Surface tailoring

Biomaterials cover a broad range of properties from those that are designed to be inert to those that are intended to elicit a particular set of biological responses. In the latter category are materials with surfaces tailored to retard blood clotting, or surfaces that bear covalently bound bioactive agents such as enzymes or antigens. 

Our main focus for this review is to briefly and critically describe some of the defluoridation techniques as a means of getting a basis to support the adsorption technique, to evaluate the defluoridation adsorbents now being utilized and those novel defluoridation adsorbents reported in literature over the last two decades, with special reference to drinking water. Emphasis is laid toward the adsorbents availability, fluoride sorption capacity and where applicable their kinetic adsorption characteristics and column performances are reported. Detailed characteristics of fluoride adsorption onto surface-tailored zeolite are provided. In addition, various adsorber configurations are reexamined and challenges to and prospects for their application to less developed countries (LDCs) are discussed. 

Characteristics of fluoride adsorption onto surface-tailored low-silica zeolite... 

Figure 3 summarizes the typical equilibrium data for fluoride sorption on 0.150-0.300 mm surface-tailored zeolite F9. Only the low-concentration range was considered where the Henry s law is applicable. Co-incidentally, fluoride ions exist in natural systems, such as groundwater, at low concentrations. It is observed that the data fit well to the linear isotherm suggesting sorption onto sites with high capacity for fluoride. From Fig. 3, the linear isotherm constant, K ( = 2.337 L/g), was obtained and coupled into the diffusion model, equation (16). 

Fig. 5. Illustration of the scheme of surface-tailored zeolite-water interface with adsorbing fluoride ions found in the region bound between planes 0 and IHP. The interaction leads to the formation of inner-sphere complexes of surface-tailored zeolite/fluoride. Sodium ions do not penetrate the IHP.

The model parameters a and t0 for the adsorption of fluoride onto surface-tailored zeolite were determined by matching equation (28) with experimental data. This was done by minimizing the objective function, , expressed as... 

While a biologically active surface performs well based on the specific biological reaction, it is a highly perturbable surface tailored for the specific reaction that could, in principle, cause other biological reactions. For instance, a heparinized surface seems to increase hemolysis (breakdown of red blood cells). When the biologically active agents wear out, the surface of the treated material returns to the untreated surface, which required the surface modification to be blood compatible in the first place. 

The surface can be further activated with suitable linkers for subsequent immobilization, and here the introduction of carboxymethyl groups has proven a versatile alternative. By choosing different sizes of dextran, ranging from lOkDa to over one million Da, surfaces tailored for speciflc applications can be created. This type of surface modification serves multiple purposes. The hydrogel-like layer provides a highly hydrophilic environment. 

Preferential dissolution of specified sites on the surface of semiconductors results in the generation of a unique etching pattern. In what follows, we shall describe some examples that we have found in recent years, especially focusing on the surface tailoring of cadmium chalcogenide and Ti02 semiconductors. 

Roach P, Farrar D, Perry CC. Surface tailoring for controlled protein adsorption effect of topography at the nanometer scale and chemistry. J Am Chem Soc 2006 128 3939 5. 

Robbins, M. E. Oh, B. K. Hopper, E. D. Schoenfisch, M. H., Nitric Oxide-Releasing Xerogel Microarrays Prepared with Surface-Tailored Poly(dimethylsiloxane) Templates. Chem. Mater. 2005,17,3288-3296. 

Forch, R., Zhang, Z., Knoll, W., 2005. Soft plasma treated surfaces tailoring of structure and properties for biomaterial applications. Plasma Processes Polym. 2, 351—372. http // dx.doi.org/10.1002/ppap.200400083. 

Ismagilov ZR, Kerzhentsev MA, Shikina NV, Lisitsyn AS, Okhlopkova LB, Bamakov CN, et al. Development of active catalysts for low Pt loading cathodes of PEMFC by surface tailoring of nanocarbon materials. Catal Today 2005 102(103) 58-66. 

J. Gurt Santanach, C. Estourn s, A. Weibel, A. Peigney, G. Chevallier and C. Laurent, Sp>ark plasma sintering as a reactive sintering tool for the preparation of surface-tailored Fe-FeA1204-A1203 nanocomposites Scripta Materialia 60(4), (2009), 195-198. 

Core sheath type (C/S) In this type of fibre one of the components is completely surrounded by another component. Core sheath type fibres can be self-bonding (e.g. two components with varying melting points with the lower melting point polymer on the sheath), surface tailored fibres (e.g. sheath containing expensive additives) or filled fibres (e.g. a core of recycled material covered by a sheath with the desired properties). 

The ORR on PtML/PdgCo/C showed the Pt mass activity is 2-3-fold higher that of commercial Pt/C. However, upon the operating conditions, the Co component is subject to diffusion out of the nanoparticles, which engenders more low-coordination sites and so inflicts the catalytic activity. Like Pd-C nanoparticles, PdjCo/C can also be surface tailored by bromine treatment to remove the low-coordination sites and improve the ORR. 

Carrette, L. Friedrich, K.A. Stimming, U. (2000). Fuel Cells Principles, Typ>es, Fuels and Applications. ChemPhysChem, Vol. 1, pp. 162-193 Cavarroc, M. Ennadjaoui, A. Mougenot, M Brault, R EscaUer, R. Tessier, Y. Durand, J. (2009). Performance of Plasma Sputtered Fuel Cell Electrodes with Ultra-Low Pt Loadings. Electrochem. Commun., Vol. 11, pp. 859-861 Cho, J. Denes, F.S. Timmons, R.B. (2006). Plasma Processing Approach to Molecular Surface Tailoring of Nanoparticles Improved Photocatalytic Activity of TiCb. Chem. Mater., Vol. 18, pp. 2989-2996... 

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