Effect of γ-Fe2O3 nanoparticles on the composition of montmorillonite and its sorption capacity for pyrene

Performance and reaction mechanism of montmorillonite/α-Fe2O3/starch bio-nanocomposite as high-efficiency photocatalytic degradation of acetaminophen: Characterization, feasibility, and pathway

The worldwide challenge of eliminating pharmaceutical contaminants requires immediate attention. Developing bio-based catalysts that are eco-friendly, reusable, and high-performance, employing starch (ST) and montmorillonite (MMT) as support, holds tremendous promise as a novel biocatalyst for pharmaceutical waste removal. In this study, a montmorillonite/α-Fe2O3/starch (MMT/α-Fe2O3/ST) bio-nanocomposite photocatalyst was successfully synthesized and used for acetaminophen (ACT) degradation under UVA-LED irradiation. The influence of operational factors, such as catalyst, ACT concentrations, and solution pH, on photocatalytic activity was examined in detail; catalyst: 0.75 g/L, pH: 7.1, leading to total ACT (10 mg/L) removal in ∼80 min. MMT/α-Fe2O3/ST showed excellent durability due to negligible Fe leaching. After four successive degradation cycles, ACT and TOC elimination efficiencies remained over 91 and 42.7 %. Compared to other anions studied, carbonate ions suppressed the most ACT degradation. Based on the radical scavenger experiments, hydroxyl and superoxide radicals and holes were involved in the MMT/α-Fe2O3/ST system. LC-MS results were used to propose ACT degradation pathways. This work illuminated the significance of biocatalysts in removing emerging pollutants from wastewater.

The important role of surface hydroxyl groups in aluminum activation during phyllosilicate mineral acidification

Phyllosilicate minerals are the important components in soils and an important source of activated aluminum (Al) during soil acidification. However, the mechanisms for Al activation in phyllosilicate minerals were not understood well. In this paper, the effect of phyllosilicate surface hydroxyl groups on Al activation during acidification was studied after the minerals were modified with inorganic and organic materials. After modification of kaolinite, montmorillonite, and illite with fulvic acid (FA-), iron oxide (Fe-), Fe combined with FA (Fe-FA-), and siloxane (Si-O-), the interlayer spaces were altered. For instance, when modified with Fe, Fe entered the interlayer spaces of kaolinite and montmorillonite and changed the interlayer spaces of both minerals but did not affect that of illite. Also, the other modification methods had significant effects on the interlayer space of montmorillonite but not on kaolinite and illite. It was observed that all the modification strategies inhibited Al activation during acidification by reducing the number of hydroxyl groups on the mineral surfaces and inhibiting protonation reactions between H⁺ and hydroxyl groups. Nevertheless, the inhibition effect varies with the type of phyllosilicate mineral. For kaolinite (Kao), the inhibition effect of the different modification methods on Al activation during acidification followed: Fe-FA-Kao > Fe-Kao > Si-O-Kao > FA-Kao. Additionally, for montmorillonite (Mon), the inhibition effect was in the order: Si-O-Mon > Fe-Mon > Fe-FA-Mon > FA-Mon, while for illite, it was: Fe-illite > Si-O-illite ≈ Fe-FA-illite > FA-illite. Thus, the hydroxyl groups on the surfaces and edges of phyllosilicate minerals play an important role in the activation of Al from the mineral structure. Also, the protonation of hydroxyl groups may be the first step during Al activation in these minerals. The results of this study can serve as a reference for the development of new technologies to inhibit soil acidification and Al activation.