Redox sorption and recovery of silver ions as silver nanocrystals on poly(aniline-co-5-sulfo-2-anisidine) nanosorbents.

Poly[aniline(AN)-co-5-sulfo-2-anisidine(SA)] nanograins with rough and porous structure demonstrate ultrastrong adsorption and highly efficient recovery of silver ions. The effects of five key factors-AN/SA ratio, Ag(I) concentration, sorption time, ultrasonic treatment, and coexisting ions-on Ag(I) adsorbability were optimized, and AN/SA (50/50) copolymer nanograins were found to exhibit much stronger Ag(I) adsorption than polyaniline and all other reported sorbents. The maximal Ag(I) sorption capacity of up to 2034 mg g(-1) (18.86 mmol g(-1)) is the highest thus far and also much higher than the maximal Hg-ion sorption capacity (10.28 mmol g(-1)). Especially at <or=2 mM Ag(I), the nanosorbents exhibit >or=99.98 % adsorptivity, and thus achieve almost complete Ag(I) sorption. The sorption fits the Langmuir isotherm well and follows pseudo-second-order kinetics. Studies by IR, UV/Vis, X-ray diffraction, polarizing microscopy, centrifugation, thermogravimetry, and conductivity techniques showed that Ag(I) sorption occurs by a redox mechanism mainly involving reduction of Ag(I) to separable silver nanocrystals, chelation between Ag(I) and -NH-/-N=/-NH(2)/-SO(3)H/-OCH(3), and ion exchange between Ag(I) and H(+) on -SO(3) (-)H(+). Competitive sorption of Ag(I) with coexisting Hg, Pb, Cu, Fe, Al, K, and Na ions was systematically investigated. In particular, the copolymer nanoparticles bearing many functional groups on their rough and porous surface can be directly used to recover and separate precious silver nanocrystals from practical Ag(I) wastewaters containing Fe, Al, K, and Na ions from Kodak Studio. The nanograins have great application potential in the noble metals industry, resource reuse, wastewater treatment, and functional hybrid nanocomposites.