Fernando Martínez

3D carbon monoliths with gyroid architecture were fabricated by digital light processing (DLP) 3D printing followed by oxidative stabilization, pyrolysis and steam activation (ACG) to develop multifunctional electrodes for electrogeneration of H2O2, adsorption and heterogeneous electro-Fenton applications. Iron oxide nanoparticles were added into the polymer precursor to produce Fe-containing monoliths with iron active sites (Fe-ACG). Carbonaceous materials revealed well developed porous structure, with Smicro values of 1192 and 885 m2/g for ACG and Fe-ACG, respectively. Steam activation also improved the electrogeneration of H2O2 with ACG through the 2 e– oxygen reduction reaction (4.0·10-4 mol/g of H2O2). However, salicylic acid scavenging experiments indicated 2.4 times higher hydroxyl radicals formation with Fe-ACG due to the efficient activation of H2O2 via heterogeneous Fenton-like mechanism. A kinetic model was developed to describe the H2O2 generation and consumption, confirming the catalytic role of the immobilized iron species. The adsorption, catalysis, electrocatalysis and intensified (external addition combined with electrogeneration of H2O2) electrocatalysis degradation of hydroxybenzene (1 g/L) were evaluated. ACG and Fe-ACG materials initially retained 70% of hydroxybenzene by adsorption; the subsequent catalytic and electrocatalytic reactions further oxidized this pollutant, with Fe-ACG achieving overall hydroxybenzene and TOC conversions of 79 and 55% by electro-Fenton, respectively. Intensified electro-Fenton resulted in the highest performance, achieving 94.6 and 68.7% of removal and mineralization, respectively. In addition, Fe-ACG cathode maintained high activity using a tertiary treated wastewater and after four consecutive reuse cycles. These results demonstrate that gyroid carbon monoliths are robust and effective multifunctional electrodes for wastewater treatment processes.

This study investigates the preparation of porous photopolymer-derived carbons (PDCs) in powder and monolithic structures through oxidative stabilization, pyrolysis, steam activation (AC-PDD adsorbent), and acid functionalization. The effects of these treatments on the physicochemical properties of the materials were evaluated, coupled with their adsorption performance toward 2-nitrophenol (2-NP) and 4-nitrophenol (4 NP), selected as model adsorbates with strong and weak lipophilicity, respectively. In single-solute batch experiments, AC-PDD demonstrated the highest maximum adsorption capacities at equilibrium reaching 586.1 and 445.6 mg g-1 for 2-NP and 4-NP, respectively. Binary-solute adsorption allowed to remove both NPs (total maximum adsorption capacity of 453.8 mg g-1) and revealed antagonistic interaction between them, deeply studied at different NP initial concentrations (20-100 mg L-1). Adsorbents were reused over multiple cycles after regeneration with ethanol and AC-PDD exhibited the highest regeneration efficiency (> 70 %). For continuous-flow assays, monoliths with gyroid lattice structure were synthesized via digital light processing 3D-printing and subsequent carbonization and steam activation, resulting in G-AC-PDD sample. G-AC-PDD monoliths showed broad breakthrough curves with longer saturation times (more than one month) and preferential retention of 2-NP over 4-NP. Dynamic adsorption capacities (356.8 and 260.2 mg g-1 for 2-NP and 4-NP, respectively) exceeded the values obtained in batch mode for binary system at the same inlet concentration and a 0.2 mL min-1 of flowrate. These results demonstrate that carbon monoliths with high uptake capacities may be produced by additive manufacturing for the efficient removal of lipophilic compounds from aqueous solutions.

Electrochemical biosensors based on purple phototrophic bacteria (PPB) offer a low-cost, real-time alternative to conventional toxicant detection methods. This study explored a single-chamber PPB-based biosensor for early-range detection of glyphosate in aquatic environments (1–30 mg/L). The results show that the pure culture Rhodobacter capsulates (R. capsulatus) is highly sensitive to low-to-medium-high glyphosate concentrations, whereas the mixed PPB-enriched consortium system exhibits stronger responses at low concentrations and maintains stable signals at higher concentrations, displaying characteristic cross-over behavior that reflects functional differentiation within the microbial systems. Mechanistic analysis indicates that glyphosate suppresses substrate metabolism and photosynthetic pigment synthesis, thereby reducing electron donor generation while increasing resistance to extracellular electron transfer, ultimately leading to decreased electron flux. Principal component analysis further confirms that the current signal arises from the coupling of metabolic activity and electrochemical processes rather than a single concentration-dependent response. The system requires no electrode modification, achieves a detection limit of 0.121 mg/L, and exhibits good stability and adaptability in complex aquatic environments. This study provides a new bioelectrochemical strategy for rapid screening and tiered monitoring of high-load pollutants.

Graphitic carbon nitride (g-C3N4) has emerged as a promising metal-free semiconductor for solar-driven environmental applications. However, its performance in photoelectrochemical systems is often limited by rapid charge recombination and poorly understood interfacial charge transport processes. In particular, the occurrence of both anodic and cathodic photocurrents in g-C3N4-based photoelectrodes under different applied biases has been widely reported, revealing a dual photoresponse behavior that remains mechanistically unexplained. In this work, g-C3N4 thin films were fabricated on fluorine-doped tin oxide substrates by electrophoretic deposition using guanidinium chloride and urea as nitrogen-rich precursors. Structural and surface characterization confirmed the formation of a porous, defect-rich carbon nitride framework with compact in-plane packing and mesoporous features. Optical analysis revealed an average band gap of 2.82 eV with limited visible-light absorption. The photoelectrochemical performance of the films was systematically evaluated as a function of film thickness and illumination direction, either through the electrode–electrolyte or substrate–electrode interface. Open-circuit potential measurements and transient photocurrent analyses demonstrated a bias-dependent switching between anodic and cathodic photocurrent responses at approximately 0.18 V versus saturated calomel electrode. Back illumination consistently produced higher photocurrent densities, suggesting that charge transport limitations within the film significantly influence the dominant photoresponse mechanism. Kinetic analysis of photocurrent transients indicated that recombination processes, rather than carrier generation, govern the observed dual behavior. These findings provide new insight into the interfacial charge transport mechanisms in carbon nitride thin films and establish synthesis–performance relationships relevant for the design of systems for solar-driven water treatment and environmental remediation.

This study investigates the potential of hydrochar derived from residual carbon sources (orange peel residues, sewage sludge, and refinery sludge) as sustainable precursors for bifunctional cathodes in electro-Fenton (EF) systems. Hydrochars were chemically activated with potassium hydroxide (KOH) in the presence of urea or melamine at temperatures of 700, 850, and 1000 ºC. KOH activation markedly enhanced porosity and surface area, while nitrogen doping introduced electroactive pyridinic and graphitic species that promote oxygen reduction and hydroxyl radical generation. Electro-Fenton degradation of phenol, used as a model pollutant, demonstrated the superior performance of KOH-activated urea-derived hydrochars compared to melamine-derived and non-activated counterparts. Among all tested materials, the urea-derived hydrochar activated at 850 °C exhibited the highest activity, achieving 90% phenol removal and 80% mineralization within 30 min under homogeneous EF conditions (pH 3, 2 mM Fe2+). Remarkably, this material also exhibited outstanding performance under heterogeneous EF conditions (circumneutral pH, without external iron addition), achieving 80% phenol removal and 70% mineralization. These results confirm the intrinsic bifunctional activity of the derived electrodes, enabling efficient hydrogen peroxide generation and catalytic decomposition into hydroxyl radicals across a wider pH range.

Reducing greenhouse gas emissions is critical for humanity nowadays, but it can be beneficial by developing engineered systems that valorize CO₂ into commodities, thus mimicking nature’s wisdom. Purple phototrophic bacteria (PPB) naturally accept CO₂ into their metabolism as a primary redox sink system in photo-heterotrophy. Dedicated use of this feature for developing sustainable processes (e.g., through negative-emissions photo-bioelectrosynthesis) requires a deep knowledge of the inherent metabolic mechanisms. This work provides evidence of tuning the PPB metabolic mechanisms upon redox stressing through negative polarization (−0.4 and −0.8 V vs. Ag/AgCl) in photo-bioelectrochemical devices. A mixed PPB-culture upregulates its ability to capture CO₂ from organics oxidation through the Calvin-Besson-Bassam cycle and anaplerotic pathways, and the redox imbalance is promoted to polyhydroxyalkanoates production. The ecological relationship of PPB with mutualist bacteria stabilizes the system and opens the door for future development of photo-bioelectrochemical devices focused on CO _up-cycling.