Preparation Of Subphthalocyanine/Semiconductor Composites And Research On Their Photocatalytic Performance

In recent years,the survival and development of human beings were seriously affected by environmental pollution and energy shortage.Photocatalytic technology can not only use semiconductor photocatalysts to catalyze the removal of pollutants in the environment,but also catalyze the conversion of solar energy into high value-added chemicals.It has huge application prospects and is one of the effective ways to solve the above problems.Graphitic carbon nitride（g-C₃N₄）has the advantages of low price,high chemical stability,and suitable energy band positions,but it has relatively small specific surface area,fast charge recombination,narrow light absorption range.Zinc oxide（ZnO）is easy to prepare,has good crystallinity and thermal stability,and is rich in morphology,but its optical band gap is too wide and the photocorrosion effect is serious.Phthalocyanine（Pc）has a chlorophyll structure,but the 18πelectron system is easy to aggregate and deactivate.By contrast,subphthalocyanine（SubPc-Br）is a 14πelectron system,and its structure is easily modified and has a unique steric configuration.Based on the above scientific problems,in this study,different types of heterojunction photocatalysts SubPc-Br/g-C₃N₄,SubPc-Br/ZnO and SubPc-Br/g-C₃N₄/ZnO were designed and prepared using SubPc-Br as photosensitizer.It was used for photocatalytic degradation of methyl blue and bromophenol blue（MB,BB）,and excellent catalytic effect was obtained.The specific studies are as follows:a.In an anhydrous and oxygen-free system with double-row tubes,SubPc-Br was synthesized by the reaction of o-dicyanobenzene and BBr₃,and g-C₃N₄nanosheets were synthesized by calcining melamine at high temperature.The crystal form,morphology and optical properties were studied by XRD,SEM and UV-vis DRS.b.A series of SubPc-Br/g-C₃N₄and SubPc-Br/ZnO heterojunction catalysts were constructed by self-assembly of SubPc-Br on the surface of g-C₃N₄and ZnO by utilizing theπstacking effect of SubPc-Br.Compared with pure g-C₃N₄,0.5SubPc-Br/g-C₃N₄（0.5means SubPc-Br loading mass is 0.5%）,the degradation rate of MB and BB reached 99.5%and 98.1%after 120 and 90 min of visible light irradiation,which are increased by 17.2%and 57.0%,respectively.Compared with pure ZnO,2.0SubPc-Br/ZnO has the best degradation performance.After 60 and 120 min of visible light irradiation,the degradation rates of MB and BB reach 99.5%and 99.3%,which are increased by 21.8%and 38.8%,respectively.Furthermore,2.0SubPc-Br/ZnO showed the ability to activate PDS to generate radical sulfate（·SO₄^-）,which accelerated the photocatalytic reaction.According to the energy band positions obtained by energy level calculation,UV-vis DRS and VB-XPS characterization,combined with the trapping experiment of active species,the interaction mechanism of SubPc-Br/g-C₃N₄and SubPc-Br/ZnO was discussed as Type-II type.Finally,it is proved that SubPc-Br acts as a sensitizer,broadening the photoresponse range and improving the carrier mobility.c.The g-C₃N₄/ZnO heterojunction was prepared by high-temperature calcination,and SubPc-Br/g-C₃N₄/ZnO composite catalyst was further constructed by introducing SubPc-Br.Compared with g-C₃N₄/ZnO,the photocatalytic efficiency of 1.0SubPc-Br/g-C₃N₄/ZnO was obviously improved,and the MB degradation rate was 98.4%after 40 min of photocatalytic reaction.And the degradation results and EPR test proved that 1.0SubPc-Br/g-C₃N₄/ZnO can activate PDS to produce·SO₄^-accelerated reaction.UV-vis DRS,PL,TPR and EIS characterizations indicated that the utilization of visible light and the separation and transfer of photogenerated electron-hole pairs were enhanced by introducing SubPc-Br.Finally,the reasons for the enhanced photocatalytic activity of SubPc-Br/g-C₃N₄/ZnO were discussed based on the capture results of active species.