Robust Fabrication of Fluorescent Cellulosic Materials via Hantzsch Reaction.

Hantzsch reaction is one of the typical multicomponent reactions (MCRs), and it is employed herein to endow cellulosic materials with fluorescent properties. For example, acetoacetyl (ACAC)-bearing cotton fabric prepared via transesterification with tert-butyl acetoacetate is subjected to an aqueous Hantzsch reaction with formaldehyde and ammonium acetate at ambient temperature. A strong fluorescent emission around 460 nm is achieved within 10 min. XPS, fluorescent spectroscopy, and elemental analysis are used to confirm the presence of 1,4-dihydropyridine (DHP) rings on the surface of the fabric. TGA, SEM, XRD, and mechanical testing results show that the modification process has minimum impact on intrinsic properties of the fabric. The strategy is also shown to be generally applicable to various forms of cellulosic materials and different aldehydes. This fast and simple approach enriches the application of MCR in modification of cellulose and cellulose derivatives.

In-plane aligned assemblies of 1D-nanoobjects: recent approaches and applications.

One-dimensional (1D) nanoobjects have strongly anisotropic physical properties which are averaged out and cannot be exploited in disordered systems. The goal of the present review is to describe the current methods for preparing macroscopic composite films in which the long axis of individual 1D-nanoobjects is more or less parallel to the x,y-plane of the substrate as well as to each other (alignment direction). Such structures are generally described as in-plane anisotropic and many of their physical properties show minima or maxima parallel to the alignment direction. Optical polarizers are a typical class of such materials, but anisotropic materials properties can enhance the performance of devices and materials over many length scales in various disciplines of materials science including electronic devices, environmental sensors, energy saving and energy generation applications, plasmonic devices, Surface-Enhanced Raman Scattering (SERS) and biological applications. The reviewed alignment methods fall into two categories: techniques in which all nanoobjects remain in the x,y-plane and the in-plane densities and alignment are controlled; and techniques allowing building complex architectures in which each stratum of multilayered or stacked films may differ in chemical nature or alignment direction or both. This review serves a purpose to provide a platform to inspire new alignment approaches with improved assembly quality and upscaling potential and new applications with enhanced performance by alignment.

Synthesis of highly branched hollow trimetallic PdAgCu nanoparticles.

An aqueous, room temperature, and surfactant-less synthetic route based on galvanic replacement and co-reduction is reported to yield PdAgCu nanoparticles (NPs) with a high density of sharp and branched tips. The PdAgCu NPs are of high-purity, uniform size and more than 90% of them adopt branched tips. Besides, the PdAgCu NPs exhibit hollow interiors, well-alloyed nature, and a tuneable localized surface plasmon resonance peak in the near infrared region. Their morphology and optical property are facilely controlled by adjusting the precursor molar ratio, amounts of AgNP seeds and Cl- ions in the growth solution. The proposed synthetic approach is anticipated to offer an attractive avenue for facile synthesis of other multi-metallic and branched NPs with controlled properties.

Multi-responsive, self-healing and adhesive PVA based hydrogels induced by the ultrafast complexation of Fe3+ ions.

Herein, a PVA (polyvinyl alcohol)-based multi-responsive hydrogel was prepared by introducing the dynamic and reversible supramolecular complexation between polyvinyl alcohol acetoacetate (PVAA) and Fe3+ ions within 20 s at room temperature. PVAA-Fe hydrogels could be achieved by the simple mixing process of a PVAA aqueous solution with FeCl3 aqueous solution. The soluble PVAA was synthesized by the reaction of PVA with tert-butyl acetoacetate (t-BAA) via transesterification in dimethyl sulfoxide (DMSO). The chemical structure of PVAA was systematically characterized by FT-IR and 1H NMR spectroscopy. The resulting hydrogel showed excellent self-healing behavior without other external stimuli. It was also demonstrated that the PVAA-Fe hydrogel exhibited multi-responsive properties, such as responsiveness to pH, redox, light irradiation and temperature. In addition, the presence of Fe3+ ions and Cl- ions in the gel imparted the PVAA-Fe hydrogel with favorable conductivity. Therefore, the strategy for the facile preparation of the hydrogel in this work could provide a benign and versatile method for achieving multi-functional soft materials for various applications such as smart devices, logic gates, and sensors.

Hydrogels with a Memory: Dual-Responsive, Organometallic Poly(ionic liquid)s with Hysteretic Volume-Phase Transition.

We report on the synthesis and structure-property relations of a novel, dual-responsive organometallic poly(ionic liquid) (PIL), consisting of a poly(ferrocenylsilane) backbone of alternating redox-active, silane-bridged ferrocene units and tetraalkylphosphonium sulfonate moieties in the side groups. This PIL is redox responsive due to the presence of ferrocene in the backbone and also exhibits a lower critical solution temperature (LCST)-type thermal responsive behavior. The LCST phase transition originates from the interaction between water molecules and the ionic substituents and shows a concentration-dependent, tunable transition temperature in aqueous solution. The PIL's LCST-type transition temperature can also be influenced by varying the redox state of ferrocene in the polymer main chain. As the polymer can be readily cross-linked and is easily converted into hydrogels, it represents a new dual-responsive materials platform. Interestingly, the as-formed hydrogels display an unusual, strongly hysteretic volume-phase transition indicating useful thermal memory properties. By employing the dispersing abilities of this cationic PIL, CNT-hydrogel composites were successfully prepared. These hybrid conductive composite hydrogels showed bi-stable states and tunable resistance in heating-cooling cycles.

Highly Swellable, Dual-Responsive Hydrogels Based on PNIPAM and Redox Active Poly(ferrocenylsilane) Poly(ionic liquid)s: Synthesis, Structure, and Properties.

Highly swellable, dual-responsive hydrogels, consisting of thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) and redox-responsive poly(ferrocenylsilane) (PFS) based poly(ionic liquid)s (PILs) are formed by photo-polymerization. PFS chains bearing cross-linkable vinylimidazolium (VIm) side groups are copolymerized with NIPAM in aqueous solutions under ultraviolet light (λ = 365 nm) in the presence of a photoinitiator. The PFS-PILs serve as a macro-cross-linker and also provide redox responsiveness. The swelling ratio, morphology, and lower critical solution temperature (LCST) of the hydrogels are studied as a function of the PNIPAM/PFS ratio. The value of the LCST is dependent on the choice of the counterion of the PIL and the PNIPAM/PFS ratio. The hydrogel is employed as a reducing environment for the in situ fabrication of gold nanoparticles (AuNPs), forming AuNP-hydrogel composites. The localized surface plasmon resonance peak of the as-synthesized Au nanoparticles inside the hydrogel could be tuned by altering the temperature.

Electrografting of stimuli-responsive, redox active organometallic polymers to gold from ionic liquids.

Robust, dense, redox active organometallic poly(ferrocenylsilane) (PFS) grafted films were formed within 5 min by cathodic reduction of Au substrates, immersed in a solution of imidazolium-functionalized PFS chains in the ionic liquid 1-ethyl-3-methylimidazolium ethyl sulfate. The electrografted polymer films were employed as an electrochemical sensor, exhibiting high sensitivity, stability, and reproducibility.

Breathing pores on command: redox-responsive spongy membranes from poly(ferrocenylsilane)s.

Redox-responsive porous membranes can be readily formed by electrostatic complexation between redox active poly(ferrocenylsilane) PFS-based poly(ionic liquid)s and organic acids. Redox-induced changes on this membrane demonstrated reversible switching between more open and more closed porous structures. By taking advantage of the structure changes in the oxidized and reduced states, the porous membrane exhibits reversible permeability control and shows great potential in gated filtration, catalysis, and controlled release.

Green, chemical-free, and high-yielding extraction of nanocellulose from waste cotton fabric enabled by electron beam irradiation.

Recycling and high-value reutilization of waste cotton fabrics (WCFs) has attracted a widespread concern. One potential solution is to extract nanocellulose. Sulfuric acid hydrolysis is a conventional method for the production of nanocellulose with high negative charge from WCFs. However, the recycling and disposal of chemicals in nanocellulose production, along with low yields, remain significant challenges. Consequently, there is a pressing need for a sustainable method to produce nanocellulose at higher yield without the use of chemicals. Herein, we propose a green, sustainable and chemical-free method to extract nanocellulose from WCFs. The nanocellulose displayed a rod-like shape with a length of 50-300 nm, a large aspect ratio of 18.4 ± 2 and the highest yield of up to 89.9 %. The combined short-time and efficient two-step process, involving electron beam irradiation (EBI) and high-pressure homogenization (HPH), offers a simple and efficient alternative approach with a low environmental impact, to extract nanocellulose. EBI induced a noticeable degradation in WCFs and HPH exfoliated cellulose to nano-size with high uniformity via mechanical forces. The as-prepared nanocellulose exhibits excellent emulsifying ability as the Pickering emulsion emulsifier. This work provides a facile and efficient approach for nanocellulose fabrication as well as a sustainable way for recycle and reutilization of the waste cotton fabrics.

Electrothermal Phase Change Composite with Flexibility over a Wide Temperature Range for Wearable Thermotherapy.

Flexible electrothermal composite phase change materials (PCMs) are promising candidates for portable thermotherapy. However, a great challenge remains to achieve high PCM loading while maintaining reasonable flexibility. Herein, the polypyrrole-decorated melamine foam (PPy@MF) was fabricated and thereafter applied to confine binary PCM mixtures composed of a high-enthalpy long-chain polyethylene glycol (PEG4000) and its short-chain homologue (PEG200) to make the novel PPy@MF-PEG4000+200 composite PCM. At a high loading of up to 74.1% PEG4000 and a high latent heat energy storage density of 150.1 J/g, the composite PCM remained flexible at temperature (-20 °C) far below its phase transition point thanks to the plasticine effect of PEG200. The composite also demonstrated good Joule heating performance, providing fast heating from 28 to 70 °C at low applied voltages (4.5-6.0 V). The energy could be stored efficiently and released to maintain the composites at the proper temperature. The electrothermal performance of the composite remained undisturbed during curved or repeated bending, showing good potential to be used for personal thermal management and thermotherapy.

Lightweight and robust cellulose/MXene/polyurethane composite aerogels as personal protective wearable devices for electromagnetic interference shielding.

The increasing electromagnetic pollution is urgently needed as an electromagnetic interference shielding protection device for wearable devices. Two-dimensional transition metal carbides and nitrides (MXene), due to their interesting layered structure and high electrical conductivity, are ideal candidates for constructing efficient conductive networks in electromagnetic interference shielding materials. In this work, lightweight and robust cellulose/MXene/polyurethane composite aerogels were prepared by mixing cellulose nanofiber (CNF) suspensions with MXene, followed by freeze-drying and coating with polyurethane. In this process, CNF effectively assembled MXene nanosheets into a conductive network by enhancing the interactions between MXene nanosheets. The prepared aerogel exhibited the shielding effectiveness of 48.59 dB in the X-band and an electrical conductivity of 0.34 S·cm-1. Meanwhile, the composite aerogel also possessed excellent thermal insulation, infrared stealth, mechanical and hydrophobic properties, and can be used as a wearable protective device to protect the human body from injuries in different scenarios while providing electromagnetic interference shielding protection.

All-cellulose composite yarn via welding engineering.

Due to the wide range of available raw materials and excellent biocompatibility, all-cellulose composites (ACCs) have received significant attention as a kind of renewable and biodegradable candidate to replace petroleum-based synthetic polymers. However, most current research of ACCs is limited to film and bulk materials. Herein, we present a simple, efficient, and scalable welding method for obtaining green, self-reinforced, high performance all-cellulose composite yarns by partially dissolving and regenerating cellulose yarns with phosphoric acid. The in-situ core-shell structure of the welded yarn results in improved strength (134.6 MPa), friction resistance (8000 cycles), moisture regain (11.89 %), and dyeing properties. Moreover, the regeneration and drying procedure can be optimized to further enhance the strength (190.5 MPa) of the welded yarn. This straightforward welding approach provides a promising and convenient route for manufacturing high-performance bio-based yarn.

High tensile regenerated cellulose fibers via cyclic freeze-thawing enabled dissolution in phosphoric acid for textile-to-textile recycling of waste cotton fabrics.

Recycling of waste cotton fabrics (WCFs) is a desirable solution to address the problems brought up by fast fashion, but it remains challenging due to inherent limitations in preparing stable and spinnable dopes by dissolving high molecular weight cellulose efficiently and cost effectively. Herein, we show that despite the prevailing concerns of cellulose degradation via glycosidic hydrolysis when dissolved in acids, fast and non-destructive direct dissolution of WCFs in aqueous phosphoric acid (a.q. PA) could be realized using a cyclic freeze-thawing procedure, which combined with subsequent adjustment of degree of polymerization (DP) and degassing yielded stable and spinnable dopes. Regenerated cellulose fibers (RCFs) with favorable tensile strength (414.2 ± 14.3 MPa) and flexibility (15.4 ± 1.5 %) could be obtained by carefully adjusting the coagulation conditions to induce oriented and compact packing of the cellulose chains. The method was shown to be conveniently extended to dissolve reactively dyed WCFs, showing great potential as a cheap and green alternative to heavily explored ionic liquids (ILs) and N-methylmorpholine-N-oxide (NMMO)-based systems for textile-to-textile recycling of WCFs.

Preparation of high antioxidant nanolignin and its application in cosmetics.

Lignin, as a natural polyphenol, displays anti-oxidant activity by trapping and binding free radicals through its free phenolic hydroxyl groups. However, the most accessible form, industrial lignins, generally has low phenolic hydroxyl content, which severely limits their application value and scenarios. Herein, we showed that potassium-glycerate deep eutectic solvent (PG-DES) treatment can be combined with laccase oxidation to afford prepared high antioxidant lignin nanoparticles (HA-LNPs) with notably improved anti-oxidant activities benefiting from both the enhanced phenolic hydroxyl content 170.8 % and reduced average particle size (59.0 nm). At concentrations as low as 60 µg/mL, HA-LNPs showed favorable effects in promoting collagen formation. When HA-LNPs were used as an active ingredient in the anti-aging mask formulation, the reactive oxygen species (ROS) scavenging activity of mask samples containing 0.4 % HA-LNPs reached 37.2 %. The data suggest great promise of HA-LNPs as a natural antioxidant for formulating in anti-aging skin care products.

Covalent layer-by-layer assembly of redox-active polymer multilayers.

Poly(ferrocenyl(3-bromopropyl)methylsilane) and poly(ethylene imine) are employed in a layer-by-layer deposition process to form covalently connected, redox-active multilayer thin films by means of an amine alkylation reaction. The stepwise buildup of these multilayers on silicon, ITO, and quartz substrates was monitored by UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), static contact angle measurements, surface plasmon resonance (SPR), atomic force microscopy, ellipsometry, and cyclic voltammetry, which provide evidence for a linear increase in multilayer thickness with the number of deposited bilayers. Upon oxidation and reduction, these covalently interconnected layers do not disassemble, in contrast to poly(ferrocenylsilane) (PFS) layers featuring similar backbone structures that are held together by electrostatic forces. The PFS/PEI multilayers are effective for the electrochemical sensing of ascorbic acid and hydrogen peroxide and show improved sensing performance at higher bilayer numbers. These covalently linked layers are readily derivatized further and can therefore be regarded as a versatile platform for creating robust, tailorable, redox-active interfaces with applications in sensing and biofuel cells.

High-tensile chitin films regenerated from cryogenic aqueous phosphoric acid.

The abuse of non-renewable fossil resources and the resulting plastic pollution have posed a great burden on the environment. Fortunately, renewable bio-macromolecules have shown great potential to replace synthetic plastics in fields ranging from biomedical applications, and energy storage to flexible electronics. However, the potential of recalcitrant polysaccharides, such as chitin, in the above-mentioned fields have not been fully exploited because of its poor processability, which is ultimately due to the lack of suitable, economical, and environmentally friendly solvent for it. Herein, we demonstrate an efficient and stable strategy for the fabrication of high-strength chitin films from concentrated chitin solutions in cryogenic 85 wt% aqueous phosphoric acid (aq. H3PO4). The regeneration conditions, including the nature of the coagulation bath and its temperature are important variables affecting the reassembly of chitin molecules and hence the structure and micromorphology of the films. Uniaxial orientation of the chitin molecules by applying tension to the RCh hydrogels further endows the films with enhanced mechanical properties of up to 235 MPa and 6.7 GPa in tensile strength and Young's modulus, respectively.

Highly stretchable porous regenerated silk fibroin film for enhanced wound healing.

Silk fibroin (SF) has received interest in tissue engineering owing to its biocompatibility, biodegradability, and favorable mechanical properties. However, the complex preparation, brittleness, and lack of pores in the structure of the silk fibroin film limit its application. Herein, we show that facile dissolution of SF in aqueous phosphoric acid followed by regeneration in aqueous ammonium sulfate ((NH4)2SO4) could afford highly stretchable films with nano-pores formed in the nonsolvent-induced phase separation process. The named phase separation, which determines the morphology and mechanical properties of the regeneration silk fibroin (RSF) films, is highly dependent on the (NH4)2SO4 concentration as well as the initial concentration of the SF solution. Therefore, the RSF films exhibit a tunable pore size ranging from 230 to 510 nm and excellent stretchability with tensile strain up to 143 ± 16%. Most interestingly, the RSF films were shown to support the proliferation of human skin fibroblasts in vitro as well as speed up full-thickness skin wound healing in a rat model. This work establishes an easy and feasible method to access porous RSF membranes that can be used for wound dressing in clinical settings.

Composite hydrogel based oxidated sodium carboxymethyl cellulose and gelatin loaded carboxymethylated cotton fabric for hemostasis and infected wound treatment.

The fabric-based wound dressings are hard to maintain a moist environment for wound healing while the hemostatic property and gas permeability of some hydrogel-based wound dressings are not ideal. This study first put forward a strategy of checkerboard-pattern wound dressing: 1) preparing the base fabric with hemostatic property, 2) printing multifunctional hydrogels onto one side of the base fabric to form checkerboard patterns, 3) modifying the other side of the base fabric to be hydrophobic. In this manner, the composite dressing not only maintained the advantages of hydrogels, but also inherited good mechanical property, hemostatic property, and gas permeability from the base fabric. Here, the cotton fabric was carboxymethylated to be MCF. To obtain multifunctional hydrogel, sodium carboxymethylcellulose was oxidated to introduce aldehyde groups to form Schiff base with amino groups in gelatin, besides, dopamine and Ag nanoparticles were introduced to endow the hydrogel with antioxidant property and antibacterial activity. The multifunctional hydrogel was printed onto one side of MCF, subsequently, the deposition of paraffin made the other side of this dressing become hydrophobic. The good performance of the obtained dressing in hemostatic process and wound healing demonstrated its potential in the field of wound treatment.

A one-pot approach to prepare stretchable and conductive regenerated silk fibroin/CNT films as multifunctional sensors.

Silk fibroin (SF)-based materials are characterized by their outstanding biocompatibility and biodegradability and are considered as the most promising candidates for next-generation flexible electronics. In order to generate such devices, SF can be mixed with carbon nanotubes (CNTs) which feature excellent mechanical, electrical, and thermal properties. However, obtaining regenerated SF with homogeneous dispersion of CNTs in a sustainable manner represents a challenging task, mainly due to the difficulty in overcoming van der Waals forces and strong π-π interactions that hold together the CNT structure. In this study, a one-pot strategy for fabricating SF/CNT films is proposed by designing SF as a modifier of CNTs through non-covalent interactions with the assistance of aqueous phosphoric acid solution. Glycerol (GL) was introduced, endowing the SF/GL/CNT composite film with excellent flexibility and stretchability. The sustainable strategy greatly simplifies the preparation process, avoiding dialysis of SF and the use of artificial dispersants. The as-fabricated SF/GL/CNT films showed an excellent mechanical strength of 1.20 MPa and high sensitivity with a gauge factor of up to 13.7 toward tensile deformation. The composite films had a sensitive monitoring capability for small strains with detection limits as low as 1% and can be assembled into versatile sensors to detect human movement. Simultaneously, the composite films showed a superb thermosensitive capacity (1.64% °C-1), which satisfied the requirement of real-time and continuous skin temperature monitoring. We anticipate that the presented one-pot strategy and the prepared composite films could open a new avenue for forthcoming technologies for electronic skins, personal health monitoring, and wearable electronics.

High-tensile regenerated cellulose films enabled by unexpected enhancement of cellulose dissolution in cryogenic aqueous phosphoric acid.

We have demonstrated, for the first time, high-efficient non-destructive and non-derivative dissolution of cellulose could be achieved in cryogenic aqueous phosphoric acid. Cellulose from different sources and of varying degree of polymerization from 200 (MCC) to 2200 (cotton fabric) could be dissolved completely to afford solutions containing 5 wt%-18 wt% cellulose, from which ultra-strong and tough cellulose films of tensile strength as high as 707 MPa could be obtained using water as the coagulant. These solutions can be stored at -18 °C for extended time without noticeable degradation while desired degree of polymerization is also attainable by tuning the storage conditions. The findings of this work call for renewal attention on phosphoric acid as a promising cellulose solvent for being non-toxic, non-volatile, easy to handle, and cost-effective.