Electrochemical oxidation of methyl orange by a Magnéli phase Ti4O7 anode

Per-and polyfluoroalkyl (PFAS) eternal pollutants: Sources, environmental impacts and treatment processes

Per- and polyfluoroalkyl substances (PFAS) have become a growing environmental concern due to their tangible impacts on human health. However, due to the large number of PFAS compounds and the analytical difficulty to identify all of them, there are still some knowledge gaps not only on their impact on human health, but also on how to manage them and achieve their effective degradation. PFAS compounds originate from man-made chemicals that are resistant to degradation because of the presence of the strong carbon-fluorine bonds in their chemical structure. This review consists of two parts. In the first part, the environmental effects of fluorinated compound contamination in water are covered with the objective to highlight how their presence in the environment adversely impacts the human health. In the second part, the focus is put on the different techniques available for the degradation and/or separation of PFAS compounds in different types of waters. Examples of removal/treatment of PFAS present in either surface or ground water are presented.

Integrated system of electro-catalytic oxidation and microbial fuel cells for the treatment of recalcitrant wastewater

The emission of recalcitrant wastewater poses serious threats to the environment. In this study, an integrated approach combining electrocatalytic oxidation (EC) for pretreatment and microbial fuel cells (MFC) for thorough pollutant degradation is proposed to ensure efficient degradation of target substances, with low energy input and enhanced bioavailability of refractory organics. When phenol was used as the pollutant, an initial concentration of 2000 mg/L phenol solution underwent EC treatment under constant current-exponential attenuation power supply mode, resulting in a COD removal rate of 54.53%, and a phenol degradation rate of 99.83%. Intermediate products such as hydroquinone and para-diphenol were detected in the solution. After subsequent MFC treatment, only minor amounts of para-diphenol were left, and the degradation rate of phenol and its intermediate products reached 100%, with an output power density of 110.4 mW m-2. When coal chemical wastewater was used as the pollutant, further examination of the EC-MFC system performance showed a COD removal rate of 49.23% in the EC section, and a 76.21% COD removal rate in the MFC section, with an output power density of 181.5 mW m-2. Microbiological analysis revealed typical electrogenic bacteria (such as Pseudomonas and Geobacter), and specific degrading functional bacteria (such as Stenotrophomonas, Delftia, and Brevundimonas). The dominant microbial communities and their proportions adapted to environmental changes in response to the variation of carbon sources.

A Comprehensive Review on Modification of Titanium Dioxide-Based Catalysts in Advanced Oxidation Processes for Water Treatment

It has become necessary to develop effective strategies to prevent and reduce water pollution as a result of the increase in dangerous pollutants in water reservoirs. Consequently, there is a need to design new catalyst materials to promote the efficiency of advanced oxidation processes (AOPs) in the field of wastewater treatment plant to ensure the mineralization of trace organic contaminants. A notable approach gaining attention involves the coupling of sulfate radicals-based AOPs to photocatalysis or electrocatalysis processes, aiming to achieve the complete removal of refractory contaminants into water and carbon dioxide. Titanium dioxide as metal oxide has received great attention for its catalytic application in water purification. TiO2 catalysts offer a multitude of advantages in AOPs. They are characterized by their high photocatalytic activity under both ultraviolet and visible light, making them environmentally friendly due to the absence of toxic byproducts during oxidation. Their versatility is remarkable, finding utility in various AOPs, from photocatalysis to photo-Fenton processes. TiO2's durability ensures long-lasting catalytic activity, which is crucial for continuous treatment processes, and their cost-effectiveness is particularly advantageous. Furthermore, their chemical stability allows it to withstand varying pH conditions. However, the large band gap energy and low electrical conductivity hinder the catalytic reaction effectiveness. This review aims to examine various approaches to enhance the catalytic performance of titanium dioxide, with the objective of enabling more efficient water purification methods.

Insights into degradation of pharmaceutical pollutant atenolol via electrochemical advanced oxidation processes with modified Ti4O7 electrode: Efficiency, stability and mechanism

A novel active Ce-doped Ti₄O₇ (Ti/Ti₄O₇-Ce) electrode was prepared and evaluated for improvement of the refractory pollutants degradation efficiency in Electrochemical advanced oxidation processes (EAOPs). The results showed that the addition of Ce in Ti/Ti₄O₇ electrode leading to great impact on •OH generation rate and electrode stability compared to pristine Ti/Ti₄O₇ electrode. Ti/Ti₄O₇-Ce electrode presented efficient oxidation capacity for pharmaceutical pollutant atenolol (ATL) in EAOPs, which could be attributed to the improvement of indirect oxidation mediated by electro-generated •OH, as the amount of •OH production was 16.5% higher than that in Ti/Ti₄O₇ within 120 min. The operational conditions greatly influenced the ATL degradation. The degradation efficiency of ATL increased as the current density, the degradation efficiency reached 100% under pH 4, but it just removed 81% of ATL under pH 10 after 120 min treatment. Results also suggested that the inhibiting effect from the ATL degradation was mostly associated with the decreased oxidation capacity induced by water hardness and natural organic matter (NOM). It displayed a satisfactory durability after 40 cycles of experimental detections in this research. The results of study suggested that Ti/Ti₄O₇-Ce was a promising electrode for the efficient degradation of PPCPs-polluted wastewater and provided constructive suggestion for the refractory pollutants of EAOPs.

In-situ fabrication of titanium suboxide-laser induced graphene composites: Removal of organic pollutants and MS2 Bacteriophage

Titanium suboxides (TSO) are identified as a series of compounds showing excellent electro- and photochemical properties. TSO composites with carbon-based materials such as graphene have further improved water splitting and pollutant removal performance. However, their expensive and multi-step synthesis limits their wide-scale use. Furthermore, recently discovered laser-induced graphene (LIG) is a single-step and low-cost fabrication of graphene-based composites. Moreover, LIG's highly electrically conductive surface aids in tremendous environmental applications, including bacterial inactivation, anti-biofouling, and pollutant sensing. Here, we demonstrate the single-step in-situ fabrication of TSO-LIG composite by directly scribing the TiO₂ mixed poly(ether) sulfone sheets using a CO₂ infrared laser. In contrast, earlier composites were derived from either commercial-grade TSO or synthesized TSO with graphene. The characteristic Ti³⁺ peaks in XPS confirmed the conversion of TiO₂ into its sub-stoichiometric form, enhancing the electro-catalytical properties of the LIG-TiO_x composite surface. Electrochemical characterization, including impedance spectroscopy, validated the surface's enhanced electrochemical activity and electrode stability. Furthermore, the LIG-TiO_x composite surfaces were tested for anti-biofouling action and electrochemical application as electrodes and filters. The composite electrodes exhibit enhanced degradation performance for removing emerging pollutant antibiotics ciprofloxacin and methylene blue due to the in-situ hydroxyl radical generation. Additionally, the LIG-TiO_x conductive filters showed the complete 6-log killing of mixed bacterial culture and MS2 phage virus in flow-through filtration mode at 2.5 V, which is ∼2.5-log more killing compared to non-composited LIG filers at 500 Lm^-2h^-1. Nevertheless, these cost-effective LIG-TiO_x composites have excellent electrical properties and can be effectively utilized for energy and environmental applications.

Electrochemical Oxidation of Organic Pollutants in Aqueous Solution Using a Ti4O7 Particle Anode

Anodes based on substoichiometric titanium oxide (Ti₄O₇) are among the most effective for the anodic oxidation of organic pollutants in aqueous solutions. Such electrodes can be made in the form of semipermeable porous structures called reactive electrochemical membranes (REMs). Recent work has shown that REMs with large pore sizes (0.5-2 mm) are highly efficient (comparable or superior to boron-doped diamond (BDD) anodes) and can be used to oxidize a wide range of contaminants. In this work, for the first time, a Ti₄O₇ particle anode (with a granule size of 1-3 mm and forming pores of 0.2-1 mm) was used for the oxidation of benzoic, maleic and oxalic acids and hydroquinone in aqueous solutions with an initial COD of 600 mg/L. The results demonstrated that a high instantaneous current efficiency (ICE) of about 40% and a high removal degree of more than 99% can be achieved. The Ti₄O₇ anode showed good stability after 108 operating hours at 36 mA/cm².

Nano-sphere RuO2 embedded in MOF-derived carbon arrays as a dual-matrix anode for cost-effective electrochemical wastewater treatment

The electrodes' activity, surface area and cost hinder the deployment of electrochemical wastewater treatment. Using an economical microfiber-based carbon felt (CF) substrate, we design RuO₂ nanospheres confined by Co_xO cooperated carbon nanoarrays (RuO₂-Co_xO@TCF) to augment noble metal utilization and thus reduce the catalyst cost. RuO₂-Co_xO@TCF anode with vertical diffusion channels exhibits rapid generation ability of oxidizing species particularity in the presence of Cl^- ions, which play a crucial role in azo bond cleavage and benzene ring chlorination of methyl orange. As a result, the catalyst shows 99.5 % color removal and ∼ 70 % mineralization efficiency at a concentration of 60 ppm. In synthetic dyeing wastewater, RuO₂-Co_xO@TCF delivers a stable total organic carbon (TOC) removal throughout ten cycling tests. Moreover, the electricity consumption of RuO₂-Co_xO@TCF is far below the reference anode, showing great promise for dye degradation and remediation of industrial wastewater.

Fabrication of PbO2/PVDF/CC Composite and Employment for the Removal of Methyl Orange

The in situ electrochemical oxidation process has received considerable attention for the removal of dye molecules and ammonium from textile dyeing and finishing wastewater. Nevertheless, the cost and durability of the catalytic anode have seriously limited industrial applications of this technique. In this work, the lab-based waste polyvinylidene fluoride membrane was employed to fabricate a novel lead dioxide/polyvinylidene fluoride/carbon cloth composite (PbO2/PVDF/CC) via integrated surface coating and electrodeposition processes. The influences of operating parameters (pH, Cl− concentration, current density, and initial concentration of pollutant) on the oxidation efficiency of PbO2/PVDF/CC were evaluated. Under optimal conditions, this composite achieves a 100% decolorization of methyl orange (MO), 99.48% removal of ammonium, and 94.46% conversion for ammonium-based nitrogen to N2, as well as an 82.55% removal of chemical oxygen demand (COD). At the coexistent condition of ammonium and MO, MO decolorization, ammonium, and COD removals still remain around 100%, 99.43%, and 77.33%, respectively. It can be assigned to the synergistic oxidation effect of hydroxyl radical and chloride species for MO and the chlorine oxidation action for ammonium. Based on the determination of various intermediates, MO is finally mineralized to CO2 and H2O, and ammonium is mainly converted to N2. The PbO2/PVDF/CC composite exhibits excellent stability and safety.

Energetic evaluation of phenol wastewater treatment by reverse electrodialysis reactor using different anodes

Efficient electrode materials are essential to convert salinity gradient energy into oxidative degradation energy and electrical energy by reverse electrodialysis reactor (REDR). In this context, comparative experiments of REDR using different anodes (Ti/IrO₂-RuO₂, Ti/PbO₂ and Ti/Ti₄O₇) were conducted. The effects of output current and electrode rinse solution (ERS) flowrate on mineralization efficiency and energy output were discussed. Results demonstrated that the COD removal rate(η_COD) rose almost linearly with output current and ERS flowrate when using Ti/Ti₄O₇ anode, but excessive operating conditions caused a slow increase or even decrease of η_COD when using Ti/IrO₂-RuO₂ or Ti/PbO₂ anodes. The order of electrode system potential loss (E_ele) for the three anodes was Ti/Ti₄O₇> Ti/PbO₂> Ti/IrO₂-RuO₂. High E_ele was beneficial to η_COD but had a negative effect on the net output power (P_net) of REDR. Regardless of the applied anodes, increasing the current and decreasing the ERS flowrate was detrimental to P_net due to higher E_ele. Based on these findings, four energy efficiency parameters were defined to evaluate energy recovery from multiple perspectives by linking energy output with mineralization capacity. They were electrode efficiency (η_ele), energy efficiency (EE), general current efficiency (GCE) and energy consumption (EC), respectively. Results showed that REDR with Ti/Ti₄O₇ anodes and suitable operating conditions achieved the optimal energy indicators and mineralization efficiency, which provided an efficient and economical option for wastewater treatment and energy recovery.

Chitin-Based Magnesium Oxide Biocomposite for the Removal of Methyl Orange from Water

In this work, a cost-effective chitin-based magnesium oxide (CHt@MgO) biocomposite with excellent anionic methyl orange (MO) dye removal efficiency from water was developed. The CHt@MgO biocomposite was characterized by FT-IR, XRD, SEM-EDX, and TGA/DTG. Results proved the successful synthesis of CHt@MgO biocomposite. Adsorption of MO on the CHt@MgO biocomposite was optimized by varying experimental conditions such as pH, amount of adsorbent (m), contact time (t), temperature (T), and initial MO concentration (C_o). The optimized parameters for MO removal by CHt@MgO biocomposite were as follows: pH, 6; m, 2 g/L; t, 120 min. Two common isotherm models (Langmuir and Freundlich) and three kinetic models (pseudo-first-order (PFO), pseudo-second-order (PSO), and intraparticle diffusion (IPD)) were tested for experimental data fitting. Results showed that Langmuir and PFO were the most suitable to respectively describe equilibrium and kinetic results on the adsorption of MO adsorption on CHt@MgO biocomposite. The maximum Langmuir monolayer adsorption capacity (q_m) on CHt@MgO biocomposite toward MO dye was 252 mg/g at 60 °C. The reusability tests revealed that CHt@MgO biocomposite possessed high (90.7%) removal efficiency after the fifth regeneration cycle.

Unique amorphous/crystalline heterophase coupling for an efficient oxygen evolution reaction

Designing amorphous/crystalline heterophase catalysts is still in the initial stage, and the study of amorphous/crystalline heterophase and carbon-free catalysts has not yet been realized. Herein, we report a unique amorphous/crystalline heterophase catalyst consisting of NiFe alloy nanoparticles (NPs) supported on Ti₄O₇ (NiFe/Ti₄O₇) for the first time, which is achieved by a heterophase supporting strategy of dual heat treatment. Surprisingly, the amorphous/crystalline heterophase is flexibly composed of amorphous and crystalline phases of alloy NPs and Ti₄O₇. The heterophase coupling endows the catalyst with a low overpotential (256 mV at 10 mA cm^-2), a small Tafel slope (47 mV dec^-1) and excellent endurance stability (over 100 h) in 1 M KOH electrolyte, which already outperforms commercial RuO₂ (338 mV and 113 mV dec^-1) and exceeds most reported representative carbon-based and titanium-based non-precious metal catalysts. The density functional theory (DFT) calculations and experimental results reveal that the unique amorphous/crystalline heterophase coupling in NiFe/Ti₄O₇ results in electron transfer between the alloy NPs and Ti₄O₇, allowing more catalytically active sites and faster interfacial electron transfer dynamics. This work provides insights into the synthesis of amorphous/crystalline heterophase catalysts and can be generalized to the heterophase coupling of other transition metal-based electrocatalysts.

Magnéli-Phase Ti4O7-Doped Laser-Induced Graphene Surfaces and Filters for Pollutant Degradation and Microorganism Removal

Laser-induced graphene (LIG) has recently become a point of attraction globally as an environmentally friendly method to fabricate graphene foam in a single step using a CO₂ laser. The electrical properties of LIG are studied in different environmental applications, such as bacterial inactivation, antibiofouling, and pollutant sensing. Furthermore, metal or nonmetal doping of graphene enhances its catalytical performance in pollutant degradation and decontamination. Magnéli phase (Ti_nO_2n-1) is a substoichiometric titanium oxide known for its high electrocatalytic behavior and chemical inertness and is being explored as a membrane or electrode material for environmental decontamination. Here, we show the fabrication and characterization of LIG-Magnéli-phase (Ti₄O₇) titanium suboxide composites as electrodes and filters on poly(ether sulfone). Unlike undoped LIG electrodes, the doped Ti₄O₇-LIG electrodes exhibit enhanced electrochemical activity, as demonstrated in electrochemical characterization using cyclic voltammetry and electrochemical impedance spectroscopy. Due to the in situ generation of hydroxyl radicals on the surface, the doped electrodes exhibit increase in methylene blue degradation and microorganism removal. Effects of voltage and doping were examined, resulting in a clear trend of degradation and decontamination performance proportional to the doping concentration and applied voltage giving the best result at 2.5 V for 10% Ti₄O₇ doping. The LIG-Ti₄O₇ surfaces also showed biofilm inhibition against mixed bacterial culture. The flow-through filtration using a LIG-Ti₄O₇ conductive filter showed complete bacterial killing with 6 log removal in the permeate at 2.5 V, an enhancement of ∼2.5 log compared to undoped LIG filters at a flow rate of ∼500 L m^-2 h^-1. The facile fabrication of Ti₄O₇-doped LIG with enhanced electrochemical properties can be effectively used for energy and environmental applications.

Magnéli phase titanium sub-oxides synthesis, fabrication and its application for environmental remediation: Current status and prospect

Sub-stoichiometric titanium oxide, also called titanium suboxides (TSO), had been a focus of research for many decades with a chemical composition of Ti_nO_2n-1 (n ≥ 1). It has a unique oxygen-deficient crystal structure which provides it an outstanding electrical conductivity and high corrosion resistance similar to ceramic materials. High electrical conductivity and ability to sustain in adverse media make these phases a point of attention for researchers in energy storage and environmental remediation applications. The Magnéli phase-based reactive electroconductive membranes (REM) and electrodes have demonstrated the electrochemical oxidation of pollutants in the water in flow-through and flow by configuration. Additionally, it has also shown its potential for visible light photochemical degradation as well. This review attempts to summarize state of the art in various Magnéli phases materials synthesis routes and their electrochemical and photochemical ability for environmental application. The manuscript introduces the Magnéli phase, its crystal structure, and catalytic properties, followed by the recent development in synthesis methods from diverse titanium sources, notably TiO₂ through thermal reduction. The various fabrication methods for Magnéli phase-base REMs and electrodes have also been summarized. Furthermore, the article discussed the environmental remediations via electrochemical and photochemical advanced oxidation processes. Additionally, the hybrid technology with REMs and electrodes is used to counter membrane biofouling and develop electrochemical sensing devices for the pollutants. The Magnéli phase materials have a bright future for both electrochemical and photochemical advanced oxidation of emerging contaminants in water and wastewater treatment.

A Case Study of Swine Wastewater Treatment via Electrochemical Oxidation by Ti4O7 Anode

With the rapid development of breeding industry, the efficient treatment of dramatically increasing swine wastewater is gradually becoming urgent. In particular, the development of application technologies suitable for the relatively small piggeries is critical due to the time cost and space requirements of conventional biological methods. In this study, Electrochemical oxidation (EO) was selected to systematically explore the treatment performance of three different swine wastewaters by Ti₄O₇ anode. It was observed that the colors changed from dark brown to light yellow after 60 min treatment at 50 mA/cm², and the removal rates of turbidity and suspended solids ranged from 89.36% to 93.65% and 81.31% to 92.55%, respectively. The chemical oxygen demand (COD), ammonia nitrogen (NH₃-N) and total phosphorus (TP) of all the three swine wastewaters were simultaneously removed to a very low concentration in 120 min, especially for sample III, 61 ± 9 mg/L of COD, 6.6 ± 0.4 mg/L of NH₃-N and 5.7 ± 1.1 mg/L of TP, which met the Discharge Standard of Pollutants for Livestock and Poultry Breeding (GB 18596-2001). Moreover, 70.93%-85.37% mineralization rates were also achieved in 120 min, confirming that EO treatment by Ti₄O₇ could efficiently remove the organic matters in wastewater. Excitation-emission matrix (EEM) and UV-vis spectrum characterization results further proved that aromatic compounds and macromolecules in wastewater were rapidly removed, which played important roles in the mineralization processes. The findings here provided an efficient and environment-friendly technology for swine wastewater treatment.

Progress in Preparation and Application of Titanium Sub-Oxides Electrode in Electrocatalytic Degradation for Wastewater Treatment

To achieve low-carbon and sustainable development it is imperative to explore water treatment technologies in a carbon-neutral model. Because of its advantages of high efficiency, low consumption, and no secondary pollution, electrocatalytic oxidation technology has attracted increasing attention in tackling the challenges of organic wastewater treatment. The performance of an electrocatalytic oxidation system depends mainly on the properties of electrodes materials. Compared with the instability of graphite electrodes, the high expenditure of noble metal electrodes and boron-doped diamond electrodes, and the hidden dangers of titanium-based metal oxide electrodes, a titanium sub-oxide material has been characterized as an ideal choice of anode material due to its unique crystal and electronic structure, including high conductivity, decent catalytic activity, intense physical and chemical stability, corrosion resistance, low cost, and long service life, etc. This paper systematically reviews the electrode preparation technology of Magnéli phase titanium sub-oxide and its research progress in the electrochemical advanced oxidation treatment of organic wastewater in recent years, with technical difficulties highlighted. Future research directions are further proposed in process optimization, material modification, and application expansion. It is worth noting that Magnéli phase titanium sub-oxides have played very important roles in organic degradation. There is no doubt that titanium sub-oxides will become indispensable materials in the future.

ZrMOX Particles for Enhanced Removal of Methyl Orange from Wastewater: Preparation, Characterization, and Adsorption Study

The wide application of organic dyes in many industries has brought challenges to the effective treatment of organic wastewater. In this study, a series of ZrMOX (M: Fe, Co, Ni, Cu) particles were prepared by the coprecipitation method to adsorb methyl orange (MO) in aqueous solution. The adsorbents were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and N2 adsorption-desorption. The selected adsorbent with the best adsorption performance was ZrFeOX with a molar ratio of 1 : 1 and calcination temperature of 573 K; the maximum adsorption capacity was 138.95 mg·g-1. The adsorption behavior of MO onto the adsorbent was studied as a function of contact time, initial concentrations, adsorption temperature, and pH conditions. The analysis results showed that pseudo-second-order, Elovich, and Langmuir models were suitable to describe the adsorption behavior of MO on the adsorbent. In addition, regeneration experiments presented that the MO removal rate reached over 96% after repeated recycling for 5 times. The adsorbent developed in this work is not only simple to prepare and low cost but also green and energy-saving, which can make some contributions to environmental governance.

Is HFPO-DA (GenX) a suitable substitute for PFOA? A comprehensive degradation comparison of PFOA and GenX via electrooxidation

Due to the potential hazard of perfluorooctanoic acid (PFOA), hexafluoropropylene oxide dimer acid (HFPO-DA, GenX) has become a typical alternative since 2009. However, GenX has recently been reported to have equal or even greater toxicity and bioaccumulation than PFOA. Considering the suitability of alternatives, it is quite essential to study and compare the degradation degree between PFOA and GenX in water. Therefore, in the present study, a comprehensive degradation comparison between them via electrooxidation with a titanium suboxide membrane anode was conducted. The degradation rate decreased throughout for PFOA, while it first increased and then decreased for GenX when the permeate flux increased from 17.3 L to 100.3 L m^-2·h^-1. The different responses of PFOA and GenX to flux might be attributed to their different solubilities. In addition, the higher k_obs of PFOA demonstrated that it had a better degradability than GenX by 2.4-fold in a mixed solution. The fluorinated byproduct perfluoropropanoic acid (PFPrA) was detected as a GenX intermediate, suggesting that ether bridge splitting was needed for GenX electrooxidation. This study provides a reference for assessing the degradability of GenX and PFOA and indicates that it is worth reconsidering whether GenX is a suitable alternative for PFOA from the point of view of environmental protection.

Systematic Study of Effective Hydrothermal Synthesis to Fabricate Nb-Incorporated TiO2 for Oxygen Reduction Reaction

Fuel cells are expected to serve as next-generation energy conversion devices owing to their high energy density, high power, and long life performance. The oxygen reduction reaction (ORR) is important for determining the performance of fuel cells; therefore, using catalysts to promote the ORR is essential for realizing the practical applications of fuel cells. Herein, we propose Nb-incorporated TiO₂ as a suitable alternative to conventional Pt-based catalysts, because Nb doping has been reported to improve the conductivity and electron transfer number of TiO₂. In addition, Nb-incorporated TiO₂ can induce the electrocatalytic activity for the ORR. In this paper, we report the synthesis method for Nb-incorporated TiO₂ through a hydrothermal process with and without additional load pressures. The electrocatalytic activity of the synthesized samples for the ORR was also demonstrated. In this process, the samples obtained under various load pressures exceeding the saturated vapor pressure featured a high content of Nb and crystalline TiNb₂O₇, resulting in an ellipsoidal morphology. X-ray diffraction results also revealed that, on increasing the Nb doping amounts, the diffraction peak of the anatase TiO₂ shifted to a lower angle and the full width at half maximum decreased. This implies that the Ti atom is exchanged with the Nb atom during this process, resulting in a decrease in TiO₂ crystallinity. At a doping level of 10%, Nb-incorporated TiO₂ exhibited the best electrocatalytic activity in terms of the oxygen reduction current (i_ORR) and onset potential for the ORR (E_ORR); this suggests that 10% Nb-doped samples have the potential for enhancing electrocatalytic activity.

Mixed metal oxide anodes used for the electrochemical degradation of a real mixed industrial wastewater

Mixed industrial wastewaters are often highly contaminated with heavy metals and organic pollutants. Treating these mixed wastewaters requires many stagewise unit operations. Our work investigates using an electrochemical oxidation-in-situ coagulation (ECO-IC) process as a pre-treatment step toward the efficient treatment of real mixed industrial wastewater rich with heavy metals and organic contaminants. The process degraded organic contaminants in the wastewater via anodic electrochemical oxidation. Simultaneously, heavy metals were precipitated in the solution by coagulants (iron hydroxides) formed in-situ by cathode-generated hydroxyl ions reacting with the significant amounts of dissolved iron in the wastewater. IrO₂-RuO₂ mixed metal oxide anodes were identified as the best electrodes for organic compound degradation demonstrating 97% degradation of methyl orange (MO) as a model compound within 15 min. These anodes were used to treat real industrial wastewater produced from the industrial cleaning of train tanker cars transporting industrial solvents. The electrochemical treatment experiments resulted in a treated solution with a lower heavy metal content, achieving 96% reduction in Fe and 30% reduction in As content. Only moderate decreases in organic content were observed up to a maximum of 13% reduction in total organic carbon after 1 h of treatment. Electrochemical treatment of the mixed industrial wastewater produced greater effective diameter of the suspended particles and distinct sediment, liquid, and suspended foam phases that could be easily separated for further treatment. ECO-IC shows promise as an efficient and chemical-free method to coagulate heavy metals in real industrial wastewaters and could be an effective pre-treatment in their separation.

Electrochemically reduced phytic acid-doped TiO2 nanotubes for the efficient electrochemical degradation of toxic pollutants

Element-doped TiO₂ nanotube arrays (TNAs) with optimized active sites provide an effective approach for significantly improving electrocatalytic performance. The challenges in such construction mainly include selection of green dopant and control of active sites. Herein, we present phytic acid as a phosphorus source for P-doped TNAs. An oxygen vacancy (Ov) and P co-doped TNAs (P-TiO_2-y) was prepared as an electrochemical oxidation anode. P-TiO_2-y exhibits excellent degradation activity due to the formation of Ti-O-P bonds and generation of Ov. P-doping was beneficial in improving the oxygen evolution potential of the electrode, which would be benefit for electrocatalytic degradation of pollutants. Using the P-TiO_2-y anode with a current density of 10 mA/cm² for tetracycline degradation, after a 3 h treatment, the removal rate, chemical oxygen demand and total organic carbon removal rates were 100%, 90.32% and 76.60%, respectively. The P-TiO_2-y also has excellent degradation performance for phenol, hydroquinone, p-nitrophenol and metronidazole.

Preparation of Fe@Fe2O3/3D graphene composite cathode for electrochemical removal of sulfasalazine

In the present study, heterogeneous electro-Fenton (EF) process was applied to remove the sulfasalazine (SU) pharmaceutical from aqueous solutions. In the first part, 3D graphene loaded with Fe@Fe₂O₃ core-shell nanowires (Fe@Fe₂O₃/3D-GO) was used as a cathode electrode in the EF process. Graphene oxide (GO) was synthesized for the synthesis of 3D graphene nanocomposites using the improved Hummers' method and subsequently 3D graphene synthesized by the hydrothermal method using glycine. Finally, Fe@Fe₂O₃/3D-GO composite was synthesized and its properties were assessed by Scanning electron microscopy, Atomic force microscopy, Brunauer-Emmett-Teller, Fourier-transform infrared spectroscopy and X-ray diffraction methods. Then, the cathode electrode was prepared using the resulting composite and its performance was evaluated using Cyclic Voltammetry analysis. In the final part of this work, the Fe@Fe₂O₃/3D-GO electrode was used as the cathode electrode in the heterogeneous EF process to remove SU from aqueous solutions. The effect of operating parameters such as applied current (mA), initial pH of solution, initial pharmaceutical concentration (mg L^-1) and process time (min) on pharmaceutical removal efficiency under heterogeneous EF process was investigated by response surface methodology. The results showed that the optimum values for applied current, pH, initial pharmaceutical concentration and electrolysis time were respectively 300 mA, 7, 30 mg L^-1 and 100 min, resulting 99.60% of SU removal. Finally, the intermediates of SU degradation were determined by Gas chromatography-mass spectrometry analysis and the amount of mineralization was determined by total organic carbon analysis. About 5.2% drop in the SU removal efficiency was observed within 8 operational runs.

Fabrication and characterization of porous titanium-based PbO2 electrode through the pulse electrodeposition method: Deposition condition optimization by orthogonal experiment

Porous titanium-based PbO₂ electrodes were successfully fabricated by pulse electrodeposition method. The primary pulse electrodeposition parameters, including pulse frequency (f), duty ratio (γ), average current density (J_a) and electrodeposition time (t) were considered in this study. An orthogonal experiment was designed based on those four factors and in three levels. SEM images and XRD results suggest that the surface morphology and structure of PbO₂ electrodes could be easily changed by varying pulse electrodeposition parameters. Orthogonal analysis reveals that the increase of f and J_a could decrease the average grain size of PbO₂ electrodes, which is conducive to create more active sites and promote the generation of hydroxide radicals. The electrochemical degradation of Azophloxine was carried out to evaluate the electrochemical oxidation performance of pulse electrodeposited electrodes. The results indicate that the influences of four factors can be ranked as follow: J_a >γ≈ t > f. The higher f, larger J_a and longer t could facilitate the optimization of the integrated electrochemical degradation performance of prepared PbO₂ electrode. The accelerated life time is dominated by J_a and t, coincident with the average weight increase of β-PbO₂ layer. The optimal parameters of pulse electrodeposition turn out to be: f = 50 Hz, γ = 30%, J_a = 25 mA cm^-2, t = 60 min. Together, the consequences of the experiments give assistance to uncover and roughly conclude the mechanism of pulse electrodeposition.