SUPPORTING INFORMATION
Synthesis of Bi2WO6 nanoplates using oleic acid as a green capping agent and its
application for thiols oxidation
Rahmatollah Rahimi, Shabnam Pordel, Mahboubeh Rabbani*
Fig S1 shows the GC-Mass chromatogram of thiophenol oxidation by Bi2WO6
nanoplates. No peaks of by-products were observed.
Fig S1. GC-Mass chromatogram of thiophenol oxidation ,Reaction conditions: thiols (1 mmol), Bi2WO6 (5
mg), dichlromethane (4 mL), H2O2 (50 µL), 60 min, room tempreture.
Possible formation mechanism
the possible formation process could be as following (Scheme 1): due to the high intrinsic
anisotropic growth of Bi2WO6 the reaction is terminated at high temperatures (175 °C in our
study) or high concentrations. The formation process of Bi2WO6 building block plates
consists of two steps. The first step is the self-aggregation which contains nucleation and
growth and the second step follows Ostwald-ripening mechanism [1]. In the first step, NO3−
ions kinetically control free ions in the solution through the reaction with free Bi 3+ ions to
form the BiONO3 intermediate species (Eq. (1),(2)), which decreases the free Bi3+ ion
concentration and hence the rate of crystal growth [2].
NO3− + H2O + Bi3+ ↔ BiONO3
2 BiONO3 + WO42− ↔ Bi2WO6 + 2 NO3−
Eq. (1)
Eq. (2)
Although the formation of smaller crystallites are kinetically preferred (as a result of the
initial agglomeration), the larger crystallites due to the thermodynamically effects are
preferred [3]. Based on the Ostwald-ripening mechanism, the smaller particles in solution
dissolve and deposite on larger particles which results in a more thermodynamically stable
state within the surface to area ratio is reduced and therefore the surface energy is minimized.
Consequently, the Bi2WO6 plates consisting of alternating (Bi2O2)n2n+ layers and perovskitelike (WO4)n2n+ layers are formed [4]. Oleic acid or omega 9 is a fatty acid found naturally in
animals and vegetables such as avocados, olive oil and canola oil. Oleic acid possesses a
hydrocarbon tail and a carboxylic acid head group which can bonded to the surface of
particles by its carboxylic acid group. As it shown in Fig. S2 in the absence of OA at the
same condition, the flower like microstructure was obtained.
Fig S2. The Bi2WO6 flower-like formation in the absence of OA
The exact role of OA in this process is not obvious at this time. It seems that OA act as a
shape-controller for the formation of final morphology. One possible function for OA could
be explained as follows: as soon as Bi2WO6 alternative layers are formed, as discussed in the
FT-IR section, OA is adsorbed onto the nanoparticles surface as a capping agent through the
hydrogen bonding and vanderwalls forces. The chemisorb oleic acid suppress the further
growth of nanoplates and hinders the nanoplates from self-organization in order to produce
flower-like microstructures.
Scheme 1
Refrences
1.
Hu, S. P., Xu, C. Y., Wang, W. S., Ma, F. X., & Zhen, L. (2014). Ceram Int.
40:11689.
2.
Chen Z, Qian L, Zhu J, Yuan Y, Qian X. (2010). Cryst Eng Comm, 12:2100.
3.
Zhang, L., Wang, W., Chen, Z., Zhou, L., Xu, H., & Zhu, W. (2007). J Mater Chem,
17:2526.
4.
Zhang, N., Ciriminna, R., Pagliaro, M., & Xu, Y. J. (2014). Chem Soc Rev, 43:5276