Science Concentrates SURFACE CHEMISTRY
Analyzing CO oxidation on Pt beam to shoot CO at an O2-bound Pt surface at precise times and then employed slice-ion imaging to determine the reaction site, speed, and escape angle for specific terrace sites produced both hyperthermal CO2 molecules flying off the surface. These A new surface chemistry technique has and thermal CO2. allowed researchers to determine the longtools had not been used together before sought mechanisms of one of the most to measure the speed and direction of surTheofanis N. Kitsopoulos at Max studied reactions in heterogeneous catalyface-generated species. Planck Institute for Biophysical Chemsis: the oxidation of carbon monoxide on a The study shows that the reaction has istry and coworkers now provide a more platinum surface. three mechanisms. Two produce thermal nuanced view (Nature 2018, DOI: 10.1038/ Catalytic CO oxidation cleans up emisCO2 and predominate at temperatures s41586-018-0188-x). They used a molecular sions from motor vehicles and below about 700 K: Either terrace industrial smokestacks. Studied CO diffuses to a step and reacts for about 40 years, it is a textbook there with an oxygen atom, or CO system for the experimental and already on a step reacts with step theoretical understanding of hetO. In the third mechanism, preerogeneous oxidations—gaseous dominant at high temperatures, reactions on catalytic surfaces. terrace CO reacts with terrace O The CO reaction is complex. Pt to make hyperthermal CO2. surfaces have two possible active The results “are phenomenal,” sites. About 99% of each surface says surface chemist Dan Killelea is flat terraces with moderate catof Loyola University Chicago. alytic activity, and the other 1% is “The ability to experimentally dishighly active steps between layers tinguish among different possible of Pt atoms. The reaction also procatalytic reaction sites on a surface duces two types of CO2 molecules: is a long-sought goal” that the new approach makes possible. hyperthermal, with high energies The strategy could be applied to and velocities, and thermal, with other heterogeneous surface reacmoderate energies and speeds. tions as well. “It has the potential Scientists have lacked analytical to shift the entire focus of efforts tools to unpack these complexito understand mechanisms of hetties, so the exact mechanisms by which CO gets oxidized have been A timed beam of CO molecules hits a Pt surface, where CO erogeneously catalyzed chemical reactions,” Killelea says.—STU a mystery. The consensus view was is oxidized to CO2. Laser slice-ion imaging (vertical blue that a single type of reaction on dashed line) measures properties of the released CO2. BORMAN
MATERIALS
‘Green’ coating protects plastics Devices that can flex and stretch, including wearable electronics, roll-up solar cells, and foldable displays, are all the rage these days. Engineers design those devices to keep working, bend after bend. A tough, transparent, eco-friendly coating applied to the plastic support might help those devices last even longer, a study suggests (ACS Nano 2018, DOI: 10.1021/acsnano.8b01057). Many plastic devices have thin coatings designed to go unnoticed. Measuring just a fraction of a micrometer in thickness, these nearly invisible films of organic and inorganic materials improve a wide range of commercial products. For example, polysi-
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C&EN | CEN.ACS.ORG | JUNE 18, 2018
loxane coatings on polycarbonate eyeglass lenses make them scratch resistant. Knowing that manufacturers are always on the lookout for new types of cost-effective coatings, a team led by Stanford University materials scientists Farhan Ansari and Reinhold H. Dauskardt looked to an unusual place for source material—the forest. The team made hybrid coatings by embedding various concentrations of nanocellulose fibrils, a tough material derived from trees, in a glass matrix composed of zirconium alkoxide and an epoxy-functionalized silane. The team used low-cost
colloidal chemistry methods to prepare the precursor solutions and then sprayed the mixtures onto flexible polymer substrates, including poly(ether imide) and poly(ethylene terephthalate), and then cured the films at low temperature. The results were highly transparent, nanometer-thick films. Tests indicate that coatings containing 20 wt % nanocellulose protect the polymer substrates by boosting hardness and fracture resistance. Microscopy analysis shows that even after 20,000 bending cycles, the films revealed no signs of delamination or cracking.—MITCH JACOBY
C R E D I T: NAT UR E
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New surface chemistry method answers mechanistic questions that have eluded chemists for 40 years
