Spectroscopic investigations at the diamond-water interface

Artificial Photosynthesis is a promising approach to tackle the increasing challenges of global warming. However, the direct conversion of CO2 to other chemicals presents major kinetic challenges, evoking exploration of abundant, cost effective and sustainable photocatalysts. Diamonds are promising candidates as H-terminated diamond surfaces exhibit excellent electron emission characteristics in water because of their negative electron affinity. However, due to their wide band gap of 5.4 eV, the generation of solvated electrons, requires the photoactivation of diamond using deep UV radiation which is scarcely available in the solar spectrum. In this thesis two strategies are investi- gated to enable visible light absorption and enhance electron emission from diamonds. Specifically, the effect of B, N and P doping on the electronic structure of diamonds were investigated using soft X-ray ab- sorption spectroscopy at C K edge. The results of our study revealed that combining nanostructuration with B-doping leads to introduction of new electronic states close to both the valence band maximum and the conduction band minimum in B-doped diamonds. As an alternative strategy, the electronic structure of nanodiamonds sensitized with Ru(bpy)3 was probed. These studies presented evidence of electronic coupling between the Ru complex and the nanodiamonds with the HOMO of Ru(bpy)3 lying above the valence band minimum of the diamonds. As a result of this band alignment, the dye acts as an electron donor and can potentially refill the photogenerated holes in the valence band of diamonds. Since photoactivation of diamonds generates solvated electrons in water, it is also important to un- derstand the diamond-water interface. To this aim, infrared spectroscopy was used to elucidate the influence of different pH conditions on the surface interactions of ND-OH surfaces at the diamond- water interface. This study provided insights that could help to determine the optimal environment that would enhance electron emission from these surfaces. Based on the results, a possible forma- tion of oxonium ions on an ND-OH surface in acidic conditions could be deduced. These oxonium ions could potentially form a charge stabilization layer with water molecules, thereby enhancing electron emission which could be advantageous for photocatalytic reductions. The results further suggested a possible aging mechanism of ND-H surfaces under long term UV irradiation. For efficient photoelectro- catalytic CO2 reduction, diamonds were also co-promoted by Cu2O to form a hybrid photocatalyst. The electronic structure of this hybrid material was probed at the Cu L edge to explain the role of diamond in this hybrid material. It was found out that diamond indeed acts as a very stable support for Cu2O thereby decelerating the process of aging and subsequent deactivation of the catalyst. With this work, we thus, aim to highlight some of the characteristics of diamonds that would enable the development of diamond based photocatalysts in the future.Die künstliche Photosynthese ist ein vielversprechender Ansatz, um den wachsenden Herausforderungen der globalen Erwärmung zu begegnen. Die direkte Umwandlung von CO2 in andere Chemikalien stellt jedoch eine große Herausforderung dar, die zur Erforschung zahlreicher, kostengünstiger und nachhaltiger Photokatalysatoren führt. Aufgrund ihrer großen Bandlücke von 5,4 eV sind Diamanten vielversprechende Kandidaten. Denn H- terminierte Diamantoberflächen weisen aufgrund ihrer negativen Elektronenaffinität in Wasser hervorragende Elektronenemissionseigenschaften auf. Die Erzeugung von solvatisierten Elektronen erfordert jedoch die Photoaktivierung von Diamanten mit tiefer UV-Strahlung, die im Sonnenspektrum kaum verfügbar ist. In der vorliegenden Arbeit wurden zwei Strategien untersucht, um die Absorption des sichtbaren Lichts zu ermöglichen und die Elektronenemission von Diamanten zu verbessern. Insbesondere wurden die elektronischen Strukturen von p- und n-Diamanten mit B-, N- bzw. P-Dotierung mittels weicher Röntgenabsorptionsspektroskopie an der C-K-Kante untersucht. Diese Untersuchungen zeigten, dass die Kombination von Nanostrukturierung mit B-Dotierung neue elektronische Zustände erzeugt, die sowohl dem Valenzbandmaximum als auch dem Leitungsbandminimum in B-dotierten Diamanten nahe kommen. Als alternative Strategie wurde die elektronische Struktur von Nanodiamanten untersucht, die mit Ru(bpy)3 sensibilisiert sind. Diese Studien zeigten eine elektronische Kopplung zwischen dem Ru-Komplex und den Nanodiamanten, wobei das HOMO von Ru(bpy)3 über dem Valenzband Minimum der Diamanten lag. Durch diese Bandausrichtung wirkt der Farbstoff als Elektronendonor und kann die photogenerierten Löcher im Valenzband der Diamanten potenziell wieder auffüllen. Da die Photoaktivierung von Diamanten im Wasser solvatisierte Elektronen erzeugt, ist es auch wichtig, die Grenzfläche zwischen Diamant und Wasser zu verstehen. Wir untersuchten die Interaktion von OH- terminierten Diamant-Oberflächen mit Wasser bei unterschiedlichen pH-Werten, um die Elektronenemission von diesen Oberflächen zu verbessern. Es stellte sich heraus, dass unter sauren Bedingungen auf einer ND-OH-Oberfläche möglicherweise Oxoniumionen gebildet werden, die mit Wassermolekülen eine ladungsstabilisierende Schicht bilden könnten. Diese wiederum könnte die Elektronenemission er- höhen und die photokatalytische Reduktion von CO2 begünstigen. Einen hybriden Photokatalysator mit Cu2O Schichten auf der Diamantenoberfläche wurde auch gebildet, als alternativen Weg für eine effiziente CO2-Photoreduktion. Die elektronische Struktur dieses Hybridmaterials wurde an der Cu-L-Kante untersucht, um die Rolle des Diamanten in diesem Hybridmaterial zu erklären. Es wurde herausgefunden, dass Diamant tatsächlich als sehr stabiler Träger für Cu2O wirkt, wodurch der Alterungsprozess und die daraus folgende Deaktivierung des Katalysators verzögert werden. Mit dieser Arbeit wollen wir daher die Eigenschaften von Diamanten beleuchten, um künftig die Entwicklung von einem diamantbasierten Photokatalysator zu ermöglichen

A multicentric evaluation of dipstick test for serodiagnosis of visceral leishmaniasis in India, Nepal, Sri Lanka, Brazil, Ethiopia and Spain

Author Correction: A multicentric evaluation of dipstick test for serodiagnosis of visceral leishmaniasis in India, Nepal, Sri Lanka, Brazil, Ethiopia and Spain PMID: 33574485Visceral leishmaniasis (VL) is one of the leading infectious diseases affecting developing countries. Colloidal gold-based diagnostic tests are rapid tools to detect blood/serum antibodies for VL diagnosis. Lack of uniformity in the performance of these tests in different endemic regions is a hurdle in early disease diagnosis. This study is designed to validate a serum-based dipstick test in eight centres of six countries, India, Nepal, Sri Lanka, Brazil, Ethiopia and Spain with archived and fresh sera from 1003 subjects. The dipstick detects antibodies against Leishmania donovani membrane antigens (LAg). The overall sensitivity and specificity of the test with 95% confidence intervals were found to be 97.10% and 93.44%, respectively. The test showed good sensitivity and specificity in the Indian subcontinent (>95%). In Brazil, Ethiopia, and Spain the sensitivity and specificity of the dipstick test (83.78-100% and 79.06-100%) were better as compared to the earlier reports of the performance of rK39 rapid test in these regions. Interestingly, less cross-reactivity was found with the cutaneous form of the disease in Spain, Brazil, and Sri Lanka demonstrating 91.58% specificity. This dipstick test can therefore be a useful tool for diagnosing VL from other symptomatically similar diseases and against cutaneous form of leishmaniasis.S

Assessment of the efficiency of listerine mouthwash as an adjuvant to conventional tooth brushing

To assess the effectiveness of Listerine mouthwash as an adjuvant to routine toothbrushing. The current trial was undertaken in 60 subjects who were categorized into two groups. Group A (Tooth brushing alone two times a day for two weeks) and Group B (Tooth brushing two times a day followed by 20 ml Listerine mouth rinse for 30 seconds twice daily, 30 minutes follow up tooth brushing). Plaque accumulation and gingival inflammation were evaluated using Modified Gingival Index, Turesky-Gillmore-Glickman- Modification of Quigley Hein Plaque Index and Approximal Plaque Index. The modified gingival index scores were significantly reduced in both groups and when pre and post treatment measurements of modified gingival index were equated in participants exercising toothbrushing accompanied by Listerine mouthwash, it was observed that the modified gingival index scores were significantly decreased. When the mean difference in plaque index values were equated in participants exercising toothbrushing accompanied by Listerine mouthwash then it was concluded that the values were significantly decreased. Listerine mouthwash could be considered as a supplement to mechanical plaque control approaches for the reason that of its exceptional antiplaque upshots, that is considered as a outcome of its excellent gradation of tenacity on the tooth surface

Bone metastases in prostate cancer - Gallium-68-labeled prostate-specific membrane antigen or Fluorine 18 sodium fluoride PET/computed tomography - the better tracer?

OBJECTIVE: The objective was to assess the roles of 68Ga-PSMA PET/CT and 18F-NaF PET/CT in evaluation of skeletal metastatic lesions in prostate cancer. METHODS: Two hundred consecutive prostate cancer patients who had undergone 68Ga-PSMA PET/CT and 18F-NaF PET/CT at baseline evaluation (n = 80) and following suspected recurrence or disease progression (restaging) (n = 120) were analyzed retrospectively. RESULTS: PSMA and NAF scans were positive for skeletal metastatic lesions in 67% (134 patients) and negative in 33% (66 patients). The scans were concordant in 80% (160 patients: 66 negative and 94 positive) and discordant in 20% (40 patients). Among 40 discordant results, 14 were baseline and 26 were restaging studies. PSMA detected more number of lesions in 11 (nine baseline and two restaging). These were true positive marrow or lytic metastatic lesions. NaF revealed more number of lesions in 29 (5 initial and 24 restaging). These were false positive on follow-up imaging. No statistical difference (P value = 0.7 by McNemar test) between the two scans for identifying absence or presence of at least one skeletal lesion was noted at baseline staging. CONCLUSION: Though, both 18F-NaF and 68Ga-PSMA are excellent tracers for evaluation of skeletal metastases in prostate cancer, there is a distinct advantage of 68Ga-PSMA PET/CT due to detection of additional skeletal lesions and absence of false positive lesions. In addition, absence of PSMA avidity in healed metastases in the restaging setting opens up new avenue for assessment of response of skeletal metastases

Impact of nitrogen, boron and phosphorus impurities on the electronic structure of diamond probed by X-ray spectroscopies

International audienceDoping diamond with boron, nitrogen or phosphorus enables a fine tuning of its electronic properties, which is particularly relevant for applications involving electron emission. However, the chemical nature of the doping sites and its correlation with electron emission properties remain to be clarified. In this work, we applied soft X-ray spectroscopy techniques to probe occupied and unoccupied electronic states in undoped, boron-, phosphorus- and nitrogen-containing single crystal diamonds. X-ray absorption, X-ray emission and X-ray photoemission spectroscopies, performed at the carbon K-edge, provide a full picture of new electronic states created by impurities in diamond. The different probing depths of fluorescence- and electron-based detection techniques enable a comparison between surface and bulk contribution

Combining nanostructuration with boron doping to alter sub band gap acceptor states in diamond materials

Diamond is a promising metal-free photocatalyst for nitrogen and carbon dioxide reduction in aqueous environment owing to the possibility of emitting highly reducing solvated electrons. However, the wide band gap of diamond necessitates the use of deep UV to trigger a photochemical reaction. Boron doping introduces acceptor levels within the band gap of diamonds, which may facilitate visible-light absorption through defect-based transitions. In this work, unoccupied electronic states from different boron-doped diamond materials, including single crystal, polycrystalline film, diamond foam, and nanodiamonds were probed by soft X-ray absorption spectroscopy at the carbon K edge. Supported by density functional theory calculations, we demonstrate that boron close to the surfaces of diamond crystallites induce acceptor levels in the band gap, which are dependent on the diamond morphology. Combining boron-doping with morphology engineering, this work thus demonstrates that electron acceptor states within the diamond band gap can be controlled

Surface structure and spectroscopie properties of fluorinated diamond materials

International audienceDepending on the surface termination, the electronic properties of diamond materials can be varied over a wide range. It is well known that fluorination generates a highly hydrophobic and lubricating surface. The strong electron-withdrawing nature of fluorine bound to carbon atoms plays a role when considering the effect of surface fluorination of diamond as a means to tune its optical and electronic properties. For submicron diamond particles, several methods including the thermal gas phase fluorination, the fluorination including XeF2 and the grafting of perfluorinated alkyl moieties have been reported. Using the reported wet-chemical fluorination technique, it is now possible to fluorinate all kinds of diamond materials in a mild and highly efficient way enabling the production of functional diamond materials for applications in catalysis, tribology or medicine

Photoelectrocatalytic conversion of CO2 : application of transition metal functionalised diamond particles

The electronic properties of diamond can not only be influenced by its termination, but also by different surface functionalisations. We present the immobilisation of transition metal complexes on linker-functionalised nanodiamond particles using the concept of click-chemistry. The resulting conjugates have been characterised using various spectroscopic methods investigating the influence on the electronic structure of the particles