In this paper, a three-dimensional ordered microporous (3DOM) inverse opal-structured ZnSe/3DOM TiO2 composite carrier was first constructed via self-assembly, vacuum impregnation and hydrothermal methods. Then, Ag-Ag2S nanoparticles were loaded onto its surface via in situ deposition and photoreduction, successfully preparing an Ag-Ag2S@ZnSe/3DOM TiO2 composite photocatalyst with a stepped, ordered pore structure. The composite exhibits highly regular multi-level interconnected channels, which are conducive to light scattering and reactant transport. Electron paramagnetic resonance (EPR), ultraviolet photoelectron spectroscopy (UPS) tests and density functional theory (DFT) confirm the formation of a double S-scheme heterojunction in the composite. Combined with the surface plasmon resonance (SPR) effect of Ag nanoparticles, it synergistically promotes efficient separation and spatial directional migration of photogenerated carriers. Under simulated sunlight, Ag-Ag2S@ZnSe/3DOM TiO2 composite demonstrates excellent multifunctional photocatalytic performances: photocatalytic degradation of crystal violet (CV) is effective under different water environments (lake water, snow water, and tap water, etc. in Qiqihar City, Heilongjiang Province, China); the photocatalytic hydrogen evolution activity is 11.68 times that of pure TiO2 after 8 h; and the antibacterial rate against Escherichia coli (E. coli) reaches 89.85% within 30 min. This work provides new strategies and mechanistic insights for developing efficient multifunctional photocatalytic systems through structural design and band regulation.

Metal organic frameworks (MOFs) have drawn the spotlight in the field of gas sensing due to their miraculous geometrical and electronic structures, as well as simple and controllable self-assembly processes. Here, NiO@Co3O4 heterostructures to be synthesized using heating reflux method by vertically wrapping ultra-thin NiO cilia on the surface of hollow ZIF-67 nanocages and applying this as a template for thermal annealing. The unique hollow structure and rich mesoporous structure provide space for gas diffusion and carrier migration. The prepared NiO@Co3O4-350 sensor achieves a high response of 47.4 and exceedingly short response/recovery time (1.3 and 9.6 s) at room temperature, with a minimum detection limit of only 10 ppb and good selectivity, repeatability and long-term stability for NO2 gas. This work highlights the significance of morphology and structure for improving gas sensing performance, which sheds a thought-provoking light on the design and preparation of composite oxide sensors.

SnO2 has attracted much attention in the field of gas sensors due to its unique structure and properties. In this work, SnO2 nanoflowers doped by Ag structures were prepared by a facile hydrothermal synthesis method. Ag doping not only increases the number of oxygen vacancies in the composite, but also alters the carrier migration behavior and significantly increases the carrier concentration, promoting the electron transport rate. Additionally, Ag doping enhanced the conductivity and catalytic activity of the composite, making it highly selective for NO2. At room temperature (RT), Ag-doped SnO2 sensor exhibit excellent gas-sensitizing properties. At the NO2 concentration of 100 ppm at RT (25 degrees C, 25 % RH) the prepared 2 at% Ag-SnO2 sensor has a response value of 73.0 (Ra/Rg), a response time of 1.4 s, and a detection limit as low as 10 ppb. Its long-term stability is up to 90 days. Doping is an effective way to improve gas sensing performance. It solves the disadvantages of low sensitivity and poor selectivity of SnO2.

Hollow NiO microspheres were prepared using one-step hydrothermal method assisted by geminal dicationic ionic liquid (DIL) 1, 2-bis (N-dodecylimidazolyl) ethane bromide ([C12-2-C12mim][Br2]). The structures of the prepared microspheres can be controlled by adjusting the concentration of ionic liquid and reaction temperature. Furthermore, the amount of ionic liquid residue in these microspheres can also be controlled by changing the calcination temperature. Among them, the NiO hollow microspheres prepared by calcining the precursor at 600 degrees C (Ni1-600) in air display the most excellent gas sensing performance, including high response (35.6-100 ppm H2S) and low working temperature (50 degrees C). The excellent gas sensing performance of the Ni1-600 is attributed to the ionic liquid residue with appropriate content, which enhances the interaction between the analyte and the sensing material. The strong interaction effectively increases the sensitivity and reduces the working temperature of the sensor. The NiO hollow microspheres are expected to be a promising candidate material for the highly sensitive H2S gas sensor at near room temperature.

A two-dimensional helical structure formed by directional helical growth of BiOCl nanosheets (NSs) on porous C3N4 thin layers was fabricated by a one-pot oil bath method and applied for the first time to gas sensing. The heterojunction interface formed by the C3N4 thin layer and BiOCl nanosheet can not only effectively inhibit the carrier recombination in the C3N4 sheet, but also form a rapid electron transfer channel between the interfaces. In addition, the microstructural control of BiOCl nanosheets spirally grown on porous C3N4 thin layers essentially increases the particular surface area and the active sites for gas and complicated interactions, hence improving the gas sensitivity of BiOCl nanosheets. The results indicate that BiC-2 has perfect detection limit and sensitivity to NO2 at room temperature. The response value at 100 ppm was 53.05 (Ra/Rg), the response time was 3.2 s, and the detection limit was 10 ppb. This provides a prospect for the future research of gas sensors based on C3N4 and BiOCl.(c) 2022 Elsevier B.V. All rights reserved.

The two-dimensional (2D) g-C3N4 nanosheets have been widely recognized for their great potential in gas sensing. However, the disadvantages brought by layer stacking of two-dimensional nanosheets also seriously affect their performance and application. In this paper, three-dimensional hydrangea-like Pd-ZIF-67/g-C3N4 was prepared for the detection of nitrogen dioxide gas at room temperature via a simple hydrothermal method. The Pd-ZIF-67/g-C3N4 gas sensor exhibited excellent sensing properties with highest sensing response (23.8-100 ppm), ultrafast response speed (0.5 s) and lowest limit of detection (10 ppb) at room temperature. Moreover, it also manifests excellent reversibility and durability, optimal stability and commendable selectivity towards NO2 gas. This excellent performance is due to the three-dimensional spatial configuration, synergistic effect and catalytic action of Pd. In general, the constructed structure and the proposed design strategy have a certain promoting role in promoting the creation of high performance gas sensors with three-dimensional heterogeneous structures based on two-dimensional nanosheets.

The reaction of copper and nickel salts with the O,N-donor Schiff base 5-bromo-2-((2-hydroxyethylimino)methyl)phenol (HL) in methanol provides two new complexes [CuL2] (1) and [Ni2L2(N-3)(2)(CH3OH)(2)]center dot CH3OH (2). The complexes have been characterized by analytical and spectroscopic measurements. The crystal structures of the complexes have been determined by X-ray crystallography. The Cu atom in the mononuclear complex1is in square planar coordination. The Ni atoms in the end-on azido bridged dinuclear complex2are octahedral coordination. The Schiff base ligands coordinate to the Cu and Ni atomsviaNO and NOO donor sets, respectively. The antimicrobial activities of the complexes were assayed.

A facile solvothermal method has been employed to fabricate ZnCo zeolite imidazolate framework (ZIF) nanoparticles intercalated graphene nanosheet (ZnCo-ZIF/GN), in which ZnCo-ZIF nanoparticles are uniformly distributed. The optimized ZnCo-ZIF/GN-120 sensor has a highly sensitive response of 54.61 for 100 ppm of NO2, and the detection limit reaches 10 ppb at room temperature (rt, 22 degrees C; relative humidity, 30%). The ZnCo-ZIF/GN-120 sensor is shown to have good selectivity, excellent stability, and repeatability for NO2 detection. The facile fabrications of the composites of ZnCo-ZIF nanoparticles and highly conductive GNs pave the way for developing advanced high-performance NO2 sensors.

The sensing materials consist of more than one metal oxides species may endow the gas sensors with superior sensing abilities. MoO3, an acidic oxide, its precursors are usually produced in acidic solution via hydrothermal/ solvothermal method and their hierarchical structures would dissolve and collapse under alkaline circumstance, hampering the functionalization of MoO3 by other conventional metal oxides which stably exist in basic solution. In this paper, a binary metal oxide, denoted as hierarchical heterostructured alpha-Fe2O3/alpha-MoO3 hollow spheres were fabricated via a simple one-step solvothermal process. The 4.55 at% alpha-Fe2O3 -decorated alpha-MoO3 sensor exhibits remarkable sensing performance for aniline (ANI) with high sensitivity and selectivity at 217 degrees C. In particular, it shows higher response (32.5) to 30 ppm ANI compared to pristine alpha-Fe2O3 (2.1) and alpha-MoO3 (3.2) sensors, respectively, along with fast response time (3.6 s). Besides, the detection limit to ANI is further decreased from 1 ppm for the pristine alpha-MoO3 sensor to 0.01 ppm. Possible oxidation product of ANI was confirmed through GC-MS technique for the first time. The gas sensing mechanism of alpha-Fe2O3/alpha-MoO3 to ANI is speculated as the oxidation of ANI to azobenzene by chemisorbed oxygen. The possibility relating to the superior reducing gas-sensing properties of alpha-Fe2O3-decorated alpha-MoO3 to ANI was demonstrated. This work provides a logical strategy to design metal oxide composites for high performance gas sensor.

Controllable synthesis of ZIF-67/EG intercalated structure for detection of ultra-trace Cd2+, Cu2+, Hg2+ and Pb2+ ions.

This work illustrates a simple polymer thermal treatment strategy to develop high-dispersed Fe2O3/Fe nanoparticles residing in honeycomb-like N-doped graphitic carbon (Fe2O3/Fe@N-GC). The as-prepared Fe2O3/Fe@N-GC composites consist of three-dimensional (3D) strutted interconnective graphitic carbon frame, which would not only refrain from restacking and facilitate the charge transfer, but also provide more reaction interface between gas molecules and materials. Benefiting from the synergistic merits of Fe2O3/Fe, N-doping graphitic carbon, high surface area and unique 3D architectures, the optimal Fe2O3/Fe@N-GC presents impressive sensitivity and selectivity for NO2 gas detection at room temperature with the response of 25.48-100 ppm, response time of 2.13 s, recovery time of 11.73 s, detection limit of 10 ppb and as long as 60 days of stability. As a result, the present Fe2O3/Fe@N-GC composite with an easy fabrication method and high sensitivity, selectivity, stabitliy towards NO2 at RT would inspire various designs based on the 3D honeycomb structure for more real applications in gas sensors.

An intercalated SnS2/aEG structure with abundant heterojunctions for enhanced NO2 gas sensing performance at room temperature.

The reactions of Ni(OAc)2 2H2O with Schiff base ligands 5-bromo-2-((cyclopentylimino)methyl)phenol (HL1) and 5-bromo-2-(((2-(isopropylamino)ethyl)imino)methyl)phenol (HL2) in methanol afforded two discrete trinuclear com-plexes [Ni3(L1)2(?2-?1:?1-OAc)2(DMF)2(BrSal)2] (1) and [Ni3(L2)2(?2-?1:?1-OAc)2(?2-?2:?1-OAc)2] (2), where BrSal is the monoanionic form of 4-bromosalicylaldehyde. The complexes were characterized by elemental analysis, IR and UV-Vis spectroscopy. The crystal structures of the complexes have been determined by X-ray crystallography. In both com-plexes, the nickel atoms are in octahedral coordination geometries. The L1 ligand coordinates to the nickel atoms through the phenolate O and imino N atoms, and the L2 ligand coordinates to the nickel atoms through the phenolate O, imino N and amino N atoms. The antimicrobial activities of the complexes were assayed.

Monodisperse alpha-Fe2O3 hollow ellipsoids have been assistantly fabricated via small amount of [C(12)mim][PF6] (IL) addition from a simple one-pot method based on hydrothermal treatment of FeCl3 center dot 6H(2)O, followed by calcination at various temperatures. The phase and microstructure of the products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption-desorption techniques. Further studies reveal that both calcination temperature and the amounts of IL have a strong effect on the structures. The well known Ostwald ripening process is responsible for the transformation from solid ellipsoids to hollow ellipsoids. The gas sensors based on the as-synthesized hollow alpha-Fe2O3 ellipsoids calcined at 300 degrees C exhibited not only high response, short recovery time and good stability to 100 ppm n-butanol at 217 degrees C, but also low detection limit (0.1 ppm) compared with those under higher calcination temperature and the products obtained without ILs-addition. IL-loading alpha-Fe2O3 hollow ellipsoids could be a promising candidate for highly sensitive n-butanol gas sensors.

Intercalated gamma-Bi2MoO6/graphene nanosheet composites (BMO/GNCs) were prepared by vacuum-assistant and solvothermal technique. In BMO/GNCs, BMO nanoparticles (NPs) were uniformly distributed on the surface and interlayer of graphene nanosheets (GNs), simultaneously along with a large number of defects and interface on GNs and BMO NPs. As synthesized with solvothermal temperature at 160 degrees C and graphite content of 80 mg, BMO/GNCs-8-160 sample exhibits the remarkable gas sensitivity, reversibility and selectivity to NO2 at room temperature (RT, 22 degrees C). The relative response rate of the sensor toward 100 ppm NO2 is 96.73, which is about 6.41 times of pure BMO NPs. Furthermore, the response time and recovery time is merely 2.5 and 34.1 s, respectively. The detection limit can reach 10 ppb with response value of 1.51. The improved NO2 sensing performance is attributed to the effective electron transfer between BMO NPs and GNs and typical structure characteristics of BMO/GNCs, which is rarely reported in the room temperature type of Bi2MoO6 sensor. (C) 2019 Elsevier Ltd. All rights reserved.

Mesoporous palladium oxide (PdO)-functionalized tin dioxide (SnO2) composite nanotubes (SPCTs) were prepared via one-step synthesis by electrospinning technology using ethanol and N,N-dimethylformamide (DMF) as solvents. Compared with pure SnO2 nanotubes, there were abundant mesopores and multiheterojunctions in PdO-functionalized SnO2 nanotubes. The sample with the molar ratio of SnO2:PdO of 100:3 (3-SPCT) exhibited excellent response (∼20.30) as a sensor with fast gas response speed (∼1.33 s) to 100 ppm nitrogen dioxide (NO2) at room temperature (RT), and the detection limit reached to 10 ppb. The improved gas sensing performance of the 3-SPCT sensor was mainly attributed to the synergistic effect: the unique SnO2 tubular structure and well-dispersed mesopores provided the gas diffusion and adsorption channels, oxygen defects and chemisorbed oxygen were taken as the electron trap and charge transfer active sites, and a large number of heterojunctions acted as electron transport channels, thereby increasing the transfer rate.

Hydrothermally prepared vertical multilayer WS2 nanosheets on the surface of few-layer MoS2 for the ultra-sensitive NO2 detection at room temperature.

MoS2 nanosheets (NSs) are a promising gas sensing material at room temperature (RT) due to their unique properties and structures. Unfortunately, the activity of pure MoS2 NSs is highly affected by the adsorption of atmospheric oxygen, which strongly influences the stability of MoS2 sensing devices and significantly hinders the practical applications of these sensors in air. Heterostructure formation may be an effective approach to modulate the intrinsic electronic properties of MoS2 NSs. In this study, thin MoO2 nanoplates (NPs) were decorated with multilayer MoS2 NSs via one-step controllable sulfurization to fabricate MoS2@MoO2 nanonetworks, and remarkable gas sensing performance was achieved with high stability in air at RT. In particular, the MSO-2 (1 h sulfurization of the MoO2 NPs) nanonetworks with n-p heterojunctions demonstrated a high response of 19.4 to 100 ppm NO2 in a short period of time (1.06 s) with rapid recovery (22.9 s) to the baseline. The excellent gas sensing performance of the MSO-2 sensor is attributed to the synergistic effect of the MoS2 NSs and thin MoO2 NPs, which created heterojunctions/defects to easily transfer electrons and provide more active sites for NO2 gas. This simple synthetic method to design and fabricate n-p heterojunction sensors will be effective in commercial gas sensing applications.

To fabricate a high-performance material for sensor devices at room temperature and further improve the synthetic approach of sensing materials, one dimensional (1D) CuO-CNTs nanocomposites were prepared with CNTs and CuO nanorods (NRs) via a facile reflux method. The 1D composite with the molar ratio of CuO and CNTs at 2.4:1 displays excellent gas sensing performance, i.e. the lowest detectable limit of 970 ppb and the short response time of 6s-97.0 ppm NO2 at room temperature. In the 1D composite, the CNTs part provides a channel to enable effective and fast carrier transport, while the CuO NRs fabricates an asymmetrical schottky contact at the interface between the composites and the Au electrode. The advantage of the synergy of CNTs and CuO which possesses superior conductivity benefits the sensing of our 1D CuO-CNTs composite by providing affluent electrons. (C) 2017 Elsevier B.V. All rights reserved.

The one dimensional (1D) ordered porous Pd@TiO2 nanofibers (NFs) array film have been fabricated via a facile one-step synthesis of the electrospinning approach. The Pd@TiO2 NFs (PTND3) contained Pd (2.0 wt %) and C, N element (16.2 wt %) display high dispersion of Pd nanoparticles (NPs) on TiO2 NFs. Adding Pd meshed with C, N element to TiO2 based NFs might contribute to generation of Lewis acid sites and Brønsted acid sites, which have been recently shown to enhance NH3 adsorption-desorption ability; Pd NPs could increase the quantity of adsorbed O2 on the surface of TiO2 based NFs, and accelerated the O2 molecule-ion conversion rate, enhanced the ability of electron transmission. The response time of PTND3 sensor towards 100 ppm NH3 is only 3 s at room temperature (RT). Meantime, the response and response time of the PTND3 to the NH3 is 1 and 14s even at the concentration of 100 ppb. Therefore, the ordered Pd@TiO2 NFs array NH3 sensor display great potential for practical applications.