[nanoPost] Nanomaterials for personal care products

Nanoporous cyclodextrin-silica nanocomposites for the trapping of malodorous organic molecules and for the controlled release of active organics

Proposed Technical Approach

Cyclodextrins (CD) are conically-shaped polysaccharides (viz., cyclic glucose polymers) well-know for their ability to form host-guest complexes with a wide variety of small organic molecules in their “donut”-shaped hydrophobic central cavity. The specific inclusion properties of CDs have promoted their use for adsorption, separation and phase transfer applications. They have recently reported the synthesis of a novel class of open-framework silica nanocomposites (denoted as CD-HMS) containing cyclodextrin (CD) groups inside their pore channels. The CD groups were covalently attached to the pore walls of the silica framework, and the pore channels were large enough (about 4 nm in diameter) to prevent clogging by the large CD molecules.

CD-HMS materials have high surface areas (200-550 m2g-1) and high adsorption capacities for organic molecules (up to 0.4 mmol g-1). Their structures also feature uniform mesoscale pore channels which allows the complete access of every framework-bound CD site for binding, while promoting very rapid access of these sites by the organic molecules (within seconds).2 Because of these optimal features, the adsorption properties of CD-HMS are expected to be vastly superior to those activated charcoal, although comparative adsorption studies between the two should be performed to verify this statement. These investigations have shown these materials to be effective in removing aromatic molecules (phenolic and nitrobenzene compounds) and pesticides from water at the ppm and ppb level.

Trapping of malodorous compounds

The group propose to test the effectiveness of CD-HMS in the removal of odorous organic molecules from aqueous and gas-phase environments. Adsorbates to be studied will include organic acids, organic amines, aldehydes, ketones, indoles, organic sulfides/disulfides, styrene and other systems of interest to the client. Thereafter, research will be expanded to include more detailed investigations on the properties of the adsorbents (uptake kinetics, long-term stability of materials, leaching studies of loaded adsorbents). Also, alternative preparative methods for these adsorbents will be investigated in order to minimize their synthesis cost, while maintaining or improving their adsorption properties.

Controlled release of active organics

The group proposes to use CD-HMS or related compounds for the controlled delivery (time-release) of organic molecules of interest to the client (including fragrant compounds, pesticides, and others). These materials are expected to be appropriate for this application because the relatively weak interaction of organic guests within the CD inclusion cavity will result in the easy yet controllable desorption of included compounds.

For these applications, the nanocomposites will first be loaded with the compound of interest (fragrance, pesticide, etc.), and the release kinetics of the compounds under different exposure conditions and environments (e.g., temperature, humidity, application form (powder, liquids, gels, wax), etc.) will be assessed. The influence of various chemical and physical characteristics of the materials (i.e., pore size, CD group loading, particle size and morphology) on the release rate of the compounds will be evaluated in order to identify materials with optimal release properties.

Appropriateness of technology for use in household or personal care products

The nanocomposites are colorless, appearing as fine or ultrafine nonabrasive white powders.  Being silica-based, they are structurally robust, chemically inert and not subject to biological degradation (unlike polymer-based resins). As the silica in these materials is in a non-crystalline form, no toxicity or carcinogenicity is foreseen in their use. The materials are prepared using aqueous (water-based) methods without the use of toxic solvents, making them environmentally safe.

Research Experience and Industrial Collaborations

During the past 9 years, the team has extensively researched the development of new nanoporous silica-based materials tailored for the selective and high capacity adsorption of various compounds, both organic and inorganic. This research program was funded mostly by government granti-ng agencies, but also by various industrial sponsors. One of the major developments made by the group in this regards involved the preparation of highly effective sorbents for heavy metal ions (in particular towards mercury and platinum-group elements) for environmental remediation and mining-related applications.

This research has lead to two industrial research/consultation contracts involving mercury adsorption (with mining giant Noranda Inc., and the Atomic Energy Commission Laboratory (Canada)). They also recently completed the evaluation of designed nanoporous adsorbents for the uptake of platinum-group elements (PGMs) for optimizing the recovery of the valuable metals from mining processes (with mining companies Inco Ltd and Placer Dome, and Materials and Manufacturing Ontario). Finally, they are at present investigating the use of functional nanoporous materials for the removal of sulfur-containing compounds from fuels (with ESSO-Imperial Oil).

Research Facilities

The group has direct access at Laurentian University to the necessary synthesis and analytical instrumentation required for the preparation of materials, their structural characterization, and their adsorption properties. These capabilities include structure determination (XRD, SEM, FTIR), surface area and porosity measurements (N2 adsorptometry), aqueous and solid chemical analysis (GC-MS, HPLC, CHN analyzer, CS analyzer, XRF, Ion chromatography, AAS, UV-vis spectroscopy, EDX, and more). 

Their team is also partnered with local private laboratories in the event that specialized analytical expertise are required (i.e., Testmark Labs for pesticide/organic speciation and assaying, Inco analytical laboratory for trace and ultratrace metal analysis).