Příprava a charakterizace karbon-silikátových nanosorbentů s vysokým specifickým povrchem

Abstract

Thesis studied preparation and characterization of carbon-silicate nanosorbents with high specific surface area and with the possibility of photocatalytic regeneration of saturated sorbent. Theoretical part begins with the structure of solids state and the bonds that occur in them. An important part is devoted to the van der Waals interactions that are present in physical sorption and the surface structure which is of great importance for the sorption capacities and the distribution of adsorption positions. The work deals with adsorption and mathematical models used for the description of adsorption processes. The main advantages and disadvantages of each model are highlighted. The process of photocatalytic reactions, their environmental applications and their use in removal of saturated sorbent materials are described next. In the regeneration process section, the mechanisms and reagents of the individual methods are analyzed. For the measurement of sorption and photocatalytic properties, an experimental reactor for the continuous measurement of photocatalytic processes developed in the Laboratory of Nanoparticulate Matter of nanotechnology center was used. The advantage of the reactor is in-situ measurement, so there is no need to interfere with the system. The vacuum freeze-drying method was used to convert samples from a water dispersion to a powder form for better handling and preservation of a high specific surface area. The developing process of sorption material with possibility of photocatalytic regeneration consisted of several steps. First, photocatalytic materials with a high specific surface based on a porous silicate structure containing zinc and graphene were prepared and characterized. The structure was deposited on the fiber structure for better handling. The material exhibited a relatively high specific surface area of 410 m2/g and much better results in photocatalytic activity than the P25 standard. Next prepared material, modified with g-C3N4, exhibited the capability of photocatalytic regeneration. Since no sorbent standard with photocatalytic regeneration effect is commercially available, titanium dioxide was used for comparison. The nanocomposite exhibited higher sorption capacities, the specific surface and rate constants of the sorption process. The sorption surface was successfully regenerated by UV irradiation, but the following cycles significantly reduced sorption capacity of the sorbent. By omitting the lyophilization process, the loss of samples was. However, the possibility of controlling the amount of used sorbent was lost. The next step was to increase the sorption capacities and to improve the regeneration properties of the sample by adjusting the preparation methodology prepared nanocomposite exhibited a high specific surface and ability of repetitive photocatalytic regeneration. Two variants were prepared, namely silicate structure containing 10 wt.% g-C3N4 and 20 wt.% g-C3N4. The material was tested for sorption of methylene blue. Photocatalytic decomposition was performed by irradiating the saturated sample with a LED source of UV radiation and natural diffuse sunlight. The regeneration efficiency for both samples exceeded 84% after the third cycle of UV regeneration and 94% after the third regeneration cycle with natural sunlight. When using a LED source emitting in the visible spectrum, the results of photocatalysis and regeneration were unproducible.