Highly enhanced response of MoS2/porous silicon nanowire heterojunctions to NO2 at room temperature

Molybdenum disulfide/porous silicon nanowire (MoS₂/PSiNW) heterojunctions with different thicknesses as highly-responsive NO₂ gas sensors were obtained in the present study. Porous silicon nanowires were fabricated using metal-assisted chemical etching, and seeded with different thicknesses. After that, MoS₂ nanosheets were synthesized by sulfurization of direct-current (DC)-magnetic-sputtering Mo films on PSiNWs. Compared with the as-prepared PSiNWs and MoS₂, the MoS₂/PSiNW heterojunctions exhibited superior gas sensing properties with a low detection concentration of 1 ppm and a high response enhancement factor of ∼2.3 at room temperature. The enhancement of the gas sensitivity was attributed to the layered nanostructure, which induces more active sites for the absorption of NO₂, and modulation of the depletion layer width at the interface. Further, the effects of the deposition temperature in the chemical vapor deposition (CVD) process on the gas sensing properties were also discussed, and might be connected to the nucleation and growth of MoS₂ nanosheets. Our results indicate that MoS₂/PSiNW heterojunctions might be a good candidate for constructing high-performance NO₂ sensors for various applications.

Molybdenum disulfide/porous silicon nanowire (MoS₂/PSiNW) heterojunctions with different thicknesses as highly-responsive NO₂ gas sensors were obtained in the present study.     

Boron-doped few-layer graphene nanosheet gas sensor for enhanced ammonia sensing at room temperature

Heteroatom doping in graphene is now a practiced way to alter its electronic and chemical properties to design a highly-efficient gas sensor for practical applications. In this series, here we propose boron-doped few-layer graphene for enhanced ammonia gas sensing, which could be a potential candidate for designing a sensing device. A facile approach has been used for synthesizing boron-doped few-layer graphene (BFLGr) by using a low-pressure chemical vapor deposition (LPCVD) method. Further, Raman spectroscopy has been performed to confirm the formation of graphene and XPS and FESEM characterization were carried out to validate the boron doping in the graphene lattice. To fabricate the gas sensing device, an Si/SiO₂ substrate with gold patterned electrodes was used. More remarkably, the BFLGr-based sensor exhibits an extremely quick response for ammonia gas sensing with fast recovery at ambient conditions. Hence, the obtained results for the BFLGr-based gas sensor provide a new platform to design next-generation lightweight and fast gas sensing devices.

A boron-doped few-layer LPCVD graphene sensor is successfully designed and demonstrated for enhanced NH₃ gas sensing applications.     

Correction: Boron-doped few-layer graphene nanosheet gas sensor for enhanced ammonia sensing at room temperature

Correction for ‘Boron-doped few-layer graphene nanosheet gas sensor for enhanced ammonia sensing at room temperature’ by Shubhda Srivastava et al., RSC Adv., 2020, 10, 1007–1014. DOI: 10.1039/C9RA08707A

The authors regret that affiliation b was incorrectly provided as Academy of Scientific and Innovative Research (AcSIR), CSIR-National Physical Laboratory Campus, Dr K S Krishnan Road, New Delhi 110012, India.The correct details are provided in the Affiliations section of this document.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Rosette-like MoS2 nanoflowers as highly active and stable electrodes for hydrogen evolution reactions and supercapacitors

MoS₂ is regarded as one of the cost-effective materials for many important applications. In this work, we report a simple one-step hydrothermal method for the directed synthesis of a rosette-like MoS₂ nanoflower modified electrode without using adhesion agents. Interestingly, owing to the hierarchical structures, the as-prepared MoS₂-based electrode exhibits significantly enhanced performance for both the hydrogen evolution reaction in acidic environments and supercapacitors. When used in the hydrogen evolution reaction, the electrode shows a low overpotential of ∼0.25 V at 10 mA cm⁻², a Tafel slope of ∼71.2 mV per decade, and long-term durability over 20 h of hydrogen evolution reaction operation at 10 mV cm⁻². In addition, as a supercapacitor electrode, it exhibits a good capacity of 137 mF cm⁻² at a current density of 10 mA cm⁻² and excellent stability in 1 M H₂SO₄ at a scan rate of 50 mV s⁻¹. The outstanding performances of the as-prepared materials may be ascribed to the unique 3D architectures of the rosette-like MoS₂ nanoflowers. This work could provide a strategy to explore low-cost and highly efficient electrocatalysts with desired nanostructures for the hydrogen evolution reaction and supercapacitors applications.

A simple strategy to synthesize interlayer spacing-enlarged rosette-like MoS₂ nanoflowers for both the hydrogen evolution reaction and supercapacitive energy storage.     

Porous 3D flower-like CoAl-LDH nanocomposite with excellent performance for NO2 detection at room temperature

The 3D flower-like CoAl-layered double hydroxide (CoAl-LDH) was successfully prepared using the functional template agent of fluoride ions via a facile one-step hydrothermal route. Various techniques proved that all the samples presented 3D flower-like microstructural morphology. Representatively, the CA-2 sample, which was synthesized with the molar ratio of Co : Al of 3.65 : 1, had considerably abundant pores in its thin nanosheets. The average pore size was 2–4 nm, the specific surface area was equal to 49.45 m² g⁻¹, and the thickness of nanosheets was approximately 3.068 nm. The CA-2 sample showed an excellent response to 0.01–100 ppm NO₂ with ultrafast response/recovery time at room temperature (RT). The detection limit of the sensor even reached 10 ppb. The superior gas sensing performance could be attributed to the synergistic effects of the functional template agent of fluoride ions and specific porous 3D flower-like nanostructure. The current study showed that the 3D flower-like CoAl-LDHs might a promising material in practical detection of NO₂ at RT.

We have synthesized 3D flower-like CoAl-LDHs consisting of ultrathin nanosheets for excellent performance for NO₂ detection at room temperature.     

Nanostructured WO3/graphene composites for sensing NOx at room temperature

WO₃ has emerged as an outstanding nanomaterial composite for gas sensing applications. In this paper, we report the synthesis of WO₃ using two different capping agents, namely, oxalic acid and citric acid, along with cetyltrimethyl ammonium bromide (CTAB). The effect of capping agent on the morphology of WO₃ material was investigated and presented. The WO₃ materials were characterized using X-ray diffraction analysis (XRD), field emission transmission electron microscopy (FETEM), field emission scanning electron microscopy (FESEM), particle size distribution (PSD) analysis, and UV-visible spectroscopic analysis. WO₃ synthesized using oxalic acid exhibited orthorhombic phase with crystallite size of 10 nm, while WO₃ obtained using citric acid shows monoclinic phase with crystallite size of 20 nm. WO₃ obtained using both capping agents were used to study their gas sensing characteristics, particularly for NO_x gas. The cross sensitivity towards interfering gases and organic vapors such as acetone, ethanol, methanol and triethylamine (TEA) was monitored and explained. Furthermore, the composites of WO₃ were prepared with graphene by physical mixing to improve the sensitivity, response and recovery time. The composites were tested for gas sensing at room temperature as well as at 50 °C and 100 °C. The results indicated that the citric acid-assisted WO₃ material exhibits better response towards NO_x sensing when compared with oxalic acid-assisted WO₃. Moreover, the sensitivity of the WO₃/graphene nanocomposite was better than that of the pristine WO₃ material towards NO_x gas. The WO₃ composite prepared using citric acid as capping agent and graphene exhibits sensing response and recovery time of 29 and 24 s, respectively.

WO₃ have been synthesized using two capping agents out of which citric acid assisted WO₃ was found to exhibit better response towards NO_x than WO₃ obtained from oxalic acid. The sensitivity was further enhanced by preparing composite with graphene.     

Nanostructured cobalt antimonate: a fast responsive and highly stable sensing material for liquefied petroleum gas detection at room temperature

Herein, cobalt antimonate (CoSb₂O₆) nanospheres were fabricated via the sol–gel spin-coating process and employed as a functional liquefied petroleum gas (LPG) sensor at room temperature (25 °C). The microstructure of the fabricated CoSb₂O₆ thin films (thickness ∼ 250 nm) was analyzed via scanning electron microscopy, which revealed the growth of nanospheres having an average diameter of ∼45 nm. The XRD analysis demonstrated the crystalline nature of CoSb₂O₆ with a crystallite size of ∼27 nm. Finally, the fabricated thin films were investigated as sensors for LPG and carbon dioxide (CO₂) at room temperature (25 °C) and 55% R.H. (relative humidity) with different concentrations in the range of 1000–5000 ppm. The sensing results demonstrated greater variations in the electrical properties of films for the incoming LPG than that of the CO₂ gas adsorption. Furthermore, to ensure the long-term stability of fabricated sensors, they were tested periodically at 10 days interval, spanning a total duration of 60 days. In summary, our fabricated LPG sensor displayed high sensitivity (1.96), repeatability, quick response time (21 s) and high long-term stability (99%). Therefore, CoSb₂O₆ nanospheres can be functionalized as a potential LPG-sensitive material characterized by high sensitivity, reliability and stability at room temperature.

Modulation in electrical resistance of the sensing layer due to interaction (adsorption and reactions) with LPG.     

Facile synthesis of few-layer MoS2 in MgAl-LDH layers for enhanced visible-light photocatalytic activity

A new photocatalyst, few-layer MoS₂ grown in MgAl-LDH interlayers (MoS₂/MgAl-LDH), was prepared by a facile two-step hydrothermal synthesis. The structural and photocatalytic properties of the obtained material were characterized by several techniques including powder X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL) and UV-vis absorption spectroscopy. The MoS₂/MgAl-LDH composite showed excellent photocatalytic performance for methyl orange (MO) degradation at low concentrations (50 mg L⁻¹ and 100 mg L⁻¹). Furthermore, even for a MO solution concentration as high as 200 mg L⁻¹, this composite also presented high degradation efficiency (>84%) and mineralization efficiency (>73%) at 120 min. The results show that the MoS₂/MgAl-LDH composite has great potential for application in wastewater treatment.

Few-layer MoS₂ was successfully grown in MgAl-LDH layers, utilizing the “space-confining” effect. The composite completed degraded 50 mg L⁻¹ and 100 mg L⁻¹ methyl orange (MO) solutions in 45 min and 105 min, respectively.     

Ruthenium-decorated vanadium pentoxide for room temperature ammonia sensing

Layer structured vanadium pentoxide (V₂O₅) microparticles were synthesized hydrothermally and successfully decorated by a facile wet chemical route, with ∼10–20 nm sized ruthenium nanoparticles. Both V₂O₅ and ruthenium nanoparticle decorated V₂O₅ (1%Ru@V₂O₅) were investigated for their suitability as resistive gas sensors. It was found that the 1%Ru@V₂O₅ sample showed very high selectivity and sensitivity towards ammonia vapors. The sensitivity measurements were carried out at 30 °C (room temperature), 50 °C and 100 °C. The best results were obtained at room temperature for 1%Ru@V₂O₅. Remarkably as short a response time as 0.52 s @ 130 ppm and as low as 9.39 s @ 10 ppm recovery time at room temperature along with high selectivity towards many gases and vapors have been noted in the 10 to 130 ppm ammonia concentration range. Short response and recovery time, high reproducibility, selectivity and room temperature operation are the main attributes of the 1%Ru@V₂O₅ sensor. Higher sensitivity of 1%Ru@V₂O₅ compared to V₂O₅ has been explained and is due to dissociation of atmospheric water molecules on 1%Ru@V₂O₅ as compared to bare V₂O₅ which makes hydrogen atoms available on Brønsted sites for ammonia adsorption and sensing. The presence of ruthenium with a thin layer of oxide is clear from X-ray photoelectron spectroscopy and that of water molecules from Fourier transform infrared spectroscopy.

Layer structured vanadium pentoxide (V₂O₅) microparticles were synthesized hydrothermally and successfully decorated by a facile wet chemical route, with ∼10–20 nm sized ruthenium nanoparticles.     

Hydrothermal synthesis of MoS2 nanosheet loaded TiO2 nanoarrays for enhanced visible light photocatalytic applications

A molybdenum disulfide (MoS₂) nanosheet-decorated titanium dioxide (TiO₂) NRA heterojunction composite was fabricated successfully through a two-step hydrothermal approach. Microstructures and optical properties of specimens were characterized by field-emission scanning electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, and ultraviolet-visible spectroscopy. The gaps of the TiO₂ nanorods have been filled with tiny MoS₂ nanosheets, which can increase the surface area of MoS₂/TiO₂ NRA composite thin films. In addition, the photocatalytic activity of the thin films were measured and discussed in greater detail. The appropriate hydrothermal reaction temperature of MoS₂ is important for the growth of perfect MoS₂/TiO₂ NRA composites with significantly enhanced photocatalytic performance. The photodegradation rate and k value of MoS₂-220/TiO₂ are 86% and 0.0105 min⁻¹, respectively, which are much larger than those of blank TiO₂. The enhanced photocatalytic performance could be attributed to the higher visible light absorption and the reduced recombination rate of photogenerated electron–hole pairs.

A molybdenum disulfide (MoS₂) nanosheet-decorated titanium dioxide (TiO₂) NRA heterojunction composite was fabricated successfully through a two-step hydrothermal approach.     

Metal-free synthesis of 1,4-benzodiazepines and quinazolinones from hexafluoroisopropyl 2-aminobenzoates at room temperature

Herein, we describe the novel reactivity of hexafluoroisopropyl 2-aminobenzoates. The metal-free synthesis of 1,4-benzodiazepines and quinazolinones from hexafluoroisopropyl 2-aminobenzoates has been developed at room temperature. These procedures feature good functional group tolerance, mild reaction conditions, and excellent yields. The newly formed products can readily be converted to other useful N-heterocycles. Moreover, the products and their derivatives showed potent anticancer activities in vitro by MTT assay.

A metal-free synthesis of 1,4-benzodiazepines and quinazolinones from hexafluoroisopropyl 2-aminobenzoates has been developed at room temperature.

Benzodiazepines (BDZs), especially 1,4-benzodiazepines, are privileged motifs in pharmaceuticals.¹ For examples, oxazepam is used to treat anxiety disorders or alcohol withdrawal symptoms; triazolam is used to treat insomnia (Scheme 1). Until now, some synthetic approaches to 1,4-benzodiazepine skeletons have been developed include isocyanide-based multicomponent reactions,² cycloadditions,³ metal-catalyzed tandem reactions,⁴ and redox-neutral [5+2] annulation with o-aminobenzaldehydes.⁵ However, these procedures have some limitations involving unavailable materials, several steps, harsh reaction conditions and low yields. α-Haloamides are widely used to synthesize N-heterocycles.⁶ Recently, some groups reported the synthesis of 1,4-benzodiazepines with α-haloamides.⁷ Kim and coworkers developed a [4+3]-annulation reaction between α-haloamides and isatoic anhydrides for 1,4-benzodiazepines, but the reaction required 80 °C reaction temperature and provided an unsatisfactory yield.^7a Singh''s group reported a two-step method to construct 1,4-benzodiazepines from α-haloamides and anthranils, but the anthranils are not readily available substrates and the second step also required 80 °C reaction temperature.^7b Quinazolinones are a significant class of heterocycles that widely occur in natural products and pharmaceuticals (Scheme 1).⁸ These compounds exhibit a range of biological activities including anticancer, antibacterial, antiinflammatory, antifungal, etc. Due to their significant value, the synthesis of quinazolinones has attracted considerable attention. The reported synthetic methods can be summarized as: (i) condensation of 2-aminobenzamides with carbonyl compounds;⁹ (ii) oxidative cyclization of primary alcohols with 2-aminobenzamides or 2-aminobenzonitriles;¹⁰ (iii) metal-catalyzed coupling/cyclization reactions;¹¹ and (iv) palladium-catalyzed carbonylation reactions.¹² But these synthetic methods also had some disadvantages. Thus, it is highly desirable to develop new available reagents for synthesizing the useful N-heterocycles such as benzodiazepines and quinazolinones with good yields under mild reaction conditions.Open in a separate windowScheme 1Structures of representative 1,4-benzodiazepine and quinazolinone drugs.In the past few years, 2-aminobenzoates have been used for the synthesis of N-heterocycles via [4+n] cyclization (Scheme 2a).¹³ However, harsh reaction conditions such as high reaction temperatures and strong bases or acids were required to effect alkoxy leaving. When we tried to synthesize benzodiazepines or quinazolinones with methyl or tert-butyl 2-aminobenzoates, we failed. Recently, hexafluoroisopropanol (HFIP) has attracted a lot of attention when used as solvent or substrate, due to its special properties.¹⁴ When we used isatoic anhydrides as substrates and NEt₃ as base in HFIP at room temperature, we unexpectedly discovered that hexafluoroisopropyl 2-aminobenzoates were completely formed. We supposed hexafluoroisopropyl 2-aminobenzoates were good synthons for the synthesis of N-heterocycles. Herein, we report metal-free procedures for the synthesis of 1,4-benzodiazepines and quinazolinones from hexafluoroisopropyl 2-aminobenzoates at room temperature with excellent yields (Scheme 2b).Open in a separate windowScheme 2Synthesis of N-heterocycles from 2-aminobenzoates.We examined the annulation reaction with hexafluoroisopropyl 2-aminobenzoate (1a) and α-bromoamide (2a) as the model substrates. Initially, when the reaction was performed with 1 equiv. of Et₃N in HFIP at room temperature for 0.5 h, 3a was formed, but cyclization product 4a was not obtained. We thought the transformation from 3a to the product 4a needing to release one molecule of HFIP, and the transformation maybe be inhibited when HFIP was used as solvent. So we removed the solvent HFIP under vacuum and added 2.0 mL DMF to react for 0.5 h. Pleasingly, the desired product 4a was obtained in 68% yield (

Transition-metal-free synthesis of aryl 1-thioglycosides with arynes at room temperature

A mild, convenient and transition-metal-free protocol for the synthesis of aryl 1-thioglycosides is presented via arynes generated in situ combined with glycosyl thiols in the presence of TBAF(tBuOH)₄. The methodology provides a general and efficient way to prepare a series of functionalized thioglycosides in good to excellent yields with a perfect control of the anomeric configuration at room temperature. In addition, the reaction conditions tolerate a variety of the pentoses and hexoses, and the reaction also performs smoothly on protected monosaccharides and disaccharides.

We have developed a convenient and transition-metal-free protocol for the synthesis of aryl 1-thioglycosides in good to excellent yields via the arynes generated in situ combined with glycosyl thiols.     

The synthesis of two-dimensional MoS2 nanosheets with enhanced tribological properties as oil additives

The use of MoS₂ nanosheets as oil additives has been proved effective to reduce friction and wear. Furthermore, it has been suggested that the synthesis of MoS₂ nanosheets with an ultrathin structure could benefit the friction and wear reduction, as they would penetrate into the contact area easily. In this paper, two-dimensional MoS₂ nanosheets were successfully fabricated by a solvothermal method with the aid of oleylamine. Meanwhile, the synthesized MoS₂ nanosheets exhibited perfect dispersing stability in paraffin oil, due to the surface modification by oleylamine molecules. The friction and wear properties of the synthesized MoS₂ nanosheets as oil additives were investigated using a ball-on-disk tribotester. The results showed that the two-dimensional MoS₂ nanosheets exhibited enhanced friction-reducing and antiwear behaviors as compared to the multilayered MoS₂ nanosheets. The prominent tribological performance of the two-dimensional MoS₂ nanosheets was attributed to the formation of a thick tribofilm inside the wear tracks, which was confirmed by XPS analyses of the rubbing interfaces.

Two-dimensional MoS₂ nansheets (2D MoS₂) with enhanced tribological properties were successfully fabricated with the aid of oleylamine.     

Correction: Gas sensing performance at room temperature of nanogap interdigitated electrodes for detection of acetone at low concentration

Correction for ‘Gas sensing performance at room temperature of nanogap interdigitated electrodes for detection of acetone at low concentration’ by Q. Nguyen Minh et al., RSC Adv., 2017, 7, 50279–50286.

The authors regret that in the original article the authorship was incorrect. J. Baggerman and S. P. Pujari were not included in the original author list. Additionally, J. F. van der Bent was spelled incorrectly in the original article. The correct author list is as presented above.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Controlled preparation of multiple mesoporous CoAl-LDHs nanosheets for the high performance of NOx detection at room temperature

By fine tuning the metal mole ratio, CoAl-LDHs (CA) with a 2D nanosheet structure were successfully prepared via a one-step hydrothermal method using urea as both precipitator and pore-forming agent. The morphology of CA samples shows uniform and thin porous hexagonal nanosheets. In particular, CA2-1, prepared with the 2 : 1 molar ratio for Co and Al, respectively, has the highest surface area (54 m² g⁻¹); its average transverse size of platelets is 2.54 μm with a thickness of around 19.30 nm and inter-plate spacing of about 0.2 μm. The sample exhibits a high sensing performance (response value of 17.09) towards 100 ppm NO_x, fast response time (4.27 s) and a low limit of detection (down to 0.01 ppm) at room temperature. Furthermore, CA2-1 shows long -term stability (60 days) and a better selectivity towards NO_x at room temperature. The excellent performance of the fabricated sensor is attributed to the special hexagonal structure of the 2D thin nanosheets with abundant mesopores, where the active sites provide fast adsorption and transportation channels, promote oxygen chemisorption, and eventually decrease the diffusion energy barrier for NO_x molecules. Furthermore, hydrogen bonds between water molecules and OH⁻ could serve as a bridge, thus providing a channel for rapid electron transfer. This easy synthetic approach and good gas sensing performance allow CoAl-LDHs to be great potential materials in the field of NO_x gas sensing.

By fine tuning the metal mole ratio, CoAl-LDHs (CA) with a 2D nanosheet structure were successfully prepared via a one-step hydrothermal method using urea as both precipitator and pore-forming agent.     

Electron-assisted synthesis of g-C3N4/MoS2 composite with dual defects for enhanced visible-light-driven photocatalysis

g-C₃N₄/MoS₂ composites were successfully prepared by an electron-assisted strategy in one step. Dielectric barrier discharge (DBD) plasma as an electron source, which has low bulk temperature and high electron energy, can etch and modify the surface of g-C₃N₄/MoS₂. The abundant N and S vacancies were introduced in the composites by plasma. The dual defects promoted the recombination and formation of heterojunctions of the g-C₃N₄/MoS₂ composite. It exhibited stronger light harvesting ability and higher charge separation efficiency than that of pure g-C₃N₄ and MoS₂. Compared with the sample by traditional calcination method, the plasma-sample showed better performance for degrading rhodamine B (RhB) and methyl orange. RhB is completely degraded within 2 hours on g-C₃N₄/MoS₂ by plasma. A mechanism for the photocatalytic degradation of organic pollutants via the composites was proposed. An electron-assisted strategy provides a green and effective platform to achieve catalysts with improved performance.

A N and S vacancies enriched g-C₃N₄/MoS₂ composite was prepared by plasma that promoted the formation of heterojunctions of the composite.     

A defect-rich ultrathin MoS2/rGO nanosheet electrocatalyst for the oxygen reduction reaction

The structural properties such as high specific surface area, good electrical conductivity, rich-defects of the catalyst surface guarantee outstanding catalytic performance and durability of oxygen reduction reaction (ORR) electrocatalysts. It is still a challenging task to construct ORR catalysts with excellent performance. Herein, we have reported column-like MoS₂/rGO with defect-rich ultrathin nanosheets prepared by a convenient solvothermal method. The structure and composition of MoS₂/rGO are systematically investigated. MoS₂/rGO shows a remarkable electrocatalytic performance, which is characterized by an outstanding onset potential of 0.97 V, a half-wave potential of 0.83 V, noticeable methanol tolerance, and durability of 93.7% current retention, superior to commercial Pt/C. The ORR process occurring on MoS₂/rGO is a typical four electron pathway. Therefore, this study achieves the design of a low-cost, highly efficient and stable nonprecious metal ORR electrocatalyst in alkaline media.

A column-like MoS₂/rGO with rich-defects nanosheets was prepared. The column-like structure, ultrathin nanosheets and the interaction of Mo atoms with graphene, and rich-defects is the guarantee of the outstanding ORR performance.     

Metal free synthesis of ethylene and propylene carbonate from alkylene halohydrin and CO2 at room temperature

Herein we describe a metal free and one-pot pathway for the synthesis of industrially important cyclic carbonates such as ethylene carbonate (EC) and propylene carbonates (PC) from molecular CO₂ under mild reaction conditions. In the actual synthesis, the alkylene halohydrins such as alkylene chloro- or bromo or iodohydrin and organic superbase, 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU) reacted equivalently with CO₂ at room temperature. The syntheses of cyclic carbonates were performed in DMSO as a solvent. Both 1,2 and 1,3 halohydrin precursors were converted into cyclic carbonates except 2-bromo- and iodoethanol, which were reacted equivalently with DBU through n-alkylation and formed corresponding n-alkylated DBU salts instead of forming cyclic carbonates. NMR analysis was used to identify the reaction components in the reaction mixture whereas this technique was also helpful in terms of understanding the reaction mechanism of cyclic carbonate formation. The mechanistic study based on the NMR analysis studies confirmed that prior to the formation of cyclic carbonate, a switchable ionic liquid (SIL) formed in situ from alkylene chlorohydrin, DBU and CO₂. As a representative study, the synthesis of cyclic carbonates from 1,2 chlorohydrins was demonstrated where the synthesis was carried out using chlorohydrin as a solvent as well as a reagent. In this case, alkylene chlorohydrin as a solvent not only replaced DMSO in the synthesis but also facilitated an efficient separation of the reaction components from the reaction mixture. The EC or PC, [DBUH][Cl] as well as an excess of the alkylene chlorhydrin were separated from each other following solvent extraction and distillation approaches. In this process, with the applied reaction conditions, >90% yields of EC and PC were achieved. Meanwhile, DBU was recovered from in situ formed [DBUH][Cl] by using NaCl saturated alkaline solution. Most importantly here, we developed a metal free, industrially feasible CO₂ capture and utilization approach to obtain EC and PC under mild reaction conditions.

Metal free, one-pot and room temperature syntheses of the industrially important cyclic carbonates such as ethylene and propylene carbonate were performed from alkylene halohydrins and CO₂.     

Low temperature NO2 gas sensing with ZnO nanostructured by laser interference lithography

ZnO conductometric gas sensors have been widely studied due to their good sensitivity, cost-efficiency, long stability and simple fabrication. This work is focused on NO₂ sensing, which is a toxic and irritating gas. The developed sensor consists of interdigitated electrodes covered by a ZnO sensing layer. ZnO has been grown by means of the aerosol assisted chemical vapor deposition technique and then nanostructured by laser interference lithography with a UV laser. The SEM and XRD results show vertically oriented growth of ZnO grains and a 2D periodic nanopatterning of the material with a period of 800 nm. Nanostructuring lowers the base resistance of the developed sensors and modifies the sensor response to NO₂. Maximum sensitivity is obtained at 175 °C achieving a change of 600% in sensor resistance for 4 ppm NO₂versus a 400% change for the non-nanostructured material. However, the most relevant results have been obtained at temperatures below 125 °C. While the non-nanostructured material does not respond to NO₂ at such low temperatures, nanostructured ZnO allows NO₂ sensing even at room temperature. The room temperature sensing capability possibly derives from the increase of both the surface defects and the surface-to-volume ratio. The long stability and the gas sensing under humid conditions have also been tested, showing improvements of sensitivity for the nanostructured sensors.

ZnO gas sensing improvement due to laser interference nanostructuration.     

Textile-supported silver nanoparticles as a highly efficient and recyclable heterogeneous catalyst for nitroaromatic reduction at room temperature

A novel textile-based nanosilver catalyst was prepared with a facile synthetic method. The textile-supported nanosilver (TsNS) proved to be an excellent heterogeneous catalyst for the reduction of nitroaromatics with a broad substrate scope. It can be recycled for up to 6 times without significantly compromising its catalytic efficacy. The TsNS catalyst was developed into a column reactor, demonstrating its practical application with the advantages of low cost, ease of operation and large scale synthesis capabilities. Scanning electron microscopy (SEM) showed that there were few changes to the catalyst''s surface after the reaction. Besides, inductively coupled plasma (ICP) analysis showed that few silver particles leaked, and the interactions between the nitro groups of the nitroaromatics and the nanosilver particles were characterized by X-ray photoelectron spectroscopy (XPS), which lead to the proposal of a four-step mechanism for the reduction reaction.

A novel textile-supported nanosilver (TsNS) catalyst was prepared and applied in nitroaromatic reduction with excellent activity, stability and recyclability.