With an ever-increasing number of applications in many advanced fields, gas sensors are becoming indispensable devices in our daily life. Among different types of gas sensors, conductometric metal oxide semiconductor (MOS) gas sensors are found to be the most appealing for advanced applications in the automotive, biomedical, environmental, and safety sectors because of the their high sensitivity, reduced size, and low cost. To improve their sensing characteristics, new metal oxide-based nanostructures have thus been proposed in recent years as sensing materials. In this review, we extensively review gas-sensing properties of core@ shell nanocomposites in which metals as the core and metal oxides as the shell structure, both of nanometer sizes, are assembled into a single metal@metal oxide core–shell. These nanostructures not only combine the properties of both noble metals and metal oxides, but also bring unique synergetic functions in comparison with single-component materials. Up-dated achievements in the synthesis and characterization of metal@metal oxide core–shell nanostructures as well as their use in MOS sensors are here reported with the main objective of providing an overview about their gas-sensing properties.

Metal-core@metal oxide-shell nanomaterials for gas-sensing applications: a review

Green and facile synthesis of Ag nanoparticles using Crataegus pentagyna fruit extract (CP-AgNPs) for organic pollution dyes degradation and antibacterial application.

Wolfberry fruit (Lycium barbarum) extract mediated novel route for the green synthesis of silver nanoparticles

Abstract Silver nanoparticles (AgNPs) have application potential in diverse areas ranging from wound healing to catalysis and sensing. The possibility for optimizing the physical, chemical and optical properties for an application by tailoring the shape and size of silver nanoparticles has motived much research on methods for synthesis of size- and shape-controlled AgNPs. The shape and size of AgNPs are reported to vary depending on choice of the Ag precursor salt, reducing agent, stabilizing agent and on the synthesis technique used. This chapter provides a detailed review on various synthesis approaches that may be used for synthesis of AgNPs of desired size and shape. Silver nanoparticles may be synthesized using diverse routes, including, physical, chemical, photochemical, biological and microwave -based techniques. Synthesis of AgNPs of diverse shapes, such as, nanospheres, nanorods, nanobars, nanoprisms, decahedral nanoparticles and triangular bipyramids is also discussed for chemical-, photochemical- and microwave-based synthesis routes. The choice of chemicals used for reduction and stabilization of nanoparticles is found to influence their shape and size significantly. A discussion on the mechanism of synthesis of AgNPs through nucleation and growth processes is discussed for AgNPs of varying shape and sizes so as to provide an insight on the various synthesis routes. Techniques, such as, electron microscopy, spectroscopy, and crystallography that can be used for characterizing the AgNPs formed in terms of their shape, sizes, crystal structure and chemical composition are also discussed in this chapter. Graphical Abstract:

Synthesis and characterization of size- and shape-controlled silver nanoparticles

Green synthesis of biocompatible silver nanoparticles mediated by Osmanthus fragrans extract in aqueous solution

Electrochemical synthesis and optical properties of organically capped silver nanoparticles

The present work investigates the influence of laser peening without coating (LPwC) on the fatigue and fretting wear behaviour of AISI 304 alloy subjected to one and five peening passes peened at 9 GW cm−2. Laser peened samples were characterised for microstructure, residual stress, phase evolution and hardness. After LPwC, the samples induced maximum compressive residual stress of −380 and −581 MPa for one and five peening passes at 50 μm from the surface. Microhardness was increased to 31 % and 71 % for one and five pass samples at 50 μm depth. The microstructure of laser peening samples was characterised using a transmission electron microscope (TEM) and electron backscattered diffraction (EBSD). Dislocation density was increased after peening with twin-twin interaction observed in both the peening cases and martensite induced at the junction of the twin-twin in five-time peened samples. Low angle grain fraction increased from 29 % (unpeened) to 41 % (one pass) and 63 % (five passes), and grain refinement was observed, where the average grain size reduced from 22.28 μm (unpeened) to 18.36 μm (one pass) and 9.51 μm (five passes) for LPwC samples. Fretting wear behaviour at various loading (5, 10 and 20 N) displayed significant improvement in wear resistance of LPwC samples, as evident from lower wear volume loss. Fatigue testing performed at R = 0.1 exhibited an improvement in fatigue life of 1.4 and 2.4 times for one and five pass samples compared to unpeened samples at a stress amplitude of 450 MPa. Fatigue fractography revealed a decrease in striation spacing for LPwC samples (979 nm/cycle and 565 nm/cycle for one- and five-time peening) with a delay in crack-propagation rate. 

K. Praveenkumar

Papers

Electrochemical synthesis and optical properties of organically capped silver nanoparticles

Effect of multiple laser peening on microstructural, fatigue and fretting-wear behaviour of austenitic stainless steel

Insights into the surface and biocompatibility aspects of laser shock peened Ti-22Nb alloy for orthopedic implant applications

Residual Stress Distribution, Phase Transformation, and Wettability Characteristics of Laser Peened Austenitic Stainless Steel

Surface Oxidation and Subsurface Deformation in a Laser-Peened Ti-6Al-4V