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The photochemical activity of the recently proposed CeO2–ZnO photocatalytic material active under visible light has been improved by means of significant modifications of its morphology. A polymeric templating agent (Pluronic) has been used in the synthesis obtaining a particle morphology based on hollow spheres that is better defined in the case of high template concentration. The charge separation ability and the light-induced surface electron transfer under irradiation with visible polychromatic light in various ranges of wavelengths has been investigated by electron paramagnetic resonance. The reactivity of the photogenerated holes has been monitored by the spin trapping technique in the presence of DMPO. The hollow spheres morphology achieved through the synthesis here reported leads to systems with a higher photoactivity under visible irradiation than the same system displaying the classic platelets morphology. A parallel increase of the photocatalytic activity of this novel system in pollution remediation reactions is therefore predictable.

Surface-functionalized nitrogen/carbon co-doped polymorphic TiO2 phase junction nanoparticles uniformly distributed in porous carbon matrix were synthesized by a simple one-step pyrolysis of titanium based metal–organic framework (MOF), NH2-MIL-125(Ti) at 700 °C under water vapour atmosphere. Introducing water vapour during the pyrolysis of NH2-MIL-125(Ti) not only functionalizes the derived porous carbon matrix with carboxyl groups but also forms additional oxygen-rich N like interstitial/intraband states lying above the valence band of TiO2 along with the self-doped carbon, which further narrows the energy band gaps of polymorphic TiO2 nanoparticles that enhance photocatalytic charge transfer efficiency. Without co-catalyst, sample N-C-TiO2/CArW demonstrates H2 evolution activity of 426 µmol gcat-1 h−1, which remarkably outperforms commercial TiO2 (P-25) and N-C-TiO2/CAr with a 5-fold and 3-fold H2 generation, respectively. This study clearly shows that water vapour atmosphere during the pyrolysis increases the hydrophilicity of the Ti-MOF derived composites by functionalizing porous carbon matrix with carboxylic groups, as well as enhancing the electrical conductivity and charge transfer efficiency due to the formation of additional localized oxygen-rich N like interstitial/intraband states. This work also demonstrates that by optimizing the anatase–rutile phase composition of the TiO2 polymorphs, tuning the energy band gaps by N/C co-doping and functionalizing the porous carbon matrix in the N-C-TiO2/C nanocomposites, the photocatalytic H2 generation activity can be further enhanced.

This study elucidates the working mechanism upon visible light exposure of the mixed C3N4–ZnO material. Structural (XRD), morphological (TEM) and optical (UV-vis spectroscopy) measurements have highlighted the intimate contact established at the interface of the biphasic solid and enhanced photoactivity arising under visible irradiation with respect to the pristine compounds. Electron paramagnetic resonance (EPR) spectroscopy analysis coupled with in situ irradiation, performed at 77 K, and supported by accurate simulations, demonstrated that the charge carrier dynamics at the C3N4–ZnO interface is governed by a direct Z-scheme heterojunction mechanism rather than that of a type-II heterojunction system. The experimental results suggest that the photoexcited electrons in the ZnO conduction band annihilate the holes in the C3N4 valence band, as in a solid direct Z-scheme system, allowing an improved charge carrier separation and stabilizing both electrons and holes at the best reductive and oxidative potentials, respectively.

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.\ud\udThe 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.

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.

The photochemical and photophysical properties of a defective zinc oxide prepared by precipitation have been investigated using mainly electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. As already reported in the literature the band gap of the oxide contains intra band gap states related to the presence of point defects (mainly cation vacancies) in the structure. The concentration and the energy levels of such defects, a fraction of them being paramagnetic, are the basis of a mechanisms of double and multiple excitations allowing visible photons with energy lower than the band gap value (hν Eg. Remarkably, some of the paramagnetic defects present in the bulk of the as prepared materials derive from excitation of VB electrons induced by ambient light illumination. The electron excitation from VB to CB has been observed upon irradiation under vacuum at 77 K with polychromatic light and applying four different filters to the emitted radiation with cut-off in the range between 400 nm and 495 nm. The process has been monitored by EPR as the photoexcitation ends up in the formation of trapped electron centers (signal at g = 1.96) and trapped hole centers (signal in the range 2.021 > g > 2.003) both clearly detected by this technique. A scheme of the energy state distribution in the band gap of the defective oxide, obtained coupling EPR and photoluminescence results, is proposed. Finally, a non-negligible fraction of the visible light generated carriers reach the surface of the nanocrystals, entailing the typical redox reactions of photocatalysis as indicated by the detection of hydroxyl radicals in solution performed by spin-trapping. For this reason, the wet chemistry prepared zinc oxide can be considered a visible light active (VLA) system.

This work aims to investigate the role of Yb dopant in the ZnO photoactivity. A new material based on ZnO doped with a small amount of Yb (1% molar) has been synthesized, characterized and tested respect to an enhancement of the photoactivity via Electron Paramagnetic Resonance spectroscopy. The prepared material has been characterized via X Ray diffraction, UV visible spectroscopy and in particular with the transmission electron microscopy. The morphological analysis with high resolution TEM allowed us to identify the formation of a new species not visible with XRD and assigned to isolated Yb2O3 nanoparticles supported on the surface of larger particles of the more abundant zinc oxide phase. The as obtained material exhibits a band gap corresponding to UV light (≈3.3 eV), but nevertheless it shows a relevant photo-activity under irradiation with photons with λ > 420 nm (visible light). This phenomenon has been investigated by means of several methods. A specific EPR-based approach allowed to monitor and quantify the charge separation following the formation of holes in the valence band (VB) of the two materials.

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.

The synthesis of a mixed CeO2–ZnO oxide results in a photocatalyst active under visible light. The characterization of the new material shows that Ce does not enter as a dopant in ZnO but rather forms isolated CeO2 nanoparticles supported on the surface of larger particles of the more abundant zinc oxide phase. The as obtained material exhibits a band gap corresponding to UV light (∼3.3 eV), but nevertheless. it shows a relevant photoactivity under irradiation with photons with λ > 420 nm (visible light). The working hypothesis is that visible light irradiation leads to a charge separation and stabilization of a fraction of the carriers connected with the formation of the CeO2/ZnO interface. This phenomenon has been investigated by means of several methods. A specific EPR-based approach allowed to monitor and quantify the charge separation following the formation of holes in the valence band (VB) of the two materials. More complex is detecting the nature of the excited electrons, as this involves the formation of EPR invisible Ce3+ ions by trapping the electrons into localized 4f states of Ce ions at the interface between the two oxides. DFT calculations provide a rational for some of the observed phenomena and a basis for the discussion of the band alignment of the two systems as a consequence of the formation of a heterojunction. The theoretical results show that indeed electrons can be excited at the interface from the VB of the two oxides into the Ce 4f states with photons of 2.3 eV, thus justifying the occurrence of a visible-light activity despite the higher band gap of the two materials.

In the present study, we investigated the effect of cerium doping in zinc oxide matrix, used as photoactive material. Cerium ions into the matrix of ZnO can act like a 'trap' for the electrons, lowering the e -/h + recombination rate and so increasing the photocatalytic efficiency of the ZnO. We synthesised doped samples using a simple precipitation route. The amount of dopant used was, 1 and 10% molar. The samples have been studied via x-ray diffraction measurements for the structural characterisation; UV-visible diffuse reflectance was used for the optical analysis; Branauer-Emmett-Teller (BET) model for the measurement of the surface area. Finally, the samples have been analysed via electron paramagnetic resonance (EPR) spectroscopy for the electronic characterisation and for testing their photoactivity. The spin trapping technique was also use to measure the amount of stable radical adducts formed via reaction of OH• radicals with molecules of the DMPO (5,5-dimethyl-1-pyrroline-N-oxide) spin probe.

In this work, nanostructured rare-earth-doped zirconia was successfully synthesized, through a simple hydrothermal method, with a rare-earth oxide (REO)-based content varying from 0.5 to 5% molar (REO = CeO2; Er2O3). The samples were characterized by using several techniques, such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy. The photoactivity of the samples was tested under irradiation with simulated solar light by both the spin trapping technique, using DMPO (5,5-dimethyl-1-pyrroline-N-oxide) as spin trapping agent, and by the photodegradation of Rhodamine B, a common textile dye. All the doped samples resulted more active than the bare zirconia, and the correlation between the physical-chemical properties and the photoactivity of the materials has been investigated.

In this paper we prepared via different synthetic processes, two ternary systems based on ZnO, CeO2 and Cu2O for the abatement of organic pollutants. The system ZnO/CeO2 was already known to be efficient in the degradation of emergent contaminants, the addition of cuprous oxides allows also to enhance reductive properties to the material thanks to its specific potential. The mixed oxides were characterized via power X Ray Diffraction, UV visible Diffuse Reflectance and Electron Paramagnetic Resonance. The materials obtained through hydrothermal synthesis shown better performances in the abatement of phenol and carbamazepine.