| Nowadays, the world is facing serious energy and environmental problems, so it is very urgent to produce a clean and sustainable energy using renewable energy source to solve such problems. Among the new energys, Hydrogen energy has many advantages, such as:it could be produced from many hydrogen-containing resources and utilized in various forms; water is the only combustion product and it has excellent chemical energy; moreover, the water produced from the burning of it can be reused to generation hydrogen. Considering above merits, hydrogen has been regarded as the most promising alternative energy in21st century by the majority of scholars around the world. Photocatalysis technique is to ues the photogenerated electrons and holes after absorbing the sunlight of the photocatalast to split water into hydrogen and oxygen. Indeed, so far there have been many reports related to different approaches for the water splitting, but to our knowledge, there have hardly investigations on natural products. We used attapulgite (ATP) and vermiculite (VMT), common and cheap clay mineral but as a high quality nanosized material with large surface area, layered and natural Fe-doping, to effectively split water in visible light irradiation and sensitized by organic dyes or CdS nanocrystals. By contrast, we have also investigated the preparation and performance of Ag/ZnO nanocomposites under the same condition.The contents of this study and important conclusions were summarized as follows:1. Organic dyes sensitized natural silicate (ATP) has been used as photocatalyst for hydrogen production from water under visible light. The samples including purified ATP, unpurified ATP as well as Ag loaded ATP were characterized by X-ray diffraction, transmission electron microscopy, ultraviolet-visible absorption spectrum, and X-ray photoelectron spectroscopy. By contrast, we could not get any hydrogen when changed ATP into montmorillonoid which is another silicate with similar composition (absence of Fe) under the same conditions, which demonstrate ATP was the host photocatalyst. We have tried four organic dyes under the same experimental conditions, and found that all of them have reduction ability, while EY is best. Loading Ag Nanocrystals (NCs), ATP showed the highest rate of hydrogen production with an apparent quantum efficiency (QE) of10.8%. Further chemical analysis as well as computational simulation proposed the natural Fe-doping (two ATP cells sharing one Fe atom.) can promote the photocatalytic precess. We have found a convenient and cheap route to produce hydrogen. In this way, no (or very small) artificial treatments including chemical synthesis, doping and nanoparticle morphology control are needed at all. Combined with the results of theoretical calculation and VB X-ray photoelectron spectroscopy, the mechanism of hydrogen evolution over EY-ATP photocatalyst was proposed.2. A series of CdS/ATP nanocomposites were synthesized via a green method. The CdS/ATP photocatalysts show high efficiency for water splitting under visible light irradiation. A loading amount3wt%CdS NCs over ATP leads to a200%increase in the photocatalytic activity. At the same time, an efficient photoelectrode was prepared by blade coating. The saturated photocurrent achieved by the CdS/ATP (3wt%) electrode under the illumination of visible light is0.35mA cm-2. Based on the Eg of ATP and CdS, the mechanism of hydrogen evolution over CdS/ATP photocatalyst was proposed.3. Inspired by the work above, we extended the host photocatalyst from1D natural nanomaterials (ATP) to2D natural nanomaterials (VMT). In this section, we use hydrothermal to combine Pt NCs to VMT and investigate the effect of the Pt NCs content on the rate of photocatalytic hydrogen evolution sensitized by EY under visible light irradiation. The rate was further increased to330μmol h-1with a high QE of22.8%when the pure VMT was coupled with3wt%of Pt NCs. VMT photoelectrode was prepared by blade coating. The photocurrent densities rise steeply up to approximately0.4mA cm-2and0.2mA cm-2respectively when irradiated from both front and back side of the electrode. Compared to the total energy (by using VASP code), we found that the most stable cell structure of VMT.4. In this study, we use chemical impregnation to combine CdS quantum dots (QDs) to VMT and investigate the effect of the CdS QDs content on the rate of photocatalytic hydrogen evolution under visible light irradiation. The as-prepared CdS-modified VMT exhibited enhanced hydrogen production activity and photoelectrochemical properties, which benefitted from the extended light absorption and the improved interfacial charge-transfer properties of VMT. The optimized hydrogen evolution rate over CdS/ATP nanocomposites (5wt%CdS) is92μmol h-1with a high QE of17.7%.5. As comparison, Ag and Ag/ZnO hybrid NCs were prepared and used as photocatalysts at the same condition. The controlled synthesis of Ag/ZnO hybrid NCs was based on a seed-mediated growth process. When Ag NCs was absent, octadecylamine (ODA) were employed as reducing agent and capping agents, the ZnO nanoparticles formed in situ in this system were protected by ODA. However, With Ag NCs as seeds, the pyramid shaped Ag/ZnO hybrid NCs were obtained with Ag nanoparticles decorated on the surface of nanopyramid. We found that dyes sensitized Ag/ZnO hybrid NCs exhibited excellent photocatalytic activities under visible light. However, by contrast, organic dyes sensitized natural silicate has a relatively high photocatalytic activity than Ag/ZnO nanocomposites under the same condition. |
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