Desorption of Coffee Pulp Used as an Adsorbent Material for Cr(III and VI) Ions in Synthetic Wastewater: A Preliminary Study

Removal of heavy metals from wastewater by aerogel derived from date palm waste

Cellulose that has been sourced from date palm leaves as a primary component was utilised. This cellulose served as the foundational material for the development of an aerogel composite. During this process, MXene (Ti3C2Tx) played a pivotal role in enhancing the overall composition of the aerogel. To ensure the stability and durability of the resulting aerogel structure, calcium ions were introduced to the mix. These ions facilitated the cross-linking process of sodium alginate molecules, ultimately leading to the formation of calcium alginate. This cross-linking step is crucial for the enhanced mechanical and chemical stability of the aerogel. Incorporating alginate and Ti3C2Tx into the cellulose aerogel enhanced its structural integrity in aqueous conditions and increased its adsorption capacity. When evaluated with synthetic wastewater, this composite exhibited remarkable adsorption capacities of 72.9, 114.4, 92.9, and 123.9 mg/g for As, Cd, Ni, and Zn ions, respectively. A systematic study was carried out to see the effect of various parameters, including contact time, MXene concentration, pH, and temperature on the adsorption of these elements. Peak adsorption was achieved at 60 min, favoring a pH range between 6 and 8 and exhibited optimal sorption efficiency at lower temperatures. The adsorption kinetics adhered closely to a pseudo-second-order, while the Freundlich model adeptly described the adsorption isotherms. An interesting result of this research was the aerogel's regenerative potential. After undergoing a basic acid treatment, the MXene/cellulose/alginate aerogel composite could be restored and reused for up to three cycles, all while maintaining its core performance capabilities even after the rigorous cross-linking processes. In three consecutive cycles, the removal percentages for As, Cd, Ni, and Zn were 48.15%, 80.38%, 56.51%, and 86.12% in cycle 1; 37.35%, 65.63%, 45.97%, and 78.42% in cycle 2; and 28.60%, 56.22%, 34.70%, and 65.83% in cycle 3, respectively. The composite was tested in conditions resembling seawater salinity. Impressively, the aerogel continued to demonstrate a significant ability to adsorb metals, reinforcing its potential utility in real-world aquatic scenarios. These findings suggest that the composite aerogel, integrating MXene, cellulose, and alginate, is an effective medium for the targeted removal of heavy metals from aquatic environments.

Simultaneous removal of Cu (II) and Cr (VI) ions from petroleum refinery wastewater using ZnO/Fe3O4 nanocomposite

The presence and removal of heavy metals such as Cu(II) as well as Cr(VI) in petroleum refinery wastewater calls for concerted efforts due to their mobility, toxicity, bioaccumulation, and non-biodegradability in the environment. In this present work, zinc oxide (ZnO), iron oxide (Fe₃O₄) nanoparticles and ZnO/Fe₃O₄ nanocomposites were synthesized via simple sol-gel and chemical reduction methods; characterized using different analytical tools and then applied as nanoadsorbent to sequester Cu(II) and Cr(VI) ions from Petroleum Refinery wastewater via batch adsorption process. Cu(II) and Cr(VI) adsorption processes were examined with respect to contact time (kinetic effect), nanoadsorbent dosage, isotherm equilibrium, and thermodynamic parameters. ZnO/Fe₃O₄ nanocomposites with higher surface area (39.450 m²/g) have a mixture of rod-like and spherical shapes as compared to ZnO and Fe₃O₄ nanoparticles with spherical shape only and surface areas of 8.62 m²/g and 7.86 m²/g) according to the high-resolution scanning electron microscopy (HRSEM) and Brunauer-Emmett-Teller (BET) analysis. The X-ray diffractometer (XRD) results revealed the formation of hexagonal wurtzite structure of ZnO and the face-centered cubic structure phase of Fe₃O₄ nanoparticles, after the formation of the ZnO/Fe₃O₄ nanocomposites the phases of the nanoparticles were not affected but the diffraction peaks shifted to higher 2θ degree. The average crystallite size of ZnO and Fe₃O₄ nanoparticles and ZnO/Fe₃O₄ nanocomposites were 20.12, 26.36 and 14.50 nm respectively. The maximum removal efficiency of Cu (II) (92.99%) and Cr (VI) (77.60%) by ZnO/Fe₃O₄ nanocomposites was higher than 85.83%; 65.19% for Cu (II) and 80.57%; 62.53 for Cr (VI) using ZnO and Fe₃O₄ nanoadsorbents individually under the following conditions: contact time (15), dosage (0.08 g) and temperature (30 °C). The experimental data for Cu (II) and Cr (VI) ion removal fitted well to the pseudo-second-order kinetic and Langmuir isotherm models. The thermodynamic study suggested that the removal of the two metal ions from petroleum wastewater was endothermic. The reusability study after the fourth adsorption-desorption cycle indicated the stability of ZnO/Fe₃O₄ nanocomposites with 85.51% and 69.42% removal efficiency of Cu (II) and Cr (VI). The results showed that ZnO/Fe₃O₄ nanocomposite achieves higher performance than ZnO and Fe₃O₄ alone in the removal of Cu (II) and Cr (VI) ions from the petroleum refinery wastewater.

Adsorption of Hexavalent Chromium Using Activated Carbon Produced from Sargassum ssp.: Comparison between Lab Experiments and Molecular Dynamics Simulations

Adsorption is one of the most successful physicochemical approaches for removing heavy metal contaminants from polluted water. The use of residual biomass for the production of adsorbents has attracted a lot of attention due to its cheap price and environmentally friendly approach. The transformation of Sargassum-an invasive brown macroalga-into activated carbon (AC) via phosphoric acid thermochemical activation was explored in an effort to increase the value of Sargassum seaweed biomass. Several techniques (nitrogen adsorption, pHPZC, Boehm titration, FTIR and XPS) were used to characterize the physicochemical properties of the activated carbons. The SAC600 3/1 was predominantly microporous and mesoporous (39.6% and 60.4%, respectively) and revealed a high specific surface area (1695 m2·g-1). To serve as a comparison element, a commercial reference activated carbon with a large specific surface area (1900 m2·g-1) was also investigated. The influence of several parameters on the adsorption capacity of AC was studied: solution pH, solution temperature, contact time and Cr(VI) concentration. The best adsorption capacities were found at very acid (pH 2) solution pH and at lower temperatures. The adsorption kinetics of SAC600 3/1 fitted well a pseudo-second-order type 1 model and the adsorption isotherm was better described by a Jovanovic-Freundlich isotherm model. Molecular dynamics (MD) simulations confirmed the experimental results and determined that hydroxyl and carboxylate groups are the most influential functional groups in the adsorption process of chromium anions. MD simulations also showed that the addition of MgCl2 to the activated carbon surface before adsorption experiments, slightly increases the adsorption of HCrO4- and CrO42- anions. Finally, this theoretical study was experimentally validated obtaining an increase of 5.6% in chromium uptake.