact network that displayed a maximum compressive stress of 2800 Pa at 60% strain. In addition, Cu (II) ions adsorption capacity of 60.92 mg/g and 84.12 mg/g was yielded for CNF-MA 1% and CNF-MA 2%, respectively. The adsorption was achieved by complexation between carboxylic and hydroxyl groups.
Furthermore, an ambient amphiphilic cellulose aerogel was prepared for both emulsified oil-in-water and water-in-oil emulsion filtration. Dicarboxylated-PEG crosslinkers of different lengths were synthesized by grafting MA on Poly (ethylene glycol) (average Mn = 600, 1500, 3350, 8000 Da) by esterification reaction. Then, ambient amphiphilic and underwater superoleophobic cellulose aerogels (CPMs) were prepared by crosslinking cellulose nanofibrils (CNF) with dicarboxylated-PEGs of different lengths. The dried aerogels showed excellent uptake capacity for various solvents possessing different polarities, and the released of the absorbed oils in water. The crosslinking efficiency decreased with increasing crosslinker length. Both crosslinking degree and network density contributed to the mechanical strength of the aerogel. Such amphiphilic aerogels were effective for both oil-in-water and water-in-oil emulsion separation. The permeation flux and separation efficiency for oil-in-water emulsions are controlled by a combination effect of size sieving and electrostatic interaction between oil droplets and the negatively charged aerogel. The aerogel also demonstrated excellent separation performance (>92%) for cellulose nanocrystal stabilized oil-in-water Pickering emulsions. For water-in-oil emulsions, the viscosity of oil showed a significant effect on the permeate flux. A separation efficiency over 97% was achieved for all studied water-in-oil emulsions.
Finally, the potential of CNF based aerogel as an absorbent for water and nutrient capture and release was examined. As an example, the as prepared CPM aerogel was buried in soil before planting pea seeds. Seed germination and growth rates in CPM aerogel containing soils was compared with normal soil. After harvesting, the fresh weight, average shoot/ root length and diameter of seedlings from each pot were compared. The results suggest that the functionalized aerogels were effective for promoting seed germination and seeding growth.
In summary, the thesis contributes to the development of CNs from two perspectives: 1) development of new and novel sustainable systems and advancing new fundamental understanding on the properties of these systems and 2) expanding their applications to other fields, such as agricultural (not often reported) and wastewater treatment. The specific applications being demonstrated are novel pesticide formulations preparation, aerogel beads for heavy metal ions removal, superwetting cellulose aerogel for oily wastewater purification, and aerogel for promoting plant growth. | en |
