Equilibrium,kinetics and enthalpy of hydrogen adsorption in MOF-177

Metal–organic framework (MOF-177) was synthesized, characterized and evaluated for hydrogen adsorption as a potential adsorbent for hydrogen storage. The hydrogen adsorption equilibrium and kinetic data were measured in a volumetric unit at low pressure and in a magnetic suspension balance at hydrogen pressure up to 100 bar. The MOF-177 adsorbent was characterized with nitrogen adsorption for pore textural properties, scanning electron microscopy for morphology and particle size, and X-ray powder diffraction for phase structure. The MOF-177 synthesized in this work was found to have a uniform pore size distribution with median pore size of 12.7 Å, a higher specific surface area (Langmuir: 5994 m²/g; BET: 3275 m²/g), and a higher hydrogen adsorption capacity (11.0 wt.% excess adsorption, 19.67 wt.% absolute adsorption) than previously reported values on MOF-177. Freundlich equation fits well the hydrogen adsorption isotherms at low and high pressures. Diffusivity and isosteric heat of hydrogen adsorption were estimated from the hydrogen adsorption kinetics and equilibrium data measured in this work.     

Effect of deashing rice straws on their derived activated carbons produced by phosphoric acid activation

We studied the effect of physically and/or chemically deashing rice straw (RS) on the adsorption capacity of their derived activated carbons (ACs) produced by chemical activation with H₃PO₄. Surface area and pore volumes were determined by nitrogen adsorption at 77 K. Methylene blue adsorption isotherms onto ACs were carried out, and we applied Langmuir and Freundlich models to fit the adsorption data. We showed that preliminary deashing does not bring significant improvement to the resultant ACs’ properties. ACs prepared by H₃PO₄ activation of raw and deashed RS have intermediate performances between those of ACs prepared by 1- and 2-step KOH activation, but are much cheaper to produce.     

Isotherms and thermodynamics for the adsorption of n-butane on pitch based activated carbon

The adsorption isotherms of n-butane on pitch based activated carbon (type Maxsorb III) at temperatures ranging from 298 to 328 K and at different equilibrium pressures between 20 and 300 kPa have been experimentally measured by a volumetric technique. The porous properties such as, the density, Brunauer–Emmett–Teller (BET) surface area, pore size, pore volume along with pore size distribution (PSD) of Maxsorb III have been determined. The Dubinin–Astakhov (DA) adsorption isotherm model describes all of the isotherm experimental data within the acceptable error ranges. The present isotherm data are compared with other published data of activated carbon (AC)/n-butane and showed the superiority of the present findings in terms of uptake capacity. The isosteric heat of adsorption (ΔH_ads) of n-butane on Maxsorb III is calculated for different loading. Using the adsorption isotherms and ΔH_ads, the thermodynamic property maps as a function of pressure, temperature and adsorbate amount are also presented.     

Adsorption Isotherms of Hydrogen on Granular Activated Carbon Derived From Coal and Derived From Coconut Shell

ABSTRACT

The development of adsorption-based storage systems requires a basic understanding of the isotherms over a wide range of pressure and temperatures for various types of adsorbents. This research is to generate experimental isothermal adsorption data for the adsorption of hydrogen gas on activated carbon. The adsorption apparatus is based on a volumetric method, and the experiments were conducted at temperatures ranging from 273 to 308 K and pressures up to 4 MPa. Two types of activated carbon, (i) a granular coal from Indonesia and (ii) a coconut-shell activated carbon that is produced in the laboratory, were used in the experiments. The experimental data are analyzed using the Langmuir, Toth, and Langmuir–Freundlich isotherm models.     

Experimental studies of ionic surfactant adsorption onto carbonate rocks

One of the main factors in chemical-based enhanced oil recovery, especially surfactant flooding, is a surfactant adsorption loss onto the reservoir rock. The main aim of this article is performing systematically a study on the adsorption behavior of an industrial ionic surfactant, which is currently employed in petroleum upstream. It is worth mentioning that sodium dodecyle sulphate was employed as an ionic surfactant in this study. Moreover, adsorption density at equilibrium condition was determined. Crushed carbonate rocks were used as rock samples. To determine adsorption behavior of the aforementioned surfactant onto carbonate surface, various surfactant concentrations were created in the range of 500 to 5,000 ppm. Furthermore, via using an electrical conductivity measurement, the surfactant concentration in each solution before and after contacting with carbonate rocks was determined. Two well-known adsorption isotherms, including Freundlich and Langmuir, were employed to specify the adsorption mechanism. Based on the experimental results the Freundlich adsorption isotherm can predict the adsorption behavior of SDS onto carbonate rock surface.     

High-Pressure Adsorption Isotherms of Carbon Dioxide and Methane on Activated Carbon From Low-Grade Coal of Indonesia

ABSTRACT

Adsorption isotherms data of methane and carbon dioxide gases on the activated carbons were measured experimentally using a volumetric method with pressure and temperatures ranging from 0 to 3.5 MPa and 27 to 65°C, respectively. Two types of activated carbons, namely, (1) Kalimantan Timur type activated carbon, which is lab-produced from Indonesian low-grade coal and (2) a commercial (Carbotech) activated carbon were used. The adsorption isotherms obtained were found to belong to type 1 of the International Union of Pure and Applied Chemistry classification. The adsorption uptakes for both carbon dioxide and methane on commercial activated carbon are higher than for the Kalimantan Timur activated carbon. This is due to higher Brunauer–Emmet–Teller surface area and pore volume of the former. Langmuir and Tóth isotherm models are correlated to predict the experimental data with acceptable accuracy.     

Hydrogen adsorption by microporous materials based on alumina-pillared clays

Hydrogen adsorption capacities of various alumina-pillared clays have been studied. The starting material for the preparation of the samples was a natural montmorillonite, which was intercalated with solutions of hydrolysed aluminium, at various Al concentration/clay weight ratios, and then calcined at various temperatures. The results of the adsorption at 77 K indicate that there is a relation between the hydrogen uptake and the microporous volume of the pillared clays. Equilibrium adsorption data were analysed using the Freundlich, Langmuir and Toth isotherm models, in order to investigate the heterogeneity of the materials.     

Removal of Phenol Using TDTAB- and HDTAB-Bentonites

Abstract

In this study, the use of modified bentonites for the removal of phenol was investigated. Two alkylammonium derivatives, tetradecyl trimethyl bromide (TDTAB) and hexadecyl trimethylammonium bromide (HDTAB), were used in the modification in amounts equivalent to 100% of CEC. Crude and modified bentonites were subjected to XRD analyses to see the changes in basal spacing (d _L ) depending on modification. The increases observed in basal spacing are 8.93 Å and 8.55 Å for TDTAB- and HDTAB-bentonites, respectively. Batch adsorption studies were carried at pH of 5.5 and 20°C. Adsorption isotherms of TDTAB- and HDTAB-bentonites have similar shape, and two regions are observed in isotherms. Adsorption behavior was modelled using Langmuir, Freundlich, BET, Bradley, Halsey, Henderson, Oswin, and Smith equations. The equations fitted better when the isotherm was divided into two concentration ranges. Adsorption efficiencies were defined in terms of relative increase in adsorbed amounts, and HDTAB-bentonite was found to be better.     

Hydrogen uptake of reduced graphene oxide and graphene sheets decorated with Fe nanoclusters

Graphene oxide (GO) has been prepared by employing modified Staudenmaier's method through thermal exfoliation of graphite oxide. High pressure hydrogen sorption isotherms up to 50 bar of GO, reduced by thermal reduction (TR-GO), chemical reduction (CR-GO) and graphene sheets decorated with Fe nanoclusters (Fe-GS) have been investigated. Thermal reduction of GO at 623 K under high vacuum yields TR-GO. Chemical reduction of GO using hydrazine forms CR-GO. Fe-GS was synthesized through arc-discharge between the ends of two graphite rods with one rod carrying Fe nanoparticles. The surface areas of these graphene samples were determined from the nitrogen adsorption isotherm employing Brunauer, Emmett and Teller (BET) method. Kelvin's equation was used to determine the pore size distribution of all graphene based samples. Hydrogen pressure-composition isotherms (PCI) were determined at 300 K and at 77 K, between 0.1 and 50 bar. Further, in this paper, we present a comparative adsorption isotherm analysis of hydrogen and helium on TR-GO. This reveals that the volume of hydrogen and helium adsorbed by TR-GO is nearly equal. The similar uptake volume determined for both hydrogen and helium indicates the possibility of monolayer adsorption of hydrogen and also nearly similar binding energy between TR-GO and H₂/He.     

Iron removal from aqueous solutions by amphistegina filter

A semi-pilot filtration unit had been assembled to determine the potential and the effectiveness of the single-media filtration of amphistegina tests and granular activated carbon (GAC) filters in the removal of iron from aqueous solutions in a comparative study. The results revealed that the maximum adsorption capacities of Fe(II) by GAC and amphistegina filters at 313 K and higher flow rate (60 l/min) were 4.19 and 1.34 mg/g, while at lower flow rate (20 l/min) were 3.68 and 3.64 mg/g, respectively. Also, Freundlich and Langmuir adsorption isotherms were used to verify the adsorption performance and thermodynamic parameters were discussed.     

Novel porous carbons synthesized from polymeric precursors for hydrogen storage

In this work, porous carbons were prepared from polymeric ion-exchangeable resin by a chemical activation method in order to obtain novel hydrogen storage materials, and the adsorption characteristics of the porous carbons were investigated. The textural properties were studied by BET and D–R methods with adsorption isotherms. The hydrogen storage behaviors of the porous carbons at 298 K and 100 bar were studied using a PCT apparatus. In the observed post-activation result, the hydrogen storage capacity was markedly improved. However, it was also found that the total amount of adsorption was not proportional to the specific surface area of the adsorbates. This indicates that hydrogen storage could be a function not only of specific surface area or total pore volume but also of microporevolume fraction or the average pore size of adsorbents.     

‘Waste’ coir pith—a potential biomass for the treatment of dyeing wastewaters

Removal of acid dyes (acid violet and acid brilliant blue) and basic dyes (rhodamine B and methylene blue) was carried out using ‘waste’ coir pith as adsorbent. Parameters like agitation time, adsorbent dosage and pH effect were studied. Adsorption followed the first-order rate expression. The equilibrium data fit well with both Langmuir and Freundlich models of adsorption. Desorption experiments confirmed that major mode of adsorption is ion-exchange for the dyes acid brilliant blue and methylene blue whereas acid violet showed mainly physical adsorption. Chemisorption seems to be the major mode of adsorption for rhodamine B.     

活性焦孔结构及表面性质对脱除烟气中SO2的影响

对两种不同方法得到的比表面积相近但脱硫性能差别甚大的活性焦,进行了孔结构、表面化学特性的表征,并进行了脱硫性能的测试.结果表明,活性焦的脱硫性能与其比表面积的关系不大,孔径分布对其存在一定的影响,而活性焦的表面化学特性(表面官能团的种类和浓度)对脱硫性能有很大的影响,在实验分析得到的C-C、C-O、CO、COOH及π-π· 5种官能团中,羰基官能团(CO)和醚基官能团(C-O)的总浓度的大小与活性焦的脱硫性能表现出极大的相关性,这两种官能团的浓度越高,活性焦的脱硫性能越强,并对应较大的苯甲酸吸附值,因此可以推断这两种官能团对活性焦的表面碱性起了主要的贡献,并且决定着活性焦脱硫活性的大小.     

Preparation and characterization of activated carbon from pistachio nut shells via microwave-induced chemical activation

In this work, pistachio nut shell, a biomass residue abundantly available from the pistachio nut processing industries, was utilized as a feedstock for the preparation of activated carbon (PSAC) via microwave assisted KOH activation. The activation step was performed at the microwave input power of 600 W and irradiation time of 7 min. The porosity, functional and surface chemistry were featured by means of low temperature nitrogen adsorption, scanning electron microscopy and Fourier transform infrared spectroscopy. Result showed that the BET surface area, Langmuir surface area, and total pore volume of PSAC were 700.53 m² g⁻¹, 1038.78 m² g⁻¹ and 0.375 m³ g⁻¹, respectively. The adsorptive property of PSAC was tested using methylene blue dye as the targeted adsorbate. Equilibrium data was best fitted by the Langmuir isotherm model, showing a monolayer adsorption capacity of 296.57 mg g⁻¹. The study revealed the potentiality of microwave-induced activation as a viable activation method.     

H2 storage on single- and multi-walled carbon nanotubes

The adsorption of hydrogen on single-walled and multi-walled carbon nanotubes (CNTs) was investigated at 77 and 298 K, in the pressure range of 0–1000 Torr. The adsorption isotherms indicate that adsorption follows the Langmuir model. Hydrogen uptakes were found to depend strongly on the nature of the CNTs. Single-walled CNTs adsorb significantly higher quantities of hydrogen per unit mass of the solid, while the opposite is true on a per unit surface area basis. This observation implies that adsorption takes place selectively on specific sites on the surface. The hydrogen uptake capacity of CNTs was also found to be affected by the purity of the materials, increasing with increasing purity. Temperature programmed desorption indicated that relatively strong adsorption bonds develop between adsorbent and adsorbate and that a single type of adsorption site exists on the solid surface.     

Optimization of the pore structure of nickel/graphite hybrid materials for hydrogen storage

Nickel/graphite hybrid materials were prepared by mixed acid treatment of graphite flakes, following metal nanoparticle deposition. The textural properties were studied by BET surface area measurement and t-plot methods with N₂/77 K adsorption isotherms. The hydrogen storage characteristics of the nickel/graphite at 298 K and 10 MPa were studied using a pressure-composition-temperature apparatus. The pore structure of the materials was studied as a function of processing conditions. In the optimum material, the hydrogen storage capacity was as high as 4.48 wt.%. The total amount of storage was not proportional to the specific surface area or metal content of the adsorbate. A dipole-induced model on nickel/carbon surfaces is proposed for the hydrogen storage mechanism.     

The adsorption refrigeration characteristics of alkaline-earth metal chlorides and its composite adsorbents

A study was conducted on the adsorption characteristics of the adsorption refrigeration working pairs using alkaline-earth metal chlorides as adsorbents and ammonia as refrigerant. The adsorption isotherms between alkaline-earth metal chlorides and nitrogen were studied. The study shows that the adsorbents of CaCl₂, SrCl₂ provide better adsorption capability associated with ammonia when compared to that of MgCl₂, BaCl₂. CaSO₄ was added into the CaCl₂, SrCl₂ with a mass ratio 20%, respectively, in order to solve the swelling and smashing problems encountered with CaCl₂, SrCl₂ adsorbent particles. The adsorption refrigeration experiments of composite adsorbents were investigated. The results show that the refrigeration capacity of the unit adsorbent of CaCl₂/CaSO₄ is 1.26 times higher than that of CaCl₂, and SrCl₂/CaSO₄ is 1.6 times higher than that of SrCl₂ at 100 °C. The mechanism of NH₃ adsorption and the gelatification of CaSO₄ were also discussed. BET (Brunauer–Emmett–Teller) specific surface area and pore structure of adsorbents were examined. Results show that the BET specific surface area and pore structure of composite adsorbents are retained well. This study indicates that the refrigeration capacity could be enhanced by compositing the adsorbents which indicates that composite adsorbents can perform better in adsorption refrigeration, and can be employed in adsorption refrigeration system using low-grade heat source.     

The porous structures of activated carbon aerogels and their effects on electrochemical performance

The pore structures of carbon aerogels were designed and controlled by changing conditions for both the microemulsion-templated sol–gel polymerization and the KOH activation processes. The resulting pore structures were characterized by means of N₂ adsorption and SEM. A new pore model is proposed and the relationship between the pore structures of the activated carbon aerogels (ACAs) and their electrochemical performance is discussed. The experimental results show that the ACAs which were prepared contain four types of pores: (A) micropores with diameters below 2 nm; (B) small mesopores with diameters from 2 to 5 nm; (C) large mesopores with diameters from 5 to 40 nm; and (D) large pores and channels with diameters over 40 nm. Appropriate activation with KOH can increase the numbers of micropores and small mesopores as well as the BET areas, resulting in an increase in the specific capacitance (C_s) of the ACA samples. The type D pores and channels play an important role in the enhancement of the electrochemical capacitance under high charge–discharge current conditions. Though ACAs with different porous models show a linear relation between C_s and BET area separately, the surface areas of micropores of the ACAs with appropriate type D pores and channels have a higher accessibility and efficiency in the storage of energy than those with closed type C pores.     

A remarkable increase in the adsorbed H2 amount: Influence of pore size distribution on the H2 adsorption capacity of Fe-BTC

Here we show the crucial role of ultramicropores on the adsorbed H₂ amount. By synthesizing Fe-BTCs via a perturbation assisted nanofusion synthesis strategy and by the control of textural porosity via Fe:BTC ratio, BET surface area (1312 m²/g), total pore volume (1.41 cm³/g), and H₂ adsorption capacity (1.10 wt% at 7.6 bar and 298 K) were enhanced by 1.6, 3.1, and 2.6 times, respectively. The reported BET surface area, and the total pore volume are the highest of those reported for Fe-BTC, to date. The enhanced H₂ adsorption capacity of Fe-BTC-3 is attributed to the ultramicropores present in its pore structure. Presence of ultramicropores maximizes van der Waals potential, and the adsorbed H₂ amount increases. By the perturbation assisted nanofusion synthesis strategy and the control over textural porosity, an Fe-BTC that possesses a H₂ adsorption capacity higher than those of reported MOFs with higher BET surface areas has been reported.     

Removal of Cu(II) from aqueous solution using the rice husk carbons prepared by the physical activation process

The adsorption of Cu(II) from aqueous solution by carbons prepared from rice husk through pyrolysis and steam activation was studied. The rice husk carbon was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), and its pore structure was also examined. After comparing different characteristics of the carbons prepared under different conditions and their adsorption abilities of Cu(II), the optimum temperature for pyrolysis and steam activation was chosen as 700 and 750 °C, respectively, using 3% (V/V) steam as the best activation gas. It was found that the Cu(II) adsorption on the rice husk derived carbons was pH and temperature dependent with an optimum pH value of 5.0, and an equilibrium time of 24 h. The adsorption kinetics and isotherms of Cu(II) by the rice husk derived carbons were also investigated under four different temperatures, and good correlation coefficients were obtained for the pseudo-second-order kinetic models, and the Langmuir isotherm model fitted very well with the experimental data. The mean free energy E (kJ mol⁻¹) obtained in the Dubinin-Radushkevitch (D-R) adsorption isortherm equation indicated a chemical ion-exchange mechanism. Several thermodynamic parameters were also caculated to predict the nature of adsorption process.