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Research on the efficient flotation desilication of low-grade magnesite is of great significance for the sustainable development of magnesium resources. Traditional collectors usually have some disadvantages, such as poor selectivity, severe environmental pollution, and weak water solubility. To strengthen the desilication flotation process of magnesite ore, the biodegradable surfactant, cocamidopropyl amine oxide (CPAO), was first utilized as the collector for the separation of the magnesite and quartz. The selective adsorption behavior and mechanism of the quartz and magnesite with the CPAO as the collector were studied through the micro-flotation experiments of the single mineral and the artificially mixed mineral, contact angle and atomic force microscopy (AFM) measurements, fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. The flotation results indicated that the CPAO showed good selectivity and could effectively separate magnesite and quartz. When the concentration of the CPAO was 10.0 mg/L in the natural pulp pH (about 7.2), the concentrates with 97.67% MgO recovery and 45.62% MgO grade were obtained. The contact angle and AFM measurements indicated that the CPAO could selectively adsorb on the quartz surface rather than the magnesite surface to improve the interface difference between them, especially its surface hydrophobicity. The results of the FTIR and XPS analyses indicated that the CPAO is selectively adsorbed on the surface of the quartz, mainly through electrostatic interaction and hydrogen bonding. In conclusion, the CPAO had good selectivity and great potential as an effective collector in the reverse flotation desilication progress of magnesite. [ABSTRACT FROM AUTHOR]

WO 3 porous films (WPFs) were synthesized by a non-hydrolytic sol-gel (NHSG) method using WCl 6 , C 2 H 5 OH, and C 3 H 7 NO as the precursors. The polyethylene glycol (PEG) was employed as a porogen to prepare the porous structure. The microstructures of WPFs were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Nitrogen adsorption-desorption isotherms were used to characterize the specific surface areas of the samples. The results indicated that the honeycomb-like WPFs were assembled by numerous WO 3 nanoparticles with the diameter of 20–60 nm. Gas sensing measurements showed that the peak sensor response to NO 2 was obtained at the operating temperature of 100 °C. The sensor based on WPFs showed excellent reversibility and fast response to NO 2 at various operating temperatures and NO 2 concentrations. The sensor also exhibited a significant NO 2 selectivity compared with NH 3 , SO 2 , CH 3 OH, and C 2 H 5 OH, demonstrating a promising application in detecting NO 2. The porous structure formation process of the WPFs was analyzed and gas sensing mechanism based on electron depletion theory as well as first principle calculations were discussed. Image 1 • WO 3 porous films with honeycomb-like nanostructure were synthesized by a non-hydrolytic sol-gel technique. • WO 3 porous films were assembled by numerous crystalline nanoparticles with the diameters of 20–60 nm. • Gas sensor based on WO 3 porous films showed high response and excellent reproducibility to NO 2. • The porous structure formation and sensing mechanism of WO 3 porous films were discussed. [ABSTRACT FROM AUTHOR]

The CuO nanorods were in-situ grown on sensing electrodes by a chemical bath method for the detection of volatile organic compounds (VOCs). The synthesized material was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). The CuO nanorods, with lengths of 100–150 nm and diameters of 35–55 nm, were uniformly formed into a thin film on the electrode surface, with a thickness of approximately 1 μm. The gas test results demonstrated that the sensor achieved a peak response of 1.32 for formaldehyde at 200 °C, and a response of 1.92 for ethanol at 175 °C. At a concentration of 50 ppm, ethanol and formaldehyde at an operating temperature of 200 °C exhibit short response/recovery times of 28 s/48 s for ethanol and 45 s/62 s for methanol, respectively, coupled with good reproducibility. Moreover, the sensor exhibited a power-law response to varying gas concentrations and showcased superior selectivity in the VOCs gas detection. This in-situ growing CuO of our work provides a facial gas sensing material fabricated method. [ABSTRACT FROM AUTHOR]

A facile strategy was designed to synthesize ZnO-SnO 2 hetero-structured nanowires followed by comprehensive studies on their sensing properties and mechanism. • ZnO-SnO 2 hetero-structured nanowires were designed and synthesized for NO 2 sensing. • ZnO-SnO 2 heterostructures were composed of ZnO nanowires and the surface-loaded SnO 2 nanoparticles. • ZnO-SnO 2 heterostructures showed overall superior sensing performance to NO 2 compared with pure ZnO nanowires. • The possible sensing enhancement mechanisms were discussed. SnO 2 nanoparticles were uniformly grown on the surfaces of ZnO nanowires by a simple hydrothermal process to form one-dimensional ZnO-SnO 2 hetero-structured nanowires. The morphology, microstructure, and composition of the pristine ZnO and ZnO-SnO 2 hetero-structured nanowires were characterized by X-ray diffraction, scanning and transmission electron microscopies and X-ray photoelectron spectroscopy. A systematic investigation on their gas sensing characteristics was performed using a static gas sensing measurement system. The ZnO-SnO 2 hetero-structured nanowires exhibited an overall enhancement in NO 2 sensing properties, which was found to be closely related to their Sn/Zn atomic ratio. The highest NO 2 response was obtained for ZnO-SnO 2 hetero-structured nanowires with Sn/Zn atomic ratio of 5% and at operating temperature of 150 °C. Compared with pristine ZnO nanowires, these hetero-structured nanowires also exhibited faster response/recovery rate and better NO 2 selectivity. The difference in sensing performance between pristine ZnO nanowires and ZnO-SnO 2 heterostructures are explained based on the surface depletion model and the potential barrier control model. [ABSTRACT FROM AUTHOR]

Mesoporous In 2 O 3 nanorod arrays were synthesized directly on a porous ceramic substrate via a one-step hydrothermal method. The morphology and structure of the obtained In 2 O 3 nanorod arrays were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results revealed that In 2 O 3 nanorod arrays with cubic phase were densely distributed on the porous ceramic substrate, showing the diameter of 120–200 nm and length of 0.5–1 μm. Especially, the nanorod was assembled by aggregated In 2 O 3 nanoparticles with the diameters of 10–30 nm, and its large specific surface ensured the highly gas sensing performance for ppb-level NO 2 detection. The response value of the mesoporous In 2 O 3 nanorod arrays to 800 ppb NO 2 was 14.9 at room temperature of 25 °C with a short response time of 14 s, and the ultraviolet light was loaded in the recovery process to shorten the recovery time to about 32 s. The growth and gas sensing mechanisms of the mesoporous In 2 O 3 nanorod arrays were discussed. It demonstrates that this work provides a low-cost route for the fabrication of room-temperature NO 2 gas sensor with high performance through in-situ growth of the sensing materials on a porous ceramic substrate. Unlabelled Image • The mesoporous In 2 O 3 nanorod arrays were synthesized on a porous ceramic substrate via one-step hydrothermal method. • The porous structure of the ceramic substrate plays an essential role in the formation of the arrays structure. • A fast recovery speed of the room temperature NO 2 sensor was realized under the UV-assisted recovery. [ABSTRACT FROM AUTHOR]

One-dimensional Zn-doped α-Fe2O3 nanowires have been controllably synthesized by using the pure pyrite as the source of Fe element through a two-step synthesis route, including the preparation of Fe source solution by a leaching process and the thermal conversion of the precursor solution into α-Fe2O3 nanowires by the hydrothermal and calcination process. The microstructure, morphology, and surface composition of the obtained products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. It was found that the formation process of α-Fe2O3 is significantly influenced by the introduction of Zn2+. The gas sensing measurements indicated that the sensor based on 1% Zn-doped α-Fe2O3 nanowires showed excellent H2S sensing properties at the optimum operating temperature of 175 °C. Notably, the sensor showed a low H2S detection limit of 50 ppb with a sensor response of 1.5. Such high-performance sensing would be ascribed to the one-dimensional structure and high specific surface area of the prepared 1% Zn-doped α-Fe2O3 nanowires, which can not only provide a large number of surface active sites for the adsorption and reaction of the oxygen and H2S molecules, but also facilitate the diffusion of the gas molecules towards the entire sensing materials. [ABSTRACT FROM AUTHOR]

[Display omitted] Detection of flammable, explosive and toxic butyl acetate helps to avoid accidents and protect health in industrial production. However, there are few reports on butyl acetate sensors, especially highly sensitive, low detection limit and highly selective ones. In this work, density functional theory (DFT) analyzes the electronic structure of sensing materials and the adsorption energy of butyl acetate. The effects of Ni element doping, oxygen vacancy constructions, and NiO quantum dot modifications on the modulation of the electronic structure of ZnO and on the adsorption energy of butyl acetate are investigated in detail. Based on the DFT analysis, the NiO quantum dot modified jackfruit-shaped ZnO is synthesized via thermal solvent method reduction. The NiO/ZnO sensor has a response 502.5 for 100 ppm butyl acetate with 100 ppb detection limit, and the response for 100 ppm butyl acetate is at least 6.2 times higher than 100 ppm methanol, 100 ppm benzene, 100 ppm triethylamine, 100 ppm isopropanol, 100 ppm ethyl acetate and 100 ppm formic acid. X-ray photoelectron spectroscopy (XPS) explores the change of oxygen vacancies in sensor accompanied with the addition of Ni element and reveales the reason for the change of oxygen vacancies. [ABSTRACT FROM AUTHOR]

[Display omitted] • DAMP was first used as a collector for the selective separation of quartz from hematite. • DAMP has good potential for hematite reverse flotation desilication. • Adsorption effect of DAMP on quartz was significantly higher than that on hematite. • OH groups, helping DAMP form stronger hydrogen bonds on quartz surface, enhance their separation. Traditional cationic collectors usually have some disadvantages, such as poor selectivity and limited water solubility, which negatively impact flotation efficiency. Thus, a novel cationic collector, 2-(dodecylamino)-2-methyl-1-propanol (DAMP) was developed to enhance the separation efficiency of hematite and quartz. The flotation behavior of DAMP was systematically investigated, and the results indicated that DAMP had good flotation performance and excellent selectivity. Optimal flotation separation of mixed hematite and quartz achieved a concentrate with a TFe grade of 67.79 % and a recovery rate of 91.26 % at a pulp pH of 7.34, using 4.0 mg/L starch and 20.0 mg/L DAMP. Furthermore, the interaction mechanisms between DAMP and the minerals were explored using zeta potential measurements, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and molecular dynamics (MD) simulation. The findings confirmed that DAMP exhibited superior selectivity compared to DDA, and the adsorption of DAMP on minerals occurred through electrostatic forces and hydrogen bonding interactions. [ABSTRACT FROM AUTHOR]

[Display omitted] • O v defect-rich phosphorus-doped porous perovskite LaFeO 3-δ nanosheets were prepared. • Characterizations and DFT results indicate that doping with P induces O v defects. • Perovskite LaFe 1-x P x O 3-δ sensor has excellent acetone sensing properties at 180 °C. • O v defects reconfigure electron distribution and promote gas adsorption. Perovskite-type oxide semiconductors (ABO 3) with defective conduction properties have been regarded as highly promising gas-sensitive materials due to their abundant structural types. However, pure ABO 3 gas sensors usually have suboptimal sensing response due to low specific surface area and few adsorption sites. Recently, surface oxygen vacancies (O v) defects have been shown to be a remarkably effective way to enhance the sensing response of gas sensors by increasing the number of adsorption sites and changing the energy level structure. In view of the above, herein, P-doped perovskite LaFe 1-x P x O 3-δ (x = 0.005, 0.01, 0.03, 0.05) with abundant O v defects were prepared by sol–gel method and fabricated as sensors for the acetone detection. Characterization and test results show that LaFe 0.99 P 0.01 O 3-δ with porous nanosheet structure has excellent acetone gas-sensitive performance. Compared to pure LaFeO 3 gas sensor, the optimal operating temperature of LaFe 0.99 P 0.01 O 3-δ is reduced to 180 °C and response value is improved nearly twofold, whose limit of detection is even at the ppb level. Crucially, the results of electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) verify that the sensing characteristics of the LaFe 1-x P x O 3-δ sensor are strongly correlated with the O v defect. In addition, further theoretical analysis shows that P doping in LaFeO 3 induces O v defects and modulates frontier electron orbital energy levels of the material, thus increasing the chemisorbed oxygen species and enhancing the intermolecular interactions. In this work, the vital function of O v defects in perovskite-type gas sensors is highlighted, which also provides an effective and feasible way to improve the performance of gas sensors. [ABSTRACT FROM AUTHOR]

While metal oxides and metal sulfides have been extensively studied for gas sensing applications, there are no extensive reports on gas sensing properties of metal diborides. Here, for the first time, we have investigated the conductometric gas sensing behavior of HfB 2 nanoparticles. The HfB 2 nanoparticles is synthesized via a sol-gel method and characterized using X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The gas sensor is fabricated by drop casting the HfB 2 nanoparticles on interdigitated Ag/Pd electrodes. The sensor exhibited a promising NO 2 sensing performance at the operating temperature of 200 °C. Interestingly, it is found that resistance of the sensor decreases upon exposure to both oxidizing and reducing gases, which does not follow the gas sensing behaviors of the widely investigated metal oxides. In addition, the sensor response is minimally influenced by oxygen background concentration. These results highlight that HfB 2 nanoparticles exhibit very unique sensing characteristics. [ABSTRACT FROM AUTHOR]

Currently, the sensing mechanism of toluene remains controversial. The sensing action of toluene is often attributed to adsorbed oxygen based on acknowledged Wolkenstein model. However, the role of lattice oxygen often remains neglected. To investigate toluene sensing mechanism, Ag quantum dot-modified Co 3 O 4 were successfully synthesized by the thermal method. X-ray photoelectron spectroscopy (XPS) of Ag-Co 3 O 4 before and after exposure to toluene reveal the role of lattice oxygen, and Gas Chromatography-Mass Spectrometry (GC-MS) and Density Functional Theory (DFT) reveal the catalytic role of Ag particles. Ag particles caused the upshift of Co D-band, more readily hybridizing the s and p orbitals in the toluene and O 2 molecules, possibly contributing to the enhanced catalytic and adsorption activity of the materials. Moreover, Ag-induced response behaviors switching from oxidation-reduction transitions were found and explained. Excitingly, the synthesized 16 at% Ag-Co 3 O 4 has good selectivity for toluene at 180 °C. And the response of 16 at% Ag-Co 3 O 4 to 100 ppm toluene reached 2113% with a detection limit 100 ppb. This work provides a novel insight into the toluene sensing mechanism, aiding the design of high-performance toluene sensors. • Ag quantum dot leads to the upward shift of Co d-band on Co 3 O 4 , activating toluene and oxygen. • Ag quantum dot modified Co 3 O 4 transfers lattice defect and reduces adsorbed oxygen. • Excess Ag particles led to a switch in the response behavior of CO 3 O 4. • Lattice oxygen has an essential role in the toluene sensing reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • 14-2G was first used as the collector in quartz-magnesite reverse flotation. • 14-2G had low foam viscosity which was consistent with the design expectation. • 14-2G displayed excellent selectivity for quartz against magnesite. • 14-2G adsorbed on quartz surfaces by electrostatic force and Hydrogen bonding. A novel cationic surfactant 2-[2-(Tetradecylamino)ethoxy]ethanol (14-2G) was designed and synthesized by introducing the –CH 2 CH 2 OCH 2 CH 2 OH group to tetradecylamine. The structure of 14-2G was characterized by Fourier transform infrared spectrum (FTIR), 1H Nuclear Magnetic Resonance, and Mass spectrum. The foam performance of 14-2G was tested and first introduced to the reverse flotation system of the quartz-magnesite as a collector. The flotation performance and adsorption mechanisms of 14-2G were investigated by micro-flotation tests, zeta potential, contact angle measurements, FTIR, and X-ray photoelectron spectroscopy (XPS). The foam collapse tests indicated that 14-2G has better foam performance and lower viscosity compared to dodecylamine (DDA). Micro-flotation test results showed that 14-2G exhibited excellent flotation ability for quartz and efficient separation performance of quartz from the quartz-magnesite mixture from natural to weak alkaline pulp pH. The contact angle measurements indicated that 14-2G can enhance the hydrophobicity of the quartz surface more than DDA. The analysis of zeta-potential, FTIR, and XPS results indicated that the adsorption of 14-2G on the quartz surface was due to the combination of electrostatic forces and hydrogen bond forces. The experimental results were consistent with the design expectations. [ABSTRACT FROM AUTHOR]

Based on the surface difference of hematite and quartz in solution, a hydroxyl-containing polyamine cationic surfactant was designed and screened with the assistant of computer simulation (molecular dynamics (MD) simulation and density functional theory (DFT) calculation) to enhance the separation efficiency in the reverse flotation system of hematite ore. And then N , N -dimethyl- N ′-(2-hydroxyethyl)- N ′-dodecyl-1.3-propanediamine (DMPDA) was synthesized in the laboratory. The computer simulation showed that the collecting ability of DMPDA would be comparable with that of N -dodecyl-1,3-propanediamine (NDEA) and N , N -Dimethyl- N ′-dodecyl-1,3-propanediamine (DPDA), while a better selectivity than that of DPDA and dodecylamine (DDA) could be obtained. The flotation performance and mechanism were studied by flotation tests, zeta potential measurements, Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The results of the flotation tests showed that DMPDA had a higher selectivity than DDA, which was in agreement with the theoretical prediction. The results of zeta potential, FTIR spectra, and XPS showed that DMPDA was adsorbed on the mineral surface mainly by electrostatic and hydrogen bonding. The introduction of the hydroxyl group could enhance the surface activity of the collector and the selective adsorption on the desired mineral surface. Based on this, a promising method for designing and screening the novel high-efficiency cation collector was proposed, which could accelerate the research and development of the cationic collectors. Unlabelled Image • The surface difference of minerals was used to design the novel surfactant. • The novel surfactant was screened by MD simulation. • DMPDA exhibited superior collector ability and selectivity than DDA. • Insertion of hydroxypropyl group could enhance the ability of cationic collector. • Better performance was achieved by weaker charges and larger sizes of polar groups. [ABSTRACT FROM AUTHOR]

Co 3 O 4 /SnO 2 flower-like structures were prepared via an one-step hydrothermal technique. Pure SnO 2 and Co 3 O 4 were used as reference, which were synthesized in the same condition by the hydrothermal technique. The products were characterized by field emission scanning electron microscopy (FESEM), X-ray diffractometer (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) nitrogen adsorption-desorption. It is revealed that p–n heterojunctions was formed. The TMA gas sensing measurement were investigated. The sensor made of 5 mol% Co 3 O 4 /SnO 2 flower-like structures exhibited response value of 9.3 to 5 ppm TMA at 175 °C, which is about 2.9 times higher than pure SnO 2 sensor and 7.2 times higher than pure Co 3 O 4 sensor at same temperature, respectively. In addition, this sensor also showed rapid response and recovery times to 5 ppm TMA (19 s and 29 s, respectively), good reproducibility and stability, lower detecting limit level (1 ppm), and good selectivity at 175 °C. The improved TMA sensing performance might be attributed to forming p–n heterojunctions at interface and Co 3 O 4 catalytic actions. Our works offer a synthesis method for fabricating Co 3 O 4 /SnO 2 flower-like structures. Moreover, the hierarchical Co 3 O 4 /SnO 2 p–n heterojunctions could be a promising candidate for TMA gas detection in the future. • Co 3 O 4 /SnO 2 flower-like structures self-assembled with porous nanosheets were synthesized by one-step hydrothermal method. • Co 3 O 4 /SnO 2 flower-like structures exhibited good sensing properties to TMA gas at a relatively low temperature of 175 °C. • The sensing enhancement mechanism of the Co 3 O 4 /SnO 2 flower-like structures was discussed. [ABSTRACT FROM AUTHOR]