Pittura mangiasmog ed ecomurales

31 Maggio 2021 by Raffaella Ganci
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Green Urban Art. Gli ecomurales riducono lo smog oppure servono alle istituzioni, alla ricerca costante di consenso, a chi propone progetti, fondazioni e associazioni, spesso a corto di soldi, agli sponsor che, attenti al rapporto costo-opportunità, sostituiscono i cartelloni pubblicitari con i muri dipinti?

Il discorso è ampio e va considerato l’intero contesto di impatto, ambientale, politico ed economico per tentare di capire se l’arte urbana venga ingaggiata nella veste di testimonial di una reale rivoluzione green, o se, invece, divenga strumento della retorica della sostenibilità, utilizzata per diffondere uno storytelling dalla trama sottile, concepito per fidelizzare elettori e consumatori, facendo leva sul diffuso ‘sentire’ ecologico.

Nei vari festival o eventi in cui la ‘sostenibilità ambientale’ passa attraverso l’arte urbana si riscontrano alcune incongruenze. Le parole corrispondono ai fatti? Gli artisti sono stati informati in modo preciso e corretto sulla procedura da seguire nell’uso dei prodotti? L’organizzazione, fornendo oltre le pitture le bombolette, si è chiesta se questa incoerenza potesse in qualche modo nuocere alla credibilità degli artisti ed al funzionamento delle vernici? Previa lettura di un esempio di scheda tecnica 1 di uno dei prodotti, alcuni video 2 suscitano qualche perplessità.

 

Le pitture mangiasmog

Le pitture mangiasmog, o fotocatalitiche, prevedono una preparazione accurata del sottofondo, una stesura uniforme dell’ultima mano entro breve tempo dalla miscelazione, la presenza di luce solare. Se utilizzate all’interno di tunnel o luoghi dove la luce solare non penetra, è necessario predisporre un impianto illuminotecnico in grado di produrre elevati quantitativi di raggi UVA.

Ciascuno di questi prodotti ha come ingrediente base per la fotocatalisi il biossido di titanio e si quotano in base a certificazioni che ne attestano la capacità di abbattimento dell’inquinamento atmosferico.

Come prevede la prassi, le certificazioni, rilasciate in seguito a test effettuati in laboratorio, si limitano a valutare il prodotto in sé, prescindendo dall’impatto ambientale dell’intero ciclo di vita (Life Cycle Assessment – LCA) del prodotto stesso 3, dall’estrazione delle materie prime, al loro trattamento, alla fabbricazione, al trasporto, alla distribuzione, all’uso, riuso, riciclo e smaltimento finale. Le certificazioni, mancando il Life Cycle Assessment, bastano per classificare come ‘verdi’ le prestazioni ambientali di un prodotto?

L’ingrediente indispensabile per questo tipo di pitture è il biossido di titanio, ricavato da anastatio, brookite, e soprattutto rutilo e ilmenite. Il processo di estrazione e smaltimento degli scarti di questi minerali è tra i più impattanti: “la concentrazione di TiO2 dei giacimenti attualmente coltivati varia tra il 5 e il 20%, implicando che oltre l’80% del materiale estratto è sterile ed è destinato a discarica. A titolo di esempio una delle più grandi miniere di ilmenite al mondo (Lac Tio Mine, Quebec, Canada) ha prodotto oltre 72 milioni di tonnellate di materiali di scarto generando discariche a cielo aperto che occupano approssimativamente 100 ettari di territorio con un’altezza variabile tra 20 e 80 metri.4 Recenti studi scientifici, preso in considerazione l’impatto ambientale delle estrazioni minerarie attraverso l’intero ciclo di vita, giungono alla conclusione che l’estrazione di uranio, rutilo e ilmenite è quella che maggiormente contribuisce al riscaldamento globale e alle emissioni di gas serra 5 .

Il processo di estrazione chimico del biossido di Titanio è altrettanto gravoso per l’ambiente: per 1 tonnellata di polveri commercializzabili si producono 7 tonnellate di scarto, i cosiddetti “gessi rossi”. La Venator Italy srl, unica azienda italiana produttrice di TiO2, è stata oggetto di verifica da parte della commissione parlamentare di inchiesta “sulle attività illecite connesse al ciclo dei rifiuti e su illeciti ambientali ad esse correlati”. La Commissione si è pronunciata in merito alla pericolosità dei “gessi rossi” e all’illeicità con cui sono stati gestiti dalla Venator nel territorio di Scarlino (Grosseto). Si è appurato che tale scarto di lavorazione, distinto in rifiuti destinati al ripristino ambientale, e come tali conferiti nell’ex cava di Poggio Speranzona a Montioni, Follonica, e in additivi per l’agricoltura, conteneva livelli di cromo e vanadio superiori a quelli consentiti dalla legge e che per le sue caratteristiche va “considerato soltanto un rifiuto che avrebbe dovuto avere come destinazione la discarica. Il mancato invio in discarica dei gessi rossi, nelle quantità sopra indicate, ha determinato per la società un notevole risparmio di spesa, per decine di milioni di euro.” A ciò si aggiunga la movimentazione che, per il solo trasporto dello scarto, sposta circa 70 camion al giorno. 6

Inoltre. Nel 2016 l’Agenzia internazionale per la ricerca sul cancro ha classificato il biossido di Titanio come potenzialmente cancerogeno per gli esseri umani 7.

La Francia, sentito il parere dell’ANSES (Agence Nationale de Sécurité Sanitaire de l’Alimentation, de l’Environnement et du Travail), ha vietato l’uso del biossido di Titanio 8 sull’evidenza di test di laboratorio che evidenziano modifiche dei meccanismi biologici cellulari nei topi, anomalie dello sviluppo negli invertebrati, ed effetti genotossici correlati alle nanoparticelle di TiO2.

E In Italia? Il Biossido di Titanio è utilizzato in vari settori industriali nella produzione di: alimenti (come additivo, E171), carta, ceramica, parti meccaniche, cosmetici, materiali cementizi e plastici, fibre sintetiche e materiali tessili, grassi lubrificanti, pellami, gomma e vetro, creme per neonati e solari, dentifrici, inchiostri, rivestimenti, vernici. Considerandolo insostituibile per la purezza del colore bianco, l’opacità e la capacità di rifrazione, Confindustria Italia si è espressa contro la possibilità di adottare le precauzioni prese dalla Francia, giudicandole ingiustificate ed inappropriate in relazione “alla percezione negativa del termine ‘cancerogeno’”, checomporterebbe il possibile divieto della vendita al pubblico di tutti i prodotti contenenti TiO2. Infatti, sebbene la proposta di classificazione riguardi la frazione inalabile del TiO2, essa impatterebbe anche sui prodotti liquidi e in pasta che contengono TiO2 anche se non è disponibile per l’esposizione all’inalazione (non è respirabile).” Nelle conclusioni del documento emergono chiaramente le ragioni del rigetto: “Non vi sono, ad oggi, valide alternative con le stesse prestazioni, motivo per cui le conseguenze nella catena di fornitura sarebbero drammatiche9.

Dati aggiornati sul giro d’affari europeo collegato al TiO2 li fornisce la Titanium Dioxide Manufacturers Association (TDMA): settore vernici e rivestimenti 27,2 miliardi di euro per il 2017; materie plastiche 350 miliardi di euro annui; industria cartaria 180 miliardi di euro annui; industria alimentare 1.089 miliardi di euro annui; industria cosmetica 77 miliardi di euro annui 10.

È di appena pochi giorni fa la comunicazione del Professore Maged Younes, presidente del gruppo di esperti EFSA (European Food Safety Authority) sugli additivi e aromatizzanti alimentari: “Tenuto conto di tutti gli studi e i dati scientifici disponibili, il gruppo scientifico ha concluso che il biossido di titanio non può più essere considerato sicuro come additivo alimentare. Un elemento fondamentale per giungere a tale conclusione è che non abbiamo potuto escludere timori in termini di genotossicità connessi all’ingestione di particelle di biossido di titanio. Dopo l’ingestione l’assorbimento di particelle di biossido di titanio è basso, tuttavia esse possono accumularsi nell’organismo umano.” Tuttavia, l’EFSA non ne vieta l’utilizzo (!!!), limitandosi “alla valutazione dei rischi legati al biossido di titanio come additivo alimentare, ovvero una valutazione delle informazioni scientifiche pertinenti sul TiO2, la sua potenziale tossicità e le stime dell’esposizione alimentare umana. Qualsiasi decisione di tipo legislativo o normativa in merito all’autorizzazione degli additivi alimentari compete ai gestori del rischio (cioè la Commissione europea e gli Stati membri).” 11

Nel 2019 l’Unione Europea ha classificato il TiO2 come cancerogeno 2 H351 per inalazione se in polvere contenente ≥ 1 % di particelle con diametro aerodinamico ≤ 10 μm. 12 In base a quanto stabilito dall’UE, le vernici fotocatalitiche confezionate sotto forma di polveri corrispondono ai parametri stabiliti dalla legge? Chi le utilizza corre dei rischi collegati all’esposizione al nano-biossido di titanio volatile? 13

Ho interpellato il Professore Nick Serpone 14, uno dei massimi esperti in fotocatalisi.

“Professore, si afferma che le pitture mangiasmog, una volta applicate, interagendo con la luce solare, eliminino inquinanti tra cui i NOx, gli ossidi di azoto, inibiscano la crescita di muffe e batteri, neutralizzino i cattivi odori, svolgendo un’azione ‘respingente’ nei confronti di tutto ciò che possiamo definire ‘sporco’. Il processo di fotocatalisi di questi prodotti convoglia, sulle superfici trattate, un gran numero di elettroni che a contatto con l’acqua e l’ossigeno presenti nell’atmosfera danno luogo a ioni ossidanti in grado di catturare le sostanze inquinanti e trasformarle in sali. Questi sali, depositandosi sulle pareti, possono, trascorso del tempo, bloccare la superficie fotocatalitica disattivandola?

Per evitare l’eventuale disattivazione, le superfici -indoor (pareti interne di edifici) e outdoor (facciate di palazzi, tunnel, etc.) – trattate con pitture fotocatalitiche devono essere ‘lavate’ con regolarità, dalla pioggia o con metodi manuali, se la pittura è utilizzata in zone aride, in tunnel o pareti interne di edifici?

Risultato del passaggio del NOx in sale è l’acido nitrico che sappiamo essere corrosivo. Pertanto, lavaggio dopo lavaggio, questo sale potrebbe inquinare il terreno, se il livello di concentrazione in sito dovesse diventare troppo alto?

Per valutare le prestazioni di un prodotto sono sufficienti i test effettuati in laboratorio o andrebbero integrati con prove condotte in ambiente aperto per valutare, nel medio e lungo termine, la capacità di assorbimento delle sostanze inquinanti della pittura utilizzata all’interno e all’esterno degli edifici?

I test di laboratorio sono in grado di riprodurre tutte le variabili dell’ambiente aperto (superfici ampie, presenza di polvere e sporcizia, variazione di luminosità e umidità, quantità variabile di NOx, periodo di rilevazione nel medio e lungo periodo), dove la pittura fotocatalitica dovrebbe rimanere attiva per mesi o anni?

Alcune di queste vernici avrebbero la capacità di neutralizzare i Coronavirus. Oltre che con i vaccini, i virus si battono anche con il pennello? 15.”

 

“Based on my 40 years’ experience in studies of semiconductor-based photocatalysis with such photocatalysts as TiO2, CdS, ZnO, CeO2, Ga2O3 (among others), and on my lengthy 2018 review article (see footnote 13), I doubt that any TiO2-based paint for that matter, can eliminate the urban-generated smog that is composed of several substances: (i) tropospheric ozone (O3); (ii) primary particulate matter such as pollen and dust; and (iii) secondary particulate matter such as sulphur oxides, nitrogen oxides (NOx), volatile organic compounds, and ammonia gas.

Extensive results presented in ‘Heterogeneous Photocatalysis and Prospects of TiO2-Based Photocatalytic DeNOxing the Atmospheric Environment’ (footnote 13) reveal that experiments in a laboratory setting are carried out under highly controlled conditions (e.g., light irradiance, gas flow, humidity, and residence time) using a small reactor (see Figure 1). Such experiments have indeed evidenced the destruction of the NOx pollutants with great efficiency; under such conditions, the NOx gases come into close contact with the photo-activated titanium dioxide and get transformed into nitrites and nitrates.  For example, studies done on behalf of Airlite at Rome’s La Sapienza reported similar findings. However, that is not the case under real environmental conditions outdoors.

 

Figure 1. (Left) a typical reactor used to test TiO2 samples under strict controlled conditions; (Right) example of a real outdoor environment (e.g., the Umberto I tunnel near the Quirinale, Rome) where the prevalent atmospheric conditions cannot be controlled.

 

Results obtained in a laboratory setting CANNOT be extrapolated to the outdoor environment because unlike a laboratory setting, in an open environment, one does not control the conditions!

 

Related to these laboratory studies, three major studies have been carried out in the last two decades, which were funded wholly or in part by the European Union to examine the use of TiO2 to destroy the NOx pollutants present in the atmosphere. The first study was carried out using Italcementi’s TX-Active® photocatalytic TiO2 by an Italcementi Consortium consisting of 8 partners from industry and research institutes from Greece, France, Italy, Denmark and Great Britain: the PICADA Project (2002–2006). The second study was done by a consortium led by German scientists who also used Italcementi’s TX-Active®, Italcementi’s TX-Active® Skim Coat, and Italcementi’s TX-Active® Skim Coat Boosted TiO2 materials: the Life+-funded Project PhotoPAQ (2010–2014). The more recent third study was led by Spanish scientists: the LIFE MINOX-STREET Project (2014–2018) in which they tested several TiO2-based photocatalytic materials.

The last 2 studies were carried out in a manner that I would have. The efficiencies of TiO2 deposited on cementitious outdoor walls to destroy the environmental NOx reported in the latter two studies was 2% or less, while the PICADA study claimed efficiencies upward of 60% ‒ “una differenza non trascurabile16.

Titanium dioxide is the white paint pigment found in white paint, but it is present in a form that is not photo-active because the TiO2 nanoparticles are passivated being coated with silica/alumina (SiO2/Al2O3). Elimination of the urban smog requires the TiO2 to be photo-active, which occurs when it is photo-activated by UVA light (the anatase TiO2 powder being the most photocatalytically active form). Being so, however, will also destroy the paint itself if TiO2 is not rendered inactive.

To get back to your question, let me do so more directly and bluntly. Only those smog components that come into actual contact 17 with the surface of the TiO2 nanoparticles on the outdoor walls will be destroyed. The method by which the TiO2 is deposited onto the walls is very important (un processo che non è trascurabile). Perhaps on a windy day, more of the smog components will come into contact with the surface TiO2 and become destroyed.

What salts are produced after the chemical reactions have taken place at the surface? Let me use the NOx pollutants as the prime example (other volatile organic compounds in the atmosphere may also be transformed through formation of intermediate species that may be toxic or whose toxicity is unknown). What happens at the surface then is an oxidation process caused by the highly oxidizing hydroxyl radicals (formed through oxidation of water) that convert the NOx into nitrites and nitrates, and since cement contains calcium, the salts formed will be calcium nitrate {Ca(NO3)2} and calcium nitrite {Ca(NO2)2}, both of which will remain on the walls surface (cioé, ricopre la superfice che contiene il TiO2) and thus will BLOCK the photo-active TiO2 from further participating in chemical reactions. Also formed is nitrous acid and nitric acid. Inasmuch as the two calcium salts are water soluble, ONLY when it rains will the calcium nitrate/nitrite salts be removed and discarded into the aqueous environment (sewage, rivers, etc…). However, there is a solution to avoid the formation of the nitrites/nitrates. This will require changing the selectivity of the TiO2 photocatalyst from being oxidative to being reductive, which will transform the NOx pollutants back to molecular nitrogen and molecular oxygen, the two principal gases in our atmosphere. 18

Nitrates are fertilizers, while Nitrites, being anti-oxidants, are often added to wines (sometimes sulfites are used) to prevent oxidation of the wine into vinegar (cioé, etanolo convertito in acido acetico tramite l’azione dell’ossigeno).

There is one additional claim made in marketing paint brochures: the removal of carbon dioxide (CO2) from the environmental atmosphere. Another falsehood? Not necessarily. Yes it does remove it to a point! Since the cement contains CaO, the CO2 will react with CaO and forms CaCO3 – also known as calcite. However, calcite remains on the walls’ surface, as it is not soluble in water so that even when it rains or when the surface is washed intentionally it stays on the walls. Accordingly, it will block (covers) the photo-active TiO2 photocatalyst in the TiO2-based paint (from whatever source) and will no longer destroy the NOx pollutants. A look at Figure 2 shows the calcite layer covering the cementitious material with the photo-active TiO2 paint on its surface. 19

 

Figure 2. (a) optical microscope image of the cross section of a concrete specimen containing TiO2 under X-polarized light—note the surface exhibits a thin calcite layer that appears in a lighter colour; (b) optical microscope image of the cross section of a concrete specimen containing TiO2 under fluorescent light—note that the calcite layer now appears dark green indicative of low porosity; and (c) SEM image of the top surface of a concrete specimen containing TiO2 (same sample as in (a,b)) wherein the surface consists of a layer of small, closely spaced, euhedral calcite crystals—TiO2 photocatalytic clusters are no longer exposed to UV light.

 

At the nanoparticulate level (that is, at the level of a few nanometers; from 0.000 000 001 to 0.000 000 100 meters), TiO2 powder is  considered a potential carcinogen if ingested orally, 20 and according to the many literature reports, TiO2 nanomaterials may be deleterious to human health. 21

The TiO2 powder from an industrial supplier usually comes as aggregated nanoparticles (several micrometers in size) that need to be broken so that when added to water and stirred vigorously (for example, by ultra sounds – sonication) it forms a colloidal solution (il latte é una soluzione colloidale). This colloidal TiO2 solution cannot simply be sprayed on a wall and expect it to bind to the cementitious wall or brick wall; it needs a chemical binder that is not affected by the photo-active TiO2.

Many of the mural art come in several different colors. The yellow and orange colors are most likely based on the pigment known as cadmium sulfide (CdS) – NOTE that cadmium is extremely toxic!! Other pigments such as chromium-based pigments are also toxic as I have indicated below.

With regard to your comment “sono riusciti a ‘intrappolare’ chimicamente il biossido di titanio?” I cannot answer this question without having seen each specific paints’ patent(s).

As normally occurs, the paint will have degraded after several years, and whatever TiO2 is left may get into the aqueous environment. It will be this ecosystem to suffer the consequences if the TiO2 paint is still photo-active.

Photo-active titanium dioxide is not a monster, however, as it also has its good sides. We have used it to destroy tens of pollutants in aqueous media (albeit in a laboratory setting; extrapolation to real applications has been challenging to say the least) from BPA flame retardants, 22 to DDT, 23 to Chlorinated Dioxins and PCBs, 24 to Haloaromatic pollutants, 25 to Creosote components (cresols), 26 to Surfactants (soaps), 27 to Biosurfactants, 28 to Herbicides, 29 to Pesticides, 30 to the recovery of precious metals (gold, platinum, rhodium) from jeweller’s wastes and disposal of Cyanide, 31 to Polymers, 32 to Pharmaceuticals (for example, the antidepressant drug Prozac), 33 to Dyes, 34 and to the elimination of Toxic Metals (lead, mercury and methylmercury). 35 As well, Japanese scientists have recently demonstrated the therapeutic effects of titanium dioxide on cancer cells, 36 while American scientists reported on the use of TiO2 to kill cancer cells. 37 So it all depends on how and under what conditions TiO2 is applied.

Can TiO2 also destroy the Covid-19 virus? Probably yes! 38 – But at the moment only under strict laboratory/clinical conditions. In this regard, it is worth noting that both Silver and Copper metals can destroy bacteria. A recent study has shown that Copper can also destroy the Coronavirus when the virus is deposited onto Copper metal. 39

Results cited in my lengthy review article (footnote 13) from the German and Spanish consortia studies demonstrate that the TiO2 deposited on the tunnel walls (that I refer to as “indoor walls”) stopped functioning after about a week because of the soot, dirt and exhaust from cars and trucks as it covered the TiO2 nanoparticles, which could no longer be photo-activated by light (see Figure 3).

 

Figure 3. Sample of a photo-active TiO2-based cementitious surface before and after one week in the Leopold II tunnel in Brussels. Courtesy of Dr. Falk Mothes of the Leibnitz Institute for Tropospheric Research (TROPOS), Germany.

 

Additionally, a careful look at my photographs (Figures 6a-6b below) shows that the paint in the tunnel Umberto I near the “Quirinale” in Rome appears degraded – it is peeling off. The blackish spots/layers seen in Figure 6b may well be claimed as being dirty cobwebs (ragnatele 40 ), but as Figure 3 shows it may just be plain dirt. Nonetheless, my personal observations indicated some degradation had occurred. In that interview 41, the respondent should have been asked about the Dives in Misericordia Church in Rome; there also the TiO2 paint on the panels installed by Italcementi 42 shows considerable degradation as demonstrated in Figure 5 (lower photograph), in stark contrast to the image in Figure 4 that shows the Dives in Misericordia Church soon after Italcementi had installed the panels around 2001/2002.

 

Figure 4. Dives in Misericordia Church, Rome, constructed of TiO2 self-cleaning and depolluting TX-Active cement (inaugurated in 2003). 43

 

An examination of what the Church looked like when I took the photographs in February 2018 (Figure 5) shows the damage done to the panel walls (lower photograph) that were painted with Italcementi’s TiO2 paint  – the damage stands out clearly. So does the “prodotto applicato crea più danni che benefici in quelle condizioni”? My view is that the product created little if anything; except that when it was inaugurated the Church looked fantastic. Would a regular white paint have given the same results?

 

Damages? Well the paint did degrade with time, as did the cementitious panel walls (see lower photograph in Figure 5). Yet it was claimed at the time that it would last for a long time. And I quote:

A structure of such architectural prestige and symbolic meaning required the use of a very special concrete, characterized not only by high mechanical performance and durability, but also by a white color of considerable brightness, capable of maintaining the aesthetic appearance unchanged over time due to its self-cleaning property…….The photocatalytic action eliminates the various pollutants – vehicle exhaust gas, flue gas from domestic heating, industrial discharge of chemicals, pesticides – which come into contact with the cement surface, transforming them into substances which do not harm the environment. This allows the original aesthetic appearance of the structure or of the work to be preserved over time. 44

Any connection to the elimination of the various pollutants was based entirely from previous laboratory studies.

So any benefits? Hardly! If we consider the more recent results from studies under actual environmental conditions by the Life+-funded Project PhotoPAQ (2010–2014) and the LIFE MINOX-STREET Project (2014–2018) undertakings.”

 

Figure 5. Photographs of the Dives in Misericordia Church taken on 24 February 2018 (Copyright by N. Serpone). Note the breaking-up of the cementitious layer on the outside sails (lower photograph).

 

When the photographs of the Umberto I tunnel were taken in 2018, not all the lights were turned ON (to save electricity?) – see Figures 6a and 6b. Without the lights ON, the TiO2 will not be photo-activated and thus no destruction of the pollutants will occur. Note the difference soon after the tunnel was renovated with the TiO2-based paint (see Figure 7).

 

Figure 6a. Photographs showing the status of the Umberto I Tunnel in Rome nearly 11 years after the renovation. Photographs taken 4 March 2018 (Copyright by N. Serpone)

 

Figure 6b. Photographs showing the status of the Umberto I Tunnel in Rome nearly 11 years after the renovation. Photographs taken 4 March 2018 (Copyright by N. Serpone)

 

Figure 7. Umberto I tunnel near the Quirinale in Rome before re-opening 45

 

One curious observation! From what we see in the schematic of Figure 8 (left) and considering the geometry of the Umberto I tunnel, the sensors to determine the extent of degradation of pollutants were located very close to the tunnel walls’ surface (perhaps at or a few centimeters from the surface). That is, because of the curvature, the sensor placed at 6 meters above the surface of the sidewalk (green stripe; left) is close enough to the tunnel walls that it senses only what happens near the walls, and not necessarily throughout the tunnel. Sensors should also have been placed about 1.5 to 2 meters above the surface to determine the extent to which the NOx were destroyed at the height at which a pedestrian would breathe the surrounding air.

For comparison, the German Life+-funded Project PhotoPAQ (2010–2014) study of the Leopold II tunnel in Brussels (Figure 9a) placed the sensors at different heights from the ground surface – namely at 1.1 meters and 3.2 meters above the ground surface, but away from the vertical walls (Figure 9b). Sensors were also placed at the ceiling some 4.4 meters above ground. 46

That study showed that the extent of photo-catalytic NOx remediation in the 160-meter more active tunnel section was at best 2% or less, in accord with the independent later study from the LIFE MINOX-STREET Project (2014–2018). Accordingly, their results showed there were hardly any benefits.

 

Figure 8. Left: schematic showing the locations of the sensors installed at the center of the tunnel, one of which was placed some 6 meters above the surface of the pedestrian sidewalk, which from the curvature of the tunnel (right) places the sensor very close to the wall surface.

 

Figure 9a. A view and the condition of the Leopold II tunnel after coating the walls and also showing the lighting system during the PhotoPAQ field trials.

 

Figure 9b.  Schematic representation of the test sites in the Leopold II tunnel during the PhotoPAQ field trials.

 

The Table below summarizes the parameters and the extent to which nitric oxide (NO; one of the NOx components) was eliminated in three different cases by the Spanish CIEMAT group 47, who investigated the NOx depolluting effect of TiO2-based photocatalytic materials in a medium-scale tunnel reactor under semi-controlled conditions using 200 ppbv of NO (ppbv = parts per billion volume) and compared the results with those from a real-scale outdoor tunnel and from a laboratory-scale reactor.

 

Table. Parameters and results of NO removal in a medium-scale tunnel reactor {UVA irradiance, > 40 W/m2; relative humidity, < 30%; dimensions, 0.4 x 0.4 x 10 m; photoactive surface, 0.4 x 10 m} compared to a real-scale tunnel and a small laboratory flow-through reactor.

 

Note the experimental differences between the Laboratory setting and the outdoor environment.

 

Clearly, the results show that the amount of NOx destroyed within the laboratory setting is significantly greater – about 2000% greater – than in the actual outdoor environment: the average yield of NO removed was ca. 2% for the Outdoor Real-Scale Tunnel Reactor; 15 ± 4% for the Outdoor Medium-Scale Tunnel Reactor; and 41% for the Laboratory Flow-through Reactor.

 

Note also the differences in the residence times: 0.017 seconds for outdoor Real-scale; 0.033 seconds for outdoor Medium-scale; and 2 seconds for Laboratory setting. THIS MAKES A BIG DIFFERENCE!! The pollutant must spend enough time on the TiO2 surface for the chemical reactions to come to some completion.

 

To make matters worse, three other studies on the usefulness of TiO2-based materials deposited on highways’ noise barriers and in an urban street were unable to determine the level of NOx destroyed because the level was below detection limits. 48

So, basically, laboratory tests have very little, if any, value in relation to the outdoors environment! Why? Because the results obtained in the laboratory cannot simply be extrapolated directly to the natural environment. Such results have only an intellectual, academic value; that is, they can only tell us if the TiO2 from X Company is better than the TiO2 from Y or Z Company at destroying the NOx and other pollutants.

In summary, whatever data/results one obtains from laboratory studies, they CANNOT be extrapolated to the ambient atmosphere since the experimentalist cannot control the conditions outdoors, which he can in a laboratory setting. In practical applications of photocatalysis then, conventional TiO2-based photocatalytic surfaces have been used to oxidize NOx to nitrate species; however, the latter species do not desorb spontaneously and consequently deactivate or block the surface-active centers of the TiO2 photocatalyst from carrying out the next cycles. To avoid such deactivation, the nitrates (or nitric acid) should typically be washed away by the rain. 49 However, being corrosive, any nitric acid formed could pollute the soil when its concentration becomes too high at the given site.

All the outdoors field trials expected the NOx to be transformed into nitrites and ultimately into nitrates on the photocatalytic surfaces to be then desorbed when raining. However, there are reports that other intermediate species are also likely to form: for instance, nitrous acid (HONO), 50 which is far more toxic than the NOx pollutants, and not least is the potential for reNOxification (that is, the nitrites and nitrates are converted back to the NOx pollutants) accompanied by the formation of ozone from the reaction of adsorbed nitrates with the TiO2 conduction band electrons that act as reducing agents. 51

In addition to the issues regarding the use of TiO2-based paints, one must also be concerned with the other pigments in the paints used in murals, as many of these pigments are toxic: for example, cadmium in cadmium sulfide (CdS) pigments, as it affects mainly the kidneys and bones, and is also a carcinogen by inhalation. 52 It can accumulate in liver, kidneys and bones, and when present in the environment, is also toxic to plants, animals and micro-organisms. 53 Other pigments include: white lead, Scheele’s green (arsenic), Cadmium red, and School Bus yellow (hexavalent chromium). 54 A list of highly toxic pigments and moderately toxic pigments is given by Caroline Robert 55:

Highly Toxic Pigments: antimony white (antimony trioxide); barium yellow (barium chromate); burnt or raw umber (iron oxides, manganese silicates or dioxide); cadmium red, orange or yellow (cadmium sulfide, cadmium selenide); chrome green (Prussian blue, lead chromate); chrome orange (lead carbonate); chrome yellow (lead chromate); cobalt violet (cobalt arsenate or cobalt phosphate); cobalt yellow (potassium cobalt nitrate); lead or flake white (lead carbonate); lithol red (sodium, barium and calcium salts of azo pigments); manganese violet (manganese ammonium pyrophosphate); molybdate orange (lead chromate, lead molybdate, lead sulfate); Naples yellow (lead antimonate); strontium yellow (strontium chromate); vermilion (mercuric sulfide); zinc sulfide; zinc yellow (zinc chromate).

Moderately Toxic Pigments: alizarin crimson; carbon black; cerulean blue (cobalt stannate); cobalt blue (cobalt stannate); cobalt green (calcined cobalt, zinc and aluminum oxides); chromium oxide green (chromic oxide); Phthalo blue and greens (copper phthalocyanine); manganese blue (barium manganate, barium sulfate); Prussian blue (ferric ferrocyanide); toluidine red and yellow (insoluble azo pigment); viridian (hydrated chromic oxide); zinc white (zinc oxide).”

 


 

Notes:

  1. Alle varie vernici si accompagna una scheda tecnica, per esempio: https://www.timerivestimenti.it/ristrutturazioni-chiavi-in-mano/wp-content/uploads/2020/04/Sunlight-ITA.pdf
  2. Super Walls – Festival Biennale della Street Art: https://www.youtube.com/watch?v=RiWavD70xzA&t=1759s,
    https://www.youtube.com/watch?v=h1XKCQScG1Y;
    https://www.youtube.com/watch?v=vTNjHHe6E80;
    SUA – San Vito Urban Art: https://www.youtube.com/watch?v=AQTdDR0_5ZQ; https://www.youtube.com/watch?v=_iPhqaDta9Y;
    Street Art for Rights: https://www.facebook.com/101082808700930/videos/307439604077657;
    https://www.facebook.com/101082808700930/videos/246522253842593.
  3. https://bit.ly/3wLw4eW.
    https://theecologist.org/2021/feb/18/can-rio-tinto-be-trusted.
  4. Il titanio e il parco del Beigua | UniGe.life:  sui pericoli ambientali connessi al “permesso di ricerca mineraria, presentato dalla Compagnia Europea del Titanio – CET s.r.l., [che] interessa per circa un 50% della sua superficie un’area classificata come Riserva Generale Orientata e per circa il 60% la Zona Speciale di Conservazione Beigua – Monte Dente – Gargassa – Pavaglione.”
  5. Farjana S. H., Huda N., Parvez Mahmud M. A., Life-Cycle environmental impact assessment of mineral industries, IOP Conf. Series: Materials Science and Engineering 351, 2018 Publisher_version_open_access_.pdf (mq.edu.au)
  6. https://www.senato.it/service/PDF/PDFServer/DF/336175.pdf
    http://documenti.camera.it/leg18/resoconti/commissioni/bollettini/pdf/2021/03/24/leg.18.bol0555.data20210324.com39.pdf
  7. IARC Publications Website – Carbon Black, Titanium Dioxide, and Talc
  8. https://www.anses.fr/fr/content/additif-alimentaire-e171-l%E2%80%99anses-r%C3%A9it%C3%A8re-ses-recommandations-pour-la-s%C3%A9curit%C3%A9-des
  9. osservazioni-di-confindustria-su-biossido-di-titanio-e-proposta-di-classificazione-armonizzata-come-cancerogeno-1b.pdf (federchimica.it)
  10. https://tdma.info/the-economic-impact-of-titanium-dioxide-in-europe/
  11. https://www.efsa.europa.eu/it/news/titanium-dioxide-e171-no-longer-considered-safe-when-used-food-additive
  12.  EUR-Lex – 32020R0217 – EN – EUR-Lex (europa.eu)
  13. H. West. M. R. Cooper, L. G. Burrelli, D. Dresser, B. E. Lippy, Exposure to airborne nano-titanium dioxide during airless spray painting and sanding, in Journal of Occupational and Environmental Hygiene XVI 3, 2019, pp. 218-228.
  14. Suo è il recente articolo Heterogeneous Photocatalysis and Prospects of TiO2-Based Photocatalytic DeNOxing the Atmospheric Environment, in the journal “Catalysts” 8(11) (2018) 533 (https://www.doi.org/10.3390/catal8110553), ora contenuto in Emerging Trends in TiO2 Photocatalysis and Applications, Mdpi AG 2020, p. 415 ss. (consultabile: https://www.google.it/books/edition/Emerging_Trends_in_TiO_sub_2_sub_Photoca/cRgREAAAQBAJ?hl=it&gbpv=1&dq=Emerging+Trends+in+TiO2+Photocatalysis+and+Applications+-+Google+Books&printsec=frontcover). Il Professore Nick Serpone ha conseguito il dottorato di ricerca in chimica fisica-inorganica presso la Cornell University (1964-1968, Ithaca, NY). È diventato membro della Concordia University (Montreal, Canada) nel 1968 come Professore Assistente, è stato fatto Professore Associato nel 1973, quindi Professore Ordinario nel 1980, University Research Professor (1998-2004) e Professore Emerito nel 2000. È stato direttore di programma della Divisione di Chimica della U.S. National Science Foundation (Washington, 1998-2001). È stato visiting professor presso le Università di Bologna (1975-1976) e Ferrara (1997-1998), professeur invité presso l’École Polytechnique Fédérale de Lausanne (1983-1984), visiting professor e direttore di ricerca presso l’École Centrale de Lyon (1990-1991), professore a contratto all’Università di Pavia (2002-2005 nel programma Rientro dei Cervelli) e a partire dal 2005 visiting professor all’Universita di Pavia, nonché visiting professor presso la Tokyo University of Science, Noda Campus (luglio-agosto 2008). I suoi principali interessi di ricerca riguardano la fotofisica e fotochimica degli ossidi metallici semiconduttori, la fotocatalisi eterogenea, la fotochimica ambientale, la fotochimica di agenti attivi nelle creme solari e l’applicazione delle microonde ai nanomateriali e al risanamento ambientale. È coautore di oltre 490 articoli e ha co-curato 12 monografie. È stato coautore di un libro con il Prof. Vincenzo Balzani (Professore Emerito, Università di Bologna) e il Dott. Nicola Armaroli (CNR, Bologna) dal titolo “Powering Planet Earth – Energy solutions for the future” (Wiley-VCH, 2013). Ha tradotto il libro “Chemistry – reading and writing the book of Nature” di Vincenzo Balzani e Margherita Venturi dell’Università di Bologna (Royal Society of Chemistry, UK; Settembre 2014). Recentemente e stato co-autore con il Prof. Stefano Protti (Università di Pavia) ed il Prof. Satoshi Horikoshi (Sophia University, Tokyo) del libro “Le Microonde ‒ tra scienze chimiche e scienze gastronomiche” (Kemia, Aracne Editrice spa, Roma, Italia; Settembre 2018). Attualmente, con tre colleghi si sta curando della monografia “AGRITECH: Innovative Agriculture Using Microwaves and Plasmas: Thermal and Non-Thermal Processing“ (Springer, Singapore, 2022). Nel luglio 2010 è stato eletto Fellow della European Academy of Sciences (EurASc), e durante il periodo 2014-2020 é stato Head of the Materials Science Division dell’Accademia EurASc (https://www.eurasc.org/user/185/nick-serpone).
  15. Vernice naturale mangia-inquinamento (avvenire.it); https://www.ilgiornale.it/news/politica/ora-virus-si-batte-pure-col-pennello-1917326.html
  16. Qui e nelle successive occorrenze in italiano nel testo, eccetto nota 42 da me inserita.
  17. J. Zhao, T. Wu, K. Wu, K. Oikawa, H. Hidaka and N. Serpone, Photoassisted Degradation of Dye Pollutants. III. Evidence for the Need of Substrate Adsorption on TiO2 Particles, Environ. Sci. Technol., 32 (1998) 2394-2400.
  18. Q. Wu, R. van de Krol, Selective photoreduction of nitric oxide to nitrogen by nanostructured TiO2 photocatalysts: Role of oxygen vacancies and iron dopant, in Journal of the American Chemical Society 134 (2012), 9369–9375.
  19. D.E Macphee, A. Folli, Photocatalytic concretes -The interface between photocatalysis and cement chemistry, in Cement and Concrete Research 85 (2016) 48–54.
  20. Justin Boucher, EU moves forward with TiO2 carcinogen classification, September 25, 2019: The European Commission (EC) is reported to be going ahead with its proposal to classify titanium dioxide (TiO2; CAS 13463-67-7) as a category 2 carcinogen due to its inhalation hazard. This follows a meeting of the CARACAL group (Competent authorities Meeting for REACH and CLP regulations) on September 18, 2019.  (EU moves forward with TiO2 carcinogen classification | Food Packaging Forum). Part 2 of Annex II to Regulation (EC) No 1272/2008 is amended as follows: Mixtures containing titanium dioxide. The label on the packaging of liquid mixtures containing 1 % or more of titanium dioxide particles with aerodynamic diameter equal to or below 10 μm shall bear the following statement: EUH211: ‘Warning! Hazardous respirable droplets may be formed when sprayed. Do not breathe spray or mist.’ The label on the packaging of solid mixtures containing 1 % or more of titanium dioxide shall bear the following statement: EUH212: ‘Warning! Hazardous respirable dust may be formed when used. Do not breathe dust.’ {EUR-Lex – 32020R0217 – EN – EUR-Lex (europa.eu)}. See also Titanium dioxide: E171 no longer considered safe when used as a food additive | European Food Safety Authority (europa.eu)
  21. M. Skocaj, M. Filipic, J. Petkovic, and S. Novak, Titanium dioxide in our everyday life; is it safe?, Radiol. Oncol. 45 (2011) 227-247; F. Grande and P. Tucci, Titanium Dioxide Nanoparticles: a Risk for Human Health?, Mini Rev. Med. Chem. 16 (2016) 762-769; E. Baranowska-Wojcik, D. Szwajgier, P. Olesczuk, and A. Winiarska-Mieczan, Effects of Titanium Dioxide Nanoparticles Exposure on Human Health-a Review, Biol. Trace Elem. Res. 193 (2020) 118-129.
  22. S. Horikoshi, T. Miura, M. Kajitani, N. Horikoshi, and N. Serpone, Photodegradation of Tetrahalobisphenol-A (X = Cl, Br) Flame Retardants in Alkaline Aqueous Media and Delineation of Factors Affecting the Process, Appl. Catal. B: Environ., 84 (2008) 797–802.
  23. R. Borello, C. Minero, E. Pramauro, E. Pelizzetti, N. Serpone, H. Hidaka, Photocatalytic degradation of DDT mediated in aqueous semiconductor slurries by simulated sunlight, Environmental Toxicology and Chemistry, 8 (1989) 997-1002.
  24. M. Barbeni, E. Pramauro, E. Pelizzetti, E. Borgarello, N. Serpone, and M.A. Jamieson, Photochemical degradation of chlorinated dioxin, biphenyls, phenols and benzene on semiconductor dispersions, Chemosphere, 15 (1986) 1913‑1916; E. Pelizzetti, M. Borgarello, C. Minero, E. Pramauro, E. Borgarello, and N. Serpone, Photocatalytic degradation of polychlorinated dioxins and polychlorinated biphenyls in aqueous suspensions of semiconductors irradiated with simulated solar light, Chemosphere, 17 (1988) 499-518.
  25. E. Pelizzetti, M. Barbeni, E. Pramauro, N. Serpone, E. Borgarello, M.A. Jamieson, H. Hidaka, Sunlight photo-degradation of haloaromatic pollutants catalyzed by semiconductor particulate materials, Chimica & Industria (Milano), 67 (1985) 623-625.
  26. R. Terzian, N. Serpone, Heterogeneous photocatalyzed oxidation of creosote components: mineralization of xylenols by illuminated TiO2 in oxygenated aqueous media, Journal of Photochemistry and Photobiology A: Chemistry, 89 (1995) 163-175.
  27. H. Hidaka, H. Kubota, M. Graetzel, N. Serpone, E. Pelizzetti, Photodegradation of the sodium dodecylbenzene sulfonate surfactant in aqueous semiconductor dispersions, Nouv. J. Chim., 9 (1985) 67‑69; E. Pelizzetti, C. Minero, V. Maurino, A. Sclafani, H. Hidaka, N. Serpone, Photocatalytic Degradation of Nonylphenol Ethoxylated Surfactants, Environ. Sci. Technol., 23 (1989) 1380-1385; H. Hidaka, J. Zhao, K. Nohara, K. Kitamura, N. Serpone, E. Pelizzetti, Photodegradation of Surfactants IX: The photocatalytic degradation of polyoxy ethylene alkyl ether homologs at the TiO2/water interface, J. Photochem. Photobiol. A: Chem., 64 (1992) 103-113; H. Hidaka, S. Yamada, S. Suenaga, H. Kubota, N. Serpone, E. Pelizzetti, Photodegradation of Surfactants. VI. Complete photocatalytic degradation of anionic, cationic, and nonionic surfactants in aqueous semiconductor dispersions, J. Mol. Catal., 59 (1990) 270-290.
  28. S. Ito, W. Worakitkanchanakul, S. Horikoshi, H. Sakai, D. Kitamoto, T. Imura, S. Chavadej, R. Rujiravanit, M. Abea, N. Serpone, Photooxidative mineralization of microorganisms-produced glycolipid biosurfactants by a titania-mediated advanced oxidation process, Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 147–152.
  29. M. Barbeni, E. Pramauro, E. Pelizzetti, M. Vincenti, E. Borgarello, and N. Serpone, Sunlight photodegradation of 2,4,5‑trichlorophenoxyacetic acid and 2,4,5-trichlorophenol on TiO2 semiconductor dispersions. Mechanism of degradation and identification of intermediate species, Chemosphere, 16 (1987) 1165-1179.
  30. H. Hidaka, K. Nohara, J. Zhao, N. Serpone, and E. Pelizzetti, Photo-oxidative degradation of the pesticide permethrin catalyzed by irradiated TiO2 semiconductor dispersions in aqueous media, J. Photochem. Photobiol. A:Chem., 64 (1992) 247-254.
  31. E. Borgarello, N. Serpone, G. Emo, R. Harris, E. Pelizzetti, and C. Minero, Light‑induced reduction of Rh(III) and Pd(II) on TiO2 dispersions, and the selective photochemical separation and recovery of Au(III), Pt(IV), and Rh(III) from dilute­ solutions, Inorg. Chem., 25 (1986) 4499‑4503; N. Serpone, E. Borgarello, M. Barbeni, E. Pelizzetti, P. Pichat, J.M. Herrmann, and M.A. Fox, Photochemical reduction of gold(III) on semiconductor dis­persions of TiO2 in the  presence of cyanide ions: Disposal of CN with H2O2, J. Photochem., 36 (1987) 373‑388 E. Borgarello, N. Serpone, G. Emo, R. Harris E. Pelizzetti, C. Minero, Light-Induced Reduction of Rhodium(III) and Palladium(II) on Titanium Dioxide Dispersions and the Selective Photochemical Separation and Recovery of Gold(III), Platinum(IV), and Rhodium(III) in Chloride Media, Inorg. Chem. 25 (1986) 4499-4503.
  32. S. Horikoshi, N. Serpone, S. Yoshizawa, J. Knowland and H. Hidaka, Photocatalyzed degradation of polymers in aqueous semiconductor suspensions. IV. Theoretical and experimental examination of the photooxidative mineralization of constituent bases in nucleic acids at titania/water interfaces, J. Photochem. Photobiol. A: Chem., 120 (1999) 63-74; S. Horikoshi, H. Hidaka, and N. Serpone, Photocatalyzed degradation of polymers in aqueous semiconductor suspensions. V. Photomineralization of lactam ring-pendant polyvinylpyrrolidone at titania/water interfaces, J. Photochem. Photobiol.A:Chem., 138 (2001) 69-77.S. Horikoshi, H. Hidaka, Y. Hisamatsu and N. Serpone, Photocatalyzed Degradation of Polymers in Aqueous Semiconductor Suspensions. 3. Optimal photooxidation of a solid polymer in a TiO2-blended polyvinylchloride film, Environ. Sci. Technol., 32 (1998) 4010-4016.
  33. F. Mendez-Arriaga, T. Otsu, T. Oyama, J. Gimenez, S. Esplugas, H. Hidaka, N. Serpone, Photooxidation of the antidepressant drug Fluoxetine (Prozac) in aqueous media by hybrid catalytic/ozonation processes, Water Research, 45 (2011) 2782-2794; T. Oyama, T. Otsu, Y. Hidano, T. Tsukamoto, N. Serpone, H. Hidaka, Remediation of aquatic environments contaminated with hydrophilic and lipophilic pharmaceuticals by TiO2-photoassisted ozonation, Journal of Environmental Chemical Engineering, 2 (2014) 84–89.
  34. T. Wu, G. Liu, J. Zhao, H. Hidaka, and N. Serpone, Photoassisted Degradation of Dye Pollutants. V. Self-Photooxidative Transformation of RhB under Visible Light Irradiation in Aqueous TiO2 Dispersions, J. Phys. Chem., B, 102 (1998) 5845-5851; T. Wu, T. Lin, J. Zhao, H. Hidaka, and N. Serpone, TiO2-assisted photodegradation of dyes. 9. Photooxidation of a squarylium cyanine dye in aqueous dispersions under visible light irradiation, Environ. Sci. Technol, 33 (1999) 1379-1387; T. Wu, G. Liu, J. Zhao, H. Hidaka, N. Serpone, Photoassisted Degradation of Dye Pollutants. V. Self-Photosensitized Oxidative Transformation of Rhodamine B under Visible Light Irradiation in Aqueous TiO2 Dispersions, J. Phys. Chem. B, 102 (1998) 5845-5851.
  35. D. Lawless, A. Res, R. Harris, N. Serpone, C. Minero, E. Pelizzetti, H. Hidaka, Removal of toxic metals from solutions by photocatalysis using irradiated platinized titanium dioxide: Removal of lead, Chimica & Industria (Milano), 72 (1990) 139-146; N. Serpone, Y.K. Ah‑You, T.P. Tran, R. Harris, E. Pelizzetti, H. Hidaka, AM1 simulated sunlight photoreduction and elimination of Hg(II) and CH3Hg(II) chloride salts from aqueous suspensions of titanium dioxide, Sol. Energy, 39 (1987) 491-498.
  36. R. Fujiwara, Y. Luo, T. Sasaki, K. Fujii, H. Ohmori, H. Kuniyasu, Cancer Therapeutic Effects of Titanium Dioxide Nanoparticles Are Associated with Oxidative Stress and Cytokine Induction, Pathobiology, 82 (2015) 243–251.
  37. D. M. Blake, P.-C. Maness, Z. Huang, E. J. Wolfrum, J. Huang, APPLICATION OF THE PHOTOCATALYTIC CHEMISTRY OF TITANIUM DIOXIDE TO DISINFECTION AND THE KILLING OF CANCER CELLS, Separation and Purification Methods, 28 (1999) 1-50.
  38. S. Khaiboullina, T. Uppal, N. Dhabarde, V. R. Subramanian, S. C. Verma, In Vitro Inactivation of Human Coronavirus by Titania Nanoparticle Coatings and UVC Radiation: Throwing Light on SARS-CoV-2, Viruses 13 (2021) 19. https://dx.doi.org/10.3390/v13010019 ; see also https://www.unr.edu/nevada-today/news/2021/covid-disinfectant and https://www.biorxiv.org/content/10.1101/2020.08.25.265223v1 ; E. V. R. Campos, A. E. S. Pereira, J. L. de Oliveira, L. Bragança Carvalho, M. Guilger-Casagrande, R. de Lima, L. F. Fraceto, How can nanotechnology help to combat COVID-19? Opportunities and urgent need, Nanobiotechnology, 18 (2020) 125; https://doi:10.1186/s12951-020-00685-4 
  39. See: Copper surfaces can inactivate SARS-CoV-2 in as little as one minute, study finds (https://www.news-medical.net/news/20210105/Copper-surfaces-can-inactivate-SARS-CoV-2-in-as-little-as-one-minute-study-finds.aspx)
    CDA Position Statement on Antimicrobial Copper and Coronavirus (COVID-19) Pandemic (https://www.copper.org/applications/antimicrobial/COVID-19.html);
    Why Copper Is Good at Killing Viruses (https://www.smithsonianmag.com/science-nature/copper-virus-kill-180974655/);
    Yes, Copper Kills Most Germs Including Viruses Like COVID-19 (https://www.insider.com/does-copper-kill-germs-and-viruses)
  40. http://www.showtechies.com/airlite-la-vernice-che-pulisce-laria/
  41. See footnote 40
  42. La chiesa Dives in Misericordia è stata consacrata nel quartiere romano di Tor Tre Teste, ed è stata progettata dall’architetto Richard Meier, vincitore di un concorso internazionale promosso dal Vicariato di Roma. In una zona periferica, carente di punti d’incontro e aree dedicate ai rapporti sociali della comunità, la chiesa svetta con le sue grandi vele (la più alta misura 26 m) e le sue superfici perfettamente bianche. Per evitare l’impiego di strutture in acciaio coperte con pannelli bianchi – una soluzione destinata a non durare nel tempo – le vele autoportanti sono state realizzate con grossi blocchi prefabbricati a doppia curvatura (conci), del peso di 12 tonnellate l’uno. Per soddisfare i requisiti estetici, e non solo, richiesti da Richard Meier, è stato utilizzato TX-Arca®, in grado di garantire un impareggiabile colore bianco durevole nel tempo”, in TX active approfondimento 2009.pmd (construction21.org). Nel 2007, in accordo con il Comune di Roma, Italcementi e C.I.M. (Calci Idrate Marcellina del gruppo Bernardoni), azienda dichiarata fallita nel 2017) intervengono nel tunnel Umberto I. “Il traforo è stato rivestito interamente con Cimax Ecosystem Paint, pittura cementizia bianca prodotta da C.I.M., a base di TX Active, il principio attivo fotocatalitico brevettato da Italcementi in grado di abbattere gli inquinanti organici e inorganici presenti nell’aria.” (https://energia-plus.it/a-roma-un-traforo-tutto-bianco-e-a-prova-di-smog_8259/).
  43. Reproduced from https://es.i-nova.net/content?articleId=96804;
    https://www.archdaily.com/20105/church-of-2000-richard-meier.
  44. https://fr.i-nova.net/content?articleId=95311
  45. Reproduced from TX_Active_Tunnel_Umberto_I_ENG (1).pdf
  46. E. Boonen, V. Akylas, F. Barmpas, A. Boreave, L. Bottalico, M. Cazaunau, H. Chen, V. Daele, T. De Marco, J. F. Doussin, et al., Construction of a photocatalytic de-polluting field site in the Leopold II tunnel in Brussels, in Journal of Environmental Management 155 (2015) 136–144.
  47. M. Pujadas, M. Palacios, L. Nunez, J. Fernandez-Pampillon, M. German, Characterization of the NOx depolluting effect of photocatalytic materials in a medium-scale tunnel reactor, in Proceedings of the Air Quality Meeting, Barcelona, Spain, 12–16 March 2018.
  48. The 2010 Report Dutch Air Quality Innovation Programme Concluded (https://laqm.defra.gov.uk/documents/Dutch_ Air_Quality_Innovation_Programme.pdf (accessed 29 September 2018); S. Jacobi, NO2-Reduzierung Durch Photokatalytisch Wirksame Oberflächen? Modellversuch Fulda, (Hesse, Germany) 2012 (https://www.hlnug.de/ fileadmin/dokumente/das_hlug/jahresbericht/2012/jb2012_059-066_I2_Jacobi_final.pdf; accessed 30 September 2018); Tera. In Situ Study of the Air Pollution Mitigating Properties of Photocatalytic Coating, Tera Environnement (Contract Number 0941C0978), Report for ADEME and Rhone-Alpes region, France (http://www.air-rhonealpes.fr/ site/media/telecharger/ 651413 ; accessed 11 May 2015).

  49. H, Wang, Z. Wu, W. Zhao, B. Guan, Photocatalytic oxidation of nitrogen oxides using TiO2 loading on woven glass fabric, in  Chemosphere 66 (2007) 185–190.
  50. S. Laufs, G. Burgeth, W. Duttlinger, R. Kurtenbach, M. Maban, C. Thomas, P. Wiesen, J. Kleffmann, Conversion of nitrogen oxides on commercial photocatalytic dispersion paints, Atmos. Environ. 44 (2010) 2341–2349; R. J. Gustafsson, A. Orlov, P. T. Griffiths, R. A. Cox, R. M. Lambert, Reduction of NO2 to nitrous acid on illuminated titanium dioxide aerosol surfaces: Implications for photocatalysis and atmospheric chemistry, in Chemical Communications (2006) 3936–3938; M. Ndour, B. D’Anna, C. George, O. Ka, Y. Balkanski, J. Kleffmann, K. Stemmler, M. Ammann, Photoenhanced uptake of NO2 on mineral dust: Laboratory experiments and model simulations, in Geophysical Research Letters 35 (2008) L05812; S. K. Beaumont, R. J. Gustafsson, R. M. Lambert, Heterogeneous photochemistry relevant to the troposphere: H2O2 production during the photochemical reduction of NO2 to HONO on UV-illuminated TiO2 surfaces, in ChemPhysChem 10 (2009) 331–333
  51. M.E. Monge, B. D’Anna, C. George, Nitrogen dioxide removal and nitrous acid formation on titanium oxide surfaces—An air quality remediation process?, in Physical Chemistry 12 (2010) 8991–8998; F. Mothes, H. Herrmann, Lab and field studies on photocatalysis to improve urban air quality—Results from the PhotoPAQ project, in Proceedings of the Life MINOx-STREET Project Ending Meeting: Results and Conclusions, CIEMAT, Madrid, Spain, 21 March 2018.
  52. M. P. Waalkes, Cadmium carcinogenesis, Mutat. Res., 533 (2003) 107-120 (https://pubmed.ncbi.nlm.nih.gov/ 14643415/);
    https://www.who.int/ipcs/assessment/public_health/cadmium/en/#:~:text=Cadmium%20exerts%20 toxic%20effects%20on,media%20relevant%20to%20population%20exposure
  53. Mehrdad R. Rahimzadeh, Mehravar R. Rahimzadeh, S. Kazemi, and A.-A. Moghadamnia, Cadmium toxicity and treatment: An update, in Caspian Journal of Internal Medicine 8 (2017) 135–145.
  54. https://info.noahtech.com/blog/the-toxic-histories-of-five-famous-pigments
  55. http://carolineroberts.blogspot.com/2009/01/toxicity-of-pigments.html