Bhupendra Joshi

Sonochemical synthesis of solar-light-driven Ag̊-PbMoO4 photocatalyst

Ag°-PbMoO4 photocatalysts were synthesized by facile sonochemical method with different mol.% of Ag nanoparticles dispersed on the surface of PbMoO4. The synthesized powders were characterized by X-ray Diffraction (XRD) Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM), and Diffuse Reflectance Spectroscopy (UV-vis DRS) to investigate the crystal structure, morphology, chemical composition, and optical properties of the photocatalyst. Photocatalytic activities of the Ag°-PbMoO4 samples were evaluated by the degradation of Indigo Carmine (IC) dye under simulated solar light irradiation. It has been observed that the sample containing 0.3 mol.% of Ag showed the best photocatalytic activity as compared to other samples. The results suggest that the dispersion of Ag nanoparticles on the surface of PbMoO4 significantly enhances the photocatalytic activity of PbMoO4. Increase in photocatalytic activity of Ag°-PbMoO4 photocatalyst has been explained on the basis of surface plasmon resonance (SPR) effect caused by the silver nanoparticles present in the photocatalyst.

Fabrication of translucent boron nitride dispersed polycrystalline silicon nitride ceramics

Optical transparency was achieved at infrared region and overall translucent silicon nitride was fabricated using hot press sintering (HPS). The increase in h-BN content decreased the optical transparency. Microstructral observations shows that the optical, mechanical and tribological properties of BN dispersed polycrystalline Si3N4 ceramics were affected by the density, α:β-phase ratio and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of α-Si3N4, AlN, MgO and h-BN at 1850°C. The composite contained from 0.25 to 2 mass % BN powder with sintering aids (9% AlN + 3% MgO). Maximum transmittance of 57% was achieved for 0.25 mass % BN doped Si3N4 ceramics. Fracture toughness was increased and wear volume and friction coefficient were decreased with increase in BN content.

Understanding Mechanism of Photocatalytic Microbial Decontamination of Environmental Wastewater

Several photocatalytic nanoparticles are synthesized and studied for potential application for the degradation of organic and biological wastes. Although these materials degrade organic compounds by advance oxidation process, the exact mechanisms of microbial decontamination remains partially known. Understanding the real mechanisms of these materials for microbial cell death and growth inhibition helps to fabricate more efficient semiconductor photocatalyst for large-scale decontamination of environmental wastewater or industries and hospitals/biomedical labs generating highly pathogenic bacteria and toxic molecules containing liquid waste by designing a reactor. Recent studies on microbial decontamination by photocatalytic nanoparticles and their possible mechanisms of action is highlighted with examples in this mini review.

Visible and near-infrared upconversion in α-sialon ceramics

α-Sialon ceramics are well known for highly stressed structural engineering applications owing to their inherently outstanding mechanical and thermo-chemical stability. However, the possibilities of the functional applications such as frequency upconversion in α-sialon ceramics have been scarcely investigated. Here, very intense visible and near-infrared frequency upconversion as well as frequency downconversion emissions are reported for the first time in Er3+, Ho3+, and Tm3+ triply doped α-sialon ceramics under 980 nm excitation. α-Sialon ceramics are prepared using a hot press sintering technique. Efficient energy transfer processes between the dopant ions are found to be responsible for the observed emissions. The upconversion process is governed by a two-photon absorption process. The energy transfer efficiency in the triply doped system is 95.8% while that in Er3+/Ho3+ and Er3+/Tm3+ systems is 71.6% and 66.3%, respectively. Triple doping results in the combination of the emission properties found in the co-doped Er3+/Ho3+ and Er3+/Tm3+ systems and it also reveals a cooperative emission behavior which is not possible with only two dopants. These findings open up the possibility of potential application of the Er3+/Ho3+/Tm3+ doped α-sialon ceramic as an optical material in which efficient luminescent properties can co-exist along with the excellent mechanical and thermo-chemical stability.

Luminescence properties of Eu2+, Gd3+ and Pr3+ doped translucent Sialon phosphors

Abstract Optical properties of hot pressed Sialon ceramics doped with different rare earth oxides (REOs) i.e. Eu2O3, Gd2O3, and Pr2O3 were investigated. The α-Sialon phase was the main phase obtained after sintering as observed by X-ray diffraction (XRD). The transparency of different samples of varying thickness measured from UV to IR region revealed that the samples were translucent in the visible region while transparent in IR region. The thin samples of 150 μm thickness had transmittance as high as 30% in the visible region. The luminescence was observed in transmittance mode to investigate the effect of sample thickness on luminescence intensity. We observed blue, yellow and red emissions in Sialon doped with Gd2O3, Eu2O3, and Pr2O3, respectively. The excitation wavelength for Gd2O3 and Pr2O3 doped samples were in UV region i.e. 280 and 270 nm, respectively, whereas, for Eu2O3 doped samples was in the blue region (460 nm). The Eu2O3 doped Sialon having 300 μm thickness showed better white light extraction as coupled with blue LED. Moreover, the fabricated phosphor samples exhibited high hardness around 20 GPa and fracture toughness above 5 MPa·m½.

Optical, mechanical and tribological properties of Y2O3, Er2O3 and Nd2O3 doped polycrystalline silicon nitride ceramics

Y2O3, Er2O3 and Nd2O3 doped polycrystalline silicon nitride ceramics were prepared by hot press sintering method at 1850°C and 30 MPa pressure. 1 wt.% of each rare earth oxides (REO) were sintered with 3 wt.% MgO, 9 wt.% AlN and 87 wt.% α-Si3N4.The optical, mechanical and tribological properties of REO doped polycrystalline silicon nitride ceramics were investigated. Optical transmittance was measured in visible and near infrared region and found to be 54% transmittance for Y2O3 doped Si3N4 ceramics. β- phase transformation was suppressed with REO addition. High hardness and high fracture toughness were achieved by addition of REO. Adding REO shows good mechanical properties as high strength and toughness. Coefficient of friction of the REO doped silicon nitride ceramics was lower than that of without REO doped silicon nitride ceramics.

Improved Tribological Behavior of Grey Cast Iron Under Low and High Viscous Lubricants by Laser Surface Texturing

The main objective of this paper was to investigate the effect of laser surface texturing (LST) on the friction and wear behavior of gray cast iron in lubricated conditions. The dimples with a diameter of 54 μm and depth of about 10 μm were produced with various dimple densities in the range from 5 to 35 %. Ball-on-disc friction tests were carried out for all the specimens in low and high viscous oils. The friction coefficient was reduced by about 35 % after the LST compared with the untextured specimen at a load of 5 N and speed of 5 cm/s. The textured specimen with a dimple density of 10 % possessed the lowest friction coefficient of all the dimpled specimens in both low and high viscous oils. However, the high viscous oil was found to be more effective to achieve a lower friction coefficient compared to the low viscous oil. The friction coefficient reduced by about 46 % in high viscous oil compared to the low viscous oil. Similarly, the lower wear was noticed for the specimen with a dimple density of 10 % and 5 % among all the specimens in both low and high viscous oils. The resistance to wear of the specimens was also found to be enhanced in high viscous oil compared to those in low viscous oil.

A Study on Mechanical and Tribological Properties of Hot Pressed Al2O3/ZrO2/h-BN/TiO2 Composites

Oxide ceramics such as alumina and zirconia are industrially utilized as cutting tools, a variety of bearings, biomaterials, and thermal and corrosion-resistant coatings due to their high hardness, chemical inertness, high melting point, and ability to retain mechanical strength at elevated temperatures. In this research, the effect of other ceramic additives (TiO2) and h-BN within alumina(α-Al2O3) and yttria-stabilized tetragonal (Y-TZP) composite was studied with respect to the mechanical and tribological properties. The lowest coefficient of frction of 0.45 was observed for the ZTA ceramic composite with hBN-TiO2. The highest hardness, fracture toughness and flexural strength were obtained as 15.7GPa, 5.2MPam-1/2, 712MPa, respectively.

Optical, Mechanical and Tribological Properties of Boronnitride Dispersed Silicon Nitride Ceramics

Transparent ceramics are used in new technology because of their excellent mechanical properties over glasses. Transparent ceramics are nowadays widely used in armor, laser windows, and in high temperature applications. Silicon nitride ceramics have excellent mechanical properties and if transparent silicon nitride is fabricated, it can be widely used. h-BN has a lubricating property and is ductile. Therefore, adding h-BN to silicon nitride ceramics gives a lubricating property and is also machinable. Translucent silicon nitride was fabricated by hot-press sintering (HPS) and 57% transmittance was observed in the near infrared region. A higher wt. % of h-BN in silicon nitride ceramics does not favor transparency. The optical, mechanical, and tribological properties of BN dispersed polycrystalline ceramics were affected by the density, -phase ratio, and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of , AlN, MgO, and h-BN at . The composite contained from 0.25 to 2 wt. % BN powder with sintering aids (9% AlN + 3% MgO). A maximum transmittance of 57% was achieved for the 0.25 wt. % BN doped ceramics. Fracture toughness increased and wear volume and the friction coefficient decreased with an increase in BN content. The properties such as transmittance, density, hardness, and flexural strength decreased with an increase in content of h-BN in silicon nitride ceramics.

Comparative study on the photocatalytic properties of Ag 3 PO 4 fabricated by different methods

A comparative study was carried out on the photocatalytic properties depending on Jodifferent morphologies of Ag3PO4 fabricated by different methods, i.e. as precipitated, oil bath heat treatment, hydrothermal, and microwave-assisted hydrothermal. The crystal structures of the prepared samples were analyzed by X-ray diffraction. The different morphologies of Ag3PO4 synthesized by different methods were observed from SEM micrographs. The micrographs show that the as-precipitated Ag3PO4 sample has smaller grain morphology whereas samples synthesized by other methods have distinct large-grain morphologies. Sharp-edged rhombic dodecahedron, cubic and polyhedral Ag3PO4 crystals were observed that were synthesized by microwave-assisted hydrothermal and hydrothermal methods. However, sharp-edged polyhedral Ag3PO4 crystals were not observed from the oil bath heat-treatment method. The optical properties of the different samples were measured by using UV–Vis diffuse reflectance spectroscopy. The samples fabricated by the microwave-assisted hydrothermal process showed better photocatalytic decoloring of methylene blue than those prepared by the hydrothermal and oil bath heat-treatment methods.Graphical Abstract