Activated carbons and amine-modified materials for carbon dioxide capture — a review

Rapidly increasing concentration of CO₂ in the atmosphere has drawn more and more attention in recent years, and adsorption has been considered as an effective technology for CO₂ capture from the anthropogenic sources. In this paper, the attractive adsorbents including activated carbons and amine-modified materials were mainly reviewed and discussed with particular attention on progress in the adsorbent preparation and CO₂ adsorption capacity. Carbon materials can be prepared from different precursors including fossil fuels, biomass and resins using the carbonization-activation or only activation process, and activated carbons prepared by KOH activation with high CO₂ adsorbed amount were reviewed in the preparation, adsorption capacity as well as the relationship between the pore characteristics and CO₂ adsorption. For the amine-modified materials, the physical impregnation and chemical graft of polyethylenimine (PEI) on the different porous materials were introduced in terms of preparation method and adsorption performance as well as their advantages and disadvantages for CO₂ adsorption. In the last section, the issues and prospect of solid adsorbents for CO₂ adsorption were summarized, and it is expected that this review will be helpful for the fundamental studies and industrial applications of activated carbons and amine-modified adsorbents for CO₂ capture.     

Physicochemical aspects of using natural scavengers in removing methylene blue (basic dye) from solution

Effluent from dyeing and finishing processes is an important source of water pollution. The effectiveness of bentonite, kaolinite and sediment from a local deposit in removing methylene blue as a cationic dye from aqueous solutions has been investigated. The adsorption equilibrium (isotherm) has been determined according to Freundlich and Langmuir equations. The optimum amount is 0.5 g for all adsorbents, and the optimum pH ranges are 2–8 for bentonite and 2–6 for kaolinite and sediment. With respect to kinetic modelling, the adsorption of methylene blue on various adsorbents was fitted to a second-order equation. Also, the thermodynamic parameters were determined. The negative free energy values indicate the feasibility of the process and spontaneous nature of adsorption. The positive ΔH° values indicate the endothermic nature of the process. Thus, Egyptian clay minerals and sediments have a great tendency to remove the dye from solutions.     

Physicochemical aspects of using natural scavengers in removing methylene blue (basic dye) from solution

Effluent from dyeing and finishing processes is an important source of water pollution. The effectiveness of bentonite, kaolinite and sediment from a local deposit in removing methylene blue as a cationic dye from aqueous solutions has been investigated. The adsorption equilibrium (isotherm) has been determined according to Freundlich and Langmuir equations. The optimum amount is 0.5 g for all adsorbents, and the optimum pH ranges are 2-8 for bentonite and 2-6 for kaolinite and sediment. With respect to kinetic modelling, the adsorption of methylene blue on various adsorbents was fitted to a second-order equation. Also, the thermodynamic parameters were determined. The negative free energy values indicate the feasibility of the process and spontaneous nature of adsorption. The positive ΔH° values indicate the endothermic nature of the process. Thus, Egyptian clay minerals and sediments have a great tendency to remove the dye from solutions.     

Leaching of arsenic from coal fly ashes 2. Arsenic pre‐leaching with sodium gluconate solution

The present study deals with the development of an efficient and reliable process for safe disposal of coal fly ash to remove arsenic that has been found to be the most easily leachable and hazardous heavy metal in coal fly ash. Pre‐leaching of fly ash prior to disposal by a natural chelating agent, sodium gluconate (SG), was proposed and studied. Several operational factors influencing arsenic leachability, such as concentration of SG solution, liquid to solid ratio, pH, length of leaching time and leaching temperature were examined. Arsenic was found to leach out substantially with SG, but almost no further release was observed from the ash pre‐leached by SG. After the pre‐leaching treatment, the desirable high buffering capacity of the ash was well sustained. SG solution was effectively regenerated by activated alumina adsorption so that it could be successfully reused for multiple leaching/adsorption cycles.     

Evaluation of micro- and nano-carbon-based adsorbents for the removal of phenol from aqueous solutions

This work reports on the adsorption efficiency of two classes of adsorbents: nano-adsorbents including carbon nanotubes (CNTs) and carbon nanofibers (CNFs); and micro-adsorbents including activated carbon (AC) and fly ash (FA). The materials were characterized by thermogravimetric analysis, transmission electron microscopy, Brunauer–Emmett–Teller (BET) specific surface area, zeta potential, field emission scanning electron microscopy, and UV spectroscopy. The adsorption experimental conditions such as pH of the solution, agitation speed, contact time, initial concentration of phenol, and adsorbent dosage were optimized for their influence on the phenol. The removal efficiency of the studied adsorbents has the following order: AC > CNTs > FA > CNFs. The capacity obtained from Langmuir isotherm was found to be 1.348, 1.098, 1.007, and 0.842 mg/g of AC, CNTs, FA, and CNFs, respectively, at 2 hours of contact time, pH 7, an adsorbent dosage of 50 mg, and a speed of 150 rpm. The higher adsorption of phenol on AC can be attributed to its high surface area and its dispersion in water. The optimum values of these variables for maximum removal of phenol were also determined. The experimental data were fitted well to Langmuir than Freundlich isotherm models.     

Removal of selenite using ‘waste’ Fe(III)/Cr(III) hydroxide: Adsorption kinetics and isotherms

Removal of selenite [Se (IV)] from aqueous solution on to industrial solid ‘waste’ Fe(III)/Cr(III) hydroxide as adsorbent was investigated in the present article. Maximum adsorption was found to be at pH 4.0. Pretreated Fe(III)/Cr(III) hydroxide was found to be more efficient for the removal of selenite compared to untreated adsorbent. Langmuir and Freundlich isotherms have been studied. The Langmuir adsorption capacity (Q ₀) of the pretreated and untreated adsorbents was found to be 15.63 and 6.04?mg?g^?1, respectively. The adsorption process fit into the second-order kinetics. Thermodynamic parameters show that the adsorption process is spontaneous and endothermic in the temperature range 32 to 60°C. Coexisting anions vanadate and phosphate significantly affect the adsorption of selenite for both the pretreated and untreated adsorbents. Molybdate, thiocyanate, sulphate, nitrate and chloride do not significantly affect the removal of selenite for pretreated adsorbent.     

黄浦江底泥对多环芳烃吸附机理的研究

本文主要介绍黄浦江底泥对以蒽为代表性物质的多环芳烃的吸附研究，着重探讨其吸附机理，在实验条件下，黄浦江底泥对蒽的吸附属多分子层吸附，可用ｄｅ ＢｏｅｒＺｗｉｋｋｅｒ公式所表示的极化模型较好地描述，这表明原描述非极性气相分子在极性吸附剂上吸附的多分子层极化模型可应用于稀溶液中溶剂化蒽分子在极性吸附剂上的吸附过程，本研究认为吸附等温线上出现阶梯状形式是由于蒽－甲醇分子的溶剂作用及底泥颗粒的表面不均匀性     

Removal of arsenic (V) from aqueous medium using manganese oxide coated lignocellulose/silica adsorbents

Arsenic (V) adsorption on manganese oxide coated rice wastes was investigated in this study. The modified adsorbents were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, and pH measurements to determine the point of zero charge. Batch adsorption equilibrium experiments were conducted to study the effects of pH, contact time, and initial concentration on arsenic removal efficiency. The adsorption capacity of rice waste was significantly improved after modification with permanganate. The Langmuir isotherm model fitted the equilibrium data better than the Freundlich model which confirms surface homogeneity of the adsorbent. Maxima adsorption capacities are determined as 10 and 12 mg/g at pH 3 for manganese oxide coated rice husk and straw, respectively. The adsorption energy indicates that the adsorption process may be dominated by chemisorption. Pseudo-second-order rate equation described the kinetics sorption of arsenic with good correlation coefficients, better than a pseudo-first-order equation. Manganese oxide coated rice husk and straw appear to be promising low cost adsorbents for removing arsenic from water.     

4种吸附剂对对氯苯酚的吸附性能

研究了常温（18℃）条件下粉末活性炭（PAC）、颗粒活性炭（GAC）、天然膨润土和天然海泡石4种吸附剂对对氯苯酚（4-CP）的静态吸附规律,考察了投加灭活活性污泥对吸附性能的影响。结果表明：4种吸附剂对4-CP的吸附符合Langmiur和Freundlich吸附等温式,且吻合良好;4种吸附剂对4-CP的饱和吸附量不同,大小顺序为：PAC〉GAC〉天然膨润土〉天然海泡石;灭活活性污泥与4种吸附剂共存时,降低了4种吸附剂对4-CP的吸附能力。     

Equilibrium studies on the adsorption of acid dye into chitin

We report the adsorption isotherm of acid dye on the surface of chitin, a unique solid adsorbent. Adsorption process offers an attractive benefit for a dyeing house treatment. Influences of essential kinetic parameters such as adsorbent particle size, reaction temperature governing the dye adsorption have been investigated. Adsorptions isotherms of dye on chitin were developed and the equilibrium data fitted well to the Langmuir, Freundlich and Redlich Peterson isotherm model. At optimum conditions maximum dye adsorption capacity of chitin estimated with the Langmuir 44.0, 85.0, 104.3 mg/g and 85.0, 114.10, 113.62 mg/g adsorbent. The results showed that chelating polymer of chitin could be considered as potential adsorbents for acid dye removal from dilute solution.     

Decolourization of pulp and paper mill effluents using heat-treated coal: a comparison with activated charcoal

A comparison between activated charcoal and heat-treated coal for decolourization of pulp and paper mill waste water was studied. The heat-treated coal was prepared in an inert atmosphere at 800°C. The adsorption dynamics that include batch contact–time study, kinetics along with adsorption isotherms were carried out. The study shows that heat-treated coal is a suitable adsorbent and can be used for the decolourization of pulp and paper mill effluent streams. The maximum removal was achieved at the initial stages of contact, and the overall adsorption was a slow process. However, the equilibrium concentration in the case of both the adsorbents reaches at almost same time. The linear plot of the Lagergren model shows its applicability and first-order kinetics.     

Sorption of pyrene from water by oil shale ash and mineral particles

The aim of this work was to estimate the sorption of pyrene from water solutions on mineral substrates, e.g., alumina, silica, and oil shale ash, from the Estonian thermal plant. Results obtained from this study indicate that the sorption of pyrene on mineral oxides and oil shale ash particles from water can be described with a linear equation. The sorptive capacity per weight of oil shale ash in aqueous systems was significantly lower compared with mineral adsorbents. The distribution coefficient (K_d) for pyrene in the system with particles of oil shale ash was 10–12 times lower as than for mineral adsorbents.     

Comparative adsorption of Pb(II) and Cd(II) ions on chestnut shell in aqueous system

In this study, high capacity Chestnut shell, a waste product from the chestnut sugar production industry, was successfully applied to remove Pb (II) and Cd (II) ions from aqueous solutions. Maximum adsorption capacities were found as 541.25?mg/g and 75.86?mg/g for Pb(II), and Cd(II) respectively. Several important parameters influencing the adsorption of Pb(II) and Cd(II) ions such as contact time, pH, temperature and effect of metal concentration were investigated systematically by batch experiments. Langmuir and Freundlich adsorption models were used to describe adsorption isotherms and constants. The thermodynamic parameters, such as standard free energy (ΔG°), standard enthalpy (ΔH°), and standard entropy (ΔS°), of the adsorption process were calculated. The adsorbents were characterised by scanning electron microscopy. It has been observed from the experimental results that in case of both Cd (II) and Pb (II), pseudo 2nd order kinetic model. From the results, Chestnut Shell are considered as an effective, low cost and environmental friendly adsorbent for the removal of Pb (II) and Cd (II) from wastewater.     

Preparation of a permanent magnetic hypercrosslinked resin and assessment of its ability to remove organic micropollutants from drinking water

A rapid and effective method based on a novel permanent magnetic hypercrosslinked resin W150 was proposed for the removal of organic micropollutants in drinking water. W150 was prepared by suspension and post-crosslinking reaction and found to possess a high specific surface area of 1149.7 m²·g^-1, a small particle size of 50 μm to 100 μm, and a saturation magnetization as high as 8 emu·g^-1. W150 was used to eliminate nitrofurazone (NFZ) and oxytetracycline (OTC) from drinking water compared with commercial adsorbents XAD-4 and F400D. The adsorption kinetics of NFZ and OTC onto the three adsorbents well fitted the pseudo-second-order equation (r>0.972), and the adsorption isotherms were all well described by the Freundlich equation (r>0.851). Results showed that the reduction in adsorbent size and the enlargement in sorbent pores both accelerated adsorption. Moreover, the effect of particle size on adsorption was more significant than that of pore width. Given that the smallest particle size and the highest specific surface area were possessed by W150, it had the fastest adsorption kinetics and largest adsorption capacity for NFZ (180 mg·g^-1) and OTC (200 mg·g^-1). For the adsorbents with dominant micropores, the sorption of large-sized adsorbates decreased because of the inaccessible micropores. The solution pH and ionic strength also influenced adsorption.     

Adsorption of vanadate(V) on Fe(III)/Cr(III) hydroxide waste

Adsorption of vanadate(V) from aqueous solution onto industrial solid ‘waste’ Fe(III)/Cr(III) hydroxide was investigated. HCl treated Fe(III)/Cr(III) hydroxide was found to be more efficient for the removal of vanadate(V) compared to untreated adsorbent. The adsorption follows second-order kinetics. Langmuir and Freundlich isotherms have been studied. The Langmuir adsorption capacity (Q ₀) of the treated and untreated adsorbents was found to be 11.43 and 4.67 mg g⁻¹, respectively. Thermodynamic parameters showed that the adsorption process was spontaneous and endothermic in the temperature range 32–60°C. Maximum adsorption was found at system pH 4.0. The adsorption mechanism was predominantly ion exchange. Effect of other anions such as phosphate, selenite, molybdate, nitrate, chloride, and sulfate on adsorption of vanadium has been examined.     

Adsorption behaviors of activated carbons for the exhaust from spray painting booths in vehicle surface coating

Adsorption performance of activated carbon adsorbers in the downstream duct of vehicle spray painting booths has been studied to understand whether fine paint particles in the off-gas would deteriorate the adsorption capacity of volatile organic compounds (VOCs) on activated carbons. Three forms of activated carbons were selected and their properties were determined using nitrogen adsorption analysis, the measurement of pH value and total ash content, energy dispersion spectrometer, field-emission scanning electron microscopy, and thermogravimetric analysis. Results show that the adsorption capacity of activated carbon strongly depends upon its available specific surface area. When the total uptake on activated carbon approaches saturation, the vapors adsorbed would commence to get displaced by the paint particles gradually as time elapses and finally the uptake of vapors and paint particles reach equilibrium. Microporous carbons, in particular, were much more susceptible to paint particles. A Langmuir-type model for the uptake on activated carbons was suggested, which successfully described the adsorption behaviors of the off-gas released from vehicle spray painting booth.     

Retention characteristics of Cu2+, Pb2+, and Zn2+ from aqueous solutions by two types of low lime fly ashes

The technical feasibility of utilization of fly ash as a low-cost adsorbent for the removal of metals from water has been studied. For two types of fly ashes, the retention capacities of copper, lead, and zinc metal ions have been studied. Contact time, initial concentration, and pH have been varied and their effect on retention mechanism has been studied. The dominant mechanisms responsible for retention are found to be precipitation due to the presence of calcium hydroxide, and adsorption due to the presence of silica and alumina oxide surfaces in the fly ash. First-order kinetic plots have revealed that the rate constant increases with increase in the initial concentration and pH. Langmuir adsorption isotherms have been plotted to study the maximum adsorption capacities for metal ions considered under different conditions. X-ray diffraction studies revealed the formation of new peaks corresponding to respective metal ions precipitates under alkaline conditions.     

Removal of fluoride by thermally activated carbon prepared from neem (Azadirachta indica) and kikar (Acacia arabica) leaves

The present investigation deals with fluoride removal from aqueous solution by thermally activated neem (Azadirachta indica) leaves carbon (ANC) and thermally activated kikar (Acacia arabica) leaves carbon (AKC) adsorbents. In this study neem leaves carbon and kikar leaves carbon prepared by heating the leaves at 400 degrees C in electric furnace was found to be useful for the removal of fluoride. The adsorbents of 0.3 mm and 1.0 mm sizes of neem and kikar leaves carbon was prepared by standard sieve. Batch experiments done to see the fluoride removal properties from synthetic solution of 5 ppm to study the influence of pH, adsorbent dose and contact time on adsorption efficiency The optimum pH was found to be 6 for both adsorbents. The optimum dose was found to be 0.5g/100 ml forANC (activated neem leaves carbon) and 0.7g/100 ml forAKC (activated kikar leaves carbon). The optimum time was found to be one hour for both the adsorbent. It was also found that adsorbent size of 0.3 mm was more efficient than the 1.0 mm size. The adsorption process obeyed Freundlich adsorption isotherm. The straight line of log (qe-q) vs time at ambient temperature indicated the validity of langergren equation consequently first order nature of the process involved in the present study. Results indicate that besides intraparticle diffusion there maybe other processes controlling the rate which may be operating simultaneously. All optimized conditions were applied for removal of fluoride from four natural water samples.     

HDTMAB改性粉煤灰对水体中磷的吸附特性

制备了十六烷基三甲基溴化铵(HDTMAB)改性粉煤灰,研究了该改性粉煤灰对水体中磷的吸附特性,结果表明:①当HDTMAB负载量为10%时,改性粉煤灰吸附磷酸盐的效果最佳;②改性粉煤灰对磷酸盐的吸附速度很快,20min可达吸附平衡;③改性粉煤灰对磷酸盐的吸附行为能较好地符合Langmuir等温吸附模型和Freundlich等温吸附模型,但在Freundlich模式下表现为两个线性区;④pH对改性粉煤灰吸附磷酸盐的性能有显著影响,随着pH的升高对磷酸盐的吸附能力逐渐增加。     

Adsorption of toluene, ethylbenzene and xylene isomers on multi-walled carbon nanotubes oxidized by different concentration of NaOCl

Multi-walled carbon nanotubes (MWCNTs) were fabricated and oxidized by different concentrations of sodium hypochlorite (NaOCl) solutions. The untreated MWCNTs and modified MWCNTs were employed as adsorbents to study their characterizations and adsorption performance of toluene, ethylbenzene and xylene isomers (TEX) in an aqueous solution. The physicochemical properties of MWCNTs were greatly affected after oxidation, which influences TEX adsorption capacity. The 3% NaOCl-oxidized MWCNTs shows the greatest enhancement in TEX adsorption, followed by the 30% NaOCl. More interestingly, the 15% NaOCl-oxidized MWCNTs has lower adsorption capacities than untreated MWCNTs. The adsorption mechanism of TEX on treated MWCNTs is attributed to the combined action of hydrophobic interaction, π-π bonding interaction between the aromatic ring of TEX and the oxygen-containing functional groups of MWCNTs and electrostatic interaction. 3% NaOCl solution could not only introduce much oxygen-containing functional groups on MWCNTs, but also lead to less damage for the pore structure. This suggests that the CNTs-3% NaOCl is efficient adsorbent for TEX and that they may possess good potential for TEX removal in wastewater treatment.