An experimental and modelling study of water vapour adsorption on SBA-15

Abstract

Many publications have been dedicated to the study of water vapour adsorption on the ordered silica-based material Santa Barbara Amorphous-15 (SBA-15). However, two aspects still need to be clarified: whether the solid is stable under repeated adsorption-desorption cycles and whether the experimental data can be predicted with a simple yet accurate analytical equilibrium model. In this study, SBA-15 showed good long-term structural stability when exposed to repeated adsorption-desorption cycles using water vapour as adsorptive up to 90 % relative humidity at 288 K, 298 K and 308 K. The reproducibility of the equilibrium isotherm was investigated using different commercial gravimetric instruments designed for water vapour adsorption measurements. The experimental measurements show a modification of the microporous structure of the solid after the first full isotherm measurement. Some water is strongly adsorbed and trapped during the first experiment on a fresh sample. After the first adsorption-desorption cycle, the water isotherm is characterized by a low value of the Henry law constant and by a nearly vertical capillary condensation and evaporation branches. Quite interestingly, the experimental scanning curves do not simply cross from one branch to the other as would be expected for cylindrical independent pores. The experimental data are correlated using new analytical models able to predict the amount adsorbed in the entire concentration range for the main adsorption-desorption branches and for the adsorption-desorption scanning curves.

Impact of Geometrical Disorder on Phase Equilibria of Fluids and Solids Confined in Mesoporous Materials

“…Let us first describe the geometric features of SCPM, also known in the literature as the corrugated pore model. 31,32,34,68,69,71 The model is shown schematically in Figure 3 and represents an interconnected chain of single pores. In the particular case considered here, a tubular pore is composed of L cylindrical pore sections, each of length l. The pore sections in the chain are labeled by index i.…”

“…Despite many relevant studies − over many years, geometric disorder has remained neglected in the quantitative analysis of the experimental findings and was mainly the focus of fundamental research mostly addressed in computer modeling studies. − Physical aspects accompanying phase transitions in disordered environments have been thoroughly studied using various realizations of the random-field Ising model, − quenched-annealed lattice gas model, , or its mean-field realizations − by using random quenched porous solids. − These studies have provided deeper insight into many experimental findings such as the return point memory or slow relaxation dynamics. , In the recent decade, this topic has been reiterated in the context of gas–liquid and solid–liquid equilibria in random pores. − …”

Measurement of water vapor adsorption isotherms in mesoporous materials using the zero length column technique

“…The ZLC experiments were conducted by performing several reversible adsorption-desorption cycles on the same batch. As discussed in a previous study (Centineo et al, 2019). during the first adsorption step the material changes irreversibly, trapping part of the water.…”

“…Following the first experiment all the isotherms become reversible and in this study we consider only these conditions and compare the results to the gravimetric experiments from repeated exposure to water (Centineo et al, 2019).…”

Influence of functionalization method on isomorphic substitution and formation of extra-framework oxides in silica for water vapor adsorption

“…Water vapor adsorption is an important process for many industries, such as chemical and petro-chemical industry, microelectronics, paper making, pharmaceuticals, food preservation and processing, thermal energy conversion and storage, humidity control and adsorption heat pumps [1][2][3]. Therefore, many new materials are being studied for water adsorption: aluminophosphates [4], titanium and zirconium silicates [5,6], mesoporous silicas [7][8][9], metal-organic frameworks [10], composite desiccants formed by hygroscopic salts in inorganic host matrices [11] and ionogels [12,13]. Among these, mesoporous silica with metallic heteroatom functionalization has been considered an interesting option for water adsorption [14].…”