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PubMed2006

Application of ion attachment mass spectrometry to evolved gas analysis for in situ monitoring of porous ceramic processing.

Ion attachment mass spectrometry was applied to evolved gas analysis-mass spectrometry (EGA-MS), generally known as thermogravimetry-mass spectrometry. Characteristic species arising from poly(vinyl alcohol) (PVA) and poly(methyl methacrylate) (PMMA) resin, used as a binder and a porogen, respectively, in the starting materials for porous ceramics, were detected in the mass spectra. The EGA curves of the characteristic mass peaks from PVA and PMMA, when plotted against the programmed temperature, successfully showed the individual pyrolysis behavior of each polymer during the firing process.

Journal Article↗

PubMed2002

The genetic secrets some fossils hold.

Most animals that once lived have gone extinct. The remains of a few of these can be found in museum collections worldwide. As modern evolutionary biology is limited to the use of extant taxa, retrieving DNA from extinct or subfossil organisms can add significant insight into past population history and resolve phylogenies that can be tentative by morphology alone. DNA is a relatively weak molecule, comparatively speaking, yet under certain conditions it persists in the fossil record, despite what in vitro chemistry predicts. While most fossil remains do not contain DNA, museum specimens can be screened for the presence of conditions that would be conducive for nucleic acid preservation by measuring the extent of amino acid racemization and by looking at the extent of protein hydrolysis by pyrolysis gas chromatography/mass spectrometry. Results from these types of analyses suggest that the preservation of DNA is linked to the temperature and its constancy at a site rather than its age. Chemical analyses of coprolites from extinct herbivores from the late Pleistocene, as well as Archaic Native Americans, show the presence of compounds from the Maillard reaction. Upon the cleaving of these products, the defecator can be identified and his diet analyzed.

Amino Acids↗

PubMed2001

Mechanisms and kinetics of thermal degradation of poly(epsilon-caprolactone).

Thermogravimetric analysis (TGA) simultaneously coupled with mass spectrometry (MS) and Fourier transform infrared spectrometry (FTIR) was developed as an original technique to study the thermal modification/degradation of poly(epsilon-caprolactone) (PCL) through in depth analysis of the evolved gas. Perfectly well-defined PCL samples with controlled end groups, predictable molecular weight, and narrow molecular weight distribution were synthesized by living "coordination-insertion" ring-opening polymerization of epsilon-caprolactone initiated by aluminum triisopropoxide. TGA analyses carried out on purified PCL samples, deprived from any residual catalyst or monomer, highlighted a two-step thermal degradation. Evolved gas analysis by both MS and FTIR showed that the first process implies a statistical rupture of the polyester chains via ester pyrolysis reaction. The produced gases were identified as H(2)O, CO(2), and 5-hexenoic acid. The second step leads to the formation of epsilon-caprolactone (cyclic monomer) as result of an unzipping depolymerization process. The influence of parameters such as polyester molecular weight, nature of the PCL end groups, and presence of catalytic residues as well as the type of purge gas were investigated. The activation energy of the thermal degradation was also studied.

Chromatography, Gel↗

PubMedDate not supplied

Thermal degradation of poly(3-hydroxyalkanoates): preparation of well-defined oligomers.

The thermal degradation of the biodegradable bacterial polyesters poly(3-hydroxybutyrate), PHB, poly(3-hydroxyvalerate), PHV, and poly(3-hydroxybutyrate-co-3-hydroxyvalerate), 0-21 mol % of hydroxyvalerate, was studied. At moderately low temperatures (170-200 degrees C), the main product is a well-defined oligomer, especially a 500-10,000 g/mol macromolecule, which contains one unsaturated end group, predominantly a trans-alkenyl end group, as well as a carboxylic end group. The process was studied regarding the effect of the copolymer composition and reaction time at 190 degrees C. During the first few hours of reaction, the thermal degradation of PHB and PHV followed a kinetic model of random scission, but eventually auto-acceleration of the pyrolysis was detected, probably due to the influence of the crotonate end groups of the oligomers formed. Ten-time scale-up experiments on a Brabender instrument were successfully undertaken.

Chromatography, Gel↗

PubMedDate not supplied

One-step synthesis of amphiphilic diblock copolymers from bacterial poly([R]-3-hydroxybutyric acid).

Catalyzed transesterification in the melt is used to produce diblock copolymers of poly([R]-3-hydroxybutyric acid), PHB, and monomethoxy poly(ethylene glycol), mPEG, in a one-step process. Bacterial PHB of high molecular weight is depolymerized by consecutive and partly simultaneous reactions: pyrolysis and transesterification. The formation of diblocks is accomplished by the nucleophilic attack from the hydroxyl end-group of the mPEG catalyzed by bis(2-ethylhexanoate) tin. The resulting diblock copolymers are amphiphilic and self-assemble into sterically stabilized colloidal suspensions of PHB crystalline lamellae.

Bacteria↗

PubMedDate not supplied

Degradation of vulcanized and nonvulcanized polyisoprene rubbers by lipid peroxidation catalyzed by oxidative enzymes and transition metals.

Despite numerous reports concerning the biodegradation of rubber materials, there has been no report of rubber degradation by fully characterized enzymes. In the present paper, we presented a new method to decompose nonvulcanized and vulcanized polyisoprene rubbers by controlling the free radical chain reactions of lipids using oxidative enzymes, manganese peroxidase (MnP), laccase (Lac), and horseradish peroxidase (HRP). Nonvulcanized synthetic polyisoprene (IR) was degraded by the free radicals from unsaturated fatty acids produced by MnP, HRP, and a combination of Lac/1-hydroxybenzotriazole. In contrast, lipoxygenase caused no apparent degradation. Degradation of IR was also observed in lipid peroxidation initiated by the Fenton reaction (FR) and Mn(III), an oxidation product produced by MnP. Vulcanized polyisoprene rubber sheets were degraded by the lipid peroxidation initiated by HRP, MnP, Mn(III), and FR. Pyrolysis GC-MS analysis demonstrated that the lipid peroxidation liberated isoprenoid fragments from the vulcanized rubbers.

Butadienes↗

PubMedDate not supplied

Effects of residual zinc compounds and chain-end structure on thermal degradation of poly(epsilon-caprolactone).

Effects of chain-end structure and residual metal compounds on thermal degradation of poly(epsilon-caprolactone) (PCL) were investigated by means of thermogravimetric and pyrolysis-gas chromatograph mass spectrometric analyses. Four types of PCL samples with different chain-end structures (alpha-carboxylic acid-omega-hydroxyl-PCL, alpha-dodecyl ester-omega-hydroxyl-PCL, alpha-carboxylic acid-omega-acetyl-PCL, and alpha-dodecyl ester-omega-acetyl-PCL) were prepared by ring-opening polymerization of epsilon-caprolactone in the presence of zinc-based catalyst and by subsequent acetylation reaction of polymers with acetic anhydride. PCL samples with different zinc contents were obtained by washing with acetic acid in chloroform solution of polymer. Thermal degradation behaviors of these PCL samples with different chain-end structures were examined under both isothermal and nonisothermal conditions. From both the isothermal and nonisothermal experiments, the thermal degradation of PCL samples containing high amounts of residual zinc compounds from synthesis process revealed the selective unzipping depolymerization step below 300 degrees C producing epsilon-caprolactone exclusively. In contrast, zinc-free PCL samples were stable at temperatures below 300 degrees C, and the thermal degradation occurred only at temperatures above 300 degrees C regardless of the chain-end structure. From (1)H NMR analysis of the residual molecules after isothermal degradation of zinc-free PCL, it was confirmed that the omega-chain-end of residual molecules was 5-hexenoic acid unit. However, the cyclic monomer and oligomers were detected as the volatile products of zinc-free PCL samples. These results suggest that the dominant reaction of thermal degradation for PCL above 300 degrees C is a competition between the random chain scission via cis elimination reaction and the cyclic rupture via intramolecular transesterification of PCL molecules.

Catalysis↗

PubMed2001

Degradation pathways of pentachlorophenol by photo-Fenton systems in the presence of iron(III), humic acid, and hydrogen peroxide.

The degradation characteristics and pathways of pentachlorophenol (PCP) by the photo-Fenton systems were studied in H2O2 aqueous solutions, which contained Fe(III) only [H2O2/Fe(III) system] and Fe(III) + humic acid (HA) [H2O2/Fe(III)/HA system] at pH 5.0. Although 40% of the PCP was degraded after 5 h of irradiation in the H2O2/Fe(III) system, more than 90% was degraded in the H2O2/Fe(III)/HA system. This shows that at pH 5.0 the degradation of PCP is clearly enhanced by the presence of HA in the photo-Fenton system. In the H2O2/Fe(III) system, the production of octachlorodibenzo-p-dioxin (OCDD) was detected, and 2-hydroxy nonachlorodiphenyl ether was also identified as a precursor of OCDD. However, no OCDD production was observed in the H2O2/Fe(III)/HA system. This indicates that the presence of HA represses the production of OCDD during the degradation of PCP by the photo-Fenton system. Such an effect by HA can be attributed to a reaction sequence wherein reaction intermediates derived from PCP, such as PCP., are incorporated into HA. This was verified by 13C NMR and pyrolysis-GC/MS studies.

Biodegradation, Environmental↗

PubMed2001

Chemical characterization of fine particle emissions from fireplace combustion of woods grown in the northeastern United States.

A series of source tests was conducted to determine the chemical composition of fine particle emissions from the fireplace combustion of six species of woods grown in the northeastern United States: red maple, northern red oak, paper birch, eastern white pine, eastern hemlock, and balsam fir. Results include fine particle emission rates for total mass, organic and elemental carbon, ionic species, elemental species including potassium, and over 250 specific organic compounds. The data are intended for use in source-apportionment studies that utilize particulate organic compounds as source-specific tracers. The cellulose pyrolysis product levoglucosan was quantified in each of the wood smokes studied and is thus a good candidate as a molecular tracer for wood combustion in general. Differences in emission rates of specific substituted phenols and resin acids can be used to distinguish between the smoke produced when burning hardwoods versus softwoods. Certain organic compounds, such as betulin from paper birch combustion and juvabione and dehydrojuvabione from balsam fir combustion, are unique to those species and can potentially be utilized to trace particulate emissions back to a specific geographical region where those individual tree species are used for firewood.

Air Pollutants↗

PubMed2001

Polycyclic aromatic hydrocarbons identified in soot extracts from domestic coal-burning stoves of Henan Province, China.

Using high-pressure liquid chromatography with ultraviolet-visible diode-array detection, we have analyzed polycyclic aromatic hydrocarbons (PAH) in the dichloromethane extracts of soot deposits from coal-burning stoves in several homes of Henan Province, China--including Linxian County, where esophageal cancer rates are some of the highest in the world. Thirty-two individual polycyclic aromatic compounds, ranging in size from three to eight fused aromatic rings, have been unequivocally identified among the soot extract components--including 20 benzenoid PAH, 6 fluoranthene benzologues, 1 cyclopentafused PAH, 1 indene benzologue, 3 oxygenated PAH, and 1 ring-sulfur-containing aromatic. Most of the identified compounds have been observed before among the products of laboratory coal pyrolysis experiments, but two of the components, the six-ring C24H14 napthol[1,2-b]fluoranthene and the eight-ring C30H16 tribenzo[e,ghi,k]perylene, have never before been documented as products of coal in any system. All of the Henan coal soot extracts are remarkably similar qualitatively in that they contain the same set of identified PAH, but absolute levels of individual species vary by up to 5 orders of magnitude, from sample to sample. The bulk of the identified component mass in all of these soot extracts lies in the five- and six-ring PAH--the largest single class being the family of five-ring C20H12 isomers, to which the samples' most abundant components, benzo[b]fluoranthene and benzo[e]pyrene, belong. The five- and six-ring PAH also account for the majority of the samples' known mutagens. The three strong mutagens identified in these soot samples are the C20H12 benzo[a]-pyrene and two C24H14 PAH, dibenzo[a,e]pyrene and naphtho-[2,1-a]pyrene. Seven moderate mutagens are found among the C20H12, C22H12, C22H14, and C24H14 PAH. A major class of mutagens, the cyclopenta-fused PAH, appears to be absent from these samples, but our detection of an oxidation product of the major mutagen cyclopenta[cd]- pyrene--itself mutagenic--suggests that these soot deposits may contain additional mutagenic cyclopentafused PAH oxidation products as well.

Air Pollutants↗

PubMed2001

Degradation characteristics of humic acid during photo-Fenton processes.

Changes in the molecular and structural characteristics of humic acid (HA) during photo-Fenton processes were studied. When aqueous solutions at pH 5.0, which contained HA, Fe(III), and H2O2, were irradiated (lambda > 370 nm), the concentrations of total organic carbon (TOC) decreased with increasing irradiation time, indicating that a portion of the HA was mineralized to CO2 during this process. To investigate the changes in molecular and structural characteristics, the HA was reisolated from the reaction mixtures after each period of irradiation. The increased elution volumes required for isolation by gel permeation chromatography indicated that the molecular size of HA decreased as a result of the irradiation. In the FTIR spectra, ether and epoxide functional groups were identified, after irradiation. These products could be formed via radical coupling and/or via peroxy radical addition reactions to the unsaturated groups in the HA, such as vinyl and aromatic groups. Moreover, an analysis of structural fragments in HA by pyrolysis-GC/MS showed that the cinnamic acid moieties (CA) disappeared, as a result of irradiation. In the molecular weight fractionated HA, the majority of the iron species were complexed with the high molecular weight HA fraction, and the CA levels of the high molecular weight fraction were larger than those in the low molecular weight fraction. These results are consistent with residues, as the reactive sites in the photo-Fenton systems. Therefore, the degradation of these sites in the high molecular weight fraction may serve as a factor in decreasing the molecular size of HA.

Carbon Dioxide↗

PubMed2001

Applications of ultrasound in NAPL remediation: sonochemical degradation of TCE in aqueous surfactant solutions.

Surfactant-enhanced pump-and-treat technologies increase the efficiency of nonaqueous-phase liquids (NAPLs) removal from soils. However, high concentrations of surfactants in groundwater impose severe limitations to water treatment. In this paper, we explore the applicability of ultrasonic irradiation as an alternative method for surfactant recovery and contaminant degradation. The combined effects of temperature, initial substrate concentration, and concentration of added surfactant (sodium dodecyl sulfate, SDS) were analyzed for the sonolysis of trichloroethylene (TCE) in batch experiments at an ultrasonic frequency of 500 kHz and 77 W/L applied power density. In the range of 5-30 degrees C, TCE sonolysis becomes faster at higher temperatures, both in the absence and in the presence of surfactant. This indicates that gas-phase pyrolysis prevails over other chemical reactions in the liquid phase. Inhibition of TCE sonolysis was observed in the presence of surfactant at all SDS concentrations. Changes in the initial TCE concentration (from 250 microM to 1.2 mM) showed no effect on the degradation rates in the presence of SDS. For surfactant levels below its critical micelle concentration (cmc), the inhibition of TCE sonolysis exhibited a highly nonlinear dependence with increasing SDS concentration. A correlation was observed in this range between the relative inhibition of sonolysis and the decreasing surface tension of the solutions. Above the cmc up to an SDS concentration of 5%, the reaction rate decreased less markedly. Micellar sequestration of the contaminant seems to be the main reason for this additional inhibition. Bubble growth prior to collapse may incorporate some of the TCE dissolved in the micelles through their adsorption in the expanding bubble walls, thus partially overcoming the scavenging effect due to micellar entrapment of the contaminant.

Micelles↗

PubMed2001

Polycyclic aromatic hydrocarbon and particulate emissions from two-stage combustion of polystyrene: the effect of the primary furnace temperature.

A study is presented on laboratory-scale combustion of polystyrene (PS) to identify staged-combustion conditions that minimize emissions. Batch combustion of shredded PS was conducted in fixed beds placed in a bench-scale electrically heated horizontal muffle furnace. In most cases, combustion of the samples occurred by forming gaseous diffusion flames in atmospheric pressure air. The combustion effluent was mixed with additional air, and it was channeled to a second muffle furnace (afterburner) placed in series. Further reactions took place in the secondary furnace at a residence time of 0.7 s. The gas temperature of the primary furnace was varied in the range of 500-1,000 degrees C, while that of the secondary furnace was kept fixed at 1,000 degrees C. Sampling for CO, CO2, O2, soot, and unburned hydrocarbon emissions (volatile and semivolatile, by GC-MS) was performed at the exits of the two furnaces. Results showed that the temperature of the primary furnace, where PS gasifies, is of paramount importance to the formation and subsequent emissions of organic species and soot. Atthe lowesttemperatures explored, mostly styrene oligomers were identified at the outlet of the primary furnace, but they did not survive the treatment in the secondary furnace. The formation and emission of polycyclic aromatic hydrocarbons (PAH) and soot were suppressed. As the temperature in the first furnace was raised, increasing amounts of a wide range of both unsubstituted and substituted PAH containing up to at least seven condensed aromatic rings were detected. A similar trend was observed for total particulate yields. The secondary furnace treatment reduced the yields of total PAH, but it had an ambiguous effect on individual species. While most low molecular mass PAH were reduced in the secondary furnace, concentrations of some larger PAH increased under certain conditions. Thus, care in the selection of operating conditions of both the primary furnace (gasifier/ burner) and the secondary furnace (afterburner) must be exercised to minimize the emission of hazardous pollutants. The emissions of soot were also reduced in the afterburner but not drastically. This indicates that soot is indeed resistant to oxidation; thus, it would be best to avoid its formation in the first place. An oxidative pyrolysis temperature of PS in the vicinity of 600 degrees C appears to accomplish exactly that. An additional afterburner treatment at a sufficiently high temperature (1,000 degrees C) may be a suitable setting for minimization of most pollutants. To obtain deeper understanding of chemical processes, the experimental results were qualitatively compared with preliminary predictions of a detailed kinetic model that describes formation and destruction pathways of chemical species including most PAH observed in the present work. The modeling was performed forthe secondary furnace assuming plug-flow conditions therein. The experimentally determined chemical composition at the outlet of the primary furnace was part of the input parameters of the model calculation.

Air Movements↗

PubMed2002

Chemical characterzation of fine particle emissions from the fireplace combustion of woods grown in the Southern United States.

The fireplace combustion of wood is a significant and largely unregulated source of fine particle pollution in the United States. Source apportionment techniques that use particulate organic compounds as tracers have been successful in determining the contribution of wood smoke to ambient fine particle levels in specific areas in California. To apply these techniques to the rest of the United States, the differences in emissions profiles between different wood smoke sources and fuel types should be resolved. To this end, a series of fireplace source tests was conducted on six fuel wood species found in the Southern United States to determine fine particulate emission factors for total mass, ionic and elemental species, elemental and organic carbon, and over 250 individual organic compounds. The wood species tested, chosen for their high abundance and availability in the Southern U.S. region, were yellow poplar, white ash, sweetgum, mockernut hickory, loblolly pine, and slash pine. The differences in the emissions of compounds such as substituted phenols and resin acids help to distinguish between the smoke from hardwood and softwood combustion. Levoglucosan, a cellulose pyrolysis product which may serve as a tracer for wood smoke in general, was quantified in the emissions from all the wood species burned. The furofuran lignan, yangambin, which was emitted in significant quantities from yellow poplar combustion and not detected in any of the other North American wood smokes, is a potential species-specific molecular tracer which may be useful in qualitatively identifying particulate emissions from a specific geographical area where yellow poplar is being burned.

Air Pollutants↗

PubMed2002

Reduced heterogeneity of a lignite humic acid by preparative HPSEC following interaction with an organic acid. Characterization of size-separates by Pyr-GC-MS and 1H-NMR spectroscopy.

Preparative high performance size exclusion chromatography (HPSEC) was used to size-fractionate a humic acid (HA) solution with 0.05 M ionic strength before and after having made the humic solution 0.5 x 10(-3) M in acetic acid (AcOH). Size-fractions were characterized by pyrolysis-gas-chromatography/mass spectrometry (Pyr-GC-MS) and 1H NMR spectroscopy. Pyr-GC-MS showed that the AcOH treatment altered the distribution of humic molecular components in the size-fractions. The unsaturated alkyl chains were moved from size-fractions of larger molecular-size into those of lower molecular-sizes. Most of the aromatic moieties, which were found in larger molecular-size fractions for the untreated HA, were spread into fractions of lower molecular size after AcOH addition to HA. Carbohydrates, which were undetectable in anyfraction of the untreated HA, appeared instead in the pyrogram of the lowest molecular-size and most hydrophilic fraction after treatment with AcOH. Our results suggested that AcOH disrupted the weakly bound association of humic supramolecularstructures and HPSEC elution separated size-fractions of different composition without losing humic matter by adsorption on the HPSEC column. The fractions with the largest apparent molecular size were the richest in alkyl chains, thereby suggesting that humic molecules were stabilized into supramolecular associations by multiple weak interactions among apolar groups such as alkyl chains and aromatic moieties. 1H NMR spectra of size-fractions were greatly simplified and more resolved after AcOH treatment. This was attributed to a less complex molecular association in the size separates which provided a larger solubility in the NMR solvent and more favorable relaxation times. Combination of the procedure used here for size-fractionation with NMR and Pyr-GC-MS methods appears to be promising to advance knowledge on the molecular composition of humic substances.

Chromatography↗

PubMed2002

De novo synthesis of PCDD/F by thermogravimetry.

On the basis of laboratory experiments with model mixtures, the steps in the de novo synthesis of halogenated compounds were studied. The study was performed using a thermobalance to evaluate the temperature of the maximum rate and the kinetics of the decomposition of the materials in the presence of air. The effect of the presence of CuCl2 and CuO with an atmosphere of HCl was studied. Analysis of the volatiles and solids after combustion in a horizontal furnace confirms the presence of organochloride compounds (including PCDD/F) at various temperatures. With the procedure that we followed, combustion is separated from pyrolysis, and it is possible to analyze the essential factors involved in the combustion process.

Benzofurans↗

PubMed2003

DDT-related compounds bound to the nonextractable particulate matter in sediments of the Teltow Canal, Germany.

Sediment samples of the Teltow Canal (Berlin, Germany) were analyzed with respect to extractable and nonextractable organic compounds. The study focused on the identification and quantitation of bound 2,2-bis(chlorophenyl)-1,1,1-trichlorethane (DDT) residues in order to obtain further information about the fate of DDT-derived compounds within the particulate matter of the aquatic environment. Various chemical degradation techniques and a complementary online pyrolysis-GC/MS method were applied to the pre-extracted sediment residues. Generally, the distribution of the bound DDT-related compounds was found to differ distinctly from the substances distribution within the extractable fraction. The main metabolite of the anaerobic degradation pathway (2,2-bis(chlorophenyl)-1,1-dichlorethane, DDD) is most abundant in the sediment extracts but occurred only in insignificant concentrations in the degradation products of all procedures applied. The most abundant DDT-metabolites released after the degradation procedures were 4,4'-DBP, 4,4'-DDA, and 4,4'-DDM. In addition, 4,4'-DDM was detected at rather high concentrations by pyrolytic analysis. The results imply a weak association to the nonextractable particulate matter based on noncovalent interactions for the observed DDT-related contaminants. The release of these compounds was initiated by the modification and degradation of the organic macromolecular matrix as well as of the inorganic material. Furthermore, numerous methoxychlor-related compounds were detected not only in the extracts but also in parts of the hydrolysis products.

DDT↗

PubMed2003

Sorption hysteresis of benzene in charcoal particles.

Charcoal is found in water, soil, and sediment where it may act as a sorbent of organic pollutants. The sorption of organic compounds to natural solids often shows hysteresis. The purpose of this study was to determine the source of pronounced hysteresis that we found in the sorption of a hydrophobic compound (benzene) in water to a maple-wood charcoal prepared by oxygen-limited pyrolysis at 673 K. Gas adsorption (N2, Ar, CO2), 13C NMR, and FTIR show the charcoal to be a microporous solid composed primarily of elemental (aromatic) C and secondarily of carboxyl and phenolic C. Nonlocal density functional theory (N2, Ar) and Monte Carlo (CO2) calculations reveal a porosity of 0.15 cm3/g, specific surface area of 400 m2/g, and appreciable porosity in ultramicropores < 10 A. Benzene sorption-desorption conditions were chosen to eliminate artificial causes of hysteresis (rate-limiting diffusion, degradation, colloids effect). Charcoal sorbed up to its own weight of benzene at approximately 69% of benzene water solubility. Sorption was highly irreversible over most of the range tested (10(-4)-10(3) microg/mL). A dimensionless irreversibility index (/i) (0 < or = /i < or = 1) based on local slopes of adsorption and desorption branches was evaluated at numerous places along the isotherm. /i decreases as C increases, from 0.9-1 at low concentration to approximately 0 (approximately fully reversible) at the highest concentrations. Using sedimentation and volumetric displacement measurements, benzene is observed to cause pronounced swelling (up to > 2-fold) of the charcoal particles. It is proposed that hysteresis is due to pore deformation by the solute, which results in the pathway of sorption being different than the pathway of desorption and which leads to entrapment of some adsorbate as the polyaromatic scaffold collapses during desorption. It is suggested that intra-charcoal mass transport may be influenced by structural rearrangement of the solid, in addition to molecular diffusion.

Adsorption↗