Rapid adsorption and reductive degradation of Naphthol Green B from aqueous solution by Polypyrrole/Attapulgite composites supported nanoscale zero-valent iron

Polypyrrole/Attapulgite-supported nanoscale zero-valent iron (PPy/APT-nZVI) composites employed to extract Naphthol Green B (NGB) from aqueous solution, were successfully fabricated by chemical oxidative polymerization and liquid-phase reduction method. Comparison experiment of different materials showed that 99.59% of NGB was removed using PPy/APT-nZVI (1:0.5) after 25 min, much higher than APT, PPy, PPy/APT and nZVI. The morphology and structure of PPy/APT-nZVI (1:0.5) composites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), which confirmed the high disperse and activity of nZVI after supported by PPy/APT. Furthermore, dynamic studies revealed that removal process was highly consistent with not only the pseudo-second-order model for adsorption but also pseudo-first-order model for degradation process, which proved the removal was controlled by chemical surface-limiting step. A possible removal mechanism, containing prompt adsorption of NGB onto the PPy/APT-nZVI (1:0.5) surface and being degraded by nZVI, was put forward. Additionally, the stability study verified the activity of nZVI can retain longer time than that of single nZVI due to such powerfully protective layers of PPy/APT.