X-ray Photoelectric Spectroscopy Research Articles

Synthesis of high purity Ti2AlC MAX phase by combustion method through thermal explosion mode: Optimization of process parameters & evaluation of microstructure

Obtaining high-purity MAX-phase powders is a challenging issue. Therefore, in this article, the effects of two key parameters, including mechanical activation time (1, 2, and 3 h), and preheating temperature (800 and 1000 °C) were investigated on the formation mechanism of Ti2AlC MAX phase using mechanically activated (assisted) self-propagating high-temperature synthesis (MA-SHS) combustion method through thermal explosion mode. For this aim, a powder mixture of titanium, aluminum, and carbon with a stoichiometry ratio of (2:1:1) was used. Differential thermal analysis (DTA) was carried out to evaluate the effect of mechanical activation and preheating temperature of the formation temperature of the target MAX phase. Subsequently, the microstructural, phase analysis, chemical composition, and determination of surface chemical states studies were carried out through scanning electron microscopy (SEM), X-ray energy distribution spectroscopy (EDS) transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and X-ray photoelectric spectroscopy (XPS), respectively. DTA results illustrated that applying mechanical activation alters the formation temperature, which leads to an increase in the purity of the MAX phase. The quantitative measurements were carried out using the Rietveld method to determine the purity of the achieved MAX phase. The results indicated that samples subjected to 2 h of mechanical activation at a preheat temperature of 1000 °C exhibited to contain 96.1 % of Ti2AlC MAX phase, which is the highest value among other specimens and the lowest amount of secondary and oxide phases (3.9 % of TiC) during the combustion synthesis process compared to other samples.

Photochemical modification of a diamond surface using a pulsed UV laser as the energy source

The use of an excimer benchtop pulsed UV laser as the energy source for the photochemical modification of the surface of diamond films is reported. Boron-doped nanocrystalline diamond (NCD) films were deposited on Si wafers via plasma-enhanced chemical vapour deposition (PECVD). The as-deposited films were characterised by scanning electron microscopy (SEM), Raman spectroscopy, and X-ray diffraction (XRD). Following characterisation, the surfaces of the films were subjected to a photochemical reaction with 2,2,2-trifluoroethyl undec-10-enoate using two different sources of radiation: a benchtop UV lamp (254 nm) and a KrF excimer pulsed UV laser (248 nm). The photochemically treated films were characterised by contact angle measurements and X-ray photoelectric spectroscopy (XPS) using non-treated films as a control. The use of a pulsed UV laser source was shown to reduce the photochemical reaction time from several hours to a few minutes.

Preparation of Nb5+ Doped Na3V2(PO4)3 Cathode Material for Sodium Ion Batteries.

Sodium-ion batteries (SIBs) have emerged as a promising alternative to lithium-ion batteries (LIBs) due to the abundance and low cost of sodium resources. Cathode material plays a crucial role in the performance of sodium ion batteries determining the capacity, cycling stability, and rate capability. Na3V2(PO4)3 (NVP) is a promising cathode material due to its stable three-dimensional NASICON structure, but its discharge capacity is low and its decay is serious with the increase of cycle period. We focused on modifying NVP cathode material by coating carbon and doping Nb5+ ions for synergistic electrochemical properties of carbon-coated NVP@C as a cathode material. X-ray diffraction analysis was performed to confirm the phase purity and crystal structure of the Nb5+ doped NVP material, which exhibited characteristic diffraction peaks that matched well with the NASICON structure. Nb5+-doped NVP@C@Nbx materials were prepared using the sol-gel method and characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Raman and Brunauer -Emmett-Teller (BET) analysis. First-principles calculations were performed based on density functional theory. VASP and PAW methods were chosen for these calculations. GGA in the PBE framework served as the exchange-correlation functional. The results showed the NVP unit cell consisted of six NVP structural motifs, each containing octahedral VO6 and tetrahedral PO4 groups to form a polyanionomer [V2(PO4)3] along with the c-axis direction by PO4 groups, which had Na1(6b) and Na2(18e) sites. And PDOS revealed that after Nb doping, the d orbitals of the Nb atoms also contributed electrons that were concentrated near the Fermi surface. Additionally, the decrease in the effective mass after Nb doping indicated that the electrons could move more freely through the material, implying an enhancement of the electron mobility. The electrochemical properties of the Nb5+ doped NVP@C@Nb cathode material were evaluated through cyclic voltammetry (CV), galvanostatic charge-discharge tests, electrochemical impedance spectroscopy (EIS), and X-ray photoelectric spectroscopy (XPS). The results showed that NVP@C@Nb0.15 achieved an initial discharge capacity as high as 114.27 mAhg-1, with a discharge capacity of 106.38 mAhg-1 maintained after 500 cycles at 0.5C, and the retention rate of the NVP@C@Nb0.15 composite reached an impressive 90.22%. NVP@C@Nb0.15 exhibited low resistance and high capacity, enabling it to create more vacancies and modulate crystal structure, ultimately enhancing the electrochemical properties of NVP. The outstanding performance can be attributed to the Nb5+-doped carbon layer, which not only improves electronic conductivity but also shortens the diffusion length of Na+ ions and electrons, as well as reduces volume changes in electrode materials. These preliminary results suggested that the as-obtained NVP@C@Nb0.15 composite was a promising novel cathode electrode material for efficient sodium energy storage.

Ornated hydrangea-like M-MO/graphitic porous carbon derived via direct carbonization of MOFs for electrooxidation of methanol in alkaline DMFC

Due to their low operating temperature, ease of storage, transportation, and low greenhouse gas emissions, direct methanol fuel cells (DMFC) are considered the best choice of fuel cells for energy conversion. Although its theoretical thermodynamic energy conversion efficiency is ~97 %, its achievable energy conversion efficiency is still in the range of 30–40 %. To improve the reaction kinetics, it is important to look for an electrocatalyst with low cost and high efficiency. In the present study, direct carbonization of [Ni, Cu, and (Ni/Cu)] metal-organic framework (MOF) was carried out under a nitrogen gas flow at 800 °C for 2.5 h, where the MOF precursor was completely converted into graphitic porous carbon well ornamented with Metal/Metal oxides (M/MO). The as-prepared nanomaterials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectric spectroscopy (XPS), Fourier transform infrared (FTIR), and the Brunauer–Emmett–Teller technique (BET). The prepared materials were used as electrocatalysts in a methanol oxidation reaction solution in an alkaline solution. The cyclic voltammetry (CV) measurements for Ni-MOF, Cu-MOF, (Ni/Cu) MOF, Ni-MOF800, Cu-MOF800, and (Ni/Cu)MOF800 showed excellent current densities of 17, 1.05, 44.25, 30, 11.56, and 53 mA∙cm−2, respectively at 0.6 V with a scan rate of 50 mV∙s−1. Whereas, the retention percent value is (96.2 %) for Ni-MOF, (93.1 %) for (Ni/Cu) MOF800, (96.7 %) for (Ni/Cu) MOF, (87.5 %) for Ni-MOF800, (97 %) for Cu-MOF, and (50.2 %) for Cu-MOF800 after an hour. Since M/MO/C800 demonstrated remarkable catalytic activity in relation to methanol oxidation and an abundance of cheap value, it is regarded as a promising candidate for future electrooxidation catalysis of MeOH in direct methanol fuel cells (DMFCs).

Fabrication of iron doped titanium dioxide photocatalytic nanocomposite supported by water-quenched blast furnace slag and photocatalytic degradation of wastewater

Metallurgical solid waste blast furnace water quenched slag (WBFS) was employed as carrier materials to prepare Fe–TiO2/WBFS composite photocatalyst using a sol-gel method for improving both the photocatalytic activity and the high-value utilization of metallurgical solid waste. The Fe3+ doping technology was adopted to increase the utilization of solar energy. The influencing factors and photocatalytic activity were systematically evaluated by thermogravimetry/differential thermal analyser (TG-DSC), X-Ray Diffraction (XRD), Brunauer-Emmett-Teller (BET) method, scanning electron microscopy-energy spectrometer (SEM-EDS), X-ray photoelectric spectroscopy (XPS), UV–Vis absorption spectrum and photoluminescence spectra technology through the degradation rate of methylene blue (MB) solution. The results showed that the Fe3+ ions were successfully incorporated into the TiO2 lattice, which had no effect on the crystalline phase of TiO2 and expanded the spectral response range of TiO2 from the ultraviolet region to the visible light region. When the calcination temperature was at 450 °C and the number of Fe–TiO2 sol loading cycles was two times, the photocatalytic activity of Fe–TiO2/WBFS presented the strongest, and the degradation ratio of MB reach the maximum value of 98.9 %. A uniform and dense anatase TiO2 thin film was wrapped on the surface of WBFS. The photocatalytic activity first improved and then weakened with an increase of calcination temperature, Fe3+ doping amounts and the loading cycles of sol. The TiO2 film changed from thin to thick and uneven to uniform, until cracking and spalling phenomenon finally occurred with an increase of Fe–TiO2 sol loading cycle from 1 to 3 times. When the Fe–TiO2/WBFS was reused for four times, the degradation rate of MB could still show 67.4 %, being far higher than that of TiO2/WBFS of 25.4 %.

Structural, Magnetic, and Mössbauer Investigation of Mg-Ni-Co ferrites doped by Sm3+ sions

Samarium-doped magnesium-nickel-cobalt nanoferrites (Mg1/3 Ni1/3Co1/3)Fe2−xSmxO4, with x = 0.00, 0.01, 0.02, 0.04, and 0.08, were synthesized by the coprecipitation method. X-ray diffractometer (XRD), transmission electron microscopy (TEM), energy dispersive x-ray (EDX), x-ray photoelectric spectroscopy (XPS), Fourier Transform Infra-Red (FTIR), Raman spectroscopy, Mössbauer spectroscopy, and magnetic measurement techniques were used, to study the structure, microstructure, and magnetic properties of the samples. The formation of the cubic spinel structure was confirmed by Rietveld analysis of the XRD data and by the appearance of the two absorption bands close to 400 cm−1 and 600 cm−1 from the FTIR spectrum. Raman spectroscopy verified the formation of the spinel phase in the samples. The elemental composition, valency, and cationic distribution were examined using x-ray photoelectric spectroscopy (XPS) measurements. Experimental findings revealed that doping with Sm3+ ions had a significant effect on the magnetic properties of nanoparticles. The saturation magnetization (M s ) and coercivity field (H c ) values fluctuate depending on the crystallite size (DXRD) of the samples from XRD analysis as the Sm3+ content increases. The magnetization dependence on the applied field was investigated at different ranges of applied fields based on the output of the statistical parameters for the curve fitted using four different forms of the law of approach to saturation. The statistical parameters and physically significant fitted parameters give information on the dependence of magnetization over various applied field regions. A thorough investigation of the output parameters from fitting into various equations reveals that the composition of Mg-Ni-Co ferrites exhibits a dependence of magnetization on the applied field. Room-temperature Mössbauer spectra displayed a mix of the magnetic sextet and central quadrupole doublet, with improvement in the magnetic sextet in the Sm-doped samples. Moreover, Mössbauer spectra at 77 K showed the demise of the quadrupole doublet in all samples and showed two sextets (tetrahedral and octahedral sites). Sm-doping reduced the values of the hyperfine magnetic field of both sextets. All Fe ions can be found in the Fe3+ state, according to the isomer shift values and there is a migration of Fe3+ ions from octahedral to tetrahedral sites upon Sm doping, which was confirmed by XPS measurements.

Angle resolved x-ray photoelectron spectroscopy assessment of the structure and composition of nanofilms—including uncertainties—through the multilayer model

The multilayer model (MLM) for assessing the structural and composition parameters of multilayered nanofilms from angle-resolved x-ray photoelectric spectroscopy is described in detail. It is compared with regularized back-transform (RBT) approaches such as the maximum entropy method (MEM) with Tikhonov-type regularizations. The advantages of MLM over MEM, such as the possibility of assessing confidence ranges, modeling structures beyond conformal multilayered nanofilms, and modeling abrupt interfaces, are discussed and exemplified. In contrast with MLM, the RBT methods have shortcomings such as the violation of the conservation of information and the inability to adequately address the dependence of the effective attenuation length on the material. Examples of the application of MLM to conformal films and systems with protrusions are shown. The covariance matrix method (CMM) is described and applied to assess uncertainties in structural parameters and composition under the MLM. The CMM constitutes the canonical method for assessing confidence ranges and adequately accounts for the covariance among structural (e.g., layer thicknesses) and composition parameters.

Self-Enhanced Antibacterial and Antifouling Behavior of Three-Dimensional Porous Cu2O Nanoparticles Functionalized by an Organic-Inorganic Hybrid Matrix.

Cu2O is currently an important protective material for domestic engineering and equipment used to exploit marine resources. Cu+ is considered to have more effective antibacterial and antifouling activities than Cu2+. However, disproportionation of Cu+ in the natural environment leads to its reduced bioavailability and weakened reactivity. Novel and functionalized Cu2O composites could enable efficient and environmentally friendly applications of Cu+. To this end, a series of three-dimensional porous Cu2O nanoparticles (3DNP-Cu2O) functionalized by organic (redox gel, R-Gel)-inorganic (reduced graphene oxide, rGO) hybrids─3DNP-Cu2O/rGOx@R-Gel─at room temperature by immobilization-reduction method was prepared and applied for protection against marine biofouling. 3DNP-Cu2O/rGO1.76@R-Gel includes rGO and R-Gel shape 3D porous Cu2O nanoparticles with diameters ∼177 nm and strong dispersion and antioxidant stability. Compared with commercial Cu2O (Cu2O-0), 3DNP-Cu2O/rGO1.76@R-Gel exhibited an ∼50% higher bactericidal rate, ∼96.22% higher water content, and ∼75% lower adhesion of mussels and barnacles. Moreover, 3DNP-Cu2O/rGOx@R-Gel maintains the same excellent, stable, and long-lasting bactericidal performance as Cu2O-0@R-Gel while reducing the average copper ion release concentration by ∼56 to 76%. This was also confirmed by X-ray diffraction, X-ray photoelectric spectroscopy (XPS), atomic absorption spectroscopy, and antifouling tests. In addition, XPS tests of rGO-Cu2+ and R-Gel-Cu2+, photocurrent tests of 3DNP-Cu2O/rGO1.76@R-Gel, and energy-dispersive spectrometry pictures of bacteria confirm that R-Gel and rGO act as electron donors and transfer substrates driving the reduction of Cu2+ (Cu2+ → Cu+) and the diffusion of Cu+. Thus, a self-growing antibacterial and antifouling system of 3DNP-Cu2O/rGO1.76@R-Gel was achieved. The mechanism of accelerated bacterial inactivation and resistance to mussel and barnacle adhesion by 3DNP-Cu2O/rGO1.76@R-Gel was interpreted. It is shown that rGO and R-Gel are important players in the antibacterial and antifouling system of 3DNP-Cu2O/rGO1.76@R-Gel.

Biobased films from amphiphilic lignin-graft-PLGA copolymer

Amphiphilic copolymers were synthesized by grafting poly(lactic-co-glycolic) acid with two lignin types: alkaline lignin and lignosulfonate. An interphase formation technique was used to produce films based on the copolymers. Films presented one side as being more hydrophobic (O-side) and smoother, and the second side more polar and with an uneven surface (W-side). Contact angle of water on the W-side was lower than the O-side corresponding to a higher lignin content and influenced by the lignin type (alkaline < lignosulfonate) and lignin: PLGA ratio. X-ray photoelectric spectroscopy analysis showed higher percentages of sulfur on the W-side, which supports a preferential partitioning of the lignin. Tensile testing demonstrated the significant impact of lignin type on the mechanical properties of the films. Alkaline films showed a higher maximum strength, a higher stiffness, and a higher tensile strength at the elastic limit compared to lignosulfonate films. However, for lignosulfonate films, ductility at break point was 4-fold higher than that of alkaline films.

Oxidative degradation of methylene blue by Ag2O@g-C3N4 photocatalysts under visible light

Ag2O@g-C3N4 catalysts with p-n heterostructure were prepared by the hydrothermal method. The catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectric spectroscopy, and UV/visible light spectroscopy. Ag2O nanoparticles were uniformly distributed on the surface of g-C3N4 and a heterostructure was formed. The sample Ag2O@g-C3N4 degraded methylene blue (MB) dye by visible light, which showed that it had good photocatalytic activity. Under the same catalytic conditions, the catalytic efficiency of Ag2O@g-C3N4 is two times higher than that of pure g-C3N4. The improvement in catalytic efficiency is due to the formation of heterostructure between Ag2O and g-C3N4, which greatly reduces the recombination rate of electrons and holes. At the same time, Ag is a good electron trapping agent, which increases the mobility of electrons and holes and inhibits the photoetching of Ag2O. Finally, the photocatalytic principle of Ag2O@ g-C3N4 was analyzed for its excellent photocatalytic performance.

A stabilized γ-CsPbI3 by poly(allylamine hydrochloride) for wide-band gap perovskites solar cells with enhanced performance

All inorganic perovskite CsPbI3 has been considered as a promising candidate for wide-bandgap solar cells due to its prominent thermal stability and suitable bandgap. However, the cesium cation in the crystal lattice of CsPbI3 seems to be too small to form a stable perovskite crystal structure, resulting in the phase instability of CsPbI3. In this study, we developed a new strategy by adding a small amount of poly(allylamine hydrochloride) (PAACl) additives into the CsPbI3 precursor solution to prepare the stabilized and distorted black phase-based CsPbI3 (γ-CsPbI3) thin films. The passivation effect through chemical bonding between PAACl and CsPbI3 was investigated systematically by Fourier transformed infrared (FTIR) and X-ray photoelectric spectroscopy (XPS) techniques. The PAACl existed in the perovskite thin films enhance the crystal quality of γ-CsPbI3 with high crystallinity and long carrier life time, and further achieved a power conversion efficiency of 17.8%. Moreover, the present CsPbI3-based perovskite solar cells showed improved stability, maintained 90% of its initial efficiency after exceeding 30 days under 30% humidity environment without encapsulation.

Solvothermal synthesis of Al2Se3/rGO nanocomposites with excellent electrochemical performance in supercapacitor

As a supercapacitor material, transition metal selenide (TMS) can be synthesised in a cost-effective and simple manner. However, it suffers from low-rate capacities and poor cyclic stability due to their easy aggregation and structural instability during charge and discharge cycles. Herein, we report the synthesis of aluminum selenide (Al2Se3) nanorods over reduced graphene oxide (rGO) nanosheets as a novel material using the solvothermal method. The successful formation of Al2Se3/rGO nanocomposite was confirmed via XRD (X-ray diffraction), SEM (scanning electron microscopy), and XPS (X-ray photoelectric spectroscopy) and was also investigated for its optical characteristics and electrochemical performance. The optimised Al2Se3/rGO sample with 5 wt% and 10 wt% rGO exhibited high specific capacitances of 701.83 Fg−1 and 1138.1 Fg−1, respectively. Moreover, Al2Se3/10%rGO nanocomposite as a positive electrode achieves energy densities of 39.57 Wh/kg and power densities of 0.006 kW/kg at current densities 2.5 A/g along with stability up to 2000 cycles, suggesting it to be a significant technological candidate in the future. This work highlights an effective and feasible approach to engineer or construct TMS/rGO nanocomposites for charge storage applications.

Self-Supporting Electrode Fabricated by Flowing Synthesis for Efficient Hydrogen Evolution Reaction

In order to achieve a balance between a good hydrogen evolution reaction (HER) performance and a low amount of catalyst loading, Pt@Ti membrane self-supporting electrodes have been fabricated by flowing synthesis. The characterizations by X-ray diffraction (XRD), X-ray photoelectric spectroscopy (XPS), and transmission electron microscopy (TEM) demonstrate the successful loading of Pt nanoparticles into the pores of a porous Ti membrane substrate. The scanning electron microscope (SEM) results demonstrate that the sizes of the Pt nanoparticles immobilized in Ti membrane pores are mostly in the range of 10–40 nm, and the average size was about 26 nm. The ICP test proves that the amount of Pt loading was only 0.760 mg cm–2. A minimum overpotential of 35 mV and a minimum Tafel slope of 30 mV dec–1 can be achieved for a Pt@Ti membrane self-supporting electrode at a current density of 10 mA cm–2 with 0.5 M H2SO4 as the electrolyte. No decay of current density is observed after a 10 h continuous electrolytic test. Besides, good HER performances can also be obtained under alkaline conditions and neutral conditions for Pt@Ti membrane self-supporting electrodes fabricated by flowing synthesis.

Lignin detaching from the oxidative delignified softwood during enzymatic hydrolysis and its effect on carbohydrate saccharification

Most studies about the influence of lignin on enzymatic digestibility of lignocellulose have focused on the content and properties, but less on the detaching behavior of lignin. The samples were prepared from Pinus massoniana wood chips by kraft cooking followed by delignification using oxygen/alkali (KP-O) and chlorine dioxide (KP-D), respectively. Two oxidative delignified samples with a similar lignin content were subject to enzymatic hydrolysis at both pH of 5.0 and 5.5 to investigate the effects of lignin detached rate (LDR) on substrate enzymatic digestibility (SED). The LDRs and the SEDs from both samples increased with the enzymatic hydrolysis time, and the situations of KP-D were much higher than those of KP-O under the same enzymatic hydrolysis time. The results of enzymatic hydrolysis at an elevated pH of 5.5 and the changes in concentration of free cellulase of the two samples indicated that the lignin detaching increased the free cellulase concentration, and thus promoted the enzymatic digestibility. Moreover, lignin distribution analysis by X-ray photoelectric spectroscopy and confocal laser scanning microscopy indicated surface lignin being preferentially detached. This work provided a reference for rationally designing pretreatment strategies, which can improve the efficiency of enzyme hydrolysis of lignocellulosic biomass.

Metagenomic Analysis of Garden Soil-Derived Microbial Consortia and Unveiling Their Metabolic Potential in Mitigating Toxic Hexavalent Chromium.

Soil microbial communities connect to the functional environment and play an important role in the biogeochemical cycle and waste degradation. The current study evaluated the distribution of the core microbial population of garden soil in the Varanasi region of Uttar Pradesh, India and their metabolic potential for mitigating toxic hexavalent chromium from wastewater. Metagenomes contain 0.2 million reads and 56.5% GC content. The metagenomic analysis provided insight into the relative abundance of soil microbial communities and revealed the domination of around 200 bacterial species belonging to different phyla and four archaeal phyla. The top 10 abundant genera in garden soil were Gemmata, Planctomyces, Steroidobacter, Pirellula, Pedomicrobium, Rhodoplanes, Nitrospira Mycobacterium, Pseudonocardia, and Acinetobacter. In this study, Gemmata was dominating bacterial genera. Euryarchaeota, Parvarchaeota, and Crenarchaeota archaeal species were present with low abundance in soil samples. X-ray photoelectric spectroscopy (XPS) analysis indicates the presence of carbon, nitrogen-oxygen, calcium, phosphorous, and silica in the soil. Soil-derived bacterial consortia showed high hexavalent chromium [Cr (VI)] removal efficiency (99.37%). The bacterial consortia isolated from garden soil had an important role in the hexavalent chromium bioremediation, and thus, this study could be beneficial for the design of a heavy-metal treatment system.

MXene quantum dots enhanced 3D-printed electrochemical sensor for the highly sensitive detection of dopamine

Using 3D-printed electrochemical sensor for the detection of biomarker has aroused widely attentions in the field of disease diagnosis. Herein, 3D printing method was employed to print 3D-printed electrode (3DE) using graphene/polylactic acid (PLA) filament. Then, synthesized MXene quantum dots (MQDs) were dropped on the activated 3DE to construct a novel sensor for highly sensitive detection of dopamine (DA). The surface physical and chemical properties of the prepared 3DEs were measured by scanning electron microscope (SEM), X-ray photoelectric spectroscopy (XPS) and contact angle experiments. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods were also performed to research the electrochemical properties of the prepared 3DEs. The constructed sensor can be used to determine DA in the concentration from 0.01 to 20 μM with an ultra-low limit of detection (3 nM). Furthermore, the sensor was further applied to detect DA in practical sample with high selectivity. The enhanced 3D-printed sensor will open the new avenue for using QDs of 2D materials in 3D-printed electrodes.

Ultra-thin CoAl layered double hydroxide nanosheets for the construction of highly sensitive and selective QCM humidity sensor

To achieve real-time monitoring of humidity in various applications, we prepared facile and ultra-thin CoAl layered double hydroxide (CoAl LDH) nanosheets to engineer quartz crystal microbalances (QCM). The characteristics of CoAl LDH were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectric spectroscopy (XPS), Brunauer–Emmett–Telle (BET), atomic force microscopy (AFM) and zeta potential. Due to their large specific surface area and abundant hydroxyl groups, CoAl LDH nanosheets exhibit good humidity sensing performance. In a range of 11.3% and 97.6% relative humidity (RH), the sensor behaved an ultrahigh sensitivity (127.8 Hz/%RH), fast response (9.1 s) and recovery time (3.1 s), low hysteresis (3.1%RH), good linearity (R2 = 0.9993), stability and selectivity. Besides, the sensor can recover the initial response frequency after being wetted by deionized water, revealing superior self-recovery ability under high humidity. Based on in-situ Fourier transform infrared spectroscopy (FT-IR), the adsorption mechanism of CoAl LDH toward water molecules was explored. The QCM sensor can distinguish different respiratory states of people and wetting degree of fingers, as well as monitor the humidity in vegetable packaging, suggesting excellent properties and a promising application in humidity sensing.

Preparation and application of graphene oxide functionalized melamine-formaldehyde aerogel coated solid-phase microextraction tube

因具有良好的萃取性能,有机气凝胶已被应用于样品前处理领域,为了进一步改善其对多环芳烃类污染物的萃取能力,利用氧化石墨烯对三聚氰胺-甲醛气凝胶进行改性,制备了一种氧化石墨烯功能化三聚氰胺-甲醛气凝胶,将其作为萃取涂层涂覆到不锈钢丝表面,通过扫描电镜和X射线光电子能谱对萃取涂层进行表征,结果表明氧化石墨烯并未破坏气凝胶的三维网络多孔结构。将4根气凝胶涂覆的不锈钢丝装进一根长度30 cm、内径0.75 mm的聚醚醚酮管内,制备了一种新型的纤维填充型固相微萃取管。将萃取管与高效液相色谱联用,构建管内固相微萃取-液相色谱在线富集分析系统。以8种多环芳烃(萘(Nap)、苊烯(Acy)、苊(Ace)、芴(Flu)、菲(Phe)、蒽(Ant)、荧蒽(Fla)和芘(Pyr))作为模型分析物,评价了萃取管的萃取性能,考察了氧化石墨烯对气凝胶萃取性能的改善,结果表明萃取效率被提升至最高2.5倍。详细考察了样品体积、样品流速、样品中有机溶剂浓度以及脱附时间对于萃取效率的影响,并建立了管内固相微萃取-液相色谱在线分析方法。该法对8种多环芳烃分析物的检出限为0.001~0.005 μg/L,萘、苊烯、苊、芴的线性范围为0.017~20.0 μg/L,菲、蒽的线性范围为0.010~20.0 μg/L,荧蒽和芘的线性范围为0.003~15.0 μg/L,精密度良好(日内重复性RSD≤4.8%,日间重复性RSD≤8.6%)。研究所发展的分析方法比已报道的某些分析方法具有更好的灵敏度、更宽的线性范围和更短的分析时间,并具有在线富集和在线分析的独特优点。将该分析方法应用于常见饮用水(包括瓶装矿泉水和饮水机的直饮水)中多环芳烃的分析检测,加标回收率试验结果(76.3%~132.8%)表明该分析方法能够高灵敏、快速、准确地检测饮用水中痕量多环芳烃污染物。经过稳定性考察,发现研究所制备的固相微萃取管在实验过程中表现出良好的使用寿命和化学稳定性。

Preparation of novel bifunctionalized magnetic nanoparticles for sequential speciation analysis of inorganic arsenic

An amino- and mercapto-bifunctionalized magnetic nanocomposite (SMNPs-(NH2 + SH)) was synthesized by modification of silica-coated magnetic nanoparticles (SMNPs) via one-pot co-condensation of 3-aminopropyltriethoxysilane (APTES) and 3-mercaptopropyltrimethoxysilane (MPTMS) for the first time. The bifunctional magnetic nanomaterial was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectrometry, X-ray photoelectric spectroscopy, elemental analysis, thermogravimetric analysis and vibrating sample magnetometry, etc. The prepared SMNPs-(NH2 + SH) nanocomposite was employed as magnetic solid-phase extraction (MSPE) sorbent for speciation of inorganic arsenic without any pre-oxidation or pre-reduction process. Different optimal conditions for the MSPE including sample solution pH and volume, adsorbent amount, loading time, eluent composition and volume, and elution time were investigated systematically. As(V) and As(III) were adsorbed simultaneously at pH 4.0, and then desorbed sequentially by 3 % (v/v) HNO3 and 3 % (v/v) HNO3 with 4 % (m/v) mercaptosuccinic acid followed by inductively coupled plasma-mass spectrometry (ICP-MS) analysis with the limits of detection of 15.2 and 24.5 ng/L respectively at an enrichment factor of 10 fold. The reliability of the stepwise speciation strategy based on SMNPs-(NH2 + SH) was validated by analyzing inorganic arsenic species in certified reference material of environmental water as well as mixed standard solutions of As(V) and As(III), and the results were in good accordance with the certified or standard values. The applicability of the SMNPs-(NH2 + SH)-MSPE-ICP-MS method for speciation analysis of inorganic arsenic was evaluated in spiked tap, rain, lake and river water samples at the recoveries of 92 %–102 % and 92 %–100 % with the relative standard deviations of 3.6 %–7.4 % and 2.3 %–8.2 % for As(V) and As(III) respectively. In consideration of the merits of single adsorbent, facile preparation, easy operation and no invasion to labile inorganic arsenic, the bifunctional material based MSPE protocol is attractive for speciation analysis of arsenic in real environmental samples.

Synthesis and characterization of amino functionalized bimetallic metal-organic frameworks as peroxymonosulfate activator for water purification: Performance and mechanistic studies

The importance of new water purification technology for maintaining clean water resources and a high quality of life is self-evident. In this study, amino functionalized bimetallic metal-organic frameworks (NH2-MIL-101(FeCo)) were prepared to activate peroxymonosulfate (PMS) for removal of organic pollutants from water. The structure, morphology, and physicochemical properties of as-prepared NH2-MIL-101(FeCo) were comprehensively evaluated by X-ray diffraction, scanning electron microscopy, N2 adsorption-desorption isotherms, and X-ray photoelectric spectroscopy. Degradation tests were performed to study effects of PMS concentration, catalyst dosage, initial pH, and common substances on the orange G (OG) removal. The acidic and alkaline conditions promoted the formation of mesoporous structures in NH2-MIL-101(FeCo) and enhanced the mass transfer processes to remove OG. 100% of OG was removed through a rate constant of 0.0711 min-1 within 45 min in NH2-MIL-101(FeCo)− 2/PMS/OG system, where 1O2, SO4•−, and ·OH played pivotal contributions in the OG removal. The catalytic activity of NH2-MIL-101(FeCo) originated from unsaturated metal sites of Fe(II) and Co(II). This work demonstrates a feasible strategy towards the synthesis of functional MOFs for removal of organic contaminants.