Wenjie Ma

Magnetic CoFe2O4 nanoparticles supported on titanate nanotubes (CoFe2O4/TNTs) as a novel heterogeneous catalyst for peroxymonosulfate activation and degradation of organic pollutants

Magnetic spinel ferrites, as heterogeneous catalysts to generate powerful radicals from peroxymonosulfate (PMS) for the degradation of organic pollutants, have received much attention in recent years due to the characteristic of environmental benefits. In this study, with titanate nanotubes (TNTs) as catalyst support, a novel CoFe2O4/TNTs hybrid was constructed by an impregnation-calcination method. Characterization results revealed that TNTs support could promise small size and good dispersion of CoFe2O4 nanoparticles. Compared to the pure CoFe2O4, the as-prepared CoFe2O4/TNTs not only exhibited better performance in catalytic decomposition of Rhodamine B, but also realized higher total organic carbon removal and less cobalt leaching, which could be attributed to the enhanced catalytic ability from smaller CoFe2O4 nanoparticles and the unique ion-exchange ability from TNTs support. Some influential factors, including reaction temperature, dosages of PMS and CoFe2O4/TNTs, and pH values were investigated and analyzed. Moreover, CoFe2O4/TNTs maintained its catalytic efficiency during the repeated batch experiments and also displayed functional advantages in the catalytic degradation of phenol. We believe the CoFe2O4/TNTs hybrid can be an efficient and green heterogeneous catalyst for the degradation of organic pollutants, and this study provides insights into the rational design and development of alternative catalysts for wastewater treatment.

Prussian blue analogues derived porous nitrogen-doped carbon microspheres as high-performance metal-free peroxymonosulfate activators for non-radical-dominated degradation of organic pollutants

Nitrogen-doped carbon materials are becoming a new type of metal-free heterogeneous catalysts in advanced oxidation processes (AOPs) for wastewater treatment and environmental remediation. In this study, porous nitrogen-doped carbon (PNC) microspheres derived from Zn–Co Prussian blue analogues (Zn–Co PBAs) are employed as heterogeneous catalysts in peroxymonosulfate (PMS) activation. The unique configuration of the metal centers/clusters bound by cyanide groups (–CN) of Zn–Co PBAs offers the PNC microspheres abundant porosity, a high graphitization degree, and rich nitrogen substitution, which lead to improvements in the catalytic performance. PNC-800 (pyrolyzed at 800 °C) exhibits better performance than other common carbon materials and homologous nitrogen-doped carbocatalysts derived from ZIF-8/ZIF-67. Based on radical quenching and trapping experiments, a non-radical pathway is proposed to dominate methylene blue (MB) degradation; and the high graphitization degree and rich surface graphitic N sites of PNC-800 are two key factors that induce the non-radical pathway. Several influential factors, including catalyst dosage, PMS concentration, pH value and reaction temperature, are investigated in detail. Notably, MB degradation over PNC-800 is almost completely insusceptible to common ions and natural organic matter, and maintains its catalytic efficiency under the background conditions of several real water samples. More interestingly, this non-radical pathway and the good catalytic performance of the PNC-800/PMS system are universal in the degradation of other typical organic pollutants. We believe that these PNC microspheres may be a promising green heterogeneous catalyst for the degradation of organic pollutants, and this study can be used for the design of high-performance carbocatalysts in non-radical systems in the future.

Pearson's principle-inspired strategy for the synthesis of amorphous transition metal hydroxide hollow nanocubes for electrocatalytic oxygen evolution

Hollow nanostructures with higher surface area offer great advantages for electrocatalytic water splitting. Here, we demonstrate the fabrication of amorphous hollow M(OH)x (M = Fe, Co, Ni) nanocubes through a template-assisted route inspired by Pearsons hard and soft acid–base (HSAB) principle with Cu2O nanocubes with different sizes (50 nm, 500 nm) as the sacrificial templates. A comparative study of the electrocatalytic oxygen evolution reaction (OER) of the hollow M(OH)x nanocubes with a similar size indicates that Ni(OH)2 has better OER catalytic activity. It has been revealed that the metal oxyhydroxides formed at the surface are actually the real active species for the OER electrocatalysis. In particular, Ni(OH)2 nanocubes obtained by the Cu2O (50 nm) template provide the best OER activity, with a low overpotential of 349 mV vs. RHE to achieve a current density of 10 mA cm−2 and a low Tafel slope of 63 mV dec−1. The hollow metal hydroxide nanostructures through the Pearsons principle-inspired strategy can be highly efficient electrocatalysts for OER applications.

Template synthesis of nitrogen-doped carbon nanocages–encapsulated carbon nanobubbles as catalyst for activation of peroxymonosulfate

Nitrogen-doped carbon nanocages–encapsulated carbon nanobubbles (CBs@NCCs) were feasibly fabricated by the in situ thermal conversion of Co–Fe Prussian blue analogues (Co–Fe PBAs) coated with polydopamine (PDA) shells. Interestingly, PBA cores can act as a self-sacrificing template and decompose during high-temperature treatment. PDA shells play a crucial role in stabilizing the steric architecture, supplementing nitrogen-doping of CBs@NCCs under high-temperature treatments. When compared with carbon nanobubbles (CBs) without the protection of carbon nanocages, CBs@NCCs possess higher specific surface area and pore volume. The contributions of a unique configuration and proper nitrogen modification are significant for improving the peroxymonosulfate (PMS) activation performance of CBs@NCCs, which is expected to be a promising alternative to other conventional carbocatalysts and metal oxides. Moreover, the applicability of the as-synthesized carbocatalysts was systematically investigated by adjusting several operating parameters, and some ubiquitous anions and natural organic matters (NOMs) were also taken into account in methylene blue (MB) degradation. The radical evolution and PMS activation mechanism are investigated by radical quenching and electron paramagnetic resonance (EPR) tests, which revealed that sulfate radicals (SO4˙−) and singlet oxygen (1O2) are simultaneously responsible for the overall MB removal in a CBs@NCCs-800/PMS system. This study may provide a broader perspective for upgrading the catalytic efficiency of various green heterogeneous carbocatalysts.