Three types of labeled silica nanoparticles were used in transport experiments in saturated sand. The goal of this study was to evaluate both the efficiency of labeling techniques (fluorescence (FITC), metal (Ag(0) core) and radioactivity (110mAg(0) core)) in realistic transport conditions and the reactive transport of silica nanocolloids of variable size and concentration in porous media. Experimental results obtained under contrasted experimental conditions revealed that deposition in sand is controlled by nanoparticles size and ionic strength of the solution. A mathematical model is proposed to quantitatively describe colloid transport. Fluorescent labeling is widely used to study fate of colloids in soils but was the less sensitive one. Ag(0) labeling with ICP-MS detection was found to be very sensitive to measure deposition profiles. Radiolabeled (110mAg(0)) nanoparticles permitted in situ detection. Results obtained with radiolabeled nanoparticles are wholly original and might be used for improving the modeling of deposition and release dynamics.

Adsorption of suspended particles to the interface of surfactant-dispersed oil droplets can alter emulsion phase and sedimentation behavior. This work examines the effects of model mineral aggregates (silica nanoparticle aggregates or SNAs) on the behavior of oil (octane)–water emulsions prepared using sodium bis(2-ethylhexyl) sulfosuccinate (DOSS). Experiments were conducted at different SNA hydrophobicities in deionized and synthetic seawater (SSW), and at 0.5mM and 2.5mM DOSS. SNAs were characterized by thermogravimetric analysis (TGA) and dynamic light scattering (DLS), and the emulsions were examined by optical and cryogenic scanning electron microscopy. In deionized water, oil-in-water emulsions were formed with DOSS and the SNAs did not adhere to the droplets or alter emulsion behavior. In SSW, water-in-oil emulsions were formed with DOSS and SNA–DOSS binding through cation bridging led to phase inversion to oil-in-water emulsions. Droplet oil-mineral aggregates (OMAs) were observed for hydrophilic SNAs, while hydrophobic SNAs yielded quickly sedimenting agglomerated OMAs.

The present study shows the current scenario of the aggregate relation between income and pollution at the household level. The indoor sampling of fine particulate matter was conducted in low– middle– and high–income group homes in Agra City, the North Central region of India. The mean indoor concentrations of PM2.5 were 46.7μg/m3, 39.2μg/m3 and 25.6μg/m3 in low– middle– and high–income group homes respectively. The full–day variation revealed that the concentrations of fine particles were higher during morning and evening hours in all the three income group homes. The indoor meteorological parameters were also monitored. Using scanning electron microscopy coupled with energy dispersive x–ray spectrometer (SEM–EDS) chemical and elemental analysis of fine particles and their probable sources has been conducted in low– middle– high–income group homes. EDS spectra indicates the elemental composition of PM2.5 which can be distributed into following groups of particles i.e. C–O rich (54%), F rich (42%) and other (4%) in low–income group homes. In middle– and high–income group homes F rich (59–65%), C–O rich (32–37%) and other (3–4%) were observed in PM2.5. The SEM images of fine particles indicates that the particles are clustered into following groups i.e. aluminosilicates/silica particles, spherical carbon rich particles, nearly spherical fluorine rich particles, Mg–Si or Mg–Si–Al particles.

A sorbent for oil spill cleanup was prepared through a novel strategy by treating polyurethane sponges with silica sol and gasoline successively. The oil sorption capacity, oil/water selectivity, reusability and sorption mechanism of prepared sorbent were studied. The results showed that the prepared sorbent exhibited high sorption capacity and excellent oil/water selectivity. 1g of the prepared sorbent could adsorb more than 100g of motor oil, while it only picks up less than 0.1g of water from an oil–water interface under both static and dynamic conditions. More than 70% of the sorption capacity remained after 15 successive sorption–squeezing cycles, which suggests an extraordinary high reusability. The prepared sorbent is a better alternative of the commercial polypropylene sorbent which are being used nowadays.

Recent scientific findings and legislations have clearly highlighted the need for comprehensive approaches and methods to evaluate natural dust contributions to an urban atmosphere. The evaluation of chemical compositions of airborne aerosols is of these methods that may employ several advanced analytical techniques and processes. In this paper, an episodic appearance of Saharan dust incursion over a megacity (Istanbul, Turkey) was investigated using size segregated particulate matter (PM) samples in fine and coarse fractions collected between February 27 and March 8, 2009. The Saharan impact was investigated using satellite observations, backward air trajectory statistics, and chemical analyses of the collected samples. In the chemical analyses, Fourier transform infrared coupled with attenuated total reflectance (ATR-FTIR) spectroscopic method was used to determine the functional groups, namely, alcohols, ammonium, aliphatic carbons, carbonyls, organonitrates, nitrate, silicate, silica, kaolinite, and calcium carbonate. Among all the measured functional groups, it was clearly seen that the intensities of IR peaks related to silicate, silica, kaolinite, and calcium carbonate were associated with the increased mass concentrations during the impact period. The observed IR peaks at 1,030 and 800 cm⁻¹for silicate ions in the samples can be used as an indicator of the large dust incursion into the atmosphere (e.g., Saharan dust episodes observed in Istanbul). This study showed that the ATR-FTIR spectroscopic method is a fast and convenient method to identify these peaks and the IR method in general is useful for identifying a large dust incursion into the atmosphere.

Adsorption and removal of cadmium ions from simulated industrial wastewater using hydrophilic and hydrophobic commercial silica nanoparticles are reported. These results are compared with those obtained using sol–gel silica nanoparticles. Two types of dense commercial pyrogenic silica nanoparticles with different chemical groups on the surface were used to adsorb cadmium ions: Aerosil A130VS and R972. The pore absence in these particles reduces the surface area and, consequently, the concentration of active chemical groups appropriated for adsorption, as compared with the sol–gel particles that are highly porous; this effect is partially compensated by the small sizes available for these commercial particles. The concentration of cadmium ions was reduced: from 109 to 0.01 ppm for A130VS, from 138 to 1.44 ppm for R972, and from 123 to 0.005 ppm for sol–gel. The flocculation kinetics was obtained using dynamic light scattering and the amount of adsorbed cadmium in the sediment using atomic absorption spectroscopy.

Corn cob silica (CCS), produced via a modification of the sol-gel method, can reduce heavy metal availability and stabilize contaminated soil on abandoned mining sites. Adding 5 % (w/w) CCS to mining site soil increased pH from 4.0 to 7.7, and cation exchange capacity increased from 94.5 to 100.3 cmol+/kg. Sequential extraction showed that adding CCS decreased heavy metal availability in the soil. Mobility factor (MF) values indicated that CCS reduced Pb mobility more than that of Zn or Cu in all fractions. Pb concentrations in leachate from all fractions using the toxicity characteristic leaching procedure (TCLP) were greatly decreased by adding 3 % (w/w) CCS. CCS similarly reduced Zn concentrations in TCLP leachate. CCS addition did not impact Cu concentrations in leachate, likely because concentrations were much lower than those of the other metals. As was generally less mobile than the heavy metals; however, As mobility and leachability tended to increase with CCS addition because its oxyanions arsenite and arsenate have low affinity for negatively charged surfaces on the CCS. Shoot and root growth of Spinacia oleracea L. (spinach) was much greater in CCS-treated soil than in unamended soil. Results demonstrate the utility of CCS to stabilize heavy metals in contaminated mining site soil, but this treatment may not be ideal for As-contaminated soils.

This paper reports about the modification of sand and fumed silica with titania in order to obtain a photocatalytic active material for the degradation of pollutants. The coating process was performed based on the sol–gel method. Tetrapropylorthotitanate was used as the titania precursor to apply a nanoscaled layer on sand grains. For silica fume, the coating process was varied. Various amounts of tetrapropylorthotitanate were used to obtain different coating thicknesses and to identify the maximum amount of titania that could be loaded on the material. All samples showed high photonic efficiencies in the degradation of nitrogen monoxide despite their low titania quantities, which were identified via x-ray fluorescence analysis. Some samples showed higher photonic efficiencies than commercial Degussa P25. Due to the preparation method, calcination of the sand composites was not necessary to yield a crystalline coating which was responsible for the high photocatalytic activity. However, silica fume composites had to be calcined possibly due to variation in the preparation method. Scanning electron micrographs revealed the structured morphology of all specimens. Energy dispersive x-ray analysis identified nanoscaled titania particles on the sand surface that could not be observed only via SEM. The results of this research are especially interesting for large scale applications of photocatalysts. As industrial sand and silica fume used are low cost materials, this new kind of photocatalyst can be applied in higher quantities and distributed onto larger areas, while saving costs at the same time.

Amorphous tin(IV) hydrogen phosphate immobilized on silica (ATHPS) was investigated as an adsorbent for the removal of Pb(II), Cu(II), and Zn(II) from aqueous solutions to determine its applicability in remediation of heavy-metal contaminated saline water. The effect of pH, contact time, initial concentration of heavy metal ions, and salinity on adsorption was studied using a batch method. Equilibrium data were interpreted in terms of Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models. The Freundlich model provided the best fit to the equilibrium data. The selectivity sequence can be given as Pb(II) > Cu(II) > Zn(II). The kinetic data correspond well to the pseudo-second-order and Elovich models. The thermodynamic parameters (i.e., ΔG ⁰, ΔH ⁰, ΔS ⁰) were evaluated to predict the nature of adsorption process. The negative ΔG ⁰ values at various treatment temperatures for each ion indicate that the adsorption processes are spontaneous and endothermic in nature. The ATHPS material can be regenerated, and the adsorption capacity in model seawater is acceptable, although a higher ionic strength can inhibit adsorption. These results show the great potential of ATHPS in removing cationic heavy metal ions from saline water.

The present study deals with the synthesis and subsequent application of Fe₃O₄@n-SiO₂nanoparticles for the removal of Cr(VI) from aqueous solutions. Rice husk, an agrowaste material, was used as a precursor for the synthesis of nanoparticles of silica. Synthesized nanoparticles were characterized by XRD and SEM to investigate their specific characteristics. Fe₃O₄@n-SiO₂nanoparticles were used as adsorbent for the removal of Cr(VI) from their aqueous solutions. The effects of various important parameters, such as initial Cr(VI) concentration, adsorbent dose, temperature, and pH, on the removal of Cr(VI) were analyzed and studied. A pH of 2.0 was found to be optimum for the higher removal of Cr(VI) ions. It was observed that removal (%) decreased by increasing initial Cr(VI) concentration from 1.36 × 10⁻²to 2.4 × 10⁻² M. The process of removal was found to be endothermic, and the removal increased with the rise in temperature from 25 to 45 °C. The kinetic data was better fitted in pseudo-second-order model in comparison to pseudo-first-order model. Langmuir and Freundlich adsorption capacities were determined and found to be 3.78 and 1.89 mg/g, respectively, at optimum conditions. The values of ΔG⁰were found to be negative at all temperatures, which confirm the feasibility of the process, while a positive value of ΔH⁰indicates the endothermic nature of the adsorption process. The present study revealed that Fe₃O₄@n-SiO₂nanoparticles can be used as an alternate for the costly adsorbents, and the outcome of this study may be helpful in designing treatment plants for treatment of Cr(VI)-rich effluents.