Showing papers on "BET theory published in 2019"

High-performance bifunctional oxygen electrocatalysts for zinc-air batteries over mesoporous Fe/Co-N-C nanofibers with embedding FeCo alloy nanoparticles

Abstract: Mesoporous Fe/Co-N-C nanofibers with embedding FeCo nanoparticles (denote as FeCo@MNC) have been prepared from electrospun Fe/Co-N coordination compounds with bicomponent polymers consisting of polyvinylpyrrolidone (PVP) and polyacrylonitrile (PAN). The as-fabricated hybrid nanofibers exhibited one-dimensional mesoporous morphology, a large BET surface area and uniformly distributed active sites (e.g FeCo alloy, Fe/Co-N). It elucidated that the co-existence of FeCo alloy and Fe/Co-N active sites could promote the catalytic activity of ORR and OER simultaneously. Essentially, the unique one-dimensional of nanofiber with observable porous morphology has indispensable contribution to charge transportation and exposure of active sites to O2 adsorption when assembled into a rechargeable zinc-air battery. As a result, FeCo@MNC exhibited a low discharge-charge voltage gap (e.g. 0.9 V, discharge-charge at 20 mA cm−2), higher power density (e.g. 115 mW cm−2, at 143 mA cm−2) and stability.

Controlled Hydrolysis of Metal-Organic Frameworks: Hierarchical Ni/Co-Layered Double Hydroxide Microspheres for High-Performance Supercapacitors.

Abstract: Pseudomorphic conversion of metal-organic frameworks (MOFs) enables the fabrication of nanomaterials with well-defined porosities and morphologies for enhanced performances. However, the commonly reported calcination strategy usually requires high temperature to pyrolyze MOF particles and often results in uncontrolled growth of nanomaterials. Herein, we report the controlled alkaline hydrolysis of MOFs to produce layered double hydroxide (LDH) while maintaining the porosity and morphology of MOF particles. The preformed trinuclear M3(μ3-OH) (M = Ni2+ and Co2+) clusters in MOFs were demonstrated to be critical for the pseudomorphic transformation process. An isotopic tracing experiment revealed that the 18O-labeled M3(μ3-18OH) participated in the structural assembly of LDH, which avoided the leaching of metal cations and the subsequent uncontrolled growth of hydroxides. The resulting LDHs maintain the spherical morphology of MOF templates and possess a hierarchical porous structure with high surface area (BET surface area up to 201 m2·g-1), which is suitable for supercapacitor applications. As supercapacitor electrodes, the optimized LDH with the Ni:Co molar ratio of 7:3 shows a high specific capacitance (1652 F·g-1 at 1 A·g-1) and decent cycling performance, retaining almost 100% after 2000 cycles. Furthermore, the hydrolysis method allows the recycling of organic ligands and large-scale synthesis of LDH materials.

Phenol adsorption on high microporous activated carbons prepared from oily sludge: equilibrium, kinetic and thermodynamic studies

Abstract: The purpose of this study was the preparation, characterization and application of high-performance activated carbons (ACs) derived from oily sludge through chemical activation by KOH. The produced ACs were characterized using iodine number, N2 adsorption-desorption, Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The activated carbon prepared under optimum conditions showed a predominantly microporous structure with a BET surface area of 2263 m2 g−1, a total pore volume of 1.37 cm3 g−1 and a micro pore volume of 1.004 cm3 g−1. The kinetics and equilibrium adsorption data of phenol fitted well to the pseudo second order model (R2 = 0.99) and Freundlich isotherm (R2 = 0.99), respectively. The maximum adsorption capacity based on the Langmuir model (434 mg g−1) with a relatively fast adsorption rate (equilibrium time of 30 min) was achieved under an optimum pH value of 6.0. Thermodynamic parameters were negative and showed that adsorption of phenol onto the activated carbon was feasible, spontaneous and exothermic. Desorption of phenol from the adsorbent using 0.1 M NaOH was about 87.8% in the first adsorption/desorption cycle and did not decrease significantly after three cycles. Overall, the synthesized activated carbon from oily sludge could be a promising adsorbent for the removal of phenol from polluted water.

Gelatin/alginate composite nanofiber membranes for effective and even adsorption of cationic dyes

Abstract: Nanofiber membranes from natural alginate are ideal adsorption materials for removing cationic dyes in solution, yet the regulations to their adsorption and desorption properties are of great challenges. In this research, gelatin/calcium alginate (GA) composite nanofiber membranes were successfully prepared via electrospinning to resolve these issues. The structural changes of composite membranes induced by the gelatin addition were confirmed by SEM, FT-IR and BET analysis. The enhanced mechanical strength of GA membranes disclosed the strong interactions between gelatin and alginate chains. Taking methylene blue (MB) as the model cationic dye, it was found the resultant composites could slow down the adsorption rate and obviously improve the adsorption evenness without apparent influences on its adsorption capacity. Moreover, the gelatin modification would generate better reusability for the composite membranes during a serial of adsorption and desorption cycles for strong electrostatic repulsions induced by protonated amino groups in gelatin chains. This effective composite strategy would pave the way for the development of natural alginate to the next generation high-performance adsorbent for cationic dyes.

Chemically activated carbon production from agricultural waste of chickpea and its application for heavy metal adsorption: equilibrium, kinetic, and thermodynamic studies

Abstract: The purpose of this study was to produce activated carbons (ACs) from chickpea (Cicer arietinum) husks by chemical activation (KOH and K2CO3) and to examine their feasibility in removing heavy metals from aqueous solutions. In the case of KOH impregnation with a ratio of 50 wt%, the most developed porosity was achieved, with a BET surface area of 2082 m2/g and a total pore volume of 1.07 cm3/g. By using the product, the maximum adsorption capacities were found to be 135.8, 59.6, and 56.2 mg/g for Pb(II), Cr(VI), and Cu(II), respectively. The experimental data were analyzed by various adsorption isotherm and kinetic models. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were also calculated. The results obtained in this study shows that adsorption onto chickpea-husk-derived activated carbon was endothermic and spontaneous for the removal of heavy metals from aqueous solutions.

Adsorption characteristics of Pb(II) using biochar derived from spent mushroom substrate.

Abstract: As a multifunctional material, biochar is considered a potential adsorbent for removing heavy metals from wastewater. Most biochars with high adsorption capacities have been modified, but this modification is uneconomical, and modifying biochar may cause secondary pollution. Thus, it is necessary to develop an efficient biochar without modification. In this study, spent P. ostreatus substrate and spent shiitake substrate were used as the raw materials to prepare biochar. Then, the physicochemical properties of the biochars and their removal efficiencies for Pb(II) were investigated. The results showed that the physicochemical properties (e.g., large BET surface area, small pore structure and abundant functional groups) contributed to the large adsorption capacity for Pb(II); the maximum adsorption capacities were 326 mg g−1 (spent P. ostreatus substrate-derived biochar) and 398 mg g−1 (spent shiitake substrate-derived biochar), which are 1.6–10 times larger than those of other modified biochars. The Pb(II) adsorption data could be well described by the pseudo-second-order kinetic model and the Langmuir model. This study provides a new method to comprehensively utilize spent mushroom substrates for the sustainable development of the edible mushroom industry.

Tunable Surface Area, Porosity and Function in Conjugated Microporous Polymers

Abstract: Simple inorganic salts are used to tune N-containing conjugated microporous polymers (CMPs) synthesized by Buchwald-Hartwig (BH) cross-coupling reactions. Poly(triphenylamine), PTPA, initially shows a broad distribution of micropores, mesopores, and macropores. However, the addition of inorganic salts affects all porous network properties significantly: the pore size distribution is narrowed to the microporous range only, mimicking COFs and MOFs; the BET surface area is radically improved from 58 m2 g-1 to 1152 m2 g-1 ; and variations of the anion and cation sizes are used to fine-tune the surface area of PTPA, with the surface area showing a gradual decrease with an increase in the ionic radius of salts. The effect of the salt on the physical properties of the polymer is attributed to adjusting and optimizing the Hansen solubility parameters (HSPs) of solvents for the growing polymer, and named the Beijing-Xi'an Jiaotong (BXJ) method.

Hydrolytically Stable Nanotubular Cationic Metal–Organic Framework for Rapid and Efficient Removal of Toxic Oxo-Anions and Dyes from Water

Abstract: Cationic framework materials capable of removing anionic pollutants from wastewater are highly desirable but relatively rarely reported. Herein, a cationic MOF (SCNU-Z1-Cl) possessing tubular channels with diameter of 1.5 nm based on Ni(II) and a nitrogen-containing ligand has been synthesized and applied to capture hazardous anionic contaminants from water. The SCNU-Z1-Cl exhibits high BET surface area of 1636 m2/g, and shows high hydrolytically stability in pH range from 4 to 10. Owing to the large tubular channels and the uncoordinated anions in the framework, the aqueous-phase anion-exchange applications of SCNU-Z1-Cl were explored with environmentally toxic oxo-anions including CrO42-, Cr2O72-, MnO4-, and ReO4-, and organic dyes. The adsorption of oxoanions exhibits high uptake kinetics and the adsorption capacities of CrO42-, Cr2O72-, MnO4-, and ReO4- are 126, 241, 292, and 318 mg/g, respectively, which were some of the highest values in the field of MOF/COF. In additional, the selectively is high when other concurrent anions are exist. The anionic dyes with different sizes including methyl orange, acid orange A, congo red, as well as methyl blue can be adsorbed by SCNU-Z1-Cl in few minutes to about 1 h. The adsorption capacities for them are 285, 180, 585, and 262 mg/g, respectively. In contrast, the adsorption kinetics for catinionic dyes with different sizes is obviously lower and exhibit a size-selectively adsorption that only cationic dye with suitable size (rhodamine B) can be adsorbed by SCNU-Z1-Cl. Consequently, SCNU-Z1-Cl can sepearate organic dyes in three different modes: size-dependent, charge-dependent, and kinetics-dependent selective adsorption. The excellent adsorption and separation properties of SCNU-Z1-Cl is attribute to the cationic framework, large tubular channel, as well as the high positive Zeta potential.

On the deactivation of Ni-Al catalysts in CO2 methanation

Abstract: This work provides detailed knowledge of long-term deactivation of Ni catalysts in CO2 methanation. NiAlOx mixed oxides with varying Ni loading as well as a 17 wt-% Ni/γ-Al2O3 catalyst were synthesized via co-precipitation and incipient wetness impregnation, respectively. The catalysts were aged at 523, 573 and 623 K under equilibrium conditions up to 165 h. Periodic activity measurements under differential conditions reveal severe deactivation. The stability of co-precipitated systems increases with decreasing Ni content on the expense of catalyst activity. Ni/γ-Al2O3 exhibits a lower stability as a comparable mixed oxide. A power law model is applied for the kinetic description of deactivation. Catalyst samples are characterized by means of temperature programmed desorption of H2 (H2-TPD) and CO2 (CO2-TPD), pulsed H2 chemisorption, XRD, FT-IR spectroscopy, XPS and N2 physisorption. Main deactivation mechanisms in the co-precipitated samples are found to be Ni particle sintering, a loss of BET surface area as well as a reduction of CO2 adsorption capacity and medium basic sites, along with structural changes of the mixed oxide phase. Ni particle growth and a decrease in BET surface area lead to deactivation of the impregnated sample. Structure-activity correlations imply a complex interplay of governing deactivation phenomena as well as structure sensitivity.

Enhanced photocatalytic activity of Pt-TiO2/WO3 hybrid material with energy storage ability

Abstract: We aimed at producing a photocatalyst having UV–vis activity with residual energy storage ability in absence of irradiation. We synthesized a series of catalysts with Pt supported over mixed titanium-tungsten oxides (TiO2/WO3). The methods were spray dried assisted sol-gel and crash precipitation. TiO2 maintained its tetragonal anatase phase and WO3 its monoclinic structure. The hybrid samples (PtxTW, where x = 0–1.2 wt.%) have significantly higher BET surface area (204.0 - 283.0 m2/g) compared to control Pt0.8T (265.0 m2/g) and Pt0.8W (54.5 m2/g) samples. XPS analysis detected the presence of metallic platinum (Pt°), which actively takes part in the enhanced photons absorption of the photocatalyst, as depicted from UV–vis-DRS study. The Pt0.8TW- optimum Pt loading- is characterized by a visible absorption edge at 501.0 nm compared to the control Pt0.8T (444.0 nm) and Pt0.8W (540.5 nm). Microscopy images showed homogenous and uniform distribution of the oxides, and Pt particles and the FTIR analyses evidenced greater adsorption of OH− groups on the hybrid samples surface. In the activity tests, the Pt0.8TW outperforms the other samples in the aqueous degradation of the model pollutant methylene blue (MB) (78.0% and 56.0% in UV and visible light), with an additional hour of energy storage ability in absence of irradiation, then reaching a final degradation of 98.0% and 77.0% under UV and Visible light, respectively. In connection to the activity tests, scavenging experiments revealed that hydrogen peroxide (H2O2) and hydroxyl radicals (OH•) were the main species responsible for the pollutant degradation.