Description Of Adsorption Process Research Articles

In Situ Probing of the Surface Properties of Droplets in the Air.

Surface properties of nanodroplets and microdroplets are intertwined with their immense applicability in biology, medicine, production, catalysis, the environment, and the atmosphere. However, many means for analyzing droplets and their surfaces are destructive, non-interface-specific, not conducted under ambient conditions, require sample substrates, conducted ex situ, or a combination thereof. For these reasons, a technique for surface-selective in situ analyses under any condition is necessary. This feature article presents recent developments in second-order nonlinear optical scattering techniques for the in situ interfacial analysis of aerosol droplets in the air. First, we describe the abundant utilization of such droplets across industries and how their unique surface properties lead to their ubiquitous usage. Then, we describe the fundamental properties of droplets and their surfaces followed by common methods for their study. We next describe the fundamental principles of sum-frequency generation (SFG) spectroscopy, the Langmuir adsorption model, and how they are used together to describe adsorption processes at planar liquid and droplet surfaces. We also discuss the history of developments of second-order scattering from droplets suspended in dispersive media and introduce second-harmonic scattering (SHS) and sum-frequency scattering (SFS) spectroscopies. We then go on to outline the developments of SHS, electronic sum-frequency scattering (ESFS), and vibrational sum-frequency scattering (VSFS) from droplets in the air and discuss the fundamental insights about droplet surfaces that the techniques have provided. Finally, we describe some of the areas of nonlinear scattering from airborne droplets which need improvement as well as potential future directions and utilizations of SHS, ESFS, and VSFS throughout environmental systems, interfacial chemistry, and fundamental physics. The goal of this feature article is to spread knowledge about droplets and their unique surface properties as well as introduce second-order nonlinear scattering to a broad audience who may be unaware of recent progress and advancements in their applicability.

A convergent SAV scheme for Cahn–Hilliard equations with dynamic boundary conditions

Abstract The Cahn–Hilliard equation is one of the most common models to describe phase separation processes in mixtures of two materials. For a better description of short-range interactions between the material and the boundary, various dynamic boundary conditions for this equation have been proposed. Recently, a family of models using Cahn–Hilliard-type equations on the boundary of the domain to describe adsorption processes was analysed (cf. Knopf, P., Lam, K. F., Liu, C. & Metzger, S. (2021) Phase-field dynamics with transfer of materials: the Cahn–Hilliard equation with reaction rate dependent dynamic boundary conditions. ESAIM: Math. Model. Numer. Anal., 55, 229–282). This family of models includes the case of instantaneous adsorption processes studied by Goldstein, Miranville and Schimperna (2011, A Cahn–Hilliard model in a domain with non-permeable walls. Phys. D, 240, 754–766) as well as the case of vanishing adsorption rates, which was investigated by Liu and Wu (2019, An energetic variational approach for the Cahn–Hilliard equation with dynamic boundary condition: model derivation and mathematical analysis. Arch. Ration. Mech. Anal., 233, 167–247). In this paper, we are interested in the numerical treatment of these models and propose an unconditionally stable, linear, fully discrete finite element scheme based on the scalar auxiliary variable approach. Furthermore, we establish the convergence of discrete solutions towards suitable weak solutions of the original model. Thereby, when passing to the limit, we are able to remove the auxiliary variables introduced in the discrete setting completely. Finally, we present simulations based on the proposed linear scheme and compare them to results obtained using a stable, nonlinear scheme to underline the practicality of our scheme.

Stable and recyclable polyporous polyurethane foam highly loaded with UIO-66-NH2 nanoparticles for removal of Cr(Ⅵ) in wastewater

Efficient and recoverable adsorption technology plays a key role in removing the heavy metal Cr(Ⅵ) from wastewater. The metal-organic frameworks (MOFs) are very unstable in aqueous solution and their structure is easy to be destroyed. Of all MOFs, UIO-66-NH 2 (Zr-MOF) is widely used to adsorb heavy metal ions in wastewater. But UIO-66-NH 2 has disadvantages of small size and easy aggregation. When it is employed as the absorbent of industrial wastewater, it is impossible to be recycled after absorption. Therefore, in this study taking advantage of the excellent properties of polyurethane foam (PUF) such as porous network, light weight and abundant binding sites, UIO-66-NH 2 were loaded on PUF by in-situ growth method to obtain a composite UIO-66-NH 2 @PUF. BET and MIR results confirmed the co-existence of macropore, micropore and mesopore. The absorption kinetics and isotherms indicated that the adsorption capacity of UIO-66-NH 2 @PUF to Cr(Ⅵ) was 92 mg/g and Langmuir model could better describe adsorption process, as well as the process belongs to monolayer adsorption. After six cycles, the removal rate of UIO-66-NH 2 @PUF still reached to 79%. XRD, EDS and determination result of Zr(Ⅳ) concentration showed that the exfoliation of Zr(Ⅳ) was negligible, which proved UIO-66-NH 2 @PUF had excellent chemical stability after repeated use. The adsorption mechanism was the comprehensive effect of ligand exchange and Lewis acid-base interaction between Zr(Ⅳ) and Cr(Ⅵ) which was concluded by XPS. Owing to these attributes, loading MOFs powder on porous carrier makes it possible to reuse MOFs and avoid secondary pollution.

Performance analysis on open thermochemical sorption heat storage from a real mass transfer perspective

Internal mass transfer coefficient is considered as a key parameter for open thermochemical sorption heat storage which usually has a large margin between theoretical and actual value. This paper aims to analyze the role of mass transfer on system performance prediction. Al2O3 and LiCl composite sorbents are prepared and adsorption behavior is tested through a thermal gravimetric analyzer and a small-scale air duct experiment. An equation of kinetic coefficient is fitted to describe adsorption process more accurate than empirical equation. For simulation, a one-dimensional model is established based on dimensionless number of heat and mass transfer, and similarity theory is built to predict output parameters. Results indicate that the sorbent with 16.44 % salt content reaches 0.39 g·g−1 maximum water uptake on the condition of 20 °C, 80 % relative humidity. It is indicated that the system using composite sorbents has a heat storage density of 345.58 kWh·m−3. Parameters that influence system output power and duration are also investigated. By adjusting air flow rate and sorption length of sorption reactor, the system can achieve temperature rise of 30 °C at the exit and a steady output of 6 h. One striking fact is that mass transfer coefficient can be used to well predict the performance of real open adsorption thermal energy storage system which is also conducive to system design and optimization.

Strength and salt/pH dependent-sorption capacity modulation of N-(alkyl)acrylamide-based semi-IPN hybrid gels reinforced with silica nanoparticles

A simple methodology was described for design of anionically modified thermosensitive organic-inorganic hybrid gels using silica nanoparticle-mediated semi-interpenetrating polymer networks. A thermosensitive copolymer poly(N-isopropylacrylamide-co-methacrylic acid), P(NIPA-MA), with linear polyacrylamide (LPA) chains was synthesized by conducting free radical polymerization under warm and cold conditions using NIPA and MA in the presence of SiO2 nanoparticles. Simple mixing of aqueous monomer solution with linear LPA chains and silica suspensions led to the formation of ionic thermosensitive hybrid gels. The effect of changes in solution environment on the swelling and elastic properties was investigated. Sodium salts of CH3COO−, NO3−, and SCN− were employed to understand specific ion effects and to gain an insight into the influence of kosmotrope and chaotrope solutes on swelling and elasticity at various ionic strength and temperature. The identity of counterion had a strong influence on swelling and compression modulus and was found to follow the reverse order of classical Hofmeister series (HS). The phase transition temperature decreased with increasing salt concentration, and transition changed from discontiuous to continuous. At low salt concentrations, the gels showed discontinuous phase transition at 50 °C, while transition temperature shifts towards 35–45 °C with increasing salt concentration. Dilution of the solution to 10−3 M resulted in a 2.0-fold reduction in compressive modulus of hybrid gels in NaAc solutions while a 3.0-fold reduction in NaSCN solutions. Compression modulus increased with shrinkage of hybrids due to increasing salt concentration. The effect of pH change of swelling medium on the swelling, phase transition profile and elasticity was evaluated. The continuity of pH-dependent swelling curve depended on swelling temperature. pH-triggered oscillation kinetics have been investigated to understand whether they can be used as a pH oscillator since the phase transition pH is close to 5.7. The swelling of NP-loaded hybrids followed a Fickian type diffusion. NP-loaded semi-IPN hybrid gels with typical feature of anionic structure were applied for adsorption of cationic dye methyl violet (MV). Different adsorption isotherm models were investigated to describe interfacial adsorption of MV which was strongly dependent on composition of hybrids. Langmuir isotherm model was found to be most appropriate to describe adsorption process. The superior properties imparted to the present system prepared with anionic modification, semi-IPN structure and NP-loading make semi-IPN hybrid gels suitable candidates for controlled release systems and for adsorbents of cationic dyes.

Borassus aethiopum activated carbon prepared for nitrate ions removal

This work aims to study nitrate ions removal using Borassus aethiopum activated carbon (BA-AC) in a synthetic medium. BA-AC was prepared through artisanal method in order to provide a low-cost activated carbon. Physico-chemical characterization of BA-AC has shown a high-specific surface area (1431 m2/g). Analysis of surface morphology by scanning electron microscopy, mean pore diameter (2.76 nm) and adsorption/desorption isotherm resulted in the mesoporous adsorbent. The existence of functional groups (C = O; C–H; C–OH) was highlighted by Fourier Transform Infrared spectroscopy. A percentage of 60.56% for nitrate ions at pH 4 was reached. Pseudo-second-order kinetic and Langmuir isotherm were the most suitable models to describe adsorption process. The thermodynamic study revealed that adsorption mechanism occurs spontaneously (ΔG° 0). Enthalpy (ΔH° = 1.89 kJ.mol−1) and entropy (ΔS° = 19.03 J.mol−1K−1) values indicate an endothermic process with an increase of disorder at the solid–liquid interface.

Remediation of Cu(II) and its adsorption mechanism in aqueous system by novel magnetic biochar derived from co-pyrolysis of sewage sludge and biomass

The novel magnetic biochar (MBC), derived from co-pyrolysis of sewage sludge and biomass loading nanosized iron oxide particles, was used as an environmentally friendly adsorbent. The loading of magnetic particles was in favor of increasing the adsorption capacity and separation from aqueous system for biochar (BC). The physical/chemical characteristics of MBC were revealed by elemental analysis, VSM, SEM-EDS, XRD, FTIR, zeta potential, and batch adsorption-desorption experiments. The nanosized γ-Fe2O3 particles grown on the surface of biochar showed ferromagnetic property. For the remediation of Cu(II) contamination, MBC-5 showed remarkable adsorption capacity of 67.68mg/g, and presented a wide pH range of 3.0-6.0. The Langmuir isothermal and pseudo-second-order model could describe adsorption process well. The adsorption mechanism of Cu(II) involved physical adsorption, ion exchange, and electrostatic surface complexation on the surface of MBCs. In the desorption experiments, MBC-5 holds the adsorption efficiency of 81.09% after fifth recycle still, which illustrated a remarkable performance of cyclic utilization by the solid waste of sewage sludge and biomass.

Fabrication of di-selective adsorption platform based on deep eutectic solvent stabilized magnetic polydopamine: Achieving di-selectivity conversion through adding CaCl2

Dynamic conversion process from selective adsorption of MG by MPDA-PDES 1 to selective adsorption of SY. • A new strategy for stabilizing and modifying MPDA by DESs was proposed. • A selective dyes adsorption method from binary dyes solution based on MPDA-PDES 1 adsorbent was established. • The addition of CaCl 2 made MPDA-PDES 1 from selectively adsorb MG to selectively adsorb SY. • MPDA-PDES 1 exhibited superior stability and can be reused six times continuously. Seeking effective synthesis strategy of adsorbents with di-selective adsorption ability to remove dyes in wastewater is of great significance for solving the increasing environmental problems. Hence, three deep eutectic solvents (DESs) were synthesized and polymerized on the surface of magnetic (Fe 3 O 4 ) polydopamine (MPDA), in which DES acted as both stabilizer and surface modifier for PDA coating. The fabricated nanoparticles (named as MPDA-PDES) were used as adsorbents for selective adsorption of binary dyes solution. Langmuir and Dubinin-Radushkevich isotherm models were suitable to describe adsorption process of malachite green (MG) and sunset yellow FCF (SY) on MPDA-PDES 1 , respectively, indicated that the adsorption of MG was monolayer uptake, and that of SY was physical adsorption. The effect of solution pH and ionic strength suggested that electrostatic interaction was mainly adsorption driving force. Interestingly, the addition of CaCl 2 in adsorption system realized dynamic transformation from selective adsorption of MG by MPDA-PDES 1 to selective adsorption of SY. And selectivity factor reduced from 37.57 to 0.30. MPDA-PDES 1 adsorbent possessed excellent anti-interference ability, regeneration and reusability, can be continuously reused six times and adsorption capacity remained basically unchanged. The adsorption of MG-SY from synthetic wastewater manifested that MPDA-PDES 1 had unlimited potential for selective removal of target dyes in actual wastewater. Mechanism exploration revealed that MPDA stabilized by DES containing long-chain alkyl groups exhibited better selective adsorption capacity for cationic dyes in binary dyes solutions. This was due to the synergistic effect of electrostatic interaction, hydrophobic interaction, hydrogen bonding and π-π stacking between MPDA-PDES 1 and dyes. Therefore, proposed DES-based PDA modification strategy improved the stability and reusability of PDA materials, and achieved outstanding selective adsorption ability because of tailorability of DES structure, which provided new ideas for design and synthesis of high-efficiency adsorbents.

Application of graphene nanosheet oxide for atrazine adsorption in aqueous solution: synthesis, material characterization, and comprehension of the adsorption mechanism.

The present study aimed to investigate the application of graphene oxide (GO) as adsorbent material for the removal of atrazine (ATZ). The material produced was characterized to investigate the characteristics and applied as an adsorbent. The material obtained after the synthesis process presented oxygenated functional groups, which contributed to the development of a good adsorbent material. Studies were carried out to verify the influence of adsorbent material mass and initial pH of ATZ solution in adsorption capacity. Kinetic study determined that pseudo-second-order model best describes adsorbate-adsorbent interaction, with equilibrium time of 72 h. The effect of temperature on the material adsorption capacity was also studied. The Langmuir isotherm is the best fit to describe adsorption process GO-ATZ and maximum adsorption capacity obtained was 23.844 ± 0.694 mg g-1, at 318 K. Variations in process energies were determined, being a spontaneous adsorption, endothermic and characteristic of physical and chemical adsorption. Finally, influence of salts in solution on adsorption capacity was studied; the conclusion was that the presence of electrolytes affects the adsorption capacity of the material.

Modeling of Mixed Mechanism Adsorption Processes Driven by Surface Adsorption and Internal Ion Exchange

In this work, a number of kinetic models describing adsorption processes that occur via a mixed mechanism of both simultaneous surface adsorption and internal ion exchange were developed. The propo...

Carbon Dioxide Adsorption Equilibrium Rates Comparative Temperature Study Using Palm Kernel Shell Sorbent.

Greenhouse effect is the serious environmental issue whereby the gaseous component involved is dangerous. One of the gases that contributed to atmosphere is carbon dioxide (CO2), in which is more than 80%, followed by methane and nitrous oxide that resulted from human activities, industrial sector and transportation. Activated carbon (AC) is the best adsorption technology due to simple design and ability to capture carbon dioxide efficiently. This paper was aimed to produce activated carbon derived from waste material, to determine adsorption rate at different pressures and temperatures and to relate adsorption kinetics and isotherms equilibrium to describe adsorption processes. Palm Kernel Shell (PKS) was selected as raw material to produce AC. Char was produced via carbonization process at 700 °C ± 20 °C for 2 h with 10 °C/min heating rate under inert gas flow. The sample is then grinded and sieved to 0.65mm to 0.8mm, followed by chemical treatment by using potassium hydroxide with ratio of 1:1 and directly undergoing microwave treatment. Adsorption rate performances were investigated by different temperatures of 25 °C and 10 °C and pressures of 5, 15 and 25 bar. The sample were characterized by thermo-gravimetric analysis, surface area analysis, and ultimate analysis. AC-PKS shows the highest surface area. As a result, increase in pressure led to increase in CO2 adsorption while decrease in temperature in CO2 adsorption. In conclusion, the findings revealed that the potential of AC-PKS to capture CO2 in order to enhance environmental sustainability and economically.

Evaluation of Adsorption Isotherm Models for Potassium Adsorption under Different Soil Types in Wolaita of Southern Ethiopia

ABSTRACT Adsorption isotherm is essential for predicting its mechanisms, which are important for potassium (K) fertilizer application and to recommendation appropriate rates for acidic soils. Thus, the objective of this study was to evaluate K adsorption characteristic of the selected soils by comparing different adsorption models with soil properties of the soil in different districts (Sodo Zurie, Damot Gale, Damot Sore and Boloso Sore) in the Wolaita Zone of Southern Ethiopia. Four adsorption isotherms are: Langmuir, Freundlich, Temkin, and Van Huay were used to describe adsorption processes. Composite surface (0-20 cm) depth soil samples from four districts sites were collected. The results revealed that the K adsorption data coincide with both models with (r2 = 0.99). However, Freundlich model was better in describing K adsorption than the other model. The adsorption maxima(ad(max), distribution coefficient, buffer capacity (BC), and adsorption capacity(a(capacity) values of soils ranged from -333 to334.5,0.54 to78.7,159.9 to 389.3, and 327 to 417mg Kkg-1 respectively, these results showed that Sodo Zurie, Bolos Sore and Demote Sore were effective model parameters. Van Huay a(capacity) 417mg Kkg-1 while the bonding energy constant Langmuir is -0.075mg Kkg-1 in Bolos Sore soil compared to other soils, which were found to be more valuable in discriminating between high K adsorption soils. Correlation between some soil properties with ad(max) were positively a highly correlated with clay, pH, organic carbon (OC) and exchangeable potassium with r2 = 0.92**, 0.93**, 0.95** and 0.96 ** respectively, but negatively correlated with bonding energy with r2= -0.79, -0.80,-0.77 and -0.72 respectively, while calcium carbonate (CaCO3) was very highly correlated with ad(max) r2= 0.99***). The Freundlich constant, Temkin BC, and Van Hauy a(capacity) were correlated with CaCO3 content soils with r2=0.12,-0.01,and 0.12,respectively, while slope (1/n) was significantly negatively correlated with soil cation exchange capacity (CEC), CaCO3, clay contents and exchangeable K and Mg2+ with r2= 0.04, -0.67, -0.78, -0.69, and –0.69, respectively. These findings reveal the extent of K depletion in the soils of Wolaita providing a baseline for K rates required for crop production and validation of all models through real-time experiments in the field; this is recommended before the models are used on a large scale basis.

Adsorption of ethanol molecules on the Al (1 1 1) surface: a molecular dynamic study.

The adsorption process of ethanol molecules on Al slabs was investigated by molecular dynamic simulations with a ReaxFF force field. The force field used in this paper has been validated by comparing adsorption energy results with quantum mechanical (QM) calculations. All simulations were performed under the canonical (NVT) ensemble. The single-molecule adsorption simulation shows that the hydroxyl group plays a more important role in the whole progress than the ethyl group. Besides, decomposition of hydroxyl groups was also observed during multimolecule adsorption processes. Simulations of adsorption processes of Al slab by ethanol molecules at different temperatures and pressures (controlled by the number of ethanol molecules) was also performed. System energy and radial distribution function (RDF) plots were invoked to describe adsorption processes and centro-symmetry parameter (CSP) analysis was adopted to study the surface properties with coating layers. Our results indicate that the whole adsorption process can be divided into two periods and the greater the pressure, the more ethanol molecules diffuse into the Al slab. How raising the temperature helps the adsorption processes is related to the initial number of molecules. The crystal structure of the Al surface will become amorphous under the constant impact of ethanol molecules.

Dynamic cum batch adsorption of a vesicant CWA (2-chloroethyl ethyl sulfide) over synthetic erionite

Erionite was synthesized under hydrothermal and static conditions and was characterized by Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and BET surface area measurement. The dynamic adsorption experiments were carried out on Temperature programed desorption (TPD) plus Chemisorption system (Micrometrics ASAP 2920 unit). Adsorption was found to be high initially and it then decreases with increase in injected volume. In batch reactor it was found that adsorption increases with increase in contact time between 2-chloroethyl ethyl sulfide and erionite only up to around 12 h after which it remains almost constant. It is exhibited from the data that maximum adsorption capacity of erionite for 2-chloroethyl ethyl sulfide was 70.26 mg/g at 25 °C. Pseudo second order kinetics was found to describe adsorption process better than pseudo first order kinetics. Freundlich and Langmuir isotherms applied on the adsorption data reveal that data fitted best for Freundlich model. Desorption pattern was analyzed which shows two types of peaks, sharp peak representing desorption of physisorbed 2-chloroethyl ethyl sulfide and a broad representing desorption of strongly chemisorbed 2-chloroethyl ethyl sulfide. Further it was observed that the adsorbent can be recycled and reused again.

ADSORPTION OF CO GAS MOLECULES ON SnO2 SURFACE

This research is devoted to the investigation of the toxic CO gas adsorption mechanism on the tin dioxide (SnO2) semiconductor. We used density functional theory (DFT) to describe adsorption processes, and we found out that the Mars-van Krevelen (MvK) adsorption mechanism is not responsible for adsorption on (101) and (001) surface orientations of SnO2, unlike (110) and (100), where CO2 molecule forms and desorbs from the surfaces. After adsorption on (101) and (001) surface orientations, CO molecule bound to the surfaces and transfer electrons to it. The charge transfer was calculated using Bader charge analysis, which showed the amount of charge transferred to the (101) and (001) surfaces is larger than to the (110) and (100) surfaces. In the case of (001) surface orientation, we considered half and full surface coverage. It was shown that during full surface coverage only one molecule can be adsorbed and transfer 2e charge. Electronic density of states (eDoS) calculation was done to explain the increase of surface conductance.

Surface and Antimicrobial Activity of Sulfobetaines

AbstractSulfobetaines belong to the group of zwitterionic surfactants. They are electroneutral salts, which have in the same molecule, two ionic centers with different charge. Due to the specific structure they exhibit excellent properties such as good solubility in water and detergency. In this paper we present surface properties and adsorption parameters of sulfobetaines in water/air systems. From the adsorption isotherms the CMC value, the surface tension and surface pressure at the CMC as well as the efficiency of adsorption were determined. Physicochemical analyses of the data allowed for the further description of adsorption process. Results showed that sulfobetaines exhibit good surface properties especially low CMC and p20 values. Additionally the antimicrobial activity of sulfobetaines solutions against gram‐positive and gram‐negative bacteria were tested by the well‐diffusion method. MIC values and growth kinetics were determined by microdilution method. Antimicrobial assays demonstrated that sulfobetaines can be good antibacterial agents, but the activity of surfactants strongly depends on alkyl chain length.

Gd-DTPA Adsorption on Chitosan/Magnetite Nanocomposites.

The synthesis of the chitosan/magnetite nanocomposites is presented. Composites were prepared by co-precipitation of iron(II) and iron(III) salts by aqueous ammonia in the 0.1 % chitosan solution. It was shown that magnetite synthesis in the chitosan medium does not affect the magnetite crystal structure. The thermal analysis data showed 4.6 % of mass concentration of chitosan in the hybrid chitosan/magnetite composite. In the concentration range of initial Gd-DTPA solution up to 0.4 mmol/L, addition of chitosan to magnetite increases the adsorption capacity and affinity to Gd-DTPA complex. The Langmuir and Freundlich adsorption models were applied to describe adsorption processes. Nanocomposites were characterized by scanning electron microscopy (SEM), differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and specific surface area determination (ASAP) methods.

Van Der Waals-Corrected Density Functional Theory Simulation of Adsorption Processes on Noble-Metal Surfaces: Xe on Ag(111), Au(111), and Cu(111)

The DFT/vdW-WF2s1 method based on the generation of localized Wannier functions, recently developed to include the van der Waals interactions in the Density Functional Theory and describe adsorption processes on metal surfaces by taking metal-screening effects into account, is applied to the case of the interaction of Xe with noble-metal surfaces, namely Ag(111), Au(111), and Cu(111). The study is also repeated by adopting the DFT/vdW-QHO-WF variant relying on the Quantum Harmonic Oscillator model which describes well many-body effects. Comparison of the computed equilibrium binding energies and distances, and the $C_3$ coefficients characterizing the adatom-surface van der Waals interactions, with available experimental and theoretical reference data shows that the methods perform well and elucidate the importance of properly including screening effects. The results are also compared with those obtained by other vdW-corrected DFT schemes, including PBE-D, vdW-DF, vdW-DF2, rVV10, and by the simpler Local Density Approximation (LDA) and semilocal (PBE) Generalized Gradient Approximation (GGA) approaches.

A Comparison Study on the Removal of Phenol From Aqueous Solution Using Organomodified Bentonite and Commercial Activated Carbon

The potential of bentonite modified with cationic surfactant (CTAB-Bent) and commercial Activated Carbon (AC) for the removal of phenol removal was assessed. Batch kinetics and isotherm studies were carried out to evaluate the effects of contact time (t), phenol initial concentration (C 0 ), adsorbent dose (C ads ), and pH of the solutions. Kinetics and isotherm of the adsorption were also determined using the most frequent models. The results of the study showed that increasing C 0 could result in the increase of adsorption capacity of both types of adsorbents. The optimum pHs for CTAB-Bent and AC were determined as 10 and 8, respectively. The equilibrium data of the phenol adsorption from the aqueous solutions was well fitted by the Langmuir isotherm models. The kinetics study revealed that pseudo-secondorder kinetics gives better description of adsorption process. The adsorption capacities, as deduced from the adsorption isotherm were 22.68 and 112.36 mg/g for CTAB-Bent and activated carbon, respectively. However, considering the market price of these adsorbents, low-cost modified bentonite can be a promising adsorption technology and an alternative adsorbent to commercial activated carbon in the future.

Van der Waals corrected DFT simulation of adsorption processes on transition-metal surfaces: Xe and graphene on Ni(111)

The DFT/vdW-WF2s1 method, recently developed to include the van der Waals interactions in the density functional theory and describe adsorption processes on metal surfaces by taking metal-screening effects into account, is applied to the case of the interaction of Xe and graphene with a transition-metal surface, namely, Ni(111). In general, the adsorption of rare-gas atoms on metal surfaces is important because it is prototypical for physisorption processes. Moreover, the interaction of graphene with Ni(111) is of great interest for practical applications, for instance concerning the efficient and large-scale production of high-quality graphene; from a theoretical point of view, it is particularly challenging, since it can be described by a delicate interplay between chemisorption and physisorption processes. The first-principles simulation of transition metals requires particular care also because they can be viewed as intermediate systems between simple metals and insulating crystals. Even in these cases the method performs well as demonstrated by comparing our results with available experimental data and other theoretical investigations. We confirm that the rare-gas Xe atom is preferentially adsorbed on the top-site configuration on the Ni(111) surface too. Our approach, based on the use of the maximally localized Wannier functions, also allow us to well characterize the bonds between graphene and Ni(111).