Decrease In Specific Surface Area Research Articles

Gas adsorption characteristics changes in shale after supercritical CO2-water exposure at different pressures and temperatures

The supercritical CO2 (ScCO2)-water-shale interaction and its influence on adsorption characteristics of shale have significant impact on the estimation of the CO2 storage capacity. In this study, the influence of ScCO2-water exposure pressures and temperatures (P = 0, 10, 15, 20 MPa, T = 308, 323, 338, 353 K) on shale CH4 and CO2 adsorption characteristics were investigated. CH4 and CO2 adsorption tests, X-ray diffraction analysis, low-pressure N2 adsorption measurement were carried out on the shale samples before and after exposure. The results shown that after ScCO2-water exposure, the CH4 and CO2 adsorption capacity were decreased gradually with the increase of exposure pressure and the decrease of exposure temperature, due to the alterations of mineral composition and pore structure in shale. After ScCO2-water exposure, the contents of shale clay minerals, organic matter and carbonate were decreased, resulting in the decrease of specific surface area and micropore volume. With the increase of exposure pressure and the decrease of exposure temperature, the solubility and extraction ability of ScCO2-water were increased, then more significant mineral composition and pore structure alterations, as well as more significant changes on the gas adsorption capacities of shale were expected. The selectivity factor of CO2 to CH4 of shale shown a gradually decreased trend with the increase of exposure pressure and the decrease of exposure temperature, respectively, and were all greater than 1 for both the untreated and ScCO2-water treated shale samples at different exposure conditions, indicating that CO2 enhanced shale gas recovery and sequestration is feasible even after ScCO2-water exposure. To predict the CO2 storage capacity in shale gas reservoirs, the combined effects of exposure pressure and temperature on the adsorption characteristics of shale should be considered at the reservoir conditions.

Study on the infiltration mechanism of injecting chelating agent into deep low permeable coal seam

Coal seam water injection technology which provides a guarantee for coal mine safety production is significant for the prevention and control of coal mine disasters. The selection of additives is very important for the implementation of coal seam water injection technology. Although the research on additives has been extensive in recent years, the mechanism of additives which can increase the permeability of coal and change mechanical properties of coal is still unclear. After selecting the chelating agent as the water injection additive, we characterized the pore structure of coal by low temperature N2 adsorption, mercury injection, scanning electron microscopy, etc., and tested the strength of coal by uniaxial hydraulic testing machine, as a result, several interesting results were found. Firstly, the minerals in the coal seam will damage the permeability of the coal seam and impede the flow of water in the coal seam. Secondly, the chelating ligand can interact with minerals like calcite and dolomite. When the concentration of the chelating agent is 500 mg/L, Ca2+ can be detected in the immersion solution and the leaching concentration of Ca2+ is 43.76 times greater than that in the ultra-pure water immersion solution. The change of pH has a greater impact on the leaching concentration of Fe and Mg, while the change of solid–liquid ratio has a smaller impact on their leaching concentration. Thirdly, as the dissolution of minerals, the size and volume of pore in coal increase, specific surface area decrease, connectivity of pore become better, the permeability of coal increase by an average of 129%, which has a promoting effect on water injection. Fourthly, the existence of minerals will affect the mechanical strength of coal. The uniaxial compressive strength of coal decreases after the chelating ligands interacted with the coal and the pH of the solution and soaking time also obviously affect the strength of coal. These results are helpful to open up a new direction for the selection of water injection additives that can realize the green and safe mining of coal.

Investigation of pore evolution and variation with magma intrusion on Permian Gufeng shale formation and their implications on gas enrichment

Magmatism can significantly alter the pore structure of shale formation due to the thermal and pressure effects, thus the gas enrichment mechanism is naturally affected. The uncertainty of shale gas development has been raised in the petrogeology community due to the magma intrusion. This study investigates pore evolution, pore alteration, and gas enrichment of gas shale in the Permian Gufeng Formation (Fm.) in the Lower Yangtze, Liqiao district. In this work, multiple techniques were used for shale characterization including total organic carbon (TOC) content quantification, reflectivity microscope tests, X-ray diffraction, high-pressure mercury injection, low-pressure nitrogen adsorption, and carbon dioxide adsorption measurements. The results show that the closer the shale approaches the intrusion, the higher the vitrinite reflectance (Ro) and quartz content, the lower the TOC and clay mineral content, and metamorphic minerals for instance augite and anatase appear in the affected shale formation. As shale is closer to the intrusion, the type of pores changes from small pores (10～100 nm) to super-large pores (1000～100,000 nm), and the super-small pores (6～10 nm) almost disappeared. In addition, a decrease in the fractal dimension of the pores was observed indicating that the heterogeneity and complexity of the pore structure are reduced. Within the contact metamorphism halo, the maximum adsorption capacity, pore volume, and specific surface area decrease with increasing proximity to the intrusion, which reduces the potential for shale gas enrichment. In basin-scale, a huge contact metamorphic range and plugging effect of the intrusion in sill intrusion generate enormous amounts of hydrocarbon and block the escape of the shale gas. Due to these factors, the intrusion can be conducive for shale gas enrichment. However, the dike that penetrates the shale reservoir is not conductive to shale gas enrichment because the fracture channels created in the contact metamorphism halo accelerate the escape of the shale gas. This study proposed critical theories of shale gas enrichment and could increase the success rate of shale gas exploration.

Pozzolanic and Cementing Activity of Raw and Pyro-Processed Saudi Arabian Red Mud (RM) Waste

This paper investigates the composition, properties and reactivity of a red mud waste generated in Saudi Arabia with a view to find alternative materials to replace construction binders of high environmental impact. The phase transformation triggered by the sintering of the RM up to 1000°C is determined with thermal and X-Ray Diffraction analyses. Reactivity is investigated with chemical and physical methods including the Chapelle test, setting times, mechanical index and microscopy. The RM is clearly pozzolanic, and its activity is mainly due to the reaction of feldespathoids and the formation of zeolitic and feldspathoid-based hydrates. The positive effects of the thermal treatment are seen below 750°C, and include the loss of water in the zeolite/feldespathoids, and the destruction of the crystal structures of the clay minerals inherited form the parent bauxite. The negative effects of the thermal treatment are evidenced over 750°C, with a decrease in specific surface area, devitrification and crystal formation, whereby the active transition aluminas and the fedespathoids/zeolites (mainly cancrinite) transform into nepheline, tricalcium aluminate (C3A) and gehlenite. Despite the occurrence of nepheline, C3A and gehlenite in the RM sintered at 1000°C, the formation of pozzolanic hydrates that cause setting and strength development are greater at lower temperature. The optimum thermal treatment that enhances pozzolanic activity lies at c.400°C, as evidenced by the highest lime combination, the greatest mechanical index and the fastest set. The RM consists of gibbsite and boehmite, inherited from the bauxite, and cancrinite, chantalite and sodalite formed during the Bayer process. Feldespathoids have formed, instead of zeolites, due to the available silica and the high alkali content of the RM. The quick lime -CaO -, added twice during the refining process, has transformed the original goethite into hematite, and produced cancrinite. The Saudi RM has high SiO2 and high alkalinity, and an abundant specific surface area available for reaction. The chloride and carbon contents are low, and no environmental toxicity is inferred from its chemistry.

Construction of molecular structure model of Tunlan coal and its microscopic physicochemical mechanism

Physicochemical structure is essential for understanding physiochemical properties of coal reservoir and coalbed methane (CBM) occurrence. In this work, ultimate analysis, 13C nuclear magnetic resonance spectra (NMR), Fourier transform infrared spectroscopy (FTIR) and gas chromatograph/mass spectrometer (GC/MS) tests were adopt to investigate the coal molecular structure information. Then, by means of molecular simulation, stable three-dimensional (3D) molecular structure and physicochemical structure models of Tunlan coal were established to reveal the physicochemical response at a molecular level. Results show that compared with the single molecular structure, angle and torsion energies in nanopore structure play a more important role in maintaining a stable and stereoscopic structure. While the electrostatic energy in non-bond energy can simulate to form nanopore space in coal. Then, with the dissolution of low molecular weight compounds (LMWCs), the pore volume (PV) of micropores increases gradually, while the corresponding specific surface area (SSA) decreases first and then increases, suggesting that pore expansion and pore increase effects are dominant in the early and the later dissolution stages, respectively. Furthermore, observing physicochemical response, total pore structure distribution depends on whether vertical or horizontal changes of basic structure units in coal make a great contribution in this evolution stage. Actually, when the aromatic layer is mainly the increase of the stacking height Lc, it is easy to result in the decrease of total SSA and PV. In contrast, for mainly the increase of the diameter La, all pores in coal present an increase characteristic to induce the increase of total SSA and PV.

Influence of ionomer on the durability of Pt/C catalyst

Ionomer is an important part of the catalytic layer in proton exchange membrane fuel cell. Its main role is to conduct protons. We investigated the effect of ionomer on the durability of Pt/C catalyst using rotating disk electrode (RDE) under two modes: the real operating conditions (mode 1) and startup/shutdown conditions (mode 2). The structural changes of Pt/C catalyst after the durability test were analyzed by identical location transmission electron microscopy (IL-TEM). Results show that the addition of ionomer improved the durability of Pt/C catalysts. After the durability test of mode 1, the addition of ionomer reduced the change of half-wave potential (∆E1/2) of oxygen reduction reaction from 23 to 11 mV, which is attributed to the growth of Pt particles rather than carbon corrosion. Ionomer delayed the decrease of electrochemical specific surface area (ECSA) of Pt/C catalyst, which is beneficial to the maintenance of Pt activity. After the durability test of mode 2, in addition to the growth of platinum particles, carbon corrosion occurred in the catalyst layer, and the growth of platinum particles was mainly due to carbon corrosion. The addition of ionomer reduced the ∆E1/2 of oxygen reduction reaction from 25 to 5 mV. Furthermore, the growth of platinum particles and carbon corrosion can be clearly seen by IL-TEM, and the corrosion of the carbon support resulted in the loss and agglomeration of platinum. The average particle size of platinum in Nafion-containing catalyst increased from 2.7 to 3.76 nm, while that of Nafion-free catalyst increased from 2.44 nm to 4.19 nm.

Multi-fractal characteristics of pore structure for coal during the refined upgrading degassing temperatures

The low-temperature nitrogen adsorption measurement is commonly used to describe the pore structure of porous medium, while the role of degassing temperature in the low-temperature nitrogen adsorption measurement does not attract enough attention, various degassing temperatures may lead to the different pore structure characterization for the same coal. In this study, the low-rank coal collected from Binchang mining area, southwest of Ordos Basin was launched the low-temperature nitrogen adsorption measurement under seven various degassing temperatures (120 °C, 150 °C, 180 °C, 210 °C, 240 °C, 270 °C and 300 °C), respectively, the dynamic change of the pore structure under refined upgrading degassing temperatures are studied, and it was also quantitative evaluated with the multi-fractal theory. The results show that the pore specific surface area and pore volume decrease linearly with the increased degassing temperatures, ranges from 12.53 to 2.16 m2/g and 0.01539 to 0.00535 cm3/g, respectively. While the average pore aperture features the contrary characteristics (various from 4.9151 to 9.9159 nm), indicating the pore structure has been changed during the refined upgrading degassing temperatures. With the upgrading degassing temperatures, the sizes of hysteresis loop decrease, and the connectivity of pore structure enhanced. The multi-fractal dimension and multi-fractal spectrum could better present the partial abnormal of pore structure during the refined upgrading degassing temperatures, and the quality index, Dq spectrum, D−10–D10 and multi-fractal spectrum could describe the homogeneity and connectivity of the pores finely. The degassing temperatures of 150 °C, 180 °C and 270 °C are selected as three knee points, which can reflect the partial abnormal of the pore structure during the refined upgrading degassing temperatures. Under the lower degassing temperature (< 150 °C), the homogeneity and connectivity of the pore feature a certain increase, following that it presents stable when the degassing temperatures various from 150 to 180 °C. The homogeneity and connectivity of the pore would further enhanced until the degassing temperature reaches to 270 °C. Because of the melting of the pore when the degassing temperature exceeds 270 °C, the complexity of pore structure increased. In this study, we advise the degassing temperature for low-temperature nitrogen adsorption measurement of low-rank coal should not exceed 120 °C.

Effect of flue gas components on the NO removal and element mercury oxidation performance of Mn-modified low-temperature catalyst

Abstract The development of a low-temperature water and sulfur-resistant catalyst with high efficiency of NO removal and element mercury Hg(0) oxidation performance is one of the main directions for the synergistic removal of multiple pollutants from flue gas. The transition metal Mn is used to modify the V-W/Ti catalyst to prepare a modified Mn-SCR catalyst. The effects of Mn loading and complex flue gas components (SO2, H2O and HCl) on the modified catalysts activity were investigated on a small fixed-bed experimental bench, respectively. As the Mn loading increases, the acid sites on the catalyst surface are significantly enhanced, the window of NO removal temperature is significantly widened, and the Hg(0) oxidation performance is nearly 100%. The optimal loading amount of Mn is 0.2(Mn/Ti, mol). When the Mn loading exceeds 0.2, the particles on the catalyst surface sinter, and the specific surface area decreases. However, little difference is observed in catalyst activity. When SO2 and H2O are present in the flue gas, dual-action catalyst activity can be significantly suppressed, but the effect of H2O on catalyst activity is greater than that of SO2. With the increase of the HCl concentration from 0 ppm to 50 ppm, the oxidation efficiency of Hg(0) and the removal efficiency of NO increased slightly.

Pore Structure Characteristics and Evolution Law of Different-Rank Coal Samples

In this study, the full-size pore structure characteristics of six different-rank coal samples were investigated and analyzed from three perspectives, namely, pore shape, pore volume, and pore specific surface area, by performing a high-pressure mercury injection experiment and a low-temperature nitrogen adsorption experiment. Next, the full-size pore volumes and pore specific surface areas of the six coal samples were accurately characterized through a combination of the two experiments. Furthermore, the relationships between volatile matter content and pore volume and between volatile matter content and pore specific surface area were fitted and analyzed. Finally, the influences of metamorphic degree on pore structure were discussed. The following conclusions were obtained. The pore shapes of different-rank coal samples differ significantly. With the increase of metamorphic degree, the full-size pore volume and pore specific surface area both decrease first and then increase. Among the pores with various sizes, micropores are the largest contributor to the full-size pore volume and pore specific surface area. The fitting curves between volatile matter content and pore volume and between volatile matter content and pore specific surface area can well reflect the influence and control of metamorphic degree on pore volume and pore specific surface area, respectively. With the increase of volatile matter content, the pore volume and the pore specific surface area both vary in a trend resembling a reverse parabola.

Amino-functionalized UiO-66 as a Novel Adsorbent for Removal of Perfluorooctane Sulfonate from Aqueous Solution

Perfluorinated compounds are a class of emerging organic water contaminants that pose risk to human health and the natural environment. Perfluorooctane sulfonate (PFOS) is the most extensively used perfluorinated compound worldwide owing to its applications in various fields. In this study, UiO-66 and UiO-66-NH2 were synthesized via a solvothermal method that uses hydrochloric acid. These were evaluated as potential adsorbents to remove PFOS from an aqueous solution. UiO-66-NH2 showed the highest adsorption capacity because its affinity for PFOS anions in water is improved despite the decrease in specific surface area caused by the introduction of amino groups. Previous studies have reported that a UiO-66 type framework is an effective PFOS adsorbent. This study presents a novel approach to enhance its adsorption performance by amino group modification.

Heating temperature effect on the hygroscopicity of expanded vermiculite

The hygroscopicity of expanded vermiculite is one of major influence factors for thermal insulating performance. To explore the water absorption properties of expanded vermiculite prepared via electrical heating method, heating temperature effect on the hygroscopicity of expanded vermiculite was investigated under various humidity circumstances. The influencing mechanisms were analyzed by means of Thermogravimetric Analysis-Differential Scanning Calorimeter technique (TG-DSC), Fourier-Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), and the Brunauer–Emmett–Teller technique (BET) for the measurement of the specific surface area. The results of water absorption experiments indicated that the hygroscopicity of vermiculite showed an inversely proportional relationship to heating temperature and the water absorption content of EV-900 was only 6.206 mg/g with a dramatic decline of 91.5% in comparison with that of RV. This decline of water absorption capacity was mainly attributed to the decrease of interlamellar spacing and specific surface area. In addition, environment humidity had a significant effect on water absorption capacity and velocity. The water absorption content of EV-400 sample increased dramatically from 48.414 mg/g at the humidity of 55%–72.929 mg/g at the humidity of 95%, and the equilibrium time reduced from 3 h to 0.5 h. This study will provide a new perspective and theoretical guidance for the development of vermiculite based thermal insulating materials.

Syngas Production via CO2 Reforming of Methane over SrNiO3 and CeNiO3 Perovskites

The development of a transition-metal-based catalyst with concomitant high activity and stability due to its distinguishing characteristics, yielding an abundance of active sites, is considered to be the bottleneck for the dry reforming of methane (DRM). This work presents the catalytic activity and durability of SrNiO3 and CeNiO3 perovskites for syngas production via DRM. CeNiO3 exhibits a higher specific surface area, pore volume, number of reducible species, and nickel dispersion when compared to SrNiO3. The catalytic activity results demonstrate higher CH4 (54.3%) and CO2 (64.8%) conversions for CeNiO3, compared to 22% (CH4 conversion) and 34.7% (CO2 conversion) for SrNiO3. The decrease in catalytic activity after replacing cerium with strontium is attributed to a decrease in specific surface area and pore volume, and nickel active sites covered with strontium carbonate. The stability results reveal the deactivation of both the catalysts (SrNiO3 and CeNiO3) but SrNiO3 showed more deactivation than CeNiO3, as demonstrated by deactivation factors. The catalyst deactivation is mainly attributed to carbon deposition and these findings are verified by characterizing the spent catalysts.

Recent advances on ZIF-8 composites for adsorption and photocatalytic wastewater pollutant removal: Fabrication, applications and perspective

• Summarize the modification and functionalization of single ZIF-8 particles. • Assess the prospects of ZIF-8 composite in adsorption and photocatalytic. • Explain the mechanism of ZIF-8 composites in treating wastewater pollutants. • Role of the synthetic parameters in the performance of ZIF-8 composites. • Provide theoretical foundation and novel ideas for studies on MOF-based materials. Zeolitic imidazolate framework-8 (ZIF-8), which consists of metal atom Zn and 2-methylimidazole, is a kind of typical MOF materials. The unique properties of ZIF-8 endue it superior adsorption capacity and good host ability for photocatalytic materials, which makes it be a high-profile material in the treatment of wastewater. However, ZIF-8 particles tent to aggregate together and result in the decrease of specific surface area. They also suffer from weak recyclability, as it is hard to separate them from water after removing pollutant. The newly emerging ZIF-8 composite materials solve the above problems, and are successfully applied in wastewater treatment. In this review, the current design and synthesis methods of ZIF-8 composites are systematically summarized. The recent research progress of ZIF-8 composites as adsorbents and photocatalysts to remove wastewater pollutants is critically introduced. Different factors affecting its efficiency and the mechanism of pollutant removal are also discussed. This review attempts to lay the mechanistic insight for the application of ZIF-8 composite in practical wastewater treatment and provides new ideas for constructing high-efficient ZIF-8 based adsorbent and photocatalyst. For the purpose of revealing the whole potentiality of ZIF-8 composite in pollutants removal and water regeneration, current challenges are introduced and future research directions are proposed at last.

A Study on the Effect of Different Ball Milling Methods on the NH3-SCR Activity of Aluminum-Laden Bayan Obo Tailings

Rich in Fe, Ce, Mn, Si and other elements which have good catalytic activity, Bayan Obo rare-earth tailings are naturally advantaged as the carrier of denitrification catalysts. In this paper, pseudo boehmite (γ-Al2O3) was mixed with Bayan Obo tailings using different ball milling methods for modification to prepare NH3-SCR catalysts. The effect of different mixing methods on the SCR denitrification activity at a low temperature was investigated and the prepared catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), temperature programed desorption (NH3-TPD), temperature programed reduction (H2-TPR) and other means. The conversion rate of NOx at 250–350 °C was above 80% and the highest conversion rate of NOx of 90% was achieved at 300 °C. SEM and XRD revealed that the tailings modified by pseudo boehmite (γ-Al2O3) using the ordinary ball milling method have loose structure and good dispersion of active substances, and specific surface area (BET) analysis shows that the tailings have the maximum specific surface area and pore volume. However, over grinding and secondary spheronization were observed in the tailings modified by pseudo boehmite (γ-Al2O3) using high energy ball milling method, leading to the decrease of specific surface area and pore volume, poor dispersion of active substances, and ultimately low denitrification rate.

Controlling the Sorption Activity of Clinoptilolites with Mechanical Activation

We have studied the effect of the phase composition of clinoptilolite rocks and the specific mechanical energy delivered to samples in a vibratory attritor on their physical properties and oil sorption capacity. Mechanical activation in air has been shown to cause amorphization, transformation of “zeolitic” water into “hydroxyl” water, and an electron density redistribution in the Al–O–Si framework of the clinoptilolite. Milling to a specific mechanical energy of 2.16 kJ/g leads to the formation of molecularly dense aggregates, which shows up as a decrease in specific surface area, demonstrated by BET measurements. An optimal approach for raising oil sorption capacity is mechanical activation of clinoptilolite–stilbite rock in air to a specific mechanical energy of 5.04 kJ/g.

Numerical Study of Flow and Heat Transfer in a Rectangular Channel Partially Filled with Porous Media at the Pore Scale Using Lattice Boltzmann Method

This work numerically presents the study of flow and heat transfer in a rectangular channel partially filled with porous media at the pore scale using lattice Boltzmann method. Quartet structure generation set is adopted to generate the structure of porous media. The effects of the relative height, porosity and specific surface area of porous media on the fluid flow and the Nusselt number are investigated in detail. The simulation results indicate that there exists a relative height of porous media where the Nusselt number and average dimensionless velocity are both up to their maximums; dimensionless velocity and Nusselt number slightly increase with the increment of porosity at small specific surface area, but have no significant change at large specific surface area; the increase rates of dimensionless velocity and Nusselt number with the increment of specific surface area decrease as porosity decreases. Based on the simulation results, correlations of Nusselt number with the fluid flow in the zone adjacent to porous media and the characteristic of porous media are established.

Effect of calcite on desulfurization and denitration performance of activated coke and its mechanism

Different contents of calcite (CaCO3) were loaded ondeminerized Ningxia anthracite during the activated coke (AC) preparation, the influence of which on the preparation, desulfurization and/or denitrification of AC was investigated. The results show thatcalcite could regulate the pore structure and surface chemistry of AC. The total specific surface area and the micropore specific surface area decrease from 746 m2/g and 645 m2/g to 408 m2/g and 244 m2/g, respectively, when the calciteaddition was up to 8%. The total volume and the micropore volume alsodecrease with calcite addition, while the volume of mesopores and macropores increases. As the calcite addition rises, the oxygen-containing functional group and π–π* are increased linearly, and the sulfur capacity of AC first increases and then decreases during single desulfurization, the NX-2%CaCO3-AC having the best desulfurization capacity (84.0 mg /g). The increase in the content of π–π* by the addition of calcite promotes the SO2 oxidation process, and also promotes the denitrification process, the NO conversion (16.9%) with the addition of 2%CaCO3 is 1.14 times higher than that of AC (7.9%), mainly owing to the increase in the number of basic groups. However, during simultaneous desulfurization and denitrification, the presence of CaO in the AC promotes the sulfur capacity but decreases the NO removal efficiency due to the competitive adsorption and ammonium salt generation.

Hydrothermal liquefaction (HTL) processing of unhydrolyzed solids (UHS) for hydrochar and its use for asymmetric supercapacitors with mixed (Mn,Ti)-Perovskite oxides

In this study, the unhydrolyzed solid (UHS) derived from corn stover was hydrothermally processed to generate heavy bio-oil (HBO) and hydrochar. In particular, hydrothermal liquefaction (HTL) was carried out in a 300 mL high temperature and high pressure reactor with the slurry of UHS in de-ionized (DI) water, and the effect of reaction temperature, initial nitrogen pressure, reaction time, and UHS to solvent ratio on hydrochar generation was investigated. HTL processed slurries were filtered to recover the solid residue, which was extracted with acetone to recover heavy bio-oil (HBO). The solid residue was thermally treated further at 400 °C to produce hydrochar, which was thoroughly characterized by BET, SEM/EDX, FTIR and Raman spectroscopy. Results indicated that as temperature of HTL process increased from 250 to 300 °C, hydrochar yield decreased. Increase in HTL temperature also resulted in decrease in BET specific surface area (SSA) and pore volume; however, increase in pore diameter. HTL parameters such as initial N2 pressure, reaction time, and UHS:water ratio was found to influence the yield, BET SSA, pore volume and pore diameter. SEM images showed porous structure whereas surface functional groups with O-H, >CC< and C–H stretching vibrations were observed with FTIR spectroscopy. Fully characterized hydrochar obtained under different HTL processing conditions was used with sol-gel synthesized (Mn,Ti)-oxide electrode and aqueous KOH electrolyte to fabricate asymmetric supercapacitors (ASC), which were tested with cyclic voltammetry to determine specific capacitance. A maximum specific capacitance was observed for the hydrochar electrode materials obtained at the HTL processing conditions of 275 °C temperature, 1 h reaction time, and UHS:water ratios of 1:30 and 1:10 with initial nitrogen pressure of 100 psig and 150 psig, respectively.

Tuning the sound frequency in the audible region during the synthesis of the precursor TiO2: Evaluation of the sound effect on the structure and photoactivity relationship

Due to their low efficiency, photocatalytic processes do not meet the requirements of commercial applicability, requiring new approaches in adjusting structural and electronic properties. Studies have been conducted in the development of the sonocatalysis technique where materials with better activity and stronger structure are observed. Although TiO2 can be easily prepared by traditional and relatively simple methods, it tends to crystallize in temperatures ranging from 673 K to 873 K. In general, this methodology promotes high shrinkage or collapse of the mesostructure and is eventually followed by an increase in nanoparticle size and a decrease in specific surface area. To obtain a non-agglomerated TiO2 crystal sample with good photocatalytic properties, we studied the audible sound frequency during the synthesis of the TiO2 precursor. All the TiO2 samples were prepared using a coprecipitation method and sonocatalysis, with some samples of TiO2 being impregnated with 10% nickel. The catalysts were prepared by keeping important variables constant during all synthesis and tuning the sound frequency on audible frequency. All the samples were synthetized in a “Synthesis Chamber” used for coprecipitation method preparations. The samples were characterized by TGA, XRD, SEM, EDX, and PTR. The photocatalysts were tested in photodegradation of the methylene blue dye under the UV-VIS light region. The influence of the chemical composition and the audible sound frequency application during the synthesis of the TiO2 precursor was evaluated establishing a relationship between the structure and photoactivity. The results suggest that sound waves applied during sample preparation have provided a good degree of crystallinity to the material, which could influence the crystallite size and the photocatalytic activity of the samples. Therefore, the audible sound associated with the “Synthesis Chamber” should be used as a tool to prepare and adjust the structural and electronic properties of the photocatalysts to promote TiO2 photoactivity.

Temporal post-discharge reactions effect on the oxidative catalytic properties of plasma-synthesized α-MnO2 nanorods

The evolution of the morphology, crystalline structure, and textural properties of α-MnO2 nanorods, which were obtained after reduction of a KMnO4 solution via gliding arc plasma process, have been followed along their ageing under temporal post-discharge conditions. When aged at 25 °C a partial transformation of α-MnO2 (cryptomelane) to γ-MnO2 (nsutite) occurred with an increase of specific surface area from 98 to 141 m2/g. In parallel, the starting nanorods were converted to nanoneedles after 24 and 48 h, and into nanosheets after 72 h. These transformations are ascribed to the evolution of maturation process of crystallites, thanks to post-discharge species (H2O2, HOONO,…). At the opposite, ageing at 100 °C induced a remarkable transformation of α-MnO2 to γ-MnO2 with a decrease of specific surface area from 98 to 35 m2/g after 3 h, which was in line with the observed agglomeration of nanorods. Finally, whereas a longer ageing at 100 °C provoked an activity diminution of the material, an augmentation of activity of plasma-synthesized α-MnO2 was recorded when implementing ageing at 25 °C.