Fluoride removal performance of glass derived hydroxyapatite

A novel sodium calcium borate glass derived hydroxyapatite (G-HAP) with different ranges of particle size was prepared by immersion sodium calcium borate glass in 0.1 M K₂HPO₄ solution by the ratio of 50 g L⁻¹ for 7 days. The unique advantage of G-HAP for the adsorption of fluoride ions in solutions was studied. The effects of size and quantity of particles, pH value and adsorption time on adsorption performance were investigated. The maximum adsorption capacity was 17.34 mg g⁻¹ if 5 g L⁻¹, <100 μm G-HAP was added to a solution with an initial pH value of 6.72 and the adsorption time was 12 h. The results showed that the micro-G-HAP could immobilize F⁻ in solution more effectively than commercial nano-HAP, which makes potential application of the G-HAP in removing the fluoride ions from wastewater. The adsorption kinetics and isotherms for F⁻ could be well fitted by a second order kinetic model and Freundlich isotherm model respectively, which could be used to describe the adsorption behavior. The mechanism of G-HAP in immobilizing F⁻ from aqueous solutions was investigated by the X-ray diffraction (XRD), infrared spectra (IR) and scanning electron microscopy (SEM).     

Quantifying effects of pH and surface loading on arsenic adsorption on NanoActive alumina using a speciation-based model

Arsenic (As) poses a significant water quality problem and challenge for the environmental engineers and scientists throughout the world. Batch tests were carried out in this study to investigate the adsorption of As(V) on NanoActive alumina. The arsenate adsorption envelopes on NanoActive alumina exhibited broad adsorption maxima when the initial As(V) loading was less than a 50 mg g⁻¹ sorbent. As the initial As(V) loading increased to 50 mg g⁻¹ sorbent, a distinct adsorption maximum was observed at pH 3.2–4.6. FTIR spectra revealed that only monodentate complexes were formed upon the adsorption of arsenate on NanoActive alumina over the entire pH range and arsenic loading conditions examined in this study. A speciation-based adsorption model was developed to describe arsenate adsorption on NanoActive alumina and it could simulate arsenate adsorption very well in a broad pH range of 1–10, and a wide arsenic loading range of 0.5–50 mg g⁻¹ adsorbent. Only four adjustable parameters, including three adsorption constants, were included in this model. This model offers a substantial improvement over existing models in accuracy and simplification in quantifying pH and surface loading effects on arsenic adsorption.     

Single and binary chromium(VI) and Remazol Black B biosorption properties of Phormidium sp.

Wastewaters of textile and leather dying industries may contain significant quantities of chromium(VI) ions besides anionic and water-soluble dyes. Moreover the temperature of these wastewaters may be a controlling parameter affecting the biosorption efficiency. In this study biosorption of chromium(VI) and Remazol Black B reactive dye by dried Phormidium sp., a thermophilic cyanobacterium, was studied as a function of initial chromium(VI) concentration and temperature in no dye and 100 mg l⁻¹ dye-containing media at an initial pH value of 2.0 at which the biomass exhibited the maximum chromium(VI) and dye uptakes. The decrease of both metal and dye uptakes with temperature indicated that the uptakes were exothermic in nature. Equilibrium uptake of chromium(VI) enhanced considerably with both chromium(VI) and 100 mg l⁻¹ dye concentrations. Moreover the presence of chromium(VI) also increased the uptake of dye. At 25 °C, 22.8 mg g⁻¹ chromium(VI) and 91.3 mg g⁻¹ dye were sorbed by the biomass in binary 100 mg l⁻¹ chromium(VI) and 100 mg l⁻¹ dye-containing medium. The Langmuir was the best suitable adsorption model for describing the biosorption of chromium(VI) individually and in dye-containing medium. The pseudo-second-order kinetic model described both the chromium(VI) and dye biosorptions kinetics accurately.     

Removal of reactive red-120 and 4-(2-pyridylazo) resorcinol from aqueous samples by Fe3O4 magnetic nanoparticles using ionic liquid as modifier

The nanoparticles of Fe₃O₄ as well as the binary nanoparticles of ionic liquid and Fe₃O₄ (IL-Fe₃O₄) were synthesized for removal of reactive red 120 (RR-120) and 4-(2-pyridylazo) resorcinol (PAR) as model azo dyes from aqueous solutions. The mean size and the surface morphology of the nanoparticles were characterized by TEM, DLS, XRD, FTIR and TGA techniques. Adsorption of RR-120 and PAR was studied in a batch reactor at different experimental conditions such as nanoparticle dosage, dye concentration, pH of the solution, ionic strength, and contact time. Experimental results indicated that the IL-Fe₃O₄ nanoparticles had removed more than 98% of both dyes under the optimum operational conditions of a dosage of 60 mg, a pH of 2.5, and a contact time of 2 min when initial dyes concentrations of 10-200 mg L⁻¹ were used. The maximum adsorption capacity of IL-Fe₃O₄ was 166.67 and 49.26 mg g⁻¹ for RR-120 and PAR, respectively. The isotherm experiments revealed that the Langmuir model attained better fits to the equilibrium data than the Freundlich model. The Langmuir adsorption constants were 5.99 and 3.62 L mg⁻¹ for adsorptions of RR-120 and PAR, respectively. Both adsorption processes were endothermic and dyes could be desorbed from IL-Fe₃O₄ by using a mixed NaCl-acetone solution and adsorbent was reusable.     

Removal of malachite green by adsorption and precipitation using aminopropyl functionalized magnesium phyllosilicate

We report a method for the removal of malachite green (MG) by adsorption and precipitation using nano-sized aminopropyl functionalized magnesium phyllosilicate (AMP) clay. MG, which is used in aquaculture and fisheries, is a carcinogenic and mutagenic compound. In response to these health risks, many efforts have been focused on adsorption of MG onto various adsorbents, which is a versatile and widely used technique for removing MG from water. Herein, we describe the adsorption and precipitation of MG using AMP clay, as well as the alkaline fading phenomenon of MG. In this study, prepared AMP clay and the precipitate product after the reaction of MG-AMP clay mixture were characterized. In addition, adsorption isotherms and kinetics, as well as thermodynamic studies are presented. Based on the results, we suggest a macro- and microscopic removal mechanism for the adsorption and precipitation of MG using AMP clay. An AMP clay dosage of 0.1 mg mL⁻¹ exhibited a maximum removal capacity of 334.80 mg g⁻¹ and 81.72% MG removal efficiency. With further increases of the AMP clay dosage, removal capacity by AMP clay gradually decreased; at dosage above 0.2 mg mL⁻¹ of AMP clay, the removal efficiency reached 100%.     

Strong adsorption of chlorotetracycline on magnetite nanoparticles

In this work, environmentally friendly magnetite nanoparticles (Fe₃O₄ MNPs) were used to adsorb chlorotetracycline (CTC) from aqueous media. Fe₃O₄ MNPs exhibit ultrahigh adsorption ability to this widely used antibiotic. The adsorption behavior of CTC on Fe₃O₄ MNPs fitted the pseudo-second-order kinetics model, and the adsorption equilibrium was achieved within 10 h. The maximum Langmuir adsorption capacity of CTC on Fe₃O₄ (476 mg g⁻¹) was obtained at pH 6.5. Thermodynamic parameters calculated from the adsorption data at different temperature showed that the adsorption reaction was endothermic and spontaneous. Low concentration of NaCl and foreign divalent cations hardly affected the adsorption. Negative effect of coexisting humic acid (HA) on CTC adsorption was also observed when the concentration of HA was lower than 20 mg L⁻¹. But high concentration of HA (>20 mg L⁻¹) increased the CTC adsorption on Fe₃O₄ MNPs. The matrix effect of several environmental water samples on CTC adsorption was not evident. Fe₃O₄ MNPs were regenerated by treatment with H₂O₂ or calcination at 400 °C in N₂ atmosphere after separation from water solution by an external magnet. This research provided a high efficient and reusable adsorbent to remove CTC selectively from aqueous media.     

Oxolane-2,5-dione modified electrospun cellulose nanofibers for heavy metals adsorption

Functionalized cellulose nanofibers have been obtained through electrospinning and modification with oxolane-2,5-dione. The application of the nanofibers for adsorption of cadmium and lead ions from model wastewater samples is presented for the first time. Physical and chemical properties of the nanofibers were characterized. Surface chemistry during preparation and functionalization was monitored using Fourier transform-infrared spectroscopy, scanning electron microscopy, carbon-13 solid state nuclear magnetic resonance spectroscopy and Brunauer Emmett and Teller. Enhanced surface area of 13.68 m² g⁻¹ was recorded for the nanofibers as compared to the cellulose fibers with a surface area of 3.22 m² g⁻¹. Freundlich isotherm was found to describe the interactions better than Langmuir: K_f = 1.0 and 2.91 mmol g⁻¹ (r² = 0.997 and 0.988) for lead and cadmium, respectively. Regenerability of the fiber mats was investigated and the results obtained indicate sustainability in adsorption efficacy of the material.     

Adsorptive separation and photocatalytic degradation of methylene blue dye on titanate nanotube powders prepared by hydrothermal process using metal Ti particles as a precursor

Titanate nanotube powders (TNTPs) with the twofold removal ability, i.e. adsorptive separation and photocatalytic degradation, are synthesized under hydrothermal conditions using metal Ti particles as a precursor in the concentrated alkaline solution, and their morphology, structure, adsorptive and photocatalytic properties are investigated. Under hydrothermal conditions, the titanate nanotubes (TNTs) with pore diameter of 3-4 nm are produced on the surface of metal Ti particles, and stacked together to form three-dimensional (3D) network with porous structure. The TNTPs synthesized in the autoclave at 130 °C for 24 h exhibits a maximum adsorption capability of about 197 mg g⁻¹ in the neutral methylene blue (MB) solution (40 mg L⁻¹) within 90 min, the adsorption process can be described by pseudo second-order kinetics model. Especially, in comparison with the adsorptive and the photocatalytic processes are performed in turn, about 50 min can be saved through synchronously utilizing the double removal ability of TNTPs when the removal ratio of MB approaches 95% in MB solution (40 mg L⁻¹) at a solid-liquid (S/L) ratio of 1:8 under ultraviolet (UV) light irradiation. These 3D TNTPs with the twofold removal properties and easier separation ability for recycling use show promising prospect for the treatment of dye pollutants from wastewaters in future industrial application.     

Efficient removal of heavy metal ions from aqueous solution using salicylic acid type chelate adsorbent

In this study, 5-aminosalicylic acid was successfully grafted onto the poly(glycidyl methacrylate) (PGMA) macromolecular chains of PGMA/SiO₂ to obtain a novel adsorbent designated as ASA-PGMA/SiO₂. The adsorption properties of ASA-PGMA/SiO₂ for heavy metal ions were studied through batch and column methods. The experimental results showed that ASA-PGMA/SiO₂ possesses strong chelating adsorption ability for heavy metal ions, and its adsorption capacity for Cu²⁺, Cd²⁺, Zn²⁺, and Pb²⁺ reaches 0.42, 0.40, 0.35, and 0.31 mmol g⁻¹, respectively. In addition, pH has a great influence on the adsorption capacity in the studied pH range. The adsorption isotherm data greatly obey the Langmuir and Freundlich model. The desorption of metal ions from ASA-PGMA/SiO₂ is effective using 0.1 mol l⁻¹ of hydrochloric acid solution as eluent. Consecutive adsorption-desorption experiments showed that ASA-PGMA/SiO₂ could be reused almost without any loss in the adsorption capacity.     

High pressure carbon dioxide adsorption on nanoporous carbons prepared by Zeolite Y templating

Nanoporous carbons were synthesized by chemical vapor deposition using furfuryl alcohol/butylene as a carbon source and zeolite Y as a hard template (ZYC). The ZYC were characterized by PXRD, N₂ sorption, and SEM. The carbon materials exhibited predominant microporosity, and the specific surface area increased from 2563 to 3010 m² g⁻¹ as the pyrolysis temperature was raised from 800 to 1000 °C. ZYC prepared at 1000 °C showed a CO₂ adsorption capacity of 986 mg g⁻¹_adsorbent at 40 bar 298 K, which surpasses the capacities of commercial carbons and mesoporous carbon CMK-3, and closely approaches the best performance of the metal organic framework MOF-177. The CO₂ adsorption capacities of the adsorbents were found to be closely correlated with the BET surface areas of the materials tested.     

Magnetic chitosan nanoparticles for removal of Cr(VI) from aqueous solution

A simple method was introduced to prepare magnetic chitosan nanoparticles by co-precipitation via epichlorohydrin cross-linking reaction. The average size of magnetic chitosan nanoparticles is estimated at ca. 30 nm. It was found that the adsorption of Cr(VI) was highly pH-dependent and its kinetics follows the pseudo-second-order model. Maximum adsorption capacity (at pH 3, room temperature) was calculated as 55.80 mg·g^? 1, according to Langmuir isotherm model. The nanoparticles were thoroughly characterized before and after Cr(VI) adsorption. From this result, it can be suggested that magnetic chitosan nanoparticles could serve as a promising adsorbent for Cr(VI) in wastewater treatment technology.     

Novel Cu (II) magnetic ion imprinted materials prepared by surface imprinted technique combined with a sol-gel process

A novel Cu (II) magnetic ion-imprinted polymer (MIIP) was synthesized by surface imprinting technique combined with a sol-gel process. The adsorbent of Cu (II)-MIIP shows higher capacity and selectivity than that of magnetic non-imprinted polymers (MNIP). Adsorption capacities of Cu (II)-MIIP and MNIP are 24.2 and 5.2 mg/g for Cu (II) ions, respectively. The selectivity coefficients of the Cu (II)-MIIP for Cu (II)/Zn (II) and Cu (II)/Ni (II) are 91.84 and 133.92, respectively. Kinetics studies show that the adsorption process obeys pseudo-second-order rate mechanism with an initial adsorption rate of 132.48 for Cu (II)-MIIP and 2.41 mg g⁻¹ min⁻¹ for MNIP. In addition, no obvious decrease was observed after up to five adsorption cycles, indicating that the Cu (II)-MIIP is of high stability.     

Zincon-modified activated carbon for solid-phase extraction and preconcentration of trace lead and chromium from environmental samples

A new method that utilizes zincon-modified activated carbon (AC-ZCN) as a solid-phase extractant has been developed for simultaneous preconcentration of trace Cr(III) and Pb(II) prior to the measurement by inductively coupled plasma optical emission spectrometry (ICP-OES). The separation/preconcentration conditions of analytes were investigated, including effects of pH, the shaking time, the sample flow rate and volume, the elution condition and the interfering ions. At pH 4, the maximum adsorption capacity of Cr(III) and Pb(II) onto the AC-ZCN were 17.9 and 26.7 mg g⁻¹, respectively. The adsorbed metal ions were quantitatively eluted by 1 mL of 0.1 mol L⁻¹ HCl. Common coexisting ions did not interfere with the separation. According to the definition of IUPAC, the detection limits (3σ) of this method for Cr(III) and Pb(II) were 0.91 and 0.65 ng mL⁻¹, respectively. The relative standard deviation under optimum condition is less than 3.5% (n = 8). The method has been applied for the determination of Cr(III) and Pb(II) in biological materials and water samples with satisfactory results.     

Synthesis,characterization and kinetic of a surfactant-modified bentonite used to remove As(III) and As(V) from aqueous solution

In this study, organobentonites were prepared by modification of bentonite with various cationic surfactants, and were used to remove As(V) and As(III) from aqueous solution. The results showed that the adsorption capacities of bentonite modified with octadecyl benzyl dimethyl ammonium (SMB3) were 0.288 mg/g for As(V) and 0.102 mg/g for As(III), which were much higher compared to 0.043 and 0.036 mg/g of un-modified bentonite (UB). The adsorption kinetics were fitted well with the pseudo-second-order model with rate constants of 46.7 × 10⁻³ g/mg h for As(V) and 3.1 × 10⁻³ g/mg h for As(III), respectively. The maximum adsorption capacity of As(V) derived from the Langmuir equation reached as high as 1.48 mg/g, while the maximum adsorption capacity of As(III) was 0.82 mg/g. The adsorption of As(V) and As(III) was strongly dependent on solution pH. Addition of anions did not impact on As(III) adsorption, while they clearly suppressed adsorption of As(V). In addition, this study also showed that desorbed rates were 74.61% for As(V) and 30.32% for As(III), respectively, after regeneration of SMB3 in 0.1 M HCl solution. Furthermore, in order to interpret the proposed absorption mechanism, both SMB3 and UB were extensively characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analyses.     

Removal of acid orange 7 by guava seed carbon: A four parameter optimization study

The preparation of carbon from waste materials is a recent and economic alternative for the removal of dyes. In this study four samples of carbon were obtained by thermal treatment at 1000 °C using as precursor the guava seed with different particle sizes. The Taguchi method was applied as an experimental design to establish the optimum conditions for the removal of acid orange 7 in batch experiments. The chosen experimental factors and their ranges were: pH (2–12), temperature (15–35 °C), specific surface area (50–600 m² g⁻¹) and adsorbent dosage (16–50 mg ml⁻¹). The orthogonal array L₉ and the larger the better response category were selected to determine the optimum removal conditions: pH 2, temperature 15 °C, S_esp 600 m² g⁻¹ and dosage 30 mg ml⁻¹. Under these conditions a total removal of acid orange 7 was achieved. Moreover, the most significant factors were the carbon specific surface area and the pH. The influence of the different factors on the adsorption of acid orange 7 from solution is explained in terms of electrostatic interactions by considering the dye species and the character of the surface.     

Heavy metal ions and organic dyes removal from water by cellulose modified with maleic anhydride

A novel type of adsorbent (CM) was synthesized by cellulose modified with maleic anhydride to remove heavy metal ions and organic dyes in this work. The synthesized adsorbent was characterized by FTIR, SEM, TGA and XRD. The degree of carboxyl group of CM was found to be 2.7 mmol g⁻¹ by the titration method. The adsorption of Hg(II) ions as heavy metal ions while basic fuchsine, methylene blue and crystal violet as organic dyes by CM was investigated. The influence of different experimental parameters such as pH, contact time, temperature on removal process was evaluated. The results indicated that the CM has a good adsorption capacity for Hg(II). The maximum adsorption capacity of Hg(II) was found to be 172.5 mg g⁻¹, and the adsorption process was described by Freundlich isotherm model of adsorption well. The process of basic fuchsine, methylene blue and crystal violet adsorbed by CM was also studied and the adsorption removal rate of those organic dyes was 88.10, 98.47 and 92.85 % under the optimum conditions, respectively. The adsorption process was depicted by the Langmuir isotherm model more correctly.     

Chloride adsorption by calcined layered double hydroxides in hardened Portland cement paste

This study investigated the feasibility of using calcined layered double hydroxides (CLDHs) to prevent chloride-induced deterioration in reinforced concrete. CLDHs not only adsorbed chloride ions in aqueous solution with a memory effect but also had a much higher binding capacity than the original layered double hydroxides (LDHs) in the cement matrix. We investigated this adsorption in hardened cement paste in batch cultures to determine adsorption isotherms. The measured and theoretical binding capacities (153 mg g⁻¹ and 257 mg g⁻¹, respectively) of the CLDHs were comparable to the theoretical capacity of Friedel's salt (2 mol mol⁻¹ or 121 mg g⁻¹), which belongs to the LDH family among cementitious phases. We simulated chloride adsorption by CLDHs through the cement matrix using the Fickian model and compared the simulation result to the X-ray fluorescence (XRF) chlorine map. Based on our results, it is proposed that the adsorption process is governed by the chloride transport through the cement matrix; this process differs from that in an aqueous solution. X-ray diffraction (XRD) analysis showed that the CLDH rebuilds the layered structure in a cementitious environment, thereby demonstrating the feasibility of applying CLDHs to the cement and concrete industries.     

Use of pH-sensitive polymer hydrogels in lead removal from aqueous solution

Three gamma crosslinked polymeric hydrogels were synthesized and evaluated as lead ion sorbents. A crosslinked poly(acrylic acid) hydrogel was compared with two 4-vinylpiridine-grafted poly(acrylic acid) hydrogels (26.74 and 48.1% 4-vinylpiridine). The retention properties for Pb(II) from aqueous solutions of these three polymers were investigated by batch equilibrium procedure. The effects of pH, contact time and Pb(II) concentration were evaluated. The optimal pH range for all polymers was 4-6. The lightly grafted polymer (PAAc-g-4VP at 26.74%) exhibited a Pb(II) removal close to 80% at 5 h and above 90% at 24 h. The maximum Pb(II) removal was 117.9 mg g⁻¹ of polymer and followed the Freundlich adsorption model. XPS characterization indicates that the carboxyl groups are involved in the Pb(II) removal.     

Adsorption of Cr(VI) on 1,2-ethylenediamine-aminated macroporous polystyrene particles

An adsorbent, 1,2-ethylenediamine-aminated macroporous polystyrene (EDA-PSt) particles was used to adsorb Cr(VI) from aqueous solution. Effect of pH value, contact time, temperature, adsorbent dosage and initial Cr(VI) concentration on adsorption amount of Cr(VI) on EDA-PSt were investigated. The results showed that the adsorption isotherm can be well described by the Langmuir equation and the adsorption kinetics fitted to the pseudo-second-order model. According to Langmuir equation, Q_m was calculated to be 175.75 mg g⁻¹. The breakthrough curve experiment showed that the dynamic adsorption capacity for Cr(VI) on EDA-PSt was 100.06 mg g⁻¹. The adsorbed Cr(VI) could be desorbed by 0.1 mol L⁻¹ NaOH and the desorption ratio was 67.28%.     

Nitrogen-containing carbons prepared from polyaniline as anode materials for lithium secondary batteries

Nitrogen-containing carbons have been prepared from polyaniline by carbonization and activation. Lithium storage performances of the carbons have been studied by galvanostatic charge/discharge. The carbon without activation shows a first discharge capacity of 729 mAh g^− 1, after activation, the capacity improved. The first discharge capacity of the carbon prepared by H₃PO₄ activation is 1083 mAh g^− 1, and that of the carbon prepared by KOH activation is as high as 2201 mAh g^− 1, whose reversible capacity is 1027 mAh g^− 1. To the carbon prepared by KOH activation, the first coulombic efficiency is just 47%, however, from the second cycle, the coulombic efficiency goes up rapidly to above 90%, the reversible capacity is still as high as 747 mAh g^− 1 after 20 cycles. It may be a promising candidate as an anode material for lithium secondary batteries.