Piezoelectricity, as a kind of physical phenomenon, is a coupling between a material’s mechanical and electrical behavior. Herein, the local accumulated charges on the surface of piezoelectric material were used to break OO bond of peroxymonosulfate (PMS) to induce its activation for the benzothiazole (BTH) removal. Taking BaTiO3 as a model piezocatalyst, up to 97 % of BTH was degraded within 30 min in BaTiO3/PMS/force system, which was respective 40 %, 79 %, 83 % higher than that in BaTiO3/force piezocatalysis, force/PMS oxidation, and BaTiO3/PMS adsorption. A significant synergistic effect was observed since the reaction rate constant of BaTiO3/PMS/force was 3 times higher than the sum of those later three processes. The possible activated mechanism was proposed based on reactive species analysis, DFT calculation and LCMS determination. The stability of the piezocatalyst and the treatment performance for real wastewater were studied to investigate the potential in practical applicability. All the results demonstrated that the BaTiO3 piezoelectricity can efficiently activate PMS to enhance BTH removal, which is a promising strategy for PMS activation, as well as a valuable insight for the piezoelectrical application in wastewater remediation.
Carboxymethyl cellulose stabilized iron sulfide (CMC-FeS) nanoparticles have been shown promising for reductive immobilization of U(VI) in water and soil. This work aimed to fill some critical knowledge gaps on the effects of the stabilizer and water chemistry, reaction mechanisms, and long-term stability of stabilized uranium. The optimal CMC-to-FeS molar ratio was determined to be 0.0010. CMC-FeS performed effectively over pH 6.0–9.0, with the best removal being at pH 7.0 and 8.0. The retarded first-order model adequately interpreted the kinetic data, representing a mechanistically sounder model for heterogeneous reactants of decaying reactivity. The presence of Ca2+ (1 mM) or bicarbonate (1 mM) lowered the initial rate constant by a factor of 1.6 and 9.5, respectively, while 1 mM of Na+ showed negligible effect. Humic acid at 1.0 mg/L (as total organic carbon) doubled the removal rate, but inhibited the removal at elevated concentrations (≥5.0 mg/L). Fourier transform infrared spectroscopy, X-ray diffractometer, X-ray photoelectron spectroscopy, and extraction studies indicated that reductive conversion of UO22+ to UO2(s) was the primary reaction mechanism, accounting for 90% of U removal at pH 7.0. S2− and S22− were the primary electron sources, whereas sorbed and structural Fe(II) acted as supplementary electron donors. The immobilized U remained stable under anoxic conditions after 180 days of aging, while 26% immobilized U was remobilized when exposed to air for 180 days. The long-term stability is attributed to the protective reduction potential of CMC-FeS, the formation of uraninite and associated structural resistance to oxidation, and the high affinity of FeS oxidation products toward U(VI).
Degradation of phenols with different substituent groups (including –OCH3, –CHO, –NHCOCH3, –NO2, and −Cl) at boron-doped diamond (BDD) anodes has been studied previously based on the removal efficiency and •OH detection. Innovatively, formations of CO2 gas and various inorganic ions were examined to probe the mineralization process combined with quantitative structure-activity relationship (QSAR) analysis. As results, all phenols were efficiently degraded within 8 h with high COD removal efficiency. Three primary intermediates (hydroquinone, 1,4-benzoquinone and catechol) were identified during electrochemical oxidation and degradation pathway was proposed. More importantly, CO2 transformation efficiency ranked as: no N or Cl contained phenols (p-CHO, p-OCH3 and Ph) > N-contained phenols (p-NHCOCH3 and p-NO2) > Cl-contained phenols (p-Cl and o,p-Cl). Carbon mass balance study suggested formation of inorganic carbon (H2CO3, CO32− and HCO3−) and CO2 after organic carbon elimination. Inorganic nitrogen species (NH4+, NO3− and NO2−) and chlorine species (Cl−, ClO3− and ClO4−) were also formed after N- and Cl-contained phenols mineralization, while no volatile nitrogen species were detected. The phenols with electron-withdrawing substituents were easier to be oxidized than those with electron-donating substituents. QSAR analysis indicated that the reaction rate constant (k1) for phenols degradation was highly related to Hammett constant (∑σo,m,p) and energy gap (ELUMO - EHOMO) of the compound (R2 = 0.908), which were key parameters on evaluating the effect of structural moieties on electronic character and the chemical stability upon radical attack for a specific compound. This study presents clear evidence on mineralization mechanisms of phenols degradation at BDD anodes.
Reservoirs play a vital role in the control and management of surface water resources. However, the long water residence time in the reservoir potentially increases the storage and accumulation of antibiotic resistant genes (ARGs). The full profiles and potential health risks of antibiotic resistomes in reservoirs are largely unknown. In this study, we investigated the antibiotic resistomes of water and sediment during different seasons in the Danjiangkou Reservoir, which is one of the largest reservoirs in China, using a metagenomic sequencing approach. A total of 436 ARG subtypes belonging to 20 ARG types were detected from 24 water and 18 sediment samples, with an average abundance of 0.138 copies/cell. The overall ARG abundance in the sediment was higher than that in the water, and bacitracin and vancomycin resistance genes were the predominant ARG types in the water and sediment, respectively. The overall ARG abundance in the dry season was higher than that in the wet season, and a significant difference in ARG subtype compositions was observed in water, but not in the sediment, between the different seasons. The potential horizontal gene transfer frequency in the water was higher than that in the sediment, and the ARGs in water mainly came from the sediment upstream of the reservoir. The metagenomic assembly identified 14 contigs as ARG-carrying pathogens including Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa, and 3 of 14 carried virulence factors. Overall, the potential public health risks posed by resistomes in the water of the Danjiangkou Reservoir were higher in the dry season than in the wet season. Based on these results, strategies including sediment control and pathogen monitoring are suggested for water safety management in drinking water reservoirs.
Fenton reaction can disinfect bacteria and degrade organic pollutants via the generation of OH through the reaction of Fe(II) and H2O2. However, its high efficiency only at very acidic conditions and the formation of Fe(III) sludge limit its practical application. Herein, magnetic Fe3O4-deposited flower-like MoS2 (MF) composites were fabricated to disinfect Escherichia coli and degrade diclofenac (DCF) with addition of small amount of H2O2 at a wide pH range (from 3.5 to 9.5). MF can efficiently inactivate bacteria and remove DCF at broad pH from 3.5 to 9.5. For example, 1.2 × 106 CFU mL-1 cells are completely disinfected by MF in 30 min at pH 6 with 5 mM H2O2, while 10 mg L-1 DCF is fully degraded in 7 min at pH 6 with 1 mM H2O2. MoS2 facilitates the conversion cycle of Fe(III)/Fe(II) and improves the generation of OH. MF can be easily collected by magnet after use. Confocal image, SEM images, the leakage of K+ and DNA were employed to determine the damage of cell membrane. Meanwhile, the theoretical density functional theory and the degradation intermediates determination were employed to provide the degradation pathway of DCF. MF exhibit excellent reusability and good catalytic performance towards sanitary sewage.
A facile method was developed to fabricate porous tube-like ZnS by sulfurizing rod-like ZIF-L with thioacetamide (TAA) at different durations and the formation mechanism of the porous tube-like ZnS was discussed in detail. The series of sulfide products (ZS-X) were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance spectroscopy (SSNMR), transmission electron microscopy (TEM), UV–visible diffuse-reflectance spectroscopy (UV–vis DRS). The photocatalytic performances of ZS-X toward Cr(VI) reduction and organic pollutant degradation were explored. It was discovered that ZS-3 (porous tube-like ZnS) exhibited excellent activities under UV light and displayed good reusability and stability after several experimental cycles. In addition, Cr(VI) reduction and organic pollutant degradation were investigated under different pH values and existence of different foreign ions. The photocatalytic activities of ZS-3 were tested toward the matrix of Cr(VI) and reactive red X–3B. The mechanism was proposed and verified by both electrochemical analysis and electron spin resonance (ESR) measurement.
Marine oil spill often causes contamination of drinking water sources in coastal areas. As the use of oil dispersants has become one of the main practices in remediation of oil spill, the effect of oil dispersants on the treatment effectiveness remains unexplored. Specifically, little is known on the removal of dispersed oil from contaminated water using conventional adsorbents. This study investigated sorption behavior of three prototype activated charcoals (ACs) of different particle sizes (4–12, 12–20 and 100 mesh) for removal of dispersed oil hydrocarbons, and effects of two model oil dispersants (Corexit EC9500A and Corexit EC9527A). The oil content was measured as n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and total petroleum hydrocarbons (TPHs). Characterization results showed that the smallest AC (PAC100) offered the highest BET surface area of 889 m2/g and pore volume of 0.95 cm3/g (pHPZC = 6.1). Sorption kinetic data revealed that all three ACs can efficiently adsorb Corexit EC9500A and oil dispersed by the two dispersants (DWAO-I and DWAO-II), and the adsorption capacity followed the trend: PAC100 > GAC12 × 20 > GAC4 × 12. Sorption isotherms confirmed PAC100 showed the highest adsorption capacity for dispersed oil in DWAO-I with a Freundlich KF value of 10.90 mg/g∙(L/mg)1/n (n = 1.38). Furthermore, the presence of Corexit EC9500A showed two contrasting effects on the oil sorption, i.e., adsolubilization and solubilization depending on the dispersant concentration. Increasing solution pH from 6.0 to 9.0 and salinity from 2 to 8 wt% showed only modest effect on the sorption. The results are useful for effective treatment of dispersed oil in contaminated water and for understanding roles of oil dispersants.
2D/1D graphitic carbon nitride hybridized with titanate nanotubes (g-C3N4/TNTs) was prepared through a hydrothermal reaction–calcination method. The photocatalyst exhibited high degradation efficiency for sulfamethazine (SMT) through photocatalysis under simulated solar light. The optimized material was composed of anatase, rutile, titanate and g-C3N4 crystalline phases. In situ transformation of titanate to anatase and rutile with specific content proportion (∼80:20, P25-type composition) leaded to formation of nanoscale “hot spots” at rutile–anatase–titanate interfaces, and then subsequent charge transfer occurred. Large specific surface area of TNTs as skeleton resulted in high-efficient interface reaction, while heterojunction with g-C3N4 further extended the adsorption to visible light region and retarded electron-hole pairs recombination. Density functional theory (DFT) calculation indicated the SMT sites with high Fukui nucleophilic (f-) index prefered to be attacked by radacils. Reduced toxicity of SMT degradation intermediates, good reusability and stability of g-C3N4/TNTs all suggested the great application potential in practical water treatment area.
A novel tubular graphitic carbon nitride (g-C3N4) modified with carbon quantum dots (CQDs) was fabricated and employed for the elimination of carbamazepine (CBZ) under visible light irradiation. The as-fabricated metal-free catalysts exhibited tubular morphologies due to the preforming of tubular protonated melamine with CQDs surface adsorption as the polymerization precursors. The surface bonded CQDs did not alter the band gap structure of g-C3N4, but greatly inhibited the charge recombination. Therefore, the CBZ degradation kinetics of tubular g-C3N4 were increased by over 5 times by the incorporation of CQDs. The main active species for CBZ degradation were found to be superoxide radical (O2−) and photo-generated holes (h+), which were further confirmed by electron spin resonance (ESR) analysis. In addition, the degradation pathways of CBZ were clarified via intermediates identification and quantum chemical computation using density functional theory (DFT) and wave function analysis. The olefinic double bond with the highest condensed Fukui index (f 0 = 0.108) in CBZ molecule was found to be the most preferable sites for radical attack. Moreover, good stability of the as-prepared photocatalysts was observed in the consecutive recycling cycles, while the slight decline of photocatalytic activity was attributed to the minimal surface oxidation.