One Pot Synthesis of Mn3o4/Graphitic Carbonnanoparticles for Simultaneous Nanomolar Detection

Supplementary Information

One pot synthesis of Mn3O4/graphitic carbonnanoparticles for simultaneous nanomolar detection of Pb(II), Cd(II) and Hg(II)

Prashanth Shivappa Adarakattia, Vijaya Kumar Gangaiaha, Craig E Banksb and Ashoka Siddaramannac*

Preparation of Mn3O4 nanoparticles video

VID_20170330_202239.mp4

Table S1. Comparison of variation of Mn3O4 crystallite size as a function of reducer

Sl. No / Fuel / No. mole of gas liberated/ mole of Mn3O4 / Crystallite size (nm) / Ref
1 / Glycine / 18.5 / NR / [29]
2 / Urea / 21.3 / 90 / [26]
3 / Citric acid / 18.5 / 60 / [26]
4 / Ethylene glycol / 17.0 / 30 / [26]
5 / Sucrose / 16.4 / 20 / Present

*NR- Not reported

The observed crystallite size are smaller than the obtained small crystallite size which is two times smaller than the reported Mn3O4 prepared through solution combustion method using urea, citric acid, ethylene glycol by Chen et al. [1], where the author reported the average crystallite sizes of 90, 60 and 30 nm respectively for urea, citric acid and ethylene glycol. The crystallite size along with number of moles of gases produced per one mole of Mn3O4 during solution combustion is summarised within Table 1 [1, 2]. From inspection of Table 1, it is observed that the average crystallite size decreases as the number of moles gasses produced during the solution combustion decreases. Using sucrose, it is about 16.4 moles per one mole of Mn3O4 and it is less than that of gases liberated by glycine, urea, citric acid and ethylene glycol.

Average crystallite size calculation from XRD data

The average crystallite size (D) has been estimated using the Scherrer formula, which assumes

D = Kλ/ cosθ

only the crystallite size is responsible for line broadening [3, 4]. Where, λ is the wavelength of the X-ray, K is the constant (K = 0.99), is the full width at half maximum (FWHM) of the diffraction peak and θ is the angle of diffraction. The FWHM of the (211) diffraction peak was fitted reasonably well using Gauss function and the FWHM of the true (211) diffraction peak was calculated using the equation 2 =B2– b2, where B and b is the measured FWHM of the sample and reference [3, 4]. The FWHM of the (211) diffraction peak is found to correspond to 0.5846 and the corresponding average crystallite size is found to be ~20 nm.The reduced crystallite size of Mn3O4 with sucrose is explained as follows. Controlled combustion reaction, smouldering type, leads to the reduced crystallite size. In order to have controlled combustion and smouldering type reaction, cations have to be distributed throughout the fuel and thereby avoid the selective precipitation. Here, the sucrose in aqueous solution is likely hydrolyzed to fructose and glucose and these further get oxidized to poly hydroxyl acid (Scheme S1, supporting information) [5]. The in situ formed poly hydroxyl acid has one carboxylic acid group and hydroxy groups, which can participate in the metal ions complexation thereby cations are uniformly distributed. Additionally, the stability for the metal complex is also supported by the development of extremely high viscosity as this high viscosity favours low cation mobility which eliminates the crystallite agglomeration.

Surface area Analysis

Figure S1: (a) N2 adsorption-desorption isotherm and (b) Pore size distribution of fabricated Mn3O4 nanoparticles

Table S2. Comparison of the synthesized Mn3O4 nanoparticles that are used to fabricate the Mn3O4 nanoparticle sensor.

Sl.No / Method of Preparation / Shape / Surface area (m2/g) / Advantages / Disadvantages / Ref
1 / Solution combustion / nanoparticle / 66 /

Simple methodology
Preparation completes in less than 5 min.
Applicable for large scale production
Reduced crystallite size (20 nm)
Excellent surface area
No Washing with organic solvent
Low preparation cost
No sophisticated instruments required
Possibility of retaining graphitic carbon (This dramatically enhances the electrochemical behaviour)
Environmentally benign (as it releases CO2, N2 and H2O)

/ Comparatively high temperature used in the preparation (450 °C) / Present
2 / Low temperature route / Particles / 80 /

Good surface area
Pretty simple method

Long reaction time up to 48 hours
Required additional washing

/ [6]
3 / Precipitation / Spherical / 38.4 /

Not required sophisticated instruments
Moderate surface area

Long reaction time up to 96 hours
Required additional calcination (873 K), washings with organic solvents
Containing carbon as impurity

/ [7]
4 / Hydrothermal / Octahedra
Partilces / 9
7 /

Good morphology

Long reaction time up to 8 hour
Required additional washing and drying
Poor surface area
Not cost effective

/ [8]
5 / Hydrothermal / Tubes / 42.18 / Moderate surface area /

Long reaction time (5 hour)
Required additional washings and drying
Not cost effective

/ [9]
6 / Sonochemical / Sphere / 75.67 /

Good surface area
Pretty simple method

/ Preparation time requires up to 3 h. / [10]

Table S2 provides a thorough comparison of the present surface area with reported Mn3O4 along with method of preparation, advantages and disadvantages. It is clear that the presented synthetic methodology reported herein is significant improved over that reported before where Mn3O4 nanoparticles are prepared via a simple, rapid and green protocol.

Figure S2. Effect of pH upon the peak currents of Pb(II), Cd(II) and Hg(II) using the Mn3O4 nanoparticle electrochemical sensor. pH 5 (acetate buffer); Scan rate: 50 mV/s.

Figure S3. Effect of deposition potential upon the peak currents of Pb(II), Cd(II) and Hg(II) using the Mn3O4 nanoparticle electrochemical sensor. pH 5 (acetate buffer); Scan rate: 50 mV/s.

Figure S4. Effect of pre-concentration time upon the peak currents of Pb(II), Cd(II) and Hg(II) using the Mn3O4 nanoparticle electrochemical sensor. pH 5 (acetate buffer); Scan rate: 50 mV/s.

Figure S5. Effect of modifier volume upon the peak currents of Pb(II), Cd(II) and Hg(II). pH 5 (acetate buffer) using the Mn3O4 nanoparticle electrochemical sensor. Scan rate: 50 mV/s.

References

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