Yang Qu

Composites of small Ag clusters confined in the channels of well-ordered mesoporous anatase TiO2 and their excellent solar-light-driven photocatalytic performance

AbstractSmall Ag clusters confined in the channels of ordered mesoporous anatase TiO2 have been fabricated via a vacuum-assisted wet-impregnation method, utilizing well-ordered mesoporous anatase TiO2 with high thermal stability as the host. The composites have been characterized in detail by X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption fine structure (XAFS) spectroscopy, N2 adsorption, UV-visible diffuse reflectance spectroscopy and transmission electron microscopy. The results indicate that small Ag clusters are formed and uniformly confined in the channels of mesoporous TiO2 with an obvious confinement effect. The presence of strong Ag-O interactions involving the Ag clusters in intimate contact with the pore walls of mesoporous TiO2 is confirmed by XAFS analysis, and favors the separation of photogenerated electron-hole pairs, as shown by steady-state surface photovoltage spectroscopy and transient-state surface photovoltage measurements. The ordered mesoporous Ag/TiO2 composites exhibit excellent solar-light-driven photocatalytic performance for the degradation of phenol. This is attributed to the synergistic effects between the small Ag clusters acting as traps to effectively capture the photogenerated electrons, and the surface plasmon resonance of the Ag clusters promoting the absorption of visible light. This study clearly demonstrates the high-efficiency utilization of noble metals in the fabrication of high-performance solar-light-driven photocatalysts.

Improved visible-light activities for degrading pollutants on TiO2/g-C3N4 nanocomposites by decorating SPR Au nanoparticles and 2,4-dichlorophenol decomposition path

It has been clearly demonstrated that the visible-light photocatalytic activities of g-C3N4 (CN) for degrading 2,4-dichlorophenol (2,4-DCP) and bisphenol A (BPA) could be improved by fabricating nanocomposites with a proper amount of nanocrystalline anatase TiO2. Interestingly, the visible-light activities of the amount-optimized nanocomposite could be further improved after decorating Au nanoparticles, with 5.11- and 3.1-time improvement respectively for 2,4-DCP and BPA compared to that of CN, even much higher than that of P25 TiO2 under UV-vis irradiation. Based on the transient-state surface photovoltage responses and photoelectrochemical measurements, it is confirmed that the exceptional visible-light activities of the fabricated Au-(TiO2/g-C3N4) nanocomposites are attributed to the extended visible-light response due to the surface plasmonic resonance (SPR) of decorated Au and its catalytic function, and to the enhanced charge separation by transferring electrons from CN and SPR Au to TiO2 in the nanocomposites. The highly promoted charge separation results in the effective availability of a large number of hydroxyl radicals (OH) participating in the photocatalytic oxidation process of 2,4-DCP. Furthermore, a possible mechanism of 2,4-DCP degradation is proposed according to the detailed analyses of produced intermediates. This work provides new idea for designing Au assisted nanocomposite photocatalysts for environmental remediation.

ZnO-dotted porous ZnS cluster microspheres for high efficient, Pt-free photocatalytic hydrogen evolution

The Pt-free photocatalytic hydrogen evolution (PHE) has been the focus in the photocatalysis field. Here, the ZnO-dotted porous ZnS cluster microsphere (PCMS) is designed for high efficient, Pt-free PHE. The PCMS is designed through an easy “controlling competitive reaction” strategy by selecting the thiourea as S2− source and Zn(Ac)2·2H2O as Zn source in ethylene glycol medium. Under suitable conditions, one of the PCMS, named PCMS-1, with high SBET specific area of 194 m2g−1, microsphere size of 100 nm and grain size of 3 nm can be obtained. The formation of PCMS is verified by TEM, XAES, XPS, Raman and IR methods. Importantly, a series of the experiments and theoretical calculation demonstrate that the dotting of ZnO not only makes the photo-generated electrons/hole separate efficiently, but also results in the formation of the active catalytic sites for PHE. As a result, the PCMS-1 shows the promising activity up to 367 μmol h−1 under Pt-free condition. The PHE activity has no obvious change after addition 1 wt.% Pt, implying the presence of active catalytic sites for hydrogen evolution in the PCMS-1. The easy synthesis process, low preparation cost of the PCMS makes their large potential for Pt-free PHE.

Modification Strategies with Inorganic Acids for Efficient Photocatalysts by Promoting the Adsorption of O2

Efficient photocatalysis for degrading environmental organic pollutants on semiconductors requires photogenerated charge carrier separation to drive the photochemical processes. To ensure charge separation, it is indispensable to make charges captured effectively. Generally, the step for capturing the photogenerated electrons by the surface adsorbed O2 is relatively slow as compared to that for capturing holes by the surface adsorbed hydroxyl groups so that it is taken as the rate-determining step. However, it is frequently neglected. Thus, it is greatly desired to develop feasible strategies to promote the adsorption of O2 for efficient photocatalysts. In this paper, we have mainly discussed surface modification with inorganic acids, such as H3PO4, HF, and H3BO3, to enhance photogenerated charge carrier separation based on oxygen adsorption promotion for photocatalytic degradation of environmental pollutants. Among these acids, the function and mechanism of H3PO4 are highlighted because of its good performance and universality. Several important photocatalyst systems, mainly including TiO2, α-Fe2O3, and g-C3N4, along with the nanostructured carbons as electron acceptors in nanocomposites, are addressed to improve the ability to adsorb O2. A key consideration in this review is the development of a strategy for the promotion of adsorbed O2 for efficient photocatalysts, along with the process mechanisms by revealing the relationships among the adsorbed O2, photogenerated charge carrier separation, and photocatalytic performance. Interestingly, it is suggested that the enrichment in surface acidity be favorable for promotion of O2 adsorption, leading to the improved charge carrier separation and then to the enhanced photoactivities of various semiconductor photocatalysts. Moreover, several outlooks are put forward.

Exceptional performance of photoelectrochemical water oxidation of single-crystal rutile TiO2 nanorods dependent on the hole trapping of modified chloride

It is highly desired to effectively trap photogenerated holes for efficient photoelectrochemical (PEC) water oxidation to evolve O2 on oxide semiconductors. Herein, it is found for the first time mainly based on the time-resolved- and atmosphere-controlled- surface photovoltage responses that the modified chloride would effectively trap photogenerated holes so as to prolong the charge lifetime and hence promote charge separation of single-crystal rutile TiO2 nanorods. Its strong capacity to trap holes, comparable to the widely-used methanol and Co(II) phosphate, is well responsible for the exceptional photoactivities for PEC water oxidation to evolve O2 on rutile nanorods with a proper amount of chloride modified, about 2.5-time high as that on the resulting anatase nanoparticles, even 10-time if the surface area is considered. Moreover, it is suggested that the hole trapping role of chemically-adsorbed chloride is related to its lonely-pair electrons, and to the subsequently-produced intermediate Cl atoms with proper electronegativity for evolving O2. Interestingly, this finding is also applicable to the chloride-modified anatase TiO2. This work will provide a feasible strategy to design high-activity nanostructured semiconductor photoanodes for PEC water oxidation, even for overall water splitting.

Synthesis of silicate-bridged ZnO/g-C3N4 nanocomposites as efficient photocatalysts and its mechanism

In this study, silicate-capped ZnO/g-C3N4 nanocomposites were successfully fabricated by a simple wet chemical process. The photocatalytic activities of g-C3N4 for the degradation of phenol and the production of H2 are greatly enhanced after coupling with an appropriate amount of nanocrystalline ZnO. This is attributed to the prolonged lifetime and increased separation of the photogenerated charges, which are mainly based on atmosphere-controlled steady-state surface photovoltage spectra and time-resolved surface photovoltage responses. Interestingly, the lifetime and separation of photogenerated charges are further improved after the introduction of silicate groups as linkers between ZnO and g-C3N4, which consequently lead to enhanced photocatalytic activities, as much as 4 times higher compared to g-C3N4. Evidently, the built silicate linkers, which act as bridges, are highly favorable for charge transfer and separation in the fabricated heterojunctional nanocomposites and also for efficient photocatalysis. The present work provides a simple and feasible idea to enhance photogenerated charge separation so as to improve the photoactivities of nanocomposites.

Coupling of Nanocrystalline Anatase TiO2 to Porous Nanosized LaFeO3 for Efficient Visible-Light Photocatalytic Degradation of Pollutants

In this work we have successfully fabricated nanocrystalline anatase TiO2/perovskite-type porous nanosized LaFeO3 (T/P-LFO) nanocomposites using a simple wet chemical method. It is clearly demonstrated by means of atmosphere-controlled steady-state surface photovoltage spectroscopy (SPS) responses, photoluminescence spectra, and fluorescence spectra related to the formed OH− radical amount that the photogenerated charge carriers in the resultant T/P-LFO nanocomposites with a proper mole ratio percentage of TiO2 display much higher separation in comparison to the P-LFO alone. This is highly responsible for the improved visible-light activities of T/P-LFO nanocomposites for photocatalytic degradation of gas-phase acetaldehyde and liquid-phase phenol. This work will provide a feasible route to synthesize visible-light responsive nano-photocatalysts for efficient solar energy utilization.

Synthesis of pure phase Mg1.2Ti1.8O5 and MgTiO3 nanocrystals for photocatalytic hydrogen production

Synthesis of pure phase Mg1.2Ti1.8O5 and MgTiO3 nanocrystals has proven to be challenging. Here, pure phase Mg1.2Ti1.8O5 and MgTiO3 nanocrystals were prepared. Furthermore, a new magnesium titanate, Mg1.2Ti1.8O5, was synthesized via a solution-based route for the first time. As hydrogen evolution photocatalysts, both pure phase Mg1.2Ti1.8O5 and MgTiO3 nanocrystals exhibit excellent hydrogen production efficiency. In comparison with pure MgTiO3 nanocrystals, the asprepared Mg1.2Ti1.8O5 nanocrystals exhibited four times as much photocatalytic hydrogen production activity, up to 40 μmol·h–1. Photoelectrochemical analysis, including linear sweep voltammetry, transient photocurrent measurement, electrochemical impedance spectroscopy, and construction of Mott-Schottky plots, demonstrated that the enhanced photocatalytic activity was attributed to the large surface area, fast photoelectron transfer, higher carrier density, and efficient charge separation of the Mg1.2Ti1.8O5 nanocrystals.

Enhanced photoelectric conversion efficiency of dye-sensitized solar cells by the synergetic effect of NaYF4:Er3+/Yb3+ and g-C3N4

TiO2-NaYF4:Er3+/Yb3+-C3N4 composite photoanodes were successfully designed for the first time. The photoelectric conversion efficiency of TiO2-NaYF4:Er3+/Yb3+-C3N4 composite cell can result an efficiency of 7.37%, which is higher than those of pure TiO2 cell and TiO2-C3N4 composite cell. The enhancement of the efficiency can be attributed to the synergetic effect of NaYF4:Er3+/Yb3+ and C3N4. Electrochemical impedance spectroscopy analysis revealed that the interfacial resistance of the TiO2-dye I3-/I− electrolyte interface of TiO2-NaYF4:Er3+/Yb3+-C3N4 composites cell was much smaller than that of pure TiO2 cell. In addition, the TiO2-NaYF4:Er3+/Yb3+-C3N4 composite cell had longer electron recombination time and shorter electron transport time than that of pure TiO2 cell.摘要本文首次成功设计并得到以TiO2-NaYF4:Er3+/Yb3+-C3N4复合材料作为光阳极的染料敏化太阳电池. 与纯TiO2和TiO2-C3N4电池相比, TiO2-NaYF4:Er3+/Yb3+-C3N4复合电池的效率明显提高. 研究表明, TiO2-NaYF4:Er3+/Yb3+-C3N4复合电池的TiO2-dye|I3-/I−界面阻抗小于纯TiO2电 池. 此外TiO2-NaYF4:Er3+/Yb3+-C3N4电池具有更长的复合时间和更短的传输时间. 电池效率的提高归结于NaYF4:Er3+/Yb3+和g-C3N4的协同效应.

Down-shifting luminescence of water soluble NaYF4:Eu3+@Ag core-shell nanocrystals for fluorescence turn-on detection of glucose

Techniques for detecting glucose are developing at a breathtaking speed because diabetes mellitus can cause many serious complications, such as blindness, high blood pressure heart disease and kidney failure. Herein, water soluble NaYF4:Eu3+@Ag core-shell nanocrystals for glucose detection with lower detection limit have been successfully developed, using NaYF4:Eu3+ cores as the energy donors and Ag shells as the efficient quenchers through energy transfer. After immobilization of glucose oxidase (GOx) on the surface of NaYF4:Eu3+@Ag core-shell nanocrystals, the Ag shells can be decomposed in the presence of glucose, accompanied by down-shifting luminescence recovery. The limit of detection of NaYF4:Eu3+@Ag was 0.12 μmol L−1. Therefore, the NaYF4:Eu3+@Ag can be easily extended to the detection of a variety of H2O2-involved analytes.摘要糖尿病可引起许多严重的并发症, 例如失明, 血压心脏病和肾衰竭等. 因此, 葡萄糖检测技术正在以惊人的速度发展. 本文合成了水溶性的NaYF4:Eu3+@Ag核-壳纳米晶体, 通过能量转移, Ag壳层可以有效吸收NaYF4:Eu3+的能量, 导致Eu3+离子荧光淬灭. 在NaYF4:Eu3+@Ag核-壳纳米晶体的表面上固定葡萄糖氧化酶(GOx)后, 通过加入一定量的葡萄糖, Ag纳米粒子可以分解成Ag+, 并伴随着Eu3+的荧光恢复. 结果表明, 该葡萄糖检测方法具有非常低的检测限(0.12 μmol L−1).