A new, more economical and sustainable material is designed that uses sunlight to decontaminate the air
image:
Image of the research team that carried out the work
view moreCredit: University of Córdoba
Nitrogen oxides (NOx) are a group of gases formed by nitric oxide and nitrogen dioxide. They are produced, above all, by the burning of fossil fuels. Due to their harmful effects on human health and the environment, in recent years they have been in the scientific community's crosshairs. A research team at the Chemical Institute for Energy and the Environment (IQUEMA), attached to the University of Cordoba, has developed a photocatalytic material capable of effectively reducing these gases, achieving results similar to others developed to date, but through a more economical and sustainable process.
Photocatalysis, or how light can decontaminate cities
There are chemical reactions that can be favored or accelerated in the presence of light. In the case of nitrogen oxides, light energy, in the presence of a material that functions as a catalyst, makes it possible to oxidize the nitrogen oxides in the atmosphere and convert them into nitrates and nitrites.
The first author of this research paper, Laura Marín, explained that, unlike other photocatalytic reactions, which only operate under ultraviolet light, this new material boasts the advantage of working effectively with visible light, which is much more abundant and makes up most of the solar spectrum, allowing greater use to be made of the sun's energy.
To do this, the research team has synthesized a new compound by combining two different types of materials: carbon nitride (which allows the reaction to be activated in the presence of visible light) and lamellar double hydroxides, which have the capacity to catalyze the reaction, in addition to featuring economical and easily scalable production.
Professor Ivana Pavlovic, one of the researchers who participated in the study, explained that the new process is capable of converting 65% of nitrogen oxides under visible light irradiation, a percentage very similar to that achieved by other photocatalysts, but with the advantage that this new system uses minerals such as magnesium and aluminum, which are "cheaper, abundant in nature, and benign, compared to other photocatalysts used to date, which contain cadmium, lead or graphene," the researcher pointed out.
Professor of Inorganic Chemistry and IQUEMA Director Luis Sánchez explained that, in this way, the work represents an important step towards the large-scale development of a system that makes it possible to decontaminate the air under real-world conditions, thus reducing one of the most common pollutant gases in cities, and one whose long-term effects can cause serious health problems.
Journal
Advanced Sustainable Systems
Article Title
The Efficient Coupling between MgAlTi Layered Double Hydroxides and Graphitic Carbon Nitride Boosts Vis Light-Assisted Photocatalytic NOx Removal
Deep-sea hydrothermal vent bacteria hold key to understanding nitrous oxide reduction
Peer-Reviewed Publicationimage:
Nitrosophilus labii HRV44T is a thermophilic chemolithoautotroph isolated from a deep-sea hydrothermal vent in the Okinawa Trough, Japan. It grows using hydrogen as an electron donor and N2O as an electron acceptor. (Photo by Muneyuki Fukushi, Hokkaido University)
view moreCredit: Muneyuki Fukushi
Scientists unearth a clue to the molecular mechanisms involved in N2O reduction by deep-sea hydrothermal vent bacteria.
Nitrous oxide (N2O) is the third most potent greenhouse gas after carbon dioxide and methane. It can also be oxidized by physical processes to form ozone-depleting substances. Atmospheric concentrations of N2O have increased since the preindustrial era, making N2O reduction a global challenge.
The only known biological sink of N2O in the biosphere is microbial denitrification. Denitrification is a series of reduction reactions starting with nitrate and ending with the reduction of N2O to nitrogen gas, with no greenhouse effect. This reaction is unique to microorganisms possessing N2O reductase (N2OR; NosZ), highlighting the importance of identifying the molecular mechanisms mediating high N2O reduction activity.
Researchers at Hokkaido University, in collaboration with colleagues at the Institute of Physical and Chemical Research (RIKEN) and the University of Washington, investigated the molecular mechanisms underlying N2O reduction of a microbial species, Nitrosophilus labii HRV44T, which had been discovered by Hokkaido University researchers in 2020, from a deep-sea hydrothermal vent. The team recently published their results in the journal iScience.
The research team developed a method that enabled them to analyze time-series gene expression at a genome-wide level, called the transcriptome, using RNA extracted from very few cells.
“Time series transcriptomic analysis of HRV44T in response to N2O was more challenging than expected,” said corresponding author Sayaka Mino, Assistant Professor at the Faculty of Fisheries Sciences, Hokkaido University. “We have performed transcriptomic analysis using methods often used in microbial studies, but we failed to capture the gene expression dynamics over short time scales because we could not get enough RNA from just a few cells. The method demonstrated in the current study requires only 1 ng of messenger RNA (mRNA), making it useful for analysis at low cell densities, from which RNA extraction is difficult.”
The time series transcriptomic profiling of HRV44T demonstrated that N2O is not a critical inducer of denitrification gene expression, including nos genes, which are expressed under anaerobic conditions even in the absence of nitrogen oxides as electron acceptors.
“We hypothesize that this feature may contribute to efficient energy metabolisms in deep-sea hydrothermal environments where alternative electron acceptors are occasionally depleted”, said Robert M. Morris, Associate Professor at the University of Washington.
Jiro Tsuchiya, the first author and a JSPS research fellow DC2 at Hokkaido University, and colleagues conducted a statistical analysis of time series data. “Our findings suggest that the denitrification gene nosZ is negatively regulated by transcriptional regulators that typically function as transcriptional activators in response to environmental changes. Although we still need to investigate this result, our study extends the understanding of the regulatory mechanisms controlling gene expression in N2O-reducers and may help increase their ability to respire N2O”, said Tsuchiya.
Deep-sea hydrothermal environments have steep chemical and physical gradients, making them hotspots for bioresources. This study demonstrates the potential for microorganisms in these environments to contribute to N2O mitigations that may help combat climate change. Search for microbial resources with high greenhouse gas reduction efficiency, optimization of their abilities, and elucidation of molecular mechanisms specific to these microorganisms will contribute to developing technologies for environmental remediation by microorganisms.
Strain HRV44T rapidly respires N2O, forming bubbles at the gas-liquid interface. (Photo by Jiro Tsuchiya, Hokkaido University)
Credit
Jiro Tsuchiya
Journal
iScience
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Time course transcriptomic profiling suggests Crp/Fnr transcriptional regulation of nosZ gene in a N2O-reducing thermophile
Porous crystals detect nitric oxide
Ultrasensitive detection of NO using a conductive 2D metal–organic framework
Wiley
Detection of nitric oxide (NO) is important for monitoring air quality because the NO released in the combustion of fossil fuels contributes to acid rain and smog. In medicine, NO is an important messenger molecule and serves as a biomarker for asthma. In the journal Angewandte Chemie, a research team now reports a material that can detect NO reversibly, with low power, and with high sensitivity and selectivity: a copper-containing, electrically conducting, two-dimensional metal–organic framework.
Metal–organic frameworks (MOFs) are latticelike structures consisting of metal “nodes” connected by organic bridges (ligands). An emerging class of MOFs are electrically conducting structures consisting of layers. These 2D-cMOFs have demonstrated great potential as chemiresistive sensors that react to the presence of specific molecules with a change to their electrical resistance, which may allow for particularly sensitive and low-power detection of toxic gases. Problems with such systems have included cross-reactivity with a variety of gases and limited reusability due to irreversible binding of the analytes.
Katherine A. Mirica, Christopher H. Hendon, and their team at Dartmouth College (Hanover, NH, USA), the University of Oregon (Eugene, OR/USA), and Ulsan National Institute of Science and Technology (South Korea), have now developed a reusable 2D-cMOF for the highly selective detection of NO. They chose to use a 2D-cMOF based on copper and hexaiminobenzene, Cu3(HIB)2. Thanks to their different synthetic strategy (the linker was added as an undissolved powder to a solution of Cu2+ ions and potassium acetate), the team produced a material with significantly higher crystallinity (rod-shaped crystallites about 500 nm in length) than has previously been attained.
The crystallites consist of stacked layers of a weblike structure of six-membered rings linked together by copper ions bound to their nitrogen atoms. Spectrometric analyses and computations revealed that the binding sites for NO were Cu-bis(iminobenzosemiquinone) units of the copper-2D-cMOFs. An analogous compound made with nickel instead of copper demonstrated no significant absorption of NO. Evidently, copper ions with a single positive charge, which are present in small amounts in the structure besides those with a twofold positive charge, play an important role in binding NO. Computational studies suggest that the adsorbed NO significantly distorts the structure, destabilizing the bound state, which is the primary cause for the desirable reversibility of the NO adsorption.
This new sensor material detects NO at room temperature and low voltage (0.1 V) with high sensitivity (detection limit about 1.8 ppb) and could be reused for at least seven cycles without regeneration. Quantitative measurements of NO were also successful in the presence of moisture, and showed high enhancement of sensor signal towards NO in comparison to other gases, such as nitrogen dioxide, hydrogen sulfide, sulfur dioxide, ammonia, and carbon monoxide and dioxide.
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About the Author
Dr. Katherine A. Mirica is an Associate Professor of Chemistry at Dartmouth College. Her main research direction focuses on the development of multifunctional porous materials capable for sensing, filtration, and detoxification of hazardous chemicals.
Journal
Angewandte Chemie International Edition
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Reversible and Ultrasensitive Detection of Nitric Oxide Using a Conductive Two-Dimensional Metal–Organic Framework
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