Research On The Enhanced Photocatalytic Performance And Mechanism Of Semiconductors Modified By Doping And Coupling

Searching for clean,efficient,renewable and stable energy is the basic of sustainable development in 21st century.The semiconductor-assisted photocatalytic reaction for water splitting attracts intense research interest because of their usefulness as an eco-friendly option for the depletion of fossil energy.In the past decades,a variety of effective semiconductors have been developed as photocatalysts to convert inexhaustible solar energy into storable hydrogen.However,most of the photocatalysts still suffer from a quite low photocatalytic activity,which greatly restricting their practical applications.Thus,how to improve the photocatalytic activity by modifying the semiconductors has been a big challeng in the field of photocatalysis.And this urges researchers to further understand the mechanism of photocatalytic hydrogen production,explore the method of improving photocatalytic activity and apply the theoretical results to design and prepare novel photocatalysts,then break the bottleneck of the development of photocatalytic hrdrogen production.Based on the above reviews,four photocatalytic systems are designed and systematically investigated,which are used to study the improved light absorption and the separation of photo-generated carriers.The research abstacts are summarized as following:1.Novel mesoporous carbonate-doped phase-junction TiO₂ nanotubes were fabricated for the first time by a general simple and cost-effective strategy,namely,olive oil-assisted electrospinning.The as-prepared mesoporous carbonate-doped phase-junction TiO₂ nanotubes show a high photocatalytic hydrogen evolution activity of 6108?mol h^-1 g^-1,which is nearly six times higher than that of the commercially available P25.This outstanding photocatalytic performance originates from the morphology,electronic,crystal and textural structures of the photocatalysts.The refined porous structure can increase the optical path by multiple reflection effect,thus enhancing light harvesting.Particularly,first-principles calculations suggest that doping TiO₂ with carbonate can effectively reduce the bandgap of TiO₂,thus the absorbance of TiO₂ in visible light region can be highly enhanced.Moreover,anatase-rutile phase junctions were elaborately introduced into TiO₂ nanotubes by changing the anneal temperature and the roles of phase junctions are studied by photoelectrochemical measurements,which reveal that appropriate phase junction interface can significantly enhance the charge separation and transfer,hence achieving about 2 and 18 times photocurrent density enhancement compared to pristine anatase and rutile phase samples,respectively.Our study not only demonstrates a facile and eco-friendly strategy to synthesize highly efficient porous TiO₂-based nanotubes photocatalysts,but also provides a new strategy for rational design and synthesis of advanced photocatalysts by combining the strong synergistic effects of the morphology,electronic,crystal and textural structures.2.A model of ultrathin copper doping ZnIn₂S₄ 2D nanosheets is put forward to study the role of doping atoms in the photocatalytic hydrogen production for the first time.The as-prepared Cu-doped ZnIn₂S₄ 2D nanosheets show a high photocatalytic hydrogen production activity of 26.2 mmol h^-1 g^-11 and an apparent quantum efficiency of 4.76%at 420 nm.This outstanding photocatalytic performance originates from the enhanced light harvesting,promoted charge carrier separation and increased surface active sites.Particularly,the theoretical calculations,time-resolved PL spectra and electrochemical analysis reveal that the doped copper atom can act as the electrons acceptor,which can effectively enhance the separation of carriers and give rise to many more charge carriers that can participate in the catalytic reaction directly.Thus,the average recovery lifetime and the density of photo-excited electrons are increased by3.24 and 2 times upon copper incorporation into the ZnIn₂S₄ crystals,respectively.This work demonstrates a method to rational design advanced photocatalysts by utilize the strong synergistic effects of electronic,crystallographic and surface structures.3.We present a step-wise strategy to prepare Pt/TiO₂/reduced graphene oxide photocatalysts and the inherent mechanism of the enhanced photocatalytic activities were systematically investigated.Experimentally,the 2 wt%rGO doped rGO/Pt-TiO₂nanocomposites showed the superior solar-driven hydrogen generation rate(1075.68?mol h^-1 g^-1),which was 81 times and 5 times higher than bare TiO₂ and Pt/TiO₂samples,respectively.X-ray photoelectron spectroscopy?XPS?and Fourier transform infrared spectra?FT-IR?demonstrated the formation of Ti-O-C bonds in the hybrid,which drove the shifting upwards of the valence band edge from+2.2 eV to+1.83 eV.Furthermore,photoelectrochemical tests indicated the electron density of PTG-2 was about one order of magnitude higher than TiO₂.Moreover,DFT calculations displayed that the bandgap had been successfully narrowed from 2.88 eV to 2.76 eV and the original blank energy region located at TiO₂ bandgap was filled with C2p orbitals,which resulted in excited electrons in TiO₂ efficiently transferring to graphene.Consequently,the DFT calculations are in good agreement with the experimental results and physical characterizations.This study affords us a rational design of a high efficiency photocatalytic system for solar energy conversion.4.Previous studies have shown that co-catalysts play a pivotal role for improving both the activity and reliability of semiconductors in photocatalytic hydrogen production,however,designing highly efficient and cost-effective co-catalysts to replace expensive and rare metals is still a big challenge.In this work,DFT?density functional theory?is utilized to guide the application of CoP NWs?nanowires?as an earth-abundant co-catalyst for photocatalytic hydrogen production.Metallic 1D CoP NWs is rationally integrated with Zn_0.5Cd_0.5S solid solution semiconductor for the first time,to induce a remarkably improved photocatalytic hydrogen production activity of12175.8?mol h^-1 g^-1,which is 22 times higher than that of the pristine Zn_0.5Cd_0.5S.This outstanding activity benefits from the collaborative advantages of excellent metallic conductivity and the rigid 1D nanostructure of CoP NWs.Moreover,the mechanism investigations demonstrate that this excellent activity arises from the strong electronic coupling,favourable band structure,highly efficient charge separation and migration based on the powerful characterizations,such as time-resolved PL decay spectra and photoelectrochemical methodology.This work brings new opportunities to employ 1D co-catalysts on photocatalysts for improving the catalytic activities in hydrogen production from water.