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A series of new granular carbonaceous adsorbents was prepared via single-stage physical and chemical activation of walnut shells. Their suitability for removing various types of organic pollutants (represented by dyes, surfactants and water-soluble polymers) from the liquid phase was assessed. The activation of the precursor was carried out with CO2 and H3PO4 using conventional heating. Activated biocarbons were characterized in terms of chemical composition, acidic–basic nature of the surface, textural and electrokinetic properties as well as thermal stability. Depending on the type of activating agent used during the activation procedure, the obtained biocarbons differed in terms of specific surface area (from 401 to 1361 m2/g) and the type of porous structure produced (microporosity contribution in the range of 45–75%). Adsorption tests proved that the effectiveness of removing organic pollutants from the liquid phase depended to a large extent on the type of prepared adsorbent as well as the chemical nature and the molecular size of the adsorbate used. The chemically activated sample showed greater removal efficiency in relation to all tested pollutants. Its maximum adsorption capacity for methylene blue, poly(acrylic acid), poly(ethylene glycol) and Triton X-100 reached the levels of 247.1, 680.9, 38.5 and 61.8 mg/g, respectively. [ABSTRACT FROM AUTHOR]

Activated carbons exhibit a high grade of porosity, which together with structural stability, regenerability and cyclability makes them capable of achieving excellent hydrogen adsorption capacity. A further advantage comes from the ease of production and the use of recyclable and biocompatible materials. A simple way to produce activated carbons from amorphous cellulose involves procedures in which a pyrolysis process is combined with physical activation in CO 2. We used this approach by optimizing the production process tuning the activation times. The aim is to evaluate the influence of this process parameter on the formation of the specific surface area, the pore volume and fraction of micropores with a typical size <2 nm. The influence of these structural parameters on the hydrogen adsorption properties was then evaluated. The textural and adsorption characteristics were investigated using a commercial volumetric apparatus (ASAP 2460, Micromeritics) at −196 °C and pressures between 0 and 1 bar, while the morphological properties were investigated using scanning electron microscopy. The results show that the nanostructured samples are characterized by a very high degree of ultra-microporosity (<0.7 nm) with an average pore size between 0.5 and 0.6 nm and a high specific surface area, reaching maximum values around 1500 m2/g and micropore volume up to 0.58 cc/g. These morphological characteristics strongly influence the hydrogen adsorption properties, where the molecules adsorbed reach values very close to the coverage of ideal monolayer. The synthesized activated carbon samples show a higher hydrogen adsorption capacity than similar commercial materials tested under the same thermodynamic conditions. [Display omitted] • Easily tuning of ultra-microporosity. • Precursor influence on storage performance. • Hierarchical porous carbons and possibility hydrogen storage at low pressure. • Fully reversible hydrogen physisorption. • Amorphous cellulose as sustainable solution. [ABSTRACT FROM AUTHOR]

Waste biomass, a renewable energy source, is inexpensive material that has great potential in sorption and electrochemical application. The selected waste materials (corncobs, coconut shells, walnuts, and pistachio husks) allow to close the production cycle and enable material recycling, which are important aspects in the hierarchy of waste management. The proposed methodology for production and activation of biochars can be used industrially due to highly porous structure, developed surface area, and sorption ability of the obtained activated carbons (AC). A significant increase (from 4 up to more than 10 times) in specific surface area (SSA) is observed for all samples after the CO2 activation process (0.5 h at 800 °C) up to 725 m2 g−1 for corncobs, 534.9 m2 g−1 for pistachio husks, 523 m2 g−1 for coconut shells, and 393 m2 g−1 for walnut husks. The highest value of SSA is achieved for the AC derived from corncobs. This material is evaluated for use as an adsorbent, revealing 99% removal of Rhodamine B (dye/AC ratio of 0.0017) and 69% removal of chromium (dye/AC ratio of 0.0028). Based on the adsorption kinetics analysis, it is demonstrated that the Cr(VI) undergoes physical adsorption, while RhB undergoes chemisorption. In addition, corncob-derived AC exhibits superior electrochemical performance in 6 M KOH compared to the nonactivated biochar. A specific capacitance of 70 F g−1 at 5 A g−1 is achieved, along with outstanding rate capability (45 F g−1 at 50 A g−1) and cycling stability (94% at 10 A g−1 after 10,000 cycles). In contrast, the nonactivated sample shows only 34 F g−1 at 5 A g−1 and 13 F g−1 at 50 A g−1, with a stability of 91.4%. [ABSTRACT FROM AUTHOR]

The main objective of the study was to prepare a series of new activated biocarbons by means of physical and chemical activation of elderberry inflorescence. The influence of carbon matrix nitrogenation/oxidation on the physicochemical properties and sorption abilities of the carbonaceous materials was investigated. The impact of initial dye concentration, pH and temperature of the system on methylene blue and rhodamine B removal efficiency was checked. It was shown that activation of elderberry inflorescences with CO2 or H3PO4, and their further modification by introducing nitrogen or oxygen functional groups, allowed us obtain a wide range of materials that differ significantly in terms of the chemical nature of the surface, degree of specific surface development and the type of porous structure generated. The samples prepared by chemical activation proved to be very effective in terms of cationic dyes adsorption. The maximum sorption capacity toward methylene blue and rhodamine B reached the level of 277.8 and 98.1 mg/g, respectively. A better fit to the experimental data was achieved with a Langmuir isotherm than a Freundlich one. It was also shown that the efficiency of methylene blue and rhodamine B adsorption from aqueous solutions decreased with increasing temperature of the system. [ABSTRACT FROM AUTHOR]

The main objective of the study was to prepare a series of new activated biocarbons by means of physical and chemical activation of elderberry inflorescence. The influence of carbon matrix nitrogenation/oxidation on the physicochemical properties and sorption abilities of the carbonaceous materials was investigated. The impact of initial dye concentration, pH and temperature of the system on methylene blue and rhodamine B removal efficiency was checked. It was shown that activation of elderberry inflorescences with CO2 or H3PO4, and their further modification by introducing nitrogen or oxygen functional groups, allowed us obtain a wide range of materials that differ significantly in terms of the chemical nature of the surface, degree of specific surface development and the type of porous structure generated. The samples prepared by chemical activation proved to be very effective in terms of cationic dyes adsorption. The maximum sorption capacity toward methylene blue and rhodamine B reached the level of 277.8 and 98.1 mg/g, respectively. A better fit to the experimental data was achieved with a Langmuir isotherm than a Freundlich one. It was also shown that the efficiency of methylene blue and rhodamine B adsorption from aqueous solutions decreased with increasing temperature of the system.

Bark residues of the forest species Cedrela fissilis were physically and chemically modified with zinc chloride (ZnCl2) as an activating agent. The two modified materials were analyzed as adsorbents in removing atrazine and 2,4-D herbicides from effluents. Firstly, the precursor material and the modified ones were characterized by different techniques to identify the structural changes that occurred in the surfaces. Through TGA, it was observed that both modified materials have thermal stability close to each other and are highly superior to the precursor. X-ray diffractions proved that the amorphous structure was not altered, the three materials being highly heterogeneous and irregular. The micrographs showed that the treatments brought new spaces and cavities on the surface, especially for the material carbonized with ZnCl2. The pHPZC of the modified materials was close to 7.5. The physically modified material had a surface area of 47.31 m2 g−1 and pore volume of 0.0095 cm3 g−1, whereas the carbonized material had a surface area of 98.12 m2 g−1 and pore volume of 0.0099 cm3 g−1. Initial tests indicated that none of the adsorbents were efficient in removing 2,4-D. However, they showed good potential for removing atrazine. The Koble-Corrigan isothermal model best fits the experimental data, with a maximum capacity of 3.44 mg g−1 and 2.70 mg g−1 for physically modified and with ZnCl2, respectively. The kinetic studies showed that the system tends to enter into equilibrium after 120 min, presenting good statistical indicators to the linear driving force model (LDF). The surface diffusion coefficients were 2.18×10−9 and 2.37×10−9 cm2 s−1 for atrazine adsorption on the physically and chemically modified materials. These results showed that the application of residues from the processing of cedar bark is promising. However, new future studies must be carried out to improve the porous development of the material and obtain greater adsorption capacities. [ABSTRACT FROM AUTHOR]

Using physical activation, a new composite adsorbent was prepared by modifying low-cost local adsorbent. This low-cost local adsorbent was also prepared from activating sludge, bentonite, and limestone (SBL). In comparison to the low-cost LCL, the adsorption capacity of the new composite adsorbent was improved. This was measured in terms of its ability to remove sulfate from wastewater. The behavior of the sulfate adsorption processes by using (SBL) as an adsorbent was investigated in batch experiments by examining different values of solution pH, contact time, adsorbent dose, and initial SO4 concentration. The high removal efficiency was exhibited by (SBL) = 96%. These results reveal the great potential of the new composite adsorbent (SBL) if applied to the absorption of sulfate ions.

Background and purpose: This study was conducted for the first time to produce activated carbon (AC) from Milkvetch wood by physical activation in order to achieve the maximum adsorbent capacity in adsorption of dye. The aim of this study was to remove acid orange 7 (AO7) dye using AC produced by physical activation with nitrogen gas. Materials and methods: AC activation was performed by physical method using nitrogen gas at 700°C. Scanning electron microscopy and isotherm technique were used to determine the structural characteristics of the adsorbent. The effect of operating parameters was investigated. The isotherms and kinetics of the dye adsorption were also studied. Results: The synthesized AC-700°C sample had a specific surface area and a total pore volume of 774 m2 /g and 181.49 m3 /g, respectively. The maximum adsorption of dye was 57.125 mg/g (removal efficiency 91.4%) that occurred at pH= 3, 0.04 g absorbent in 50 ml of solution, and 50 mg/l of dye in 75 min. The adsorption data followed the Langmuir adsorption isotherm model and the pseudo-second order model kinetics. Also, the ability to reuse the adsorbent using the heating method showed that the synthesized adsorbent can be used for three consecutive times with good performance. Correlation coefficients (R2 ) for genetic program and neural network were 0.98 and 0.99, respectively, indicating the agreement of laboratory data with the models. Conclusion: The as-prepared AC by physical activation has a high potential for adsorption of AO7 dye from aqueous solutions. [ABSTRACT FROM AUTHOR]

Activated carbon (AC) is a carbonaceous material used to adsorb and remove pollutants. One of the requirements for the material to be considered a precursor in the AC production is its high levels of carbon. Therefore, a promising alternative for the use of forest biomass and its residues would be the application of these materials as precursors in the AC production. Owing to the productive capacity of activated carbon in Brazil and the considerable availability of forest biomass, the objective of the study was to approach the production and market of activated carbon in Brazil. This study is a bibliographic review focused on the use of forest resources for the AC production. AC production occurs by three methods: physical, chemical and physico-chemical activation. At the national level, the main production method is the physical one, since it has the least cost. However, the Sector still requires the researches and technologies aimed at the standardisation and improvements in the whole production chain. [ABSTRACT FROM AUTHOR]

This study investigated the alternative cheap eco-friendly materials date palm (Phoenix dactylifera) fibers for the preparation of activated carbon (AC) by physical activation with CO2 at different parameters of pyrolysis: pyrolysis temperature, the particle size and the duration of pyrolysis. The physical characterization (porosity and surface) was determined by the adsorption–desorption of nitrogen at 77 K (BET) and Dubinin–Radushkevich (D-R) equations, as well as the analysis by scanning electron microscopy. The chemical characterization (surface function), which was carried out by the Boehm titration, the pH zero-point charge (pHzpc) and Fourier transform infrared spectroscopy, confirmed the acidic character of the material. The adsorption of phenol from aqueous solutions onto the prepared AC was investigated. The adsorption process followed the Langmuir isotherm model with a maximum adsorption capacity of 31.75 mg g–1 for date palm fibers. [ABSTRACT FROM AUTHOR]

In this study, Cinnamon sticks, a low-cost farming by-product abundant in Egypt, were tested as a precursor for the production of porous carbons with high surface area and large pore volume using a two-step preparation method carbonization followed by physical activation in the presence of carbon dioxide. The influences of the pyrolysis temperature and activation hold-up time on the porosity of the activated carbon were studied. The BET surface area and the total pore volume of the prepared carbon were utilized as the criteria for selecting the optimum preparation parameters. The optimum temperature for pyrolysis was found to be at a temperature of 900 °C, hold-up time of two-hour, a nitrogen flow rate of 150 cm3/min, and a heating rate of 10 °C/min. However, the optimum activation conditions were at a temperature of 900 °C, a CO2 flow rate of 150 cm3/min, a heating rate of 20 °C/min. and hold-up time of 120 min. Steadiness data were tailored to Langmuir, Freundlich, and Temkin isotherms, and the equilibrium data were best described by the Langmuir isotherm model, with a maximum monolayer adsorption capacity of 12.37 mg/g at 25 °C. The extreme monolayer adsorption capacity declined with rising temperature confirming the exothermic character of the adsorption interaction.

Physical adsorption on activated carbons has shown to be a very attractive methodology for CO2 separation from flue gas streams and biogas. In this context, the goal of this work was to prepare granular activated carbons intended for CO2 adsorption from an abundant and low-cost biomass residue (coconut shell) by using practical and cost-effective procedures. By the first time, parameters involved in chemical activation with dehydrating agents (H3PO4 or ZnCl2) and/or physical activation with CO2 were systematically screened in depth in order to obtain materials with improved performance for CO2 adsorption on a volume basis. Compared with the commonly used mass basis, the data expressed on a volume basis are very important for industrial applications because they permit to estimate the efficiency of a fixed bed adsorption column. The work permitted to prepare granular activated carbons with a blend of relatively high gravimetric CO2 uptake and bulk density, so that high volumetric CO2 uptakes were attained. The highest values were 2.67 and 1.17 mmol/cm3 for CO2 pressures of 1.0 and 0.15 bar, respectively. It is remarkable that the obtained results were similar to those reported by other authors for carbons chemically activated with KOH, the activation methodology that has been widely claimed as the one that produce ACs with the best performances for CO2 adsorption, but which involves severe restrictions. Therefore, the present work can be considered a very important step in paving the way toward making CO2 adsorption an each time more interesting technology to reduce the emissions of anthropogenic greenhouse gases.

An increasing level of carbon dioxide (CO2) in the atmosphere has ultimately resulted in global warming and climate change. The high-performance activated carbon (AC-WL) was synthesized from walnut shell, a low-cost biomass by-product, by physical activation using a tube furnace. The adsorption behavior of CO2 from the CO2/N2 mixture was investigated using a fixed bed. The surface and morphological characterizations of the produced activated carbons were measured using a BET analyzer and a scanning electron microscope (SEM). The effect of temperature, flow rate, CO2 level, and partial pressure on breakthrough behavior was analyzed, and the adsorption response presented in terms of breakthrough point and adsorption capacity. The breakthrough and saturation periods vary significantly with change in temperature. The steepness of the breakthrough curves signifies good utilization of adsorbent capacity at breakthrough point. The increase in temperatures and flow rates lead to an increase in the length of mass transfer zone. The adsorption capacity of 1.58 mmol/g was obtained at 1.30 bars and 293 K with higher capacity utilization factor of 0.8492.These results suggest that the walnut-based activated carbon is favorable for capturing CO2. [ABSTRACT FROM AUTHOR]

Activated carbon refers to a wide range of carbonised materials of high degree of porosity and high surface area. Activated carbon has many applications in the environment and industry for the removal, retrieval, separation and modification of various compounds in liquid and gas phases. Selection of the chemical activator agent is a major step controlling the performance and applicability of activated carbon. Here, we review chemical activators used to produce activated carbon. We compare the impregnation method with the physical mixing method used in activating with alkali hydroxides. We selected 81 articles from Google Scholar, PubMed, Scopus, Science Direct, Embase and Medlin databases. Eighteen articles report the activation with potassium hydroxide, 17 with phosphoric acid, 15 with zinc chloride, 11 with potassium carbonate, nine with sodium hydroxide, and 11 with new activating agents. Activation with phosphoric acid is commonly used for lignocellulosic material and at lower temperatures. Zinc chloride generates more surface area than phosphoric acid but is used less due to environmental concerns. Potassium carbonate, in comparison with potassium hydroxide, produces higher yields and a higher surface area for the adsorption of large pollutant molecules such as dyes. Activating with potassium hydroxide in terms of surface area and efficiency shows better results than sodium hydroxide for various applications. Also, the comparison of the physical mixing method and the impregnation method in activation with alkali metals indicates that the activated carbon obtained through physical mixing had a higher porosity than the activated carbon produced by the impregnation method. [ABSTRACT FROM AUTHOR]

Residues after supercritical extraction of hops were chosen as activated bio-carbons precursor. The actual adsorbent was prepared by physical activation of the starting material. Some amount of the activated bio-carbon was divided into two parts. One of them was washed with distilled water, while the other part of the activated bio-carbon was washed first with a 5% solution of HCl and then with distilled water. The activated bio-carbons obtained were subjected to textural characterization and determination of pH and the content of surface oxygen groups. Carbonaceous adsorbents obtained were tested for removal of gas pollutant of acidic character (nitrogen dioxide) and liquid organic (methylene blue) and inorganic (iodine) pollutants. The maximum sorption capacity of the carbonaceous adsorbents towards iodine was 1395 mg/g, while towards methylene blue it was 238 mg/g. The results have shown that physical activation of the residue after supercritical extraction of hops is possible to be used as precursor of activated bio-carbons showing high adsorption capacity towards nitrogen dioxide reaching a maximum of 72.1 mg/g. The effectiveness of nitrogen dioxide removal depends on bio-carbons preparation and the conditions of adsorption. [ABSTRACT FROM AUTHOR]

Activated bio-char prepared from the pyrolysis and CO 2 -based physical activation of Sargassum macro-algae was developed as a sustainable and cost-effective adsorbent for malachite green (MG) and methylene blue (MB) adsorption. Prepared activated bio-char was characterized with CHNS, FESEM, Raman, FT-IR and N 2 adsorption/desorption methods. Langmuir isotherm and pseudo second order kinetics model best fitted equilibrium and kinetics data. The maximum adsorption capacity for MG and MB were 500 and 204.8 mg/g. The effect of solution pH and temperature on adsorption efficiency was studied and discussed. Acid treatment easily regenerated the adsorbent. After 5 cycles, the MB and MG adsorption efficiency reached 89 % and 78 %, respectively. A Density Functional Theory (DFT) calculation showed that pH-N-(CH 3) 2 of MB was strongly attracted to the -COOH functional groups in activated bio-char. For MG, the order of preferred interactions between the ph-N-(CH 3) 2 groups and the functional groups of adsorbent was -CONH 2 >-COOH>-COH. [Display omitted] • Mesoporous Sargassum macroalgae-derived activated biochar with high surface area. • A green and low-cost adsorbent with diverse functional groups and S/N doped carbons. • Regeneration of the adsorbent with acid treatment. • Investigation of the nature of adsorbent-adsorbate interactions by DFT calculation. [ABSTRACT FROM AUTHOR]

Sugarcane bagasse soot is an agro-industrial residue rich in carbon that can be transformed into value-added materials, such as activated carbons. Therefore, this work aimed at producing activated carbon from sugarcane bagasse soot, using CO at 800, 850, and 900 °C, and investigating its efficiency to adsorb methylene blue as model contaminant. The results showed that the surface area and pore volume increased in the obtained carbons, with high specific areas (up to 829 m/g), and the isotherms of the N adsorption describe mesoporous materials. The morphology of the prepared activated carbons showed that sugarcane bagasse soot and the activated carbons kept the fibrous structure of sugarcane bagasse, but after activation, they have cavities that resemble a honeycomb. Adsorption studies with methylene blue dye showed that the activation process resulted in adsorption capacities up to 11 times higher than sugarcane bagasse soot, which is comparable with commercial activated carbon. Dye adsorption kinetics could be described by a pseudo-second-order dependency in the studied materials, and the adsorption isotherms were better fitted by the Langmuir model. It is emphasized that cost-effective materials that are similar to commercial activated carbon were obtained. [ABSTRACT FROM AUTHOR]

Biogas produced from biomass is carbon neutral. In fact, the carbon feedstock of biomass is converted into gas phase. Biogas use in high efficient energy systems, such as Solid Oxide Fuel Cells is a viable choice. One of the most important drawbacks for such systems is related to the interaction between trace compounds and anode section. Gas cleaning through physical removal mechanisms is the simplest and cheapest method adopted in the literature. Coupled with this solution, the recovery of waste materials is an efficient application of the circular economy approach. In this work, a physical activation process was investigated experimentally for waste-derived materials at a temperature of 700 °C. The removal of H2S was considered as the most abundant trace compound. Activated biochar showed an adsorption capacity comparable to commercial sorbents, while the performance of ashes are still too poor. An important parameter to be considered is the biogas humidity content that enters in competition with trace compounds that must be removed.

The release of colored compounds containing wastewaters into the environment and surface water resources is known as a serious threat to public health and aquatic ecosystems. Accordingly, in the present study, cost-effective and efficient activated carbons (ACs) were prepared employing agricultural wastes (walnut shell) over a two-stage physical activation under CO2 at various activation temperature (700–1000 °C) and time (30–120 min). The prepared ACs were characterized by various analyses of SEM, XRD, FTIR, BET, and also their adsorption performance was checked via the measure of methylene blue (MB) number in order to determine selected activated carbon. According to the reported results, the AC produced at the activation temperature and time of 900 °C and 60 min, respectively, indicated better physicochemical properties and more favorable performance compared to others. The selected AC had the highest BET surface area (S BET) of 903.9 m2/g and the greatest adsorption capacity of 307.4 mg/g as the MB number. Furthermore, the adsorption capacity as iodine number and pH of point of zero charge (pH PZC) were reported to be 1150 mg/g and 4.6, respectively, for the selected AC. In the following, the performance of the selected AC was further evaluated as adsorption of synthetic (MB) and natural dyes from biologically treated wastewaters under different conditions. Maximum absorption capacity of the MB was obtained to be 307.45 mg/g at optimum conditions (the adsorbent dosage of 1 g/L, adsorbate concentration of 400 mg/L, contact time of 3 h, and agitation speed of 150 rpm). Moreover, the selected AC demonstrated appreciable performance at adsorbent dosage of 1 g/L and the contact time of 240 min using three biologically treated wastewaters. The highest adsorption capacity of 395.7 mg/g was obtained by the biologically treated baker's yeast wastewater as the adsorbate. The selected AC revealed the highest conformity with the Langmuir isotherm model (R2 = 0.9999) and the Pseudo-second-order kinetic model (R2 = 0.9994). • The walnut shell-based activated carbons (ACs) were physically synthesized. • The impact of activation temperature and time on the ACs properties was studied. • The AC performance was evaluated as natural dye removal from field samples. [ABSTRACT FROM AUTHOR]

Oil sands coke was activated with CO2 at 900°C in a tubular fixed bed reactor. Samples activated in a CO2 stream with 50% air contained a significant number of functional groups. Some activated samples were post-oxidised in air at 350°C to increase their surface functionality. Post-oxidation was necessary for the adsorption of ferric cations by the coke samples activated, except for the sample activated with 50% air. However, non-oxidised samples were also able to adsorb molybdate anions. Both organic and inorganic constituents of oil sands tailings water were successfully removed, but some inorganic species leached into water. [ABSTRACT FROM AUTHOR]

Abstract: The use of rubber-seed shell as a raw material for the production of activated carbon with physical activation was investigated. The produced activated carbons were characterized by Nitrogen adsorption isotherms, Scanning electron microscope, Thermo-gravimetric and Differential scanning calorimetric in order to understand the rubber-seed shell activated carbon. The results showed that rubber-seed shell is a good precursor for activated carbon. The optimal activation condition is: temperature 880°C, steam flow 6kgh−1, residence time 60min. Characteristics of activated carbon with a high yield (30.5%) are: specific surface area (SBET) 948m2 g−1, total volume 0.988m3 kg−1, iodine number of adsorbent (q iodine) 1.326gg−1, amount of methylene blue adsorption of adsorbent (q mb) 265mgg−1, hardness 94.7%. It is demonstrated that rubber-seed shell is an attractive source of raw material for producing high capacity activated carbon by physical activation with steam. [Copyright &y& Elsevier]

Industrial valorisation of low cost and renewable biomass as raw precursor of activated carbon for environmental applications is an interesting alternative to costly commercial activated carbons. In this study, the possible use of Mediterranean, Posidonia oceanica fibrous biomass, as a precursor for chars and physically activated carbons, is investigated. Firstly, the raw marine material was chemically and biochemically characterised throughout dry-basis elemental, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis. Then, several P. oceanica chars were prepared and characterised under different pyrolysis times and temperatures. In addition, physically activated carbons (PACs) were produced via water steam flow under various activation periods. The results showed that the pyrolysis induces the creation of pores at different levels with respect to the involved temperature. Thereafter, the physical activation tends to enhance the development of the porous structure. In that issue, the performed Brunauer–Emmett–Teller (BET) and Barrett–Joiner–Halenda (BJH) analysis revealed that the prepared PACs have a mainly mesoporous inner morphology with a varying fraction of micropores. [Copyright &y& Elsevier]

Abstract: This paper focuses on physical activation (CO2) and chemical activation (H3PO4, NaOH and KOH) of sewage sludge-based precursors. Our results show that (i) a simple acid washing treatment leads to a significant increase in the adsorption capacity of some precursors; (ii) under the experimental conditions tested, CO2 physical activation and chemical activation with H3PO4 were ineffective for an efficient porosity development and (iii) choosing an appropriate protocol, it is possible to obtain highly porous materials (700–1700m2 g−1) by chemical activation of sludge-based precursors with alkaline hydroxides. The efficiency of the chemical activation with NaOH or KOH is very much influenced by the method used for mixing the activating agent and the precursor. The BET values of the materials obtained when physically mixing ground hydroxides with the precursor almost doubled the values obtained if other mixing methods are employed. Increasing the hydroxide:precursor ratio leads to an enhancement of the adsorption capacity of the adsorbents, with BET values ranging from 689 to 1224m2 g−1 for NaOH activation and from 853 to 1686m2 g−1 for KOH activation. [Copyright &y& Elsevier]

A series of regeneration experiments with physical activation were carried out on bleaching earth waste from the soybean refining process in a rotary reactor. The influence of activation parameters on the spent clay by varying the holding time of 1∼4 hours and temperature of 700∼900°C was determined. The variations of pore properties as well as the change of chemical characteristics in the resulting solids were also studied. Results showed that the resulting samples were type IV with hysteresis loops corresponding to type H3 from nitrogen adsorption–desorption isotherms, indicating slit-shaped mesoporous characteristics. However, the regenerated clays had smaller surface areas (70∼117 m2/g) than that (245 m2/g) of fresh bleaching earth. Under the physical activation conditions investigated, the holding time of 1 hour and temperature of 700°C were found to be optimal conditions for producing mesoporous clay with physical activation. The adsorption of paraquat on regenerated sample was also evaluated. The isotherm showed that the regenerated sample still had a high affinity for this herbicide. Thus, the regeneration of this agro-industrial waste is one option for utilizing the clay resource, and it may be used for water treatment applications to remove organic contaminants. [ABSTRACT FROM AUTHOR]

Binder-less activated char briquettes from sewage sludge were prepared and used for the liquid-phase adsorption of methylene blue. The properties of sludge char briquettes prepared under the different initial sludge moisture content, compression pressure, and heating rate were systematically investigated through the tests of thermogravimetric analysis (TGA), scanning electron microscopy (SEM), surface and mechanical properties, burn-off rates, methylene blue adsorption kinetics and isotherms. All of the prepared briquettes presented hierarchical structures and microporous/mesoporous characteristics, and the increase of initial sludge moisture content from 10 to 30 wt% resulted in a great increase of surface area (S BET), total pore volume (V T), apparent density, and a slight decrease of mechanical performance. The decrease of compression pressure markedly enhanced the equilibrium adsorption capacity (q e, exp), owing to the decreased diffusion resistance and blockage of diffusion pathways inside briquettes. In consideration of the mechanical performance and adsorption capacity, the optimum preparation condition was obtained at the initial moisture content of 30 wt%, compression pressure of 25 MPa, and heating rate of 10 °C/min, in which the axial compressive strength (ACS) and q e, exp of the prepared briquettes were as high as 22.2 ± 3.1 kg/m2 and 316.9 mg/g. The results also showed that the equilibrium adsorption data fit well into the pseudo-first order model system, and the adsorption isotherms followed the Langmuir isotherm model, suggesting that the adsorption process was attributed to physical adsorption, and was inclined to happen on the adsorption sites with the same energy level. Finally, the thermal regeneration tests demonstrated that the binder-less briquette had a good regeneration performance and was worthy of reusing for industrial applications. [Display omitted] • Binder-less sludge briquettes showed a characteristic of hierarchical porous structures. • Briquettes prepared with sludge of higher moisture content showed higher S BET. • Briquettes prepared with sludge of lower moisture content showed higher mechanical performance. • Briquettes maintained 90% of initial adsorption capacity after thermal regeneration for three times. [ABSTRACT FROM AUTHOR]

The waste materials left after supercritical extraction of hop cones and marigold flowers were tested as precursors of activated bio-carbons. Adsorbents were produced by means of the physical (also called thermal) activation method using CO2 as the gasifying agent. All the activated bio-carbons were tested for the removal of NO2 and H2S from the gas phase under dry and wet conditions. The effects of the type of precursor and the activation procedure on the porous structure development, the acid-base properties of the surface, as well as the sorption capacities of the materials produced were also checked. The final products were bio-carbons of medium developed surface area with a basic surface nature, characterized by their high effectiveness in removal of gas pollutants of acidic character, especially nitrogen dioxide (sorption capacities in the range from 12.5 to 102.6 mg/g). It was proved that the toxic gas removal efficiency depends considerably on the sorption conditions and the activation procedure. All materials showed greater effectiveness in gas removal when the process of adsorption was carried out in the presence of steam. [ABSTRACT FROM AUTHOR]

• Mesoporous structure promotes adsorption of CO 2 and NH 3 more significantly. • Effect of functional groups in the micropores is greater than that of pore structures. • NH 3 inhibits the construction of O-containing functional groups by H 2 O. • Combination of simulation and experiment is used for biochar adsorption research. CO 2 emission reduction has become a global consensus, and the most potential carbon emission reduction technology-Carbon Capture and Storage (CCS) is still in the development stage. In order to make up for the shortcomings of CCS technology, the idea of functionalized biochar-ammonia carbon capture system is proposed. Corn straw was used as raw materials, and activated biochar were prepared by one-step/two-step H 2 O/NH 3 ·H 2 O activation, to construct a hierarchical-functionalized structure of biochar, and explore its adsorption characteristics of CO 2 and NH 3. Various methods such as solid characterization, temperature programmed desorption, molecular dynamics and quantum chemical simulation were used to explore the structure-effect relationship between the physicochemical properties of biochar and the adsorption of CO 2 and NH 3. The results show that the pore structure of gas-physical activated biochar is dominated by micropores. The one-step method is beneficial to the construction of functional groups on biochar surface, while the two-step one is conducive to the improvement of pore formation and its aromatization. During NH 3 ·H 2 O activation, NH 3 would inhibit the formation of O-containing functional groups on the surface of biochar by H 2 O. Compared with O-containing groups, the N-containing functional groups on biochar surface have greater adsorption energy for CO 2 and NH 3 adsorption. The adsorption sites of CO 2 and NH 3 are mainly in the micropores (d < 0.7 nm), and the contribution of functional groups in the micropores to the adsorption of CO 2 and NH 3 is greater than the pore structure. This study provided theoretical basis for the development of new biochar-ammonia CO 2 capture system. [ABSTRACT FROM AUTHOR]

Chichá-do-cerrado (Sterculia Striata St. Hil. et Naud) is a Brazilian native plant whose nuts have interesting nutritional value. However, the fruit shells (CH) have never been evaluated for potential uses. This study aimed to characterize the biochar (BC–CH) and the activated carbons synthesized by chemical (K–CH) and physical (C–CH) processes. The activated carbons were evaluated on metformin adsorption and treatment of a synthetic mixture. Pyrolysis increased the carbon content and the H/C ratio indicated higher aromatization for C–CH. BC–CH presented low surface area, which was increased mainly with KOH activation (1273.6 m2 g−1). FTIR demonstrated the degradation of lignocellulosic compounds and zeta potential inferred a higher number of oxygenated groups for C–CH. Regarding the adsorption studies, the kinetics demonstrated an equilibrium time of 60 min and the isotherm resulted in a maximum experimental adsorption capacity of 33.75 and 45.50 mg L−1 for C–CH and K–CH, respectively. Interestingly, C–CH presented the highest removal percentage of the synthetic mixture, indicating the role of Cu (II) interactions and synergistic effects. In summary, it was verified the potential of the adsorbents in wastewater treatment, and the importance of evaluating the composition of the aqueous matrix, which can alter the adsorption mechanisms. ga1 • Chichá-do-cerrado as precursor of activated carbons was never evaluated before. • KOH-activated carbon had the highest surface area (1273.6 m2 g−1). • The oxygenated functional groups were more preserved in CO 2 -activated carbon. • The removal of metformin, caffeine, reactive black 5 and Cu (II) were evaluated. • Synergistic effects were suggested in the synthetic mixture. [ABSTRACT FROM AUTHOR]

This study was designed to prepare an adsorbent without any complex modification process for the removal of atrazine (AZN) from aqueous phase. Thus, Mobil composition of matter No. 41 (MCM-41) was synthesized and modified by physical activation at high temperature (650 °C). The synthesized adsorbent was tested by XRD, SEM, EDX, FT-IR and BET to confirm the successful synthesis as well as effectiveness for the adsorption of AZN. The average particle size of prepared material was found to be about 500 nm, while the BET calculations showed that adsorbent was porous with a specific surface area of 25.9 m2/g. Later, it was used in batch removal studies of AZN for which, it showed a high adsorption capacity of 89.99 (mg/g). The pH of 6, temperature of 313 K was found to be the optimized conditions for the maximum removal of AZN. Of the four kinetic models studied, the pseudo-first-order yielded a superior fit in comparison with the other three models. The results indicated that the five linearized adsorption equilibrium isotherm models (Langmuir, Freundlich, Dubinin-Radushkevich, Temkin and Harkins-Jura models) closely correlate the AZN adsorption removal process with Pearson correlation coefficient (R2) values of 0.9955, 0.8551, 0.8736, 0.8913 and 0.7253, respectively. The energy functions obtained by thermodynamic analysis suggested that the AZN sorption follows a non-spontaneous and endothermic path. Unlabelled Image • A thermally active adsorbent MCM-41 was fabricated for the rapid adsorption of atrazine. • Preparation of adsorbent does not involve any complex chemical treatment. • Change in the pH, temperature and initial adsorbate concentration massively affects the removal rate of atrazine. • Langmuir and pseudo first order made a best fit implying the physical adsorption. [ABSTRACT FROM AUTHOR]