Three-dimensional Photocatalysts For Environmental Purification And Energy Conversion

In this work,a series of original researches on the environmental purification and energy conversion of three-dimensional photocatalysts have been carried on.In terms of environmental purification,a new idea of synergistic removal of organic contaminant in water via adsorption enrichment joined with photocatalytic degradation was presented,which provides new insights into the fabrication of three-dimensional nanocomposites and facilitates their potential application for the synergistic removal of various aquatic pollutants in the water purification field.In terms of energy conversion,self-supported oxygen-doped carbon nitride aerogel was successfully fabricated through a facile self-assembly method combined with hydrothermal process,without adopting any harmful solvents or cross-linking agents,which paves a facile colloid chemistry strategy to assemble self-supported 3D aerogels that could be widely adopted in the sustainability field.TCNQ@TiO₂ visible photocatalyst with core-shell structure was synthesized by adsorption methods.Under visible irradiation,the photogenerated holes on the HOMO orbit of TCNQ can be injected into the VB of TiO₂,resulting in the oxidation of organic pollutant directly.However,the energy of the holes injected into the VB of TiO₂ is not high enough to mineralize phenol completely.Under UV irradiation,the photogenerated electrons on the CB of TiO₂ can be injected into the LUMO orbit of TCNQ,which is too low that electrons could not combine with O₂ easily,interdicting the formation of superoxide radicals and resulting in the decrease of photoactivity.Polyaniline?PANI?hydrogel with three-dimensional network nanostructure was synthesized by polymerizing aniline.TiO₂ nanoparticles were located onto the 3D matrix of the PANI hydrogel.This PANI/TiO₂ composite 3D hydrogel is efficient in removing organic contaminants owing to the synergistic effect of adsorption-enrichment and the succedent in-situ photocatalytic degradation.In this process,organic contaminant was first adsorbed and enriched onto the surface of the TiO₂ nanoparticles through 3D network nanostructure of PANI hydrogel.Then the organic contaminant was in situ degraded.The 3D network structured PANI/TiO₂ composite hydrogel has the advantage of high reactivity in nano-sized materials and posesses the characteristics of separation-free in bulk materials,indicating that the composite hydrogel is ease of recycling.Polyaniline?PANI?/carbon nitride nanosheets?CNNS?composite hydrogel with three-dimensional hierarchical nanostructure was synthesized via in-situ polymerization.The 3D hierarchical structure was robust and stable,making the composite hydrogel separation-free and ease of recycling.It is highly excellent in removing organic pollutant for PANI/CNNS composite hydrogel on account of the cooperation of adsorptive preconcentration and the following photocatalytic oxidation.Pollutants were firstly adsorbed and concentrated into the 3D hierarchical nanostructure of the composite hydrogel.Then the pollutants were in-situ oxidized via photocatalysis.The promoted photocatalytic performance could be mainly ascribed to the outstanding interfacial charge separation and photoelectrochemical performance.Self-supported oxygen-doped carbon nitride aerogel?OCNA?was successfully fabricated through a facile self-assembly method combined with hydrothermal process,without adopting any harmful solvents or cross-linking agents.The fabrication mechanism of OCNA was discussed.OCNA exhibited much faster charge separation efficiency,longer carriers' lifetime than bulk carbon nitride?BCN?.More importantly,oxygen-doping led to a more negative conduction band?CB?position and narrower band gap?Eg?.Hence,the spectral response range of OCNA was extended dramatically and the hydrogen evolution rate?HER?of OCNA?? > 510 nm?was about 26 times as high as that of BCN prepared herein.OCNA exhibited a remarkable apparent quantum yield?AQY?of 20.42% at 380 nm,7.43% at 420 nm,4.78% at 450 nm and 1.71% at 500 nm,superior to most of the reported C₃N₄-based materials.