Decoding Upconversion-Emitting Phase in Complex Composites Through Single-Particle-Level Upconversion Imaging and Density Functional Theory Calculations.

The crystal structure and phase stability of a host lattice plays an important role in efficient upconversion phenomena. In stable hosts, lanthanides doping should not generally change the crystal structure of the host itself. But when phase of a system drastically changes after lanthanide doping resulting in multiple phases, accurate identification of upconverting phase remains a challenge. Herein, an attempt to synthesize lanthanide-doped NiMoO4 by microwave hydrothermal method produced MoO3/Yb2Mo4O15/NiMoO4 micro-nano composite upconversion phosphor. A combined approach of density functional theory (DFT) calculations and single-particle-level upconversion imaging has been employed to elucidate the phase stability of different phases and upconversion properties within the composite. Through single-particle-level imaging under 980 nm excitation, an unprecedented resolution in visualizing individual emitting and non-emitting regions within the composite has been achieved, thereby allowing to accurately assign the Yb2Mo4O15 as a sole upconversion emitting phase in the composite. Result of the DFT calculation further shows that the Yb2Mo4O15 phase is the most thermodynamically preferred over other lanthanide-doped phases in the composite. This comprehensive understanding not only advances the knowledge of upconversion emission from composite materials but also holds promise for tailoring optical properties of materials for various applications, including bioimaging, sensing, and photonics, where controlled light emission is crucial.

Ho-SiAlON Ceramics as Green Phosphors under Ultra-Violet Excitations.

In most inorganic phosphors, increasing the concentration of activators inevitably causes the concentration quenching effect, resulting in reduced emission intensity at a high level of activator doping and the conventional practice is to limit the activator concentration to avoid the quenching. In contrast, SiAlON ceramics preserve their chemical composition over a very wide range of doping of activator ions, which favors the adjustment and optimization of the luminescence properties avoiding concentration quenching. Here, we investigate the photoluminescence properties of Ho-doped SiAlON (Ho-SiAlON) ceramics phosphors prepared by the hot-press method. Ho-SiAlON ceramics show strong green visible (554 nm) as well as infrared (2046 nm) broadband downshifting emissions under 348 nm excitation. It is shown that there is no concentration quenching, even at a very high level of Ho doping. The emission intensity of the 554 nm band increased two-fold when the Ho concentration is doubled. The results show that the Ho-SiAlON ceramics can be useful for efficient green phosphors.

A sustainable composite of rice-paper/BaMoO4 nanoparticles for the photocatalytic elimination of the recalcitrant 2,6-dichlorobenzamide (BAM) pesticide in drinking water and its mechanisms of degradation.

This research reports the use of biodegradable and flexible composites for the removal of the 2,6-dichlorobenzamide (BAM) pesticide from drinking water. Rice paper (a biodegradable substrate) and Ag/BaMoO4 (MOBA) nanoparticles were employed to fabricate these composites. The SEM images showed that the MOBA nanoparticles with sizes of 300-800 nm decorated the surface of the biodegradable substrate and formed porous agglomerates, which have sizes of 1-3 µm. The MOBA powders were dispersed in drinking water polluted with BAM and were exposed to 4 h of UV-VIS irradiation, producing a maximum degradation of 82% for the BAM. Moreover, the flexible and biodegradable rice/MOBA composite produced a maximum removal percentage of 95% for the BAM. Also, we studied the effect of pH of the initial solution utilizing both powders and composites. From here, we found that a pH of 10 leads to a complete degradation of BAM after 4h, while a pH of 3 degraded only 37-47% of BAM for the same reaction time. According to the scavenger experiments, the •OH radical and the h+ were the main oxidizing agents for the BAM. Overall, the biodegradable photocatalytic composites are a reliable and a low-cost alternative to eliminate pesticides from the drinking water and can find application in water purification processes.

Current status on synthesis, properties and applications of CsPbX3(X = Cl, Br, I) perovskite quantum dots/nanocrystals.

The quantum confinement effect and interesting optical properties of cesium lead halide (CsPbX3; X = Cl, Br, I) perovskite quantum dots (QDs) and nanocrystals (NCs) have given a new horizon to lighting and photonic applications. Given the exponential rate at which scientific results on CsPbX3NCs are published in the last few years, it can be expected that the research in CsPbX3NCs will further receive increasing scientific interests in the near future and possibly lead to great commercial opportunities to realize these materials based practical applications. With the rapid progress in the single-photon emitting CsPbX3QDs and NCs, practical applications of the quantum technologies such as single-photon emitting light-emitting diode, quantum lasers, quantum computing might soon be possible. But to reach at cutting edge of stable perovskite QDs/NCs, the study of fundamental insight and theoretical aspects of crystal design is yet insufficient. Even more, it has aroused many unanswered questions related to the stability, optical and electronic properties of the CsPbX3QDs. Aim of the present review is to illustrate didactically a precise study of recent progress in the synthesis, properties and applications of CsPbX3QDs and NCs. Critical issues that currently restrict the applicability of these QDs will be identified and advanced methodologies currently in the developing queue, to overcome the roadblock, will be presented. And finally, the prospects for future directions will be provided.

Effects of Annealing Temperature on the Crystal Structure, Morphology, and Optical Properties of Peroxo-Titanate Nanotubes Prepared by Peroxo-Titanium Complex Ion.

This study addresses the effects of annealing temperatures (up to 500 °C) on the crystal structure, morphology, and optical properties of peroxo groups (-O-O-) containing titanate nanotubes (PTNTs). PTNTs, which possess a unique tubular morphology of layered-compound-like hydrogen titanate structure (approximately 10 nm in diameter), were synthesized using peroxo-titanium (Ti-O-O) complex ions as a precursor under very mild conditions-temperature of 100 °C and alkali concentration of 1.5 M-in the precursor solution. The nanotubular structure was dismantled by annealing and a nanoplate-like structure within the range of 20-50 nm in width and 100-300 nm in length was formed at 500 °C via a nanosheet structure by decreasing the specific surface area. Hydrogen titanate-based structures of the as-synthesized PTNTs transformed directly into anatase-type TiO2 at a temperature above 360 °C due to dehydration and phase transition. The final product, anatase-based titania nanoplate, was partially hydrogen titanate crystal in nature, in which hydroxyl (-OH) bonds exist in their interlayers. Therefore, the use of Ti-O-O complex ions contributes to the improved thermal stability of hydrogen titanate nanotubes. These results show a simple and environmentally friendly method that is useful for the synthesis of functional nanomaterials for applications in various fields.

Enhancement of NOx photo-oxidation by Fe- and Cu-doped blue TiO2.

The present work is focused on the removal of NOx with reduced blue TiO2 with Fe (blue Fe-TiO2)- and Cu (blue Cu-TiO2)-doped photocatalyst. TiO2 was reduced via lithium in EDA (blue TiO2). Fe and Cu ions were doped in the reduced TiO2 (blue Fe-TiO2 and blue Cu-TiO2). The material resulted in a core-shell structure of amorphous and anatase phase. XPS suggests the existence of Ti3+ species and oxygen vacancies within the structure of TiO2. Additionally, valence bond (VB)-XPS shows the generation of intermediate levels at the band edge of the doped photocatalyst. Photocurrent, electrochemical impedance spectroscopy and cyclic voltammetry confirmed the enhanced charge-separation process in doped reduced TiO2. The photocatalysts were tested for the photo-oxidation of NOx. Blue Fe-TiO2 reveals the efficiency of 70% for NO elimination and 44.74% for NO2 formation. The improved efficiency of the doped photocatalyst is related to the re-engineered structure with Ti3+ species, oxygen vacancies, and charge traps. Electron spin resonance (ESR) measurement was carried out for blue Fe-TiO2 to confirm the formation of reactive oxygen species (ROS). Furthermore, ion chromatography was used to investigate the mechanism of NOx oxidation. In conclusion, the doped blue TiO2 has a strong tendency to photo-oxidize NOx gasses.

Electronic structure, thermodynamic stability and high-temperature sensing properties of Er-α-SiAlON ceramics.

α-SiAlON ceramics have been in use as engineering ceramics in the most arduous industrial environments such as molten metal handling, cutting tools, gas turbine engines, extrusion molds, thermocouple sheaths, protective cover for high-temperature sensors, etc., owing to their outstanding mechanical, thermal and chemical stability. Taking advantage of the intrinsic properties of α-SiAlONs, we investigate, in this paper, the possibility of using the Er-doped α-SiAlON (Er-α-SiAlON) ceramic as a high-temperature sensing material via its unique near-infrared to visible upconversion property. We first use neutron diffraction and density functional theory calculations to study the electronic structure and thermodynamic stability of Er-α-SiAlON. It is found that the interstitial doping of Er stabilizes the α-SiAlON structure via chemical bonds with O-atoms with N:O ratio of 5:2 in the seven-fold coordination sites of the Er3+ ion. Temperature-dependent upconversion emissions are then studied under 980 and 793 nm excitations over a temperature range of 298-1373 K and the fluorescence intensity ratio (FIR) technique has been employed to investigate the temperature sensing behavior. Temperature-dependent Raman behavior is also investigated. We demonstrate that using Er-α-SiAlON as a sensing material, the limit of temperature measurement via the FIR technique can be pushed well beyond 1200 K.

Microwave hydrothermal synthesis and upconversion properties of BiVO4 nanoparticles.

Nanomaterials are the subject of extensive investigations due to their applications in medicine, multimodal imaging, volumetric displays, and photonics. Here, lanthanide-doped bismuth vanadate (BiVO4) upconverting nanoparticles (UCNPs) have been reported. The nanoparticles have been synthesized by a microwave hydrothermal method. As-synthesized nanoparticles are highly crystalline in the tetragonal zircon phase with particles about 200 nm in size. Under 980 nm excitation, intense multicolor visible and near-infrared upconversion emissions are observed. Moreover, broadband infrared downshifting emissions are also observed. Time-resolved emission measurements have been carried out to investigate the involved upconversion and energy transfer mechanism. The BiVO4-based UCNPs may provide a new class of nanomaterials for multifunctional applications.

Influence of SiC and TiC nanoparticles reinforcement on the microstructure, tribological, and scratch resistance behavior of electroless Ni-P coatings.

Two different ceramic carbide nanoparticles (SiC, and TiC) were separately incorporated into the Ni-P matrix via the electroless deposition method. As prepared Ni-P, Ni-P-SiC, and Ni-P-TiC coatings were subjected to heat treatment at 400 °C for 1 h. The surface morphology, microstructural transformation, Vicker's microhardness, tribological and scratch resistance properties were studied with reference to the different carbide reinforcements as well as heat treatment. Inter-nodular space, craters and kinks are created due to the branching effect of nodules in the surface of the Ni-P-SiC (TiC) composite coatings. After the heat treatment, the matrix phase transformation was not altered due to the incorporation of SiC or TiC into the Ni-P coating; however, a slight increase in residual stress was identified from the XRD analysis. In addition, the content of carbon deposition was found to be higher in the matrix of Ni-P-SiC composite coating than that in the Ni-P-TiC coating. The agglomeration of SiC particles was higher than TiC particles in the coating matrix, which was also supported by the result of Zeta potential measurement. Heat treatment improved wear and coefficient of friction in the Ni-P-SiC and Ni-P-TiC composite coatings. Compared to Ni-P-SiC coating, Ni-P-TiC coating revealed the enhanced tribological and scratch resistance performance after the heat treatment.

Visible light driven MoS2/α-NiMoO4 ultra-thin nanoneedle composite for efficient Staphylococcus aureus inactivation.

MoS2/α-NiMoO4 ultra-thin nanoneedle composite was synthesized by microwave hydrothermal process in one step. The nanocomposite revealed the complete destruction of multidrug resistant Staphylococcus aureus (S. aureus) within 150 min under visible light irradiation. According to electron spin resonance measurement and radical trapping experiment, it has been established that O2¯ acts as a major active species for bacterial inactivation in visible light. The bacterial inactivation was further proved by membrane deformities in bacterial cell membrane, DNA fragmentation, and protein destruction. TEM- elemental mapping confirms the inactivation of S. aureus by reactive oxygen species (ROS) but not the toxicity of photocatalyst. Transient photocurrent responses, electrochemical impedance spectroscopy, and cyclic voltammetry measurements reveal the efficient separation of electron-hole pairs in the composite photocatalyst. The composite photocatalyst shows greater ROS production, higher degree of DNA fragmentation and protein degradation, detrimental effects on the morphology of the bacterial cell wall, outstanding transient photocurrent responses, reduction of interfacial charge transfer resistance, superb oxidation/reduction potential, strong visible light absorption, and adequate separation of photogenerated electron-hole pairs as compared to host photocatalyst. The photocatalytic inactivation mechanism was explained. So, this promising composite photocatalyst can be applied for inactivation of multidrug resistant bacteria in biological waste water.

Visible light-Driven AgBr/AgCl@MIL-101(Fe) Composites For Removal of Organic Contaminant From Wastewater.

Microwave-solvothermal synthesized MIL-101(Fe) was successfully loaded by silver halides (AgCl and AgBr) by simple precipitation method. The XRD, FESEM mapping, XPS and DRS measurements reveal the successful fabrication of composite photocatalyst. The results suggested that silver halides altered surface charge, surface area and pore size distribution of MIL-101(Fe). The 20%AgBr@MIL-101(Fe) composite has strong tendency to remove the cationic/anionic dyes (96% of rhodamine B, 100% of malachite green and 92% of methyl orange) from wastewater after 30 min of adsorption and 90 min under visible light irradiation. The composite photocatalyst revealed the photodegradation stability up to four cycles. The formation of mesopores improves the adsorption ability of the composites for large organic molecules, while loaded silver halides might inhibit the recombination of electron-hole pairs; those were responsible for enhancing the photocatalytic degradation of organic pollutants. ESR suggested O 2 · - , · OH were responsible for dye degradation in visible light by composite photocatalysts. The photocatalytic mechanism of the composite was also explained in this work.

Morphologies controlled ZnO for inactivation of multidrug-resistant Pseudomonas aeruginosa in solar light.

The different morphology and size of the zinc oxide (ZnO) were synthesized by a co-precipitation process via variation of calcination temperature from 400 °C to 900 °C. The nanorod, flower, hexagon, pentagon, and microflambeau morphologies were obtained. The flower morphology of ZnO tends to inactivate multidrug-resistant Pseudomonas aeruginosa (P. aeruginosa) completely within 45 min under solar light irradiation better than other morphologies due to efficient separation electron-hole pairs. The prevention of charge recombination was confirmed by transient photocurrent response and electrochemical impedance spectra measurements. Electron spin resonance spectroscopy suggests that [Formula: see text] OH·, and h+ are responsible for P. aeruginosa inactivation in solar light. Furthermore, P. aeruginosa inactivation was confirmed by transmission electron microscope (TEM) images, DNA fragmentation (gel electrophoresis) and protein degradation (Bradford assay). The TEM mapping illustrates the damage of bacteria by active species but not the release of Zn2+ ions in the bacterial cell. So, this work provides a detailed investigation of morphology/size-dependent photocatalytic inactivation of a multidrug-resistant pathogen in solar light.

Bimetallic MOF-templated synthesis of alloy nanoparticle-embedded porous carbons for oxygen evolution and reduction reactions.

Pyrolysis of metal-organic frameworks (MOFs) to produce metal nanoparticles embedded inside a porous carbon matrix (M@PC) has drawn a lot of attention in recent years. Notably, Fe nanoparticles trapped in a carbon matrix (Fe@PC) have been reported to efficiently promote oxygen evolution and reduction reactions (OER/ORR). However, research on the effect of doping in Fe particles has been scarce because of the difficulty in synthesizing alloys of small size at elevated temperature. Herein, we focus on the development of bimetallic MOFs composed of Fe and a second metal M (M = Cr, Ni, Co, and Mn) made from a preassembled cluster and their sacrificial use to synthesize FeM@PC composites. After optimising the pyrolysis conditions and determining the optimal structure of an MOF template, the materials were used in the electrocatalytic OER and ORR in 0.1 M KOH aqueous solution. Results showed that Co-Fe alloy composites exhibited the best activity for the OER with a 210 mV cathodic shift to achieve 10 mA cm-2 compared to that of pure Fe@PC. On the other hand, the oxygen reduction reaction most efficiently proceeded on the Mn-Fe alloy composite, showing an 80 mV anodic shift in comparison with all other doped materials.

Upconversion luminescence properties of BaMoO4: Yb3+, Ln3+ (Ln3+ = Er3+/Tm3+, Er3+/Tm3+/Ho3+) micro-octahedrons.

Yb3+, Ln3+ (Ln3+ = Er3+/Tm3+, Er3+/Tm3+/Ho3+) doped BaMoO4 micro-octahedrons were synthesized by a hydrothermal process. The as-prepared phosphors were characterized by x-ray powder diffraction, field emission scanning electron microscopy, elemental mapping, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. The upconversion luminescence properties of the samples were investigated under 980 nm near infrared excitation. The different concentrations of Er3+, Tm3+, and Ho3+ were used for tuning the multicolor (blue, green, and red) emissions. The multicolor emissions were investigated by Commission Internationale de l'Elcairage chromaticity and decay lifetime. The photon process as well as the energy transfer mechanism between the Yb3+ to Er3+, Tm3+, and Ho3+ were described.

Understanding the multifunctionality in Cu-doped BiVO4 semiconductor photocatalyst.

A visible light-induced, Cu-doped BiVO4 photocatalyst was synthesized by a microwave hydrothermal method. The photocatalytic efficiency was investigated in the degradation of model water pollutants like Methylene Blue (dye) and ibuprofen (pharmaceuticals), as well as the inactivation of Escherichia coli (bacteria). The Cu-doped BiVO4 samples showed better efficiency than undoped BiVO4, and the 1wt.% Cu-doped BiVO4 sample showed the best efficiency. The degradation of Methylene Blue reached 95%, while the degradation of ibuprofen reached 75%, and the inactivation of E. coli reached 85% in irradiation with visible light. The appearance of additional absorption band shoulders and widening of the optical absorption in the visible range makes the prepared powder an efficient visible light-driven photocatalyst. Moreover, the formation of an in-gap energy state just above the valance band as determined by density functional theory (DFT) first principle calculation, facilitates the wider optical absorption range of the doped system. Similarly, this in-gap energy state also acts as an electron trap, which is favorable for the efficient separation and photoexcited charge carriers' transfer process. The formation of oxygen vacancies due to doping also improved the separation of the charge carrier, which promoted the trapping of electrons and inhibited electron hole recombination, thus increasing the photocatalytic activity. No decrease in the efficiency of the 1wt.% Cu-doped BiVO4 photocatalyst in the degradation of ibuprofen over three consecutive cycles revealed the stability of the photocatalyst towards photocorrosion. These findings highlight the multifunctional applications of Cu-doped BiVO4 in wastewater containing multiple pollutants.

Microwave hydrothermal synthesis and upconversion properties of Yb3+/Er3+ doped YVO4 nanoparticles.

Yb3+ and Er3+ doped YVO4 (Yb3+/Er3+:YVO4) nanoparticles with highly efficient near-infrared to visible upconversion properties have been synthesized by microwave hydrothermal process. Uniform-sized Yb3+/Er3+:YVO4 nanoparticles were synthesized within 1 h at 140 °C which is relatively faster than the conventional hydrothermal process. Under 980 nm laser excitation, strong green and less strong red emissions are observed which are attributed to 2H11/2, 4S3/2 to 4I15/2 and 4F9/2 to 4I15/2 transitions of Er3+ respectively. The emission intensity is found to depend strongly on the concentration of Yb3+. The quadratic dependence of upconversion intensity on the excitation power indicates that the upconversion process is governed by two-photon absorption process.

Fabrication of Ag-decorated BiOBr-mBiVO4 dual heterojunction composite with enhanced visible light photocatalytic performance for degradation of malachite green.

A visible light active Ag-decorated BiVO4-BiOBr dual heterojunction photocatalyst was prepared using a facile hydrothermal method, followed by the photodeposition of Ag. The photocatalytic activity of the synthesized samples was investigated by monitoring the change in malachite green (MG) concentration upon visible light irradiation. The synthesized sample was highly effective for the degradation of non-biodegradable MG. The enhanced activity observed was ascribed to the efficient separation and transfer of charge carriers across the dual heterojunction structure as verified by photoluminescence measurements. The removal of MG was primarily initiated by hydroxyl radicals and holes based on scavenger's effect. To gain insight into the degradation mechanism, both high performance liquid chromatography and high resolution-quantitative time of flight, electrospray ionization mass spectrometry measurements during the degradation process were carried out. The degradation primarily followed the hydroxylation and N-demethylation process. A possible reaction pathway is proposed on the basis of all the information obtained under various experimental conditions.

Visible-light-induced Ag/BiVO4 semiconductor with enhanced photocatalytic and antibacterial performance.

An Ag-loaded BiVO4 visible-light-driven photocatalyst was synthesized by the microwave hydrothermal method followed by photodeposition. The photocatalytic performance of the synthesized samples was evaluated on a mixed dye (methylene blue and rhodamine B), as well as bisphenol A in aqueous solution. Similarly, the disinfection activities of synthesized samples towards the Gram-negative Escherichia coli (E. coli) in a model cell were investigated under irradiation with visible light (λ ≥ 420 nm). The synthesized samples have monoclinic scheelite structure. Photocatalytic results showed that all Ag-loaded BiVO4 samples exhibited greater degradation and a higher mineralization rate than the pure BiVO4, probably due to the presence of surface plasmon absorption that arises due to the loading of Ag on the BiVO4 surface. The optimum Ag loading of 5 wt% has the highest photocatalytic performance and greatest stability with pseudo-first-order rate constants of 0.031 min-1 and 0.023 min-1 for the degradation of methylene blue and rhodamine B respectively in a mixture with an equal volume and concentration of each dye. The photocatalytic degradation of bisphenol A reaches 76.2% with 5 wt% Ag-doped BiVO4 within 180 min irradiation time. Similarly, the Ag-loaded BiVO4 could completely inactivate E. coli cells within 30 min under visible light irradiation. The disruption of the cell membrane as well as degradation of protein and DNA exhibited constituted evidence for antibacterial activity towards E. coli. Moreover, the bactericidal mechanisms involved in the photocatalytic disinfection process were systematically investigated.

Insight Into Malachite Green Degradation, Mechanism and Pathways by Morphology-Tuned α-NiMoO4 Photocatalyst.

The microwave hydrothermal process was used for the synthesis of various morphologies of α-NiMoO4 by simply adjusting the pH during experimental conditions. The effect of morphology/size on the photocatalytic performances for degradation of malachite green (MG) has been investigated under UV-Vis/visible light irradiation. Nanorod morphology has strong tendency to degrade (88.18%) the MG as compared to spherical quantum-sized (57.65%) and layered square microsheet (37.98%) under UV-Vis irradiation in 180 min. The active species trapping experiment revealed that active species (OH• , O2•- and h+ ) play a crucial role for MG degradation. The high BET surface area, greater amount of oxygen defect and efficient separation of electron-hole pair are responsible for MG degradation. About seventeen types of organic fragments of MG were confirmed by high resolution-quadruple time of flight electrospray ionization mass spectroscopy (HR-QTOF ESI/MS) technique on the basis of retention time and molecular masses. Degradation mechanism and pathways were proposed that follow the demethylation, nitration, decarboxylation, hydrolysis, decarboxylation and oxidation reaction. The reduction of total organic carbon revealed the mineralization of MG during photocatalytic degradation process. Therefore, this article represents the investigation of MG degradation by various morphology of α-NiMoO4 and detailed degradation mechanism and pathways.

Graphene Coating via Chemical Vapor Deposition for Improving Friction and Wear of Gray Cast Iron at Interfaces.

This study reports the influence of CVD-graphene on the tribological performance of gray cast iron (GCI) from the internal combustion engine (ICE) cylinder liners by performing a ball-on-disk friction tests. The graphene-coated specimen exhibited a significant reduction (∼53%) of friction as compared to that of the uncoated specimen, whereas wear resistance increased by 2- and 5-fold regarding the wear of specimen and ball, respectively. Extremely low shear strength and highly lubricating nature of graphene contribute to the formation of a lubricative film between the sliding surfaces and decreases the interaction between surfaces in the dry environment. Under the applied load, a uniform film of iron oxides such as Fe2O3, Fe3O4, and FeOOH is found to be formed between the surfaces. It is proposed that the graphene encapsulation with the metal debris and oxides formed between the specimens increases the lubricity and decreases the shear force. The transformation of graphene/graphite into nanocrystalline graphites across the contact interfaces following the amorphization trajectory further increases the lubricity of the film that ultimately reduces friction and wear of the material.