Toxins in water, such as metal ions and dyes, have become a global challenge to humanity by causing several serious illnesses. Removal of these toxins from water is needed for human health and environmental concerns. This work investigated the use of hemp seeds as an environmentally friendly adsorbent for applications in water treatment. Pristine hemp seeds (PHSs) were carbonized at 500 and 700 °C to obtain carbon-based hemp seeds (CHS-500 and CHS-700 for the removal of cadmium and methylene blue. The morphological and functional groups of the carbonized adsorbents and pristine hemp seeds were determined by SEM and FTIR. Isotherm studies showed that the Langmuir model best described the adsorption process based on homogenous surfaces. The maximum adsorption capacities were obtained with CHS-700 with a 36.88 and 52.61 mg/g uptake of cadmium and methylene blue, respectively. The effect of contact time showed that the sorption process rate was rapid initially, followed by a slower increment due to the saturation of active sites. ΔS° values were positive, demonstrating the increased randomness and degree of freedom of cadmium and methylene blue in water. The adsorption trends for cadmium and methylene blue by CHS-500 and CHS-700 increased as the temperature rose; a decrease was observed for adsorption by PHSs. This result suggests that the adsorption was endothermic for CHS-500 and CHS-700 and exothermic for PHSs. The pseudo-second-order model better described the uptake of both pollutants by the adsorbents. This research illustrates the great potential of carbon-based hemp seeds in removing cadmium and methylene blue dye from water.

Carbon from black cumin seeds was modified with 10 and 20% sulfuric acid to obtain the activated adsorbents. Pristine carbon from black cumin seeds, 10 and 20% H2SO4 activated carbon from black cumin seeds were labelled CBC, ACBC-10 and ACBC-20, respectively. The adsorbents were characterized by SEM, XRD, FTIR, TGA and BET. The adsorbents maximum trend for Cd(II) was ACBC-10 > ACBC-20 > CBC. The maximum capacity trend for methylene blue dye was ACBC-20 > ACBC-10 > CBC. The kinetic model best fitted pseudo second order for Cd(II) which gave r2 values of 0.991-0.998. The methylene blue fitted pseudo first order model with r2 values ranging from 0.993-0.997. Pseudo first order suggested that the adsorption mechanism for methylene blue onto adsorbents involved van der Waal forces of attraction. The equilibrium data fitted Langmuir isotherm model for CBC, ACBC-10 and ACBC-20 with r2 of 0.994 to 0.998 for the removal of methylene blue whilst the removal of Cd(II) followed Freundlich with r2 ranging from 0.992 to 0.997. This suggested that the different adsorption processes were involved between the adsorbate and the adsorbents. Gibb′s free energy (ΔGº) for Cd(II) and methylene blue onto CBC, ACBC-10 and ACBC-20 suggested that the reaction was spontaneous. The adsorption of Cd(II) and methylene blue was endothermic, positive values (ΔHº). This suggested that the enthalpy (ΔHº) had a weak interactive force process whose low energy is associated with electrostatic attraction.

The aim of the present study was to utilise pristine and magnetite-sucrose functionalized Nigella Sativa seeds as the adsorbents for the uptake of chromium(VI) and lead(II) ions from synthetic wastewater. Prestine Nigella Sativa seeds were labelled (PNS) and magnetite-sucrose functionalized Nigella Sativa seeds (FNS). The PNS and FNS composites were characterized by Fourier-transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD). The FTIR analysis of both adsorbents revealed the presence of vibrations assigned to 1749 and 1739 cm^-1 (-C=O) for ketonic group for both adsorbents. The amide (-NH) peak was observed at 1533 and 1527 cm^-1 on FNS and PNS composites, respectively, whilst the carboxyl group (-COOH) were observed at 1408 cm^-1 on both adsorbents. The XRD results of FNS and PNS composites showed a combination of spinel structure and [ ]-Fe₂O₃ phase confirming the formation of iron oxide. The influence of operational conditions such as initial concentration, temperature, pH, and contact time was determined in batch adsorption system. The kinetic data of Cr(VI) and Pb(II) ions on both adsorbents was described by pseudo-first-order (PFO) model which suggested physisorption process. The sorption rate of Cr(VI) ions was quicker, it attained equilibrium in 20 min, and the rate of Pb(II) ions was slow in 90 min. Freundlich isotherm described the mechanism of Pb(II) ions adsorption on PNS and FNS composites. Langmuir best fitted the uptake of Cr(VI) ions on PNS and FNS. The results for both adsorbents showed that the removal uptake of Pb(II) ions increased when the initial concentration was increased; however, Cr(VI) uptake decreased when the initial concentration increased. The adsorption of Cr(VI) and Pb(II) ions on both adsorbents increased with temperature.

Present study reports on the sorption study of chromium(VI), cadmium(II) ions and methylene blue dye by pristine, defatted and carbonized Nigella sativa L. seeds from aqueous solution. The removal of oil from pristine Nigella sativa L. (PNS) seeds was carried out by defatting the Nigella sativa with acetone and N,N-dimethylformamide and then labelled ANS and DNS, respectively. Thereafter the defatted ANS and DNS adsorbents were carbonized at 600 ºC for 2 h under nitrogen and labelled as CANS and CDNS. The results of pristine, defatted and carbonized seeds were compared. The removal of Cr(VI), Cd(II) and methylene blue dye from aqueous solutions was investigated by varying adsorbate concentration, solution pH, reaction contact time and temperature of the solution. The SEM images indicated that the surface morphology of PNS was irregular, whilst ANS and DNS had pores and cavities. CANS and CDNS was heterogeneous and had pores and cavities. FTIR spectroscopy showed that the adsorbents surfaces had bands that indicated a lot of oxygen containing groups. The pH of the solution had an influence on the removal uptake of Cr(VI), Cd(II) and methylene blue. The sorption of Cr(VI) decreased when pH of the solution was increased due to different speciation of Cr(VI) ions whilst the removal of Cd(II) and methylene blue increased when solution pH was increased. Pseudo first order kinetic model well described the adsorption of Cr(VI), Cd(II) and methylene blue onto PNS. On the other hand, the kinetic data for ANS, CANS, DNS and CDNS was well described by pseudo second order. Furthermore, the removal mechanism onto PNS and ANS was better described by Freundlich multilayer model. The CANS, DNS and CDNS fitted Langmuir monolayer model. Thermodynamic parameters indicated that the sorption processes of Cr(VI), Cd(II) and methylene blue was endothermic and effective at high temperatures for all adsorbents. The ΔSº and ΔHº had positive values this confirmed that the sorption of Cr(VI), Cd(II) and methylene blue onto all adsorbents was random and endothermic, respectively. The values of ΔGº confirmed that the sorption of Cr(VI), Cd(II) and methylene blue on all adsorbents was spontaneous and predominated by physical adsorption process. The CANS had highest adsorption capacity of 99.82 mg/g for methylene blue, 96.89 mg/g for Cd(II) and 87.44 mg/g for Cr(VI) followed by CDNS with 93.90, 73.91 and 65.38 mg/g for methylene blue, Cd(II) and Cr(VI), respectively. The ANS capacities were 58.44, 45.28 and 48.96 mg/g whilst DNS capacities were 48.19, 32.69 and 34.65 mg/g for methylene blue, Cd(II) and Cr(VI), respectively. PNS had the lowest sorption capacities at 43.88, 36.01 and 19.84 mg/g for methylene blue, Cd(II) and Cr(VI), respectively.

This research assessed the adsorption of a pharmaceutical compound, ibuprofen, using rose geranium (Pelargonium graveolens L.) leaves to prepare low-cost activated carbon through orthophosphoric acid (H₃PO₄) activation. The activated carbon from rose geranium leaves (AC-RGL) was characterized by TGA, SEM and FTIR. The results were compared with those from natural rose geranium leaves (Raw-RGL). The influence of chemical parameters for the uptake of ibuprofen on both adsorbents was evaluated through adsorption experiments. The results were subjected to adsorption models, kinetics models and thermodynamic studies to determine the distribution of ibuprofen in the solid and liquid phases. The results for both Raw-RGL and AC-RGL best fitted the Freundlich model, and the kinetic studies were shown to be pseudo-first order. The thermodynamic evaluation suggested exothermic and spontaneous process sorption for ibuprofen on both adsorbents. The maximum sorption capacities for AC-RGL and Raw-RGL were 113.76 and 74.12 mg/g, respectively. This work confirms that low-cost rose geranium leaves can be used as a potential adsorbent for the sorption of ibuprofen in solution.