Dengwei Jing

Heterojunctions in g-C3N4/TiO2(B) nanofibres with exposed (001) plane and enhanced visible-light photoactivity

The formation of heterojunctions is an efficient strategy to extend the light response range of TiO2-based catalysts to the visible light region. In addition to the bandgap edge match between the narrow bandgap semiconductors and the TiO2 substrate, a stable phase interface between the sensitiser and TiO2 is crucial for the construction of heterojunctions, since it acts as a tunnel for the efficient transfer of photogenerated charges. Herein, the coincidence site density (1/Σ) of graphite-like carbon nitride (g-C3N4) nanoflakes and two types of TiO2 nanofibres [anatase and TiO2(B)] was calculated by near coincidence site lattice (NCSL) theory. It was found that the coincidence site density of g-C3N4 and TiO2(B) nanofibre with an exposed (001) plane is 3 times of that of the g-C3N4 and anatase nanofibre with exposed (100) plane. This indicated that the g-C3N4 nanoflakes are more favoured to form stable heterojunctions with TiO2(B) nanofibres. As expected, a stable phase interface was formed between the plane of (22–40) of g-C3N4 and the plane (110) of TiO2(B) which had same d-spacing of 0.35 nm and the same orientation. Under visible light irradiation, the photogenerated electrons could efficiently migrate to the TiO2(B) nanofibres from the g-C3N4 through the heterojunctions. So the g-C3N4/TiO2(B) system exhibited better photodegradation ability for sulforhodamine B (SRB) dye than the g-C3N4/anatase system, although the photoactivity of the anatase nanofibres was much better than that of the TiO2(B) nanofibres.

Twin-induced one-dimensional homojunctions yield high quantum efficiency for solar hydrogen generation

Efficient charge separation is of crucial importance for the improvement of photocatalytic activity for solar hydrogen evolution. Here we report efficient photo-generated charge separation by twin-induced one-dimensional homojunctions with type-II staggered band alignment, using a ternary chalcogenate, i.e. Cd0.5Zn0.5S nanorod as a model material. The quantum efficiency of solar hydrogen evolution over this photocatalyst, without noble metal loading, reaches 62%. Unlike traditional heterojunctions, doping or combination of additional elements are not needed for the formation of this junction, which permits us to tune the band structures of semiconductors to the specific application in a more precise way. Our results highlight the power of forming long-range ordered homojunctions at the nanoscale for photocatalytic and photoelectrochemical applications.

Site-selected doping of upconversion luminescent Er3+ into SrTiO3 for visible-light-driven photocatalytic H2 or O2 evolution.

A series of upconversion luminescent erbium-doped SrTiO(3) (ABO(3)-type) photocatalysts with different initial molar ratios of Sr/Ti have been prepared by a facile polymerized complex method. Er(3+) ions, which were gradually transferred from the A to the B site with increasing Sr/Ti, enabled the absorption of visible light and the generation of high-energy excited states populated by upconversion processes. The local internal fields arising from the dipole moments of the distorted BO(6) octahedra promoted energy transfer from the high-energy excited states of Er(3+) with B-site occupancy to the host SrTiO(3) and thus enhanced the band-to-band transition of the host SrTiO(3). Consequently, the erbium-doped SrTiO(3) species with B-site occupancy showed higher photocatalytic activity than those with A-site occupancy for visible-light-driven H(2) or O(2) evolution in the presence of the corresponding sacrificial reagents. The results generally suggest that the introduction of upconversion luminescent agents into host semiconductors is a promising approach to simultaneously harnessing low-energy photons and maintaining redox ability for photocatalytic H(2) and O(2) evolution and that the site occupancy of doped elements in ABO(3)-type perovskite oxides greatly determines the photocatalytic activity.

Simple pyrolysis of cobalt alginate fibres into Co3O4/C nano/microstructures for a high-performance lithium ion battery anode

Cobalt tetroxide (Co3O4) has attracted much attention as a promising anode material for rechargeable lithium-ion batteries (LIBs) owing to its high theoretical capacity (890 mA h g−1). However, its poor electronic conductivity and weak ability to accommodate large volume changes during a repeated charging–discharging process, which results in the poor cycling performance, have hindered the practical application of Co3O4. In this article, Co3O4/C fibres were prepared by simple pyrolysis of wetspun cobalt alginate fibres. The composites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). It was found that the resulting material possesses a unique hierarchical nano/microstructure in which Co3O4 nanoparticles (NPs) are capsulated in a micro-sized carbonaceous fibrous matrix. This nano/microstructure can combine the merits of the Co3O4 nanostructure and the carbonaceous microfibre matrix, and thus exhibits a high reversible capacity of 780 mA h g−1 at 89 mA g−1 after 100 cycles as well as excellent cycling stability and rate performance when used as an anode material. This finding could open up a new direction in sustainable use of natural seaweed resources as new energy storage materials.

Enhanced photodynamic therapy of mixed phase TiO2(B)/anatase nanofibers for killing of HeLa cells

Photodynamic therapy (PDT), which is a procedure that uses photosensitizing drug to apply therapy selectively to target sites, has been proven to be a safe treatment for cancers and conditions that may develop into cancers. Nano-sized TiO2 has been regarded as potential photosensitizer for UV light driven PDT. In this study, four types of TiO2 nanofibers were prepared from proton tri-titanate (H2T3O7) nanofiber. The as-obtained nanofibers were demonstrated as efficient photosensitizers for PDT killing of HeLa cells. MTT assay and flow cytometry (FCM) were carried out to evaluate the biocompatibility, percentage of apoptotic cells, and cell viability. The non-cytotoxicity of the as-prepared TiO2 nanofibers in the absence of UV irradiation has also been demonstrated. Under UV light irradiation, the TiO2 nanofibers, particularly the mixed phase nanofibers, displayed much higher cell-killing efficiency than Pirarubicin (THP), which is a common drug to induce the apoptosis of HeLa cells. We ascribe the high cellkilling efficiency of the mixed phase nanofibers to the bandgap edge match and stable interface between TiO2(B) and anatase phases in a single nanofiber, which can inhibit the recombination of the photogenerated electrons and holes. This promotes the charge separation and transfer processes and can produce more reactive oxygen species (ROS) that are responsible for the killing of HeLa cells.

Concentrating PV/T Hybrid System for Simultaneous Electricity and Usable Heat Generation: A Review

Photovoltaic (PV) power generation is one of the attractive choices for efficient utilization of solar energy. Considering that the efficiency and cost of PV cells cannot be significantly improved in near future, a relatively cheap concentrator to replace part of the expensive solar cells could be used. The photovoltaic thermal hybrid system (PV/T), combining active cooling with thermal electricity and providing both electricity and usable heat, can enhance the total efficiency of the system with reduced cell area. The effect of nonuniform light distribution and the heat dissipation on the performance of concentrating PV/T was discussed. Total utilization of solar light by spectral beam splitting technology was also introduced. In the last part, we proposed an integrated compound parabolic collector (CPC) plate with low precision solar tracking, ensuring effective collection of solar light with a significantly lowered cost. With the combination of beam splitting of solar spectrum, use of film solar cell, and active liquid cooling, efficient and full spectrum conversion of solar light to electricity and heat, in a low cost way, might be realized. The paper may offer a general guide to those who are interested in the development of low cost concentrating PV/T hybrid system.

Modeling of anisotropic flow and thermodynamic properties of magnetic nanofluids induced by external magnetic field with varied imposing directions

Magnetic field can enhance both thermal conductivity and Lorentz force resistance of the magnetic nanofluids (MNFs), in which the former is favored while the latter often leads to pressure drop of the flow. It is assumed that there would exist a balance between the magnetic field induced thermal conductivity and Lorentz force if one can appropriately adjust the angle of the imposing magnetic field with respect to the direction of the flow. In the present study, the effects of direction of magnetic field ( α) on anisotropic thermodynamic properties of magnetic nanofluids in channel were studied. The effects of direction of magnetic field on thermal conductivity, Nusselt number, global total entropy generation, and other parameters, such as velocity, temperature, and concentration, have been discussed in detail. A greater α can lead to a larger thermal conductivity normal to the walls of channel and a more uniform temperature field. However, the velocity of magnetic nanofluid tends to decrease. There is a t...

A novel Sn2Sb2O7 nanophotocatalyst for visible-light-driven H2 evolution

AbstractA novel pure cubic-phase pyrochlore structure tin(II) antimonate nanophotocatalyst, stoichiometric Sn2Sb2O7, has been prepared by a modified ion-exchange process using an antimonic acid precursor, and employed in visible-light-driven photocatalytic H2 evolution for the first time. The physicochemical properties (crystal phase, chemical composition and state, textural properties, and optical properties) of the material were investigated by different instrumental techniques. Compared with the antimonic acid precursor, the as-prepared Sn2Sb2O7 had a narrower bandgap, smaller crystal size, and larger BET surface area. The as-prepared Sn2Sb2O7 was validated as a promising candidate for visible-light-driven photocatalytic H2 evolution with a constant rate of 40.10 μmol·h−1·gcat−1.

Photocatalytic hydrogen production over CdS: effects of reaction atmosphere studied by in situ Raman spectroscopy

CdS is a well-known and efficient photocatalyst for photocatalytic hydrogen production. However, CdS is prone to photocorrosion in the photocatalytic reaction, in which CdS itself is oxidized by the photogenerated holes. Most of the work reported, to date, has focused only on the structure of CdS. However, less attention was paid to the kinetic changes of CdS during the photocatalytic reaction, which, in our opinion, is a crucial step for its practical utilization. In this report, we have developed a facile in situ Raman analysis, aiming to clarify the microstructural changes of CdS during the photocatalytic reaction process. In this study, photocatalytic hydrogen production over CdS in an Ar or air atmosphere was studied using various techniques in addition to in situ Raman spectroscopy. With Raman spectroscopy, a significant increase in the surface lattice strain of CdS was only observed when it was exposed to air, while the electron–phonon interactions remained the same regardless of the atmosphere. A direct correlation between the interfacial crystal lattice and photocorrosion of the CdS photocatalyst during photocatalytic hydrogen production was found based on our in situ Raman investigation. Finding the photocorrosion of the CdS photocatalyst at its very early stage using our in situ Raman technique is expected to provide meaningful guidance for the design of active and stable chalcogenide photocatalysts, which, however, cannot be achieved using traditional characterization techniques.

Tin(II) Antimonates with Adjustable Compositions: Effects of Band‐Gaps and Nanostructures on Visible‐Light‐Driven Photocatalytic H2 Evolution

A series of tin(II)–antimonate photocatalysts with varied Sn content were prepared by altering the ion‐exchange time and reaction temperature to control their physicochemical properties, especially their band‐gaps and nanostructures. Furthermore, the effect of these catalysts on visible‐light‐driven photocatalytic H2‐evolution was also investigated. With an increase in Sn content, the narrowed band‐gaps enhanced the absorption of photons to excite the photogenerated charge carriers. A decrease in nanocrystal size approaching stoichiometric compositions impeded the recombination of the photogenerated charge carriers; the increased surface areas and pore volumes, owing to the nanostructural transformation, accelerated the redox reactions. Consequently, the photocatalytic activities gradually improved and the highest rate was observed for stoichiometric Sn2Sb2O7. As a result, the as‐prepared tin(II) antimonates—especially Sn2Sb2O7—were confirmed to be stable and efficient photocatalysts for visible‐light‐driven H2 evolution. Moreover, the activities of these photocatalysts could be improved by tuning their physicochemical properties to jointly optimize all of the processes in the photocatalytic reaction.