Magnetic Fe-doped silicon carbide induced microwave activated persulfate for decabromodiphenyl ether removal: Mechanism and unique degradation pathway.

In this work, the magnetic nanocomposite Fe@SiC was prepared by a hydrothermal method and determined by SEM, XRD, XPS, FTIR and VNA. Fe3O4 particles were loaded onto SiC with great success, and the synthesized composites had favorable microwave absorption properties. Fe@SiC was used to activate persulfate in a microwave field for the degradation of BDE209 in soil. Specifically, the synergistic interaction between microwaves and Fe@SiC showed excellent catalytic performance in activating PS to degrade BDE209 (90.1% BDE209 degradation in 15 min). The presence of •OH, O2•- and 1O2 was demonstrated based on quench trapping and EPR experiments. LC‒MS was applied to determine the intermediates and propose the possible degradation pathway for BDE209 in the MW/Fe@SiC/PS system, and it was found that BDE209 produced almost no lower brominated diphenyl ethers. Therefore, the toxicity of BDE209 was found to be reduced using toxicity assessment software. Overall, this work provides an effective approach for the degradation of BDE209 in environmental remediation.

Simultaneous adsorption of As(III) and Pb(II) by the iron-sulfur codoped biochar composite: Competitive and synergistic effects.

Simultaneous elimination of As(III) and Pb(II) from wastewater is still a great challenge. In this work, an iron-sulfur codoped biochar (Fe/S-BC) was successfully fabricated in a simplified way and was applied to the remediate the co-pollution of As(III) and Pb(II). The positive enthalpy indicated that the adsorption in As-Pb co-pollution was an endothermic reaction. The mechanism of As(III) removal could be illustrated by surface complexation, oxidation and precipitation. In addition to precipitation and complexation, the elimination mechanism of Pb(II) also contained ion exchange and electrostatic interactions. Competitive and synergistic effects existed simultaneously in the co-contamination system. The suppression of As(III) was ascribed to competitive complexation of the two metals on Fe/S-BC, while the synergy of Pb(II) was attributed to the formation of the PbFe2(AsO4)2(OH)2. Batch experiments revealed that Fe/S-BC had outstanding ability to remove As(III) and Pb(II), regardless of pH dependency and interference by various coexisting ions. The maximum adsorption capacities of the Fe/S-BC for As(III) and Pb(II) were 91.2 mg/g and 631.7 mg/g, respectively. Fe/S-BC could be treated as a novel candidate for the elimination of As(III)-Pb(II) combined pollution.

Remediation of cadmium and lead contaminated soils using Fe-OM based materials.

Iron oxide-lignin composites (GLS) were prepared based on the significant role of Fe-OM in the environmental behaviour of heavy metals and lignin binding with iron oxide preferentially in soil. GLS was applied in Cd/Pb immobilization and the stability under acid rain was investigated. The results show that the iron oxide appeared weakly crystalline or amorphous similar to 2-line ferrihydrite after the addition of lignin. Agglomerates of nanoparticles with higher adsorption capacity were observed for GLS. The mobility factor (MF) of Cd/Pb in the soil decreased rapidly after adding GLS. At the 3% dosage, the MF of Cd and Pb in the soil was decreased by 58.94% and 78.15% respectively, which was approximately 5 times that of goethite (GE). The mobile and exchangeable Cd/Pb were converted to organic, amorphous Fe oxide-bound and residue fractions. Under acid rain conditions, MF continues to decline for the GLS group, increasing the organic and amorphous Fe oxide-bound fractions, while for control group (CK) and GE, the trend was the opposite. Lignin could inhibit iron oxide dissolution and stabilize the combination of Cd/Pb and iron oxides in soil. The better stability performance of GLS for Cd/Pb may be related to the higher adsorption capacity and microstructural difference after iron oxide combined with lignin.

Peroxydisulfate activation by nano zero-valent iron graphitized carbon materials for ciprofloxacin removal: Effects and mechanism.

Since the discovery of the potential hazards of ciprofloxacin (CIP) to the ecosystem and human health, there has been an urgent need to develop effective technologies to solve the severe issue. In this work, the nanozero-valent iron graphitized carbon matrix (xFe@CS-Tm) were prepared via a hydrothermal method to activate peroxydisulfate (PDS) for degradation of CIP. Specifically, 0.5Fe@CS-T7 exhibited the excellent catalytic performance for PDS activation to degrade CIP. Moreover, the catalyst exhibited vigorous interference resistance at various pH values, in the presence of various inorganic anions and under humic acid conditions. The characterization results demonstrated that Fe was successfully embedded on the carbon matrix and became the active sites to promote ROS production. It is demonstrated that O2•- was the main active species rather than •OH and SO4•-, based on quench trapping, EPR experiments and steady state concentrations calculations. The possible pathways of CIP degradation were proposed using LC-MS results and density functional theory. The outcomes of the toxicity estimation software tool found that the toxicity of CIP was reduced. This study not only investigated a novel methodology for the degradation of antibiotic wastewater but also provides a feasible pathway for carbon-neutral wastewater treatment.

Role of sulfide-modified nanoscale zero-valent iron on carbon nanotubes in nonradical activation of peroxydisulfate.

Sulfamethoxazole (SMX) is highly persistent and difficult to remove, making it urgent to find an efficient method for alleviating the enormous environmental pressure of SMX. In this study, sulfide-modified nanoscale zero-valent iron on carbon nanotubes (S-nZVI@CNTs) was prepared to activate peroxydisulfate (PDS) for the degradation of SMX. The results showed that SMX was completely removed within 40 min (kobs=0.1058 min-1) in the S-nZVI@CNTs/PDS system. By analyzing quenching experiments and electron paramagnetic resonance (EPR), singlet oxygen (1O2) was the main active species of the S-nZVI@CNTs/PDS system. 1O2 might be mediated by the abundant carbonyl groups (CO) on carbon nanotubes through spectroscopic analyses. In addition, sulfur doping transitioned the activation pathway to a nonradical pathway. Spectroscopic analyses and electrochemical experiments confirmed that the formation of CNTs-PDS complexes and S-nZVI could promote electron transfer on the catalyst surface. Furthermore, the main degradation intermediates of SMX were identified, and five possible transformation pathways were proposed. The S-nZVI@CNTs/PDS system possessed advantages including high anti-interference (Cl-, NO3-, HA), a strong applicability, recyclability and a low PDS consumption, offering new insight into the degradation of antibiotic wastewater.

[Influencing Mechanism of Eh, pH and Iron on the Release of Arsenic in Paddy Soil].

The massive release of soil arsenic and its enrichment in rice are significantly associated with the flooded and anaerobic management in paddy soil. Soil redox potential (Eh), pH and iron oxides exert remarkable impacts on arsenic release, which remain to be explored. In this study, long-term aerobic and anaerobic as well as intermittent aerobic incubation treatments were applied to investigate the influences of Eh, pH and iron content on arsenic release. It was found that anaerobic and flooded treatment contributed to the highest arsenic release. With decreasing Eh, significant enhancement in As(Ⅲ) and As(Ⅴ) contents in soil solution was observed. Particularly, As(Ⅲ) and As(Ⅴ) contents during the second phase increased by 1.37 and 0.99 µg·L-1compared with those in the first phase. Conversely, significant reduction in soil arsenic release (P<0.05) occurred when intermittent aerobic treatment was adopted, and the lowest level of arsenic release was observed along with the longest treatment time (6 d). The exponent relationships between arsenic and soil Eh, pH and Fe2+ content were also established, which indicated that arsenic release could be accelerated by lower pH and elevated Eh. In addition, a significant positive correlation was also found between iron(Ⅱ) content and arsenic content in soil solution. Since low Eh and elevated pH served as critical factors driving arsenic release, intermittent and aerobic water management was proved to be an effective method for the inhibition of arsenic release and uptake and accumulation of arsenic by rice.

[Effect of Different Iron Minerals on Bioaccessibility of Soil Arsenic Using in vitro Methods].

To explore the effects of different iron minerals on soil arsenic bioaccessibility, ferrihydrite, goethite and hematite were used in PBET, SBRC and IVG in-vitro experiments in this study. The relationship between arsenic bioavailability in gastric, small intestinal phases and arsenic speciation was also studied. The results showed that when 1% ferrihydrite was added, arsenic bioavailability in gastric phase was 2.22%, 5.11% and 7.43% by PBET, SBRC and IVG methods, respectively, while in the small intestinal phase it was 3.39%, 2.33% and 6.18%. At an elevated ferrihydrite dosage of 2%, significant difference in arsenic bioavailability was observed in both phases (P<0.05). According to in vitro experiments, the addition of the same amount of different iron minerals had contributed to the decrease in arsenic bioavailability to varying extents in contrast with the blank group, in the descending order of ferrihydrite(F1) > goethite(G1) > hematite(H1) (F2 > G2 > H2). Total arsenic in exchangeable (F1) and specifically sorbed (F2) state was found positively correlated with arsenic bioavailability in gastric phase by PBET, SBRC and IVG methods, the correlation coefficient of which being r=0.93, P=0.002, r=0.90, P=0.004 and r=0.89,P=0.006, respectively. It was also found that arsenic bioavailability in gastric phase was positively correlated with total arsenic in F1 and F2 states by PBET(r=0.94,P=0.001) and IVG (r=0.87,P=0.009) methods, but no significant correlation was observed by SBRC method. Additionally, three in vitro experiments showed that amorphous iron bound arsenic had significant negative correlation with arsenic bioavailability in gastric phase and small intestinal phase, except that no correlation was found in small intestinal phase by SBRC method.

Synthesis, characterization, and secondary sludge dewatering performance of a novel combined silicon-aluminum-iron-starch flocculant.

Flocculation is one of the most widely used cost-effective pretreatment method for sludge dewatering, and a novel environmentally friendly and efficient flocculant is highly desired in the sludge dewatering field. In this study, a novel combined silicon-aluminum-ferric-starch was synthesized by grafting silicon, aluminum, and iron onto a starch backbone. The synthesized starch flocculant was characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy, X-ray powder diffraction, and thermogravimetric analysis. The dewatering performance of secondary sludge was evaluated according to the capillary suction time, settling volume percentage, and specific resistance to filtration. The results indicated that the copolymer exhibited: (1) a good dewatering efficiency over a wide pH range of 3.0-11.0, (2) superior sludge dewatering performance compared to those of polyaluminum chloride (PACl), polyacrylamide (PAM), ferric chloride, and (3) a discontinuous surface with many channels or voids that helps to mobilize the impermeable thin layer of secondary sludge during filter pressing. Such a novel copolymer is a promising green flocculant for secondary sludge dewatering applications.

Flocculation mechanism by a novel combined aluminum-ferrous-starch flocculant (CAFS).

A combined flocculant (CAFS) was prepared with Al(2)(SO(4))(3)·18H(2)O, FeSO(4)·7H(2)O and starch. The flocculation mechanism of reactive brilliant red X-3B was studied. The results showed that CAFS was a cationic polymeric flocculant with high charge density, and its mesh starch chains grafted polyaluminum and polyferrous. At the preliminary stage, the main flocculation mechanism was adsorption and charge neutralization. At a later stage, the high molecular weight and flexible linear chains of CAFS initiated bridge-aggregation and sweep-flocculation. Moreover, the zeta potential and dynamic changes of flocs were closely related to flocculant dosages and the pH. The optimum dosage of CAFS and pH value were 0.990 mg/L and 5.0. Taken together, these results suggested CAFS as a novel flocculant in water treatment, with good results for the studied conditions.