Acid/Base-treated activated carbons: characterization of functional groups and metal adsorptive properties

Preparation and characterization of activated carbon from acorn shell by physical activation with H2O-CO2 in two-step pretreatment

Activated carbons have been prepared by physical activation with H2O-CO2 in two-step pre-treatment including ZnCl2-HCl from acorn shell at 850 °C. The active carbons were characterized by N2 adsorption at 77 K. Adsorption capacity was demonstrated by the iodine numbers. The surface chemical characteristics of activated carbons were determined by FTIR spectroscopic method. The microstructure of the activated carbons prepared was examined by scanning electron microscopy. The maximum BET surface area of the obtained activated carbon was found to be around 1779 m(2)/g.

The Application of Response Surface Methodology for Lead Ion Removal from Aqueous Solution Using Intercalated Tartrate-Mg-Al Layered Double Hydroxides

Layered double hydroxide intercalated with tartrate (tartrate-Mg-Al) was used as an adsorbent to remove lead ions from aqueous solutions. The effects of various optimization parameters such as contact time, solution pH, lead ion concentrations, and adsorbent dosage were investigated by the use of Response Surface Methodology (RSM). The Response Surface Methodology (RSM) based on a four-level four-variable Central Composite Rotatable Design (CCRD) was employed to evaluate the interactive effects of the various optimization parameters. The parameters were contact time (6–10 h), solution pH (1–3), adsorbent dosage (0.06–0.1 g), and lead ion concentrations (10–30 mg/L). The percentage of lead ions removal for each of the parameters studied was determined by Inductively Coupled Plasma-Optical Emission Spectrophotometer. Simultaneously by increasing contact time and amount of dosage of tartrate-Mg-Al used the percentage of lead ions removal from aqueous solution will increase; however, the percentage removal decreases with an increase in pH and concentrations of lead ions. The experimental percentage removal recorded under optimum conditions was compared well with the maximum predicted value from the RSM, which suggest that Central Composite Rotatable Design of RSM can be used to study the removal of lead from aqueous solution by the use of tartrate-Mg-Al as an adsorbent.

Retention of heavy metals in a Typic Kandiudult amended with different manure-based biochars

Although nutrient-rich manure biochars are expected to be an effective heavy metal stabilizer in agricultural and contaminated soils, systematic studies are lacking to predict the influence of manure variety and pyrolysis temperature on metal-binding potentials. In this study, biochars produced from five manure varieties (dairy, paved feedlot, swine solids, poultry litter, and turkey litter) at two pyrolytic temperatures (350 and 700°C) were examined for the stabilization of Pb, Cu, Ni, and Cd in a weathered, acidic Norfolk loamy sand (fine-loamy, kaolinitic, thermic, Typic Kandiudult). Equilibrium concentrations in the aqueous phase were determined for heavy metals (Cu, Ni, Cd, and Pb) and additional selected elements (Na, P, S, Ca, Mg, Al, and K); these were analyzed by positive matrix factorization to quantitatively determine the factors responsible for the biochar's ability to bind the selected heavy metals in soil. Concurrently with the greatest increase in pH and highest equilibrium Na, S, and K concentrations, poultry litter, turkey litter, and feedlot 700°C biochar exhibited the greatest heavy metal retention. In contrast, manure varieties containing disproportionately high (swine) and low (dairy) ash, P, and other elements were the least effective stabilizers. Regardless of the manure type, proton nuclear magnetic resonance analyses showed the removal of leachable aliphatic and nitrogen-containing heteroaromatic functional groups at the higher (700°C) pyrolysis temperature. Consistently greater Cu retention by the 700°C biochar indicated the mobilization of Cu by 350°C biochar-born dissolved organic carbon; however, the influence of other temperature-dependent biochar characteristics cannot be ruled out.

Surface activated carbon nanospheres for fast adsorption of silver ions from aqueous solutions

We report the synthesis and activation of colloidal carbon nanospheres (CNS) for adsorption of Ag(I) ions from aqueous solutions. CNS (400-500 nm in diameter) was synthesized via simple hydrothermal treatment of glucose solution. The surface of nonporous CNS after being activated by NaOH was enriched with -OH and -COO(-) functional groups. Despite the low surface area (<15m(2)/g), the activated CNS exhibited a high adsorption capacity of 152 mg silver/g. Under batch conditions, all Ag(I) ions can be completely adsorbed in less than 6 min with the initial Ag(I) concentrations lower than 2 ppm. This can be attributed to the minimum mass transfer resistance as Ag(I) ions were all deposited and reduced as Ag(0) nanoparticles on the external surface of CNS. The kinetic data can be well fitted to the pseudo-second-order kinetics model. The adsorbed silver can be easily recovered by dilute acid solutions and the CNS can be reactivated by the same treatment with NaOH solution. The excellent adsorption performance and reusability have also been demonstrated in a continuous mode. The NaOH activated CNS reported here could represent a new type of low-cost and efficient adsorbent nanomaterials for removal of trace Ag(I) ions for drinking water production.

Adsorption of copper(II) onto sewage sludge-derived materials via microwave irradiation

The materials with adsorbent properties were produced from urban sewage sludge by two different procedures via microwave irradiation: (1) by one single pyrolysis stage (SC); (2) by chemical activation with ZnCl(2) (SZ). The BET, SEM and FT-IR have been used to evaluate the pore structural parameters and surface chemistry of the adsorbents, respectively. Subsequently they were used for adsorption of Cu(II) from aqueous solutions. The effects of various experimental parameters, such as pH, temperature were investigated in a batch-adsorption technique. The results showed that the adsorption of Cu(II) was maximal at pH 5.0. The kinetic study demonstrated that the adsorption process was followed the second-order kinetic equation. The experimental adsorption isotherm data were well fitted with Langmuir model and the maximum adsorption capacity of Cu(II) were found to be 3.88 and 10.56 mg/g for SC and SZ, respectively, in the solution of pH 5.0. Thermodynamic parameters such as changes in the enthalpy (ΔH(0)), entropy (ΔS(0)) and free energy (ΔG(0)) indicate that Cu(II) adsorption onto SC and SZ is an endothermic and spontaneous process in nature at 15-45°C. These results indicate that the sewage sludge-derived material via microwave induced ZnCl(2) activation is an effective and alternative adsorbent for the removal of Cu(II) from aqueous solution.

Activated carbon modifications to enhance its water treatment applications. An overview

The main objective of this study was to list and compare the advantages and disadvantages of different methodologies to modify the surface of activated carbons (ACs) for their application as adsorbents to remove organic and inorganic pollutants from aqueous phase. These methodologies have been categorized into four broad groups: oxidation, sulfuration, ammonification, and coordinated ligand anchorage. Numerous investigations into the removal of metals from water have modified carbon surfaces to increase their content of acidic surface functional groups by using H(2)O(2), O(3) and HNO(3). Because these treatments can reduce the AC surface area, researchers are seeking alternative methods to modify and/or create surface functional groups without the undesirable effect of pore blockage. The nitrogenation or sulfuration of the AC surface can increase its basicity favoring the adsorption of organic compounds. The introduction of nitrogen or sulfur complexes on the carbon surface increases the surface polarity and, therefore, the specific interaction with polar pollutants. Different coordinated ligands have also been used to modify ACs, showing that coordinated ligand anchorage on the AC surface modifies its textural and chemical properties, but research to date has largely focused on the use of these modified materials to remove heavy metals from water by complexes formation.

Distinct photoacidity of honokiol from magnolol

Honokiol, 5,5'-diallyl-2,4'-dihydroxy- biphenyl, by comparison with its isomer magnolol, 5,5'-diallyl- 2,2'-dihydroxy- biphenyl, has been characterized by steady-state and time-resolved spectroscopy as well as (1)H NMR. Honokiol shows more complex pH dependence of absorption and fluorescence characteristics compared with magnolol. Honokiol possesses much weaker acidity than magnolol both in the ground and excited states. Its weak photoacidity is similar to that of 4-hydroxy- biphenyl or 4, 4'-dihydroxy- biphenyl rather than 2-hydroxy- biphenyl or 2, 2'-hydroxy- biphenyl. The electron effect and geometry configuration of substitution has been discussed.

Sorption of aqueous Zn[II] and Cd[II] by multiwall carbon nanotubes: the relative roles of oxygen-containing functional groups and graphenic carbon

Exposure of multiwalled carbon nanotubes (MWCNTs) to oxidizing acids and other oxidants introduces oxygen-containing functional groups such as hydroxyl, carboxyl, and carbonyl groups onto the surface. This research evaluated how changes in oxygen concentration and distribution of oxygen-containing functional groups influenced the sorption of aqueous zinc and cadmium on MWCNTs. Sorption results with natural char, activated carbon, and a suite of MWCNTs (of varying surface oxygen content) were obtained. Results confirmed that surface oxygen enhances the sorption of both Zn[II] and Cd[II] from aqueous solution. Although Zn[II] sorbed more strongly than Cd[II] for all materials studied, surface oxidation had more effect on the sorption of Cd[II] than of Zn[II]. Additional sorption experiments with Zn[II] and 16 MWCNTs of varying surface oxidation level and functional group distribution revealed the relative contributions of different types of surface sites to sorption. Sorption isotherms were fit using a two-site Langmuir adsorption model that incorporated the independent characterization of functional group distribution. Results showed that carboxyl-carbon sites were over 20 times more energetic for zinc sorption than unoxidized carbon (graphenic-carbon) sites, though both site types are important contributors to sorption.

Copper and cadmium sorption onto kraft and organosolv lignins

The relative metal sorption ability of kraft and organosolv lignins was examined as a function of solution chemistry (pH, ionic strength (I), sorbate-to-sorbent ratio) and reaction time. The surface charge characteristics and functional group composition of these lignins, especially kraft lignin, are favorable for metal sorption. Sorption of Cu and Cd increased with increasing pH and decreasing I. Description of sorption isotherms required the more complex Sips equation, as compared to the simpler Langmuir and Freundlich formulations, indicative of the presence of binding sites with varying affinities on these lignin biosorbents. Sorption capacity varied in the following order: softwood organosolv lignin<hardwood organosolv lignin<hardwood kraft lignin<softwood kraft lignin with sorption maximum of 21.5, 40, 66.7, and 80.6 micromol/g, respectively, for Cu, and 8.2, 18.3, 25.2, and 28.7 micromol/g for Cd. Both Cu and Cd sorption kinetics were rapid with equilibrium levels attained within 80 min and faster uptake was noticed for Cu. Strong competitive effects exhibited by H(+) and Na(+) in limiting Cu and Cd sorption are suggestive of the occurrence of weak ion-exchange type interactions involving the carboxylic and phenolic functional groups. Additional pretreatment and surface modifications of these biosorbents might be required to increase metal sorption capacity and enhance their use in waster/wastewater treatment.

Characteristics and defluoridation performance of granular activated carbons coated with manganese oxides

Using a redox process, granular activated carbon (GAC) was coated with manganese oxides to enhance its ability to adsorb fluoride from an aqueous solution. Compared with plain GAC, the fluoride adsorption capacity of this new adsorbent was improved and at least three times greater than that of uncoated GAC. The surface characteristics of coated GAC were observed with scanning electron microscopy. The surface area of the new adsorbent was calculated using the Brunauer-Emmett-Teller method. X-ray diffraction revealed that manganese oxides are amorphous. X-ray photoelectron spectroscopy demonstrated that manganese existed primarily in the oxidation state +IV. Kinetic and equilibrium adsorption data showed that the adsorption process follows the pseudo-second order kinetic and Freundlich equation models. The sorption data also indicated that the removal of fluoride by adsorption is a highly complex process, involving both boundary layer diffusion and intra-particle diffusion. The pH value of solution influences fluoride removal, and the optimum equilibrium pH value of fluoride adsorption is 3.0.

Uptake of arsenate by an alginate-encapsulated magnetic sorbent: process performance and characterization of adsorption chemistry

Arsenate removal by a calcium alginate-encapsulated magnetic sorbent was studied. The morphology, microstructure, and composition properties of the sorbent were explored using X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX). The SEM study demonstrates that there are many protuberances and pores on the sorbent surface; the XRD analysis reveals that the sorbent consists of Fe(3)O(4). The EDX analysis indicates that the adsorption on the surfaces of sorbent is highly location dependent. The interaction characteristics between the arsenic and the functional groups on the sorbent were studied by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). These studies indicate that the lattice oxygen in magnetite and the oxygen in hydroxyl of the calcium alginate play important roles in the sorption of arsenate ions onto the sorbent. More importantly, the XPS analysis demonstrates that the arsenate is reduced to arsenite after its adsorption onto the sorbent. It is proposed that divalent iron and the alcoholic group in alginate provide electrons to arsenate. A conceptual model for the adsorption is proposed to illustrate the mechanisms.

Effect of surface acidic oxides of activated carbon on adsorption of ammonia

The influence of surface acidity of activated carbon (AC) was experimentally studied on adsorption of ammonia (NH(3)). Coconut shell-based AC was modified by various acids at different concentrations. There were five different acids employed to modified AC, which included nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, and acetic acid. Acidic functional groups on the surface of ACs were determined by a Fourier transform infrared spectrograph (FTIR) and by the Boehm titration method. Specific surface area and pore volume of the ACs were measured by a nitrogen adsorption apparatus. Adsorption amounts of NH(3) onto the ACs were measured by a dynamic adsorption system at room temperature according to the principle of the ASTM standard test method. The concentration of NH(3) in the effluent stream was monitored by a gas-detecting tube technique. Experimental results showed that adsorption amounts of NH(3) on the modified ACs were all enhanced. The ammonia adsorption amounts on various activated carbons modified by different acids are in the following order: nitric acid>sulfuric acid>acetic acid approximately phosphoric acid>hydrochloric acid. It is worth to note that the breakthrough capacity of NH(3) is linearly proportional to the amount of acidic functional groups of the ACs.

Catalytic ozonation of phenolic wastewater with activated carbon fiber in a fluid bed reactor

The effect of activated carbon fiber (ACF) on the ozonation of phenol in water in a fluid bed reactor was investigated. It was observed that this combined process could increase the yield of the oxidation process significantly for phenol and COD (chemical oxygen demand) removal, especially for the phenol removal. The efficiency of ozonation increased with an increase in the dose of ACF. Higher initial phenol concentration only caused a slight decrease of phenol and COD removal. The results of repeated use found that ozonation could efficiently regenerate ACF in situ in the reactor, which was considered easy to handle without the costly ex situ regeneration of the industrial treatment process. The Boehm titrations and FTIR studies indicate that the ozonation process in water can significantly change the composition of acidic surface oxygen-containing groups of ACF, leading to the increase of carboxylic, hydroxylic, and carbonylic groups and the slight decrease of the lactonic groups. Furthermore, this process can also increase the surface area and total pore volume of ACF. Due to the new micropore formation and some pore enlargement, the micropores became smaller, and the mesopores and macropores got bigger.

Sorption of lead from aqueous solution by chemically modified carbon adsorbents

An indigenously prepared, steam activated and chemically modified carbon from husk and pods of Moringa oleifera (M. oleifera), an agricultural waste, was comparatively examined as an adsorbent for the removal of lead from aqueous solutions. Studies were conducted as a function of contact time, initial metal concentration, dose of adsorbent, agitation speed, particle size and pH. Maximum uptake capacities were found to be, 98.89, 96.58, 91.8, 88.63, 79.43% for cetyltrimethyl ammonium bromide (CTAB), phosphoric, sulfuric, hydrochloric acid treated and untreated carbon adsorbents, respectively. Bangham, pseudo-first- and second-order, intra-particle diffusion equations were implemented to express the sorption mechanism by utilized adsorbents. Adsorption rate of lead ions was found to be considerably faster for chemically modified adsorbents than unmodified. The results of adsorption were fitted to both the Langmuir and Freundlich models. Satisfactory agreement between the metal uptake capacities by the adsorbents at different time intervals was expressed by the correlation coefficient (R(2)). The Langmuir model represented the sorption process better than the Freundlich one, with R(2) values ranging from 0.994 to 0.998.

Simultaneous adsorption of copper ions and humic acid onto an activated carbon

In this study, simultaneous adsorption of copper ions and humic acid (HA) from Aldrich onto an activated carbon is investigated. It is found that the HA adsorption in the absence of copper decreases as the pH is increased. It leads to a reduction of 34.7% in the specific surface area of carbon. There exists a critical concentration (CC) of HA for copper adsorption. At HA concentrations < CC, a decrease in copper adsorption is observed; however, the HA improves the adsorption at HA concentrations > CC. An increase in ionic strength can enhance the copper uptake; however, zinc and/or cobalt ions have an insignificant influence on copper adsorption. The adsorption is significantly increased by citric acid, whereas addition of EDTA slightly decreases the uptake. An intraparticle diffusion model is successfully used to describe the copper adsorption kinetics.