The prospect of engineering the bandgap in semiconductor nanostructures all the way from ultraviolet to visible is highly significant in various applications such as photocatalysis, sensing, optoelectronics and biomedical applications. Since many semiconductors have their bandgaps in the UV region, various techniques are used to tune their bandgaps to the visible region. Doping and co-doping with metals and non-metals have been found to be highly effective in bandgap narrowing as doping creates a continuum of mid-bandgap states which effectively reduces the bandgap. Other than these techniques, the modulation of intrinsic vacancies is an effective way to control the bandgap. Among all semiconductors, titanium dioxide (TiO2) is a well-studied material for UV photocatalytic applications. TiO2 has oxygen and titanium vacancies as intrinsic defects which influence the bandgap based on its phase of existence. The oxygen vacancies generate unpaired electrons associated with Ti3+ species, resulting in the creation of donor levels within the bandgap. Trivacancies give a p-type nature to TiO2 due to excess holes and generate acceptor levels in the bandgap. The existence of a continuum of such intrinsic defect states within the bandgap appears to narrow the bandgap and enhances the visible light absorption in TiO2, although the effect is an apparent narrowing. Doping and co-doping of TiO2 with metals such as Au, Ag, Fe, Co, Ni, Pt and Pd and non-metals such as B, C, N, Br and Cl, doping with Ti3+ ions and hydrogenation have all been found to narrow the bandgap of TiO2. In this review, we focus on such intrinsic vacancy-modulated bandgap narrowing in TiO2. This review covers significant recent advancements in bandgap engineering of TiO2.

A review on optical bandgap engineering in TiO2 nanostructures via doping and intrinsic vacancy modulation towards visible light applications

The determination of the most stable structures of metal clusters supported at solid surfaces by computer simulations represents a formidable challenge due to the complexity of the potential-energy surface. Here, we combine a high-dimensional neural network potential, which allows us to predict the energies and forces of a large number of structures with first-principles accuracy, with a global optimization scheme employing genetic algorithms. This very efficient setup is used to identify the global minima and low-energy local minima for a series of copper clusters containing between four and ten atoms adsorbed at the ZnO(101¯0) surface. A series of structures with common structural features resembling the Cu(111) and Cu(110) surfaces at the metal-oxide interface has been identified, and the geometries of the emerging clusters are characterized in detail. We demonstrate that the frequently employed approximation of a frozen substrate surface in global optimization can result in missing the most relevant structures.

Global optimization of copper clusters at the ZnO(101¯0) surface using a DFT-based neural network potential and genetic algorithms

The invention relates to a clean process method for extracting vanadium, chromium and iron from vanadium slag step by step. The clean process method comprises the following steps of: selectively oxidizing the vanadium slag to obtain a roasted product; leaching the obtained roasted product by using a leaching agent to extract vanadium, carrying out liquid-solid separation to obtain vanadium-containing leach liquor and vanadium-extracted tailings, and carrying out product transformation on the vanadium-containing leach liquor to prepare vanadium series products; adding the obtained vanadium-extracted tailings and a silicon fixing agent to a sodium hydroxide solution, selectively fixing silicon, then oxidizing to extract chromium, then carrying out liquid-solid separation to obtain chromium-containing leach liquor and chromium-extracted tailings, and carrying out product transformation on the chromium-containing leach liquor to prepare chromium series products; mixing the chromium-extracted tailings with a reducing agent, and carrying out magnetizing roasting and magnetic separation to obtain silicon slag and ion concentrate powder/iron-enriched slag/reduced iron powder. The clean process method disclosed by the invention realizes the step-by-step extraction and high-efficiency separation of valuable components such as vanadium, chromium and iron which are contained in the vanadium slag, prevents the mutual entrainment of vanadium, chromium and iron products; in addition, the clean process method disclosed by the invention realizes the near zero discharge of waste water and the recycling of final slag and is clean and pollution-free.

Clean process method for extracting vanadium, chromium and iron from vanadium slag step by step

Semiconductor-based heterojunction photocatalysts with a special active crystal surface act as an essential part in environmental remediation and renewable energy technologies. In this study, an RGO/CdS/TiO2 step-scheme with high energy {001} TiO2 facets was successfully fabricated via a microwave-assisted solvothermal method. The photocatalytic performance of as-prepared samples was assessed by degrading methylene blue under visible light irradiation. We found that the photocatalytic activity of the RGO/CdS/TiO2 step-scheme heterojunction was related to the proportion of TiO2. A ternary sample with a TiO2 content of 10 wt% exhibited superior photocatalytic performance, and approximately 99.7% of methylene blue was degraded during 50 min of visible illumination which was much higher than the percentages found for TiO2, CdS, RGO/TiO2, and RGO/CdS. The greatly improved photocatalytic performance is due to the exposure of the reactive {001} surface of TiO2 and the formation of a CdS/TiO2 heterojunction step-scheme, which effectively inhibits the recombination of charge carriers at the heterogeneous interfaces. Moreover, the incorporation of graphene further enhances the visible light harvesting and serves as an electron transport channel for rapidly separating photogenerated carriers. Based on the PL, XPS, photoelectrochemical properties and the free radical capturing experiment results, a possible photodegradation mechanism was proposed.

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Microwave-assisted synthesis of an RGO/CdS/TiO2 step-scheme with exposed TiO2 {001} facets and enhanced visible photocatalytic activity

The invention discloses a method for separating and recovering vanadium and chromium from vanadium-chromium slag. The method comprises the following steps: (1) carrying out first roasting on the vanadium-chromium slag and first sodium-containing materials and carrying out solid-liquid separation after leaching the product obtained after first roasting in water, thus obtaining first solid phases and a first liquid phase; (2) carrying out solid-liquid separation after carrying out vanadium precipitation on the first liquid phase, thus obtaining second solid phases and a second liquid phase; (3) carrying out secondary roasting on the first solid phases and second sodium-containing materials and carrying out solid-liquid separation after leaching the product obtained after secondary roasting in water, thus obtaining third solid phases and a third liquid phase; (4) carrying out solid-liquid separation after contacting the second liquid phase with the third liquid phase and carrying out precipitation, thus obtaining fourth solid phases and a fourth liquid phase; (5) calcining the second solid phases and the fourth solid phases and extracting vanadium; and (6) reducing the fourth liquid phase and precipitating chromium. By the method, vanadium and chromium can be simply separated and recovered from the vanadium-chromium slag at high yield.

Method for separating and recovering vanadium and chromium from vanadium-chromium slag

Black TiO2 has attracted widespread attention due to its visible light absorption and wide range of applications. However, the currently reported preparation methods for black TiO2 are not suitable for large-scale production due to its being prepared under high vacuum and over a long time. We have successfully prepared black TiO2 under normal pressure and short time conditions. The as-prepared black titanium dioxide was characterized by XRD, XPS, TEM, UV-visible absorption spectrum and other characterization methods. The result shows that the as prepared black titanium dioxide had a disordered structure and oxygen vacancy defects on the surface, and exhibits excellent visible and near infrared absorption performance. The black TiO2 sample was prepared under 650 °C 60 min exhibits excellent visible light photocatalytic performance, and can degrade 56% MO after visible light irradiation for 120 min.

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A facile method for the preparation of black TiO2 by Al reduction of TiO2 and their visible light photocatalytic activity

The invention relates to a method for recycling vanadium-chromium resources, belonging to the field of resource recycling. The invention aims at providing a method for recycling vanadium-chromium resources. The method for recycling vanadium-chromium resources comprises the following steps: a. mixing vanadium-chromium slag with calcium carbonate to obtain a primary mixture material, and oxidizing-roasting the primary mixture material to obtain a primary roasting clinker; b. performing acid leaching to the primary roasting clinker to obtain acid leaching liquor and acid leaching slag; c. drying acid leaching slag, grinding and mixing together with sodium carbonate to obtain a secondary mixture material, oxidizing-roasting the secondary mixture material to obtain secondary roasting clinker; d. performing water leaching to the secondary roasting clinker, to obtain water leaching liquor and water leaching slag; and e. respectively separating and extracting vanadium, chromium and iron from the acid leaching liquor, water leaching liquor and water leaching slag. The method for recycling vanadium-chromium resources has the advantages of being high in vanadium and chromium recycling rate, simple in technology, low in equipment requirement, less in environmental pollution and the like.

Method for recycling vanadium-chromium resources

The invention belongs to the technical field of metallurgy, and relates to a titanium alloy material and a preparation method thereof, in particular to a titanium-silicon alloy and a preparation method thereof The titanium-silicon alloy material comprises, by weight, 37-60 parts of Ti and 40-63 parts of Si The preparation method of the titanium-silicon alloy material comprises the following steps of a, preparing materials, b, mixing uniformly, c, roasting and d, cooling, wherein in the step a, 357-385 parts of titanium pigment, 269-32 parts of silicon powder and 25-346 parts of calcium oxide, by weight, are taken; in the step b, the materials prepared in the step a are mixed uniformly; in the step c, the raw materials mixed uniformly in the step b are roasted, the roasting temperature is 1450-1600 degrees and the roasting time is 10-30min; in the step d, the raw materials after the roasting in the step c are cooled, and effective separation between the titanium-silicon alloy and slag is realized The titanium-silicon alloy is prepared through one-step synthesis by employing an electro-silicothermic process to reduce titanium pigment, the preparation method is simple in technology, the preparation of the titanium-silicon alloy is not required to be carried out in an inert gas or vacuum environment, the energy consumption is low, the titanium-silicon alloy can be produced and prepared in scale, and the titanium-silicon alloy and the preparation method have great application prospects

Aluminum-silicon alloy material and preparation method thereof

Method for preparing titanium-aluminum alloy

We used a revised genetic algorithm (GA) to explore the potential energy surface (PES) of AuxM− (x = 9–12; M = Si, Ge, Sn) clusters. The most interesting finding in the structural study of AuxSi− (x = 9–12) is the 3D (Au9Si− and Au10Si−) → quasi-planar 2D (Au11Si− and Au12Si−) structural evolution of the Si-doped clusters, which reflects the competition of Au–Au interactions (forming a 2D structure) and Au–Si interactions (forming a 3D structure). The AuxM− (x = 9–12; M = Ge, Sn) clusters have quasi-planar structures, which suggests a lower tendency of sp3 hybridization and a similarity of electronic structure for the Ge or Sn atom. Au9Si− and Au10Si− have a 3D structure, which can be viewed as being built from Au8Si− and Au9Si− with an extra Au atom bonded to a terminal gold atom, respectively. In contrast, the quasi-planar structures of AuxM− (x = 9–12; M = Ge, Sn) reflect the domination of the Au–Au interactions. Including the spin–orbit (SO) effects is very important to calculate the simulated spectrum (structural fingerprint information) in order to obtain quantitative agreement between theoretical and future experimental PES spectra.

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Huang Ping

Papers

A facile method for the preparation of black TiO2 by Al reduction of TiO2 and their visible light photocatalytic activity

Method for recycling vanadium-chromium resources

Aluminum-silicon alloy material and preparation method thereof

Method for preparing titanium-aluminum alloy

Structural exploration of AuxM− (M = Si, Ge, Sn; x = 9─12) clusters with a revised genetic algorithm