Continuous adsorption in highly ordered porous matrices made by nanolithography

Abstract

The exposed surface area of porous materials is usually determined by measuring the mass of adsorbed gas as a function of vapour pressure. Here we report a comprehensive study of adsorption in systems with closed bottom, not interconnected pores exhibiting different degrees of disorder, produced with methods encompassing nanolithography and dry and wet etching. Detailed adsorption studies of these matrices show hysteresis loops, as found always in pores having sizes of tens to hundreds of nanometres. The observed variations in the loop shape are associated with changes in the pore morphology. In regular pores formed by vertical and smooth walls, continuous adsorption is found for the first time in agreement with thermodynamic considerations valid for ideal pores. This suggests that irregularities in the walls and pore openings are the key factors behind the hysteresis phenomenon. Interestingly, pores having rough walls but a pyramidal shape also do not show any hysteresis.

Fabrication of Self-Ordered Alumina Films with Large Interpore Distance by Janus Anodization in Citric Acid

“…Moreover, JA only needs very simple and inexpensive apparatuses, which are accessible for common researchers to controllable fabrication of micro or sub-micro arrays that are made up of metal, inorganic and polymer materials. Thus, it is potential to become an alternative technology for traditional top-down nanofabrication technologies to explore novel physical, chemical and biological properties of nanomaterials with large period arrays or hybrid micro and nanostructure2627282930.…”

“…As combined with other processing (e.g. nanoimprinting and electrochemical deposition), the large D int PAA fabrication technology is very promising to become an alternative technology for traditional top-down nanofabrications26272829 to efficiently and controllably fabricate advanced materials with arrayed microstructure or hybrid micro- and nanostructure30 possessing novel properties and so on.…”

“…These findings open a new way to explore large period PAA films, and are very helpful to develop new surface coating for aluminum and fabricate advanced chemical and biological sensors. The Janus anodization process is potential to become an alternative technology for traditional top-down nanofabrication technologies to efficiently and controllably fabricate microstructure or hybrid micro- and nanostructure with novel properties2627282930.…”

A molecular simulation study of adsorption and desorption in closed end slit pores: Is there a hysteresis loop?

“…Reversible isotherms have been reported for closed end pores when the interaction between adsorbate and adsorbent is weaker (Mistura et al, 2013); this raises the question of whether a reduction in this interaction is the reason for reversibility. Figure 7 shows the isotherms for a graphite-like (lamellar) surface in which the well depth ( ss /k) of an atom in the adsorbent is reduced from 28K to 10K.…”

“…However, these real materials may have irregularities on the surface that could be responsible for the hysteresis (Bruschi et al, 2008;Puibasset, 2009). In an experimental adsorption study of very wide closed end pores where effects due to the external adsorbent field are expected to be negligible, no hysteresis was found (Mistura et al, 2013). In this paper we explore the effects of various parameters on the existence and properties of the hysteresis loop in closed end pores.…”