Preparation and characterization of cellulose nanocrystals from rice straw

Pure cellulose have been isolated from rice straw at 36% yield and hydrolyzed (64% H₂SO₄, 8.75 mL/g, 45 °C) for 30 and 45 min to cellulose nanocrystals (CNCs), i.e., CNC30 and CNC45, respectively. CNC45 was smaller (11.2 nm wide, 5.06 nm thick and 117 nm long) than CNC30 (30.7 nm wide, 5.95 nm thick and 270 nm long). Freeze-drying of diluted CNC suspensions showed both assembled into long fibrous structures: ultra-fine fibers (∼400 nm wide) from CNC45 and 1-2 μm wide broad ribbons interspersed with CNC clusters from CNC30. The self-assembled fibers from CNC30 and CNC45 were more highly crystalline (86.0% and 91.2%, respectively) and contained larger crystallites (7.36 nm and 8.33 nm, respectively) than rice straw cellulose (61.8%, 4.42 nm). These self-assembled fibers had essentially nonporous or macroporous structures with the CNCs well aligned along the fiber axis. Furthermore, the self-assembled ultra-fine fibers showed extraordinary structural stability, withstanding vigorous shaking and prolong stirring in water.     

Utilization of residues from agro-forest industries in the production of high value bacterial cellulose

Bacterial cellulose (BC), a very peculiar form of cellulose, is gaining considerable importance due to its unique properties. In this study, several residues, from agro-forestry industries, namely grape skins aqueous extract, cheese whey, crude glycerol and sulfite pulping liquor were evaluated as economic carbon and nutrient sources for the production of BC. The most relevant BC amounts attained with the residues from the wine and pulp industries were 0.6 and 0.3 g/L, respectively, followed by biodiesel crude residue and cheese whey with productions of about, 0.1 g/L after 96 h of incubation. Preliminary results on the addition of other nutrient sources (yeast extract, nitrogen and phosphate) to the residues-based culture media indicated that, in general, these BC productions could be increased by ∼200% and ∼100% for the crude glycerol and grape skins, respectively, after the addition organic or inorganic nitrogen.     

High performance edible nanocomposite films containing bacterial cellulose nanocrystals

Bacterial cellulose obtained from Gluconacetobacter xylinus in the form of long fibers were acid hydrolyzed under controlled conditions to obtain cellulose nanocrystals. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) confirmed the formation of rod like cellulose nanocrystals having an average diameter and length of 20 ± 5 nm and 290 ± 130 nm respectively. These nanocrystals were used to prepare gelatin nanocomposite films and characterized for elucidating its performance. The formation of percolated networks of cellulose nanocrystals within gelatin matrix resulted in improving the mechanical properties of nanocomposites. The moisture sorption and water vapor permeability (WVP) studies revealed that the addition of cellulose nanocrystals reduced the moisture affinity of gelatin, which is very favorable for edible packaging applications. Results of this study demonstrated the use of bacterial cellulose nanocrystals (BCNCs) in the fabrication of edible, biodegradable and high-performance nanocomposite films for food packaging applications at relatively low cost.     

Synthesis and characterization of pure cubic zirconium oxide nanocrystals by decomposition of bis-aqua, tris-acetylacetonato zirconium(IV) nitrate as new precursor complex

Pure zirconium oxide (ZrO₂) nanocrystals with diameters 10-30 nm are fabricated from bis-aqua, tris-acetylacetonato zirconium(IV) nitrate; [Zr(acac)₃(H₂O)₂](NO₃); by thermal decomposition. The different combinations of oleylamine, or polyethyleneglycol (PEG) and triphenylphosphine, were added as surfactants to control the particle size. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) spectroscopy, photoluminescence spectroscopy (PL), Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) to depict the phase and morphology. The synthesized ZrO₂ nanoparticles have a cubic structure. The FT-IR spectrum showed the purity of obtained ZrO₂ nanocrystals with cubic phase. The UV-Visible absorption peak for ZrO₂ was observed at 233 nm (5.3 eV in photon energy). The band at 363 nm for cubic ZrO₂ nanocrystals was found.     

Green synthesis of silver nanoparticles using cellulose extracted from an aquatic weed; water hyacinth

As part of the desire to save the environment through “green” chemistry practices, we herein report an environmentally benign synthesis of silver nanoparticles (Ag-NPs) using cellulose extracted from an environmentally problematic aquatic weed, water hyacinth (WH), as both reducing and capping agent in an aqueous medium. By varying the pH of the solution and reaction time, the temporal evolutions of the optical and morphological properties of the as-synthesised Ag-NPs were investigated. The as-synthesised cellulose capped silver nanoparticles (C–Ag-NPs) were characterised using Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–vis), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The maximum surface plasmon resonance (SPR) peak decreased as the pH increased indicating that an increase in the pH of the solution favoured the formation of smaller particles. In addition, instantaneous change in the colour of the solution from colourless to brown within 5 min at pH 11 showed that the rate of reduction is faster at this pH compared to those at lower pH. The TEM micrographs showed that the materials are small, highly monodispersed and spherical in shape. The average particle mean diameters were calculated to be 5.69 ± 5.89 nm, 4.53 ± 1.36 nm and 2.68 ± 0.69 nm nm at pH 4, 8 and 11 respectively. The HRTEM confirmed the crystallinity of the material while the FTIR spectra confirmed the capping of the as-synthesised Ag-NPs by the cellulose. It has been shown therefore that based on this synthetic method, this aquatic plant can be used to the advantage of mankind.     

Structure and properties of hydroxyapatite/cellulose nanocomposite films

The aim of this study was to develop a new inorganic-organic hybrid film. Nanohydroxyapaptite (nHAP) particles as the inorganic phase was mixed with cellulose in 7 wt.% NaOH/12 wt.% urea aqueous solution with cooling to prepare a blend solution, and then inorganic-organic hybrid films were fabricated by coagulating with Na₂SO₄ aqueous solution. The structure and properties of the hybrid films were characterized by high resolution transmitting electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), thermo-gravimetric analysis (TGA), Fourier transform infra-red (FT-IR) spectra, wide angle X-ray diffraction (WAXD) and tensile testing. The results revealed that the HAP nanoparticles with mean diameter of about 30 nm were uniformly dispersed and well immobilized in the hybrid film as a result of the role of the nano-and micropores in the cellulose substrate. A strong interaction existed between HAP and cellulose matrix, and their thermal stability and mechanical strength were improved as a result of good miscibility. Furthermore, the results of 293T cell viability assay indicated that the HAP/cellulose films had excellent biocompatibility and safety, showing potential applications in biomaterials.     

Synthesis and size regulation of gold nanoparticles by controlled thermolysis of ammonium gold(I) thiolate in the absence or presence of amines

Controlled thermolysis of gold(I) complex with no use of solvent was investigated as a novel synthetic method of gold nanoparticles. A series of precursors, ammonium gold(I) thiolate [RN(CH₃)₃][Au(SC₁₂H₂₅)₂] (R = C₈H₁₇, C₁₂H₂₅, and C₁₄H₂₉) and [(C₁₈H₃₇)₂N(CH₃)₂][Au(SC₁₂H₂₅)₂], have been prepared and the thermolysis of those precursors was conducted at 180 °C for 5 h under an N₂ atmosphere, providing spherical gold nanoparticles stabilized by alkyl groups derived from the precursor, gold(I) complex. In spite of thermolysis process, the average diameter of gold nanoparticles deriving from [C₁₂H₂₅N(CH₃)₃][Au(SC₁₂H₂₅)₂] was 22 nm, but the size distribution ranges from 11 to 76 nm. For the purpose of the size regulation of the gold nanoparticles, equimolar primary, secondary, or tertiary alkylamines are added as stabilizer and mild reductant to the controlled thermolysis of gold(I) complex at lower temperature of 165 °C for 5 h. The gold nanoparticles obtained by the controlled thermolysis in the presence of stearylamine are well regulated and almost monodispersed nanoparticles with average diameter of 7.5 nm. Such size regulation resulted from the inhibition of the growth of gold nuclei by transforming reaction from ammonium and thiolate moieties to neutral tertiary amine, thiol and sulfide, which function as stabilizer for gold nanoparticles.     

Biocompatible elastomer of waterborne polyurethane based on castor oil and polyethylene glycol with cellulose nanocrystals

Biocompatible waterborne polyurethane (WPU) based on castor oil (CO)/polyethylene glycol (PEG) filled with low level loadings of Eucalyptus globulus cellulose nanocrystals (ECNs) was prepared. The ECNs obtained by sulfuric hydrolysis, consisted of ‘rod-like’ crystals with an average length and diameter of 518.0 ± 183.4 nm and 21.7 ± 13.0 nm, respectively. The nanocomposites with low level loadings of ECNs showed significant enhancement in tensile strength and Young's modulus from 5.43 to 12.22 MPa and from 1.16 to 4.83 MPa, respectively. SEM results showed well dispersion of ECNs in the WPU matrix. Furthermore, it was verified that the nanosized ECNs favored the hard-segments (HSs)/soft-segments (SSs) microphase separation of the WPU, causing shifts of the SS glass transition temperature (T_g,s) and the HS melting temperature (T_m,h) toward higher temperatures.     

Image analysis of modified cellulose fibers from sugarcane bagasse by zirconium oxychloride

Surface modification of natural fibers has been made using different methods. In this paper, cellulose fibers from sugarcane bagasse were bleached and modified by zirconium oxychloride in situ. The chemically modified cellulose fibers were compared to those of bleached ones. Cellulose fibers were modified with ZrO₂·nH₂O nanoparticles through the use of zirconium oxychloride in acidic medium in the presence of cellulose fibers using urea as the precipitating agent. The spatial distribution characterization of hydrous zirconium oxide on cellulose fibers was carried out by combining both processing and image analyses obtained by SEM and statistical methodologies. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TG) were also used to characterize the nanocomposite. Results indicated that ZrO₂·nH₂O nanoparticles of about 30-80 nm diameter deposited on cellulose fibers were heterogeneously dispersed.     

Novel regenerated cellulose films prepared by coagulating with water: Structure and properties

Regenerated films were successfully prepared from cellulose/NaOH/urea solution by coagulating with water at temperature from 25 to 45 °C. The results of solid ¹³C NMR, wide angle X-ray diffraction, scanning electron microscopy (SEM) and tensile testing revealed that the cellulose films possessed homogeneous structure and cellulose II crystalline, similar to that prepared previously by coagulating with 5 wt% H₂SO₄. By changing the coagulation temperature from 25 to 45 °C, tensile strength of the films was in the range of 85-139 MPa. Interestingly, the RC35 film coagulated at 35 °C exhibited the highest tensile strength (σ_b = 139 MPa). The inclusion complex associated with cellulose, NaOH and urea hydrates in the cellulose solution were broken by adding water (non-solvent), leading to the self-association of cellulose to regenerate through rearrangement of the hydrogen bonds. This work provided low-cost and “green” pathway to prepare cellulose films, which is important in industry.     

In situ preparation of magnetic Fe3O4-chitosan nanoparticles for lipase immobilization by cross-linking and oxidation in aqueous solution

A new and simple method has been proposed to prepare magnetic Fe₃O₄-chitosan (CS) nanoparticles by cross-linking with sodium tripolyphosphate (TPP), precipitation with NaOH and oxidation with O₂ in hydrochloric acid aqueous phase containing CS and Fe(OH)₂, and these magnetic CS nanoparticles were used to immobilize lipase. The effects on the sequence of adding NaOH and TPP, the reaction temperature, and the ratio of CS/Fe(OH)₂ were studied. TEM showed that the diameter of composite nanoparticles was about 80 nm, and that the magnetic Fe₃O₄ nanoparticles with a diameter of 20 nm were evenly dispersed in the CS materials. Magnetic measurement revealed that the saturated magnetisation of the Fe₃O₄-CS nanoparticles could reach 35.54 emu/g. The adsorption capacity of lipase onto nanoparticles could reach 129 mg/g; and the maximal enzyme activity was 20.02 μmol min⁻¹ mg⁻¹ (protein), and activity retention was as high as 55.6% at a certain loading amount.     

Biodegradable and biocompatible polyampholyte microgels derived from chitosan, carboxymethyl cellulose and modified methyl cellulose

Two biocompatible and biodegradable polyampholyte microgels, namely chitosan-carboxymethyl cellulose (CS-CMC) and chitosan-modified methyl cellulose (CS-ModMC) were synthesized by an inverse microemulsion technique. The CS-CMC microgel system was pH-responsive while the CS-ModMC system possessed both pH and thermo-responsive properties. For CS-CMC system, the number of -OCH₂COOH and -NH₂ groups was determined to be 1.5 and 1.1 meq/g of microgel, respectively. In the pH range of 4-9, the zeta potential values varied from +10 to −40 mV, while the hydrodynamic radius varied from 160 nm in the swollen state (acidic and basic pH) to 110 nm in the “collapse” state (neutral pH). Furthermore, TEM micrographs confirmed the swelling/deswelling behaviour of CS-CMC microgel particles at acidic, neutral and basic conditions. For CS-ModMC system, the number of -OCH₂COOH and -NH₂ groups was determined to be 0.8 and 0.6 meq/g microgel, respectively. In the pH range of 4-9, the surface charge on the microgels varied from +25 to −60 mV and the hydrodynamic radii were 190 nm at low pH, 80 nm at neutral pH, to 120 nm at a high pH. In vitro drug release studies confirmed that CS-CMC microgels could encapsulate and release a model drug, thus they could potentially be used as biocompatible and biodegradable drug carriers.     

Carboxymethylation of cellulose using reactive extrusion

Carboxymethyl cellulose was prepared using a continuous, reduced solvent, reactive extrusion process with a short reaction time. The effects of the amounts of NaOH (30 g, 40 g and 50 g), water:ethanol ratio (100%, 70%, 50%, 30% and 10% H₂O) and their interactions on the physical, chemical and morphological properties of carboxymethyl cellulose were studied. Experiments were conducted using to a 5 × 3 blocked factorial design. X-ray diffraction analyses revealed higher degrees of crystallinity and fractions of cellulose-II crystalline structure when 100% H₂O was used as compared to that for 70%, 50%, 30% and 10% H₂O and a commercially available brand of carboxymethyl cellulose, AQUASORB A500. Statistical analysis revealed a significant interaction between the effects of NaOH and H₂O on the degrees of substitutions. The degrees of substitutions decreased with increasing amounts of NaOH and tended to increase with increasing alcohol concentrations. Liquid uptake measurements revealed that the extent of saline uptake, measured at intervals of 1 min, 5 min and 10 min, by carboxymethyl cellulose prepared with 100% H₂O, especially when 40 g and 50 g NaOH was used, was higher than that for 70%, 50%, 30% and 10% H₂O and AQUASORB A500. This may have been because of the higher crystallinity in carboxymethyl cellulose prepared with 100% H₂O. Carboxymethyl cellulose prepared with 70% H₂O and 30 g and 50 g NaOH had the highest saline absorption, using the soak method, before and after centrifugation, respectively. Scanning electron microscopy for carboxymethyl cellulose prepared with 100% and 10% H₂O, through images at 120X magnification, revealed fibers 100 μ to >800 μ in length and 0.8-3.3 μ in breadth. Some non fibrous particles, 0.8-6.7 μ in dimensions, also were observed for 100% H₂O. Images at 900× magnification revealed partially damaged fiber surfaces.     

Germanium tetra(tertiary butoxide): Synthesis, structure and its utility as a precursor for the preparation of europium doped germanium oxide nanoparticles

Germanium tetra(tertiary butoxide), [Ge(O^tBu)₄], has been prepared by the reaction of GeCl₄ with KOBu^t in benzene. It is a monomeric crystalline solid having a distorted tetrahedral configuration, defined by the coordination of four OBu^t groups around germanium atom. The TG analysis showed that the compound is thermally stable and volatilizes at around 130 °C. Europium doped and un-doped germanium oxide nanoparticles were prepared based on the urea hydrolysis of Ge(O^tBu)₄/Eu(OOCCH₃)₃ in ethylene glycol medium at 150 °C followed by heating the resulting product at 750 °C. The nanoparticles were characterized by XRD, TEM and PL measurements. The europium doped nanoparticles, which were nearly monodispersed (∼30 nm), showed luminescence and the Eu³⁺ ions were occupying the surface of the GeO₂ nanoparticles.     

Self-assembly of 6-O- and 6'-O-hexadecylsucroses mixture under aqueous conditions

In this paper, we report the self-assembly of 6-O- and 6′-O-hexadecylsucroses mixture under aqueous conditions. The mixture was synthesized by a five-step sequence from sucrose. The SEM image of a sample prepared by drying a dispersion of the mixture in water showed nanoparticles with the diameter of ∼50 nm and aggregates that were formed by further assembly of them. The XRD measurement of the sample exhibited the diffraction pattern assignable to face-centered cubic (FCC) structure and the diameter of a sphere, which took part in the FCC structure, was calculated to be 5.1 nm. This value was relatively close to that observed in the DLS measurement of a dispersion of the mixture in water and estimated for a spherical micelle based on the molecular sizes of the two sucrose ethers. On the basis of the above findings, the following self-assembly process of the mixture under aqueous conditions was proposed. The mixture formed the spherical micelles with the diameter of ∼5-7 nm in water. The micelles regularly organized according to the FCC structure during the drying process from the aqueous dispersion to construct the nanoparticles with the diameter of ∼50 nm. Several numbers of the nanoparticles further assembled to form the aggregates.     

Hydrothermal synthesis of bacterial cellulose/AgNPs composite: A “green” route for antibacterial application

Antibacterial materials based on cellulose have been widely used in many fields. In this work, an environmentally benign and facile approach for production of silver nanoparticles (AgNPs) was proposed for the first time by hydrothermal synthesis using bacterial cellulose (BC) as both the reducing and stabilizing agent, without any chemical reagents introduced. Some key reaction parameters were optimized to achieve a high antibacterial activity of the BC/AgNPs composite. Under the optimal conditions, a small size and a narrow distribution of AgNPs, 17.1 ± 5.9 nm, was formed on the BC matrix, with a silver content of 1.78% (w/w) and a MIC value of 1.30 × 10⁻⁴ μg/CFU. Moreover, a sustained release of silver and a prolonged antibacterial performance of the composite against Staphylococcus aureus were found over a long period time of 72 h, which were important for practical applications.     

Synthesis of silver nanoparticles by solar irradiation of cell-free Bacillus amyloliquefaciens extracts and AgNO3

Silver nanoparticles (AgNPs) were obtained by solar irradiation of cell-free extracts of Bacillus amyloliquefaciens and AgNO₃. Light intensity, extract concentration, and NaCl addition influenced the synthesis of AgNPs. Under optimized conditions (solar intensity 70,000 lx, extract concentration 3 mg/mL, and NaCl content 2 mM), 98.23 ± 0.06% of the Ag⁺ (1 mM) was reduced to AgNPs within 80 min, and the ζ-potential of AgNPs reached −70.84 ± 0.66 mV. TEM (Transmission electron microscopy) and XRD (X-ray diffraction) analysis confirmed that circular and triangular crystalline AgNPs with mean diameter of 14.6 nm were synthesized. Since heat-inactivated extracts also mediated the formation of AgNPs, enzymatic reactions are likely not involved in AgNPs formation. A high absolute ζ-potential value of the AgNPs, possibly caused by interaction with proteins likely explains the high stability of AgNPs suspensions. AgNPs showed antimicrobial activity against Bacillus subtilis and Escherichia coli in liquid and solid medium.     

Synthesis of soluble coordination polymer nanoparticles using room-temperature ionic liquid

We report a new family of soluble cyano-bridged coordination polymer nanoparticles M₃[Cr(CN)₆]₂/[BMIM][BF₄] (where M²⁺ = Ni, Mn, V^IVO; BMIM = 1-butyl-3-methylimidazolium). These nanoparticles of ca. 6 nm were synthesised in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, which acts both as a stabilizing agent and a solvent. The magnetic properties of frozen colloids containing the nanoparticles show that the relaxation of magnetisation is strongly influenced by interparticle interactions leading to the appearance of spin-glass-like dynamics in these systems.     

Optically active amphiphilic hyperbranched polyglycerols as templates for palladium nanoparticles

We report a systematic study on the encapsulation of palladium nanoparticles in optically active amphiphilic hyperbranched polyglycerols with different optical signs and different degrees of polymerization, namely (−)-P(G₄₀C16_0.5) 1 and (+)-P(G₇₃C16_0.5) 2. Several issues have been addressed here: (a) relatively wide size distributions (1-5 nm) of palladium nanoparticles have been achieved, (b) a remarkable template effect (1, DP_n = 40, 1.2 ± 0.1 nm; 2, DP_n = 73, 2.3 ± 0.1 nm average particle size) has been observed using TEM technique, as shown by the particle size dependent on the degree of polymerization of the polymers, (c) NaBH₄ is found to be a convenient reducing agent to produce small particle size compared with gaseous hydrogen, (d) catalytic Heck reaction of 2,3-dihydrofuran and aryl triflate has been tested successfully without enantiocontrol.     

Integrated hydrogen production process from cellulose by combining dark fermentation, microbial fuel cells, and a microbial electrolysis cell

Hydrogen gas production from cellulose was investigated using an integrated hydrogen production process consisting of a dark fermentation reactor and microbial fuel cells (MFCs) as power sources for a microbial electrolysis cell (MEC). Two MFCs (each 25 mL) connected in series to an MEC (72 mL) produced a maximum of 0.43 V using fermentation effluent as a feed, achieving a hydrogen production rate from the MEC of 0.48 m³ H₂/m³/d (based on the MEC volume), and a yield of 33.2 mmol H₂/g COD removed in the MEC. The overall hydrogen production for the integrated system (fermentation, MFC and MEC) was increased by 41% compared with fermentation alone to 14.3 mmol H₂/g cellulose, with a total hydrogen production rate of 0.24 m³ H₂/m³/d and an overall energy recovery efficiency of 23% (based on cellulose removed) without the need for any external electrical energy input.