The design of Si‐(B)‐C materials is investigated, with detailed insight into the precursor chemistry and processing, the precursor‐to‐ceramic transformation, and the ceramic microstructural evolution ...at high temperatures. In the early stage of the process, the reaction between allylhydridopolycarbosilane (AHPCS) and borane dimethyl sulfide is achieved. This is investigated in detail through solid‐state NMR and FTIR spectroscopy and elemental analyses for Si/B ratios ranging from 200 to 30. Boron‐based bridges linking AHPCS monomeric fragments act as crosslinking units, extending the processability range of AHPCS and suppressing the distillation of oligomeric fragments during the low‐temperature pyrolysis regime. Polymers with low boron contents display appropriate requirements for facile processing in solution, leading to the design of monoliths with hierarchical porosity, significant pore volume, and high specific surface area after pyrolysis. Polymers with high boron contents are more appropriate for the preparation of dense ceramics through direct solid shaping and pyrolysis. We provide a comprehensive study of the thermal decomposition mechanisms, and a subsequent detailed study of the high‐temperature behavior of the ceramics produced at 1000 °C. The nanostructure and microstructure of the final SiC‐based ceramics are intimately linked to the boron content of the polymers. B4C/C/SiC nanocomposites can be obtained from the polymer with the highest boron content.
Ceramic structure synthesis: Si‐(B)‐C materials are designed from boron‐modified polycarbosilanes as processable and functional precursors, with detailed insight into the precursor chemistry and processing and the precursor‐to‐ceramic transformation (see figure). Materials with an original structural organization at the nanoscale and complex geometries at both micro‐ and macroscale are generated.
•High quality boron-doped diamond film electrodes were synthesized on Nb substrates.•Electrochemical oxidation on boron-doped diamond anode is an effective method for treating landfill leachate ...concentrates.•Optimal operating conditions for electrochemical oxidation of landfill leachate concentrates is determined.•87.5% COD removal and 74.06% NH3N removal were achieved after 6h treatment.
In the present study, the high quality boron-doped diamond (BDD) electrodes with excellent electrochemical properties were deposited on niobium (Nb) substrates by hot filament chemical vapor deposition (HFCVD) method. The electrochemical oxidation of landfill leachate concentrates from disc tube reverse osmosis (DTRO) process over a BDD anode was investigated. The effects of varying operating parameters, such as current density, initial pH, flow velocity and cathode material on degradation efficiency were also evaluated following changes in chemical oxygen demand (COD) and ammonium nitrogen (NH3N). The instantaneous current efficiency (ICE) was used to appraise different operating conditions. As a result, the best conditions obtained were as follows, current density 50mAcm−2, pH 5.16, flow velocity 6Lh−1. Under these conditions, 87.5% COD and 74.06% NH3N removal were achieved after 6h treatment, with specific energy consumption of 223.2kWhm−3. In short, these results indicated that the electrochemical oxidation with BDD/Nb anode is an effective method for the treatment of landfill leachate concentrates.
Mechanochemistry has been applied for the first time to an iridium(I)‐catalyzed C−H borylation reaction. By using either none or just a catalytic amount of a liquid, the mechanochemical C−H ...borylation of a series of heteroaromatic compounds proceeded in air to afford the corresponding arylboronates in good‐to‐excellent yields. A one‐pot mechanochemical C−H borylation/Suzuki–Miyaura cross‐coupling sequence for the direct synthesis of 2‐aryl indole derivatives is also described. The present study constitutes an important milestone towards the development of industrially attractive solvent‐free C−H bond functionalization processes in air.
The first application of mechanochemistry to a catalytic C−H borylation reaction is described. By using either none or just a catalytic amount of a liquid, a series of heteroaromatic compounds was efficiently reacted with bis(pinacolato)diboron in the presence of an iridium(I)/dtbpy catalyst under mechanochemical conditions to afford the corresponding C−H borylation products in good‐to‐excellent yield.
Microbial fuel cell (MFC) is a hybrid technology that produces electricity and recovers resources from wastewater through biocatalytic and electrochemical reactions. Metallurgical facilities in Bor, ...Serbia, are a source of copper-rich metallurgical wastewater, and the Town of Bor is a source of municipal wastewater rich in organic matter. The aim of this paper is to investigate the possibility of application of MFC for the treatment of metallurgical and municipal wastewater that are released into the Bor River in Serbia. A prototype of MFC was constructed for this study, and 3 sets of experiments were performed using model solutions and real wastewater. Copper was successfully removed from the treated model solution with 99.42 % efficiency. Solid copper particles were obtained with a particle size of about 1 ?m. Maximum chemical oxygen demand (COD) removal rate of 191.7 mg L-1 h-1 was observed in the anodic compartment. The impact of this study is significant because MFC was implemented for the simultaneous treatment of two types of wastewaters, one containing metals and the other containing organic matter, and both types of wastewater are released into the same river.
Si24: An Efficient Solar Cell Material Linghu, Jiajun; Shen, Lei; Yang, Ming ...
Journal of physical chemistry. C,
07/2017, Letnik:
121, Številka:
29
Journal Article
Recenzirano
Si24, a recently synthesized allotrope of silicon, has received much attention due to its quasi-direct band gap around 1.3 eV. To explore its potential application as a solar cell device, we ...investigated the doping effect on the electronic properties of Si24 using first-principles calculations. It is found that Si24 can be easily doped as both p- and n-type, and the dopants are readily ionized. Furthermore, the incorporation of these dopants only reduces the band gap of Si24 slightly, which remains in the ideal region for solar cells. Boron and phosphorus are identified as the most promising elements for the p-type and n-type doping in Si24, respectively, due to their low formation energies, small ionization energies, and small reductions in the band gap. These properties suggest great potential in constructing a novel Si24-based p-n junction which is highly desired for future industrial application of photovoltaic devices.
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•Mg-Al LDH was firstly prepared in ChCl:2 urea deep eutectic solvent (I-LDH).•I-LDH display smaller size distribution and monolayer.•I-LDH and its calcinated product can be applied in ...boron removal.
Ultra-thin layered double hydroxides (LDHs) with small particle sizes were synthesized using a deep eutectic solvent (DES). Products were characterized and applied towards boron removal. The results showed that the LDHs were successfully prepared in a DES (I-LDH) with a narrow diameter distribution (10–40nm) and a monolayer of around 0.7nm. Due to the reduced size, the interaction between the carbonate and metal layers was weak; therefore, I-LDH was found to have a higher sorption capacity to boron than that of LDH prepared through the urea method. The calcinated products (I-CLDH) also exhibited excellent sorption efficiency. The sorption mechanisms of I-LDH, I-CLDH, and U-CLDH were studied. Ion exchange was found to be the predominant mechanism of boron removal by I-LDH. However, for samples after calcination, two stages were present; the first stage included surface complexation and electrostatic attraction, and the second stage included immobilizing boric acid into Mg(OH)2 and attracting borate as an interlayer anionic species into the newly formed LDHs. In addition, pH was found to have a slight influence on sorption performance, although co-existing anions, especially carbonates, played a role in hindering sorption. Base on the Langmuir sorption isotherm, the sorption density of I-CLDH showed a good capacity for removing borate due to the ultrathin structure and high surface area. In addition, the influence of temperature, shaking speed, and dosage on borate sorption by I-CLDH has been studied. I-CLDH was also tested for borate removal from actual wastewater.
In the electrophilic C−H borylation of electron‐rich aromatic compounds with catecholborane, the catalytic generation of the boron electrophile is initiated by heterolysis of the B−H bond by various ...Lewis and Brønsted acids, with a boronium ion formed exclusively. After ligand dissociation, the corresponding borenium ion undergoes regioselective electrophilic aromatic substitution on aniline derivatives as well as nitrogen‐containing heterocycles. The catalysis is optimized using B(C6F5)3 as the initiator and proceeds without the addition of an external base or dihydrogen acceptor. Temperatures above 80 °C are generally required to secure efficient turnover in these Friedel–Crafts‐type reactions. Mechanistic experiments reveal that regeneration of the boronium/borenium ion with dihydrogen release is rate‐determining. This finding finally led to the discovery that, with added alkenes, catalytic C−H borylations can, for the first time, be carried out at room temperature.
Be positive: B(C6F5)3 initiates the acceptor‐free electrophilic aromatic substitution of anilines and azoles (and thiophenes) with catecholborane (catBH). Elevated reactions temperatures are required to overcome the rate‐determining step—the regeneration of the boronium/borenium ion. The addition of alkenes, for example, norbornene (nbe), changes the situation dramatically, with the reaction occurring at ambient temperature. PG=protecting group.
In this study, boron removal from geothermal water with an air gap membrane distillation (AGMD) system was examined. The utilization idea of the waste heat sources in geothermal power plants for ...membrane distillation process is the basis of this research. During the study, six different types of commercial membranes were used and the influence of operating parameters such as feed temperature and velocity, coolant temperature and velocity and air gap distance on the permeate flux and rejection performances were investigated. First, the operating parameters were optimized and the experiments were performed with three different saline water concentrations (0.1–1.5–3% (w/v)). Then, the effect of boron concentration on permeate flux was investigated by using a synthetic geothermal water. Finally, a real geothermal water was used for the determination of AGMD system performance and min. 99.5% boron removal efficiency was achieved for all membranes. The results showed that permeate water boron concentrations were <0.5 mg/L for all membranes which are in accordance with irrigation standards. As a result, the air gap width, feed velocity and temperature were found as dominant factors affecting the permeate flux. And also, it was observed that feed water boron concentration did not affect permeate water flux.
•Air gap membrane distillation (AGMD) is used for the removal of boron from geothermal water.•Feed water flow rate, feed temperature and the air gap width are the main controlling parameters of AGMD.•The permeate water flux is not significantly affected by the feed water boron concentrations.•The boron values of the permeate waters are below 0.5 mg/L which were suitable for irrigation standarts.
Catalytic enantioselective conjunctive cross‐coupling between 9‐BBN borate complexes and aryl electrophiles can be accomplished with Ni salts in the presence of a chiral diamine ligand. The reactions ...furnish chiral 9‐BBN derivatives in an enantioselective fashion and these are converted to chiral alcohols and amines, or engaged in other stereospecific C−C bond forming reactions.
Conjunctive coupling: Ni‐Catalyzed conjunctive couplings furnish chiral 9‐BBN derivatives in an enantioselective fashion and these are converted to chiral alcohols and amines, or they can be engaged in other stereospecific C−C bond forming reactions.
In this work, a family of pH-responsive fluorescent probes has been designed in a rational manner with the aid of quantum chemistry tools, covering the entire pH range from 0–14. Relying on the ...boron–dipyrromethene (BODIPY) core, all the probes as well as selected reference dyes display very similar spectroscopic properties with ON–OFF fluorescence switching responses, facilitating optical readout in simple devices used for detection and analysis. Embedding of the probes and reference dyes into hydrogel spots on a plastic strip yielded a test strip that reversibly indicates pH with a considerably small uncertainty of ∼0.1 pH units. These strips are not only reusable but, combined with a 3D-printed case that can be attached to a smartphone, the USB port of which drives the integrated LED used for excitation, allows for autonomous operation in on-site or in-the-field applications; the developed Android application software (“app”) further simplifies operation for unskilled users.
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