Photodegradation of amitriptyline in Fe(III)-citrate-oxalate binary system: Synergistic effect and mechanism

An Overview of Degradation Strategies for Amitriptyline

Antidepressant drugs play a crucial role in the treatment of mental health disorders, but their efficacy and safety can be compromised by drug degradation. Recent reports point to several drugs found in concentrations ranging from the limit of detection (LOD) to hundreds of ng/L in wastewater plants around the globe; hence, antidepressants can be considered emerging pollutants with potential consequences for human health and wellbeing. Understanding and implementing effective degradation strategies are essential not only to ensure the stability and potency of these medications but also for their safe disposal in line with current environment remediation goals. This review provides an overview of degradation pathways for amitriptyline, a typical tricyclic antidepressant drug, by exploring chemical routes such as oxidation, hydrolysis, and photodegradation. Connex issues such as stability-enhancing approaches through formulation and packaging considerations, regulatory guidelines, and quality control measures are also briefly noted. Specific case studies of amitriptyline degradation pathways forecast the future perspectives and challenges in this field, helping researchers and pharmaceutical manufacturers to provide guidelines for the most effective degradation pathways employed for minimal environmental impact.

Mechanisms of interfacial catalysis and mass transfer in a flow-through electro-peroxone process

To investigate the catalytic mechanism and mass transfer efficiency in the removal of amitriptyline using an electro-peroxide process, a CuFe₂O₄-modified carbon cloth cathode was prepared and utilized in a reaction unit. The results demonstrated a remarkable efficacy of the system, achieving 91.0% amitriptyline removal, 68.3% mineralization, 41.2% mineralization current efficiency, and 0.24 kWh/m³ energy consumption within just five minutes of treatment. The study revealed that the exposed Fe atoms of the ferrite nanoparticles, with a size of 22.7 nm and 89.7% crystallinity, functioned as mediators to bind the adsorbed O atoms. The 3d_xy, 3d_xz, and 3d²_z orbitals of Fe atoms interacted with the 2p_z orbital of O atoms of H₂O₂ and O₃ to form σ and π bonds, facilitating the adsorption-activation of H₂O₂ and O₃ into hydroxyl radicals. These hydroxyl radicals (∼ 1.15 × 10¹³ mol/L) were distributed at the cathode-solution interface and rapidly consumed along the direction of liquid flow. The flow-through cathode design improved the mass transfer of aqueous O₃ and in-situ generated H₂O₂, leading to an increased yield of hydroxyl radicals, as well as the contact time and space between hydroxyl radicals and amitriptyline. Ultimately, this resulted in a higher degradation efficiency of the system.

Enhanced degradation of 2,6-dimethylphenol by photocatalytic systems using TiO2 assisted with H2O2 and Fe(III)

In this study, several photocatalytic degradation systems were investigated using 2,6-dimethylphenol (2,6-DMP) as a model compound. Highly reactive species are formed in four systems, Fe(III), TiO₂, TiO₂/H₂O₂ and TiO₂/Fe(III) where complete degradation of 2,6-DMP was achieved under UV radiation. Photodegradation of the 2,6-DMP has been described by pseudo-first order kinetic model in the presence of TiO₂. In UV/TiO₂-H₂O₂ system, the addition of H₂O₂ in the TiO₂ suspension improves the degradation rate of 2,6-DMP from 70% to 100% for a H₂O₂ concentration of 10^-2 M in 3 h. In homogeneous system, HO^• and Fe²⁺ can be generated by the irradiation of Fe(III) solution. The speciation of Fe(III) obtained from Visual MINTEQ soft showed the formation of several species and Fe(OH)²⁺ were the most predominant and active species in a pH range of 2.5-3.5. At a low concentration of TiO₂ (30 mg L^-1), an important positive effect due to the iron addition has been shown in TiO₂/Fe(III) system, the entrance of metallic ions at different concentrations enhanced the photocatalytic activity of TiO₂. A degradation percentage of 90% was achieved in the UV/TiO₂-Fe(III) system under optimal conditions against 57% in UV/TiO₂ system. Strong synergistic effect was observed in the UV/TiO₂-H₂O₂ binary system. On the basis of literature, a pathway for 2,6-DMP degradation was proposed. The mechanism of degradation of the 2,6-DMP did not involve only HO^• radicals, an interaction of Fe(III) in the excited state with 2,6-DMP occurred giving rise to the formation of 2,6-dimethylphenoxyl radical.

Rapid Redox Cycling of Fe(II)/Fe(III) in Microdroplets during Iron-Citric Acid Photochemistry

Fe(III) and carboxylic acids are common compositions in atmospheric microdroplet systems like clouds, fogs, and aerosols. Although photochemical processes of Fe(III)-carboxylate complexes have been extensively studied in bulk aqueous solution, relevant information on the dynamic microdroplet system, which may be largely different from the bulk phase, is rare. With the help of the custom-made ultrasonic-based dynamic microdroplet photochemical system, this study examines the photochemical process of Fe(III)-citric acid complexes in microdroplets for the first time. We find that when the degradation extent of citric acid is similar between the microdroplet system and the bulk solution, the significantly lower Fe(II) ratio is present in microdroplet samples due to the rapider reoxidation of photogenerated Fe(II). However, by replacing citric acid with benzoic acid, no much difference in the Fe(II) ratio between microdroplets and bulk solution is observed, which indicates distinct reoxidation pathways of Fe(II). Moreover, the presence of ^•OH scavenger, namely, methanol, greatly accelerates the reoxidation of photogenerated Fe(II) in both citric acid and benzoic acid situations. Further experiments reveal that the high availability of O₂ and the citric acid- or methanol-derived carbon-centered radicals are responsible for the rapider reoxidation of Fe(II) in iron-citric acid microdroplets by prolonging the length of HO₂^•- and H₂O₂-involved radical reaction chains. The results in this study may provide a new understanding about iron-citric acid photochemistry in atmospheric liquid particles, which can further influence the photoactivity of particles and the formation of secondary organic aerosols.

Effect of Fe(III)-bicarboxylic complexes in removal pollutant under UV and sunlight in aqueous solutions

In this study, we have applied Fe(III)-bi-carboxylic acid solutions containing citrate and oxalate ligands to degrade 3-méthylphénol (3MP) in aqueous solutions both under UV and sunlight. Under irradiation at 365 nm, the photodegradation of 3MP is markedly better in the presence of the Fe(III)Ox complex than in the Fe(III)Cit complex this fact is explained by an excess of H₂O₂ and Fe(II) generated by Fe(III)Ox photolysis creating the Fenton process. We mixtures were realized by varying the composition of the Fe(III)Cit and Fe(III)Ox in order to see the additives of the degradation efficiency of the pollutant. The results show that the addition of Fe(III)Ox to the Fe(III)Cit system evidently augmented the photodegradation rate at pH = 5.5. The Fe(III)Ox/Fe(III)Cit ratio is optimized at [Fe(III)Ox] (0.15/0.15)/[Fe(III)Cit] (0.15/0.6). Synergistic effect in the Fe(III)Ox/Fe(III)Cit binary system was confirmed. The addition of tertiobutanol (T-buOH) noticeably inhibited the photodegradation, indicating the involvement of ^•OH in the process. To verify the feasibility of photochemical processes in the environment, tests on the photodegradation of 3MP were performed under natural irradiation. The degradation was improved under excitation by sunlight in the presence of Fe(III)-bi-carboxylic acid solutions containing citrate and oxalate ligands. These results are very encouraging for the application of this system for the treatment of organic pollutants in aqueous solution.

Phenanthrene decomposition in soil washing effluents using UVB activation of hydrogen peroxide and peroxydisulfate

In this work, the decomposition of phenanthrene (PHE) in mimic and real soil washing (SW) effluents was investigated using UVB light assisted activation of hydrogen peroxide (H₂O₂) and peroxydisulfate (PDS) oxidation processes. The impact of oxidant concentration, initial pH, and coexisting inorganic anions (Cl^-, HCO₃^- and NO₃^-) on PHE removal was evaluated. PHE degradation efficiency under UVB irradiation followed the order of UVB/PDS > UVB/H₂O₂ > UVB. The increase of PHE decomposition efficiency was observed with increasing oxidant dose in the range of 2-30 mM upon the two processes. It was found Cl^- played different roles in the two activation systems depending on the solution pH and Cl^- concentration. The influence of HCO₃^- on PHE elimination was negligible in the UVB/PDS process, while an inhibitory effect was observed in the UVB/H₂O₂ system. Nitrate inhibited the PHE decay in both UVB/H₂O₂ and UVB/PDS processes at the investigated pH 3.3, 7.1 and 8.6. Finally, the application of the two activation processes to the treatment of real SW effluents indicated that up to 85.0% of PHE degradation could be reached under 6 h UVB irradiation with PDS, indicating UVB/PDS process is a promising alternative for SW effluent treatment.

Photodegradation of para-arsanilic acid mediated by photolysis of iron(III) oxalate complexes

Organic arsenicals are important environment pollutants due to wide use in livestock and toxicity of degradation products. In this work we report about the efficient photodegradation of the p-arsanilic acid (p-ASA) and its decomposition products in the Fe(III)-oxalate assisted approach under nature-relevant conditions. At neutral pH under near-visible UV irradiation the Fe(III) oxalate complexes generate the primary oxidizing intermediate, OH radical (the quantum yield of ϕ^OH ∼ 0.06), which rapidly reacts with p-ASA with high rate constant, (8.6 ± 0.5) × 10⁹ M^-1s^-1. Subsequent radical reactions result in the complete photooxidation of both p-ASA and basic aromatic photoproducts with the predominant formation of inorganic arsenic species, mainly As(V), under optimal conditions. Comparing with the direct UV photolysis, the presented Fe(III)-oxalate mediated degradation of p-ASA has several advantages: higher efficiency at low p-ASA concentration and complete degradation of organic arsenic by-products without use of short-wavelength UV radiation. The obtained results illustrate that the Fe(III)-oxalate complexes are promising natural photosensitizers for the removal of arsenic pollutants from contaminated waters.

Safe and efficient degradation of metronidazole using highly dispersed β-FeOOH on palygorskite as heterogeneous Fenton-like activator of hydrogen peroxide

In this study, the highly dispersed β-FeOOH on palygorskite (H-β-FeOOH/PAL) was prepared and investigated as Fenton catalyst for H₂O₂ activation towards metronidazole (MTZ). Based on electron spin resonance and probe techniques, hydroxyl radicles (^•OH) as main reactive oxygen species was confirmed, and much more ^•OH were generated over H-β-FeOOH/PAL than T-β-FeOOH/PAL using traditional impregnation method. The enhanced Fe(III) to Fe(II) cycle due to the highly dispersed β-FeOOH leads to the fast degradation of metronidazole over H-β-FeOOH/PAL. 92.8% of MTZ degradation efficiency was achieved within 180 min by adding 17 mmol/L H₂O₂ and 40 mg/L of H-β-FeOOH/PAL at pH 6.0. The bacterial cytotoxicity during MTZ degradation process also decreased with reaction time and achieved zero at 66 min, indicating MTZ was not only efficiently degraded but also safely transformed. Besides, the possible MTZ degradation pathway was further proposed based on the intermediates identified by HPLC-MS.

A TiO2/crosslinked carboxymethyl starch composite for high-efficiency adsorption and photodegradation of cationic golden yellow X-GL dye

In this paper, a crosslinked carboxymethyl starch (CCMS) was prepared with corn starch as the raw material, epichlorohydrin as the crosslinking agent, and chloroacetic acid as the etherifying agent through a series of crosslinking, alkalization, and etherification reactions, respectively. Nano-TiO₂ was loaded onto the surface of the CCMS by the sol-gel method to obtain a TiO₂/CCMS composite. The TiO₂/CCMS composite was characterized by XPS, XRD, SEM, and BET. XPS showed that the surface chemical composition of the TiO₂/CCMS composite material contained titanium; XRD diffraction patterns indicated that the crystal form of the TiO₂/CCMS composite was a combination of the CCMS and anatase TiO₂. The surface morphology obtained by SEM showed that there were nano-TiO₂ particles on the surface of the CCMS. The specific surface area of the TiO₂/CCMS composite was larger than that of CCMS. The adsorption-photodegradation performance of the TiO₂/CCMS composite was also studied under UV irradiation, and the results showed that significant adsorption-photodegradation synergies occurred.