Preparation of novel activated carbons from H2SO4-pretreated corncob hulls with KOH activation for quick adsorption of dye and 4-chlorophenol.

Corncob hull was immersed in 25 wt% H(2)SO(4) and was carbonized in an oven at 290 °C for 2h to obtain the char. The char was then activated for 1h at 780 °C by KOH at weight ratio of KOH/char of 2.5, 3.0, and 3.5. SEM photos of the carbons revealed that the cell wall of corncob hull was etched into thin film structure. It was shown that the adsorption isotherms of methylene blue and 4-chlorophenol on the carbons were well fitted by the Langmuir equation. Moreover, the adsorption kinetics could be satisfactorily described by the Elovich equation. The normalized standard deviations are less than 2.8%. The high fraction of adsorption amount adsorbed within 1 min to that at saturation demonstrated the advantage of the prepared activated carbons. The fraction of adsorption amount within 1 min to that at saturation (q(1)/q(mon)) for the adsorption of 4-CP is high up to 0.807. Such quick adsorption behavior was mainly attributed to the presence of the thin film structure of carbons.

A review and experimental verification of using chitosan and its derivatives as adsorbents for selected heavy metals.

A literature survey on liquid-phase adsorption of selected heavy metals including Cu(II), Zn(II), Ni(II), Cd(II), Pb(II), Hg(II), and Cr(VI) on chitosan (CTS) and its derivatives was made from the viewpoint of adsorption capacity. This parameter was obtained from the Langmuir fit of isotherm data. The magnitude of adsorption capacity of heavy metals on pristine CTS was also used to discuss the mechanism of adsorption; that is, how many amino groups in CTS chains would coordinate with one heavy metal ion. Furthermore, a newly defined parameter, the approaching equilibrium factor R(L), was proposed to quantitatively indicate the favorability of the related adsorption process and to judge the correctness of adsorption capacity determined by the Langmuir equation.

Kinetic studies on the adsorption of phenol, 4-chlorophenol, and 2,4-dichlorophenol from water using activated carbons.

This study uses rate parameters in pseudo-first-order (PFO) and pseudo-second-order (PSO) equations (k(1) and k(2)q(e), respectively) to judge the extent for approaching equilibrium in an adsorption process. Out of fifty-six systems collected from the literature, the adsorption processes with a k(2)q(e) value between 0.1 and 0.8 min(-1) account for as much as 70% of the total. These are classified as fast processes. This work compares the validity of PFO and PSO equations for the adsorption of phenol, 4-chlorophenol (4-CP), and 2,4-dichlorophenol (2,4-DCP) on activated carbons prepared from pistachio shells at different NaOH/char ratios. The activated carbons, recognized as microporous materials, had a surface area ranging from 939 to 1936 m(2)/g. Findings show that the adsorption of phenol, 4-CP, and 2,4-DCP on activated carbons had a k(2)q(e) value of 0.15-0.58 min(-1), reflecting the fast process. Evaluating the operating time by rate parameters revealed that k(2)q(e) was 1.6-1.8 times larger than k(1). These findings demonstrate the significance of using an appropriate kinetic equation for adsorption process design.

Preparation of activated carbons from unburnt coal in bottom ash with KOH activation for liquid-phase adsorption.

In this work, unburnt coal (UC) in bottom ash from coal-fired power plants was soaked in KOH solution and activated for 1 h at 780 degrees C. The yield of activated carbons varied from 47.8 to 54.8% when the KOH/UC weight ratio changed from 2 to 4. Pore properties of these activated carbons including the BET surface area, pore volume, pore size distribution, and pore diameter were characterized based on N(2) adsorption isotherms. It was shown that the isotherms for the adsorption of methylene blue, acid blue 74, and 4-chlorophenol from aqueous solutions on these activated carbons at 30 degrees C were well fitted by the Langmuir equation (correlation coefficient r(2) > 0.9968). The adsorption capacities of methylene blue, acid blue 74, and 4-chlorophenol were obtained to be 2.40-2.88, 0.57-1.29, and 2.34-5.62 mmol/g, respectively. Moreover, the adsorption kinetics could be suitably described by the Elovich equation.

Analyzing a liquid-solid phase countercurrent two- and three-stage adsorption process with the Freundlich equation.

Adsorbent consumption advantages of a countercurrent two- and three-stage process are described. The Freundlich equation and equilibrium-stage were used to deduce these adsorption processes; it was proved that large adsorbent savings were obtained from operations of these systems in most cases. Microporous activated carbon was prepared from plum kernels with KOH chemical activation. Isotherm equilibrium adsorptions of three dyes (BB1, MB, and AB74) and three phenols (phenol, 4-CP, and 2,4-DCP) were used to explain both the superior adsorption capability of activated carbon and the advantages of analyzing adsorption system operations with the Freundlich equation, and to calculate the countercurrent two- and three-stage adsorption processes and explain the design procedures. A continuous-flow countercurrent three-stage adsorption process was developed to provide for design in practical application.

Liquid-solid phase countercurrent multi-stage adsorption process for using the Langmuir equation.

Mass balance and the Langmuir equation were used to deduct the countercurrent multi-stage adsorption process. The relationships between the Langmuir parameter (K(L)y(i)) and the required amounts of adsorbent in countercurrent two-, three- and infinite-stage processes were obtained to find the optimum number of stages as well as the reduction in the adsorbent consumption of the countercurrent multi-stage process of an adsorption system. Pistachio shell activated carbons with BET surface areas of 1013, 1398, and 1919m(2)/g were obtained by KOH activation with CO(2) gasification at gasification times of 0, 10, and 30min. The isotherm adsorption of four adsorbates were investigated and analyzed with the Langmuir equation. The activated carbons studied in this work show compared with other published literatures, the K(L)y(i) and q(mon) values in this work showed excellent adsorption performance. The amount of activated carbon for a countercurrent two- and single stage adsorption operation was calculated, a saving of 66-87% adsorbent was obtained. A simple countercurrent two-stage adsorption system was designed for use in engineering applications.

High adsorption capacity NaOH-activated carbon for dye removal from aqueous solution.

In this study, the surface coverage ratio (Sc/Sp) and monolayer cover adsorption amount per unit surface area (qmon/Sp) were employed to investigate the adsorption isotherm equilibrium of the adsorption of dyes (AB74, BB1 and MB) on NaOH-activated carbons (FWNa2, FWNa3 and FWNa4); the adsorption rate of the Elovich equation (1/b) and the ratio of 1min adsorption amount of adsorbate to the monolayer cover amount of adsorbate (q1/qmon) were employed to investigate adsorption kinetics. The qmon/Sp of NaOH-activated carbons was better than that of KOH-activated carbons prepared from the same raw material (fir wood). The Sc/Sp values of the adsorption of all adsorbates on adsorbent FWNa3 in this study were found to be higher than those in related literature. Parameters 1/b and q1 of the adsorption of dyes on activated carbons in this study were higher than those on KOH-activated carbons; the q1/qmon value of FWNa3 was the highest. The pore structure and the TPD measurement of the surface oxide groups were employed to explain the superior adsorption performance of FWNa3. A high surface activated carbon (FWNa3) with excellent adsorption performance on dyes with relation to adsorption isotherm equilibrium and kinetics was obtained in this study. Several adsorption data processing methods were employed to describe the adsorption performance.

Inferring the favorable adsorption level and the concurrent multi-stage process with the Freundlich constant.

This paper proposes a method for inferring a favorable level for the adsorption isotherm curve with the Freundlich constant (1/n), explains that a favorable level is only a function of 1/n, and then, five favorable levels are classified according to 1/n value. The adsorbent consumption ratio of the concurrent multi-stage to single-stage system was deduced in order to investigate the relationship between favorable level and the most suitable number of stages. Activated carbon (TGBAC) was prepared from Taiwan Giant Bamboo with steam activation. The isotherm equilibrium of the adsorption of three phenols (phenol, 3-CP, and 4-CP), two dyes (MB and BB 69), and tannic acid on TGBAC was obtained. According to the Freundlich constant (1/n), the adsorption of MB was inferred in a strongly favorable zone. The favorable zone for BB69, phenol, 3-CP, and 4-CP was determined. The tannic acid, the pseudo-linear zone and their most suitable number of stages were also determined. The 1/n values and favorable levels summarized from more than a hundred sources/studies indicate that the favorable levels of the adsorption of dyes and phenols on TGBAC are excellent. This paper proposes a simple method for inferring the favorable level and the most suitable number of stages for the concurrent multi-stage adsorption system.

Preparation of highly porous carbon from fir wood by KOH etching and CO2 gasification for adsorption of dyes and phenols from water.

Fir wood was first carbonized for 1.5 h at 450 degrees C, then soaked in a KOH solution KOH/char ratio of 1, and last activated for 1 h at 780 degrees C. During the last hour CO2 was poured in for further activation for 0, 15, 30, and 60 min, respectively. Carbonaceous adsorbents with controllable surface area and pore structure were chemically activated from carbonized fir wood (i.e., char) by KOH etching and CO2 gasification. The pore properties, including the BET surface area, pore volume, pore size distribution, and pore diameter, of these activated carbons were first characterized by the t-plot method based on N2 adsorption isotherms. Fir-wood carbon activated with CO2 gasification from 0 to 60 min exhibited a BET surface area ranging from 1371 to 2821 m2 g(-1), with a pore volume significantly increased from 0.81 to 1.73 m2 g(-1). Scanning electron microscopic (SEM) results showed that the surfaces of honeycombed holes in these carbons were significantly different from those of carbons without CO2 gasification. The adsorption of methylene blue, basic brown 1, acid blue 74, p-nitrophenol, p-chlorophenol, p-cresol, and phenol from water on all the carbons studied was examined to check their chemical characteristics. Adsorption kinetics was in agreement with the Elovich equation, and all equilibrium isotherms were in agreement with the Langmuir equation. These results were used to compare the Elovich parameter (1/b) and the adsorption quantity of the unit area (q(mon)/Sp) of activated carbons with different CO2 gasification durations. This work facilitated the preparation of activated carbon by effectively controlling pore structures and the adsorption performance of the activated carbon on adsorbates of different molecular forms.

Comparisons of porous and adsorption properties of carbons activated by steam and KOH.

In this work, fir woods and pistachio shells were used as source materials to prepare porous carbons, which were activated by physical (steam) and chemical (KOH) methods. Pore properties of these activated carbons including the BET surface area, pore volume, pore size distribution, and pore diameter were first characterized by a t-plot method based on N(2) adsorption isotherms. Highly porous activated carbons with BET surface area up to 1009-1096 m(2)/g were obtained. The steam and KOH activation methods produced carbons with mesopore content in the range 9-15 and 33-49%, respectively. The adsorption equilibria and kinetics of tannic acid, methylene blue, 4-chlorophenol, and phenol from water on such carbons at 30 degrees C were then investigated to check their chemical characteristics. The Freundlich equation gave a better fit to all adsorption isotherms than the Langmuir equation. On the other hand, the intraparticle diffusion model could best follow all adsorption processes. In comparison with KOH-activated carbons, it was shown that the rate of external surface adsorption with steam-activated carbons was significantly higher but the rate of intraparticle diffusion was much lower.