1. Department of Materials Science and Engineering; Massachusetts Institute of Technology; Cambridge MA 02139-4307 USA
2. College of Chemistry and Chemical Engineering; Key Laboratory of Biomass Fibers and Eco-dyeing & Finishing; Wuhan Textile University; Wuhan 430200 P. R. China
3. School of Metallurgy; Northeastern University; Shenyang 110819 P. R. China
4. Department of Chemistry; University of Texas; Austin TX 78712 USA