Synthesis and Catalytic Applications of Non-Metal Doped Mesoporous Titania

Abstract

Mesoporous titania (mp-TiO 2 ) has drawn tremendous attention for a diverse set of applications due to its high surface area, interfacial structure, and tunable combination of pore size, pore orientation, wall thickness, and pore connectivity. Its pore structure facilitates rapid diffusion of reactants and charge carriers to the photocatalytically active interface of TiO 2 . However, because the large band gap of TiO 2 limits its ability to utilize visible light, non-metal doping has been extensively studied to tune the energy levels of TiO 2 . While first-principles calculations support the efficacy of this approach, it is challenging to efficiently introduce active non-metal dopants into the lattice of TiO 2 . This review surveys recent advances in the preparation of mp-TiO 2 and their doping with non-metal atoms. Different doping strategies and dopant sources are discussed. Further, co-doping with combinations of non-metal dopants are discussed as strategies to reduce the band gap, improve photogenerated charge separation, and enhance visible light absorption. The improvements resulting from each doping strategy are discussed in light of potential changes in mesoporous architecture, dopant composition and chemical state, extent of band gap reduction, and improvement in photocatalytic activities. Finally, potential applications of non-metal-doped mp-TiO 2 are explored in water splitting, CO 2 reduction, and environmental remediation with visible light.

Band edge positions as a key parameter to a systematic design of heterogeneous photocatalyst

“…Nonmetal doping can broaden the visible light absorption region by raising the valence band edge significantly if the nonmetal has a comparable radius and lower electronegativity compared to the nonmetal ions in the photocatalyst structure [47]. For example, nitrogen, carbon and fluorine have been cited in the literatures as an effective nonmetal doping of the semiconductor TiO2 due to their comparably radius (rN = 0.75, rC = 0.77, rF = 0.72) and lower electronegativity (ENN = 3.0, ENC= 2.5, ENF = 4.0) compared to the oxygen atom (ro = 0.73, ENo = 3.5) who forms the TiO2 valence band [48].…”

“…Mid gap approximation for non-metal doped. The mid gap positions of different non-metal anions have been taken from[47]. Surface sensitization electrode potential requirements.…”

First-Principles View on Photoelectrochemistry: Water-Splitting as Case Study

“…For more detailed discussion about mono-doping and co-doping effects on the photocatalytic properties of TiO 2 , we refer the reader to the review articles of Ref. [89][90][91]. Meng et al [92] used Cu dopants to move the conduction band minimum (CBM) of α-Fe 2 O 3 above the hydrogen redox level, while Ti dopants create very shallow donor levels and chang the band-gap slightly.…”

Kinetic studies on using photocatalytic coatings for removal of indoor volatile organic compounds

“…Typically, there are two types of doped impurity elements in TiO2: metals and non-metals. Metals includes manganese, iron, cobalt, and nickel [14,15], and non-metals include boron, carbon and nitrogen [16][17][18][19]. The metal and non-metal elements can also be co-doped in TiO2, e.g., iron-nitrogen co-doped [20], which helps to further reduce the band-gap and improve the photocatalytic activity.…”