Characteristics of nitrogen-enriched activated carbon prepared from waste medium density fiberboard by potassium hydroxide

Most waste of medium density fiberboard (MDF) is burnt, which could release toxic gases and pollutants to the environment. So, the re-using waste of MDF is highly desired. The nitrogen atoms of waste medium density fiberboard originate from urea–formaldehyde resin adhesive used in the manufacturing process, so nitrogen-enriched activated carbons could prepared easily. Nitrogen-enriched activated carbons were prepared from waste MDF by potassium hydroxide. The activation temperature was ranged from 600 to 900 °C, and the chemical agent/waste MDF varied from 1 to 5. Iodine number was used to evaluate the adsorption ability of waste MDF activated carbons. The pore properties including surface area, pore volume and pore size distribution were determined by N₂ adsorption. The method of elemental analysis and XPS were used to estimate how nitrogen functional groups changed with different activation conditions. The results showed that the adsorption of iodine number of activated carbons was ranged from 661 to 1350 mg/g. The surface area of waste MDF activated carbons was different from 941 to 1876 m²/g and total pore volume was from 0.455 to 0.949 cm³/g. The pore size distribution indicated that waste MDF activated carbons included both micropores and mesopores, and the analysis of element implied that the contents of nitrogen varied from 0.41 to 2.31 %.     

Study of Cr(VI) adsorption onto nitrogen-containing activated carbon preparation from bamboo processing residues

Nitrogen-containing bamboo charcoals were prepared using bamboo processing residues, and modified by melamine or urea. The iodine value of the products we obtained was analyzed, and two samples were chosen for the Cr(VI) adsorption. The experimental results show that under the KOH and carbon ratio of 3:1 (w₁/w₂), activation temperature 800 °C and activation time 1 h, the activated carbons modified by melamine boasted the iodine value of 1144 mg/g and the activated carbons modified by urea boasted the iodine value of 1263 mg/g. In addition, the equilibrium adsorption capacity is 95.3 mg/g for the activated carbons modified by melamine with the adsorbent dosage of 1.0 g/L at an initial pH 2 in the presence of 100 mg/L K₂Cr₂O₇ at 30 °C for 180 min and it is 94.2 mg/g for the activated carbons modified by urea in the same reaction condition. The pseudo-second-order kinetic model can better reflect the two kinds of nitrogen-containing activated carbons adsorption kinetic process of Cr(VI). The adsorption process conforms to the Langmuir model, indicating that the process is single molecular layer adsorption.     

Response surface methodology approach for methyl orange dye removal using optimized Acacia mangium wood activated carbon

The existing approach of response surface methodology was extended to study the adsorption of methyl orange dye on optimized Acacia mangium wood-based activated carbon with a Brunauer, Emmett and Teller surface area of 1,767 m²/g. The experiments were carried out in a batch system, and the optimal condition was determined by means of the face-centered central composite design of response surface methodology. The effect of activated carbon dose, temperature and contact time on the adsorption capacity and percentage removal of methyl orange dye molecules were optimized. The experimental results indicated that the optimal conditions for the maximum adsorption capacity were 0.515 g/L, 55.0 °C and 24 h for adsorbent dose, temperature and contact time, respectively. Under these conditions, the maximum adsorption capacity and percentage removal were found to be 181 mg/g and 90.5 %, respectively. At optimized conditions of methyl orange dye removal, studies of the kinetic and thermodynamic behavior of adsorption revealed that it followed the pseudo-second-order rate model and was spontaneously endothermic in nature.     

Removal of Cr(VI) from aqueous solutions by larch bark

The ability of larch (Larix leptolepis Gold.) bark to remove Cr(VI) from dilute aqueous solutions was investigated. The research parameters included the solution pH, contact time, temperature and initial concentration of Cr(VI) in solution. Of the parameters studied, the solution pH was found to be the most crucial. The Cr(VI) removal decreased steadily throughout the pH range studied (pH 2–6), while the Cr adsorption peaked at pH 3. Because the chemical reduction of Cr(VI) to trivalent state occurred to lesser extents even in strong acidic media, the Cr(VI) removal was mainly governed by physico-chemical adsorption. The positive value of the heat adsorption (ΔH ⁰) indicates the endothermic nature of the Cr(VI) adsorption. The relatively slow rate and irreversible nature of the adsorption as well as the order of the magnitude of the heat adsorption value suggest that the adsorption is of a chemical type. The adsorption data obtained from the equilibrium experiments were well fitted to both the Langmuir and Freundlich isotherms.     

Sorption of Cr(VI) on the wood of Japanese larch treated with concentrated sulfuric acid

A carbonaceous sorbent was prepared from the wood of Japanese larch (Larix leptolepis) by dehydration with concentrated sulfuric acid in a 69% yield. The abilities of the sorbent to remove Cr(VI) from aqueous solutions were investigated. Research parameters included the initial solution pH, temperature, and initial concentration of Cr(VI) in solution. The removal of Cr(VI) was highly solution pH dependent and was mainly governed by physicochemical sorption under weak acidic conditions. The equilibrium data fit well in the Langmuir isotherm model. The Langmuir constants were calculated at different temperatures, and the sorption capacity increased with rising temperature, indicating the endothermic nature of the Cr(VI) sorption onto the sorbent. The desorption experiments suggest that the Cr(VI) sorption is generally irreversible, owing to strong interaction of HCrO ₄ ⁻ with the active sites of the sorbent.     

竹活性炭处理六价铬废水的试验研究

用竹子加工的下脚料制得的竹活性炭,对六价铬废水进行净化处理。结果表明,竹活性炭对六价铬废水处理效果良好,实验探讨了竹活性炭处理六价铬废水的一般规律及影响因素。     

Pore structure and the properties of electric double layer capacitor electrode of bamboo-derived activated carbon prepared by superheated steam

Bamboo-derived activated carbon prepared by superheated steam (BAC) exhibited performance for utilization as an electric double layer capacitor (EDLC) electrode. Pore structure and EDLC performances were investigated by comparison with phenol resin-derived activated carbon (MSP-20), which is commercially available and often used for the purpose. The nitrogen adsorption isotherm showed that BAC had a large BET-specific surface area of 1268 g/m² with a developed pore structure, especially of the mesopore, in comparison with MSP-20. It is considered that inherent ash in bamboo promoted activation, in addition to physical activation by superheated steam. Capacitance per electrode volume (C_V) was 52 F/cm³ with BAC. Because the density of BAC is high (0.78 g/cm³) compared with that of MSP-20 (0.58 g/cm³), sufficient C_V for usage was obtained, although the capacitance per electrode mass (C_M) at 5 mA/cm² itself of BAC (67 F/g) was lower than that of MSP-20 (126 F/g). With IR drop, the resistance value of BAC (9.7 Ω) was lower than that of MSP-20 (10.5 Ω). Especially, the diffusion resistance of BAC disclosed to be smaller than that of MSP-20. These results indicated that BAC produced by steam activation is a promising material with a pore structure suitable for ion transfer in EDLC.     

Adsorption of trivalent chromium from dilute solution by conifer leaves

Summary  Chromium(III), Cr(III) adsorption capacities of the leaves of 34 conifer species were examined. Among these, Ginkgo biloba, Taxus cuspidata, Cephalotaxus harringtonia var. nana, and Taxodiaceae and Cupressaceae spp. showed large capacities to adsorb Cr(III). The adsorption capacities of conifer leaves for Cr(III) (3.12–5.09 mg Cr g⁻¹ adsorbent) compared favorably with those of commercial activated carbons (1.23–2.75 mg g⁻¹). Factors affecting Cr(III) adsorption were studied using G. biloba leaves. The factors included solution pH, contact time, temperature, and the initial concentration of Cr(III). The amount of Cr(III) adsorbed on the adsorbent increased steadily with increasing pH in a pH range from 2 to 5, with increasing contact time, and with increasing temperature ranging 20 to 40 °C. The Cr(III) adsorption was also affected by the initial concentration of Cr(III) in the solution.  A linear relationship was observed between the amount of Cr(III) adsorbed and the equilibrium concentration of Cr(III) in the solution when graphed logarithmically. The maximum capacity of G. biloba leaves was 27.5 mg Cr g⁻¹ adsorbent by column experiments. Received 13 January 1998     

Photocatalytic activity of TiO<Subscript>2</Subscript> crystallite-activated carbon composites prepared in supercritical isopropanol for the decomposition of formaldehyde

 An effort was made to develop photocatalytic TiO₂ crystallite–activated carbon (TiO₂-AC) composites from tetraisopropyl titanate (TPT)-soaked activated carbon in supercritical isopropanol. It was subsequently found that TPT in supercritical isopropanol could be effectively converted to the anatase form of the TiO₂ crystallites. The prepared composites, composed of activated carbon as an adsorbent and the anatase form of TiO₂ as a photocatalyst, were evaluated for their adsorption capacity and subsequent photocatalytic activity against formaldehyde, one of the harmful air pollutants in the environment. As a result, the supercritically treated TiO₂–AC composites, particularly at 300°C and 350°C, had much higher formaldehyde-decomposing ability compared to a noncomposite comprising a simple mixture of activated carbon and TiO₂ granules. This indicates that the supercritical treatment can be effective for preparing the photocatalytic composites that have a high synergetic effect of adsorption and photocatalytic decomposition of formaldehyde for environmental cleaning. Received: May 18, 2001 / Accepted: March 8, 2002 On leave from Fujian Forestry College, Fujian 353001, P.R. China Acknowledgments The authors express their sincere thanks to Miss H. Tokoro and Mr. D. Kusdiana for their kind, valuable help and cooperation and to Dr. H. Miyafuji for SEM observations of samples, all at the Graduate School of Energy Science, Kyoto University. Correspondence to:S. Saka     

活性碳纤维增强中密度纤维板力学性能的研究

研究了聚丙烯腈基活性碳纤维(PAN-ACF)对中密度纤维板(MDF)力学性能的影响,通过对比测试添加PAN-ACF中密度纤维板的静曲强度和内结合强度,得出聚丙烯腈基活性碳纤维对中密度纤维板性能的影响。     

Reinforcement of fiberboard containing lingo-cellulose nanofiber made from wood fibers

Wood-based materials are fabricated with adhesives composed of various materials derived from fossil fuels. It is difficult to identify replacements for these chemical adhesives. This study explored nanofiber technologies as an alternative to these adhesives. In this study, we focused on reinforcement effects of lingo-cellulose nanofiber (LCNF) on fiberboards made from softwood and hardwood fiber. We discuss the density effects of reinforcement with LCNF because the density of medium-density fiberboard (MDF), which is widely used for construction, is standardized at about 0.60–0.80 g/cm³. Fiberboards were manufactured with three densities (0.60, 0.75, and 1.00 g/cm³). For softwood fiberboards, the bending properties for LCNF-mixed boards were higher than those for the control fiberboards at all densities. In this paper, control fiberboard means fiberboard with fiber only. For hardwood fiberboards, the bending properties for LCNF-mixed fiberboard for 1.00 g/cm³-density board were higher than those for the control fiberboard. For internal bond strength (IB), the IB for LCNF-mixed fiberboard was higher than that for the control fiberboard. The thickness swelling (TS) and weight change (WC) with water absorption for fiberboards containing LCNF were lower than those for control fiberboards. As a conclusion, physical and mechanical properties of the resulting fiberboards were significantly improved with the addition of LCNF, especially for softwood fiberboards, due to close binding between LCNF and wood fibers.     

Consumption of O<Subscript>2</Subscript>, evolution of CO<Subscript>2</Subscript> and reduction of Cr(VI) during fixation of chromium based wood preservatives in wood

Norway spruce dust was impregnated with aqueous solutions of chromated copper wood preservatives. Immediately after treatment, observation of CO₂ evolution and O₂ consumption were performed. Significant quantities of CO₂ were released during reaction of chromium (K₂Cr₂O₇) containing solutions with wood or brown rotted wood. Nevertheless, during reaction of cellulose with these preservatives we did not observe evolution of CO₂. The presence of copper did not influence on concentration of CO₂. Opposite to CO₂ evolution, treatment of wood and brown rotted wood resulted in O₂ consumption. The oxygen concentration decrease in the measuring chamber was approximately 5 times greater than increase of concentration of carbon dioxide. Electron paramagnetic resonance (EPR) observations of chromium fixation showed that chromium is reduced from Cr(VI) to Cr(III) with Cr(V) as an intermediate on wood, brown rotted wood and cellulose. However, the reduction on wood and brown rotted wood was faster than the reduction on cellulose, as determined from changes of Cr signals in EPR spectra. So, evolution of CO₂ and consumption of O₂ as well as EPR signals of Cr species thus indicate that brown rotted wood, consisting of lignin and hemicelluloses in contact with Cr(VI) reacts more intensively than cellulose, and possibly, oxidation mechanisms of lignin and cellulose with Cr(VI) are different. Received: 20 July 2000     

Epichlorohydrin and aspartic acid incorporated into sawdust and application as sorbent for methylene blue

In this paper, a new cation exchanger is prepared by activating sawdust with epichlorohydrin, followed by coupling the epoxy-activated sawdust with aspartic acid. The sawdust cation exchanger (SCE) was investigated for its methylene blue (MB) removal capacity from aqueous solution. The removal experiments were performed under various conditions such as different initial pH, SCE dosage, dye concentration, ionic strength, and contact time in a batch system. The highest sorption capacity of MB was obtained beyond pH 4. The 2.0 g/l or more of SCE could remove above 95% of MB from 250 mg/l of dye solution. Increasing the ionic strength of the solution caused decline of MB sorption. The sorption isotherm conformed well to the Langmuir model. The sorption process could be described by the pseudo-second-order kinetic model.     

Optimization study for preparation of activated carbon from Acacia mangium wood using phosphoric acid

A study on the preparation of activated carbon from Acacia mangium wood was conducted, and the operating factors, such as activating agent concentration, activation temperature and activation time, were optimized using response surface methodology. In order to determine the effects of the operating factors namely H₃PO₄ concentration (6.48–48.5 %), activation temperature (364–1,036 °C) and activation time (19–146 min) on the characteristics of activated carbon, a three-level rotatable central composite design was used. The second-order mathematical model was proposed by regression analysis of the experimental data gathered from 20 batch runs. The optimum H₃PO₄ concentration, activation temperature and activation time were found to be 40 %, 900 °C and 45 min, respectively. At optimum conditions of the operating factors, the percent yield and surface area were 20.3 % and 1,767 m²/g, respectively. The activated carbon was found to be largely composed of mesopores. About 95 % of the total surface area was attributed to mesopores.     

木质颗粒活性炭吸附Cr（Ⅵ）的工艺条件

本文分别从静态和动态实验对影响活性炭吸附Ｃｒ（Ⅵ）的主要因素如炭种、表面含氧官能团的类型和数量、预处理及Ｃｒ（Ⅵ）浓度、ｐＨ值、温度、接触时间、解吸方法和条件进行了探讨和研究，确定了木质颗粒活性炭吸附Ｃｒ（Ⅵ）的合理的工艺条件。     

Thermal treatment of sawdust and coal-tar pitch mixture to produce porous carbon materials by chemical activation

In this work, different activated carbons were prepared from composites based on birch sawdust and coal-tar pitch by chemical activation with zinc chloride, phosphoric acid, and potassium hydroxide followed by carbonization. The influence of different chemical agents (ZnCl₂, KOH, and H₃PO₄), final temperature of carbonization and media on yield and structural properties of the carbonic product was studied. It was shown that chemical agents allow increasing yield of carbonic residue. Composite modification by H₃PO₄ or ZnCl₂ facilitates the formation of molded porous carbonic residue during the carbonization process. However, addition of KOH to the composite leads to formation of powder-like carbonic residue having a specific surface area of 1,600 m² g^?1 at 800 °C. It was established that all samples aged in air medium at 800 °C have higher values of specific surface area in comparison with the same samples aged in argon medium at similar conditions.     

活性炭的Zeta电位对其吸附各种染料规律的影响2．活性炭对阴离子染料酚红的吸附

通过在不同ｐＨ下活性炭吸附阴离子染料酚红规律的研究，发现ｐＨ对活性炭吸附酚红的影响，一方面是ｐＨ不同时活性炭表面ζ电位的带电性不同；另一方面是酚红的溶解度随ｐＨ而变化，这两个因素决定了活性炭对酚红的吸附性能。当ｐＨ小于活性炭的ｐＨ＿ｚｐｃ时活性炭表面ζ电位带正电，随着ｐＨ的降低，ζ电位增加，对阴离子酚红的吸附量随之增大。反之，当ｐＨ大于ｐＨ＿ｚｐｃ时，随着ｐＨ的增大，ζ电位降低以及酚红溶解度的增大，吸附量很快下降直至趋于零。此外还通过活性炭对阴离子染料酚红在不同ｐＨ下的吸附动力学和吸附热大学参数的估算，进一步揭示了活性炭在不同ｐＨ下对酚红的吸附机理。     

中纤板废水的预处理研究

用混凝剂聚合硫酸铁(PFS)和助凝剂聚丙烯酰胺(PAM)对中纤板废水进行预处理,考察了PFS和PAM投加量,以及投加后各自的搅拌时间,这4个因素对混凝效果的影响。结果表明,4个因素的较优水平分别为1.8g/L、15mg/L和30、90s时,废水中CODcr和SS的去除率分别达到了64.59%和91.06%;且PFS投加量对试验结果的影响最为显著。     

Fire performance of carbonized medium density fiberboard manufactured at different temperatures

Authors established a new manufacturing technology for crack-free carbonized boards by pressing and carbonizing the medium-density fiberboard. Industrialization of new functional carbon materials was performed by investigating the fundamental properties of the carbonized boards. To be used as a construction material, the carbonized board needs to satisfy the fire performance regulation. In this study, the carbonized boards were manufactured from medium-density fiberboard (c-MDF) at different temperatures and then fire performance including flame retardancy and smoke toxicity was analyzed using a cone calorimeter and noxious gas analyzer. The results show that as the carbonization temperature increases, weight loss ratio decreases and flame retardancy increases. In the c-MDF at 800 and 1000 °C, no external damage was observed after combustion. These c-MDFs satisfy the total heat release (standard below 8 MJ/m²) and heat release rate (standard below 200 kW/m²) regulations according to the Building Standard Law of Korea and Japan. In addition, the c-MDFs showed the lower total smoke release (TSR, 0.213 m²/m²) than that of virgin MDF (94.281 m²/m²). The c-MDF at 800 and 1000 °C were, therefore, classified as a class III flame retardancy material and can be used as indoor finishing material.     

Adsorption of mercury by sugi wood carbonized at 1000°C

The ability of sugi wood carbonized at 1000°C to adsorb mercury was examined using aqueous solutions of mercuric chloride. Parameters studied include contact time, pH, adsorption temperature, and initial concentration of mercury in solution. Results showed that sugi wood carbonized at 1000°C could effectively remove mercury from aqueous solutions. The carbonized wood showed high adsorption ability for mercury at a wide pH range (pH 3–9), but its ability drastically decreased at pH 11. Adsorption decreased with increases in adsorption temperatures, indicating that the processes were exothermic in nature. Adsorption was found to follow the Freundlich isotherm model. The adsorption capacity of carbonized sugi wood was comparable to that of commercial activated carbon.