Clasificación de las nulidades procesales

It is very important to compare the characteristic of nZVI, such as sample G; synthesised using only H. Caffrum leaf extract (1 g), the nZVI, sample N; synthesised with both sodium borohydride (500 mg) and H. Caffrum leaf extract (200 mg) and conventional nZVI, sample C; synthesised using sodium borohydride (1 g) by using common analytical equipment such as XRD, TEM, SEM, FT-IR, XPS and TGA. Finger print identification of the synthesised nZVI was analysed by using the X-ray Diffraction spectra (XRD) as described in section 3.8.1.

Figure 4.7: X-ray Diffraction pattern of nZVI C, N and G (G; synthesised using only H.

Caffrum leaf extract (1 g), N; synthesised with both sodium borohydride (500 mg) and H. Caffrum leaf extract (200 mg) and C; synthesised using sodium borohydride (1 g) only)

A broad peak at 44.6o 2θ presented in this study is a confirmation of the presence of nano zero valent iron in its crystalline form as described by Taha and Ibrahim (2014). This pattern is in accordance with diffraction pattern of body-centered cubic α-Fe (JCPDS No. 06-0696). Both the conventionally synthesised nano zero valent iron, C and the nano zero valent iron modified by simultaneous addition of H. caffrum extract, N have identical XRD spectra patterns with peaks as described above. However, the appearance of small peaks around 22.7o and 63.2o on close inspection of the XRD spectrum of C is a confirmation of the presence of ϒ-FeOOH (Lepidrocite) phase (JCPDS No. 17-0536). This is a consequence of the oxidation of nZVI in moist air due to its instability and absence of the capping agent or surface protecting substances. Therefore, C is an “iron-zero” core surrounded by higher oxidation state iron oxides (Fe2+/ Fe3+). The result is in agreement with previous publications on nano zero valent iron (Hoag et al., 2009; Kozma et al., 2016; Liu and Zhang, 2014). Besides, the XRD spectra of nano zero valent synthesised with only the leaf extract from H. caffrum (G) lack the typical well defined iron peaks. It is possible for the H. caffrum to bind with iron metal and form a metal chelating amorphous compound with a decreased XRD intensity (Su et al., 2018). Consequently, nano-

sized crystal substances formed has capacity for scattering the X-rays in many directions leading to a broader XRD main peak. Both the capping and surface oxidation of nZVI can alter its surface functionalities and increases its size. The determination of the surface functionality and size of nZVI can be better done with TEM (section 3.8.2) and SEM (section 3.8.3) analysis.

30 40 50 60 70 80 90 100 110 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 F re q u e n c y Diameter (nm) c 65 nm

Figure 4.8: TEM image of C showing the agglomeration (Scale: 200 nm) and particle size distribution (30 nm to 100 nm) with the particle size bar chart (low frequency bar)

30 40 50 60 70 80 90 0 2 4 6 8 10 F re q u e n cy Diameter (nm) 50 nm N

Figure 4.9: TEM image of N (Scale: 200 nm) particle identifying the H. caffrum location and size distribution with the particle size bar chart

H. caffrum Agglomerated nZVI

High Resolution Transmission Electron Microscopy (HRTEM) images of nZVI samples (C and N) are as presented in Figure 4.8 and Figure 4.9 respectively. It was observed through the TEM images that the nZVI, sample C had a crystalline form of zero valent iron (Fe0) with a number of agglomerated particles while nZVI, sample N is composed of relatively well dispersed crystals of zero valent iron. The sizes of nZVI, sample C is 65 nm at average but widely distributed between 30 nm and 100 nm while the sizes of nZVI, sample N is 50 nm at average with a narrow distribution, giving it a more uniform sizes compared with nZVI, sample C. Sizes of the synthesised nano particles during the current investigation are in concordance with the previously published reports on the nZVI (Markova et al., 2014; Thomé et al., 2015; Yaacob et al., 2012). The surface morphology of the synthesised nano iron particles were also analysed by the SEM as described in the section 3.7.3.

Conventionally synthesised nZVI, sample C, as revealed by SEM analysis shows the chain-like agglomeration of particles in which several layers of small particles clump together to form bigger agglomerates while SEM analysis of N shows better dispersed spherical shaped nano particles (Figure 4.10).

The differences in the capping agent‟s structural bonds and intermolecular forces are responsible for surface morphological differences exhibited in the synthesised nano zero valent irons as visible in the observed TEM and SEM images. Unlike the nZVI samples C and N, both the TEM and SEM methods cannot be use to characterise nZVI, sample G. The structural bonds and intermolecular forces of the dried leaf extract of H. caffrum (HF) as well as the nZVI, samples C, N and G were investigated by the FT-IR analysis described in section 3.8.6. The result of FT-IR analysis is presented in Figure 4.11.

500 1000 1500 2000 2500 3000 3500 4000 40 60 80 100 % T ra n s m it a n c e Wavenumber (cm-1) C G N HC 1056 1253 1385 1615 2907 2987 3286 _G HC C N 875

Figure 4.11: FT-IR spectra of H. caffrum (HF) plant extract and synthesised nano zero valent irons G, N and C

There are broad OH stretching vibration of around 3286 cm-1 on the FT-IR spectra of C, G and HF. The OH spectrum in the FT-IR of C is due to the sorbed water which resulted in formation

of (ϒ-FeOOH) Lepidrocite on the surface of nZVI. Meanwhile, the metal oxide peaks at 875 cm-

1

on the FT-IR spectrum of C and N was the resultant effect of continous oxidation at their outer layers. This result is a confirmation of the claim that the surface of the synthesised nZVI is predominantly iron at higher oxidation state (Ashokkumar and Ramaswamy, 2014; Liu and Zhang, 2014). Besides, the spectra of G and HF also show intense broad OH stretching vibrations due to the contribution of benzylic OH from the polyphenolic plant extract. The intense aromatic skeletal vibration peaks around 1615 cm-1 in the FT-IR spectra of HC and G suggest the binding of the polyphenolic groups to the active surfaces of the synthesised nano iron particles. These peaks suggest the presence of aromatic groups in the compounds while their high intensity in G is a confirmation of the existence of Fe-O complex as previously documented by Lu et al. (2010) and Wang (2013). Similarly, symmetric and asymmetric carbonyl peaks at 1253 and 1385 cm-1 as well as the observed C-O stretching peak at 1042 cm-1 are present on the spectra of HC, G and N. There are specific distinctions between H. caffrum (polyphenol) containing nano iron (G and N) and the one synthesised with only NaBH4 (C). The carbonyl

containing sugar base in H. caffrum serves as surface modifier in the novel nanoparticle G and N, hence it prevents agglomeration and enhances the activity in nZVI (N). This is possible through the polymer entanglement and hydrogen bonding of the sugar moiety of the polyphenolic plant extract (Lu et al., 2010; Thekkae et al., 2017). However, the amount of H. caffrum needed for the stability of nZVI must be optimised to prevent possible loss of its activity.