A critical review of recent advancements in the photocatalysis process, mechanism, and degradation pathways for the removal of phthalates from the contaminated water matrix

Phthalates, a sort of plasticizer, are widely utilized in various consumer products and pose significant environmental and health risks due to their persistence and potential toxicity. This review explores the occurrence, sources, environmental impact, and remediation strategies for phthalates. Various remediation techniques have been investigated to address phthalate contamination. Among these, photocatalysis, an advanced oxidation process (AOP), has emerged as a viable approach due to its ability to mineralize organic contaminants into innocuous byproducts. The review discusses the recent advancements in photocatalytic processes, the underlying mechanisms, and degradation pathways for phthalate removal. The mechanism of photocatalytic degradation includes the generation of reactive oxygen species like hydroxyl radicals (OH•) and superoxide radicals (O2-•) and their role in breaking down phthalate molecules. It also highlights recent advancements in photocatalytic materials, such as metal-doped semiconductors and composite materials, which enhance the removal efficiency. The review concludes by emphasizing the need for integrated approaches to achieve effective and sustainable phthalate remediation. Future research should focus on developing efficient and cost-effective photocatalytic materials, optimizing reactor design, and scaling up photocatalytic processes for practical applications. The review also highlights the challenges and limitations of photocatalytic processes, including low quantum efficiency, catalyst deactivation, and mass transfer limitations. Potential areas of study are put forward to address these challenges and further advance the application of photocatalysis for phthalate removal. This review intends to help the development of efficient photocatalytic technologies for the remediation of phthalate-contaminated water by providing a complete overview of the present state of the art.

Compound-specific isotopic analysis to characterize the photocatalytic reaction of TiO2 nanoparticles with diethyl phthalate

In this study compound-specific isotope analysis (CSIA) has been used to explore the degradation mechanism of nano titanium dioxide (TiO₂) catalyzes photodegradation of diethyl phthalate (DEP). TiO₂ is a popular photosensitizer with potential in waste water treatment and application in advanced oxidation processes. The degradation process of DEP can be described with a first-order kinetics in the applied concentration ranges. The larger degradation rate constant has been found at neutral conditions. The ¹³C and ²H isotope fractionation associated with the nano TiO₂ catalyzes photodegradation of DEP at pH 3, 7 and 11 yield normal isotope effects. In the TiO₂/UV/DEP and TiO₂/H₂O₂/UV/DEP systems, the correlation of ¹³C and ²H fractionation (Λ) were calculated to be 2.7 ± 0.2, 2.8 ± 0.2 at pH 3, 2.2 ± 0.4, 2.5 ± 0.2, 2.3 ± 0.6 at pH 7 and 2.6 ± 0.3, 2.2 ± 0.3, 2.7 ± 0.2 and 2.3 ± 0.3 at pH11, respectively. The dominant free radical species in studied systems were explored by combining free radical quenching method and electron paramagnetic resonance analysis. The hydroxyl radicals have been found as the main radical species at all pH conditions studied. Furthermore, the ¹³C and ²H fractionation suggested that the addition of •OH on the benzene ring of DEP is the main conversion pathway. Therefore, CSIA is a promising technology for the identification of reaction pathways of DEP for example in water treatment systems.

Insights into the Titania (TiO2) Photocatalysis on the Removal of Phthalic Acid Esters (PAEs) in Water

In this era of globalization, plastic is regarded as one of the most versatile innovations, finding its uses ranging from packaging, automotive, agriculture, and construction to the medical and pharmaceutical industries. Unfortunately, the single-use nature of plastics leads to ecological and environmental problems. Among conventional disposal management of plastic waste are landfilling dumping, incineration, and recycling. However, not all plastic waste goes into disposal management and ends up accumulating in lakes, rivers, and seas. In the aquatic environment, the action of photochemical weathering plastics has resulted in the release of chemical additives such as phthalic acid esters (PAEs), an important plasticizer added to plastic products to improve their softness, flexibility, and durability. Nowadays, PAEs have been ubiquitously detected in our environment and numerous organisms are exposed to PAEs to some extent. As PAEs carry endocrine disruptive and carcinogenicity properties, an urgent search for the development of an efficient and effective method to remove PAEs from the environment is needed. As a viable option, titania (TiO2) photocatalysis is a promising tool to combat the PAEs contamination in our environment owing to its high photocatalytic activity, cost-effectiveness, and its ability to totally mineralize PAEs into carbon dioxide and water. Hence, this paper aims to highlight the concerning issue of the contamination of PAEs in our aquatic environments and the summary of the removal of PAEs by TiO2 photocatalysis. This review concerning the significance of knowledge on environmental PAEs would hopefully spark huge interest and future development to tackle this plastic-associated pollutant. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Phthalates removal from wastewater by different methods - a review

Phthalate esters are commonly used as plasticizers to improve the durability and workability of polymeric materials, locating and identifying them in various contexts has become a major challenge. Because of their ubiquitous use in plastic packaging and personal care items, as well as their tendency to leach out of these materials, phthalates have been detected in a variety of aquatic situations, including surface water, groundwater, drinking water, and wastewater. Phthalate esters have been shown to affect reproductive health and physical growth by disrupting the endocrine system. As a result, developing energy-efficient and effective technologies to eliminate these harmful substances from the atmosphere has become more important and urgent. This paper examines the existing techniques for treating phthalates and degradation mechanisms, as well as knowledge gaps and future research directions. These technologies include adsorption, electrochemical, photocatalysis, membrane filtration and microbial degradation. Adsorption and photo catalysis are the most widely used techniques for phthalate removal, according to the literature survey papers.

Insights into photocatalytic degradation of phthalate esters over MSnO3 perovskites (M = Mg, Ca): Experiments and density functional theory

In this study, the physicochemical and photocatalytic properties of two kinds of stannate perovskite oxides (MgSnO₃ and CaSnO₃) were investigated under simulated sunlight, where dimethyl phthalate (DMP) and diethyl phthalate (DEP) were selected as the probe pollutants. The results of photochemical characterization showed that MgSnO₃ perovskite exhibited better photocatalytic performance than CaSnO₃ perovskite. MgSnO₃ perovskite could effectively degrade 75% of DMP and 79% of DEP through pseudo-first-order reaction kinetics, which remained good in pH 3.0 to 9.0. Quenching experiments and electron paramagnetic resonance (EPR) characterization indicated that photogenerated holes (h⁺), superoxide (O₂^-), and hydroxyl radicals (OH) worked in the photo-degradation, while O₂^- played the most important role. Furthermore, intermediates identification and density functional theory (DFT) calculations were used to explore the degradation mechanism. For both DMP and DEP, the reactive oxygen species (ROS, including O₂^- and OH) were responsible for the hydroxylation of benzene ring and the breaking of the aliphatic chain, while h⁺ was prone to break the aliphatic chain. This work is expected to provide new insights on the photocatalytic mechanism of stannate perovskites for environmental remediation.

Catalytic oxidation of dimethyl phthalate over titania-supported noble metal catalysts

Semi-volatile organic compounds (SVOCs) are organic compounds with the boiling point ranging between 240/260 ℃ and 380/400 ℃. Detailed knowledge regarding catalytic removal of SVOCs from indoor environment is very limited as it remains challenge to explore such reaction due to the viscosity nature of target contaminants. Here, we established a facile methodology to explore the heterogeneous catalytic oxidation reaction of dimethyl phthalate (DMP), a model SVOC, over the surface of supported catalyst. DMP was found to be gradually oxidized over the surface of titania supported catalysts including palladium (Pd), platinum and ruthenium with increasing temperature. The cleavage of side chain of DMP occurs at 75 ℃ over the surface of Pd/TiO₂, which is significantly lower than that of the other two catalysts. Carbon dioxide was observed as the main product of the catalytic oxidation reaction. However, aromatic products and small molecule products were still observed as side-product in different temperature range. Density functional theory calculations further show that DMP can react with reactive oxygen species to form phthalic acid. While the cleavage of the DMP side chain occurs to form products such as methyl benzoate. This work thus provides basic knowledge about indoor SVOCs catalytic oxidation removal.

Mechanistic evaluation of heterocyclic aromatic compounds mineralization by a Cu doped ZnO photo-catalyst

In this study, a Cu doped ZnO photo-catalyst was used for the degradation of the heterocyclic compounds, pyridine and quinoline.