Fabrication And Photo/Electro Catalytic Performance Of Composites Based On Octamethyl Substituted Metal Phthalocyanine

Photocatalytic and electrocatalytic reactions are considered as the most common and effective energy and environmental application techniques.Especially,the light energy-driven photocatalytic reactions have been explored for treating the pollutants in the wastewater to solve the ecological issues.On the other hand,the electrochemical CO₂ reduction reaction（CO₂RR）is the most effective method to convert atmospheric CO₂ to fuels/chemicals.The design of catalysts is a key factor for the photo/electrocatalytic reactions to achieve significant outcomes.As a typical metal macrocyclic complex,metal phthalocyanines have strong visible light and near-infrared absorption,high carrier mobility,high stability,sufficient electron delocalization,the highly active center metal,and easy accessibility making it become one of the most widely studied photo/electrocatalytic materials.Metal phthalocyanines with simple structures are stable and insoluble.Most studies have focused on complex compound with substituent groups to improve their photo/electrochemical properties and solubility.However,the complicated synthesis process limited their yield and stability,which increased the cost of preparing the material for industrial purposes.This research project highlighted the octamethyl-substituted metal phthalocyanine with a relatively simple structure,and the nanostructures were prepared by the self-assembly method.The composites based on their nanostructures were further designed and synthesized and investigated their photocatalytic reduction of Cr（VI）,photocatalytic oxidation of Rhodamine B（Rh B）,and electrocatalytic CO₂RR.This work broadens the practical value of poorly soluble phthalocyanines with the fundamental understanding of the formation mechanism of the nanostructure and photo/electrocatalytic reactions,and provides ideas for its application in more efficient photoelectrical synergistic catalysis.Phthalonitrile route was adopted for the preparation of four different metal-centered（Fe,Co,Ni,and Cu）unsubstituted metal phthalocyanines（MPc）and non-peripheral octamethyl substituted metal phthalocyanines（N-MMe₂Pc）catalysts.The peripheral octamethyl-substituted nickel phthalocyanine（Ni Me₂Pc）was also synthesized.The phthalocyanine molecules were self-assembled to form nanostructures（nanorods）by precipitation method;the methyl group could hinder the aggregation of phthalocyanine molecules,resulting in the lesser size nanorods formations（N-MMe₂Pc NR）.On the other hand,because of the introduction of methyl groups,four N-MMe₂Pc NR were pure H-aggregates,in which all phthalocyanine molecules were arranged in face-to-face stacking.The strongerπ-πinteraction in N-MMe₂Pc NR promoted the light absorption and electrical conductivity,which is conducive to improving its photo/electrocatalytic activity.Theπ-πstacking enhancement effect was also found in Ni Me₂Pc NR,but no pure H-aggregates were formed,indicating that the peripheral substitution did not induce formation of H-aggregates as much as the non-peripheral substitution.In the photocatalytic reduction of Cr（VI）,the Cu Pc/RGO and N-Cu Me₂Pc/RGO nanocomposites were prepared by an in situ precipitation method.The remarkable improvement in the photocatalytic reduction of Cr（VI）of nanocomposites was attributed to the efficient transfer of photogenerated electrons to the RGO surface,which inhibited the carrier recombination in the phthalocyanine and enhanced the charge transfer rate.The removal rate of Cr（VI）by N-Cu Me₂Pc/RGO reached 99.0%after 2 h of light irradiation,and the reaction rate constant was 0.0320 min^-1,which was about 1.5 times faster than that of Cu Pc/RGO.The large specific area,higher conductivity,and broader light absorption of the composite significantly promoted the removal efficiency.N-Cu Me₂Pc/RGO also had excellent photocatalytic stability and maintained good photocatalytic performance in industrial chrome plating wastewater,which proves our designed catalysts’s commerzilation.In photocatalytic oxidation of Rh B,Siloxene nanosheets with a large specific surface area were synthesized by the topological reaction;then N-Cu Me₂Pc NR was successfully loaded onto Siloxene by impregnation method to form nanocomposites.The photocatalytic oxidation of Rh B was greatly improved,which was assigned to the accelerated separation efficiency of photogenerated carriers due to the heterostructure formation.The composite formed by 1:10 mass ratio（P1S10）achieved the best degradation efficiency of 55.9%within 1 h illumination,and the reaction rate was 3.9 and 7.5 times higher than that of Siloxene and N-Cu Me₂Pc NR,respectively.With the assistance of PMS,the best degradation efficiency of P1S10was increased to 95.3%,and the reaction rate reached 0.0453 min^-1.The P1S10/PMS/Vis system had excellent photocatalytic cycling stability,and·SO₄^-,·OH,and·O^2-radicals played a significant role in this system.During the electrocatalytic CO₂RR,the CO selectivity(FE_CO)of N-Co Me₂Pc NR was higher than Co Pc NR.DFT calculations demonstrated that the octamethyl substitution significantly enhanced the central metal’s CO adsorption and activation process.Different ratios of N-Co Me₂Pc/NRGO（x:10）nanocomposites were prepared by the impregnation method.The composite at a ratio of 6:10 in an H-type cell with0.5 mol L^-1 KHCO₃ as electrolyte achieved the best FE_CO（90.0%）at-0.8 V（vs.NHE）,the corresponding partial current density(j _CO)was 9.7 m A cm^-2.In the flow cell,j _COimproved to 14.8 m A cm^-2 at the same potential,which was attributed to the improved mass transfer efficiency in the flow cell.The FE_CO of N-Co Me₂Pc/NRGO（6:10）was further improved to 94.1%at lower potential（-0.6 V）,corresponding to j _CO(56.4 m A cm^-2)and TOF_CO(6.2 s^-1)in the KOH electrolyte as the results of the HER inhibition and lesser ohmic resistance of the system.