Metallic adsorption

Diehl R D and McGrath R 1996 Structural studies of alkali metal adsorption and coadsorption on metal surfaces Surf. Sc/. Rep. 23 43... 

Physics and Chemistry of Alkali Metal Adsorption," in H. P. Bonzel, A. M. Bradshaw, and G. Erti, eds.. Material Science Monograph, Vol. 57, Elsevier, New York, 1989. 

Besides trace metals, adsorptive stripping voltammetry has been shown to be highly suitable for measuring organic compounds (including cardiac or anticancer drugs, nucleic acids, vitamins, and pesticides) that exhibit surface-active properties. 

Hydrogen adsorption from solution Oxygen adsorption from solution Underpotential deposition of metals Adsorption of probe molecules from solution ... 

T. Aruga, and Y. Murata, Alkali-metal adsorption on metals, Progress in Surface Science 31, 61-130 (1989). 

We have reviewed experiments on two classes of systems, namely small metal particles and atoms on oxide surfaces, and Ziegler-Natta model catalysts. We have shown that metal carbonyls prepared in situ by reaction of deposited metal atoms with CO from the gas phase are suitable probes for the environment of the adsorbed metal atoms and thus for the properties of the nucleation site. In addition, examples of the distinct chemical and physical properties of low coordinated metal atoms as compared to regular metal adsorption sites were demonstrated. For the Ziegler-Natta model catalysts it was demonstrated how combination of different surface science methods can help to gain insight into a variety of microscopic properties of surface sites involved in the polymerization reaction. 

There is further emphasis on adsorption isotherms, the nature of the adsorption process, with measurements of heats of adsorption providing evidence for different adsorption processes - physical adsorption and activated adsorption -and surface mobility. We see the emergence of physics-based experimental methods for the study of adsorption, with Becker at Bell Telephone Laboratories applying thermionic emission methods and work function changes for alkali metal adsorption on tungsten. 

Less complex techniques have been reported to be useful to study the acidic and alkaline treatment processes of biosorbents and the role of carboxyl and carboxylate groups in metal adsorption. Rakhshaee and coworkers101 used potentiometric titration curves to assess the content of such groups in L. minor biomass treated with NaOH and HC1. The results showed an increase (up to 25%) in the adsorption of Hg(II), Cr(III), Cr(VI), and Cu(II) with NaOH-treated biomass as a consequence of an increase of -COO- groups (0.92-2.42 mmol/g). On the contrary, the -COOH groups increase observed (1.50-2.41 mmol/g) due to the acidic treatment led to a decrease in the metal ions uptake (up to 33%) despite activation by the chloride salts. 

Demirbas, A., Heavy metal adsorption onto agro-based waste materials A review, Journal of Hazardous Material, 157, 220-229, 2008. 

Reed, B. and Nonavinakere, S., Metal adsorption by activated carbon—effect of complexing ligands, competing adsorbates, ionic strength, and background electrolyte, Sep Sci Technol, 27 (14), 1985-2000, 1992. 

Electrochemical reactions are driven by the potential difference at the solid liquid interface, which is established by the electrochemical double layer composed, in a simple case, of water and two types of counter ions. Thus, provided the electrochemical interface is preserved upon emersion and transfer, one always has to deal with a complex coadsorption experiment. In contrast to the solid/vacuum interface, where for instance metal adsorption can be studied by evaporating a metal onto the surface, electrochemical metal deposition is always a coadsorption of metal ions, counter ions, and probably water dipols, which together cause the potential difference at the surface. This complex situation has to be taken into account when interpreting XPS data of emersed electrode surfaces in terms of chemical shifts or binding energies. 

Soil pH strongly affects adsorption of Cd, Zn, and Pb in soils, but less so for Cu. In addition, Ca2+ is the major soil solution cation of arid soils. Ca2+ has been shown to be important in inhibiting divalent heavy metal sorption in calcareous soils. Theoretically, the presence of Ca2+ in soil solution may reduce metal adsorption in arid soils. However, high pH increases overall metal adsorption in arid soils. 

Metal sorption on Fe/Al oxides is an inner sphere complexion. The formation of a surface-metal bond releases protons for every metal ion adsorbed. Heavy metal sorbed on Fe oxides can be exchanged only by other metal cations having a similar affinity or by H (McBride, 1989). Metal adsorption on Fe oxides is an initial rapid adsorption reaction, followed by slow diffusion (Barrow et al., 1989). Metal ions (Ni2+, Zn2+ and Cd2+) slowly... 

Cavallaro and McBride (1984a) observed that the removal of Fe oxides from two clay soils reduced Zn adsorption. Shuman (1976) reported that the removal of Fe oxides resulted in an increase or decrease in Zn adsorption, but later in another similar study (1988) he found that the removal of either amorphous or crystalline Fe oxides increased Zn adsorption capacity and decreased Zn-bonding energy. The author explained that adsorption sites on the Fe oxide coatings were not as numerous as those released when the coatings were removed. Elliott et al. (1986) observed that DCB extraction of Fe oxides from two subsoils of the Atlantic Coastal Plain increased heavy metal adsorption. Wu et al. (1999) found that Cu adsorption on the fine clay fraction increased after dithionite treatment with possible exposure of much more high-affinity sites for Cu on the fine clay. 

In summary, the removal of organic matter and Fe oxides significantly changes the physicochemical and surface chemical properties of soils. Thus, this pretreatment affects the overall reactivity of heavy metals in soils. The removal of organic matter and Fe oxides may either increase or decrease heavy metal adsorption. The mechanisms responsible for the changes in metal adsorption in soils with the removal of organic matter and Fe oxides include increases in pH, surface area, CEC and electrostatic attraction, decreases in the ZPC, shifts of positive zeta potentials toward... 

Both organic and inorganic ligands such as Cl and dissolved organic carbon (fulvie acid and carboxylic acids) decrease metal adsorption. In the arid soils with higher pH, folic acids increase the solubility of metals such as Cu and Zn. The interaction between the transition of heavy metals and silicate surfaces was reviewed by McBride (1991). 

Johnson KJ, Cygan RT, Fein JB (2006) Molecular simulations of metal adsorption to bacteria surfaces. Geochim Cosmochim Acta 70 5075-5088 Jokic A, Frenkel AI, Vairavamurthy MA, Huang PM (2001) Bimessite catalysis of the Maillard reaction and its significance in natural humification. Geophys Res Lett 28 3899-3902... 

Daughney CJ, Fein JB, Yee N (1998) A comparison of the thermodynamics of metal adsorption onto two common bacteria. Chem Geol 144 161-176... 

Daughney CJ, Fowle DA, Fortin D (2001) The effect of growth phase on proton and metal adsorption by Bacillus subtilis. Geochim Cosmochim Acta 65 1025-1035... 

Fein JB, Daughney CJ, Yee N, Davis TA (1997) A chemical equilibrium model for metal adsorption onto bacterial surfaces. Geochim Cosmochim Acta 61 3319-3328... 

Fein JB, Martin AM, Wightman PG (2001) Metal adsorption onto bacterial surfaces development of a predictive approach. Geochim Cosmochim Acta 65 4267 4273... 

Carrizosa MJ, Hermosin MC, Koskinen WC, Cornejo J (2004) Interactions of two sulfonylurea herbicides with organoclays. Clays Clay Miner 52 643-649 Celis R, Hermosin MC, Cornejo J (2000) Heavy metal adsorption by functionalized clays. Environ Sci Technol 34 4593-4599 Chappell MA, Laird DA, Thompson ML, Li H, Teppen BJ, Johnston CT, Boyd SA (2005) Influence of smectite hydration and swelling on atrazine sorption behavior. Environ. Sci Technol 39 3150-3156 Chiou CT (1989) Theoretical considerations of the partition uptake of nonionic organic compounds by soil organic matter. In Sawhney BL, Brown K (eds) Reactions and movement of organic chemicals in soils. Soil Science Society of America, Madison, WI, pp 1-29... 

However, the platelet nanofibers (PL-CNF) carry only about two-thirds of the loaded cobalt, and the nanotubes (MW-CNT) showed the most inefficient functionalization performance, exhibiting barely 50% of metal adsorption. 

In the case of trace metals, adsorption is typically much faster than the time intervals for which it is practically possible to separate the cells. Therefore, in practice, values of kf and kr are most often estimated by assuming that water loss from the hydrated cation is rate-limiting (Eigen-Wilkins mechanism, see Section 4.3.1 above). In some cases, uptake transients can be observed at the start of a short-term uptake experiment or by using pulse-chase experiments for which a metal solution containing a radioactive tracer is replaced by a solution... 

Despite the intriguing results suggesting a kinetically limiting surface adsorption of Fe in oceanic surface waters [192], few other experiments have been performed that specifically examine the kinetics of the metal adsorption process. Among other complications, kinetic control of the transport would be expected to cause undersaturation of the carriers that could could produce a gradient of variable [metal]/[ligand] that would affect the overall flux. This would appear to be an area that is ripe for future research. 

Lion, L. W., Altmann, R. S. and Leckie, J. O. (1982). Trace-metal adsorption characteristics of estuarine particulate matter evaluation of contributions of iron/ manganese oxide and organic surface coatings, Environ. Sci. Technol., 16, 660-666. 

---