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Bisphenol-A (BPA) is an important industrial chemical generally introduced into the environment through the wastes of factories producing, for example, paper, plastics and plastic products-making industries. Consequently, factory effluents and sewage containing BPA are sources of contamination in the aquatic environments. The objective of this research is to study the efficiency of BPA removal from aqueous solutions using two chitosans, (1) synthesized chitosan; a waste derived adsorbent from waste seafood shell and which was synthesized in our laboratory and (2) commercial chitosan a chitosan sample obtained commercially. The effects of process parameters such as solution pH, adsorbent dose, contact time, and initial concentration of BPA have been examined and compared. The results obtained from this study indicated that the efficiency of removal declines with increased contaminant concentration and decreased adsorbent dose. The optimal pH for maximum adsorption for both chitosan adsorbents was 5. The adsorption data were fitted into six isotherm models namely Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Redlich–Peterson and Sips and the isotherm parameters were determined. Furthermore, the kinetics of the process were correlated by three kinetic models, namely, the pseudo-first-order, pseudo-second-order and intra-particle diffusion models. The kinetic experiments revealed that both chitosan adsorbents follow the pseudo-second-order kinetic model. The isotherm studies demonstrated that both adsorbents follow the Langmuir model. Based on the results, chitosan, synthesized (SC) and commercial (CC), is an efficient, novel and inexpensive alternative for the removal of BPA from aqueous solution. [ABSTRACT FROM AUTHOR]

In the present study, multi-walled carbon nanotubes (MWCNTs) have been used for the rapid removal of four trihalomethanes (THMs) from aqueous solutions. The adsorption capacity of THMs onto MWCNTs was reasonably constant in the pH range of 5-7 but decreased as the pH exceeded 7. Four equilibrium isotherm models, namely, Langmuir, Freundlich, Temkin, and Sips, were applied to determine the best-fit equilibrium expressions. The results showed that all four experimental adsorption isotherms were best correlated by using the Sips model. The maximum adsorption capacities for the CHCl, CHClBr, CHClBr and CHBr were found to be 10.98, 6.85, 6.57, and 5.95 mg/g, respectively. The rate of adsorption followed the pseudo-second-order kinetic model. Furthermore, four nonlinear regression-based equations were also derived to model THM adsorption from aqueous solutions by MWCNTs. The modeling results clearly indicated that the empirical formulations satisfactorily described the behavior of the present adsorption process for CHCl ( R = 0.949), CHClBr ( R = 0.945), CHClBr ( R = 0.936), and CHBr ( R = 0.919). The overall results confirmed that MWCNTs could be a promising adsorbent material for THMs removal from aqueous solutions. [ABSTRACT FROM AUTHOR]

In the present paper, the removal of ethidium bromide (EtBr) from aqueous solutions in a batch system using natural (NP) and aluminium-coated pumice (ACP) as alternative low-cost adsorbents was investigated. The maximum adsorption capacity, q m (mg/g) was 58.82 and 76.92 mg/g for NP and ACP, respectively, operating at an initial pH of 8, an adsorbent dose of 8 g/L, a contact time of 210 min and an initial EtBr concentration of 30 mg/L. The equilibrium data of both adsorbents fitted the Freundlich isotherm model, indicating the heterogeneity of the adsorbent surface. In addition, the adsorption rate of both adsorbents was well described by the pseudo-second-order kinetics model. This indicated chemisorption was the rate-controlling step of the adsorption process which occurred by ion exchange. Within the performed study, a three-layer artificial neural network (ANN) model was also developed to predict the efficiency of EtBr removal. Computational results clearly demonstrated that the ANN model was able to predict the combined effect of initial pH, adsorbent dose, contact time and initial EtBr concentration on the adsorption efficiency with a very high determination coefficient ( R 2 = 0.998) and a low relative error (RE = 0.037). [ABSTRACT FROM AUTHOR]

This paper explores the possibility of employing Oxidized Multiwalled Carbon Nanotubes (MWCNT-COOH) for the removal of toxic Linear Alkyl benzene Sulfonate (LAS). LAS is among the most toxic industrial and house hold waste surfactants. This study discusses the feasibility of removing LAS from aqueous solutions using MWCNT-COOH. The effects of operational parameters such as solution pH, LAS concentration and contact time on the removal of LAS were studied. The four linear forms of Langmuir, Freundlich, Dubinin Radushkevich (D-R) and Temkin models were applied to determine the best fit of equilibrium expressions. Our results showed that the experimental adsorption isotherm complies with Freundlich model. The maximum adsorption capacity was determined to be 62.5 mg/g with an initial LAS concentration of 4 mg/L at pH 3 in 45 min. Fitting of the experimental results to kinetic models showed the relevance of the pseudo second-order (R 2 > 0.99) model for LAS. Our results confirmed that MWCNT-COOH would be promising adsorbents for LAS removal in aqueous solution. [ABSTRACT FROM AUTHOR]

Azinphos-methyl and chlorpyrifos are the organophosphorous pesticides which pose serious threats to the environment including their detrimental effect on humans and, therefore, their removal from the environment is a must. Hence, in the present paper the ultrasound technique was applied to remove the above-mentioned hazardous compounds. For this, the effect of influential parameters such as pH, initial pesticide concentration, frequency, electric power and treatment time on the ultrasound degradation of azinphos-methyl and chlorpyrifos was well investigated and elucidated. The results obtained showed that azinphos-methyl and chlorpyrifos were effectively and rapidly degraded by the ultrasound technique. Thus, the operating optimal conditions (initial pH 9, initial pesticide concentration 1 mg/L, frequency 130 kHz, electric power 500 W and treatment time 20 min) lead to a degradation of 78.50% for azinphos-methyl and of 98.96% for chlorpyrifos with in 20 min of contact time. Two multiple regression-based equations were derived to describe the degradation process of the pesticides by the ultrasound treatment. The result of this study showed that the polynomial equations satisfactorily described the behavior of the present process for various operating conditions. [ABSTRACT FROM AUTHOR]

In the present study, defluoridation study of liquid phase with the help of multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) were well investigated and elucidated. The impact of different experimental conditions such as solution pH, initial fluoride concentration, adsorbent dose, and contact time was well studied and optimized for the maximum fluoride removal from water. The experimental data were fitted by the Freundlich, Langmuir and Dubinin–Radushkevich (D–R) isotherm models and the related equilibrium constants were calculated. The results of the isotherm studies showed that fluoride removal by both adsorbents followed the Freundlich isotherm model. Kinetic studies were conducted and the results demonstrated that the experimental data were fitted well with the pseudo-second order kinetic model. Furthermore, two multiple regression-based equations were also derived to model the removal of fluoride from aqueous solutions by the carbon nanotubes. This study demonstrated that the polynomial equations satisfactorily described the behavior of the present defluoridation process for both MWCNTs ( R 2 = 0.913) and SWCNTs ( R 2 = 0.941). [ABSTRACT FROM AUTHOR]