Degradation Of Pollutants In Water Research Articles

Preparation of direct Z-scheme hierarchical MoS2/MnO2 composite for efficient adsorption and wide spectrum photocatalytic degradation of organic pollutants in water

Developing semiconductor-based heterogeneous photocatalysts with high adsorption performance and wide light response range is a significant technology for removing organic pollutants from water. Herein, a novel hierarchical dendritic-like direct Z-scheme MoS2/MnO2 composite with MoS2 hollow tubular decorated by MnO2 nanosheets was successfully fabricated by vacuum freeze-drying. When the mass ratio of MoS2/MnO2 is 3:1, the highest adsorption-photocatalytic removal rate of 94.5% and 95.1% in 120 min for RhB was attained under visible (Vis) and ultraviolet (UV) light irradiation, respectively. After three repeated uses, the removal rate of RhB still reached 91.1%. The enhanced adsorption-photocatalytic performance of the composite can be well illustrated according to the hierarchical composite structure, production of •OH, •O2− and h+ active species, oxygen-doping in the MoS2 and the direct Z-scheme photocatalytic mechanism. This work gives a good strategy to frame hierarchical Z-scheme photocatalysts for efficient adsorption and wide-spectrum photocatalytic removal of organic pollutants from water.

Cs2SnI6 perovskites nanostructures as excellent photocatalytic degradation of organic dye pollutants in water under visible light: Synthesis and characterization

Pollution of surface waters containing chemical dye combinations and/or biological materials can have adverse effects on human health and other organisms, even in small quantities. The photocatalytic oxidation procedure has been widely regarded as a commercially viable method of removing environmental pollutants. In recent research, Caesium-hexaiodostannate nanostructures (Cs2SnI6) were prepared through a co-precipitation approach and their photocatalytic performance was analyzed. A number of surfactants were examined for their influence on the structure, purity, and morphology of the sample. It was found in the SEM data that the presence of surfactants has a negative impact on the morphology, which may be due to the inability to remove surfactants by calcination at high temperatures. Photocatalytic activity of Cs2SnI6 catalysts was demonstrated over a variety of organic dyes, including methylene blue (MB), rhodamine b (RhB), methyl orange (MO), and methyl violet (MV). Upon exposure to visible light for 180 min, 5 ppm methylene blue showed the greatest degradation (84.0%). Cs2SnI6 nanostructures are being applied for the first time in photocatalytic applications. Due to their wide bandgap (1.7 eV) in the visible region, they may be a suitable candidate for water purification. Moreover, the results indicated that the efficiency of photocatalysis was affected by various parameters, including pH, dye concentration, dye types, catalyst dosages, and surfactants. In the recyclability test, Cs2SnI6 nanostructures were found to be stable, and the removal efficiency was reduced by 6.9% after the fifth run.

Advanced Oxidation Processes for Degradation of Water Pollutants—Ambivalent Impact of Carbonate Species: A Review

Advanced oxidation processes (AOPs) hold great promise in the removal of organic contaminants. Reactive oxygen species (ROS) produced in AOPs react with target pollutants to initially form several intermediate compounds that finally undergo complete mineralization. Such observations are reported, especially for laboratory-scale experiments performed in pure water. On the other hand, while considering real contaminated wastewater matrices, particularly industrial effluents, there are many co-existing ions. Carbonate ions are one of the major inorganic ions commonly existing in water resources. Hence, these ions have a significant impact on the respective water treatment processes. This review focused on the effect of carbonate ions on the degradation of pollutants in AOPs. In AOPs, carbonate radicals are formed by the scavenging reaction of the respective ions with ROS. The reactivity of these radicals towards the pollutant varies with respect to the structure and functionality. Therefore, depending on the functionalities of the contaminants, these ions show both positive and negative effects. Thus, this review aims to summarize the effects of carbonate species on the degradation of organic contaminants during AOPs and their environmental impacts. The carbonates enhanced the degradation of several emerging organic pollutants, including aniline, bisphenol A, rhodamine B, acid orange 7, naphthalene, and phenol derivatives. Carbonate presence was also revealed to have a positive contribution in cases of drug degradation, including sulfamethoxazole, propranolol, sulfamethazine, salbutamol, trimethoprim, azithromycin, naproxen, oxcarbazepine, and oxytetracycline.

Heterogeneous activation of persulfate using delafossite AgFeO2/α-MnO2 for efficient degradation of tartrazine under visible light

For the first time, delafossite AgFeO2/α-MnO2 nanocomposites were successfully synthesized and used as heterogeneous persulfate (PS) activators for degradation of water pollutants. The potential of several systems, such as AgFeO2/α-MnO2/light, AgFeO2/α-MnO2/PS/light, etc., as well as reaction conditions, stability, and radicals involved, were all assessed for degradation of tartrazine (TZ). The exceptional activity of optimal AgFeO2/α-MnO2 (AFM50) nanocomposite was attained because of improved redox cycling between Ag0/Ag+, Fe2+/Fe3+, Mn3+/Mn4+ cycles, enhanced electron transfer, reduced e−/h+ pair recombination, long electron lifetime, high charge transfer and mobility, and electron density, which facilitated efficient PS activation and subsequent generation of various reactive oxidizing species. Interestingly, AFM50 showed exceptional degradation efficiency (67.4%) under dark conditions. The AFM50/PS/Vis system also demonstrated excellent stability and activity for degrading several dyes (rhodamine B (97.8%), methyl orange (94.5%), methylene blue (100%), and congo red (97.7%)). Based on quenching experiments, active radicals (•OH, SO4•-, O2•-), and non-radical (h+, 1O2), all contributed towards efficient degradation of TZ. Following that, a reasonable PS activation mechanism was proposed. This study propounds insightful synergistic activation of PS using delafossite AgFeO2/α-MnO2 nanocomposite under visible light and dark conditions, as well as its potential application in wastewater treatment plants.

Activation of peroxymonosulfate by an Enteromorpha prolifera derived biochar supported CoFe2O4 catalyst for highly efficient lomefloxacin hydrochloride degradation under a wide pH range

Heterogeneous catalysts with high-activity and wide pH tolerance are urgently needed for water pollutant degradation. In this work, CoFe2O4-loaded biochar prepared from the marine biomass Enteromorpha prolifera (CFO@EPBC) was successfully developed as an efficient heterogeneous catalyst for the degradation of lomefloxacin hydrochloride (LMH) by activating peroxymonosulfate (PMS). The crystalline structure, porous structure and surface chemistry of CFO@EPBC were characterized. The catalytic performance of CFO@EPBC activated PMS for the decomposition of LMH was estimated, and the reusability, stability and applicability of CFO@EPBC were also evaluated. The results showed that CFO@EPBC displayed 35.2-, 3.7- and 6.6-times degradation rates (kobs) towards LMH than that of EPBC, CoFe2O4 and EPBC + CoFe2O4, respectively, demonstrating remarkable synergistic interaction between EPBC and CoFe2O4. More importantly, excellent catalytic ability of the CFO@EPBC/PMS system for LMH degradation under a wide initial pH range (3–11) was observed due to a suitable pHzpc of catalysts. Also, CFO@EPBC showed a good application prospect for treating LMH in different types of water matrixes (river water and seawater). Reactive oxygen species (SO4·−, ·OH, ·O−2 and 1O2) produced marked effects during the degradation process, while the radical process played a dominant role. This study also demonstrates a typical case for turning trash into treasure using Enteromorpha prolifera, providing a new idea for the value-added transformation of other similar bio-wastes.

NIR-response amorphous FeOOH anchored BiO2-x for chlorophenols photodegradation via molecular oxygen activation

Chlorophenols (CPs) are universal and toxic pollutants in nature, as they have been widely detected in surface water, groundwater, sediment, ambient air, soil, and the human body. In this work, novel FeOOH/BiO2-x binary heterostructure composites with UV-Vis-NIR full-spectrum response were successfully constructed by anchoring highly dispersed amorphous FeOOH on BiO2-x nanosheets. A series characterization indicated the binary components were successfully obtained. The FeOOH/BiO2-x photocatalysts exhibited highly enhanced photocatalytic activity for the degradation of chlorophenols under UV-Vis-NIR full-spectrum irradiation. The amorphous FeOOH could effectively broaden the light response range, modulate the energy band structure and promote the separation and transfer of photogenerated electron-holes pairs, thus boosting the activation of molecular oxygen to generate •O2–. Furthermore, FeOOH/BiO2-x maintained excellent photocatalytic performance upon real solar light of varied irradiance for consecutive 7 days, indicative of great potential towards phenolic pollutants degradation in water. The redox couples of Fe3+/Fe2+ and Bi(3+x)+/Bi3+ also accelerate the efficient generation of reactive oxygen species over FeOOH/BiO2-x with improved durability. This work not only contributes to the design of full-spectrum responsive photocatalysts, but also provides a rational strategy for molecular oxygen activation towards the elimination of emerging contaminants.

Latest advances in layered covalent organic frameworks for water and wastewater treatment

This review provides an overview of recent progress in the development of layered covalent organic frameworks (LCOFs) for the adsorption and degradation of pollutants in water and wastewater treatment. LCOFs have unique properties such as high surface area, porosity, and tunability, which make them attractive adsorbents and catalysts for water and wastewater treatment. The review covers the different synthesis methods for LCOFs, including self-assembly, co-crystallization, template-directed synthesis, covalent organic polymerization (COP), and solvothermal synthesis. It also covers the structural and chemical characteristics of LCOFs, their adsorption and degradation capacity for different pollutants, and their comparison with other adsorbents and catalysts. Additionally, it discussed the mechanism of adsorption and degradation by LCOFs, the potential applications of LCOFs in water and wastewater treatment, case studies and pilot-scale experiments, challenges, and limitations of using LCOFs, and future research directions. The current state of research on LCOFs for water and wastewater treatment is promising, however, more research is needed to improve their performance and practicality. The review highlights that LCOFs have the potential to significantly improve the efficiency and effectiveness of current water and wastewater treatment methods and can also have implications for policy and practice.

Plasma microbubbles vs gas-liquid DBD energized by low-frequency high voltage nanopulses for pollutants degradation in water: Destruction mechanisms, composition of plasma-activated water and energy assessment

The main scope of this study was the direct comparison of gas-liquid DBD and plasma microbubbles (PMB) driven by high voltage nanopulses in terms of pollutant destruction mechanisms, plasma-activated water composition and cost-effectiveness. The comparison between gas-liquid DBD and PMB was evaluated in terms of water physicochemical properties and plasma species concentrations, performance towards the degradation of dyes with different structure, energy yield and electrical energy per order (EEO) whereas the role of various critical parameters including feeding gas, gas flow rate, applied voltage, water matrix and pollutant concentration was investigated. Different plasma-liquid interactions between the two systems led to high concentrations of long-lived species (NO3–, NO2–, H2O2, O3) and a significant decrease in solution pH in gas-liquid DBD compared to low concentrations of long-lived species and near-neutral pH in PMB. PMB bears important advantages, including higher .OH concentrations, faster degradation kinetics and lower energy requirements compared to gas-liquid DBD whereas the decisive species were found to depend on the target pollutant. The energy yield of the current nanopulsed-driven PMB system was extremely high (82.1 g/kWh) whereas its EEO (0.25 kWh/m3) was one of the lower ever reported. However, the low concentrations of long-lived species and almost neutral pH may act negatively for the removal of contaminants whose degradation is favored at lower pH and/or high long-lived species concentrations. This study provides insights into both gas-liquid DBD and PMB systems contributing on the further exploitation of the plasma-based wastewater treatment.

Carbonaceous Catalyst Activated Persulfate for Degradation of Antibiotic Pollutants in Water

In recent years, the frequent use of antibiotics has led to the continuous release of antibiotics into the water environment, which not only poses a potential threat to public health, but also contributes to the generation and spread of antibiotic resistance. In addition, due to the high environmental persistence and low biodegradability of antibiotics, it is difficult to be effectively degraded by traditional water treatment processes. Therefore, it is urgent to develop clean and efficient treatment technologies. Advanced oxidation processes (AOPs), which can effectively remove refractory organic pollutants from water, has become a promising water treatment technology. In this regard, persulfate (PS)-based AOPs (PS-AOPs) has attracted extensive attention of researchers. In this system, PS can be activated by energy and catalysts to produce highly oxidizing active species, and achieve efficient degradation of antibiotics. Due to its rich surface functional groups, high specific surface area and high adsorption properties, researches on the activation of PS by carbonaceous materials have been reported continuously. In this paper, the research progress of carbon nanotubes, graphene, biological carbon, active carbon and hetero-atom doped carbon materials as catalysts to activate PS and degrade antibiotics is reviewed. In addition, the structure and properties of different carbon materials and the activation mechanism of free radical and non-free radical mediated by carbon materials were introduced, and the effects of PS dosage, catalyst dosage, temperature and pH on the degradation of antibiotics were discussed. Finally, this paper points out the important development direction in the future, that is, the development of environmental protection, high efficiency, low cost carbon materials and further research on the actual wastewater treatment performance.

Efficient photocatalytic degradation of water contaminants via Ag decorated porphyrin-based organic framework materials

With high specific surface area, strong photoabsorption efficiency and outstanding semiconducting properties, porphyrin-based organic frameworks (MOFs) have become the focus of research on efficient photocatalysts. However, the rapid compounding of electrons and holes results in low efficiency of photogenerated electrons, hindering the photocatalytic performance of this type of catalyst. In this work, MOF-525 composite catalysts modified with Ag (Ag@MOF-525) were prepared by photoreduction method and applied to the visible photocatalytic degradation of pollutants in water. Owing to the formation of a Schottky barrier on the surface of porphyrin-based MOFs with Ag nanoparticles (AgNPs), the unique surface plasmon resonance (SPR) effect is generated, which promoted the absorption of visible light by MOF-525; meanwhile, Ag acts as an electron trap, resulting in an effective suppression of electron-hole complexation, boosting the electron transfer between them and the semiconductor MOFs and improving the efficiency of the photogenerated carriers, thus promoting the improvement of photocatalytic activity. Taking rhodamine B (RhB) and tetracycline (TC) as the target degradants, Ag@MOF-525 showed higher photocatalytic activity compared with the MOF structural unit (TCPP) and MOF-525. The degradation rate of RhB was achieved at 91% in 60 min; and the degradation rate of TC, which is very difficult to mineralize, was also achieved at 81% in 200 min. Through a series of detailed analyses including XRD, HRTEM and DRS on the structure, composition and light response range of the samples, it is demonstrated that the successful loading of singlet Ag could effectively extend the light response range of MOF-525 and promote the separation of electrons and holes. In addition, the radical trapping experiments indicated that h+ and •O2− are the main active species and possible degradation mechanisms are discussed.

Germanane and butyl-functionalized germanane as visible-light photocatalysts for the degradation of water pollutants

Germanane, a two-dimensional Ge lattice in which each atom is hydrogen-terminated in the z-direction, possesses a remarkable combination of electronic and optical properties that are attractive for applications ranging from chemical sensing to electrocatalysis and photocatalysis. In this work, we studied germanane (GeH) and the novel butyl-functionalized germanane (GeBuxH(1−x)) as photocatalysts for water purification under visible light irradiation and utilizing challenging conditions in terms of photocatalyst loading (1 mg per g of aqueous solution containing 200 ppm of pollutant). The synthesized GeH and GeBuxH(1−x) have significantly higher specific surface area (121 m2 g−1 and 76 m2 g−1, respectively) than other germanane derivatives reported to date and display optical band gaps suitable for visible light absorption (1.40 eV and 1.55 eV, respectively). In terms of photocatalytic performance, GeH displayed the best activity in the degradation of rhodamine B (61% removal after 3 h under visible radiation), while GeBuxH(1−x) proved to be the best photocatalyst for the degradation of phenol (33% removal after 3 h under visible radiation). In both cases, the activity under visible radiation surpassed that of P25 TiO2 and could be enhanced significantly by sonication in water before interaction with the pollutants. Recycling tests showed that GeH could be reused with no or negligible loss of photocatalytic activity, whereas GeBuxH(1−x) showed a minor decrease in activity upon reuse.

In-house vs. commercial boron-doped diamond electrodes for electrochemical degradation of water pollutants: A critical review

Boron-doped diamond (BDD) electrodes are eco-friendly and widely used in efficient water remediation through electrochemical advanced oxidation processes (EAOPs). These anodes can completely mineralize a wide range of pollutants, only requiring electrical energy. Over the last 2 decades, numerous commercially available BDD electrodes have emerged, but little is known about their electrooxidation performance, particularly if compared to laboratory-produced anodes by different research groups. In this critical review, a comparison between in-house-made and commercially available BDD electrodes based on a systematic literature review (SLR) is carried out. SLR was quite useful in locating and selecting the scientific publications relevant to the topic, enabling information gathering on dissemination, growth, and trends in the application of BDD electrodes in the degradation of water pollutants. More specifically, data concerning the origin of the employed BDD electrodes, and their physicochemical properties were extracted from a thorough selection of articles. Moreover, a detailed analysis of the main parameters affecting the BDD electrodes’ performance is provided and includes selection and pre-treatment of the substrate material, chemical vapor deposition (CVD) method, deposition parameters, characterization methods, and operational conditions. This discussion was carried out fully based on the numerous performance indicators found in the literature. Those clearly revealed that there are only a few analogous points across works, demonstrating the challenge of establishing an accurate comparison methodology. In this context, we propose a figure-of-merit equation which aims at normalizing BDD degradation results for a specific contaminant, even if working under different experimental conditions. Two case studies based on the degradation of solutions spiked with phenol and landfill leachate treatment with commercial or in-house-made BDD electrodes are also presented. Although it was not possible to conclude which electrode would be the best choice, we propose a set of guidelines detailing a consistent experimental procedure for comparison purposes in the future.

Weak visible-light photo-piezoelectric synergistic catalyst based on the Bi2Fe4O9/Carbon-dots/g-C3N4 heterostructure

The photocatalytic efficiency towards water pollutant degradation has been limited due to the intermittence of the sunlight, low light utilization and rapid recombination of photoexcited electron-hole pairs. Here a photo-piezoelectric synergistic catalyst of Bi2Fe4O9/Carbon-dots/g-C3N4 heterostructure has been fabricated by loading Bi2Fe4O9 on the Carbon-dots modified g-C3N4 with opened g-C3N4 layer distance, which combined large surface area and photocatalytic activity of Carbon-dots/g-C3N4, and excellent piezoelectric effect of Bi2Fe4O9 for better electron-hole separation efficiency, achieved highly efficient antibiotics and dye degradation even under very weak visible-light treatment and mechanical stress. This heterostructure may fully use wave energy and light irradiation in numerous natural water environmental conditions and enhance the catalytic degradation efficiency, even in cloudy weather or at night when the photocatalytic activity is invalidated.

Low‐temperature synthesis of maize straw biochar‐ZnO nanocomposites for efficient adsorption and photocatalytic degradation of methylene blue

AbstractAs a new type of environmental functional material, biochar composites have become the focus of considerable interest in wastewater treatment research owing to their excellent adsorption and photocatalytic properties. However, the fabrication of cost‐effective biochar composites with high photocatalytic efficiencies at low synthesis temperatures remains challenging. In this study, biochar was prepared using an environmentally friendly hydrothermal method at a low temperature with maize straw as the waste material, instead high costs pyrolysis process. Hexagonal zinc oxide nanoparticles were grown in and on the biochar framework using the chemical deposition method. The adsorption and photocatalytic degradation performance of aqueous methylene blue (MB) solutions were investigated. We demonstrated that the photocatalytic degradation performance of the biochar‐ZnO composites was considerably higher than that of the most other reports. The degradation of the MB solutions (60 mg/L) reached 98.0 % in 240 min under low‐power ultraviolet light (50 W) irradiation. We propose that the synergetic effect of the high adsorption of the porous biochar and the photocatalytic activity of ZnO led to a high degradation efficiency. This study provides theoretical and practical guidance for the preparation of photocatalytic composites obtained from waste biomass materials by a cost‐efficient, fast, and environmentally friendly method, and the efficient degradation of dye pollutants in water.

Recent Progress of Single-Atom Photocatalysts Applied in Energy Conversion and Environmental Protection.

Photocatalysis driven by solar energy is a feasible strategy to alleviate energy crises and environmental problems. In recent years, significant progress has been made in developing advanced photocatalysts for efficient solar-to-chemical energy conversion. Single-atom catalysts have the advantages of highly dispersed active sites, maximum atomic utilization, unique coordination environment, and electronic structure, which have become a research hotspot in heterogeneous photocatalysis. This paper introduces the potential supports, preparation, and characterization methods of single-atom photocatalysts in detail. Subsequently, the fascinating effects of single-atom photocatalysts on three critical steps of photocatalysis (the absorption of incident light to produce electron-hole pairs, carrier separation and migration, and interface reactions) are analyzed. At the same time, the applications of single-atom photocatalysts in energy conversion and environmental protection (CO2 reduction, water splitting, N2 fixation, organic macromolecule reforming, air pollutant removal, and water pollutant degradation) are systematically summarized. Finally, the opportunities and challenges of single-atom catalysts in heterogeneous photocatalysis are discussed. It is hoped that this work can provide insights into the design, synthesis, and application of single-atom photocatalysts and promote the development of high-performance photocatalytic systems.

Reduced graphene oxide decorated transition metal manganese vanadium oxide nanorods for electrochemical supercapacitors and photocatalytic degradation of pollutants in water

BackgroundGraphene-based nanostructured metal oxides have great attention in the field of electrochemistry and photochemistry due to their electrochemical, optical, and electronic properties. This Mn2V2O7-rGO hybrid catalyst demonstrated excellent stability and reusability, indicating that it is an efficient, cost-effective, and environmentally friendly catalyst. MethodsOur research aims to develop effective supercapacitor (SC) electrodes and photocatalysts by incorporating reduced graphene oxide (rGO) into manganese vanadium oxide (Mn2V2O7) nanorods to generate a Mn2V2O7-rGO hybrid composite via a single-step hydrothermal process. As prepared catalysts are investigated using different analytical methods such as optical, morphological, XPS, and ESR for radical analysis. Significant findingsThe Mn2V2O7-rGO nanorods coated on a carbon sheet exhibited a specific capacitance of 882 Fg−1 at 0.6 current density. The Mn2V2O7-rGO supercapacitor also exhibited long-term cyclic stability, with 88% of its original specific capacitance remaining after 2000 cycles. These findings open a new pathway for SCs as promising electrode materials. The Mn2V2O7-rGO hybrid was then tested for photocatalytic activity using ciprofloxacin (CIP). The photocatalytic reduction process destroyed >96% of the CIP after 60 min. The prepared catalyst was then used to investigate the electron transfer mechanism. The combination of rGO and Mn2V2O7 formed a conductive nano-network, yielding a highly active material.

Unravelling the synergy of Ce dopant and surface oxygen vacancies confined in FeTiO3 perovskite for peroxymonosulfate activated degradation of wide range of pollutants

In this study, ferrite titanate (FeTiO3) as a low-cost, eco-friendly and a new type of perovskite catalyst was utilized in sulfate-based advanced oxidation process. Structural and chemical modulation strategy was implemented by doping cerium (Ce) atoms via hydrothermal technique. The morphological, optical and structural properties of the catalysts were investigated with the aid of XRD, SEM-EDS, TEM, XPS, UV–vis DRS and PL analyses. XPS analysis confirmed that Ce existed as Ce(III) and Ce(IV) oxidation states, indicating the presence of Ce(III)/Ce(IV) redox couple, which assisted the oxidative degradation process. The introduction of Ce into the FeTiO3 structure also resulted in higher content of oxygen vacancies, regulated the redox cycle, and reduced the energy barrier for Fenton activation. The photocatalytic performances of Ce-doped FeTiO3 perovskites for peroxymonosulfate activation were investigated towards removal of sunset yellow azo dye which is one of the most used synthetic food dyes. The effects of Ce concentrations in FeTiO3, initial solution pH, water media, scavengers and re-usability were studied systematically. Moreover, the photodegradation activities of the catalyst with respect to different dye and antibiotic components were also investigated. The catalyst was proven to be stable after eight consecutive runs. The findings showed that the incorporation of Ce as a peroxymonosulfate activator greatly facilitated the degradation of water pollutants.

Tannin-functionalized Mn3O4 as support for FeNiB alloy to construct sono-Fenton-like reaction for the degradation of antibiotic pollutants in water

In this paper, iron-based amorphous alloy (FeNiB) supported on Tannin-functionalized Mn3O4(Mn3O4-TA@FeNiB) were prepared and used as a heterogeneous catalyst to degrade ciprofloxacin (CIP) and norfloxacin (NOR) in aqueous solution by the ultrasound (US)-assisted Fenton-like process. The physicochemical properties of the resulting Mn3O4-TA@FeNiB were characterized by SEM, TEM, XRD, BET, FTIR, XPS and other techniques. The results showed that 92.04% and 90.34% of CIP and NOR at their initial concentration of 10 mg L−1 were removed by the sono-Fenton-like system after 60 min in comparison with 85.24% and 82.52% of CIP and NOR removal after 300 min by Mn3O4-TA@FeNiB alone and the rate constants of the former were 6.65 and 6.80 times higher than those of the latter, respectively. Excellent catalytic performances were benefited from synergistic interactions between US, H2O2 and Mn3O4-TA@FeNiB. Mn3O4-TA as a support and stabilizer could effectively load and disperse FeNiB, meanwhile providing reactive area and active sites (Mn2+/Mn3+). FeNiB was corroded to produce Fe2+ and Ni2+, thus forming reversible redox reactions between polyvalent metals, which ensured Fenton-like reaction to be effectively proceeded. While US accelerated the oxidation process to generate more reactive species, which resulted in higher catalytic efficiencies and reaction rates of CIP and NOR degradation. Metal leaching and cycling experiments showed that Mn3O4-TA@FeNiB exhibited good stability and reusability. Finally, the degradation intermediates of CIP were analyzed and the possible degradation mechanisms and pathways were proposed. These results indicated that Mn3O4-TA@FeNiB had great potential as an effective and low-cost catalyst in US-assisted Fenton-like process for removal of the emerging pollutants.

Engineered tourmaline/g-C3N4 composites for photocatalytic Fenton-like oxidation: Synergy of spontaneous interface polarization and surface iron circulations induced by minerals

The peroxymonosulfate/peroxydisulfate (PMS/PDS) activation induced by photocatalytic reduction reaction is an economical and green means for oxidative degradation of organic pollutants in water. However, its efficiency is largely limited by the rapid recombination of photogenerated electron-holes. Herein, we report a graphitic carbon nitride (g-C3N4)-based photocatalytic persulfate activation system fine-tuned by a natural polarized Fe-containing mineral, tourmaline. The tourmaline/g-C3N4 composite photocatalyst was prepared to activate PMS for efficient carbamazepine (CBZ) degradation. In this system, the electrons and holes were produced by tourmaline/g-C3N4 composites under light excitation. Subsequently, PMS was activated by photogenerated electrons from g-C3N4 and Fe2+ on the surface of tourmaline to generate SO4•−, where partial SO4•− further reacted with H2O/OH– to produce •OH. Finally, the CBZ was oxidized by SO4•−, •OH and photo-induced holes. Under optimal conditions, with the presence of PMS, the degradation rate of CBZ conducted by tourmaline/g-C3N4 is 6.2 and 7.7 times of pristine g-C3N4 and tourmaline. It is revealed that the polarization electric field of tourmaline not only boosted the separation and migration of electron-hole of g-C3N4, but also optimized the electronic structure of g-C3N4 for intensified light absorption and improved reduction ability. Moreover, the Fe2+/Fe3+ cycle of tourmaline also facilitated the utilization of photogenerated electrons from g-C3N4 for PMS activation reactions. This study has innovatively constructed a photocatalytic PMS activation system enhanced by introducing natural Fe-containing polarized minerals, providing a new strategy for sustainable and low-cost advanced oxidation processes for water treatment.

Activation of peroxymonosulfate by g-C3N4/ε-MnO2 microspheres for nonradical pathway degradation of organic pollutants in water: Catalytic mechanism and degradation path

ε-MnO2 has the potential to activate persulfate for the elimination of organic contaminants. However, the sluggish electron transfer caused by the excessive structural defects and the easy agglomeration during preparation and reaction severely suppresses the catalytic activity of ε-MnO2. Herein, g-C3N4 modified ε-MnO2 composites (g-C3N4/ε-MnO2) are synthesized by precipitation method coupling with calcination, and their catalytic activities are investigated vis peroxymonosulfate (PMS) activation for removal of acid orange 7 (AO7) in aqueous solution. Characterization results show that the g-C3N4 nanosheets modified ε-MnO2 nanoparticles are assembled to form the hierarchical microspheres, which not only can provide abundant active sites but also can effectively promote electron mobility for the degradation of AO7. Consequently, the g-C3N4/ε-MnO2 composites deliver high catalytic performance in activating PMS, resulting in 98.5 % of AO7 is degraded in 80 s, which is much better than the bare ε-MnO2. Nonradical pathways dominate the degradation process of AO7 and 1O2 is the main ROS. Density functional theory calculations demonstrate that PMS activation is more easily achieved on the surface of the g-C3N4/ε-MnO2 than the bare g-C3N4 and ε-MnO2. The possible degradation mechanisms for g-C3N4/ε-MnO2/PMS system include the interaction between PMS and ε-MnO2 and electron transfer to PMS in the redox cycle of Mn(II), Mn(III), and Mn(IV). This work provides insight into the promotion of efficient MnO2 catalysts in PMS activation for the degradation of organic pollutants.