Thermally activated, acid-activated, and acid-leached of thermally activated kaolinites were prepared from the Egyptian ore. The physical and chemical properties were studied using N₂sorption at −196°C, FTIR, SEM, and the total surface acidity. The sorption ofNH4+ions on the investigated sorbents was controlled with the solution pH, sorbent dosage, and initial concentration ofNH4+solution. Kinetic and equilibriumNH4+sorption at 30°C were employed. Four kinetic models were applied to the kinetic sorption data; pseudo-second-order, Elovich, and intraparticle diffusion models fitted well the kinetic data whereas pseudo-first-order model was less applicable. Elovich parameters refer to physical sorption type ofNH4+on nonuniform sites and the intraparticle diffusion controls the sorption ofNH4+by kaolinites to a small extent. The equilibrium sorption data followed Langmuir and D-R models; the negative value ofΔGindicates a spontaneous sorption and the mean sorption energy obtained shows also physical sorption. The sorption capacities of nonactivated and activated Egyptian kaolinites towardsNH4+sorption (10.87–45.45 mg·g⁻¹) were good sorbents as compared with those uptaken by other clays reported in the literature and proved to be more active besides being less expensive and highly available.

In this paper, carbonaceous hydrochar adsorbents with highly functionalized surface active sites were prepared from cellulose and lignin constitutes of rice straw via hydrothermal treatment at 180oC for 20h followed by carbonization process at 500oC for 2h without external gas flow. Two carbonaceous samples were obtained from cellulose and lignin and denoted as RC-C and RL-C, respectively. The resulting hydrochar adsorbents were characterized using means of SEM, TEM, FTIR, Boehm's titration and adsorption of N2 gas at -196oC. Kinetic and equilibrium adsorption studies using methylene blue (MB) dye as model pollutant compound in industrial wastewaters were determined. The calculated adsorption efficiencies of the adsorbents were considerably depended on the initial dye concentration, contact time and temperature. The obtained adsorption results were found to describe well using the pseudo-second order kinetic and Langmuir isotherm models. Monolayer adsorption capacity of RC-C and RL-C reached to 100 and 40 mg/g towards MB dye, respectively. Based on these findings, the produced hydrochars from cellulose and lignin of rice straw can be emerged as low-cost and valuable adsorbents for removing dye contaminants from wastewater.

Background: Application of nanotechnology in wastewater treatment is the solution to cope with the conflict between people’s increasing demand for water and the world-wide water shortage. The main goal of this study is to prepare modified carbon nanostructures (CNSs) from sugarcane bagasse waste (SCB) as effective adsorbents for removing toxic Cr(VI) ions from their aqueous solutions. Methods: The preparation of CNSs was performed via catalytic hydrothermal/carbonization of SCB. The resultant CNSs sample was oxidized by oxidation with HNO₃/H₂O₂ (O-CNSs) and then followed by coating with diethylenetriamine (N-CNSs). Transmission electron microscope (TEM), scanning electron microscope attached to energy-dispersive X-ray (SEM/EDX), fourier transform infrared (FTIR) and nitrogen adsorption analyses were used to determine the morphology and surface properties of CNSs. Adsorption and desorption studies of Cr(VI) ions onto these modified CNSs were investigated. Effects of initial concentration of Cr(VI), pH of solution and temperature in the batch mode were estimated. Adsorption studies were analyzed by Langmuir, Freundlich and Dubinin- Radushkevich models. Pseudo-first-order, pseudo-second-order and intraparticle diffusion models were undertaken to follow the adsorption mechanism. Results: The prepared samples composed of carbon nanotubes and graphene sheets were evident by TEM and SEM. The adsorption of Cr(VI) is exothermic in nature, well-fitted with Langmuir, described by pseudo-second order kinetic model and then is uncontrolled by intraparticle diffusion step. It was found that the adsorption of Cr(VI) was higher uptake over O-CNSs (56 mg/g) than that by NCNSs (44 mg/g). This was ascribed to that the first sample is enriched with acidic O-functional groups and possessed higher specific surface area (188 m²/g). Desorption studies were achieved by HNO₃ and NaOH reagents for recovering the Cr(VI) from O-CNSs. Results revealed that about 90% of Cr(VI) can be recovered by HNO₃ more than that by NaOH till the third run. Conclusions: Two modified CNSs samples were successfully prepared from SCB. Adsorption of Cr(VI) is highly relied on initial concentration of Cr(VI), pH and temperature. The main factors controlling the adsorption behavior of Cr(VI) are the acidic functional groups and the accessible surface area on O-CNSs. Furthermore, the O-CNSs attained high stability in recycling tests for Cr(VI) removal.