Adsorption Behaviors of CO2 and NH3 on Chemically Surface-Treated Activated Carbons

Comparative Study of Three Dyes' Adsorption onto Activated Carbon from Chenopodium quinoa Willd and Quillaja saponaria

The present study shows porous activated carbon obtained from Chenopodium quinoa Willd and Quillaja saponaria and their use as potential adsorbents to remove three types of dyes from aqueous solutions. The adsorption results were compared with commercial charcoal to check their efficiency. All porous carbon materials were activated using carbon dioxide and steam and fully characterized. Moreover, the steam-activated samples exhibited a high total pore volume with a BET surface area of around 800 m2 g−1. Batch adsorption experiments showed that commercial charcoal is the charcoal that offered the best adsorption efficiency for tartrazine and sunset yellow FCF. However, in the case of crystal violet, all activated carbons obtained from Chenopodium quinoa Willd and Quillaja saponaria showed the best captures, outperforming commercial charcoal. Molecular dockings of the dyes on the commercial charcoal surface were performed using AutoDock Vina. The kinetic results of the three isotherm’s models for the present data follow the order: Langmuir~Freundlich > Temkin.

The Role of CO2 as a Mild Oxidant in Oxidation and Dehydrogenation over Catalysts: A Review

Carbon dioxide (CO2) is widely used as an enhancer for industrial applications, enabling the economical and energy-efficient synthesis of a wide variety of chemicals and reducing the CO2 levels in the environment. CO2 has been used as an enhancer in a catalytic system which has revived the exploitation of energy-extensive reactions and carry chemical products. CO2 oxidative dehydrogenation is a greener alternative to the classical dehydrogenation method. The availability, cost, safety, and soft oxidizing properties of CO2, with the assistance of appropriate catalysts at an industrial scale, can lead to breakthroughs in the pharmaceutical, polymer, and fuel industries. Thus, in this review, we focus on several applications of CO2 in oxidation and oxidative dehydrogenation systems. These processes and catalytic technologies can reduce the cost of utilizing CO2 in chemical and fuel production, which may lead to commercial applications in the imminent future.

Removal of CO2 in a multistage fluidized bed reactor by diethanol amine impregnated activated carbon

To mitigate the emission of carbon dioxide (CO2), we have developed and designed a four-stage fluidized bed reactor. There is a counter current exchange between solid adsorbent and gas flow. In this present investigation diethanol amine (DEA) impregnated activated carbon made from green coconut shell was used as adsorbent. This type of adsorbent not only adsorbs CO2 due to the presence of pore but also chemically reacts with CO2 and form secondary zwitterions. Sampling and analysis of CO2 was performed using Orsat apparatus. The effect of initial CO2 concentration, gas velocity, solid rate, weir height etc. on removal efficiency of CO2 have been investigated and presented. The percentage removal of CO2 has been found close to 80% under low gas flow rate (0.188 m/s), high solid flow rate (4.12 kg/h) and weir height of 50 mm. From this result it has been found out that multistage fluidized bed reactor may be a suitable equipment for removal of CO2 from flue gas.

Effects of Microporosity and Surface Chemistry on Separation Performances of N-Containing Pitch-Based Activated Carbons for CO2/N2 Binary Mixture

In this study, N-containing pitch-based activated carbons (NPCs) were prepared using petroleum pitch with a low softening point and melamine with a high nitrogen content. The major advantage of the preparation method is that it enables variations in chemical structures and textural properties by steam activation at high temperatures. The adequate micropore structures, appropriate chemical modifications, and high adsorption enthalpies of NPCs are favorable for CO₂ adsorption onto carbon surfaces. Furthermore, the structure generates a considerable gas/N-containing carbon interfacial area, and provides selective access to CO₂ molecules over N₂ molecules by offering an increased number of active sites on the carbon surfaces. The highest CO₂/N₂ selectivity, i.e., 47.5, and CO₂ adsorption capacity for a CO₂/N₂ (0.15:0.85) binary gas mixture, i.e., 5.30 wt%, were attained at 298 K. The NPCs also gave reversible and durable CO₂-capturing performances. All the results suggest that NPCs are promising CO₂ sorbents, which can meet the challenges of current CO₂ capture and separation techniques.

Characterization and lead adsorption properties of activated carbons prepared from cotton stalk by one-step H3PO4 activation

Activated carbons were prepared from cotton stalk by one-step H(3)PO(4) activation and used as adsorbent for the removal of lead(II). Taguchi experimental design method was used to optimize the preparation of the adsorbents. The results showed that the optimized conditions were: impregnation with a 50% (w/v) phosphoric acid solution with a mass ratio of 3:2 and activation temperature at 500 degrees C for 60 min with the rate of achieving the activation temperature equal to 10 degrees C min(-1). The cotton stalk activated carbon (CSAC) prepared at these conditions have 1.43 mmol g(-1) acidic surface groups and 1570 m(2) g(-1) BET surface area. Adsorption isotherms for lead(II) on the adsorbents were measured by conducting a series of batch adsorption experiments. The Langmuir maximum adsorption amount of lead(II) on CSAC was more than 119 mg g(-1), which was superior to the ordinary commercial activated carbon (CAC) on the market. Compared with the CAC, the CSAC had a wider applicable pH range from 3.5 to 6.5 for lead(II) uptake. The final pH values at equilibrium after adsorption were lower than the initial pH value, indicating that the ion-exchange process was involved in the adsorption. This is also confirmed by the result that the increase of acidic surface groups favored the adsorption process. Thermodynamic study indicated that the adsorption was a spontaneous and endothermic process.

Can carbon surface oxidation shift the pore size distribution curve calculated from Ar, N(2) and CO(2) adsorption isotherms? Simulation results for a realistic carbon model

Using the virtual porous carbon model proposed by Harris et al, we study the effect of carbon surface oxidation on the pore size distribution (PSD) curve determined from simulated Ar, N(2) and CO(2) isotherms. It is assumed that surface oxidation is not destructive for the carbon skeleton, and that all pores are accessible for studied molecules (i.e., only the effect of the change of surface chemical composition is studied). The results obtained show two important things, i.e., oxidation of the carbon surface very slightly changes the absolute porosity (calculated from the geometric method of Bhattacharya and Gubbins (BG)); however, PSD curves calculated from simulated isotherms are to a greater or lesser extent affected by the presence of surface oxides. The most reliable results are obtained from Ar adsorption data. Not only is adsorption of this adsorbate practically independent from the presence of surface oxides, but, more importantly, for this molecule one can apply the slit-like model of pores as the first approach to recover the average pore diameter of a real carbon structure. For nitrogen, the effect of carbon surface chemical composition is observed due to the quadrupole moment of this molecule, and this effect shifts the PSD curves compared to Ar. The largest differences are seen for CO(2), and it is clearly demonstrated that the PSD curves obtained from adsorption isotherms of this molecule contain artificial peaks and the average pore diameter is strongly influenced by the presence of electrostatic adsorbate-adsorbate as well as adsorbate-adsorbent interactions.

Adsorption of Ammonia Ions and Ammonium from Aqueous Solutions on Modified Activated Carbons

The adsorption process of ammonia ions and ammonium from aqueous solutions on the intact activated carbon obtained from nutshells through activation with phosphoric acid and oxidized with H2O2 and later impregnated with salt containing Co2+, Ag+, Ni2+, Cu2+, has been investigated. The efficiency of ammonia ions and ammonium elimination from various water categories, using both activated carbon (the intact CAN-7 and CAN-7 oxidized with H2O2 and impregnated with Co2+, Ag+, Ni2+, Cu2+ ions) has been demonstrated.

Structure evolution and optimization in the fabrication of PVA-based activated carbon fibers

The structure and composition evolution of polyvinyl alcohol (PVA) fibers during the fabrication of activated carbon fibers (ACF) by a newly developed method were systematically elucidated. The pore structure of the fibers was significantly influenced by the carbonization and activation conditions. The elemental composition and chemical structure evolution of the fibers during the heat treatment processes were evaluated by elemental analysis, Fourier transform infrared spectrophotometry (FTIR), and X-ray photoelectron spectroscopy (XPS). Crystal structure evolution of the fibers during the heat treatment processes was elucidated by X-ray diffraction (XRD) analysis. Based on these understandings, the process conditions were optimized using an L(9)(3)(4) orthogonal array design matrix. Appropriate process parameters for the fabrication of PVA-ACFs were established as carbonizing the dehydrated fiber at 300 degrees C for 60 min, and then lifting the temperature to 900 degrees C with a heating speed of 10 degrees C/min in an inert atmosphere, thereafter keeping the fiber at 900 degrees C for 60 min in an oxidizing atmosphere.

Effect of electrochemical oxidation of activated carbon fiber on competitive and noncompetitive sorption of trace toxic metal ions from aqueous solution

A viscose-rayon-based activated carbon cloth (ACC) was electrochemically oxidized to enhance its cation sorption capacity for comparison with as-received ACC. The ACCs were characterized by sodium capacity measurement, pH titration, zeta potential measurement, elemental analysis, Brunauer-Emmet-Teller surface area, and pore size distribution. Batch sorption experiments showed that electrochemically oxidized ACC (EO) is more effective for the removal of lead and copper ions compared to unoxidized ACC (UO) for both competitive and noncompetitive sorption. For electrochemically oxidized fibers the copper and lead sorption capacities of ACC increased 17 and 4 times, respectively, for noncompetitive sorption and 8.8 and 8.6 times, respectively, for competitive sorption. However, reduction in the sorption capacities for both metals was observed for the competitive sorption. The sorption of lead and copper onto EO was by ion exchange, while that onto UO was likely to be due to surface complex formation. The affinity order of the two metal ions sorbed by UO and EO is Pb(2+)>Cu(2+). The effect of pH on sorption isotherms indicated that metal uptake increased with an increase in solution pH.

Quantum Chemical Prediction of Reaction Pathways and Rate Constants for Dissociative Adsorption of COx and NOx on the Graphite (0001) Surface

We present predictions of reaction rate constants for dissociative adsorption reactions of CO(x) (x = 1, 2) and NO(x) (x = 1, 2) molecules on the basal graphite (0001) surface based on potential energy surfaces (PES) obtained by the integrated ONIOM(B3LYP:DFTB-D) quantum chemical hybrid approach with dispersion-augmented density functional tight binding (DFTB-D) as low level method. Following an a priori methodology developed in a previous investigation of water dissociative adsorption reactions on graphite, we used a C(94)H(24) dicircumcoronene graphene slab as model system for the graphite surface in finite-size molecular structure investigations, and single adsorbate molecules reacting with the pristine graphene sheet. By employing the ONIOM PES information in RRKM theory we predict reaction rate constants in the temperature range between 1,000 and 5,000 K. We find that among CO(x) and NO(x) adsorbate species, the dissociative adsorption reactions of CO(2) and both radical species NO and NO(2) are likely candidates as a cause for high temperature oxidation and erosion of graphite (0001) surfaces, whereas reaction with CO is not likely to lead to long-lived surface defects. High temperature quantum chemical molecular dynamics simulations (QM/MD) at T = 5,000 K using on-the-fly DFTB-D energies and gradients confirm the results of our PES study.

Role of copper chloride on the surface of activated carbon in adsorption of methyl mercaptan

In this paper, adsorption characteristics of methyl mercaptan on virgin activated carbon and copper chloride impregnated activated carbons were studied by using a dynamic adsorption method in a fixed bed. The activated carbons were characterized by nitrogen adsorption, XRD, TGA and solubility tests. The impregnation of copper chloride on the activated carbon significantly enhanced the adsorption capacity of methyl mercaptan, despite a notable decrease in microporosity. It is likely that copper chloride may act as adsorption site for methyl mercaptan. Copper chloride on the activated carbon in a range of 3-20 wt% Cu content was present mostly in the amorphous form of CuCl(2), according to the results of the solubility, XRD and TGA tests. Starting at 10 wt% in Cu loading, the adsorption capacity for methyl mercaptan decreases gradually. It is likely that a decrease in the degree of copper chloride dispersion and an accessibility of small pores may lead to the decrease in the adsorption capacity of the activated carbon for methyl mercaptan.

Adsorption of NH3 onto activated carbon prepared from palm shells impregnated with H2SO4

Adsorption of ammonia (NH3) onto activated carbons prepared from palm shells impregnated with sulfuric acid (H2SO4) was investigated. The effects of activation temperature and acid concentration on pore surface area development were studied. The relatively large micropore surface areas of the palm-shell activated carbons prepared by H2SO4 activation suggest their potential applications in gas adsorption. Adsorption experiments at a fixed temperature showed that the amounts of NH3 adsorbed onto the chemically activated carbons, unlike those prepared by CO2 thermal activation, were not solely dependent on the specific pore surface areas of the adsorbents. Further adsorption tests for a wide range of temperatures suggested combined physisorption and chemisorption of NH3. Desorption tests at the same temperature as adsorption and at an elevated temperature were carried out to confirm the occurrence of chemisorption due to the interaction between NH3 and some oxygen functional groups via hydrogen bonding. The surface functional groups on the adsorbent surface were detected by Fourier transform infrared spectroscopy. The amounts of NH3 adsorbed by chemisorption were correlated with the contents of elemental oxygen present in the adsorbents. Mechanisms for chemical activation and adsorption processes are proposed based on the observed phenomena.

Influence of copper content on NO removal of the activated carbon fibers produced by electroplating

In this study, the activated carbon fibers (ACFs) on which copper metal was deposited by electroplating were used to remove nitric oxide (NO). N(2)/77 K adsorption isotherm characteristics, including the specific surface area and micropore volume, were investigated by BET and T-plot methods. NO removal efficiency was confirmed by gas chromatographic technique. From the experimental results, the copper content supported on ACFs led to an increase in the NO conversion, in spite of the decrease of the specific surface area or the micropore volume of ACFs. Consequently, the presence of Cu on ACFs played an important role in improving the NO reduction into O(2) and N(2), which was mainly attributed to the catalytic reactions of Cz-NO-Cu.

Studies on pore structures and surface functional groups of pitch-based activated carbon fibers

The present study concerns the physical activation and chemical oxidation of pitch-based activated carbon fibers (ACFs) as ways to improve the adsorption properties. The surface oxides of the ACFs studied were determined by Boehm's titration and the pore structures were studied by the BET method with N(2)/77 K adsorption. Also, the adsorption properties of the ACFs were investigated with chromium ion adsorption by different adsorption models. As a result, it was observed that carboxyl groups were largely created after nitric acid treatment on ACFs. The affinity for chromium ions increases with increasing specific surface area, micropore volume, and surface functionalities of ACFs as the activation time increases.

In Situ Sol–Gel Preparation of Polysaccharide/Titanium Oxide Hybrid Colloids and Their Electrorheological Effect

A new type of organic/inorganic hybrid colloid, made of modified carboxylmethyl starch (CMS) and titanium oxide (TiO(2)), was synthesized by an in situ sol-gel technique. IR spectra analysis shows strong a interaction of functional groups between two components, whose dispersion is almost at the molecular level. Due to the highly active surfaces hybrid particles and their characteristic dielectric behavior in accordance with the previous theoretic calculation, the suspensions of hybrids in silicone oil display a remarkable ER effect. The static yield stress can be above 20 kPa (shear rate 5 S(-1)) under a direct current field of 4 kV/mm at room temperature, much higher than that of simple blends of starch and titanium dioxide. In the meanwhile, the temperature dependence and sedimentation stability were optimized. Based on existing experimental results, we propose that dielectric properties and surface (interface) activity are two necessary conditions fulfilling the requirement of high ER activity. The combination of both factors may effectively reduce the activation energy needed for ERF restructuring.

Effect of KOH Activation on the Formation of Oxygen Structure in Activated Carbons Synthesized from Polymeric Precursor

In this work, the influence of KOH activation on the surface chemistry of activated carbons (ACs) synthesized from polystyrene-based cation exchangeable resin (PSI) has been investigated. The surface chemistry of ACs has been characterized by using Fourier transformed infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), pH measurement, and Boehm's titration method. As a result, PSI can be successfully converted into ACs with high porosities. The total oxygen content on the ACs studied increases with increasing the KOH-to-PSI ratio. FT-IR and XPS analyses show that the resulting carbons possess a number of oxygen surface functional groups, such as carbonyl, quinone, phenol, ether, and carboxylic acid groups. The highest oxygen content and acid value are observed at a KOH-to-PSI ratio of 4 (KPS-4). However, its pH and surface basicity are higher than those of a KOH-to-PSI ratio of 2 (KPS-2), indicating the formation of basic species, such as quinone and pyrone groups. Although the oxygen-containing groups with basic character exist in the resulting carbons, all the samples are still acidic in character.

Preparation and Structural Characterization of Activated Carbons Based on Polymeric Resin

In this work, activated carbons (ACs) with high porosity were synthesized from polystyrene-based cation-exchangeable resin (PSI) by chemical activation with KOH as the activating agent. And the influence of the KOH-to-PSI ratio on the porosity of the ACs studied was investigated by using nitrogen adsorption isotherms at 77 K and a scanning electron microscope (SEM). As a result, PSI could be successfully converted into ACs with well-developed micro- and mesopores. The specific surface area and pore volumes increased with an increase in the KOH-to-PSI ratio. However, it was found that the addition of KOH did lead to the transformation of the micropores to the meso- and macropores. From the results of pore size analysis, quite different pore size distributions were observed, resulting from the formation of new pores and the widening of the existing micropores during KOH activation. A SEM study showed that the resulting carbons possessed a well-developed pore structure and the pore size of the ACs studied increased with the KOH-to-PSI ratio.

Pore Structure and Surface Properties of Chemically Modified Activated Carbons for Adsorption Mechanism and Rate of Cr(VI)

Effects of hydrochloric acid and sodium hydroxide treatments of activated carbons (ACs) on chromium(VI) reduction were studied. The surface properties were determined by pH, acid-base values, FT-IR, and X-ray photoelectron spectrometer (XPS). And the porous structure of the activated carbons was characterized by adsorption of N(2)/77 K. The Cr(VI) adsorption experiments were carried out to analyze the influence of porous texture and surface properties changed by the chemical surface treatments of ACs on adsorption rate with carbon-solution contact time. From the experimental results, it was observed that the extent of adsorption and reduction processes depends on both microporous structure and functional groups. And the adsorption of Cr(VI) ion was more effective in the case of acidic treatment on activated carbons, resulting from the increases of acid value (or acidic functional group) of activated carbon surfaces. However, basic treatment on activated carbons was not significantly effective on the adsorption of Cr(VI) ion, probably due to the effects of the decrease of specific surface area and basic Cr(VI) in nature.

Anodic Surface Treatment on Activated Carbons for Removal of Chromium(VI)

In this work, the effect of anodic surface treatment on activated carbons and its Cr(VI) adsorption properties were investigated under reaction-treatment time conditions with 35 wt% HCl solution. The acid-base surface values were determined by Boehm's titration technique. The pore and surface characteristics were studied in terms of BET volumetric measurement with N(2) adsorption. As an experimental result, the acidic surface functional groups of activated carbons increased with increasing the HCl reaction-treatment time. It was found that the surface characteristics, including specific surface area, total pore volume, net heat of adsorption, and BET's C, slightly decrease in anodic surface treatments on activated carbons. In addition, an increase in reaction-treatment time led to increases of the first rate (K(1)) of Cr(VI) adsorption and diffusion coefficient (D). These values are evidence that adsorption is controlled more by the acid-base interactions between electron-donor substances and acidized activated carbons as electron acceptor than by the pore and surface structures of activated carbons. Copyright 2001 Academic Press.

Role of Chemically Modified Carbon Black Surfaces in Enhancing Interfacial Adhesion between Carbon Black and Rubber in a Composite System

The surface and adsorption characteristics of carbon blacks treated with H(3)PO(4), KOH, and C(6)H(6) were investigated. The equilibrium spreading pressure (pi(e)), surface energy (gamma(s)), and specific surface area (S(BET)) were studied by the BET method with N(2) adsorption. In this work, an interpretation based on the nitrogen amount adsorbed for filling a monolayer (a(0)) was proposed for the determination of the Gibbs free energy of nitrogen adsorption, allowing evaluation of the equilibrium spreading pressure or London dispersive component of the surface free energy of the carbon blacks studied. Also, the microstructures of the carbon blacks treated were investigated by transmission electron microscopy. Acidic treatment led to significant decreases in adsorption amount, S(BET), and surface free energy of the carbon blacks, due to aggregation of the microstructures and increasing weight of the swollen specimen in an equilibrium state. Polar basic and nonpolar chemical treatments resulted in an increase of the equilibrium spreading pressure or London dispersive component of surface free energy of the carbon blacks without significantly changing the surface and adsorption properties and microstructures. Results from the surface energetics and parameter of polymer-filler interaction (chi) showed that the tearing energy of the composites is greatly dependent on the carbon blacks studied in the treatment. Copyright 2000 Academic Press.

Influence of Anodic Surface Treatment of Activated Carbon on Adsorption and Ion Exchange Properties

The effect of anodic surface treatment of activated carbon on adsorption and ion exchange characteristics was investigated in the condition of 35 wt% NaOH electrolyte for 60 s. The acid and base values were determined by a titration technique, and surface and pore structures were studied in terms of BET volumetric measurement with N(2) adsorption. The ion exchange capacity of the anodized activated carbons was characterized by a dry weight capacity technique. It was observed that an increase in current intensity leads to an increase in the surface functional groups of activated carbons, resulting in increasing pH, acid-base values, and anion-cation exchange capacities, without significant change of surface and pore structures (i.e., specific surface area, total pore volume, micropore volume, and average pore diameter). Also, anodically treated activated carbons are more effectively evaluated on the base value or cation exchange capacity than on the opposite properties in this electrolytic system. Copyright 1999 Academic Press.