Коллоидный журнал

This study examines the influence of the activation ratio on the properties of potassium hydroxide-activated carbon (KOH-AC) derived from safflower stems and its performance in hexavalent chromium Cr(VI) adsorption. The adsorbent was characterized using Brunauer–Emmett–Teller (BET) surface area analysis, Scanning Electron Microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier Transform Infrared spectroscopy (FTIR), and X-ray diffraction (XRD) to evaluate porosity, morphology, and crystallinity. Key adsorption parameters—including pH, contact time, initial concentration, temperature, and adsorbent dosage—were systematically investigated. The optimal activation ratio (KOH-activated carbon with 4:1 KOH to carbon; KAC-4) yielded a highly porous carbon with a BET surface area of 2089.5 m²/g and a maximum Cr(VI) adsorption capacity of 132.3 mg/g. The highest removal efficiency was achieved at pH 5.2. Kinetic analysis revealed that adsorption followed a pseudo-second-order model, indicating chemisorption, while thermodynamic results suggested an exothermic and non-spontaneous process with decreased adsorption at higher temperatures—implying a dominant physisorption mechanism governed by electrostatic interactions. The Freundlich isotherm provided the best fit, confirming multilayer adsorption on a heterogeneous surface.

Overall, KOH-activated carbon from safflower stems proved to be a promising, low-cost, and sustainable adsorbent for Cr(VI) removal, supporting agricultural waste valorization and circular economy initiatives.

Live and dead microalgae have the potential to remove mineral nutrients such as nitrogen from water resources. In this research, the efficiency of biocomposites prepared from different ratios of dried biomass of Chlorella sorokiniana microalgae together with kaolin and iron chloride for nitrate removal from water was investigated. The effect of pH on the nitrate adsorption capacity of microalgal biomass for different initial nitrate concentrations (30 and 50 mg L^-1) was studied. The optimum pH value was found to be about 5. The adsorption efficiency decreased at higher pH. The best performance was achieved by the 50% algae + 50% clay biocomposite, with an adsorption capacity of 14.25 mg g^-1 (47.5%) of nitrate at a concentration of 30 mg L^-1. The biocomposite of 50% algae + 35% clay + 15% FeCl₃ also showed similar performance in nitrate adsorption at a concentration of 30 mg L^-1 (46.06%). With increasing nitrate concentration, the removal by microalgal biomass and biocomposites did not increase. Adding FeCl₃ to the biocomposite did not increase nitrate adsorption compared to the 50% algae + 50% clay biocomposite. The lowest removal rate of 2.46 mg g^-1 related to dry biomass was obtained at a concentration of 50 mg L^-1. The morphological structure of the adsorbent was investigated by SEM microscopy and the functional groups by FTIR method. Based on the obtained results, it can be concluded that the prepared composite has a high ability to remove nitrate from water sources.