Prospects of Supercritical Fluids in Realizing Graphene‐Based Functional Materials

Supercritical‐fluids science and technology predate all the approaches that are currently established for graphene production by several decades in advanced materials design. However, it has only recently been proposed as a plausible approach for graphene processing. Since then, supercritical fluids have emerged into contention as an alternative to existing technologies because of their scalability and versatility in processing graphene materials, which include composites, aerogels, and foams. Here, an overview is presented of such materials prepared through supercritical fluids from an advanced materials science standpoint, with a discussion on their fundamental properties and technological applications. The benefits of supercritical‐fluid processing over conventional liquid‐phase processing are presented. The benefits include not only better performances for advanced applications but also environmental issues associated with the synthesis process. Nevertheless, the limitations of supercritical‐fluid processing are also stressed, along with challenges that are still faced toward the achievement of the great expectations from graphene materials.     

In situ growth of SiC wires on CVI densification of SiC foam

Silicon carbide (SiC) foam prepared by polymer infiltration and pyrolysis (PIP) process was further densified with β-SiC by chemical vapor infiltration (CVI) technique. Scanning electron microscopy and high-resolution transmission electron microscopy images confirmed the presence of highly entangled and branched in situ grown SiC wires of uniform diameter (∼500 nm) over the struts of open-cell SiC foam. A uniform rate increase in diameter from nanometer to micron range (∼11 μm) was observed with an increase in the CVI reaction period. X-ray diffraction results showed the formation of highly crystalline β-SiC structure along the <111> direction with stacking faults. The formation of SiC wires was explained by the vapor–liquid–solid mechanism and evenness of the surface and uniform growth rate of SiC confirmed the homogeneous concentration of gaseous species during CVI reaction. The compressive strength increased with relative density, with maximum values of 5.5 ± 1.26 MPa for ultimate SiC foam (ρ = 400 kg/m³) prepared by hybrid PIP/CVI technique. The thermo-oxidative stability of the resultant foam was evaluated up to 1650°C under air and shows excellent thermal stability compared to SiC foam prepared by PIP route. The densified SiC foam can find potential applications in the field of hot gas filters, catalyst supports, microwave absorption properties, and heat insulation for high-temperature applications.     

Nanoscale Assembly of 2D Materials for Energy and Environmental Applications

Rational design of 2D materials is crucial for the realization of their profound implications in energy and environmental fields. The past decade has witnessed significant developments in 2D material research, yet a number of critical challenges remain for real-world applications. Nanoscale assembly, precise control over the orientational and positional ordering, and complex interfaces among 2D layers are essential for the continued progress of 2D materials, especially for energy storage and conversion and environmental remediation. Herein, recent progress, the status, future prospects, and challenges associated with nanoscopic assembly of 2D materials are highlighted, specifically targeting energy and environmental applications. Geometric dimensional diversity of 2D material assembly is focused on, based on novel assembly mechanisms, including 1D fibers from the colloidal liquid crystalline phase, 2D films by interfacial tension (Marangoni effect), and 3D nanoarchitecture assembly by electrochemical processes. Relevant critical advantages of 2D material assembly are highlighted for application fields, including secondary batteries, supercapacitors, catalysts, gas sensors, desalination, and water decontamination.     

Humic acid-immobilized polymer/bentonite composite as an adsorbent for the removal of copper(II) ions from aqueous solutions and electroplating industry wastewater

In this study, humic acid (HA) was immobilized onto amine-modified polyacrylamide/bentonite composite (Am-PAA-B) which was prepared by direct intercalation polymerization technique and the product (HA-Am-PAA-B) was used as an adsorbent for the removal of copper(II) ions from aqueous solutions. The surface characteristics of bentonite, Am-PAA-B and HA-Am-PAA-B were investigated. The adsorbent behaved like a cation exchanger and more than 99.0% Cu(II) ions’ removal was observed at the pH range 5.0–6.0. Kinetic and isotherm experiments showed that amount of Cu(II) ions adsorbed increases with increase of the initial concentration and temperature. The adsorption kinetic data were interpreted by pseudo-first-order and pseudo-second-order rate equations. The suitability of Langmuir, Freundlich and Dubinin–Radushkevich (D-R) adsorption models to the equilibrium data was investigated. The Langmuir isotherm was found to provide the best theoretical correlation of the experimental equilibrium data. The thermodynamic and kinetic activation parameters were derived to predict the nature of adsorption process and discussed in detail. The isosteric heat of adsorption was constant even after increase in surface loading. The removal efficiency of HA-Am-PAA-B was tested using electroplating industry wastewater. The desorption of adsorbed Cu(II) ions was achieved by 0.1 M HCl and four adsorption/desorption cycles were performed without significant decrease in the adsorption capacity.     

Synthesis and characterization of humic acid immobilized-polymer/bentonite composites and their ability to adsorb basic dyes from aqueous solutions

A new polyacrylamide-bentonite composite with amine functionality (Am-PAA-B) was prepared by direct polymerization in the presence of N,N'-methylenebisacrylamide as a crosslinking agent and potassium peroxydisulphate as an initiator followed by reaction with ethylenediammine. The Am-PAA-B was modified by immobilizing humic acid and tested as an adsorbent to remove basic dyes (Malachite Green, Methylene Blue and Crystal Violet) from aqueous solutions. XRD, conductometric and potentiometric titrations were used to characterize the adsorbent. The adsorbent behaved like a cation exchanger and more than 99.0% removal of dyes was observed at the pH range 5.0 to 8.0. The adsorption kinetic data were interpreted by pseudo-second-order rate equation and the film diffusion was the rate-limiting step. The equilibrium data were fitted well with the Freundlich isotherm model. Desorption of dyes was achieved by treatment with 0.1 M HNO₃ and four adsorption desorption cycles were performed without significant decrease in adsorption capacity.     

Catalytic pyrolysis of cellulose with oxides: effects on physical properties and reaction pathways

Clean Technologies and Environmental Policy - Fast pyrolysis is a potential technology for converting lignocellulosic biomass into bio-oil, a potential substitute for crude oil and a source of...     

Evaluating the performance of bagging-based k-nearest neighbor ensemble with the voting rule selection method

Multimedia Tools and Applications - Label ranking based prediction problems help to find a mapping between instances and ranked labels. To improve the prediction performance of label ranking...     

Meta-analysis on big data of bioactive compounds from mangrove ecosystem to treat neurodegenerative disease

Scientometrics - The mangrove ecosystem is one of the wealthiest organic and salt containing ecosystem. It has a large biomass consisting of bacteria, fungi, plants and other potential organisms....     

Preparation and characterization of iron(III) complex of an amino‐functionalized polyacrylamide‐grafted lignocellulosics and its application as adsorbent for chromium(VI) removal from aqueous media

The growth and decay processes of optically induced birefringence in two novel azobenzene compounds [one was a hyperbranched poly(aryl ether) containing azobenzene groups, and the other was a hydrogen‐bonded complex] were studied. The temperature dependence of the birefringence signal was investigated. The curves for the buildup and decay of birefringence fit well to biexponential functions. The dependence of the fitting parameters on the temperature is also discussed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010