Hierarchically porous poly(ethylenimine) modified poly(styrene-co-divinylbenzene) microspheres for the adsorption of gold nanoparticles and simultaneously being transformed as the nanoparticles immobilized catalyst.

With the extensive applications of gold nanoparticles (AuNPs) and the confirmation of their toxicity on human health and environment, it was urgent to remove AuNPs from environment. The hierarchically porous poly(ethylenimine) modified poly(styrene-co-divinylbenzene) microsphere (PEI-PS-DVB) was prepared and characterized by scanning electron microscopy, X-ray diffraction, transform infrared spectrometry, energy dispersive X-ray spectrometry, elemental analysis, contact angle, zeta potential analysis, N adsorption-desorption and mercury intrusion porosimetry. PEI-PS-DVB possessed abundant flow-through pores (70-120 nm) and meso/micropores (<50 nm); the former pores enabled full availability of the adsorbent to relatively large adsorbate, i.e. AuNPs, with fast mass transfer, while the latter ones ensured large surface area for high adsorption capacity. Thanks to its plentiful nitrogen and special hierarchical pores, PEI-PS-DVB was suitable for the adsorption of AuNPs by electrostatic interaction and special affinity between nitrogen and Au. The adsorption obeyed the pseudo-first-order kinetic and Langmuir isotherm models. The maximum adsorption capacity based on Langmuir model was 806.5 mg/g. Moreover, PEI-PS-DVB adsorbing AuNPs could be the efficient catalyst for the reduction of 4-nitrophenol with satisfactory reusability. The developed hierarchically porous PEI-PS-DVB was a promising adsorbent for AuNPs with high adsorption capacity, and recycling usage of waste AuNPs conformed to the green and sustainable concept.