•The basic-oxide-rich precursor La3NbO7 has low effective positive charge on Nb(V).•Formation of low-valent Nb defects is inhibited in LaNbON2 prepared from La3NbO7.•Removal of the secondary product La2O3 gives rise to additional pores in LaNbON2.The presence of low-valent Nb-based point defects and low surface area are common issues within niobium oxynitrides. Herein, La3NbO7 which has richer basic oxide and lower positive Mulliken charge on Nb(V) than LaNbO4, was prepared via NaCl-KCl mixed flux synthesis and converted to perovskite-type LaNbON2 via thermal ammonolysis. Removal of secondary product La2O3 from ammonolysis of La3NbO7 gives rise to additional nanopores in LaNbON2 besides the pores resulted from nitridation. This makes a bigger specific surface area (23 m2/g) than conventional LaNbON2 prepared from LaNbO4 (11 m2/g). Moreover, UV–vis spectrum of LaNbON2 from La3NbO7 reveals much lower defect absorption than LaNbON2 from LaNbO4; thermogravimetric analysis shows that the mass-gain stage attributed to oxidation of low-valent Nb is present in curve of LaNbON2 from LaNbO4 while absent in that of LaNbON2 from La3NbO7. These indicate that the formation of low-valent Nb defects in LaNbON2 is inhibited when using La3NbO7 as precursor.

Metal nitrides are a significant class of multifunctional materials that have attracted a huge and ever-increasing interest for their new structural and redox chemical, as well as physical, characteristics. In this work, we present a designed synthesis of Sn3N4 nanoparticles through a soft urea route for the first time. The strategy includes the synthesis of gel-like tin–urea precursor and subsequent transformation to Sn3N4 nanoparticles via thermal treatment of the as-prepared precursor under NH3 flow. Various techniques were employed to characterize the structure and morphology of the as-prepared Sn3N4 samples. When innovatively utilized as sensing material for a gas sensor, Sn3N4 nanoparticles exhibited high sensitivity, excellent cyclability, and long-term stability to ethanol at the operating temperature of 120 °C, which is lower than those of metal oxide-based ethanol sensors. This research work provides an efficient method for preparing Sn3N4nanoparticles that are promising sensing materials for ethanol gas sensors.

•Solvothermal approach followed by calcination is used to obtain mesoporous (Ag, Ag2O) co-loaded TiO2.•Co-loaded (Ag, Ag2O):TiO2 microspheres exhibit visible light photocatalysis.•Nitridation of (Ag, Ag2O) co-loaded TiO2 deleteriously impacts its photocatalytic performance.•TiN phase formation is not observed even after prolonged nitridation.•Nitridation results (a) reduction of Ag2O to Ag and (b) Ag agglomeration and grain growth.A simple solvothermal approach with post-calcination is used to obtain (Ag, Ag2O) co-loaded TiO2 microspheres with high specific surface area (43.8 m2g-1) and desirable visible light photocatalytic degradation (64% after 2 h visible light irradiation). Generally, N-doping of TiO2 via nitridation using NH3 improves the visible light absorption property of material. However, nitridation of (Ag, Ag2O) co-loaded TiO2 results in a deleterious impact on the photocatalytic performance (around 20% after 2 h visible light irradiation). This is because nitridation of Ag-Ag2O-TiO2 results in (a) reduction of Ag2O to Ag and (b) Ag agglomeration and grain growth on TiO2 particles. These results in fact imply that in as-synthesized (Ag, Ag2O) co-loaded TiO2 systems, local surface plasmonic resonance (associated with of 5–12 nm Ag particles) aids in enhanced broad band visible light absorption; furthermore the heterojunction between TiO2 and Ag2O improves efficiency with which photogenerated carriers become available for photocatalysis. In all cases we show through selective radical quenching experiments that singlet oxygen is the primary reason for the dye degradation observed.Solvothermal approach followed by calcination is used to obtain Ag and Ag2O co-loaded TiO2 microspheres (Ag-Ag2O-TiO2) with high specific surface area (43.8 m2g-1) and good photocatalytic performance. Interestingly nitridation of (Ag, Ag2O) co-loaded TiO2 deleteriously impacts photocatalytic performance; this is due to (a) reduction of Ag2O to Ag and (b) Ag agglomeration and grain growth.Download high-res image (270KB)Download full-size image

•Co3O4/NiCo2O4 double-shelled nanocages were prepared via a metal-organic framework route.•The strategy includes the synthesis of ZIF-67/Ni-Co hydroxide and Co3O4/NiCo2O4 DSNCs.•The Co3O4/NiCo2O4 DSNCs shows excellent sensing performance to acetone.Co3O4/NiCo2O4 double-shelled nanocages (DSNCs) were successfully prepared through a metal-organic frameworks (MOFs) route. The strategy includes the synthesis of zeolite imidazolate framework-67 (ZIF-67)/Ni-Co layer doubled hydroxides precursor and subsequent transformation to Co3O4/NiCo2O4 DSNCs by thermal annealing of the as-prepared precursor in air. Various techniques such as XRD, SEM/EDS, BET and TEM were employed for the characterization of microstructure and morphology of the as-prepared Co3O4/NiCo2O4 DSNCs. The use of as-prepared Co3O4/NiCo2O4 DSNCs as a gas sensing material in a gas sensor gave an enhanced sensitivity to acetone compared with result obtained in Co3O4 nanocages (NCs). In addition, excellent reversibility and selectivity of the sensor were observed. These properties make the Co3O4/NiCo2O4 DSNCs a good candidate for acetone detection.

•The Mo-N-co-doped mesoporous TiO2 microspheres were synthesized via a solvothermal method and further nitriding treatment.•The properties of TiO2 microspheres can be tuned by Mo-N-co-doping.•Photocatalytic rate is much higher than Pure TiO2 catalyst powder and Mo doped TiO2 microspheres.•The higher activity is attributed to the large BET surface area, narrow band gap and intense light absorbance in visible region.Mo-N-co-doped mesoporous TiO2 microspheres were synthesized via a solvothermal method, followed by nitriding treatment under ammonia gas flow. The efficiency of the samples was investigated by monitoring the degradation of Rhodamine-B under visible light irradiation. The experimental results revealed that Mo-N-co-doped mesoporous TiO2 microspheres showed better performances than Mo-TiO2 microspheres. It was observed that; 0.1% molar quantity of Mo doped on TiO2 at 500 °C for 2 h under nitriding conditions gave highest photocatalytic activities. The nitridation under ammonia gas of Mo-TiO2 samples created oxygen vacant sites and led to incorporation of substitutional and interstitial Nitrogen. The enhanced visible light photocatalytic activities of Mo-N-co-doped TiO2 photocatalyst was attributed to the large surface areas, narrow band gap and intense light absorbance in visible region. This study may create a promising and eco-friendly method towards synthesis of metal and non-metals co-doped on semiconductor materials to improve their photocatalytic activities and applications.Download high-res image (192KB)Download full-size image

•Iron (III) and nitrogen co-doped mesoporous TiO2 microspheres (Fe-N-TiO2) are prepared.•Fe3+/Fe2+ dopant trap energy level introduced within the band gap in Fe (∼1 at%) doped TiO2.•Subjecting Fe-TiO2 samples to ammonothermal process induces oxygen vancancies, and causes substitutional and interstitial N.•Co-dopants are distributed uniformly in the best photocatalysts.•Active species generated is shown to be singlet molecular oxygen (1O2).Iron (III) and nitrogen co-doped mesoporous TiO2 microspheres (Fe-N-TiO2) are prepared using a self-assembly based solvothermal process followed by an ammonothermal method. Among all samples, 1 mol.% of Fe dopants and 500 °C nitridation (for 2 h) gives the highest visible light photoactivity. Results imply that the Fe3+/Fe2+ dopant trap energy level introduced within the band gap in mildly Fe (∼1 at%) doped TiO2 and the mesoporous nature of the material, both aid in the observed catalytic performance. Subjecting Fe-TiO2 samples to ammonothermal process induces oxygen vancancies, and substitutional and interstitial N. This reduces optical band gap, and introduces local states. The lower band gap and local states together aid in the absorption of visible light and separation of charge carriers. Co-dopants are distributed uniformly in the best photocatalysts. The active species generated in the photocatalytic system is shown to be singlet molecular oxygen (1O2) using selective radical quenchers.Download high-res image (146KB)Download full-size image

Highly crystalline (110) layered perovskite Sr2Nb2O7, (111) layered perovskite Sr5Nb4O15 and complex perovskite Sr4Nb2O9 were prepared by NaCl-KCl flux growth method from SrCO3 and Nb2O5. This flux synthesis achieves single strontium niobate phase in contrast to mixed niobates from the solid state reaction with the same heating parameters. A little excess of Sr source was found to be required for the synthesis of Sr5Nb4O15 and Sr4Nb2O9 at elevated temperature due to slight evaporation. The three strontium niobates were converted to perovskite SrNbO2N via thermal ammonolysis under NH3 flow at 900 °C. Post-wash treatment was performed to remove the byproduct SrO. This makes additional nanopores in SrNbO2N in the cases of Sr5Nb4O15 and Sr4Nb2O9, and results in increasing surface areas of SrNbO2N with Sr:Nb ratios in the precursors (from 9.9 to 19.8 and 35.5 m2/g). On the other hand, the UV–Vis diffusion reflectance spectra reveal decreasing light absorption by defects in SrNbO2N in this order. This suggests fewer low-valent Nb defects in SrNbO2N prepared from precursor with higher Sr:Nb ratio. SrNbO2N prepared from Sr4Nb2O9 would be advantageous for applications that require high surface area and low defect density of the material.

Usually oxygen cannot participate in the selective oxidation reaction of thioether to sulfoxide, which is attributed to its inactive feature. Although UV-light irradiation can activate O2, this process also results in UV-induced hole (hvb+) generation. This oxidative species and O2 can be consumed for the formation of free radical intermediates that leads to uncontrolled auto-oxidation products resulting in low selectivity. Current work aims to develop an approach for the aerobic oxidation of thioether to sulfoxide by exploring the synergy between triethylamine and mesoporous Co–N–TiO2 (nitrided @ 500 °C for 2 h) microspheres (with a large surface area: 124 m2 g−1); the oxidation is carried out via visible-light photoredox catalysis. Triethylamine, due to its electron donating ability, acts as a redox mediator. With a lower band gap and level of conduction band minimum (−0.605 V vs. NHE), the Co–N–TiO2 sample has the ability to be an efficient and selective catalyst. Excellent conversion from the selective oxidation of thioanisole (76.4%) under 12 h visible light irradiation is observed. It may be noted that Co doping into TiO2 alone does not aid in obtaining a good photocatalyst; in fact this sample shows the Moss–Burstein effect. We have also shown that the reported photocatalyst is applicable for the conversion of several other thioethers to sulfoxides; generally high conversion rates and selectivities are observed. The reaction mechanisms are studied using UV-visible absorption spectra and the oxidation–extraction photometry (OEP) method. This result is likely useful for further exploration of surface complex photocatalysts for many other aerobic oxidation reactions.

Bimetallic nitrides are now being considered as one of the emerging advanced functional materials due to their characteristic features and remarkable physicochemical properties. Herein, we report a new crystalline bimetallic nitride (Co3ZnN) that belongs to the cubic crystal phase, which was successfully synthesized through direct nitridation of metallic salts as precursors. Co3ZnN nanoparticles were then supported on nitrogen-doped XC-72 carbon black (N-CB), and this typical Co3ZnN/N-CB nanohybrid discovered can serve as an efficient non-noble metal electrocatalyst with a 4e− reaction pathway for ORR, and demonstrated excellent electrocatalytic performance with high activity and stability.

A highly crystallized mesoporous Ni3N with core–shell structure was prepared from a green and template free method. The Ni3N was characterized by using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area analysis, and the measured Ni3N has a specific surface area of 85.89 m2 g−1 and a narrow pore size distribution centered at 5 nm. After air oxidization, the Ni3N/NiO composite was further evaluated for NO2 gas sensing at room temperature, and the Ni3N/NiO-based sensor exhibited excellent selectivity for NO2 gas. A good linear relationship between the sensor response and the NO2 gas concentrations was observed. The enhanced NO2 sensing performance can be attributed to the highly crystallized mesoporous and core–shell structures of the synthesized Ni3N/NiO.

•In2O3 nanoparticles were synthesized via a facile template-free method.•The synthesis was conducted in water-glycerol-ethylene glycol mixed solvent without any templates.•The In2O3 nanoparticles-based sensor exhibits excellent acetone sensing performances.Ordered In2O3 nanoparticles (In2O3 NPs) were successfully prepared via a template-free method. The synthesis was conducted in a water-glycerol-ethylene glycol mixed solvent without any templates, and the ultra-fine nanostructured In2O3 has a uniform size of about 20–30 nm. The In2O3 nanoparticles exhibited improved sensitivity, fast response, and high selectivity to acetone. The enhanced acetone performance results from a large surface area with enough sensing active sites, and small particle size for effective electron depletion.

•The preparation of metal–nonmetal codoped mesoporous anatase TiO2 microspheres.•The high surface area of doped TiO2 mesoporous microspheres.•The enhanced Vis-light activity of N-doped TiO2 by codoping with W.Mesoporous anatase TiO2 microspheres were prepared via solvothermal method. Ammonium tungstate was used as the W source, and ammonia gas flowing in an ammonothermal reactor as the N source for codoping. TiO2:(W,N) mesoporous microspheres, which were prepared from solvothermal treatment at 160 °C for 16 h and thermal ammonolysis at 500 °C for 2 h after calcination, have high specific surface area of 106 m2 g−1. XPS results indicate the presence of NO, Ni and W6+ in the codoped mesoporous TiO2 microspheres. Monodoping with N shifts the absorption band edge of anatase TiO2 from ultraviolet region to visible region. Although codoping with W makes the visible light absorbance decrease a little, the photocatalytic degradation of a cationic dye rhodamine B (RhB) on mesoporous TiO2:(W,N) microspheres is increased to 1.7 times of that on mesoporous TiO2:N microspheres. This may due to decreasing recombination centers by W-doping charge compensation.

Micro-sized or monolithic electrode materials with sufficient mesoporosity and a high intrinsic conductivity are highly desired for high-energy batteries without the trade-off of electrolyte infiltration and accommodation of volume expansion. Here metallic nitrides consisting of mesoporous microparticles were prepared based on a mechanism of solid–solid phase separation and used as conversion anodes for Li and Na storage. Their superior capacity and rate performance during thousands of cycles benefit from the preservation or self-reconstruction of hierarchically conductive wiring networks. The conversion efficiency is also highly dependent on the reaction pathway and product. Exploring more conductive and percolating mass/charge transport networks particularly in a deep sodiation state is a potential solution for activation of Na-driven conversion electrochemistry.

Copper nitrides are defect-tolerant semiconductors with properties that are promising for solar energy conversion applications. Currently, there are few known ternary copper nitride materials. Here, we synthesized a previously unreported CuNbN2 using an ion-exchange reaction and subsequently determined its properties. CuNbN2 has a layered delafossite-type structure with NbN6 octahedra arranged in layers separated by linear N–Cu–N bonds. Experimental measurements and theoretical calculations agree that CuNbN2 has a 1.3–1.4 eV optical absorption threshold; theory also indicates that the lowest energy indirect band gap is 0.9 eV. The calculated CuNbN2 electron and hole effective masses are quite isotropic (mout /min = 1.3–2.1) and low (m = 0.3–0.7 me), as for the layered crystal structure. On the basis of these results, we propose a new lattice-matched delafossite tandem solar cell approach with Cu(Nb,Ta)N2 absorbers, p-type CuAlO2 contacts, and n-type ZnO contacts. Interestingly, first-principles calculations indicate that CuNbN2 is thermodynamically unstable with respect to disproportionation, yet the successful synthesis and potentially useful photovoltaic properties of this metastable material are possible. We theoretically examine a wide range of ternary copper nitrides for thermodynamic stability and optoelectronic properties with the goal of accessing their potential for solar energy conversion. It is found that the majority of these materials are thermodynamically unstable but that some of them should have properties that are promising for solar energy conversion applications and thus are worth experimental synthesis attempts.

Micro-sized or monolithic electrode materials with sufficient mesoporosity and a high intrinsic conductivity are highly desired for high-energy batteries without the trade-off of electrolyte infiltration and accommodation of volume expansion. Here metallic nitrides consisting of mesoporous microparticles were prepared based on a mechanism of solid–solid phase separation and used as conversion anodes for Li and Na storage. Their superior capacity and rate performance during thousands of cycles benefit from the preservation or self-reconstruction of hierarchically conductive wiring networks. The conversion efficiency is also highly dependent on the reaction pathway and product. Exploring more conductive and percolating mass/charge transport networks particularly in a deep sodiation state is a potential solution for activation of Na-driven conversion electrochemistry.