Development, dilemma and potential strategies for the application of nanocatalysts in wastewater catalytic ozonation: A review

With the continuous development of nanomaterials in recent years,the application of nanocatalysts in catalytic ozone oxidation has attracted more and more researchers’attention due to their excellent catalytic properties.In this review,we systematically summarized the current research status of nanocatalysts mainly involving material categories,mechanisms and catalytic efficiency.Based on summary and analysis,we found most of the reported nanocatalysts were in the stage of laboratory research,which was caused by the nanocatalysts defects such as easy aggregation,difficult separation,and easy leakage.These defects might result in severe resource waste,economic loss and potentially adverse effects imposed on the ecosystem and human health.Aiming at solving these defects,we further analyzed the reasons and the existing reports,and revealed that coupling nano-catalyst and membrane,supported nanocatalysts and magnetic nanocatalysts had promising potential in solving these problems and promoting the actual application of nanocatalysts in wastewater treatment.Furthermore,the advantages,shortages and our perspectives of these methods are summarized and discussed.

Efficient and recyclable palladium enriched magnetic nanocatalyst for reduction of toxic environmental pollutants

In this paper,highly stable,powerful,and recyclable magnetic nanoparticles tethered Nheterocyclic carbene-palladium(Ⅱ)((CH_(3))_(3)-NHC-Pd@Fe_(3)O_(4))as magnetic nanocatalyst was successfully synthesized from a simplistic multistep synthesis under aerobic conditions through easily available low-cost chemicals.Newly synthesized(CH_(3))_(3)-NHC-Pd@Fe_(3)O_(4) magnetic nanocatalyst was characterized from various analytical tools and catalytic potential of the(CH_(3))_(3)-NHC-Pd@Fe_3 O_4 magnetic nanocatalyst was studied for the catalytic reduction of toxic 4-nitrophenol(4-NP),hexavalent chromium(Cr(Ⅵ)),Methylene Blue(MB)and Methyl Orange(MO)at room temperature in aqueous media.UV-Visible spectroscopy was employed to monitor the reduction reactions.New(CH_(3))_(3)-NHC-Pd@Fe_(3)O_(4) magnetic nanocatalyst exhibited excellent catalytic activity for the reduction of toxic environmental pollutants.Moreover,(CH_(3))_(3)-NHC-Pd@Fe_(3)O_(4) magnetic nanocatalyst could be easily and rapidly separated from the reaction mixture with the help of an external magnet and recycled minimum five times in reduction of 4-NP,MB,MO and four times in Cr(Ⅵ)without significant loss of catalytic potential and remains stable even after reuse.

A magnetic-void-porous MnFe_(2)O_(4)/carbon microspheres nano-catalyst for catalytic ozonation:Preparation,performance and mechanism

Wastewater treatment is essential to guarantee human health and ecological security.Catalytic ozonation with nanocatalysts is a widely studied and efficient treatment technology.However,this method has always been limited by nanocatalysts disadvantages such as easily loss,difficult to separate and reuse,and catalytic ability decay caused by aggregation,which could cause severe resources waste and potential risk to human health and ecosystem.To remedy these challenges,a magnetic-void-porous MnFe_(2)O_(4)/carbon microsphere shell nanocatalyst(CMS-MnFe_(2)O_(4))was successfully synthesized using renewable natural microalgae.The separation test showed CMS-MnFe_(2)O_(4) was rapidly separated within 2 min under an external magnetic field.In catalytic ozonation of oxalic acid(OA),CMS-MnFe_(2)O_(4) showed efficient and stable catalytic efficiency,reaching a maximum total organic carbon removal efficiency of 96.59% and maintained a 93.88% efficiency after 4 cycles.The stable catalytic efficiency was due to the supporting effects of the carbon microsphere shell,which significantly enhanced CMS-MnFe_(2)O_(4) chemical stability and reduced the metal ions leaching to 10-20% of MnFe_(2)O_(4) through electron transfer.To explore the catalytic mechanism,radical experiments were conducted and a new degradation pathway of OA involving superoxide anions rather than hydroxyl radicals was proposed.Consequently,this study suggests that an efficient,recyclable,stable,and durable catalyst for catalytic ozonation could be prepared.

MnFe2O4@PANI@Ag Heterogeneous Nanocatalyst for Degradation of Industrial Aqueous Organic Pollutants

This paper reports a stable heterogeneous nanoparticles catalyst MnFe2O4@PANI@Ag for the degradation of azo dyes. In this synthesizing method, MnFe204 is used as magnetic core and polyaniline （PANI） a linker to stabilize the Ag nanoparticles （NPs） on the surface of catalyst. The method has a high ability to prevent Ag NPs from aggregation on the PANI surface, thus resulting in small size and highly dispersed Ag NPs. The composition and nano-structural features of polycrystalline sample were studied by X-ray powder diffractometry, Fourier transform infrared spectroscopy, and scanning electron microsco- py. Vibrating sample magnetometer measurements proved the super-paramagnetic property of the catalyst, and UV results demonstrated that MnFe2O4@PANI@Ag has a high ability to reduce the azo dyes, which come from industrial wastes in the form of pollutant. The nanocomposites could be readily separated by magnet and reused for the next four reductions with high generation efficiency.