Sorption mechanisms of phenanthrene, lindane, and atrazine with various humic acid fractions from a single soil sample

The sorption behavior of organic compounds (phenanthrene, lindane, and atrazine) to sequentially extracted humic acids and humin from a peat soil was examined. The elemental composition, XPS and (13)C NMR data of sorbents combined with sorption isotherm data of the tested compounds show that nonspecific interactions govern sorption of phenanthrene and lindane by humic substances. Their sorption is dependent on surface and bulk alkyl carbon contents of the sorbents, rather than aromatic carbon. Sorption of atrazine by these sorbents, however, is regulated by polar interactions (e.g., hydrogen bonding). Carboxylic and phenolic moieties are key components for H-bonding formation. Thermal analysis reveals that sorption of apolar (i.e., phenanthrene and lindane) and polar (i.e., atrazine) compounds by humic substances exhibit dissimilar relationships with condensation and thermal stability of sorption domains, emphasizing the major influence of domain spatial arrangement on sorption of organic compounds with distinct polarity. Results of pH-dependent sorption indicate that reduction in sorption of atrazine by the tested sorbents is more evident than phenanthrene with increasing pH, supporting the dependence of organic compound sorption on its polarity and structure. This study highlights the different interaction mechanisms of apolar and polar organic compounds with humic substances.     

Identification and characterization of sorption domains in soil organic matter using strucuturally modified humic acids

The sorption of phenanthrene was examined in humic acids (HAs) from different sources: a compost, a peat soil, and a mineral soil. Sub-samples of each HA were subjected to bleaching or hydrolysis to remove predetermined chemical groups from their structures. Bleaching successfully removed a large percentage of rigid, aromatic moieties, whereas hydrolysis removed the mobile, carbohydrate components. Phenanthrene sorption by all HAs was nonlinear (N < 1). However, the phenanthrene isotherms of the bleached HAs were more linear than those of the untreated HAs, whereas the removal of the carbohydrate components by hydrolysis produced more nonlinear isotherms. The introduction of pyrene to the phenanthrene sorption system yielded more linear isotherms for all the HAs, indicative of competitive sorption. Proton spin-spin (1H T2) relaxation determined by nuclear magnetic resonance (NMR) was used to identify separate rigid (condensed) and flexible (expanded) 1H populations and to determine their distribution. These 1H domains were highly sensitive to temperature and correlated well with reported glass transition temperatures for HAs. In combination with the chemical treatments, sorption, and spectroscopic data, we were able to observe some significant relationships among chemical groups, sorption behavior, and structural characteristics.     

New structural information on a humic acid from two-dimensional 1H-13C correlation solid-state nuclear magnetic resonance

New information on the chemical structure of a peat humic acid has been obtained using a series of two-dimensional 1H-13C heteronuclear correlation solid-state NMR (HETCOR) experiments with different contact times and with spectral editing by dipolar dephasing and 13C transverse relaxation filtering. Carbon-bonded methyl groups (C-CH3) are found to be near both aliphatic and O-alkyl but not aromatic groups. The spectra prove that most OCH3 groups are connected directly with the aromatic rings, as is typical in lignin. As a result, about one-third of the aromatic C-O groups is not phenolic C-OH but C-OCH3. Both protonated and unprotonated anomeric O-C-O carbons are identified in the one- and two-dimensional spectra. COO groups are found predominantly in OCHn-COO environments, but some are also bonded to aromatic rings and aliphatic groups. All models of humic acids in the literature lack at least some of the features observed here. Compositional heterogeneity was studied by introducing 1H spin diffusion into the HETCOR experiment. Comparison with data for a synthetic polymer, polycarbonate, indicates that the separation between O-alkyl and aromatic groups in the humic acid is less than 1.5 nm. However, transverse 13C relaxation filtering under 1H decoupling reveals heterogeneity on a nanometer scale, with the slow-relaxing component being rich in lignin-like aromatic-C-O-CH3 moieties and poor in COO groups.     

Sorption of polar and nonpolar aromatic organic contaminants by plant cuticular materials: role of polarity and accessibility

In both forest and agricultural soils, plant derived cuticular materials can constitute a significant part of soil organic matter. In this study, the sorption of nonpolar (naphthalene and phenanthrene) and polar (phenol and 1-naphthol) aromatic organic pollutants to aliphatic-rich cuticularfractions of green pepper (Capsicum annuum) (i.e., bulk (PC1), dewaxed (PC2), nonsaponifiable (PC3), nonsaponifiable-nonhydrolyzable (PC4), and dewaxed-hydrolyzed residue (PC5)) were examined to better understand the influence of polarity and accessibility on their sorption behavior. The polarity and structures of cuticular fractions were characterized by elemental analysis, Fourier transform infrared spectroscopy, and solid-state 13C NMR. The sorption isotherms fit well to the Freundlich equation. Sorption of the tested organic compounds to PC4, which had more condensed domains, was nonlinear (Freundlich N(s) values of 0.766-0.966). For naphthalene and phenanthrene, the largest sorption capacity (K(oc)) occurred in PC5, which contained the highest paraffinic carbons (63%) and the lowest polarity: approximately 2 and aproximately 3 times higher than the respective carbon-normalized octanol-water partition coefficient (K(owc)), indicating that PC5 was a powerful sorption medium. For phenol and 1-naphthol, the largest K(oc) values occurred in PC4 with polar aromatic cores: approximattely 17 and approximately 7 times higher than the respective K(owc), suggesting that PC4 was much more accessible and compatible to polar aromatic pollutants than nonpolar aromatic pollutants. There was little or no correlation of K(oc) with either aliphatic or aromatic components of the tested aliphatic-rich sorbents because the polarity and accessibility apparently played a regulating role in the sorption of organic contaminants.     

Accurate quantification of aromaticity and nonprotonated aromatic carbon fraction in natural organic matter by 13C solid-state nuclear magnetic resonance

An improved approach for accurately determining the aromatic carbon fraction (fa) and nonprotonated aromatic carbon fraction (faN) in natural organic matter by solid-state 13C NMR is described. Quantitative peak areas are obtained from direct polarization 13C nuclear magnetic resonance (NMR) under high-speed magic angle spinning (MAS). The problem of overlap between aromatic and alkyl carbon resonances around 90-120 ppm in 13C NMR spectra is solved by a 13C chemical shift anisotropy (CSA) filter technique. After correction for residual spinning sidebands, an accurate value of the aromaticity fa is obtained. To obtain a quantitative faN fraction, dipolar dephasing was adapted for high-speed MAS 13C NMR; the separation of the signals of nonprotonated alkyl and aromatic carbons was achieved by CSA filtering plus dipolar dephasing. The method is demonstrated on a peat humic acid, yielding fa = 45 +/- 2% and faN = (0.64 +/- 0.07) x 45%.     

Aggregation and disaggregation of humic supramolecular assemblies by NMR diffusion ordered spectroscopy (DOSY-NMR)

Diffusion ordered nuclear magnetic resonance spectroscopy (DOSY-NMR) was applied to a number of fulvic (FA) and humic (HA) acids of different origin. Spectral separation achieved by DOSY based on diffusion coefficients (D), and correlated to molecular sizes by calibration standards, showed that carbohydrates had the largest molecular size in FA, whereas alkyl or aromatic components were the most slowly diffusing moieties in HA. At increasing concentrations, these components had invariably lower D values in DOSY spectra for all humic samples,thereby indicating an aggregation into apparently larger associations, whose increased hydrodynamic radius was confirmed by viscosity measurements. When humic solutions were broughtfrom alkaline to acidic pH (3.6), components diffusivity detected by DOSY increased significantly, suggesting a decrease of aggregation and molecular size. A general comparison of HA and FA molecular sizes was achieved by multivariate statistical analysis. While a larger extent of aggregation and disaggregation was observed for HA than for FA, no aggregation was detected, under similar conditions, for a true macropolymeric standard. Such difference in diffusion between a polymeric molecule and humic samples, is in line with the supramolecular nature of humic matter. The possible formation of humic micelles was also investigated by both changes of diffusivity in DOSY spectra and shift of 1H NMR signals. Except for HA of peat and soil origin, revealing a self-assembling in micelle-like structures at the 4 mg mL(-1) concentration, no other humic sample showed evidence of critical micelle concentration (cmc) up to 20 mg mL(-1). These results indicated that DOSY-NMR spectroscopy is a useful technique to evaluate components of different molecular size in natural humic superstructures.     

Phenanthrene sorption by aliphatic-rich natural organic matter

Contaminant sorption, an important process that may limit bioavailability, hinder remediation, encourage environmental persistence, and control mobility in the environment, has been the focus of numerous studies. Despite these efforts, the fundamental understanding of sorptive processes in soil and sedimentary environments has not been resolved. For instance, many have suggested that contaminants, such as polycyclic aromatic hydrocarbons (PAHs), solely interact with aromatic domains of organic matter. Until now, studies have neglected the aliphatic components that are known to be a recalcitrant and significant part of soil and sedimentary organic matter (SOM). In this investigation, the sorption of phenanthrene to several aliphatic-rich SOM samples was measured. The samples included the following: SOM precursors (algae, degraded algae, cellulose, collagen, cuticle, and lignin), two kerogen samples, and a highly aromatic humic acid. All samples were characterized by cross polarization magic angle spinning carbon-13 (CPMAS 13C) NMR and carbon, hydrogen, and nitrogen analysis. Batch experiments demonstrated that the highest organic carbon normalized sorption coefficients (Koc values) were obtained with the Pula kerogen sample (log Koc = 4.88) that only contains 6.5% aromatic carbon. Other aliphatic-rich samples, namely the Green River kerogen, degraded algae, and collagen samples produced comparable log Koc values (4.64, 4.66, and 4.72, respectively) to that of the highly aromatic humic acid (log Koc = 4.67). Phenanthrene uptake was the least for cellulose and lignin, two major soil components. A comparison of phenanthrene Koc values and paraffinic carbon content revealed a positive correlation (Koc = 798 +/- 96.1 * paraffinic carbon (%), r2 = 0.56) and indicates that amorphous polymethylene carbon is an important consideration in phenanthrene sorption. This study establishes that aliphatic SOM domains have a strong affinity for phenanthrene and likely, other PAHs. Therefore, aliphatic structures, that are an important component of SOM, require more attention in the examination of sorption processes in terrestrial and sedimentary environments.     

Binding of atrazine to humic substances from soil,peat and coal related to their structure

Partition coefficients for the binding affinities of atrazine to 16 different humic materials were determined by the ultrafiltration HPLC technique. Sources included humic acids (HA), fulvic acids (FA), and combined humic and fulvic fractions (HF) from soil, peat, and coal humic acid. Each of the humic materials was characterized by elemental composition, molecular weight, and composition of main structural fragments determined by 13C solution-state NMR. The magnitude of K(OC) values varied from 87 to 575 L/kg of C, demonstrating relatively low binding affinity of humic substances (HS) for atrazine. On the basis of the measured K(OC) values, the humic materials can be arranged in the following order: coal HA approximately = gray wooded soil HA > chernozemic soil HA and HF > sod-podzolic soil HA approximately = peat HF > sod-podzolic soil FA > peat dissolved organic matter. The magnitude of the K(OC) values correlated strongly with the percentage of aromatic carbon in HS samples (r = 0.91). The hydrophobic binding was hypothesized as the key interaction underlying the binding of atrazine to HS.     

Noncovalent interactions between monoaromatic compounds and dissolved humic acids: a deuterium NMR T1 relaxation study

Deuterium nuclear magnetic resonance spectroscopy (2H NMR) spin-lattice relaxation (T1) experiments were used to examine solution-phase, noncovalent interactions between deuterated monoaromatic compounds (phenol-d5, pyridine-d5, benzene-d6) and Suwannee River, soil, and peat humic acids. Noncovalent interactions, in aqueous solution, were examined as a function of solution pH, monoaromatic hydrocarbon functional groups, and humic acid identity. Benzene interacted with dissolved humic acids at all pH values; however, these interactions increased with decreasing pH and generally were proportional with the humic acid percent aromaticity. Pyridine behaved similarly as benzene; however, two modes of interaction between pyridine and humic acids were detected as a function of pH and humic acid type: bonding with the lone pair of electrons of pyridine's nitrogen and pi-pi interactions between the aromatic ring of pyridine and aromatic components of humic acid. The latter interaction was favored by increasing humic acid percent aromaticity and decreasing solution pH. On the other hand, because of its strong capacity for hydrogen bonding, phenol interacted preferentially with water, except at pH values 5 or lower and with humic acids with 45% or greater aromaticity. Under these conditions, strong interactions between phenol and humic acids were observed. These results demonstrate that solution-phase, noncovalent interactions between monoaromatic compounds and humic acids are a function of solution pH, percent aromaticity, and the monoaromatic functional group.     

Sorption equilibrium of a wide spectrum of organic vapors in Leonardite humic acid: experimental setup and experimental data

The environmental fate of volatile and semivolatile organic compounds is determined by their partitioning between air and soil constituents, in particular soil organic matter (SOM). While there are many studies on the partitioning of nonpolar compounds between water and SOM, data on sorption of polar compounds and data for sorption from the gas phase are rather limited. In this study, Leonardite humic acid/air partition coefficients for 188 polar and nonpolar organic compounds at temperatures between 5 and 75 degrees C and relative humidities between < 0.01% and 98% have been determined using a dynamic flow-through technique. To the best of our knowledge, this is by far the largest and most diverse and consistent data set for sorption into humic material published so far. The major results are as follows: the relative humidity affected the experimental partition coefficients by up to a factor of 3; polar compounds generally sorbed more strongly than nonpolar compounds due to H-bonding (electron donor/ acceptor interactions) with the humic acid; no glass transitions in the range of 5-75 degrees C that would be relevant with respect to the sorption behavior of hydrated Leonardite humic acid were observed; our experimental data agree well with experimental partition coefficients from various literature sources.     

Sorption of peat humic acids to multi-walled carbon nanotubes

Sorption of humic acids (HAs) from a peat soil by multiwalled carbon nanotubes (MWCNTs) was examined in this work. Sorption rate of HAs to MWCNTs was dominantly controlled by their diffusion from liquid-MWCNT boundary to MWCNT surfaces. Size exclusion chromatography analysis did not detect preferential sorption of HA fractions to MWCNTs at equilibrium, whereas the components with lower molecular weight in some HA fractions (e.g., HA1) would more preferentially be sorbed to MWCNTs at the initial sorption stage. Equilibrium sorption intensity of HAs by MWCNTs was dependent on their surface area and a sum of meso- and macropore volume. The surface area and sum of meso- and macroporosity-normalized sorption coefficient (K(d)) values of a given HA by MWCNTs increased with increasing outer diameter of MWCNTs, because MWCNTs with larger outer diameter were more strongly dispersed by HAs thereby making more sorption sites exposed for HA sorption. Van der Waals interaction between the alkyl components rather than the aromatic ones of HAs with MWCNTs was likely the key driving force for their sorption. This study highlights the sorption rate-controlling step of HAs from a same source to MWCNTs and the major factors affecting their sorption intensity at equilibrium.     

Characterization of water-soluble organic carbon in urban atmospheric aerosols using solid-state 13C NMR spectroscopy

Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy has been used to investigate the distribution of carbon functional groups in urban Atlanta aerosol fine (PM2.5) particles. Carbonaceous aerosol particles comprise a significant fraction of the ambient particle mass and are environmentally significant as they may influence radiative and cloud-nucleating properties and can also produce adverse health effects upon inhalation. The water-soluble organic carbon (WSOC) fraction was extracted from multiple 24 h integrated high-volume quartz filter samples and further separated into recovered hydrophobic and hydrophilic fractions using an approach similar to that used to extract humic and fulvic acids from aqueous samples. Solid-state 13C NMR results indicate that WSOC in urban atmospheric aerosol particles is mostly aliphatic in nature (approximately 95% by C mass) with major contributions from alkyl and oxygenated alkyls (approximately 80%), carboxylic acid (approximately 10%), and aromatic functional groups (approximately 4%). The aromatic C is associated with the recovered hydrophobic fraction of WSOC. These spectra have been compared to the 13C NMR results obtained from Suwannee River humic acid and a fractionated biomass burning sample. WSOC, and more importantly, its recovered hydrophobic fraction, is found to be only qualitatively similar to aqueous humic material. The biomass burning sample is significantly different from urban Atlanta WSOC and is composed of substantial amounts of sugar derivatives and phenolic compounds, as expected. The NMR results demonstrate the potential of this technique to investigate aerosol WSOC composition and to study its variations with changes in parameters such aerosol sources.     

Mobile aliphatic domains in humic substances and their impact on contaminant mobility within the matrix

Using a novel NMR option, magic angle spinning pulsed field gradient (MAS PFG) NMR, the mobility of aliphatic domains in humic substances in the presence of toluene (about 4.5 wt. %) has been monitored. Results show a strong correlation between the diffusivities of the mobile aliphatic chains and those of the adsorbed toluene molecules in the matrix as a function of temperature. Particularly, a strong influence of structural relaxation of the humic matrix on the diffusivity of toluene is observed. Our findings confirm that the aliphatic domains in humic substances play an important role in the mobility of sorbed contaminants within this matrix. These findings further confirm the potential of MAS PFG NMR method in monitoring diffusion processes in particulate humic substances.     

Investigating the role of mineral-bound humic acid in phenanthrene sorption

Contaminant-soil interaction studies have indicated that physical conformation of organic matter atthe solid-aqueous interface is important in governing hydrophobic organic compound (HOC) sorption. To testthis, organo-clay complexes were constructed by coating montmorillonite and kaolinite with peat humic acid (PHA) in Na+ or Ca2+ dominated solutions with varying pH and ionic strength values. The solution conditions encouraged the dissolved PHA to adopt a "coiled" or "stretched" conformation prior to interacting with the clay mineral surface. Both kaolinite and montmorillonite organo-clay complexes exhibited higher phenanthrene sorption (Koc values) with decreasing pH, indicating that the coiled configuration provided more favorable sorption conditions. Evidence from 1H high-resolution magic angle spinning (HR-MAS) nuclear magnetic resonance (NMR) indicated that polymethylene groups were prevalent at the surface of the organo-clay complexes and may enhance sorptive interactions. Preferential sorption of polymethylene groups on kaolinite and aromatic compounds on montmorillonite may also contribute to the difference in phenanthrene sorption by PHA associated with these two types of clay. This study demonstrates the importance of solution conditions in the sorption of nonionic, hydrophobic organic contaminants and also provides evidence for the indirect role of clay minerals in sorption of contaminants at the soil-water interface.     

A distributed reactivity model for sorption by soils and sediments 13. Simulated diagenesis of natural sediment organic matter and its impact on sorption/desorption equilibria

Subcritical water treatment was used to effect rapid compositional and functional changes to peat organic matter that mimic those of the natural diagenesis process. Elemental, solid state 13C NMR, FTIR, and calorimetry analyses all indicated that the organic matter of the artificially aged peat was chemically similar to that of geologically mature coal kerogens. This paper extends the work of the previous paper in this series, which investigated the effects of subcritical water treatment of humic topsoil on subsequent phenanthrene sorption and desorption equilibria. As opposed to the previous study, however, changes in sorptive reactivity herein were unequivocally related to changes in organic matter rather than other soil constituents, and organic matter functional changes due to the simulated diagenesis were more accurately characterized. Phenanthrene sorption capacity and isotherm nonlinearity both increased with increasing degrees of artificial aging, supporting the viewpoint that hydrophobic organic contaminant sorption equilibrium properties can be directly related to the degree of diagenesis of geosorbent organic matter. In addition, this work investigated effects of subcritical water treatment of a geologically mature, kerogen-containing shale sample. In contrast to the peat, the functional characteristics of the shale were unchanged by this treatment, and subsequent phenanthrene sorption equilibria were altered far less.     

Identification of black carbon derived structures in a volcanic ash soil humic acid by Fourier transform ion cyclotron resonance mass spectrometry

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), coupled with cross-polarization magic angle spinning 13C nuclear magnetic resonance (NMR) spectroscopy and Kendrick mass defect analysis, was used to study the molecular composition of an aromatic carbon-rich humic acid extracted from a dark black soil from Iwata, Japan. Black carbon, produced by the incomplete combustion of fossil fuels and organic matter, has been suggested as a major component of humic acids having intense peaks in the aromatic and carboxyl regions of the 13C NMR spectrum. Taking advantage of the high resolving power of FT-ICR MS to make precise formula assignments, three different types of highly carboxylated polycyclic aromatic compounds were identified in the sample: linearly fused aromatic structures, aromatic structures linked by carbon-carbon single bonds, and highly condensed aromatic structures. These carboxylated aromatic structures have a low mass defect in their mass spectra due to their abundance of oxygen and deficiency of hydrogen. This mass defect is observed in the vast majority of peaks present in the entire mass spectrum, differentiating them from structures that are hydrogen-rich (e.g., fatty acids, proteins, carbohydrates). Thus, we conclude that the bulk of the sample analyzed is comprised of these heavily carboxylated, hydrogen-deficient, condensed aromatic structures, features believed to be characteristic of black carbon-like material.     

Characterisation and evaluation of humic acids extracted from urban waste as liquid fertilisers

In this work a comparative study of humic acids extracted from organic wastes (sewage sludge and compost) and those currently used in the humic acid companies (humic acids from leonardite and peat) was carried out. Humic acids were characterised by means of chemical analysis (elemental and functional analysis) and spectroscopic techniques (¹³C NMR, gel filtration and infrared spectra) in order to relate their characteristics with their effect on plant growth. Chemical and spectroscopic analysis emphasised the different nature of the studied humic acids. The humic acids derived from the less evolved organic materials (sludge and compost) showed higher aliphatic nature, higher nitrogen compound content, lower oxidation degree and more heterogeneous composition than those extracted from more evolved materials (peat and leonardite). However, all these differences did not lead to significant differences in plant growth, but all these humic acids showed an increase of the yield respect to the control. ©1997 SCI     

Immobilizing humic acid in a sol-gel matrix: a new tool to study humic-contaminants sorption interactions

Humic substances originated from aquatic, soil, or sediment environments are mixtures of humic compounds with various characteristics. Sorption interactions with isolated, well defined humic fractions can be studied either in an aqueous phase ("dissolved humic substances"), or in a solid-phase, by coating mineral particles with the humic materials, or simply by working with humic acid particles (powder) at low pH to minimize dissolution. Each attitude, by definition, can be studied by different experimental techniques and has a different meaning for understanding natural environmental processes. In this study, a new tool for studying sorption interactions is presented. Sol-gel was used as an inert matrix to immobilize (entrap) various humic acids (HAs), and then used to study the interactions of several polycyclic aromatic hydrocarbons (PAHs) with the entrapped HA. Linear and nonlinear sorption coefficients were highly correlated with contaminant hydrophobicity. Sorption of pyrene to immobilized HA was in the order of soil HA > Aldrich HA approximately = peat HA. It was concluded that the entrapped HAs retained their original properties in the gel matrix and were accessible to the external contaminant through the pore network. Additionally, binding coefficients of pyreneto dissolved humic substances and to dissolved organic matter (DOM) were determined from the reduction in pyrene sorption to immobilized HA in the presence of dissolved humic material or DOM in solution. Binding coefficients of pyrene were in the order of the following: dissolved Aldrich HA > dissolved peat fulvic acid (FA) > DOM derived from mature compost > DOM derived from fresh compost.     

Sorption and conformational characteristics of reconstituted plant cuticular waxes on montmorillonite

Plant cuticular waxes are essential barriers that regulate the transport of water and organic molecules to intact cuticular membranes. They also compose a significant fraction ofthe recalcitrant aliphatic components of soil organic matter (SOM). In this study, we examined the sorption and desorption of three polycyclic aromatic hydrocarbons (PAHs), naphthalene (NAPH), phenanthrene (PHEN), and pyrene (PYR), by cuticular waxes of green pepper (Capsicum annuum) that had been reconstituted by loading them onto montmorillonite (at four different loadings). The reconstituted wax samples, with and without sorbed PAHs, were characterized by solid-state 13C NMR to supply the evidence of melting transition. The sorption isotherms fit well to a Freundlich equation. Sorption isotherms were practically linear except for that of PYR sorption to the low-load wax-montmorillonite sample. The organic-carbon-normalized sorption coefficients (Koc) depended on PAH's lipophilicity (e.g., octanol-water partition coefficient) and increased with increasing wax-load on clay. Desorption was dependent on PAH's molecular sizes and sorbed amounts and on the wax load of the clay. Desorption hysteresis was observed only at high loads of NAPH and PHEN, and it decreased with both increasing wax load and molecular size (i.e. NAPH > PHEN > PYR). Contributing to hysteresis, the melting transition of the reconstituted waxes after sorbing the PAHs was confirmed by solid-state 13C NMR data. Upon adsorption, the intensity of the NMR peak at 29 ppm (attributed to mobile amorphous paraffinic domains) increased, and a peak at 167 ppm (-COOH) appeared, reflecting the transition of solid amorphous to mobile amorphous domains in the reconstituted waxes. The intensity of melting induced by PAH adsorption decreased with increasing PAH molecular size.