science

Photocatalytic concrete

Photocatalytic concrete is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Photocatalytic concrete rather than just read about it. In short: Photo-catalytic concrete is a formulation of concrete used as pavers and other structural concrete that includes titanium dioxide (TiO2) as an admixture or superficial layer. Titanium dioxide is a heterogeneous photocatalyst that uses sunlight and moisture to absorb and render oxides of nitrogen (NO and NO2) into nitrate ions (NO3−), which are then either washed away by rain or soaked into the concrete to form stabl…

Key takeaways

Photocatalytic concrete belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Photocatalytic concrete to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Photocatalytic concrete from memory before moving on to harder problems.

Reference excerpt

Photo-catalytic concrete is a formulation of concrete used as pavers and other structural concrete that includes titanium dioxide (TiO2) as an admixture or superficial layer. Titanium dioxide is a heterogeneous photocatalyst that uses sunlight and moisture to absorb and render oxides of nitrogen (NO and NO2) into nitrate ions (NO3−), which are then either washed away by rain or soaked into the concrete to form stable compounds.

History The technique of photocatalytic concrete was firstly used in architecture during construction of the Italian Church of Dio Padre Misericordioso. Richard Meier construction also known as Jubilee Church is confined to 2000 anniversary of the Christianity that was celebrated in 2000. In order to avoid frequent cleanings of new church's concrete "sails", new development was used - white self-cleaning coating of the walls. However, back then it wasn't known that this colouring plaster containing titanium dioxide and white pigment absorbs exhaust gases and other elements of city fog. This discovery raised question of wide application of similar materials in urban construction. According to studies, the air at a distance of 2.5 m from a facade coated with titanium dioxide contains 70% less various combustion products than other city buildings. So the people inhale less harmful substances while passing by the buildings treated this way. Options for using photocatalytic cement to cover asphaltic roads are also being considered. As an experiment it was used at 230-meter stretch of highway near Milan. Measurements allowed to see that at this road average traffic load of 1000 vehicles per hour, the reduction of nitrogen oxides in the air at ground level was 60%. Some were skeptical about this discovery: in their opinion, it is necessary to reduce the level of harmful substances emissions, and not to eliminate their consequence - smog. Moreover effectiveness of practically all catalysts weakens as time passes.

Mechanism When titanium dioxide is exposed to ultraviolet radiation from sunlight, it absorbs the radiation and electron excitation occurs. The following reactions then occur on the surface of the titanium dioxide crystals: Photolysis of water:

H2O → H+ + OH (hydroxyl radical) + e− O2 + e− → O2− (a superoxide ion) The overall reaction is therefore:

H2O + O2 → H+ + O2− + OH The hydroxyl radical is a powerful oxidizing agent and can oxidize nitrogen dioxide to nitrate ions:

NO2 + OH → H+ + NO3− The superoxide ion is also able to form nitrate ions from nitrogen monoxide:

NO + O2− → NO3− The oxidation of NOx to nitrate ions occurs very slowly under normal atmospheric conditions because of the low concentrations of the reactions. The photochemical oxidation with the aid of titanium dioxide is much faster because of the energy absorbed by the coating on the block and also because the reactants are held together on the surface of the block. The reaction using titanium dioxide shows a greater oxidizing power than most other metal-based catalysts. Photo-catalytic blocks have replaced ordinary paving in around 30 towns in Japan, originally having been tested in Osaka in 1997 and have been used in the City of Westminster (London). The aim of these blocks is to reduce atmospheric pollution levels and therefore lower the amount of photochemical smog.

References

Worked examples

Example 1 — a first encounter with Photocatalytic concrete

Start with the simplest possible case. Write down what Photocatalytic concrete claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Photocatalytic concrete before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Photocatalytic concrete ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Photocatalytic concrete

In research: Photocatalytic concrete appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Photocatalytic concrete in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Photocatalytic concrete is common in secondary-school and first-year university syllabi. It links to neighbouring topics Catalysts, Concrete, NOx control, so understanding it makes those chapters shorter.
In everyday life: Look for Photocatalytic concrete outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Photocatalytic concrete in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Photocatalytic concrete means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Photocatalytic concrete out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Photocatalytic concrete in simple terms?

Why does Photocatalytic concrete matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Photocatalytic concrete?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Photocatalytic concrete.