Optimization of Disperse Blue 3 mineralization by UV-LED/FeTiO3 activated persulfate using response surface methodology

Response surface methodology based on Box-Behnken design (BBD) was successfully applied for the optimization of the UV-LED/FeTiO3 activated persulfate (PS) process. Disperse Blue 3 (DB3) azo dye oxidation was carried out in a quartz jacketed stirred batch reactor using 405 nm UV at 10 W/m−2 as radiation source. The effects of temperature, catalyst concentration and persulfate dose upon the total organic carbon (TOC) removal were investigated. Optimum operating conditions were found to be: ilmenite: 320 mg/L−1, PS: 1.56 g/L−1 and 67°C. Under these conditions, 96% mineralization was achieved. Ecotoxicity of the final effluent was evaluated using Aliivibrio fischeri bacteria, finding a negligible toxicity.Comunidad Autónoma de Madrid and MINECO have supported this work through projects S2013/MAE-2716 and CTM2016-76454-R, respectively. Jefferson E. Silveira and Wendel S. Paz gratefully acknowledge the support from CAPES: Science Without Borders Program, Ministry of Education Brazil, under grants BEX-1046/13-6 and BEX-9476/13-0 respectively

Hyperfine magnetic field in ferromagnetic graphite

Information on atomic-scale features is required for a better understanding of the mechanisms leading to magnetism in non-metallic, carbon-based materials. This work reports a direct evaluation of the hyperfine magnetic field produced at 13C nuclei in ferromagnetic graphite by nuclear magnetic resonance (NMR). The experimental investigation was made possible by the results of first-principles calculations carried out in model systems, including graphene sheets with atomic vacancies and graphite nanoribbons with edge sites partially passivated by oxygen. A similar range of maximum hyperfine magnetic field values (18-21T) was found for all systems, setting the frequency span to be investigated in the NMR experiments; accordingly, a significant 13C NMR signal was detected close to this range without any external applied magnetic field in ferromagnetic graphite

Consistency between ARPES and STM measurements on SmB6_6

Strongly correlated topological surface states are promising platforms for next-generation quantum applications, but they remain elusive in real materials. The correlated Kondo insulator SmB$_6$ is one of the most promising candidates, with theoretically predicted heavy Dirac surface states supported by transport and scanning tunneling microscopy (STM) experiments. However, a puzzling discrepancy appears between STM and angle-resolved photoemission (ARPES) experiments on SmB$_6$. Although ARPES detects spin-textured surface states, their velocity is an order of magnitude higher than expected, while the Dirac point -- the hallmark of any topological system -- can only be inferred deep within the bulk valence band. A significant challenge is that SmB$_6$ lacks a natural cleavage plane, resulting in ordered surface domains limited to 10s of nanometers. Here we use STM to show that surface band bending can shift energy features by 10s of meV between domains. Starting from our STM spectra, we simulate the full spectral function as an average over multiple domains with different surface potentials. Our simulation shows excellent agreement with ARPES data, and thus resolves the apparent discrepancy between large-area measurements that average over multiple band-shifted domains and atomically-resolved measurements within a single domain

Nitrate removal in saline water by photo-reduction using natural FeTiO as catalyst

As climate change progresses, there is an increasing interest on the use of non-conventional water sources such as brackish or saline waters. Nowadays, the main threat in Europe detected in these waterbodies is nitrate contamination. Within the multiple available methods studied for nitrate reduction, photocatalysis presents promising results, but this technology has not yet been tested in saline water. This work tackles the elimination of nitrate ([NO3−] =50 mg/L) in brackish and saline water ([sea salt] = 5–33 g/L) using ilmenite as photocatalyst and oxalic acid as an environmental-friendly reducing agent. The main challenge when working in saline water is to overcome oxalic acid scavenging by Ca2+ present in the water matrix. This can be solved either working at over stoichiometric concentrations of oxalic acid (≈300% stoich. dose) or acidifying the reaction media. The addition of hydrochloric acid ensures the protonation of oxalic acid, reducing drastically its precipitation as CaC2O4. Working at [C2O42−] = 180 mg/L, [FeTiO3] = 450 mg/L and [HCl 37%] = 13 mM, 73% total nitrogen (TN) elimination was reached after 420 min. Reaction temperature was also evaluated in the range of 20–80 °C, which allowed to calculate the Ea=9.8 kJ/mol. Finally, the effect of dissolved O2 on the TN reduction was assessed. Overall, photocatalytic nitrate reduction presents itself as a feasible technology regardless of the water salinit

Few-layer antimonene electrical properties

Antimonene -a single layer of antimony atoms- and its few layer forms are among the latest additions to the 2D mono-elemental materials family. Numerous predictions and experimental evidence of its remarkable properties including (opto)electronic, energetic or biomedical, among others, together with its robustness under ambient conditions, have attracted the attention of the scientific community. However, experimental evidence of its electrical properties is still lacking. Here, we characterized the electronic properties of mechanically exfoliated flakes of few-layer (FL) antimonene of different thicknesses (∼ 2–40 nm) through photoemission electron microscopy, kelvin probe force microscopy and transport measurements, which allows us to estimate a sheet resistance of ∼ 1200 Ω sq−1 and a mobility of ∼ 150 cm2V−1s−1 in ambient conditions, independent of the flake thickness. Alternatively, our theoretical calculations indicate that topologically protected surface states (TPSS) should play a key role in the electronic properties of FL antimonene, which supports our experimental findings. We anticipate our work will trigger further experimental studies on TPSS in FL antimonene thanks to its simple structure and significant stability in ambient environmentsWe acknowledge financial support through the “Maríade Maeztu” Programme for Units of Excellence in R&D (CEX2018-000805-M), the Spanish MINECO through projects PCI2018-093081, FIS2016-80434-P, PID2019-109539GB-C43, PID2019- 106268GB-C31 and -C32, MAT2016-77608-C3-1-P and -3-P, MAT2013-46753-C2-2-P and MAT2017-85089-C2-1R, the EU Graphene Flagship funding (Graphene Flagship Core3 881603 and JTC2017/2D-Sb&Ge), the EU via the ERC-Synergy Program (GrantERC-2013-SYG-610256 NANOCOSMOS), the Comunidad Autónoma de Madrid through MAD2D-CM, S2018/NMT-4321 (NanomagCOST-CM) and the European StructuralFunds via FotoArt CM project (S2018/NMT-4367), and the Fundación Ramón Areces. S.P. acknowledges financial support by the VILLUM FONDEN via the Centre of Excellence for Dirac Materials (Grant No. 11744

Exfoliation of Alpha-Germanium: A Covalent Diamond-Like Structure

2D materials have opened a new field in materials science with outstanding scientific and technological impact. A largely explored route for the preparation of 2D materials is the exfoliation of layered crystals with weak forces between their layers. However, its application to covalent crystals remains elusive. Herein, a further step is taken by introducing the exfoliation of germanium, a narrow-bandgap semiconductor presenting a 3D diamond-like structure with strong covalent bonds. Pure α-germanium is exfoliated following a simple one-step procedure assisted by wet ball-milling, allowing gram-scale fabrication of high-quality layers with large lateral dimensions and nanometer thicknesses. The generated flakes are thoroughly characterized by different techniques, giving evidence that the new 2D material exhibits bandgaps that depend on both the crystallographic direction and the number of layers. Besides potential technological applications, this work is also of interest for the search of 2D materials with new properties

Dynamically tuned non-classical light emission from atomic defects in hexagonal boron nitride

Luminescent defects in hexagonal boron nitride (h-BN) have recently emerged as a promising platform for non-classical light emission. On-chip solutions, however, require techniques for controllable in-situ manipulation of quantum light. Here, we demonstrate the dynamic spectral and temporal tuning of the optical emission from h-BN via moving acousto-mechanical modulation induced by stimulated phonons. When perturbed by the propagating acoustic phonon, the optically probed radiative h-BN defects are periodically strained and their sharp emission lines are modulated by the deformation potential coupling. This results in an acoustically driven spectral tuning within a 2.5-meV bandwidth. Our findings, supported by first-principles theoretical calculations, reveal exceptionally high elasto-optic coupling in h-BN of ~50 meV/%. Temporal control of the emitted photons is achieved by combining the acoustically mediated fine-spectral tuning with spectral detection filtering. This study opens the door to the use of sound for scalable integration of h-BN emitters in nanophotonic and quantum information technologiesThis work was supported in part by the collaborative project “Single-Photon Generation in 2D Crystals for Quantum Information” (MDM-2014-0377) funded by the Condensed Matter Physics Center (IFIMAC) as well as by the Spanish MINECO under contracts MAT2014-53119-C2-1-R, MAT2016-77608-C3-1-P and MAT2017-83722-R. S.L. is a recipient of the Ramón and Cajal Research Grant (RyC-2011-09528) funded by the Spanish MINECO. J.J.P.B. acknowledges financial support from Spanish MINECO through Grant FIS2016-80434-P, the Fundación Ramón Areces, the Comunidad Autónoma de Madrid through MAD2D-CM Program (S2013/MIT-3007) and the European Union Seventh Framework Programme under Grant agreement No. 604391 Graphene Flagship. W.S.P. was funded by the CNPq Fellowship programme (Pós-doutorado júnior) under grant 405107/2017-0 and acknowledges the computer resources at FinisTerrae2 and the technical support provided by Barcelona Supercomputing Center (RES-FI-2018-2-0036). We thank Eduardo J.H. Lee (UAM) for his help in sample preparatio

Dynamically tuned non-classical light emission from atomic defects in hexagonal boron nitride

Luminescent defects in hexagonal boron nitride (h-BN) have recently emerged as a promising platform for non-classical light emission. On-chip solutions, however, require techniques for controllable in-situ manipulation of quantum light. Here, we demonstrate the dynamic spectral and temporal tuning of the optical emission from h-BN via moving acousto-mechanical modulation induced by stimulated phonons. When perturbed by the propagating acoustic phonon, the optically probed radiative h-BN defects are periodically strained and their sharp emission lines are modulated by the deformation potential coupling. This results in an acoustically driven spectral tuning within a 2.5-meV bandwidth. Our findings, supported by first-principles theoretical calculations, reveal exceptionally high elasto-optic coupling in h-BN of ~50 meV/%. Temporal control of the emitted photons is achieved by combining the acoustically mediated fine-spectral tuning with spectral detection filtering. This study opens the door to the use of sound for scalable integration of h-BN emitters in nanophotonic and quantum information technologies. © 2019, The Author(s)