The Design And Exploration Of Photocatalyst Based On Photocatalytic Hydrogen Production From Water

Energy is the footstone of survival and development of human society.Nowadays,fossil fuel is the main component of world energy,such as petroleum,natural gas and coal.However,fossil fuel faces two key problems:limited resources reserve and non-friendly for environment.It is urgent for looking for eco-friendly renewable energy.Hydrogen,clean,efficient,safe and renewable,has been considered as the optimal secondary energy.Photocataly can directly convert the low-density solar energy into high-density hydrogen,attracts extensive attention of world-wide researchers.Photocatalytic hydrogen production is a complex system,closely links with many factors,for example,cocatalyst,sacrificial agent,reaction condition,and photocatalyst.Among them,photocatalyst is the most important one.The narrow scope of light absorption and low carrier separation efficiency are the two challenges for the development of photocatalyst.For gain efficient photocatalyst,people takes a lot of efforts,mainly focus on modification of conventional semiconductor photocatalyst and exploration of new semiconductor photocatalyst.Organic-inorganic coupling is a common way to enhance the photocatalytic activity of semiconductors.In this thesis,we synthesized two organic-inorganic coupling photocatalysts NdVO4/g-C3N4 and PDINH/TiO2,and evaluated their photocatalytic H2 production activities;We designed a kind of organic-inorganic coupling photocatalysts Pd-PPy-TiO2,which allows for precisely locating Pd and PPy on TiO2.In addition,we explored the applications in the field of photocatalytic hydrogen production of infrared nonlinear semiconductor ZnGeP2 as well as their organic-inorganic coupling photocatalysts Pt/PPy/ZnGeP2 and ZnGeP2/g-C3N4;We studied the applications in photocatalytic H2 production of DNA-like inorganic metal free double helical semiconductors SnIP and Pt/PPy/SnIP organic-inorganic coupling.The main research contents and results as follows:In chapter one,we first briefly discussed the research background,principal mechanism and research progress of photocataly,and introduced several photocatalysts for hydrogen production,for example,TiO2,CdS and g-C3N4.In addition,we also analyzed the influence factors of photocatalytic hydrogen production,and aimed at the constraints of semiconductor photocatalysts(narrow range of light absorption and low carrier separation efficiency),summarized the common methods for synthesizing efficient semiconductor photocatalysts.At last,from two aspects of constructing organic-inorganic coupling and exploration novel semiconductor photocatalysts,we summarized the research significance and content of our thesis.In chapter two,we synthesized two organic-inorganic coupling photocatalysts NdVO4/g-C3N4 and PDINH/TiO2,and evaluated their photocatalytic H2 production activities.(1)Organic-inorganic coupling photocatalyst NdVO4/g-C3N4 was prepared by solid-state sintering method,which displayed much higher photocatalytic H2 production activity than NdVO4 and g-C3N4,among them,3.0%NdVO4/g-C3N4 had the highest photocatalytic H2 production rate,which was about 5.5 times than that of g-C3N4.The apparent quantum efficiency for H2 production over 3.0%NdVO4/g-C3N4 reached as high as 6.57%using irradiation at 365 nm.In addition,NdVO4/g-C3N4 displayed higher photcurrent intensity and lower PL intensity than those of NdVO4 and g-C3N4,indicating that NdVO4/g-C3N4 had a higher charge separation efficiency.It could be formed a typical type Ⅱ energy band structure between NdVO4 and g-C3N4,which can improve the charge separation efficiency and further enhance the photocatalytic acvitity.(2)Perylene-3,4,9,10-tetracarboxylic diimide(PDINH),a typical n-type organic semiconductor,was chosen to improve the photocatalytic activity of TiO2 through constructing PDINH/TiO2 organic-inorganic hybrid,which displayed much higher H2 production rate under UV-visible light irradiation.The apparent quantum efficiency for H2 production over 0.5%PDINH/TiO2 reached as high as 70.69%using irradiation at 365 nm.The photocatalytic hydrogen evolution of different samples with irradiation light at a certain wavelength of 365,420,450,520,600 nm were also evaluated,the results indicated the light absorption was not the key factor for enhanced photocatalytic activity of PDINH/TiO2.The-C=O…H hydrogen bond existed in the interfaces between PDINH and TiO2 and the distance of newly generated-C=O…H hydrogen bond was explored to be 1.75 A.The theoretical calculation showed that substantial charge transfer occurs from the molecular PDINH to TiO2(101)surface through the-C=O…H hydrogen bond.In chapter three,we studied the impact of loading position on photocatalytic activity of organic-inorganic hybrid.TiO2-Pd-PPy was prepared via one-step simultaneous photoreduction of palladium chloride and photooxidation of pyrrole monomers on TiO2(P25).The places where Pd and PPy nanoparticles deposited were just the active sites that the photo-induced electrons and holes participated in the photocatalytic reaction.Different from other reported synthetic methods,TiO2-0.5Pd-0.6PPy synthesized by the method in our paper displayed much higher photocatalytic H2 production activity than TiO2-0.5Pd-0.6PPy synthesized by other methods,which was about 3.1 and 11.7 times than those of TiO2-0.5Pd and TiO2 under UV-visible light irradiation,respectively.Thanks for the better separation of charge carriers and photo response of Pd and PPy particles,higher photocatalytic activities for H2 production were achieved.In chapter four,we studied the applications in photocatalytic H2 production of infrared nonlinear semiconductor ZnGeP2 as well as their organic-inorganic coupling photocatalysts Pt/PPy/ZnGeP2 and ZnGeP2/g-C3N4.(1)ZnGeP2 photocatalyst was prepared by one zone temperature method in a vacuum quartz ampoule.The photocatalytic activities for H2 production under visible and near-infrared light irradiation were also measured.Due to the P3-in ZnGeP2 is easily oxidized by photo-induced holes,adding H3PO2 into photocatalytic reaction solution and ultrasonic treatment for ZnGeP2 can improve the photocatalytic activity and stability of ZnGeP2.(2)Organic-inorganic coupling photocatalyst Pt/PPy/ZnGeP2 was prepared by one-step coprecipitation method.Compared to pure ZnGeP2,the light absorption of Pt/PPy/ZnGeP2 had not been expanded,however,the photocatalytic activities for H2 production and photostability of Pt/PPy/ZnGeP2 had been improved largely,which was ascribed to the higher charge separation efficiency.A typical Z type energy band structure between Pt,PPy and ZnGeP2 could be formed,this type heterogeneous structure could effectively promote the separation of carriers,thus improve the H2 production rate and photo-stability of ZnGeP2 photocatalyst.(3)Organic-inorganic coupling photocatalyst ZnGeP2/g-C3N4 was prepared by ultrasonic self-assembly method,which displayed better photocatalytic activity than those of ZnGeP2 and g-C3N4,among them,4.0%ZnGeP2/g-C3N4 had the best H2 production rate of 85 μmol h-1 under visible light irradiation,which is about 34 and 3.0 times than those of ZnGeP2 and g-C3N4,respectively.The apparent quantum efficiency for H2 production over 4.0%ZnGeP2/g-C3N4 reached as high as 5.6%using irradiation at 420 nm.Thanks for the good light absorption and efficient separation of carriers,ZnGeP2/g-C3N4 had an enhanced photocatalytic H2 production rate.In chapter five,we studied the application in photocatalytic H2 production of DNA-like inorganic metal free double helical semiconductors SnIP and Pt/PPy/SnIP organic-inorganic coupling photocatalyst.(1)SnIP photocatalyst was prepared with high-purity Sn,P and SnI2 as raw materials in a vacuum quartz ampoule.SnIP had a DNA-like double helical structure,which displayed good light absorption and efficient separation of carriers.From the XPS changes of each element before and after photocatalytic reaction in pure water,it could be found that the Sn and P in SnIP had great changes because that Sn and P were oxidized.Through adding H3PO2 into reaction system,the H2 production rate and photo-stability of SnIP had been improved largely.(2)Organic-inorganic coupling photocatalyst Pt/PPy/SnIP was prepared by one-step coprecipitation method,which displayed higher H2 production rate and photo-stability than those of SnIP.Although the light absorption of SnIP had not been expanded after loading Pt and PPy,the carrier separation efficiency of SnIP had been improved in some extent,which was associated with the band gap position of PPy and SnIP.It could be formed a typical type Ⅱ energy band structure between PPy and SnIP,which can improve the charge separation efficiency and further enhanced the photocatalytic acvitity.In chapter six,we firstly summarized the main research contents and results in our thesis,and then concluded the innovation point and discussed the shortages and problems of this thesis.Finally,we made a prospect and expectation for next work.