Surface Area Measurement Techniques Research Articles

Theoretical and experimental approaches to the preparation, characterization and application of a newly synthesized mesoporous Zn-MOF as a selective ionophore for Ni(II) ion in carbon paste electrode matrix

A novel carbon paste electrode (CPE) chemically modified with a newly synthesized Zn-metal organic framework (Zn-MOF) was synthesized for Ni(II) ion determination with impressing enhancement in sensitivity and selectivity over the preceding studies. Due to their electrocatalytic and substantial surface area criteria, MOFs are a reasonably new category of fascinating materials for precise electrochemical detection. Under the sonication condition, a novel Zn-MOF depending on a Schiff base ligand in nano size was synthesized, and it was characterized using different characterization methods such as powdered X-ray diffraction (PXRD), FT-IR, BET surface area, contact angle and scanning electron microscope (SEM) combined with energy dispersive X-ray analyzer (EDX). The BET surface area and contact angle measurement techniques results were 2901.08 m2 g−1 and 143.49°, respectively, for the synthesized MOF. It was concluded that under the ideal experimental circumstances, the produced Zn-MOF can extract and sense nickel ions from aqueous solution selectively. Several crucial factors were optimized to gain the ultimate electrochemical response. Response mechanism was proved by the aid of study of morphological change and functional groups chemical shifts. Ultimately, a calibration with a Nernstian slope of 28.75 mV decade−1 over linear concentration limits from 5.0 × 10−8 to 1.0 × 10−1 mol L−1 (R2 = 0.9990) and detection limit of 5.0 × 10−8 mol L−1 was obtained. The relative standard deviations and recovery ranges of the proposed approach for determining the Ni(II) ion in various water and food tests (n = 5) were 0.94–2.35% and 97.0–104%, respectively.

Highly reusable plant-based biosorbent for the selective methylene blue biosorption from dye mixture in aqueous media

The natural Polygonum cognatum (P. cognatum) was utilized as a selective biosorbent for the biosorption of methylene blue (MB) from dye mixtures (MB/RhB and MB/MO), separately. P. cognatum was characterized by using SEM–EDX, FT-IR, TGA, BET surface area and zeta measurement techniques. The effects of diverse parameters on the biosorption were investigated, and the kinetic and isotherm models were applied to obtain data to exhibit the biosorption mechanism. The characterization results showed that P. cognatum had various functional groups and also roughness, irregularity and cavities on the structure with the BET surface area of 57.65 m2/g. P. cognatum biosorbed the MB selectively with an attractive efficiency from MB/RhB and MB/MO mixtures and the maximum biosorption capacity of P. cognatum was calculated as 426.39 mg g−1 for MB at pH ~ 5. The selective biosorption could be ascribed to the electrostatic and weak interactions between smaller cationic dye (MB) and negatively charged biosorbent surface with a zeta potential value of − 26.30 mV at pH 5. The pseudo-second order kinetic and Langmuir isotherm models have well-defined the biosorption process. Moreover, P. cognatum showed high biosorption (97.54%) and desorption (100%) efficiencies after ten repeated cycles for MB biosorption. P. cognatum with a high biosorption capacity could be a reusable biosorbent for the selective MB biosorption from dye mixtures. Polygonum cognatum (P. cognatum) selectively biosorbed MB over RhB and MO from the dye mixtures with the maximum biosorption capacity of 426.39 mg g−1. The selective biosorption could be attributed to the electrostatic and weak interactions between smaller cationic dye (MB) and negatively charged biosorbent surface. P. cognatum showed highly reusability after ten repeated cycles for MB biosorption.

Effect of nickel on combustion synthesized copper/ fumed‐SiO 2 catalyst for selective reduction of CO 2 to CO

In this study, we explore the effect of nickel incorporation in Cu/fumed‐SiO2 catalyst for CO2 reduction reaction. Two catalysts, Cu and CuNi supported on fumed silica were synthesized using a novel surface restricted combustion synthesis technique, where the combustion reaction takes place on the surface of the inert fumed‐SiO2 support. An active solution consisting of a known amount of metal nitrate precursors and urea (fuel) was impregnated on fumed silica. The catalyst loading was limited to 1 wt% to ensure localized combustions on the surface of fumed‐SiO2 by restricting the combustion energy density. The synthesized catalysts were tested for CO2 hydrogenation reaction using a tubular packed bed reactor between temperature 50°C and 650°C, where Cu/SiO2 showed high CO2 conversion to carbon monoxide, and the addition of Ni further improved the catalytic performance and showed some tendency for methane formation along with CO. Moreover, both the catalysts were highly stable under the reaction conditions and did not show any sign of deactivation for ~42 hours time on stream (TOS). The catalysts were characterized using X‐ray diffractometer (XRD), scanning electron microscope/energy dispersive X‐ray spectrometer (SEM/EDX), transmission electron microscope (TEM), and the Brunauer‐Emmet‐Teller (BET) surface area measurement technique to understand their structural properties and to assess the effect of CO2 conversion reaction. In situ DRIFTS was also used to investigate the reaction pathway followed on the surface of the catalysts.

Optimizing acido-basic profile of support in Ni supported La2O3+Al2O3 catalyst for dry reforming of methane

The increasing alarm of global warming always draws interest in reactions like dry reforming of methane (DRM) where both global warming gases (CO2 and CH4) are converted into value-added chemical building blocks, such as syngas. Nickel catalyst active sites along with support acid-base profiles play a key role in DRM. Herein, xLa2O3+(100-x) Al2O3 (x = 0, 10, 15, 20%) supports are prepared and followed by NiO dispersion over the produced support by impregnation method. It was tested for DRM reaction and characterized with TGA, XRD, TEM, IR, Surface area and porosity measurement, H2-TPR, CO2-TPD and NH3-TPD techniques. Upon increasing the basic lanthana proportion in the acidic alumina support, the crystallinity of alumina and acidity of total support decline. Up to 15% Lanthana addition in support claims a low acid and rich basic surface including super basic sites (related to unidentate carbonates) which governed optimum catalytic performance 64% CH4 conversion, 79% CO2 conversion and H2/CO ~ 1 up to 460-min in time on stream test. 20% lanthanum oxide loading led to inferior performance due to rapid loss of surface area, pore-volume, pore diameter, acidity and medium basic strength sites. Fine-tuning of acid-base lanthana-alumina support with dispersed Ni species are a means for understanding DRM.

AN EGGSHELL HYDROXYAPATITE - GRAPHENE OXIDE NANOCOMPOSITE FOR THE REMOVAL OF HEAVY METALS FROM WASTE WATER

Heavy metal pollution is a serious environmental problem that can be remediated by various adsorbents. So, a new hydroxyapatite / graphene oxide nanocomposite (HAp/GO) material was synthesized from waste eggshell as a green and eco-friendly adsorbent for the effective removal of heavy metals (e.g., Cd, Pb, Cr, Ni, Co) from wastewaters. Nano-structured HAp was synthesized by calcination of the waste eggshell followed by hydrothermal treatment in the presence of phosphate solution. However, GO was synthesized using the Hummar’s method (Guerrero-Contreras and Caballero-Briones, 2015). The HAp/GO nanocomposite was synthesized from the HAp and GO precursors by ultrasonic treatment. The morphology, composition, crystal structure, functionality and stability of the synthesized sorbent were evaluated using Fourier transform infrared spectrophotometry (FTIR), high-resolution transmission electron microscopy (HR-TEM), scanning electron microscope (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), Raman spectrometry and N2-BET (Barrett–Emmett–Teller) surface area measurement techniques. The equilibrium concentrations of heavy metals were measured using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The effect of the initial concentration of heavy metals, the dosage of HAp/GO, temperature effect and the solution pH on the adsorption capacity was investigated. The synthesized HAp/GO was adopted to achieve superior simultaneous removal efficiencies (≥ 90 %) for (Cd, Pb, Cr, Ni, Co) metal ions. .

Direct surface area measurement from digital images via brightness histogram method

A direct, shape- and scale-independent digital image measurement method of the surface area (SA) of individual objects is proposed. The algorithms presented herein utilize the brightness histogram of 8-bit greyscale images, and thus are referred to as a brightness histogram surface area measurement algorithm (BHSAMA). The proposed SA measurement technique allows the uncertainty of the single measurement reading to be evaluated by traditional error propagation. Furthermore, the numerical value of the propagated uncertainty reflects the pixel brightness gradient of the edge pixels. This fact alone presents a significant advantage to the current methods utilizing image segmentation and/or edge detection whose measurement uncertainties cannot be quantitatively analysed. The proposed method does not involve any shape-related approximations. Five examples illustrating the method are discussed. For method verification purposes, a series of digital simulations using a control sample of predetermined size is undertaken. The accuracy of the single measured SA reading is between 0.5% and 1.5%. The uncertainty of the measured SA is evaluated and discussed further as a function of two types of simulated blurred edge region. The two presented BHSAMA techniques can have a wide range of applicability, from nanoparticles to cell biology to aerial imagery.

Green synthesis of graphene oxide (GO)-anchored Pd/Cu bimetallic nanoparticles using Ocimum sanctum as bio-reductant: an efficient heterogeneous catalyst for the Sonogashira cross-coupling reaction.

To explore the synergism between two metal centers we have synthesized graphene oxide (GO) supported Pd/Cu@GO, Pd@GO and Cu@GO nanoparticles through bio-reduction of Pd(NO3)2 and CuSO4·5H2O using Tulsi (Ocimum sanctum) leaf extract as the reducing and stabilizing agent. The graphene oxide (GO) was obtained by oxidation of graphite following a simplified Hummer's method. The as-prepared nanomaterials have been extensively characterized by FTIR, powder X-ray diffraction (PXRD), HRTEM, TEM-EDS, XPS, ICP-AES and BET surface area measurement techniques. The morphological study of Pd/Cu@GO revealed that crystalline bimetallic alloy type particles were dispersed on the GO layer. The activity of Pd@GO, Cu@GO and Pd/Cu@GO as catalysts for the Sonogashira cross-coupling reaction have been investigated and it was found that the Pd/Cu@GO nanostructure showed highly superior catalytic activity over its monometallic counterparts, substantiating the cooperative influence of the two metals. The inter-atom Pd/Cu transmetalation between surfaces was thought to be responsible for its synergistic activity. The catalyst showed higher selectivity towards coupling of aryl iodides with both aliphatic and aryl alkynes resulting in moderate to excellent isolated yield of the desired products (45–99%). The products have been characterized by GC-MS and 1H-NMR spectroscopic techniques and compared with authentic samples. The Pd/Cu@GO catalyst could be easily isolated from the reaction products and reused for up to at least ten successive runs effectively.

TiO2@NbSe2 decorated nanocomposites for efficient visible-light photocatalysis

In this article, 2D NbSe2 nanosheets are combined with TiO2 nanoparticles to prepare visible-light active composite photocatalysts using sol gel reflux synthesis. The concentration of NbSe2 is varied as 0.5, 1, 2 and 3 weight percent with respect to TiO2. The prepared samples are characterized via scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), UV–Vis spectroscopy and Brunauer–Emmett–Teller (BET) surface area measurement techniques to determine morphology, dimensional aspects of nanosheets, phase, optical properties and surface area of the nanocomposites, respectively. From SEM images TiO2 nanoparticles are observed on the surface of NbSe2 sheets in all the samples. AFM gives an estimate of thickness of NbSe2 nanosheets ranging from 25 to 40 nm corresponding to 30–50 layers. XRD confirms the presence of both components in nanocomposites. UV–Vis spectrum of NbSe2 nanosheets reveals its visible-light absorption capability and a narrow band gap. The surface area values as obtained from BET technique vary from 120 m2/g for TiO2 NPs alone to 162 m2/g for 2 wt% NbSe2 in TiO2 nanocomposites. To study the visible-light photocatalytic behavior the composites are employed for the photodegradation of rhodamine B (RhB) dye under visible-light irradiation. The prepared nanocomposites substantiate to be highly effective photocatalysts for degradation of organic dye due to visible-light absorption offered by NbSe2 together with increased surface area. The sample having 2 wt% NbSe2 shows best performance with almost complete (i.e., 98%) RhB degradation in just 60 min of visible-light irradiation. NbSe2 can facilitate the increased induction of electrons into the CB of TiO2 by visible-light absorption and higher surface area in composites also adds to substantially improved photocatalytic activity exhibited by the nanocomposites.

Measuring Surface Area of Skin Lesions with 2D and 3D Algorithms

Purpose The treatment of skin lesions of various kinds is a common task in clinical routine. Apart from wound care, the assessment of treatment efficacy plays an important role. In this paper, we present a new approach to measure the skin lesion surface in two and three dimensions. Methods For the 2D approach, a single photo containing a flexible paper ruler is taken. After semi-automatic segmentation of the lesion, evaluation is based on local scale estimation using the ruler. For the 3D approach, reconstruction is based on Structure from Motion. Roughly outlining the region of interest around the lesion is required for both methods. Results The measurement evaluation was performed on 117 phantom images and five phantom videos for 2D and 3D approach, respectively. We found an absolute error of 0.99±1.18 cm2 and a relative error 9.89± 9.31% for 2D. These errors are <1 cm2 and <5% for five test phantoms in our 3D case. As expected, the error of 2D surface area measurement increased by approximately 10% for wounds on the bent surface compared to wounds on the flat surface. Using our method, the only user interaction is to roughly outline the region of interest around the lesion. Conclusions We developed a new wound segmentation and surface area measurement technique for skin lesions even on a bent surface. The 2D technique provides the user with a fast, user-friendly segmentation and measurement tool with reasonable accuracy for home care assessment of treatment. For 3D only preliminary results could be provided. Measurements were only based on phantoms and have to be repeated with real clinical data.

Synthesis, Characterization and Photocatalytic Efficiency of ZnO/MWCNT Nanocomposites Prepared Under Different Solvent Conditions.

Here we report the application of zinc oxide (ZnO) coated multi-walled carbon nanotube (MWCNT) composites in the photocatalytic decomposition of acetaldehyde (AA). Zinc oxide nanoparticles were successfully coated on the multi-walled carbon nanotube via impregnation process using zinc acetate (Zn(CH₃COO)₂×2H₂O) as precursor and sodium dodecyl sulfate (SDS) treated multiwalled carbon nanotube as raw material under different solvent conditions. The applied solvents during preparation were ethanol (EtOH) and water (H₂O). As-prepared materials were characterized by thermal analysis (TG), X-ray diffraction (XRD), specific surface area measurement (BET) and transmission electron microscopy (TEM) techniques. Photocatalytic efficiencies of as-prepared composites were investigated in a stationary reactor equipped with UV lamp. Decomposition of acetaldehyde was followed by using gas chromatography (GC). Observations revealed that using impregnation method and different solvents the preparation of ZnO/MWCNT nanocomposites can be controlled easily. The highest degradation rate was achieved with the nanocomposite was synthetized using ethanol as solvent. The photocatalytic experiments revealed that the composite has higher photocatalytic activity than that of both the zinc oxide nanoparticles and the mechanical mixture of multi-walled carbon nanotube and zinc oxide.

Structural characterization of chitosan-smectite nanocomposite and its application in the development of a novel potentiometric monohydrogen phosphate-selective sensor

Chitosan-smectite biocomposite was prepared by intercalation of protonated chitosan molecules into the interlayer space of smectite in monolayer arrangement through cation exchange mechanism and the obtained biocomposite was successfully used as an electroactive component in the structure of a PVC membrane potentiometric sensor for the direct and highly selective determination of monohydrogen phosphate ions. The comparative elemental, structural, thermal and morphological analysis of starting-smectite, neat chitosan and chitosan-smectite were investigated by utilizing EDX, XRD, ATR-FTIR, TG/DTG/DTA, SEM and surface area measurement techniques. The optimum membrane composition, detection limit, response time, pH working range and repeatability of the proposed electrode were determined.

Well-connected microsphere-nanoparticulate TiO2 composites as high performance photoanode for dye sensitized solar cell

Anatase TiO2 microspheres with smooth and fibrous morphology (SμS and FμS) resembling laddu and dandelion are synthesized by solvothermal and hydrothermal methods, respectively. A detailed analysis of these two microstructures using XRD, UV–vis spectroscopy, electron microscopy and surface area measurement techniques are presented. Photoanodes fabricated using these microspheres and their composites with nanoparticles (Degussa P25) are tested for photovoltaic (PV) performance using a standard Grätzel-type dye-sensitized solar cell (DSSC) configuration. The DSSC made up of SμS and FμS microspheres exhibit an efficiency (η) of 8.4% and 6.4% respectively, in comparison to η≈7.1% for nanoparticulate P25. Further enhancement in η is realized in the composite photoanode films made of porous SμS/FμS microspheres filled with nanoparticulate P25 TiO2. High power conversion efficiency of 8.9% (for cell area of 0.5cm2 and thickness of ~25µm) was achieved in composite photoanode film consisting of 80wt% SμS and 20wt% P25. Electrochemical impedance spectroscopy studies reveal a low interfacial resistance in composite photoanodes, which is desired for efficient electron generation and transport. Composite microspheres filled with P25 nanoparticles in their voids show enhanced efficiency than the mesoporous TiO2 microspheres. Thus, SμS-nanoparticle composite TiO2 film possesses essential attributes necessary for an efficient photoanode viz. large surface area for dye adsorption, good connectivity between nanocrystallites for the efficient electron transport, and higher scattering properties for better light harvesting efficiency.

Intrinsic gasification rate of oil sands fluid coke with carbon dioxide and steam

Petroleum coke is a byproduct of oil sands upgrading which can be utilized as a low‐cost feedstock for further value‐added operations such as gasification. The design and scale up of gasifiers for oil sands coke demands reliable data on the intrinsic reaction rates, which are currently missing from the literature. The intrinsic gasification rates for char‐CO2, and char‐H2O reactions were determined for Canadian oil sands fluid coke. Four different specific surface area measurement techniques were used to normalize the specific reaction rate calculated from the weight loss profiles of TGA: N2‐BET surface area, two micro‐porosity measurement techniques based on Density Functional Theory (DFT) and Dubinin‐Radushkevich (DR) models, and finally active surface area (ASA) measured by CO2 chemisorption at different levels of conversion (char conversion). The specific reaction rates, calculated at different levels of conversion were divided by different surface areas, in order to find the specific surface area that results in the best reduction in the variability of reaction rate, r(X), by using surface area as a regressor variable. Overall, ASA was found to be the best regressor for deriving the intrinsic rates. Surface areas based on the N2‐BET technique were also proven to be a better choice for normalizing the specific rates compared to the ones based on DFT and DR models.

Two-level Full Factorial Design for Selectivity Modeling and Studying Simultaneous Effects of Temperature and Ethanol Concentration in Methanol Dehydration Reaction

Using surface analysis, simultaneous effects of temperature (260-380oC) and ethanol concentration (0-1%) on dimethyl ether (DME) selectivity, yields of hydrocarbon and DME, and methanol conversion were investigated in methanol dehydration reaction over γ-Al2O3 catalyst. Methanol conversion and yield of hydrocarbon/DME were found to be significantly affected by temperature and the temperature-ethanol concentration interactions. In addition, DME selectivity and yield of DME were found to be influenced by the process temperature, and ethanol concentration as well as their interactions. BET surface area measurement and scanning electron microscopy technique (SEM) confirmed that the catalyst deactivation was intensified at higher temperatures by increasing ethanol concentration. Using statistical regression, a mathematical model was developed, and then validated, to describe simultaneous effects of temperature and feedstock ethanol concentration on DME selectivity. Although the model was statistically significant, curvature was not significant. Therefore, a two-level full factorial design of experiment approach was followed as a promising strategy for DME selectivity modeling and interpretation of data in this work.

INVESTIGATION OF THERMAL AND STRUCTURAL PROPERTIES OF NATURAL AND ION-EXCHANGED ANALCIME

In this study, the thermal and structural properties of natural analcime zeolite obtained from the Canakkale-Kucukkuyu-Ayvacik region and its cationic forms (HA, FeA, AgA and CuA) were characterized using a range of methods. These included X-ray fluorescence (XRF), X-ray diffraction (XRD), thermogravimetric analysis (TG), differential thermogravimetric analysis (DTG), differential thermal analysis (DTA) and specific surface area measurement techniques. Cationic forms were prepared by using 1 M HCl, 1 M Fe(NO 3 ) 3 .9H 2 O, 1 M AgNO 3 and 1 M Cu(NO 3 ) 2 .3H 2 O solutions. Quantitative XRD analysis showed that the natural zeolite was mainly composed of analcime accompanied by quartz, feldspar, montmorillonite and amorphous substance s. AgA and HA samples showed different thermal and structural behaviors due to their rearranged crystal structure and chemical composition. Adsorption properties of samples were determined by using adsorption isotherms and specific surface areas obtained by the Brunauer-Emmet-Teller (BET) method. The specific surface areas of the ion-exchanged analcime zeolites were found to be higher in comparison to natural analcime. Among all the modified forms, it was found that the H-form of the analcime sample has the largest surface area HA (41.88 m 2 /g).

CaO-ZrO2 nanocomposite oxide prepared by urea hydrolysis method as heterogeneous base catalyst for synthesis of chromene analogues

A series of CaO–ZrO2 nanocomposite oxides containing 2–50mol% of CaO were synthesized employing urea as a mild hydrolyzing agent. The nanocomposite systems were characterized using XRD, Fourier analysis, TPD, Raman, XPS, TGA-DSC, FESEM, HRTEM, and BET surface area measurement techniques. XRD study indicated selective stabilization of the tetragonal zirconia phase in the composite oxide. Upto 20mol% CaO, the Ca2+ ions substituted for Zr4+ ions in the zirconia lattice to form a substitutional solid solution. Beyond 20 mol% CaO, the presence of a mixed phase system consisting of the solid solution phase, CaO and nonstoichiometric Zr0.93O2 phase was observed. The composite oxides contain crystallites with size <20nm as observed from Fourier and HRTEM analysis. TPD study revealed a significant enhancement in the basicity of zirconia as a result of Ca2+ incorporation. XPS study confirmed presence of different lattice oxygen as potential basic sites. Raman spectral data indicated the presence of oxygen vacancy and distortion in oxygen sublattice due to Ca2+ incorporation to zirconia. Microscopic investigation of the composite oxide suggested a gradual morphological change from rod shape particles to flake like and subsequently to cubic morphology with increase in CaO content in the composite. The CaO–ZrO2 nanocomposite oxides were used as an efficient and recyclable heterogeneous base catalyst for synthesis of chromene analogues. Structurally diverse 2-amino-4H-chromenes and 2-amino-2-chromenes were synthesized in high yield and purity under mild condition using CaO-ZrO2 material as catalyst and multicomponent condensation approach.

Microemulsion synthesized silica/ZnO stable core/shell sensors highly selective to ethanol with minimum sensitivity to humidity

Silica/ZnO core/shell and composite nanostructured sensors containing 15–90wt% zinc oxide were prepared by a two- and one-step microemulsion method, respectively. The samples were characterized by XRD, EDX, FESEM, TEM and BET surface area measurement techniques and used for detection of 300ppm of C2H5OH, CO, C2HCl3, C3H8, C2H4O, C3H6O or C6H5CH3 and 1% CH4 in air at 200–450°C. For core/shell samples, containing less than 40wt% ZnO, 7.5–20.5nm porous layers of ZnO nanoparticles is formed on the silica spherical particles. At higher ZnO loadings, separate bulk ZnO nanoparticle aggregates are also formed. Heterogeneous nucleation on the silica surface is preferred at the low ZnO concentrations, while homogeneous nucleation occurs at the higher ones too. On the other hand, mixtures of ZnO nanostructures including plate and particle morphologies as well as silica nanoparticles are observed in the composite samples. Core/shell sensors are sensitive and selective to ethanol with responses at least 10 times higher than those to interfering gases. However, the composite sensors with less than 70wt% ZnO have no response to any gas. The core/shell sensor containing 40wt% ZnO shows a very slow drift in the response to ethanol in 14days and only 3–14% lower response in 56% relative humidity.

Highly sensitive and selective Gd2O3-doped SnO2 ethanol sensors synthesized by a high temperature and pressure solvothermal method in a microreactor

Gd2O3-doped SnO2 nanoparticles as highly sensitive and selective ethanol sensor materials with uniform size distributions were synthesized in ethylene glycol at 250°C and 20bar in a continuous tubular microreactor. The samples were characterized by DLS, XRD, SEM, EDX, TEM, FTIR, and BET surface area measurement techniques. As 5wt% Gd2O3 is added to SnO2, the average particle and crystallite sizes of the samples decrease from 22 and 11.9nm to 10 and 3.8nm, respectively. The responses of Gd2O3-doped SnO2 sensors containing 0–10.0wt% Gd2O3 calcined at 450°C were measured in presence of 300ppm CO, 10–1000ppm ethanol and 1.0 vol% of methane in air at 150–430°C. The sensor containing 10wt% Gd2O3 is highly sensitive and selective to ethanol in presence of CO, methane, and three volatile organic compounds, at 150°C. At the same low temperature, as the Gd2O3 content of the sensor increases from 2.5 to 10%, its response to ethanol dramatically enhances by about 263 times and the resistance in air changes by more than 4 orders of magnitude. Relative humidities higher than 50% eliminate the 10% Gd2O3–SnO2 sensor responses to CO and CH4 and the sensor shows absolute selectivity to ethanol.

Structural, thermal, morphological and surface charge properties of dodecyltrimethylammonium-smectite composites

The present investigation was undertaken to obtain information about the structural, thermal, morphological, surface charge and textural properties of the synthesized dodecyltrimethylammonium-smectite composites at various surfactant concentrations by means of powder X-ray diffraction, attenuated total reflection Fourier transform infrared, thermal analyses, scanning electron microscopy, electrophoretic mobility and surface area measurement techniques. The basal spacing values of organo-smectites varied between 13.55 and 17.00 Å that point out the successful intercalation of the surfactant cations into smectite layers with different molecular arrangements either lateral monolayer or lateral bilayer. Intercalation of surfactant cations led to appreciable decreases in the intensities of the bands at 3402 and 1635 cm−1 which originate from OH stretching and bending vibration of sorbed water molecules, respectively. Thermal analysis data showed that all organo-smectites had lower adsorbed water losses than raw and sodium-smectite and the removal of surfactant species occurred in the temperature range of 130–720 °C. The specific surface areas, pore volumes and micropore surface areas of organo-smectites decreased while the average pore width of these species increased with respect to that of raw smectite. The surfactant cations located in the interlayer spaces caused significant alterations in electrophoretic mobility values and morphology of raw smectite.

Gallia–ZnO nanohybrid sensors with dramatically higher sensitivity to ethanol in presence of CO, methane and VOCs

Gallia–ZnO nanohybrid sensors are fabricated and their response to ethanol, CO, methane, acetone and toluene are investigated. Gallia–ZnO samples containing 0–50wt% Ga2O3 were prepared via a facile co-precipitation method using zinc chloride and gallium nitrate aqueous solutions without any template and calcined at 500°C. The samples were characterized by XRD, EDX, SEM, PL and BET surface area measurement techniques. The samples with up to 5wt% gallia show hexagonal; wurtzite structure of ZnO, while those containing 10wt% gallia present additional weak ZnGa2O4 reflexes amplified for the samples with higher gallia contents. The highest responses of 177.3 and 44.3–300ppm ethanol and CO are observed for the sensors containing 1 and 0wt% Ga2O3, respectively. The sensor containing 3wt% Ga2O3–ZnO with a response of 120 is selective to ethanol in presence of CO, acetone, toluene and methane at 300°C. Also, the sensor containing 50wt% Ga2O3 is selective to ethanol and show negligible responses to 300ppm of CO, acetone, toluene and 1% methane at the same temperature.