Activated carbons with metal containing bentonite binders as adsorbents of hydrogen sulfide

Wood-based activated carbon was ground and mixed with 10% bentonite binders containing either iron, zinc or copper cations adsorbed within the interlayer space and/or on the external surface of bentonite flakes. To better understand the role of transition metals, carbon was also impregnated with iron, zinc and copper salts. The structure of materials after modification was determined using nitrogen adsorption. The modification resulted in a decrease in porosity, especially in micropore volume, as a result of combined mass dilution effect and adsorption/re-adsorption of metals in small pores. Introduction of bentonite binders containing adsorbed metal increased the capacity of carbon for hydrogen sulfide only in the case of material containing copper. Copper also significantly increases the performance of carbon as an H₂S adsorbent when impregnation is applied whereas the effects of other metals used in this study are much less pronounced. It is likely that copper present in the small pores acts as a catalyst for oxygen activation causing hydrogen sulfide oxidation. As a result of this process, elemental sulfur is formed which, when present in small pores, is oxidized to weakly adsorbed SO₂. The SO₂ is removed from the surface when continuous reaction with hydrogen sulfide occurs. Thus, even though binding carbon with spent bentonites after copper adsorption increases the capacity of carbon toward H₂S removal, the formation of SO₂, another undesirable pollutant, does detract somewhat from the procedure.     

Characteristics of unburned carbons and their application for humic acid removal from water

Two unburned carbons (UCs) were separated from coal fly ash and their physicochemical properties were characterised using N₂ adsorption, XRD, SEM, XPS, FT-IR and potentiometric mass titration. Chemical treatments using HNO₃ and KOH were also conducted on one of the unburned carbons. The adsorption of humic acid from aqueous solution was performed on these untreated and chemically treated UCs. It was found that the UCs showed different porous structure and surface chemical properties, which influenced their adsorption behaviour. UCs exhibited high adsorption capacity for humic acid. After chemical treatment, the textural structure and surface functional groups of the unburned carbon were changed and the adsorption behaviour showed significant difference. Acid treatment did not change the surface area but reduced the functional groups while basic treatment significantly enhanced the surface area in microporous section but still reduced the surface functional groups. Particle size and pH solution will also influence the adsorption capacity. The adsorption will increase with decreasing particle size for humic acid. Higher pH solution will reduce humic acid adsorption on unburned carbon. Ionic strength will also affect humic acid adsorption showing positive effect on adsorption capacity.     

Comparison of a single grain activated carbon and column adsorption system

Results from a single grain activated carbon adsorption study indicate that the effective diffusion coefficient was from 0.65×10⁻⁶ to 7.4×10⁻⁶ cm²/s for H₂S in the concentration range of 20–300 ppmv at 23 °C for both virgin activated carbon (FAC) and impregnated-regenerative activated carbon (IRAC). The effective diffusivity of the IRAC was nearly two times the FAC for H₂S adsorption. The surface reaction of H₂S-impregnated regenerative activated carbon was faster than that of H₂S and virgin activated carbon. The single grain activated carbon kinetic curve and a time scale conversion method were used to predict the breakthrough curve and the adsorption capacity of the column adsorption system. The single grain activated carbon adsorption system measured the breakthrough curve more efficiently than column adsorption. The prediction error was between 10 and 30%. Improvement can be further achieved by enhanced experimental approaches. It has a great potential for scale-up.     

Adsorption of dyes on activated carbons: influence of surface chemical groups

The surface chemistry of a commercial activated carbon has been selectively modified, without changing significantly its textural properties, by means of chemical treatments, using HNO₃, H₂O₂, NH₃, and thermal treatments under a flow of H₂ or N₂. The resultant samples were characterized in terms of their surface chemistry and textural properties, and subsequently tested in the removal of different classes of dyes. It was shown that the surface chemistry of the activated carbon plays a key role in dye adsorption performance. The basic sample obtained by thermal treatment under H₂ flow at 700 °C is the best material for the adsorption of most of the dyes tested. For anionic dyes (reactive, direct and acid) a close relationship between the surface basicity of the adsorbents and dye adsorption was shown, the interaction between the oxygen-free Lewis basic sites and the free electrons of the dye molecule being the main adsorption mechanism. For cationic dyes (basic) the acid oxygen-containing surface groups show a positive effect but thermally treated samples still present good performances, showing the existence of two parallel adsorption mechanisms involving electrostatic and dispersive interactions. The conclusions obtained for each dye individually were confirmed in the colour removal from a real textile process effluent.     

The Adsorption and Desorption Characteristics of EDTA-Chelated Copper Ion by Activated Carbon

Abstract

This paper addresses the effect of EDTA, a strong agent, on the removal of copper ion from solutions using activated carbon adsorption. Experimental studies indicate the presence of EDTA significantly altered the adsorption behavior of copper on the activated carbon due to the formation of copper chelate species in the solution. The adsorption isotherms and kinetics were found to be strong functions of solution pH and the ratio of copper ion and EDTA concentrations. Adsorption of EDTA-Cu chelates was found to be more favorable than those of free copper ion and unbound EDTA species in the solution. Experimental results indicated that the desorption of chelated copper ion from activated carbon by NaOH and HClO⁴ solutions was influenced by the initial adsorption conditions. A significantly higher quantity of copper ion was recovered with HClO⁴ than with NaOH. Combining the adsorption and desorption data of copper and EDTA, and an understanding of the species distribution of copper in the presence of EDTA, the behavior of the adsorption of EDTA-chelated copper on the activated carbon was described. The predominant adsorbed copper species was the chelated form, CuEDTA^2-, which can be adsorbed on activated carbon surfaces with either the Cu end or the EDTA end bonding directly to the surface.     

Study of SO2 adsorption and thermal regeneration over activated carbon-supported copper oxide catalysts

The mechanisms of SO₂ adsorption and regeneration over activated carbon-supported copper oxide sorbent/catalysts were analyzed. Studies were carried out in a fixed-bed reactor equipped with a non-dispersive infrared gas analyzer to detect the reaction products and by using X-ray powder diffraction (XRPD) and temperature-programmed desorption (TPD) experiments to characterize the nature of the sulfate species and surface oxygen complexes. The results indicate that SO₂ was catalytically oxidized to SO₃ over a copper phase in the presence of gaseous oxygen, and then reacted with a copper site to form a sulfate linked to copper without desorption into the gas phase. The activated carbon support did not participate in this sulfation reaction. After the adsorption of SO₂, the exhausted sorbent/catalysts could be regenerated by direct heat treatment in inert gas at temperatures between 260 and 480 °C, while the neighboring surface oxygen complexes on the carbon surface were acting as the reducing agents to reduce CuSO₄ to Cu. During the subsequent adsorption process, the copper is rapidly oxidized by oxygen in the flue gas.     

Influence of HNO3 oxidation on the structure and adsorptive properties of corncob-based activated carbon

An investigation of the impact of strong oxidation with HNO₃ on the porosity and adsorption characteristics of char and activated carbons, derived from corncobs, is presented. Texture parameters, as obtained from N₂ adsorption at 77 K, showed a considerable decrease in surface area of the activated carbons with enhanced pore widening. The extent of porosity modification was found to depend on the scheme of activation of the precursor, simple carbonization, steam pyrolysis, steam gasification of the char, or chemical activation with H₃PO₄. Surface-chemical changes were detected by FTIR spectroscopy, where absorption bands assigned to carboxyl, carboxylate, carbonyl, and phenolic groups were observed. A SEM study demonstrated the erosive effect of HNO₃, detected by the presence of disintegration of the carbon grains, with the porous structure probably containing very large macropores. As a consequence of the oxidation process, elemental analysis showed high contents of O, H and N, and TG confirmed that the weight loss distribution in the thermogram becomes slower at higher temperatures. The removal of phenol decreased as a result of the formation of oxygen functionalities. Mono-nitrophenols were adsorbed in smaller amounts than phenol, and p-nitrophenol showed a relatively higher uptake than the other two mono-nitrophenols, whereas the uptake of Methylene Blue was improved. Removal of Pb²⁺ from aqueous non-buffered solution was considerably enhanced by chemical oxidation, which may be related to pore widening, increased cation-exchange capacity by oxygen groups, and the promoted hydrophilicity of the carbon surface.     

Carbon coated monoliths as support material for a lactase from Aspergillus oryzae: Characterization and design of the carbon carriers

Tunable carbon-coated monoliths as carriers for enzyme adsorption are presented. Depending on enzyme properties and reaction conditions, the carrier can be adjusted to optimize enzyme loading. Carbon-ceramic composites were prepared by sucrose carbonization, polyfurfuryl alcohol (PFA) carbonization, and by growth of carbon nanofibers (CNFs) over deposited Ni. All carbons were treated in air and subsequently in 1 M HNO₃, and analyzed with respect to porosity, morphology and surface chemistry. The composites were applied as a carrier for a lactase from Aspergillus oryzae. The CNFs proved to be the best carrier, with respect to enzyme loading. Untreated fibers could adsorb 115 mg lactase/g carbon. After air/HNO₃ treatment this value increased to 360 mg/g. Porosity was not affected by air and air/HNO₃ treatment, implying that lactase adsorption mainly depends on surface chemistry. A clear trend was observed between oxygen content of different CNFs and lactase adsorption. Ni could be removed completely from the fiber tips of CNFs by different concentrated acids—nitric acid, hydrochloric acid, and oxalic acid. However, with HCl and HNO₃ the porosity and surface chemistry were affected. Treatment in oxalic acid removed Ni from the tips by complexation, without changing the porosity. For these samples, 30% of the Ni remained present in the sample as residual NiC₂O₄. This was confirmed by TGA-MS and XRD.     

Mechanisms of surfactant adsorption on non-polar, air-oxidized and ozone-treated carbon surfaces

Ozone treatment of fly ash carbon has recently been reported to inhibit the adsorption of commercial surfactants in concrete paste, thus mitigating the known negative effects of carbon on ash utilization. This paper examines the general mechanism of surfactant adsorption on carbon and its suppression by surface oxidation. Experimental results are presented for two carbon types (carbon black, fly ash carbon), both raw and surface oxidized (by ozone and molecular oxygen) and several commercial anionic and non-ionic surfactants (Darex II, SDS, Tergitol). The treated carbon surfaces were characterized with XPS, FT-IR, thermal desorption in N₂ and H₂/He, surface acidity, hygroscopic behavior, interfacial energy and its components through contact angle measurement involving standard liquid probes. Surface oxidation is found to decrease surfactant adsorption in each of the carbon/oxidant/surfactant systems examined, and its effect correlates with the amount of surface oxides by XPS. The combined results suggest that surfactant adsorption primarily occurs on non-polar carbon surface patches where it is driven by hydrophobic interactions. The main mechanism of oxidative suppression is the destruction of this non-polar surface, though micropore blockage and increased negative surface charge may also contribute for some systems.     

Adsorption characteristics of methyl mercaptan, dimethyl disulfide, and trimethylamine on coconut-based activated carbons modified with acid and base

The influence of surface modification of activated carbon on the adsorption of methyl mercaptan (MM), dimethyl disulfide (DMDS), and trimethylamine (TMA) was investigated by treatments with 1N-HNO₃ solution and 1N-NaOH solution. The surface modifications changed the concentrations of functional groups on the surface of activated carbon. Also, the surface modifications changed breakthrough time and equilibrium adsorption capacity of MM, DMDS, and TMA. The adsorption capacities of MM and DMDS were increased by acid treatment, but decreased by base treatment. On the other hand, the adsorption capacity of TMA was decreased by both acid and base treatments. But the difference ranges of equilibrium adsorption capacities according to acidity and basicity of the surface were relatively small.     

柠檬酸改性糠醛渣的制备

研究了柠檬酸改性糠醛渣的制备过程和条件。首先对糠醛渣进行预处理,然后分别用20%的异丙醇和20%的氢氧化钠溶液处理,最后用柠檬酸对其进行改性,得到柠檬酸改性糠醛渣。讨论了反应时间,反应温度,柠檬酸溶液浓度,固液比等因素对改性的影响。结果表明:当反应时间60 min,反应温度80℃,柠檬酸质量浓度100 g/L,固液比1︰3时获得的改性糠醛渣吸附亚甲基蓝效果最好,去除率可达到98.2%。     

Novel Synthesized Gemini Surfactant as Corrosion Inhibitor for Carbon Steel in HCl Solution

A quaternary ammonium gemini surfactant containing an ester spacer, namely (diethylhexanedioate)diyl‐α,ω‐bis(dimethyl myristyl ammonium bromide) ( 14‐DEHA‐14 ) was synthesized using a two‐step procedure with dimethyl hexanedioate, dimethylaminoethanol, and 1‐bromotetradecane. The chemical structure of the compound was confirmed by infrared (IR) spectrum, ¹H nuclear magnetic resonance (NMR), and elemental analysis. The critical micelle concentration was determined by conductivity and tensiometry measurements, and its inhibition effect on corrosion of carbon steel in dilute (1.0 M) hydrochloric acid solution was investigated by weight loss measurements. The results show that the synthesized gemini surfactant acts as an excellent corrosion inhibitor in 1.0 M HCl solution. The adsorption of the inhibitor via chemical adsorption onto the carbon steel surface obeyed the Langmuir adsorption isotherm. A possible corrosion mechanism of the compound is discussed in relation to the calculated thermodynamic parameters and adsorption isotherm.     

The anodic dissolution of copper in hydrochloric acid solutions

The electrodissolution of copper in hydrochloric acid solutions at the rotating ring-disk electrode was found to be controlled by both mass transfer and reaction in the apparent-Tafel region in HCl concentrations of between 0.1 and 1.0 M. The proposed mechanism describes the adsorption of CuCl_ads on the corroding copper surface and the diffusion of CuCl⁻₂ from the copper surface. The reaction in the limiting-current region was found to be controlled by the diffusion of Cl⁻ to the copper surface through a porous CuCl layer that forms on the surface. The thickness of this porous layer is dependent on the stirring conditions, and independent of the Cl⁻ concentration. Cu²⁺ is also produced at the Cu surface during electrodissolution. A mechanism describing the formation of a porous film of CuCl on the surface, the diffusion of Cl⁻ through this film and the formation of Cu²⁺ has been proposed.     

The effect of activated carbon surface moisture on low temperature mercury adsorption

Experiments with elemental mercury (Hg⁰) adsorption by activated carbons were performed using a bench-scale fixed-bed reactor at room temperature (27°C) to determine the role of surface moisture in capturing Hg⁰. A bituminous-coal-based activated carbon (BPL) and an activated carbon fiber (ACN) were tested for Hg⁰ adsorption capacity. About 75-85% reduction in Hg⁰ adsorption was observed when both carbon samples’ moisture (∼2 wt.% as received) was removed by heating at 110°C prior to the Hg⁰ adsorption experiments. These observations strongly suggest that the moisture contained in activated carbons plays a critical role in retaining Hg⁰ under these conditions. The common effect of moisture on Hg⁰ adsorption was observed for both carbons, despite extreme differences in their ash contents. Temperature programmed desorption (TPD) experiments performed on the two carbons after adsorption indicated that chemisorption of Hg⁰ is a dominant process over physisorption for the moisture-containing samples. The nature of the mercury bonding on carbon surface was examined by X-ray absorption fine structure (XAFS) spectroscopy. XAFS results provide evidence that mercury bonding on the carbon surface was associated with oxygen. The results of this study suggest that surface oxygen complexes provide the active sites for mercury bonding. The adsorbed H₂O is closely associated with surface oxygen complexes and the removal of the H₂O from the carbon surface by low-temperature heat treatment reduces the number of active sites that can chemically bond Hg⁰ or eliminates the reactive surface conditions that favor Hg⁰ adsorption.     

Experimental Investigation on the Removal of p-Toluic Acid from Aqueous Solution using Functionalized Polymeric Sorbent

Polystyrene-divinylbenzene copolymer (PsDVB) was covalently functionalized with monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA) by a simple method. The functionalized sorbents were characterized in terms of functionality and morphology, and used for the removal of p-toluic acid (p-TA) from aqueous solution. It was found that DEA-PsDVB has higher adsorption capacity than MEA- and TEA-PsDVB due to more accessible nitro and hydroxyl groups on its surface. Further investigation on the adsorptive properties of DEA-PsDVB indicated that the maximum uptake of p-TA occurred at the optimum pH of 5.3. The kinetics data was successfully represented by the pseudo-first-order model, and the behavior of the adsorption isotherms followed the Freundlich model well. Thermodynamic studies showed that the adsorption of p-TA onto DEA-PsDVB was an endothermic and spontaneous process along with the positive change in entropy. The regeneration of DEA-PsDVB was performed with 0.1 M NaOH solution, and results showed that 99% of the initial capacity was conserved after eight successive adsorption/regeneration cycles.     

Copper and strontium adsorption by a novel carbon material manufactured from pecan shells

A novel carbon material (PS276a) was produced from pecan shells, a waste product of the agricultural industry. Preparation of this material involved the impregnation of the pecan shell feedstock with a phosphoric acid solution. Activation was followed by a water wash and a sodium hydroxide treatment. The carbon produced was characterized by adsorption of N₂ and revealed a pore structure with an average pore diameter of 74.8 Å. Equilibrium sorption isotherms prepared for this carbon demonstrate that it has a significantly higher capacity for copper and strontium sorption than that of a commercial material used for comparison. A maximum of 95 mg Cu²⁺ and 180 mg Sr²⁺ are adsorbed per gram of this carbon at pH 3.6 and 8.5, respectively. Demonstrated process advantages of this carbon material and preparation technique include low temperature manufacture, in-situ regeneration potential, and adsorbate recovery capability.     

Efficient Removal of Ammonia by Hierarchically Porous Carbons from a CO2 Capture Process

The amine-based post-combustion carbon capture process is one of the most efficient methods for treating large-scale CO₂, but it produces hazardous products due to chemical transition and degradation of the absorbents. In this study, carbon-based materials were used as adsorbents for the removal of NH₃, and their adsorption capacities, adsorption rates, and stabilities were examined by comparing commercial activated carbon (AC) with hierarchically porous carbon (HPC). HPC-Step4 possessed a higher number of total acid sites, resulting in higher NH₃ adsorption compared to AC. Despite the similar porosity, HPC-Step4 exhibited a higher adsorption rate constant and the improved kinetics was attributed to its increased portion of mesopores, enhancing the diffusion rate of the adsorbate. Furthermore, HPC-Step4 exhibited better reaction stability than AC.     

Improving the pore structure and adsorption properties of industrial active carbons

The paper describes the possibility of improving the pore structure and adsorption properties of industrial active carbons (AC) by means of their modification with ɛ-caprolactam (CL). Application of ɛ-caprolactam (a product of large-scale organic synthesis) as a modifying substance allows the targeted regulation of the specific surface area and volume of AC mesopores, while the conditions of modification change the chemical composition of the surface of carbon adsorbents and, as a result, their adsorption properties. The process of modification includes three stages. The first is the adsorption of CL from aqueous solution and heating at 300°C in the presence of atmospheric oxygen. The second is carbonization in an argon flow at 900°C, and the third is the vapor-gas activation of the resultant adsorbents at 900°C. Each stage is followed by determining the parameters of the pore structure by N₂ adsorption and the adsorption parameters with respect to benzene, iodine, aqueous solutions of ɛ-caprolactam, and copper sulfate (CuSO₄). When modifying the carbonized samples with an initial ɛ-caprolactam content of 2%, we observe the growth of mesopores over 100% of volume, relative to AG-OV-1 original industrial activated carbon. Depending on the stage of modification, an increase in adsorption is observed, relative to the AG-OV-1 original carbon: benzene adsorption rises by 50%, the adsorption of iodine from aqueous solution rises by 20%, the adsorption of ɛ-caprolactam from aqueous solution grows by more than 30%, and the adsorption of copper(II) ions rises by more than 70%. The procedure for the production of the described modified adsorbent has no rivals abroad; it is protected by a patent and can be used in industry. It is possible to use inexpensive industrial carbons as the original material. The procedure allows the production of carbon adsorbents with predetermined structural and adsorption properties.     

Interaction and stabilization of DMF-based alumina suspensions with citric acid

The understanding of the detailed interaction between particles and dispersants in non-aqueous solutions is important for industrial applications. Herein, we report the investigation on the alumina suspension with citric acid in N,N′-dimethylformamide (DMF). The interaction was characterized by monitoring the evolution of UV-vis spectra, zeta potential values, and FT-IR spectra. The dispersion stability was examined by sedimentation test. It is found that the adsorption of citric acid on the surface of alumina particles depends on the apparent pH (pH_a) values of the solution. The adsorption follows the Langmuir type. The DMF-based alumina suspension exhibits a high stability due to the adsorption of citric acid on alumina particles, and shows the highest stability at pH_a 2.6 where the maximum adsorption occurs for citric acid.