Nitrogen Adsorption Desorption Research Articles

Preparation and performance of MOF-808 (Zr-MOF) for the efficient adsorption of phenoxyacetic acid pesticides

The organic herbicides of chlorophenoxyacetic acids, including 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA), have posed serious threats to aquatic ecosystems and human health due to extensive use, high solubility and degradation-resistant. In this study, the efficient adsorbent (MOF-808) was synthesized through solvothermal synthesis method and further evaluated for the adsorption performances of 2,4-D and MCPA. Results showed that MOF-808 exhibited the Type I nitrogen adsorption–desorption isotherm with a specific surface area of 2,155 m2·g−1, pore volume of 0.59 cm3·g−1 and pore size of 1.41 nm. It was suggested that the pseudo-second-order and Langmuir model were much better to illustrate the adsorption performances of MOF-808 for both 2,4-D and MCPA, and the maximum adsorption capacities of 793 and 775 mg·g−1 were achieved, respectively; besides, the adsorption processes were spontaneous and primarily driven by chemical adsorption with contributions from physical-chemical adsorption. Additionally, the adsorption capacities for 2,4-D and MCPA were decreased with the increasing of pH and cations concentrations; the optimal pH was 3.0 for 2,4-D and 4.0 for MCPA, and the effects of four cations on pesticides adsorption followed the order of Ca2+ > Mg2+ > Na+ > K+. Reuse experiments demonstrated that MOF-808 could retain a high removal rate of 95.9 % (2,4-D) and 95.8 % (MCPA) at the fifth cycle. The spectral analysis revealed that the adsorption mechanisms of 2,4-D and MCPA by MOF-808 involved electrostatic interactions, π-π interactions, hydrogen bonding, and complexation. In conclusion, the well-defined physicochemical properties and outstanding adsorption performance of the synthesized MOF-808 may provide a potential application for the removal of chlorophenoxyacetic acid herbicides from real wastewater.

Enhanced electrocatalytic nitrate reduction via carbon material integration between Cu and Ni-foam: Mechanisms and performance analysis

This study investigates the electrocatalytic reduction of nitrates using three novel electrodes: Cu@CNFs/NF, Cu@CNTs/NF, and Cu@CB/NF, synthesized via an impregnation-calcination-electrodeposition technique. The emphasis is on the role of different carbon materials, which serve as the base or matrix for Cu, and their influence on nitrate reduction and nitrogen selectivity. Experimental results indicated that all three-electrode variants outperformed the conventional Cu/NF electrode in nitrate reduction and nitrogen selectivity. Among these, the Cu@CNFs/NF electrode emerged as the standout performer, achieving an impressive nitrate reduction rate of up to 98 % and a nitrogen selectivity of 51 % under the optimized experimental conditions (pH 7, nitrate concentration of 100 mg∙L-1 as NO3–-N, a current density of 8 mA cm−2, a sodium sulfate concentration of 0.5 g∙L-1, 120 min, anode: Ti/RuO2-IrO2). Stability tests confirmed that the Cu@CNFs/NF electrode maintained over 97 % nitrate removal efficiency across ten cycles, highlighting its robustness and potential for practical water treatment applications. A significant enhancement in nitrogen selectivity of Cu@CNFs/NF to 96 % was observed when using 0.75 g∙L-1 NaCl as the electrolyte during an extended electrolysis period of 180 min, underscoring its potential to optimize catalytic efficiency. Characterization data from SEM, XRD, and other analyses substantiate that the incorporation of carbon materials augments the active sites of copper; Nitrogen adsorption–desorption experiments further illustrate that the integration of carbon materials leads to an increase in mesoporous volume. This increase promotes adsorptive interactions, enhances the conversion of intermediates, and contributes to the improvement of nitrate reduction and nitrogen selectivity. These results highlight the potential of tailored carbon material integration for enhancing the electrocatalytic performance of electrodes in practical water treatment applications.

Rational Use of Waste from Oil Extraction Production — Bleaching Clay Waste

The results of studies of the physic-chemical and sorption properties of bleaching clay waste, the prospects for its use for the purification of polluted waters, as well as the possibility of subsequent disposal of used materials are presented. Using the method of low-temperature nitrogen adsorption-desorption, it was found that the studied bleaching clay waste has a specific surface area of 185.53 m2/g and has a mesoporous structure. The sorption properties of clay waste were studied and it was found that at a dosage of 1.5 g/dm3, the purification efficiency of the standard solutions containing Cu2+ ions with a concentration of 10 mg/dm3 is 96.7 %. It has been found that the maximum sorption capacity, determined under static conditions for clay fired at a temperature of 350 °C, is 0.41 mmol/g. The use of bleaching clay as filler pigments in the manufacture of paints and varnishes has been proposed and demonstrated.

Immobilization of Laccase in β-Cyclodextrin Composite Hydrogel for Efficient Degradation of Dye Pollutants

A stable and efficient biocatalyst was prepared by encapsulating Trametes versicolor laccase using an acrylic acid-grafted β-cyclodextrin hydrogel (Lac-CD-PAA). Scanning electron microscopy and nitrogen adsorption-desorption experiments showed that there were regularly distributed channels in the spongy Lac-CD-PAA. In addition, a large number of mesopores and macropores existed in the wall of the hydrogel lamellae. This network structure reduced the diffusion resistance of the hydrogel to the target substrate. The relative activity of the resulting Lac-CD-PAA could be maintained at 35.8% after six cycles of use. Lac-CD-PAA exhibited higher thermal and chemical stability compared to free laccase. The negative charge on the surface of Lac-CD-PAA gives it the ability to pretreat cationic dyes. In six consecutive methylene blue decolorization tests, Lac-CD-PAA decolorized better than free laccase. The results showed that the prepared β-cyclodextrin-based composite hydrogel was a good carrier for laccase.

Shale pore characteristics and their impact on the gas-bearing properties of the Longmaxi Formation in the Luzhou area

Deep shale has the characteristics of large burial depth, rapid changes in reservoir properties, complex pore types and structures, and unstable production. The whole-rock X-ray diffraction (XRD) analysis, reservoir physical property parameter testing, scanning electron microscopy (SEM) analysis, high-pressure mercury intrusion testing, CO2 adsorption experimentation, and low-temperature nitrogen adsorption–desorption testing were performed to study the pore structure characteristics of marine shale reservoirs in the southern Sichuan Basin. The results show that the deep shale of the Wufeng Formation Longyi1 sub-member in the Luzhou area is superior to that of the Weiyuan area in terms of factors controlling shale gas enrichment, such as organic matter abundance, physical properties, gas-bearing properties, and shale reservoir thickness. SEM is utilized to identify six types of pores (mainly organic matter pores). The porosities of the pyrobitumen pores reach 21.04–31.65%, while the porosities of the solid kerogen pores, siliceous mineral dissolution pores, and carbonate dissolution pores are low at 0.48–1.80%. The pores of shale reservoirs are mainly micropores and mesopores, with a small amount of macropores. The total pore volume ranges from 22.0 to 36.40 μL/g, with an average of 27.46 μL/g, the total pore specific surface area ranges from 34.27 to 50.39 m2/g, with an average of 41.12 m2/g. The pore volume and specific surface area of deep shale gas are positively correlated with TOC content, siliceous minerals, and clay minerals. The key period for shale gas enrichment, which matches the evolution process of shale hydrocarbon generation, reservoir capacity, and direct and indirect cap rocks, is from the Middle to Late Triassic to the present. Areas with late structural uplift, small uplift amplitude, and high formation pressure coefficient characteristics favor preserving shale gas with high gas content and production levels.

Intensification of Cr(VI) adsorption using activated carbon adsorbent modified with ammonium persulfate

Granular activated carbon has been modified by ammonium persulfate as a new adsorbent for Cr(VI) adsorption from aqueous solutions. The adsorbent was characterized by nitrogen adsorption–desorption isotherm data and infrared spectroscopy. The impact of different factors, such as the initial pH level of the solution, time, temperature, ionic strength, and initial concentration of the Cr(VI) ion, on the adsorption efficiencies of the adsorbent has been studied by batch experiments. Kinetic studies and the adsorption thermodynamics of Cr(VI) with ammonium persulfate-modified activated carbon adsorbent were carefully studied. The results showed that the Cr(VI) adsorption follows a pseudo-second-order kinetic model and the adsorption reaction is endothermic and spontaneous. The adsorption isotherm was scrutinized, and the fitting results showed that the Langmuir model could well represent the adsorption process. The maximum adsorption capacity of Cr(VI) onto persulfate-modified activated carbon was 108.69 mg g−1. The research results showed that using persulfate-modified activated carbon adsorbent can greatly remove Cr(VI) from aqueous solutions.

Sol-Gel Synthesis of TiO2 with Pectin and Their Efficiency in Solar Cells Sensitized by Quantum Dots.

In this study, titanium oxide TiO2 nanoparticles were produced using the sol-gel approach of green synthesis with pectin as the reducing agent. The synthetized TiO2 nanoparticles with pectin were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), visible light absorption (UV-Vis) and the BET method. The structure and morphology of the TiO2 powder were described with SEM, revealing uniform monodisperse grains with a distribution of 80% regarding sizes < 250 nm; the resulting crystal phase of synthetized TiO2 was identified as an anatase and rutile phase with a crystallinity size estimated between 27 and 40 nm. Also, the surface area was determined by nitrogen adsorption-desorption using the Brown-Emmet-Teller method, with a surface area calculated as 19.56 m2/g, typical of an IV type isotherm, indicating mesoporous NPs. UV-Vis spectra showed that sol-gel synthesis reduced the band gap from the 3.2 eV common value to 2.22 eV after estimating the optical band gap energy using the adsorption coefficient; this translates to a possible extended photo response to the visible region, improving photoactivity. In addition, the power conversion of the photoelectrode was compared based on similar assembly techniques of TiO2 electrode deposition. Quantum dot crystals were deposited ionically on the electrode surface, as two different paste formulations based on a pectin emulsifier were studied for layer deposition. The results confirm that the TiO2 paste with TiO2-synthesized powder maintained good connections between the nanocrystalline mesoporous grains and the deposited layers, with an efficiency of 1.23% with the transparent paste and 2.27% with the opaque paste. These results suggest that pectin could be used as a low-cost, functional sol-gel catalysis agent for the synthesis of controlled NPs of metal oxide. It demonstrates interesting optical properties, such as an increase in photo response, suggesting further applications to photocatalysts and biomedical features.

Ag0, Re0, and Ag@Re heterogeneous persulfate activators for reactive radical based oxidation of water contaminant

Silver-rhenium bi-metallic nanoparticles (Ag-Re) were prepared by the combination of colloidal sols of silver and rhenium at room temperature. The silver and rhenium sols were synthesized by using the chemical reduction of silver nitrate and ammonium perrhenate with sodium borohydride in presence of cetyltrimethylammonium bromide (CTAB). The morphology (shape, size, elemental composition, oxidation states, and crystalline nature) and textural properties (pore size, pore volume, and surface area) of Ag0-Re0 were determined with EDX, SEM, TEM, XPS, XRD, and nitrogen adsorption-desorption isotherm. The Ag0-Re0 was used as heterogeneous persulfate (S2O82−) activator to generate reactive radical species (SO4−• and HO•) for the degradation of xylenol orange (XO) at 434 nm. The Ag-Re exhibits higher XO degradation efficiency than that of mono-metallic Ag0 and Re0 nanoparticles, respectively. The degradation efficiency strongly depends on the concentrations of S2O82−, XO, pH, temperature, and amount of Ag0-Re0. The role of SO4−• and HO• were established by using ethanol, and tertiary butanol as radical scavengers. The activation energy was found to be 85.2, 63.5, and 32.6 kJ/mol, respectively, to the degradation of XO by activated S2O82− with Re0, Ag0, and Ag0-Re0.

Physico-chemical characteristics of Ca/P ratio on the composition and structure of oxygenated apatite

Phosphocalcic apatites have osteoconductive and bioactive properties that make them suitable for bone reconstruction. But, they are inactive against pathogenic microorganisms that can infect bone tissue. To overcome this limitation, we synthesized oxygen-doped phosphocalcic apatites that can release molecular oxygen as a bioactive molecule. We investigated how the calcium-to-phosphorus ratio (Ca/P) gave impacts on the chemical and structural composition of the oxygen-doped phosphocalcic apatites. We here used the double decomposition method, which involved mixing calcium nitrate and diammonium phosphate solutions in an ammonia buffer. We then characterized the products using several analysis, including infrared absorption spectroscopy, X-ray diffraction, thermal analysis, nitrogen adsorption-desorption, and elemental chemical analysis. It was found that the oxygen-doped phosphocalcic apatites were calcium-deficient and had a well-defined crystallinity at room temperature. After calcination at 900°C, the crystallinity improved further. The thermal analysis showed two mass losses: one at 50°C due to water adsorption and another at 450°C due to CO2 release. The specific surface area was about 100 ± 2 m2/g without any change with the Ca/P ratio. The quantity of molecular oxygen increased with the Ca/P ratio and reached an optimal value of the order of 3.6 ×10-4 mol for Ca/P=1/65 with the chemical formula of Ca9.9(PO4)6(OH)1.25(O2)0.74(CO3)0.01. It is important to make further analysis to know more about the properties of oxygenated apatite, and to combine this apatite with polymers purposely to have biomedical composites. It then can be concluded that the oxygen-doped phosphocalcic apatites could be a promising biomaterial for bone infection prevention and treatment. This research highlights an oxygenation treatment of phosphocalcic apatite and brings new ideas and possibilities for future research and development to get better understanding of the behavior of these biomaterials to be more effective, especially in the biological field. As a perspective, improving the biological properties in these biomaterials needs to be further explored, including experimental parameters for the obtainment of more conclusive results.

Identification of suitable catalyst among HZSM-5, HY and γ-Al2O3 to obtain upgraded pyrolysis oil with augmented liquid oil yield

This study examines catalytic ability of various zeolite materials in converting discarded tire pyrolyzed oil by employing a moderate sized pyrolysis plant of a 10 L working volume. The study revealed that the yield of liquid fractions using γ-Al2O3 was greater than that of HZSM-5 and HY, while the yield of condensates were limited in the absence of catalyst. The tire waste pyrolysis oil catalytcially enhanced by alumina catalyst analyzed using Fourier transform infrared spectroscopy exhibited the stretching bands corresponding to aromatic and non-aromatic compounds. The GC MS analysis revealed that the cyclic unsaturated fragment percentages in liquids were decreased by the catalysts to 53.9% with HY, 59.0% with γ-Al2O3, and 62.2% with HZSM-5, which in turn was converted into aromatic chemicals. Nitrogen adsorption desorption analysis revealed that γ-Al2O3 has an enhanced surface area of 635 m2/g which improved its catalytic performance. The cracked liquid oil had viscosity (10.36 cSt), values of pour and flash temperatures of −2.2 °C and 41 °C respectively, analogous to petroleum diesel. The upgraded pyrolysis oil (10%) is blended with gasoline (90%), and emission analysis was performed. Moreover, liquid oil needs post treatment (refining) for its use as energy source in transportation application. The novelty of this research is in its comparative analysis of multiple catalysts under controlled conditions using a small pilot-scale pyrolysis reactor, which provides insights into optimizing the pyrolysis process for industrial applications.

Hygroscopic Mg–Al LDHs composite microspheres for highly efficient hyperspectral camouflage in the VIS and NIR wavebands

In order to enhance the hyperspectral camouflage efficacy of stealth coatings against a natural vegetative backdrop, LiCl, known for its significant hygroscopic properties, was incorporated into green Mg–Al layered double hydroxide (Mg–Al LDHs) material. Micron-sized composite microspheres were subsequently synthesized via the spray-drying granulation technique. The structure, morphology, and chemical composition of these microspheres were thoroughly characterized by X-ray diffraction, scanning electron microscopy, laser particle size analysis, nitrogen adsorption–desorption isotherms, and Fourier-transform infrared spectroscopy. The effect of LiCl content on the moisture absorption capacity and near-infrared reflectance spectra of the microspheres was systematically evaluated. We found that incorporating an optimal amount of LiCl into the internal pores of the Mg–Al LDHs microspheres did not compromise their smooth surface morphology and uniform particulate distribution. Notably, when the LiCl content was 10%, the maximum saturation moisture uptake ratio of the coating increased to 0.75 g/g. This hygroscopicity significantly enhanced the absorption and scattering of near-infrared radiation by the coating while concurrently improving its ability to modulate the shape and reflectance of both the visible and near-infrared spectral curves. Spectral congruence between the synthetic coating and natural green foliage was quantified at 97.41%. Moreover, this performance was maintained over 10 cycles of programmed drying and re-humidification, and the coating consistently demonstrated stable hygroscopic properties and sustained over 95% spectral congruence. These optimized artificial coatings were found to effectively confuse hyperspectral classification algorithms, thus blending seamlessly into a natural foliage backdrop. This study provides a new method for regulating VIS and NIR spectral (visible–near infrared spectrum) features, which will be critical for applications in advanced hyperspectral camouflage materials.

Preparation of bulk micro–mesoporous silica-supported ZnO via silicic acid as a desulfurizer

Silicic acid solution, which is prepared from water glass followed by extraction with tetrahydrofuran (THF), is focused on an environmentally friendly and inexpensive source of silica. In this study, we aimed the preparation of bulk porous silica with low environmental impact and cost, and desulfurization of its supported ZnO was investigated. Bulk porous silica was prepared by the condensation of silicic acid/THF in the presence of Pluronic P123. Suitable condition was investigated for the formation of crack-free bulk body with high surface area and reproducibility under the molar ratio of H2O/Si and Si/Pluronic P123 on 121 and 100, respectively. From nitrogen adsorption–desorption measurements, this bulk porous silica was categorized into micro–mesoporous silica. Moreover, Pluronic P123 was extracted and recycled. Bulk porous silica-supported 15 wt% ZnO was prepared by the impregnation of ZnCl2 followed by calcination in air. The desulfurization ability was 8.7 mg/g.Graphical

Effect of Temperature on CO2 Adsorption onto Amine-Functionalized KIT-6 Adsorbents.

The mesoporous silica KIT-6 was synthesized and functionalized with 3-aminopropyltriethoxysilane (APTES) by grafting at 110 °C. The composites were prepared with three different concentrations of APTES: 20, 30 and 40 wt.%. The as-prepared samples were characterized by thermal gravimetric analysis in air and nitrogen atmosphere (TG/DTA), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction and nitrogen adsorption-desorption. In this study, CO2 adsorption-desorption was investigated using temperature programmed desorption mass spectrometry (TPD-MS) at different temperatures. The adsorption capacity of the prepared composites is 2.23 mmol CO2/g at 40 °C and decreases to 0.95 mmol/g at 70 °C. Regarding the efficiency of the amino groups, the best result was obtained for APTES-grafted KIT-6 at 40 °C, with 0.512 mmol CO2/mmol NH2. The results showed good cyclical stability in adsorption capacities even after nine adsorption-desorption cycles.

Ruthenium-modified catalyst Ru-CeO2 significantly enhances mercury removal from sulfur-containing coal flue gas

In this study, we innovatively synthesized Ru-CeO2 catalysts by doping ruthenium dioxide (RuO2) with cerium dioxide (CeO2), which significantly enhanced the removal efficiency of mercury (Hg0) from coal-fired flue gases and tolerance to high sulfur environments. We effectively responded to the complex challenges in coal-fired flue gases. Nitrogen adsorption-desorption, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were employed to characterize the catalyst. It was found that the mercury removal efficiency of the Ru-CeO2 catalyst was significantly higher than that of unmodified CeO2 at 125°C, demonstrating excellent mercury removal performance and sulfur resistance. In addition, in the field of mercury removal and sulfur resistance, the innovative combination of characterization technique and density functional theory (DFT) was used to deeply explore the adsorption behaviors of Hg0 and SO2 on the surface of the catalyst and their mechanisms, revealing the changes in surface charge distribution and the increase in active sites caused by ruthenium doping. The changes in the electronic structure of the active sites on the catalyst surface were revealed by DFT calculations, which provide a scientific basis for the optimization and screening of catalysts in the future and are of great significance to the field of coal-fired flue gas purification and catalyst science.

Zn-doped aerogel for Ni2+ adsorption (Zn-A-Ni) and reuse of Zn-A-Ni to create Zn, Ni-co-doped carbon aerogel for applications in adsorption and energy storage

In order to solve the problem of heavy metal pollution, in this study, Zn-doped aerogel (Zn-A) was used as a material to remove Ni2+ from wastewater. Zn-A was synthesized from sodium alginate and nipa palm shell-derived cellulose via the sol–gel method combined with freeze-drying. Zn-A has the ability to adsorb Ni2+ up to 194.2 mg/g (Zn-A-Ni). After adsorbing Ni2+, Zn-A-Ni was pyrolyzed to form Zn, Ni-co-doped carbon aerogel (Zn-CA-Ni), which has high potential for manufacturing electrodes in supercapacitors (specific capacitance reaches 124.0F/g) and crystal violet treatment (adsorption capacity reaches 38.7 mg/g). Furthermore, Zn-A and Zn-CA-Ni were characterized through modern methods: Scanning electron microscope, energy dispersive X-ray, Fourier-transform infrared spectroscopy, X-ray diffraction analysis, and Nitrogen adsorption–desorption isotherm. The ability to adsorb Ni2+ of Zn-A and adsorb crystal violet of Zn-CA-Ni was determined through ultraviolet–visible spectroscopy measurement. In addition, the electrochemical properties of Zn-CA-Ni were also analyzed through cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy.

Development and characterization of magnetic-based biodegradable periodic mesoporous organosilica nanoparticles for enhanced biomedical applications

Herein, magnetic-based biodegradable periodic mesoporous organosilica (BPMO) nanoparticles were successfully synthesized via a co-precipitation method to form a magnetic iron oxide (Fe3O4) core, followed by the condensation of organosilica precursors to produce BPMO shells. The physicochemical properties of the resulting hybrid nanoparticles were evaluated using powder X-ray diffraction, nitrogen adsorption–desorption isotherms, thermogravimetric analysis, Fourier transform infrared spectroscopy, and vibrating sample magnetometry. The synthesized particles exhibited a spherical morphology with an average diameter of approximately 250 nm. A core–shell structure was formed by depositing a 100-nm biodegradable organosilica layer onto the magnetic Fe3O4 cluster, endowing the nanoparticles with both magnetic and biodegradable mesoporous characteristics. Notably, despite the silica coating, the saturation magnetization remained high, reaching 35.8 emu/g, suggesting the potential for using these nanoparticles in magnetic-based biomedical applications. Furthermore, Fe3O4@BPMO nanoparticles were demonstrated to be efficiently uptaken by OVCAR8 ovarian cancer cells and spheroids, indicating that these nanoparticles are promising as magnetic nanocarriers for anti-cancer drug delivery and can be used in magnetic resonance imaging and magnetic hyperthermia.

Deciphering the influence of support in the performance of NiFe2O4 catalyst for the production of hydrogen fuel and nanocarbon by methane decomposition

Wet chemical synthesis route was used to synthesis nickel ferrite (NiFe2O4) nanoparticle. Later on the synthesized NiFe2O4 were supported on the surface of three traditional supports such as Al2O3, MgO and TiO2 to get NiFe2O4/Al2O3, NiFe2O4/TiO2 and NiFe2O4/MgO catalysts. The activity profile of each catalyst was evaluated in a fixed-bed reactor for direct methane decomposition at 800 °C. For both fresh and spent catalysts, many characterization techniques have been employed mainly XRD, FESEM, HRTEM, Raman spectroscopy, TGA, and nitrogen adsorption-desorption isotherm. X-ray powder diffraction studies revealed that all synthesized catalysts have a cubic spinel crystal structure. The XRD confirm the presence of NiFe2O4 particles in the component of fresh NiFe2O4/MgO, NiFe2O4/TiO2 and NiFe2O4/Al2O3 catalysts. Temperature Program Reduction (TPR) unveiled the presence of Ni oxides and Fe oxides by displaying reduction peaks in their respective temperature regions. The N2 adsorption-desorption isotherms of the fresh all catalysts reveal that these catalysts have a mesoporous structure. Activity data concluded NiFe2O4/MgO to be the most active catalysts among the tested catalysts methane conversion magnitude of 41.13 % and H2 formation rate of 84.40 × 10−5 mol H2 g−1 min−1. On the other hand, the H2 formation rate drastically declined and very poor activity of both NiFe2O4/TiO2 and NiFe2O4/Al2O3 catalysts was observed in the current work. XRD patterns, FESEM images and TGA analysis of spent NiFe2O4/MgO catalyst shown the filamentous carbon formation which secondarily confirm its higher activity, while its absence in catalysts of NiFe2O4/TiO2 and NiFe2O4/Al2O3. TGA analysis of the carbon deposited on the NiFe2O4/MgO catalyst showed that the amount of carbon was approximately 64 wt%. It was suggested that the formation of nickel-iron carbide revealed by XRD studies of spent catalysts may be the factor related to their poor activity while discussing the structure-activity relationship. Likewise, the higher degree of dispersion related to NiFe2O4/MgO as displayed by XRD, FESEM and TPR investigations, played a vital role in accelerating the rate of hydrogen formation.

In English

Fullerenes are interesting objects of research in view of their promising use as a nano-sized additive to coatings, films, adsorbents, as well as active components in medicine, pharmacy, cosmetology. This paper considers the possibility of modifying commercial adsorbents - silica gel and cation-exchanger based on activated carbon with available and inexpensive linear carbon radicals. Behentrimonium chloride (C22H45(CH3)3N+Cl-) and cetyl alcohol (C16H33OН) were chosen as the latter. The obtained adsorbents were compared with a commercial sample of silica gel modified with a linear hydrocarbon radical –C18Н37. The adsorbents were described by the methods of IR spectroscopy, thermogravimetry, the main characteristics of the porous structure were determined by the method of low-temperature adsorption-desorption of nitrogen. Modification of adsorbents based on silica gel leads to a decrease in the specific surface area to 202.4 and 236.5 m2/g and the total pore volume to 0.32 and 0.39 cm3/g, which is almost 2 half source material. Increasing the fraction of micropores contributes to better separation rates of large molecules. Treatment of cation-exchanger based on activated carbon by cation modifier leads to a significant decrease in the specific surface area, as well as to an increase in the size of pores with the predominant formation of mesopores. It is shown that the modification of silica gel is carried out both through silanol and siloxane groups, in contrast to the commercial sample of silica gel. The approximate number of modifier groups on the surface of the original SiO2 matrix was estimated, which is one modifier group ~ per 11 SiO2 molecules. To study the behavior of adsorption of C60, C70 fullerenes and their mixtures on adsorbents, column experiments were carried out with changes in the geometrical parameters of the column and the initial concentrations of the solutions. The results showed that the modified silica gels are potential adsorbents for the separation of a mixture of fullerenes with a ratio of 65/25. Silica gel modified with cetyl alcohol C16H33OH showed the best separation efficiency. By the help of an adsorbent, it is possible to separate C60 - 90.52 % from a less concentrated solution and 87.26 % from a more concentrated solution. To increase the purity of the product, it is necessary to pass the solution through the sorbent 2–3 times. The competitive capability of the proposed modified silica gels, together with economic efficiency, ease of modification, and the possibility of fullerene separation characterize the proposed adsorbents as potential materials for practical application. Due to the significantly lower cost and simpler manufacturing methods, the proposed adsorbents can be used for separation at a large scale.

Determination of quinolone antibiotics in surface water by MnFe2O4@TiO2 magnetic solid phase extraction-high performance liquid chromatography

The magnetic solid phase extraction material (MnFe2O4@TiO2) was prepared by coating TiO2 on MnFe2O4 through an in-situ formation method. The structure and properties of MnFe2O4@TiO2 were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), nitrogen adsorption–desorption experiment, and vibrating sample magnetometer (VSM). The conditions for magnetic solid phase extraction (MSPE) of quinolone antibiotics were optimized, and an MSPE-HPLC method was established to determine quinolone antibiotics in water samples. The optimal conditions for MSPE are MnFe2O4@TiO2 amount of 15 mg, extraction time of 15 min, 5 mL of methanol solution with 20 % ammonia as eluent, and elution time of 1 min. Under the optimal conditions, 50 mL 0.1 mg/L mixed standard solutions of fleroxacin, ofloxacin, norfloxacin, ciprofloxacin, and enrofloxacin have achieved enrichment multiples of 67.8, 72.1, 59.6, 55.8, and 60.7, respectively. The linear range of five antibiotics determined by MSPE-HPLC is 0.004–1 mg/L with the relative standard deviations (RSDs) of 2.1 %–4.9 % and the limits of detection (LODs) of 0.0006–0.0020 mg/L. The method is applied to the determination of the five antibiotics in rice paddy water and fish pond water; the recoveries range from 78.9 to 105.8 %, and the RSDs (n = 5) are 3.6 %–8.7 %.

High nitrogen-doped porous carbon material from porous aromatic framework; an approach to bi-functional Metal-free electrocatalyst

This study successfully synthesized nitrogen-doped porous carbon materials through pyrolysis of the azo-bridged calix[4]resorcinarene porous aromatic framework. This was the first time that N was introduced into porous carbon materials by using the azo group (N = N) as a nitrogen source. Nitrogen-doped porous carbon materials (N-C-x) were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and nitrogen adsorption–desorption isotherms. The efficiency of the fabricated electrocatalysts was assessed toward oxygen reduction reaction (ORR) in whole-range pH and oxygen evolution reaction (OER) in the base media. N-C-900 displayed outstanding activity among the prepared samples. In the ORR, the onset potential for N-C-900 was 0.99 V, 0.925 V, and 0.98 V vs. RHE in base, natural, and acidic electrolytes, respectively, which were close to commercial Pt/C in the same electrolyte. In OER, the optimal catalyst N-C-900 had an overpotential of 220 mV and a Tafel slope of 212 mV.dec-1, similar to RuO2.