Use of chemically activated cotton nut shell carbon for the removal of fluoride contaminated drinking water:Kinetics evaluation☆

Chemically activated cotton nut shell carbons (CTNSCs) were prepared by different chemicals and they were used for the removal of fluoride from aqueous solution. Effects of adsorption time, adsorbent dose, pH of the solution, initial concentration of fluoride, and temperature of the solution were studied with equilibrium, ther-modynamics and kinetics of the adsorption process by various CTNSC adsorbents. It showed that the chemical y activated CTNSCs can effectively remove fluoride from the solution. The adsorption equilibrium data correlate well with the Freundlich isotherm model. The adsorption of fluoride by the chemical y activated CTNSC is spon-taneous and endothermic in nature. The pseudo first order, pseudo second order and intra particle diffusion kinetic models were applied to test the experimental data. The pseudo second order kinetic model provided a better correlation of the experimental data in comparison with the pseudo-first-order and intra particle diffusion models. A mechanism of fluoride adsorption associating chemisorption and physisorption processes is presented allowing the discussion of the variations in adsorption behavior between these materials in terms of specific surface area and porosity. These data suggest that chemically activated CTNSCs are promising materials for fluoride sorption.     

Random forest model for removal of bromophenol blue using activated carbon obtained from Astragalus bisulcatus tree

In this research, activated carbon (AC) simply was prepared from a local, abundant tree in south of Iran. The AC with low cost and toxicity is a good candidate for bromophenol blue (BPB) removal from aqueous media. The AC with nano scale pore diameter is applicable for this dye removal following optimization of the influence of various parameters including contact time, pH, initial dye concentration and amount of adsorbent. Subsequently, experimental data was analyzed by four kinetic models including pseudo first and second-order, Elovich and the intraparticle diffusion equations and subsequently their respective parameters such as rate constants, equilibrium adsorption capacities and correlation coefficients was investigated and based on well known criterion their applicability was judged. The result shows that adsorption of BPB onto proposed adsorbent at all conditions such as versatile adsorbent dosages and initial BPB concentrations sufficiently described by the combination of the pseudo second-order equation and interparticle diffusion model. It was found that equilibrium rate of the BPB adsorption at various adsorbent dosage well fitted by Langmuir. Investigation of experimental result by two approaches (multiple linear regressions (MLR) and random forest (RF)) models show that RF is a powerful tool for prediction of BPB adsorption by activated carbon obtained from Astragalus bisulcatus tree. The optimal tuning parameters for RF model are obtained based on the n_tree = 100, m_try = 2. For the training data set, the MSE values of 0.0006 and the coefficient of determination (R²) values of 0.9895 for RF model and the MSE value of 0.0104 and the R² value of 0.823 for MLR model are obtained.     

Comparison between microwave and conventional thermal reactivations of spent activated carbon generated from vinyl acetate synthesis

Microwave and traditional thermal reactivations of activated carbon (AC) used as catalyst support in vinyl acetate synthesis have been investigated. Experiments have been carried out by using a single mode microwave device (MW) operating at 2450 MHz and a conventional electric furnace (CF) under steam and CO₂ atmosphere, respectively. The surface properties of the spent AC and the reactivated samples were characterized by means of N₂ adsorption and SEM, and compared the effects of different heating mechanisms and activating agents on the adsorption capacities and pore structures of the reactivated AC. These results indicated that the AC obtained by microwave irradiation showed higher adsorption capacities for iodine, methylene blue (MB) and acetate acid, higher BET surface areas and mesoporosity than those obtained by conventional thermal heating. The reactivated samples activated by steam had a narrower and more extensive microporosity as well as higher BET than those activated by carbon dioxide under the same heating equipment. From the results, it was concluded that microwave heating combined with steam as an activating agent could remarkably increase the reactivating efficiency compared to the traditional thermal heating.     

Adsorption of Cd(II), Hg(II) and Zn(II) from aqueous solution using mesoporous activated carbon produced from Bambusa vulgaris striata

Mesoporous activated carbon (surface area of 608 m²/g) has achieved high efficiency in removal of cadmium, mercury and zinc ions from water solution. The proposed low-cost adsorbent was physically activated with water steam from the bamboo species Bambusa vulgaris striata. The batch studies suggested an activated carbon dose of 0.6 g/L, solution pH of 9 and an equilibrium time of 16 h in static conditions. The pseudo-second order equations represented the adsorption kinetics with high correlation. Fitting of the experimental results to the Langmuir, Freundlich, Redlich–Peterson and Toth isotherm models showed an almost homogeneous surface coverage and presence of physical adsorption. The highest adsorption capacities, calculated from the Langmuir model, are 239.45, 248.05 and 254.39 mg/g of cadmium, mercury and zinc, respectively.     

Study of adsorption behavior using activated carbon for removal of colored impurities from 30% caprolactam solution produced by means of SNIA-toluene-technology

We studied the adsorption removal of the colored impurities from caprolactam solution by granular activated carbons. It was observed that removal was favored at lower pH (pH 3.84 or below) and higher temperature. The effects of concentration, dosage of activated carbons, contact time have been also reported. Uptake of colored impurities was very rapid in the first 100 minutes and reached equilibrium after 24 h. The batch adsorption kinetics was found to follow the pseudo-second-order model and the rate constants of adsorption for all these kinetic models have been calculated. Three isotherm expressions Langmuir, Freundlich and Trinomial were shown to fit with the experimental results successfully. The mass transfer coefficientβ and the effective diffusion coefficient in aqueous phase Deff was calculated under a temperature 35–80 °C. The value of the mean free energy of adsorption E signifies that the adsorption of colored impurities onto activated carbon has a physical nature.     

Preparation and characterization of mesoporous activated carbon from waste tires

Activated carbons were produced from waste tires and their characteristics were investigated. Rubber separated from waste tires was first carbonized at 500 °C in N₂ atmosphere. Next, the obtained chars were activated with steam at 850 °C. As a result, fairly mesoporous activated carbons with mesopore volumes and BET surface areas up to 1.09 cm³/g and 737 m²/g, respectively, were obtained. To further improve the porous properties of the activated carbons, the char was treated with 1 M HCl at room temperature for 1 day prior to steam activation. This treatment increased mesopore volumes and BET surface areas of the activated carbons up to 1.62 cm³/g and 1119 m²/g, respectively. Furthermore, adsorption characteristics of phenol and a dye, Black 5, on the activated carbon prepared via acid treatment were compared with those of a commercial activated carbon in the liquid phase. Although the prepared carbon had a larger micropore volume than the commercial carbon, it showed a slightly lower phenol adsorption capacity. On the other hand, the prepared carbon showed an obviously larger dye adsorption capacity than the commercial carbon, because of its larger mesopore volume.     

Evaluation of phenanthrene removal from soil washing effluent by activated carbon adsorption using response surface methodology

Soil washing is a promising technology for the remediation of polycyclic aromatic hydrocarbons (PAH)-contaminated sites, but surfactant needs to be recovered to reduce remediation cost and avoid secondary pollution. In this study, activated carbon (AC), prepared from waste walnut shells, was applied to the adsorptive removal of phenanthrene (PHE) from synthetic soil washing effluent with Tween 80 as a model surfactant. Box-Behnken statistical experiment design (BBD) and response surface methodology (RSM) were used to investigate the influence of AC dosage, Tween 80 concentration and adsorption time, and their potential interaction effect on PHE removal. A response surface model was established based on the BBD experimental results. The goodness of fit of the model was confirmed by determination coefficient, coefficient of variation (CV) and residuals analysis. The RSM model indicates that AC dosage or adsorption time had positive effect on PHE removal while Tween 80 concentration had negative effect. The interaction effect between AC dosage and Tween 80 concentration was significant but the other two interaction effects were not. The 3D response surface plots were developed based on the RSM equation. The RSM model was validated by an additional experiment and the obtained result of PHE removal was very close to the model prediction, indicating the RSM model can effectively predict the PHE removal from soil washing effluent with activated carbon adsorption.     

磷酸活化烟草杆制备中孔活性炭的研究

以烟草杆为原料,以磷酸为活化剂,采用一步炭化法制备了活性炭。采用正交实验研究了磷酸质量分数、浸渍时间、炭化温度及保温时间对活性炭得率和吸附性能的影响,在最佳工艺条件(磷酸质量分数30%,浸渍时间48 h,炭化温度750℃,保温时间20 min)下,所制备的活性炭其碘吸附值为889.36 mg/g,亚甲基蓝吸附值为21.5 mL/(0.1 g),得率为36.90%。同时测定了该活性炭的液氮吸附等温线,并通过BET、H K方程、D A方程和密度函数理论(DFT)表征了活性炭的孔结构。结果表明,该活性炭为中孔型,BET比表面积为892 m2/g,总孔体积为0.467 8 mL/g,微孔占总孔体积的37.06%,中孔占62.85%,大孔占0.07%。最后采用电子探针和透射电镜分析了活性炭的微观结构,其结构与氮吸附测定的结果较为一致。     

Adsorption removal of thiophene and dibenzothiophene from oils with activated carbon as adsorbent: effect of surface chemistry

Commercial coconut-based activated carbons (AC), before and after being treated using 65 wt% HNO₃ at different temperatures (termed as AC–Hs), were used as adsorbents to remove thiophene (T) or dibenzothiophene (DBT) from model oils. The fresh AC sample and all of the AC–Hs samples were characterized by Boehm titration, Fourier-transform infrared spectroscopy, and thermal analysis, which yield the information of the surface chemistry properties of the carbon materials. The results show that in comparison to the fresh AC sample, the quantity of oxygen-containing functional groups on the surface of AC–Hs samples increases as the pretreatment temperature of the fresh AC sample increases. The adsorption capabilities of the AC samples for removal of T and DBT from model oils were evaluated in a batch-type reactor. It has been found that the refractory DBT can be removed easily over the untreated commercial AC with the removal efficiency even being higher than that of T. In the case of acid modified AC–Hs samples, the efficiency for removal of T has been greatly improved, but this is not the case for the removal of DBT. The possible mechanism for adsorption removal of T and DBT over activated carbons is discussed in terms of the quantity of surface oxygen-containing functional groups of adsorbents and the chemical structure of sulfur compounds. The effect of olefin (1-octene) and aromatic hydrocarbons (benzene) in the model oils on the selective adsorption DBT over AC is also evaluated, revealing that in the case of DBT, the competitive adsorption is involved in the process, and the removal efficiency levels off at a level over 80%.     

The importance of finite adsorption kinetics in the sorption of hydrocarbon gases onto a nutshell-derived activated carbon

An activated carbon sample was synthesized from nutshells using a sequential step of carbonization and CO₂ physical activation. Sorption equilibria and kinetics of hydrocarbon gases were measured on this sample at various temperatures and concentrations. The structural heterogeneity of the carbon is characterized by its micropore distribution, which is derived from the analysis of isotherms. The finite kinetics (FK) model [Do, D.D., Wang, K., 1998b. Predictions of adsorption equilibria of non-polar hydrocarbons onto activated carbon. Langmuir 14, 7271-7277; Do, D.D., Wang, K., 1998a. Dual diffusion and finite mass exchange model for adsorption kinetics in activated carbon. A.I.Ch.E. Journal 44, 68.] was employed to describe the sorption kinetics of pure gases and to predict those of binary gas mixtures. The performance of the FK model is compared to that of the HMSD model which assumes the same surface heterogeneity but infinite rates of interchange between the bulk and adsorbed phases. It is demonstrated that the finite kinetics play an important role in the simulation/prediction of desorption kinetics and sorption kinetics of binary gas mixtures.     

Synthesis and characterization of carbon/AlOOH composite for adsorption of chromium(VI) from synthetic wastewater

In this work, flake like carbon/AlOOH composite has been synthesized and evaluated as a new adsorbent for the removal of Cr(VI) from synthetic wastewater. Different characterization tools such as, SEM, EDAX, XRD and XPS were performed to characterize the composite material. Batch adsorption studies for Cr(VI) removal were performed under the influence of various operational parameters such as solution pH, contact time, initial solution concentration and temperature. Results obtained revealed that adsorption of Cr(VI) onto carbon/AlOOH composite followed the pseudo-second order kinetics and Freundlich isotherm model. Thermodynamic results suggests that adsorption of Cr(VI) onto carbon/AlOOH composite was spontaneous and endothermic in nature.     

Effect of ZnO loading to activated carbon on Pb(II) adsorption from aqueous solution

The effect of zinc oxide loading to granular activated carbon on Pb(II) adsorption from aqueous solution was studied in comparison with zinc oxide particles and oxidized activated carbon. Cu(II), Cd(II) and nitrobenzene were used as reference adsorbates to investigate the adsorption. The BET surface area and point of zero charge (pH_PZC) in the aqueous solution were measured for the adsorbents. The adsorption isotherms were examined to characterize the adsorption of heavy metals and organic molecules. The heavy metal adsorption was improved by both the zinc oxide loading and the oxidation of activated carbon. In contrast, the adsorption of nitrobenzene was considerably reduced by the oxidation, and slightly decreased by the zinc oxide loading. The zinc oxide loading to the activated carbon was found to be effectively used for the Pb(II) adsorption whereas only a part of surface functional groups was used for the zinc oxide particles and the oxidized activated carbon. From the experimental results, the surface functional groups responsible for the Pb(II) adsorption on the zinc oxide loaded activated carbon were considered to be hydroxyl groups that formed on the oxide, while those on the oxidized activated carbon were considered to be carboxylic groups.     

Kinetics of adsorption on activated carbon: application of heterogeneous vacancy solution theory

The kinetics of single component adsorption on activated carbon is investigated here using a heterogeneous vacancy solution theory (VST) of adsorption. The adsorption isotherm is developed to account for the adsorbate non-ideality due to the size difference between the adsorbate molecule and the vacant site, while incorporating adsorbent heterogeneity through a pore-width-related potential energy. The transport process in the bidisperse carbon considers coupled mass transfer in both macropore and micropore phases simultaneously. Adsorbate diffusion in the micropore network is modeled through effective medium theory, thus considering pore network connectivity in the adsorbent, with the activation energy for adsorbate diffusion related to the adsorption energy, represented by the Steele 10-4-3 potential for carbons. Experimental data of five hydrocarbons, CO₂ and SO₂ on Ajax carbon at multiple temperatures, as well as three hydrocarbons on Norit carbon at three temperatures are first fitted by the heterogeneous VST model to obtain the isotherm parameters, followed by application of the kinetic model to uptake data on carbon particles of different sizes and geometry at various temperatures. For the hydrocarbons studied, the model can successfully correlate the experimental data for both adsorption equilibrium and kinetics. However, there is some deviation in the fit of the desorption kinetics for polar compounds such as CO₂ and SO₂, due to the inadequacy of the L-J potential model in this case. The significance of viscous transport in the micropores is also considered here and found to be negligible, consistent with recent molecular simulation studies.     

Adsorption of cationic dye from aqueous solutions by activated carbon

Batch sorption experiments were carried out to remove a cationic dye, methylene blue (MB), from its aqueous solutions using a commercial activated carbon as an adsorbent. Operating variables studied were pH, stirring speed, initial methylene blue concentration and temperature. Adsorption process was attained to the equilibrium within 5 min. The adsorbed amount MB dye on activated carbon slightly changed with increasing pH, and temperature, indicating an endothermic process. The adsorption capacity of methylene blue did not significantly change with increasing stirring speed. The experimental data were analyzed by various isotherm models, and found that the isotherm data were reasonably well correlated by Langmuir isotherm. Adsorption measurements showed that the process was very fast and physical in nature. Thermodynamic parameters such as the adsorption entropy (ΔS^o) and adsorption enthalpy (ΔH^o) were also calculated as 0.165 kJ mol⁻¹ K⁻¹ and 49.195 kJ mol⁻¹, respectively. The ΔG^o values varied in range with the mean values showing a gradual increase from −0.256 to −0.780 to −2.764 and −7.914 kJ mol⁻¹ for 293, 313, 323 and 333 K, respectively, in accordance with the positive adsorption entropy value of the adsorption process.     

Kinetics and equilibrium of dissolved oxygen adsorption on activated carbon

The macroscopic adsorption behavior of dissolved oxygen on a coconut shell-derived granular activated carbon has been studied in batch mode at 301 and 313 K for initial dissolved oxygen concentrations of 10-30 mg/l and oxygen/carbon ratios of 2-180 mg/g. BET (Brunauer, Emmett, and Teller) surface area, micropore volume, and pore size distribution were determined from N₂ isotherm data for fresh and used samples of carbon. The surface groups were characterized using Boehm titrations, potentiometric titrations, and FTIR study. The material is characterized by its high specific surface area , microporocity (micropore volume ), its basic character ( total basic groups) and its high iron content (15,480 ppm Fe). BET n-layer isotherm describes adsorption equilibrium suggesting cooperative adsorption and important adsorbate-adsorbate interactions. Kinetic data suggest a process dependent on surface coverage. At low coverage a Fickian, intraparticle diffusion rate model assuming a local equilibrium isotherm (oxygen dissociation reaction) adequately describes the process. The calculated diffusion coefficients (D) vary between and for initial oxygen concentration of 10 and 20 mg/l, respectively. Sensitivity analysis shows that the oxygen dissociation equilibrium constant determines the equilibrium concentration, whereas the diffusion coefficient controls the kinetic rate of the adsorption process having no effect at the final equilibrium concentration. A combined kinetic mass transfer model with concentration-dependent diffusion (parabolic form) has been developed and successfully applied on the dissolved oxygen adsorption system at high surface coverage. For equilibrium uptake of the estimated mean mass transfer coefficient and adsorption rate constant are and , respectively.     

Effects of compressed carbon dioxide treatment on the specificity of oxidase enzymatic complexes from mate tea leaves

This work evaluates the enzymatic activity of peroxidase (POD) and polyphenoloxidase (PPO) present in the crude extract of mate tea leaves (Ilex paraguariensis St. Hill) submitted to compressed CO₂. The effects of temperature, exposure time, solvent reduced density, pressure, and depressurization rate on the activity of peroxidase and polyphenoloxidase were evaluated through a fractionated factorial experimental planning. Results show that temperature of 30 °C, pressure of 70.5 bar, exposure time of 1 h, depressurization rate of 10 kg m⁻³ min⁻¹ and carbon dioxide reduced density of 0.60 led to an enhancement of around 25% in the peroxidase activity and a polyphenoloxidase activity loss of 50%. Using this experimental condition, thermal stability at low temperature (−4 °C) and the influence of successive pressurization/depressurization cycles were determined. Results suggest that it is possible to increase the specificity of the enzymatic extract towards enhancing POD or PPO activity depending on the experimental condition employed, and that the processing of enzymatic complexes with compressed CO₂ may be a promising route to increase the specificity of enzymatic extracts.     

From pollutant to solution of wastewater pollution: Synthesis of activated carbon from textile sludge for dye adsorption

Adsorption is an important process in wastewater treatment,and conversion of waste materials to adsorbent offers a solution to high material cost related to the use of commercial activated carbon.This study investigated the adsorption behaviour of Reactive Black 5(RB5)and methylene blue(MB)onto activated carbon produced from textile sludge(TSAC).The activated carbon was synthesized through chemical activation of precursor followed with carbonization at 650°C under nitrogen flow.Effects of time(0–200 min),pH(2–10),temperature(25–60°C),initial dye concentration(0–200 mg·L~(-1)),and adsorbent dosage(0.01–0.15 g)on dye removal efficiency were investigated.Preliminary screening revealed that TSAC synthesized via H_2SO_4activation showed higher adsorption behaviour than TSAC activated by KCl and ZnCl_2.The adsorption capacity of TSAC was found to be 11.98 mg·g~(-1)(RB5)and 13.27 mg·g~(-1)(MB),and is dependent on adsorption time and initial dye concentration.The adsorption data for both dyes were well fitted to Freundlich isotherm model which explains the heterogeneous nature of TSAC surface.The dye adsorption obeyed pseudo-second order kinetic model,thus chemisorption was the controlling step.This study reveals potential of textile sludge in removal of dyes from aqueous solution,and further studies are required to establish the applicability of the synthesized adsorbent for the treatment of waste water containing toxic dyes from textile industry.