The remarkable achievement by Fujishima and Honda (1972) in the photo-electrochemical water splitting results in the extensive use of TiO 2 nanomaterials for environmental purification and energy storage/conversion applications. Though there are many advantages for the TiO 2 compared to other semiconductor photocatalysts, its band gap of 3.2 eV restrains application to the UV-region of the electromagnetic spectrum ( λ  ≤ 387.5 nm). As a result, development of visible-light active titanium dioxide is one of the key challenges in the field of semiconductor photocatalysis. In this review, advances in the strategies for the visible light activation, origin of visible-light activity, and electronic structure of various visible-light active TiO 2 photocatalysts are discussed in detail. It has also been shown that if appropriate models are used, the theoretical insights can successfully be employed to develop novel catalysts to enhance the photocatalytic performance in the visible region. Recent developments in theory and experiments in visible-light induced water splitting, degradation of environmental pollutants, water and air purification and antibacterial applications are also reviewed. Various strategies to identify appropriate dopants for improved visible-light absorption and electron–hole separation to enhance the photocatalytic activity are discussed in detail, and a number of recommendations are also presented.

/pdf/visible-light-activation-of-tio2-photocatalysts-advances-in-37hmh9krsz.pdf

Visible-light activation of TiO2 photocatalysts: Advances in theory and experiments

As an alternative to the gold standard TiO2 photocatalyst, the use of zinc oxide (ZnO) as a robust candidate for wastewater treatment is widespread due to its similarity in charge carrier dynamics upon bandgap excitation and the generation of reactive oxygen species in aqueous suspensions with TiO2. However, the large bandgap of ZnO, the massive charge carrier recombination, and the photoinduced corrosion–dissolution at extreme pH conditions, together with the formation of inert Zn(OH)2 during photocatalytic reactions act as barriers for its extensive applicability. To this end, research has been intensified to improve the performance of ZnO by tailoring its surface-bulk structure and by altering its photogenerated charge transfer pathways with an intention to inhibit the surface-bulk charge carrier recombination. For the first time, the several strategies, such as tailoring the intrinsic defects, surface modification with organic compounds, doping with foreign ions, noble metal deposition, heterostructuring with other semiconductors and modification with carbon nanostructures, which have been successfully employed to improve the photoactivity and stability of ZnO are critically reviewed. Such modifications enhance the charge separation and facilitate the generation of reactive oxygenated free radicals, and also the interaction with the pollutant molecules. The synthetic route to obtain hierarchical nanostructured morphologies and study their impact on the photocatalytic performance is explained by considering the morphological influence and the defect-rich chemistry of ZnO. Finally, the crystal facet engineering of polar and non-polar facets and their relevance in photocatalysis is outlined. It is with this intention that the present review directs the further design, tailoring and tuning of the physico-chemical and optoelectronic properties of ZnO for better applications, ranging from photocatalysis to photovoltaics.

/pdf/zinc-oxide-based-photocatalysis-tailoring-surface-bulk-xudspiii2k.pdf

Zinc oxide based photocatalysis: tailoring surface-bulk structure and related interfacial charge carrier dynamics for better environmental applications

Using elliptical iron glycolate nanosheets as precursors, elliptical Fe3O4/C core-shell nanorings (NRs) [25 ± 10 nm in wall thickness, 150 ± 40 nm in length, and 1.6 ± 0.3 in long/short axis ratio] are synthesized via a one-pot hydrothermal route. The surface-poly(vinylpyrrolidone) (PVP)-protected-glucose reduction/carbonization/Ostwald ripening mechanism is responsible for Fe3O4/C NR formation. Increasing the glucose/precursor molar ratio can enhance carbon contents, causing a linear decrease in saturation magnetization (Ms) and coercivity (Hc). The Fe3O4/C NRs reveal enhanced low-frequency microwave absorption because of improvements to their permittivity and impedance matching. A maximum RL value of -55.68 dB at 3.44 GHz is achieved by Fe3O4/C NRs with 11.95 wt % C content at a volume fraction of 17 vol %. Reflection loss (RL) values (≤-20 dB) are observed at 2.11-10.99 and 16.5-17.26 GHz. Our research provides insights into the microwave absorption mechanism of elliptical Fe3O4/C core-shell NRs. Findings indicate that ring-like and core-shell nanostructures are promising structures for devising new and effective microwave absorbers.

Facile Hydrothermal Synthesis of Fe3O4/C Core-Shell Nanorings for Efficient Low-Frequency Microwave Absorption.

Photocatalysis for solar-driven reactions promises a bright future in addressing energy and environmental challenges. The performance of photocatalysis is highly dependent on the design of photocatalysts, which can be rationally tailored to achieve efficient light harvesting, promoted charge separation and transport, and accelerated surface reactions. Due to its unique feature, semiconductors with hollow structure offer many advantages in photocatalyst design including improved light scattering and harvesting, reduced distance for charge migration and directed charge separation, and abundant surface reactive sites of the shells. Herein, the relationship between hollow nanostructures and their photocatalytic performance are discussed. The advantages of hollow nanostructures are summarized as: 1) enhancement in the light harvesting through light scattering and slow photon effects; 2) suppression of charge recombination by reducing charge transfer distance and directing separation of charge carriers; and 3) acceleration of the surface reactions by increasing accessible surface areas for separating the redox reactions spatially. Toward the end of the review, some insights into the key challenges and perspectives of hollow structured photocatalysts are also discussed, with a good hope to shed light on further promoting the rapid progress of this dynamic research field.

https://espace.library.uq.edu.au/view/UQ:7823631/UQ7823631_OA.pdf

Hollow Nanostructures for Photocatalysis: Advantages and Challenges.

Among the most challenging problems that human beings appear to face are depleting energy sources and increasing environmental pollutions. Heterogeneous photocatalytic processes are the most reward...

Magnetically separable nanocomposites based on ZnO and their applications in photocatalytic processes: A review

Magnetic nest-like γ-Fe2O3/ZnO double-shelled hollow nanostructures have been successfully synthesized via a multi-step process. The materials have been thoroughly characterized by different techniques. These interesting nest-like hollow nanostructures are composed of ZnO nanoflakes grown on the surface of γ-Fe2O3 hollow spheres. Importantly, these magnetic hollow nanostructures show very high visible-light photocatalytic activity for the degradation of different organic dyes including methylene blue (MB), Rhodamine-B (RhB), and methyl orange (MO). It is further demonstrated that these γ-Fe2O3/ZnO hybrid photocatalysts are highly stable and can be used repeatedly.

A magnetically separable photocatalyst based on nest-like γ-Fe2O3/ZnO double-shelled hollow structures with enhanced photocatalytic activity

We report a novel strategy for fabrication of one-dimensional (1D) Fe3O4/C/CdS coaxial nanochains via a magnetic field-induced assembly and microwave-assisted deposition method. First, 1D pearl chain-like Fe3O4/C core–shell nanocables are successfully assembled via the hydrothermal reaction of Fe3O4 nanospheres and glucose in water in the presence of an external magnetic field. The carbonaceous layer is about 10 nm in thickness, and it acts as the stabilizer for the Fe3O4 nanochains. Afterwards, CdS nanoparticles are facilely deposited onto the 1D Fe3O4/C nanochains via a rapid microwave-irradiation route to form 1D Fe3O4/C/CdS coaxial nanochains. Further investigation has revealed that these magnetic nanocomposites possess significantly improved activity as a recyclable photocatalyst for the degradation of organic pollutants when exposed to visible light irradiation. This new synthesis strategy is not restricted to the specific material discussed in this work and should be versatile for a wide range of magnetically separable photocatalysts containing 1D magnetic nanochains as the support and an outer layer of active semiconductor nanocrystals.

Magnetic-field induced formation of 1D Fe3O4/C/CdS coaxial nanochains as highly efficient and reusable photocatalysts for water treatment

Twinning is an important deformation mechanism for Mg alloys, which is intimately related to their mechanical behaviors, such as yield strength, strain hardening, ductility and so on. Therefore, a fundamental understanding of twinning behavior and mechanism under various conditions is essential for improving the mechanical properties of Mg alloys. This study aims to extend understanding the mechanism of {10–12} twin variant selection and twin patterns in compression of basal textured AZ31 Mg alloy sheet along transverse direction. Various twin patterns such as independent or intersecting multi-twins in a grain, paired twins in two neighboring grains, and twin chains across many grains were observed in the 3% compressed AZ31 sample. The variant selection of {10–12} twins in the various twin patterns were studied by a combined analysis of Schmid factor and strain compatibility factor, m′. Multiple twin variants can be formed in a grain and the non-Schmid twin variant could be induced by the impingement of a neighboring twin at grain boundary. Paired {10–12} twins are likely formed when the Schmid factors of both twins and their strain compatibility factor are very high. The paired twins can propagate throughout the grains and transfer to more neighboring grains (termed as twin–twin transfer behavior). Such continuous twin–twin transfer behavior across more than three neighboring grains results in the formation of twin chains. In addition, strain accommodation among the different twin variants in the same grain, and the orientation relationship between the paired twins and their common grain boundary direction are discussed. A comprehensive understanding of the twin patterns and variant selection was achieved by such a combined analysis of Schmid factor and strain accommodation factor.

Understanding of variant selection and twin patterns in compressed Mg alloy sheets via combined analysis of Schmid factor and strain compatibility factor

Changfa Guo

Papers

A magnetically separable photocatalyst based on nest-like γ-Fe2O3/ZnO double-shelled hollow structures with enhanced photocatalytic activity

Magnetic-field induced formation of 1D Fe3O4/C/CdS coaxial nanochains as highly efficient and reusable photocatalysts for water treatment

Understanding of variant selection and twin patterns in compressed Mg alloy sheets via combined analysis of Schmid factor and strain compatibility factor

Characteristics of long {10-12} twin bands in sheet rolling of a magnesium alloy

Magnetite (Fe3O4) tetrakaidecahedral microcrystals: Synthesis, characterization, and micro-Raman study