Showing papers in "Applied Surface Science in 2021"

Raman study of D* band in graphene oxide and its correlation with reduction

Abstract: Reduced graphene oxide (rGO) is a graphene-like material that exhibits high productivity for a wide range of industrial applications. To promote the application of rGO, it is important to not only produce high-quality rGO but also precisely evaluate the output. The intensity ratio of the D to G band in the Raman scattering is commonly used to assess the defect density of the carbon materials; however, this ratio is limited to evaluate the reduction degree of rGO because of the ambiguity arising from the superposition of the bands. In this study, we investigate the relationship between the intensity ratio of D* to G band and the reduction of graphene oxide (GO) to evaluate the degree of reduction of rGO. The spectral analysis of GO and rGO, along with systematic research of the thermally reduced GO synthesized via thermal treatment (100–900 °C) revealed a strong linkage between the D*/G intensity ratio and the C/O atomic ratio. The atomic vibrational relationships were elucidated by the assignment of the D* band, based on the density functional perturbation theory calculations. These findings explain the atomic vibrational properties of rGO and provide an indicator of the quality of rGO to optimize its performance for applications.

CeO2/3D g-C3N4 heterojunction deposited with Pt cocatalyst for enhanced photocatalytic CO2 reduction

Abstract: The conversion of CO2 into high value-added carbon-based compounds through photocatalytic reduction technology is considered as one of the more promising strategies to solve the greenhouse effect. And construction of heterojunction photocatalysts can promote the separation of photoelectron-hole pairs, so as to achieve higher activity of photocatalytic CO2 reduction. Hence, Pt@CeO2/3DCN heterojunction are prepared by calcination method and photoreduction technology. The photocatalytic results revealed that Pt@CeO2/3DCN show better photocatalytic activity for reducing CO2 into CO and CH4, compared with 3DCN. Especially, Pt@45CeO2/3DCN shows the maximum photocatalytic activity of 4.69 and 3.03 μmol·h−1·g−1 for CO and CH4 under UV light irradiation, respectively, and the reduction activity did not decrease significantly after five cycles. The enhanced photoreduction of CO2 performance can be ascribed to the synergistic effects of the oxygen vacancies in CeO2 for CO2 activation and heterojunction for electron separation. Besides, Pt nanoparticles (NPs) on CeO2/3DCN can further promote the transfer of electrons, resulting in higher photocatalytic activity.

N, S self-doped hollow-sphere porous carbon derived from puffball spores for high performance supercapacitors

Abstract: A novel N, S self-doped hollow-sphere porous carbon is directly prepared from abundant biomass puffball spores via a simple carbonization and KOH activation process for the first time. The electrochemical properties and porous structure of these carbons are explored by adjusting the amount of KOH. It is found that the obtained N, S self-doped hollow-sphere porous carbon with a KOH to carbon mass ratio of 4 (NS-HPC-4) exhibits the largest specific surface area (1431 m2/g), a well-developed hierarchical porous structure and moderate N/S contents. As a result, the NS-HPC-4 electrode in the supercapacitor delivers a large specific capacitance of 285 F/g at 0.5 A/g in KOH electrolyte. Furthermore, the symmetric supercapacitor based on NS-HPC-4 exhibits an energy density of 10.9 Wh/kg at a power density of 400.4 W/kg in 2 M KOH aqueous electrolyte, and achieves a high energy density of 58.4 Wh/kg at a high power density of 876.0 W/kg in 1 M Et4NBF4/AN organic electrolyte. These excellent results confirm that puffball spores derived porous carbons are promising candidates to be used in high performance supercapacitors.

Fe3O4 nanorods decorated on polypyrrole/reduced graphene oxide for electrochemical detection of dopamine and photocatalytic degradation of acetaminophen

Abstract: The increase in the world’s population has exerted tremendous pressure on the research community to solve the related health and environmental issues. Hence, it is an important and challenging task to design a multifunctional catalyst that both aids medical diagnostics and removes organic pollutants from aqueous environments. Herein, we developed iron oxide nanorods uniformly coated on the polypyrrole/reduced graphene oxide (Fe3O4@PPy/rGO) nanohybrids by the chemical reflux method. The optimized Fe3O4@PPy/rGO nanohybrids show better electrochemical detection of dopamine (DA) with a low detection limit (0.063 µM) and a better linearity range (0 to 100 µM), with a coefficient of determination of 0.994. The Fe3O4@PPy/rGO nanohybrids reveal an excellent DA recovery rate of 97– 98% during real sample analysis. In addition, photocatalytic studies reveal that 84% acetaminophen (ACP) degradation by Fe3O4@PPy/rGO nanohybrids was noticed with the persulfate. The effect of co-existing photocatalytic studies affirms that the higher ACP photodegradation rate constant of 9.13 × 10−4 M−1 s−1 was obtained in the presence of the Cl− ion. The present work provides a new pathway for the development of a metal oxide with a conducting polymer and graphene-based catalyst for multi-functional applications for the electrochemical sensing and photodegradation of organic pollutants.

Step-scheme WO3/CdIn2S4 hybrid system with high visible light activity for tetracycline hydrochloride photodegradation

Abstract: Photocatalytic degradation is an ideal choice for the treatment of antibiotic contaminant in water environment because of the characters of environmental-benign and sustainable. In this work, the visible-light-driven WO3/CdIn2S4 hybrid photocatalysts with different WO3 content were successfully fabricated by hydrothermal method. The phase structure, surface composition, optical properties, specific surface areas and charge separation were systematically by a series of measurements. The photocatalytic activity of resultant WO3/CdIn2S4 hybrid photocatalysts was evaluated by photocatalytic degradation for removal of tetracycline hydrochloride (TCH) and the results reveal that optimized photocatalytic efficiency in WO3/CdIn2S4 hybrid photocatalysts can be achieved by modulating the weight ratio of WO3 to CdIn2S4. The 70 wt% WO3/CdIn2S4 hybrid photocatalyst exhibited the best photodegradation activity. Significant enhancement of photocatalytic activity in WO3/CdIn2S4 hybrid photocatalysts is ascribed to effective charge separation due to the construction of step-scheme heterojunction. The photocatalytic mechanism involving charge transfer and separation, and degradation path using step-scheme WO3/CdIn2S4 hybrid photocatalysts were in-depth investigated and discussed. It is anticipated that our current investigation could open an avenue for design and preparation of step-scheme hybrid photocatalysts for environmental remediation.

CoFe2O4 nanoparticles loaded N-doped carbon nanofibers networks as electrocatalyst for enhancing redox kinetics in Li-S batteries

Abstract: Lithium sulfur (Li-S) batteries have been paid more attention to meet the demand of high capacity energy storage. However, most substrates applied to electrodes, which have both high conductivity and full coverage of adsorption-catalysis synergies, are difficult to achieve. Herein, the combination of electrospinning and hydrothermal method is developed to fabricate the composite membrane of ferri-based spinel CoFe2O4 (CFO) loaded nitrogen doped carbon nanofibers (CFONC) applied to positive current collector with Li2S6 catholyte and binder-free of Li-S batteries. Benefiting from the improved catalytic performances in redox reaction of lithium polysulfides due to the abundant active sites which originate from CFO, the CFONC composite with S loading of 4.74 mg exhibits an initial specific discharge capacity of 1096 mAh g−1 at 0.2 C and a high specific discharge capacity of 681 mAh g−1 after 500 cycles with a capacity decay as small as 0.076% per cycle. Even with S loading of 7.11 mg, the cell of CFONC delivers a high initial capacity of 6.1 mAh and maintains 4.8 mAh after 300 cycles. The results show that the efficient chemical anchoring polysulfides and catalyzing redox reaction by multifunctional CFONC composites is a feasible strategy for the large-scale application of lithium sulfur batteries with high performance in the future.

Towards reliable X-ray photoelectron spectroscopy: Sputter-damage effects in transition metal borides, carbides, nitrides, and oxides

Abstract: Ar+ sputter etching is often used prior to X-ray photoelectron spectroscopy (XPS) analyses with the intention to remove surface oxides and contaminants. Since the XPS probing depth is comparable to the thickness of the ion-beam modified layer the signal from the latter dominates the spectra. We check here the conditions for reliable XPS analysis by studying ion irradiation effects for single-phase Group IVB transition metal (IVB-TM) boride, carbide, nitride, and oxide thin film specimens. The extent of sputter damage, manifested by changes in the surface composition, binding energy shift, peak broadening, and the appearance of new spectral features, varies greatly between material systems: from subtle effects in the case of IVB-TM carbides to a complete change of spectral components for IVB-TM oxides. The determining factors are: (i) the nature of compounds that may form as a result of ion-induced mixing in the affected layer together with (ii) the final elemental composition after sputtering, and (iii) the thickness of the Ar+-affected layer with respect to the XPS probing depth. Our results reveal that the effects of Ar+ ion irradiation on XPS spectra cannot be a priori neglected and a great deal of scrutiny, if not restraint, is necessary during spectra interpretation.

Effective and structure-controlled adsorption of tetracycline hydrochloride from aqueous solution by using Fe-based metal-organic frameworks

Abstract: Removal of tetracycline hydrochloride (TCH) is vital to the environment yet challenging. Here, three Fe-based MOFs (metal–organic frameworks) with significantly different porous properties and open metal sites were applied as adsorbents to remove TCH, and the adsorption mechanism was investigated using experiments and computations. The experimental results showed structure-controlled TCH adsorption. The adsorption ability of the three MOFs was in the order MIL-101(Fe) > MIL-88A(Fe) > MIL-53(Fe); these results were closely related to the BET surface area, pore volume and open metal sites. Among these MOFs, MIL-101(Fe), with a high pore volume, high BET surface area, large number of open metal sites and high binding energy (Ebind), exhibited excellent TCH adsorption performance (qm = 420.6 mg g−1). The Ebind of MIL-53(Fe) is higher than that of MIL-88A(Fe), but the lower BET surface areas and porosity might limit its adsorption capacity. Zeta potential and XPS results showed that TCH adsorption was driven by electrostatic interactions and coordination between TCH and unsaturated Fe sites. The π-π interactions (TCH benzene ring and the MOF’s ligand) and pore fillings may be important for TCH removal. The results obtained will help in understanding surface interactions between MOFs and TCH and fabricating efficient MOFs-based adsorbents for pollutant removal.

Selective, sensitive, and stable NO2 gas sensor based on porous ZnO nanosheets

Abstract: In this study, we synthesized porous (porosity: ~16%, average pore size: ~60 nm) ZnO nanosheets (thickness: ~80 nm) using a conventional solvothermal method to investigate NO2 gas sensing properties. Porous ZnO nanosheets triggered the detection of NO2 gas with high sensitivity. Responses of 2.93 – 0.5 ppm and 74.68 – 10 ppm NO2 gas at 200 °C were observed in the porous ZnO nanosheet-based gas sensor. In addition, improved sensing properties with high selectivity to NO2 gas, reasonable stability, and high response even in the presence of water vapor molecules were obtained. We found that the enhanced NO2 gas response of the porous ZnO nanosheet-based gas sensor was due to the synergetic effects of the high surface area, ZnO/ZnO homojunctions, and structural defects. We developed a highly sensitive NO2 gas sensor with improved reliability using morphologically engineered ZnO, which was prepared via a simple and scalable chemical-synthesis route.

Investigation of phosphate removal mechanisms by a lanthanum hydroxide adsorbent using p-XRD, FTIR and XPS

Abstract: Macroscopic batch experiments and microscopic spectroscopic characterization by powder X-ray diffraction (p-XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were employed to accurately study the phosphate adsorption process onto lanthanum hydroxide adsorbent. The relatively low La release after phosphate adsorption suggested the formation of surface co-precipitation of lanthanum phosphate beyond the Lewis acid-base interaction under the acidic conditions. The maximum adsorption capacities calculated by the Langmuir isotherm at pH 4.0 and 8.0 were 122.0 mg/g and 109.9 mg/g, respectively. Cl−, SO42– and HCO3– on phosphate removal negligibly impacted on phosphate adsorption, while acetate slightly retarded the adsorption. The fitted FTIR spectra of P−O stretching vibration bands in 900–1200 cm−1 range indicated that diprotonated bidentate binuclear or monoprotonated bidentate mononuclear complexes were the dominant surface configurations at pH 4–9. Diprotonated bidentate binuclear complexes were dominant at pH 3 and monoprotonated bidentate binuclear complexes were the major configurations at pH > 9. The high resolution scans of La 3d, O 1s and P 2p spectra before and after phosphate adsorption and lanthanum phosphate indicated that inner-sphere surface complexes formed through the ligand exchange reaction, which were further determined to be rhabdophane (LaPO4·0.5H2O) by p-XRD analysis.

CdS/BiOBr heterojunction photocatalyst with high performance for solar-light-driven degradation of ciprofloxacin and norfloxacin antibiotics

Abstract: Sunlight active CdS/BiOBr heterojunction photocatalyst was fabricated by a solvothermal route. To the best of our knowledge, the novelty of the research is based on the decoration of the hexagonal CdS nanoparticles on the surface of the tetragonal BiOBr microflowers for the creation of a heterostructure photocatalyst used for the removal of the antibiotics. The CdS/BiOBr-1:3 heterojunction exhibited 100% removal of norfloxacin and ciprofloxacin under simulated visible light. In addition, complete degradation of the antibiotics under natural sunlight was also achieved. Construction of the CdS/BiOBr heterojunction is a promising strategy for the improvement of photocatalytic performance due to a decrease in the charge carrier recombination rate at the interface, an increase in the visible light absorption range, and an enhancement of the surface area of the resultant product. The removal of the pollutants fit very well with the first-order reaction. The photogenerated hole played a crucial role in the removal of the antibiotics. Confirmation of the stability of the CdS/BiOBr heterojunction was also elucidated. The photoactivity of the photocatalyst remained the same after the fifth cycle implying the excellent cycling ability of the sample. This research demonstrates the promising potential of the CdS/BiOBr heterojunction for degradation of toxic antibiotics presented in water.

Construction of CeO2/BiOI S-scheme heterojunction for photocatalytic removal of elemental mercury

Abstract: In this work, a series of CeO2/BiOI S-scheme heterojunction photocatalysts were prepared through a simple co-precipitation and hydrothermal method. In addition, various characterization methods were adopted to confirm the successful preparation of the photocatalyst, and density functional theory (DFT) was applied to evaluate and calculate the band structure, density of states and electrostatic potential, and to further determine the construction of the S-scheme heterojunction. Furthermore, photocatalytic activity of the samples was evaluated by removing Hg0 under visible light, and the mechanism of photocatalytic mercury removal was proposed. The experimental results show that compared with single CeO2 and BiOI, the photocatalytic activity of the prepared CeO2/BiOI S-structure heterojunction has been significantly improved. Moreover, the significant enhancement of photocatalytic activity not only benefits from Ce4+/Ce3+ activation centers and oxygen vacancies, but also from the S-scheme heterojunction. This work provides effective guidance for exploring the effective construction of Bi-based composite photocatalysts with S-scheme heterojunctions.

Magnetic NiFe2O4 nanoparticles decorated on N-doped BiOBr nanosheets for expeditious visible light photocatalytic phenol degradation and hexavalent chromium reduction via a Z-scheme heterojunction mechanism

Abstract: In the present work, new Z-scheme N-BiOBr/NiFe2O4 nanocomposites were successfully constructed by a facile hydrothermal method. Various analytical characterization techniques were employed to examine the physicochemical and optical absorption properties of prepared photocatalysts. The prepared N-BiOBr/NiFe2O4 nanocomposites considerably enhanced the simultaneous visible light removal of phenol and Cr(VI) when compared with single-phase component photocatalysts. Especially, the N-BiOBr/NiFe2O4-15 nanocomposite demonstrated the top-flight photoactivity. The formed Z-scheme system in the nanocomposite significantly decreased the charge carrier recombination and improved the photoactivity. Photoluminescence and photoelectrochemical measurements were conducted to confirm the evidence of efficient charge carrier separation by the nanocomposites. Moreover, the N-BiOBr/NiFe2O4-15 nanocomposite can be magnetically separated and possessed good recycle performance up to five successive runs. The active species capturing experiments demonstrated that the hydroxyl radicals can degrade the phenol efficiently and that photogenerated electrons can reduce the Cr(VI). Finally, the mechanism of excellent photoactivity of N-BiOBr/NiFe2O4 nanocomposite was discussed.

Exploring the enhanced catalytic performance on nitro dyes via a novel template of flake-network Ni-Ti LDH/GO in-situ deposited with Ag3PO4 NPs

Abstract: A novel catalyst composed of Ag3PO4 bridged by Ni/Ti LDH-graphene heterojunction structure was successfully prepared by a simple in-situ deposition method, which has excellent catalytic performance for 4-NP and 2-NA. Various characterizations to the samples such as XRD, SEM, TEM, STEM-EDS, XPS, TG–DSC, and UV–vis DRS were adopted. Because the ternary structure is mixed with each other to form more heterojunctions and higher specific surface area, the ternary composite Ag3PO4/Ni-Ti LDH/GO has excellent catalytic and cycle performance. Compared to the precursors Ag3PO4/GO and Ni-Ti LDH/GO, the finally as-obtained nanocomposite Ag3PO4/Ni-Ti LDH/GO degraded 4-NP and 2-NA solutions represented more dominant degradation efficiency. In addition, the pseudo-first-order rate constants of the composite catalyst for 4-NP and 2-NA are 0.178 min−1 and 0.089 min−1, respectively. The complex and irregular surfaces of Ni-Ti LDH/GO provided an ideal carrier with abundant active sites for in-situ depositing and stabilizing of Ag3PO4 NPs, formed the Ag3PO4/Ni-Ti LDH/GO hybrid possessed an acceptable catalytic performance on the degradation of azo dyes, which could be applied in the efficient treatment of wastewater from industries.

Flexoelectricity-induced enhancement in carrier separation and photocatalytic activity of a photocatalyst

Abstract: In this paper, we have elucidated the role of flexoelectricity in the photoexcited carrier separation and photocatalysis enhancement by comparatively investigating the photocatalytic, flexocatalytic and flexo-photocatalytic activities of centrosymmetric Ag2MoO4 photocatalyst for degrading methylene blue (MB). Ultrasonic vibration was used to induce the flexoelectric effect in Ag2MoO4, and the flexo-photocatalytic experiment was performed by simultaneously irradiating the reaction solution with simulated sunlight and ultrasonic wave. It is demonstrated that the photo-flexocatalysis of Ag2MoO4 is much higher than its single photocatalysis and flexocatalysis, implying an obvious flexoelectricity-enhanced mechanism of photocatalysis. To incorporate the photo-flexocatalysis of Ag2MoO4 into practical application in environmental purification, the effects of initial MB concentration, catalyst dosage, pH and various anions on the flexo-photocatalytic degradation of MB over Ag2MoO4 were investigated. Flexo-photocatalytic degradation of methyl orange (MO)/rhodamine B (RhB)/MB mixture dyes and other organic pollutants including tetracycline hydrochloride (TC) and ciprofloxacin (CIP) were also investigated, further confirming the excellent flexo-photocatalytic performance of Ag2MoO4.

Space-confined carbonization strategy for synthesis of carbon nanosheets from glucose and coal tar pitch for high-performance lithium-ion batteries

Abstract: A space-confined carbonization strategy is developed to synthesize carbon nanosheets (CNSs) from various carbon precursors such as glucose and coal tar pitch (CTP) using expanded vermiculite as template The carbonization process of the glucose and CTP molecules occurs in the confined space in the expanded vermiculite, which leads to the formation of well-defined carbon nanosheets (G-CNSs and CTP-CNSs) These carbon nanosheets not only have acceptable specific surface area (381 and 297 m2·g−1) and total pore volume (0379 and 0558 cm3·g−1) with abundant heteroatom functional groups (eg O and N), but also possess lamellar structure consisting of multi-layer graphene with appreciate interlayer spacing and favorable hierarchical pore structure Such distinctive microstructure features ensure both kinds of CNSs applied as anode materials for lithium-ion batteries to exhibit superior electrochemical behaviors Particularly, CTP-CNSs exhibit a high initial reversible capacity (1147 mAh/g at 005 A/g), outstanding rate capability (510 mAh/g at a high current density of 2 A/g), and superior long-term cycling stability (623 mAh/g with a Coulombic efficiency of 997% at 2 A/g after 500 cycles) This result suggests such anode material outperformed many other carbon materials reported in the literature, proving the applicability of the preparation route developed in the current work

Double ligand MOF-derived pomegranate-like Ni@C microspheres as high-performance microwave absorber

Abstract: Metal-organic framework (MOF)-derived functional composites have received extensive attention, especially in microwave absorption (MA) materials. However, the delicate design of the spatial structure, designed components, and heterojunction interfaces of MOF derivatives remains a great challenge in the MA application. Herein, a simple double organic ligand strategy and controllable pyrolysis treatment were used to regulate the Ni-MOF derived pomegranate-like Ni@C Microspheres. Their morphology and crystallization can be accurately controlled by a simple hydrothermal method. After pyrolysis, hierarchical magnetic-carbon Ni@C microspheres were obtained which consists of many nickel-carbon core–shell units within the carbon layer. MOF-derived Ni@C microspheres possessed plentiful interfaces, unique three-dimensional conduction network, and magnetic-dielectric synergy system. The pomegranate-like Ni@C microspheres shown excellent microwave absorption performance of a maximum reflection loss (−46.9 dB at 3.5 mm), which can be attributed to the dielectric attenuation, magnetic loss, and matched impedance. Precision regulation of MOF precursors and MOF derivatives provide a novel platform of magnetic-dielectric Ni@C composites that offers excellent MA applications.

Ru doped bimetallic phosphide derived from 2D metal organic framework as active and robust electrocatalyst for water splitting

Abstract: The exploration of earth-abundant, highly active, and stable electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a vital but challenging step for sustainable energy conversion processes. Herein, a super-low ruthenium (Ru) (0.6 wt%) doped bimetallic phosphide derived from 2D MIL-53(NiFe) MOF nanosheets (i.e., Ru-NiFeP/NF) on nickel foam was developed via a continuous two-step hydrothermal followed by phosphorization process. The as-obtained Ru-doped NiFeP/NF with optimized electronic structure and enhanced electric conductivity delivers admirable performance for HER in a wide pH range, which requires overpotentials of 29, 105, and 56 mV to reach current density of 10 mA·cm−2 in acid, neutral, and alkaline media, respectively. For the OER, only requires an overpotential of 179 mV to achieve 10 mA·cm−2 in alkaline media. In a two-electrode alkaline electrolyzer, the as-prepared Ru-NiFeP/NF electrodes only need 1.47 V to yield 10 mA·cm−2, which is superior to the integrated RuO2 and Pt/C couple electrode (1.5 V). This work highlights the rational design of MOF-derivates and electronic structure engineering strategy by heteroatom doping, which can be extended to design and prepare other high-performance MOF-based electrocatalysts.

Selectively Se-doped Co3O4@CeO2 nanoparticle-dotted nanoneedle arrays for high-efficiency overall water splitting

Abstract: Transition metal oxides are well-known for their excellent activity and stability during oxygen evolution reaction process, while their hydrogen evolution reaction performance still is unsatisfactory. Herein, we firstly introduced the selectively Se-doped Co3O4@CeO2 nanoparticle-dotted nanoneedle arrays through three continuous operations of mild hydrothermal, air calcination and selective selenation. The remarkable HER and OER performance of SCCN-1 resulted from abundant oxygen vacancy as well the heterostructure and was testified by the overpotentials at a certain current density: 48 mV@10 mA cm−2 and 175 mV@50 mA cm−2 for HER; 188 mV@20 mA cm−2 and 293 mV@50 mA cm−2 for OER. In addition, the SCCN-1//SCCN-1 electrode couple only required a small cell voltage of 1.49 V to deliver a current density of 10 mA cm−2, which outperformed most recently reported bifunctional catalyst and exhibited outstanding stability in 1.0 M KOH over 12 h for overall water splitting process. Density functional theory calculations show that Se-doped Co3O4 exhibits stronger water adsorption energy compared to CeO2, which proves that Se-doped Co3O4 is a true reactive center. It's worth noting that this selective Se doping strategy is versatile to improve the HER activity of transition metal oxides and further use for catalyzing water splitting process.

Magnetic core-shell MnFe2O4@TiO2 nanoparticles decorated on reduced graphene oxide as a novel adsorbent for the removal of ciprofloxacin and Cu(II) from water

Abstract: An efficient nanocomposite adsorbent of magnetic core-shell MnFe2O4@TiO2 nanoparticles loaded on reduced graphene oxide (MnFe2O4@TiO2-rGO) was successfully synthesized via a hydrothermal followed by sol-gel route. By using the ciprofloxacin (CIP) and Cu2+ as target pollutants, the adsorption properties of MnFe2O4@TiO2-rGO were systematically learned as well as the factors dependance on the adsorption properties, such as temperature, adsorption time, initial pollutant concentration and pH. The adsorption thermodynamics and kinetics for CIP and Cu2+ were also explored. According to the experimental results, the maximum adsorption capacities for CIP and Cu2+ are 122.87 and 225.99 mg/g, respectively. Their adsorption behaviors conform to the Langmuir isotherm and follow a pseudo-second-order kinetic model at all temperature. It is proposed that adsorption is spontaneous and endothermic chemisorption. Furthermore, the MnFe2O4@TiO2-rGO adsorbent can be easily recycled from polluted solution by external magnetic field. After the adsorbent recycled 6 times, the adsorption capacities for CIP and Cu2+ could still reach up to 76.56 and 118.45 mg/g, respectively. Based on the excellent adsorption performance, magnetic separation and recycling performance, therefore, it is highly believed that our MnFe2O4@TiO2-rGO adsorbent has huge potential applications in the field of water purification.

Tunable electronic and magnetic properties of MoSi2N4 monolayer via vacancy defects, atomic adsorption and atomic doping

Abstract: The two dimensional MoSi2N4 (MSN) monolayer exhibiting rich physical and chemical properties was synthesized for the first time last year. We have used the spin-polarized density functional theory to study the effect of different types of point defects on the structural, electronic, and magnetic properties of the MSN monolayer. Adsorbed, substitutionally doped (at different lattice sites), and some kind of vacancies have been considered as point defects. The computational results show all defects studied decrease the MSN monolayer band gap. We found out the H-, O-, and P-doped MSN are n-type conductors. The arsenic-doped MSN, and MSN with vacancy defects have a magnetic moment. The MSN with a Si vacancy defect is a half-metallic which is favorable for spintronic applications, while the MSN with a single N vacancy or double vacancy (N + S) defects are metallic, i.e., beneficial as spin filters and chemical sensors.

Adsorption of SF6 decomposition gases (H2S, SO2, SOF2 and SO2F2) on Sc-doped MoS2 surface: A DFT study

Abstract: By detecting the decomposition gases of sulfur hexafluoride (SF6), the type of internal fault of gas insulated switchgear (GIS) can be determined In this paper, the scandium atom doped molybdenum sulfide material (Sc-MoS2) was proposed, and the adsorption behaviors of four typical SF6 decomposing gases (H2S, SO2, SOF2, SO2F2) on the surfaces of intrinsic MoS2 and Sc-MoS2 are studied based on density functional theory (DFT) method The adsorption models were established to calculate the electronic properties and adsorption parameters of the adsorption systems The results show that Sc-MoS2 has excellent adsorption properties for SO2, SOF2 and SO2F2, but weak adsorption for H2S Moreover, the adsorption effect for target gases was obviously enhanced by the introduction of Sc atom as the active center of the system The findings are beneficial to refine the gas sensing mechanism of MoS2 materials and lay a foundation for SF6 decomposition gases detection based on MoS2 sensors

Hydrogel derived FeCo/FeCoP embedded in N, P-codoped 3D porous carbon framework as a highly efficient electrocatalyst for oxygen reduction reaction

Abstract: Numerous studies have been focused on renewable energy conversion devices (e.g. fuel cell and Zn-air battery) to mitigate the climate changing and serious environmental degradation. Herein, hydrogel derived FeCo/FeCoP embedded in N, P-doped three-dimensional porous carbon framework (FeCo/FeCoP@NP-CF) was prepared by the high-temperature pyrolysis and subsequent acid-etching. Polyacrylamide (PAM) would absorb water here to form hydrogel and act as the C and N sources, which is conducive to capture and in-situ reduce metal ions. The hybrid porous carbon framework had interconnection, highly open structures and molecular accessible hierarchical surfaces. The resultant FeCo/FeCoP@NP-CF displayed remarkable oxygen reduction reaction (ORR) characteristics with a more positive half-wave potential (E1/2) of 0.85 V in 0.1 M KOH electrolyte, surpassing commercial Pt/C (E1/2 = 0.84 V). This work offers some valuable guidelines for synthesis of non-noble metal catalysts in energy technologies.

Fabrication of BiOBr/MoS2/graphene oxide composites for efficient adsorption and photocatalytic removal of tetracycline antibiotics

Abstract: Bismuth oxybromide/molybdenum disulfide/graphene oxide (BiOBr/MoS2/GO) heterojunction composites were fabricated to modulate the adsorption ability and photocatalytic degradation performance toward oxytetracycline (OTC). The flowerlike BiOBr/MoS2/GO composites demonstrated excellent photocatalytic activies for the OTC degradation. Specifically, OTC, tetracycline, chlorotetracycline, and doxycycline were simultaneously removed with degradation rates higher than 98% under visible light irradiation within 40 min. Radical trapping experiments indicated that photogenerated holes (h+), hydroxyl radicals ( OH), and superoxide radicals ( O2−) played crucial roles in photocatalytic OTC degradation. Further, Possible transformation pathway and photocatalytic mechanism were proposed by investigating the intermediates in OTC degradation process.

Experimental and computational investigation on interaction mechanism of Rhodamine B adsorption and photodegradation by zeolite imidazole frameworks-8

Abstract: The adsorption of Rhodamine B (Rh.B) was achieved by Zeolite imidazolate framework-8 (ZIF-8) in the dark condition, and the adsorption rate was noticeably increased under visible and UV light irradiations. According to fluorescence spectroscopic studies, ZIF-8 under UV light generated hydroxyl radicals for the effective degradation of Rh.B dyes. These featured mechanisms were systematically elucidated by investigating the zeta potentials of ZIF-8/Rh.B; blue-shifted π –π* transition of aromatic system; chemical shift of 13C NMR spectra; FTIR spectra; and high surface area and abundant mesopores of ZIF-8. Furthermore, the interaction mechanism between Rh.B with ZIF-8 was studied using a density functional theory (DFT) coupled with a spectroscopic technique. Herein, nine ZIF-8 clusters and Rh.B molecules were optimized in aqueous solution using the polarizable continuum model to address the solvation effect. The DFT calculations suggested that π-π stacking interactions between the xanthene ring of Rh.B and the imidazole rings of ZIF-8 and electrostatic interactions between electron-deficient Zn centers and Rh.B predominantly contributed to the adsorption of Rh.B on the ZIF-8. The experimental and computations studies provide a new insight for the sophisticated design of ZIF-8 nanostructures for removing organic pollutants efficiently through the combined adsorption and degradation under solar light irradiation.

Ultrathin mesoporous g-C3N4/NH2-MIL-101(Fe) octahedron heterojunctions as efficient photo-Fenton-like system for enhanced photo-thermal effect and promoted visible-light-driven photocatalytic performance

Abstract: Ultrathin mesoporous g-C3N4/NH2-MIL-101(Fe) octahedron heterojunctions photocatalysts are successfully constructed through the solvothermal method of loading the ultrathin mesoporous g-C3N4 (U-g-C3N4) onto NH2-Iron metal-organic framework (Fe-MOF). The homogeneous growth of U-g-C3N4 on NH2-MIL-101(Fe) is not only distinctly conducive to the illumination to MOF substrate but also the diffusion of reactants and products. Due to the presence of iron trivalent in Fe-MOF, the Fenton-like system is formed, which can further promote the photocatalytic efficiency. The optimum heterojunction photocatalyst, M101-U6 (6% mass ratio of ultrathin g-C3N4), reveals a highest photocatalytic efficiency to degrade 2,6-dichlorophen and 2,4,5-trichlorophenol, up to 98.7 and 97.3% respectively within 3 h. Meanwhile, the yield of hydrogen peroxide for M101-U6 is raised to 69 μM within 3 h, about 2.2 times superior to the single ultrathin g-C3N4, significantly promoting the formation of hydroxyl radicals. In addition, the photo-thermal effect of M101-U6 is enhanced for this heterojunction photocatalyst and Fenton-like coupling system, which could further improve the photocatalytic degradation performance. This two-in-one strategy of combining photocatalysis with Fenton-like has broad prospects on establishing novel photocatalysts for eliminating high-toxic organic pollutants and generating O2 concurrently in aquatic environment.

Nickel metal–organic framework (Ni-MOF) derived NiO/C@CNF composite for the application of high performance self-standing supercapacitor electrode

Abstract: Compared to conventional electrode, a self-standing structure electrode is an effective way to achieve high performance of supercapacitor by maximizing the use of active material. We present a new combination of nickel oxide–carbon composites fabricated by directly carbonizing a nickel metal–organic framework (Ni-MOF)@carbon nanofiber (CNF) for a self-standing electrode of the supercapacitor application. The new scheme utilizes the CNF film as a substrate with high electron transferring capability and as a backbone of a self-standing electrode as well. It is observed that the MOF-derived NiOs with a diameter of ~ 8 nm are uniformly distributed in the carbon matrix and result in the improvement of the electrical conductivity. The self-standing electrode, NiO/C@CNF composite, provides a high rate capability with high specific capacitances of 742.2 and 671.1F g−1 (at 1 and 10 A g−1), respectively. An asymmetric supercapacitor (ASC) constructed from the NiO/C@CNF and the activated carbon exhibits an excellent specific energy density of 58.43 Wh kg−1 at a power density of 1,947 W kg−1. It is also confirmed that the ASC shows a good cycle stability from the long-term cycling test. It is demonstrated that the proposed nickel oxide–carbon composite has a potential as promising self-standing electrode materials for supercapacitors.

DFT exploration of sensor performances of two-dimensional WO3 to ten small gases in terms of work function and band gap changes and I-V responses

Abstract: A combination of density functional theory (DFT) and nonequilibrium Green function (NEGF) based simulation was employed to investigate the prospects of two-dimensional (2D) WO3 materials for gas sensing applications. The target gas molecules considered are O2, N2, NH3, NO, CO, CO2, CH4, C2H6, HCHO, and H2S. Our computed binding energies suggested that the interactions between the gas molecules and 2D WO3 nano-layers cleaved from (0 0 1) plane of WO3 bulk crystal are stronger than those with some other 2D materials like graphene and borophene. The electronic properties of adsorption systems such as band gaps, work functions and partial density of states were calculated and compared to the bare substrates. The results demonstrate high sensitivity and selectivity of the 2D WO3 nano-layers towards NH3, NO, HCHO, O2 and H2S. The computation of transport properties such as transmission functions and current-voltage (I-V) characteristics indicated that the presence and absence of gas molecules on the 2D WO3 nano-layers can well realize the electronic device characteristics (ON and OFF) of gas sensors. Theoretical recovery times were also calculated to estimate the reusability of the 2D WO3 nano-layers based gas sensors. Our results suggest that the 2D WO3 nano-layers are promising candidates for sensing applications to NH3, NO, HCHO, O2 and H2S, better than graphene and borophene.

Ti3C2 MXene-bridged Ag/Ag3PO4 hybrids toward enhanced visible-light-driven photocatalytic activity

Abstract: As a novel transition metal carbides and/or carbonitrides, MXene possess two-dimensional characteristic, abundant surface hydrophilic functional groups, and excellent electrical conductivity that bestow a possibility to building MXene-based photocatalysts. Inspired by this, an emerging Ti3C2 MXene cocatalyst bridged Ag/Ag3PO4 to induce a highly visible-light-driven photocatalytic activity, synthesized by electrostatic self-assembly method and the partial reduction of Ag+ ions to Ag0 in MXene solution is reported. The resultant hybrids reveal a well-defined hybrid structures with Ag/Ag3PO4 anchoring on the layer structured Ti3C2 nanosheets. Benefiting from the unique structural features, the Ag/Ag3PO4/Ti3C2 hybrids present Ti3C2 content-dependent photocatalytic activity toward the methyl orange (MO) degradation and Cr(VI) reduction under visible-light irradiation. Remarkably, the Ag/Ag3PO4/Ti3C2 hybrid with 3 wt% Ti3C2 content achieves the greatest MO degradation efficiency and Cr(VI) reduction efficiency after irradiation for 1 h, which are increased to 1.72 and 1.46 times higher than that obtained on pristine Ag3PO4 nanoparticles, respectively. Such impressive photocatalytic activity is related to the synergeric effects derived from Ag, Ag3PO4, and Ti3C2, which greatly enhance visible light absorption, promote separation and transfer of photo-generated electron-hole pairs. This work highlights that the MXene-based photocatalysts would be desirable candidates for environmental purification of organic pollutants and heavy metal ions.

Ti3C2Tx MXene playing as a strong methylene blue adsorbent in wastewater

Abstract: Layer-structured MXenes recently attract a great deal of interest due to their intriguing properties. Despite the broad and intensive research, some of their application areas have been scarcely highlighted. In this work, it was demonstrated that the mostly F-terminated Ti3C2Tx MXene could play as a strong adsorbent of methylene blue (MB) in wastewater. For this, the MXene was synthesized by Al-selective etching of Ti3AlC2 MAX phase using HF. At a standard condition, the MXene turned out to be terminated mostly with F functional groups. Remarkably, the mostly F-terminated MXene adsorbed approximately 92% of MB in 20 μM of MB aqueous solution within 5 min. It was found that the surface termination groups could be controlled simply by adjusting cleaning cycles, and the MB removal efficiency had a strong dependence on the pH of MXene suspension. Furthermore, the MXene exhibited relatively good recyclability, enabling its repeated use. The adsorption capability of the MXene was revealed to become weaker for the other organic dyes. The results of this work may give an insight into practical application of MXene for remediation of polluted water.