Averrhoa carambola: A Renewable Source of Oxalic Acid for the Facile and Green Synthesis of Divalent Metal (Fe, Co, Ni, Zn, and Cu) Oxalates and Oxide Nanoparticles

Nguimezong Nguefack Marius Borel,Ekane Peter Etape,Josepha Foba-Tendo,Jude Namanga Eko,Lambi John Ngolui,Divine Mbom Yufanyi

doi:10.1155/2014/767695

Nguimezong Nguefack Marius Borel, Ekane Peter Etape + Show 4 more

Open Access

https://doi.org/10.1155/2014/767695

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Abstract

A green, simple, and environmentally benign synthetic approach has been utilised to obtain some bivalent metal oxalates from Averrhoa carambola juice extract, without any purification or special treatment of the juice. The main acid components (oxalic acid and ascorbic acid) of the juice were identified by HPLC technique. The effect of temperature on the purity of the product has been investigated. The as-synthesized metal oxalates were thermally decomposed at low temperatures to their respective metal oxide nanoparticles. The metal oxalates and their respective thermal decomposition products were characterized by Fourier Transform Infrared spectroscopy, X-ray diffraction analysis, and thermogravimetry.

Highlights

Metal carboxylates have been widely investigated and have been used as precursors in the production of metal oxide nanomaterials [1,2,3,4,5,6]
The as prepared complexes and their various thermal decomposition products have been characterized by FTIR, powder XRD, and Thermogravimetric analysis (TGA)
The absence of the peaks of other acids indicates that they are either absent or if present they are in trace proportions. This observation supports that of several authors who found that the principal acids in the mature fruits are ascorbic and oxalic acids [7, 14, 15]

Summary

Introduction

Metal carboxylates have been widely investigated and have been used as precursors in the production of metal oxide nanomaterials [1,2,3,4,5,6]. We here explore the feasibility of using this naturally available and sustainable resource (Averrhoa carambola L.) rather than the commercial sources for the synthesis of metal oxalates The use of these natural renewable resources is of environmental significance and in the case of free oxalic acid rich fruits (e.g., Averrhoa carambola L.) could result in a significant reduction in the level of the free acid, adding value to the elimination of toxic components through reaction with metal ions of biological and technological importance. In order to render the synthesis cost effective and ecofriendly, we decided to proceed with a synthetic pathway where the fruit juice is used directly without initial purification steps or prior extraction of the acid This decision was guided by the fact that in the natural condition of the juice (pH 2.6–3.1) oxalic acid has a better chance to react preferentially with the metal ions owing to its relative high acidic strength (pKa1 (1.23) and pKa2 (4.19)). The as prepared complexes and their various thermal decomposition products have been characterized by FTIR, powder XRD, and TGA

Experimental

Results and Discussion

Conclusion