Yilin Chen

Enhanced photocatalytic H2 evolution on ZnS loaded with graphene and MoS2 nanosheets as cocatalysts

Graphene and MoS2 nanosheets modified ZnS nanoparticles were successfully prepared by a simple one-pot hydrothermal route in the presence of graphene and MoS2 nanosheets. The resultant ZnS/graphene/MoS2 nanocomposites exhibited significantly enhanced photocatalytic activity and good recurrence stability in H2 evolution from water splitting. When the loading content of graphene was 0.25 wt% and that of MoS2 was 2 atom%, the ZnS/graphene/MoS2 nanocomposite reached a high H2-evolution rate of 2258 μmol h−1 g−1 under a 300 W Xe lamp irradiation, which is about 2 times that of ZnS alone. The synergistic effect of cocatalysts contribute to the high performance of the hybrid photocatalyst, where graphene serves as an excellent electron acceptor and transporter, and MoS2 nanosheets provide a source of active reactive sites. It demonstrates that the exfoliated MoS2 nanosheets, achieved by the liquid exfoliation from natural molybdenite, can be used as an efficient cocatalyst to prepare high-performance photocatalysts in hydrogen evolution from water splitting.

Enhancement of photocatalytic H2 evolution over nitrogen-deficient graphitic carbon nitride

Nitrogen-deficient graphitic carbon nitride (g-C3N4−x) was synthesized by a hydrothermal treatment using ammonium thiosulfate as an oxidant. The as-prepared photocatalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption–desorption, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), elemental analysis (EA), electron paramagnetic resonance (EPR), UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and photoluminescence (PL) spectroscopy. The visible-light-driven photocurrent measurement was performed by several on–off cycles of intermittent irradiation. The photocatalytic activity of catalysts was evaluated by splitting water under visible-light irradiation (λ > 420 nm). Results demonstrated that the photoactivity of g-C3N4−x was enhanced greatly by the deficiency of the terminal amino species on the catalysts. The average H2 evolution rate on g-C3N4−x was 31.6 μmol h−1, which was ca. 3 times higher than that on pristine g-C3N4. It was revealed that the unique nitrogen-deficient structure of g-C3N4−x played an important role in broadened visible-light absorption and efficient electron–hole separation, mainly accounting for the improved photocatalytic activity.

Fe-doped and ZnO-pillared titanates as visible-light-driven photocatalysts

Fe-doped cesium titanate was obtained by a solid state reaction with a mixture of Cs(2)CO(3), TiO(2), and Fe(2)O(3). ZnO-pillared doped titanate nanocomposite was successfully fabricated by exfoliating doped titanate and restacking its nanosheets with ZnO nanoparticles. The resulting nanocomposite was characterized by powder X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, N(2) adsorption-desorption measurement, thermogravimetric analysis and UV-vis spectroscopy. It was revealed that the present nanocomposite exhibits greatly increased specific surface area with mesoporous texture and that there exists an electronic coupling between the host sheets and the guest nanoparticles in the pillared system. The results of degradation of methylene blue under visible light radiation suggest that doping iron ions improves the material spectral response region and that hybridizing with ZnO nanopillars can suppress the recombination of photogenerated electron-hole pairs.

Interstratified nanohybrid assembled by alternating cationic layered double hydroxide nanosheets and anionic layered titanate nanosheets with superior photocatalytic activity.

Oppositely charged 2D inorganic nanosheets of ZnAl-layered double hydroxide and layered titanate were successfully assembled into an interstratified nanohybrid through simply mixing the corresponding nanosheet suspensions. Powder X-ray diffraction and high-resolution transmission electron microscope clearly revealed that the component nanosheets in the as-obtained nanohybrid ZnAl-Ti3O7 retain the 2D sheet skeletons of the pristine materials and that the two kinds of nanosheets are well arranged in a layer-by-layer alternating fashion with a basal spacing of about 1.3 nm, coincident with the thickness summation of the two component nanosheets. The effective interfacial heterojunction between them and the high specific surface area resulted in that the nanohybrid exhibits a superior photocatalytic activity in the degradation of methylene blue with a reaction constant k of 2.81 × 10(-2)min(-1), which is about 9 and 4 times higher than its precursors H2Ti3O7 and ZnAl-LDH, respectively. Based on UV-vis, XPS and photoelectrochemical measurements, a proposed photoexcitation model was provided to understand its photocatalytic behavior.

Heterostructured Tin oxide-pillared tetratitanate with enhanced photocatalytic activity.

An effective active heterostructured photocatalyst of porous SnO(2)-pillared tetratitanate nanocomposite is synthesized by assembling tetratitanate nanosheets with SnO(2) nanoparticles via an exfoliation-restacking route. The nanocomposite was characterized by powder X-ray diffraction, high-resolution transmission electron microscope, thermogravimetric analysis, UV-vis DRS, X-ray photoelectron spectroscopy, and N(2) adsorption-desorption measurements. It was found that the pillared nanaocomposite is mesoporous with a gallery height of about 2 nm and a specific surface area of 154 m(2)/g. The pillared nanaocomposite exhibited enhanced photocatalytic activity in the photodegradation of Rhodamine B under UV light irradiation. The improved performance is attributed to the electronic coupling between the host and the guest components, as well as its high surface area and mesoporosity.

Study of the Photocatalytic Performance of Oxygen-deficient TiO 2 Active in Visi-ble Light: Study of the Photocatalytic Performance of Oxygen-deficient TiO 2 Active in Visi-ble Light

采用氢气还原法制备氧缺陷型二氧化钛(TiO 2- x ), 考察氧气氛中不同返烧温度对TiO 2- x 性能的影响. 利用X射线光电子能谱、电子自旋共振谱、紫外-可见漫反射光谱和荧光光谱等技术对样品的表面化学状态、氧缺陷位的种类、光吸收性能和光生载流子的分离效率等性质进行了表征, 并以气相的苯为模型污染物, 研究催化剂样品在可见光(λ > 400 nm)照射下的光催化氧化能力. 结果表明, 与未返烧的催化剂相比, 返烧后TiO 2- x 对苯的光催化氧化降解能力显著提高, 反应4 h、催化剂活性稳定后, 经300℃返烧的TiO 2- x 样品对苯的转化率为36.9 %, 是未返烧样品的5.3倍. 还原过程中生成的体相氧缺陷位(束缚单电子的氧空位)是催化剂具有可见光催化性能的主要原因, 返烧热处理减少了催化剂表面氧缺陷位(Ti 3+ )的浓度并有效地抑制了光生载流子的复合.采用氢气还原法制备氧缺陷型二氧化钛(TiO 2- x ), 考察氧气氛中不同返烧温度对TiO 2- x 性能的影响. 利用X射线光电子能谱、电子自旋共振谱、紫外-可见漫反射光谱和荧光光谱等技术对样品的表面化学状态、氧缺陷位的种类、光吸收性能和光生载流子的分离效率等性质进行了表征, 并以气相的苯为模型污染物, 研究催化剂样品在可见光(λ > 400 nm)照射下的光催化氧化能力. 结果表明, 与未返烧的催化剂相比, 返烧后TiO 2- x 对苯的光催化氧化降解能力显著提高, 反应4 h、催化剂活性稳定后, 经300℃返烧的TiO 2- x 样品对苯的转化率为36.9 %, 是未返烧样品的5.3倍. 还原过程中生成的体相氧缺陷位(束缚单电子的氧空位)是催化剂具有可见光催化性能的主要原因, 返烧热处理减少了催化剂表面氧缺陷位(Ti 3+ )的浓度并有效地抑制了光生载流子的复合.

Visible-light-driven photocatalytic performance of nitrogen-doped Ti{sub 1−x}Zr{sub x}O{sub 2} solid solution

Nitrogen-doped Ti1-xZrxO2 solid solutions have been synthesized by a multi-step sol-gel process followed by hydrothermal treatment in ammonia solution. XRD, XPS and UV-vis diffuse reflectance analyses indicated that nitrogen was doped in the surface layer of catalyst, introducing surface states located close to valence band. However, Zr4+. was successfully incorporated into the bulk lattice of TiO2 so as to induce the up-shift of conduction band. Compared to pristine TiO2 and nitrogen-doped TiO2, nitrogen-doped Ti1-xZrxO2 exhibited much higher efficiency for the degradation of Acid Red 88 solution and gaseous benzene under visible light irradiation, attributed to the synergetic effect of nitrogen and zirconium on the energy band. Specifically, the presence of surface states in the band gap enabled the extended visible light response and the up-shift of conduction band facilitated the excited electron interfacial transfer and hence suppressed efficiently the recombination of charge carriers