Increase In Specific Surface Area Research Articles

Mesoporous honeycomb-like ZnO as ultraviolet photocatalyst synthesized via solution combustion method

Single phase zinc oxide (ZnO) powders were obtained via solution combustion method using various amounts of mixture of polyvinylpyrrolidone and citric acid as fuel. The powders had honeycomb-like structure which transformed to spongy structure accompanied by the increase of specific surface area from 19 to 141 m2/g with the increase of fuel content. The methylene blue, methyl orange and rhodamine B dyes were photodegraded in the presence of ZnO powders under ultraviolet irradiation. The highest photodegradation (94%) was obtained for methylene blue by ZnO powders prepared at fuel to oxidant ratio of 1. However, the photodegradation decreased to 52 and 88% for methyl orange and rhodamine B dyes, respectively.

Pellet silica-based titanate adsorbents with high selectivity for strontium removal from synthetic radioactive solutions

The selective removal of strontium ion (Sr2+) from seawater has aroused great attention since the occurrence of the Fukushima nuclear accident. Inorganic ion adsorbents show promise in the treatment of large amounts of polluted water. Among of them, the titanates present a stability and selectivity towards strontium, but limited by poor mechanical and granulometric properties. In this work, a novel silica-based titanate (Na2TinO2n+1/SiO2) was synthesized by sol-gel method and then characterized by X-ray diffraction (XRD), thermal analysis (TG-DSC), XPS and BET. Characterization suggested that the crystal of the titanate was greatly affected by temperature, leading to the difference of the adsorption properties. The silica-based material showed a significant increase in specific surface area; and the adsorption process was found to be an ion-exchange reaction occurred inside these particles. Finally, the material calcined at 500 °C was selected to conduct the following batch experiments. Results suggested that the adsorption data of Sr2+ fitted the Langmuir adsorption model well; the pH from 3 to 10 contributed to a better Sr2+ adsorption behavior, with adsorption amount approaching 33.31 mg/g; the adsorption could reach equilibrium within 5 min with data fitted by the pseudo second kinetic model. And the selectivity coefficient revealed that this material had higher selectivity towards Sr2+ contrast to other alkali and alkaline-earth metals. Based on above static experimental results, the dynamic treatment was designed and carried out in a glass column. This test demonstrated that Na2TinO2n+1/SiO2 could remove the strontium from the simulated seawater effectively and efficiently with no leakage. Generally, this work provides an excellent material to removing Sr2+ from high salinity solution with good column compatibility.

N-doped reduced graphene oxide decorated NiSe2 nanoparticles for high-performance asymmetric supercapacitors

This work reports the preparation of N-doped reduced graphene oxide decorated NiSe2 nanoparticles (N-rGO/NiSe2) in the presence of different amount of graphene oxide reactant by a simple two-step process, which contains hydrothermal preparation of Ni(OH)2 precursor and then solvothermal synthesis of N-rGO/NiSe2 composites with different content of N-rGO. The as-prepared N-rGO/NiSe2 composites is characterized by power X-ray diffraction, Raman spectroscopy, high-resolution X-ray photoelectron spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy and N2 adsorption–desorption isotherm. The results show that N-rGO acts as supporter of NiSe2 nanoparticles to prevent them from aggregation, leading to the increase in specific surface area and electrical conductivity of material. The optimized N-rGO/NiSe2 composite can deliver high specific capacitance of 2451.4 F g−1 at a current density of 1 A g−1. Using activated carbon (AC) as negative electrode and the optimized N-rGO/NiSe2 composite as positive electrode, an asymmetric supercapacitor is constructed. This fabricated asymmetric supercapacitor can work stably under the potential window of 0–1.6 V, and presents the maximum energy density of 40.5 Wh kg−1 at a power density of 841.5 W kg−1. Moreover, the N-rGO/NiSe2//AC asymmetric supercapacitor exhibits good cyclic stability.

CuZn Catalysts Superior to Adkins Catalysts for Dimethyl Adipate Hydrogenolysis

AbstractIndustrial hydrogenolysis of esters to alcohols relies on the use of Adkins catalysts whose production and disposal is an environmental burden. This work is focused on CuZn catalysts that represent an ecological alternative to Adkins catalysts. Four CuZn catalysts with Cu/Zn atomic ratio ranging from 0.5 to 2.0 and single phase CuO and ZnO catalysts were prepared by co‐precipitation and their hydrogenolysis activity was compared with a commercial Adkins catalyst. Dimethyl adipate was used to test the catalyst performance in a flow reactor at temperatures ranging from 175 to 205 °C and hydrogen pressure of 16 MPa. The increase in ZnO content was directly responsible for the reduction in copper crystallite size and increase in the catalyst specific surface area. The CuZn catalysts exhibited higher conversion than the Adkins catalyst despite their specific surface area declined during the experiments more significantly than that of the Adkins catalyst. Nonetheless, the TOF of CuZn catalysts exceeded that of the commercial Adkins catalyst.

Synthesis and Functionalization of Filamentous Carbon Material via Decomposition of 1,2-Dichlorethane over Self-Organizing Ni-Mo Catalyst

Segmented carbon filaments produced by catalytic decomposition of 1,2-dichloroethane over Ni-Mo (8 wt.% Mo) self-organizing catalyst were subjected to functionalization in two different regimes. The structure, textural properties and chemical composition of surface were studied using SEM, Raman spectroscopy, adsorption (BET) and XPS. It was shown that oxidation of carbon nanomaterial in concentrated HNO3 results in enhancement of O-containing groups concentration (from 2.2 to 6.8 wt.%), increase in specific surface area (from 224 to 280 m2/g) and slight structural disorder of graphitic material (increase of ID/IG ratio from 2.15 to 1.84).

Evaluation of physical, mechanical and biological properties of poly 3-hydroxybutyrate-chitosan-multiwalled carbon nanotube/silk nano-micro composite scaffold for cartilage tissue engineering applications.

Nano-micro scaffolds are developed for long-term healing tissue engineering like cartilage. The poly 3-hydroxybutyrate (P3HB)-chitosan/silk and P3HB-chitosan-1 wt% multi-walled carbon nanotubes functionalized by COOH (MWNTs)/silk nano-micro scaffolds are fabricated through electrospinning the solution on a knitted silk which is saturated (S) or unsaturated (U) with P3HB as a mediator to enhance the interaction at nano/microinterface. Consuming MWNTs lead to a decrease in fiber diameter, while an increase in specific surface area, tensile strength and bioactivity properties. The saturation condition as well as MWNTs leads to intensification in the hydrophilicity properties. The nanolayer in all scaffolds lead to an increase in tensile strength in comparison with the pure knitted silk. The scaffold containing MWNTs showed slower degradation rate. MWNTs beside the chitosan and silk provide an appropriate environment for attachment and growth of chondrocytes. The P3HB-chitosan-MWNTs/silk (S) nano-microscaffold can be appropriate for a long-term tissue engineering application like cartilage.

Окислительная переработка пропана в важные нефтехимические продукты на нанесенных ванадиевых катализаторах

The paper presents the data on activity of the deposited catalyst based on vanadium. The developed catalyst allows conducting the process of oxidative conversion of propane into ethylene and hydrogen using CO2 as an oxidant. The study of the activity of the developed vanadium catalyst at the oxidative conversion of propane showed that the maximum ethylene yield was 24.5% at: C3H8:CO2=2:1, T=700°C and W=1000 h-1. The increase of temperature to 800°C resulted in the in formation of 27.5% hydrogen. By methods of BET and XRD the developed catalyst 5% V/Al2O3, is differed by increase of specific surface area and bonding of the carrier with active phase, contributing to increase of efficiency of the developed catalyst in the oxidative conversion of propane to ethylene and hydrogen.

Highly sensitive and selective isoprene sensing performance of ZnO quantum dots for a breath analyzer

We report the quantum-size effect on the sensing properties of ZnO nanoparticles for the detection of isoprene. For this purpose, two types of ZnO particles with different sizes, including nanoparticles (NPs, ˜25 nm) and quantum dots (QDs, ˜5 nm), were prepared by a wet chemical method. The ZnO QDs exhibited excellent sensing performance to 1 ppm isoprene compared to NPs. The maximum sensing response and response time were ˜42 and 8 s at 350 °C for the QDs, while ˜5.6 and 40 s at 500 °C for the NPs, respectively. The higher sensing response, rapid response, and lower optimal working temperature of the ZnO QDs can be attributed to an increase in oxygen vacancies, band gap, and specific surface area owing to the small size effect. Both ZnO NPs and QDs showed the lower limit of 0.01 ppm for detecting isoprene. It is noted that the sensing properties of ZnO QDs to 1 ppm isoprene are superior to previously reported isoprene sensors that are based on semiconducting metal oxides. Furthermore, we demonstrated that the low concentration (0.4–6.2 ppm) of isoprene can be selectively detected within ˜83 s using a recently developed miniaturized gas chromatography integrated with the ZnO QD sensor.

Design of nanoscale structured composite particles through mechanical process for fabricating a powder layer with rapid drying properties

Nanoscale structured composite particles consisting of spherical porous SiO2 particles with nanoscaled surface roughness as the core particles and SiO2 nanoparticles as the depositing particles were designed using a high-shear mechanical composing process to develop a powder material that can form a layer with apparent rapid drying properties. The spherical porous SiO2 core particles and depositing nanoparticles were selected to enhance the water extension on the core particle surface and amongst the composite particles in the powder layer, respectively. The effects of the composite particle nanoparticle content on the morphology of the composite particles and their relationships with the water droplet extending and drying properties in the powder layer of the designed composite particles were systematically investigated based on FE-SEM observations, characterization of N2 adsorption/desorption isotherms, and 1H spin-spin relaxation rate measurements of composite particles. The FE-SEM observations show that the pulverized nanoparticles could be successfully attached to porous core particles without the core particles collapsing. The reduction of the specific surface area and increase of the particle specific external surface area after the compositing process strongly supported the fact of nanoparticle attachment. While a small amount of nanoparticle attachment decreased the water droplet extended area, wet area circularity, and apparent drying rate, 15 wt% loading of the pulverized nanoparticles resulted in a drastic increase of the water extended area, wet area circularity, and apparent drying rate.

In-situ synthesis of MnCo2O4.5 nanosheets on reduced graphene oxide for a great promotion in the thermal decomposition of ammonium perchlorate

In this work, ternary transition metal oxides MnCo2O4.5 nanosheets was anchored on reduced graphene oxide (RGO/MnCo2O4.5 NSs) in an in-situ way for catalyzing ammonium perchlorate (AP). XRD, FT-IR, Raman, EDX, XPS, SEM, TEM, HR-TEM, SAED and nitrogen absorption-desorption techniques were applied to characterize the structure and morphology of the catalyst. The catalytic performances for the thermal decomposition of AP were investigated using DSC and TG. The results show that the MnCo2O4.5 nanosheets are vertically grown on RGO sheets to form a hierarchically porous structure, which is remarkably effective to avoid both the aggregation of MnCo2O4.5 NSs and the re-stacking of RGO. The introduction of RGO will significantly lead to an increase in conductivity and specific surface area. Just for that reason and the synergetic effect between RGO and MnCo2O4.5 NSs, the synthesized RGO/MnCo2O4.5 NSs composites gets the low-temperature decomposition peak of AP disappeared, the high-temperature decomposition temperature reduced by as high as 124.1 °C, the activation energy decreased from 221.04 to 129.85 kJ·mol−1, and the reaction rate increased incredibly up to 186.8 times when compared with corresponding data of the pure AP. Furthermore, the catalytic mechanism of the RGO/MnCo2O4.5 NSs has been discussed either based upon the electron-transfer theory.

Factors influencing the gas adsorption thermodynamic characteristics of low-rank coal

Low-temperature nitrogen and isothermal adsorption experiments were conducted on six typical low-rank coal samples from the Fukang mining area, Xinjiang, PR China. Using different temperatures, the effects of the coal’s pore structure on gas adsorption and other thermodynamic characteristics were analyzed. The Clausius–Clapeyron equation was used to calculate the isosteric heat of adsorption, and the standard adsorption equilibrium constant was derived to calculate the adsorption free-energy and entropy. The relationships between pore structure characteristics and gas adsorption thermodynamic parameters were investigated. The results showed that the adsorption free-energy and enthalpy of the coal samples decreased with an increase in temperature. Adsorption heat and adsorption entropy were affected by an increase in pore volume and specific surface area. The specific surface area and transition pore volume exhibited quadratic relationships with the free-energy and total pore volume, whereas the mesopore volume exhibited a positive linear relationship with the adsorption free-energy. No prominent relationships among average pore diameter, adsorption heat, adsorption free-energy, and adsorption entropy were observed. No correlation was identified between micropore volume and adsorption free-energy. Fractal dimension was linearly and positively related to the adsorption heat and entropy but had no effect on the free-energy.

Photoelectrochemical properties of BiVO4 thin films with NaOH chemical treatment

BiVO4 thin films were prepared by a mature and simple electrochemical deposition method on F-doped SnO2 substrate electrode (FTO). The influence of a chemical treatment using sodium hydroxide (NaOH) on the photoelectrochemical properties of BiVO4 thin films was studied. It was found that NaOH can etch the crystal surface of BiVO4, which leads to the increase in specific surface area and improved photoelectrochemical activity. The photocurrent density of the BiVO4 thin films showed an enhancement of photoelectronic current from 0.50 to 0.65 mA·cm−2 at 1.23 V (vs. RHE) after the treatment for 5 h by NaOH, which supplies a stronger potential for H2O oxidation.

Enhanced Methane Sensing Properties of WO₃ Nanosheets with Dominant Exposed (200) Facet via Loading of SnO₂ Nanoparticles.

Methane detection is extremely difficult, especially at low temperatures, due to its high chemical stability. Here, WO3 nanosheets loaded with SnO2 nanoparticles with a particle size of about 2 nm were prepared by simple impregnation and subsequent calcination using SnO2 and WO3·H2O as precursors. The response of SnO2-loaded WO3 nanosheet composites to methane is about 1.4 times higher than that of pure WO3 at the low optimum operating temperature (90 °C). Satisfying repeatability and long-term stability are ensured. The dominant exposed (200) crystal plane of WO3 nanosheets has a good balance between easy oxygen chemisorption and high reactivity at the dangling bonds of W atoms, beneficial for gas-sensing properties. Moreover, the formation of a n–n type heterojunction at the SnO2-WO3 interface and additionally the increase of specific surface area and defect density via SnO2 loading enhance the response further. Therefore, the SnO2-WO3 composite is promising for the development of sensor devices to methane.

Photocatalytic Degradation of 2,4-Dichlorophenol by TiO2 Intercalated Talc Nanocomposite

Novel nanocomposites have been prepared by intercalating TiO2 nanoparticles into talc. The nanocomposites have been verified by X-ray diffraction (XRD) from the appearance of a characteristic diffraction peak of TiO2. Thermal behavior of the prepared samples is examined by thermogravimetric analyzer (TGA), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS), which have shown no TiO2 particles on the surface of the talc. The TiO2 particles are found in the layers of talc by transmission electron microscopy (TEM) and the Brunauer-Emmett-Teller (BET) method, which have shown the increase of specific surface areas and total pore volumes and the decline of average pore diameters. As the strong adsorption ability of talc can intensify the power of photon absorption and capture-recombination carriers, more than 99.5% of 2,4-dichlorophenol can be degraded in 1 h by the nanocomposite under an ultraviolet lamp in neutral solution and room temperature after reaching adsorption equilibrium, and the result of adsorbance is in accord with the first-order kinetic. The degradation rate was maintained at about 99% after 20 times. Therefore, the prepared talc/TiO2 nanocomposite is an efficient, stable, and recyclable material for wastewater treatment.

Structure and crystal phase transition effect of Sn doping on anatase TiO2 for dichloromethane decomposition.

Efficient removal of chlorinated volatile organic compounds (CVOCs) has received great attention because of the considerable harm that they cause to the environment and to human health. Developing novel catalysts and exploring the catalytic activation and deconstruction mechanism of CVOCs molecule are always the focus in this field. Here, a set of Sn doped TiO2 catalysts were investigated for the decomposition of dichloromethane (DCM). Rietveld refinement of the XRD patterns showed that Sn ions can uniformly disperse into TiO2 and induce the crystal transition of anatase. Meanwhile, such decorating can induce an increase in specific surface area and affect the surface oxygen vacancy concentration of these samples, which have been demonstrated by N2 adsorption and XPS, respectively. Catalytic performance tests indicated that the Sn0.2Ti0.8O2 has the best activity for DCM decomposition, and a lower CH3Cl selectivity than that of pure TiO2. Computational results suggested the dominant surface (110) of rutile Sn0.2Ti0.8O2 is more beneficial for the adsorption/dissociation of DCM molecule than that of anatase TiO2 (101). That's because the anchoring of DCM to Sn sites and electron enrichment on the surface bridge oxygen atoms of rutile Sn0.2Ti0.8O2 (110) can promote the nucleophilic substitution process for breaking of CCl bonds.

The impact of depositional environment and tectonic evolution on coalbed methane occurrence in West Henan, China

A deeper understanding of the mechanisms by which geological factors (depositional environment and tectonic evolution) control the occurrence of coalbed methane (CBM) is important for the utilization of CBM resources via surface-drilled wells and the elimination of coal-methane outbursts, the latter of which is a key issue for coal mine safety. Based on drill core data, high-pressure isothermal adsorption experiments, scanning electron microscopy experiments, mercury intrusion porosimetry, and X-ray diffraction experiments, the impact of the depositional environment and tectonic evolution on CBM occurrence of the II-1 coal seam of the Shanxi Formation in West Henan was analyzed. Results showed that the depositional environment led to the epigenetic erosion of tidal flat coal-accumulating structures by shallow-delta distributary channel strata. This resulted in the replacement of the original mudstone-sandy mudstone coal seam immediate roof with fine-to-medium grained sandstones, reducing methane storage capacity. Epigenetic erosion by the depositional environment also increased coal body ash content (from 6.9% to 21.4%) and mineral content, filling the cleat system and reducing porosity, reducing methane storage capacity. The maximum methane adsorption capacity of the coal body reduced from 35.7 cm3/g to 30.30 cm3/g, and Langmuir pressure decreased from 1.39 MPa to 0.909 MPa. Hence, the methane adsorption capacity of the coal body decreased while its capacity for methane desorption increased. Owing to the tectonic evolution of West Henan, tectonically deformed coal is common; as it evolves from primary cataclastic coal to granulitic coal, the angle of the diffraction peak increases, d002 decreases, and La, Lc, and Nc increase; these traits are generally consistent with dynamic metamorphism. This is accompanied by increases in the total pore volume and specific surface area of the coal body, further increasing the capacity for methane storage. Increases in micropore volume and specific surface area also increase the ability of the coal body to adsorb methane.

Upgradation of Zhaotong Lignite through microwave drying

Upgradation of the rank of lignite is mandatory for its effective utilization as a potential energy source. Microwave drying is being explored in the present work as an effective upgradation technique. The effects of operating variables such as sample mass, particle size and sample thickness were investigated. The work also attempts to compare the quality of lignite dried using conventional hot air and microwave drying utilizing characterization techniques such as SEM, FT-IR, BET. The SEM analysis demonstrate a considerable increase in number of pores, fractures and cracks in the upgraded lignite structure after microwave drying as compared to hot air drying. The FT-IR analysis indicate an overall reduction in the number of absorbance peaks and a significant reduction in the oxygen-containing functional groups with microwave drying as compared to hot air drying. The BET analysis reveal a 30 fold increase in specific surface area with microwave drying as compared to hot air drying. The major proportion of pores in the lignite after microwave drying were either mesopores or micropores, while that dried with conventional hot air were macropores. Microwave drying as compared with hot air drying is more effective having higher fixed carbon content. The moisture re-adsorption capacity weakened after microwave drying, while it increased with increase in particle size.

Microscopic investigations on the air-void characteristics of wet-mix shotcrete

This paper aims to perform microscopic investigations on the air-void characteristics of wet-mix shotcrete before and after the spraying process. Both air-void analysis (AVA) and image analysis (IA) were used to monitor the air-void characteristics of both fresh and hardened mixtures such as air content, spacing factor, and air-void specific surface area. To gain a comprehensive understanding on the air-void characteristics, a total of 28 mixtures were fabricated with different aggregate gradations, slumps, air entrainments, and the types and replacement levels of supplementary cementitious materials (i.e., fly ash, silica fume, metakaolin, and ground-granulated blast furnace slag (GGBFS)). The results have shown that: (1) both pumping and shooting significantly altered the air-void characteristics; (2) the pumping process increased the air content and air-void specific surface area while decreasing the spacing factor; and (3) a decrease in air content and an increase in air-void specific surface area were observed after shooting. In addition, the findings of this study revealed that the air-void characteristics of wet-mix shotcrete were more closely associated with the pumping and shooting operations rather than the mixture characteristics such as aggregate gradation, slump, air entrainment, and mineral admixtures addition.

Relating early hydration, specific surface and flow loss of cement pastes

Flow loss in superplasticized systems has been mainly explained in qualitative and comparative ways over the past years. This is due to the intrinsic complexity of the underlying mechanism involving a change in the agglomeration degree as a result of cement hydration. The lack of robust and reliable experimental methodologies must have additionally discouraged researchers from attempting to understand the phenomena of flow loss in quantitative terms. Thanks to new analytical methods, it was possible to prove that after the so-called onset point, yield stress increases exponentially with the increase of both heat rate measured by isothermal calorimetry and specific surface. This paper also identifies the existence of a direct proportionality between the increase of heat rate and the increase of specific surface area during the acceleration period, most likely reflecting the nucleation and growth nature at this stage of the cement hydration.

Calcined products of Mg–Al layered double hydroxides/single-walled carbon nanotubes nanocomposites for expeditious removal of phenol and 4-chlorophenol from aqueous solutions

We reported a facile method for preparing calcined products of layered double hydroxides/single-walled carbon nanotubes (CLDH/SWCNT) nanocomposites. A large number of “pore channels” with diameters between 30 and 150 nm were formed in CLDH/SWCNT nanocomposites. This led to a significant increase in specific surface area and pore volume of nanocomposites. Experimental data showed that the removal rates of phenol and 4-chlorophenol by CLDH/SWCNT can reach 91.7% and 99.5%, respectively. By fitting the Langmuir adsorption isotherm, the maximum adsorption capacities of CLDH/SWCNT for phenol and 4-chlorophenol adsorption under optimal conditions (pH 6, adsorbent dosage of 3.5 g/L, contact time of 24 h, and temperature of 303 K) were 219.0 and 255.6 mg/g, respectively. Remarkably, after 10 cycles of recycling, the material can still effectively adsorb target pollutants. Compared to most existing adsorbents, CLDH/SWCNT nanocomposites have the advantages of high maximum adsorption capacity, wide range of effective pH for adsorption, fast adsorption speed and excellent recyclability. Due to their superior adsorption performance, CLDH/SWCNT may become an excellent adsorbent with high potential for treating phenolic pollutants.