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  • 1. Goetz, Lee A.
    et al.
    Jalvo, Blanca
    Rosal, Roberto
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Superhydrophilic anti-fouling electrospun cellulose acetate membranes coated with chitin nanocrystals for water filtration2016In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 510, p. 238-248Article in journal (Refereed)
    Abstract [en]

    Electrospun cellulose acetate (CA) random mats were prepared and surface coated with chitin nano crystals (ChNC) to obtain water filtration membranes with tailored surface characteristics. Chitin nano crystals self-assembled on the surface of CA fibers into homogenous nanostructured networks during drying that stabilized via hydrogen bonding and formed webbed film-structures at the junctions of the electrospun fibers. Coating of CA random mats using 5% chitin nanocrystals increased the strength by 131% and stiffness by 340% accompanied by a decrease in strain. The flux through these membranes was as high as 14217 L m(-2) h(-1) at 0.5 bar. The chitin nanocrystal surface coating significantly impacted the surface properties of the membranes, producing a superhydrophilic membrane (contact angle 0) from the original hydrophobic CA mats (contact angle 132 degrees). The coated membranes also showed significant reduction in biofouling and biofilm formation as well as demonstrated improved resistance to fouling with bovine serum albumin and humic acid fouling solutions. The current approach opens up an easy, environmental friendly and efficient route to produce highly hydrophilic membranes with high water flux and low fouling for microfiltration water purification process wash water from food industry for biological contaminants.

  • 2. Herrera, Martha A.
    et al.
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Oksman, Kristiina
    Barrier and mechanical properties of plasticized and cross-linked nanocellulose coatings for paper packaging applications2017In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, no 9, p. 3969-3980Article in journal (Refereed)
    Abstract [en]

    Barrier, mechanical and thermal properties of porous paper substrates dip-coated with nanocellulose (NC) were studied. Sorbitol plasticizer was used to improve the toughness, and citric acid cross-linker to improve the moisture stability of the coatings. In general, the addition of sorbitol increased the barrier properties, maximum strength and toughness as well as the thermal stability of the samples when compared to the non-modified NC coatings. The barrier properties significantly improved, especially for plasticized NC coating's, where the oxygen permeability value was as low as 0.7 mL mu m day(-1) m(-2) kPa(-1) at 49% RH and the water vapor permeability was reduced by 60%. Furthermore, we found that the cross-linked plasticized NC coating had a smoother surface (50% lower roughness) compared to non-modified ones. This study shows that the environmentally friendly additives sorbitol and citric acid had positive effects on NC coating properties, increasing its potential use in paper-based packaging applications.

  • 3. Hooshmand, Saleh
    et al.
    Aitomäki, Yvonne
    Berglund, Linn
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Oksman, Kristiina
    Enhanced alignment and mechanical properties through the use of hydroxyethyl cellulose in solvent-free native cellulose spun filaments2017In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 150, p. 79-86Article in journal (Refereed)
    Abstract [en]

    In this study, the addition of hydroxyethyl cellulose (HEC) in cellulose nanofiber filaments is shown to improve the solvent-free processing and mechanical properties of these biobased fibers as well as their compatibility with epoxy. An aqueous dope of cellulose nanofiber (CNF) with HEC was spun and the resulting filaments cold-drawn. The HEC increased the wet strength of the dope allowing stable spinning of low concentrations of CNF. These lower concentrations promote nanofiber alignment which is further improved by cold-drawing. Alignment improves the modulus and strength and an increase of over 70% compared to the as-spun CNF only filaments was achieved. HEC also decreases hydrophilicity thus increasing slightly the interfacial shear strength of the filaments with epoxy resin. The result is continuous biobased fibers with improved epoxy compatibility that can be prepared in an upscalable and environmentally friendly way. Further optimization is expected to increase draw ratio and consequently mechanical properties.

  • 4. Jalvo, Blanca
    et al.
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Rosal, Roberto
    Coaxial poly(lactic acid) electrospun composite membranes incorporating cellulose and chitin nanocrystals2017In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 544, p. 261-271Article in journal (Refereed)
    Abstract [en]

    In this study, we used electrospinning to produce core-shell nanofibers of poly(lactic acid) as core and polyacrylonitrile/ cellulose nanocrystals (CNC) or polyacrylonitrile/chitin nanocrystals (ChNC) as shell. Electrospun materials prepared at different nanocrystal concentrations were tested and assayed as microfiltration membranes. The coaxial membranes presented a maximum pore size in the 1.2-2.6 mu m range and rejections > 85% for bacterial cells (0.5 x 2.0 mu m) and > 99% for fungal spores (> 2 mu m). The morphological and mechanical properties and the water permeability of the nanocomposite membranes were studied. The morphological characterization showed random fibers of beadless and well-defined core/shell structured fibers with diameter generally below the micron size with presence of secondary ultrafine nanofibers. Tensile strength and Young's modulus of elasticity improved with respect to coaxial membranes without nanocrystals with best mechanical properties achieved at 5 wt% CNC and 15 wt% ChNC loadings. The enhancement was attributed to the reinforcing effect of the percolating network of cellulose nanocrystals. Water permeability increased for all membranes loaded with nanocrystals with respect to the coaxial fibers without nanocrystals, the highest corresponding to ChNC composites with up to a 240% increase over non-loaded membranes. Composite membranes prepared with CNC in their shell were hydrophilic, in contrast with the hydrophobic PLA core, while coaxial fibers with ChNC were superhydrophilic. CNC membranes were negatively charged but ChNC originated neutral or positively charged membranes due to the contribution of deacetylated chitin structural units. Upon exposure to E. coli cultures, composite membranes containing ChNC showed a high antimicrobial action and were essentially free of bacterial colonization under strong biofilm formation conditions.

  • 5. Karim, Zoheb
    et al.
    Claudpierre, Simon
    Grahn, Mattias
    Oksman, Kristiina
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Nanocellulose based functional membranes for water cleaning: Tailoring of mechanical properties, porosity and metal ion capture2016In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 514, p. 418-428Article in journal (Refereed)
    Abstract [en]

    Multi-layered nanocellulose membranes were prepared using vacuum-filtration of cellulose nanofibers suspensions followed by dip coating with cellulose nanocrystals having sulphate or carboxyl surface groups. It was possible to tailor the specific surface area, pore structure, water flux and wet strength of the membranes via control of drying conditions and acetone treatment. Cellulose nanofibers coated with cellulose nanocrystal with carboxyl surface groups showed the highest tensile strength (95 MPa), which decreased in wet conditions (approximate to 3.7 MPa) and with acetone (2.7 MPa) treatment. The membrane pore sizes, determined by nitrogen adsorption/desorption were in nanofiltration range (74 angstrom) and the acetone treatment increased the average pore sizes to tight ultrafiltration range (194 angstrom) with a concomitant increase (7000%) of surface area. The water flux, also increased from zero to 25 L m(-2) h(-1) at a pressure differential of 0.45 MPa, for acetone treated membranes. Modeling of the permeance showed that the middle layer of cellulose nanofibers was responsible for the majority of the resistance to flux and the flux can be improved by increasing the porosity or decreasing the thickness of this layer. The membranes irrespective of the surface functionality showed exceptional capability (approximate to 100%) to remove Ag+, Cu2+ and Fe3+/Fe2+ ions from mirror industry effluents. Surface adsorption followed by micro-precipitation was considered as the possible mechanism of ion removal, which opens up a new generation of ultra filtration membranes with high rejection towards metal ions.

  • 6. Karim, Zoheb
    et al.
    Hakalahti, Minna
    Tammelin, Tekla
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    In situ TEMPO surface functionalization of nanocellulose membranes for enhanced adsorption of metal ions from aqueous medium2017In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 7, no 9, p. 5232-5241Article in journal (Refereed)
    Abstract [en]

    The current work demonstrates an innovative approach to develop nanocellulose based membranes with high water permeability, mechanical stability and high functionality via (1) tailoring the composition of the support layer of sludge microfibers/cellulose nanofibers (CNFSL) and (2) in situ TEMPO functionalization of the thin functional layer of cellulose nanocrystals (CNCBE) to enhance the metal ion adsorption capacity. SEM studies showed a porous network structure of the cellulose support layer and a denser functional layer with CNCBE embedded within gelatin matrix. AFM studies indicated the presence of a nanoscaled coating and increased roughness of membranes surface after TEMPO modification whereas FT-IR and conductometric titration confirmed the introduction of carboxyl groups upon TEMPO oxidation. The contact angle measurement results showed improved hydrophilic nature of membranes after in situ TEMPO functionalization. High networking potential of CNFSL made the membrane support layer tighter with a concomitant decrease in the average pore size from 6.5 to 2.0 mm. The coating with CNCBE further decreased the average pore size to 0.78 and 0.58 mm for S/CNCBE and S-CNFSL/CNCBE, respectively. In parallel, a drastic decrease in water flux (8000 to 90 L MPa-1 h(-1) m(-2)) after coating with CNCBE was recorded but interestingly in situ functionalization of top CNCBE layer did not affect water flux significantly. The increase in adsorption capacity of approximate to 1.3 and approximate to 1.2 fold was achieved for Cu(II) and Fe(II)/Fe(III), respectively after in situ TEMPO functionalization of membranes. Biodegradation study confirmed the stability of layered membranes in model wastewater and a complete degradation of membranes was recorded after 15 days in soil.

  • 7. Karim, Zoheb
    et al.
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Kokol, Vanja
    Wei, Jiang
    Grahn, Mattias
    High-flux affinity membranes based on cellulose nanocomposites for removal of heavy metal ions from industrial effluents2016In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, no 25, p. 20644-20653Article in journal (Refereed)
    Abstract [en]

    Fully biobased affinity membrane processing and its application in the removal of heavy metal ions from mirror industry effluents were successfully demonstrated; indicating the potential use of these membranes in point-of-use or point-of-entry water cleaning products that are cheap, environmentally friendly and efficient. Layered cellulose nanocomposite membranes were fabricated using cellulose microfiber sludge as a support layer and cellulose nanocrystals (CNCSL, CNCBE or PCNCSL) in a gelatin matrix as the functional layer. Scanning electron microscopy (SEM) studies revealed the bi-layered morphology of the membrane and well-individualized nanocelluloses in the functional layer. Bubble point measurements confirmed the membrane pore structure in the microfiltration range (5.0- 6.1 mu m), which provided very high water permeability (900-4000 L h (1) m (2)) at <1.5 bars. A tensile strength of 16 MPa in dry conditions and a wet strength of 0.2 MPa, was considered sufficient for use of these membranes in spiral wound modules. Mirror industry effluent laden with metal ions (Ag+ and Cu2+/Fe3+/Fe2+) when treated with cellulose nanocomposite membranes, showed high ion removal capacity, being 100% for PCNCSL followed by CNCBE than CNCSL. The removal of metal ions was expected to be driven by interactions between negatively charged nanocellulose and the positively charged metal ions.

  • 8.
    Liu, Peng
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Garrido, Beatriz
    Oksman, Kristiina
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Adsorption isotherms and mechanisms of Cu(II) sorption onto TEMPO-mediated oxidized cellulose nanofibers2016In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, no 109, p. 107759-107767Article in journal (Refereed)
    Abstract [en]

    2,2,6,6-Tetramethyl-1-piperidinyloxy (TEMPO) mediated oxidized cellulose nanofibers (TOCNF) have shown potential in the removal of metal ions from contaminated water owing to their abundant carboxylate groups on their surface, functioning as metal sorption sites. The current work aims to study the kinetics and thermodynamics of the sorption behavior of Cu(II) onto TOCNF, and verify the correlation between Delta[H+] and the corresponding Delta[Cu(II)] in aqueous solution during sorption. Sorption of Cu(II) onto TOCNF was found to be an exothermic process with fast kinetics; reaching equilibrium Cu(II) adsorption in less than 1 min. The sorption data fits well with Langmuir isotherm models. The SEM imaging of the TOCNF after Cu(II) sorption revealed interesting copper-containing nanoparticles, which was further analyzed by using XRD. Besides, a linear correlation between Delta[H+] and the corresponding D [Cu(II)] in the solution was found, which indicates that the Cu(II) sorption capacity might be well predicted and calculated by Delta[H+] or pH variation during Cu(II) ion sorption onto TEMPO oxidized nanocellulose fibers and have potential to develop online sensors for tracking metal ion removal.

  • 9. Liu, Peng
    et al.
    Oksman, Kristiina
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Surface adsorption and self-assembly of Cu(II) ions on TEMPO-oxidized cellulose nanofibers in aqueous media2016In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 464, p. 175-182Article in journal (Refereed)
    Abstract [en]

    TEMPO-mediated oxidized cellulose nanofibers (TOCNFs) have shown potential in the bioremediation of metal ions from contaminated water due to their interaction with positively charged metal ions via electrostatic interactions involving surface carboxyl groups. Copper is one of the most common pollutants in industrial effluents and is thus the target metal in the current study. The specific surface adsorption of Cu (II) was similar for TOCNFs with different degrees of functionalization and directly impacted the zeta potential. SEM imaging of the TOCNF after Cu(II) adsorption revealed interesting nanostructured clusters that were attributable to Cu(II) ions first being adsorbed by carboxylate groups on the TOCNF and subsequently being reduced and self-assembled to Cu(0) nanoparticles (NPs) or copper oxide NPs by microprecipitation. TOCNF turned superhydrophilic and resulted in faster water filtration after copper adsorption due to the stronger polarity of the copper ions or the self-assembled Cu(0) NPs creating voids or highly water-permeable channels at the interface between the interconnected TEMPO-oxidized nanofibers. Thus, the adsorption of Cu(II) ions and self-assembly into the Cu NPs on TOCNF favors a faster water purification process and provides a viable route to reuse/recycle TOCNFs studded with Cu nanoparticles as biocidal materials.

  • 10.
    Nair, Santhosh S.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Porous composite membranes based on cellulose acetate and cellulose nanocrystals via electrospinning and electrospraying2017In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 175, p. 149-157Article in journal (Refereed)
    Abstract [en]

    Porous and non-porous cellulose acetate (CA) - cellulose nanocrystal (CNC) electrospun nanocomposite fibers and electrosprayed-electrospun composite membranes were fabricated using two different binary solvent systems. To evaluate the expression of CNC as the active entity in the membrane, dye adsorption studies were carried out using Victoria Blue. To overcome the low surface area of thick porous fibers, a porous electrosprayed-electrospun composite has developed which exhibited 98% dye removal compared to non-porous counterparts (67.9%). The porous membrane with CNC showed an increase of 38 mV in surface zeta potential compared to 9 mV increases in the case of the nonporous membrane and after the dye adsorption, it maintained the negative charge, indicating that further adsorption is feasible. Moreover, the mechanical properties of porous fibers were found to be ten-fold better than that of nonporous fibers. Creating porous CA-CNC composites is demonstrated as a tool for ensuring better exposure of active materials during the adsorption reaction.

  • 11.
    Naseri, Narges
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Deepa, B.
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Oksman, Kristiina
    Girandon, Lenart
    Nanocellulose-Based Interpenetrating Polymer Network (IPN) Hydrogels for Cartilage Applications2016In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 17, no 11, p. 3714-3723Article in journal (Refereed)
    Abstract [en]

    Double cross-linked interpenetrating polymer network (IPN) hydrogels of sodium alginate and gelatin (SA/G) reinforced with 50 wt % cellulose nanocrystals (CNC) have been prepared via the freeze-drying process. The IPNs were designed to incorporate CNC with carboxyl surface groups as a part of the network contribute to the structural integrity and mechanical stability of the hydrogel. Structural morphology studies of the hydrogels showed a three-dimensional (3D) network of interconnected pores with diameters in the range of 10-192 mu m and hierarchical pores with a nanostructured pore wall roughness, which has potential benefits for cell adhesion. Significant improvements in the tensile strength and strain were achieved in 98% RH at 37 degrees C for CNC cross-linked IPNs. The high porosity of the scaffolds (>93%), high phosphate buffered saline (PBS) uptake, and cytocompatibility toward mesenchymal stem cells (MSCs) are confirmed and considered beneficial for use as a substitute for cartilage.

  • 12. Naseri, Narges
    et al.
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Oksman, Kristiina
    Electrospinnability of bionanocomposites with high nanocrystal loadings: The effect of nanocrystal surface characteristics2016In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 147, p. 464-472Article in journal (Refereed)
    Abstract [en]

    This paper deals with the effect of solution properties and nanoparticle surface chemistry on the spinnability of a chitosan/polyethylene oxide (PEO) with high concentration (50 wt%) of chitin and cellulose nanocrystals and the properties of the resultant nanocomposite fibers/fiber mats. Electrospinning dispersions with cellulose nanocrystals having sulphate surface groups showed poor spinnability compared to chitin nanocrystals with amide and amino groups. Chitin nanocrystal based dispersions showed good spinnability and continuous fiber formation whereas cellulose nanocrystal system showed discontinuous fibers and branching. The viscosity and surface tension are shown to impact this behavior, but conductivity did not. Poor spinnability observed for cellulose nanocrystal based fibers was attributed to the coagulation of negatively charged cellulose nanocrystals and positively charged chitosan. The study showed that the nanocrystal surface charge and interactions with the chitosan/PEO matrix have a significant impact on the spinnability of bionanocomposites.

  • 13. Naseri, Narges
    et al.
    Poirier, Jean-Michel
    Girandon, Lenart
    Fröhlich, Mirjam
    Oksman, Kristiina
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    3-Dimensional porous nanocomposite scaffolds based on cellulose nanofibers for cartilage tissue engineering: tailoring of porosity and mechanical performance2016In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, no 8, p. 5999-6007Article in journal (Refereed)
    Abstract [en]

    Fully bio-based 3-dimensional porous scaffolds based on freeze-dried cellulose nanofibers (70-90 wt%) stabilized using a genipin crosslinked matrix of gelatin and chitosan were prepared. Morphology studies using scanning electron microscopy showed that the scaffolds have interconnected pores with average pore diameters of 75-200 mu m and nanoscaled pore wall roughness, both favorable for cell interactions with cartilage repair. X-ray tomography confirmed the 3-dimensional homogeneity and interconnectivity of the pores as well as the fibrillar structure of the scaffolds. The compression modulus of the scaffolds (1-3 MPa) at room conditions was higher than natural cartilage (approximate to 1 MPa). The lowered compression modulus of 10-60 kPa in phosphate buffered saline (PBS) at 37 degrees C was considered favorable for chondrogenesis. The current study therefore successfully addressed the challenge of tailoring the pore structure and mechanical properties simultaneously for cartilage regeneration. Furthermore, the scaffolds' high porosity (approximate to 95%), high PBS uptake and good cytocompatibility towards chondrocytes are considered beneficial for cell attachment and extracellular matrix (ECM) production.

  • 14.
    Sultan, Sahar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    3D printed scaffolds with gradient porosity based on a cellulose nanocrystal hydrogel2018In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 10, no 9, p. 4421-4431Article in journal (Refereed)
    Abstract [en]

    3-Dimensional (3D) printing provides a unique methodology for the customization of biomedical scaffolds with respect to size, shape, pore structure and pore orientation useful for tissue repair and regeneration. 3D printing was used to fabricate fully bio-based porous scaffolds of a double crosslinked interpenetrating polymer network (IPN) from a hydrogel ink of sodium alginate and gelatin (SA/G) reinforced with cellulose nanocrystals (CNCs). CNCs provided favorable rheological properties required for 3D printing. The 3D printed scaffolds were crosslinked sequentially via covalent and ionic reactions resulting in dimensionally stable hydrogel scaffolds with pore sizes of 80-2125 m and nanoscaled pore wall roughness (visible from scanning electron microscopy) favorable for cell interaction. The 2D wide angle X-ray scattering studies showed that the nanocrystals orient preferably in the printing direction; the degree of orientation varied between 61-76%. The 3D printing pathways were optimised successfully to achieve 3-dimensional scaffolds (Z axis up to 20 mm) with uniform as well as gradient pore structures. This study demonstrates the potential of 3D printing in developing bio-based scaffolds with controlled pore sizes, gradient pore structures and alignment of nanocrystals for optimal tissue regeneration.

  • 15.
    Voisin, Hugo
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Peng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nanocellulose-Based Materials for Water Purification2017In: Nanomaterials, ISSN 2079-4991, Vol. 7, no 3, article id 57Article, review/survey (Refereed)
    Abstract [en]

    Nanocellulose is a renewable material that combines a high surface area with high strength, chemical inertness, and versatile surface chemistry. In this review, we will briefly describe how nanocellulose is produced, and present-in particular, how nanocellulose and its surface modified versions affects the adsorption behavior of important water pollutants, e.g., heavy metal species, dyes, microbes, and organic molecules. The processing of nanocellulose-based membranes and filters for water purification will be described in detail, and the uptake capacity, selectivity, and removal efficiency will also be discussed. The processing and performance of nanocellulose-based membranes, which combine a high removal efficiency with anti-fouling properties, will be highlighted.

  • 16. Zhu, Chuantao
    et al.
    Dobryden, Illia
    Rydén, Jens
    Öberg, Sven
    Holmgren, Allan
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Adsorption Behavior of Cellulose and Its Derivatives toward Ag(I) in Aqueous Medium: An AFM, Spectroscopic, and DFT Study2015In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 45, p. 12390-12400Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to develop a fundamental understanding of the adsorption behavior of metal ions on cellulose surfaces using experimental techniques supported by computational modeling, taking Ag(I) as an example. Force interactions among three types of cellulose microspheres (native cellulose and its derivatives with sulfate and phosphate groups) and the silica surface in AgNO3 solution were studied with atomic force microscopy (AFM) using the colloidal probe technique. The adhesion force between phosphate cellulose microspheres (PCM) and the silica surface in the aqueous AgNO3 medium increased significantly with increasing pH while the adhesion force slightly decreased for sulfate cellulose microspheres (SCM), and no clear adhesion force was observed for native cellulose microspheres (CM). The stronger adhesion enhancement for the PCM system is mainly attributed to the electrostatic attraction between Ag(I) and the negative silica surface. The observed force trends were in good agreement with the measured zeta potentials. The scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) analyses confirmed the presence of silver on the surface of cellulose microspheres after adsorption. This study showed that PCM with a high content of phosphate groups exhibited a larger amount of adsorbed A(I) than CM and SCM and possible clustering of Ag(I) to nanoparticles. The presence of the phosphate group and a wavenumber shift of the P-OH vibration caused by the adsorption of silver ions on the phosphate groups were further confirmed with computational studies using density functional theory (DFT), which gives support to the above findings regarding the adsorption and clustering of Ag(I) on the cellulose surface decorated with phosphate groups as well as IR spectra.

  • 17.
    Zhu, Chuantao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Peng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Self-Assembled TEMPO Cellulose Nanofibers: Graphene Oxide-Based Biohybrids for Water Purification2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 24, p. 21048-21058Article in journal (Refereed)
    Abstract [en]

    Nanocellulose, graphene oxide (GO), and their combinations there off have attracted great attention for the application of water purification recently because of their unique adsorption capacity, mechanical characteristics, coordination with transition metal ions, surface charge density, and so on. In the current study, (2,2,6,6-tetramethylpiperidine-1-oxylradical) (TEMPO)-mediated oxidized cellulose nanofibers (TOCNF) and GO sheets or graphene oxide nanocolloid (nanoGO) biohybrids were prepared by vacuum filtration method to obtain self-assembled adsorbents and membranes for water purification. The porous biohybrid structure, studied using advanced microscopy techniques, revealed a unique networking and self-assembling of TOCNF, GO, and nanoGO, driven by the morphology of the GO phase and stabilized by the intermolecular H-bonding between carboxyl groups and hydroxyl groups. The biohybrids exhibited a promising adsorption capacity toward Cu(II) due to TOCNF and formed a unique arrested state in water because of ionic cross-linking between adsorbed Cu(II) and the negatively charged TOCNF and GO phase. The mechanical performance of the freestanding biohybrid membranes investigated using PeakForce Quantative NanoMechanics characterization confirmed the enhanced modulus of the hybrid membrane compared to that of the TOCNF membrane. Besides, the TOCNF+nanoGO membrane shows unique hydrolytic stability and recyclability even under several cycles of adsorption and desorption and strong sonication. This study shows that TOCNF and nanoGO hybrids can generate new water-cleaning membranes with synergistic properties because of their high adsorption capacity, flexibility, hydrolytic stability, and mechanical robustness.

  • 18.
    Zhu, Chuantao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Sweden.
    Nanocellulose-Functionalized AFM Probes for Investigating Surface Interactions by Force SpectroscopyManuscript (preprint) (Other academic)
  • 19.
    Zhu, Chuantao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Monti, Susanna
    CNR - Institute of Chemistry of Organometallic Compounds, Area della Ricerca, via Moruzzi 1, 56124 Pisa, Italy.
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Sweden.
    TEMPO Cellulose Nanofiber - Graphene Oxide Biohybrids: Disclosing Self-Assembly and Cu(II) Adsorption using Advanced Microscopy and ReaxFF Molecular Dynamics SimulationsManuscript (preprint) (Other academic)
  • 20.
    Zhu, Chuantao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Soldatov, Alexander
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Advanced microscopy and spectroscopy reveal the adsorption and clustering of Cu(II) onto TEMPO-oxidized cellulose nanofibers2017In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 9, no 22, p. 7419-7428Article in journal (Refereed)
    Abstract [en]

    TEMPO (2,2,6,6-tetramethylpiperidine-1-oxylradical)-mediated oxidation nanofibers (TOCNF), as a biocompatible and bioactive material, have opened up a new application of nanocellulose for the removal of water contaminants. This development demands extremely sensitive and accurate methods to understand the surface interactions between water pollutants and TOCNF. In this report, we investigated the adsorption of metal ions on TOCNF surfaces using experimental techniques atthe nano and molecular scales with Cu(II) as the target pollutant in both aqueous and dry forms. Imaging with in situ atomic force microscopy (AFM), together with a study of the physiochemical properties of TOCNF caused by adsorption with Cu(II) in liquid, were conducted using the PeakForce Quantitative NanoMechanics (PF-QNM) mode at the nano scale. The average adhesion force between the tip and the target single TOCNF almost tripled after adsorption with Cu(II) from 50 pN to 140 pN. The stiffness of the TOCNF was also enhanced because the Cu(II) bound to the carboxylate groups and hardened the fiber. AFM topography, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) mapping and X-ray photoelectron spectroscopy (XPS) indicated that the TOCNF were covered by copper nanolayers and/or nanoparticles after adsorption. The changes in the molecular structure caused by the adsorption were demonstrated by Raman and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). This methodology will be of great assistance to gain qualitative and quantitative information on the adsorption process and interaction between charged entities in aqueous medium.

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