Ab initio study of adsorption properties of hazardous organic molecules on graphene: Phenol, phenyl azide, and phenylnitrene

Adsorption Affinities of Small Volatile Organic Molecules on Graphene Surfaces for Novel Nanofiller Design: A DFT Study

The adsorption of organic molecules on graphene surfaces is a crucial process in many different research areas. Nano-sized carbon allotropes, such as graphene and carbon nanotubes, have shown promise as fillers due to their exceptional properties, including their large surface area, thermal and electrical conductivity, and potential for weight reduction. Surface modification methods, such as the "pyrrole methodology", have been explored to tailor the properties of carbon allotropes. In this theoretical work, an ab initio study based on Density Functional Theory is performed to investigate the adsorption process of small volatile organic molecules (such as pyrrole derivatives) on graphene surface. The effects of substituents, and different molecular species are examined to determine the influence of the aromatic ring or the substituent of pyrrole's aromatic ring on the adsorption energy. The number of atoms and presence of π electrons significantly influence the corresponding adsorption energy. Interestingly, pyrroles and cyclopentadienes are 10 kJ mol-1 more stable than the corresponding unsaturated ones. Pyrrole oxidized derivatives display more favorable supramolecular interactions with graphene surface. Intermolecular interactions affect the first step of the adsorption process and are important to better understand possible surface modifications for carbon allotropes and to design novel nanofillers in polymer composites.

Adsorption Characteristics of Phenolic Compounds on Graphene Oxide and Reduced Graphene Oxide: A Batch Experiment Combined Theory Calculation

A series of phenolic compounds containing 2-phenylphenol (PPE), bisphenol A (BPA), 4-isopropylphenol (IPE), 4-methylphenol (ME) and phenol (PE) were selected to investigate their major influence factors for their adsorption on graphene oxide (GO) and reduced graphene oxide (RGO) by studying their adsorption isotherms and kinetics. It was found that the adsorption of all tested phenols fitted well with the Freundlich model. In comparison, the adsorption ability of RGO with a stronger π-π interaction was superior to GO, which was confirmed by using naphthalene probe measurements. The thermodynamic characteristics, by studying the effect of the adsorption temperatures (298, 313 and 333 K), demonstrated that the adsorption process was spontaneous, exothermic and entropy-decreasing. The chemical structures of the phenols also affected their adsorption on GO and RGO. It was found that the adsorption capacities of phenols were, in order, PE (0.271 mmol g−1 on GO and 0.483 mmol g−1 on RGO) < ME (0.356 and 0.841 mmol g−1) < IPE (0.454 and 1.117 mmol g−1) < BPA (0.4 and 1.56 mmol g−1) < PPE (0.7 and 2.054 mmol g−1), which depended on the π-electron density of the benzene ring by means of a density functional theory (DFT) calculation. Undoubtedly, the reduction of GO and an increase in π-electron density on the chemical structures of phenols facilitated the adsorption.

Adsorption of Monocyclic Carbon Rings on Graphene: Energetics Revealed via Continuum Modeling

Gas-phase spectroscopic detection of tiny carbon clusters is a recent success story in the area of carbon cluster research. However, experimental production and isolation of these clusters are extremely difficult because of their high reactivity. One possibility to isolate the generated clusters would be to deposit them on graphene and to desorb them for subsequent use. One of the pertinent questions toward realizing this would be the energetics of the adsorption process. Therefore, in this work, the energetics for the adsorption of the monocyclic carbon rings (C _n with n = 10, 12, 14, 16, 18, 20, and 22) on a graphene sheet are investigated using the analytical approaches, developed earlier by Hill and co-workers. The adsorption process here is driven by the noncovalent interactions between the carbon rings and the graphene sheet. The analyses of the interaction energies as a function of both the vertical distance Z and the rotational angle ϕ are performed in order to determine the preferred orientations, equilibrium positions, and binding energies for the adsorption of various carbon rings on graphene. We find that the preferred orientation of the rings with respect to the graphene sheet is the parallel orientation. The results from continuum, discrete-continuum, and discrete models are in good agreement. Further, computations using density functional theory and quantum mechanics/molecular mechanics approaches are performed, and comparisons of the computed energetics with the data from the models are reported. Finally, we highlight the scope and the limitations of the analytical models.

Stacking Modes-Induced Chemical Reactivity Differences on Chemical Vapor Deposition-Grown Trilayer Graphene

Trilayer graphene (TLG) synthesized by chemical vapor deposition (CVD), in particular the twisted TLG, exhibits sophisticated electronic structures that depend on their stacking modes. Here, we computationally and experimentally demonstrate the chemical reactivity differences of CVD-TLG induced by the stacking modes and corroborated by a photoexcited phenyl-grafting reaction. The experimental results show that the ABA stacking TLGs have the most inert chemical property, yet 30°-30° stacking twisted TLGs are the most active. Further, density functional theory calculations have shown that the chemical reactivity difference can be quantitatively explained by the differences in the number of hot electrons generated in their valence band during irradiation. The activity difference is further verified by the calculated adsorption energy of phenyl on the TLGs. Our work provides insight into the chemistry of TLG and addresses the challenges associated with selective functionalization of TLG with phenyl groups. The understandings developed in this project can also guide the future development of TLG-based functional devices.

Study of Grains and Boundaries of Molybdenum Diselenide and Tungsten Diselenide Using Liquid Crystal

Direct observation of grains and boundaries is a vital factor in altering the electrical and optoelectronic properties of transition metal dichalcogenides (TMDs), that is, MoSe₂ and WSe₂. Here, we report visualization of grains and boundaries of chemical vapor deposition grown MoSe₂ and WSe₂ on silicon, using optical birefringence of two-dimensional layer covered with nematic liquid crystal (LC). An in-depth study was performed to determine the alignment orientation of LC molecules and their correlation with other grains. Interestingly, we found that alignment of liquid crystal has discrete preferential orientations. From computational simulations, higher adsorption energy for the armchair direction was found to force LC molecules to align on it, compared to that of the zigzag direction. We believe that these TMDs with three-fold symmetric alignment could be utilized for display applications.

Dioxin sensing properties of graphene and hexagonal boron nitride based van der Waals solids: a first-principles study

The changes in the electronic properties of single and bilayers of graphene and hexagonal boron nitride two dimensional sheets have been investigated upon interaction with 2,3,7,8-tetrachlorodibenzo-p-dioxin by employing the DFT calculations.

Thermodynamic and kinetic properties of the adsorption of 4-nitrophenol on graphene from aqueous solution

Graphene is a newly discovered material and is considered to be the new wonder material for many applications. The recent possibility of obtaining pure and fully characterized graphene opens the door to the study of the adsorption of toxic materials on graphene. The adsorption behavior of p-nitrophenol on graphene was studied in aqueous medium. The effect of each of pH, temperature, and dosage was emphasized. The highest calculated adsorption capacity of 4-nitrophenol was found to be 15.5 mg/g, assuming Langmuir fitting starting from 11.1 mg/g initial concentration at 298 K and pH = 6. Fitting the data using the Freundlich isotherm model predicted a favorable adsorption process (n > 1). The rise and saturation areas of the isotherms were fitted as pseudo first-order and pseudo second-order processes, respectively, with relatively good fit (k1 = 0.0023/s, k2 = 0.68 g mg−1 s−1). The thermodynamic properties indicated a spontaneous and exothermic process.

Density functional studies of small silicon clusters adsorbed on graphene

The structural and electronic properties of small Si_n clusters (n = 1–6, 10) adsorbed on graphene are studied by use of density functional theory within periodic boundary conditions.