Electrolyte ion effects on Cd2+ binding at Al2O3 surface: specific synergism versus bulk effects

Influences of dissolved organic matters on the adsorption and bioavailability of sulfadiazine: Molecular weight- and type-dependent heterogeneities

The bioavailability of contaminants in aquatic environments was highly related with the existing forms (soluble or adsorbed) and properties of dissolved organic matters (DOMs). In this study, the molecular weight (MWs)-dependent effects of DOMs on the adsorption and bioavailability of sulfadiazine were explored. Colloid ZnO and Al2O3 were employed as the representative colloidal particles, and algae-derived organic matter (AOM) and humic acid (HA) were selected as typical autochthonous and allochthonous DOMs. The ultrafiltration procedure was applied to divide the bulk DOMs into high MW (HMW-, 1 kDã0.45 μm) and low MW (LMW-, <1 kDa) fractions. Results showed that HMW-DOM contained more aromatic and protein-like substances as compared to the LMW counterparts. In addition, presence of AOM promoted sulfadiazine adsorption capabilities by 1.19-4.54 folds and mitigated the inhibition ratio by 0.56-0.78 folds, whereas those of HA inhibited sulfadiazine adsorption by 0.27-0.84 folds and enhanced the biotoxicity by 1.21-1.45 folds. Regardless of different DOM types, HMW-fraction exhibited highest effects on sulfadiazine adsorption and bioavailability, followed by the bulk- and LMW-fractions. Two-dimensional correlation spectroscopy showed that sulfadiazine was adsorbed on colloidal surfaces prior to AOM, and the subsequent adsorption of AOM can provide additional sites for sulfadiazine adsorption, which decreased the concentrations of aqueous sulfadiazine as well as the biotoxicity to Microcystis aeruginosa (M. aeruginosa). The HA, however, was preferentially adsorbed on colloidal surfaces, which hindered the subsequent sulfadiazine adsorption and resulted in a high sulfadiazine abundance in aqueous solution as well as the enhanced biotoxicity to M. aeruginosa. This study highlighted the importance of the types and MWs of DOMs in influencing the behaviors and ecological effects of aquatic contaminants.

Understanding fluoride adsorption from groundwater by alumina modified with alum using PHREEQC surface complexation model

Fluoride is recognized as a vital ion for human and animal growth because of the critical role it plays in preventing skeletal and dental problems. However, when it is ingested at a higher concentration it can cause demineralization of teeth and bones resulting in fluorosis, therefore, the production of high-adsorptive capacity material which is also cost-effective is necessary for the treatment of fluorides. In this study, aluminium foil is valorised into alumina nanoparticles. The as-prepared alumina was modified with alum in two different ratios of 1:0.5 and 1:1 (alumina to alum w/w%) and later used as adsorbents for the removal of fluoride from groundwater. The adsorbents were characterized by Fourier transform infrared spectroscopy, point of zero charge and X-ray diffraction. Different factors that influence the removal efficiency of fluorides such as pH, initial concentrations, contact time and adsorbent dosage were studied and optimized using a simulated fluoride solution. The optimum conditions obtained were used to test real groundwater. The static experiment conditions were used to calibrate a PHREEQC geochemical model which was later used to simulate the fluoride sorption onto the modified alumina at different conditions. PHREEQC was also coupled with parameter estimation software to determine equilibrium constants for the surface reactions between the fluoride species and the adsorbent in a way that the simulations accurately reflect the outcomes of laboratory experiments. Isotherm studies were carried out on the adsorbents. Both Langmuir and Freundlich's non-linear models fitted well for the equilibrium data. However, with a higher coefficient of regression and low chi-square test values, the adsorption process was more of chemisorption on a monolayer surface. Kinetic studies were also carried out by using the non-linear equations from the pseudo-first-order and pseudo-second-order models. The pseudo-second-order model fitted well for the equilibrium data. The mechanism for the fluoride ion adsorption was also studied by the intraparticle (IP) diffusion model and was found that IP was not the rate-determining factor, and therefore the most plausible mechanism for the sorption process was ion exchange or attraction of fluoride ions to the sorbent surface. The findings obtained from this research show that readily available aluminium waste could be valorised into a useful product that could be employed in the removal of fluoride from water samples, including groundwater, that may contain too much fluoride and pose a risk to the general public's health.

Assessing Spatial Variability of Soil Properties in Mediterranean Smallholder Farming Systems

Smallholder farming systems are typical of the European Mediterranean region. Small farms of less than 2 hectares cover approximately 15% of cropland in the southern EU and only 5% across the EU. The greater variability of cultivated species per unit of cropland (ha), the different approaches, and empirical application of cultivation practices by smallholder farmers increase the spatial variability of soil properties. Therefore, a decision support tool for effective management practices was formed based on a soil indicators set, which is sensitive to changes under agricultural management practices and different LUs. The data for this task were collected from 364 crop fields. The data were clustered and correlated based on (a) the existing soil units (SU): Fluvisols, Cambisols, Luvisols, and Calcisols, and (b) the LU: pastureland, annual, and permanent crops. Principal component analysis (PCA) identified up to seven main components that can better explain soil variability properties. The results indicated that the selected soil indicators can explain only 70.98% of soil variability. Clustering the parameters based on LU and SU can explain up to 80% and 82% of soil properties’ variability, respectively. Factor analysis could function as a decision support tool for soil fertility management by farmers or policy makers, who aim to achieve higher yields, promote sustainable practices, maintaining, at the same time, a low cost of cultivation.

Effect of land-use types on edaphic properties and plant species diversity in Mediterranean agroecosystem

Land-use intensification, contrary to sustainable land management, has an impact on the healthiness of the environmental agroecosystem. To assess the environmental implications in abandoned land, olive groves and maize crops, the most sensitive and reliable edaphic indicators were measured to estimate plant species diversity and potentially toxic elements in soil, among different types of land-use. Species diversity presents a decrease in maize crops and olive groves compared to abandoned land. The families with the greatest species diversity were Poaceae, Asteraceae and Fabaceae in each land-use. From the results of the canonical correspondence analysis among species, sampling sites and selected environmental variables, a clear separation between species and sampling sites belonging to different types of land-use was found, presenting strong correlation with specific edaphic parameters (pH, Soil Organic Matter, Silt, Electrical Conductivity, Total Nitrogen, NO3-, P, K, Zn and Cu). Species diversity was reduced in maize crops due to anthropogenic interventions such as the excessive use of nitrogen and phosphate fertilizers and herbicides. Despite the fact that the lowest richness of plant species was found in olive groves, non-removal of crop residue preserves soil organic matter. In 7.4% of soil samples in olive groves, Cutotal concentrations were over 100 mg kg⁻¹ denoting polluted soils, while the potentially toxic concentrations of bioavailable copper fraction (CuDTPA) probably lead to a decrease of species diversity. Future researches should therefore focus on the accumulation of toxic elements in agricultural land to preserve species diversity and a healthy environment.

The interaction of metallic ions onto activated carbon surface using computational chemistry software

Activated carbon was prepared from the seeds of aguaje palm ( Mauritia flexuosa L.f.) by a chemical activation with phosphoric acid. This activated carbon was used for adsorbing metal ions: Pb(II), Cd(II), and Cr(III). To understand the mechanism of adsorption of these heavy metals (Cr, Cd, and Pb), the activated carbon surface was oxidized with nitric acid (1 M) increasing the oxygenated surface groups showing an increasing in their adsorption capacities of these metals. The oxidized activated carbon slightly increased the maximum adsorption capacity to 5–7%. The order of adsorption for unoxidized and oxidized activated carbons was Pb> Cd> Cr. This experimental information was corroborated by molecular modeling program Hyperchem 8 based adsorption mainly on two factors: the electron density and orbitals—highest occupied molecular orbital and lowest unoccupied molecular orbital.Activated carbons were characterized by adsorption/desorption of N2, obtaining an increase of microporous surface area for oxidized activated carbon. An increase of surface acidity and a reduction of isoelectric points were observed in oxidized activated carbon. According to these results, the adsorption of metal ions is favored in contact with an oxidized activated carbon, which has more amount of phenolic and carboxylic functional groups. Similarly, decreasing the isoelectric point indicates that the surface has a higher negative charge. The surface information was corroborated by Hyperchem, which indicates that the surface of the oxidized activated carbon has a higher electron density, indicating a larger amount of electrons on its surface, which means the surface of oxidized activated carbon charges negatively and thereby attracts metal ions.

The effect of chelating anions on the retention of Co(II) by γ-alumina from aqueous solutions under the unadjusted pH condition of supported catalyst preparation

This study analyzes the effect of the addition of acetate, citrate, and nitrilotriacetate anions on the retention of Co(II) cations by the γ-alumina surface in view of the preparation of alumina supported cobalt catalysts. The emphasis was placed on the way the Co(II) species attach to the solid surface when adsorbed from aqueous solutions under the unadjusted pH condition. The individual adsorption isotherms onto γ-Al₂O₃ support for cobalt and a given ligand were determined by following the solution depletion method in single-solute and bi-solute systems. These adsorption data were supplemented by the results of potentiometric titrations. In the case of bi-solute systems, the adsorption procedures allowed either co-impregnation of γ-alumina with equimolar solutions of cobalt and ligand salts or pre-impregnation of γ-alumina with the ligand anions and the subsequent adsorption of cobalt. Changes in the pH of the equilibrium solid-liquid suspension were also monitored along the adsorption isotherms. The adsorption of Co(II) onto γ-Al₂O₃ in the presence of acetate and nitrilotriacetate led to the formation of the type A (i.e., solid-metal-ligand) ternary complexes. The use of citrate anions together with Co(II) cations was shown to improve the impregnation process through the formation of ternary complexes of type B (i.e., solid-ligand-metal). The comparison with a system containing tricarballylate anions allowed concluding that the presence of the hydroxyl group in the citrate anion enhanced its affinity for the alumina surface by contributing to the inner-sphere character of its surface-bound complexes.

The molecular properties of biochar carbon released in dilute acidic solution and its effects on maize seed germination

It is not yet clear whether the carbon released from biochar in the soil solution stimulates biological activities. Soluble fractions (AQU) from wheat and maize biochars, whose molecular content was thoroughly characterized by FTIR, ¹³C and ¹H NMR, and high-resolution ESI-IT-TOF-MS, were separated in dilute acidic solution to simulate soil rhizospheric conditions and their effects evaluated on maize seeds germination activity. Elongation of maize-seeds coleoptile was significantly promoted by maize biochar AQU, whereas it was inhibited by wheat biochar AQU. Both AQU fractions contained relatively small heterocyclic nitrogen compounds, whose structures were accounted by their spectroscopic properties. Point-of-Zero-Charge (PZC) values and van Krevelen plots of identified masses of soluble components suggested that the dissolved carbon from maize biochar behaved as humic-like supramolecular material capable to adhere to seedlings and deliver bioactive molecules. These findings contribute to understand the biostimulation potential of biochars from crop biomasses when applied in agricultural production.

pH-dependent surface charging and points of zero charge. IV. Update and new approach

The recently published points of zero charge (PZC) and isoelectric points (IEPs) of various materials are compiled to update the previous compilation [M. Kosmulski, Surface Charging and Points of Zero Charge, CRC Press, Boca Raton, FL, 2009]. Unlike in previous compilations by the same author [Chemical Properties of Material Surfaces, Dekker, New York, 2001; J. Colloid Interface Sci. 253 (2002) 77; J. Colloid Interface Sci. 275 (2004) 214; J. Colloid Interface Sci. 298 (2006) 730], the materials are sorted not only by the chemical formula, but also by specific product, that is, by brand name (commercially available materials), and by recipe (home-synthesized materials). This new approach indicated that the relatively consistent PZC/IEP reported in the literature for materials having the same chemical formula are due to biased choice of specimens to be studied. Specimens which have PZC/IEP close to the "recommended" value are selected more often than other specimens (PZC/IEP not reported before or PZC/IEP reported, but different from the "recommended" value). Thus, the previously published PZC/IEP act as a self-fulfilling prophecy.