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Membrane breaks through performance barrier
RESEARCH NEWS
Membrane breaks through performance barrier SURFACE SCIENCE
Engineers have developed a new method for creating high-performance membranes from crystal sieves called zeolites; the method could increase the energy efficiency of chemical separations up to 50 times over conventional methods and enable higher production rates. Researchers led by chemical engineer Michael Tsapatsis of the University of Minnesota [Choi et al., DOI: 10.1126/science.1176095] reported this discovery in the July 31, 2009, issue of Science. Tsapatsis’s team developed a rapid heating treatment to remove structural defects in zeolite membranes that limit their performance, a problem that has plagued the technology for decades. This discovery could increase the energy efficiency of producing important chemical solvents for example; renewable biofuels such as ethanol and butanol. Conventional methods of creating zeolite membranes involves growing a film of crystals with small organic ions added to direct the crystal structure and pore size; two zeolite properties that help determine which molecules can pass through the material. Then they slowly heat the zeolite film in a process called
Membranes + defects (top), after RTP – defects (below).
calcination to decompose the ions and open the pores. This method for creating zeolite films often leaves cracks at the boundaries between grains of zeolite crystals. In an effort to minimize the formation of cracks and other defects, the heating rate during calcination must be very gentle, extending the length of the process to well over 40 hours. Tsapatsis’s team developed a treatment called Rapid Thermal Processing (RTP), a treatment in which zeolite film is heated to 700 degrees Celsius within one minute and kept at that
temperature for no more than two minutes. Acting as an annealing method, RTP refines the granular structure of the zeolite crystal film. When the researchers examined the RTP-treated films they found no evidence of cracks at grain boundaries. Although they found other types of defects, these don’t seem to affect the membrane properties or performance. In a comparison to conventionally-made zeolite membranes, Tsapatsis said, “We observed a dramatic improvement in the separation performance of the RTP-treated membranes.” A second round of RTP treatment improved separation performance even further to a level on par with current industry separation methods. The researchers demonstrated the RTP process on relatively thick (several micrometers) zeolite membranes. Tsapatsis and collaborators are now working towards making zeolite membranes 10 to 100 times thinner to allow molecules to pass through more quickly. They hope to eventually implement RTP treatment with its beneficial effects to these membranes as well. Jonathan Agbenyega
Climbing the walls – gecko-style BIOMATERIALS Two scientists have discovered that the ability of the gecko to grip onto smooth surfaces is actually triggered by gravity, and that it is the steepness of a surface that makes them deploy their gripping mechanism. These findings and future results may have applications in the medical world, space travel, and in robotics, to name but a few. The researchers, from the University of Calgary and Clemson University, have been examining how and when geckos use their specialized toepads to attach to surfaces under different circumstances. Published in the online edition of the Proceedings of the Royal Society [DOI: 10.1098/rspb.2009.0946], the research showed that the adhesive system was turned on when a surface was inclined to at least 10 degrees, regardless of the type of surface involved. It was known how geckos are able to stick to most surfaces but not what actually triggered the use of the adhesion system. The setae, the bristles that cover their toes, and the microscopic, hair-like filaments called spatulae that are attached to them, give the geckos the ability to grip, but it is also crucial that
they are able to turn the adhesion system on and off easily as they move across a surface. An interest in evolutionary biology and how animals respond to particular challenges led the researchers to explore how natural selection has created an system that enables geckos to deploy their special grip when needed. A key insight of their research was in showing the importance of feedback and perception for the gecko, when it was realised that geckos never use their clinging mechanism when on the horizontal, even when that surface is extremely slippery. Russell explains that “it may be disadvantageous for geckos to use their adhesive system on level surfaces. We know that it would slow them down, but we don’t know if there are other physical limitations that would render such a system less effective if not assisted by gravitational loading that can be experienced in body orientations beyond the horizontal.” The hope is that an understanding of the geckos’ in-built traction system will have commercial potential, from a use in space exploration, to military
Figure of a Gecko applications such as in bomb disposal, to medical uses such as bandages, or even in the area of robotics. As Higham points out, “a robot could potentially be faster when moving on a level surface by not adhering. When the robot encounters an incline, it could then deploy the system and climb.” Russell and Higham now aim to continue by observing different types, sizes and ages of gecko, to see how the adhesive system is deployed in other species of geckos, which will help them better understand the extensive diversity of such systems.
Laurie Donaldson
SEPTEMBER 2009 | VOLUME 12 | NUMBER 9
11
Membrane breaks through performance barrier SURFACE SCIENCE
Engineers have developed a new method for creating high-performance membranes from crystal sieves called zeolites; the method could increase the energy efficiency of chemical separations up to 50 times over conventional methods and enable higher production rates. Researchers led by chemical engineer Michael Tsapatsis of the University of Minnesota [Choi et al., DOI: 10.1126/science.1176095] reported this discovery in the July 31, 2009, issue of Science. Tsapatsis’s team developed a rapid heating treatment to remove structural defects in zeolite membranes that limit their performance, a problem that has plagued the technology for decades. This discovery could increase the energy efficiency of producing important chemical solvents for example; renewable biofuels such as ethanol and butanol. Conventional methods of creating zeolite membranes involves growing a film of crystals with small organic ions added to direct the crystal structure and pore size; two zeolite properties that help determine which molecules can pass through the material. Then they slowly heat the zeolite film in a process called
Membranes + defects (top), after RTP – defects (below).
calcination to decompose the ions and open the pores. This method for creating zeolite films often leaves cracks at the boundaries between grains of zeolite crystals. In an effort to minimize the formation of cracks and other defects, the heating rate during calcination must be very gentle, extending the length of the process to well over 40 hours. Tsapatsis’s team developed a treatment called Rapid Thermal Processing (RTP), a treatment in which zeolite film is heated to 700 degrees Celsius within one minute and kept at that
temperature for no more than two minutes. Acting as an annealing method, RTP refines the granular structure of the zeolite crystal film. When the researchers examined the RTP-treated films they found no evidence of cracks at grain boundaries. Although they found other types of defects, these don’t seem to affect the membrane properties or performance. In a comparison to conventionally-made zeolite membranes, Tsapatsis said, “We observed a dramatic improvement in the separation performance of the RTP-treated membranes.” A second round of RTP treatment improved separation performance even further to a level on par with current industry separation methods. The researchers demonstrated the RTP process on relatively thick (several micrometers) zeolite membranes. Tsapatsis and collaborators are now working towards making zeolite membranes 10 to 100 times thinner to allow molecules to pass through more quickly. They hope to eventually implement RTP treatment with its beneficial effects to these membranes as well. Jonathan Agbenyega
Climbing the walls – gecko-style BIOMATERIALS Two scientists have discovered that the ability of the gecko to grip onto smooth surfaces is actually triggered by gravity, and that it is the steepness of a surface that makes them deploy their gripping mechanism. These findings and future results may have applications in the medical world, space travel, and in robotics, to name but a few. The researchers, from the University of Calgary and Clemson University, have been examining how and when geckos use their specialized toepads to attach to surfaces under different circumstances. Published in the online edition of the Proceedings of the Royal Society [DOI: 10.1098/rspb.2009.0946], the research showed that the adhesive system was turned on when a surface was inclined to at least 10 degrees, regardless of the type of surface involved. It was known how geckos are able to stick to most surfaces but not what actually triggered the use of the adhesion system. The setae, the bristles that cover their toes, and the microscopic, hair-like filaments called spatulae that are attached to them, give the geckos the ability to grip, but it is also crucial that
they are able to turn the adhesion system on and off easily as they move across a surface. An interest in evolutionary biology and how animals respond to particular challenges led the researchers to explore how natural selection has created an system that enables geckos to deploy their special grip when needed. A key insight of their research was in showing the importance of feedback and perception for the gecko, when it was realised that geckos never use their clinging mechanism when on the horizontal, even when that surface is extremely slippery. Russell explains that “it may be disadvantageous for geckos to use their adhesive system on level surfaces. We know that it would slow them down, but we don’t know if there are other physical limitations that would render such a system less effective if not assisted by gravitational loading that can be experienced in body orientations beyond the horizontal.” The hope is that an understanding of the geckos’ in-built traction system will have commercial potential, from a use in space exploration, to military
Figure of a Gecko applications such as in bomb disposal, to medical uses such as bandages, or even in the area of robotics. As Higham points out, “a robot could potentially be faster when moving on a level surface by not adhering. When the robot encounters an incline, it could then deploy the system and climb.” Russell and Higham now aim to continue by observing different types, sizes and ages of gecko, to see how the adhesive system is deployed in other species of geckos, which will help them better understand the extensive diversity of such systems.
Laurie Donaldson
SEPTEMBER 2009 | VOLUME 12 | NUMBER 9
11