| The photocatalytic water splitting for hydrogen production can store the solarenergy by converting it into chemical energy, which is a promising approach tosolve the energy and environment problems. ZnS, an ideal photocatalytic hydrogenproduction materials, can facilitate the rapid generation of electron-hole pairs byphotoexcitation and possess the appropriate energy band structure with a strongerreduction ability of photogenerated electrons. However, the drawbacks of ZnS arethe limited light response of the UV light due to its wide band gap as well as highrecombination rate of photogenerated charge carriers. It is found that wurtzite ZnSwith an inner-polar electric field between zinc-rich and sulfur-rich crystal face arebenefit for phtocatalytic hydrogen production. ZnS3D hierarchical nanostructuresexhibit low density, high crystallinity, and large specific surface area, etc.Additionally, constructing heterostructure photocatalysts can effectively extend thephotoresponse to visible spectral region. In this dissertation, firstly, based on thetheory of ZnS crystal growth, we prepared uniform wurtzite ZnS chestnut-likehollow hierarchical microspheres (CHHMs) by a stepwise epitaxial growth processthrough controlling the experimental conditions leading to a high nucleation rate anda low crystal growth rate. And then, we synthesized ZnO/CuS-ZnS ternaryheterostructures by developing a hydrothermal process followed by a cation andanion exchange method. Meanwhile, We discussed the optical properties andphotocatalytic activities for hydrogen production of these two micro/nano-structures.The main results are as follows:1. Wurtzite ZnS chestnut-like hollow hierarchical microspheres were preparedvia a solvothermal method, together with a gas-bubble inducing method usingZn(Ac)22H2O and SC(NH2)2as raw materials, ethylenediamine as complexingagent. In our protocol, through changing the existence of Zn2+using NH3fromdecomposing SC(NH2)2, that is transforming the [Zn(EN)m(H2O)2(3-m)]2+to a higherstability ternary complex ([Zn(EN)m(NH3)2(3-m)]2+), the concentration of Zn2+wassuccessfully reduced to a low level. Thereby the growth condition was balancedleading to a high nucleation rate and a low crystal growth rate. Such novel ZnS CHHMs exhibit an excellent photocatalytic hydrogen evolution activity of82.68μmol h-1using0.35M Na2S，0.25M Na2SO3as sacrificial agent under the simulantsolar light irradiation, which can be attributed to the hollow hierarchical structure,the wurtzite phase, single-crystal and mesoporous charaters and uniformity. Thestudy here suggests that the meticulous control over the structural characteristics isan effective way to enhance the photocatalytic activity.2. ZnO/CuS-ZnS sheet-shaped ternary heterostructures were successfullyprepared by a facile hydrothermal process followed by a cation and anion exchangemethod. The difference of solubility product constant is the main driving force forthe cation and anion exchange reactions. This effective design of the heterostructureconfiguration facilitates the oriented transfer of interfacial electrons and holes. CuScontacts with ZnO and ZnS intimately, which induces the double IFCT effect, whilethe contaction of ZnO and ZnS induces the hole transfer from ZnS to ZnO. In thiscase, the separation of electron-hole charge pairs is greatly enhanced, moreover, thephotoresponse is extended towards the visible spectral region. As a consequence, theZnO/CuS-ZnS ternary heterostructures showed a higher visible light photocatalyticH2-production activity of93.4mol h-1than those of CuS/ZnO and/or CuS/ZnS, andphysical mixed ZnO+CuS+ZnS. The apparent quantum efficiency of thisheterostructures is13.8%under420nm visible light irradiation. The study heresuggests that constructing heterostructures based on the charge transfer mechanismis an effective way to enhance the photocatalytic activity. |
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