Weiping Xiong

Effective removal of Cr(VI) through adsorption and reduction by magnetic mesoporous carbon incorporated with polyaniline

Magnetic mesoporous carbon incorporated with polyaniline (PANI–Fe/OMC) is developed for enhanced adsorption and reduction of toxic Cr(VI) to non-toxic Cr(III). Several physicochemical techniques including TEM, FTIR and XPS analyses confirmed that magnetic iron nanoparticles and amino groups have been successfully bound on the mesoporous matrix. The adsorption capacity of the functionalized material is two- and ten-fold that of the magnetic mesoporous carbon (Fe/OMC) and pristine mesoporous silicon (SBA-15), respectively. Solution pH exhibited a remarkable impact on the Cr(VI) adsorption and the maximum uptake amount (172.33 mg g−1) occurred at pH 2.0. The good fitting of adsorption process using pseudo-second-order and Langmuir models indicated the chemisorption process of Cr(VI) removal. The regeneration study revealed that PANI–Fe/OMC can be reused without loss of their activity in repetitive adsorption tests. Moreover, the resultant adsorbent can be effectively applied in actual wastewater treatment due to the excellent removal performance in fixed-bed column and real water samples. The interaction between Cr(VI) and PANI–Fe/OMC was investigated by FTIR and XPS analyses. The results indicate that the amino groups on the surface of PANI–Fe/OMC are involved in Cr(VI) uptake, and simultaneously some toxic Cr(VI) are reduced to non-toxic Cr(III) during the removal process.

Comprehensive evaluation of the cytotoxicity of CdSe/ZnS quantum dots in Phanerochaete chrysosporium by cellular uptake and oxidative stress

The growing potential of quantum dots (QDs) in biological and biomedical applications has raised considerable concern due to their toxicological impact. Consequently, it is urgent to elucidate the underlying toxicity mechanism of QDs. In this work, we comprehensively investigated the cellular uptake of four CdSe/ZnS QDs (COOH CdSe/ZnS 525, COOH CdSe/ZnS 625, NH2 CdSe/ZnS 525, and NH2 CdSe/ZnS 625) and induced physiological responses in Phanerochaete chrysosporium (P. chrysosporium) through inductively coupled plasma optical emission spectroscopy, confocal laser scanning microscopy, and the determination of malondialdehyde content, superoxide level, superoxide dismutase activity, catalase activity and glutathione level. The results showed that the four CdSe/ZnS QDs accumulated largely in the hyphae and caused oxidative stress to P. chrysosporium in the tested concentration range (10–80 nM). Furthermore, the cellular uptake and cytotoxicity were related to the physicochemical properties of the QDs, such as particle size and surface charges. Negatively charged CdSe/ZnS QDs with small size could be more easily ingested by P. chrysosporium than large ones; thus small size CdSe/ZnS QDs were more cytotoxic to P. chrysosporium. On the other hand, small negatively charged CdSe/ZnS QDs resulted in greater cytotoxicity than large negatively charged CdSe/ZnS QDs. The obtained results offer valuable information for revealing the toxicity mechanism of QDs in living cells.

Adsorption of phosphate from aqueous solution using iron-zirconium modified activated carbon nanofiber: Performance and mechanism

Phosphate (P) removal is significant for the prevention of eutrophication in natural waters. In this paper, a novel adsorbent for the removal of P from aqueous solution was synthesized by loading zirconium oxide and iron oxide onto activated carbon nanofiber (ACF-ZrFe) simultaneously. The adsorbent was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The results showed that P adsorption was highly pH dependent and the optimum pH was found to be 4.0. The isotherm of adsorption could be well described by the Langmuir model and the maximum P adsorption capacity was estimated to be 26.3mgP/g at 25°C. The kinetic data were well fitted to the pseudo-second-order equation, indicating that chemical sorption was the rate-limiting step. Moreover, co-existing ions including sulfate (SO42-), chloride (Cl-), nitrate (NO3-) and fluoride (F-) exhibited a distinct effect on P adsorption with the order of F->NO3->Cl->SO42-. Further investigations by FT-IR spectroscopy and pH variations associated with the adsorption process revealed that ligands exchange and electrostatic interactions were the dominant mechanisms for P adsorption. The findings reported in this work highlight the potential of using ACF-ZrFe as an effective adsorbent for the removal of P in natural waters.

Co-occurrence and interactions of pollutants, and their impacts on soil remediation—A review

ABSTRACT With the development of industrialization and agriculture, the phenomenon of soil contamination by combination of potentially toxic elements and organic pollutants has been a terrible environmental issue. The co-occurring pollutants exhibit complicated interactions in chemical processes, adsorption behaviors, and biological processes. These interactions are of concern for any kind of remediation to be implemented, since they make great influence on soil remediation efficiency. Exploring the interactions and impacts of multiple pollutants is important for actual soil remediation. This review expounds several interactions of pollutants in soil, which would be helpful to better understand their impacts on remediation efficiency and further study directions in this field.

One-step calcination method for synthesis of mesoporous g-C3N4/NiTiO3 heterostructure photocatalyst with improved visible light photoactivity

A novel g-C3N4/NiTiO3 composite was fabricated by one-step calcination method using dicyandiamide, tetrabutyl titanate and nickel acetate as the precursors. The samples were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, N2 adsorption/desorption isotherms, UV-vis diffuse reflection spectroscopy and photoluminescence spectroscopy. It was indicated that the hybrids owned a large surface area, mesoporous structure and improved visible light absorption. The optimal g-C3N4 content in the g-C3N4/NiTiO3 composite was 18.4 wt%, and the corresponding visible-light removal rate for nitrobenzene was 0.0132 min−1, about 1.6 times higher than that of pure NiTiO3. The enhanced photocatalytic activity may be attributed to the large surface area, stronger absorption in the visible region and efficient electron–hole separation.

Interactions of carbon nanotubes and/or graphene with manganese peroxidase during biodegradation of endocrine disruptors and triclosan

Molecular-level biodegradation processes of bisphenol A (BPA), nonylphenol (NP) and triclosan (TCS) mediated by manganese peroxidase (MnP) were investigated with and without single-walled carbon nanotube (SWCNT) and/or graphene (GRA). Although the incorporation of SWCNT, GRA or their combination (SWCNT+GRA) did not break up the complexes composed of manganese peroxidase (MnP) and these substrates, they had different effects on the native contacts between the substrates and MnP. GRA tended to decrease the overall stability of the binding between MnP and its substrates. SWCNT or SWCNT+GRA generally had a minor impact on the mean binding energy between MnP and its substrates. We detected some sensitive residues from MnP that were dramatically disturbed by the GRA, SWCNT or SWCNT+GRA. Nanomaterials changed the number and behavior of water molecules adjacent to both MnP and its substrates, which was not due to the destruction of H-bond network formed by sensitive regions and water molecules. The present results are useful for understanding the molecular basis of pollutant biodegradation affected by the nanomaterials in the environment, and are also helpful in assessing the risks of these materials to the environment.

Adsorption of tetracycline antibiotics from aqueous solutions on nanocomposite multi-walled carbon nanotube functionalized MIL-53(Fe) as new adsorbent

Adsorption of tetracycline antibiotics from aqueous solutions by a multi-walled carbon nanotube (MWCNT) loaded iron metal-organic framework (MIL-53(Fe)) composite was studied. The adsorbent was characterized by environmental scanning electron microscope, energy dispersive X-ray spectroscopy, brunauer-emmett-teller, thermogravimetric analysis, X-ray diffraction, fourier transform infrared spectrum, and X-ray photoelectron spectrum. The adsorption kinetics of tetracycline hydrochloride (TCN), oxytetracycline hydrochloride (OTC), and chlortetracycline hydrochloride (CTC) were all well fitted to the pseudo-second-order equation as well as the adsorption isotherms could be well delineated via Langmuir equations. The main influencing factors such as pH and ionic strength were studied in detail. At initial pH of 7.0, maximum adsorption capacity of TCN, OTC and CTC on MWCNT/MIL-53(Fe) was 364.37, 325.59, 180.68 mg·g-1 at 25 °C, which was 1.25, 8.28 and 3.34 times than that of single MWCNT, respectively. The adsorption capacity of TCS for this adsorbent was in the order: TCN > OTC > CTC, which was determined by the adsorbate molecule magnitude. In addition, π-π adsorbate-adsorbent interactions played an important role during the adsorption process. The excellent reusability and great water stability indicated the potential application of this novel composite in the removal of TCS from aqueous solutions.

Efficient degradation of sulfamethazine in simulated and real wastewater at slightly basic pH values using Co-SAM-SCS /H 2 O 2 Fenton-like system

The presence of antibiotics in aquatic environments has attracted global concern. Fenton process is an attractive yet challenging method for antibiotics degradation, especially when such a reaction can be conducted at neutral pH values. In this study, a novel composite Fe/Co catalyst was synthesized via the modification of steel converter slag (SCS) by salicylic acid-methanol (SAM) and cobalt nitrate (Co(NO3)2). The catalysts were characterized by N2-Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results indicated that the Co-SAM-SCS/H2O2 Fenton-like system was very effective for sulfamethazine (SMZ) degradation at a wide pH range. At initial pH of 7.0, the degradation rate of SMZ in Co-SAM-SCS/H2O2 system was 2.48, 3.20, 6.18, and 16.21 times of that in Fe-SAM-SCS/H2O2, SAM-SCS/H2O2, Co(NO3)2/H2O2 and SCS/H2O2 system, respectively. The preliminary analysis suggested that high surface area of Co-SAM-SCS sample and synergistic effect between introduced Co and SAM-SCS are responsible for the efficient catalytic activity. During the degradation, three main intermediates were identified by high performance liquid chromatography-mass spectrometry (HPLC-MS) analysis. Based on this, a possible degradation pathway was proposed. The SEM images, XRD patterns and XPS spectra before and after the reactions demonstrate that the crystal and chemical structure of Co-SAM-SCS after five cycles are almost unchanged. Besides, the Co-SAM-SCS presented low iron and cobalt leaching (0.17 mg/L and 2.36 mg/L, respectively). The studied Fenton-like process also showed high degradation of SMZ in river water and municipal wastewater. The progress will bring valuable insights to develop high-performance heterogeneous Fenton-like catalysts for environmental remediation.

Rapid startup of thermophilic anaerobic digester to remove tetracycline and sulfonamides resistance genes from sewage sludge

Spread of antibiotic resistance genes (ARGs) originating from sewage sludge is highlighted as an eminent health threat. This study established a thermophilic anaerobic digester using one-step startup strategy to quickly remove tetracycline and sulfonamides resistance genes from sewage sludge. At least 20days were saved in the startup period from mesophilic to thermophilic condition. Based on the results of 16S rDNA amplicons sequencing and predicted metagenomic method, the successful startup largely relied on the fast colonization of core thermophilic microbial population (e.g. Firmicutes, Proteobacteria, Actinobacteria). Microbial metabolic gene pathways for substrate degradation and methane production was also increased by one-step mode. In addition, real-time quantitative PCR approach revealed that most targeted tetracycline and sulfonamides resistance genes ARGs (sulI, tetA, tetO, tetX) were substantially removed during thermophilic digestion (removal efficiency>80%). Network analysis showed that the elimination of ARGs was attributed to the decline of their horizontal (intI1 item) and vertical (potential hosts) transfer-related elements under high-temperature. This research demonstrated that rapid startup thermophilic anaerobic digestion of wastewater solids would be a suitable technology for reducing quantities of various ARGs.

Interaction of carbon nanotubes with microbial enzymes: conformational transitions and potential toxicity

Wide industrial, environmental and biomedical applications of carbon nanotubes (CNTs) are allowing them to enter the environment. Their toxicity to microorganisms has been experimentally reported, but the underlying molecular mechanism is still unclear. Here, we investigated the conformational transitions in widely distributed microbial enzymes in the presence and absence of single-walled carbon nanotubes (SWCNTs) by molecular dynamics (MD) simulations. Our study identifies a new mechanism by which SWCNTs produce possible toxicity to microbes by inducing significant changes in enzymatic conformations. The protein–protein interactions undergo significant transitions in two monomers, either towards or away from each other in the presence of SWCNTs. The significant conformational changes in microbial enzymes may inactivate the microbial enzymes and disturb the microbial metabolism.