ABSTRACT Nano MnO2 powder was synthesized by low temperature solution combustion method using oxalyl dihydrazide (ODH) fuel. The final product was well characterized by Powder X-ray diffraction (PXRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning electron microscopy (SEM) for crystallographic purity, phase formation and surface morphology respectively. PXRD results show that pure MnO2 was synthesized at 300 0 C with no other impurities. SEM micrograph shows the product has highly porous structure with large voids, typical of combustion derived material. An adsorption characteristic of the porous MnO2 was studied over direct green dye (DG). The optimum dose of MnO2 for removal of 10 ppm DG azo dye was found to be 0.4 g L -1 

B M Nagabhushana

For Correspondence

Hari Krishna

K H Shivaprasad

Kumar

Pradeep Bm

Sriram Karikkat

T H Udayashankara

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RESEARCH AND REVIEWS: JOURNAL OF MATERIAL SCIENCES 
 
 
Synthesis, Characterization of Nano MnO2 and its Adsorption Characteristics Over 
an Azo Dye. 
 
BM Pradeep Kumara, Sriram Karikkatb, R Hari Krishnac, TH Udayashankarab,  KH Shivaprasada, 
and BM Nagabhushanac*. 
 
aDepartment of Chemistry, V. S. K. University, Bellary -583105, India. 
bDepartment of Environmental Engineering, Sri Jayachamarajendra College of Engineering,  Mysore -570 006, India 
cDepartment of Chemistry, M. S. Ramaiah Institute of Technology, Bangalore 560 054, India. 
 
 
Research Article 
 
Received: 22/11/2013 
Revised: 12/12/2013 
Accepted: 19/12/2013 
 
*For Correspondence 
 
Department of Chemistry, M. S. 
Ramaiah Institute of Technology, 
Bangalore 560 054, India. 
 
Keywords: Nano MnO2, Solution 
combustion, Adsorbtion, Direct 
green dye 
 
 
ABSTRACT 
 
 Nano MnO2 powder was synthesized by low temperature solution 
combustion method using oxalyl dihydrazide (ODH) fuel. The final product 
was well characterized by Powder X-ray diffraction (PXRD), Fourier 
Transform Infrared Spectroscopy (FTIR) and Scanning electron microscopy 
(SEM) for crystallographic purity, phase formation and surface morphology 
respectively. PXRD results show that pure MnO2 was synthesized at   300 
0C with no other impurities. SEM micrograph shows the product has highly 
porous structure with large voids, typical of combustion derived material. 
An adsorption characteristic of the porous MnO2 was studied over direct 
green dye (DG). The optimum dose of MnO2 for removal of 10 ppm DG azo 
dye was found to be   0.4 g L-1. 
 
 
INTRODUCTION 
 
 The textile industries are becoming a major source of environmental contamination because an alarming 
amount of dye pollutants are generated during the dyeing processes[1]. In fact, about 700000 tonnes of different 
dyes are produced annually in the world, among which about 50000 tonnes of dyes are discharged into the 
environment[2]. Organic dyes are one of the largest pollutants released into wastewater from textile and other 
industrial processes, which have shown severe impacts on human physiology[3,4]. Some dyes like azo-dyes and 
fluorescein dyes have been found to be highly cytotoxic for the mammalian tissues[5,6]. The organic groups present 
in dyes result in the formation of certain reactive intermediates, which trigger the morphological and genetic 
alterations, thereby making the dye cytotoxic and carcinogenic. Synthesis, properties and application potential of 
semiconductor nanoparticles manifesting photocatalytic activity in various redox-processes have been and the 
subject of great interest to the present day[7,8]. In addition several novel adsorbents have been reported to possess 
great adsorption potential due to their enhanced adsorptive capacity[9]. Nano-structure compounds have gained 
importance in this category due their anticipated high surface area and improved reactive sites[10,11]. Nano-MnO2 
has great potential applications in environment protection field as a new generation of environmental friendly 
catalyst. There are a number of research results which show that the functional activity of semiconductor materials 
depends on the structure. Manganese oxide is one of the most interesting materials, which has a wide variety of 
structure with large surface area. The diverse structures, chemical properties of manganese oxides are taken 
advantage of in potential applications such as cation–exchange[12], ion and molecule separation[13–14], 
adsorbents[15], sensor[16], battery[17], catalysis[18] etc. It is also used for a wide catalytic applications, such as 
degradation of dyes[19,20], photocatalytic oxidation of organic pollutants and waste water treatment[21], nitric oxide 
reduction[22], ozone decomposition[23], selective oxidation of CO[24], alcohols[18] etc., The diverse chemical properties 
makes the MnO2 material unique. MnO2 with different physical and chemical properties, such as crystallinity, 
amount of combined water, specific surface areas, and electrochemical performance, can be yielded under 
different synthesis conditions.  
 
       Nanostuctured materials become more and more attractive in recent years, because these materials 
possess favorable and enhanced physical and chemical properties. Much effort has been made toward the 
preparation of MnO2 nanostructures with different morphologies[25,26,27]. However, very few reports on the synthesis 
of MnO2 nanostructures with Solution combustion. In this paper, we report a facile, energy saving method to 
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synthesize MnO2 nano powders with highly porous structure via solution combustion route and its potential 
application in removal of organic dye from aqueous solution. 
 
EXPERIMENTAL 
 
Synthesis of nano MnO2 
 
 The synthesis process involved the combustion of redox mixtures in which Manganese nitrate 
[Mn(NO3)2.H2O] acted as an oxidizing reactant and oxalyl di-hydrazide (ODH) [C2H6N4O2] as a reducing one. The 
initial composition of solution containing manganese nitrate and ODH was calculated based on the total oxidizing 
and reducing valences of the oxidizer and the fuel using the concepts of propellant chemistry[28]. All the reagents 
were of analytical purity, and used without further purification. Manganese nitrate and ODH were mixed with 
minimum quantity of doubled distilled water in a cylindrical petri dish and stirred for few minutes until clear solution 
is formed. The dish was introduced into a muffle furnace maintained at 300 0 C. The solution initially undergoes 
dehydration, followed by decomposition with the evolution of large amounts of gases. The mixture then froths and 
swells forming foam, very soon the flames spread the entire volume forming black porous product. The entire 
combustion process is over in 5 min. The foam was grinded to obtain fine powder of MnO2. 
 
Instruments used 
 
 The PXRD patterns of MnO2 samples were obtained using a Philips PW/1050/70/76 X-ray diffractometer 
using CuKα radiation at a scan rate of 2°/min. The morphology of powders was examined using JEOL (JSM-840A) 
scanning electron microscopy (SEM). FTIR spectra were recorded using Nicollet IMPACT 400 D FTIR spectrometer, 
in the range 400–4000 cm−1 as KBr pellet. The absorption spectra were recorded with a UV-visible 
spectrophotometer (Elico-159). 
 
RESULTS AND DISCUSSION 
 
Characterization of nano-catalyst 
 
Powder X-ray diffraction (PXRD) 
 
 Figure 1. shows the PXRD pattern of the MnO2 powder prepared using ODH as fuel in stoichiometric fuel-to-
oxidant ratio at 300 ◦C. The typical PXRD patterns show broad diffraction peaks corresponding to Braggs reflections 
from (120), (131), (300), (160)  and (003) planes which corresponds to gamma phase MnO2 (according with JCPDS 
14-644) with no other impurity peaks. The crystallite size was estimated using Scherrer’s formula given by the 
relation 
      
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 1: PXRD pattern of MnO2 nano powder 
 
 
D=0.9λ/βCosθ         …………..(i) 
 
The crystallite size estimated by this method is found to be in the range 15-20 nm. 
 
Scanning Electron Microscopy (SEM) 
 
 SEM micrograph (Fig.2) shows the overall appearance of the combustion derived product.The particles are 
almost spherical with varying sizes, might be due to non uniform distribution of temperature during combustion.   It 
can be observed that product aggregation is constituted by many irregular particles with a variety of pores and 
10 20 30 40 50 60 70 80
00
3
16
030
0
13
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In
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 (a
.u
.)
2Degree
12
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JCPDS: 14-644
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voids due to the evolution large amount of gases that are formed as by product during synthesis. This type of 
structure is typical of combustion derived samples. Highly porous nature of MnO2 facilitates and enhances the 
adsorption characteristics.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 2: SEM micrograph of nano MnO2. 
 
Fourier Transform Infrared Spectrum (FTIR) 
 
 The FT-IR spectrum was used to identify the functional groups and other impurities present in the final 
product. Fig. 3 represents the spectrum of the MnO2 nano powder prepared by solution combustion method. The 
broad band at 3438 cm−1 is believed to be associated with the stretching vibrations of hydrogen-bonded surface 
water molecules and hydroxyl groups. Additionally, the bands at 1645 and 1386 cm−1 correspond to the existence 
of large numbers of residual hydroxyl groups, which imply the O-H vibrating mode of traces of adsorbed water. The 
band located at 539 cm−1 can be ascribed to the Mn-O vibrations of MnO2 nano powder. The FTIR analysis 
presented here is consistent with the   results reported in the literatures[29, 30]. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
                                    
Figure. 3. FTIR spectra of MnO2 nanopowder 
 
ADSORPTION ACTIVITY OF NANO MnO2 OVER DIRECT GREEN DYE 
 
 Direct green dye has a molecular formula of C34H22N8Na2O10S2 and its molecular weight of 767.7.    Direct 
dyes colour cellulose fibres directly without the use of mordant. They are used for dyeing wool, silk, nylon, cotton, 
rayon etc. Direct dyes colour cellulose fibres directly without the use of mordant. It has a strong, though apparently 
non-covalent affinity to cellulose fibres. However, its tendency to change colour when touched by sweaty fingers 
and its toxicity has proven to be a disadvantage to its best use.   
 
         In order to evaluate adsorption activity of the combustion derived MnO2 sample, batch adsorption studies 
of direct green dye was done. A typical experiment constitutes 50 ml of 10 ppm dye solution and different amount 
of adsorbent were taken in a glass reactor. The mixture was stirred in dark for 30 minutes to establish the 
4000 3500 3000 2500 2000 1500 1000 500
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%
 T
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m
it
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 (
a
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.)
Wavenumber (cm
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adsorption equilibrium between the dye molecules and the catalyst surface. The decolourization efficiency (%) was 
calculated as follows  
 
% Removal = Co-C/Co X 100  ….. (ii) 
 
Where C0 is the initial concentration of dye and C is the concentration of dye after adsorption. 
 
Effect of MnO2 dose 
 
 Experiments were carried out using different amounts of MnO2, keeping dye concentration constant at 10 
ppm [Fig. 4]. It was found that the adsorption increases up to 20 mg/50 ml of the dye solution, beyond which it 
shows a sudden reduction. The increase in the adsorption efficiency of DG with increase in the amount of 
adsorbent may be due to increase in the active sites available on the adsorbent. Decrease in adsorption beyond 20 
mg is due to desorption of dye due to increased collutions between adsorbent.The percentage removal of DG is 
about around 67 % at neutral pH for 30 min contact time.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure  4: UV-Vis spectra of  (a) blank DG dye (b) 10 mg MnO2  (c) 20 mg MnO2   (d) 30 mg MnO2 (e) 40 mg MnO2. 
 
CONCLUSIONS 
 
 In this study, highly porous and crystalline nano MnO2 was synthesized by low temperature combustion 
synthesis. The adsorbent consists of monocrystalline particles of 15-20 nm size. The ability of MnO2 to adsorb DG 
was investigated by batch adsorption studies. The amount of dye adsorbed was found to vary with adsorbent 
dosage. The amount of dye uptake (mg/g) was found to increase with increase in adsorbent dose upto 0.4 g L -1 and 
beyond which it decreases. It can be concluded that the combustion derived nano porous MnO2 is an efficient 
adsorbent for the removal of DG from aqueous solution. 
 
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Synthesis, Characterization of Nano MnO2 and its Adsorption Characteristics Over an Azo Dye

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Synthesis, Characterization of Nano MnO2 and its Adsorption Characteristics Over an Azo Dye

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