Our work on hydroxyapatite accepted in J. Chem. Eng. Japan

Our work on the electrochemical synthesis of hydroxyapatite has been accepted for publication in the Journal of Chemical Engineering of Japan (Impact Factor 0.61). This journal is an official publication of the Society of Chemical Engineers, Japan. It is dedicated to providing timely original research results in the broad field of chemical engineering ranging from fundamental principles to practical applications.

An Experimental and theoretical investigation of the formation of hydroxyapatite particles prepared by an electrochemical method

Adrian Nur and Heru Setyawan

NurGrapAbs

Abstract

Electrochemical synthesis of hydroxyapatite particles was performed galvanostatically from a homogeneous solution of Na2H2EDTA×2H2O, KH2PO4 and CaCl2. The electrogeneration of OH ions by water reduction at the cathode plays an important role in the formation of hydroxyapatite by an electrochemical method. The OH ions induce the liberation of Ca2+ ions and the dissociation of phosphoric acid, which serve as the reactants for the formation of hydroxyapatite. We found that the final product obtained, i.e., brushite or hydroxyapatite (HA), corresponds to the pH of the solution. Brushite is formed when the pH is < 7, and HA is formed when the pH > 7. Aging the suspension for 72 h at 40transforms brushite to HA even at pH < 7. The presence of Ca2+ during aging accelerates brushite conversion. EDTA serves as a chemical agent to mediate particle nucleation and growth. The reaction mechanism and its kinetic model proposed for the HA formation could predict the experimental results well.

Paper in Adv. Powder Technol. is available on line

Our paper accepted in Advanced Powder Technology (see before) is now available on line at here.

Thermal stability of silica-coated magnetite nanoparticles prepared by an electrochemical method

Fauziatul Fajaroh, Heru Setyawan, Adrian Nur, I. Wuled Lenggoro

ABSTRACT

Magnetite nanoparticles have been prepared by electrooxidation of iron in water. Surface modifications have been conducted by coating the nanoparticles with silica by a one-step synthesis in dilute sodium silicate solution. The mean size of particles was approximately 10-30 nm for the uncoated particles and 9-12 nm for the coated particles. The results obtained from thermal gravimetric/differential thermal analysis (TG/DTA) revealed that the silica layer formed by the electrochemical method was stable and could serve as a protective layer. Annealing the nanoparticles at 550°C for 30 min converts magnetite into maghemite for the silica-coated particles, and it further converts the uncoated particles into hematite. The conversions cause the saturation magnetization to decrease for all samples.

HIGHLIGHTS

  1. Silica-coated magnetite nanoparticles were succesfully prepared by one-step method.
  2. We investigate the thermal stability of the silica-coated magnetite nanoparticles.
  3. The silica layer is stable under heating up to 550°C.
  4. The silica layer can protect magnetite from being converted to other oxide species.

GRAPHICAL ABSTRACT

Thermal stability of SiO2-coated Fe3O4 nanoparticles

Our paper entitled: “Thermal stability of silica-coated magnetite nanoparticles prepared by an electrochemical method” has been accepted for publication in the journal Advanced Powder Technology published by Elsevier B.V. on behalf of the Society of Powder Technology Japan.Below are the highlights, graphical abstract and abstract of the article.

Advanced Powder Technology

Thermal stability of silica-coated magnetite nanoparticles prepared by an electrochemical method

Fauziatul Fajaroh, Heru Setyawan, Adrian Nur, I. Wuled Lenggoro

HIGHLIGHTS

  1. Silica-coated magnetite nanoparticles were succesfully prepared by one-step method.
  2. We investigate the thermal stability of the silica-coated magnetite nanoparticles.
  3. The silica layer is stable under heating up to 550°C.
  4. The silica layer can protect magnetite from being converted to other oxide species.

GRAPHICAL ABSTRACT

ABSTRACT

Magnetite nanoparticles have been prepared by electrooxidation of iron in water. Surface modifications have been conducted by coating the nanoparticles with silica by a one-step synthesis in dilute sodium silicate solution. The mean size of particles was approximately 10-30 nm for the uncoated particles and 9-12 nm for the coated particles. The results obtained from thermal gravimetric/differential thermal analysis (TG/DTA) revealed that the silica layer formed by the electrochemical method was stable and could serve as a protective layer. Annealing the nanoparticles at 550°C for 30 min converts magnetite into maghemite for the silica-coated particles, and it further converts the uncoated particles into hematite. The conversions cause the saturation magnetization to decrease for all samples.

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