Synergetic Removal of Pb(II)- and Sulfonamide-Mixed Pollutants using Ni/Co Layered Double Hydroxide Nanocages Coupled with Peroxymonosulfate

Abstract

Organic pollutants are often present in wastewater coupled with toxic metallic ions, which are harmful to both human beings and the ecological environment, and their simultaneous removal is of great significance. In this work, hollow Ni/Co layered double hydroxide (LDH) nanocages were synthesized through the hydrothermal method by using zeolitic imidazolate framework-67 as a self-sacrificial template, and it was further used as a catalyst to activate peroxymonosulfate (PMS) for sulfonamide (SA) degradation and an adsorbent for Pb(II) removal simultaneously. The materials were characterized using various techniques, and the effect of parameters including the dosage of the catalyst and PMS, initial temperature, and pH on the performances of the LDH nanocage was investigated. Nearly 80% of SA (15 mg/L) could be degraded via PMS activation, whereas ∼93% of Pb(II) (20 mg/L) could be removed simultaneously within 60 min. During the reaction, there were redox cycles for both Co and Ni over the surface of LDH, but Pb did not participate in the process, and it had a slightly negative effect on SA degradation. The quenching experiments and the electron paramagnetic resonance results showed that the radicals ( • OH,, and 1 O 2 ) generated from PMS activation participated in the process. Finally, the possible mechanism and degradation pathways were proposed, based on the intermediate products identified, and the toxicity of the intermediate products was evaluated.

Synergistic Removal of U (VI), Pb(II), and HA on nZVI/MoS2 Composites Investigated by Batch, Spectroscopic, and Modeling Techniques

“…Figure A–C shows the effect of pH on U­(VI), Pb­(II), and HA removal, respectively. The removal amount of U­(VI) increased gradually with an increase in pH from 2.0 to 8.0, while a slight decrease in U­(VI) adsorption was observed at pH > 8, which was similar to previous studies. , This phenomenon could be explained by the electrostatic interaction. It was reported that U­(VI) ions mainly presented as positively charged species (i.e., UO 2 2+ ) at pH < 4.0.…”

“…The kinetic model as an important tool has been widely introduced for demonstrating reaction mechanisms of pollutants such as physical/chemical adsorption. , The adsorption kinetics of U­(VI), Pb­(II), and HA on MoS 2 and nZVI/MoS 2 were fitted using pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models, which are provided in the Supporting Information (SI). As shown in Figure S1A–S1B and Table S1 in SM, the removal kinetics of U­(VI), Pb­(II), and HA on MoS 2 and nZVI/MoS 2 can be fitted by the PSO model due to a high correlation coefficient ( R 2 > 0.995), suggesting the chemical adsorption process. ,,, In addition, the initial adsorption rate of U­(VI) and HA on MoS 2 (0.0099 and 0.0084 /min, respectively; Figure S1) was significantly lower than that of nZVI/MoS 2 (0.0254 and 0.0383 /min, respectively), revealing the fast adsorption equilibrium of nZVI/MoS 2 . The removal amount of Pb­(II) on nZVI/MoS 2 (78 mg/g after 24 h) was slightly higher than that of U­(VI) (74 mg/g), which was consistent with previous studies. , Consequently, the adsorption rate was primarily dominated by surface and internal diffusion; then, the removal rate was determined by the surface chemical reaction. , …”

“…With the rapid development of modern industrialization and civilization, the increasing production of various environmental pollutants (e.g., organics, heavy metals, and radionuclides) has been paid more attention due to the high toxicity, carcinogenicity, and hazardous bioaccumulation. − For instance, uranium (e.g., dissolved U­(VI) and sparingly dissolved U­(IV)) has been widely used as basic raw materials for nuclear energy. , Lead (Pb­(II)) as a typical heavy metal has been utilized in various industries such as milling, processing, printing, storage batteries, and smelting. ,− Natural organic matter (NOM, such as humic acid (HA) and fulvic acid (FA)) is an integral component of aquatic systems, which possesses a complex structure with a high molecular weight. − Additionally, the fate and transport of heavy metal/radionuclides are significantly influenced by organics due to the formation of stable complexes. ,− Thus, it is of great importance to remove heavy metals, radionuclides, and HA simultaneously in actual environmental remediation. − Various removal methods, including ion exchange, chemical precipitation, membrane separation, redox, osmosis, and adsorption, have been widely investigated to remove environmental pollutants in recent years. , Among them, adsorption and redox are simple and effective techniques. , The development of cost-efficient adsorbents with high adsorption performance, large reduction ability, and exceptional selective enrichment is of great significance for the elimination of radionuclides, heavy metals, and organics from aqueous solutions …”