Three carbonaceous porous materials (biochar and activated carbon) were developed from the Tectona grandis tree sawdust. The applied process of two-stage preparation included pre-treatment through hydrothermal carbonization at 190 °C and subsequent pyrolysis at 800 °C. Two chemical activating agents (K₂CO₃ and ZnCl₂) were used to prepared activated carbons (K₂CO₃-AC and ZnCl₂-AC), respectively. They were characterized by textural property, morphology, and surface element components and applied to remove Cr(VI) from solution at various solution pH values and initial Cr(VI) concentrations. Results showed that the textural parameters (S_BET and V_Total) of the prepared material were 1757 m²/g and 1.027 cm³/g for Zn-Cl₂-AC, 1013 m²/g and 0.418 cm³/g for K₂CO₃-AC, and 792 m²/g and 0.345 cm³/g for biochar. The adsorption process reached the highest efficiency at pH 3.0. The Langmuir maximum adsorption capacity indicated the decreasing order: ZnCl₂-AC (127 mg/g) > K₂CO₃-AC (103 mg/g) > biochar (83.5 mg/g). The removal mechanism of Cr(V) from solution was regarded as an adsorption-coupled reduction, namely (1) partial reduction of Cr(VI) into Cr(III) during the adsorption process and (2) adsorption of the Cr(VI) anions through electrostatic attraction and pore filling and the reduced Cr(III) cations through complexation, Cπ–cation interaction, cation exchange, and pore filing. Therefore, the prepared biochar and activated carbon can server as promising adsorbents to efficiently remove both Cr(VI) and Cr(III) from water.

This study proposed a novel and low-cost adsorbent prepared from dredging sediment (DSD) for effective removal of dye in aqueous solutions. The adsorption efficiency and behavior of the DSD adsorbent toward the crystal violet (CV), a cationic dye, were investigated via batch experiments. The results showed that DSD samples contain mainly clay minerals (illite and kaolinite) and other mineral phases. In addition, DSD is a mesoporous material (V_mesopore = 94.4%), and it exhibits a relatively high surface area (~39.1 m²/g). Adsorption experiments showed that the solution’s pH slightly affects the adsorption process, and a pH of 11 gave a maximum capacity of 27.2 mg/g. The kinetic data of CV dye adsorption is well described by the pseudo–second-order and the Avrami models. The Langmuir and Liu isotherm models provide the best fit for the adsorption equilibrium data. The monolayer adsorption capacity of Langmuir reached 183.6, 198.0, and 243.6 mg/g at 293, 308, and 323 K, respectively. It was also found that the adsorption process was spontaneous (−ΔG°), exothermic (−∆H°), and increased the randomness (+∆S°) during the adsorption operation. The primary mechanisms in CV dye adsorption were ion exchange and pore filling, whereas electrostatic attraction was a minor contribution. In addition, three steps involving intraparticle diffusion occur at the same time to control the adsorption process. The results of this study highlight the excellent efficiency of DSD material as an ecofriendly sorbent for toxic dyes from water media.

This paper aims at studying the preparation of Zn-Al-LDH anionic clay and its adsorption proprieties in removing orthophosphate ions from aqueous medium. The LDH phase was synthesized by co-precipitation method and then calcined at 500 °C. Structural and textural properties of the prepared LDHs were determined by using x-ray diffraction, FTIR, BET, SEM and pH_PZC analysis. Batch adsorption experiments were carried out under different parameters such as stirring time, pH and initial orthophosphate concentration. Results show that the prepared LDHs are efficient in removing orthophosphate and the maximum uptake was observed after 2 h. Experimental kinetic data are well described by the pseudo-second order model. It was also found that the adsorption process is significantly affected by the pH value. The sorption mechanisms include ion exchange, reconstitution of LDH phase and/or electrostatic attraction. Also, the isotherm study reveals that the Freundlich equation best fit the equilibrium data.