Synthesis of SnO 2 Nanoparticles by High Potential Electrolysis

SnO2 nanoparticles have been synthesized by high voltage electrolysis. Tin bare was used for anode and cathode. The effect of potentials and electrolyte were studied. The particles obtained after electrolysis was characterized using X-ray Diffraction (XRD). The diffractogram is in agreement with the standard diffraction pattern of SnO2 which is identified as tetragonal structure. The Fourier Transform Infrared (FTIR) spectrum indicates that there is a vibration of Sn–O asymmetric at 580 cm1. The optimum potential for SnO2 nanoparticles synthesis is 60 V at 0.06 M HCl which shows the highest UV-Vis spectrum. The absorption peak of SnO2 nanoparticles by UV-Vis spectrophotometer appears at about 207 nm. The particle size analysis shows that the SnO2 nanoparticles obtained have the size distribution in a range of 25-150 nm with the highest volume at 83.11 nm. Copyright © 2017 BCREC Group. All rights reserved

Several scientists reported that the SnO2 nanoparticles could be synthesized using wet chemical methods.Those method are biogenic synthesis [5], gel combustion [10], hydrothermal route [11,12], sol-gel [13][14][15], microemulsion [16], solvothermal [17], thermal decomposition [18], sonochemical [19], and precipitation [20,21].All methods were proved to produce SnO2 nanoparticles.Unfortunately, these methods are relatively time-consuming and complicated processes.They are not suitable for fabrication cost and facile preparation process [22].Another method which can be developed for nanoparticle synthesis is an electrochemical method, which it is proposed in this work.The efficiency of the procedure offers several advantages including control of particles size, excellent yields, operational simplicity and minimum environmental [23].It has been applied for some research, such as influence CTAB and sonication on nickel hydroxide nanoparticles synthesis [24], synthesis nickel hydroxide by electrolysis at high voltage [25], and influence of Ni(OH)2 nanoparticles on insulin sensor sensitivity [26,27].
Based on the explanation, most of researchers produced SnO2 nanoparticles using techniques which require Tin(IV) chloride as a reagent.This reagent is relatively expensive and difficult to be found in Indonesia.There have been limited studies concerned on synthesis of SnO2 from tin bare which is cheaper and easier to be found in Indonesia.Therefore, this research intent to produce a nano-size SnO2 using tin bare as the reagent by high potential electrolysis.

Materials
Pure tin metal sheets (99.9%) with 1 mm thickness and hydrochloric acid (AR grade 37%) were purchased from Merck.The sheet was adjusted into a dimension of 4 mm × 10 cm before used for anode and cathode.Demineralized water was used for all cleaning and chemical preparation.

Methods
The SnO2 nanoparticles were synthesized by electrolysis with a tin sheet as anode and cathode.The scheme of the electrolysis cells is shown in Figure 1.The electrolysis was performed at various potentials, i.e. 10; 20; 30; 40; 50; 60; 70; 80; 90; and 100 V, in 100 mL 0.02 M HCl as electrolyte solution to see the influence of the potential applied.Various concentration of electrolyte solution was also applied to observe the formation of SnO2 nanoparticles duriing electrolysis.The concentration was 0.005; 0.01; 0.02; 0.03; 0.04; 0.05; and 0.06 M HCl, at a fixed potential of 60 V. Continues stirring was also applied during all the electrolysis experiment.Electrolysis was stopped after 15 minutes, and then both electrodes were released from the electrolysis cell, dried at room temperature, and weighed to observe the weight different of the both electrodes before and after electrolysis.The solution obtained was also cooled at room temperature and ready for characterization.The plasmon band peak of SnO2 nanoparticles solution was observed The nanoparticles structure was analyzed by Philips X'Pert MPD (Multi-Purpose Diffractometer) XRD using Cu Kα1 radiation (λ = 1.540598 nm) and Kα2 (λ = 1.544426 nm).The FTIR spectrum was recorded from 4000 to 400 cm -1 by a Shimadzu Fourier Transform Infrared (FTIR) spectrophotometer.Malvern Zetasizer Nano Series Instruments was used to measure the particle size obtained.

Synthesis of SnO2 nanoparticles
The most probable reaction on cathode occurs as Eqn.(1).

Cathode (Sn):
(1) H2 production at the cathode can be observed by bubbles formation during electrolysis process.Meanwhile, the reaction on the anode has three possibilities as described in Eqns.( 2), (3), or (4): Anode (Sn): (2) The oxidation of Sn was observed by the lost weight of the Sn bare (Table 1 shows the mass of tin metal that dissolved during the synthesis process).The Sn can be oxidized to be Sn 2+ or Sn 4+. .Formation of O2 as Eqn.( 4) was also observed by the bubbles produced at the surface of the anode.
The nanoparticles were obtained characterized using XRD.The diffractogram is shown in  211), (310), ( 112), (202), and (321) for SnO2 nanoparticles, respectively.The three strong peaks are assigned to the (110), (101), and (211), respectively.All diffraction peaks are in good agreement with the SnO2 standard diffraction pattern.The results indicate the product obtained is SnO2 nanoparticles with a tetragonal structure [18].
The FTIR analysis is also in agreement with the SnO2 spectrum (Figure 3).In this spectrum, the absorption at 934 cm -1 is described to surface oxygen of Sn-O [18] and 580 cm -1 is assigned to the Sn-O asymmetric vibrations [22].The presences of two peaks in product confirm the presence of SnO2.We found that the product has absorption from several functional groups.The peaks at 3396 and 1626 cm -1 are assigned to the stretching vibration of OH groups and the bending vibration of absorbed molecular water.Bending vibrations of H-O-H in the water were observed at 1401 cm -1 .It also appeared that the absorption at 1159 is assigned to vibration of different types of surface hydroxyl groups.The product in optimum condition (0.06 M HCl at 60 V) was analyzed by zeta sizer (Figure 4).The average size of SnO2 nanoparticles obtained is 83.11 nm.

The effect of potential
The optimum conditions in this experiments occurred at the potential of 60 V with the maximum value of absorbance and wavelength are 2.583 and 203 nm, as shown in Figure 5.Comparison with the other potential, in this condition, the greatest mass reduction occurs at the anode.Increasing the applied potential increases the value of absorbance at the maxi-  mum wavelength.This indicates that the tin bare dissolves more with the potential.This is due to the potential act as a controller parameter in electron pressure that causes a reduction or oxidation reaction [28].The equation states E = I.R, so the greater potential increases the electric current.The electrical current is proportional to the mass of the anode which is oxidized into ions.The ions are only formed under the effect of an electric field that flows through the solution [29].

The effect of electrolyte solution
Increasing the acid concentration increases the dissolution of tin metal (Table 2).It shows that the greatest mass reduction obtained at 0.06 M HCl.The HCl was ionized into H + and Cl -ions.Whereas, chloride ions from ionization can activate the dissolution of the tin metal (Sn 2+ or Sn 4+ ) at anode [29].Observations on the maximum wavelength are presented in Figure 6.UV-Vis spectra show the absorbance value increase with increasing of the acid concentration.It was achieved at 0.06 M HCl with the absorbance and wavelength values are 3.068 and 207 nm, respectively.The SnO2 nanoparticles were formed (the oxidation number of tin increase from 0 to 2) in solutions as follows: (5) (6) This reaction can be continued to oxidize Sn 2+ to Sn 4+ as the following: (7) The other possibility reaction can also occur.The oxidation number of tin increases from 0 to +4, the SnO2 nanoparticles was formed with the following reaction: (8) (9)

Conclusions
Based on the results, it was concluded that SnO2 nanoparticles could be synthesized from the tin metal using an electrochemical method in HCl solution.The optimum condition for the

Figure 6 .
Figure 6.UV-Vis spectrum of SnO2 nanoparticles at various HCl concentrations

Table 1 .
Reduced mass of tin after electrolysis process at various potential in 0.02 M HCl

Table 2 .
Reduced mass of tin after electrolysis process at various concentration at potential 60 V