Reducing atmospheric pollutants with a new paint-on graphene-based coating for concrete

via Graphene Flagship

Graphene Flagship partners the University of Bologna, Politecnico di Milano, CNR, NEST, Italcementi HeidelbergCement Group, the Israel Institute of Technology, Eindhoven University of Technology, and the University of Cambridge have developed a graphene-titania photocatalyst that degrades up to 70% more atmospheric nitrogen oxides (NOx) than standard titania nanoparticles in tests on real pollutants.

Atmospheric pollution is a growing problem, particularly in urban areas and in less developed countries. According to the World Health Organization, one out of every nine deaths can be attributed to diseases caused by air pollution. Organic pollutants, such as nitrogen oxides and volatile compounds, are the main cause of this, and they are mostly emitted by vehicle exhausts and industry.

To address the problem, researchers are continually on the hunt for new ways to remove more pollutants from the atmosphere, and photocatalysts such as titania are a great way to do this. When titania is exposed to sunlight, it degrades nitrogen oxides – which are very harmful to human health – and volatile organic compounds present at the surface, oxidising them into inert or harmless products.

Now, the Graphene Flagship team working on photocatalytic coatings, coordinated by Italcementi, HeidelbergCement Group, Italy, developed a new graphene-titania composite with significantly more powerful photodegradation properties than bare titania. “We answered the Flagship’s call and decided to couple graphene to the most-used photocatalyst, titania, to boost the photocatalytic action,” comments Marco Goisis, the research coordinator at Italcementi. “Photocatalysis is one of the most powerful ways we have to depollute the environment, because the process does not consume the photocatalysts. It is a reaction activated by solar light,” he continues.

By performing liquid-phase exfoliation of graphite – a process that creates graphene – in the presence of titania nanoparticles, using only water and atmospheric pressure, they created a new graphene-titania nanocomposite that can be coated on the surface of materials to passively remove pollutants from the air. If the coating is applied to concrete on the street or on the walls of buildings, the harmless photodegradation products could be washed away by rain or wind, or manually cleaned off.

To measure the photodegradation effects, the team tested the new photocatalyst against NOx and recorded a sound improvement in photocatalytic degradation of nitrogen oxides compared to standard titania. They also used rhodamine B as a model for volatile organic pollutants, as its molecular structure closely resembles those of pollutants emitted by vehicles, industry and agriculture. They found that 40% more rhodamine B was degraded by the graphene-titania composite than by titania alone, in water under UV irradiation. “Coupling graphene to titania gave us excellent results in powder form – and it could be applied to different materials, of which concrete is a good example for the widespread use, helping us to achieve a healthier environment. It is low-maintenance and environmentally friendly, as it just requires the sun’s energy and no other input,” Goisis says. But there are challenges to be addressed before this can be used on a commercial scale. Cheaper methods to mass-produce graphene are needed. Interactions between the catalyst and the host material need to be deepened as well as studies into the long-term stability of the photocatalyst in the outdoor environment.

Ultrafast transient absorption spectroscopy measurements revealed an electron transfer process from titania to the graphene flakes, decreasing the charge recombination rate and increasing the efficiency of reactive species photoproduction – meaning more pollutant molecules could be degraded.

Xinliang Feng, Graphene Flagship Work Package Leader for Functional Foams and Coatings, explains: “Photocatalysis in a cementitious matrix, applied to buildings, could have a large effect to decrease air pollution by reducing NOx and enabling self-cleaning of the surfaces – the so-called “smog-eating” effect. Graphene could help to improve the photocatalytic behaviour of catalysts like titania and enhance the mechanical properties of cement. In this publication, Graphene Flagship partners have prepared a graphene-titania composite via a one-step procedure to widen and improve the ground-breaking invention of “smog-eating” cement. The prepared composite showed enhanced photocatalytic activity, degrading up to 40% more pollutants than pristine titania in the model study, and up to 70% more NOx with a similar procedure. Moreover, the mechanism underlying this improvement was briefly studied using ultrafast transient absorption spectroscopy.”

Enrico Borgarello, Global Product Innovation Director at Italcementi, part of the HeidelbergCement Group, one of the world’s largest producers of cement, comments: “Integrating graphene into titania to create a new nanocomposite was a success. The nanocomposite showed a strong improvement in the photocatalytic degradation of atmospheric NOx boosting the action of titania. This is a very significant result, and we look forward to the implementation of the photocatalytic nanocomposite for a better quality of air in the near future.”

The reasons to incorporate graphene into concrete do not stop here. Italcementi is also working on another product – an electrically conductive graphene concrete composite, which was showcased at Mobile World Congress in February this year. When included as a layer in flooring, it could release heat when an electrical current is passed through it. Goisis comments: “You could heat your room, or the pavement, without using water from a tank or boiler. This opens the door to innovation for the smart cities of the future – particularly to self-sensing concrete,” which could detect stress or strain in concrete structures and monitor for structural defects, providing warning signals if the structural integrity is close to failure.

Learn more: Smog-eating graphene composite reduces atmospheric pollution



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A new type of reinforced concrete that doesn’t need any maintenance

via Inside Construction

A pedestrian bridge designed by Deakin University researchers for a North Geelong park will use a new type of reinforced concrete that doesn’t need any maintenance.

The bridge over Cowies Creek at Deppeler Park will be made from sustainable concrete with carbon and glass fibre reinforcement that should ensure the bridge requires no maintenance over its 100 year life-span.

Deakin researchers Dr Mahbube Subhani and Dr Kazem Ghabraie designed the bridge for North-Geelong based engineering firm Austeng when Austeng won a tender to build two pedestrian bridges from the City of Greater Geelong (COGG).

Dr Subhani said the new design would avoid the usual problem of corrosion that occurs in conventional steel reinforced concrete construction.

“We have replaced the steel reinforcing bar normally used in steel reinforced concrete with more durable carbon and glass fibre reinforced polymer,” Dr Subhani said.

“Structures made with steel reinforced concrete require maintenance about every five years and major maintenance or rehabilitation every 20 years.

“This bridge should not require any maintenance for the whole of its design life,” Dr Subhani said.

Carbon and glass fibre reinforced polymer is stronger than steel and five times lighter than reinforced steel.

It also needs much less energy to make – just 25 per cent of the energy required to produce steel.

“The geopolymer concrete used in the bridge construction is also environmentally sustainable,” Dr Subhani said.

“Instead of cement, the concrete has been made using fly ash, a by-product of coal combustion.

“Cement is responsible for seven per cent of the world’s total CO2 emissions so this structural element has the potential to cut down the maintenance cost as well as reduce CO2 emissions.”

The beam was cast by geopolymer concrete manufacturer, Rocla, and pre-testing has already shown the bridge can successfully carry the design load.

COGG maintains about 160 recreational bridges and that number is growing through subdivision development.

Dr Subhani and his design team hope that their environmentally sustainable maintenance-free bridge is a potential candidate for new and replacement bridges throughout the city.

Learn more: Deakin researchers design maintenance-free bridge for Geelong park


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Replacing Portland cement in concrete with fly ash from coal-fired power plants

A scanning electron microscope image shows raw, type C fly ash particles made primarily of calcium oxide as a byproduct of coal-fired power plants. Rice University engineers have made a cementless, environmentally friendly binder for concrete that shows potential to replace Portland cement in many applications. Courtesy of the Multiscale Materials Laboratory

Rice engineers use byproduct from coal-fired power plants to replace Portland cement

Rice University engineers have developed a composite binder made primarily of fly ash, a byproduct of coal-fired power plants, that can replace Portland cement in concrete.

The material is cementless and environmentally friendly, according to Rice materials scientist Rouzbeh Shahsavari, who developed it with graduate student Sung Hoon Hwang.

Fly ash binder does not require the high-temperature processing of Portland cement, yet tests showed it has the same compressive strength after seven days of curing. It also requires only a small fraction of the sodium-based activation chemicals used to harden Portland cement.

The results are reported in the Journal of the American Ceramic Society.

More than 20 billion tons of concrete are produced around the world every year in a manufacturing process that contributes 5 to 10 percent of carbon dioxide to global emissions, surpassed only by transportation and energy as the largest producers of the greenhouse gas.

Manufacturers often use a small amount of silicon- and aluminum-rich fly ash as a supplement to Portland cement in concrete. “The industry typically mixes 5 to 20 percent fly ash into cement to make it green, but a significant portion of the mix is still cement,” said Shahsavari, an assistant professor of civil and environmental engineering and of materials science and nanoengineering.

Previous attempts to entirely replace Portland cement with a fly ash compound required large amounts of expensive sodium-based activators that negate the environmental benefits, he said. “And in the end it was more expensive than cement,” he said.

The researchers used Taguchi analysis, a statistical method developed to narrow the large phase space — all the possible states — of a chemical composition, followed by computational optimization to identify the best mixing strategies.

This greatly improved the structural and mechanical qualities of the synthesized composites, Shahsavari said, and led to an optimal balance of calcium-rich fly ash, nanosilica and calcium oxide with less than 5 percent of a sodium-based activator.

“A majority of past works focused on so-called type F fly ash, which is derived from burning anthracite or bituminous coals in power plants and haslow calcium content,” Shahsavari said. “But globally, there are significant sources of lower grade coal such as lignite or sub-bituminous coals. Burning them results in high-calcium, or type C, fly ash, which has been more difficult to activate.

“Our work provides a viable path for efficient and cost-effective activation of this type of high-calcium fly ash, paving the path for the environmentally responsible manufacture of concrete. Future work will assess such properties as long-term behavior, shrinkage and durability.”

Shahsavari suggested the same strategy could be used to turn other industrial waste, such as blast furnace slag and rice hulls, into environmentally friendly cementitious materials without the use of cement.

Learn more: Cementless fly ash binder makes concrete ‘green



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Self-healing concrete that uses a specific type of fungi as a healing agent

Assistant professor Congrui Jin (center) with two Binghamton University graduate students from the Mechanical Engineering Department. Image Credit: Jonathan Cohen.

Binghamton University researchers have been working on a self-healing concrete that uses a specific type of fungi as a healing agent.

America’s crumbling infrastructure has been a topic of ongoing discussion in political debates and campaign rallies. The problem of aging bridges and increasingly dangerous roads is one that has been well documented and there seems to be a consensus from both democrats and republicans that something must be done.

However, spending on infrastructure improvement has continually gone down. The New York Times reported in 2016, based on a report for the Bureau of Economic Analysis, that “in the 1950s and ’60s, federal, state and local governments were spending twice as much on the nation’s public infrastructure, relative to the size of the economy, as they are today.”

The hesitancy to invest in America’s infrastructure may come from a number of sources, but the fact remains that most want something to be done before the consequences are too severe.

Binghamton University assistant professor Congrui Jin has been working on this problem since 2013, and recently published her paper “Interactions of fungi with concrete: significant importance for bio-based self-healing concrete” in the academic journal Construction & Building Materials.

This research is the first application of fungi for self-healing concrete, a low-cost, pollution-free and sustainable approach.

Why is infrastructure crumbling?

Jin’s studies have looked specifically at concrete and found that the problem stems from the smallest of cracks in the concrete.

“Without proper treatment, cracks tend to progress further and eventually require costly repair,” said Jin. “If micro-cracks expand and reach the steel reinforcement, not only the concrete will be attacked, but also the reinforcement will be corroded, as it is exposed to water, oxygen, possibly CO2 and chlorides, leading to structural failure.”

These cracks can cause huge and sometimes unseen problems for infrastructure. One potentially critical example is the case of nuclear power plants that may use concrete for radiation shielding.

What can be done?

While remaking a structure would replace the aging concrete, this would only be a short-term fix until more cracks again spring up. Jin wanted to see if there was a way to fix the concrete permanently.

“This idea was originally inspired by the miraculous ability of the human body to heal itself of cuts, bruises and broken bones,” said Jin. “For the damaged skins and tissues, the host will take in nutrients that can produce new substitutes to heal the damaged parts.”

Jin worked with associate professor Ning Zhang from Rutgers University, and professor Guangwen Zhou and associate professor David Davies from Binghamton University with support from the Research Foundation for the State University of New York’s Sustainable Community Transdisciplinary Area of Excellence Program. Together, the team set out to find a way to heal concrete.

The team found an unusual answer, a fungus called Trichoderma reesei.

When this fungus is mixed with concrete, it originally lies dormant — until the first crack appears.

“The fungal spores, together with nutrients, will be placed into the concrete matrix during the mixing process. When cracking occurs, water and oxygen will find their way in. With enough water and oxygen, the dormant fungal spores will germinate, grow and precipitate calcium carbonate to heal the cracks,” explained Jin.

“When the cracks are completely filled and ultimately no more water or oxygen can enter inside, the fungi will again form spores. As the environmental conditions become favorable in later stages, the spores could be wakened again.”

The research is still in fairly early stages with the biggest issue being the survivability of the fungus within the harsh environment of concrete. However, Jin is hopeful that with further adjustments the Trichoderma reesei will be able to effectively fill the cracks.

“There are still significant challenges to bring an efficient self-healing product to the concrete market. In my opinion, further investigation in alternative microorganisms such as fungi and yeasts for the application of self-healing concrete becomes of great potential importance,” said Jin.

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Revolutionizing the world of concrete with graphene

Innovative new ‘green’ concrete using graphene (Photo credit Dimitar Dimov)

A new greener, stronger and more durable concrete that is made using the wonder-material graphene could revolutionise the construction industry.

Experts from the University of Exeter have developed a pioneering new technique that uses nanoengineering technology to incorporate graphene into traditional concrete production.

The new composite material, which is more than twice as strong and four times more water resistant than existing concretes, can be used directly by the construction industry on building sites. All of the concrete samples tested are according to British and European standards for construction.

Crucially, the new graphene-reinforced concentre material also drastically reduced the carbon footprint of conventional concrete production methods, making it more sustainable and environmentally friendly.

The research team insist the new technique could pave the way for other nanomaterials to be incorporated into concrete, and so further modernise the construction industry worldwide.

The research is published in the journal Advanced Function Materials, on Monday, April 23 2018.

Professor Monica Craciun, co-author of the paper and from Exeter’s engineering department, said: “Our cities face a growing pressure from global challenges on pollution, sustainable urbanization and resilience to catastrophic natural events, amongst others.

“This new composite material is an absolute game-changer in terms of reinforcing traditional concrete to meets these needs. Not only is it stronger and more durable, but it is also more resistant to water, making it uniquely suitable for construction in areas  which require maintenance work and are difficult to be accessed .

“Yet perhaps more importantly, by including graphene we can reduce the amount of materials required to make concrete by around 50 per cent – leading to a significant reduction of 446kg/tonne of the carbon emissions.

“This unprecedented range of functionalities and properties uncovered are an important step in encouraging a more sustainable, environmentally-friendly construction industry worldwide.”

Previous work on using nanotechnology has concentrated on modifying existing components of cement, one of the main elements of concrete production.

In the innovative new study, the research team has created a new technique that centres on suspending atomically thin graphene in water with high yield and no defects, low cost and compatible with modern, large scale manufacturing requirements.

Dimitar Dimov, the lead author and also from the University of Exeter added: “This ground-breaking research is important as it can be applied to large-scale manufacturing and construction. The industry has to be modernised by incorporating not only off-site manufacturing, but innovative new materials as well.

“Finding greener ways to build is a crucial step forward in reducing carbon emissions around the world and so help protect our environment as much as possible. It is the first step, but a crucial step in the right direction to make a more sustainable construction industry for the future.”

Learn more: Scientists create innovative new ‘green’ concrete using graphene


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