Removal of Cu<Superscript>2+</Superscript> ions from aqueous solution by amino-functionalized magnetic sawdust composites

In this study, amino-functionalized magnetic γ-Fe₂O₃/sawdust composites (MSC-NH₂) were investigated as biological absorption materials for removing Cu²⁺ ions from aqueous solution. These composites were fabricated by precipitated γ-Fe₂O₃ nanoparticles on sawdust substrate and then functionalized with 1,6-hexanediamine. Characterization of MSC-NH₂ was performed by means of SEM, TEM, XRD, FTIR, BET, MPMS and XPS analysis to discuss the uptake mechanism. As a result, the amino groups are grafted upon the sawdust surfaces. The MSC-NH₂ could be effectively used to remove Cu²⁺ from aqueous solution and be separated conveniently from the solution with the help of an external magnet. Batch experiments show that the adsorption equilibrium is achieved in 150 min, and the adsorption capacity is 7.55 mg/g at pH 6 and room temperature. The isotherm analysis indicates that the sorption data could be represented by Langmuir isotherm models. The kinetics is evaluated utilizing the Lagergren pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion models. Thermodynamic parameters reveal the spontaneous, endothermic and chemical nature of 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.     

Comparative sorption of copper and nickel from aqueous solutions by natural neem (<Emphasis Type="Italic">Azadirachta indica</Emphasis>) sawdust and acid treated sawdust

This study investigates the potential use of neem (Azadirachta indica) sawdust treated with hydrochloric acid for the removal of copper (II) and nickel (II) ions from wastewater. The effects of different system variables, viz, adsorbent dosage, initial metal ion concentration, pH and contact time were studied. The results showed that as the amount of the adsorbent was increased, the percentage of metal ion removal increased accordingly. Optimum pH value for metal adsorption is determined as 5.0 for Cu (II) and 4.0 for Ni (II) ions. Maximum metal is sequestered in 150 min for Cu (II) and 180 min for Ni (II) after the beginning of every experiment. Similar experiments were carried out with acid treated sawdust to compare the results. The adsorption of metal ions followed a first order rate equation. Both Freundlich and Langmuir adsorption models are suitable for describing the sorption of Cu (II) and Ni (II) on the two forms of sawdust. Furthermore, the natural organic matter (neem sawdust) is characterized by FTIR spectra and surface area analysis. At optimal conditions the maximum adsorption capacity is found to be 48.3 and 286 mg/g for Cu (II) and 31.5 and 74.1 mg/g for Ni (II) in natural and acid treated forms, respectively.     

Preparation and adsorption properties of macroporous tannin resins

1 Introduction Plant polyphenols are a large and diverse class of poly-atomic phenols which occur naturally in some parts of plants. Their molecular weight ranges from 500 to 3,000 g·mol–1. Plant polyphenols are abundant in nature and their production capacity is only second to that of cellulose, hemicellulose and lignin (Sun, 1988). Polyphenols can be divided into two kinds given their chemical constitution: hydrolysable tannin and condensed tannin (Song and Di, 2000). Benzene rings in th…     

Study of Cr(VI) adsorption onto nitrogen-enriched activated carbon from waste medium density fiberboard

Nitrogen-enriched activated carbons were prepared from waste medium density fiberboard waste by using NaOH, K₂CO₃ and KOH. The content of nitrogen in the activated carbon was 0.92, 0.74 and 1.33 % by analysis. The influence of contact time, pH, Cr(VI) initial concentration and the amount of activated carbon on the Cr(VI) adsorption capacity were investigated. The maximum adsorption capacity of Cr(VI) could reach 89.21 mg/g at pH 2 and a contact time of 9 h. The kinetics adsorption followed nicely the pseudo-second-order rate expression. In adsorption isotherm, the Langmuir model fitted better than the Freundlich model. Pure Poplar activated carbon was also prepared as the adsorbent for Cr(VI) removal as control sample. This study indicated that the nitrogen-enriched activated carbon prepared from waste medium density fiberboard can be used effectively for the removal of Cr(VI) compound from aqueous solutions.     

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.     

Water sorption mechanisms of commercial wood adhesive films

As water moves inside the wood, the gluelines might act as barriers that are potentially leading to local moistening. Even low amounts of water may influence the mechanical performance of glued wood products. Dynamic vapor sorption analysis was performed to assess the sorption processes of six commercial wood adhesives. Vapor sorption isotherms were compared with vapor uptake dynamics. Phenol–resorcinol–formaldehyde showed high moisture uptake of 18 %, while vapor diffusion speed was low. Fish glue showed a water uptake of 45 % at otherwise moderate vapor uptake speed. Melamine–formaldehyde resin gained 22 % water, and polyvinyl acetate absorbed 10 %. The latter was also the fastest vapor absorbing adhesive. Polyurethane only absorbed 3.5 % of moisture at medium uptake speed. Mechanisms of water diffusion seem to be driven by (1) the available free volume in the polymer and (2) the interacting ionic groups of the polymer chain. While the free volume could be linked to the accumulated moisture, the ionic group interaction might determine the measured vapor diffusion dynamics.     

Biosorption of methylene blue from aqueous solutions on β-cyclodextrin grafting wood flour copolymer: kinetic and equilibrium studies

The preparation, characterization, and environmental application of β-cyclodextrin/citric acid/wood flour (β-CD/CA/WF) graft copolymer wood-based biosorbent for methylene blue (MB) biosorption were investigated in this paper. The Fourier transform infrared spectroscopy and the technique of phenolphthalein probe were used to characterize the grafting β-CD. Furthermore, the biosorption behavior of MB on β-CD/CA/WF graft copolymer was studied under various conditions of pH, contact time, and initial MB concentration. The results indicated that the biosorption of MB was dependent on both the initial MB concentration and the initial pH. Langmuir isotherm model fitted the isotherm data better than the Freundlich model. The adsorption kinetics followed the pseudo-second-order kinetic model, and intraparticle diffusion was one of the effective rate-controlling steps for the entire biosorption period. Equilibrium and kinetic results have implied that β-CD/CA/WF graft copolymer could be considered as a promising material for the adsorption of dye from aqueous solutions.     

Sorption of metal ions from aqueous solution to spruce bark

The concentrations and protonation constants of the functional groups like carboxyl and phenolic hydroxyl groups in spruce bark were determined by a potentiometric acid–base titration method. The non-cellulosic carbohydrates in spruce bark were also characterized by acid methanolysis and GC, including determination of the uronic acid units, which are the key units involved in metal sorption. Sorption of metal ions to bark takes place by ion exchange, mainly by complexation to these functional groups. The sorption equilibrium time, studied by using a batch method, was approximately 5 min. The metal sorption capacity of spruce bark and the affinity order of metal ions were studied with four different metal ion mixtures using a column chromatographic method. Because a method of competition was used, concentration of metal ions adsorbed to bark depends on the metal ions present in the mixtures studied. In the sorption experiments with same metal ion mixtures, inner bark of spruce exhibited higher sorption capacity than outer bark. By combination of the results from several experiments, the following affinity order was obtained Fe³⁺ ? Pb²⁺ ? Cu²⁺ ? Cd²⁺ > Zn²⁺ > Ni²⁺ > Ba²⁺ > Ca²⁺ > Sr²⁺ > Mn²⁺ > Mg²⁺ ? K⁺ ~ Na⁺ ~ Li⁺. Bark has a great potential as an effective and inexpensive sorbent for removal of metal ions from, e.g., waste water.     

落叶松基复合材料SiO2@C的制备及其对染料的吸附行为研究

以落叶松木屑为原料,SiO2为孔结构调控剂,采用一步原位掺杂法制备了落叶松基SiO2@C复合材料,探讨了炭化温度、模板剂SiO 2对复合材料孔结构及吸附性能的影响。利用扫描电镜(SEM)、透射电镜(TEM)、氮气的吸附/脱附、拉曼光谱、X射线衍射仪(XRD)、傅里叶红外光谱(FT-IR)仪和X射线光电子能谱(XPS)对复合材料进行表征,并以乙基紫染料为模型物研究了复合材料的吸附行为。研究表明:随着炭化温度由700℃升高至900℃,SiO2@C复合材料的形貌由交联的球形形貌转变为网状结构,孔隙结构由整体无序向局部有序转变,比表面积由538 m^2/g提高到780 m^2/g;经900℃炭化制备的复合材料SiO2@C-900具有较高的比表面积和有序的孔隙结构,对乙基紫染料的吸附值高达378 mg/g,在温度55℃,pH值7的最佳吸附条件下,对乙基紫染料的脱除率达99%;重复利用5次后,脱除率仍在97%以上,说明复合材料稳定性良好。SiO2@C复合材料对染料的吸附符合Langmuir吸附等温模型,吸附动力学符合准二级动力学,即主要是化学吸附。     

新型转极性离子化合物对香樟木屑的溶解和再生性能研究

为实现生物质的溶解,同时克服传统离子液体溶解生物质的缺点,制备了新型转极性离子化合物1,8-二氮杂二环十一碳-7-烯(DBU)/CH3OH/CO_2(DCC)的甲醇溶液,考察了不同温度、时间和溶液浓度对香樟木屑的溶解性能和再生效果,分析了溶解前后香樟木屑中纤维素、半纤维素和木质素的溶解率及结晶度的变化,并对溶解前后的木屑进行FT-IR、XRD和SEM表征,对溶解液中再生的物质进行FT-IR和UV分析。结果表明:较高温度(≥120℃)下,香樟木屑在DCC的甲醇溶液中的溶解率随温度升高和时间延长而有所增加;DCC甲醇溶液对半纤维素和木质素的溶解能力较强,对纤维素的溶解能力较弱;2.5 mol/L的DCC甲醇溶液在溶解温度180℃,溶解时间6 h时,木屑溶解率达到48.6%,半纤维素溶解率达62.4%,木质素溶解率为55.7%,纤维素溶解率为19.6%,溶解效果与传统离子液体相当。FT-IR、XRD和SEM分析表明,DCC甲醇溶液溶解木屑时,主要溶解木屑中无定形的半纤维素、木质素和少量非晶态的纤维素。FT-IR和UV分析表明溶解液中再生的物质是木质素,其质量分数在90%以上。DCC甲醇溶液重复使用3次时,每溶解一次其溶解能力下降2~3个百分点。     

染色木材pH值与缓冲容量的比较分析

分别用酸性染料与活性染料,对大青杨和桦木单板进行直接染色和NaOH溶液预处理后染色,测量2种染色单板的pH值和缓冲容量,并与未染色单板进行对比.结果表明,NaOH溶液预处理、酸性染料、活性染料的染色对2种单板的pH值及缓冲容量的影响规律一致;染色可小幅度增加木材pH值,显著降低酸缓冲容量;预处理则可较大幅度增加pH值,并一定程度上增加酸缓冲容量;大青杨单板经2种工艺染色后,其酸缓冲容量均有明显下降;桦木单板直接染色酸缓冲容量减小,而预处理后染色则酸缓冲容量增大.     

Sorption of copper and lead by citric acid modified wood

The sorption characteristics of citric acid modified wood to remove copper and lead ions from aqueous solution under batch conditions have been investigated. Sorption was pH dependent with increasing uptake at higher pH values. The kinetics of sorption for both ions was rapid with 90% sorption taking place within the first 60 min regardless of its initial concentration. Sorption can be explained by a second-order kinetics model from which the rate constant, the equilibrium sorption capacity and the initial rate were calculated. From these parameters, the predictive models for Cu and Pb sorbed (q _t) in time t and at an initial concentration (C _o) are given by q _t=C _o t[0.31C _o–2.29+(0.04C _o+5.19)t] and q _t=C _o t/[0.06C _o–6.59+(0.01C _o+4.48)t] for Cu and Pb, respectively. Using these models the predicted and experimental uptakes of Cu and Pb were compared and discussed. Maximum sorption capacities of modified wood under present experimental conditions were 23.70 and 82.64 mg/g for Cu and Pb, respectively. However, for untreated wood the corresponding values were 2.56 and 7.71 mg/g indicating a tenfold increase in sorption upon citric acid modification. Ethylene diamine tetraacetic acid and nitrilotriacetic acid complexed with both ions render sorption less favorably. However, salicylic acid had little influence. In a binary system, Pb ions were more favorably sorbed than Cu ions which could be due to the larger ionic radius of the former ions.     

STUDIES ON STEPWISE STABILITY CONSTANTS OF COORDINATION COMPOUNDS FROM SULFONATED SHEOAK TANNIN WITH METAL IONS

The stepwise stability constants of coordination compounds from sulfonatedsheoak tannin with metal ions have been determined by pH potential method with catechol asmodel compounds at 20℃and constant ionic strength.     

Prediction of bending stiffness and moment carrying capacity of sugi cross-laminated timber

Cross-laminated timber (CLT) panels consist of several layers of lumber stacked crosswise and glued together on their faces. Prototype sugi CLT floor panels were manufactured and bending tests were carried out under the different parameters of lumber modulus of elasticity (MOE), number of layers, thickness of lumber and thickness of CLT panels. On the basis of above tests, bending stiffness and moment carrying capacity were predicted by Monte Carlo method. MOE of lumber was measured by using grading machine and tensile strength of lumber was assumed to be 60 % of bending strength based on the obtained bending test. Bending stiffness EI of CLT panels could be estimated by adopting composite theory and equivalent section area. Experimental moment carrying capacity showed 12 % higher value than the calculated moment carrying capacity by average lumber failure method, and also showed 45 % higher value than the calculated moment carrying capacity by minimum lumber failure method due to the reinforcement of the outer layer by the neighboring cross layer.     

Removal of cadmium (II) from aqueous solutions by adsorption using meranti wood

Meranti wood, an inexpensive material, has been utilized as an adsorbent for the removal of cadmium (II) from aqueous solutions. Various physico-chemical parameters such as equilibrium contact time, solution pH, initial metal ion concentration, and adsorbent dosage level were studied. Langmuir, Freundlich, Dubinin-Radushkevich (D-R) and Temkin isotherms were used to analyze the equilibrium data at different temperatures. The experimental data fitted well with the Langmuir adsorption isotherm, indicating the monolayer adsorption of the cadmium (II). The monolayer adsorption capacity of meranti wood for cadmium (II) was found to be 175.43, 163.93 and 153.84?mg/g at 30, 40, and 50°C, respectively. The thermodynamics of cadmium (II) adsorption on meranti wood indicates its spontaneous and exothermic nature. Kinetic studies showed that the adsorption followed a pseudo-second-order kinetic model. The results indicated that the meranti wood could be an alternative for more costly adsorbents used for cadmium (II) removal.     

The water vapor sorption mechanism and its hysteresis in wood: the water/void mixture postulate

A new method of wood moisture sorption analysis is presented using sorption isotherms of a series of mildly heat-treated specimens with varied and known elemental composition. This method allows the determination of the occupancy of accessible sorption sites in wood as a function of relative humidity h, θ(h) ≈ h, found in agreement with the literature data on the non-freezing water occupancy of hydroxyl groups for h < 0.9. Complementary sorption isotherm shape analysis identifies an empirical power law occupancy function, θ(h) = h ^α , α ≈ 0.73, which is close to the former two determinations in the same humidity range. The validity of widely accepted surface sorption theories for wood with a strongly bound primary layer and loosely bound secondary layers is disproven. To explain the found occupancy function, θ(h) ≈ h, a near-ideal liquid mixture of moisture and polar dynamic microvoids in the cell wall substance is postulated. The power law occupancy function is used to calculate the humidity-dependent number of sorption sites in adsorption/desorption isotherms to show that (1) the number of sorption sites from the adsorption line monotonically increases with increasing humidity—argued to represent the equilibrium number of sorption sites at each humidity, and (2) the number of sorption sites from the desorption line fails to fully return to that of the (equilibrium) adsorption line. Hysteresis is quantitatively explained as the result of non-equilibrium excess sorption sites being occupied according to the occupancy law. The relaxation of non-equilibrium excess sorption sites is satisfactorily modeled by a first-order rate equation. Applying the analysis to study mild thermal modification of moisture sorption isotherms revealed that (1) moisture contents decrease directly linear to the removed amount of sorption sites at all humidity <0.95, and (2) the absolute hysteresis is nearly unaffected as a result of counter-acting effects of the reduced number of sorption sites and reduced amount of relaxation.     

Differential adsorption of Al, Ca, and Mg by roots of red spruce (Picea rubens Sarg.)

The surface adsorption characteristics of red spruce (Picea rubens) roots were examined as a function of changes in external acidity and cation concentrations. Root cation exchange capacity varied significantly with changes in pH, increasing from 110 micromol(c) g(-1) at pH 3.5 to 155 micromol(c) g(-1) at pH 4.5, and reaching 250 micromol(c) g(-1) at pH 7.0. In general, Al adsorption by spruce roots was much greater than either Ca or Mg adsorption under the same initial conditions. However, root affinity for the divalent cations was proportionately much more sensitive to pH changes than was root affinity for Al. The fractions of adsorbed Ca and Mg increased by 50 to 100% as pH increased from 3.5 to 4.5, whereas the fraction of adsorbed Al remained relatively constant at both initial pH conditions. Competition experiments at pH 3.5 and 4.5 indicated that Al adsorption was strongly favored over Ca adsorption, except at low Al concentrations (~10 micromol l(-1)), high solution Ca(2+)/Al(3+) ion activity ratios (> 1.5 to 5.0), and at the higher pH. These results suggest that cell wall exchange sites in red spruce roots will tend to become progressively saturated with Al under the prevailing conditions of many acidic forest soils. To the extent that root adsorbed Al interferes with the active uptake of Ca and Mg, this process of competitive cation adsorption can contribute to impaired mineral nutrition in the spruce forest community.     

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.     

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。