Looking for photochemistry inside particles

At the Swiss Light Source (SLS), a new photochemical reaction cell was developed for the X-ray microscope at the PolLux beamline. This allowed the researchers to mimic sunlight mediated chemical reactions in airborne particles we normally inhale. Utilizing the new reaction cell, the X-ray microscope was used to image the interior of particles for the chemistry that produced a high concentration of persistent carbon centered radicals (CCR) and reactive oxygen species (ROS), which are harmful compounds when inhaled and can cause damage in the respiratory tract. Two main factors were 1) a very high particle viscosity that effectively locks the CCRs in a glass-like state and 2) oxygen deficiency, or anoxia, to prevent smaller ROS to be formed with a shorter lifetime that easily diffuse out of the particle before inhalation. When relative humidity in air is <60%, particles can become highly viscous or even glass-like, which drastically reduces the mobility of all molecules. Although sunlight induced radical formation is likely to be unhindered, high viscosity would instead inhibit molecular diffusion and block oxygen from accessing the particle interior. This leads to preservation of large amounts of radicals. Amazingly, this may apply to all organic light absorbing atmospheric compounds making radical abundance and persistence an unforeseen issue until now.

Particles composed of citric acid and iron were investigated as a model for iron containing organic particles. About 1 in 20 airborne particles contain iron in urban areas at a significant concentration as identified by previous studies. The oxidation state of iron was mapped across individual particles using X-ray spectromicroscopy to reveal where photochemical reactions, oxidation and molecular diffusion took place inside. Oxidation and formation of ROS took place rapidly, but surprisingly, only near the particle surfaces, i.e. an oxidized reaction front extending only hundreds of nanometers was directly observed. This was entirely due to the rapid depletion of oxygen in the particle due to slow molecular transport and fast reaction cycling. In addition to X-ray microscopy, the researchers used an electrodynamic balance (collaboration with ETHZ) and a coated wall flow tube reactor to study these radical forming particles and constrain the overall reactive cycle and the production and release of radicals to air.

Read more on the PSI website

Image: A chemical scheme and X-ray image showing particles oxidized only near their surface. Light in iron-organic particles start a cycle of oxidizing reactions (purple text) forming carbon centered radicals (yellow text) and reactive oxygen species (red text). We directly imaged oxidation happening only near the particle surfaces indicated by the brighter colour in micrometer and submicrometer viscous particles in the right image.

Credit: PSI

Cooking pollution more resilient than previously thought

Following research undertaken at Diamond, particulate emissions from cooking have been discovered to stay in the atmosphere for longer than initially thought, causing a prolonged contribution to poor air quality and human health.

A new study, led by researchers at the University of Birmingham, demonstrated how cooking emissions can survive in the atmosphere over several days, rather than being broken up and dispersed.

The team collaborated with Diamond, the University of Bath and the Central Laser Facility to show how these fatty acid molecules react with molecules found naturally in the earth’s atmosphere. During the reaction process, a coating is formed around the outside of the particle that protects the fatty acid inside from gases such as ozone which would otherwise break up the particles.

This research was made possible by using Diamond’s powerful X-ray beamline (I22). For the first time researchers we able to recreate the reaction process in a way that enables it to be studied in laboratory conditions.

Read more on the Diamond website

New materials for the reduction of vehicle pollution

Research develops nanostructured material with high oxygen storage and release capacity for the improvement of catalytic converters

Complete combustion of both fossil and biofuels generates carbon dioxide (CO2) and water as final products. However, incomplete combustion of these substances can occur in automobile engines, generating important pollutants such as carbon monoxide (CO), hydrocarbons, and nitrogen oxides (such as NO and NO2).
To reduce the emission of these toxic substances, an equipment called a catalytic converter is used in the exhaust of vehicles. Materials called catalysts promote and accelerate chemical reactions without being consumed during the process. They retain on their surface the reactant molecules, weakening the bonds between the atoms and causing the pollutants to be converted into less harmful gases.
The action of the catalytic converter happens in three stages. The first stage converts the nitrogen oxides into nitrogen (N2) and oxygen (O2) gases. The second stage breaks down bonds of unburnt hydrocarbons and carbon monoxide, turning them into CO2. Finally, the third stage has an oxygen sensor to regulate the intake of air and fuel to the engine, so that the amount of oxygen is always close to the most efficient for the different reactions.

>Read more on the Brazilian Light Laboratory (LNLS) website

“Molecular scissors” for plastic waste

A research team from the University of Greifswald and Helmholtz-Zentrum-Berlin (HZB) has solved the molecular structure of the important enzyme MHETase at BESSY II.

MHETase was discovered in bacteria and together with a second enzyme – PETase – is able to break down the widely used plastic PET into its basic building blocks. This 3D structure already allowed the researchers to produce a MHETase variant with optimized activity in order to use it, together with PETase, for a sustainable recycling of PET. The results have been published in the research journal Nature Communications.

Plastics are excellent materials: extremely versatile and almost eternally durable. But this is also exactly the problem, because after only about 100 years of producing plastics, plastic particles are now found everywhere – in groundwater, in the oceans, in the air, and in the food chain. Around 50 million tonnes of the industrially important polymer PET are produced every year. Just a tiny fraction of plastics is currently recycled at all by expensive and energy-consuming processes which yield either downgraded products or depend in turn on adding ‘fresh’ crude oil.

>Read more on the BESSY II at HZB website

Image: At the MX-Beamlines at BESSY II, Gottfried Palm, Gert Weber and Manfred Weiss could solve the 3D structure of MHETase.
Credit: F. K./HZB

Urea susbstitutes noble metal catalysts

… for the photodegradation of organic polluants.

A new laser-based technique developed by the Institute of Materials Science (ICMAB-CSIC) uses urea, a common substance in the chemical industry and a low-cost alternative to noble metal co-catalyst, to enable a more efficient, one-step production of hybrid graphene-based organic-inorganic composite layers for environmental remediation, photodegradation of antibiotic contaminants from wastewater. The composition and chemical bonds of the urea-enriched thin layers were studied in detail using synchrotron light at the ALBA Synchrotron.
Human activity is increasing the amount of pollutants in water and air, as well as in all sorts of materials at home and work place. The existence of antibiotic contamination is undeniably one of the most threatening challenges to date, at a time when antibiotic-resistant bacteria has already been flagged as the next world-wide pandemic crisis.
Semiconductor photocatalysts have long been investigated for environmental remediation because they can degrade or mineralize a wide range of organic contaminants as well as pathogens. Research focuses on addressing some drawbacks that prevent their use on a large scale. On the one hand, many photocatalysts are activated only by UV radiation which represents solely a small fraction of the total available solar emission. On the other hand, the recombination of the photogenerated  electron-hole pairs that enable the decomposition of the pollutant is usually faster than the oxidation reactions that cause the degradation of organic molecules. As a consequence, noble metal co-catalysts acting as electron scavengers, such as gold or platinum, are needed in the process.

Image: Researchers Ángel Pérez  del Pino and Enikö György from the ICMAB-CSIC together with Ibraheem Yousef, scientists responsible of MIRAS beamline at ALBA.

Mine tailings dumped into the sea analysed with synchrotron light

The case of Portmán Bay, at the Spanish Mediterranean coast, is one of the most extreme cases in Europe causing great impact on the marine ecosystem by disposal of mine tailings.

For more than 40 years, 60 million tonnes of mine waste were dumped directly into the sea, resulting from the open pit mining that took place in Sierra Minera in Cartagena. As a consequence, the Bay was literally filled with metal-rich artificial soil. Since 2014, a research group from the University of Barcelona (UB) has been studying Portmán Bay. Now, they have analysed samples of these sediments at ALBA because with synchrotron light they can obtain unprecedented information about the heavy metals contamination, such as arsenic.

Very few people know about Portmán Bay, where took place one of the most extreme cases of coastal ecological impact by mine activity in Europe. Figures speak for itself: the mining company Peñarroya dumped more than 60 million tonnes of mine waste into the sea through a 2km-long pipeline located at the west part of the bay. Over the years, the bay became totally filled with a mountain of artificial sediment. The shoreline moved 600m seaward and the trace of the pollution reached 12km out to sea.

>Read more on the ALBA website

Image: Miquel Canals putting sample supports, which were specifically designed and printed with 3D technology at ALBA, at the CLAESS beamline to be analysed with synchrotron light; with Carlo Marini, beamline scientist and Andrea Baza, PhD student from UB.

Scientist discover that charcoal traps ammonia pollution

Discovery could have implications for agricultural management and climate change mitigation

Cornell University scientists Rachel Hestrin and Johannes Lehmann, along with collaborators from Canada and Australia, have shown that charcoal can mop up large quantities of nitrogen from the air pollutant ammonia, resulting in a potential slow-release fertilizer with more nitrogen than most animal manures or other natural soil amendments. The results were published Friday in Nature Communications.

Ammonia is a common component of agricultural fertilizers and provides a bioavailable form of the essential nutrient nitrogen to plants. However, ammonia is also a highly reactive gas that can combine with other air pollutants to create particles that travel deep into the lungs, leading to a host of respiratory issues. It also indirectly contributes to climate change when excess fertilizer inputs to soil are converted into nitrous oxide, a potent greenhouse gas.

In Canada, ammonia emissions have increased by 22 per cent since 1990, and 90 per cent are produced by agriculture, particularly from manures, slurries and fertilizer applications. Mitigating this pollutantwithout limiting fertilizers and food growth for our growing world populationis key to a sustainable future.

>Read more on the Canadian Light Source website

Image: Rachel Hestrin (right) on the beamlines at Canadian Light Source with fellow Cornell researcher Angela Possinger.