MXenes vs. clays: emerging and traditional 2D layered nanoarchitectonics

Although MXene materials are considered an emerging research topic, they are receiving considerable interest because, like metals and graphene, they are good electronic conductors but with the particularity that they have a marked hydrophilic character. Having a structural organization and properties close to those of clay minerals (natural silicates typically with a lamellar morphology), they are sometimes referred to as "conducting clays" and exhibit colloidal, surface and intercalation properties also similar to those of clay minerals. The present contribution aims to inform and discuss the nature of MXenes in comparison with clay phyllosilicates, taking into account their structural analogies, outstanding surface properties and advanced applications. The current in-depth understanding of clay minerals may represent a basis for the future development of MXene-derived nanoarchitectures. Comparative examples of the preparation, and studies on the properties and applications of various nanoarchitectures based on clays and MXenes have been included in the present work.

Green Carbon Nanostructures for Functional Composite Materials

Carbon nanostructures are widely used as fillers to tailor the mechanical, thermal, barrier, and electrical properties of polymeric matrices employed for a wide range of applications. Reduced graphene oxide (rGO), a carbon nanostructure from the graphene derivatives family, has been incorporated in composite materials due to its remarkable electrical conductivity, mechanical strength capacity, and low cost. Graphene oxide (GO) is typically synthesized by the improved Hummers’ method and then chemically reduced to obtain rGO. However, the chemical reduction commonly uses toxic reducing agents, such as hydrazine, being environmentally unfriendly and limiting the final application of composites. Therefore, green chemical reducing agents and synthesis methods of carbon nanostructures should be employed. This paper reviews the state of the art regarding the green chemical reduction of graphene oxide reported in the last 3 years. Moreover, alternative graphitic nanostructures, such as carbons derived from biomass and carbon nanostructures supported on clays, are pointed as eco-friendly and sustainable carbonaceous additives to engineering polymer properties in composites. Finally, the application of these carbon nanostructures in polymer composites is briefly overviewed.

CANDYBOTS: A New Generation of 3D-Printed Sugar-Based Transient Small-Scale Robots

Sugars are ubiquitous in food, and are among the main sources of energy for almost all forms of life. Sugars can also form structural building blocks such as cellulose in plants. Because of their inherent degradability and biocompatibility characteristics, sugars are compelling materials for transient devices. Here, an additive manufacturing approach for the production of magnetic sugar-based composites is introduced. First, it is shown that sugar-based 3D architectures can be 3D printed by selective laser sintering. This method enables not only the caramelization chemistry but also the mechanical properties of the sugar architectures to be adjusted by varying the laser energy. It is also demonstrated that mixtures of sugar and magnetic particles can be processed as 3D composites. As a proof of concept, a sugar-based millimeter-scale helical swimmer, which is capable of corkscrew motion in a solution with a viscosity comparable to those of biological fluids, is fabricated. The millirobot quickly dissolves in water, while being manipulated through magnetic fields. The present fabrication method can pave the way to a new generation of transient sugar-based small-scale robots for minimally invasive procedures. Due to their rapid dissolution, sugars can be used as an intermediate step for transporting swarms of particles to specific target locations.

From Solute, Fluidic and Particulate Precursors to Complex Organizations of Matter

The organization of matter from its constitutive units recruits intermediate states with distinctive degrees of self-association and molecular order. Existing as clusters, droplets, gels as well as amorphous and crystalline nanoparticles, these precursor forms have fundamental contributions towards the composition and structure of inorganic and organic architectures. In this personal account, we show that the transitions from atoms, molecules or ionic species to superstructures of higher order are intertwined with the interfaces and interactions of precursor and intermediate states. Structural organizations distributed across different length scales are explained by the multistep nature of nucleation and crystallization, which can be guided towards functional hybrid materials by the strategic application of additives, templates and reaction environments. Thus, the non-classical pathways for material formation and growth offer conceptual frameworks for elucidating, inducing and directing fascinating material organizations of biogenic and synthetic origins.

Nitrogen- and oxygen-containing activated carbons from sucrose for electrochemical supercapacitor applications

High surface area nitrogen- and oxygen-containing activated carbons have been synthesized from sucrose and ammonium nitrateviacombustion route for supercapacitor applications.

Characteristics of cesium ion sorption from aqueous solution on bentonite- and carbon nanotube-based composites

The technology development of Cs(+) capture from aqueous solution is crucial for the disposal of nuclear waste and still remains a significant challenge. Previous researches have been proven that ion exchanges with the cations and hydroxyl exchange are the main sorption mechanisms for Cs(+). Therefore, how important are the cation exchange and the hydroxyl exchange mechanisms to Cs(+) sorption? And whether can we improve the sorption capacity of the material by increasing the amount of hydroxyl groups? With these in mind, we herein designed the chitosan-grafted carbon nanotubes (CS-g-CNTs) and the chitosan-grafted bentonite (CS-g-bentonite) by plasma-induced grafting method. The interactions of Cs(+) with CNTs, bentonite, CS-g-CNTs and CS-g-bentonite composites were investigated. The sorption of Cs(+) is mainly dominated by strong cation exchange in monovalent Group I and divalent Group II. And the cation-exchange mechanism is much more effective than the hydroxyl group exchange. The effect of hydroxyl groups is dependent on the property of the matrix. We cannot improve the Cs adsorption capacity of material for Cs(+) only by increasing the amount of hydroxyl groups in any case. The spatial structure and the cation-exchange capacity of the material are important factors for choosing the sorbent for Cs(+) removal from radioactive waste water.

Clay-supported graphene materials: application to hydrogen storage

The present work refers to clay-graphene nanomaterials prepared by a green way using caramel from sucrose and two types of natural clays (montmorillonite and sepiolite) as precursors, with the aim of evaluating their potential use in hydrogen storage. The impregnation of the clay substrates by caramel in aqueous media, followed by a thermal treatment in the absence of oxygen of these clay-caramel intermediates gives rise to graphene-like materials, which remain strongly bound to the silicate support. The nature of the resulting materials was characterized by different techniques such as XRD, Raman spectroscopy and TEM, as well as by adsorption isotherms of N2, CO2 and H2O. These carbon-clay nanocomposites can act as adsorbents for hydrogen storage, achieving, at 298 K and 20 MPa, over 0.1 wt% of hydrogen adsorption excess related to the total mass of the system, and a maximum value close to 0.4 wt% of hydrogen specifically related to the carbon mass. The very high isosteric heat for hydrogen sorption determined from adsorption isotherms at different temperatures (14.5 kJ mol(-1)) fits well with the theoretical values available for hydrogen storage on materials that show a strong stabilization of the H2 molecule upon adsorption.

Novel biodegradable nanocomposite based on XG-g-PAM/SiO2: application of an efficient adsorbent for Pb2+ ions from aqueous solution

This article highlights the development of a novel nanocomposite based on nanosilica filled modified natural polymer (i.e. xanthan gum grafted with polyacrylamide:XG-g-PAM) for removal of Pb(2+) ions from aqueous solution. The chemical, structural, textural, and rheological characteristics of the nanocomposite (XG-g-PAM/SiO(2)) revealed stronger interaction of silica nanoparticles with polymer matrix and showed maximum adsorption capacity (Q(max)=537.634 mg g(-1)) of Pb(2+) ion, which is significantly higher than other reported adsorbents. This developed novel material also finds potential application as an efficient adsorbent for the treatment of battery industry wastewater. The enhanced adsorption efficiency may be because of its higher hydrodynamic radius and hydrodynamic volume. The adsorption kinetic parameters were best described by pseudo-second-order model. The adsorption equilibrium data fitted well with Langmuir isotherm. The thermodynamic studies confirm that the adsorption is spontaneous and endothermic. Desorption studies affirmed the regenerative efficacy of loaded Pb(2+).