Electrochemical degradation of p-nitrophenol on carbon nanotube and Ce-modified-PbO2 electrode

Catalytic electrodes' characterization study serving polluted water treatment: environmental healthcare and ecological risk assessment

Pesticide residues in the environment have irreparable effects on human health and other organisms. Hence, it is necessary to treat and degrade them from polluted water. In the current work, the electrochemical removal of the fenitrothion (FT), trifluralin (TF), and chlorothalonil (CT) pesticides were performed by catalytic electrode. The characteristics of SnO2-Sb2O3, PbO2, and Bi-PbO2 electrodes were described by FE-SEM and XRD. Dynamic electrochemical techniques including cyclic voltammetry, electrochemical impedance spectroscopy, accelerated life, and linear polarization were employed to investigate the electrochemical performance of fabricated electrodes. Moreover, evaluate the risk of toxic metals release from the catalytic electrode during treatment process was investigated. The maximum degradation efficiency of 99.8, 100, and 100% for FT, TF, and CT was found under the optimal condition of FT, TF, and CT concentration 15.0 mg L-1, pH 7.0, current density 7.0 mA cm-2, and electrolysis time of 120 min. The Bi-PbO2, PbO2, and SnO2-Sb2O3 electrodes revealed the oxygen evolution potential of 2.089, 1.983, 1.914 V, and the service lifetime of 82, 144, and 323 h, respectively. The results showed that after 5.0 h of electrolysis, none of the heavy metals such as Bi, Pb, Sb, Sn, and Ti were detected in the treated solution.

Electrochemical study of a novel high-efficiency PbO2 anode based on a cerium-graphene oxide co-doping strategy: Electrodeposition mechanism, parameter optimization, and degradation pathways

A novel and efficient Ti/SnO₂-Sb/PbO₂-GO-Ce electrode was successfully fabricated based on the co-deposition of Ce ions and graphene oxide (GO) into β-PbO₂ crystals and used as an anode for electrocatalytic oxidation of phenol. The electrodeposition mechanism, parameter optimization, mechanism analysis, and potential degradation pathways were discussed in depth. The co-doping of GO and Ce resulted in the high directional specificity of β(301), orderly and dense grain arrangement of PbO₂ crystals. At the same time, the oxygen evolution potential, •OH generation capacity and lifetime were also improved. The effects of experimental parameters on phenol removal efficiency were evaluated, including the applied current density, electrode gap, supporting electrolyte, initial NaCl concentration, initial pH, and initial phenol concentration. Under the optimal conditions, the removal efficiency of phenol can reach 375.6 g m^-2 h^-1 for 20 min electrolysis, which is about 1.2 times that of the pure PbO₂ electrode. The active oxygen species (•OH, ClO^- and HClO) were important attributes to the degradation of phenol. Additionally, a potential degradation pathway for phenol was proposed. After 10 successive recycles, there was no significant difference of the electro-generated •OH, cell voltage and phenol removal rate, which confirms the stability and admirable reusability of Ti/SnO₂-Sb/PbO₂-GO-Ce electrode.

Improvement of stability and reduction of energy consumption for Ti-based MnOx electrode by Ce and carbon black co-incorporation in electrochemical degradation of ammonia nitrogen

Ti-based electrode coated with MnO_x catalytic layer has presented superior electrochemical activity for degradation of organic pollution in wastewater, however, the industrial application of Ti-based MnO_x electrode is limited by the poor stability of the electrode. In this study, the novel Ti-based MnO_x electrodes co-incorporated with rare earth (Ce) and conductive carbon black (C) were prepared by spraying-calcination method. The Ti/Ce:MnO_x-C electrode, with uniform and integrated surface and enhanced Mn(IV) content by C and Ce co-incorporation, could completely remove ammonia nitrogen (NH₄⁺-N) with N₂ as the main product. The cell potential and energy consumption of Ti/Ce:MnO_x-C electrode during the electrochemical process was significantly reduced compared with Ti/MnO_x electrode, which mainly originated from the enhanced electrochemical activity and reduced charge transfer resistance by Ce and C co-incorporation. The accelerated lifetime tests in sulfuric acid showed that the actual service lifetime of Ti/Ce:MnO_x-C was ca. 25 times that of Ti/MnO_x, which demonstrated the significantly promoted stability of MnO_x-based electrode by Ce and C co-incorporation.

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.

Improved 4-nitrophenol removal at Ti/RuO2-Sb2O4-TiO2 laser-made anodes

In this study, binary and ternary mixed metal oxide anodes of Ti/RuO₂-Sb₂O₄ and Ti/RuO₂-Sb₂O₄-TiO₂ were prepared using two different heating methods: conventional furnace and alternative CO₂ laser heating. The produced anodes were physically and electrochemically characterized by using different techniques. The main difference found in the laser-made anodes was their more compact morphology, without the common deep cracks found in anodes made by typical thermal decomposition, which showed an important correlation with the prolonged accelerated service life. The correlation between the physicochemical properties of the anodes with their performance towards the 4-nitrophenol oxidations is discussed. The results demonstrated that the ternary anode (Ti/RuO₂-Sb₂O₄-TiO₂) is very promising, presenting a kinetic 5.7 times faster than the respective binary anode and the highest removal efficiency when compared with conventionally made anodes. Also, the lowest energy consumption per unit of mass of contaminant removed is seen for the laser-made Ti/RuO₂-Sb₂O₄-TiO₂ anode, which evidences the excellent cost-benefit of this anode material. Finally, some by-products were identified, and a degradation route is proposed. Graphical abstract.

Preparation and characterization of ZnO/PEG-Co(II)-PbO2 nanocomposite electrode and an investigation of the electrocatalytic degradation of phenol

A ZnO/PEG (polyethylene glycol) -Co(II)-PbO₂ nanocomposite electrode was constructed by using the anodic electrodeposition method and used for the electrocatalytic degradation phenol. The results showed that the electrode surface formed numerous PbO₂ nanosphere structures, and the average size of a single nanosphere is approximately 0.4 μm. XRD and EDS results showed the active layer consisted of β-PbO₂, and contained small amounts of cobalt and carbon. The electrochemical measurements showed that the electrode possessed a lower activation energy (E_a = 17.517 kJ∙mol^-1) and charge transfer resistance (R_ct = 7.564 Ω cm²) and a larger exchange current density (i°=1.476 × 10^-4 mA cm^-2). The phenol degradation process was controlled by the adsorption process and kinetic parameters were obtained with an initial concentration of 100 mg L^-1. The electrode possessed a shorter half-life, larger reaction rate constant, and degradation efficiency (RE = 91.1 %) after 180 min. Reaction order was also calculated, and the degradation followed the pseudo-first-order reaction kinetics. HPLC results showed that the degradation pathway is as follows: firstly, phenol is gradually decomposed into o-diphenol, p-diphenol and benzoquinone under hydroxyl radicals attack. Then, benzoquinone is broken into maleic acid and fumaric acid. Finally, these acidic compounds are broken into oxalic acid, which is eventually mineralized.

Degradation of pesticide Cartap in Padan 95SP by combined advanced oxidation and electro-Fenton process

The electro-Fenton process combined with a boron-doped diamond-positive electrode in a one-compartment cell has shown efficient degradation of Cartap (95% in Padan 95SP) by hydroxyl radicals (•OH) generated in the electro-Fenton and the electrochemical oxidation processes. The influence of added NaOCl in a pretreatment step, effects of H2O2 concentration, Fe2+-ion addition, presence of further metals acting as co-catalysts, and solution pH on the efficiency of Cartap degradation were studied. The concentration of Cartap was determined by UV-vis spectroscopy according to the 5,5-dithiobis-(2-nitrobenzoic acid) procedure. The efficiency reaches approximately 80% when measured as total carbon concentration decrease, even with increased concentrations of H2O2, Fe2+, or metal ions added as co-catalyst. This limitation is presumably due to recalcitrant intermediates, which cannot be destroyed by •OH.

A Novel Porous Ni, Ce-Doped PbO2 Electrode for Efficient Treatment of Chloride Ion in Wastewater

The porous Ti/Sb-SnO2/Ni-Ce-PbO2 electrode was prepared by using a porous Ti plate as a substrate, an Sb-doped SnO2 as an intermediate, and a PbO2 doped with Ni and Ce as an active layer. The surface morphology and crystal structure of the electrode were characterized by scanning electron microscope(SEM), energy dispersive spectrometer(EDS), and X-Ray diffraction(XRD). The electrochemical performance of the electrodes was tested by linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and electrode life test. The results show that the novel porous Ni-Ce-PbO2 electrodes with larger active surface area have better electrochemical activity and longer electrode life than porous undoped PbO2 electrodes and flat Ni-Ce-PbO2 electrodes. In this work, the removal of Cl− in simulated wastewater on three electrodes was also studied. The results show that the removal effect of the porous Ni-Ce-PbO2 electrode is obviously better than the other two electrodes, and the removal rate is 87.4%, while the removal rates of the other two electrodes were 72.90% and 80.20%, respectively. In addition, the mechanism of electrochemical dechlorinating was also studied. With the progress of electrolysis, we find that the increase of OH- inhibits the degradation of Cl−, however, the porous Ni-Ce-PbO2 electrode can effectively improve the removal of Cl−.

Preparation of novel Ti-based MnOx electrodes by spraying method for electrochemical oxidation of Acid Red B

At different calcination conditions, titanium-based manganese oxides (MnO_x) electrodes were fabricated by spraying method without adhesive. The MnO_x/Ti electrodes were applied in electrochemical oxidation of wastewater treatment for the first time. The surface morphologies of electrodes were tested by scanning electron microscopy. The formation of different manganese oxidation states on electrodes was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. The electrochemical properties of the electrodes have been performed by means of cyclic voltammetry and electrochemical impedance spectroscopy. The characterizations revealed that the MnO_x/Ti-350(20) electrode, prepared at calcination temperature of 350 °C for 20 min, exhibited fewer cracks on the electrode surface, larger electrochemically effective surface area and lower charge transfer resistance than electrodes prepared at other calcination conditions. Moreover, Acid Red B was used as target pollutant to test the electrode activity via monitoring the concentration changes by UV spectrophotometer. The results showed that the MnO_x/Ti-350(20) electrode presented the best performance on decolorization of Acid Red B with the lowest cell potential during the process of electrochemical oxidation, and the chemical oxygen demand (COD) conversion was 50.7%. Furthermore, the changes of Acid Red B during the electrochemical oxidation process were proposed by the UV-vis spectra.

Fast removal of methylene blue from aqueous solution using coal-based activated carbon

Coal-based activated carbons (CACs) were prepared from three long flame coals with different ash and volatile matter content. CACs prepared by coal with high ash (6.74%) and volatile matter content (34.31%) showed better adsorption efficiency towards MB (547.35 mg g⁻¹) due to higher surface area and pore volume. The effect of coal to activating agent ratio (CAR) was also investigated in a batch reactor. The porosity development is closely related to the CAR. The calculated monolayer adsorption amount (714.29 mg g⁻¹) was found on YLC-AC-3 with a surface area of 1212.50 m² g⁻¹. The equilibrium data were favorably described by the Langmuir and Freundlich isotherm models, and adsorption kinetics fitted well to the pseudo-second order model. The removal efficiency remains at 98.21% after five runs. The results of the present study suggest that CACs are potential and effective adsorbents in fast removal of dyes from aqueous solution.

A monolayer adsorption amount of MB (714.29 mg g⁻¹) was found on a coal-based activated carbon prepared by a simple method.

Efficient 2-Nitrophenol Chemical Sensor Development Based on Ce2O3 Nanoparticles Decorated CNT Nanocomposites for Environmental Safety

Ce₂O₃ nanoparticle decorated CNT nanocomposites (Ce₂O₃.CNT NCs) were prepared by a wet-chemical method in basic medium. The Ce₂O₃.CNT NCs were examined using FTIR, UV/Vis, Field-Emission Scanning Electron Microscopy (FESEM), X-ray electron dispersive spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (XRD). A selective 2-nitrophenol (2-NP) sensor was developed by fabricating a thin-layer of NCs onto a flat glassy carbon electrode (GCE, surface area = 0.0316 cm²). Higher sensitivity including linear dynamic range (LDR), long-term stability, and enhanced electrochemical performances towards 2-NP were achieved by a reliable current-voltage (I-V) method. The calibration curve was found linear (R² = 0.9030) over a wide range of 2-NP concentration (100 pM ~ 100.0 mM). Limit of detection (LOD) and sensor sensitivity were calculated based on noise to signal ratio (~3N/S) as 60 ± 0.02 pM and 1.6×10⁻³ μAμM^-1cm^-2 respectively. The Ce₂O₃.CNT NCs synthesized by a wet-chemical process is an excellent way of establishing nanomaterial decorated carbon materials for chemical sensor development in favor of detecting hazardous compounds in health-care and environmental fields at broad-scales. Finally, the efficiency of the proposed chemical sensors can be applied and utilized in effectively for the selective detection of toxic 2-NP component in environmental real samples with acceptable and reasonable results.

Electrosynthesis and performance of WC and Co3O4 co-doped α-PbO2 electrodes

α-PbO₂ uniformly co-doped with Co₃O₄ and WC particles was prepared as a functional electrode for oxygen evolution.

Preparation and characterization of Cu–rare earth/Al2O3 catalysts and their application in the electrochemical removal of p-nitrophenol

Cu and rare earth composite catalysts (Cu–rare earth/Al₂O₃) were prepared on Al₂O₃ particles using an impregnation method for the electro-catalytic oxidation of p-nitrophenol in this study.

Adsorption-desorption characteristics of methyl ethyl ketone with modified activated carbon and inhibition of 2,3-butanediol production

Activated carbon (AC) is seldom applied for recovering ketone-based volatile organic compounds because of safety concerns. Adsorption of methyl ethyl ketone (MEK) with AC is a highly exothermic reaction that potentially causes fires in AC beds. Moreover, 2,3-butanediol (BDO) is produced in the desorbed solvent, causing yellowing and odor of the recovered solvent. This study applied a continuous adsorption-desorption apparatus for evaluating the operating capacities and BDO concentration in recovered MEK containing modified and original ACs. AC-1 (TAKETA- G2X) was used as the target for modification. The experimental results indicate that using MgO as the modifier increases the ignition point by 12°C and that applying KNO3 as the modifier reduces the AC ignition point by 28°C (compared with AC-1). The BDO concentration of the desorbed MEK solvent can be reduced by increasing the loading of the modifying agent (Ethanolamine) (Im-1: 3.1 wt%; Im-5: 6.2 wt%). Moreover, applying the AC pretreated with nitrogen (Im-6) as adsorbent significantly reduces the BDO concentration (from 0.123 wt% to 0.073 wt%). Because desorption and purging procedures were performed in N2 atmospheres, the BDO concentrations of the desorbed MEK solvents were relatively low and ranged from 0.032 wt% to 0.043 wt%. When the MEK concentration was reduced to 2000 ppm, lower BDO concentrations (0.012-0.022 wt%) were measured in the recovered MEK solvent. The way to modify activated carbon and a better desorbing sequence to effectively inhibit the oxidation of MEK to BDO are developed. The results obtained indicate that the BDO concentration in the desorbed solvent was lower than the original MEK solvent (0.023 wt%). Different approaches can be applied simultaneously to achieve high inhibition effects; however, carbon adsorption performance may be negatively affected.

IMPLICATIONS

The study is motivated to improve the quality of recovered solvent and reduce fire hazards, particularly when AC is applied for adsorbing a ketone-based solvent (e.g., MEK). The experimental results indicate that the BDO concentration in the recovered solvent can be reduced and the ignition point of AC can be increased by modifying the AC with an appropriate agent.

Fabrication and characterization of β-PbO2/α-PbO2/Sb–SnO2/TiO2nanotube array electrode and its application in electrochemical degradation of Acid Red G

A novel β-PbO₂/α-PbO₂/Sb–SnO₂/TiO₂nanotube array electrode was fabricated and investigated for the treatment of Acid Red G (ARG) in aqueous solution.