AC Adsorption Research Articles

Adsorption of food dyes from aqueous solution on a sweet potato residue-derived carbonaceous adsorbent: Analytical interpretation of adsorption mechanisms via adsorbent characterization and statistical physics modeling

The adsorption of three food dyes, namely allura red AC, carmine and tartrazine, on a sweet potato residue-derived activated carbon (SPAC) was analyzed via experimental and theoretical tools. In a first step, SPAC was characterized by BET, FTIR and XRD to unravel its textural and surface properties. Adsorption isotherms of the three dyes were obtained at different temperatures ranging from 30 to 50 °C. Classical models were first applied to model the adsorption isotherms, but they were unable to describe the adsorption mechanisms. An alternative approach based on the application of mono- and multi-layer models from statistical physics theory was then used to better investigate the adsorption mechanisms. This alternative approach indicated that carmine and allura red AC adsorption followed a monolayer behavior, whereas the adsorption of tartrazine was a multi-layer process. These dyes were adsorbed via different configurations (horizontal, non-horizontal, horizontal and non-horizontal at the same time), depending on the system and the temperature. Tartrazine dye was removed via an aggregation process at different temperatures, while carmine was aggregated only at high temperatures. This aggregation process was absent for the allura red AC adsorption. Endothermic physisorption processes was observed for dye adsorption under these experimental conditions. The theoretical analysis indicated that SPAC is a promising material for the removal of these dyes, particularly in the case of allura red AC dye molecule. Overall, this study reports a combination of experimental and theoretical results to provide a new perspective at the molecular level of the removal of dye molecules using a low-cost activated carbon.

The production of activated carbon from Acacia erioloba seedpods via phosphoric acid activation method for the removal of methylene blue from water

Wastewater treatment requires a lot of granular activated carbon to absorb the dissolved organic components. This article describes a low-cost process for making highly active adsorption activated carbons from biomass, which could be used for wastewater treatment. A one-step carbonization and chemical activation with phosphoric acid at 500 °C produced low-cost acacia-derived porous activated carbons. The activated carbons' moisture, ash, volatile matter, and fixed carbon content were determined using proximate analysis. The activated carbon's adsorption qualities were also determined by studying its bulk density, surface morphology, power of hydrogen, iodine number, and methylene blue number index. To test the produced activated carbons for water treatment, batch adsorption dynamics were performed at room temperature for the removal of methylene blue from aqueous solution. Compared to activation using H2SO4, H3PO4 proves superior in generating well-developed pores, leading to a mesoporosity and microporosity structure with a larger surface area and high adsorption capacity. Brunauer–Emmett–Teller determined the sample's specific surface area, which was found to be 387 m2/g. The iodine number for 50, 100, and 200 μm activated carbon particles size was 620, 592, and 632 mg/g, respectively. The adsorption of MB on AC material better fits with Langmuir's adsorption isotherm; hence, particles are adsorbed on well-pronounced heterogeneous surfaces. The sips model is found to best represent the equilibrium data with R2 values of 0.994, suggesting the heterogeneous surface adsorption of MB on AC. Therefore, the adsorption of AC by MB involves physical and chemical processes. The produced AC hence appears to remove dissolved organic contaminants from raw water.

Simultaneous removal of PCDD/Fs and mercury by activated carbon from a full-scale MSW incinerator in southeast China.

This study emphasized on the removal performance of polychlorinated-ρ-dibenzodioxins and dibenzofurans (PCDD/Fs) and mercury by different activated carbon injection (ACI) rates from a full-scale (700 t/d) MSW incinerator. The result exhibited that the emission standard of PCDD/Fs and mercury could be met when the ACI rate reached 50mg/Nm3 and 30mg/Nm3, respectively. Lower chlorinated PCDD/Fs and PCDFs showed higher removal efficiencies compared with highly chlorinated PCDD/Fs and PCDDs, which could be attributed to the larger competitiveness of highly volatile congeners in AC adsorption than the lower volatile ones. AC turned out to have different adsorption selectivity for CP-routes PCDD/Fs congeners, among which 1379-TCDD was preferred to be absorbed while others exhibited little or poor selectivity for AC adsorption. The removal efficiency of PCDD/Fs was positively correlated with ACI rate at 99% confidence interval with a linear relationship (R2 = 0.98). Also, the outlet concentration of mercury decreased with the increase of ACI rate in a nearly linear function (R2 = 0.96). These results will be meaningful for the rational use of AC for pollutants control.

The alkaline sites integrated into biomass-carbon reinforce selective adsorption of acetic acid: In situ implanting MgO during activation operation

The adsorption separation of volatile organic compounds affords an efficient potential solution to address VOC emission. In this work, we reported alkaline sites-modified biomass-carbon adsorbents through in situ implanting MgO for reinforcing the adsorption abatement of polar VOCs. We revealed that the dispersed MgO alkaline sites in situ formed over the activated carbon during the KOH activation process by placing the magnesium acetate and KOH into grapefruit peel-based biochar together, which avoids the repeated postmodification. By tuning the mass proportion of Mg precursor and KOH activator, the optimized loading of magnesium oxide in AC was explored and compared with the MgO post-modified AC using a two-step procedure. The physicochemical properties of MgO-modified AC were characterized by various techniques. Impressively, MgO occupied a higher surface formation ratio (82.6%) in whole Mg species of the in-situ synthesized 10MgO/C compared to that (51.4%) in postimpregnated 10MgO/C-P. The adsorption properties of polar acetic acid and nonpolar benzene over the above comparative adsorbents were systematically studied by the gas-static adsorption method. The results revealed that the optimal sample of 10MgO/C afforded excellent structural properties (SBET = 2646 m2 g−1, Vtotal = 1.59 cm3 g−1) and a large adsorption capacity of polar acetic acid reaching 16.64 mmol g−1 at 30 °C. More importantly, compared to unmodified and nitrogen-doped AC, 10MgO/C showed improved acetic acid adsorption capacity, reversible desorption behavior, and lower adsorption heat. The calculation of Ideal Adsorption Solution Theory (IAST) for selective adsorption separation of the CH3COOH/C6H6 binary mixture(50/50) over 10MgO/C showed the highest selectivity (3.42). This work offers new insight into the in-situ modification of AC and polar VOCs selective adsorption separation.

Nanoscale zero-valent iron/silver@activated carbon-reduced graphene oxide: Efficient removal of trihalomethanes from drinking water

AC-supported nanoscale zero-valent iron composites (nZVI/AC) exhibit significant environmental implications for trihalomethanes (THMs)-contaminated water remediation. To improve the adsorption and degradation capability of AC, herein, a composite (nZVI/Ag@AC-RGO) consisting of AC, reduced graphene oxide (RGO), nanoscale zero-valent iron (nZVI), and silver (Ag) was synthesized and characterized using several techniques, such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, N2 adsorption-desorption isotherms, and X-ray photoelectron spectroscopy (XPS). The analysis of textural and morphological structures showed that a tightly-attached RGO film, amorphous iron, and weak crystal silver nanoparticles with a size of 20–30 nm were evenly immobilized on the support. Specific surface area increased by 19.12% after supporting RGO, while it decreased after supporting nZVI and Ag due to the partial blockage of micropores. The Fe surface was concurrently coated by iron oxides (Fe2O3, FeOOH) and Ag. THMs were eliminated through multilayer reaction processes. The values of the adsorption constant (KF) of chloroform (CHCl3), dichlorobromoethane (CHBrCl2), dibromochloroethane (CHBr2Cl), and tribromomethane (CHBr3) adsorbed by nZVI/Ag@AC-RGO increased by 34.4, 33.7, 81.6, and 67.3%, respectively, compared to pristine AC. THMs with more Br atoms exhibited better removal efficiency and adsorption capacity, along with a higher oxidation degree of the Fe surface. CHBrCl2 and CHBr2Cl mainly decomposed into chloromethane (CH3Cl) and dichloromethane (CH2Cl2), and CHBr3 and CHCl3 primarily degraded into dibromomethane (CH2Br2) and CH2Cl2, respectively, along with generating Cl− and Br−. Conclusively, THMs-contaminated water could be remediated by coupling AC pre-enrichment and the reactivity of nZVI/Ag.

N-doped activated carbon for high-efficiency ofloxacin adsorption

Preparation of high specific surface area activated carbon from rice husk for the removal of ofloxacin from medical wastewater. The optimum conditions for the preparation of activated carbon were a nitrogen doping ratio of 1:1:4 and an activation temperature of 800 °C (AC). The samples were characterised by N 2 adsorption isotherms, BET, FT-IR, TGA, XPS and SEM. The data showed that the specific surface area of AC was up to 1818.20 m 2 g −1 with a total pore volume of 1.12 cm 3 g −1 . AC formed N-containing functional groups on the surface and had good thermal stability. Scientific batch experiment studies were conducted to investigate the effect of pH, initial concentration, temperature and coexisting ions on the ofloxacin adsorption. The q e reached a maximum value of 780 ± 20 mg g −1 and maintained a removal efficiency of 51.1% after four regeneration cycles. The adsorption equilibrium data and the adsorption process were well represented by Langmuir model and general-order kinetic model, respectively. Thermodynamic studies of adsorption had shown that the adsorption process was autogenous and endothermic. Possible adsorption mechanisms for this material were also analysed. Finally, treatment of synthetic medical wastewater with AC resulted in a high removal rate of 98.3%. The superior adsorption properties combined with ease of preparation, ease of separation and excellent regeneration properties, make this material potentially effective for the removal ofloxacin from real medical wastewater. • Optimal preparation conditions for N-doped AC were studied. • The maximum sorption capacity of AC was 780 mg g −1 . • Various mechanisms for efficient adsorption of N-doped AC were analyzed. • Removal of ofloxacin from synthetic medical wastewater.

Development of a biosponge based on Luffa cylindrica and crosslinked chitosan for Allura red AC adsorption

A new bioadsorbent from Luffa cylindrica and cross-linked chitosan was proposed in the present study. Luffa was used as a natural support medium for chitosan crosslinked with glutaraldehyde (LCsG) and epichlorohydrin (LCsE). Biosponges were applied to remove Allura red from aqueous solutions. LCsG and LCsE were produced using different concentrations of chitosan (1%, 3% and 5% (m v−1)) and crosslinking agents (0.5%, 1.0% and 1.5% (v v−1)). Based on the FT-IR spectra, functional groups characteristic of chitosan crosslinked with glutaraldehyde and epichlorohydrin confirmed the crosslinking. In addition, the biosorbent revealed highly efficient functional groups and morphology with irregularities favorable for adsorption. It was found that the increase in the percentage of glutaraldehyde and epichlorohydrin increased the sample's swelling degree, and the degree of cross-linking was greater than 80% for all LCsG. The results regarding the degree of swelling and degree of crosslinking corroborated with the evaluation of the biosponge's adsorptive potential. The Sips model predicted the equilibrium isotherms, with a maximum adsorption capacity of 89.05 mg g−1 for LCsG and 60.91 mg g−1 for LCsE. The new procedure was successful. Luffa was excellent support for chitosan, resulting in an attractive, low-cost bioadsorbent, preventing renewable sources.

Comparative study on polychlorinated biphenyl sorption to activated carbon and biochar and the influence of natural organic matter

The sorption isotherms of polychlorinated biphenyls (PCBs) on carbons (coal based activated carbon named AC and hardwood derived biochar named BC) and natural organic matter (NOM) loaded carbons were examined and carbon-water partition coefficients (KC-W-PCB) were calculated. The purpose was to accurately predict the effectiveness of in-situ carbon treatments on the sediment impacted with hydrophobic organic chemicals (HOCs). For 1 month sorption, AC KC-W-PCB values were significantly higher than BC, corresponding to the much larger surface area (particularly in mesopores) for AC. BC KC-W-PCB values were correlated with PCB total surface area (TSA) and octanol-water partition coefficient (logKow). After loading with NOM, AC adsorption to PCBs strongly reduced and the fitted Freundlich exponents (n) decreased with increasing NOM level. However, NOM loading slightly impacted BC sorption and exhibited an opposite effect on BC n values. It is illustrated that the sorption mechanisms are different between AC and BC thereby the influences of NOM on sorption characteristics differ vastly. As the sorption time increased from 1 month to 6 months, an increase is observed in BC sorption extent but simultaneously NOM reduction effect on BC sorption increases, implying that more accurately evaluating BC application as an in-situ sorbent amendment for HOC impacted sediment need further investigation. On the contrary, AC adsorption attenuation caused by NOM coating greatly decreases over time, encouraging AC application as a sediment amendment.

Influence of alkaline activation temperature on the porous structure of the activated brown coal and its capacity to adsorb phenol

The purpose of this work was to evaluate the influence of alkaline activation temperature (t) on the pore structure of activated carbons produced from brown coal (ACs) and their adsorption capacity towards the sorption of phenol from aqueous solutions. The ACs were prepared by heating (t=400–8500C, 1 hr) of brown coal impregnated with KOH; the prepared samples were designated as AC(t). Based on the nitrogen adsorption-desorption isotherms (77 K), the total volume and surface (S) of all pores and separately micro- and subnanopores were determined. Maximum phenol adsorption capacities of ACs (Am) were registered at the temperature of 250С. The activation temperature was stated to be the most significant factor influencing the ACs capacity to adsorb phenol. The growth of temperature from 4000С to 8500С in the case of AC(800) results in an exponential increase in the value of Аm from 27 mg g–1 to 240 mg g–1 (a maximal value) according to the following equation: Аm=6.038exp(0.0045t) (R2=0.952). The kinetics of phenol adsorption obeys the second order model (R20.982). The AC(800) adsorption isotherm is described by the Freundlich equation (R2=0.988) within the equilibrium concentrations Ce=0.001–2.5 mg cm–3 with the heterogeneity factor nF=3.23 indicating physical adsorption. The same model for Ce0.001 mg cm–3 (R2=0.951) gives nF=0.52, which suggests chemical adsorption. The specific adsorptive capacity АS=Аm/S sharply decreases from 2.11 mg m–2 to 0.21 mg m–2 with increasing the temperature from 4000С to 5500С and remains constant (0.200.01 mg m–2) for ACs prepared at higher temperatures. The invariability of AS indicates the temperature independence of adsorption centers concentrations of ACs prepared within 550–8500С.

Wooden Activated Carbon Production for Dioxin Removal via a Two-Step Process of Carbonization Coupled with Steam Activation from Biomass Wastes.

A two-step process of carbonization coupled with steam activation was proposed for wooden activated carbon production from four kinds of biomass waste materials. The TG-FTIR results show that the carbonization process started at around 250 °C and finished at 500 °C for the coconut shell, pinewood, and plywood. The carbonization temperature of corn straw was lower than those of the other three samples, which was attributed to the higher concentration of ash content. FTIR results for the volatile compounds during carbonization show that CH4, CO, CO2, and hydrocarbons are the main detected gaseous species. The CH4 and CmHn yields of pinewood and plywood are higher than those of the coconut shell and corn straw. The carbonization results on the tubular furnace reactor show that furfural and phenol and its derivatives are the main tar compounds in waste carbonization. Carbonization experiments show that a temperature of 500 °C and residence time of 30 min are the optimized parameters for the three biomass wastes. The char yields are 26.4, 25.73, and 30.38% for pinewood, plywood, and coconut shell, respectively. CFD modeling has proven that using 20% of the volatiles could achieve lowest pollution and provide heat for carbonization of biomass waste. The steam activation results show that an activation temperature of 800 °C and activation time of 30 min are suitable for all three biomass samples, which could obtain optimized AC yields and adsorption quality for dioxin.

The adsorption properties of functionalization vetiver grass-based activated carbon: the simultaneous adsorption of phosphate and nitrate.

In this work, zirconium chloride octahydrate/CTAB/vetiver grass-activated carbon (ZR/CTAB/VGAC) was prepared from vetiver grass-activated carbon (VGAC), using zirconium chloride octahydrate (ZR) and cetyltrimethylammonium bromide (CTAB) as modifiers. The optimized conditions of the simultaneous phosphate and nitrate removal by ZR/CTAB/VGAC were discussed, including amount of adsorbent, initial concentration, pH, contact time, and temperature. The simultaneous removal efficiency of phosphate and nitrate was 96.50% and 51.17% under optimized conditions. The structural and morphology of ZR/CTAB/VGAC was investigated by using automatic volumetric adsorption analyzer (BET), scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDAX), and Fourier transform infrared spectroscopy (FTIR). It was found that the removal efficiencies of phosphate and nitrate were enhanced dramatically because ZR and CTAB were introduced on the surface of VGAC after modification. Moreover, the adsorption data fitted significantly well with Freundlich isotherm model. It was described well by pseudo-second-order kinetic model. Phosphate and nitrate adsorbed via chemisorption (ion exchange) by ZR, CTAB, and functional groups of the surface of ZR/CTAB/VGAC. Electrostatic adsorption of AC in ZR/CTAB/VGAC also played an important role in the adsorption process. ZR/CTAB/VGAC is an excellent adsorbent, which could be applied to remove nitrate and phosphate from wastewater.

Modulation of the driving forces for adsorption on MIL-101 analogues by decoration with sulfonic acid functional groups: superior selective adsorption of hazardous anionic dyes.

Toxic dyes pose a dramatic threat to human health and the environment when they are directly released into the water environment. Therefore, new porous materials with excellent adsorption performances are urgently needed to remove toxic dyes from wastewater. Herein, we report a sulfo-modified metal-organic framework (MIL-101-SO3H), which exhibits superior adsorption performance toward toxic dyes. The free -SO3H groups were successfully introduced into the MIL-101(Cr) skeleton to modulate the adsorption driving forces (i.e., hydrogen bonding, electrostatic attractions, and π-π stacking interactions together with adsorption spaces and steric hindrance) between the toxic dyes and MIL-101-SO3H adsorbent by varying the monosodium 2-sulfoterephthalic acid-to-terephthalic acid molar ratio in the reaction mixture. The experimental adsorption uptake by MIL-101-SO3H-1 was found to be 688.9 (methyl orange), 2592.7 (Congo red), and 213.2 (acid chrome blue K, AC) mg g-1, which was respectively 69.6, 89.6, and 51.5% higher than those of undecorated MIL-101. This adsorption behavior was attributed to the dye molecular structure, pore volumes, surface charge status, and functional groups of the adsorbents as well as the adsorption capacity of the dyes. The results revealed that the uncoordinated -SO3H groups increased the electrostatic attraction and hydrogen bonding between the MIL-101-SO3H adsorbent and linear anionic dyes. This increased the adsorption capacity toward the linear anionic dyes, overriding the effect of the pore volumes. On the other hand, the steric hindrance between the nonlinear anionic dye AC and MIL-101-SO3H adsorbent decreased the AC adsorption uptake of the latter, overriding the effects of hydrogen bonding and electrostatic attraction. In addition, the adsorption performance toward the cationic dye methylene blue increased, owing to the hydrogen bonding interactions, thereby overriding the effect of electrostatic repulsion and adsorption spaces. Thus, it is concluded that the adsorption behavior of the modified MIL-101-SO3H adsorbent is governed by the synergetic interplay between the electrostatic attraction, hydrogen bonding, and π-π stacking interactions as well as the steric hindrance and pore volumes of the adsorbent.

Efficient Cr(VI) removal from wastewater by activated carbon superparamagnetic composites

Activated carbon decorated with superparamagnetic iron oxide nanoparticles, AC/SPION, with high efficiency for removal of Cr(VI) from aqueous media in pH 3 to 8 range was realized, by exploiting the adsorption and reducing capability of AC and magnetite nanoparticles, allied to magnetic separation. However, iron(II) species was demonstrated to be very interesting as co-adsorbent since broaden the optimal pH range (pH 4 to 10) and enhance the removal capacity more than four times, by reducing hexavalent chromium to Cr(III) at the same time that produce iron(III) hydroxide, a colloidal material that tend to precipitate on the nanocomposite increasing its adsorption properties. Finally, AC/SPION can be dispersed in water maximizing the efficiency, and the chromium species loaded material can be easily separated with a magnet providing an alternative for the treatment of large volumes of contaminated wastewater. In fact, final effluents with Cr concentrations in the low μg/L range, suitable for direct disposal according to EPA recommendations, can be produced by the iron(II) assisted process demonstrating its potentiality in real applications.

Treatment of Ablution Greywater for Recycling by Alum Coagulation and Activated Carbon Adsorption

A considerable amount of ablution greywater (AGW) is being produced at mosques for cleaning certain parts of the body before performing prayers. In this study, alum coagulation followed by batch and continuous AC adsorption tests was conducted to examine the removal efficiency of turbidity, COD, and BOD to evaluate the recycling potential of AGW. In coagulation experiments, optimal overall removals of turbidity (95.8%), COD (31.6%) and BOD (50.0%) were achieved at 20 mg/L of alum dose. Further, the overall removal efficiencies were enhanced by AC adsorption for COD up to 70.8% and BOD up to 57.2% at 20 min adsorption equilibrium time with 0.2 g/L of optimal AC dose. The adsorption data was well fitted to the pseudo-second-order kinetics model. Both the Langmuir and Freundlich isotherm models were found suitable to characterize the adsorption of COD and BOD on AC. Maximum adsorption capacities were calculated 175 mg/g for COD and 88 mg/g for BOD. Continuous experiments of the AGW treatment process resulted in residual turbidity less than 1 NTU and both the COD and BOD values less than 10 mg/L. Treated AGW was found suitable for unrestricted irrigation, toilet flushing, and firefighting. The estimated cost for a full-scale treatment process (1.02 US$/ $$\hbox {m}^{3})$$ came out to be less than the existing cost of water production (1.09 US$/ $$\hbox {m}^{3})$$ in Saudi Arabia. The study revealed that the combination of alum coagulation and AC adsorption is a sustainable treatment option for recycling of AGW in arid and semiarid regions.

Superior adsorptive removal of anionic dyes by MIL-101 analogues: the effect of free carboxylic acid groups in the pore channels

MIL-101-COOH nanoparticles functionalized with free carboxylic acid groups exhibited superior CR, MO, and AC adsorption capacities via their distinctive adsorption mechanisms.

Optimization and toxicity assessment of a combined electrocoagulation, H2O2/Fe2+/UV and activated carbon adsorption for textile wastewater treatment

In this study, the potential application of sequential Electrocoagulation + Fenton (F) or Photo-Fenton (PF) + Active carbon adsorption (EC + F/PF + AC) processes were analyzed as alternatives for the treatment of an industrial textile wastewater resulting from an industrial facility located in Medellín (Colombia). In order to maximize the organic matter degradation, each step of the treatment was optimized using the Response Surface Methodology. At first, the optimal performance of EC was achieved with Fe electrodes operating at pH = 7, jEC = 10 mA/cm2 and 60 rpm, during 10 min of electrolysis. At these conditions, EC let to remove 94% of the dye's color, 56% of the COD and 54% of the TOC. Next, sequentially applied Fenton or photo-Fenton process (i.e., EC + F/PF), operating at the optimized conditions (pH = 4.3, [Fe2+] = 1.1 mM, [H2O2] = 9.7 mM, stirring velocity = 100 rpm and reaction time = 60 min.), improved the quality of the treated effluent. The EC + F let to achieve total color reduction, as well as COD and TOC removals of 72 and 75%, respectively. The EC + PF reached 100% of color, 76% of COD and 78% of TOC reductions. The EC + F/PF processes were more efficient than EC in elimination of low molecular weight (<5 kDa) compounds from wastewater. Moreover, the BOD5/COD ratio increased from 0.21 to 0.42 and from 0.21 to 0.46 using EC + F and EC + PF processes, respectively. However, EC + F/PF were not fully effective for the removal of acute toxicity to Artemia salina: 20% and 60% of reduction in toxicity using EC + F and EC + PF, respectively, comparing to very toxic (100%) raw textile wastewater. Thus, activated carbon adsorption was applied as an additional step to complete the treatment. After AC adsorption, the acute toxicity decreased to 10% and 0% using EC + F and EC + PF, respectively. The total operational costs, including chemical reagents, electrodes, energy consumption and sludge disposal, were of 1.65 USD/m3 and 2.3 USD/m3 for EC + F and EC + PF, respectively.

Single and mixture adsorption of clofibric acid, tetracycline and paracetamol onto Activated carbon developed from cotton cloth residue

Abstract The aim of this work is to investigate the feasibility of the preparation of adsorbent materials from waste textiles (cotton) for the removal of pharmaceutical products such as clofibric acid (AC), tetracycline (TC) and paracetamol (PC). Our results showed that the adsorbents prepared by chemical activation in the presence of phosphoric acid and pyrolysis at 600 °C lead to microporous materials with high surface areas. The adsorbents exhibit acid and basic groups at their porous surface and the acid character overrides the basic character. Kinetic data for AC and PC adsorption are found to follow a pseudo-second order kinetic equation with the exception of adsorption of TC which is well described by the pseudo-first-order model. The equilibrium data for the adsorption of pharmaceuticals compounds onto Activated Carbon Cloths (ACCs) were analyzed by testing different models. Additionally, the Langmuir model provided a good description of the experimental isotherms for PC and TC, whereas AC isotherm rather follows the Freundlich model. On the basis of the Langmuir analysis, the maximum adsorption capacities were determined to be 109, 105 mg g−1 for TC and PC, respectively. The activated carbon cloth also showed high efficiency for the removal of a mixture of 3 pharmaceuticals, except for AC. This study highlights that activated carbon prepared from the cotton cloths waste using phosphoric acid at 50% (ACC 50%) is a promising adsorbent because of its relatively high efficiency and potential of reuse.

A density functional theory study on adsorption and decomposition of acetic acid over silicon carbide nanotubes

In this study, the adsorption behavior of acetic acid (CH3COOH, AC) over (6,0) zigzag silicon-carbide nanotube (SiCNT) surface are investigated by carrying out density functional theory calculations. The structures of AC-SiCNT complexes are optimized and characterized by frequency calculations at the M06-2X/6-31G* computational level. To understand the catalytic activity of the surface, the interaction between the AC and SiCNT is analyzed by detailed electronic analysis such as adsorption energy (Eads), density of states (DOS), electron density difference and activation barrier. The calculated Eads values are in the range of −0.55 to −3.56eV. In order to investigate the curvature effect on the adsorption energies of the AC molecule, the AC adsorption on (5,0) and (7,0) SiCNTs is also studied. Our results indicate that the AC adsorption over the narrower (5,0) SiCNT is more thermodynamically favorable process than (6,0) one. So it seems that the curvature of small-diameter SiCNTs facilitates the sp3-hybridization of Si atoms and thus helps in the binding of AC on the tube surface. For the gas-phase AC decomposition over the SiCNT, the reaction proceeds through an acetate mechanism, which is consistent with the experimental results obtained on metal or metal oxide surfaces.

Impact of AC/O3 pretreatment on ultrafiltration processing sewage effluent for fouling alleviation

To resolve membrane fouling in the ultrafiltration process of sewage effluent, the impact of activated carbon catalytic ozonation (AC/O3) on fouling control was investigated. The influence of initial pH on AC/O3 for fouling alleviation was further explored. The results revealed that AC/O3 pretreatment greatly mitigated the membrane fouling. The total fouling, reversible fouling, and irreversible fouling were all decreased. The initial pH influenced the alleviation effect of AC/O3 on fouling control obviously, although it only slightly impacted the AC adsorption pretreatment on fouling alleviation. Besides, there was no obvious impact of pH on the ultrafiltration process. Compared with the adjustment of initial pH during ultrafiltration and the pretreatment methods such as AC adsorption and preozonation, AC/O3 displayed the greatest effect on both fouling alleviation and permeate quality improvement under all pH conditions. It was the component transformation of sewage effluent after AC/O3 pretreatment that caused the alleviation of membrane fouling. With the increase in initial pH, the high-MW biopolymers as well as humic substances in the effluent organic matter could be preferentially removed by AC/O3, which mitigated the flux decline during the ultrafiltration process and decreased the reversible and irreversible fouling.

INFLUENCE OF PHYSICAL-CHEMICAL PROPERTIES OF ACTIVE CARBONS ON GALLIC ACID ADSORPTION

The adsorption of gallic acid on active carbons of different ranks with different pore structure and chemical state of the surface is investigated. The regularities and features of the adsorption process are established. It is revealed that the adsorption isotherm of gallic acid from the aqueous solution with activated carbon of AG-OB-1 rank refers to the L-type isotherms by Giles's classification, and AC adsorption isotherm of ABG and Purolat-Standard ranks - to the S-type isotherms. L-type isotherm gives evidence concerning the flow of physical adsorption. With S-type isotherm is the adsorption described, at which the strength of the interaction between the solute and the adsorbent is less than the force of interaction between the adsorbed molecules, which can be explained by the formation of hydrogen bonds. It was found that the maximum adsorption of gallic acid with carbon sorbents changes in the following sequence - Purolat-standard > ABG > AG-OV-1. The mechanism of adsorption of gallic acid on active carbons is offered. Proceeding from the structure, the chemical state and the main adsorption parameters of active carbon, we can assume that the adsorption of gallic acid has physical nature. It can take place in pores, both due to dispersion interaction (of van der Waals forces) and due to the interaction between the active carbon surface functional groups, containing oxygen with carboxyl and hydroxyl groups of gallic acid. The values of adsorptive capacity testify to the dependence of the adsorption efficiency on the structure and physical-chemical properties of the sorbent. It has been determined that by the absorption of gallic acid specific interaction makes greater contribution. It is shown that the results obtained can be applied to create adsorption technologies on removing gallic acid from the sewage containing individual components and from the mixture with other polyphenols, including beer wort.