Shuang-Yan Huan

Easily separated silver nanoparticle-decorated magnetic graphene oxide: Synthesis and high antibacterial activity

Silver nanoparticle-decorated magnetic graphene oxide (MGO-Ag) was synthesized by doping silver and Fe3O4 nanoparticles on the surface of GO, which was used as an antibacterial agent. MGO-Ag was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Energy dispersive X-ray (EDS), X-ray diffraction (XRD), Raman spectroscopy and magnetic property tests. It can be found that magnetic iron oxide nanoparticles and nano-Ag was well dispersed on graphene oxide; and MGO-Ag exhibited excellent antibacterial activity against Escherichia coli and Staphylococcus aureus. Several factors were investigated to study the antibacterial effect of MGO-Ag, such as temperature, time, pH and bacterial concentration. We also found that MGO-Ag maintained high inactivation rates after use six times and can be separated easily after antibacterial process. Moreover, the antibacterial mechanism is discussed and the synergistic effect of GO, Fe3O4 nanoparticles and nano-Ag accounted for high inactivation of MGO-Ag.

Polyurethane foam membranes filled with humic acid-chitosan crosslinked gels for selective and simultaneous removal of dyes

Polyurethane foam membrane filled with humic acid-chitosan crosslinked gels (HA-CS-PUF) for dye removal was prepared by soaking the foams into humic acid-chitosan (HA-CS) crosslinked gels and hot-pressing them into membranes. Scanning electron microscope, derivative thermogravimetry and X-ray photoelectron spectroscopy were used to characterize the HA-CS-PUF membrane. Results showed that the interaction of HA and CS was mainly through ionic cross-linking between carboxyl and protonated amino groups. Three types of dyes, including positively charged methylene blue (MB), neutrally charged rhodamine B (RB) and negatively charged methyl orange (MO), were used to test membranes properties through static adsorption and membrane filtration experiments. It revealed that adsorption process was better fitted with Pseudo-second-order and Freundlich model. In membrane filtration experiments, we found that the retention rates of membrane 1 (ratio of HA to CS was 0:1) to MO and RB were 99.7% and 65%, respectively, and nearly no retention to MB. While membrane 4 (ratio of HA to CS was 0.2:1) can retain 97.7% of MO, 71.6% of RB and 62.1% of MB. Based on the experimental results, membrane 1 possessed the ability of selectively separating MB from MO/MB and RB/MB solutions, and membrane 4 can simultaneously retain RB and MB from RB/MB solution.

Graphene sponge decorated with copper nanoparticles as a novel bactericidal filter for inactivation of Escherichia coli

Nanotechnology has great potential in water purification. However, the limitations such as aggregation and toxicity of nanomaterials have blocked their practical application. In this work, a novel copper nanoparticles-decorated graphene sponge (Cu-GS) was synthesized using a facile hydrothermal method. Cu-GS consisting of three-dimensional (3D) porous graphene network and well-dispersed Cu nanoparticles exhibited high antibacterial efficiency against Esherichia coli when used as a bactericidal filter. The morphological changes determined by scanning electron microscope and fluorescence images measured by flow cytometry confirmed the involvement of membrane damage induced by Cu-GS in their antibacterial process. The oxidative ability of Cu-GS and intercellular reactive oxygen species (ROS) were also determined to elucidate the possible antibacterial mechanism of Cu-GS. Moreover, the concentration of released copper ions from Cu-GS was far below the drinking water standard, and the copper ions also have an effect on the antibacterial activity of Cu-GS. Results suggested that Cu-GS as a novel bactericidal filter possessed a potential application of water disinfection.

Ultrathin reduced graphene oxide/MOF nanofiltration membrane with improved purification performance at low pressure

Here we demonstrated an alternative partial reduction graphene oxide/metal-organic frameworks nano-scale laminated membrane for dyes and heavy metal ions removal at low pressure. Compared with pure prGO membranes, the novel UiO-66-(COOH)2/prGO membranes with loose structure and excellent selective permeability demonstrated significant enhancements of permeation for low-pressure nanofiltration. The UiO-66-(COOH)2/prGO membranes possess more nanochannels structure, high surface charge and stability, which were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The experiment result indicated that the flux of composite membranes for pure water was 20.0 ± 2.5 Lm-2h-1bar-1, about 2.9 times higher than that (6.5 ± 1.2 Lm-2h-1bar-1) of the pristine prGO membranes at the same prGO loading. The high rejection of UiO-66-(COOH)2/prGO membranes for organic dyes (98.2 ± 1.7% for negatively charged congo red and 92.55 ± 2.5% for positively charged methylene blue) were exhibited. Moreover, the rejection for heavy metal ions also can be efficiently improved up to 96.5-83.1% for Cu2+ and 92.6-80.4% for Cd2+, indicating the positive effect of the electrostatic interaction on the nanochannels for ions. Therefore, it is reasonable to believe that novel UiO-66-(COOH)2/prGO membranes have great potential application in water treatment.

Carbon nanotube-impeded transport of non-steroidal anti-inflammatory drugs in Xiangjiang sediments

Carbon nanotubes (CNTs), usually with a superior affinity with organic chemicals, are expected to ultimately released to the environment through their manufacturing, usage, and eventual disposal, which will influence the mobility and environmental risk of nonsteroidal anti-inflammatory drugs (NSAIDs). In this study, batch and column experiments were performed to examine the effects of two kinds of multi-walled carbon nanotubes (MWCNTs: MWCNT2040, MWCNT0815) and one kind of single-walled carbon nanotubes (SWCNTs) on the environmental fate of two NSAIDs, paracetamol (PA) and diclofenac sodium (DS), in sediments. Impact ways of CNTs including addition in inflow and mixing with sediments were investigated. The adsorption capacity of NSAIDs on sediments increased with increasing CNTs/sediments ratios and in an order of MWCNT2040<MTWCNT0815<SWCNT. In column tests, PA showed a higher mobility than DS. With CNTs in inflow, the amounts of NSAIDs leached from sediment columns reduced because of the association with CNTs. For the sediment columns mixed with CNTs, breakthrough of the two NSAIDs was dramatically retarded, and the NSAIDs were hard to separate from CNT-polluted sediments. Our work provides useful insights into fate, transport and risk assessment of NSAIDs in the presence of CNTs.

Zirconium-based metal organic frameworks loaded on polyurethane foam membrane for simultaneous removal of dyes with different charges

Treating dye wastewater by membrane filtration technology has received much attention from researchers all over the world, however, current studies mainly focused on the removal of singly charged dyes but actual wastewater usually contains dyes with different charges. In this study, the removal of neutral, cationic and anionic dyes in binary or ternary systems was conducted by using zirconium-based metal organic frameworks loaded on polyurethane foam (Zr-MOFs-PUF) membrane. The Zr-MOFs-PUF membrane was fabricated by an in-situ hydrothermal synthesis approach and a hot-pressing process. Neutrally charged Rhodamine B (RB), positively charged Methylene blue (MB), and negatively charged Congo red (CR) were chosen as model pollutants for investigating filtration performance of the membrane. The results of filtration experiments showed that the Zr-MOFs-PUF membrane could simultaneously remove RB, MB, and CR not only from their binary system including RB/MB, RB/CR, and MB/CR mixtures, but also from RB/MB/CR ternary system. The removal of dyes by Zr-MOFs-PUF membrane was mainly attributed to the electrostatic interactions, hydrogen bond interaction, and Lewis acid-base interactions between the membrane and dye molecules. The maximum removal efficiencies by Zr-MOFs-PUF membrane were 98.80% for RB at pH ≈ 7, 97.57% for MB at pH ≈ 9, and 87.39% for CR at pH ≈ 3. Additionally, when the NaCl concentration reached 0.5 mol/L in single dye solutions, the removal efficiencies of RB, MB, and CR by Zr-MOFs-PUF membrane were 93.08%, 79.52%, and 97.82%, respectively. All the results suggested that the as-prepared Zr-MOFs-PUF membrane has great potential in practical treatment of dye wastewater.