Water Molecules on the Epoxide Groups of Graphene Oxide Surfaces

Nylon Fabric/GO Based Self-Powered Humidity Sensor Based on the Galvanic Cell Principle with High Air Permeability and Rapid-Response

Flexible humidity sensors have received more and more attention in people's lives, and the problems of gas permeability and power supply issues of the device have long been areas in need of improvement. In this work, inspired by the high air permeability of daily wear clothing and galvanic batteries, a self-powered humidity sensor with high air permeability and fast response is designed. A nylon fabric/GO net (as a humidity sensitive layer and solid electrolyte) is obtained by spraying technique. This structure enables the sensor to have fast response/recovery (0.78 s/0.93 s, calculated at 90% of the final value), ultra-high response (0.83 V) and excellent stability (over 150 cycles) at 35 °C. Such sensors are useful for health monitoring, such as non-contact monitoring of human respiratory rate before and after exercise, and monitoring a level of humidity in the palms, arms, and fingers. This research provides an idea for developing a flexible wearable humidity sensor that is both breathable and self-powered and can also be mass-produced similar to wearable clothing.

Variations in the Effective Work Function of Graphene in a Sliding Electrical Contact Interface under Ambient Conditions

Control of work function (WF) in graphene is crucial for graphene application in electrode material replacement and electrode surface protection in optoelectronic devices. Although efforts have been made to manipulate the effective WF of graphene to optimize its application, most studies have focused on graphene employed in static electrical contact interfaces. In this work, we investigated WF variations of supported single-layer graphene (SLG) in sliding electrical contact under ambient conditions, which was achieved by sliding an electrically biased conductive atomic force microscopy (cAFM) probe on the SLG surface. The effective WF, structural properties, and chemical compositions of rubbed SLG were subsequently measured by Kelvin probe force microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, respectively. We found that the effective WF of the rubbed SLG was governed by both the tunneling triboelectric effect (TTE) and tribochemical-induced surface functionalization. The TTE charges generated by the sliding cAFM probe tunneled through the structural defects of the SLG and were trapped underneath the SLG. The SLG will be either p-doped or n-doped depending on the type of TTE charges and the polarity of electric bias applied to the cAFM probe during the rubbing process. However, the applied electric bias also led to the electrolysis of a water meniscus formed at the cAFM probe-SLG contact, resulting in surface oxidation and the increase of SLG WF. Further absorption of ambient water molecules on the oxygenated functional groups gradually reduced the SLG WF. The influence of TTE and surface functionalization on the SLG WF depends on the magnitude and polarity of applied electric biases, relative humidity, and physical properties of the supporting substrates. Our results demonstrate that the effective WF of SLG in a sliding electrical contact interface will vary with time and might need to be considered for related applications.

Experimental and DFT Studies of Hybrid Silver/Cdots Nanoparticles

In this work, the combination of experimental and theoretical results was employed to confirm an interaction between Cdots and AgNPs in the silver/Cdots hybrid nanoparticles. The experimental data obtained by UV-vis, IR, ζ potential, and TGA techniques were correlated and interpreted by calculations obtained by DFT. In particular, an interaction between the -COO^- functional group of the Cdots with AgNPs was revealed. As consequence of this interaction, a frequency shift and a higher absorption intensity in the IR of the -OH group in the Cdots was theoretically predicted and also observed in the experimental IR spectra. Moreover, a bonding and charge distribution analysis was also carried out. These results constitute new physical insight for the Ag@Cdots system. Additionally, based in this type of interaction, energy calculations explained the negative charge surrounding the AgNPs, which was detected by ζ potential measurements. This systematic methodology not only is useful for this nanoparticles system but also could be used to analyze the interaction between the components that constitute other types of hybrid nanoparticles.

Roll-to-roll graphene oxide radon barrier membranes

Graphene oxide as a radon barrier in living environments was introduced by intercalating the polymer resin-coated layer inside a multilayer membrane with an area of 1 × 10 m and a thickness of 2.5 mm, prepared by the roll-to-roll method. A 5 μm-thick graphene oxide polymer resin (GOPR) layer was coated on polyethylene terephthalate (PET) film (100 μm) between the two styrene-butadiene-styrene (SBS)-modified bitumen asphalt layers fitted for construction sites. The inserted graphene oxide materials were characterized by means of infrared, Raman, and X-ray photoelectron spectroscopy (XPS). Dispersion-corrected density functional theory (DFT) calculations suggested weaker binding energies on the oxide surfaces and higher penetration energy barriers of graphene nanopores for radon (²²²Rn) than in the cases of the atmospheric gas molecules Ar, H₂O, CO₂, H₂, O₂, and N₂. Theoretical calculations of the graphene nanopores supported the higher barrier energies of ²²²Rn than most ambient gases. The roll-to-roll prepared graphene materials exhibited good barrier properties for ²²²Rn as well as for the ambient gases. The purpose of our experimental and theoretical study is to provide a better understanding of using graphene-based materials to reduce the risk of carcinogenic radon gas in construction sites and residential buildings for practical applications.

In-Situ Deposition of Graphene Oxide Catalyst for Efficient Photoelectrochemical Hydrogen Evolution Reaction Using Atmospheric Plasma

The vacuum deposition method requires high energy and temperature. Hydrophobic reduced graphene oxide (rGO) can be obtained by plasma-enhanced chemical vapor deposition under atmospheric pressure, which shows the hydrophobic surface property. Further, to compare the effect of hydrophobic and the hydrophilic nature of catalysts in the photoelectrochemical cell (PEC), the prepared rGO was additionally treated with plasma that attaches oxygen functional groups effectively to obtain hydrophilic graphene oxide (GO). The hydrogen evolution reaction (HER) electrocatalytic activity of the hydrophobic rGO and hydrophilic GO deposited on the p-type Si wafer was analyzed. Herein, we have proposed a facile way to directly deposit the surface property engineered GO.