Trithiocyanurate-functionalized hydrochar for effectively removing methylene blue and Pb (II) cationic pollutants.

Functionalization can change the physicochemical properties of hydrochar and improve its ability to adsorb pollutants. Herein, a trithiocyanurate-functionalized hydrochar (TTHC) was obtained from acylation of chloroacetyl chloride and hydrochar and modification with trithiocyanuric acid in alkaline conditions. TTHC can efficiently remove cationic methylene blue (MB) and Pb(II) from wastewater. The removal can be expressed with pseudo-second-order kinetic and Langmuir models. The MB and Pb(II) removed uptakes by TTHC at 298 K exceeded 909.9 and 182.8 mg g-1 respectively, and the removal rates reached 90% and 98% within 120 min respectively. Characterizations show TTHC is functionalized with trithiocyanurate, and rich in thiolate and aromaticity, and tends to adsorb MB/Pb(II) via multiple adsorption mechanisms. After five sorption-desorption regeneration cycles, TTHC maintained 80% and 99% adsorption capacities for MB and Pb(II) respectively. Therefore, TTHC is a promising efficient sorbent for removing MB and Pb(II) from effluents.

Adsorption of lead ions and methylene blue on acrylate-modified hydrochars.

Hydrochars are promising sorbents for wastewater treatment. Herein, two acrylate-modified hydrochars (AMHC1 and AMHC2) were obtained by grafting acrylic acid on the surface of two hydrochars (MHC1 and MHC2 hydrothermally carbonized in water and acidic medium respectively) with free radical polymerization. Characterizations show that MHC2 is more prone to free radical polymerization than MHC1 does, and has higher carboxylate content after modification. The adsorption amounts of AMHC2 over methylene blue (MB) and Pb(II) are much higher than those of AMHC1. Pseudo-second-order kinetic and Langmuir isotherm equations well fit the Pb(II) and MB sorption data of AMHC2. The Pb(II) adsorptive mechanism is mainly inner-surface complexation accompanied by ion exchange and cation-π interaction. MB adsorption involves ion exchange, electrostatic interaction, H-bonding and π-π interaction. Hence, the one-step modification method of free radical polymerization under alkaline condition has great potential for preparing carboxylate-modified hydrochars to adsorb cationic pollutants.