A 'green' adsorbent: effect of chemical modification of biosorbents on the adsorption of methylene blue and malachite green.

The dyes methylene blue and malachite green were adsorbed onto the as-prepared and chemically-modified biosorbents obtained from the mesocarp of crushed calabash (Lagenaria siceraria). The aim was to investigate the adsorption capacity of the natural biosorbent, neutralized biosorbent (0.1 mol L-1 NaOH, followed by 0.1 mol L-1 HCl), acid biosorbent (0.1 mol L-1 HCl) and basic biosorbent (0.1 mol L-1 NaOH). The maximum adsorption capacities for methylene blue were, in ascending order: 11.37 mg g-1 for acid biomass < 11.87 mg g-1 for basic biomass < 16.55 mg g-1 for neutralized biomass < 18.83 mg g-1 for natural biomass. In ascending order, for malachite green the maximum adsorption capacities were: 12.80 mg g-1 for basic biomass < 13.31 mg g-1 for acid biomass < 18.74 mg g-1 for natural biomass < 19.67 mg g-1 for neutralized biomass. A comparison of the thermodynamic parameters Gibbs free energy, enthalpy and entropy obtained for the natural biosorbent with those obtained for the chemically-modified biosorbents indicated that the chemical modification proposed led to a change in the materials. The removal capacity, the Freundlich isotherms and the pH of the biosorbents underwent changes with the chemical modification carried out, promoting a novel approach for the use of this biosorbent.

Evaluation of PAH contamination in soil treated with solid by-products from shale pyrolysis.

The aim of this work was to evaluate the concentrations of polycyclic aromatic hydrocarbons (PAHs) in soils to which solid shale materials (SSMs) were added as soil conditioners. The SSMs were derived from the Petrosix pyrolysis process developed by Petrobras (Brazil). An improved ultrasonic agitation method was used to extract the PAHs from the solid samples (soils amended with SSMs), and the concentrations of the compounds were determined by gas chromatography coupled to mass spectrometry (GC-MS). The procedure provided satisfactory recoveries, detection limits, and quantification limits. The two-, three-, and four-ring PAHs were most prevalent, and the highest concentration was obtained for phenanthrene (978 ± 19 µg kg(-1) in a pyrolyzed shale sample). The use of phenanthrene/anthracene and fluoranthene/pyrene ratios revealed that the PAHs were derived from petrogenic rather than pyrogenic sources. The measured PAH concentrations did not exceed national or international limit values, suggesting that the use of SSMs as soil conditioners should not cause environmental damage.

Preferential solvation bromophenol blue in water-alcohol binary mixture.

In this study, the perichromic behavior of bromophenol blue (BPB) in various binary solvent mixtures was investigated. The binary mixtures considered were comprised of water and methanol (MeOH), ethanol (EtOH), n-propanol (n-PrOH), isopropanol (iso-PrOH) or t-butanol (t-BuOH). The investigation of a preferential solvation model that considers the addition of small quantities of alcohol to water in the presence of bromophenol blue (BPB) is described in this paper. The data obtained were employed to study the preferential solvation (PS) of the probe. It was observed that with increases in the molar fraction of water the spontaneity of the system decreases. This can be explained by the high solubility of BPB in ethanol, with ∆G > 0 at higher wavelengths (region rich in water with violet solution) and ∆G < 0 at lower wavelengths (region rich in alcohol with yellow solution). The pK of the binary mixture changed in all solvents and for all ratios, and the higher the water ratio is the lower the pKIn will be. In binary mixture, an increase in the hydrogen bond acceptor (HBA) nature of the solvents tested resulted in a bathochromic effect on the absorption band of BPB (Δλ = 12 nm). All of the data obtained showed a good nonlinear fit with the mathematical model (SD ≤ 6.6 × 10-3), suggesting that BPB has other potential applications besides its use as a pH indicator.