Novel environmental sorbents and methods for their characterization

摘要

An overview of current trends in the application and characterization of new environmental sorbents is presented. These sorbents can take a broad spectrum of chemical forms and different geometrical surface structures. This is reflected in the wide range of their applications. The main types of adsorbents of practical environmental importance contain carbon adsorbents (active carbons, activated carbon fibers, carbon molecular sieves, mesocarbon microbeads, carbonaceous nanomaterials), mineral adsorbents (silica gels, activated alumina, oxides of metals, hydroxides of metals, zeolites, clay minerals, pillared clays, porous clay heterostructures, inorganic nanomaterials) and such solids as synthetic polymers, metallorganic microporous and mesoporous materials, composite adsorbents and the so-called mixed adsorbents. Strong efforts are also directed on the development and broader application of the ion-exchange method that deals with the production of novel organic and inorganic ion exchangers of suitably chosen physicochemical properties. Main trends in the development of new selective materials referred to great ion-exchange capacity achievement as well as improvement of chemical, thermal and mechanical resistance is discussed in perspective of their impact on adsorption for environment (e.g., selective removal of relatively low levels of toxic or noble metal ions). Application of solid sorbents requires their many - faceted characterization and achievements in this field accelerate their synthesis and applications. The two groups of methods most commonly used are direct physical techniques and indirect methods such as sorption, chromatography, and thermal analysis. The former group of methods comprises electron and scanning microscopy, atomic force microscopy (AFM), X-ray diffraction, X-ray spectroscopy, small-angle X-ray spectroscopy (SAXS), solid-state NMR, Raman spectroscopy, etc. that provides direct information about physicochemical properties of solids sorbents. On the other hand, the second group of methods is very important because classical adsorption/desorption measurements are unavoidable to collect information on the adsorption behavior of a solid with regard to a given pollutant. This lectures presents the overview referring to a brief description and classification of modern environmental adsorbents, summarizes the adsorption / desorption methods aimed at their characterization and demonstrates various theoretical approaches to evaluate the adsorption energy and micropore-size distributions from the gas / solid and liquid / solid adsorption isotherms. Moreover, a special emphasis is placed on the molecular simulations of adsorption processes that include the understanding the synthesis of the novel adsorbents through simulation techniques and improved methods for their characterization.