Uranium adsorption by non-treated and chemically modified cactus fibres in aqueous solutions

The adsorption efficiency of Opuntia ficus indica fibres regarding the removal of hexavalent uranium [U(VI)] from aqueous solutions has been investigated prior and after the chemical treatment (e.g. phosphorylation and MnO₂-coating) of the biomass. The separation/removal efficiency has been studied as a function of pH, uranium concentration, adsorbent mass, ionic strength, temperature and contact time. Evaluation of the experimental data shows that biosorption is strongly pH-depended and that the MnO₂-coated product presents the highest adsorption capacity followed by the phosphorylated and non-treated material. Experiments with varying ionic strength/salinity don’t show any significant effect on the adsorption efficiency, indicating the formation of inner-sphere surface complexes. The adsorption reactions are in all cases exothermic and relatively fast, particularly regarding the adsorption on the MnO₂-coated product. The results of the present study indicate that adsorption of uranium from waters is very effective by cactus fibres and particularly the modified treated fibres. The increased adsorption efficiency of the cactus fibres is attributed to their primary and secondary fibrillar structure, which result in a relative relative high specific surface available for sorption.     

In situ synthesis of MnO<Subscript>2</Subscript>-loaded biocomposite based on microcrystalline cellulose for Pb<Superscript>2+</Superscript> removal from wastewater

We fabricated a new MnO₂-loaded biocomposite based on microcrystalline cellulose (MCC–MnO₂) by an in situ synthesis method and investigated its adsorption behavior and mechanism for Pb²⁺ removal from aqueous medium. As-prepared MCC–MnO₂ was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) analyses. The effects of pH value, initial Pb²⁺ concentration, contact time, and solution temperature on the uptake of Pb²⁺ onto MCC–MnO₂ were investigated using a batch system. Adsorption equilibrium could be achieved in 3 h for various studied initial concentrations, and a pseudo-second-order model could fit the adsorption behavior well. The equilibrium data could be well described by the Langmuir isotherm model, and the maximum monolayer adsorption capacity of MCC–MnO₂ (with 7.98% MnO₂ loading) for Pb²⁺ was estimated to be 247.5 mg/g at 313 K. Thermodynamic studies indicated a spontaneous and endothermic adsorption process. X-ray photoelectron spectroscopy (XPS) was used to analyze the adsorption mechanism, revealing that the chemical speciation of Pb²⁺ on MCC–MnO₂ was similar to the compound PbO. Moreover, no variations in the valence of Mn were observed after adsorbing Pb²⁺. The regeneration study showed that the adsorption capacity retained about 89.6% of its initial value at the fifth sequential regeneration cycle, indicating that this material is an efficient and renewable hybrid adsorbent for Pb²⁺ removal.     

Photogenic MnO2/Ag metal nanocomposites and their dye adsorbing activities

• Manganese dioxide/silver (MnO₂/Ag) nanoparticles were fabricated by using KMnO₄-NaBH₄ redox reaction at room temperature. The optical and structural properties of MnO₂/Ag were determined using UV–visible and Fourier transform infrared spectroscopies. The morphology was established with scanning and transmission electron microcopies, and X-ray diffraction. MnO₂/Ag showed excellent adsorbing activity to the removal of Congo red. The various kinetic models were used to determine the rate of dye removal. Congo red adsorption onto MnO₂Ag proceeds through the pseudo-second-order kinetic model. Langmuir adsorption capacity (Q⁰_max = 97.1 mg/g), and sorption intensity (n = 1.6) were estimated with Langmuir and Freundlich adsorption isotherm models for 250 mg/L Congo red. Elovich model suggest the adsorption of Congo red with the MnO₂Ag proceeds through the film diffusion. The positive values of enthalpy changes (ΔH⁰), entropy changes (ΔS⁰), and negative Gibbs free energy changes (ΔG⁰) showed that the Congo red adsorption process was endothermic, spontaneous, and chemisorption process followed with physical mechanism. The results showed that the removal efficiency decreases from 98% to 89% after the six consecutive experiments.

     

基于医用纱布负载的二氧化锰纳米颗粒用于亚甲蓝染料的去除

以医用纱布(medical gauze,MG)同时作为模板和还原剂,通过原位氧化还原反应,简便地制备了MG负载的MnO₂纳米颗粒(MnO₂ NPs/MG),并对其形貌、成分进行表征。结果表明,MnO₂ NPs均匀地分散于MG纤维表面。结合MnO₂纳米材料的吸附性能和MG复合材料的操作便捷性,将MnO₂ NPs/MG进一步应用于亚甲蓝染料的去除。结果表明,在中性条件下,通过简单的浸泡搅拌,MnO₂ NPs/MG对亚甲蓝的去除率可达85.09%,并且可以通过增大吸附材料用量与染料初始浓度的比例提高去除率。等温吸附和动力学研究证明,MnO₂ NPs/MG对亚甲蓝的吸附符合Langmuir吸附等温模型和拟二级动力学模型。     

基于医用纱布负载的二氧化锰纳米颗粒用于亚甲蓝染料的去除

以医用纱布（medical gauze,MG）同时作为模板和还原剂,通过原位氧化还原反应,简便地制备了MG负载的MnO₂纳米颗粒（MnO₂ NPs/MG）,并对其形貌、成分进行表征。结果表明,MnO₂ NPs均匀地分散于MG纤维表面。结合MnO₂纳米材料的吸附性能和MG复合材料的操作便捷性,将MnO₂ NPs/MG进一步应用于亚甲蓝染料的去除。结果表明,在中性条件下,通过简单的浸泡搅拌,MnO₂ NPs/MG对亚甲蓝的去除率可达85.09%,并且可以通过增大吸附材料用量与染料初始浓度的比例提高去除率。等温吸附和动力学研究证明,MnO₂ NPs/MG对亚甲蓝的吸附符合Langmuir吸附等温模型和拟二级动力学模型。     

Influence of Surface Coating on Fluoride Removal by Magnetite

Al(OH)₃- and ZrO(OH)₂-coated magnetites were prepared and used for fluoride removal from aqueous samples. The influence of pH, sorbent mass, and ions such as chloride, sulfate, and phosphate on the removal of fluoride was characterized. The sorption process was highly pH dependent, and the optimal sorption was obtained from pH 4 to 5 for ZrO(OH)₂- and pH 4 to 7 for Al(OH)₃-coated magnetites. The sorption isotherm was well described by the Langmuir equation for the sorbents. The maximum adsorption capacity of ZrO(OH)₂-coated magnetite (57.47?mg-F?g^?1-sorbent) was higher than for Al(OH)₃-coated magnetite (23.87?mg-F?g^?1-sorbent). The ion-exchange reaction occurred in 5?min and more than 99% of fluoride was removed from solution. When the ZrO(OH)₂-coated magnetite was used, the presence of foreign ions negatively affected the fluoride removal. The prepared sorbents showed an excellent performance for the removal of fluoride in water samples.     

MnO2上氧气第一个电子转移步骤的从头计算研究

采用裸露簇和嵌入簇模型, 对β-MnO₂ (001), (110), (111)三个晶面以及O₂在(110)晶面的单址吸附模式(Pauling和Griffths模式), 进行从头计算. 从β-MnO₂ (001), (110), (111)三个晶面的电子结构差异以及O₂在(110)晶面吸附的吸附能、几何结构、集居数以及净电荷数分析得到: (001), (110), (111)三个晶面中(110)晶面的催化活性最高, 其活性顺序为(110)＞(111)＞(001). 氧气在(110)晶面的吸附, Pauling和Griffths两种吸附模式均存在, 属于化学吸附中的离子吸附. 氧气与MnO₂固体间发生了单电子转移, 氧气得到电子被还原成O₂^-, 转移电子属于整个体系, 具有离域性.     

Nanofiltration and electrodialysis: alternatives in heavy metal containing high salinity process water treatment

Desalination is priority in process water treatment and several different technologies can be applied to minimize the total salinity of water. Our aim was to study desalination and simultaneous elimination of heavy metal residues from process waters. Nanofiltration (NF) and electrodialysis (ED) treatment technologies were applied for high salinity model solutions and high salinity, heavy metal containing real process waters originating from electroplating industry. Efficiencies of two technologies were compared in respect to salt and heavy metal removal both for model solutions (NaCl and Na₂SO₄) and three real process water samples. Initial concentrations of model solutions chosen accordingly the most common process water salt composition. Both technologies showed similar efficiency of heavy metal (Ni²⁺ and Cu²⁺) removal; however, they provide different demineralization rates, rejection, and extraction percentage for sodium and chloride ions. ED experiments of model solutions showed complete desalination after 1 h operating time at 6 V applied voltage; on the other hand, the increasing conductivities of NF permeates verified the selectivity of NF membrane, therefore, representing partial desalination. These phenomena were confirmed by demineralisation rate values as well (NF: for NaCl: 41.5–66.6%, for Na₂SO₄: > 96.6%; ED: both for NaCl and Na₂SO₄ > 98%). Significantly. higher demineralisation rates were achieved by ED (37.3–99.2%) than NF (20.2–62.3%) during the treatment of real process waters. We successfully demonstrated that ED is more efficient for simultaneous salt and heavy metal removal for process waters originating of electroplating industry.     

Preparation and Pb (II) adsorption in aqueous of 2D/2D g‐C3N4/MnO2 composite

A novel g‐C₃N₄/MnO₂ composite was prepared by in situ deposition of MnO₂ on graphitic carbon nitride (g‐C₃N₄) nanosheets, and its adsorption properties were evaluated for removal of Pb (II) in aqueous. Fourier transform‐infrared, spectrometer scanning electron microscopy and transmission electron microscopy characterization showed the g‐C₃N₄/MnO₂ composite had a two‐dimensional/two‐dimensional (2D/2D) structure with ample active sites. The Brunauer–Emmett–Teller specific surface area of g‐C₃N₄/MnO₂ composites (234.9 m²/g) was 13.5 times larger than that of g‐C₃N₄ (17.37 m²/g), providing better conditions for adsorption. The adsorption kinetic data were better fitted with the pseudo‐second‐order model. The Langmuir model was more suitable for describing the experimental equilibrium data of g‐C₃N₄/MnO₂, and the maximum adsorption capacity was 204.1 mg/g for Pb (II). The adsorption of g‐C₃N₄/MnO₂ composite for Pb (II) was an endothermic and spontaneous process, and reached adsorption equilibrium rapidly within initial 150 min. This composite was an excellent adsorbent because of its higher adsorption capacity and facile preparation progress.     

U(VI) adsorption by biochar fiber–MnO2 composites

The removal of U(VI) by biochar fibers from aqueous solutions has been investigated prior and after MnO₂ surface-deposition. The removal efficiency has been studied as a function of pH, U(VI) concentration, ionic strength, temperature and contact time. The fibers morphology and surface complexes were analyzed by SEM–EDX and FTIR, respectively. Evaluation of the experimental data indicates that the composite presents extraordinary adsorption capacity (q_max = 3.8 mmol g⁻¹, 904 mg g⁻¹), which is attributed to the formation of inner-sphere surface complexes, and that the adsorption reaction is a relatively fast, endothermic and entropy-driven process.

     

Simultaneous Removal of Antibiotics and Heavy Metals with Poly(Aspartic Acid)-Based Fenton Micromotors

The discharge of diverse pollutants has led to a complex water environment and posed a huge health threat to humans and animals. Self-propelled micromotors have recently attracted considerable attention for efficient water remediation due to their strong localized mass transfer effect. However, a single functionalized component is difficult to tackle with multiple contaminants and requires to combine different decontamination effects together. Here, we introduced a multifunctional micromotor to implement the adsorption and degradation roles simultaneously by integrating the poly(aspartic acid) (PASP) adsorbent with a MnO₂-based catalyst. The as-prepared micromotors are well propelled in contaminated waters by MnO₂ catalyzing hydrogen peroxide. In addition, the catalytic ramsdellite MnO₂(R-MnO₂) inner layer is decorated with Fe₂O₃ nanoparticles to improve their catalytic performance, contributing to an excellent degradation ability with 90% tetracycline (TC) removal in 50 minutes by enhanced Fenton-like reactions. Combining the attractive adsorption capability of poly (aspartic acid) (PASP), the composite micromotors offer an efficient removal of heavy metal ions in short time. Moreover, the designed micromotors are able to simultaneously remove antibiotic and heavy metals in mixed contaminants circumstance just in single treatment. This multifunctional micromotor with distinctive decontamination ability exhibits a promising prospective in treating multiple pollutants in the future.     

The adsorption of CaOH+ on (001) basal and (010) edge surface of Na‐montmorillonite: a DFT study

Ca²⁺ cations were generally added to facilitate the coagulation of stable fine clay mineral dispersion due to the specific adsorption of their first hydrolysis CaOH⁺ species at pH near 10. The adsorption of CaOH⁺ on dry and hydrated (001) basal surface and (010) surface of Na‐montmorillonite was investigated by using density functional theory method combined with the periodic slab model method. The adsorption energies and geometries, Mulliken charge, electron density difference, and density of state were presented and discussed. It was found that the adsorption energy of CaOH⁺ on (010) edge surface of Na‐montmorillonite (?328.8 kJ/mol) was much larger than that (?126.9 kJ/mol) on (001) basal surface. The presence of waters could increase the adsorption energy of CaOH⁺ on (001) surface but affect that on (010) surface slightly. The protons in Si–OH and Al–OH₂ groups as well as the OH₂ ligands in Al–OH₂ group on (010) edge surface were easily dissociated and coordinated to CaOH⁺ to form new waters. CaOH⁺ was the most steady adsorption species among CaOH⁺, Ca²⁺ cation, and H₂O molecule on both (001) and (010) surfaces. Copyright © 2016 John Wiley & Sons, Ltd.     

Determination of <Superscript>226</Superscript>Ra in sediments by ICP-MS: A comparative study of three sample preparation approaches

Three protocols (Method I: ion chromatography (IC) and extraction chromatography (EC), Method II: precipitation followed by IC, and Method III: adsorption onto MnO₂ followed by IC-EC) were investigated to determine their applicability for the separation and pre-concentration of ²²⁶Ra in sediments. ²²⁶Ra recoveries, measured using the isotope dilution method with ²²⁸Ra as yield tracer, and the removal of spectral and non-spectral interferences were evaluated. The formation of polyatomic interferences at m/z = 226 from elements found in the matrix of sediments was also investigated to assess the level of separation required. Methods I and III were found to be the most effective with respect to recoveries and interference removal. The efficiency of a rapid microwave based protocol for the complete digestion of 1 g of sediment is also described. The method was tested and ²²⁶Ra concentrations in the millibecquerel range (fg) were determined in a standard reference material and sediment cores collected from Lake Baikal.     

Adsorption of strontium ions from aqueous solution using hydrous,amorphous MnO2–ZrO2 composite: a new inorganic ion exchanger

Hydrous, amorphous MnO₂–ZrO₂ composite was prepared as a new inorganic composite material under various conditions for removal of Sr²⁺ ion from aqueous solutions. The physico-chemical characterization was carried out by Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy and thermogravimetry. The maximum sorption capacity for synthesized composite was evaluated as 1.5 meq/g sorbent and batch experiments were carried out as a function of contact time, aqueous phase pH, temperature and initial metal ions concentration of adsorptive solution. The results indicated that under optimal conditions, Sr²⁺ ions could be efficiently removed using MnO₂–ZrO₂ composite from aqueous solutions when pH > 5. The equilibrium isotherms were determined and the sorption data were successfully modeled using Langmuir model. Kinetics of the process was studied by considering a pseudo second-order model. This model predicted chemisorption as the adsorption mechanism. The results of thermodynamic investigation reveal that the adsorption process of the studied ion is entropy driven.     

Removal of Carbon Disulfide from Gas Streams Using Dielectric Barrier Discharge Plasma Coupled with MnO2 Catalysis System

The removal of gaseous carbon disulfide (CS₂) via dielectric barrier discharge (DBD) combined with MnO₂ catalysis has been investigated. CS₂ removal and energy yield (EY) had been examined as a function of catalyzer position in DBD reactor, initial CS₂ concentration, input power, and gas residence time. The results showed that DBD combined with MnO₂ catalyst can improve the CS₂ energy and removal efficiency, and MnO₂ catalyst placed in afterglow area can enhance the CS₂ removal efficiency by about 10 % as compared with DBD treatment only. When increasing initial CS₂ concentration and flow rate, a higher EY is obtained. The possible CS₂ removal pathways by DBD combined with MnO₂ were proposed based on the product identification by FT-IR.     

Effect of substituting Ru4+ and other tetravalent ions in the B-site of rare earth manganates on the magneto-transport properties and charge-ordering

Substitution of Ti and Zr in the B-site of La_0.7Ca_0.3MnO₃ lowers the T_C and the temperature of insulator—metal transition. Substitution of Ru in the B-site of La_0.7Ca_0.3MnO₃, however, does not alter the T_C or T_IM significantly. More importantly, the effect of substitution of Ti and Zr in the B-site of the charge-ordered Nd_0.5Ca_0.5MnO₃ progressively destroys the charge-ordering in this insulating material. In contrast, substitution by Ru in the B-site renders the material ferromagnetic with the T_C increasing with the Ru content and the material also shows insulator-metal transition. This marked effect of Ru substitution on the charge-ordering is also seen in Nd_0.5Sr_0.5MnO₃ where the T_C increases with Ru content while charge-ordering gets destroyed. The extraordinary effect of Ru in favouring the ferromagnetic metallic state and destroying the charge-ordering is attributed mainly to its unique electronic configuration (t_2g⁴e_g⁰.     

Lead Extraction from Natural Waters—A Simple and Rapid Technique

Abstract

A technique is described for the concentration of lead from fresh and saline waters before analysis by atomic absorption spectrophotometry. The lead is adsorbed on managanese dioxide supported on glass fibre filters. Quantitative adsorption of up to 75 mg Pb/g MnO₂ was achieved, with a maximum adsorption of 190 mg Pb g^?1. The technique, which allows rapid processing of large samples, is suited to field use.     

Adsorption of Copper (II) Ions onto Surfactant-Modified Oil Palm Leaf Powder

Il palm leaf powder (OPLP), an agricultural solid waste was used as adsorbent for the removal of copper (II) ions after modification with an anionic surfactant, sodium dodecyl benzene sulfonate (SDBS), CH₃(CH₂)₁₁C₆H₄SO₃Na. The copper (II) ions adsorption is highly dependent on pH and maximum removal was observed at pH 6, above which copper (II) started to precipitate. The equilibrium adsorption data were fitted into the Langmuir and Freundlich isotherms. The Freundlich isotherm model fitted well to data with 0.989 regression coefficient (R²). The kinetics of the adsorption of copper (II) ions onto the surfactant-modified OPLP was best described by a pseudo-second-order model. Comparison of this SDBS-modified-OPLP to previously investigated adsorbents showed comparably good result, offering this material as a promising adsorbent for the treatment of waste waters containing lower concentrations of copper (II) ions.     

Hydrogen production from bio-oil by chemical looping reforming

Hydrogen is a green energy carrier. Chemical looping reforming of biomass and its derivatives is a promising way for hydrogen production. However, the removal of carbon dioxide is costly and inefficient with the traditional chemical absorption methods. The objective of this article is to find a new material with low energy consumption and high capacity for carbon dioxide storage. A metal organic framework (MOF) material (e.g., CuBTC) was prepared using the hydrothermal synthesis method. The synthesized material was characterized by X-ray diffraction, ?196 °C N₂ adsorption/desorption isotherms, and thermogravimetry analysis to obtain its physical properties. Then BET, t-plot, and density functional theory (DFT) methods were used to acquire its specific surface area and pore textural properties. Its carbon dioxide adsorption capacity was evaluated using a micromeritics ASAP 2000 instrument. The results show that the decomposition temperature of the synthesized CuBTC material is 300 °C. Besides, high CO₂ adsorption capacity (4 mmol g^?1) and low N₂ adsorption capacity were obtained at 0 °C and atmospheric pressure. These results indicate that the synthesized MOF material has a high efficiency for CO₂ separation. From this study, it is expected that this MOF material could be used in adsorption and separation of carbon dioxide in chemical looping reforming process for hydrogen production in the near future.     

Thorium adsorption on graphene oxide nanoribbons/manganese dioxide composite material

A functional graphene oxide nanoribbons/manganese dioxide composite material (MnO₂-GONRs) was synthesized by hydrothermal method using graphene oxide nanoribbons (GONRs) as raw material which were formed by longitudinal unzipping of multi-walled carbon nanotubes with KMnO₄ and H₂SO₄. The microstructure of MnO₂-GONRs was characterized by SEM and FT-IR. The various factors affecting the adsorption of Th(IV) in aqueous solution such as pH, solid–liquid ratio, contact time, initial concentration and temperature were investigated by batch static adsorption experiments, and the adsorption mechanism is also discussed. The results showed that MnO₂-GONRs had a good adsorption effect on Th(IV) with a maximum adsorption of 166.11 mg/g.