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Recent advances in the removal of persistent organic pollutants (POPs) using multifunctional materials:a review
Abstract
Persistent organic pollutants (POPs) have gained heightened attentions in recent years owing to their persistent property and hazard influence on wild life and human beings. Removal of POPs using varieties of multifunctional materials have shown a promising prospect compared with conventional treatments. Herein, three main categories, including thermal degradation, electrochemical remediation, as well as photocatalytic degradation with the use of diverse catalytic materials, especially the recently developed prominent ones were comprehensively reviewed. Kinetic analysis and underlying mechanism for various POPs degradation processes were addressed in detail. The review also systematically documented how catalytic performance was dramatically affected by the nature of the material itself, the structure of target pollutants, reaction conditions and treatment techniques. Moreover, the future challenges and prospects of POPs degradation by means of multiple multifunctional materials were outlined accordingly. Knowing this is of immense significance to enhance our understanding of POPs remediation procedures and promote the development of novel multifunctional materials.
... Hazardous organic pollutants, such as dyes released into water bodies, contaminate water sources, affecting the health of humans, animals, and plants that depend on the water source. These dyes are reported to be toxic, carcinogenic, and mutagenic [3,4]. Therefore, removing toxic organic compounds from polluted waters to protect public health is an increasingly important and urgent issue. ...
... In practice, these values are lower. Therefore, it is possible that only a part of Cd 2+ and MoO 4 2ions adsorbs on the matrix and reacts with each other to form CdMoO 4 . ...
... The peak at 1383 cm -1 presents the C-O stretching vibrations of carboxyl groups[58]. The FTIR spectrum of pure CdMoO 4 exhibits a strong band at 777 cm -1 and a weak peak at 438 cm -1 , representing the stretching and bending vibration of the Mo-O-Mo bonds in the MoO4 2tetrahedron group. In addition, a broad peak at 3460 cm -1 and two sharp peaks at 1630 and 1395 cm -1 on this spectrum correspond to the valence and bending vibrations of the O-H bond of adsorbed water[43,44]. ...
CdMoO4/g-C3N4/GO composites were first synthesized by a hydrothermal process for the photocatalytic degradation of rhodamine B (RhB) under visible light illumination. The findings show that CdMoO4 is highly dispersed onto g-C3N4 and graphene oxide (GO) sheets. The surface area of the composite increased 27–30.5 times that of CdMoO4, and its band gap energy decreased by about 1.26 times. These features significantly improve the photocatalytic activity of the composite in the RhB decomposition reaction under visible light. The RhB degradation efficiency of the CdMoO4/g-C3N4/GO composite is 5.7, 1.36, and 1.65 times that of CdMoO4, CdMoO4/g-C3N4, and CdMoO4/GO composites, respectively. The active species trapping experiments show that the main forms in RhB degradation are •O2– , •OH, and h +. The stability of the photocatalyst is retained even after the 5th reuse. In addition, RhB degradation products were identified with the high-performance liquid chromatography-mass spectrometry method, and the pathway of photocatalytic degradation was also addressed.
... The oxidation process, which is complemented by Fig. 6.9 Degradation of POPs. (Sun et al., 2020) a few weak competitors, including hydrodechlorination, hydrodebromination, C-C bridge bond breaking, etc., is the predominant pathway in POP heat degradation. Through incremental electron uptake from O 2 deposited on the catalyst surface, oxygen species can be refilled. ...
... Photocatalysis mainly makes use of diverse semiconductors as its photocatalysts, including metal oxides, like TiO 2 (Dong et al., 2015), ZnO (Ong et al., 2018) (Li et al., 2014), silver phosphate (Ag 3 PO 4 ) (Liang et al., 2018), bi-based photocatalytic materials, and graphenebased photocatalytic materials (Sun et al., 2020). ...
The method’s QA/QC process begins with sample collection (water, sediment, and biota). The collection techniques utilized must yield a representative sample that remains unchanged throughout the collection. Silica rubber, low-density polyethylene (LDPE) bags, and semipermeable membrane device (SPMD) are powerful sampling tools that have recently been created and employed in aquatic environments. Extraction and fractionation techniques are presented. The most commonly used equipment for determining POPs is high-performance liquid chromatography (HPLC) and gas chromatography. The accuracy and precision of the procedures described should be verified.
... The oxidation process, which is complemented by Fig. 6.9 Degradation of POPs. (Sun et al., 2020) a few weak competitors, including hydrodechlorination, hydrodebromination, C-C bridge bond breaking, etc., is the predominant pathway in POP heat degradation. Through incremental electron uptake from O 2 deposited on the catalyst surface, oxygen species can be refilled. ...
... Photocatalysis mainly makes use of diverse semiconductors as its photocatalysts, including metal oxides, like TiO 2 (Dong et al., 2015), ZnO (Ong et al., 2018) (Li et al., 2014), silver phosphate (Ag 3 PO 4 ) (Liang et al., 2018), bi-based photocatalytic materials, and graphenebased photocatalytic materials (Sun et al., 2020). ...
... Hexachlorobenzene-a known carcinogen-raises similar concerns. These findings magnify the call for targeted interventions against persistent organic pollutants (POPs), which are commonly not removed by routine treatment methods [42,43]. ...
Groundwater pollution in landfill-adjacent regions presents a critical environmental and public health issue. This study evaluates groundwater quality in Xiangyang City, focusing on drinking water sources and key pollution points near landfill sites. The investigation involved a comprehensive field survey, systematic sampling, and laboratory analysis to determine pollutant types, sources, and concentrations. A total of 13 landfill sites were examined, with 178 groundwater samples analyzed for physical, chemical, and biological indicators during both wet and dry seasons. The findings reveal that 27.0% of groundwater samples meet Class I standards, while 46.1% and 27.0% fall into Class IV and V categories, respectively, indicating a significant prevalence of poor-quality groundwater. Seasonal variations were observed, with both wet and dry seasons showing consistent distributions of Class I, IV, and V samples. Heavy metals such as lead and arsenic, along with organic pollutants like polychlorinated biphenyls and pesticides (e.g., hexachlorobenzene), were significant contaminants in several sites. Key indicators such as nitrate, ammonia nitrogen, manganese, and total hardness consistently exceeded standard limits, with the most affected sites including L4 and L5 in Xiangyang. This study identifies leachate infiltration as the primary cause of pollution, exacerbated by geological and agricultural non-point sources. Based on these findings, a robust framework for monitoring and controlling groundwater pollution is proposed, emphasizing stricter regulations, advanced monitoring systems, and cross-regional coordination. The results underscore the urgency of immediate intervention to safeguard groundwater quality in landfill-adjacent regions.
... In this process, wastes are treated using dispersed metallic alkali. Chlorine in halogenated non-aqueous waste combines with metallic alkali to form salt and non-halogenated trash (Sun et al. 2020). ...
The occurrence of persistent organic pollutants (POPs) in almost every sphere of life and their notorious effects have been a global concern for quite a few decades, regardless of the fact that notable conventions have banned the standard POPs. Control measures and numerous technologies are being researched, but still exhibits challenges to completely curb these chemicals’ destructive effects. The negative impacts of the POPs in terms of environmental and human health are a growing concern. In recent years, studies have proven that the list of POPs keeps increasing, and their concentrations levels are widely varied region wise. The current review presents sources and classification of POPs. Furthermore, the deleterious consequences due to POPs on environment and human health have been illustrated. A few potential methodologies that can be implemented to control the hazardous effects of POPs have been discussed.
... In this sense, heterogeneous photocatalysis is an Advanced Oxidation Process (AOP) that guarantees improved pollutant degradation rates under ambient operating conditions. In addition, it ensures a decrease in the concentration of pollutants by reducing toxicity at high degradation rates [11][12][13]. Among the semiconductors nanoparticles studied as promising photocatalysts, the highlights are titanium dioxide (TiO 2 ), zinc oxide (ZnO), iron (III) oxide (Fe 2 O 3 ), aluminium oxide (Al 2 O 3 ) and cerium (IV) oxide (CeO 2 ) [14][15][16]. ...
... However, due to the sharp increase in the world's human population, accelerating urbanization, industrialization, and pollution from anthropogenic sources, natural inland waters have undergone significant change, with detrimental consequences for both aquatic ecosystems and people [22,23]. Thus, these organic pollutants produced from many industries are creating rising alarms and gaining great importance [24][25][26]. Synthetic dyes are considered one of the most common pollutants that are discharged as effluents into freshwater and other aquatic ecosystems from different industries such as textile and cloth dyeing, paper manufacturing, printing, color photography, food products, pharmaceuticals, and cosmetics [27]. Annually, about 800,000 tons of synthetic dyes are produced (50% azo dyes) [28], and approximately 10-15% of these dyes are discharged into aquatic ecosystems and cause an undeniable environmental problem due to their stability against light, temperature, and biodegradation [29]. ...
The current study aimed to investigate the potentiality of yeast isolate Rhodotorula toruloides Y1124 to be used as a feedstock for biodiesel production, and the reutilization of the de-oiled yeast biomass wastes as a biosorbent for the biosorption of Congo red from aquatic solutions was investigated. From screening results, eight yeast isolates were referred to as oleaginous microorganisms, of which yeast isolate Rhodotorula toruloides Y1124 was the highest lipid-accumulating isolate and was used as a feedstock for biodiesel production. The highest lipid accumulation (64.8%) was significantly dependent on the glucose concentration, pH, and incubation temperature according to Plackett–Burman and central composite design results. Under optimized conditions, the estimated amount of biodiesel synthesis from Rhodotorula toruloides biomass represented 82.12% of total analytes. The most prevalent fatty acid methyl esters were hexadecanoic and 11-octadecenoic, comprising 30.04 and 39.36% of total methyl esters which were compatible with plant oils. The optimum biosorption conditions for Congo red removal were pH 6, a 15 min contact time, and an initial dye concentration of 40 mg L−1. The biosorption isothermal and kinetics fitted well with the Langmuir model and the maximal biosorption capacity (qmax) was 81.697 mg g−1. Therefore, the current study may offer a sustainable feedstock with potential viability for both the synthesis of biodiesel and the removal of organic dyes.
... POPs are persistent and bioaccumulative with the potential of long-range transport via multiple environmental media (86). Many POPs have been listed in the Stockholm Convention of the United Nations Environment Programme, and the list is growing (87). ...
Groundwater deterioration due to enrichment with contaminants of either geogenic or anthropogenic origin has adversely affected safe water supply for drinking and irrigation, with pervasive impacts on human health and ecosystem functions. However, the spatiotemporal evolution and public health effects of groundwater quality remain unclarified, posing a grand challenge for the safe and sustainable supply of global groundwater resources. This article provides a state-of-the-art review of the complexity and dynamics of groundwater quality, as well as the impacts of various groundwater substances on human health. In particular, knowledge is growing about the health impacts of key substances ranging from nutritional elements (e.g., Ca ²⁺ , Mg ²⁺ ) to pollutants (e.g., heavy metals/metalloids, persistent organic pollutants, and emerging contaminants) and, further, to pathogenic microorganisms to which the human body can be exposed through multiple patterns of groundwater use. Proliferating concerns at the same time call for enhancing, science-based governance directives, economic policies, and management strategies coordinating groundwater quality. We propose that safeguarding groundwater-dependent public health needs concerted efforts in source control, cross-scale rehabilitation, and social hydrology-based groundwater governance.
Expected final online publication date for the Annual Review of Environment and Resources, Volume 48 is October 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... POPs have a low solubility, which makes them resistant to biological, chemical, and photo-degradation. It is also challenging to break down POPs using conventional wastewater-treatment methods [19,20]. In the recent past, POP cleanup was accomplished using cutting-edge wastewater-treatment technology or by combining one or more techniques. ...
... Among the 22 pesticides investigated here, nine are banned in Brazil (aldicarb, aldrin, carbofuran, carbendazim, chlordane, DDT, lindane, methamidophos, and molinate; Table 1). Aldrin, chlordane, DDT, and lindane are classified as persistent organic pollutants (POPs), characterized by their high persistence, high capacity for bioaccumulation, high toxicity, and potential for long-range transport (Sun et al., 2020). The Stockholm Convention controls POPs by restricting or banning their use (http://www.pops.int/). ...
Pesticide contamination in water resources is a global threat. Although usually found at low concentrations, pesticides raise considerable toxicological concerns, mainly when mixtures are considered. The occurrence of 22 pesticides (2,4 D, alachlor, aldicarb, aldrin, atrazine, carbendazim, carbofuran, chlordane, chlorpyrifos, DDT, diuron, glyphosate, lindane, mancozeb, methamidophos, metolachlor, molinate, profenofos, simazine, tebuconazole, terbufos, and trifluralin) was investigated, through consolidated database information, in surface freshwaters of Brazil. Moreover, scenarios of environmental risk assessment considering isolated compounds and mixtures were performed, as well as a meta-analytic approach for toxicity purposes. Pesticides in freshwater have been reported from 719 cities (12.9% of Brazilian cities), where 179 (3.2%) showed pesticide occurrence above the limit of detection or quantification. Considering cities with more than five quantified, 16 cities were prone to environmental risks considering individual risks. However, the number increased to 117 cities when the pesticide mixture was considered. The mixture risk was driven by atrazine, chlorpyrifos, and DDT. The national maximum acceptable concentrations (MAC) for nearly all pesticides are higher than the predicted no-effect concentration (PNEC) for the species evaluated, except aldrin. Our results show the need to consider mixtures in the environmental risk assessment to avoid underestimation and review MAC to protect aquatic ecosystems. The results presented here may guide the revision of the national environmental legislation to ensure the protection of Brazilian aquatic ecosystems.
... In adsorption processes, the pollutant molecules in water interact and get attached to the surface of a solid material (called adsorbent), and are then removed from solution. 3,17 A lot of different materials can be used as adsorbents, allowing the removal of different pollutants, but there is always a strong need of new adsorbent materials in order to provide viable and effective depollution processes with adsorbents that are low-cost, easily removed from polluted media and ideally also recyclable. 3 In recent years, a lot of attention has been paid to nanomaterials for depollution applications because they display high surface area, 18 allowing a high contact surface with the pollutant molecules and thus making them attractive for adsorption applications. Among promising nano-sized adsorbents, graphene and graphene-based materials are well-known to be highly efficient adsorbents of organic pollutants, due to π-π stacking interactions between the aromatic rings of graphene and the unsaturated organic pollutant molecules including the aromatics. ...
Regarding the importance of water pollution by persistent organic pollutants and the need for innovative processes to extract them efficiently, we designed magnetic few-layers graphene-based composite nanomaterials (CNs) for high...
We reported the fabrication of a substrate with cavity-nanorod and decorated by Ag-nanoplates (C-NR@Ag). The cavities on the substrate are formed by metal assistant chemical etching (MACE), and Ag-nanoplates in...
Background: Leachate, containing challenging-to-degrade organic substances and persistent toxins, poses significant environmental concerns. Advanced oxidation processes (AOPs) have emerged as a promising solution for effective leachate treatment. This research provides a comprehensive review of the impact of various AOPs in leachate treatment. Methods: This systematic review was conducted, encompassing commonly used AOPs such as ozone, peroxone, O3 /catalyst, Fenton, photo-Fenton, UV/TiO2 , photolytic persulfate, O3 /UV, and O3 /H2 O2 / UV. Extensive searches were performed using reputable databases, including EBSCO, PubMed, Web of Science, and Google Scholar. Specific keywords and inclusion/exclusion criteria were applied. Data regarding leachate treatment parameters were meticulously summarized and analyzed using descriptive statistical methods. Results: The efficiency of AOPs in removing leachate organic matter varied, with chemical oxygen demand (COD) removal ranging from 41% to 83% in treatment systems. The order of effectiveness was found to be: O3 /UV/H2 O2>photo-Fenton>UV/TiO2>Fenton>persulfate (PS)>O3 /UV>O3 /H2 O2>O3 / catalyst>ozonation (O3 ). The highest COD removal efficiency of 83.75% was achieved using the O3 /UV/ H2 O2 AOP approach. The removal efficiency of color also varied, ranging from 32% to 100%, depending on the leachate’s characteristics, concentration, and specific treatment process utilized. Conclusion: AOPs, particularly the hybrid approach using O3 /UV/H2 O2 , significantly enhance waste leachate treatment by effectively degrading persistent organic compounds through the generation of hydroxyl radicals. Further research is required to optimize AOPs and improve their efficiency in waste leachate treatment.
The continuous rise of emerging contaminants (ECs) in the environment has been a growing concern due to their potentially harmful effects on humans, animals, plants, and aquatic life, even at low concentrations. ECs include human and veterinary pharmaceuticals, hormones, personal care products, pesticides, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organic dyes, heavy metals (HMs), and others. The world's growing population contributes to the release of many kinds of chemicals into the environment, which is estimated to be more than 200 billion metric tons annually and results in over 9 million deaths. The removal of these contaminants using conventional physical, chemical, and biological treatments has proven to be ineffective, highlighting the need for simple, effective, inexpesive, practical, and eco-friendly alternatives. Thus, this article discusses the utilization of subcritical water oxidation (SBWO) and subcritical water extraction (SBWE) techniques to remove ECS from the environment. Subcritical water (water below the critical temperature of 374.15 °C and critical pressure of 22.1 Mpa) has emerged as one of the most promising methods for remediation of ECs from the environment due to its non-toxic properties, simplicity and efficiency of application. Furthermore, the impact of temperature, pressure, treatment time, and utilization of chelating agents, organic modifiers, and oxidizing agents in the static and dynamic modes was investigated to establish the best conditions for high ECs removal efficiencies.
This paper aims to emphasize the occurrence of various emerging contaminant (EC) mixtures in natural ecosystems and highlights the primary concern arising from the unregulated release into soil and water, along with their impacts on human health. Emerging contaminant mixtures, including pharmaceuticals, personal care
products, dioxins, polychlorinated biphenyls, pesticides, antibiotics, biocides, surfactants, phthalates, enteric viruses, and microplastics (MPs), are considered toxic contaminants with grave implications. MPs play a crucial role in transporting pollutants to aquatic and terrestrial ecosystems as they interact with the various components
of the soil and water environments. This review summarizes that major emerging contaminants (ECs), like trimethoprim, diclofenac, sulfamethoxazole, and 17α-Ethinylestradiol, pose serious threats to public health and contribute to antimicrobial resistance. In addressing human health concerns and remediation techniques, this
review critically evaluates conventional methods for removing ECs from complex matrices. The diverse physiochemical properties of surrounding environments facilitate the partitioning of ECs into sediments and other organic phases, resulting in carcinogenic, teratogenic, and estrogenic effects through active catalytic interactions and mechanisms mediated by aryl hydrocarbon receptors. The proactive toxicity of ECs mixture complexation
and, in part, the yet-to-be-identified environmental mixtures of ECs represent a blind spot in current literature, necessitating conceptual frameworks for assessing the toxicity and risks with individual components and mixtures. Lastly, this review concludes with an in-depth exploration of future scopes, knowledge gaps, and challenges, emphasizing the need for a concerted effort in managing ECs and other organic pollutants.
The implementation of photoelectrochemical water purification technology can address prevailing environmental challenges that impede the advancement and prosperity of human society. In this study, Cu, which is abundant on Earth, was fabricated using an electrochemical deposition process, in which the preferential orientation direction and carrier concentration of the Cu-based oxide semiconductor were artificially adjusted by carefully controlling the OH– and applied voltage. In particular, Cu2O grown with a sufficient supply of OH– ions exhibited the (111) preferred orientation, and the (200) surface facet was exposed, independently achieving 90% decomposition efficiency in a methyl orange (MO) solution for 100 min. This specialized method minimizes the recombination loss of electron–hole pairs by increasing the charge separation and transport efficiency of the bulk and surface of the Cu2O multifunctional absorption layer. These discoveries and comprehension not only offer valuable perspectives on mitigating self-photocorrosion in Cu2O absorbing layers but also provide a convenient and expeditious method for the mass production of water purification systems that harness unlimited solar energy. These properties enable significant energy saving and promote high-speed independent removal of organic pollutants (i.e., MO reduction) during the water purification process.
The accumulation, fate, and destiny of persistent organic pollutants (POPs) in aquatic systems are all influenced by a variety of factors. The primary fate of POPs in the marine environment is through atmospheric deposition at the air-sea interface. Diffuse vapor exchange, aerosol-vapor partitioning, precipitation scavenging of vapors and particle-sorbed chemicals, and dry particle deposition are the processes that contribute to the exchange of POPs between the air and the sea. A second important route for POPs is when they attach to settling particles in municipal or industrial effluents and are deposited in the bottom sediment (BS). POPs have a high bioaccumulation and biomagnification potential. It is advised to use a variety of remediation methods to remove POPs from aquatic environments. The emphasis is on models for predicting the annual contribution rate of POPs. The greatest challenges for the safety environment are raising managerial capacity and public awareness about POPs. Numerous international agreements have been formed to limit POP emissions and lessen environmental pollution, such as the Stockholm Convention on POPs, which is ratified by 186 countries. An international negotiating committee (INC) (12 POPs) was established by the United Nation Environment Program (UNEP) Governing Council in 1997 through decision 19/13C. At a Conference of Plenipotentiaries convened in Stockholm, Sweden, in 2001, the Stockholm Convention was adopted and made available for signature. In 2004, the Convention became operative. In the end, the Stockholm Convention included perfluorooctanoic acid (PFOA) and its salts in 2019. The Stockholm Convention review, which was finished in 2022, found that many governments still needed to improve the domestic legal, administrative, and other measures to manage POPs. This included creating or updating national laws and regulations pertaining to POPs and their waste.
Perfluorooctane Sulfonate (PFOS) is widely used in various commercial applications, including food packaging, fabrics, and fire-fighting foams. This toxic and carcinogenic compound could be present in water and food products, which could be fatal to living beings. Zeolite-based materials are promising PFOS sorbents due to their high anion exchange capacity and specific surface area. In this study, a natural Clinoptilolite-type zeolite was modified with Hexadecyl Trimetilammonium Bromide (HDTMA) for PFOS remediation in aqueous solutions. The modification introduced an inversion of Clinoptilolite's natural surface net charge, i.e., from negative to positive, making it effective in capturing PFOS. At pH 7, the modified material (Clinop_HDTMA) showed ~ 96–98% removal of PFOS at a low concentration range of 0.5–1 mg L−1. The adsorption isotherm and kinetic data followed the Freundlich and pseudo second-order model, respectively, which suggested the involvement of physicochemical forces in the adsorption process. Thus, this study demonstrates a viable and cost-effective solution to remove PFOS ions from wastewater.
Persistent organic pollutants (POPs) are one of the important concerns in the environmental sciences and ecotoxicology fields. Various deadly illnesses and environmental problems are caused by them. It is a major issue in society that there are no new and effective ways to eliminate POPs from the atmosphere. Nanotechnology is a rapidly developing area that has uses in every aspect of life. A lot of attention is being paid to the investigation of novel synthetic methods for shaping and controlling the size of nanomaterials due to their outstanding uses and qualities. One of the most significant groups of nanoparticles is the magnetic nanoparticles. A novel class of magnetic separation techniques for water treatment has been made possible through the utilization of magnetic nanoparticles as nano adsorbents. Our aim in this study is to give a concise, focused review of POP, emphasize the sources, types, and potentially hazardous impacts they have on living organisms, and to offer some observations on their detection and monitoring strategies. To draw attention to certain significant conventional removal technologies and recent developments including nanotechnology, magnetic nanoparticles, and their synthesis. Finally, hybrid nanotechnology for POP removal has been investigated.
Landfilling and open dumping have been the most widely used municipal solid waste (MSW) management strategies over the past decades due to lower costs and less treatment efforts. However, landfilling continues to be an acceptable final disposal strategy for MSW. Non-sanitary landfill sites (lacking modern environmental technology) that rely on direct landfilling without waste pre-treatment pose a significant threat to the entire ecosystem. Many of these sites are situated in environments adjacent to residential districts or water bodies, affecting the local environment and population health. The assessment of the environmental impact of landfills is thus a key issue in the literature that has recently received more attention as a result of growing environmental concerns. This chapters reviews the major impacts due to waste mismanagement worldwide, particularly in developing countries where the unsustainable management of solid waste is common. Potential analytes and composition found in MSW landfills and their related risk assessment are also highlighted in this book chapter with a focus on heavy metals accumulation. This narrative literature review assessed global issues due to improper waste management and showing how potential contaminants found within landfills waste can affect the environment and human health. It can also be of reference for scholars and stakeholders to evaluate and estimate the potential risk posed by poor MSW management in order to improve sustainability at a global level.
The adsorption and degradation capacities of dichlorodiphenyltrichloroethane (DDT) on a photocatalyst composed of TiO2 supported on the mesoporous material MCM-41 (TiO2/MCM-41) were investigated using density functional theory and real-time density functional theory methods. The van der Waals interactions within the PBE functional were adjusted by using the Grimme approach. The adsorption of DDT was evaluated through analyses involving adsorption energy, Hirshfeld atomic charges, Wiberg bond orders, molecular electrostatic potential, noncovalent interaction analysis, and bond path analysis. The findings reveal that DDT undergoes physical adsorption on pristine MCM-41 or MCM-41 modified with Al or Fe due to the very small bond order (only about 0.15–0.18) as well as the change in total charge of DDT after adsorption is close to 0. However, it chemically adsorbs onto the TiO2/MCM-41 composite through the formation of Ti···Cl coordination bonds because the maximum bond order is very large, about 1.0 (it can be considered as a single bond). The adsorption process is significantly influenced by van der Waals interactions (accounting for approximately 30–40% of the interaction energy), hydrogen bonding, and halogen bonding. MCM-41 is demonstrated to concurrently function as a support for the TiO2 photocatalyst, creating a synergistic effect that enhances the photocatalytic activity of TiO2. Based on the computational results, a novel photocatalytic mechanism for the degradation of DDT on the TiO2/MCM-41 catalyst system was proposed.
Billions of people globally live under conditions of water stress and water shortage, or with contaminated water sources. Anthropogenic contaminants pose an extra challenge as water purification technology must be constantly developed or upgraded to deal with newly fabricated pollutants.
One of the UN sustainable development goals is to ensure availability and sustainable management of water and sanitation for all. Therefore, it is vital to develop novel materials and technologies for producing clean drinking water in a human safe, economically reasonable and environmentally sustainable way.
Novel Materials and Water Purification introduces recent approaches to the fabrication of novel material’ for water purification and discusses several significant applications including removal of heavy metals and pharmaceuticals. This is a timely work of high interest to researchers and learners in the fields of water science, water management and materials science.
The increasing presence of chemical contaminants in the environment due to demands associated with a growing population and industrial development poses risks to human health due to their exposure. Electrochemical...
Currently, nanomaterials are an important class of materials in the field of synthesis of efficient and selective catalysts with desired properties due to their unique physical and chemical properties. The presence of nanosized particles of transition metals undoubtedly improves the course of the hydrodechlorination of polychlorinated biphenyls (PCBs) and makes it possible to reduce the content of the noble metal in the catalyst. In order to obtain active and stable heterogeneous catalysts for the neutralization of persistent organic pollutants (POPs), the correct choice of carrier and method of catalyst synthesis is required. In this work, the synthesis of a nickel nanocatalyst was carried out using the wet impregnation method for the hydrodechlorination of PCBs. Commercial activated carbon grade BAU-A was pre-modified with hydrochloric acid and used as a carrier (AC m ) of the catalyst. Using modern physical and chemical methods, the main properties of the synthesized nanocatalyst were investigated. The IR spectroscopy has established that the carboxyl and carbonyl groups of AC m are the main functional groups that fix nickel in the bulk of the carrier. The nickel nanocatalyst has a developed surface, where nickel nanoparticles are deposited in micro- and mesopores of the carrier. The degree of conversion of 2,2',3,3',4-pentachlorobiphenyl is 84.21%, which indicates the catalytic activity of nickel nanocatalysts with respect to POPs.
Peroxymonosulfate‐based advanced oxidation processes (PMS‐AOPs) for in situ persistent organic pollutant (POP) remediation in aqueous solutions can be a promising technology. However, this technology is constrained by its high toxicity and cost of metal oxide and non‐metal catalysts for PMS activation. Here, we investigated the catalytic performance of a widely available natural mineral, manganese ore (MO), for PMS activation. A series of natural MO samples in an aqueous solution were prepared via the Fenton‐like reaction. The samples' crystalline structure, surface morphology, textural properties, and other surface characteristics of the selected MO were systematically characterized. The effects of PMS concentration and process parameters on the degradation performance of four chosen model pollutants, that is, phenol, tetrabromobisphenol A (TBBPA), rhodamine B (RhB), and methylene blue (MB), were evaluated. The experimental results showed that natural MO increased catalytic activity and enhanced the PMS oxidation processes, with 98%, 90%, and 75% removal efficiencies on phenol, TBBPA, and RhB, respectively, within 1.5 h. The reduction in the initial pH solution from 10 to 7 and the increase in temperature from 15 to 45°C enhanced the MB degradation rate (decolorization) by 55 and 46%, respectively, within 2 h. During the PMS activation process, SO 4 •− , • OH, and ¹ O 2 species were generated, but only SO 4 •− and • OH radicals with strong oxidative potentials contributed to the catalytic degradation. The dissolved metals from the experiments were found well within the limit of drinking water standards, verifying that the MO + PMS catalytic system is suitable for commercial applications. This work provides insights into the development potential and prospects of using natural minerals for PMS activation and POP degradation, which can accelerate their industrial applications.
The intensification of industrial activities and urbanization have significantly increased the discharge of huge amount of toxic and recalcitrant pollutants into
the water bodies. Among these, persistent organic pollutants (POPs) are considered
highly toxic to aquatic ecosystem as well as human and animals due to their pervasive
and bio-accumulative in behaviour. Moreover, these pollutants are not effectively
eliminated by conventional wastewater treatment systems due to their recalcitrant
nature; thus, trace concentrations of these persistent pollutants are detected in the
effluent of wastewater treatment plants (WWTPs). In this regard, to achieve the safe
discharge of POPs laden wastewater into the receiving water bodies, electrochemical technologies, such as electrocoagulation (EC), anodic electrochemical oxidation (AO) and electro-Fenton (EF), have demonstrated the potential to effectively
eliminate the POPs from contaminated water. Thus, this chapter aims to annotate the
basic principles, advantages, disadvantages, application status of electrode materials,
electrocatalysts and latest advancement in the field of electrochemical technologies. Moreover, the factors affecting the performance, bottlenecks, future research directions and status of commercialization of electrochemical technologies also have been articulated in the present chapter for the benefit of the researchers for commercial utilization of these technologies in near future.
The global decline in the atmosphere caused by the release of hazardous material, produced by the entry of chemical and physical or biological elements from anthropogenic, geogenic, or biogenic activities, is becoming a severe problem worldwide. This raises many human and animal health problems, and it can wipe out all living things, further complicating the use of conventional treatment technologies. However, the majority of the work has been done for the removal of oxides of carbon, nitrogen, and sulfur; however, dangerous chemicals such as hydrocarbons, aliphatic, aromatic, complex compounds and chlorofluorocarbons that are released into the air from a variety of sources must be eradicated before they reach an unsafe level. Hence, this study illuminates current advances in nanotechnology and their critical role to include the overpowering need to monitor and treat growing dangerous wastes more efficiently at low cost and with less energy. Interestingly, the main features of this article are to outline the benefits of nanotechnology above traditional methods quickly and to relevantly highlight the removal of toxic chemicals, bioaerosols, heavy metals, and organic and inorganic pollutants from the air spectrum. Nanotechnological methods such as thermal breakdown, adsorption, absorption, air filtration, and photocatalytic degradation will be used in the future to get rid of these dangerous substances. Nanotechnology possesses three essential characteristics that enable its application to environmental areas: purification and remediation (cleanup), contaminants identification (detection and sensing), and pollution prevention. In conclusion, nanotechnology is utilized to avoid pollution from a variety of sources that are damaging to various systems owing to its unique physical and chemical features.
The increase in the world’s population in the twentieth century resulted in the subsequent increase in the demand for food. To enhance the constant supply of food for this large population and sustainable crop production, different types of agrochemicals such as fertilizers, pesticides, fungicides, and herbicides were used by farmers for decades. Pesticides are mainly categorized as herbicides, fungicides, and insecticides based on the target they killed. Pesticides and herbicides are designed to kill and prevent pests and unwanted weeds respectively. As their mode of action is not species specific, they often harm other organisms including crops in the agricultural field when used in excess amounts. Over time, insects and weeds become adapted and develop resistance to such chemicals, which necessitates the excessive amount of usage and development of new chemical compounds to protect crops. In many developing countries cheap compounds, such as dichloro-diphenyl-trichloroethane (DDT), hexachlorocyclohexane (HCH), and lindane are popular among farmers, even though they are environmentally persistent and have a toxic effect on soil flora and fauna. Thus, the pesticide and herbicide compounds have emerged as a new global concern owing to their several phytotoxic effects. Moreover, the development of leaf and crop growth rate, and the nutritive composition of seeds, specifically the content of proteins, fall sharply following pesticide treatment. The herbicides and pesticides cause several cytotoxic and genotoxic effects which ultimately challenge the stability of the plant genome through the production of reactive oxygen compounds. To combat these stress conditions, plants have evolved several biochemical, physiological, transcriptional, and epigenetic strategies that together help to maintain the growth and development of plants. In this present book chapter, we summarize the harmful effects of pesticides and herbicides on crop plants and the different strategies evolved by plants to combat these emerging stress compounds to sustain growth and eventually survivability.
A perfluorooctanoic acid (PFOA), as the most important representative of perfluorocarboxylic acids (PFCAs), is environmentally persistent and bioaccumulative. Among treatment techniques for PFOA decomposition, photocatalytic degradation of PFOA has received considerable attention. A series of candidate photocatalytic materials, including TiO2‐, carbonaceous‐, Ga2O3‐, In2O3‐based, etc., have been successfully proposed to eliminate PFOA. Overall, there are two types of mechanisms for photocatalytic degradation of PFCAs, including conventional mechanism and charge transfer mechanism. For a conventional mechanism, the mechanism of PFOA photodegradation over bulk TiO2 via two pathways: photo‐redox and β‐scission. For the charge transfer mechanism, the PFOA degradation pathway in water‐soluble H3PW12O40 is mainly via charge‐transfer excited complex ([PW12O40]3−*). Finally, attention on critical challenges and prospects for photodegradation of PFOA are also intensified. © 2020 Society of Chemical Industry
Nanoparticles of four noble metal doped titanium dioxide (i.e., Pd/TiO2, Ag/TiO2, Pt/TiO2 and Cu/TiO2) were synthesized and investigated for their effectiveness to degrade polybrominated diphenyl ethers (PBDEs) under UV light. All the investigated noble metal additives can greatly enhance the performance of TiO2 to degrade 2,2′,4′,4′-tetrabromodiphenyl ether (BDE-47). However, the debromination pathways of BDE-47 in Ag/TiO2 and Cu/TiO2 systems are just contrary to those in Pd/TiO2 and Pt/TiO2 systems, and there was an induction period in the former systems but not in the latter systems. The hydrogenation experiment suggests a direct H-atom transfer mechanism in Pd/TiO2 and Pt/TiO2 systems, while in Ag/TiO2 and Cu/TiO2 systems, electron transfer is still the dominant mechanism. Electronic method was applied to explain why BDE-47 exhibit different debromination pathways based on different degradation mechanism. In addition, oxygen was proved to be able to capture both electrons and H atoms, and thus can greatly inhibit the degradation of PBDEs in all investigated systems. Finally, the merit and demerit of each metal doped TiO2 were discussed in detail, including the reactivity, stability and the generation of byproducts. We proposed our study greatly enhance our understanding on the mechanisms of PBDE degradation in various metal doped TiO2 systems. Keywords: Polybrominated diphenyl ethers, Debromination pathways, Photocatalytic degradation, Mechanisms, Titanium dioxide
A relatively new approach to the design of photocatalytic and gas sensing materials is to use the shape-controlled nanocrystals with well-defined facets exposed to light or gas molecules. An abrupt increase in a number of papers on the synthesis and characterization of metal oxide semiconductors such as a TiO2, α-Fe2O3, Cu2O of low-dimensionality, applied to surface-controlled photocatalysis and gas sensing, has been recently observed. The aim of this paper is to review the work performed in this field of research. Here, the focus is on the mechanism and processes that affect the growth of nanocrystals, their morphological, electrical, and optical properties and finally their photocatalytic as well as gas sensing performance.
The effect of NaCl addition on the properties, activity, and deactivation of a V2O5-WO3/nano-TiO2 catalyst was investigated during catalytic decomposition of gas-phase polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). The extent of deactivation relates directly to the NaCl loading of the catalyst. Poisoning by sodium neutralizes acid sites, interacts strongly with active VOx species, and reduces the redox capacity of catalysts. In addition, NaCl is also a chlorine source and may actually accelerate the synthesis of new PCDD/Fs. Washing a catalyst with dilute sulfuric acid largely restores catalytic activity, breaking the interaction of Na⁺ ions and dispersed vanadia and removing Na from the catalyst surface. Consequently, catalyst acidity and redox capacity almost recover. Furthermore, sulfate residues react with surface adsorbed water to generate Brønsted acid sites, ensuing a surge of strong acidity of the catalysts.
Soil contamination by persistent organic pollutants (POPs) poses a great threat to historically polluted soil worldwide. In this study, soils were characterized, and organochlorine pesticides contained in the soils were identified and quantified. Individual electrokinetic (IE), EK-Fenton-coupled technologies (EF), and enhanced EK-Fenton treatment (E-1, E-2, and E-3) were applied to remediate soils contaminated with hexachloro-cyclohexane soprocide (HCH) and dichloro-diphenyl-trichloroethane (DDT). Variation of pH, electrical conductivity, and electroosmotic flow was evaluated during the EK-Fenton process. The IE treatment showed low removal efficiency for HCHs (30.5%) and DDTs (25.9%). In the EF treatment, the highest removal level (60.9%) was obtained for α-HCH, whereas P,P-DDT was the lowest (40.0%). Low solubility of pollutants impeded the HCH and DDT removal. After enhanced EK-Fenton treatment, final removal of pollutants decreased as follows: β-HCH (82.6%) > γ-HCH (81.6%) > α-HCH (81.2%) > δ-HCH (80.0%) > P,P-DDD (73.8%) > P,P-DDE (73.1%) > P,P-DDT (72.6%) > O,P-DDT (71.5%). The results demonstrate that EK-Fenton is a promising technology for POP removal in historically polluted soil.
This study is focused on the effective removal of recalcitrant pollutants hexaclorocyclohexanes (HCHs, isomers α, β, γ, and δ) and chlorobenzenes (CBs) present in a real groundwater coming from a landfill of an old lindane factory. Groundwater is characterized by a total organic carbon (TOC) content of 9 mg L⁻¹, pH0 = 7, conductivity = 3.7 mS cm⁻¹, high salt concentration (SO4²⁻, HCO3⁻, Cl⁻), and ferrous iron in solution. The experiments were performed using a BDD anode and a carbon felt (CF) cathode at the natural groundwater pH and without addition of supporting electrolyte. The complete depletion of the four HCH isomers and a mineralization degree of 90% were reached at 4-h electrolysis with a current intensity of 400 mA, the residual TOC (0.8 mg L⁻¹) corresponding mainly to formic acid. A parallel series reaction pathway was proposed: HCHs and CBs are transformed into chlorinated and hydroxylated intermediates that are rapidly oxidized to non-toxic carboxylic acids and/or mineralized, leading to a rapid decrease in solution pH.
In this study, novel ZnS@In2S3 core@shell hollow nanospheres were fabricated by a facile refluxing method for the first time, and the formation mechanism of hollow structure with interior architecture was discussed based on ion-exchange Ostwald ripening. As the photocatalytic material for degradation of gaseous o-Dichlorobenzene (o-DCB), the as-synthesized core@shell hollow nanospheres were found to show significantly enhanced catalytic performance for effective separation of photo-generated charges. Moreover, the mechanisms of enhanced activity were elucidated by band alignment and unique configuration. Such photocatalyst would meet the demands for the control of persistent organic pollutant (POPs) in the atmospheric environment.
This study investigates electrooxidation of short (C3-C6) and long (C7-C-18) chain perfluorocarboxylic acids (PFCAs) including perfluorooctane sulfonate (PFOA) using Si/BDD electrode. The effect of operational parameters (supporting electrolyte type, applied current density, and initial pH) were explored for PFOA removal. At the optimized conditions, 74% TOC removal and 37% defluorination ratio were gained for 10 mg L-1 of PFOA solution which evidences that the shorter chain PFCAs were formed. The PFOA degradation pathway followed one direct electron transfer from PFOA molecule to anode surface. Then two different degradation pathways were proposed. The first proposed degradation mechanism involved the reaction of perfluoroheptyl radical and hydroxyl radical, the release of HF and hydrolysis. The second mechanism involved the reaction between perfluoroheptyl radical and O2, formation of C7F15O and perfluorohexyl radical with releasing COF2. The removal of short- (C3-C6) and long-chain PFCAs (C7-C18) was also characterized. More than 95% of removal efficiency was gained for all long-chain PFCAs, excluding C7. The removal ratios of short-chain PFCAs (C3-C6) were 39%, 41%, 66% and 70% for C3, C4, C5 and C6, respectively. Contrary to long-chain PFCAs, chain-length dependence for short-chain PFCAs were observed. Defluorination ratio of short-chain PFCAs was only 45% signifying that defluorination partially occurred. Water matrix did not significantly affect the degradation of short-chain PFCAs in deionized water (DI), river water and secondary effluent of a wastewater treatment plant (WWTP). In contrast, defluorination ratio of long-chain PFCAs was noticeably affected by water matrix with the order of DI water > WWTP effluent > river water.
This study examined the degradation of perfluorooctanesulfonate (PFOS) in an electrochemical system using Magnéli phase titanium suboxide (Ti4O7) as the anode. In particular, the influence of chloride on the treatment process was examined. Tests were also conducted with boron doped diamond (BDD) electrodes for comparison. Experimental data demonstrated that PFOS was effectively degraded by electrochemical oxidation on both BDD and Magnéli phase Ti4O7 anodes. It appeared that PFOS degradation occurred via direct electron transfer (DET) in combination with attack by hydroxyl radicals adsorbed on the anode surface (HO•ads) that were formed by anodic oxidation of water. The presence of Cl− inhibited the degradation of the PFOS on Ti4O7 electrode by suppressing the oxidation of water, but accelerated PFOS degradation on BDD electrode, where the oxidation of Cl− via DET occurred. Formation of chlorate and perchlorate was slower on Ti4O7 than on the BDD anode. The mechanisms governing the behavior of PFOS and chloride reactions on BDD and Ti4O7 anodes were explored by experiments in combination with density functional theory (DFT) computations.
Perfluorooctanoic acid (PFOA) has attracted considerable attention worldwide due to its widespread occurrence and environmental impacts. This research focused on the photocatalytic process for the treatment of PFOA in water and wastewater. Gallium oxide (Ga2O3) and peroxymonosulfate (PMS) were mixed directly in PFOA solution, which was irradiated under different light sources. The treatment system showed excellent performance that 100% PFOA was degraded within 90 min and 60 min under 254 nm and 185 nm UV irradiation, respectively. Moreover, the degradation efficacy was unaffected by initial PFOA concentration from 50 ng L-1 to 50 mg L-1. Acidic solution (pH 3) improved the degradation process. The quantum yield in the PMS/Ga2O3 system under UV light (254 nm) was estimated to be 0.009 mol E-1. Scavengers such as tert-butanol (t-BuOH), disodium ethylenediaminetetraacetate (EDTA-Na2) and benzoquinone (BQ) were added into PFOA solution to prove that sulfate radicals (SO4•-), superoxide radical (O2•-) and photogenerated electrons (e-) were the main active species with strong redox ability for PFOA degradation in PMS/Ga2O3/UV system. Combined with the intermediates analysis, PFOA was degraded stepwise from long chain compound to shorter chain intermediates. In addition, PFOA in real wastewater exhibited similar degradation efficiency, together with 75-85% TOC removal by Ga2O3/PMS under 254 nm UV irradiation. Therefore, Ga2O3/PMS system was highly effective for PFOA photodegradation under UV irradiation, which has potential to be applied for the perfluoroalkyl substances (PFAS) treatment in water and wastewater.
Lindane (γ-hexachlorocyclohexane) and its isomers (HCH) are some of the most common and most easily detected organochlorine pesticides in the environment. The widespread distribution of lindane is due to its use as an insecticide, accompanied by its persistence and bioaccumulation, whereas HCH were disposed of as waste in unmanaged landfills. Unfortunately, certain HCH (especially the most reactive ones: γ- and α-HCH) are harmful to the central nervous system and to reproductive and endocrine systems, therefore development of suitable remediation methods is needed to remove them from contaminated soil and water. This paper provides a short history of the use of lindane and a description of the properties of HCH, as well as their determination methods. The main focus of the paper, however, is a review of oxidative and reductive treatment methods. Although these methods of HCH remediation are popular, there are no review papers summarising their principles, history, advantages and disadvantages. Furthermore, recent advances in the chemical treatment of HCH are discussed and risks concerning these processes are given.
Modified nanoscale zero-valent iron (nZVI) is a promising functional material for the remediation of combined pollutants involving polychlorinated biphenyls (PCBs) and heavy metals. However, the interaction between the two types of pollutants has not been systematically studied for this method of treatment. In this study, 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB153), Cu ²⁺ , and Ni ²⁺ were selected as the target pollutants. To understand the interaction between pollutants, the efficiencies of nZVI, sulfidated nZVI (S-nZVI), and carboxymethylcellulose stabilized nZVI (CMC-nZVI) were investigated for removal of PCB153, Cu ²⁺ /Ni ²⁺ , and combined pollution system (PCBs-Cu ²⁺ /Ni ²⁺ ). Results showed that the removal kinetics of the two types of pollutants by the three materials fitted a pseudo-first-order model well and that the reaction mechanisms were similar. Among the three materials, CMC-nZVI showed the highest reactivity to degrade PCB153 (pseudo-first-order kinetic constants (k obs ) = 2.7 × 10 ⁻⁴ min ⁻¹ ) and remove Cu ²⁺ (k obs = 2.890 min ⁻¹ ), while S-nZVI showed higher affinity for the removal of Ni ²⁺ (k obs = 0.931 min ⁻¹ ). For the combined pollution system, PCB153 had little effect on the removal of heavy metals by the three materials, while the effect of heavy metals on PCB153 degradation was related to the types of heavy metals and the materials. Cu ²⁺ had no significant effect on PCB153 degradation by the three materials, while the coexistence of Ni ²⁺ promoted PCB153 degradation by nZVI and CMC-nZVI. XPS and electrochemical analysis showed that Cu ⁰ and Ni ⁰ were produced on the surface of the three materials. Ni is a more effective catalyst and promoted the electron transfer efficiency of the materials and had a positive impact on the dechlorination reaction.
Electrochemical oxidation based on SO4•‒ and •OH generated from sulfate electrolyte is a cost-effective method for degradation of persistent organic pollutants (POPs). However, sulfate activation remains a great challenge due to lack of active and robust electrodes. Herein, B/N codoped diamond (BND) electrode is designed for electrochemical degradation of POPs via sulfate activation. It is efficient and stable for perfluorooctanoic acid (PFOA) oxidation with first-order kinetic constants of 2.4 h⁻¹ and total organic carbon removal efficiency of 77.4% (3 h) at relatively low current density of 4 mA cm⁻². The good activity of BND is mainly originated from the B and N codoping effect. PFOA oxidation rate at sulfate electrolyte is significantly enhanced (2.3-3.4 times) compared with those at nitrate and perchlorate electrolytes. At sulfate, PFOA oxidation rate decreases slightly in the presence of •OH quencher while it declines significantly with SO4•‒ and •OH quenchers, indicate both SO4•‒ and •OH contribute to PFOA oxidation but SO4•‒ contribution is more significant. Based on intermediates analysis, proposed mechanism for PFOA degradation is that PFOA is oxidized to shorter chain perfluorocarboxylic acids gradually by SO4•‒ and •OH until it is mineralized.
Reductive debromination has been widely studied for the degradation of polybrominated diphenyl ethers (PBDEs), although the reaction mechanisms are not so clear. In the present study, the photocatalytic degradation and debromination of ten PBDEs were carried out with CuO/TiO2 nanocomposites as the photocatalyst under anaerobic condition. The pseudo-first-order rate constants were obtained for the photocatalytic debromination of PBDEs, and their relative rate constants (kR) were evaluated against kR= 1 for BDE209. Unlike the generally accepted summary that kR is dependent on total Br number (N) of PBDEs, kR is found to depend on Br number on a phenyl ring with more Br atoms than the other one. In other word, a phenyl ring substituted by more Br is more reactive for the reductive debromination. The calculated LUMO energies (ELUMO) of all PBDEs are well correlated to more reactive phenyl ring with more Br, compared with N of two phenyl rings. The result was explained by LUMO localization on the Br-rich phenyl ring, suggesting the reductive debromination occurs on the phenyl ring.
The new persistent organic pollutant (POP), 1,2,5,6,9,10-hexabromocyclododecane (HBCD), has been widely detected in various environmental media and proved to be biotoxic. However, the research on catalytic degradation of HBCD is in its infancy. Herein, we examined the degradation of α-HBCD, β-HBCD and γ-HBCD, over Fe 3 O 4 micro/nanomaterial at 200 °C. The pseudo-first-order kinetic rate constants were in the range of 0.04–0.15 min ⁻¹ , with half-life values of 5–19 min. γ-HBCD is slightly less stable than β-HBCD, but both of them readily convert into α-HBCD, as consistent with the Gibbs free energies of isomers themselves. The four products containing pentabromocyclododecene, two isomers of tetrabromocyclododecene and 1,5,9-cyclododecatriene were detected by conventional GC–MS. Interestingly, a high-throughput non-target product detection were performed by ESI-FT-ICR-MS, where up to 59 types of intermediate products were determined. It is tentatively proposed that different types of bromine-removed products (C 12 H 17 Br 5 , C 12 H 18 Br 4 , C 12 H 18 , C 12 H 19 Br 5 , C 12 H 24 and C 12 H 19 Br 5 O) and cyclododecane ring-opened products (C 12 H 19 Br 7 , C 12 H 20 Br 6 O and C 12 H 20 Br 6 ) form via elimination reaction, nucleophilic substitution, hydrodebromination and addition reaction. Besides, most of the products that were detected contained oxygen. The average carbon oxidation state (OS c ¯) of the products indicate that the oxidation reaction is the dominant reaction type. Deep oxidation products, such as small molecular organic acids (formic, acetic, propionic, and butyric acids) and gas-phase oxidation products (CO 2 and CO) were further detected by ion chromatography and GC-FID, respectively. This study might provide an alternative technique for the low-cost treatment of HBCD waste.
Here we present the highly enhanced sunlight photocatalytic efficiency and photocorrosion resistance of biomimetic ZnO-modified micro/nanofern fractal architectures, which are synthesized by using a novel, simple, inexpensive and green electrochemical deposition approach in high stirring conditions. Such fern-like hierarchical structures simultaneously combine enhanced angle independent light trapping and surface/bulk modifications of the ZnO morphology to drastically increase: i) the light trapping and absorption in the visible near-infrared range, and ii) the surface to volume ratio of the architecture. This combination is crucial for boosting the sunlight photocatalytic efficiency. To modulate the electronic properties for extending the operation of the ZnO photocatalysts into the visible domain we have used three different modification approaches: sulfidation (leading to a ZnS shell), Ag decoration, and Ni-doping. The different ZnO-modified bioinspired fern-like fractal structures have been used to demonstrate their efficiency in the photodegradation and photoremediation of three different persistent organic pollutants –methylene blue, 4-nitrophenol, and Rhodamine B – under UV light, simulated and natural UV-filtered sunlight. Remarkably, the [email protected] [email protected] structures exhibited an outstanding photocatalytic activity compared to the pristine ZnO catalyst, with over 6-fold increase in the pollutant degradation rate when using solar light. In fact, the catalytic performance of the [email protected] micro/nanoferns for the photoremediation of persistent organic pollutants is comparable to or better than the most competitive state-of-the-art ZnO photocatalysts, but showing a negligible photocorrosion. Ag-decorated ZnO, and Ni-doped ZnO exhibited similar excellent visible-sunlight photodegradation efficiency. Although the Ni-doped photocatalysts showed a relatively poor photocorrosion resistance, it was acceptable for Ag-decorated ZnO. Therefore, the easy fabrication and the capacity to drastically enhance the sunlight photocatalytic efficiency of the [email protected] bioinspired micro/nanoferns, together with their practically negligible photocorrosion and simple recyclability in terms of non-catalyst poisoning, makes them very promising photocatalysts for water remediation.
Humic acids (HA) are the most important photosensitizers in the ocean and generate highly reactive oxygen species (ROS), known as photochemically produce reactive intermediates (PPRI), which degrade organic pollutants. Thus, to reveal the fate of organic pollutants in an aqueous environment, it is important to understand the natural photodegradation phenomenon caused by HA. Three ROS generated from HA, ¹ O 2 , O 2 - [rad] , and [rad] OH, were measured using different probe compounds and instrumental techniques. In this study, HBCD (hexabromocyclododecane), a newly listed one of persistent organic pollutants (POPs) under the Stockholm Convention, was studied to understand the phototransformation mechanism, which has not been sufficiently investigated in terms of its environmental fate and transport, despite the distinctive features of its diastereoisomers. The results showed that the diastereoisomer-specific distributions of α-, β-, and γ-HBCD were related to the acceleration and retardation of photodegradation in the presence of AHA (Aldrich Humic Acid) under simulated solar light, and only α-HBCD was rapidly photodegraded as the amount of AHA increased relative to the absence of AHA. This study provides the first characterization of the behavior of photosensitized HBCD degradation in aquatic systems.
This article gives an overview of nanotechnologies applied in remediation of water contaminated by poly- and perfluoroalkyl substances (PFASs). The use of engineered nanomaterials (ENMs) in physical sorption and photochemical reactions offers a promising solution in PFAS removal because of the high surface area and the associated high reactivities of the ENMs. Modification of carbon nanotubes (CNTs) (e.g., oxidation, applying electrochemical assistance) significantly improves their adsorption rate and capacity for PFASs removal and opens a new door for use of CNTs in environmental remediation. Modified nanosized iron oxides with high adsorption capacity and magnetic property have also been demonstrated to be ideal sorbents for PFASs with great recyclability and thus provide an excellent alternative for PFAS removal under various conditions. Literature shows that PFOA, which is one of the most common PFASs detected at contaminated sites, can be effectively decomposed in the presence of either TiO2-based, Ga2O3-based, or In2O3-based nano-photocatalysts under UV irradiation. The decomposition abilities and mechanisms of different nano-photocatalysts are reviewed and compared in this paper. Particularly, the nanosized In2O3 photocatalysts have the best potential in PFOA decomposition and the decomposition performance is closely related to the specific surface area and the amount of photogenerated holes on the surfaces of In2O3 nanostructures. In addition to detailed review of the published studies, future prospects of using nanotechnology for PFAS remediation are also discussed in this article.
In this work, microwave-assisted hydrothermal process is applied to the PCDD/F degradation of municipal solid waste incineration (MSWI) fly ash. The effects of water-washing pretreatment and the Na2HPO4 reagent on the degradation efficiency of PCDD/Fs are investigated. The PCDD/F content in MSWI fly ash is detected by high-resolution gas chromatography-mass spectrometry (HRGC/MS). The experimental results show that the efficiency of total PCDD/F degradation increases from 60.6% to 83.3% after water-washing pretreatment, with 5 wt % Na2HPO4 added for 2 h of microwave heating at 220 °C. With more Na2HPO4 (10 wt %), the degradation efficiency of PCDD/Fs reaches 91.8%, and remarkably, the WHO-TEQ is as low as 0.255 ng g⁻¹. Analysis of the degradation pathway of PCDD/Fs indicates that a chlorination reaction happens during the microwave-assisted hydrothermal process, as do dechlorination and destruction reactions. Water-washing effectively weakens the chlorination reaction for the decrease of chlorine in fly ash, which contributes to PCDD/F degradation. The reagent Na2HPO4 has a greater effect on the dechlorination of high-chlorinated congeners. Furthermore, the results indicate that the removal efficiency of PCDDs is higher than that of PCDFs under microwave conditions. Several linear correlations between indicative congener content and I/WHO-TEQ values are summarized. Overall, microwave-assisted hydrothermal process is a promising disposal method and should receive further study for large-scale application.
2,2′,4,4′-Tetrabrominateddiphenyl ether (BDE-47), as one of polybrominated diphenyl ethers (PBDEs), has been proven to be global contaminant owing to widespread utilization as flame retardant. Herein, a novel visible-light-driven (VLD) artificial indirect Z-scheme system of [email protected]3PO4/g-C3N4/rGO is finely designed for BDE-47 removal assisted with abundant solar energy. The novel hybrid composite exhibits an enhanced reductive debromination activity with removal efficiency of 93.4% under visible light irradiation (λ > 420 nm) for 120 min, which is 173.65 times higher than pristine g-C3N4 catalyst. A series of experiments in terms of the environmental effects of initial concentration, pH, solvent and light source are performed to optimize the photocatalytic performance. The presence of rGO as an excellent storing and shuttling medium, can further facilitate the charge carrier separation in the indirect Z-scheme system for the enhanced photo-reduction debromination performance. The accumulated electrons on the solid catalyst can attack the ortho-Br of BDE-47 to formation of BDE-28, and then so on. The protons (H⁺) can be reduced to atomic hydrogen (H°), which can greatly weaken para-Br of BDE-47 to generation of BDE-17. Furthermore, the remaining holes can react with CH3OH to generate [rad]CH2OH radical, and then further directly produce electron for debromination process. A possible debromination pathway for BDE-47 was proposed. This work provides a green and promising strategy utilizing solar energy to remove BDE-47 in the liquid medium by virtue of VLD composite.
A multipollutant (Hg0/NO/dioxin)-containing gas stream generating system is developed to investigate the effectiveness of V2O5-WO3/TiO2 catalyst for multi-pollutant control. The results indicate that plate-type 1.52 wt% V2O5 performs much better than two other catalysts for oxidizing Hg0. With a higher vanadium loading of 1.52 wt% V2O5, higher Hg0 conversions (53% → 75%) are observed compared to 0.66 wt% V2O5 (45% → 68%) and 0.26 wt% V2O5 (32% → 63%) for simulated flue gas streams. In addition, the mercury oxidation activity significantly increases with increasing concentration of hydrogen chloride. For the removal of PCDD/Fs, the results show that the removal efficiencies of PCDD/F congeners achieved with V2O5-WO3/TiO2 range from 50% to 65%. It is observed that the removal efficiency of highly chlorinated PCDD/Fs is slightly higher than that of low chlorinated PCDD/Fs. Overall, plate-type catalyst of 1.52 wt% V2O5 shows the highest Hg0/NO/dioxin conversion and reduction efficiency among three catalysts evaluated.
Fast and deep debromination of polybrominated diphenyl ethers (PBDEs) under mild conditions is a challenge in the field of pollution control. A strategy was developed to achieve it by exploiting Cu/TiO2 composites as a noble-metal-free catalyst. Towards the debromination of 2,2’,4,4’-tetrabromodiphenyl ether (BDE47) as a typical PBDE, the use of Cu/TiO2 as a catalyst and hydrazine hydrate (N2H4•H2O) as a reducing agent yielded a degradation removal of 100% and a debromination efficiency of 87.7% in 3 seconds. A complete debromination of BDE47 at 1500 mg L-1 was possible by successively adding N2H4•H2O. A debromination pathway involving active H-atom species was proposed for the catalytic transfer hydrogenation (CTH) of PBDEs according to the identified degradation intermediates. A mechanism was further clarified by density functional theory calculations: electrons deliver from N2H4•H2O to metallic Cu atom via a coordination of N in N2H4•H2O with Cu atoms, electron-trapped Cu atom interacts with adsorbed BDE47 to form a transition complex, and then the debromination of this complex occurs on the surface of Cu nanoparticles due to the hydrogen donation of N2H4•H2O through the CTH process. The new method provides an economic and highly efficient method to remove brominated pollutants.
Catalytic oxidation is regarded an effective technique to control the emissions of chlorinated benzenes (CBzs) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from waste incinerators. Among the numerous factors affecting the degradation efficiency of CBzs and PCDD/Fs, limited attention has been paid to the impact of hydrochloric acid (HCl) present in the flue gas. This study investigates how HCl affects the catalytic degradation of 1,2-dichlorbenzene (1,2-DCBz) at different reaction times and temperature regimes. The results showed that the removal efficiency of 1,2-DCBz, which was achieved by the V2O5/WO3-TiO2 (VWTi) catalyst, decreased the largest by 10% in the presence of HCl. Furthermore, it was found that the increasing concentration of water vapor hindered the degradation efficiency of 1,2-DCBz. No relationship between the process temperature and the destruction efficiency of PCDD/Fs was observed in the presence of HCl. Potential increasing of the removal efficiency of 1,2-DCBz was confirmed by adding different amount of activated carbon (AC) in the presence of HCl.
Polybrominated diphenyl ethers (PBDEs) are typical flame retardant that have arose widely environmental concerns. Previous studies have found that PBDEs can generate lower BDEs and polybrominated dibenzofuran (PBDFs) under UV exposure, but these two processes were not well understood. In this study, we have investigated them through the case study of three BDE congeners (i.e. BDE-29, BDE-25 and BDE-21), which all have an ortho-, a meta- and a para-bromine substituents. The results shows that the vulnerability rank order of brominated position for these three BDE congeners are totally different, the bromine substituent at each position (ortho-, meta- or para-) can be preferentially removed, indicating it is not scientific to summarize the debromination pathways of PBDEs by comparing the brominated position. The lowest unoccupied molecular orbital (LUMO) of PBDEs in first excited state are well consistent with their actual debromination pathways, suggesting it is a good descriptor to predict the photodebromination pathways of PBDEs. In addition, the PBDEs with an ortho-bromine substituent can generate lower PBDFs, and the first step is to generate lower BDEs with an ortho-carbon radical, followed by ring closure reaction to generate PBDFs.
The effective removal of recalcitrant organochlorine pesticides including hexachlorocyclohexane (HCH) present in a real groundwater coming from a landfill of an old lindane (γ-HCH) factory was performed by electrochemical oxidation using a BDD anode and a carbon felt cathode. Groundwater (ΣHCHs = 0.42 mg L-1, TOC0 = 9 mg L-1, pH0 = 7, conductivity = 3.7 mS cm-1) was treated as received, achieving the complete depletion of the HCH isomers and a mineralization degree of 90% at 4 h electrolysis at constant current of 400 mA. Initial groundwater contains high chloride concentration (Cl0- = 630 mg L-1) that is progressively decreased due to its oxidation to different oxychlorine species: Cl2, HClO, ClO-, ClO2-ClO3-and ClO4-some of them (Cl2, HClO, ClO-) playing an important role in the oxidation of organic pollutants. The oxidation rate of chloride (and its oxidized intermediates) depends on the applied current value. Although some of the species generated from them are active oxidants, the presence of inorganic salts is detrimental to the efficiency of the electrochemical process when working at current densities above 100 mA due to the high consumption of hydroxyl radicals in wasting reactions. The initial organic carbon content is not crucial for the extension of the process but high organic loads are more profitable for cost effectiveness. The addition of a supporting electrolyte to the solution could be interesting since it increases the conductivity, reducing the cell potential and therefore, decreasing the energy consumption.
The photoreduction of polybrominated diphenyl ethers (PBDEs) － a kind of persistent organic pollutants with high hydrophobicity was achieved on graphene in aqueous solution. We first observed that reduced graphene oxide (RGO) exhibited higher reaction rate than graphene oxide (GO). FT-IR and elementary analysis indicated that GO firstly was reduced to RGO at the beginning of the irradiation, and RGO is the real photoactive species. The theoretical calculations and absorption experiments reveal a new photochemical debromination pathway based on the weak interaction, such as hydrophobic interaction, π-π interaction and halogen binding interaction between the PBDEs and RGO. These interactions enable the photoinduced electron transfer from the RGO to PBDEs and lead to the efficient reductive debromination of PBDEs. This study provides a green and low-cost method to removal of the high hydrophobicity halogen organic pollutants in water with environmental benign carbon nanomaterials.
In order to find a catalyst to destroy polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) with high efficiency, a homemade VOx-CeOx/TiO2catalyst was prepared, and then tested in the flue gas of a waste incinerator at temperatures of 180-240 °C. The results shows the best removal efficiency (93.4%) was attained already at 200 °C, yet degradation efficiency further raised with temperature, until 240 °C. Ozone (500 ppm) was also introduced into the system to increase the activity of catalyst, and removal efficiency of PCDD/Fs increased further to 97.4% and 98.8% at 200 and 240 °C, respectively. In addition, a lab-scale reaction system was installed to study the degradation mechanism of PCDD/Fs. Octa-chlorinated dibenzo-p-dioxin (OCDD) was selected as the study object due to the most stable structure and maximum chlorine atom number. The intermediate products resulting from the conversion of OCDD were monitored using gas chromatography/mass spectrometry and Fourier transform infrared spectroscopy and a possible reaction pathway was proposed. Dechlorination persists until the complete conversion of OCDD. Oxidation decomposes OCDD-molecules mainly into organic substances having one, two or more benzene rings, yet also alkanes, cycloalkanes and heterocompounds of sulphur, nitrogen, and halogens appear. However, more work is still needed to fit those trace products into mechanistic schemes.
This study focuses on the effect of electrode materials on abatement of lindane (an organochlorine pesticide) by electrooxidation process. Comparative performances of different anodic (platinum (Pt), dimensionally stable anode (DSA) and boron-doped diamond (BDD)) and cathodic (carbon sponge (CS), carbon felt (CF) and stainless steel (SS)) materials on lindane electrooxidation and mineralization were investigated. Special attention was paid to determine the role of chlorine active species during the electrooxidation process. The results showed that better performances were obtained when using a BDD anode and CF cathode cell. The influence of the current density was assessed to optimize the oxidation of lindane and the mineralization of its aqueous solution. A quick (10 min) and complete oxidation of 10 mg L-1lindane solution and relatively high mineralization degree (80% TOC removal) at 4 h electrolysis were achieved at 8.33 mA cm-2current density. Lindane was quickly oxidized by in-situ generated hydroxyl radicals, (M(•OH)), formed from oxidation of water on the anode (M) surface following pseudo first-order reaction kinetics. Formation of chlorinated and hydroxylated intermediates and carboxylic acids during the treatment were identified and a plausible mineralization pathway of lindane by hydroxyl radicals was proposed.
Polybrominated diphenyl ethers (PBDEs) are a family of important organic pollutants, and methods for their complete debromination are urgently needed. It is known that highly-brominated PBDEs are easily photocatalytically reduced to lower-brominated congeners, and the lower-brominated congeners are relatively susceptible to photocatalytic oxidation but not to further reduction. The present work developed a one-pot photocatalytic consecutive reduction and oxidation method (O-CRO) for the complete debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE47). It was observed that BDE47 was resistant to photocatalytic reduction on TiO2 but underwent a slow oxidation in aerobic aqueous solutions (rate constant k = 0.065 h⁻¹). The use of a reduced graphene oxide and TiO2 (RGO/TiO2) composite only slightly improved the photocatalytic oxidation of BDE47 in air-H2O systems (k = 0.12 h⁻¹), but achieved a rapid photocatalytic reduction of BDE47 (k = 0.81 h⁻¹) in anoxic ACN-H2O systems; however, the debromination was only 25.0% even after 14 h because the reduction intermediates (i.e., tri-BDEs) were minimally reduced. To conduct the O-CRO process, we developed an anoxic RGO/TiO2-H2O system containing a small amount of methanol. This system yielded the complete debromination and mineralization of BDE47 within 14 h. The mechanism for the debromination and mineralization of BDE47 was clarified. This method overcame the drawbacks of the separated two-step reduction and oxidation method and will find promising applications for the degradation of halogenated organic pollutants.
Ozone assisted carbon nanotubes (CNTs) supported vanadium oxide/titanium dioxide (V/Ti-CNTs) or vanadium oxide-manganese oxide/titanium dioxide (V-Mn/Ti-CNTs) catalysts towards gaseous PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) catalytic oxidations at low temperature (150 °C) were investigated. The removal efficiency (RE) and decomposition efficiency (DE) of PCDD/Fs achieved with V-Mn/Ti-CNTs alone were 95% and 45% at 150 °C under a space velocity (SV) of 14000 h-1; yet, these values reached 99% and 91% when catalyst and low concentration (50 ppm) ozone were used in combined. The ozone promotion effect on catalytic activity was further enhanced with the addition of manganese oxide (MnOx) and CNTs. Adding MnOxand CNTs in V/Ti catalysts facilitated the ozone decomposition (creating more active species on catalyst surface), thus, improved ozone utilization (demanding relatively lower ozone addition concentration). On the other hand, this study threw light upon ozone promotion mechanism based on the comparison of catalyst properties (i.e. components, surface area, surface acidity, redox ability and oxidation state) before and after ozone treatment. The experimental results indicate that a synergistic effect exists between catalyst and ozone: ozone is captured and decomposed on catalyst surface; meanwhile, the catalyst properties are changed by ozone in return. Reactive oxygen species from ozone decomposition and the accompanied catalyst properties optimization are crucial reasons for catalyst activation at low temperature.
In this work, an all solid Z-scheme g-C3N4/Ag3PO4/NCDs photocatalyst has been prepared through decorating the direct Z-scheme g-C3N4/Ag3PO4 photocatalyst with nitrogen-doped carbon dots (NCDs). The g-C3N4/Ag3PO4/NCDs photocatalyst exhibits excellent photocatalytic activity for the degradation of methylene blue (MB), rhodamine B (RhB) and phenol under visible light irradiation. The solutions of MB (10 mg L⁻¹) and RhB (10 mg L⁻¹) can be efficiently degraded within 20 min and 15 min, respectively, and the phenol (50 mg L⁻¹) can be degraded to 36% within 80 min, which are much better than those of Ag3PO4 and g-C3N4/Ag3PO4, indicating that the introduction of NCDs into g-C3N4/Ag3PO4 can effectively improve the photocatalytic activity. Moreover, the photocatalytic performance of g-C3N4/Ag3PO4/NCDs shows just a slight decrease after four degradation cycles, indicating a high stability of the g-C3N4/Ag3PO4/NCDs photocatalyst. A possible photocatalytic mechanism based on the experimental results is proposed. It is revealed that NCDs on the ternary g-C3N4/Ag3PO4/NCDs can enhance the light harvesting capacity and molecular oxygen activation ability of the photocatalyst, and serve as excellent electronic transmission medium to promote the transfer and separation of photo-generated electron-hole pairs. This study demonstrates that NCDs decorated photocatalysts are very promising for environment and related applications.
Novel palladium (Pd) and ruthenium (Ru) Bimetal Quantum Dots (BQDs) co-anchored on Titania nanotube arrays electrodes (NAEs) bearing double Schottky junctions with superior photoelectrochemical conversions and photoelectrocatalytic reductive dechlorination (PECRD) properties were successfully developed and constructed by facial two-step electrochemical strategy. The PECRD of toxic Pentachlorophenol and photoelectrochemical conversions over the afore-designed bimetallic Pd and Ru BQDs co-anchored TiO2 (101) nanotube array electrodes (Ru-Pd BQDs/TiO2 NAEs) composites have been systematically investigated both theoretically and practically. A remarkable enhancement of photoelectrochemical conversion efficiency of 14.10% as compared to that of the pure TiO2 NAEs (0.45%) in the Ru-Pd BQDs/TiO2 NAEs composites has been successfully achieved, and pentachlorophenol (PCP) species could be PECRD over 90% under the optimum conditions. Various physico-chemical techniques including UV–vis spectroscopy, XRD, SEM/TEM/EDX, PL, EIS, SPV and XPS were employed to systematically characterize the crystal-, electronic and micro-interfacial structures of the composites with double Schottky junction, respectively. All of the studies implied that the marvelous enhancement of separation efficiency of photo-generated electron–hole pairs is mainly caused by the Schottky-barriers as derived from the interfacial interaction within the Ru-Pd BQDs/TiO2 NAEs metal-semiconductor composites. The Ru-Pd BQDs/TiO2 NAEs bearing double Schottky-junctions would greatly facilitate the interfacial charge transfer followed by fully utilization of the photo-generated electrons for PECRD of PCP species. The DFT calculations clearly indicated that the number of impurity (i.e., co-anchored Ru-Pd BQDs) energy levels near Fermi surface increased, promoting electron energy transition and reduces the band gap, which suggesting a better reduction capability. Overall, this work shall provide brand new insight for molecular design of Bimetal Quantum Dots (BQDs) assembled onto Tatiana NAEs composites with superior performance for both environmental eliminations and green energy conversions and could significantly deepen our understanding to the catalytic dechlorination pathways of typical environmental toxic polychlorinated compounds over multifunctional nanocatalytic materials.
Triclosan (TCS) is widely used as antiseptic or preservative in many personal care products (PCPs), such as cosmetics, hand wash, toothpaste and deodorant soaps, among others. It is characterized by acute toxicity, resistance to biodegradation, environmental persistence and relatively high lipophilicity. In order to protect the environment and natural resources from the negative effects of the discharge of polluted wastewater with TCS, the application of efficient remediation technologies able to degrade the pollutant to harmless levels becomes crucial. Electrochemical oxidation, among all advanced oxidation processes (AOPs), has been reported as very effective in the complete degradation of a number of persistent pollutants; therefore, its performance using boron-doped diamond (BDD) anodes, and response to operation variables, has been studied in this work. As expected, complete degradation of TCS was achieved in all the studied conditions; however, going a step further and knowing that TCS is a precursor of polychlorinated dibenzo‑p‑dioxins and dibenzofurans (PCDD/Fs), their quantitative presence in the oxidation media has been assessed. Results showed the dominance of dichlorinated (DCDD) and trichlorinated (TrCDD/Fs) in the homologue profile of total PCDD/Fs, reaching values up to 1.48 × 105 pg L-1 in samples with initial concentration of TCS of 100 mg L-1 and NaCl as electrolyte. Under these conditions, the International Toxicity Equivalency Factor (I-TEF) achieved values up to 2.76 × 102 pg L-1. Nevertheless, the presence of copper in the oxidation medium tends to reduce I-TEF values. Finally, considering the information reported in literature, a mechanism describing the formation of low chlorinated PCDD/Fs from TCS oxidation reactions is proposed.
Nowadays, an increasing emission of chemically resistant perfluorinated compounds (PFCs) to the natural environment, together with a global presence of those anthropogenic pollutants in both natural and treated waters and in both human and animal organisms, poses a great environmental challenge. A limited efficiency of their removal by commonly employed technologies prompts a search for more efficient and more cost-effective methods. Recent decades brought in water management an intense progress in Advance Oxidation Processes, based on decomposition of pollutants by free radicals, which can be produced in different ways. This review presents the recent advances in those methods for decomposition of the most commonly occurring PFCs in the natural environment – perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). For this purpose, there have been developed particular methods based on an oxidation and reduction of target pollutants, generally abbreviated as AO/RPs. The review, which was based on 180 cited references, includes photolytic and photocatalytic methods, electrochemical processes as well as sonolytic and radiolytic methods with the use of ionizing radiation, wet chemnical oxidation methods, ozonation and Fenton processes. Attempts on comparison of the developed methods, their applications to real samples and molecular mechanisms of occurring transformations are provided.
Persistent organic pollutants (POPs) are carbon-based chemical substances that are resistant to environmental degradation and may not be completely removed through treatment processes. Their persistence can contribute to adverse health impacts on wild-life and human beings. Thus, the solar photocatalysis process has received increasing attention due to its great potential as a green and eco-friendly process for the elimination of POPs to increase the security of clean water. In this context, ZnO nanostructures have been shown to be prominent photocatalyst candidates to be used in photodegradation owing to the facts that they are low-cost, non-toxic and more efficient in the absorption across a large fraction of the solar spectrum compared to TiO2. There are several aspects, however, need to be taken into consideration for further development. The purpose of this paper is to review the photo-degradation mechanisms of POPs and the recent progress in ZnO nanostructured fabrication methods including doping, heterojunction and modification techniques as well as improvements of ZnO as a photocatalyst. The second objective of this review is to evaluate the immobilization of photocatalyst and suspension systems while looking into their future challenges and prospects.
A series of graphene oxide (GO)/Ag3PO4 composites were synthesized using ion exchange-chemical precipitation method with different GO content, and the photocatalytic reduction degradation effect on decabromodiphenyl ether (BDE-209) over GO/Ag3PO4 was also studied. The optimized composite exhibited superior photocatalytic activity. When the content of GO was 7%, the degradation efficiency of BDE-209 could reach 97.33% in anoxic water with methanol as electron donors after 8 h of visible light irradiation, being 3 times that over pure Ag3PO4 and the BDE-209 reduction generated 3Br-8Br PBDEs congeners. The photocatalytic degradation of BDE-209 has been further investigated under different reaction conditions, such as photocatalyst dosage and pH of reaction system. According to analysis of the intermediates's generation, accumulation and distribution, we proposed that the BDE-209 reduction mechanism was the multi-electron reduction process. GO not only trapped electrons to improve the charge separation on Ag3PO4, but also fleetingly transferred the accumulated electrons to BDE-209. This study indicates that GO/Ag3PO4 could be a promising material for environmental treatment of persistent pollutants.
Adsorptive removal and photocatalytic degradation of Persistent Organic Pollutants (POPs) in water have been emerged as energy- and cost-effective technologies. Both have attracted considerable attention to treat the world's wastewater. As a class of recently developed versatile porous materials, MOFs have shown huge potential and bright perspective in adsorptive removal and photocatalytic degradation of POPs for water remediation. This mini-review introduces the classification of POPs, and summarizes the current research progress on adsorptive and photocatalytic removal for each group of POPs using the emerging MOFs and functional MOFs. Possible interactions between the POPs and active sites on the MOFs are discussed to understand the adsorption/photocatalysis mechanism. The outlooks on adsorptive removal and photocatalytic degradation of POPs using MOFs are given, albeit often with barriers as addressed. The integration of adsorption and photocatalysis using MOFs is discussed.
In the present work, a cobalt phthalocyanine-supported reduced graphene oxide material (rGO-CoPc) was used as a catalyst for the degradation of rhodamine B (RhB) and pentachorophenol (PCP) in the presence of peroxymonosulfate (PMS). Inductively coupled plasma (ICP-OES), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were employed to characterize the properties of the composite and Co loading in the material. The catalytic activity of the rGO1-CoPc1 catalyst (rGO:CoPc = 1:1) was evaluated by UV–vis absorption spectroscopy at varying PMS concentrations and catalyst dosages. The complete dye removal was achieved in 9 min by rGO1-CoPc1/PMS system with a high initiation rate constant of 1.019 min⁻¹ using RhB (25 µM), PMS (0.1 mM) and rGO1-CoPc1 (0.5 mg/mL). The removal efficiency was found to be as high as 100% after 11 cycles, suggesting a long-lasting catalytic activity of the of rGO1-CoPc1/PMS system. Quenching experiments suggested that sulfate (SO4[rad]−) radicals are the dominant species in the degradation process although hydroxyl (OH[rad]) radicals are also involved in the reaction mechanism. Furthermore, the catalyst was successfully applied for the efficient degradation of pentachlorophenol (PCP). A full degradation of PCP (25 µM) was achieved within 20 min using rGO1-CoPc1 (0.5 mg/mL) and PMS (0.6 mM). This study demonstrated that the use of rGO-CoPc as a heterogeneous catalyst for PMS activation is useful for the advanced oxidation processes (AOP) for practical wastewater treatment.
Degradation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in real-field soil was conducted using an integrated photocatalysis-solvent migration system of BiVO4/Bi2O3 and n-hexane. The photocatalyst BiVO4/Bi2O3 was synthesized, and its performance was found to be affected by the BiVO4 content, with 20 wt % BiVO4 showing the best performance owing to its p-n heterojunction being well formed. Migration was affected by the amount of n-hexane, with 15% n-hexane giving the most effective transportation of PCDD/Fs. 37.2% of 17 PCDD/Fs was removed in 60 h by the integrated photocatalysis-solvent migration system, although the reaction zone covered 8.5% of the volume of the soil. The result showed that migration via n-hexane fulfilled the aim of carrying contaminants from inside of the soil to the surface. Electron-scavenging experiments with BiVO4/Bi2O3 showed an 18.4% of performance in removal compared to no-scavenging condition, which showed that the main reactions driving BiVO4/Bi2O3 visible-light photocatalysis for aryl-chloride were found to be reduction-based. Owing to the hindering effect of Cl atoms, degradation by hydroxyl radical could proceed after initial dechlorination. This study establishes the applicability of integrated photocatalysis-solvent migration systems in real-field settings, and is the first report of a visible-light photocatalyst, BiVO4/Bi2O3, for the degradation of PCDD/Fs in soil.
As a typical congener of Polybrominated diphenyl ethers (PBDEs), 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) has attracted more and more attention due to its high biological toxicity and environmental abundance. In this study, a novel polyanionic cellulose stabilized Pd/Fe (PAC-Pd/Fe) nanoparticle was successfully synthesized for BDE47 degradation under ambient condition. Batch experiments showed that BDE47 degradation followed pseudo first-order kinetic model. Pd loading played a crucial role as it affected the formation of activated hydrogen species H∗ and accelerated electron transfer. At Pd loading of 0.3 wt%, nearly 100% BDE47 was degraded completely within 10 min by 0.4 g L⁻¹PAC-Pd/Fe nanoparticles. When compared with strong acidic (pH 3) and alkaline (pH 9 and 11) conditions, weak acidic condition (pH 5) was more favorable for BDE47 degradation, with nearly 100% BDE47 was removed within 7.5 min. In the presence of HA inhibited the degradation of BDE47, and the degradation efficiencies within 15 min decreased from 100%, 88.6%, 79.5% to 73.1% as HA concentration increased from 0, 10, 40 to 70 mg L⁻¹. The degradation of BDE47 by PAC-Pd/Fe nanoparticles was a reductive debromination process, and a stepwise debromination from n-Br to (n-1)-Br BDEs was the dominant reaction, in which the para-Br was more susceptible to remove than ortho-Br. This study suggests PAC-Pd/Fe nanoparticle can be utilized as a promising remediation technology for PBDEs contaminated wastewater.
Polycyclic aromatic hydrocarbons (PAHs) are persistent and harmful pollutants with high priority concern in the environment. To efficiently and energy-savingly remove PAHs from water, this work prepared a novel graphite oxide-TiO2-Sr(OH)2/SrCO3 nanocomposite and evaluated its photocatalytic activity for degradation of phenanthrene (a model PAH) under simulated solar irradiation. The presence of 50 mg/L of the photocatalyst enhanced the pseudo-first-order photodegradation rate constant of phenanthrene by 11.6 times from 0.0005 ± 0.0000 min⁻¹ (control) to 0.0058 ± 0.0004 min⁻¹. Superoxide radicals (O2⁻) and hydroxyl radicals (OH) were found to be the key reactive species in the photocatalytic process. Based on analysis of intermediates and established photocatalysis chemistry, the degradation pathway was elucidated. The effects of various water quality parameters were investigated, including temperature, pH, ionic strength, humic acid and two surfactants (Tween 80 and sodium dodecyl sulfate (SDS)), and the underlying mechanisms were illustrated. Based on the effects of individual water quality parameters, two predictive models were established by addition or multiplication to predict the photocatalytic degradation rate under complex water matrices. Based on experimental results with seawater and in the presence of three model oil dispersants, the multiplicative model was shown to present a robust and accurate prediction of the phenanthrene photodegradation rate with a predicted correlation coefficient (r²pred.) of 0.9483. This study not only developed a new photocatalyst of high activity under solar light, but also provided useful information for its practical application under various water quality conditions.
This study investigates the efficiencies and mechanisms of the catalytic degradation of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) first, in simulated laboratory conditions and then, in a commercial municipal solid waste incineration (MSWI) plant. Five commercially available V2O5-WO3/TiO2 (VWTi) catalysts were tested. The degradation efficiency of PCDD/Fs in the simulated flue gas ranged 22.8–91.7% and was generally higher than that in the MSWI flue gas of 8.0–85.4%. The degradation efficiency of PCDD/Fs in the real flue gas of the MSWI plant was largely hindered by the complex composition of the flue gas, which could not be completely reproduced in the simulated laboratory conditions. Furthermore, the degradation of the higher chlorinated PCDD/Fs was easier compared to the lower chlorinated ones in the presence of the VWTi catalysts, which was primarily driven by the tendency of the higher chlorinated PCDD/Fs to be adsorbed on the surface of the catalyst and further destructed due to their lower vapor pressure. In addition, powdered catalysts should be preferred over the honeycomb shaped ones as they exposed higher PCDD/Fs degradation efficiencies under equal reaction conditions. The chemical composition and a range of the relevant to the study properties of the catalysts, such as surface area, crystallinity, oxidation ability, and surface acidity, were analyzed. The study ultimately supports the identification of the preferred characteristics of the VWTi catalysts for the most efficient degradation of toxic PCDD/Fs and elucidates the corresponding deactivation reasons of the catalysts.
NixCo1-xFe2Oz composite oxide nanosphere was successfully prepared, to degrade 2-monochlorobiphenly (CB-1) in continuous-flow fixed-bed microreactor at GHSV of 20000 h⁻¹. The five cycles of temperature-dependent run experiments between 150 and 350 °C showed its superior activity with a CB-1 conversion of more than 95% above 300 °C over Ni0.5Co0.5Fe2Oz. Importantly, the sustainable higher reactivity could be observed over prolonged 600 min reaction times after the 5th run test. The degradation products detected as biphenyl and monochlorobenzene with yield ratio of 129, account for 0.24% and 0.0011% of initial CB-1 respectively. This indicated the weak occurrence of hydrodechlorination and breakage of CC bridge bond during the degradation of CB-1. The possibly dominant occurrence of oxidative degradation probably follows Mars–van Krevelen mechanism, resulting in the generation of the formic, acetic, propanoic and butyric acids and so on. Due to the high oxygen mobility over Ni0.5Co0.5Fe2Oz nanosphere, the consumed oxygen species could be compensated rapidly by the gas phase oxygen via O2 → O2⁻ → 2O⁻ → 2O²⁻. The interaction among different elements in Ni0.5Co0.5Fe2Oz nanosphere confirmed by the derivation of the electron cloud, enhanced the mobility of the reactive oxygen species, which would be beneficial for the oxidation of chlorinated biphenyls.
This review focuses on heterogeneous photocatalysis of perfluoroalkyl substances (PFAS) which are of worldwide concern as emerging persistent organic contaminants. Heterogeneous photocatalysis is an effective and advanced technology for PFAS removal from water with relatively high efficacy. During photocatalysis, various short chain perfluorocarboxylic acids (PFCA) are produced as intermediates and the efficacy is related to the photo-generated hole (h+) and photo-generated electron (e-). PFAS photodegradation in water under UV irradiation is most effective by using In2O3 as the catalyst, followed by Ga2O3 and TiO2. Significantly, modifying the chemical composition or morphology of the catalyst can improve its efficacy for PFAS removal. In2O3 porous nanoplates were found to have the best performance of 100% PFAS decomposition under UV light with rate constant (kt) and half-time (τ1/2) of 0.158 min-1 and 4.4 min, respectively. Catalysts perform well in acidic solution and increasing temperature to a certain extent. The photocatalytic performance is reduced when treating wastewater due to the presence of dissolved organic matter (DOM), with the catalysts following the order: needle-like Ga2O3 > In2O3 > TiO2. Future studies should focus on the development of novel photocatalysts, and their immobilization and application for PFAS removal in wastewater.
Photocatalytic solar energy conversion is considered one of the most promising pathways to address the global energy shortage and environmental crisis. Layered bismuth oxyhalides are a new class of photocatalytic materials with a strong light response to boost solar energy conversion due to their appealing energy band structure and unique layered structure. This critical review summarizes recent progress in designing and tuning new bismuth oxyhalide materials to boost solar energy conversion. We start with methods to prepare and tune bismuth oxyhalides to enhance photocatalysis: structural engineering via control of the bismuth-rich state, elemental doping, defect control, interface engineering, solid solutions, inner coupling, and heterojunction construction. Then advancements in versatile photocatalytic applications of bismuth oxyhalide–based photocatalysts in the areas of oxygen evolution, hydrogen evolution, CO2 reduction, nitrogen fixation, organic syntheses, disinfection, and pollutant removal are discussed. Finally, the major challenges and opportunities regarding the future exploration of bismuth oxyhalide–based materials in photocatalysis are presented. The present review will deepen understanding regarding bismuth oxyhalides and open new directions in designing and optimizing advanced bismuth oxyhalide–based materials for energy and environmental applications.