Drastic sensitivity enhancement in 29Si MAS NMR of zeolites and mesoporous silica materials by paramagnetic doping of Cu2+

Abstract

The paramagnetic doping of Cu²⁺ in both mesoporous silica materials and microporous silicate crystals (zeolites) can be used effectively to enhance the signal intensity of ²⁹Si solid state magic angle spinning NMR, as a result of shortening of the spin–lattice relaxation time, T₁, by the paramagnetic effect, because of the Cu²⁺ electronic relaxation time in the range of 10⁻⁸ s. This leads to drastically reduced data-collection times, typically 80-fold shorter than that in mesoporous silica. We found that the estimated range of the paramagnetic effect of Cu²⁺ doping in porous silicates was at least 1 nm.