In this work, four different techniques were concurrently applied to study the interplay between local electroactivity and electrode surface characteristics of free-standing, polycrystalline boron-doped diamond (BDD). Scanning electron microscopy, electron back-scatter diffraction, Raman mapping and scanning electrochemical microscopy were used to probe the electrode morphology, grain orientation and boundaries, composition, and local electrochemical activity, respectively. Both nucleation and growth BDD surfaces together with the cross-section area were carefully investigated for the first time in a single study using the combination of all four techniques. This enabled us to obtain significant insights into the highly heterogeneous nature of the polycrystalline BDD material. Notably, boron dopants were confirmed to be non-uniformly distributed over the BDD material, which is characterized by a distinct columnar structure and composition of grains of various orientations. Particularly, the highest electrochemical activity was recorded on the highest doped (111) crystal orientation. In contrast, the averagely boron-doped (100)-oriented facet showed non-conductive nature. This highlights that the local electrochemical activity of the BDD surface is strongly grain-dependent and the most significant factors governing the obtained responses are crystallographic orientation and boron doping. Moreover, increased boron and sp² carbon content in the boundary regions was recognized by Raman mapping. However, such localized enrichment in impurities did not translate into enhanced electrochemical activity, which implies that boron atoms at the inter-grain areas are predominantly inactive. Finally, it is crucial to consider all characteristics of the polycrystalline BDD including crystal orientation, which is particularly relevant if micro- and nanoscale probing is intended.

Electrochemical wastewater treatment is a promising technique to remove recalcitrant pollutants from wastewater. However, the complexity of elucidating the underlying degradation mechanisms hinders its optimisation not only from a techno-economic perspective, as it is desirable to maximise removal efficiencies at low energy and chemical requirements, but also in environmental terms, as the generation of toxic by-products is an ongoing challenge. In this work, we propose a novel combined experimental and computational approach to (i) estimate the contribution of radical and non-radical mechanisms as well as their synergistic effects during electrochemical oxidation and (ii) identify the optimal conditions that promote specific degradation pathways. As a case study, the distribution of the degradation mechanisms involved in the removal of benzoic acid (BA) via boron-doped diamond (BDD) anodes was elucidated and analysed as a function of several operating parameters, i.e., the initial sulfate and nitrate content of the wastewater and the current applied. Subsequently, a multivariate optimisation study was conducted, where the influence of the electrode nature was investigated for two commercial BDD electrodes and a customised silver-decorated BDD electrode. Optimal conditions were identified for each degradation mechanism as well as for the overall BA degradation rate constant. BDD selection was found to be the most influential factor favouring any mechanism (i.e., 52-85% contribution), given that properties such as its boron doping and the presence of electrodeposited silver could dramatically affect the reactions taking place. In particular, decorating the BDD surface with silver microparticles significantly enhanced BA degradation via sulfate radicals, whereas direct oxidation, reactive oxygen species and radical synergistic effects were promoted when using a commercial BDD material with higher boron content and on a silicon substrate. Consequently, by simplifying the identification and quantification of underlying mechanisms, our approach facilitates the elucidation of the most suitable degradation route for a given electrochemical wastewater treatment together with its optimal operating conditions.

In this work, we pioneered the preparation of diamond-containing flexible electrodes using 3D printing technology. The herein developed procedure involves a unique integration of boron-doped diamond (BDD) microparticles and multi-walled carbon nanotubes (CNTs) within a flexible polymer, thermoplastic polyurethane (TPU). Initially, the process for the preparation of homogeneous filaments with optimal printability was addressed, leading to the development of two TPU/CNT/BDD composite electrodes with different CNT:BDD weight ratios (1:1 and 1:2), which were benchmarked against a TPU/CNT electrode. Scanning electron microscopy revealed a uniform distribution of conductive fillers within the composite materials with no signs of clustering or aggregation. Notably, increasing the proportion of BDD particles led to a 10-fold improvement in conductivity, from 0.12 S m^-1 for TPU/CNT to 1.2 S m^-1 for TPU/CNT/BDD (1:2). Cyclic voltammetry of the inorganic redox markers, [Ru(NH₃)₆]^3+/2+ and [Fe(CN)₆]^3-/4-, also revealed a reduction in peak-to-peak separation (ΔE_p) with a higher BDD content, indicating enhanced electron transfer kinetics. This was further confirmed by the highest apparent heterogeneous electron transfer rate constants (k⁰_app) of 1 × 10^-3 cm s^-1 obtained for both markers for the TPU/CNT/BDD (1:2) electrode. Additionally, the functionality of the flexible TPU/CNT/BDD electrodes was successfully validated by the electrochemical detection of dopamine, a complex organic molecule, at millimolar concentrations by using differential pulse voltammetry. This proof-of-concept may accelerate development of highly desirable diamond-based flexible devices with customizable geometries and dimensions and pave the way for various applications where flexibility is mandated, such as neuroscience, biomedical fields, health, and food monitoring.

The ongoing challenge of water pollution by contaminants of emerging concern calls for more effective wastewater treatment to prevent harmful side effects to the environment and human health. To this end, this study explored for the first time the implementation of single-crystal boron-doped diamond (BDD) anodes in electrochemical wastewater treatment, which stand out from the conventional polycrystalline BDD morphologies widely reported in the literature. The single-crystal BDD presented a pure diamond (sp³) content, whereas the three other investigated polycrystalline BDD electrodes displayed various properties in terms of boron doping, sp³/sp² content, microstructure, and roughness. The effects of other process conditions, such as applied current density and anolyte concentration, were simultaneously investigated using carbamazepine (CBZ) as a representative target pollutant. The Taguchi method was applied to elucidate the optimal operating conditions that maximised either (i) the CBZ degradation rate constant (enhanced through hydroxyl radicals (^•OH)) or (ii) the proportion of sulfate radicals (SO₄^•−) with respect to ^•OH. The results showed that the single-crystal BDD significantly promoted ^•OH formation but also that the interactions between boron doping, current density and anolyte concentration determined the underlying degradation mechanisms. Therefore, this study demonstrated that characterising the BDD material and understanding its interactions with other process operating conditions prior to degradation experiments is a crucial step to attain the optimisation of any wastewater treatment application.

This paper investigates the electrical properties of boron-doped diamond-graphene (B:DG) nanostructures, focusing on their semiconductor characteristics. These nanostructures are synthesized on fused silica glass and Si wafer substrates to compare their behaviour on different surfaces. A specialized measurement system, incorporating Python-automated code, was developed for an in-depth analysis of electronic properties under various contact configurations. This approach allowed for a detailed exploration of charge transport mechanisms within the nanostructures. The research highlights a decrease in resistivity with increased deposition time, as shown by Arrhenius plot analysis. This trend is linked to the formation and evolution of multi-wall graphene structures. SEM images showed nanowall structures formed more readily on amorphous fused silica substrates, enabling unrestricted growth. TOF-SIMS analysis revealed uneven boron atom distribution through the film depth. A significant finding is a reduction in conductive activation energy in samples grown in microwave plasma from 197 meV to 87 meV as deposition time increased from 5 to 25 min. Furthermore, the study identifies a shift in transport mechanisms from variable range hopping (VRH) below 170 K to thermally activated (TA) conduction above 200 K. These insights advance our understanding of the electronic behaviours in B:DG nanostructures and underscore their potential in electronic device engineering, opening new paths for future research and technological developments.

The challenge of doping synthetic diamond with phosphorus stems from the atomic size mismatch between phosphorus and carbon atoms, which previously hindered achieving high phosphorus doping levels. This limitation delayed the exploration of phosphorus-doped diamond (PDD) in electrochemical applications, where it holds potential as a novel and appealing electrode material because PDD uniquely combines diamond's exceptional properties with phosphorus atoms inducing n-type conductivity. In this study, heavily doped PDD electrodes were successfully developed using chemical vapour deposition, followed by comprehensive microstructural and electrochemical characterisations. The influence of phosphorus doping, manipulated via high phosphine gas concentration or time-dependant precursor gas flow control, on the PDD properties was thoroughly examined. PDD layers grown at higher phosphine concentrations demonstrated enhanced phosphorus incorporation, leading to a higher prevalence of fine nano-crystalline diamond grains and non-diamond carbon components, while also slowing the growth rate. Notably, a distinct PDD sample produced under dynamic gas flow with lower phosphine concentration revealed larger grain sizes, increased effective deposition rate, and improved phosphorus levels compared to its counterpart synthesized under static conditions. Cyclic voltammetry in a 1 mol L⁻¹ KCl solution revealed a low double-layer capacitance (<11 µF cm⁻²) in all as-grown PDD electrodes. However, significant differences between the samples emerged during the experiments conducted with redox probes [Ru(NH₃)₆]^3+/2+ and [Fe(CN)₆]^3−/4−. Particularly, higher phosphorus content promoted well-developed voltammograms, significantly reduced peak-to-peak separation values, faster electron transfer rates, and increased peak currents. Furthermore, the possibility of using heavily P-doped diamond electrodes for the detection of two organic analytes, dopamine and ascorbic acid, was successfully manifested. All in all, the as-grown, highly P-doped diamond electrodes proved their ability, first time ever, to record well-defined signals of both inorganic redox probes and complex organic compounds, unravelling their potential in electroanalysis and sensor development and broadening the scope of PDD utilisation.

Metal-free graphitic carbon nitrides are on the rise as polymer photocatalysts under visible light illumination, taking shares in a range of promising photocatalytic reactions, including water splitting. Their simple synthesis and facile structural modification afford them exceptional tunability, enabling the creation of photocatalysts with distinct properties. While their metal-free nature marks a significant step towards environmental sustainability, the high energy consumption required to produce carbon nitride photocatalysts remains a substantial barrier to their widespread adoption. Furthermore, the process of condensation at approximately 550 °C typically results in solid yields of less than 15 %, significantly challenging their economic viability. Here, we report on lowering manufacturing conditions of carbon nitride photocatalysts whilst enhancing photocatalytic activity by introducing binaphthyl diamine as a structural mediator. At 450 °C in 2 hours, carbon nitride photocatalyst shows a lower bandgap and enables visible light induced hydrogen evolution (194 μmol h⁻¹) comparable to benchmark carbon nitride photocatalysts.