Selenization governs the intrinsic activity of copper-cobalt complexes for enhanced non-radical Fenton-like oxidation toward organic contaminants.

Non-radical oxidation pathways in the Fenton-like process have a superior catalytic activity for the selective degradation of organic contaminants under complicated water matrices. Whereas the synthesis of high-performance catalysts and research on reaction mechanisms are unsatisfactory. Herein, it was the first report on copper-cobalt selenide (CuCoSe) that was well-prepared to activate hydrogen peroxide (H2O2) for non-radical species generation. The optimized CuCoSe+H2O2 system achieved excellent removal of chlortetracycline (CTC) in 10 min at neutral pH along with pleasing reusability and stability. Moreover, it exhibited great anti-interference capacity to inorganic anions and natural organic matters even in actual applications. Multi-surveys verified that singlet oxygen (1O2) was the dominant active species in this reaction and electron transfer on the surface-bound of CuCoSe and H2O2 likewise played an important role in direct CTC oxidation. Where the synergetic metals of Cu and Co accounted for the active sites, and the introduced Se atoms accelerated the circulation efficiency of Co3+/Co2+, Cu2+/Cu+ and Cu2+/Co2+. Simultaneously, the produced Se/O vacancies further facilitated electron mediation to enhance non-radical behaviors. With the aid of intermediate identification and theoretical calculation, the degradation pathways of CTC were proposed. And the predicted ecotoxicity indicated a decrease in underlying environmental risk.

Enhanced peroxymonosulfate activation by hierarchical porous Fe3O4/Co3S4 nanosheets for efficient elimination of rhodamine B: Mechanisms, degradation pathways and toxicological analysis.

Fenton-like catalysts have usually superior catalytic activities, however, some drawbacks of ion leaching and difficult-to-recovery limit their applications. In this work, a hierarchical porous Fe3O4/Co3S4 catalyst was fabricated via a simple phase change reaction to overcome these shortcomings. The introduced iron cooperates with cobalt achieving high-efficiency activation of peroxymonosulfate (PMS) to eliminate Rhodamine B (RhB). The results showed that 0.05 g/L Fe3O4/Co3S4 and 1 mM PMS could quickly remove 100% of 200 mg/L RhB within 20 min, and the removal rate of RhB remained above 82% after 5 cycles. Moreover, the as-prepared Fe3O4/Co3S4 possessed a great magnetic separation capacity and good stability of low metal leaching dose. Radical quenching experiments and electron paramagnetic resonance (EPR) techniques proved that sulfate radicals (SO4•-) were the dominant reactive oxygen species responding for RhB degradation. X-ray photoelectron spectroscopy (XPS) pointed out that the synergism of sulfur promoted the cycling of Co3+/Co2+ and Fe3+/Fe2+, boosting the electron transfer between Fe3O4/Co3S4 and PMS. Moreover, the degradation pathways of RhB were deduced by combining liquid chromatography-mass spectrometry (LC-MS) analysis and density functional theory (DFT) calculations. The toxicities of RhB and its intermediates were evaluated as well, which provided significant assistance in the exploration of their ecological risks.

Fluoride sensing performance of fluorescent NH2-MIL-53(Al): 2D nanosheets vs. 3D bulk.

Due to their ultra-thin morphology, larger specific surface area and more exposed active sites, two-dimensional (2D) metal-organic framework (MOF) nanosheets can break the limitations of three-dimensional (3D) MOFs in sensitivity, response speed and the limit of detection for sensing applications. In this work, fluorescent NH2-MIL-53(Al) nanosheets were developed as a fluoride detection sensor compared with the 3D bulk counterpart. The morphological and structural characteristics of the obtained products were systematically characterized, and the favourable chemical and fluorescence stability of the NH2-MIL-53(Al) nanosheets were explored. The fluorescent NH2-MIL-53(Al) nanosheets showed high sensitivity, fast response speed (as short as 10 seconds), low limit of detection (15.2 ppb), and wide linear detection range (5-250 µM), and all performances were better than those of their bulk counterpart. In addition, the sensing mechanism was investigated to be based on the transformation of the NH2-MIL-53(Al) framework that induced the release of fluorescent ligands, resulting in an exceptionally enhanced fluorescence. This work highlights the advantages of 2D MOF nanosheets in fluorescence sensing applications.

Enhanced Fenton-like degradation of sulfadiazine by single atom iron materials fixed on nitrogen-doped porous carbon.

The use of single-atom iron catalysts in heterogeneous Fenton-like reactions has demonstrated tremendous potential for antibiotic wastewater treatment. In this study, single-atom iron fixed on nitrogen-doped porous carbon materials (Fe-ISAs@CN) was synthesised using a metal organic framework (MOF) as a precursor. Fe-ISAs@CN was applied as a heterogeneous Fenton catalyst to activate H2O2 for the degradation of sulfadiazine (SDZ) in an aqueous solution. The physical and chemical properties of Fe-ISAs@CN were characterised by scanning electron microscopy (SEM), transmission electron microscope (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and rotating disk electrode (RDE) measurements. The results of our degradation experiments indicated that Fe-ISAs@CN exhibited remarkable activity and stability for the degradation of SDZ over a wide pH range; even after five cycles, Fe-ISAs@CN retained a high catalytic efficiency (>80%). The 5,5-dimethyl-1-oxaporphyrin-n-oxide (DMPO)-X signal captured by electron paramagnetic resonance (EPR) spectroscopy indicated that a large amount of hydroxyl radicals (OH) was produced in the reaction system. Quench tests indicated that the OH was the main active substance in the degradation of SDZ. The degradation products of the reaction were analysed by High Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS), and possible degradation pathways for the SDZ degradation were proposed.

MSU-Net: Multi-Scale U-Net for 2D Medical Image Segmentation.

Aiming at the limitation of the convolution kernel with a fixed receptive field and unknown prior to optimal network width in U-Net, multi-scale U-Net (MSU-Net) is proposed by us for medical image segmentation. First, multiple convolution sequence is used to extract more semantic features from the images. Second, the convolution kernel with different receptive fields is used to make features more diverse. The problem of unknown network width is alleviated by efficient integration of convolution kernel with different receptive fields. In addition, the multi-scale block is extended to other variants of the original U-Net to verify its universality. Five different medical image segmentation datasets are used to evaluate MSU-Net. A variety of imaging modalities are included in these datasets, such as electron microscopy, dermoscope, ultrasound, etc. Intersection over Union (IoU) of MSU-Net on each dataset are 0.771, 0.867, 0.708, 0.900, and 0.702, respectively. Experimental results show that MSU-Net achieves the best performance on different datasets. Our implementation is available at https://github.com/CN-zdy/MSU_Net.

The rationality of using core-shell nanoparticles with embedded internal standards for SERS quantitative analysis based glycerol-assisted 3D hotspots platform.

Surface enhanced Raman spectroscopy (SERS) is a promising sensing technique that can provide unique chemical and structural fingerprint information, but gaining reliable SERS quantitative data with high sensitivity and stability still remains a challenge. Although using a molecule as an internal standard (IS) can improve the SERS quantitative capability, the reliability and SERS measuring conditions for signal fluctuations during calibration based on IS are yet to be explored when the embedded IS molecules and target objects are located in different environments. Herein, a 3D hotspot matrix SERS platform based on Au@4-MPy@AgNPs was constructed in water with the assistance of glycerol and the dynamic signal changes from the IS, i.e. 4-Mpy, and target molecules were monitored during the process of evaporation with high sensitivity and stability. In contrast to the traditional water-dispersed drying film system, the variation trends of IS and target molecules were consistent in the glycerol-assisted liquid film protection system. Therefore, it is reasonable to calibrate the signal fluctuation by utilizing the embedded IS based on the construction strategy of a glycerol-assisted 3D hotspot platform. This work demonstrates a rational, reliable and precise SERS quantitative technique for testing analyte concentrations in practical systems and has great application prospects in the field of analytical chemistry.

Multimodal Glioma Image Segmentation Using Dual Encoder Structure and Channel Spatial Attention Block.

Multimodal medical images provide significant amounts of complementary semantic information. Therefore, multimodal medical imaging has been widely used in the segmentation of gliomas through computational neural networks. However, inputting images from different sources directly to the network does not achieve the best segmentation effect. This paper describes a convolutional neural network called F-S-Net that fuses the information from multimodal medical images and uses the semantic information contained within these images for glioma segmentation. The architecture of F-S-Net is formed by cascading two sub-networks. The first sub-network projects the multimodal medical images into the same semantic space, which ensures they have the same semantic metric. The second sub-network uses a dual encoder structure (DES) and a channel spatial attention block (CSAB) to extract more detailed information and focus on the lesion area. DES and CSAB are integrated into U-Net architectures. A multimodal glioma dataset collected by Yijishan Hospital of Wannan Medical College is used to train and evaluate the network. F-S-Net is found to achieve a dice coefficient of 0.9052 and Jaccard similarity of 0.8280, outperforming several previous segmentation methods.

Highly fluorescent scandium-tetracarboxylate frameworks: selective detection of nitro-aromatic compounds, sensing mechanism, and their application.

Recently, exploring new luminescent metal-organic frameworks (LMOFs) to selectively detect nitro-aromatic compounds (NACs) has been a hot topic of research. Simultaneously, it is still a challenging issue to understand the sensing mechanism of luminescent MOFs interacting with NACs at the molecular level. In this work, highly fluorescent Sc-tetracarboxylate frameworks (Sc-EBTC) have been successfully synthesized through a solvothermal method. The as-prepared Sc-EBTC crystals have good thermal stability, chemical stability as well as strong fluorescence (λex = 320 nm and λem = 400 nm), and they can detect various NACs rapidly (as short as 30 s), selectively and efficiently by the "turn-off" fluorescence mechanism. The detection limits of Sc-EBTC toward 2,4-DNP and 4-NP are quantified to be 5.71 ppb and 6.26 ppb, respectively. Furthermore, to better understand the sensing mechanism, we attempt to use solid-state NMR and X-ray photoelectron spectroscopy to vividly characterize the charge transfer caused by the interaction between NAC molecules and the MOF at the molecular level. Additionally, test strips were made successfully for the practical detection of the NACs. This study demonstrates that the MOF constructed from the H4EBTC ligands might be a promising candidate for the detection of trace NACs.

Ultra-Sensitive and Selective Detection of Arsenic(III) via Electroanalysis over Cobalt Single-Atom Catalysts.

Achieving highly sensitive and selective detection of trace-level As(III) and clarifying the underlying mechanism is still a intractable problem. The electroanalysis of As(III) relies on the electrocatalytic ability of the sensing interface. Herein, we first adopt single-atom catalysts as the electrocatalyst in As(III) detection. Cobalt single-atoms anchored on nitrogen-doped carbon material (Co SAC) were found to have an extraordinary sensitivity of 11.44 µA ppb-1 with excellent stability and repeatability, which so far is the highest among non-noble metal nanomaterials. Co SAC also exhibited a superior selectivity toward As(III) compared with some bivalent heavy metal ions (HMIs). Combining X-ray absorption spectroscopy (XAFS), density functional theory (DFT) calculation, and reaction kinetics simulation, we demonstrated that Co single atoms stabilized in N2C2 support serve as active sites to catalyze H3AsO3 reduction via the formation of Co-O hybridization bond, leading to a lower energy barrier, promoting the breakage of As-O bonds. Importantly, the first electron transfer is the rate-limiting step of arsenic reduction and is found to be more favorable on Co-SAC both thermodynamically and kinetically. This work not only expands the potential applicaiton of single-atom catalysts in the detection and treatment of As(III), but also provides atomic-level catalytic insights into HMIs sensing interfaces.

Identifying Phase-Dependent Electrochemical Stripping Performance of FeOOH Nanorod: Evidence from Kinetic Simulation and Analyte-Material Interactions.

Metal hydroxide nanomaterials are widely applied in the energy and environment fields. The electrochemical performance of such materials is strongly dependent on their crystal phases. However, as there are always multiple factors relating to the phase-dependent electrochemistry, it is still difficult to identify the determining one. The well-defined crystal phases of α- and ß-FeOOH nanorods are characterized through the transmission electron microscopy by a series of rotation toward one rod, where the cross-section shape and the growth direction along the [001] crystalline are first verified for 1D FeOOH nanostructures. The electrosensitivity of the two materials toward Pb(II) is tested, where α-FeOOH performs an outstanding sensitivity whilst it is only modest for ß-FeOOH. Experiments via Fourier transform infrared spectroscopy, X-ray absorption fine structure (XAFS), etc., show that α-FeOOH presents a larger Pb(II) adsorption capacity due to more surficial hydroxyl groups and weaker PbO bond strength. The reaction kinetics are simulated and the adsorption capacity is found to be the determining factor for the distinct Pb(II) sensitivities. Combining experiment with simulation, this work reveals the physical insights of the phase-dependent electrochemistry for FeOOH and provides guidelines for the functional application of metal hydroxide nanomaterials.

Nano-hybrids of needle-like MnO2 on graphene oxide coupled with peroxymonosulfate for enhanced degradation of norfloxacin: A comparative study and probable degradation pathway.

In this work, 1D MnO2 nano-needles were prepared and grown on the graphene oxide (GO) nano-sheets successfully. The morphology and structure of materials were explored. The MnO2 nano-needles with a length of 200-400 nm were distributed uniformly on the GO nano-sheets. As a result of GO substrate, the MnO2/GO nano-hybrids (MnO2/GO) have the much larger surface area and more surface oxygen-containing functional groups than MnO2 nano-needles, which are beneficial for enrichment and degradation of the norfloxacin (NOR). Results showed that more than 80% NOR was degraded within 20 min at the dose of 10 mM PMS and 0.8 g/L catalysts. Moreover, the optimal pH in MnO2/PMS and MnO2/GO/PMS system were both acidic condition. Furthermore, the mechanism of PMS activation by MnO2/GO was investigated through radical identification using quenching experiments and EPR techniques. According to this, the HSO5- of PMS reacted with Mn (IV)/Mn(III) to form a redox loop, and GO played an important role in the degradation process. Finally, the transformation intermediates of NOR were identified and four probable degradation pathways were speculated. This work would provide a potential contribution towards NOR removal in the environmental remediation.

A nanoscale "yarn ball"-like heteropoly blue catalyst for extremely efficient elimination of antibiotics and dyes.

Fenton system is one of the most popular methods to eliminate antibiotics and dyes in aquatic environment. However, the existed Fenton system is limited by various factors such as potential second pollution and narrow pH range. In this study, we report that the bottlenecks for high strength antibiotics and dyes wastewater treatment at a wide pH range can be well tackled by the nanoscale "yarn ball"-like Mo/W-containing heteropoly blue (HPB) catalyst Mg2Ti6Mo23O119SiW12 (1). This novel catalyst displayed extremely efficient elimination for several typical organic contaminants such as malachite green (MG), tetracycline (TC) and methyl orange (MO). Compared with other materials reported in previous papers, the catalytic performance of 1 in degradation of the organic contaminants of high concentrations increased several times. More than 90% of antibiotics and dyes are degraded within 60 min. Electron spin resonance (ESR) experiments and UV-vis spectra confirmed that the catalytic mechanisms of 1 could mainly ascribe to the 1/H2O2 process and the possible photocatalytic oxidation of adsorbed H2O by holes (h+) in the valence band (VB) of 1 surface generated ·OH for extremely efficient degradation of organic contaminants. This work widens the optimal pH values up to neutral condition and it's significant for the expansion of the heterogeneous Fenton-like catalyst family and its application in the field of water treatment.

Mesoporous zirconia nanostructures (MZN) for adsorption of As(III) and As(V) from aqueous solutions.

Mesoporous zirconia nanostructures (MZN) were synthesized by hydrothermal method to efficiently remove highly mobile and toxic arsenite (As(III)) and arsenate (As(V)) from aqueous solutions. The as-synthesized MZN were characterized by Brunauer-Emmett-Teller (BET), X-Ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM), and Energy-dispersive X-ray spectroscopy (EDX) techniques. The batch adsorption experimental results showed that the As(III) and As(V) removal capacities of the MZN were 105.03 and 110.29 mg/g, respectively, under neutral pH conditions, which were better than many recently reported adsorbents. The adsorption behavior of As(III) and As(V) on the MZN could be well described by pseudo-second-order and Langmuir isotherms models. Moreover, As(III) and As(V) adsorption on the MZN was spontaneous and endothermic. Some of the common co-existing ions had slightly affected the arsenic removal proficiency of MZN. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to investigate the adsorption mechanism of As(III) and As(V) on the as-synthesized MZN. The as-synthesized MZN demonstrated quite fast and good treatment of simulated real arsenic (As(III,V)) contaminated water. This study suggested that the as-synthesized MZN are potential candidate for practical applications of As(III) and As(V) removal from the aqueous solutions.

Metal coordination-functionalized Au-Ag bimetal SERS nanoprobe for sensitive detection of glutathione.

We demonstrated a surface-enhanced Raman spectroscopy (SERS) nanoprobe, neocuproine-Cu (Nc-CuII)-functionalized Au-Ag "nanobowls" (Au-Ag NBs/Nc-CuII), for detection of glutathione (GSH). Detection was accomplished with alternation of SERS spectra from Nc-CuII into Nc-CuI resulting from the reaction of GSH with Nc-CuII on Au-Ag NBs. This nanoprobe exhibited high selectivity and sensitivity (µM) towards GSH.

Synthesis of ultra-large ZrO2 nanosheets as novel adsorbents for fast and efficient removal of As(III) from aqueous solutions.

Consumption of water having excessive arsenic (As) contamination can cause adverse health effects on human beings. In this study, novel ultra-large zirconium oxide (ZrO2) nanosheets were successfully synthesized using graphene oxide (GO) templates and their adsorption-ability was studied for arsenite (As(III)). Owing to higher values of surface area, numbers of available hydroxyl groups and strong chemisorption binding affinity towards As(III), the synthesized novel ultra-large ZrO2 nanosheets showed high adsorption-ability for As(III) over a wide pH range. Experimental results demonstrated that the maximum adsorption-ability of the ZrO2 nanosheets for As(III) reached to 74.9 mg/g at pH 6. BET, zeta potential, effect of initial pH, FTIR and XPS have been used to analyze the As(III) adsorption process on the ZrO2 nanosheets. The experiments for effects of co-existing ions indicated that ZrO2 nanosheets possessed good anti-interference ability towards co-existing ions. Furthermore, the ZrO2 nanosheets demonstrated very fast and excellent treatment of simulated real As(III) polluted water, consequently the effluent concentration met the standard regulated by World Health Organization. This study suggested that the as-prepared ZrO2 nanosheets could be potentially applied in practical drinking water treatment.

Morphology-tunable WMoO nanowire catalysts for the extremely efficient elimination of tetracycline: kinetics, mechanisms and intermediates.

The presence of antibiotics in aquatic environments has attracted global concern. The Fenton system is one of the most popular methods for eliminating antibiotics in aquatic environments, but the existing Fenton system is limited due to the potential for secondary pollution, and the narrow pH range (∼3-5). In this study, we report that the bottlenecks for high-strength tetracycline (TC) wastewater treatment under neutral conditions can be tackled well by a class of mixed-valence W/Mo containing oxides (WMoO-x) with tunable morphologies. Triethanolamine was selected as a structure-directing agent to control the morphologies of the catalysts going from ultrathin nanowires (UTNWs) to wire-tangled nanoballs (WTNBs). As a proof of concept, the most efficient catalyst in the batch samples, WMoO-1 ultrathin nanowires, was employed as a model material for TC degradation, in which the coordinatively unsaturated metal atoms with oxygen defects serve as the sites for TC chemisorption and electron transfer. As a result, 91.75% of TC was degraded in 60 min for the initial TC concentration of 400 µM. Furthermore, LC-MS analysis confirmed that the TC could be degraded to nontoxic by-products without benzene rings, and finally mineralized to CO2 and H2O. ICP-MS and cycle experiments showed the good stability and reusability of WMoO-1 UTNWs in the Fenton-like system. The findings of this work provide fresh insights into the design of nanoscale catalyst morphology and reaffirm the versatility of doping in tuning catalyst activity, extending the range of the optimal pH values to neutral conditions. This is significant for the expansion of the heterogeneous Fenton-like family and its application in the field of water treatment.

Dual-modality optical projection tomography reconstruction method from fewer views.

In optical projection tomography (OPT), for longitudinal living model studies, multiple measurements of the same sample are required at different time points. It is important to decrease both the total acquisition time and the light dose to the sample. We improved the ordered subsets expectation maximization reconstruction algorithm for OPT, which reduces the acquisition time and number of projections greatly compared with filtered back projection (FBP), and obtained satisfactory reconstructed images. Using zebrafish, in transmission and fluorescence mode, we demonstrate the capability of the method to reconstruct image from downsampled projection subsets. The result shows that the reconstruction image quality of the proposed method using 30 projections is comparable to that of FBP using 720 projections. The total acquisition procedure can be finished in a few seconds. The method also provides OPT with the remarkable capability to resist noises and artifacts. Projection image and fused image of zebrafish.

EDTA-Fe(III) Fenton-like oxidation for the degradation of malachite green.

Industrial waste, urban sewage and aquaculture have led to severely increased grades of environment pollutants such as dyes, pesticides and fertilizer. The use of technologies for purifying contaminated waters can be difficult and toxic due to the anti-photolysis, anti-oxidation and anti-bio-oxidation characteristics of organic pollutants, and there is therefore a significant need for new approaches. Here, we report methods of Fenton oxidation and EDTA-Fe(III) Fenton-like oxidation which can be used to degrade malachite green (MG: a dye and antibiotic-like substance) from contaminated water. Compared with the degradation rate (59.34%) of the Fe(III)/H2O2 Fenton process, the EDTA-Fe(III) Fenton-like oxidation got a better degradation rate (92.7%) at neutral pH conditions. By conducting a series of parallel controlled experiments (changing parameters such as the reactant concentration, temperature, and pH), we report the relationships between the degradation effect and different parameters, and we fitted their pseudo first order kinetic curves. Furthermore, we repeated to adjustment of the concentrations of MG in solutions to test the cycle performance and catalytic activities of EDTA-Fe(III)/H2O2 system and it showed good repeatability in the first five rounds and all of them keep the degradation efficiencies greater than 80%. By conducting comparative spin-trapping electron paramagnetic resonance (EPR) experiments, we showed indirectly that the OH contributes to the degradation of MG. Additionally, the results of the EPR experiments showed that EDTA contributes to the generation of OH in the EDTA-Fe(III)/H2O2 Fenton-like system. By conducting total organic carbon (TOC) analysis experiments, we found that EDTA was also oxidized to some extent during the degradation of MG. In all, the findings of this work widen the range of the optimal pH values up to neutral condition for degradation of MG by use of EDTA-Fe(III) Fenton-like system. And this system could be used as one approach for the degradation of organic pollutants at neutral conditions and provide some initial information regarding EDTA-Fe(III) Fenton-like oxidations. It's significant for the expansion of the homogenous Fenton-like family and its application in the field of water treatment.

Defect- and phase-engineering of Mn-mediated MoS2 nanosheets for ultrahigh electrochemical sensing of heavy metal ions: chemical interaction-driven in situ catalytic redox reactions.

An ultrasensitive electrochemical detection of heavy metal ions is achieved via defect- and phase-engineering of Mn-mediated MoS2 nanosheets. We find for the first time that chemical interactions between Pb(ii) and active S atoms in Mn-MoS2 facilitate the electron transfer and in situ catalytic redox reactions.

Size-tunable Ag nanoparticles sensitized porous ZnO nanobelts: controllably partial cation-exchange synthesis and selective sensing toward acetic acid.

Porous ZnO nanobelts sensitized with Ag nanoparticles have been prepared via a partial cation-exchange reaction assisted by a thermal oxidation treatment, employing ZnSe·0.5N2H4 nanobelts as precursors. After partially exchanged with Ag+ cations, the belt-like morphology of the precursors is still preserved. Continuously calcined in air, they are in situ transformed into Ag nanoparticles sensitized porous ZnO nanobelts. The size of the Ag nanoparticles can be tuned through manipulating the amount of exchanging Ag+ cations. Considering the porous and belt-like nanostructure, sensing characteristics of ZnO and the catalytic activity of Ag nanoparticles, the gas sensing performances of the as-prepared Ag nanoparticles sensitized porous ZnO nanobelts have been carefully investigated. The results indicate that Ag nanoparticles significantly enhance the sensing performances of porous ZnO nanobelts toward typical volatile organic compounds. Especially, a good selectivity has been demonstrated toward acetic acid gas with a low detection limit less than 1 ppm. Furthermore, they also display a good reproducibility with a short response/recovery time due to the thin, uniform and porous sensing film, which is fabricated with the assembled technique and in situ calcined approach. Finally, their sensing mechanism has been further discussed.