Efficient separation of dyes using two-dimensional heterogeneous composite membranes.

Two-dimensional materials are widely used in membrane separation, but the loose distribution and severe expansion between graphene oxide (GO) nanosheets limit its application. Here, we introduce a two-dimensional MOF material into the GO membrane to enhance its water permeance and separation performance. The MOF/GO composite membrane was prepared by vacuum filtration. The MOF and GO nanosheets were tightly stacked through the π-π effect, and the shortened transmission path and enhanced pore structure greatly improved the water permeance of the composite membrane. The MOF/GO membrane exhibited a high water permeance of 56.94 L m-2 h-1 bar-1. The rejection rates of methylene blue and was as methyl orange dyes were as high as 99.79% and 99.11%, respectively. At increased dye concentration, the rejection rate of methylene blue was still maintained greater than 99%. Dye rejection after 18 h of continuous operation remains above 90%. This work provides new ideas for improving membrane separation materials. The combination of two-dimensional heterogeneous materials can result in synergistic advantages for the development of composite membranes with high water permeance and high rejection rate.

Ultrafast and Selective Nanofiltration Enabled by Graphene Oxide Membranes with Unzipped Carbon Nanotube Networks.

Carbon nanomaterials have proven their wide applicability in molecular separation and water purification techniques. Here, an unzipped carbon nanotubes (CNT) embedded graphene oxide (GO) membrane (uCNTm) is reported. The multiwalled CNTs were longitudinally cut into multilayer graphene oxide nanoribbons by a modified Hummer method. To investigate the varying effects of different bandwidths of unzipped CNTs on their properties, four uCNTms were prepared by a vacuum-assisted filtration process. Unzipped-CNTs with different bandwidths were made by unzipping multiwalled CNTs with outer diameters of 0-10, 10-20, 20-30, and 30-50 nm and named uCNTm-1, uCNTm-2, uCNTm-3, and uCNTm-4, respectively. The uCNTms exhibited good stability in different pH solutions, and the water permeability of the composite membranes showed an increasing trend with the increase of the inserted uCNTm's bandwidth up to 107 L·m-2·h-1·bar-1, which was more than 10 times greater than that of pure GO membranes. The composite membranes showed decent dye screening performance with the rejection rate of methylene blue and rhodamine B both greater than 99%.

Utilizing the interfacial reaction of naphthalenyl thiosemicarbazide-modified carbon dots for the ultrasensitive determination of Fe (III) ions.

Since thiosemicarbazide contains numerous nitrogen and sulfur atoms in its structural formula that enhance its strong coordinating abilities with metal ions, it is always selected as the mother molecule for the design of metal-ion sensors. In this report, a thiosemicarbazide derivative (4-naphthalenyl-3-thiosemicarbazide (NTSC)) was synthesized via a single step process and covalently conjugated onto the surfaces of carbon dots (CDs). The modified CDs demonstrated excellent monodispersity, good photostability, and tunable luminescence properties. More importantly, the CDs retained a highly specific Fe3+ recognition capacity in contrast to other competing metal ions. Fe3+ can efficiently quench the fluorescence of CDs even at fairly low concentration (30µM) with a detection limit as low as 1.68nM. The fluorescence quenching kinetics are likely to involve static quenching, which is caused by specific interactions between NTSC-CDs and Fe3+ toward the formation of a ground state complex. Due to their excellent optical performance, low toxicity, and good biocompatibility the NTSC-CDs may be applied to the imaging and monitoring of Fe3+ in bacillus subtilis. In effect we successfully fabricated an effective fluorescent nanosensor for both the quantitative detection of Fe3+ in aqueous solutions, and its real-time imaging in vivo.

Hybridization-induced Ag(I) dissociation from an immobilization-free and label-free hairpin DNA: toward a novel electronic monitoring platform.

A novel silver ion (Ag(+))-assisted hairpin DNA through C-Ag(+)-C coordination chemistry was designed for immobilization-free and label-free electrochemical monitoring of human immunodeficiency virus (HIV) DNA on a negatively charged indium-tin oxide electrode, based on hybridization-induced dissociation of silver ions from the hairpin DNA.