Chitosan-derived nitrogen-doped carbon electrocatalyst for a sustainable upgrade of oxygen reduction to hydrogen peroxide in UV-assisted electro-Fenton water treatment

The urgency to move from critical raw materials to highly available and renewable feedstock is currently driving the scientific and technical developments. Within this context, the abundance of natural resources like chitosan paves the way to synthesize biomass-derived nitrogen-doped carbons. This work describes the synthesis of chitosan-derived N-doped mesoporous carbon in the absence (MC-C) and presence (N-MC-C) of 1,10-phenanthroline, which acted as both a porogen agent and a second nitrogen source. The as-prepared MC-C and N-MC-C were thoroughly characterized and further employed as catalytic materials in gas-diffusion electrodes (GDEs), aiming to develop a sustainable alternative to conventional GDEs for H2O2 electrogeneration and photoelectro-Fenton (PEF) treatment of a drug pollutant. N-MC-C presented a higher content of key surface N-functionalities like the pyrrole group, as well as an increased graphitization degree and surface area (63 vs 6 m2/g), comparable to commercial carbon black. These properties entailed a superior activity of N-MC-C for the oxygen reduction reaction, as confirmed from its voltammetric behavior at a rotating ring-disk electrode. The GDE prepared with the N-MC-C catalyst showed greater H2O2 accumulation, attaining values close to those obtained with a commercial GDE. N-MC-C- and MC-C-derived GDEs were employed to treat drug solutions at pH 3.0 by the PEF process, which outperformed electro-oxidation. The fastest drug removal was achieved using N-MC-C, requiring only 16 min at 30 mA/cm2 instead of 20 min required with MC-C. The replacement of the dimensionally stable anode by a boron-doped diamond accelerated the degradation process, reaching an almost complete mineralization in 360 min. The main degradation products were identified, revealing the formation of six different aromatic intermediates, alongside five aliphatic compounds that comprised three nitrogenated structures. The initial N was preferentially converted into ammonium.Peer ReviewedPostprint (published version

Bimetallic FeCu-MOF derivatives as heterogeneous catalysts with enhanced stability for electro-Fenton degradation of lisinopril

A bimetallic FeCu/NC core-shell catalyst, consisting in nanoparticles where zero-valent Fe and Cu atoms, slightly oxidized on their surface, are encapsulated by carbon has been successfully prepared by modifying the synthesis route of MIL(Fe)-88B. FeCu/NC possessed well-balanced textural and electrochemical properties. According to voltammetric responses, in-situ Fe(III) reduction to Fe(II) by low-valent Cu was feasible, whereas the high double-layer capacitance confirmed the presence of a great number of electroactive sites that was essential for continuous H2O2 activation to •OH via Fenton's reaction. Electrochemical impedance and distribution of relaxation times (DRT) analysis informed about the strong leaching resistance of FeCu/NC. To validate the promising features of this catalyst, the advanced oxidation of the antihypertensive lisinopril (LSN) was investigated for the first time. The heterogeneous electro-Fenton (HEF) treatment of 16.1 mg L-1 LSN solutions was carried out in a DSA/air-diffusion cell. At pH 3, complete degradation was achieved within 6 min using only 0.05 g L-1 FeCu/NC; at near-neutral pH, 100 % removal was also feasible even in actual urban wastewater, requiring 60–75 min. The FeCu/NC catalyst demonstrated high stability, still maintaining 86.5 % of degradation efficiency after 5 cycles and undergoing low iron leaching. It outperformed the monometallic (Fe/NC and Cu/NC) catalysts, which is explained by the Cu(0)/Cu(I)-catalyzed Fe(II) regeneration mechanism that maintains the Fenton's cycle. LC-MS/MS analysis allowed the identification of two main primary LSN by-products. It can then be concluded that the FeCu/NC-based HEF process merits to be further scaled up for wastewater treatment.Peer ReviewedPostprint (published version

Valorization of bottom ash from municipal solid waste incineration: recovery of copper by electrowinning

Postprint (published version

Electrochemically-assisted thermal-based technologies for soil remediation

In situ thermal remediation (ISTR) technologies are considered a good option to both, evaporate volatile organic contaminants (VOCs) and enhance the mass transport of dissolved chemicals, avoiding the drawbacks associated with soil excavation. Subsurface heating can be promoted by using direct current (DC) or alternating current (AC), thanks to the Joule effect that arises when electricity is converted into heat as it flows through a low conductivity medium like soil. In this chapter, after a short introduction about existing ISTR technologies, electrochemical ISTR (i.e., electrothermal methods), is reviewed with detail. The fundamentals, mathematical considerations, and modelling are described, thereby presenting some examples that clearly reveal the temperature dependence of key physical properties of soil and water, as well as the scale effect. Several companies that have successfully scaled-up the DC and AC electrothermal techniques are mentioned throughout the chapter. A key idea to keep in mind is that the lowest effective temperature should be the one chosen in ISTR to avoid collateral effects like excessive energy consumption and negative effects on soil properties, including loss of fertility. Coupling of electrical heating with simultaneous in situ chemical oxidation (ISCO) via generation of highly oxidizing species like sulfate radicals enables the operation at milder temperature, thus reducing the electrical power consumption and allowing the degradation of pollutants in addition to their desorption/volatilization.Peer ReviewedPostprint (published version

Paired electrochemical removal of nitrate and terbuthylazine pesticide from groundwater using mesh electrodes

Groundwater is one of the main freshwater resources on Earth, but its contamination with NO3- and pesticides jeopardizes its viability as a source of drinking water. In this work, a detailed study of single electro-oxidation (EO) and electrodenitrification and paired EO/electrodenitrification processes has been undertaken with simulated and actual groundwater matrices containing 100 mg dm-3 NO3- and/or 5 mg dm-3 terbuthylazine pesticide. Galvanostatic electrolyses were made with 500 cm3 of solutions at pH 4.0-10.5 and 250-1000 mA in tank reactors with a RuO2 or boron-doped diamond (BDD) anode and one or two Fe cathodes, all of them in the form of meshes. Most of NO3- removals agreed with a pseudo-first-order kinetics. In Cl--free media, NH4+ predominated as electroreduction product. In chloride media, a greater amount of N-volatiles was determined alongside a slower electrodenitrification, especially with RuO2 due to the partial re-oxidation of electroreduction products like NH4+ by active chlorine. The pesticide decays were also fitted to a pseudo-first order kinetics, and its presence led to a smaller release of N-volatiles. Overall, BDD always favored the pesticide degradation thanks to the action of BDD( OH), whereas RuO2 was preferred for electrodenitrification under some conditions. The EO/electrodenitrification of groundwater was successful once the matrix was softened to minimize its hardness. The NO3- concentration was reduced below the limit established by the WHO. Overall, the BDD/Fe cell was more suitable than the RuO2/Fe cell because it accelerated the pesticide removal with a simultaneous high degree of NO3- electroreduction. However, it produced toxic chlorate and perchlorate. A final post-treatment with an anion exchange resin ensured a significant removal of both ions, thus increasing the viability of the electrochemical approach to treat this type of water. Chromatographic analyses revealed the formation of ten heteroaromatic products like desethyl-terbuthylazine and cyanuric acid, alongside oxalic and oxamic as final short-chain carboxylic acids.Peer ReviewedPostprint (author's final draft

Groundwater treatment using a solid polymer electrolyte cell with mesh electrodes

This article reports the high performance of a solid polymer electrolyte cell, equipped with a Nafion¿ N117 membrane packed between a Nb/BDD mesh anode and a Ti/RuO2 mesh cathode, to degrade the insecticide imidacloprid spiked at 1.2 - 59.2 mg L-1 into low conductivity groundwater by electrochemical oxidation. The natural water matrix was first softened using valorized industrial waste in the form of zeolite as reactive sorbent. Total removal of the insecticide, always obeying a pseudo-first-order kinetics, and maximum mineralization degrees of 70%-87% were achieved, with energy consumption of 26.4±1.6 kWh m-3. Active chlorine in the bulk and •OH at the BDD surface were the main oxidants. Comparative studies using simulated water with analogous anions content revealed that the natural organic matter interfered in the groundwater treatment. Trials carried out in ultrapure water showed the primary conversion of the initial N and Cl atoms of imidacloprid to NO3 - and Cl- ions, being the latter anion eventually transformed into ClO3 - and ClO4 - ions. 6- Chloro-nicotinonitrile, 6-chloro-pyridine-3-carbaldehyde, and tartaric acid were identified as oxidation products