Enhanced resistance to chloride interference in Hg(II) adsorption by thiourea-functionalized poly(pyrrole methane)

Adsorption method is an effective method to remove highly toxic mercury ions from water, but the inhibition of chloride ions (Cl⁻) on Hg(II) adsorption cannot be ignored. In this study, a thiourea-functionalized poly(pyrrole methane) (PPD4AlBA/thio) was successfully prepared through a Schiff base reaction to significantly enhance resistance to Cl- interference during Hg(II) adsorption process. The initial adsorption rate ( h _initial ) of unfunctionalized poly(pyrrole methane) was reduced by 80.9% (from 1071.63 to 204.42 mg·g⁻¹·min⁻¹), the maximum theoretical adsorption capacity ( Q _max ) was reduced by 79.5% (from 1294 to 265 mg·g⁻¹ at 318 K), and the distribution coefficient ( K _d) was reduced by 2 orders of magnitude (the initial concentration was 10 mg L⁻¹). However, the inhibitory effect of Cl⁻ on PPD4AlBA/thio was significantly weakened, which only inhibited the h _initial by 28.7% (from 1508.42 to 1074.79 mg·g⁻¹·min⁻¹), the Q _max by 50.6% (from 1572 to 777 mg·g⁻¹ at 318 K), and the distribution coefficient increased slightly at the initial concentration of 10 mg L⁻¹. Mechanistic studies revealed that the C S group in the thiourea structure played a crucial role in weakening the inhibition of Cl⁻ on Hg(II) adsorption. Additionally, the -NH₂ and C=N-N groups also serviced as additional adsorption sites contributing to the Hg(II) adsorption.