Selective adsorption of organic homologues onto activated carbon from dilute aqueous solutions: Solvophobic interaction approach: Part IV. Effect of simple structural modifications with aliphatics

Abstract

Preferential adsorption of organic compounds onto activated carbon from dilute aqueous solutions is studied to develop a comprehensive theoretical basis for predicting the adsorption of structurally different isomers for different homologous series. The fundamental multidimensional approach of the solvophobic (c+) thermodynamic theory is further refined and used to correlate the extent of adsorption for the comprehensive theory with the overall standard net free energy change (ACnet/RT) for the association-adsorption reaction in solution, and for the simplified theory with the cavity surface area of the solute (TSA).Experimental adsorption isotherms of two homologous series (12 aliphatic alcohols and 21 aliphatic ketones) were measured and used to test and compare the c+ theory with seven independent parameters characterizing the sorbates. Several experimental innovations for measuring equilibrium adsorption isotherms are introduced to reduce the possible loss of sorbate during the procedure and to provide reproducible and reliable results.Comparing the coefficients of linear correlation (r), the results for 12 aliphatic alcohols give greater than 99% confidence that the r-values are different for hGnet/RT and molecular weight (MW). For the 15 aliphatic ketones, greater than 90% confidence interval is obtained for different r-values for TSA and MW, These results support the contention that simple structural modifications of aliphatic homologous compounds can be used to predict the effect of solutesolvent-sorbent interactions on adsorption. The c+ theory can thus be used to rankorder adsorption intensity of these compounds from the aqueous phase onto activated carbon. SCOPEDuring the past century, little effort has been expended in trying to understand the fundamentals underlying the process of adsorption of solutes from a solvent onto a solid sorbent (Miller, 1980a,b). Several simultaneous developments, such as the need to clean our surface water, the development of extremely sensitive analytical techniques, and the wide use of reverse-phase liquid chromatography, have spurred interest in this field.Most researchers used a phenomenological approach in which equilibrium adsorption models mostly derived from gas-and vapor-phase adsorption, were used to describe adsorption from the liquid phase. This approach either a priori ignored the presence of the solvent, assuming that the dominant interaction was between the solute and sorbent, or included the solvent effect without specifying its role quantitatively. Freundlich (1926), in his classic monograph, describes the first attempts 90 years ago by Traube and others to include the solvent-solute interaction effect through interfacial tension at the solid-liquid interface. Although Defay et al. (1966) a comprehensive interaction theory among solute, solvent, and sorbent is still lacking. Recent attempts to include the solventeffect in aqueous phase adsorption include a semiempirical approach based on partial solubility parameters called the net adsorption energy appro...

QSAR Models To Predict Effect of Ionic Strength on Sorption of Chlorinated Benzenes and Phenols at Sediment–Water Interface

“…Many semi-theoretical models describing the QSARs have been proposed to predict the sorption parameters including the octanol-water partitioning coefficient, the LSE model, (Nirmalakhandan and Speece, 1993;Luehrs et al, 1996), the MCI model (Blum et al, 1994;Nirmalakhandan and Speece, 1988), and the solvophobic theory (Belfort et al, 1984). While utilising the above QSARs, it is hypothesised that the sorption coefficients normalised to the organic carbon fraction of the sediment (K exp oc ) values for pollutants in fact depend upon the background ionic strength of the system and the validity of this approach has been demonstrated by incorporating the ionic strength term into the three QSARs namely octanol-water partitioning coefficient model (Kow model), the LSE model, and the MCI model.…”

“…Many semi-theoretical quantitative structure activity relationships (QSARs) have been proposed to parameterise sorption onto soils/sediments (Baker et al, 1997;Meylan et al, 1992), sorption onto activated carbon (Blum et al, 1994;Luehrs et al, 1996;Belfort et al, 1984), sorption onto wastewater solids (Dobbs et al, 1989), adsorption of organic vapours onto activated carbon (Urano et al, 1982;Nirmalakhandan and Speece, 1993;Prakash et al, 1994), dissolution of compounds (Kamlet et al, 1986;Lane and Loehrs, 1995;Speece, 1988, 1989;Dunnivent et al, 1992), Henry's law constants (Nirmalakhandan and Speece, 1988;Dunnivent et al, 1992;Nirmalakhandan et al, 1997;Brennan et al, 1998), chemical biotransfer (Dowdy et al, 1996), chemical toxicity (Blum and Speece, 1990;Xu and Nirmalakhandan, 1998); and octanolwater partition coefficients (Sablijic et al, 1993). It is well known that the physico-chemical interactions depend on chemical properties of the pollutant such as aqueous solubilities, octanol/water partition coefficients, or structural characteristics including substituted groups on the pollutant molecule, molar volume of the molecule, topology as well as the intrinsic properties like polarity and polarisability of the pollutant molecules (Westall et al, 1985;Kamlet et al, 1986).…”

“…Lately, more attention has been given to applications of QSARs to predict sorption parameters at the soil or sediment interface (Meylan et al, 1992) because such parameterisation can help in a variety of situations including prediction of local and regional impact of aquatic environment, understanding relative importance of fate (Baker et al, 1997) and transport processes in aquatic systems such as oceans, rivers, aquifers, and lakes, remediation of soils, sediments, and aquifers, bioaccumulation, biomagnification, toxicity to life forms, and bioavailability. Some of the most commonly used QSARs for prediction of sorption capacities at the soil-water interface include the octanol-water partitioning coefficient model (Means et al, 1980;Karickhoff, 1981;Piwomi and Banerjee, 1989;Chiou, 1983;Schwarzenbach et al, 1993), the Linear Solvation Energy model (Nirmalakhandan and Speece, 1993;Luehrs et al, 1996), Molecular Connectivity Indices model (Blum et al, 1994;Nirmalakhandan and Speece, 1988;Xu and Nirmalakhandan, 1998); the Solvophobic Theory (Belfort et al, 1984); and the combination of polarisability parameter, molecular connectivity index, and hydrogen bonding index model (Nirmalakhandan et al, 1997). All these QSARs have essentially tried to focus on several complex physico-chemical surface interactions including adsorption, absorption, ion exchange, pore diffusion, redox reaction, precipitation, dissolution, acid/base hydrolysis, formation of co-ordinated complexes giving rise to the polynuclear species (Weber et al, 1991;Banerji et al, 1993;Gao et al, 1998).…”

Washing of Marine Coastal Sand in a Batch Reactor: Sorption and Desorption of BTEX

“…For example, specific studies have been carried out for washing soils/sediments contaminated with organics 2,4,15 and inorganics 1,8,9,13,16 and also modeling the sorption and desorption phenomenon. 17 Many isolated research efforts on development and application of quantitative structure activity relationships (QSARs) for predicting the sorption and desorption equilibrium at the activated carbon/water interface or activated carbon/air interface [18][19][20][21][22] have been reported in the literature. However, no studies on modeling the soil-washing techniques and incorporating the QSARs for prediction of the thermodynamic limits of sorption and desorption into the soil-washing model have been reported.…”

“…Some of the semi-theoretical models describing the QSARs proposed to predict the sorption parameters include the octanol-water partitioning coefficient (Kow model), the linear solvation energy model (LSE model), 19,20 the molecular connectivity indices model (MCI model) 18,21 and the Solvophobic Theory. 22 Among the various QSAR formulations tried (Kow, LSE, and MCI models) for the nonionic hydrophobic organic solvents (such as BTEX), it has been concluded that the MCI group of models is the most suitable QSAR based on an elaborate goodness-of-fit exercise, χ 2 test, and standard error of estimator analyses.…”