1. Introduction

Oxide semiconductors (ZnO, TiO₂, CuO, Al₂O₃ and SnO₂) have attracted researchers across the globe due to less cost, easy processing technique and less toxicity. Among the oxide semiconductors SnO has a wide range of applications [1], extending from gas sensing [2], bio enzyme sensors [3], solar cell applications [4] and hazardous elemental absorbers. Nanomaterials can increase the efficiency of above mentioned applications due to enhanced surface area [5]. Nano tin oxide can be prepared using several techniques such as sol-gel, electrodeposition, ball milling, and laser ablation [6-9]. Sol-gel has been the preferred choice for synthesis of nano-oxides due to its less cost, easy processing techniques and control over the particle morphology [10].  Aloe vera, neem, tea, and coffee have been used in synthesis of nanomaterials as a reducing agent to study the effect of variation of morphology or surfactants. [11]. Aloe vera has been reported as a good reducing/stabilizing agent for silver nanoparticles [12]. This study investigated the effect of aloe vera on the oxide nanomaterials. It was followed by investigating the SnO morphology after addition of few drops of aloe vera.

2. Experimental

Tin chloride (1.9 g) was mixed with 100 ml water in a beaker. The solution was stirred by a magnetic stirrer to get a white solution. Sodium hydroxide (2 g) was dissolved in the solution and stirred for 1 h to obtain a pale white solution. The pH of the solution was adjusted in the range of 10.5-11 by addition of NaOH. The solution was heated up to 250 °C for 2 h to obtain the SnO₂ powder from Sn(OH)₂. This is further hand milled to get the nano-powder.

The above procedure is repeated with inclusion of aloe vera extract during the stirring process. Aloe vera contained 75 active constituents such as sugars, lipids, amino acids, and salicylic acid [13]. The composition of aloe vera contains 99% water and derivatives of anthroquinonoe and glycosace which are aromatic compounds. The aromatic compounds may not react with the Sn(OH)₂ phase, but they can introduce some functional groups in solution due to decomposition.

The prepared micro and nano SnO were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM) to identify the structural features, functional groups, and the morphology. The summary of the preparation process is presented in Fig. 1.

3. Results and Discussion  

XRD pattern of the prepared SnO₂ (Fig. 2) shows diffraction peaks at 25, 33, 51, and 660.The observed peaks are indicative of SnO₂ in accordance with JCPDS  41-1445 [14]. SnO₂ prepared with aloe vera drops (Fig. 3) also shows diffraction peaks at same diffraction angles, but broadening of peaks are observed. Scherer equation is used to calculate the crystallite size of prepared nanoparticle. d= 0.91λ /(β Cosθ) Where,d= crystallite size  (nm), λ= wavelength of the incident rays (1.54A), β= Full Width at Half Maximum value (radian) & θ= Position (radian), diffraction angle. The size is found to be 6 nm for SnO₂ and 13 nm for aloe vera - SnO₂. The Williamsons Hall plot (Fig 4 & Fig 5) between βcos θ and 4sin θ is plotted for both the powders. The intercept of the plot gives   is used to measure the particle size. The intercept of the plot gives 0.91 λ/D, where D is the crystallites size to be determined. The particle size of the SnO₂ and SnO₂ in the aloe vera solution is 23 and 49 nm, respectively.

Fig. 1. Preparation of SnO₂ and SnO₂ with Aloe Vera Solution.

Fig. 2. XRD pattern of SnO₂.

Fig. 3. XRD pattern of SnO₂ with aloe vera.

Fig.4. Williamson Hall plot of SnO₂.

Fig 5. Williamson Hall plot of SnO₂ with aloe vera solution.

Fig 6. FT-IR of SnO₂.

The FTIR spectrum of the SnO₂ (Fig. 6) shows wave numbers of 3382.27, 958.61, 517.36 /cm which can be identified with O-H, C-H and Sn-O bonds. The FTIR spectrum of the SnO₂ with aloe vera (Fig. 7) shows wave numbers between 3500 to 4000 /cm in addition to the peaks present in Sn-O. The peaks confirm the presence of anthro quinones which are derived from Aloe vera solution.

Fig 7. FTIR of SnO₂ with Aloe vera solution.

The SEM   image of SnO₂ and SnO₂ with Aloe vera is shown in Fig. 8.a and Fig. 8.b respectively. A heterogeneous range of particle size is observed for both the materials. The particle size of SnO ranging from 100 nm to 500 nm.

But the particle size for the SnO₂ with Aloe vera ranges from 100 nm to 20 µm. Therefore, the aloe vera solution has agglomerated the SnO₂ and results in a phase transformation from

nano to micro size.

Fig 8. a, SEM image of SnO₂. and b,SnO₂ with Aloe Vera solution.

 The PL spectra of both the samples is illustrated in Fig. 9. The samples are excited at a wavelength of 265 nm. The SnO₂ samples show peaks at 363, 419, 485 nm which corresponds to 3.41, 2.95 and 2.55 eV respectively. The SnO₂ prepared with Aloe vera solution shows peaks at 362, 419, 485 nm which corresponds to 3.42, 2.95 and 2.55 eV respectively. Inclusion of Aloe Vera solution in the precursor changes the photon intensity at all the three wavelengths. SnO₂ prepared with aloe vera solution shows high intensity in comparison to SnO₂ and the difference in intensity increases from UV to visible range.

Fig 9. PL spectra of SnO₂ and SnO₂ with Aloe vera.