Showing papers on "BET theory published in 2018"

Phosphorus-Doped Graphitic Carbon Nitride Nanotubes with Amino-rich Surface for Efficient CO2 Capture, Enhanced Photocatalytic Activity, and Product Selectivity

Abstract: Phosphorus-doped graphitic carbon nitrides (P-g-C3N4) have recently emerged as promising visible-light photocatalysts for both hydrogen generation and clean environment applications because of fast charge carrier transfer and increased light absorption. However, their photocatalytic performances on CO2 reduction have gained little attention. In this work, phosphorus-doped g-C3N4 nanotubes are synthesized through the one-step thermal reaction of melamine and sodium hypophosphite monohydrate (NaH2PO2·H2O). The phosphine gas generated from the thermal decomposition of NaH2PO2·H2O induces the formation of P-g-C3N4 nanotubes from g-C3N4 nanosheets, leads to an enlarged BET surface area and a unique mesoporous structure, and creates an amino-rich surface. The interstitial doping phosphorus also down shifts the conduction and valence band positions and narrows the band gap of g-C3N4. The photocatalytic activities are dramatically enhanced in the reduction both of CO2 to produce CO and CH4 and of water to produce...

Evaluation of the BET Theory for the Characterization of Meso and Microporous MOFs

Abstract: Surface area determination with the Brunauer–Emmett–Teller (BET) method is a widely used characterization technique for metal–organic frameworks (MOFs). Since these materials are highly porous, the use of the BET theory can be problematic. Several researchers have evaluated the BET method to gain insights into the usefulness of the obtained results and interestingly, their findings are not always consistent. In this review, the suitability of the BET method is discussed for MOFs that have a diverse range of pore widths below the diameters of N2 or Ar and above 20 A. In addition, the surface area of MOFs that are obtained by implementing different approaches, such as grand canonical Monte Carlo simulations, calculations from the crystal structures or based on experimental N2, Ar, or CO2 adsorption isotherms, are compared and evaluated. Inconsistencies in the state‐of‐the‐art are also noted. Based on the current literature, an overview is provided of how the BET method can give useful estimations of the surface areas for the majority of MOFs, but there are some crucial and specific exceptions which are highlighted in this review.

Tetracycline antibiotic removal from aqueous solutions by MOF-5: Adsorption isotherm, kinetic and thermodynamic studies

Abstract: This study examines time-varying adsorption of aqueous tetracycline (TC) by metal-organic framework, MOF-5 The employed MOF-5 is firstly synthesized under room temperature condition Its structural, chemical, and physical features are then determined applying FTIR, XRD, SEM, TGA, N2 adsorption, and TEM characterization techniques Cubic arrangement, 843% crystallinity, up to 450 °C thermal stability and approximately 2510 m2/g BET surface area with the both micro- and meso-cavities are its revealed characteristics The impacts of the operative factors (adsorbent dosage, contact time, initial TC concentration, initial pH and temperature) on TC removal efficiency are examined following a two-step experimental design procedure (two-level categorical screening followed by response surface methodology for correlative model development) Additionally, to define the most appropriate condition/conditions, model-based optimization is implemented and verified in practice (more than %96 TC removal is achieved) Further thermodynamic and kinetic assessments respectively signify the both physisorption (Langmuir adsorption isotherm with maximum capacity of 233 mg/g) and chemisorption (pseudo-second-order model) mechanisms in this adsorption system To sum up, MOF-5 as a suitable adsorbing agent will possibly have significant effects on pharmaceutical wastewater treatment and can be considered for advanced studies as an appropriate candidate regarding practicable remediation techniques

CO2 methanation over nickel-ZrO2 catalyst supported on carbon nanotubes: A comparison between two impregnation strategies

Abstract: Ni-ZrO2 catalysts supported on CNT synthesized by sequential and co-impregnation were tested in the CO2 methanation reaction. The catalysts were characterized using different physico-chemical techniques including BET surface area analysis, TGA, H2-TPR analysis, CO2-TPD analysis, XRD analysis, TEM-EDS analysis and XPS. Both samples were found to be active in the CO2 methanation; however, the catalyst prepared by co-impregnation was notably less active and selective to CH4 than the catalyst synthesized by sequential impregnation method. The characterization results gave significant insight on the disposition of active phases in CNT surface. The catalyst prepared by co-impregnation showed NiO nanoparticles surrounded by ZrO2 in core-shell structures that growth over the CNT, reducing reactant access to Ni and Ni – ZrO2 interface. Additionally, TEM analysis of this catalyst prepared by sequential impregnation showed NiO nanoparticles available and deposited either on the surface or next to the ZrO2 nanoparticles, increasing the extent of the Ni – ZrO2 interface thus improving the catalytic performance.

Nitrogen-doped porous carbon: highly efficient trifunctional electrocatalyst for oxygen reversible catalysis and nitrogen reduction reaction

Abstract: Simple yet efficient design of an outstanding multifunctional electrocatalyst is crucial for advanced energy conversion and storage devices. Herein, we report the synthesis of an N-enriched hierarchically porous carbon electrocatalyst, which demonstrated excellent overall oxygen electrode activity (ΔE = EOER,10 − EORR,1/2 of 0.770 V) and impressive durability in 0.1 M KOH. The activity of our material integrates a high BET surface area (1547.13 m2 g−1), accessible N dopant and suitable porous architectures. The material is formed by mixing cicada sloughs with ZnCl2, as the inorganic pore-fabricating agent, with ball milling followed by annealing treatment. Unexpectedly, the nitrogen reduction reaction (NRR) with excellent production yield (NH3: 15.7 μg h−1 mg−1 cat., faradaic efficiency: 1.45%) and selectivity is achieved at −0.2 V vs. RHE under ambient conditions. The present trifunctional catalytic activities are markedly better than leading results reported in recent literature. These results highlight the significance of deliberate structural engineering in the preparation of multifunctional electrocatalysts for versatile electrochemical reactions.

Promotional removal of HCHO from simulated flue gas over Mn-Fe oxides modified activated coke

Abstract: A series of MnxFey/AC catalysts synthesized by impregnation method were investigated on the efficient and stable removal of HCHO in the fix-bed reactor. Extensive characterizations, BET, SEM, XRD, H2-TPR, XPS and FT-IR, were conducted to study the physicochemical properties, HCHO oxidation and surface reaction of catalysts. The optimal Mn0.75Fe6.02/AC showed enhanced HCHO removal efficiency of 98.30%, as well as excellent performance for simultaneous removal of HCHO (89.96%) and Hg0 (77.51%). NO and SO2 balanced in N2 would inhibit the removal of HCHO, while the addition of 6% O2 weakened the negative effect of SO2 and NO + 6% O2 facilitated the removal of HCHO. Besides, the slight promotion effect of water vapor was contributed to the regeneration of consumed −OH via the activation of surface oxygen by adsorbed H2O. Characterization results indicated that Mn0.75Fe6.02/AC possessed larger BET surface area, well-developed porosity and better dispersion of active components. Mn0.75Fe6.02/AC exhibited higher reducibility due to the synergistic effect between MnOx and FeOx, and the interaction between Mn-Fe oxides and AC support. At the same time, the oxygen-containing functional groups (C-O-, COO), abundant active surface oxygen and –OH facilitated both adsorption and oxidation of HCHO. Besides, the formate and carbonate intermediates formed on the surface of Mn0.75Fe6.02/AC in HCHO removal process, which could be further oxidized into CO2 and H2O. On the basis of above investigations, the mechanism of enhanced HCHO catalytic removal over MnxFey/AC was proposed.

Sustainable Synthesis of High-Surface-Area Graphite Oxide via Dry Ball Milling

Abstract: A sustainable route to produce graphite oxide (GO) is presented using dry ball milling. The production method was based on pristine graphite flakes in a planetary ball mill. The prepared GO was characterized using UV–vis spectroscopy, BET surface area analysis, thermal analysis, SEM-EDX, TEM, XPS, elemental analysis, and Raman spectroscopy. The degree of graphite oxidation was controllable by the milling time and milling material, and the carbon-based yields ranged from 86 to 97%. The maximum oxygen/carbon ratios of the produced GOs were 0.16 and 0.15 after 24 h of ball milling with steel and zirconia balls, respectively. The BET surface area increased with increasing milling time from 1 m2 g–1 for pristine graphite up to 730 m2 g–1 for the ball-milled samples. Furthermore, the intensity ratios of the D and G bands (ID/IG) from the Raman spectra were 0.84 and 0.77 for GO produced with the steel and zirconia balls, respectively. The in-plane sp2 crystallite sizes (La) of graphite (168 nm) decreased to 20 (...

Bone char-derived metal-free N- and S-co-doped nanoporous carbon and its efficient electrocatalytic activity for hydrazine oxidation

Abstract: Bone char (BC) was successfully used, for the first time, both as a self-template/a pore-former and a precursor of heteroatoms (N and S atoms) during carbonization of sucrose, allowing for the synthesis of nanoporous N- and S-co-doped carbon (NSC) material possessing high surface area and excellent electrocatalytic activity. BC’s ability to help with the formation of nanopores in the carbon material was indirectly confirmed by making a control material, denoted as pyrolyzed sucrose or PS, under the same condition but without including BC in the reaction media. N2 gas porosimetry showed that NSC had a very large BET surface area (1108 m2 g−1), which is about 60% higher than that of PS (443 m2 g−1). Comparison of the SEM images of the two materials also indicated some differences in their textural and morphological features. XPS analysis showed that NSC had a higher content of S (2.29%) than PS (0.21%) and that the S atoms were distributed mostly in the form of thiophenic moieties (32.3% for the PS and 59.2% for the NSC). Although some of the S groups were originated from sulfuric acid, which was used for the dehydration of sucrose during the synthesis of the materials, this result indicated that BC was the major source of the S dopant atoms in NSC as well as the major reason for the formation of thiophenic groups in this material. Furthermore, while PS’s structure did not have N dopants, NSC’s lattice had about 1.39% of N dopant atoms that existed in the form of pyridinic, pyrrolic and graphitic groups and that were also originated from BC. X-ray diffraction and Raman spectroscopy revealed that NSC’s lattice had a higher density of defects than PS. Owing to its high surface area and optimal density of heteroatom dopant groups and defect sites, NSC exhibited excellent electrocatalytic activity toward the hydrazine oxidation reaction (HzOR), or the lowest overpotential ever reported for this reaction, along with a high current density. Besides making it among the most efficient electrocatalysts for HzOR, its electrocatalytic performance can make this metal-free material a good alternative to the conventional metal-based electrocatalysts that are commonly used in HzOR-based fuel cells.

A porous rhodium(III)-porphyrin metal-organic framework as an efficient and selective photocatalyst for CO2 reduction

Abstract: A rhodium(III)-porphyrin zirconium metal-organic framework (Rh-PMOF-1(Zr)) has been prepared from the self-assembly of a Rh-based metalloporphyrin tetracarboxylic ligand Rh(TCPP)Cl (TCPP = tetrakis(4-carboxyphenyl)porphyrin) with ZrCl4. The framework of Rh-PMOF-1 is stable up to 270 °C as disclosed by the variable-temperature powder X-ray diffraction (VT-PXRD) measurements, and possesses good chemical stability over a wide range of solvents including water. The single-crystal structural analysis reveals that Rh-PMOF-1 contains 3-D channels (1.9 × 1.9 nm2), and the Rh-porphyrin units are exposed to the cavities. The calculation based on the N2 adsorption at 77 K shows Rh-PMOF-1(Zr) has a high BET surface area (3015 m2g−1). The luminescence decay of Rh-PMOF-1 is well fitted to a tri-exponential curve featuring a long average lifetime of 207 μs at 298 K under vacuum, which represents a rare example of room-temperature phosphorescence of Rh-porphyrin complexes. Under 1 atm, it displays CO2 uptake up to 42, 53 and 98 cm3g−1 at 308, 298 and 273 K, respectively. Catalytic results show that, under the visible light (≥400 nm) irradiation without any additional photosensitizer, Rh-PMOF-1 is powerful to catalyze CO2 reduction to the formate ion with up to 99% selectivity, and can be recycled and reused for 3 runs. Theoretical study was further carried out to reveal the energy levels of the frontier orbitals of Rh-PMOF-1 and the preferred binding sites of CO2 in the framework.

Solvothermal synthesis of well-designed ceria-tin-titanium catalysts with enhanced catalytic performance for wide temperature NH3-SCR reaction

Abstract: Ternary mixed ceria-titanium catalysts doping tin were synthesized by a solvothermal method and applied to selective catalytic reduction (SCR) of NO with NH3. The Sn doping catalyst showed better low-temperature activity compared with unmodified catalyst, which exhibited an extraordinarily wide operation window ranging from 180 to 460 °C and better the tolerance of H2O or SO2. Powder X-ray diffraction (XRD), laser Raman spectroscopy (Raman), fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), BET surface area by N2-adsorption-desorption, hydrogen temperature-programmed reduction (H2-TPR), ammonia temperature-programmed desorption (NH3-TPD) were performed to study the structure, redox ability and surface acidity for the CeSnTiOx catalyst. Notably, the addition of Sn could prominently modify and optimize the structure of mixed metal oxides. Meanwhile, it was verified that synergistic interaction between of Ce and Sn surprisingly produced, and crystal defects, oxygen vacancies, acid sites as well as the specific surface areas evidently increased. In addition, the uniform pore channel was also beneficial to NH3-SCR. Especially, the electron interaction between Sn and Ce in reaction could greatly improve the SCR performance and H2O/SO2 durability.