Adsorption of an active molecule on the surface of halloysite for controlled release application: Interaction, orientation, consequences

Abstract

The goal of the study was to check the possible use of halloysite nanotubes as a controlled release natural antioxidant device with quercetin as the active component. The mineral was thoroughly characterized by various techniques including the determination of particle and tube morphology, specific surface area, pore size and volume, as well as surface energy. The high surface energy of halloysite predicted strong adsorption of active molecules on its surface and consequently difficult release. FTIR spectroscopy confirmed the existence of strong interactions, energetically heterogeneous halloysite surface and multilayer coverage at large loadings. FTIR and XRD experiments proved the complete lack of intercalation and showed that below 3.5 wt% quercetin loading, most of the molecules are located within the halloysite tubes. Molecular modelling indicated the parallel orientation of quercetin molecules with the surface. Critical concentrations derived from various measurements agreed well with each other further confirming that up to about 4.0 wt% loading, quercetin is bonded very strongly to the halloysite surface. As a consequence, the dissolution of active molecules is very difficult or impossible, especially into apolar media, thus neither stabilization nor controlled release effect can be expected below that concentration.

Long term stabilization of PE by the controlled release of a natural antioxidant from halloysite nanotubes

“…Very few attempts are made to determine the surface energy of the nanotubes, their pore size and volume although these determine both the amount of active molecules accommodated inside the tubes as well as the kinetics and amount of released material. The detailed characterization of halloysite nanotubes done earlier [40,41] showed that their average length is 203 ± 119 nm, external diameter 50 ± 23 nm and internal diameter 15 ± 6 nm accompanied by a pore volume of 0.039 cm 3 Preferential and very strong adhesion of quercetin within the tubes is demonstrated even better by the correlation between the intensity of the vibration appearing at 1563 cm -1 and the amount of quercetin adsorbed on the surface of the tubes. As the correlation presented in Fig.…”

“…The detailed study of the release characteristics of the quercetin/halloysite complex has shown that numerous factors must be considered, which are often partially or completely neglected [40,41]. Very few attempts are made to determine the surface energy of the nanotubes, their pore size and volume although these determine both the amount of active molecules accommodated inside the tubes as well as the kinetics and amount of released material.…”

“…The approach resulted in improved homogeneity and stability, but at rather large, 2-3 wt%, antioxidant content. With these results in mind, we thoroughly characterized a commercial halloysite product and checked the release of quercetin from it into various solvents [40,41]. The analysis of the results allowed us to draw conclusions about competitive interactions and their role in the release of the stabilizer into polyethylene.…”

Kutatómunka a BME Fizikai Kémia és Anyagtudományi Tanszékén

“…Ennek fényében tehát olyan HNT/polimer kompozitokat tanulmányoztunk, melyekben különbözõ stabilizátorokat juttatunk be a HNT csövek belsõ felületére (5. ábra), hogy idõben hosszan elnyújtott stabilizáló hatást érjünk el például poliolefinekben. 36,37 A töltõanyag jellemzése során, az irodalomban egyedülálló módon, inverz gázkromatográfiával határoztuk meg az ásvány felületi energiáját, aminek döntõ szerepe van a kölcsönhatások erõsségében. Részletes vizsgálatainkkal bizonyítottuk, hogy az antioxidáns molekulái preferáltan kötõdnek meg a nanocsövek belsõ felületén és az összetétel helyes megválasztása mellett, elnyújtott stabilizáló hatás is biztosítható a módosított nanocsövekkel.…”

A neutral Cu-based MOF for effective quercetin extraction and conversion from natural onion juice

“…5 Due to various pharmacological and biological applications of quercetin and its metal complexes, adsorption and extraction of quercetin from natural resources have been extensively investigated. Porous organic materials, including silica nanoparticles, 6 polytetrauoroethylene lms, 7 macroporous acrylic resin 8 and halloysite, 9 have been employed in the adsorption and extraction of quercetin. However, most of these materials cannot be effectively recycled.…”