ABSTRACT
Single atom catalysts (SACs) are atomic-level-engineered materials with high intrinsic activity. Catalytic centers of SACs are typically the transition metal (TM)-nonmetal coordination sites, while the functions of coexisting non-TM-bonded functionalities are usually overlooked in catalysis. Herein, the scalable preparation of carbon-supported cobalt-anchored SACs (CoCN) with controlled CoâN sites and free functional N species is reported. The role of metal- and nonmetal-bonded functionalities in the SACs for peroxymonosulfate (PMS)-driven Fenton-like reactions is first systematically studied, revealing their contribution to performance improvement and pathway steering. Experiments and computations demonstrate that the CoâN3C coordination plays a vital role in the formation of a surface-confined PMS* complex to trigger the electron transfer pathway and promote kinetics because of the optimized electronic state of Co centers, while the nonmetal-coordinated graphitic N sites act as preferable pollutant adsorption sites and additional PMS activation sites to accelerate electron transfer. Synergistically, CoCN exhibits ultrahigh activity in PMS activation for p-hydroxybenzoic acid oxidation, achieving complete degradation within 10 min with an ultrahigh turnover frequency of 0.38 min-1, surpassing most reported materials. These findings offer new insights into the versatile functions of N species in SACs and inspire rational design of high-performance catalysts in complicated heterogeneous systems.
ABSTRACT
Industrial and disinfection wastewater typically contains high levels of organic pollutants and residue hydrogen peroxide, which have caused environmental concerns. In this work, dual-asymmetric MnO2 @polymer microreactors are synthesized via pollutant polymerization for self-driven and controlled H2 O2 decomposition. A hollow and asymmetric MnO2 nanotube is derived from MnO2 nanorods by selective acid etching and then coated by a polymeric layer from an aqueous phenolic pollutant via catalytic peroxymonosulfate (PMS)-induced polymerization. The evolution of particle-like polymers is controlled by solution pH, molar ratios of PMS/phenol, and reaction duration. The polymer-covered MnO2 tubing-structured micromotors presented a controlled motion velocity, due to the reverse torque driven by the O2 bubbles from H2 O2 decomposition in the inner tunnels. In addition, the partially coated polymeric layer can regulate the exposure and population of Mn active sites to control the H2 O2 decomposition rate, thus avoiding violent motions and massive heat caused by vigorous H2 O2 decomposition. The microreactors can maintain the function of mobility in an ultra-low H2 O2 environment (<0.31 wt.%). This work provides a new strategy for the transformation of micropollutants to functional polymer-based microreactors for safe and controlled hydrogen peroxide decomposition for environmental remediation.
ABSTRACT
Efficient separation of photogenerated electron-hole pairs is always one of the key factors boosting visible light photodegradation efficiency. Till now, there are few reports on the synergistic competitive consumption of photogenerated active species and the synergistic adsorption of organic contaminants to promote the performance of a designed heterojunction. Herein, we design and construct a novel BiOBr/Ag6Si2O7 heterojunction with the dual synergistic effects towards methylene blue (MB) and methyl orange (MO). The dual synergistic effects could avoid the combination of photogenerated h+/e- pairs, improve the adsorption efficiency, and even regulate the photodegradation efficiency. Thus, for an aqueous mixture of MB and MO, the BiOBr/Ag6Si2O7 photocatalyst exhibits largely improved adsorption capacities of the dyes by a multi-layer adsorption mode. Moreover, the photocatalyst could further promote the photodegradation rate of MO while slow that of MB due to the competitive consumption of photogenerated active species, showing a sequential selectivity phenomenon. Thanks to the dual synergistic effects, the adsorption capacity of MO increases 1379% higher than that of neat MO solution, and the photodegradation time decrease from 30 to 12â¯min with a rate constant of 0.22â¯min-1, 38% higher than that of neat MO solution.
ABSTRACT
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.
ABSTRACT
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-Fe2O3 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-Fe2O3 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-1. 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-Fe2O3/bacterial cellulose membrane.
