Insights into the impacts of chloride ions on the oxidation of 2,4-dinitrotoluene using ferrous activated persulfate: Removal efficiency, reaction mechanism, transformation pathway, and toxicity assessment

Preparation of hydrophobic and lipophilic carboxymethyl cellulose composite aerogel using ferrous ion/ persulfate and its directed oxidation for oil-water emulsion separation

In particular, efficient oxidative demulsification is an effective method for oil-water separation. However, the inactivation of free radicals owing to the rapid release of transition metals is the main factor that reduces the effectiveness. In this study, a hydrophobic and lipophilic CP/SiO2@Fe2+ composite aerogel was prepared using carboxymethyl cellulose as substrate, polyvinyl alcohol as reinforcement, and SiO2 nanoparticles as hydrophobic modifier. The resulting aerogel had a water contact angle of 139°, oil absorption yield of 99.9 %, higher specific surface area 132.13 m2·g-1, low density of 0.021 g·cm-3, and high porosity of 98.60 %. Fe2+ was slowly released from the composite aerogel after efficient Fe2+ loading of 65.77 mg·g-1. The drug exhibited a low release rate of 87.72 % after 9 h, which was higher than that of the composite aerogel. This promoted the efficient presence of SO4-· activated from persulfate oxidation in the catalytic oxidative demulsification system over a long period. The green and efficient separation of oily-water was achieved by the synergistic effect of the adsorption of the hydrophobic and lipophilic composite aerogel and targeted and efficient oxidative demulsification. These results demonstrate the advantages of high separation efficiency, durability, stability of the CP/SiO2@Fe2+ composite aerogel for oil-water separation.

Degradation of organic pollutants by the Cl-/PMS process

The viewpoints on whether high concentrations of chloride ion (Cl-) promote or inhibit the oxidation activity of activated persulfates are still inconclusive. Furthermore, the degradation of organic pollutants by the persulfates in the presence of high Cl- concentrations without any activation medium has not yet been studied. In this work, the efficiency and mechanism of degradation of organic pollutants such as carbamazepine (CBZ), sulfadiazine (SDZ), and phenol (PN) by Cl--activated PMS (denoted as Cl-/PMS) were investigated. Results showed that Cl- could effectively activate PMS for the complete removal of CBZ, SDZ, and PN with reaction kinetic constants of 0.4516 min-1, 0.01753 min-1, and 0.06805 min-1, respectively. Parameters such as PMS dose, Cl- concentration, solution pH, and initial concentrations of organic pollutants that affect the degradation efficiencies of the Cl-/PMS process were optimized. Unlike conventional activated persulfates, it was confirmed that the free chlorine was the main active species in the Cl-/PMS process. Finally, the degradation by-products of CBZ and SDZ as well as their toxicity were detected, and a possible degradation pathway for CBZ and SDZ was proposed. Though higher toxic chlorinated by-products were generated, the Cl-/PMS process was still an efficient oxidation method for the removal of organic pollutants in aqueous solutions which contain high concentrations of Cl-.

Magnetic MoS2/Fe3O4 composite as an effective activator of persulfate for the degradation of tetracycline: performance, activation mechanisms and degradation pathways

The activated persulfate (PS) process could produce sulfate radical (SO4·-) and rapidly degrade organic pollutants. The application of Fe3O4 as a promising PS activator was limited due to the rapid conversion of Fe2+ to Fe3+ on its surface. Mo4+ on MoS2 surface could be used as a reducing site to convert Fe3+ to Fe2+, but the separation and recovery of MoS2 was complex. In this study, MoS2/Fe3O4 was prepared to accelerate the Fe3+/Fe2+ cycle on Fe3O4 surface and achieved efficient separation of MoS2. The results showed that MoS2/Fe3O4 was more effective for PS activation compared to Fe3O4 or MoS2, with a removal efficiency of 91.8% for 20 mg·L-1 tetracycline (TC) solution under the optimal conditions. Fe2+ and Mo4+ on MoS2/Fe3O4 surface acted as active sites for PS activation with the generation of SO4•-, •OH, •O2-, and 1O2. Mo4+ acted as an electron donor to promote the Fe3+/Fe2+ cycling and thus improved the PS activation capability of MoS2/Fe3O4. The degradation pathways of TC were inferred as hydroxylation, ketylation of dimethylamino group and C-N bond breaking. This study provided a promising activated persulfate-based advanced oxidation process for the efficient degradation of TC by employing MoS2/Fe3O4 as an effective activator.

Hydrophilic magnetic Ti3C2Tx-based nanocomposite as an efficient boron adsorbent: Synthesis, characterization, and application

It is widely recognized that wastewater containing boron is an environmental issue. Therefore, the development of adsorbents with excellent adsorption capacity, stability, and recyclability is essential in water treatment applications. A Fe3O4/PDA/Ti3C2Tx/PEI/DHHA nanocomposite has been prepared that can be used to separate and recover boric acid by adjusting the pH of the solution, based on the affinity theory of boric acid and cis-diol. Through series characterization, it was determined that the adsorbent possessed good magnetic properties, high hydrophilicity and high loading capacities. In this study, 4-formylphenylboronic acid (FPBA) was selected as the model compound. The nanocomposite exhibited an adsorption equilibrium time of 10 h and an adsorption capacity of 98.99 mg/g at pH = 8.5 and 25 °C. The Langmuir isothermal model and the quasi-secondary kinetic model are both appropriate for describing the adsorption process. Thermodynamic results suggest that adsorption is a spontaneous chemisorption process. Furthermore, the nanocomposite retains good regeneration performance after five adsorption-desorption cycles.