Elucidation of the oxidation-reduction reactions in the synthesis of Co-based nanoparticles through polyol process using 1, 2-butanediol (BEG): a theoretical study

Abstract

The role of BEG 1,2-butanediol as a reducing agent in Co-based nanoparticle synthesis in the polyol process has not been well-detailed yet. So, we focused on the determination of the main active species derived from 1,2-butanediol (BEG) in Co-based nanoparticle synthesis and their reducing abilities through density functional theory (DFT) calculations. In the reaction medium, BEG is deprotonated by the hydroxyl ions introduced in the solution then oxidized by the metal ions. The progression of reduction and dissociation reactions of metal ions is relatively related to the reducing ability of polyols. Three species which are: dianion, monoanion and neutral molecule of BEG were considered in our investigation. The highest occupied orbital energy was estimated for the different configurations. Considering the experimental and theoretical studies, the monoanion state was suggested as the most active form. A comparative study was carried out between three polyols: BEG, PEG (1, 2-propanediol) and EG (Ethylen glycol), which are the most used solvents in Co-based nanoparticle synthesis. We showed that the highest occupied orbital energy of BEG monoanion state is relatively high compared to PEG and EG ones. Thus, BEG could reduce metal ions more easily by giving its electrons and its use can make the reaction kinetics faster.

Selection Criteria for Metal Precursors and Solvents for Targeted Synthesis of Metallic Nanostructures Via Kinetic Control in the Polyol Process

“…However, the above research findings were confined to one type of solvent and precursor, namely “EG” and “cobalt acetate”. Recently, by using B3LYP/6-31G­(d), the reduction ability of 1,2-butanediol for Co salts has been evaluated by Mrad et al . However, there are some questions about their results.…”

“…However, the above research findings were confined to one type of solvent and precursor, namely "EG" and "cobalt acetate". Recently, by using B3LYP/6-31G(d), the reduction ability of 1,2-butanediol for Co salts has been evaluated by Mrad et al 43 However, there are some questions about their results. First, it is unclear why they chose 1,2-butanediol as the simplest polyol; it is hard to obtain all stable conformers using energy surfaces.…”

New insights into pertinent Fe-complexes for the synthesis of iron via the instant polyol process

“…[33][34][35] Ethylene glycol is widely used to reduce metals in polyols while Mrad et al predicted theoretically that the highest occupied orbital energy for 1,2-butanediol was relatively higher than that of the commonly used polyols. 36 Indeed, ethylene glycol was chosen as the preferred model polyol to identify the active species involved in the reduction of Co. 22 Kaneko et al studied the reducing ability of vicinal and terminal polyols using Co as a model system concluding that the terminal polyol, 1,4 butanediol has the highest reduction ability, and this could apply to most of the magnetic elements. 37 More recently, the authors have shown that vicinal polyols are suitable for reducing Fe ions, while terminal polyols produce Fe oxides under the same experimental conditions.…”

In situ investigation of the formation mechanism of α-Bi2Rh nanoparticles in polyol reductions

“…6,[15][16][17][18] Although the (microwave-assisted) polyol process is well established and there are also several empirical studies on the dependence on diverse reaction parameters, such as starting materials, 19 concentrations, 20 temperature 21 and the influence of auxiliaries, 22 the mechanism of particle formation has been thoroughly studied mainly for mono-metallic reactions. 13,[23][24][25][26] Schaak et al performed first systematic studies on the more complex formation of binary and ternary compounds, such as AuCuSn 2 . 27 More recently, Jouini et al and Han et al investigated the formation of Ag 3 Sn and NiSn 5 particles, respectively, 28,29 and Balachandran et al studied extensively the formation and design of copper-cobalt alloys.…”