Deep-sea molecular sieves surface in lab.

Several decades ago, scientists discovered deep on the ocean floor nodules containing materials that performed remarkably well in the laboratory as catalysts that speed oxidation reactions. Unfortunately these porous manganese oxides - called todorokites - never became commercially useful because they were scarce and occurred as mixtures too difficult to separate. Predicting that the pure materials could serve as "molecular sieves" that adsorb substances into their crystalline channels, researchers long hoped to make synthetic todorokites.

Now chemists can create the promising materials in the lab, a team from the University of Connecticut in Storrs and the Texaco Research Center in Beacon, N.Y., announces in the April 23 SCIENCE. Unlike the products of previous attempts, the synthetic todorokite retains its basic properties at temperatures up to 500 degrees C. And it fulfills scientists' original hopes.

"These substances make good oxidation catalysts, sorbents, and electrical conductors," says Connecticut's Steven L. Suib. "They're very interesting materials."

Todorokite captured the attention of chemists because of its large pores and ability to selectively soak up and then release positively charged cations, much as zeolites do (SN: 8/3/91, p.77). Todorokite offers intriguing possibilities for catalysis and electrical conduction because its manganese accepts varied numbers of electrons.

To build their crystals, Suib's group developed a new synthesis method using doubly charged manganese cations and potassium permanganate mixed together at a very alkaline pH of 13.8. A layer of clay-like material precipitated, to which they added magnesium cations that settled into specific grooves. For a week, the crystals grew around these cations, forming tunnels. Then the material was heated to about 170 degrees C for five days to set the structure. The new todorokite - a black powder - performs as well as commercial oxidation catalysts commonly used in processing hydrocarbons, the team reports.

Kathleen Carrado at Argonne (III.) National Laboratory calls this work "extremely relevant to industrially important technologies." She and her colleagues propose to study synthetic todorokites for use as cathodes in rechargeable lithium batteries. Suib's group is now modifying its synthesis technique to make derivatives for a wide variety of applications.