The effects of picolinic acid and pH on the adsorption of Cu(II) by activated carbon fibers

The adsorption characteristics of Cu(II) on activated carbon fibers (ACFs) from simulated wastewater was investigated in the picolinic acid concentration range from 0.15 to 15 mM by varying pH from 2 to 8. When pH is below 4, the removal fraction of Cu(II) ions decreased with the decrease of pH. The removal fraction of Cu(II) ions is almost constant above pH 4. The removal efficiency of Cu(II) ions increased as the molar ratio of picolinic acid to Cu(II), specific surface area of ACFs and pH of the solution increased. In the case of [Pic]/[Cu(II)]=10, complete adsorption of Cu(II) was performed on ACF, even at pH 2.     

Phosphoric acid activated carbon discs for methane adsorption

Phosphoric acid has been used as activating agent in the preparation of binderless activated carbon discs. The granular precursor was impregnated with different solutions of phosphoric acid, hot pressed in discs, heat treated under a flow of nitrogen and washed with distilled water to extract the excess acid. The role of the impregnation ratio and the temperature of conforming have been analysed. The discs have a bulk density higher than the granular activated carbon because there is a considerable reduction of the interparticle space, the contribution of non-microporous volume being small. The discs exhibit a high volume of microporosity accessible to both nitrogen and methane molecules. Best results (storage capacity of 131, v/v) were obtained when using an impregnation ratio X_P=0.35 g phosphorous/g precursor (maximum micropore volume and minimum interparticle space) and conforming at 100 °C (higher temperatures reduce the volume of micropores). Some discs were additionally activated under a flow of carbon dioxide, the maximum methane storage capacity (near 150, v/v) being obtained when burn-off is in the 10-40% range.     

Effects of activated carbon surface chemistry and pore structure on the adsorption of organic contaminants from aqueous solution

The objective of this research was to develop activated carbon selection criteria that assure the effective removal of trace organic contaminants from aqueous solution and to base the selection criteria on physical and chemical adsorbent characteristics. To systematically evaluate pore structure and surface chemistry effects, a matrix of activated carbon fibers (ACFs) with three activation levels and four surface chemistry levels was prepared and characterized. In addition, three granular activated carbons (GACs) were studied. Two common drinking water contaminants, relatively polar methyl tertiary-butyl ether (MTBE) and relatively nonpolar trichloroethene (TCE), served as adsorbate probes. TCE adsorbed primarily in micropores in the 7-10 Å width range while MTBE adsorbed primarily in micropores in the 8-11 Å width range. These results suggest that effective adsorbents should exhibit a large volume of micropores with widths that are about 1.3 to 1.8 times larger than the kinetic diameter of the target adsorbate. Hydrophobic adsorbents more effectively removed both TCE and MTBE from aqueous solution than hydrophilic adsorbents, a result that was explained by enhanced water adsorption on hydrophilic surfaces. To assure sufficient adsorbent hydrophobicity, the oxygen and nitrogen contents of an activated carbon should therefore sum to no more than about 2 to 3 mmol/g.     

Ligand adsorption on different activated carbon materials for catalyst anchorage

Adsorption of naphtoic acid was investigated as a initial stage for the preparation of catalysts by heterogenisation of metal complexes. Four granular activated carbons and a carbon cloth showing different physical and chemical properties were used as sorbents. Adsorption of naphtoic acid was accomplished by all materials, being clear that an oxygen-rich surface chemistry has a negative effect on the physical adsorption of this molecule. The naphtoic acid molecule accommodates on the surface of narrow micropores. After adsorption, the samples were subjected to conditions similar to those used in hydrogenation reactions in order to quantify the amount of naphtoic acid that leaches from the surface of the adsorbent. According to the purpose of this research, all the carbons retain enough naphtoic acid.     

Surface chemistry of a viscose-based activated carbon cloth modified by treatment with ammonia and steam

The influence of ammonia treatment at 800 °C on the catalytic activity of a viscose-based activated carbon cloth (ACC) was evaluated for the oxidative retention of H₂S or SO₂ at room temperature. Change in the surface chemistry was observed by X-ray spectroscopy of nitrogen (N1s) and by temperature programmed desorption (TPD). Dynamic adsorption of H₂S or SO₂ in moist air onto a packed bed of activated carbon cloth was monitored by measurement of the breakthrough curves at room temperature. ACC modified by ammonia showed noteworthy enhanced SO₂ and H₂S loading relative to the untreated ACC. Improved SO₂ retention rate could be replicated several times after regeneration by washing at room temperature, in contrast to the case with H₂S. The likely reasons for the behavior of H₂S and SO₂ on the ammonia-treated ACC are discussed with reference to the recent literature.     

Mercury (II) adsorption by activated carbon made from sago waste

The preparation of activated carbon (AC) from sago industry waste is a promising way to produce a useful adsorbent for Hg (II) removal, as well as dispose of sago industry waste. The AC was prepared using sago industry waste with H₂SO₄ and (NH₄)₂S₂O₈ and physico-chemical properties of AC were investigated. Adsorptive removal of mercury (II) from aqueous solution onto AC prepared from sago industry waste has been studied under varying conditions of agitation time, metal ion concentration, adsorbent dose, particle size and pH to assess the kinetic and equilibrium parameters. Adsorption equilibrium was obtained in 105 min for 20 mg l⁻¹ and 120 min for 30, 40, and 50 mg l⁻¹ Hg (II) concentrations. The Langmuir and Freundlich equilibrium isotherm models were found to provide an excellent fitting of the adsorption data, with r² 0.9999 and 0.9839, respectively. The adsorption capacity of Hg (II) (Q_o) obtained from the Langmuir equilibrium isotherm model was found to be 55.6 mg g⁻¹ at pH 5.0 for the particle size range of 125-250 μm. The percent removal increased with an increase in pH from 2 to 10. This adsorbent was found to be effective and economically attractive.     

Simultaneous pentachlorophenol decomposition and granular activated carbon regeneration assisted by microwave irradiation

This paper describes an integrated granular activated carbon (GAC) adsorption/microwave (MW) irradiation process used for the treatment of high concentration pentachlorophenol (PCP) wastewater. Firstly, PCP in water was adsorbed onto GAC, then the PCP was decomposed and GAC regenerated by MW irradiation. The liquid and gas produced during irradiation were collected through condensing, and absorbed by a 0.1 mol l⁻¹ NaOH solution, respectively. The determination of the PCP concentrations in the distillate, absorption solution and GAC was accomplished by a HPLC. The results suggested that when irradiated with 850 W MW for 10 min, most of the PCP adsorbed by GAC and whatever fragments formed were decomposed to CO₂, H₂O and HCl or tightly bound to GAC, and less than 2% of PCP was transformed into intermediates in the distillate. Some dechlorination and dehydroxylation products were identified by the GC/MS analysis, and the degradation mechanism was proposed. It was also confirmed that GAC could be reused after several adsorption/MW regeneration cycles and its adsorption capacity could maintain a relatively high level, even higher than that of virgin GAC, as indicated by BET results, iodine values and PCP adsorption isotherms.     

Improvement of the reduction capacity of activated carbon fiber

The reduction property of activated carbon fibers (ACFs) enables them to be used in the recovery of noble metals from wastewater, or in the extraction of gold or silver from ore leaching solutions. In order to effectively recover or extract noble metals, it is important to enhance the reduction capacity of ACFs and to improve the particle size of the noble metal reduced and adsorbed on the surface of activated carbon fibers. In this paper, the effect of the preparation method and surface modification of ACFs on their reduction capacity was studied. The results show that the preparation methods of ACFs have significant influence on their reduction-adsorption capacities for silver ions in solution—those ACFs prepared with phosphoric acid or zinc chloride activation have much higher reduction capacities. Moreover, surface modification of ACFs with some inorganic oxidants such as nitric acid, potassium permanganate, or hydrogen peroxide, though resulting in a small decrease of specific surface area or pore volume, will enhance the reduction capacity of oxidized ACFs for silver ions. Furthermore, methylene blue, aniline, or p-nitrophenol present in solution or adsorbed on ACFs can also significantly increase the reduction capacities of sisal-based ACFs for silver ions.     

Simultaneous adsorption of MIB and NOM onto activated carbon. I. Characterisation of the system and NOM adsorption

The objective of this work was to increase the understanding of the adsorption competition between an odour compound, 2-methylisoborneol, and natural organic material (NOM). Part I describes the characterisation of six commercially available activated carbons, undertaken using nitrogen gas adsorption, surface titrations, and Fourier transform infrared spectroscopy. The natural organic material (NOM) from one raw water and four fractions obtained from an isolation and fractionation procedure undertaken on the same raw water, were characterised using ¹³C NMR, high-performance size exclusion chromatography, UV-visible absorbance and elemental analysis. Simultaneous adsorption of NOM and MIB indicated that the adsorption of the NOM was largely dependent on the pore volume distribution of the activated carbons, and less influenced by the variation in surface chemistry. Larger NOM molecules showed greater relative rates of adsorption where the access to the internal structure of the carbon was restricted by size exclusion, due to the shorter diffusion distances to adsorption sites travelled by the larger molecules. As the concentration of MIB was extremely low compared with that of the NOM in these experiments, no effect of MIB on NOM adsorption was seen. Part II reports the significant effect of the NOM solutions on the adsorption of MIB.     

Improved activated carbon by thermal treatment in methane and steam: Physicochemical influences on MIB sorption capacity

Thermal treatment by steam or by methane plus steam altered the physicochemical properties of a commercial lignite-based activated carbon; and improved the carbon’s sorption capacity for the odorant 2-methylisoborneol (MIB). Rapid small scale column tests (RSSCTs) revealed that favorable thermal treatment allowed an activated carbon to remove this odorant for up to six times longer before initial MIB breakthrough than did its commercial lignite counterpart. For these RSSCTs (135 ppt), clarified water from a water treatment plant (2.07 mg/L TOC) was spiked with ¹⁴C-MIB; and liquid scintillation protocols facilitated ¹⁴C-MIB detection at 1-3 ppt. The more favorable thermal treatment at 1000 °C increased pore volumes with 5-400 Å widths by twofold; and the bed volume to initial MIB breakthrough correlated fairly well (R² = 0.9) with pore volume in the range of 5-60 or 5-400 Å. Thermal tailoring altered the carbon’s apparent point of zero charge: from pH 6.5 for the commercial lignite carbon, to pH 9.2 for tailored carbon. When methane and steam were used together, the C, H, N and O contents were virtually the same as for the commercial lignite. In contrast, when steam was employed alone, the percent of oxygen increased, and the percent of H, C and N therefore decreased slightly.     

Adsorption of trace polar methy-ethyl-ketone and non-polar benzene vapors on viscose rayon-based activated carbon fibers

The adsorption of polar methy-ethyl-ketone (MEK) and non-polar benzene vapors on viscose rayon-based activated carbon fiber (ACF) was investigated. The pore texture and surface composition of ACF were characterized by nitrogen adsorption at 77 K and X-ray photoelectron spectroscopy (XPS), respectively. Gas adsorption on the samples was measured by the gravimetric method and the Dubinin-Radushkevich (DR) equation was used to fit the experimental adsorption isotherms. The experimental results show that ACF with different pore texture and surface composition exhibited different adsorption and desorption behavior for polar and non-polar vapors. The effect of adsorbate polarity on the adsorption capacity at lower concentrations was more significant in the case of adsorbents with a smaller surface area. It was found that evacuation treatment greatly increased the adsorption rate.     

Preparation and modification of activated carbon fibres by microwave heating

Thermal treatment of activated carbon fibres (ACF) has been carried out using a microwave device, instead of a conventional furnace. The results show that microwave treatment affects the porosity of the ACFs, causing a reduction in micropore volume and micropore size. More importantly, the results also show that microwave treatment is a very effective method for modifying the surface chemistry of the ACFs with the production of pyrone groups, detected by FTIR. As a result very basic carbons, with points of zero charge approximately equal to 11, are readily obtained.     

Flue gas treatment by activated carbon obtained from oil-fired fly ash

The treatment of the solid particulates derived from the combustion of heavy oils (that is, oil-fired fly ash) with acidic solutions (HCl and HF) followed by activation at 900 °C with CO₂ and then with O₂ (1%) in N₂ at 800 °C, produces activated carbon having high surface area values (measured both by N₂ adsorption at 77 K and by CO₂ adsorption at 273 K) and surface basic characteristics. This carbon appears to be suitable for SO₂ and NO_X adsorption and hence for industrial flue gas treatment processes. By submitting the activated carbon thus obtained to some adsorption/desorption cycles of gaseous mixtures having a similar composition to that of flue gases, its general characteristics (surface areas, sorbent properties etc.) change as expected of a typical activated carbon. Based on the results obtained, these particulate materials, produced in large amounts by heavy oil combustion, are assumed to be fully exploitable for flue gas treatment.     

The role of adsorbent pore size distribution in multicomponent adsorption on activated carbon

The impact of adsorbent pore size distribution (PSD) on adsorption mechanism for the multi solute system was evaluated in this study. Anoxic and oxic adsorption equilibrium for the single solute (phenol), binary solute (phenol/2-methylphenol) and ternary solute (phenol/2-methylphenol/2-ethylphenol) systems on one granular activated carbon (GAC) F400 and two types of activated carbon fibers (ACFs), namely, ACC-10 and ACC-15, were determined. F400 has a wide PSD, while ACC-10 and ACC-15 have narrow PSD and their critical pore diameters are 8.0 Å and 12.8 Å, respectively. In single solute adsorption, the increase of adsorptive capacity under oxic conditions as compared to anoxic ones was related to the PSD of the adsorbent. Binary solute adsorption on ACC-10 and ternary solute adsorption on ACC-15 indicated no impact of the presence of molecular oxygen on the adsorptive capacity and the adsorption isotherms were well predicted by the ideal adsorbed solution theory (IAST). Significant differences between oxic and anoxic isotherms were noticed for other multicomponent adsorption systems. The narrow PSD of ACFs was effective in hampering the oligomerization of phenolic compounds under oxic conditions. Such a phenomenon will provide accurate predictions of fixed bed adsorbers in water treatment systems.     

Adsorption of resorcinol and catechol on granular activated carbon: Equilibrium and kinetics

Investigations were conducted in the batch mode for studying the adsorption behavior of resorcinol and catechol on granular activated carbon from a basic salt medium (BSM) at pH≈7.1 and temperature≈30 °C. The isotherm data were correlated with six isotherm models, namely Langmuir, Freundlich, Redlich–Peterson, Radke–Prausnitz, Toth, and Fritz–Schlunder’s using a nonlinear regression technique. It is observed that the catechol isotherm data may be represented by Redlich–Peterson, Radke–Prausnitz, Toth, and Fritz–Schlunder models with similar accuracy (max. dev. 12%). And the resorcinol data may be represented by Freundlich, Redlich–Peterson, Radke–Prausnitz, and Fritz–Schlunder models equally well (max. dev. 15%). Freudlich being a simple model is recommended for resorcinol. At the conditions investigated in this study, catechol is adsorbed to a greater extent than resorcinol. This is due to the compound’s solubility and position of the –OH group on the benzene aromatic ring. The kinetics of adsorption have been found to be diffusion controlled and the value of effective particle diffusion coefficients is of the order of 10⁻¹³ m²/s. Three distinct phases of kinetics—rapid, medium, and slow—have been observed. These results should be useful for the design of adsorbers for removing these pollutants.     

NOx adsorption-temperature programmed desorption and surface molecular ions distribution by activated carbon with chemical modification

Activated carbon, the surface of which has been modified with KOH, was used in this study. The study examined adsorption and desorption behaviors and the accompanied surface reaction mechanism as well as the distribution of molecular ions on the surface. The peaks of NO_x desorption behavior may be classified into three bond categories depending on adsorption strength. NO desorption occurs at the earliest stage as chemical adsorption occurs earlier, in a sort of competition, than physical adsorption due to strong basic OH⁻ ion of surface. It was confirmed that the adequate temperature for NO_x desorption was near 390 °C. The potassium that existed on the surface remained without being consumed even with complete desorption of NO_x.