Molecular dynamics simulation of doxorubicin adsorption on a bundle of functionalized CNT

In this study, molecular dynamics simulation is used to investigate the adsorption of an anticancer drug, doxorubicin, on bundles of functionalized single-walled carbon nanotubes (SWNTs) in an aqueous solution. Carboxylic group has been selected as the functional group. Molecular dynamics (MD) simulations are performed for both separated systems containing a SWNT bundle and a functionalized carbon nanotube bundle, and results are compared with existing experimental data. MD results show that doxorubicin can be adsorbed on CNTs using different methods such as entrapment within CNT bundle, attachment to the side wall of the CNT, and adsorption on the CNT inner cavity. For functionalized CNT, the adsorption of drugs on the functional groups is essential for predicting the enhancement of drug loading on the functionalized nanotubes. Furthermore, the adsorption behavior of doxorubicin on CNTs is fitted with Langmuir and Freundlich isotherm models. The results show that Langmuir model can predict the adsorption behavior of doxorubicin on CNTs more accurately than Freundlich model does. As predicted by this isotherm model, the adsorption process of doxorubicin on CNTs is relatively difficult, but it can be improved by increasing the functional groups on the CNTs surface.     

Removal of color from biomethanated distillery spentwash by treatment with activated carbons

This work examined 19 carbon samples prepared by acid and thermal activation of various agro-residues viz. bagasse, bagasse flyash, sawdust, wood ash and rice husk ash for color removal from biomethanated distillery effluent. Phosphoric acid carbonized bagasse B (PH) showed the maximum color removal (50%). However, commercial activated carbons AC (ME) and AC (LB) showed better performance of over 80% color removal. Besides color removal, activated carbon treatment also showed reduction in chemical oxygen demand (COD), total organic carbon (TOC), phenol and total Kjeldahl nitrogen (TKN). The performance was related to the characteristics of the investigated samples. Further, adsorption isotherms for melanoidins, which is the primary coloring compound in distillery spentwash, followed the Langmuir isotherm implying monolayer adsorption.     

Adsorption of Neutral Red onto Mn-impregnated activated carbons prepared from Typha orientalis

Activated carbon was prepared from an inexpensive and renewable carbon source, Typha orientalis, by H(3)PO(4) activation and then impregnated with different Mn salts and tested for its Neutral Red (NR) adsorption capacities. The amount of Mn impregnated in the activated carbon was influenced by the anion species. Impregnation with Mn decreased the surface area, changed the pore size and crystal structure, and introduced more acidic functional groups such as carboxyl, lactone and phenol groups. The optimum adsorption performance for all the activated carbons was obtained at pH 3.7, Mn-Carbon dose of 0.100g/100ml solution and contact time 4.5h. The adsorption isotherms fit the Langmuir isotherm equation. The kinetic data followed the pseudo-second-order model. The thermodynamic parameters indicated that the processes were spontaneous and endothermic. According to these results, the prepared Mn modified activated carbons are promising adsorbents for the removal of Neutral Red from wastewater.     

Preparation of high adsorption capacity bio-chars from waste biomass

Bio-chars with high adsorption capacity derived from rice-husks and corncobs were prepared at different retention times (RTs) in a pyrolysis reactor. At a fixed pyrolysis temperature, the pyrolysis RT is a key factor influencing the surface areas and functional group contents of the bio-chars, and further influencing their adsorption capacities. The results indicate that the bio-char prepared at RT of 1.6 s exhibits a higher phenol adsorption capacity (589 mg g⁻¹) than other bio-chars and many activated carbons reported in the literature. An adsorption mechanism based on acid-base interaction and hydrogen binding between phenol and the functional groups was proposed to elucidate the adsorption process. An economic evaluation of the use of bio-chars as adsorbents was made.     

Hydrogen dissociation on diene-functionalized carbon nanotubes

Chemical functionalization of a zigzag carbon nanotube (CNT) with 1, 3-cyclohexadiene (CHD), previously reported by experimentalists, has been investigated in the present study using density functional theory in terms of energetic, geometric, and electronic properties. Then, the thermodynamic and kinetic feasibility of H₂ dissociation on the pristine and functionalized CNTs have been compared. The dissociation energy of the H₂ molecule on the pristine and functionalized CNT has been calculated to be about ?1.00 and ?1.55 eV, while the barrier energy is found to be about 3.70 and 3.51 eV, respectively. Therefore, H₂ dissociation is thermodynamically more favorable on the CNT-CHD system than on the pristine tube, while the favorability of the dissociation on the pristine tube is higher in term of kinetics.     

Semicontinuous and continuous degradation of phenol by Pseudomonas putida P8 adsorbed on activated carbon

Summary The semicontinuous and continuous degradation of phenol by Pseudomonas putida P8 which was immobilized on activated carbon was investigated. The amount of bacteria immobilized on the activated carbon surface dependend on the cell concentration in the suspension and on the type of activated carbon. In a continuous process running for four weeks the biomass, which accumulated in the activated carbon fixed bed, was removed periodically. The average phenol degradation rate in this process was 360 mg/1 h. The degradation activity of the bacteria for phenol, measured by the activity of the catechol-2,3-dioxygenase, was stimulated by the activated carbon. During the fermentation processes the carbon particles were covered with a biofilm. The bacteria grew, especially in the caverns and the entrances of the macropores, whereby the phenol adsorption by the activated carbon was decreased.     

Influence of preparation conditions in the textural and chemical properties of activated carbons from a novel biomass precursor: the coffee endocarp

In this work a novel biomass precursor for the production of activated carbons (AC) was studied. The lignocellulosic material used as precursor is the coffee bean endocarp, which constitutes an industrial residue from the Portuguese coffee industry. Activation by carbon dioxide and potassium hydroxide produces activated carbons with small external areas and pore volumes up to 0.22 and 0.43cm3g(-1), respectively, for CO2 and KOH activation. All the AC's produced are very basic in nature with point of zero charge higher than 8. SEM/EDX studies indicate the presence of K, O, Ca and Si. By FTIR it was possible to identify the formation on the AC's surface of several functional groups, namely phenol, alcohol, quinone, lactone, pyrone and ether as well as SiH groups. The tailoring of the porous and chemical structure of the activated carbons produced is possible by selecting the appropriate production conditions.     

Phenol degradation by microorganisms adsorbed on activated carbon

Summary The phenol degradation by Candida sp. and Pseudomonas sp. immobilized on activated carbon was investigated. Thanks to its great adsorptive surface, activated carbon is suited as supporting material for microorganisms and also provides a high adsorption capacity for phenol.The immobilization by adsorption avoids any unphysiological treatment of the microorganisms. One gram activated carbon adsorbed in 10 h about 4×10⁹ Pseudomonas cells and 3×10⁸ Candida cells. While the free cells did not tolerate more than 1.5 g/l phenol, the adsorbed microorganisms survived at temporary high phenol concentrations up to 15 g/l, and they degraded about 90% of the adsorbed phenol.The activated carbon operated like a depot: the adsorbed phenol diffused out of the carbon and could be metabolized by the microorganisms. The results give an explanation of the stimulating effect of activated carbon in the treatment of waste waters observed until now.     

Degradation of phenol by a defined mixed culture immobilized by adsorption on activated carbon and sintered glass

Summary A defined mixed culture of the yeast Cryptococcus elinovii H1 and the bacterium Pseudomonas putida P8 was immobilized by adsorption on activated carbon and sintered glass, respectively. Depending on its adsorption capacity for phenol the activated carbon system could completely degrade 17 g/l in batch culture, whereas the sintered glass system was able to degrade phenol up to 4 g/l. During semicontinuous degradation of phenol (1 g/l) both systems reached constant degradation times with the fourth batch that lasted 8 h when using the activated carbon system and 10 h in the sintered glass system. In the course of continuous degradation of phenol the activated carbon system reached a maximum degradation rate of 9.2 g l^–1 day^–1 compared to 6.4 g l^–1 day^–1degraded by the sintered glass system. 2-Hydroxymuconic acid semialdehyde could be identified and quantitatively determined as a metabolite of phenol degradation by P. putida P8. Increased membrane permeability under the influence of phenol was demonstrated by the examination of K⁺ efflux from P. putida P8. Offprint requests to: H.-J. Rehm     

Comparative evaluation for the sorption capacity of four carbonaceous sorbents to phenol

Sorption kinetics and isotherms of phenol by four carbonaceous sorbents (activated carbon (AC), mesoporous carbon (MPC), bamboo biochar (BBC) and oak wood biochar (OBC)) were compared in this study. MPC has the fastest sorption rate and initial sorption potential, which were indicated by sorption rate constants and initial sorption rate “h” in a pseudo-second-order kinetic model. The ordered and straight pore structure of MPC facilitated the accessibility of phenol. The AC showed the greatest sorption capacity towards phenol with maximum sorption of 123 mg/g as calculated by the Langmuir model. High surface area, complexity of pore structure, and the strong binding force of the π–π electron-donor-acceptor interaction between phenol molecules and AC were the main mechanisms. The BBC and OBC had much slower sorption and lower sorption capacity (33.04 and 29.86 mg/g, respectively), compared to MPC (73.00 mg/g) and AC, indicating an ineffective potential for phenol removal from water.     

Effects of manufacturing conditions on the adsorption capacity of heavy metal ions by Makino bamboo charcoal

The objective of this study was to investigate the effects of manufacturing conditions on the adsorption capacity of heavy metal ions by Makino bamboo charcoal. Results show that the specific surface area and iodine number of bamboo charcoal activated at 900 degrees C were larger than those of bamboo charcoal activated at 800 degrees C. The specific surface area of bamboo charcoal activated at 800 degrees C by carbon dioxide was larger than that of charcoal activated by steam. However, a contrary result was observed when the activation temperature was 900 degrees C. The total volume and proportion of micropores in bamboo charcoal activated by carbon dioxide were greater than those in the other sample groups. However, the total volume and bulk volume of meso- and macropores, and average pore diameter for bamboo charcoal activated by steam were greater than those in the other sample groups. Using 5g bamboo charcoal (10-30 mesh) with a soaking time of 24h, a better adsorption effect on Pb2+ (100%), Cu2+ (100%), and Cr3+ (88-98%) was found. However, medium frequencies were observed for the adsorption of Cd2+ (40-80%) and Ni2+ (20-60%). Very limited adsorption of As5+ was detected in this study. For the same charcoal grain sizes, the adsorption capacity of 0.5g of charcoal was better than that of 0.1g. The improved adsorption effect of the sample group activated by steam was compared with the sample group activated by carbon dioxide.     

Enhancement of the activated sludge process by activated carbon produced from surplus biological sludge

Surplus biological sludge from wastewater treatment operations was converted into activated carbon and then added to the aerated vessel of an activated sludge process treating phenol and glucose. The addition of activated carbon, either sludge-based or commercial, enhanced phenol removal from 58 to 98.7% and from 87 to 93% for COD with feed concentrations of 100 mg phenol l^–1 and 2500 mg COD l^–1. No differences were found between the activated sludge-activated carbon bench scale continuous reactors operating with either commercial or sludge-based activated carbon in spite of the higher adsorption capacity of the former.     

Biochar derived from anaerobically digested sugar beet tailings: characterization and phosphate removal potential

Two biochars were produced from anaerobically digested and undigested sugar beet tailings through slow-pyrolysis at 600 °C. The digested sugar beet tailing biochar (DSTC) and raw sugar beet tailing biochar (STC) yields were around 45.5% and 36.3% of initial dry weight, respectively. Compared to STC, DSTC had similar pH and surface functional groups, but higher surface area, and its surface was less negatively charged. SEM-EDS and XRD analyses showed that colloidal and nano-sized periclase (MgO) was presented on the surface of DSTC. Laboratory adsorption experiments were conducted to assess the phosphate removal ability of the two biochars, an activated carbon (AC), and three Fe-modified biochar/AC adsorbents. The DSTC showed the highest phosphate removal ability with a removal rate around 73%. Our results suggest that anaerobically digested sugar beet tailings can be used as feedstock materials to produce high quality biochars, which could be used as adsorbents to reclaim phosphate.     

Biofiltration of a mixture of volatile organic compounds on granular activated carbon

The performance of a biofilter packed with Active Carbon (AC) was evaluated. The effluent (alcohol, ketones, esters, aromatic and chlorinated compounds) treated was a representative mixture of most common industrial emissions. To achieve a better knowledge of multicomponent adsorption mechanisms, and to underline the interest of inoculating AC, a control abiotic humidified filter had been operated in the same conditions as the biofilter. For a load of 110 g VOC m(-3) AC h(-1), after 55 days of operation, the removal efficiency was higher in the biotic than in the abiotic filter (85% vs 55%, respectively). Moreover, in the biofilter, at steady state, the elimination of all compounds was almost complete except for chlorinated compounds and p-xylene (removal efficiency of 25% and 64%, respectively). The microbial colonization of AC involved a decrease of the adsorption sites accessibility and enhanced the treatment of VOCs (volatile organic compounds) having a lower affinity for activated carbon. Moreover, while aromatic compounds and MIBK were eliminated along the overall height of the biofilter, pollutants with reduced affinity for AC, such as methanol, acetone, and halogenated compounds were only treated on the second half of the reactor. Thus, the affinity for activated carbon was an important parameter controlling the biodegradation process. Nevertheless, the use of AC as packing material in biofilters treating complex mixtures of VOCs is limited. Actually, similar removal efficiency could be reached, in the same conditions, for a biofilter packed with granular peat. Furthermore, for the biofilter packed with AC, the column height necessary to remove biodegradable compounds, with reduced affinity for the support, was important.     

Adsorption of Phenolic Compounds and Methylene Blue onto Activated Carbon Prepared from Date Fruit Pits

Activated carbon has been prepared from date fruit pits. The carbon, prepared at different burn‐off rates, showed a high uptake of methylene blue. At 92 % burn‐off (weight loss percent of the carbonized pits upon activation), methylene blue uptake was 590 mg/g. With this high capacity, the carbon was then used to study the adsorption of phenol, 2‐nitrophenol, 2,4‐dinitrophenol, and 2,4,6‐trinitrophenol. The prepared activated carbon showed an adsorption capacity better than that of many activated carbons in current use. The experimental adsorption data for the single components were regressed using both Langmuir and Freundlich isotherm models and the fit was generally satisfactory. The experimental adsorption data of the binary system phenol‐2‐nitrophenol were compared with the predicted results using two predictive models: the generalized Langmuir and the IAS models. The data were better represented by the IAS theory than the generalized Langmuir model even though the fit of the experimental data was not adequate.     

The impact of Gelrite and activated carbon on the elemental composition of two conifer embryogenic tissue initiation media

The elemental composition of plant tissue culture media was studied in response to (1) different levels of Gelrite and activated carbon (AC) in semisolid media and (2) different levels and types of AC in liquid media. Doubling the level of Gelrite from 2 g/l to 4 g/l reduced available magnesium (20%), calcium (16%), zinc (17%) and manganese (24%) and increased potassium (6%). AC adsorbed copper (90-95%) and zinc (35-51%) from both liquid and semisolid media. Two significantly different ACs gave minor differences in adsorption. No adsorption was indicated for inorganic anions. Nonacid-washed AC released significant levels of magnesium (44% increase), calcium (16% increase) and silica (a 75% increase to 1.8 mg/l). The elemental composition of media may need to be adjusted when increasing the Gelrite level or adding AC.     

XPS evidence for the formation of Ni(II) complexes on treated activated carbon

X-ray photoelectron spectroscopy (XPS) was applied to a solid-state investigation on adsorbed systems obtained by contacting different samples of an activated carbon (Chemviron Filtrasorb 400) with solutions containing (a) 1,10-phenanthroline (phen); (b) NiCl₂·6H₂O. (c) Ni²⁺ ions and phen in a 1:3 molar ratio.XPS results on these systems are discussed with particular regard to the chemical state of the ligand (interaction of functional groups with the substrate) and of the metal ions on carbon (assessment of Ni oxidation state; detection of Ni complexes on carbon and information on their stoichiometries and structures). Various effects of successive chemical treatments on the above reported carbon species were also revealed by XPS, such as:(i) the formation of a ‘carbon–ligand’ system (activated carbon with ligand firmly present on it) after acid elution of the activated carbon treated with Ni–phen complexes in solution, and (ii) the adsorption of Ni²⁺ ions on this ‘carbon–ligand’ system, with fomation of Ni–phen complexes on carbon.     

Development of easy made low cost bindless monolithic electrodes from biomass with controlled properties to be used as electrochemical capacitors

The aim of the work now reported is the development of low cost electrodes in the monolithic shape without the need for a pos-production step with potential to be used in supercapacitors. The tested materials were activated carbon fibres prepared and activated carbons made from coffee endocarp. The main functional groups identified were quinone, lactone, Si-H, phenol, hydroxyl, carbonyl and ether for activated carbon samples and amine, amide, pyrone, lactone, carbonyl and hydroxyl for activated carbon fibres samples. The nanostructure of the materials is predominantly microporous but with a significant variety of porosity development with BET surface area and pore volume given by α(s) method range from 89 to 1050 m(2) g(-1) and 0.04 to 0.50 cm(3) g(-1), respectively. The electrochemical properties of the materials were investigated using classic cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. The higher specific capacitance achieved was 176 F g(-1).     

Caffeine adsorption of montmorillonite in coffee extracts

The growth in health-conscious consumers continues to drive the demand for a wide variety of decaffeinated beverages. We previously developed a new technology using montmorillonite (MMT) in selective decaffeination of tea extract. This study evaluated and compared decaffeination of coffee extract using MMT and activated carbon (AC). MMT adsorbed caffeine without significant adsorption of caffeoylquinic acids (CQAs), feruloylquinic acids (FQAs), dicaffeoylquinic acids (di-CQAs), or caffeoylquinic lactones (CQLs). AC adsorbed caffeine, chlorogenic acids (CGAs) and CQLs simultaneously. The results suggested that the adsorption selectivity for caffeine in coffee extract is higher in MMT than AC. The caffeine adsorption isotherms of MMT in coffee extract fitted well to the Langmuir adsorption model. The adsorption properties in coffee extracts from the same species were comparable, regardless of roasting level and locality of growth. Our findings suggest that MMT is a useful adsorbent in the decaffeination of a wide range of coffee extracts.