Surface-functionalized nitrogen/carbon co-doped polymorphic TiO 2 phase junction nanoparticles uniformly distributed in porous carbon matrix were synthesized by a simple one-step pyrolysis of titanium based metal-organic framework (MOF), NH 2 -MIL-125(Ti) at 700°C under water vapour atmosphere. Introducing water vapour during the pyrolysis of NH 2 -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 TiO 2 along with the self-doped carbon, which further narrows the energy band gaps of polymorphic TiO 2 nanoparticles that enhance photocatalytic charge transfer efficiency. Without co-catalyst, sample N-C-TiO 2 /C ArW demonstrates H 2 evolution activity of 426 mmol g cat -1 h À1 , which remarkably outperforms commercial TiO 2 (P-25) and N-C-TiO 2 /C Ar with a 5-fold and 3-fold H 2 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 TiO 2 polymorphs, tuning the energy band gaps by N/C co-doping and functionalizing the porous carbon matrix in the N-C-TiO 2 / C nanocomposites, the photocatalytic H 2 generation activity can be further enhanced.

The synthesis of a mixed CeO 2 −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 CeO 2 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 CeO 2 /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 Ce 3+ 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.

No abstract

No abstract

No abstract

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.

No abstract

This study elucidates the working mechanism upon visible light of the mixed C3N4-ZnO material. Structural (XRD) morphological (TEM) and optical (UV-vis) measurements have highlighted the intimate contact established at the...