Mechanical Exfoliation of Expanded Graphite to Graphene-Based Materials and Modification with Palladium Nanoparticles for Hydrogen Storage.

Hydrogen is a promising green fuel carrier that can replace fossil fuels; however, its storage is still a challenge. Carbon-based materials with metal catalysts have recently been the focus of research for solid-state hydrogen storage due to their efficacy and low cost. Here, we report on the exfoliation of expanded graphite (EG) through high shear mixing and probe tip sonication methods to form graphene-based nanomaterial ShEG and sEG, respectively. The exfoliation processes were optimized based on electrochemical capacitance measurements. The exfoliated EG was further functionalized with palladium nanoparticles (Pd-NP) for solid-state hydrogen storage. The prepared graphene-based nanomaterials (ShEG and sEG) and the nanocomposites (Pd-ShEG and Pd-sEG) were characterized with various traditional techniques (e.g., SEM, TEM, EDX, XPS, Raman, XRD) and the advanced high-resolution pair distribution function (HRPDF) analysis. Electrochemical hydrogen uptake and release (QH) were measured, showing that the sEG decorated with Pd-NP (Pd-sEG, 31.05 mC cm-2) and ShEG with Pd-NP (Pd-ShEG, 24.54 mC cm-2) had a notable improvement over Pd-NP (9.87 mC cm-2) and the composite of Pd-EG (14.7 mC cm-2). QH showed a strong linear relationship with an effective surface area to volume ratio, indicating nanoparticle size as a determining factor for hydrogen uptake and release. This work is a promising step toward the design of the high-performance solid-state hydrogen storage devices through mechanical exfoliation of the substrate EG to control nanoparticle size and dispersion.

Spatially Resolved Optical Spectroscopic Measurements with Simultaneous Photoelectrochemical Mapping Using Scanning Electrochemical Probe Microscopy.

A deep understanding of the properties of semiconductor films at the micro-/nanoscale level is fundamental toward designing effective photoelectrocatalysts. Here, we integrated spatially resolved optical spectroscopy (SR-OS) with scanning photoelectrochemical microscopy (SPECM) to collect UV/vis spectra and quantify photocurrents of localized sites on a nanostructured BiVO4 thin film. Direct measurement of absorbance allowed for the determination of band gap energy at each location. Absorbance and photocurrent maps were obtained and used to investigate heterogeneities on the films. Scanning electrochemical cell microscopy (SECCM) was also coupled with SR-OS to acquire quantitative photoelectrochemical data at the FTO/BiVO4 film interface, revealing higher photocurrents at the boundary regions. As a droplet-based technique, SECCM was employed to estimate the wetted area by measuring the maximum height of droplet stretch at each point, allowing for the calculation of photocurrent density. This novel approach provides an advantageous mean to correlate localized photocatalytic activities and band gap energies.

Experimental and computational studies of photoelectrochemical degradation of atrazine by modified nanoporous titanium dioxide.

The presence of herbicides like Atrazine (ATZ) in groundwater from non-target runoff of the agriculture industry becomes a big concern due to its potential negative impacts on the environment and human health. The use of advanced oxidative processes (AOP) to remove harmful contaminants has been shown to be effective for wastewater treatment. Herein, we report on an advanced photoelectrochemical (PEC) approach based on electrochemically modified nanoporous TiO2 electrode for efficient degradation of ATZ. The electrochemical treated TiO2 electrodes were shown to have a six-fold increase in the photo-current density over the untreated ones. This increase in PEC activity was attributed to the increase in Ti3+ sites after the electrochemical modification, which was corroborated by low-temperature electron paramagnetic resonance (EPR) studies. The removal of ATZ by the PEC process resulted in a rate constant of 1.91 × 10-3 s-1, compared to 3.12 × 10-4 s-1 obtained by a strictly photocatalytic process. Liquid-Chromatography Mass-Spectrometric measurements showed the modified TiO2 electrodes highly effective at removing ATZ, with 96.1% removed after 10 h. Monitoring of the common degradation products desethyl atrazine (DEA), desisopropyl atrazine (DIA) and desethyl desisopropyl atrazine (DDA) revealed very low concentrations throughout the degradation process, indicating that further degradation was achieved. Quantum mechanical-based test for overall free radical scavenging activity (QM-ORSA) computational studies were performed and a mechanism for the N-dealkylation processes of ATZ has been proposed.

Unraveling the Chemosensing Mechanism by the 7-(Diethylamino)coumarin-hemicyanine Hybrid: A Ratiometric Fluorescent Probe for Hydrogen Peroxide.

The hemicyanine hybrid containing the 7-(diethylamino)coumarin (ACou) donor attached to the cationic indolenium (Ind) acceptor through a vinyl linkage (ACou-Ind) represents a classic ratiometric fluorescent probe for detecting nucleophilic analytes, such as cyanide and reactive sulfur species (RSS), through addition reactions that disrupt dye conjugation to turn off red internal charge transfer (ICT) fluorescence and turn on blue coumarin emission. The chemosensing mechanism for RSS detection by ACou-Ind suggested in the literature has now been revised. Our studies demonstrate that thiolates react with ACou-Ind through conjugate addition to afford C4-SR adducts that lack coumarin fluorescence due to photoinduced electron transfer quenching by the electron-rich enamine intermediate. Thus, ACou-Ind serves as a turn-off probe through loss of red ICT fluorescence upon RSS addition. The literature also suggests that blue coumarin emission of thiolate adducts is enhanced in the presence of reactive oxygen species (ROS) due to ROS-mediated cellular changes. Our studies predict that such a scenario is unlikely and that thiolate adducts undergo oxidative deconjugation in the presence of H2O2, the pervasive ROS. Under basic conditions, H2O2 also reacts directly with ACou-Ind to generate intense coumarin fluorescence through an epoxidation process. The relevance of our chemosensing mechanism for ACou-Ind was assessed within live zebrafish, and implications for the utility of ACou-Ind for unraveling the interplay between RSS and ROS are discussed.

Methods for Enhanced Fluorescence Detection of Proteins by using Entrapped Gold Nanoparticles in Membranes.

Measuring protein levels from biofluids can provide important insight into human health and disease during various physiological and pathological conditions. In many situations, sensitive methods are required for protein quantification because at the early stages of many diseases, proteins in biofluids are present at very low concentrations. Here, a new and simple method is presented in the form of Basic and Alternative Protocols for an immunoassay performed on a nitrocellulose membrane, followed by the addition of gold nanoparticles prior to measuring fluorescence with a microscope. The assay protocol was optimized to achieve 3D metal-enhanced fluorescence (MEF) with increased antibody-binding capacity and enhanced fluorescence signals, improving assay sensitivity. Using different concentrations of spiked fluorescently labeled IgGs in pooled normal human plasma, a lower detection limit of 29 ng/ml was achieved. This limit of detection was found to be a thousand-fold lower than the conventional 2D assay and one order of magnitude lower than when the assay was performed on a 3D membrane without MEF. This method provides an easy way to improve immunoassay sensitivity, and it can be simply transferred to other labs. It also can extend to fluorescence detection of other analytes beyond proteins. © 2022 Wiley Periodicals LLC. Basic Protocol: Assay in nitrocellulose membrane with entrapped AuNPs using commercially available AuNPs Alternative Protocol: Assay in nitrocellulose membrane with entrapped AuNPs using lab-made AuNPs.

Entrapping gold nanoparticles in membranes for simple-to-use enhanced fluorescence detection of proteins.

Quantifying proteins under different physiological and pathological conditions can give important insights into human health and disease, since proteins are the functional components of cells. In order to be able to use protein expression levels to diagnose diseases, sensitive protein quantification techniques are required, because some proteins can be present in low concentrations in biofluids at early stages of a disease. Here, a novel and simple-to-implement signal enhancement method for fluorescence-based protein detection is presented, in which an immunoassay was conducted on a nitrocellulose membrane, and a solution of gold nanoparticles was then pipetted onto the membrane before signal acquisition with a fluorescence microscope. The gold nanoparticles were entrapped and adsorbed into the 3D membrane matrix upon drying due to the hydrophobic interactions with the membrane. Through optimizing the concentration and size of the nanoparticles and comparison of different membranes, we were able to achieve metal enhanced fluorescence (MEF). This new gold nanoparticle-based MEF method, together with the 3D membrane platform that improves antibody and gold nanoparticle binding capacity, provided higher signal intensity and assay sensitivity for fluorescence-based protein quantification. Fluorescently-labeled IgG protein was spiked in human plasma with different concentrations, and the lower limit of detection was determined to be 29 ng/mL, three orders of magnitude lower than that of conventional 2D assays and one order of magnitude lower than that of 3D membrane assays without applying gold nanoparticles. This method offers a simple way of improving the sensitivity of fluorescence-based immunoassays that can be easily adopted in a biological lab with basic lab set up. Furthermore, it can be potentially extended to the fluorescence detection of other analytes beyond proteins.

Highly boosted gas diffusion for enhanced electrocatalytic reduction of N2 to NH3 on 3D hollow Co-MoS2 nanostructures.

Transition metal chalcogenide MoS2 catalysts are highly selective for the electrochemical reduction of dinitrogen (N2) to ammonia (NH3) in aqueous electrolytes. However, due to the low solubility of N2 in water, limited N2 diffusion and mass transport have heavily restricted the yield and the faradaic efficiency (FE). Here, we have demonstrated a highly efficacious assembled gas diffusion cathode with hollow Co-MoS2/N@C nanostructures to significantly improve the electrochemical reduction of N2 to NH3. Our results revealed that the synthesized Co-MoS2 heterojunctions with abundant graphitic N groups exhibited a superb NH3 yield of 129.93 µg h-1 mgcat-1 and a high faradaic efficiency of 11.21% at -0.4 V vs. the reversible hydrogen electrode (RHE), as well as excellent selectivity and stability. The strategy described in this study offers new inspiration to design high-performance electrocatalyst assemblies for the sustainable environmental and energy applications.

Graphene-Oxide-Based Electrochemical Sensors for the Sensitive Detection of Pharmaceutical Drug Naproxen.

Here we report on a selective and sensitive graphene-oxide-based electrochemical sensor for the detection of naproxen. The effects of doping and oxygen content of various graphene oxide (GO)-based nanomaterials on their respective electrochemical behaviors were investigated and rationalized. The synthesized GO and GO-based nanomaterials were characterized using a field-emission scanning electron microscope, while the associated amounts of the dopant heteroatoms and oxygen were quantified using x-ray photoelectron spectroscopy. The electrochemical behaviors of the GO, fluorine-doped graphene oxide (F-GO), boron-doped partially reduced graphene oxide (B-rGO), nitrogen-doped partially reduced graphene oxide (N-rGO), and thermally reduced graphene oxide (TrGO) were studied and compared via cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that GO exhibited the highest signal for the electrochemical detection of naproxen when compared with the other GO-based nanomaterials explored in the present study. This was primarily due to the presence of the additional oxygen content in the GO, which facilitated the catalytic oxidation of naproxen. The GO-based electrochemical sensor exhibited a wide linear range (10 mM-1 mM), a high sensitivity (0.60 µAµM-1cm-2), high selectivity and a strong anti-interference capacity over potential interfering species that may exist in a biological system for the detection of naproxen. In addition, the proposed GO-based electrochemical sensor was tested using actual pharmaceutical naproxen tablets without pretreatments, further demonstrating excellent sensitivity and selectivity. Moreover, this study provided insights into the participatory catalytic roles of the oxygen functional groups of the GO-based nanomaterials toward the electrochemical oxidation and sensing of naproxen.

Sulfur vacancy-rich N-doped MoS2 nanoflowers for highly boosting electrocatalytic N2 fixation to NH3 under ambient conditions.

In this communication, optimized sulfur vacancy-rich nitrogen-doped MoS2 nanoflowers were developed, which served as excellent N2 reduction reaction (NRR) electrocatalysts for the conversion of N2 to NH3 under ambient conditions. Electrochemical results demonstrated that the as-prepared N-doped MoS2 electrode afforded a superior NH3 yield and high faradaic efficiency, which exceeded those of the recently reported MoS2 catalysts. The possible NRR catalytic mechanism and electron transfer pathway were further elucidated via density functional theory calculations.