Tag Archives: water

No more butts: biodegradable filters a step to boot litter problem.

 

Robertson, R, W Thomas, J Suthar and D Brown. 2012.  Accelerated degradation of cellulose acetate cigarette filters using controlled-release acid catalysis. Green Chemistry http://ds.doil.org/10.1039/C2GC16635F.

 


Synopsis by Marty Mulvihill and Wendy Hessler, Aug 14, 2012

Context

Every year over 6 trillion cigarettes are manufactured globally. Approximately 99 percent have a filter tip. After the cigarette is smoked, the used filter is called a butt and is thrown out. When littered, cigarette butts often take years to break down.

Most filters are made using cellulose acetate fibers. More than 2 billion pounds of cellulose acetate is produced every year to meet the world demand for filters. To make it, acetic anhydride is added to cellulose fibers made from wood or cotton. The reaction creates a type of plastic that provides a stronger, more rigid filter.

By itself, cellulose fibers degrade naturally in the environment. Cellulose acetate plastic degrades very slowly.

The slow degradation, along with indoor smoking bans, mean increasingly large numbers of cigarette butts are found in public places, including parking lots, parks and beaches every year. Cigarette waste is the number one reported item collected during beach clean-ups, according to the Ocean Conservancy. In some coastal towns as many as 1 in 10 cigarette butts end up polluting the waterways.

The discarded butts are more than just an eyesore. The filters contain chemical residue from the tobacco. The residue can be toxic to marine animals. Cigarette butts are commonly found in the stomachs of dead shore birds.

One way to decrease the litter would be to create cigarette filters that degrade quickly. Previous attempts used plant-based products like cornstarch, hemp, flax or cotton. One brand of biodegradable filter, Greenbutts, incorporates plant seeds that would germinate after disposal. To date, cigarette manufacturers have not widely adopted alternative filters.

The demand for degradable filters may increase as states – including New York – consider levying taxes on non-biodegradable cigarette filters. In response, there is renewed interest to make cigarette filters degrade faster.

What did they do?

A group of chemists wondered if a cellulose acetate plastic filter could be converted back into natural, degradable cellulose after it was used. If so, the cigarette butts should degrade much more quickly.

They guessed that small amounts of acid added to the filter should speed the degradation process.

First, they measured the degradation rate of cellulose acetate using a wide range of acids with different strengths. Combinations of acids were also tested to find which worked best to make cigarette filters that retained their structure and function while degrading faster.

Next, they created an effective additive based on which acids worked best. The additive needed to be acidic, non-toxic and allow the cigarette to burn normally. To find one, they looked to acids common in food, including citric acid, phytic acid and vitamin C (ascorbic acid), as well as stronger mineral acids not commonly considered safe food additives.

The new filter design was tested. A smoking machine “smoked” the cigarettes, and the butts were left outside and monitored.

What did they find?

In the first tests, the butts exposed to water and a small amount of acid broke down faster than those not exposed to acid. Strong acids worked best to efficiently speed the degradation of the cellulose acetate fibers. In particular they found that sulfuric acid was the most effective catalyst.

Sulfuric acid, however, is not safe to put into cigarette filters. The researchers devised a way to generate the stronger acid only after the cigarette was smoked. The smoker would not be exposed to any additional harmful compounds, and the filter would degrade more quickly.

To make the acid additive, the researchers combined safer chemicals – cellulose sulfate, citric acid and phytic acid – into a tablet. When the tablet got wet, these ingredients mixed and released small amounts of sulfuric acid that degraded the filter material. The tablets were coated with ethyl cellulose and cellulose acetate to shield the acid precursors from premature exposure to water.

After 14 days outside, the butts containing the acid tablet were more acidic and tested positive for the presence of sulfuric acid, while the control butts remained unchanged. At the end of the 90-day trial, the new filters were considerably more degraded than the controls. Unfortunately they had not degraded as much as expected based on the laboratory experiments.

What does it mean?

Small amounts of strong acid increase the degradation rate of the cellulose acetate fibers found in cigarette butts. Although the idea worked in principle, the outside trials did not live up to the promise of the laboratory results.

The research is important because it is a step towards making a truly degradable and functional cigarette filter. This research shows how green chemistry can improve existing technology. The researchers designed the new filters for degradation while making safer chemical choices. This approach will ultimately minimize waste and hopefully prevent some of the toxic exposures to birds and other wildlife.

Under laboratory conditions, the acid converted the filter plastic into a biodegradable material within 30 to 60 days, depending on temperature. The food grade acids and materials generated the strong acid only after the cigarette had been smoked. These preliminary results indicate that acidic additive in the filter could reduce the time it takes for cigarette butts to degrade in the environment.

Several problems will need to be resolved before large manufacturers could adopt the use of acid tablets in cigarette filters. The filter’s effectiveness – improved degradation and materials safety of materials – will need to be quantified in clinical and environmental trials. This will take more research to design and incorporate the acid precursors into the filter body.

Cost and performance are also issues. The acid materials must be incorporated into cigarettes at a low cost without harming the performance of the product.

Researchers will llkely pursue this technology as well as other approaches to a biodegradable cigarette filter in an effort to reduce cigarette butt litter.

Resources

Clean Virginia Waterways and Longwood University. 2012. Cigarette butt litter. http://www.longwood.edu/cleanva/cigarettelitterhome.html.

Novotny, T, K Lum, E Smith, V Wang, and R Barnes. 2009. Cigarettes butts and the case for an environmental policy on hazardous cigarette waste. International Journal of Environmental Research and Public Health http://dx.doi.org/10.3390/ijerph6051691.

Ocean Conservancy. A rising tide of ocean debris, International Coastal Clean-up 2009 Report. http://www.oceanconservancy.org/pdf/A_Rising_Tide_full_lowres.pdf.

Register, K. 2000. Cigarette butts as litter: Toxic as well as ugly. Underwater Naturalist: Bulletin of the American Littoral Society http://www.longwood.edu/CLEANVA/ciglitterarticle.htm.

Pie Chart

Analysis of Green Chemistry publications over the past four years.

This figure is taken from Green chemistry: state of the art through an analysis of the literature by V. Dichiarante, D. Ravelli and A. Albini. Green Chemistry Letter and Reviews Vol. 3, No. 2, June 2010, 105-113.

 

As the label indicates, the pie chart shows a distribution of green chemistry topics as analyzed by articles produced in the year 2008. The majority of the pie chart (about 50%) is attributed to catalysis – or starting a reaction, under more favorable conditions that require less resources, whether those resources are heat, energy, reagents etc. Specifically, metal catalysts were the most cited catalysts used in many different reactions, specifically in those involving enzymes. Acids are also seen in this category, and according to the article, are used mainly in condensation reactions. The next largest section of the pie (about 40%) is attributed to media, or where/in what the reaction takes place. Many reactions require some liquid for a reaction to take place. Many of these liquids, especially in organic chemistry, are volatile or toxic compounds. As a result, most of the research done with green chemistry and the media of reactions use either no solvent, which allows for most reduction of waste. Water has also gained a prominent role in green chemistry literature as it is our universal solvent and usually can be recycled in a reaction. Ionic liquids are the third major media hit; they are liquids that have charged compounds in the solution to help guide a reaction. Ionic liquids are usually not volatile and are stored more easily compared to their organic counterparts. Finally, the last 10% of the pie chart goes to ‘new methods,’ or novel ways to do old reactions. Using microwaves to start and maintain a reaction is the most prominent method, followed by some research advances in photochemistry and ultrasounds, using light or sound respectively in reactions.

A more sensitive material detects heavy metals at 100 times lower levels.

Synopsis by Wim Thielemans, Aug 04, 2011

Zhang, Y, Y Liu, X Ji, CE Banks and W Zhang. 2011. Sea cucumber-like hydroxyapatite: Cation exchange membrane-assisted synthesis and its application in ultra-sensitive heavy metal detection. Chemical Communications http://dx.doi.org/10.1039/c1cc10489f.

A nano-sized membrane that looks like a hard, hairy sponge can detect minute amounts of lead and cadmium in water, report researchers who devised a new method in the laboratory to grow the natural material – called hydroxyapatite – that makes up the membrane.

Hydroxyapatite has unique properties that are already being exploited in a variety of sensors in an effort to move away from using gold, mercury and other toxic substances. The new method – which is still being researched – takes its use even further by developing crystal-like protrusions and structures that increase the material’s surface area. Its higher interaction with the surrounding water dramatically improves the material’s sensitivity; it can measure levels up to 100 times lower than other available devices.

Heavy metals such as lead and cadmium are a major health and environmental problem. They contaminate soil and water and accumulate in plants and animals. People are exposed to heavy metals through many sources, including food, water, air and dust. In humans, exposure to heavy metal is linked to many disorders such as organ damage, developmental problems and psychological changes.

Governments regulate heavy metal emissions, but the metals still contaminate many streams, lakes and other water bodies. As regulation tighten, it is thus important to monitor for these pollutants at more sensitive levels in waterways, tap water and drinking water.

The researchers grew the hydroxyapatite – which is a major component of human teeth and bones – on a membrame for four to seven days to create a crystal-like material with a high surface area. A higher surface area allows for increased surface-water interaction.

The hydroxyapatite can efficiently exchange calcium from its own structure with lead and cadmium in the water. The metal content in the water is then determined by applying a varying voltage over the hydroxyapatite and measuring the electrical current that flows through it.

The detection limit for lead was determined to be 9 X 10-10 grams per liter (g/L) – that is, a decimal point followed by nine zeros and a nine. Cadmium was detected down to 3 X 10-9 g/L. These detection limits are on the order of parts per trillion. They could detect a single drop in the volume of 20 Oympic size swimming pools. This makes the innovative material 10 to 100 times more sensitive than other hydroxyapatite-based sensors.

The high surface area hydroxyapatite was formed by controlling its growth using a Nafion membrane. Nafion is a polymer that allows only positive ions to pass through it. Hydroxyapatite was formed by combining two reactants – calcium and phosphate – added on opposite sides of the membrane in water. Only calcium – with its positive charge – can pass through the membrane The hydroxyapatite forms on the membrane’s surface as calcium reaches the other side and combines with the water and phosphate.

The new method to prepare high surface area hydroxyapatite is very promising. However, applying it to detect heavy metals will take further work to optimise. For example, the authors only tested their device to detect a single metal. They did not yet report the effectiveness when several metals are present or when other non-metallic pollutants are present in the water.

The researchers will also need to optimise how to form the high surface area hydroxyapatite. For wide use, faster preparation methods will need to be developed.

See more science at Environmental Health News.

Pollution and predators: a double whammy for tadpoles.

Pollution and predators: a double whammy for tadpoles.

Synopsis by Roxanne Karimi, Aug 16, 2011

Reeves, MK, M Perdue, GD Blakemore, DJ Rinella and M Holyoak. 2011. Twice as easy to catch? A toxicant and a predator cue cause additive reductions in larval amphibian activityEcosphere http://dx.doi.org/10.1890/ES11-00046.1.

Low levels of copper can make tadpoles sluggish, putting them at a disadvantage with predators.

Copper levels in water that are considered safe by regulatory agencies can slow wood frog tadpoles enough to make them easier prey for predators, report researchers in the journal Ecosphere. The slowing combined with the normal quiet triggered when a natural predator approaches can so diminish a tadpole’s movements that it is even more vulnerable to predators that can injure or eat it.

The results of the study highlight how low levels of contaminants can indirectly influence animal fitness in unexpected ways. It also shows the importance of examining toxicity effects in a broader ecological context.

There is considerable concern over the effects of multiple stressors on tadpoles, because worldwide, certain amphibian populations are declining. While experts debate the causes, they generally agree that more than one factor may be at play in their demise, including contaminants, disease and atmospheric changes.

More broadly, frogs, salamanders and other amphibians are important because they act as sentinal creatures that indicate the health of the environment. Their unique absorbent skin and dependence on water at some point in their life cycle means they are highly sensitive to environmental changes.

Copper is a trace metal that enters waterways from road runoff and is also a waste product of hard rock mining. While copper is considered essential for growth and survival, high doses lead to toxic effects in many aquatic organisms.

Previous studies have found that copper can interfere with smell and alter fish behavior by impairing homing ability. Other studies show that tadpoles change their behavior in response to environmental cues, such as chemicals released when a predator eats another tadpole.

This new study looks at what happens to tadpoles when exposure to what is considered safe, low levels of copper in the water is combined with a routine, ecological stress – in this case, the presence of a dragonfly predator.

In an earlier study, the researchers found that copper and predators were associated with limb abnormalities, that smaller frogs were found in sites with high copper levels and that the smaller animals were more likely to have limb abnormalities than larger frogs.

To understand how the combined presence of copper and predators might detrimentally alter tadpole behavior and lead to limb abnormalities, the authors collected tadpoles undergoing hind limb development from multiple sites within the Kenai National Wildlife Refuge. They exposed the tadpoles to a low, nontoxic level of copper (5 micrograms per liter), a predator chemical cue or both. They recorded the number of times the tadpoles moved in two hours.

The tadpoles exposed to copper at this low concentration were half as likely to move compared to tadpoles not exposed to copper at all. Predator cues also reduced tadpole activity, but to a lesser extent than copper. Older tadpoles responded less to predators and were more likely to remain active than younger tadpoles. When combined, copper and predators reduced tadpole activity in an additive way. The change in behavior was particularly strong in less developed tadpoles.

While reduced activity can help avoid predation, the additional slowing from the contaminants can lead to less feeding, which can delay growth and development, increase vulnerablity to predators and decrease survival and reproduction. These results help explain the researchers’ previous study in which they found smaller frogs with more abnormal limbs in copper-laden water. The scientists think that the slower-moving tadpoles are more vulnerable to dragonfly predators, which tend to eat the tadpoles developing hind limbs. In this case, the copper indirectly leads to hind limb abnormalities.

The findings show how low levels of copper, thought to be nontoxic to amphibians, can lead to a change in behavior that is likely to be harmful. However, further studies will need to directly measure the effect of copper on feeding or growth and address whether reduced activity leads to changes in survival or reproduction.

See more science at Environmental Health News.

 

Novel, sugar-based surfactants more stable and sustainable.

Synopsis by Evan Beach and Wendy Hessler. Jan 12, 201

Foley, PM, A Phimphachanh, ES Beach, JB Zimmerman, and PT Anastas.  2011.  Linear and cyclic C-glycosides as surfactants. Green Chemistry http://dx.doi.org/10.1039/C0GC00407C.


2011-0106ecoproducts
xrrr/flickr

Context

Surfactants – the active ingredients in many household products, including cleaners and personal care products – are produced on the scale of millions of tons per year. In nearly every application, after a few minutes of use, they are rinsed with water either down the drain or directly into the environment.

Unsurprisingly, there have been harmful effects from such large-scale releases. When surfactants are slow to break down in the environment, problems range from unsightly foaming to toxic effects on aquatic organisms. Some of these chemicals – for example, the widely used nonylphenol ethoxylates – have been implicated in endocrine disruption. The term is used to describe substances that can alter hormone activity in the body.

There has been a push in recent years toward sugar-based surfactants because of improved biodegradability and lower toxicity. They are also derived from natural and renewable sources, adding another “green chemistry” benefit.

Sugar-based surfactants have been commercially available for more than a decade. Formulations of the alkyl polyglycosides (APGs) are used in a variety of consumer products for laundry, hair and skin care. On an ingredient label they are usually identified as a variety of “glucosides,” for example decyl glucoside or lauryl glucoside. The use of APGs is growing at a faster rate than petroleum-based surfactants.

However, chemists are trying to improve APGs. Many of the sugar-derived chemicals can fall apart when exposed to acids in water because the link between the water-loving and oil-loving ends of the APG molecules is vulnerable. Also, depending on the variety of the APG produced, the manufacturing process relies on high temperature and pressure and energy-consuming purification steps.

What did they do?

Researchers investigated a new process to make a stronger chemical bond in one particularly weak spot of sugar-based surfactant molecules. The researchers transformed a precursor chemical by treating it with a chemical mix that included alkyl aldehydes.

Several sugar derivatives with straight or cyclic tails were produced, depending on the conditions that were used to convert the intermediary chemical. The new chemicals were tested for surface tension and foaming and the results were compared to current APG surfactant performance.

The researchers showed that the new surfactants could be prepared in a two-step reaction under mild conditions, using only a minimum of solvent. It was not necessary to purify the products by column chromatography, a procedure that would consume large volumes of potentially hazardous solvents. This improves the prospects for producing the chemicals on a large scale.

The scientists show that the technical performance of the new surfactants is as good as existing APG technology. This was determined by measuring surface activity – how efficient the chemicals are at reducing the surface tension of water. It is important for surface tension to drop quickly with just a small amount of added chemical, for surfactant applications. The best chemical tested in the study worked at just 40 milligrams (the weight of a few grains of rice) per liter.

The researchers also explored the foaming properties of the new chemicals. Foaming is desirable for some personal care products like shampoos, but would be a disadvantage in laundry applications and some industrial cleaners. The Yale chemicals were low foamers compared to a conventional surfactant, sodium dodecyl sulfate (SDS). But when mixed with SDS, the resulting foam lasted longer. Thus they could be useful in either low- or high-foam formulations.

The biodegradability of the new chemicals was not measured, but U.S. Environmental Protection Agency software suggests that the changes made to improve acid stability will not affect how microbes disassemble the chemicals. The glucose end of the molecule contains many carbon-oxygen bonds that are common places for microbial attack. If the surfactants are made from long, straight-chain aldehydes, that should also provide bacteria with a familiar food source.

What does it mean?

The new sugar-based surfactants may offer more stable and sustainable varieties to use in consumer products. The novel chemicals are more stable under harsh conditions and work just as well in laboratory tests as the sugar-based surfactants currently used. In addition, their chemical production is a significant improvement over current methods in that it uses less resources and produces a wider array of chemicals with surfactant properties.

2010-0106surfactantsmolecules
Evan Beach

This new family of sugar-based surfactants complements APGs that are already on the market. A wider variety of molecular structures means that manufacturers of green consumer products are more likely to come up with formulations that meet all the goals of function, performance, economy and low environmental footprint.

Replacing the weak spot in APGs with a sturdier alternative allows the sugar-based chemicals to be used in more applications. The two parts of the new molecule are linked with a bond between two carbon atoms instead of a bond between an oxygen and a carbon atom. The stronger carbon-carbon bond is unaffected by strong acid. That robustness could help in industrial applications and heavy-duty household formulations, for example acidic tile cleaners.

The new surfactants are made from glucose, which is widely found in nature. It is one of the components of table sugar and is the repeating chain unit in cellulose, which gives plants their supporting structure. Glucose acts as the water-loving part of the surfactant. The oil-loving part of the surfactant is made from aldehydes. Aldehydes are a diverse set of chemicals; some occur in nature and others are produced from petrochemicals. In this study, the aldehydes could be obtained by treating plant oils.

The researchers say their next step will be to explore algae as a possible source for all of the surfactants’ starting materials. The carbohydrate portion of algal biomass could provide the sugar, and algal oils could give the right kinds of aldehydes. Algae oils are particularly rich in carbon-carbon double bonds that can react with ozone to produce aldehydes. If that approach is successful, surfactant production could supplement algae-to-fuel technology.

Bacteria clean up metal waste, then serve as catalysts.

Synopsis by Evan Beach, Dec 09, 2010

Gauthier, D, LS Sobjerg, KM Jensen, AT Lindhart, M Bunge, K Finster, RL Meyer and T Skrydstrup. 2010. Environmentally benign recovery and reactivation of palladium from industrial waste by using gram-negative bacteria. ChemSusChem 3:1036-1039.

A group of Danish scientists has developed a method to recycle valuable metals that would ordinarily have to be mined and refined before ending up in chemists’ hands. Their discovery means that the metals could be sourced instead from electronic waste or polluted water and soil.

The researchers used two species of bacteria and added hydrogen gas to recover the waste metals – palladium, platinum and rhodium – in a cheaper and more efficient way than conventional processes. Interest in using microbes to remove metals from waste is growing among scientists who are searching for the best methods.

This is the first time that researchers report that they can remove these platinum group metals from industrially contaminated water without altering the bacteria or diluting the liquid. Remarkably, the bacteria could remove up to 100 percent of the palladium from the polluted water.

Mining, industrial activities and manufacturing release these specific metals into the environment, where they can contaminate soil and water. All three of the metals examined are widely used in automotive, chemical, glass, electrical, medical and jewelry applications.

The microbes used in the study are naturally tolerant of metals. One species can be found in typical soils, and the other is more commonly found in industrial areas, near mines and metal factories.

The bacteria bind and absorb metal ions dissolved in water. Hydrogen gas can also remove metal from the water. Metal uptake and recovery are enhanced when the two are combined.

The contaminated water used in the study contained a mixture of eight different metals and was deep orange colored. Hydrogen gas and bacteria with and without added palladium were added to test tube samples.

The liquid cleared after 24 hours, indicating the metals had been removed. The bacteria were most selective for palladium – the recovery rates were 96-100 percent, compared to 70-74 percent for platinum and 55-57 percent for rhodium.

After recovering the bacteria, researchers asked what could be done with the metal-rich material. They went a step further and found a productive use. They showed that the microbes could drive a common chemical reaction that uses palladium to connect two hydrocarbon building blocks, a method often used in synthesizing pharmaceuticals. The conversion rates were 50-100 percent. The effectiveness was higher when the bacteria were pretreated with a small amount of pure palladium before exposure to the wastewater.

Further experiments will be aimed at understanding how the metals compete for the absorption sites on the bacterial surface, and thus, produce treatment methods that select for specific metals. In turn, the selective, one-metal binding could result in more active catalysts to be used in conventional processes.

Less is more for greener insecticide.

Romanelli, GP, EG Virla, PR Duchowicz, AL Gaddi, DM Ruiz, DO Bennardi, E del Valle Ortiz and JC Autino.  2010.  Sustainable synthesis of flavonoid derivatives, QSAR study and insecticidal activity against the fall armyworm, Spodoptera frugiperda (Lep.: Noctuidae). Journal of Agricultural and Food Chemistry 58:6290-6295.

Synopsis by Evan Beach
Aug 23, 2010

No solvent and no corrosive acids. That’s part of the recipe for a new, less polluting method of making chemicals that kill an important crop pest. Taking their inspiration from natural plant chemicals called flavones, the authors of the study developed a way to make, compare, and test the insecticides, and used the information to create a predictive computer model.

The cleaner synthesis was used to control fall armyworms, one of the main threats to corn crops in many parts of the world. The new method avoids toxic solvents and strong mineral acids that were needed in earlier processes.

Instead, it relies on a metal catalyst that works at low levels: one catalyst molecule per 200 molecules of starting material. The catalyst could be easily recovered at the end of the chemical reaction and recycled several times, reducing waste.

Flavones protect plants against a variety of bacteria and insects. Some flavones also show beneficial effects in humans as antioxidants, anti-inflammatory agents, antimicrobials and anticancer agents.

The researchers made synthetic flavones using the greener technique and found that the chemicals were effective against the armyworm larvae. Based on these results, the researchers then created a computer model to predict which natural flavones might be worth testing as pesticides. They analyzed the structures of more than a dozen plant flavones and found two with characteristics in common with the chemicals that worked against armyworms.

One of the natural flavones, luteolin, occurs naturally in the human diet, in carrots, peppers, celery, and some spices. The other, apigenin, is common in citrus fruit, tea, and a variety of vegetables. Both chemicals are often cited for their therapeutic effects in humans.

The next step is for scientists to test whether these two natural flavones do indeed kill insects, as predicted by the model. While the natural flavones would probably have minimal environmental impacts if applied as pesticides, the synthetic flavones reported in the study were not tested for environmental persistence or toxicity to organisms besides armyworms. Those experiments would confirm whether the greener preparation leads to greener pesticides.

Fuel cell gets energy from water.

Aug 09, 2010

Dreizler, AM, and E Roduner.  2010.  A fuel cell that runs on water and air. Energy and Environmental Science 3:761-764.


Synopsis by Evan Beach and Wendy Hessler
2010-0723hyrogenfuelcell
Flickr/eston

Chemists in Germany have figured out a way to extract energy from just water and oxygen. The discovery uses existing fuel cell technology and minimal additional chemicals, providing a safer way to generate electricity for low-power applications.

Context

Concern about the impacts of petroleum as the world’s major energy source has driven research into alternative energy sources, such as solar radiation, wind and biomass.

One of the tools for converting these sustainable energy sources into usable forms of electricity is the fuel cell. Fuel cells are devices that use chemical reactions to change energy from one form to another.

Because of their efficiency and their ability to harvest energy from diverse sources, fuel cells show promise as one of the keys to sustainable power generation.  Fuel cell technology has already matured to the point where it can be used in power plants to supply electricity to buildings, and portable fuel cells have been demonstrated in prototype cars as well as military vehicles.  Smaller fuel cells can be used in place of batteries for electronic devices like radios or laptop computers.

A fuel cell has an anode and a cathode, just like the positive and negative terminals of a battery. Chemical reactions occur at the two electrodes.

Generally, conventional fuel cells get power from a carrier molecule – usually hydrogen – that is added to the device. The fuel cell harvests electrons from the carrier molecule, producing electrical current.  When hydrogen is used in fuel cells, it combines with oxygen in air to make water as a byproduct, also releasing heat.  Fuel cells generally do not require wind or sun and operate quietly.

Tens of thousands of scientific studies have focused on fuel cell technology in attempts to find the chemical fuels and components that produce the greatest energy efficiency. While many varieties of fuel cells have been demonstrated, one thing they have in common is that they depend on energy that was previously generated – in effect they are just tools for converting one form of energy into another. A fuel cell that consumes hydrogen generated from natural gas, for example, still depletes fossil resources. In other types of fuel cells, the carrier molecules are toxic, or the byproducts produced are harmful.  Ideally a fuel cell would derive its energy from a renewable source and avoid unsafe chemicals in the process.

To move toward this goal, there is another way to drive the reactions inside a fuel cell. This not-so-common approach is to use entropy. Entropy is a measure of disorder, and nature favors increasing disorder: it is one of the fundamental laws of thermodynamics.

What did they do?

The authors purchased a commercially available fuel cell, the kind that would ordinarily be used to harvest power from methanol, an energy carrier chemical commonly used in fuel cells. They poured water into the anode side of the cell. The cathode side was exposed to a temperature-controlled stream of air.

In the study, the pH of the water was changed by adding sulfuric acid or sodium hydroxide, and the electrical current and voltage were measured with a multimeter.  The pH was adjusted because it affects the rate at which electrons can be harvested by the cell.

What did they find?

The fuel cell was driven by evaporation of water from one end of the cell, “pulling” the chemical reactions forward. This form of entropy powered the cell.

Considering the chemical reactions involved, at one end of the cell, water breaks down to make oxygen, hydrogen ions, and electrons. At the other end of the cell, the oxygen, hydrogen ions and electrons recombine to make water. In other words, the chemical input (water) is the same as the output. The net enthalpy, or heat balance, is zero, because any heat released at one side of the cell would be balanced by an equal absorption of heat at the other side, so release of heat cannot be the driving force for the fuel cell.

However, this fuel cell used two different forms of water: liquid and vapor. Liquid water is fed into the cell and vapor escapes. Vapor is more disordered than liquid, so the entropy increases and the chemical reaction moves forward. The electrons are forced through a circuit in the process, to make electricity.

The researchers found that temperature and pH affected performance. The optimum temperature was 70 degrees celsius (about 160 degree farenheit) and the voltage was highest at pH 11 (about the same pH as household ammonia).

What does it mean?

This paper reports a unique approach in developing fuel cells. It takes advantage of the fact that a chemical reaction can be “downhill” or spontaneous even if no heat is released, as long as there is an increase in entropy.

The fuel cell design reported in this study uses this technique to drive the overall chemical reaction.

Remarkably, the fuel cell setup can be used to generate electricity from water and air, producing just water and oxygen as byproducts. This is extremely attractive compared to hydrogen, methanol or other common fuel cell chemicals that only carry energy that was generated elsewhere. For example, it is possible to derive hydrogen from solar or wind power, but in practice most hydrogen comes from natural gas or oil, and a fuel cell would only be capturing the energy from those non-renewable sources.

In addition, the use of water as the energy source avoids problems of flammability and toxicity. Many existing fuel cell technologies based on liquids have the drawbacks that the fuels, byproducts or sometimes both are very hazardous. For example, methanol fuel cells can produce formaldehyde, a cancer-causing chemical.  The authors noted that high pH gave better results; in other words the use of a pH-raising additive like sodium hydroxide would be necessary to give optimum performance.  This could be considered a drawback but it might be possible through further research to improve the reaction rate by other means.

Because evaporation of water is critical to the process, the researchers suggested that the technology would be most effective in dry, windy areas.

The main limitation of the water fuel cell is that it needs more space, and materials, to generate the same amount of power as a denser fuel cell.  The researchers suggest that the water fuel cell is perhaps 100 times less dense than would be practical for most applications. The performance, though, is similar to fuel cells that produce electricity from microbial activity. The researchers suggest the cell would be adequate to power sensors or wireless transmitters.

Further research on these fuel cells might compare the amount of energy used to construct the fuel cell and its component parts, including membranes and metal catalysts, to the amount of energy that could be generated in the fuel cell’s expected lifetime.

Resources

Demirci, UB. 2010. How green are the chemicals used as liquid fuels in direct liquid-feed fuel cells? Environment International 35:626-631.

Fuel cell basics. Smithsonian Institute.

Fuel Cell Technology Program. U.S. Department of Energy.

Tollefson, J. 2010. Hydrogen vehicles: Fuel of the Future? Nature 464:1262-1264.

Hydrogen fuel cells

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2 August High hopes in the search for clean-burning hydrogen. As General Motors gets ready to sell its new Chevrolet Volt plug-in car this year, and with Nissan right behind with its all-electric Leaf hatchback, there’s not a lot of talk about hydrogen fuel-cell cars. Toronto Star, Ontario.

28 July US seeks solar flair for fuels. The US Department of Energy has launched an ‘artificial photosynthesis’ initiative with the ambitious goal of developing, scaling up and ultimately commercializing technologies that directly convert sunlight into hydrogen and other fuels. Nature.

18 July The case of the poisoned fuel cell. Hydrogen fuel cells have their own Achilles’ heel: They are easily poisoned by carbon monoxide. Now, researchers report that they’ve created novel catalysts for fuel cell cars that strongly resist carbon monoxide contamination, potentially solving a problem that has vexed the industry for years. Science.

15 July UK firm B9 eyes hydrogen as gas plant alternative. Britain’s B9 Gas is exploring hydrogen fuel cells as an alternative cheap, low-carbon way to generate electricity instead of burning gas, the clean fossil-fuel company said on Wednesday. Reuters.

10 July UK hydrogen cars are coming – if you can fill up. Britain’s hydrogen fuel cell car fleet may hit top gear within five years, but only if there is enough investment in filling stations, the UK Hydrogen and Fuel Cells Association told Reuters on Friday. Reuters.

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New membrane makes fresh water from sea and sewage feasible.

New membrane makes fresh water from sea and sewage feasible.

Jul 20, 2010

Yin Yip, N, A Tiraferri, WA Phillip, JD Schiffman and M Elimelech. 2010.
High performance thin-film composite forward osmosis membrane. Environmental Science & Technology http://dx/doi.org/10.1021/es1002555.

Synopsis by Adelina Voutchkova
A special membrane turns salty sea water into fresh water, paving the way for large-scale desalination that would provide desperately needed drinking water.

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Researchers at Yale University have developed a custom membrane that can clean and purify water from oceans, salty ground water or sewage water with far less energy input than currently is required to do a similar job.

The membrane may be a big step forward in reaching the goal of reliable and affordable sources of fresh water.  Finding sustainable sources of clean drinking water is a major global challenge, especially in most of the developing world. The need is apparent in both urban areas, due to growing population and demand, and rural regions, where sometimes scarce water supplies are quickly drying up.

As fresh water becomes more scarce, desalination and filtering will be increasingly necessary to satisfy the world’s unquenchable thirst for this precious commodity. Yet, neither of the existing desalination technologies – distilling sea water water vapors by boiling then collecting the water vapors or reverse osmosis where water is pushed through membranes to filter the salt – are feasible on a large scale. Both require high amounts of energy to either boil the water or create pressure.

A newer approach does not require external heat or pressure but lacks an adequte membrane to filter the water. The techique uses a mixture of dissolved carbon dioxide and ammonia gas in water on one side and salty or dirty water on the other side of the membrane. The gas/water mixture draws the clean water through the membrane and leaves the salt and dirt on the other side. A small amount of heat is then applied to drive off the carbon dioxide and ammonia, leaving just pure, fresh water.

However, no current membranes can stand up to the ammonia.

Now, researchers report that they have developed one – a thin-film composite forward osmosis membrane. They describe the elaborate technology in the journal Environmental Science and Technology. The membrane is permeable enough to allow water to flow freely through it but resistant enough to keep the ammonia and chemicals in sewage from passing through it.

This landmark development is a beginning. More research is needed to bring down the costs of the membranes and make this technology accessible in all parts of the world.