Interface Defects and Carrier Regulation in MOF-Derived Co3O4/In2O3 Composite Materials for Enhanced Selective Detection of HCHO.

Gas sensors for real-time monitoring of low HCHO concentrations have promising applications in the field of health protection and air treatment, and this work reports a novel resistive gas sensor with high sensitivity and selectivity to HCHO. The MOF-derived hollow In2O3 was mixed with ZIF-67(Co) and calcined twice to obtain a hollow Co3O4/In2O3 (hereafter collectively termed MZO-6) composite enriched with oxygen vacancies, and tests such as XPS and EPR proved that the strong interfacial electronic coupling increased the oxygen vacancies. The gas-sensitive test results show that the hollow composite MZO-6 with abundant oxygen vacancies has a higher response value (11,003) to 10 ppm of HCHO and achieves a fast response/recovery time (11/181 s) for HCHO at a lower operating temperature (140 °C). The MZO-6 material significantly enhances the selectivity to HCHO and reduces the interference of common pollutant gases such as ethanol, acetone, and xylene. There is no significant fluctuation of resistance and response values in the 30-day long-term stability test, and the material has good stability. The synergistic effect of the heterostructure and oxygen vacancies altered the formaldehyde adsorption intermediate pathway and reduced the reaction activation energy, enhancing the HCHO responsiveness and selectivity of the MZO-6 material.

Bi-Doped and Bi Nanoparticles Loaded CeO2 Derived from Ce-MOF for Photocatalytic Degradation of Formaldehyde Gas and Tetracycline Hydrochloride.

Bi/CeO2 (BC-x) photocatalysts are successfully prepared by solvothermal loading Bi nanoparticles and Bi-doped CeO2 derived by Ce-MOF (Ce-BTC). Formaldehyde gas (HCHO) and tetracycline hydrochloride (HTC) are used to evaluate the photocatalytic activity of the synthesized Bi/CeO2. For BC-1000 photocatalyst, the degradation of HTC by 420 nm < λ < 780 nm light reaches 91.89% for 90 min, and HCHO by 350 nm < λ < 780 nm light reaches 94.66% for 120 min. The photocatalytic cycle experiments prove that BC-1000 has good cyclic stability and repeatability. The results of photoluminescence spectra, fluorescence lifetime, photocurrent response, and electrochemical impedance spectroscopy showed that the SPR (Surface Plasmon Resonance) effect of Bi nanoparticles acted as a bridge and promoted electron transfer and enhanced the response-ability of Bi/CeO2 to visible light. Bi-doping produced more oxygen vacancies to provide adsorption sites for adsorbing oxygen and generated more ·O2 - thus promoting photocatalytic reactions. The mechanism of photocatalytic degradation is analyzed in detail utilizing active free radical capture experiments and electron paramagnetic resonance (EPR) characterization. The experimental results indicate that ·O2 - and h+ active free radicals significantly promote the degradation of pollutants.

Double-Solvent-Induced Derivatization of Bi-MOF to Vacancy-Rich Bi4O5Br2: Toward Efficient Photocatalytic Degradation of Ciprofloxacin in Water and HCHO Gas.

MOF-derived photocatalytic materials have potential in degrading ciprofloxacin (CIP) in water and HCHO gas pollutants. Novel derivatization means and defect regulation are effective techniques for improving the performance of MOF-derived photocatalysis. Vacancy-rich Bi4O5Br2 (MBO-x) were derived in one step from Bi-MOF (CAU-17) by a modified double-solvent method. MBO-50 produced more oxygen vacancies due to the combined effect of the CAU-17 precursor and double solvents. The photocatalytic performance of MBO was evaluated by degrading CIP and HCHO. Thanks to the favorable morphology and vacancy structure, MBO-50 demonstrated the best photocatalytic efficiency, with 97.0% removal of CIP (20 mg L-1) and 90.1% removal of HCHO (6.5 ppm) at 60 min of light irradiation. The EIS Nyquist measurement, transient photocurrent response, photoluminescence spectra, and the calculation of energy band information indicated that the vacancy sites can effectively capture photoexcited electrons during the charge transfer process, thus limiting the recombination of electrons and holes, improving the energy band structure, and making it easier to produce superoxide anion radical (·O2-) and to degrade CIP and HCHO. The improvement of photocatalytic performance of MBO-50 in HCHO degradation due to the bromine vacancy generation and filling mechanism was discussed in detail. This work provides a promising new idea for the modulation of MOF-derived photocatalytic materials.

The Z-Scheme MIL-88B(Fe)/BiOBr Heterojunction Promotes Fe(III)/Fe(II) Cycling and Photocatalytic-Fenton-Like Synergistically Enhances the Degradation of Ciprofloxacin.

The Z-scheme MIL-88B/BiOBr (referred to as MxBy, whereas x and y are the mass of MIL-88B(Fe) and BiOBr) heterojunction photocatalysts are successfully prepared by a facile ball milling method. By adding low concentration H2 O2 under visible light irradiation, the Z-scheme heterojunction and photocatalytic-Fenton-like reaction synergistically enhance the degradation and mineralization of ciprofloxacin (CIP). Among them, M50B150 showed efficient photodegradation efficiency and excellent cycling stability, with 94.6% removal of CIP (10 mg L-1 ) by M50B150 (0.2 g L-1 ) under 90 min of visible light. In the MxBy heterojunctions, the rapid transfer of photo-generated electrons not only directly decomposed H2 O2 to generate ·OH, but also improved the cycle of Fe3+ /Fe2+ pairs, which facilitated the reaction with H2 O2 to generate ·OH and ·O2 - radicals. In addition, the effects of photocatalyst dosages, pH of CIP solution, and coexisting substances on CIP removal are systematically investigated. It is found that the photocatalytic- Fenton-like reaction can be carried out at a pH close to neutral conditions. Finally, the charge transfer mechanism of the Z-scheme is verified by electron spin resonance (ESR) signals. The ecotoxicity of CIP degradation products is estimated by the T.E.S.T tool, indicating that the constructed photocatalysis-Fenton-like system is a green wastewater treatment technology.

Efficient Photocatalytic Degradation of Tetracycline under Visible Light by an All-Solid-State Z-Scheme Ag3PO4/MIL-101(Cr) Heterostructure with Metallic Ag as a Charge Transmission Bridge.

The Z-type Ag/Ag3PO4/MIL-101(Cr) heterojunction photocatalyst (referred to as AAM-x) was successfully prepared by a simple in situ precipitation method. The photocatalytic activity of the AAM-x samples was evaluated using a common tetracycline (TC) antibiotic. All AAM-x materials are more effective in removing TC than Ag3PO4 and MIL-101(Cr). Among them, AAM-3 exhibited efficient photodegradation efficiency and excellent structural stability, and the removal rate of TC (20 mg L-1) by AAM-3 (0.5 g L-1) under 60 min of visible light was 97.9%. The effects of photocatalyst dosage, pH, and inorganic anions were also systematically investigated. According to the X-ray photoelectron spectroscopy analysis, metallic silver particles appeared on the surface of the Ag3PO4/MIL-101(Cr) mixture during the catalyst synthesis. The results of photoluminescence spectra, photocurrent response, EIS, and fluorescence lifetime showed that AAM-3 has a high photogenic charge separation efficiency. An all-solid-state Z-type heterojunction mechanism including Ag3PO4, metallic Ag, and MIL-101(Cr) is proposed to rationalize the excellent photocatalytic performance and photostability of AAM-x composites and to explain the effect of metallic Ag acting as a charge transfer bridge. The TC intermediates were identified using liquid chromatography-mass spectrometry and possible routes of TC degradation were also discussed. This work provides a viable idea for removing antibiotics by an Ag3PO4/MOF-based heterogeneous structured photocatalyst.

Atomically Dispersed Pt on Three-Dimensional Ordered Macroporous SnO2 for Highly Sensitive and Highly Selective Detection of Triethylamine at a Low Working Temperature.

Triethylamine (TEA) is a widely used volatile organic chemical, which is harmful and can cause headache, dizziness, and respiratory discomfort. Developing an efficient sensor to detect trace amounts of TEA is significant for industrial and healthcare monitoring. In this work, SnO2 with a three-dimensional ordered macroporous structure (3DOM) was prepared through a polymethylmethacrylate sphere template route. The TEA sensing performance of the 3DOM SnO2 was enhanced through Pt loading. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy images and X-ray absorption fine-structure analysis indicate that Pt on the 3DOM 0.20% Pt/SnO2 surface mainly exists in the state of atomic dispersion, which results in more active sites, higher Hall mobility and active oxygen contents, and lower response energy barriers. The 0.20% Pt/SnO2 sensor has a low operating temperature of 80 °C and a low limit of detection (0.32 ppb). Because of the uniform adsorption of TEA on the atomically dispersed Pt, the 3DOM Pt/SnO2 sensor exhibits high selectivity.

Selective Catalytic Oxidation of Methane to Methanol in Aqueous Medium over Copper Cations Promoted by Atomically Dispersed Rhodium on TiO2.

Direct conversion of methane into value-added chemicals, such as methanol under mild conditions, is a promising route for industrial applications. In this work, atomically dispersed Rh on TiO2 suspended in an aqueous solution was used for the oxidation of methane to methanol. Promoted by copper cations (as co-catalyst) in solution, the catalysts exhibited high activity and selectivity for the production of methanol using molecular oxygen with the presence of carbon monoxide at 150 °C with a reaction pressure of 31 bar. Millimole level yields of methanol were reached with the selectivity higher than 99 % using the Rh/TiO2 catalysts with the promotion of the copper cation. CO was the reductive agent to generate H2 from H2 O, which led to the formation of H2 O2 through the reaction of H2 and O2 . Atomically dispersed Rh activated the C-H bond in CH4 and catalyzed the oxidation using H2 O2 . Copper cations maintained the low-valence state of Rh. Moreover, copper acted as a scavenger for suppressing the overoxidation, thus leading to the high selectivity of methanol.

Atomically Dispersed Au on In2O3 Nanosheets for Highly Sensitive and Selective Detection of Formaldehyde.

As an important industrial chemical, formaldehyde is used in various fields but is harmful to health. Developing a convenient detection device for formaldehyde is significant. Based on atomically dispersed Au on In2O3 nanosheets, a formaldehyde sensor was fabricated in this work. The highly dispersed Au obtained by the ultraviolet (UV) light-assisted reduction method helps improve the sensing performance. A meager loading amount (0.01 wt %) of Au on In2O3 nanosheets exhibits high sensitivity toward ppb-level formaldehyde. Au acts as an electron sink and promotes the oxidation of formaldehyde. Atomically dispersed Au on In2O3 nanosheets decreases the activation energy and increases the number of active sites, which result in a highly efficient conversion of formaldehyde and a marked resistance change of the fabricated sensors. The selective adsorption and oxidation of formaldehyde on single atom Au's uniform sites establish excellent selectivity. Besides, the sensor exhibits short response/recovery time and excellent stability, with promising applications in formaldehyde detection.

Cobalt oxide nanorods with special pore structure for enhanced ethanol sensing performance.

Cobalt oxide (Co3O4) nanorods with special pore structure were successfully synthesized by a facile hydrothermal method with proper temperature calcination. The relationship between morphologies, structures and gas sensing properties under different calcination temperature were investigated by using XRD, SEM, TEM and XPS method. The Co3O4 sample calcinated at 300 °C displayed the highest response of 143 and fast response/recovery time to 100 ppm ethanol at relatively low operating temperature of 185 °C. The mechanism for enhanced gas sensing performances of Co3O4 nanorods to ethanol could be attributed to the large specific surface area and abundant pore structure through the unique Co3O4 nanorods. The particular surface components under the proper calcination temperature are also the possible reasons for such excellent sensing performances.

One-Step Synthesis of Co-Doped In2O3 Nanorods for High Response of Formaldehyde Sensor at Low Temperature.

Uniform and monodisperse Co-doped In2O3 nanorods were fabricated by a facile and environmentally friendly hydrothermal strategy that combined the subsequent annealing process, and their morphology, structure, and formaldehyde (HCHO) gas sensing performance were investigated systematically. Both pure and Co-doped In2O3 nanorods had a high specific surface area, which could offer abundant reaction sites to gas molecular diffusion and improve the response of the gas sensor. Results revealed that the In2O3/1%Co nanorods exhibited a higher response of 23.2 for 10 ppm of HCHO than that of the pure In2O3 nanorods by 4.5 times at 130 °C. More importantly, the In2O3/1%Co nanorods also presented outstanding selectivity and long-term stability. The superior gas sensing properties were mainly attributed to the incorporation of Co, which suggested the important role of the amount of oxygen vacancies and adsorbed oxygen in enhancing HCHO sensing performance of In2O3 sensors.

Humidity-Sensing Performance of 3DOM WO3 with Controllable Structural Modification.

The development of humidity sensors with excellent sensing performance is a great challenge in the field of material chemistry. Here, we synthesized 3DOM WO3 nanomaterials through a poly(methyl methacrylate) template method, and first, we applied it to humidity measurement. For the goal of better sensing performance, the structural modification of Li/K-codoping was adopted, and the test results showed that Li/K-codoped 3DOM WO3 possessed highly improved humidity sensing performances, such as high response, low-humidity hysteresis, good long-term stability, great repeatability, decent response, and recovery properties. To deeply understand the great effect of Li/K-codoping on sensing performance, the pure, Li-monodoped, and Li/K-codoped 3DOM WO3-based humidity sensors were compared, and we found that the structure defects and adsorbed oxygen as well as the co-effect of Li/K dopants were key factors for the improved sensing performance. Additionally, a possible humidity sensitive mechanism was proposed to further study the promotion effect of Li/K-codoping on humidity sensing process.

Manipulating the Defect Structure (VO) of In2O3 Nanoparticles for Enhancement of Formaldehyde Detection.

Because defects such as oxygen vacancies (VO) can affect the properties of nanomaterials, investigating the defect structure-function relationship are attracting intense attention. However, it remains an enormous challenge to the synthesis of nanomaterials with high sensing performance by manipulating VO because understanding the role of surface or bulk VO on the sensing properties of metal oxides is still missing. Herein, In2O3 nanoparticles with different contents of surface and bulk VO were obtained by hydrogen reduction treatment, and the role of surface or bulk VO on the sensing properties of In2O3 was investigated. The X-ray diffraction, ultraviolet-visible spectrophotometer, electron paramagnetic resonance, photoluminescence, Raman, X-ray photoelectron spectroscopy, Hall analysis, and the sensing results indicate that bulk VO can decrease the band gap and energy barrier and increase the carrier mobility, hence facilitating the formation of chemisorbed oxygen and enhancing the sensing response. Benefiting from bulk VO, In2O3-H10 exhibits the highest response, good selectivity, and stability for formaldehyde detection. However, surface VO does not contribute to the improvement of formaldehyde-sensing performance, and the black In2O3-H30 with the highest content of surface VO exhibits the lowest response. Our work provides a novel strategy for the synthesis of nanomaterials with high sensing performance by manipulating VO.

Structural and electronic engineering of 3DOM WO3 by alkali metal doping for improved NO2 sensing performance.

Novel alkali metal doped 3DOM WO3 materials were prepared using a simple colloidal crystal template method. Raman, XRD, SEM, TEM, XPS, PL, Hall and UV-Vis techniques were used to characterize the structural and electronic properties of all the products, while the corresponding sensing performances targeting ppb level NO2 were determined at different working temperatures. For the overall goal of structural and electronic engineering, the co-effect of structural and electronic properties on the improved NO2 sensing performance of alkali metal doped 3DOM WO3 was studied. The test results showed that the gas sensing properties of 3DOM WO3/Li improved the most, with the fast response-recovery time and excellent selectivity. More importantly, the response of 3DOM WO3/Li to 500 ppb NO2 was up to 55 at room temperature (25 °C). The especially high response to ppb level NO2 at room temperature (25 °C) in this work has a very important practical significance. The best sensing performance of 3DOM WO3/Li could be ascribed to the most structure defects and the highest carrier mobility. And the possible gas sensing mechanism based on the model of the depletion layer was proposed to demonstrate that both structural and electronic properties are responsible for the NO2 sensing behavior.

Highly Sensitive and Selective Ethanol Sensor Fabricated with In-Doped 3DOM ZnO.

ZnO is an important n-type semiconductor sensing material. Currently, much attention has been attracted to finding an effective method to prepare ZnO nanomaterials with high sensing sensitivity and excellent selectivity. A three-dimensionally ordered macroporous (3DOM) ZnO nanostructure with a large surface area is beneficial to gas and electron transfer, which can enhance the gas sensitivity of ZnO. Indium (In) doping is an effective way to improve the sensing properties of ZnO. In this paper, In-doped 3DOM ZnO with enhanced sensitivity and selectivity has been synthesized by using a colloidal crystal templating method. The 3DOM ZnO with 5 at. % of In-doping exhibits the highest sensitivity (∼88) to 100 ppm ethanol at 250 °C, which is approximately 3 times higher than that of pure 3DOM ZnO. The huge improvement to the sensitivity to ethanol was attributed to the increase in the surface area and the electron carrier concentration. The doping by In introduces more electrons into the matrix, which is helpful for increasing the amount of adsorbed oxygen, leading to high sensitivity. The In-doped 3DOM ZnO is a promising material for a new type of ethanol sensor.

Strong metal-support interaction in novel core-shell Au-CeO2 nanostructures induced by different pretreatment atmospheres and its influence on CO oxidation.

Yolk-shell Au/CeO2 (Y-Au/CeO2) and encapsulated Au/CeO2 (E-Au/CeO2) nanocatalysts were prepared by using silica templates. A strong metal-support interaction (SMSI) in the Au/CeO2 nanostructures induced by different pretreatment atmospheres and its influence on CO oxidation were studied. E-Au/CeO2 pretreated in O2 had the best performance, followed by Y-Au/CeO2 pretreated in O2, Y-Au/CeO2 pretreated in H2, and E-Au/CeO2 pretreated in H2. The reasons for the different activities were discussed. There were two kinds of strong metal-support interactions (SMSI) between Au and CeO2 termed as R-SMSI (pretreated in reductive atmosphere) and O-SMSI (pretreated in oxidation atmosphere). Because of the smaller size of the Au and the larger contact area, both the R-SMSI and O-SMSI of E-Au/CeO2 were larger than those of Y-Au/CeO2. The O-SMSI was accompanied by the formation of cationic Au species that were beneficial to the enhancing of activity. As expected, the activity of E-Au/CeO2 pretreated in O2 with a Au size less than 5 nm was higher than that of Y-Au/CeO2 pretreated in O2 with 25 nm Au. However, it is surprisingly found that the activity of Y-Au/CeO2 pretreated in H2 with 25 nm Au was higher than that of E-Au/CeO2 pretreated in H2 with a Au size less than 5 nm. R-SMSI resulted in the formation of a AuCe alloy that had a negative effect on the activity. Compared with E-Au/CeO2 pretreated in H2, Y-Au/CeO2 pretreated in H2 exhibited a smaller relative content of the AuCe alloy, leading to a better activity of Y-Au/CeO2 pretreated in H2.

Controllable defect redistribution of ZnO nanopyramids with exposed {101Ì 1} facets for enhanced gas sensing performance.

ZnO nanopyramids (NPys) with exposed crystal facets of {101̅1} were synthesized via a one-step solvothermal method, having a uniform size with a hexagonal edge length of ∼100 nm and a height of ∼200 nm. Technologies of XRD, TEM, HRTEM, Raman, PL, and XPS were used to characterize the morphological and structural properties of the products, while the corresponding gas sensing properties were determined by using ethanol as the target gas. For the overall goal of defect engineering, the effect of aging temperature on the gas sensing performance of the ZnO NPys was studied. The test results showed that, at the aging temperature of 300 °C, the gas sensing property has been improved to the best, with the fast response-recovery time and the excellent selectivity, because the ZnO300 has the most electron donors for absorbing the largest content of O(2-). Model of defect redistribution was used to explicate the changing of the surface defects at different aging temperatures. The findings showed that, in addition to VO, Zni was the dominant defect of the {101̅1} crystal facet. The gas sensing performance of the ZnO NPys was determined by the contents of VO and Zni, with all of the defects redistributed on the surface. All of the results will be noticeable for the improvement of the sensing performance of materials with special crystal facet exposing.

Three dimensionally ordered macroporous Pd-LaMnO3 self-regeneration catalysts for methane combustion.

Three-dimensionally ordered macroporous (3DOM) Pd-LaMnO3 self-regeneration catalysts were successfully prepared. After reduction treatment at 500 °C, the catalyst exhibited the best catalytic activity for methane combustion. The excellent catalytic performance was attributed to the ordered porous structure, the large surface area, and the strong interaction between segregated Pd and the LaMnO3 substrate.

Synthesis of titania and titanate nanomaterials and their application in environmental analytical chemistry.

TiO(2) nanoparticles and H(2)Ti(2)O(5).H(2)O, Na(2)Ti(2)O(4)(OH)(2) nanotubes were synthesized by solvothermal method and their applications in the degradation of active Brilliant-blue (KN-R) solution were investigated. The experimental results revealed that the synthesized TiO(2) nanoparticles had a good crystallinity and a narrow size distribution (about 4-5 nm); the obtained H(2)Ti(2)O(5).H(2)O, Na(2)Ti(2)O(4)(OH)(2) were tubelike products with an average diameter of approximately 20-30 and approximately 200-300 nm length. The three catalysts we synthesized had some hydroxyl groups and the maximum absorption boundaries of the samples were all red-shifted, which indicated the samples had a promising prospect in photocatalysis. The results of the photocatalytic experiments indicated that the photocatalytic activity of the samples was: TiO(2)>H(2)Ti(2)O(5).H(2)O>Na(2)Ti(2)O(4)(OH)(2), which was in good accordance with the fact of FTIR and UV-vis absorption spectra. The formation mechanism of these nanostructures was also discussed.