Machine-Learning-Assisted Material Discovery of Pyridine-Based Polymers for Efficient Removal of ReO4.

Efficient capture of 99TcO4- is the focus in nuclear waste management. For laboratory operation, ReO4- is used as a nonradioactive alternative to 99TcO4- to develop high-performance adsorbents for the treatment. However, the traditional design of new adsorbents is primarily driven by the chemical intuition of scientists and experimental methods, which are inefficient. Herein, a machine learning (ML)-assisted material genome approach (MGA) is proposed to precisely design high-efficiency adsorbents. ML models were developed to accurately predict adsorption capacity from adsorbent structures and solvent environment, thus predicting and screening the 2450 virtual pyridine polymers obtained by MGA, and it was found that halogen functionalization can enhance its adsorption efficiency. Two halogenated functional pyridine polymers (F-C-CTF and Cl-C-CTF) predicted by this approach were synthesized that exhibited excellent acid/alkali resistance and selectivity for ReO4-. The adsorption capacity reached 940.13 (F-C-CTF) and 732.74 mg g-1 (Cl-C-CTF), which were better than those of most reported adsorbents. The adsorption mechanism is comprehensively elucidated by experiment and density functional theory calculation, showing that halogen functionalization can form halogen-bonding interactions with 99TcO4-, which further justified the theoretical plausibility of the screening results. Our findings demonstrate that ML-assisted MGA represents a paradigm shift for next-generation adsorbent design.

Oxidation of emerging contaminants by S(IV) activated ferrate: Identification of reactive species.

Studies on the Fe(VI)/S(IV) process have focused on improving the efficiency of emerging contaminants (ECs) degradation under alkaline conditions. However, the performance and mechanisms under varying pH levels remain insufficiently investigated. This tudy delved into the efficiency and mechanism of Fe(VI)/S(IV) process using sulfamethoxazole (SMX) and ibuprofen (IBU) as model contaminants. We found that pH was crucial in governing the generation of reactive species, and both Fe(V/IV) and SO4•- were identified in the reaction system. Specifically, an increase in pH favored the formation of SO4•-, while the formation of Fe(VI) to Fe(V/IV) became more significant at lower pH. At pH 3.2, Fe(III) resulting from the Fe(VI) self-decay reactedwith HSO3-to produce SO4•-and •OH. Under near-neutral conditions, the coexistance of Fe(V/IV) and SO4•- in abundance contributed to the optimal oxidation of both pollutants in the Fe(VI)/S(IV) process, with the removal exceeding 74% in 5 min. Competitive quenching experiments showed that the contributions of Fe(V/IV) to SMX and IBU destruction dimished, while the contributions of radicals increased with an increase in pH. However, this evolution was slower during SMX degradation compared to IBU degradation. A comprehensive understnding of pH as the key factor is essential for the optimization of the sulfite-activated Fe(VI) oxidation process in water treatment.

Mechanistic insight into selective adsorption and easy regeneration of carboxyl-functionalized MOFs towards heavy metals.

The development of heavy metal adsorbents with high selectivity has become a research hotspot due to the interference of coexisting ions (e.g., Na+, Ca2+) in the actual wastewater, but the more difficult regeneration caused by high adsorption selectivity severely limits its practical applications. Herein, a carboxyl adsorbent, MIL-121, demonstrated high adsorption selectivity for heavy metals at 10,000 mg/L of Na+ (removal > 99% for Cu2+) as well as unexpected easy regeneration (desorption > 99%) at low H+ concentration (10-3.5-10-3.0 M), which is hundreds of times lower than that of ever reported selective adsorbents (> 10-1 M H+). X-ray photoelectron spectrometry (XPS), extended X-ray absorption fine structure (EXAFS) coupled with Density functional theory (DFT) simulation unveil that the -COOH groups in MIL-121 for heavy metals adsorption is specific inner-sphere coordination with higher binding energy (1.31 eV for Cu), and less energy required for regeneration (0.26 eV for H). Similar high selectivity and easy regeneration were also satisfied with other heavy metals (e.g., Pb2+, Ni2+), and removal of heavy metals remained > 99% in 10 consecutive adsorption-desorption cycles. For actual copper electroplating wastewater treatment, MIL-121 could produce ~ 3600 mL clean water/g sample, outperforming 300 mL that of the benchmark commercial adsorbent D-113. This study shows the potential of MIL-121 for heavy metal wastewater treatment and provides mechanistic insight for developing adsorbents with high selective adsorption and easy regeneration.