RESUMO
PURPOSE: This research aimed to develop activated carbons from tobacco by double (thermal-physical) and triple activations (thermal-chemical-physical) for high-efficiency removal of Cd2+. METHODS: The adsorbents were characterized by their chemical composition, point of zero charge (pHPZC), SEM, FT-IR, BET, and BJH. The subsequent adsorption studies were conducted: optimal conditions (CCD on adsorbent dose versus pH of Cd2+ solution), kinetics, equilibrium, thermodynamics, and desorption studies. RESULTS: The activated carbons have irregular and heterogeneous morphology, surface functional groups COO-, C-O, C-O-C, C=O and O-H, pHPZC of 11.11 and 10.86, and enhanced SSA (especially for CT NaOH + CO2 = 103.40 g m-2). The optimal conditions for Cd2+ adsorption occur using 4.0 g L-1, pH from 3.0 to 7.0, with most of the Cd2+ adsorbed in the first 10-20 min. The goodness of the fit found for pseudo-first order, pseudo-second order, intraparticle diffusion, Langmuir, Freundlich, Dubinin-Radushkevich, Sips, and Temkin suggest the occurrence of Cd2+ chemisorption and physisorption in mono and multilayers. The values of ∆G° < 0 kJ mol-1 indicate that the observed phenomena are energetically favorable and spontaneous; the values of ∆H° < 0 and the effective desorption rates (58.52% and 44.64%) suggest that the adsorption of Cd2+ is ruled mainly (but not only) by physical interactions. CONCLUSION: Our excellent results on Cd2+ removal allow us to state that tobacco use as a raw material for adsorbent development is a renewable and eco-friendly technique, allowing the production of highly effective activated carbons and providing an adequate destination for this waste. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40201-021-00740-8.
RESUMO
The validation of chromatographic methods is a costly process, however necessary, especially with regard to the validation of methods that accurately determine concentrations of pesticides in different environmental compartments. This research aimed at the development and validation of a simple and fast method for the determination of chlorpyrifos concentrations in water by means of a gas chromatograph with electron capture detection (GC/ECD), and to investigate chlorpyrifos dynamics of adsorption in a Rhodic Ferralsol in Southern Brazilian conditions. The developed chromatographic method was based in EPA 8141 method. Parameters to be checked for method validation were: Selectivity/specificity, linearity, precision, accuracy, robustness, limit of detection (LOD) and limit of quantitation (LOQ). Were employed the following methodologies for the validation process: ANVISA Resolution 899, DOQ-CGCRE-008 and FDA Bioanalytical Method Validation Guide. Also, through laboratory tests, the sorption dynamics of chlorpyrifos in Rhodic Ferralsol was evaluated. Thus, the soil was contaminated with increasing concentrations of chlorpyrifos, which were subjected to solid-liquid extraction with SPE cartridge Chromabond® C18 ec. The obtained results were submitted to the models of Langmuir, Freundlich, Dubinin-Radushkevich and Sips. By this method, chlorpyrifos peaks are obtained at 16.9 min, demonstrating practicality and low cost. This method exhibits precision and sensitivity, with satisfactory LQ and LQ values. The models of Langmuir, Freundlich, Dubinin-Radushkevich and Sips suggest the occurrence of simultaneous adsorption in mono and multilayer of chlorpyrifos in Rhodic Ferralsol colloids, as well as the predominance of a chemical, high energy binding process (irreversible). However, the chemisorption of chlorpyrifos is more related to the good fit found for Dubinin-Radushkevich sorption energy values (9.861 and 11.079 KJ mol-1) and Qm values estimated by Langmuir (485.55 and 389.61 µg g-1 for linear and nonlinear model).
