High Electrochemical Performance Phosphorus-Oxide Modified Graphene Electrode for Redox Supercapacitors Prepared by One-Step Electrochemical Exfoliation

Unraveling Structural and Acidic Properties of Al-SBA-15-supported Metal Phosphates: Assessment for Glucose Dehydration

5-Hydroxymethylfurfural (5-HMF) synthesized through glucose conversion requires Lewis acid (L) site for isomerization and Brønsted acid (B) site for dehydration. The objective of this work is to investigate the influence of the metal type of Al-SBA-15-supported phosphates of Cr, Zr, Nb, Sr, and Sn on glucose conversion to 5-HMF in a NaCl-H2 O/n-butanol biphasic solvent system. The structural and acid property of all supported metal phosphate samples were fully verified by several spectroscopic methods. Among those catalysts, CrPO/Al-SBA-15 provided the best performance with the highest glucose conversion and 5-HMF yield, corresponding to the highest total acidity of 0.65 mmol/g and optimal L/B ratio of 1.88. For CrPO/Al-SBA-15, another critical parameter is the phosphate-to-chromium ratio. Moreover, DFT simulation of glucose conversion to 5-HMF on the surface of the optimized chromium phosphate structure reveals three steps of fructose dehydration on the Brønsted acid site. Finally, the optimum reaction condition, reusability, and leaching test of the best catalyst were determined. CrPO/Al-SBA-15 is a promising catalyst for glucose conversion to high-value-added chemicals in future biorefinery production.

Structural Control and Electrical Behavior of Thermally Reduced Graphene Oxide Samples Assisted with Malonic Acid and Phosphorus Pentoxide

We present a detailed study of the structural and electrical changes occurring in two graphene oxide (GO) samples during thermal reduction in the presence of malonic acid (MA) (5 and 10 wt%) and P2O5 additives. The morphology and de-oxidation efficiency of reduced GO (rGO) samples are characterized by Fourier transform infrared, X-ray photoelectron, energy-dispersive X-ray, Raman spectroscopies, transmission electron and scanning electron microscopies, X-ray diffraction (XRD), and electrical conductivity measurements. Results show that MA and P2O5 additives are responsible for the recovery of π-conjugation in rGO as the XRD pattern presents peaks corresponding to (002) graphitic-lattice planes, suggesting the formation of the sp2-like carbon structure. Raman spectra show disorders in graphene sheets. Elemental analysis shows that the proposed reduction method in the presence of additives also suggests the simultaneous insertion of phosphorus with a relatively high content (0.3–2.3 at%) in rGO. Electrical conductivity measurements show that higher amounts of additives used in the GO reduction more effectively improve electron mobility in rGO samples, as they possess the highest electrical conductivity. Moreover, the relatively high conductivity at low bulk density indicates that prepared rGO samples could be applied as metal-free and non-expensive carbon-based electrodes for supercapacitors and (bio)sensors.

A Simple and Expeditious Route to Phosphate-Functionalized, Water-Processable Graphene for Capacitive Energy Storage

Phosphate-functionalized carbon-based nanomaterials have attracted significant attention in recent years owing to their outstanding behavior in electrochemical energy-storage devices. In this work, we report a simple approach to obtain phosphate-functionalized graphene (PFG) via anodic exfoliation of graphite at room temperature with a high yield. The graphene nanosheets were obtained via anodic exfoliation of graphite foil using aqueous solutions of H3PO4 or Na3PO4 in the dual role of phosphate sources and electrolytes, and the underlying exfoliation/functionalization mechanisms are proposed. The effect of electrolyte concentration was studied, as low concentrations do not lead to a favorable graphite exfoliation and high concentrations produce fast graphite expansion but poor layer-by-layer delamination. The optimal concentrations are 0.25 M H3PO4 and 0.05 M Na3PO4, which also exhibited the highest phosphorus contents of 2.2 and 1.4 at. %, respectively. Furthermore, when PFG-acid at 0.25 M and PFG-salt at 0.05 M were tested as an electrode material for capacitive energy storage in a three-electrode cell, they achieved a competitive performance of ∼375 F/g (540 F/cm3) and 356 F/g (500 F/cm3), respectively. Finally, devices made up of symmetric electrode cells obtained using PFG-acid at 0.25 M possess energy and power densities up to 17.6 Wh·kg-1 (25.3 Wh·L-1) and 10,200 W/kg; meanwhile, PFG-salt at 0.05 M achieved values of 14.9 Wh·kg-1 (21.3 Wh·L-1) and 9400 W/kg, with 98 and 99% of capacitance retention after 10,000 cycles, respectively. The methodology proposed here also promotes a circular-synthesis process to successfully achieve a more sustainable and greener energy-storage device.

Highly Sensitive and Contactless Ammonia Detection Based on Nanocomposites of Phosphate-Functionalized Reduced Graphene Oxide/Polyaniline Immobilized on Microstrip Resonators

Ammonia is a key compound in a variety of industrial sectors, including automotive, chemical, and food. Its hazardous effects on the environment and human health require the implementation of proper safety guidelines and monitoring techniques. An attractive approach is to add sensing functionality to low-cost wireless communication devices to allow for the monitoring/mapping of the chemical environment across a large area. This study outlines a highly sensitive contactless ammonia gas sensor with the potential for continuous and wireless mapping of ammonia emissions by integrating an antenna on the device. The devices were fabricated by casting a novel advanced sensing nanocomposite, polyaniline (PANI), and phosphate-functionalized reduced graphene oxide (P-rGO) on split-ring resonators (SRRs). P-rGO incorporation in PANI produced a positive-sensing synergistic effect to multiply the sensing response severalfold to ammonia and dimethylamine gases. Furthermore, we identified that the modification of the semiconductive behavior of the nanosheets, achieved via phosphate functionalization, is the key factor to the positive-sensing synergy observed in the nanocomposites because of the formation of localized heterojunctions. The prepared SRRs exhibited remarkably a low detection limit, ∼1 ppm, to ammonia gas, as well as good stability and selectivity, which paves the path for a novel generation of wireless, chipless, potentially fully printable, and passive sensor platforms.

Facile one-pot synthesis of water-dispersible phosphate functionalized reduced graphene oxide toward high-performance energy storage devices

Phosphate functionalized carbon nanomaterials have attracted significant attention because of their potential applications in energy storage applications. Herein we report a facile one-pot method to prepare water dispersible phosphate functionalized reduced graphene oxide and demonstrate the potential of the novel materials for energy storage applications. The synthesis method shows promise to promote a wider adoption of reduced graphene oxide for high performance applications.

Boron-, sulfur-, and phosphorus-doped graphene for environmental applications

The control of environmental pollutants is a global concern. Recently, heteroatom-doped graphene has drawn increasing attention due to their widespread applications in removing and detecting environmental pollutants. Owing to the introduction of heteroatoms into pristine graphene, the properties of heteroatom-doped graphene have been significantly enhanced in physic, chemistry, and biology. This review focuses on the approaches for synthesis and characterization of boron-, sulfur-, and phosphorus-doped graphene and their applications in the fields of adsorption, catalysis, and detection for environmental pollutants. The mechanisms of environmental applications, including π-π interactions, complexation, hydrophobic interactions, electronic conductivity, and active sites and reactive radicals, are elaborated. Furthermore, the challenges associated with the use of heteroatom-doped graphene materials and their prospective applications are also proposed.