Chemical modification of activated carbon monoliths for CO2 adsorption

The development of materials with potential application for CO₂ capture is a topic of great scientific interest. Activated carbons (AC) can be conveniently used as CO₂ adsorbents thanks to their microporous structure and tunable chemical properties. In this work, two AC honeycomb monoliths were synthesized starting from African palm stones through activation either with H₃PO₄ or with ZnCl₂ solution. Surface functionalization was performed in order to add nitrogen groups, aiming at an enhancement of CO₂ adsorption capacity. This chemical modification was performed either with ammonia in gas phase or a with 30 % ammonium hydroxide aqueous solution on both AC monolith samples. The original and modified monoliths were characterized by N₂ adsorption at 77 K, infrared spectroscopy, Boehm titration, and immersion calorimetry in benzene and water. CO₂ adsorption on both raw and functionalized AC monoliths was evaluated in volumetric equipment at a temperature of 273 K and until 1 bar, and adsorption capacity ranging between 120 and 220 mg_CO2 g _AC ^?1 was obtained. The experimental results indicated that both methods of chemical modification determined an increase in the content of superficial nitrogen groups and thus an increase in CO₂ adsorption capacity, the treatment with ammonium hydroxide being slightly preferable.     

Thermal decomposition of lignocellulosic materials: comparison of the results obtained in different experimental systems

An experimental system that allows the use of large particle sizes and the simulation of different operating conditions was built to study the thermal decomposition of lignocellulosic materials. The values of solid conversion and of temperature obtained at different points using spherical particles of pine wood 2 cm in diameter are shown. The conversion values are compared with those calculated from the equations obtained in a thermobalance for small particle sizes.     

Enthalpic characterization of activated carbons obtained from <Emphasis Type="Italic">Mucuna Mutisiana</Emphasis> with different burn-offs

Immersion enthalpies of activated carbon samples obtained by activation with steam at temperatures between 600 and 900 °C and activation times between 1 and 10 h were determined. The calorimetric liquids of immersion are CCl₄, water, NaOH, and HCl 2 M solutions, and the values of the immersion enthalpies are related to other properties of the activated carbons such as the surface area B.E.T., the micropore volume, the content of acid, and basic surface groups. The highest values for the immersion enthalpies take place for the polar solvent CCl₄ and for HCl solution, with values between 4.0 and 75.2 J g⁻¹ and 9.15 and 48.3 J g⁻¹, respectively.     

CO<Subscript>2</Subscript> adsorption on binderless activated carbon monoliths

A series of activated carbon monoliths have been prepared by chemical activation of two lignocellulosic precursors, coconut shell (CACM) and African palm stones (PACM). The incorporation of a conforming step between the impregnation with H₃PO₄ and the activation step allows the successful development of disc-shape monoliths without the use of a binder. Textural characterization results using N₂ adsorption at 77 K show that the effect of the activating agent highly depends on the nature of the carbon precursor used. While chemical activation with phosphoric acid has mainly no effect when using coconut shell, a large development of both micro- and mesoporosity is observed for African palm stones. Large concentrations of the activating agent produce the partial shrinkage of the narrow microporous structure independently of the precursor used. Concerning the adsorption of CO₂ at atmospheric pressure and 273 K, both series of activated carbon monoliths exhibit an improved adsorption behaviour with the activation degree up to an optimum value around ∼164 mg CO₂/g, for sample CACM-32, and ∼162 mg CO₂/g, for sample PACM-28, the amount adsorbed decreasing thereafter. Apparently, the total amount of CO₂ adsorbed under these experimental conditions is defined by the volume of narrow micropores (V _n ).     

Low-temperature catalytic adsorption of NO on activated carbon materials

The catalytic adsorption of NO on activated carbon materials provides an appropriated alternative for the control of low-concentration emissions of this air pollutant. The surface complexes formed upon NO adsorption at 30 degrees C were studied by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD). The effects of the addition of O2 and the presence of copper as a catalyst were studied. Copper assisted the oxygen transfer to the carbon matrix. For the Cu-impregnated carbon sample, the presence of O2 favored NO adsorption by increasing the breakthrough time, the adsorption capacity, and the formation of nitrogen and oxygen complexes of higher thermal stabilities, which mainly desorbed as NO and CO2.     

Removal of phenols from water and petroleum industry refinery effluents by activated carbon obtained from coconut coir pith

Coir pith obtained from the coir industry as waste biomass was used to prepare activated carbon by chemical activation using phosphoric acid (H₃PO₄). The influences of activation temperature and lasting time of activation on specific surface areas (SSA) of the activated carbons were observed. Physical characteristics of the activated carbon were investigated using X-ray diffraction (XRD), infra-red spectroscopy (IR), surface area analyzer, scanning electron microscopy (SEM), thermal analysis and potentiometric titration. The feasibility of using activated carbon for the removal of phenol (P), p-chlorophenol (PCP) and p-nitrophenol (PNP) from water and petroleum refinery industry effluents was investigated. The effects of contact time, adsorbent dose, ionic strength and initial concentration on the adsorption of phenols onto the activated carbon were investigated. The optimum pH for the maximum removal of phenols was 6.0. The equilibrium adsorption data of phenols were correlated to Langmuir and Freundlich isotherm models, the latter being the best fit of the experimental data. Dynamics of the sorption process and mass transfer were investigated using McKay and Urano-Tachikawa models. Adsorption kinetic data fits the Urano-Tachikawa kinetic model. The utility of the adsorbent was tested by using petroleum refinery industry effluent. The adsorbed phenols can be recovered by treatment with 0.1 M NaOH solution.     

Adsorption characteristics of activated carbons obtained from corncobs

Dried, crushed, corncobs were carbonized at 500°C and steam activated (in one- or two-step schemes), or activated with H₃PO₄. The products were characterized by N₂ adsorption at 77 K, using the BET, _s and DR methods. Adsorption capacity was demonstrated by the iodine and phenol numbers, and the isotherms of methylene blue and Pb²⁺ ions, from aqueous solutions. A distribution of porosity in the carbons was estimated within the various ranges (ultra-, super-, meso- and macropores). Simple carbonization yields a poor adsorbing carbon; only its uptake for iodine was high and proposed to be due to an addition reaction on residual unsaturation of the parent lignocellulosic structures. Enhanced porosity was best associated with chemical activation and/or steam pyrolysis at 700°C. These activated carbons proved highly porous and rich in mesopores, and showed high adsorption capacity for methylene blue and Pb²⁺ ions. Phenol uptake was found to depend on surface chemical nature of the carbon rather than its porous properties. Corncobs were postulated to be feasible as feedstock to produce good adsorbing carbons, under the one-step activation schemes outlined here.     

Analysis of the microporous structure of the low-cost activated carbon fibres obtained from flax and jute cloth

The paper presents the results of research devoted to obtaining the low-cost activated carbon fibres from waste flax and jute cloth by carbonisation in inert atmosphere and activation with air as well as to the analysis of the microporous structure of materials obtained on the basis of the nitrogen, argon and benzene adsorption isotherms, using among others, the unique LBET method with implemented of the new models of the multilayer adsorption on the heterogeneous surfaces of the carbonaceous adsorbents. As part of the research conducted, imaging of the surface of the low-cost activated carbon fibres obtained has also been done using scanning electron microscopy.     

The environmental applications of activated carbon/zeolite composite materials

Over the past couple of years, the resurgence of placing an effective and sustainable amendment to combat against the auxiliary industrial entities, remains a highly contested agenda from a global point. With the renaissance of activated carbon, there has been a steadily growing interest in the research field. Recently, the adoption of zeolite composite, a prestigious advanced catalyst which formulates the enhancement of adsorption rate and hydrogen storage capability, has fore fronted to be a new growing branch in the scientific community. Confirming the assertion, this paper presents a state of art review of activated carbon/zeolite composite technology, its fundamental background studies, and environmental implications. Moreover, its major challenges together with the future expectation are summarized and discussed. Conclusively, the expanding of activated carbon/zeolite composite represents a potentially viable and powerful tool, leading to the plausible improvement of environmental preservation.     

Kinetics of thermochemical pretreatment of lignocellulosic materials

The results of an experimental study of the acid hydrolysis of hardwood are presented in the form of values for the three parameters, activation energy, power on the acid concentration, and pre-exponen-tial factor, of the first order kinetic constants for each of the following reaction participants: xylan remaining, glucan remaining, xylose formed, and xylose decomposed. These are used as a base for a quantitative theory to predict the temperature, time, and acid concentrations needed for effective pretreatment of the substrate for subsequent enzymatic hydrolysis of the glucan. This theory is based on the assumption that successful pretreatment requires >90% removal of the xylan, <10% removal of the glucan, and >80% xylose yield. This theory is compared with selected published data.     

HPLC characterization of phenolics in lignocellulosic materials

Summary The application of HPLC with an electrochemical detector for the determination of phenolics in lignocellulosic materials is reported. The separation of phenolic acids and aldehydes (gallic acid, p-hydroxybenzoic acid, vanillic acid, p-coumaric acid, syringic acid, ferulic acid, vanillin, syringaldehyde and p-hydroxybenzaldehyde) on two different columns (reversed phase C6 and styrene-divinylbenzene PLRP-S) is shown. Chromatograms of phenolic compounds in neutral, basic and oxidative extracts of wheat straw treated with NaOH and white rot fungusStropharia rugosoannulata are reported along with quantitative results.     

Structural influence of the carbon chain length in hybrid materials obtained from zirconium n-propoxide and diols

Zirconium n-propoxide Zr(OPr ⁿ )₄ has been chemically modified by 1,3-propanediol and 1,3-butanediol with molar ratio r=0.5, 1 and 2. The properties of the hybrid organic-inorganic materials obtained after drying at 100°C for 24 hours have been measured by thermal analysis, X-ray diffraction, infra-red spectroscopy and ¹³C NMR with cross-polarisation at magic angle spinning. Chemical modification of the zirconium precursor at a molecular level has been clearly detected, with a bridging coordination mode for both diols. If the coordination mode of the diols cannot be changed by increasing the carbon chain length, it was found using ¹³C CP MAS NMR that the local order is much more well-defined when the reactivity of both OH groups are not the same. Thus, using 1,3-butanediol which has a primary and a secondary OH group, it is possible to obtain after complete modification (r=2) a highly homogeneous hybrid polymer which transforms directly into tetragonal zirconia below 400°C. With other diols (1,2-ethanediol and 1,3-propanediol), the hybrid materials transform into tetragonal zirconia above 400°C through a decomposition process involving several steps. Then playing with the carbon chain length and/or the steric hindrance around the OH groups provides an easy way to monitor the ultrastructure of these hybrid materials, and allows a better control of the gel oxide transformation.     

Preparation of activated carbon from Turbinaria turbinata seaweeds and its use as supercapacitor electrode materials

Turbinaria turbinata brown seaweeds were tested as carbon electrode material in symmetric, electrochemical supercapacitors. The electrochemical properties of the carbon materials were characterised for their application as supercapacitors using cyclic voltammetry, galvanostatic charge/discharge method and electrochemical impedance spectroscopic analyses. Our initial results showed that the optimal behaviour was obtained for the sample prepared by pyrolysis at 800 °C. The average surface area of the carbon was 812 m²/g. Electrochemical tests with an organic electrolyte gave the following interesting results: a capacitance of 74.5 F/g, a specific series resistance of 0.5 Ω cm² and an ionic resistivity of 1.3 Ω cm². These results show the promising capacitive properties of carbon derived from seaweeds and their application in electrochemical supercapacitors.     

Hybrid/porous materials obtained from nano-emulsions

Nano-emulsions known also as mini-emulsions, ultrafine emulsions or submicron emulsions are a specific kind of emulsions that have a sub-micrometer droplet size and a low polydispersity. Nano-emulsions, being kinetically stable systems, require energy input in order to be formed, either from mechanical devices or from the intrinsic physicochemical potential of the components. The properties of the nano-emulsions make them suitable for applications in various domains such as drug delivery, cosmetics, pesticides and in particular for the preparation of inorganic or hybrid nanostructured materials. This review discusses the recent progresses made in this latest field. We focus on inorganic or hybrid nanoparticles, nanocapsules, hollow spheres or composites prepared by combining the nano-emulsion technique and the sol–gel process. In that case nano-emulsions act as template. We also outline the most recent development, which consists in using the nano-emulsions as imprints to get hierarchical porous silica materials.     

Preparation and characterisation of anion-exchange latex-coated silica monoliths for capillary electrochromatography

Silica monoliths coated with functionalised latex particles have been prepared for use in monolithic ion-exchange capillary electrochromatography (IE-CEC) for the separation of inorganic anions. The ion-exchange monoliths were prepared using 70 nm quaternary ammonium, anion-exchange latex particles, which were bound electrostatically to a monolithic silica skeleton synthesised in a fused silica capillary. The resulting stationary phases were characterised in terms of their chromatographic performance and capacity. The capacity of a 50 microm diameter 25 cm latex-coated silica monolith was found to be 0.342 nanoequivalents and 80,000 theoretical plates per column were typically achieved for weakly retained anions, with lower efficiency being observed for analytes exhibiting strong ion-exchange interaction with the stationary phase. The electroosmotic flow (EOF) was reversed after the latex-coating was applied (-25.96 m2 V(-1) s(-1), relative standard deviation (RSD) 2.8%) and resulted in anions being separated in the co-EOF mode. Ion-exchange interactions between the analytes and the stationary phase were manipulated by varying the ion-exchange selectivity coefficient and the concentration of a competing ion (phosphate or perchlorate) present in the electrolyte. Large concentrations of competing ion (greater than 1M phosphate or 200 mM perchlorate) were required to completely suppress ion-exchange interactions, which highlighted the significant retention effects that could be achieved using monolithic columns compared to open tubular columns, without the problems associated with particle-packed columns. The latex-coated silica monoliths were easily produced in bulk quantities and performed reproducibly in acidic electrolytes. The high permeability and beneficial phase ratio makes these columns ideal for micro-LC and preconcentration applications.     

吸汞载银活性炭纤维和吸汞活性炭纤维的热脱附特性研究

70℃下分别对载银活性炭纤维(载银量14.07%)和活性炭纤维的片状吸附体进行气态汞吸附实验,测定出载银活性炭纤维汞饱和吸附量为192.3 mg/g,活性炭纤维汞饱和吸附量为29.4 mg/g,分别为普通活性炭的48倍～192倍和7倍～29倍.采用热重分析法(TGA)研究了两种吸附剂汞饱和后的热脱附再生特性.结果表明,汞饱和载银活性炭纤维的汞脱附发生在100℃～650℃,在70 min内从50℃升温至650℃,才乏脱附率为94.73%;汞饱和活性炭纤维的汞脱附发生在100℃～230℃,在40 min内从50℃升温至350℃ ,汞脱附率为69.93%.扫描电镜分析发现,载银活性炭纤维因吸附汞而富集的银,经热脱附后变成均匀弥散于纤维表面的亚微米级和纳米级球状银颗粒;吸汞活性炭纤维经热脱附后物理吸附汞基本消失,而氧化汞颗粒反而变多,说明物理吸附的汞易于脱附,氧化汞难以脱附,同时在热脱附过程中存在金属汞向氧化汞的转化.     

Equilibrium,kinetics and thermodynamics study of phenols adsorption onto activated carbon obtained from lignocellulosic material (<Emphasis Type="Italic">Eucalyptus Globulus labill</Emphasis> seed)

Activated carbon was prepared from lignocellulosic material (Eucalyptus Globulus labill seed) by chemical activation with ZnCl₂ at two different concentrations (10 and 25 % m/v) named ACS25 and ACS10. The textural characteristics of the activated carbons (ACs) were determined by N₂ adsorption isotherms; these exhibit B.E.T. surface areas of 250 and 300 m² g^?1 for ACS25 and ACS10, respectively, with micropore volume contents of 0.140 and 0.125 cm³ g^?1 in the same order. In addition, the FTIR and Boehm methods were conducted for the chemical characterisation of ACs, where many groups with basic character were found, which favours the adsorption of phenols. The prepared carbonaceous adsorbents were used in the adsorption of wide pollutants monosubstituted phenol derivatives: phenol, 4-nitrophenol and 4-chlorophenol. The effect of temperature on the thermodynamics, kinetic and equilibrium of phenols adsorption on ACs was thoroughly examined. The adsorption kinetics adjusted properly for a pseudo-second-order kinetic model. However, the Elovich model (chemisorption) confirms that phenols adsorption did not occur via the sharing of electrons between the phenolic ring and basal plane of ACs because is not properly adjusted, so the process is given by physisorption. The thermodynamic parameters [i.e. Gibbs free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°)] were also evaluated. The overall adsorption process was exothermic and spontaneous in nature. The values found in the thermodynamic study, confirm that the adsorption process corresponds to a clearly physical process.     

Hybrid process for the conversion of lignocellulosic materials

Because of the recalcitrant nature of lignocellulosic materials, it is important to pretreat the biomass in order to obtain a suitable material for the bioconversion. In this study, two different types of pretreatments were performed. The first experiment used a 2-gal Parr reactor operated at 140, 150,160, and 170‡C with sulfuric acid concentrations varying from 0.5 to 2%. A second pretreatment was performed with a two-stage low-temperature process. The first-stage pretreatment was performed at 100 or 120‡C with sulfuric acid concentrations of 0.5, 2, and 5% followed by a secondstage pretreatment at 120‡C with 2% acid concentration. The best residues for enzymatic hydrolysis and simultaneous saccharification and fermentations (SSF) came from the higher temperature pretreatment with the Parr reactor. However, a large portion of the xylose fraction was degraded to furfural and glucose was degraded to HMF. On the contrary, the two-stage low temperature pretreatment resulted in a very low percentage of xylose degradation, and no glucose degradation. The residues from this two-stage pretreatment performed satisfactorily toward the production of ethanol by SSFs. This study discusses the results obtained from these experiments.