Iron mining wastes collected from Mariana disaster: Reuse and application as catalyst in a heterogeneous electro-Fenton process

Unlocking the Potential of Nanobubbles: Achieving Exceptional Gas Efficiency in Electrogeneration of Hydrogen Peroxide

The electrogeneration of hydrogen peroxide (H2 O2 ) via the oxygen reduction reaction is a crucial process for advanced water treatment technologies. While significant effort is being devoted to developing highly reactive materials, gas provision systems used in these processes are receiving less attention. Here, using oxygen nanobubbles to improve the gas efficiency of the electrogeneration of H2 O2 is proposed. Aeration with nanobubbles is compared to aeration with macrobubbles under an identical experimental set-up, with nanobubbles showing a much higher gas-liquid volumetric mass transfer coefficient (KL a) of 2.6 × 10-2 min-1 compared to 2.7 × 10-4 min-1 for macrobubbles. Consequently, nanobubbles exhibit a much higher gas efficiency using 60% of O2 delivered to the system compared to 0.19% for macrobubbles. Further, it is observed that the electrogeneration of H2 O2 using carbon felt electrodes is enhanced using nanobubbles. Under the same dissolved oxygen levels, nanobubbles boost the reaction yield to 84%, while macrobubbles yield only 53.8%. To the authors' knowledge, this is the first study to investigate the use of nanobubbles in electrochemical reactions and demonstrate their ability to enhance gas efficiency and electrocatalytic response. These findings have important implications for developing more efficient chemical and electrochemical processes operating under gas-starving systems.

Decentralized approach toward organic pollutants removal using UV radiation in combination with H2O2-based electrochemical water technologies

The current literature lacks a comprehensive discussion on the trade-off between pollutant degradation/mineralization and treatment time costs in utilizing UV light in combination with H2O2-based electrochemical advanced oxidation processes (EAOPs). The present study sheds light on the benefits of using the photoelectro-Fenton (PEF) process with UVA or UVC for methylparaben (MetP) degradation in real drinking water. Although light boosts the photodegradation of refractory Fe(III) complexes and the photolysis of H2O2 (with UVC only), the energy-intensive nature of light-based treatments is acknowledged. To help tackle the high energy consumption issue, a novel approach was employed: partial application of UVA or UVC light after a predetermined electro-Fenton electrolysis time. The proposed treatment approach yielded satisfactory comparable results to those obtained from the application of PEF/UVA or PEF/UVC in terms of total organic carbon removal (ca. 100%), with notably lower energy consumption (ca. 50%). The study delves into the combined method's feasibility, analyzing pollutant degradation/mineralization process and overall energy consumption. The research identifies possible degradation routes based on intermediate detection and radical quenching experiments. Finally, toxicological assessments evaluate the toxicity levels of MetP and its intermediates. The findings of this study bring meaningful contributions to the fore and point to the highly promising potential of the proposed approach, in terms of sustainability and cost-effectiveness, when applied for decentralized water treatment.

Enhanced catalytic reduction of emerging contaminant by using magnetic CuFe2O4@MIL-100(Fe) in Fenton-based electrochemical processes

Fenton-based electrochemical processes (FEPs) using newly engineered 3D photocatalyst nanocomposites have garnered significant attention owing to their ability to remove emerging contaminants. Despite the development of numerous materials, there is still a need to enhance their efficiency, stability, and recyclability to address the limitations of FEPs. This study seeks to address this issue by investigating sustainable methods to engineer novel 3D core-shell photocatalyst composites for application in FEPs. These materials can update the photo-assisted PEFs activity, and magnetism can be helpful for the easy recyclability of the catalyst. Herein, we successfully synthesized a magnetic and photoactive CuFe₂O₄@MIL-100(Fe) (CM) composite through sustainable methods and assessed its morphological structure and physicochemical and photocatalytic properties. The catalytic performance of CM was investigated in an undivided RuO₂/air-diffusion cell to treat Cefadroxil. The results show that heterogeneous photoelectro-Fenton (HPEF) (100% in 120 min) has higher degradation efficiency than electro-Fenton (100% in 210 min) and electrooxidation (73.3% in 300 min) processes. The superior degradation efficiency of HPEF is attributed to the formation of a large amount of hydroxyl radicals indicating the excellent photocatalytic activity of the material due to the direct excitation of the Fe-O cluster, which boosts the redox reaction of Fe²⁺/Fe³⁺. Key operational parameters such as pH, catalyst concentration, current density, and CuFe₂O₄ proportion on MIL-100(Fe) in the composite were optimized in the HPEF process. The optimized composite exhibited good stability and easy recyclability, allowing high removal efficiency, which can be kept up after five cycles of 90 min. High degradation performance was observed using natural sunlight radiations. Additionally, possible catalytic degradation mechanisms in HPEFs were proposed based on radical quenching experiments. This study has significant potential to contribute to the development of more sustainable and effective water treatment strategies.

An FeP/carbon composite derived from a phytic acid-Fe3+ complex for sulfathiazole degradation through peroxymonosulfate activation

Peroxymonosulfate (PMS) activation-based advanced oxidation technology possesses great potential for antibiotic-containing wastewater treatment. Herein, we developed an iron phosphide/carbon composite and verified its capability and superiority towards a model antibiotic pollutant (sulfathiazole, STZ) degradation through PMS activation. Benefiting from the chelating ability of phytic acid (PA) with metal ions and its abundance on phosphorous element, a PA-Fe³⁺ complex was firstly formed and then served as sole precursor for iron phosphide formation by anoxic pyrolysis. Well crystalized FeP particle were found loading on the simultaneously formed thin layer carbon structure. Catalytic activity evaluation showed that FeP/carbon composite could remove over 99% of STZ (20 mg L^-1) in 20 min adsorption and 30 min catalysis process under the reaction conditions of catalyst dosage 0.2 g L^-1, PMS loading 0.15 g L^-1. A pseudo-first-order reaction rate constant of 0.2193 min^-1 was obtained, which was among the highest compared with reported studies. Further investigations indicated that the developed FeP/carbon composite worked well in a wide solution pH range of 3-9. Reaction mechanism study showed that reactive species of SO₄^-• and ¹O₂ generated from PMS activation played major roles for STZ degradation. Based on liquid chromatography-mass spectroscopy (LC-MS) analysis, a few STZ degradation intermediate products were identified, which facilitated the proposal of STZ degradation pathways. The possible ecological risk of STZ and related degradation intermediates were also considered by toxicity assessment using the Ecological Structure Activity Relationships (ECOSAR) Class Program. The obtained acute and chronic toxicity values implied the relatively low ecological risk of FeP/carbon-PMS reaction system for STZ treatment.

Efficient degradation of Rhodamine B in water by CoFe2O4/H2O2 and CoFe2O4/PMS systems: A comparative study

In this work, a comparative study of efficient degradation of Rhodamine B (RhB) in CoFe₂O₄/H₂O₂ and CoFe₂O₄/PMS systems was performed. Batch experiments indicated that the RhB degradation rate of CoFe₂O₄/H₂O₂ system reached 95.5% at 90 min under the condition of 0.5 g L^-1 of CoFe₂O₄ dosage, 10 mM of H₂O₂ concentration and 3.0 of initial pH. At certain conditions of initial pH = 7.0, 0.3 g L^-1 of CoFe₂O₄ dosage, 7 mM of PMS concentration, CoFe₂O₄/PMS system could completely degrade RhB within 90 min. EPR and quenching experiments indicated that •OH was the main active species of CoFe₂O₄/H₂O₂ system, and •OH, SO₄•^-, •O₂^- and ¹O₂ participated in RhB degradation of CoFe₂O₄/PMS system. The circulate of Co(II)/Co(III) and Fe(II)/Fe(III) on the CoFe₂O₄ surface promoted the formation of free radical species in the two system. In CoFe₂O₄/PMS system, the formed •O₂^- and SO₅•^- realized the generation of non-free radical species (¹O₂). The LC-MS results indicated that N-de-ethylation, chromophore cleavage, opening rings and mineralization were the main steps for the RhB degradation of the two systems. After five cycles of degradation experiment, the CoFe₂O₄/H₂O₂ and CoFe₂O₄/PMS systems still maintained the high degradation rate (85.2% and 92.4%) and low mass loss (2.7% and 3.09%). In addition, CoFe₂O₄/PMS system had better potential value for the actual water and multi-pollutant degradation than CoFe₂O₄/H₂O₂ system. Finally, the toxicity analysis and cost assessment of the two oxidation systems were preliminarily evaluated.

Industrial symbiosis in Brazil: A systematic literature review

This study describes how industrial symbiosis is reposed in studies dealing with the Brazilian context. This study was based on a systematic literature review in the Scopus and Web of Science databases, relying on the Prisma method and a research protocol. The results embrace quantitative and qualitative aspects such as the number of publications, the territorial scope of the studies, authors and keywords networks. The sample was also segregated into three categories, theoretical works, opportunities and formed networks, reporting the presence of industrial symbiosis in Brazil in the extant literature. The main contribution of this research is to aggregate the studies already published in the international literature, demonstrate how the IS is reported and how they can be expanded in territories or business cases not yet portrayed.

Mixed industrial wastewater treatment by the combination of heterogeneous electro-Fenton and electrocoagulation processes

Mixed industrial wastewater treatment efficiency of combined electro-Fenton (EF) and electrocoagulation (EC) processes was investigated in the present study. Alkali modified laterite soil was used as a heterogeneous EF catalyst and found superior performance than the raw laterite soil. Initially, the effect of catalyst dosage, initial pH, and applied voltage on the performance of EF process was carried out. A total of 54.57% COD removal was observed after 60 min of the EF treatment. Further treatment was carried out with EC process at different voltages. A total of 85.27% COD removal after 2 h treatment was observed by combining two electrochemical processes. Performance of EF followed by EC (EF + EC) process was compared with EC followed by EF (EC + EF) process. Even though efficiency is the same, EF + EC is a better strategy than EC + EF as it nullifies the neutralization requirement after EF process in addition to high mineralization efficiency, enhanced biodegradability, and lesser sludge generation.

A comprehensive study on the heterogeneous electro-Fenton degradation of tartrazine in water using CoFe2O4/carbon felt cathode

In this study, cobalt ferrite coated carbon felt (CoFe₂O₄/CF) was synthesized by solvothermal method and applied as cathode for electro-Fenton (EF) treatment of tartrazine (TTZ) in water. The materials were characterized by SEM, XRD, FTIR, CV, and EIS to explore their physical, chemical, and electrical properties. The effects of solvothermal temperature and metal content on the TTZ removal were examined, showing that 220 °C with 2 mM of Co and 4 mM of Fe precursors were the best synthesis condition. Various influencing factors such as applied current density, pH, TTZ concentration, and electrolytes were investigated, and the optimal condition was found at 8.33 mA cm^-2, pH 3, 50 mgTTZ L^-1, and 50 mM of Na₂SO₄, respectively. By radical quenching test, , ¹O₂, and HO were recognized as the key reactive oxygen species and the reaction mechanism was proposed for the EF decolorization of TTZ using CoFe₂O₄/CF cathode. The reusability and stability test showed that the highly efficient CoFe₂O₄/CF cathode is very promising for practical application in wastewater treatment, especially for dyes and other recalcitrant organic compounds to improve its biodegradability.

Magnetic nanostructured material as heterogeneous catalyst for degradation of AB210 dye in tannery wastewater by electro-Fenton process

Degradation of the Acid Black 210 dye (AB210) in synthetic and industrial effluent samples was performed, for the first time, using a heterogeneous electro-Fenton (EF) process with a CoFe₂O₄/NOM magnetic hybrid catalyst (Hb200). The technique was compared with electrochemical oxidation using electrogenerated hydrogen peroxide (AO-H₂O₂). The catalyst was synthesized by the sol-gel technique, using water with a high content of natural organic matter (NOM) as an eco-friendly solvent. Analyses using XRD, FTIR, and TEM showed the formation of hybrid nanostructures with average size of 4.85 nm. Electrochemical assays were performed with a GDE/BDD electrode pair, electrogenerated H₂O₂, and current density of 45.4 mA cm^-2. For the synthetic solution of AB210 at pH 3, the EF process presented higher efficiency, compared to AO-H₂O₂, with the optimum condition achieved using a lower mass of the catalyst (30 mg) and a higher concentration of the dye (55 mg L^-1). The EF method also showed superior performance in the treatment of an industrial effluent with high organic load, at pH 6, with almost complete mineralization of AB210 (95%) in 7 h, while the AO-H₂O₂ process achieved 82% mineralization. The Hb200 hybrid maintained excellent catalytic activity during reuse in 3 cycles, with only 10% lower mineralization efficiency in the last cycle. GC-MS analysis showed that most of the contaminants in the effluent, including bis(2-ethylhexyl) phthalate, one of the most toxic, were eliminated or transformed after the EF treatment with Hb200.

Study on the efficient removal of azo dyes by heterogeneous photo-Fenton process with 3D flower-like layered double hydroxide

As organic dyes are the main pollutants in water pollution, seeking effective removal solutions is urgent for humans and the environment. A novel environmentally friendly three-dimensional CoFe-LDHs (3D CoFe-LDHs) catalyst was synthesized by one-step hydrothermal method. Scanning electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectra, X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller technique as well as UV-Vis diffuse reflectance spectra were used to characterize the prepared samples. The experimental results revealed that 3D CoFe-LDHs exhibited a rapid decolorization of methyl orange and Rhodamine B by heterogeneous photo-Fenton process after reaching the adsorption equilibrium, and the final decolorization efficiency reached 91.18% and 93.56%, respectively. On the contrary, the decolorizing effect of 3D CoFe-LDHs on neutral blue was relatively weak. The initial concentrations of azo dyes, pH and H₂O₂ concentration affected the decolorization of dyes and the catalyst maintained excellent reusability and stability after reuse over five cycles. The quenching experiments found that •OH, •O₂ ^- and h⁺ were the main active substances and reaction mechanisms were further proposed. The study suggests that the synergistic effect of photocatalysis and Fenton oxidation process significantly improved the removal of azo dyes and the synthesized catalyst had potentially promising applications for difficult-to-biodegrade organic pollutants in wastewater.