Chalcogenide aerogels

Porous chalcogenide aerogels is another broad class of non-oxidic framework that prepared by template-free routes [71-73]. These materials possess a continuous nanostructured chalcogenide framework that is penetrated by a random network of nanopore channels. Because these high surface area structures are random and not exhibit long-range pore periodicity, such systems are outside of the scope of this review and will not be covered further. 

Given the sol-gel chemistry demonstrated by this approach, this would appear to be a fertile area for the development of new chalcogenide aerogels. Nevertheless, there are some distinct drawbacks. In addition to problems balancing reaction kinetics and thermodynamics to drive gel formation (in lieu of precipitation), oxygen contamination is a common problem. Even when gels form, the networks that have been prepared to date are very weak and do not lead to monoliths (45). 

Metal chalcogenide aerogels prepared by condensation of metal chalcogenide nanoparticles (quantum dots) exhibit unique optical properties. What are these properties and how does the aerogel dimensionality determine the extent of quantum confinement You may wish to consult Chapter 16 on semiconducting nanoparticles in answering this question. 

Figure 17.2. A. Proposed structure of the Pt2[Ge4Sio] chalcogenide aerogel based on pair distribution function (PDF) analysis of X-ray data. Relevant inter-atomic distances are indicated. B. Different types of Zintl clusters (teal balls = Ge, Sn red balls = S, Se) employed in chalcogel formation with Pt ". Reproduced with permission from Science, 317 490-493 (2007). Copyright 2007, American Association for the Advancement of Science.

Figure 17.5. Plot showing adsorption isotherms of CO2 and H2 at 273 K on a C0M0S4 aerogel with a surface area of 340 m /g. The chalcogenide aerogel shows a selectivity of CO2 over H2 of nearly 16 times. Reproduced with permission from Nat. Chem., 1 217-224 (2009). Copyright 2009 Macmillan Publishers Ltd.

An alternate approach to chalcogenide aerogel synthesis is to start with discrete nanoparticles of metal chalcogenides and condense them together to form a gel network. A method for doing just that was reported in 1997 by Gacoin and coworkers [21-25]. 

Mohanan JL, Arachchige lU, Brock SL (2005) Porous semiconductor chalcogenide aerogels. Science 307 397-400... 

PDMS aerogel A composite between PDMS and a metal chalcogenide aerogel... 

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