Electro-reversible adsorption as a versatile tool for the removal of diclofenac from wastewater

All-in-one continuous electrochemical monitoring of 2-phenylphenol removal from water by electro-Fenton treatment

The biggest allure of heterogeneous electro-Fenton (HEF) processes largely fails on its high efficiency for the degradation of a plethora of hazardous compounds present in water, but still challenging to search for good and cost-effective electrocatalyst. In this work, carbon black (CB) and oxidised carbon black (CBox) materials were investigated as cathodes in the electrochemical production of hydrogen peroxide involved in HEF reaction for the degradation of 2-phenylphenol (2PP) as a target pollutant. The electrodes were fabricated by employing carbon cloth as support, and the highest H2O2 production yields were obtained for the CBox, pointing out the beneficial effect of the hydrophilic character of the electrode and oxygen-type functionalization of the carbonaceous surface. HEF degradation of 2PP was explored at -0.7 V vs. Ag/AgCl exhibiting the best conversion rates and degradation grade (total organic carbon) for the CBox-based cathode. In addition, the incorporation of an electrochemical sensor of 2PP in line with the HEF reactor was accomplished by the use of screen-printed electrodes (SPE) in order to monitor the pollutant degradation. The electrochemical sensor performance was evaluated from the oxidation of 2PP in the presence of Fe2+ ions by using square wave voltammetry (SWV) technique. The best electrochemical sensor performance was based on SPE modified with Meldola Blue showing a high sensitivity, low detection limit (0.12 ppm) and wide linear range (0.5-21 ppm) with good reproducibility (RSD 2.3 %). The all-in-one electrochemical station has been successfully tested for the degradation and quantification of 2PP, obtaining good recoveries analysing spiked waters from different water matrices origins.

Comparative study on electro-regeneration of antibiotic-laden activated carbons in reverse osmosis concentrate

Electro-regeneration is emerging as a new technique to regenerate spent carbon adsorbents through an electrochemical process. In this study, sequential adsorption and electro-regeneration of ciprofloxacin (CIP)-laden carbon were investigated using both pristine and iron (Fe)-doped F400 activated carbon in distilled, deionized (DI) water and reverse osmosis (RO) concentrate water. The impact of reactor flow rate and sequential adsorption/electro-regeneration cycles on the regeneration efficiency were also evaluated. The results indicate that the breakthrough points for both adsorbents in DI water, where 100 % of the CIP molecules were adsorbed, occurred at around 7,800 bed volumes (BVs). Conversely, electro-regeneration for both adsorbents, where 94 % of the CIP molecules were desorbed, took place at 380 BVs. The main distinction between the two activated carbons lies in the initial range of BVs (<400 BVs).Fe doping on F400 appears to enhance its surface selectivity for CIP uptake, which can easily diffuse into the meso/macropore regions of Fe-doped F400. In contrast, pristine F400, being highly microporous, necessitated more contact time to fill its high-energy sites, resulting in a higher affinity for CIP adsorption. Over the four sequential adsorption/electro-regeneration cycles in DI water, a similar regeneration efficiency was observed at 190 BVs. As the flow rate increased from 2 to 6 mL/min, the CIP uptake on pristine F400 decreased in DI water, calculating 138, 74 and 57 mg/g for flow rates of 2, 4, and 6 mL/min, respectively. When the RO concentrate water was compared with DI water, the pristine F400 quickly reached saturation due to pore blockage caused by organic matter in RO concentrate. During electro-regeneration, up to 100 % of adsorbed CIP molecules were desorbed at around 120 BVs in RO concentrate, which is 3X faster than DI water. The effectiveness of this technology can be enhanced by implementing continuous flow systems, thereby improving the overall efficiency of CIP removal in RO concentrate.

Toward decentralized wastewater treatment: A flow-through module using microtubular gas diffusion electrodes for micropollutants removal

Electro-Fenton (EF) represents an eco-friendly and cost-effective advanced oxidation process that can remove highly persistent and hazardous pharmaceuticals, e.g., contrast media agents, from water bodies. However, up to date, EF modules incorporate a planar carbonaceous gas diffusion electrode (GDE) cathode containing fluorinated compounds as polymeric binders. Here, we introduce a novel flow-through module that deploys freestanding carbon microtubes (CMT) as microtubular GDEs, omitting any risks of secondary pollution by highly-persistent fluorinated compounds (e.g., Nafion). The flow-through module was characterized for electrochemical hydrogen peroxide (H₂O₂) generation and micropollutant removal via EF. H₂O₂ electro-generation experiments illustrated high production rates (1.1 ± 0.1-2.7 ± 0.1 mg cm^-2 h^-1) at an applied cathodic potential of - 0.6 V vs. SHE, depending on the porosity of CMTs. Diatrizoate (DTZ), as the model pollutant, with a high initial concentration of 100 mg L^-1 was successfully oxidized (95-100 %), reaching mineralization (TOC-total organic carbon removal) efficiencies up to 69 %. Additionally, Electro-adsorption experiments demonstrated the capability of positively charged CMTs to remove negatively charged DTZ with a capacity of 11 mg g^-1 from a 10 mg L^-1 DTZ solution. These results reveal the potential of the as-designed module to serve as an oxidation unit coupled with other separation techniques, e.g., electro-adsorption or membrane processes.

Activity and stability of bifunctional perovskite/carbon-based electrodes for the removal of antipyrine by electro-Fenton process

Bifunctional perovskite/carbon-black(CB)/polytetrafluoroethylene(PTFE) electrodes for electro-generation and catalytic decomposition of hydrogen peroxide to oxidizing hydroxyl radicals have been fabricated. These electrodes were tested for electroFenton (EF) removal of antipyrine (ANT) as a model antipyretic and analgesic drug. The influence of the binder loading (20 and 40 wt % PTFE) and type of solvent (1,3-dipropanediol and water) was studied for the preparation of CB/PTFE electrodes. The electrode prepared with 20 wt % PTFE and water exhibited a low impedance and remarkable H₂O₂ electro-generation (about 1 g/L after 240 min, a production rate of ca. 6.5 mg/h·cm²). The incorporation of perovskite on CB/PTFE electrodes was also studied following two different methods: i) direct deposition on the CB/PTFE electrode surface and ii) addition in the own CB/PTFE/water paste used for the fabrication. Physicochemical and electrochemical characterization techniques were used for the electrode's characterization. The dispersion of perovskite particles in the own electrode matrix (method ii) exhibited a higher EF performance than the immobilisation onto the electrode surface (method i). EF experiments at 40 mA/cm² and pH 7 (non-acidified conditions) showed ANT and TOC removals of 30% and 17%, respectively. The increase of current intensity up to 120 mA/cm² achieved the complete removal of ANT and 92% of TOC mineralisation in 240 min. The bifunctional electrode also proved high stability and durability after 15 h of operation.

Ecofriendly and sustainable Sargassum spp.-based system for the removal of highly used drugs during the COVID-19 pandemic

Analgesic consumption increased significantly during the COVID-19 pandemic. A high concentration of this kind of drug is discarded in the urine, reaching the effluents of rivers, lakes, and seas. These medicines have brought serious problems for the flora and, especially, the ecosystems’ fauna. This paper presents the results of removing diclofenac, ibuprofen, and paracetamol in an aqueous solution, using Sargassum spp. from the Caribbean coast. The study consisted of mixing each drug in an aqueous solution with functionalized Sargassum spp in a container under constant agitation. Therefore, this work represents an alternative to solve two of the biggest problems in recent years; first, the reduction of the overpopulation of sargassum through its use for the remediation of the environment. Second is the removal of drug waste used excessively during the COVID-19 pandemic. Liquid samples of the solution were taken at intervals of 10 min and analyzed by fluorescence to determine the concentration of the drug.

The sorption capacity for diclofenac, ibuprofen, and paracetamol was 2.46, 2.08, and 1.41 μg/g, corresponding to 98 %, 84 %, and 54 % of removal, respectively. The removal of the three drugs was notably favored by increasing the temperature to 30 and 40 °C, reaching efficiencies close to 100 %. Moreover, the system maintains its effectiveness at various pH values. In addition, the Sargassum used can be reused for up to three cycles without reducing its removal capacity. The wide diversity of organic compounds favors the biosorption of drugs, removing them through various kinetic mechanisms. On the other hand, the Sargassum used in the drugs removal was analyzed by X-ray diffraction, FTIR spectroscopy, TGA analysis, and scanning electron microscopy before and after removal. The results showed an evident modification in the structure and morphology of the algae and demonstrated the presence of the biosorbed drugs. Therefore, this system is sustainable, simple, economical, environmentally friendly, highly efficient, and scalable at a domestic and industrial level that can be used for aquatic remediation environments.

Application of Raney Al-Ni Alloy for Simple Hydrodehalogenation of Diclofenac and Other Halogenated Biocidal Contaminants in Alkaline Aqueous Solution under Ambient Conditions

Raney Al-Ni contains 62% of Ni₂Al₃ and 38% NiAl₃ crystalline phases. Its applicability has been studied within an effective hydrodehalogenation of hardly biodegradable anti-inflammatory drug diclofenac in model aqueous concentrates and, subsequently, even in real hospital wastewater with the aim of transforming them into easily biodegradable products. In model aqueous solution, complete hydrodechlorination of 2 mM aqueous diclofenac solution (0.59 g L⁻¹) yielding the 2-anilinophenylacetate was achieved in less than 50 min at room temperature and ambient pressure using only 9.7 g L⁻¹ of KOH and 1.65 g L⁻¹ of Raney Al-Ni alloy. The dissolving of Al during the hydrodehalogenation process is accompanied by complete consumption of NiAl₃ crystalline phase and partial depletion of Ni₂Al₃. A comparison of the hydrodehalogenation ability of a mixture of diclofenac and other widely used halogenated aromatic or heterocyclic biocides in model aqueous solution using Al-Ni was performed to verify the high hydrodehalogenation activity for each of the used halogenated contaminants. Remarkably, the robustness of Al-Ni-based hydrodehalogenation was demonstrated even for the removal of non-biodegradable diclofenac in real hospital wastewater with high chloride and nitrate content. After removal of the insoluble part of the Al-Ni for subsequent hydrometallurgical recycling, the low quantity of residual Ni was removed together with insoluble Al(OH)₃ obtained after neutralization of aqueous filtrate by filtration.

Heterogeneous Electro-Fenton-like Designs for the Disposal of 2-Phenylphenol from Water

The hunt for efficient and environmentally friendly degradation processes has positioned the heterogeneous advanced oxidation processes as an alternative more interesting and economical rather than homogenous processes. Hence, the current study lies in investigating the efficiency of different heterogeneous catalysts using transition metals in order to prevent the generation of iron sludge and to extend the catalogue of possible catalysts to be used in advanced oxidation processes. In this study, nickel and zinc were tested and the ability for radical-generation degradation capacity of both ions as homogeneous was evaluated in the electro-Fenton-like degradation of 2-phenylphenol. In both cases, the degradation profiles followed a first-order kinetic model with the highest degradation rate for nickel (1 mM) with 2-phenylphenol removal level of 90.12% and a total organic reduction near 70% in 2 h. To synthesise the heterogeneous nickel catalyst, this transition metal was fixed on perlite by hydrothermal treatment and in a biochar or carbon nanofibers by adsorption. From the removal results using the three synthesized catalysts, it is concluded that the best catalysts were obtained by inclusion of nickel on biochar or nanofibers achieving in both with removal around 80% before 1 h. Thus, to synthetize a nickel electrocatalyst, nickel doped nanofibers were included on carbon felt. To do this, the amount of carbon black, nickel nanofibers and polytetrafluoroethylene to add on the carbon felt was optimized by Taguchi design. The obtained results revealed that under the optimised conditions, a near-complete removal was achieved after 2 h with high stability of the nickel electrocatalyst that open the applicability of this heterogeneous system to operate in flow systems.