Cyanide contaminated water treatment by di-nuclear Cu(II)-cryptate: A supramolecular approach

Y A popular Cu(II) based metallo-cage cryptate, Complex 1 [LCu2(ClO4)(4)], is synthesized by using a bicyclic cryptand, L (synthesized in large scale of approximate to 28 gm/batch) and Cu(ClO4)(2) for its application towards the removal of toxic CN- from cyanide contaminated water and cyanide containing industrial blast furnace (BF) wastewater. Complex 1, having very low solubility in aqueous medium, showed efficient removal of CN- (initial CN- conc. of 80 ppm to final conc. of 4.21 ppm; approximate to 95 % removal of CN-) from standard aqueous solution of CN- (NaCN in water) within 10 min, through heterogeneous phase mixing as observed from Ion Selective Electrode (ISE) based measurements. Mechanistic investigation towards the binding of cyanide with complex 1 through spectroscopic studies indicated the initial formation of CN- bridged green dimeric copper (II) complex upon addition of one equivalent of CN- which subsequently decomposed upon addition of further equivalents of CN- to produce a colourless solution. Finally, as a real-time application, complex 1 was treated with cyanide contaminated industrial wastewater in the presence of other interfering anions (e.g. Cl-, SO42-, NO3-, NO2-, SCN-, F- etc.) which showed fast and efficient removal of cyanide (initial CN- conc. of 6.7 ppm to final conc. of 1.3 ppm; approximate to 77 % removal of CN- in 30 min) of BF wastewater from lab scale to pilot plant scale. Interestingly, the complex 1 showed recyclability up to six cycles in terms of removal of cyanide with high efficiency (approximate to 72-74 % removal of CN-).