Fabrication of magnetically responsive core-shell adsorbents for thiophene capture: AgNO₃-functionalized Fe₃O₄@mesoporous SiO₂ microspheres

Deep desulfurization of transportation fuels via π-complexation adsorption is an effective method for the selective capture of aromatic sulfur compounds. Taking into consideration that the desulfurization of transportation fuels proceeds in the liquid phase, separation and recycling of adsorbents should be greatly facilitated if the adsorbents were endowed with magnetism. In this paper, magnetically responsive core-shell π-complexation adsorbent microspheres, AgNO₃/Fe₃O₄@mSiO₂ (mSiO₂ denotes mesoporous silica), which comprises a core of magnetite particles and a shell of mesoporous silica dispersed with AgNO ₃, was developed for the first time. The silica shell exhibits highly open mesopores with perpendicularly aligned pore channels, large surface area (694 m² g^-1) and uniform pore size (2.3 nm), which is quite beneficial to the accommodation of Ag(i) active species. As a result, AgNO₃ can be well dispersed in the pores of silica shells and are highly accessible to adsorbate molecules. Our results show that the adsorbent is active in the adsorptive removal of a typical aromatic sulfur compound, thiophene, via π-complexation under ambient conditions. More importantly, the superparamagnetism allows the adsorbent to be separated conveniently from the adsorption system in several seconds by the use of an external field. After desulfurization, the adsorbents were regenerated by washing with isooctane and subsequent thermal dispersion in Ar. The regenerated adsorbent after six cycles still shows a good adsorption capacity (0.145 mmol g^-1 or 4.64 mg g^-1), which is comparable to the fresh adsorbent (0.147 mmol g ^-1 or 4.70 mg g^-1). The magnetically responsive π-complexation adsorbent may be a promising candidate for the deep purification of transportation fuels.