Chalcogenide Surfaces

Another possible approach to model mesoporous materials is to mimic the synthesis process of the real material. This strategy has been used by Gelb and Gubbins [62] to develop realistic models for Vycor and controlled pore glasses. The input of such an approach is the representation of the templating surfactants using simplified potentials to describe the interactions involved in the system. Siperstein et al. [63] 

Glassy Bulk S102 obtained by first principles or classical calculationsi  

TEM apparatus. In Fig. 13.5 the darker areas in both TEM images represent the pore walls while the lighter areas represent the pore voids and areas with low densities. The TEM image for the MCM-41 for the atomistic sample of the mesoporous silica captures all the features of the TEM image for the real sample. 

Nitrogen adsorption at low temperature is a routine characterization technique of nanoporous materials. For instance, the specific surface of porous materials is usually assessed from adsorption experiments (prior to capillary condensation of the fluid) on the basis of the Brunauer, Emmett, and Teller (BET) method. The BET model corresponding to the N2 adsorption isotherm at 77 K in the atomistic model of MCM-41 materials fits very well the simulated data with a correlation coefficient = 0.999 (see [39] for the comparison). We found Sbet 1000 m /g (the latter value is obtained by considering as the surface area occupied by an adsorbed N2 molecule, A 2 = 0.162 nm ) and C = 100. The value obtained for C 

Coasne and Ugliengo [39] provided also a theoretical picture of adsorption in regular silica pores. In particular, they show that the simulated adsorption/desorption isotherm can be described using available theoretical models. In case of capillary condensation (such as for N2 in the present work), the thermodynamically approach known as the Derjaguin-Broekhoff-DeBoer model [72, 73], provides a comprehensive picture of adsorption and capillary condensation in nanopores. 

---

Fig. 13.2 (color online) Side (top) and top (bottom) views of glassy silica (left) and chalcogenide (right) slab models. The silica surface possesses a 5 OH/nm surface density of hydroxyl groups while the chalcogenide surface possesses a 2.3 SH/nm of thiol groups, color code silica Si yellow, O red, and H white-, chalcogenide S yellow, Ge blue, and H white... 

Thus, it was established that adsorption of metal hydroxide species on the surface of the substrate provides a nucleation layer which is chemically converted to the metal chalcogenide. The forming metal chalcogenide layer acts then as a catalytic surface for subsequent anion and cation adsorption. 

As an illustrative example of this method for electrochemical synthesis of sulfide compounds consisfed in utilizing a sulfur-modified mefal surface as a template for fhe elecfrodeposition of mefal sulfide films, Tacconi and Rajeshwar described fhe firsf aflempl fo obfain all-elecfrodeposifed indium sulfide tiiin films, by a dual batii procedure [95] (cf conventional deposition of indium chalcogenides). The... 

Somasundaram S, Chenthamarakshan CR, Tacconi NR, Ming Y, Rajeshwar K (2004) Photoassisted deposition of chalcogenide semiconductors on the titanium dioxide surface Mechanistic and other aspects. Chem Mater 16 3846-3852... 

Mirovsky Y, Tenne R, Cahen D, Sawatzky G, Polak M (1985) Ternary chalcogenide-based photoelectrochemical cells V. Surface Analyses of the CulnX2/aqueous polysulfide interface (X = S, Se) by X-ray photoelectron spectroscopy Absence of Se/S exchange in the CulnSe2/Sn system. J Electrochem Soc 132 1070-1076... 

---