Tag Archives: magnetite

Reaktor elektrokimia untuk produksi nanopartikel berhasil di-scale up

Peneliti di laboratorium Elektrokimia dan Korosi, Departemen Teknik Kimia ITS berhasil melakukan scale up reaktor elektrokimia untuk memproduksi nanopartikel. Sebelumnya, sebuah proses sederhana untuk memproduksi nanopartikel magnetite (Fe3O4) dengan elektro-oksidasi besi dalam air telah berhasil dikembangkan (Fajaroh dkk., 2012). Proses ini dapat dikatakan proses yang ramah lingkungan karena bahan yang digunakan hanya lempengan besi dan air saja, tanpa tambahan bahan kimia lainnya. Namun sayang sekali, kapasitas produksinya sangat rendah. Untuk mendapat kurang dari 1 gram dibutuhkan waktu lebih daripada 20 jam.

Hal ini dicoba diatasi dengan melakukan perancangan ulang konfigurasi elektroda besi dalam volume reaktor yang sama (Nurlilasari dkk., 2019). Dalam hal ini elektroda yang berupa lempengan besi disusun berjajar menjadi beberapa baris, dalam hal ini hanya 4 baris, dan dalam satu baris dibagi menjadi 2, dan kemudian dihubungkan dengan catu daya listrik searah dengan sambungan monopolar (Gambar 1 & 2). Dengan konfigurasi ini, kapasitas produksi dapat ditingkatkan hingga mencapai 30 kali. Kelebihan lainnya, elektroda besi tidak perlu dilapisi terlebih dahulu dengan lapisan besi yang relatif murni dengan elektrodeposisi.

Gambar 1. Reaktor elektrokimia dengan satu pasang elektroda yang dikembangkan sebelumnya (kiri); dn reaktor elektrokimia monopolar (kanan).
Gambar 2. Susunan reaktor elektrokimia skala laboratorium untuk produksi nanopartikel magnetite dengan elektroda besi dalam elektrolit air.

Nanopartikel yang dihasilkan berukuran antara 20-25 nm dan berbentuk bola. Nanopartikel ini memiliki sifat ferromagnet dengan magnetisasi jenuh sekitar 50 emu/g. Bahan ini bisa dipakai untuk berbagai keperluan, a.l.: katalis, ferofluida, biomedis dan remediasi lingkungan, dan bahan yang menjanjikan untuk baterai litium-ion dan superkapasitor. Selain itu, bahan seperti ini sudah banyak digunakan sebagai pigmen hitam dan dalam alat perekam magnetik.

Salah satu aplikasi yang sudah diuji di Lab adalah pemakaian nanopartikel magnetite yang diproduksi dengan metoda di atas untuk katalis reaksi reduksi oksigen (RRO) dalam larutan 0,6 M KOH yang jenuh oksigen (Gambar 3). Uji kinerja katalitik menunjukkan bahwa mekanisme RRO adalah melalui 4-elektron. Jadi, bahan memiliki potensi yang besar untuk digunakan sebagai elektroda baterai logam-udara yang salah satunya adalah untuk pembangkit listrik stasioner daerah terpencil. (hs)

Gambar 3. Foto rangkaian alat uji kinerja nanopartikel magnetite sebagai elektrokatalis RRO.

Daftar Pustaka

Fajaroh, F., Setyawan, H., Widiyastuti, W., Adv. Powder Technol. 23(3), 328-333 (2012). DOI: 10.1016/j.apt.2011.04.007

Nurlilasari, P., Widiyastuti, W., Setyawan, H., Faizal, F., Wada, M., Lenggoro, I.W., Chem. Eng. Sci., 201, 112-120 (2019).In Press, DOI: 10.1016/j.ces.2019.02.027

Most cited Advanced Powder Technology articles

aptsem

SEM image and particle size distribution of magnetite nanoparticles

Our article published in Advanced Powder Technology in 2012 is listed in the most cited articles of Advanced Powder Technology, for articles published in the journal since 2011. Our article is

Fauziatul Fajaroh | Heru Setyawan | W. Widiyastuti | Sugeng Winardi

The data for the citation number were extracted from SCOPUS database. The complete list of the most cited articles can be read in

http://www.journals.elsevier.com/advanced-powder-technology/most-cited-articles

Electrochemical-induced particle formation

One of our research work is dealing with the synthesis of particles by electrochemical method. One of them is synthesis of magnetite (Fe3O4) nanoparticles. How can electrochemical process induce particle formation? This article will give some discussion about electrochemical-induced particle formation with an example about the formation of magnetite nanoparticles.

One important thing that must be noted is that particles may be formed from solution if the solubility of a dissolved solid (solute) in solvent is exceeded, i.e., the solutiion must be supersaturated. Supersaturation refers to a state in which liquid (solvent) contains more solute than can ordinarily be accommodated at that temperature. Such process often referred to as crystallization, or precipitation if the particle formation is induced by chemical reaction. Crystallization is widely used in industries to produce some important products such as sugar, salt, monosodium glutamate, etc.

On an industrial scale, a large supersaturation driving force is necessary to initiate primary nucleation (the first step of nucleation). The supersaturation may be driven by a combination of high solute concentration and rapid cooling. Once the condition for nucleation is met, nucleation begins. Then, particles may be grown through surface growth and coagulation, and particle size distribution begins to take shape.

Regarding with the formation of magnetite nanoparticles from aqueous system in an electrochemical system, what is the driving force to initiate primary nucleation, i.e., to reach supersaturation? It has been shown that, as illustrated by the Pourbaix diagram, iron oxides and/or hydroxides (Fe2O3, Fe3O4, Fe(OH)2, Fe(OH)3) can be in electrochemical equilibrium with water at high potentials in neutral and basic solutions. Under basic conditions, Fe3O4 may be formed by the corrosion process in an aqueous medium. Therefore, if a layer of iron film adheres weakly to an anode surface, Fe2+ ions would be released from the surface during the electrooxidation of the iron.

Hence, the mechanisms of formation of Fe3O4 can be described as follows. Fe2+ ions produced by iron oxidation at anode react with OH- ions coming from water reduction at cathode. Fe(OH)2 is then partially oxidized by O2 produced by water oxidation at anode to form FeOOH. Fe3O4 is formed when an appropriate proportion of Fe(OH)2 and FeOOH is created. The overall mechanism may be illustrated schematically below (Fajaroh et al, Adv. Powder Technol., 23, 328-333, 2012).

Mechanism of particle formation of Fe3O4

Electrosynthesis of magnetite nanoparticles

We have successfully synthesized magnetite (Fe3O4) nanoparticles and SiO2-coated magnetite nanoparticles by an enviromentally friendly electrochemical method. The results have been published in: (i) Advanced Powder Technology and (ii) Journal of Nanoparticle Research. Below is summary of the articles

Advanced Powder Technology (2011), in press
Synthesis of magnetite nanoparticles by surfactant-free electrochemical method in an aqueous system
Method: electro-oxidation of iron in water
Material: magnetite (Fe3O4)
Particle size: 10-30 nm
Properties: ferromagnetic
Impurities: FeOOH

SEM image and particle size distribution

Journal of Nanoparticle Research (2012) 14:807
One-step synthesis of silica-coated magnetite nanoparticles by electrooxidation of iron in sodium silicate solution
Method: electro-oxidation of iron in sodium silicate solution
Material: SiO2-coated magnetite
Size: 6-10 nm
Properties: superparamagnetic
Impurities: none

SEM image and particle size distribution