Search

The development of cost effective and environmentally benign adsorbents for arsenic removal is absolutely required due to arsenic contamination of water sources in many regions around the globe. The use of materials which are locally available in the affected regions is important for successful implementation of the developed technologies in rural areas. In this regard, we treated volcanic rocks (red scoria and pumice) locally available in Ethiopia with an aluminum sulphate solution and evaluated these materials for their capacity to remove As(V) from aqueous systems. The adsorbents were characterized using ICP-OES, EDX, SEM and BET. The experimental sorption data fitted well a Freundlich isotherm and the pseudo-second-order model was found to be more suitable than the pseudo-first-order model to describe the adsorption kinetics. The Langmuir maximum adsorption capacity was 0.18 mg/g for aluminum-treated red scoria (Al-Rs) and 2.68 mg/g for aluminum-treated pumice (Al-Pu). The effect of pH, adsorbent dose, initial As(V) concentration and interfering ions on arsenic adsorption were studied. The leaching of aluminum from the adsorbent during the adsorption process was also investigated. Results of column experiments indicated that Al-Pu is suitable to treat low concentration of As(V) contaminated water. The Al-Pu adsorbent is recyclable with only about 9% loss of its original efficiency after the 3 rd adsorption cycle (99.5%–90.2%). The data obtained from both batch and column studies indicate that Al-Rs and Al-Pu remove As(V) effectively from aqueous systems, with the latter being more efficient. [ABSTRACT FROM AUTHOR]

Mesoporous carbons were synthesized via both soft and hard template methods and compared to a commercial powder activated carbon (PAC) for the adsorption ability of bisphenol-A (BPA) from an aqueous solution. The commercial PAC had a BET-surface of 1027 m2/g with fine pores of 3 nm and less. The hard templated carbon (CMK-3) material had an even higher BET-surface of 1420 m2/g with an average pore size of 4 nm. The soft templated carbon (SMC) reached a BET-surface of 476 m2/g and a pore size of 7 nm. The maximum observed adsorption capacity (qmax) of CMK-3 was the highest with 474 mg/g, compared to 290 mg/g for PAC and 154 mg/g for SMC. The difference in adsorption capacities was attributed to the specific surface area and hydrophobicity of the adsorbent. The microporous PAC showed the slowest adsorption, while the ordered mesopores of SMC and CMK-3 enhanced the BPA diffusion into the adsorbent. This difference in adsorption kinetics is caused by the increase in pore diameter. However, CMK-3 with an open geometry consisting of interlinked nanorods allows for even faster intraparticle diffusion. [ABSTRACT FROM AUTHOR]

Abstract: The reaction kinetics of the liquid-phase transesterification of ethyl acetate with methanol to methyl acetate and ethanol have been investigated in a temperature range from 303.15K to 333.15K as a model reaction for the transesterification of triglycerides in the production of biodiesel. The reaction has been catalyzed by the acidic ion-exchange resin Lewatit K1221. The effect of the initial reactant molar ratio and the temperature on the reaction kinetics was investigated and kinetic models, based on pseudo-homogeneous (PH), Eley–Rideal (ER) and Langmuir–Hinshelwood (LH) mechanisms, were used to describe the reaction rate. Because of the pronounced non-ideality of the reaction mixture, the kinetics were expressed in terms of activities. Additional experiments, based on a D-optimum design of experiments, were performed to obtain more precise parameter estimates as required for final model discrimination. The kinetic model with the surface reaction of adsorbed methanol with ethyl acetate from the bulk as the rate-determining step according to an Eley–Rideal mechanism was found to best describe the observed kinetics. The corresponding rate equation agrees with a reaction mechanism in which physically adsorbed methanol reacts with protonated ethyl acetate. [Copyright &y& Elsevier]

Mesoporous MIL-101(Cr) is used as host for a ship-in-a-bottle type adsorbent for selective U(VI) recovery from aqueous environments. The acid-resistant cage-type MOF is built in-situ around N,N-Diisobutyl-2-(octylphenylphosphoryl)acetamide (CMPO), a sterically demanding ligand with high U(VI) affinity. This one-step procedure yields an adsorbent which is an ideal compromise between homogeneous and heterogeneous systems, where the ligand can act freely within the pores of MIL-101, without leaching, while the adsorbent is easy separable and reusable. The adsorbent was characterized by XRD, FTIR spectroscopy, nitrogen adsorption, XRF, ADF-STEM and EDX, to confirm and quantify the successful encapsulation of the CMPO in MIL-101, and the preservation of the host. Adsorption experiments with a central focus on U(VI) recovery were performed. Very high selectivity for U(VI) was observed, while competitive metal adsorption (rare earths, transition metals...) was almost negligible. The adsorption capacity was calculated at 5.32 mg U/g (pH 3) and 27.99 mg U/g (pH 4), by fitting equilibrium data to the Langmuir model. Adsorption kinetics correlated to the pseudo-second-order model, where more than 95% of maximum uptake is achieved within 375 min. The adsorbed U(VI) is easily recovered by desorption in 0.1 M HNO 3 . Three adsorption/desorption cycles were performed. [ABSTRACT FROM AUTHOR]

The synthesis of soft template mesoporous carbons was optimized with a Definitive Screening Design (DSD), a recently developed design of experiments (DOE) method. Such a design enables to investigate the effect of synthesis parameters including their interactions or quadratic effects, on the material properties. The mesopore formation was influenced mostly by the ratio precursor/surfactant, other significant effects were curing time and carbonization temperature. The micropore formation was significantly influenced by the curing time and the carbonization temperature. The DSD was used to optimize the mesoporous surface area which could improve its potential as adsorbent. Via a validation experiment, a material with optimal mesoporous surface area (393 m 2 /g) was synthesized, showing a total surface area of 712 m 2 /g and a large pore volume of 0.78 cm 3 /g. The different mesoporous carbons, synthesized according to the DSD, were tested for the adsorption of bisphenol A (BPA). This allowed to investigate the effect of material properties on the adsorption capacity, which varied between 12 and 163 mg/g. Via regression analysis, the mesoporous surface area and the carbon content of the mesoporous carbons were identified as the main factors influencing the adsorption of BPA. [ABSTRACT FROM AUTHOR]