Grafting chelating groups on 2D carbon for selective heavy metal adsorption

Electrochemical exfoliation of graphite using aqueous ammonium hydrogen carbonate solution and the ability of the exfoliated product as a hydrogen production electrocatalyst support

Electrochemical exfoliation of graphite has attracted much attention as a practical mass production of two-dimensional graphene-like materials. There is an increasing desire to find new and improved methods to create unique exfoliated products with excellent functionality. We used aqueous ammonium hydrogen carbonate solution as a new electrolyte for anodic oxidative exfoliation of graphite. The exfoliated product has a porous two-dimensional structure, and it can be dispersed in water for over five years. The oxidized and defected porous surface serves as an ideal support for molecular metal complexes, effectively functioning as heterogeneous electrocatalysts for hydrogen production.

Highly sensitive detection of Pb2+ with a non-contact, near-infrared responsive hydrogel-functionalized optical fiber sensor

Most sensors use acidic eluent to realize the desorption of Pb2+, which inevitably causes damage to the sensing membrane. A near-infrared responsive hydrogel sensing membrane (PNIPAm/PVA/GO) was prepared by free radical polymerization, which was modified on U-shaped optical fiber sensors for the selective determination of Pb2+. Graphene oxide (GO) is the functional recognition monomer, and the double-crosslinked network of polyvinyl alcohol (PVA) and Poly(N-isopropylacrylamide) (PNIPAm) acts as the mechanical stress skeleton while increasing the Pb2+ adsorption sites and inhibiting the agglomeration of GO. The "self-healing" of the sensing membrane achieves non-destructive desorption without causing secondary pollution to the environment by utilizing the high photothermal conversion efficiency of GO and the temperature response characteristics of PNIPAm. The sensor exhibited a sensitivity of 0.2191 nm/ppb in the 0-100 ppb range; the limit of detection was calculated to be 0.27 ppb. The experimental results show that the sensor has good reproducibility, stability, and selectivity. Further, the proposed signal analysis method based on convolutional neural networks realizes the measurement of Pb2+ at different pH values. This method can effectively solve the problem of increased selectivity while leading to desorption difficulties and provides a new idea for realizing green, clean, and efficient detection of Pb2+.

Stabilizing Zn/electrolyte Interphasial Chemistry by a Sustained-Release Drug Inspired Indium-Chelated Resin Protective Layer for High-Areal-Capacity Zn//V2O5 Batteries

For zinc-metal batteries, the instable chemistry at Zn/electrolyte interphasial region results in severe hydrogen evolution reaction (HER) and dendrite growth, significantly impairing Zn anode reversibility. Moreover, an often-overlooked aspect is this instability can be further exacerbated by the interaction with dissolved cathode species in full batteries. Here, inspired by sustained-release drug technology, an indium-chelated resin protective layer (Chelex-In), incorporating a sustained-release mechanism for indium, is developed on Zn surface, stabilizing the anode/electrolyte interphase to ensure reversible Zn plating/stripping performance throughout the entire lifespan of Zn//V2O5 batteries. The sustained-release indium onto Zn electrode promotes a persistent anticatalytic effect against HER and fosters uniform heterogeneous Zn nucleation. Meanwhile, on the electrolyte side, the residual resin matrix with immobilized iminodiacetates anions can also repel detrimental anions (SO4 2- and polyoxovanadate ions dissolved from V2O5 cathode) outside the electric double layer. This dual synergetic regulation on both electrode and electrolyte sides culminates a more stable interphasial environment, effectively enhancing Zn anode reversibility in practical high-areal-capacity full battery systems. Consequently, the bio-inspired Chelex-In protective layer enables an ultralong lifespan of Zn anode over 2800 h, which is also successfully demonstrated in ultrahigh areal capacity Zn//V2O5 full batteries (4.79 mAh cm-2).

Selective ion transport in large-area graphene oxide membrane filters driven by the ionic radius and electrostatic interactions

Filters made of graphene oxide (GO) are promising for purification of water and selective sieving of specific ions; while some results indicate the ionic radius as the discriminating factor in the sieving efficiency, the exact mechanism of sieving is still under debate. Furthermore, most of the reported GO filters are planar coatings with a simple geometry and an area much smaller than commercial water filters. Here, we show selective transport of different ions across GO coatings deposited on standard hollow fiber filters with an area >10 times larger than typical filters reported. Thanks to the fabrication procedure, we obtained a uniform coating on such complex geometry with no cracks or holes. Monovalent ions like Na+ and K+ can be transported through these filters by applying a low electric voltage, while divalent ions are blocked. By combining transport and adsorption measurements with molecular dynamics simulations and spectroscopic characterization, we unravel the ion sieving mechanism and demonstrate that it is mainly due to the interactions of the ions with the carboxylate groups present on the GO surface at neutral pH.