RESUMO
The formation of aggregates between carboxylated (PVCOOH) or neutral hydrolyzed (PVOH) poly(vinyl alcohol) and hexadecylpyridinium chloride (C16PyCl) was examined by conductimetry, turbidimetry, and isothermal titration calorimetry (ITC) in the presence of different NaCl concentrations. The interaction between the polymers and C16PyCl in pure water showed a critical aggregation concentration (cac = 0.8 mmol L-1) only for the neutral polymer. PVCOOH interacted with the surfactant through electrostatic attraction, forming macroscopic aggregates. Integral enthalpy changes for aggregate formation (ΔHagg) obtained from ITC curves varied from -0.61 (for the PVOH system in pure water) to -4.14 kJ mol-1 (for PVOH in the presence of 10.0 mmol L-1 NaCl), indicating that the formation of the aggregates was enthalpically favored. However, hydrophobic interactions drove the process for low surfactant concentration for both polymers. Saturation concentrations (C2) obtained from conductimetry were smaller than those from ITC, revealing that the binding of C16PyCl on the chain of the polymers at higher surfactant concentrations shows the same electric properties as that of free micelles on the solution. Increase of the ionic strength favored the aggregation and decreased the complexity of the ITC curves, suggesting that the reorganization of the surfactant monomers on the polymeric chain with the increase in their concentration was suppressed.
Assuntos
Polímeros , Álcool de Polivinil , Polímeros/química , Cloreto de Sódio , Tensoativos/química , Termodinâmica , Calorimetria , ÁguaRESUMO
A new one-pot synthesis method optimized by a 23 experimental design was developed to prepare a biosorbent, sugarcane bagasse cellulose succinate pyromellitate (SBSPy), for the removal of Cu(II) and Zn(II) from single-component aqueous solutions, in batch and continuous modes. The bi-functionalization of the biosorbent with ligands of different chemical structures increased its selectivity, improving its performance for removing pollutants from contaminated water. The succinate moiety favored Cu(II) adsorption, while the pyromellitate moiety favored Zn(II) adsorption. Sugarcane bagasse (SB) and SBSPy were characterized using several techniques. Analysis by 13C Multi-CP SS NMR and FTIR revealed the best order of addition of each anhydride that maximized the chemical modification of SB. The maximum adsorption capacities of SBSPy for Cu(II) and Zn(II), in batch mode, were 1.19 and 0.95 mmol g-1, respectively. Homogeneous surface diffusion, intraparticle diffusion, and Boyd models were used to determine the steps involved in the adsorption process. Isothermal titration calorimetry was used to assess changes in enthalpy of adsorption as a function of SBSPy surface coverage. Fixed-bed column adsorption of Cu(II) and Zn(II) was performed in three cycles, showing that SBSPy has potential to be used in water treatment. Breakthrough curves were well fitted by the Thomas and Bohart-Adams models.