Thermodynamic study on aniline adsorption on chemical modified multi-walled carbon nanotubes

Optical Absorption Investigations for efficient Crystal Violet Dye removal from wastewater via Carbon nanotubes: Montmorillonite based Nanocomposite

The current study reports a facile method to fabricate functionalized multi-walled carbon nanotubes and montmorillonite clay mineral-based nano-composite matrix and its detailed characterization using spectroscopic and morphological techniques. The nanocomposites have been studied for their potential applications in the treatment of contaminated water using batch adsorption studies. The investigations conducted using optical absorption spectroscopic measurements for the adsorption process indicate that the nanocomposite matrix can effectively remove almost 98% of the dye from aqueous solution. The nanocomposites have showed fast and strong adsorption behaviour for the dye with the maximum adsorption capacity (q_m ) of ~ 467.3 mg g^-1 in 25 min. The experimental data at equilibrium were also correlated with the theoretical adsorption isotherm and kinetic models. The results demonstrate that the experimental data fits well to the Freundlich adsorption isotherm model and conforms to second order kinetics. Furthermore, the nanocomposite exhibits good recyclability without any marked decrease in the adsorption performance even after five adsorption cycles of usage which indicates its potential application as reusable adsorbent for the efficient removal of hazardous dyes from contaminated water.

The Application of Carbon Nanotube/Graphene-Based Nanomaterials in Wastewater Treatment

The treatment of organic wastewater is of great significance. Carbon nanotube (CNT)/graphene-based nanomaterials have great potential as absorbent materials for organic wastewater treatment owing to their high specific surface area, mesoporous structure, tunable surface properties, and high chemical stability; these attributes allow them to endure harsh wastewater conditions, such as acidic, basic, and salty conditions at high concentrations or at high temperatures. Although a substantial amount of work has been reported on the performance of CNT/graphene-based nanomaterials in organic wastewater systems, engineering challenges still exist for their practical application. Herein, the adsorption mechanism of CNT- and graphene-based nanomaterials is summarized, including the adsorption mechanism of CNTs and graphene at the atomic and molecular levels, their hydrophilic and hydrophobic surface properties, and the structure-property relationship required for adsorption to occur. Second, the structural modification and recombination methods of CNT- and graphene-based adsorbents for various organic wastewater systems are introduced. Third, the engineering challenges, including the molding of macroscopically stable adsorbents, adsorption isotherm models and adsorption kinetic behaviors, and reversible adsorption performance compared to that of activated carbon (AC) are discussed. Finally, cost issues are discussed in light of scalable and practical application of these materials.

Green Carbon Material for Organic Contaminants Adsorption

Eco-friendly and economical adsorbents are desirable for removing organic pollutants from the environment. Herein, a kind of green carbon material, electrolytic carbon (EC) prepared by the electrochemical conversion of greenhouse gas (CO₂) in molten carbonate, is verified as an effective adsorbent for aniline and other small aromatic organic molecules. The EC consists of nanoparticles and nanoflakes, featuring the specific surface area of ∼641 m²/g with an enriched micropore structure. It exhibits a large adsorption capacity (Q_max > 114.1 mg/g) for aniline, especially in water with a lower contamination level. The adsorption conforms to the pseudo-second-order equation kinetically and the Freundlich model thermodynamically in the temperature range of 303-323 K. Moreover, it is found that the adsorption performance of the material can be further improved through reducing surface oxygen functional groups by a simple thermotreatment. Its adsorption capacity for aniline is enhanced by 1.7 times, demonstrating that the π-π dispersive interaction plays a primary role for the efficient adsorption. This adsorption mechanism is further confirmed by the excellent adsorption performance of the carbon materials for other analogue aromatic compounds (phenol, nitrobenzene). The super performance of the CO₂-derived carbon adsorbents will be helpful for capturing CO₂ as well as for removing organic pollutants.

Relationship between the structure and catalytic performance of MoS2 with different surfactant-assisted syntheses in the hydrodesulfurization reaction of 4,6-DMDBT

Surfactants are important factors in the hydrothermal synthesis of MoS₂ with different morphologies. Herein, we report the synthesis of MoS₂via the hydrothermal method combined with a single-source precursor with the assistance of different surfactants (CTAB/SDS/SDBS). The synthesis mechanisms of MoS₂ with different morphologies and their effects on 4,6-DMDBT in hydrodesulfurization (HDS) have been systematically studied. MoS₂-CTAB was prepared by the adsorption of molybdate radicals, nucleation and formation. MoS₂-SDS and MoS₂-SDBS were synthesized via four steps, namely, adsorption, insertion, exfoliation and assembly, and the relationship between the morphology-structure-performance of MoS₂ in the hydrodesulfurization of 4,6-DMDBT was investigated. It was established that the desulfurization rate of MoS₂, HYD ratio and selectivity of the MoS₂ increased in the order: MoS₂-SDBS > MoS₂-CTAB > MoS₂-SDS, which exhibited a positive correlation with the average number of layers and dispersion, and a negative correlation with the average slab length and the ratio of the Mo edge/corner sites of MoS₂. Among all the MoS₂, MoS₂-SDBS exhibited the best HDS performance.

Surfactants are important factors in the hydrothermal synthesis of MoS₂ with different morphologies.

Effects of Various Surfactants on the Dispersion of MWCNTs-OH in Aqueous Solution

Dispersion of carbon nanotubes (CNTs) is a challenge for their application in the resulting matrixes. The present study conducted a comparison investigation of the effect of four surfactants: Alkylphenol polyoxyethylene ether (APEO), Silane modified polycarboxylate (Silane-PCE), I-Cationic polycarboxylate (I-C-PCE), and II-Cationic polycarboxylate (II-C-PCE) on the dispersion of hydroxyl functionalized multi-walled carbon nanotubes (MWCNTs–OH). Among the four surfactants, APEO and II-C-PCE provide the best and the worst dispersion effect of CNTs in water, respectively. Dispersion effect of MWCNTs–OH has been characterized by optical microscope (OM), field emission-scanning electron microscope (FE-SEM), and Ultraviolet–visible spectroscopy (UV–Vis).The OM images are well consistent with the UV–Vis results. Based on the chemical molecular structures of the four surfactants, the mechanism of MWCNTs–OH dispersion in water was investigated. For each kind of surfactant, an optimum surfactant/MWCNTs–OH ratio has been determined. This ratio showed a significant influence on the dispersion of MWCNTs–OH. Surfactant concentration higher or lower than this value can weaken the dispersion quality of MWCNTs–OH.

Degradation pathways of aniline in aqueous solutions during electro-oxidation with BDD electrodes and UV/H2O2 treatment

In this work, it has been studied the mineralization of aniline, a toxic substance of low biodegradability typically found in many industrial wastewaters, through electro-oxidation using boron doped diamond (BDD) electrodes and photo-oxidation (UV photolysis and UV/H₂O₂ treatments). It was observed that in electro-oxidation and UV/H₂O₂, it was feasible to reach aniline mineralizations higher than 85%. Two different degradation routes have been observed during the aniline oxidation in these two treatments. The first route was the mineralization pathway, in which aniline was oxidized to CO₂, water and nitrate. The second route was the polyaniline pathway in which polyanilines of high molecular weight are formed. The intermediate compounds involved in both degradation routes are different depending on the treatment used. In the electro-oxidation, denitrification processes were also observed. From an economical point of view, electro-oxidation of aniline using BDD electrodes is more interesting than UV/H₂O₂ due it has an 87% lower operational cost. So, electro-oxidation using BDD electrodes seems to be a more suitable technique for the mineralization of wastewater containing aniline than UV or H₂O₂ based technologies.

A key parameter on the adsorption of diluted aniline solutions with activated carbons: The surface oxygen content

A total of 11 different commercial activated carbons (AC) with well characterized textural properties and oxygen surface content were tested as adsorbents for the removal of aniline as a target water pollutant. The maximum adsorption capacity of aniline for the studied AC was from 138.9 to 257.9 mg g(-1) at 296.15 K and it was observed to be strongly related to the textural properties of the AC, mainly with the BET surface area and the micropore volume. It was not observed any influence of the oxygen surface content of the AC on the maximum adsorption capacity. However, it was found that at low aniline aqueous concentration, the presence of oxygen surface groups plays a dominant role during the adsorption. A high concentration of oxygen surface groups, mainly carboxylic and phenolic groups, decreases the aniline adsorption regardless of the surface area of the AC.

Aqueous adsorption and removal of organic contaminants by carbon nanotubes

Organic contaminants have become one of the most serious environmental problems, and the removal of organic contaminants (e.g., dyes, pesticides, and pharmaceuticals/drugs) and common industrial organic wastes (e.g., phenols and aromatic amines) from aqueous solutions is of special concern because they are recalcitrant and persistent in the environment. In recent years, carbon nanotubes (CNTs) have been gradually applied to the removal of organic contaminants from wastewater through adsorption processes. This paper reviews recent progress (145 studies published from 2010 to 2013) in the application of CNTs and their composites for the removal of toxic organic pollutants from contaminated water. The paper discusses removal efficiencies and adsorption mechanisms as well as thermodynamics and reaction kinetics. CNTs are predicted to have considerable prospects for wider application to wastewater treatment in the future.

Influence of functional groups on desorption of organic compounds from carbon nanotubes into water: insight into desorption hysteresis

Adsorption-desorption of nitrobenzenes, phenols, and anilines on five multiwalled carbon nanotubes (MWCNTs) with different degrees of surface oxidation were investigated to examine the influence of functional groups of both organic chemicals and CNTs on desorption hysteresis. Desorption hysteresis was not observed for nitrobenzenes, phenols, and 4-nitroaniline from all MWCNTs. Significant desorption hysteresis was observed for aniline and 4-methylaniline on surface-oxidized MWCNTs but not on unoxidized MWCNTs. Formation of an irreversible amide bond (i.e.,-CONH-) by amidation reaction of amino group of anilines with oxygen-containing groups (i.e., carboxyl or lactonic groups) on MWCNTs was observed. We proposed that desorption hysteresis could be attributed to the immobilization of organic compounds on the surface of CNTs resulting from the irreversible chemical reaction/binding. The irreversible chemical immobilization is compound functional group selective and dependent on the surface oxygen-containing groups of CNTs. Hysteresis index (HI) values of aniline or 4-methylaniline on MWCNTs increased with the amounts of oxygen-containing groups on MWCNTs. Moreover, HI values of anilines on a given oxidized MWCNT followed an order of 4-nitroaniline < 4-chloroaniline < aniline < 4-methylaniline.

Synthesis and properties of Fe3O4-activated carbon magnetic nanoparticles for removal of aniline from aqueous solution: equilibrium, kinetic and thermodynamic studies

In this study, powder activated carbon (PAC) and magnetic nanoparticles of iron (III) oxide were used for synthesis of Fe₃O₄-activated carbon magnetic nanoparticles (AC-Fe₃O₄ MNPs) as an adsorbent for the removal of aniline. The characteristics of adsorbent were evaluated by SEM, TEM, XRD and BET. Also, the impact of different parameters such as pH, contact time, adsorbent dosage, aniline initials concentration and solution temperature were studied. The experimental data investigated by Langmuir and Freundlich adsorption isotherms and two models kinetically of pseudo first-order and pseudo second-order. The results indicated that the adsorption followed Langmuir and pseudo second-order models with correlation r² > 0.98 and r² > 0.99, respectively. The equilibrium time was obtained after 5 h. According to Langmuir model, the maximum adsorption capacity was 90.91 mg/g at pH = 6, and 20°C. The thermodynamic parameters indicated that adsorption of aniline on magnetic activated carbon was exothermic and spontaneous. This synthesized AC-Fe₃O₄ MNPs due to have advantages such as easy and rapid separation from solution could be applied as an adsorbent effective for removal of pollutants such as aniline from water and wastewater.

Adsorption of diuron, fluridone and norflurazon on single-walled and multi-walled carbon nanotubes

The sorption behaviors of diuron (DIU), fluridone (FLU) and norflurazon (NOR) by a single-walled carbon nanotube (SWCNT) and three multi-walled carbon nanotubes (MWCNT) samples including MWCNT10 (<10nm, outer diameter), MWCNT20 (10-20 nm), and MWCNT40 (20-40 nm) were investigated. All adsorption isotherms were nonlinear and were well fitted with the Freundlich model and Dubinin Ashtakhov (DA) model. The linear relationships between the organic carbon (OC)-normalized saturated adsorption capacity (Q(0)(OC)) and surface area (SA) suggest that SA is presumably responsible for the adsorption of DIU and NOR on CNTs. While FLU, DIU, and NOR OC-normalized distribution coefficients (logK(OC)) of CNTs increased with increasing their hydrophobicity (logK(OW)) and the positive relationships between the logK(OW)-normalized logK(OC) (i.e., logK(OC)/logK(OW)) of FLU, DIU, and NOR and their hydrogen bonding ability indicate that the adsorption of FLU, DIU and NOR was mainly controlled by the hydrophobic interaction and hydrogen bonding. The higher logK(OC) or Q(0)(OC) values of MWCNT10 and SWCNT relative to other large MWCNTs and carbonaceous adsorbents suggest that MWCNT10 has the potential to serve as an adsorbent used to reduce the mobility of herbicides in agricultural and environmental applications.

Removal of methylene blue from aqueous solution with magnetite loaded multi-wall carbon nanotube: kinetic, isotherm and mechanism analysis

In this study, we have demonstrated the efficient removal of cationic dye, methylene blue (MB), from aqueous solution with the one-pot solvothermal synthesized magnetite-loaded multi-walled carbon nanotubes (M-MWCNTs). The as-prepared M-MWCNTs were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. The effects of contact time, initial dye concentration, and solution pH on the adsorption of MB onto M-MWCNTs were systematically studied. It was shown that the MB adsorption was pH-dependent. Adsorption kinetics was best described by the pseudo-second-order model. Equilibrium data were well fitted to the Langmuir isotherm model, yielding maximum monolayer adsorption capacity of 48.06 mg g(-1). FTIR analysis suggested that the adsorption mechanism was possibly attributed to the electrostatic attraction and π-π stacking interactions between MWCNTs and MB.

Synergistic removal of aniline by carbon nanotubes and the enzymes of Delftia sp. XYJ6

Synergistic removal of aniline by carbon nanotubes and the enzymes of Delftia sp. XYJ6, a newly isolated bacterial strain for biodegrading aniline, was investigated. It showed that biodegradation rate of aniline was increased with the augment of protein concentration in cell-free extract of Delftia sp. XYJ6. The adsorption amount of aniline by multi-walled carbon nanotubes (MWCNTs) was slightly higher than that by single-walled carbon nanotubes (SWCNTs), however the adsorption amount of protein of Delftia sp. XYJ6 by MWCNTs was lower than that by SWCNTs. Much more amount of aniline could be removed by CE of Delftia sp. XYJ6 in the presence of SWCNTs than MWCNTs, which indicated that an efficient reaction between aniline and enzymes of Delftia sp. XYJ6 on the surface of SWCNTs played a key role in the rapid enzymatic biodegradation of aniline. This study is not previously reported and may be useful in basic research and the removal of aniline from wastewater.

Adsorption property and mechanism of composite adsorbent PMAA/SiO2 for aniline

In this paper, functional monomer methacrylic acid (MAA) was grafted onto the surface of silica gel particles using 3-methacryloxypropyl trimethoxysilane (MPS) as intermedia, and grafting particles PMAA/SiO(2) were prepared. The adsorption properties and mechanism of PMAA/SiO(2) towards aniline were researched through batch and column adsorption methods. The experimental results showed that PMAA/SiO(2) possesses strong adsorption ability for aniline with interaction of hydrogen bond. The saturated adsorption amount could reach up to 140 mg g(-1). The empirical Langmuir isotherm was found to agree well with the equilibrium adsorption data. pH and temperature were found to have great influence on the adsorption amount. Finally, PMAA/SiO(2) was observed to possess excellent reusability properties as well.

Equilibrium, kinetic and thermodynamic studies on the adsorption of 2-nitroaniline onto activated carbon prepared from cotton stalk fibre

Activated carbon prepared from cotton stalk fibre has been utilized as an adsorbent for the removal of 2-nitroaniline from aqueous solutions. The influence of adsorbent mass, contact time and temperature on the adsorption was investigated by conducting a series of batch adsorption experiments. The equilibrium data at different temperatures were fitted with the Langmuir, Freundlich, Tempkin, Redlich-Peterson and Langmuir-Freundlich models. The Langmuir-Freundlich isotherm was found to best describe the experimental data. The adsorption amount increased with increasing temperature. The maximum adsorption capacity of 2-nitroaniline was found to be 383 mg/g for initial 2-nitroaniline concentration of 200mg/L at 45 degrees C. The kinetic rates were modeled by using the Lagergren-first-order, pseudo-second-order and Elovich models. The pseudo-second-order model was found to explain the adsorption kinetics most effectively. It was also found that the pore diffusion played an important role in the adsorption, and intraparticle diffusion was the rate-limiting step at the first 30 min for the temperatures of 25, 35 and 45 degrees C. FTIR and (13)C NMR study revealed that the amino and isocyanate groups present on the surface of the adsorbent were involved in chemical interaction with 2-nitroaniline. The negative change in free energy (Delta G degrees) and positive change in enthalpy (Delta H degrees) indicated that the adsorption was a spontaneous and endothermic process.

Aqueous adsorption of aniline, phenol, and their substitutes by multi-walled carbon nanotubes

Aqueous adsorption of a series of phenols and anilines by a multiwalled carbon nanotube material (MWCNT15), which depends strongly on the solution pH and the number and types of solute groups, was investigated in this study. The pH-dependent adsorption coefficients, Kd, could be predicted by the established models including solute pKa and solution pH values. Phenol or aniline substitution with more groups has higher adsorption affinity, and nitro, chloride, or methyl groups enhanced adsorption in the following order: nitro group > chloride group > methyl group. All adsorption isotherms of nondissociated phenols and anilines are nonlinear and fitted well bythe Polanyi-theory based Dubinin-Ashtakhov (DA) model. Linear quantitative relationships combining DA model parameters (E and b) with solute solvatochromic parameters were developed to evaluate the adsorptive behaviors of nondissociated species. For the saturated sorbed capacity, Q0, the logarithmic values of phenols and anilines were relatively constant with a mean value of 1.90. Besides the van der Waals force, H-bonding interactions from solutes as hydrogen-bonding donors, and followed by pi-electron polarizability, may play important roles on the adsorption of phenols and anilines by carbon nanotubes in the aqueous environment