Fast Method for Testing the Photocatalytic Performance of Modified Gypsum

Heterogeneous vs homogenous photocatalysis: what dominates in the degradation of methyl orange and methylene blue mixtures?

Photocatalysis has been oft proposed as a green solution for pollution remediation, however, majority of the existing literature only studies the degradation of solitary analytes. The degradation of mixtures of organic contaminants is inherently more complicated due to a variety of photochemical processes that occur in parallel. Here, we describe a model system comprised of methylene blue and methyl orange dyes whose degradation carried out by two common photocatalysts, P25 TiO₂ and g-C₃N₄. With P25 TiO₂ as the catalyst, the degradation rate of methyl orange slowed by 50% when degraded in a mixture compared to when alone. Control experiments with radical scavengers showed this to occur due to competition between the dyes for oxidative photogenerated species. In the presence of g-C₃N₄, methyl orange's degradation rate in the mixture increased by 2300% due to two homogeneous photocatalysis processes sensitized by methylene blue. Homogenous photocatalysis was found to be fast relative to heterogeneous photocatalysis by g-C₃N₄ but slow relative to photocatalysis by P25 TiO₂ and explains the change observed between the two catalysts. Changes in dye adsorption to the catalyst when in a mixture were also explored but not found to coincide with changes in degradation rate.

A New Preparation Method of Cement with Photocatalytic Activity

The studies of some mechanical properties and photocatalytic activity of new cements with photocatalytic activity are presented. The new building materials were obtained by addition of semi-product from titanium white production. Semi-product was calcined at 300 and 600 °C for one, three, and five hours and then this material was added to cement matrix in an amount of 1 and 3 wt.%. New materials were characterized by measuring the flexural and compressive strength and the initial and the final setting time. The photocatalytic activity was tested during NOx photooxidation. The cement with photocatalytic activity was also characterized by sulphur content measurements. The measurement of reflectance percentage of TiO2-loaded cements in comparison with pristine cement and TiO2 photocatalyst calcined at 600 °C were also performed. It should be emphasized that although in some cases, the addition of photocatalyst reduced the flexural and the compressive strength of the modified cements, these values were still within the norm PN-EN 197-1:2012. It was also found that the initial and the final setting time is connected with the crystal size of anatase, and the presence of larger crystals significantly delays of the setting time. This was probably caused by a water adsorption on the surface of anatase crystals.

Environmental Applications of Photocatalytic Processes

Photocatalytic processes have been investigated in different environmental fields, but their applications at full scale are still scarce [...]

Combined Effect of Photocatalyst, Superplasticizer, and Glass Fiber on the Photocatalytic Activity and Technical Parameters of Gypsum

In this study, gypsum plasters enriched with the modified photocatalyst TiO2/N and additive components were prepared and analyzed in detail. The aim of this work was to recognize the combined impact of a photocatalyst, polycarboxylic superplasticizer (SP), and glass fiber (F) on the properties of the composed building materials. The mutual compatibility was verified in relation to self-cleaning and air-purifying activity as well as to the technical parameters defined in standards for gypsum materials. The measurements revealed that photocatalytic gypsum material can have high mechanical strength and limited shrinkage as a result of superplasticizer contribution in form of a water-reducing and well-dispersive agent. Normal consistency was achieved by the addition of 0.01 wt % of SP to photocatalytic gypsum mortar or by the addition of 0.2 wt % of SP with a 12% reduction of water. This study also explains why glass fiber fulfills the role of inner reinforcement only if a superplasticizer is simultaneously added to the gypsum matrix. It is possible, by the combined effect of TiO2/N, a polycarboxylic superplasticizer, and glass fiber, to achieve NOx degradation at a high level. Moreover, the significantly improved self-cleaning properties of the complex gypsum plasters surfaces from dye pollutants in comparison to a gypsum plaster with solely a TiO2/N photocatalyst indicate the synergistic effect of the three considered additives.

Photocatalytic Activity and Mechanical Properties of Cements Modified with TiO2/N

In this paper, studies of the mechanical properties and photocatalytic activity of new photoactive cement mortars are presented. The new building materials were obtained by the addition of 1, 3, and 5 wt % (based on the cement content) of nitrogen-modified titanium dioxide (TiO₂/N) to the cement matrix. Photocatalytic active cement mortars were characterized by measuring the flexural and the compressive strength, the hydration heat, the zeta potential of the fresh state, and the initial and final setting time. Their photocatalytic activity was tested during NOx decomposition. The studies showed that TiO₂/N gives the photoactivity of cement mortars during air purification with an additional positive effect on the mechanical properties of the hardened mortars. The addition of TiO₂/N into the cement shortened the initial and final setting time, which was distinctly observed using 5 wt % of the photocatalyst in the cement matrix.