No abstract

Fast diffusion rate of ions and sufficiently exposed active sites are important for catalysts. As a superior but rarely studied Fenton‐type catalyst, unsatisfactory ion diffusion rate of manganese silicate is the exact obstacle for improving its catalytic activity. Here, hierarchical manganese silicate hollow nanotubes (MnSNTs) assembled by tunable secondary structures are precisely fabricated by an efficient hydrothermal method and systematically investigated as Fenton‐type catalysts for the first time. The open end and thin mesoporous walls of the hollow nanotubes help shorten the diffusion pathway of ions and enhance the mass transport. Moreover, the numerous standing small nanosheets endow MnSNTs with higher specific surface area and larger pore volume than the large nanosheets and nanoparticles, and thus expose more active sites for adsorption and catalytic decomposition. MnSNTs are highly efficient in adsorption and catalytic decomposition of cationic dyes with an excellent recycling stability. About 98.1% of methylene blue is catalytically decomposed in 45 min at an ambient temperature of 25 °C. When the temperature increases to 60 °C, only 2 min are required, with a 530% higher kinetic constant than reported.

High activity and long-term stability are particularly important for peroxymonosulfate (PMS)-based degradation processes in wastewater treatment, especially under a flowing state. However, if the highly active nanomaterials are in a powder form, they could disperse well in water but would not be convenient for application under varied flow rates. A metal oxide/bacterial cellulose hybrid membrane fixed in a flowing bed is expected to solve these problems. Herein, α-FeO nanodisk/bacterial cellulose hybrid membranes as high-performance sulfate-radical-based visible light photocatalysts are synthesized for the first time. The bacterial cellulose with excellent mechanical stability and film-forming feature not only benefits the formation of a stable membrane to avoid the separation and recycling problems but also helps disperse and accommodate α-FeO nanodisks and thus enhances the visible light absorption performances, leading to an excellent PMS-based visible light degradation efficiency under both stirring and flowing states. Particularly, the optimized hybrid membrane photocatalyzes both cationic and anionic organic dyes under a flowing bed state for at least 84 h with the catalytic efficiency up to 100% and can be easily separated after the reaction, confirming its remarkable catalytic performance and long-term stability. Even under varied flow rates during the continuous process, it efficiently degrades rhodamine B and orange II from 3 to 16 mL h. When the flow rate goes back from high to low, the hybrid membrane quickly recovers its original performance, demonstrating the high activity and stability of the α-FeO/bacterial cellulose membrane.

Electrochemical advanced oxidation processes (EAOPs) are a class of promising technologies for wastewater remediation. The challenge of EAOPs is the in situ generation and activation of hydrogen peroxide (H2O2) to evolve reactive oxygen species (ROS) simultaneously with low energy consumption and high performances. In this work, we designed an EAOP system, coupling FeOCl nanoparticles on oxygen-enriched carbon nanotubes (O-CNTs) and a nickel foam (FeOCl/O-CNTs/NF) cathode for electro-Fenton (EF) reactions and an IrO2/Ti anode for anodic oxidation (AO) simultaneously. Specifically, the defects and oxygen functional groups on O-CNTs introduced by a modified Hummers’ method could induce the charge redistribution of O-CNTs for outstanding two-electron oxygen-reduction-reaction performances (H2O2 selectivity of 73%) and provide more anchoring sites for the loading of active cocatalyst nanoparticles. Thus, abundant FeOCl nanoparticles were successfully loaded onto O-CNTs. Such a FeOCl/O-CNTs/NF cathode exhibited a high H2O2 production rate of 95 mmol gcat –1 h–1 because of the improved exposure of catalytic active sites supported on nickel foam to attain a large specific surface area. •OH was generated from H2O2 via both heterogeneous and homogeneous EF processes induced by the FeOCl/O-CNTs/NF cathode and leached ferrous ions accordingly. Sulfamethoxazole (SMX) was completely removed within 30 min at a low specific energy consumption of 0.024 kWh g–1 SMX–1. Thus, the simultaneous FeOCl/O-CNTs/NF-based EF system and AO provide an efficient and cost-effective technology for organic contaminant remediation.

Macroscopic three-dimensional catalytic materials could overcome the poor operability and avoid secondary pollution of common powdery counterparts, especially in flow-type setups. However, conventional isotropic graphene-based aerogels and foams have randomly distributed graphene sheets, which may cause stream erosion and reduce the flux seriously. Herein, for the first time, we design and fabricate a novel anisotropic CoFe2O4@graphene hybrid aerogel (CFO@GA-A) with a hydrothermal synthesis followed by directional-freezing and freeze-drying for a tube-like flow-type setup analogous to a wastewater discharge pipeline. The long and vertically aligned pores inside the aerogel provide an exceptional flux of 1100 L m–2 h–1, 450% higher than that of the rough and zigzag paths in the isotropic CoFe2O4@graphene hybrid aerogel (CFO@GA-I), and the leaching of metal ions is obviously inhibited by relieving the erosion of CoFe2O4. Besides, the CFO@GA-A could sustain the scour of high-speed flowing wastewater and maintain its structural stability. Therefore, organic contaminants of indigo carmine, methyl orange, orange II, malachite green, phenol, and norfloxacin could readily flow over the nanocatalysts and be degraded rapidly within 7.5–12.5 min at varied flow rates from 60 to 120 mL h–1. The CFO@GA-A also exhibits a much better long-term stability with removal efficiencies toward indigo carmine at 100%, 91%, and 85% for at least 30 h (60 mL h–1), 25 h (90 mL h–1), and 21 h (120 mL h–1), respectively. On the contrary, the CFO@GA-I exhibits unsatisfactory removal efficiencies of <40%. Interestingly, CFO@GA-A could also serve as building blocks to stack on each other for degrading intense flowing wastewater, exhibiting an outstanding composability. The high-flux and long-term stability make the CFO@GA-A promising as an ideal catalytic material for wastewater treatments.