A ligand-modulated photostable Mn(I)-carbonyl complex for preferential conversion of CO2 to CO in water.

A strategically designed redox-active ligand ensures proper electronic balance in an Mn(I)-carbonyl template to induce photostability and water solubility. This newly designed Mn-carbonyl complex showcased rapid CO2 reduction with preferential production of CO (faradaic efficiency ∼88%) as the only C1 product in pure water, even from a flue gas resource.

Beyond S and Se: Electrocatalytic Hydrogen Production by Tellurolate-Bridged Co(III)-Mn(I) Heterodinuclear Complexes.

In the pursuit of efficient electrocatalysts for the hydrogen evolution reaction (HER), a series of manganese and cobalt heterodinuclear complexes have been synthesized and characterized that have a stark resemblance with the [NiFe]-hydrogenase active site structure. Irradiation of [Mn2(CO)10] in the presence of 1.5 eq of [NaEPh] [E = S, Se, Te] followed by reaction with [Cp*CoCl]2 led to the formation of half-sandwiched trichalcogenate-bridged heterodinuclear complexes [{Mn(CO)3}(µ-EPh)3(CoCp*)] [E = S (C1); Se (C2) and Te (C3)]. The reaction of these heterodinuclear trichalcogenate-bridged complexes with [LiBH4·THF] yielded the corresponding dichalcogenate hydride-bridged heterobimetallic complexes [(CO)3Mn(µ-EPh)2(µ-H)(CoCp*)] [E = S (C5); Se (C6) and Te (C7)], which closely imitate the Ni-R intermediate of [NiFe]-hydrogenase. The resultant complexes (C5-C7) displayed impressive H2 production in DMF in the presence of HBF4, whereas the Te-based complex (C7) showcased the highest TON (184 h-1) with an impressive Faradaic efficiency of >98%. The DFT investigations revealed a unique role of bridging chalcogens in catalysis, wherein, depending on the identity of the chalcogen (S, Se, or Te), protonation could occur via two distinct routes. This study represents a rare example of the full trio of S/Se/Te-based heterodinuclear complexes whose electrocatalytic HER activity has been probed under analogous conditions.

Green H2 Generation from Seawater Deploying a Bifunctional Hetero-Interfaced CoS2-CoFe-Layered Double Hydroxide in an Electrolyzer.

This work illustrates the practicality and economic benefits of employing a hetero-interfaced electrocatalyst (CoS2@CoFe-LDH), containing cobalt sulphide and iron-cobalt double-layer hydroxide for large-scale hydrogen generation. Here, the rational synthesis and detailed characterization of the CoS2@CoFe-LDH material to unravel its unique heterostructure are essayed. The CoS2@CoFe-LDH operates as a bifunctional electrocatalyst to trigger both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline seawater (pH 14.0) while showcasing low overpotential requirement for HER (311 mV) and OER (450 mV) at 100 mA cm- 2 current density. The identical CoS2@CoFe-LDH on either electrode in an H-cell setup results in simultaneous H2 and O2 production from seawater with a ≈98% Faradaic efficiency with an applied potential of 1.96V@100 mA cm- 2. Next, this CoS2@CoFe-LDH catalyst is deployed on both sides of a membrane electrode assembly in a one-stack electrolyzer, which retains the intrinsic bifunctional reactivity of the catalyst to generate H2 and O2 in tandem from alkaline seawater with an impeccable energy efficiency (50 kWh kg-1-of-H2). This electrolyzer assembly can be directly linked with a Si-solar cell to produce truly green hydrogen with a solar-to-hydrogen generation efficiency of 15.88%, highlighting the potential of this converting seawater to hydrogen under solar irradiation.

Expedited Proton Relay in Enzyme-Inspired Cobaloximes Facilitate Organic Transformations.

Developing a water-soluble, oxygen-tolerant, and acid-stable synthetic H2 production catalyst is vital for renewable energy infrastructure. To access such an effective catalyst, we strategically incorporated enzyme-inspired, multicomponent outer coordination sphere elements around the cobaloxime (Cl-Co-X) core with suitable axial coordination (X). Our cobaloximes with axial imidazole or L-histidine coordination in photocatalytic HAT including the construction of anilines via a non-canonical cross-coupling approach is found superior compared to commonly used cobaloxime catalysts. The reversible Co(II)/Co(I) process is influenced by the axial N ligand's nature. Imidazole/L-histidine with a higher pKa promptly produces H2 upon irradiation, leading to the improved reactivity compared to previously employed axial (di)chloride or pyridine analogue.

Nanoporous air filtering systems made from renewable sources: benefits and challenges.

There is a crucial need for air purification systems due to increasing air contamination, while conventional air-filtering materials face challenges in eliminating gaseous and particulate pollutants. This review examines the development and characteristics of nanoporous polymeric materials developed from renewable resources, which have rapidly advanced in recent years. These materials offer more sustainable alternatives for nanoporous structures made out of conventional polymers and significantly impact the properties of porous polymers. The review explores nanoporous materials' production from renewable sources, filtering mechanisms, physicochemical makeup, and sensing capabilities. The recent advancements in this field aim to enhance production techniques, lower pressure drop, and improve adsorption efficiency. Currently, supporting approaches include using adsorbent layers and binders to immobilize nanoporous materials. Furthermore, the prospects and challenges of nanoporous materials obtained from renewable sources used for air purification are discussed.

Cancer phototherapy by CO releasing terpyridine-based Re(I) tricarbonyl complexes via ROS generation and NADH oxidation.

Here, we have synthesized and characterized three visible light responsive terpyridine based-Re(I)-tricarbonyl complexes; [Re(CO)3(ph-tpy)Cl] (Retp1), [Re(CO)3(an-tpy)Cl] (Retp2), and [Re(CO)3(py-tpy)Cl] (Retp3) where ph-tpy = 4'-phenyl-2,2':6',2″-terpyridine; an-tpy = 4'-anthracenyl-2,2':6',2″-terpyridine, py-tpy = 4'-pyrenyl-2,2':6',2″-terpyridine. The structures of Retp1 and Retp2 were confirmed from the SC-XRD data, indicating distorted octahedral structures. Unlike traditional PDT agents, these complexes generated reactive oxygen species (ROS) via type I and type II pathways and oxidized redox crucial NADH (reduced nicotinamide adenine dinucleotide) upon visible light exposure. Retp3 showed significant mitochondrial localization and demonstrated photoactivated anticancer activity (IC50 ∼ 2 µM) by inducing ROS-mediated cell death in cancer cells selectively (photocytotoxicity Index, PI > 28) upon compromising mitochondrial function in A549 cells. Their diagnostic capabilities were ultimately assessed using clinically relevant 3D multicellular tumor spheroids (MCTs).

A Two-Dimensional Cu-Based Nanosheet Producing Formic Acid Via Glycerol Electro-Oxidation in Alkaline Water.

The sluggishness of the complementary oxygen evolution reaction (OER) is reckoned as one of the major drawbacks in developing an energy-efficient green hydrogen-producing electrolyzer. An array of organic molecule oxidation reactions, operational at a relatively low potential, have been explored as a substitute for the OER. Glycerol oxidation reaction (GOR) has emerged as a leading alternative in this context because glycerol, a waste of biodiesel manufacturing, has become ubiquitous and accessible due to the significant growth in the biodiesel sector in recent decades. Additionally, the GOR generates several value-added organic compounds following oxidation that enhance the cost viability of the overall electrolysis reaction. In this study, a low-cost, room temperature operable, and energy-efficient synthetic methodology has been developed to generate unique two-dimensional CuO nanosheets (CuO NS). This CuO NS material was embedded on a carbon paper electrode, which showcased excellent glycerol electro-oxidation performance operational at a moderately low applied potential. Formic acid is the major product of this CuO NS-driven GOR (Faradaic efficiency ~80 %), as it is formed primarily via the glyceraldehyde oxidation pathway. This CuO NS material was also active for oxidizing other abundant alcohols like ethylene glycol and diethylene glycol, albeit at a relatively poor efficiency. Therefore, this robust CuO NS material has displayed the potential to be used in large-scale electrolyzers functioning with HER/GOR reactions.

Bioinspired graphene-based metal oxide nanocomposites for photocatalytic and electrochemical performances: an updated review.

Considering the rapidly increasing population, the development of new resources, skills, and devices that can provide safe potable water and clean energy remains one of the vital research topics for the scientific community. Owing to this, scientific community discovered such material for tackle this issue of environment benign, the new materials with graphene functionalized derivatives show significant advantages for application in multifunctional catalysis and energy storage systems. Herein, we highlight the recent methods reported for the preparation of graphene-based materials by focusing on the following aspects: (i) transformation of graphite/graphite oxide into graphene/graphene oxide via exfoliation and reduction; (ii) bioinspired fabrication or modification of graphene with various metal oxides and its applications in photocatalysis and storage systems. The kinetics of photocatalysis and the effects of different parameters (such as photocatalyst dose and charge-carrier scavengers) for the optimization of the degradation efficiency of organic dyes, phenol compounds, antibiotics, and pharmaceutical drugs are discussed. Further, we present a brief introduction on different graphene-based metal oxides and a systematic survey of the recently published research literature on electrode materials for lithium-ion batteries (LIBs), supercapacitors, and fuel cells. Subsequently, the power density, stability, pseudocapacitance charge/discharge process, capacity and electrochemical reaction mechanisms of intercalation, and conversion- and alloying-type anode materials are summarized in detail. Furthermore, we thoroughly distinguish the intrinsic differences among underpotential deposition, intercalation, and conventional pseudocapacitance of electrode materials. This review offers a meaningful reference for the construction and fabrication of graphene-based metal oxides as effective photocatalysts for photodegradation study and high-performance optimization of anode materials for LIBs, supercapacitors, and fuel cells.

Production of hydrogen from alcohols via homogeneous catalytic transformations mediated by molecular transition-metal complexes.

Hydrogen obtained from renewable sources such as water and alcohols is regarded as an efficient clean-burning alternative to non-renewable fuels. The use of the so-called bio-H2 regardless of its colour will be a significant step towards achieving global net-zero carbon goals. Challenges still persist however with conventional H2 storage, which include low-storage density and high cost of transportation apart from safety concerns. Global efforts have thus focussed on liquid organic hydrogen carriers (LOHCs), which have shown excellent potential for H2 storage while allowing safer large-scale transformation and easy on-site H2 generation. While water could be considered as the most convenient liquid inorganic hydrogen carrier (LIHC) on a long-term basis, the utilization of alcohols as LOHCs to generate on-demand H2 has tasted instant success. This has helped to draw a road-map of futuristic H2 storage and transportation. The current review brings to the fore the state-of-the-art developments in hydrogen generation from readily available, feed-agnostic bio-alcohols as LOHCs using molecular transition-metal catalysts.

A Clinico-Epidemiological Study of Cutaneous Adverse Drug Reactions in a Tertiary Care Centre of Eastern India.

Background: Adverse drug reactions (ADRs) are major problems in the drug therapy. Cutaneous adverse drug reactions (CADRs) are the most common ADRs. The pattern of CADRs differs among various drugs. Aims: To record various morphological patterns of CADRs and their causal relationships among patients attending in a tertiary care centre. Materials and Methods: An observational, cross-sectional, clinical study was conducted for a duration of one and a half years in a tertiary care centre in eastern India. Patients presenting with suspected CADRs were included if drug identity could be ascertained. Clinical profiling and drug history were recorded, and causality assessment was carried out as per the Naranjo scale. Result: The commonest CADR in our study was fixed drug eruption (FDE) 48.61%, followed by SJS-TEN spectrum 16.66%, maculopapular rash 11.11% and so on. Severe cutaneous adverse drug reactions (SCARs) such as SJS, TEN, SJS-TEN Overlap, AGEP and DRESS accounted for 18 cases (25%). The most common culprit drugs were antimicrobials (54.16%), followed by nonsteroidal anti-inflammatory drugs (15.27%) and anticonvulsants (12.5%). Most of the CADRs were in probable category. Conclusion: The pattern of CADRs and the drugs causing them in our study population are similar to some previous studies but somewhat different from most of the previous Indian studies. The incidence of SCARs was significantly higher than in previous other studies in India and abroad.

Green Light-Triggered Photocatalytic Anticancer Activity of Terpyridine-Based Ru(II) Photocatalysts.

The relentless increase in drug resistance of platinum-based chemotherapeutics has opened the scope for other new cancer therapies with novel mechanisms of action (MoA). Recently, photocatalytic cancer therapy, an intrusive catalytic treatment, is receiving significant interest due to its multitargeting cell death mechanism with high selectivity. Here, we report the synthesis and characterization of three photoresponsive Ru(II) complexes, viz., [Ru(ph-tpy)(bpy)Cl]PF6 (Ru1), [Ru(ph-tpy)(phen)Cl]PF6 (Ru2), and [Ru(ph-tpy)(aip)Cl]PF6 (Ru3), where, ph-tpy = 4'-phenyl-2,2':6',2″-terpyridine, bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and aip = 2-(anthracen-9-yl)-1H-imidazo[4,5-f][1,10] phenanthroline, showing photocatalytic anticancer activity. The X-ray crystal structures of Ru1 and Ru2 revealed a distorted octahedral geometry with a RuN5Cl core. The complexes showed an intense absorption band in the 440-600 nm range corresponding to the metal-to-ligand charge transfer (MLCT) that was further used to achieve the green light-induced photocatalytic anticancer effect. The mitochondria-targeting photostable complex Ru3 induced phototoxicity with IC50 and PI values of ca. 0.7 µM and 88, respectively, under white light irradiation and ca. 1.9 µM and 35 under green light irradiation against HeLa cells. The complexes (Ru1-Ru3) showed negligible dark cytotoxicity toward normal splenocytes (IC50s > 50 µM). The cell death mechanistic study revealed that Ru3 induced ROS-mediated apoptosis in HeLa cells via mitochondrial depolarization under white or green light exposure. Interestingly, Ru3 also acted as a highly potent catalyst for NADH photo-oxidation under green light. This NADH photo-oxidation process also contributed to the photocytotoxicity of the complexes. Overall, Ru3 presented multitargeting synergistic type I and type II photochemotherapeutic effects.

Harnessing the cobalt complex for bidirectional O2/H2O transformation in neutral water via electrocatalysis/photocatalysis.

Bidirectional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts are crucial for renewable energy transduction via electrolyzers and fuel cell. Here, we present a protocol for harnessing the cobalt complex for bidirectional O2/H2O transformation in neutral water via electrocatalysis/photocatalysis. We describe steps for monitoring ORR and OER in neutral aqueous solution, measuring O2 concentration, and identifying the probable catalytic mechanism for ORR and OER. We then detail procedures for examining catalyst behavior under photocatalytic conditions in neutral aqueous surroundings. For complete details on the use and execution of this protocol, please refer to Saini et al.1.

Highly Stable Self-Regenerating Organic Multi-Redox Systems derived from Bicyclic (Alkyl)(amino)carbenes (BICAACs).

An extended class of organic multi-redox systems was derived from bicyclic(alkyl)amino carbenes (BICAACs). The highly-conjugated system undergoes a total of 4 redox events spanning a 1.8 V redox range. These organic compounds exhibited four different stable redox states (dication, radical cation, neutral and radical anion), and all of them were characterized either by single crystal X-ray study and/or various spectroscopic studies. Three of the four redox states are stable to air and moisture. The availability of stable multiple redox states demonstrated promise towards their efficacy in the symmetric H-cell charge/discharge cycling. Among various redox states, the dication/neutral state works efficiently and continuously for 1500 cycles in 2e- charge/discharge process outside glovebox in commercially available DMF with minimum capacity loss (retaining nearly 90 % Coulombic efficiency). Surprisingly, the efficiency of the redox cycle was retained even if the system was exposed to air for 30 days when it slowly regenerated to the initial deep blue radical cation, and it exhibited another 100 charge/discharge cycles with a minimal capacity loss. Such a stable H-cell cycling ability is not well known among organic molecule-based systems.

Augmenting Antimicrobial Resistance Surveillance: Rapid Detection of ß-Lactamase-Expressing Drug-Resistant Bacteria through Sensitized Luminescence on a Paper-Supported Hydrogel.

The emergence of antimicrobial resistance (AMR) in pathogenic bacteria, expedited by the overuse and misuse of antibiotics, necessitates the development of a rapid and pan-territorially accessible diagnostic protocol for resistant bacterial infections, which would not only enable judicious prescription of drugs, leading to infection control but also augment AMR surveillance. In this study, we introduce for the first time a "turn-on" terbium (Tb3+) photoluminescence assay supported on a paper-based platform for rapid point-of-care (POC) detection of ß-lactamase (BL)-producing bacteria. We strategically conjugated biphenyl-4-carboxylic acid (BCA), a potent Tb3+ sensitizer, with cephalosporin to engineer a BL substrate CCS, where the energy transfer to terbium is arrested. However, BL, a major resistance element produced by bacteria resistant to ß-lactam antibiotics, triggers a spontaneous release of BCA, empowering terbium sensitization within a supramolecular scaffold supported on paper. The remarkable optical response facilitates quick assessment with a binary answer, and the time-gated signal acquisition ensues improved sensitivity with a detection limit as low as 0.1 mU/mL. Furthermore, to ensure accessibility, particularly in resource-limited areas, we have developed an in loco imaging device as an affordable alternative to high-end instruments. The integration of the assay with the device readily identified the BL-associated drug-resistant strains in the mimic urinary tract infection samples within 2 h, demonstrating its excellent potential for in-field translation. We believe that this rapid paper-based POC assay, coupled with the in loco device, can be deployed anywhere, especially in developing regions, and will enable extensive surveillance on antibiotic-resistant infections.

A homogeneous cobalt complex mediated electro and photocatalytic O2/H2O interconversion in neutral water.

The O2/H2O redox couple is vital in various renewable energy conversion strategies. This work delves into the Co(L-histidine)2 complex, a functional mimic of oxygen-carrying metalloproteins, and its electrochemical behavior driving the bidirectional oxygen reduction (ORR) and oxygen evolution (OER) activity in neutral water. This complex electrocatalyzes O2 via two distinct pathways: a two-electron O2/H2O2 reduction (catalytic rate = 250 s-1) and a four-electron O2 to H2O production (catalytic rate = 66 s-1). The formation of the key trans-µ-1,2-Co(III)-peroxo intermediate expedites this process. Additionally, this complex effectively oxidizes water to O2 (catalytic rate = 15606 s-1) at anodic potentials via a Co(IV)-oxo species. Additionally, this complex executes the ORR and OER under photocatalytic conditions in neutral water in the presence of appropriate photosensitizer (Eosin-Y) and redox mediators (triethanolamine/ORR and Na2S2O8/OER) at an appreciable rate. These results highlight one of the early examples of both electro- and photoactive bidirectional ORR/OER catalysts operational in neutral water.

Density Functional Theory-Guided Photo-Triggered Anticancer Activity of Curcumin-Based Zinc(II) Complexes.

Photodynamic therapy (PDT) has evolved as a new therapeutic modality for cancer treatment with fewer side effects and drug resistance. Curcumin exhibits PDT activity, but its low bioavailability restricts its clinical application. Here, the bioavailability of curcumin was increased by its complex formation with the Zn(II) center. For a structure-activity relationship study, Zn(II)-based complexes (1-3) comprising N^N-based ligands (2,2'-bipyridine in 1 and 2 or 1,10-phenanthroline in 3) and O^O-based ligands (acetylacetone in 1, monoanionic curcumin in 2 and 3) were synthesized and thoroughly characterized. The X-ray structure of the control complex, 1, indicated a square pyramidal shape of the molecules. Photophysical and TD-DFT studies indicated the potential of 2 and 3 as good visible light type-II photosensitizers for PDT. Guided by the TD-DFT studies, the low-energy visible light-triggered singlet oxygen (1O2) generation efficacy of 2 and 3 was explored in solution and in cancer cells. As predicted by the TD-DFT calculations, these complexes produced 1O2 efficiently in the cytosol of MCF-7 cancer cells and ultimately displayed excellent apoptotic anticancer activity in the presence of light. Moreover, the molecular docking investigation showed that complexes 2 and 3 have very good binding affinities with caspase-9 and p-53 proteins and could activate them for cellular apoptosis. Further molecular dynamics simulations confirmed the stability of 3 in the caspase-9 protein binding site.

Polypyridyl-based Co(III) complexes of vitamin B6 Schiff base for photoactivated antibacterial therapy.

Herein, five novel polypyridyl-based Co(III) complexes of Schiff bases, viz., [Co(dpa)(L1)]Cl (1), [Co(dpa)(L2)]Cl (2), [Co(L3)(L2)]Cl (3), [Co(L3)(L1)]Cl (4), and [Co(L4)(L1)]Cl (5), where dpa (dipicolylamine) = bis(2-pyridylmethyl)amine; H2L1 = (E)-2-((2-hydroxybenzylidene)amino)phenol; H2L2 = (E)-5-(hydroxymethyl)-4-(((2-hydroxyphenyl)imino)methyl)-2-methylpyridin-3-ol; L3 = 4'-phenyl-2,2':6',2''-terpyridine (ph-tpy); and L4 = 4'-ferrocenyl-2,2':6',2''-terpyridine (Fc-tpy), were synthesized and characterized. Complexes 1, 3, and 4 were structurally characterized by single-crystal XRD, indicating an octahedral CoIIIN4O2 coordination core. The absorption bands of these complexes were observed in the visible range with a λmax at ∼430-485 nm. Complex 5 displayed an extra absorption band near 545 nm because of a ferrocene moiety. These absorptions in the visible region reflect the potential of the complexes to act as visible-light antimicrobial photodynamic therapy (aPDT) agents. All of these complexes showed reactive oxygen species (ROS)-mediated antibacterial effects against S. aureus (Gram-positive) and E. coli (Gram-negative bacteria) upon low-energy visible light (0.5 J cm-2, 400-700 nm) exposure. Additionally, 1-5 did not show any toxicity toward A549 (Human Lung adenocarcinoma) cells, reflecting their selective bacteria-killing abilities.

Energy-efficient CO2/CO interconversion by homogeneous copper-based molecular catalysts.

Facile conversion of CO2 to commercially viable carbon feedstocks offer a unique way to adopt a net-zero carbon scenario. Synthetic CO2-reducing catalysts have rarely exhibited energy-efficient and selective CO2 conversion. Here, the carbon monoxide dehydrogenase (CODH) enzyme blueprint is imitated by a molecular copper complex coordinated by redox-active ligands. This strategy has unveiled one of the rarest examples of synthetic molecular complex-driven reversible CO2 reduction/CO oxidation catalysis under regulated conditions, a hallmark of natural enzymes. The inclusion of a proton-exchanging amine groups in the periphery of the copper complex provides the leeway to modulate the biases of catalysts toward CO2 reduction and CO oxidation in organic and aqueous media. The detailed spectroelectrochemical analysis confirms the synchronous participation of copper and redox-active ligands along with the peripheral amines during this energy-efficient CO2 reduction/CO oxidation. This finding can be vital in abating the carbon footprint-free in multiple industrial processes.

Role of Partial Vacancy and Structural Distortion in the Stability of Nonstoichiometric Phases Ni7-δInSe2-xSx (1.26 ≥ δ ≥ 0.94; 0 ≤ x ≤ 1.33).

This study explores the structure and stability of partly disordered sulfur-substituted Ni5.74InSe2 (I4/mmm, a = 3.6766(1) Å, c = 18.8178(10) Å, Z = 2). The structure of Ni7-δInSe2-xSx (x = 0.2, 0.36, 0.66, 0.80, 0.94) compounds is isotypic to their parent Ni5.74InSe2 and can be viewed as alternating heterometallic Cu3Au-type ∞2[Ni3In] slabs and defective Cu2Sb-type ∞2[Ni4-δ(Se/S)2] slabs along the [001]-axis. Similar to the parent Se-compound, the Ni-Ch (Ch = chalcogen) fragment is non-stoichiometric and possesses a partially occupied Ni-site. It was observed that with sulfur insertion at the selenium site of Ni5.74InSe2, the interatomic distance between the partially occupied nickel and mixed (S/Se) sites decreases from ∼2.24 to ∼1.95 Å, and the occupancy of the disordered nickel site simultaneously increases. The limiting composition Ni6.06InSe0.67S1.33 (x = 1.33, δ = 0.94) is formed in the sulfur-rich region. Its average structure resembles the Ni6SnS2-type and has a similar motif to Ni5.74InSe2; the only difference is that Cu3Au-type ∞2[Ni3In] alternates with two types of Ni-Ch fragments (Cu2Sb or Li2O type units). By using first-principles electronic structure calculations, we explained the presence of partially disordered nickel sites in the Ni-Ch fragment and rationalized why the nickel site occupancy increases with sulfur insertion.

ZnGa2-xAlxO4 (x = 0 ≤ 2) spinel for persistent light emission and HER/OER bi-functional catalysis.

Spinel materials have demonstrated diverse applications in various fields, especially in the energy sector. Since the pure spinel structure has the limitations of poor inherent activity and low conductivity, defect engineering through octahedral B-site modulation is expected to enhance various properties. Here in this work, we have synthesized ZnGa2-xAlxO4 (x = 0 ≤ 2) spinel and moved from one terminal (ZnGa2O4) to the other (ZnAl2O4) by varying the Ga/Al ratio using solvent-free solid-state reaction. Dopant and rare earth element-free (RE) ZnGa2O4 spinel showed excellent blue luminescence with photoluminescent quantum yields (PLQY) of 13% while exhibiting persistent light emission close to 60 min. The Al3+ incorporation at Ga3+ site doesn't yield any improvement in persistent luminescence lifetime owing to quenching of shallow traps as suggested by thermoluminescence (TL) studies. Moreover our materials have demonstrated bifunctional electrocatalytic activity towards both oxygen evolution (OER) and hydrogen evolution reaction (HER) which has never been reported for ZnGa2-xAlxO4. X-ray photoelectron spectroscopy (XPS) and positron annihilation lifetime spectroscopy (PALS) suggested that mixed Al/Ga-containing spinels possessed enhanced oxygen vacancies/defects. This makes them better electrocatalyst towards OER and HER compare to ZnGa2O4 and ZnAl2O4. The ZnGa1.75Al0.25O4 composition by virtue of enhanced oxygen vacancies and less charge transfer resistance (47.3 ohms) demonstrated best electrocatalytic activity for OER compared to the other synthesized catalysts at the same applied potential (1.6 V). On the other hand, the ZnGa1Al1O4 composition demonstrated excellent faradaic efficiency of ∼ 90% towards HER. From this work we can achieve multifunctional applications towards optoelectronics and electrocatalysis just by modulating Al/Ga ratio in ZnGa2-xAlxO4.