Preparation and characteristics of rice-straw-based porous carbons with high adsorption capacity

To prepare porous carbons with high adsorption capacity from rice straws, two different kinds of precursors, i.e. one as the raw rice straws (one-stage process) and the other as pre-carbonized rice straws (two-stage process), were activated with KOH of various impregnation ratios. The two-stage process was found very effective for manufacturing porous carbons with high surface area and adsorption capacities for MB and I₂. For example, the porous carbon that was carbonized at 700°C and subsequently activated at 900°C exhibited the surface area of 2410 m²/g, the adsorption capacities of 800 and 1720 mg/g for MB and I₂, respectively, and the total pore volume of 1.4 ml/g. In the two-stage method, there was a preferential optimum impregnation ratio of KOH to a precursor carbon, i.e. 4:1, with which high surface area of porous carbons could be achieved. The formation of uni- and bidentate carboxylic salt structure, induced by reaction between KOH and oxygen containing carbon, that facilitates the formation of azo group (-NN-) on a subsequent heat treatment was considered as one of the key factors for the presence of optimum impregnation ratio of KOH. In contrast, the porous carbons of only moderate adsorption capacity could be obtained from the one-stage method. The original morphology of rice straw was sustained during the two-stage process, yet not during the one-stage process.     

Hydrogen adsorption on metal-organic framework (MOF-5) synthesized by DMF approach

Metal-organic frameworks (MOFs), especially MOF-5, are believed to be promising new porous materials for hydrogen adsorption. A comparative study of material synthesis, characterization and hydrogen adsorption was performed to examine the effects of different synthesis conditions on crystal structure, pore textural property and hydrogen adsorption performance of MOF-5 materials. Three MOF-5 samples synthesized with dimethyl formamide (DFM) as solvent and slightly different procedures have shown similar phase structure and chemical composition, diverse crystal structures, varying pore textural properties and different hydrogen adsorption performance. It was established from the experimental results that higher order of crystallinity in the MOF-5 materials generates better adsorbents with larger crystal size, higher specific surface area, uniform pore size distribution (PSD), larger hydrogen adsorption capacity and faster hydrogen diffusion rate in MOF-5 adsorbents. The best MOF-5 sample synthesized in this work (MOF-5(γ)) has a Langmuir specific surface area of 1157 m²/g; it can adsorb 0.5 wt.% of hydrogen at 77 K and 800 mmHg; and results in hydrogen diffusivity inside MOF-5 crystal of 2.3 × 10⁻⁹ cm²/s. The density functional theory reasonably predicts the presence of mesopores and macropores in all three MOF-5 samples synthesized in this work.     

SnO2 submicron porous cube derived from metal-organic framework for n-butanol sensing at room temperature

SnO₂ is a typical metal oxide semiconductor gas sensitive material, which has been studied deeply. However, pure SnO₂ sensing materials usually have good performance at high operating temperatures. In this study, we reported an n-butanol sensor with high selectivity and fast response based on SnO₂ submicron porous cube prepared by heating and decomposing the Sn-based metal-organic framework material (Sn-MOF) in air at a certain temperature. SnO₂ submicron porous cube prepared at 450 °C shows good response and selectivity for n-butanol. And it has a response (%) of 175% to 100 ppm n-butanol and a relatively fast response/recovery time of 184 s/183 s at room temperature. The (110) crystal plane with sufficient oxygen-rich vacancy can adsorb O₂ and n-butanol molecules more effectively. Therefore, its sensitivity to n-butanol gas can be significantly improved. This work provides a good idea for further research on pure metal oxide semiconductor room temperature gas sensors.     

Reversible water inclusion in a porous magnetic material synthesized from copper(II) incorporated metal-organic framework showing alternate ferro- and antiferromagnetic interactions

X-ray structural analysis shows that {[Cu₂(CTA) (H₂O)] · 5 H₂O}_n constitutes infinite one-dimensional parallel chains along the c-axis with water columns running down the crystallographic a-axis. The inclusion of water molecules is reversible and is confirmed by X-ray powder diffraction studies. The magnetic data (2–300 K) reveal that there are alternate ferro- (J = 0.29 cm⁻¹) and antiferromagnetic (J = −2.5 cm⁻¹) interactions.     

A new analysis method for the determination of the pore size distribution of porous carbons from nitrogen adsorption measurements

A new analysis method has been developed for the determination of the pore size distribution of porous carbons from nitrogen adsorption measurements. The method is based on a molecular model for the adsorption of nitrogen in porous carbon. It allows, for the first time, the distribution of pore sizes to be determined over both the micropore and mesopore size ranges using a single analysis method. In addition to carbons, this method is also applicable to a range of adsorbents, such as silicas and aluminas.     

Magnetic mesoporous carbon material with strong ciprofloxacin adsorption removal property fabricated through the calcination of mixed valence Fe based metal-organic framework

As an efficient and low cost adsorbent to remove fluoroquinolones antibiotics (such as ciprofloxacin and norfloxacin) in waste water, magnetic mesoporous carbon material has attracted increasing concern all over the world. Here, a convenient strategy to fabricate magnetic mesoporous carbon material has been explored with Fe containing metal-organic framework (MOF) as precursor. With this method, a magnetic mesoporous carbon material, Fe₃O₄/C , which possesses high surface area, is obtained through the calcination of a mixed valence Fe based MOF. For Fe₃O₄/C, its ciprofloxacin adsorption capacity reaches as high as 868.6 mg/g. Magnetic measurement reveals its ferromagnetic feature of Fe₃O₄/C with magnetization saturation 22.81 emu g^?1 and this guarantees its excellent magnetic separation performance. Furthermore, Fe₃O₄/C also exhibits outstanding stability during ciprofloxacin containing waste water treatment.     

Hybrid metal-organic framework nanomaterials with enhanced carbon dioxide and methane adsorption enthalpy by incorporation of carbon nanotubes

Two hybrid materials composed of metal-organic framework (JUC-32) nanoparticles and carboxyl-modified multi-wall carbon nanotubes (MWCNTs) were synthesised successfully in situ and characterized by TEM, PXRD, and TGA. The gas adsorption properties of these two hybrid materials were compared with the original JUC-32 material and a physical mixture of JUC-32 and MWCNTs. The results indicated that the composite materials absorbed larger amounts of CO₂ and CH₄ per specific surface area than the original materials, and that the adsorption enthalpies of CO₂ and CH₄ had significantly increased.     

Gas adsorption on activated carbons from PET mixtures with a metal salt

Activated carbons were prepared from carbonized PET by steam activation via pretreatment by mixing PET with a metal salt [Ca(NO₃)₂·4H₂O, Ca(OH)₂, CaCO₃, ZnO, and AlNH₄(SO₄)₂·12H₂O], and with acid treatment after carbonization. The porous properties of the activated carbons were determined by the nitrogen adsorption method. The adsorption isotherms of CO₂, C₂H₆, nC₄H₁₀ and iC₄H₁₀ at 298 K on the prepared activated carbons were measured to determine practical applications and to obtain a better understanding of the porous structure of the prepared carbons. Steam-activated carbons via pretreatment have a larger mesoporosity than carbons with no pretreatment. The metal salt used in the pretreatment for steam activation has no influence on the microporous structure, but it does influence the mesoporous structure of the prepared carbons. Activated carbons prepared via pretreatment show a large adsorption capacity for nC₄H₁₀ and iC₄H₁₀. These carbons are suitable as adsorbents for canisters, etc. Application of the potential theory to adsorption data for the prepared carbons suggests that the pretreatment contributes to the formation of pores larger than 0.50 nm at high burnoff.     

The unusually formation of porous silica nano-stalactite structure by high temperature heat treatment of SiO2 aerogel synthesized from rice hull

The SiO₂ aerogel has attracted the attention of many researchers in recent years in terms of energy saving due to its properties such as very low density, high porosity, and superior insulation. The primary purpose of this study was to synthesize SiO₂ aerogel. For this purpose, the sodium silicate obtained from rice hull ash was used as pre-initiator and dried at ambient pressure and SiO₂ aerogel was synthesized. BET surface area of the obtained SiO₂ aerogel was found as 241 m²/g. The difference of this study is the structures obtained after this stage. After obtaining SiO₂ aerogel, it was subjected to heat treatment at a high temperature to increase the BET area of aerogel and after examining under SEM, it was noticed that some uncommon structures that have not seen before formed. After observing nano-stalactite type structures in the sample, the study was expanded on the causes of the formation of these structures. It was seen that this structure forming after heat treatment was a stalactite composed of SiO₂ nanoparticles having a crystal structure. This study examined the formation mechanism and some properties of this structure which was not encountered in previous studies. Brunauer-Emmett-Teller (BET), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis were conducted in order to determine the physical and chemical properties of both synthesized SiO₂ aerogel and nano-stalactite type structure.     

On the methane adsorption capacity of activated carbons: in search of a correlation with adsorbent properties

BACKGROUND: There exists now a widely held view that the methane storage capacity on an activated carbon is not related to any of the routinely determined properties of the adsorbent, such as surface area or micropore volume. This has been confirmed and a correlation pursued with other physical and/or chemical properties of both commercially available carbons and those prepared in the laboratory. Textural characteristics (from nitrogen adsorption isotherms at 77 K) considered were BET‐equivalent specific surface area, DR micropore volume and Horvath–Kawazoe micropore size distribution. Chemical properties were evaluated using Fourier transform infrared (FTIR) spectroscopy, thermal programmed decomposition (TPD) and Boehm titrations. Both kinetic and equilibrium methane adsorption experiments were performed at 273 and 298 K and up to 3.5 MPa. RESULTS: Using phosphoric acid to activate peach stones together with additional thermal treatment enabled the production of activated carbons with 137 v/v methane adsorption capacity at 298 K. CONCLUSIONS: The presence of acidic surface functional groups has a detrimental influence on methane uptake, due to the chemical inertness of the adsorbate and/or to pore blockage of the adsorbent. Basic surface functional groups (pyrone), together with a desirable pore size distribution centered at ca 0.8 nm, are thought to be responsible for improved methane adsorption capacity on such activated carbons. Copyright © 2009 Society of Chemical Industry     

A continuous method to prepare porous polystyrene membranes with high adsorption ability for polycyclic aromatic hydrocarbons

A convenient and continuous method to prepare porous polystyrene (PS) membranes via a microlayer coextrusion and template method is proposed. The porous PS membranes can be obtained via the acid etching of a CaCO₃ template embedded in the membranes. Scanning electron microscopy, thermogravimetric analysis, and Fourier transform infrared spectroscopy of the porous PS membranes show that most of the CaCO₃ particles can be etched away. The effects of etching time, CaCO₃ content, and membrane thickness on the porous structures are investigated, which can be used to regulate and control the porous structure. To demonstrate the adsorption performance of porous PS membranes on polycyclic aromatic hydrocarbons, pyrene is used as the model compound. Compared with that of solid PS membranes, porous PS membranes exhibit much higher adsorption performance for trace pyrene. The adsorption kinetics and isotherm of porous PS membranes can be well fit by pseudo‐second‐order kinetics and a Freundlich isotherm model. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45917.     

Liquid-phase adsorption of phenol by activated carbons prepared from bituminous coals with different oxygen contents

Activated carbons prepared from two bituminous coals were used to adsorb phenol in aqueous solutions. The major difference between the coal precursors is the oxygen content. The carbon preparation consisted of carbonization of the coals followed by activation in CO ₂ to various extents of burn-off. Experimental results show that the amount of phenol adsorbed generally increases with the BET surface area of the carbon. The carbons prepared from the coal with a higher oxygen content have larger surface areas, and, therefore, exhibit higher capacities for phenol. The surface area of the carbon increases with the extent of carbon burn-off, whereas the increase in the adsorptive capacity due to the increasing burn-off level does not show a linear relationship with the increase in area; the ratio of the capacity to BET surface area is not constant and decreases with the burn-off level. This has been attributed to the accessibility of phenol to the surface being affected by the length of diffusion path, which is an increasing function of the burn-off level or the particle size. The amount of phenol adsorbed decreases with the temperature for these carbons. It was found, according to the Langmuir model, that the adsorption process was significantly affected by the oxygen content in the coal precursors. © 1999 Society of Chemical Industry     

Effect of the porous texture and surface chemistry of activated carbons on the adsorption of a germanium complex from dilute aqueous solutions

The effect of the adsorption properties and surface chemistry of activated carbons on the adsorption of germanium (IV) from dilute aqueous solutions (50 ppm) was investigated. A large number of activated carbons were obtained by activating three precursors, one coal and two lignocellulosic chars, with alkaline hydroxides, NaOH and KOH, and different activating agent/precursor ratios (from 1/1 to 5/1). The characterization of their textural properties, assessed by N₂ and CO₂ isotherms, and their oxygen surface chemistry, assessed by temperature-programmed desorption experiments, confirm that a large variety of materials with different surface areas, pore size distributions and surface chemistries are available for this study. To increase the Ge adsorption, an organic compound (catechol) was used as a ligand in order to form a germanium complex. Such a complex works very well, allowing its good adsorption on the activated carbons. The results showed that to achieve the highest Ge adsorption, the activated carbon should show a high apparent surface area, a wide microporosity and a moderate oxygen surface content that may assure the wettability of the solution but that does not produce large repulsive interactions.     

Zirconia nano-powders with controllable polymorphs synthesized by a wet chemical method and their phosphate adsorption characteristics & mechanism

Adsorption is a simple and efficient phosphorus removal method used to control the eutrophication of water bodies. A simple and gentle atmospheric pressure hydrothermal method by adjusting the dosage of ammonium chloride and sodium hydroxide was used to synthesize amorphous, monoclinic, and tetragonal zirconia nano-powders with high specific surface areas (383.91 m²/g, 330.01 m²/g, and 234.36 m²/g) and particle size of about 40 nm for phosphate adsorption. When pH = 6.3, the phosphate adsorption capacity of the amorphous monoclinic phase and the tetragonal phase respectively reached 102.58 mg P/g, 68.11 mg P/g, and 37.25 mg P/g and the adsorption process of the three crystal forms of zirconia powders conformed to the Langmuir adsorption model. In the first 2 min of rapid adsorption, amorphous zirconia completed 76.23% of the adsorption process and the monoclinic phase also completed more than 60%. The adsorption process of the three crystal forms of zirconia was completed within 240 min and conformed to the pseudo-second-order kinetic model. Their adsorption characteristics of the three crystal forms of zirconia decreased with the increase in pH. While the pH was above than the isoelectric point of the solution, the adsorption capacity was significantly reduced. The large specific surface area and high hydroxyl content of the zirconia nano-powder made a great contribution to the adsorption process.     

Luminescence properties of Br-doped ZnS nanoparticles synthesized by a low temperature solid-state reaction method

Br-doped ZnS nanoparticles were synthesized using a low temperature solid-state reaction method. Influence of Br doping concentration on the crystal structures, crystallite sizes, and luminescence properties of the Br-doped ZnS nanoparticles was investigated. The Br-doped ZnS nanoparticles had a cubic zincblende crystal structure, and had an average crystallite size of about 8.0–9.5 nm. Both the lattice constant and average crystallite size of the Br-doped ZnS nanoparticles decreased with Br doping concentration. It was found that the luminescence intensity of the Br-doped ZnS nanoparticles remarkably increased with Br doping concentration. The emission intensity of the 5% Br-doped ZnS nanoparticles was about 13 times stronger than the undoped ZnS nanoparticles. Mechanism for the enhanced luminescence of the Br-doped ZnS nanoparticles was discussed. This work suggests that the low temperature solid-state reaction method can be used to synthesize Br-doped ZnS nanoparticles with strong luminescence properties.     

Fabrication of bimodal mesoporous carbons from petroleum pitch by a one-step nanocasting method

A one-step nanocasting method to prepare a bimodal mesoporous carbon from a highly hydrophobic carbon precursor, i.e., petroleum pitch, has been successfully developed by adopting tetrahydrofuran and hydrofluoric acid as solvent and catalyst, respectively, for the gelation reaction of tetraethyl orthosilicate and water. Experimental results show that the introduction of proper amounts of petroleum pitch does not hamper this gelation reaction, thus forming a uniform silica/carbon composite. It was found that the as-prepared nanoporous carbon has a three-dimensional 3.4 nm-sized wormholelike mesoporous network with well-distributed 17.1 nm-sized particlelike mesopores. Such a bimodal mesoporous carbon has a high Brunauer-Emmett-Teller surface area (782 m² g⁻¹) and a very large total pore volume (3.0 cm³ g⁻¹).     

Stereolithography as a manufacturing method for a hierarchically porous ZSM-5 zeolite structure with adsorption capabilities

Hierarchically porous structures are important in adsorption applications and can be used in gas treatment. Hierarchy in adsorbents offers flow channels on different scales, resulting in fast gas flow into a structure. Additive manufacturing, a technology capable of forming intricate geometries, was seen as a potential method to form porous adsorption structures. Stereolithography was chosen as the fabrication method for hierarchically porous zeolite structures because of its high resolution and superior forming capability. The focus of this study was on tailoring the properties of light-cured resin to maximize stability during shaping and shape retention in the debinding stage. Successful slurry preparation was required for demonstrating that monoliths with channel geometry and retained adsorption properties can be manufactured with stereolithography. The final printed structures exhibited hierarchical porosity consisting of flow channels, macropores between the primary particles and the characteristic microporosity of zeolite framework. The structure was manufactured by using blue light to cure layers of resin containing ZSM-5 zeolite. An appropriate debinding heat-treatment cycle was generated based on the TGA and DSC thermal analysis results. The properties of the porous structure were analysed by comparing the BET surface area, XRD patterns and SEM images of as-received powder and a debound piece. The measured BET adsorption properties of the final monoliths remained comparable to the as-received ZSM-5 powder. Based on this study, stereolithography can be utilized to manufacture porous zeolite structures.     

高温抗烧结吸附剂对SeO2捕集性能

使用气固瞬时反应装置在700~1100℃下对不同氧化物（氧化镁、氧化铁、氧化铝、氧化钙）的硒捕集性能进行研究,确定吸附产物性质。基于此选取相应的典型矿物及双组分抗烧结吸附剂改善硒高温吸附能力。结果表明：900℃前氧化钙捕集效果最好,但1100℃时其吸附量迅速降低到167.59μg/g;γ-氧化铝在高温下捕集效果较好,1100℃时吸附量可达415.04μg/g,这与其优异的孔隙结构有关。钙基矿物方解石因其具有一定的抗烧结能力和发达的孔隙结构,表现出更好的高温捕集能力,1100℃时吸附量可提高到1064.97μg/g。双组分吸附剂高温捕集能力展现出不同程度的提高。钙-铝基吸附剂高温捕集性能提高相对较小;而钙-硅基吸附剂在高温下效果远高于单组分吸附剂,与氧化钙相比,1100℃时可提高1787.21μg/g。     

Preparation of zirconia ceramics from powder synthesized by a sol-gel method

Differential thermal and x-ray-phase analysis methods are used to study properties of ZrO₂ powder stabilized with yttrium oxide, prepared by sol-gel technology using an organo-mineral solution. Optimization of powder preparation, including firing and deagglomeration treatment, makes it possible to prepare dense ceramic with a sintering temperature of 1350°C with an average grain size of 250 – 290 nm. Deagglomerated powder may be used as an addition in the preparation of high quality refractories based on oxide raw material.     

Neutron adsorption performance of Dy2TiO5 materials obtained from powders synthesized by the molten salt method

Dy₂TiO₅ powders were synthesized by molten salt and solid-state methods. The influences of molten medium on phase compositions and microstructures were analyzed. The addition of molten salt lowered significantly the synthesis temperature and resulted in uniform powders. Green bodies compacted from the prepared powders were pressureless sintered at 1600 °C. Sinterability, mechanical properties and neutron absorption performance of the sintered pellets were studied. Results showed that molten salt synthesis resulted in materials with higher fracture toughness and bending strength, excellent hardness and neutron adsorption performance compared to the solid-state process. The neutron absorption rate reached 86.6% for 8 cm thick pellets.