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).     

Template-free solvothermal synthesis of hierarchical boehmite hollow microspheres with strong affinity toward organic pollutants in water

Three-dimensional hierarchical boehmite hollow microspheres with a very high yield at low cost were successfully synthesized via a one-pot template-free solvothermal route using aluminum chloride hexahydrate as precursor in a mixed ethanol–water solution with assistance of trisodium citrate. The as-synthesized products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption/desorption techniques. The results show that Cl⁻ and addition amount of trisodium citrate have significant effect on the morphologies of the resultant products, and 6–8 mmol of trisodium citrate is optimal for the synthesis of boehmite hollow microspheres assembled from randomly interconnecting and aligned nanorods with solvothermal time no less than 15 h. A synergistic mediation mechanism of citrate ions and Cl⁻ to form boehmite hollow spheres via self-assembly morphology evolution was proposed based on the experimental results. Interestingly, the typical boehmite hollow microspheres with a surface area of 102 m² g⁻¹, pore volume of 0.37 cm3 g⁻¹, and the average pore size of 14.6 nm show superb adsorption properties for Congo red with maximum capacity of 114.7 mg g⁻¹ which is higher than that of a commercial boehmite. This simple synthetic route is a very promising way for the design and synthesis of new functional hierarchical nanostructured materials with desired adsorptive properties.     

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%.     

MgO-templated porous carbons-based CO2 adsorbents produced by KOH activation

Nanoporous (styrene–divinylbenzene)-based ion exchange resin-based carbons (MPCs) were prepared by MgO-templating synthesis and activated by KOH. MPCs were prepared from a (styrene–divinylbenzene)-based ion exchange resin by the carbonization of a mixture with Mg gluconate at 900 °C. And then, the prepared MPCs were treated with KOH at KOH/MPCs ratios ranging from 0.5 to 4 at 800 °C. Low KOH/MPCs ratios (KOH/MPCs ratio = 1) tended to favor the formation of micropores, whereas higher KOH/MPCs (KOH/MPCs ratio = 4) led to the formation of mesopores. The treated MPCs with a KOH/MPCs ratio = 1 exhibited the best CO₂ adsorption value of 266 mg g⁻¹ at 1 bar. However, the treated MPCs with a KOH/MPCs ratio = 3 exhibited the best CO₂ adsorption value of 1385 mg g⁻¹ at 30 bar. This result indicated that the CO₂ adsorption capacity of nanoporous carbons attributed to the mesopore volume fraction at higher pressure.     

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.     

Removal of indigo carmine dye from water to Mg-Al-CO(3)-calcined layered double hydroxides

Layered double hydroxides (LDHs) calcined, denoted as CLDHs, have been shown to recover their original layered structure in the presence of appropriate anions. In the light of this so-called "memory effect", the removal of indigo carmine (IC), an anionic dye, from aqueous solution by calcined Mg-Al-CO(3) LDHs was investigated in batch mode. We looked at the influence of pH values, dye-adsorbent contact time, initial dye concentration and various temperatures of heating of LDHs on the decolorization rate of IC. The adsorption isotherms, described by Freundlich model are L-type. The characterization of the solids CLDHs, both fresh and after removal of IC, by X-ray diffraction and infrared spectroscopy shows that the IC adsorption on CLDHs is enhanced by reconstruction of a matrix hydrotalcite intercaled by the dye, and the intercalation of the organic ion was clearly evidenced by the net increase in the basal spacing from 0.76 nm for [Mg-Al-CO(3)] to 2.13 nm for the organic derivative.     

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.     

One-pot synthetic method to prepare highly N-doped nanoporous carbons for CO2 adsorption

A one-pot synthetic method was used for the preparation of nanoporous carbon containing nitrogen from polypyrrole (PPY) using NaOH as the activated agent. The activation process was carried out under set conditions (NaOH/PPY = 2 and NaOH/PPY = 4) at different temperatures in 600–900 °C for 2 h. The effect of the activation conditions on the pore structure, surface functional groups and CO₂ adsorption capacities of the prepared N-doped activated carbons was examined. The carbon was analyzed by X-ray photoelectron spectroscopy (XPS), N2/77 K full isotherms, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The CO₂ adsorption capacity of the N-doped activated carbon was measured at 298 K and 1 bar. By dissolving the activation agents, the N-doped activated carbon exhibited high specific surface areas (755–2169 m² g⁻¹) and high pore volumes (0.394–1.591 cm³ g⁻¹). In addition, the N-doped activated carbons contained a high N content at lower activation temperatures (7.05 wt.%). The N-doped activated carbons showed a very high CO₂ adsorption capacity of 177 mg g⁻¹ at 298 K and 1 bar. The CO₂ adsorption capacity was found to be dependent on the microporosity and N contents.     

Nitrate removal from aqueous solutions by cross-linked chitosan beads conditioned with sodium bisulfate

The investigation of adsorption of nitrate onto chitosan beads modified by cross-linking with epichlorohydrin (ECH) and surface conditioning with sodium bisulfate was performed. The results indicated that both cross-linking and conditioning increased adsorption capacity compared to normal chitosan beads. The maximum adsorption capacity was found at a cross-linking ratio of 0.4 and conditioning concentration of 0.1 mM NaHSO₄. The maximum adsorption capacity was 104.0 mg g⁻¹ for the conditioned cross-linked chitosan beads at pH 5, while it was 90.7 mg g⁻¹ for normal chitosan beads. The Langmuir isotherm model fit the equilibrium data better than the Freundlich model. The mean adsorption energies obtained from the Dubinin-Radushkevich isotherm model for all adsorption systems were in the range of 9.55–9.71 kJ mol⁻¹, indicating that physical electrostatic force was potentially involved in the adsorption process.     

Adsorption of mercury cation on chemically modified clay

A montmorillonite clay (M) sample from the Amazon region, Brazil, was intercalated with pyridine (Py), dimethyl sulfoxide (DS) and 3-aminopropyltriethoxysilane (APS). The chemically modified montmorillonite (M_P/APS) sample showed modification of its physical-chemical properties including: specific area 41.39 m² g⁻¹ (M) to 198.45 m² g⁻¹ (M_P/APS). Solid-state ²⁹Si CPMAS/NMR of the silylated montmorillonite samples showed Q² and Q³ signals as well as T² and T³ signals. The appearance of T² and T³ signals can be attributed to the grafting of APS to the interlayer surface silanol groups. The natural and modified clays were used for mercury cation adsorption from aqueous solutions at room temperature and pH 3.0. The energetic effects (Δ_intH°, Δ_intG° and Δ_intS°) caused by mercury cation adsorption were determined through calorimetric titrations.     

Synthesis and characterization of CTAB-silica nanocapsules and its adsorption behavior towards Pd(II) ions in aqueous solution

The silica nanocapsules (SiNC) with CTAB (SiNC-CTAB) and free CTAB (SiNC-FREE) were prepared by the microemulsion polymerization process, in which the cetyltrimethylammonium bromide (CTAB) was used as a structure directive as well as a cationic functionalized agent. The structure and properties of these adsorbents were characterized by a field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), nitrogen adsorption–desorption (NAD) analyzer, Fourier transform infrared (FTIR) spectrophotometer, thermogravimetric analyzer (TGA) and pH at point zero charges (pH_pzc) determination. The adsorbents were then characterized for their adsorption behavior towards Pd(II) ions in aqueous solution performed in a batch adsorption experiment. The maximum adsorption capacity of Pd(II) ions onto SiNC-CTAB obtained from the adsorption isotherm was 124.50 mg g⁻¹, which was over 2.4 times higher than that of the SiNC-FREE (51.28 mg g⁻¹). The diffusion modeling analysis by the Weber Morris model indicated that the film diffusion is the controlling step, while the chemical reaction modeling obeyed the pseudo-second order kinetic model. The SiNC-CTAB was found to be reusable in which a good adsorption performance of up to 4 adsorption cycles was observed.     

Physical,photoelectrochemical properties of CuIn3Se5 and relevance for hydrogen production

CuIn₃Se₅, prepared by the fusion technique crystallizes in the P-chalcopyrite structure and exhibits n-type conduction ascribed to indium excess. The electrical conductivity follows an Arrhenius-type law with activation energy of 0.35 eV and an electron mobility of 10⁻⁴ cm² V⁻¹ s⁻¹ in conformity with small polaron hopping. The optical gap (1.19 eV), determined from the diffuse reflectance spectrum, is properly matched to the sun spectrum. CuIn₃Se₅ is chemically stable and a corrosion rate of only 1.2 μmol year⁻¹ is found at neutral pH. The slope and the intercept to C⁻² = 0 of the Mott Schottky plot gives respectively an electron density of 3.75 × 10¹⁶ cm⁻³ and a flat band potential of −0.22 V_SCE. The conduction band (−0.74 V_SCE) therefore lies below the potential of H₂O/H₂ couple and as application, H₂ photo-production is successfully achieved over CuIn₃Se₅. The best performance is obtained in S₂O₃²⁻ solution (10⁻² M, pH ∼ 7) with an evolution rate of 0.54 mL g⁻¹ min⁻¹. The conversion efficiency (0.13%) is due to the formation of small depletion width (230 nm) and a large diffusion length compared to a very large penetration depth (∼1 μm). Attempts have been made to improve the photoactivity and the hetero-system CuIn₃Se₅/WO₃ is compared favorably with respect to CuIn₃Se₅. The photoactivity is ascribed to electrons transfer from the sensitizer CuIn₃Se₅-conduction band (CB), acting as electrons pump, to WO₃-CB (−0.4 V_SCE) resulting in the enhanced water reduction.     

Design of magnetic and fluorescent Mg-Al layered double hydroxides by introducing Fe3O4 nanoparticles and Eu ions for intercalation of glycine

We describe a novel route for the preparation of magnetic and fluorescent magnesium-aluminum layered double hydroxides by introducing Fe₃O₄ nanoparticles and Eu³⁺ ions. From the powder X-ray diffraction results, it was found that the Fe₃O₄ nanoparticles were highly dispersed in the inner void of octahedral lattice, and the Eu³⁺ ions substituted for the Al³⁺ ions and entered into hydrotalcite lattice through isomorphous replacement. Moderate introduction of Fe₃O₄ nanoparticles and Eu³⁺ ions did not change the lamellar structure of magnesium-aluminum layered double hydroxides. Glycine can also be intercalated into this magnetic and fluorescent layered double hydroxides by ion-exchange method. After intercalation of glycine, the basal spacing of magnetic and fluorescent layered double hydroxides increased from 7.6 to 8.8 Å, indicating that glycine was successfully intercalated into the interlayer space of layered double hydroxides. Magnetic measurements reveal that these novel layered double hydroxides possess paramagnetic property at room temperature, and the emission and excitation spectra indicate the layered double hydroxides exhibit fluorescent property.     

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.     

Calcium phenylphosphonate as a host for 4-aminobenzoic acid—Synthesis, characterization, and cation adsorption from ethanol solution

Crystalline lamellar calcium phenylphosphonate retained 4-aminobenzoic acid inside its cavity without leaching. The intense infrared bands in the 1160–695 cm⁻¹ interval confirmed the presence of the phosphonate groups attached to the inorganic layer, with sharp and intense peaks in X-ray diffraction patterns, which gave basal distances of 1532 and 1751 pm for the original and the intercalated compounds, respectively. The thermogravimetric curves of both layered compounds showed the release of water molecules and the organic moiety in distinct stages, to yield a final Ca(PO₃)₂ residue. Solid-state ³¹P nuclear magnetic resonance spectra presented only one peak for the phenylphosphonate groups attached to the main inorganic polymeric structure near 12.4 ppm. The adsorption isotherms from ethanol gave the maximum adsorption capacities of 1.68 and 0.50 mmol g⁻¹ for copper and cobalt, respectively, whose average stability constants followed Co > Cu; the number of ligands was determined as four for both cations.     

Anion-exchange properties of nickel–aluminum layered double hydroxide prepared by liquid phase deposition

The optimum coordination structure of Ni–fluoro complexes for the preparation of Ni–Al LDH by LPD process and the diverse anion-exchange properties of as-deposited Ni–Al on α-alumina powder were quantitatively evaluated for the industrial application of new positive material for alkali secondary batteries. The [NiF_6−x−y(NH₃)_x(OH⁻)_y]ⁿ⁺ was more suitable than [NiF₆]⁴⁻ as the precursor of the deposition of Ni–Al LDH in the LPD reaction, and the improved LPD reaction achieved the synthesis of high purity and high crystallinity Ni–Al LDH. All anion-exchanged Ni–Al LDHs for OH⁻–, Cl⁻–, SO₄²⁻–, and CH₃COO⁻–forms kept the high crystallinity and showed the enlargement of interlayer distances. The tilting angle of the intercalated CH₃COO⁻ anions was about 15°. Anion-exchange capacity remained constant at a minimum of 0.8 meq g⁻¹ in pH >10, increased as pH decreased, and reached a maximum of 8 meq g⁻¹ at pH 2. Anion-exchange of OH⁻–form of Ni–Al LDH was accelerated by the neutralization of hydroxide ions in interlayers, in addition, the anion-exchange capacity and the crystallinity of Ni–Al LDH could be controlled by the amount of doped aluminum ions.     

Raman spectroscopic investigation of Friedel's salt

Friedel's salt (FS) forms upon chloride binding in monosulphoaluminate (AFm) phase. This removes chlorides from the pore solution, hence, delays the initiation of steel-bar corrosion. Apparently, characterising and, in particular, monitoring the formation and the status of FS facilitate the prediction of the service life of reinforced concrete structures. Raman spectroscopy offers a potential for investigating FS. The current work characterised FS, including the synthesised pure FS, and the FS formed in a Portland cement (PC) paste powder, using a bench-mounted Raman spectrometer. The results revealed the full Raman spectra of pure FS between 200 and 4000 cm⁻¹, including the featured Raman bands at 534/568 cm⁻¹ and 783 cm⁻¹ which correspond to the Al-OH stretching and bending vibration of FS respectively. Furthermore, similar Raman bands of FS were identified in PC paste sample subjected to accelerated chloride attack, further confirming the potential of Raman spectroscopy for distinguishing FS in cementitious materials.     

Facile synthesis of carbon coated LiFePO4 nanocomposite with excellent electrochemical performance through in situ formed lithium stearate pyrolysis route

Carbon coated LiFePO₄ (LiFePO₄/C) nanocomposite is successfully synthesized at a comparatively low temperature (400 °C) via a pyrolysis process of in situ formed lithium stearate. The obtained products are characterized by X-ray diffraction, electron microscopy, thermogravimetry, infrared and X-ray photoelectron spectroscopy. Experimental results indicate that the in situ formed lithium stearate can decompose at ∼290 °C, which is beneficial for the formation of carbon coating and reduction of Fe³⁺ species, and then the crystallized LiFePO₄/C nanocomposite can be formed at 400 °C without other intermediate products. As cathode material of Li-ion battery, the obtained LiFePO₄/C nanocomposite exhibits a good rate and cycling performance with a high discharge capacity of ∼160 mAh g⁻¹ (>94% theoretical capacity of LiFePO₄) at a current density of 1 C (170 mA g⁻¹), and ∼96% of its initial capacity can be retained after 200 charging/discharging cycles. Even at a high current density (10 C), the LiFePO₄/C nanocomposite still presents a discharge capacity as high as ∼100 mAh g⁻¹. The excellent electrochemical performances of the present LiFePO₄/C nanocomposite mainly originate from the good crystallinity, small particles and enhanced electronic conductivity of the materials coated and linked by carbon layers.     

Preparation and electrochemical properties of lamellar MnO2 for supercapacitors

Lamellar birnessite-type MnO₂ materials were prepared by changing the pH of the initial reaction system via hydrothermal synthesis. The interlayer spacing of MnO₂ with a layered structure increased gradually when the initial pH value varied from 12.43 to 2.81, while the MnO₂, composed of α-MnO₂ and γ-MnO₂, had a rod-like structure at pH 0.63. Electrochemical studies indicated that the specific capacitance of birnessite-type MnO₂ was much higher than that of rod-like MnO₂ at high discharge current densities due to the lamellar structure with fast intercalation/deintercalation of protons and high utilization of MnO₂. The initial specific capacitance of MnO₂ prepared at pH 2.81 was 242.1 F g⁻¹ at 2 mA cm⁻² in 2 mol L⁻¹ (NH₄)₂SO₄ aqueous electrolyte. The capacitance increased by about 8.1% of initial capacitance after 200 cycles at a current density of 100 mA cm⁻².     

Porous graphene gels: Preparation and its electrochemical properties

Ultra-light porous 3D network graphene oxide (GO) gels were prepared using a simple process of aqueous gel precursor freezing, solvent exchange, and ethanol drying rather than supercritical drying technology. The GO sheets were consolidated by cross-linked sodium alginate (SA) and the obtained GO–SA gel was reduced by glucose to prepare graphene nanosheet–SA (GN–SA) gel. The gels were characterized by FTIR, XRD, SEM, and nitrogen adsorption–desorption measurements. SA was proven to attach to GO or GN surfaces to form gels composed of macropores and mesopores. GO–SA gel exhibited a bulk density of 16.79 mg cm⁻³, and adsorbed water 17.4 times, ethanol 20.5 times, and soybean oil 22.4 times the weight of GO–SA gel, while GN–SA gel exhibited a lower bulk density of 12.93 mg cm⁻³, and adsorbed water 12.2 times, ethanol 16.9 times and soybean oil 32.3 times the weight of GN–SA gel. The electrochemical performance of the GN–SA gel was analyzed using cyclic voltammetry, electrochemical impedance spectrometry, and chronopotentiometry. The results revealed that GN–SA gel displayed superior capacitive performance with large capacitance (114.12 F g⁻¹) and excellent cyclic performance.