Photo-assisted Electrochemical Oxidation Research Articles

Hybrid process of adsorption and electrochemically based green regeneration of bentonite clay for ofloxacin and ciprofloxacin removal.

Removal of emerging contaminants, such as antibiotics, from wastewater by adsorption is a simple, low-cost, and high-performance process; however, regeneration and reuse of the exhausted adsorbent are necessary to make the process economically viable. This study aimed to investigate the possibility of electrochemical-based regeneration of clay-type materials. For this, the calcined Verde-lodo (CVL) clay was saturated with the antibiotics ofloxacin (OFL) and ciprofloxacin (CIP) in one-component systems by an adsorption process and then subjected to photo-assisted electrochemical oxidation (0.45 A, 0.05 mol/L NaCl, UV-254 nm, and 60 min), which promotes both pollutant degradation and adsorbent regeneration. The external surface of the CVL clay was investigated by X-ray photoelectron spectroscopy before and after the adsorption process. The influence of regeneration time was evaluated for the CVL clay/OFL and CVL clay/CIP systems, and the results demonstrate high regeneration efficiencies after 1 h of photo-assisted electrochemical oxidation. Clay stability during regeneration was investigated by four successive cycles in different aqueous matrices (ultrapure water, synthetic urine, and river water). The results indicated that the CVL clay is relatively stable under the photo-assisted electrochemical regeneration process. Furthermore, CVL clay was able to remove antibiotics even in the presence of natural interfering agents. The hybrid adsorption/oxidation process applied here demonstrated the electrochemical-based regeneration potential of CVL clay for the treatment of emerging contaminants, since it can be operated quickly (1h of treatment) and with lower consumption of energy (3.93 kWh kg-1) than the traditional method of thermal regeneration (10 kWh kg-1).

Integrated approach of photo-assisted electrochemical oxidation and sequential biodegradation of textile effluent

Synthetic azo dyes are extensively used in the textile industries, which are being released as textile effluent into the environment presence of azo dyes in the environment is great environmental concern therefore treatment of textile effluent is crucial for proper release of the effluent into the environment. Electrochemical oxidation (EO) is extensively used in the degradation of pollutants because of its high efficiency. In this study, photo-assisted electrooxidation (PEO) followed by biodegradation of the textile effluent was evaluated. The pretreatment of textile effluent was conducted by EO and PEO in a tubular flow cell with TiO2–Ti/IrO2–RuO2 anode and titanium cathode under different current densities (10, 15, and 20 mA cm−2). The chemical oxygen demand level reduced from 3150 mg L−1 to 1300 and 600 mg L−1under EO and PEO, respectively. Furthermore, biodegradation of EO and PEO pretreated textile effluent shows reduction in chemical oxygen demand (COD) from 1300 mg L−1 to 900 mg L−1and 600 mg L−1to 110 mg L−1, respectively. The most abundant genera were identified as Acetobacter, Achromobacter, Acidaminococcus, Actinomyces, and Acetomicrobium from the textile effluent. This study suggests that an integrated approach of PEO and subsequent biodegradation might be an effective and eco-friendly method for the degradation of textile effluent.

Photo-assisted electrochemical advanced oxidation processes for the disinfection of aqueous solutions: A review

Disinfection is usually the final step in water treatment and its effectiveness is of paramount importance in ensuring public health. Chlorination, ultraviolet (UV) irradiation and ozone (O3) are currently the most common methods for water disinfection; however, the generation of toxic by-products and the non-remnant effect of UV and O3 still constitute major drawbacks. Photo-assisted electrochemical advanced oxidation processes (EAOPs) on the other hand, appear as a potentially effective option for water disinfection. In these processes, the synergism between electrochemically produced active species and photo-generated radicals, improve their performance when compared with the corresponding separate processes and with other physical or chemical approaches. In photo-assisted EAOPs the inactivation of pathogens takes place by means of mechanisms that occur at different distances from the anode, that is: (i) directly at the electrode’s surface (direct oxidation), (ii) at the anode’s vicinity by means of electrochemically generated hydroxyl radical species (quasi-direct), (iii) or at the bulk solution (away from the electrode surface) by photo-electrogenerated active species (indirect oxidation).This review addresses state of the art reports concerning the inactivation of pathogens in water by means of photo-assisted EAOPs such as photo-electrocatalytic process, photo-assisted electrochemical oxidation, photo-electrocoagulation and cathodic processes. By focusing on the oxidation mechanism, it was found that while quasi-direct oxidation is the preponderant inactivation mechanism, the photo-electrocatalytic process using semiconductor materials is the most studied method as revealed by numerous reports in the literature. Advantages, disadvantages, trends and perspectives for water disinfection in photo-assisted EAOPs are also analyzed in this work.

Degradation of hydroxychloroquine by electrochemical advanced oxidation processes

In this work, the degradation of hydroxychloroquine (HCQ) drug in aqueous solution by electrochemical advanced oxidation processes including electrochemical oxidation (EO) using boron doped diamond (BDD) and its combination with UV irradiation (photo-assisted electrochemical oxidation, PEO) and sonication (sono-assisted electrochemical oxidation, SEO) was investigated. EO using BDD anode achieved the complete depletion of HCQ from aqueous solutions in regardless of HCQ concentration, current density, and initial pH value. The decay of HCQ was more rapid than total organic carbon (TOC) indicating that the degradation of HCQ by EO using BDD anode involves successive steps leading to the formation of organic intermediates that end to mineralize. Furthermore, the results demonstrated the release chloride (Cl−) ions at the first stages of HCQ degradation. In addition, the organic nitrogen was converted mainly into NO3− and NH4+ and small amounts of volatile nitrogen species (NH3 and NOx). Chromatography analysis confirmed the formation of 7-chloro-4-quinolinamine (CQLA), oxamic and oxalic acids as intermediates of HCQ degradation by EO using BDD anode. The combination of EO with UV irradiation or sonication enhances the kinetics and the efficacy of HCQ oxidation. PEO requires the lowest energy consumption (EC) of 63 kWh/m3 showing its cost-effectiveness. PEO has the potential to be an excellent alternative method for the treatment of wastewaters contaminated with HCQ drug and its derivatives.

Mineralization of formic acid from catalytic nitrate reduction effluent by UV-based and electrochemical processes

Abstract In this work, UV-based and electrochemical processes were proposed for formic acid (FA) mineralization, from an effluent generated on the nitrate catalytic reduction reaction. The results show that although direct photolysis (DP) does not have the ability to mineralize FA, heterogeneous photocatalysis (HP), photo-assisted electrochemical oxidation (PEO) and electrochemical oxidation (EO) have. In fact, it has been shown that FA mineralization is governed by the electrochemical process. When nitrate was added in the FA solution, all process exhibited an increase in FA mineralization, mainly for DP. For UV-based process, this fact can be linked to the nitrate photolysis generating hydroxyl radicals ( H O • ). On the other hand, the mineralization increase observed on the EO process, is associated with the increase in charge transfer, considering that the generation of oxidants is a rate-limiting-step, showing pseudo-zero-order constants for DP and HP, and pseudo-first-order for PEO and EO. The best results of FA mineralization with the smallest energy consumption was obtained by the electrochemical process. Besides, EO was not negatively influenced by the addition of nitrate.

Atomically tunable photo-assisted electrochemical oxidation process design for the decoration of ultimate-thin CuO on Cu2O photocathodes and their enhanced photoelectrochemical performances

A representative method of forming CuO thin films on Cu2O photoabsorbers is simple annealing oxidation at high temperature in a controlled oxygen atmosphere, but the typical oxidation process is irregular, resulting in a high density of defect sites.

Removal of sulfide and recycling of recovered product from tannery lime wastewater using photoassisted-electrochemical oxidation process

Investigation and optimization of photoassisted electro-oxidation process for removal of high concentration of sulfide and COD from tannery lime wastewater was done. Electro oxidation process with UV-light were evaluated with different current densities such as 15, 20, 25mA/cm2 with cylindrical electrodes (MMO and Ti sheet). 100% sulfide, 92% of COD and 70% total organic carbon (TOC) were effectively reduced by the current density of 25mA/cm2 in the photo-assisted electrochemical oxidation process. In Electro-oxidation process alone, the COD and TOC were not reduced effectively. Water/mixed salt (47% Na2SO4 and 53% NaCl) were recovered and reused for dye fixation process.

Antibiotics mineralization by electrochemical and UV-based hybrid processes: evaluation of the synergistic effect

ABSTRACTAntibiotics are not efficiently removed in conventional wastewater treatments. In fact, different advanced oxidation process (AOPs), including ozone, peroxide, UV radiation, among others, are being investigated in the elimination of microcontaminants. Most of AOPs proved to be efficient on the degradation of antibiotics, but the mineralization is on the one hand not evaluated or on the other hand not high. At this work, the UV-based hybrid process, namely Photo-assisted electrochemical oxidation (PEO), was applied, aiming the mineralization of microcontaminants such as the antibiotics Amoxicillin (AMX), Norfloxacin (NOR) and Azithromycin (AZI). The influence of the individual contributions of electrochemical oxidation (EO) and the UV-base processes on the hybrid process (PEO) was analysed. Results showed that AMX and NOR presented higher mineralization rate under direct photolysis than AZI due to the high absorption of UV radiation. For the EO processes, a low mineralization was found for all antibiotics, what was associated to a mass-transport limitation related to the low concentration of contaminants (200 µg/L). Besides that, an increase in mineralization was found, when heterogeneous photocatalysis and EO are compared, due to the influence of UV radiation, which overcomes the mass-transport limitations. Although the UV-based processes control the reaction pathway that leads to mineralization, the best results to mineralize the antibiotics were achieved by PEO hybrid process. This can be explained by the synergistic effect of the processes that constitute them. A higher mineralization was achieved, which is an important and useful finding to avoid the discharge of microcontaminants in the environment.

A one-pot approach: Oxychloride radicals enhanced electrochemical oxidation for the treatment of textile dye wastewater trailed by mixed salts recycling

Abstract The efficacy of a photo-assisted electrochemical oxidation for the mineralization of real textile effluents (wash water and dye-bath effluent) was investigated by employing a non-photoactive dimensionally stable anode in a tubular flow cell. Under optimized conditions, the photo-assisted electrochemical oxidation was performed at a pH of 2, with a chloride concentration of 2 g L−1, a current density of 10 mA cm−2, and a flow rate of 50 mL min−1. The process efficiency was assessed through ultraviolet–visible spectroscopy, high performance liquid chromatography, Fourier transform-Infra red spectroscopy, nuclear magnetic resonance spectroscopy, chemical oxygen demand and total organic carbon analyses. The results obtained have shown that, in case of wash water effluent, 96% of chemical oxygen demand and 68% of total organic carbon were removed in 180 min of photo-assisted electrochemical oxidation, whereas a simple electrochemical oxidation removed only 70% of chemical oxygen demand and 27% of total organic carbon, in the same time. The energy consumptions were about to 29.8 and 39.5 Wh g−1 of chemical oxygen demand in photo-assisted electrochemical oxidation and electrochemical oxidation. The higher efficiency of photo-assisted electrochemical oxidation is attributed to the formation of oxychloride radicals at acidic pH, as confirmed by electron paramagnetic resonance analysis. The analytical results revealed that the degradation mechanism of photo-assisted electrochemical oxidation is entirely different from that of electrochemical oxidation; in particular, the byproducts formed in the photo-assisted process are free from chlorinated organic compounds and exhibit zero toxicity towards Lemna minor. The photo-assisted electrochemical oxidation proved to be effective also in the case of dye bath effluents with a high organic load: about 90% of the chemical oxygen demand was removed within 5 h at 10 mA cm−1. The recovered salts from the color-free dye-bath effluent were recycled for further dyeing purposes.

Photo-assisted electrochemical oxidation of the urea onto TiO2-nanotubes modified by hematite

The electrochemical oxidation of the urea in near neutral pH is investigated on platinum electrode. It is shown that oxidation reaction is practically inhibited up to the potentials of ∼0.9V. The same reaction is investigated onto electrochemically obtained titanium dioxide nanotubes modified by hematite using facile, low-cost successive ion layer adsorption and reaction (SILAR) method. It is shown that such system possesses electrocatalytic activity at very low potentials, and activity can be further improved by the illumination of the electrode in the photo-assisted reaction. The possible application of the photoactive anode is considered in the application of urea based water electrolysis and urea based fuel cell.

Degradation of the commercial surfactant nonylphenol ethoxylate by advanced oxidation processes

Four different oxidation process, namely direct photolysis (DP) and three advanced oxidation processes (heterogeneous photocatalysis – HP, eletrochemical oxidation – EO and photo-assisted electrochemical oxidation – PEO) were applied in the treatment of wastewater containing nonylphenol ethoxylate (NPnEO). The objective of this work was to determine which treatment would be the best option in terms of degradation of NPnEO without the subsequent generation of toxic compounds. In order to investigate the degradation of the surfactant, the processes were compared in terms of UV/Vis spectrum, mineralization (total organic carbon), reaction kinetics, energy efficiency and phytotoxicity. A solution containing NPnEO was prepared as a surrogate of the degreasing wastewater, was used in the processes. The results showed that the photo-assisted processes degrade the surfactant, producing biodegradable intermediates in the reaction. On the other hand, the electrochemical process influences the mineralization of the surfactant. The process of PEO carried out with a 250W lamp and a current density of 10mA/cm2 showed the best results in terms of degradation, mineralization, reaction kinetics and energy consumption, in addition to not presenting phytotoxicity. Based on this information, this process can be a viable alternative for treating wastewater containing NPnEO, avoiding the contamination of water resources.

Degradation of phenol by synergistic chlorine-enhanced photo-assisted electrochemical oxidation

Hybridization of a UV-C photoreactor with an electrochemical cell led to the discovery of a distinctive synergistic mechanism for the degradation and mineralization of phenol when free chlorine-producing anodes were utilized in the presence of chloride. After 6h, photochemical (UV) treatment resulted in 29% phenol mineralization and electrochemical (EL) treatment resulted in 35% and 52% mineralization using boron-doped diamond (BDD) and ruthenium oxide on titanium (DSA-Cl2) anodes, respectively. However, the photo-assisted electrochemical (UVEL) process removed 88% and 96% of total organic carbon (TOC) after 6h with BDD and DSA-Cl2 anodes, respectively. The hybrid UVEL process generated highly reactive hydroxyl and chlorine radicals by the photolysis of in situ electrogenerated free chlorine. As a result, the UVEL treatment produced fewer chlorinated by-products compared to EL alone. UVEL with DSA-Cl2 had the highest TOC removal after 6h (96%), one of the highest mineralization rates (0.38h−1), and the lowest energy demand per order TOC removed (EEO=104kWhm−3order−1) without any residual toxicity after dechlorination. Generally, conventional advanced oxidation processes (UV/O3 and UV/H2O2) were most effective at mineralization up to 50%, but UVEL appeared more cost effective for mineralization beyond 75%.

Combined electro-photochemical oxidation for iron removal from ground water

Iron in water presents health hazard, its presence in water may cause taste and staining problems. Currently applied water treatment techniques consist of a combination of different methods to achieve the elimination of harmful pollutants. The aim of this study is to investigate the efficiency of the photo-assisted electrochemical oxidation process for the removal of dissolved iron as a cheaper technology. This process could be used at room temperature and low pressure without the need for special equipment and complex operation. The photoelectrochemical cell used in this study was composed of carbon cathode, aluminum anode and high pressure mercury lamp. The effect of the irradiation time, initial concentration of iron, amount of electrolyte and current intensity on the removal efficiency of iron was investigated through series of batch runs in a photo-electrochemical reactor. Results indicated that higher iron removal was obtained at neutral pH of the solution, 20 min irradiation time, 125 ppm of NaCl a...

Photo-assisted electrochemical oxidation of isopropanol to acetone on a chemically modified electrode

The photocatalytic oxidation of isopropanol, as sensitized by photoexcited quinone derivatives which are chemically bound on a carbon electrode, has been observed. The quantum efficiency for the photosensitized reaction of bound quinones to that of quinone in solution is compared. From the observation of photocurrents, when bound quinones on glassy carbon are photolyzed, it is concluded that some of the excited molecules of the chemically bound quinones react with isopropanol and are not quenched during the lifetime of the excited state at the carbon electrode surface.

Photo-assisted electrochemical oxidation of isopropanol to acetone on a chemically modified electrode

The photocatalytic oxidation of isopropanol, as sensitized by photoexcited quinone derivatives which are chemically bound on a carbon electrode, has been observed. The quantum efficiency for the photosensitized reaction of bound quinones to that of quinone in solution is compared. From the observation of photocurrents, when bound quinones on glassy carbon are photolyzed, it is concluded that some of the excited molecules of the chemically bound quinones react with isopropanol and are not quenched during the lifetime of the excited state at the carbon electrode surface.

Photo-assisted electrochemical oxidation of isopropanol to acetone sensitized by photoexcited anthraquinone derivatives chemically bound on a carbon electrode

Photo-assisted electrochemical oxidation of isopropanol to acetone sensitized by photoexcited anthraquinone derivatives chemically bound on a carbon electrode