•CuO hollow microspheres composed of nanobars were successfully synthesized by hydrothermal method.•The effect of reaction time and temperature on morphologies was investigated and a synthesis mechanism was proposed.•Good formaldehyde sensing properties of CuO hollow microspheres were obtained.CuO hollow microspheres were synthesized via a facile hydrothermal process. Copper nitrate trihydrate (Cu(NO3)2·3H2O) was used as copper source and cetyltrimethylammonium bromide (CTAB) was used as soft template. The morphology and crystal structure of products were systematically investigated by XRD, FESEM, TEM, FT-IR and BET. CuO hollow microspheres were identified as monoclinic structure. The hollow microspheres were assembled by a number of nanobars which were composed of smaller nanograins. The formaldehyde gas sensing properties of CuO products with different morphologies were investigated. The results indicated that the sensor based on CuO hollow microspheres exhibited high gas response, fast reversible and response, good selectivity and stability to formaldehyde gas. This is attributed to hollow structures with the largest specific surface area and an effective gas diffusion path in favor of mass transportation and gas diffusion.

Flower-like NiO hierarchical architectures were synthesized by a solvothermal process without using any other surfactant. Absolute ethanol and distilled water were adopted as solvent, and nickel nitrate hexahydrate was employed as the nickel source. The morphology and crystal structure were mainly investigated. Through annealing the as-obtained products, flower-like NiO hierarchical architectures with a cubic structure were synthesized, which were assembled by a number of thin nanosheets with a thickness of about 30 nm. The formaldehyde gas sensing measurements showed that well-defined NiO flower-like structures with large surface area exhibited higher responses compared with microsheets/nanosheets at a relatively lower operating temperature of 200 °C. Moreover, a reversible and fast response to formaldehyde gas at various gas concentrations, good selectivity and stability were obtained. The results indicated that the flower-like NiO hierarchical architectures are promising materials for gas sensors.

•Porous MgO nanoplates were synthesized through a facile precursor calcination method.•The adsorption capacity for fluoride is larger than 185.5 mg g−1.•The porous MgO nanoplates can efficiently removal fluoride at a wide pH rang of 2–10.•A novel hydroxyl and carbonate co-exchange mechanism was reported.•The porous MgO nanoplates is quite stable during the fluoride removal process.Porous MgO nanoplates were successfully synthesized through a facile and cost-effective precursor calcination method. The as-prepared porous MgO nanoplates were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller measurements. The fluoride removal performance of the porous MgO nanoplates has been investigated. The fluoride adsorption rate of the absorbent was very fast, and the adsorption kinetics could be fitted into a pseudo-second-order model. The adsorption isotherm can be well fitted in Freundlich model, while the adsorption capacity was over 185.5 mg/g at pH 7. Furthermore, the porous MgO nanoplates can efficiently remove fluoride from water in a wide pH range of 2–10, which is favorable for practical application. The effect of co-existing anions on fluoride removal also has been investigated. The result indicated that the existence of carbonate, bicarbonate and phosphate can influenced the fluoride adsorption performance. Furthermore, the fluoride adsorption mechanism was investigated by the FTIR and XPS analysis. The results show that both the hydroxyl and surface carbonates can exchange with fluoride ions, revealing a hydroxyl and carbonate co-exchange mechanism. Moreover, the as-prepared porous MgO nanoplates is quite stable, only less than 0.18% of the absorbent was dissolved during the adsorption experiment. The results indicated that the as-prepared porous MgO nanoplates can be used as a potential suitable candidate for fluoride removal.

•Ag/SnO2/graphene ternary nanocomposites have been synthesized by a wet-chemical method.•The lowest detection concentration of the synthesized ternary nanocomposites to acetone is 0.005 ppm.•The roles of Ag nanoparticle, SnO2 nanoparticle, and graphene in gas sensing process are discussed.Combined with the π-conjugate system of graphene, the SnO2/graphene nanocomposites exhibited highly sensitive to benzene as reported previously. However, the SnO2/graphene nanocomposites presented lower sensitive to other volatile organic compounds (VOCs) than benzene. For further improving the sensitivity to VOCs, noble metal was added to those nanocomposites. Here, Ag/SnO2/graphene ternary nanocomposites have been synthesized by a wet-chemical method. The synthesized ternary nanocomposites exhibit high sensitive to VOCs, especially acetone. The lowest detection concentration to acetone is 0.005 ppm. The sensing mechanism is speculated and the role of Ag nanoparticle, SnO2 nanoparticle, and graphene are clearly discussed.

•Chlorobenzene sensor has been fabricated by the Pt-decorated porous single-crystalline ZnO nanosheets.•The Pt-decorated PSC ZnO NSs showed good response to low concentrations of chlorobenzene from 10 to 500 ppb.•The enhancement sensing mechanism of Pt nanoparticle decoration has also been discussed in detail.Detection of chlorobenzene is a challenge for metal oxide gas sensors because of its stable molecule structure. In this work, Pt-decorated porous single-crystalline ZnO nanosheets (PSC ZnO NSs) were successfully synthesized via a one-pot hydrothermal method followed by a liquid phase reduction process. The morphology and structure of the as-prepared sample were well characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectrum (EDS) and ICP-MS analysis. From gas-sensing test, it can be found that the decoration of Pt nanoparticles largely enhanced the sensing performance of the PSC ZnO NSs. The Pt-decorated PSC ZnO NSs showed good response to low concentrations of chlorobenzene from 10 to 500 ppb. In contrast, the Au and Ag-decorated PSC ZnO NSs had still no response to 500 ppb of chlorobenzene. The enhancement sensing mechanism of Pt nanoparticle decoration has also been discussed in detail.

•1D ZnO nanostructures were synthesized on SiO2 substrate without using any catalyst.•The effect of source temperature and Ar flow rate on morphologies was investigated.•H2 gas sensing properties of the 1D ZnO nanostructures were in situ investigated.One-dimensional (1D) ZnO nanostructures were synthesized on SiO2 substrate by a catalyst-free thermal evaporation method using metallic Zn powders as a raw material. The crystal structure and morphology of the ZnO nanostructures were investigated by SEM, XRD and BET. The results showed that the 1D nanostructures obtained on the SiO2 substrate were hexagonal ZnO. Source temperature and Ar flow rate were an important parameter for the growth of the 1D nanostructures and particular type of ZnO nanostructures could be grown in a specific temperature and Ar flow rate. The H2 sensing properties of prepared 1D ZnO nanostructures were in situ investigated. The sensor exhibited high sensitivity and fast response to H2 gas. The highest sensitivity observed upon exposure to H2 at 1000 ppm was 5.3 at 200 °C, which demonstrates the potential application of the 1D ZnO nanostructures for fabricating gas sensors compatible with semiconductor technology.

•Flower-like hierarchical structures consisting of porous single-crystalline ZnO nanosheets were synthesized.•The flower-like hierarchical structured ZnO exhibited higher response and shorter response and recovery times.•The sensing mechanism of the flower-like hierarchical has been systematically analyzed.Flower-like hierarchical structures consisting of porous single-crystalline ZnO nanosheets (FHPSCZNs) were synthesized by a one-pot wet-chemical method followed by an annealing treatment, which combined the advantages between flower-like hierarchical structure and porous single-crystalline structure. XRD, SEM and HRTEM were used to characterize the synthesized FHPSCZN samples. The sensing properties of the FHPSCZN sensor were also investigated by comparing with ZnO powder sensor, which exhibited higher response and shorter response and recovery times. The sensing mechanism of the FHPSCZN sensor has been further analyzed from the aspects of electronic transport and gas diffusion.

Hierarchical meso-macroporous SnO2 was synthesized by a sol–gel process using carbonaceous spheres as sacrificial templates. The morphology of meso-macroporous structures can be controlled by adjusting the sintering temperature. Compared with the traditional SnO2, the hierarchical meso-macroporous SnO2 exhibited higher gas response and shorter response and recovery times in detecting indoor air pollutants including ethanol, benzene and toluene. With regard to the gas sensing property, mesopores provide plenty of active sites for surface chemical reactions, on the one hand. On the other hand, the gas diffusion in the sensing film can be improved by macropores greatly. The morphology and structures were characterized by field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) respectively.

To detect polychlorinated biphenyls (PCBs), a novel porous anodic alumina (PAA) based capacitive sensor working at room temperature has been developed. The parallel nanopores of PAA not only provide large surface area for PCB adsorption, but also benefit for the enhancement of capacitive response. By dropping the PCB methanol solution on the surface of PAA, it is convenient to load PCB into the nanopores by solvent evaporation. 3,3′,4,4′-tetrachlorobiphenyl (PCB77) was chosen as a typical sample of PCBs to investigate the sensing properties of the capacitive sensor. The capacitance of the PAA membrane shows remarkable enhancement after PCB77 solution was loaded while no significant change can be seen after the pure solvent was loaded. The capacitive sensor also shows good response to PCB77 even in the presence of the interferent of benzene. The sensing mechanism has been qualitatively discussed based on a parallel plate capacitor model. The detection limit is down to 8 × 10−8 M towards PCB77. The novel PAA based capacitive sensor exhibits great potential for practical application in trace detection of PCBs.

An effort has been made to develop a kind of mesoporous SnO2 gas sensor for detecting indoor air pollutants such as ethanol, benzene, meta-xylene. Mesoporous SnO2 material has been prepared by sol-gel method joined into multiwall carbon nanotubes as template. The field emission scanning electron microscope (FSEM) was used to characterize the samples, by which the mesoporous structure of SnO2 was obviously observed. The investigation results suggest that the as-prepared mesoporous SnO2 has a good response and reversibility to indoor environmental air pollutants. At last, the selectivity of the mesoporous sensor was investigated.

Hierarchical meso-macroporous SnO2 was synthesized by a sol–gel process using carbonaceous spheres as sacrificial templates. The morphology of meso-macroporous structures can be controlled by adjusting the sintering temperature. Compared with the traditional SnO2, the hierarchical meso-macroporous SnO2 exhibited higher gas response and shorter response and recovery times in detecting indoor air pollutants including ethanol, benzene and toluene. With regard to the gas sensing property, mesopores provide plenty of active sites for surface chemical reactions, on the one hand. On the other hand, the gas diffusion in the sensing film can be improved by macropores greatly. The morphology and structures were characterized by field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) respectively.