A*STAR team uses graphene oxide to create a cathode for improved li-ion batteries

A*STAR researchers have found that incorporating organic materials into lithium ion batteries could lower their cost and make them more environmentally friendly. The team has developed an organic-based battery cathode that has significantly improved electrochemical performance compared to previous organic cathode materials. The new material is also robust, remaining stable over thousands of battery charge/discharge cycles.

An electron-deficient, rigid organic molecule called hexaazatrinaphthalene (HATN) was previously investigated as an organic cathode material for lithium ion batteries. However, its promising initial performance declined rapidly during use, because the molecule began to dissolve into the battery’s liquid electrolyte. A new cathode material, in which HATN was combined with graphene oxide in an attempt to prevent the organic material from dissolving, has now been developed by Yugen Zhang and his colleagues from the A*STAR Institute of Bioengineering and Nanotechnology.

“Graphene oxide has excellent electronic conductivity, and surface oxygen functionality that may form hydrogen-bonding interactions with HATN,” Zhang says. He explains that this made graphene oxide a promising candidate for forming a HATN-graphene oxide nanocomposite.

The nanocomposite’s performance reportedly exceeded expectations. The materials combined to form core-shell nanorods in which the HATN was coated with graphene oxide. “Graphene oxide and HATN formed a very nice composite structure, which solved the dissolution issue of HATN in electrolyte and gave the cathode very good cycling stability,” Zhang says. A lithium ion battery using this material as its cathode retained 80% of its capacity after 2000 charge/discharge cycles.

The team saw even better performance when they combined graphene oxide with a HATN derivate called hexaazatrinaphthalene tricarboxylic acid (HATNTA). A battery made from this material retained 86% of its capacity after 2,000 charge/discharge cycles. The improved performance is probably due to the polar carboxylic acid groups on the HATNTA molecule, which attached the molecule even more strongly to the graphene oxide.

The team is continuing to develop new materials to improve the performance of organic cathodes, Zhang says. Aside from investigating alternatives to graphene oxide, the team also is working on HATN-based porous polymers for use as organic cathode materials, which should enhance the flow of ions during battery charge and discharge.

Source: Journal of Materials Chemistry A

Nanosheets Make Batteries Better: New method may be the next step for high performance lithium-ion batteries.

Lithium-ion batteries are used to power many things from mobile phones, laptops, tablets to electric cars. But they have some drawbacks, including limited energy storage capacity, low durability and long charging time.

Now, researchers at the Institute of Bioengineering and Nanotechnology (IBN) at Singapore’s Agency for Science, Technology and Research (A*STAR) have developed a way of producing more durable and longer lasting lithium-ion batteries. This finding was reported in Advanced Materials. Led by IBN Executive Director Professor Jackie Y. Ying, the researchers invented a generalized method of producing anode materials for lithium-ion batteries. The anodes are made from metal oxide nanosheets, which are ultrathin, two-dimensional materials with excellent electrochemical and mechanical properties.

These nanosheets are 50,000 times thinner than a sheet of paper, allowing faster charging of power compared to current battery technology. The wide surface area of the nanosheets makes better contact with the electrolyte, thus increasing the storage capacity. The material used is also highly durable and does not break easily, which improves the battery shelf life. Existing methods of making metal oxide nanosheets are time-consuming and difficult to scale up.

The IBN researchers came up with a simpler and faster way to synthesize metal oxide nanosheets using graphene oxide. Graphene oxide is a 2D carbon material with chemical reactivity that facilities the growth of metal oxides on its surface. Graphene oxide was used as the template to grow metal oxides into nanosheet structures via a simple mixing process, followed by heat treatment. The researchers were able to synthesize a wide variety of metal oxides as nanosheets, with control over the composition and properties. The new technique produces the nanosheets in one day, compared to one week for previously reported methods.

It does not require the use of a pressure chamber and involves only two steps in the synthesis process, making the nanosheets easy to manufacture on a large scale. Tests showed that the nanosheets produced using this generalized approach have excellent lithium-ion battery anode performance, with some materials lasting three times longer than graphite anodes used in current batteries. “Our nanosheets have shown great promise for use as lithium-ion anodes.

This new method could be the next step toward the development of metal oxide nanosheets for high performance lithium-ion batteries. It can also be used to advance other applications in energy storage, catalysis and sensors,” said Ying.

The article can be found at: AbdelHamid et al. (2017) Generalized Synthesis of Metal Oxide Nanosheets and Their Application as Li-Ion Battery Anodes. ——— Source: A*STAR.

Read more from Asian Scientist Magazine at: https://www.asianscientist.com/2017/07/tech/nanosheet-lithium-batteries/

 

Researchers at A*STAR Discover Nano-Structured Coatings Absorb Pollutants from Drinking Water

Low-cost iron hydroxide coatings with unique fin-like shapes can clean heavily contaminated water with a simple dipping procedure.

As one of the primary components of rust, iron hydroxides normally pose corrosive risks to health. A team at Agency for Science, Technology and Research (A*STAR), Singapore, has found a way to turn these compounds into an environmentally friendly coating that repeatedly absorbs large amounts of pollutants, such as dyes, from drinking water at room temperature.

Conventional activated charcoal treatments have trouble removing heavy metals and bulky organic compounds from water. Instead, iron hydroxides are being increasingly used because they can form stable chemical bonds to these unwanted pollutants. Researchers have recently found that turning iron particles into miniscule nanomaterials boosts their active surface areas and enhances chemical absorption processes.

Separating iron hydroxide nanomaterials from water, however, remains difficult. Commercial filtration systems and experimental magnetic treatments introduce significant complexity and cost into treatment plants. Failure to remove these substances may lead to acute or chronic health issues if they are ingested.

To improve handling of the nanosized iron hydroxides, Sing Yang Chiam from A*STAR’s Institute of Materials Research and Engineering and co-workers decided to attach them to a solid, sponge-like support known as nickel foam. This type of material could safely trap and remove contaminants by immersion into dirty water, and then be regenerated with a simple chemical treatment. But immobilizing the nanoparticles also diminishes their valuable high surface areas — a paradox the team had to solve.

“We were not totally convinced that a coating approach could perform as well as traditional powders and particles,” says Chiam. “So we were really pleased when some nice test results came through.”

The A*STAR team found their answer by synthesizing iron hydroxide coatings with a hierarchy of structural features, from nano- to micrometer scales. To do so, they turned to electrodeposition, a green synthesis method that deposits aqueous metal ions on to nickel foam at mild voltages. After optimizing the uniformity and adhesion of their multiscale coatings, they tested their material in water contaminated by a ‘Congo red’ dye pollutant. Within half an hour, the water became almost colorless, with over 90 per cent of the dye attached to the special coating.

 

The Institute of Materials Research and Engineering team. Credit: © 2017 A*STAR Institute of Materials Research and Engineering

 

Close-up views of the coating’s nanostructure using scanning electron microscopy revealed that elongated, fin-like protrusions were key to recovering active surface area for high-performance pollutant removal. “Even though these coatings have some of the highest capacities ever reported, they are only operating at a fraction of their theoretical capacity,” says Chiam. “We are really excited about tapping their potential.”

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Story Source:

Materials provided by The Agency for Science, Technology and Research (A*STAR). Note: Content may be edited for style and length.

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Journal Reference:

1. Junyi Liu, Lai Mun Wong, Gurudayal Gurudayal, Lydia Helena Wong, Sing Yang Chiam, Sam Fong Yau Li, Yi Ren. Immobilization of dye pollutants on iron hydroxide coated substrates: kinetics, efficiency and the adsorption mechanism. J. Mater. Chem. A, 2016; 4 (34): 13280 DOI: 10.1039/C6TA03088B

Drug Delivery that Hits the (Quantum) Dot

Cultured fibroblasts took up both the (green) quantum dots and the (red) doxorubicin.

Credit: Image courtesy of The Agency for Science, Technology and Research (A*STAR)

Brightly fluorescent nanocrystals, called quantum dots, can be used to test the delivery of drugs packaged into nanocapsules.

Drug treatments are made more efficient by delivering them to specific sites in the body where they are needed. For example, specific targeting of anticancer drugs to tumour sites could reduce required doses, provide more sustained effects and minimise side effects. Such targeting is possible by encapsulating drugs in polymeric nanoparticles, or nanocapsules, that transport them through the body to their targets. However, the properties of various nanocapsules and of drugs can vary, and testing the effectiveness of different systems can be difficult.

Some drugs are inherently fluorescent and can therefore be easily visualised, making their transport and targeting easy to track. However, many drugs cannot be visualised in this way, making it impossible to know whether they are delivered to targets appropriately or efficiently. Researchers at the Agency for Science, Technology and Research (A*STAR) Institute of Materials Research and Engineering aimed to develop an effective strategy for assessing new delivery systems.

The team first demonstrated that the uptake of a drug by target cells depends on the properties of the nanocapsules rather than the properties of the drug. They packaged the anticancer drug doxorubicin — which is inherently fluorescent and exists in water-soluble and water-insoluble forms — into nanocapsules, and found that cultured cancer cells took up both forms of the drug with the same efficiency.

The researchers then showed that when quantum dots — semiconductor nanocrystals that glow when hit by light — were put in nanocapsules in place of doxorubicin, they were delivered to several different types of cancer cells the same way as the drug. The scientists concluded that quantum dots could be used in place of both water-soluble and water-insoluble drugs to test the feasibility and effectiveness of different polymeric nanoparticles as drug carriers.

Having validated their technique, the researchers now hope to qualitatively and quantitatively evaluate possible polymeric nanoparticle systems, thereby enabling improvements in drug delivery.

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Story Source:

The above post is reprinted from materials provided by The Agency for Science, Technology and Research (A*STAR).Note: Materials may be edited for content and length.

 

The Agency for Science, Technology and Research (A*STAR). “Drug delivery that hits the dot.” ScienceDaily. ScienceDaily, 29 May 2016.

Graphene’s stabilizling influence on Supercapacitors

Supercapacitors can be charged and discharged tens of thousands of times, but their relatively low energy density compared to conventional batteries limits their application for energy storage. Now, A*STAR researchers have developed an ‘asymmetric’ supercapacitor based on metal nitrides and graphene that could be a viable energy storage solution (“All Metal Nitrides Solid-State Asymmetric Supercapacitors”).

llustration of the asymmetric supercapacitor, consisting of vertically aligned graphene nanosheets coated with iron nitride and titanium nitride as the anode and cathode, respectively. (©WILEY-VCH Verlag)

A supercapacitor’s viability is largely determined by the materials of which its anodes and cathodes are comprised. These electrodes must have a high surface area per unit weight, high electrical conductivity and capacitance and be physically robust so they do not degrade during operation in liquid or hostile environments.

Unlike traditional supercapacitors, which use the same material for both electrodes, the anode and cathode in an asymmetric supercapacitor are made up of different materials. Scientists initially used metal oxides as asymmetric supercapacitor electrodes, but, as metal oxides do not have particularly high electrical conductivities and become unstable over long operating cycles, it was clear that a better alternative was needed.

Metal nitrides such as titanium nitride, which offer both high conductivity and capacitance, are a promising alternative, but they tend to oxidize in watery environments that limits their lifetime as an electrode. A solution to this is to combine them with more stable materials.

Hui Huang from A*STAR’s Singapore Institute of Manufacturing Technology and his colleagues from Nanyang Technological University and Jinan University, China, have fabricated asymmetric supercapacitors which incorporate metal nitride electrodes with stacked sheets of graphene.

To get the maximum benefit from the graphene surface, the team used a precise method for creating thin-films, a process known as atomic layer deposition, to grow two different materials on vertically aligned graphene nanosheets: titanium nitride for their supercapacitor’s cathode and iron nitride for the anode. The cathode and anode were then heated to 800 and 600 degrees Celsius respectively, and allowed to slowly cool. The two electrodes were then separated in the asymmetric supercapacitor by a solid-state electrolyte, which prevented the oxidization of the metal nitrides.

The researchers tested their supercapacitor devices and showed they could cycle 20,000 times and exhibited both high capacitance and high power density. “These improvements are due to the ultra-high surface area of the vertically aligned graphene substrate and the atomic layer deposition method that enables full use of it,” says Huang. “In future research, we want to enlarge the working-voltage of the device to increase energy density further still,” says Huang.

Source: A*STAR

Read more: Graphene’s stabilizling influence on supercapacitors

A*STAR: Detecting Breast Cancer Using Nanoscale Polymers (Contrasting Agents & Photacoustic Imaging)

Photoacoustic imaging is a ground-breaking technique for spotting tumors inside living cells with the help of light-absorbing compounds known as contrast agents. A*STAR researchers have now discovered a way to improve the targeting efficacy and optical activity of breast-cancer-specific contrast agents using conjugated polymer nanoparticles.

Generating photoacoustic signals requires an ultrafast laser pulse to irradiate a small area of tissue. This sets off a series of molecular vibrations that produce ultrasonic sound waves in the sample. By ‘listening’ to the pressure differences created by the acoustic waves, researchers can reconstruct and visualize the inner structures of complex objects such as the brain and cardiovascular systems.

Diagnosing cancer with photoacoustic imaging requires contrast agents that deeply penetrate tissue and selectively bind to malignant cells. In addition, they need a high optical response to near-infrared laser light, a spectral region that is particularly safe to biological materials. Traditional contrast agents have been based on gold and silver nanostructures, but the complex chemical procedures needed to optically tune these nanocompounds have left researchers looking for alternatives.

Photoacoustic imaging of model breast cancer cells in mice reveals that a polymer-based contrast agent can illuminate tumor sites within one hour. Credit: Dove Medical Press Limited 

Malini Olivo and her colleagues from the A*STAR Singapore Bioimaging Consortium and the A*STAR Institute of Materials Research and Engineering investigated different contrast agents based on conjugated polymers. These organic macromolecules, which contain alternating double and single carbon bonds, have delocalized electrons in their frameworks that can produce useful optical properties such as photoluminescence. The researchers identified a conjugated polymer known as PFTTQ—a compound with multiple aromatic rings, alkyl chains, sulfur and nitrogen atoms—as a promising in vivo photoacoustic agent because of its biocompatible structure and light absorption that peaks in the near-infrared range.

To direct this contrast agent to cancer cells, the team synthesized ‘dot’-like nanostructures with an inner core of PFTTQ surrounded by water-soluble polyethylene glycol chains, terminated by an outer layer of folate molecules—a vitamin that specifically binds to folate receptor proteins commonly expressed by breast cancer tumors. Experiments with MCF-7 model breast cancer cells implanted in mice revealed the merits of this approach: in just one hour after administering the folate–conjugated polymer dots, strong photoacoustic signals emerged from the tumor positions. The folate functionality played a critical role in this bioimaging procedure, quadrupling the photoacoustic signals compared to unmodified PFTTQ dots.

“The folate–PFTTQ nanoparticles have great potential for diagnostic imaging and other biomedical applications,” says Olivo. “We are working to expand the library of biocompatible polymers to use as molecular photoacoustic contrast agents.”

Explore further: Dual-action chemical agents improve a high-resolution and noninvasive way to detect cancer

More information: “Molecular photoacoustic imaging of breast cancer using an actively targeted conjugated polymer.” International Journal of Nanomedicine 10, 387–397 (2015). dx.doi.org/10.2147/IJN.S73558