Surface modification of TiO2 with copper clusters for band gap narrowing

Surface modification of photocatalytic materials to give better activity, and potentially extending the response into the visible spectrum, is an area of active research. In this work, DFT modelling suggests that surface modification of rutile and anatase TiO2 with partially oxidised copper clusters can induce a red shift in the photo-action spectrum. Copper clusters were synthesised and characterised separately before TiO2 nanoparticle surface modification. Characterisation of copper clusters and photocatalysts modified with copper clusters showed that ex-situ synthesis can control the size of surface clusters. Sub-nanometre clusters of copper maintained their size and morphology upon attachment to the photocatalyst surface. The copper clusters we determined to be a mixture of Cu(0) and Cu(I), and no significant change in the oxidation state was observed following surface modification or following photoelectrochemical measurements. Experimental measurements including UV–vis spectroscopy and valence band XPS showed a small red shift the band gap correlating to the DFT predictions. Photoelectrochemical characterisation showed an enhancement in the UV photocurrent response and a small red shift in the effective band gap for the surface modified TiO2

Enhanced Photocatalytic Degradation of the Imidazolinone Herbicide Imazapyr upon UV/Vis Irradiation in the Presence of CaxMnOy-TiO2 Hetero-Nanostructures: Degradation Pathways and Reaction Intermediates

[Abstract] The determination of reaction pathways and identification of products of pollutants degradation is central to photocatalytic environmental remediation. This work focuses on the photocatalytic degradation of the herbicide Imazapyr (2-(4-methyl-5-oxo-4-propan-2-yl-1H-imidazol-2-yl) pyridine-3-carboxylic acid) under UV-Vis and visible-only irradiation of aqueous suspensions of CaᵪMnOᵧ-TiO₂, and on the identification of the corresponding degradation pathways and reaction intermediates. CaᵪMnOᵧ-TiO₂ was formed by mixing CaᵪMnOᵧ and TiO₂ by mechanical grinding followed by annealing at 500 °C. A complete structural characterization of CaᵪMnOᵧ-TiO₂ was carried out. The photocatalytic activity of the hetero-nanostructures was determined using phenol and Imazapyr herbicide as model pollutants in a stirred tank reactor under UV-Vis and visible-only irradiation. Using equivalent loadings, CaᵪMnOᵧ-TiO₂ showed a higher rate (10.6 μM·h⁻¹) as compared to unmodified TiO₂ (7.4 μM·h⁻¹) for Imazapyr degradation under UV-Vis irradiation. The mineralization rate was 4.07 μM·h⁻¹ for CaᵪMnOᵧ-TiO₂ and 1.21 μM·h⁻¹ for TiO₂. In the CaᵪMnOᵧ-TiO₂ system, the concentration of intermediate products reached a maximum at 180 min of irradiation that then decreased to a half in 120 min. For unmodified TiO₂, the intermediates continuously increased with irradiation time with no decrease observed in their concentration. The enhanced efficiency of the CaᵪMnOᵧ-TiO₂ for the complete degradation of the Imazapyr and intermediates is attributed to an increased adsorption of polar species on the surface of CaᵪMnOᵧ. Based on LC-MS, photocatalytic degradation pathways for Imazapyr under UV-Vis irradiation have been proposed. Some photocatalytic degradation was obtained under visible-only irradiation for CaᵪMnOᵧ-TiO₂. Hydroxyl radicals were found to be main reactive oxygen species responsible for the photocatalytic degradation through radical scavenger investigations.This research received external funding from the British Council under the STREAM-MENA Institutional Links Scheme Grant number 278072873. This is a collaboration between Ulster University (UK), Technion Institute (Israel) and Rabat University (Morocco). MC acknowledges support from Ministerio de Economía y Competitividad (Spain) through project CTQ2015-71238-R (MINECO/FEDER). AS would like to acknowledge the financial support received from Ulster University (UK) through the VCRS scholarship. PS would like to acknowledge funding from Invest Northern Ireland for the BioDevices projectBritish Council; 27807287

Formal Quantum Efficiencies for the Photocatalytic Reduction of CO2 in a Gas Phase Batch Reactor

The photocatalytic reduction of CO2 to fuels, or useful products, is an area of active research. In this work, nanoengineering and surface modification of titania were investigated as approaches for improving the CO2 reduction efficiency in a fixed-bed gas phase batch photoreactor under UV–vis irradiation. Titania nanotubes were prepared by a hydrothermal method, and TiO2 (P25) was surface modified with copper clusters. Unmodified TiO2 (P25) was used as the bench-mark comparison. The titania nanotubes and Cu-TiO2 materials showed higher efficiency for the photocatalytic reduction of CO2 to yield CH4 as compared to P25. Carbon monoxide yields were similar for all photocatalysts tested. The photocatalytic reduction of CO2 was observed on all photocatalyst tested, with the nanotubes proving to be the most efficient for the production of CH4. The product yields per mass of catalyst observed in this work are similar to those reported in the literature (with similar reactor parameters) but the calculated formal quantum efficiencies for CO2 reduction are very low (4.41 × 10−5 to 5.95 × 10-4)

The Direct 3D Printing of Functional PEEK/Hydroxyapatite Composites via a Fused Filament Fabrication Approach

The manufacture of polyetheretherketone/hydroxyapatite (PEEK/HA) composites is seen as a viable approach to help enhance direct bone apposition in orthopaedic implants. A range of methods have been used to produce composites, including Selective Laser Sintering and injection moulding. Such techniques have drawbacks and lack flexibility to manufacture complex, custom-designed implants. 3D printing gets around many of the restraints and provides new opportunities for innovative solutions that are structurally suited to meet the needs of the patient. This work reports the direct 3D printing of extruded PEEK/HA composite filaments via a Fused Filament Fabrication (FFF) approach. In this work samples are 3D printed by a custom modified commercial printer Ultimaker 2+ (UM2+). SEM-EDX and µCT analyses show that HA particles are evenly distributed throughout the bulk and across the surface of the native 3D printed samples, with XRD highlighting up to 50% crystallinity and crystalline domains clearly observed in SEM and HR-TEM analyses. This highlights the favourable temperature conditions during 3D printing. The yield stress and ultimate tensile strength obtained for all the samples are comparable to human femoral cortical bone. The results show how FFF 3D printing of PEEK/HA composites up to 30 wt% HA can be achieved