High yield combustion synthesis of nanomagnesia and its application for fluoride removal

Synthesis, characterization, and evaluation of fluoride removal capacity of calcium-impregnated Euphorbia neriifolia carbon (Ca-Enc)

Fluoride ions must be removed from drinking water in order to prevent fluorosis. Many conventional techniques have been examined for the defluoridation of water all over the world. As far as fluoride ions are concerned, adsorption is the most promising method for the removal of them from aqueous environments. In the present study, we aim to find out how well Euphorbia neriifolia plants can remove fluoride from water using activated and carbonized adsorbents. The Euphorbia neriifolia plant stem was pulverized, dried, and activated using calcium ions extracted from used eggshells collected nearby. The synthesized adsorbent material before and after adsorption of fluoride ions was systematically characterized using FTIR, XRD, SEM with EDAX, TGA, and zero-point charge. The defluoridation capacity of the as-prepared adsorbent material was investigated using batch adsorption studies. Various influencing factors such as contact time, solution pH, initial fluoride concentration, mass of the adsorbent, temperature, and co-existing ions were systematically investigated towards the removal of fluoride ion on prepared adsorbent material. This study was conducted to identify the optimal conditions of prepared adsorbent for the maximum removal of fluoride ions from aqueous solution. A groundwater sample with fluoride content of more than 1.5 ppm was taken and studied in this present work. A basic quality indicator of the synthesized material was examined, and its ability to remove fluoride was determined. The findings provide insight into the selective elimination of fluoride ions from aqueous environment.

Comparison of fluorine removal performance and mechanism of spheroidal magnesium oxide before and after lanthanum modification

Firstly, spherical magnesium oxide was synthesized by simple magnesium salt and specific reaction conditions. Then, lanthanum-modified spherical magnesium oxide (LSMO) was prepared by impregnation of lanthanum salt. The adsorption mechanism of the adsorbent was investigated by XRD, SEM, XPS, and FT-IR. Through the study of fluorine removal performance, for the solution with fluoride ion concentration of 10 mg·L^-1, the fluorine removal efficiency of lanthanum-modified spherical magnesium oxide (15LSMO) (93.1%) with 15% impregnation mass ratio is higher than that of SMO (82.7%). In addition, in the pH range of 2-11 or in the presence of interfering ions, the fluoride removal effect of 15LSMO still meets the fluoride removal efficiency of more than 90%. The research enhanced the profound insights into the effect and mechanism of fluorine removal of lanthanum modified materials.

Comparative study of low-cost fluoride removal by layered double hydroxides, geopolymers, softening pellets and struvite

Excessive F^- in drinking water due to natural and anthropogenic activities is a serious health hazard affecting humans worldwide. In this study, a comparative assessment was made of eight mineral-based materials with advantageous structural properties for F^- uptake: layered-double-hydroxides (LDHs), geopolymers, softening pellets and struvite. These materials are considered low-cost, for being either a waste or by-product, or can be locally-sourced. It can be concluded that Ca-based materials showed the strongest affinity for F^- (Ca-Al-CO₃ LDHs, slag-based geopolymer, softening pellets). The Langmuir adsorption capacity of Ca-Al-CO₃ LDHs, slag-based geopolymer and softening pellets was observed to be 20.83, 5.23 and 1.20 mg/g, respectively. The main mechanism of F^- uptake on Ca-Al-CO₃ LDHs, Mg-Al-Cl LDHs, slag-based geopolymers and softening pellets was found to be sorption at low initial F^- concentrations (<10 mg/L) whereas precipitation as CaF₂ is proposed to play a major role at higher initial F^- concentrations (>20 mg/L). Although the softening pellets had the highest Ca-content (96-97%; XRF), their dense structure and consequent low BET surface area (2-3 m²/g), resulted in poorer performance than the Ca-based LDHs and slag-based geopolymers. Nevertheless, geopolymers, as well as struvite, were not considered to be of interest for application in water treatment, as they would need modification due to their poor stability and/or F^- leaching.

Sorption of Fluoride and Bacterial Disinfection Property of Biosynthesized Nanofibrous Cellulose Decorated Ag-MgO-Nanohydroxyapatite Composite for Household Water Treatment

An innovative and sustainable approach to integrating modified Ag–MgO–nanohydroxyapatite on a nanofibrous cellulose template (CNF-AgMgOnHaP) as a multifunctional adsorbent via a hydrothermal bioreduction route using Citrus paradisi peel extract was developed and examined. The surface morphology and mineralogical properties of CNF-AgMgOnHaP by UV–vis spectroscopy, SEM-EDS, XRD, FTIR, TEM, and BET techniques are reported. Batch fluoride sorption studies and its disinfection potential against common bacteria in surface water were evaluated. The results showed the successful synthesis of a modified multistructural CNF-AgMgOnHaP composite with an improved BET surface area of 160.17 m²/g. The sorption of fluoride by the adsorbent was found to strongly depend on the different sorption conditions with a maximum F⁻ sorption capacity of 8.71 mg/g at 303 K, and pH of 5 with 0.25 g dosage at 10 min contact time (25 ± 3 °C). Equilibrium fluoride sorption onto the CNF-AgMgOnHaP was best described by the Freundlich isotherm model across all the operating temperatures. The overall kinetic results showed that the adsorption mechanisms not only depend on using the pseudo-second-order process but are also governed by the mass transfer of the adsorbate molecules from the external surface onto the pores of the adsorbent. The thermodynamic parameters revealed that the adsorption process of F⁻ onto CNF-AgMgOnHaP was endothermic and spontaneous at the sorbent/solution interface. The synthesized composite also provides some antibacterial activity against common infectious microbes from contaminated drinking water. The overall results suggested that the CNF-AgMgOnHaP nanocomposite possesses the potential for the simultaneous decontamination of pollutants and microbes in drinking water.

Synthesis and evaluation of Ca-doped ferrihydrite as a novel adsorbent for the efficient removal of fluoride

Ferric hydrate has been extensively applied for the removal of various types of pollutants from wastewater because of its low cost and high efficiency. However, its wide-scale application has been greatly restricted by high-dose and low-adsorption capacity. Therefore, a novel Ca-doped ferrihydrite adsorbent has been synthesized and used for the enhanced removal of fluoride from wastewater in the presence of other co-existing ions. At 5 mg/L initial fluoride concentration and pH 5, the removal efficiency of fluoride approached to 97.5% and remained stable. Similarly, with the increase of dose from 100 to 300 mg/L, the fluoride removal linearly increased to 98% and remained plateau at neutral pH. Also, the presence of co-existing ions such as NO₃^-, SO₄^2-, Cl^-, and natural organic matter has not significantly influenced the removal performance of the adsorbent. Fluoride removal best fit the pseudo-second-order reaction kinetics and Langmuir isotherm model. The prepared adsorbent exhibited a maximum adsorption capacity of 53.21 mg/g for fluoride uptake from water. The SEM-EDX confirmed the doping of Ca onto the ferrihydrite where the elemental peaks of Ca and Fe emerged at the energy value of about 3.6 Kev and 7.1 Kev respectively in EDX analysis. In addition, SEM results of Ca-doped ferrihydrite adsorbent illustrated that a large microplates type of products was acquired after synthesis. The regeneration results confirmed that adsorbent could retain their original adsorption capacity after five regeneration cycles. The current study suggested that Ca-doped ferrihydrite has the application potential for the enhanced adsorption of fluoride from the water phase.

Controlled preparation of cerium oxide loaded slag-based geopolymer microspheres (CeO2@SGMs) for the adsorptive removal and solidification of F- from acidic waste-water

A new cerium oxide loaded slag-based geopolymer microspheres (CeO₂@SGMs) was prepared by a two-step i.e. dispersion-suspension-solidification and in-situ co-precipitation method. The optimal parameters for the preparation of 0.02CeO₂@SGMs were slag (30 g), 1.7 M water glass (12.86 g), water (8 g) and 0.02 mol/L of Ce⁴⁺. 0.02CeO₂@SGMs was characterized by SEM, XRD, BET, EDX, FTIR, XPS and PSD techniques. The leaching concentration of Ca²⁺ (95.65 mg/L) was only 1/5 of the SGMs at pH 2 after the modification of CeO₂. Adsorption data fitted well with Freundlich isotherm model suggesting multilayer adsorption mechanism with a maximum adsorption capacity for F^- by 0.02CeO₂@SGMs of 121.77 mg/g at 298 K. The negative values of thermodynamic parameters (ΔH⁰ and ΔS⁰) indicated the exothermic nature of the adsorption process with reduced chaos of the whole system. 0.02CeO₂@SGMs exhibited excellent dynamic adsorption performance at 4 mL/min F^- solution flow rate. The influence of various co-existing anions on adsorption of F^- over 0.02CeO₂@SGMs followed an order of: Cl^- ≈ NO₃^- < SO₄^2- << PO₄^3-. Attributed to the facile preparation process, cost-effectiveness and environmental friendliness, the newly designed 0.02CeO₂@SGMs can be deemed of promising industrial applications for the abatement of F^- from wastewater.

Glycerol mediated solution combustion synthesis of nano magnesia and its application in the adsorptive removal of anionic dyes

This study reports solution combustion synthesis of magnesia nanoparticles (nMgO) using magnesium nitrate as oxidiser and glycerol as fuel. Size, morphology, crystal structure and surface properties of synthesised nMgO were analysed by PXRD, SEM, TEM, FTIR and Point of Zero Charge. The XRD pattern of nMgO confirmed prepared samples were single cubic-phase without any impurities. TEM analysis proved nMgO was in nano regime with an average particle diameter of 20–40 nm. FTIR spectra show the presence of characteristic peaks of nMgO and support the XRD results. The prepared nMgO was employed as an adsorbent for the removal of two anionic dyes viz. Indigo Carmine (IC) and Orange G (OG). Furthermore, various adsorption isotherms and kinetic models were performed to understand the kinetics and mechanism of the adsorption process. Experimental results demonstrated that the adsorption equilibrium data fit well to Sips isotherm (R2 > 0.98) and the saturated adsorption capacities of nMgO were found to be 262 mg g−1 for IC and 126 mg g−1 for OG. Adsorption kinetics analysis revealed that the adsorption followed pseudo-first-order model, with both film and pore diffusion governing the rate of adsorption. Excellent adsorption capacity combined with efficient regeneration proved the potential of the prepared nMgO as an adsorbent for the removal of harmful dyes from industrial effluent.

Characterisation and utilisation of solid waste from coal combustion to modelling of sorption equilibrium in a bi-component system metal-dye

It was found that the chemical enhancement of fly ash from coal combustion by tetrabutylammonium bromide treatment yields an effective and economically feasible material for the treatment of chromium and basic dye Rhodamine B containing effluents. Characterisation of coal fly ash and treatment with tetrabutylammonium bromide were done by using a Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, confocal three-dimensional microscope, X-ray diffraction and laser particle sizer. The studies of equilibrium in a bi-component system by means of extended Langmuir, extended Langmuir-Freundlich and Jain-Snoeyink models were analysed. The estimation of parameters of sorption isotherms in a bi-component system metal-dye has shown that the best-of-fit calculated values of experimental data for both sorbates have been the Jain-Snoeyink model and the extended Langmuir model, but only in the case of a Rhodamine B. The maximum monolayer adsorption capacity of the fly ash-tetrabutylammonium bromide was found to be 863 mg g^-1 and 670 mg g^-1 for chromium and Rhodamine B, respectively.

Synthesis of MgO micro-rods coated with charred dextrose and its application for the adsorption of selected heavy metals from synthetic and real groundwater

MgO micro-rods supported on porous carbon were synthesized by an economical method and applied for the adsorption of three different heavy metals ions (As (III), Cd (II) and Pb (II)). Here, we used dextrose as the source of carbon during the synthesis. The synthesized material has been characterized by different techniques like XRD, TEM, FE-SEM, BET and FT-IR for the determination of various physical properties. Compared with MgO synthesized without dextrose, the carbon-supported MgO or C-MgO demonstrated consistent rod-shaped morphology, higher surface area and better absorptivity. The adsorption data were analysed using various isotherm models and the Freundlich isotherm model seemed to provide the best fit to the data. The adsorption kinetics data on the other hand was well explicated by the pseudo second-order kinetic model. The maximum adsorption capacity of C-MgO was 508.47 mg g^-1 for As (III), 566.01 mg g^-1 for Cd (II) and 476.19 mg g^-1 for Pb (II), respectively after 6 h of reaction. To check the real-life usability and efficiency of C-MgO, it was added to a groundwater sample which had 169.55 ppb of As (III) and within 20 min it was adsorbed with 99% efficiency. Reusability studies reveal that C-MgO could be used up to 6 times with more than 60% efficiency. This study shows that C-MgO has high adsorptive ability, is an economic and non-toxic material with versatile applications and can be used for groundwater remediation in real life.

Fluoride removal from water by composite Al/Fe/Si/Mg pre-polymerized coagulants: Characterization and application

Fluoride, an anionic pollutant, is possibly to be found in excessive concentrations especially in groundwaters and can show detrimental effects on human health, in concentrations higher than the commonly applied legislation limit of 1.5 mg/L The most commonly applied method for water de-fluoridation is performed by Al-based coagulants, which however presents some important limitations, such as the applied relatively high dosage, producing rather excessive amounts of chemical sludge. In this study, the use of novel pre-polymerized Al-based coagulants was examined, regarding their efficiency towards fluoride removal, as compared with the conventionally applied AlCl₃. The novel coagulants were characterized by measuring the main physico-chemical properties, the aluminum species distribution, the zeta potential, the particles' size distribution and the produced flocs' sizes. The results showed that the Mg-containing coagulant (PSiFAC-Mg_30-10-15) was the most efficient, when applied in pH values relevant to fluoride-containing groundwaters; it was also the only coagulant, which increases its efficiency at pH values > 7. The uptake capacity of coagulants, regarding fluoride, to reach the residual/equilibrium concentration limit of 1.5 mg F/L (Q_1.5-value) at the pH value 7.0 ± 0.1 were found 170, 134 and 94 mg F/g Al for the cases of PSiFAC-Mg_30-10-15, AlCl₃·6H₂O and PSiFAC-Na_1.5-10-15, respectively. Accordingly, at the pH value 7.8 ± 0.2 the Q_1.5-values were found 189, 118 and 41 mg F/g Al for the same coagulants; whereas considering the residual aluminum concentration this was ranged at 15 ± 5, 25 ± 5 and 30 ± 5 μg Al/L, respectively. In addition, (beneficial) increase of residual magnesium concentration, when applying the coagulant PSiFAC-Mg_30-10-15 was 15 ± 5 mg/L.

Potential use of ZnO@activated carbon nanocomposites for the adsorptive removal of Cd2+ ions in aqueous solutions

Nowadays, the pollution in water resources has become a major concern, both environmentally and in perspective of human health. The bioaccumulation of pollutants, especially heavy metal ions through the food chain, poses a hazardous risk to humans and other living organisms. Nanomaterials and their composites have been recognized for their potential to resolve such problems. Herein, ZnO nanoparticles were synthesized and characterized via different microscopic/spectroscopic techniques. ZnO nanoparticles (i.e., 20 to 50 nm) were obtained in high yield via a facile chemical approach. The ratio of ZnO nanoparticles and activated carbon was optimized to achieve enhanced electrostatic interactions for the effective adsorption of cadmium ions (Cd²⁺). The adsorptive performance of the nanocomposite was further assessed in relation to several key parameters (e.g., contact time, solution pH, and adsorbent/adsorbate dosage). The nanocomposites (1 mg/ml) offered amaximum adsorption capacity of 96.2 mg/g for Cd²⁺ ions as confirmed through adsorption isotherms for a best interpretation of the adsorption phenomenon. The favourable adsorption capacity of the synthesized ZnO/activated carbon (9:1) nanocomposites supported their use as an efficient sorbent material in practical performance metrics (e.g., partition coefficient of 0.54 mg g^-1μM^-1) for the adsorption of Cd²⁺ ions.

Enhanced distribution of humic acid-modified nanoscale magnesia for in situ reactive zone removal of Cd from simulated groundwater

Efficient injection and distribution of nanoparticles in porous media are considered a formidable technical hurdle for injection-based in situ remediation. One approach to enhance the mobility of nanoparticles in an aquifer is to use surface modifiers. In this study, nanoscale magnesia (NMgOs), an innovative and effective remedial material for cadmium (Cd) removal from groundwater, was modified with the negatively charged and eco-friendly humic acid to enhance its mobility in aquifers. A two-dimensional reactor (60 × 50 × 10 cm), with 2 injection wells and 30 monitoring wells was designed, constructed, and sand-packed in the laboratory to simulate a saturated aquifer. The simulated aquifer was pre-contaminated with Cd to simulate a plume in groundwater. The distribution of injected unmodified NMgOs and humic acid-modified NMgOs slurry were evaluated in the reactor. The radius of influence (ROI) of humic acid-modified NMgOs was estimated to be approximately 5 cm based on visual observation, while no ROI was apparent for the unmodified NMgOs because of their aggregation at the bottom of the injection wells. The concentrations of Cd and magnesium (Mg) were monitored in all 30 monitoring wells at different time intervals to evaluate the effectiveness of Cd removal. The breakthrough curve analysis revealed that humic acid enhances the transport of NMgOs in the saturated porous media. Furthermore, the results of scanning electron microscopy-energy dispersive x-ray (SEM-EDX) characterization of silica sand before and after injection of NMgOs verified the presence of 5.78% of Mg from humic acid-modified NMgOs and 0.19% from unmodified NMgOs at 35 cm downgradient of the injection wells, which are consistent with the conclusion drawn from the breakthrough curves.

Fluoride Removal from Aqueous Solutions Using Poly(Styrene Sulfonate)/Nanoalumina Multilayer Thin Films

In the present study, fluoride removal from drinking water is investigated using layer-by-layer (LbL) fabricated poly(sodium 4-styrene-sulfonate) (PSS)/Al2O3 thin films. The surface morphology of the fabricated thin films is characterized using atomic force microscopy and field emission-scanning electron microscopy. Optical profilometry is used to determine the self-assembly of the multilayer thin films. The effect of various parameters such as adsorbent dosage, contact time, initial fluoride content, number of bilayers, surface area, and pH is thoroughly studied. Fluoride removal increases with the number of bilayers and number of slides (total surface area). The amount of fluoride adsorbed increases from 11.32 to 26 mg L-1 when the number of substrates increases from 1 to 5. A 68% removal of fluoride is observed when 20 bilayers of PSS/Al2O3 thin films with three slides at an initial fluoride concentration of 5 mg L-1 are used, thereby bringing down the fluoride concentration level below the World Health Organization permissible limit. Slide reusability studies reveal that the fabricated thin films can be used for ten cycles without affecting the fluoride removal properties of the film. This study demonstrates the potential application of immobilized PSS/Al2O3 thin films as an effective adsorbent for drinking water purification.

A Comparative Study on Removal of Hazardous Anions from Water by Adsorption: A Review

This paper presents a comparative review of arsenite (As(III)), arsenate (As(V)), and fluoride (F−) for a better understanding of the conditions and factors during their adsorption with focus on (i) the isotherm adsorption models, (ii) effects of pH, (iii) effects of ionic strength, and (iv) effects of coexisting substances such as anions, cations, and natural organics matter. It provides an in-depth analysis of various methods of arsenite (As(III)), arsenate (As(V)), and fluoride (F-) removal by adsorption and the anions’ characteristics during the adsorption process. The surface area of the adsorbents does not contribute to the adsorption capacity of these anions but rather a combination of other physical and chemical properties. The adsorption capacity for the anions depends on the combination of all the factors: pH, ionic strength, coexisting substances, pore volume and particles size, surface modification, pretreatment of the adsorbents, and so forth. Extreme higher adsorption capacity can be obtained by the modification of the adsorbents. In general, pH has a greater influence on adsorption capacity at large, since it affects the ionic strength, coexisting anions such as bicarbonate, sulfate, and silica, the surface charges of the adsorbents, and the ionic species which can be present in the solution.

Comparison of adsorption of Cd(II) and Pb(II) ions on pure and chemically modified fly ashes

The study investigates chemical modifications of coal fly ash (FA) treated with HCl or NH4HCO3 or NaOH or Na2edta, based on the research conducted to examine the behaviour of Cd(II) and Pb(II) ions adsorbed from water solution on treated fly ash. In laboratory tests, the equilibrium and kinetics were examined applying various temperatures (293 - 333 K) and pH (2 - 11) values. The maximum Cd(II) and Pb(II) ions adsorption capacity obtained at 293 K, pH 9 and mixing time 2 h from the Langmuir model can be grouped in the following order: FA-NaOH > FA-NH4HCO3 > FA > FA-Na2edta > FA-HCl. The morphology of fly ash grains was examined via small-angle X-ray scattering (SAXS) and images of scanning electron microscope (SEM). The adsorption kinetics data were well fitted by a pseudo-second-order rate model but showed a very poor fit for the pseudofirst order model. The intra-particle model also revealed that there are two separate stages in the sorption process, i.e. the external diffusion and the inter-particle diffusion. Thermodynamics parameters such as free energy, enthalpy and entropy were also determined. A laboratory test demonstrated that the modified coal fly ash worked well for the Cd(II) and Pb(II) ion uptake from polluted waters.

Facile green fabrication of nanostructure ZnO plates, bullets, flower, prismatic tip, closed pine cone: Their antibacterial, antioxidant, photoluminescent and photocatalytic properties

Green synthesis of multifunctional Zinc oxide nanoparticles (NPs) with a variety of morphologies were achieved by low temperature solution combustion route employing neem (Azadirachta indica) extract as fuel. The nanoparticles were characterized by PXRD, FTIR, XPS, Raman and UV-Visible spectroscopic studies. The Morphologies were studied by SEM and TEM analysis. The NPs were subjected for photoluminescence, photocatalytic, antibacterial and antioxidant activity studies. PXRD pattern confirmed the hexagonal wurtzite structure of the product. SEM images indicated the transformation of mushroom like hexagonal disks to bullets, buds, cones, bundles and closed pine cone structured NPs with increase in the concentration of neem extract in reaction mixture. The NPs exhibited prominent green emission due to the presence of intrinsic defect centers. The as-formed bullet shaped ZnO with 4ml of neem extract was found to decolorize Methylene blue (MB) under Sunlight and UV light irradiation. The antibacterial studies indicated that ZnO NPs of concentration 500, 750 and 1000μg resulted in significant antibacterial activity on Klebsiella aerogenes and Staphylococcus aureus but not against Escherichia coli and Pseudomonas aeruginosa in agar well diffusion method. Further, ZnO NPs exhibited significant antioxidant activity against scavenging DPPH free radicals. The current investigation demonstrated green engineering method for the synthesis of multifunctional ZnO NPs with interesting morphologies using neem extract.

Simultaneous adsorptive removal of fluoride and phosphate by magnesia–pullulan composite from aqueous solution

The presence of fluoride and phosphate could affect the adsorption rate of another one while simultaneous adsorption on MgOP.

Low temperature synthesis of pure cubic ZrO2 nanopowder: structural and luminescence studies

Pure cubic zirconia (ZrO2) nanopowder is prepared for the first time by simple low temperature solution combustion method without calcination. The product is characterized by Powder X-ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infra Red spectroscopy (FTIR) and Ultraviolet-Visible spectroscopy (UV-Vis). The PXRD showed the formation of pure stable cubic ZrO2 nanopowders with average crystallite size ranging from 6 to 12 nm. The lattice parameters were calculated from Rietveld refinement method. SEM micrograph shows fluffy, mesoporous, agglomerated particles with large number of voids. TEM micrograph shows honey comb like arrangement of particles with particle size ∼10 nm. The PL emission spectrum excited at 210 nm and 240 nm consists of intense bands centered at ∼365 and ∼390 nm. Both the samples show shoulder peak at ∼420 nm, along with four weak emission bands at ∼484, ∼528, ∼614 and ∼726 nm. TL studies were carried out pre-irradiating samples with γ-rays ranging from 1 to 5 KGy at room temperature. A well resolved glow peak at 377 °C is recorded which can be ascribed to deep traps. With increase in γ radiation there is linear increase in TL intensity which shows the possible use of ZrO2 as dosimetric material.

Synthesis of Nanocrystalline MgO Particles by Combustion Followed by Annealing Method Using Hexamine as a Fuel

In this work, nanocrystalline MgO particles were prepared through combustion method using magnesium nitrate as oxidizer and hexamine as a fuel. The materials obtained by combustion method were subsequently annealed at800°Cfor 3 h to improve the crystallinity and phase purity. The obtained MgO nanomaterials were characterized by powder X-ray diffraction analysis (XRD), infrared (IR) spectroscopy, photoluminescence (PL), near-infrared (NIR) spectroscopy, and scanning electron microscopy (SEM). The cubic crystal structure with lattice parameter,a= 0.4210(4) nm with average crystalline size of 22 nm, is obtained for the nano-MgO particles. The PL emission spectrum of nanocrystalline MgO materials exhibits three emission peaks at 432, 465, and 495 nm which are due to various structural defects. The SEM results expose the fact that the MgO nanomaterials are seemingly porous and highly agglomerated with fine particles. Owing to the higher reflectance of prepared nanocrystalline MgO, it can be used as NIR reflective pigments. The present results prove that the combustion technique using hexamine can produce the materials with high crystallinity. To the best of our knowledge, this is the first report on the synthesis of nanocrystalline MgO materials by combustion method using hexamine as a fuel.

Sulfate-doped Fe3O4/Al2O3 nanoparticles as a novel adsorbent for fluoride removal from drinking water

A novel adsorbent of sulfate-doped Fe3O4/Al2O3 nanoparticles with magnetic separability was developed for fluoride removal from drinking water. The nanosized adsorbent was characterized and its performance in fluoride removal was evaluated. Kinetic data reveal that the fluoride adsorption was rapid in the beginning followed by a slower adsorption process, nearly 90% adsorption can be achieved within 20 min and only 10-15% additional removal occurred in the following 8 h. The fluoride adsorption isotherm was well described by Elovich model. The calculated adsorption capacity of this nanoadsorbent for fluoride by two-site Langmuir model was 70.4 mg/g at pH 7.0. Moreover, this nanoadsorbent performed well over a considerable wide pH range of 4-10, and the fluoride removal efficiencies reached up to 90% and 70% throughout the pH range of 4-10 with initial fluoride concentrations of 10 mg/L and 50 mg/L, respectively. The observed sulfate-fluoride displacement and decreased sulfur content on the adsorbent surface reveal that anion exchange process was an important mechanism for fluoride adsorption by the sulfate-doped Fe3O4/Al2O3 nanoparticles. Moreover, a shift of the pH of zero point charge (pHPZC) of the nanoparticles and surface analysis based on X-ray photoelectron spectroscopy (XPS) suggest the formation of inner-sphere fluoride complex at the aluminum center as another adsorption mechanism. With the exception of PO4(3-), other co-existing anions (NO3(-), Cl(-) and SO4(2-)) did not evidently inhibit fluoride removal by the nanoparticles. Findings of this study demonstrate the potential utility of the nanoparticles as an effective adsorbent for fluoride removal from drinking water.

A practical silver nanoparticle-based adsorbent for the removal of Hg2+ from water

In this work, we describe the use of silver nanoparticles of 9 ± 2 and 20 ± 5 nm core diameter, protected by mercaptosuccinic acid (MSA) and supported on activated alumina for the removal of mercuric ions present in contaminated waters, at room temperature (28 ± 1 °C). These two nanoparticle samples were prepared by using two Ag:MSA ratios 1:6 and 1:3, respectively, during synthesis and were loaded on alumina at 0.5 and 0.3% by weight. The mechanism of interaction of silver nanoparticles with Hg(2+) ions was studied using various analytical techniques such as ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DLS), inductively coupled plasma-optical emission spectrometry (ICP-OES), energy dispersive analysis of X-rays (EDAX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Interactions of the metal ion with the metal core, the surface head group and the monolayer functionality were investigated. A high removal ability of 0.8 g of mercury per gram of Ag@MSA was achieved in the case of 1:6 Ag@MSA. These two materials show better uptake capacity of Hg(2+) in the pH range of 5-6. The ease of synthesis of the nanomaterial by wet chemistry, capability to load on suitable substrates to create stable materials and affordable cost will make it possible to use this approach in field applications, especially for the treatment of Hg(2+) contaminated waters.

A novel cellulose-manganese oxide hybrid material by in situ soft chemical synthesis and its application for the removal of Pb(II) from water

We report an in situ soft chemical synthesis of a novel hybrid material, cellulose-nanoscale-manganese oxide composite (C-NMOC), and its application for Pb(II) removal from aqueous solutions. For comparison, detailed Pb(II) adsorption studies were also performed with nanoscale-manganese oxide powder (NMO), prepared through a similar route. Various spectroscopic and microscopic techniques were used to characterize the as-synthesized materials. X-ray photoelectron spectroscopic (XPS) measurements confirmed the existence of Mn(IV) phase in NMO whereas C-NMOC showed largely the Mn(III) phase. The existence and uniform distribution of manganese oxide in cellulose fiber materials was confirmed by SEM and EDAX analyses. The adsorption studies reveal that the Pb(II) uptake onto C-NMOC is a fast process and >90% of the uptake occurred within the first 10 min contact time. The Sips isotherm predicted the equilibrium data well and the maximum Pb(II) uptake capacity of C-NMOC (4.64% Mn loading) was estimated to be 80.1 mg g(-1). The Pb(II) adsorption capacity of C-NMOC (per gram of Mn present) was several times higher than commercial manganese oxide (beta-MnO2) and at least twice larger than NMO. The experimental evidence reveals that physisorption plays a dominant role in Pb(II) adsorption by both NMO and C-NMOC.