Abstract Activated Carbon Research Articles

Role of Activated Carbon Precursor for Mercury Oxidation and Removal: Oxidized Surface and Carbene Site Interaction

Activated carbon (AC) is widely accepted for the removal of inorganic contaminants like mercury; however, the raw material used in the production of activated carbon is not always taken into consideration when evaluating its efficacy. Mercury oxidation and adsorption mechanisms governed by carbene sites are more likely to occur when graphitic-like activated carbons (such as those produced from high-ranking coals) are employed versus lignocellulosic-based ACs; this is likely due to the differences in carbon structures where lignocellulosic materials are less aromatic. In this research, the team studied bituminous coal-based ACs in comparison to coconut shell and wood-based (both less aromatic) ACs for elemental mercury removal. Nitric acid of 0.5 M, 1 M, and 5 M concentrations along with 10 M hydrogen peroxide were used to oxidize the surface of the ACs. Boehm titrations and FTIR analysis were used to quantify the addition of functional groups on the activated carbons. A trend was observed herein, resulting in increasing nitric acid molarity and an increased quantity of oxygen-containing functional groups. Gas-phase mercury removal mechanisms including physisorption, oxygen functional groups, and carbene sites were evaluated. The results showed significantly better elemental mercury removal in the gas phase with a bituminous coal-based AC embodying similar physical and chemical characteristics to that of its coconut shell-based counterpart. The ACs treated with various oxidizing agents to populate oxygen functional groups on the surface showed increased mercury removal. It is hypothesized that nitric acid treatment creates oxygen functional groups and carbene sites, with carbene sites being more responsible for mercury removal. Heat treatments post-oxidation with nitric acid showed remarkable results in mercury removal. This process created free carbene sites on the surface and shows that carbene sites are more reactive to mercury adsorption than oxygen. Overall, physisorption and oxygen functional groups were also dismissed as mercury removal mechanisms, leaving carbene-free sites as the most compelling mechanism.

Enhancement of Cu(II) adsorption on activated carbons by non-thermal plasma modification in O2, N2 and O2/N2 atmospheres

Abstract Activated carbon (AC) was modified by using non-thermal plasma in O2, N2 and O2/N2 atmospheres to increase its Cu(II) adsorption capacity and quantify the influences of the modifying atmospheres. SEM, BET, FT-IR and XPS were used to characterize the surface physical and chemical properties of AC. The results show that the AC modified by using plasma had significantly better Cu(II) adsorption performance than the raw AC. Among the O2, N2 and O2/N2 atmospheres, the AC with plasma modification in N2 showed best Cu(II) adsorption performance and the Cu(II) adsorption capacity was 369.5% higher than the raw AC. The AC modified in O2 atmosphere can form C—COOH groups, while the AC modified in N2 atmosphere can form C—NH2 groups. These two groups are both beneficial for Cu(II) adsorption, where the —NH2 groups are more effective for Cu(II) adsorption compared to —COOH groups. The chemisorption dominated the Cu(II) adsorption on the plasma modified AC and the adsorption performance was dependent on the surface functional groups properties of AC.

Preparation of composite adsorbents of activated carbon supported MgO/MnO2 and adsorption of Rhodamine B.

Activated carbon (AC) was modified by MgO and MnO2 through an impregnation-precipitation-calcination procedure. The batch experiments of adsorption of Rhodamine B (RB) by a modified adsorption material, an MgO-MnO2-AC composite, were carried out and the characteristics of the composite adsorbent were evaluated. The results showed that manganese/magnesium loading changed the surface area, pore volume and increased the number of active adsorption sites of AC. The highest Brunauer-Emmett-Teller (BET) surface area (1,036.18 m2·g-1) was obtained for MgO-MnO2-AC compared with AC. The content of AC loaded with magnesium and manganese was 34.24 and 5.51 mg·g-1 respectively. The adsorption of RB on MgO-MnO2-AC was significantly improved. The maximum adsorption capacity of RB on MgO-MnO2-AC was 16.19 mg·g-1 at 25 °C under the RB concentration of 50 mg·L-1. The adsorption of RB by AC and MgO-MnO2-AC increased with the initial concentration of RB. The adsorption of RB increased first and then decreased when pH was between 3 and 11. The results indicated that the pseudo-second-order kinetic equation and Langmuir equation can be used to describe the adsorption of RB on MgO-MnO2-AC.

Lithium-Ion Capacitor with Three-Dimensional Porous HAC/SP/PVDF as Positive Electrode

Activated carbon (AC) was acidified with dilute sulfuric acid (H2SO4) as an acidifying agent to obtain acidified activated carbon (HAC). The positive electrode was prepared by mixing HAC with a conductive agent (SP) or polyvinylidene fluoride. Carbon nanotubes and mesocarbon microbeads, as negative materials, were prelithiated and used as the negative eletrode. The positive electrode and negative electrode were assembled into the lithium ion capacitor. Materials and electrodes were characterized by scanning electron microscopy; elemental analysis, chemical bond analysis and specific surface area analysis of acidified activated carbon were made by x-ray energy spectrum analysis, an intelligent Fourier transform infrared spectrometer and specific surface space as well as a porosimetry analyzer (BET); The electrochemical capability of lithium ion capacitors was tested by constant current charge and discharge as well as electrochemical impedance. From the results, it can be concluded that the activated carbon acidified successfully grafted with hydroxyl (OH) and carboxyl (COOH) functional groups has increased the surface area by about 60% compared with AC. Under this situation, the charge and discharge current density is 50 mA/g. Also the capacitor has a mass ratio of 40.17 F/g, whose maximum power density is 0.98 kW/kg (700 mA/g) and maximum energy density is 52.34 Wh/kg (50 mA/g). Impedance tests showed that it has low impedance characteristics; the capacitance retention rate is above 60% after 2000 cycles of charge and discharge; the energy density can still reach 21.68 Wh/kg with a power density of 0.98 kW/kg. The electrochemical capability of the lithium ion capacitor was improved with acidified activated carbon as positive electrode.

Application of waste tyre-based powdered activated carbon for the adsorptive removal of cylindrospermopsin toxins from environmental matrices: Optimization using response surface methodology and desirability function

Activated carbon (AC) derived from waste tyre was investigated for the removal of cylindrospermopsin (CYN) from aqueous solutions and spiked real water samples. Response surface methodology based on Box–Behnken design was used for the optimization of experimental conditions. Based on the desirability score of 1.0, the percentage recovery of CYN was optimized at 104% and the optimum conditions were found to be 50.0 mg for the mass of adsorbent, 60 min for contact time and sample pH value of 3. The experimental equilibrium data best fitted Langmuir isotherm model and the maximum monolayer adsorption uptake of the waste tyre-based AC (WTAC) was 107 µg g−1. Kinetic studies demonstrated that the adsorption data were best described by pseudo-second-order. Finally, the optimized adsorption process was applied for the removal of CYN from real samples.

Activated carbons from common nettle as potential adsorbents for CO2 capture

Abstract Activated carbons (ACs) prepared from common nettle (Urtica Dioica L.) were studied in terms of carbon dioxide adsorption. ACs were prepared by KOH chemical activation in a nitrogen atmosphere at temperatures (ranging from 500 to 850°C). The pore structure and the surface characterization of the ACs were specified based on adsorption-desorption isotherms of nitrogen measured at –196°C and carbon dioxide at 0°C. The specific surface area was calculated according to the BET equation. The pore volume was estimated using the DFT method. The highest values of the specific surface area (SSA) showed activated carbons produced at higher carbonization temperatures. All samples revealed presence of micropores and mesopores with a diameter range of 0.3–10 nm. The highest value of the CO2 adsorption, 4.22 mmol/g, was found for the material activated at 700°C.

Reduction of chlorate and regeneration of activated carbon used for chlorate adsorption

AbstractActivated carbon (AC) from coal, coconut and palm kernel shell was regenerated after adsorbing chlorate from chlor-alkali plant brine solutions. Hydrochloric acid (HCl) of 17% w/w concentration showed the ability to regenerate AC, with some chlorine gas being released. Regeneration with HCl yielded enhanced adsorption of chlorate. AC from coconut shell adsorbed chlorate better than coal and palm kernel shell AC. Higher chlorate concentration in the influent and lower influent pH resulted in better adsorption. Regeneration of the AC with 17% w/w HCl reduced chlorate to chlorine derivatives. The AC released 107 mg/g of chlorine during the first regeneration and 160–178 mg/g after the second regeneration. During regeneration, coal AC released the highest amount of chlorine at 0.51–0.59 mg/g of chlorate adsorbed followed by palm kernel shell with 0.34–0.36 mg/g, while coconut shell AC released 0.18 mg/g. Scanning electron micrograph of the coconut shell AC carried out after each regeneration showed the structure of AC remained intact, with active sites surfacing on the regenerated AC. Using AC for chlorate adsorption followed by regeneration with 17% w/w HCl may reduce the release of brine and chlorate to the environment from chlor-alkali plants.

Preparation, adsorptive properties and chemical regeneration studies of high-porous activated carbon derived from Platanus orientalis leaves for Cr(VI) removal.

Activated carbon (AC) was prepared from Platanus orientalis leaves by H3PO4 activation using a microwave heating method and characterized by SEM (scanning electron microscopy), Brunauer-Emmett-Teller (BET) surface area analysis and FTIR (Fourier transform infrared spectroscopy) techniques. AC exhibited a surface area of 1089.67 m2/g and a relatively high pore volume of 1.468 cm3/g. Utilization of AC for the removal of Cr(VI) from aqueous solution was researched. The adsorption efficiency was highly pH dependent and adsorption capacity of AC for Cr(VI) could reach up to 135.24 mg/g. Adsorption equilibrium could be quickly reached within 2 h. A kinetic study indicated that the adsorption of Cr(VI) conformed to the pseudo-second-order model (R2 > 0.99). An intraparticle diffusion model was applied to describe the adsorption kinetics, and the results showed that there are other factors that affect the rate. Chemical regeneration for AC saturated with Cr(VI) was performed and HNO3 displayed the best regeneration performance among the four chemical regeneration agents (HNO3, H2SO4, NaOH, NaCl). The regeneration performance increased at first and then decreased with the rise of HNO3 concentration, and regeneration reaction could reach equilibrium within 4 h in the first cycle. The FTIR spectra revealed that HNO3 successfully introduced N-H bonds onto the AC surface in the regeneration process.

Mercury (II) adsorption from aqueous solution using nitrogen and sulfur co-doped activated carbon.

Activated carbon (AC) was modified with urea, thioglycolic acid and thiourea to obtain nitrogen doped activated carbon (ACN), sulfur doped activated carbon (ACS) and nitrogen and sulfur co-doped activated carbon (ACNS), respectively. The AC samples were characterized by elemental analysis, N2 adsorption-desorption, determination of the pH of the point of zero charge (pHpzc) and X-ray photoelectron spectroscopy, and tested for adsorption behaviors of Hg(II) ions. The experimental data of equilibrium isotherms fitted well with the Langmuir model. ACNS showed the highest adsorption capacity of 511.78 mg/g, increasing more than 2.5 times compared to the original ACA. The adsorption process followed pseudo-second-order kinetics. The thermodynamic parameters of ΔH°, ΔS°, and ΔG° at 30 °C were -20.57 kJ/mol, -0.032 kJ/mol K and -10.87 kJ/mol, respectively. It was concluded that the Hg(II) ions' adsorption on ACNS was exothermic, spontaneous and physiosorptive in nature. Finally, the adsorption capacity of ACNS reduced by just 8.13% even after the sixth cycle compared to the initial cycle.

Preparation and Utilization of the Precursor Activated Carbon from Carbon Enriched Fuel Oil Fly Ash: Part II Removal and Speciation of Chromium(III and VI) from Wastewater

Activated carbon (AC) prepared from residual fly (FA) was activated by combined CO2-steam gasification and physically modified with procaine hydrochloride (PQ+Cl-). Modified AC was used as low cost and effective solid phase extractor (SPE) for removal, total determination and chemical speciation of chromium(III&VI) in wastewater. Pseudo-second order rate equation is proposed for assigning the kinetics of chromium(VI) sorption in aqueous HCl (1.0 mol L-1) by PQ+Cl-- modified AC . The data were correlated with surface structure of the SPE. A dual separation mechanism of chromium(VI) as a binary complex ion associate [PQ+.CrO3Cl-] in/on the modified AC via "weak base anion exchanger" and an added component of “surface adsorption” is proposed. At 2 mL min-1 flow rate Sorption of spiked chromium(VI) at known concentrations (0.5-20 mg mL-1) from water onto modified AC packed columns at 2 mL min-1 was achieved. The sorbed chromium(VI) species were successfully recovered (106.0±2- 110 ±3%, n=3) from AC packed column with NaOH (10 mL, 1.0 mol L-1). Chromium(III) after oxidation to chromium(VI) was also enriched and eluted from the AC packed column and analyzed. Modified PQ+Cl- AC packed column was also used for total determination and speciation of chromium(III & VI) species at trace levels in environmental water samples. Good apparent recovery percentage (94.6±6.3-102.0± 8.5 %) of chromium species was achieved confirming the analytical utility of the modified AC-packed column for removal, total determination and speciation of chromium(III & VI) species in environmental water samples.

The atomic scale structure of saccharose-based carbons

Activated carbons (ACs) have a wide range of applications, in which the largely expanded specific surface plays a major role. The question of their structure came back to the limelight with the discovery of nanotubes fullerenes, which suggested that curved surfaces may be present in their structure and which incorporates well into the ideas of ACs porous structure. The source of those curved surfaces is atomic defects present inside the in-plane graphitic honeycomb lattice. Such defects have a crucial influence on the macroscopic morphology as well as physical properties of the material. The activated carbon (AC) in this work was derived from carbonised saccharose by activation with NaOH. Both materials – before and after activation were investigated. The main methods used in this study are wide angle neutron scattering and wide angle X-ray scattering combined with computer simulations. Confirmation of the proposed structures was sought with high-resolution transmission electron microscopy and Raman scattering. In this case, the use of classical crystallography to interpret experimental data was impossible due to the lack of periodic three-dimensional symmetry. Due to this fact, the data was analysed both in real and reciprocal space in the form of a pair correlation function and a structure factor. The experimental data were compared with calculated atomistic models. As a validation, the discrepancy factor between the theoretically and experimentally obtained functions was used. The presented innovative approach can be applied to different carbon materials with varying degrees of disorder.

Wood based activated carbons for supercapacitor electrodes with sulfuric acid electrolyte

Abstract Activated carbons (ACs) based on wood charcoal were synthesized via sodium hydroxide activation and studied as electrode material in supercapacitors (sulfuric acid electrolyte). In focus were the porous structure of the ACs and their electrochemical properties as a function of the synthesis conditions. The data of surface area and pore volume and pore size dimensions (determined by N2 adsorption and evaluated based on three theories) of the ACs activated at 700°C and with NaOH/carbonizate ratios of 2 and 3.7 are reported, such as the specific capacitance (F g−1), specific resistance (Ohm cm), electrolyte volume (mm3 g−1) and the specific power capacity of a cell (Wh kg−1) of the supercapacitors made of various ACs. It was established that the porosity is increasing with increasing activation temperature and activator rate while the specific capacitance of the device increased up to 390 F g−1 based on elementary cell mass.

Lignocellulosic-Based Activated Carbon Prepared by a Chemical Impregnation Method as Electrode Materials for Double Layer Capacitor

Activated carbons (ACs) were prepared from a lignocellulosic-based waste material by a chemical impregnation method using KOH, NaOH or CaCl2 as the activating agent. These ACs were characterized by different techniques such as N2 adsorption, FTIR, XRD and SEM. Electrostatic properties viz. pH and pHpzc of AC suspensions in aqueous media were measured. The concentration of surface oxygenated functional groups of the ACs was estimated following the Boehm titration method. Cyclic voltammetry was conducted in H2SO4 after fabricating two-electrode capacitor cells of the ACs. The correlation of AC surface chemistry and morphology with electrochemical performance (capacitance) of powdered electrodes is analyzed and discussed.

Activated Carbon as Heterogeneous Catalyst of Catalytic Ozonation Activity for Improvement RB 49 Dye Degradation

Activated carbon (AC) catalyst was successfully improved activity for the degradation of Reactive blue 49 dye (RB 49) in catalytic ozonation system. The degradation of the RB 49 dye was visualized by UV-Visible spectroscopy. As the RB 49 degradation kinetics were investigated by different initial parameters, initial RB 49 concentrations, AC catalyst loading, H2O2 dosage and additives. The degradation efficiency of AC catalytic ozonation towards RB 49 was found to be 95% when compared to 45% using pure ozone. The concentration of AC catalyst ranged from 0, 0.01, 0.05 and 0.1 g/L. We found that the maximum pseudo first and second order rate constant were 0.186 min-1 and 1.416 L.mg-1min-1 for 0.05 g/L AC. The results showed that the optimum of AC concentration in system was 0.05 g/L. In addition, this research studied the effect of auxiliary chemicals such as NaCl, Na2CO3, Na2SO4 and H2O2 upon dye degradation in AC catalytic ozonation system.

Porosity Development of Activated Carbons Prepared from Wild Almond Shells and Coir Pith Using Phosphoric Acid

Activated carbons (ACs) are prepared from wild almond shells (AS) and coir pith (CP) using phosphoric acid as an activating agent. Various process parameters like acid concentration, impregnation ratio, activation temperature, and time are optimized for better iodine adsorption capacity and yield. The impregnation ratio and the activation temperature are found to be the key parameters governing the porosity, surface area, and the yield of AC. The Brunauer-Emmett-Teller (BET) analysis of ACs shows that the surface areas are 1133.25 and 1210.58 m2/g with the yields of 32.8 and 40.7%, respectively, produced from wild AS and CP. The maximum adsorption capacities for methylene blue are as high as 788.88 and 708.33 mg/g. The equilibrium data is best described by the Langmuir and the Temkin isotherm, while the adsorption follows second-order kinetics, indicating that the intraparticle diffusion is one of the rate-controlling steps.

Effect of micropore and mesopore structure on CO2 adsorption by activated carbons from biomass

Activated carbons (ACs) were produced by a one step process with CO 2 as the physical activation agent at 800 °C. The ACs were further activated chemically using KOH, HNO 3 or CH 3 COOH and heat-treated at 300 or 600 °C for 1 or 2 h to modify their properties. The effect of CO 2 concentration, activation time, types of chemical agents and the post heat-treatment conditions on CO 2 capture were investigated. Results showed that the optimum conditions for AC production from corn stalks was at 800 °C for 30 min with a CO 2 concentration of 20% during the physical activation. Chemical agents and further heat-treatment modified the pore structure of the ACs, resulting in a performance improvement for CO 2 adsorption. The BET surface area of one sample (HNO 3 activation + 100 °C water bath 1 h + post heat-treatment at 600 °C for 2 h) was 639. 8 m 2 /g. The maximum CO 2 adsorption capacity of the sample was 7.33 wt%, which is higher than that of a commercial AC (6.55 wt%). The CO 2 adsorption is dominantly dependent on the mesopore volume when the BET surface area is smaller than 500 m 2 /g while the adsorption is closely associated with micropore area when the BET surface area is larger than 500 m 2 /g. The adsorption kinetics agreed well with the Bangham kinetic model. [New Carbon Materials 2015, 30(2): 156–166]

The influence of the acidic scouring treatment on the wastewater treatment of TiO2 loaded activated carbon electrode

Activated carbon (AC) electrodes were loaded with TiO2 by using sol–gel method after a pretreatment process, the effect of the acidic pretreatment of the TiO2 loaded electrode on its deionization efficiency of the wastewater containing NaCl solutions was studied; the physical, chemical and electrochemical properties of the electrode were characterized. The physical and chemical properties of the activated carbon before and after loaded with TiO2 nanoparticles are characterized by using scanning electron microscopy, energy dispersion spectrum analyzer, Brunauer–Emmett–Teller gas adsorption method, thermal gravimetric analysis, Fourier transform infrared spectroscopy respectively . Electrochemical properties were characterized by employing electrochemical workstation and electrical adsorption deionization test. It was found that both the specific capacitance and the ions removal efficiency of the activated carbon loaded with TiO2 had an increase of 16.4 and 49.8 % respectively in comparison with original activated carbon electrode. It was believed that this is due to the presence of crystal anatase TiO2 nanoparticles (the mass content of titanium element in the TiO2/AC complex is about 24.91 %) on the surface and pores in the activated carbon; while Ti–O–C bonds was found on the surface of the activated carbon, its surface wetting properties was significantly improved. However, it was also noticed that and the specific surface area of the activated carbon was decreased from 680.5 to 523.35 m2 g−1. This might lead to the decrease of the physical adsorption properties of the activated carbon electrodes, but its Electrical double-layer capacitance increases, electrical adsorption efficiency was improved.

Preparation and Characterization of Microporous Activated Carbon from Raw Anthracite

Activated carbon (AC) is a kind of artificial carbon materials with highly developed pore structure and high specific surface area. As sound adsorption materials, the AC shows excellent adsorption property, good chemical stability, high mechanical strength and easy-to-regeneration characteristics, which makes it a widely application in the fields of chemical industry, environmental protection, food and pharmaceutical industry, electrode materials, and so on [1-3].

Preparation of activated carbon from wet sludge by electrochemical-NaClO activation

Activated carbon (AC) from sludge is one potential solution for sewage sludge disposal, while the drying sludge is cost and time consuming for preparation. AC preparation from the wet sludge with electrochemical-NaClO activation was studied in this work. Three pretreatment processes, i.e. chemical activation, electrolysis and electrochemical-reagent reaction, were introduced to improve the sludge-derived AC properties, and the optimum dosage of reagent was tested from the 0.1:1 to 1:1 (mass rate, reagent:dried sludge). It was shown that the electrochemical-NaClO preparation is the best method under the test conditions, in which AC has the maximum Brunauer, Emmett and Teller area of 436 m2/g at a mass ratio of 0.7. Extracellular polymeric substances in sludge can be disintegrated by electrochemical-NaClO pretreatment, with a disintegration degree of more than 45%. The percentage of carbon decreased from 34.16 to 8.81 after treated by electrochemical-NaClO activation. Fourier transform infrared spectra showed that a strong C–Cl stretching was formed in electrochemical-NaClO prepared AC. The maximum adsorption capacity of AC reaches 109 mg/g on MB adsorption experiment at pH 10 and can be repeated for three times with high removal efficiency after regeneration.

A Study of the Adsorption of Aromatic Compounds Using Activated Carbons Prepared from Chestnut Shell

Activated carbons (ACs) prepared from chestnut shell were used as adsorbents for the removal of benzoic acid, salicylic acid and phenol from aqueous solutions. Adsorption studies were carried out by modifying activation temperature, concentration of activating acid and pH. The samples presented a microporous texture with acidic groups on the surface. It was found that the adsorption process not only depended on the porosity and the functional groups present in the AC, but was also affected by the solubility, the number and type of substituent groups, the superficial acidity in the adsorbate and the adsorbate-adsorbent interactions. The order of removal capacity was determined as follows: salicylic acid > benzoic acid > phenol. The differences in energy between the orbital frontier of the electronic densities of the adsorbent and the adsorbates, predicted by the HyperChem program, explained the experimental data pretty well.