Facile synthesis of hexamine–silicotungstic acid hybrid and its photocatalytic activity toward degradation of dyes

A new organic hybrid of silicotungstic acid was prepared by means of an easily available, very cheap, and non-toxic amine via a facile precipitation method. Characterization of hybrid was carried out by elemental analyses, Fourier transform infrared spectroscopy, powder X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, and scanning electron microscopy. Dye adsorption and photocatalytic properties of the prepared water-insoluble hybrid were examined by studying the decolorization of model dyes such as methylene blue and methyl, orange and their mixture solutions under ultraviolet, visible, and sunlight irradiation. The effect of different factors containing the initial concentration, pH, catalyst dosage, H₂O₂ dosage, and salt adding was investigated on the decolorization of dyes. The results showed that the hybrid is a good heterogeneous photocatalyst in the degradation of methylene blue, methyl orange and their mixture and can be recovered and reused. The methylene blue is removed via combination of adsorption and photocatalytic degradation under ultraviolet, visible, and sunlight through direct oxidation by hybrid. The methyl orange is removed via ultraviolet and solar photocatalytic degradation through indirect oxidation by ^·OH radicals. While the visible light is not able to degrade methyl orange solution alone in the presence of hybrid, it degrades the methyl orange mixed with methylene blue solution.     

纳米TiO2/天然矿物复合材料的环境效应

本文系统论述了国内外有关纳米TiO2/矿物复合材料的研究和应用现状,重点介绍了负载纳米TiO2的矿物种类及其复合材料在环境科学研究中的应用。分别介绍了氧化物、层状硅酸盐、架状硅酸盐和硅藻土,重点论述了层状硅酸盐类。纳米TiO2/矿物复合材料主要应用于降解有机污染物(如有机染料、苯酚、甲基橙、亚甲基蓝、邻氯苯酚、DDVP、HCH、DDT、DDE、DDD、反式氯丹和顺式氯丹等),将其变为H2O、CO2等无害小分子化合物,不产生二次污染。纳米TiO2/天然矿物复合材料对污染物的降解效果优于单相TiO2,在环境方面的应用很有潜力。     

Removal of textile dyes from aqueous solution by conducting polymer modified clinoptilolite

In this work, clinoptilolite was modified with conducting polyaniline polymer and then the nanocomposite was used as an adsorbent for methyl orange (MO) as a model dye. Cations located in clinoptilolite structure like Na⁺, K⁺, Mg²⁺, Ca²⁺ were exchanged with anilinium cations and then the polymerization of anilinium cations in and outside of the clinoptilolite channels resulted in the formation of polyaniline/clinoptilolite nanocomposite. The resulted nanocomposite was used for the removal of MO from aqueous solution. The effect of various factors like contact time, concentration of dye as well as the amount of adsorbent on the removal efficiency of dye was investigated. The adsorption isotherms were investigated. It was found that the equilibrium adsorption data were well described by the Langmuir isotherm model. The kinetic studies indicated that the adsorption process was controlled by pseudo-second-order equation. High adsorption capacity and low contact time as well as the low cost of modified clinoptilolite proved that it is an efficient adsorbent for the removal of MO from aqueous solutions.     

Adsorption kinetic studies for removal of methylene blue using activated carbon prepared from sugar beet pulp

Sugar beet pulp is an abundant, renewable and low-cost precursor for production of activated carbon. In the present study, sugar beet pulp based activated carbon was prepared by using phosphoric acid as activating agent for adsorption of methylene blue. The conditions of preparation process had a significant influence on the adsorption of methylene blue, and the optimal preparation conditions were obtained as follows: liquid-to-solid ratio of 5, temperature of 450 °C and phosphoric acid concentration of 3 mol/L. The properties of sugar beet pulp based activated carbon were characterized by nitrogen adsorption isotherm. The adsorption increases as the increase of contact time, adsorption temperature and pH, and initial concentration of methylene blue. Batch kinetic studies showed that an equilibrium time of 100 min was needed for the adsorption, and the adsorbance of methylene blue is 244.76 mg/g at equilibration. Kinetic models, Weber’s pore diffusion model and Boyd’s equation were applied to the experimental data to study the mechanism of adsorption and the controlled step. The results showed that the adsorption kinetics followed the pseudo-second-order type kinetic model, intraparticle diffusion was not the rate-limiting mechanism and adsorption process was controlled by film diffusion.     

Nanofiltration process on dye removal from simulated textile wastewater

Dyestuffs removal from industrial wastewater requires special advanced technologies, since dyes are usually difficult to remove by biological methods. In this study nanofiltration process was used for removal of different dyestuffs from solutions. The rate of dye removal by spiral wound nanofiltration membrane in film thin composite MWCO=90 Dalton, was evaluated for four classes of dyes acidic, disperse, reactive and direct in red and blue dyes medium. Dye absorbance was measured by spectrophotometric method (2120 Standard Method 1998). Effects of feed concentration, pressure and total dissolved solids concentration were also studied. Results showed that increasing dye concentration lead to higher color removal up to 98 % and at different pressures for acidic and reactive blue were up to 99.7 %. Different types of dyes had no effect on dye removal and permeate flux. During 2 h. of the operation time, permeate flux decline was increased. Permeate fluxes for different types of red dyes were from 16.6 to 12.6 (L/m²/h.) and for blue dyes were from 16.6 to 10.45 (L/m²/h.). Presence of sodium chloride in dye solutions increased dye rejections nearby 100 %. Chemical oxygen demand removal efficiencies for reactive blue, disperse blue, direct and disperse red dyes were also approximately 100 %.     

Adsorption of a cationic dye (methylene blue) by Iranian natural clays from aqueous solutions: equilibrium,kinetic and thermodynamic study

Removal of dyes by low-cost adsorbents is an effective method in wastewater treatment. Iranian natural clays were determined to be effective adsorbents for removal of a basic dye (methylene blue) from aqueous solutions in batch processes. Characterizations of the clays were carried out by X-ray diffraction, Brunauer–Emmett–Teller surface area analysis and field-emission scanning electron microscopy. Effects of the operational parameters such as adsorbent dosage, initial dye concentration, solution pH and temperature were investigated on the adsorption performance. Adsorption isotherms like Langmuir, Freundlich and Temkin were used to analyze the adsorption equilibrium data and Langmuir isotherm was the best fit. Adsorption kinetics was investigated by pseudo-first-order, pseudo-second-order and intraparticle diffusion models and the results showed that the adsorption system conforms well to the pseudo-second-order model. The thermodynamic parameters of adsorption (ΔS°, ΔH° and ΔG°) were obtained and showed that the adsorption processes were exothermic.     

Removal of hexavalent chromium from aqueous solution by lignocellulosic solid wastes

The batch removal of Cr(VI) from aqueous solution using lignocellulosic solid wastes such as sawdust and pine leaves under different experimental conditions was investigated in this study. The influence of pH, temperature, contact time, initial concentration of Cr(VI) and particle size on the chromium removal was investigated. Adsorption of Cr(VI) is highly pH-dependent and the results indicate that the optimum pH for the removal is 2. The capacity of chromium adsorption at equilibrium by these natural wastes increased with absorbent concentration. Temperature in the range of 20–60 °C showed a restricted effect on the adsorption capacity of pine leaves, but had a considerable effect on the adsorption capacity of sawdust. The capacity of chromium adsorption at the equilibrium increased with the decrease in particle sizes. The suitability of adsorbents was tested with Langmuir and Freundlich isotherms and their constants were evaluated. Results indicated that the Freundlich model gave a better fit to the experimental data in comparison with the Langmuir equation. The study showed that lignocellulosic solid wastes such as sawdust and pine leaves can be used as effective adsorbents for removal of Cr(VI) from wastewater.     

Analysis of shake flask experiments results conducted on residues from hydrometallurgical processes

Hydrometallurgical facilities processing sulfide based ores produce waste residues in the form of sludges that contain concentrations of metals, as well as metal sulfides. As a part of the waste characterization and risk assessment process, a statistical design of experiment was used to assess the significant factors and interactions in the residue leaching process. Two shake flask experiments, a 2⁴ factorial design and 2³ central composite design were employed to evaluate the effect of mixing time, test pH, solid/liquid ratio and residue type on acidity, alkalinity, sulfate and metal concentration and pH of the resulting filtered leachate. The results indicate that the variable tested mixing time and solid/liquid ratio most strongly affect metal concentration in the filtrate from waste residue samples tested over a moderate test pH range. When tests were conducted over a longer test period and at lower test pH values, test pH and residue type were dominant factors contributing to residue filtrate metal concentration.     

Detoxification of toxic dyes using biosynthesized iron nanoparticles by photo-Fenton processes

Environmental contamination resulting from dyes has become a serious concern for today’s world. The textile effluents are highly colored, and the disposal of these in water bodies causes severe damage to the environment by reducing the solar light penetration which may affect the photosynthetic activity and the aquatic life in water. Further, the high water solubility of dyes also leads to surface and ground water contamination. Thus, in this study, we attempt to develop a cost-effective and eco-friendly method for removal of toxic dyes from aqueous using biosynthesized iron nanoparticles (INPs). Various complimentary instruments such as a thermogravimetric analysis, scanning electron microscopy/energy dispersive X-ray spectrometer, and X-ray diffraction were employed for identification and characterization of INPs. The biosynthesized INPs were applied as a Fenton-like catalyst for decolorization of toxic dyes solution like methylene blue, methyl orange, allura red, brilliant blue, and green S using hydrogen peroxide under solar radiation. The decolorization of the toxic dyes solution using INPs was monitored by UV–visible spectrophotometer, and the data obtained were utilized to evaluate the kinetic rate of the reactions. The kinetic data suggest that the decolorization of all studied toxic dyes solution follows first-order rate with rate constant values in the range of 13.1 × 10^?3–17.7 × 10^?3 min^?1. Therefore, such a clean method employing non-toxic plant extract in INP synthesis and the application of INPs as a Fenton-like catalyst in toxic dyes decolorization can be considered as an alternative technique to the expensive and toxic chemical methods.     

Adsorption of Cd ions from aqueous solutions by iron modified pomegranate peel carbons: kinetic and thermodynamic studies

The experimental conditions for preparation of pomegranate peel carbon and Fe(III) modified pomegranate peel carbon were studied. The effects of main experimental parameters on carbon preparation such as carbonization time, carbonization temperature and Fe(III) impregnation ratio in pomegranate peel were investigated. The prepared carbons in various conditions were characterized by consideration of the production yield, ash content, iodine number, pH of zero point charge and their ability for adsorption of methylene blue. After preparation of carbons, their efficiency for removal of Cd²⁺ species from aqueous solution was investigated. The effect of experimental parameters such as Cd²⁺ initial concentration, pH of solution and contact time was studied by batch adsorption experiments. The fitting of experimental data in thermodynamic isotherms matched the linear results with Langmuir and Freundlich isotherms. The adsorption capacity for Cd²⁺ species on Fe(III) modified pomegranate peel carbon was 22.72 mg/g and the adsorption kinetic presented the pseudo-second-order kinetic model.     

Evaluation of the use of modified coal ash as a potential sorbent for organic waste streams

Fly ash was modified by hydrothermal treatment with 7 M NaOH. The resultant product displayed an 8-fold increase in surface area. The primary crystalline component of the modified fly ash was identified by X-ray diffraction to be hydroxysodalite (Na₆Al₆Si₆O₂₄8H₂O). The cation exchange capacity of the modified ash was significantly increased over that of the raw fly ash (188 vs 2 meq g⁻¹). Adsorption experiments showed that the modified fly ash adsorbed a cationic dye (methylene blue) to a much greater extent than an anionic dye (alizarin sulfonate). Saturation adsorption revealed that the capacity of the ash for methylene blue had increased 10-fold during modification when compared to the raw ash. Adsorption is thus ascribed to be a surface effect rather than involving incorporation into the channels of the hydroxysodalite structure.     

Use of Tunisian raw clay to remove dye from aqueous solution

This paper presents the first attempt to investigate the potential of Tunisian palygorskite-rich clay (Pal-clay) on the effectiveness of a textile dye “Direct orange 34” (DO34) removal. Important parameters which affect adsorption, such as initial solution pH, contact time, adsorbent mass, initial dye concentration, and temperature, were investigated. The raw Pal-clay was characterized using X-ray diffractometer (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), cation exchange capacity (CEC), specific surface area (SSA) analysis, and point of zero charge (PZC) determination. The results showed that the Pal-clay has a high selectivity for DO34 and had maximum removal efficiency reaching up to about 91 %. The highest adsorption capacity was obtained at 25 °C and pH of 2. The dye uptake process fitted well to the pseudo-second-order kinetic expression and was best described by the Langmuir and Freundlich isotherms. Intra-particle diffusion studies showed that the adsorption mechanism was not exclusively controlled by the diffusion step and was more likely to be governed by external mass transfer. Thermodynamic parameters such as change in free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were also calculated. The parameters revealed that the adsorption of dye by the raw clay is spontaneous and exothermic. The results indicate that the Pal-clay has a moderate adsorption capacity towards anionic dye.     

A novel approach for textile dye degradation by zinc,iron–doped tin oxide/titanium moving anode

The present contribution reports a moving iron (Fe), zinc (Zn)–doped tin oxide/titanium (SnO₂/Ti) anode-based system designed and operated for the electro-oxidation of methyl orange dye effluent. Electrochemical oxidation of the dye was carried out at a current density of 1.8 A/dm² for 120 min. Similar experiments were repeated with pure SnO₂-based static and moving anode-based systems and the Fe, Zn-doped SnO₂ static anode-based electro-oxidation system. Post oxidation, the surface of the electrodes was critically examined by scanning electron microscopy. Dye samples were analysed at regular intervals during the electro-oxidation process by chemical oxygen demand and colour removal measurements and characterized by UV–Vis spectroscopy and Fourier transform infrared spectroscopy at the end of the oxidation process. The obtained results elucidate the superiority of Fe, Zn-doped SnO₂/Ti moving anode-based system for methyl orange dye effluent electro-oxidation. The moving anode prevents passive layer formation and decreases polarization resistance. Doping of Fe and Zn provides the anode-enhanced mechanical strength and electrocatalytic activity. The combined effects of axial anode movement and doping are responsible for improved performance of the moving anode system reported in this contribution.     

微生物电化学体系中金红石可见光还原降解偶氮染料的实验研究

利用双室微生物电化学装置对微生物和半导体矿物协同作用下偶氮类染料废水的还原脱色降解进行了系统的实验研究.不同光照条件及不同阴极电极材料的对比实验结果显示,偶氮染料甲基橙(MO)可作为终端电子受体直接从固体电极上获得电子被还原脱色;各对比实验中,在微生物催化与半导体矿物光催化协同作用条件下,MO还原脱色效率最高.电化学交流阻抗谱(EIS)的拟合结果显示金红石涂布阴极电极光照下极化内阻(Rp)为443.4 Ω,较无光条件下的1378 Ω显著降低,证明光照下金红石阴极的电子转移过程受其光催化作用的驱动.不同初始浓度下MO的生物-半导体催化还原反应符合准一级动力学模型,其反应速率随MO初始浓度降低而增加.通过对脱色产物的进一步分析,推测该实验中MO的还原脱色反应机制为: 阳极初始电子供体在微生物的催化作用下将电子通过阳极电极和外电路传递给阴极半导体矿物电极,进而在半导体矿物的光催化作用下通过光生电子还原终端电子受体MO,使MO中的偶氮键断裂,生成无色的联氨类衍生物.     

Biosorption of methylene blue from aqueous solutions by Typha angustata phytomass

The objective of this study was to investigate the biosorption of an azo dye (Methylene blue) by a wetland phytomass (Typha angustata) under post-phytoremediation scenario. Thus, the phytomass was used without any chemical modification. The batch adsorption experiments were conducted to evaluate the effects of contact time and temperatures (25–45 °C) on the adsorption of methylene blue (MB) from aqueous solution by cattail phytomass (CP). More than 80 % of MB dye was removed from the aqueous solution within first 10 min of the experiment. Langmuir isotherm was modeled to describe the monolayer adsorption of MB dye (R ² = 0.995) with the maximum adsorption capacity of 8.1 mg/g at 25 °C. Pseudo-second-order kinetic model adequately described the kinetics of absorption process (R ² = 0.999). The adsorption of MB on the cattail phytomass was a spontaneous and endothermic process that was governed by chemisorption. Hence, CP could be applied as a potential low cost biosorbent to treat dyeing wastewater.     

Preparation of magnetic microgels for catalytic reduction of 4-nitrophenol and removal of methylene blue from aqueous medium

This work describes the synthesis of poly(acrylic acid) microgels and fabrication of magnetic cobalt nanoparticles in the prepared microgels. Cobalt nanoparticles were fabricated by loading the cobalt (II) ions in microgels from aqueous solution and their subsequent reduction with sodium borohydride (NaBH₄). Bare and composite microgels were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The catalytic properties of the prepared microgel composites were investigated by using them as catalyst for the reduction of 4-nitrophenol and methylene blue. The effect of temperature and catalyst dose on the rate of reduction of these toxic pollutants was investigated. The reusability of prepared catalysts was also studied for the five consecutive cycles, and an increase in catalytic activity was observed after every cycle. The prepared bare and magnetic microgels were found as very effective adsorbent for the removal of methylene blue from aqueous medium. Very rapid adsorption rate was found for the removal of methylene as its 100 mg was adsorbed on per gram of dried hydrogels in about 25 min. The effects of different parameters like amount of adsorbate and concentration of adsorbent on the adsorption process were studied. Langmuir, Freundlich and Temkin adsorption isotherms were applied, and it was found that adsorption of MB follows Freundlich model better than others. Furthermore, pseudo-first-order and pseudo-second-order kinetic models were also applied and adsorption of MB was found to abide by pseudo-second-order kinetics.     

海洋铁锰结核对次甲基蓝的氧化性脱色

利用锰氧化物具有高的吸附与氧化还原化学活性的特点,研究了采自东太平洋的铁锰结核对阳离子染料次甲基蓝氧化性脱色特征。结果表明,铁锰结核表面的非均相氧化是次甲基蓝脱色的主要机制。在通常的染料废水浓度范围内,铁锰结核可有效地对次甲基蓝染料废水氧化脱色。随染料浓度降低,铁锰结核投放量增加和粒度减小,次甲基蓝的脱色率明显提高。次甲基蓝的矿化程度(TOC去除率)较高,但仍低于脱色率。pH对次甲基蓝脱色的影响主要体现在对表面配位体形成和对体系还原电位的影响,当pH<4.0时,脱色率随酸度的增加明显提高;当pH在4.0~10.0时,溶液pH值对脱色率影响有限。在铁锰结核连续循环体系中,溶解Mn2 浓度和pH的增加是脱色率不断下降的主要原因。     

Dye adsorption on electrochemical exfoliated graphene oxide nanosheets: pH influence,kinetics and equilibrium in aqueous solution

Graphene oxide nanosheets were synthesized by electrochemical exfoliation. X-ray diffraction, scanning electron microscopy, atomic force microscopy, Raman spectrometry and Fourier transform infrared spectrometry were used to characterize crystal structure, particle size, thickness and function groups of the nanosheets. The nanosheets were examined for adsorption of methyl orange, an anionic dye, in aqueous solution at different pHs and temperatures. The maximum adsorption capacity of methyl orange on graphene oxide nanosheets obtained from the Langmuir isotherm was 138.69 mg/g at pH 2.0, which is larger than that of other carbonaceous adsorbents. The large adsorption affinity of graphene oxide nanosheets to methyl orange might be due to the presence of hydrogen bonding and π–π interaction between methyl orange and graphene oxide nanosheets. Adsorption kinetics followed a pseudo-second-order kinetic model, and the isotherm adsorption results were fitted with Langmuir isotherm model in a monolayer adsorption manner. The thermodynamic studies indicated that the adsorption reaction was a spontaneous physisorption process.     

Direct calculation of thermodynamic properties of the barite/celestite solid solution from molecular principles

 Thermodynamic properties of the barite–celestite solid solution were calculated using molecular principles. Cation–cation (Ba–Ba, Sr–Sr, and Ba–Sr) interaction energies were derived from a number of random and ordered cation distributions which were energy-optimized using force potentials as incorporated in the program package GULP. With these interaction energies, diagrams for the enthalpy and free energy of mixing could be computed for the entire range of the solid solution between the barite and celestite end members and for a number of annealing temperatures. These thermodynamic data show that the solid solution is nonideal. The system has a tendency for Ba²⁺ and Sr²⁺ cations to order onto alternating layers ||(100). However, this ordering scheme is thermodynamically only relevant for annealing temperatures below approximately 500 K and systems that are kinetically inhibited during crystal growth. For sufficiently long annealing times at room temperature, the solid solution tends to exsolve with barite–celestite interfaces ||(100). The cell parameters a and c were calculated to have almost linear behavior for the whole solid solution, suggesting close to ideal behavior according to Vegard's law. In contrast, b tends to deviate positively from linearity, in agreement with experimental values. Received: 6 April 1999 / Revised, accepted: 29 September 1999     

Modeling of air stripping from volatile organic compounds in biological treatment processes

The removal of volatile organic compounds from biological treatment processes occurs through several mechanisms. These include biodegradation, adsorption onto solids, and air stripping or volatilization to the atmosphere. Volatilization results in fugitive emissions to the atmosphere, which is largely uncontrolled. Recent regulations have called for increased evaluation and control of inadvertent volatile organic compounds emissions from treatment processes. The use oxygen as a parallel volatile compound is extremely useful for prediction of volatile organic compounds removal by air stripping. In this study, the simultaneous biodegradation and air stripping of volatile organic compounds, based on steady state mass balance are examined and a general approach to estimating the dominant removal mechanism is developed. A Monte Carlo simulation technique was used to estimate air stripping over a wide range of operating conditions. Several volatile organic compounds were selected for this study. The results showed the values drived from the model correspond with the experimental data for benzene, toluene, methylene chloride, trichloroethylene, and methyl isobutyl ketone.