Tag Archives: sunlight

Historic and other buildings get protection from pollution?

This Sept. 15, 2017 news item on Nanowerk announces a new product for protecting buildings from pollution,

The organic pollution decomposing properties of titanium dioxide (TiO2 ) have been known for about half a century. However, practical applications have been few and hard to develop, but now a Greek paint producer claims to have found a solution

A Sept. 11, 2017 Youris (European Research Media Center) press release by Koen Mortelmans which originated the news item expands on the theme,

The photocatalytic properties of anatase, one of the three naturally occurring forms of titanium dioxide, were discovered in Japan in the late 1960s. Under the influence of the UV-radiation in sunlight, it can decompose organic pollutants such as bacteria, fungi and nicotine, and some inorganic materials into carbon dioxide. The catalytic effect is caused by the nanostructure of its crystals.

Applied outdoors, this affordable and widely available material could represent an efficient self-cleaning solution for buildings. This is due to the chemical reaction, which leaves a residue on building façades, a residue then washed away when it rains. Applying it to monuments in urban areas may save our cultural heritage, which is threatened by pollutants.

However, “photocatalytic paints and additives have long been a challenge for the coating industry, because the catalytic action affects the durability of resin binders and oxidizes the paint components,” explains Ioannis Arabatzis, founder and managing director of NanoPhos, based in the Greek town of Lavrio, in one of the countries home to some of the most important monuments of human history. The Greek company is testing a paint called Kirei, inspired by a Japanese word meaning both clean and beautiful.

According to Arabatzis, it’s an innovative product because it combines the self-cleaning action of photocatalytic nanoparticles and the reflective properties of cool wall paints. “When applied on exterior surfaces this paint can reflect more than 94% of the incident InfraRed radiation (IR), saving energy and reducing costs for heating and cooling”, he says. “The reflection values are enhanced by the self-cleaning ability. Compared to conventional paints, they remain unchanged for longer.”

The development of Kirei has been included in the European project BRESAER (BREakthrough Solutions for Adaptable Envelopes in building Refurbishment) which is studying a sustainable and adaptable “envelope system” to renovate buildings. The new paint was tested and subjected to quality controls following ISO standard procedures at the company’s own facilities and in other independent laboratories. “The lab results from testing in artificial, accelerated weathering conditions are reliable,” Arabatzis claims. “There was no sign of discolouration, chalking, cracking or any other paint defect during 2,000 hours of exposure to the simulated environmental conditions. We expect the coating’s service lifetime to be at least ten years.”

Many studies are being conducted to exploit the properties of titanium dioxide. Jan Duyzer, researcher at the Netherlands Organisation for Applied Scientific Research (TNO) in Utrecht, focused on depollution: “There is no doubt about the ability of anatase to decrease the levels of nitrogen oxides in the air. But in real situations, there are many differences in pollution, wind, light, and temperature. We were commissioned by the Dutch government specifically to find a way to take nitrogen oxides out of the air on roads and in traffic tunnels. We used anatase coated panels. Our results were disappointing, so the government decided to discontinue the research. Furthermore, we still don’t know what caused the difference between lab and life. Our best current hypothesis is that the total surface of the coated panels is very small compared to the large volumes of polluted air passing over them,” he tells youris.com.

Experimental deployment of titanium dioxide panels on an acoustic wall along a Dutch highway – Courtesy of Netherlands Organisation for Applied Scientific Research (TNO)

“In laboratory conditions the air is blown over the photocatalytic surface with a certain degree of turbulence. This results in the NOx-particles and the photocatalytic material coming into full contact with one another,” says engineer Anne Beeldens, visiting professor at KU Leuven, Belgium. Her experience with photocatalytic TiO2 is also limited to nitrogen dioxide (NOx) pollution.

In real applications, the air stream at the contact surface becomes laminar. This results in a lower velocity of the air at the surface and a lower depollution rate. Additionally, not all the air will be in contact with the photocatalytic surfaces. To ensure a good working application, the photocatalytic material needs to be positioned so that all the air is in contact with the surface and flows over it in a turbulent manner. This would allow as much of the NOx as possible to be in contact with photocatalytic material. In view of this, a good working application could lead to a reduction of 5 to 10 percent of NOx in the air, which is significant compared to other measures to reduce pollutants.”

The depollution capacity of TiO2 is undisputed, but most applications and tests have only involved specific kinds of substances. More research and measurements are required if we are to benefit more from the precious features of this material.

I think the most recent piece here on protecting buildings, i.e., the historic type, from pollution is an Oct. 21, 2014 posting: Heart of stone.

A different type of ‘smart’ window with a new solar cell technology

I always like a ‘smart’ window story. Given my issues with summer (I don’t like the heat), anything which promises to help reduce the heat in my home at that time of year, has my vote. Unfortunately, solutions don’t seem to have made a serious impact on the marketplace. Nonetheless, there’s always hope and perhaps this development at Princeton University will be the one to break through the impasse. From a June 30, 2017 news item on ScienceDaily,

Smart windows equipped with controllable glazing can augment lighting, cooling and heating systems by varying their tint, saving up to 40 percent in an average building’s energy costs.

These smart windows require power for operation, so they are relatively complicated to install in existing buildings. But by applying a new solar cell technology, researchers at Princeton University have developed a different type of smart window: a self-powered version that promises to be inexpensive and easy to apply to existing windows. This system features solar cells that selectively absorb near-ultraviolet (near-UV) light, so the new windows are completely self-powered.

A June 30, 2017 Princeton University news release, which originated the news item, expands on the theme,

“Sunlight is a mixture of electromagnetic radiation made up of near-UV rays, visible light, and infrared energy, or heat,” said Yueh-Lin (Lynn) Loo, director of the Andlinger Center for Energy and the Environment, and the Theodora D. ’78 and William H. Walton III ’74 Professor in Engineering. “We wanted the smart window to dynamically control the amount of natural light and heat that can come inside, saving on energy cost and making the space more comfortable.”

The smart window controls the transmission of visible light and infrared heat into the building, while the new type of solar cell uses near-UV light to power the system.

“This new technology is actually smart management of the entire spectrum of sunlight,” said Loo, who is a professor of chemical and biological engineering. Loo is one of the authors of a paper, published June 30, that describes this technology, which was developed in her lab.

Because near-UV light is invisible to the human eye, the researchers set out to harness it for the electrical energy needed to activate the tinting technology.

“Using near-UV light to power these windows means that the solar cells can be transparent and occupy the same footprint of the window without competing for the same spectral range or imposing aesthetic and design constraints,” Loo added. “Typical solar cells made of silicon are black because they absorb all visible light and some infrared heat – so those would be unsuitable for this application.”

In the paper published in Nature Energy, the researchers described how they used organic semiconductors – contorted hexabenzocoronene (cHBC) derivatives – for constructing the solar cells. The researchers chose the material because its chemical structure could be modified to absorb a narrow range of wavelengths – in this case, near-UV light. To construct the solar cell, the semiconductor molecules are deposited as thin films on glass with the same production methods used by organic light-emitting diode manufacturers. When the solar cell is operational, sunlight excites the cHBC semiconductors to produce electricity.

At the same time, the researchers constructed a smart window consisting of electrochromic polymers, which control the tint, and can be operated solely using power produced by the solar cell. When near-UV light from the sun generates an electrical charge in the solar cell, the charge triggers a reaction in the electrochromic window, causing it to change from clear to dark blue. When darkened, the window can block more than 80 percent of light.

Nicholas Davy, a doctoral student in the chemical and biological engineering department and the paper’s lead author, said other researchers have already developed transparent solar cells, but those target infrared energy. However, infrared energy carries heat, so using it to generate electricity can conflict with a smart window’s function of controlling the flow of heat in or out of a building. Transparent near-UV solar cells, on the other hand, don’t generate as much power as the infrared version, but don’t impede the transmission of infrared radiation, so they complement the smart window’s task.

Davy said that the Princeton team’s aim is to create a flexible version of the solar-powered smart window system that can be applied to existing windows via lamination.

“Someone in their house or apartment could take these wireless smart window laminates – which could have a sticky backing that is peeled off – and install them on the interior of their windows,” said Davy. “Then you could control the sunlight passing into your home using an app on your phone, thereby instantly improving energy efficiency, comfort, and privacy.”

Joseph Berry, senior research scientist at the National Renewable Energy Laboratory, who studies solar cells but was not involved in the research, said the research project is interesting because the device scales well and targets a specific part of the solar spectrum.

“Integrating the solar cells into the smart windows makes them more attractive for retrofits and you don’t have to deal with wiring power,” said Berry. “And the voltage performance is quite good. The voltage they have been able to produce can drive electronic devices directly, which is technologically quite interesting.”

Davy and Loo have started a new company, called Andluca Technologies, based on the technology described in the paper, and are already exploring other applications for the transparent solar cells. They explained that the near-UV solar cell technology can also power internet-of-things sensors and other low-power consumer products.

“It does not generate enough power for a car, but it can provide auxiliary power for smaller devices, for example, a fan to cool the car while it’s parked in the hot sun,” Loo said.

Here’s a link to and a citation for the paper,

Pairing of near-ultraviolet solar cells with electrochromic windows for smart management of the solar spectrum by Nicholas C. Davy, Melda Sezen-Edmonds, Jia Gao, Xin Lin, Amy Liu, Nan Yao, Antoine Kahn, & Yueh-Lin Loo. Nature Energy 2, Article number: 17104 (2017 doi:10.1038/nenergy.2017.104 Published online: 30 June 2017

This paper is behind a paywall.

Here’s what a sample of the special glass looks like,

Graduate student Nicholas Davy holds a sample of the special window glass. (Photos by David Kelly Crow)

Using only sunlight to desalinate water

The researchers seem to believe that this new desalination technique could be a game changer. From a June 20, 2017 news item on Azonano,

An off-grid technology using only the energy from sunlight to transform salt water into fresh drinking water has been developed as an outcome of the effort from a federally funded research.

The desalination system uses a combination of light-harvesting nanophotonics and membrane distillation technology and is considered to be the first major innovation from the Center for Nanotechnology Enabled Water Treatment (NEWT), which is a multi-institutional engineering research center located at Rice University.

NEWT’s “nanophotonics-enabled solar membrane distillation” technology (NESMD) integrates tried-and-true water treatment methods with cutting-edge nanotechnology capable of transforming sunlight to heat. …

A June 19, 2017 Rice University news release, which originated the news item, expands on the theme,

More than 18,000 desalination plants operate in 150 countries, but NEWT’s desalination technology is unlike any other used today.

“Direct solar desalination could be a game changer for some of the estimated 1 billion people who lack access to clean drinking water,” said Rice scientist and water treatment expert Qilin Li, a corresponding author on the study. “This off-grid technology is capable of providing sufficient clean water for family use in a compact footprint, and it can be scaled up to provide water for larger communities.”

The oldest method for making freshwater from salt water is distillation. Salt water is boiled, and the steam is captured and run through a condensing coil. Distillation has been used for centuries, but it requires complex infrastructure and is energy inefficient due to the amount of heat required to boil water and produce steam. More than half the cost of operating a water distillation plant is for energy.

An emerging technology for desalination is membrane distillation, where hot salt water is flowed across one side of a porous membrane and cold freshwater is flowed across the other. Water vapor is naturally drawn through the membrane from the hot to the cold side, and because the seawater need not be boiled, the energy requirements are less than they would be for traditional distillation. However, the energy costs are still significant because heat is continuously lost from the hot side of the membrane to the cold.

“Unlike traditional membrane distillation, NESMD benefits from increasing efficiency with scale,” said Rice’s Naomi Halas, a corresponding author on the paper and the leader of NEWT’s nanophotonics research efforts. “It requires minimal pumping energy for optimal distillate conversion, and there are a number of ways we can further optimize the technology to make it more productive and efficient.”

NEWT’s new technology builds upon research in Halas’ lab to create engineered nanoparticles that harvest as much as 80 percent of sunlight to generate steam. By adding low-cost, commercially available nanoparticles to a porous membrane, NEWT has essentially turned the membrane itself into a one-sided heating element that alone heats the water to drive membrane distillation.

“The integration of photothermal heating capabilities within a water purification membrane for direct, solar-driven desalination opens new opportunities in water purification,” said Yale University ‘s Menachem “Meny” Elimelech, a co-author of the new study and NEWT’s lead researcher for membrane processes.

In the PNAS study, researchers offered proof-of-concept results based on tests with an NESMD chamber about the size of three postage stamps and just a few millimeters thick. The distillation membrane in the chamber contained a specially designed top layer of carbon black nanoparticles infused into a porous polymer. The light-capturing nanoparticles heated the entire surface of the membrane when exposed to sunlight. A thin half-millimeter-thick layer of salt water flowed atop the carbon-black layer, and a cool freshwater stream flowed below.

Li, the leader of NEWT’s advanced treatment test beds at Rice, said the water production rate increased greatly by concentrating the sunlight. “The intensity got up 17.5 kilowatts per meter squared when a lens was used to concentrate sunlight by 25 times, and the water production increased to about 6 liters per meter squared per hour.”

Li said NEWT’s research team has already made a much larger system that contains a panel that is about 70 centimeters by 25 centimeters. Ultimately, she said, NEWT hopes to produce a modular system where users could order as many panels as they needed based on their daily water demands.

“You could assemble these together, just as you would the panels in a solar farm,” she said. “Depending on the water production rate you need, you could calculate how much membrane area you would need. For example, if you need 20 liters per hour, and the panels produce 6 liters per hour per square meter, you would order a little over 3 square meters of panels.”

Established by the National Science Foundation in 2015, NEWT aims to develop compact, mobile, off-grid water-treatment systems that can provide clean water to millions of people who lack it and make U.S. energy production more sustainable and cost-effective. NEWT, which is expected to leverage more than $40 million in federal and industrial support over the next decade, is the first NSF Engineering Research Center (ERC) in Houston and only the third in Texas since NSF began the ERC program in 1985. NEWT focuses on applications for humanitarian emergency response, rural water systems and wastewater treatment and reuse at remote sites, including both onshore and offshore drilling platforms for oil and gas exploration.

There is a video but it is focused on the NEWT center rather than any specific water technologies,

For anyone interested in the technology, here’s a link to and a citation for the researchers’ paper,

Nanophotonics-enabled solar membrane distillation for off-grid water purification by Pratiksha D. Dongare, Alessandro Alabastri, Seth Pedersen, Katherine R. Zodrow, Nathaniel J. Hogan, Oara Neumann, Jinjian Wu, Tianxiao Wang, Akshay Deshmukh,f, Menachem Elimelech, Qilin Li, Peter Nordlander, and Naomi J. Halas. PNAS {Proceedings of the National Academy of Sciences] doi: 10.1073/pnas.1701835114 June 19, 2017

This paper appears to be open access.

Trying to push past the 30% energy conversion ceiling for solar cells

A Nov. 21, 2016 news item on Nanowerk describes some work in Japan which suggests that more energy conversion for solar cells is possible,

Solar energy could provide a renewable, sustainable source of power for our daily needs. However, even the most state-of-the-art solar cells struggle to achieve energy conversion efficiency of higher than 30%. While current solar-powered water heaters fare better in terms of energy efficiency, there are still improvements to be made if the systems are to be used more widely.

One potential candidate for inclusion in solar water heaters is “nanofluid,” that is, a liquid containing specially-designed nanoparticles that are capable of absorbing sunlight and transforming it into thermal energy in order to heat water directly.

A Nov. 20, 2016 (Japan) International Center for Materials Nanoarchitectonics (WPI-MANA) press release (received via email), explains further,

Nanoparticle Boost for Solar-powered Water Heating

Now, Satoshi Ishii and his co-workers at the International Center for Materials Nanoarchitectonics (WPI-MANA) and the Japan Science and Technology Agency have developed a new nanofluid containing titanium nitride (TiN) nanoparticles, which demonstrates high efficiency in heating water and generating water vapor.

The team analytically studied the optical absorption efficiency of a TiN nanoparticle and found that it has a broad and strong absorption peak thanks to lossy plasmonic resonances. Surprisingly, the sunlight absorption efficiency of a TiN nanoparticle outperforms that of a carbon nanoparticle and a gold nanoparticle.

They then exposed each nanofluid to sunlight and measured its ability to heat pure water. The TiN nanofluid had the highest water heating properties, stemming from the resonant sunlight absorption. It also generated more vapor than its carbon‒based counterpart. The efficiency of the TiN nanofluid reached nearly 90 %. Crucially, the TiN particles were not consumed during the process, meaning a TiN‒based heating system could essentially be self‒sustaining over time.

TiN nanofluids show great promise in solar heat applications, with high potential for use in everyday appliances such as showers. The new design could even contribute to methods for decontaminating water through vaporization.

90% is a very exiting conversion rate. Of course, now they need to make sure they can achieve those results consistently, get those results outside the laboratory, and scale up to industrial standards.

Here’s a link to and a citation for the paper,

Titanium Nitride Nanoparticles as Plasmonic Solar Heat Transducers by Satoshi Ishii, Ramu Pasupathi Sugavaneshwar, and Tadaaki Nagao. J. Phys. Chem. C, 2016, 120 (4), pp 2343–2348 DOI: 10.1021/acs.jpcc.5b09604 Publication Date (Web): December 21, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall and it’s almost a year old. I wonder what occasioned the push for publicity.

Clothes washers and dryers begone! Nano-enhanced textiles can self-clean

It will be a while yet even it this technique proves to be viable commercially, still, the possibilities tantalize: self-cleaning textiles. A March 22, 2016 news item on ScienceDaily announced research in Australia that may, one day, change your life,

A spot of sunshine is all it could take to get your washing done, thanks to pioneering nano research into self-cleaning textiles.

Researchers at RMIT University in Melbourne, Australia, have developed a cheap and efficient new way to grow special nanostructures — which can degrade organic matter when exposed to light — directly onto textiles.

The work paves the way towards nano-enhanced textiles that can spontaneously clean themselves of stains and grime simply by being put under a light bulb or worn out in the sun.

A March 22, 2016 RMIT media release (also on EurekAlert), which originated the news item, expands on the theme,

Dr Rajesh Ramanathan said the process developed by the team had a variety of applications for catalysis-based industries such as agrochemicals, pharmaceuticals and natural products, and could be easily scaled up to industrial levels.

“The advantage of textiles is they already have a 3D structure so they are great at absorbing light, which in turn speeds up the process of degrading organic matter,” he said.

“There’s more work to do to before we can start throwing out our washing machines, but this advance lays a strong foundation for the future development of fully self-cleaning textiles.”

The researchers from the Ian Potter NanoBioSensing Facility and NanoBiotechnology Research Lab at RMIT worked with copper and silver-based nanostructures, which are known for their ability to absorb visible light.

When the nanostructures are exposed to light, they receive an energy boost that creates “hot electrons”. These “hot electrons” release a burst of energy [emphasis mine] that enables the nanostructures to degrade organic matter.

The challenge for researchers has been to bring the concept out of the lab by working out how to build these nanostructures on an industrial scale and permanently attach them to textiles.

The RMIT team’s novel approach was to grow the nanostructures directly onto the textiles by dipping them into a few solutions, resulting in the development of stable nanostructures within 30 minutes.

When exposed to light, it took less than six minutes for some of the nano-enhanced textiles to spontaneously clean themselves.

“Our next step will be to test our nano-enhanced textiles with organic compounds that could be more relevant to consumers, to see how quickly they can handle common stains like tomato sauce or wine,” Ramanathan said.

I wonder if these “hot electrons” mean that when they release “a burst of energy” your clothing will heat up when exposed to light? This image supplied by the researchers does not help to answer the question but it is intriguing,

Caption: Close-up of the nanostructures grown on cotton textiles by RMIT University researchers. Image magnified 150,000 times. Credit: RMIT University

Caption: Close-up of the nanostructures grown on cotton textiles by RMIT University researchers. Image magnified 150,000 times. Credit: RMIT University

Here’s a link to and a citation for the paper,

Robust Nanostructured Silver and Copper Fabrics with Localized Surface Plasmon Resonance Property for Effective Visible Light Induced Reductive Catalysis by Samuel R. Anderson, Mahsa Mohammadtaheri, Dipesh Kumar, Anthony P. O’Mullane, Matthew R. Field, Rajesh Ramanathan, and Vipul Bansal. Advanced Materials Interfaces DOI: 10.1002/admi.201500632 Article first published online: 7 JAN 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

Graphene oxide-silver nanoparticle composite along with sunlight removes* endocrine disruptors from the environment

Removing pollutants from the environment with a combination of silver nanoparticles, graphene, and ordinary sunlight may be possible according to a Nov. 6, 2014 news item on Azonano,

Many pollutants with the potential to meddle with hormones — with bisphenol A (BPA) as a prime example — are already common in the environment. In an effort to clean up these pollutants found in the soil and waterways, scientists are now reporting a novel way to break them down by recruiting help from nanoparticles and light. The study appears in the journal ACS [American Chemical Society] Applied Materials & Interfaces.

A Nov. 5, 2014 ACS press pak news item (also on EurekAlert), which originated the Azonano piece, describes the work further,

Nikhil R. Jana and Susanta Kumar Bhunia explain that the class of pollutants known as endocrine disruptors has been shown to either mimic or block hormones in animals, including humans. That interference can cause reproductive and other health problems. The compounds are used to make many household and industrial products, and have been detected in soil, water and even human breast milk. Scientists have been working on ways to harness sunlight to break down endocrine disruptors to make them less of a health threat. But the approaches so far only work with ultraviolet light, which at a mere 6 percent of sunlight, means these methods are not very efficient. Jana and Bhunia wanted to find a simple way to take advantage of visible light, which comprises 52 percent of sunlight.

For inspiration, the researchers turned to an already-developed graphene composite that uses visible light to degrade dyes. They tweaked the composite and loaded it with silver nanoparticles that serve as an antenna for visible light. When they tested it, the new material successfully degraded three different kinds of endocrine disruptors: phenol, BPA and atrazine. They conclude that their composite is a promising way to harness visible light to break down these potentially harmful compounds and other organic pollutants.

The authors acknowledge funding from India’s Department of Science & Technology.

Here’s a link to and a citation for the paper,

Reduced Graphene Oxide-Silver Nanoparticle Composite as Visible Light Photocatalyst for Degradation of Colorless Endocrine Disruptors by Susanta Kumar Bhunia and Nikhil R. Jana. ACS Appl. Mater. Interfaces, Article ASAP DOI: 10.1021/am505677x Publication Date (Web): October 8, 2014

Copyright © 2014 American Chemical Society

This article is behind a paywall.

The authors have provided a diagram illustrating the effectiveness of a control material, graphene-oxide alone, silver nanoparticles alone, and a graphene-oxide silver nanoparticle composite at reducing organic pollutants when used in conjunction with sunlight,

[downloaded from http://pubs.acs.org/doi/abs/10.1021/am505677x]

[downloaded from http://pubs.acs.org/doi/abs/10.1021/am505677x]

* ‘Remove’ in head corrected to ‘removes’ on Nov. 7, 2014.