Effect of Erbium on the Photocatalytic Activity of TiO₂/Ag Nanocomposites under Visible Light Irradiation

Abstract

Erbium co-doped TiO2 /Ag catalysts are synthesized by using a simple, one-step solvothermal method and characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, Raman analysis, X-ray photoelectron spectroscopy, and diffuse reflectance spectroscopy. The catalysts exhibit anatase crystal structures with increased visible light absorption compared with pure TiO2 . Enhanced photocatalytic activity is observed with Er co-doped TiO2 /Ag nanocomposites for Rhodamine B degradation under visible light irradiation. The photocatalytic activity of 1 % Er co-doped TiO2 /Ag is much higher than that of TiO2 /Ag, TiO2 /Er, pure TiO2 , and commercial Degussa P25. The kinetics of the degradation process are studied and the pseudo-first-order rate constant (k) and half-life time (t1/2 ) of the reaction are calculated. The enhanced activity might be accredited to the efficient separation of electron-hole pairs by silver and higher visible light absorption of TiO2 induced by Er.

Phase Equilibrium of TiO2 Nanocrystals in Flame‐Assisted Chemical Vapor Deposition

“…As a metastable form of titania, anatase has garnered considerable interest owing to its wide ranging applications, from dye‐sensitized solar cells and photoelectric chemical catalysis to chemical sensors . Doped TiO 2 can exhibit rich electronic, electrochemical, catalytic and photocatalytic properties that are the basis of many emerging applications.…”

Structure–Activity Relationships of Er3+ and MWCNT-Modified TiO2: Enhancing the Textural and Optoelectronic Properties of TiO2

“…Remarkable, is the shift of peak I in Er:TiO 2 from 529.5 to 527.7 eV, which is due to the Ti–O bond resulting from the interaction between TiO 2 and Er 3+ , where Er 3+ reduced Ti 4+ to Ti 3+ and Ti 2 O 3 has formed. Peaks II and III in the samples are a result of the presence of hydroxyl groups forming Ti–OH; as well as carbonyl and carboxylic species from the Er:TiO 2 /MWCNT nanocomposite. , …”

“…The shift to lower 2θ values in Er:TiO 2 has been argued to be due to Er 3+ ions successfully incorporating into the TiO 2 lattice . However, Er 3+ ions have a larger ionic radius (88 pm) than Ti 4+ (61 pm); therefore, it is unlikely that Er 3+ ions enter the lattice to replace Ti 4+ but instead migrate to the surface of TiO 2 during the crystallization process and form Ti–O–Er bonds from the small concentration of Er 2 O 3 segregating at the crystal boundary, which is in turn responsible for the decrease in particle sizes as it hinders TiO 2 crystal growth. , …”

“…The separation between the peaks is ∼5.8 eV, which intimates that Ti 4+ is the dominant state in the octahedral environment of anatase titania. 32,46 Additionally, the high intensity of the peaks at ∼458 and 464 eV (denoted I and III) in TiO 2 and Er:TiO 2 /MWCNT samples show that Ti 4+ is the dominant state, while the Ti 3+ component (denoted II and IV) has a minor relative contribution. However, in the Er:TiO 2 sample, Ti 3+ has a higher relative contribution than Ti 4+ .…”

“…31 However, Er 3+ ions have a larger ionic radius (88 pm) than Ti 4+ (61 pm); therefore, it is unlikely that Er 3+ ions enter the lattice to replace Ti 4+ but instead migrate to the surface of TiO 2 during the crystallization process and form Ti−O−Er bonds from the small concentration of Er 2 O 3 segregating at the crystal boundary, which is in turn responsible for the decrease in particle sizes as it hinders TiO 2 crystal growth. 32,33 The partial oxidation of the MWCNTs during synthesis of Er:TiO 2 /MWCNT may have provided for trace amounts of carbon to dope TiO 2 hence the decrease in unit cell parameters a and V of Er:TiO 2 /MWCNT and; the marked 2θ shift to higher values and the corresponding peak broadening with a smaller crystallite size. 34,35 A curious observation is the nonlinear lattice parameter variation: viz there is both an expansion and contraction of unit cell parameters, and therefore, Er 3+ doping cannot be unequivocally determined.…”