Monitoring adsorption by small angle neutron scattering in tandem with digital reconstruction-simulation techniques

The sorption of benzene at 310 K in a model mesoporous silica gel was monitored by in situ small angle neutron scattering (SANS) measurements along an adsorption isotherm with a specially constructed cell using contrast-matching conditions for the condensed fluid. The silica gel was produced by a sol–gel process to give a porous network formed by the packing of nearly monosized sol particles. Since the scattering length density of the solid matrix and the fluid were identical, the autocorrelation functions of the binary sorbent/sorbate-pore system could be determined by Fourier transforming the scattering curves obtained at different equilibrium pressures. On the other hand, a Monte-Carlo based, central attraction procedure of non-overlapping spherical particles has been employed as a process-based representation method to simulate the sphere pack pore structure of the adsorbent. The reconstructed material revealed a similar autocorrelation function with the original silica gel. Density functional theory (DFT) was subsequently employed to simulate sorption in the reconstructed material and the autocorrelation functions of the virtual system were calculated for different adsorbate loadings and found to be in agreement with the experimental data.