Mechanisms of NOx entrapment into hydrated cement paste containing activated carbon — Influences of the temperature and carbonation

Different Roles of Water in Photocatalytic DeNOx Mechanisms on TiO2: Basis for Engineering Nitrate Selectivity?

“…This observation is important because it suggests that the nitrate selectivity of TiO 2 is not only influenced by molecular water but also by the level of photo-induced structural defects (i.e. oxide ion vacancies) in the photocatalyst, as indicated in reaction (13). This relationship between defect concentration and nitrate selectivity in TiO 2 has been suggested before 38 and these results may provide some support for this, although in the present case, the linear dependency of selectivity with physisorbed water content suggests that defect concentration is not a limiting factor.…”

“…in glass and concrete products, and its photocatalytic activity, i.e. the rate of normalized NOx concentration decrease, has been exclusively used as an indicator of efficiency [11][12][13][14][15][16][17] . The nature of the exposure regimes (of the photocatalyst to light and reactants) is the primary differentiating factor for the various approaches to supporting photocatalysts and has led to a number of innovative and effective strategies for performance improvements [18][19][20] .…”

NO2 AND VOCS DEPOLLUTION IN GARAGE PROTOTYPES USING INNOVATIVE CONCRETES AND MORTARS

“…Calcium Silicate Hydrates (C-S-H) of the hydrated cement pastes showed a high absorption capacity but this effect is temporary [7]. Indeed, the NO 2 reduction rate by the reference cement paste is affected by carbonation caused by atmospheric CO 2 : this gas converts the highly alkaline hydrates to calcium carbonates [13], which are less reactive with NO 2 .…”

“…Indeed, the NO 2 reduction rate by the reference cement paste is affected by carbonation caused by atmospheric CO 2 : this gas converts the highly alkaline hydrates to calcium carbonates [13], which are less reactive with NO 2 . Previous laboratory-scale experiments [7], [14] showed that the addition of a small rate of activated carbon (AC, SA2 from Cabot Corp.) powder into the cement paste increases the NO 2 reduction rate (even in presence of ambient concentrations of CO 2 ) and prolongs the depolluting effect. According to these previous works, we hypothesized [7] that the NO 2 absorption in the alkaline cement pastes could be governed by two consecutive phenomena: (i) NO 2 physisorption on the activated carbon (AC) powder; and (ii) reaction of the adsorbed NO 2 with the alkaline pore solution of the surrounding cement paste, which depends on its carbonation.…”

“…We have previously shown that ordinary Portland cement pastes are porous alkaline material that can absorb NO2 at ambient temperature until the complete carbonation of the paste [7]. In addition, the activated carbons are known to be excellent adsorbents for NO 2 [8] and can be added to the mix of mortar and concrete without affecting their mechanical properties and intrinsic durability [9].…”