The pesticide gibberellic acid (GA3) is a potential endocrine disruptor and environmental toxin; therefore, research into its environmental fate is warranted. Batch studies were conducted to investigate the sorption and desorption characteristics of GA3 on aquifer media. The results demonstrated special sorption characteristic of GA3 on ferrihydrite compared to goethite, hematite, montmorillonite, and kaolinite, where the sorption kinetics of GA3 on ferrihydrite was fitted well with the pseudo-second-order, Elovich, and intra-particle diffusion models. The sorption kinetics of GA3 on ferrihydrite indicated an initial high sorption rate followed by a slow reaction process. The initial high GA3 sorption rate may be related to electrostatic sorption and surface complexation reactions on the outer surfaces and at the macropore entrances of ferrihydrite. While the slow step was controlled by GA3 diffusion into mesopore of ferrihydrite. Analysis of the desorption hysteresis indicated a high hysteresis index (HI) ranging from 0.68 to 17.32, and a low desorption percentage ranging from 18 to 48%. After sufficient desorption, the calculated maximum residual GA3 quantity due to surface complexation reactions with the ferrihydrite coordinated unsaturated sites was 9.05 ± 0.12 mg g−1. The calculated maximum quantity of GA3 trapped within the mesopore was 16.23 ± 0.91 mg g−1.

•The increasing pH decreased the adsorption of diclofenac (DCF) to goethite.•DCF adsorption to goethite was well fitted with Pseudo-second-order model.•The carboxyl group (COOH) might be involved in the adsorption.•DCF and goethite formed bidentate chelate and bridging bidentate complexes.The adsorption of diclofenac (DCF), one of the widely used non-steroidal anti-inflammatory drugs, onto the surface of goethite was investigated with batch experiments. The adsorption at different pH values (5.3, 7.4, and 10.0) were well fitted with the pseudo-second-order model. The results showed that the adsorption of DCF onto goethite was strongly depended on solution pH. The amount of adsorbed DCF decreased with increasing pH duo to electrostatic repulsive interactions. Fourier transform infrared (FTIR) results indicated that carboxyl group (COOH) might be involved in the adsorption, and DCF formed bidentate chelate and bridging bidentate complexes on the surface of goethite.

Carbon nitride has been considered as promising metal-free polymers for low-cost photocatalysis. Most prevailing concern about this fantastic material focuses on g-C3N4, while the potential of other derivatives have been overlooked. Herein, in order to determine the desired derivatives for environmental pollutant treatment, the impact of degree of thermal polymerization on the microstructure of carbon nitride was investigated. Interestingly, melem-based derivatives exhibit 4- and 6-fold enhanced activities than g-C3N4, when used as synergetic photocatalysts for the simultaneous treatment of heavy metal ions and organic contaminants. According to the fundamental study of reactive species formation, a microstructure-dependent photocatalytic mechanism was established. Hydrogen bond-facilitated trapping of photogenerated holes and superior ability for oxygen molecular activation contributed to the high-performance of melem-based derivatives. In contrast, g-C3N4 shows inferior performance during superoxide radical-dominated photodegradation reactions, as its microstructure is favorable for the generation of . Our research not only sheds new insights into the microstructure design of metal-free carbon nitride photocatalysts, but also has immense scientific and technological values for high-efficiency and synergetic environmental applications.Download high-res image (82KB)Download full-size image

The efficacy of two oxidant systems, iron-activated hydrogen peroxide (H2O2) and iron-activated hydrogen peroxide coupled with persulfate (S2O82−), was investigated for treatment of two chlorinated organic compounds, trichloroethene (TCE) and 1,2-dichloroethane (DCA). Batch tests were conducted at multiple temperatures (10–50 °C) to investigate degradation kinetics and reaction thermodynamics. The influence of an inorganic salt, dihydrogen phosphate ion (H2PO4−), on oxidative degradation was also examined. The degradation of TCE was promoted in both systems, with greater degradation observed for higher temperatures. The inhibition effect of H2PO4− on the degradation of TCE increased with increasing temperature for the iron-activated H2O2 system but decreased for the iron-activated hydrogen peroxide-persulfate system. DCA degradation was limited in the iron-activated hydrogen peroxide system. Conversely, significant DCA degradation (87% in 48 h at 20 °C) occurred in the iron-activated hydrogen peroxide-persulfate system, indicating the crucial role of sulfate radical (SO4−∙) from persulfate on the oxidative degradation of DCA. The activation energy values varied from 37.7 to 72.9 kJ/mol, depending on the different reactants. Overall, the binary hydrogen peroxide-persulfate oxidant system exhibited better performance than hydrogen peroxide alone for TCE and DCA degradation.

•We investigate adsorption of levofloxacin (LEV) onto goethite.•The maximum amount of LEV onto goethite is observed at pH 6.•Less LEV is adsorbed in the presence of Ca2+ due to the complexation with Ca2+.•Phosphate decreases LEV adsorption strongly.Adsorption of levofloxacin (LEV), one of the extensively used antibiotics, onto goethite was investigated using batch experiments. The adsorption of LEV on goethite was pH-dependent. A maximum adsorption was reached at pH 6. Above or below pH 6, the adsorption decreased. In the presence of calcium (Ca2+), a decrease in adsorption was observed, due to probably formation of Ca2+–LEV complexes in solutions. Phosphate also showed a significant inhibition on LEV adsorption over a pH range of 3–10. Phosphate competed with LEV for binding sites on the surface of goethite, and the electrostatic competition between LEV and phosphate on goethite surface might be another reason for the decrease in adsorption. These results indicated that Ca2+ and phosphate have a great influence on the distribution of LEV in soils and waters, which will eventually affect its antibacterial activity in the environment.

Pollution of groundwater with chlorinated aliphatic hydrocarbons (CAHs) is a serious environmental problem which is threatening human health. Microorganisms are the major participants in degrading these contaminants. Here, groundwater contaminated for a decade with CAHs was investigated. Numerical simulation and field measurements were used to track and forecast the migration and transformation of the pollutants. The diversity, abundance, and possible activity of groundwater microbial communities at CAH-polluted sites were characterized by molecular approaches. The number of microorganisms was between 5.65E+05 and 1.49E+08 16S rRNA gene clone numbers per liter according to quantitative real-time PCR analysis. In 16S rRNA gene clone libraries constructed from samples along the groundwater flow, eight phyla were detected, and Proteobacteria were dominant (72.8 %). The microbial communities varied with the composition and concentration of pollutants. Meanwhile, toluene monooxygenases and methane monooxygenases capable of degradation of PCE and TCE were detected, demonstrating the major mechanism for PCE and TCE degradation and possibility for in situ remediation by addition of oxygen in this study.

•The retention Cr(VI) by HA follows a complexation-coupled reduction mechanism.•HA functional groups changing sequence was determined by a novel method of 2DCOS.•Carboxyl and phenol account for complexation and reduction of Cr(VI) respectively.•Functional groups for Cr(VI) retention are mainly located at aromatic domains.Undissolved humic acid (HA) is known to substantially effect the migration and transformation of hexavalent chromium [Cr(VI)] in soils. The mechanisms of Cr(VI) retention in soils by undissolved HA have been reported; however, past studies are inconclusive about the types of HA functional groups that are involved in Cr(VI) retention and the retention mechanisms. Utilizing a two-dimensional correlation spectroscopy (2DCOS) analysis for FTIR and 13C CP/MAS NMR, this study investigated the variations of HA function groups and molecular structures after reactions with aqueous Cr(VI) under different pH conditions. Based on the changing sequence of functional groups interpreted from the 2DCOS results, a four-step mechanism for Cr(VI) retention was determined as follows: (1) electrostatic adsorption of Cr(VI) to HA surface, (2) complexation of adsorbed Cr(VI) by carboxyl and ester, (3) reduction of complexed Cr(VI) to Cr(III) by phenol and polysaccharide, and (4) complexation of reduced Cr(III) by carboxylic groups. These functional groups that are involved in Cr(VI) retention were determined to occur in aromatic domains.Download high-res image (347KB)Download full-size image