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, 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.

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.

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.

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.

Fabrication of patterned boron-doped diamond (BDD) in an inexpensive and straightforward way is required for a variety of practical applications, including the development of BDD-based electrochemical sensors. This work describes a simplified and novel bottom-up fabrication approach for BDD-based three-electrode sensor chips utilizing direct inkjet printing of diamond nanoparticles on silicon-based substrates. The whole seeding process, accomplished by a commercial research inkjet printer with piezo-driven drop-on-demand printheads, was systematically examined. Optimized and continuous inkjet-printed features were obtained with glycerol-based diamond ink (0.4% vol/wt), silicon substrates pretreated by exposure to oxygen plasma and subsequently to air, and applying a dot density of 750 drops (volume 9 pL) per inch. Next, the dried micropatterned substrate was subjected to a chemical vapor deposition step to grow uniform thin-film BDD, which satisfied the function of both working and counter electrodes. Silver was inkjet-printed to complete the sensor chip with a reference electrode. Scanning electron micrographs showed a closed BDD layer with a typical polycrystalline structure and sharp and well-defined edges. Very good homogeneity in diamond layer composition and a high boron content (∼2 × 10²¹ atoms cm^-3) was confirmed by Raman spectroscopy. Important electrochemical characteristics, including the width of the potential window (2.5 V) and double-layer capacitance (27 μF cm^-2), were evaluated by cyclic voltammetry. Fast electron transfer kinetics was recognized for the [Ru(NH₃)₆]^3+/2+ redox marker due to the high doping level, while somewhat hindered kinetics was observed for the surface-sensitive [Fe(CN)₆]^3-/4- probe. Furthermore, the ability to electrochemically detect organic compounds of different structural motifs, such as glucose, ascorbic acid, uric acid, tyrosine, and dopamine, was successfully verified and compared with commercially available screen-printed BDD electrodes. The newly developed chip-based manufacture method enables the rapid prototyping of different small-scale electrode designs and BDD microstructures, which can lead to enhanced sensor performance with capability of repeated use.

In this work, non-modified boron-doped diamond (BDD) was employed first time ever as the sensing material for the in-depth voltammetric study of the antiretroviral drug nevirapine (NVP) used to treat HIV infections. Two types of electrode surface pre-treatments, anodic oxidation and alumina-polishing, yielded BDD of different surface chemistry, denoted as O-BDD and p-BDD, respectively. Induced alterations in BDD surface composition reflected in distinct voltammetric responses of NVP, also dependant on the pH of the medium. The electrochemical oxidation of NVP on both electrodes, whose mechanism is proposed herein, has an irreversible character and is controlled by diffusion. The analytical figures of merit were assessed in a pH 2.0 buffer on O-BDD, and in supporting electrolytes of pH 5.0 and 13.0 on p-BDD using differential pulse voltammetry. Overall, NVP provided signals of excellent intra- and inter-day repeatability (RSD ≤ 5.0%) which remained unaffected even in the presence of common interfering compounds (e.g., glucose, ascorbic acid, uric acid, and dopamine). Even though the O-BDD electrode outperformed the p-BDD electrode in terms of sensitivity and the lowest detection limit achieved (0.04 μM), both O-BDD and p-BDD provided highly favourable analytical parameters fulfilling the requirements for clinical application for NVP sensing and monitoring in biofluids. This was also proved by electroanalysis of NVP in synthetic serum samples where recovery values between 96.3 and 103.0% were successfully achieved. Finally, unique properties of BDD allowed to develop a direct, modification-free, and reliable protocol for NVP detection, which paves the way for the full sensor development.