O Oxido de Zinco

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The influence of TiO2 and ZnO powder mixtures on photocatalytic activity and rheological behavior of cement pastes[pic 6][pic 7]

1. Senff a,⇑, D.M. Tobaldi b, P. Lemes-Rachadel c, J.A. Labrincha b, D. Hotza c

a Center of Mobility Engineering, Federal University of Santa Catarina (UFSC), 89218-000 Joinville, SC, Brazil

b Department of Materials and Ceramics Engineering/CICECO, University of Aveiro, 3810-193 Aveiro, Portugal

c Department of Chemical Engineering (EQA), Graduate Program on Materials Science and Engineering (PGMAT), Federal University of Santa Catarina (UFSC), 88040-900 Florianópolis, SC, Brazil

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h i g h l i g h t s  [pic 9]

• Experimental design was used to formulate cement pastes containing TiO2 and ZnO.
• Ternary mixture having the smallest amount of nano-TiO2 was the better photocatalyst.
• Statistically nano-TiO2 was confirmed as the strongest influent factor to rheology.[pic 10]

a r t i c l e i n f o  

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Article history:

Received 20 August 2013

Received in revised form 12 April 2014 Accepted 23 April 2014

Available online 20 May 2014

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Keywords: Nano-titania Zinc oxide Rheology Cement paste

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a b s t r a c t  

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The photocatalytic activity of titania nano/microparticles (nT and mT) and zinc oxide microparticles (mZ) as well as the rheological behavior of cement pastes with the addition of those particles were evaluated applying design of experiments (DoE). Such additives ranged from 0 to 1.2 wt.% in the cement paste, while the water/cement ratio (0.45) and superplasticizer (0.45 wt.%) remained invariable. Thus, pure blends and binary or ternary mixtures were studied. Pure blends containing nT or mT and ternary mixtures 0.67mT:0.17nT:0.17mZ reached the best and comparable performances in terms of photocata- lytic activity. The rheological parameters (plastic viscosity and yield stress) values changed along time in distinct levels described by a quadratic model. Samples with nT became less fluid, and the yield stress was the main rheological parameter affected. The  kinetics of hydration  was not significantly  affected  by additions up to 120 min testing, but showed noticeable distinctions for longer periods: mZ (delayed) and nT (shortened), while mT required about the same time to reach the maximum exothermic peak than reference paste.

© 2014 Elsevier Ltd. All rights reserved.

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1. Introduction

The use of titania (TiO2) and zinc oxide (ZnO) particles in con- struction materials has been recently suggested. Those oxides have photocatalytic properties that can be explored for environmental pollution remediation, self-cleaning and self-disinfection purposes [1,2]. For example, TiO2 and ZnO layers deposited on the surface of ceramic tiles were able to attenuate 70–90% of the color given by azo dyes in aqueous solution (e.g. Orange II solutions), when exposed to artificial visible light irradiation, or under the sunlight [3–5]. Other works reported an apparent synergistic effect of tita- nia polymorphs as powder and in water suspensions [6]. The com- bined use of anatase and rutile (mass ratio of 4:1) seemed also to

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⇑ Corresponding author.

E-mail address: [e-mail] (L. Senff).

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improve catalytic performance [7]. ZnO is frequently looked as an alternative to titania, since it can absorb a larger energy fraction of the solar spectrum and more light quanta [8].

Recently, the investigations have shown that NOx photocatalytic degradation of mortars containing TiO2 up to 1 h under solar light ranged from 65% to 80%, while Orange II degradation after 9 h under visible light changed from 18% to 50% [9]. Moreover, the photocatalytic activity depends on the porosity of the surface layer in the case of paving blocks added with titania [10]. On the other hand, the presence of finer TiO2 particles tends to reduce the water permeability [11]. Since the degradation rate of NOx tends to reduce for higher relative humidity values, the overall performance is kept acceptable in distinct environments, and the wear resis- tance of the surface is also acceptable [12,13]. Lately, less common nanoparticles (Al2O3, ZnO, ZrO2) have been also applied in cemen- titious composites, attempting to achieve distinct effects, while the

http://dx.doi.org/10.1016/j.conbuildmat.2014.04.121 0950-0618/© 2014 Elsevier Ltd. All rights reserved.

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192        L. Senff et al. / Construction and Building Materials 65 (2014) 191–200[pic 16][pic 17]

microstructural, physical and mechanical properties were deter- mined [14–16]. In addition, TiO2 sol–gel coatings were applied in the surface of adobe substrates, assuring novel functionalities (e.g. higher water resistance and bactericidal behavior), while the common properties were improved [17].

Cement based materials containing the mentioned finer particles have shown several benefits under distinct perspectives for sustainable construction practice, as well as, the kinetics of hydration acceleration [18]. However, a considerable drawback regarding these fine particles is the tendency of mixtures to hinder the flowability. Thus, a systematic study that clarifies the role of each individual mixture component and the synergetic action on a particular characteristic of the material is crucial to optimize  its rheological, chemical and mechanical behavior [19–22].