Applications of Carbon-Based Materials in Activated Peroxymonosulfate for the Degradation of Organic Pollutants: A Review

Degradation of methyl parathion in thermally activated peroxymonosulfate processes: Kinetics, reaction mechanism and toxicity evaluation

Methyl parathion, as widely utilized organophosphorus pesticide, was commonly detected in aquatic environments. Heat-activated peroxymonosulfate (PMS) represented an emerging advanced oxidation process. In this study, the degradation efficiency and reaction mechanism of methyl parathion by heat-activated PMS system were investigated by experimental and theoretical aspects. The findings indicated that the degradation efficacy of methyl parathion improved with the increase in temperature, PMS concentration and pH. The radical quenching experiments revealed that the primary reactive radical initiating methyl parathion degradation was ·OH. Moreover, we determined that the coexistence mechanism existed in the heat-activated PMS process involving both PMS direct oxidative and radical oxidative degradation of methyl parathion. Then, the possible reactions of methyl parathion with ·OH and SO4˙- in the water environment were calculated at SMD/M06-2X/6-311++G(3df,2p)//SMD/M06-2X/6-311+G(d,p) level to clarify the detailed reaction mechanism. It was found that two reactive radicals were more prone to react with methyl parathion via addition reaction at the P=S bond. The total reaction rate constants of methyl parathion with ·OH and SO4˙- slightly decreased as the temperature increased from 298 K to 333 K. Eventually, the toxicity evaluation by the QSAR-based toxicity prediction software demonstrated that the aquatic toxicity of most products was lower than methyl parathion, but still has positive mutagenicity and toxic developmental toxicity. This work offered novel insights into the reaction mechanism of methyl parathion with activated PMS and could also help to clarify the fate of methyl parathion in the water environment.

Novel hemin-derived Fe/N-C magnetic catalyst for enhanced peroxymonosulfate activation and diclofenac degradation

In this study, Fe involved N-doped carbon catalysts labelled as PA@Hemx (x = pyrolysis temperature) was synthesized through a one-step pyrolysis of hemin (Hem) and polyacrylate (PA). The reported method enables high dispersion and exposure of both Fe and N active sites on PA derived carbon. The PA@Hemx samples were then used for peroxymonosulfate (PMS) activated diclofenac (DCF) degradation. Results from the characterization studies verified the successful incorporation of hemin in the composite. Approximately 99.2 % DCF degradation at pH = 6.01 was achieved in 60 min using 0.1 g L-1 PA@Hem700 and 1.0 mM PMS. The pseudo-second-order kinetic model and Langmuir model were used to described the uptake and equilibrium process in DCF/PA@Hem700 system. Scavenging and electron-spin-resonance studies showed a non-radical singlet oxygen species (1O2) dominates over •OH and SO4•- radicals in the system. The role of electron transfer was also verified via chronoamperometry and electrochemical-impedance spectroscopy techniques. Furthermore, the PA@Hem700/PMS remained highly active towards DCF degradation even in the presence of common anions, humic acid, and various water matrices. The developed catalyst exhibited a TOC removal of 65.8 %. The study also established the potential of PA@Hem700/PMS to degrade other organic pollutants (e.g., tetracycline (TC), simazine (SIM), and sulfamethoxazole (SMX)). The results from this study are expected to advance research on synthesizing other novel polymer-based Fe/N-C catalysts for degrading organic pollutants.

Single-step synthesis of nitrogen and phosphorus co-doped biochar and its application in dye removal: synergistic effects of adsorption and peroxymonosulfate activation

In the field of advanced oxidation processes (AOPs), the development of catalysts with environmental friendliness and economic benefits faces multiple difficulties, mainly reflected in the catalytic efficiency, selection specificity, and complexity of the synthesis process. This study, we reported a nitrogen and phosphorus co-doped carbon catalyst (CANP800-1) synthesized by a one-step pyrolysis method. The co-doped catalyst was able to achieve 100 % removal of Acid Orange 7 (AO7) in about 30 min and had a high apparent rate constant (kobs = 0.125 min-1), which is better than unmodified carbon and other single-doped comparative materials. Structural analyses pinpointed that N, P co-doped enhanced specific surface area (1179 m2/g), introduced abundant mesopores, and created a wealth of active sites (such as graphitic nitrogen, C-P bonds) synergistically promoting adsorption and peroxymonosulfate (PMS) activation. The CANP800-1/PMS system had significant adaptability to various water matrices, including pH, coexisting ions, natural organic matter, and real water conditions. A mechanistic investigation confirmed that singlet oxygen (1O2) was essential to the reaction process, while electrochemical studies and DFT simulations validated that N/P-induced enhancement of electron transfer and PMS adsorption took place. This study established an innovative metal-free catalytic system that exhibited remarkable effectiveness in sustainable water treatment, providing distinctive solutions and a theoretical basis for ongoing technical difficulties in industrial wastewater treatment.

Efficient simultaneous degradation of multiple sulfonamide antibiotics in soil using biocarbon-based nanomaterials as catalysts for persulfate activation

There is an urgent need to develop effective and sustainable methods to decrease sulfonamide (SA) contamination of soil. Herein, a non-homogeneous system of zero-valent metal-biochar-based composites was proposed and tested for persulfate (PS) activation. This system employed zero-valent iron (Fe0) as an electron donor to catalyze the cleavage of the OO bond in PS, thereby generating reactive oxygen species (ROS) that degrade SAs. Notably, the incorporation of elemental sulfur (S) significantly mitigated the passivation of Fe0, leading to an enhanced degradation capability of the system. The system decomposes 84-97 % of SAs at their concentration in soil suspension 10 mg/kg in 3 h. Among the coexistence of several SAs, the system showed the fastest degradation rate of sulfisoxazole with a kobs of 0.0305 min-1, nearing complete removal within 3 h. The system is resistant to the impact of organic matter in soil. It allows to decrease concentration of sulfadiazine in actual contaminated soil on 73 % in 2 h. The system remains effective with decreasing concentrations of PS from 20 mM to 2.5 mM, which lowered the operating cost. T.E.S.T software evaluation showed a significant reduction in the bioaccumulation toxicity and developmental toxicity of the degradation products, suggesting that the system is environmentally friendly. The high efficiency of the catalytic system, the simplicity and economy of the manufacturing process, the resistance to interference in real soil, and the environmental friendliness make this technology promising for mitigating the problem of the environment contamination by SAs.

The loading of Fe ions on N-doped carbon nanosheets to boost photocatalytic cascade for water disinfection

The pervasive presence of pathogenic bacteria in water environment poses a serious threat to public health. Here, a photocatalytic cascade was developed to reveal great water disinfection. Firstly, N-doped carbon nanosheets (N-CNSs) about 30-50 nm in size were synthesized by a hydrothermal strategy. It revealed wide-spectrum photocatalysis for H2O2 generation via a typical two-step single-electron process. A Fenton agent (Fe ion) was loaded, N-CNSs-Fe can in-situ convert photocatalytic H2O2 into ·OH with high oxidation potential. Moreover, its Fenton active is three times greater than pure Fe2+ owing to electron enrichment from N-CNSs to Fe for Fe3+/Fe2+ cycle. Further investigation displayed that Fe loading also could decrease bad gap and promote charge separation to boost photocatalysis. In addition, N-CNSs-Fe possesses positive surface potential to exhibit strong interaction with negative bacteria, facilitating the capture. Therefore, the nanocomposite can effectively inactivate E. coli with a lethality rate of 99.7 % under stimulated sunlight irradiation. In addition, it also was employed to treat a complex lake water sample, revealing great antibacterial (95.1 %) and dye-decolored (92.3 %) efficiency at the same time. With novel biocompatibility and antibacterial ability, N-CNSs-Fe possessed great potential for water disinfection.