RESUMO
Microplastics (MP) have received great attention due to the mass-produced residues discharged into the environment. MP are ideal for adhering to organic pollutants that can be easily dispersed, thus posing risks to human health. Furthermore, little has been reported on how different functional groups in polycyclic aromatic hydrocarbons (PAH) derivatives influence the adsorption behavior on MP. To better understand this process, groups methyl (-CH3) and hydroxyl (-OH) were selected and commercial and waste high-density polyethylene (HDPE, ≤ 1 mm) were used as adsorbents, and Naphthalene (Nap), 1-Methyl-Naphthalene (Me-Nap) and α-Naphthol as adsorbates. The results showed different behaviors for nonpolar and polar adsorbates. Dispersion forces were the main type of interaction between HDPE and Nap/Me-Nap, while dipole-induced dipole forces and H-bonding were the chief interactions involving MP and polar compounds. Regardless the HDPE source, Nap and Me-Nap have a Type III isotherm, and α-Naphthol presents a Type II isotherm. Nap and Me-Nap fitted to Freundlich isotherm of an unfavorable process (n = 2.12 and 1.11; 1.87 and 1.31, respectively), with positive values of ΔH° (50 and 77.17; 66 and 64.63 kJ mol-1) and ΔS° (0.070 and 0.0145; 0.122 and 0.103 kJ mol-1) for commercial and waste MP, respectively. Besides, the adsorption isotherm of α-Naphthol on commercial and waste HDPE fitted to the Langmuir model (Qmax = 42.5 and 27.2 µmol g-1, respectively), presenting negative values of ΔH° (-43.71 and -44.10 kJ mol-1) and ΔS° (-0.037 and -0.025 kJ mol-1). The adsorption kinetic study presents a nonlinear pseudo-second-order model for all cases. The K2 values follow the order Me-Nap > Nap > α-Naphthol in both MP. Therefore, this experimental study provides new insights into the affinity of PAH derivatives for a specific class of MP, helping to understand the environmental fate of residual MP and organic pollutants.
Assuntos
Poluentes Ambientais , Hidrocarbonetos Policíclicos Aromáticos , Poluentes Químicos da Água , Humanos , Microplásticos/química , Plásticos , Polietileno , Adsorção , Poluentes Químicos da Água/análise , Naftalenos/química , Termodinâmica , Hidrocarbonetos Policíclicos Aromáticos/análise , Cinética , Concentração de Íons de HidrogênioRESUMO
Removal of Cr(VI) from the aqueous phase using numerous activated carbons (AC) has been broadly studied in the last decades. Nevertheless, the diversity of activation methods, AC properties, and adsorption conditions precludes the standardization of specific characteristics required to achieve better adsorption results. This work reviewed the pertinent literature on Cr(VI) adsorption onto AC published over the past four decades. Pearson's correlation matrix and principal component analysis (PCA) assisted in identifying the parameters and AC characteristics that have the greatest influence on the maximum adsorption capacity (qm). Two hundred thirty-six adsorption assays were found reporting data on 110 ACs and different parameters. Of these, 39.8% of the studies contemplated the variables qm, pH, temperature (T), surface area (SBET), micropore volume (Vmicro), and mesopore volume (Vmeso), and only 19.5% reported the point of zero charge (pHPZC). Statistical analysis disclosed that SBET and Vmicro have a strong positive correlation with qm, while Vmeso, T, and pH show little or no correlation. The difference between pH and pHPZC (PZCdiff) indicated a significant anticorrelation with qm, thus evidencing that lower PZCdiff values enhance adsorption. The findings are useful for all researchers that work with Cr(VI) adsorption on AC since they provide a start point concerning the required adsorbent characteristics and process conditions to be employed.
Assuntos
Carvão Vegetal , Poluentes Químicos da Água , Adsorção , Carvão Vegetal/química , Cromo/química , Concentração de Íons de Hidrogênio , Cinética , Poluentes Químicos da Água/químicaRESUMO
The DPPH method has been reported with misconceptions in a large number of studies, thus precluding comparison of results. Attention is drawn to a common mistake in the unit used to express the IC50 of ascorbic acid and other antioxidant substances. Concentration of the antioxidant is widely misused with a total disregard for the DPPH⢠concentration, while the molar ratio of antioxidant/DPPH⢠would be the correct choice. Data from 26 studies with widely varying IC50 values were renormalized according to reaction stoichiometry, resulting in values which are more coherent and closer to the ideal one of 0.25 for at least 15 of them. In addition, the model which is currently being used to calculate the DPPH⢠concentration can lead to an overestimation of around 7%, as it does not take into account the small contribution of the reaction product. In view of that, we present a mathematical model to correct the overestimation of the DPPH⢠concentration.
RESUMO
Naphthalene (NAP) is found as a pollutant in water, soil, and air, and adsorption is the most prominent removal process of this compound, among the methods studied. A study concerning the types of adsorbents and the parameters with the greatest influence on the adsorption process is interesting to direct future works on new adsorbents. The use of multivariate data analysis tools becomes an appealing way to compile data obtained from bibliographic reviews and to establish a behavior in NAP adsorption. This work aims to evaluate the parameters with greater influence on NAP adsorption process regarding adsorption capacity (qeexp) with the principal component analysis (PCA), and to group common NAP adsorbents by chemical characteristics through hierarchical cluster analysis (HCA). The variables qeexp, S, [NAP]0, T, CT, and [Ads] were used to perform PCA with correlation matrix. For the HCA, the variables S, [NAP]0, T, CT, and [Ads] with average linkage method (UPGMA) and Euclidean distance were used. Through PCA, it is possible to infer that S and [NAP]0 are the factors with greater influence in qeexp of NAP, while T, CT, and [Ads] have little correlation. PCA also shows that activated charcoal is the adsorbent with higher qeexp. HCA grouped the adsorbents into four groups by their chemical classes, except group A. Both PCA and HCA methods show themselves as potential tools to evaluate a data set of NAP adsorption processes.