Eco-Friendly Polysaccharide-Based Synthesis of Nanostructured MgO: Application in the Removal of Cu2+ in Wastewater

Abstract

The present study described three synthesis routes using different natural polysaccharides as low-cost non-toxic fuels and complexing agents for obtaining MgO. Cassava starch, Aloe vera leaves (mainly acemannan) gel, and citric pectin powder were mixed with magnesium nitrate salt and calcined at 750 °C for 2 h. The samples were named according to the polysaccharide: cassava starch (MgO-St), citrus pectin (MgO-CP), and Aloe vera (MgO-Av). X-ray diffraction identified the formation of a monophasic periclase structure (FCC type) for the three samples. The N2 adsorption/desorption isotherms (B.E.T. method) showed an important difference in textural properties, with a higher pore volume (Vmax = 89.76 cc/g) and higher surface area (SA = 43.93 m2/g) obtained for MgO-St, followed by MgO-CP (Vmax = 11.01 cc/g; SA = 7.01 m2/g) and MgO-Av (Vmax = 6.44 cc/g; SA = 6.63 m2/g). These data were consistent with the porous appearance observed in SEM images. Porous solids are interesting as adsorbents for removing metallic and molecular ions from wastewater. The removal of copper ions from water was evaluated, and the experimental data at equilibrium were adjusted according to the Freundlich, Langmuir, and Temkin isotherms. According to the Langmuir model, the maximum adsorption capacity (qmax) was 6331.117, 5831.244, and 6726.623 mg·g−1 for the adsorbents MgO-St, MgO-Av, and MgO-CP, respectively. The results of the adsorption isotherms indicated that the synthesized magnesium oxides could be used to decrease the amount of Cu2+ ions in wastewater.

Synthesis of Periclase Phase (MgO) from Colloidal Cassava Starch Suspension, Dual Application: Cr(III) Removal and Pigment Reuse

“…The values obtained for chromium removal can be compared to studies reported in the literature with materials typically used for Cr 3+ and Cr 6+ removal, as shown in Table 6. In addition, the adsorption capacity of Cr 3+ by MgO can be highlighted by the ion exchange process that occurs when MgO is added to different concentrations of Cr 3+ ion solutions [14]. In Cr(VI) removal studies by Alvares et al [31], zeolites were used in a discontinuous system for tannery effluent, opting for 0.0057 mg/g in the removal tests, with considerably low values.…”

“…According to Balaba et al [14], the metal removal mechanism by MgO involves at least three steps, shown in Equations ( 3)-( 5).…”

“…Starch is a biodegradable polysaccharide consisting of amylose and amylopectin molecules made up of D-glucose units [13]. Natural polysaccharides act as low-cost, non-toxic alternative additives produced from plants, acting as complexing agents for central metal ions, and can adapt to the growth of MgO [14]. Several other studies have shown the advantages of opting for biosynthesis and green fabrication using natural fuels, e.g., Naveed et al 2023 [15] in their studies using aqueous extract of Nigella sativa seeds in the synthesis of zero-valent iron nanoparticles (ZVI-NPs) and evaluation of their heavy metal remediation capabilities.…”