Fabrication of melamine formaldehyde/graphene oxide composite for efficient static and dynamic adsorption of lead ions from aqueous medium.

The present work discusses the synthesis, characterization, and environmental applications of graphene oxide (GO), melamine formaldehyde resin (MF), and melamine formaldehyde/graphene oxide composite (MGO) for the efficient removal of Pb2+ from aqueous medium via batch and column procedures. TGA, XRD, TEM, zeta potential, nitrogen adsorption/desorption, ATR-FTIR, and other characterization techniques revealed that MGO is characterized by a greater surface area (609 m2/g), total pore volume (1.0106 cm3/g), pHPZC (6.5), and the presence of various surface chemical functional groups. The synthesized solid adsorbents were used in both static and dynamic adsorption processes to remove Pb2+, with varying application parameters such as pH, starting concentration, adsorbent dosage, and shaking time in the case of static adsorption method. While through the column adsorption process the effects of column bed height, flow rate, and starting Pb2+ were taken into consideration. Results of the batch adsorption demonstrated that MGO had the highest Langmuir adsorption capacity (201.5 mg/g), and the adsorption fit the nonlinear Langmuir adsorption model and Elovich kinetic models. The adsorption of Pb2+ onto all prepared solid materials is endothermic, spontaneous, and physical in nature, as demonstrated by thermodynamic studies. Column adsorption of Pb2+ well fitted by Thomas and Yoon Nelson nonlinear adsorption models. MGO showed a maximum column adsorption capacity of 168 mg/g when applying 4 cm, 15 mL/min, and 150 mg/L as bed height, flow rate, and initial Pb2+, respectively. With only a 12.6% reduction in its adsorption capacity, column regeneration showed that MGO exhibited a high degree of reusability even after five cycles of adsorption/desorption studies.

Fabrication and characterization of Araucaria gum/calcium alginate composite beads for batch and column adsorption of lead ions.

In this work, we developed five solid adsorbents such as calcium alginate beads (CG), Araucaria gum (AR) extracted from Araucaria heterophylla tree by chemical precipitation procedures, and Araucaria gum/calcium alginate composite beads (CR21, CR12, and CR11) prepared with different calcium alginate: Araucaria gum ratios (2:1, 1:2, and 1:1, respectively). The synthesized solid adsorbents were characterized utilizing TGA, XRD, nitrogen adsorption/desorption analysis, ATR-FTIR, pHPZC, swelling ratio, SEM, and TEM. Through the batch and column adsorption strategies, we evaluated the effect of adsorbent dose, pH, initial Pb (II) concentration, shaking time, bed height, and flow rate. The data of batch technique indicated that CR11 demonstrated a maximum batch adsorption capacity of 149.95 mg/g at 25 °C. Lead ions adsorption was well fitted by pseudo-second order and Elovich according to kinetic studies, in addition to Langmuir and Temkin models based on adsorption isotherm studies onto all the samples. Thermodynamic investigation showed that Pb (II) adsorption process is an endothermic, physical, and spontaneous process. The highest column adsorption capacity (161.1 mg/g) was achieved by CR11 at a bed height of 3 cm, flow rate of 10 mL/min, and initial Pb+2 concentration of 225 mg/L with 68 min as breakthrough time and 180 min as exhaustion time. Yoon-Nelson and Thomas models applied well the breakthrough curves of Pb (II) column adsorption. The maximum column adsorption capacity was decreased by 11.4 % after four column adsorption/desorption processes. Our results revealed that CR11 had an excellent adsorption capacity, fast kinetics, and good selectivity, emphasizing its potential for its applications in water treatment.

Polymorphic phase transformations of 3-chloro-trans-cinnamic acid and its solid solution with 3-bromo-trans-cinnamic acid.

We have investigated the polymorphic phase transformations above ambient temperature for 3-chloro-trans-cinnamic acid (3-ClCA, C9H7ClO2) and a solid solution of 3-ClCA and 3-bromo-trans-cinnamic acid (3-BrCA, C9H7BrO2). At 413 K, the γ polymorph of 3-ClCA transforms to the ß polymorph. Interestingly, the structure of the ß polymorph of 3-ClCA obtained in this transformation is different from the structure of the ß polymorph of 3-BrCA obtained in the corresponding polymorphic transformation from the γ polymorph of 3-BrCA, even though the γ polymorphs of 3-ClCA and 3-BrCA are isostructural. We also report a high-temperature phase transformation from a γ-type structure to a ß-type structure for a solid solution of 3-ClCA and 3-BrCA (with a molar ratio close to 1:1). The γ polymorph of the solid solution is isostructural with the γ polymorphs of pure 3-ClCA and pure 3-BrCA, while the ß-type structure produced in the phase transformation is structurally similar to the ß polymorph of pure 3-BrCA.