Polycyclic Aromatic Hydrocarbons Adsorption onto Graphene: A DFT and AIMD Study

Polycyclic aromatic hydrocarbons in water environments: Impact, legislation, depollution processes and challenges, and magnetic iron oxide/graphene-based nanocomposites as promising adsorbent solutions

Environmental pollution is a big challenge of today's world, as population continues to grow, and industrialisation and urbanisation increase. Out of the different micropollutants in the atmosphere and aquatic environments, polycyclic aromatic hydrocarbons are of particular importance because they have known severe associated health risks to human life and they have high stability, leading to their persistence in the environment. They are generally present in the environment in low concentrations, but, even at these levels, they pose threats. This review thus focuses on this family of pollutants, on their occurrence and consequences, as well as the current methodologies employed to remove them from water environments and the challenges that remain. This work then focuses on the potential of magnetic iron oxide/graphene nanocomposites for the adsorption of PAHs, extensively discussing past and undergoing works, as well as the interactions between these adsorbents and PAHs.

Tailoring DNA Surface Interactions on Single-Layer Graphene: Comparative Analysis of Pyrene, Acridine, and Fluorenyl Methyl Linkers

This study investigates the effect of different linkers and solvents on the immobilization of DNA probes on graphene surfaces, which are crucial for developing high-performance biosensors. Quartz crystal microbalance with dissipation (QCM-D) measurements were used to characterize in situ and real-time the immobilization of ssDNA and hybridization efficiency on model graphene surfaces. The DNA probes immobilization kinetics and thermodynamics were systematically investigated for all the pairings between three bifunctional linkers─1-pyrenebutyric acid succinimidyl ester (PBSE), Fluorenylmethylsuccinimidyl carbonate (FSC), and Acridine Orange (AO) succinimidyl ester─and three organic solvents (DMF, DMSO, and 10% DMF/ethanol). The linker's spatial orientation and effective surface modification for DNA probe attachment were also evaluated based on footprints and DNA probe surface coverage. Graphene surfaces functionalized with PBSE in DMF achieved the highest DNA probe surface density (up to 1.31 × 1013 molecules cm-2) and fastest kinetic, p values above 4, and hybridization efficiencies of at least 70%, with 20 to 30% of ssDNA directly adsorbed nonspecifically on the functionalized graphene surface, which has significant implications for the design of sensitive biosensors. The efficiency of the ethanolamine-NHS blocking reaction was estimated to be 80%. The surface packing density of the linker was estimated at 25% of the entire surface coverage for PBSE, and about 22 and 13% for AO and FSC, respectively. Overall, the surface coverage achieved for probe DNA was in the same order of magnitude as that obtained on flat gold surfaces (≥1013 molecules cm-2), typically used in biosensors. These findings highlight the importance of the selected conditions for graphene surface modification to achieve high DNA probe surface density on graphene materials. These results underscore the critical role of interface engineering in achieving target functional outcomes in biosensing technology.

Transferable machine learning interatomic potential for carbon hydrogen systems

In this study, we developed a machine learning interatomic potential based on artificial neural networks (ANN) to model carbon-hydrogen (C-H) systems. The ANN potential was trained on a dataset of C-H clusters obtained through density functional theory (DFT) calculations. Through comprehensive evaluations against DFT results, including predictions of geometries and formation energies across 0D-3D systems comprising C and C-H, as well as modeling various chemical processes, the ANN potential demonstrated exceptional accuracy and transferability. Its capability to accurately predict lattice dynamics, crucial for stability assessment in crystal structure prediction, was also verified through phonon dispersion analysis. Notably, its accuracy and computational efficiency in calculating force constants facilitated the exploration of complex energy landscapes, leading to the discovery of a novel C polymorph. These results underscore the robustness and versatility of the ANN potential, highlighting its efficacy in advancing computational materials science by conducting precise atomistic simulations on a wide range of C-H materials.

Single and Competitive Adsorption of Naphthalene, Phenanthrene, and Pyrene on Polystyrene Nanofibers

In this investigation, polystyrene (PS) nanofibers were prepared by electrospinning for the adsorption of naphthalene (Nap), phenanthrene (Phe), and pyrene (Pyr) from an aqueous solution. Surface morphology and physicochemical characteristics of PS nanofibers were analyzed using Fourier transform infrared spectroscopy (FT-IR) and point-of-zero-charge calorimetry (pHpzc). The effects of pH, ion concentration, and temperature on the adsorption were also investigated. The adsorption mechanism of target pollutants on PS nanofibers was investigated by a batch adsorption method. The adsorption kinetic studies showed that the adsorption of the three polycyclic aromatic hydrocarbons (PAHs) on PS nanofibers conformed to the pseudo-second-order kinetic model in both single and ternary systems. Meanwhile, in a single system, the three PAHs adsorbed on nanofibers were controlled by both intraparticle diffusion and liquid film diffusion, whereas the adsorption of Nap in a ternary system was controlled mainly by intraparticle diffusion, and the adsorption of Phe and Pyr was controlled mainly by liquid film diffusion. The isotherm data indicated that the Freundlich model performed better than the Langmuir model for the adsorptions of Nap, Phe, and Pyr on PS nanofibers in both the single system and the ternary system. Due to competitive adsorption, the adsorption capacities of Nap and Pyr on PS nanofibers decreased from 105.816 and 19.098 mg g-1 in the single system to 23.626 and 12.126 mg g-1 in the ternary system, but the adsorption of Phe was not affected. π-π interactions and pore filling may be jointly involved in the adsorption of PAHs on PS nanofibers.

Theoretical study on electrocatalytic carbon dioxide reduction over copper with copper-based layered double hydroxides

The conversion of CO2 into valuable fuels and multi-carbon chemical substances by electrical energy is an effective strategy to solve environmental problems by using renewable energy sources. In this work, the density functional theory (DFT) method is used to reveal the electrocatalytic mechanism of CO2 reduction reaction (CO2RR) over the surface of CuAl-Cl-layered double hydroxides (LDHs) with Cu monoatoms (Cu@CuAl-Cl-LDH), Cu2 diatoms (Cu2@CuAl-Cl-LDH), orthotetrahedral Cu4 clusters (Td-Cu4@CuAl-Cl-LDH) and planar Cu4 clusters (Pl-Cu4@CuAl-Cl-LDH). The active sites, density of states, adsorption energy, charge density difference and free energy are calculated. The results show that CO2RR over all the above five catalysts can generate C2 products. Pl-Cu4@CuAl-Cl-LDH tends to generate C2H5OH, while the remaining four structures all tend to produce C2H4. Cuδ+ favors CO2RR, and Td-Cu4@CuAl-Cl-LDH with a larger positively charged area at the active site has the better electrocatalytic performance among the calculated systems with a maximum step height of 0.78 eV. The selectivity of the products C2H4 and C2H5OH depends on the dehydration of the intermediate *C2H2O to *C2H3O or *CCH; if the dehydration produces *CCH intermediate, the final product is C2H4, and if no dehydration occurs, C2H5OH is produced. This work provides theoretical information and guidance for further rational design of efficient CO2RR catalysts for energy saving and emission reduction.

Evaluation interaction of graphene oxide with heparin for antiviral blockade: a study of ab initio simulations, molecular docking, and experimental analysis

CONTEXT

Heparin, one of the drugs reused in studies with antiviral activity, was chosen to investigate a possible blockade of the SARS-CoV-2 spike protein for viral entry through computational simulations and experimental analysis. Heparin was associated to graphene oxide to increase in the binding affinity in biological system. First, the electronic and chemical interaction between the molecules was analyzed through ab initio simulations. Later, we evaluate the biological compatibility of the nanosystems, in the target of the spike protein, through molecular docking. The results show that graphene oxide interacts with the heparin with an increase in the affinity energy with the spike protein, indicating a possible increment in the antiviral activity. Experimental analysis of synthesis and morphology of the nanostructures were carried out, indicating heparin absorption by graphene oxide, confirming the results of the first principle simulations. Experimental tests were conducted on the structure and surface of the nanomaterial, confirming the heparin aggregation on the synthesis with a size between the GO layers of 7.44 Å, indicating a C-O type bond, and exhibiting a hydrophilic surface characteristic (36.2°).

METHODS

Computational simulations of the ab initio with SIESTA code, LDA approximations, and an energy shift of 0.05 eV. Molecular docking simulations were performed in the AutoDock Vina software integrated with the AMDock Tools Software using the AMBER force field. GO, GO@2.5Heparin, and GO@5Heparin were synthesized by Hummers and impregnation methods, respectively, and characterized by X-ray diffraction and surface contact angle.

Ab initio study of water anchored in graphene pristine and vacancy-type defects

CONTEXT

In this paper, we have addressed two issues that are relevant to the interaction of water in pristine and vacant graphene through first-principles calculations based on the Density Functional Theory (DFT). The results showed that for the interaction of pristine graphene with water, the DOWN configuration (with the hydrogen atoms facing downwards) was the most stable, presenting binding energies in the order of -13.62 kJ/mol at a distance of 2.375 Å in the TOP position. We also evaluated the interaction of water with two vacancy models, removing one carbon atom (Vac-1C) and four atoms (Vac-4C). In the Vac-1C system, the most favourable system was the DOWN configuration, with binding energies ranging from -20.60 kJ/mol to -18.41 kJ/mol in the TOP and UP positions, respectively. A different behaviour was observed for the interaction of water with Vac-4C; regardless of the configuration of the water, it is always more favourable for the interaction to occur through the vacancy centre, with binding energies ​​between -13.28 kJ/mol and -20.49 kJ/mol. Thus, the results presented open perspectives for the technological development of nanomembranes as well as providing a better understanding of the wettability effects of graphene sheets, whether pristine or with defects.

METHOD

We evaluated the interaction of pristine and vacant graphene with the water molecule, through calculations based on Density Functional Theory (DFT); implemented by the SIESTA program. The electronic, energetic, and structural properties were analyzed by solving self-consistent Kohn-Sham equations. In all calculations, a double ζ plus a polarized function (DZP) was used for the numerical baise set. Local Density Approximation (LDA) with the Perdew and Zunger (PZ) parameterisation along with a basis set superposition error (BSSE) correction were used to describe the exchange and correlation potential (Vxc). The water and isolated graphene structures were relaxed until the residual forces were less than 0.05 eV/Å^-1 in all atomic coordinates.

Determination of polycyclic aromatic hydrocarbons in Chinese herbal medicines by gas chromatography-mass spectrometry with graphene-functionalized nickel foam

Graphene-functionalized nickel foam (NF) sorbent materials were prepared and characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Thermogravimetric analysis. For the separation and detection of polycyclic aromatic hydrocarbons (PAHs) in five Chinese medicine samples, namely dandelion, fructus aurantii, peppermint, mulberry leaf and embryo chrysanthemum, a method combining dispersive micro-solid phase extraction and gas chromatography-mass spectrometry (GC-MS) was developed. Four conditions affecting the extraction efficiency, such as the type of desorption solvent, the amount of sorbent, the extraction time and the volume of water sample, were optimized. The results of the methodological validation showed that NF@SiO₂@G was able to adsorb PAHs well and with good reproducibility. All analytes showed good linearity in the concentration range of 20-2000 ng/mL with coefficient of determination R²≥0.9956. The limit of detection was 0.98-13.34 ng/mL, and the limit of quantification ranged from 3.25 to 44.47 ng/mL. Both the intra-day and inter-day precision were lower than 15.46%, and the spiked recoveries were in the range of 75.5-118.4%. The total contents of the 16 PAHs contained in these five Chinese herbal medicines (CHMs) were varied from 450 to 1557 µg/kg. The results indicated that the graphene-functionalized NF sorbent combined with GC-MS can effectively detect PAHs in CHMs.

Modeling the Adsorption of Polycyclic Aromatic Hydrocarbons on Graphynes: An Improved Lennard-Jones Formulation

Research on the development of theoretical methodologies for modeling noncovalent interactions governing the adsorption of polycyclic aromatic hydrocarbons (PAHs) on graphene and other two-dimensional materials is being intensely pursued in recent times. Highly accurate empirical potentials have emerged as a viable alternative to first-principles calculations for performing large-scale simulations. Herein, we report exploration of the potential energy surfaces for the adsorption of cata-condensed and peri-condensed PAHs on graphynes (GYs) using the improved Lennard-Jones (ILJ) potential. Initially, the ILJ potential is parametrized against benchmark electronic structure calculations performed on a selected set of PAH-GY complexes using dispersion-corrected density functional theory. The accuracy of the parametrization scheme is then assessed by a comparison of the adsorption features predicted from the ILJ potential with those computed using electronic structure calculations. The potential energy profiles as well as the single point energy calculations and geometry reoptimizations performed on the minimum-energy configurations predicted by the ILJ potential for a broader range of PAH-GY complexes provided a validation of the parametrization scheme. Finally, by an extrapolation of the PAH adsorption energies on various GYs, we estimated the interlayer cohesion energies for the van der Waals bilayer heterostructures of GYs with graphene to be in the range of 25-50 meV/atom.

A Comprehensive DFT Investigation of the Adsorption of Polycyclic Aromatic Hydrocarbons onto Graphene

To better understand graphene and its interactions with polycyclic aromatic hydrocarbons (PAHs), density-functional-theory (DFT) computations were used. Adsorption energy is likely to rise with the number of aromatic rings in the adsorbates. The DFT results revealed that the distance between the PAH molecules adsorbed onto the G ranged between 2.47 and 3.98 Å depending on the structure of PAH molecule. The Non-Covalent Interactions (NCI) plot supports the concept that van der Waals interactions were involved in PAH adsorption onto the Graphene (G) structure. Based on the DFT-calculated adsorption energy data, a rapid and reliable method employing an empirical model of a quantitative structure–activity relationship (QSAR) was created and validated for estimating the adsorption energies of PAH molecules onto graphene.

Assessment of reusable graphene wool adsorbent for the simultaneous removal of selected 2-6 ringed polycyclic aromatic hydrocarbons from aqueous solution

The United States Environmental Protection Agency categorized polycyclic aromatic hydrocarbons (PAHs) as hazardous to humans upon acute and/or chronic exposure. This study investigated the simultaneous adsorption of several PAHs onto graphene wool (GW), thereby providing holistic insights into the competitive adsorption of PAHs onto graphene-based materials. SEM, TEM and FTIR provided evidence for the adsorption of PAHs and successful regeneration of the adsorbent accompanied by distinct morphological changes. Isotherm experiments revealed that adsorption of PAHs was significantly influenced by hydrophobic interactions between the sorbate and hydrophobic surface of GW. The Freundlich multilayer isotherm model best fit the experimental data obtained for both multi-component PAH and single-solute experiments as indicated by the Error Sum of Squares (SSE) obtained from nonlinear regression analysis. Experiments revealed that competitive adsorption had a limiting effect on the overall adsorption capacity as q_max and K_d were higher in single-solute than multi-component PAH experiments. The results suggest that partition distribution coefficients (K_d) between the solid-liquid interphase played a significant role in the overall adsorption and a positive correlation between K_d and LogK_ow of PAHs was established in single-solute experiments. Sorption-desorption experiments revealed that PAHs were adsorbed with a maximum removal efficiency of 100% at an optimum GW dosage of 2 g/L. Adsorption thermodynamics revealed that PAH adsorption onto GW is spontaneous and endothermic. The adsorbent was regenerated and reused for up to six times and its efficiency remained fairly constant.

Uptake and effects of graphene oxide nanomaterials alone and in combination with polycyclic aromatic hydrocarbons in zebrafish

Because of its surface characteristics, once in the aquatic environment, graphene could act as a carrier of pollutants, such as polycyclic aromatic hydrocarbons (PAHs), to aquatic organisms. In this study we aimed to (1) assess the capacity of graphene oxide (GO) to sorb PAHs and (2) to evaluate the toxicity of GO alone and in combination with PAHs on zebrafish embryos and adults. GO showed a high sorption capacity for benzo(a)pyrene (B(a)P) (98% of B(a)P sorbed from a nominal concentration of 100 μg/L) and for other PAHs of the water accommodated fraction (WAF) of a naphthenic North Sea crude oil, depending on their log K_ow (95.7% of phenanthrene, 84.4% of fluorene and 51.5% of acenaphthene). In embryos exposed to different GO nanomaterials alone and with PAHs, no significant mortality was recorded for any treatment. Nevertheless, malformation rate increased significantly in embryos exposed to the highest concentrations (5 or 10 mg/L) of GO and reduced GO (rGO) alone and with sorbed B(a)P (GO-B(a)P). On the other hand, adults were exposed for 21 days to 2 mg/L of GO, GO-B(a)P and GO co-exposed with WAF (GO + WAF) and to 100 μg/L B(a)P. Fish exposed to GO presented GO in the intestine lumen and liver vacuolisation. Transcription level of genes related to cell cycle regulation and oxidative stress was not altered, but the slight up-regulation of cyp1a measured in fish exposed to B(a)P for 3 days resulted in a significantly increased EROD activity. Fish exposed to GO-B(a)P and to B(a)P for 3 days and to GO + WAF for 21 days showed significantly higher catalase activity in the gills than control fish. Significantly lower acetylcholinesterase activity, indicating neurotoxic effects, was also observed in all fish treated for 21 days. Results demonstrated the capacity of GO to carry PAHs and to exert sublethal effects in zebrafish.

Theoretical study of small aromatic molecules adsorbed in pristine and functionalised graphene

Small aromatic molecules are precursors for several biological systems such as DNA, proteins, drugs, and are also present in several pollutants. The understanding of the interaction of these small aromatic molecules with pristine and functionalised graphene (fGr) can generate different applications. We performed ab initio simulations based on the density functional theory to evaluate the interaction between the aromatic compounds, benzene, benzoic acid, aniline and phenol, with pristine and fGr. The results show that the binding energy for all cases is less than 103.24 kJ/mol (1.07 eV) without substantial modification of the electronic properties, indicating that the interaction occurs through a physical adsorption regime. The results are promising because they suggest that pristine graphene and functionalised graphene are suitable for removing these pollutants, or for carrying molecules for biological applications influenced by π-π and H-bonds interaction.

Ultrasound-assisted magnetic solid-phase extraction of polycyclic aromatic hydrocarbons and nitrated polycyclic aromatic hydrocarbons from water samples with a magnetic polyaniline modified graphene oxide nanocomposite

A novel magnetic graphene oxide nanocomposite modified with polyaniline (Fe₃O₄@GO-PANI) was synthesized and applied for the magnetic solid-phase extraction of polycyclic aromatic hydrocarbons (PAHs) (i.e. fluorene, phenanthrene and pyrene) and nitrated polycyclic aromatic hydrocarbons (N-PAHs) (i.e. 2-nitrofluorene, 9-nitroanthracene, 1-nitropyrene and 3-nitrofluoranthene) prior to their determination by gas chromatography-mass spectrometry. The prepared nanomaterial was characterized by scanning electron microscopy, X-ray diffraction, and Fourier transform-infrared spectroscopy. The main experimental parameters affecting the extraction and desorption steps of the MSPE procedure were investigated and optimized. Under optimum conditions, coefficients of determination (r²) ranged between 0.9970 and 0.9995, limits of detection (LODs, S/N = 3) ranged between 0.04-0.05 ng mL^-1 for PAHs and 0.01-0.11 ng mL^-1 for N-PAHs, while the relative standard deviation for intra-day and inter-day repeatability were lower than 10.0% for PAHs and N-PAHs. The method was successfully applied to the analysis of tap, mineral and river water samples. Relative recoveries in spiked water samples ranged between from 91.6 to 114% and from 92.3 to 110% for PAHs and N-PAHs, respectively. The proposed method is simple, rapid, sensitive and the Fe₃O₄@GO-PANI sorbent can be reused for at least 15 times without significant decrease in extraction recovery.

Pristine graphene covalent functionalization with aromatic aziridines and their application in the sensing of volatile amines - an ab initio investigation

Food quality is of paramount importance for public health safety. For instance, fish freshness can be assessed by sensing the volatile short chain alkylamines produced by spoiled fish. Functionalized graphene is a good candidate for the design of gas sensors for such compounds and therefore of interest as the basic material in food quality sensor devices. To shed theoretical insight in this direction, in the present work we investigate via first-principles density functional theory (DFT) simulations: (i) graphene functionalization via aziridine appendages and (ii) the adsorption of short chain alkylamines (methylamine MA, dimethylamine DMA, and trimethylamine TMA) on the chemically functionalized graphene sheets. Optimal geometries, adsorption energies, and projected density of states (PDOS) are computed using a DFT method. We show that nitrene reactive intermediates, formed by thermal or photo splitting of arylazides - p-carboxyphenyl azide (1a), p-carboxyperfluorophenyl azide (1b), and p-nitrophenyl azide (1c) - react with graphene to yield functionalized derivatives, with reaction energies >-1.0 eV and barriers of the order of 2.0 eV, and open a ∼0.3 to 0.5 eV band gap which is in principle apt for applications in sensing and electronic devices. The interaction between the amines and functionalized graphene, as demonstrated from the calculations of charge density differences showing regions of charge gain and others of charge depletion between the involved groups, occurs through hydrogen bonding with interaction energies ranging from -0.04 eV to -0.76 eV, and induce charge differences in the system, which in the case of p-carboxyperfluorophenyl azide (1b) are sizeable enough to be experimentally observable in sensing.

An Overview and Evaluation of Highly Porous Adsorbent Materials for Polycyclic Aromatic Hydrocarbons and Phenols Removal from Wastewater

Polycyclic aromatic hydrocarbons (PAHs) and phenolic compounds had been widely recognized as priority organic pollutants in wastewater with toxic effects on both plants and animals. Thus, the remediation of these pollutants has been an active area of research in the field of environmental science and engineering. This review highlighted the advantage of adsorption technology in the removal of PAHs and phenols in wastewater. The literature presented on the applications of various porous carbon materials such as biochar, activated carbon (AC), carbon nanotubes (CNTs), and graphene as potential adsorbents for these pollutants has been critically reviewed and analyzed. Under similar conditions, the use of porous polymers such as Chitosan and molecularly imprinted polymers (MIPs) have been well presented. The high adsorption capacities of advanced porous materials such as mesoporous silica and metal-organic frameworks have been considered and evaluated. The preference of these materials, higher adsorption efficiencies, mechanism of adsorptions, and possible challenges have been discussed. Recommendations have been proposed for commercialization, pilot, and industrial-scale applications of the studied adsorbents towards persistent organic pollutants (POPs) removal from wastewater.

Polycyclic aromatic hydrocarbons in edible oils and fatty foods: Occurrence, formation, analysis, change and control

Numerous studies have demonstrated that dozens of polycyclic aromatic hydrocarbons (PAHs) are mutagenic, genotoxic and strongly carcinogenic. PAHs are found to be widely present in foods contaminated through multiple paths. Due to their lipophilic nature, these compounds easily accumulate in edible oils and fatty foods where they can range from no detection to over 2000μg/kg. Compared to precursor PAHs, researchers have seldom studied the presence of PAH derivatives, especially in food matrices. This chapter includes the physical and chemical characteristics of PAHs and their types, occurrence, sample pretreatment and instrumental determination methods, and their formation, change and control in edible oils and fatty foods. The occurrence and formation of PAH derivatives in foods are much less investigated compared to those of their precursor PAHs. Although the removal of matrix effects and accuracy remain difficult for current rapid determination methods, a prospective research direction of PAH analysis for large-scale screening is in demand. To date, physical absorption, chemical oxidation and biodegradation have been widely used in PAH removal techniques. Specific types of bacteria, fungi, and algae have also been used to degrade PAHs into harmless compounds. However, most of them can only degrade a range of LPAHs, such as naphthalene, anthracene and phenanthrene. Their ability to degrade HPAHs requires further study. Moreover, it is still a great challenge to maintain food nutrition and flavor during the PAH removal process using these methods.

Comprehensive review of polycyclic aromatic hydrocarbons in water sources, their effects and treatments

Polycyclic aromatic hydrocarbons (PAHs) are principally derived from the incomplete combustion of fossil fuels. This study investigated the occurrence of PAHs in aquatic environments around the world, their effects on the environment and humans, and methods for their removal. Polycyclic aromatic hydrocarbons have a great negative impact on the humans and environment, and can even cause cancer in humans. Use of good methods and equipment are essential to monitoring PAHs, and GC/MS and HPLC are usually used for their analysis in aqueous solutions. In aquatic environments, the PAHs concentrations range widely from 0.03 ng/L (seawater; Southeastern Japan Sea, Japan) to 8,310,000 ng/L (Domestic Wastewater Treatment Plant, Siloam, South Africa). Moreover, bioaccumulation of ∑16PAHs in fish has been reported to range from 11.2 ng/L (Cynoscion guatucupa, South Africa) to 4207.5 ng/L (Saurida undosquamis, Egypt). Several biological, physical and chemical and biological techniques have been reported to treat water contaminated by PAHs, but adsorption and combined treatment methods have shown better removal performance, with some methods removing up to 99.99% of PAHs.

Can Adsorption on Graphene be Used for Isotopic Enrichment? A DFT Perspective

We have explored the theoretical applicability of adsorption on graphene for the isotopic enrichment of aromatic compounds. Our results indicate that for nonpolar molecules, like benzene, the model compound used in these studies shows a reasonable isotopic fractionation that is obtained only for the deuterated species. For heavier elements, isotopic enrichment might be possible with more polar compounds, e.g., nitro- or chloro-substituted aromatics. For benzene, it is also not possible to use isotopic fractionation to differentiate between different orientations of the adsorbed molecule over the graphene surface. Our results also allowed for the identification of theory levels and computational procedures that can be used for the reliable prediction of the isotope effects on adsorption on graphene. In particular, the use of partial Hessian is an attractive approach that yields acceptable values at an enormous increase of speed.