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News Article | July 31, 2017
Site: www.eurekalert.org

Inspired by nature, an inexpensive green technique that enables common materials to repel liquid has been developed by KAUST scientists and could lead to diverse applications from underwater drag reduction to antifouling. Making surfaces liquid repellent, referred to as omniphobicity, is used in a range of industrial processes from reducing biofouling and underwater drag to membrane distillation, waterproofing and oil-water separation. Producing such a veneer generally relies on applying perfluorinated coatings; however, these degrade under harsh physical and chemical environments, increasing costs and both health and environmental impacts and limiting their use. Rendering conventional materials, such as plastics and metals, omniphobic has been a tantalizing goal for some time; this challenge led Himanshu Mishra and colleagues from the KAUST Water Desalination and Reuse Center to seek inspiration from nature. The researchers first tested microtextures comprising doubly reentrant pillars: they were inspired by a US-based research team who, in 2014, demonstrated these pillars exhibited unprecedented omniphobicity in air, even when the materials were intrinsically wetting. "At first, these results seemed to defy conventional wisdom as roughening intrinsically wetting surfaces makes them even more wetting," said Mishra. "So we decided to investigate these microtextures for ourselves." The team confirmed that intrinsically wetting surfaces with doubly reentrant micropillars do indeed exhibit omniphobicity in air, but they also found that it was catastrophically lost in the presence of localized physical defects or damage or upon immersion in wetting liquids. "These were serious limitations because real surfaces get damaged during use," said Mishra. "This inspired us to look to nature and investigate the skins of springtails." Patterns on the skin of springtails--tiny soil-dwelling insects that live in moist conditions--exploit surface textures that contain doubly reentrant cavities, keeping them dry. By using photolithography and dry-etching tools at the KAUST Nanofabrication Core Lab, the researchers recreated these doubly reentrant microcavities on silica surfaces. Taking advantage of the doubly reentrant features showed that the microcavities trapped air and prevented penetration of liquids, even under elevated pressures. In addition, their compartmentalized nature prevented any loss of omniphobicity in the presence of localized damage or defects or upon immersion in wetting liquids. "Having demonstrated the proof of concept, we now plan to translate the fabrication process from the lab to the Workshop Core Lab in KAUST to create doubly reentrant cavities on common materials, such as polyethylene terephthalate and low-carbon steels," said Mishra. "This may help to unlock their potential for applications to reduce hydrodynamic drag and antifouling."


News Article | July 31, 2017
Site: phys.org

Making surfaces liquid repellent, referred to as omniphobicity, is used in a range of industrial processes from reducing biofouling and underwater drag to membrane distillation, waterproofing and oil-water separation. Producing such a veneer generally relies on applying perfluorinated coatings; however, these degrade under harsh physical and chemical environments, increasing costs and both health and environmental impacts and limiting their use. Rendering conventional materials, such as plastics and metals, omniphobic has been a tantalizing goal for some time; this challenge led Himanshu Mishra and colleagues from the KAUST Water Desalination and Reuse Center to seek inspiration from nature. The researchers first tested microtextures comprising doubly reentrant pillars: they were inspired by a US-based research team who, in 2014, demonstrated these pillars exhibited unprecedented omniphobicity in air, even when the materials were intrinsically wetting. "At first, these results seemed to defy conventional wisdom as roughening intrinsically wetting surfaces makes them even more wetting," said Mishra. "So we decided to investigate these microtextures for ourselves." The team confirmed that intrinsically wetting surfaces with doubly reentrant micropillars do indeed exhibit omniphobicity in air, but they also found that it was catastrophically lost in the presence of localized physical defects or damage or upon immersion in wetting liquids. "These were serious limitations because real surfaces get damaged during use," said Mishra. "This inspired us to look to nature and investigate the skins of springtails." Patterns on the skin of springtails—tiny soil-dwelling insects that live in moist conditions—exploit surface textures that contain doubly reentrant cavities, keeping them dry. By using photolithography and dry-etching tools at the KAUST Nanofabrication Core Lab, the researchers recreated these doubly reentrant microcavities on silica surfaces. Taking advantage of the doubly reentrant features showed that the microcavities trapped air and prevented penetration of liquids, even under elevated pressures. In addition, their compartmentalized nature prevented any loss of omniphobicity in the presence of localized damage or defects or upon immersion in wetting liquids. "Having demonstrated the proof of concept, we now plan to translate the fabrication process from the lab to the Workshop Core Lab in KAUST to create doubly reentrant cavities on common materials, such as polyethylene terephthalate and low-carbon steels," said Mishra. "This may help to unlock their potential for applications to reduce hydrodynamic drag and antifouling." More information: Domingues, E.M., Arunachalam, S. & Mishra, H. Prevention of catastrophic wetting transitions on intrinsically wetting surfaces by doubly reentrant cavities. Applied Materials & Interfaces 9, 21532-21538 (2017)


News Article | June 19, 2017
Site: www.eurekalert.org

Materials called transition-metal carbides have remarkable properties that open new possibilities in water desalination and wastewater treatment. A KAUST team has found compounds of transition metals and carbon, known as a MXenes but pronounced "maxenes," can efficiently evaporate water using power supplied by the sun1. Renyuan Li, a Ph.D. student at KAUST, has investigated a MXene in which titanium and carbon combine with the formula Ti3C2. "This is a very exciting material," said Associate Professor Peng Wang, Li's supervisor at the KAUST Water Desalination and Reuse Center. Wang explains his excitement comes from their finding that Ti3C2 can trap the energy of sunlight to purify water by evaporation with an energy efficiency that is "state of the art." He says this clearly justifies more research toward practical applications. Other researchers had explored the ability of MXenes to act as electromagnetic shielding materials due to their ability to absorb wavelengths of electromagnetic radiation beyond the visible range. So the KAUST discovery began with a simple question. "We decided to investigate, what is the interaction with this MXene and sunlight?" Wang explained. With his group's focus on desalination technology, using the sun's energy to convert water into steam was an obvious target. The KAUST team's first observation was that Ti3C2 converts the energy of sunlight to heat with 100% efficiency. Also important, however, was that the sophisticated system developed during this research to measure light-to-heat conversion showed that various other materials, including carbon nanotubes and graphene, also achieved almost perfectly efficient conversion. "I suggest the focus of the field should now move away from finding new photothermal materials toward finding applications for the many perfect ones we now have," said Wang. To investigate MXene's possibilities in water purification, the researchers then fabricated a thin and flexible Ti3C2 membrane incorporating a polystyrene heat barrier to prevent the heat energy from escaping. This created a system that could float on water and evaporate some of the water with 84% efficiency at the illumination levels of natural sunlight. For Wang, the next challenge is how to move from this basic research finding toward practical applications. Wang hopes to break through what he calls "the 85% efficiency barrier," taking photo-thermal purification of water into new territory. In addition to maximizing the system's light-trapping capacity, the researchers want to investigate ways to capture the water vapor and yield a complete water purifying process. Wang is already in talks with one potential industrial partner.


Scientists have long assumed that the capacity of water-harvesting surfaces to interact with water—their wettability—should be a crucial factor in their performance, but this latest research at KAUST reveals a surprise. "Whether a surface 'loves' or 'hates' water does not matter that much for its final water-harvesting performance," says Peng Wang of the KAUST Water Desalination and Reuse Center. Wang's use of the terms love and hate reflects the technical distinction between surfaces that are hydrophilic (water loving) and hydrophobic (water hating). Research at KAUST aims to improve the efficiency of collection methods for water harvesting—an important source of drinking water in regions with little rainfall but high humidity—through considering the influence of attributes of different surfaces, including wettability and edge effect. Wang performed experimental and theoretical studies on the effect of surface wettability, edge structures and wettability hysteresis working with his Ph.D. student Yong Jin and Lianbin Zhang, a former researcher from his KAUST lab, who is now at Huazhong University in China. Rather than the surface's wettability properties being paramount, the team's research showed that variation in the edge of the surface structures significantly affects water-droplet formation, and that rough-edged structures mimicking some found in nature are highly effective. "Trying to develop artificial surfaces like the surface of a cactus seems a good way to go," says Wang. His earlier work also explored the water-catching power of the exoskeleton of desert beetles. Water harvesting can be achieved passively by either exposing a surface to humid air or actively, for example, by cooling the surface to encourage water condensation—similar to the operation of a domestic dehumidifier. Passive harvesting has a long history, with suspended fabrics used in several cultures to gather water from the air. "The field of water harvesting is both mature and primitive at the same time," explains Wang. "It is mature because of its ancient origins yet primitive because of the limited understanding of the efficiency of different surfaces." The team's future plans in this field will complement their related interest in using solar energy to evaporate seawater and wastewater to then condense purified liquid water from the resulting vapor. "The knowledge we are obtaining from studying atmospheric water harvesting will definitely be a help for other research," says Wang. Explore further: Using sunlight to the max More information: Yong Jin et al. Atmospheric Water Harvesting: Role of Surface Wettability and Edge Effect, Global Challenges (2017). DOI: 10.1002/gch2.201700019


News Article | August 14, 2017
Site: www.eurekalert.org

Water harvesting is an age-old technique of collecting atmospheric water vapor. Researchers are looking to nature to learn about the efficiency of surfaces used to collect the vapor. Scientists have long assumed that the capacity of water-harvesting surfaces to interact with water--their wettability--should be a crucial factor in their performance, but this latest research at KAUST reveals a surprise. "Whether a surface 'loves' or 'hates' water does not matter that much for its final water-harvesting performance," says Peng Wang of the KAUST Water Desalination and Reuse Center. Wang's use of the terms love and hate reflects the technical distinction between surfaces that are hydrophilic (water loving) and hydrophobic (water hating). Research at KAUST aims to improve the efficiency of collection methods for water harvesting--an important source of drinking water in regions with little rainfall but high humidity--through considering the influence of attributes of different surfaces, including wettability and edge effect. Wang performed experimental and theoretical studies on the effect of surface wettability, edge structures and wettability hysteresis working with his Ph.D. student Yong Jin and Lianbin Zhang, a former researcher from his KAUST lab, who is now at Huazhong University in China. Rather than the surface's wettability properties being paramount, the team's research showed that variation in the edge of the surface structures significantly affects water-droplet formation, and that rough-edged structures mimicking some found in nature are highly effective. "Trying to develop artificial surfaces like the surface of a cactus seems a good way to go," says Wang. His earlier work also explored the water-catching power of the exoskeleton of desert beetles. Water harvesting can be achieved passively by either exposing a surface to humid air or actively, for example, by cooling the surface to encourage water condensation--similar to the operation of a domestic dehumidifier. Passive harvesting has a long history, with suspended fabrics used in several cultures to gather water from the air. "The field of water harvesting is both mature and primitive at the same time," explains Wang. "It is mature because of its ancient origins yet primitive because of the limited understanding of the efficiency of different surfaces." The team's future plans in this field will complement their related interest in using solar energy to evaporate seawater and wastewater to then condense purified liquid water from the resulting vapor. "The knowledge we are obtaining from studying atmospheric water harvesting will definitely be a help for other research," says Wang.


News Article | June 19, 2017
Site: phys.org

Renyuan Li, a Ph.D. student at KAUST, has investigated a MXene in which titanium and carbon combine with the formula Ti3C2. "This is a very exciting material," said Associate Professor Peng Wang, Li's supervisor at the KAUST Water Desalination and Reuse Center. Wang explains his excitement comes from their finding that Ti3C2 can trap the energy of sunlight to purify water by evaporation with an energy efficiency that is "state of the art." He says this clearly justifies more research toward practical applications. Other researchers had explored the ability of MXenes to act as electromagnetic shielding materials due to their ability to absorb wavelengths of electromagnetic radiation beyond the visible range. So the KAUST discovery began with a simple question. "We decided to investigate, what is the interaction with this MXene and sunlight?" Wang explained. With his group's focus on desalination technology, using the sun's energy to convert water into steam was an obvious target. The KAUST team's first observation was that Ti3C2 converts the energy of sunlight to heat with 100% efficiency. Also important, however, was that the sophisticated system developed during this research to measure light-to-heat conversion showed that various other materials, including carbon nanotubes and graphene, also achieved almost perfectly efficient conversion. "I suggest the focus of the field should now move away from finding new photothermal materials toward finding applications for the many perfect ones we now have," said Wang. To investigate MXene's possibilities in water purification, the researchers then fabricated a thin and flexible Ti3C2 membrane incorporating a polystyrene heat barrier to prevent the heat energy from escaping. This created a system that could float on water and evaporate some of the water with 84% efficiency at the illumination levels of natural sunlight. For Wang, the next challenge is how to move from this basic research finding toward practical applications. Wang hopes to break through what he calls "the 85% efficiency barrier," taking photo-thermal purification of water into new territory. In addition to maximizing the system's light-trapping capacity, the researchers want to investigate ways to capture the water vapor and yield a complete water purifying process. Wang is already in talks with one potential industrial partner. Explore further: MOFs provide a better way to remove water from gas More information: Renyuan Li et al. MXene TiC: An Effective 2D Light-to-Heat Conversion Material, ACS Nano (2017). DOI: 10.1021/acsnano.6b08415


News Article | June 19, 2017
Site: www.cemag.us

Materials called transition-metal carbides have remarkable properties that open new possibilities in water desalination and wastewater treatment. A KAUST team has found compounds of transition metals and carbon, known as a MXenes but pronounced "maxenes," can efficiently evaporate water using power supplied by the sun1. Renyuan Li, a Ph.D. student at KAUST, has investigated a MXene in which titanium and carbon combine with the formula Ti3C2. "This is a very exciting material," said Associate Professor Peng Wang, Li's supervisor at the KAUST Water Desalination and Reuse Center. Wang explains his excitement comes from their finding that Ti3C2 can trap the energy of sunlight to purify water by evaporation with an energy efficiency that is "state of the art." He says this clearly justifies more research toward practical applications. Other researchers had explored the ability of MXenes to act as electromagnetic shielding materials due to their ability to absorb wavelengths of electromagnetic radiation beyond the visible range. So the KAUST discovery began with a simple question. "We decided to investigate, what is the interaction with this MXene and sunlight?" Wang explained. With his group's focus on desalination technology, using the sun's energy to convert water into steam was an obvious target. The KAUST team's first observation was that Ti3C2 converts the energy of sunlight to heat with 100% efficiency. Also important, however, was that the sophisticated system developed during this research to measure light-to-heat conversion showed that various other materials, including carbon nanotubes and graphene, also achieved almost perfectly efficient conversion. "I suggest the focus of the field should now move away from finding new photothermal materials toward finding applications for the many perfect ones we now have," said Wang. To investigate MXene's possibilities in water purification, the researchers then fabricated a thin and flexible Ti3C2 membrane incorporating a polystyrene heat barrier to prevent the heat energy from escaping. This created a system that could float on water and evaporate some of the water with 84% efficiency at the illumination levels of natural sunlight. For Wang, the next challenge is how to move from this basic research finding toward practical applications. Wang hopes to break through what he calls "the 85% efficiency barrier," taking photo-thermal purification of water into new territory. In addition to maximizing the system's light-trapping capacity, the researchers want to investigate ways to capture the water vapor and yield a complete water purifying process. Wang is already in talks with one potential industrial partner.


Zhang Z.,Water Desalination and Reuse Center | Yang X.,Water Desalination and Reuse Center | Hedhili M.N.,King Abdullah University of Science and Technology | Ahmed E.,Water Desalination and Reuse Center | And 2 more authors.
ACS Applied Materials and Interfaces | Year: 2014

In this article, we report that the combination of microwave heating and ethylene glycol, a mild reducing agent, can induce Ti3+ self-doping in TiO2. A hierarchical TiO2 nanotube array with the top layer serving as TiO2 photonic crystals (TiO2 NTPCs) was selected as the base photoelectrode. The self-doped TiO2 NTPCs demonstrated a 10-fold increase in visible-light photocurrent density compared to the nondoped one, and the optimized saturation photocurrent density under simulated AM 1.5G illumination was identified to be 2.5 mA cm-2 at 1.23 V versus reversible hydrogen electrode, which is comparable to the highest values ever reported for TiO2-based photoelectrodes. The significant enhancement of photoelectrochemical performance can be ascribed to the rational coupling of morphological and electronic features of the self-doped TiO 2 NTPCs: (1) the periodically morphological structure of the photonic crystal layer traps broadband visible light, (2) the electronic interband state induced from self-doping of Ti3+ can be excited in the visible-light region, and (3) the captured light by the photonic crystal layer is absorbed by the self-doped interbands. © 2013 American Chemical Society.


Yu H.,King Abdullah University of Science and Technology | Qiu X.,King Abdullah University of Science and Technology | Nunes S.P.,Water Desalination and Reuse Center | Peinemann K.-V.,King Abdullah University of Science and Technology
Angewandte Chemie - International Edition | Year: 2014

The combination of nonsolvent-induced phase separation and the self-assembly of block copolymers can lead to asymmetric membranes with a thin highly ordered isoporous skin layer. The effective pore size of such membranes is usually larger than 15 nm. We reduced the pore size of these membranes by electroless gold deposition. We demonstrate that the pore sizes can be controlled precisely between 3 and 20 nm leading to a tunable sharp size discrimination in filtration processes. Besides fractionation of nanoparticles and biomaterials, controlled drug delivery is an attractive potential application. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Zhang Z.,Water Desalination and Reuse Center | Zhang L.,Water Desalination and Reuse Center | Hedhili M.N.,King Abdullah University of Science and Technology | Zhang H.,Water Desalination and Reuse Center | Wang P.,Water Desalination and Reuse Center
Nano Letters | Year: 2013

A visible light responsive plasmonic photocatalytic composite material is designed by rationally selecting Au nanocrystals and assembling them with the TiO2-based photonic crystal substrate. The selection of the Au nanocrystals is so that their surface plasmonic resonance (SPR) wavelength matches the photonic band gap of the photonic crystal and thus that the SPR of the Au receives remarkable assistance from the photonic crystal substrate. The design of the composite material is expected to significantly increase the Au SPR intensity and consequently boost the hot electron injection from the Au nanocrystals into the conduction band of TiO2, leading to a considerably enhanced water splitting performance of the material under visible light. A proof-of-concept example is provided by assembling 20 nm Au nanocrystals, with a SPR peak at 556 nm, onto the photonic crystal which is seamlessly connected on TiO2 nanotube array. Under visible light illumination (>420 nm), the designed material produced a photocurrent density of ∼150 μA cm-2, which is the highest value ever reported in any plasmonic Au/TiO2 system under visible light irradiation due to the photonic crystal-assisted SPR. This work contributes to the rational design of the visible light responsive plasmonic photocatalytic composite material based on wide band gap metal oxides for photoelectrochemical applications. © 2012 American Chemical Society.

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