Glyphosate adsorption onto porous clay heterostructure (PCH): kinetic and thermodynamic studies

The synthesis of PCH from natural bentonite produces a porous heterostructure material effective for the adsorption of glyphosate from water. The adsorption process takes place through an interaction between the silanol group of montmorillonite and/or the PCH adsorbent with the functional groups of glyphosate. The glyphosate adsorption isotherms, recorded for all the studied samples, have been established to be of Langmuir type. The kinetic of the herbicide adsorption on the PCH was best described by the pseudo-second-order model. With the increase in temperature from 25 to 50 °C, the sorption capacities of the materials studied towards glyphosate increased. The process of glyphosate adsorption was found to be endothermic and spontaneous in nature, as indicated by positive values of ΔH and negative values of ΔG. According to the results obtained, the herbicide sorption was more effective in a basic environment. The maximum amount of adsorbed glyphosate is almost doubled with PCH from 13.5 mg/g of natural clay to 27.5 mg/g of PCH. Graphic abstract

Porous Clay Heterostructure with Alginate Encapsulation for Toluene Removal

A volatile organic compound adsorbent based on a porous clay heterostructure (PCH) with alginate biopolymer was successfully prepared. From N2 adsorption–desorption analysis, the specific surface area, pore volume, and pore size of bentonite were dramatically increased after introducing the porous structure. Following complexation with alginate (Alg-PCH), the pore volume and pore size were not significantly affected by pore structure. The thermal stability of Alg-PCH shows enhanced thermal stability compared to alginate and alginate beads. The morphology layered structure of Alg-PCH was carried out by transmission electron microscopy (TEM), suggesting the disorder and re-order of the c-axis layer stacking by porous structure and complexation with alginate, respectively, which was well-matched with X-ray diffraction results. To optimize the preparation of Alg-PCH, various reaction conditions (alginate, CaCl2 concentration, bead size, and weight ratio between alginate and PCH) were utilized. According to the toluene adsorption–desorption experiments, the preparation conditions for Alg-PCH were selected as a 2 mm extrusion tip, 0.5% of alginate, and 2% of CaCl2 solution with a 1:50 alginate:PCH weight ratio. Additionally, it shows 61.63 mg/g adsorption capacity with around 49% desorption efficacy under atmospheric temperature and pressure.

ZnO-Porous Clay Heterostructure from Saponite as Green Catalyst for Citronellal Cyclization

Green conversion in organic synthesis is one of the interesting and important topics in green chemistry. The use of heterogeneous catalysis instead of homogeneous catalysis offers some advantages, such as easy separation and reusability. In this research, a heterogeneous acid catalyst was prepared from saponite by immobilizing ZnO in the form of a pillared clay (Zn/PILS) and Zn supported on porous clay heterostructure (Zn/PCH). Physicochemical studies involving X-ray diffraction measurement, surface analysis using a gas sorption analyzer, and surface acidity measurement were performed. Results indicated that the increasing surface acidity and the high specific surface area of the material were the relevant physicochemical properties that facilitate environment-friendly citronellal cyclization. The higher values for both parameters in Zn/PCH than in Zn/PILS linearly affected citronellal conversion and the selectivity for isopulegol production. Zn/PCH demonstrated a conversion rate of 98.9% for a 3-hour reaction and a selectivity of 100% for isopulegol production, and it exhibited reusability properties. Copyright © 2020 BCREC Group. All rights reserved

Study of the Surface Charge of a Porous Clay Heterostructure (PCH) and Its Adsorption Capacity of Alkaline Metals

A Porous Clay Heterostructure (PCH) was prepared by chemical modification of a natural clay, by intercalation of a cationic surfactant. Its surface charge properties as well as its adsorption capacity for alkali metals were studied using a potentiometric titration method. The PCH developed a pH-dependent charge (sH), probably due to the presence of amphoteric silanol groups (SiO2) coming from the pillars of silica interlayered during the pillared process. The PCH presented a region of zero charge in the range of pH of 4.0 to 7.7. The sH acquired by the PCH was adjusted with good correlation to the electric double layer model of Gouy-Chapman (r2 = 0.9925). The surface charge conferred the PCH ion exchange capacity for the studied metals (Li, Na, K, Rb and Cs) at high pH values (10 < pH), in comparable quantities (3.5 to 6 meq/g) to some Dowex resins. The results of this study suggest that PCH could have applications in the recovery of toxic metals from waste waters.