Furthermore, a broad band at 3,600 to 3,100 cm-1 corresponding to water and hydroxyl SBI-0206965 purchase groups on the wire surface can be observed. The peak at 1,629 cm-1 indicates the bSelleck Ferrostatin-1 ending modes of the water molecules adsorbed on the surface of the ZnO material. In the ZnO-NH2 spectrum, the deformations of primary amine (N-H) are located at 833 and 1,609 cm-1. The band between 3,500 and 3,300 cm-1 corresponds to the N-H stretching vibration, from 3,000 to 2,800 cm-1 to the stretching vibration of the C-H groups, belonging to the propyl chain. Figure 3 Fourier transform infrared spectroscopy and thermogravimetric analysis of ZnO. (a) Fourier transform infrared spectroscopy and (b) thermogravimetric
analysis on the ZnO (black lines) and amino-functionalized ZnO (red lines) samples. A tentative quantification of the aminopropyl groups is based on thermogravimetry (Figure 3b) and the available surface area (0.96 m2/g) of the ZnO wires, as calculated by the BET model from nitrogen sorption PF-01367338 mw measurements (as reported in Additional file 1: Figure S1). The weight loss of the functionalized sample is slightly higher with respect to the sample with unfunctionalized ZnO, in particular, the first derivative of the thermogravimetric curve (DTG, red dot curve) shows a peak from 300°C to 400°C, indicative of the loss of organic
materials. The weight loss in this temperature range can be generally attributed to the materials adsorbed or anchored to the ZnO surface, including the amine functionalizing agent. Calculation based on the weight loss of both samples returns a value of about 2 μmol/g of sample (0.37 mg/g) of organic material; thus, in absence of any contamination, one could assume this value as the maximum over amount of aminopropyl group attached to the surface. By taking into account the value of specific surface area, the hypothetic maximum aminopropyl group density is about 0.38 mg/m2 or 1.78 molecules/nm2. From the thermogravimetric curve,
we also calculated about 2.11 mg/g (2.19 mg/m2) of hydroxyl groups on the bare ZnO surface (black curve), whereas after the functionalization with APTMS, the groups are reduced to 1.17 mg/g (1.22 mg/m2). This decrease of hydroxyl group is clearly attributed to the effective anchoring of the aminopropyl groups to the ZnO surface, since an average of two/three methoxysilane ending groups of the APTMS molecule condense with the respective hydroxyl group on the ZnO surface during the functionalization reaction (Figure 1, left). All these findings, combined with the FTIR spectroscopy, confirm the successful functionalization of ZnO with aminopropyl groups. In addition, the reduction of the hydrophilic hydroxyl groups on the wire surface after functionalization leads a useful indication about the degree of wettability of the ZnO and ZnO-NH2 surfaces.