Multiscale MXene Engineering for Enhanced Capacitive Deionization via Adaptive Surface Charge Tailoring

Capacitive deionization (CDI), renowned for its eco-friendly and low-energy approach to water treatment, encounters challenges in achieving optimal deionization efficiency and cycle stability despite recent advancements. In this study, the CDI electrodes were crafted with multilevel pore structures using modified cellulose (MCNF) and porous activated MXene (PAMX), aiming to the impact of surface modification on adsorption efficiency, stability, and overall performance. The experimental results demonstrated the superiority of the electrode, specifically the formulation integrating sulfonic acid-treated cellulose and PAMX (SCNF@PAMX). This configuration exhibited remarkably a higher desalination rate (3.91 mg·g-1·min-1) and enhanced desalination capacity (31.24 mg·g-1), with cycling performance exceeding 90%. Density functional theory calculations underscored the formidable adsorption energy of SCNF for Na+ (2.15 eV), surpassing that of other modified electrodes. The enhancement of deionization performance and efficiency through surface charge modification, altering Na+ electrostatic adsorption, lays a solid foundation for advancing more efficient and durable seawater desalination technologies.

Structural Color from Cellulose Nanocrystals or Chitin Nanocrystals: Self-Assembly, Optics, and Applications

Widespread concerns over the impact of human activity on the environment have resulted in a desire to replace artificial functional materials with naturally derived alternatives. As such, polysaccharides are drawing increasing attention due to offering a renewable, biodegradable, and biocompatible feedstock for functional nanomaterials. In particular, nanocrystals of cellulose and chitin have emerged as versatile and sustainable building blocks for diverse applications, ranging from mechanical reinforcement to structural coloration. Much of this interest arises from the tendency of these colloidally stable nanoparticles to self-organize in water into a lyotropic cholesteric liquid crystal, which can be readily manipulated in terms of its periodicity, structure, and geometry. Importantly, this helicoidal ordering can be retained into the solid-state, offering an accessible route to complex nanostructured films, coatings, and particles. In this review, the process of forming iridescent, structurally colored films from suspensions of cellulose nanocrystals (CNCs) is summarized and the mechanisms underlying the chemical and physical phenomena at each stage in the process explored. Analogy is then drawn with chitin nanocrystals (ChNCs), allowing for key differences to be critically assessed and strategies toward structural coloration to be presented. Importantly, the progress toward translating this technology from academia to industry is summarized, with unresolved scientific and technical questions put forward as challenges to the community.

Controlling the critical parameters of ultrasonication to affect the dispersion state, isolation, and chiral nematic assembly of cellulose nanocrystals

Cellulose nanocrystals (CNCs) are typically extracted from plants and present a range of opto-mechanical properties that warrant their use for the fabrication of sustainable materials. While their commercialization is ongoing, their sustainable extraction at large scale is still being optimized. Ultrasonication is a well-established and routinely used technology for (re-) dispersing and/or isolating plant-based CNCs without the need for additional reagents or chemical processes. Several critical ultrasonication parameters, such as time, amplitude, and energy input, play dominant roles in reducing the particle size and altering the morphology of CNCs. Interestingly, this technology can be coupled with other methods to generate moderate and high yields of CNCs. Besides, the ultrasonics treatment also has a significant impact on the dispersion state and the surface chemistry of CNCs. Accordingly, their ability to self-assemble into liquid crystals and subsequent superstructures can, for example, imbue materials with finely tuned structural colors. This article gives an overview of the primary functions arising from the ultrasonication parameters for stabilizing CNCs, producing CNCs in combination with other promising methods, and highlighting examples where the design of photonic materials using nanocrystal-based celluloses is substantially impacted.

Improving the decorative performance of UV-curable coatings with iridescent cellulose nanocrystal film

Cellulose nanocrystals (CNC) possess remarkable mechanical properties, a high aspect ratio, a large specific surface area, and a unique nanostructure, making them a popular choice in various fields. In this study, a CNC suspension was prepared through acid hydrolysis, and subsequently, a film exhibiting iridescence and chiral nematic structure was formed on the cured UV-WA surface via evaporation-induced self-assembly. The mean diameter and length of CNC were determined to be 25.1-33.3 nm and 281.3-404.2 nm, respectively, through transmission electron microscope analysis. The experimental results revealed that the color of the film significantly changes with variations in the CNC suspension concentration. Notably, the formation of the iridescent film is dependent on the concentration of CNC, with concentrations between 1.2% and 2.9% being optimal, and the aspect ratio of the CNC nanoparticles being around 11.3. X-ray diffraction analysis confirmed that the CNC nanoparticles possess the same crystal structure as microcrystalline cellulose (cellulose I). Fourier transform infrared spectroscopy revealed that the C[double bond, length as m-dash]C bond present in the liquid UV-curable coating disappeared upon UV irradiation. The performance of the CNC iridescent film, with varying thickness, was evaluated using UV-vis spectroscopy. The thermogravimetric analysis results indicate that the addition of CNC enhances the membrane's thermal stability and heat resistance. The results indicate that as the thickness of the CNC iridescent film increases, the corresponding UV-vis spectra display a redshift. The UV-WA/CNC shows potential in the field of decoration and establishing a straightforward, cost-effective, and efficient method for producing photonic materials with structural colors.

Accelerating Cellulose Nanocrystal Assembly into Chiral Nanostructures

Cellulose nanocrystal (CNC) suspensions self-assembled into chiral nematic liquid crystals. This property has enabled the development of versatile optical materials with fascinating properties. Nevertheless, the scale-up production and commercial success of chiral nematic CNC superstructures face significant challenges. Fabrication of chiral nematic CNC nanostructures suffers from a ubiquitous pernicious trade-off between uniform chiral nematic structure and rapid self-assembly. Specifically, the chiral nematic assembly of CNCs is a time-consuming, spontaneous process that involves the organization of particles into ordered nanostructures as the solvent evaporates. This review is driven by the interest in accelerating chiral nematic CNC assembly and promoting a long-range oriented chiral nematic CNC superstructure. To start this review, the chirality origins of CNC and CNC aggregates are analyzed. This is followed by a summary of the recent advances in stimuli-accelerated chiral nematic CNC self-assembly procedures, including evaporation-induced self-assembly, continuous coating, vacuum-assisted self-assembly, and shear-induced CNC assembly under confinement. In particular, stimuli-induced unwinding, alignment, and relaxation of chiral nematic structures were highlighted, offering a significant link between the accelerated assembly approaches and uniform chiral nematic nanostructures. Ultimately, future opportunities and challenges for rapid chiral nematic CNC assembly are discussed for more innovative and exciting applications.

Electrochemical paper-based antigen sensing platform using plant-derived monoclonal antibody for detecting SARS-CoV-2

The current approaches of diagnostic platforms for detecting SARS-CoV-2 infections mostly relied on adapting the existing technology. In this work, a simple and low-cost electrochemical sensing platform for detecting SAR-CoV-2 antigen was established. The proposed sensor combined the innovative disposable paper-based immunosensor and cost-effective plant-based anti-SARS-CoV-2 monoclonal antibody CR3022, expressed in Nicotiana benthamiana. The cellulose nanocrystal was modified on screen-printed graphene electrode to provide the abundant COOH functional groups on electrode surface, leading to the high ability for antibody immobilization. The quantification of the presence receptor binding domain (RBD) spike protein of SARS-CoV-2 was performed using differential pulse voltammetry by monitoring the changing current of [Fe(CN)6]3-/4- redox solution. The current change of [Fe(CN)6]3-/4- before and after the presence of target RBD could be clearly distinguished, providing a linear relationship with RBD concentration in the range from 0.1 pg/mL to 500 ng/mL with the minimum limit of detection of 2.0 fg/mL. The proposed platform was successfully applied to detect RBD in nasopharyngeal swab samples with satisfactory results. Furthermore, the paper-based immunosensor was extended to quantify the RBD level in spiked saliva samples, demonstrating the broadly applicability of this system. This electrochemical paper-based immunosensor has the potential to be employed as a point-of-care testing for COVID-19 diagnosis.

Biomimetic Chiral Photonic Materials with Tunable Metallic Colorations Prepared from Chiral Melanin-like Nanorods for UV Shielding, Humidity Sensing, and Cosmetics

Many biological species combine the helical organization of cellulose or chitin microfibrils with broadband light absorption of black melanin to produce brilliant structural colors with metallic and glossy effects and other diverse functions. In this work, based on core-shell CNC@PDA chiral nanorods consisting of cellulose nanocrystals (CNCs) as the core and melanin-like polydopamine (PDA) as the shell that can form well-defined chiral liquid crystal phases, we report chiral photonic materials that closely mimic the unique coloration mechanisms and functionalities mastered by several biological species. The photonic films formed by such single CNC@PDA nanorods have brilliant iridescent structural colors originating from selective reflection of circularly polarized lights by the helical organization of CNC@PDAs across the films. Furthermore, the colors of such films have background-independent brightness, high visibility, and metallic effects that arise from the light absorption of the PDA component. Especially, the color ranges and metallic effects of the films can be conveniently tuned by varying the thickness of the PDA shell. In addition, the UV absorption and hygroscopic properties of PDA endow these CNC@PDA films with efficient broadband UV shielding and sensitive humidity-induced dynamic color changes. Due to the mussel-like superior adhesion of PDA, CNC@PDA-based photonic coatings can be formed conformably onto diverse kinds of substrates. A shiny eye shadow with viewing angle-dependent colorful patterns was used to demonstrate the potential applications. With combinations of multiple unique properties in one photonic material fabricated from a single building block, these CNC@PDA-based films are expected to have potential applications in cosmetics, UV protection, anticounterfeiting, chiral reflectors, etc.

Ultrasonication pretreatment assisted rapid co-assembly of cellulose nanocrystal and metal ion for multifunctional application

Co-assembly of metal ion and cellulose nanocrystals (CNC) is a promising strategy to fabricate novel iridescent CNC materials with advanced applications. By combining ultrasonication pretreatment and vacuum-assisted self-assembly (VASA) technique, a facile and rapid strategy is proposed to prepare the Mn²⁺-doped carboxylated CNC (C-CNC) iridescent films with multifunctional application. The ultrasonication pretreatment temporarily disassembles the aggregates of C-CNC nanorods caused by the electrostatic interaction between negative charged C-CNC and Mn²⁺. The subsequent VASA process accelerates the self-assembly of chiral liquid crystals prior to the re-agglomeration of C-CNC by the bridge effect of Mn²⁺. Furthermore, the as-prepared Mn²⁺/CNC film exhibits a rapid and visible color change in ammonia atmosphere along with the formation of MnO₂. The reversible change can be realized by the stimulation of reducing agent. The derived MnO₂/C-CNC composite film displays efficient removal of methylene blue dye in aqueous solution by both of adsorption and degradation procedure.

Cellulose Nanocrystals/Graphene Hybrids-A Promising New Class of Materials for Advanced Applications

With the growth of global fossil-based resource consumption and the environmental concern, there is an urgent need to develop sustainable and environmentally friendly materials, which exhibit promising properties and could maintain an acceptable level of performance to substitute the petroleum-based ones. As elite nanomaterials, cellulose nanocrystals (CNC) derived from natural renewable resources, exhibit excellent physicochemical properties, biodegradability and biocompatibility and have attracted tremendous interest nowadays. Their combination with other nanomaterials such as graphene-based materials (GNM) has been revealed to be useful and generated new hybrid materials with fascinating physicochemical characteristics and performances. In this context, the review presented herein describes the quickly growing field of a new emerging generation of CNC/GNM hybrids, with a focus on strategies for their preparation and most relevant achievements. These hybrids showed great promise in a wide range of applications such as separation, energy storage, electronic, optic, biomedical, catalysis and food packaging. Some basic concepts and general background on the preparation of CNC and GNM as well as their key features are provided ahead.

Robust Chiral Organization of Cellulose Nanocrystals in Capillary Confinement

We showed large area uniformly aligned chiral photonic bioderived films from a liquid crystal phase formed by a cellulose nanocrystal (CNC) suspension placed in a thin capillary. As a result of the spatial confinement of the drying process, the interface between coexisting isotropic and chiral phases aligns perpendicular to the long axis of the capillary. This orientation facilitates a fast homogeneous growth of chiral pseudolayers parallel to the interface. Overall, the formation of organized solids takes hours vs weeks in contrast to the slow and heterogeneous process of drying from the traditional dish-cast approach. The saturation of water vapor in one end of the capillary causes anisotropic drying and promotes unidirectional propagation of the anisotropic phase in large regions that results in chiral CNC solid films with a uniformly oriented layered morphology. Corresponding ordering processes were monitored in situ at a nanoscale, mesoscale, and microscopic scale with complementary scattering and microscopic techniques. The resulting films show high orientation order at a multilength scale over large regions and preserved chiral handedness causing a narrower optical reflectance band and uniform birefringence over macroscopic regions in contrast to traditional dish-cast CNC films and those assembled in a magnetic field and on porous substrates. These thin films with a controllable and well-identified uniform morphology, structural colors, and handedness open up interesting possibilities for broad applications in bioderived photonic nanomaterials.

Inverse Thermoreversible Mechanical Stiffening and Birefringence in a Methylcellulose/Cellulose Nanocrystal Hydrogel

We show that composite hydrogels comprising methyl cellulose (MC) and cellulose nanocrystal (CNC) colloidal rods display a reversible and enhanced rheological storage modulus and optical birefringence upon heating, i.e., inverse thermoreversibility. Dynamic rheology, quantitative polarized optical microscopy, isothermal titration calorimetry (ITC), circular dichroism (CD), and scanning and transmission electron microscopy (SEM and TEM) were used for characterization. The concentration of CNCs in aqueous media was varied up to 3.5 wt % (i.e, keeping the concentration below the critical aq concentration) while maintaining the MC aq concentration at 1.0 wt %. At 20 °C, MC/CNC underwent gelation upon passing the CNC concentration of 1.5 wt %. At this point, the storage modulus ( G') reached a plateau, and the birefringence underwent a stepwise increase, thus suggesting a percolative phenomenon. The storage modulus ( G') of the composite gels was an order of magnitude higher at 60 °C compared to that at 20 °C. ITC results suggested that, at 60 °C, the CNC rods were entropically driven to interact with MC chains, which according to recent studies collapse at this temperature into ring-like, colloidal-scale persistent fibrils with hollow cross-sections. Consequently, the tendency of the MC to form more persistent aggregates promotes the interactions between the CNC chiral aggregates towards enhanced storage modulus and birefringence. At room temperature, ITC shows enthalpic binding between CNCs and MC with the latter comprising aqueous, molecularly dispersed polymer chains that lead to looser and less birefringent material. TEM, SEM, and CD indicate CNC chiral fragments within a MC/CNC composite gel. Thus, MC/CNC hybrid networks offer materials with tunable rheological properties and access to liquid crystalline properties at low CNC concentrations.

Biomimetic Structural Materials: Inspiration from Design and Assembly

Nature assembles weak organic and inorganic constituents into sophisticated hierarchical structures, forming structural composites that demonstrate impressive combinations of strength and toughness. Two such composites are the nacre structure forming the inner layer of many mollusk shells, whose brick-and-mortar architecture has been the gold standard for biomimetic composites, and the cuticle forming the arthropod exoskeleton, whose helicoidal fiber-reinforced architecture has only recently attracted interest for structural biomimetics. In this review, we detail recent biomimetic efforts for the fabrication of strong and tough composite materials possessing the brick-and-mortar and helicoidal architectures. Techniques discussed for the fabrication of nacre- and cuticle-mimetic structures include freeze casting, layer-by-layer deposition, spray deposition, magnetically assisted slip casting, fiber-reinforced composite processing, additive manufacturing, and cholesteric self-assembly. Advantages and limitations to these processes are discussed, as well as the future outlook on the biomimetic landscape for structural composite materials.