Synthesis of Highly Stable Cobalt Nanomaterial Using Gallic Acid and Its Application in Catalysis

We report the room temperature (25–30°C) green synthesis of cobalt nanomaterial (CoNM) in an aqueous medium using gallic acid as a reducing and stabilizing agent. pH 9.5 was found to favour the formation of well dispersed flower shaped CoNM. The optimization of various parameters in preparation of nanoscale was studied. The AFM, SEM, EDX, and XRD characterization studies provide detailed information about synthesized CoNM which were of 4–9？nm in dimensions. The highly stable CoNM were used to study their catalytic activity for removal of azo dyes by selecting methyl orange as a model compound. The results revealed that 0.4？mg of CoNM has shown 100% removal of dye from 50？μM aqueous solution of methyl orange. The synthesized CoNM can be easily recovered and recycled several times without decrease in their efficiency. 1. Introduction Metal nanoparticles have attracted much attention in nanoscale science and engineering technology over the past decades due to their unusual chemical and physical properties, such as catalytic activity, novel electronic, and optical and magnetic properties. Their main application areas include catalysts, absorbents, chemical and biological sensors, optoelectronics, information storage, and photonic and electronic devices [1]. Cobalt nanomaterial (CoNM) exhibits high resistance to oxidation, corrosion, and wear. CoNM have been prepared by several synthetic methods including solvothermal process [2], thermal decomposition method [3], hydrothermal microemulsion process [4], high temperature solution phase method [5], and reduction by NaBH4 at room temperature [6]. Among all, the wet chemical reduction method has the advantage over the others in easy control of the reaction process. However, most of the wet chemical reduction methods reported to date rely strongly on the use of environmentally and biologically hazardous organic solvents and reducing agents (i.e., hydrazine, sodium borohydride, dimethyl formamide, formaldehyde, sodium hypophosphite, or hydroxylamine hydrochloride, etc.) [1]. Recently, there is an increased emphasis on the subject of green chemistry, to avoid the problems related to toxic chemicals and solvents. Nanomaterials prepared by green rout are environmentally benevolent. Raveendran et al. [7] prepared silver nanoparticles using water as a solvent, β-D-glucose as a reducing agent, and starch as a protecting agent. Liu et al. [8] synthesized gold nanocrystals using β-D-glucose as both the reducing and stabilizing agent. In addition Xiong et al. [1], worked on the synthesis of highly stable nanosized copper