A ceramic electrode of ZrO2-Y2O3 for the generation of oxidant species in anodic oxidation. Assessment of the treatment of Acid Blue 29 dye in sulfate and chloride media

Fe-doped g-C3N4 with duel active sites for ultrafast degradation of organic pollutants via visible-light-driven photo-Fenton reaction: Insight into the performance, kinetics, and mechanism

The photo-Fenton process provides a sustainable and cost-effective strategy for removing refractory organic contaminants in wastewater. Herein, a high-efficient Fe-doped g-C3N4 photocatalyst (Fe@CN10) with a unique 3D porous mesh structure was prepared by one-pot thermal polymerization for ultrafast degradation of azo dyes, antibiotics, and phenolic acids in heterogeneous photo-Fenton systems under visible light irradiation. Fe@CN10 exhibited a synergy between adsorption-degradation processes due to the co-existence of Fe3C and Fe3N active sites. Specifically, Fe3C acted as an adsorption site for pollutant and H2O2 molecules, while Fe3N acted as a photocatalytic active site for the high-efficient degradation of MO. Resultingly, Fe@CN10 showed a photocatalytic degradation rate of MO up to 140.32 mg/L min-1. The dominant ROS contributed to the removal of MO in the photo-Fenton pathway was hydroxyl radical (•OH). Surprisingly, as the key reactive species, singlet oxygen (1O2) generated from superoxide radical (•O2-) also efficiently attacked MO in a photo-self-Fenton pathway. Additionally, sponge/Fe@CN10 was prepared and filled in the continuous flow reactors for nearly 100% degradation of MO over 150 h when treating artificial organic wastewater. This work provided a facile route to prepare highly-active Fe-doped photocatalysts and develop a green photocatalytic system for wastewater treatment in the future.

Development of SDS-Modified PbO2 Anode Material Based on Ti3+ Self-Doping Black TiO2NTs Substrate as a Conductive Interlayer for Enhanced Electrocatalytic Oxidation of Methylene Blue

Efficient and stable electrode materials are urgently required for wastewater treatment in the electrocatalytic degradation of toxic and refractory organic pollutants. Ti3+ self-doping black TiO2 nanotube arrays (Ti/B-TiO2-NTs) as an interlayer were used for preparing a novel PbO2 electrode via an electrochemical reduction technology, and a sodium dodecyl sulfate (SDS)-modified PbO2 catalytic layer was successfully achieved via an electrochemical deposition technology. The physicochemical characterization tests showed that the Ti/B-TiO2-NTs/PbO2-SDS electrodes have a denser surface and finer grain size with the introduction of Ti3+ in the interlayer of Ti/TiO2-NTs and the addition of SDS in the active layer of PbO2. The electrochemical characterization results showed that the Ti3+ self-doping black Ti/TiO2-NTs/PbO2-SDS electrode had higher oxygen evolution potential (2.11 V vs. SCE), higher electrode stability, smaller charge-transfer resistance (6.74 Ω cm-2), and higher hydroxyl radical production activity, leading to it possessing better electrocatalytic properties. The above results indicated that the physicochemical and electrochemical characterization of the PbO2 electrode were all enhanced significantly with the introduction of Ti3+ and SDS. Furthermore, the Ti/B-TiO2-NTs/PbO2-SDS electrodes displayed the best performance on the degradation of methylene blue (MB) in simulated wastewater via bulk electrolysis. The removal efficiency of MB and the chemical oxygen demand (COD) could reach about 99.7% and 80.6% under the optimal conditions after 120 min, respectively. The pseudo-first-order kinetic constant of the Ti/B-TiO2-NTs/PbO2-SDS electrode was 0.03956 min-1, which was approximately 3.18 times faster than that of the Ti/TiO2-NTs/PbO2 electrode (0.01254 min-1). In addition, the Ti/B-TiO2-NTs/PbO2-SDS electrodes showed excellent stability and reusability. The degradation mechanism of MB was explored via the experimental identification of intermediates. In summary, the Ti3+ self-doping black Ti/TiO2-NTs/PbO2-SDS electrode is a promising electrode in treating wastewater.

Tetracycline removal from aqueous solution by electrooxidation using ruthenium-coated graphite anode

This paper reports the electrochemical oxidation treatment of 80 mL of acidic aqueous solutions with 0.2 mM of the drug tetracycline in 25 mM Na₂SO₄ using a lab-scale electrochemical cell. The performance of tetracycline removal with Ru-coated graphite by the chemical bath deposition (CBD) and raw graphite anode has been demonstrated. The effects of operating parameters were tested such as pH, applied current, supporting electrolyte concentration, and initial tetracycline concentration. The best tetracycline degradation was obtained with Ru-coated graphite anode due to its higher oxidation power, which allowed the complete degradation of refractory compounds. The modified surface structure of the Ru-coated graphite anode was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy-dispersive X-ray (EDX). The EO process with Ru-coated graphite anode allowed 93.8% tetracycline abatement after 100 min of electrolysis at an applied current of 100 mA. In all cases, tetracycline decay obeyed pseudo-first-order kinetics. The tetracycline removal performance of graphite electrodes with nano coating on graphite has offered a performing alternative. A Comparative study revealed that electrolysis with Ru-coated graphite acted as a better electrode material than raw graphite for the catalytic reaction.

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.

Highly porous seeding-free boron-doped ultrananocrystalline diamond used as high-performance anode for electrochemical removal of carbaryl from water

Boron-doped diamond (BDD) electrodes are regarded as the most promising catalytic materials that are highly efficient and suitable for application in advanced electrochemical oxidation processes targeted at the removal of recalcitrant contaminants in different water matrices. Improving the synthesis of these electrodes through the enhancement of their morphology, structure and stability has become the goal of the material scientists. The present work reports the use of an ultranano-diamond electrode with a highly porous structure (B-UNCD_WS/TDNT/Ti) for the treatment of water containing carbaryl. The application of the proposed electrode at current density of 75 mA cm^-2 led to the complete removal of the pollutant (carbaryl) from the synthetic medium in 30 min of electrolysis with an electric energy per order of 4.01 kWh m^-3 order^-1. The results obtained from the time-course analysis of the carboxylic acids and nitrogen-based ions present in the solution showed that the concentrations of nitrogen-based ions were within the established maximum levels for human consumption. Under optimal operating conditions, the proposed electrode was successfully employed for the complete removal of carbaryl in real water. Thus, the findings of this study show that the unique, easy-to-prepare BDD-based electrode proposed in this study is a highly efficient tool which has excellent application potential for the removal of recalcitrant pollutants in water.

The Effect of Yttria Content on Microstructure, Strength, and Fracture Behavior of Yttria-Stabilized Zirconia

Yttria-stabilized zirconia (YSZ) is well-known as a material with perfect mechanical, thermal, and electrical properties. It is used for manufacturing various high-temperature components for aerospace and energy generation, as well as wear- and corrosion-resistant devices in medicine. This work investigated the effect of a Y2O3 addition to ZrO2 on the microstructure and mechanical properties of YSZ ceramics produced by one sintering schedule. ZrO2 ceramics doped with 3, 4, 5, 6, 7, and 8 mol% Y2O3 (designated 3YSZ through to 8YSZ) were prepared by using conventional sintering at 1550 °C for 2 h in argon. The effect of yttria content was analyzed with respect to grain size, morphology of the microstructural features, phase composition, parameters of fracture surface, and flexural strength. The 7YSZ ceramics sintered at 1550 °C for 2 h showed the highest level of flexural strength due to the formation of the fine-grained microstructure containing mainly the monoclinic and tetragonal zirconia phases. The fracture micromechanism in the studied YSZ ceramics is discussed.

Electrochemical oxidation of ciprofloxacin in different aqueous matrices using synthesized boron-doped micro and nano-diamond anodes

The present work investigates the electrocatalytic performance of two different morphologies of boron doped-diamond film electrode (microcrystalline diamond - MCD, and nanocrystalline diamond - NCD) used in electrochemical oxidation for the removal of the antibiotic ciprofloxacin (CIP). A thorough study was conducted regarding the formation of the MCD and NCD films through the adjustment of methane in CH₄/H₂ gas mixture, and the two films were compared in terms of crystalline structure, apparent doping level, and electrochemical properties. The physicochemical results showed that the NCD film had higher sp² carbon content and greater doping level; this contributed to improvements in its surface roughness, as well as its specific capacitance and charge transfer, which consequently enhanced its electrocatalytic activity in comparison with the MCD. The results obtained from CIP removal and mineralization assays performed in sulfate medium also showed that the NCD was more efficient than the MCD under all the current densities investigated. The effects of CIP concentration and the evolution of the final by-products, including short-chain carboxylic acids and inorganic ions, were also investigated. The electrochemical performance of the NCD was evaluated in different aqueous matrices, including chloride medium, real wastewater and simulated urine. The application of the NCD led to complete or almost complete CIP degradation, regardless of the medium employed. The kinetic constant rates obtained under the different media investigated were as follows: synthetic urine (0.0416 min^-1 - R² = 0.991) < real wastewater (0.0923 min^-1 R² = 0.997) < synthetic matrix containing chloride (0.1992 min^-1 - R² = 0.995); this shows that the pollutant degradation was affected by the type of aqueous matrix and the oxidants that were electrogenerated in situ. The results obtained from the analysis of electrical energy per order (EE/O) showed that the treatment of simulated urine spkiked with required the highest energy consumption, followed by the real effluent and synthetic matrix containing chloride. The present study proves the viability of electrocatalytic nanostructured materials to the treatment of antibiotics in complex matrices.

Green production of hydrochar nut group from waste materials in subcritical water medium and investigation of their adsorption performance for crystal violet

This study evaluates the production of hydrochars from the outer shells of the nut group (peanut, hazelnut, walnut, and pistachio) in an eco-friendly subcritical water medium (SWM) and their effects as adsorbents on the removal of crystal violet (CV) from an aqueous solution. The prepared hydrochars were characterized using Brunauer Emmett-Teller (BET) analysis, scanning electron microscope (SEM), Fourier transforms infrared spectroscopy (FTIR), and zeta potential. The adsorption process was optimized based on pH, adsorbent dose, dye concentration, and contact time. The hazelnut hydrochar was found to have the maximum removal efficiency (91%). Optimum conditions were pH of 8, particle size <45 μm, adsorption time of 60 min, and dye concentration of 25 mg/L. The results of all hydrochars were fitted to the second-order kinetics. Langmuir, Freundlich, and Redlich-Peterson isotherms models were used to explain the relationship between adsorbent and adsorbate. For all hydrochars, CV adsorption was found to be feasible and inherently spontaneous. The use of materials with no commercial value like; the outer shells of the nut group, is considered a method for waste reduction using the SWM method. PRACTITIONER POINTS: Hydrochars of nut group were synthesized in the subcritical water medium. Adsorption ability of the hydrochars in the adsorption of crystal violet were investigated. Adsorption isotherms were used to explain the relationship between adsorbent and adsorbate. The hazelnut hydrochar provided the maximum removal efficiency (91%). Hazardous water pollutant effectively removed using an eco-friendly method.

Tin dioxide decorated on Ni-encapsulated nitrogen-doped carbon nanotubes for anodic electrolysis and persulfate activation to degrade cephalexin: Mineralization and degradation pathway

In this study, bamboo-shaped carbon nanotubes exhibiting high nitrogen content and Ni encapsulation (Ni@NCNT) were effectively synthesized by a simple pyrolysis method. The catalytic peroxydisulfate activation for cephalexin (CPX) degradation was investigated using the prepared material. SnO₂ was further decorated and fabricated on the anode material (SnO₂/Ni@NCNT) for electrochemical degradation of CPX in an aqueous solution. Transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy indicated that the SnO₂ nanoparticles were uniformly distributed on the surface of Ni@NCNT. Electrochemical characterization employing cyclic voltammetry and linear sweep voltammetry demonstrated that SnO₂/Ni@NCNT displayed higher oxygen evolution potential and electrocatalytic activity than Ni@NCNT. Mineralization of CPX in wastewater was performed using electrolysis coupled with persulfate oxidation. The analysis revealed a synergistic strengthening effect. The electropersulfate oxidation resulted in higher total organic carbon (TOC) removal (70.3%) than the sum of electrooxidation (48.1%) and persulfate oxidation (9.2%) toward CPX. This phenomenon might result from the regeneration of sulfate radicals (SO₄^•-) on the anode and complementary oxidation by SO₄^•- and OH. Persulfate oxidation alone was shown to result in low TOC removal, although CPX was mostly degraded. Additionally, the CPX degradation pathway involving electropersulfate oxidation was proposed and it is indicated that CPX molecules were completed decomposed by the examination of short chain acids, mineralized ions, and ecotoxicity evolution indicated that the antibiotic was completely degraded. This study provides a new approach for the design and preparation of novel electrode materials and electrochemical degradation facilities for the removal of pollutants via persulfate activation.

Green synthesis of Quercus coccifera hydrochar in subcritical water medium and evaluation of its adsorption performance for BR18 dye

In this study, we investigated the production conditions of Quercus coccifera hydrochar, which is an inexpensive and easy available adsorbent, for the adsorption of Basic Red 18 (BR18) azo dye. The hydrochar was produced in the eco-friendly subcritical water medium (SWM). The effects of the pH (2-10), adsorbent size (45-106 μm), adsorbent dose (0.5-1.5 g/L), dye concentration (40-455 mg/L), and contact time (5-120 min) were studied via optimization experiments. The optimum conditions were pH 10, particle size of 45 μm, particle amount of 1.5 g/L, dye concentration of 455 mg/L, and 60 min. The removal efficiency increased sharply for the first 5 min; after that the removal efficiency reached a steady state at 60 min, with a maximum removal of 88.7%. The kinetic studies for the adsorption of BR18 dye in aqueous solution using hydrochar showed pseudo-second-order kinetics. The Langmuir and Freundlich isotherm models were used to explain the relationship between adsorbent and adsorbate, and Freundlich isotherm was the most suitable model because of its high regression coefficient (R²) value. The intraparticle diffusion model was used to determine the adsorption mechanism of BR18 onto Q. coccifera acorn hydrochar. Desorption studies were also carried out using different types of acid and different molarities.

A novel gradient current density output mode for effective electrochemical oxidative degradation of dye wastewater by boron-doped diamond (BDD) anode

In order to solve the problems of high energy consumption and low current efficiency in electrochemical oxidation (EO) degradation under the traditional constant output process (COP), a gradient output process (GOP) of current density is proposed in this paper. That is, the current density is gradually reduced in a fixed degradation time, and the Reactive Blue 19 simulated dye wastewater was used as the degradation target. The general applicability of the process was further confirmed by studying the optimal gradient current density output parameters, the dye concentration, electrolyte concentration and other dye compounds with different molecular structures. The corresponding results show that the chemical oxygen demand (COD) removal (78%) and the color removal (100%) under the GOP are similar to those in the COP, and the overall energy consumption is reduced by about 50% compared with that in the traditional constant current mode. Moreover, the current efficiency in the middle and late stages of EO process has increased by 8.6 times compared with COP.

Yellow 2G dye degradation by electro-Fenton process using steel electrode as catalysis and its phytotoxicity effect

The heterogeneous electro-Fenton process degradation of Yellow 2G from wastewater was studied using a batch reactor. The COD of the wastewater used in treatment experiments was 163 mg O₂·L^-1 and the BOD₅ was 17 mg O₂·L^-1 (hardly biodegradable). The treatment of the wastewater at different current densities (2.5 mA·cm^{- 2}-12.5 mA·cm^{- 2}), solution pH (3 and 6.6), reaction times (5-25 min), electrolyte nature (NaCl, Na₂SO₄) and electrolyte concentrations (0.15 g·L^{- 1}-1 g·L^{- 1}) was investigated. According to the results, the heterogeneous electro-Fenton process was suitable for the decolorization of wastewater containing Yellow 2G. The optimum conditions were current density of 12.5 mA·cm^-2, initial pH of the wastewater neutral, 25 min of electrolysis treatment using an additive steel electrode as a source of catalysis and in the presence of 1 g NaCl·L^-1. We obtained easily biodegradable water with a mineralization rate equal to 85% and non-toxicity confirmed by the pea grain germination test.