Metal-free pyridinium-based polymeric ionic liquids as catalyst for H2 generation from NaBH4

Abstract

Monodispersed poly(2-vinyl pyridine) (p(2-VP)) polymeric particles were synthesized with a self-emulsion polymerization (SEP) technique. Polymeric ionic liquid (PIL) particles such as poly(2-vinyl pyridine)-ethane (p(2-VP)++C2), poly(2-vinyl pyridine)-butane (p(2-VP)++C4), and poly(2-vinyl pyridine)-hexane (p(2-VP)++C6) particles were then prepared from monodispersed p(2-VP) particles by modifying with 1,2-dibromobutane (DBE) 1,4-dibromobutane (DBB) and 1,6-dibromobutane (DBH), respectively. The hydrodynamic diameter of the prepared particles was found be in the range of 350–400 nm, and the zeta potential of p(2-VP)++Cn (n: 2, 4 and 6) particles were found to be in the range of 26–28 mV. The prepared PIL particles (p(2-VP)++C6 etc.) were shown to be very effective catalysts in H2 generation by methanolysis of NaBH4. Various parameters, such as the effect of modifying agents on PIL particle, the amount of PIL particles, the amount of NaBH4 and temperature, affecting the H2 production rate were investigated. Hydrogen generation rate (HGR) was calculated as 5433 ± 141 mL H2 g−1 min−1 for 50 mg p(2-VP)++C6 particles in the methanolysis of 500 mM NaBH4. The activation energy (Ea) of methanolysis of NaBH4 catalyzed by p(2-VP)++C6 particles was calculated as 20.84 ± 0.76 kJ mol−1, which is much lower than similar studies reported in the literature.