Heather J. Shipley

Inorganic nano-adsorbents for the removal of heavy metals and arsenic: a review

Adsorption is widely popular for removal of heavy metals due to its low cost, efficiency, and simplicity. The focus of this review will be the use of inorganic adsorbents engineered at the nanoscale. The applicability of iron oxide (hematite, magnetite and maghemite), carbon nanotubes (CNT), and metal oxide based (Ti, Zn) and polymeric nanoadsorbents are examined. The advantages and limitations of the type of nanoadsorbent and its functionality are evaluated. Current developments and next generation adsorbents are also reviewed. Finally, scopes and limitations of these adsorbents will be addressed while investigating the types of metal ions that are harmful.

Adsorption of arsenic to magnetite nanoparticles: effect of particle concentration, pH, ionic strength, and temperature.

Little work has been conducted on the adsorption of arsenic to the mixed iron [Fe(II)/(III)] oxide magnetite and the effect that environmental parameters, such as pH, ionic strength, and temperature, have on adsorption. Magnetite nanoparticles are unique because of their affinity for both arsenate and arsenite and increased adsorption capacity from their bulk counterparts. This article shows the effect of various magnetite nanoparticle concentrations on arsenic adsorption kinetics. The adsorption data show the ability of the magnetite nanoparticles to remove arsenate and arsenite from solution in both synthetic and natural waters, and the data fit a first-order rate equation. Because of the increased surface area of these particles, less than 1 g/L of magnetite nanoparticles was needed. The results suggest that arsenic adsorption to the nanoparticles was not significantly affected by the pH, ionic strength and temperature in the ranges tested, which are typical of most potable water sources.

Adsorption and desorption of bivalent metals to hematite nanoparticles

The use of commercially prepared hematite nanoparticles (37.0 nm) was studied as an adsorbent in the removal of Cd(II), Cu(II), Pb(II), and Zn(II) from aqueous solutions. Single-metal adsorption was studied as a function of metal and adsorbent concentrations, whereas binary metal competition was found to be dependent on the molar ratio between the competing metals. Competitive effects indicated that Pb had strong homogenous affinity to the nanohematite surface, and decreased adsorption of Cd, Cu, and Zn occurred when Pb was present in a binary system. Metal adsorption strength to nanohematite at pH 6.0 increased with metal electronegativity: Pb > Cu > Zn ∼ Cd. Equilibrium modeling revealed that the Langmuir-Freundlich composite isotherm adequately described the adsorption and competitive effects of metals to nanohematite, whereas desorption was best described by the Langmuir isotherm. The desorption of metals from nanohematite was found to be pH dependent, with pH 4.0 > pH 6.0 > pH 8.0, and results showed that greater than 65% desorption was achieved at pH 4.0 within three 24-h cycles for all metals.

A sorption kinetics model for arsenic adsorption to magnetite nanoparticles

IntroductionArsenic is a well known water contaminant that causes toxicological and carcinogenic effects. In this work magnetite nanoparticles were examined as possible arsenic sorbents. The objective of this work was to develop a sorption kinetics model, which could be used to predict the amount of arsenic adsorbed by magnetite nanoparticles in the presence of naturally occurring species using a first-order rate equation, modified to include adsorption, described by a Langmuir isotherm.DiscussionArsenate and arsenite adsorption to magnetite nanoparticles was studied, including the effect of naturally occurring species (sulfate, silica, calcium magnesium, dissolved organic matter, bicarbonate, iron, and phosphate) on adsorption.ConclusionThe model accurately predicts adsorption to magnetite nanoparticles used in a batch process to remove arsenic from spiked Houston, TX tap water, and contaminated Brownsville, TX groundwater.

Transport of aluminum oxide nanoparticles in saturated sand: Effects of ionic strength, flow rate, and nanoparticle concentration

The effect of ionic strength (IS), flow rate, and nanoparticle concentration on the transport and deposition of aluminum oxide nanoparticles (Al2O3 NPs) in saturated sand was investigated. Mobility of Al2O3 NPs was influenced by IS, the highest mobility was observed in DI water (97% elution of the influent) and decreased with increasing ionic strength. Decreased mobility of the NPs was due to aggregation as the IS increased. Varying flow conditions did not have a significant effect on mobility. However, increased and faster elution was observed when the influent concentration was increased from 50 mg/L to 400 mg/L. The influent and effluent nanoparticle sizes were also measured using dynamic light scattering. For most conditions, the size was observed to be below 100 nm and there was no significant change to the influent and effluent particle sizes. Significant elution was observed although conditions were electrostatically favorable, which was attributed to the small, stable size (~82 nm) of the particles and blocking. DLVO theory was also applied to the data to better understand the mechanisms of mobility. It is necessary to consider these mechanisms for a reliable prediction of transport through the subsurface and potential removal methods such as filtration.

Excretion and toxicity of gold–iron nanoparticles

UNLABELLED Though gold nanoparticles have been considered bio-inert, recent studies have questioned their safety. To reduce the potential for toxicity, we developed a nanoclustering of gold and iron oxide as a nanoparticle (nanorose) which biodegrades into subunits to facilitate rapid excretion. In this present study, we demonstrate acid and macrophage lysosomal degradation of nanorose via loss of the near-infrared optical shift, and clearance of the nanorose in vivo following i.v. administration in C57BL/6 mice by showing gold concentration is significantly reduced in 11 murine tissues in as little as 31 days (P < 0.01). Hematology and chemistry show no toxicity of nanorose injected mice up to 14 days after administration. We conclude that the clustering design of nanorose does enhance the excretion of these nanoparticles, and that this could be a viable strategy to limit the potential toxicity of gold nanoparticles for clinical applications. FROM THE CLINICAL EDITOR The potential toxicity of nanomaterials is a critically important limiting factor in their more widespread clinical application. Gold nanoparticles have been classically considered bio-inert, but recent studies have questioned their safety. The authors of this study have developed a clustering gold and iron oxide nanoparticle (nanorose), which biodegrades into subunits to facilitate rapid excretion, resulting in reduced toxicity.

Evaluation of desorption of Pb (II), Cu (II) and Zn (II) from titanium dioxide nanoparticles

The adsorption-desorption of toxic compounds onto engineered nanoparticles is an important process that governs their potential as sorbents for treatment applications, their toxicity and their environmental risks. This study was aimed to investigate the desorption of Pb (II), Cu (II) and Zn (II) from commercially prepared nano-TiO(2) (anatase) using batch techniques, with the evaluation of isothermal, kinetic and thermodynamic properties. Results showed that desorption was pH dependent and that more than 98% of all metals desorbed at pH 2. Short term kinetic studies were fit with a pseudo second order model and showed that a significant amount of desorption occurred in the first fifteen minutes. Surface complexation modeling determined a trend of adsorption affinity to be Pb > Zn > Cu and with adjustable surface complexation constant (K(int)) provided good fit to the experimental data. The thermodynamic studies found that desorption was exothermic and non-spontaneous in most cases. The XPS study showed that no change in oxidation state occurred due to desorption and suggested that Pb desorption was due to inner-sphere surface complexation. The results suggest three important points that will improve the capabilities of researchers to understand Pb (II), Cu (II) and Zn (II) adsorption-desorption to nano-TiO(2): (1) the desorption of metals was enhanced at lower pH values suggesting its potential to be regenerated for treatment applications; (2) the possible mechanism for adsorption-desorption varies for different metals; and (3) nano-TiO(2) could interact with metals in the environment if released due to their high sorption capacity and reversible adsorption at lower pH values which could affect the fate and behavior of metals in the environment and enhance nanoparticle toxicity.

Modeling and sensitivity analysis on the transport of aluminum oxide nanoparticles in saturated sand: Effects of ionic strength, flow rate, and nanoparticle concentration

Aluminum oxide nanoparticles have been widely used in various consumer products and there are growing concerns regarding their exposure in the environment. This study deals with the modeling, sensitivity analysis and uncertainty quantification of one-dimensional transport of nano-sized (~82 nm) aluminum oxide particles in saturated sand. The transport of aluminum oxide nanoparticles was modeled using a two-kinetic-site model with a blocking function. The modeling was done at different ionic strengths, flow rates, and nanoparticle concentrations. The two sites representing fast and slow attachments along with a blocking term yielded good agreement with the experimental results from the column studies of aluminum oxide nanoparticles. The same model was used to simulate breakthrough curves under different conditions using experimental data and calculated 95% confidence bounds of the generated breakthroughs. The sensitivity analysis results showed that slow attachment was the most sensitive parameter for high influent concentrations (e.g. 150 mg/L Al2O3) and the maximum solid phase retention capacity (related to blocking function) was the most sensitive parameter for low concentrations (e.g. 50 mg/L Al2O3).

Evaluation of hydrogen sulphide concentration and control in a sewer system

This study focused on monitoring hydrogen sulphide (dissolved and atmospheric) generation and wastewater volumetric flow in a 21.4 km sewer line of the City of San Antonio, Texas. The results were used to evaluate daily and seasonal trends of atmospheric and dissolved sulphide, and to better apply sulphide control using ferrous sulphate to prevent odour and sewer pipe deterioration. As part of this study, the evaluation of a cost-effective dosing strategy with ferrous sulphate was performed to better control the sulphide contents in wastewater. Dosing studies were performed in the laboratory to find the required ratio of ferrous sulphate for acceptable sulphide removal. The results indicate a 1.25 mole ratio requirement, to reduce sulphide by 93%. Over a typical daily diurnal cycle, necessary dosing rates to maintain sulphide concentrations below 2 mg varied between 0 and 36,777 mol d−1 with a daily average rate of 14,438 mol d−1. If, instead of dosing at the maximum required rate, dosing was matched over the diurnal cycle, chemical savings would amount to 22,339 mol d−1 while achieving sulphide control. The approximate cost of the ferrous sulphate solution dosed is

Identification of a new high-molecular-weight Fe−citrate species at low citrate-to-Fe molar ratios: Impact on arsenic removal with ferric hydroxide

0.14 per mol and this amount of chemical savings translates into roughly