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A novel magnetic copper-based metal organic framework (M-MOF-199) has been successfully prepared using Fe 3 O 4 –graphene oxide (GO) nanocomposite for solid phase extraction of five triazole pesticides from environment water samples. High-performance liquid chromatography coupled with tandem mass spectrometry was used for sample quantification and determination. The results suggest that Fe 4 O 3 –GO is a thin single-layer structure anchoring Fe 3 O 4 and M-MOF-199 is coated on its surface. Under the optimized conditions, the limits of detection of the triazole pesticides are 0.05–0.1 (S/N = 3) with correlation coefficients larger than 0.992. The recoveries in spiked water samples are 72.3%–91.53% with relative standard deviations ranging from 1.5% to 9.1%. Furthermore, the results show that M-MOF-199 is a promising hybrid adsorbent for magnetic dispersive solid phase extraction and removal of triazole pesticides from environmental water samples. [ABSTRACT FROM AUTHOR]

A novel magnetic copper-based metal–organic framework (M-MOF) was prepared using a Fe 4 O 3 –graphene oxide (GO)–β-cyclodextrin (β-CD) nanocomposite as the magnetic core and support, and used for adsorption and removal of neonicotinoid insecticide pollutants from aqueous solution. M-MOF characterization suggested that 1 Fe 4 O 3 –GO–β-CD consisted of a thin single layer with anchored Fe 3 O 4 . The M-MOF was coated on the Fe 4 O 3 –GO–β-CD surface. The M-MOF had a large Brunauer–Emmett–Teller surface area (250.33 m 2 g −1) and high super-paramagnetism with saturation magnetization of 10.47 emu g −1 . Adsorption model analysis showed that the equilibrium data for thiacloprid fitted Langmuir monolayer adsorption and the other insecticides tested showed Freundlich bimolecular layer adsorption. The results show that M-MOF is a promising hybrid adsorbent for rapid removal of neonicotinoid insecticide pollutants from environmental waters. [ABSTRACT FROM AUTHOR]

Three reduced graphene oxide (rGO) with different defect contents were prepared at 250, 600 and 1000 °C, respectively, using thermal reduction method, and their effects on the oxidative coupling processes of 4-methoxyphenol (MOP) in aqueous solution were investigated. In the presence of rGOs, the oxidation of MOP was dramatically accelerated. At the same surface area dose, the catalytic efficiencies of three rGOs followed an ascending order of rGO 250 ≤ rGO 600 < rGO 1000 . Using liquid chromatography-mass spectrometry and molecular modeling computation, we identified the coupling products (dimer, trimer, and tetramer), and revealed that ortho C O and ortho-ortho C C coupling between two MOP radicals were the main reaction pathways. Dissolved oxygen and structural defects of rGOs played important roles in the oxidation of MOP. It is proposed that dissolved oxygen reacted with the defect sites of rGO to produce surface-bound superoxide species, which captured H atom from the phenolic hydroxyl group of MOP to generate MOP radical and H 2 O 2 . A portion of H 2 O 2 can be catalyzed further by rGO to hydroxyl radical, which continued to react with MOP to produce MOP radical and H 2 O. [ABSTRACT FROM AUTHOR]

The mediation effect of reduced graphene oxide (rGO) on the oxidative transformation of 1,4-hydroquinone (H 2 Q) to 1,4-benzoquinone (BQ) in aqueous solution was investigated using a batch method and electron paramagnetic resonance. The results showed that the autoxidation of H 2 Q was spin-restricted and extremely slow in acidic and neutral pH range, but this process can be dramatically accelerated when rGO was added. In the presence of 33.3 mg L −1 rGO, more than 76.0% of H 2 Q was oxidized to BQ within 36 h. The enhancement effects of rGO were attributed to the combined contribution of the high chemical reactivity of graphenic edges and defects on rGO and the high electron conductivity of graphene basal surface of rGO. It is proposed that dissolved oxygen reacted with graphenic edges and defects of rGO to produce surface-bound oxygen intermediates, which capture H atoms from the phenolic hydroxyl groups of H 2 Q and facilitate the generation of semiquinone radical (SQ − ). The generated SQ − continued to transfer an electron to molecular oxygen to yield superoxide radical (O 2 − ) and BQ. As a chain-carrying radical, O 2 − further reacted with H 2 Q to produce SQ − and H 2 O 2 . [ABSTRACT FROM AUTHOR]

Abstract: The effects of humic acid (HA) on copper (Cu(II)) adsorption onto few-layer reduced graphene oxide (FRGO) and few-layer graphene oxide (FGO) were investigated using a batch equilibration method, micro-Fourier transform infrared spectroscopy, and extended X-ray absorption fine structure spectroscopy (EXAFS). The results showed that HA was adsorbed on FRGO through π–π interaction. The adsorbed HA introduced O-containing functional groups and negative charges to FRGO surfaces, increasing Cu(II) adsorption through chemical complexation and electrostatic attraction. In contrast, HA was adsorbed onto FGO mainly through polar interactions, due to its rich O-containing functional groups. The adsorbed HA had little effect on Cu(II) adsorption onto FGO because the shielding effect of HA on Cu(II) adsorption was offset by newly introduced adsorption sites of HA on FGO. EXAFS results suggested that Cu(II) was adsorbed on FRGO and FGO mainly through the coordination with their O-containing functional groups. When HA was added at pH 4.0 and 6.0, more Cu(II) was adsorbed on HA-coated FRGO. At pH 8.0, a portion of Cu(II) in solution precipitated on FRGO surface, while the presence of HA led to the formation of FRGO-HA-Cu ternary surface complexes instead of Cu(II) precipitation. [Copyright &y& Elsevier]

• rGO promoted the oxidative coupling of BPs in water in the dark. • HO-PBDEs and HO-PBBs were the main reaction products. • Dissolved oxygen was the oxidant of BPs oxidation. • Dissolved oxygen oxidized BPs by forming of reactive oxygen species. The widespread use of bromophenols in industrial products has led to their emergence in natural water environments. This study investigated the oxidative coupling reactions of 2,6-dibromophenol (2,6-diBP), 2,4-dibromophenol (2,4-diBP) and 3,5-dibromophenol (3,5-diBP) during the water purification by reduced graphene oxide (rGO). Results showed that rGO markedly promoted the oxidation of three bromophenols (BPs). The oxidation efficiencies of three BPs were related to their homolytic bond dissociation energies and decreased following the order of 2,6-diBP > 2,4-diBP > 3,5-diBP. Mass spectrometry and density functional theory calculation revealed that C O and C C coupling among BPs radicals were the main reaction pathways, with the hydroxylated polybrominated diphenyl ethers (HO-PBDEs) and the hydroxylated polybrominated biphenyls (HO-PBBs) being the main reaction products. The oxidant of the reaction was dissolved oxygen, which was first transformed to the surface-bound reactive oxygen species on graphene defects and then oxidized BPs into HO-PBDEs and HO-PBBs. To our knowledge, this is the first report indicating that HO-PBDEs and HO-PBBs could be generated during the adsorption of BPs by rGO. Given the enhanced toxicity of HO-PBDEs and HO-PBBs, caution should be taken when treating BPs-containing water with rGO. [ABSTRACT FROM AUTHOR]

Substituent effects of 4-nitrophenol (4-NP), phenol (PE), 4-methylpheol (4-MP), and 4-methoxyphenol (4-MOP) on their oxidative coupling reactions mediated by reduced graphene oxide (rGO) were examined using a batch method. The reaction products were identified as the oligomers of their individual parent compound, and C C and C O coupling between phenolic radicals were the main reaction pathways. The oxidative kinetics were well described with pseudo-first order model. The rate constants ( k obs ) of 4-NP, PE, 4-MP and 4-MOP were 0.47 × 10 −3 , 1.00 × 10 −3 , 2.03 × 10 −3 , and 3.53 × 10 −3  h −1 , respectively, following the order 4-NP < PE < 4-MP < 4-MOP. The k obs of four phenolic compounds was negative linear correlation with their homolytic bond dissociation energies (BDE(O H)), suggesting that BDE(O H) was an effective indicator to predict the oxidation susceptibility of phenolic compounds in rGO system. Dissolved oxygen played a critical role in the oxidation reactions through the formation of superoxide anion (O 2 − ) on rGO. These O 2 − further cleaved the O H bond of phenolic compounds to produce phenolic radicals, which interacted each other and led to the following oxidative coupling reactions. The finding of this study is important for predicting the environmental fate of rGO and phenolic compounds. [ABSTRACT FROM AUTHOR]