Surface modifications of activated carbon by gamma irradiation

Four commercial activated carbons with different chemical and textural characteristics were modified by gamma irradiation under five different conditions: irradiated in absence of water, in presence of ultrapure water, in ultrapure water at pH = 1.0 and 1000 mg L⁻¹ Cl⁻, in ultrapure water at pH = 7.5 and 1000 mg L⁻¹ Br⁻, and in ultrapure water at pH = 12.5 and 1000 mg L⁻¹ NO₃⁻. Changes in surface chemistry were studied by X-ray photoelectron spectroscopy; pH of point of zero charge, total acidic groups and total basic groups, which were determined by assessment with HCl and NaOH; and textural changes were determined by obtaining the corresponding adsorption isotherms of N₂ and CO₂. Outcomes show that the activated carbon surface chemistry can be modified by gamma irradiation and that the changes depend on the irradiation conditions. Modifications in the sp² hybridization of the surface carbons suggest that the irradiated carbons undergo graphitization. Measurements of structural parameters indicate that the irradiation treatment does not modify the textural properties of the carbons. Finally, studies of pristine and irradiated activated carbons using diffuse reflectance spectroscopy with the Kubelka–Munk function revealed a reduction in band gap energy in the irradiated carbons associated with an increase in sp² hybridization of the carbon atoms.     

High-yield,in-situ fabrication and integration of horizontal carbon nanotube arrays at the wafer scale for robust ammonia sensors

This paper reports the successful experimental demonstration of the localized growth of horizontal, dense carbon nanotube (CNT) arrays in situ and at the wafer scale. The selectivity and directionality of the CNT catalytic growth process along with the adequate design and fabrication of the catalyst support enables the direct integration of nanotubes arrays into heterogeneous devices. This novel CNT integration method is developed to manufacture conductance based gas sensors for ammonia detection and is demonstrated to produce a yield above 90% at the wafer scale. Owing to its flexibility, the integration process can be useful for a wide range of applications and complies with industrial requirements in terms of manufacturability and yield, requirements for the acceptance of CNTs as alternate materials. A state-of-the-art CNT array resistivity of 1.75 × 10⁻⁵ Ω m has been found from the CNT characterization. When exposed to low NH₃ concentrations, the CNT sensors show good repeatability, long-term stability, and high design robustness and tackle the reproducibility challenge for CNT devices. Individual device calibration is not needed. The ammonia adsorption isotherm on the sensor is well fitted by Freundlich equation. The extrapolated detection limit is about 1 ppm. The dependence of the sensitivity with temperature indicates that ammonia sensing is likely to involve an endothermic process. Finally, relative humidity cross sensitivity has been found to have no adverse effect on the ammonia response enabling NH₃ monitoring in ambient conditions.     

Effect of microstructure on the electrochemical performance of Ni-ScSZ anodes

The effects of NiO powder morphology and sintering temperature on the microstructure and the electrochemical performance of Nickel-scandia-stabilized zirconia (Ni-ScSZ) cermet anodes for solid oxide fuel cells (SOFCs) were investigated. The particle size and agglomeration of the starting powders were found to affect both the microstructure and electrochemical performance of the Ni-ScSZ cermet anodes. The lowest polarization resistance, 0.690 Ω cm² at 700 °C, was measured for the Ni-ScSZ anode prepared with fine NiO powder (~0.5 µm grain size). This was attributed to the increase in the number of reaction sites afforded by the small grains and well-dispersed Ni and ScSZ phases. The effect of the anode sintering temperature was also found to affect the anode microstructure, adhesion with the electrolyte, and consequently anode polarization resistance. The lowest polarization resistance was observed for the anode sintered at 1400 °C and this was 3–5 times lower than the corresponding values for anodes sintered at lower temperatures.     

Adsorption of rhodium(III) ions onto poly(1,8-diaminonaphthalene) chelating polymer: Equilibrium,kinetic and thermodynamic study

In the present work, poly(1,8-diaminonaphthalene) (poly(1,8-DAN)) was synthesized by the reaction of 1,8-diaminonaphthalene (1,8-DAN) with ammonium persulfate (APS) and then the equilibrium, kinetics and thermodynamics of rhodium(III) adsorption onto poly(1,8-DAN) were studied. Poly(1,8-DAN), Rh(III)-poly(1,8-DAN) and Rh(III)-1,8-DAN complex were characterized by UV–vis. and FTIR spectroscopy, thermal analysis, potentiometric titration and electrical conductivity. In the adsorption studies, the effects of acidity, the temperature and the concentration of rhodium(III) were examined. It was found that poly(1,8-DAN) has Rh(III) adsorption capacity (q_m) of 11.11 mg/g polymer. The adsorption data fitted better to the Freundlich isotherm then the Langmuir isotherm, and the kinetics of the adsorption fitted to pseudo second order kinetic model. The ΔG° values were calculated as ?7.33 at 20 and ?11.31 kJ/mol at 60 °C. The enthalpy (ΔH°), entropy (ΔS°) and the activation energy (E_a) of the adsorption were found as 21.335 kJ/mol, 97.057 J/mol K and 70.210 kJ/mol, respectively. It was predicted that the adsorption of Rh(III) onto poly(1,8-DAN) was an endothermic chemical adsorption process governed by both ionic interaction and chelating mechanisms. It was also observed that the adsorption of Rh(III) lowered the electrical conductivity of the pol(1,8-DAN).     

Production of 2-phenylethanol in hybrid system using airlift reactor and immersed hollow fiber membrane module

To minimize capital and operative costs in many bioproductions of chemical specialities, where the product inhibits the bioreaction, a hybrid system based on the application of membrane extraction integrated in the bioreactor to remove the product is a suitable solution. Integration can be done by an external module for membrane extraction or, as a more effective solution, by an extraction membrane module immersed directly in the bioreactor. In this second case, it is not necessary to use microfiltration to prevent membrane fouling or to use another pump for shell flow in the membrane module. Moreover, the system is very compact, highly effective, resistant to failures and its mathematic simulation is also possible. These statements are proved in this paper where a hybrid system consisting of an airlift reactor and immersed extraction hollow fiber membrane module was used for the biotransformation of l-phenylalanine to the desired rose-like aroma, 2-phenylethanol, by yeasts Saccharomyces cerevisiae. Two biotransformation experiments were carried out using different feeding and aeration strategies. In both experiments, high conversion of l-phenylalanine (up 100%) and high volumetric production of 2-phenylethanol (up 18.6 g L⁻¹) were reached. Both biotransformation experiments were mathematically predicted with good agreement between experimental data and simulations.     

Simulation of magnetic suspensions for HGMS using CFD,FEM and DEM modeling

Properties of magnetic suspensions depend on the fluid, the particles and the magnetic background field. The simulation is aimed at understanding the influence of magnetic properties in High Gradient Magnetic Separation processes. In HGMS magnetic particles are collected on magnetic wires for separation. External magnetic forces are calculated or simulated using the Finite Element Method and embedded first in a Computational Fluid Dynamics simulation. In the simulation, elliptic and rectangular wires aligned in field direction reach higher separation efficiencies than cylindrical wires. Magnetic forces from FEM with implemented dipole forces in a Discrete Element Method code show magnetically induced agglomeration and yield an acceptable agreement with experiments. Particle deposition on wires is investigated under the influence of different parameters. The porosity of the deposit is dependent on the magnetization of the wire and particles. A centrifugal force of 60 g has an important influence.     

High pressure enhances activity and selectivity of Candida rugosa lipase immobilized onto silica nanoparticles in organic solvent

High hydrostatic pressure has been increasingly utilized to improve functions of enzymes, and most of such studies are currently focused on free enzymes in aqueous solution or organic solvent. In this work, Candida rugosa lipase (CRL) was immobilized onto silica nanoparticles and its activity and enantioselectivity in organic solvent were evaluated at high pressures under different water activities. The application of high hydrostatic pressures (50–200 MPa) led to improved activities of immobilized CRL for transesterification of (R)-1-phenylpropan-2-ol with vinyl acetate by 4–6 folds. Additionally the immobilization of CRL resulted in a significant change of selectivities, shifting the enantiomeric excess from the (R)- towards (S)-1-phenylpropan-2-yl acetate product at atmospheric pressure. The application of high pressures led to either enantiomeric excess towards (R)-1-phenylpropan-2-yl or no enantiomeric selectivity, depending on the water activities in the organic solvent and the level of pressures. The interesting behaviour of immobilized CRL under high pressures offers new opportunities to modulate enzyme functions through combination of high pressures and enzyme immobilization.     

Solid state 27Al NMR and X-ray diffraction study of alumina–carbon composites

The structural and chemical transformations occurring in alumina–carbon composites upon heat treatment were investigated by using a combination of X-ray diffraction (XRD) and solid-state ²⁷Al nuclear magnetic resonance (NMR) spectroscopy. Two different carbon precursors were employed: a commercial activated carbon and a char obtained by carbonization of the endocarp of babassu coconut at 700 °C. The alumina–carbon composites were prepared by aqueous impregnation of the carbon supports with aluminum nitrate and, after filtering and drying, the as-synthesized powders were heat-treated under argon flow at temperatures up to 1000 °C. The Al compounds present in the as-synthesized samples were identified by XRD and solid-state ²⁷Al NMR as nanocrystalline aluminum oxyhydroxides or hydroxides, depending on the synthesis conditions. All Al-containing phases were XRD-amorphous in the char-derived nanocomposites, with the presence of a distribution of AlO₆ (octahedral Al site), AlO₅ (pentacoordinated Al) and AlO₄ (tetrahedral Al site) units revealed by solid-state ²⁷Al NMR spectroscopy. The heat treatments caused the formation of transition aluminas dispersed over the carbon supports, with the occurrence of different amounts of AlO₆, AlO₅ and AlO₄ units depending on the heat treatment temperature and on the type of carbon precursor used for the preparation of the composites.     

Investigation of the chemical and morphological structure of thermally rearranged polymers

Reacting ortho-functional poly(hydroxyimide)s via a high-temperature (i.e., 350 °C–450 °C) solid-state reaction produces polymers with exceptional gas separation properties for separations such as CO₂/CH₄, CO₂/N₂, and H₂/CH₄. However, these reactions render these so-called thermally rearranged (TR) polymers insoluble in common solvents, which prevent the use of certain experimental characterization techniques such as solution-state nuclear magnetic resonance (NMR) from identifying their chemical structure. In this work, we seek to identify the chemical structure of TR polymers by synthesizing a partially soluble TR polymer from an ortho-functional poly(hydroxyamide). The chemical structure of this TR polymer was characterized using 1-D and 2-D NMR. By use of cross-polarization magic-angle spinning ¹³C NMR, the structure of the polyamide-based TR polymer was compared to that of a polyimide-based TR polymer with a nearly identical proposed structure. The NMR spectra suggest that oxazole functionality is formed for both of these TR polymers. Furthermore, gas permeation results are provided for the precursor polymers and their corresponding TR polymer. The differences in transport properties for these polymers result from differences in the isomeric nature of oxazole-aromatic linkages and morphological differences related to free volume and free volume distribution.     

Enzymatic modification of sesame seed protein,sourced from waste resource for nutraceutical application

The functional characteristics which include protein solubility at different pH, emulsifying and foaming properties, degree of hydrolysis, molecular weight distribution, antioxidant and ACE inhibitory activity of sesame protein hydrolysates prepared with pepsin, papain and alcalase enzymes were evaluated. The rate of degree of hydrolysis was found to reach maximum (25–30%) within the first time fragment i.e 10 min but 80% of hydrolysis was obtained in 120 min with alcalase. SDS-PAGE of hydrolysates with papain, pepsin and alcalase evinced bands of low molecular weight protein of 14.3 kDa and even lower for alcalase treatment of 120 min. Hydrolysates so formed were of improved functional properties as evident from emulsifying and foaming property. Hydrolysis with different proteases enhanced the protein solubility significantly at pH 7.0. Antioxidative assay revealed radical scavenging activity of the hydrolysates with papain hydrolysates showing maximum antioxidative efficacy. The ultra-filtered peptide fractions which showed comparable ACE inhibitory activity were sequenced by MALDI-TOF and matched to that of previously identified ACE inhibitory peptides. The results corroborate the ACE inhibitory effect of the peptides. Hence, these highly bioactive protein hydrolysates produced from waste sesame meals can be successfully employed in various functional food formulations.     

Extraction of essential oils from Mentha piperita using advanced techniques: Microwave versus ohmic assisted hydrodistillation

Ohmic and microwave assisted hydrodistillation (OAHD and MAHD, respectively) are advanced hydrodistillation (HD) techniques utilizing ohmic and microwave heating processes for extraction of essential oils. OAHD and MAHD of essential oils from the aerial parts of peppermint were studied and the results were compared with those of the traditional HD. The results showed that OAHD and MAHD methods require less than half an hour for extraction process while HD require about 1 h. Scanning electron microscopy of mint leaves undergone OAHD and MAHD provided evidences as to a sudden rupture of essential oil glands. GC–MS analysis did not indicate any noticeable changes in the compounds of the essential oils obtained by novel studied methods in comparison with HD. The results introduced OAHD as the greenest technique in terms of energy consumption. MAHD was superior in terms of rate of essential oils accumulation and also extraction duration parameter.     

Functionalization of carbon nanomaterials for advanced polymer nanocomposites: A comparison study between CNT and graphene

The allotropes of carbon nanomaterials (carbon nanotubes, graphene) are the most unique and promising substances of the last decade. Due to their nanoscale diameter and high aspect ratio, a small amount of these nanomaterials can produce a dramatic improvement in the properties of their composite materials. Although carbon nanotubes (CNTs) and graphene exhibit numerous extraordinary properties, their reported commercialization is still limited due to their bundle and layer forming behavior. Functionalization of CNTs and graphene is essential for achieving their outstanding mechanical, electrical and biological functions and enhancing their dispersion in polymer matrices. A considerable portion of the recent publications on CNTs and graphene have focused on enhancing their dispersion and solubilization using covalent and non-covalent functionalization methods. This review article collectively introduces a variety of reactions (e.g. click chemistry, radical polymerization, electrochemical polymerization, dendritic polymers, block copolymers, etc.) for functionalization of CNTs and graphene and fabrication of their polymer nanocomposites. A critical comparison between CNTs and graphene has focused on the significance of different functionalization approaches on their composite properties. In particular, the mechanical, electrical, and thermal behaviors of functionalized nanomaterials as well as their importance in the preparation of advanced hybrid materials for structures, solar cells, fuel cells, supercapacitors, drug delivery, etc. have been discussed thoroughly.     

Evaluation of commercial PTFE membranes in desalination by direct contact membrane distillation

In this study, nine flat-sheet commercially available hydrophobic PTFE membranes were used in desalination by direct contact membrane distillation and their characteristics were investigated under different operating conditions including feed temperature, feed flow rate, cold stream flow rate, and feed concentration. Membrane properties, i.e. pore size, thickness, support layer, and salt rejection were also studied. Moreover, membrane module designs including flow arrangements (co-current, counter-current and tangential) for process liquid and depth both on hot and cold sides were tested experimentally. Finally, the long-term performance of the selected membranes for direct contact membrane distillation as a stand-alone desalination process was investigated. The results indicated that increasing feed temperature, hot feed flow rate, and module depth on the cold side led to increase permeate flux. On the other hand, increasing membrane thickness and module depth on the hot side (at constant flow rate) had negative effects on the flux. The highest permeation flux and salt rejection was achieved when the membranes with a pore size of 0.22 μm were used in the cross-current follow arrangement of hot and cold streams. In addition, the requirements for support layer for a successful DCMD process has been extensively discussed.     

Anisotropic behavior of hydrogen in the formation of pentagonal graphene domains

Variously shaped graphene domains are of significant interest since the electronic properties of pristine graphene are strongly dependent on its size, shape, and edge structures. With the consideration that the reactivity of graphene is governable by the p-electron structure at its edge, a number of attempts have been made to grow variously shaped graphene domains and to define their edge structures. In this work, we explored the anisotropic behavior of hydrogen in the formation of graphene domains during atmospheric pressure chemical vapor deposition. As increasing the hydrogen or reducing the methane partial pressure, the formation of pentagonal graphene domains was accelerated through anisotropic growth and etching. Their edge structures were characterized using polarization-dependent D and G peak Raman spectroscopy. This work contributes significantly to improving graphene-based engineering by allowing graphene shapes and domain edges to be tuned, and also provides greater insight into the electronic properties of graphene devices.     

Optimization of the various modes of flexible operation for post-combustion CO2 capture plant

One option to mitigate the adverse effect of power plant output loss from adding a CO₂ capture plant is to operate it in flexible modes in which the capture level and/or regeneration rate are dynamically varied in response to varying electricity market demand and price. This can help the plant meet peak electricity demand and improve its overall profit. However, the benefit is offset by higher capital costs and/or CO₂ emission penalty. Various modes of flexible operation including capture level reduction and solvent storage have been optimized for a given post-combustion capture system with typical daily electrical energy price patterns and the results are compared with those from a fixed point operation. Effects of varying storage capacities and energy price patterns have also been evaluated. Simultaneous use of the two flexible modes is also optimized and the result showed significantly higher cost savings compared to the individual uses.     

Preparation and studies of transparent conductive monolayers of multiwall carbon nanotubes on quartz and flexible polymer with the use of modified Langmuir technique

An improved Langmuir method is described and applied to produce transparent, conductive and flexible single layer of multiwall carbon nanotubes. This paper presents properties of multiwall carbon nanotubes spread on water subphase and in a form of Langmuir–Schaefer layers on a quartz plate and on flexible polymeric foil. The results show very high homogeneity of the monolayers on a very large area obtained with the use of the proposed modified Langmuir method and indicate their relatively high radiation transmission and electrical conductivity. Laser scanning confocal and scanning electron microscopic images of the layers are presented. The microscopic visualization of the nanolayers is supported by spectroscopic studies (transmittance, photoacoustics) in the range from ultraviolet to mid-infrared. Moreover, electric measurements (current versus voltage characteristics) of the carbon material on the polymeric foil are presented.The obtained results of the investigated multiwall carbon nanotubes are discussed in a view of potential application in optoelectronics.     

Role of activated carbon on micropollutans degradation by ionizing radiation

The objective of this study was to analyze the influence of the presence of activated carbon on the degradation of the triiodinated contrast medium diatrizoate (DTZ) by the simultaneous use of gamma radiation and activated carbon. Four commercial activated carbons (Ceca, Witco, Sorbo, and Merck) with different textural and chemical characteristics were used for this purpose. The percentage DTZ removal obtained was considerably higher with the gamma radiation/activated carbon (GM/AC) system than with radiolysis in the absence of activated carbon, and it depended on the specific activated carbon employed. First, we optimized the amount of activated carbon required to maximize the amount of DTZ removed by the GM/AC system (0.06 g). The degradation constants were higher with the GM/AC system than with radiolysis alone, evidencing a synergic effect that favors pollutant removal. This synergic effect is independent of the textural but not the chemical characteristics of the activated carbon, observing a higher synergic activity for carbons with a higher surface content of oxygen, specifically quinone groups. We also highlight that the synergic effect of the activated carbon requires adsorbent–adsorbate electrostatic interaction and is absent when this interaction is hindered.     

Carbon nanotube networks on different platforms

Carbon nanotube (CNT) networks are an emerging class of material with potential applications that range from biotechnology to sensors. However, the design and fabrication of CNT networks with specific properties necessitates a deep understanding on how a variety of factors affect the performance of these materials. Of particular interest is how the substrate on which the CNT networks are assembled also influences on the applicational aspects of the CNT network. In this review, we overview the variety of substrates reported as CNT networks supports, and the different applications of these networks. Substrates can be varied from rigid to flexible to porous materials. Interestingly, the method of network preparation and the nature of the scaffold have a direct influence on the properties and the potential applications of the final material.     

Engineering proteolytically-degradable artificial extracellular matrices

Hydrogels are widely used as provisional matrices for tissue engineering and regenerative medicine, showing also great promise as platforms for 3D cell culture. Different bio-functionalization strategies have been proposed to enhance the biological performance of hydrogels, particularly when they lack intrinsic bioactivity. In this context, the design of artificial materials that mimic structural and functional features of the natural extracellular matrix (ECM) has been pursued. This review presents an overview on bioengineering approaches of integrating protease-sensitive motifs into hydrogels, for the creation of cell-responsive biomimetic scaffolding materials that degrade in response to their proteolytic microenvironment. The successful incorporation of protease-sensitive motifs in several synthetic and natural polymers, which has been achieved using various chemical routes, is described. In each case, the selected peptide sequences and their target proteases are highlighted, along with the main achievements of the study. A critical analysis of current limitations and recent advances is also provided, along with suggestions for further improvements.