Heteroaggregation of carbon nanomaterials with mineral-based nanomaterials: A review

Production and widespread use of carbon nanomaterials (CNMs) have caused the release of increasing amounts into the environment and then raised concern over the safety to global ecosystems. For assessing these potential toxicity risks of CNMs, heteroaggregation of CNMs with natural colloids as an environmental behavior with vital importance for determining the fate and transport of CNMs in aqueous phase and sediments are of great interest. In natural aquatic systems, heteroaggregation of CNMs with mineral-based nanomaterials (MNMs) is expected to be the dominant process due to their abundance. In this article, a critical review of the current studies, about research progresses on the heteroaggregation of CNMs with MNMs were provided though many aspects. The performances of heteroaggregation divided into four forms, adsorption, coagulation, sedimentation, and flocculation via different testing instruments and methods for displaying results. The performance of heteroaggregation could be affected by characteristics of CNMs and MNMs, such as ion dissolution, concentration, size, crystallinity, aspect ratio, surface charges, functional groups, special structure and assemblage. Meanwhile, environmental conditions (pH, ionic strength, natural organic matter, UV-irradiation, sunlight, temperature, and surfactant) were very likely to change their particle properties and interactions. The involved major mechanisms of heteroaggregation include electric force, bridging, and hydrogen bonding/Lewis acid-base interactions. It's believed that this review could be not only important for the fundamental investigation of behavior and fate of carbon nanomaterials, but also significant for the applied science and engineering of control and removal of carbon nanomaterials in aqueous environments.