Efficient remediation of the field soil contaminated with PAHs by amorphous porous iron material activated peroxymonosulfate

Green mechanochemical activation of solid persulfate to remove PAHs in soil: Performance and mechanism

Due to the high biotoxicity and persistence of polycyclic aromatic hydrocarbons (PAHs), the remediation of PAHs-contaminated soil becomes an intractable problem. Persulfate-based advanced oxidation processes are widely used to degrade PAHs in aquatic environment. However, they are not convenient for used in soil due to the heterogeneity and complexity of soil matrix. In this study, a green and convenient ball milling process is introduced to activate persulfate for the remediation of PAHs-contaminated soil. About 82.5% PAHs were removed with 10% wt. Na2S2O8 (PS) addition and ball-milling for 2 h under 500 r/min. The degradation of PAHs is attributed to the attack of radicals (SO4·- and·OH) generated from the activation of PS by mechanochemistry. Moreover, stable Si-O bonds were disrupted during ball-milling process, and formed free electron on the surface of soil particles. This facilitates the electron transfer from oxidants to contaminants. The particle size, surface element composition, functional group, and thermogravimetric analysis confirmed the slight disturbance of ball-milling-assisted PS process on the physical and chemical properties of soil. Therefore, ball-milling assisted PS approach would be a promising technology for the remediation of PAHs-contaminated soil.

Photocatalytic degradation of fluoranthene in soil suspension by TiO2/α-FeOOH with enhanced charge transfer capacity

Polycyclic aromatic hydrocarbons (PAHs) in soil are potentially harmful to human health. However, the use of photocatalysis technology to treat soil contaminated with PAHs remains challenging. Therefore, TiO2/α-FeOOH composite photocatalyst has been synthesized by hydrothermal method and sol-gel method and applied to photocatalytic degradation of fluoranthene in soil. The morphology, elements, crystal structure, optical properties, electrochemical characteristics, and photocatalytic activity of TiO2/α-FeOOH have been characterized. Results showed that TiO2 is tightly fixed on the surface of α-FeOOH, and TiO2/α-FeOOH had higher photocatalytic activity on photocatalytic degradation of fluoranthene in soil under simulated sunlight. The degradation efficiency of TiO2/α-FeOOH is 3.0 and 4.8 times higher than that of TiO2 and α-FeOOH, respectively. This is attributed to enhanced photocatalytic ability by enhancing the transfer capacity of electrons and holes and broadening the spectrum absorption range. The highest degradation efficiency was achieved when the pH of the soil is neutral, the ratio of water/soil is 10:1, and the dosage of catalyst is 50 mg/g. In addition, it was proved that •O2-, h+, and 1O2 are the main active substances in the photocatalysis of TiO2/α-FeOOH. The possible mechanism of a Z-type electron transfer structure was also proposed. The degradation products of fluoranthene were detected, and the degradation pathway was deduced.

Targeted degradation of naphthalene by peroxymonosulfate activation using molecularly imprinted biochar

Polycyclic aromatic hydrocarbons (PAHs) in aquatic environments are threatening ecosystems and human health. In this work, an effective and environmentally friendly catalyst based on biochar and molecular imprinting technology (MIT) was developed for the targeted degradation of PAHs by activating peroxymonosulfate. The results show that the adsorption amount of naphthalene (NAP) by molecularly imprinted biochar (MIP@BC) can reach 82% of the equilibrium adsorption capacity within 5 min, and it had well targeted adsorption for NAP in the solution mixture of NAP, QL and SMX. According to the comparison between the removal rates of NAP and QL by MIP@BC/PMS or BC/PMS system in respective pure solutions or mixed solutions, the MIP@BC/PMS system can better resist the interference of competing pollutants (i.e., QL) compared to the BC/PMS system; that is, MIP@BC had a good ability to selectively degrade NAP. Besides, the removal rate of NAP by MIP@BC/PMS gradually decreased as pH increased. The addition of Cl- greatly promoted the targeted removal of NAP in the MIP@BC/PMS system, while HCO3- and CO32- both had an inhibitory effect. Furthermore, SO4•-, O2•- and 1O2 produced by BC activating PMS dominated the NAP degradation, and it was inferred that the vacated imprinted cavities after NAP degradation can continue to selectively adsorb NAP and this could facilitate the reusability of the material. This study can promote the research on the targeted degradation of PAHs through the synergism of biochar/PMS advanced oxidation processes and MIT.

New insights into the degradation mechanism of ibuprofen in the UV/H2O2 process: role of natural dissolved matter in hydrogen transfer reactions

Ibuprofen (IBU), a widely used antipyretic and analgesic, has been frequently detected in various natural water systems. Advanced oxidation processes (AOPs) are effective ways to remove pollutants from water. The degradation of IBU under UV/H2O2 conditions in the presence of various kinds of natural dissolved matter was investigated using density functional theory (DFT). The eco-toxicological properties were predicted based on a quantitative structure-activity relationship (QSAR) model. The calculated results showed that two H-abstraction reactions occurring at the side chain are predominant pathways in the initial reaction. H2O, NH3, CH3OH, C2H5OH, HCOOH and CH3COOH can catalyze the H transfer in the degradation process through decreasing the energy barriers and the catalysis effects follow the order of NH3 > alcohols > acids > H2O. The catalysis effects differ under acid or alkaline conditions. The overall rate coefficient of the reaction of IBU with ˙OH is calculated to be 5.04 × 109 M-1 s-1 at 298 K. IBU has harmful effects on aquatic organisms and human beings and the degradation process cannot significantly reduce its toxicity. Among all products, 2-(4-formylphenyl)propanoic acid, which is more toxic than IBU, is the most toxic with acute and chronic toxicity, developmental toxicity, mutagenicity, genotoxic carcinogenicity and irritation/corrosivity to skin. The findings in this work provide new insights into the degradation of IBU and can help to assess its environmental risks.

Efficiency and mechanism on photocatalytic degradation of fluoranthene in soil by Z-scheme g-C3N4/α-Fe2O3 photocatalyst under simulated sunlight

Polycyclic aromatic hydrocarbons (PAHs) in soil have potential harm on human health. However, remediation of PAH-contaminated soils through photocatalytic technology remains a challenge. Therefore, the photocatalyst g-C₃N₄/α-Fe₂O₃ was synthesized and applied to photocatalytic degradation of fluoranthene in soil. The physicochemical properties of g-C₃N₄/α-Fe₂O₃ and various degradation parameters, such as catalyst dosage, the ratio of water/soil, and initial pH, were investigated in detail. In soil slurry reaction system (water/soil=10:1, w/w), the optimal degradation efficiency on fluoranthene was 88.7% after simulated sunlight irradiation for 12 h (contaminated soil=2 g, initial fluoranthene concentration=36 mg/kg, catalyst dosage=5%, and pH=6.8), and the photocatalytic degradation followed pseudo-first-order kinetics. The degradation efficiency of g-C₃N₄/α-Fe₂O₃ was higher compared with P25. Degradation mechanism analysis showed that •O₂^- and h⁺ are the main active species in photocatalytic degradation process of fluoranthene by g-C₃N₄/α-Fe₂O₃. Coupling g-C₃N₄ and α-Fe₂O₃ enhances the interfacial charge transport capacity via Z-scheme charge transfer route and inhibits the recombination of photogenerated electrons and holes of g-C₃N₄ and α-Fe₂O₃, then significantly improves the production of active species and photocatalytic activity. Results showed that photocatalytic treatment of soil by g-C₃N₄/α-Fe₂O₃ is an effective strategy for remediation of soils contaminated by PAHs.