Efficient photoactivation of peroxymonosulfate by Z-scheme nitrogen-defect-rich NiCo2O4/g-C3N4 for rapid emerging pollutants degradation

Enhanced activation of peroxymonosulfate by ZIF-67/g-C3N4 S-scheme photocatalyst under visible light assistance for degradation of polyethylene terephthalate

Photocatalyst-activated peroxymonosulfate (PMS) degradation of pollutants is already widely used for wastewater treatment under visible light. Polyethylene terephthalate (PET) is widely used in daily life, but waste plastics have an irreversible negative impact on the environment. In this paper, the ZIF-67/g-C3N4 S-scheme heterojunction catalyst was synthesized as a photocatalyst to achieve a good effect on PET degradation in coordination with PMS. The results indicated that PET could be degraded up to 60.63 ± 2.12 % under the combined effect of catalyst, PMS, and light. In this experiment, the influence of catalyst-to-plastic ratio, PMS concentration, aqueous pH, and inorganic anions on plastic degradation by the photocatalytic synergistic PMS system was discussed, and the excellent performance of this system for degrading PET was highlighted through a comparative test. Electron spin resonance (ESR) and free radical quenching experiments demonstrated that SO4•- contributes the largest amount to the PET degradation performance. Furthermore, results from gas chromatography and liquid chromatography-mass spectrometry (LC-MS) indicated that the plastic degradation products include CO, CH4, and organic small-molecule liquid fuels. Finally, a possible mechanism for the light/PMS system to degrade PET in water was suggested. This paper provides a feasible solution to treat waste microplastics in water.

Linker Encouraged Solid State Synthesis of MOF Derived Z-Scheme NiCo2O4/NiO/C toward Efficient Removal of Organic and Inorganic Pollutants from Water

Here, we represent a solid-state route for the construction of MOF derived multifunctional Z-scheme NiCo2O4/NiO/C applied for the photocatalytic removal of methylene blue (dye) and tetracycline (drug) and the reduction of Cr(VI) (heavy metal). The developed solid-state method yielded a highly effective NiCo2O4/NiO/C catalyst by mechanically grinding independently produced Ni and Co-MOFs and subsequently pyrolyzing them. The use of different linkers in the Ni MOF (H3-BTC linker) and Co-MOF (2-methylimidazole linker) proved to be effective in constructing the NiCo2O4/NiO/C composite, ensuring a nonaggregated distribution on a carbon framework. Such a synthesized Z-scheme NiCo2O4/NiO/C composite has performed exceptionally well to achieve excellent degradation of MB (98.23% in 120 min) and TC (92.85% in 25 min) and Cr(VI) reduction (98.22% in 20 min), with excellent recyclability and stability. The NiCo2O4/NiO/C composite, synthesized using Ni and Co-MOFs prepared with different linkers, outperformed its counterpart prepared using Ni and Co-MOFs with identical linkers (either 2-methylimidazole or H3BTC). This study paves the way for the future synthesis of MOF derived bimetallic composites for photocatalytic applications.

Ultrathin BiOCl-OV/CoAl-LDH S-scheme heterojunction for efficient photocatalytic peroxymonosulfate activation to boost Co (IV)=O generation

Sustainable and rapid production of high-valent cobalt-oxo (Co(IV)=O) species for efficiently removing organic pollutants is challenging in permoxymonosulfate (PMS) based advanced-oxidation-processes (AOPs) due to the limitation of the high 3d-orbital electronic occupancy of Co and slow conversion from Co(III) to Co(II). Herein, S-scheme BiOCl-OV/CoAl-LDH heterojunction were constructed by ultrathin BiOCl with the oxygen-vacancy (OV) self-assembled with ultrathin CoAl-LDH. OV promoted the formation of charge transfer channel (Bi-O-Co bonds) at the interface of the heterojunction and reduced electron occupation of the Co 3d-orbital to facilitate the generation of Co(IV)=O in the BiOCl-OV/CoAl-LDH/PMS/Visible-light system. S-scheme heterojunction accelerated the photogenerated electrons to allow rapid conversion of Co(III) to Co(II), promoting the fast two-electron transfer from Co(II) to Co(IV)=O. Consequently, the developed BiOCl-OV/CoAl-LDH/PMS/Visible-light system showed excellent degradation efficiency for most of organic pollutions, and exhibited very high removal capability for the actual industrial wastewater. This study provides a new insight into the evolution of Co(IV)=O and the coordinative mechanism for photocatalysis and PMS activation.

Efficient Photocatalytic Activation of Peroxymonosulfate by Cobalt-Doped Oxygen-Vacancies-Rich BiVO4 for Rapid Tetracycline Degradation

In this work, cobalt-doped oxygen-vacancies-rich BiVO4 (Co/BiVO4-Vo) was successfully synthesized for the degradation of tetracycline (TC) by activated peroxymonosulfate (PMS) under visible light. The morphologies, microstructures, and optical properties of the photocatalysts were analyzed in detail. Co/BiVO4-Vo exhibited significantly enhanced degradation, removing 92.3% of TC within 10 min, which was greater than those of pure BiVO4 (62.2%) and oxygen-vacancies-rich BiVO4 (BiVO4-Vo) (72.0%), respectively. The photogenerated charge separation and transport properties were explored through surface photovoltage (SPV), photoluminescence spectrum (PL), and UV-vis diffuse reflectance spectroscopy (UV-vis DRS) measurements. Additionally, an in-depth investigation was conducted on the photocatalytically assisted advanced oxidation processes based on SO4•- (SR-AOPs) for the degradation of organic pollutants. The experimental results showed that the introduction of oxygen vacancies and Co doping achieved an effective separation of photogenerated carriers, which could accelerate the cycling between Co3+ and Co2+ and further activate PMS. The results of free radical capture experiments and electron spin resonance (ESR) experiments showed that reactive oxygen species (ROSs) such as 1O2, •O2-, and SO4•- played a dominant role in the removal of pollutants. This work provides a novel insight into the further development of efficient and rapid PMS photoactivators for environmental remediation of water bodies.

Enhanced antibiotic degradation via photo-assisted peroxymonosulfate over graphitic carbon nitride nanosheets/CuBi2O4: Highly efficiency of oxygen activation and interfacial charge transfer

Improving the activation capacity of peroxymonosulfate (PMS) to increase radical and non-radical production is critical for antibiotic degradation. However, how to boost reactive oxygen species (ROS) and speed interfacial charge transfer remains an essential challenge. We report a coupling system of 10 %CNNS/CuBi2O4 photocatalyst and sulfate radical-based advanced oxidation processes (SO4--AOPs) to enhance the activation of PMS and improve antibiotic degradation. Owing to highly efficient oxygen activation and interfacial charge transfer, the degradation efficiency of the photo-assisted PMS system was as high as 51.6 times and 2.8 times that of photocatalyst and SO4--AOPs alone, respectively. Importantly, the highly efficient oxygen activation resulted in the production of O2-, which in turn could utilize the excess electrons generated through efficient interfacial charge transfer to convert into non-radical 1O2. The total organic carbon (TOC) elimination effectiveness of the photo-assisted PMS system reached 82 % via the synergy of radicals and non-radicals (O2-, OH, 1O2, SO4-, h+). This system also had excellent potential for reducing the generation and toxicity of disinfection by-products (DBPs), as evidenced through significant reductions in concentrations of trichloromethane (TCM), dichloroacetic acid (DCAA), and trichloronitromethane (TCNM) by 76 %, 64 %, and 35 %, respectively, providing an effective and eco-friendly strategy for antibiotic treatment.

An innovative Z-type Sb2S3/In2S3/TiO2 heterostructure: superior performance in the photocatalytic removal of levofloxacin and mechanistic insight

In this study, Sb2S3/In2S3/TiO2 (SIT) heterojunction photocatalysts were prepared by a simple two-step hydrothermal method and applied to the photocatalytic degradation of levofloxacin (LEV). After 160 min of reaction under visible light, the SIT heterojunction photocatalyst degraded 10 mg L-1 LEV at a rate of 86.7%. The degradation of LEV follows pseudo-first-order kinetics with a rate constant 1.16 × 10-2 min-1, which is 1.42, 1.22 and 1.05 times higher than that of TiO2, SI and IT, respectively. Meanwhile, the SIT photocatalysts also showed high photocatalytic activity for other antibiotics. The enhanced photocatalytic activity of the ternary heterostructures was attributed to the full-spectrum response and the synergistic effect of the dual Z-type heterojunctions, which improved the visible light absorption and facilitated the charge separation. In addition, ˙OH and ˙O2- play a dominant role in the photodegradation process. This work contributes to the design of novel photocatalytic materials with dual Z-type heterojunctions and efficient photocatalysts for the degradation of antibiotics.

Nanotechnology-assisted treatment of pharmaceuticals contaminated water

The presence of pharmaceutical compounds in wastewater due to an increase in industrialization and urbanization is a serious health concern. The demand for diverse types of pharmaceutical compounds is expected to grow as there is continuous improvement in the global human health standards. Discharge of domestic pharmaceutical personal care products and hospital waste has aggravated the burden on wastewater management. Further, the pharmaceutical water is toxic not only to the aquatic organism but also to terrestrial animals coming in contact directly or indirectly. The pharmaceutical wastes can be removed by adsorption and/or degradation approach. Nanoparticles (NPs), such as 2D layers materials, metal-organic frameworks (MOFs), and carbonaceous nanomaterials are proven to be more efficient for adsorption and/or degradation of pharmaceutical waste. In addition, inclusion of NPs to form various composites leads to improvement in the waste treatment efficacy to a greater extent. Overall, carbonaceous nanocomposites have advantage in the form of being produced from renewable resources and the nanocomposite material is biodegradable either completely or to a great extent. A comprehensive literature survey on the recent advancement of pharmaceutical wastewater is the focus of the present article.

Efficient photocatalytic reduction of p-nitrophenol under visible light irradiation based on Ag NPs loaded brown 2D g-C3N4 / g-C3N4 QDs nanocomposite

Recently, low-cost graphitic carbon nitride (g-C3N4) revealed high photocatalytic activities and provided solutions to environmental pollution. In this study, we synthesized brown mesoporous 2D g-C3N4 by calcination dicyandiamide with pluronic P123. This is followed by loading of Ag NPs on the prepared 2D g-C3N4 by photodeposition process. After that, a ternary composite 2% Ag/ 2D g-C3N4 / g-C3N4 QDs heterojunction photocatalyst has been successfully prepared. The prepared nanomaterials were comprehensively characterized by various analysis techniques such as XRD, UV-Vis., BET, XPS, SEM, TEM. This new system exhibited a large surface area with porous structure and a wide absorption of visible light. The results verified that Ag NPs decoration enhanced the charge separation of photo-generated carriers of g-C3N4 2D and g-C3N4 QDs, promote significant enhancement in the photocatalytic activity for reduction of p-nitrophenol with a rate constant (k) value of 0.49729 / min in 6 min. This rate is about two-fold higher than that observed for pure g-C3N4 2D and g-C3N4 QDs as well as shows an improvement compared to 2% Ag/ g-C3N4 2D and g-C3N4 2D/ g-C3N4 QDs. The results open the door to design highly efficient 2D/0D nanocomposite photocatalysts for a wide variety of environmental applications.

The synergistic degradation of pollutants in water by photocatalysis and PMS activation

In recent years, the synergistic degradation of water pollutants through advanced oxidation technology has emerged as a prominent research area due to its integration of various advanced oxidation technologies. The combined utilization of peroxymonosulfate (PMS) activation technology and photocatalysis demonstrates mild and nontoxic characteristics, enabling the degradation of water pollutants across a wide pH range. Moreover, this approach reduces the efficiency of electron hole recombination, broadens the catalyst's light response range, facilitates electron transfer of PMS, and ultimately improves its photocatalytic performance. The paper reviews the current research status of photocatalytic technology and PMS activation technology, respectively, while highlighting the advancements achieved through the integration of photocatalytic synergetic PMS activation technology for water pollutant degradation. Furthermore, this review delves into the mechanisms involving both free radicals and nonradicals in the reaction process and presents a promising prospect for future development in water treatment technology. PRACTITIONER POINTS: Degradation of water pollutants by photocatalysis and PMS synergistic action has emerged. Synergism can enhance the generation of free radicals. This technology can provide theoretical support for actual wastewater treatment.

Facile design of surface electric field driven tourmaline/g-C3N4 layered stacked photocatalysts with enhanced photocatalytic activity for antibiotic removal

In the field of photocatalysis, Graphitic carbon nitride (g-C₃N₄) has received a lot of attention for its superior functionality and benefits. However, it suffers from the fatal defect of low charge separation efficiency, which is well addressed by tourmaline's self-contained surface electric field. In this work, tourmaline/g-C₃N₄ (T/CN) composites were successfully synthesized. Due to its surface electric field effect, tourmaline and g-C₃N₄ are stacked on top of each other. It makes its specific surface area increase greatly and more active sites are exposed. Additionally, the rapid separation of photogenerated electron holes under the action of electric field promotes the photocatalytic reaction. T/CN exhibited excellent photocatalytic performance under visible light, with 99.9% Tetracycline (TC 50 mg L^-1) removal after 30 min. Compared to tourmaline (0.0160 min^-1) and g-C₃N₄ (0.0230 min^-1), the T/CN composite's reaction rate constant (0.1754 min^-1) was 11.0 and 7.6 times higher. A series of characterizations also determined the structural properties and catalytic performance of the T/CN composites, which were found to have a larger specific surface area, narrower band gap, and higher charge separation efficiency compared to the monomer. In addition, the toxicity of tetracycline intermediates and their degradative pathways were investigated, and the toxicity of the intermediates was found to be reduced. Given the quenching experiments and active substance determination, it was also found that h⁺ and ·O₂^- play a major role. This work provides more inspiration for photocatalytic material performance research as well as green innovation for environmental management.

Donor-acceptor engineered g-C3N4 enabling peroxymonosulfate photocatalytic conversion to 1O2 with nearly 100% selectivity

Singlet oxygen (¹O₂) is a thrilling active species for selectively oxidating organic substances. However, the efficient and selective generation of ¹O₂ maintains a great challenge. Here, we develop a donor-acceptor structured g-C₃N₄ by covalently engineering benzenetricarboxaldehyde (BTA) onto the fringe of g-C₃N₄. The g-C₃N₄-BTA exerts high-efficiency ¹O₂ generation with nearly 100% selectivity via peroxymonosulfate (PMS) photocatalytic activation upon visible light illumination, exhibiting obviously boosted efficiency for selective elimination of atrazine (ATZ). The consequences of experiments and theoretical calculations demonstrate that BTA units serve as electron-withdrawing sites to trap photogenerated electrons and facilitate the adsorption of PMS on the electron-deficient heptazine rings of g-C₃N₄. As such, PMS can be in-situ oxidated by the photogenerated holes to selectively produce ¹O₂. Besides, the g-C₃N₄-BTA/PMS system delivers high stability and strong resistance to the coexisting organic ions and natural organic matter, demonstrating great potential for selectively removing targeted organic contaminants with high efficiency.

Advanced Functional Carbon Nitride by Implanting Semi-Isolated VO2 Active Sites for Photocatalytic H2 Production and Organic Pollutant Degradation

It is critical to facilitate surface interaction for liquid-solid two-phase photocatalytic reactions. This study demonstrates more advanced, efficient, and rich molecular-level active sites to extend the performance of carbon nitride (CN). To achieve this, semi-isolated vanadium dioxide is obtained by controlling the growth of non-crystalline VO₂ anchored into sixfold cavities of the CN lattice. As a proof-of-concept, the experimental and computational results solidly corroborate that this atomic-level design has potentially taken full advantage of two worlds. The photocatalyst comprises the highest dispersion of catalytic sites with the lowest aggregation, like single-atom catalysts. It also demonstrates accelerated charge transfer with the boosted electron-hole pairs, mimicking heterojunction photocatalysts. Density functional theory calculations show that single-site VO₂ anchored into the sixfold cavities significantly elevates the Fermi level, compared with the typical heterojunction. The unique features of semi-isolated sites result in a high visible-light photocatalytic H₂ production of 645 µmol h^-1 g^-1 with only 1 wt% Pt. They also represent an excellent photocatalytic degradation for rhodamine B as well as tetracycline, surpassing the activities obtained from many conventional heterojunctions. This study presents exciting opportunities for the design of new heterogeneous metal oxide for a variety of reactions.

Direction regulation of interface carrier transfer and enhanced photocatalytic oxygen activation over Z-scheme Bi4V2O11/Ag/AgCl for water purification

Molecular oxygen activation is essential to the photocatalytic oxidation reaction, which is highly dependent on the construction of active sites and efficient charge transfer of photocatalysts. In this study, we constructed Bi₄V₂O₁₁/Ag/AgCl Z-type heterojunction photocatalysts with significantly enhanced molecular oxygen activation capacity. The systematic characterization and analysis including X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations confirmed that the formation of efficient Z-type heterostructure could be attributed to the introduction of Ag nanoparticles (NPs), which regulated the electron transfer direction from Bi₄V₂O₁₁ to AgCl. Owing to the advantage of enhanced charge transfer efficiency, the O₂^- generation capacity of Bi₄V₂O11/Ag/AgCl Z-scheme heterojunction was as high as 4.6 times that of pure Bi₄V₂O₁₁. Consequently, Bi₄V₂O₁₁/Ag/AgCl showed good degradation performance against tetracycline (TC), ciprofloxacin (CIP), ranitidine hydrochloride (RAN) and 2,4-dichlorophenoxyacetic acid (2,4-D) under visible light, and their degradation rates were 8.2 times, 5.9 times, 3.8 times and 11.9 times higher than those of Bi₄V₂O₁₁, respectively. This study provides an effective and feasible strategy to design photocatalyst with improved molecular oxygen activation efficiency.

MOFFeCo/B-CN composites achieve efficient degradation of antibiotics in a non-homogeneous concurrent photocatalytic-persulfate activation system

We synthesized an M_FeCoB_0.4CN_x% (MOF-Fe/Co nanosheets/boron-doped g-C₃N₄) composite catalyst for enhancing the concurrent photocatalytic-persulfate activation (CPPA) system and achieved efficient degradation of antibiotics. The role of MOF-Fe/Co is to activate persulfate, while boron-doped g-C₃N₄ can generate photogenerated electrons for the reduction of Co³⁺/Fe³⁺ to enhance the regeneration of the active center. The rate constant for Tetracycline degradation by the CPPA system was 4.74 and 7.54 times higher than the photocatalytic and persulfate-activated systems, respectively. This composite was shown to be practical and economically viable for antibiotic degradation. The degradation behavior was explored based on experiments, and molecular orbitals and Fukui functions were obtained by density functional theory calculations. Mechanisms were investigated using reactive oxygen species trapping studies and electron spin resonance, and the process was explained in terms of the charge population and electron density difference of MOF-Fe/Co nanosheets. The CPPA system is an ecologically benign technology for removing antibiotic-related risks to the environment and human health.

Construction of Ag nanocluster-modified Ag3PO4 containing silver vacancies via in-situ reduction: With enhancing the photocatalytic degradation activity of sulfamethoxazole

Photocatalytic removal of sulfonamide antibiotics is an effective strategy to solve environmental pollution. Ag3PO4 is a promising anode material for photocatalytic material with photocatalytic degradation ability under ultraviolet light or natural light. Unfortunately, due to its instability, Ag+ could be reduced to Ag0 which loaded onto the surface of Ag3PO4 during the photocatalytic process, causing self-photocorrosion and resulting in the reduction of photocatalytic activity and stability. Herein, Ag3PO4 nanoparticles loaded with Ag nanoclusters containing Ag vacancies (Ag/Ag3PO4-VAg) were constructed by an in-situ reduction strategy to achieve effectively photocatalytic degradation behavior. The Ag nanoclusters loaded on the surface of Ag3PO4 can not only effectively inhibit the self-photocorrosion but also affords a localized surface plasmon resonance (LSPR) effect in the photocatalytic process, thus leading to the efficient generation and rapid transfer of photogenerated carriers behavior. In addition, the Ag vacancies in Ag3PO4 are crucial to increasing the adsorption energy of H2O for further enhancing the capture and accumulation of electrons. In detail, according to Zeta potential analysis, the strong adsorption sites of sulfamethoxazole (SMX) molecules are generated at the interface of Ag and Ag3PO4, which promote the activation of SMX molecules. A 100 ml of 20 mg/L SMX could be completely degraded within 15 min with an apparent rate constant (Kapp) of 0.306 min-1, which far exceeds the activity of most of the photocatalysts. This work may provide an attractive strategy to address the activity, stability of Ag3PO4 and and realizing the green remediation of SMX wastewater.

NH2-MIL-125(Ti) modified graphitic carbon nitride with carbon vacancy for efficient photocatalytic NO removal

This paper reports the application of NH₂-MIL-125(Ti) modified carbon nitride C_v-C₃N₄ with carbon vacancies in the removal of NO. We performed a series of characterizations of the complex and compared various ratios with the individual components. The results of UV spectrum analysis show that the composite's range of light absorption expanded due to the modification of Ti metal-organic framework. Furthermore, the results of photocurrent and electrical impedance indicate the compound has a better ability to generate and transfer electrons. The increase in the compound's NO removal efficiency (up to 63%) indicates that MOF has a positive effect on C_v-C₃N₄ modification-a good method for photocatalysis. Moreover, the compound can promote photocatalysis in a favorable direction.

Construction lamellar BaFe12O19/Bi3.64Mo0.36O6.55 photocatalyst for enhanced photocatalytic activity via a photo-Fenton-like Mo6+/Mo4+redox cycle

The novel BaFe₁₂O₁₉/Bi_3.64Mo_0.36O_6.55 composite materials were constructed as magnetically recyclable photo-Fenton-like degradation systems. The composite catalyst not only promoted the effective transfer of photo-generated electrons and improved the Mo⁶⁺/Mo⁴⁺ cycle consequent, but also activated hydrogen peroxide to generate oxidizing free radicals. BaFe₁₂O₁₉/Bi_3.64Mo_0.36O_6.55-0.25 exhibited an outstanding degradation performance for tetracycline hydrochloride it is 1.3 times to Bi_3.64Mo_0.36O_6.55. The thermal catalytic performance of the Bi_3.64Mo_0.36O_6.55 monomer is similar to that of the BaFe₁₂O₁₉/Bi_3.64Mo_0.36O_6.55 material without light. However, the removal rate of BaFe₁₂O₁₉/Bi_3.64Mo_0.36O_6.55 material reaches 84.5% after 60 min with light, far exceeding that of Bi_3.64Mo_0.36O_6.55 material. By way of the contrast experiment with light and without light, it is further demonstrated that interfacial interaction between BaFe₁₂O₁₉ and Bi_3.64Mo_0.36O_6.55 acted a key role in the photocatalytic reaction system. It is also a good advantage that pollutants can be efficiently degraded without adjusting the pH. The characterization of photocurrent and X-ray photoelectron spectroscopy (XPS) also further proved the synergy between the two materials, which is useful to the separation of electrons and holes. The synergy ultimately improves the degradation performance. Besides, BaFe₁₂O₁₉/Bi_3.64Mo_0.36O_6.55 can be easily separated by an external magnetic field after the photocatalytic activity reaction owing to BaFe₁₂O₁₉'s magnetic properties. It provides a new research idea for the construction and iron-based heterogeneous Fenton-like system for magnetic degradation of antibiotics.

Carbon nitride-based Z-scheme heterojunctions for solar-driven advanced oxidation processes

Solar-driven advanced oxidation processes (AOPs) via direct photodegradation or indirect photocatalytic activation of typical oxidants, such as hydrogen peroxide (H₂O₂), peroxymonosulfate (PMS), and peroxydisulfate (PDS), have been deemed to be an efficient technology for wastewater remediation. Artificial Z-scheme structured materials represent a promising class of photocatalysts due to their spatially separated charge carriers and strong redox abilities. Herein, we summarize the development of metal-free graphitic carbon nitride (g-C₃N₄, CN)-based direct and indirect Z-scheme photocatalysts for solar-driven AOPs in removing organic pollutants from water. In the work, the classification of AOPs, definition and validation of Z-schemes are summarized firstly. The innovative engineering strategies (e.g., morphology and dimensionality control, element doping, defect engineering, cocatalyst loading, and tandem Z-scheme construction) over CN-based direct Z-scheme structure are then examined. Rational design of indirect CN-based Z-scheme systems using different charge mediators, such as solid conductive materials and soluble ion pairs, is further discussed. Through examining the relationship between the Z-scheme structure and activity (charge transfer and separation, light absorption, and reaction kinetics), we aim to provide more insights into the construction strategies and structure modification on CN-based Z-schemes towards improving their catalytic performances in AOPs. Lastly, limitations, challenges, and perspectives on future development in this emerging field are proposed.

Durable and eco-friendly peroxymonosulfate activation over cobalt/tin oxides-based heterostructures for antibiotics removal: Insight to mechanism, degradation pathway

Potential leaching of Co ions could decrease the catalytic activity and cause secondary pollution of water, thereby threatening ecological safety and human health. In response, the in-situ generation of well-dispersed Co₂SnO₄ and SnO₂ with fine interfacial feature was constructed for PMS activation toward efficient tetracycline degradation and lower cobalt ion leaching feature. The synergistic effect of Co₂SnO₄ and SnO₂ endowed Co₂SnO₄-SnO₂ an outstanding catalytic performance for tetracycline degradation in alkaline condition. Meanwhile, the catalysts can effectively degrade the quinolones, dyes and mixture pollutant solution. The excellent performance can attributed to the in-situ introduction of SnO₂, which stabilizes the microstructure and provides an effective electronic pathway to enhance the activity of Co₂SnO₄ in the Co₂SnO₄-SnO₂. In optimized condition, the tetracycline degradation efficiency was enhanced to 94.9% within 20 min and maintained the stability at least four cycles. The degradation rate constant of Co₂SnO₄-SnO₂ was 0.149 min^-1, which was about 1.93, 2.98, 11.5 times higher than of Co₂SnO₄, Co₃O₄ and SnO₂, respectively. Notably, the leaching performance of Co₂SnO₄-SnO₂ was greatly suppressed to be 7.45 ug/L, which was lower than that of Co₂SnO₄ (6.41 mg/L) and Co₃O₄ (1.12 mg/L). Radical quenching and EPR experiments showed that singlet oxygen (¹O₂), rather than hydroxyl active species and sulfate radicals, played a predominating role for PMS activation in the Co₂SnO₄-SnO₂/PMS system. The intermediates and degradation routes for tetracycline degradation were characterized by liquid chromatograph-tandem mass spectrometry. This study expected to provide a novel strategy to construct heterostructural catalysts with lower cobalt ion leaching for the activation of PMS.

Enhanced adsorption and catalytic degradation of antibiotics by porous 0D/3D Co3O4/g-C3N4 activated peroxymonosulfate: An experimental and mechanistic study

In this work, Co₃O₄/g-C₃N₄ catalyst with highly efficient adsorption and degradation of antibiotics was developed based on the combination of three-dimensional (3D) porous morphological controls of g-C₃N₄ and the loading of Co₃O₄ quantum dots (Co₃O₄ QDs). It was discovered that the catalyst can effectively activate peroxymonosulfate (PMS) through a non-photochemical path, and a high tetracycline elimination rate of 99.7% can be achieved within 18 min. The characterization and density functional theory calculation results demonstrated that the porous 3D structure can not only promote the substrate adsorption reaction but also provide large surface area and countless exposed active sites for catalytic reaction. The introduction of Co₃O₄ QDs lowered activation energy barrier and lead to high energy of PMS adsorption. More efficient charge migration between the catalyst and PMS further accelerated PMS activation. Thus, leading to the excellent catalytic performance. In addition, non-free radical mediated degradation mechanism of catalytic activity was also proposed. This work provides a scheme for designing novel and efficient PMS activators for the removal of abusive antibiotics from aqueous environments.

Enhanced visible light photo-Fenton-like degradation of tetracyclines by expanded perlite supported FeMo3Ox/g-C3N4 floating Z-scheme catalyst

In the conventional Fenton system, the relatively low efficiency of Fe (II) regeneration is a significant drawback. To address this shortcoming, a novel floating Z-scheme photo-Fenton catalyst FeMo₃O_x/g-C₃N₄/EP was prepared by a facile dip-calcination method, in which iron and molybdenum oxides with mixed valence states (FeMo₃O_x) and graphitic carbon nitride (g-C₃N₄) were loaded on the expanded perlite. The removal efficiencies reached the maximum at 98.0%, 93.1% and 97.1% for tetracycline, oxytetracycline and chlortetracycline, respectively, after 60 min dark adsorption and 60 min photo-Fenton process. The aid of dual ion (Fe and Mo) synergy system and photoreduction by Z-scheme photocatalyst enhanced the Fe (II) regeneration, resulting in the excellent performance. Radical scavenger experiment, electron spin resonance spectra (ESR) and X-ray photoelectron spectra (XPS) were used to confirm the mechanism of free radicals' formation and Fe/Mo redox cycling. ·OH, ·O₂^- and ¹O₂ played important roles in the pollutant's degradation, while the generation of ·O₂^- was enhanced due to the floatability in this system. The possible degradation pathways of TC were put forward according to the results of mass spectrum and Orbital-Weighted Fukui Function. Overall, this work provides new insights on the cooperation between iron-based mix oxides and semiconductor in the photo-Fenton system.

Construction of BiVO4/NiCo2O4 nanosheet Z-scheme heterojunction for highly boost solar water oxidation

The sluggish water oxidation process is a severe obstacle for solar-driven water splitting. Therefore, it is imperative to develop a suitable photocatalyst with reduced energy barrier for strong oxidation. In this study, a Z-scheme BiVO₄/NiCo₂O₄ (BVO/NCO) heterojunction system was designed by decorating ultrathin nickel-cobalt (NiCo₂O₄) spinel nanosheets on BiVO₄ as an efficient photocatalyst for water oxidation. The unique structure of the system significantly reduced the energy barrier and improved the oxidation ability of BiVO₄ to efficiently enhance the separation and transfer of the photogenerated carriers. Thus, the photocatalyst delivered an excellent O₂ evolution performance of 1640.9 μmol∙g^-1∙h^-1 and showed 124% improved efficiency as compared to pristine BiVO₄ and a quantum efficiency of 5.39% at 400 nm for O₂ evolution. Additionally, the theoretical calculations revealed that the formation of *OOH was the rate-determining step for water oxidation. The decoration with NiCo₂O₄ significantly reduced the energy barrier between *O and *OOH, which eventually improved the photocatalytic performance of BVO/NCO. The results hold great promise for the potential application of spinel-based materials in efficient photocatalytic O₂ evolution and offer fundamental insights into the design of efficient water oxidation heterojunctions.

Generation of singlet oxygen over CeO2/K, Na-codoped g-C3N4 for tetracycline hydrochloride degradation in a wide pH range

Singlet oxygen (1O2) were widely studied for catalytic oxidation and photo dynamic therapy (PDT) and so on due to its unique properties, such as its long lifetime, wide pH tolerance,...

Surface engineering of copper sulfide-titania-graphitic carbon nitride ternary nanohybrid as an efficient visible-light photocatalyst for pollutant photodegradation

Advanced photocatalyst is a key for photocatalytic water purification in the environmental pollutant remediation. In this study, graphitic carbon nitride (g-CN) modified by CuS and TiO₂ ternary nanohybrid (CuS-TiO₂-g-CN) with close interfacial contact among CuS, TiO₂ and g-CN was fabricated through a facile and green method. Compared to the binary g-CN-based counterparts, the CuS-TiO₂-g-CN possesses multiple photo-generated charge transfers owing to the synergistic action of CuS, TiO₂ and g-CN. And hence the separation efficiency of photo-generated electron-hole pairs can be improved for the CuS-TiO₂-g-CN. The optical and photoelectrochemical measurements prove that the CuS-TiO₂-g-CN has narrower band gap energy and higher transient photocurrent density than those of g-CN and TiO₂-g-CN. Therefore, the CuS-TiO₂-g-CN shows notably higher photocatalytic activity and stability towards the degradation of Rhodamine B (RhB) than g-CN and TiO₂-g-CN under visible-light irradiation. Moreover, a possible visible-light photocatalytic mechanism of CuS-TiO₂-g-CN for degrading RhB was also proposed on the basis of the experimental results and literature reports.

Green and efficient synthesis of Co-MOF-based/g-C3N4 composite catalysts to activate peroxymonosulfate for degradation of the antidepressant venlafaxine

Based on single metal-organic framework (MOF) composite catalyst ZIF-67/g-C₃N₄ (ZG), the composite catalysts ZIF-67/MOF-74(Ni)/g-C₃N₄ (ZNG) and ZIF-67/MIL-100(Fe)/g-C₃N₄ (ZMG) with double MOFs were synthesized, used to effectively activate peroxymonosulfate (PMS) for degrade venlafaxine (VEN). Various characterization methods (XRD, FT-IR, Raman, SEM, EDS, TEM and TG) showed that ZIF-67 and g-C₃N₄; ZIF-67, MOF-74(Ni) and g-C₃N₄; as well as ZIF-67, MIL-100(Fe) and g-C₃N₄ successfully formed heterostructures. The series of catalytic degradation results showed that within 120 min, the degradation rate of VEN by ZMG achieved 100% and the mineralization rate reached 51.32%. The removal rate of VEN by ZNG was 91.38%, while that by ZG was only 27.75%. Free radical quenching tests and EPR further confirmed the production of OH and SO₄^-, which could be conducive to the degradation of VEN. The mechanism analysis of PMS activation confirmed that the interaction of Fe²⁺/Co³⁺ was stronger than that of Ni²⁺/Co³⁺, and it was an important driving force to significantly enhance the synergistic effect. Finally, Gauss theory calculation and HPLC-MS/MS were used to analyze the intermediate products of VEN. It was verified that the main chemical reactions in the degradation process of VEN were hydroxylation, dehydration, demethylation and tertiary amine substitution.