Visible light-driven NH2Cl activation by g-C3N4 photocatalysis producing reactive nitrogen species to degrade bisphenol A

The photolysis of monochloramine (NH2Cl), a widely used disinfectant, under UVC irradiation produces different radicals for the micropollutant degradation. For the first time, this study demonstrates the degradation of bisphenol A (BPA) via the NH2Cl activation by graphitic carbon nitride (g-C3N4) photocatalysis using visible light-LEDs at 420 nm, termed as the Vis420/g-C3N4/NH2Cl process. The process produces center dot NH2, center dot NH2OO, center dot NO and center dot NO2 via the e(-)CB- and O-2(center dot-)-induced activation pathways and center dot NHCl and NHClOO center dot via the h+VB-induced activation pathway. The produced reactive nitrogen species (RNS) enhanced 100% of the BPA degradation compared with the Vis420/g-C3N4. Density functional theory calculations confirmed the proposed NH2Cl acti-vation pathways and further demonstrated that e(-) CB/O-2(center dot-) and h+VBinduced the cleavage of N-Cl and N-H bonds in NH2Cl, respectively. The process converted 73.5% of the decomposed NH2Cl to nitrogen-containing gas, compared with that of approximately 20% in the UVC/NH2Cl process, leaving much less ammonia, nitrite and nitrate in water. Among different operating conditions and water matrices tested, of particular significance is natural organic matter of 5 mgDOC/L only reduced 13.1% of the BPA degradation compared against that of at least 46% reduction in the UVC/NH2Cl process. Only 0.017-0.161 mu g/L of disinfection byproducts were pro-duced, two orders of magnitudes lower than that in the UVC/chlorine and UVC/NH2Cl processes. The combined use of visible light-LEDs, g-C3N4 and NH2Cl significantly improves the micropollutant degradation and reduces the energy consumption and byproduct formation of the NH2Cl-based AOP.

Automated summary

This study demonstrates the degradation of bisphenol A (BPA) via the activation of monochloramine (NH2Cl) by graphitic carbon nitride (g-C3N4) photocatalysis using visible light-LEDs at 420 nm. The reactive nitrogen species (RNS) produced in this process enhance 100% of the BPA degradation compared with the traditional method. The process also significantly reduces the formation of disinfection byproducts.