A modified homogeneous precipitation method has been used to synthesize ZnS nanoparticles. Starch and polyvinyl alcohol (PVA) were utilized as capping molecules, and later, the ZnS–PVA-capped nanoparticles were then incorporated with chitosan to form ZnS–chitosan nanocomposites for the removal of Cr( vi ) ion from wastewater. The optical measurements of the synthesized ZnS nanoparticles showed the band gap which was blue-shifted when compared with the bulk ZnS material. The crystalline structures were determined by X-ray diffraction, and the crystalline sizes were estimated from the Scherer formula. XRD spectra confirmed the formation of hexagonal phase for the uncapped ZnS nanoparticles with an average crystalline size of 3.71 nm whereas the starch- and PVA-capped ZnS nanoparticles showed the formation of cubic phase structures with crystalline sizes of 3.26 and 2.88 nm. The TEM image showed spherical particles with regular morphologies and significantly narrow size distributions. The calculated average particle diameters were in good agreement with the estimated XRD result. The removal of Cr( vi ) ion from wastewater was studied through the adsorption process. The effect of pH, dosage, and contact time was investigated. More than 95% of the metal ion recovery was achieved through using ZnS–chitosan nanocomposites.

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.

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.

The whole world is faced with a huge challenge of the shortage of clean water due to industrialization and the intimidation of climate change. Poor water quality distresses many areas of human’s well-being. Although there are existing technologies for water treatments, many of these methods utilize toxic substances which create more problems into the environment. The preparation of bis(N-benzyl-salicydenaminato)zinc (II) complex and the synthesis of zinc oxide nanoparticles via the thermal decomposition of zinc complex together with the fabrication of ZnO-chitosan nanocomposites for the removal of iron (II) ions from wastewater is reported. The optical properties of the synthesized nanoparticles showed band edges that are red-shifted in wavelengths when the decomposition temperature was increased. The XRD patterns displayed the hexagonal ZnO phase for the synthesized nanoparticles. TEM images revealed spherical-shaped particles which became agglomerated when the temperature was increased. The parameters such as pH, contact time, and initial concentration were investigated during the water treatment. The pH = 6 was found to be optimum, and the highest percentage removal was recovered after three hours for both adsorbents.