EPR studies of free radical reactions of C60 embedded in mesoporous MCM-41 materials in aqueous solution

Abstract

The channels of the molecular sieve MCM-41 are employed as nanoreactors to study free radical attacks on C 60 in aqueous media. Samples of C 60 embedded in the nanochannels of mesoporous materials were prepared by the chemical binding of C 60 to the amino-modified surface of MCM-41 solids. The spin trapping/EPR technique was employed to study the reactions of hydroxyl and methyl radicals with the embedded C 60 in the nanochannels. The study enables us to examine the chemistry of C 60 in aqueous solution, and the efficacy of free radical scavenging by C 60 embedded in the nanochannels. The study further reveals the proximity effect of free radical reactions in a nano-restricted environment.

High loading of C60 in nanochannels of mesoporous MCM-41 materials

“…These EPR studies further confirm that C À 60 can be embedded in the channels of MCM-41-NH 2 by the synthetic method as described earlier. Other detailed EPR studies of free radical attack on C 60 embedded in the nanochannels of MCM-41-NH 2 solids has been reported elsewhere [16].…”

“…From the data of elemental analysis (see Table 1), there is 0.018 mmol C 60 bound on the surface per gram MCM-41-NH 2 that gives 1.21% for the calculated percentage of C 60 binding on MCM-41-NH 2 . These low loading samples inhibited us to perform many of the planned experiments, such as the study of free radical reactions of C 60 embedded in mesoporous materials [16].…”

“…in a linear array), the average distance between C 60 molecules would be 3.1-2.3 nm, only 3.1-2.3 times greater than the close contact distance of 1.0 nm. Thus, we have an extraordinarily dense distribution of C 60 in the confined space, which is very advantageous for other applications, such as free radical reactions of C 60 in the nanochannel pore [16] and optical studies [17].…”

“…1 We shall demonstrate high concentration of C 60 can be embedded in the channels of MCM-41 solids by surface modification with amino-functional group and other chemical consideration. These high loading of C 60 in the surface modified MCM-41 solids allowed us to study the free radical reactions of C 60 in aqueous solution by the EPR technique [16]. The study revealed the efficiency of free radical (hydroxyl and methyl radicals) attacks on C 60 in a nanoreactor environment is higher than that in a non-restricted environment.…”

Nano-structure and property transformations of carbon systems under γ-ray irradiation: a review

“…In fact, it reacts with a number of different types of radicals and normally it undergoes multiple addition reactions, leading to adducts with different stability. [72][73][74][75] When they were irradiated in molecularly dispersed forms, the behavior of fullerenes was investigated by Cataldo et al 76 In presence of air the interference of oxygen is evident and the radiolysis should be conducted in high vacuum to avoid the interference of oxygen. A detailed analysis of the kinetics of the multiple additions of benzyl radicals to the fullerene cage was made spectrophotometrically with the determination of the addition rate constants at the each addition step and the average number of benzyl groups added to the fullerene cage as function of the radiation dose.…”