Activation of peroxymonosulfate by a floating oxygen vacancies - CuFe2O4 photocatalyst under visible light for efficient degradation of sulfamethazine

Real "zero energy consumption" for efficient antibiotics degradation by floating photocatalysis: modeling, degradation pathway and toxicity assessment

Floating photocatalysis is a real "zero energy consumption" and practicable green water treatment technology because of no need for reactor and pump, and direct contact with sunlight to produce more free radicals compared to traditional immersion photocatalysts. To realize "green" and "safe" practical application, efficiency for different water quality bodies and toxicity assessment of degradation products are key factors. In this work, an economic and efficient floating photocatalyst Bi doped P25-TiO2 (Bi@P25)/expanded perlite (EP), named BTEP was successfully constructed, exhibiting stronger visible light absorption and faster photogenerated carriers separation ability due to Bi doping and formation of Bi-O-Si bond. Ciprofloxacin (CIP) degradation efficiency (10 mg/L) in deionized water and three types of ambient water reached 97.8 % and 52.9 %-75.2 %, respectively, based on the major active species (h+ and •O2-). Three degradation pathways were determined and the reduced toxicity of most intermediates proved the process is green and safe. BTEP had strong adaptability over a wide pH range (3-9). The degradation efficiency is promoted by higher temperatures, while depressed by humic acid (HA) (still maintain over 65.3 % at 15 mg/L of HA). Moreover, the Random Forest model is the most suitable to achieve degradation efficiency prediction of different water parameters duo to the lowest root mean square error (RMSE) value (9.52) and the highest R2 value (0.9045). The BTEP based floating photocatalysis promotes the practical application of solar photocatalytic technology and realizes zero energy consumption to remove pollutants.

Removal of sulfonamides by persulfate-based advanced oxidation: A mini review

Sulfonamides (SAs) are known for their persistence and have become one of the most frequently detected pharmaceuticals and personal care products (PPCPs) in the environments. The widespread presence of SAs in natural waters, wastewater, soil, and sediment has prompted growing concern due to their potential threats to both human health and ecological systems. Persulfate-based advanced oxidation processes (PS-AOPs) have emerged as a promising technology for effectively mitigating the presence of these pollutants in the environment. This review offers a comprehensive overview of the degradation of SAs by PS-AOPs. The various activation methods of persulfate for the purpose of removing SAs are elaborated upon in detail. The factors influencing the removal efficiency of SAs through PS-AOPs is thoroughly discussed. Additionally, the conceivable mechanisms and degradation pathways associated with various types of SAs are discussed. Lastly, existing challenges are identified, and future prospects pertaining to the utilization of PS-AOPs for efficient SA removal are presented.

Electronic coupling of iron-cobalt in Prussian blue towards improved peroxydisulfate activation

Prussian blue analogs (PBAs) have attracted extensive attention in the field of aqueous organic degradation due to the tremendous potential for peroxydisulfate (PDS) activation. However, the relationship between the d-band center of the catalyst and the activation behavior of PDS remained largely unexplored. Herein, a series of Fe-Co PBAs-based catalysts with different Fe/Co ratios (Fe-Co PBAs-1 = 1: 0.52; Fe-Co PBAs-2 = 1: 1.21, and Fe-Co PBAs-3 = 1: 1.48) have been prepared by a facile hydrothermal procedure and subsequent acid treatment (Fe-Co PBAs-xH). The as-prepared Fe-Co PBAs-xH exhibited superior PDS activation performance and excellent recyclability in the degradation of methylene blue (MB). Density functional theory calculations revealed that the electron-occupied state of the Fe-Co PBAs was shifted to the Fermi level, indicating a strong interaction and easier electron transfer. Moreover, the d-band center of Fe-Co PBAs was upshifted relative to that of Fe PBAs, suggesting easier adsorption of MB and PDS, which was beneficial to enhancing catalytic activation and subsequent dissociation. Radicals such as •OH, 1O2, O2•-, and SO4•- were determined by the radical quenching experiment and electron paramagnetic resonance (EPR) testing in the Fe-Co PBAs-3H/PDS system, and the order of MB degradation by the free active radical is •OH > 1O2 > O2•- > SO4•-. The degradation pathway and potential ecotoxicity of MB and its intermediates were also studied. This work can provide new insights to construct the efficient catalysts for the activation of PDS and the degradation of organic pollutants.

Hydroxylamine hydrochloride-driven activation of NiFe2O4 for the degradation of phenol via peroxymonosulfate

In this study, hydroxylamine hydrochloride (HA) was employed to enhance the activation of NiFe2O4 towards peroxymonosulfate (PMS) for the effective degradation of phenol. NiFe2O4 particles were synthesized via a simple hydrothermal method, followed by characterization of their surface morphology, and microstructure. Upon the addition of HA to the system of NiFe2O4/PMS, the degradation activity is significantly enhanced. The degradation efficiency of phenol reached 98.5% after 60 min using 0.6 g/L NiFe2O4, 3 mmol/L PMS, 2 mmol/L HA at pH 7, which increased by 4.76 times compared to the system without HA. The study further explored the activation mechanism of the NiFe2O4/HA/PMS system, revealing that HA significantly enhanced the conversion of Fe3+/Fe2+ and the leaching of metal ions, thereby accelerating the reaction rate. In addition, the NiFe2O4/HA/PMS system proved effective across a broad range of pH values. This study provides new insights and perspectives into enhancing peroxymonosulfate activation coupled with metal oxides catalysts through the use of reducing agents.

Interface Structure Strengthening of a Mesoporous Silicon/Expanded Perlite Microevaporator for Efficient Solar-Driven Interfacial Evaporation

Solar-driven interfacial evaporation is one of the cutting-edge technologies for seawater desalination and wastewater purification. Herein, a floating carbon-coated silica microsphere/expanded perlite integrated interfacial microevaporator (HEPCL) is reported. The carbon nanolayer allows the HEPCL to have better broadband light absorption performance than natural graphite and graphene oxide. Through the low density of expanded perlite, HEPCL particles can self-float on the water surface and self-aggregate into an integrated whole under surface tension, which enhances the heat collection capacity. The hierarchical porous structure of the HEPCL has a continuous water absorption capacity. Notably, water molecules adsorbed in the HEPCL have a high desorption energy, which reduces the water evaporation enthalpy (1621 kJ/kg), making it easy to remove with external energy. Thanks to the design merits, the HEPCL achieves a water evaporation rate of 1.551 kg m-2 h-1 (efficiency of 94.85%) under 1 sun irradiation and may inspire a practicable solution of water scarcity.

Recent progress in defect-engineered metal oxides for photocatalytic environmental remediation

Rapid industrial advancement over the last few decades has led to an alarming increase in pollution levels in the ecosystem. Among the primary pollutants, harmful organic dyes and pharmaceutical drugs are directly released by industries into the water bodies which serves as a major cause of environmental deterioration. This warns of a severe need to find some sustainable strategies to overcome these increasing levels of water pollution and eliminate the pollutants before being exposed to the environment. Photocatalysis is a well-established strategy in the field of pollutant degradation and various metal oxides have been proven to exhibit excellent physicochemical properties which makes them a potential candidate for environmental remediation. Further, with the aim of rapid industrialization of photocatalytic pollutant degradation technology, constant efforts have been made to increase the photocatalytic activity of various metal oxides. One such strategy is the introduction of defects into the lattice of the parent catalyst through doping or vacancy which plays a major role in enhancing the catalytic activity and achieving excellent degradation rates. This review provides a comprehensive analysis of defects and their role in altering the photocatalytic activity of the material. Various defect-rich metal oxides like binary oxides, perovskite oxides, and spinel oxides have been summarized for their application in pollutant degradation. Finally, a summary of existing research, followed by the existing challenges along with the potential countermeasures has been provided to pave a path for the future studies and industrialization of this promising field.

Promoting oxygen vacancies utility for tetracycline degradation via peroxymonosulfate activation by reduced Mg-doped Co3O4: Kinetics and key role of electron transfer pathway

Developing cobalt-based catalysts with a high abundance of oxygen vacancies (Vo) and exceptional Vo utility efficiency for the prompt removal of stubborn contaminants through peroxymonosulfate (PMS) activation poses a significant challenge. Herein, we reported the synthesis of the reduced Mg-doped Co3O4 nanosheets, i.e. Mg-doped Co3O4-r, via Mg doping and followed by NaBH4 reduction, aiming to degrade tetracycline (TC). Various characterization results illustrated that NaBH4 reduction imparted higher Vo utility efficiency to Mg-doped Co3O4-r, along with an ample presence of reduced Co2+ species and an increased surface area, thereby substantially elevating PMS activation capability. Notably, Mg-doped Co3O4-r achieved more than 97.9% degradation of 20 mg/L TC within 10 min, showing an over 8-fold increase in reaction rate relative to the Mg-doped Co3O4 (kobs: 0.3285 min-1 vs 0.0399 min-1). The high removal efficiency of TC was sustained across a broad pH range of 3-11, even in the presence of common anions and humic acid. Radical quenching trials, EPR outcomes, and electrochemical analysis indicated that neither radicals nor 1O2 were the primary active species. Instead, electron transfer pathway played a dominant role in TC degradation. The Mg-doped Co3O4-r displayed excellent recyclability and versatility. Even after the fifth cycle, it maintained an impressive 83.0% removal of TC. Furthermore, it exhibited rapid degradation capabilities for various pollutants, including levofloxacin, pefloxacin, ciprofloxacin, malachite green, and rhodamine B. The TC degradation pathway was proposed based on LC-MS determination of its degradation intermediates. This study showcases an innovative strategy for the rational design of an efficient cobalt-based activator, leveraging electron transfer pathways through PMS activation to degrade antibiotics effectively.

Floating photocatalysts as promising materials for environmental detoxification and energy production: A review

The oxygenation process of the catalyst surface, the incident-light harvesting capability, and facile recycling of utilized photocatalysts play key role in the outstanding photocatalytic performances. The typical existing photocatalysts in powder form have many drawbacks, such as difficult separation from the treated water, insufficient surface oxygenation, poor active surface area, low incident-light harvesting ability, and secondary pollution of the environment. A great number of scientific works introduced novel and fresh ideas related to designing floating photocatalytic systems by immobilizing highly active photocatalysts onto a floatable substrate. Thanks to direct contact with the illuminated light and oxygen molecules in the interface of water/air, the photocatalytic performance is maximized through production of more reactive species, employed in the photocatalytic reactions. Furthermore, facile recovering of the utilized photocatalysts for next processes avoids secondary pollution as well as diminishes the process's price. This review highlights the performance of developed floating photocatalysts for diverse applications. Furthermore, different floating substrates and possible mechanisms in floating photocatalysts are briefly mentioned. In addition, several emerging self-floating photocatalytic systems are taken attention and discussed. Specially, coupling photo-thermal and photocatalytic effects seems to be a good strategy for introducing a new class of floating photocatalyst to utilize the free, abundant, and green sunlight energy for the aims of water desalination and purification. Despite of a large number of attempts about the floating photocatalysts, there are still plenty of rooms for more in-depth research to be carried out for attaining the required characteristics of the large scale utilizations of these materials.

Interfacial coupling of CuFe2O4 induced hotspots over self-assembled g-C3N4 nanosheets as an efficient photocatalytic bacterial disinfectant

Most bacterial disinfectants contain high levels of extremely toxic and environmental hazardous chemicals, which pose a significant threat to the ecosystem. Semiconductor photocatalysis exhibits attractive prospects as an emerging greener technology for waste water disinfection. However, the fast recombination of charge carriers limits its practical application. Herein, self-assembled polymeric feather-like g-C3N4 (GCN) nanosheets modified with ferromagnetic CuFe2O4 (CFO) nanospheres were successfully applied as a reusable visible light photocatalytic disinfectant. As expected, the g-C3N4/CuFe2O4 (GCF) nanohybrid displayed superior photocatalytic inactivation efficiency of 0.157log within 120 min towards Escherichia coli DH5α (E. coli) compared with pristine GCN and CFO. The characterization results revealed the synergistic heterostructure interfaces, high surface area, and the transformative self-assembly of GCN to feather-like structure providing a rich active site for improved charge separation efficiency, and wide spectral response, therefore the superior performance of GCF. The radical trapping assay proclaimed that both O2•- and •OH radical played major role in the photocatalytic inactivation among the other reactive oxygen species (ROS). Furthermore, the chemical oxygen demand (COD), protein estimation, and DNA estimation assay results validated the cell damage caused by the photocatalyst. Besides that, GCN showed applicability in real-time wastewater samples with improved efficiency than in the saline solution. The excellent magnetic characteristics facilitated the recycling of the catalyst with insignificant leaching, magnetic induction, and distinguished separation. The results of this work signify the well-designed GCF as a high-performance and reusable photocatalyst for real-world pathogenic bacterial disinfection operations.

Fabrication of water-floating litchi-like polystyrene-sphere-supported TiO2/Bi2O3 S-scheme heterojunction for efficient photocatalytic degradation of tetracycline

The exploration of advanced photocatalysts for antibiotic degradation is critical, but it remains a challenge due to the lack of rational structural design and in-depth insights into molecular oxygen activation. Water-floating photocatalysts could be one of the best choices owing to their technical features in terms of reasonability and efficiency involving a high oxygenation of photocatalyst surface, fully solar irradiation, and simple recycling and reuse. Herein, a floatable litchi-like architecture of a polystyrene-sphere-supported TiO2/Bi2O3 (PS@TiO2/Bi2O3) S-scheme heterojunction was skillfully constructed and evaluated for photodegradation of model tetracycline (TC) antibiotics. By integrating the advantages of floatability and S-scheme, the TC removal rate of the optimal PS@TiO2/Bi2O3-0.4 catalyst can reach 88.4% under 1 h illumination, which is higher than that of pristine Bi2O3 (60.8%) and PS@TiO2 (40.1%). Moreover, PS@TiO2/Bi2O3-0.4 exhibits high recyclability and stability, and there is no significant loss of activity after five cycles of repeated use. With the aid of liquid chromatography-mass spectrometry analysis and density functional theory calculations, a reasonable degradation pathway for TC was proposed. The present work provides a recyclable and efficient approach for the photodegradation of TC, expecting to guide the innovative exploitation of other environmental systems.

Effective removal of azithromycin by novel g-C3N4/CdS/CuFe2O4 nanocomposite under visible light irradiation

In this study, the visible light active pristine, binary and ternary g-C₃N₄/CdS/CuFe₂O₄ nanocomposite is prepared through a coprecipitation-assisted hydrothermal technique. The characterization of the as-synthesized catalysts was conducted using various analytical techniques. When compared with pristine and binary nanocomposites, the ternary g-C₃N₄/CdS/CuFe₂O₄ nanocomposite exhibits higher photocatalytic degradation of azithromycin (AZ) under a visible light source. Ternary nanocomposite exhibits high AZ removal efficiency of about 85% within 90 min of the photocatalytic degradation experiment. Enhanced the visible light absorption ability and the suppression of photoexcited charge carriers is also achieved by forming heterojunctions between pristine materials. The ternary nanocomposite exhibited ∼2 times higher degradation efficiency than CdS/CuFe₂O₄ nanoparticles and ∼3 times higher degradation efficiency than CuFe₂O₄. The trapping experiments were conducted and it shows superoxide radicals (O₂^•-) are the predominant reactive species involved in the photocatalytic degradation reaction. This study provided a promising approach for the treatment of contaminated water using g-C₃N₄/CdS/CuFe₂O₄ as a photocatalyst.

Accelerated radical generation from visible light driven peroxymonosulfate activation by Bi2MoO6/doped gCN S-scheme heterojunction towards Amoxicillin mineralization: Elucidation of the degradation mechanism

A novel S-scheme photocatalyst Bi₂MoO₆ @doped gCN (BMO@CN) was prepared through a facile microwave (MW) assisted hydrothermal process and further employed to degrade Amoxicillin (AMOX), by peroxymonosulfate (PMS) activation with visible light (Vis) irradiation. The reduction in electronic work functions of the primary components and strong PMS dissociation generate abundant electron/hole (e^-/h⁺) pairs and SO₄^*-,*OH,O₂^*-reactive species, inducing remarkable degeneration capacity. Optimized doping of Bi₂MoO₆ on doped gCN (upto 10 wt%) generates excellent heterojunction interface with facile charge delocalization and e^-/h⁺ separation, as a combined effect of induced polarization, layered hierarchical structure oriented visible light harvesting and formation of S-scheme configuration. The synergistic action of 0.25 g/L BMO(10)@CN and 1.75 g/L PMS dosage can degrade 99.9% of AMOX in less than 30 min of Vis irradiation, with a rate constant (k_obs) of 0.176 min^-1. The mechanism of charge transfer, heterojunction formation and the AMOX degradation pathway was thoroughly demonstrated. The catalyst/PMS pair showed a remarkable capacity to remediate AMOX-contaminated real-water matrix. The catalyst removed 90.1% of AMOX after five regeneration cycles. Overall, the focus of this study is on the synthesis, illustration and applicability of n-n type S-scheme heterojunction photocatalyst to the photodegradation and mineralization of typical emerging pollutants in the water matrix.

Materials Based on Co, Cu, and Cr as Activators of PMS for Degrading a Representative Antibiotic-The Strategy for Utilization in Water Treatment and Warnings on Metal Leaching

A chromate of copper and cobalt (Φy) was synthesized and characterized. Φy activated peroxymonosulfate (PMS) to degrade ciprofloxacin (CIP) in water. The Φy/PMS combination showed a high degrading capability toward CIP (~100% elimination in 15 min). However, Φy leached cobalt (1.6 mg L^-1), limiting its use for water treatment. To avoid leaching, Φy was calcinated, forming a mixed metal oxide (MMO). In the combination of MMO/PMS, no metals leached, the CIP adsorption was low (<20%), and the action of SO₄•^- dominated, leading to a synergistic effect on pollutant elimination (>95% after 15 min of treatment). MMO/PMS promoted the opening and oxidation of the piperazyl ring, plus the hydroxylation of the quinolone moiety on CIP, which potentially decreased the biological activity. After three reuse cycles, the MMO still presented with a high activation of PMS toward CIP degradation (90% in 15 min of action). Additionally, the CIP degradation by the MMO/PMS system in simulated hospital wastewater was close to that obtained in distilled water. This work provides relevant information on the stability of Co-, Cu-, and Cr-based materials under interaction with PMS and the strategies to obtain a proper catalyst to degrade CIP.

Effective photodegradation of antibiotics by guest-host synergy between photosensitizer and bismuth vanadate: Underlying mechanism and toxicity assessment

The removal of antibiotics in wastewater has attracted increasing attention. Herein, a superior photosensitized photocatalytic system was developed with acetophenone (ACP) as the guest photosensitizer, bismuth vanadate (BiVO₄) as the host catalyst and poly dimethyl diallyl ammonium chloride (PDDA) as the bridging complex, and used for the removal of sulfamerazine (SMR), sulfadiazine (SDZ) and sulfamethazine (SMZ) in water under simulated visible light (λ > 420 nm). The obtained ACP-PDDA-BiVO₄ nanoplates attained a removal efficiency of 88.9%-98.2% for SMR, SDZ and SMZ after 60 min reaction and achieved kinetic rate constant approximately 10, 4.7 and 13 times of BiVO₄, PDDA-BiVO₄ and ACP-BiVO₄, respectively, for SMZ degradation. In the guest-host photocatalytic system, ACP photosensitizer was found to have a great superiority in enhancing the light absorption, promoting the surface charge separation-transfer and efficient generation of holes (h⁺) and superoxide radical (·O₂^-), greatly contributing to the photoactivity. The SMZ degradation pathways were proposed based on the identified degradation intermediates, involving three main pathways of rearrangement, desulfonation and oxidation. The toxicity of intermediates was evaluated and the results demonstrated that the overall toxicity was reduced compared with parent SMZ. This catalyst maintained 92% photocatalytic oxidation performance after five cyclic experiments and displayed a co-photodegradation ability to others antibiotics (e.g., roxithromycin, ciprofloxacin et al.) in effluent water. Therefore, this work provides a facile photosensitized strategy for developing guest-host photocatalysts, which enabling the simultaneous antibiotics removal and effectively reduce the ecological risks in wastewater.

Synergetic Photocatalytic Peroxymonosulfate Oxidation of Benzotriazole by Copper Ferrite Spinel: Factors and Mechanism Analysis

The development of oxidation processes with the efficient generation of powerful radicals is the most interesting and thought-provoking dimension of peroxymonosulfate (PMS) activation. This study reports the successful preparation of a magnetic spinel of CuFe₂O₄ using a facile, non-toxic, and cost-efficient co-precipitation method. The prepared material exhibited a synergetic effect with photocatalytic PMS oxidation, which was effective in degrading the recalcitrant benzotriazole (BTA). Moreover, central composite design (CCD) analysis confirmed that the highest BTA degradation rate reached 81.4% after 70 min of irradiation time under the optimum operating conditions of CuFe₂O₄ = 0.4 g L^-1, PMS = 2 mM, and BTA = 20 mg L^-1. Furthermore, the active species capture experiments conducted in this study revealed the influence of various species, including ^•OH, SO₄^•-, O₂^•-, and h⁺ in the CuFe₂O₄/UV/PMS system. The results showed that SO₄^•- played a predominant role in BTA photodegradation. The combination of photocatalysis and PMS activation enhanced the consumption of metal ions in the redox cycle reactions, thus minimizing metal ion leaching. Additionally, this maintained the reusability of the catalyst with reasonable mineralization efficiency, which reached more than 40% total organic carbon removal after four batch experiments. The presence of common inorganic anions was found to have a retardant effect on BTA oxidation, with the order of retardation following: HCO₃^- > Cl^- > NO₃^- > SO₄^2-. Overall, this work demonstrated a simple and environmentally benign strategy to exploit the synergy between the photocatalytic activity of CuFe₂O₄ and PMS activation for the treatment of wastewater contaminated with widely used industrial chemicals such as BTA.

Ice-templated synthesis of tungsten oxide nanosheets and their application in arsenite oxidation

Tungsten oxide (WO₃) nanosheets were prepared as catalysts to activate hydrogen peroxide (H₂O₂) in arsenite (As(III)) oxidation. Ice particles were employed as templates to synthesize the WO₃ nanosheets, enabling easy template removal via melting. Transmission electron microscopy and atomic force microscopy revealed that the obtained WO₃ nanosheets were plate-like, with lateral sizes ranging from dozens of nanometers to hundreds of nanometers and thicknesses of <10 nm. Compared to that of the WO₃ nanoparticle/H₂O₂ system, a higher efficiency of As(III) oxidation was observed in the WO₃ nanosheet/H₂O₂ system. Electron spin resonance spectroscopy, radical quenching studies, and As(III) oxidation experiments under anoxic conditions suggested that the hydroperoxyl radical (HO₂^●) acted as the primary oxidant. The WO₃ nanosheets possessed numerous surface hydroxyl groups and electrophilic metal centers, enhancing the production of HO₂^● via H₂O₂ activation. Various anions commonly present in As(III)-contaminated water exhibited little effect on As(III) oxidation in the WO₃ nanosheet/H₂O₂ system. The high oxidation efficiency was maintained by adding H₂O₂ when it was depleted, suggesting that the catalytic activity of the WO₃ nanosheets did not deteriorate after multiple catalytic cycles.

Improvement of peroxymonosulfate utilization efficiency for sulfamethazine degradation by photo-electron activating peroxymonosulfate: Performance and mechanism

Enhancing the utilization efficiency of oxidant is of great importance for advanced oxidation processes (AOPs). Herein, nitrogen-doped titania dioxide/carbon (NTC7) catalyst was fabricated via pyrolyzing NH₂-MIL-125 under nitrogen atmosphere at 700 °C. Excitation of NTC7 under visible light can successfully achieve efficient activation of peroxymonosulfate (PMS) (NTC7 + PMS + Vis). Degradation performance and PMS activation mechanism were systematically investigated using sulfamethazine (SMT) as the target pollutant. It was found that the photo-generated electrons excited from NTC7 under visible light played the dominant role in enhancing the productive consumption of PMS. Its utilization increased by 66 % (Δ[PMS]/Δ[SMT] = 7.0) in NTC7 + PMS + Vis process and the degradation rate was 2.14 times higher than that of NTC7 + PMS process. The ketonic CO groups and structural defects were responsible for the generation of ¹O₂ in dark activation while radicals (•OH, O₂^•-) were more inclined to be continuously produced in NTC7 + PMS + Vis process. The involved degradation pathways, intermediates, and toxicity assessment have been studied in detail. This work provides an effective approach to enhance the utilization efficiency of oxidant for pollutant degradation by AOPs.

Enhanced activation of peroxymonosulfate by a floating FeMo3Ox/C3N4 photocatalyst under visible-light assistance for oxytetracycline degradation: Performance, mechanisms and comparison with H2O2 activation

In this study, a floating FeMo₃O_x/C₃N₄-EP (FM-C-P) composite with highly stability and reusability was synthesized by an impregnation/calcination process and used to activate peroxymonosulfate (PMS) for oxytetracycline (OTC) degradation under visible light irradiation. The results demonstrated that 98.1% of OTC (50 mg/L) removal can be achieved by the activation of PMS (5 mM) using FM-C-P (1 g/L) in 30 min under visible light irradiation. The pseudo-first-order rate constant was calculated to be 0.181 min^-1. The degradation process with PMS was hardly affected by pH (3-11) and co-existing substance. ·SO₄^-, ·OH, ·O₂^- and ¹O₂ were produced in the Vis/PMS/FM-C-P system and ¹O₂ was determined to be the main reactive oxygen species (ROSs). The high efficiency of ROSs production mainly contributed to two mechanisms. Firstly, via the combination of ≡Fe (II)-·SO₅^- and free state ·SO₅^-, ¹O₂ could be generated on the Fe-N_x site. Secondly, photo-induced electrons in the FeMo₃O_x/g-C₃N₄ heterojunction could react with Fe (III) and Mo (VI) to form catalytically active species Fe (II) and Mo (IV). Moreover, the proposed degradation pathway and the toxicity of intermediated products was analyzed. Overall, this study was expected to deepen the understanding of the photo-assisted PMS activation and the generation of ¹O₂ with the presence of metal-oxide/C₃N₄ heterojunction.

Visible LED photocatalysis combined with ultrafiltration driven by metal-free oxygen-doped graphitic carbon nitride for sulfamethazine degradation

A novel visible light emitting diode (LED) photocatalysis combined ultrafiltration (UF) system driven by metal-free O-doped C₃N₄ was established for sulfamethazine (SMZ) removal in environmental remediation. Among different O-doping ratios, 8%O-C₃N₄ exhibited the optimal SMZ degradation efficiency (89.36%) and the flux of 8%O-C₃N₄/LED/UF system could reach up to 38.92 L/m²/h. Benefitting from the O-doping, the synergetic effect of the expansion of visible-light absorption, enhancement of electron redox capacity, and improvement of e^--h⁺ separation efficiency could produce the intensified photoactivity. Superoxide radical (O₂^•-) and single oxygen (¹O₂) were proved to be the primary active species by EPR and quenching tests. Moreover, the influence of several parameters such as photocatalyst dosage, SMZ concentration, raw turbidity and humic acid concentration in 8%O-C₃N₄/LED/UF system on SMZ removal were systematically studied. Under simulated surface water matrix, 8%O-C₃N₄/LED/UF system could also remove 96.88% SMZ and stable membrane flux stabilized as high as 33.36 L/m²/h. This study makes a demonstration for applying highly-effective powdery photocatalysts in the actual wastewater treatment and designing future photocatalytic reactors.

Hollow Nanospheres Organized by Ultra-Small CuFe2O4/C Subunits with Efficient Photo-Fenton-like Performance for Antibiotic Degradation and Cr(VI) Reduction

Hollow transition metal oxides have important applications in the degradation of organic pollutants by a photo-Fenton-like process. Herein, uniform, highly dispersible hollow CuFe2O4/C nanospheres (denoted as CFO/C-PNSs) were prepared by a one-pot approach. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images verified that the CFO/C-PNS catalyst mainly presents hollow nanosphere morphology with a diameter of 250 ± 30 nm. Surprisingly, the photodegradation test results revealed that CFO/C-PNSs had an excellent photocatalytic performance in the elimination of various organic contaminants under visible light through the efficient Fenton catalytic process. Due to the unique hollow structure formed by the assembly of ultra-small CFO/C subunits, the catalyst exposes more reaction sites, improving its photocatalytic activity. More importantly, the resulting magnetically separable CFO/C-PNSs exhibited excellent stability. Finally, the possible photocatalytic reaction mechanism of the CFO/C-PNSs was proposed, which enables us to have a clearer understanding of the photo-Fenton mechanism. Through a series of characterization and analysis of degradation behavior of CFO/C-PNS samples over antibiotic degradation and Cr(VI) reduction, •OH radicals generated from H2O2 decomposition played an essential role in enhancing the reaction efficiency. The present work offered a convenient method to fabricate hollow transition metal oxides, which provided impetus for further development in environmental and energy applications. Highlights: Novel hollow CuFe2O4/C nanospheres were prepared by a facile and cost-effective method. CuFe2O4/C exhibited excellent photo-Fenton-like performance for antibiotic degradation. Outstanding photocatalytic performance was attributed to the specific hollow cavity-porous structure. A possible mechanism for H2O2 activation over hollow CuFe2O4/C nanospheres was detailed and discussed.