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Low-cost solar-powered water filter removes lead, other contaminants

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Low-cost solar-powered water filter removes lead, other contaminants

A new invention that uses sunlight to drive water purification could help solve the problem of providing clean water off the grid.

The device resembles a large sponge that soaks up water but leaves contaminants – like lead, oil and pathogens – behind. To collect the purified water from the sponge, one simply places it in sunlight. The researchers described the device in a paper published this week in the journal Advanced Materials.

The inspiration for the device came from the pufferfish, a species that takes in water to swell its body when threatened, and then releases water when danger passes, said the device’s co-inventor Rodney Priestley, the Pomeroy and Betty Perry Smith Professor of Chemical and Biological Engineering, and Princeton’s vice dean for innovation.

“To me, the most exciting thing about this work is it can operate completely off-grid, at both large and small scales,” Priestley said. “”It could also work in the developed world at sites where low-cost, non-powered water purification is needed.””

Xiaohui Xu, a Princeton Presidential Postdoctoral Research Fellow in the Department of Chemical and Biological Engineering and co-inventor, helped develop the gel material at the heart of the device.

“”Sunlight is free,” Xu said, “and the materials to make this device are low-cost and non-toxic, so this is a cost-effective and environmentally friendly way to generate pure water.””

The authors noted that the technology delivers the highest passive solar water- purification rate of any competing technology.

One way to use the gel would be to place it in a water source in the evening and the next day place it in the sunlight to generate the day’s drinking water, Xu said.

The gel can purify water contaminated with petroleum and other oils, heavy metals such as lead, small molecules, and pathogens such as yeast. The team showed that the gel maintains its ability to filter water for at least ten cycles of soaking and discharge with no detectable reduction in performance. The results suggest that the gel can be used repeatedly.

To demonstrate the device in real-world conditions, Xu took the device to Lake Carnegie on the Princeton University campus.

Xu placed the gel into the cool water (25 degree Celsius, or 77 degrees Fahrenheit) of the lake, which contains microorganisms that make it unsafe to drink, and let it soak up the lake water for an hour.

At the end of the hour, Xu lifted the gel out of the water and set it on top of a container. As the sun warmed the gel, pure water trickled into the container over the next hour.

The device filters water much more quickly than existing methods of passive solar-powered water purification methods, the researchers said. Most other solar-powered approaches use sunlight to evaporate water, which takes much longer than absorption and release by the new gel.

Other water filtration methods require electricity or another source of power to pump water through a membrane. Passive filtration via gravity, as with typical household countertop filters, requires regular replacement of filters.

At the heart of the new device is a gel that changes depending on temperature. At room temperature, the gel can act as a sponge, soaking up water. When heated to 33 degrees Celsius (91 degrees Fahrenheit), the gel does the opposite – it pushes the water out of its pores.

The gel consists of a honeycomb-like structure that is highly porous. Closer inspection reveals that the honeycomb consists of long chains of repeating molecules, known as poly(N-isopropylacrylamide), that are cross-linked to form a mesh. Within the mesh, some regions contain molecules that like to have water nearby, or are hydrophilic, while other regions are hydrophobic or water-repelling.

At room temperature, the chains are long and flexible, and water can easily flow via capillary action into the material to reach the water-loving regions. But when the sun warms the material, the hydrophobic chains clump together and force the water out of the gel.

This gel sits inside two other layers that stop contaminants from reaching the inner gel. The middle layer is a dark-colored material called polydopamine that transforms sunlight into heat and also keeps out heavy metals and organic molecules. With PDA in place, the sun’s light can heat up the inner material even if the actual outdoor temperature is not very warm.

The final external layer is a filtering layer of alginate, which blocks pathogens and other materials from entering the gel.

Xu said that one of the challenges to making the device was to formulate the inner gel to have the correct properties for water absorption. Initially the gel was brittle, so she altered the composition until it was flexible. Xu synthesized the materials and conducted studies to assess the device’s ability to purify water, aided by coauthors Sehmus Ozden and Navid Bizmark, postdoctoral research associates in the Princeton Institute for the Science and Technology of Materials.

Sujit Datta, assistant professor of chemical and biological engineering, and Craig Arnold, the Susan Dod Brown Professor of Mechanical and Aerospace Engineering and director of the Princeton Institute for the Science and Technology of Materials, collaborated on the development of the technology.

The team is exploring ways to make the technology widely available with the help of Princeton Innovation, which supports University researchers in the translation of discoveries into technologies and services for the benefit of society.

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Research team achieves significant solar cell efficiency milestone

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Research team achieves significant solar cell efficiency milestone


Research team achieves significant solar cell efficiency milestone

by Simon Mansfield

Sydney, Australia (SPX) May 26, 2024






A research team has created a tandem solar cell using antimony selenide as the bottom cell material and a hybrid perovskite material as the top cell, achieving over 20 percent power conversion efficiency. This advancement highlights antimony selenide’s potential for bottom cell applications.

Photovoltaic technology converts sunlight into electricity, offering a clean energy source. Scientists aim to enhance the efficiency of solar cells, achieving over 20 percent in conventional single-junction cells. Surpassing the Shockley-Queisser limit in these cells would be costly, but tandem solar cells can overcome this limit by stacking materials.



The team focused on antimony selenide for tandem cells, traditionally used in single-junction cells. “Antimony selenide is a suitable bottom cell material for tandem solar cells. However, because of the rarity of reported tandem solar cells using it as a bottom cell, little attention has been paid to its application. We assembled a tandem solar cell with high conversion efficiency using it as the bottom cell to demonstrate the potential of this material,” said Tao Chen, professor of Materials Science and Engineering at the University of Science and Technology of China.



Tandem cells absorb more sunlight than single-junction cells, converting more light into electricity. The team created perovskite/antimony selenide tandem cells with a transparent conducting electrode, optimizing the spectral response and achieving over 17 percent efficiency. By optimizing the antimony selenide bottom cell, they reached 7.58 percent efficiency.



The assembled four-terminal tandem cell achieved 20.58 percent efficiency, higher than independent subcells. The tandem cell is stable and uses nontoxic elements. “This work provides a new tandem device structure and demonstrates that antimony selenide is a promising absorber material for bottom cell applications in tandem solar cells,” said Chen.



The team aims to develop an integrated two-terminal tandem cell and further improve performance. “The high stability of antimony selenide provides great convenience for the preparation of two-terminal tandem solar cell, which means that it may have good results when paired with quite a few different types of top cell materials.”



Research Report:Sb2Se3 as a bottom cell material for efficient perovskite/Sb2Se3 tandem solar cells


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Flower or power? Campaigners fear lithium mine could kill rare plant

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Flower or power? Campaigners fear lithium mine could kill rare plant


Flower or power? Campaigners fear lithium mine could kill rare plant

By Romain FONSEGRIVES

Rhyolite Ridge, United States (AFP) May 23, 2024






Delicate pink buds sway in the desert breeze, pregnant with yellow pompoms whose explosion will carpet the dusty corner of Nevada that is the only place on Earth where they exist.

Under their roots lie vast reserves of lithium, vital for the rechargeable electric car batteries that will reduce planet-heating pollution.

But campaigners fear the extraction of the precious metal could destroy the flower’s tiny habitat.

“This mine is going to cause extinction,” says Patrick Donnelly, an environmentalist who works at the Center for Biological Diversity, a non-governmental organization.

“They somehow claim that they’re not harming the (plant). But can you imagine if someone built an open-pit mine 200 feet from your house? Wouldn’t that affect your life profoundly?”

The plant in question is Tiehm’s buckwheat.

There are only around 20,000 known specimens, growing in a few very specific places on a total surface area equivalent to around five soccer fields.

In 2022, the wildflower was classified as endangered by US federal authorities, with mining cited as a major threat to its survival.

The plant and the lithium reserve on which it grows embody one of the key challenges and contradictions of the global climate struggle: how much damage can we inflict on the natural world as we seek to halt or reverse the problems we have already created?

– ‘Coexist’ –

Bernard Rowe, boss of Australian miner Ioneer, which holds the mineral rights to the area, says the lithium produced at Rhyolite Ridge “will be sufficient to provide batteries for about 370,000 vehicles” a year.

“We’ll do that year-on-year for 26 years,” he said.

Those nearly 10 million vehicles will go a long way towards meeting the goal President Joe Biden has set of cutting down the nation’s fleet of gas-guzzlers as a way to slash US production of planet-warming pollutants.

So-called zero-emission cars make up around 7.5 percent of new vehicle sales in the United States today — more than double the percentage just a few years earlier.

In California, the figure is more than 20 percent.

And while expansion in the sector has slowed, the category remains the fastest-growing, according to Kelley Blue Book.

And it’s not only in the United States: Global demand for lithium will increase five to seven times by 2030, according to the International Energy Agency.

The difficulty for US manufacturers is that much of the world’s lithium supply is dominated by strategic rival China, as well as Australia and Chile.

“The United States has very, very little domestic production,” said Rowe.

“So it’s important to develop a domestic supply chain to allow for that energy transition, and Rhyolite Ridge will be an integral part of that.”

Ioneer’s plans show that over the years the mine is in operation — it is projected to start producing lithium in late 2027 — around a fifth of the plant’s habitat will be directly affected.

But the company, which has spent $2.5 million researching the plant, says mining will not affect its survival; it is already growing well in greenhouses and biologists think it can be replanted.

“We’re very confident that the mine and Tiehm’s buckwheat can coexist,” Rowe said.

– ‘Greenwashing’ –

Donnelly counters that Ioneer is “basically greenwashing extinction.”

“They’re saying. ‘We’re going to save this plant,’ when actually they are going to send it to its doom,” he said.

Under the company’s plans, the strip mine will use hundreds of trucks, which Donnelly says will raise clouds of dust that will affect photosynthesis and harm the insects that pollinate the plants.

Ioneer says it has already planned mitigation methods, like dust curtains, and keeping the roads wet.

Still, Donnelly says, why not just move the mine? But Rowe counters that it’s not as simple as just digging somewhere else.

Ioneer has invested $170 million since 2016 to demonstrate the feasibility of this site, which it believes is one of the best around.

“Many of these other deposits haven’t had that amount of work, so they’re not viable alternatives to a project like this,” he said.

The US Department of Energy has offered Ioneer a $700 million loan for the project, if the Bureau of Land Management signs off on an operating permit.

Donnelly insists the issue is not just the future of one obscure wildflower, but rather just one example of large-scale biodiversity loss that is threatening millions of plants and animals.

“If we solve the climate crisis, but we drive everything extinct while we do it, we’re still going to lose our world,” he said.

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Tesla breaks ground on huge Shanghai battery plant

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Tesla breaks ground on huge Shanghai battery plant


Tesla breaks ground on huge Shanghai battery plant

by AFP Staff Writers

Shanghai (AFP) May 23, 2024






Tesla broke ground on a massive battery factory in Shanghai on Thursday, Chinese state media reported, making it the US electric car giant’s second plant in the financial hub.

The project was announced last April after boss Elon Musk presented a vague but ambitious plan to investors to turbocharge growth.

However, the company last month reported a 55 percent drop in quarterly earnings, reflecting a decline in EV sales in an intensively competitive market.

The new Shanghai factory should make 10,000 units per year of Tesla’s Megapack batteries, state news agency Xinhua said.

Tesla says Megapacks are intended to store energy and stabilise supply for power grids, with each unit able to store more than three megawatt-hours of power.

The factory is expected to start mass production in 2025, state media said in May.

“I believe the new plant is a milestone for both Shanghai and Tesla,” the company’s vice president Tao Lin told Xinhua.

“In a more open environment, we can… supply the global market with large-scale energy-storage batteries manufactured in China.”

Musk has extensive business interests in China and is a fairly frequent visitor.

In April, he met Chinese Premier Li Qiang, and received a key security clearance for Tesla’s locally produced EVs.

Musk’s interests in China have long raised eyebrows in Washington — President Joe Biden has said in the past that his links to foreign countries were “worthy” of scrutiny.

The battery plant will be Tesla’s second in the Chinese city after its enormous Shanghai Gigafactory, which broke ground in 2019.

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