Review of Nanocoatings for Building Application

Available online at www.sciencedirect.com ScienceDirect Procedia Engineering 145 (2016) 1541 – 1548 International Conference on Sustainable Design, Engineering and Construction Review of Nanocoatings for Building Application Haleh Boostania*, Sama Modirroustab a Department of architecture, Eastern Mediterranean University, Famagusta, North Cyprus. Department of Architecture and Urban Development, Imam Khomeini International University, Qazvin, Iran. b Abstract Nanocoatings are regarded as the most promising high-performance materials for construction applications. Thanks to their selfassembly effect, they represent remarkable characteristics against environmental agents compared to conventional coating materials in construction industry. They also show high performance in contradiction of energy efficiency, CO 2 emission, and the air quality improvement. In this study, a review of nanocoatings on the basic reaction mechanisms and materials, in general, and for building application, in particular, is presented. © Published by by Elsevier Ltd.Ltd. This is an open access article under the CC BY-NC-ND license © 2016 2015The TheAuthors. Authors. Published Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of the International Conference on Sustainable Design, Engineering Peer-review under responsibility of the organizing committee of ICSDEC 2016 and Construction 2015. Keywords: Building industry; Nanocoatings; Nanomaterials; Self-assembly; Sustainable development; 1. Introduction There is a growing interest in the application of nanomaterials in building industry mainly because of their positively perceived characteristics including thermal properties, moisture behavior, energy efficiency, air quality improvement, self-cleaning, and anti-bactericidal effects [1-62]. Considering its high demands, the construction industry was the only industry that identified nanotechnology as a promising emerging technology in the UK Delphi Survey in the early 1990s [1]. The fundamentals of nanotechnology, nanomaterials and their applications in buildings were reviewed by several authors on a number of occasions [1-10]. Zhu et al. [1], Golabchi et al. [2], Pacheco-Torgal et al. [3], Ge and Gao [4], and Bitnnar et al. [5] stressed the role of nanotechnology in building industry. Leydecker [6], Kutschera et al. [7], Geckeler and Nishide [8], and Sanchez et al. [9] introduced advanced, hybrid, and organic– * Corresponding author. Tel.: +90-533-8371384. E-mail address: boostani.haleh@gmail.com 1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ICSDEC 2016 doi:10.1016/j.proeng.2016.04.194 1542 Haleh Boostani and Sama Modirrousta / Procedia Engineering 145 (2016) 1541 – 1548 inorganic nanomaterials. In addition, Schodec et al. [10] suggested design criteria by implementing nanomaterials and nanotechnologies for engineers and architects. In this review, fundamentals of nanocoatings are investigated for building application in particular. 2. What is Self-assembly Effect in Nanocoatings Nanocoatings are increasingly used by the construction industry on building surfaces, such as walls, doors, and windows, as they open new horizons for sustainable and environment-friendly buildings. Providing a protective layer bound to the base material, they create a surface of the desired protective or functional properties. The key mechanism concept of nanocoatings is their self-healing capabilities through a process of self-assembly [11]. Selfassembly is a phenomenon where the components of a system assemble themselves spontaneously via an interaction to form a larger functional unit (Fig. 1). This spontaneous organization can be because of direct specific interaction and/or indirectly through their environment [12]. The spatial arrangements of the self-assembled nanoparticles are the key concept of nanocoatings application. Fig. 1. The Process of Self-assembly through a Set of Specific Interactions among Nanoparticles. 3. Previous Research Works on Nanocoatings 3.1. Hydrophilic and Hydrophobic Coatings Fig. 2 shows a self-cleaning glass system based on a thin film Titanium Oxide (TiO2) coating [13-18]. The glass cleans itself in two stages. The photocatalytic stage of the process breaks down the organic dirt on the glass using ultraviolet light (Fig. 2 (B)) and makes the glass superhydrophilic. During the following superhydrophilic stage, rain washes away the dirt, leaving almost no streaks (Fig. 2 (C)), because water spreads evenly on superhydrophilic surfaces [19]. The films also have good photoinduced anti-bacterial and anti-reflective properties. The doping of a small amount of silver into the TiO2 porous film can enhance its anti-bacterial effect without UV light irradiation. On the contrary, hydrophobic coatings [20-24] are mostly used to make the surfaces water and corrosion resistant. Fig. 3 shows a hydrophobic system based on Silicon Oxide (SiO2) coating. The contact angles of a water droplet exceeds 150° and the roll-off angle is less than 10° [25]. Both hydrophilic and hydrophobic coating mechanisms are applicable for flat building surfaces and base materials such as tiles, stones, and woods. Haleh Boostani and Sama Modirrousta / Procedia Engineering 145 (2016) 1541 – 1548 Fig. 2. A Self-cleaning Glass System Based on Titanium Oxide (TiO2) Thin Film Coating. Fig. 3. A Hydrophobic System Based on Silicon Oxide (SiO2) Coated Surface. 3.2. Flame Retardant Coatings Want et al. [26-28] proposed flame-retardant nanocoatings by adding nano-size magnesium Aluminium-ayered Double Hydroxides (LDHs), Titanium Oxide (TiO2) and Silicon Oxide (SiO2). Mizutani et al. [29] used emulsiontype paint prepared using a Nano-Composite Emulsion (NCE) contained nano-size particles of silica and polyacrylate. The results clarified the excellent antipollution property and the high flame resistance of the product. 3.3. Wear Resistant Coatings Barna et al. [30] have stressed the incorporation of silicon dioxide (SiO2), Titanium Oxide (TiO2), Aluminium Oxide (Al 2O3), and Zirconium Oxide (ZrO2) nanoparticles for increasing the hardness and mechanical properties of coatings, thereby improving their wear-and- scratch resistance. In addition, because of their small size, nanoparticles do not affect the transparency or the gloss of the coatings. Nanocoatings can thus be used to maintain the surface appearance and durability of parquet floorings or the windowpanes. 3.4. Anti-graffiti Coatings Quagriliani et al. [31, 32] and Munafo [33] found nano-structured Titanium Oxide (TiO2) based coatings promising on historical and stone surfaces. Rabea et al [34] used silica nanoparticles on a permanent anti-graffiti polyurethane coating, which positively affected the anti-graffiti performance against ageing cycles. 3.5. Corrosion Resistant Coatings Hamdy and Butt [35, 36] successfully used the effect of chromate conversion coatings for the corrosion protection of aluminium alloys. Feng et al. [28] proposed nano-Al2O3 particles incorporation to composite coatings in order to improve the corrosion and oxidation resistance. Moreover, Montemore [38] reviewed the most recent self-healing and smart coating alternatives for enhanced corrosion protection. 1543 1544 Haleh Boostani and Sama Modirrousta / Procedia Engineering 145 (2016) 1541 – 1548 3.6. Energy Efficient Coatings 3.6.1. Phase Change Materials (PCMs) Karlessi et al [39] have investigated the performance of organic Phase Change Materials (PCMs) used as Latent Heat Storage (LHS) system incorporated in building coatings. The result demonstrated lower surface temperatures than that for conventional coating materials. With a high thermal conductivity nanoparaffin composites [40] are capable of storing and releasing large amounts of energy by heat absorption or heat release when the material changes from solid to liquid and vice versa [41-45]. Also Motahar et al [46] found Mesoporous Silica (MPSiO2) nanoparticles efficient as a novel composite for thermal storage. Fig. 4 shows functional mechanism of (PCMs). In principal they incorporate to external surfaces, e.g. walls, windows, floors [47-49] to be exposed to the air for a certain temperature range. 3.6.2. Electrochromic Materials Nanochromic materials, e.g. Tungsten Oxide (WO3) [50], Nickel Oxide (NiO2), Titanium Oxide (TiO2), and Vanadium Oxide (VO2) [51, 52], can be applied as thin film layer(s) on the window glasses as the energy efficient coatings [53]. Baetens et al [52] found electrochromic windows as the most promising to reduce cooling loads, heating loads, and lighting energy in buildings where they have been found most reliable and able to modulate the transmittance up to 68% of the total solar spectrum. 3.6.3. Photovoltaic Coatings Fig. 5 presents a photovoltaic (PV) system of converting solar energy to direct current electricity [55]. In this regard, Jayaweera et al [56] found that use of nano-porous Titanium oxide (TiO2) films onto a thin film of stannic Oxide (SnO2) is successful for producing more electricity. Furthermore, Han et al [57] proposed the anti-reflection technique using a nanoscale dot-pattern array as one of the most effective methods to achieve high efficiency in (PV) systems. 3.7. Nanocoatings Categorization Based on the previous research works conducted over nanocoatings in terms of type, application and their synthetics, all mentioned factors are given in table 1, to have a brief deduction on the subject’s objectives. Fig. 4. The Process of PCMS Functional Mechanism [54]. 1545 Haleh Boostani and Sama Modirrousta / Procedia Engineering 145 (2016) 1541 – 1548 Fig. 5. A Photovoltaic (PV) System of Converting Solar Energy into Direct Current Electricity [58]. Table 1. Nanocoating Categorization. Types of Coating Application Synthetics Energy Efficiency Hydrophilic Window frame and Window pane, Tiles, Brick, Stone, Paint Thin films comprised of: Titanium Oxide (TiO2) and Silver Non-energy Efficient Hydrophobic Tiles, Brick, Stone, Wood , Paint Silicon Oxide (SiO2) Non-energy Efficient Flame retardant Aluminium, Magnesium, Aluminium Hydroxides (LDHs) Titanium Oxide (TiO2) and Silicon Oxide (SiO2). Non-energy Efficient Wear and Scratch Resistance Transparent surfaces, Parquet floorings, Glasses and the window panes Silicon Oxide (SiO2), Titanium Oxide (TiO2), Aluminium Oxide (Al2O3) and Zirconium Oxide (ZrO2) Non-energy Efficient Anti-graffiti Stone, Facade plaster Titanium Oxide (TiO2) Non-energy Efficient Corrosion Resistant Aluminium alloys Aluminium Oxide (Al2O3) Non-energy Efficient External walls, window panes, Flooring Mesoporous Silicon Oxide (MPSiO2) Energy Efficient Electro Chromic Window panes Titanium Oxide (TiO2), Energy Efficient Photovoltaic Solar cells Titanium Oxide (TiO2), Stannic dioxide (SnO2) Energy Efficient Phase Change Material 4. Environmental and Economic Feasibility Analyses The increasing use of nanomaterials in consumer products has raised certain concerns over their safety to human health and the environment. There are currently a number of major uncertainties and knowledge gaps in regard to behavior, chemical, and biological interactions and toxicological properties of nanomaterials [59-62]. As dealing with these uncertainties will require the generation of new basic knowledge, it is unlikely that they will be resolved in the immediate future. One has to consider the whole life cycle of nanoproducts to ensure that possible impacts can be systematically discovered [64-66]. Life Cycle Assessment (LCA), as a formalized life cycle concept, may be used to assess the relative environmental sustainability performance of nanomaterials in comparison with their conventional equivalents [67]. Fig. 6. shows the life cycle of a row material from fundamental to application. 1546 Haleh Boostani and Sama Modirrousta / Procedia Engineering 145 (2016) 1541 – 1548 Fig. 6. The Life Cycle of a Row Material from Fundamental to the Application [70]. Although the initial investment required for nanomaterials is higher than that for conventional materials [10], their energy consumption is drastically low. Thiele et al [69] conducted an energy analysis of concrete containing Phase Change Materials (PCMs) for building envelopes for two different cities in the US. The study showed that the annual cooling load reduction varies from 15% to 30%. The major portion of energy consumption worldwide is based on oil and coal, two energy sources with the most CO2 emissions and the green gas effects [70]. Moreover, Baetens et al [51] found electerocromic windows as the most promising to reduce cooling loads, heating loads and lighting energy in buildings up to 68%. Achieving solutions to environmental issues that we face today requires long-term potential actions for sustainable development. In this regard, renewable energy resources appear to be the one of the most efficient and effective solutions [71]. Such strategies typically involve three major targets: energy savings on the demand side, efficiency improvements in the energy production, and replacement of fossil fuels by various sources of renewable energy [72]. As previously mentioned, application of nanocoatings and nanomaterials in construction industry would be an efficient strategy to meet sustainable development targets. 5. Conclusion This paper reviewed nanocoatings on the basic reaction mechanisms and materials as well as for building applications in particular. The key concept in basic mechanism of nanocoatings is based on self-healing capabilities through a self-assembly process, where the components of a system assemble themselves spontaneously via an interaction to form a larger functional unit. The previous research works have revealed the effect of using nanomaterials for a more efficient self-assembly process through implementation of different and multifunctional nanocoatings. 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