Microporous Active Carbons Research Articles

Efficient decaffeination with recyclable magnetic microporous carbon from renewable sources: Kinetics and isotherm analysis

Rapid global urbanization and population growth have ignited an alarming surge in emerging contaminants in water bodies, posing health risks, even at trace concentrations. To address this challenge, novel water treatment and reuse technologies are required as current treatment systems are associated with high costs and energy requirements. These drawbacks provide additional incentives for the application of cost-effective and sustainable biomass-derived activated carbon, which possesses high surface area and low toxicity. Herein, we synthesized microporous activated carbon (MAC) and its magnetic derivative (m-MAC) from tannic acid to decaffeinate contaminated aqueous solutions. Detailed characterization using SEM, BET, and PXRD revealed a very high surface area (>1800 m2/g) and a highly porous, amorphous, heterogeneous sponge-like structure. Physicochemical and thermal analyses using XPS, TGA, and EDS confirmed thermal stability, unique surface moieties, and homogeneous elemental distribution. High absorption performance (>96 %) and adsorption capacity (287 and 394 mg/g) were recorded for m-MAC and MAC, respectively. Mechanistic studies showed that the sorption of caffeine is in tandem with multilayer and chemisorptive mechanisms, considering the models’ correlation and error coefficients. π-π stacking and hydrogen bonding were among the interactions that could facilitate MAC-Caffeine and m-MAC-Caffeine bonding interactions. Regeneration and reusability experiments revealed adsorption efficiency ranging from 90.5 to 98.4 % for MAC and 88.6–93.7 % for m-MAC for five cycles. Our findings suggest that MAC and its magnetic derivative are effective for caffeine removal, and potentially other organic contaminants with the possibility of developing commercially viable and cost-effective water polishing tools.

Thermal pretreatment of willow branches impacts yield and pore development of activated carbon in subsequent activation with ZnCl2via modifying cellulose structure

Development of pore structures of activated carbon (AC) from activation of biomass with ZnCl2 relies on content and structure of cellulose/hemicellulose in feedstock. Thermal pretreatment of biomass could induce dehydration and/or aromatization to change structure of cellulose/hemicellulose. This might interfere with evolution of structures of AC, which was investigated herein via thermal pretreatment of willow branch (WB) from 200 to 360 °C and the subsequent activation with ZnCl2 at 550 °C. The results showed that thermal pretreatment at 360 °C (WB-360) could lead to substantial pyrolysis to form biochar with yield of 31.9%, accompanying with nearly complete destruction of cellulose crystals and remarkably enhanced aromatic degree. However, cellulose residual in WB-360 could still be activated to form AC-360 with specific surface area of 1837.9 m2·g−1, which was lower than that in AC from activation of untreated WB (AC-blank, 2077.8 m2·g−1). Nonetheless, the AC-200 from activation of WB-200 had more developed pores (2113.9 m2·g−1) and superior capability for adsorption of phenol, due to increased permeability of ZnCl2 to the largely intact cellulose structure in WB-200. The thermal pretreatment did increase diameters of micropores of AC but reduced overall yield of AC (26.8% for AC-blank versus 18.0% for AC-360), resulting from accelerated cracking but reduced intensity of condensation. In-situ IR characterization of the activation showed that ZnCl2 mainly catalyzed dehydration, dehydrogenation, condensation and aromatization but not cracking, suppressing formation of derivatives of cellulose and lignin in bio-oil. The thermal pretreatment formed phenolic —OH and C=O with higher chemical innerness, which changed reaction network in activation, shifting morphology of fibrous structures in AC-blank to "melting surface" in AC-200 or AC-280.

Electrochemical Properties of Activated Carbon Electrodes for Supercapacitor Application: The Effect of Various Electrolyte Concentrations of Na2SO4

To achieve the high accomplishment of the supercapacitor, various electrolyte concentrations of Na2SO4 (0.5 M, 1 M, and 2 M) were added to the activated carbon (AC) electrode. The AC has a moderate surface area of 1,500 m2/g and a pore size of 1 nm (micropore scale). The AC electrode was deposited from the mixture of AC, carbon black, and polytetrafluoroethylene (PTFE) with a weight ratio of 8:1:1 using the doctor blade method. Cyclic Voltammetry (CV), Galvanostatic Charge Discharge (GCD), and Electrical Impedance Spectroscopy (EIS) were used to characterize the electrodes electrochemically. Based on CV, GCD, and EIS characterizations, the measured specific capacitance of 17.2 F/g and ESR of 4.4 W exhibit the best performance due to their high ionic conductivity. We can conclude that 2 M Na2SO4 is a viable option for the ionic electrolyte of the microporous AC for the high performance of a supercapacitor.

Utilization of inherent minerals in coal for high-performance activated carbon production: The mechanism of deSO2 and/or deNOx enhanced by in situ transformed calcium sulfide (CaS)

Calcium sulfide (CaS) is transformed from the interaction between inherent pyrite and calcite in coal during activated carbon (AC) preparation by vapor activation, which could impact AC's textural and performance. For elucidating the contribution of in situ transformed CaS on the AC structure and SO2/NO removal, as-obtained AC-XCaS (X is the CaS content) were produced by Taixi coal and calcium sulfide (0–4 wt.%) through steam activation. The textural evolution and denitrification and/or desulfurization were also investigated. The results indicated that: (1) Calcium sulfide declined the burn-off linearly. The graphitization degree of ACs presents first enhancing and then decreasing trend with the CaS content increased. Calcium sulfide promotes the AC's micropore porosity development by catalyzing the corrosion of steam on the carbon surface. The specific surface area including total BET and micropore from 954 m2/g and 894 m2/g (AC) first raised to 1017 m2/g and 962 m2/g (AC-1CaS) and then decreased to 808 m2/g and 768 m2/g (AC-4CaS), respectively. Meanwhile, calcium sulfide improves the AC's amounts of C–O and C=O. (2) Calcium sulfide strengthens AC's removal ability of NO and SO2 evidently. The maximum desulfurization capacity is up to 67.1 mg/g of AC-4CaS, which is higher by 50.8% than 44.5 mg/g of AC. Calcium sulfide enhances AC's surface chemical feature and finally favors the adsorption of SO2/O2/H2O. Meanwhile, calcium sulfide catalyzes the desulfurization reaction. The AC-3CaS's NO conversion is up to 22.7%, which is higher 39.3% than 16.3% of AC. Calcium sulfide favors oxygen dissociation to form intermediate C(O), which could strengthen the adsorption of NH3 and NO. (3) During simultaneous removal of SO2 and NO, calcium sulfide shows that anti-SO2 poisoning ability is promising. The results of this research could complement the reference by utilizing coal with high-inorganic-iron/calcium/sulfur for high-performance AC preparations.

Optimized preparation of activated carbon with high porosities based on puck shells (Afrostyrax lepidophyllus) by response surface methodology and physico-chemical characterization.

From recent research, lignocellulosic materials assert themselves as good precursors for the manufacture of highly carbonaceous and porous materials. Hence, the perspective of this work is the preparation of the low-cost activated carbons (ACs) based on puck shells (Afrostyrax lepidophyllus) with a large surface area. To achieve this, chemical activation using phosphoric acid and sodium hydroxide as an activating agent was carried out. The response surface methodology through Box-Behnken design was used to optimize the preparation conditions. Box-Behnken design was used to optimize the preparation conditions. The factors whose influences have been studied are the concentration of activating agent (0.5-1.5 mol l-1), the carbonization temperature (300-500°C) and the residence time (30-100 min). The AC obtained by phosphoric acid was named CRP and impregnated with sodium hydroxide CRB. The ideal conditions for the preparation of the ACs obtained from the maximum iodine number (647.29 for CRP and 575.15 mg g-1 for CRB) were: 1.5 mol l-1 for the concentration of activating agent at a carbonization temperature of 500°C during 62 min for CRP and 0.85 mol l-1 for the concentration of activating agent at a carbonization temperature of 500°C during 59 min for CRB. These two materials prepared were characterized by several techniques pH at the point of zero charge (pHpzc), Boehm titration, Fourier transform infrared spectroscopy, XRD analysis, BET method, Raman spectroscopy and scanning electron microscopy, which confirmed the acidic nature of CRP and the basic nature of CRB carbons. The specific surface of the micropores was 509.05 and 27.53 m2 g-1, respectively. It provides a new valorization of agricultural waste for the preparation of effective-cost microporous ACs as an adsorbent that can be applied in water treatment industries.

Synthesis of microporous-activated carbon via direct H3PO4 and KOH activation of Pterospermum acerifolium fruits: process optimization and characterization

Synthesis of microporous-activated carbon via direct H3PO4 and KOH activation of Pterospermum acerifolium fruits: process optimization and characterization

Microporous activated carbon filled anti-freezing hydrogels used for low-temperature applications

Self-healing and anti-freezing hydrogels have attracted great attention as their ability to work stably in harsh environments. In this manuscript, we design a dual self-healing and anti-freezing hydrogels based on functionalized microcapsules and phytic acid (PA). Based on mussel-inspired chemistry, polydopamine (PDA) is wrapped on microporous activated carbon (MAC) to obtain functional microcapsule (LO@MAC@PDA), which is loaded with linseed oil (LO). The stronger hydrogen bonds between PA and water weakens the intermolecular between water, effectively reducing the freezing point of the hydrogel and enabling the hydrogel to maintain good flexibility at −20 °C. The dual self-healing effect of LO@MAC@PDA gives the hydrogel a self-healing efficiency of 93.5% at −20 °C. The PA-LMP/PVA hydrogel is assembled into hydrogel-based flexible sensors to achieve sensitive detection of human motion at low temperatures. We expect that this simple strategy to expand the temperature range for using of hydrogel-based flexible sensors.

Degradation Mechanisms of a Li—S Cell using Commercial Activated Carbon

<p>In lithium–sulfur (Li–S) batteries, encapsulation of sulfur in activated carbon (AC) materials is a promising strategy for preventing the dissolution of lithium polysulfide into electrolytes and enhancing cycle life, because instead of solid–liquid–solid reactions, quasi-solid-state (QSS) reactions occur in the AC micropores. While a high weight fraction of sulfur in S/AC composites is essential for achieving a high energy density of Li–S cells, the deterioration mechanisms under such conditions are still unclear. In this study, we report the deterioration mechanisms during charge–discharge cycling when the discharge products overflow from the AC. Analysis using scanning electron microscopy and energy-dispersive X-ray spectrometry confirms that the sulfur in the S/AC composites migrates outside the AC as cycling progresses, and it is barely present in the AC after 20 cycles, which corresponds to the capacity decay of the cell. Impedance analysis clearly shows that the electrical resistance of the S/AC composite and the charge-transfer resistance of QSS reactions significantly increase as a result of sulfur migration. On the other hand, the charge–discharge cycling performance under limited-capacity conditions, where the discharge products are encapsulated inside the AC, is extremely stable. These results reveal the degradation mechanism of a Li–S cell with micro-porous carbon and provide crucial insights into the design of a S/AC composite cathode and its operating conditions needed to achieve stable cycling performance.</p>

A quantitative evaluation of the large pore-size effect on the electric double-layer capacitance for high voltage by 19F-NMR

Electric double-layer capacitors (EDLCs) afford long cycle life and high-power density by dielectric ion adsorption and desorption on the surface of porous materials. However, high potential charges/discharges lower the capacitance of EDLCs. In this study, we quantitatively evaluated the large pore-size effect of activated carbons (ACs) on the electric double layer capacitances at various voltages based on a hierarchical domain model from a structural point of view. ACs with highly developed microporous and mesoporous (2–4 nm) structures were prepared using KOH activation. The AC with small amount of mesopores showed a specific capacitance of 30.35 F/g at a voltage of 2.7 V, where it significantly lowered to 20.93 F/g at a high voltage of 3.3 V. Meanwhile, the highly microporous AC with abundant mesopores had a higher specific capacitance (40.77 F/g at 2.7 V to 38.22 F/g at 3.3 V). 19F-NMR results indicate that the amounts of solvated ions in the mesopores significantly increased in all the ACs after charging at a higher voltage. The mitigation of the high-voltage capacitance drop might occur because of the mesopore structure that functions as a buffer space for the electric double layer.

Adsorption and photocatalytic degradation of 2-chlorophenol in water: Evaluating the performance of TiO2/activated carbon vs. using a mixture of TiO2 and activated carbon

The work reported here compared between two photocatalytic degradation strategies of 2-chlorophenol (2-CP). The first strategy utilized titanium dioxide (TiO2) immobilized on activated carbons (AC) to produce TiO2/AC photocatalysts of various TiO2 loadings. Various immobilization techniques were used: chemical vapour deposition (CVD), direct air hydrolysis (DAH), high-temperature impregnation (HTI). In the first strategy, characterization, adsorption and photocatalytic degradation of 2-CP using TiO2/AC revealed that: 1) deposition of anatase TiO2 occurred in the micro pores of AC; 2) adsorption capacity decreased with increasing anatase TiO2 loading on TiO2/AC; 3) adsorption kinetics followed pseudo first order kinetics where 40 % of 2-CP was adsorbed; 4) photocatalytic degradation caused removal of all 2-CP and 80 % of total organic carbon (TOC), while no chloride ion (Cl−) was produced. In the second strategy, naked TiO2 (anatase) and mixtures of (anatase and AC) were involved to investigate the effect of presence of AC on degradation ability of anatase TiO2 towards 2-CP. The results showed that: 1) naked TiO2 (anatase) caused better degradation of 2-CP than TiO2/AC (Cl− was liberated; complete degradation of 2-CP occurred; some TOC remained in the suspension); 2) presence of AC with anatase TiO2 in the reaction mixture negatively affected Cl− production, but positively affected 2-CP and TOC disappearance; 3) when all 2-CP was adsorbed on AC, production of Cl− was inhibited but continued at a reduced rate. This might indicat that both dissolved and adsorbed 2-CP contributed to the degradation process.

A high-capacity, high-power organic electrode via supercritical CO2 impregnation into activated carbon micropores.

Herein, we report the impregnation of chloranil into activated carbon micropores using scCO2. The sample prepared under 105 °C and 15 MPa showed a specific capacity of 81 mAh gelectrode-1, except for the electric double layer capacity at 1 A gelectrode-Polytetrafluoroethylene (PTFE)-1. Additionally, approximately 90% of the capacity was retained even at 4 A gelectrode-PTFE-1.

Mesoporous and microporous carbons from one-pot hydrothermal products for supercapacitor electrodes: effects of porous structures and surface functionality

Mesoporous carbons were prepared from carbon dots via physical activation. Mesoporous carbons exhibit higher Cg than high-surface-area microporous carbons, and the efficiency of the surface area for mesopores is much higher than for micropores.

Catalysis/CO2 sorption enhanced pyrolysis-gasification of biomass for H2-rich gas production: Effects of activated carbon, NiO active component and calcined dolomite

This study aims to reveal the effects of activated carbon (AC), NiO active component and calcined dolomite addition on the H2-rich gas production from pyrolysis-gasification of biomass, the experiments were conducted on a two-staged fixed-bed reactor with sawdust (SD) as biomass feedstock. It was found that the H2-rich gas production was largely enhanced by AC catalyst due to its catalytic effect on volatiles gasification as well as its self-gasification during the process. Lower impregnation ratio of ZnCl2 or H3PO4 to biomass was preferable to the H2 production. H3PO4 activation char (PAC) might keep more active structures with higher AC yields compared with ZnCl2 activation char (ZAC). NiO would mainly enter into the micropores of AC, possibly covered some of the active sites on AC surface, thus caused the decrease in AC self-gasification, although certain catalytic effect of NiO on H2 production was also observed. Additional calcined dolomite introduction together with NiO/AC catalyst could further increase the H2 concentration and yield. A remarkable synergistic strengthening effect was found between NiO/PAC-SD catalyst and calcined dolomite, the maximum H2 concentration and yield of 62.54 vol% and 1343.52 mL/g biomass were achieved with the addition of NiO/PAC-SD-1 and calcined dolomite due to the combination of in situ CO2 sorption enhancing effect and NiO/PAC-SD-1 catalytic effect as well as the enhanced AC self-gasification. It is thus illustrated that the catalysis/sorption enhanced pyrolysis-gasification of biomass using NiO/AC catalyst and calcined dolomite is an effective way to produce a H2-rich gas and shows a good prospect in the carbon-constrained future.

Multivariable optimization of activated carbon production from microwave pyrolysis of brewery wastes - Application in the removal of antibiotics from water

This study aimed at optimizing the one-step chemical activation and microwave pyrolysis of an agro-industrial waste to obtain a microporous activated carbon (AC) with superior textural and adsorptive properties by a fast, low-reagent and low-energy process. Spent brewery grains were used as precursor, and the antibiotics sulfamethoxazole (SMX), trimethoprim (TMP) and ciprofloxacin (CIP) were considered as target adsorbates. A fractional factorial design was applied to evaluate the effect of the main factors affecting the preparation of AC (activating agent, activating agent:precursor ratio, pyrolysis temperature and residence time) on relevant responses. Under optimized conditions (K2CO3 activation, pyrolysis at 800 °C during 20 min and a K2CO3:precursor ratio of 1:2), a microporous AC with specific surface area of 1405 m2 g-1 and large adsorption of target antibiotics (82–94%) was obtained and selected for further studies. Equilibrium times up to 60 min and maximum Langmuir adsorption capacities of 859 µmol g-1 (SMX), 790 µmol g-1 (TMP) and 621 µmol g-1 (CIP) were obtained. The excellent textural and adsorptive properties of the selected material were achieved with a very fast pyrolysis and low load of activating agent, highlighting the importance of optimization studies to decrease the environmental and economic impact of waste-based AC.

The competing role of moisture in adsorption of gaseous benzene on microporous carbon

The effects of moisture on adsorption of gaseous benzene have been investigated using microporous activated carbon (AC). Here, the performance metrics of an AC bed are explored in terms of the interplay between benzene concentrations (1–20 Pa) and relative humidity (RH, 0–100%). At lower benzene levels (<10 Pa), the adsorption capacity of AC bed was affected sensitively by water vapor with the performance reduction by 27–65% at 100% RH (e.g., relative to 0% RH). In contrast, the negative effect of water on AC performance was not so evident at higher benzene levels (~20 Pa) with only less than 5.3% decrease in the adsorption capacity. A test on the combinatory effects of temperature (25, 40, and 60 °C) and humudity (0 and 100% RH) confirms the relative dominance of temperature over moisture conditions in lowering AC performance. The isotherm analysis of benzene indicates complex fitting results of microporous AC across varying RH levels. The kinetic analysis further demonstrates that the physical nature of benzene is best explained by the pseudo-first order fitting. The test of temperature-swing cycles between adsorption–desorption clarifies the slight decreases in the adsorption capacity (reduction of 11.9% at 0% RH and 3.4% at 50% RH) at lower RH levels, although there is a prominent reduction (35.5%) at the saturated RH. As a whole, the commercial AC product is verified as an excellent adsorbent for purifying the atmosphere from gaseous aromatic pollutants like benzene under dynamically varying environmental conditions (e.g., in the presence of competing component like water vapor at different temperature conditions).

An updated study on NO catalytic oxidation over activated carbon: The effect of pore structure and a dual-site mechanism

NO catalytic oxidation (NOCO) to NO2 is widely believed to be a fundamental step in selective catalytic reduction (SCR) over activated carbon (AC). Thus, the enhancement of NOCO over AC is significant. The effect of the pore structure on NOCO is discussed first. A series of microporous AC samples with various microporous surface areas were prepared, in which a strong positive correlation existed between NO conversion and the microporous surface area. With an increase in the microporous surface area, the NO conversion increased from 13.10% for MAC1 to 41.18% for MAC4. Concurrently, a hierarchical AC sample with an approximate hierarchy degree (the ratio of Vmes+mac to Vt) of 50% demonstrated higher NO conversion than microporous AC when the microporous surface areas were similar. HAC2 exhibited the largest NO conversion (51.58%). Therefore, the microporous surface area and degree of hierarchy are key factors that enhance NO conversion. NOCO has been demonstrated to be an O-enriched process. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) results revealed that carbonyl groups were generated during the NOCO process. Density functional theory calculations were then performed. Carbonaceous models with unsaturated C atom, carbonyl, and lactone groups were constructed, and the corresponding NOCO reaction paths were calculated. A dual-site NOCO mechanism was proposed by combining the experimental and calculation results. Two types of active sites existed: unsaturated C atoms and high-spin density C atoms that affected the kinetic and steady-state stages of NOCO, respectively. The total amount of high-spin density C atoms strongly depends on the microporous surface area. The study of NOCO was updated, which contributed to the preparation of highly efficient AC for NOCO.

Efficient micropore sizes for carbon dioxide physisorption of pine cone-based carbonaceous materials at different temperatures

Biomass-based activated carbons (ACs) are widely used as CO2 capturing materials. Most plant-based biomass contains a phytolith component that mainly comprises silica, which is an obstacle for developing the porosity of ACs. The silica elimination process (SE) has rarely been studied for developing the porosity of ACs. Here, we prepared pre-carbonized pine cones (CPC) as a starting material to investigate optimizing the micropores of ACs according to the preparation sequence. One was prepared by chemical activation (CA) and the subsequent SE (CPC-CA-SE/ACs) and the other was carried out the SE before CA (CPC-SE-CA/ACs). It was found significant differences on the pore development between two samples, the former showed a specific surface area of 1787 m2 g−1 and the microporosity of ∼92 % while the latter were 2047 m2 g−1 and ∼74 %, respectively. The highest CO2 adsorption capacities were exhibited in CPC-CA-SE/ACs of 6.57 mmol g−1 at 273 K and 1 bar, resulting from the effective pore size (< 1.1 nm). Furthermore, the highest CO2 capture performance of 0.75 mmol g−1 in the typical flue gas condition (15 % CO2/85 % N2) and superior regeneration properties during 10 adsorption–desorption cycles at 313 K were achieved in CPC-CA-SE/ACs. From the results, we found that the preparation sequence had a strong effect on the textural properties of the resultant of biomass-based ACs and their CO2 capture performance.

Microporous-activated carbons of type I adsorption isotherm derived from sugarcane bagasse impregnated with zinc chloride

Microporous-activated carbons of type I adsorption isotherm derived from sugarcane bagasse impregnated with zinc chloride

A systematic preparation mechanism for directional regulation of pore structure in activated carbon including specific surface area and pore hierarchy

Currently, the simultaneous and directional regulation of specific surface area (SBET) and pore hierarchy (the percentage of mesoporous and macroporous volume to total pore volume, Vmes+mac/Vt) of activated carbon (AC) lacks a systematic preparation mechanism. In this study, AC samples were prepared from coconut husks, and the effect of carbonization methods, activation methods, and process parameters on the development of the pore structure were explored. N2 adsorption–desorption results indicated that AC samples prepared via conventional carbonization were microporous. Hierarchical AC samples were obtained by the combination of hydrothermal carbonization at 240 °C and physical activation. CaCl2 impregnation was found to be beneficial to the preparation of meso-/macroporous AC samples. Based on these results, a series of AC samples with typically varied pore hierarchies (18.05–76.73 %) with similar specific surface areas (∼450.0 m2 g−1) were obtained. AC samples with similar pore hierarchies and different specific surface areas were also prepared, including microporous AC (SBET: 330.5–761.4 m2 g−1; Vmes+mac/Vt: 12.21–14.06 %), hierarchical AC (SBET: 445.9–780.7 m2 g−1; Vmes+mac/Vt: 51.04–54.89 %), and meso-/macroporous AC samples (SBET: 371.1–516.0 m2 g−1; Vmes+mac/Vt: 67.39–75.25 %). A systematic preparation mechanism for the directional regulation of the pore structure of AC is proposed, which is significant for the preparation of high-efficiency AC for different applications.

Perfluoroalkyl substances (PFAS) adsorption in drinking water by granular activated carbon: Influence of activated carbon and PFAS characteristics

Perfluoroalkyl substances (PFAS) persistence in the environment leads to their presence in drinking water, that is of high concern due to their potential human health risk. Adsorption onto activated carbon (AC) has been identified as an effective technique to remove PFAS. Adsorption isotherms and breakthrough curves, determined by rapid small-scale column tests (RSSCTs), were studied for eight PFAS and four granular ACs, characterized by different origins, porosities and numbers of reactivation cycles. Both batch and RSSCT results highlighted the strong interaction of AC and PFAS characteristics in adsorption capacity. The most important factor affecting AC performance is the surface charge: a positively-charged AC showed higher adsorption capacities with greater Freundlich constants (KF) and later 50% breakthroughs compared to the AC with neutral surface. Among the positively-charged ACs, a microporous AC demonstrated higher adsorption capacities for hydrophilic and marginally hydrophobic PFAS, while the mesoporous AC performed better for more hydrophobic PFAS, possibly due to lower pore blockage by organic matter. These results were confirmed at full-scale through a one-year monitoring campaign, in which samples were collected at the inlets and outlets of GAC systems in 17 drinking water treatment plants spread in a wide urban area, where the four analyzed ACs are used.