Nanodiamond surface redox chemistry: influence of physicochemical properties on catalytic processes

Abstract

Modification of an electrode with an immobilised layer of nanodiamond is found to significantly enhance the recorded currents for reversible oxidation of ferrocene methanol (FcMeOH). Current enhancement is related to nanodiamond diameter, with enhancement increasing in the order 1000 nm < 250 nm < 100 nm < 10 nm < 5 nm. We attribute the current enhancement to two catalytic processes: i) electron transfer between the solution redox species and redox-active groups on the nanodiamond surface; ii) electron transfer mediated by FcMeOH(+) adsorbed onto the nanodiamond surface. The first process is pH dependent as it depends on nanodiamond surface functionalities for which electron transfer is coupled to proton transfer. The adsorption-mediated process is observed most readily at slow scan rates and is due to self-exchange between adsorbed FcMeOH(+) and FcMeOH in solution. FcMeOH(+) has a strong electrostatic affinity for the nanodiamond surface, as confirmed by in situ infrared (IR) experiments.

Electrocatalytic processes promoted by diamond nanoparticles in enzymatic biosensing devices

“…Thus, HMF is partially bonded to the DNP surface. This result agrees well with previous studies, where infrared experiments confirmed the strong electrostatic affinity of the oxidized form of HMF for negatively charged diamond nanoparticles surfaces [17]. The negative charge of commercial DNP powders arises from acid cleaning steps that leave oxygen groups on the surface, particularly carboxyl groups [21][22].…”

“…Depending on the specific synthesis conditions and purification procedures employed in their fabrication, the resulting nanomaterials can present different sizes and physicochemical properties and, therefore, differences in their surface chemistry [14], which clearly affect their subsequent behavior. In particular, previous studies have shown that DNPs diameter has a great influence on their reactivity [17,21]. Thereby, the percentage of the number of atoms on the DNPs surface, the number of functionality groups and the sp 2 /sp 3 carbon ratio are parameters greatly dependent on the size.…”

“…4, the modification of a gold electrode with DNPs4 enhances the electrochemical response of the redox compound in solution, HMF, with respect to the unmodified electrode. This enhancement is a consequence of the following catalytic feedback mechanism [17,18]: after oxidation of HMF(Fe II ) to HMF(Fe III ) over the electrode surface, an electron transfer from DNPs to HMF(Fe III ) occurs, allowing a rapid regeneration of HMF(Fe II ) and enhancing oxidation currents. Accordingly, enhancements of reduction currents are produced when HMF(Fe II ), obtained from reduction of HMF(Fe III ) over the electrode, gives an electron to DNPs, regenerating HMF(Fe III ).…”

“…Therefore, DNPs can be either oxidized or reduced depending on their potential relative to the underlying electrode or to a redox probe [13,14]. Recently, the electrochemical behavior of neutral redox probes in solution has also been studied employing DNPs modified electrodes, showing an oxidation/reduction current even higher than that obtained for charged species [17]. However, the employment of DNPs in biosensors development is still scarce.…”

Diamond Nanostructures and Nanoparticles: Electrochemical Properties and Applications

“…Holt and her colleague [60][61][62][63][64][65] made extensive investigation on the electrochemistry of detonation diamond nanoparticles. Differential pulse voltammetry of electrode-immobilised layers of diamond nanoparticles in the absence of solution redox species revealed oxidation and reduction peaks, resulting from direct electron transfer reactions of diamond nanoparticles themselves [60].…”