Electrodeposition preparation of Ce-doped Ti/SnO2-Sb electrodes by using selected addition agents for efficient electrocatalytic oxidation of methylene blue in water

Preparation of Ti/SnO2-Sb2O4-La Electrode with TiO2 Nanotubes Intermediate Layer and the Electrochemical Oxidation Performance of Rhodamine B

A La-doped Ti/SnO2-Sb2O4 electrode with TiO2-NTs intermediate layer (Ti/TiO2-NTs/SnO2-Sb2O4-La) was created via the electrodeposition technique. The physicochemical and electrochemical properties of the electrode were analyzed through FESEM, XRD, XPS, CV, and LSV electrochemical tests. The results showed that TiO2-NTs were tightly packed on the surface of Ti substrate, thus improving the binding force of the SnO2-Sb2O4-La coating, offering greater specific surface area, more active spots, higher current response, and longer lifespan for the degradation of rhodamine B. The lifespan of the Ti/TiO2-NTs/SnO2-Sb2O4-La electrode reached 200 min (1000 mA cm-2, 1 M H2SO4), while the actual service life was up to 3699 h. Under the conditions of initial pH 3.0, Na2SO4 concentration of 0.1 M, current density of 30 mA cm-2, and initial rhodamine B concentration of 20 mg L-1, the color and TOC removal rate of rhodamine B reached 100% and 86.13% within 15 and 30 min, respectively. Rhodamine B was decomposed into acids, esters, and other molecular compounds under the action of •OH and SO4•- free radicals and electrocatalysis, and finally completely mineralized into CO2 and H2O. It is anticipated that this work will yield a novel research concept for producing DSA electrodes with superior catalytic efficacy and elevated stability.

Electrocatalytic oxidation of gaseous toluene in an all-solid cell using a foam Ti/Sb-SnO2/β-PbO2 anode

Mineralization of benzene, toluene, and xylene (BTX) with high efficiency at room temperature is still a challenge for the purification of indoor air. In this work, a foam Ti/Sb-SnO2/β-PbO2 anode catalyst was prepared for electrocatalytically oxidizing gaseous toluene in an all-solid cell at ambient temperature. The complex Ti/Sb-SnO2/β-PbO2 anode, which was prepared by sequentially deposing Sb-SnO2 and β-PbO2 on a foam Ti substrate, shows high electrocatalytic oxidation efficiency of toluene (80%) at 7 hr of reaction and high CO2 selectivity (94.9%) under an optimized condition, i.e., a cell voltage of 2.0 V, relative humidity of 60% and a flow rate of 100 mL/min. The better catalytic performance can be ascribed to the high production rate of ⋅OH radicals from discharging adsorbed water and the inhibition of oxygen evolution on the surface of foam Ti/Sb-SnO2/β-PbO2 anode when compared with the foam Ti/Sb-SnO2 anode. Our results demonstrate that prepared complex electrodes can be potentially used for electrocatalytic removal of gaseous toluene at room temperature with a good performance.

Robust Self-Supported SnO2-Mn2O3@CC Electrode for Efficient Electrochemical Degradation of Cationic Blue X-GRRL Dye

Exploration of highly efficient and robust catalyst is pivotal for electrocatalytic degradation of dye wastewater, but it still is a challenge. Here, we develop a three-dimensional self-supported SnO₂-Mn₂O₃ hybrid nanosheets grown on carbon cloth (noted by SnO₂-Mn₂O₃@CC) electrode via a simple hydrothermal method and annealing treatment. Benefitting from the interlaced nanosheets architecture that enlarges the surface area and the synergetic component effect that accelerates the interfacial electronic transfer, SnO₂-Mn₂O₃@CC electrode exhibits a superior electrocatalytic degradation efficiency for cationic blue X-GRRL dye in comparison with the single metal oxide electrode containing SnO₂@CC and Mn₂O₃@CC. The degradation efficiency of cationic blue X-GRRL on SnO₂-Mn₂O₃@CC electrode can reach up to 97.55% within 50 min. Furthermore, self-supported architecture of nanosheets on carbon cloth framework contributes to a robust stability compared with the traditional electrode via the multiple dip/brush coating accompanied by the thermal decomposition method. SnO₂-Mn₂O₃@CC electrode exhibits excellent recyclability, which can still retain a degradation efficiency of 94.12% after six cycles. This work may provide a new pathway for the design and exploration of highly efficient and robust electrooxidation catalysts for dye degradation.

Fabrication of high performance Ti/SnO2-Nb2O5 electrodes for electrochemical textile wastewater treatment

Textile wastewater contains many organic compounds and colors that affect aquatic life and human health when discharged into the environment. High coloration due to excess dyes entering the wastewater causes coloration to the receiving water stream, affects the photosynthesis process of aquatic species, and adversely affects the landscape. SnO₂-based electrodes have been extensively used in electrochemical water treatment, but their low durability decreases the pollutant treatment ability. Therefore, it is necessary to add another stable oxide to improve the performance and stability of SnO₂ electrodes. This study aims to fabricate Ti/SnO₂-Nb₂O₅ electrodes for the textile wastewater treatment using the electrochemical oxidation method. Different molar ratios of SnO₂:Nb₂O₅ coating were prepared using the sol-gel method and then coated on the Ti substrates for calcination in 60 min at 500 °C. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer Emmett Teller (BET), and cyclic voltammetry (CV) were used to determine the surface and electrochemical properties of Ti/SnO₂-Nb₂O₅ electrodes. The SEM images show that SnO₂-Nb₂O₅ electrode surfaces have the appearance of typical cracking structures of mixed metal oxides electrodes. The XRD spectrum show the SnO₂ peaks of facet (110), (101), (200), (301), (321) and Nb₂O₅ peaks of facet (001), (002), (100), (101), (102) on Ti substrates. Furthermore, the specific surface area of the Ti/SnO₂-Nb₂O₅ electrode ranges from 37.354 m²/g (SnO₂:Nb₂O₅ = 9:1) to 71.885 m²/g (SnO₂:Nb₂O₅ = 1:9). The electrochemical properties of SnO₂:Nb₂O₅ electrodes showed high oxygen, chlorine evolution potential and high organic pollutant degradation in textile wastewater with COD removal at 83 %, decolorization at 74 % and the generation of many free radicals such as HO^•, H₂O₂, O₃, Cl₂. The results demonstrate that the Ti/SnO₂-Nb₂O₅ electrode with the mole ratio of 3:7 is the best in textile wastewater treatment with the longest service life (39 h).

Electrochemical Oxidation of Methyl Orange in an Active Carbon Packed Electrode Reactor (ACPER): Degradation Performance and Kinetic Simulation

The efficient removal and kinetic modelling of methyl orange (MO) degradation using an electrocatalytic oxidation method in an activated carbon (AC) packed electrode reactor (ACPER) were conducted. A significantly high (81.2%) chemical oxygen demand (COD) and 100.0% MO decolorization efficiency were observed under the experimental conditions of current density of 3.0 mA·cm⁻², flow velocity of 0.3 L·h⁻¹, and treatment duration of 1.68 h using a β-PbO₂/Ti anode. The high removal efficiency is ascribed to the anode expansion effect after AC packing. The anode expansion coefficient (λ) of the ACPER was calculated to be 0.63 from the cyclic voltammetry (CV) measurement, which means the further current utilization for MO oxidation. Based on the current utilization efficiency on anodic and particle electrode surfaces, a phase-reaction kinetics model was proposed for the simulation of MO COD removal efficiency. Our simulation results showed that the newly established average current efficiency (ACE) and energy consumption (E_sp) model well matched the MO experimental degradation data. Our work broadens the scope of the application of ACPER in the treatment industry wastewater containing organics and provides a new strategy for the energy utilization evaluation during the removal of organic matter by electrocatalytic oxidation.

Research trends in the development of anodes for electrochemical oxidation of wastewater

The review focuses on the recent development in anode materials and their synthesis approach, focusing on their compatibility for treating actual industrial wastewater, improving selectivity, electrocatalytic activity, stability at higher concentration, and thereby reducing the mineralization cost for organic pollutant degradation. The advancement in sol–gel technique, including the Pechini method, is discussed in the first section. A separate discussion related to the selection of the electrodeposition method and its deciding parameters is also included. Furthermore, the effect of using advanced heating approaches, including microwave and laser deposition synthesis, is also discussed. Next, a separate discussion is provided on using different types of anode materials and their effect on active •OH radical generation, activity, and electrode stability in direct and indirect oxidation and future aspects. The effect of using different synthesis approaches, additives, and doping is discussed separately for each anode. Graphene, carbon nanotubes (CNTs), and metal doping enhance the number of active sites, electrochemical activity, and mineralization current efficiency (MCE) of the anode. While, microwave or laser heating approaches were proved to be an effective, cheaper, and fast alternative to conventional heating. The electrodeposition and nonaqueous solvent synthesis were convenient and environment-friendly techniques for conductive metallic and polymeric film deposition.

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.

An easily fabricated nano-hydroxyapatite modified glassy carbon electrode for the degradation of methylene blue

According to the existing photocatalytic properties and adsorption properties of hydroxyapatite, the electrochemical properties of hydroxyapatite have been studied to provide ideas for the design of new mineral electrocatalysts.

Influence of Cu–Zn co-doping on the degradation performance of a Ti/SnO2–Sb anode

A Ti/SnO2–Sb–Cu–Zn electrode was prepared for the electrocatalytic oxidation of Acid Red 18 (AR18).

Preparation of Ti/SnO2-Sb/Rare Earth Electrodes Containing Different Contents of Ni Intermediate Layer for Efficient Electrochemical Decolorization of Rhodamine B

Water contamination by dyes discharged from many industries is an environmental issue of great matter. Electrochemical oxidation is an advanced approach for wastewater treatment. In this study, the composite electrodes of Ti/SnO2-Sb-Ni/rare earth have been modified using rare earth elements (Re) Gd, Ce, Eu, and Er and various molar ratios of tin and nickel intermediate layer, and their electrochemical oxidation effects were scrutinized. To analyze the decolorization performance of the electrodes, Rhodamine B (RhB) dye was utilized as a target pollutant. Accelerated life testing indicated that the longer service life could be observed in Ni (3.5%)/Re and Ni (5%)/ Re electrodes compared with other modified Ni (0%, 1%, and 2%)/Re electrodes. Compared with the color removal efficiencies of the Ni (2%)/Re electrodes, the decolorization rate of 90% after treatment for 60 min and the low energy consumption of 3.621 kW h·m−3 can be achieved at the Ni (2%)/Gd electrode under the experimental condition of 100 mg·L−1 RhB. The best decolorization rate was observed at the Ni (2%)/Re electrodes among other Ni and no adding Ni-doped Re electrodes. The characterization of the electrodes was described, consisting of surface morphology, oxygen evolution potential, and a crystallographic and elemental combination of the coatings.

Organic synthesis of fixed CO2 using nitrogen as a nucleophilic center

In this review, recent progress in the application of CO2 as an electrophilic reagent and nitrogen as a nucleophilic center under different catalytic conditions in organic synthesis is summarized. The used catalytic methods in the reactions of CO2 and nitrogen are classified as metal catalysis, metal-free catalysis, photocatalysis and electrocatalysis. Various catalytic conditions have been used to solve the problems of thermodynamic properties and stability of CO2. The transformation mechanisms of these reactions are discussed.

Degradation of aqueous cefotaxime in electro-oxidation - electro-Fenton -persulfate system with Ti/CNT/SnO2-Sb-Er anode and Ni@NCNT cathode

Due to the potential threatening of antibiotics in aqueous environment, a novel electro-oxidation (EO) - electro-Fenton (EF) -persulfate (PS) system with the addition of peroxydisulfate and Fe²⁺ was installed for the degradation of cefotaxime. Ti/CNT/SnO₂-Sb-Er with an ultra-high oxygen evolution potential (2.15 V) and enhanced electrocatalytic surface area was adopted as anode. The OH production and electrode stability test demonstrated great improvement in the electrochemical performances. Ni@NCNT cathode was tested with higher H₂O₂ generation by the presence of nitrogen functionalities due to the acceleration of electron transfer of O₂ reduction. Experiment results indicated CNT and ErO₂ modification increased the molecular and TOC removal of cefotaxime. Coupling processes of EO-EF and EO-PS both resulted in shorter electrolysis time for complete cefotaxime removal, however, the mineralization ability of EO-PS process was lower than EO-EF, which might result from the immediate vanishing of PS. Thus, a further improved treatment EO-EF-PS system achieved an 81.6% TOC removal towards 50 mg L^-1 cefotaxime after 4 h electrolysis, under the optimal working condition Fe²⁺ = PS = 1 mM. The influence of current density and initial concentration on the performance of all processes was assessed. Methanol and tert-butanol were added in the system as OH and SO₄^- scavengers, which illustrating the mechanism of EO-EF-PS oxidizing process was the result of the two free radicals. Major intermediates were deduced and the degradation pathway of cefotaxime was analyzed. This research provides a potential coupling process with high antibiotic removal efficiency and effective materials for practical uses.

Optimized terbium doped Ti/PbO2 dimensional stable anode as a strong tool for electrocatalytic degradation of imidacloprid waste water

The presence of pesticides in water has emerged as a momentous environmental issue over the past decades. Herein, a terbium doped Ti/PbO₂ (denoted as Ti/PbO₂-Tb) dimensionally stable Ti/PbO₂-Tb anode has been successfully prepared by one-step electrodeposition path for electrocatalytic degradation of imidacloprid (IMD) wastewater with high efficiency. Ti/PbO₂-Tb electrode presents higher oxygen evolution potential, lower charge transfer resistance, stronger stability, longer service lifetime and outstanding electrocatalytic activity than Ti/PbO₂ electrode. The optimum condition for IMD oxidation is obtained by analyzing the effects of some critical operating parameters including temperature, initial pH, current density and electrolyte concentration. It is proved that 70.05% of chemical oxygen demand and 76.07% of IMD are removed after 2.5 h of degradation under current density of 8 mA cm^-2, pH 9, temperature 30 °C and 7.0 g L^-1 NaCl electrolyte. In addition, the electrode displays commendable energy saving property as well as favorable reusability. The degradation mechanism of IMD is proposed by analyzing the intermediates identified by LC-MS. The present research provides a feasible strategy to degrade IMD wastewater by Ti/PbO₂-Tb electrode.

High electrochemical activity of a Ti/SnO2-Sb electrode electrodeposited using deep eutectic solvent

Electrodeposition is an economical and efficient way to prepare Ti/SnO₂-Sb electrode for electrochemical oxidizing pollutants in wastewater. The solvent used for electrodeposition has a great effect on electrode performance. The conventional Ti/SnO₂-Sb electrode electrodeposited using aqueous solvent has poor electrochemical activity and short service life. In this study, a Ti/SnO₂-Sb electrode was prepared via electrodeposition using a deep eutectic solvent (DES). This new Ti/SnO₂-Sb-DES electrode performed a rate constant of 0.571 h^-1 for methylene blue decolorization and long accelerated service life of 12.9 h (100 mA cm^-2; 0.5 M H₂SO₄), which were 1.7 times and 3.2 times as high as that of the electrode prepared in aqueous solvent, respectively. The enhanced properties were related to the 1.3 times increased electrochemically active surface area of Ti/SnO₂-Sb-DES electrode which had a rough, multilayer and uniform surface structure packed with nano-sized coating particles. In conclusion, this study developed a facile, green and efficient pathway to prepare Ti/SnO₂-Sb electrode with high performance.

Comparative study on treatment of methylene blue dye wastewater by different internal electrolysis systems and COD removal kinetics, thermodynamics and mechanism

In this study, Fe/Cu, Fe/Al/Cu, Fe/Cu/C and Fe/Al/Cu/C internal electrolysis systems (IESs) were constructed and used to treat methylene blue dye (MB) wastewater. The effects of filler mass ratio, filler dosage, solution pH, reaction time and reaction temperature on COD removal were discussed, while the kinetics, thermodynamics and mechanism of COD removal were also investigated. The results showed that when the COD removal rates were basically the same, the reaction times of Fe/Al/Cu, Fe/Cu/C and Fe/Al/Cu/C IESs were shorter, and the filler dosages were lower. For the four systems, the appropriate pH was around 5, while the suitable reaction temperature was in the range of 20-25 °C. The COD removals of these four IESs were generally greater than 90%. The COD removal processes of the four systems could be better described by the improved pseudo-second-kinetic model, and the liquid film diffusion was the rate-controlling step. Moreover, the COD removal was a spontaneous and endothermic process. MB was degraded into inorganic substances in four steps. In addition, the FTIR characterization of the fillers before and after reaction suggests the four IESs have good stability.

Enhanced oxidation potential of Ti/SnO2-Cu electrode for electrochemical degradation of low-concentration ceftazidime in aqueous solution: Performance and degradation pathway

In order to develop an efficient electrode to remove pharmaceutical and personal care products from wastewater, copper and antimony doped Ti/SnO₂ electrode were prepared by thermal decomposition. Electrochemical characterization was undertaken on Ti/SnO₂-Cu using cyclic voltammetry and linear sweep voltammetry, indicating an ultra-high 2.1 V of oxygen evolution potential, better stability, and superior corrosion resistance rather than traditional Ti/SnO₂-Sb electrode. Competitive degradation experiments showed more efficient removal rate was achieved on Ti/SnO₂-Cu electrode, which could remove more than 90% ceftazidime within 60 min. The microstructure and crystal orientation of the modified electrodes were investigated by scanning electron microscopy, which indicated that the crystal of the Ti/SnO₂-Cu electrode grew in more porous and uniform condition, covered with closely arranged layers of the coating. X-ray photoelectron spectroscopy and X-ray diffractions suggested that Cu₂O was successfully coated on the Ti/SnO₂-Cu electrode surface. The operating parameters of electrochemical degradation process were also investigated, including current density, initial concentration, electrode distance, stirring rate and supporting electrolyte. Consequently, the intermediate products of electrochemical degradation were monitored by liquid chromatography-mass spectrometry and a major degradation pathway was proposed.