Studies on the effect of electrode pretreatment on the coverage of self-assembled monolayers of dodecanethiol on gold by electrochemical reductive desorption determination

Abstract

This paper examines the effect of five major pretreatments on the surface coverage Γ_m of dodecanethiol self-assembled monolayer on polycrystalline gold electrode (C₁₂SH-SAMs-Au). It is based on the electrochemical reductive desorption in the alkaline solution by cyclic voltammetry (CV). The five different pretreatment methods include: aqua regia pretreatment, reductive annealed pretreatment, UV/O₃ pretreatment, piranha reagents pretreatment and simple polishing pretreatment, and then all above pretreatments following the same procedure of electrochemistry cleaning. The experimental results show that the surface coverage Γ_m for C₁₂SH-SAMs-Au by the five pretreatment methods are: aqua regia pretreatment (8.0 × 10⁻¹⁰ mol cm⁻²) ∼ reductive annealed pretreatment (7.8 × 10⁻¹⁰ mol cm⁻²) > UV/O₃ pretreatment (5.0 × 10⁻¹⁰ mol cm⁻²) ∼ piranha reagents pretreatment (4.1 × 10⁻¹⁰ mol cm⁻²) ∼ simple polishing pretreatment (4.0 × 10⁻¹⁰ mol cm⁻²). This indicates that Au surfaces pretreated by aqua regia and reductive annealing can achieve the best results, and the Γ_m values obtained are consistent with the theoretical coverage values (Γ_m ≈ 8.0 × 10⁻¹⁰ mol cm⁻²); however, the Γ_m values for other three pretreatment methods (UV/O₃, piranha reagents and simple polishing) are not satisfactory, obtaining only almost half of the theoretical Γ_m value. Thus, we recommend aqua regia and reductive annealed pretreatments as the best methods for self-assembling the alkyl thiol monolayer (C_nSH-SAMs-Au), whereas UV/O₃, piranha reagents and simple polishing pretreatments are not recommended.