WO₃ as an Electron Exchange Matrix: A Novel and Efficient Treatment Method for Nitro Compounds

To minimize the use of the chemicals that have traditionally been needed to treat toxic organic compounds, a WO₃ electron exchange matrix (EEMWO₃), which requires fewer chemical solvents in line with green chemistry engineering principles, was developed for waste degradation. The EEMWO₃ was tested for its ability to remove 4-nitrophenol and 2-nitrophenol, which were chosen as models for common oxidizing toxic compounds. The nitrophenol was added in an initial amount of 7.19 × 10^-5 mol, which is a larger concentration than that reported to cause health problems. The conversion values were ∼(10-50)%, depending on the type of EEMWO₃ and on the substrate used. Ca. 10% of the WO₃ units in the matrix were observed to be reduced by BH₄^- to W(V), a value that is orders of magnitude better than that previously reported for EEM. The results indicate that the structure and the surface area of the EEMWO₃ are important parameters in the degradation process. The monoclinic hydrotungstite (WO₂(OH)₂·H₂O) was the reactive species. The same parameters also affected the recyclability of the process, and three cycles were possible with the commercial WO₃. The tungsten oxide functioned as an active EEM without an entrapped redox species and as a skeleton, indicating that one does not have to worry about the number of active species that can be entrapped in the matrix. It can be concluded that EEMWO₃ is an efficient treatment method for toxic, oxidizing organic compounds and that it is a greener method whose use requires fewer chemicals than conventional methods.