Monolithic Neat Graphene Oxide Aerogel for Efficient Catalysis of S → O Acetyl Migration

Chemoselectivity Streamlines the Approach to Linear and Y-Shaped Thiol-Polyethers Starting from Thiocarboxylic Acids

Thiol-functionalized polyethers, especially poly(ethylene oxide) (PEO), have extensive applications in biomedicine and materials sciences. Herein, we report a simple one-pot synthesis of α-thiol-ω-hydroxyl polyethers through ring-opening polymerization (ROP) of epoxides using thiocarboxylic acid initiators followed by in situ aminolysis. The efficient and chemoselective metal-free Lewis pair catalyst avoids transthioesterification thus achieving well-controlled molar mass, low dispersity, and high end-group fidelity. Kinetic and calculation results demonstrated a fast-initiation mode of the ROP for the strong nucleophilicity of the thiocarboxylate anion and its weak interaction with Lewis acid. The method is expanded for α-thiol-ω-dihydroxyl (Y-shaped) PEO by virtue of the stability of thioester during the ROP. The thiol functionality in linear/Y-shaped PEO is further corroborated by the intensified interaction with gold surface and the resultant protein resistance behavior.

Application of Unsupervised Learning for the Evaluation of Aerogels' Efficiency towards Dye Removal-A Principal Component Analysis (PCA) Approach

Water scarcity is a growing global issue, particularly in areas with limited freshwater sources, urging for sustainable water management practices to insure equitable access for all people. One way to address this problem is to implement advanced methods for treating existing contaminated water to offer more clean water. Adsorption through membranes technology is an important water treatment technique, and nanocellulose (NC)-, chitosan (CS)-, and graphene (G)- based aerogels are considered good adsorbents. To estimate the efficiency of dye removal for the mentioned aerogels, we intend to use an unsupervised machine learning approach known as "Principal Component Analysis". PCA showed that the chitosan-based ones have the lowest regeneration efficiencies, along with a moderate number of regenerations. NC2, NC9, and G5 are preferred where there is high adsorption energy to the membrane, and high porosities could be tolerated, but this allows lower removal efficiencies of dye contaminants. NC3, NC5, NC6, and NC11 have high removal efficiencies even with low porosities and surface area. In brief, PCA presents a powerful tool to unravel the efficiency of aerogels towards dye removal. Hence, several conditions need to be considered when employing or even manufacturing the investigated aerogels.

Rapid adsorption of directional cellulose nanofibers/3-glycidoxypropyltrimethoxysilane/polyethyleneimine aerogels on microplastics in water

Currently, cellulose-based aerogel materials are a hot topic owing to their high specific surface area and high porosity, as well as the green, degradable and biocompatible characteristics of cellulosic materials. Modification of cellulose to enhance the adsorption properties of cellulose-based aerogels has important research significance in solving the problem of water body pollution. In this paper, cellulose nanofibers (CNFs) were modified with polyethyleneimine (PEI), and modified aerogels with directional structures were prepared by a simple reaction and freeze-drying method. The adsorption behavior of the aerogel followed the adsorption kinetic models and isotherm models. More significantly, the aerogel could rapidly adsorb microplastics, reaching equilibrium within 20 min. Furthermore, the fluorescence displayed directly expresses the occurrence of the adsorption behavior of the aerogels. Therefore, the modified cellulose nanofiber aerogels were of reference significance for microplastic removal from water bodies.

Dense, Three-Dimensional, Highly Absorbent, Graphene Oxide Aerogel Coating on ZnCo2O4/ZnO Particles Exerts a Synergistic Catalytic Effect for Ammonium Perchlorate Thermal Decomposition

As a new type of carbon material, graphene oxide aerogel (GA) is widely used in catalysis due to its porous structure, high-efficiency adsorption, and superb conductivity. In this study, GA was prepared into a dense coating layer surrounding ZnCo₂O₄/ZnO particles to form a composite GA-ZnCo₂O₄/ZnO by means of a hydrothermal, blast drying, and vacuum-freeze-drying approach applied to catalyze the thermal decomposition of ammonium perchlorate (AP). The physicochemical properties of the obtained GA-ZnCo₂O₄/ZnO were characterized by different analytical methods. Scanning electron microscopy (SEM) analysis exhibited that GA is coated on the surface of ZnCo₂O₄/ZnO, forming a dense layer. Brunner Emmet Teller (BET) measurement results show that GA-ZnCo₂O₄/ZnO has a smooth macropore distribution curve and a larger specific surface area. Moreover, The catalytic effect investigation on AP with GA-ZnCo₂O₄/ZnO: the high temperature decomposition (HTD) peak temperature of AP in the presence of 5 wt % GA-ZnCo₂O₄/ZnO was reduced from 441 to 294 °C, and the exotherm of AP was expanded from 205 to 1275 J/g at a heating rate of 15 °C/min. Through the calculation, GA-ZnCo₂O₄/ZnO makes the activation energy and Gibbs free energy of the AP pyrolysis lower so that the reaction is easier to occur. Thermogravimetric-mass (TG-MS) spectrometry revealed that during thermal decomposition of AP, GA-ZnCo₂O₄/ZnO leveraged the synergistic catalysis of ZnCo₂O₄/ZnO and GA that boosted the flow of electrons from ClO₄^- to O₂ and increased the absorption of the gas product to accelerate the AP pyrolysis. These results provided a facile strategy to prepare GA-based composite catalysts with extraordinary application prospects in the domain of solid propellants.

Ultrahigh-strength carbon aerogels for high temperature thermal insulation

Carbon aerogels with nanoporous structure are attractive for thermal insulation under extreme conditions, but their practical applications are usually plagued by the inherent brittleness and easy-oxidation characteristic at high temperature. Herein, silica-modified carbon aerogels (SCAs) with extraordinarily high strength are prepared via a facile sol-gel polymerization of phenolic resin and siloxane, followed by ambient pressure drying and carbonization. The resulting SCAs possess medium-high density of ∼0.5 g·cm^-3 and mesoporous structure with the mean pore size of 33 nm. During carbonization process, the siloxane could be gradually transformed into the amorphous SiO₂ particles and crystalline SiC particles, which are coated on the surface of carbon nanoparticle and consequently improve the oxidation-resistance of carbon aerogels. Due to the density-porosity trade-off, the SCAs have high compressive strength of 10.0 MPa and satisfied thermal conductivities of 0.118 W·m^-1·K^-1 at 25 °C and 0.263 W·m^-1·K^-1 at 1000 °C. Furthermore, needled carbon fiber-reinforced SCAs (CF-SCAs) with ultrahigh compressive strength of 210.5 MPa are prepared, which exhibit good thermal conductivities of 0.207 W·m^-1·K^-1 at 25 °C and 0.407 W·m^-1·K^-1 at 1000 °C. The ultrahigh mechanical strength, good oxidation-resistance, good thermal insulation as well as the facile preparation make the SACs great promising in high-temperature insulations especially under harsh conditions.

Nanoporous Crystalline Composite Aerogels with Reduced Graphene Oxide

High-porosity monolithic composite aerogels of syndiotactic polystyrene (sPS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) containing reduced graphene oxide (r-GO) were prepared and characterized. The composite aerogels obtained by supercritical carbon dioxide (scCO₂) extraction of sPS/r-GO and PPO/r-GO gels were characterized by a fibrillar morphology, which ensured good handling properties. The polymer nanoporous crystalline phases obtained within the aerogels led to high surface areas with values up to 440 m² g⁻¹. The role of r-GO in aerogels was studied in terms of catalytic activity by exploring the oxidation capacity of composite PPO and sPS aerogels toward benzyl alcohol in diluted aqueous solutions. The results showed that, unlike sPS/r-GO aerogels, PPO/r-GO aerogels were capable of absorbing benzyl alcohol from the diluted solutions, and that oxidation of c.a. 50% of the sorbed benzyl alcohol molecules into benzoic acid occurred.

Hydrophilic and Compressible Aerogel: A Novel Draw Agent in Forward Osmosis

Forward osmosis (FO) technology is an efficient route to obtain purity water for drinking from wastewater or seawater. However, there are some challenges in draw solution to limit its application. We first introduce a novel sodium alginate-graphene oxide (SA-GO) aerogel as draw agent for highly efficient FO process. The GO nanosheets covalently cross-linked to SA matrix to form a three-dimensional and highly porous aerogel to provide excellent water flux and operation stability, together with the property of compressibility served by SA-GO aerogel resulting in easy water production and regeneration process. When deionized water was used as the feed solution, the SA-GO aerogel exhibited a higher water flux (15.25 ± 0.65 L m^-2 h^-1, abbreviated as LMH) than that of 1 mol L^-1 NaCl (1 M), and there was no nonreverse osmosis phenomenon. The water fluxes were stabilized in the range of 5-6.5 LMH during recycle process of absorbing and releasing water as high as 100 times. It also had a great desalination capacity (water flux was 7.49 ± 0.61 LMH) with the seawater (Huanghai coast) as the feed solution. Moreover, the water production and regeneration process of the SA-GO aerogel can be rapidly and cost-effectively accomplished with low-strength mechanical compression (merely 1 kPa). The results present that the SA-GO aerogels as a promising, innovative draw agent can make the FO process simpler, more efficient, and lower energy consumption. It can be a potential material for hydration bags to fast and repeatable product fresh water from saline water or wastewater.

Fabrication of Graphene Aerogels with Heavily Loaded Metallic Nanoparticles

Natural biomaterials with hierarchical structures that enable extraordinary capability of detecting chemicals have inspired the interest in producing materials that can mimic these natural structures. This study reports the fabrication of hierarchically-structured, reduced graphene oxide (rGO) aerogels with heavily loaded palladium (Pd), platinum (Pt), nickel (Ni), and tin (Sn) metallic nanoparticles. Metal salts chelated with ethylenediaminetetraacetic acid (EDTA) were mixed with graphene oxide (GO) and then freeze-dried. The subsequent reduction produces rGO/metal nanoparticle aerogels. SEM and EDS results indicated that a loading of 59, 67, 39, and 46 wt % of Pd, Pt, Ni, and Sn nanoparticles was achieved. Pd/rGO aerogels of different Pd nanoparticle concentrations were exposed to H₂ gas to monitor the resistance change of the composites. The results suggest that rGO aerogels can achieve a higher nanoparticle loading by using chelation to minimize electrostatic interactions between metal ions and GO. Higher loading of Pd nanoparticles in graphene aerogels lead to improved hydrogen gas sensing performance.

Redissolution of Flower-Shaped Graphene Oxide Powder with High Density

As a sort of scalable precursor of graphene, single-layer graphene oxide (GO) has received widespread attention. However, producing dried GO powder which can redisperse in solvents on a molecular level is still under challenge. Here, we have developed a strategy to obtain flower-shaped GO powder (fGO) via a low-temperature spray-drying method. Such GO powder can be redissolved in various solvents including water, with a concentration higher than 3 wt %. The excellent solubility of fGO is totally preserved even after being compressed into a high-density disk (1.26 g/cm(3)). The aqueous solution of fGO can form liquid crystals, which can be assembled into macroscopic graphene papers. By tracking the dissolution process of fGO, we reveal a "swelling-dissociation-stretching" behavior of the GO particles. For the first time, nuclear magnetic resonance (NMR) solution relaxation is applied to in situ monitor the degree of unfolding (DU) of fGO during dissolution. We discover that the classic polymer dissolution mechanism of linear polymer can extend to GO, a two-dimensional macromolecule. Our findings not only provide a solution for the problems in the transportation, storage and applications of GO, but also open a new way to adjust the microstructure of crumpled GO in large scale.

Three-dimensional macro-structures of two-dimensional nanomaterials

This review summarizes the recent progress and efforts in the synthesis, structure, properties, and applications of three-dimensional macro-structures of two-dimensional nanomaterials.

Group interval-controlled polymers: an example of epoxy functional polymers via step-growth thiol–yne polymerization

Here, we successfully synthesized a series of epoxy GICPs via one-step UV-triggered thiol–yne polymerization of commercial glycidyl propargyl ether and dithiols at 0 °C..

Direct solvothermal preparation of nanostructured fluoride aerogels based on AlF3

AlF3-based aerogels, a new class of inorganic aerogels, are prepared in a novel direct process that combines fluoride sol-gel synthesis with high temperature supercritical drying. The bulk structure of the solid products depends decisively on the applied solvent(s); very voluminous bulk aerogels are obtained only with MeOH that is used either alone or in combination with some other polar solvents. MeOH acts as a methoxylation agent; and formed methoxy (MeO) species are remarkably stable and deactivate the surface acidic sites. Removal of MeO species under moderate conditions results in catalytically active fluorides with a preserved nanostructure. In preparations with MeOH, preferential growth of anisotropic nanoparticles (nanorods) is the key step that leads to the formation of very open aerogel structures. Another process, dehydration of alcohols, results in some hydroxylation and hydration that lead to the formation of distinctive surface and bulk OH/H2O species. The structure of AlF3-based aerogels is consistent with the hexagonal tungsten bronze (HTB) β-AlF3 although their composition corresponds to a formula AlF3-x(OH, OMe)x·yH2O (x = 0.1 ± 0.05). Some other characteristics of the fluoride nanoparticles, like crystallinity, particle size, and uniformity, can be effectively controlled by the temperature of the solvothermal process. The described methodology allows a controllable preparation of catalytically active fluorides in the form of regularly shaped and uniformly sized nanoparticles.

A green approach for the decoration of Pd nanoparticles on graphene nanosheets: An in situ process for the reduction of C–C double bonds and a reusable catalyst for the Suzuki cross-coupling reaction

In situ synthesis of Pd nanoparticles on graphene nanosheets with simultaneous reduction of alkene to alkane using hydrogen gas were utilized as efficient catalysts for the Suzuki cross-coupling reaction.

Discovery of neat silica gel as a catalyst: an example of S → O acetyl migration reaction

For the first time, we reported pristine silica gel as an efficient fixed-bed catalyst for S → O acetyl migration to obtain important thiol compounds under mild reaction conditions.