Preparation Of Cobalt Complex Modified 2D Sheet Materials And Their Photocatalytic Activities In Dehalogenation Reaction

Vitamin B₁₂ and its derivatives are highly efficient and environmental friendly catalysts.A large number of studies reported in the literature mainly study the photocatalytic dehalogenation activity of these catalysts under anaerobic conditions.However,there are few reports under aerobic conditions.In the early work of the research team,the B₁₂ catalyst was fixed on the surface of mesoporous TiO₂microspheres and P25 TiO₂ nanospheres.They show high photocatalytic dehalogenation activity.Due to its large proportion,two-dimensional layered materials have broad application prospects in lots of fields.In order to expand the type of B₁₂-based composite photocatalyst,two two-dimensional titanium-containing layered materials were replaced here:thin-layer TiO₂ nanosheets and multilayer Ti₃C₂?OH?₂ nanosheets as carriers.Three composite catalysts B₁₂-TiO₂-N3,Co-TiO₂-N3 and B₁₂-Ti₃C₂?OH?₂-N3 were used to study photocatalytic dehalogenation reaction to esters.The main contents are as follows:First,using ultra-thin TiO₂ nanosheets as carrier,two kinds of cobalt complexes:[CN?H₂O?Cob???7COOH]Cl and[Co?dmgH?₂4-COOHpyCl]and good photoelectric performance N3 dye were co-immobilized on the surface of TiO₂ nanosheets in one step to prepare two composite catalysts B₁₂-TiO₂-N3 and Co-TiO₂-N3.The morphology and structures of the two composites were characterized by EDX,XRD et al.According to the change of UV-Vis absorption spectrum,the loading amount of B₁₂ and N3 in the composite B₁₂-TiO₂-N3 were determined to be 6.3×10^-5 mol/g and3.2×10^-4 mol/g respectively;The loadings of Co and N3 in Co-TiO₂-N3 were 1.7×10^-5mol/g and 7.2×10^-5 mol/g respectively.The catalyst B₁₂-TiO₂-N3 could achieve complete dechlorination of trichlorotoluene under visible light irradiation for 2 h,while the catalyst Co-TiO₂-N3 achieved this reaction under 3 h.Both catalysts can be reused without loss.Second,we co-immobilized the B₁₂ derivative[CN?H₂O?Cob???7COOH]Cl and photosensitizer N3 dye onto the surface of Ti₃C₂?OH?₂ nanosheets by a one-step method to prepare the composite B₁₂-Ti₃C₂?OH?₂-N3.The morphology and structure of the composite was characterized by EDX,XRD et al.According to the change of UV-visible absorption spectrum,the loading capacity of B₁₂ and N3 in the composite B₁₂-Ti₃C₂?OH?₂-N3 were 2.3×10^-5 mol/g and 9.8×10^-5 mol/g.The results of photocatalysis showed that under aerobic conditions,the yield of methyl benzoate was only 66%under visible light irradiation for 3 h.Compared with the composite B₁₂-TiO₂-N3,the catalytic activity is relatively low.It is speculated that the Ti₃C₂?OH?₂ nanosheets are thick and multi-layered,the photosensitizer has poor photosensitivity,which affects the electron transmission between the photosensitizer and the catalyst,and substrate molecules and catalyst molecules are insufficient contact which leads to low catalytic activity.