Summer Research Fellowship Programme of India's Science Academies

Synthesis of iron-oxide nanoparticles for scavenging of arsenic and fluoride, synthesis of polyoxotungstates for versatile applications

Jyotismita Das

Student, Department of Chemistry, B. Borooah College, Dr. Bhubaneshwar RG Baruah Rd Ulubari, Guwahati, Assam 781007

Dr. Priyabrata Banerjee

Senior Scientist, Surface Engineering and Tribology Group, CSIR-Central Mechanical Engineering Research Institute, Mahatma Gandhi Avenue, Durgaur 713209



Rapid industrialization and population explosion in the world has been dramatically deteriorating the global climate and natural ecosystem owing to voluminous waste generation. It contains various pollutants including heavy metal ions, toxic organic compounds, pharmaceuticals, organic and inorganic dyes and dissolved inorganic solids. Contamination of drinking water sources continues to pose a challenge in almost all parts of the world. Among the inorganic pollutants, arsenic and fluoride have lured massive connotation towards obtaining secure drinking water predominantly owing to two major reasons. Chronic deadly effects on human health caused by high intake accompanied by their natural abundance in drinkable water sources. Literature is replete with plethora of adsorbent materials for the mitigation of arsenic and fluoride from water, but in recent decades there has been a surging interest in the application of nanomaterials in environmental applications. In its relevance the incorporation of bimetallic iron oxide based materials are known for their affinity towards Arsenic and fluoride removal. So, in this work synthesis of iron oxide nanoparticles has been done that serves as a potential adsorbent for removal of arsenic and fluoride. Additionally a vast number of studies are related with polyoxometalate due to their attractive electronic and molecular properties that give rise to a variety of applications. The applications include catalysis, medicines and material science. Their versatile nature originates from the ability to polymerize metal oxide based polyhedra to form a range of clusters from low to high nuclearities. Within this eight week we have synthesized Polyoxotungstates owing to its ability to utilize organic based guest analytes in trapping.

Keywords: bimetallic nanomaterials, adsorption, polyoxometallate, multifarious properties, disparate applicability.


FT-IRFourier-transform infrared Spectroscopy
UV-VIS Ultra Violet – Visible Spectroscopy
EDXEnergy-dispersive X-ray Spectroscopy 
FESEMField Emission Scanning Electron Microscopy



Contamination of drinking water resources continues to be a challenging and burning issue in almost all parts of the world. The World Health Organization (WHO) reports that around 748 million people around the world lack access to safe drinking water and thus one of the Sustainable Development Goals (SDG6) of the United Nations is to ensure Universal access of safe drinking water to all by 2030. Ground water consists of a number of naturally occurring and anthropogenic generated ions which may compromise the quality of water and make it unfit for drinking purpose[2]. Among the various inorganic contaminants in ground water, arsenic and fluoride have been determined to be the contaminants most detrimental to health. Studies have also indicated that two contaminants when ingested together may function independently, synergistically or antagonistically with respect to one another. There are reports that reveal the the co-existence of both arsenic and fluoride in ground water resources. The major challenge is towards the design and synthesis of next generation materials that would be safe, non-corrosive and extensively used for mitigation of these raw water contaminants (arsenic and fluoride herein). This will ultimately pave the way towards fetching potable water from contaminated ground water resources.

    Effect of Arsenic Poisoning

    Arsenic poisoning is a medical condition that occurs due to elevated levels of arsenic in the body. If arsenic poisoning occurs over a brief period of time symptoms may include vomiting, abdominal pain, encephalopathy, and watery diarrhoea that contains blood. Long-term exposure can result in thickening of the skin, darker skin, abdominal pain, diarrhea, heart disease, numbness, and cancer.

    Ingestion of excess fluoride, most commonly in drinking-water, can cause fluorosis which affects the teeth and bones. Moderate amount leads to dental effects, but long-term ingestion of large amounts can lead to potentially severe skeletal problems. Paradoxically, low levels of fluoride intake help to prevent dental caries. The control of drinking-water quality is therefore critical in preventing fluorosis. Fluorosis is caused by excessive intake of fluoride. The dental effects of fluorosis are developed much earlier than the skeletal effects in people exposed to large amounts of fluoride. Clinical dental fluorosis is characterized by staining and pitting of the teeth. In more severe cases all the enamel may be damaged.

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      Dental and Skeletal Fluorosis

      Literature is replete with plethora of materials that have been tested as possible adsorbents for the removal of arsenic [3] and fluoride from water. These primarily include alumina, iron based oxides, rare metal oxides, activated carbon [4], and bone char to name a few. In the recent decades, there has been a surging interest in the extensive exploration of nanomaterials towards environmental applications such as in contaminant removal or toxic ion mitigation. Among these the use of iron oxide based materials are significantly known for their moderate affinity towards removal of both arsenic and fluoride.

      Therefore, in the present study, an attempt has been made in order to study the feasibility of bimetallic iron oxide nanoparticles as adsorbents for removal of arsenic and fluoride. In order to achieve this, iron oxide nanoparticles were synthesized, characterized for arsenic and fluoride removal efficiency.

      Literature Review

      Iron oxide nanoparticles play a major role in various areas of chemistry, physics and material science.[1-2] The application of magnetic technology to solve environmental problems has received considerable attention in the recent years. Literature is replete with reports demonstrating that magnetic Fe3O4 can be used for removal of alkalinity and hardness, desalination, decolourization of pulp milk effluent and removal of natural organic compounds. After adsorption of the target specific analytes, Fe3O4 can be separated from the medium by a simple magnetic process. Synthesis of Fe3O4 nanoparticles is highly efficient for potential applications and fundamental research.

      Materials And Methods:

      Procedure of synthesis of hydrous Zinc incorporated ferric oxides

      Hydrous iron oxide incorporated transition metal (Zn) based nanoparticles have been prepared by the following method:

      For synthesizing 1:1 nanoparticles 16.89 g of FeCl3 (0.25M) and 18.59 g of ZnNO3 (0.25M) have been taken in two separate 1000ml beaker. 5ml of conc. HCl is added in each beaker. The volume is made up by distilled water addition. Then in a plastic container a magnet is kept which is mounted on a magnetic stirrer. The RPM (rotation per minute) is set (600-700) after addition of FeCl3 solution followed by ZnNO3 solution. A separating funnel containing NH4OH is set up; dropwise NH3 will trickle and mix. After a certain intervals of the time pH of the solution is constantly monitored with pH paper.

      The pH should retain within (6~7). The container is then unmounted. It is then allowed to settle for overnight and is then filtered under suction / vaccum pump. The brown mass so obtained is then dried inside an oven at 80-1000C had been treated with cold water, and re-dried at the temperature. Finally, the dried material was ground, sieved to particles size in order to obtain fine nano sized particles. After drying we have to grind it to obtain fine nano sized iron particles.

      Results and Discussion


      Figure displays the FESEM images (Fig. 3a and b) along with the elemental composition prevailing over the surface of the asynthesized nanoparticles in tabular form (Table 1). In the image (a) single particle has been visualized wherein the shape of particles is revealed. Whereas the image (b) showed the granulated micro structure of the asynthesized powder (nanoparticles). The average grain size was observed to be ~ 200 nm. Owing to non-uniform distribution of grain growth and its subsequent non-similar size is beneficial towards permitting penetration of the target specific analyte solution bearing ions of varying sizes.  

      Untitled 3.png
        The FESEM images at (a) high resolution and (b) low resolution of the aysnthesized bimetallic nanoparticles.

        From the EDX study (Table 1) the respective abundance of the constituent elements could be concluded along with the weight percentage of atomic composition of the elements of the bimetallic iron nanoparticle surface.

        Table 1: Elemental composition of the asynthesized nanoparticles

        Element Weight% Atomic%  
        C K 10.5 19.31  
        O K 42 60.25  
        Cl K 4.03 2.72  
        Fe K, ZnK 38.89, 4.58 15.70, 2.02  

        FT-IR Spectra

        The FT-IR spectra of the asynthesized bimetallic nanoparticles exhibit a few marker peaks (3408 cm-1, 1630 cm-1, 1400 cm-1) (Fig. 4) that correspond to the functionalities prevailing within the same and also authenticate the formation of it. The M-O stretching band is observed at 1400 cm-1. The bending of O–H band appears around υ = 1630 cm−1. The more intense FTIR stretching band of hydroxyl group is found to be around 3408 cm−1.

        Untitled 4.png
          FT-IR Spectrum of the asynthesized bimetallic nanoparticles.


          Bimetallic iron oxide nano particles were synthesized by chemical co-precipitation method and it was experimentally observed that the grain size of the nano particles is in between 190-210 nm. The nanoparticles were characterized by FT-IR and FESEM analysis. The composition of the nanoparticles was sanguined by EDX analysis. These nanoparticles are supposed to adsorb fluoride and arsenic properly from ground water resources. In the future work emphasis will be solely levied towards full fledged characterization and comparison of the asynthesized material after adsorption of the targeted analytes and in depth study of the plausible mechanistic course of interaction of the same.



          In the domain of chemistry, a polyoxometalate (POM) is particularly defined as a polyatomic ion, usually an anion that consists of three or more transition metal oxyanion linked together by shared oxygen atom to form closed 3-dimensional frameworks. The metal atoms are usually colourless or orange, diamagnetic anions. Two broad families are recognized, isopolymetalates composed of only one kind of metal and oxide and heteropolyoxometalates, composed of one metal, oxide, and a main group oxyanion (phosphate, silicate, etc.). Many expectations to this general statement exist.

          Polyoxometalates have been subjected to a vast number of studies due to their attractive electronic and molecular properties that give rise to a variety of applications e.g. in catalysis, medicine and material science. Their versatile nature originates from the ability to polymerize metal-oxide based polyhedral to form a range of clusters from low to high nuclearities. In particular, the ability for molybdenum-based systems to form very large clusters has been demonstrated by a number of nanosized cluster system. Therefore, the ability to assemble large cluster systems from smaller known building blocks in a predetermined way is a great challenge; as such route could be a direct way to systematically control the overall cluster architecture and properties. In this project, synthesis of polyoxometalate (in particular polyoxotungstate) for exhibiting versatile applications.

           Literature Review

          Again, the Polyoxotungstates with the Keggin structure are among the most studied polyoxometalates. These include the parent Keggin anion {XW12O40}n-, the lacunary {XW11O39}(n+4)- and the metal substituted anions {XW11M(L)O39}-, X= P, Si, B and others, M = transition or p- block metal ions, L= H2O or other monodentate ligands [5-8]. The association of Keggin type polyoxotungstate with cations has been shown to be different from the “traditional” one (group 1 metal, NH4+, low tetra-alkylammonium cations) has recently been shown to provide very interesting compounds with relevant new properties. This include new magnetic, conducting and support properties among others.

          Procedure of Synthesis of Polyoxotungstate


          Na2WO4. 2H2O (0.2g) and triethanolamine- hydrochloride (0.2g) were dissolved in H2O (10ml) in a plastic flask and the solution was adjusted to a pH of 2.2 with HCl (6N). After heating the reaction mixture to 90°C for 24 hours, 0.01289 g ZrOCl2.8H2O were added to the hot solution and mixture was cooled down without further stirring. The sample was stored undisturbed for crystallization, which yielded colourless needle shaped material.


          Physical properties

          Colour: Colour of the obtained polyoxotungstate crystal is white and it is a solid crystalline material.

          Solubility: Na2WO4.2H2O and ZrOCl2 are soluble in water and DMSO.

          The prepared crystal is soluble only in aqueous medium, slightly soluble in MeOH and DMSO and insoluble in other solvents.

          FT-IR Spectra

          The FT-IR spectrum of the precursors i.e. Triethanolamine (Fig 5a), sodium tungstate (Fig 5b) and the prepared polyoxotungstate crystal (Fig 5c) are depicted below. The IR spectrum of expected polyoxotungstate shows a clear difference from the IR spectrum of its precursor and also it shows clear indication of tungsten oxide stretching frequencies. Hence from the above FT-IR graphs we can have a clear indication of formation of a polyoxotungstate.

          Untitled 5.png
            (a) FT-IR spectra of Triethanolamine, (b) FT-IR spectra of sodium tungstate (c) FT-IR spectra of polyoxotungstate crystal.

            UV-Vis Spectra

            The UV-VIS spectrum of the polyoxotungstate is depicted in Fig. 6. It is clear from the graph that the polyoxotungstate material has a clear peak at 258nm which is coincident with the literature value of polyoxometallates and the cause behind this absorbance is charge transfer between metal and oxygen in the polyoxotungstate crystal.

            Untitled 6.png
              UV-VIS plot of the synthesized polyoxotungstate.

               FE-SEM AND EDX ANALYSIS:

              FE-SEM image of the synthesized polyoxotungstate is shown below in Fig. 7. From the figure we can conclude that the desired material has block shaped morphology and also it is a highly crystalline material. EDX analysis confirms its composition as the EDX plot shows a high abundance of W, O and also Zr.

                FESEM and EDX image of the synthesized crystal.

                X-ray mapping

                X-ray mapping images of the polyoxotungstate are shown below (Fig. 8). The abundance of the constituents is shown here with their respective positions.

                  X-ray mapping images of the polyoxotungstate. (a) part of the crystal where X-ray mapping was done. (b) abundance of Tungsten. (c) abundance of Chlorine (d) abundance of Zirconium


                  Polyoxotungstate has been successfully synthesized and characterized properly through FT-IR, FESEM and EDX. Crystalline nature of the material was confirmed by FESEM analysis and composition of the material was confirmed by EDX analysis.


                  First of all I would like to express my heartfelt thanks to Indian Academy of Sciences for providing me such a wonderful opportunity to enhance my research skill.

                  My immense gratitude to CSIR-Central Mechanical Engineering Research Institute, Durgapur for giving me an opportunity to work as a summer research fellow in this premiere research institute.

                  I would like to express my sincerest gratitude to Dr Priyabrata Banerjee, Senior Scientist, Surface Engineering and Tribology Group, CSIR-CMERI for his constant encouragement and guidance during the project. I will always be grateful to him for his support and kindness. It would be impossible to count all the ways that he has helped me in my career. Thank you so much Sir for being an excellent mentor and for guiding me on the right path. I only hope I can return the favour sometime in the future.

                  I owe a debt of gratitude to Ms. Suparna Paul, SRF and Mr. Anindya Roy, JRF for their constant assiatance throughout my project. I thank all my labmates for their continuing support throughout.

                  Lastly I am very much grateful to my parents for their constant love and support. Special thanks to Dr Apurba Kalita and Dr Diganta Choudhury, Department of Chemistry B.Borooah College, Guwahati for being my motivators and support system.


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                  [2] P. L. Hariani, M. Faizal, R. Marsi, and D. Setiabudidaya,Synthesis and Properties of Fe3O4 Nanoparticles by Co-precipitation Method to Removal Procion Dye. International Journal of Environmental Science and Development, 2013, 4(5), 336-340.

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                  [6] W. C. Chen, L. K. Yan, C. X. Wu, X. L. Wang, K. Z. Shao, Z. M. Su and E. B. Wang, Assembly of Keggin-/Dawson-type Polyoxotungstate Clusters with Different Metal Units and SeO32− Heteroanion Templates. Inorg. Chem. 2006, 45, 1915-1923.

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                   [8] D. L. Long, H. Abbas, P. Ko¨ gerler and L. Cronin, A High-Nuclearity “Celtic-Ring” Isopolyoxotungstate, [H12W36O120]12-, That Captures Trace Potassium Ions. J. Am. Chem. Soc. 2004, 126, 43, 13880-13881.  

                  Written, reviewed, revised, proofed and published with