Reports: G10 48520-G10: Synthesis of Novel Oxynitride Structures by Soft Chemical Routes

Neal M. Abrams, State University of New York College of Envrionmental Science and Forestry

The essence of this research is to explore novel low-temperature solvothermal routes to obtain stable and metastable oxynitride materials.  The ability to synthesize new oxynitride materials provides fundamental understanding of low temperature synthetic techniques as well as potentially new water-splitting photocatalysts.  Additionally, as an educator I am passionate about involving undergraduates in the research process.  I have developed this research project with undergraduate researchers in mind so they too can become part of the discovery process.  To date, four undergraduate students have participated in the project, including three full-time summer research students.

As the first solid-state inorganic chemist in the department, I have been given me the opportunity to obtain all of the necessary pieces of equipment needed for my research. Chronologically, the project began with the acquisition of equipment and supplies required to complete the proposed work.  To this end, funds from the PRF award have been able to fully or partially fund the purchase of 1) a box furnace, 2) tube furnace, 3) UV-vis spectrophotometer, 4) departmental FTIR spectrometer,
5) high-pressure reaction bomb, 6) Xenon lamp and power supply 7) assorted lab supplies, and 8) provide stipend support for the PI, two summer students, and 9) travel to an ACS National Meeting (Boston). 

Over the course of this year, the original project was split into two sub-areas.  In the first and original proposed work, undergraduate students have been at work synthesizing literature compounds and attempting to synthesize these same compounds through novel solvothermal methods.  To date, compounds have been limited to lanthanum titanium oxynitride, LaTiO2N and cerium oxynitride, Ce0.5Zr0.5OxN1-x. The students have used sol-gel methods to synthesize mixed-metal precursor compounds using literature-based polymerized-complex (PC) methods via in-situ ethylene glycol-citric acid polymerization.  The PC method is used as it facilitates the synthesis of stoichiometric high surface area oxide compounds that can be reduced to an oxynitride under flowing ammonia or potentially using high-pressure solvothermal techniques.  To date, we have successfully synthesized the above named oxide precursors, as evidenced by XRD and elemental analysis.  Over the course of the summer, we worked to systematically ascertain the appropriate reaction conditions (precursor, reducing agent concentration, temperature) for these oxynitrides. We are synthesizing these compounds under low-temperature, high-pressure solvothermal conditions in aprotic solvents (toluene) and aggressive reducing agents such as sodium azide.  Solvothermal methods are desired as the solvent can reduce the diffusion barrier among solid-phase reactants. To date, we have successfully synthesized a nitrogen containing Ce0.5Zr0.5O2 precursor that, when annealed, results in the oxynitride as evidenced by both thermogravimetric and X-ray analysis.  This is very exciting as it is the first example of low temperature oxynitride synthesis. We are now working to qualify the importance of the solvothermal technique compared to a standard “dry” solid-state reaction under similar temperature conditions.  We are also studying the LaTiO2N compound for photocatalytic light-splitting properties.

Towards the end of last year’s summer research season, one student began to explore novel biomimetic templating techniques with oxynitride compounds.  This was expanded upon during the 2009-2010 academic year and this past summer.  We have successfully templated oxides and oxynitrides, SrAlO4 and LaTiO2N specifically, from wood (pine) using a similar polymerized-complex reaction method and we are currently working to improve the process to yield more durable replicas.  We are also working to determine the appropriate pre-treatment methods for the wood template.  This second-project has the potential to make a significant impact in the field of high-surface area materials and green chemistry, since the template materials are not only natural and renewable, but the oxynitride products are known water-splitting photocatalysts.  This work is being carried out in conjunction with an ESF faculty member specializing in wood anatomy and is the subject of an ESF new-research award and new collaboration with a German colleague.  Work was recently presented at the ACS National Meeting in Boston.

Students in my lab have received an excellent background in various chemistries and techniques, ranging from organic to inorganic and materials work and from simple distillation to x-ray powder diffraction.  For all of the students involved in the project to date, this has been the first, if not only, opportunity for them to explore this type chemistry.  One research student, Josh McEnaney, carried on from the semester’s work whereas the other, Jessica Nordby, was not only new to my lab, but new to the College.  She is an incoming transfer student from a local community college.  Although her chemistry background was not as founded in textbook learning, she showed exceptional prowess in reading the literature and developing experimental protocols.  Both students are active in our Chemistry Club, keeping them very involved with both Outreach and Research while being academically top-performing students.   

Professionally, the ACS PRF award has allowed me to explore my proposed research and explore new research avenues, making connections among on- and off-campus colleagues, and seek additional funding for continued support.  I was able to travel to the Boston ACS national meeting (partially funded by the Younger Chemists Committee (YCC), as well).  I was recently awarded an “ESF Seed” award by the College ($8,000), an award designed for new startup projects, specifically the biomimcry aspect of my work.   PRF recently granted me a one-year extension for this award, allowing me more time to explore this research and prepare for more funding opportunities.

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