Preparation And Photoelectric Properties Of Porous Photonic Prystal Composed Of Carbon Nitride And Bismuth Oxide

In recent years,using semiconductor photocatalytic technology to convert solar energy into fuel or chemical energy has gradually become a hot technology to solve energy and environmental problems.Beyond the ultraviolet band,semiconductor materials with visible light absorption have received more and more attention.In addition to the optical absorption efficiency,the recombination of photo generated carriers is also an important factor affecting the photocatalytic performance of semiconductors.Using heterojunction to achieve carrier separation is an effective way to solve this problem.Compared with the traditional type II heterojunction,the Z-type heterojunction model is expected to effectively utilize the redox potential of the composites.At the same time,the inverse opal photonic crystal structure has both three-dimensional structural order suitable for optical control,and porous morphology suitable for photoelectrochemical properties.Besides,the slow light effect and multiple scattering effect of photonic crystal structure can also play a role in enhancing the absorption performance of materials,adjusting the absorption range,in addition,even inhibition of carrier recombination is expected.At present,the research of Z-type heterojunction photocatalyst based on photonic crystal structure is still relatively limited,which needs to be further explored.Therefore,in this paper,g-C₃N₄/TiO₂-Bi₂O₃composite porous photonic crystal structure with Z-type carrier migration potential was successfully constructed,and the individual and composite properties of each part were briefly studied.The main contents of this paper are as follows:(1)The study of the TiO₂ loaded g-C₃N₄ with hierarchical porous photonic crystal structure.The opal photonic crystal template was prepared by vertical deposition.The template was filled by sol-gel method using tetrabutyl titanate,tetraethyl orthosilicate and cyanamide.The inverse opal structure of TiO₂-Si O₂ loaded with g-C₃N₄ was constructed by calcining the template.Then,the target structure of TiO₂ loaded g-C₃N₄hierarchical porous structure was obtained by removing Si O₂ with ammonium hydrogen fluoride.The microstructure of the composite was characterized by SEM and the composition of the composite was characterized by XPS.Comparing the difference between the two structures by the position of photonic band gap in the reflection spectrum,the introduction of mesoporous made the reflection peak of the reflection spectrum blue shifted by about 20 nm,which also confirmed the formation of mesoporous.The absorption spectra and photoelectrochemical tests of composite materials with different structures and different g-C₃N₄ contents were compared.The results show that due to the multiple scattering effect,the introduction of porous structure can improve the absorption efficiency of the composites in the visible region to a certain extent.Compared with inverse opal structure,the photocurrent density of hierarchical porous structure with mesoporous structure increased by 42.9%at 1.23V(Vs RHE)bias.The loading of g-C₃N₄ extends the absorption spectrum to the visible region,and the photocurrent density of the hierarchical porous structure loaded with g-C₃N₄ is about 2.73 times higher than that of the pure TiO₂ inverse opal.When the molar ratio of cyanamide,the precursor of g-C₃N₄,was increased from 20.0%to 33.3%,the photocurrent density increased by 25.0%.The construction of hierarchical porous structure and the loading of g-C₃N₄ can significantly enhance the visible spectrum absorption and photoelectric response of the composite structure.(2)Study on the Bi₂O₃ inverse opal structure.The polystyrene opal template of 219nm,238 nm,303 nm and 358 nm was filled with bismuth nitrate pentahydrate by sol-gel method.After drying,pre-crystallization and annealing,the Bi₂O₃ inverse opal structure with different pore sizes was constructed.The surface structure of inverse opal was characterized by SEM.The synthesis of bismuth oxide was confirmed by EDS.The valence of bismuth(+3)in bismuth oxide was confirmed by XPS.XRD patterns show that the prepared Bi₂O₃ is monoclinic phase.The reflection spectrum reflected the effect of different particle size templates on the photonic band gap of Bi₂O₃ inverse opal structure.With the increase of particle size,the characteristic peaks of photonic crystal in the reflection spectrum were red shifted.The photoelectric response of Bi₂O₃ inverse opal with different pore sizes was studied by photoelectrochemical measurement.The photocurrent density of Bi₂O₃ inverse opal prepared by 303nm template was about 25%higher than that of other samples,due to the band edge absorption enhancement of the photonic band gap is just at the spectral response of Bi₂O₃(about 442 nm).(3)Study on the g-C₃N₄/TiO₂-Bi₂O₃ composite porous photonic crystal structure.The above-mentioned two materials were compounded in two ways to construct:1)laminated composite structure of TiO₂ loaded g-C₃N₄ inverse opal and Bi₂O₃ inverse opal,and 2)Bi₂O₃ filled composite TiO₂ loaded g-C₃N₄ porous structure.The cross sectional appearance of the upper and lower levels of porous composite inverse opal structure is characterized by SEM.The absorption spectra and photoelectrochemical tests were performed to explore the influence of different composite methods,different g-C₃N₄ content,different pore size on the optical absorption and photoelectric properties of the composites.The absorption spectra showed that the visible light absorptivity of the composite was significantly higher than that of pure g-C₃N₄/TiO₂ and Bi₂O₃,and the photocurrent density at 1.23V(Vs RHE)bias was increased by about 0.80 and 1.00 time,respectively.There was no obvious difference in the absorptive properties of the two composites.However,photoelectrochemical tests showed that the photocurrent density of Bi₂O₃ filled composite TiO₂ loaded g-C₃N₄ porous structure increased by about17.5%at 1.23V(Vs RHE)bias compared with laminated composite structure of TiO₂loaded g-C₃N₄ inverse opal and Bi₂O₃ inverse opal.