Series Of Activated Carbons Research Articles

Surface Chemistry of Cherry Stone-Derived Activated Carbon Prepared by H3PO4 Activation

The preparation of activated carbons (ACs) from cherry stones and chemical activation with H3PO4 can be controlled by the experimental variables during the impregnation step in order to obtain a tailored porous structure of the as-prepared ACs. This control not only extends to the ACs’ texture and porosity development, but also to the chemical nature of their surface. The spectroscopic and elemental characterization of different series of ACs is presented in this study. The spectroscopic band features and assignments strongly depend on the H3PO4 concentration and/or the semi-carbonization treatments applied to the feedstock before impregnation, which ultimately influence different characteristics such as the AC hydrophilicity. Different surface chemistries arise from the different tailored impregnation solutions, showing a practical outcome for future applications of the as-prepared ACs.

Activated carbon preparation based on the direct molten-salt electro-reduction of CO2 and its performance for VOCs adsorption

The conversion of CO2 into activated carbon (AC) for the adsorption of volatile organic compounds (VOCs) is a green strategy to treat waste by waste. In this study, CO2 was converted into a series of mesopore-enriched AC (MS-AC500, MS-AC550, and MS-AC600) by molten salt (MS) electrochemical method under different temperatures, and the prepared adsorbents were employed for the rapid adsorption of VOCs. The results showed that MS-AC500, MS-AC550, and MS-AC600 had a rich internal pore structure with specific surface area and pore volume of 816.70, 1062.05, 1255.50 m2/g and 0.58, 0.73, 0.84 cm3/g, respectively. The pore structures and surface chemistry of the adsorbents were positively correlated with the adsorption capacity, the adsorption amounts of MS-AC500, MS-AC550, and MS-AC600 were 244.89, 306.38, 414.39 mg/g for toluene and 279.29, 366.19, 460.10 mg/g for chlorobenzene, respectively. The superior adsorption capacity for chlorobenzene is mainly because chlorobenzene is a polar molecule and the C-O bonds inside the adsorbents have an attractive effect on the unpaired electrons inside the polar molecule. Simulation of the adsorption process of the adsorbents confirmed that the adsorption of both toluene and chlorobenzene was a physical adsorption process. Moreover, the adsorption-desorption cycle of chlorobenzene was more stable than that of toluene, and the durability of the adsorbent was above 95% after 5 cycles. This study can remove VOCs while reducing CO2 greenhouse gas, providing a feasible green route to treat waste by waste.

Shaping metal-organic framework (MOF) with activated carbon and silica powder materials for CO2 capture

Metal-organic framework (MOF) UTSA-16 (Co) was shaped into pellets with diameters of 0.2 mm using activated carbon (AC), silica, and 8% polyvinyl butyral (PVB)/ethanol solution as a binder. A series of AC and silica pellets was prepared with different percentages of the UTSA-16 (Co) MOF. As the percentage of UTSA-16 (Co) increased, the CO2 adsorption capacity and CO2/N2 selectivity of the AC and silica pellets increased. AC/UTSA-16 (Co)− 30% pellets showed 83% enhancement in CO2 adsorption capacity and 800% improvement in CO2/N2 selectivity at 298 K compared to the AC pellet. The stability of AC-UTSA-16 (Co) pellets was analyzed by exposing them to SO2 and NO2 for 2 days. The performance of AC was further investigated by preparing an AC composite pellet using UTSA-16 (Zn). AC/UTSA-16 (Zn)− 30% pellets showed 75% enhancement in CO2 adsorption capacity and 1000% improvement in CO2/N2 selectivity than parent AC pellet. CO2 adsorption–desorption cycles were performed to examine the long-term stability of the pellet composites. The pellets were characterized by scanning electron microscopy (SEM) for particle morphology, thermogravimetric analysis (TGA) for thermal stability, and Brunauer–Emmett–Teller (BET) method for structural properties.

Boosting Zn-ion storage capacity of pitch coke-based activated carbon via pre-oxidation assisted KOH activation strategy

Activated carbons (ACs) with unique structure are desired for high-performance of Zinc-ion supercapacitors (ZICs). Herein, a series of ACs were prepared using air pre-oxidation assisted KOH activation technology from pitch coke (PHC). The results show that pre-oxidation promotes the development of pore and the regulation of surface chemical composition of obtained ACs. Based on this experiment, the as-prepared AC-330 delivers suitable oxygen functional groups, high specific surface area of 3223 m 2 g −1 and high small-sized mesopore (2–4 nm) volume of 0.72 cm 3 g −1 . All these unique structures endow AC-330 with a satisfactory specific capacity of 212.5 mAh g −1 at 0.1 A g −1 , and it can still remain at 85 mAh g −1 even when the current density increased up to 20 A g −1 with an excellent capacity retention of 40%. Fortunately, it can also deliver high energy-power density parameters (170 Wh kg −1 at 170.4 W kg −1 and 67.2 Wh kg −1 at 32.3 kW kg −1 ). • Pitch coke-based porous carbon (AC) was obtained via pre-oxidation assisted KOH activation. • The obtained AC has well-developed mesoporous structure for rapid ion transport. • Ion diffusion coefficient as a function of V 2–4 nm /V mic ratio was investigated. • The maximum energy density and power output of ZICs are 170 Wh/kg and 32.3 kW kg −1 , respectively.

Reduction of C═C Double Bonds by Hydrazine Using Active Carbons as Metal-Free Catalysts

A series of active carbons with or without chemical oxidation by nitric acid have been prepared, and their activity was evaluated as metal-free catalysts for the C═C double bond hydrogenation using hydrazine as reducing agent in the presence of oxygen. It was observed that an optimal treatment by nitric acid results in a sample with enhanced catalytic activity that is superior to that measured under the same conditions for the other carbon materials. Kinetic data suggest that the active sites in the process could be quinone/hydroquinone type redox centers introduced in the oxidative treatment of AC by nitric acid. Nitric acid-oxidized active carbon has a wide substrate scope and also exhibits a chemoselective C═C hydrogenation with respect to nitro group reduction compared to conventional Pd/C catalyst.

Asphalt-derived high surface area activated porous carbons for the effective adsorption separation of ethane and ethylene

We reported novel asphalt–based activated carbons (A-ACs) with high C2H6/C2H4 adsorption capacity and selectivity. A series of A-ACs were prepared by a one-step preparation method and characterized. The adsorption performances of A-ACs for ethane/ethylene were examined. Results showed that the sample A-ACs prepared at 800°C and the KOH/asphalt ratio=4 exhibited ultra-high BET area of 3111m2/g and its pore volume reached 1.92cm3/g. Their surface O and N contents gradually decreased with activation temperature or KOH/asphalt ratio at which A-ACs were prepared. More interestingly, A-ACs showed significantly preferential adsorption of C2H6 over C2H4. It could be ascribed to the stronger interaction of C2H6 with the surfaces of A-ACs by hydrogen bonds compared to C2H4, which were revealed by Density functional theory calculation. Its C2H6 adsorption capacity was up to 7.2mmol/g at 100kPa and 25°C and its C2H6/C2H4 adsorption selectivity for typical cracked gas mixture (15:1 ethylene/ethane) was in the range of 3.2–16.3 at the pressure below 100kPa, higher than the most reported ethane-adsorbents. Additionally, the isosteric heat of ethane and ethylene adsorption on A-ACs were lower than those on π-complexation adsorbents. Therefore, these excellent adsorption properties would make A-ACs as a type of promising adsorbents for adsorption separation of C2H6/C2H4.

Physico-chemical characterization of activated carbon–metal oxide photocatalysts by immersion calorimetry in benzene and water

From a commercial activated carbon (AC) and Al3+, Fe3+, Zn2+, SnCl2, TiO2 and WO 4 2− in water, three series of AC–metal (hydr)oxide (MO) samples prepared by wet impregnation in two successive steps of soaking at 80 °C and oven-drying at 120 °C (S1) and subsequent heat treatment at 200 (S2) or 850 °C (S3) were characterized texturally by N2 adsorption at −196 °C and by immersion calorimetry in benzene and water. The mass changes associated with the preparation of the samples are usually stronger for S1 and S3 than for S2. The incorporation of MO to AC causes a greater decrease in the micropore volume and pore narrowing only for the SnCl2-impregnated sample. The opposite effects on the microporous structure are noted for most S2 and S3, as compared to S1. For AC, −∆i H(C6H6) is 114.0 J g−1 and −∆i H(H2O) is 30.5 J g−1. For the AC–MO samples, −∆i H(C6H6) and S tot(C6H6) are generally lower than for AC and vary by S3 > S2 > S1. However, −∆i H(H2O), S tot(H2O) and [O] are usually lower for S3. S tot(C6H6) is higher for the samples prepared using the metal ions. The results of immersion calorimetry for AC and AC–MO samples provide one with valuable information concerning the dependence of the hydrophobicity and hydrophilicity of the samples on the method used in their preparation.

Temperature dependence of dc electrical conductivity of activated carbon–metal oxide nanocomposites. Some insight into conduction mechanisms

From a commercial activated carbon (AC) and six metal oxide (Al2O3, Fe2O3, SnO2, TiO2, WO3 and ZnO) precursors, two series of AC–metal oxide nanocomposites are prepared by wet impregnation, oven-drying at 120°C, and subsequent heat treatment at 200 or 850°C in inert atmosphere. The temperature-dependent dc electrical conductivity of AC and the as-prepared nanocomposites is measured from room temperature up to ca. 200°C in air atmosphere by the four-probe method. The decrease in conductivity for the hybrid materials as compared to AC is the result of a complex interplay between several factors, including not only the intrinsic conductivity, crystallite size, content and chemical nature of the supported nanoparticles, which ultimately depend on the precursor and heat treatment temperature, but also the adsorption of oxygen and water from the surrounding atmosphere. The conductivity data are discussed in terms of a thermally activated process. In this regard, both AC and the prepared nanocomposites behave as semiconductors, and the temperature-dependent conductivity data have been interpreted on the basis of the classical model proposed by Mott and Davis. Because of its high content of heteroatoms, AC may be considered as a heavily doped semiconductor, so that conduction of thermally excited carriers via acceptor or donor levels is expected to be the dominant mechanism. The activation energies for the hybrid materials suggest that the supported metal oxide nanoparticles strongly modify the electronic band structure of AC by introducing new trap levels in different positions along its band gap. Furthermore, the thermally activated conduction process satisfies the Meyer–Neldel rule, which is likely connected with the shift of the Fermi level due to the introduction of the different metal oxide nanoparticles in the AC matrix.

Preparation and Microstructural Characterization of Activated Carbon-Metal Oxide Hybrid Catalysts: New Insights into Reaction Paths

In catalysis processes, activated carbon (AC) and metal oxides (MOs) are widely used either as catalysts or as catalyst supports because of their unique properties. A combination of AC and MO nanoparticles in a single hybrid material usually entails both chemical and microstructural changes, which may largely influence the potential catalytic suitability and performance of the resulting product. Here, the preparation of a wide series of AC−MO hybrid catalysts is studied. Three series of such catalysts are prepared by support first of MO (Al2O3, Fe2O3, SnO2, TiO2, WO3, and ZnO) precursors on a granular AC by wet impregnation and oven-drying at 120 °C, and by subsequent heat treatment at 200 or 850 °C in inert atmosphere. Both the chemical composition and microstructure are mainly investigated by powder X-ray diffraction. Yield and ash content are often strongly dependent on the MO precursor and heat treatment temperature, in particular for the Sn catalysts. With the temperature rise, trends are towards the transformation of metal hydroxides into metal oxides, crystallinity improvement, and occurrence of drastic composition changes, ultimately leading to the formation of metals in elemental state and even metal carbides. Reaction paths during the preparation are explored for various hybrid catalysts and new insights into them are provided.

Influence of moderate pre-oxidation treatment on the physical, chemical and phosphate adsorption properties of iron-containing activated carbon

A novel adsorbent based on iron oxide dispersed over activated carbon (AC) were prepared, and used for phosphate removal from aqueous solutions. The influence of pre-oxidation treatment on the physical, chemical and phosphate adsorption properties of iron-containing AC were determined. Two series of ACs, non-oxidized and oxidized carbon modified by iron (denoted as AC-Fe and AC/O-Fe), resulted in a maximum impregnated iron of 4.03% and 7.56%, respectively. AC/O-Fe showed 34.0%–46.6% higher phosphate removal efficiency than the AC-Fe did. This was first attributed to the moderate pre-oxidation of raw AC by nitric acid, achieved by dosing Fe(II) after a pre-oxidation, to obtain higher iron loading, which is favorable for phosphate adsorption. Additionally, the in-situ formed active site on the surface of carbon, which was derived from the oxidation of Fe(II) by nitric acid dominated the remarkably high efficiency with respect to the removal of phosphate. The activation energy for adsorption was calculated to be 10.53 and 18.88 kJ/mol for AC-Fe and AC/O-Fe, respectively. The results showed that the surface mass transfer and intra-particle diffusion were simultaneously occurring during the process and contribute to the adsorption mechanism.

Comparative study of nanopores in activated carbons by HRTEM and adsorption methods

Detailed analysis of nanopores (IUPAC micropores at pore half-width x<1nm) of carbonised porous phenolformaldehyde resin microbeads used as a precursor of activated carbon (AC) and CO2 activated carbon (at 50% burn-off) has been performed on the basis of high-resolution transmission electron microscopy (HRTEM) image analysis and nitrogen adsorption data analysed using several density functional theory (DFT) methods. The results of quenched solid DFT (QSDFT) and nonlocal (NLDFT) are in agreement with the pore size distributions of nanopores based on the HRTEM image analysis. Development of porosity with progressive activation degree in a series of ACs leads to enhancement of the deviation of the pore shape from the used pore models. The TG/DTA data and Raman spectra show nonlinear but weak changes in the AC characteristics with increasing burn-off degree.

Characteristics of an activated carbon monolith for a helium adsorption compressor

An activated carbon monolith (ACM) with a high helium adsorption/desorption capacity, high density, low pressure drop, low thermal expansion and good mechanical properties was prepared and applied successfully in a helium adsorption compressor as a part of a 4.5 K sorption cooler. The activated carbon (AC) used in the monolith preparation was selected from a series of ACs prepared from an anthracite and bituminous coals activated using KOH, NaOH and CO 2, and having a variety of surface areas, micropore size distributions and packing densities. The selected AC was combined with a binder to prepare an ACM with suitable mechanical properties for machining. The results of this study, related to an helium sorption compressor includes: packing density, mechanical properties (compression strength, vibration tests), thermal expansion, pressure-drop measurements and also helium adsorption isotherms measured at high pressure (up to 35 bar) and low temperatures (from 20 K up to 150 K).

Adsorption of mercury from single and multicomponent metal systems on activated carbon developed from cherry stones

The adsorption of mercury from a single/multi-solute aqueous solution by activated carbon (AC) prepared from cherry stones (CS) by chemical activation with H3PO4, ZnCl2 or KOH is studied. Three series of AC (i.e., P, H3PO4; Z, ZnCl2; K, KOH) were prepared by controlling the impregnation ratio and carbonization temperature. The textural characterization of AC was carried out by gas adsorption, mercury porosimetry and density measurements. The surface chemistry was analyzed by the pH of the point of zero charge (pHzpc), FT-IR spectroscopy and Boehm’s method. Experiments of mercury adsorption were conducted by the batch method, using aqueous solutions of mercury and of mercury, cadmium and zinc without pH adjustment. The ACs possess a wide range of pore volumes and sizes. Their microporosity is usually well developed. The meso- and macropore volumes are higher for the P carbons and K carbons, respectively. BET surface areas as a rule range between 1000 and 2000 m2 g−1. The pHzpc is much lower for the P carbons. The content of acidic oxygen surface groups is lower for the K carbons, whereas the content of basic groups is higher for these carbons. The kinetics of the adsorption process of mercury is faster for ACs with high volumes of large size pores. However, the surface groups have a marked unfavorable influence on the kinetics. The pseudo-second order rate constant (k2×10−3, g/mol h) is higher by the order Z-4-800 (67.69)>K-3-800 (43.45)>P-3.44-400 (36.98). The incorporation of zinc and cadmium to the mercury solution usually decelerates the adsorption process for the P carbons and Z carbons and accelerates it for the K carbons. The amount adsorbed of mercury is much larger for the K carbons than for the other ACs. For the Z carbons, competition effects of zinc and cadmium on the adsorption of mercury are negligible, which indicates that mercury adsorbs specifically on surface active sites of these adsorbents.

Relationship between the nanoporous texture of activated carbons and their capacitance properties in different electrolytes

A series of activated carbons (ACs) with progressively changing nanotextural characteristics was obtained by heat-treatment of a bituminous coal at temperatures ranging from 520 to 1000 °C, and subsequent activation by KOH at 700 °C or 800 °C. As the pre-treatment temperature increases, the total pore volume V T decreases from 1.28 to 0.30 cm 3 g −1, and the BET specific surface area from 3000 to 800 m 2 g −1. The specific capacitance determined for each series of ACs using symmetric two electrode cells in 6 mol L −1 KOH varies almost linearly with the BET surface area, suggesting that the charge accumulation is controlled primarily by the surface area development. A further analysis of the electrochemical behaviour in different electrolytic media—aqueous and organic—shows that an adequate pore size is more important than a high surface area in order to obtain high values of capacitance. Theoretical values of volumetric capacitance could be evaluated without considering the size of ions, which is always uncertain in solution, and compared with the experimental data as a function of the pore width. The efficiency of pore filling, i.e., of double layer formation, is optimal when the pore size is around 0.7 nm in aqueous media and 0.8 nm in organic electrolyte. A study of the performance of the positive and negative electrodes during the charge/discharge of the capacitor, reveals an additional pseudo-faradaic contribution due to oxygenated functionalities within the working potential window of the negative electrode. This effect is more pronounced for the ACs series obtained at 700 °C, because of their higher oxygen content.

Monitoring Changes in Surface and Structural Properties of Porous Carbons Modified by Different Oxidizing Agents

A series of active carbons and carbon blacks was oxidized with various oxidizing agents such as hydrogen peroxide, perchloric acid, and nitric acid. Their surface and structural properties were evaluated by use of nitrogen and water vapor adsorption isotherms, as well as high-resolution thermogravimetry. A comparative analysis of differential thermogravimetric curves and adsorption isotherms of nitrogen and water vapor for the samples studied showed that the surface properties of oxidized carbons depend on the type of oxidizing agent as well as oxidation conditions. This comparison shows that the modification of carbons with concentrated nitric acid caused the most pronounced surface and structural changes. These changes were much smaller for the samples modified with perchloric acid and hydrogen peroxide.