Tiju Thomas

Solar energy harnessing and conversion has attracted considerable research interest. Photo(electro)catalysis based approaches offer one of the methods for moving forward. In recent times, cobalt-based nitrides, with their excellent catalytic properties and unique electronic structure, have attracted attention in the field of solar energy conversion. Here, we mainly focus on photo(electro)catalytic solar energy conversion over cobalt-based nitride catalysts. The classification of cobalt-based nitrides, including single monometallic cobalt-based nitrides, transition metal doped cobalt-based nitrides and bimetal cobalt-based nitrides, and their current mainstream synthesis strategies are discussed. In addition, the latest advances of cobalt-based nitrides with various functional roles in photo(electro)catalytic solar energy conversion are discussed. Finally, a summary is given of the challenges and opportunities in cobalt-based nitride photoelectrocatalysts.

The effects of gadolinium (Gd) on lead free sodium bismuth titanate (Na0.5Bi0.5TiO3, NBT) ceramics are investigated. X-ray diffraction (XRD) studies indicate that perovskite phase (rhombohedral, R3c) is formed for all Gd doped NBT (Gdx:NBT) compositions (x = 0, 0.02, 0.04, 0.06, 0.08). XRD peak shifts to the higher angles for all compositions except for x = 0.08. Amphoteric nature of Gd in NBT sites are observed i.e., it occupies Bi-site up to x = 0.06 and then distributes to Ti-site. Octahedral distortion (c/a) increases in the range 0.02 ≤ x ≤ 0.06 and then decreases. Raman spectra suggest that the introduction of Gd+3 ion induces structural changes without disturbing the long range order. The material can be readily excited using UV (360 nm) and shows emission peaks at ~592 nm and 687 nm. Optical property evaluation indicates that the lowest band gap (Eg = 2.78 eV) is observed at x = 0.08. When x > 0.04, the photoluminescence (PL) intensity decreases indicating the onset of concentration quenching. The critical energy distance (found to be 14 Å) and Dexter's theory based analysis indicate that concentration quenching is attributable to multipole-multipole (specifically dipole-dipole) interactions in the system. Commission International de Eclairage (CIE) chromatic color coordinates are reported for all doped systems; the observed patterns mirror PL analysis results. For instance, PL intensity shrinks beyond 4 at%; this corresponds to a regression in the CIE trajectory with respect to concentration.

Arsenic (As) toxicity is a significant threat to global public health. Moreover, the lacks of social awareness and understanding of the impact of As in affected communities are also of concern. Therefore, subppm level detection of As in environmental waters and associated public awareness are crucial for remediation programs. We developed a sustainable As sensing methodology by merging the fundamental concepts of As cytotoxicity with an alternative approach for selectivity. A cellular platform was prepared on an electrospun scaffold using As-sensitive keratinocyte cells. Arsenic-induced reactive oxygen species (ROS) were quantified using a fluorimetric probe, 2′,7′-dichlorofluorescin diacetate, commonly used to detect oxidative stress within cells. Experiments were conducted with a mixture of arsenite and arsenate, the predominant forms of As present in natural conditions, in a 1:1 ratio. We also quantified unknown As concentrations in real water samples. The selectivity to As was achieved by exposing the contaminated water composed of several ions to an As adsorbing material, namely, confined metastable 2-line ferrihydrite (CM2LF). An adsorption-desorption protocol enabled As extraction in field conditions. The ROS resulting from cells' responses to the As extract were used as the signature of As concentration. The sensor could precisely quantify even 5 ppb of As in tap water, and the theoretical limit of detection (LOD) was 2.7 ppb. A sustainable device using the cellular platform is proposed for As detection in field conditions that can also be used for social awareness, demonstrating the impact of As on human biology in affected regions.

Hydrogen peroxide is a widely used industrial oxidant, the large-scale production of which continues to be done by an indirect process. Direct electrosynthesis of hydrogen peroxide from aerial oxygen and water is a sustainable alternative, but this remains challenging because hydrogen peroxide is highly reactive and robust catalysts are vital. Here, we report direct and continuous electrosynthesis of hydrogen peroxide under alkaline conditions using a nitrogen-doped-carbon-supported nickel catalyst. Both experiment and theoretical calculations confirm that the existence of nickel particles suppresses the further reduction of hydrogen peroxide on Ni-N-C matrix. In air-saturated 0.1 M potassium hydroxide, the energy-efficient non-precious metal electrocatalyst exhibits a consistent Faraday efficiency over 95% at a steady rate of hydrogen peroxide production (15.1 mmol min−1 gcat−1) for 100 h. This sustainable, efficient, and safe process is an important step toward continuous production of hydrogen peroxide.

The authors regret that there was an error in the Conclusions section of their article. The sentence ‘Hydrogen is generated at as high rate as 720 mL/min or 32 mmol/min for 0.5 mg of Al salt at room temperature.’ should be: “Hydrogen is generated at as high rate as 720 mL/min or 32 mmol/min for 0.5 g of Al salt at room temperature.” The authors would like to apologise for any inconvenience caused.

Reaction of Al metal with water is a well-known technique for large scale production of hydrogen. However, this method suffers from kinetic limitations due to formation of a passivation layer on Al, preventing optimal operations. Using high resolution Scanning Kelvin Probe Force Microscopy (SKPFM), we show the origin of formation of ‘nano-galvanic couple’ on in situ formed nano-aluminum amalgam surfaces in a water splitting system; passivation based limitations are completely bypassed in this approach. Furthermore, they offer an opportunity to beneficiate and recover mercury in contaminated water. The nano-galvanic corrosion due to substantial lateral variation in surface contact potential is responsible for the observed high throughput of hydrogen production (720 mL/min per 0.5 g Al salt). It may be noted that this process fares better than in situ prepared nano-Al based hydrogen production, wherein 600 mL/min of hydrogen is obtained for 0.5 g Al salt. Investigations using Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) provide evidence for passivation-bypassed hydrolysis and favourable kinetics for in situ derived nano-AlHg hydrolytic agents (when compared to nano-Al). This study, to the best of our knowledge, reports the first direct proof of nano-galvanic couple formation on in-situ prepared nanoaluminum amalgam surface; paving a direct way to overcome the long standing passivation problem in Al hydrolysis. It is found that the hydrogen production rate and standard deviation (SD) of the contact potential of nanoaluminum amalgam are directly related to the rate of addition of the reducing agent, offering an opportunity for kinetic control for the in situ hydrolytic process.

The reaction of β-hydroxyethylation is essential to the current practice of organic chemistry. Here, we proposed a new and green route to synthesize 2-hydroxyethyl n-alkyl sulfide with n-alkyl mercaptan and ethylene carbonate (EC) in the presence of alkali carbonates as catalysts and revealed the mechanism by experiments and theoretical calculations. The reaction reported proceeds rapidly with high yields when it is performed at 120 °C and the catalytic loading is ∼1 mol%. This protocol is applicable to other mercaptans to synthesize the corresponding β-hydroxyethyl sulfide. Density functional theory-based calculations show the energy profile for the reaction pathway. The rate-determining step is the ring-opening of EC. A negatively charged O atom of alkali carbonates approaches the S atom of -SH under the influence of hydrogen bonds. An activated S atom that carries more negative charge serves as a nucleophilic reagent and assists in the ring-opening of EC by reducing the Mayer bond orders of the C1-O1 bond in EC. Alkali cations also contribute to the C1-O1 bond cleavage. The energy barrier for the ring-opening of EC decreases with the decrease of electronegativity of alkali cations. Subsequent transference of a H atom leads to the formation of β-hydroxyethyl sulfide, the dissociation of CO2 and the reduction of K2CO3

Visible-light-driven photo-fenton-like catalytic activity and photoelectrochemical (PEC) performance of nitrogen-doped brownmillerite KBiFe2O5 (KBFO) are investigated. The effective optical bandgap of KBFO reduces from 1.67 to 1.60 eV post N-doping, enabling both enhancement of visible light absorption and photoactivity. The photo-fenton activity of KBFO and N-doped KBFO samples were analysed by degrading effluents like Methylene Blue (MB), Bisphenol-A (BPA) and antibiotics such as Norfloxacin (NOX) and Doxycycline (DOX). 20 mmol of Nitrogen-doped KBFO (20N-KBFO) exhibits enhanced catalytic activity while degrading MB. 20N-KBFO sample is further tested for degradation of Bisphenol-A and antibiotics in the presence of H2O2 and chelating agent L-cysteine. Under optimum conditions, MB, BPA, and NOX, and DOX are degraded by 99.5% (0.042 min-1), 83% (0.016 min-1), 72% (0.011 min-1) and 95% (0.026 min-1) of its initial concentration respectively. Photocurrent density of 20N-KBFO improves to 8.83 mA/cm2 from 4.31 mA/cm2 for pure KBFO. Photocatalytic and photoelectrochemical (PEC) properties of N-doped KBFO make it a promising candidate for energy and environmental applications.

The development of full-color/white carbon-dot-based light-emitting diodes (LEDs) has been achieved, which show promising applications in full-color and flexible displays, backlights, and novel lighting sources. The gram-level synthesis of these full-color carbon dots (CDs) from citric acid by controlling the temperature has been achieved. By increasing the temperature from 120 to 180 °C, two, four, and six light-emitting CDs can be obtained, for which the emission wavelength shifts from 440 to 585 nm. This result reveals that temperature has a huge impact on the evolution of surface states, that is, increasing the temperature brings about enhanced surface functionalization and passivation, resulting in a red shift of the emission wavelength and enhancement of quantum yield. Then, full-color CDs/polymer composite phosphors are fabricated for efficient phosphor-based LED devices with quench-resistant solid-state fluorescence. By regulating the proportion of various CDs/polymer phosphors, white LEDs are realized with Commission Internationale de L'Eclairage coordinates of (0.32, 0.33) and a color rendering index of 82.7. The as-prepared CD-based full/white color LEDs can prove to be promising candidates for alternative light sources.

Conversion of Cr(VI) to Cr(III) in mitigating pollution of water bodies is of significant importance to public health due to the fact that Cr(VI) is known to be a potent carcinogen, while Cr(III) is relatively low in toxicity. Photocatalytic approaches are considered as important means to achieve this reduction. Here, TiO2/SnS2 core-shell nanostructures have been produced using a single-step hydrothermal method and its photocatalytic activity is tested for the reduction of aqueous Cr(VI). The structural and optical properties of the as-synthesized products are characterized by XRD, HRTEM, Raman, FTIR, XPS and DRS techniques. The present work reveals that by calcining the core-shell nanoparticles in Ar atmosphere a defective Ti3O5 phase is formed as the core with low band gap, and hence, offers improved light absorption in the visible range. However, its photoactivity was found to be lower than that of the core-shell nanoparticles annealed in oxidizing atmosphere. The observed lower photoreduction was due to the presence of midgap states which acted as recombination centres and hence, reduced the photocatalytic activity.