Photocatalytic Active Self-Cleaning Cement-Based Materials. Compositions, Properties, Application

Abstract

The paper reviews the available technologies for producing photocatalytic active self-cleaning materials based on cement, including concretes and dry building mixtures. Used photocatalytic additives and their influence on the cement system are considered. The applied methods for assessing the photocatalytic activity of self-cleaning cement materials are presented. The compositions of concrete mixtures, their properties, areas and prospects of application are analyzed. The main problems of development, production and application of photocatalytic active self-cleaning materials based on cement are presented. The main directions to increase the self-cleaning ability of photocatalytic active materials based on cement are: optimization of the microstructure of the photocatalyst and the composite with its use in the direction of creating a developed surface of the photocatalyst - hierarchical microstructure; it intensifies the diffusion processes of photocatalytic reaction reagents and increases the contact area photocatalyst with a pollutant; it absorbs and accumulates ultraviolet radiation waves; optimization of the phase composition of titanium dioxide - search for the ratio of the anatase and rutile phases, at which the maximum photocatalytic activity is achieved; choosing of economically feasible method for periodical updating of the surface of concrete products carbonized during operation in order to restore self-cleaning ability.

Evaluation of the effectiveness of mineral additives in cement systems in the development of “core – shell” photocatalytic compositions

“…The narrow spectral range of action, characterized by insensitivity to the main visible region of the solar spectrum, is another significant disadvantage of titanium dioxide. In particular, the band gap of rutile and anatase is 3.0 and 3.2 eV, respectively, which is higher than that of other known semiconductors (for example, GaAs, CdSe, Fe 2 O 3 , CDs, GaP, WO 3 , SiC with band gap of 1.4-3.0 eV [11]).…”

“…due to their decomposition to low-toxic or non-toxic products (oxygen, carbon dioxide, water, sulfates, nitrates and nitrites) as a result of redox reactions occurring in the structure of the material when irradiated with light [1][2][3][4][5][6][7][8]. Achieving the self-cleaning mechanism of the outer layers of composites with photocatalysts through more efficient flushing of pollutants with water due to surface hydrophilization is another positive aspect of the use of such materials, which makes it possible to maintain the original purity and color of building products and structures for a long time under the influence of adverse environmental factors [6,[9][10][11].…”

“…Anatase form of titanium dioxide is currently the most widely studied and successfully used photocatalyst [4,5,7,8,[9][10][11][12][13][14][15] due to its chemical stability, non-toxicity, and the special band structure, which determines its high photocatalytic activity. However, photocatalysis using titanium dioxide also has a number of disadvantages.…”

“…The preparation of photocatalytically active compositions by deposition of TiO 2 nanoparticles on particulate carriers ("core -shell" systems) is a promising direction. The photocatalytic activity of such systems grows due to an increase in the TiO 2 active surface and its more uniform distribution in the material volume [11].…”

“…It is worth noting that natural and technogenic pozzolanic materials of silica and aluminosilicate compositions, in particular, diatomite, silica fume, metakaolin, mordenite, zeolite, etc. [11,17], are among the most effective substrates in the synthesis of "core -shell" photocatalytic nanomodifiers for cement systems. The prospect of using this kind of raw material as a carrier lies in its wide applicability in building composites, as well as increased values of porosity and amorphous phase content, which contribute to the formation of an active acid-base surface, which has a high chemical affinity with cement hydration products and provides improved adhesion of the photocatalytic material to cement matrix [18,[22][23][24][25][26][27].…”