Construction Of 3D Hierarchical Cobalt-Based Heterojunction And The Study Of Mechanisms For Visible-light Photocatalytic Degradation Of Pollutants

Recently,photocatalysis as one of the most promising energy conversion technology for remediation contaminants has been widely investigated for it is green and environmental benignity.The key of this technology is photocatalyst.However,most of photocatalysts still suffer from two fundamental drawbacks:the low separation efficiency of photo-generated electron-hole pairs and the narrow response range to solar light.Herein,tremendous efforts has been made to explore efficiency,hight stably and visible light driven novel materials.In this study,several 3D hierarchical cobalt-based heterojunction catalysts with excellent visible light response have been prepared and were uesd to tretment the contaminants in the waste-water.Moreover,the possible mechanisms for them enhancing photocatalytic performance were elucidated in detail.Magnetic microsphere CoMn₂O₄/CF?MS-CoMn₂O₄/CF?with a 3D architecture was constructed using the wastepaper as cellulose fibers?CF?substrates by solvothermal synthesis method with further calcination treatment,and was further used for photocatalytic degradation of tetracycline?TC?and methylene blue?MB?in water.The constructed composite displays excellent dual functions which can not only rapid catalytic oxidation of TC?MB?,but also has high adsorption capacity.Comparied with the bare MS-CoMn₂O₄,the removal efficiency for TC and MB are90.0%and 92.9%within 120min,respectively.At the same time,MS-CoMn₂O₄/CF is easily recycled via an external magnetic field and the reusability analysis revealed that3D hierarchical MS-CoMn₂O₄/CF hybrid exhibt superb cycling stability after 5 cycles.The improved adsorption ability and photocatalytic activity is mainly attributed to introduce CF supporter in the composite,which can served as trapping centers for photogenerated electrons,improving the efficient separation of photogenerated carriers and transport pathway of electrons.Furthermore,CF can help to enrich and further improve the photocatalytic activity of organic contaminations.The possible mechanism for enhancing photocatalytic performance is elucidated in detail.Hollow porous Co₂SnO₄-SnO₂/graphite carbon?Co₂SnO₄-SnO₂/GC?nanocube heterojunction with 3D hierarchical structre was designed and constructed by calcining CoSn?OH?₆ precursors followed a immersion carbon coating?using the recyclable napkin as graphite carbon source?.The generation of Co₂SnO₄ and SnO₂ in situ via calcining CoSnO₃ and which ensured to forme intimate interfacial contacts among Co₂SnO₄,SnO₂ and GC.Therefore,the obtained Co₂SnO₄-SnO₂/GC exhibits remarkable dual catalytic behavior including the high catalytic efficiency for photocatalytic degradation of CTC?TC?and catalytic reduction of p-NP.The photocatalytic degradation efficency for CTC and TC were 83.0%and 80.0%with in80min visible light irradiation.Moreover,the catalytic reduction efficency for p-NP nearly was 100%within 10min.Co₂SnO₄-SnO₂/GC can be recycled more than 4times due to graphite carbon protective layer on the surface of catalysts.The possible mechanisms of catalytic reactions over Co₂SnO₄-SnO₂/GC were discussed detailed.That is the multiple heterojunctions structure features and the synergistic effects of them,greatly enhance the charge carrier generation and suppress the charge recombination would be beneficial to improve its catalytic activity.Porousdouble-shellCu₂O@CuCo₂O₄hollowmicrospheres?PDS-Cu₂O@CuCo₂O₄-HS?with excellent visible light response is successfully designed and synthesized as a Z-Scheme photocatalyst and and was further used for photocatalytic degradation of Chlortetracycline?CTC?and photocatalytic redunction Nitrobenzene?NB?in water.The growth of Cu₂O NPs on CuCo₂O₄-HS outer surface was carried out at room temperature via solution reactions in order to form a double-shell configuration that could provide the homogeneous heterojunction interface and large surface area.Importantly,PDS-Cu₂O@CuCo₂O₄-HS can utilize multiple reflections of light in sphere structure to achieve enhanced photocatalytic activity.Moreover,the fabrication of a spontaneous Z-scheme system not only effectively separate photoexcited charge carriers,but also can retain prominent redox ability.PDS-Cu₂O@CuCo₂O₄-HS exhibits remarkable photocatalytic activity for CTC oxidation,NB reduction under simulated solar light irradiation,and the photocatalytic degradation efficency for CTC is 87.0%and the reduction efficency is79.0%.Compared with single-target photocatalytic systems,the degradation efficiency of CTC?97.8%?and the reduction efficiency of NB?95.0%?were simultaneously improved.Meanwhile,the synergistic photocatalytic mechanism in CTC and NB systems was systematically discussed.The novel 3D marigold flower-like hierarchical architecture CoO@MnCo₂O₄possessing excellent visible light response was successfully synthesized by anchoring CoO nanoparticles?NPs?on MnCo₂O₄ flower using a facile solvothermal method followed thermal annealing treatment under N₂ atmosphere for the first time,and was further used for photocatalytic degradation of tetracycline?TC?and photocatalytic redunction Hexavalent chromium Cr???in water.This strategy relies on the formation of a p-n heterostructure with matching energy band gaps,in which CoO NPs tightly adhere to the surface of hierarchical MnCo₂O₄ microflowers,and the flower-like MnCo₂O₄ act as scaffold to disperse CoO NPs.Moreover,the unique 3D hierarchical microflowers structure not only provide a higher specific surface area,sufficient active sites and enhanced light harvesting,but also significantly decrease the aggregation of CoO particles.The as-fabricated CoO@MnCo₂O₄ hybrid not only presented remarkable performance for PCO of TC?the photocatalytic efficiency is ca.86.6%? but also exhibited excellent PCR of Cr????the photocatalytic efficiency is91.9%?under visible light irradiation.Meanwhile,the photocatalyst also can be used for treatment a mixture of them and exhibited promoted photocatalytic efficiency,the photocatalytic efficiency for them are 94.0%and 96.1%,respcetively.That's the primary reason that h⁺and e^-can play their own roles to accomplish PCO and PCR,respectively.The appearance photocatalytic mechanism of the p-n heterostructure system was also discussed in detail.