Search

The dielectric response of thin, flexible films, prepared from graphene oxide (GO) and 2,2,6,6-tetramethylpiperidin-1-yloxyl (TEMPO) oxidized cellulose nanofibres (TCNF) is studied using the solution casting method, and further subjected to the UV irradiation treatment under nitrogen atmosphere for GO reduction. The reduction of GO and its interactions with TCNF has been proven by ATR-FTIR, FESEM, UV–Vis, Raman, and XRD spectroscopy measurements. The film’s improved storage modules and deformability by temperature are demonstrated by dynamic mechanical analysis. The dielectric constant of the TCGO-3 (contains 3 wt.% GO) composite film reaches up to 74.05, whereas its 5 h UV treated counterpart even up to 119.2 at a high frequency of 1 MHz. The ac conductivity of the latter film sample reaches ~ 0.0053 Sm− 1. These outstanding dielectric responses of such films indicate their potential to be utilized in energy storage devices, as well as demonstrating their preparation in an environmentally friendly way.

We report remarkable adsorption capacities of graphene oxide-incorporated 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-modified cellulose nanofibrils (CNF) composite films for Basic Violet 1 and Rhodamine 6g dyes. The morphology of composites shows the formation of open-pore capillary microstructures, typically in only one direction, with a large surface-to-volume ratio and abundance of adsorption voids within the surface down the bulk of the films. The experimental adsorption capacities of Basic Violet 1 and Rhodamine 6g are compared with the theoretical capacities obtained from the pseudo-second-order kinetic model. Moreover, the incorporation of graphene oxide has been found to provide an excellent platform for the stability of adsorbents on CNF and TEMPO-oxidized CNF (TCNF). It is found that TCNF have a remarkable increment in adsorption capacities, typically 100 and 200 times more than CNF, becoming promising industrially viable substrate material for the removal of Basic Violet 1 and Rhodamine 6g.

Nanocellulose has been established to be one of the most promising green resources of modern times due to its inherent properties and renewability. In this chapter, we present the fundamentals of nanocellulose-based composite materials and their significance in electronics applications. The composites involving various types, including films, papers, and aerogels comprising nanocellulose incorporated with conducting polymers, carbon nanomaterials, metal nanoparticles and oxides, etc. have been discussed. The underlying mechanism for nanocellulose composites to be utilized for electronics device fabrication includes flexible and printed electronics, energy storage and conversion devices, and dielectric and microwave absorbing systems has been systematically presented. The ability of nanocellulose to provide mechanical supports for freestanding flexible and thermally stable electronic devices has been widely exploited. This chapter aims at providing an outline in the fabrication process and significance of nanocellulose composites in the entire electronics.

We report on an effective dry method to reduce graphene oxide (GO) in films of cellulose nanofibrils (CNF) by UV irradiation in the presence of nitrogen gas. The reduction of GO and the removal of carbonyl and carboxyl moieties were confirmed by infrared and UV-vis spectroscopy, potentiometric charge titration and X-ray photoelectron spectroscopy (XPS). The crystallinity of native and reduced composites was elucidated by X-ray diffraction measurements. The resulting reduced graphene oxide–CNF nanocomposite films remain flexible and show improved dielectric properties. After 5 hours of UV irradiation a 3 wt% graphene oxide loaded film increased its dielectric constant from 68.9 to 88.9, which shows significant enhancement compared to previous reports. The AC conductivity of reduced GO films reaches values of 9.37 × 10−4 S m−1. The electrochemical performance of the samples was tested by cyclic voltammetry and electrochemical impedance spectroscopy. UV treated samples showed a higher capacitive nature than untreated samples. The UV induced reduction of GO in the presence of CNF is seen as a promising alternative to solvent based methods.

Metallic implants have dominated the biomedical implant industries for the past century for load-bearing applications, while the polymeric implants have shown great promise for tissue engineering applications. The surface properties of such implants are critical as the interaction of implant surfaces, and the body tissues may lead to unfavourable reactions. Desired implant properties are biocompatibility, corrosion resistance, and antibacterial activity. A polymer coating is an efficient and economical way to produce such surfaces. A lot of research has been carried out on chitosan (CS)-modified metallic and polymer scaffolds in the last decade. Different methods such as electrophoretic deposition, sol-gel methods, dip coating and spin coating, electrospinning, etc. have been utilized to produce CS coatings. However, a systematic review of chitosan coatings on scaffolds focussing on widely employed techniques is lacking. This review surveys literature concerning the current status of orthopaedic applications of CS for the purpose of coatings. In this review, the various preparation methods of coating, and the role of the surface functionalities in determining the efficiency of coatings are discussed. Effect of nanoparticle additions on the polymeric interfaces and in regulating the properties of surface coatings are also investigated in detail.

This study aims to report the synthesis of nitrogen-doped carbon dots (N-CDs) derived from biomass, tannic acid and polyethyleneimine, which is a N-doping agent. The N-doping of CDs is found to enhance singlet oxygen (1O2) generation under visible light irradiation. Additionally, the N-CDs work as both a reducing agent and stabiliser, and hence the N-CDs can directly reduce chloroauric acid to form gold nanoparticles (Au NPs) without adding other reducers and stabilisers. The as-prepared N-CD–Au NP nanocomposite possesses 2.3 times higher photosensitising ability for producing 1O2 than N-CDs. To the best of our knowledge, this is the first report on the enhancement of the photosensitising ability of N-CDs by Au NPs. We suggest that the plasmon coupling of Au NPs with the N-CDs causes the energy transfer from the N-CDs to the ground state oxygen (3O2), thus resulting in an increased 1O2 generation.

The fabrication of superadsorbent for dye adsorption is a hot research area at present. However, the development of low-cost and highly efficient superadsorbents against toxic textile dyes is still a big challenge. Here, we fabricated hydrophobic cellulose nanofiber aerogels from cellulose nanofibers through an eco-friendly silanization reaction in liquid phase, which is an extremely efficient, rapid, cheap, and environmentally friendly procedure. Moreover, the demonstrated eco-friendly silanization technique is easy to commercialize at the industrial level. Most of the works that have reported on the hydrophobic cellulose nanofiber aerogels explored their use for the elimination of oil from water. The key novelty of the present work is that the demonstrated hydrophobic cellulose nanofibers aerogels could serve as superadsorbents against toxic textile dyes such as crystal violet dye from water and insulating materials for building applications. Here, we make use of the possible hydrophobic interactions between silane-modified cellulose nanofiber aerogel and crystal violet dye for the removal of the crystal violet dye from water. With a 10 mg/L of crystal violet (CV) aqueous solution, the silane-modified cellulose nanofiber aerogel showed a high adsorption capacity value of 150 mg/g of the aerogel. The reason for this adsorption value was due to the short-range hydrophobic interaction between the silane-modified cellulose nanofiber aerogel and the hydrophobic domains in crystal violet dye molecules. Additionally, the fabricated silane-modified cellulose nanofiber hydrophobic aerogels exhibited a lower thermal conductivity value of 0.037 W&middot, m&minus, 1 K&minus, 1, which was comparable to and lower than the commercial insulators such as mineral wools (0.040 W&middot, 1) and polystyrene foams (0.035 W&middot, 1). We firmly believe that the demonstrated silane-modified cellulose nanofiber aerogel could yield an eco-friendly adsorbent that is agreeable to adsorbing toxic crystal violet dyes from water as well as active building thermal insulators.

Relatively low viscosity with poor resolution and shape fidelity make soft gelatine hydrogel still challenging to use as an ink or bio-ink for 3D printing, despite its good shear-thinning behaviour and high potential in tissue engineering due to its biocompatibility and similarities to biological tissues. A horizontally-induced cooling platform has thus been proposed to accelerate the physical stabilisation of each printed deposit during such a multilayer printing by fastening its phase-change (gelation) transition, which would affect its flow (shear-thinning) and gel strength (viscoelasticity), and thus enable scaffolds to be created with more precise porosities and geometries. In order to verify the physical properties (sol-gel transitions, gelation point, gel strength) and the kinetics of gelatine solutions (5 and 10 wt%) during such printing conditions, the viscosity and oscillatory rheology as a function of kinetically different cooling / heating rates (5−48 °C/min) have been performed in the range from 37 to 0 vs. -30 °C. The gelation of 10 wt% gelatine was shown to decrease by 4 °C (to 18 °C) when the plate was cooled to 0 °C, and the cooling speed rate was changed from 5 to 42 °C/min, which increased its complex viscosity (η*) for 485 Pa (to 1135 Pa) by forming tight and in a flow direction-oriented clusters of multi/triple-helices, being confirmed with FTIR spectroscopy. The lower plate temperature (-30 °C) didn't change solutions' gelation transition significantly, while it only increased the η* (from 43 to 470 Pa) of 5 wt% hydrogels at lower cooling speed (5−12 °C/min) by forming larger and more disordered aggregates, getting immobilised by fast crystallisation of the aqueous medium. It can be concluded that, besides the gelatine concentration, the cooling speed has a major impact on its physical stabilisation by yielding macromolecularly differently structured gels, which shall affect the printability, as well as give different porous structures.

International audience; An array of highly conductive, lightweight and flexible cellulose nanopapers as effective attenuators of electromagnetic radiations within 8.2–12.4 GHz (X band) were formulated via in situ polymerization of pyrrole monomers on to cellulose nanofibers (CNFs). It is quite obvious that the free hydroxyl groups on the surface of CNFs facilitate the formation of intense intermolecular hydrogen bonding with PPy which is envisaged for its excellent electromagnetic shielding performance with an average shielding effectiveness of ca. –22 dB (>99% attenuation) at 8.2 GHz for a paper having 1 mm thickness. The fabricated papers displayed a predominant absorption mechanism (ca. 89%) rather than reflection (ca. 11%) for efficiently attenuating electromagnetic radiations, which has a considerable importance in the modern telecommunication sector. Thus, the designed PPy/CNF papers would replace the conventional metal‐based shields and pave way for the development of green microwave attenuators functioning via a strong absorption mechanism. The PPy/CNF nanopapers exhibited a DC conductivity of 0.21 S/cm, a prime requisite for the development of highly efficient electromagnetic shields. Undoubtedly, such nanopapers can be employed in wide range of applications such as electrodes for supercapacitors and other freestanding flexible paper‐based devices.

Magnesium (Mg) and its alloys are third-generation biomedical implant material in the biomedical field. The limitation of using Mg in medical applications is its rapid corrosion rate. In the present work, for the first time, AZ91 magnesium alloy surface treated with the inductively coupled Ar/O2 Plasma process to decrease the corrosion rate of the alloy. The oxidation mechanism and surface analysis have been investigated in detail. The electrochemical studies in SBF solution reveal that plasma modified surface increases the corrosion resistance of the alloy compared to the untreated surface.

A series of flexible, lightweight, and highly conductive cellulose nanopapers were fabricated through in situ polymerization of aniline monomer on to cellulose nanofibers with a rationale for attenuating electromagnetic radiations within 8.2-12.4 GHz (X band). The demonstrated paper exhibits good conductivity due to the formation of a continuous coating of polyaniline (PANI) over the cellulose nanofibers (CNF) during in situ polymerization, which is evident from scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction analysis. The free hydroxyl groups on the surface of nanocellulose fibers promptly form intermolecular hydrogen bonding with PANI, which plays a vital role in shielding electromagnetic radiations and makes the cellulose nanopapers even more robust. These composite nanopapers exhibited an average shielding effectiveness of ca. -23 dB (99% attenuation) at 8.2 GHz with 1 mm paper thickness. The fabricated papers exhibited an effective attenuation of electromagnetic waves by a predominant absorption mechanism (ca. 87%) rather than reflection (ca. 13%), which is highly desirable for the present-day telecommunication sector. Unlike metal-based shields, these demonstrated PANI/CNF papers have given a new platform for designing green microwave attenuators via an absorption mechanism. The prime novelty of the present study is that these robust PANI/CNF nanopapers have the ability to attenuate incoming microwave radiations to an extent that is 360% higher than the shielding effectiveness value reported in the previous literature. This makes them suitable for use in commercial electronic gadgets. This demonstrated work also opens up new avenues for using cellulose nanofibers as an effective substrate for fabricating conductive flexible papers using polyaniline. The direct current conductivity value of PANI/CNF nanopaper was 0.314 S/cm, which is one of the key requisites for the fabrication of efficient electromagnetic shields. Nevertheless, such nanopapers also open up an arena of applications such as electrodes for supercapacitors, separators for Li-S, Li-polymer batteries, and other freestanding flexible paper-based devices.

The effect of structure (density and porosity) and composition (ratio) of composites prepared from cellulose nanofibrils (CNF) and reduced graphene oxide (RGO) as film-like xerogels and porous cryogels, respectively, were investigated related to their dielectric performance and electrochemical storage abilities. A very small content (5 wt%) of RGO incorporated xerogelic film of a denser and layered structure shows relatively high dielectric constant of similar to 85 and similar to 164 and an ac electrical conductivity of 0.0028 S/m(2) and 0.0072 S/m(2) at 270 K and 370 K, respectively, at a high frequency of 1 MHz showing their suitability for high temperature dielectric storage applications. On the other hand, a high specific capacitance of similar to 460 F/g and electrochemical resistance of 12-15 Omega cm(2) was observed for well-aligned and longitudinal-oriented micro-porous cryogel, indicate on its suitability as electrodes for electrochemical storage devices. (C) 2018 Elsevier Ltd. All rights reserved.