Enhancing Electrochemical Reactivity with Magnetic Fields: Unraveling the Role of Magneto-Electrochemistry.

Electrocatalysis performs a vital role in numerous energy transformation and repository mechanics, including power cells, Electric field-assisted catalysis, and batteries. It is crucial to investigate new methods to improve electrocatalytic performance if effective and long-lasting power systems are developed. The modulation of catalytic activity and selectivity by external magnetic fields over electrochemical processes has received a lot of interest lately. How the use of various magnetic fields in electrocatalysis has great promise for building effective and selective catalysts, opening the door for the advancement of sophisticated energy conversion is discussed. Furthermore, the challenges and possibilities of incorporating magnetic fields into electrocatalytic systems and suggestions for future research areas are discussed.

Carbon Dots for Multiuse Platform: Intracellular pH Sensing and Complementary Intensified T1-T2 Dual Imaging Contrast Nanoprobes.

Measurement of pH in living cells is a great and decisive factor for providing an early and accurate diagnosis factor. Along with this, the multimodal transverse and longitudinal relaxivity enhancement potentiality over single modality within a single platform in the magnetic resonance imaging (MRI) field is a very challenging issue for diagnostic purposes in the biomedical field of application. Therefore, this work aims to design a versatile platform by fabricating a novel nanoprobe through holmium- and manganese-ion doping in carbon quantum dots (Ho-Mn-CQDs), which can show nearly neutral intracellular pH sensing and MRI imaging at the same time. These manufactured Ho-Mn-CQDs acted as excellent pH sensors in the near-neutral range (4.01-8.01) with the linearity between 6.01 and 8.01, which could be useful for the intracellular pH-sensing capability. An innumerable number of carboxyl and amino groups are present on the surface of the prepared nanoprobe, making it an excellent candidate for pH sensing through fluorescence intensity quenching phenomena. Cellular uptake and cell viability experiments were also executed to affirm the intracellular accepting ability of Ho-Mn-CQDs. Furthermore, with this pH-sensing quality, these Ho-Mn-CQDs are also capable of acting as T1-T2 dual modal imaging contrast agents in comparison with pristine Ho-doped and Mn-doped CQDs. The Ho-Mn-CQDs showed an increment of r1 and r2 relaxivity values simultaneously compared with only the negative contrast agent, holmium in holmium-doped CQDs, and the positive contrast agent, manganese in manganese-doped CQDs. The above-mentioned observations elucidate that its tiny size, excitation dependence of fluorescence behavior, low cytotoxicity, and dual modal contrast imaging capability make it an ideal candidate for pH monitoring in the near-neutral range and also as a dual modal MRI imaging contrast enhancement nanoprobe at the same time.

1D/2D interface engineering of a CoPc-C3N4 heterostructure for boosting the nitrogen reduction reaction to NH3.

Herein, we demonstrate the construction of a 1D/2D heterostructure of cobalt phthalocyanine (CoPc)-carbon nitride (C3N4) for electrochemical N2 reduction to NH3. Improved performance originates from the higher exposure of active surface sites. The electrochemical NRR performance showed an NH3 formation rate of 423.8 µg h-1 mgcat-1, a high faradaic efficiency (FE) of 33%, and stability for 20 h. This study provides a new strategy for designing a highly efficient 1D/2D electrocatalytic system for ammonia synthesis.

Selective Electrocatalytic Oxidation of Nitrogen to Nitric Acid Using Manganese Phthalocyanine.

Ammonia is produced through the energy-intensive Haber-Bosch process, which undergoes catalytic oxidation for the production of commercial nitric acid by the senescent Ostwald process. The two energy-intensive industrial processes demand for process sustainability. Hence, single-step electrocatalysis offers a promising approach toward a more environmentally friendly solution. Herein, we report a 10-electron pathway associated one-step electrochemical dinitrogen oxidation reaction (N2OR) to nitric acid by manganese phthalocyanine (MnPc) hollow nano-structures under ambient conditions. The catalyst delivers a nitric acid yield of 513.2 µmol h-1 gcat-1 with 33.9% Faradaic efficiency @ 2.1 V versus reversible hydrogen electrode. The excellent N2OR performances are achieved due to the specific-selectivity, presence of greater number of exposed active sites, recyclability, and long period stability. The extended X-ray absorption fine structure confirms that Mn atoms are coordinated to the pyrrolic and pyridinic nitrogen via Mn-N4 coordination. Density functional theory-based theoretical calculations confirm that the Mn-N4 site of MnPc is the main active center for N2OR, which suppresses the oxygen evolution reaction. This work provides a new arena about the successful example of one step nitric acid production utilizing a Mn-N4 active site-based metal phthalocyanine electrocatalyst by dinitrogen oxidation for the development of a carbon-neutral sustainable society.

Scalable Production of Cobalt Phthalocyanine Nanotubes: Efficient and Robust Hollow Electrocatalyst for Ammonia Synthesis at Room Temperature.

Electrocatalytic ammonia (NH3) synthesis through the nitrogen reduction reaction (NRR) under ambient conditions presents a promising alternative to the famous century-old Haber-Bosch process. Designing and developing a high-performance electrocatalyst is a compelling necessity for electrochemical NRR. Specific transition metal based nanostructured catalysts are potential candidates for this purpose owing to their attributes such as higher actives sites, specificity as well as selectivity and electron transfer, etc. However, due to the lack of a well-organized morphology, lower activity, selectivity, and stability of the electrocatalysts make them ineffective at producing a high NH3 yield rate and Faradaic efficiency (FE) for further development. In this work, stable ß-cobalt phthalocyanine (CoPc) nanotubes (NTs) have been synthesized by a scalable solvothermal method for electrochemical NRR. The chemically synthesized CoPc NTs show excellent electrochemical NRR due to high specific area, greater number of exposed active sites, and specific selectivity of the catalyst. As a result, CoPc NTs produced a higher NH3 yield of 107.9 µg h-1 mg-1cat and FE of 27.7% in 0.1 M HCl at -0.3 V vs RHE. The density functional theory calculations confirm that the Co center in CoPc is the main active site responsible for electrochemical NRR. This work demonstrates the development of hollow nanostructured electrocatalysts in large scale for N2 fixation to NH3.

Effect of annealing on the defect-mediated blue phosphorescence in ZnO nanocrystals.

Recently, UV/NUV excitable RGB phosphors with precisely tunable PL emission properties have been in high demand for their suitability in the fabrication of white LEDs. In this paper, we report to have tuned the PL intensity, shade, and color temperature of the defect-mediated blue phosphorescence of ZnO nanopowders by systematic annealing at different temperatures. The ZnO nanopowder was prepared by a facile and cost-effective aqueous solution-precipitation method. The as-synthesized nanopowder was annealed at different temperatures ranging from 150 °C to 850 °C and all these samples were characterized by XRD, FESEM, EDX, BET, Raman spectroscopy, and UV-Vis spectroscopy to have insight into their microstructural, compositional, and band-structure details. Optical studies of the samples were conducted by PL and τ-PL spectroscopy. Color coordinates of the samples were obtained from the CIE plots derived from the PL spectra. The CIE coordinates were further used to calculate the CCT values of the samples. τ-PL spectroscopy was carried out to measure the life-time of the photogenerated electrons. PL studies of the samples revealed that the blue emissions have red, yellow, and blue components originating from crystalline point defects, viz. zinc interstitial (Zni), and oxygen interstitial (Oi). Annealing at different temperatures triggered changes in the defect concentrations leading to the corresponding changes in the intensity, shade, and color temperature of the blue phosphorescence.

Blue Emitting BaAl2O4:Ce3+ Nanophosphors with High Color Purity and Brightness for White LEDs.

In this work, strongly blue emitting Ce3+-activated BaAl2O4 nanophosphors were successfully synthesized by a sol-gel technique. The crystal structure, morphology, and microstructure of the nanophosphors have been studied by X-ray powder diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. The photoluminescence spectra show the impact of concentration variation of Ce3+ on the photoluminescence emission of the phosphor. These nanophosphors display intense blue emission peaking at 422 nm generated by the Ce3+ 5d → 4f transition under 350 nm excitation. Our results reveal that this nanophosphor has the capability to take part in the emergent domain of solid-state lighting and field-emission display devices.

Efficient Fluoride Removal and Dye Degradation of Contaminated Water Using Fe/Al/Ti Oxide Nanocomposite.

The trimetallic Fe/Al/Ti (1:1:1) nanocomposite (FAT), synthesized by an adaptable tuned chemical route, offers a new approach for water treatment, for example, the de-fluoridation and photodegradation soluble dye methylene blue (MB) at pH 7. FAT acted as a good fluoride scavenger in the presence of other co-ions and within a widespread pH range (pH 2-11). The photodegradation efficiencies were >90% for different concentrations of MB solutions. The characterization of FAT includes thermogravimetric analysis, X-ray diffraction, Fourier transform-infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and ζ-potential analysis. Furthermore, the regeneration efficiencies of both the water treatments were checked, where the removal efficiency was not hampered significantly even after five batches. Spectroscopic techniques were adopted to perform the kinetic studies and to propose the probable mechanistic paths.

White light emitting lanthanide based carbon quantum dots as toxic Cr (VI) and pH sensor.

Although, great attention is paid to synthesize fluorescent carbon quantum dots (CQDs) for versatile applications, the field remains still attractive to achieve white light using these nano materials. In the present work, CQDs are synthesized from citric acid and lanthanide ions viz. Europium (Eu) and Terbium (Tb) are doped in CQD moiety to explore superior optical response for multifunctional applications. By proper tuning of excitation wavelength, perfect white light with Commission Internationale de l'Elcairage (CIE) index (0.345, 0.344) is obtained using these Europium Terbium co-doped CQDs (Eu-Tb-CQD). The observed photoluminescence of white light emitting lanthanide based CQD is pH dependent and will be used as a visual pH sensor. These luminescent Eu and Tb co-doped CQDs are also very useful to detect toxic Cr (VI) with excellent selectivity and sensitivity as compared to pure CQDs. It shows high quenching efficiency (∼95%) in presence of only 160 µM Cr(VI). The selectivity and lower detection limit are also obtained as ∼80% and 0.175 µM respectively.

Multitasking behaviour of a small organic compound: solid state bright white-light emission, mechanochromism and ratiometric sensing of Al(iii) and pyrophosphate.

The solid state bright white light emission and mechanochromic behavior of 1-(1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-2-ol, 1H, are described. Further, 1H can be used as a highly sensitive ratiometric luminescence sensor for Al3+ and pyrophosphate in solution.

Postsynthesis Spontaneous Coalescence of Mixed-Halide Perovskite Nanocubes into Phase-Stable Single-Crystalline Uniform Luminescent Nanowires.

All inorganic mixed-halide perovskite, CsPb(Br xI1- x)3 (0 ≤ x ≤ 1), nanocrystals possess tunable photoluminescence with high quantum yield in the visible window. However, the photoluminescence degrades rapidly with postsynthetic aging due to the spontaneous ion separation and phase instability. Here we show that the postsynthetic aging of CsPb(Br xI1- x)3 nanocubes spontaneously forms highly uniform single-crystalline nanowires with a diameter of 9 ± 0.5 nm and length of up to several micrometers. The nanowires show bright photoluminescence with an absolute photoluminescence quantum yield of 41%. Rietveld refinement identifies the stable orthorhombic phase of the nanowires, implying a phase transition from the cubic crystallographic phase of the nanocubes during the morphology evolution. Transient absorption spectroscopy reveals a faster excited-state decay dynamic with a large exciton delocalization length in 1D nanowires. Our findings elucidate the insights into the postsynthesis morphology evolution of mixed-halide perovskite nanocrystals leading to luminescent nanowires with excellent crystal phase stability for potential optoelectronic applications.

Enhanced Photoluminescence Properties of Low-Dimensional Eu3+-Activated Y4Al2O9 Phosphor Compared to Bulk for Solid-State Lighting Applications and Latent Fingerprint Detection-Based Forensic Applications.

In recent years, nanoscale phosphors have become vital in optoelectronic applications and to understand the improved performance of nanophosphors over bulk material, detailed investigation is essential. Herein, trivalent europium-activated Y4Al2O9 phosphors were developed by solid-state reaction and solvothermal reaction methods and their performance as a function of their dimension was studied for various applications. Under 394 nm optical excitation, the photoluminescence (PL) emission, excited state lifetime of the nanophosphor, exhibits greater performance than its bulk counterpart. The homogeneous spherical structure of the nanophosphors as compared with solid lumps of bulk phosphors is the basis for almost 40% of the enhancement in nanophosphors' intense red emission compared to the bulk. Moreover, the thermal stability of the nanophosphor is much better than the bulk phosphor, which clearly indicates a key advantage of nanophosphor. The superior performance of Eu3+-doped Y4Al2O9 nanophosphors over their bulk counterparts has been demonstrated for industrial phosphor-converted light-emitting diodes and visualization of latent fingerprint.

Crystal phase induced upconversion enhancement in Er3+/Yb3+ doped SrTiO3 ceramic and its temperature sensing studies.

Through doping of Er3+/Yb3+ ions the SrTiO3 perovskite ceramic is turned into an optically active material keeping its ferroelectric property intact. A huge enhancement of around 20 times in upconversion (UC) emission intensity is observed due to the transformation of cubic crystal structure to tetragonal phase. The intensity ratio of green to red band is found too high to neglect the contribution from the red emission band, which is not observed normally in such type of relatively moderate phonon frequency materials containing Yb3+/Er3+ ions. The change in emission intensity is reflected in the decay time measurement. Optical temperature sensing behavior based on FIR technique also has been discussed for Er3+/Yb3+ doped SrTiO3 ceramic.

Cost-Effective, Wireless, Portable Device for Estimation of Hexavalent Chromium, Fluoride, and Iron in Drinking Water.

The quality of drinking water often remains unknown to people because of the inadequacy of cost-effective testing systems that can be used in the field. Major portable instruments for water-quality analysis include ion-selective electrodes (ISE) or colorimeters. These are low-cost devices, but in the case of multiple-analyte detection, such as that of hexavalent chromium (Cr), fluoride (F-), and iron (Fe), with a single instrument, no portable systems are available, to the authors' knowledge. In this paper, we demonstrate the use of a low-cost (approximate price of INR 1500 or US$20), portable colorimetric system that can be operated with Android smartphones wirelessly to estimate the contamination levels of Cr(VI), F-, and Fe in drinking water. This system also generates absorption spectra by recording the absorbance of the analyte using a light-dependent-resistor (LDR) sensor. An Android-application software named Spectruino was developed to calculate the concentrations of the analytes. We strongly believe that this cost-effective, portable system will be very useful in improving human health by ensuring drinking-water quality throughout India.

Resonant energy transfer in a van der Waals stacked MoS2 - functionalized graphene quantum dot composite with ab initio validation.

Graphene-based van der Waals (vdW) heterostructures can facilitate exciting charge transfer dynamics in between structural layers with the emission of excitonic quasi-particles. However, the chemical formation of such heterostructures has been elusive thus far. In this work, a simple chemical approach is described to form such van der Waals (vdW) heterostructures using few layer MoS2 sheet embedded quantum dots (QDs) and amine-functionalized graphene quantum dots (GQDs) to probe the energy transfer mechanism for tunable photoluminescence (PL). Our findings reveal an interesting non-radiative Förster-type energy transfer with the quenching of functional GQD PL intensity after GQD/MoS2 composite formation, which validates the existing charge transfer dynamics analogous to 0D and 2D systems. The non-radiative type of energy transfer characteristic from GQD into the MoS2 layer through vdW interactions has been confirmed by photoluminescence, time decay analyses and ab initio calculations with the shifting of the Fermi level in the density of states towards the conduction band in the stacked configuration. These results are encouraging for the fundamental exploration of optical properties in other chemically prepared QD/2D based heterostructures to understand the charge transfer mechanism and fingerprint luminescence quenching for future optoelectronic device and optical sensing applications.

White light emitting MgAl2O4:Dy3+,Eu3+ nanophosphor for multifunctional applications.

Feeble white emission with a low Colour Rendering Index (CRI) has become the principal gridlock for the extensive commercialization of phosphor converted white LEDs (pc-WLEDs). Fusion of red, green and blue emitting rare-earth (RE) ions in a suitable host can overcome these drawbacks but the energy migration between multiple RE ions at single excitation wavelength defines the key standpoint in designing such white light emitting phosphors. Apart from the abovementioned obstacles, recently traditional optical temperature sensors based on RE ions have faced difficulties due to their low relative sensitivity and large detection error. Keeping these points in mind, in this work, a series of MgAl2O4:Dy3+,Eu3+ nanophosphors are synthesized among which 2% Dy3+,0.2% Eu3+ doped MgAl2O4 nanophosphors demonstrate strong white emission with CIE co-ordinates of (0.31, 0.33), and high quantum yield (∼67%), which could be directly utilized for pc-WLED based solid state lighting devices. Detailed investigation of PL properties reveals that Eu3+ ions can be well sensitized by Dy3+ under near-ultraviolet excitation of 351 nm. Dexter's theory & Reisfeld's approximation are employed for an in-depth analysis of the inter-RE energy transfer (ET) mechanism, which signposts that the dipole-quadrupole interaction phenomenon is responsible for the ET process from Dy3+ to Eu3+. Additionally, the validated ET plays a pivotal role in demonstrating the self-referencing ratiometric temperature sensor behaviour supported by a distinct high temperature thermal quenching trend between Dy3+ and Eu3+ ions. Hence the obtained nanophosphors are highly promising for utilizing in WLED based solid state lighting and self-referencing ratiometric temperature sensor applications.

Dual doped biocompatible multicolor luminescent carbon dots for bio labeling, UV-active marker and fluorescent polymer composite.

We report on metal-non-metal doped carbon dots with very high photoluminescent properties in solution. Magnesium doping to tamarind extract associated with nitrogen-doping is for the first time reported here which also produce very high quantum yield. Our aim is to develop such dual doped carbon dots which can also serve living cell imaging with easy permeation towards cells and show non-cytotoxic attributes. More importantly, the chemical signatures of the carbon dots unveiled in this work can support their easy solubilization into water; even in sub-ambient temperature. The cytotoxicity assay proves the almost negligible cytotoxic effect against human cell lines. Moreover, the use of carbon dots in UV-active marker and polymer composites are also performed which gave clear distinguishable features of fluorescent nanoparticles. Hitherto, the carbon dots can be commercially prepared without adopting any rigorous methods and also can be used as non-photo-bleachable biomarkers of living cells.

Neutralizing the Charge Imbalance Problem in Eu3+-Activated BaAl2O4 Nanophosphors: Theoretical Insights and Experimental Validation Considering K+ Codoping.

In recent years, rare-earth-doped nanophosphors have attracted great attention in the field of luminescent materials for advanced solid-state lighting and high-resolution display applications. However, the low efficiency of concurrent red phosphors creates a major bottleneck for easy commercialization of these devices. In this work, intense red-light-emitting K+-codoped BaAl2O4:Eu3+ nanophosphors having an average crystallite size of 54 nm were synthesized via a modified sol-gel method. The derived nanophosphors exhibit strong red emission produced by the 5D0 → 7F J (J = 0, 1, 2, 3, 4) transitions of Eu3+ upon UV and low-voltage electron beam excitation. Comparative photoluminescence (PL) analysis is executed for Eu3+-activated and K+-coactivated BaAl2O4:Eu3+ nanophosphors, demonstrating remarkable enhancement in PL intensity as well as thermal stability due to K+ codoping. The origin of this PL enhancement is also analyzed from first-principles calculations using density functional theory. Achievement of charge compensation with the addition of a K+ coactivator plays an important role in increasing the radiative lifetime and color purity of the codoped nanophosphors. Obtained results substantially approve the promising prospects of this nanophosphor in the promptly growing field of solid-state lighting and field emission display devices.

Nickel-Doped Silver Sulfide: An Efficient Air-Stable Electrocatalyst for Hydrogen Evolution from Neutral Water.

A low-cost, platinum-free electrocatalyst for hydrogen (H2) generation via the water splitting reaction holds great promise to meet the demand of clean and sustainable energy sources. Recent studies are mainly concerned with semiconducting materials like sulfides, selenides, and phosphides of different transition metals as electrocatalysts. Doping of the transition metals within the host matrix is a good strategy to improve the electrocatalytic activity of the host material. However, this activity largely depends on the nature of the dopant metal and its host matrix as well. To exploit this idea, here, in the present work, we have synthesized semiconducting Ag2S nanoparticles and successfully doped them with different transition metals like Mn, Fe, Co, and Ni to study their electrocatalytic activity for the hydrogen evolution reaction from neutral water (pH = 7). Among the systems doped with these transition metals, the Ni-doped Ag2S (Ni-Ag2S) system shows a very low overpotential (50 mV) with high catalytic current in neutral water. The trend in electrocatalytic activity of different transition metals has also been explained. The Ni-Ag2S system also shows very good stability in ambient atmosphere over a long period of time and suffers no catalytic degradation in the presence of oxygen. Structural characterizations are carried out using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy to establish the phase purity and morphology of the materials.

Amorphous Carbon Nanotubes-Nickel Oxide Nanoflower Hybrids: A Low Cost Energy Storage Material.

Amorphous carbon nanotubes (a-CNTs) have been synthesized by a simple low-temperature process and have been grafted with chemically synthesized nickel oxide microflowers with different concentrations. The phase and morphology of the as-prepared pure and hybrid samples were characterized by X-ray diffraction and field emission scanning and transmission electron microscopes. Thermal properties of the samples were estimated by using thermal gravimetric and differential thermal analysis. The optical properties of the sample were characterized by UV-vis spectroscopic, Raman spectroscopic, and Fourier-transformed infrared spectroscopic analysis. The electrochemical performance of all hybrid samples has been done in detail for different scan rates as well as from charge-discharge analysis. It has been seen that because of the nickel oxide grafting, the electrochemical performance of pure a-CNTs gets enhanced significantly. The value of the specific capacitance of the hybrid comes out to be around 120 F/g for the best sample, which is almost 12 times higher compared to that of the pure a-CNTs. The result has been explained in terms of change in effective surface area as well as change in conductivity of the hybrid samples.