Porous Carbonaceous Adsorbents Research Articles

Synthesis of N/P/S Co-doped porous carbons by carbonizing polyphosphazene microspheres for highly selective adsorption of Pb (II)

Heteroatom-doping has emerged as a promising approach for enhancing the properties of carbon materials, particularly in the treatment of heavy-metal wastewater. However, the simultaneous synthesis of multi-heteroatom co-doped carbon materials poses significant complexity and challenges. Consequently, there is an increasing demand for the development of non-toxic and straightforward methods to prepare such materials. In this study, we present a novel approach for the synthesis of N/P/S co-doped porous carbonaceous adsorbents using polyphosphazene as precursors. Our focus is specifically on their effectiveness in adsorbing Pb (II). The results reveal that the synthesized adsorbents, denoted as carbonized polyphosphazene or CZ-600 exhibited a high carbon content co-doped with N, P and S atoms, as well as an abundance of oxygen-containing functional groups and a porous structure. These characteristics collectively contribute to the exceptional adsorption capacity of CZ-600 for Pb (II), with a maximum adsorption capacity of 121.7 mg/g and an equilibrium time as short as 20 min. Further investigations of the adsorption process involve fitting adsorption isotherm, kinetic, and thermodynamic models, revealing chemical adsorption as the predominant mechanism, supported by contributions from micropore adsorption and electrostatic interactions. This work proposes a sustainable and efficient solution for the treatment heavy-metal wastewater, which not only advances the understanding of heteroatom-doped carbon materials but also provides valuable insights into their practical applications in environmental remediation.

Removal of Ciprofloxacin from Water by a Potassium Carbonate-Activated Sycamore Floc-Based Carbonaceous Adsorbent: Adsorption Behavior and Mechanism.

In this study, a porous carbonaceous adsorbent was prepared from sycamore flocs by pyrolysis method and K2CO3 activation. The effects of preparative conditions of the material on its adsorptive property were explored. The optimal material (SFB2-900) was obtained with a K2CO3/biochar mass ratio of 2:1 at an activation temperature of 900 °C, possessing a huge surface specific area (1651.27 m2/g). The largest adsorption capacity for ciprofloxacin on SFB2-900 was up to 430.25 mg/g. The adsorption behavior was well described by the pseudo-second-order kinetic model and the Langmuir isothermal model. Meanwhile, this process was spontaneous and exothermic. The obtained material showed excellent adsorption performance in the conditions of diverse pH range, ionic strength, and water quality of the solution. The optimum adsorption conditions (pH = 7.01, dosage = 0.6 g/L, and C0 = 52.94 mg/L) determined based on the response surface methodology were in accordance with the practical validation consequences. The good regeneration effect of SFB2-900 manifested that this material had great practical application potential. Combining the experimental results and density functional theory calculation results, the adsorption mechanisms mainly included pore filling, π-π EDA interactions, electrostatic interactions, and H-bonds. The material could be regarded as a novel and high-efficiency adsorbent for antibiotics. Additionally, these findings also provide reference for the reuse of waste biomass in water treatment.

Understanding the synergy between N-doped ultra-microporous carbonaceous adsorbent and nitrogen functionalities for high performance of CO2 sorption

Porous carbonaceous adsorbents are believed to encourage contenders to CO2 uptake however their high production cost has urged researchers towards cheap renewable. In this study, nitrogen-doped carbonaceous adsorbents with high ultra-microporous structure were synthesized by carbonization and activation of chitosan along with urea and KOH simultaneously at various temperatures (600−900 °C). The effects of temperature, urea modification, and chemical activation on nitrogen functionalities and development of porous structure were analyzed. Results showed that porous carbons synthesized with urea and KOH modification at 700 °C exhibit the highest CO2 adsorption value (5.92 mmol g−1 at 0 °C and 4.45 mmol g−1 at 25 °C). Enhanced adsorption by NCABC-700 was found due to synergistic effect of nitrogen as well as high specific surface area (1404 m2 g−1) and micropore volume (0.68 cm3 g−1), respectively. Furthermore, best fitting of Freundlich isotherm model explained heterogeneous nature of adsorbent. Isosteric heat of adsorption with a value of 42.2 kJ mol-1, also indicated the presence of N containing functional groups and a high number of micropores that created a strong interaction between adsorbent and adsorbate, helping in high CO2 uptake.

Polyethyleneimine-modified biochar for enhanced phosphate adsorption.

Biochar, a low-cost porous carbonaceous adsorbent, has low adsorption capacity for anion contaminants. The objective of this study was to improve biochar's ability to adsorb phosphorus (P) through polyethyleneimine (PEI) modification to form an amine-functionalized biochar. Biochars prepared by pyrolysis of bamboo biomass, before and after PEI modification, were characterized using the Fourier transformed infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), elemental analysis, and batch sorption experiments. The effects of pH, coexisting anions, and ionic strength on P adsorption by PEI-modified biochar were also investigated. Results indicated that PEI was successfully grafted onto biochar which resulted an increase in surface amine group and in P adsorption. The peak of P adsorption occurred at pH of three and adsorption of P was decreased with increasing of ionic strength and when coexisting ions, such as HCO3-, SO42-, NO3-, and Cl-, were coexisted. The electrostatic interaction between P and surface functional groups of PEI-modified biochar served as the primary mechanism controlling the adsorption process. These results indicate that chemically functionalized biochar with amine groups can enhance P adsorption.

Chemically activated nanoporous carbon adsorbents from waste plastic for CO2 capture: Breakthrough adsorption study

Abstract This paper describes the preparation of O-enriched porous carbonaceous adsorbents derived from low cost, abundantly available polyethylene terephthalate (PET) waste with high carbon content by directly carbonising at different temperatures (500–800 °C) and then chemically activating using variable impregnation ratios of KOH to carbon. The prepared carbon adsorbents were characterized for their textural and surface chemical properties using nitrogen sorption, CHN, FTIR, XRD, SEM, HRTEM, and XPS techniques. Further, to assess their CO2 adsorption-desorption performance under dynamic conditions, breakthrough experiments were conducted in a fixed-bed adsorption set up. Porous carbon obtained at 700 °C with KOH to carbon mass ratio of 3 (Act-3-700) exhibited best textural properties with BET surface area of 1690 m2g-1 and micropore volume of 0.78 cm3 g−1 and showed highest CO2 uptake of 1.31 mmol g−1 at 30 °C and 12.5% CO2 concentration. Four adsorption–desorption cycles establish the adsorbent's remarkable stability and regeneration. Furthermore, fractional order kinetic model explained the CO2 adsorption kinetics and Freundlich isotherm showed superior fit with the adsorption equilibrium data suggesting heterogeneous nature of the adsorbent surface. Negative values of Gibbs free energy ΔG° and adsorption enthalpy ΔH° indicate the spontaneous and exothermic nature of adsorption process.

N-doped porous carbons from low-temperature and single-step sodium amide activation of carbonized water chestnut shell with excellent CO2 capture performance

The aim of this study is to exploit low-cost N-doped porous carbonaceous adsorbents with excellent CO2 adsorption properties. Herein, the N-enriched porous carbons were obtained through a single-step sodium amide activation of carbonized water chestnut shell at 400–500 °C. The optimal sample possesses high CO2 uptake of 4.50 mmol/g (25 °C) and 6.04 mmol/g (0 °C) at atmospheric pressure. Additionally, this sample displays high CO2/N2 selectivity, stable cyclic ability, moderate CO2 isosteric heat of adsorption, fast CO2 adsorption rate, and high dynamic CO2 uptake. In addition to the two well-known factors i.e. volume of narrow micropore and N content, the pore size distribution is also found to play major role in deciding CO2 adsorption performance for these adsorbents. The features of excellent CO2 adsorption properties, low-cost raw materials, low reaction temperature and facile preparation demonstrate that these adsorbents are prospective in the application of CO2 capture.

Preparation of porous carbon directly from hydrothermal carbonization of fructose and phloroglucinol for adsorption of tetracycline

Hydrothermal carbonization of biomass is a promising method to prepare carbonaceous materials. Generally, post physical or chemical activation is necessary to increase surface area and porosity of the carbon. Herein, porous carbonaceous material (FPC) with large surface area (481.7m2/g) and pore volume (0.73cm3/g) was prepared directly from hydrothermal carbonization of fructose and phloroglucinol in hydroalcoholic mixture. Structure characteristics of the FPC and its adsorption capacity for a representative antibiotic tetracycline in aqueous solution were investigated. This work provides a green and efficient method to fabricate porous carbonaceous adsorbent that has great potential applications in chemical and environmental fields.

Soluble hydrocarbons uptake by porous carbonaceous adsorbents at different water ionic strength and temperature: something to consider in oil spills.

Nowadays, petrochemical operations involve risks to the environment and one of the biggest is oil spills. Low molecular aromatics like benzene, toluene, and naphthalene dissolve in water, and because of their toxicological characteristics, these produce severe consequences to the environment. The oil spill cleanup strategies are mainly designed to deal with the heavy fractions accumulated on the water surface. Unfortunately, very limited information is available regarding the treatment of dissolved fractions.A commercial (Filtrasorb 400) and modified activated carbons were evaluated to remove benzene, toluene, and naphthalene from water, which are the most soluble aromatic hydrocarbons, at different ionic strengths (I) and temperatures (0-0.76M and 4-25°C, respectively). This allowed simulating the conditions of fresh and saline waters when assessing the performance of these adsorbents. It was found that the hydrocarbons adsorption affinity increased 12% at a I of 0.5M, due to the less negative charge of the adsorbent, while at a high I (≃0.76M) in a synthetic seawater, the adsorption capacity decreased 21% that was attributed to the adsorbent's pores occlusion by water clusters. Approximately, 40h were needed to reach equilibrium; however, the maximum adsorption rate occurred within the first hour in all the cases. Moreover, the hydrocarbons adsorption and desorption capacities increased when the temperature augmented from 4 to 25°C. On the other hand, thermally and chemically modified materials showed that the interactions between adsorbent-contaminant increased with the basification degree of the adsorbent surface.

A corn stalk-derived porous carbonaceous adsorbent for adsorption of ionic liquids from aqueous solution

Corn stalks were used to prepare a porous carbonaceous material with a high surface area of 2442 m2 g−1 by the hydrothermal carbonization of corn stalks followed by chemical activation.

Mathematical modeling of the Ni(II) removal from aqueous solutions onto pre-treated rice husk in fixed-bed columns: a comparison

One of the efficient techniques for the removal of heavy metals from wastewater is adsorption. In this paper, the adsorption of Ni on a new porous carbonaceous adsorbent, pre-treated rice husk particles, was investigated in both batch and column experiments. The equilibrium isotherm was described well by both the Langmuir and Freundlich isotherm. The Langmuir constants, qm and b, were estimated to be 8.0 and 0.15 l/mg, respectively. Different conditions of flow rate, bed heights, and initial nickel concentrations were considered in the column experiments. It was observed that the adsorption capacity of the packed-bed column and the breakthrough time were increased with an increase in the bed height and a decrease in the flow rate and the influent Ni concentration. The traditional Bohart–Adams, Thomas, and Yoon–Nelson models in accompany with the mass transport model were used to describe the adsorption process in the columns. The experimental breakthrough curves were described satisfactorily by all the aforementioned continuous models. However, the predicted maximum adsorption capacity using Bohart–Adams and Thomas models was less than the one obtained from batch equilibrium experiments. Whereas, there was a good agreement between the batch equilibrium results and the continuous mass transport model regarding the maximum adsorption capacity, indicating the prediction of column performance using batch experiments.

Optimization and Comparison of Cd Removal from Aqueous Solutions Using Activated and Non-activated Carbonaceous Adsorbents Prepared by Pyrolysis of Oily Sludge

New porous carbonaceous adsorbents were prepared from an oily sludge generated in a fuel oil storage tank using pyrolysis with and without activation by KOH at 600 °C. The pore characteristics of the activated carbonaceous adsorbent (AC), due to the formation of micropores and mesopores structure, were considerably better than those of non-activated carbonaceous adsorbent (NA). The adsorption of Cd from aqueous solutions on the produced carbonaceous adsorbents was optimized using the Taguchi method. Under optimum conditions, the Cd adsorption efficiency for the NA and AC was obtained to be 77.7 and 98.2 %, respectively. The initial concentration and the adsorbent dose were the most significant factors affecting the removal of Cd by NA and AC, respectively. The adsorption data for the AC were well fitted by the Langmuir, Freundlich, and Redlich-Peterson isotherms models. The regeneration and reuse of the adsorbents in the three cycles of Cd adsorption-desorption were possible. The carbonaceous adsorbents had acceptable efficiency for the removal of Cd from a mine wastewater. Based on the obtained results, the oily sludges available in huge amounts in the petroleum industry proved to be a potential precursor resource for the production of the porous carbonaceous adsorbents, particularly for application in the wastewater treatment.

Chemically activated fungi-based porous carbons for hydrogen storage

A set of porous carbons has been prepared by chemical activation of various fungi-based chars with KOH. The resulting carbon materials have high surface areas (1600–2500m2/g) and pore volumes (0.80–1.56cm3/g), regardless of the char precursors. The porosities mainly derived from micropores in activated carbons strongly depend on the activation parameters (temperature and KOH amount). All activated carbons have uniform micropores with pore size of 0.8–0.9nm, but some have a second set of micropores (1.3–1.4nm pore size), further broadened to 1.9–2.1nm as a result of increasing either the activation temperature to 750°C or KOH/char mass ratio to 5/1. These fungi-based porous carbons achieve an excellent H2 uptake of up to 2.4wt% at 1bar and −196°C, being in agreement with results from other porous carbonaceous adsorbents reported in the literature. At high pressure (ca. 35bar), the saturated H2 uptake reaches 4.2–4.7wt% at −196°C for these fungi-based porous carbons. The results imply a great potential of these fungi-based porous carbons as H2 on-board storage media.

Adsorption of tetracycline and chloramphenicol in aqueous solutions by bamboo charcoal: A batch and fixed-bed column study

Adsorption of two antibiotics, tetracycline (TC) and chloramphenicol (CAP), on a new porous carbonaceous adsorbent, bamboo charcoal (BC), is investigated in batch and fixed bed column experiments. Adsorption isotherms of TC and CAP obtained from batch experiments are better fitted by Freundlich and Dubinin–Radushkevich models compared with Langmuir model. In the fixed bed column experiments, lower bed height, higher flow rate and lower influent contaminant concentration lead to greater adsorption of TC and CAP on BC. A mass transfer model that incorporates both surface and intraparticle diffusion theory into the convection–dispersion equation (CDE) is developed to identify the key process controlling the rate of TC and CAP adsorption. The results demonstrate that the surface diffusion is the rate-limiting step for antibiotics adsorption onto BC, which is consistent with the results of traditional Adams–Bohart model. π–π Electro-donor–acceptor (EDA), cation-π bond in conjunction with hydrogen bonding interaction are the main mechanisms for the adsorption of TC and CAP on BC, while the hydrophobic interaction and electrostatic interaction have minor contributions.

Mechanistic aspects of nitrogen-heterocyclic compound adsorption on bamboo charcoal

Adsorption of three nitrogen-heterocyclic compounds (NHCs), pyridine, indole, and quinoline, on a new porous carbonaceous adsorbent, bamboo charcoal (BC), is investigated. Different structures and surface properties of BC are created by HNO3 and NaOH treatment as well as by microwave (MW) radiation. HNO3 treatment decreases surface area, micropore volume, and surface hydrophobicity, whereas NaOH treatment increases surface area and micropore volume. MW treatment dramatically increases hydrophobicity and fraction of aromatic structure. Adsorption isotherms of NHCs are nonlinear and better fitted by Freundlich model (FM) compared with Langmuir model (LM) and Polanyi–Manes model (PMM). The maximum adsorption capacities for pyridine, indole, and quinoline reach 42.92, 93.24, and 91.74mgg−1, respectively, at an initial concentration of 200mgL−1. Surface area, hydrophobicicty, and electrostatic and π–π electron-donor–acceptor (EDA) interactions are accountable for NHC adsorption. A model relating NHC adsorption (log K) and adsorbent–adsorbate physicochemical properties is developed to measure the relative contribution of these interactions giving the sequence of surface area>hydrophobic interaction>electrostatic interaction>π–π EDA interaction.

The significance of physical factors on the adsorption of polyaromatic compounds by activated carbons

The adsorption of three synthetic organic compounds (SOCs) (i.e., phenanthrene, biphenyl, and 2-chlorobiphenyl), with similar physicochemical properties but different molecular conformations (i.e., planar and nonplanar), by an activated carbon and an activated carbon fiber was investigated. The physical characteristics of the carbons were obtained from low temperature nitrogen adsorption isotherms using BET, DR, and DFT models. Their surface chemistry was characterized by water vapor adsorption, pH of the point of zero charge, acid/base uptakes, and elemental analysis. The results indicated that adsorbent pore structure characteristics and adsorbate molecular conformation are important in the adsorption of SOCs by porous carbonaceous adsorbents. To predict the adsorption of SOCs by activated carbons, accurate characterization of pore shape and size distribution in primary micropores is important. The results indicated that adsorbate molecules can access and fill more efficiently the slit-shape pores than ellipsoidal pores, whereas the ellipsoidal pores create higher adsorption potential than slit-shape pores. Both molecular conformation and dimensions of adsorbate affect the adsorption. Planar molecules appear to access and pack in slit-shape pores more efficiently as compared to nonplanar molecules. Nonplanar molecular conformation weakens the interactions between adsorbate molecules and carbon surfaces.

Production of porous carbonaceous adsorbent from physical activation of sewage sludge: application to wastewater treatment

With an objective of production of carbonaceous sorbent for industrial effluent treatment, physical activation by steam of biological sludge collected from the municipal wastewater treatment plant of Nantes (France) was studied and optimised using experimental design. Thus, this activation process consists of a carbonisation under N2 atmosphere at 600 degrees C for 1 h, followed by a thermal oxidation using steam (760 degrees C, 0.5 h, 2.5 L/Umin). The global mass yield of the process is equal to 38%. The thermal treatment allows a specific surface area of up to 225 m2/g to be reached, the porous structure being composed of both micropores and mesopores. The content of acidic surface groups is 0.71 mEq/g whereas that of basic surface groups is 0.55 mEq/g. The adsorption properties of the sorbent made from sludge are estimated with regard to various pollutants representative of industrial pollution of wastewaters and compared with those of commercial activated carbon. Whereas the adsorption capacities of organic micropollutants are quite low because of proportionality to the microporosity, the important mesoporosity of the sorbent leads to interesting properties for macromolecules removal from aqueous solutions, such as dyes (q(m) = 175-200 mg/g). Furthermore, the surface functional groups and Ca2+ ions within the materials allow high copper ion adsorption capacities of 140 mg/g to be obtained. Finally, a techno-economic approach shows that the sludge activation process seems to be economically competitive with regard to incineration.

Use of porous pyrolytic carbon for analytical and microscale high-performance liquid chromatographic bioseparations

Porous carbonaceous adsorbent was prepared by carbonization of saccharose in silica gel pores followed by leeching out of the silica matrix. The product of pyrolysis was then deactivated by hydrogenation. The resulting adsorbent shows intermediate sorption properties between those of the highly polar pyrolytic glassy carbon and the hydrophobic graphitized carbon. The microparticulate mesoporous carbon was examined for its use in capillary HPLC separations. The separation of selected stereoisomers in a 320 μm I.D. capillary column packed with the porous carbon particles is described and discussed. Additionaly, the porous carbon filled with dextran gel was tested as a material for direct HPLC analysis of drugs in human serum.

Porous structure of pan-based activated carbon fibers

The porous structure of polyacrylonitrile (PAN)- based activated carbon fibers (ACFs) was studied by means of nitrogen adsorption over a wide range of relative pressure and scanning electron microscopy (SEM). The specific surface area of samples was evaluated using the standard BET method. The micropore volume was obtained from the Dubinin-Astokhov and Horvath-Kawazoe equations. An average micropore size was calculated from the Dubinin-Radushkevich equation. The pore size distributions of the samples were calculated by employing the regularization method according to Density Functional Theory (DFT). It was shown that adsorption measurement provides profound insight into the structural heterogeneity of porous carbonaceous adsorbents. The analysis results by means of different methods had a good consistence with one another.

Catalytic oxidation and decomposition of CH2Cl2 on supported CrO3 at low temperature

CrO3 supported on porous carbonaceous adsorbent and γ‐alumina was used between 200 and 400 °C to oxidise CH2Cl2. The following parameters were studied in a fixed bed integral reactor: type of support, temperature, spatial rates and amounts of CH2 Cl2 in air. The kinetic study of the reaction revealed an order one with respect to CH2 Cl2 and a Mars‐Van Krevelen mechanism appeared quite satisfactory for explaining the experimental results. Conversions of CH2Cl2 as high as 99% were achieved at 340°C on CrO3/γ‐Al2O3 at concentration up to 15000 ppm CH2Cl2 in air.

Characterization of Carbonaceous Adsorbents by Soil Fulvic and Humic Acid Adsorption

AbstractSix porous carbonaceous adsorbents, selective for nonpolar organic adsorbates, were evaluated for dissolved soil humic adsorption and testing. Amberlite XAD 8 resin was similarly tested. Soil fulvic (FA) and humic (HA) acids were used as models for naturally occurring dissolved organic C in soil. The adsorbents were tightly packed as spherical capsules identical to previous studies using ion exchange resins for soil adsorption of plant nutrients. Static or passive adsorption from solution was applied. Kinetic studies (0–264 or 0–336 h) indicated a high initial adsorption rate followed by slower adsorption, common for porous adsorbents. Intraparticle diffusion was rate limiting. Adsorption differences between adsorbents are probably caused by molecular‐size exclusion effects due to pore size. The capsules of Carboxen‐Carbotrap resin mixture were capable of doubling adsorption, requiring no additional time, in response to doubling the FA (43–85 mg C L−1) or HA (46–90 mg C L−1) concentration. This effect was seen across the whole adsorption‐time range. The constant partitioning isotherm model described adsorption, indicating linear adsorption (r2 > 0.96, P < 0.01) with temperatures ranging from 13 to 50 °C, at pH 7.0, and within the concentration ranges of FA (9–126 mg C L−1) and HA (11–138 mg C L−1). This suggests a usefulness for these adsorbents at neutral pH and typical temperatures in waters for dissolved humic adsorption. Subsequently, initial solution concentrations of FA and HA were predicted from resin‐extractable C, indicating a potential for quantifying humic concentrations in solutions. Under identical conditions, XAD 8 resin did not demonstrate the testing attributes found with these carbonaceous adsorbents.