Advances in Microwave Synthesis of Nanoporous Materials

Usually, porous materials are synthesized by using conventional electric heating, which can be energy- and time-consuming. Microwave heating is commonly used in many households to quickly heat food. Microwave ovens can also be used as powerful devices in the synthesis of various porous materials. The microwave-assisted synthesis offers a simple, fast, efficient, and economic way to obtain many of the advanced nanomaterials. This review summarizes the recent achievements in the microwave-assisted synthesis of diverse groups of nanoporous materials including silicas, carbons, metal-organic frameworks, and metal oxides. Microwave-assisted methods afford highly porous materials with high specific surface areas (SSAs), e.g., activated carbons with SSA ≈3100 m² g^-1 , metal-organic frameworks with SSA ≈4200 m² g^-1 , covalent organic frameworks with SSA ≈2900 m² g^-1 , and metal oxides with relatively small SSA ≈300 m² g^-1 . These methods are also successfully implemented for the preparation of ordered mesoporous silicas and carbons as well as spherically shaped nanomaterials. Most of the nanoporous materials obtained under microwave irradiation show potential applications in gas adsorption, water treatment, catalysis, energy storage, and drug delivery, among others.

Improved energy storage performance of PbZrO3 antiferroelectric thin films crystallized by microwave radiation

Energy storage dielectric capacitors based on a physical charge-displacement mechanism have attracted much attention due to their high power density and fast charge–discharge characteristics. How to improve the energy storage capacity of dielectric materials has become an important emerging research topic. Here, antiferroelectric PbZrO₃ films were prepared by chemical solution deposition on Pt/Ti/SiO₂/Si substrates and crystallized by microwave radiation. The effects of microwave radiation on the antiferroelectric properties and energy storage performance were investigated. In contrast to ordinary heating, microwave radiation can crystallize the amorphous PbZrO₃ films into the perovskite phase at 750 °C in only 180 seconds. The PbZrO₃ films have a highly (100)-preferred orientation and dense microstructure, which is beneficial to enhance the stability of antiferroelectric phase and the electric breakdown strength. The PbZrO₃ films show a recoverable energy storage density of 14.8 J cm⁻³ at 740 kV cm⁻¹, which is approximately 40% higher than that of the PbZrO₃ films crystallized by ordinary heating. The results reveal that microwave radiation is an effective method to improve energy storage performance of antiferroelectric films.

We prepared amorphous PZO films by chemical solution deposition and then crystallized the films by microwave radiation. Using microwave radiation in the crystallization of AFE thin films is an effective method to improve their energy storage performance.

Bioanodes containing catalysts from onion waste and Bacillus subtilis for energy generation from pharmaceutical wastewater in a microbial fuel cell

Performance of the FAOW8 + B. subtilis bioanode in an MFC (a 14-day test) using pharmaceutical wastewater (pH = 9.2) as a substrate.

Recent Advancement in Bio-precursor derived graphene quantum dots: Synthesis, Characterization and Toxicological Perspective

Graphene quantum dots (GQDs), impressive materials with enormous future potential, are reviewed from their inception, including different precursors. Considering the increasing burden of industrial and ecological bio-waste, there is an urgency to develop techniques which will convert biowaste into active moieties of interest. Amongst the various materials explored, we selectively highlight the use of potential carbon containing bioprecursors (e.g. plant-based, amino acids, carbohydrates), and industrial waste and its conversion into GQDs with negligible use of chemicals. This review focuses on the effects of different processing parameters that affect the properties of GQDs, including the surface functionalization, paradigmatic characterization, toxicity and biocompatibility issues of bioprecursor derived GQDs. This review also examines current challenges and s the ongoing exploration of potential bioprecursors for ecofriendly GQD synthesis for future applications. This review sheds further light on the electronic and optical properties of GQDs along with the effects of doping on the same. This review may aid in future design approaches and applications of GQDs in the biomedical and materials design fields.

Graphene Modified Multifunctional Personal Protective Clothing

Personal protective clothing is intended to protect the wearer from various hazards (mechanical, biological, chemical, thermal, radiological, etc.) and inhospitable environmental conditions that may cause harm or even death. There are various types of personal protective clothing, manufactured with different materials based on hazards and end user requirements. Conventional protective clothing has impediments such as high weight, bulky nature, lack of mobility, heat stress, low heat dissipation, high physical stress, diminishing dexterity, diminishing scope of vision, lack of breathability, and reduced protection against pathogens and hazards. By virtue of the superlative properties of graphene, fabrics modified with this material can be an effective means to overcome these limitations and to improve properties such as mechanical strength, antibacterial activity, flame resistance, conductivity, and UV resistance. The limitations of conventional personal protective equipment are discussed, followed by necessary measures which might be taken to improve personal protective equipment (PPE), the unique properties of graphene, methods of graphene incorporation in fabrics, and the current research status and potential of graphene-modified performance textiles relevant to PPE.

Commercial Silk-Based Electronic Yarns Fabricated Using Microwave Irradiation

Electronic textiles (e-textiles) are being developed because of their potential applications in wearable and flexible electronics. However, complex procedures and chemical agents are required to synthesize carbon-based e-textiles. Pyroprotein-based e-textiles, obtained by the pyrolysis of silk proteins, consume large amounts of time and energy due to the high-temperature process (from 800 to 2800 °C). In this study, we report a novel method of fabricating pyroprotein-based electronic yarns (e-yarns) using microwave irradiation. Microwaves were applied to pyroprotein treated at 650 °C to remove numerous heteroatoms in a short time without the high-temperature process and chemical agents. The structural modulation was confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy. We found a reduction in heteroatoms and enlargement of the carbon region. The temperature-dependent resistance was well explained by the fluctuation-induced tunneling model, which also showed structural modification. The electrical conductivity of the fabricated e-yarns was comparable to that of pyroprotein-based e-textiles heat-treated at 1000 °C (order of 10² S/cm) and showed electrical stability under bending.

Advances in Microwave-Assisted Production of Reduced Graphene Oxide

Efficient reduction of graphene oxide to obtain high-quality graphene nanosheets is desirable for energy storage, catalysis, electronics and environmental remediation. In this brief review, we mainly focus on the microwave-assisted production of reduced graphene oxide in three categories: (1) microwave-assisted chemical reduction of graphene oxide; (2) microwave-assisted thermal reduction of graphene oxide; (3) microwave-assisted simultaneous thermal exfoliation & thermal reduction of graphite oxide. We also summarize common techniques for characterizing reduction efficiency and quality of as-obtained rGO.

Synthesis of Graphite Oxide with Different Surface Oxygen Contents Assisted Microwave Radiation

Graphite oxide is synthesized via oxidation reaction using oxidant compounds that have lattice defects by the incorporation of unlike functional groups. Herein, we report the synthesis of the graphite oxide with diverse surface oxygen content through three (B, C, D) different modified versions of the Hummers method assisted microwave radiation compared with the conventional graphite oxide sample obtained by Hummers method (A). These methods allow not only the production of graphite oxide but also reduced graphene oxide, without undergoing chemical, thermal, or mechanical reduction steps. The values obtained of C/O ratio were ~2, 3.4, and ~8.5 for methodologies C, B, and D, respectively, indicating the presence of graphite oxide and reduced graphene oxide, according to X-ray photoelectron spectroscopy. Raman spectroscopy of method D shows the fewest structural defects compared to the other methodologies. The results obtained suggest that the permanganate ion produces reducing species during graphite oxidation. The generation of these species is attributed to a reversible reaction between the permanganate ion with π electrons, ions, and radicals produced after treatment with microwave radiation.

Synthesis of graphene-transition metal oxide hybrid nanoparticles and their application in various fields

Single layer graphite, known as graphene, is an important material because of its unique two-dimensional structure, high conductivity, excellent electron mobility and high surface area. To explore the more prospective properties of graphene, graphene hybrids have been synthesised, where graphene has been integrated with other important nanoparticles (NPs). These graphene-NP hybrid structures are particularly interesting because after hybridisation they not only display the individual properties of graphene and the NPs, but also they exhibit further synergistic properties. Reduced graphene oxide (rGO), a graphene-like material, can be easily prepared by reduction of graphene oxide (GO) and therefore offers the possibility to fabricate a large variety of graphene-transition metal oxide (TMO) NP hybrids. These hybrid materials are promising alternatives to reduce the drawbacks of using only TMO NPs in various applications, such as anode materials in lithium ion batteries (LIBs), sensors, photocatalysts, removal of organic pollutants, etc. Recent studies have shown that a single graphene sheet (GS) has extraordinary electronic transport properties. One possible route to connecting those properties for application in electronics would be to prepare graphene-wrapped TMO NPs. In this critical review, we discuss the development of graphene-TMO hybrids with the detailed account of their synthesis. In addition, attention is given to the wide range of applications. This review covers the details of graphene-TMO hybrid materials and ends with a summary where an outlook on future perspectives to improve the properties of the hybrid materials in view of applications are outlined.

Effect of few-layer graphene films as electrodes on the electrical properties of ferroelectric capacitors

An FLG/PZT/Pt capacitor exhibits comparable polarization compared with a Pt/PZT/Pt capacitor but the magnitude of leakage current density for the FLG/PZT/Pt capacitor is largely decreased due to the van der Waals gap at the FLG/PZT interface.

Graphene oxide: strategies for synthesis, reduction and frontier applications

In this review article, we describe a general introduction to GO, its synthesis, reduction and some selected frontier applications. Its low cost and potential for mass production make GO a promising building block for functional hybrid materials.