Novel Low Temperature Routes to Metal Sulfides

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TECHNICAL SUMMARY:Non-oxide materials have increasingly attracted the interest of researchers, as many advanced applications in optoelectronics, catalysis, energy and other fields require properties that are difficult or impossible to achieve with oxides. While these materials can be air-sensitive, the improvement in performance offsets the difficulties in handling and protecting the compounds. Metal sulfides have received attention because of their catalytic, electronic and optical properties. Many applications depend on the quality of the sulfide materials. Homogeneity, low oxidation state, glassy structure, or high surface area are often desirable. Traditional solid-state methods require high temperatures to overcome diffusion-related kinetic barriers, restricting products to thermodynamically stable phases, and prohibiting control over grain size or surface area. The growing demand for advanced materials has led to the exploration of a variety of alternative low temperature methods. This proposal introduces a novel low temperature route by extending non-hydrolytic sol-gel (NHSG) chemistry to the synthesis of metal sulfides. The specific objectives of the proposed research are: 1) To gain a thorough understanding of synthetic variable space of non-hydrolytic sol-gel processes for selected binary metal sulfide systems, 2) to explore phase space by NHSG chemistry to discover new binary metal sulfides, and 3) to explore NHSG routes for the synthesis of ternary or quarternary sulfides. Students will be trained in novel low temperature routes, synthesis of air-sensitive materials, and a number of solid-state characterization methods applied to air-sensitive materials. Naturally occurring sulfide mineral crystals will be used in outreach projects to expose the public to basic crystallography, as well as to the importance of sulfides. Solar cell materials or geomarkers like troilite will be used as examples to connect with non-scientists. This research is supported by the NSF Solid-State and Materials Chemistry/Division of Materials Research program.NON-TECHNICAL SUMMARY: Most metals readily form oxides when heated in air. This has made them the most widely explored class of solids, and resulted in many applications. However, some applications require properties that are difficult or impossible to achieve with oxides, which has spurred interest in the synthesis and characterization of non-oxide materials like metal sulfides. Metal sulfides have found use as catalysts in oil cracking, solid lubricants, solar cells, electrodes in battery materials, light emitting diodes, and many other technologically important fields. Some of these applications require materials with very high purity, controlled oxidation state, crystal structure, and morphology. This proposal will explore a novel synthetic method, which will allow the preparation of metal sulfides at low temperatures, and can offer control over oxidation state, crystal structure, surface area, and the resulting properties of the materials. In addition, it is likely that new metal sulfides with unexplored properties will be obtained by this approach. These materials will be characterized in detail, and their properties may lead to novel applications. Graduate and undergraduate students will be trained in synthesis and characterization of solid-state materials, with particular emphasis on handling air-sensitive materials. Women and minority students will be actively recruited. Exchange students will work on the project on six month internships, adding to the diversity of the research group. In addition, outreach programs related to naturally occurring sulfide minerals and technologically important sulfides will be designed to give the general public an appreciation for crystallography and materials chemistry, with particular emphasis on the less well known non-oxide materials. This research is supported by the NSF Solid-State and Materials Chemistry/Division of Materials Research program.