A temperature-jump relaxation technique is used to monitor reversible adsorption/desorption kinetics at the reversed-phase C1 -silica/solution interface. A Joule discharge is used to heat a packed bed of trimethylchlorosilane-derivatized silica gel on a microsecond time scale. Single-exponential relaxation kinetics are observed for adsorption of an ionic fluorescent probe, l-anilino-8naphthalenesulfonate, to a Cl-silica surface from methanol/ water solution. The relaxation rate increases with concentration of solute in solution, which shows that adsorption kinetics are detectable in the relaxation. The adsorption rate of the ionic probe is slower than diffusioncontrolled, exhibiting significant influence over the adsorption equilibrium constant The adsorption rate of .ZV-phenyi-1 -naphthylamine is indistinguishable from the diffusion limit, indicating a negligible barrier to adsorption for this neutral species.Separations in reversed-phase liquid chromatography result from complex thermodynamic and kinetic processes involving the transfer of solutes between the mobile and stationary phases.Knowledge of kinetics in this process is important for the design of effective column materials and for fundamental understanding of the chemistry of bonded phases and the retention behavior of analytes. The kinetics of chromatographic retention on bonded hydrocarbon stationary phases are not well-understood. Two approaches to gaining information about adsorption/desorption kinetics in chromatographic systems have been developed.Chromatographic techniques have been used to investigate these kinetics by measuring plate heights versus flow velocity and correcting for the estimated contributions from dispersion and diffusion.1 Despite questions raised about the assumptions underlying this method1 2 and errors associated with the fitting of peak shapes to determine kinetic parameters,3 two general conclusions can be made from band-broadening studies of adsorption/desorption kinetics: that slow rates of desorption dominate kinetic contributions to band broadening and that barriers to adsorption are much smaller and difficult to detect in the shape of eluted peaks.A more direct approach to measuring adsorption/desorption rates is the use of relaxation kinetic methods. In relaxation kinetics, the equilibrium of a reversible process is shifted by a rapid change of conditions, such as temperature, pressure, or

BACKGROUND Taking advantage of their voluminous availability as agricultural or industrial waste and ease of chemical modification, it is always a promising strategy to fabricate waste biomass materials as adsorbents for selective uptake of concerned metal ions. In the present paper, an environmentally “green” adsorbent was developed by introduced triethylamine (TEA) group on persimmon waste and its potentiality for adsorption, desorption behavior, and mechanism of molybdenum were evaluated. RESULTS As compared to the persimmon tannin waste based other adsorbents, TEA‐CPT gel exhibited reasonable uptake capacity (287.21 mg g−1) and selectivity for the adsorption of molybdenum. Chelation action between the O‐atom of molybdenum poly‐anions and the N‐atom of tertiary amine is considered to be responsible for selective binding and sorption of molybdenum over co‐existing metal ions. In addition, the adsorbed molybdenum was very effectively eluted with low concentration NH3H2O solution (1%) in column experiment and the regenerated adsorbent exhibited undiminished sorption efficiency for at least six cycles. CONCLUSION Results show that the TEA‐CPT gel modified by triethylamine has the good stability and the selectivity, etc make it a promising candidate for selective recovery of molybdenum from aqueous system. © 2014 Society of Chemical Industry

The influence of the alkyl chain length on the kinetics of solute retention at reversed-phase chromatographic surfaces is examined. A Joule-discharge temperature-jump relaxation experiment was used to monitor reversible sorption/desorption kinetics at C4- and C8-modified silica/solution interfaces. Biexponential sorption/desorption relaxation kinetics were observed for a charged fluorescent probe, 1-anilino-8-naphthalenesulfonate (ANS), on both C4- and C8-silica surfaces. Both relaxation rates on C4 surfaces were sufficiently slow to be measured and increased linearly with solute concentration. One of the relaxations on a C8 surface is too fast to be resolved from the heating rate, similar to behavior of the solute on a longer chain C18-silica. These observations suggest that sorption kinetics on the intermediate chain length surfaace, C4-silica, are different from kinetics on longer chain length surfaces, C8- and C18-silica. From a fit of the data to a two-step kinetic model, the rates of both adsorption and partition of the ionic probe on the C4 chain are estimated; both rates exhibit significant influence over the equilibrium constant. The relaxation rate of a neutral probe, N-phenyl-1-naphthylamine, is also measured; the results indicate a fast (diffusion-controlled) adsorption step, followed by a detectable barrier to partition that is similar to the partition barrier for ANS on the C4-silica surface. These results show that the alkyl chain length of modified silica strongly influences retention kinetics.

In the present study, crab shell chitin (CSC) has been used for the recovery of Mo(VI) from Cu/Fe containing solutions. The CSC gel showed a high affinity for Mo(VI) compared with other adsorbents, and the maximum adsorption capacity was evaluated as 252.27 mg g −1 in the case of pH 1, which could be explained by the structure of the CSC gel, containing more reactive −OH and/or −NH groups binding Mo(VI) ions. The experimental results fit satisfactorily to the Langmuir isotherm in comparison to the Freundlich, Temkin, and Dubinin−Radushkevich models. Biosorption kinetics data were successfully modeled using a nonlinear pseudo-second-order model. The sorption mechanism was investigated in detail through FTIR, EDS, and the percentage of positively charged amide analyses. Moreover, its excellent adsorption properties and applicability for Mo(VI) were demonstrated by the recovery and separation of Mo(VI) from Cu or/and Fe binary and ternary mixtures.

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