Showing papers on "Langmuir published in 2016"

Nanocomposite of carbon nanotubes/silica nanoparticles and their use for adsorption of Pb(II): from surface properties to sorption mechanism

Abstract: This paper demonstrates the synthesis of multi-wall carbon nanotubes and silica nanocomposite (CNT/SiO2). Successful realization of MWCNT/SiO2 nanostructure was observed by scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and high-resolution transmission electron microscopy studies. The as-prepared nanocomposite was evaluated as an adsorbent to remove lead, Pb(II), from aqueous solutions. The resulting MWCNT/SiO2 manifests propitious adsorption performance (~95%) over silica nanoparticles (~50%) and CNTs (~45%). Lagergren’s pseudo-first order, pseudo-second order and intraparticle diffusion models were used to analyse the kinetic data obtained at different initial Pb(II) concentrations. The adsorption kinetic data were described well by the pseudo-second order model with R2 of 0.99. The activation energy (Ea) of the adsorption process was calculated as 15.8 kJ mol−1. Adsorption data were described well by the Langmuir and Temkin models. Th...

Thermodynamic parameters of cadmium adsorption onto orange peel calculated from various methods: A comparison study

Abstract: Thermodynamic adsorption investigation plays a key role in estimating adsorptive mechanisms (i.e., physical or chemical). Accuracy estimation of the thermodynamic parameters is directly dependent on the equilibrium constant between two phases (KC; dimensionless). In this study, the thermodynamic parameters were calculated from the KC constants derived from the adsorption isotherm constants (i.e., Langmuir, Freundlich, and Henry) and partition coefficient, with and without dimensionality consideration. Results showed that the optimal selection of KC is strongly dependent on: the adsorption characteristics (i.e., Henry, Freundlich, and Langmuir) where equilibrium data are actually located; and the correlation coefficient of the van’t Hoff equation. Both the Langmuir and Freundlich constants (dimensionless) are appropriate to calculate the thermodynamic parameters. The Langmuir constants from its four linear forms can be applied to calculate the thermodynamic parameters without significant difference. The Cd(II) biosorption process onto the orange peel (OP) occurred spontaneously (−ΔG°), in an exothermic nature (−ΔH°), and with increased randomness (+ΔS°). The biosorption process involved physical adsorption with minimal activation energy (Ea) and adsorption energy (E). The biosorption phenomenon reached fast equilibrium and reversibility. The negatively charged carboxylic groups (–COO−) on the OP’s surface play an important role (approximately 90%) in Cd2+ biosorption through electrostatic attractions (out-sphere complexes).

Selective adsorption and separation of organic dyes from aqueous solution on polydopamine microspheres.

Abstract: Polydopamine (PDA) microspheres, synthesized by a facile oxidation polymerization route, were evaluated as a potential adsorbent for selective adsorption and separation of organic dyes. The adsorption processes towards nine water-soluble dyes (anionic dyes: methyl orange (MO), eosin-Y (EY), eosin-B (EB), acid chrome blue K (ACBK), neutral dye: neutral red (NR), and cationic dyes: rhodamine B (RhB), malachite green (MG), methylene blue (MB), safranine T (ST)) were thoroughly investigated. The adsorption selectivity of organic dyes onto PDA microspheres was successfully applied for the separation of dyes mixtures. Various influential factors such as solution pH, temperature, and contact time were employed to ascertain the optimal condition for adsorption of representative organic dyes including MB, MG and NR. The pseudo-first-order and pseudo-second-order kinetics models were used to fit the adsorption kinetics process. Five isothermal adsorption models (Langmuir, Dubnin-Radushkevich, Temkin, Freundlich and Harkins-Jura) were used to investigate the adsorption thermodynamics properties. The results showed that the PDA microspheres owned good selective adsorption ability towards cationic dyes. The adsorption kinetics process conformed to the pseudo-second-order kinetics model and the Langmuir isotherm model was more appropriate for tracing the adsorption behavior than other isotherm models. Thus, we can conclude PDA microspheres may be a high-efficiency selective adsorbent towards some cationic dyes.

Removal of methylene blue dye from artificially contaminated water using citrus limetta peel waste as a very low cost adsorbent

Abstract: In the present work, the potential of citrus limetta peel (CLP) as a low cost adsorbent for the removal of Methylene blue (MB) dye was investigated. Batch adsorption studies were conducted to find out how adsorption was affected by various factors like contact time, initial dye concentration, adsorbent dosage, pH and temperature. The experimental data was analysed in the light of Langmuir, Freundlich and Temkin isotherm models. The data was found to be best represented by Langmuir adsorption isotherm with maximum adsorption capacity for monolayer coverage was found to be 227.3 mg/g. The data were analysed in the light of different available kinetic models and was observed to be best followed pseudo-second order kinetics. Desorption of MB-loaded CLP was studied with various desorbing agents and HCl was found to be most effective desorbing agent among HCl, NaOH, NaCl, CH3COOH and deionised doubly distilled water (DDDW). Results suggest that CLP is a very effective low cost adsorbent for the removal of dyes from wastewater.

Adsorptive Removal of Toxic Dye Using Fe3O4–TSC Nanocomposite: Equilibrium, Kinetic, and Thermodynamic Studies

Abstract: Herein, trisodium citrate based magnetite nanocomposite (Fe3O4–TSC) was used for malachite green (MG) dye expulsion from aqueous medium. The adsorption tests were executed at different parameters. The maximum adsorption were took place at pH 4 in 40 min. The equilibrium studies were demonstrated using Langmuir and Freundlich isotherms and better agreement was attained with the Langmuir model. The maximum adsorption capacity (qe) was calculated 435 mg g–1 using Langmuir equation. The kinetic parameters displayed that MG adsorption onto Fe3O4–TSC followed pseudo-second-order kinetic model. Furthermore, the thermodynamic analysis suggested the adsorption of MG onto Fe3O4–TSC was impulsive and exothermic. The desorption studies showed the best recovery of MG dye in 0.1 M HCl. Finally, it was found that Fe3O4–TSC can be effortlessly separated from mixed solutions using external magnetic field.

Adsorption of rhodamine B and methylene blue dyes using waste of seeds of Aleurites Moluccana, a low cost adsorbent

Abstract: Removal of the cationic dyes rhodamine B (RhB) and methylene blue (MB) by waste seeds Aleurites moluccana (WAM) was studied in a batch system. The adsorbent was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), point of zero charge measurement, and the Boehm titration method. The effects of contact time and pH were investigated for the removal of cationic dyes. An increase in pH from 3 to 9 was accompanied by an approximately three-fold increase in the amount of dye adsorbed. The adsorptions equilibrium values were obtained and analyzed using the Langmuir, Freundlich, Sips, and Redlich–Peterson equations, the Sips isotherm being the one that showed the best correlation with the experimental values. The maximum adsorption capacities of the dyes were 178 mg/g for the MB and 117 mg/g for the RhB. The kinetic sorption was evaluated by the pseudo-first-order, pseudo-second-order, and intraparticle diffusion models, where it was observed that sorption follows the pseudo-second-order kinetic model. The study of thermodynamics showed that the adsorption is a spontaneous and endothermic process. The results indicate that waste seeds of A. moluccana could be used as a low cost material for the removal of cationic dyes from wastewater.

β-Cyclodextrin modified graphitic carbon nitride for the removal of pollutants from aqueous solution: experimental and theoretical calculation study

Abstract: A novel β-cyclodextrin modified, multifunctional, layer-by-layer graphitic carbon nitride (g-C3N4/β-CD) was successfully synthesized and applied as an effective adsorbent for the removal of methyl orange (MO) and Pb(II) from aqueous solutions under various environmental conditions (e.g., solution pH, solid content, contact time and temperature). The kinetic results indicated that the adsorption was dominated by chemisorption, and the higher adsorption capacity of g-C3N4/β-CD was attributed to it having more oxygen-containing functional groups than g-C3N4. The Langmuir, Freundlich and Sips models were applied to simulate the adsorption isotherms of MO and Pb(II), and the results demonstrated that the adsorption of MO was attributed to multilayer adsorption, while the coverage adsorption of Pb(II) on the g-C3N4/β-CD was monolayer adsorption. The thermodynamic parameters showed that the adsorption of both MO and Pb(II) was spontaneous and endothermic. The DFT calculations further evidenced the surface complexation and electrostatic interaction of Pb(II) on the g-C3N4 and g-C3N4/β-CD, whereas, the interaction of MO with g-C3N4 and g-C3N4/β-CD was mainly attributed to hydrogen bonds and strong π–π interactions. The results demonstrated that g-C3N4/β-CD is a promising material for the efficient removal of organic and inorganic pollutants in environmental pollution remediation.