Simultaneous decomplexation of Pb-EDTA and elimination of free Pb ions by MoS2/H2O2: Mechanisms and applications.

The critical challenge of effectively removing Pb-EDTA complexes and Pb(II) ions from wastewater is pivotal for environmental remediation. This research introduces a cutting-edge bulk-MoS2/H2O2 system designed for the simultaneous decomplexation of Pb-EDTA complexes and extraction of free Pb(II) ions, streamlining the process by eliminating the need for subsequent treatment stages. The system exhibits outstanding efficiency, achieving 98.1% decomplexation of Pb-EDTA and 98.6% removal of Pb. Its effectiveness is primarily due to the generation of reactive oxygen species, notably •OH and O2•- radicals, facilitated by bulk-MoS2 and H2O2. Key operational parameters such as reagent dosages, Pb(II): EDTA molar ratios, solution pH, and the presence of coexisting ions were meticulously evaluated to determine their impact on the system's performance. Through a suite of analytical techniques, the study confirmed the disruption of Pb-O and Pb-N bonds, further elucidating the decomplexation process. It also underscored the synergistic role of bulk-MoS2's adsorption properties and the formation of PbMoO4-like precipitates in enhancing Pb elimination. Demonstrating the bulk-MoS2/H2O2 system as a robust, one-step solution that meets stringent Pb emission standards, this study provides in-depth insights into the removal mechanisms of Pb-EDTA, affirming its potential for broader application in wastewater treatment practices.

Singlet oxygen generation in light-assisted peroxymonosulfate activation by carbon nitride: Role of elevated crystallinity.

Carbon nitride (CN) is an emerging 2D non-metal semiconductor material that could be used in photocatalysis and advanced oxidation processes (AOPs) for pollutants degradation. The radical-induced degradation by CN in photocatalysis or photo-assisted AOPs was widely reported in previous studies. Nevertheless, how the non-radical degradation by CN materials could be achieved under irradiation is neither well understood nor controlled. In this work, crystalline carbon nitride (CCN) was synthesized via a facile molten-salt method, and used to activate peroxymonosulfate (PMS) under visible light (>420 nm) to selectively and efficiently degrade tetracycline (TC). Compared to the traditional polymeric carbon nitride (PCN), CCN was found to be a superior PMS activator with the assistance of visible light, which was ascribed to the increased crystallinity of CN tri-s-triazine units and the increased number of catalytic sites, thereby optimizing the photoelectric properties. The activation performance could be further improved by copper loading, with TC degradation rate nearly six times more than that of PCN. EPR trapping and quenching tests showed that singlet oxygen (1O2) was the dominant reactive oxygen species in the CCN/PMS/visible light system, attributing to the increased graphitic N sites and formation of electron-deficient C in C-N bonding between neighboring tri-s-triazine units upon crystallinity elevation in CCN. In contrast to the conventional radical-based photocatalysis and AOP processes, the visible light-assisted non-radical AOP degradation was highlighted for the selectivity and the remarkable resistance to the impacts of background inorganic anions or natural organic matter (up to 10 mg/L) in the actual water matrix. This work revealed the 1O2 generation mechanism by CN-based materials under the joint assistance of visible light illumination and crystallinity elevation, and its excellent removal performance demonstrates the great potential of CCN-based materials in the practical wastewater treatment.

Redispersion Behavior of 2D MoS2 Nanosheets: Unique Dependence on the Intervention Timing of Natural Organic Matter.

The aggregation-redispersion behavior of nanomaterials determines their transport, transformation, and toxicity, which could be largely influenced by the ubiquitous natural organic matter (NOM). Nonetheless, the interaction mechanisms of two-dimensional (2D) MoS2 and NOM and the subsequent influences on the redispersion behavior are not well understood. Herein, we investigated the redispersion of single-layer MoS2 (SL-MoS2) nanosheets as influenced by Suwannee River NOM (SRNOM). It was found that SRNOM played a decisive role on the redispersion of MoS2 2D nanosheets that varied distinctly from the 3D nanoparticles. Compared to the poor redispersion of MoS2 aggregates in the absence or post-addition of SRNOM to the aggregates, co-occurrence of SRNOM in the dispersion could largely enhance the redispersion and mobility of MoS2 by intercalating into the nanosheets. Upon adsorption to SL-MoS2, SRNOM enhanced the hydration force and weakened the van der Waals forces between nanosheets, leading to the redispersion of the aggregates. The SRNOM fractions with higher molecular mass imparted better dispersity due to the preferable sorption of the large molecules onto SL-MoS2 surfaces. This comprehensive study advances current understanding on the transport and fate of nanomaterials in the water system and provides fresh insights into the interaction mechanisms between NOM and 2D nanomaterials.