Carbon-mineral adsorbents prepared by pyrolysis of waste materials in the presence of tetrachloromethane

Natural bentonite spent in the process of plant oil bleaching was used as an initial material for preparation of carbon-mineral adsorbents. The spent bleaching earth was treated using four procedures: T (thermal treatment); H (hydrothermal treatment); C (thermal treatment with addition of CCl4 vapor); M (modification of porous structure). Raw bentonite, RB (raw bleaching earth), and carbon materials prepared using plant oil were compared. The physicochemical characteristics of the adsorbents were determined using different methods: nitrogen adsorption/desorption, XRD, TEM, and MS-TPD. Carbon-mineral adsorbents contain from 5.23 to 19.92% C (w/w) and carbon adsorbents include from 84.2 to 91.18% C (w/w). Parallel processes of organic substance carbonization, porous structure modification, sublimation or evaporation of metal chlorides, and removal of hydrogen chloride take place during pyrolysis of waste mineral materials in the CCl4 atmosphere.     

Preparation of complex carbon-silica adsorbents with different properties

Summary The surface properties of complex adsorbents prepared through the pyrolysis of benzyl and n-heptyl alcohols and their mixtures on the surface of silica gel were investigated. The reactions were carried out in an autoclave at 500°C. A series of adsorbents having different porous structure, chemical nature of the adsorption centers and their topography were obtained. The best resolution of different mixtures was obtained by the carbon-silica adsorbent prepared through the pyrolysis of n-heptanol.     

Formation of phenoxy and cyclopentadienyl radicals from the gas-phase pyrolysis of phenol

The formation of radicals from the gas-phase pyrolysis of phenol over a temperature range of 400-1000 degrees C was studied using the technique of low temperature matrix isolation electron paramagnetic resonance (LTMI EPR). Cooling the reactor effluent in a CO2 carrier gas to 77 K produces a cryogenic matrix that exhibits complex EPR spectra. However, annealing by slowly raising the matrix temperature yielded well-resolved, identifiable spectra. All annealed spectra over the temperature range of 700-1000 degrees C resulted in the generation of EPR spectra with six lines, hyperfine splitting constant approximately 6.0 G, g = 2.00430, and peak-to-peak width approximately 3 G that was readily assignable, based on comparison with the literature and theoretical calculations, as that of cyclopentadienyl radical. Annihilation procedures along with microwave power saturation experiments helped to clearly identify phenoxy radicals in the same temperature region. Conclusive identifications of cyclopentadienyl and phenoxy radicals were based on pure spectra of these radicals under the same experimental conditions generated from suitable precursors. Cyclopentadienyl is clearly the dominant radical at temperatures above 700 degrees C and is observed at temperatures as low as 400 degrees C. The low-temperature formation is attributed to heterogeneous initiation of phenol decomposition under very low pressure conditions. The high cyclopentadienyl to phenoxy ratio was consistent with the results of reaction kinetic modeling calculations using the CHEMKIN kinetic package and a phenol pyrolysis model adapted from the literature.     

Multifunctionality and crystal dynamics of a highly stable, porous metal-organic framework [Zn4O(NTB)2

A porous metal-organic framework [Zn(4)O(NTB)(2)].3DEF.EtOH (1), in which (3,6)-connected nets are doubly interpenetrated to generate curved three-dimensional channels, has been prepared. Framework 1 exhibits high permanent porosity (Langmuir surface area, 1121 m(2)/g; pore volume, 0.51 cm(3)/cm(3)), high thermal stability (up to 430 degrees C), high hydrogen adsorption capacity (1.9 wt % at 77 K and 1 atm), selective organic guest binding ability (K(f)()( )(): MeOH > pyridine > benzene > dodecane), and guest-dependent blue luminescence (lambda(max) depending on guest identity). Most interestingly, the framework sustains single crystallinity even at 400 degrees C and 10(-)(5) Torr, and the framework components undergo reversible dynamics, mainly rotational motion, in response to removal and rebinding of the guest molecules.     

Synthesis and characterization of mesoporous ceria/alumina nanocomposite materials via mixing of the corresponding ceria and alumina gel precursors

Mesoporous ceria/alumina, CeO(2)/Al(2)O(3), composites containing 10, 20 and 30% (w/w) ceria were prepared by a novel gel mixing method. In the method, ceria gel (formed via hydrolysis of ammonium cerium(IV) nitrate by aqueous ammonium carbonate solution) and alumina gel (formed via controlled hydrolysis of aluminum tri-isopropoxide) were mixed together. The mixed gel was subjected to subsequent drying and calcination for 3 h at 400, 600, 800 and 1000 degrees C. The uncalcined (dried at 110 degrees C) and the calcined composites were investigated by different techniques including TGA, DSC, FTIR, XRD, SEM and nitrogen adsorption/desorption isotherms. Results indicated that composites calcined for 3 h at 800 degrees C mainly kept amorphous alumina structure and gamma-alumina formed only upon calcinations at 1000 degrees C. On the other hand, CeO(2) was found to crystallize in the common ceria, cerinite, phase and it kept this structure over the entire calcination range (400-1000 degrees C). Therefore, high surface areas, stable surface textures, and non-aggregated nano-sized ceria dispersions were obtained. A systematic texture change based on ceria ratio was observed, however in all cases mesoporous composite materials exposing thermally stable texture and structure were obtained. The presented method produces composite ceria/alumina materials that suit different applications in the field of catalysis and membranes technology, and throw some light on physicochemical factors that determine textural morphology and thermal stability of such important composite.     

Structural features and thermal degradation properties of various lignin macromolecules obtained from poplar wood (Populus albaglandulosa)

Four different lignins obtained from poplar wood (milled wood lignin: ML, organosolv lignin: OL, ionic liquid lignin: IL and Klason lignin: KL) were subjected to several types of chemical/thermal analyses to compare their structural features and thermal decomposition properties. The ML, OL, IL and KL yield from poplar wood was 5.5, 3.9, 5.8, 19.5 wt%, respectively. Functional group analysis revealed that during the OL and KL extraction processes, the condensation reaction involved with phenolic hydroxyl groups of lignins significantly prevailed, which led to a highly condensed OL and KL structure. Thermogravimetric analysis (TGA) results showed that OL and KL thermal stability was much higher than that of ML and IL. The derivatization followed by reductive cleavage (DFRC) data showed that the thermal stability was highly associated with the frequency of arylglycerol-β-aryl ether (β-O-4) linkages in the lignin polymers. Pyrolysis-GC/MS (Py-GC/MS) analysis confirmed that acetic acid and several types of phenolic compounds were the main lignin pyrolysis products. The maximum sum of ML (13.8 wt%), OL (9.9 wt%) and IL (11.8 wt%) pyrolysis products was obtained at the pyrolysis temperature of 600 °C, whereas KL (1.6 wt%) was significantly lower due to its high thermal stability and condensation degree. The S- and G-type pyrolysis products (S/G) ratio varied from 1.61 to 1.93 for ML, 2.28 to 5.28 for OL, 2.06 to 2.86 for IL and 1.40 to 2.20 for KL, depending on the pyrolysis temperature, which ranged between 400 °C and 700 °C.     

Simultaneous Removal of Polymers with Different Ionic Character from Their Mixed Solutions Using Herb-Based Biochars and Activated Carbons

Nettle and the sage herbs were used to obtain carbonaceous adsorbents. For the biochar preparation the precursors were dried and subjected to conventional pyrolysis. Activated carbons were obtained during precursor impregnation with phosphoric(V) acid and multistep pyrolysis. The textural parameters and acidic-basic properties of the obtained adsorbents were studied. The activated carbons prepared from the above herbs were characterized by the largely developed specific surface area. The obtained carbonaceous adsorbents were used for polymer removal from aqueous solution. Poly(acrylic acid) (PAA) and polyethylenimine (PEI) were chosen, due to their frequent presence in wastewater resulting from their extensive usage in many industrial fields. The influence of polymers on the electrokinetic properties of activated carbon were considered. PAA adsorption caused a decrease in the zeta potential and the surface charge density, whereas PEI increased these values. The activated carbons and biochars were used as polymer adsorbents from their single and binary solutions. Both polymers showed the greatest adsorption at pH 3. Poly (acrylic acid) had no significant effect on the polyethylenimine adsorbed amount, whereas PEI presence decreased the amount of PAA adsorption. Both polymers could be successfully desorbed from the activated carbons and biochar surfaces. The presented studies are innovatory and greatly required for the development of new environment protection procedures.     

Preparation and modification of complex pyrolytic carbon-silica adsorbents

Summary The surface properties of complex adsorbents prepared through the pyrolysis of dichloromethane on the surface of silica gel were investigated. The reaction was carried out in a specially constructed reactor at 400–500°C. The construction and performance of the reactor are described. The modification of the silica gel surface by pyrogenic carbon results in its chemical but not energetical homogeneity. Such adsorbents usually show strong adsorptive properties which limits their use in chromatography. A simple method of homogenizing the porous structure and energetic properties of the adsorptive centers of such adsorbents is presented. The method consists of an additional pyrolysis of an alcohol or other substances on the surface of the carbon-silica adsorbent. Such reactions were carried out under both static and dynamic conditions. The properties of the modified adsorbent depend on the reaction conditions and on the type of the additionally pyrolysed substance.     

Magnesium indium oxide (MgIn2O4) spinel thin films: chemical spray pyrolysis (CSP) growth and materials characterizations

MgIn(2)O(4), which has an inverse spinel structure, has been adopted as the transparent material in optoelectronic device fabrication due to its high optical transparency and electrical conductivity. Such a technologically important material was prepared by the spray pyrolysis technique. Precursors prepared for the cationic ratio Mg/In=0.5 were thermally sprayed onto glass substrates at 400 and 450 degrees C. We report herein the preparation and characterization of the films by X-ray diffraction (XRD), energy-dispersive absorption X-ray spectroscopy (EDAX), and atomic force microscopy (AFM). The XRD results showed the single phase formation of the material that revealed the presence of Mg(2+) and In(3+) in the inverse spinel-related structure. The FTIR and EDAX results further confirmed that the nanocrystalline films were mainly composed of magnesium, indium, and oxygen, in agreement with XRD analysis. We surmised from the AFM micrographs that the atoms have enough diffusion activation energy to occupy the correct site in the crystal lattice. For the 423-nm-thick magnesium indium oxide films grown at 400 degrees C, the electrical conductivity was 5.63x10(-6) Scm(-1) and the average optical transmittance was 63% in the visible range (400-700 nm). Similar MgIn(2)O(4) films deposited at 450 degrees C have a conductivity value of 1.5x10(-5) Scm(-1) and an average transmittance of 75%. Hall coefficient observations showed n-type electrical conductivity and high electron carrier concentration of 2.7x10(19) cm(-3).     

Effect of expanded graphite lattice in exfoliated graphite nanofibers on hydrogen storage

A graphite exfoliation technique, using intercalation of a concentrated sulfuric/nitric acid mixture followed by a thermal shock, has successfully exfoliated a herringbone graphite nanofiber (GNF). The exfoliated GNF retains the overall nanosized dimensions of the original GNF, with the exfoliation temperature determining the degree of induced defects, lattice expansion, and resulting microstructure. High-resolution transmission electron microscopy indicated that the fibers treated at an intermediate temperature of 700 degrees C for 2 min had dislocations in the graphitic structure and a 4% increase in graphitic lattice spacing to 3.5 A. The fibers treated at 1000 degrees C for 36 h were expanded along the fiber axis, with regular intervals of graphitic and amorphous regions ranging from 0.5 to >50 nm in width. The surface area of the starting material was increased from 47 m(2)/g to 67 m(2)/g for the 700- degrees C treatment and to 555 m(2)/g for the 1000- degrees C treatment. Hydrogen uptake measurements at 20 bar indicate that the overall hydrogen uptake and operative adsorption temperature are sensitive to the structural variations and graphitic spacing. The increased surface area after the 1000- degrees C treatment led to a 1.2% hydrogen uptake at 77 K and 20 bar, a 3-fold increase in hydrogen physisorption of the starting material. The uptake of the 700- degrees C-treated material had a 0.29% uptake at 300 K and 20 bar; although low, this was a 14-fold uptake over the starting material and higher than other commonly used pretreatment methods that were tested in parallel. These results suggest that selective exfoliation of a nanofiber is a means by which to control the relative binding energy of the hydrogen interaction with the carbon structure and thus vary the operative adsorption temperature.     

Primary thermal degradation processes occurring in poly(phenylenesulfide) investigated by direct pyrolysis–mass spectrometry

The thermal degradation Processes which occur in poly(phenylenesulfide) (PPS) have been studied by direct pyrolysis-mass spectrometry (DPMS). The structure of the compounds evolved in the overall temperature range of PPS decomposition (400–700°C) suggests the occurrence of several thermal decomposition steps. At the onset of the thermal degradation (430–450°C) this polymer decomposes with the formation of cyclic oligomers, generated by a simple cylization mechanism either initiated at the—SH end groups or by the exchange between the inner sulfur atoms along the polymer chain. At higher temperature (> 500°C) another decomposition reaction takes over with the formation of aromatic linear thiols. The formation of thiodibenzofuran units by a subsequent dehydrogenation reaction occurs in the temperature range of 550–650°C; in fact, pyrolysis products with a quasi-ladder structure have also been detected. Ultimately, above 600°C, extrusion of sulfur from the pyrolysis residue occurs with the maximum evolution at the end of decomposition (about 700°C). It appears, therefore, that the residue obtained at high temperature tends to have a crosslinked graphite-like structure from which the bonded sulfur is extruded. © 1994 John Wiley & Sons, Inc.     

Silica adsorbent prepared from spent diatomaceous earth and its application to removal of dye from aqueous solution

The objective of this work is to study the activation regeneration of spent diatomaceous earth (SDE) for the preparation of silica adsorbents using thermal regeneration and acid/alkaline activation methods. Under the experimental conditions investigated, it was found that the alkaline activation method carried out by sodium hydroxide under controlled conditions is significantly superior to other heat and activation methods. The porosities of solids thus obtained are over 0.2, indicating that they are basically mesoporous. The optimal porous material thus prepared was used as a mineral adsorbent for methylene blue at 25 degrees C. The adsorption equilibrium revealed that the silica adsorbent can take up over 50 mg/g at relatively low concentrations in aqueous medium from the fittings of Langmuir and Freundlich isotherms with high correlations. On the other hand, the adsorption kinetic of methylene blue under various adsorbent dosages can be well described with a pseudo-second-order reaction model.     

Formation and characterization of high surface area thermally stabilized titania/silica composite materials via hydrolysis of titanium(IV) tetra-isopropoxide in sols of spherical silica particles

A direct synthetic route leading to titania particles dispersed on nonporous spherical silica particles has been investigated; 5, 10, and 20% (w/w) titania/silica sols mixtures were achieved via hydrolyzation of titanium tetra-isopropxide solution in the mother liquor of a freshly prepared sol of spherical silica particles (St?ber particles). Titania/silica materials were produced by subsequent drying and calcination of the xerogels so obtained for 3 h at 400 and 600 degrees C. The materials were investigated by means of thermal analyses (TGA and DSC), FT-IR, N(2) gas adsorption-desorption, powder X-ray diffraction (XRD), and transmission electron microscopy (TEM). In spite of the low surface area (13.1 m(2)/g) of the pure spherical silica particles calcined at 400 degrees C, high surface area and mesoporous texture titania/silica materials were obtained (e.g., S(BET) ca. 293 m(2)/g for the 10% titania/silica calcined at 400 degrees C). Moreover, the materials were shown to be amorphous toward XRD up to 600 degrees C, while reasonable surface areas were preserved. It has been concluded that dispersion of titania particles onto the surface of the nonporous spherical silica particles increase their roughness, therefore leading to composite materials of less firm packing and mesoporosity.     

Adsorption of a reactive dye on chemically modified activated carbons--influence of pH

The surface chemistry of a commercial activated carbon with a slightly basic nature was modified by appropriate treatments in order to obtain two additional samples, respectively with acidic and basic properties, without changing its textural parameters significantly. Different techniques (N2 adsorption at 77 K, temperature programmed desorption, and determination of acidity, basicity, and pH at the point of zero charge) were used to characterize the adsorbents. Kinetic and equilibrium adsorption data of a selected textile reactive dye (Rifafix Red 3BN, C.I. reactive red 241) on the mentioned materials were obtained at the pH values of 2, 7, and 12. The kinetic curves are fitted using the second-order model. The respective rate constants seem to diminish progressively with the initial concentration for the more diluted solutions tested, reaching a constant value at higher concentrations, which depends on the experimental system under consideration (adsorbent and pH). In general, the Langmuir model provides the best fit for the equilibrium data. The different uptakes obtained are discussed in relation to the surface chemical properties of the adsorbents. It is shown that the adsorption of the reactive (anionic) dye on the basic sample (prepared by thermal treatment under H2 flow at 700 degrees C) is favored. This conclusion is explained on the basis of the dispersive and electrostatic interactions involved. Moreover, it is also shown that the optimal adsorption condition for all the activated carbons tested corresponds to solution pH values not higher than the pH(pzc) of the adsorbents, which may be interpreted by taking into account the electrostatic forces present.     

The effect of chemical activation method on properties of activated carbons obtained from pine cones

A method for obtaining carbonaceous adsorbents from pine cones by chemical activation with NaOH is described. Activated carbons were obtained by two methods of activation (physical mixing and impregnation) and two variants of thermal treatment. It has been shown that pine cones can be successfully used as cheap precursor of carbonaceous adsorbents of well-developed surface area, large pore volume and good sorption properties. All activated carbon samples obtained show strongly microporous structure and surface of acidic character. The best physicochemical properties and greatest sorption capacity towards iodine were found for the carbon samples obtained by physical mixing of the precursor with the activating agent and then subjected to thermal activation at 600°C.     

Study of thermal behavior of vitamin D3 by pyrolysis-GC-MS in combination with boiling point-retention time correlation

The thermal behavior of vitamin D3 was studied based on pyrolysis-GC-MS technique. It was pyrolyzed at 600 degrees C, 750 degrees C, 900 degrees C, respectively. The pyrolysis product were separated With an HP-5 column and identified by the NIST mass spectral search program in combination with the correlation of boiling point and retention time (BP-RT). There are totally 50 components, including mono aromatics and polycyclic aromatic hydrocarbons (PAHs), were determined. It is shown that the contents of the PAHs are increasing with the increasing of the pyrolysis temperature. The contents of the determined components vary from 0.04% to 37.08%.     

Nanostructured carbon arrays from block copolymers of polyacrylonitrile

Arrays of graphitic carbon nanoclusters were obtained by pyrolysis of nanoscale phase-separated block copolymers of polyacrylonitrile and poly(n-butyl acrylate). Upon heating in an inert atmosphere to temperatures ranging from approximately 400 to 1200 degrees C, polyacrylonitrile domains were converted into carbon nanoclusters, maintaining the overall shape and spacing, whereas the poly(n-butyl acrylate) phase was sacrificed. Preservation of the original nanoscale morphology of a block copolymer was possible only if pyrolysis was preceded by oxidation at temperatures of approximately 230 degrees C, in analogy with thermal stabilization of polyacrylonitrile precursor in the process used in the manufacturing of carbon fibers. Preorganization of the carbon precursor through self-assembly in block copolymers of polyacrylonitrile appears to be an attractive and robust strategy for templated synthesis of well-defined nanostructured carbon materials.     

Effects of vacuum pyrolysis conditions on the characteristics of activated carbons derived from pistachio-nut shells

Preparation of effective adsorbents from pistachio-nut shells was carried out. Optimization of the vacuum pyrolysis parameters prior to activation was carried out to study the effects of vacuum pyrolysis temperature, hold time, and heating rate on the properties of chars and activated carbons, while CO2 activation conditions were fixed at a temperature of 900 degrees C, an activation time of 30 min, a heating rate of 10 degrees C/min, a CO2 flow rate of 100 cm3/min, and a nitrogen flow rate of 150 cm3/min. The optimum vacuum pyrolysis conditions for preparing activated carbons with high surface area and pore volume were identified. The microstructure and microcrystallinity of the activated carbons prepared were examined by scanning electron microscopy and powder X-ray diffraction techniques respectively while the Fourier transform infrared spectra determined any changes in the surface functional groups produced during different preparation stages. Experimental results show that it is feasible to prepare activated carbons with high BET surface area from pistachio-nut shells.     

Synthesis and characterization of electrical conducting porous carbon structures based on resorcinol–formaldehyde

Electrical conducting carbon (ECC) porous structures were explored by changing the pyrolysis temperature of organic xerogel compounds prepared by sol–gel method from resorcinol–formaldehyde (RF) mixtures in acetone using picric acid as catalyst. The effect of this preparation parameter on the structural and electrical properties of the obtained ECCs was studied. The analysis of the obtained results revealed that the polymeric insulating xerogel phase was transformed progressively with pyrolysis temperature into carbon conducting phase; this means the formation of long continuous conducting path for charge carriers to move inside the structure with thermal treatment and the samples exhibited tangible percolation behaviour where the percolation threshold can be determined by pyrolysis temperature. The temperature-dependent conductivity of the obtained ECC structures shows a semi-conducting behaviour and the I(V) characteristics present a negative differential resistance. The results obtained from STM micrographs revealed that the obtained ECC structures consist of porous electrical conducting carbon materials.     

H2S adsorption/oxidation on materials obtained using sulfuric acid activation of sewage sludge-derived fertilizer

Sewage sludge-derived fertilizer, Terrene, was used as a precursor of adsorbents tested for removal of hydrogen sulfide from moist air. The adsorbents were obtained by pyrolysis of sulfuric acid-treated granular fertilizer at 600, 800, and 950 degrees C in a nitrogen atmosphere. The highest H(2)S removal capacity was obtained for the sample carbonized at 950 degrees C. This is a result of a combined effect of the specific chemistry of the inorganic phase and the development of microporosity within the carbon deposit. On the surface of the materials studied hydrogen sulfide is converted to elemental sulfur, sulfides, and sulfates as a result of the reaction with salts/oxides and the presence of an oxidizing atmosphere. The pores are gradually filled as the surface reactions proceed. The removal of H(2)S occurs until all the small micropores are filled with the reaction/oxidation products.