Sonochemical synthesis of graphene oxide supported Pt–Pd alloy nanocrystals as efficient electrocatalysts for methanol oxidation

A review on Pd-M bimetallic electrochemical sensors: Techniques, performance, and applications

Environmental pollution, food safety, and medical diagnostics pose severe threats to human health, making the development of effective detection technologies crucial. Electrochemical sensors, as an efficient detection method, are extensively employed in detecting environmental pollutants, food additives, and biomolecules. Pd-M bimetallic materials, known for their excellent electrocatalytic performance, are extensively utilized as electrode modification materials. Although earlier reviews have covered the sensing applications of bimetallic materials, they have not targeted discussed Pd-based bimetallic materials. This paper systematically summarizes the preparation methods of Pd-M bimetallic materials, explores their structural and morphological regulation, and elaborates on their recent applications in pesticide detection, environmental pollutant detection, food additive detection, drug detection, and biosensing. It enumerates the detection performance of various Pd-M bimetallic material-modified electrochemical sensors for the aforementioned analytes in detail, including specific modification materials, linear range, detection limits, and sensitivity parameters.

The unique Pd@Pt/C core-shell nanoparticles as methanol-tolerant catalysts using sonochemical synthesis

Over the past decades, there were a few reports on the use of sonochemical method to prepare noble metals catalysts for fuel cells. However, the synthetic processes were conducted under high frequency (200 kHz)/long reaction time in most cases. In this work, Pd and PdxPt nanoparticles were prepared by sonochemical method under low frequency (20 kHz) in a shorter time (20-40 mins). In the first time, a sequentialsonochemical synthesis was explored to achieve a core/shell structure of PdxPt nanoparticles. Consequently, the unique core-shell structure was formed with two shells surrounding the Pd core. The Pd core was firstly grown. In the second step, the Pd²⁺ ion existing in the Pd core reduced simultaneously with Pt⁴⁺ ion in the solution as the first layer of PdPt alloy. Further, the Pt layer was formed subsequently. The Pd-based catalysts exhibited a superior ORR selective activity and exceptional methanol-tolerance property compared with the commercial Pt/C catalyst. In 0.5 M CH₃OH + 0.5MH₂SO₄ solution, the best performance was achieved on Pd₃Pt/C catalyst with increased overpotential of 24 mV. However, overpotentials was increased 174 mV on commercial Pt/C catalyst. The excellent performance of the Pd₃Pt/C catalyst is ascribed to its combination of preferable growth of the Pd (1 1 1) plane, small particle size (∼4 nm), unique core/shell structure as well as the electronic effects between Pd and Pt. These results have demonstrated that the sequential ultrasonic synthesis is an effective method for the synthesis of binary/trinary catalysts in a green approach.

State of the art and recent advances in the ultrasound-assisted synthesis, exfoliation and functionalization of graphene derivatives

Sonochemistry, an almost a century old technique was predominantly employed in the cleaning and extraction processes but this tool has now slowly gained tremendous attention in the synthesis of nanoparticles (NPs) where particles of sub-micron have been produced with great stability. Following this, ultrasonication techniques have been largely employed in graphene synthesis and its dispersion in various solvents which would conventionally take days and offers poor yield. Ultrasonic irradiation allows the production of thin-layered graphene oxide (GO) and reduced graphene oxide (RGO) of up to 1nm thickness and can be produced in single layers. With ultrasonic treatment, reactions were made easy whereby graphite can be directly exfoliated to graphene layers. Oxidation to GO can also be carried out within minutes and reduction to RGO is possible without the use of any reducing agents. In addition, various geometry of graphene can be produced such as scrolled graphene, sponge or foam graphene, smooth as well as those with rough edges, each serving its own unique purpose in various applications such as supercapacitor, catalysis, biomedical, etc. In ultrasonic-assisted reaction, deposition of metal NPs on graphene was more homogeneous with custom-made patterns such as core-shell formation, discs, clusters and specific deposition at the edges of graphene sheets. Graphene derivatives with the aid of ultrasonication are the perfect catalyst for various organic reactions as well as an excellent adsorbent. Reactions which used to take hours and days were significantly reduced to minutes with exceedingly high yields. In a more recent approach, sonophotocatalysis was employed for the combined effect of sonication and photocatalysis of metal deposited graphene. The system was highly efficient in organic dye adsorption. This review provides detailed fundamental concepts of ultrasonochemistry for the synthesis of graphene, its dispersion, exfoliation as well as its functionalization, with great emphasis only based on recent publications. Necessary parameters of sonication such as frequency, power input, sonication time, type of sonication as well as temperature and dual-frequency sonication are discussed in great length to provide an overview of the resultant graphene products.

Ruthenium based metallopolymer grafted reduced graphene oxide as a new hybrid solar light harvester in polymer solar cells

A new class of pyridyl benzimdazole based Ru complex decorated polyaniline assembly (PANI-Ru) was covalently grafted onto reduced graphene oxide sheets (rGO) via covalent functionalization approach. The covalent attachment of PANI-Ru with rGO was confirmed from XPS analysis and Raman spectroscopy. The chemical bonding between PANI-Ru and rGO induced the electron transfer from Ru complex to rGO via backbone of the conjugated PANI chain. The resultant hybrid metallopolymer assembly was successfully demonstrated as an electron donor in bulk heterojunction polymer solar cells (PSCs). A PSC device fabricated with rGO/PANI-Ru showed an utmost ~6 fold and 2 fold enhancement in open circuit potential (Voc) and short circuit current density (Jsc) with respect to the standard device made with PANI-Ru (i.e., without rGO) under the illumination of AM 1.5 G. The excellent electronic properties of rGO significantly improved the electron injection from PANI-Ru to PCBM and in turn the overall performance of the PSC device was enhanced. The ultrafast excited state charge separation and electron transfer role of rGO sheet in hybrid metallopolymer was confirmed from ultrafast spectroscopy measurements. This covalent modification of rGO with metallopolymer assembly may open a new strategy for the development of new hybrid nanomaterials for light harvesting applications.

Sonochemical and sustainable synthesis of graphene-gold (G-Au) nanocomposites for enzymeless and selective electrochemical detection of nitric oxide

In this study, a sonochemical approach was utilised for the development of graphene-gold (G-Au) nanocomposite. Through the sonochemical method, simultaneous exfoliation of graphite and the reduction of gold chloride occurs to produce highly crystalline G-Au nanocomposite. The in situ growth of gold nanoparticles (AuNPs) took place on the surface of exfoliated few-layer graphene sheets. The G-Au nanocomposite was characterised by UV-vis, XRD, FTIR, TEM, XPS and Raman spectroscopy techniques. This G-Au nanocomposite was used to modify glassy carbon electrode (GCE) to fabricate an electrochemical sensor for the selective detection of nitric oxide (NO), a critical cancer biomarker. G-Au modified GCE exhibited an enhanced electrocatalytic response towards the oxidation of NO as compared to other control electrodes. The electrochemical detection of NO was investigated by linear sweep voltammetry analysis, utilising the G-Au modified GCE in a linear range of 10-5000μM which exhibited a limit of detection of 0.04μM (S/N=3). Furthermore, this enzyme-free G-Au/GCE exhibited an excellent selectivity towards NO in the presence of interferences. The synergistic effect of graphene and AuNPs, which facilitated exceptional electron-transfer processes between the electrolyte and the GCE thereby improving the sensing performance of the fabricated G-Au modified electrode with stable and reproducible responses. This G-Au nanocomposite introduces a new electrode material in the sensitive and selective detection of NO, a prominent biomarker of cancer.

Multi-component electrocatalyst for low-temperature fuel cells synthesized via sonochemical reactions

This review presents recent advances in multi-component electrocatalysts for low-temperature fuel cells (FCs) synthesized via sonochemical reactions. As a feasible approach to develop novel electrocatalysts that can overcome the many problems of the prevailing Pt electrocatalysts, Pt- or Pd-based alloy and core-shell M@Pt nanoparticles (NPs) have been pursued. Synthesizing NPs with desirable properties often turn out to be challenging. Sonochemistry generates extreme conditions via acoustic cavitation, which have been utilized in the syntheses of various Pt and Pd NPs and Pt- and Pd-based alloy NPs. Especially, it has been reported that several M@Pt core-shell NPs can be synthesized by sonochemistry, which is hard to achieve by other methods. The principles of sonochemistry are presented with examples. Also alloy NPs and core-shell NPs synthesized by sonochemistry and those by other methods are compared.

Carrier separation and charge transport characteristics of reduced graphene oxide supported visible-light active photocatalysts

Extending the absorption to the visible region by tuning the optical band-gap of semiconductors and preventing charge carrier recombination are important parameters to achieve a higher efficiency in the field of photocatalysis.

Recent advances in noble metal based composite nanocatalysts: colloidal synthesis, properties, and catalytic applications

This Review article provides a report on progress in the synthesis, properties and catalytic applications of noble metal based composite nanomaterials. We begin with a brief discussion on the categories of various composite materials. We then present some important colloidal synthetic approaches to the composite nanostructures; here, major attention has been paid to bimetallic nanoparticles. We also introduce some important physiochemical properties that are beneficial from composite nanomaterials. Finally, we highlight the catalytic applications of such composite nanoparticles and conclude with remarks on prospective future directions.