A computational method to quantify the adsorption of gas by porous zeolites should help labs know what to expect before they embark upon slow, costly experiments, according to researchers at Rice University.
The new method created by engineers in Rice’s Multiscale Materials Modeling Lab accurately calculated the ability of two zeolites, small cage-like molecules with enormous surface area, to trap and store gas molecules.
Among other possibilities, the work could help in the race to meet Department of Energy (DOE) standards that call for the creation by 2015 of materials that can hold 5.5 percent of their weight in hydrogen to fuel vehicles.
“We think we can get there,” said Rice materials scientist Rouzbeh Shahsavari, who calculated capacities for two of what he called “remarkably large and colossal cages” and found that one comes close to the mark.
The study by Shahsavari, graduate student Navid Sakhavand and former Rice postdoctoral researcher Prakash Muthuramalingam, now a postdoctoral researcher at Université Paris-Est, appears online in the American Chemical Society’s Journal of Physical Chemistry.
The lab analyzed a dizzying array of potential interactions for two synthetic microporous materials known as zeolitic imidazolate frameworks, ZIF-95 and ZIF-100. Those “colossal cages” may be only nanometers wide, but the molecules they can store that the lab looked at — hydrogen, methane and nitrogen – are much smaller. The zeolites’ enormous surface area inside and out gives gas molecules plenty of room to bind.
Aside from storing hydrogen for fuel, ZIFs show potential for size-selective catalysis, environmental remediation and for use as molecular sieves. “Imagine people are designing fit-for-purpose ZIFs,” Sakhavand said. “Before jumping into the experiment and synthesizing them, we can help them rapidly screen the gas uptake for each particular ZIF at various temperatures and pressures.”
The researchers’ primary goal was to prove the accuracy of their method when compared with a host of experimental results on hydrogen storage carried out elsewhere. Shahsavari said the researchers modeled the interactions between molecules of the three gases with each other and with the binding ligands in the zeolites at 77 and 300 kelvins (-321 and 80 degrees Fahrenheit, respectively) and at various pressures.
For hydrogen, they determined that both zeolites stored about three times as much gas at 77 K and at 100-bar pressure (100 times that of the atmosphere at sea level) than they would at room temperature. ZIF-100, in particular, adsorbed 3.4 percent of its weight in hydrogen, which approaches the DOE standard, Shahsavari said.
“We didn’t reach that DOE target with this design, but if we can functionalize the ZIFs by adding ligand-binding moieties (the functional groups in a molecule) into the pore space, then we might be able to. We’re working on that,” he said.
They were also able to calculate both subtle and significant differences between the adsorptive qualities based on various input parameters of gas, pressure, temperature and type of zeolite. For example, they came to the counterintuitive conclusion that ZIF-100, the larger of the two zeolites, could adsorb more small-molecule hydrogen but fewer of the larger methane molecules than ZIF-95 under similar conditions.
“So our method not only accurately predicts the properties of these porous materials, but also provides fundamental insights that can be leveraged to further improve their properties,” Shahsavari said.
The Rice lab’s method involved several steps. First, the team performed first-principle calculations to describe the very weak atomic interactions – the van der Waals-related London dispersion forces — among each of the three types of gas molecules and the two ZIFs. The next step used those results to align the potentials among various atomic pairs. Those were plugged into large-scale Monte Carlo simulations to predict how much of each gas each porous zeolite could adsorb.
“Because we combined two methods, each appropriate for a different length scale, we were able to predict the maximum capacity of these materials with high accuracy while maintaining reasonable computational time,” Shahsavari said.
The method may seem simple, but calculating integrative forces between thousands of gas molecules and each ZIF was not. It took the combined power of Rice’s DAVinCI and SUGAR supercomputers to find results for all the variations. Even so, calculations for a single data point – one molecule, one zeolite, one temperature – often took 96 processing cores three days to complete.
Shahsavari said the method should also be good for analyzing the potential for zeolites as membranes to separate gases. “It can work not only for single molecules, but also gas mixtures,” he said. “This provides a good computational framework so one can do rapid screening for the desired properties.”
Rice University, the National Institutes of Health, the National Science Foundation and an IBM Shared University Research Award in partnership with CISCO, Qlogic and Adaptive Computing supported the research. The Data Analysis and Visualization Cyber Infrastructure (DAVinCI) and Shared University Grid at Rice (SUGAR) supercomputers are administered by Rice’s Ken Kennedy Institute for Information Technology.
Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation’s top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,708 undergraduates and 2,374 graduate students, Rice’s undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice has been ranked No. 1 for best quality of life multiple times by the Princeton Review and No. 2 for “best value” among private universities by Kiplinger’s Personal Finance. To read “What they’re saying about Rice,” go to http://tinyurl.com/AboutRiceU.
David Ruth | EurekAlert!
Etching Microstructures with Lasers
25.10.2016 | Fraunhofer-Institut für Lasertechnik ILT
Applying electron beams to 3-D objects
23.09.2016 | Fraunhofer-Institut für Organische Elektronik, Elektronenstrahl- und Plasmatechnik FEP
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
19.01.2017 | Earth Sciences
19.01.2017 | Life Sciences
19.01.2017 | Physics and Astronomy