Increase In Specific Surface Area Research Articles

CCCM SPECIFIC SURFACE ESTIMATION IN PROCESS OF LOW-TEMPERATURE OXIDATION

The low-temperature oxidation process of carbon-carbon composite materials (CCCM) with a pyrocarbon matrix has been examined. Oxidation at temperatures of 450 to 700 °C is characterized by internal burnout of the carbon phase without a noticeable change in the experimental samples external volume. Oxidation resistance analysis of CCCM structural components was performed. CCCM and carbon fibers specific surface area were estimated by the low-temperature adsorption of nitrogen and krypton using the Brunauer-Emmett-Teller model and the theory of density functional model. Pore size distribution was calculated by the semi-empirical Horvath-Kawazoe method. A significant increase (about 10-15 times) in specific surface area of the composite material, together with a rise in free volume ~5%, was accompanied by total weight loss of about 5%. Specific surface area changes occur as a result of anisotropic etching of carbon fibers surface with the formation of micropores with 0.5–2.0 nm diameter range. Although macropores are formed mainly due to the oxidation of thermosetting binder pyrolysis residue, they do not contribute to the specific surface increase but solely provide access to micropores. Microporosity evolution leads to an increase of structural discontinuity degree and, ultimately, to the loss of matrix-filler contact boundary. As a result, an overall weakening of material mechanical characteristics is to be noted. Thus, oxidative degradation is closely related to the increase in void space. A follow-up study is on-going. In fact, an open question remains, namely whether the oxidative process occurs differently in the micropores of diameter less than 2 nm and how it may contribute to the oxidative stress resistance behavior of CCCM.

Catalyst layer, method for producing the same, membrane electrode assembly and electrochemical cell

In this research, selective catalytic oxidation was applied to remove high-concentration hydrogen sulfide in landfill gas. The removal efficiency of H2S was the best with V/TiO2 catalyst produced by wet impregnation among. The optimum vanadium content was 10 %. In addition, selective conversion to elemental sulfur and generation of SO2 could be controlled by adjusting O2/H2S ratio. The larger the cell per square inch that affected the performance of the honeycomb-type catalyst, the greater the removal efficiency of H2S according to increase in specific surface area. An analysis of long-term performance of the honeycomb-type catalyst with landfill gas including CH4 and CO2 revealed that more than 90 % of H2S was removed. In addition, the performance of the catalyst could be recovered by thermal regeneration. Considering that the performance of a catalyst can be recovered for durability and regeneration, V/TiO2 coated honeycomb-type catalyst can be used in the actual process.

Preparation of hydrogen storage carbon materials using bio-oil heavy components as carbon-containing precursor

A new method for preparing carbon materials using bio-oil heavy components has been proposed and their hydrogen capacity at low temperature was explored. The effects of different templates and mass ratio of template to bio-oil on specific surface area, pore size distribution and yield of carbon materials were studied. The thermal decomposition pathway of calcium citrate was proposed. Carbon materials prepared by calcium citrate have larger specific surface area (1688 m2 g−1), more uniform pore size distribution and higher yield (17.76%). The specific surface area and the microporosity first increased and then decreased with increasing mass ratio of template to bio-oil, and reached the maximum value when the mass ratio was 1:1. The yield of carbon materials increased with increasing mass ratio. Hydrogen adsorption capacity (0.73–1.80 wt%) of carbon materials increased along with the increase of specific surface area and microporosity. Furthermore, the interaction between carbon and hydrogen molecules is strong, as shown by the isosteric heat of adsorption of between 6.13 and 10.56 kJ/mol. This paper provides an economical and environmental-friendly method for the preparation of hydrocarbon storage materials, and also a new idea for the utilization of bio-oil heavy components.

Thermal performance of a flat-plate solar collector using aqueous colloidal dispersions of graphene nanoplatelets with different specific surface areas

The effects of using aqueous nanofluids containing covalently functionalized graphene nanoplatelets with triethanolamine (TEA-GNPs) as novel working fluids on the thermal performance of a flat-plate solar collector (FPSC) have been investigated. Water-based nanofluids with weight concentrations of 0.025%, 0.05%, 0.075%, and 0.1% of TEA-GNPs with specific surface areas of 300, 500, and 750 m2/g were prepared. An experimental setup was designed and built and a simulation program using MATLAB was developed. Experimental tests were performed using inlet fluid temperatures of 30, 40, and 50 °C; flow rates of 0.6, 1.0, and 1.4 kg/min; and heat flux intensities of 600, 800, and 1000 W/m2. The FPSC’s efficiency increased as the flow rate and heat flux intensity increased, and decreased as inlet fluid temperature increased. When using nanofluids in the FPSC, the measured temperatures of absorber plate and tube wall decreased down to 3.35% and 3.51%, respectively, with the increase in weight concentration and specific surface area, while the efficiency increased up to 10.53% for 0.1- wt% TEA-GNPs nanofluid with specific surface area of 750 m2/g, in comparison with water. When using water as heat transfer fluid, very good agreement was obtained between the experimental and predicted values of absorber plate temperature, tube wall temperature, and collector’s efficiency with maximum differences of 3.02%, 3.19%, and 3.26%, respectively. While, when using nanofluids, higher differences were found, up to 4.74%, 4.7%, and 13.47% for TEA-GNPs nanofluid with specific surface area of 750 m2/g, respectively. Accordingly, the MATLAB code was capable of simulating the thermal performance of FPSCs utilizing nanofluids as their heat transfer fluids with acceptable accuracy. Values of performance index were all greater than 1, and increased as weight concentration increased up to 1.104 for 0.1- wt% TEA-GNPs nanofluid with specific surface area of 750 m2/g, implying higher positive effects on efficiency than negative effects on pressure drop. Accordingly, the investigated nanofluids can efficiently be used in FPSCs for enhanced energy efficiency, and the 0.1- wt% water-based TEA-GNPs nanofluid with specific surface area of 750 m2/g was comparatively the superior one.

Influence of agricultural organic inputs and their aging on the transport of ferrihydrite nanoparticles: From enhancement to inhibition

Organic matter effectively regulates nanoparticles transport. However, little is known about the effect of agricultural organic inputs on the transport of ferrihydrite nanoparticles (FHNPs) during aging. In this study, columns were filled with sand mixed with varying proportions of pristine, water-processing, or alkali-processing biochar or swine manure and used to simulate the release of organic matter and changes in surface roughness of sand grains during field aging. The influence of these factors on FHNPs transport was investigated using column experiments. The dissolved organic matter (DOM) (0.008–24.8 mg L−1) released from agricultural organic inputs decreased the zeta potential of the FHNPs from 30.8 mV to 14.6–-48.9 mV and further caused electrostatic repulsion, osmotic repulsion, and elastic-steric repulsion between FHNPs and mixed sand, thus enhancing FHNPs transport. Ferrihydrite nanoparticles transport increased with increasing content of biochar and swine manure due to the increased amount of DOM. However, with the presence of organic inputs, surface roughness up to a certain degree (the increase in specific surface area up to 4.6 m2) became the dominant inhibition factor affecting FHNPs transport. After DOM release, agricultural organic inputs decreased the enhancement of FHNPs transport; with the increase input, their rougher surface gradually increased inhibition of FHNPs transport. The strongest FHNPs retention in the alkali-processing biochar (0.2–10%) or swine manure (1–2%) mixed sand columns indicated that fully aged agricultural organic inputs strongly inhibited FHNPs transport. Our findings provided novel insights into the critical influence of agricultural organic inputs and their aging on FHNPs transport, which changed gradually from enhancement to inhibition gradually.

Modification of Bael fruit shell and its application towards Natural organic matter removal with special reference to predictive modeling and control of THMs in drinking water supplies

Abstract The study emphasized on evaluating the potential of acid-modified Bael fruit shell (AM-BFS) for Natural organic matter (NOM) removal following thermo-chemical treatment using ortho-phosphoric acid (H3PO4) and heating at 500 0C. Acid treated Bael fruit shell (BFS) resulted in an increase in both specific surface area (8 times) & external surface area (13 times) and resulted in 82% removal of NOM. FTIR analysis showed the presence of the O-H group, amide group (N-H), alkyl (C-H), and Nitrile group (C ≡ N) however no new bond formation occurred during the adsorption process resulting into intact structural stability of the adsorbent. The results of FTIR analysis were in line with Langmuir isotherm and indicated monolayer adsorption with a maximum adsorption capacity of 192 mg/g. Correlation matrix analysis revealed that pH, temperature, residual chlorine, TOC, DOC, and UV254 were the most influential parameters leading to high THM formation. A multi-linear regression (MLR) model was developed to determine the kinetics of the THMs formation. The higher value of the determination coefficient (R2-0.983), coupled with the Durbin-Watson value of 2.106, proves the statistical significance of the model and confirms its applicability with the least error of precision (-2.02% ± 3.813). Response surface methodology (RSM) also efficiently predicted and validated the experimental findings. Facile synthesis technique and easy availability of raw material make this adsorbent more promising and competitive than activated carbon and other natural adsorbents reported in the literature.

Chemical‐looping gasification of coal with CuFe2O4 oxygen carriers: The reaction characteristics and structural evolution

AbstractIn this study, coal gasification to produce synthesis gas by chemical looping was investigated with CuFe2O4 oxygen carriers (OCs), including the reaction characteristics and structural evolution process. It was found that the presence of a CuFe2O4 OC increases the gasification reaction rate of coal in comparison to the use of inert bed material (silica sand). The CuFe2O4 OC enhanced the performance of hematite and improved the ability to produce syngas of CuO OCs. During the chemical looping process, CuFe2O4 was reduced to Fe3O4 and Cu. Furthermore, N2 adsorption/desorption and scanning electron microscopy images verified that the released O2 and the generated CO2 by the CuFe2O4 OCs improved the carbon conversion and facilitated the pore opening and expansion shown by the increase in specific surface area. This can be used as a theoretical reference that can be used to gain a better understanding of the microscopic mechanism for how CuFe2O4 OCs can accelerate the chemical looping gasification of coal.

Application of microwave for promoting biooxidation of refractory high-sulphide concentrates: influencing factors analysis

ABSTRACTTo promote biooxidation efficiency of a refractory high-sulphide gold concentrate, microwave technology has been applied. Two factors were investigated in the microwave stage including initial solution pH and microwave irradiation time. The results show that biooxidation efficiency of the gold concentrate increases with the increasing initial solution pH. The effect of microwave irradiation on biooxidation efficiency becomes negligible after 300 s. The optimal experiment conditions were initial solution pH of 7.00 and microwave irradiation time of 300 s. Using the irradiated sulphide concentrate, the biooxidation period decreased and the biooxidation efficiency increased. After microwave irradiation, the mineral particle surface was destroyed and became bumpy. Microwave contributed to the decrease of mineral particle size and the increase of specific surface area. A mechanism model shows that the increasing mineral surface area caused by microwave irradiation leads to the enhancement of biooxidation efficiency.

Designing of Carbon Nitride Supported ZnCo2O4 Hybrid Electrode for High-Performance Energy Storage Applications

This study reports a unique graphitic-C3N4 supported ZnCo2O4 composite, synthesized through a facile hydrothermal method to enhance the electrochemical performance of the electrode. The g-C3N4@ZnCo2O4 hybrid composite based electrode exhibits a significant increase in specific surface area and maximum specific capacity of 157 mAhg−1 at 4 Ag−1. Moreover, g-C3N4@ZnCo2O4 electrode maintained significant capacity retention of 90% up to 2500 cycles. Utilizing this composite in the development of the symmetric device, g-C3N4@ZnCo2O4//g-C3N4@ZnCo2O4 displays a specific capacity of 121 mAhg−1. The device exhibits an energy density of 39 Whkg−1 with an equivalent power density of 1478 Wkg−1. A good cycling stability performance with an energy efficiency of 75% and capacity retention of 71% was observed up to 10,000 cycles. The superior performance of g-C3N4@ZnCo2O4 is attributed to the support of the g-C3N4 which increases the surface area, electroactive sites and provides chemical stability for electrochemical performance. The outstanding performance of this exclusive device symbolizes remarkable progress in the direction of high-performance energy storage applications.

Pore distribution characteristics of various rank coals matrix and their influences on gas adsorption

Methane is primarily stored in coal matrix pores and pore size distribution has an important effect on gas adsorption/desorption. Investigation of the relationship between pore size distribution and adsorption performance of coal is of significance for the understanding of the evolution of coalbed methane reservoirs. In this study, a series of laboratory experiments (nitrogen, carbon dioxide and methane adsorption) were carried out to determine the pore size distribution and adsorption capacity of coal samples of various coal ranks. The relationship between pore size distribution, Langmuir volume and the metamorphic degree of coals were established. The factors influencing methane adsorption of coals were also analyzed. The results show that the matrix pores are mainly cylindrical, thin bottleneck-, ink bottleneck- and parallel plate-shaped. With the increase in coal rank, both the total pore volume and the specific surface area initially decrease and then increase. Matrix pores, including micro-, transitional- and mesopores, show a similar asymmetric U-shaped trend in the pore volume and the specific surface area with an increase in coal rank. The percentages by volume and by specific surface area increase for the micropores and declines for the transitional pores and mesopores. In the low-pressure zone, micro- and transitional pores play a dominant role in methane adsorption; however, in the high-pressure zone, the influence of mesopores on methane adsorption is pronounced.

Advanced Mg, Zn, Sr, Si Multi-Substituted Hydroxyapatites for Bone Regeneration.

PurposeCompositional tailoring is gaining more attention in the development of advanced biomimetic nanomaterials. In this study, we aimed to prepare advanced multi-substituted hydroxyapatites (ms-HAPs), which show similarity with the inorganic phase of bones and might have therapeutic potential for bone regeneration.MaterialsNovel nano hydroxyapatites substituted simultaneously with divalent cations: Mg2+ (1.5%), Zn2+ (0.2%), Sr2+ (5% and 10%), and Si (0.2%) as orthosilicate (SiO44-) were designed and successfully synthesized for the first time.MethodsThe ms-HAPs were obtained via a wet-chemistry precipitation route without the use of surfactants, which is a safe and ecologically friendly method. The composition of synthesized materials was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The materials were characterized by X-ray powder diffraction (XRD), FT-IR and FT-Raman spectroscopy, BET measurements and by imaging techniques using high-resolution TEM (HR-TEM), FE-SEM coupled with EDX, and atomic force microscopy (AFM). The ion release was measured in water and in simulated body fluid (SBF).ResultsCharacterization methods confirmed the presence of the unique phase of pure stoichiometric HAP structure and high compositional purity of all synthesized nanomaterials. The doping elements influenced the crystallite size, the crystallinity, lattice parameters, morphology, particle size and shape, specific surface area, and porosity. Results showed a decrease in both nanoparticle size and crystallinity degree, coupled with an increase in specific surface area of these advanced ms-HAP materials, in comparison with pure stoichiometric HAP. The release of biologically important ions was confirmed in different liquid media, both in static and simulated dynamic conditions.ConclusionThe incorporation of the four substituting elements into the HAP structure is demonstrated. Synthesized nanostructured ms-HAP materials might inherit the in vivo effects of substituting functional elements and properties of hydroxyapatite for bone healing and regeneration. Results revealed a rational tailoring approach for the design of a next generation of bioactive ms-HAPs as promising candidates for bone regeneration.

Carbon foam composites based on expanded graphite for electrochemical application

Polymer composites containing modified graphite structures as fillers have been successfully processed exhibiting attractive features for different applications. Carbon foams derived from polymer precursor is brittle and the addition of some reinforcement to produce them is of great interest not only to improve their mechanical properties, but also to use them for multifunctional purposes. Considering the advantages provided by different modified graphite structures added to polymer composites, including low price, ease of dispersion, good thermal stability, electrical conductivity, and mechanical properties, expanded graphite (EG) was chosen as filler for the carbon foams processing to produce reticulated vitreous carbon (RVC) composites. Poly(furfuryl alcohol) was used as the carbon matrix precursor and different amounts of EG were dispersed in the resin to impregnate the polyurethane foam template. The RVC_EG composites were analyzed by scanning electron microscopy, Raman spectroscopy, X-ray diffraction, compression test, and cyclic voltammetry. EG presence on RVC_EG composites showed synergic effects contributing to their crystallinity, compressive strength, and charge transfer reactions improvement as well as their specific electrochemical surface area increase. Therefore, the effectiveness of the resulting carbon composite was mainly attributed to the good interaction between EG and carbon matrix.

Influences of Calcination Atmosphere on Nickel Catalyst Supported on Mesoporous Graphitic Carbon Nitride Thin Sheets for CO Methanation.

Nickel (Ni) catalysts supported on mesoporous graphitic carbon nitride (mpg-C3N4) were synthesized through simple impregnation method with air and nitrogen calcination atmosphere for CO methanation. The effects of pretreatment gas on catalyst structure, surface characteristics, and Ni species reducibility were investigated. Under air-calcination condition, the increase in specific surface area of the catalyst can be ascribed to the creation of mesopores and exfoliation of bulk mpg-C3N4 to form thin sheets. However, excessive Ni content on the catalyst accelerated the decomposition of the mpg-C3N4 support during calcination. The catalysts calcined in nitrogen showed lower surface area and fewer number of pores compared to air-treatment. The Ni/mpg-C3N4 catalyst calcined in air with Ni loading 10% exhibited enhanced medium-temperature activity for CO methanation with 79.7% CO conversion and 73.9% CH4 selectivity. This finding can be explained by the formation of mpg-C3N4 thin sheets, which increased the number of catalyst active sites. The CO methanation performance of Ni/mpg-C3N4 catalysts calcined in air was superior to those calcined in nitrogen. Interestingly, CO2 formed by water-gas shift reaction at 320 °C also contributed to the overall methane formation through CO2 methanation. Therefore, mpg-C3N4 thin sheets can be an interesting support for nickel catalyst for COx methanation.

Improved ethanol gas-sensing properties of optimum Fe–ZnO mesoporous nanoparticles

Fe-doped ZnO (Fe–ZnO) mesoporous nanoparticles have been synthesized via a facile hydrothermal method, which utilizes pluronic triblock copolymer polyethylene glycol–polypropylene glycol–polyethylene glycol (PEO-PPO-PEO) as the pore-forming agent. Fe–ZnO composites have an unique porous structure. Their pore sizes increase with Fe-doping concentration and reach a maximum as Fe concentration is 15 at.%; the specific surface area of synthesized mesoporous Fe–ZnO nanoparticles reaches a maximum as the Fe concentration is about 11 at.%. Electron microscopy, vapor pressure isotherm measurements and photoluminescence (PL) were used to characterize synthesized Fe–ZnO composites. Fe–ZnO-based gas sensors exhibit excellent response in detecting ethanol; the sensing response of Fe(11 at.%)–ZnO reaches 319.8, which is significantly higher than most of the ZnO-based gaseous sensors. The improved sensitivity is ascribed to the increase of oxygen-related defects and specific surface area of Fe–ZnO composites.

Natural Cellulose-Full-Hydrogels Bioinspired Electroactive Artificial Muscles: Highly Conductive Ionic Transportation Channels and Ultrafast Electromechanical Response

The design of smart full-hydrogel actuators constructed with natural carbohydrate polymers applied in biomedical and tissue engineering is very important but challenging. Herein, inspired by the efficient transportation of nerve impulses from human muscle, a very simple and natural enhancement strategy was proposed for the preparation of high-efficiency ion transportation channels and high-performance cellulose-all-hydrogel electroactive human-like muscles. Simulating the mechanisms that nerve excitation in human muscle are transmitted through, e.g., releasing ions into efficient channels, co-doped conductive nanoparticles of manganese dioxide (MnO2)/polyaniline/multi-walled carbon nanotubes (MWCNTs)/reduced graphene oxide (r-GOx) are applied to construct ionic electrolyte membrane (IEM) with superconductive ion channels based on a natural cellulose polymer as a skeleton template, and the obtained product demonstrated outstanding ion transportation efficiency, mechanical properties and electrochemical properties. Bioinspired artificial muscles prepared by IEM exhibit excellent actuation performance including superfast response speed, deflection displacement (16.284 mm), and output force (4.153 mN). These advantages are largely attributed to the superconductive ion channels formed by the codoping of conductive nanoparticles, and this anisotropic feature also contributes to the increase in porosity and specific surface area within the IEM. This study reveals that the bioinspired idea of developing efficient ion transportation channels provides an innovative inspiration for accelerating the actuation performance of artificial muscles.

Leaching Ni and Co from Saprolitic Laterite Ore by Employing Atmospheric Acid Leaching Solution with High Concentration of FeCl3 at Mild Conditions

Limonitic and saprolitic laterite ores are used to produce Ni by employing different kinds of processes. Acid leaching is an energy-saving process for pure Ni metal production. The high concentration of Fe in atmospheric acid leaching solution caused difficulties in metal-ions separation. In this work, saprolitic laterite ore was leached by atmospheric acid leaching solution of limonitic laterite ore at moderate temperatures. Conditions affecting the leaching of valuable metals and the conversion ratio of Fe were investigated. The results showed that optimal output was obtained after 1.5 h of leaching at 150°C with 1.0 liquid/solid ratio (volume/weight). X-ray diffraction analysis and mineral liberation analysis indicate that some nickel was adsorbed by leached residues, resulting in the loss of nickel. The physiochemical properties of leached residues could be changed due to the presence of Al and Cr. The decrease in zeta potential and the increase in specific surface area resulted in the increase of Ni adsorption.

Batch grinding studies by a ball mill for hematite ore

Most of the industrial operations need size reduction in some form or other. Compression, impact, attrition and cutting are the principle reduction. It is now an established fact that size of fineness by some grinding technique accounts for more than half of the total cost. In the present study hematite ore of hardness 5.5–6.5, specific gravity 5.26 has been subjected to grinding tests in a ball mill. The experiments were conducted at three feed sizes (i. e., −10 + 8 mm, −8 + 5.6 mm, −5.6 + 4.7 mm) and three ball sizes (i.e. 1 inch, ½ inch, ¼ inch). As the grinding time increases, specific surface and energy consumption per unit specific surface area also increases. As the specific surface area increases, energy consumption also increases. As the size of the ball increases specific surface area and energy consumption per unit specific surface area are also increased. Similarly, as the size of the ball decreases energy consumption also decreases uniformly for a particularly feed size. Energy consumption of feed decreased with quantity of feed. The new specific surface area generated also decreases with increase in feed quantity. Energy consumption per unit surface area of the feed is decreased with increase in feed quantity.

Microbial aging of hydrochar as a way to increase cadmium ion adsorption capacity: Process and mechanism

Microbially-aged hydrochar were prepared to investigate how aging affected their ability to remove Cd2+ from aqueous solutions. Based on aging time in an anaerobic fermenter, four samples were produced: HC, M20-HC, M40-HC, and M60-HC. Results indicated increases in specific surface area, pH, and negative charge on hydrochar surface with aging process. Also, there were a decrease in O/C and an increase in surface functional groups, such as –COOH. The adsorption experiments confirmed the positive correlation between aging time and adsorption performance. The 60-day-aged M60-HC treatment displayed the maximum adsorption capacity, which was 3.8 times higher than that of HC. The Langmuir and pseudo-second-order kinetic equations fitted well with isothermal and kinetic data, respectively. Thermodynamic study indicated that Cd2+ adsorption is dominated by chemisorption. This study showed that microbial aging process is an effective and promising measure to improve hydrochar adsorption capacity for Cd2+.

In English

Physical and mechanical properties of carbon nanotube (CNT) powders depend on the method of their synthesis and chemical refinement. In order to create new composite materials that contain CNT powders as a filler, it is necessary to achieve functionalization of powder surface. Functionalization of MWCNT-A brand CNT powder surface using pulse processing by high voltage electric discharges (HVED) in liquid leads to changes in distribution of its particles by size, a decrease in amorphous carbon content and in powder thermostability. Sedimentation separation of powder after HVED processing leads to formation of powder in three size ranges (0.118–0.139, 2.639–20.895 and 2.44–33.701 µm). Thermochemical modification of CNT powders leads to an increase in specific surface area, total volume of pores and micropores, their mean radii, a decrease in impurities content, changes in distribution of its particles by size, a decrease in amorphous carbon content and in powder thermostability. Electrochemical reconstruction of the surface of specimens of initial MWCNT-A brand CNT powder allows decreasing impurities content, free energy of surface saturation by water vapor, specific magnetic susceptibility, electrokinetic potential as well as increasing specific surface area, pores total volume and hydrogen adsorption. Consecutive application of these methods leads to a decrease in impurities content in MWCNT-A brand CNT powder and to changes of its physical and chemical characteristics. Mass share of impurities decreases 3.7 times, mass share of soluble impurities decreases 7 times, specific magnetic susceptibility increases 5.2 times, electrokinetic potential increases 7.8 times. Specific electric resistivity increases 1.3 times, which leads to changes of adsorption and structural characteristics of powder: specific surface area increases 1.4 times and free energy of surface saturation by water vapor decreases by 11.9 %, which means that surface becomes more hydrophobic. As a result of such changes, rate of hydrogen adsorption on powders surface increases by 46 % and the current density at the potential of –0.6 V increases by 50 %.

In English

The nanocomposites based on TiO 2 doped with sulfur (S/TiO 2 ), carbon (C/TiO 2 ), carbon and sulfur (S/C/TiO 2 ) have been obtained. The powders were characterized by XRD, XPS, BET, SEM, EDX, TEM and UV-VIS spectroscopy. EDX and XPS spectroscopies prove that titanium dioxide powder includes only Ti and O elements, composites C/TiO 2 include the elements Ti, O, C, composites S/TiO 2 - Ti, O, S and composites C/S/TiO 2 - Ti, O, C, and S. XRD analysis revealed phase of anatase in all composites, rutile phase appeared with increasing of sulfur amount in sulfur-containing powders. It has been found that composites consist of roundish agglomerates in the range of 5–30 mm. Sulfur additives decrease grain growth of titanium dioxide particles from 14 to 9–10 nm in S/TiO 2 composites, carbon leads to increase in particle size from 14 to 19 nm, simultaneous modification of titanium dioxide by carbon and sulfur leads to the formation of particles with sizes of 7–8 nm. Analysis of nitrogen sorption–desorption isotherms for all synthesized samples has shown the presence of a hysteresis loop which is the evidence for mesoporous structure of the powders. The isotherms correspond to type IV of IUPAC classification for mesoporous materials with H1 type for C/TiO 2 and H 2 type for S/TiO 2 , and C/S/TiO 2 of hysteresis loop. The modification of TiO 2 by carbon and sulfur leads to increase of specific surface area (of about 1.8 times in the case of C/TiO 2 , about 3.3 times for S/TiO 2 and about 4.7 times for C/S/TiO 2 ), average pore volume and decrease of radius pore volume compared with TiO 2 . Absorption spectra of nanocomposites showed a bathochromic shift as compared with the absorption band of pure TiO 2 . It has been found that modification leads to band gap narrowing. Nanocomposite samples showed higher photocatalytic activity in the destruction of safranine T under UV and visible irradiation compared to pure TiO 2 . It may be related to the participation of dopants in the inhibition of electron-hole recombination, prolongation of charges lifetime, increasing efficiency of interfacial charge separation and formation of doping electronic states.