Synergistic effect of B-TiO2 and MIL-100(Fe) for high-efficiency photocatalysis in methylene blue degradation

Nowadays, the magnetic properties of solids play a main role in different kinds of applications. In particular, magnetic order, like ferromagnetism (FM) or antiferromagnetism (AFM), is a phenomenon that attracts the interest of a large scientific community. From the materials research side, there is still the need of new materials with magnetic order above room temperature (RT). Interestingly, although there are a large number of magnetic compounds including oxides with ordering temperatures above RT (especially with transition metals like Fe, Co, Ni, etc.), its percentage with respect to the total number of magnetically ordered materials remains rather small. From the theoretical side, magnetic order still belongs to one of the most complex phenomena in solid-state physics. Its origin is given by the exchange interaction, a quantum mechanical mechanism

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pssb.201900623

Defect-Induced Magnetism in Nonmagnetic Oxides: Basic Principles, Experimental Evidence, and Possible Devices with ZnO and TiO 2

Nanostructured metal sulfides have been widely studied due to their unique electrical, chemical, magnetic and optical properties and the promising application prospects. Pyrite iron disulfide (FeS2) receives high attention because of its suitable band gap, exceptionally high optical absorption coefficient in the visible region and the advantages of earth abundance, nontoxicity and low fabrication cost. It exhibits promising applications in photovoltaics, rechargeable batteries, dye-sensitized solar cells, photodetectors, photocapacitors and photocatalysis. This paper provides a comprehensive review of the FeS2 nanostructures, including the preparation methods, properties and applications. We begin from a short background of FeS2, describing the structure, fundamental physical, chemical and electronic properties. Then a detailed investigation of FeS2 nanostructures with different shapes and the corresponding methods are described. Finally, the application prospects of FeS2 nanostructures in plentiful novel devices are introduced.

Pyrite FeS2 nanostructures: Synthesis, properties and applications

Making semiconductors ferromagnetic has been a long dream. One approach is to dope semiconductors with transition metals (TM). TM ions act as local moments and they couple with free carriers to develop collective magnetism. However, there are no fundamental reasons against the possibility of local moment formation from localized sp states. Recently, ferromagnetism was observed in nonmagnetically doped, but defective semiconductors or insulators including ZnO and TiO2. This kind of observation challenges the conventional understanding of ferromagnetism. Often the defect-induced ferromagnetism has been observed in samples prepared under non-optimized condition, i.e. by accident or by mistake. Therefore, in this field theory goes much ahead of experimental investigation. To understand the mechanism of the defect-induced ferromagnetism, one needs a better controlled method to create defects in the crystalline materials. As a nonequilibrium and reproducible approach of inducing defects, ion irradiation provides such a possibility. Energetic ions displace atoms from their equilibrium lattice sites, thus creating mainly vacancies, interstitials or antisites. The amount and the distribution of defects can be controlled by the ion fluence and energy. By ion irradiation, we have generated defect-induced ferromagnetism in ZnO, TiO2 and SiC. In this short review, we also summarize some results by other groups using energetic ions to introduce defects, and thereby magnetism in various materials. Ion irradiation combined with proper characterizations of defects could allow us to clarify the local magnetic moments and the coupling mechanism in defective semiconductors. Otherwise we may have to build a new paradigm to understand the defect-induced ferromagnetism.

Defect-induced ferromagnetism in semiconductors: a controllable approach by particle irradiation

Oxygen vacancies and Ti-related defects (OTDs) are the main lattice defects of , which have great influence on its photocatalytic activity. To understand the relationship between the defects and photocatalytic activities, detailed discussions based on the electronic driven force provided by these defects are carried out during the three commonly accepted processes in photocatalytic reactions. It is found that these defects inevitably (i) influence the energy structure of the pristine as the isolate acceptor/donor level or hybrid with the original orbital, (ii) provide a disordered short-range force that confuses the charge carriers transferring to surface active sites, (iii) act not only as the surface active sites for trapping the charge carriers but also as the main chemisorption sites for , , and organic species. These effects of the defects make them one of the key factors that determine the efficiency of heterogeneous photocatalysis. Clarifying the role of the defects will further facilitate the exploration and the construction of high-performance photocatalysts for practical applications.

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Function of Lattice Defects toward Photocatalytic Processes: View of Electronic Driven Force

The magnetic properties and defect types of virgin and N-doped TiO2 single crystals are probed by superconducting quantum interference device (SQUID), X-ray photoelectron spectroscopy (XPS), and positron annihilation analysis (PAS). Upon N doping, a twofold enhancement of the saturation magnetization is observed. Apparently, this enhancement is not related to an increase in oxygen vacancy, rather to unpaired 3d electrons in Ti3+, arising from titanium vacancies and the replacement of O with N atoms in the rutile structure. The production of titanium vacancies can enhance the room temperature ferromagnetism (RTFM), and substitution of O with N is the onset of ferromagnetism by inducing relatively strong ferromagnetic ordering.

https://iopscience.iop.org/article/10.1088/1674-1056/22/3/037504/pdf

Defect types and room temperature ferromagnetism in N-doped rutile TiO2 single crystals

This paper reports how pyrite films were prepared by thermal sulfurization of magnetron sputtered iron films and characterized by x-ray absorption near edge structure spectra and x-ray photoelectron spectroscopy on a 4B9B beam line at the Beijing Synchrotron Radiation Facility. The band gap of the pyrite agrees well with the optical band gap obtained by a spectrophotometer. The octahedral symmetry of pyrite leads to the splitting of the d orbit into t2g and eg levels. The high spin and low spin states were analysed through the difference of electron exchange interaction and the orbital crystal field. Only when the crystal field splitting is higher than 1.5 eV, the two weak peaks above the white lines can appear, and this was approved by experiments in the present work.

https://iopscience.iop.org/article/10.1088/1674-1056/18/7/018/pdf

X-ray absorption near the edge structure and x-ray photoelectron spectroscopy studies on pyrite prepared by thermally sulfurizing iron films

The design of a pulsing system for an intense slow positron beam is described in this paper. Slow positron annihilation lifetime measurement is an important method to study the depth-dependent characteristics of the surface and near surface. The start signal for slow positron lifetime measurement can be obtained from the pulsing system, which consists of a reflection type chopper, a prebuncher and a buncher. On the basis of the simulation of dynamics process by Parmela, the frequency of the buncher and the positron energy have been chosen to be 150MHz and 330eV respectively. The designed time resolution of this system is about 150ps (FWHM).

王宝义

Papers

Defect types and room temperature ferromagnetism in N-doped rutile TiO2 single crystals

X-ray absorption near the edge structure and x-ray photoelectron spectroscopy studies on pyrite prepared by thermally sulfurizing iron films

Design of a Pulsing System for Beijing Intense Slow Positron Beam