Influence of Rainfall and Basic Water Quality Parameters on the Distribution of Endocrine-Disrupting Chemicals in Coastal Area

Occurrence and distribution of three typical endocrine-disrupting chemicals (EDCs), nonylphenol mixture (NPs), bisphenol A (BPA), and 17α-ethynilestradiol (EE2), were investigated in the seawater, suspended solid, and sediment around the coastline of Shenzhen city. Field surveys were conducted in both dry season and rainy season to access the influence of rainfall and basic water quality parameters on the distribution of target EDCs. In the seawater, NPs, BPA, and EE2 ranged from 31 to 1,777 ng/l, from 11 to 777 ng/l, and from 10 to 269 ng/l, respectively. In the suspended solid, NPs, BPA, and EE2 were in the range from 3 to 289 ng/l, from 1 to 75 ng/l, and from 1 to 29 ng/l, respectively. In the sediment, NPs, BPA, and EE2 varied from 9 to 355 ng/g dry weight (dw), from 3 to 156 ng/g dw, and from 7 to 144 ng/g dw, respectively. With the increasing rainfall, the concentrations of target EDCs decreased in seawater and sediment and increased in suspended solid at all the sampling locations. Among the six measured basic water quality parameters, the volatile suspended solid value was positively related with the partition property of target EDCs between suspended solid and seawater. Based on the results of principal component analysis, dissolved organic carbon, total nitrogen, and total phosphorous had close relationships with the distribution of target EDCs in the seawater. Temperature and dissolved oxygen had little relationship with the distribution of target EDCs in the coastal area.     

Removal of Bisphenol A and 17β-Estradiol by Single-Walled Carbon Nanotubes in Aqueous Solution: Adsorption and Molecular Modeling

Single-walled carbon nanotubes, both before (SWNTs) and after treatment (t-SWNTs) with acidified ammonium persulfate, were successfully used to adsorb bisphenol A (BPA) and 17??-estradiol (E2) from aqueous systems. The surface characteristics of the SWNTs and t-SWNTs were analyzed by measuring their surface charge and by imaging their morphological properties through transmission electron microscopy. The extent of defects on the SWNT scaffold generated through acid etching was analyzed by Raman spectroscopy. A total of 19.4, 15.4, and 14.3?mg/g of BPA was adsorbed on SWNTs, while a total of 8.0, 6.4, and 5.1?mg/g was adsorbed on t-SWNTs with a 72-h contact time at 280, 295, and 315?K, respectively. A significantly high fraction of E2 (27.2?mg/g) was absorbed by both SWNTs and t-SWNTs, as compared to BPA. The adsorption kinetics was analyzed using a pseudo-second-order model. Sorption experiments showed that t-SWNTs adsorbed less than half as much BPA as SWNTs, but their E2 adsorption was similar. The sorption mechanism was investigated by performing molecular-level calculations. Adsorption energies calculated using density functional theory show preferential sorption of E2 to SWNTs and graphene (?26.2?kcal/mol on SWNT and ?34.1?kcal/mol on graphene) compared to BPA (?17.1?kcal/mol on SWNT and ?22.5?kcal/mol on graphene), which were consistent with the experimental findings. Thus, ab initio calculations can mechanistically explain the adsorption differences of BPA and E2 on SWNTs.     

A Study on Al(III) and Fe(II) Ions Sorption by Cattle Manure Vermicompost

Cattle manure vermicompost has been used for the adsorption of Al(III) and Fe(II) from both synthetic solution and kaolin industry wastewater. The optimum conditions for Al(III) and Fe(II) adsorption at pH?2 (natural pH of the wastewater) were particle size of ≤250?µm, 1 g/10 mL adsorbent dose, contact time of 4 h, and temperature of 25°C. Langmuir and Freundlich adsorption isotherms fitted reasonably well in the experimental data, and their constants were evaluated, with R ² values from 0.90 to 0.98. In synthetic solution, the maximum adsorption capacity of the vermicompost for Al(III) was 8.35 mg g^?1 and for Fe(II) was 16.98 mg g^?1 at 25°C when the vermicompost dose was 1 g 10 mL^?1, and the initial adjusted pH was 2. The batch adsorption studies of Al(III) and Fe(II) on vermicompost using kaolin wastewater have shown that the maximum adsorption capacities were 1.10 and 4.30 mg g^?1, respectively, at pH?2. The thermodynamic parameter, the Gibbs free energy, was calculated for each system, and the negative values obtained confirm that the adsorption processes were spontaneous.     

Removal of Pentachlorophenol by Adsorption on Magnetite-immobilized Chitin

The application of magnetite-immobilized chitin in pentachlorophenol (PCP) removal was demonstrated in this study. The physicochemical parameters for immobilization of chitin by magnetite, and for PCP adsorption using magnetite-immobilized chitin were optimized. For chitin immobilization, the optimized conditions were: magnetite to chitin (m:c) ratio at 1:2, initial pH 6, 25°C, 200 rpm and 60 min in batch system. The immobilization efficiency (IE) was 99.4% and immobilization capacity (IC) was 2.0 mg chitin mg^?1 magnetite. High initial pH (pH?>?11) and temperature (>30°C) lowered the IE and IC. For PCP (10 mg l^?1) adsorption, the optimized conditions were: 1,500 mg l^?1 immobilized chitin, initial pH 6, 25°C, 200 rpm and 60 min in batch system. The removal efficiency (RE) was 57.9% and removal capacity (RC) was 5.4 mg g^?1. The adsorption ability of immobilized chitin decreased with pH and temperature increased. However, increasing the amount of immobilized chitin (24,000 mg l^?1) can increase the RE up to 92%. Both chitin immobilization and PCP adsorption exhibited Langmuir and Freundlich adsorption isotherms. Results in this study indicated that magnetite-immobilized chitin was a cost-effective and environmental friendly adsorbent to remove environmental pollutants such as PCP.     

Biosorption of Chromium (III) and Chromium (VI) by Untreated and Pretreated Cassia fistula Biomass from Aqueous Solutions

The present study explained the effect of pretreatments on the biosorption of Cr (III) and Cr (VI) by Cassia fistula biomass from aqueous solutions. For this purpose Cassia fistula biomass was pretreated physically by heating, autoclaving, boiling and chemically with sodium hydroxide, formaldehyde, gluteraldehyde, acetic acid, hydrogen peroxide, commercial laundry detergent, orthophosphoric, sulphuric acid, nitric acid, and hydrochloric acid. The adsorption capacity of biomass for Cr (III) and Cr (VI) was found to be significantly improved by the treatments of gluteraldehyde (95.41 and 96.21 mg/g) and benzene (85.71 and 90.81 mg/g) respectively. The adsorption capacity was found to depend on pH, initial metal concentration, dose, size, kinetics, and temperature. Maximum adsorption of both the Cr (III) and Cr (VI) was observed at pH 5 and 2. When Freundlich and Langmuir isotherms were tested, the latter had a better fit with the experimental data. The kinetic studies showed that the sorption rates could be described better by a second order expression than by a more commonly applied Lagergren equation.     

Residual Organic Compound Removal from Aqueous Solution Using Commercial Coconut Shell Activated Carbon Modified by a Mixture of Seven Metal Salts

The modified activated carbon (MAC) derived from commercial coconut shell activated carbon (AC) with mixture of seven metal salts was used as an adsorbent to remove target residual organic compound (sucrose) from aqueous solutions in batch modes. The results indicated that the highest adsorption capacity of sucrose onto MAC reached when the AC was modified at the ratio of impregnation of AC with mixture of seven metal salts, including nitrate silver (AgNO₃), manganese nitrate (Mn (NO₃)₂), potassium bichromate (K₂Cr₂O₇), nitrate cobalt (Co (NO₃)₂·6H₂O), nitrate copper (Cu (NO₃)₂·3H₂O), nitrate nickel (Ni (NO₃)₂·6H₂O) and nitrate iron (Fe (NO₃)₂·9H₂O) of 3% (w/w). The most appropriate conditions for sucrose adsorption onto MAC in batch experiments obtained at pH 7, contact time of 120 min, 800 mg MAC/50 mL of sucrose solution with initial concentration of 1500 mg/L. At this condition, the highest adsorption capacity of sucrose onto MAC reached 28.28 mg/g. The Langmuir, Freundlich, and Sips adsorption isothermal equilibrium models can adequately describe the adsorption properties of sucrose on MAC. The adsorption kinetic of sucrose onto MAC obeyed pseudo-first-order and pseudo-second-order models with the chemical sorption process. The saturated MAC was recovered by heat from an oven. The highest recovery efficiency of saturated MAC obtained at 180 °C in 120 min. The highest adsorption capacity of sucrose onto recovered MAC was 24.31 mg/g, appropriately adsorption capacity of initial MAC.     

Analysis and Occurrence of Endocrine Disruptors in Brazilian Water by HPLC-Fluorescence Detection

A method for simultaneous analysis of bisphenol A (BPA) and 17α-ethinylestradiol (EE2) in water supply was developed using solid-phase extraction and high-performance liquid chromatography with fluorescence detection. The linearity was evaluated between 2.5 and 200 μg L^?1 (r> for the analytes. The limits of quantification were 1.5 and 2.1 ng L^?1 for BPA and EE2, respectively. The extraction was made with C18 cartridges, and recoveries obtained varied between 70 and 102 % for the strengthening of 5 μg L^?1. After the validation, the method was applied in the determination of pollutants in surface water and water supply of Sao Luis, Brazil, where BPA was found in two of the eight samples analyzed, with concentrations of 1.11 and 3.61 μg L^?1.     

Copper Biosorption by Biomass of Marine Alga: Study of Equilibrium and Kinetics in Batch System and Adsorption/Desorption Cycles in Fixed Bed Column

Copper biosorption onto chemically modified biomass of marine alga Sargassum filipendula was investigated in a batch reactor and a fixed bed column. Experiments were carried out in the batch reactor to obtain kinetic and equilibrium data and to assess the copper desorption efficiency of different eluent solutions. The pseudo-first-order, pseudo-second-order, and Langmuir kinetic models were used to correlate kinetic data. The experimental data fitted well to the pseudo first order and Langmuir kinetic models. Langmuir and Freundlich models were applied to describe the equilibrium data obtained at a fixed temperature of 30°C and at pH values of 3.0, 4.0, 5.0, and 6.0. The maximum capacities of copper biosorption onto the algal biomass were 1.43, 1.59, 2.40, and 2.36 mequiv./g at pH 3.0, 4.0, 5.0, and 6.0, respectively. The efficiencies of two eluent solutions (calcium chloride and hydrochloric acid) for copper removal from the biomass were evaluated at different concentrations (0.1, 0.2, 0.5, and 1.0 mol/L). The efficiencies of the calcium chloride solutions varied from 1% to 14%, while efficiencies varying from 95% to 99% were obtained when hydrochloric acid solutions were applied. Three adsorption/desorption cycles were carried out in a fixed bed column using 0.1 mol/L hydrochloric acid as eluent solution. The results showed that an increase in the number of cycles led to a reduction in the adsorption capacity of the alga. The desorbed copper fraction presented no significant variation, remaining around 63% in the three adsorption/desorption cycles.     

Pb(II) Removal Using TiO<Subscript>2</Subscript>-Embedded Monolith Composite Cryogel as an Alternative Wastewater Treatment Method

Different from direct application of free nanoparticles (NPs) in water treatment, a composite material is used to reduce the release and potential toxic effects of NPs with maintained adsorption capacity and kinetics. Novel monolithic composites with TiO₂ NPs incorporated into the walls of macroporous cryogels were synthesized and evaluated for material characteristics and their efficiency for removal of Pb(II) from aqueous solution in batch test and continuous mode. The uniformly distributed 6% TiO₂-cryogel is shown to be optimal for minimizing TiO₂ NP losses while maximizing Pb(II) removal. Under (25.0 ± 0.1) °C with the initial Pb(II) concentration of 10 mg/l, TiO₂-cryogels exhibit excellent adsorption characteristic for Pb(II) removal with adsorption capacity up to 23.27 mg/g TiO₂, which is even a little higher than that of TiO₂ NPs (21.58 mg/g TiO₂), and the results fit well with Langmuir–Freundlich isotherm. Both adsorbents work well in higher pH range with the highest removal rate at pH 6 for TiO₂-cryogel, and the adsorption mechanism might be strong chemical interaction. Pseudo-second-order process can better describe the adsorption process rather than pseudo-first-order for both adsorbents. The external mass transfer process of Pb(II) on TiO₂ NPs is much faster than that on TiO₂-cryogel, and the ultimate equilibrium time is about the same (3 h) on both adsorbents. The synthesized composites could also withstand a continuous treatment, and the effect of competing and co-existing constituents such as Cd²⁺, SO₄ ^2? and dissolved organic matter (DOM) is almost negligible. The composite design with small particles embedded into cryogels is proved to successfully keep the adsorption activity of TiO₂ NPs and prevent them from releasing into the environment in engineering practice.     

Spectrophotometric Determination of Nickel(II) in Soil and Standard Alloy Samples Using 5-Methyl-2-acetylfuran-4-methyl-3-thiosemicarbazone (5-MAFMT)

A simple and selective spectrophotometric method was developed for the determination of nickel(II) using 5-methyl-2-acetylfuran-4-methyl-3-thiosemicarbazone (5-MAFMT) as a chromogenic reagent forming a yellow-colored complex at pH 9.5. The complex was instantaneous and stable for 5 h. The system obeyed Beer’s law in the concentration range of 0.06–0.60 µg/mL of nickel(II), with a correlation coefficient of 0.999. The molar absorptivity and Sandell’s sensitivity of the complex species were found to be 1.87 × 10⁴ L/mol.cm and 1.2 × 10^–3 µg/cm² at 361 nm, respectively. The limit of detection was 0.0713 µg/mL with the relative standard deviation (RSD) ≤1.0%. The proposed method is rapid, simple, sensitive, and successfully applied for the determination of nickel(II) when present alone or in the presence of other ions that are usually associated with nickel(II). The method was tested for nickel (II) determination in soil and various standard alloy samples. The recovery of nickel(II) in alloy samples using the developed method was >98% confirming the suitability of the method. Comparisons of the results with those obtained using an atomic absorption spectrophotometer for nickel(II) determination also tested the validity of the method at the 0.05 level.     

HS-protein associates in the aqueous/oil system: composition and colloidal properties

Purpose

Despite experiments with humic substances and positively charged proteins, the colloidal behavior of HS-protein mixture in the system of two immiscible liquids has been neglected. In this context, the main objective of this study was to reveal the interference of HS and globular proteins on its partition in an aqueous/organic liquid system and the adsorption at liquid/liquid interface as a model of natural organic matter interaction with proteins in nature at hydrophobic/hydrophilic surfaces.

Materials and methods

Coal humic acids (HA) and two globular proteins lysozyme and albumin were under the test. Aqueous phase was prepared in phosphate-buffered saline (pH 7.2?±?0.1, 0.16 M); p-xylene was chosen as an organic phase. Experiments were performed for fixed concentration of protein (0.1 g L^?1 for lysozyme and 0.06 g L^?1 for albumin) and varied HA concentration from 0.2 to 50 mg L^?1. Radiotracer method including tritium thermal activation and scintillation phase method, dynamic light scattering, and optical microscopy were used to control mixed adsorption layer at the aqueous/p-xylene interface and composition of each contact phase.

Results and discussion

The results suggest that if both HA and protein are negatively charged (HA-albumin mixture), the mechanism of interaction between them in the bulk of water and at liquid/liquid interface is controlled by HA concentration. At low HA concentrations, free protein prevents HA adsorption at liquid/liquid interface and its transition to the organic phase via coulomb repulsion. At high HA concentration, the formation of hydrophilic complexes occurs via both electrostatic attraction between positively charged amino acid residues and the hydrophobic interaction. In HA-lysozyme mixture, the interaction between protein and HA is preferably provided by electrostatic attraction that provides higher hydrophobicity of HA-lysozyme complex compared with free HA. An increase in HA concentration results in partial recharge of the conjugate that leads to lysozyme amount reduction at the interface. We also measured the composition of spontaneously formed precipitate of HA-lysozyme conjugate and followed its self-organization.

Conclusions

This work demonstrates colloidal chemical behavior of net positively and negatively charged model protein by coal humic acids under environmentally relevant solution conditions in the system of two immiscible liquids that were used as a model of natural membrane. For the first time, quantities of both protein and HA in mixed adsorption layer at the liquid/liquid interface in the cases of positively and negatively charged protein have been determined.     

A Comparison of Inorganic Solid Wastes as Adsorbents of Heavy Metal Cations in Aqueous Solution and Their Capacity for Desorption and Regeneration

The adsorption capacity of seven inorganic solid wastes [air-cooled blast furnace (BF) slag, water-quenched BF slag, steel furnace slag, coal fly ash, coal bottom ash, water treatment (alum) sludge and seawater-neutralized red mud] for Cd²⁺, Cu²⁺, Pb²⁺, Zn²⁺ and Cr³⁺ was determined at two metal concentrations (10 and 100 mg?L^?1) and three equilibrium pH values (4.0, 6.0 and 8.0) in batch adsorption experiments. All materials had the ability to remove metal cations from aqueous solution (fly and bottom ash were the least effective), their relative abilities were partially pH dependant and adsorption increased greatly with increasing pH. At equimolar concentrations of added metal, the magnitude of sorption at pH 6.0 followed the general order: Cr³⁺????Pb²⁺????Cu²⁺?>?Zn²⁺?=?Cd²⁺. The amounts of previously sorbed Pb and Cd desorbed in 0.01 M NaNO₃ electrolyte were very small, but those removed with 0.01 M HNO₃, and more particularly 0.10 M HNO₃, were substantial. Water treatment sludge was shown to maintain its Pb and Cd adsorption capability (pH 6.0) over eight successive cycles of adsorption/regeneration using 0.10 M HNO₃ as a regenerating agent. By contrast, for BF slag and red mud, there was a very pronounced decline in adsorption of both Pb and Cd after only one regeneration cycle. A comparison of Pb and Cd adsorption isotherms at pH 6.0 for untreated and acid-pre-treated materials confirmed that for water treatment sludge acid pre-treatment had no significant effect, but for BF slag and red mud, adsorption was greatly reduced. This was explained in terms of residual surface alkalinity being the key factor contributing to the high adsorption capability of the latter two materials, and acid pre-treatment results in neutralization of much of this alkalinity. It was concluded that acid is not a suitable regenerating agent for slags and red mud and that further research and development with water treatment sludge as a metal adsorbent are warranted.     

Distribution Coefficient and Adsorption–desorption Rates of di (2-ethylhexyl) Phthalate (DEHP) onto and from the Surface of Suspended Particles in Fresh Water

The commonly used plastic softener, di (2-ethylhexyl) phthalate (DEHP), also a known Endocrine Disrupting Compound, was found contaminated in various aquatic environments, including river water in Thailand. The data of adsorption kinetics from this study indicated that DEHP can adsorb onto pure bentonite and natural suspended sediment with average adsorption rate constants of 0.0056 and 0.0039 min^?1 respectively. The average distribution coefficients between suspended particles and water found in this study for pure bentonite and natural suspended sediment were 0.045 and 0.043 l g^?1 respectively. Although the studies were carried out in pH 4.0, 7.0 and 10.0, there were no obvious influences of pH on adsorption rates and distribution coefficients of DEHP onto both pure bentonite and natural suspended particles. The desorption rate was very small and was estimated to be less than 0.03 μg min^?1. The results indicated that suspended sediment could become a long term release of DEHP and facilitate the transport of DEHP mainly due to fast adsorption rate and relatively high adsorption capacity.     

Removal of Cyanide and Zinc–Cyanide Complex by an Ion-Exchange Process

Removal efficiencies of cyanide and a zinc–cyanide complex in solutions were studied by using an ion-exchange process at pH 10.0 and 12.0. An anion-exchange resin, AMBERLITE® IRA-402 Cl, was used to perform packed bed continuous experiments. For the initial 200 mg/l cyanide solution, the packed bed gave a cyanide effluent concentration of 0.2 mg/l at 80 bed volumes for both pH 10.0 and 12.0. Comparatively, in the mixture of 200 mg/l cyanide and 100 mg/l zinc, packed bed volumes were obtained as 80 and 90 at pH 10.0 and 12.0, respectively, to have 0.2 mg/l cyanide effluent concentrations. The packed beds were exhausted at 250 and 400 bed volumes for cyanide and zinc–cyanide complex solutions, respectively. Speciation calculations in Zn(II)/cyanide/OH^? were used to interpret the results. The exchange capacities of the resin were determined as ～1.2 and ～0.9 meq/ml resin for cyanide and zinc–cyanide complex solutions, respectively, and were independent of pH in the studied pH range.     

Activated Biochar Prepared by Pomelo Peel Using H<Subscript>3</Subscript>PO<Subscript>4</Subscript> for the Adsorption of Hexavalent Chromium: Performance and Mechanism

Adsorption of hexavalent chromium (Cr(VI)) using pomelo peel activated biochar (PPAB) as a adsorbent was investigated. The characterization of the adsorbent was studied by Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and zeta potentials analysis. The results showed that the PPAB had a high microporous structure and the existence of organic compounds such as hemicellulose, cellulose, and lignin. Various parameters including initial Cr(VI) concentration, pH, and adsorbent dosage were studied. The results indicated that the adsorption process was pH dependent and maximum adsorption capacity of Cr(VI) was 57.637 mg/g at pH 2.0 and 35 °C with PPAB dosage of 0.05 g. The adsorption kinetics fitted well to the pseudo-second-order model and the correlation coefficients were greater than 0.999. The adsorption isotherm data could be better described with the Langmuir model, suggesting the homogeneous and monolayer adsorption. Moreover, the scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and Fourier transform infrared spectrum (FTIR) results showed that the surface of PPAB had plenty of developed pores after activation and the modification process was deemed to proceed between the O–H groups from pomelo peel and H₃PO₄ molecules. The main adsorption mechanism was attributed electrostatic interaction and ion exchange between the surface of PPAB and Cr(VI).     

Adsorptive Potential of 2-Mercaptobenzimidazole-Immobilized Organophilic Hydrotalcite for Mercury(II) Ions from Aqueous Phase and Its Kinetic and Equilibrium Profiles

An organophilic calcined hydrotalcite (OHTC) was prepared by treating calcined hydrotalcite (HTC) with sodium dodecylbenzene sulphonate (an anionic surfactant) to achieve a high loading of thiol functionality through the immobilization of 2-mercaptobenzimidazole (MBI) as a chelating agent. The adsorbent (MBI-OHTC) obtained was characterized using XRD, FTIR, SEM, TG/DTG, surface area analysis and potentiometric titration. The adsorption of MBI-OHTC to remove Hg(II) ions from aqueous solutions was studied as a function of pH, contact time, metal ion concentration, ionic strength and adsorbent dose. The optimum pH range for the maximum removal of Hg(II) was 6.0–8.0. The maximum value of Hg(II) adsorption was found to be 11.63 and 21.52 mg g^?1 for an initial concentration of 25 and 50 mg l^?1, respectively at pH 8.0. The equilibrium conditions were achieved within 3 h under the mixing conditions employed. A reversible pseudo-first-order used to test the adsorption kinetics. The adsorption mechanism consisted of external diffusion and intraparticle diffusion and the intraparticle mass transfer diffusion was predominated after 20 min of experiment. Extent of adsorption decreased with increase of ionic strength. The experimental isotherm was analyzed with two parameters (Langmuir and Freundlich) and three parameters (Redlich–Peterson) equations. The isotherm data were best modeled by the Freundlich isotherm equation. Complete removal (≈100%) of Hg(II) from 1.0 l of chlor-alkali industry wastewater containing 9.86 mg Hg(II) ions, was possible with 3 g of the adsorbent dose at pH 8.0. About 95.0% of Hg(II) can be recovered from the spent adsorbent using 0.1 M HCl.     

Adsorption Behaviour of Basic Dyes on the Humic Acid Immobilized Pillared Clay

In this work, the adsorption of three basic dyes, namely methylene blue (MB), crystal violet (CV) and rhodamine B (RB) on the humic acid (HA) immobilized pillared clay (PILC) (HA-PILC) was studied. The adsorption capacity of dyes at 30 °C using HA–PILC was foundto be 2.6, 2.0 and 2.3 times greater than that using PILC for the removal of MB, CV and RB, respectively for an initial concentrationof 250 μmol dm^-3. The adsorption process was pH dependent. The maximum dye adsorption on HA-PILC was observed at a pH of 5.0–7.0 (removal of 95.2–99.2% for MB, 92.7–97.3% for CV and 83.4–91.0% for RB) with no significant increase in removalsbeyond a pH of 7.0. The adsorption process could be best describedby the Urano and Tachikawa model showing that particle diffusion controlled adsorption. Equilibrium adsorption data were analyzed using the Langmuir, Freundlich and Redlich-Peterson isotherms. Dye adsorption was best described by the Freundlich model. The monolayer adsorption capacities of HA-PILC calculated using the Langmuir isotherm were 608.4, 484.7 and 413.1 μmol g^-1 for MB, CV and RB, respectively. The linear Sheindorf-Rebhun-Sheintuch equation (Multicomponent Freundlich-type), was applied to the isotherm data obtained for each binary-solute combination of MB, CV and RB. The study showed that HA-PILC was an excellent media for the removal of basic dyes from aqueous solutions, based on adsorption kinetics and capacity.     

Copper Binding by Activated Biochar Fibres Derived from <Emphasis Type="Italic">Luffa cylindrica</Emphasis>

The adsorption of copper (Cu(II)) from aqueous solutions by activated Luffa cylindrica biochar fibres has been investigated by means of batch equilibrium experiments and FTIR spectroscopy. The effect of various physicochemical parameters, such as pH, initial metal concentration, ionic strength, mass of the adsorbent, contact time and temperature, has been evaluated by means of batch type adsorption experiments. FTIR spectroscopy, as well as acid-base titrations, was used for the characterization of the material and the surface species formed. According to the experimental results even at pH 3, the relative sorption is above 85% and the adsorption capacity of the activated biochar fibres for Cu(II) is q _max = 248 g kg^?1. Moreover, the interaction between the surface carboxylic moieties and Cu(II) results in the formation of very stable inner-sphere complexes (?G ^o = ?11.2 kJ mol^?1 at pH 3 and ?22.4 kJ mol^?1 at pH 5.5).     

Adsorption of humic acid fractions with different molecular weight by magnetic polyacrylic anion exchange resin

Purpose

Anion exchange resin has been shown to be efficient for adsorption of humic acid (HA). However, the mechanism of the effect(s) of the molecular weight (MW) of HA on the adsorption by anion exchange resin needs to be further explored. The objective of this work was to investigated the effect(s) of HA MW on their adsorption and desorption behavior by interacting with anion exchange resin.

Materials and methods

HA fractions with different MW were obtained by ultrafiltration and characterized. For adsorption kinetic study, the magnetic polyacrylic anion exchange resin (NDMP) was shaken with each HA fraction. The amounts of HA in the solutions at different sampling times were obtained by measurement of the total organic carbon. For isotherm study, batch experiments were performed to obtain the isotherms of each HA fractions. The effects of pH value and the regeneration efficiency for HA fractions with different MW were all investigated.

Results and discussion

The characterization reveals that aromaticity of HA increases as the MW rises, while the negative charge follows the order: HA3 (2,500–1,000 Da)?>?HA4 (>10,000 Da)?>?HA2 (1,000–2,500 Da)?>?HA1 (<1,000 Da). The adsorption amount of HA increases as the negative surface charge rises. Thus, HA3 has the largest adsorption amount by NDMP resin among HA fractions, while the adsorption amount of HA1 is the smallest. HA2 adsorption could be modeled by Freundlich equation, suggesting the interaction between HA2 and NDMP is a heterogeneous process. However, the adsorption isotherms of HA3 and HA4 were both better described by Langmuir equation than Freundlich equation. In addition, the resin fouling follows the order: HA2?>?HA1?>?HA4?>?HA3.

Conclusions

The aromaticity of HA freactions increases as MW rises. HA fractions with 1,000?–?2,500 Da have the largest surface negative charge, while the fractions with MW lower than 1,000 Da are almost electroneutral. The adsorptions of HA fractions onto NDMP suggest there is little effect of size exclusion on adsorption, and the adsorption behavior mainly depends on the negative charge of HAs.     

Removal of Copper,Lead, Methylene Green 5, and Acid Red 1 by Saccharide-Derived Spherical Biochar Prepared at Low Calcination Temperatures: Adsorption Kinetics,Isotherms, and Thermodynamics

Spherical biochar derived from saccharides (glucose, sucrose, and xylose) was prepared through two steps: pre-hydrothermal carbonization at 190 °C and calcination at low temperatures (200–325 °C). The spherical biochar was characterized by Brunauer–Emmett–Teller (BET) surface area analysis, Fourier transform infrared spectroscopy, zeta potential, scanning and transmission electron microscopies, and X-ray diffraction. The result indicated that the spherical biochar exhibited low S _BET (15–22 m²/g), but abundant superficial active oxygen-containing functional groups. The spherical biochar possessed a negatively charged surface within solution pH 2.0–11. The adsorption process of Pb²⁺, Cu²⁺, and methylene green 5 (MG5) was strongly dependent on the solution pH and reached fast equilibrium at approximately 60 min. The maximum Langmuir adsorption capacity (Q°_max) exhibited the following order: glucose-biochar > sucrose-biochar > xylose-biochar prepared at 300 °C. The selective adsorption order of glucose-biochar was Cu²⁺ (0.894 mmol/g) > Pb²⁺ (0.848 mmol/g) > MG5 (0.334 mmol/g). The electrostatic attraction played a determining role in the adsorption mechanism of pollutant cations. The adsorption of anionic dye (acid red 1) on the spherical biochar was negligible because of electrostatic repulsion. The spherical biochar can serve as a newer and promising adsorbent to remove toxic pollutant cations from water media.