Abstract
TiO2 is a semiconductor material with high chemical stability and low toxicity. It is widely used in the fields of catalysis, sensing, hydrogen production, optics and optoelectronics. However, TiO2 photocatalyst is sensitive to ultraviolet (UV) light; this is why its photocatalytic activity and quantum efficiency are reduced. To enhance the photocatalytic efficiency in the visible light range as well as to increase the number of the active sites on the crystal surface or inhibit the recombination rate of photogenerated electron–hole pairs electrons, various metal ions were used to modify TiO2. This review paper comprehensively summarizes the latest progress on the modification of TiO2 photocatalyst by a variety of metal ions. Lastly, the future prospects of the modification of TiO2 as a photocatalyst are proposed.
Highlights
In the past, industrial development has been accompanied by the discharge of a large number of organic pollutants, which has caused great harm to the environment and living beings in general [1,2]
Researchers have proposed two ways to enhance the photocatalytic performance of titanium dioxide (TiO2): one is to prevent photogenerated electrons from recombining with photogenerated holes so that they can effectively participate in the catalytic degradation reaction process; the other is to introduce other elements into TiO2 lattice, thereby reducing the bandgap energy of the catalyst and expanding its photoresponse range
It has been previously reported that the modification of TiO2 with Zr can improve physicochemical characteristics including an increase in the specific surface area [156], decrease in crystallite size as a result of dissimilar coordination geometry and nuclei [157]; enhance surface acidity [158], the transition temperature between anatase and rutile [156,158], and the adsorption and the hydrophilic properties [159], and enhance thermal stability and imbalance of charge resulting from the formation of capture traps as well as the formation of Ti-O-Zr bonds
Summary
Industrial development has been accompanied by the discharge of a large number of organic pollutants, which has caused great harm to the environment and living beings in general [1,2]. These treatment methods have some shortcomings, and the treatment effect on organic wastewater is not very ideal. Recent studies have been devoted to a promising approach, the advanced oxidation processes (AOP) for the degradation of organic pollutants from wastewaters [3,4,5,6,7,8,9,10], due to its ability to completely mineralize the targeted pollutants [11]. AOPs are a chemical purification treatment used to remove inorganic/organic materials in wastewater and water via oxidation through reactions with hydroxyl radicals (·OH). Photocatalytic degradation is a part of AOP for the degradation of organic pollutants which has proven as an effective technology [15,16]. It is more effective in comparison with the AOP as it can mineralize various organic components and the semiconductors used are not expensive
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