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The current luminescent metal-organic framework (MOF) based fluorescence detection mostly focuses on achiral molecules. The stereospecific recognition and determination of MOF-based detection remain challenging. A novel luminescent terbium-based MOF (Tb-MOF) based biosensing system with excellent performance for stereoselective detection of D-amino acids (D-AAs) was introduced in this paper. D-Amino acid oxidase catalyzes stereospecific oxidative deamination of D-AAs, producing H2O2. The generated H2O2 effectively quenches the fluorescence of Tb-MOF. Under optimum conditions, the D-AAs were detected with excellent efficiency. The linear working range was 0.5-100 mM for D-Alanine (D-Ala) and 0. 5-5 mM for D-Proline (D-Pro), respectively. The limit of detection (Ksv detection) for D-Ala and D-Pro was 0.09 mM and 0.14 mM, respectively. The detection can be performed within 30 min with high selectivity and long-term stability. The fluorescent sensing platform required simple fabrication and operation and was free from complicated reaction processes and expensive reagents. The present sensing system was successfully applied in D-AA detection in human serum with good recovery, indicating its potential application in detection in biological samples. [ABSTRACT FROM AUTHOR]

The supercells of pure anatase TiO2, nitrogen and/or vanadium doping anatase TiO2 were calculated by first-principles with the plane-wave ultrasoft pesudopotentials method. The effects of different ions doping on the crystal structure, electronic structure, optical properties and photocatalytic activity were investigated by means of the calculational data. At the same time realizing visible-light response, nitrogen and vanadium codoping TiO2 photocatalysts have strong redox potential, and its photocatalytic efficiency would be remarkably improved due to enhancement of electron–hole pairs’ separation. The conclusions would have important significance for understanding and further developing of TiO2 photocatalyst that are activity under visible-light irradiation. [ABSTRACT FROM AUTHOR]

Molecular imprinting technology (MIT); often described as a method of designing a material to remember a target molecular structure (template); is a technique for the creation of molecularly imprinted polymers (MIPs) with custom-made binding sites complementary to the target molecules in shape; size and functional groups. MIT has been successfully applied to analyze; separate and detect macromolecular organic compounds. Furthermore; it has been increasingly applied in assays of biological macromolecules. Owing to its unique features of structure specificity; predictability; recognition and universal application; there has been exploration of the possible application of MIPs in the field of highly selective gas sensors. In this present study; we outline the recent advances in gas sensors based on MIT; classify and introduce the existing molecularly imprinted gas sensors; summarize their advantages and disadvantages; and analyze further research directions. [ABSTRACT FROM AUTHOR]

The vanadium-doped TiO2 nanoparticles were prepared by a sol-gel method with Ti(OBu)4 as a precursor. The powders were characterized by XRD, FT-IR, TEM, XPS and UV-Vis absorption spectrum. The photocatalytic activity of the powders for methyl orange degradation was investigated under a fluorescent lamp. The results show that the doping V presents mainly in the form of V5+, and vanadium doping can restrain the crystal growth and promote the phase transfer from anatase to rutile. Vanadium doping can widen the light absorption range of TiO2, and the absorption threshold wavelength is red shifted from 380 nm to about 650 nm. As a result, the photocatalytic activity of the V-TiO2 nanoparticles is higher than that of P25 under the fluorescent lamp. [ABSTRACT FROM AUTHOR]

We have systematically investigated the modification mechanism of anatase TiO2 doped with nitrogen using the plane-wave ultrasoft pseudopotentials method based on density functional theory. The crystal structure, impurity formation energy, electronic structure and optical properties of TiO2 supercells containing subsitutional nitrogen, interstitial nitrogen or oxygen vacancies were calculated. TiO2 doped with substitutional nitrogen has shallow acceptor states above the valence band. In contrast, TiO2 doped with interstitial nitrogen has isolated impurity states in the middle of the band gap. These impurity energy levels are mainly hybridized by N 2p states with O 2p states and Ti 3d states. TiO2 containing oxygen vacancy has shallow donor states below the conduction band, which consists of Ti 3d states. Except for containing oxygen vacancies, the band gaps of N-doped TiO2 are narrowed in the range 0.03-0.23 eV, and thus their fundamental absorption edges extend to the visible-light region. By nitrogen doping, the octahedral dipole moments in TiO2 increase due to the changes in lattice parameters, bond length and charges on atoms, which is very effective for the separation of photoexcited electron-hole pairs. The calculated results are consistent with the existing experimental data. Based on these results, the effects on the electronic structure and photocatalytic activity of anatase TiO2 doped with nitrogen were analysed and compared in detail, and the mechanism by which anatase TiO2 doped with nitrogen has higher photocatalytic activity than that of pure TiO2 was explained. The conclusions have important significance for understanding and further developing TiO2 photocatalysts that are active under visible-light irradiation. [ABSTRACT FROM AUTHOR]

Mixed phase TiO2 nanoparticles with element doping by Sm and C were prepared via a facile sol-gel procedure. The UV-Vis light-diffuse reflectance spectroscopy analysis showed that the absorption region of co-doped TiO2 was shifted to the visible-light region, which was attributed to incorporation of samarium and carbon into the TiO2 lattice during high-temperature reaction. Samarium effectively decreased the anatase-rutile phase transformation. The grain size can be controlled by Sm doping to achieve a large specific surface area useful for the enhancement of photocatalytic activity. The photocatalytic activities under visible light irradiation were evaluated by photocatalytic degradation of methylene blue (MB). The degradation rate of MB over the Sm-C co-doped TiO2 sample was the best. Additionally, first-order apparent rate constants increased by about 4.3 times compared to that of commercial Degusssa P25 under the same experimental conditions. Using different types of scavengers, the results indicated that the electrons, holes, and OH radicals are the main active species for the MB degradation. The high visible-light photocatalytic activity was attributed to low recombination of the photo-generated electrons and holes which originated from the synergistic effect of the co-doped ions and the heterostructure. [ABSTRACT FROM AUTHOR]

The prevalently used immunoassays for fast screening of aftatoxins (AFs) usually cannot meet the requirement for simultaneous determination of total AFs (aflatoxin B1 + aflatoxin B2 + aflatoxin G1 + aflatoxin G2) due to the deficiency of highly group-specific antibodies. This paper describes a two-step chromogenic reaction based method to quantitatively detect total AFs in rice using colorimetric measurement without antibody. In the method, colorless AFs transform into green-colored indophenol products through the reaction with sodium hydroxide and 2,6-dibromoquinone-4-chloroimide (DBQC) successively, allowing selectively determining total AFs up to 3.9 µg/kg over other competitive mycotoxins under optimal conditions by a UV-vis spectrophotometer. In addition, the colorimetric measurement results of the rice samples agree well with that of a standard HPLC method, demonstrating the good reliability and applicability of the method. Uniquely, the method has potential for on-site detection of total AFs in rice when using a nylon membrane-based device. [ABSTRACT FROM AUTHOR]

Abstract: Through self-assembly approach, ZnO nanoparticles were prepared in the pores of mesostructured SnO2 and the assembled composite of ZnO nanoparticles/mesostructured SnO2 was obtained. Powder X-ray diffraction (XRD) results clearly showed the existence of mesostructure in the assembled composite after calcining at high temperature. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the morphology and showed ZnO nanoparticles in pores of mesostructured SnO2. Room temperature photoluminescence (RTPL) of the assembly solid of ZnO nanoparticles/mesostructured SnO2 was measured. Two emission bands were observed, one being an exciton emission with the peak position of about 406nm and the other the visible emission with the peak position of about 500nm. Compare with the nanostructured ZnO bulk, the photoluminescence intensity of the assembled composite of ZnO nanoparticles/mesostructured SnO2 was enhanced. The luminescence intensity of the assembled composite of ZnO nanoparticles/mesostructured SnO2 is five to six times higher than that of nanostructured ZnO bulk. It was suggested that the intensity enhancement of the exciton emission was due to band-edge exciton transition and the green emission was corresponded to the increase of the oxygen defect states in ZnO particle surface. [Copyright &y& Elsevier]

Xylene is a volatile organic compound which is harmful to the human health and requires precise detection. The detection of xylene by an oxide semiconductor gas sensor is an important research direction. In this work, Co3O4 decorated flower-like SnO2 nanorods (SnO2/Co3O4 NRs) were synthesized by a simple and effective two-step method. The SnO2/Co3O4 NRs show high xylene response (Rg/Ra = 47.8 for 100 ppm) and selectivity at the operating temperature of 280 °C, and exhibit high stability in continuous testing. The resulting SnO2/Co3O4 NRs nanocomposites show superior sensing performance towards xylene in comparison with pure SnO2 nanorods. The remarkable enhancement in the gas-sensing properties of SnO2/Co3O4 NRs are attributed to larger specific surface area and the formation of p–n heterojunction between Co3O4 and SnO2. These results demonstrate that particular nanostructures and synergistic effect of SnO2 and Co3O4 enable gas sensors to selectively detect xylene. [ABSTRACT FROM AUTHOR]

To address the urgent issues of hazardous gas detection and the prevention of environmental pollution, various functional materials for gas sensing and catalytic reduction have been studied. Specifically, the p-type perovskite LaFeO3 has been studied widely because of its promising physicochemical properties. However, there remains several problems to develop a controllable synthesis of LaFeO3-based p-n heterojunctions. In this work, α-Fe2O3 was further compounded with LaFeO3 to form a porous and hollow α-Fe2O3/LaFeO3 heterojunction to improve its gas-sensing performance and photocatalytic efficiency via a microwave-assisted hydrothermal method. While evaluated as sensors of acetone gas, the optimized sample exhibits excellent performance, including a high response (48.3), excellent selectivity, good reversibility, fast response, and recovery ability. Furthermore, it is an efficient catalyst for the degradation of methylene blue. This can be attributed to the enhancement effect of its larger specific surface area, fast diffusion, enhanced surface activities, and p-n heterojunction. Additionally, this work provides a rapid and rational synthesis strategy to produce metal oxides with both enhanced gas-sensing performance and improved photocatalytic properties. [ABSTRACT FROM AUTHOR]

Silver-doped LaFeO3 molecularly imprinted polymers (SLMIPs) were synthesized by a sol–gel method combined with molecularly imprinted technology as precursors. The precursors were then used to prepare SLMIPs cage (SLM-cage) and SLMIPs core–shell (SLM-core–shell) structures by using a carbon sphere as the template and hydrothermal synthesis, respectively. The structures, morphologies, and surface areas of these materials were determined, as well as their gas-sensing properties and related mechanisms. The SLM-cage and SLM-core–shell samples exhibited good responses to methanol gas, with excellent selectivity. The response and optimum working temperature were 16.98 °C and 215 °C, 33.7 °C and 195 °C, respectively, with corresponding response and recovery times of 45 and 50 s (SLM-cage) and 42 and 57 s (SLM-core–shell) for 5 ppm methanol gas. Notably, the SLM-cage and SLM-core–shell samples exhibited lower responses (≤5 and ≤7, respectively) to other gases, including ethanol, ammonia, benzene, acetone, and toluene. Thus, these materials show potential as practical methanol detectors. [ABSTRACT FROM AUTHOR]