Photocatalytic TiO2-Based Coatings for Mortars on Facades: A Review of Efficiency, Durability, and Sustainability
Abstract
:1. Introduction
2. Methods
3. Overview
Paper | Photocatalytic Coating Composition | Applying Method | Doping Substance/Nanocomposite If Applicable | Substrate Evaluated |
---|---|---|---|---|
Khannyra et al. [50] | TiO2/SiO2 and N-TiO2/SiO2 synthesized via sol–gel method. TiO2 proportion of 4% w/v concerning silica oligomer and concentrations of 0, 3.33, 6.66, 8 and 10 M for the nitrogen doping, regarding the synthesis of TiO2/SiO2 and N-TiO2/SiO2. P25 used for comparison. (S0N0T; SN10TiO2; SP25; SN8TiO2; SN3.33TiO2; STiO2; SN6.66TiO2) | Brushed to saturation three times; sols extra removed by paper | Nitrogen | Portland cement mortar |
Gryparis et al. [51] | TiO2/C-dots composites synthesized using a hydrothermal strategy. TiO2 and several C-dot loadings: TC0, TC25, TC50, TC62.5 and TC75. Each catalyst was added in 4% w/w to a hydrophobic consolidant, synthesized using a sol–gel process. A commercial catalyst Au (1%)/TiO2 (TAu) was also tested under solar conditions | Brushed three times | C-dot loading | Cement mortar |
Pei et al. [11] | Graphene/TiO2 nanocomposites prepared using a sol-gel assisted electrospray method. Suspensions in methanol of graphene/TiO2 nanocomposites (2.5%) and commercial TiO2 nanoparticles (2.5%) by weight of the cementitious materials used for the cement mortar | Sprayed | Graphene | Portland cement mortar |
Zahabizadeh et al. [52] | Nano-TiO2 aqueous suspension sprayed over the surface of mortar specimens after 1.5, 5, 9, 24 and 32 h and 7 days after the beginning of the hydration process | 5 mg/cm² to 80 mg/cm² sprayed | - | Cement mortar |
Zuena et al. [53] | Two distinct sols obtained by mixing TEOS, ethanol, TiO2 nanoparticles, and loaded NC (silica nanocapsules) or MNP (silica mesoporous nanocapsules). Total nanoparticle concentration: 0.1% w/w. Tested coatings: Si-TiO2-NC, Si-TiO2-MNP and Si-Control | Applied using a brush until the surface remained wet for more than 1 min | Silica nanodevices loaded with a commercial biocide (2-mercaptobenzothiazole) | Lime-based mortar |
Speziale et al. [54] | Two heterostructures of TiO2-ZnO (weight/weight 50/50 and 10/90). Dispersions into plain hydroalcoholic and 3D superhydrophobic medium. Further improvement by addition of superplasticizers (polycarboxylate ether (PCE), melamine sulfonate (MEL), polynaphthalene sulfonate (PNS) and polyacrylate (PA)) in a 1% w/w percentage concerning the weight of photocatalyst. Optimized coatings—Dispersion 1: superhydrophobic coatings (SPHB) 3 w/w% TiO2-ZnO 50/50 + 5% w/w PCE with respect to the nanoparticles. Dispersion 2: SPHB 3 w/w% TiO2-ZnO 10/90 + 5% w/w MEL with respect to the nanoparticles. Dispersion 3: SPHB 1.5 w/w% TiO2-ZnO 50/50 + 2.5% w/w PCE with respect to the nanoparticles. Dispersion 4: SPHB 1.5 w/w% TiO2-ZnO 10/90 + 2.5% w/w MEL with respect to the nanoparticles | 1 mL deposited with a pipette | ZnO | Lime-based mortar |
Hot et al. [15] | TiO2-based powders obtained from waste due to chemical milling baths of the aeronautical industry. 5 g of TiO2-based powder mechanically dissolved in 100 mL of distilled water solution containing 3.5 g of dispersant and 0.1 g of anti-foaming agent | Applied using a brush: 2–3 layers. 0, 1.4, 1.7, 4.4, 5.4, 5.5, 5.6, 6 g TiO2/m² | - | Cement mortar |
Kim et al. [55] | Recycled TiO2 nanoparticles produced from Ti-salt flocculated sludge obtained from dye wastewater. Suspension: dispersion of 20, 40, or 60 mg of TiO2 powder in 5 mL of distilled water with 10 mg of mussel adhesive protein (MAP) | 5 mL sprayed | - | Cement mortar |
Pondelak et al. [56] | Nanocomposites based on layered double hydroxides (LDHs) associated with a photocatalytically active TiO2. Up to 10 wt.% of TiO2 intercalated into the LDH. Preparation of a photocatalytic suspension | Three layers sprayed | ZnAl layered double hydroxide | Lime-based mortar |
Saeli et al. [24] | Photocatalytic hydroxyapatite (TiHAp). HAp derived from Atlantic codfish bone wastes prepared with 1 wt% TiO2. Suspensions of 1 wt% and 5 wt% TiHAp in distilled water | 1.5 mL deposited with a pipette | - | Natural hydraulic lime-based mortar |
Wang et al. [57] | Two core-shell nanocomposites with different deposited densities of TiO2 nanoparticles on each SiO2 nanosphere. SiO2@TiO2 photocatalysts (0.025 mg) added into water (2 mL), solution sprayed on one surface (4 cm × 4 cm) of slices. P25 used as reference | 2 mL sprayed | SiO2 | Cement paste and mortar |
Krishnan et al. [58] | For laboratory studies: TiO2 mixed in a commercial silicate coating in two contents of 1.6% or 2.5% (by volume of the liquid silicate). For field study: silicate containing 0.7% photocatalytic TiO2 | Individual coatings applied in three coats | - | Cement mortar |
Rosales et al. [59] | Synthesis with sonochemistry: mixing of titanium dioxide sol and silicon dioxide sol. Synthesis without sonochemistry: mixing of titanium dioxide particles and silicon dioxide sol | - | SiO2 | Cement mortar |
Wu et al. [60] | Photocatalytic top layer prepared by mixing a transparent silicate coating with 1.46% photocatalytic TiO2 by volume. 3 layers: white silicate coating, transparent silicate coating and photocatalytic layer | Each layer applied using a brush | - | Portland cement mortar |
Pérez-Nicolás et al. [61] | Dispersions with 1 wt% of the photocatalytic additive in water with superplasticizer (three polycarboxylate-based polymers and a commercial polynaphthalene sulfonate (PNS); 1 wt% in relation to the photocatalysts). Average percentage of photocatalytic additive with respect to the binder weight: 0.005% | 28.5 mg sprayed | Bare TiO2, Fe-TiO2 and V-TiO2 | Cement and air lime mortar |
Hot et al. [62] | TiO2 aqueous dispersions: dilution of a commercial stable aqueous dispersion of ultrafine TiO2 anatase particles. TiO2 dry matter content in solution: 18 wt%, 12 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt% and 1 wt% | Applied using brush | - | Cement mortar |
Guo et al. [29] | Commercially available TiO2 containing paint with about 10% TiO2 by weight: TiO2 water suspension prepared from a 0.03 g/L P25 distilled deionized water suspension | Three layers applied using a brush | - | Self-compacting architectural mortar |
Mendoza et al. [63] | Commercial TiO2 suspensions and homemade titania sol (TEA)—stabilized suspension. SiO2 sol applied on cement surface previously to the TiO2 layer for RhB removal evaluation | SiO2 and TiO2 layer sprayed | - | Cement mortar |
Rudic et al. [64] | Layered double hydroxides and photocatalytic active TiO2 particles in suspension. 1 wt% of the synthesized nanocomposite (TiO2-LDH) in a stabilized suspension | Three layers sprayed | Zn and Al salts | Lime-based renders |
Vulic et al. [65] | 3 wt% TiO2 suspensions introduced onto calcined ZnAl-LDH (layered double hydroxides) powder. Nanocomposite powder (1 g) suspended in 100 mL demineralized water. Nanocomposite suspension: 1 wt% of solid phase | Three layers sprayed | ZnAl-LDH | Cement and pozzolanic mortar |
Bengtsson and Castellote [66] | Two commercial paints (applied directly on the surface). Six TiO2 powders, applied in a solution at a concentration of 8.37 g/L, final TiO2 mass load of 5 g/m2. One of the powders was a homemade S-, N-, and C-doped catalyst (S-TiO2). Samples of the catalysts also submitted to treatments of exposure to water and calcinations (except for the paints and one powder) | 300 g/m² of paint applied with metal roller. 3 mL of dispersions | S, N and C for one of the eight different catalysts tested | White cement mortar |
Martinez et al. [67] | Acrylic polymer binder, water as solvent, additives (thickeners and wetting agents). Photocatalyst: particle suspension commercialized (40 wt% TiO2 P25). Final photocatalytic coating with 10% (wt) of TiO2 | 40 g/m² (≈5 µm) applied using a brush | - | Cement mortar |
Krishnan et al. [25] | Commercially available silicate coating material (containing potassium silicate, silica sol, and organic additives, solid content of 13.5%). 5%, 10%, 15%, and 20% of TiO2 by mass of solid silicate mixed with the silicate coating material | Three coats | - | Portland cement mortar |
Smits et al. [26] | TiO2 P25, P90 and Hombikat dispersed in ethanol; E-UV commercially available in liquid form | One layer deposited with a pipette (24 ± 2 mg, 267 µg/cm²) | - | Cement mortar |
Guo et al. [21] | Two coating techniques. 1: suspension of 25 g/L P25 ethanol suspension with 25 g/L glycerol; substrate materials dipped into it for 5 min. Coated mortar calcinated at 450 °C for 120 min to burn organic materials and bond the TiO2 film to the substrate. 2: suspension of methanol and P25 (25g/L); mortar dipped for 5 min, and over-dried at 60 °C for 120 min | Dip-coating | - | Self-compacting glass mortars |
Vulic et al. [22] | Wet impregnation of TiO2 onto Zn–Al layer double hydroxides (LDHs) for the preparation of Ti–Zn–Al LDH nanocomposites. Nanocomposite suspension prepared using sol–gel method with H2O2 solution | Three layers sprayed | Ti–Zn–Al LDH | Cement mortar |
Martinez et al. [68] | Acrylic binder, water as solvent, additives (thickeners and wetting agents). The photocatalyst was a commercial slurry solution. Different amounts of binders (2.3%, 5.0%, 7.5%, 11.5%, 15.0%) and various concentrations of photocatalyst (0%, 5%, 10%, 15%, 20%) | 40 g/m² applied using a brush | - | Mortar |
Fonseca et al. [69] | Aqueous solutions of anatase photocatalyst P25 (1% (v/v) in distilled water) | Sprayed | - | Two external walls of the National Palace of Pena |
Bengtsson and Castellote [70] | Colloidal suspension of TiO2 in deionised water at a concentration of 8.37 g/L, final TiO2 mass load of 5 g/m2 | Layers of around 10 μm | - | White mortar |
4. Photocatalytic Efficiency
4.1. Self-Cleaning Ability
4.2. Depolluting Effect
4.3. Antimicrobial Properties
5. Durability of Thin TiO2-Based Coatings
6. Sustainability Potentials and Concerns
7. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Paper | Subjects Addressed | |||
---|---|---|---|---|
Self-Cleaning Ability | Depolluting Effect | Antimicrobial Effect | Durability | |
Khannyra et al. [50] | X | X | X | |
Castro-Hoyos et al. [1] | X | X | X | X |
Gryparis et al. [51] | X | |||
Singh et al. [47] | X | X | ||
Pei et al. [11] | X | X | X | |
Zahabizadeh et al. [52] | X | |||
Zuena et al. [53] | X | |||
Gopalan et al. [42] | X | X | X | |
Speziale et al. [54] | X | X | X | |
Hot et al. [15] | X | |||
Rosales and Esquivel [48] | X | |||
Kim et al. [55] | X | X | ||
Pondelak et al. [56] | X | X | ||
Saeli et al. [24] | X | X | ||
Wang et al. [57] | X | |||
Krishnan et al. [58] | X | X | ||
Rosales et al. [59] | X | X | ||
Wu et al. [60] | X | |||
Pérez-Nicolás et al. [61] | X | X | ||
Khitab et al. [49] | X | X | ||
Hot et al. [62] | X | |||
Guo et al. [29] | X | X | ||
Mendoza et al. [63] | X | X | ||
Rudic et al. [64] | X | |||
Vulic et al. [65] | X | X | ||
Bengtsson and Castellote [66] | X | X | ||
Martinez et al. [67] | X | |||
Krishnan et al. [25] | X | X | ||
Smits et al. [26] | X | |||
Guo et al. [21] | X | X | X | |
Vulic et al. [22] | X | |||
Martinez et al. [68] | X | |||
Fonseca et al. [69] | X | |||
Bengtsson and Castellote [70] | X |
Paper | Photocatalytic Coating Composition | Deposition Method | Doping Substance/Nanocomposite If Applicable | Substrate Evaluated |
---|---|---|---|---|
Hischier et al. [33] | 3 coatings: paint containing nano-TiO2 together with pigment-grade TiO2; paint containing only pigment-grade TiO2; nano-TiO2 integrated into a (protection) coating laid separately on top of a traditional paint | Painting | - | - |
Pini et al. [72] | TiO2 acid nanosuspension | Dip-coating | - | Softened glass |
Tichá et al. [73] | TiO2 photocatalytic commercial suspension | Painting | - | - |
Hischier et al. [43] | Paint systems containing manufactured nanomaterials (MNM): paint containing nano-TiO2 together with pigment-grade TiO2; paint containing only pigment-grade TiO2 | Painting | - | Facade |
Babaizadeh and Hassan [34] | Mixture of TiO2 anatase nanoparticles suspended in an aqueous liquid at 2% by volume | Sprayed | - | Residential window glass |
Fufa et al. [74] | Coating with primer and stain or water-based acrylic blue tinted paint with brush. Treatments modified with TiO2 and clay nanoparticles or a combination of the two | Applied with brush | - | Norway spruce wood |
Paper | Dye or Contamination Agent | Exposure Conditions |
---|---|---|
Khannyra et al. [50] | 20 µL/cm² of 1mM MB solution dissolved in ethanol dropped over the treated and untreated samples | A 2500 W xenon arc lamp. 300 W/m² of irradiance. 60 min of irradiation |
Gryparis et al. [51] | Two drops (around 0.025 mL each) of MB applied over the coatings | UV-A light: 36 W LED curing lamp, with 33.6 mW/cm² irradiance. Artificial solar light: two 15 W tubular fluorescent lamps, around 13.6 mW/cm² irradiance. 48 h of irradiation |
Pei et al. [11] | 0.1 mL of RhB 10−3 mol/L deposited on the mortar surfaces = 5 cm² circular homogenous stained area | Three visible light lamps, resulting in 3.5 W/m² of irradiation. 72 h of irradiation |
Zahabizadeh et al. [52] | Immersion of samples in 30 mL of a 5 mg/L (5 ppm) RhB solution | Lamp with 300 W to simulate solar irradiation with 1 mW/cm² irradiance. 8 h of irradiation |
Zuena et al. [53] | Covering with 750 µL of a solution of 1 mM of methyl orange in ethanol | Laboratory test: samples in a ventilated chamber and irradiated for 72 h with 365 nm UV light. In-situ: specimens exposed to natural solar light over the month of November 2020 in Rome |
Speziale et al. [54] | 0.2 mL of RhB solution (10−3 M) poured with a micropipette on the surface of the specimens | UV–vis illumination with 300 W lamp. Loss of colour observed at different times over 48 h of irradiation |
Pondelak et al. [56] | Preabsorption test (24 h) with RhB solution, after which the RhB solution was replaced | UV-A intensity: 0.8 mW/cm². Visible light intensity: 0.3 W/m². Irradiation for 30 min, 90 min, 150 min, 210 min and 24 h |
Wang et al. [57] | 2 mL of RhB solution (80 mg/L) sprayed onto the surface of treated cement pastes | UV lamp (20 W). Intensity of UV light on the surface: 0.04 mW/cm2. 9 h of irradiation |
Krishnan et al. [58] | Black Carbon loadings of 8 mg/cm2 and 24 mg/cm2 | Three xenon lamps, 200 h of irradiation |
Rosales et al. [59] | RhB solution (concentration of 50 ppm) evenly applied with a pipette to 3 standardized positions on the samples | Light with a peak wavelength of 360 nm and an intensity of 10.3 W/m2. UV-A irradiation for 26 h |
Wu et al. [60] | 50 mg of commercially available black carbon powder dispersed in 100 g of deionized water. 8 μg/cm2 applied on the surface of the coated specimens | Simulated solar irradiation with wavelength from 295 to 3000 nm, intensity of 0.55 W/m2/nm at a wavelength of 340 nm. Exposure for 300 h |
Guo et al. [29] | 0.1 mL RhB solution (concentration of 5 × 10−4 g/mL) applied evenly on 3 standardized positions (5 cm2 e.a.) | Intensity of 3.1–3.4 W/m² and 0.5–0.6 W/m² for UV-A and visible light irradiation. Irradiation for 26 h |
Mendoza et al. [63] | 1.5 mL of 10−4 M RhB deposited on the surfaces in a circular homogeneous spot with 1.56 × 10−4 moles m−2 RhB | Six fluorescent lamps: 30 W/m2 of irradiance. 5 days of irradiation |
Vulic et al. [65] | Preabsorption with RhB solution (24 h) and then RhB solution replaced (10 ppm dm−3) | Intensity of UV-A and visible light spectra: 8 W/m² and 0.3 W/m², respectively. Irradiation for 210 min |
Bengtsson and Castellote [66] | RhB initial concentration: 1.368E−4 mol/m²; tobacco solution initial concentration: 2.359 g/m² | UV light. Irradiance: 5 W/m². Irradiation for 22 h |
Krishnan et al. [25] | RhB dissolved in deionized water (concentration of 0.05 g/L), 5 mL applied on the specimen surface. Surface loading: 4.2 µg/cm² | UV light: wavelength from 295 nm to 400 nm with average intensity of ≈0.35 W/m² and peak intensity of 0.68 W/m² at 340 nm. Irradiation for 100 h |
Smits et al. [26] | Dispersion of 0.1% carbon black in 8:2 water:isopropanol solution. Four drops applied on each sample = thickness of the soot layer around 0.12 µm (≈22 µg cm²) | UV-A illumination: five lamps of 25 W; most intense wavelength at 368 nm; maximum incident light intensity: 340 µW/cm²; luminance: 4600 lux. Artificial solar irradiation: four full spectrum daylight lamps of 14 W with reflectors; maximum incident light intensity: 70 µW/cm² and 31,000 lux. Irradiation for over 400 h |
Vulic et al. [22] | Bottomless glass tube (inner diameter 33 mm, height 70 mm) fixed on each specimen and filled with a 10 ppm dm−3 MB solution. Specimens surrounded by the same MB solution. Preabsorption test (24 h), after which the MB solution was replaced | UV irradiation with light intensity of 0.922 mW/cm² for 30, 90, 150 and 210 min |
Paper | Gas Flow | Exposure Conditions |
---|---|---|
Khannyra et al. [50] | NO gas supply volume fraction ranging from 1136 ppb to 1188 ppb depending on the sample | UV-A light, irradiation intensity of 1 mW/cm². Irradiation for 5 h |
Pei et al. [11] | Gas mixture with a flow rate of 3 L/min and a NO concentration of 1 ppm | Two visible lamps, 420 nm, irradiation intensity of 10 W/m². Irradiation for 12 h |
Speziale et al. [54] | Initial NO concentration of 500 ppbv at a 3.0 L/min | UV–vis radiation. Illumination source: a 300 W lamp. Irradiation for 30 min |
Hot et al. [15] | Initial NO concentration of 400 ppb after dilution with air | Two different UV light intensities: 20 W/m² and 5 W/m². Irradiation for 10 min |
Kim et al. [55] | 1 ppm ± 0.015 ppm of NO gas at a flow rate of 3.0 L/min | UV light of 10 W/m², 352 nm lamp. Irradiation for 5 h |
Saeli et al. [24] | Inlet gas mixture prepared with synthetic air and NOx at a concentration of 0.2 ppm. Flow rate of 1 L/min | Solar lamp leading to light intensity of 3.6 W/m2 in the UVA range and 25 W/m2 in the visible-light range. Irradiation for 45 min |
Pérez-Nicolás et al. [61] | 500 ppb NO stream, 0.78 L/min flow | Two different lamps: 300 W for UV illumination, and 250 W for solar and visible irradiation, with intensities of 43.4 W/m2 and 36.7 W/m2. Irradiation for 30 min |
Hot et al. [62] | NO diluted to 400 ppb and flow rate constant at 1.5 L/min | Three illumination conditions: UV light at 1 W/m², UV light at 3.3 W/m², and visible light at 2.4 W/m². Irradiation for 60 min |
Mendoza et al. [63] | NOx concentration 0.55 ± 0.05 mg/L (0.4 mg/L NO + 0.15 mg/L NO2) at a constant 1.5 L/min flow | 300 W lamp (λMax = 365 nm) that provides 20 W/m² of irradiance. Irradiation for 40 min |
Bengtsson and Castellote [66] | Initial NO concentration: 1000 ppbv; initial NO2 concentration: 50 ppbv | Irradiance 10 W/m². Irradiation for 120 min |
Martinez et al. [67] | Concentrations: 2.2 ppmV benzene, 9.5 ppmV toluene, 1.7 ppmV ethylbenzene, 1.7 ppmV o-xylene, 1.6 ppmV m-xylene, 1.6 ppmV p-xylene. Flow rate of 100 mL/min | 18 W blacklight blue fluorescent tube. Light intensity of 6.0 W/m2. Conversion of VOC calculated for 24 h of UV irradiation |
Guo et al. [21] | Flow of the testing gas: 1000 ppb NO. Rate of 3 L/min | UV intensity of 10 W/m2. Irradiation for 60 min |
Martinez et al. [68] | Flow rate 1.5 L/min; initial NO concentrations: 400 ppb, 1000 ppb, 1500 ppb, 2000 ppb | 300 W bulb with an emission spectrum close to that of daylight. Light intensity of 5.8 W/m2. Irradiation for 1 h |
Bengtsson and Castellote [70] | Initial NO concentration of 1000 ppb. Flow rate of 5.2 L/min | UVA radiation at an optimum of 365 nm. Irradiation for 120 min |
Paper | Microorganism Studied | Method |
---|---|---|
Guo et al. [21] | Escherichia coli K12, a UV-resistant bacterium | Concentration of E. coli K12 of ≈1 × 105 colony forming units (CFU)/mL in sterilized 0.9% (w/v) sodium chloride solution. 1 mL of cell suspension applied with a pipette on mortar samples. Irradiation with UV lamps with 10 W/m² of intensity. After 20, 40, 60, 90, and 120 min of irradiation, collection of cell suspension by washing the sample with 20 mL of 0.9% sodium chloride. 100 µL of diluted suspension spread on a nutrient agar plate and incubated. The examination of the viable count of the CFU indicated the loss of variability |
Fonseca et al. [69] | Studies in situ encompassing two existing external walls already covered by organisms located in National Palace of Pena (Sintra, Portugal). One of the walls was directed to East-Northeast, did not receive direct sunlight, presented high humidity, and was widely colonized by lichenic and algal communities. The second wall faced East, received direct sunlight for most of the day and had a scattered presence of lichens | Photocatalytic coatings compared with conventional biocides (Biotin T applied using a brush at 2% (v/v), and Anios sprayed without dilution). Anatase aqueous solution applied on 50 cm² of the walls and compared with the biocides. Colour measurements and photograph records comparing the treated areas before and after two weeks of the suspension application used to evaluate the results |
Paper | Property | Method |
---|---|---|
Khannyra et al. [50] | Adhesion of the coating to the substrates | Peeling test by sticking a piece of adhesive tape on the surface and determining the increase of weight on the tape after its detachment |
Pei et al. [11] | Photocatalyst regeneration after NO photodegradation | Deactivated graphene/TiO2 nanocomposites exposed to UV irradiation in a continuous flow without NO under 50% RH for 0 h, 6 h, 12 h, 24 h, 36 h, and 48 h. NO removal rates of commercial TiO2 assessed after 0 h, 6 h, and 12 h. The regeneration was evaluated using a subsequent photocatalysis experiment |
Speziale et al. [54] | Photocatalytic activity (NOx abatement) and water repellence assessment (WCA) for optimized coatings | Exposure to accelerated climatic ageing. Cycles with changes in temperature, relative humidity, UV–vis irradiation, and rain periods. 25 min steps of: (1) 35 °C, UV–vis radiation, 40% RH; (2) 20 °C, 90% RH, rainwater; (3) 0 °C, 60% RH; (4) −5 °C, 50% RH. Steps continuously repeated for 3 days |
Kim et al. [55] | Adhesion/bonding strength of the MAP-dispersed TiO2 nanoparticle-coated film on substrates | Adhesion analyser (centrifugation technique) |
Pondelak et al. [56] | Abrasion resistance and photocatalytic activity using RhB degradation | Exposure to rinsing (constant flow of tap water (250 mL/min) through a pipe system (nozzle diameter of 0.90 mm) for 30 min) and freezing–thawing cycles (50 cycles encompassing 5.5 h at 15 °C in water, followed by removal of the water and reduction of the temperature to −4 °C within 2 h; then, cooling of the substrates to −10 °C for 4 h. Lastly, the water was poured into the chamber again) |
Saeli et al. [24] | Presence of the photocatalytically active layer on the surface and photocatalytic efficiency using NOx abatement | For the evaluation of the layer presence, exposure during 24 h in an ageing chamber at 35 °C, with aerosol of distilled water at 100% humidity, and test with X-ray diffraction (XRD). For NOx abatement, three repeated runs of the test, with no thermal or chemical regeneration treatment + test after two years of external exposure |
Krishnan et al. [58] | Appearance changes | Field exposure for ~42 months in Singapore. Appearance changes monitored with L* and solar reflectance (SR) measurements |
Rosales et al. [59] | Adhesion of the coating to the substrates | Grid of 1 mm × 1 mm with 11 cuts of 20 mm in length on the coated mortar. Scotch tape, three inches long, placed in the centre of the grid and soft pressed with an eraser. Removal of the tape from the opposite end of the application. Comparison with patterns. RhB removal assessed before and after adherence test (0 h, 4 h and 26 h) |
Pérez-Nicolás et al. [61] | Photocatalytic activity using NO abatement | Accelerated climatic ageing. 7 cycles of 24 h, with varying conditions of temperature, relative humidity, rain, and UV light |
Guo et al. [29] | Photocatalytic removal of RhB | Lab-simulated accelerated facade weathering, encompassing wet (1.5 L of tap water for 12 h) and dry (switching off the pumps for 12 h) conditions, and day (three UV-A and two visible lamps; UV-A intensity of 350 ± 10 mW/cm²) and night conditions (switching off the lamps). Weathering for one and two weeks |
Rudic et al. [64] | Adhesion of the coating to the substrates | Two adhesion tests: one based on the standard tensile/pull-off method [83] and the other on modified test with semi-transparent pressure-sensitive tape [84] |
Vulic et al. [65] | Photocatalytic activity, contact angle, surface roughness, and micro-hardness | Rain rinsing (constant tap water flow (250 mL/min) through a pipe system (nozzle diameter of 0.90 mm) for 30 min) |
Krishnan et al. [25] | RhB degradation | 5 cycles of 100 h, at the beginning of each RhB was applied. After each cycle, intermittent UV irradiation exposure (18 h UV and 6 h rest). Total duration of UV exposure of 2500 h, similar to at least 2.4 years on a tropical warm and humid condition |
Guo et al. [21] | NO removal and antibacterial abilities | Three weathering conditions: normal weathering with no additional treatment; samples washed 10 times using 500 mL of deionized water to simulate rain; abrasive process with a wet cotton towel to scrape the surface with the TiO2 layer (manually applied back and forth motion for 20 cycles) |
Paper | Scenarios | Reference Study Period/ Functional Unit | LCA Software and Database | System Boundaries | Impact Assessment Method | Environmental Impact/Damage Categories Assessed |
---|---|---|---|---|---|---|
Hischier et al. [33] | 180: 6 functionality options, 5 data sources for nano-TiO2 production, 2 nanoparticles’ release scenarios, 3 LCIA factors of the releases. Lifetime: traditional paint: 20 years; nano paint: 27 years (alternatives with 20% and 50% longer lifetime than traditional); nano coating: 15 years (alternatives with 10 and 20 years) | 80 years/ 1 m² of wall, protected over a time period of 80 years | Software OpenLCA (version 1.4.2) and database Ecoinvent data v3.1, cut-off approach | Project-specific data for product stage (production of traditional paint, nano-TiO2, nano-paint, and nano-coating, where applicable), construction stage (1st and further application of paint/coating), use and end-of-life. Background system: production of further ingredients, and production and end-of-life of packaging materials | USEtox and ReCiPe | Global warming potential, fossil resource depletion potential, freshwater eutrophication potential, tropospheric acidification potential, freshwater ecotoxicity potential, human toxicity potential/ ecosystem diversity, human health, resource availability |
Pini et al. [72] | Uncoated flat glass (conventional material), nanoTiO2 coated float glass (10 years or 30 years, obtained with two refunctionalization processes) | 30 years/ 1 m² of nanoTiO2 self-cleaning coated float glass | Software SimaPro 8 and databases included in the software (like Ecoinvent v2) | Supply of raw materials, packing, installation, and end-of-life; production, maintenance, and disposal of facilities; environmental burdens related to the production of chemicals, packaging, and auxiliary materials; emissions into air and water, solid waste; transportation of solid waste to a treatment facility | Modified IMPACT 2002+ v2.10 and USEtox method v1.03 | Carcinogens, non-carcinogens, respiratory inorganics, ionizing radiation, ozone layer depletion, respiratory organics, aquatic ecotoxicity, terrestrial ecotoxicity, terrestrial acidification/nutrification, land occupation, aquatic acidification, aquatic eutrophication, global warming, non-renewable energy, mineral extraction, radioactive waste, carcinogens inhaled, human toxicity—cancer, human toxicity—non-cancer, ecotoxicity, human toxicity—cancer—indoor, human toxicity—non-cancer—indoor/ human health, ecosystem quality, climate change, resources, radioactive waste, carcinogens inhaled |
Tichá et al. [73] | Application of photocatalytic coating to the ceiling (100 m²)—for the mechanical air purifier, a maximum input power of 110 W was chosen. 3 scenarios for lighting and power regime/period of operation | 1 year/ Purification of 100 cubic meters of air in an enclosed space over a period of one year | Software SimaPro 8.0.4 and database Ecoinvent 3 | Cradle-to-grave: from raw material acquisition through production, use, end-of-life treatment, recycling, and final disposal | CML-IA baseline V3.01/EU25 | Abiotic depletion, abiotic depletion (fossil fuels), global warming (GWP100a), ozone layer depletion, human toxicity, freshwater aquatic ecotoxicity, marine aquatic ecotoxicity, terrestrial ecotoxicity, photochemical oxidation, acidification, eutrophication |
Hischier et al. [43] | Substitution of nano-TiO2 for parts of another active ingredient in the paint (pigment-grade TiO2) | 80 years/ Protection of one square meter of (indoor or outdoor) wall during a period of 80 years | Software OpenLCA and database Ecoinvent v2.2 | Foreground system: production of MNM and paint, 1st and further application of paint, use phase, end-of-life treatment (paint). Background: extraction resources, production of further ingredients, copolymer, filler materials, energy supply, production, and end-of-life packaging materials | ReCiPe method and USEtox model | Global warming potential, freshwater eutrophication potential, fossil fuel depletion potential, terrestrial acidification potential/ecotoxicity, human toxicity, ecosystem diversity, human health, resource availability |
Babaizadeh and Hassan [34] | Comparison of titanium dioxide-coated glass with uncoated glass (float glass) with the same specifications | 40 years/ One square meter of titanium dioxide-coated glass | - | Extracting and processing the raw data, manufacturing, use phase, and end-of-life for coated and uncoated windows | BEES 4.0 model | Global warming, acidification potential, eutrophication potential, fossil fuel depletion, indoor air quality, water intake, criteria air pollutants, human health, smog formation potential, ozone depletion potential, ecological toxicity |
Fufa et al. [74] | Spruce coated with unmodified water-based paint and modified with 1 wt% nano-TiO2 | 50 years/ 0.01 m² coated exterior wooden cladding | - | Production, construction, use and maintenance, and demolition | ReCiPe | Global warming, human toxicity, photochemical oxidation formation, acidification, and eutrophication |
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Bersch, J.D.; Flores-Colen, I.; Masuero, A.B.; Dal Molin, D.C.C. Photocatalytic TiO2-Based Coatings for Mortars on Facades: A Review of Efficiency, Durability, and Sustainability. Buildings 2023, 13, 186. https://doi.org/10.3390/buildings13010186
Bersch JD, Flores-Colen I, Masuero AB, Dal Molin DCC. Photocatalytic TiO2-Based Coatings for Mortars on Facades: A Review of Efficiency, Durability, and Sustainability. Buildings. 2023; 13(1):186. https://doi.org/10.3390/buildings13010186
Chicago/Turabian StyleBersch, Jéssica D., Inês Flores-Colen, Angela B. Masuero, and Denise C. C. Dal Molin. 2023. "Photocatalytic TiO2-Based Coatings for Mortars on Facades: A Review of Efficiency, Durability, and Sustainability" Buildings 13, no. 1: 186. https://doi.org/10.3390/buildings13010186