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Fe-Mn binary oxides (FMBOs) with different molar ratios of Fe and Mn (1:1–8:1) synthesized in a redox-precipitation method were investigated for the activation of a combination of persulfate (PS) and hydrogen peroxide (HP) for the degradation of 2,4-dinitrotoluene (2,4-DNT). X-ray diffraction and field-emission scanning electron microscopy were used to demonstrate FMBOs with different molar ratios exhibited no significant influence on crystallinity and morphology. The degradation efficiency and kinetics of 2,4-DNT in the FMBOs/PS/HP system were investigated. The results showed that F4.5M1BO exhibited better effectively heterogeneous catalytic activity in the activation of the combined PS and HP. The effects of initial HP and PS concentrations, F4.5M1BO dose, initial pH, and coexisting anions on the degradation efficiency and kinetics of 2,4-DNT were comprehensively investigated. A possible activation mechanism in the F4.5M1BO/PS/HP system was proposed based on electron paramagnetic resonance, radical scavenger tests, X-ray photoelectron spectroscopy, and Fourier transformation infrared spectroscopy. The results showed that Fe(II), Mn(II), and Mn(III) ( is representative of the element in solid form) are active sites on the surface of F4.5M1BO that effectively activated the combined PS and HP to generate the dominant SO4 − and HO . Furthermore, the proportions of lattice oxygen, surface adsorbed species, and adsorbed molecular water activated of the combined PS and HP. The strong synergistic interaction reaction among Fe(III), Mn(III), Mn(IV), and HP could be deduced and confirmed. These findings provide new insight into the potential of F4.5M1BO as a heterogeneous catalyst in the activation of the combined PS and HP for improving the degradation of refractory organic pollutants.

Recently, increasing attention has been paid to the activated peroxymonocarbonate (APMC) process, because it is envisioned to be engineered for the chemical oxidation remediation of groundwater in karstic regions with elevated levels of naturally occurring bicarbonate. In the present study, we explored the feasibility of using metal sulfides (CuFeS2, CuS, and FeS2) as the catalysts for heterogeneous APMC (H-APMC) processes. Among the three synthesized metal sulfides, the CuFeS2 catalyst exhibited reversible redox properties, thereby it had the best performance to activate peroxymonocarbonate (PMC) for the degradation of 2,4-dichlorophenol (2,4-DCP). The X-ray photoelectron spectroscopy analysis and density-functional-theory calculations both revealed that, for the CuFeS2-catalyzed APMC process, iron sites of CuFeS2 acted as the catalytic active sites. Electron spin resonance and chemical quenching experiments revealed that the intermediated reactive species for a CuFeS2-catalyzed APMC process included hydroxyl radicals ( OH), singlet oxygen (1O2), superoxide radicals ( O2−), and carbonate radicals ( CO3−). It was also found that, under a low bicarbonate condition (≤25 mM), the concentration of H2O2 was not the limiting factor that controlled the degradation rate of 2,4-DCP. Instead, bicarbonate concentration and catalyst dosage significantly influenced the performance of CuFeS2-catalyzed APMC process. Al2O3-supported CuFeS2 catalyst (Al2O3@CuFeS2) was prepared and tested as fillers for practical application. The flowing experiment using fixed-bed reactor showed that the Al2O3@CuFeS2 fillers could effectively activate PMC and thereby degraded the 2,4-DCP. Runoff of the coated CuFeS2 component occurred during the experiment, but the leached copper and iron species from the fillers were constantly at a low and safe level (

Understanding the formation of high fluoride (F-) groundwater in water-scarce northern China is critical for the sustainable development of the region. This study investigates the effects of F- enrichment in groundwater from seven typical regions of northern China, including Datong, Guide, Junggar, Yinchuan, Taiyuan, and Tarim basins and the North China Plain. A literature survey of 534 samples of selected regions showed that 45.13% of groundwater F- exceeded the 1.0 mg/L of Chinese drinking water guideline. Based on the geological background and hydrogeochemical analysis, in Datong and Yinchuan basins and part of the North China Plain, the main types of groundwater are soda water and controlling processes of F- enrichment are salinization, mineral dissolution, and desorption. In Taiyuan and Guide basins with Cl-Na water type, F- enrichment is mainly affected by salinization, cation exchange, and evaporation. The hydrogeochemical characteristics of high F- groundwater in Tarim and Junggar basins reflect the extent of salinization and weathering dissolution of minerals in groundwater. According to PCA, the contribution of salinization and mineral dissolution to F- enrichment is relatively high. Under the alkaline condition, groundwater with high Cl-, HCO3-, and Na+ concentration favors F- enrichment. Based on HCA, index clustering category I explains the influence of pH and buried depth on F- enrichment, and category II explains the effect of different ions. It is concluded that F- enrichment in groundwater is related to hydrogeochemical processes and hydrogeological conditions. The hydrogeochemical and alkaline conditions of groundwater are regulated by mineral dissolution, ion exchange, and evaporation, resulting in different degrees of F- enrichment.

Mercury (Hg2+) contamination in water is associated with potential toxicity to human health and ecosystems. Many research studies have been ongoing to develop new materials for the remediation of Hg2+ pollution in water. In this study, a novel thiol- and amino-containing fibrous adsorbent was prepared by grafting 2-amino-5-mercapto-1,3,4-thiadiazol (AMTD) onto PAN fiber through a microwave-assisted method. The synthesized functional fiber was characterized by FTIR, SEM, and elemental analysis. Adsorption tests depicted that for mercury uptake, PANMW-AMTD fiber exhibited enhanced adsorption capacity compared with other fibrous adsorbents and selective adsorption feature under the interference of other metal ions, including Pb2+, Cu2+, Cd2+, and Zn2+. The influence of pH on the adsorption process was investigated and the effect of temperature revealed that the adsorption sorption process was endothermic and the adsorption performance of PANMW-AMTD was elevated with the increase of temperature. Kinetic studies of PANMW-AMTD fiber followed the pseudo-second-order and the adsorption isotherm of Hg2+ was well fitted by Sips and Langmuir equations, given the maximum adsorption amount of 332.9 mg/g. XPS results suggested that a synergetic coordination effect of sulfur and nitrogen in functional fiber with mercury took responsibility for the adsorption mechanism in the uptake process. In addition, the prepared PANMW-AMTD fiber could easily be regenerated with 0.1 M HCl for five times without significant reduction of mercury removal efficiency. Thus, this study will facilitate the research on novel functional material for the removal of mercury from water.

Water level (WL) changes are an important factor in the fate and transport of nitrogen in the saturated-unsaturated zone. In this study, the fate of nitrogen was investigated under simulated conditions of replenishment, runoff, and discharge. Three patterns of water level changes of ascent, stability, and descent were simulated under laboratory conditions to study nitrogen transport and transformation. Three columns (I, II, and III) were used to simulate the conditions of replenishment, steady water level, and discharge, respectively. The nitrate-nitrogen (NO3 (-)-N), nitrite-nitrogen (NO2 (-)-N), and ammonia-nitrogen (NH4 (+)-N) concentrations observed at different depths were compared among the three columns at 46.5 and 251.5 h. The results indicated that the NO3 (-)-N concentration decreased with time in both the saturated and unsaturated zones of the three columns (columns I, II, and III). The maximum decreasing concentrations of NO3 (-)-N in the three columns were 14.3, 37.97, and 38.17 mg/L, respectively. However, NH4 (+)-N in the saturated zone increased with time, whereas the NH4 (+)-N concentration decreased in both the saturated and unsaturated zones of other columns. No significant change in NO2 (-)-N concentration was observed in the experiment. These results suggest that water level changes must be considered in the remediation of groundwater nitrate pollution in the field.

In this study, scrap irons (SI)/granular activated carbons (GAC) micro-electrolysis treatment and persulfate-releasing materials (PRM) treatment were employed to construct the combination reduction and oxidation system to treat 2,4-dinitrotoluene (2,4-DNT) contaminated groundwater. The 2,4-DNT treatment efficiencies in the PRM pre-treatment before SI/GAC micro-electrolysis treatment (FM-1 = PRM + SI/GAC) and SI/GAC micro-electrolysis pre-treatment before the PRM treatment (FM-3 = SI/GAC + PRM) were investigated in two separated columns. As control groups, the separated SI and GAC instead of the SI/GAC mixture were used in another two separated columns (FM-2 = PRM + SI + GAC; FM-4 = SI + GAC + PRM). The highest treatment efficiencies of 2,4-DNT in the FM-1 and FM-3 systems reached 79% and 93% during 5 PV, respectively. We found that the filling position of SI, GAC and PRM significantly affected the variations of pH, oxidation-reduction potential, Fe2+ and S2O82− concentrations in the combined systems. These results indicated that the SI/GAC micro-electrolysis pre-treatment of 2,4-DNT before the PRM treatment (FM-3) is more beneficial. The fifteen main intermediates in the combined system were identified by the detection of liquid chromatograph mass spectrometer. Furthermore, the possible treatment pathways of 2.4-DNT were proposed on the basis of identified intermediates. The treatment mechanisms in the FM-1 and FM-3 systems were proposed with the reduction mechanism in the SI/GAC micro-electrolysis system and the oxidation mechanism in the PRM treatment. Therefore, the combination of the reduction pre-treatment with the SI/GAC micro-electrolysis system and the oxidation post-treatment with persulfate can effectively treat the nitroaromatic compounds contaminated groundwater.