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FESEM images of the samples electrodeposited at 0.25 mA/cm 2 : a) TiO2-NTs; b) 0.25 MnOx/Ti; c) 0.25 MnOx/TiO2-NTs; d) 0.25c MnOx/Ti (s); e) 0.25c MnOx/Ti; f) 0.25c MnOx/TiO2-NTs.  

FESEM images of the samples electrodeposited at 0.25 mA/cm 2 : a) TiO2-NTs; b) 0.25 MnOx/Ti; c) 0.25 MnOx/TiO2-NTs; d) 0.25c MnOx/Ti (s); e) 0.25c MnOx/Ti; f) 0.25c MnOx/TiO2-NTs.  

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Article
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More and more attention has recently been paid to the electrochemical treatment of wastewater for the degradation of refractory organics, such as phenol and its derivatives. The electrodeposition of different types of manganese oxides (MnOx) over two substrates, namely metallic titanium and titania nanotubes (TiO2-NTs), is reported herein. X-Ray Di...

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... Thanks to their quasi one-dimensional arrangement, TiO 2 NTs are able to provide high surface area and superior electron transport properties, resulting in a performance enhancement in the different fields of application. For these reasons TiO 2 NTs have been extensively studied as an active component in biomedical devices [23], sensors [24], Li-ion batteries [25], water photo-electrolysis [26], dye-sensitized solar cells [27], and pollutant photo and electrocatalytic degradation [28]. Moreover, they can be easily converted in titanate by a hydrothermal treatment allowing the formation, for example, of barium titanate (BaTiO x ) [29] useful as piezoelectric or lithium titanate (LiTiO x ) [30], a well-known candidate for lithium ion batteries or lithium sieve for raw material recovery. ...
Article
The electric response of a system formed by an electrolyte in contact with porous electrode is investigated. The simple case in which only the positive ions are mobile is considered. The first scenario is the one in which the mobile ions can be immobilized by means of an irreversible reaction. We show that the existing model, based on this assumption, is not suitable to describe in a proper manner the electric response of the cell to an external electric excitation, because in a one dimensional problem the electric current density, usually defined as the sum of the conduction and displacement currents, is not position independent. Consequently, it cannot be used to analyze the current–voltage characteristics, or the electrical impedance of the cell. A generalization of the model, in which the mobile ions are instead immobilized by a reversible reaction, allows the impedance of the cell to be determined in such a way to be meaningful for the investigations carried out with the impedance spectroscopy technique. Special attention is devoted to the problem of a cell limited by one blocking electrode and one transparent electrode, which corresponds to a porous electrode of TiO2 immersed in an electrolytic solution. The model is subsequently generalized in such a way that the ionic diffusion is regulated by a time fractional equation to take into account the porous nature of the medium. In order to validate the theoretical model, we select a case of study that well represent the modeled system in which the working electrode is made up of lithium titanate (LiTiOx) nanotubes in contact with an organic electrolyte. The theoretical predictions of the resulting model are in good agreement with the experimental data on the full frequency range explored.
... The high redox activity, earth abundance and low toxicity make Mn a perfect catalyst for environmental applications [26]. Indeed, Mn was successfully applied for the removal of various refractory organic contaminants, including aniline [27], formaldehyde [28,29], phenol [30][31][32], as well as volatile organic contaminants [33,34]. Several studies proposed the removal of sulfide through dosing of potassium permanganate [35,36]. ...
... Moreover, it can improve adhesion and enhance the electron transfer between the coating and the substrate, thus ensuring a rapid recovery of the MnxOy coating [30,40,41]. We have investigated the impact of the operating parameters (i.e., applied potential, pH, sulfide concentration) on the sulfide removal kinetics and the formed reaction products. ...
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Manganese oxide-coated TiO2 nanotube array (NTA) was synthesized and applied for the (electro)catalytic oxidation of sulfide. By setting the electrodeposition parameters and calcination temperature, the coating obtained was MnO2 or Mn2O3, with rod or needle like morphology. Excellent catalytic activity of the Ti/TiO2 NTA/MnxOy anodes resulted in robust and selective oxidation of sulfide to elemental sulfur via an inner sphere complex between the sulfide ion and Mn-oxide. The penetration of the MnxOy inside the NTA improved adhesion and enhanced the electron transfer, thus enabling complete and rapid electrocatalytic re-oxidation of the Mn-oxide coating. At pH 8, the final product of sulfide oxidation was colloidal sulfur, S8, which prevented anode passivation and enabled a stable (electro)catalytic activity in the subsequent applications. This was observed in both synthetic electrolyte and real sewage, thus demonstrating the efficiency of the Ti/TiO2 NTA/MnxOy anode for sulfide oxidation in complex waste streams.
... Compared with our previous studies of TiO 2 , MnO x were reported as a better catalyst for the electro-oxidation of refractory organics [18][19][20][21], and porous Ti has been used to prepare composite membranes as support due to its superior chemical, thermal and mechanical stabilities [22][23][24]. In this work, MnO x /Ti (MT) composite membrane, the MnO x layers including various crystal forms coated on Ti support, were prepared by sol-gel method and then optimized further by acidification to obtain acidified MnO x /Ti (AMT) composite membrane. ...
Article
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A novel electrocatalytic membrane reactor (ECMR), assembled by MnOx/Ti (MT) composite membrane as an anode, was used to degrade phenolic wastewater. The MT composite membrane, MnOx layer with the various crystal forms coated on porous tubular Ti support, was prepared by sol–gel method and then activated further by acidification to obtain acidified MnOx/Ti (AMT) composite membrane. The XRD results showed that the crystallite size of MnOx layer distinctly decreased after acidification. This is because of the Ti support had a great effect on the crystal form and crystallite size of MnOx, especially after acidification. The results of XPS analysis showed that the interaction between Ti support and MnOx layer had great influence on the Mn–O, Ti–O binding energies and active oxygen species of MT and AMT. Treated by ECMR with AMT, the phenol, COD and TOC removal rates of the synthetic phenolic wastewater were 96.45%, 84.97% and 71.26%, which were obviously higher than that of MT, 62.87%, 50.34% and 41.25%, respectively. It was revealed that acidified MnOx as the catalysts in AMT composite membrane, with the specific crystal form, refined crystallite size and active oxygen species, exhibited a great potential in the electrocatalytic oxidative degradation of the phenolic wastewater.
... Therefore, it is urgent to develop a novel treatment process with high efficiency and low energy for dye wastewater. At present, advanced oxidation processes (AOPs) have been considered to be a promising method for wastewater treatment, mainly including photocatalysis, catalytic ozonation, wet air oxidation, electrochemical advanced oxidation process (EAOPs), and Fenton or Fenton-like reaction, etc. [5,6]. Among these methods, EAOPs have attracted more attention because of its high efficiency, easy operation, mild reaction conditions, less pollution, and small occupation [7]. ...
Article
Geopolymers have been developed to various catalysts due to their advantages. However, low conductivity restricts their application in the electrocatalysis field. In this study, an α-Fe2O3/circulating fluidized bed fly ash based geopolymer (CFAG) composite anode was fabricated using a facile dip-coating method by loading α-Fe2O3 in the matrix of CFAG. The effects of α-Fe2O3 content on the composition, surface morphology and electrochemical performance of α-Fe2O3/CFAG composite anode were investigated. The X-ray diffraction (XRD) and scanning electron microscope (SEM) results demonstrated that α-Fe2O3 was successfully inlaid with the surface of amorphous CFAG matrix. The electrochemical measurements indicated that α-Fe2O3/CFAG composite anode had higher oxygen evolution potential, greater electrochemical activity area, and smaller electrochemical impe-dance than CFAG. The as-prepared composite anode was applied for electrocatalytic degradation of indigo carmine dye wastewater. It was discovered that the highest degradation efficiency over 10α-Fe2O3/CFAG reached up 92.6%, and the degradation of indigo carmine followed pseudo-first-order kinetics. Furthermore, 10α-Fe2O3/CFAG composite anode presented excellent stability after five cycles. The active hydroxyl radical was generated over the α-Fe2O3/CFAG composite anode, which acted as strong oxidizing agents in the electro-catalytic degradation process.
... Although Mn x O y -coated electrodes have been extensively investigated and applied in the energy field [12], only a few studies have explored environmental applications of these materials for water treatment. For example, several studies reported that Mn x O y nanostructures are capable of efficient elelctrooxidation of refractory organics, such as aniline [13], formaldehyde [14,15], phenol [16][17][18] with its derivatives [19][20][21] and low molecular weight organic acids [22,23] as well as some volatile organic contaminants [24,25]. Besides that morphological characteristics of certain Mn x O y forms achieve efficient adsorption of metals from wastewater by retaining ions inside Mn x O y three-dimensional network [26][27][28]. ...
Article
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Sulfide and its removal is a major concern in wastewater treatment as it represents a threat to human health and the structural integrity of the water distribution system. In this study, we demonstrated for the first time an exceptional performance of manganese oxide-coated graphite felt (GF-MnxOy) electrodes for selective sulfide oxidation to sulfur. Oxidation state, loading, morphology and crystallinity of MnxOy coating was tuned using electrodeposition synthesis method to enable an efficient and selective sulfide oxidation to sulfur. Excellent (electro)catalytic activity of GF-MnxOy yielded up to 25-fold increase in sulfide removal rates compared to pristine GF, both in the open circuit (OC, no applied potential) and under anodic polarization at 0.4 V vs Standard Hydrogen Electrode (SHE). Although anodic polarization did not further enhance sulfide oxidation rate compared to OC, it enabled a continuous re-oxidation of the reduced MnxOy coating after its reaction with sulfide. Thus, restoring of the catalytic properties of MnxOy coating enabled higher sulfide removal rates compared with the OC experiment. The formed elemental sulfur remained at the surface of GF-MnxOy leading to a gradual electrode passivation. The deposited sulfur was successfully dissolved by reversing the polarity of the GF-MnxOy electrode to -0.8 V vs SHE. However, full electrode recovery and restoring of the initial sulfide removal rates could not be achieved as cathodic polarization at -0.8 V vs SHE during longer time (>3 hours) required to remove S⁰ also caused a partial dissolution of the MnxOy coating. (Electro)catalytic sulfide removal was somewhat decreased in real sewage (2.42 ± 0.02 h⁻¹ vs 0.93 ± 0.15 h⁻¹ in NaNO3 supporting electrolyte and real sewage, respectively). The selectivity of the process towards deposition of elemental sulfur was decreased in real sewage due to partial production of colloidal sulfur, which was presumably caused by diffusion limitation imposed by presence of other ions. Due to lesser extend of GF-Mn2O3 electrode passivation in real sewage, sulfide removal rates remained stable over six subsequent application cycles. In summary, MnxOy-based electrodes demonstrated exceptional (electro)catalytic activity and selectivity for sulfide oxidation to sulfur and thus its complete separation from water. Upscaling of the proposed electrochemical system and its application for the treatment of complex wastewater streams requires further efforts to maintain the selectivity towards deposited sulfur as a final product and allow its complete recovery.
... Phenol emissions from many industrial process such as coal processing, oil refineries and petrochemicals manufacturer are the major contributor to the global wastewater, being harmful and dangerous to environment and human being due to their toxicity and hard biodegradability characteristics (Vaiano et al., 2018;Wang et al., 2018). Various techniques have been developed to remove phenol from wastewater, such as adsorption, biological treatment, photo-catalysis, electro-oxidation, and membrane-based separation (Archana et al., 2016;Loh et al., 2016;Massa et al., 2017). In recent years, heterogeneous Fenton oxidation process using porous solid catalysts shows a promising alternative for the decomposi-tion of organic contaminants in polluted water (Martínez et al., 2018;Wang et al., 2017). ...
Article
Microfibrous-structured catalysts are materials that address the mass/heat transfer limitation and achieve catalytic process intensification, showing great promise for enabling practical environmental catalysis such as continuous wastewater treatment process. In this work, Fe3O4-doped ordered mesoporous carbon (OMC) catalyst supported on porous sintered metal fibers (Fe-OMC/SMFs) was prepared using a new yet simple “one-pot” method and used as a Fenton-like heterogeneous catalyst. The obtained catalysts were carefully characterized by TGA-DTG, BET, XRD, SEM-EDS, XPS and H2-TPR techniques. Structured reactor was designed and developed using developed microfibrous-structured catalysts, demonstrating an excellent catalytic performance for continuous heterogeneous Fenton oxidation of phenol. Specifically, both phenol and H2O2 conversions increased slightly as carbonization temperatures increasing from 400 to 1000 °C. Compared to Fe-OMC pellet catalyst, the developed structured catalyst showed an improved catalytic activity (i.e. ∼100 % phenol/H2O2 conversions), and remarkable long-term stability (i.e. ∼100 % phenol conversion over a 7-h longevity test). Additionally, the developed Fe-OMC/SMFs catalyst showed Fe leaching amounts of ∼10 mg L⁻¹ during reaction, being significantly lower than that of Fe-OMC pellet catalyst (i.e. ∼500 mg L⁻¹). Experimental results revealed that well-dispersed Fe3O4 nanoparticles in OMC and three-dimensional microfibrous networks and large void volume of SMFs support are significantly benefit to enhance mass transfer and contacting efficiency between active sites and reactants, and thus achieve the process intensification of catalytic degradation of phenol.
... In pH = 10, we remark that the solutions become a little bit turbid after oxidation. This indicates the formation of polymeric intermediate products by the hydroxyl group that makes the degradation much more difficult (Massa et al., 2017;Rabaaoui et al., 2013). Therefore, a pH 3 was chosen as the optimal value. ...
Article
Full-text available
The commercial imidacloprid (IMD) insecticide [1-(6-chloro-3-pyridinyl) methyl-4,5-dihydro-N-nitro-1H-imidazole-2-amine] is widely used for the enhancement of crop production, but the intensive use of this insecticide has caused serious environmental problems. This work presents an electrochemical process for the removal of this insecticide using galvanostatic electrolysis at modified tantalum surface by lead dioxide film anode (Ta(PbO2)) anode. The electrolytic process was monitored by chemical oxygen demand (COD). The influence of operating parameters, such as current density, initial concentration of IMD, temperature and initial pH value was investigated. The COD decay follows a pseudo first-order kinetic and the process was under mass transport control. COD removal reach 97% when using an apparent current density of 100 mA cm −2 , initial COD of 953 mg L −1 and at 25 °C after 4.5 h electrolysis time.
... In pH = 10, we remark that the solutions become a little bit turbid after oxidation. This indicates the formation of polymeric intermediate products by the hydroxyl group that makes the degradation much more difficult (Massa et al., 2017;Rabaaoui et al., 2013). Therefore, a pH 3 was chosen as the optimal value. ...
... The DSA is mainly composed of titanium-based coating electrode, which is an electrode prepared by active metal oxides coated on the titanium substrate surface. Currently, the coated metal oxides are mainly SnO 2 [8][9][10], PbO 2 [10], Sb 2 O 5 [8], RuO 2 [11][12][13], IrO 2 [13,14], MnO 2 [15], Ta 2 O 5 [16] and two or more of them in complexes [8,16,17]. PbO 2 , RuO 2 and IrO 2 have been extensively studied both in theory and by experiments, because of their high oxygen evolution reaction (OER) compared to other oxides. ...
... Because of the enhanced electron capture capacity by MnO x , the Ti/SnO 2 -Sb-Mn/b-PbO 2 electrode exhibited better performance. Massa et al. [15] electrodeposited different types of manganese oxides on metallic titanium and titania nanotubes for electro-oxidation of phenol. The results showed that MnO 2 and Mn 2 O 3 both could promote the direct and indirect oxidation of phenol. ...
Article
Full-text available
The titanium-based electrodes with MnOx nanoparticles coating (MnOx/Ti) and MnOx nanoparticles mixed with multi-walled carbon nanotubes (MnOx–CNTs/Ti) were fabricated by spraying–calcination method. The physicochemical properties of electrodes were investigated by SEM, XRD and XPS, which indicated that the surface coating of MnOx–CNTs/Ti, with MnOx nanoparticles dispersed uniformly on the CNTs, was smoother and with higher integrity than MnOx/Ti. Acid Red B was used as model pollutant to investigate the electro-catalytic activity of the electrodes, and the results revealed that the removal efficiency of Acid Red B reached 93.6% and 98.0% by MnOx/Ti and MnOx–CNTs/Ti, respectively, and the cell potential during the process of degradation by MnOx–CNTs/Ti was relatively low and stable. The electrochemical results confirmed that MnOx–CNTs/Ti possessed smaller charge transfer resistance and higher oxygen evolution current compared with MnOx/Ti, which can enhance the electro-catalytic activity and reduce the energy consumption by accelerating the transfer of electrons on the electrode surface. The accelerated lifetime tests of electrodes were carried out and showed that actual service lifetimes of MnOx–CNTs/Ti were 38 times of that for MnOx/Ti calculated by the experienced formula, which demonstrated that the durability of MnOx-based electrode was significantly promoted by addition of CNTs on Ti substrate.
... Traditionally, EO usually takes titanium as substratum, which is coated with a catalyst layer of metal oxide such as PbO 2 (Farinos and Ruotolo, 2017), antimony doped tin oxide (ATO) (Haddad et al., 2017), etc. For an instance, Ti/ATO anode are effective for the removal of refractory organics, such as phenol (Liang et al., 2015), dye and other substrates (Massa et al., 2017) in wastewater. While EO also generates Cl 2 and O 3 , etc, as the anodic by-products, which may reduced the current efficiency. ...
Article
Recently, a novel proof-of-concept oxygen reduction reaction (ORR) based electro-oxidation (EO) process has been developed, which was accomplished by integrating anodic electrochemical oxidation coupled with an in situ electro-peroxone process, by harnessing the anodic by-product O3 reacted with ORR cathode generated H2O2. To further enhance EO coupled in situ electro-peroxone, a nickel and antimony doped tin oxide anodic catalyst layer, namely NATO, was fabricated on Ti mesh to improve anodic oxidation and reinforce the generation of O3, thus promoting in situ Electro-peroxone. As a result, O3 generation rate was enhanced by 12.6%. Complete phenol, as a model organic compound, and 95% of TOC removal were achieved, respectively, during ORR-EO. Through kinetics and instrument analysis, results show that the amount of intermediates accumulated during phenol degradation was much less in this Ti/NATO based ORR-EO system than in a traditional EO system. Moreover, 35.7% of the energy consumption was saved for ORR-EO, owing to its reduced applied voltage and the enhanced in situ electro-peroxone process.