The scaling-up of electrochemical CO2 reduction requires circumventing the CO2 loss as carbonates under alkaline conditions. Zero-gap cell configurations with a reverse-bias bipolar membrane (BPM) ...represent a possible solution, but the catalyst layer in direct contact with the acidic environment of a BPM usually leads to H2 evolution dominating. Here we show that using acid-tolerant Ni molecular electrocatalysts selective (>60%) CO2 reduction can be achieved in a zero-gap BPM device using a pure water and CO2 feed. At a higher current density (100 mA cm–2), CO selectivity decreases, but was still >30%, due to reversible product inhibition. This study demonstrates the importance of developing acid-tolerant catalysts for use in large-scale CO2 reduction devices.
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•TiO2-rGO composite showed higher photocatalytic activity than TiO2-P25.•Reactive oxygen species produced under UV and visible irradiation were investigated.•Under UV–Vis irradiation ...TiO2-rGO produced hydroxyl radicals, hydrogen peroxide and singlet oxygen.•Under visible light singlet oxygen was detected from TiO2-rGO and TiO2-P25 catalysts.•A mechanism for the photocatalytic synthesis of singlet oxygen from H2O2 is discussed.
Photocatalysis has been shown to be effective for the disinfection of water contaminated with pathogenic microorganisms. In order to increase the solar efficiency of photocatalysis on titanium dioxide (TiO2) it is necessary to modify the TiO2 so that visible photons may be utilised in addition to the UV. TiO2 – reduced graphene oxide composites (TiO2-rGO) were prepared by the photocatalytic reduction of exfoliated graphene oxide (GO) using P25 (Evonik-Aeroxide) as the photocatalyst. The composites were tested for the inactivation of E. coli as the model microorganism under UV–Vis and visible only irradiation at relatively low light intensities to help elucidate the mechanism of disinfection. The results showed a 6log inactivation of E. coli after 120min of treatment with unmodified TiO2-P25 and the same level of inactivation was achieved after 90min with TiO2-rGO under UV–Vis irradiation. Under visible irradiation only, the TiO2-rGO gave a 5.3log inactivation of E. coli following 180min of treatment whereas the unmodified P25 gave only a 1.7log-reduction in the same time, similar to that observed in the light control. Using probes, the main reactive oxygen species involved in the disinfection process were determined to be hydrogen peroxide, hydroxyl radicals, and singlet oxygen under UV–Vis irradiation; and only singlet oxygen under visible only irradiation. Scavenger studies were also performed to further elucidate the mechanism of disinfection.
The thermal stability of anatase titanium dioxide (TiO2) is a prerequisite to fabricate photocatalyst-coated indoor building materials for use in antimicrobial and self-cleaning applications under ...normal room light illumination. Metal doping of TiO2 is an appropriate way to control the anatase to rutile phase transition (ART) at high processing temperatures. In this work, ART of indium (In)-doped TiO2 (In–TiO2) was investigated in detail in the range of 500–900 °C. In–TiO2 (In mol % = 0–16) was synthesized via a modified sol–gel approach. These nanoparticles were further characterized by means of powder X-ray diffraction (XRD), Raman, photoluminescence (PL), transient photocurrent response, and X-ray photoelectron spectroscopy (XPS) techniques. XRD results showed that the anatase phase was maintained up to 64% by 16 mol % of In doping at 800 °C of calcination temperature. XPS results revealed that the binding energies of Ti4+ (Ti 2p1/2 and Ti 2p3/2) were red-shifted by In doping. The influence of In doping on the electronic structure and oxygen vacancy formation of anatase TiO2 was studied using density functional theory corrected for on-site Coulomb interactions (DFT+U). First-principles results showed that the charge-compensating oxygen vacancies form spontaneously at sites adjacent to the In dopant. DFT+U calculations revealed the formation of In - 5s states in the band gap of the anatase host. The formation of In2O3 at the anatase surface was also examined using a slab model of the anatase (101) surface modified with a nanocluster of composition In4O6. The formation of a reducing oxygen vacancy also has a moderate energy cost and results in charge localization at In ions of the supported nanocluster. PL and photocurrent measurements suggested that the charge carrier recombination process in TiO2 was reduced in the presence of In dopant. The photocatalytic activity of 2% In–TiO2 calcined at 700 °C is more comparable with that of pure anatase.
A room temperature H2S sensor based on pure and Au modified ZnO nanowires has been demonstrated. Modification of ZnO nanowires with Au resulted in a remarkable 16-fold increase in the sensor response ...over pure ZnO NWs toward 5ppm H2S at room temperature. A sensing mechanism based on the formation of nano-Schottky type barrier junction at the interface between Au and ZnO has been proposed. The enhanced response is attributed to the alteration of barrier properties by the adsorption or desorption of adsorbed species and/or H2S gas molecules. Observance of higher resistivity and a higher work function (0.2eV) for Au modified samples further corroborates the finding. Low temperature resistivity measurements indicate that the charge transport is governed by the thermal conduction and the nearest neighbor hopping mechanism.
Pulsed electrolysis can significantly improve carbon dioxide reduction on metal electrodes, but the effect of short (millisecond to seconds) voltage steps on molecular electrocatalysts is largely ...unstudied. In this work, we investigate the effect pulse electrolysis has on the selectivity and stability of the homogeneous electrocatalyst Ni(cyclam)2+ at a carbon electrode. By tuning the potential and pulse duration, we achieve a significant improvement in CO Faradaic efficiencies (85%) after 3 h, double that of the system under potentiostatic conditions. The improved activity is due to in situ catalyst regeneration from an intermediate that occurs as part of the catalyst’s degradation pathway. This study demonstrates the wider opportunity to apply pulsed electrolysis to molecular electrocatalysts to control activity and improve selectivity.
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.
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In recent years, core-shell nanofibrous drug delivery systems have received increasing attention due to their ability to incorporate two or more active pharmaceutical ingredients ...(APIs) individually into the desired layer (either core or sheath) and thereby finely tune the release profiles of even incompatible drugs in one system. This study aims to perform formulation and solid-state characterisation of levofloxacin-loaded polylactic acid (PLA) - naproxen-sodium-loaded polyvinyl pyrrolidone (PVP) bicomponent core-shell fibrous sheets and examine the electro spinnability of the precursor combinations. The selected drugs have potential therapeutic relevance in similar systems intended for wound healing; however, in this study, they are used as model drugs to understand the physicochemical properties of a drug loaded system. In order to determine the best core- and shell-solution combination, a full factorial experimental design is used. A combination of various morphological (scanning electron microscopy and transmission electron microscopy) and microstructural characterisation techniques (X-ray photoelectron spectroscopy and Raman spectroscopy) was applied to non-invasively obtain information about the structure of the fibres and the embedded drugs. The results indicate that core-shell fibres of different compositions could be successfully prepared with various structural homogeneities. The best core-shell structure was obtained using a combination of 15% (w/w) shell concentration and 8% (w/w) PLA solution concentration. In addition to the conventional core-shell structural verification methods, the Raman spectroscopy method was implemented to reveal not only the core-shell structure of the PLA/PVP nanofibers but also the form of the embedded drugs. The Raman mapping of the fibres confirm the above results, and it is shown that an amorphous solid dispersion is formed as a result of the coaxial electrospinning process.
The increasing CO2 concentration in the atmosphere exerts a significant influence on global warming and climate change. The capture and utilization of CO2 by conversion to useful products is an area ...of active research. In this work, the photodriven reduction of CO2 was investigated using graphitic carbon nitride (g-C3N4) as a potential photocatalyst. The photocatalytic reduction of CO2 was investigated with g-C3N4 powder immobilized on a glass support in a batch gas-phase photoreactor. The experiments were carried out under UV–vis irradiation at 70 °C and an initial pressure of 2.5 bar. The only gas-phase product detected during the irradiation of the g-C3N4 in the presence of CO2 was CO, and the rate of production was observed to decrease over time. Oxygen-doped g-C3N4 was also tested for CO2 reduction but had efficiency lower than that of the parent g-C3N4. Repeated cycles of photocatalytic CO2 reduction showed a decline in the activity of the g-C3N4. In the absence of CO2 some CO generation was also observed. Characterization of used and unused materials, using FTIR and XPS, showed an increase in the oxygen functional groups following UV–vis irradiation or thermal treatment. While others report the use of g-C3N4 as a photocatalyst, this work highlights the important need for replicates and control testing to determine material stability.
There is continued focus on the development of new biomaterials and associated biological testing methods needed to reduce the time taken for their entry to clinical use. The application of Raman ...spectroscopy to the study of individual cells that have been in contact with biomaterials offers enhanced in vitro information in a potentially non-destructive testing regime. The work presented here reports the Raman spectral analysis of discreet U-2 OS bone cells after exposure to hydroxyapatite (HA) coated titanium (Ti) substrates in both the as-deposited and thermally annealed states. These data show that cells that were in contact with the bioactive HA surface for 7 days had spectral markers similar to those cultured on the Ti substrate control for the same period. However, the spectral features for those cells that were in contact with the annealed HA surface had indicators of significant differentiation at day 21 while cells on the as-deposited surface did not show these Raman changes until day 28. The cells adhered to pristine Ti control surface showed no spectral changes at any of the timepoints studied. The validity of these spectroscopic results has been confirmed using data from standard in vitro cell viability, adhesion, and proliferation assays over the same 28-day culture period. In this case, cell maturation was evidenced by the formation of natural bone apatite, which precipitated intracellularly for cells exposed to both types of HA-coated Ti at 21 and 28 days, respectively. The properties of the intracellular apatite were markedly different from that of the synthetic HA used to coat the Ti substrate with an average particle size of 230 nm, a crystalline-like shape and Ca/P ratio of 1.63 ± 0.5 as determined by SEM-EDX analysis. By comparison, the synthetic HA particles used as a control had an average size of 372 nm and were more-rounded in shape with a Ca/P ratio of 0.8 by XPS analysis and 1.28 by SEM-EDX analysis. This study shows that Raman spectroscopy can be employed to monitor single U-2 OS cell response to biomaterials that promote cell maturation towards de novo bone thereby offering a label-free in vitro testing method that allows for non-destructive analyses.
Electrolyzers for CO2 reduction containing bipolar membranes (BPM) are promising due to low loss of CO2 as carbonates and low product crossover, but improvements in product selectivity, stability, ...and cell voltage are required. In particular, direct contact with the acidic cation exchange layer leads to high levels of H2 evolution with many common cathode catalysts. Here, Co phthalocyanine (CoPc) is reported as a suitable catalyst for a zero‐gap BPM device, reaching 53% Faradaic efficiency to CO at 100 mA cm−2 using only pure water and CO2 as the input feeds. It is also shown that the cell voltage can be lowered by constructing a customized BPM using TiO2 water dissociation catalyst, however this is at the cost of decreased selectivity. Switching the pure‐water anolyte to KOH improved both the cell voltage and CO selectivity (62% at 200 mA cm−2), but cation crossover could cause complications. The results demonstrate viable strategies for improving a BPM CO2 electrolyzer toward practical‐scale CO2‐to‐chemicals conversion.
CO2 electrolyzers are usually operated with a high local pH at the cathode but this can cause issues with bicarbonate salt formation. Operating with a low local pH is desirable but challenging as H2 evolution can occur. Here, it is shown that a Co molecular catalyst performs with high selectivity and CO2 utilization in a zero‐gap bipolar membrane electrolyzer cell.
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