Green Synthesis of Date Palm Seed Extract–Derived Iron Sulfide Nanoparticles for Effective Removal of Hexavalent Chromium

In this study, we investigated the removal of hexavalent chromium (Cr(VI)) through an innovative approach, which employed iron sulfide nanoparticles synthesized via a green chemistry technique, utilizing extracts derived from date palm seeds (referred to as ds-FeS). Batch studies, which were well represented by the Langmuir isotherm model, were conducted to determine the maximum removal capacities (q_m) of ds-FeS nanoparticles at three different initial pH conditions (pH = 3, 7, and 9). Additionally, batch kinetic studies were conducted under varying conditions of initial Cr(VI) load (3.5, 9, 27, and 38 mg/g of nanoparticles), nanoparticle dose (25, 37, 50, and 75 g/g of Cr(VI)), and initial pH (3, 5, 7, and 9). Results demonstrated the positive impact of acidic pH during Cr(VI) removal by ds-FeS wherein the highest q_m of 31.3 mg/g and initial rate of 6.95 mg/g·min (pseudo-second order kinetics) were observed at pH 3. Conversely, with an increase in pH to neutral and alkaline conditions, a decline in both q_m and initial rates was observed. Measurements of solution pH, total chromium, and particle surface chemistry using X-ray diffraction and Fourier transform infrared spectrometry techniques revealed the crucial roles of reduction, surface precipitation, and complexation processes in Cr(VI) removal by ds-FeS nanoparticles. Overall, this study demonstrates the promising potential of environmentally friendly, date palm seed–derived iron sulfide nanoparticles for Cr(VI) removal.