Comparing the adsorption behaviors of Cd,Cu and Pb from water onto Fe-Mn binary oxide,MnO2 and FeOOH

The adsorption potential of FMBO, FeOOH, MnO₂ for the removal of Cd²⁺, Cu²⁺ and Pb²⁺ in aqueous systems was investigated in this study. Comparing to FMBO and FeOOH, MnO₂ offered a much higher removal capacity towards the three metal ions. The maximal adsorption capacity of MnO₂ for Cd²⁺, Cu²⁺ and Pb²⁺ were 1.23, 2.25 and 2.60 mmol·g^-1, respectively. And that for FMBO were 0.37, 1.13, and 1.18 mmol·g^-1 and for FeOOH were 0.11, 0.86 and 0.48 mmol·g^-1, respectively. The adsorption behaviors of the three metal ions on the three adsorbents were all significantly affected by pH values and heavy metal removal efficiency increased with pH increased. The Langmuir and Freundlich adsorption models were used to describe the adsorption equilibrium of the three metal ions onto the three adsorbents. Results showed that the adsorption equilibrium data fitted well to Langmuir isotherm and this indicated that adsorption of metal ions occurred on the three metal oxides adsorbents limited to the formation of a monolayer. More negative charged of MnO₂ surface than that of FMBO and FeOOH could be ascribed by lower pH_iep of MnO₂ than that of FMBO and FeOOH and this could contribute to more binding sites on MnO₂ surface than that of FMBO and FeOOH. The higher metal ions uptake by MnO₂ than FMBO and FeOOH could be well explained by the surface charge mechanism.     

Preparation of a permanent magnetic hypercrosslinked resin and assessment of its ability to remove organic micropollutants from drinking water

A rapid and effective method based on a novel permanent magnetic hypercrosslinked resin W150 was proposed for the removal of organic micropollutants in drinking water. W150 was prepared by suspension and post-crosslinking reaction and found to possess a high specific surface area of 1149.7 m²·g^-1, a small particle size of 50 μm to 100 μm, and a saturation magnetization as high as 8 emu·g^-1. W150 was used to eliminate nitrofurazone (NFZ) and oxytetracycline (OTC) from drinking water compared with commercial adsorbents XAD-4 and F400D. The adsorption kinetics of NFZ and OTC onto the three adsorbents well fitted the pseudo-second-order equation (r>0.972), and the adsorption isotherms were all well described by the Freundlich equation (r>0.851). Results showed that the reduction in adsorbent size and the enlargement in sorbent pores both accelerated adsorption. Moreover, the effect of particle size on adsorption was more significant than that of pore width. Given that the smallest particle size and the highest specific surface area were possessed by W150, it had the fastest adsorption kinetics and largest adsorption capacity for NFZ (180 mg·g^-1) and OTC (200 mg·g^-1). For the adsorbents with dominant micropores, the sorption of large-sized adsorbates decreased because of the inaccessible micropores. The solution pH and ionic strength also influenced adsorption.     

Simultaneous removal of arsenate and fluoride from water by AI-Fe （hydr）oxides

A1-Fe （hydr）oxides with different A1/Fe molar ratios （4：1, 1：1, 1：4, 0：1） were prepared using a co- precipitation method and were then employed for simultaneous removal of arsenate and fluoride. The 4A1 ： Fe was superior to other adsorbents for removal of arsenate and fluoride in the pH range of 5.0-9.0. The adsorption capacity of the A1-Fe （hydr）oxides for arsenate and fluoride at pH 6.50.3 increased with increasing A1 content in the adsorbents. The linear relationship between the amount of OH released from the adsorbent and the amount of arsenate or fluoride adsorbent by 4A1 ： Fe indicated that the adsorption of arsenate and fluoride by A1- Fe （hydr）oxides was realized primarily through quantita- tive ligand exchange. Moreover, there was a very good correlation between the surface hydroxyl group densities of A1-Fe （hydr）oxides and their adsorption capacities for arsenate or fluoride. The highest adsorption capacity for arsenate and fluoride by 4A1 ： Fe is mainly ascribed to its highest surface hydroxyl group density besides its largest pHpzc. The dosage of adsorbent necessary to remove arsenate and fluoride to meet the drinking water standard was mainly determined by the presence of fluoride since fluoride was generally present in groundwater at much higher concentration than arsenate.     

Preparation of a novel anion exchange group modified hyper-crosslinked resin for the effective adsorption of both tetracycline and humic acid

A novel hyper-crosslinked resin (MENQ) modified with an anion exchange group was prepared using divinylbenzene (DVB) and methyl acrylate (MA) as comonomers via four steps: suspension polymerization, post-crosslinking, ammonolysis and alkylation reactions. The obtained resin had both a high specific surface area (793.34 m²·g^-1) and a large exchange capacity (strong base anion exchange capacity, SEC: 0.74 mmol·g^-1, weak base anion exchange capacity, WEC: 0.45 mmol·g^-1). XAD-4 was selected as an adsorbent for comparison to investigate the adsorption behavior of tetracycline (TC) and humic acid (HA) onto the adsorbents. The results revealed that MENQ could effectively remove both TC and HA. The adsorption capacity of XAD-4 for TC was similar to that of MENQ, but XAD-4 exhibited poor performance for the adsorption of HA. The adsorption isotherms of TC and HA were well-fitted with the Freundlich model, which indicated the existence of heterogeneous adsorption through cation-π bonding and π–π interactions. The optimal solution condition for the adsorption of TC was at a pH of 5–6, whereas the adsorption of HA was enhanced with increasing pH of the solution.     

Fabrication,characterization and evaluation of mesoporous activated carbons from agricultural waste: Jerusalem artichoke stalk as an example

This work explores the feasibility of Jerusalem artichoke stem (JAS), an agricultural waste, as an alternative precursor for fabrication of mesoporous activated carbon (MAC) via conventional ZnCl₂ activation. The as-prepared JAS-MACs were characterized by thermogravimetric, nitrogen gas adsorption isotherm and high resolution scanning electron microscopy analysis. The interacting effects of chemical dosage, activation temperature and time on the mesoporosity, mesopore volume and carbon yield were investigated, and further optimized by response surface methodology (RSM). The Brunauer-Emmett-Teller surface area, mesoporosity and mesopore volume of the JAS-MAC prepared under optimum condition were identified to be 1631 m²·g^-1, 90.16% and 1.11 cm³·g^-1, respectively. Compared with commercial activated carbons, this carbon exhibited a comparable monolayer adsorption capacity of 374.5 mg·g^-1 for Methylene Blue dye. The findings suggest that RSM could be an effective approach for optimizing the pore structure of fabricated activated carbons.     

Mass-transfer processes of chromium(VI) adsorption onto guava seeds

The chromium(VI) biosorption onto guava seeds, as an alternative method for Cr⁶⁺ removal from aqueous solutions, was investigated. The parameters affecting kinetics and equilibrium of Cr⁶⁺ adsorption onto guava seeds were studied. An external mass-transfer diffusion coefficient k and intra-particle diffusion coefficient k_i were determined to measure the rate-limiting step of adsorption. A single external mass-transfer diffusion model and intra-particle diffusion models were used. The effects of initial pH, sorbent mass, and initial Cr⁶⁺ concentrations on mass-transfer coefficients were investigated. The external mass-transfer coefficient has an average value of 7.2×10^-3 cm s^-1, while the intra-particle mass-transfer diffusion coefficient was 0.34 mg g^-1 min^-0.5. This indicates that external diffusion to the guava seeds surface and intra-particle diffusion are both involved in the sorption process. The isotherm equilibrium data were well fitted by the Langmuir and Freundlich models with an average correlation coefficient R²=0.98. The maximum removal of Cr⁶⁺ was obtained at pH 1 (about 100% for adsorbent dose of 15 g l^-1 and 25 mg l^-1 initial concentration of Cr⁶⁺). The results indicated that the guava seeds exhibit acceptable sorption capacity.     

Fe3O4@SA/Ce微球的表征及对染料的吸附特性

以天然高分子化合物海藻酸钠(sodium alginate,SA)为骨架,结合磁性Fe₃O₄和稀土铈离子Ce(Ⅲ)通过溶液反应制备出一种新型的磁性海藻酸铈复合微球(Fe₃O₄@SA;Ce).采用X射线衍射(XRD)、孔结构比表面积分析(BET)、扫描电子显微镜(SEM)、红外光谱(FT-IR)及振动样品强磁计(VSM)对Fe₃O₄@SA;Ce的结构进行了表征,并以直接桃红12B(direct red 12B,DR 12B)和直接橙S(direct orange S,DO S)两种染料为吸附对象,探讨了Fe₃O₄@SA;Ce的吸附剂性能、吸附动力学和热力学.结果表明,Fe₃O₄@SA;Ce对室温下自然pH染料溶液中DR 12B和DO S均表现出良好的吸附效果,吸附量分别可达464 mg·g^-1和730 mg·g^-1.在不同温度下(298、313、328 K),Fe₃O₄@SA;Ce对DR 12B和DO S的吸附过程均可用拟二级吸附动力学方程准确描述.通过等温吸附研究,发现Fe₃O₄@SA;Ce对两种染料的等温吸附较好地符合Freundlich模型.各种表征结果表明,SA与Ce(Ⅲ)和Fe₃O₄交联反应后生成的Fe₃O₄@SA;Ce凝胶球表面有大量深浅不一的褶皱沟纹,形貌发生了显著变化.作为一种绿色环保、制备方法简单、可高效吸附的磁性高分子复合吸附剂,Fe₃O₄@SA;Ce对高浓度染料具有很好的吸附效果,期望能够在染料废水处理中得到广泛应用.     

Removal of lead from aqueous solution by hydroxyapatite/manganese dioxide composite

A novel composite adsorbent, hydroxyapatite/manganese dioxide (HAp/MnO₂), has been developed for the purpose of removing lead ions from aqueous solutions. The combination of HAp with MnO₂ is meant to increase its adsorption capacity. Various factors that may affect the adsorption efficiency, including solution pH, coexistent substances such as humic acid and competing cations (Ca²⁺, Mg²⁺), initial solute concentration, and the duration of the reaction, have been investigated. Using this composite adsorbent, solution pH and coexistent calcium or magnesium cations were found to have no significant influence on the removal of lead ions under the experimental conditions. The adsorption equilibrium was described well by the Langmuir isotherm model, and the calculated maximum adsorption capacity was 769 mg·g⁻¹. The sorption processes obeyed the pseudo-second-order kinetics model. The experimental results indicate that HAp/MnO₂ composite may be an effective adsorbent for the removal of lead ions from aqueous solutions.     

钾改性蒙脱石磁性微球对铯的吸附性能

本研究以钙基蒙脱石(Ca-MMT)为原料,通过K⁺作用制得改性蒙脱石粉(K-MMT),经海藻酸钠交联作用,将改性蒙脱石与永磁体(BaFe₁₂O₁₉)结合,制成钾改性蒙脱石磁性微球(KMBC).对比了Ca-MMT、K-MMT、KMBC对Cs+的吸附差异,并通过SEM-EDS、FTIR、XRD、XPS分析了K-MMT的微观结构及理化性质.试验结果表明,K⁺对蒙脱石的改性以离子交换为主,改性后晶体层间距变小,吸附量K-MMT>KMBC>Ca-MMT,分别为57.08、45.13、45.05 mg·g^-1;K-MMT对Cs⁺的吸附属于吸热反应,反应在2 h内可达到平衡,35℃时KMBC的最大吸附量为136.08 mg·g^-1;随着pH的增加,KMBC对Cs+的吸附量呈先增大后减小的趋势;吸附机理主要包括离子交换和内层扩散.     

Dual-functional sites for synergistic adsorption of Cr(VI) and Sb(V) by polyaniline-TiO2 hydrate: Adsorption behaviors,sites and mechanisms

• PANI/Ti(OH)_n^(4–n)+ exhibited excellent adsorption capacity and reusability. • Adsorption sites of Cr(VI) were hydroxyl, amino/imino group and benzene rings. • Sb(V) was adsorbed mainly through hydrogen bonds and Ti-O-Sb. • The formation of Cr-O-Sb in dual system demonstrated the synergistic adsorption. • PANI/TiO₂ was a potential widely-applied adsorbent and worth further exploring. Removal of chromium (Cr) and antimony (Sb) from aquatic environments is crucial due to their bioaccumulation, high mobility and strong toxicity. In this work, a composite adsorbent consisting of Ti(OH)_n^(4–n)+ and polyaniline (PANI) was designed and successfully synthesized by a simple and eco-friendly method for the uptake of Cr(VI) and Sb(V). The synthetic PANI/TiO₂ composites exhibited excellent adsorption capacities for Cr(VI) and Sb(V) (394.43 mg/g for Cr(VI) and 48.54 mg/g for Sb(V)), wide pH applicability and remarkable reusability. The adsorption of Cr(VI) oxyanions mainly involved electrostatic attraction, hydrogen bonding and anion-π interactions. Based on X-ray photoelectron spectroscopy and FT-IR analysis, the adsorption sites were shown to be hydroxyl groups, amino/imino groups and benzene rings. Sb(V) was adsorbed mainly through hydrogen bonds and surface complexation to form Ti-O-Sb complexes. The formation of Cr-O-Sb in the dual system demonstrated the synergistic adsorption of Cr(VI) and Sb(V). More importantly, because of the different adsorption sites, the adsorption of Cr(VI) and Sb(V) occurred independently and was enhanced to some extent in the dual system. The results suggested that PANI/TiO₂ is a promising prospect for practical wastewater treatment in the removal of Cr(VI) and Sb(V) from wastewater owing to its availability, wide applicability and great reusability.     

Removal of Cr(VI) from aqueous solution using waste weed, Salvinia cucullata

Biosorption studies of Cr(VI) were carried out using waste weed, Salvinia cucullata. Various adsorption parameters were studied, such as agitation speed, contact time, pH, particle size, and concentrations of adsorbent and adsorbate. The equilibrium was achieved in 12 h. A lower pH favoured adsorption of Cr(VI). The kinetics followed pseudo-second-order rate equations. The adsorption isotherm obeyed both the Langmuir and Freundlich models. The calculated activation energy (1.1 kJ mol^-1) suggested that the adsorption followed a diffusion-controlled mechanism. Various thermodynamic parameters such as Δ G^°, Δ H^°, and Δ S^° were also calculated. The positive values of enthalpy indicated the endothermic nature of the reaction, and Δ S^° showed the increasing randomness at the solid liquid interface of Cr(VI) on the adsorbent, which revealed the ease of adsorption reaction. These thermo-dynamic parameters showed the spontaneity of the reaction. The maximum adsorption of uptake (232 mg g^-1) compared well with reported values of similar adsorbents. The rate-determining step was observed to follow an intra-particle diffusion model.     

Adsorption of humic acid from aqueous solution on bilayer hexadecyltrimethyl ammonium bromide-modified zeolite

Surfactant-modified natural zeolites (SMNZ) with different coverage types were prepared by loading hexadecyltrimethyl ammonium bromide (HTAB) onto the surface of a natural zeolite. The adsorption behavior of humic acid (HA) on SMNZ was investigated. Results indicate that the adsorbent SMNZ exhibited a higher affinity toward HA than the natural zeolite. HA removal efficiency by SMNZ increased with HTAB loading. Coexisting Ca²⁺ in solution favored HA adsorption onto SMNZ. Adsorption capacity decreased with an increasing solution pH. For typical SMNZ with bilayer HTAB coverage, HA adsorption process is well described by a pseudo-second-order kinetic model. The experimental isotherm data fitted well with the Langmuir model. Calculated maximum HA adsorption capacities for SMNZ with bilayer HTAB coverage at pH 5.5 and 7.5 were 63 and 41 mg·g^-1, respectively. E2/E3 (absorbance at 250 nm to that at 365 nm) and E4/E6 (absorbance at 465 nm to that at 665 nm) ratios of the residual HA in solution were lower than that of the original HA solution. This indicates that the HA fractions with high polar functional groups, low molecular weight (MW), and aromaticity had a stronger tendency for adsorption onto SMNZ with bilayer HTAB coverage. Results show that HTAB-modified natural zeolite is a promising adsorbent for removal of HA from aqueous solution.     

Reduction of hexavalent chromium with scrap iron in a fixed bed reactor

The reduction of hexavalent chromium by scrap iron was investigated in continuous long-term fixed bed system. The effects of pH, empty bed contact time (EBCT), and initial Cr(VI) concentration on Cr(VI) reduction were studied. The results showed that the pH, EBCT, and initial Cr(VI) concentration significantly affected the reduction capacity of scrap iron. The reduction capacity of scrap iron were 4.56, 1.51, and 0.57 mg Cr(VI)·g^-1 Fe⁰ at pH 3, 5, and 7 (initial Cr(VI) concentration 4 mg·L^-1, EBCT 2 min, and temperature 25°C), 0.51, 1.51, and 2.85 mg Cr(VI)·g^-1 Fe⁰ at EBCTs of 0.5, 2.0, and 6.0 min (initial Cr(VI) concentration 4 mg·L^-1, pH 5, and temperature 25°C), and 2.99, 1.51, and 1.01 mg Cr(VI)·g^-1 Fe⁰ at influent concentrations of 1, 4, and 8 mg·L^-1 (EBCT 2 min, pH 5, and temperature 25°C), respectively. Fe(total) concentration in the column effluent continuously decreased in time, due to a decrease in time of the iron corrosion rate. The fixed bed reactor can be readily used for the treatment of drinking water containing low amounts of Cr(VI) ions, although the hardness and humic acid in water may shorten the lifetime of the reactor, the reduction capacity of scrap iron still achieved 1.98 mg Cr⁶⁺·g^-1 Fe. Scanning electron microscope equipped with energy dispersion spectrometer and X-ray diffraction were conducted to examine the surface species of the scrap iron before and after its use. In addition to iron oxides and hydroxide species, iron-chromium complex was also observed on the reacted scrap iron.     

硝酸钙投加频次对污泥生物调理效果的影响

在接种了反硝化菌的剩余污泥中投加硝酸钙药剂,利用反硝化菌消耗NO₃^-进行反硝化作用去除污泥中易生物降解的有机物,利用Ca²⁺的中和、架桥作用,改善污泥的脱水性能.固定NO₃^-总投加浓度为100 mg·g^-1 TS,在6 d的时间内,按1次、2次、3次、6次的投加频次向污泥中投加硝酸钙.结果表明,1次投加对污泥脱水性能的提升最显著,较对照组而言,污泥CST降低了65.0%,SRF降低了73.2%,污泥脱水性能明显改善;投加硝酸钙后,污泥胞外聚合物中蛋白质含量大幅降低,S层、L层蛋白质分别从13.47 mg·L^-1、11.66 mg·L^-1降低至0.52 mg·L^-1、1.43 mg·L^-1;投加硝酸钙的污泥Zeta电位更趋于电中性.研究还发现,一次性投加硝酸钙产生了更多NO₂^-,有利于污泥结合水,即微生物细胞质的释放.释放出的有机碳被反硝化菌用作碳源,又增强了反硝化效果,从而促进了污泥EPS的破坏与降解,从而改善了污泥的脱水性能.     

Adsorption property of direct fast black onto acid-thermal modified sepiolite and optimization of adsorption conditions using Box-Behnken response surface methodology

The adsorption of direct fast black onto acid-thermal modified sepiolite was investigated. Batch adsorption experiments were performed to evaluate the influences of experimental parameters such as initial dye concentration, initial solution pH and adsorbent dosage on the adsorption process. The three-factor and three-level Box-Behnken response surface methodology (RSM) was utilized for modeling and optimization of the adsorption conditions for direct fast black onto the acid-thermal modified sepiolite. The raw sepiolite was converted to acid-thermal modified sepiolite, and changes in the fourier transform infrared spectrum (FTIR) adsorption bands of the sample were noted at 3435 cm^-1 and 1427 cm^-1. The zeolitic water disappeared and the purity of sepiolite was improved by acid-thermal modification. The decolorization rate of direct fast black adsorbed increased from 68.2% to 98.9% on acid-thermal modified sepiolite as the initial solution pH decreased from 10 to 2. When the adsorbent dosage reached to 2.5 g·L^-1, 2.0 g·L^-1, 1.5 g·L^-1 and 1.0 g·L^-1, the decolorization rate was 90.3%, 86.7%, 61.0% and 29.8%, respectively. When initial dye concentration increased from 25 to 200 mg·L^-1, the decolorization rate decreased from 91.9% to 60.0%. The RSM results showed that the interaction between adsorbent dosage and pH to be a significant factor. The optimum conditions were as follows: the adsorbent dosage 1.99 g·L^-1, pH 4.22, and reaction time 5.2 h. Under these conditions, the decolorization rate was 95.1%. The three dimensional fluorescence spectra of direct fast black before and after treatment showed that the direct fast black was almost all adsorbed by the acid-thermal modified sepiolite.     

Enhanced adsorption of phosphate by loading nanosized ferric oxyhydroxide on anion resin

Ferric oxyhydroxide loaded anion exchanger （FOAE） hybrid adsorbent was prepared by loading nanosized ferric oxyhydroxide （FO） on anion exchanger resin for the removal of phosphate from wastewater. TEM and XRD analysis confirmed the existence of FO on FOAE. After FO loading, the adsorption capacity of the hybrid adsorbent increased from 38.70 to 51.52mg.g-1. Adsorption processes for both FOAE and anion resin were better fit to the pseudo first order model. Batch adsorption experiments revealed that higher temperature （313K）, higher initial phosphate concentration （50 mg.L-1） and lower solution pH （pH value of 2） would be more propitious to phosphate adsorption. Competition effect of coexisting anions on phosphate removal can be concluded as sulfate 〉 nitrate 〉 chloride. Freundlich isotherm model can describe the adsorption of phosphate on FOAE more accurately, which indicated the heterogeneous adsorption occurred on the inner-surface of FOAE.     

生物炭对土壤中阿特拉津吸附特征的影响

为探究生物炭对土壤中阿特拉津的吸附特征及影响因素,采用批处理实验研究了灭菌(T1)、5%秸秆生物炭+灭菌(T2)、未灭菌(T3)和5%秸秆生物炭+未灭菌(T4)条件下对土壤中阿特拉津吸附特征及土壤理化性质的影响.结果表明,在最初0—12 h内,不同处理下阿特拉津吸附量均随时间的延长而快速增加,而在12—96 h内增加较为缓慢并逐渐趋于平衡.在96 h时,T2和T4处理下阿特拉津最大吸附量分别达到46.22 mg·kg^-1和46.43 mg·kg^-1,而未添加生物炭的T1和T3处理则有所降低,分别为44.20 mg·kg^-1和43.09 mg·kg^-1.准二级动力学模型更好地拟合不同处理下土壤对阿特拉津吸附特征,T2和T4处理下吸附速率常数K分别为0.257 kg·mg^-1·h^-1和0.339 kg·mg^-1·h^-1,显著高于未添加生物炭处理的T1和T3处理(K分别为-0.083 kg·mg^-1·h^-1和-0.261 kg·mg^-1·h^-1).内扩散模型显示添加生物炭后,土壤对阿特拉津的吸附是一个由边界扩散、内部孔隙扩散等多因素控制的复杂化学过程.添加生物炭可显著提高土壤pH、有机碳、碱解氮、速效磷和速效钾含量,其中土壤有机碳含量与阿特拉津最大吸附量之间存在显著的正相关关系(P<0.05).由此可见,添加生物炭可以提高土壤对阿特拉津的固持能力,减少其淋溶迁移风险,从而达到修复阿特拉津污染土壤的目的.     

Separation/degradation behavior and mechanism for cationic/anionic dyes by Ag-functionalized Fe3O4-PDA core-shell adsorbents

● PDA-Fe₃O₄-Ag was made by hydrothermal and oxidation self-polymerization method. ● PDA-Fe₃O₄-Ag had great magnetic separation performance. ● PDA-Fe₃O₄-Ag had good adsorption and degradation performance for ionic dyes. ● PDA-Fe₃O₄-Ag showed NR and MO degradation potential of 91.2% and 87.5%, respectively. High-performance adsorbents have been well-studied for the removal of organic dye pollutants to promote environment remediation. In this study, an Ag nanoparticle-functionalized Fe₃O₄-PDA nanocomposite adsorbent (PDA-Fe₃O₄-Ag) was synthesized, and the adsorption/separation performance of commonly used cationic and anionic organic dyes by the PDA-Fe₃O₄-Ag adsorbent were assessed. Overall, PDA-Fe₃O₄-Ag exhibited a significantly higher adsorption capacity for cationic dyes compared to anionic dyes, the highest of which was more than 110.0 mg/g (methylene blue (MB)), which was much higher than not only the adsorption capacities of the anionic dyes in this study but also other dye adsorption capacities reported in the literature. The dye adsorption kinetics data fitted well to both the pseudo second-order kinetics model and the Langmuir isotherm model, suggesting a monolayer-chemisorption-dominated adsorption mode. Thermodynamics analysis indicated that the adsorption process was both endothermic and spontaneous. Furthermore, the PDA-Fe₃O₄-Ag adsorbent achieved high photodegradation removal rates of the dyes, especially neutral red (NR) and methyl orange (MO), which were 91.2% and 87.5%, respectively. With the addition of PDA-Fe₃O₄-Ag, the degradation rate constants of NR and MO increased from 0.08 × 10⁻² and 0 min⁻¹ to 2.11 × 10⁻² and 1.73 × 10⁻² min⁻¹, respectively. The high adsorption and photocatalytic degradation performance of the PDA-Fe₃O₄-Ag adsorbent make it an excellent candidate for removing cationic and anionic dyes from the industrial effluents.     

Removal of arsenic (V) from aqueous medium using manganese oxide coated lignocellulose/silica adsorbents

Arsenic (V) adsorption on manganese oxide coated rice wastes was investigated in this study. The modified adsorbents were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, and pH measurements to determine the point of zero charge. Batch adsorption equilibrium experiments were conducted to study the effects of pH, contact time, and initial concentration on arsenic removal efficiency. The adsorption capacity of rice waste was significantly improved after modification with permanganate. The Langmuir isotherm model fitted the equilibrium data better than the Freundlich model which confirms surface homogeneity of the adsorbent. Maxima adsorption capacities are determined as 10 and 12 mg/g at pH 3 for manganese oxide coated rice husk and straw, respectively. The adsorption energy indicates that the adsorption process may be dominated by chemisorption. Pseudo-second-order rate equation described the kinetics sorption of arsenic with good correlation coefficients, better than a pseudo-first-order equation. Manganese oxide coated rice husk and straw appear to be promising low cost adsorbents for removing arsenic from water.     

Mercury removal from aqueous solution using petal-like MoS2 nanosheets

• Synthesized few-layered MoS₂ nanosheets via surfactant-assisted hydrothermal method. • Synthesized MoS₂ nanosheets show petal-like morphology. • Adsorbent showed 93% of mercury removal efficiency. • The adsorption of mercury is attributed to negative zeta potential (-21.8 mV). Recently, different nanomaterial-based adsorbents have received greater attention for the removal of environmental pollutants, specifically heavy metals from aqueous media. In this work, we synthesized few-layered MoS₂ nanosheets via a surfactant-assisted hydrothermal method and utilized them as an efficient adsorbent for the removal of mercury from aqueous media. The synthesized MoS₂ nanosheets showed petal-like morphology as confirmed by scanning electron microscope and high-resolution transmission electron microscopic analysis. The average thickness of the nanosheets is found to be about 57 nm. Possessing high stability and negative zeta potential makes this material suitable for efficient adsorption of mercury from aqueous media. The adsorption efficiency of the adsorbent was investigated as a function of pH, contact time and adsorbent dose. The kinetics of adsorption and reusability potential of the adsorbent were also performed. A pseudo-second-order kinetics for mercury adsorption was observed. As prepared MoS₂ nanosheets showed 93% mercury removal efficiency, whereas regenerated adsorbent showed 91% and 79% removal efficiency in the respective 2^nd and 3^rd cycles. The adsorption capacity of the adsorbent was found to be 289 mg/g at room temperature.