# Low-Cost Goethite Nanorods for As (III) and Se (VI) Removal from Water
## 3 Results and Discussion  
### Structural and Morphological Study  
The color (dark yellowish-brown) of the obtained solution and powder (Figure 1) is the first indication of the synthesis of the \(\alpha\)-_FeOOH_ phase [26]. Besides, the X-ray diffraction (XRD) (D8 Advance X-ray Diffractometer, Bruker, Billerica, Massachusetts, USA) pattern obtained from the as-synthesized sample is displayed in Figure 2a. The diffraction peaks are indexed to the orthorhombic structure phase of \(\alpha\)-_FeOOH_ (_JCPDS_ file No. 81 0463) [27]. The diffractogram revealed the presence of no other diffraction peaks of impurities phases thus suggesting the pure phase synthesis. Of note, the difference in peak broadening indicates the high surface defects and the presence of asymmetry in the crystallite geometries. Accordingly, the average crystallite size of \(\alpha\)-_FeOOH_ was estimated by Scherrer's formula at -11.34 nm. Later on, most of these fine crystallites under the van der wall forces get attracted in a certain direction to form rod-like particle features [12]. Fourier transforms infrared (FTIR) spectrophotometer (Model: Thermo Scientific Nicolet 380, Thermo Fisher Scientific, Waltham, Massachusetts, USA) was used to study the presence of different chemical groups in the sample. The spectrum obtained from the sample is exhibited in Figure 2b. Figure 1: Photographs of \(\alpha\)-_FeOOH_: (**a**) solution; (**b**) powder. Figure 2: (**a**) X-ray diffraction diagram (XRD); (**b**)Fourier transforms infrared (FTIR) graph; (**c**) Raman spectrum; (**d**) Differential scanning calorimetry (DSC) and thermo-gravimetric analysis (TGA) thermal analysis; (**e**) Zeta potential; (**f**) Energy dispersive spectroscopy (EDS) of \(\alpha\)-_FeOOH_ nanorods NRs. The band at 670 cm\({}^{-1}\) is assigned to Fe-O stretching of \(\alpha\)-_FeOOH_[28]. The band at 856 cm\({}^{-1}\) is attributed to the \(\delta\)-OH in-plane bending of \(\alpha\)-_FeOOH_[28]. Also, the peaks at \(\sim\)1632 and \(\sim\)1392 cm\({}^{-1}\) are allocated to the O-H vibrational mode of absorbed H\({}_{2}\)O species and structural O-H groups on the surface of \(\alpha\)-_FeOOH_, respectively. The prominent peak at 3347 cm\({}^{-1}\) is related to the vibrational stretching mode of O-H groups attracted to the surface. Of note, the FTIR analysis shows the absence of carboxyl legends, plausibly due to the use of water solvent and not alcoholic solvents. Raman scattering data was obtained using an Nd-YAG laser (532 nm laser). Figure 2c depicts the Raman spectrum obtained from the sample. In general, it is a powerful characterization tool for those materials with dynamic phase transformation such as iron oxides [11]. Raman bands at \(\sim\)249, \(\sim\)298, \(\sim\)391, \(\sim\)485, \(\sim\)520, \(\sim\)547, and \(\sim\)677 cm\({}^{-1}\) in a single sample are specific to the \(\alpha\)-_FeOOH_[29; 30]. One wide and intense band at 1319 cm\({}^{-1}\) was attributed to a two-magnon scattering [29]. Figure 2d elucidates TGA-DSC (Thermo-gravimetric analysis-differential scanning calorimetry) profile measurements that provide precise information on the thermal stability of the \(\alpha\)-_FeOOH_ sample. Thermo-gravimetric analysis (TGA) ([PERSON], Waltham, Massachusetts, USA) is a proper technique to study the dehydration process of iron oxy-hydroxides. It accurately estimates the water weight loss (red curve of Figure 2d) as a function of temperature under inert or reactive atmospheres. Weight loss leads to dynamic changes of crystallization and phase transformation in such an iron oxy-hydroxide phase transform to iron oxide. Besides, it affords valuable information on the chemical reaction and oxidation rate changes as a function of temperature. A considerable weight loss was observed below 150 \({}^{\circ}\)C, which can be ascribed to the loss of surface-bonded water molecules and partial endothermic dehydration of iron oxy-hydroxide.