Carbonaceous Adsorbents Research Articles

Conversion of waste plastics into carbonaceous adsorbents and their application for wastewater treatment

ABSTRACT Potentially poisonous elements (PPEs) water pollution has become one of the key issues in the field of water treatment. In recent years, it has threatened ecosystems as well as human health. This study aims to remove PPEs such as chromium (Cr6+), copper (Cu2+), lead (Pb2+), and Zinc (Zn2+) from both vehicle wash wastewater and aqueous solutions through batch experiments utilising carbonaceous adsorbents. Carbonaceous adsorbents were prepared from waste polyethylene terephthalate (wPET) and waste polystyrene (wPS) by carbonisation under a N2 atmosphere followed by chemical activation with 1 M KOH and 1 M HCl. The carbonaceous adsorbents were characterised by Fourier transform infrared spectroscopy, surface area analysis, as well as scanning electron microscopy. The results show that, except for Cr6+, the adsorption of PPEs from aqueous solutions is highly dependent on pH, and the highest removal rate was recorded at pH 6.0. However, the largest Cr6+ adsorption was noted at pH 3.0. Using 0.2 g of adsorbent, the adsorption reached equilibrium after 90 min. Results demonstrated that highest removal of Pb2+, Cu2+, Cr6+, and Zn2+ from aqueous solution achieved over wPET-AC adsorbent was 98.40%, 97.60%, 96.80% and 99.90%, respectively, whereas that of wPS-AC adsorbent was 96.30%, 95.64%, 94.22% and 97.60%, respectively. Root mean square error (RMSE) was also calculated for the validation of data. Isotherms as well as kinetics models are used to evaluate the adsorption capacity of carbonaceous adsorbents for PPEs. The experimental results have shown that the pseudo-second-order as well as Langmuir models are the most suitable for the data. Thermodynamic studies have shown that the adsorption of PPEs is spontaneous as well as endothermic in nature. This study shows that the novel carbonaceous adsorbent wPET-AC and wPS-AC has great potential to remove PPEs from vehicle wash wastewater.

Adsorption characteristics of the carbonaceous adsorbents for organic compounds in a model exhaust gas from thermal treatment processing

ABSTRACT This study investigated the adsorption characteristics of the carbonaceous adsorbents for organic compounds in gas to gain technical knowledge useful for the appropriate operation and management of the incineration plants and industrial heat treatment facilities. The experiments in the study were performed using a dynamic method, employing a small column packed with test adsorbent, into which flowed the model gas, primarily over a temperature range of 150°C to 190°C. Three activated carbon materials and an activated coke were used, with specific surface areas ranging from 250 to 1,100 m2/g-adsorbent. Organic components in the gas were produced and supplied at a concentration of tens of mg/m3, and gaseous mercury was supplied at a concentration of around 100 μg/m3. The experimental results showed the following: 1) The adsorption capacity of every carbonaceous material for organic vapor decreased with increasing temperature, with roughly a three-fold difference in the capacity, between 150°C and 190°C in the dry gas. The equilibrium adsorption amount of benzene could be estimated based on the specific surface area of the adsorbent. 2) Gas moisture reduced the equilibrium adsorption amount of adsorbates by about half. 3) The estimation of the treatment performance for actual adsorption processing suggested the possibility of decreased removal efficiency at higher temperatures above 175°C. Overall, the precise process design should be made based on future practical studies. Implications: Adsorptive characteristics of activated carbon materials were examined for benzene and chlorobenzene in gas within the temperature range of 150°C to 190°C. The adsorption amount of benzene at high temperature and low concentration range below 20 ppm was in the range of 103 to 104 mg/kg-adsorbent. There was a clear difference between the adsorption parameters of activated carbon and coke for the benzene adsorption, depending on their specific surface area values and other factors.

Amine-Modified Biochar for the Efficient Adsorption of Carbon Dioxide in Flue Gas

Biochar-based carbonaceous adsorbents are gaining interest due to their high availability, ease of modification, and low cost; however, they show limited adsorption of CO2 in flue gas due to common textural properties. In this study, TEPA-modified biochar was used to prepare a solid amine adsorbent for the efficient capture of CO2 in flue gas. First, the porous biochar was prepared with FeCl3, Mg(NO3)2, and H2O (g) as activators and walnut shells as carbon sources. Next, the biochar was modified with TEPA to obtain a solid amine adsorbent. Porous texture properties and sample surface functional groups were characterized, and we measured the adsorption CO2 of the amine-modified biochar in a breakthrough adsorption device. Results showed that biochar has a large specific surface area (744.38 m2 g−1), a total pore volume of 1.41 cm3 g−1, and a high mesoporous volume ratio (82.7%). The high pore volume provided a more efficient support space for loading tetraethylenepentamine (TEPA). The adsorbent had an excellent CO2 adsorption capacity, corresponding to 2.82 mmol g−1, which increased to 3.31 mmol g−1 and kept water resistance at 10% H2O (g) simulated flue gas (SFG). The FTIR analysis showed that H2O (g) inhibited urea production after cyclic adsorption. Therefore, solid amine adsorbent created by amine-modified biochar has potential advantages in its application for capturing CO2 in SFG.

A sustainable, low-cost carbonaceous hydrochar adsorbent for methylene blue adsorption derived from corncobs

In this study, activated carbon from corncobs was successfully synthesized by hydrothermal carbonization and hydrochemical activation at low temperatures, followed by pyrolysis. A developed method of hydrochemical activation of hydrochar that uses only small amounts of chemicals is a promising approach. After activation, the activator residues in the hydrothermal product can constantly act as a chemical activator during pyrolysis to form corncob-activated carbon (AHC-KOH), which had specific surface area of 965.028 m2/g and oxygenated functional groups of 0.3780 mmol/g, 31.67 and 4 times, respectively, of those of the inactivated sample. AHC-KOH was used to study the adsorption characteristics of methylene blue (MB). The MB adsorption efficiency of AHC-KOH was the highest at 489.560 mg/g, which was considerably higher than that of activated carbons produced from other biomasses. The isotherm equilibrium and adsorbent kinetics parameters of MB adsorption on AHC-KOH were also determined using the Langmuir isotherm model (R2 = 0.99) and pseudo-second-order kinetic model (R2 > 0.99). Thus, the results indicate that an inexpensive adsorbent produced from corncobs using the above method is a promising material for wastewater treatment.

Nanoarchitectonics of polyaniline-derived porous carbons for efficient adsorptive denitrogenation of liquid fuel

Highly porous polyaniline-derived carbons (pDCs) were used as adsorbents to adsorb/remove hazardous organonitrogens (ONs) from liquid fuel for the first time. The nitrogen-rich pDCs were obtained via the carbonization of polyaniline (pANI) under an inert atmosphere. Further, the pDCs were activated in the presence of KOH (as a chemical activating agent) at different pyrolysis temperatures (600 to 800 °C) to increase the porosity or surface area of the pDCs. One pDC prepared at 700 °C (named pDC-700) showed very efficient adsorptions of representative ONs (indole and quinoline) from liquid fuel. The pDC-700 had a maximum adsorption capacity of 458 mg/g of quinoline which is the highest among the reported values with carbon-based adsorbents. The maximum adsorption capacity of the same adsorbent for the adsorption of indole (385 mg/g) was also very competitive against other carbonaceous adsorbents. The high adsorption capacities of the pDC-700 could be interpreted by a synergistic effect of an efficient hydrogen bonding (between the heteroatoms of pDC-700 and the adsorbates) and high microporosity of the adsorbent (SABET > 2000 m2/g). In addition, a simple solvent washing could regenerate the pDC-700 for the successive utilization in adsorptions effectively.

Efficient adsorption of acetaminophen from the aqueous phase using low-cost and renewable adsorbent derived from orange peels

Pharmaceutically active compounds (PhACs) are frequently detected emerging pollutants in water resources worldwide that provoke pernicious influences on human health and the ecosystem. Developing effective carbonaceous adsorbents from biomass for the efficient removal of PhACs has lately drawn significant research attention. Herein, an efficient and cost-effective activated carbon was produced via ZnCl2-activation, employing orange peels as a precursor (named hereafter as OPAC). OPAC was well-characterized and applied in the sequestration of acetaminophen (N-acetyl-para-aminophenol, APAP), a broadly used non-steroidal anti-inflammatory drug, from water media using the batch technique. OPAC exhibited excellent performance, and more than 95.5% APAP was removed after 90 min, in the pH range of 2.0–8.0, using 1 g/l adsorbent at 25 °C. Additionally, the equilibrium and the kinetic studies outcomes unveiled the suitability of the Langmuir and the pseudo-second-order kinetic models, respectively, to describe the adsorption process. Based on the pH-adsorption dependence and OPAC properties, the presumable mechanism was mainly dominated by non-electrostatic interactions, including hydrogen bonding, π-π interactions, and pore diffusion. Thermodynamically, the process was found to be spontaneous and endothermic. Ultimately, OPAC manifested outstanding recyclability, with at least 95% of the initial efficiency being preserved after five cycles, making it more attractive from the environmental and economic perspectives.

One-step synthesis of carbonaceous adsorbent from soybean bio-residue by microwave heating: Adsorptive, antimicrobial and antifungal behavior

In this work, the transformation of soybean industrial bio-residue with limited practical applications, into a multifunctional carbonaceous adsorbent (SBAC) via one-step microwave-irradiation has been succeeded. The surface porosity, chemical compositions, functionalities and surface chemistry were featured by microscopic pore-textural analysis, elemental constitution analysis, morphological characterization and Fourier transform infra-red spectroscopy. The adsorptive performance of SBAC was evaluated in a batch experiment by adopting different classes of water pollutants, specifically methylene blue (MB), acetaminophen and 2,4-dichlorophenoxyacetic acid (2,4-D). The equilibrium uptakes were analyzed with respect to the non-linearized Langmuir, Freundlich and Temkin isotherm equations. The unique features of SBAC, specifically the antimicrobial and antifungal efficacies were examined against gram-positive/negative bacteria and fungi species. An ordered microporous-mesoporous structure of SBAC, with the BET surface area and total pore volume of 1696m2/g and 0.94m3/g, respectively, has been achieved. The equilibrium data of MB and acetaminophen were found to be in good agreement with the Langmuir isotherm model, with the monolayer adsorption capacities (Qo) of 434.57mg/g and 393.31mg/g, respectively. The adsorptive experiment of 2,4-D was best fitted to the Freundlich isotherm equation, with the Qo of 253.17mg/g. The regeneration performance of the spent SBAC under microwave-irradiation could maintain at 69.42-79.31%, even after five (5) adsorption-regeneration cycles. SBAC exhibited excellent inhibition efficiencies against gram-positive/negative bacteria and fungi species, with the inhibition zones at 14.0-28.0mm. This newly developed SBAC appears to be a new powerful candidate for the remediation of different classes of water contaminants, and novel antibacterial and antifungal agents against biological contaminations. The novel concept of "turn waste into wealth" in a cost-effective and energy saving manner for environmental preservation has been successfully accomplished.

Hydrothermal synthesis of magnetic-biochar nanocomposite derived from avocado peel and its performance as an adsorbent for the removal of methylene blue from wastewater

In this work hydrothermally prepared magnetic iron oxide coated biochar nanocomposite (Fe3O4-BC), from raw avocado peel (raw AVP) and ferric chloride hexahydrate, effectively adsorbed aqueous methylene blue (MB) dye. Successful Fe3O4-BC formation was confirmed by TEM, FT-IR, XRD, and SEM. BET analyses measured a higher surface area (25.98 m2/g vs. 18.89 m2/g) and smaller-pore diameter (8.25 nm vs. 13.01 nm) for Fe3O4-BC compared to raw AVP. The Tempkin and Langmuir isotherm models successfully modeled the Fe3O4-BCMB adsorption equilibrium data, indicating uniform adsorption binding energy and homogeneous single layer adsorption. The maximum Langmuir adsorption capacity qmax = 62.1 mg/g for MB compared well with previously reported values for low cost carbonaceous adsorbents. The temporal experimental data was best represented by the pseudo-second order and two-phase pseudo-first-order kinetic models suggesting that chemisorption dominated. Thermal studies indicated spontaneous endothermic adsorption (ΔG < 0, ΔH > 0). Fe3O4-BCshowed remarkable stability and reusability during four consecutive adsorption–desorption cycles. Compared to literature, Fe3O4-BC adsorption was markedly faster requiring between 1 and 3 orders of magnitude less time to reach equilibrium. Consequently, a significantly lower treatment time would be required industrially which, coupled with magnetic separation, reusability, and relatively high adsorption capacity of the adsorbent, highlights the unprecedented industrial potential of Fe3O4-BC nanocomposite as an adsorbent for the treatment of MB polluted waters.

The Sorption of Sulfamethoxazole by Aliphatic and Aromatic Carbons from Lignocellulose Pyrolysis

Massive biomass waste with lignocellulose components can be used to produce biochar for environmental remediation. However, the impact of lignocellulose pyrolysis on biochar structure in relation to the sorption mechanism of ionizable antibiotics is still poorly understood. In this paper, diverse techniques including thermogravimetric analysis and 13C nuclear magnetic resonance were applied to investigate the properties of biochars as affected by the pyrolysis of cellulose and lignin in feedstock. Cellulose-derived biochars possessed more abundant groups than lignin-derived biochars, suggesting the greater preservation of group for cellulose during the carbonization. Higher sorption of sulfamethoxazole (SMX) was also observed by cellulose-derived biochars owing to hydrogen bond interaction. Sorption affinity gradually declined with the conversion aliphatic to aromatic carbon, whereas the enhanced specific surface area (SSA) subsequently promoted SMX sorption as evidenced by increased SSA-N2 and SSA-CO2 from 350 to 450 °C. The decreased Kd/SSA-N2 values with increasing pH values implied a distinct reduction in sorption per unit area, which could be attributed to enhanced electrostatic repulsion. This work elucidated the role of carbon phases from thermal conversion of lignocellulose on the sorption performance for sulfonamide antibiotics, which will be helpful to the structural design of carbonaceous adsorbents for the removal of ionizable antibiotics.

Carbon-dot hydrogels as superior carbonaceous adsorbents for removing perfluorooctane sulfonate from water

Efficiently removing perfluorooctane sulfonate (PFOS) from wastewaters is a hot topic in environmental field. Herein, crosslinking the nano-sized and zero-dimensional carbon dots (CDs) with polyethylene glycol diglycidyl ether (PEG) and polypropylene glycol diglycidyl ether (PPG) resulted in CD hydrogels that were verified by TEM, SEM, FTIR and XPS. The obtained CD hydrogels could efficiently adsorb PFOS from water through their CD moieties. The kinetic curves were fitted well by the pseudo-second order model, indicating the involvement of chemisorption in the rate-limiting step. The adsorption isotherm measurements showed that the hydrogel with the highest CD content had a PFOS maximum uptake capacity of ca. 2.82 g/g (5.64 mmol/g) in the neutral water, which was much higher than the ever-reported carbonaceous materials, and also ranked the top three among the superior positively-charged adsorbents. The superior PFOS adsorption of CD hydrogels could be attributed to good dispersion of the nanoscale CDs in the PEG/PPG hydrogel matrix, leading to the substantial exposure of the binding sites of CDs towards PFOS molecules. Moreover, CD hydrogels did not show pronounced loss of adsorption capacity after experiencing five adsorption-desorption cycles. As for the real wastewaters, CD hydrogels could efficiently treat not only the high concentration of PFOS in the neutral firefighting wastewaters, but also the extremely low concentration of PFOS in the neutral environmental wastewater, where the residual PFOS concentration could be reduced less than 5 ng/L, satisfying the standard of the U.S. Environmental Protection Agency.

Designed synthesis of porous carbons for the separation of light hydrocarbons

The separation of light hydrocarbon mixtures (C1–C3) generated from petrochemical industry is vital and challenging process for obtaining valuable pure chemical feedstocks. In comparison to the energy intensive conventional separation technologies (cryogenic distillation, absorption and hydrogenation), the adsorptive separation is considered as a low energy cost and high efficiency process. Porous carbons have been demonstrated as excellent adsorbents for the separation of light hydrocarbons, owing to their designable structure and tailorable properties. This review summarizes the recent advances of using porous carbons as adsorbents for the separation of light hydrocarbons, including methane/nitrogen, methane/alkane, methane/carbon dioxide, ethylene/ethane and propylene/propane. We discuss the separation mechanisms and highlight the material features including pore structure, surface chemistry and target molecular properties that determine the separation performance. Furthermore, the challenges and development direction associated with carbonaceous adsorbents for light hydrocarbon separation are discussed, meanwhile the guidelines for the design of porous carbons are proposed.

Development of a novel and efficient biochar produced from pepper stem for effective ibuprofen removal

A potential biochar from pepper stems (PS-biochar) was developed via a one-stage pyrolysis process of precursor at 700 °C and employed to adsorb ibuprofen (IBP) in water media. Results showed that PS-biochar was a carbonaceous mesoporous adsorbent with well-developed porosity (SBET = 727.5 m2/g and VTotal = 0.36 cm3/g) and rich surface functional groups. Mechanism of IBP adsorption consisted mainly of π- π interaction, pore filling, and H-bonding. The Langmuir monolayer capacity (569.6 mg/g) was very high compared to values reported in similar studies. The successful PS-biochar regeneration after four cycles in the batch system confirmed the high performance of the NaOH (0.1 M) as a desorbing agent. Therefore, the prepared biochar can be considered as a cost-effective and high-performance material for water decontamination.

Removal of Doxycycline from Water using Dalbergia sissoo Waste Biomass Based Activated Carbon and Magnetic Oxide/Activated Bioinorganic Nanocomposite in Batch Adsorption and Adsorption/Membrane Hybrid Processes.

The carbonaceous adsorbents, an activated carbon (AC) and a bioinorganic nanocomposite (MAC), were prepared using Dalbergia sissoo sawdust as waste biomass, in this study. Both the adsorbents were characterized by FTIR, EDX, SEM, XRD, TG/DTA, surface area, and a pore size analyzer. The adsorbents were used for the removal of an antibiotic, doxycycline (DC) antibiotic, from wastewater in order to minimize a load of antibiotics in industrial effluents and consequently the drug resistance problem. Initially, the effectiveness of adsorbent was confirmed using batch adsorption experiments where isothermal models like Langmuir, Freundlich Temkin, Jovanovic, and Harkins–Jura were utilized to govern the maximum adsorption capacity of AC and MAC while pseudo-first- and second-order kinetic models were used to estimate the values of different kinetic parameters. Langmuir model best accommodated the equilibrium data whereas the pseudo-second-order kinetic model finest trimmed the kinetics data. The effect of pH on adsorption was also evaluated where maximum removal was observed between pH 5 and 7 by both adsorbents. The effect of temperature on adsorption was evaluated where the entropy change (ΔS0) comes out to have a numerically positive value whereas Gibbs free energy change (ΔG0) and enthalpy change (ΔH0) were negative indicating the spontaneous nature and feasibility of the procedure. The robust technology of membrane separation is rapidly replacing the conventional technologies but at the same time suffers from the problem of membrane fouling. As pretreatment, the AC and MAC were used in hybrid with ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) membranes whereas permeate fluxes and percent retention of DC were compared for naked membrane operations and AC/membrane and MAC/membrane process. The permeate fluxes for MAC/membrane processes were greater as compared to AC/membrane and naked membrane processes showing the effectiveness of the bioinorganic composite as foul control and consequently recovery of DC from effluents. The percent retention of the UF membrane was lower as compared to NF and RO membranes. Improvement in percent retention for UF/AC, UF/MAC, NF/AC, NF/MAC, RO/AC, and RO/MAC was observed. The bioinorganic composite MAC contains a magnetic iron oxide which was effectively removed from slurry after use through the magnetic process and that was the main reason for high permeate fluxes in MAC/membrane operations.

Carbonaceous adsorbents from polymers-rubber and plastic wastes for adsorption of methylene blue

Carbonaceous adsorbents from polymers-rubber and plastic wastes for adsorption of methylene blue

Preparation of Sulfur-impregnated Carbonaceous Adsorbent via Mechanochemical Treatment

Preparation of Sulfur-impregnated Carbonaceous Adsorbent via Mechanochemical Treatment

A Comprehensive Insight on Adsorption of Polyaromatic Hydrocarbons, Chemical Oxygen Demand, Pharmaceuticals, and Chemical Dyes in Wastewaters Using Biowaste Carbonaceous Adsorbents

Recent trends in adsorption of hazardous organic pollutants including Polyaromatic Hydrocarbons (PAHs), Chemical Oxygen Demand (COD), Pharmaceuticals, and Chemical Dyes in wastewater using carbonaceous materials such as activated carbon (AC) and biochar (BC) have been discussed in this paper. Utilization of biomass waste in the preparation of AC and BC has gained a lot of attention recently. This review outlines the techniques used for preparation, modification, characterization, and application of the above-mentioned materials in batch studies. The approaches towards understanding the adsorption mechanisms have also been discussed. It is observed that in the majority of the studies, high removal efficiencies were reported using biowaste adsorbents. Regarding the full potential of adsorption, varying values were obtained that are strongly influenced by the adsorbent preparation technique and adsorption method. In addition, most of the studies were concentrated on the kinetic, isotherm equilibrium, and thermodynamic aspects of adsorption, suggesting the dominant isotherm and kinetic models as Langmuir or Freundlich and pseudo-second-order models. Due to development in biosorbents, adsorption has been found to be increasingly economical. However, application of these adsorbents at commercial scale has not been adequately investigated and needs to be studied. Most of the studies have been conducted on synthetic solutions that do not completely represent the discharged effluents. This also needs attention in future studies.

Recent Advances in Carbon-Based Adsorbents for Adsorptive Separation of Light Hydrocarbons.

Light hydrocarbons (LHs) separation is an important process in petrochemical industry. The current separation technology predominantly relies on cryogenic distillation, which results in considerable energy consumption. Adsorptive separation using porous solids has received widespread attention due to its lower energy footprint and higher efficiency. Thus, tremendous efforts have been devoted to the design and synthesis of high-performance porous solids. Among them, porous carbons display exceptional stability, tunable pore structure, and surface chemistry and thus represent a class of novel adsorbents upon achieving the matched pore structures for LHs separations. In this review, the modulation strategies toward advanced carbon-based adsorbents for LHs separation are firstly reviewed. Then, the relationships between separation performances and key structural parameters of carbon adsorbents are discussed by exemplifying specific separation cases. The research findings on the control of the pore structures as well as the quantification of the adsorption sites are highlighted. Finally, the challenges of carbonaceous adsorbents facing for LHs separation are given, which would motivate us to rationally design more efficient absorbents and separation processes in future.

Thiol-Functionalization Carbonaceous Adsorbents for the Removal of Methyl-Mercury from Water in the ppb Levels

Mercury is a highly toxic pollutant of major public health concern, and human exposure is mainly related to the aqueous phase, where its dominant form is methyl-mercury (MeHg). In the current work, two carbon-based adsorbents, i.e., a commercial activated carbon and a sunflower seeds’ biochar, were modified by the introduction of thiol-active groups onto their surfaces for the MeHg removal from natural-like water in ppb concentration levels. The examined thiol-functionalization was a two-step process, since the raw materials were initially treated with nitric acid (6 N), which is a reagent that favors the formation of surface carboxyl groups, and subsequently by the thiol surface bonding groups through an esterification reaction in methanol matrix. The adsorbents’ capacity was evaluated toward the Hgtotal legislative regulation limit (1 μg/L) in drinking water (denoted as Q1). The respective isothermal adsorption results revealed an increased affinity between MeHg and thiol-functionalized materials, where the commercial carbon showed slightly higher capacity (0.116 μg Hg/mg) compared with the biochar (0.108 μg Hg/mg). This variation can be attributed to the respective higher surface area, resulting, also, to higher thiol groups loading. Regarding the proposed mechanism, it was proved that the S-Hg bond was formed, based on the characterization of the best performed saturated adsorbent.

Alternative Materials for the Enrichment of Biogas with Methane.

Carbonaceous adsorbents have been pointed out as promising adsorbents for the recovery of methane from its mixture with carbon dioxide, including biogas. This is because of the fact that CO2 is more strongly adsorbed and also diffuses faster compared to methane in these materials. Therefore, the present study aimed to test alternative carbonaceous materials for the gas separation process with the purpose of enriching biogas in biomethane and to compare them with the commercial one. Among them was coconut shell activated carbon (AC) as the adsorbent derived from bio-waste, rubber tire pyrolysis char (RPC) as a by-product of waste utilization technology, and carbon molecular sieve (CMS) as the commercial material. The breakthrough experiments were conducted using two mixtures, a methane-rich mixture (consisting of 75% CH4 and 25% CO2) and a carbon dioxide-rich mixture (containing 25% CH4 and 75% CO2). This investigation showed that the AC sample would be a better candidate material for the CH4/CO2 separation using a fixed-bed adsorption column than the commercial CMS sample. It is worth mentioning that due to its poorly developed micropore structure, the RPC sample exhibited limited adsorption capacity for both compounds, particularly for CO2. However, it was observed that for the methane-rich mixture, it was possible to obtain an instantaneous concentration of around 93% CH4. This indicates that there is still much potential for the use of the RPC, but this raw material needs further treatment. The Yoon–Nelson model was used to predict breakthrough curves for the experimental data. The results show that the data for the AC were best fitted with this model.

Adsorption of fluoride from industrial wastewater using polymer adsorbents: a review

Fluoride pollution in ground and surface water originates from naturally occurring reactions and industrial activities such as the disposal of industrial wastewater. Amongst different fluoride removal technologies including chemical precipitation, membrane filtration, ion exchange processes, and electrodialysis, adsorption is an attractive method for fluoride removal from wastewater due to its low operational cost, simplicity, and good sustainability. Various adsorbents are used for fluoride removal including, metal oxides and hydroxide, carbonaceous adsorbents, zeolite, polysaccharides, and polyresin adsorbents. This review studies the application of modified polysaccharides and polyresin adsorbents for the removal of fluoride from wastewater. The relationship between the adsorption conditions and the resulting adsorption capacity is thoroughly discussed. Based on the reported studies, modified polysaccharides and polyresins adsorbents can effectively remove fluoride from wastewater achieving high adsorption capacity, the highest being 92.39 mg/g for aluminum impregnated amberlite at pH 3. Furthermore, aluminum impregnated adsorbents reported a higher fluoride adsorption capacity than other modification methods where the three adsorbents with the highest fluoride adsorption capacity are: aluminum impregnated amberlite 92.39 mg/g at pH 3> zirconium immobilized crossed linked chitosan 48.26 mg/g at pH 6 > chitosan/aluminum hydroxide beads 17.68 mg/g at pH 4. In addition, polymeric adsorbents are also highly sustainable as they can be regenerated multiple times to be reused. Therefore, the high adsorption capacity and good regeneration potential allow polymeric adsorbents to serve as promising and sustainable adsorbents to remove fluoride from industrial wastewater.