Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate

Abstract

A novel and generic sol-gel method has been developed for the production of high purity metal oxide nanopowders using sodium alginate. This has been demonstrated successfully employing nickel oxide (NiO) as a model material in this instance. The results of this investigation indicate that the final particle size of~20 nm can be obtained after calcination of the predried beads at 500°C for 3 h in ambient air. An insight into the calcination process has been obtained using simultaneous thermo-gravimetric analysis and differential scanning calorimetry (TGA/DSC) and high temperature X-ray diffraction (HT-XRD). Powder X-ray diffraction (XRD) confirms that the obtained samples are single phase cubic NiO powders with no trace of impurity. During the phase transformation, NiO + NiO 2 have been found to coexist between 250°C and 350°C and a reaction scheme is proposed to account for this. The mean crystallite sizes calculated from XRD analysis using Rietveld refinement method is in good agreement with the morphological features observed using transmission electron microscopy (TEM). The NiO nanopowders produced in this study exhibit negligible strain as indicated using Rietveld refinement procedure. The XRD and TEM analyses indicate that there is a significant influence of calcination temperature and time on the particle size, which increases with increasing temperature and annealing time. This new sol-gel method is a simple, environmentally friendly, and nontoxic route for a large scale production of high purity single phase nanopowders in a cost-effective manner at significantly low temperatures. The process described in this study can yield 200 kg of NiO nanopowders per ton of dried Ni-ALG beads.J. Nino-contributing editor Manuscript No. 30902.

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“…In TGA curve weight losses of 10% was observed in the first stage due to the removal of adsorbed water. Evaporation of bounded water and dissociation of alginate structure (GG-O-MM, MM-O-GM) along with evolution of bridging oxygen [13] were observed in the range 150-210 °C with corresponding weight loss of 17%. A weight loss of 23% was observed in the range 217-375 °C due to further loss of bridging oxygen and partially reacting with some of carbon atoms in the chain to form CO 2 .…”

“…Sol gel processes are used to fabricate the electrolyte and electrode materials of SOFC with preferred properties or functionalities, as they are capable of providing good control of crystal structure, composition, microstructure and morphology [11]. Nanopowders of CGO (Cerium Gadolinium Oxide) and NiO have been successfully prepared by Leeds Alginate Process (LAP) for electrolyte and anode applications in a SOFC which is a unique polysaccharide mediated ion-exchange process developed by Kale et al [12,13].…”

Hybrid alginate based aerogels by carbon dioxide induced gelation: Novel technique for multiple applications

“…The use of metal alginates as intermediate precursors has been widely reported in literature. For example, nickel oxide (an antiferromagnetic material with catalytic and magnetic properties) can be processed using nickel-alginate crosslinking as an intermediate step [45]. Mixed metal alginate aerogels with controllable amounts of individual metal content can be prepared,which could further be calcined at low temperatures into oxidation catalysts (e.g.…”

Ion-exchange kinetics and thermal decomposition characteristics of Fe2+-exchanged alginic acid membrane for the formation of iron oxide nanoparticles

“…For nanopowders, particle size effects show a far better description of the XRD broadening in comparison to the micro-strain [6,7,16]. …”

“…Most of the research in understanding sodium alginate mediated ion-exchange process in related to pharmaceutical science and food chemistry [2][3][4][5]. Not much has been done to understand this phenomenon with respect to the production of high surface area ceramic oxide particles until recently [6,7]. It has been discovered that, during gelation and subsequent calcinations of the metal alginate gels, the ions become immobile and cannot readily come closer to each other, hence providing an excellent basis for producing small metal oxide particles [6,7] in nano to micrometer size range.…”