Influence of complexing agents in redox behaviour of Sb on gold surface

Abstract

Electrochemical redox behaviour of Antimony (Sb) in Nitrilotriacetic acid (NTA) and Tartaric acid (TA) was investigated, owing to its relevance in nuclear, semiconducting and catalysis industry. A quasi-reversible to irreversible nature of Sb reduction was revealed from the type of chelant controlled the Sb availability as dissolved oxygenated species both in electrolyte and in the adsorbed form. Existence of two stable Sb-NTA complexes (denoted as Sb-NTA-a & Sb-NTA-b) was proposed based on the reduction peaks of Sb-NTA complexes observed in cyclic voltammetry. The stability constant of Sb-NTA-a is found to be lower when compared to Sb-TA. A more negative reduction potential compared to -0.3 V for Sb-NTA-b complex, indicates the formation of a stable species. Standard rate constant for Sb reduction evaluated by extended Nicholson method, supported the irreversible Sb reduction, and point towards the difficulty in dissolution of reduced Sb in presence of chelants. NTA acted as a habit modifier, where Sb2O3 acquired an octahedral shape with cubic crystal structure. The presence of NTA, thus modified both the kinetics of Sb reduction and the morphology of Sb deposits. These findings provide additional insights into the active role of chelants used for Sb mitigation both in nuclear and environmental applications.

Keywords

• Electrodeposition
• Antimony deposition
• Nitrilotriacetic acid
• Tartaric acid