Reduced graphene oxide decorated with Ag/CeO2 nanocomposite towards room temperature photocatalytic esterification of aldehydes
Graphical abstract
Introduction
In the emerging field of nanochemistry, preparation, and in-situ characterization of efficient heterogeneous nanocatalyst with nano levels and morphology have attracted considerable attention among the researcher [1]. Cerium oxide (CeO2) being striking on rare earth oxides with good redox properties and wide range applications in various fields of electronics, medicine, and chemistry [2], [3]. On the other end, contact of noble metals (gold, silver) with constant support theatre a noteworthy role on the various physical & chemical properties, surface volume ratios, and effortlessly accessible active sites for the chemical transformations [4]. CeO2 has proved to be an adequate support to various metals due to their high thermal stability and redox properties [3]. Therefore, combination of Ag-doped CeO2 nanomaterialwith needed shape, size, and morphology still remains a major obstacle. However, due to poor steric and diffusion factor in most of the cases, the Ag NPs weakened by self-aggregation or precipitation, and loss the activity. To dazed those drawbacks often, these nanoparticles are supported on silicon-based materials, macromolecules, and carbon-based materials where the specific surface area is considerably enlarged and the nanoparticles can be uniformly dispersed in the pores [5]. Graphene oxide (GO) has confirmed to be very competent carbon support for decorating various metallic nanoparticles due to its significant surface area/surface active sites and its nanosheets available at both sides [6], [7]. Therefore, due to its high synergistic effect between nanoparticles and GO, the nanoparticles can be evenly dispersed in the pores leads to enhance performance of the material. Recently, very few studies have been established with transition metals and oxides decorated on porous graphene nanosheets, which act as resourceful heterogeneous catalysts for various organic transformation reactions [8]. Taking into account these advantages, we report the herein in-situ synthesis of silver supported cerium oxide nanocomposite decorated on reduced graphene oxide and studied its application for esterification of aldehyde under visible light irradiation.
Esters are significant and common intermediates widely used as precursors in various organic synthesis from laboratories and numerous organic industries [9]. Several synthetic procedures have been developed for the synthesis of ester. The two-step synthesis procedure involving the activation of a carboxylic acid followed by substitution with alcohol is the most common traditional pathway [10]. Furthermore, there required and alternative approach that considers environmental concerns and the direct route for the synthesis of ester. Photocatalysis has proved itself as an efficient rote for various organic transformations due to its combine effectiveness of catalyst with the potential of sunlight which is essential from the green chemistry point of view [11]. Herein, we report a sustainable alternative route for direct esterification of aldehyde in presence of silver decorated cerium oxide deposited on reduced graphene oxide (RGO) catalyst under visible light irritation.
Section snippets
Catalyst preparation
Synthesis of graphene oxide was performed using graphite powder using an improved method [12]. An aqueous solution of 5 mmol of Ce(NO3)3·6H2O (1.63 g) and 0.5 mmol of AgNO3 (0.084 g) was slowly added to 1.8 mg mL−1 GO aqueous solution (20 mL) with constant stirring and followed by the addition of 0.5 mmol of polyethylene glycol of molecular weight 4000 (PEG 4000) and 20 mmol of urea (1.2 g). Furthermore, the reaction mixture was transferred into 100 mL Teflon liner autoclave for the
Result and discussion
One-pot hydrothermal synthesis of Ag supported CeO2 embedded rGO was synthesized using urea as hydroxylation agent and polyethylene glycol of molecular weight 4000 as a surfactant. It is interesting to mention that both PEG and urea played a dual role. Urea not only acts as a hydroxylation agent but also serves as a reducing agent for graphene oxide. Similarly, PEG also played an essential role in reducing agents for Ag+ and surfactant to control the size of the nanocomposite [4], [13]. The
Conclusion
In this work, we have demonstrated a cost-effective way to synthesis nanocomposite embedded reduced graphene oxide via an in-situ synthesis method. The synthesized nanoparticles were employed as visible light active photocatalyst for the selective conversion of aldehydes into esters. To the best of our knowledge, this noble synthesis procedure has never been explored for the synthesis of Ag/CeO2-rGO. The catalyst shows excellent photocatalytic activity for esterification of the aldehyde with a
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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