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

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

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Triplet ground state of the neutral oxygen-vacancy donor in rutile TiO 2

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

曹兴忠

Papers

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