Insights into the degradation and detoxication mechanisms of aqueous capecitabine in electrochemical oxidation process

Insights into electrochemical oxidation of tris(2-butoxyethyl) phosphate (TBOEP) in aquatic media: Degradation performance, mechanisms and toxicity changes of intermediate products

Tris (2-butoxyethyl) phosphate (TBOEP) has gained significant attention due to its widespread presence and potential toxicity in the environment. In this study, the degradation of TBOEP in aquatic media was investigated using electrochemical oxidation technology. The anode Ti/SnO2-Sb/La-PbO2 demonstrated effective degradation performance, with a reaction constant (k) of 0.6927 min-1 and energy consumption of 1.24 kW h/m3 at 10 mA/cm2. CV tests, EPR tests, and quenching experiments confirmed that indirect degradation is the main degradation mechanism and ·OH radicals were the predominant reactive species, accounting for up to 93.8%. The presence of various factors, including Cl-, NO3-, HCO3- and humic acid (HA), inhibited the degradation of TBOEP, with the inhibitory effect dependent on the concentrations. A total of 13 intermediates were identified using UPLC-Orbitrap-MS/MS, and subsequent reactions led to their further degradation. Two main degradation pathways involving bond breaking, hydroxylation, and oxidation were proposed. Both Flow cytometry and the ECOSAR predictive model indicated that the intermediates exhibited lower toxic than the parent compound, resulting in a high detoxification rate of 95.9% for TBOEP. Although the impact of TBOEP on the phylum-level microbial community composition was found to be insignificant, substantial alterations in bacterial abundance were noted when examining the genus level. The dominant genus Methylotenera, representing 17.4% in the control group, decreased to 6.9% in the presence of TBOEP and slightly increased to 8.7% in the 4-min exposure group of degradation products. Electrochemical oxidation demonstrated its effectiveness for the degradation and detoxification of TBOEP in aqueous solutions, while it is essential to consider the potential impact of degradation products on sediment microbial communities.

Decontamination of wastewater containing contaminants of emerging concern by electrooxidation and Fenton-based processes - A review on the relevance of materials and methods

In recent years, there has been an increasingly growing interest regarding the use of electrochemical advanced oxidation processes (EAOPs) which are considered highly promising alternative treatment techniques for addressing environmental issues related to pollutants of emerging concern. In EAOPs, electrogenerated oxidizing agents, such as hydroxyl radical (HO^•), can react non-selectively with a wide range of organic compounds, degrading and mineralizing their structures to unharmful molecules like CO₂, H₂O, and inorganic ions. To this date, a broad spectrum of advanced electrocatalysts have been developed and applied for the treatment of compounds of interest in different matrices, specifically aiming at enhancing the degradation performance. New combined methods have also been employed as alternative treatment techniques targeted at circumventing the major obstacles encountered in Fenton-based processes, such as high costs and energy consumption, which still contribute significantly toward inhibiting the large-scale application of these processes. First, some fundamental aspects of EAOPs will be presented. Further, we will provide an overview of electrode materials which have been recently developed and reported in the literature, highlighting different anode and cathode structures employed in EAOPs, their main advantages and disadvantages, as well as their contribution to the performance of the treatment processes. The influence of operating parameters, such as initial concentrations, pH effect, temperature, supporting electrolyte, and radiation source, on the treatment processes were also studied. Finally, hybrid techniques which have been reported in the literature and critically assess the most recent techniques used for evaluating the degradation efficiency of the treatment processes.

Regulating electron distribution of Fe/Ni-N4P2 single sites for efficient photo-Fenton process

Regulating local electron density by introducing single-atom is an effective strategy to improve the activity of heterogeneous photo-Fenton processes. Here N, P coordinated Fe and Ni single-atom catalysts on carbon nitrides (CN-FeNi-P) were prepared to activate H₂O₂ for contaminant mineralization under visible light irradiation. The as-prepared CN-FeNi-P presented a higher moxifloxacin degradation activity in photo-Fenton system, which was up to 3.7 times that of pristine CN, meanwhile, its TOC removal reached to 95.9 % in 60 min. Based on density functional theory calculations, the Ni single-atoms serve as the optimal reactive sites to produce •OH. The strong interaction between Fe and Ni single-atoms by P-bridging and the modulated local electron structure after introducing P into coordination environment can lower •OH formation energy. This study provides new doping strategies to design single-atom catalysts and expands the family of the Fenton-like system for advanced oxidation technologies.

Highly dispersed Ag and g-C3N4 quantum dots co-decorated 3D hierarchical Fe3O4 hollow microspheres for solar-light-driven pharmaceutical pollutants degradation in natural water matrix

The efficient removal of pharmaceutical pollutants presents a great challenge for the conventional sewage treatment system. Herein, we document the nanosheets assembled 3D hierarchical Fe₃O₄ hollow microspheres co-modified by Ag and g-C₃N₄ quantum dots (Ag/CNQDs@Fe₃O₄) for efficient degradation of two classic anticancer drugs, i.e., capecitabine (CAP) and 5-fluorouracil (5-FLU) under visible light in 1 h. Benefiting from the unique hierarchically hollow structure, the intrinsic strengths of each component and their interactions, synergistic reinforcing mechanism is constructed, furnishing more accessible reactive places, promoting the diffusion of pollutants/oxidants, improving charge separation ability, and raising light utilization rate. Consequently, Ag/CNQDs@Fe₃O₄ can not only show superior photocatalytic properties, but also greatly boost PMS activation to yield sufficient oxidative radicals. More notably, the studied system also features excellent stability and strong tolerance to real water samples, and maintains appreciable performance even under natural sunlight illumination. The predominant active species, possible ADs decomposition pathways, and underlying reaction mechanism for the Ag/CNQDs@Fe₃O₄/PMS/vis system are thoroughly explored. This work presents significant advancement in enabling an integrated technology of PMS and photocatalysis to realize its great potential in environment restoration.

Formation of stable imine intermediates in the coexistence of sulfamethoxazole and humic acid by electrochemical oxidation

The electrochemical degradation performance of sulfamethoxazole (SMX) was studied in the presence of humic acid (HA) by using a Ti/Ti₄O₇/β-PbO₂ anode. The electrochemical degradation efficiency of SMX decreased from 93.4% to 45.8% in 50 min after the addition of 25 mg L^-1 HA. The pseudo-first-order kinetic rate constant decreased by 71.4%, and the E_EO value increased from 63.8 Wh L^-1 to 90.9 Wh L^-1. HA and its degradation intermediates could compete for free radicals, especially for ·OH, with SMX. The analytical results obtained using UPLC-ESI-Q-TOF-MS showed that 18 degradation intermediates were identified in the coexistence of SMX and HA. Four imine intermediates were formed through the reactions between the aniline moieties of SMX and quinone groups in the HA structure through covalent bonds. Furthermore, the relative abundances of the intermediates demonstrated that the imine intermediates were complex and stable during electrochemical degradation.

Effective degradation of aqueous carbamazepine on a novel blue-colored TiO2 nanotube arrays membrane filter anode

The effective electrochemical oxidation of aqueous carbamazepine (CBZ) using a novel blue-colored TiO₂ nanotube arrays (BC-TiO₂NTA) membrane filter anode was studied. The BC-TiO₂NTA was characterized using SEM, TEM, BET, mercury intrusion porosimetry, XPS, XRD, CV, and LSV. The BC-TiO₂NTA had reserved pore structure, formed mesopores, specific and electroactive surface areas of 2.01 m² g^-1 and 9.32 cm² cm^-2, respectively. The oxygen evolution potential was 2.61 V vs. SCE. CBZ could be degraded by OH, SO₄^- and O₂^- on BC-TiO₂NTA in accordance to pseudo-first-order kinetic, which was greatly enhanced in flow-through mode. The optimal kinetic rate constant of CBZ degradation of 0.403 min^-1 was achieved at 3 mA cm^-2, while energy consumption per order was 0.086 kW h m^-3. The mineralization efficiency and mineralization current efficiency were 50.8 % and 9.5 % at 180 min, respectively. The presence of Cl^- (0.3-3 mM) accelerated electrochemical degradation of CBZ, while NO₃^- (0.1-2 mM) inhibited the reaction. Based on density functional theory calculation and UPLC-Orbitrap-MS/MS measurement, we found that electrochemical degradation of CBZ was initialized by cleavage of -CONH₂ group and attack of OH on the olefinic double bond of the central heterocyclic ring.

Occurrence, statutory guideline values and removal of contaminants of emerging concern by Electrochemical Advanced Oxidation Processes: A review

A wide variety of chemical compounds are used in human activities; however, part of these compounds reach surface water, groundwater and even water considered for potable uses. Due to the limited efficiency of water treatment by the Water and Wastewater Treatment Plants, the presence of these compounds in natural and human consumption waters can be very harmful due to their high persistence and adverse effects; these characteristics define the contaminants of emerging concern (CECs). Water treatment by Electrochemical Advanced Oxidation Processes (EAOPs) has been evaluated as a promising process for the removal of persistent and recalcitrant organic contaminants. With this background, the present review aims to gather studies and information published between 2015 and 2020 regarding the occurrence of CECs in surface, potable and groundwater, its treatment by EAOPs, the main operating conditions and by-product generation of EAOPs, contaminant toxicity assessments and international statutory guideline values concerning CEC standards and allowable concentrations in the environment and treated drinking water. Therefore, in this review it was found that the compounds bisphenol A (BPA), diethyltoluamide (DEET), 17α-ethinyl estradiol (EE2), perfluorobutanoic acid (PFBA), carbamazepine, caffeine and atrazine were the most frequently detected in water sources, with concentrations ranging from 35.54-4800, 1.21-98, 0.005-38.5, 5-742.904, 0.0071-586, 0.89-1040, and 100-323 (ng L-1), respectively. Among the operational conditions of EAOPs, current density, pH and oxidant concentration are the main operational parameters that have an influence on these treatment technologies, besides the by-products generated, which might be removed by the integration of EAOPs with biological digestion treatments. Regarding the values of water quality standards, many CECs do not have established standard allowable concentration values, which represents a concern toward the possible toxic effects of these compounds on non-target organisms.