Efficient photoelectrocatalytic degradation of pollutants over hydrophobic carbon felt loaded with Fe-doped porous carbon nitride via direct activation of molecular oxygen.

Developing a photoelectric cathode capable of efficiently activating molecular oxygen to degrade pollutants is a coveted yet challenging goal. In pursuit of this, we synthesize a Fe doped porous carbon nitride catalyst (Fe-CN) using an ionothermal strategy and subsequently loaded it on the hydrophobic carbon felt (CF) to fabricate the Fe-CN/CF photoelectric cathode. This cathode benefits from the synergistic effects between the porous CN support and the highly dispersed Fe species, which enhance O2 absorption and activation. Additionally, the hydrophobic CF serves as a gas diffusion layer, accelerating O2 mass transfer. These features enable the Fe-CN/CF cathode to demonstrate notable photoelectrocatalytic (PEC) degradation efficiency. Specifically, under optimal conditions (cathodic bias of -0.3 VAg/AgCl, pH 7, and a catalyst loading of 3 mg/cm2), the system achieves a 76.4% removal rate of tetracycline (TC) within 60 min. The general application potential of this system is further underscored by its ability to remove approximately 98% of 4-chlorophenol (4-CP) and phenol under identical conditions. Subsequent investigations into the active species and degradation pathways reveal that 1O2 and h+ play dominant role during the PEC degradation process, leading to gradually breakdown of TC into less toxicity, smaller molecular intermediates. This work presents a straightforward yet effective strategy for constructing efficient PEC systems that leverage molecular oxygen activation to degrade pollutants.

Ultrasound-based advanced oxidation processes for landfill leachate treatment: Energy consumption, influences, mechanisms and perspectives.

Advanced oxidation processes (AOPs) based on ultrasound (US) have attracted considerable attention in recent years due to its advantages in the degradation of landfill leachate. The review summarizes the existing treatment methods of leachate from lab-scale, compares their advantages and disadvantages by focusing on the degradation of emerging contaminants (ECs) in the leachate. Then the US-based AOPs are introduced emphatically, including their degradation mechanisms, influencing factors, energy consumption, further optimization methods as well as the possibility of field-scale application are systematically described. Moreover, this review also expounds on the advantages of dual-frequency US (DFUS) technology compared with single-frequency US, and a theoretically feasible DFUS process is proposed to treat ECs in the leachate. Finally, suggestions and prospects for US technologies in treating landfill leachate are put forward to aid future research on landfill leachate treatment. Meaningfully, this manuscript will provide reference values of US-based technologies in landfill leachate treatment for the practical use, facilitating the development of US-based AOPs in landfill leachate management and disposal.

In Situ Synthesis of Bi2S3/BiFeO3 Nanoflower Hybrid Photocatalyst for Enhanced Photocatalytic Degradation of Organic Pollutants.

Photocatalytic degradation of Malachite Green oxalate (MG) in a water body is of significant importance to our health protection, as it could cause various serious diseases. However the photocatalytic activity of most catalysts is still unsatisfactory, due to the poor reactive oxygen species production as a result of sluggish charge separation. Here, innovative nanoflower-shaped Bi2S3/BiFeO3 heterojunctions are prepared via a facile sol-gel method, exhibiting an enhanced reactive oxygen species generation, which leads to the excellent photocatalytic performance toward MG degradation. We verify that interfacing BiFeO3 with Bi2S3 could form a fine junction and offers a built-in field to speed up charge separation at the junction area; as a result, this shows much higher charge separation efficiency. By virtue of the aforementioned advantages, the as-prepared Bi2S3/BiFeO3 heterojunctions exhibit excellent photocatalytic performance toward MG degradation, where more than 99% of MG is removed within 2 h of photocatalysis. The innovative design of nanoflower-like Bi2S3/BiFeO3 heterojunctions may offer new viewpoints in designing highly efficient photocatalysts for environmentally related applications.

Few-Layer Meets Crystalline Structure: Collaborative Efforts for Improving Photocatalytic H2O2 Generation over Carbon Nitride.

Although the conversion of O2 and H2O to H2O2 over graphite carbon nitride (g-C3N4) has been realized by means of the photocatalytic process, the catalytic activity of pristine g-C3N4 is still restricted by the rapid charge recombination and inadequate exposure of the active site. In this work, we propose a straightforward strategy to solve these limitations by decreasing the thickness and improving the crystallinity of g-C3N4, resulting in the preparation of few-layered crystalline carbon nitride (FL-CCN). Benefiting from the minimal thickness and highly ordered in-plane triangular cavities within the structure, FL-CCN processes an extended π-conjugated system with a reduced charge transfer resistance and expanded specific surface area. These features accelerate the efficiency of photogenerated charge separation in FL-CCN and contribute to explore of its surface active sites. Consequently, FL-CCN exhibits a significantly improved H2O2 evolution rate (63.95 µmol g-1 h-1), which is 7.8 times higher than that of pristine g-C3N4 (8.15 µmol g-1 h-1), during the photocatalytic conversion of O2 and H2O. This systematic investigation offers valuable insights into the mechanism of photocatalytic H2O2 generation and the development of efficient catalysts.

Restricted reaction of layered double hydroxide nanoparticles with phosphate in a confined microsphere space.

Over the past decades, considerable efforts have been made to find useful solutions for phosphate pollution control. The state transition of nanomaterials from freely dispersed to encapsulated provides a realizable route for their application in phosphate elimination. The separation convenience offered by encapsulation has been widely recognized, however, the unique binding mode of nanostructures and phosphate in the confined space remains unclear, limiting its further development. Here, carboxymethyl cellulose (CMC) microspheres were used as hosts to deploy layered double hydroxide (LDH) nanoparticles. On this basis, we described an attempt to explore the adsorption behavior of LDH and phosphate in the microsphere space. Compared to their freely dispersed analogues, LDH particles exhibited higher structural stability, wider pH adaptability, and better phosphate selectivity when spatially confined in the CMC microsphere. Nevertheless, the kinetic process was severely inhibited by three orders of magnitude. Besides, the saturated phosphate adsorption capacity was also reduced to 74.6 % of the freely dispersed system. A combinative characterization revealed that the highly electronegative CMC host not only causes electrostatic repulsion to phosphate, but also extracts the electron density of the metal center of LDH, weakening its ability to act as a Lewis acid site for phosphate binding. Meanwhile, the microsphere encapsulation also hinders the ion exchange function of interlayer anions and phosphate. This study offers an objective insight into the reaction of LDH and phosphate in the confined microsphere space, which may contribute to the advanced design of encapsulation strategies for nanoparticles.

Bioprotective Respirator Assembled by Defective Carbon Nitride for Long-Term Light Triggered Health Protection.

Wearing face masks is the best way to stop the spread of respiratory infections. However, if masks are not sterilized, changing them too frequently can actually increase the risk of cross-contamination. Herein, the construction of an antipathogen photocatalytic mask with carbon vacancy-modified carbon nitride nanosheets (g-C3N4-VC Ns) coated on the non-woven fabrics of the out layer of the mask, offering effective and long-term protection against damaging pathogens when exposed to light is reported. The introduced carbon vacancies are found capable of creating energy-disordered sites and inducing energetic electric force to overcome the Coulomb interactions between electron-hole pairs, thus promoting the electron-hole separation to achieve a high generation of reactive oxygen species (ROS). Thanks to its high activity in generating ROS upon exposure to light, the as-prepared photocatalytic mask shows high pathogen sterilization performance. This, in turn, prolongs the mask's protective lifetime, decreases the need for regular replacement, and decreases medical waste production. The work demonstrated here opens new viewpoints in designing pathogens biocidal protective devices for health protection, offering significant promise in specific environment self-protection.

Toxicity of Tetracycline and Metronidazole in Chlorella pyrenoidosa.

Antibiotics have become a new kind of organic pollutant as they are widely used in the water environment of China. Tetracycline (TC) is a class of broad-spectrum antibiotics produced or semi-synthesized by actinomycetes. Metronidazole (MTZ) is the first generation of typical nitroimidazoles. The content of nitroimidazoles is relatively high in medical wastewater, and their ecotoxicity is worthy of attention because they are difficult to completely eliminate. In this paper, the effects of TC and MTZ on the growth, cell morphology, extracellular polymer and oxidative stress of Chlorella pyrenoidosa (C. pyrenoidosa) were studied, and the toxic interactions between TC and MTZ mixture components were analyzed. The results showed that the 96h-EC50 of TC and MTZ was 8.72 mg/L and 45.125 mg/L, respectively. The toxicity of TC to C. pyrenoidosa was higher than that of MTZ, and the combined toxicity effect of TC and MTZ was synergistic after the combined action of a 1:1 toxicity ratio. In addition, the algal cells of C. pyrenoidosa died to varying degrees, the membrane permeability of algal cells was increased, the membrane was damaged, the surface of algal cells exposed to higher concentration of pollutants was wrinkled, and their morphology was changed. The extracellular polymer of C. pyrenoidosa was affected by a change in concentration. The effect of pollutants on the reactive oxygen species (ROS) level and malondialdehyde (MDA) content of C. pyrenoidosa also had an obvious dose-effect relationship. This study contributes to the assessment of the possible ecological risks to green algae due to the presence of TC and MTZ in aquatic environments.

Dissolved organic matter promotes photocatalytic degradation of refractory organic pollutants in water by forming hydrogen bonding with photocatalyst.

Removing refractory organic pollutants in real water using photocatalysis is a great challenge because coexisting dissolved organic matter (DOM) can quench photogenerated holes and thus prevent generation of reactive oxygen species (ROS). Herein, for the first time, we develop a hydrogen bonding strategy to avoid the scavenging of photoexcited holes, by which DOM even promotes photocatalytic degradation of refractory organic pollutants. Theoretical calculations combined with experimental studies reveal the formation of hydrogen bonding between DOM and a hydroxylated S-scheme heterojunction photocatalyst (Mo-Se/OHNT) consisting of hydroxylated nitrogen doped TiO2 (OHNT) and molybdenum doped selenium (Mo-Se). The hydrogen bonding is demonstrated to change the interaction between DOM and Mo-Se/OHNT from DOM-Ti (IV) to a hydrogen bonded complexation through the hydroxyl/amine groups of DOM and the OHNT in Mo-Se/OHNT. The formed hydrogen network can stabilize excited-state of DOM and inject its electron to the conduction band rather than the valence band of the OHNT upon light irradiation, realizing the key to preventing hole quenching. The electron-hole separation in Mo-Se/OHNT is consequently improved for generating more ROS to be involved in removing refractory organic pollutants. Moreover, this hydrogen bonding strategy is generalized to nitrogen doped zinc oxide and graphitic carbon nitride and applies to real water. Our findings provide a new insight into handling the DOM problem for photocatalytic technology towards water and wastewater treatment.

Highly Efficient Degradation of Tetracycline Hydrochloride in Water by Oxygenation of Carboxymethyl Cellulose-Stabilized FeS Nanofluids.

The transformation of organic pollutants by stabilized nano-FeS in oxic conditions is far less understood than in anoxic states. Herein, carboxymethyl cellulose-stabilized FeS (CMC-FeS) nanofluids are prepared at a CMC-to-FeS mass ratio of 1/2 and their performance of tetracycline hydrochloride (TC) degradation under oxic conditions was investigated. Here, we showed that TC could be efficiently removed by oxygenation of CMC-FeS nanofluids at neutral initial pH. We found that CMC-FeS dosages as low as 15 mg/L can achieve the TC removal efficiency as high as 99.1% at an initial TC concentration of 50 mg/L. Oxidative degradation plays a predominated role in TC removal (accounting for 58.0%), adsorption has the second importance (accounting for 37.0%), and reduction has minor impact (accounting for 4.1%) toward TC removal. Electron spin resonance assays, fluorescent detection using coumarin as a probe, and radical scavenging experiments confirm that hydroxy radicals (•OH), both in free and surface-bound forms, contribute to oxidation of TC. Humic acids brought detrimental effects on TC removal and therefore should be biologically degraded in advance. This work offers a facile and cost-effective solution to decontaminate TC in natural and engineered water bodies.

Improved Dewaterability of Waste Activated Sludge by Fe(II)-Activated Potassium Periodate Oxidation.

Fe(II)-activated potassium periodate (KIO4) oxidation was used to improve the dewaterability of waste-activated sludge for the first time. Compared with those of raw sludge, the capillary suction time (CST), specific resistance filtration (SRF), and water content of filter cake (WC) of sludge treated using the Fe(II)/KIO4 process under the optimal conditions (i.e., the initial pH = 6.8, KIO4 dose = 1.4 mmol/g volatile suspended solids, Fe(II)/KIO4 molar ratio = 1.2) decreased by 64.34%, 84.13%, and 6.69%, respectively. For conditioned sludge flocs, the Zeta potential and particle size were increased, and hydrophilic proteins in extracellular polymeric substances (EPS) were partly degraded, accompanied by the transformation of tightly bound EPS into soluble EPS and the conversion of dense sludge flocs into loose and porous ones. During Fe(II)/KIO4 oxidation, Fe(IV) and the accompanying •OH were determined as the predominant reactive species and the underlying mechanism of sludge EPS degradation was proposed. This work provides a prospective method for conditioning the sludge dewaterability.

Selective Photocatalytic Transformation of Lignin to Aromatic Chemicals by Crystalline Carbon Nitride in Water-Acetonitrile Solutions.

The photocatalytic conversion of lignin to aromatic compounds in aqueous solutions is a promising approach. We herein report a crystalline carbon nitride prepared by high-temperature thermal polymerization and alkali-metal molten salt treatment, which was then applied in the selective conversion of lignin to aromatic compounds. The results showed that the tri-s-tri-C3N4 presented a relatively high activity and selectivity for the conversion of lignin in aqueous solutions. In a 95% water-acetonitrile solution, it achieved a relatively high conversation rate of lignin, reaching 62.00%, and the selectivity of the C-C bond cleavage was high, at 86.8%. The characterization results obtained by TEM, UV-vis/DRS, PL, and transient photocurrent response showed that the ultra-high activity of tri-s-tri-C3N4 was mainly due to the improvements in crystallinity and light absorption. Mechanism studies showed that the dispersion of the catalyst and the combination of lignin and catalyst in aqueous solvents with different acetonitrile ratios were the main factors affecting lignin conversion. As the water content in the solutions increased, the primary active sites were converted from h+ to ·O2-. This study revealed the interactions between lignin, photocatalysts, and reaction solutions, providing a theoretical basis for the photocatalytic conversion of lignin in aqueous solutions.

Carbon Quantum Dots-Functionalized UiO-66-NH2 Enabling Efficient Infrared Light Conversion of 5-Hydroxymethylfurfuryl with Waste Ethanol into 5-Ethoxymethylfurfural.

The catalytic etherification of 5-hydroxymethylfurfural (HMF) with the waste ethanol into high-energy-density 5-ethoxymethylfurfural (EMF) has been considered as a promising way to simultaneously alleviate the energy crisis and environmental pollution. However, the energy consumption is rather high as the synthesis of EMF requires a high temperature to open the etherification reaction. Herein, we demonstrate a clever design and construction of acidified biomass-derived carbon quantum dots (BCQDs)-modified UiO-66-NH2 that is immobilized on cermasite (H+/BCQDs/UiO-66-NH2@ceramsite), which can use the IR light as driven energy and wasted ethanol to trigger the catalytic conversion of HMF into EMF. The temperature on the surface of the immobilized catalyst could reach as high as 139 °C within 15 min IR irradiation. Due to the aforementioned advantages, the as-prepared catalyst exhibited excellent IR-triggered catalytic performance toward EMF production, where the EMF yields and selectivity were as high as 45% and 65%, respectively. The high catalytic performance originates from the outstanding photo-to-thermal conversion by the introduction of BCQDs, as well as the strong interactions between BCQDs and UiO-66-NH2 that boosts the etherification reactions. The immobilization of catalyst on cermasite not only benefits catalyst recycling, but more importantly reduces catalyst loss during practical applications. The conceptual study shown here provides new viewpoints in designing energy-effective materials for the conversion of wastes into high-value-added resources.

Energy-transfer-mediated oxygen activation in carbonyl functionalized carbon nitride nanosheets for high-efficient photocatalytic water disinfection and organic pollutants degradation.

Polymeric photocatalysts are promising candidates for water purification, however their catalytic performance are still unsatisfactory due to the fast charge recombination that leads to low reactive oxygen radicals production. In this study, a conceptual energy-transfer-mediated photocatalytic oxygen activation system over polymeric carbon nitride without the need of electron-hole separation is proposed, exhibiting remarkable singlet oxygen triggered bacteria inactivation performance as well as organic pollutants degradation. By structure and excitonic effect modulation, the oxygen activation process changes from the traditional electron-transfer mechanism to the final energy-transfer pathway, leading to the selective generation of singlet oxygen with high efficiency. The generated singlet oxygen is found to fervently attack the bacteria membrane, creating irreparable pores or holes on the cell membrane for cytoplasmic contents leaking out to accelerate bacteria destruction. The work demonstrated here offers a new photocatalytic oxygen activation pathway for achieving high-efficient reactive oxygen species generation performance without the need of charge separation.

Three-Dimensional Branched Crystal Carbon Nitride with Enhanced Intrinsic Peroxidase-Like Activity: A Hypersensitive Platform for Colorimetric Detection.

Graphitic carbon nitride (g-C3N4) as a metal-free nanozyme has attracted huge attention for catalytic applications. However, the catalytic activity of pure g-C3N4 causes very moderate H2O2 activation. Herein, a novel three-dimensional (3D) branched carbon nitride nanoneedle (3DBC-C3N4) nanozyme has been proposed to overcome such shortcoming. This unique 3D branched structure of 3DBC-C3N4 facilitated effective mass transfer during catalytic reaction and induced a lightning rodlike effect to accelerate electron collection at the tip area for H2O2 activation. With improved H2O2 activation for hydroxyl radical (•OH) generation, 3DBC-C3N4 showed excellent peroxidase-like activity toward 3,3',5,5'-tetramethylbenzidine oxidation in the presence of H2O2. As for H2O2, the Vmax value of 3DBC-C3N4 was found to be 20 times higher than that of natural horseradish peroxidase. Moreover, the 3D branched structure of 3DBC-C3N4 offered large interface for the reversible conjugation of single-stranded DNA, which enhanced the colorimetric sensitivity. Moreover, 3DBC-C3N4 exhibited high sensitivity toward oxytetracycline detection, with the detection limit and quantitative limit of 1 and 50 µg/L, respectively.

Preparation of graphene/TiO2 composites by nonionic surfactant strategy and their simulated sunlight and visible light photocatalytic activity towards representative aqueous POPs degradation.

A series of graphene/TiO2 composites were fabricated using a single-step nonionic surfactant strategy combined with the solvothermal treatment technique. Their phase structure, morphology, porosity, optical absorption property, as well as composition and structure, were characterized. The as-prepared composites were successfully applied to degrade aqueous persistent organic pollutants (POPs) such as rhodamine B, aldicarb, and norfloxacin in simulated sunlight (λ>320 nm) and visible light (λ>400 nm) irradiation. The degradation mechanism and kinetics of aqueous POPs were studied in detail. The mineralization of aqueous POPs and the recyclability of the composites were also tested in the same condition.