Reduction of perchlorate in dilute aqueous solutions over monometallic nano-catalysts: Exemplified by tin

Perchlorate removal in a clean, cost-effective and publicly acceptable manner is of the utmost importance as far as drinking water treatment is concerned. An electrodialytically assisted catalytic membrane system was developed for the reduction of perchlorate in dilute aqueous solutions. The catalyst support (membrane) was a stainless steel mesh coated with specific monometallic catalysts. A total of 18 metals covering the first, the second and the third row of the periodical table were tested. Results indicated that the perchlorate reduction rate followed the order: Cd > Pt > Cr > Mo > Sc ≫ Rh > Ru ∼ Sn > Pd > V ∼ Ti > Zn > Mn > Ni > Zr > Co > Cu > Pb. Due to its environmental benignity and relatively low material cost, tin was selected for further evaluation in spite of its moderate reaction rate. Results indicated that perchlorate reduction took place rapidly in the concentration range of 2–100 ppm at room temperature and chloride was the major end product. The reaction followed the Langmuir–Hinshelwood rate expression. Based on the activation energy obtained, i.e., 49.8 kJ mol−1 K, it is clear that surface reaction, not mass transfer, was the rate-limiting step. SEM images showed the formation of metallic catalyst in the size of nano-scale over the stainless steel mesh support. X-ray photoelectron spectroscopy (XPS) survey of the metallic catalyst indicated the presence of metal oxide and elemental metals. X-ray diffraction (XRD) spectra showed the presence of amorphous metallic catalysts.