Removal of dyes from colored textile wastewater by orange peel adsorbent: equilibrium and kinetic studies

The use of low-cost and ecofriendly adsorbents has been investigated as an ideal alternative to the current expensive methods of removing dyes from wastewater. Orange peel was collected from the fields of orange trees in the north of Iran and converted into a low-cost adsorbent. This paper deals with the removal of textile dyes from aqueous solutions by orange peel. Direct Red 23 (DR23) and Direct Red 80 (DR80) were used as model compounds. The adsorption capacity Q0 was 10.72 and 21.05 mg/g at initial pH 2. The effects of initial dye concentration (50, 75, 100, 125 mg/l), pH, mixing rate, contact time, and quantity of orange peel have been studied at 25 degrees C. The Langmuir and Freundlich models were used for this study. It was found that the experimental results show that the Langmuir equation fit better than the Freundlich equation. The results indicate that acidic pH supported the adsorption of both dyes on the adsorbent. Orange peel with concentrations of 8 and 4 g/l has shown adsorption efficiencies of about 92 and 91% for DR23 and DR80, respectively. Furthermore, adsorption kinetics of both dyes was studied and the rates of sorption were found to conform to pseudo-second-order kinetics with a good correlation (R > or = 0.998). Maximum desorption of 97.7% for DR23 and 93% for DR80 were achieved in aqueous solution at pH 2. Finally, the effect of adsorbent surface was analyzed by scanning electron microscope (SEM). SEM images showed reasonable agreement with adsorption measurements.     

Adsorption/desorption of Cd(II), Cu(II) and Pb(II) using chemically modified orange peel: Equilibrium and kinetic studies

Waste materials from industries such as food processing may act as cost effective and efficient biosorbents to remove toxic contaminants from wastewater. This study aimed to establish an optimized condition and closed loop application of processed orange peel for metals removal. A comparative study of the adsorption capacity of the chemically modified orange peel was performed against environmentally problematic metal ions, namely, Cd²⁺, Cu²⁺ and Pb²⁺, from aqueous solutions. Chemically modified orange peel (MOP) showed a significantly higher metal uptake capacity compared to original orange peel (OP). Fourier Transform Infrared (FTIR) Spectra of peel showed that the carboxylic group peak shifted from 1637 to 1644 cm⁻¹ after Pb (II) ions binding, indicated the involvement of carboxyl groups in Pb(II) ions binding. The metals uptake by MOP was rapid and the equilibrium time was 30 min at constant temperature and pH. Sorption kinetics followed a second-order model. The mechanism of metal sorption by MOP gave good fits for Freundlich and Langmuir models. Desorption of metals and regeneration of the biosorbent was attained simultaneously by acid elution. Even after four cycles of adsorption-elution, the adsorption capacity was regained completely and adsorption efficiency of metal was maintained at around 90%.     

Biosorption of uranium(VI) from aqueous solution by Citrus limon peels: kinetics,equlibrium and batch studies

Citrus limon peel (exocarp) was chemically treated and used for removal of U(VI) ions from aqueous solution in a batch system. Optimization of U(VI) sorption parameters, i.e. medium pH, adsorbent amount, contact time, initial U(VI) ions concentration and temperature on the removal performance of both native and modified peels was studied. Adsorption capacity of the modified peel was near up to 4 times higher than of unmodified. The correlation regression coefficients show that the adsorption process can be well-defined by Langmuir equation. Additionally, it conforms to the pseudo-second order kinetic and Weber–Morris diffussion models well.

     

Magnetic carbon nanotubes synthesis by Fenton's reagent method and their potential application for removal of azo dye from aqueous solution

We report a simple and easy method to fabricate magnetic carbon nanotubes (CNTs) by Fenton's reagent method without the addition of any cations. H(2)O(2) was added slowly into the FeSO(4) solution mixed with purified CNTs, and the resulting reactants were placed into a quartz tube to undergo heat treatment under a nitrogen/hydrogen flow. Iron oxide (Fe(2)O(3)) nanoparticles were uniformly dispersed on CNTs without any pretreatment such as strong acid or covalent functionalization processes. The as-produced magnetic CNTs were used as an adsorbent for removal of methyl orange (MO) dye from aqueous solutions. Adsorption experiments indicated that the magnetic CNTs have good adsorption capacity (q(e)) of MO (28 mg/g). The Freundlich isotherm model fitted the experiment data better than the Langmuir isotherm mode. The mean energy of adsorption was calculated as 3.72 kJ/mol based on the Dubinin-Radushkevich model, which suggests that the removal process was dominated by physical adsorption. Kinetic regression results showed that the adsorption kinetics was more accurately represented by a pseudo second-order model. Intra-particle diffusion was involved in the adsorption process, but it was not the only rate-controlling step. More importantly, a new photocatalytic regeneration technology can be enabled by the high nanoscale iron oxide loading (50%). The magnetic CNT adsorbents could be effectively and quickly separated by applying an external magnetic field and regenerated by UV photocatalysis. Therefore, CNTs/λ-Fe(2)O(3) hybrid is a promising magnetic nanomaterial for preconcentration and separation of organic pollutants for environmental remediation.     

Modified bentonite by polyhedral oligomeric silsesquioxane and quaternary ammonium salt and adsorption characteristics for dye

To remove methylene blue dye from water by adsorption, bentonites were modified by polyhedral oligomeric silsesquioxane (POSS) and three kind of quaternary ammonium surfactants (dodecyl trimethyl ammonium bromide, tetrabutyl ammonium bromide, cetyl trimethylammonium bromide) in aqueous solution. Systematic adsorption experiments were carried out, the adsorption mechanism was studied, and the factors governing the adsorption of methylene blue on modified bentonite were discussed. The adsorption capacity of methylene blue on all three modified bentonites in 1000 mg·L⁻¹ solutions quickly reached equilibrium within 2000 s, and the removal rate was basically 100%; however, the removal rate in raw bentonite samples was only 60%. The pseudo second-order kinetic model can provide satisfactory kinetic data fitting. The obtained adsorption isotherms fit well with the Dubinin-Radushkevich isotherm model. The thermodynamic results showed that the adsorption process was a spontaneous endothermic physical adsorption process. With increasing pH and KCl concentration, the removal of methylene blue increased significantly. The results of this study confirmed that the modified bentonite is a candidate material as a cationic dye adsorbent.     

Cyanex272功能化的橘子皮对Cd(Ⅱ)的吸附动力学和热力学

本文采用橘皮(OP)吸附剂从水介质中去除Cd(Ⅱ).用萃取剂Cyanex272对生物质进行预处理活化,找到了去除Cd(Ⅱ)的最佳操作条件.通过用几种模型拟合实验数据后,发现最佳拟合模型为Langmuir模型和准二级动力学模型.不同吸附剂对Cd(Ⅱ)的吸附量顺序依次为272SCO>SCO>272CO>272OP>CO>OP.272SCO的最大吸附量为0.8663mol·g^-1,Cd(Ⅱ)的吸附量严格依赖于pH,所有吸附剂的最适合pH范围为5.5~6.0.对于吸附剂的再生,以0.1mol·L^-1 HCl为最佳解吸剂,解吸率接近100%.萃取剂Cyanex 272预处理后的橘皮可作为一种高效、低成本的吸附剂,用于去除水溶液中的镉.     

Adsorption of Cu(II) in aqueous solution by sodium dodecyl benzene sulfonate-modified montmorillonite

The pristine montmorillonite (P-Mt) was modified with sodium dodecyl benzene sulfonate (SDBS) to form SDBS montmorillonite (SDBS-Mt) for the purpose of enhancing the removal performance of Cu(II) from aqueous solution. The materials were characterized by means of XRD, SEM-EDS, BET, and FTIR to analyze the surface morphology and structure. SDBS-Mt displayed a higher adsorption capacity than P-Mt. The adsorption kinetic model and the adsorption isotherm model are depicted by the pseudo-second-order kinetic equation and the Langmuir equation, respectively. The adsorption of Cu(II) on SDBS-Mt is a spontaneous and endothermic process. The order of influence of coexisting cations on the adsorption of Cu(II) is Ni(II) > Co(II) > Zn(II). In addition, the adsorbent has great regeneration performance after five cycles of regeneration. The main mechanisms of Cu(II) adsorption by SDBS-Mt may include electrostatic attraction, ion exchange, and complexation of sulfonate groups. In brief, SDBS-Mt may be a promising, simple, and low-cost adsorbent for the treatment of Cu(II) in aqueoussolutions.     

Efficient Removal of Pb(II) from Aqueous Medium Using Chemically Modified Silica Monolith

The adsorptive removal of lead (II) from aqueous medium was carried out by chemically modified silica monolith particles. Porous silica monolith particles were prepared by the sol-gel method and their surface modification was carried out using trimethoxy silyl propyl urea (TSPU) to prepare inorganic–organic hybrid adsorbent. The resultant adsorbent was evaluated for the removal of lead (Pb) from aqueous medium. The effect of pH, adsorbent dose, metal ion concentration and adsorption time was determined. It was found that the optimum conditions for adsorption of lead (Pb) were pH 5, adsorbent dose of 0.4 g/L, Pb(II) ions concentration of 500 mg/L and adsorption time of 1 h. The adsorbent chemically modified SM was characterized by scanning electron microscopy (SEM), BET/BJH and thermo gravimetric analysis (TGA). The percent adsorption of Pb(II) onto chemically modified silica monolith particles was 98%. An isotherm study showed that the adsorption data of Pb(II) onto chemically modified SM was fully fitted with the Freundlich and Langmuir isotherm models. It was found from kinetic study that the adsorption of Pb(II) followed a pseudo second-order model. Moreover, thermodynamic study suggests that the adsorption of Pb(II) is spontaneous and exothermic. The adsorption capacity of chemically modified SM for Pb(II) ions was 792 mg/g which is quite high as compared to the traditional adsorbents. The adsorbent chemically modified SM was regenerated, used again three times for the adsorption of Pb(II) ions and it was found that the adsorption capacity of the regenerated adsorbent was only dropped by 7%. Due to high adsorption capacity chemically modified silica monolith particles could be used as an effective adsorbent for the removal of heavy metals from wastewater.     

改性黏土负载多乙烯多胺对H_2S的高效捕集

以工业建材级黏土矿石粉为原料,经酸处理或煅烧改性后,利用其多孔性负载多乙烯多胺制得吸附材料,并考察了其硫化氢脱除性能.实验结果表明,经400℃煅烧改性的材料的硫化氢脱除效果最佳.考察了负载方法、吸附温度、水蒸气预处理和负载量等因素对吸附的影响,发现在较低温度以及预加湿的情况下,硫化氢的脱除效果最显著,脱除率接近100%.负载量为33.3%的吸附剂的穿透硫容及饱和硫容均优于其它负载量的吸附剂.再生实验表明,吸附剂可以在较低温度下轻易再生,且多次再生后脱硫效果无显著下降.红外光谱和比表面积测试结果表明,该吸附剂对硫化氢的吸附以化学吸附为主.     

Application of polyaniline as an efficient and novel adsorbent for azo dyes removal from textile wastewaters

In this work, application of polyaniline coated onto wood sawdust (PAni/SD) for the removal of methyl orange (MO) as a typical azo dye from aqueous solutions is introduced. The effects of some important parameters such as pH, initial concentration, sorbent dosage, and contact time on the uptake of MO solution were also investigated. In order to get a better comparison, adsorption experiments were also carried out using commercial grade of granulated activated carbon (GAC) and sawdust without coating (SD) at the same time. It was found that PAni/SD can be used to remove azo dyes such as MO from aqueous solutions very efficiently. Experimental data were analyzed by the Langmuir and Freundlich models of adsorption. Kinetic parameters for the adsorption of MO dyes for the selected adsorbents are also reported. In order to study the possibility of desorption for frequent application, chemical regeneration of the used adsorbents was also investigated. Desorption or recovery of dye and regeneration of adsorbent (PAni/SD) was found to be quite possible and of high performance. Application of modified sawdust with polyaniline for the removal of azo dye is very promising for textile wastewater treatment.     

Low-temperature synthesis of nanoparticle-assembled, transparent, and low-crystallized hydroxyapatite blocks

The mesoporous carbon CMK-3 adsorbent was prepared, characterized, and used for the removal of anionic methyl orange dye from aqueous solution. Adsorption experiments were carried out as batch studies at different contact time, pH, initial dye concentration, and salt concentration. The dye adsorption equilibrium was rapidly attained after 60 min of contact time. Removal of dye in acidic solutions was better than in basic solutions. The adsorption of dye increased with increasing initial dye concentration and salt concentration. The equilibrium data were analyzed by the Langmuir and Freundlich models, which revealed that Langmuir model was more suitable to describe the methyl orange adsorption than Freundlich model. Experimental data were analyzed using pseudo-first-order and pseudo-second-order kinetic models. It was found that kinetics followed a pseudo-second-order equation. Thermodynamic study showed that the adsorption was a spontaneous and exothermic process.     

胍改性凹凸棒土对甲基橙的吸附

采用十六烷基胍改性凹凸棒土对甲基橙废水进行脱色处理,考察了吸附时间、吸附剂用量和染料浓度等因素对脱色效果的影响。 结果表明,十六烷基胍改性凹凸棒土对甲基橙废水具有很好的脱色性能,其对甲基橙废水脱色率达98%以上,与原凹凸棒土相比有显著提高。 平衡吸附量qe与平衡浓度ρe之间关系符合Langmuir等温吸附方程。 吸附热值小于40 kJ/mol,表观表现为物理吸附。     

载铁(β-FeOOH)球形棉纤维素吸附剂去除地下水砷(Ⅲ)的研究

制备了一种载铁(β-FeOOH)球形棉纤维素吸附剂,并用于地下水中As(Ⅲ)的去除.吸附剂对As(Ⅴ)和As(Ⅲ)在吸附容量、选择性和速率等方面都具有良好的性能,无需预氧化As(Ⅲ),其适用pH范围宽,不必调节原水的pH.吸附剂孔隙度大,机械强度好,活性成分铁的载入量高,吸附As(Ⅲ)的活性好.Langmuir和Freundlich方程能较好地描述吸附平衡方程,其吸附动力学符合Lagergren准二级方程.吸附As(Ⅲ)的最佳pH范围为6-9.SO42-和Cl-等干扰离子均不影响As(Ⅲ)的去除.柱吸附实验表明,即使在较高流速和As(Ⅲ)进水浓度下,吸附剂对As(Ⅲ)的去除依然具有很高的穿透容量和饱和容量.吸附剂可以用NaOH溶液再生,洗脱和再生效率较高.活性成分β-FeOOH形态稳定,柱实验和再生时铁均无泄漏.     

Experimental and Theoretical Insights on Methylene Blue Removal from Wastewater Using an Adsorbent Obtained from the Residues of the Orange Industry

Chemical and thermochemical transformations were performed on orange peel to obtain materials that were characterized and further tested to explore their potential as adsorbents for the removal of methylene blue (MB) from aqueous solutions. The results show the high potential of some of these materials for MB adsorption not only due to the surface area of the resulting substrate but also to the chemistry of the corresponding surface functional groups. Fitting of the kinetic as well as the equilibrium experimental data to different models suggests that a variety of interactions are involved in MB adsorption. The overall capacities for these substrates (larger than 192.31 mg g⁻¹) were found to compare well with those reported for activated carbon and other adsorbents of agro-industrial origin. According to these results and complementary with theoretical study using Density Functional Theory (DFT) approximations, it was found that the most important adsorption mechanisms of MB correspond to: (i) electrostatic interactions, (ii) H-bonding, and (iii) π (MB)–π (biochar) interactions. In view of these findings, it can be concluded that adsorbent materials obtained from orange peel, constitute a good alternative for the removal of MB dye from aqueous solutions.     

苯并噻吩在酸改性NaY分子筛上的吸附

以NaY分子筛为母体,通过柠檬酸、磷酸改性分别得到吸附剂NaY-C和NaY-P.采用SEM、XRD、XRF、N₂物理吸附及NH₃-TPD表征可知,柠檬酸改性后得到的NaY-C吸附剂介孔表面积增加,分子筛骨架结构保持不变.同时,磷酸改性使得NaY分子筛表面弱酸量减少强酸量增加,改性后所得吸附剂NaY-P的强酸量大于NaY-C.吸附实验表明,NaY-C和NaY-P均可完全脱除模拟油品中的苯并噻吩,同时NaY-C吸附剂对0^#柴油的脱硫能力优于NaY-P吸附剂.再生实验中NaY-C和NaY-P吸附剂对模拟油品的脱硫率由第一次的100%分别下降至第6次的91.97%和85.96%.由此可知,柠檬酸改性NaY分子筛所得NaY-C吸附剂的脱硫能力优于NaY-P,原因是吸附剂上的介孔更易于发生吸附脱硫.     

Treatment of methyl orange by calcined layered double hydroxides in aqueous solution: adsorption property and kinetic studies

Adsorption of a weak acid dye, methyl orange (MO) by calcined layered double hydroxides (LDO) with Zn/Al molar ratio of 3:1 was investigated. In the light of so called "memory effect," LDO was found to recover their original layered structure in the presence of appropriate anions, after adsorption part of MO(-) and CO(2-)(3) (come from air) intercalated into the interlayer of LDH which had been supported by XRD and ICP. The results of adsorption experiments indicate that the maximum capacity of MO at equilibrium (Q(e)) and percentage of adsorption (eta%) with a fixed adsorbent dose of 0.5 g L(-1) were found to be 181.9 mg g(-1) and 90.95%, respectively, when MO concentration, temperature, pH and equilibrium time were 100 mg L(-1), 298 K, 6.0 and 120 min, respectively. The isotherms showed that the adsorption of MO by Zn/Al-LDO was both consistent with Langmuir and Freundlich equations. The adsorption process was spontaneous and endothermic in nature and followed pseudo-second-order kinetic model. The calculated value of E(a) was found to be 77.1 kJ mol(-1), which suggests that the process of adsorption of methyl orange is controlled by the rate of reaction rather than diffusion. The possible mechanism for MO adsorption has also been presumed. In addition, the competitive anions on adsorption and the regeneration of Zn/Al-LDO have also been investigated.     

Design and evaluation of functionalized multi-walled carbon nanotubes by 3-aminopyrazole for the removal of Hg(II) and As(III) ions from aqueous solution

Carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were chemically modified with 3-aminopyrazole (MWCNTs-f) and applied as an efficient adsorbent to mercury and arsenic adsorption from aqueous solutions. The adsorbents were characterized by FT-IR, EDX, FE-SEM, TGA, and BET. The effects of pH, adsorbent dose, and initial ions concentration on the adsorption efficiency and the optimum conditions were investigated by central composite design. The optimum conditions were obtained at pH 7.6–7.9, adsorbent dose 20 mg, and initial ions concentration 20 ppm. So the maximum adsorption efficiencies in these conditions were 80.5 and 72.4% for the removal of Hg(II) and As(III) by MWCNTs-f, respectively. The quadratic model was used for the analysis of variance and indicated that adsorption of metal ions strongly depends on pH. Also, the pseudo-second-order model has been achieved from the adsorption kinetic studies. Furthermore, the experimental data were well fitted to the Langmuir isotherm and the maximum adsorption capacities obtained were 112 and 133 mg g^?1 for the adsorption of Hg(II) and As(III) by MWCNTs-f, respectively. Moreover, a thermodynamic study revealed that the adsorption reactions were spontaneous and endothermic with the increase in randomness. In addition, a desorption study showed the favorable regeneration ability of MWCNTs-f even after three adsorption–desorption cycles. Therefore, the MWCNTs-f adsorbent has good potential for the removal of Hg(II) and As(III) pollutants from aqueous solutions.     

Utilization of Waste Biomass (Kitchen Waste) Hydrolysis Residue as Adsorbent for Dye Removal: Kinetic,Equilibrium, and Thermodynamic Studies

Kitchen waste hydrolysis residue (KWHR), which is produced in the bioproduction process from kitchen waste (KW), is usually wasted with potential threats to the environment. Herein, experiments were carried out to evaluate the potential of KWHR as adsorbent for dye (methylene blue, MB) removal from aqueous solution. The adsorbent was characterized using FT-IR and SEM. Adsorption results showed that the operating variables had great effects on the removal efficiency of MB. Kinetic study indicated pseudo-second-order model was suitable to describe the adsorption process. Afterwards, the equilibrium data were well fitted by using Langmuir isotherm model, suggesting a monolayer adsorption. The Langmuir monolayer adsorption capacity was calculated to be 110.13 mg/g, a level comparable to some other low-cost adsorbents. It was found that the adsorption process of MB onto KWHR was spontaneous and exothermic through the estimation of thermodynamic parameters. Thus, KWHR was of great potential to be an alternative adsorbent material to improve the utilization efficiency of bioresource (KW) and lower the cost of adsorbent for color treatment.     

改性埃洛石材料的制备及其对亚甲基蓝吸附行为的研究

使用硅烷偶联剂KH550改性埃洛石纳米管获得改性材料HNTs-APTS,并对其吸附亚甲基蓝的行为进行研究。利用傅立叶变换红外光谱仪(FTIR)、X-衍射仪(XRD)对改性前后的埃洛石进行表征。考察了吸附时间和温度对吸附过程的影响,并采用Lagrange准二级动力学方程、Langmuir等温线方程及Freundlich等温线方程对实验数据进行拟合。结果表明,KH550成功负载到埃洛石表面;改性后材料的吸附能力大大提高。改性埃洛石对亚甲基蓝的吸附约在60 min达平衡,最大吸附容量为21.66 mg/g。其吸附过程符合准二级动力学方程,热力学较好地符合Langmuir等温线方程,且吸附过程为自发吸热,升高温度有利于吸附的进行。改性材料可重复再生6次,具有良好的再生性能,可在工业处理亚甲基蓝废水中使用。