Yueping Fang

Engineering heterogeneous semiconductors for solar water splitting

There is a growing interest in the conversion of water and solar energy into clean and renewable H2 fuels using earth-abundant materials due to the depletion of fossil fuel and its serious environmental impact. This critical review highlights some key factors influencing the efficiency of heterogeneous semiconductors for solar water splitting (i.e. improved charge separation and transfer, promoted optical absorption, optimized band gap position, lowered cost and toxicity, and enhanced stability and water splitting kinetics). Moreover, different engineering strategies, such as band structure engineering, micro/nano engineering, bionic engineering, co-catalyst engineering, surface/interface engineering of heterogeneous semiconductors are summarized and discussed thoroughly. The synergistic effects of the different engineering strategies, especially for the combination of co-catalyst loading and other strategies seem to be more promising for the development of highly efficient photocatalysts. A thorough understanding of electron and hole transfer thermodynamics and kinetics at the fundamental level is also important for elucidating the key efficiency-limiting step and designing highly efficient solar-to-fuel conversion systems. In this review, we provide not only a summary of the recent progress in the different engineering strategies of heterogeneous semiconductors for solar water splitting, but also some potential opportunities for designing and optimizing solar cells, photocatalysts for the reduction of CO2 and pollutant degradation, and electrocatalysts for water splitting.

Photocatalysis fundamentals and surface modification of TiO2 nanomaterials

Abstract As a green and sustainable technology, heterogeneous photocatalysis using semiconductors has received much attention during the past decades because of its potential to address energy and environmental problems. Among various semiconductors, TiO 2 has been regarded as the best and most widely investigated photocatalyst in the past 10 years. Based on the fundamentals of photocatalysis and surface chemistry of TiO 2 nanomaterials, we herein summarize and discuss the achievements in the different surface modification strategies employed to date such as surface doping and sensitization, construction of surface heterojunctions, loading of nano-sized co-catalysts, increase in the accessible surface areas, and usage of surface F effects and exposure of highly reactive facets. Especially, the interesting synergistic effects of these different surface modification strategies deserve more attention in the near future. Studying these important advances in photocatalysis fundamentals, and surface chemistry and modification may offer new opportunities for designing highly efficient TiO 2 -based and non-TiO 2 -based photocatalysts for solar fuel production, environmental remediation, organic photosynthesis, and other related fields such as solar cell device fabrication, thermal catalysis, and separation and purification.

Design and fabrication of semiconductor photocatalyst for photocatalytic reduction of CO 2 to solar fuel

The shortage of fossil fuels and the disastrous pollution of the environment have led to an increasing interest in artificial photosynthesis. The photocatalytic conversion of CO2 into solar fuel is believed to be one of the best methods to overcome both the energy crisis and environmental problems. It is of significant importance to efficiently manage the surface reactions and the photo-generated charge carriers to maximize the activity and selectivity of semiconductor photocatalysts for photoconversion of CO2 and H2O to solar fuel. To date, a variety of strategies have been developed to boost their photocatalytic activity and selectivity for CO2 photoreduction. Based on the analysis of limited factors in improving the photocatalytic efficiency and selectivity, this review attempts to summarize these strategies and their corresponding design principles, including increased visible-light excitation, promoted charge transfer and separation, enhanced adsorption and activation of CO2, accelerated CO2 reduction kinetics and suppressed undesirable reaction. Furthermore, we not only provide a summary of the recent progress in the rational design and fabrication of highly active and selective photocatalysts for the photoreduction of CO2, but also offer some fundamental insights into designing highly efficient photocatalysts for water splitting or pollutant degradation.摘要近年来, 严 重的化石燃料短缺以及环境污染问题使得人工光合作用引起了科研工作者的广泛关注, 光催化转换CO2成为有价值的太阳能燃料被认为是解决能源危机以及环境问题的最好的方法之一. 有效地控制半导体表面的催化反应以及光生载流子是制备高活性以及高选择性半导体CO2还原光催化剂的关键因素, 至今, 研究人员已经提出了许多策略来增强光催化转换CO2的活性以及选择性. 本文在分析提高光催化效率和选择性限制因素的基础上, 尝试从几个不同方面总结了近些年来提高光催化CO2还原效率的方法以及它们的设计原理, 包括增强半导体可见光响应、 促进光生电子空穴分离、 提高CO2的吸附和活化、 加速CO2还原的动力学以及抑制不良反应等方面. 因此, 本文不仅系统地总结了近年来高活性高选择性光催化CO2还原光催化剂的设计进展, 而且为高效光解水产氢和污染物降解光催化剂的设计提供了重要参考.

Enhanced photocatalytic H2 evolution over noble-metal-free NiS cocatalyst modified CdS nanorods/g-C3N4 heterojunctions

In this report, CdS nanorods/g-C3N4 heterojunctions loaded with a noble-metal-free NiS cocatalyst were for the first time fabricated by an in situ hydrothermal method. The as-synthesized heterostructured photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy, UV-visible spectroscopy, nitrogen absorption, photoluminescence (PL) spectra, transient photocurrent responses and electrochemical impedance spectroscopy (EIS) measurements. Their photocatalytic activity for hydrogen production was evaluated using an aqueous solution containing triethanolamine under visible light (λ ≥ 420 nm). The results clearly demonstrated that the ternary hybridization of the NiS cocatalyst, 1D CdS nanorods and 2D g-C3N4 nanosheets is a promising strategy to achieve highly efficient visible-light-driven photocatalytic H2 evolution. Among all the photocatalysts employed, the ternary hybrid g-C3N4–CdS–9% NiS composite materials show the best photocatalytic performance with a H2-production rate of 2563 μmol h−1 g−1, which is 1582 times higher than that of the pristine g-C3N4. The enhanced photocatalytic activity was ascribed to the combined effects of NiS cocatalyst loading and the formation of the intimate nanoheterojunctions between 1D CdS nanorods and 2D g-C3N4 nanosheets, which were favorable for promoting charge transfer, improving the separation efficiency of photoinduced electron–hole pairs from the bulk to the interfaces and accelerating the surface H2-evolution kinetics. This work would not only provide a promising photocatalyst candidate for applications in visible-light H2 generation, but also offer a new insight into the construction of highly efficient and stable g-C3N4-based hybrid semiconductor nanocomposites for diverse photocatalytic applications.

A carbon nitride/TiO2 nanotube array heterojunction visible-light photocatalyst: synthesis, characterization, and photoelectrochemical properties

A carbon nitride/TiO2 nanotube array (CN/TNT) heterojunction photocatalyst with visible-light response was prepared by a simple electrochemical method. The photocatalyst was characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The photoelectrochemical properties and photocatalytic activities of the obtained-samples were systematically tested under visible light irradiation. The activity of heterojunction photocatalyst CN/TNTs is higher than that of TNTs. The obviously increased performance of CN/TNTs is ascribed mainly to enhancement of electron–hole separations both at the interface and in the semiconductors.

Sonochemical Preparation of Hierarchical ZnO Hollow Spheres for Efficient Dye‐Sensitized Solar Cells

Hierarchical ZnO hollow spheres (400-500 nm in diameter) consisting of ZnO nanoparticles with a diameter of approximately 15 nm have been successfully prepared by a facile and rapid sonochemical process. The formation of hierarchical ZnO hollow spheres is attributed to the oriented attachment and subsequent Ostwald ripening process according to time-dependent experiments. The as-prepared ZnO hollow spheres are used as a photoanode in dye-sensitized solar cells and exhibit a highly efficient power conversion efficiency of 4.33%, with a short-circuit current density of 9.56 mA cm(-2), an open-circuit voltage of 730 mV, and a fill factor of 0.62 under AM 1.5 G one sun (100 mW cm(-2)) illumination. Moreover, the photovoltaic performance (4.33%) using the hierarchical ZnO hollow spheres is 38.8% better than that of a ZnO nanoparticle photoelectrode (3.12%), which is mainly attributed to the efficient light scattering for the former.

利用Ni(OH) x 助催化剂修饰提高g-C 3 N 4 纳米片/WO 3 纳米棒Z型纳米体系的可见光产氢活性的研究

Abstract Novel WO 3 /g-C 3 N 4 /Ni(OH) x hybrids have been successfully synthesized by a two-step strategy of high temperature calcination and in situ photodeposition. Their photocatalytic performance was investigated using TEOA as a hole scavenger under visible light irradiation. The loading of WO 3 and Ni(OH) x cocatalysts boosted the photocatalytic H 2 evolution efficiency of g-C 3 N 4 . WO 3 /g-C 3 N 4 /Ni(OH) x with 20 wt%defective WO 3 and 4.8 wt%Ni(OH) x showed the highest hydrogen production rate of 576 μmol/(g–h), which was 5.7, 10.8 and 230 times higher than those of g-C 3 N 4 /4.8 wt%Ni(OH) x , 20 wt%WO 3 /C 3 N 4 and g-C 3 N 4 photocatalysts, respectively. The remarkably enhanced H 2 evolution performance was ascribed to the combination effects of the Z-scheme heterojunction (WO 3 /g-C 3 N 4 ) and loaded cocatalysts (Ni(OH) x ), which effectively inhibited the recombination of the photoexcited electron-hole pairs of g-C 3 N 4 and improved both H 2 evolution and TEOA oxidation kinetics. The electron spin resonance spectra of • O 2 − and • OH radicals provided evidence for the Z-scheme charge separation mechanism. The loading of easily available Ni(OH) x cocatalysts on the Z-scheme WO 3 /g-C 3 N 4 nanocomposites provided insights into constructing a robust multiple-heterojunction material for photocatalytic applications.

Photocatalytic reduction of carbon dioxide to methanol by Cu2O/SiC nanocrystallite under visible light irradiation

Abstract The Cu2O/SiC photocatalyst was obtained from SiC nanoparticles (NPs) modified by Cu2O. Their photocatalytic activities for reducing CO2 to CH3OH under visible light irradiation have been investigated. The results indicated that besides a small quantity of 6H-SiC, SiC NPs mainly consisted of 3C-SiC. The band gaps of SiC and Cu2O were estimated to be about 1.95 and 2.23 eV from UV-Vis spectra, respectively. The Cu2O modification can enhance the photocatalytic performance of SiC NPs, and the largest yields of methanol on SiC, Cu2O and Cu2O/SiC photocatalysts under visible light irradiation were 153, 104 and 191 μmol/g, respectively.

Electrochemical route to the preparation of highly dispersed composites of ZnO/carbon nanotubes with significantly enhanced electrochemiluminescence from ZnO

ZnO nanostructures were electrochemically deposited on the surfaces of carbon nanotubes (CNTs) supported on a Zn foil cathode, leading to the facile formation of ZnO/CNT composites with uniform mixing, high dispersion and high-quality interfaces. The electrochemical deposition method circumvents the need for bridging molecules to bring together the two phases and has the key advantage of controllability. By increasing the deposition time, the individual CNTs were first fully covered with ZnO and then the morphology of the deposited ZnO nanostructures was gradually changed from spherical nanoparticles to lily-like nanoflowers. The lily-like structures of ZnO/CNT nanocomposites showed enhanced electrochemiluminescence (ECL). Significantly, the ECL intensity of the lily-like structure of ZnO/CNT nanocomposites was almost an order of magnitude larger than that of pure ZnO nanoflowers, and the ECL starting voltage shifts positively from −1.06 to −0.41 V. These have been attributed to the presence of CNTs which decrease the barriers of ZnO reduction during the ECL process and the special structure of ZnO on the surface of CNTs as well. This work has demonstrated a new strategy to directly coat CNTs with oxides, probably many other inorganic materials, with tunable coverage and nanostructure. Furthermore, the significantly enhanced ECL of ZnO by interfacing with the CNTs highlights the importance and potential utility of such nanostructuring in the development of optoelectronic and biomedical devices.

Controlled synthesis of SnO2@carbon core-shell nanochains as high-performance anodes for lithium-ion batteries

A new low-flow-rate inert atmosphere strategy has been demonstrated for the synthesis of perfect SnO2@carbon core-shell nanochains (SCNCs) by carbonization of an SnO2@carbonaceous polysaccharide (CPS) precursor at a relatively high temperature. This strategy results in the thorough carbonization of CPS whilst avoiding the carbothermal reduction of SnO2 at 700 °C. It has been investigated that a moderate carbon content contributes to the 1-D growth of SCNCs, and the thickness of the carbon shell can be easily manipulated by varying the hydrothermal treatment time in the precursor process. Such a unique nanochain architecture could afford a very high lithium storage capacity as well as resulting in a desirable cycling performance. SCNCs with about 8 nm carbon shell synthesized by optimized routes were demonstrated for optimal electrochemical performances. More than 760 mAh g¬1 of reversible discharge capacity was achieved at a current density of 300 mA g−1, and above 85% retention can be obtained after 100 charge-discharge cycles. TEM analysis of electrochemically-cycled electrodes indicates that the structural integrity of the SnO2@carbon core-shell nanostructure is retained during electrochemical cycling, contributing to the good cycleability demonstrated by the robust carbon shell.