Physical Science and Engineering | Physical Science & Engineering

Tuesday, May 11, 2021

MOF metallic mastery

The tightly defined ratios of metals in metallic organic frameworks makes them ideal starting materials for novel catalyst creation.

Share this

The tightly defined ratios of metals in MOFs makes them ideal starting materials for novel catalyst creation.

Heating bimetallic metal organic frameworks (MOFs) until their porous structure collapses into nanoparticles can be a highly effective way to make catalysts. This novel approach to catalyst design has now been used by KAUST and Spanish researchers to make a robust catalyst that converts carbon dioxide (CO2) into carbon monoxide (CO) gas with unprecedented selectivity.

The benefit of this method pioneered at KAUST is that it can generate mixed metal catalytic nanoparticles that have proven challenging or impossible to make by conventional means.

Capturing CO2 emissions and catalytically converting the greenhouse gas into CO, a valuable chemical feedstock, is one option for reducing greenhouse gases associated with climate change. Precious metals can catalyze this reaction, but they are costly and supplies are limited, says Samy Ould-Chikh, a research engineer in KAUST.

“Iron oxide catalysts are an inexpensive alternative,” Ould-Chikh says. “However, in the presence of CO, the iron is carburized forming iron carbide, which leads to by-product formation and catalyst deactivation.”

Adding titanium to the catalyst particles could stabilize iron oxide against carburization. Chemical incompatibilities between iron and titanium precursors, however, had made it impossible to synthesize nanoparticles incorporating a homogenous mixture of the two metals in the necessary ratio. To overcome this limitation, the team turned to MOFs, porous materials made from metal ions connected together by carbon-based linkers.

“The use of MOFs allows us to perfectly control the iron-titanium ratio on the parent MOF,” says research engineer Adrian Ramirez Galilea. Heating decomposes the organic part of the MOF, leaving the two metals behind, homogenously mixed in the desired ratio and in neat octahedral nanoparticles that mirror the structure of the parent MOF.

The nanoparticles converted CO2 to CO with 100 percent selectivity, with no sign of deactivation after several days of use. “Our initial calculations suggested that nanoparticles with such atomic ratios should be able to do the job; however, the results far exceeded our original expectations,” Gascon says.

As well as continuing to explore the properties and reactivity of the iron-titanium nanocatalyst, the team is examining other metal catalyst systems made from MOFs in the same way. “The use of MOFs opens the way to synthesize new catalysts that were not possible to make using conventional approaches,” Ramirez Galilea says.

“We are looking at different metal combinations for applications ranging from traditional thermal catalysis to photo and photothermal catalysis,” adds Jorge Gascon, who led the research. “This paper is just the tip of the iceberg.”

- KAUST Discovery

Sunday, May 09, 2021

Congratulations Professor Han!

Professor Yu Han has been named a Fellow of the Royal Society of Chemistry.

Share this

KAUST Professor of Chemical Science and Chemical Engineering Programs, Professor Yu Han, has been named a Fellow of the Royal Society of Chemistry (FRSC).

The Royal Society of Chemistry (RSC) is the United Kingdom’s professional body for chemists and the largest organization in Europe for advancing the chemical sciences. The designation Fellow of the Royal Society of Chemistry (FRSC) is given to elected Fellows who have made an outstanding contribution to the advancement of chemical sciences, or to the advancement of the chemical sciences as a profession.

At KAUST, Professor Han is affiliated with the Advanced Membranes & Porous Materials and KAUST Catalysis Center Research Centers.

Research

“Professor Han's research interests at KAUST include the synthesis of nanoporous and nanostructured materials, the resolution of their complicated structures and the development of novel applications for these materials in catalysis, separation, adsorption, sensing, and laser.” Read Professor Han’s full profile.

Thursday, May 06, 2021

2D materials offer unique stretching properties

Calculations predict that atom-thin sheets of carbon chalcogenides will grow wider when stretched in any direction.

Share this

Like most materials, an elastic band gets thinner when it is stretched. But some materials behave in the opposite way — they grow thicker when stretched and thinner when compressed. These counterintuitive substances, known as auxetic materials, tend to have a high resistance to shear or fracture and are used in applications such as medical implants and sensors. But typically, this auxetic effect is only seen when the material is distorted in one particular direction.

Now, Minglei Sun and Udo Schwingenschlögl have predicted that a group of carbon-based materials, formed into atom-thin sheets, should show this auxetic effect in every direction. This phenomenon has never been observed before in any 2D anisotropic material, a growing family of flat materials that include several potentially auxetic materials.

The KAUST researchers calculated several key characteristics of three 2D materials called carbon sulfide, carbon selenide and carbon telluride, which unite carbon with elements collectively known as chalcogens. The calculations rely on density functional theory, a commonly used approach based on quantum mechanics, and they describe characteristics of the materials such as their structural stability, mechanical behavior and electronic properties.

All auxetic materials have a negative Poisson's ratio, a number that describes how a material deforms when it is stretched or compressed. But the researchers found that the three materials are uniquely auxetic because they have an omnidirectional negative Poisson’s ratio. “We were surprised that we found a series of 2D anisotropic materials with negative Poisson’s ratio in all directions,” says Sun.

Sun and Schwingenschlögl’s calculations predict that all three materials should be stable at room temperature, suggesting that it may be possible to synthesize and isolate them. They also explain the materials’ omnidirectional auxetic effect in terms of their crystal structures and chemical bonding. Carbon telluride shows the strongest auxetic effect, which is larger in all directions than the highest values seen in most other 2D auxetic materials. It also has the highest fracture strain of the three materials investigated by the KAUST researchers.

According to the team, the materials should be semiconductors that are able to absorb near-infrared or visible light. The three carbon chalcogenides “turn out to be direct or quasi-direct bandgap semiconductors with impressive absorption of solar radiation,” says Sun. This implies that the materials might be useful in photovoltaic devices or as light-powered catalysts. “Our next step is to predict more 2D auxetic materials with negative Poisson’s ratio in all directions,” says Schwingenschlögl.

- KAUST Discovery

Tuesday, May 04, 2021

Closing in on state-of-the-art semiconductor solar cells

Mixed-cation single crystals narrow the gap between perovskite and top-performing semiconductor solar cells.

Share this

A synthetic approach that improves absorber layers in perovskite solar cells could help them achieve their full potential and draw closer to the performance of leading gallium arsenide devices.

Solar cells that rely on perovskite thin films to capture sunlight are the fastest growing photovoltaic technology. Cheaper and easier to manufacture and incorporate into devices than conventional semiconductors, lead halide perovskites also effectively absorb visible light and display long charge carrier diffusion lengths — an indicator of their ability to maintain light-induced electrons and holes separation and facilitate charge transport.

Performance of solar cells hinges on absorber materials with a high-quality crystal structure and a narrow bandgap to maximize sunlight harvesting. This optimal bandgap range spans energies of 1.1 to 1.4 eV, which corresponds to near-infrared wavelengths.

Absorber layers containing polycrystalline lead halide perovskites have provided high-efficiency solar cells. Their performance, however, has been affected by considerable structural disorder and defects. Formamidinium lead triiodide features the smallest bandgap to date, but this bandgap exceeds the optimal range for single-junction devices. One way to reduce the bandgap of perovskites involves forming lead–tin alloys in the absorber, but this introduces crystal defects and instability.

Now, a team from KAUST has developed an approach using a microns-thick absorber layer consisting of perovskite single crystals to minimize the bandgap. The crystals contain a mixture of methylammonium and formamidinium organic cations.

The researchers incorporated the mixed-cation perovskite into unconventional inverted p–i–n solar cells, in which the absorber is sandwiched between an electron transport top layer and a hole transport bottom layer. The resulting solar cells exhibited an efficiency of 22.8 percent, surpassing the best-performing devices using single-crystal methylammonium lead triiodide.

“We had known that mixed-cation single-crystal absorbers could outperform single-cation absorbers due to their lower bandgap and superior optoelectronic qualities. However, this had not been realized before because of challenges in crystal growth and device integration,” says Abdullah Alsalloum, a Ph.D. student in Osman Bakr’s group.

The external quantum efficiency of the mixed-cation perovskite film, which measures its effectiveness when converting incoming light into charge carriers, shifted toward near-infrared wavelengths from that of polycrystalline formamidinium lead triiodide, consistent with its smaller bandgap. “By utilizing a thicker single-crystal absorber layer, we expanded the absorption range of the film so that it’s very close to the optimal range,” Alsalloum says.

The team is working on enhancing device performance and stability to get even closer to the top-performing gallium arsenide solar cells. “Future studies include optimizing device interfaces and exploring more favorable device structures,” Alsalloum adds.

- KAUST Discovery

Monday, May 03, 2021

Congratulations Antonia!

Energy Resources & Petroleum Engineering (ERPE) Ph.D. Student Antonia Sugar wins the Young Presenters of Note from EAGE (European Association of Geoscientists and Engineers).

Share this

KAUST Ph.D. Student of ERPE program, member of the Advanced Reservoir Modeling & Simulation Group supervised by Prof. Hussein Hoteit and ANPERC, Antonia Sugar, wins the Young Presenters of Note of EAGE (European Association of Geoscientists and Engineers) for outstanding presentation at IOR2021.

EAGE aims to “promote the development and application of geosciences and related engineering subjects, to promote innovation and technical progress and to foster the communication, fellowship, and cooperation between those working in, studying or otherwise being interested in these fields.”

Education

Before coming to KAUST, Antonia took her B.Sc. in Petroleum Engineering at the Oil and Gas University of Ploiesti in Romania and her M.Sc. in Reservoir Engineering, Montanuniversität Leoben in Austria.

Sunday, May 02, 2021

Understanding aromaticity in catalysis to unlock new opportunities

The chemical concept of aromaticity is inspiring new developments in the area of catalysis.

Share this

Aromaticity, a concept usually used to explain the striking stability and unusual reactivity of certain carbon-based molecules, could inspire the design of new catalysts with novel uses, KAUST researchers have shown.

Chemists first came upon the anomalous behavior of aromatic molecules in the nineteenth century while studying benzene. The unexpected stability of this six-carbon cyclic structure comes down to its electrons.

In general, bonding electrons hold a specific pair of atoms together in a discrete chemical bond. But in benzene, six electrons form a delocalized ring across the molecule. A host of other molecules share this feature. “Many classic examples of organic and organometallic reactivity can be explained on this basis,” says Théo Gonçalves, a research scientist in Kuo-Wei Huang’s lab. “But although the concept is well known, there are limited practical chemical applications of aromaticity,” he adds.

One area of practical application is in the field of catalysis. The Huang group recently developed an unusual family of catalysts called PN3(P) pincer complexes. In most catalysts, the central metal ion is where all the bond breaking and making takes place. In PN3(P) complexes, the pincer ligands around the metal can also be active participants in the catalytic process. “Our PN3(P) ligand platform enables catalytic applications beyond conventional systems where metal is the center of reactivity,” Huang says.

As the team studied pincer complexes’ catalytic behavior, they showed that a six-membered ring structure transiently forms during catalysis and that aromaticity was coming into play. “We have provided strong evidence that during the catalytic cycle, our catalysis benefits from the additional energy coming from aromatization of the ring,” Gonçalves says. “Tuning the degree of aromatization will gently tune the reaction output.”

The PN3(P) pincer family possesses high catalytic performance for reactions such as the selective hydrogen production from formic acid for reducing carbon dioxide (CO2) and for forming esters and imines. But the real value of the research could be from the new insights it generates into the role of aromaticity in catalysis, and the new horizons that open up as a result. “Prior to our work, the importance of the aromaticity was not highlighted in this field,” Gonçalves says. “Fundamentally understanding aromatization and dearomatization will allow redesign of catalysts towards better performance and perhaps novel reactivity.”

“Our discovery is not about identifying a new or better catalyst for a known reaction, but about opening a new field for unlimited new opportunities in the future,” Huang adds.

- KAUST Discovery

Thursday, April 29, 2021

An ocean 13 million years in the making

A detailed analysis combining seafloor mapping and earthquake and gravity data shows that the oceanic crust under the Red Sea is older than previously thought.

Share this

Spreading of the seafloor in the Red Sea basin is found to have begun along its entire length around 13 million years ago, making its underlying oceanic crust twice as old as previously believed.

The formation history and age of the Red Sea basin has long been contested, largely because the crust under the sea is widely overlain by thick layers of salt and sediment, making it difficult to observe directly.

“Existing geological models of the Red Sea often contradict each other, largely due to limited high-resolution data and the influence of overlaying salt layers,” says Froukje van der Zwan from KAUST, who worked on the project. “For example, magnetic methods do not work well because of the salt layers, where lava erupting under the salt blankets develops significantly different magnetic signatures than those from other oceans.”

“We decided to start afresh without preconceptions and make use of gravity and earthquake data, which allowed us to ‘see through’ the salt layers to the crust beneath,” explains van der Zwan.

Areas of thick crust, such as mountains and volcanoes, and denser rock types have a high gravity index, and oceanic crust displays different gravity properties compared with continental crust. These differences are mapped by satellites monitoring the gravitational field of the Earth, and the resulting “vertical gravity gradient” (VGG) data are readily available.

The international team combined VGG data with high-resolution seafloor maps, rock chemistry and earthquake data to gain a comprehensive overview of the basin. Their results indicate that the Red Sea has the fairly simple geological structure of a young ocean, with large volcanoes running the length of the slow-spreading rift. These features are typical of mid-ocean ridges around the world and suggest that the entire Red Sea is not a young sea, but rather a maturing “teenage” ocean basin of around 13 million years old.

“Most of the basin is underlain by oceanic crust, and the continental crusts on either side are further apart than previously indicated,” says van der Zwan.

The new model explains features found in the northern Red Sea that are unaccounted for in earlier models. Furthermore, dating the spreading of the seafloor changes the understanding of the region’s geological history and could help researchers better understand the formation of other oceans, such as the South Atlantic.

“With a stronger sense of where the earth plate boundaries are, we may improve our understanding of regional seismic activity,” says van der Zwan. “Our model will enable us to conduct detailed studies of the ocean crust, active fault systems and the volcanic explosion craters that we found.”

- KAUST Discovery

Tuesday, April 27, 2021

Explaining electric fields in sandstorms

The intense sparks that occasionally accompany charged sandstorms can arise from turbulent movements of airborne dust.

Share this

A complex weather phenomenon that has puzzled researchers since the nineteenth century can now be accurately modeled using a computer simulation framework developed at KAUST.

One lesser-known aspect of sandstorms is that they can generate high-magnitude electrical fields capable of disrupting communication equipment. Recent studies have shown that sand can pick up static electricity through collisions that take place near the ground. Less certain, though, is how the electrified sand behaves once airborne. The observed field strengths require some means of separating oppositely charged particles from each other over large scales.

Ravi Samtaney and his team at KAUST realized that because very few collisions take place between sand particles in the atmosphere, another physical mechanism could be behind electric field formation. They proposed that turbulence — stochastic motion of sand particles embedded in the airflow — might cause sand grains to spontaneously separate. Proving this theory, however, would require some means of simplifying a problem with many dynamic variables.

“Resolving all those sand particles and turbulent motions would require unrealistic computational power,” says Samtaney. “So we use what’s called a large-eddy simulation, where the tiny fluctuations get smoothed over and only large ones remain. We are situating the model inside the sandstorm, for several minutes or hours, to see what is statistically steady”.

As part of his Ph.D. research, Mustafa Rahman joined Samtaney’s group to tackle this problem. He helped develop an approach where the turbulent eddies of sandstorms are modeled inside a virtual box that stretches from ground level to kilometer-scale heights in the atmosphere. They controlled the sandstorm’s strength with an algorithm that introduces different densities of charged particles into the box, just above the desert floor.

“Near the ground, the turbulent air becomes coupled with the sand transport and they influence each other,” says Rahman. “These mechanisms are tricky to model with conventional techniques.”

The team spent months of modeling and coding on Shaheen-II, KAUST’s massively parallel supercomputer, to resolve the large eddies in sufficient detail. Their computations revealed that smaller-sized grains tended to follow the turbulent flow, but larger grains did not. Because the two size classes of sand grains had opposite charges, this turbulence-based separation created an electric field that sustained itself and reinforced further charge separation, ultimately producing electric fields close to several hundred thousand volts per meter, which accurately match field measurements.

“Reproducing the electric field measurements means our simulation framework may be used as a predictive tool, even for rovers and satellites dealing with dust devils on Mars,” says Samtaney.

- KAUST Discovery

Thursday, April 22, 2021

Congratulations Professor Pedro!

Associate Professor Pedro Castaño is named an Early Career Fellow of the Industrial & Engineering Chemistry (I&EC) of the American Chemical Society (ACS).

Share this

KAUST AssociateProfessor of Chemical Engineering Program and member of the KAUST Catalysis Center (KCC), Pedro Castaño, has been named an Early Career Fellow of Industrial & Engineering Chemistry (I&EC) of the American Chemical Society (ACS) in recognition of the innovative contributions to applied chemistry and engineering.

The Industrial & Engineering Chemistry (I&EC) is a multi-disciplinary Division helping individuals convert science into commercially relevant products and processes.

Research

Professor Castaño’s research interests focus on engineering reactions and sustainable catalytic processes. In particular, (1) developing advanced reactors, heterogeneous catalysts, and models for these processes; and (2) understanding the fundamental relationships between structure, performance, deactivation of catalysts with the reaction media and reactor performance-dynamics.

In the Applied Physics Program Faculty and students engage in interdisciplinary research at the interface between fundamental physical concepts and cutting-edge technologies. They strive to exploit basic physical phenomena at the nanoscale to design innovative solutions in several applied physics specialties, such as optics and photonics, semiconductor devices, quantum electronics and novel materials for energy applications.

Find out More

The Chemical Engineering Program offers students the opportunity to develop real-world solutions to global challenges by performing rigorous coursework studies and cutting-edge research in areas including the development of new materials and processes for gas and liquid separations, for water desalination, catalysis, sustainable energy and nanotechnology as well as the advancement of new ideas in process design and control and reactor design.

Find out More

The Chemical Science Program provides a modern, research-oriented education in Chemistry. Making use of the outstanding facilities at KAUST, the program distinguishes itself with a clear focus on current challenges related to catalysis and materials.

Find out More

In the Earth Science and Engineering Program Faculty and their students engage in interdisciplinary research to understand and model geophysical processes due to the complex and changing nature of our planet. The curriculum provides a sound graduate-level education in geophysical sciences and their applications in two distinct specializations represented by two tracks:

• Fluid Earth Systems;
• Solid Earth Systems.

Find out More

Faculty and students in the Energy Resources and Petroleum Engineering (ErPE) program at KAUST engage in interdisciplinary research to understand and model hydro-chemo-thermo-mechanical coupled processes in the subsurface, with emphasis on multiphase and reactive fluid flow (oil, gas, brine, water and steam).

Find out More

The Material Science and Engineering Program equips students with fundamental and applied knowledge of nanomaterials and devices; energy conversion materials and devices; biomaterials; and advanced characterization techniques.

Find out More

The Mechanical Engineering Program focuses on the following broad areas of research: structures and mechanics of solids, fluid dynamics, thermal sciences, combustion, energy, and control and dynamics. Courses in the program provide a solid foundation in each area, covering subjects such as mechanical behavior of engineering materials, continuum mechanics, thermodynamics, experimental and numerical combustion, control design, dynamic analysis, modeling, and simulation.

Find out More

Latest News VIEW MORE

MOF metallic mastery

Congratulations Professor Han!

Research

2D materials offer unique stretching properties

Closing in on state-of-the-art semiconductor solar cells

Congratulations Antonia!

Education

Understanding aromaticity in catalysis to unlock new opportunities

An ocean 13 million years in the making

Explaining electric fields in sandstorms

Congratulations Professor Pedro!

Latest Events SEE ALL

Eid Al-Fitr

Summer Semester 2021 starts

Last day to add a class and/or drop a class without a W grade

Functional Metal Organic Frameworks for Surface Organometallic Chemistry and Carbon Conversion

MORE INFORMATION

LOCATION

Spring Semester 2021 Graduation date

VIRTUAL SUMMER SCHOOL: Utilizing unstructured data in Geoscience

Last day to drop a class with a W grade

Summer Semester 2021 session ends

WATCH THE DIVISION VIDEO

GRADUATE PROGRAMS

Applied Physics

Chemical Engineering

Chemical Science

Earth Science and Engineering

Energy Resources and Petroleum Engineering

Material Science and Engineering

Mechanical Engineering

FACULTIES AND RESEARCH

Faculty Research Group Labs

Affiliated Research Centers

Research

Education

MORE INFORMATION

LOCATION

​​WATCH THE DIVISION VIDEO

​​GRADUATE PROGRAMS

Applied Physics

Chemical Engineering

Chemical Science

Earth Science and Engineering

Energy Resources and Petroleum Engineering

Material Science and Engineering

Mechanical Engineering

​FACULTIES AND RESEARCH

Faculty Research Group Labs

Affiliated Research Centers

WATCH THE DIVISION VIDEO

GRADUATE PROGRAMS

FACULTIES AND RESEARCH