Acidic Oxygen-containing Functional Groups Research Articles

Study on Molecular Model Construction and Gas Adsorption Simulation of Anthracite in the Qinshui Basin.

Uncovering gas adsorption characteristics of coal at the molecular scale is of great theoretical significance for the study of gas occurrence, coalbed methane exploitation, and carbon dioxide sequestration. In this study, based on proximate analysis, ultimate analysis, 13C nuclear magnetic resonance, and Fourier-transform infrared spectroscopy experiments, the existence forms and relative contents of elements of anthracite in the Qinshui Basin were tested and analyzed, and a macromolecular structure model was constructed. Besides, three types of acidic oxygen-containing functional groups, namely, carboxyl groups, phenolic hydroxyl groups, and lactone groups, were added to the molecular model. Furthermore, CH4 adsorption simulation was conducted on the original molecular model of anthracite and models with three types of acidic functional groups added. The following research results were obtained. The molecular formula of the constructed macromolecular model of anthracite in the Qinshui Basin is C193H138N2O7. The molecular structure of coal becomes more compact and curved after structural optimization and annealing optimization. For the four models, the CH4 adsorption characteristics of coal molecules all conform to the Langmuir equation under the same simulation conditions. Among them, the original model has the largest CH4 adsorption capacity, while the addition of oxygen-containing functional groups reduces the CH4 adsorption capacity to varying extents. The reduction of CH4 adsorption capacity follows the order: adding carboxyl groups > adding phenolic hydroxyl groups > adding lactone groups, which is mainly attributed to the different adsorption heats and adsorptive potential wells triggered by the addition of acidic functional groups in molecules.

Tuning the reactivity of carbon surfaces with oxygen-containing functional groups

Oxygen-containing carbons are promising supports and metal-free catalysts for many reactions. However, distinguishing the role of various oxygen functional groups and quantifying and tuning each functionality is still difficult. Here we investigate the role of Brønsted acidic oxygen-containing functional groups by synthesizing a diverse library of materials. By combining acid-catalyzed elimination probe chemistry, comprehensive surface characterizations, 15N isotopically labeled acetonitrile adsorption coupled with magic-angle spinning nuclear magnetic resonance, machine learning, and density-functional theory calculations, we demonstrate that phenolic is the main acid site in gas-phase chemistries and unexpectedly carboxylic groups are much less acidic than phenolic groups in the graphitized mesoporous carbon due to electron density delocalization induced by the aromatic rings of graphitic carbon. The methodology can identify acidic sites in oxygenated carbon materials in solid acid catalyst-driven chemistry.

Performance optimization and kinetic analysis of HNO3 coupled with microwave rapidly modified coconut shell activated carbon for VOCs adsorption

As a typical carbon-based material, activated carbon (AC) has satisfied adsorption performance and is of great significance in the field of volatile organic compounds (VOCs) pollutants removal. In order to further reveal the optimization mechanism of AC adsorption performance, coconut shell-based AC was selected as the research object, and different concentrations of HNO3 coupled with microwave were used for rapid modification and activation. The characteristic changes of pore structure and surface chemical of AC before and after rapid modification were analyzed, and the performance changes of VOCs absorption were discussed from the perspective of reaction kinetics. The pore structure and surface chemical properties of before and after modification were analyzed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Brunauer-Emmeta-Teller (BET) analysis, Fourier Transform Infrared Spectroscopy (FTIR), and Boehm titration. The results showed that HNO3 coupled with microwave could significantly eliminate impurities in the pores of AC. After impregnation in HNO3 at a concentration of 1.5 mol L−1 and under microwave irradiation of 900 W, the number of micropore on the surface of samples increased slightly. When the impregnation concentration of HNO3 continued to increase, the two adjacent pore structures of the samples merged, which lead to a large decrease in the number of micropore and a corresponding increase in the proportion of mesoporous. Meanwhile, the specific surface area SBET of the modified NAC-6 sample increased to 1,140.40 m2 g−1, and the total acidic oxygen-containing functional groups on the surface increased by 0.459 mmol g−1 compared to that of the unmodified raw carbon. Furthermore, by analyzing the experimental results of formaldehyde adsorption on AC samples, it was concluded that the saturated adsorption capacity of the modified NAC-6 sample was 43% higher than that of the raw carbon. This study provides a more convenient and faster modification method for AC in the field of gas phase pollutants purification, which is helpful to realize the practical engineering application of AC with high efficiency, energy saving and sustainable.

Coke powder improving the performance of desulfurized activated carbon from the cyclic thermal regeneration

Thermal regeneration is widely used in industry for the activated carbon/coke for flue gas desulfurization. But the serious carbon and mechanical loss of AC results in the rapid dropping of desulfurization performance. This paper studies the effect of coke powder (CP) as an additive for improving the performance of AC for the flue gas desulfurization/regeneration. Results show that the addition of CP decreased the carbon and mechanical loss by 33% and 41% after 10 cycles, and improve the cyclic desulfurization performance by slowing down the decrease of sulfur capacity. Physicochemical structure analyses confirmed that the addition of CP maintained the structural stability and prevented the generation of acidic oxygen-containing functional groups as well as the reduction of π − π* basic functional group. The conducive effect might be attributed to the reduction of the redox reaction from the addition of CP. This study suggests that AC with CP addition has a great potential for the application on the activated carbon/coke flue gas desulfurization (ACFGD).

Optimizing the Desorption Technology of Total Flavonoids of Ginkgo Biloba from Separating Materials of Activated Carbon.

Activated carbon adsorption is one of the processes used to produce ginkgolides from the extract of Ginkgo biloba (EGB) in most enterprises. However, the problem is that the ginkgolides can be eluted by ethanol after the Ginkgo biloba extracts are adsorbed by activated carbon, while total ginkgo flavonoids (TGFs) would form dead adsorption, leading to the ineffective utilization of TGFs. In this paper, the maximum adsorption capacity of TGFs by activated carbon was 226.7 mg/g activated carbon at pH 5, and the adsorption of TGFs was easier and more favorable to monolayer adsorption. On this basis, the technical process of desorption of TGFs from activated carbon preparation technology was optimized by using the response surface optimization technique. Under the optimum process (the elution volume was 116.75 mL, the ethanol concentration in the eluent was 73.4%, the elution temperature was 31.5 °C, and the ammonia concentration was 5.7%), the desorption rate of TGFs was 74.56%. Scanning electron microscopy morphological analysis showed that the used activated carbon had a wide pore size distribution, with the micropore pore size mainly concentrated around 0.64 and 1.00 nm and the mesopore pore size mainly concentrated between 2.89 and 39.5 nm. In addition, the molecular weight of ginkgo flavonoids is mainly distributed between 500 and 1000 Da, which can be transported to the micropores through the mesopore channels. On the other hand, there is a force between the flavonoids and the acidic oxygen-containing functional groups on the pore surface, which is the main reason for the formation of dead adsorption. The obtained results contribute to further improving the process of adsorbing and desorbing TGFs from EGB and lay a foundation for the development of more suitable activated carbon.

Effects of acid modification on the structure and adsorption NH4+-N properties of biochar

The adsorption by biochar can effectively alleviate the problem of ammonia inhibition in biogas engineering. Based on batch adsorption experiments, the effect of acid modifier on physicochemical and adsorption NH4+-N properties of biochar was explored, and anaerobic digestion (AD) with addition of modified biochar (MB) was designed and carried out. The results showed that after modification, the adsorption capacity of biochar was significantly improved, and the maximum adsorbance of MB was 1.57 times higher than that of original biochar. Acid modifier had demineralization and increased the number of acidic oxygen-containing functional groups. Chemical adsorption was the dominant adsorption mechanism, mainly including surface electrostatic adsorption and the interaction between ammonium ions and surface functional groups of biochar. With the addition of MB, gas production rate of the AD of chicken manure was increased and the effective gas production period was shortened to 18 days. This research has guidance significance for alleviation ammonia inhibition during the AD by adding MB.

Influence of cerium doping on Cu-Ni/activated carbon low-temperature CO-SCR denitration catalysts.

In this study, to evaluate the effects of two methods for activation of nitric acid, air thermal oxidation and Ce doping were applied to a Cu–Ni/activated carbon (AC) low-temperature CO-SCR denitration catalyst. The Cu–Ni–Ce/AC0,1 catalyst was prepared using the ultrasonic equal volume impregnation method. The physical and chemical structures of Cu–Ni–Ce/AC0,1 were studied using scanning electron microscopy, Brunauer–Emmett–Teller analysis, Fourier-transform infrared spectroscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, CO-temperature programmed desorption (TPD) and NO-TPD characterisation techniques. It was found that the denitration efficiency of 6Cu–4Ni–5Ce/AC1 can reach 99.8% at a denitration temperature of 150 °C, a GHSV of 30 000 h−1 and 5% O2. Although the specific surface area of the AC activated by nitric acid was slightly lower than that activated by air thermal oxidation, the pore structure of the AC activated by nitric acid was more developed, and the number of acidic oxygen-containing functional groups was significantly increased. Ce metal ions were inserted into the graphite microcrystalline structure of AC, splitting it into smaller graphene fragments, whereby the dispersibility of Cu and Ni was improved. In addition, many reaction units were formed on the catalyst surface, which could adsorb more CO and NO reaction gases. With the increase in Ce doping, the relative proportions of Cu2+/Cun+, Ni3+/Nin+ and surface adsorbed oxygen (Oα) in the Cu–Ni–Ce/AC0,1 catalyst increased. In addition, after the introduction of Ce into Cu–Ni/AC, the amount of weak and medium acids significantly increased. This may be due to the Ce species or its influence on the Cu/Ni species. Further, the active sites of the acid were more exposed. According to the results of the study, a composite metal oxide CO-SCR denitration mechanism is proposed. Through the oxidation–reduction reaction between the metals, the reaction gas of CO and NO is adsorbed and the incoming O2 is converted into (Oα), which promotes the conversion of NO into NO2. The CO-SCR reaction is accelerated, and the rate of low-temperature denitration was increased. Overall, the results of this study will provide theoretical support for the research and development of low-temperature denitration catalysts for sintering flue gas in iron and steel enterprises.

Research Progress of Adsorption and Photocatalysis of Formaldehyde on TiO2/AC

Based on the increasingly serious formaldehyde pollution, effective degradation of formaldehyde has become a practical problem that humans urgently need to solve. Among many treatment methods, activated carbon has the advantages of large specific surface area, high adsorption efficiency, and uniform pore size distribution. As a kind of clean photocatalytic material for formaldehyde degradation, titanium dioxide supported by activated carbon has become a research hotspot to develop adsorption-catalytic materials for formaldehyde degradation. In this paper, the research progress of activated carbon and its modification, the photocatalytic principle and modification of titanium dioxide, and TiO2/AC materials are reviewed. The results show that the pore size distribution gradient and acidic oxygen-containing functional groups of activated carbon play key roles in the formaldehyde adsorption process. TiO2 doped with metal ions and nonmetal ions can significantly improve the photocatalytic activity. The TiO2/AC material can greatly improve the photocatalytic rate and achieve the technical goal of efficient and clean degradation for formaldehyde.

Design of Paracetamol Delivery Systems Based on Functionalized Ordered Mesoporous Carbons.

The oxidized ordered mesoporous carbons of cubic and hexagonal structure obtained by two templating methods (soft and hard) were applied for the first time as delivery systems for paracetamol—the most common antipyretic and analgesic drug in the world. The process of carbon oxidation was performed using an acidic ammonium persulfate solution at 60 °C for 6 h. The functionalization was found to reduce the specific surface area and pore volume of carbon materials, but it also led to an increasing number of acidic oxygen-containing functional groups. The most important element and the novelty of the presented study was the evaluation of adsorption and release ability of carbon carriers towards paracetamol. It was revealed that the sorption capacity and the drug release rate were mainly affected by the materials’ textural parameters and the total amount of surface functional groups, notably different in pristine and oxidized samples. The adsorption of paracetamol on the surface of ordered mesoporous carbons occurred according to different mechanisms: donor–acceptor complexes and hydrogen bond formation. The adsorption kinetics was assessed using pseudo-first- and pseudo-second-order models. The regression results indicated that the adsorption kinetics was more accurately represented by the pseudo-second-order model. Paracetamol was adsorbed onto the carbon materials studied following the Langmuir type isotherm. The presence of oxygen-containing functional groups on the surface of ordered mesoporous carbons enhanced the amount of paracetamol adsorbed and its release rate. The optimal drug loading capacity and expected release pattern exhibited oxidized ordered mesoporous carbon with a hexagonal structure obtained by the hard template method.

Enhanced adsorption of aqueous acetone by modified powdered activated carbon

ABSTRACT Acetone, a small molecule organic compound, is freely soluble and volatile. To improve the removal rate of acetone, three different types of powdered activated carbon (PAC) were compared and then modified with formic acid and NaOH to optimize the adsorption capacities of PAC. The adsorption mechanism and the effect of physical–chemical properties of PAC to the adsorption were clarified. Results show that PAC produced from wood performed best adsorption capacities. The pseudo-second-order model and the Freundlich model accurately described the adsorption behaviour, while lower temperature was more conducive to the adsorption process. PAC giving a higher acetone adsorption capacity had a larger specific surface area, a richer micropore structure, a larger micropore volume, a smoother surface, with more acidic, oxidizing functional groups. The adsorption removal efficiency of modified PACs with formic acid was improved from 60.89% to 82.93%, while NaOH modification decreased the adsorption capacity. The positive effect of formic acid was attributed to the formation of novel acidic oxygen-containing functional groups, which was supported from the NaOH treatment that removed original acidic oxygen-containing functional groups, contrarily the formation of novel alkaline reducing functional groups did not restore the acetone adsorption capacity. We conclude that wooden PAC is a suitable adsorbent for acetone, in particular after pretreatment with formic acid.

Performance Recovery in Degraded Carbon-Based Electrodes for Capacitive Deionization.

Limitations of capacitive deionization (CDI) and future commercialization efforts are intrinsically bound to electrode stability. In this work, thermal treatments are explored to understand their ability to regenerate aged CDI electrodes. We demonstrate that a relatively low thermal treatment temperature of ∼500 °C can sufficiently recover the lost salt adsorption capacity of degraded electrodes. Furthermore, a systematic study of electrode replacement clarifies that the desalination ability loss and regeneration for a CDI cell are isolated to the aged anode, as expected. Characterizations of surface functionalities support that the acidic oxygen-containing functional groups formed in situ during cycling undergo thermal decomposition during treatment. The modified Donnan model quantitatively confirms that the surface charges originate from the formation/decomposition of functional groups. Accordingly, the lost pore volume and the increased resistance are recovered during thermal treatments, while the surface morphologies and pore structure of the electrodes are well-preserved. Therefore, thermal treatment can be applied practically to extend the lifetime of aged electrodes. This study also offers insights into strategies for minimizing electrode degradation or in situ regeneration such that the technology gains momentum for future commercialization.

Effect of Pyrolysis Temperature on Acidic Oxygen-Containing Functional Groups and Electron Storage Capacities of Pyrolyzed Hydrochars

Hydrothermal carbonization (HTC) is a thermochemical process, where biomass is treated with subcritical water. Hydrochar, the solid product of HTC, is a carbon-rich material containing acidic funct...

Elucidating dominant factors of PO43–, Cd2+ and nitrobenzene removal by biochar: A comparative investigation based on distinguishable biochars

Biochars produced from crab shell (CSB), oak sawdust (OB), Jerusalem artichoke tuber (JAB) and sorghum grain (SB) displayed distinguishable adsorption-related characteristics, such as specific surface area (SSA), ash content and acidic oxygen-containing functional groups (AFGs), which linked to the biochar adsorption mechanisms of most pollutants. Herein, PO43–, Cd2+, and nitrobenzene (NB) were employed for adsorption by these biochars to elucidate the dominant factors for the adsorption. Adsorption performance of the three pollutants onto these four biochars varied considerably, as exemplified by the excellent adsorption of PO43– and Cd2+ onto CSB (225.3 and 116.0 mg/g, respectively) as compared with onto the other three biochars (4.2–37.1 mg/g for PO43– and 9.7–41.0 mg/g for Cd2+). OB displayed the best adsorption of NB (72.0 mg/g), followed by SB (39.5 mg/g), JAB (31.1 mg/g), and CSB (23.6 mg/g). The kinetics and isotherm adsorption assessments couple with material characterization suggested that the sorption of selected pollutants on biochars was attributed to the multiple mechanisms involved, including coprecipitation, chemical bonds, cation exchange, physical absorption, and complexation. Further path analysis suggested that AFGs and ash content in biochars were more important than SSA with regards to pollutant removal, especially, with ash playing a crucial role in the removal of Cd2+ and PO43–, and AFGs being mainly responsible for NB adsorption. These findings might offer guidance on the preparation or modification of biochar with a targeted function for pollutant removal through an understanding the dominant factors.

The modification of the mesoporous carbon CMK-3 with the aqua regia and its adsorption desulfurization mechanism

ABSTRACTOrdered mesoporous carbon CMK-3 was synthesized and modified with aqua regia. Dibenzolthiophene (DBT) was employed to evaluate the adsorptive desulfurization performance of the adsorbents. It was found that such modification considerably enhanced the saturated sulfur capacity and breakthrough sulfur capacity toward DBT by 2 times, respectively. The modified CMK-3 possessed good reused performance. In order to make a deep study of main reasons for such increase, some characterizations including XRD, BET, TEM, FTIR, XPS, and Boehm titration were carried out. Based on the characterization results, the increased adsorption performance of modified CMK-3 was mainly attributed to the changes of the surficial acidic oxygen-containing functional groups. On such surface, the phenolic hydroxyl and the carboxyl groups have the chemical interactions with the S and the aromatic rings of DBT. Such interaction concerning the carboxyl groups devoted itself to the desulfurization more than the phenolic hydroxyl, and the cracking of the C-S bond of DBT also happen.

A study on the preparation of pitch-based high-strength columnar activated carbon and mechanism of phenol adsorption from aqueous solution.

Coal tar pitch was ground into powder and hydroformed with high pressure. After pre-oxidation, the pitch was activated by CO2 at high temperature. The effects of different preparation conditions on the yield, pore structure and phenol adsorption capacity of activated carbon were investigated, and activated carbon prepared under suitable conditions had good adsorption performance. A pore volume of 1–10 nm is the main absorption structure according to the analysis of pore size distribution and phenol adsorption capacity. The activated carbon showed high mechanical strength through compressive strength tests. Graphite nanocrystals around 5 nm were observed in the TEM images, and it illustrates that grain refinement results in the high strength. These nanocrystal stacked structures are easier to make and enlarge pores by activation than graphite layer stacked structures. Surface functional groups are considered not to be the active sites of phenol adsorption as suggested by the results of FTIR and Boehm's titration, and acidic oxygen-containing functional groups are harmful to phenol adsorption, which happen to be removed in the reductive preparation atmosphere. The donor–acceptor complex mechanism can be ruled out, and the π–π interactions are considered the most likely mechanism. The Langmuir and Redlich–Peterson models are better fitted to the adsorption isotherms. Adsorption kinetics fit the intraparticle diffusion model best. Comparison of different activated carbons shows that suitable pore size is important for phenol adsorption. Thermodynamic parameters demonstrate that the adsorption process is spontaneous and exothermic, and the entropy increases. Pitch-based high-strength columnar activated carbon is an effective and low cost adsorbent for phenol wastewater treatment. This carbon nanocrystal material also provides a new direction for catalyst carriers.

Adsorption of creatinine on active carbons with nitric acid hydrothermal modification

The adsorption of creatinine on active carbons was studied. Original active carbon (AC) and AC samples modified by nitric acid hydrothermal modification were assessed for their ability to adsorb creatinine. The pore structure and surface properties of the AC samples were characterized by N2 adsorption, temperature programmed desorption (TPD), Fourier Transform Infrared spectroscopy (FTIR), and X-ray photoelectron spectrometer (XPS). It indicated that 4M HNO3 hydrothermal modification with 180 °C was an efficient method in improvement of the creatinine adsorption. The improved adsorption capacity can be attributed mainly to an increase in the acidic oxygen-containing functional groups. The adsorption of creatinine over AC may involve an interaction with the acidic oxygen-containing groups on AC. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherm and isotherm constants. Equilibrium data fitted very well to the Freundlich model in the entire saturation range (3.58–59.08mg L−1). The maximum adsorption capacities of AC modified with 180 °C is 62.5mg g−1 according to the Langmuir model. Pseudo first-order and second-order kinetic models were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted well to the second-order kinetic model, which indicates that the chemical adsorption was the rate-limiting step, instead of mass transfer.

Study on the Impact of Degummed on Pineapple Leaf Fiber’s Structures and Formaldehyde Adsorptions

The micro-structural and formaldehyde adsorption abilities of pineapple leaf raw and degummed fibers are characterized by using SEM, FT-IR, chemical composition analysis and determination of acidic oxygen-containing functional groups and more other methods. Test results show that after being degummed, pineapple leaf fibers possess smoother surfaces, obvious grooves, better single-fiber separations and non-significant cross-sectional cavities. Hemicellulose’s characteristic absorption peaks disappear basically and their contents are reduced from 20.62% to 2.65%. The intensities of lignins’ characteristic absorption peaks drop and their contents are decreased from 3.68% to 1.20%. The locations of celluloses’ characteristic absorption peaks do not change too significantly and their contents are increased from 61.18% to 84.45%. The numbers of carboxyl, lactone and phenolic hydroxyl in acid oxygen-containing functional groups are reduced. Pineapple leaf raw fibers have higher formaldehyde adsorption abilities. After degumming, formaldehyde adsorption abilities of pineapple leaf fibers are similar, but all slightly lower than raw fibers.

Effect of oxidative modification of coal tar pitch-based mesoporous activated carbon on the adsorption of benzothiophene and dibenzothiophene

This work examines the effect of modification of coal tar pitch-based mesoporous activated carbon (MC) by HNO3 oxidation on the liquid-phase adsorption of benzothiophene (BT) and dibenzothiophene (DBT) in the model fuel oil. The pore structure and surface properties of the MC samples were characterized by N2 adsorption, SEM, FT-IR and Boehm titration. The results show that after oxidative modification, the specific surface area decreased, while the mesopore ratio and the density of the surface oxygen-containing groups increased remarkably. Moreover, the average pore sizes of MCs were not changed. The oxidative modification considerably enhanced the adsorption capacity toward BT and DBT by 1.3 times and 0.9 times, respectively. The improved adsorption performance upon the HNO3 oxidation can be attributed mainly to an increase in the acidic oxygen-containing functional groups. The higher the concentration of nitric acid and the oxidation temperature were, the more the amounts of surface acidic oxygen-functional groups were, and thus the higher the amounts adsorbed of BT and DBT on corresponding carbon were. The resulting oxidized MC afforded a maximum capacity of 53.0mg DBT and 32.8mg BT g−1 of MC follow saturation kinetics with respect to the total acidity on the surface of the MC. The competitive adsorption effects of naphthalene and phenanthrene against DBT on the oxidized MCs are obvious, and the effect of phenanthrene is greater than that of naphthalene. The MCs could be easily regenerated by washing with toluene. The regenerated adsorbent afforded 98%, 95% and 91% of the initial adsorption capacity after the first three regeneration cycles, respectively.

Effects of Plasma Polymerized Acrylic Acid Film on the Adhesion of Ag Tracks Screen-Printed on Polyimide

The adhesion of conductive patterns printed on polymer substrates is an indispensible issue for the commercialization of printable and flexible electronic devices. Plasma treatment has been widely used to improve the interfacial adhesion between a metal and a flexible polymer substrate. This study aims to investigate the influence of a polymerized acrylic acid layer coated by atmospheric-pressure plasma (APP) on the adhesion of a screen-printed silver (Ag)/polyimide (PI) system. The acidic oxygen-containing functional groups were incorporated onto a PI film by plasma polymerization of acrylic acid and, on it, the conductive tracks were constructed with a Ag nanopaste via screen printing. The Ag tracks were sintered at various temperatures ranging from 150 to 300°C for 30 min in air. The adhesion was evaluated by a roll-type 90% peel test. The peel strength of the screen-printed Ag/PI system with the acrylic acid film approximately quadrupled. To understand this adhesion enhancement, field emission scanning microscopy (FE-SEM), atomic force microscopy (AFM), contact angle analyzer, and X-ray photoelectron spectroscopy (XPS) were utilized. It was confirmed from these analyses that a hydrophilic film was formed due to the plasma polymerization process, and the carbon-oxygen (C–0)and carbonyl (C=0) bonds increased at the interfacial surface. Under the optimized conditions, a maximum adhesion of 245.5 N/m was obtained, and the stronger adhesion with the acrylic acid coating influenced the improvement in the flexibility of the film.

Optimization Conditions of Modified Activated Carbon and the Adsorption of Phenol

To optimize the conditions of modification and understand the absorption mechanism of activated carbon, the orthogonal test was used to select the best conditions of ammonia-modified activated carbon. The changes of activated carbon’s specific surface area, pore volume and surface acidic oxygen-containing functional groups were determined before and after modification by ammonia, and the equilibrium adsorption model for phenol was also explored. The results show that under the conditions of ammonia concentration of 10%, soaking time of 2h, activation time of 2.5h and activation temperature of 500°C, the best removal rate could be obtained. The specific surface area and pore volume of modified activated carbon were increased, whereas the acidic oxygen-containing groups of its surface were significantly reduced by 57.88% after modification. It means the surface polarity of carbon was decreased, and which was conducive to the adsorption of phenol, since phenol was a weakly polar substance. Both Freundlich and Langmuir model could reflect the adsorption behavior of modified activated carbon for phenol, while the Freundlich model was more properly, but for the unmodified activated carbon, Freundlich model was more suited to describe the adsorption behavior of phenol than Langmuir model.