Combined Effect of Functionality and Pore Size on Dehydrogenation of Ammonia Borane via Its Nanoconfinement in Polyacrylamide-Grafted Organically Modified Mesoporous Silica

Organically modified poly(acrylamide) (PAM)-grafted mesoporous silica nanoparticles (MSNs) have been evaluated for the first time as a hybrid material for hydrogen release experiments via nanoconfinement of ammonia borane (AB). PAM was grafted from two different types of R group (isobutyric acid and phenylethyl)-containing in-built reversible addition-fragmentation chain transfer (RAFT) agent-primed MSNs (PAM-COOH-MSNs and PAM-Ph-MSNs). To evaluate the suitability of these PAM-grafted MSNs as an efficient hybrid material for hydrogen release at a lower dehydrogenation temperature compared to neat AB, which was nanoconfined in PAM-grafted MSNs (AB-PAM-COOH-MSNs and AB-PAM-Ph-MSNs). The hydrogen release from AB-nanoconfined PAM-grafted MSNs was performed using temperature-programmed desorption-mass spectrometry (TPD-MS). Significantly, it was observed that AB-PAM-COOH-MSNs and AB-PAM-Ph-MSNs justified the nanoconfinement by a lower onset of hydrogen release temperature in comparison to neat AB. The possible mechanism for the lower dehydrogenation temperature of PAM-COOH-MSNs in comparison to that of PAM-Ph-MSNs was attributed to the size reduction of AB and the interaction between functional groups of polymers and MSNs with AB. Additionally, impurities such as diborane and ammonia during hydrogen release were suppressed for both PAM-grafted MSNs. Justifying the evidence for AB-PAM-COOH-MSNs in comparison to AB-PAM-Ph-MSNs, it can be proposed that organically modified poly(acrylamide)-grafted MSNs can be used as efficient nanocarriers for ammonia borane nanoconfinement and hydrogen release.