Corrosion inhibition during synthesis of Cu₂O nanoparticles by 1,3-diaminopropylene in solution

Abstract

Corrosion inhibition for Cu₂O nanoparticles in solution using the regulators of 1,3-dimorpholinpropylene and 1,3-diethylaminopropylene was studied by experimental and theoretical calculation methods. The inhibition mechanism of regulators was related to the arrangement of cetyltrimethylammonium (CTAB) molecules on the surface of Cu₂O nanoparticles. Control of the type and amount of regulators has been demonstrated to produce well-dispersed and active Cu₂O nanoparticles (∼100 nm). The oxidation temperature of Cu₂O nanoparticles decreased from 297.9–404.4 °C (blank) to 232.3–334.3 °C (containing regulator). For 1,3-dimorpholinpropylene, its arc structure and active sites (C_4C_5, N_2 and O_2) facilitate the formation of stable protective film over Cu₂O surface.

Introduction

In the past few years, many efforts have been focused on the fabrication of Cu₂O nanoparticles due to their unique chemical and physical properties [1], [2], [3], [4]. Applications of Cu₂O nanoparticles are diverse, involving heterogeneous catalysis, biosensors, nonlinear optical devices and other areas of nanotechnology [5], [6], [7], [8], [9]. To date, many methods have been developed to prepare Cu₂O nanoparticles [10], [11], [12], [13], [14], [15], [16]. Among them, solution reduction has been proved to be one of the most powerful and practical approaches in the synthesis of Cu₂O nanoparticles. Using this method, Cu₂O nanoparticles with various shapes (such as cubic, pyramidal and tetrahedral) have been achieved [17], [18], [19], [20], [21], [22]. However, the synthesis of well-dispersed and active Cu₂O nanoparticles was difficult, partially because the surfactant molecules were ineffectively adsorbed on the surface of nanoparticles, resulting in the agglomeration and oxidation propensity of nanoparticles. Recently, Mott and co-workers [23] reported that the oxidation of copper nanoparticles can be controlled in the presence of regulators (oleic acid and oleyl amine). The surface of nanoparticles was covered by a capping shell, which inhibited the agglomeration and oxidation of nanoparticles. Regulators were proposed to play an important role in the arrangement of surfactant molecules on the surface of nanoparticles, which is quite intriguing. Generally, organic compounds containing hetero-atoms (e.g., N, O and S atoms) could be used as regulators [24], [25], [26], [27], [28]. 1,3-Dimorpholinpropylene and 1,3-diethylaminopropylene belong to the low-toxic compounds in the series of 1,3-diaminopropylene [29]. These compounds are constituted by multi-adsorption centers (N, O and CC) in their molecular structures, presenting very interesting properties. It should be valuable to explore the application of 1,3-diaminopropylene as corrosion inhibitors for the Cu₂O nanoparticles. As far as we know, it is the first time to investigate the protective properties of these new compounds on the Cu₂O nanoparticles in solution.

In this paper, 1,3-dimorpholinpropylene and 1,3-diethylaminopropylene were synthesized by alkylation reaction and used as regulators for the arrangement of CTAB molecules on the surface of Cu₂O nanoparticles in aqueous reduction condition. Cu²⁺ in solution was mildly reduced to Cu⁺ using Vitamin C as reducing agent at room temperature. The interaction between the regulators structures and their arrangement of CTAB molecules over Cu₂O surface were discussed from density functional theory (DFT) calculations, such as the highest occupied molecule orbital, the lowest unoccupied molecule orbital, energy difference, global hardness and dipole moments.