The surface area and pore volume of carbonaceous materials, which are commonly determined by N2 and/or CO2 gas-physisorption, are important parameters when describing environmental processes such as ...adsorption. Their measurement requires prior degassing of samples, which can change the nature of the material. Current guidelines for biochar characterization recommend different degassing temperatures. To investigate how degassing temperatures affect gas-physisorption we systematically degassed a range of materials (four biochars, carbon nanotubes, and Al2O3 reference material) at different temperatures (105, 150, 200, 250 and 300°C; for ≥14h each). Degassing temperatures had no effect on Al2O3 or carbon nanotubes but the measured surface areas and pore volumes of biochars increased by up to 300% with degassing temperature. An equation is presented for predicting surface area obtained at different degassing temperatures. Elemental analysis and results from sorption batch experiments suggest that surface area and pore volume may increase as biochar components volatilize during degassing. Our results showed that degassing temperatures change material properties and influence gas-physisorption measurements, and therefore need to be standardized. These results may also apply to the characterization of other complex materials, including carbon nanotubes coated with natural organic matter and fouled activated carbon.
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•Specific surface area and pore volume increase with degassing temperature.•Upon degassing, non-carbonized organic fractions in the biochar volatilize.•Standardization of degassing protocols is urgently needed in the biochar community.•A simple equation is presented to make results from different studies more comparable.
•The specific surface area of monolayer GO is measured to be approximately 2391 m2/g.•The specific surface area of GO can be measured based on the shear viscosity of GO/water solutions.•The specific ...surface area of monolayer GO is calculated to be about 2418 m2/g.
Many applications of graphene oxide concern specific surface area. Monolayer graphene has a high specific surface area of about 2630 m2/g, but the specific surface area of monolayer graphene oxide reported in literature (usually 2–1000 m2/g) is much smaller. To date, the exact measurement of the specific surface area of monolayer graphene oxide still remains a challenge. Here we demonstrate that this specific surface area can be measured in water by a rheology-based method. Graphene oxide was fully exfoliated in water to obtain monolayer graphene oxide/water solutions. Its specific surface area was theoretically calculated to be about 2418 m2/g, and was measured to be approximately 2391 (±1292) m2/g. The measured value is obviously larger than those in literature, and is close to the theoretical value. The advantages and disadvantages of this new method have been discussed.
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•Malachite green adsorption behavior on four types of commercial activated carbons was studied.•The effect of pore and surface chemical properties for malachite green adsorption is ...confirmed.•Malachite green adsorption performance on activated carbon depends on the total specific surface area.
Malachite green (MG) separation from wastewater has always been a research focus in the field of environment. Removal of MG from aqueous solution using activated carbon has been studied or verified. Because of the different preparation materials and processes, the physicochemical properties of activated carbons differ significantly, and it is not clear which parameter affects on MG adsorption and to what extend it is. Four types of commercial activated carbon were selected to study their MG adsorption performances systematically, such as adsorption contact time, equilibrium adsorption capacities, Langmuir and modified Langmuir equations fitting, adsorption thermodynamics and effect of pH. The study of contact time showed that MG adsorption on four activated carbons fits the pseudo-second-order equation in the initial stage. However, the adsorption kinetics is found to follow pseudo-first-order equation with the increase of adsorption capacities. Consistent with the results reported in the literature, the adsorption mechanism of MG on activated carbon is monolayer physisorption. We associated MG adsorption behavior on four activated carbons with the specific surface area from different pore structures and content of surface chemical groups, respectively. The results showed that the strong acidic groups have the detrimental influence on the MG adsorption, while the total specific surface area has a notable effect, showing a positive linear relationship between the total specific surface area and the adsorption capability. Therefore, the total specific surface area could be used as a key parameter to determine the adsorption performance of MG on activated carbon.
Hydrogen (H2) has been deemed as the most promising and valuable alternative to nonrenewable fossil fuels. Photocatalytic and electrocatalytic water splitting are considered to be the most efficient ...and environmentally friendly approaches for the sustainable H2 evolution reaction (HER). Graphene with a 3D framework has been utilized for the HER due to its unique structure and properties, including its hierarchical network, large specific surface area, diverse pore distribution, outstanding light absorption ability, and excellent electrical conductivity. The large specific surface area and hierarchically porous structure of 3D graphene can not only maximize the exposure of active sites but also promote electron transfer and gas product diffusion. In addition, the free‐standing 3D graphene monolith is easily recycled compared with powder phase support, which can prevent the loss of active catalysts. By making full use of the aforementioned merits, 3D graphene‐based composite materials show great promise as high‐performance catalysts toward photocatalytic and electrocatalytic HER. In this review, recent advances in fabricating 3D graphene‐based composite materials and their applications in both photocatalytic and electrocatalytic HER are summarized and discussed. Furthermore, the current challenges and future vision associated with the design, fabrication, and integration of 3D graphene‐based composite materials toward HER are put forward.
Three‐dimensional (3D) graphene is utilized for the photocatalytic and electrocatalytic H2 evolution reaction (HER) due to its unique structure and properties, including large specific surface area, hierarchical network, and excellent electrical conductivity. 3D graphene‐based composite materials exhibit high photocatalytic and electrocatalytic HER activity. This review summarizes the recent advances of 3D graphene‐based composite materials toward photocatalytic and electrocatalytic HER.
As a non-aqueous medium for increasing permeability in coal seams, liquid nitrogen fracturing has been widely studied. The changes of the pores in coal fractured by liquid nitrogen have important ...effects on coalbed methane (CBM) migration. It is difficult to thoroughly characterize the pore structure in coal using a single method. Therefore, this study carried out a detailed study of the pores in coal samples fractured by liquid nitrogen using both nitrogen adsorption and mercury intrusion. The results show that combining these methods can accurately determine pore sizes and specific surface areas in the samples tested. The maximum liquid nitrogen adsorption capacity and the injected mercury volume in the samples were positively correlated with the freezing times and freeze–thaw cycles. This indicated that the number of pores in the coal gradually increased. Cumulative total pore and seepage pore volumes in the samples showed a positive exponential correlation with freezing time. The volume increases also correlated with the number of freeze–thaw cycles and this increase followed a quadratic function. The cumulative specific surface areas also varied with freezing time but the areas first rose and then fell as the freeze–thaw cycles increased. Liquid nitrogen freezing time significantly affects the micropores and specific surface area. However, freezing time has only a minor effect on the larger seepage pores and the total pore volume. Liquid nitrogen freeze–thaw cycles help the formation of connections between micropores and larger pores and thus promote the development of fracture networks. This provides favorable conditions for CBM production.
Gas physisorption is an experimental technique based on equilibrium Van der Waals interactions between gas molecules and solid particles, that quantifies the specific surface area (SSA), pore size ...distribution (PSD), and pore volume of solids and powders. The performance of catalysts, absorbents, chromatography column materials, and polymer resins depends on these morphological properties. Here we introduce the basic principles and procedures of physical adsorption, especially nitrogen physisorption, as a guide to students and researchers unfamiliar with the field. The Brunauer‐Emmett‐Teller theory (BET) is a common approach to estimate SSA that extends the Langmuir monolayer molecular adsorption model to multilayer layers. It relies on an equilibrium adsorption isotherm, measured at the normal boiling point of the adsorbate, eg, 77 K or 87 K for N2 and Ar, respectively. Web of Science indexed 45 400 articles in 2016 and 2017 that mentioned N2 adsorption porosimetry—BET and BJH (Barrett‐Joyner‐Halenda) keywords. The VOSViewer bibliometric tool grouped these articles into four research clusters: adsorption, activated carbon in aqueous solutions for removal of heavy metal ions; synthesis of nanoparticles and composites; catalysts performance in oxidation and reduction processes; and photocatalytic degradation with TiO2. According to the literature, the accuracy of the density function theory (DFT) method is higher than with the BJH theory and it is more reliable.
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•Water treated reduced the pore volume and specific surface area.•Compared with water treated, mesopore volume increased in ionic liquid treated coal.•After ionic liquid treated, the ...pore becomes rougher and more complex.•Ionic liquid treated can change pore structures and improve coalbed methane mining.
In order to study the variation of pore characteristics and fractal dimensions, coal samples are treated by ionic liquid with different concentrations. Then the N2 isotherm adsorption/desorption experiment is carried out. The results show that water treatment caused a decrease in total pore volume. While the total pore volume in ionic liquid treated coal samples are larger than that in water treated coal sample. In comparison with water treated coal sample, the volumes of micropores in ionic liquid treated coal samples are reduced and the specific surface areas are increased. However, the volume and specific surface area of the mesopores are opposite to those in the water treated coal sample. The fractal dimensions D1 and D2 are calculated. The results show D1 decreases in water treated coal sample while increases in ionic liquid treated coal samples. D2 decreases obviously in water treated coal sample. Besides, it is lower than that in ionic liquid treated coal samples. Those indicate single water treatment will decrease the surface roughness and structural complexity of pores, while ionic liquid treatment will increase it. This study is of great significance to enhance the CBM exploitation and reduce the water block effect.
Porous carbon spheres (PCS) with different specific surface areas and porous structures were prepared by templated self-assembly method. The as-prepared PCS had uniform radically distributed ...channels, single cavity and dispersed dendritic pore structures respectively. The whole blood clotting time tests showed the good hemostatic properties of PCS, even better than Celox. It's probably the specific surface area made the difference over the hemostatic performance of PCS. The possible reason is that the higher specific surface area can increase the contact area between PCS and blood, promote blood coagulation rapidly. And the oxygen polar functional groups on the surface of PCS can rapidly stimulate platelets and red blood cells when in contact with blood. Both of the hemolysis rate and cell viability experiments proved that PCS had good biocompatibility. The hemostatic effect of PCS in vivo were preliminary validated on the mouse tail-cutting model and the rabbit liver injury model, and all PCS could efficiently control the caudal and hepatic hemorrhage. Especially, PCSF127 with a pore size of 3 nm and specific surface area of 335 m2 g−1 showed the best hemostatic efficiency, and it was expected to be an ideal candidate for rapid hemostasis in the battlefield or pre-hospital.
Porous carbon spheres with different pore structures and specific surface areas were prepared by templated self-assembly synthesis method. The negative charges carried by the porous carbon spheres activate coagulation factor FXII to trigger a coagulation cascade reaction to complete rapid hemostasis, and the hydroxyl groups on the surfaces, as oxygen polar groups, can rapidly stimulate erythrocytes and platelets when contacting with blood, thereby having a good application prospect in the fields of rapid hemostasis and wound care. Display omitted
•Porous carbon spheres (PCS) were prepared with templated self-assembly.•The microstructure made the difference over the hemostatic performance of PCS.•PCS could efficiently control the caudal and hepatic hemorrhage.
Porous carbon-based electrode materials have been widely used in supercapacitors (SCs) because of their good physicochemical stability, high specific surface area, adjustable pore structure, and ...excellent electrical conductivity. The factors influencing their SC performance are analyzed, which include specific surface area, pore structure, surface heteroatoms, structural defects and electrode structure. The high surface area accessible to ions provides abundant active sites for their storage, while a suitable pore structure is important for the accommodation and diffusion of ions, thereby influencing the specific capacitance and rate performance of the electrodes. An appropriate pore size with a narrow distribution is required to increase the volumetric energy density while mesopores are favorable for ion transport, so a good balance between micro and mesopore volumes is important to improve both the energy and power densities of the SCs. Structural defects, surface heteroatoms and a rational electrode structural design all play significant roles in the capacitance performance.
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•Conventional surface area calculations of biochars based on N2 can be unreliable.•N2 induced adsorption stress artificially enlarges the surface area of certain biochars.•The ...Brunauer-Emmett-Teller method enhances errors from N2 adsorption measurement.•Pore specific methods enable a reliable adjustment of the surface area calculation.•A modified calculation method is proposed to ensure comparability between biochars.
A large specific surface area is one of the structural characteristics which makes biochar a promising material for novel applications in agriculture and environmental management. However, the high complexity and heterogeneity of biochar’s physical and chemical structure can render routine surface area measurements unreliable. In this study, N2 and CO2 characterization of twelve biochars from three feedstocks with production temperatures ranging from 400 °C to 900 °C were used to evaluate materials with varying structural properties. The results indicate that the frequently reported peak in the surface area of biochars around 650 °C is an artefact of N2 measurements and not confirmed by CO2 analysis. Contradicting results indicate an influence of the structural rigidity of biochar on N2 measurements due to pore deformation in certain biochars. Pore non-specific calculation models like the Brunauer-Emmett-Teller method do not allow for adjustments to these changes. Instead, the use of a pore specific model and the exclusion of pores smaller than 1.47 nm was found to achieve more representative results. The proposed calculation was validated on an external dataset to highlight the applicability of the method. Our results provide novel insights for understanding the structural evolution of biochar related to production temperature.
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