## 3 Results and Discussion
### Effects of Surfactant in Directing the Size and Morphology of Alanate Nanostructures
As such, LiAlH\({}_{4}\) particles synthesized with TDA would inevitably be larger than that of DDA due to the reduction of COOH into OH. Figure 3: The average particle size of LiAlH\({}_{4}\) and NaAlH\({}_{4}\) stabilized by DDA (RNH\({}_{2}\)), TDA (RCOOH), and DDT (RSH) at 1 mM. Error bars represent standard deviation of the mean particle size (Figure S17). The concentration of the surfactants can also be expected to affect the nucleation and growth process of LiAlH\({}_{4}\) and NaAlH\({}_{4}\) particles, owing to the concentration dependent organizational structures of the surfactant in solution and associated critical micelle concentration (CMC). As shown in Figure 5, which summarized the evolution of particle size as determined by TEM upon changing the surfactant concentration (Figures S3-S14), a relationship can be drawn between the surfactants' concentration and particle size. For the amine stabilized LiAlH\({}_{4}\), it can be seen that particle size decreases with an increase in surfactant concentration, with the smallest particles obtained at a surfactant concentration of 10 mM. A similar trend was observed with thiol-stabilized LiAlH\({}_{4}\) with the exception of LiAlH\({}_{4}\)-ODT. LiAlH\({}_{4}\) stabilized with ODT exhibited a different trend where at 10 mM, the average particle size increased from 22 \(\pm\) 6 to 200 \(\pm\) 78 nm. This suggested that a concentration of 10 mM is far exceeding the CMC of ODT in diethyl ether. Under these conditions LiAlH\({}_{4}\) particles would start to agglomerate to form larger particles. Indeed, it was reported that surfactants with longer carbon chains would display lower CMC than the ones with shorter chains [56]. Therefore, ODT would have lower CMC than DDT. Additionally, it has been previously reported that the CMC decreases as the size of surfactants' head group increases [57; 58]. Based on these considerations, ODT which has a larger head group can be assumed to have lower CMC than ODA with smaller head group. A similar correlation of particle size and surfactant concentration was observed with thiol-stabilized NaAlH\({}_{4}\) such as DDT and ODT (Figure 5d and Figures S12-S14) where a spherical-like particles were produced. Upon increasing the concentration of surfactant from 0.1 mM to 1 mM, a significant reduction in average particle size was observed (e.g., from 108 \(\pm\) 25 to 26 \(\pm\) 6 nm). Nevertheless, heptanethiol (HTT) failed to restrict the particle size of NaAlH\({}_{4}\), possibly due to the low steric hindrance. For the NaAlH\({}_{4}\) stabilized by HXA, DDA, and ODA (Figure 5c and Figures S8-S11), the size of the nanostructure decreases when the concentration increases from 0.1 to 1 mM. Unfortunately, it was not possible to determine the size of these particles at a 10 mM surfactant concentration because of the severe particles' agglomeration (Figures S9-S11). Figure 4: FTIR spectra of (**a**) LiAlH\({}_{4}\)-TDA-10 in black and (**b**) NaAlH\({}_{4}\)-TDA-1 in red. When comparing the size of LiAlH\({}_{4}\) and NaAlH\({}_{4}\) nanoparticles, it can be seen that the stabilization effects (i.e., smaller particles) are more pronounced in NaAlH\({}_{4}\) than with LiAlH\({}_{4}\). This can be explained by: (1) the higher reactivity of LiAlH\({}_{4}\) with the surfactants, e.g., DDT, ODT, and TDA as compared to NaAlH\({}_{4}\); and the higher amount of possible by-product (e.g., LiOH formed during the reaction between LiAlH\({}_{4}\) and the surfactants), which may potentially weaken the interaction with the surfactant; (2) differences in the evaporation rates of the solvent (THF and diethyl ether boiling point is 66 \({}^{\circ}\)C and 34.6 \({}^{\circ}\)C respectively), which may affect the growth of nanoparticles due to differences in nucleation rate and; (3) the tendency of NaAlH\({}_{4}\) to bind to THF, and this may affect the growth of NaAlH\({}_{4}\) nanoparticles by possibly preventing further Ostwald ripening [59; 60; 61]. Interestingly, different morphologies were observed when increasing the concentration of TDA (Figure 6).