The effect of cobalt doping on the efficiency of semiconductor oxides in the photocatalytic water remediation

Abstract The effect of cobalt doping on semiconductors materials synthesized via solution and hydrothermal methods was investigated by testing its photocatalytic efficiency on pollutants abatement. X Ray Diffraction technique was used to evaluate samples crystallographic phases allowing to identify different species due to the introduction of the dopants. Diffuse Reflectance UV–vis Spectroscopy was employed to determine the bandgap as well as the absorption corresponding to d-d transitions for cobalt doped systems. Finally, Electron Paramagnetic Resonance Spectroscopy was adopted to perform a pre-screening of the photoactivity of the prepared samples. The Co-doped TiO2 and ZnO materials photoactivity was assessed on phenol degradation, selected as pollutant probe, under UVA irradiation. Doping TiO2 with cobalt in low amounts (0.25% and 0.5%) prepared by hydrothermal method leads to an enhancement on phenol degradation. Also, the presence of Co-doped ZnO obtained by hydrothermal process if prepared with defined cobalt amount (0.5 or 1%) promote an increasing on phenol abatement. Ketoprofen was used to evaluate the doping effect, being the Co-doped ZnO material more efficient on ketoprofen mineralization comparing with bare material. The ketoprofen and its transformation products were easily abated and, in wastewater, they were completely eliminated within 1 h, endorsing that inserting cobalt can improve the ZnO photocatalysis efficiency for water remediation

Rare earth ions doped ZnO: Synthesis, characterization and preliminary photoactivity assessment

This work reports the effect of doping zinc oxide with lanthanide ions on structural, EPR and UV visible properties. Bare and doped samples were synthesized using the simple and green hydrothermal process. Different rare earth ions (RE = La, Ce, Pr, Er and Yb) with 1% molar ratio RE/Zn were used. The samples have been studied using X Ray Diffraction, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and UV visible diffuse reflectance spectroscopy. Finally, electron paramagnetic resonance (EPR) spectroscopy, was used to assess the materials photoactivity under UV irradiation, both in solid state, to see the charge carriers’ generation and in solution, evaluating the OH• radical formation using the DMPO (5,5-Dimethyl-1-Pyrroline-N-Oxide) spin trapping technique. The results suggest that the synthesized materials could be interesting systems for the photocatalytic abatement of emerging organic persistent pollutants in wastewater treatment plants

Photocatalytic performances of rare earth element-doped zinc oxide toward pollutant abatement in water and wastewater

The photocatalytic performance of pristine and rare earth elements (La, Ce, Pr, Er, Yb) doped zinc oxide was tested toward the abatement of a model pollutant in MilliQ water and wastewater matrices. ZnO doped with Ce, Er and particularly with Yb exhibited photoactivity higher than bare zinc oxide and the benchmark TiO2 P25, especially in wastewater matrix. Several electrochemical investigations were performed via chronopotentiometry and cyclic voltammetry aimed to shed light on the reasons why the diverse materials behaved differently. From the overall data a complex picture emerged, where there is not a single property of the materials evidently outperforming the others. Nonetheless, from the analysis of whole data a limited role of doping emerged for La and Pr, doping with Er improved the photocurrent, doping with Yb favored a better accumulation of photoelectrons, and doping with Ce promoted a faster electron transfer

Control of Membrane Fouling in Organics Filtration Using Ce-Doped Zirconia and Visible Light

Membrane fouling has been a major issue in the development of more efficient water treatment processes. Specifically in surface waters filtration, organic matter, such as humic-like substances, can cause irreversible fouling. Therefore, this study evaluates the activity of a photocatalytic layer composed of Ce-doped zirconia nanoparticles in improving the fouling resistance during filtration of an aqueous solution of humic acid (HA). These nanoparticles were prepared by hydrothermal and sol-gel processes and then characterized. Before the filtration experiments, the photodegradation of HA catalyzed by Ce-doped zirconia nanoparticles in dispersion was studied. It was observed that the sol-gel prepared Ce-ZrO2 exhibited higher HA removal in practically neutral pH, achieving 93% efficiency in 180 min of adsorption in the dark followed by 180 min under visible-light irradiation using light-emitting diodes (LEDs). Changes in spectral properties and in total organic carbon confirmed HA degradation and contributed to the proposal of a mechanism for HA photodegradation. Finally, in HA filtration tests, Ce-ZrO2 photocatalytic membranes were able to recover the flux in a fouled membrane using visible-light by degrading HA. The present findings point to the further development of anti-fouling membranes, in which solar light can be used to degrade fouling compounds and possibly contaminants of emerging concern, which will have important environmental implications

New insight into zinc oxide doped with iron and its exploitation to pollutants abatement

This study aims to investigate how the photocatalytic efficiency of zinc oxide can be improved by introducing doping species into its crystal lattice. New materials based on zinc oxide doped with iron, have been synthesized using different methods, characterized and tested toward the abatement of selected organic molecules. The different synthetic strategies followed comprised sol-gel, precipitation and hydrothermal processes, in order to identify which one is capable of guaranteeing the best photocatalytic performances.The photoactivity of the new semiconductors was firstly tested using phenol as a model molecule subjected to irradiation under UV-A light. Phenol abatement is particularly favoured when using ZnO prepared via hydrothermal method and doped with iron at 0.5%. These materials were then tested toward the elimination of ketoprofen, an emerging pollutant substance, from water and real wastewater. Ketoprofen and its transformation products are completely abated within 30 min in pure water or in 1 h in wastewater

New insight into zinc oxide doped with iron and its exploitation to pollutants abatement

This study aims to investigate how the photocatalytic efficiency of zinc oxide can be improved by introducing doping species into its crystal lattice. New materials based on zinc oxide doped with iron, have been synthesized using different methods, characterized and tested toward the abatement of selected organic molecules. The different synthetic strategies followed comprised sol-gel, precipitation and hydrothermal processes, in order to identify which one is capable of guaranteeing the best photocatalytic performances.The photoactivity of the new semiconductors was firstly tested using phenol as a model molecule subjected to irradiation under UV-A light. Phenol abatement is particularly favoured when using ZnO prepared via hydrothermal method and doped with iron at 0.5%. These materials were then tested toward the elimination of ketoprofen, an emerging pollutant substance, from water and real wastewater. Ketoprofen and its transformation products are completely abated within 30 min in pure water or in 1 h in wastewater

Comparison of the photocatalytic activity of ZnO/CeO2 and ZnO/Yb2O3 mixed systems in the phenol removal from water: a mechanicistic approach

In this paper we compare the photocatalytic activity of two semiconductors based on ZnO: ZnO/CeO2 and ZnO/Yb2O3. The two samples were prepared via hydrothermal synthesis and fully characterized by X-ray diffraction technique, diffuse reflectance Ultra Violet- Visible spectroscopy (UV-Vis), high resolution transmission electron microscopy and finally with electron paramagnetic resonance spectroscopy. The prepared materials were also tested in their photocatalytic performances both through Electron Paramagnetic Resonance (EPR) analyzing the formation of charge carriers and with the abatement of a probe molecule like phenol, in presence and in absence of scavengers