Advanced Functionalized Materials Based on Layer-by-Layer Assembled Natural Cellulose Nanofiber for Electrodes: A Review.

The depletion of fossil fuel resources and its impact on the environment provide a compelling motivation for the development of sustainable energy sources to meet the increasing demand for energy. Accordingly, research and development of energy storage devices have emerged as a critical area of focus. The electrode materials are critical in the electrochemical performance of energy storage devices, such as energy storage capacity and cycle life. Cellulose nanofiber (CNF) represents an important substrate with potentials in the applications of green electrode materials due to their environmental sustainability and excellent compatibility. By utilizing the layer-by layer (LbL) process, well-defined nanoscale multilayer structure is prepared on a variety of substrates. In recent years, increasing attention has focused on electrode materials produced from LbL process on CNFs to yield electrodes with exceptional properties, such as high specific surface area, outstanding electrical conductivity, superior electrochemical activity, and exceptional mechanical stability. This review provides a comprehensive overview on the development of functional CNF via the LbL approach as electrode materials.

Aqueous Sol-Gel Synthesis and Shaping of Covalent Organic Frameworks.

The intrinsic fragility and insoluble nature of covalent organic frameworks (COFs) have strongly impeded their processability for practical applications. Herein, an aqueous-based sol-gel synthetic strategy is reported for the synthesis and shaping of COFs with task-specific applications that satisfy the principles of green chemistry for gram-scale production of crystalline materials. Our successful approach involves three pivotal aspects: the "prodrug mimic" design of water-soluble monomers, the utilization of hydrolyzable bonds, and the manipulation of reaction kinetics. The generality of the method is demonstrated by the successful preparation of representative high-surface area two-dimensional (2D) COFs with several commonly used amines. By virtue of this strategy, a COF colloidal dispersion is achieved and can be formulated into processable fluids, structured films, and COF monoliths. Remarkably, the obtained lightweight (∼0.020 g cm-3) and robust aerogels displayed outstanding adsorption capacity (exceeding 57 times its own weight) toward a variety of organic solvents and exhibited superior thermal insulating properties compared to the widely used sponge and cotton. This work demonstrates a versatile strategy for the synthesis and shaping of processable COF materials in water that will contribute to the development of COF monoliths for advanced applications.

Surface Modification, Topographic Design and Applications of Superhydrophobic Systems.

Superhydrophobic surfaces with expanded wetting behaviors, like tunable adhesion, hybrid surface hydrophobicity and smart hydrophobic switching have attracted increasing attention due to their broad applications. Herein, the construction methods, mechanisms and advanced applications of special superhydrophobicity are reviewed, and hydro/superhydrophobic modifications are categorized and discussed based on their surface chemistry, and topographic design. The formation and maintenance of special superhydrophobicity in the metastable state are also examined and explored. In addition, particular attention is paid to the use of special wettability in various applications, such as membrane distillation, droplet-based electricity generators and anti-fogging surfaces. Finally, the challenges for practical applications and future research directions are discussed.

Sustainable Superhydrophobic Surface with Tunable Nanoscale Hydrophilicity for Water Harvesting Applications.

Superwettable surfaces show great potential in water harvesting applications, however, a scalable water harvesting surface remains elusive due to the trade-off between water deposition and transport. Herein, we report a unique superhydrophobic surface with tunable nanoscale hydrophilicity constructed by structured Pickering emulsions. Preferential exposure of the cellulose nanocrystal's outer surface and wax microspheres accelerates droplet deposition allowing for the manipulation of droplet mobility. Appropriate tuning of the wetting characteristics of the surfaces, optimizing the hydrophobicity and density of the water affinity nanodomains enhance the water deposition rate without the sacrifice of water transport rate, achieving an optimal water harvesting flux of 3.402 L m-2 h-1 for a plate and 5.02 L m-2 h-1 for a mesh. This hydrophilic/superhydrophobic surface allows the controllable manipulation of droplet nucleation and removal to enhance the water harvesting efficiency.

Use of isothermal titration calorimetry to study surfactant aggregation in colloidal systems.

BACKGROUND: Isothermal titration calorimetry (ITC) is a general technique that allows for precise and highly sensitive measurements. These measurements may provide a complete and accurate thermodynamic description of association processes in complex systems such as colloidal mixtures. SCOPE OF THE REVIEW: This review will address uses of ITC for studies of surfactant aggregation to form micelles, with emphasis on the thermodynamic studies of homologous surfactant series. We will also review studies on surfactant association with polymers of different molecular characteristics and with colloidal particles. GENERAL SIGNIFICANCE: ITC studies on the association of different homologous series of surfactants provide quantitative information on independent contribution from their apolar hydrocarbon chains and polar headgroups to the different thermodynamic functions associated with micellization (Gibbs energy, enthalpy and entropy). Studies on surfactant association to polymers by ITC provide a comprehensive description of the association process, including examples in which particular features revealed by ITC were elucidated by using ancillary techniques such as light or X-ray scattering measurements. Examples of uses of ITC to follow surfactant association to biomolecules such as proteins or DNA, or nanoparticles are also highlighted. Finally, recent theoretical models that were proposed to analyze ITC data in terms of binding/association processes are discussed. MAJOR CONCLUSIONS: This review stresses the importance of using direct calorimetric measurements to obtain and report accurate thermodynamic data, even in complex systems. These data, whenever possible, should be confirmed and associated with other ancillary techniques that allow elucidation of the nature of the transformations detected by calorimetric results, providing a complete description of the process under scrutiny.

Poly(2-oxazoline)-based nanogels as biocompatible pseudopolypeptide nanoparticles.

Hydrophilic nanogels based on partially hydrolyzed poly(2-ethyl-2-oxazoline) were synthesized in dilute aqueous media in the presence of 1,6-hexanediol diglycidyl ether as a cross-linker. Nanogel formation was monitored by DLS and HSQC NMR spectroscopy, and the final nano-objects were characterized by DLS, TEM, AFM, and NanoSight analyses. Nanogels with a hydrodynamic radius of 78 nm exhibiting a slight positive surface charge were obtained. MTS assays (cell metabolic activity test) evidenced that nanogels were nontoxic in the investigated concentration range (i.e., 0.1 to 400 µg/mL) and that no specific interaction with bovine serum albumin was observed.

Stimuli-responsive Pickering emulsions: recent advances and potential applications.

Pickering emulsions possess many advantages over traditional surfactant stabilized emulsions. For example, Pickering emulsions impart better stability against coalescence and, in many cases, are biologically compatible and environmentally friendly. These characteristics open the door for their use in a variety of industries spanning petroleum, food, biomedicine, pharmaceuticals, and cosmetics. Depending on the application, rapid, but controlled stabilization and destabilization of an emulsion may be necessary. As a result, Pickering emulsions with stimuli-responsive properties have, in recent years, received a considerable amounts of attention. This paper provides a concise and comprehensive review of Pickering emulsion systems that possess the ability to respond to an array of external triggers, including pH, temperature, CO2 concentration, light intensity, ionic strength, and magnetic field. Potential applications for which stimuli-responsive Pickering emulsion systems would be of particular value, such as emulsion polymerization, enhanced oil recovery, catalyst recovery, and cosmetics, are discussed.

Crystallisation-driven self-assembly of poly(2-isopropyl-2-oxazoline)-block-poly(2-methyl-2-oxazoline) above the LCST.

The solution behaviour in water of a polyoxazoline-type block copolymer, namely poly(2-isopropyl-2-oxazoline)-block-poly(2-methyl-2-oxazoline), denoted as P(iPrOx-b-MeOx), above the lower critical solution temperature (LCST) of the PiPrOx block was exploited to induce a temporary or permanent self-assembly. Spherical micelles were first obtained and could be disassembled in a reversible manner when kept for a short period of time (i.e. t < 90 min) above the LCST, and cooled down to room temperature. In contrast, annealing the copolymer solution for more than 90 min at 65 °C induced the crystallisation of the PiPrOx block, as evidenced by wide angle X-ray scattering (WAXS) experiments. This crystallisation-driven self-assembly phenomenon resulted in different morphologies, including spherical and distorted crystallised micelles and micron-size fibers, their relative proportion varies with the annealing time. Formation of micron-size range fiber-like structures might be explained by the re-organization of parent crystallised micelles. The crystal structure, as determined by WAXS, appeared to be identical to that of the PiPrOx homopolymer.

Modified cellulose nanocrystal for vitamin C delivery.

Cellulose nanocrystal grafted with chitosan oligosaccharide (CNC-CSOS) was used to encapsulate vitamin C and prepare CNCS/VC complexes using tripolyphosphte via ionic complexation. The stability of vitamin C and the antioxidant activity of the CNCS/VC complexes were elucidated. The formation of the complex was confirmed using DSC and UV-vis spectrophotometry, and TEM was used to study the morphology of the complexes. The encapsulation efficiency of vitamin C at pH 3 and 5 was 71.6% ± 6.8 and 91.0 ± 1.0, respectively. Strong exothermic peaks observed in isothermal titration calorimetric (ITC) studies at pH 5 could be attributed to additional electrostatic interactions between CNC-CSOS and vitamin C at pH 5. The in vitro release of vitamin C from CNCS/VC complexes showed a sustained release of up to 20 days. The vitamin C released from CNCS/VC complex displayed higher stability compared with the control vitamin C solution, and this was also confirmed from the ITC thermograms. CNC-CSOS possessed a higher scavenging activity and faster antioxidant activity compared with its precursors, i.e., oxidized CNC and CSOS and their physical mixtures. Complexing vitamin C into CNC-CSOS particles yielded a dynamic antioxidant agent, where the vitamin C is released over time and displayed sustained antioxidant properties. Therefore, CNCS/VC can potentially be used in cosmeceutical applications as topical formulations.

Enzyme-degradable self-assembled nanostructures from polymer-peptide hybrids.

The peptide PVGLIG, which is known to be selectively cleaved by the tumor-associated enzyme matrix metalloproteinase-2 (MMP-2), was conjugated to α-alkene poly(trimethylene carbonate) (PTMC) blocks of varying sizes via UV-initiated thiol-ene "click" chemistry. The PTMC precursor was synthesized by metal-free ring-opening polymerization using allyl alcohol as an initiator and an N-heterocyclic carbene as an organic catalyst. The unprecedented PVGLIG-b-PTMC hybrids were self-assembled in aqueous solution and various submicrometer-sized morphologies obtained by a nanoprecipitation process. Characterization of particle morphology was carried out by multiangle dynamic light scattering (DLS) and static light scattering (SLS) evidencing spherical nanoparticles with different morphologies and narrow size distributions. Microstructure details were also observed on transmission electron micrographs and were in good agreement with light scattering measurements showing the assembly of core-shell, large compound micelles, and vesicle morphologies, the particle morphology varying with the hydrophilic weight fractions (f) of the hybrids. These nanostructures displayed selective degradation in the presence of the cancer-associated enzyme MMP-2, as probed by the morphological change both by TEM and DLS. All these results demonstrated that PVGLIG-b-PTMC hybrids were suitable to target the tumor microenvironment.

Thermo-adaptive interfacial solar evaporation enhanced by dynamic water gating.

Solar-driven evaporation offers a sustainable solution for water purification, but efficiency losses due to heat dissipation and fouling limit its scalability. Herein, we present a bilayer-structured solar evaporator (SDWE) with dynamic fluidic flow mechanism, designed to ensure a thin water supply and self-cleaning capability. The porous polydopamine (PDA) layer on a nickel skeleton provides photothermal functionality and water microchannels, while the thermo-responsive sporopollenin layer on the bottom acts as a switchable water gate. Using confocal laser microscopy and micro-CT, we demonstrate that this unique structure ensures a steady supply of thin water layers, enhancing evaporation by minimizing latent heat at high temperatures. Additionally, the system initiates a self-cleaning process through bulk water convection when temperature drops due to salt accumulation, thus maintaining increased evaporation efficiency. Therefore, the optimized p-SDWE sample achieved a high evaporation rate of 3.58 kg m-2 h-1 using 93.9% solar energy from 1 sun irradiation, and produces 18-22 liters of purified water per square meter of SDWE per day from brine water. This dynamic water transport mechanism surpasses traditional day-night cycles, offering inherent thermal adaptability for continuous, high-efficiency evaporation.

Tailoring Hydronium ion Driven Dissociation-Chemical Cross-Linking for Superfast One-Pot Cellulose Dissolution and Derivatization to Build Robust Cellulose Films.

Concepts of sustainability must be developed to overcome the increasing environmental hazards caused by fossil resources. Cellulose derivatives with excellent properties are promising biobased alternatives for petroleum-derived materials. However, a one-pot route to achieve cellulose dissolution and derivatization is very challenging, requiring harsh conditions, high energy consumption, and complex solubilizing. Herein, we design a one-pot tailoring hydronium ion driven dissociation-chemical cross-linking strategy to achieve superfast cellulose dissolution and derivatization for orderly robust cellulose films. In this strategy, there is a powerful driving force from organic acid with a pKa below 3.75 to dissociate H+ and trigger the dissolution and derivatization of cellulose under the addition of H2SO4. Nevertheless, the driving force can only trigger a partial swelling of cellulose but without dissolution when the pKa of organic acid is above 4.26 for the dissociation of H+ is inhibited by the addition of inorganic acid. The cellulose film has high transmittance (up to ∼90%), excellent tensile strength (∼122 MPa), and is superior to commercial PE film. Moreover, the tensile strength is increased by 400% compared to cellulose film prepared by the ZnCl2 solvent. This work provides an efficient solvent, which is of great significance for emerging cellulose materials from renewable materials.

Application of Pickering emulsions in probiotic encapsulation- A review.

Probiotics are live microorganisms that confer health benefits to host organisms when consumed in adequate amounts and are often incorporated into foods for human consumption. However, this has negative implications on their viability as large numbers of these beneficial bacteria are deactivated when subjected to harsh conditions during processing, storage, and passage through the gastrointestinal tract. To address these issues, numerous studies on encapsulation techniques to protect probiotics have been conducted. This review focuses on emulsion technology for probiotic encapsulation, with a special focus on Pickering emulsions. Pickering emulsions are stabilized by solid particles, which adsorb strongly onto the liquid-liquid interfaces to prevent aggregation. Pickering emulsions have demonstrated enhanced stability, high encapsulation efficiency, and cost-effectiveness compared to other encapsulation techniques. Additionally, Pickering emulsions are regarded as safe and biocompatible and utilize natural materials, such as cellulose and chitosan derived from plants, shellfish, and fungi, which may also be viewed as more acceptable in food systems than common synthetic and natural molecular surfactants. This article reviews the current status of Pickering emulsion use for probiotic delivery and explores the potential of this technique for application in other fields, such as livestock farming, pet food, and aquaculture.

Cellulose-based aerogel beads for efficient adsorption- reduction- sequestration of Cr(VI).

The reduction and sequestration of toxic Cr(VI) via a one-step process in an aqueous solution is critical to eliminate its environmental risk. In this study, amine functionalized cellulose-based aerogel beads (CGP) was developed for simultaneous and efficient adsorption- reduction- sequestration of Cr(VI). CGP showed a maximum Cr(VI) adsorption capacity of 386.40 mg/g at 25 °C due to its strong electrostatic attraction towards Cr(VI). The simultaneous Cr(VI) adsorption- reduction- sequestration performance of CGP over a wide Cr(VI) concentration range was examined. The mechanism was investigated in-depth via the analysis of adsorption kinetics, XPS spectra, and FTIR spectra. Moreover, the Cr immobilization stability of CGP after adsorption was evaluated in simulated neutral, acidic, and alkaline conditions. The effect of pH, temperature, ionic strength and the presence of interfering ions on CGP adsorption performance were investigated by batch adsorption experiments. Fixed-bed column adsorption study was performed to explore the application potential of CGP beads in a wastewater treatment process.

Synthesis of silver nanoclusters in colloidal scaffold for biolabeling and antimicrobial applications.

A robust method to prepare silver nanoclusters (AgNCs) inside a methacrylic acid-ethyl acrylate (MAA-EA) nanogel is proposed, where AgNCs were produced within the nanogel scaffold via UV-photoreduction. The impact of UV irradiation time on the formation of AgNCs and their application in biolabeling and antimicrobial properties were examined. The AgNCs formation is described by two stages; (1) Agn (n = 2-8) nanoclusters formation between 0 and 25 min, and (2) larger silver nanoparticles (AgNPs) formed via aggregation inside the nanogel. The antimicrobial performance depended on the size and concentration of silver ions (Ag+). A maximum inhibitory concentration (MIC) of 1.1 ppm was observed for antimicrobial test with yeast, and a MIC of 11 and 22 ppm was recorded for Escherichia. coli and Staphylococcus aureus respectively. Combining with the green illumination property of AgNCs (emitted at 525 nm) with dead yeast, it could be used for biolabeling. By tuning the size through photoirradiation, the nanogel templated AgNCs is a promising candidate for antimicrobial and biolabeling applications.

Topographical Design and Thermal-Induced Organization of Interfacial Water Structure to Regulate the Wetting State of Surfaces.

Smart surfaces with superhydrophobic/superhydrophilic characteristics can be controlled by external stimuli, such as temperature. These transitions are attributed to the molecular-level conformation of the grafted polymer chains due to the varied interactions at the interface. Here, tunable surfaces were prepared by grafting two well-known thermo-responsive polymers, poly(N-isopropylacrylamide) (PNIPAM) and poly(oligoethylene glycol)methyl ether acrylate (POEGMA188) onto micro-pollen particles of uniform morphology and roughness. Direct Raman spectra and thermodynamic analyses revealed that above the lower critical solution temperature, the bonded and free water at the interface partially transformed to intermediate water that disrupted the "water cage" surrounding the hydrophobic groups. The increased amounts of intermediate water produced hydrogen bonding networks that were less ordered around the polymer grafted microparticles, inducing a weaker binding interaction at the interface and a lower tendency to wet the surface. Combining the roughness factor, the bulk surface assembled by distinct polymer-grafted-pollen microparticles (PNIPAM or POEGMA188) could undergo a different wettability transition for liquid under air, water, and oil. This work identifies new perspectives on the interfacial water structure variation at a multiple length scale, which contributed to the temperature-dependent surface wettability transition. It offers inspiration for the application of thermo-responsive surface to liquid-gated multiphase separation, water purification and harvesting, biomedical devices, and printing.

Flexible, anti-damage, and non-contact sensing electronic skin implanted with MWCNT to block public pathogens contact infection.

If a person comes into contact with pathogens on public facilities, there is a threat of contact (skin/wound) infections. More urgently, there are also reports about COVID-19 coronavirus contact infection, which once again reminds that contact infection is a very easily overlooked disease exposure route. Herein, we propose an innovative implantation strategy to fabricate a multi-walled carbon nanotube/polyvinyl alcohol (MWCNT/PVA, MCP) interpenetrating interface to achieve flexibility, anti-damage, and non-contact sensing electronic skin (E-skin). Interestingly, the MCP E-skin had a fascinating non-contact sensing function, which can respond to the finger approaching 0-20 mm through the spatial weak field. This non-contact sensing can be applied urgently to human-machine interactions in public facilities to block pathogen. The scratches of the fruit knife did not damage the MCP E-skin, and can resist chemical corrosion after hydrophobic treatment. In addition, the MCP E-skin was developed to real-time monitor the respiratory and cough for exercise detection and disease diagnosis. Notably, the MCP E-skin has great potential for emergency applications in times of infectious disease pandemics. Electronic Supplementary Material: Supplementary material (fabrication of MCP E-skin, laser confocal tomography, parameter optimization, mechanical property characterization, finite element simulation, sensing mechanism, signal processing) is available in the online version of this article at 10.1007/s12274-021-3831-z.

Stimuli-responsive water-soluble fullerene (C60) polymeric systems.

This review documents the advances in stimuli-responsive water-soluble fullerene (C(60)) polymeric systems. Stimuli-responsive polymers, when grafted onto C(60) impart "smart" and "responsive" characteristics, and these novel materials adopt various morphologies when subjected to external stimuli, such as pH, temperature, and salt. Various synthetic approaches for producing C(60)-polymers are outlined and discussed. The responsive behavior, water solubility, and self-assembly characteristics of these C(60)-polymers make them attractive for applications such as drug delivery, temperature sensors, and personal care.

Co(III)-Salen immobilized cellulose nanocrystals for efficient catalytic CO2 fixation into cyclic carbonates under mild conditions.

Searching for green, recyclable and highly efficient catalyst for the synthesis of cyclic carbonates from CO2 is of great importance because it is profitable for reducing the greenhouse effects and meets the principles of green chemistry. Herein, a series of cellulose nanocrystals, either the pristine or modified ones (TEMPO oxidized and Co(III)salen immobilized), were explored as catalysts for cycloaddition of epoxides and carbon dioxide. The impact of surface properties on the performance of the as-made catalysts was investigated. Co(III)-salen grafted cellulose nanocrystals was proven to be the most effective catalyst in this study, which could afford excellent yield up to 99 % after 24 h even under low CO2 pressures of 0.1 MPa. They can be easily recovered and reused for at least 4 times, demonstrating their excellent stability. We found that the surface functional groups such as enriched sulfate or carboxylic groups could also account for the enhanced catalytic activity. This work highlights the applications of green and sustainable nanoparticles in a cycloaddition reaction and offers a sustainable solution in industrial catalysis related to CO2 conversions.