Values Of Thermodynamic Constants Research Articles

Investigation of Adsorption of Cobalt-phthalocyanine from Aqueous Waste Stream Using UVM-7/Ag

The effect adsorption of cobalt-phthalocyanine-3,4’,4”,4”’- tetrasulfonicacid tetrasodium salt [Co(tsPc)-4•4Na＋] onto UVM-7/Ag mesoporous material was investigated. In addition, X-ray diffraction (XRD), scanning electron microscopy (SEM), and nitrogen adsorptiondesorption measurement were used to examine the morphology and the microstructure of the obtained composite. Various parameters including solution adsorbent dosage, contact time, initial dye concentration and temperature were systematically studied. Equilibrium data fitted well the Langmuir models; moreover, the fitness suggests that the adsorption be monolayer and physical in nature. Kinetic studies showed that the adsorption process could be better described by the Lagergren pseudosecond- order models. Thermodynamic constant values (ΔG < 0, ΔH< 0 and ΔS< 0) demonstrated that the adsorption reactions of Co(tspc)-4 onto UVM-7/Ag were feasible, spontaneous, and exothermic under the examined conditions.

Functionalized agricultural biomass as a low-cost adsorbent: Utilization of rice straw incorporated with amine groups for the adsorption of Cr(VI) and Ni(II) from single and binary systems

The adsorption of Cr(VI) and Ni(II) applying amine-functionalized modified rice straw (MRS) as an adsorbent in single and binary systems was investigated. The MRS was characterized by Fourier transform infrared spectroscopy (FTIR), Thermo-gravimetric Analysis (TG), Brunauer–Emmett–Teller (BET) analysis, Scanning Electron Microscope (SEM) and the Energy Dispersive Spectrometer (EDS) analysis. The adsorption study was conducted systematically by varying adsorbent dosage, initial pH value, temperature and initial metal ion concentration. The results showed that the maximum adsorption capacity for Cr(VI) was 15.82mg/g with MRS dosage 10g/L at pH 2.0, temperature 318K and initial metal ion concentration 200mg/L, and 3.95mg/g for Ni(II) at pH 7.0, temperature 318K and initial metal ion concentration 80mg/L with MRS dosage 10g/L, respectively. The adsorption data were suitable for Langmuir isotherm model better both in single and binary systems. The pseudo-second-order model could better describe the adsorption process in single and binary systems. In binary systems, the existence of Ni(II) hindered the adsorption of Cr(VI) but the removal of Ni(II) was enhanced with the existence of Cr(VI) ions. Thermodynamic constant values (ΔG0<0, ΔH0>0, ΔS0>0) illustrated that the adsorption of Cr(VI) and Ni(II) onto MRS were spontaneous and endothermic.

Design and operation of fixed bed laterite column for the removal of fluoride from water

Laterite, the geomaterial, is used as an adsorbent for the removal of fluoride from drinking water. The equilibrium data obtained through batch study is fitted to the Langmuir and Freundlich isotherm. The values of thermodynamic constants and the separation factor indicate that fluoride removal on laterite is feasible. The solution movement through the laterite column bed was predicted from the mass balance concept. The nature of breakthrough curve was found to be influenced by several operational parameters, adsorption capacity and adsorption rate. The governing influence of primary adsorption zone formation was characterized by different secondary parameters. The laterite bed capacity under dynamic condition was determined from the breakthrough curve and is higher compared to that evaluated from static mode. Sharp breakthrough curve was obtained at higher feed fluoride concentration and lesser bed height. Column capacity does not change up to a flow rate of 6.5 cm3 min−1 even for the highest concentration studied. It is found that a maximum of 80.4% of retained fluoride was eluted at pH ≥ 9.8. In a typical set with initial fluoride concentration of 20 mg dm−3 and bed height 20 cm the retention–elution process was repeated for a number of times. It is found that the capacity though decrease with the cycle number, it remains within 68% after five cycles.

Interaction of Alkyltin(IV) Compounds with Ligands of Interest in the Speciation of Natural fluids: Complexes of (CH3)2Sn2+ with Carboxylates

Complex formation by (CH3)2Sn 2+ with acetate (ac), malonate (mal), 1,2,3-propanetricarboxylate (tricarballylate, tca) and 1,2,3,4-butanetetracarboxylate (btc) ligands in aqueous solution is reported. The study has been performed by potentiometry ([H + ]‐glass electrode) at T = 25 °C, and in the 0 < I < 1 mol dm 2 3 ionic strength range. In order to evaluate the salt effects on the formation constants of the complex species, and to contribute to the definition of the chemical speciation of diorganotin(IV) compounds in natural waters where carboxylic ligands are naturally present, interactions of NaCl (which is the major component of all natural fluids), with the components of the systems under investigation have also been considered. A model for the ionic strength dependence of the formation constant was used in order to calculate the values of thermodynamic constants, at infinite dilution, for all the proposed species, by considering hydrolytic species too. A relationship between the charges on the different ligands considered and the stabilities of the complex species formed is also discussed. © 1997 by John Wiley & Sons, Ltd.