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Fundamental Nitro-Oxidation Method Study

A simple nitro-oxidation method to extract cellulose nanofibers from raw biomass has been developed in our lab. This method involves the use of nitric acid or nitric acid-sodium nitrite mixtures to defibrillate and oxidize cellulose components. Experiments indicate that the method greatly reduces the need for multichemicals, and offered significant benefits in lowering the consumption of water and electric energy, when compared with conventional multiple-step processes at bench scale (e.g., TEMPO oxidation). Additionally, the effluent produced by this approach could be efficaciously neutralized using base to produce nitrogen-rich salts as fertilizers. Nanofibers with low crystallinity were found to be effective for removal of heavy metal ions for drinking water purification. 


Efficient Heavy Metal Ions Remediation

The research is mainly focusing on the remediation of heavy metal ions in drinking water by functional modified cellulose material. For instance, micro dialdehyde cellulose-cysteine (MDAC-cys) and nano dialdehyde-cysteine (NDAC-cys), have been synthesized from wood pulp cellulose, the most abundant and sustainable biopolymer in the world. Their comparative behaviors in arsenic (III) remediation from drinking water is determined by AFS detection technique and confirmed by SEM characterization. Under Freundlich fitting model, MDAC-cys exhibits 982 mg/g adsorption capacity and NDAC-cys presents 1011 mg/g adsorption capacity by their thiol groups, in the presence of 2500 ppm As (III) impurities. Also, cellulose nanofiber (CNF) extracted from jute fiber through Nitro-oxidation method were used to remove Hg ions and Tl ions, high efficiency of remediation has obtained through ICP-MS analysis.

Scaling up this method is another an ongoing project in the aims of preparing large amounts of CNF at one time due to the simplicity and efficiency of this method.






Bionanomaterials derived from Nitro-Oxidized Carboxy Cellulose Nanofibers for Effective Removal of Fluoride from Water

Water shortage is a global concern of growing population. Worldwide, over 7% of total population lacks access to clean drinking water due to high fluoride contamination. In this study, we demonstrate a new way to remove high concentration fluoride ions from water using renewable and sustainable nanocellulose materials.  In specific, we have developed carboxycellulose nanofibers (NOCNF) from untreated (raw) jute biomass using a simple and cost-effective nitro-oxidation approach. The resulting NOCNF, having an average width of 6.6 nm and an average length of 750 nm, possessed 1.12 mmol/g carboxylate content. These nanofibers were further modified into composite substrate which can remove fluoride ions from water. The mechanism of removal involved stronger electrostatic interactions between oppositely charged ions, the material is highly efficient in removal fluoride from water.

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Ammonium Remediation Using Nitro-Oxidized Cellulose

Current sources of ammonium pollution come largely from agriculture, urban sewage and industrial wastewater, which is expected to rise as the world population continues to increase. As the demands for food and water expand, new means for more sustainable water purification and effective plant fertilization are necessary. In our previous study, we demonstrated the cost-effective nitro-oxidation method using the combination of nitric acid and sodium nitrite that can simultaneously carboxylate and defibrillate raw biomass and yield carboxylated nanocellulose.1 Raw jute fibers were chosen to generate nitro-oxidized cellulose nanofibers (NOCNF) having a length of 300-400 nm and cross-sectional width of 5-10 nm. A 0.126 wt.% NOCNF suspension contained a carboxylate concentration of 1.03 mmol/g and zeta potential of -116.2 mV. Further characterizations of the ammonium-adsorbed NOCNF include electron microscopy, thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, and elemental analysis. The ammonium-adsorbed NOCNF may be used as a cheap, biodegradable and slow release fertilizer for plant growth. This research indicates that with NOCNF extracted from agricultural residual, a new nexus of food, energy and water systems may be obtained.


Superhydrophobic Cellulosic Membrane for Membrane Distillation

Water scarcity affects 40% of the global population and is one of the biggest technological challenges of the world. Membrane distillation (MD) is an emerging desalination process capable of treating highly saline or contaminated water, which can help to alleviate water stress. MD is a thermally driven separation process in which only vapor molecules can pass through a porous “hydrophobic” membrane. Petroleum-based polymeric membranes that are currently employed in water filtration techniques have a large carbon footprint. There is need to employ sustainable, low-cost and environmentally friendly options to reduce the carbon footprint without compromising performance. Our aim is to develop a composite porous hydrophobic/hydrophilic membrane prepared using ‘cellulosic’ micro/nano fibers, which have the advantage of being biodegradable and biocompatible. The hydrophobic top layer should be a thin membrane (30-60 µm) to stop liquid penetration followed by a thick hydrophilic layer (more than 90 µm thick). The porosity of the top layer should be in the range of 30-85%. The proposed plan is to prepare top hydrophobic layer from carboxylated cellulosic nanofibers (obtained from wood and other low value biomass like jute fibers) crosslinked with wet strength additives. Fillers like precipitated calcium carbonate may be used to obtain a rough structure required for a hydrophobic surface. This top layer could be treated with bio waxes to obtain a superhydrophobic top layer with high contact angle to avoid liquid penetration. The bottom thick hydrophilic layer primarily meant for water transportation and securing the wet integrity of the hybrid membrane will be prepared from cellulosic microfibers. This composite cellulosic membrane may replace the synthetic polymeric membranes in membrane distillation.


Preparation and Characterization of Cationic Cellulose Materials for Waste Water Treatment

Cellulose is a significant class of natural polymeric materials. The abundant active functional groups in their polymeric chains makes them exceptionally suitable, after certain modification process, to interact with the surface charge of specific particles in waste water. The objective of this study is to modify the surface of cellulose extracted from different biomass sources, so as to serve as flocculants or adsorbents in waste water treatment applications. Since this targets are those particles with negatively-charged surfaces (i.e., activated sludge, metal complex and anionic dyes), the surface of the cellulose needs to be positively-charged in order to act as a flocculant or adsorbent, so that the cellulose chain acts as a binder to attract and retain the negatively-charged particles and form flocs or precipitation. 
In this study, cellulose from different renewable and sustainable biomass sources (i.e., wood pulp, jute, algae, sugar cane and bamboo) were extracted. Then, these cellulosic materials underwent an oxidation process by sodium periodate into dialdehyde cellulose (DAC). Ultimately, cationic flocculants (c-DAC) were produced by the cationization reaction of the DAC with a cationic reagent, Girard’s reagent T. The preliminary results indicate that the performance of the cationic bio-flocculants/adsorbents prepared from the three bioresources (wood pulp, sugar cane, and bamboo) in promoting the waste activated sludge dewatering, hexavalent chromium removal and Congo red adsorption were effective and could be a potential alternative to the fossil fuel-derived synthetic flocculant/adsorbent. 


Understanding the Link between Structure and Process of Nanocellulose Materials

The research project has the overall aim to understand continuous processes of assembling cellulose nanofibrils (CNF) into nanostructured materials with tunable properties. Such a process typically consists of three main steps: (1) hydrodynamic alignment of dispersed CNF with shear and/or extensional flow, (2) a transition from dispersion to gel, thus locking the aligned structure and (3) drying of the gel. The target is to study the dynamics of the fibrils under the actual processing conditions, which is approached mainly experimentally using in-situ small angle X-ray scattering (SAXS/WAXS) techniques and polarized optical microscopy (POM) of the flowing system. Additionally, using numerical simulations of flowing Brownian particles, experimental observables (e.g. X-ray scattering patterns) can be calculated and compared with experimental results. In order to pinpoint the important system parameters of the full process from raw material to end product, the influence of these parameters will be compared along the process. For example, using a different raw material source (e.g. wood, bamboo or agricultural waste) might influence the fibril alignment in the flow but also the dynamics during the gel transition as well as the properties of the final material. Understanding on a fundamental level how such parameters influence the full process will be crucial in the development of continuously producing high performing materials that can be both biobased and biodegradable.

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Study of Polyamide Barrier Layers in Reverse Osmosis Membranes

Fresh water scarcity is an urgent challenge in many regions around the world, where desalination of brackish water and seawater has become one of the most promising solutions.  In desalination, the reverse osmosis (RO) membrane technology, developed in 1960s, is the most state-of-the art solution. However, the relatively low filtration efficiency of RO membranes is still the major hurdle that limits the overall performance of desalination. Currently, interfacial polymerization is a common approach to fabricate RO membranes, in which two reactive monomers: such as m-phenyldiamine (MPD) and Tirmesoyl chloride (TMC), dissolved in two immiscible phases (i.e., aqueous and organic phases, respectively), can react at the interface to form a thin polyamide barrier layer. To overcome the low filtration efficiency (low flux), it is important to learn the formation mechanism of polyamide layer and the resulting structure. For this purpose, we first investigated the freestanding polyamide layer without the scaffold support. In specific, grazing-incidence wide-angle X-ray scattering (GIWAXS) was used to inspect the inter-molecular structure of free-standing polyamide layer, with the layer thickness was controlled at around 18 nm, where reflectometer was used to determine the film thickness and surface smoothness. The RO membrane based on the same polyamide barrier layer was tested by a high-pressure desalination system at 800 psi, to correlate the polyamide structure with desalination performance. 


Next-generation High-flux Anti-fouling Cellulose-based Hierarchical Membranes

Membrane process is a filtration process by which the undesirable particles, colloids, organic and inorganic components, pathogens and their excretions, and viruses are retained, while smaller water molecules pass through the porous matrix of the membrane, resulting in the production of clean water. The main challenge with membranes is the fouling issue which refers to the pore clogging of the membranes followed by the formation of a cake layer. Hydrophilicization of the polymeric membranes is a promising method to reduce this undesirable phenomenon. However, the introduced hydrophilicity may gradually weaken by aging.

Cellulose nanofibers (CNFs), on the other hand, exhibit super-hydrophilic properties due to the abundance of hydroxyl and carboxyl functional surface groups. Therefore, due to its innate hydrophilicity and negatively-charged surface functional moieties, the use of functionalized CNF for fabrication of low fouling, high-flux hierarchical membranes for water purification has great potential in a range of practical applications. We are developing an innovative hierarchical membrane with high water flux and good antifouling properties. In this membrane, a highly porous nanofibrous scaffold prepared by the electrospinning technique is used as the substrate in order to maximize flux and reduce energy consumption in membrane operations. Since, the electrospun scaffold is highly susceptible to fouling, its surface is coated with a layer of CNF, as the barrier layer, which facilitates the reduction in the interaction between the membrane and the foulant molecules/particles and thus, mitigates fouling. This state-of-the-art membrane has recently gained widespread attention from industry because of its high performance and low maintenance costs.


Nanosized Titanium Dioxide Embedded in Nanocellulose Scaffold as Photocatalyst for Dye Degradation and Bacterial Inactivation

Nanocelluloses, which can be derived from any cellulosic biomass, have emerged as appealing nanoscale scaffolds for a wide range of applications, while titanium dioxide (TiO2) has been widely used in some applications from paint pigments, photocatalysts, photovoltaics to electrical energy storage. In this study, nanosized TiO2 was prepared by thermal decomposition of titanium oxysulfate precursor in the presence of cellulose nanocrystals (CNC). The resultant TiO2@CNC composite was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), solution small-angle X-ray scattering (SAXS), and other supplemental methods. The TiO2 particles had size of 2 – 3 nm and was uniformly distributed on the CNC surface. The composite exhibited excellent performance for dye degradation (within 5 cycles) and antibacterial activity. We believe optimization on the nanostructure of this unique nanocomposite system will lead to better performance and novel applications in water treatments.

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