The effective, stable, and secure catalysts are essential for sulfate radical (SO₄^·−)-based advanced oxidation processes (SR-AOPs) to the degradation of organic contaminants in water. Heterogeneous supported cobalt-based catalysts are commonly used to activate peroxymonosulfate (PMS) to achieve the degradation. In this work, we synthesized Co₃O₄@Al₂O₃ three-dimensional (3D) mesoporous nanocomposite (denoted as Co₃O₄@Al₂O₃ 3DPNC) in just one step by calcining cheap and green deep eutectic solvent (DES) solution containing Co salt. Co₃O₄@Al₂O₃ 3DPNC with the high specific surface area (93.246 m²/g), uniform pore distribution (3.829 nm) and rich porosity (0.255 cm³/g) were attained in a beautiful hierarchical structure which exhibited the open 3D propeller-like microstructure, two-dimensional lamellar substructure with rich folds, as well as the decoration of highly dispersed Co₃O₄ nanoparticles on mesoporous amorphous Al₂O₃. The excellent chemical and thermal stability of Al₂O₃ ensures the high stability of the catalyst, and the formation of the complex hierarchical structure makes the active Co₃O₄ be homogenously dispersed for effective catalysis. The catalyst demonstrated outstanding performance for catalytic degradations of organic pollutants (acetaminophen, oxytetracycline, 5-sulfosalicylic acid, orange G and Rhodamine B) by generated SO₄^·−, ·OH and ¹O₂. With a very low cobalt content (equal to 28.2 mg/L of Co), the catalyst exhibited very high stability and excellent reusability in the recycling usages, while the leaching of the cobalt element (< 0.145 mg/L) was also at a low level. Our catalyst achieved effective degradations of acetaminophen in cycles without losing its stable hierarchical nanostructure.

The development of novel nanozymes for environmental contamination remediation is a worthwhile research direction. However, most of the reported nanozymes cannot degrade efficiently due to the limitation of the internal active sites not being able to come into direct contact with contaminants. Therefore, we reported Fe-N-C single-atom nanozymes (SAzymes) with atomically dispersed FeN₄ active sites anchored on a three-dimensional hierarchically ordered microporous-mesoporous-macroporous nitrogen doped carbon matrix (3DOM Fe-N-C) for the degradation of a targeted environmental pollutant (rhodamine B (RhB)). The three-dimensional (3D) hierarchically ordered porous structure may accelerate mass transfer and improve the accessibility of active sites. This structure and high metal atom utilization endow Fe-N-C SAzyme with enhanced tri-enzyme-mimic activities, comprising oxidase-mimic, peroxidase-mimic, and catalase-mimic activities. Based on its excellent peroxidase-mimic activity, 3DOM Fe-N-C can degrade RhB by hydroxyl radicals (·OH) generated in the presence of hydrogen peroxide. This study provides a new idea for designing porous Fe-N-C SAzymes for environmental contamination remediation.

Eco-friendly chemical oxygen demand (COD) sensors are highly desired with respect to the importance of COD determination in environmental protection. In this work, a new FTO/TiO₂/PbO₂ (FTO = fluorine-doped tin oxide) electrode was fabricated with a two-step method and used as an eco-friendly electrochemical COD sensor. The interlayer TiO₂ was employed to strengthen the adhesion of PbO₂ on the FTO substrates by providing a large TiO₂/PbO₂ interface area. The effects of the factors including applied potential, supporting electrolyte concentration and stirring speed on the sensing performance were investigated. Under the optimized conditions, linear responses to the COD of water with different COD sources were achieved, and a linear range from 5 to 120 mg/L was obtained in the case of sucrose as the COD source. The relative standard deviations (RSD) were determined to be less than 9% for the glucose solutions with the COD of 7.5, 12.5 and 17.5 mg/L. For real sample analysis, the obtained results were comparable with those measured with the conventional dichromate method, with a relative error less than 11%.

The development of highly active catalysts is the key to the successful application of sulfate radical (SO₄^·−)-based advanced oxidation processes (AOPs) to wastewater treatment. Herein, bimetallic oxide CoMn₂O₄ hierarchical porous nanosheets (CoMn₂O₄ HPNSs) were constructed using glucose/urea deep eutectic solvent (DES) as sustainable solvent and self-formed sacrificial carbon templates. The prepared CoMn₂O₄ HPNS exhibited outstanding peroxymonosulfate (PMS) activation performance, achieving the rapid degradation of refractory organic compounds in wastewater, including 5-sulfosalicylic acid (100%), acetaminophen (100%), oxtetracycline (100%), and sulfamethoxazole (91%) within 20 min. This excellent performance was attributed not only to the synergistic catalytic effect of Co-Mn bimetals, but also to the hierarchical porous structure which exposes more active sites and accelerates the migration of PMS and organic pollutants. In addition, CoMn₂O₄ HPNS also showed excellent reusability and high stability in multiple cycles of degradation. The active species quenching results and electron paramagnetic resonance measurements revealed that SO₄^·− greatly contributed to organic degradation, while ¹O₂ and ·OH also involved. Moreover, a series of other transition metal oxides (Co₃O₄, Fe₂O₃, Mn₃O₄, NiO, and CoFe₂O₄) with hierarchical porous nanosheet structures were successfully fabricated with this method. This study provides a simple, general, and low-cost strategy for fabricating hierarchical porous transition metal oxides, which are promising for the environmental remediation or many other applications in the future.

Electrochemical nitrogen reduction reaction (NRR) is a promising method for the synthesis of ammonia (NH₃). However, the electrochemical NRR process remains a great challenge in achieving a high NH₃ yield rate and a high Faradaic efficiency (FE) due to the extremely strong N≡N bonds and the competing hydrogen evolution reaction (HER). Recently, bismuth telluride (Bi₂Te₃) with two-dimensional layered structure has been reported as a promising catalyst for N₂ fixation. Herein, to further enhance its NRR activity, a general doping strategy is developed to introduce and modulate the crystal defects of Bi₂Te₃ nanosheets by adjusting the amount of Ce dopant (denoted as Ce_x-Bi₂Te₃, where x represents the designed molar ratio of Ce/Bi). Meanwhile, the crystal defects can be designed and controlled by means of ion substitution and charge compensation. At −0.60 V versus the reversible hydrogen electrode (RHE), Ce_0.3-Bi₂Te₃ exhibits a high NH₃ yield (78.2 μg·h⁻¹·mg_cat⁻¹), a high FE (19.3%), and excellent structural and electrochemical stability. Its outstanding catalytic activity is attributed to the tunable crystal defects by Ce doping. This work not only contributes to enhancing the NRR activity of Bi₂Te₃ nanosheets, but also provides a reliable approach to prepare high-performance electrocatalysts by controlling the type and concentration of crystal defects for artificial N₂ fixation.

Atomically dispersed catalysts have been widely studied due to their high catalytic activity and atom utilization. Single-atom catalysts have achieved breakthrough progress in the degradation of emerging organic contaminants (EOCs) by activating peroxymonosulfate (PMS). However, the construction of atomically dispersed catalysts with diatomic/multiatomic metal active sites by activating PMS to degrade pollutants is still seldom reported, despite the unique merits of atom-pair in synergistic electronic modulation and breaking stubborn restriction of scaling relations on catalytic activity. We have synthesized Fe₁-N-C, Fe₂-N-C, and Fe₃-N-C catalysts with monoatomic iron, diatomic iron, and triatomic iron active center, respectively. The results show that the catalytic degradation activity of Fe₂-N-C is twice that of Fe₁-N-C and Fe₃-N-C due to its unique Fe₂N₆ coordination structure, which fulfilled the complete degradation of rhodamine B (RhB), bisphenol A (BPA), and 2,4-dichlorophenol (2,4-DP) within 2 min. Electron paramagnetic resonance (EPR) and radical quenching experiments confirmed that the reaction was a non-radical reaction on the catalyst surface. And singlet oxygen and Fe(IV) are the key active species.

Polymer stabilizers are widely used to synthesize gold nanoparticles (Au NPs) to prevent their aggregation and improve their stability. Although stabilizers are known to greatly influence both the structure and size of Au NPs, limited efforts explore their effects on the activity of Au NPs for biocatalysis. Herein, different polymers are used as stabilizers to synthesize Au NPs. For the glucose oxidase-like activity, we find that without the spatial barrier from stabilizers, naked Au NPs show significantly high catalytic activity as well as the worst stability. Among the polymers, polyacrylic acid-stabilized Au NPs exhibit the highest activity, whose V_max (0.74 μM·s⁻¹) is higher than that of the natural glucose oxidase (0.37 μM·s⁻¹) due to the smallest particle size (< 2 nm) and the weak spatial resistance of polyacrylic acid. These variable catalytic results derive from the comprehensive effects including size, steric hindrance, and electronic effect. However, further selectivity and activity tests have exposed shortcomings. They possess universal activities for aldose oxidation, whereas cannot retain activities in typical physiological environments. Our findings highlight the role of polymer stabilizers in imposing effects on the glucose oxidase-like activity of Au NPs and provide a basis for further Au NPs engineering and applications.

Transition metal phosphides (TMPs) are essential catalysts for some general catalytic reactions. However, their potentials for biological catalysis have seldom been explored. Herein, we investigated the enzyme-like properties of four TMPs (FeP, CoP, Ni₂P, and Cu₃P) towards two sugar-related reactions. Among the four TMPs, Cu₃P nanoparticles (NPs) efficiently catalyzed the hydrolysis of glycosidic bonds as glycoside hydrolase mimics, and FeP NPs possessed both glucose oxidase-like (GOx-like) and peroxidase-like activities, which combined into a cascade reaction for glucose’s simple and one-step colorimetric biosensor without GOx. Cu₃P and FeP NPs with distinctive enzyme-like activities have shown unique biological catalysis potentials for further applications with an attractive and challenging goal of developing nanomaterials to mimic natural enzymes, which encourages more efforts to reveal TMP’s capabilities towards biocatalysis.

High-entropy-oxides (HEOs), a new class of solids that contain five or more elemental species, have attracted increasing interests owing to their unique structures and fascinating physicochemical properties. However, it is a huge challenge to construct various nanostructured, especially low-dimensional nanostructured HEOs under the high temperature synthetic conditions. Herein, a facile strategy using glucose-urea deep eutectic solvent (DES) as both a solvent and the carbon source of structure-directed template is proposed for the synthesis of various HEOs with two-dimentional (2D) nanonets and one-dimentional (1D) nanowires, including rock-salt (Co, Cu, Mg, Ni, Zn)O, spinel (Co, Cr, Fe, Mn, Ni)₃O₄, and perovskite La(Co, Cr, Fe, Mn, Ni)O₃. The as-prepared HEOs possessed five or more uniformly dispersed metal elements, large specific surface areas (more than 25 m²·g⁻¹), and a pure single-phase structure. In addition, high cooling rate (cooling in air or liq-N₂-quenching) was indispensable to obtain a single-phase rock-salt (Co, Cu, Mg, Ni, Zn)O because of phase separation caused by copper. By taking advantage of unique features of HEOs, rock-salt (Co, Cu, Mg, Ni, Zn)O can function as a promising candidate for lithium-ion batteries (LIBs) anode material, which achieved excellent cycling stability. This work provides a feasible synthetic strategy for low-dimensional hierarchical HEOs, which creates new opportunities for the stable HEOs being highly active functional materials.

Self-powered glucose biosensor (SPGB) is of great interest due to the advantages including single configuration, good stability and particularly no need of external power sources. Herein, a mediator-free SPGB with high sensitivity and good selectivity is constructed based on a hybrid enzymatic biofuel cell (EBFC) composed of a glucose oxidase/cobalt phthalocyanine/1-pyrenebutyric acid/ buckypaper (GOD/CoPc/PBA/BP) bioanode and a MnO₂/PBA/BP capacitive cathode. The efficient electron transfer from GOD to electrodes is achieved successfully through the anode oxidation of hydrogen peroxide (H₂O₂), one nature product of glucose oxidation catalyzed by GOD, thus avoiding the potential drawbacks posed by the use of redox mediators. CoPc servers as an efficient catalyst to lower the anode potential required by the reaction of H₂O₂ to 0.17 V. The MnO₂/PBA/BP capacitive cathode is utilized because it can not only provide a high discharge potential and adequate capacitance to match the bioanode well, but also exhibit no potential interference to the anodic reaction. The concentration of glucose can be detected simply by measuring the output of the SPGB and a wide linear detection range from 0.5 to 8 mM has been obtained with high sensitivities of 48.66 and 32.12 μA·cm^-2·mM^-1 with and without stirring, respectively. The recoveries of glucose in grape juice and human serum are in the range from 99.5% to 101.2% with the relative standard deviation (RSD) less than 8%, indicating the good promise of the SPGB in sensing glucose in real samples.