One-step preparation of Fe O /N-GN/CNTs heterojunctions as a peroxymonosulfate activator for relatively highly-efficient methylene blue degradation

Skin-Inspired and Self-Powered Piezoionic Sensors for Smart Wearable Applications

Bio-inspired by tactile function of human skin, piezoionic skin sensors recognize strain and stress through converting mechanical stimulus into electrical signals based on ion transfer. However, ion transfer inside sensors is significantly restricted by the lack of hierarchical structure of electrode materials, and then impedes practical application. Here, a durable nanocomposite electrode is developed based on carbon nanotubes and graphene, and integrated into piezoionic sensors for smart wearable applications, such as facial expression and exercise posture recognitions. The nanocomposite electrode provides abundant channels for ion transfer because of its hierarchically porous structure. Carbon nanotubes not only prevent restacking of graphene nanolayers, but also connect them across out-plane dimension. The piezoionic skin sensors present a high degree of linearity in a wide strain range with high sensitivity, and long cycling life with bending strains beyond 20 000 s. Further, a smart bracelet based on flexible sensors is fabricated for accurate posture recognition of badminton exercise, valuable to athlete training.

Peroxymonosulfate activation by magnetic CoNi-MOF catalyst for degradation of organic dye

In this work, Fe₃O₄/CoNi-MOF was synthesized by a simple solvothermal method. The catalytic performance of 0.2-Fe₃O₄/CoNi-MOF toward PMS activation was studied by degradation of 20 mg/L methylene blue (MB). The results indicated that 0.2-Fe₃O₄/CoNi-MOF had good catalytic ability, the removal rate of MB was 99.4% within 60 min with 125 mg/L PMS and 150 mg/L catalyst. Quenching experiment and electron paramagnetic resonance (EPR) analysis revealed that the singlet oxygen (¹O₂), superoxide radical (•O₂^-) and sulfate radical (SO₄^•-) played a crucial role in the catalytic degradation process. Meantime, mechanism of PMS activation by 0.2-Fe₃O₄/CoNi-MOF was proposed, the electrons donated by Fe²⁺ can also enhance the Co-Ni cycles. In conclusion, Fe₃O₄/CoNi-MOF composite catalyst has the advantages of simple preparation, excellent catalytic activity and reusability, which is an effective catalyst for water pollution control.

Carbon materials in persulfate-based advanced oxidation processes: The roles and construction of active sites

Many researchers have paid more attention to the progress of carbon materials owing to their advantages, such as high activity, low cost, large surface area, high conductivity and high stability. Carbon materials have been widely used in persulfate-based advanced oxidation processes (PS-AOPs), especially for graphene (G), carbon nanotubes (CNTs) and biochar (BC). Various strategies are applied to promote their activity, however, up to now, the relationship between the structures of carbon materials and their activities in PS-AOPs has not been specifically reviewed. The methods to switch reaction pathway (radical and nonradical pathways) in carbon-persulfate-based AOPs have not been systematically explored. Hereon, this review illustrated the active sites of G, CNTs, BC and other carbon materials, and generalized the modification methods to promote the activity of carbon materials and to switch reaction pathway in PS-AOPs. The roles of carbon materials in PS-AOPs were discussed around reactive oxygen species (ROS) and the structures. ROS are frequently complex in AOPs, but main ROS generation is related to the active sites on carbon materials. The structures of carbon materials (e.g., metal-carbon bonds, the electron-deficient C atoms, unbalanced electron distribution and graphitized structures) play a decisive role in the nonradical pathway. Finally, future breakthroughs of carbon materials were proposed for practical engineering and multi-field application.

Synergistic oxytetracycline adsorption and peroxydisulfate-driven oxidation on nitrogen and sulfur co-doped porous carbon spheres

Metal-free carbonaceous catalysts are receiving increasing attention in wastewater treatment. Here, nitrogen and sulfur co-doped carbon sphere catalysts (N,S-CSs₉₀₀-OH) were synthesized using glucose and L-cysteine via a hydrothermal method and high temperature alkali activation. The N,S-CSs₉₀₀-10%-OH exhibited excellent catalytic performance for the degradation of oxytetracycline (OTC). The degradation rate was 95.9% in 60 min, and the reaction equilibrium rate constant was 0.0735 min^-1 (k_0-15 min). The synergistic effect of adsorption-promoting degradation was demonstrated in the removal process of OTC. The excellent adsorption capacity of N,S-CSs₉₀₀-10%-OH ensured the efficient oxidation of OTC. N,S-CSs₉₀₀-10%-OH reduced the activation energy of the OTC degradation reaction (Ea=18.23 kJ/mol). Moreover, the pyrrolic N, thiophene S and carbon skeleton played an important role in the degradation of OTC based on density function theory, and the catalytic mechanism was expounded through radical and nonradical pathways. The active species involved in the reaction were O₂^•-, ¹O₂, SO₄^•- and •OH, of which O₂^•- was the primary reactive species. This study provides a new insight into the reaction mechanism for efficient treatment of organic pollutants using metal-free doped porous carbon materials.

2D N-Doped Porous Carbon Derived from Polydopamine-Coated Graphitic Carbon Nitride for Efficient Nonradical Activation of Peroxymonosulfate

Nitrogen-doped carbon materials attract broad interest as catalysts for peroxymonosulfate (PMS) activation toward an efficient, nonradical advanced oxidation process. However, synthesis of N-rich carbocatalysts is challenging because of the thermal instability of desirable nitrogenous species (pyrrolic, pyridinic, and graphitic N). Furthermore, the relative importance of different nitrogenous configurations (and associated activation mechanisms) are unclear. Herein, we report a "coating-pyrolysis" method to synthesize porous 2D N-rich nanocarbon materials (PCN-x) derived from dopamine and g-C₃N₄ in different weight proportions. PCN-0.5 calcined at 800 °C had the highest surface area (759 m²/g) and unprecedentedly high N content (18.5 at%), and displayed the highest efficiency for 4-chlorophenol (4-CP) degradation via PMS activation. A positive correlation was observed between 4-CP oxidation rates and the total pyridinic and pyrrolic N content. These N dopants serve as Lewis basic sites to facilitate 4-CP adsorption on the PCN surface and subsequent electron-transfer from 4-CP to PMS, mediated by surface-bound complexes (PMS-PCN-0.5). The main degradation products were chlorinated oligomers (mostly dimeric biphenolic compounds), which adsorbed to and deteriorated the carbocatalyst. Overall, this study offers new insights for rational design of nitrogen-enriched carbocatalysts, and advances mechanistic understanding of the critical role of N species during nonradical PMS activation.

Interior engineering of seaweed-derived N-doped versatile carbonaceous beads with Co x O y for universal organic pollutant degradation

The rational optimization of catalytic composites with excellent catalytic activities and long-term cycling stabilities for environmental remediation is still maintained as highly desired but is an ongoing challenge. Here, seaweed-derived N-doped versatile carbonaceous beads with Co x O y (Co-NC-0.25-700 °C) are employed as a novel catalyst to activate peroxymonosulfate (PMS) for methylene blue (MB) degradation. Profiting from the improved structure-activity relationship and the synergistic effects between the "egg-box" structure and the Co x O y loaded on the N-doped carbonaceous beads, Co-NC-0.25-700 °C exhibited relatively high performance and comparative long-term stability. The universal applicability of Co-NC-0.25-700 °C was investigated by degrading other types of organic pollutants in various systems. For this type of newly fabricated high-performance versatile composites, structure-property relationships were plausibly proposed. Notably, the degradation efficiency and the catalyst structure could be tailored by the amount of polyethyleneimine (PEI) introduced in the preparation process and by the pyrolysis temperature. More favorably, the coupling of the magnetic properties and bead-like shape endows the resultant composites with remarkable reusability and recyclability, as compared to powder state materials. Another interesting finding is that MB degradation over Co-NC-0.25-700 °C is minimally affected by common ions (Cl-, NO3 -, SO4 2-, etc.), and holds a certain catalytic activity under the background conditions of two simulated real water conditions (running water and seawater). Of particular interest, a microreactor filled with Co-NC-0.25-700 °C was utilized as a verification model for practical applications of the reaction in continuous-flow. More far-reaching, the simulations of actual water conditions and the design of a continuous-flow reactor represent a giant step towards universal applications for organic pollution treatment.