Carbon capture technology can be further improved for efficiency by simply irradiating one of the components, according to research from a Khalifa University team of chemical engineers

Reducing greenhouse gas emissions, particularly carbon dioxide (CO2), is paramount in combating climate change. Along with a paradigm shift from fossil fuels to renewable energy sources, deployment of carbon capture and storage technologies is a key strategy to actively limit the global average rise in temperature to less than 1.5 ⁰C relative to pre-industrial levels.

Carbon capture, utilization and storage (CCUS) is the most widely accepted and promising strategy for mitigating point source CO2 emissions, with technologies being increasingly demonstrated across a number of industries globally. These technologies typically include capturing CO2 from emission sources such as power plants, followed by compression prior to transportation to long-term storage sites. These approaches can be further improved for increased efficiency and reduced energy consumption and cost.

The team found that activating the graphene oxide using ultraviolet light improves the surface, structural, and morphological properties for enhanced selective carbon dioxide affinity.

Team members included Eng. Anish Mathai Varghese, Research Associate, Dr. K. Suresh Kumar Reddy, Research Scientist, and Dr. Georgios Karanikolos, Associate Professor of Chemical Engineering. Their results were published in

Successful carbon capture needs a sorbent material that will selectively grab CO₂ in a stream of mixed gases and then readily release it when desired so that the material can be reused, while the captured CO₂ can be utilized or sent for long-term storage.

In adsorption, CO₂ collects in the pores in the material that serve as active capture sites. When, for instance, temperature is lowered, CO₂ adheres to the surface, and when temperature is raised, CO₂ is released. Changes in pressure can also bring about these capture and release cycles.

Currently, aqueous amine solutions, which are solutions containing water and organic compounds called amines that contain nitrogen atoms attached to hydrogen and carbon atoms, are used to capture CO₂ in industrial applications. Amine solutions are excellent at capturing the CO₂, making them the most popular and developed carbon capture technology. However, their disadvantage is that in order to recover the trapped CO₂ from the amine solution, the solution has to be heated, requiring large amounts of thermal energy and resulting in some amines being lost to the environment in this high-energy process.

To overcome the shortcomings of amine solutions, solid sorbent materials are a viable alternative. Solid sorbents can selectively adsorb CO₂, however some solid sorbent materials perform better than others.

“Adsorption is gaining increased attention due to advantages that include low energy consumption, ease of implementation, cost-effectiveness, and generation of harmless byproducts,” Eng. Varghese explained. “To be suitable for large scale carbon capture, however, the adsorbent materials need to offer certain features and properties, including low energy consumption, chemical and thermal stability, low manufacturing cost, and mechanical robustness. As such, a large variety of materials are being investigated globally, like metal-organic frameworks, zeolites, covalent organic materials, and porous polymers, among many others. We developed a hybrid metal-organic framework adsorbent using copper ions, and UV-activated graphene oxide.”

Metal-organic frameworks offer superior textural properties, high structural flexibility, and can be combined with various functional groups for different applications. However, MOFs typically possess low thermal and chemical stability, restricting their use in harsh environments. To overcome this, the research team used a MOF-based hybrid known as HKUST-1 or MOF-199. This MOF is particularly promising for CO2 capture thanks to its extended porous structure with large surface area and pore volume, along with good chemical stability, ease of synthesis and commercial viability. It is a 3D porous framework combining copper ions with oxygen atoms.

The team went a step further too: they used UV-irradiated graphene oxide to increase the hybrid MOF’s CO2 adsorption capacity by 45 percent.

UV irradiation of the graphene oxide affected the distribution of the copper ions on the surface of the resulting MOF, which enhanced the pore shape and structure to allow for better CO2 selectivity and adsorption.

“These results show that UV treatment is a simple and scalable technique that can enhance the characteristics and performance of MOF/GO hybrid adsorbents for CO2 capture,” Eng. Varghese said. “Our hybrid material is an excellent adsorbent in humid conditions, which is beneficial since water vapor is often present in CO2-containing mixtures, such as in post-combustion of fuels.”

This material now has the potential to be further developed and scaled-up, with UV activation of graphene before capture application serving as an easy and low-cost pre-treatment technology.

Jade Sterling
Science Writer
12 April 2022

The post UV Radiation of Graphene Oxide Improves Carbon Capture Efficiency in Metal-Organic Frameworks appeared first on Khalifa University.

The ‘memimpedance’ device can control current flow in a circuit, and could make electronics like wearable sensors, flexible medical devices and biodegradable electronics more efficient

A team from Khalifa University has developed a novel electronic ‘memimpedance’ device that can act as a switch and induce tunable resistor and capacitor behavior simultaneously in an electronic circuit.

A resistor is an electrical component that regulates the flow of electrons in a circuit, while a capacitor is an electrical component that collects and stores electrical charge.

The need to control electron flow is what gave rise to transistors, which are at the heart of all electronics today. Transistors are three terminal electronic switches that either permit or prevent electrons from flowing from one terminal to another based on the control provided by the third terminal, which serves as a gate. Other elements, including resistors and capacitors, also play a role in regulating current flow in electronics.

Enter memristors. Memristors are resistors with memory. They were physically realized for the first time in 2008, though they were conceptualized theoretically for decades before that, and have gained popularity for their potential use in computers.  They are simpler than transistors, smaller, use less energy, can alter their resistance and “remember” the most recent resistance they had. This means they have the potential to replace silicon-based transistors and could be used to create faster, more efficient computer chips that integrate memory with logic.

When memristor and memcapacitor behaviors happen simultaneously in the same device, it is called memimpedance. A memimpedance device, therefore, is designed to control, or tune, the memristor and memcapacitor behavior in an integrated circuit.

Dr. Heba Abunahla, Research Scientist in the Electrical Engineering and Computer Science Department at Khalifa University, and a team from the KU System-on-Chip Lab (SoCL), developed a memimpedance device made out of silver-reduced graphene oxide-silver that can tune the resistance and capacitance behaviors in a circuit.

Dr. Abunahla published her research in the journal, with co-authors Dr. Baker Mohammad, Professor, Dr. Yawar Abbas, Research Scientist, and Dr. Anas Alazzam, Associate Professor.

“Memimpedance has many advantages compared to resistance or capacitance only devices, especially its ability to tune the overall circuit impedance,” Dr. Abunahla said.

Circuit impedance measures how much a circuit impedes the flow of charge. As electrons move through a circuit, they collide with the internal structure of the conductor, which creates friction and slows them down.

The amount of resistance depends on the conductor’s material, shape and size, but conductors generally have low resistance to current. In addition to resistance, circuit impedance also considers capacitance, which is the ability of a component to collect and store electrical charge.

A device that can tune a circuit’s overall impedance would be particularly useful in applications like wearable sensors, flexible medical devices and biodegradable electronics.

Dr. Abunahla and the SoCL team successfully demonstrated that their memimpedance device would, when a suitable voltage was applied, tune the circuit resistance and capacitance concurrently.

They developed the memimpedance device with a unique structure using silver-reduced graphene oxide-silver.

“Using graphene-related materials as a switching material is a great asset due to their low cost and adaptability, and they are environmentally friendly,” Dr. Abunahla said.

The team’s memimpedance device has a planar structure, meaning all the atoms of the molecule sit on a single two-dimensional plane.

“Fabricating the device with a planar design boosts its potential to be deployed in sensing applications, such as wearable electronics. The planar structure allows for a bigger surface area and better interaction with the environment, which increases the efficiency of the sensing unit,” Dr. Abunahla added.

The researchers fabricated the device on a flexible polymer substrate using a lithography process. They deposited the graphene oxide directly onto the polymer substrate, then immersed it in an acid to create a thin layer of reduced graphene oxide measuring around 60 nanometers thick. They then used a standard lift-off process to pattern a film of silver electrodes onto the substrate.

They intentionally selected a polymer substrate instead of a silicon-based substrate, which is traditionally used to make memristors, because silicon-based devices pose challenges when they are stacked together to create 3D circuits.

The KU memimpedance device, however, is well suited for stacking and to produce 3D integrated circuits, which can achieve better performance than traditional 2D circuits.

Using silver-reduced graphene oxide-silver in a planar structure, fabricated on a flexible substrate using a standard production process, makes the resulting device cost-effective and deployable in flexible electronics and many other potential applications

“This work will be a great asset for tunable emerging applications, especially for communication and AI systems,” Dr. Abunahla said.

Jade Sterling
Science Writer
6 October 2021

The post Khalifa University Researchers Develop Next-Generation Electronic Tuning Device as New Building Block for Modern Computers appeared first on Khalifa University.

KU researchers publish the first ever review paper on layered graphene for strain and pressure sensor applications

A class of nanomaterials known as cellular graphene are emerging as a promising avenue for developing more efficient, flexible and wearable strain and pressure sensors. However, a strong understanding of how to best develop cellular graphene with highly tailored mechanical properties for optimal pressure and strain sensing capability has been lacking, until now.

A team of researchers from Khalifa University and the University of Cambridge, led by KU Professor of Aerospace Engineering Dr. Kin Liao, has written the first-ever comprehensive review paper on the design and development of cellular graphene for the application of strain and pressure sensors. Their was published earlier this month in the journal Matter by Cell Press.

Graphene is an ultrathin 2D material that possesses incredibly unique properties. It is the thinnest, strongest material known to exist and can conduct heat and electricity better than perhaps any other material. However, it is difficult to translate graphene’s 2D strength into useful 3D applications, like sensors. In response, researchers have been figuring out how to manipulate graphene to create three-dimensional representations of it.

“Graphene is a 2D material, like a sheet of paper,” explained Dr. Liao. “When one assembles these tiny sheets in a three-dimensional form, like a sponge, it becomes cellular graphene, also known as graphene foam or graphene sponge. Cellular graphene are structures deliberately designed and processed from graphene sheets. This kind of meta-material has properties that can be actively designed for a variety of applications.”

One application that cellular graphene is particularly well suited for is strain and pressure sensing. By converting very small changes in pressure into larger, significant changes in an electrical current, pressure sensors have a wide range of applications. They are used in a number of personal devices and biomedical devices, and for industrial monitoring, navigation, and ultrasonic imaging.

“Cellular graphene is an extremely promising candidate material for the type of flexible, wearable and ultra-sensitive strain and pressure sensors needed to support emerging applications, particularly in healthcare technology,” Dr. Liao shared. “For example, strain and pressures sensors with high sensitivity and a large sensing range are critical for the accurate measurement of human physiological parameters, such as subtle microcirculation dynamics or whole body movements.”

“Traditional metal-based strain and pressure gauges do not satisfy these emerging requirements because of their outdated design and less effective sensing mechanisms. Therefore, nanomaterials like carbon nanotubes, graphene, and metallic nanowires and nanoparticles, have been applied in the design and fabrication of novel strain and pressure sensors over the last few years.”

The demand for smaller, more sensitive and more reliable strain and pressure sensors that may be incorporated into emerging technologies like biomedical sensors is growing rapidly. The worldwide pressure sensor market is pegged to reach US$11.4 billion by 2024.

Dr. Liao’s paper aims to uncover some of the major challenges currently facing the development of cellular graphene-based strain and pressure sensors, which include issues of precise control of the cellular structure, as well as achieving durability and stability.

The paper is a significant contribution to the research community and to the advancement of cellular graphene-based sensors, as it consolidates the most recent research findings from around the world and critically analyzes a spectrum of different cellular graphene fabrication processes, systematically comparing the fabrication method against the materials’ strain and pressure sensing performance.

The review paper is a result of the research work that has been carried out by Dr. Liao’s research group over the past few years. The main research interest of his group is 2D and 3D assembly of heterogeneous two-dimensional materials (including graphene), and their advanced applications in strain- and pressure-sensing, electromagnetic interference shielding, and electrochemical energy storage. Currently a team lead by Dr. Liao and Dr. Rashid Abualrub, Interim Chair and Professor of Aerospace Engineering, is developing cellular graphene lattice, or intricately designed microstructures built by graphene sheets, derived from 3D printed scaffolds.

Most importantly, the paper points out that future research efforts should focus on in-depth understanding of structure-property-function correlations of cellular graphene-based sensors and generalization of design principles to be applied during fabrication of other 2D materials-based sensors. (“Structure” refers to whether the cellular graphene consists of struts or spherical cells or cells of other geometry, in micrometer scale; “property” refers to thermo-electro-mechanical properties that depend on or are derived from a specific structure of the foam, such as a closed spherical cell structure; and “function” refers to how those properties can be utilized to make something useful, such as sensors.)

The potential applications of cellular graphene and 2D materials are diverse. Thus, Dr. Liao’s review will benefit a broad range of researchers in the UAE and around the world on future research directions in strategic areas not only in strain sensing and biomedical applications but also in energy storage.

Erica Solomon
Senior Editor
13 November 2019

The post Flexible, Wearable and Ultra-Sensitive Strain and Pressure Sensors with Cellular Graphene appeared first on Khalifa University.