Nanotechnology simplifies hydrogen production for clean energy

In the first-ever experiment of its kind, researchers have demonstrated that clean energy hydrogen can be produced from water splitting by using very small metal particles that are exposed to sunlight. In the article, “Outstanding activity of sub-nm Au clusters for photocatalytic hydrogen production”, published in the journal Applied Catalysis B: Environmental, Alexander Orlov, PhD, an Assistant Professor of Materials Science & Engineering at Stony Brook University, and his colleagues from Stony Brook and Brookhaven National Laboratory, found that the use of gold particles smaller than one nanometer resulted in greater hydrogen production than other co-catalysts tested.
Experimental and theory predicted optical properties of supported sub-nanometer particles.
Experimental and theory predicted optical properties of supported sub-nanometer particles.
“This is the first ever demonstration of the remarkable potential of very small metal nanoparticles [containing fewer than a dozen atoms] for making fuel from water,” said Professor Orlov.
Using nanotechnology, Professor Orlov’s group found that when the size of metal particles are reduced to dimensions below one nanometer, there is a tremendous increase in the ability of these particles to facilitate hydrogen production from water using solar light. They observed a “greater than 35 times increase” in hydrogen evolution as compared to ordinary materials.
Experimental and theory predicted optical properties of supported sub-nanometer particles. In order to explain these fascinating results, Professor Orlov collaborated with Brookhaven National Lab computational scientist Dr. Yan Li, who found some interesting anomalies in electronic properties of these small particles. Professor Orlov noted that there is still a tremendous amount of work that needs be done to understand this phenomenon.
“It is conceivable that we are only at the beginning of an extraordinary journey to utilize such small particles [of less than a dozen atoms in size] for clean energy production,” he said.
“In order to reduce our dependence on fossil fuels it is vital to explore various sustainable energy options,” Professor Orlov said. “One possible strategy is to develop a hydrogen-based energy economy, which can potentially offer numerous environmental and energy efficiency benefits. Hydrogen can conceivably be a promising energy source in the future as it is a very clean fuel, which produces water as a final combustion product. The current challenge is to find new materials, which can help to produce hydrogen from sustainable sources, such as water.”
Source: Stony Brook University

Overview of nanomaterials for cleaning up the environment

Researchers have presented an extensive analysis of the role of nanomaterialsin environmental remediation and monitoring. Nanomaterials can be used to clean up toxins and bacteria from natural waters, wastewaters and the air (see paper in Energy & Environmental Science: “A review on nanomaterials for environmental remediation”).
Nanomaterials’ unique properties allow them to remove pollutants from the environment. The extremely small size of nanomaterial particles, typically in the range between 1 and 100 nanometres, creates a large surface area in relation to their volume, which makes them highly reactive, compared to non-nano forms of the same materials.
Silver, iron, gold, titanium oxides and iron oxides are some of the commonly used nanoscale metals and metal oxides cited by the researchers that can be used in environmental remediation. Silver nanoparticles, for example, have proved to be effective antimicrobial agents and can treat wastewater containing bacteria, viruses and fungi. Nanoscale titanium dioxide can also kill bacteria and disinfect water when activated by light.
Gold nanoparticles may potentially be another useful material for removing contaminants, such as toxic chlorinated organic compounds, pesticides and inorganic mercury, from water. They can also be used to remediate air. In combination with titanium dioxide, goldnanoparticles have been shown to convert the toxic air pollutant, sulphur dioxide, to sulphur. Titanium dioxide nanomaterials are commonly used in some processes to disinfect water, in addition to breaking down halogenated compounds, and removing dyes and metal toxins from drinking water and wastewater.
The researchers point to studies that show that carbon nanomaterials are particularly suited to removing a broad range of pollutants. Carbon nanotube clusters, for example, are used to purify water by adsorbing bacteria that contaminate the water. Heavy metals, such as cadmium, as well as organic pollutants including benzene and 1,2-dichlorobenzene can also be removed from water by carbon nanotube materials.
The researchers suggest that nanoparticles can be attached to host polymer materials, such as porous resins, cellulose and silica, to reduce potential harm to human health and the environment derived from the release of nanoparticles into the environment. The nanoparticles fixed to the host material are thus bulkier and can be more easily removed and captured from wastewater. Nanoparticles, such as nanoscale zinc oxide, fixed in this way, are used, for example, to break down organochlorine pesticides, halogenated herbicides and azo dyes.
In addition to remediating pollution, nanoparticles can be used as sensors to monitor toxins, heavy metals and organic contaminants in land, air and water environments and have been found to be more sensitive and selective than conventional sensors. Sensor strips composed of nylon 6 nano-fibre nets are one example. These are used to detect formaldehyde, a toxic air pollutant widely used in the manufacture of household materials and building products. The yellow sensor strips turn red upon exposure to formaldehyde.
The researchers acknowledge that ongoing work is needed to further improve the shape, sizes, structures, functionality and manufacture of nanomaterials that show promise in cleaning up contaminants that enter water, land and air environments from industries, transport and other human activities. A better understanding of the behaviour of nanomaterials and their potential harm to the environment is also required.

Graphene-based nanocomposite to adsorb water pollutants

(Nanowerk News) Researchers succeeded in the production of particles with smaller size but higher surface area, and consequently more number of active sites, to adsorb pollutants by synthesizing cerium oxide–titanium dioxide nanoparticles and obtaining cerium oxide–titanium dioxide nanocomposite (see paper in Journal of Hazardous Materials: “Assembly of CeO2–TiO2 nanoparticles prepared in room temperature ionic liquid on graphene nanosheets for photocatalytic degradation of pollutants”).
Among semi-conductive photocatalysts, titanium dioxide (TiO2) is an important candidate to be used in many industries due to its high optical stability and non-toxicity. However, it is impossible to use this component in visible light because its energy gap is placed in the range of ultraviolet.
In this research, researchers from Sharif University of Technology in association with researchers from University of Mohaghegh Ardebili and Nanoscience and Nanotechnology Research Center tried to move the energy gap of TiO2 towards longer wavelengths through the synthesis of carbon-based TiO2 / CeO2 nanocomposite. They also aimed to increase the photocatalytic activity of TiO2.
Results of the research showed that the synthesis of TiO2 in an ionic solution and the addition of cerium oxide to the structure of TiO2 decreased the particle size, increased the surface area, and slowed down the phase exchange from anatase to rutile at higher temperatures. As a result, it caused the creation of nanoparticles with higher thermal stability. High activity of the nanocomposite in the degradation of pollutants is explained by the unique structure of graphene, which increases adsorption on the catalyst surface and decreases the re-composition of ion carriers.

Titanate nanotubes and nanofibers for radioactive waste clean-up in water

Radioactive cesium and iodine ions are products of uranium fission and can be easily dissolved in water during an accident at a nuclear reactor like the one in Fukushima earlier this year. The fear is that these fission products could get into the groundwater and could make their way into the food chain.

Natural inorganic cation exchange materials, such as clays and zeolites, have been extensively studied and used in the removal of radioactive ions from water via ion exchange and are subsequently disposed of in a safe way. However, synthetic inorganic cation exchange materials – such as synthetic micas, g-zirconium phosphate, niobate molecular sieves, and titanate – have been found to be far superior to natural materials in terms of selectivity for the removal of radioactive cations from water. Radioactive cations are preferentially exchanged with sodium ions or protons in the synthetic material. More importantly, a structural collapse of the exchange materials occurs after the ion exchange proceeds to a certain extent, thereby forming a stable solid with the radioactive cations being permanently trapped inside. Hence, the immobilized radioactive cations can be disposed safely.

“Based on our earlier work, we have now demonstrated a potentially cost-effective method to remediate cesium and iodine ions from contaminated water by using the unique chemistry of titanate nanotubes and nanofibers to chemisorb these ions,” HuaiYong Zhu, a professor of chemistry at the Queensland University of Technology, tells Nanowerk.

The team, which reported their findings in the September 20, 2011 online edition of Angewandte Chemie International Edition (“Capture of Radioactive Cesium and Iodide Ions from Water by Using Titanate Nanofibers and Nanotubes”), also found that the new sorbents can not only take up these ions but efficiently trap them for safe disposal because of their unique structural and chemical features.

“The sorbents take up cesium ions via an exchange with sodium ions in the nanostructures; the rapid uptake of cesium ions eventually triggers a phase transition of the titanate and traps the cesium ions inside permanently for safe disposal,” explains Zhu. “This is because the fibers and tubes consist of negatively charged thin layers – as thin as two oxygen atoms – and phase transition of the layers with low rigidity can be readily induced.”

In order to capture and immobilize iodine ions from water, the researchers anchored silver oxide nanocrystals on the external surfaces of titanate nanotubes and nanofibers by chemical bonds owing to their crystallographic similarity. These composites can efficiently capture iodine ions forming silver iodine precipitate on the titanates.

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Basics of TiO2 sunscreen

Ultraviolet (UV) Radiation

Ultraviolet radiation can be divided into three regions: UVA (320–400 nm), UVB(290–320 nm) and UVC (200–290 nm). Although UVC is the most damaging UV radiation, it is filtered out by the ozone layer in the stratosphere before reaching the earth’s surface. The radiation in the UVB region (partially filtered by ozone) can penetrate both the stratum corneum and the epidermis of human skin. It has
sufficient energy to cause damage, such as sunburn, to human skin. This is particularly true for fair-skinned individuals. The UVA radiation, which is unfiltered by ozone, has deeper penetration of human skin to the dermis; it, thereby, stimulates the formation of melanin and produces a tan, which acts as the first line of defense for the protection from sunburn. UVA radiation, therefore, is also called the “tanning region.” Although having considerably lower energy than UVB, UVA photons can cause delayed damages to the skin.

The fundamental function of a sunscreen is to serve as a filter that can prevent the penetration of ultraviolet radiation. The substances most commonly used in commercial sunscreen preparations include p-aminobenzoic acids (PABA), cinnamates, oxybenzone, salicylates, and metal oxides, such as TiO2 and ZnO. In addition to their ability to scatter sunlight, inorganic particles, such as TiO2, do
absorb strongly in the UVA and UVB regions.

Rutile and Anatase TiO2

In addition to its amorphous state, two of the most common crystalline forms of TiO2 are rutile and anatase. The two crystalline forms share many similarities, such as their physical appearance, refractive index, density, low toxicity, and high stability in the presence of strong acids and bases. As a physical blocker for sunlight, bot
crystalline forms would serve the purpose well. Their photochemical properties, however, are very different. TiO2 is a semiconductor. When a semiconductor particle absorbs light, it promotes an electron from its valence band to its conduction band, leading to a charge separation. In rutile TiO2, the charge separation is quickly diminished through a charge recombination within the particle and the energy is released as heat. This translates to a low photoactivity and an effective conversion of UV light into heat. As a result, any photoinduced reactions that can pose damage to the skin are avoided. The low photoactivity and its desirable UV absorption spectrum, which cover the entire erythemal curve make rutile TiO2 an ideal choice as UV blocker for sunscreen preparations.

For amorphous and anatase TiO2, the lifetime of the charge separation is much longer than that on a rutile particle. The electron and electron hole, therefore, have greater opportunity to undergo redox reactions on the surface; therefore, anatase has been extensively used for applications involving such electron transfer processes as
photocatalysis for environmental waste treatment and photovoltaic design for solar energy storage. Extensive reviews on these interesting topics are available. Due to their photoactivity, amorphous and anatase TiO2 are not suitable for sunscreen applications.

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Nanoparticles Used in Common Household Items Cause DNA Damage- Study.

Titanium dioxide (TiO2) nanoparticles, found in everything from cosmetics to sunscreen to paint to vitamins, caused systemic genetic damage in mice, according to a comprehensive study conducted by researchers at UCLA’s Jonsson Comprehensive Cancer Center.

The TiO2 nanoparticles induced single- and double-strand DNA breaks and also caused chromosomal damage as well as inflammation, all of which increase the risk for cancer. The UCLA study is the first to show that the nanoparticles had such an effect, said Robert Schiestl, a professor of pathology, radiation oncology and environmental health sciences, a Jonsson Cancer Center scientist and the study’s senior author.

Once in the system, the TiO2 nanoparticles accumulate in different organs because the body has no way to eliminate them. And because they are so small, they can go everywhere in the body, even through cells, and may interfere with sub-cellular mechanisms.

The study appeared the week of November 16 2009 in the journal Cancer Research.

In the past, these TiO2 nanoparticles have been considered non-toxic in that they do not incite a chemical reaction. Instead, it is surface interactions that the nanoparticles have within their environment- in this case inside a mouse — that is causing the genetic damage, Schiestl said. They wander throughout the body causing oxidative stress, which can lead to cell death.

It is a novel mechanism of toxicity, a physicochemical reaction, these particles cause in comparison to regular chemical toxins, which are the usual subjects of toxicological research, Schiestl said.

“The novel principle is that titanium by itself is chemically inert. However, when the particles become progressively smaller, their surface, in turn, becomes progressively bigger and in the interaction of this surface with the environment oxidative stress is induced,” he said. “This is the first comprehensive study of titanium dioxide nanoparticle-induced genotoxicity, possibly caused by a secondary mechanism associated with inflammation and/or oxidative stress. Given the growing use of these nanoparticles, these findings raise concern about potential health hazards associated with exposure.”

The manufacture of TiO2 nanoparticles is a huge industry, Schiestl said, with production at about two million tons per year. In addition to paint, cosmetics, sunscreen and vitamins, the nanoparticles can be found in toothpaste, food colorants, nutritional supplements and hundreds of other personal care products.

“It could be that a certain portion of spontaneous cancers are due to this exposure,” Schiestl said. “And some people could be more sensitive to nanoparticles exposure than others. “I believe the toxicity of these nanoparticles has not been studied enough.”

Schiestl said the nanoparticles cannot go through skin, so he recommends using a lotion sunscreen. Spray-on sunscreens could potentially be inhaled and the nanoparticles can become lodged in the lungs.

The mice were exposed to the TiO2 nanoparticles in their drinking water and began showing genetic damage on the fifth day. The human equivalent is about 1.6 years of exposure to the nanoparticles in a manufacturing environment. However, Schiestl said, it’s not clear if regular, everyday exposure in humans increases exponentially as continued contact with the nanoparticles occurs over time.

“These data suggest that we should be concerned about a potential risk of cancer or genetic disorders especially for people occupationally exposed to high concentrations of titanium dioxide nanoparticles, and that it might be prudent to limit their ingestion through non-essential drug additives, food colors, etc.,” the study states.

Next, Schiestl and his team will study exposure to the nanoparticles in mice that are deficient in DNA repair, to perhaps help find a way to predict which people might be particularly sensitive to them.

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Silver nanopacticles to identify prostate cancer cells

A team of researchers at UC Santa Barbara has developed a breakthrough technology that can be used to discriminate cancerous prostate cells in bodily fluids from those that are healthy. The findings are published this week in the Proceedings of the National Academy of Sciences (“Quantitative ratiometric discrimination between noncancerous and cancerous prostate cells based on neuropilin-1 overexpression”).

Cancerous and non-cancerous cells are incubated with silver nanoparticle biotags, and then analyzed by shining the red laser on them. The biotags are shown on the cells' surface. Those glowing red in the middle are the cancer biomarkers, and those glowing green are standard biomarkers that bind to many cell types. A high ratio of red to green is found on the cancer cells.

While the new technology is years away from use in a clinical setting, the researchers are nonetheless confident that it will be useful in developing a microdevice that will help in understanding when prostate cancer will metastasize, or spread to other parts of the body.

“There have been studies to find the relationship between the number of cancer cells in the blood, and the outcome of the disease,” said first author Alessia Pallaoro, postdoctoral fellow in UCSB’s Department of Chemistry and Biochemistry. “The higher the number of cancer cells there are in the patient’s blood, the worse the prognosis.

“The cancer cells that are found in the blood are thought to be the initiators of metastasis,” Pallaoro added. “It would be really important to be able to find them and recognize them within blood or other bodily fluids. This could be helpful for diagnosis and follow-ups during treatment.”

The team developed a novel technique to discriminate between cancerous and non-cancerous cells using a type of laser spectroscopy called surface enhanced Raman spectroscopy (SERS) and silver nanoparticles, which are biotags.

The team is working to translate the technology into a diagnostic microdevice for studying cancer cells in the blood. Cells would be mixed with nanoparticles and passed through a laser, then discriminated by the ratio of two signals.

The two types of biotags used in this research have a particular affinity that is dictated by the peptide they carry on their surface. One type attaches to a cell receptor called neuropilin-1, a recently described biomarker found on the surface membrane of certain cancer cells. The other biotag binds many cell types (both cancerous and non-cancerous) and serves as a standard measure as the cells are analyzed.
In this study, the team mixed the two biotags and added them to the healthy and tumor cell cultures. The average SERS signal over a given cell image yielded a ratio of the two signals consistent with the cells’ known identity.

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