Preparation, characterization, and application of Ti/TiO2-NTs/Sb-SnO2 electrode in photo-electrochemical treatment of industrial effluents under mild conditions

Characterization and electrochemical properties of TiO2-rNTs/SnO2-Sb/PbO2 electrodes for the mineralization of persistent organic pollutants using anodic oxidation coupled Electro-Fenton treatment: Effect of precursor selection

The present study compares the effect of using different solvents on the electrochemical properties of the reduced TiO2 nanotubes (TiO2-rNTs) layered Ti/TiO2-rNTs/SnO2-Sb/PbO2 anodes. The electrodes are prepared using three different solvent-based precursors: (i) isopropanol, (ii) ethylene glycol and citric acid (Pechini method), and (iii) 2-hydroxyethylammonium acetate (2HEAA) ionic liquid (IL) via the thermal decomposition route. The decomposition mechanism of precursor solutions was explored using the thermogravimetric (TGA) analysis. Further, the physicochemical properties of the electrodes are examined using Field emission Scanning Electron microscopy (FE-SEM), X-ray diffraction spectroscopy (XRD), and X-ray photoelectron emission spectroscopy (XPS). The results revealed that solvents with higher viscosity and slower decomposition rates support better film uniformity and higher stability of the electrode. The TiO2 -rNTs bottom layer and PbO2 top layer helped obtain higher film stability, increased working potential window (2.2 V vs. SHE) of the electrode, and the repeatability of the results. The performance of different electrodes based on the precursor solution is found as IL ≫ Pechini > Isopropanol. 4-chlorophenol (4-CP) is used as a model pollutant to test the performance of IL-Ti/TiO2-rNTs/SnO2-Sb/PbO2 anode in an anodic oxidation (AO) coupled electro-Fenton (EF) treatment. Further, the reliability of the electrode is evaluated by mineralizing other persistent organic pollutants (POPs) like tetracyclin, phenol, 2-chlorophenol (2-CP), and 2,4-dichlorophenol (2,4-DCP). Under the optimized conditions, the proposed system was able to mineralize the tetracyclin, phenol, 2-CP, 2,4-DCP, and 4-CP up to 78.91, 82.07, 74.96, 78.78, and 69.3 %, respectively. Moreover, the degradation mechanism of chlorophenols is proposed.

Acute Aquatic Toxicity to Zebrafish and Bioaccumulation in Marine Mussels of Antimony Tin Oxide Nanoparticles

Antimony tin oxide (Sb₂O₅/SnO₂) is effective in the absorption of infrared radiation for applications, such as skylights. As a nanoparticle (NP), it can be incorporated into films or sheets providing infrared radiation attenuation while allowing for a transparent final product. The acute toxicity exerted by commercial Sb₂O₅/SnO₂ (ATO) NPs was studied in adults and embryos of zebrafish (Danio rerio). Our results suggest that these NPs do not induce an acute toxicity in zebrafish, either adults or embryos. However, some sub-lethal parameters were altered: heart rate and spontaneous movements. Finally, the possible bioaccumulation of these NPs in the aquacultured marine mussel Mytilus sp. was studied. A quantitative analysis was performed using single particle inductively coupled plasma mass spectrometry (sp-ICP-MS). The results indicated that, despite being scarce (2.31 × 10⁶ ± 9.05 × 10⁵ NPs/g), there is some accumulation of the ATO NPs in the mussel. In conclusion, commercial ATO NPs seem to be quite innocuous to aquatic organisms; however, the fact that some of the developmental parameters in zebrafish embryos are altered should be considered for further investigation. More in-depth analysis of these NPs transformations in the digestive tract of humans is needed to assess whether their accumulation in mussels presents an actual risk to humans.

Application of Electrochemical Oxidation for Water and Wastewater Treatment: An Overview

In recent years, the discharge of various emerging pollutants, chemicals, and dyes in water and wastewater has represented one of the prominent human problems. Since water pollution is directly related to human health, highly resistant and emerging compounds in aquatic environments will pose many potential risks to the health of all living beings. Therefore, water pollution is a very acute problem that has constantly increased in recent years with the expansion of various industries. Consequently, choosing efficient and innovative wastewater treatment methods to remove contaminants is crucial. Among advanced oxidation processes, electrochemical oxidation (EO) is the most common and effective method for removing persistent pollutants from municipal and industrial wastewater. However, despite the great progress in using EO to treat real wastewater, there are still many gaps. This is due to the lack of comprehensive information on the operating parameters which affect the process and its operating costs. In this paper, among various scientific articles, the impact of operational parameters on the EO performances, a comparison between different electrochemical reactor configurations, and a report on general mechanisms of electrochemical oxidation of organic pollutants have been reported. Moreover, an evaluation of cost analysis and energy consumption requirements have also been discussed. Finally, the combination process between EO and photocatalysis (PC), called photoelectrocatalysis (PEC), has been discussed and reviewed briefly. This article shows that there is a direct relationship between important operating parameters with the amount of costs and the final removal efficiency of emerging pollutants. Optimal operating conditions can be achieved by paying special attention to reactor design, which can lead to higher efficiency and more efficient treatment. The rapid development of EO for removing emerging pollutants from impacted water and its combination with other green methods can result in more efficient approaches to face the pressing water pollution challenge. PEC proved to be a promising pollutants degradation technology, in which renewable energy sources can be adopted as a primer to perform an environmentally friendly water treatment.

Ti/SnO2-Sb2Ox-TiO2 Electrodeposited from Methanesulfonate Electrolytes: Preparation, Properties, and Performance

In this study, Ti/SnO2-Sb2Ox-TiO2 electrodes were produced using a sol-enhanced electrodeposition technique from methanesulfonate electrolytes. The surface microstructures of Ti/SnO2-Sb2Ox-TiO2 were observed, and their phase constituents were determined. The surface features were analyzed by X-ray photoelectron spectroscopy. Linear sweep voltammetry and degradation tests were also conducted to determine the degradation performance. The results show that the addition of TiO2 sol affects the microstructures of Ti/SnO2-Sb2Ox-TiO2 electrodes, while a uniform coating surface can be obtained at a proper sol concentration in electrolytes. Adding TiO2 sol also causes deep oxidation of Sb and generates more adsorbed oxygen on the electrode surface. The favorable surface features and the well-dispersed TiO2 in the coatings of 10 mL/L TiO2 modified Ti/SnO2-Sb2Ox-TiO2 electrodes award them the best electrocatalytic performance, and their uniform coating surface prolongs the electrode service life.

Characterization and comparison of Ti/TiO2-NT/SnO2-SbBi, Ti/SnO2-SbBi and BDD anode for the removal of persistent iodinated contrast media (ICM)

In this study, we investigated the impact of a TiO₂ nanotube (NT) interlayer on the electrochemical performance and service life of Sb and Bi-doped SnO₂-coatings synthesized on a titanium mesh. Ti/SnO₂-SbBi electrode was synthetized by a thermal decomposition method using ionic liquid as a precursor solvent. Ti/TiO₂-NT/SnO₂-SbBi electrode was obtained by a two-step electrochemical anodization, followed by the same process of thermal decomposition. The synthesized electrodes were electrochemically characterized and analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy. Terephthalic acid (TA) experiments showed that Ti/SnO₂-SbBi and Ti/TiO₂-NT/SnO₂-SbBi electrodes formed somewhat higher amounts of hydroxyl radicals (HO) compared with the mesh boron doped diamond (BDD) anode. Electrochemical oxidation experiments were performed using iodinated contrast media (ICM) as model organic contaminants persistent to oxidation. At current density of 50 A m^-2, BDD clearly outperformed the synthesized mixed metal oxide (MMO) electrodes, with 2 to 3-fold higher oxidation rates observed for ICM. However, at 100 and 150 A m^-2, Ti/SnO₂-SbBi had similar performance to BDD, whereas Ti/TiO₂-NT/SnO₂-SbBi yielded even higher oxidation rates. Disappearance of the target ICM was followed by up to 80% removal of adsorbable organic iodide (AOI) for all three materials, further demonstrating iodine cleavage and thus oxidative degradation of ICM mediated by HO. The presence of a TiO₂ NT interlayer yielded nearly 4-fold increase in anode stability and dislocated the oxygen evolution reaction by +0.2 V. Thus, TiO₂ NT interlayer enhanced electrode stability and service life, and the electrocatalytic activity for the degradation of persistent organic contaminants.

Semiconductor Electrode Materials Applied in Photoelectrocatalytic Wastewater Treatment—an Overview

Industrial sources of environmental pollution generate huge amounts of industrial wastewater containing various recalcitrant organic and inorganic pollutants that are hazardous to the environment. On the other hand, industrial wastewater can be regarded as a prospective source of fresh water, energy, and valuable raw materials. Conventional sewage treatment systems are often not efficient enough for the complete degradation of pollutants and they are characterized by high energy consumption. Moreover, the chemical energy that is stored in the wastewater is wasted. A solution to these problems is an application of photoelectrocatalytic treatment methods, especially when they are coupled with energy generation. The paper presents a general overview of the semiconductor materials applied as photoelectrodes in the treatment of various pollutants. The fundamentals of photoelectrocatalytic reactions and the mechanism of pollutants treatment as well as parameters affecting the treatment process are presented. Examples of different semiconductor photoelectrodes that are applied in treatment processes are described in order to present the strengths and weaknesses of the photoelectrocatalytic treatment of industrial wastewater. This overview is an addition to the existing knowledge with a particular focus on the main experimental conditions employed in the photoelectrocatalytic degradation of various pollutants with the application of semiconductor photoelectrodes.

Hazardous waste treatment technologies

This is a review of the literature published in 2018 on topics related to hazardous waste management in water, soils, sediments, and air. The review covers treatment technologies applying physical, chemical, and biological principles for contaminated water, soils, sediments, and air. PRACTITIONER POINTS: The management of waters, wastewaters, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) was reviewed according to the technology applied, namely, physical, chemical and biological methods. Physical methods for the management of hazardous wastes including adsorption, coagulation (conventional and electrochemical), sand filtration, electrosorption (or CDI), electrodialysis, electrokinetics, membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, persulfate-based, Fenton and Fenton-like, and potassium permanganate processes for the management of hazardous were reviewed. Biological methods such as aerobic, anaerobic, bioreactor, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed.

Preparation of a SnO2–Sb electrode on a novel TiO2 network structure with long service lifetime for degradation of dye wastewater

Developing effective electrodes with long service lifetime for electrochemical degradation of dyes is of paramount importance for their practical industrial applications. We constructed a novel SnO₂–Sb electrode (Ti/TiO₂-NW/SnO₂–Sb electrode) based on a uniform TiO₂ network structure decorated Ti plate (Ti/TiO₂-NW) for a long-term electrocatalytic performance. The SnO₂–Sb coating layer on this electrode was grown on the Ti/TiO₂-NW by pulse electrodeposition. The introduction of the three-dimensional TiO₂-NW enhances the bonding strength between the Ti substrate and the SnO₂–Sb surface coating. An accelerated life test shows that the service life of Ti/TiO₂-NW/SnO₂–Sb electrode is 11.15 times longer than that of the traditional Ti/SnO₂–Sb electrode. The physicochemical properties of the electrodes were characterized through SEM, EDS, XRD and HRTEM. In addition, through LSV, EIS, CV and voltammetric charge analysis, it is found that compared with the traditional electrode, the Ti/TiO₂-NW/SnO₂–Sb electrode possesses a higher oxygen evolution potential, a lower charge transfer resistance and a larger electrochemical active surface area. Besides, this novel electrode also exhibits an outstanding electrocatalytic oxidation ability for degradation of acid red 73 in simulated sewage. After a 5 hours' test, the removal efficiency of acid red 73 and the COD reached 98.6% and 71.8%, respectively, which were superior to those of Ti/SnO₂–Sb electrode (89.1% and 58.8%). This study highlights the excellent stability of the Ti/TiO₂-NW/SnO₂–Sb electrode and provides an energy-efficient strategy for dye degradation.

A novel TiO₂ network structure modified SnO₂–Sb electrode has been prepared by electrodeposition with long service lifetime and low energy consumption.