Rare earth co-doped ZnO photocatalysts: Solution combustion synthesis and environmental applications

Abstract

A novel europium (Eu) and terbium (Tb) co-doped ZnO nanoparticles had been synthesized by a facile, cost efficient and rapid combustion method. The physical and chemical properties of the as-synthesized nanoparticles were determined by XRD, SEM, EDS, BET, FTIR, XPS, UV-vis DRS, PL, EIS and photocurrent density. XRD patterns confirm that Eu and Tb ions are stably inserted into the framework of ZnO, and the crystallite size decreases to 21 nm compared to that of pure ZnO (32 nm) as the amount of co-dopants increases to optimal value (3 mol% of each). With the insertion of Eu and Tb ions into ZnO, the recombination rate of photo generated charge carriers is found to be low. It is observed that doped Eu and Tb ions can enter the lattice structure of ZnO with a suitable doping concentration, and the obtained doped ZnO have ordered hexagonal wurtzite structures and nearly spherical morphology with high specific surface area and high porosity. Meanwhile, the introduction of Eu and Tb ions can effectively extend the spectral response from UV to visible region for the catalysts, thus reducing the band gap from 3.25 to 2.91 eV. Further analysis by means of XPS measurement showed that the existence of mixture of Eu 2+/ Eu 3+ and Tb 3+/ Tb 4+ oxidation states and high content of the surface chemisorbed oxygen species also contributed to the high photocatalytic activity. It was found that Eu and Tb co-doped ZnO shows highly efficient and stable visible light activity and provides a 100% MB degradation within 15 min, while the degradation time for Eu doped ZnO and Tb doped ZnO is reduced gradually to 50 and 42 min, respectively to obtain the 100% MB degradation. It was also found that the photocatalytic hydrogen evolution activity over Eu and Tb co-doped ZnO can be significantly increased to 533.8 and 792 µmol with 0.2 wt% catalyst dose and initial solution pH 9, respectively under similar conditions with good stability. Moreover, simultaneous introduction of Eu and Tb effectively promoted the yield of CH 4 to 4.59 µmol, which was 3.4 fold higher in comparison to pure ZnO. Thus the present approach could provide a versatile strategy for the synthesis of novel and efficient visible light activated photocatalysts.

Synthesis of a New Phosphonate-Based Sorbent and Characterization of Its Interactions with Lanthanum (III) and Terbium (III)

“…In the case of Tb (III), the deconvolution is more difficult due to poorly resolved signals. More specifically, the analysis of the Tb 4 d 5/2 signal tends to indicate that two forms of Tb may coexist at ~149 eV and 152–151 eV; the REE may coexist as bound Tb (III) but also under its oxidized form, i.e., Tb (IV), respectively [ 68 , 69 ].…”

Highly Enhanced OER Performance by Er-Doped Fe-MOF Nanoarray at Large Current Densities

“…Importantly, the doping of rare-earth elements can effectively regulate the electronic and geometric structures of electrocatalysts, thus improving their electrical conductivity and internal catalytic activity. [22]. However, there still are few reports about enhancing the intrinsic OER activity of MOFs by rare-earth element doping, especially under large currents [23,24].…”

“…Xu et al reported that Ni–Fe–Ce–LDH microcapsules exhibited a high OER activity owing to the optimized electronic structure of 3D LDHs through Ce species doping [ 21 ]. Ahmad et al found that doped Eu and Tb ions could enter the lattice of ZnO, and the resulting ZnO had a large specific surface area and high porosity [ 22 ]. However, there still are few reports about enhancing the intrinsic OER activity of MOFs by rare-earth element doping, especially under large currents [ 23 , 24 ].…”

Direct Synthesis of Magnetic CoFe2O4 Nanoparticles as Recyclable Photo-Fenton Catalysts for Removing Organic Dyes

“…This method is essentially an exothermal redox reaction between fuels and oxidizers. 18 − 20 In general, the oxidizers are metal nitrates and the fuels are glycine, citric acid, urea, etc. 21 Additionally, the energy generated by exothermal reactions can be used to sustain the reaction system.…”