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MXenes have demonstrated potential for various applications owing to their tunable surface chemistry and metallic conductivity. However, high temperatures can accelerate MXene film oxidation in air. Understanding the mechanisms of MXene oxidation at elevated temperatures, which is still limited, is critical in improving their thermal stability for high-temperature applications. Here, we demonstrate that Ti3C2Tx MXene monoflakes have exceptional thermal stability at temperatures up to 600 °C in air, while multiflakes readily oxidize in air at 300 °C. Density functional theory calculations indicate that confined water between Ti3C2Tx flakes has higher removal energy than surface water and can thus persist to higher temperatures, leading to oxidation. We demonstrate that the amount of confined water correlates with the degree of oxidation in stacked flakes. Confined water can be fully removed by vacuum annealing Ti3C2Tx films at 600 °C, resulting in substantial stability improvement in multiflake films (can withstand 600 °C in air). These findings provide fundamental insights into the kinetics of confined water and its role in Ti3C2Tx oxidation. This work enables the use of stable monoflake MXenes in high-temperature applications and provides guidelines for proper vacuum annealing of multiflake films to enhance their stability. [ABSTRACT FROM AUTHOR]

Traditionally, rechargeable lithium metal battery systems relied on simple metal cationic species to enable metal nucleation and deposition. However, this mechanism is less applicable to room‐temperature rechargeable aluminum batteries (RABs), which utilize complex ionic species. This work takes advantage of two different MXenes, Mo2Ti2C3Tx and Ti3C2Tx, which have different metal‐termination group bond strengths, interlayer spacings, and surface termination compositions, to amplify and visualize the differences between two promising RAB electrolytes (i.e., urea/AlCl3 and EMImCl/AlCl3). This work allowed us to deduce the following: 1) despite lower coulombic efficiencies, smoother Al deposits are observed when the urea/AlCl3 electrolyte is used; 2) unknown side reactions occur in all the different scenarios, however, they are likely less reversible in the EMImCl/AlCl3 electrolyte; 3) metal‐halogen exchange reactions can occur in all scenarios, forming Al(OF)x and AlFx species; 4) the free urea in urea/AlCl3 electrolyte behaves differently from the urea in aqueous solutions. Overall, due to the characteristics of aluminum, RABs involve vastly different internal mechanisms, resulting in the need for audacious attempts toward system understanding. [ABSTRACT FROM AUTHOR]

Water quality monitoring has become more critical in recent years to ensure the availability of clean and safe water from natural aquifers and to understand the evolution of water contaminants across time and space. The conventional water monitoring techniques comprise of sample collection, preservation, preparation, tailed by laboratory testing and analysis with cumbersome wet chemical routes and expensive instrumentation. Despite the high accuracy of these methods, the high testing costs, laborious procedures, and maintenance associated with them don't make them lucrative for end end-users and field testing. As the participation of ultimate stakeholders, that is, common man for water quality and quantity can play a pivotal role in ensuring the sustainability of our aquifers, thus it is essential to develop and deploy portable and user-friendly technical systems for monitoring water sources in real-time or on-site. The present review emphasizes here on possible approaches including optical (absorbance, fluorescence, colorimetric, X-ray fluorescence, chemiluminescence), electrochemical (ASV, CSV, CV, EIS, and chronoamperometry), electrical, biological, and surface-sensing (SPR and SERS), as candidates for developing such platforms. The existing developments, their success, and bottlenecks are discussed in terms of various attributes of water to escalate the essentiality of water quality devices development meeting ASSURED criterion for societal usage. These platforms are also analyzed in terms of their market potential, advancements required from material science aspects, and possible integration with IoT solutions in alignment with Industry 4.0 for environmental application. [ABSTRACT FROM AUTHOR]

To advance the MXene field, it is crucial to optimize each step of the synthesis process and create a detailed, systematic guide for synthesizing high‐quality MXene that can be consistently reproduced. In this study, a detailed guide is provided for an optimized synthesis of titanium carbide (Ti3C2Tx) MXene using a mixture of hydrofluoric and hydrochloric acids for the selective etching of the stoichimetric‐Ti3AlC2 MAX phase and delamination of the etched multilayered Ti3C2Tx MXene using lithium chloride at 65 °C for 1 h with argon bubbling. The effect of different synthesis variables is investigated, including the stoichiometry of the mixed powders to synthesize Ti3AlC2, pre‐etch impurity removal conditions, selective etching, storage, and drying of MXene multilayer powder, and the subsequent delamination conditions. The synthesis yield and the MXene film electrical conductivity are used as the two parameters to evaluate the MXene quality. Also the MXenes are characterized with scanning electron microscopy, x‐ray diffraction, atomic force microscopy, and ellipsometry. The Ti3C2Tx film made via the optimized method shows electrical conductivity as high as ≈21,000 S/cm with a synthesis yield of up to 38 %. A detailed protocol is also provided for the Ti3C2Tx MXene synthesis as the supporting information for this study. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials have sought intensive research attention from diverse scientific disciplines due to their unique and exciting properties. The most well-known 2D material is graphene that finds applications in various physical and life sciences fields. There has been a surge in the protocols available to synthesize graphene during the last two decades. Furthermore, several of these protocols have been revisited to improve the quality and yield of graphene that has resulted in a large body of literature. Young researchers, however, may not be entirely aware of these approaches. This review attempts to highlight the synthesis schemes that students and researchers could quickly adopt—even those having limited access to sophisticated tools. This review focuses on the top-down synthesis schemes that use low-end readily available equipment, benefitting the inexperienced and under-equipped researchers. This review's primary goal is to reach out to the young students, researchers, and technocrats working in diverse fields (not limited to nanoscience), to provide them with a roadmap for graphene synthesis. We will also present students entering academia with exciting applications that can be undertaken in university laboratories and high schools. [ABSTRACT FROM AUTHOR]

In the present work, green synthesized plasmonic copper nanostructures derived from carbon quantum dots (PCQDs) activated ZnO microarrays (MAs) based catalyst system is developed and studied for photocatalytic activity and photoelectrocatalytic water splitting. CQDs are synthesized from pharmaceutical waste and used as a reducing agent to synthesize PCQDs of an average size of 10±2 nm. PCQDs decorated ZnO (PCQDs/ZnO) MAs exhibited enhanced photocurrent density of ∼7.1 mA/cm2 at 1.23 V (vs. RHE), which is ∼11 fold to ZnO MAs alone (0.65 mA/cm2). The catalyst exhibits an ABPE of 1.07% at 0.7 V (vs. RHE), IPEC of 8.8% for 450 nm, and hydrogen production rate of 435 μmol/h. The enhanced PEC characteristics are assigned to the improved photons collection and better charge transfer for their participation in oxidation/reduction reaction. The same is well supported with DFT studies for the PCQDs/ZnO MAs catalyst for the first time. [ABSTRACT FROM AUTHOR]

Hydrogels have long been developed for a plethora of applications such as soft electronics, energy storage, the development of actuators, sensors, and, most importantly, biomedical applications. The biomedical applications of hydrogels are the most sought after and highly researched because of the various advantages of hydrogels. Having said that, the practical applications of the hydrogels are still restricted and efforts are being made to introduce other materials that add to the advantages of the hydrogels and impart new and exciting properties to the formed composite. In this regard, 2D materials beyond graphene such as phosphorene, antimonene, and germanene have gained significant attention. These are the newest addition to the existing 2D material family. These materials are highly optically active, which is vital while considering biomedical applications. The biomedical applications include antibacterial activity, chemotherapy, photothermal therapy, wound treatment, drug delivery, tissue engineering, and many more. This review intends to give the readers a brief overview of the trends and advancements in using these beyond graphene 2D material/hydrogel composites for biomedical applications. [ABSTRACT FROM AUTHOR]

The article focuses on two-dimensional (2D) materials, which have a wide range of applications spanning electronics, optics, energy storage, and more. Researchers have developed high-throughput computational strategies to predict and guide the synthesis of 2D materials through chemical exfoliation, enhancing efficiency and expanding the variety of materials available.

We herein demonstrate polypyrrole decorated micro-porous laboratory filter paper (PFP) as photoanode (PA) for efficient and stable water splitting. The straddling band position with water redox and the measured band gap of ~1.98 eV, make these PFP-PAs effective for water splitting reactions. The results manifest excellent photo-anodic PEC activity of these PFP-PAs, yielding a photocurrent density of ~9.5 mA/cm2 (at 1.23 V vs. RHE) in a three-electrode configuration. The incident photon-to-current efficiency (IPCE) and applied bias photon-to-current efficiency (ABPE) was measured to be 43.19% and ~1%, respectively. Moreover, the robustness of these flexible PFP-PAs was visualized by the provided stability for more than ~160 min in alkaline conditions. The current study provides a proof-of-concept for the realization of a cost-effective, flexible, and efficient paper-based artificial catalyst (like a natural leaf) for solar-driven water splitting. Image 1 • In-situ fabricated polypyrrole based flexible filter paper photo electrode (PFP-PEs). • Exhibit a bandgap of ~1.98 eV and reported as PEs for water splitting. • Photocurrent density of ~9.5 mA/cm2 (at 1.23 V vs. RHE) in 3-electrode system. • IPCE and ABPE was measured to be 43.19% and ~1%, respectively. • PFP-PEs stable for 160 min in alkaline conditions for PEC water splitting. [ABSTRACT FROM AUTHOR]

The ever-increasing demand for renewable and clean energy sources has prompted the development of novel materials for photoelectrochemical (PEC) water splitting, but efficient solar to hydrogen conversion remains a big challenge. In this work, we report a bio-nanohybrid strategy in a photo-system to simultaneously enhance the charge separation and water splitting efficiency of photoanode (PA) by introducing Bacteriorhodopsin (bR), a natural proton pumping photosystem and GaN nanowall network (NWN), a direct band gap and corrosion-resistant semiconductor. The experimental study reveals that this combination of bR and GaN NWN has huge potential as a light-activated sensitizer as well as proton pumping source to achieve enhance photocurrent density in hydrogen evolution reaction (HER). Consequently, this synergistic effect in bR/GaN NWN PA gives rise to largely enhanced applied bias photon-to-current efficiency (ABPE) ~7.8% and photocurrent density (28.74 mA/cm2 at 1.0 V vs RHE). It is worth mentioning that the photocurrent density of bR/GaN NWN, to the best of our knowledge, is superior to previously reported bR-based PAs and bio-photoelectric devices reported till today for solar-to-hydrogen fuel generation. Image 1 • First report on GaN NWN as photoanode with bR into electrolyte. • Measured photocurrent density is 28.74 mA/cm2 at 1.0 V (vs RHE). • Largely enhanced applied bias photon-to-current efficiency (ABPE) ~7.8%. [ABSTRACT FROM AUTHOR]

• Green synthesized Au and Ag loaded TiO 2 nanofiber photoanodes for solar water splitting. • One step green synthesis of Ag and Au nanostructures using green synthesized carbon dots. • Highest photocurrent density achieved with Au@CNL/TNF based photoanodes. • Waste to Value added approach derived photoanodes for solar hydrogen production. We herein present the Au and Ag NPs synthesized via chemical reduction with green synthesized carbon nano lights (CNL) as a visible light photosensitizer for TiO 2 nanofibers (TNFs) towards photoelectrochemical water splitting. The synthesized photoanodes (PA1: TNFs, PA2: Ag@CNLs/TNFs and PA3: Au@CNLs/TNFs) were probed ex-situ for morphological, structural, optical and electronic properties before being used for the PEC experiments. We first show the efficient photocatalytic activity of these photoanodes for the degradation of methylene blue under visible light irradiation. Followed by the photoelectrochemical (PEC) water splitting investigation, which reveals the substantially improved photocurrent density to 13 mA/cm2 and 18 mA/cm2, for PA2 and PA3, respectively under simulated AM 1.5 solar illumination at 1.36 V vs RHE, ~15 fold enhancement compared to that obtained for a PA1. This improvement we attributed to the synergic consequence, improved absorption and effective charge carrier separation & transport due to surface plasmonic effect, which is well evident in the decrease of measured charge transfer resistance (R ct), for PA2 (15.1 Ω) and PA3 (6.71 Ω), as compared to PA1 (139 Ω). [ABSTRACT FROM AUTHOR]

Abstract Arsenic poisoning of water resources has been of universal concern because of its serious health impact and on the ecosystem. As such, several efforts have been made on promising optical detection of arsenic utilizing various transduction platforms. However, the substantial role of sensor material cannot be ignored in the design of cost-effective, environment-friendly, and user acceptable sensor systems for on-site/in-field application. The goal is to employ sensor materials that enable detection of arsenic with high sensitivity, selectivity, reproducibility, and stability. In the present review, we have covered and critically deliberated upon the progress made over 2013–2018 in sensor materials, including colorimetric dyes, organic fluorophores, nanostructures (metal, carbon, semiconductor, metal oxides, etc.), and bioreceptors (aptamers, peptides, whole cells, etc.), for optical detection of arsenic in water. The possible integration of microfluidics/paper fluidics and imaging with existing optical sensor materials to realize a user friendly system for varied settings is also discussed. Graphical abstract Image 1 Highlights • Aquatic arsenic pollution: A global problem. • Optical chemo sensors for arsenic detection in water. • Nano materials in arsenic optical detection. • Environment friendly carbon nanostructures as emerging sensor probes. • Role of paper analytical devices and Imaging techniques in arsenic quantification. [ABSTRACT FROM AUTHOR]

Abstract Herein, we report an electrochemically synthesized Au/ZnO nanocomposite (NC) onto a disposable ITO electrode for selective detection of selenium (IV), the utmost toxic chemical species of selenium, in water using the square wave anodic stripping voltammetry as transduction technique. The NC is synthesized via one-step electrochemical reduction method. Raman, XPS, and EDAX analysis confirm the synthesis of the nanocomposite, while XRD and HR-TEM investigations reveal their crystalline nature, with a uniform distribution of spherical Au nanoparticles onto hexagonal ZnO. CV and EIS analysis of fabricated electrodes support their electro-analytical application. The analytical characteristics of the fabricated NC were optimized in terms of deposition potential, deposition time, electrolyte, pH and square wave characteristics (frequency, step-size, amplitude, etc.) to achieve a detection and quantification limit of 2.89 ppb and 8.75 ppb, respectively, with 2.55% (n = 3) RSD and 0.19 μA/ppb sensitivity. The NC is also tested against a variety of cations and anions, commonly found in water, such as Pb (II), Cu (II), Mg (II), Fe (III), Cd (II), iodide, phosphate, sulphate, bromide, etc. The observed electrode insulation towards these interfering ions is assigned to a high adsorption coefficient of ZnO towards selenium (IV) in the fabricated NC electrodes. The sensor performance is also validated against ion chromatography technique and spiked water sample collected from the field. The presented sensor electrodes could be a potential substitute for existing mercury and bulk electrodes for their easy integration into the field-deployable electrochemical analyzer for selenium screening in water. Graphical abstract Image 1 Highlights • Electrochemically synthesized Au/ZnO NC/ITO electrodes for Se(IV) sensing. • Wide detection window and detection limit below WHO permissible level. • High selectivity utilizing ZnO high adsorption coefficient towards selenite. • Low cost and selective electrodes for easy integration with portable analyzer. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials like conventional graphene, hexagonal boron nitride (h-BN, monolayer), and transition metal dichalcogenides (2D TMDCs) have gotten a lot of attention lately because of their unparalleled possibilities for a variety of applications. MBenes, a family of two-dimensional (2D) transition metal borides, have recently attracted significant attention. Their elemental compositions, surface terminations, geometrical forms, and properties (chemical and physical) are unique and fascinating. These two-dimensional compounds hold promising potential for environmental applications because of their exceptional electrical conductivity, high hydrophilicity, rich surface chemistry, and outstanding stability. The newly discovered MBenes are incredibly stable, with isotropic and ultrahigh Young's modulus. Furthermore, MBenes have superior catalytic activity, optical and thermal properties. Given many potential MBenes, theoretical and experimental applications are expected soon. This review presents the synthetic approaches, properties (optical, thermal, mechanical, and electrochemical), and diverse applications of MBenes-based heterostructures. The numerous strategies for further investigation MBenes for applications in the energy sector (storage and conversion) are highlighted. [ABSTRACT FROM AUTHOR]

• The recent advances achieved in photoanodes/cathodes for PEC water splitting are reviewed. • Key challenges in the fabrication of highly efficient and stable photoelectrodes are explicated. • Deliberations are also given on emerging photoelectrode materials for PEC water splitting. • Strategies and outlooks for the future improvement of solar-driven PEC devices are highlighted. The development of alternative clean and renewable fuels has become the need of the hour due to the decreasing supply of fossil fuels. Solar hydrogen produced from water is a sustainable, green substitute for fossil fuels for a variety of applications (e.g., transport, power generation, and industrial energy). However, cost-effective, efficient, and stable production of hydrogen fuel from water is a challenge for real-world applications. In pursuit of cost-effective and large-scale commercialization (e.g., photoproduction) of hydrogen from water, attempts were made to describe an up-to-date knowledge on photoelectrochemical (PEC) water splitting processes. In this respect, solar hydrogen production based on semiconductor photoelectrodes (PEs) is regarded as a highly effective option. In this review, we summarize the development of the PEC-based water splitting processes with respect to the efficiency and stability of the PEs. This study is thus expected to help open new paths for the establishment of a sustainable, renewable, and clean energy economy. [ABSTRACT FROM AUTHOR]

• CDs (~5 nm and 13% QY) and Ag@CDs biosynthesis using Cannabis sativa leaf extract. • Characterization of nanoparticles using FT-IR spectroscopy, HRTEM and XRD. • Antibacterial analysis against E. coli , S. aureus and dental microflora. The present was the first report on the synthesis of Carbon dots (CDs) using the acetone leaf extract of Cannabis sativa , an abundant weed plant as a sole carbon precursor. The obtained ~5 nm spherical CD particles (exhibiting 13% absolute quantum yield) were further employed to synthesize silver@CDs (Ag@CDs). CDs and Ag@CDs characterization revealed characteristic functional groups attributing to the aromatic, carboxylated and hydroxylated moieties. Ether and acetone leaf extracts of C. sativa exhibited strong antibacterial activity against dental microflora. Statistical analysis indicated 42 µg/mL as the significant MIC of Ag@CDs against Escherichia coli and Staphylococcus aureus (ρ < 0.0001). The results suggested weed abundance as an excellent natural carbon reserve and the biosynthesized Ag@CDs carry a great potential for the antibacterial application. [ABSTRACT FROM AUTHOR]

Heavy metal pollution of water resources is of worldwide concern, stimulating the development of breakthroughs in detection and remedy technologies. In the digital age, imaging solutions have been applied to almost every sector of civil society, from health and manufacturing to diagnostics, defense, and personal security. The next generation of monitoring sensors and systems for water quality and pollutants is developing at a rapid pace. The present review discusses various aspects of imaging-assisted quantification of heavy metals in water, including transduction techniques (colorimetric and photoluminescence), sensor materials (organic linkers, metal nanoparticles, carbonaceous & semiconductor quantum dots, etc.), the roles of equipment and readout tools (color charts, image scanners, digital cameras, mobile phones, etc.), substrates (organic and inorganic), and sampling methods. To the best of our knowledge, no such efforts have been made previously to critically and comprehensively analyze various aspects on the new imaging-based technologies in the environmental sector. Image 1 • This review analyzes advances over colorimetric sensor materials for heavy metals. • Advances over colorimetric readouts (e.g., smartphones) are evaluated. • Deliberations are made on commercial colorimetric kits and mobile apps for sensing. • Performance evaluation are made for their translation into field-deployable systems. • Integration of microfluidic and smartphones has been realized with chromogenic probes. [ABSTRACT FROM AUTHOR]

MXenes, a family of 2D transition‐metal carbides and nitrides, have excellent electrical conductivity and unique optical properties. However, MXenes oxidize in ambient conditions, which is accelerated upon heating. Intercalation of water also causes hydrolysis accelerating oxidation. Developing new tools to readily characterize MXenes' thermal stability can enable deeper insights into their structure–property relationships. Here, in situ spectroscopic ellipsometry (SE) is employed to characterize the optical properties of three types of MXenes (Ti3C2Tx, Mo2TiC2Tx, and Ti2CTx) with varied composition and atomistic structures to investigate their thermal degradation upon heating under ambient environment. It is demonstrated that changes in MXene extinction and optical conductivity in the visible and near‐IR regions correlate well with the amount of intercalated water and hydroxyl termination groups and the degree of oxidation, measured using thermogravimetric analysis. Among the three MXenes, Ti3C2Tx and Ti2CTx, respectively, have the highest and lowest thermal stability, indicating the role of transition‐metal type, synthesis route, and the number of atomic layers in MXene flakes. These findings demonstrate the utility of SE as a powerful in situ technique for rapid structure–property relationship studies paving the way for the further design, fabrication, and property optimization of novel MXene materials. [ABSTRACT FROM AUTHOR]

A diverse range of materials (e.g., metallic nanoparticles, semiconductor oxides, composites, polymers, and MOFs) have been reported for sensing applications in water samples based on several transduction techniques (e.g., absorbance, fluorescence, Raman, colorimetry, voltammetry, and plasmon resonance). Recently, carbon quantum dots (CQDs) have gained significant interest as fluorescent and small carbonaceous nanostructures for designing sensing devices (either as-produced or through modification) for heavy metals due to their excellent properties (e.g., photostability, facile surface modification, optical tunability, and environmental friendliness). This review provides a comprehensive overview on the role of CQDs as sensors for heavy metals in water. This work will help open up opportunities for the use of CQDs under the diverse field conditions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • First report on the synthesis of blue luminescent Carbon dots from Carica papaya waste. • Facile synthesis method and very high quantum yield of 23.7%. • We functionalized green synthesized CDs with EDTA and demonstrated for total chromium sensing in water. • The green sensor wide detection range of 10–1000 ppb and a very low detection limit of 0.708 ppb for total Cr. • Selectivity tested against a battery of ions in competitive and comparative assays. Abstract The work presents the facile green synthesis of blue luminescent C-dots (CDs) using papaya waste (Carica papaya) as a precursor. The as-synthesized CD S exhibit a quantum yield of 23.7% and are of size < 10 nm, while their polymerized architecture is confirmed by NMR spectroscopic analysis. The presence of various carbonyl and carboxyl surface groups confirmedthrough FT-IR is utilized for their surface modification with Ethylenediaminetetraacetic acid (EDTA) to detect chromium in water with high sensitivity and selectivity. The sensor demonstrated a fashioned decrease in fluorescence intensity on chromium (Cr (III), Cr (VI), Cr (III) + Cr (VI)) addition in a wide detection window of 10–1000 ppb. The theoretical detection (LOD, 3 s/sensitivity) and quantification (LOQ, 10 s/sensitivity) limits for total chromium were found to be 0.708 ppb and 2.4 ppb, respectively. The study presents fruit waste-derived and modified green CD S based chromium sensing platform for their potential integration with optical analyzers in water pollutants monitoring. [ABSTRACT FROM AUTHOR]

Rechargeable magnesium batteries (RMBs) are promising next‐generation low‐cost and high‐energy devices. Among all RMBs, anode‐free magnesium metal batteries that use in situ magnesium‐plated current collectors as negative electrodes can afford optimal energy densities. However, anode‐free magnesium metal batteries have remained elusive so far, as their practical application is plagued by low Mg plating/stripping efficiency due to nonuniform Mg deposition on conventional anode current collectors. Herein, for the first time, an anode‐free Mg‐metal battery is developed by employing a 3D MXene (Ti3C2Tx) film with horizontal Mg electrodeposition. The magnesiophilic oxygen and reactive fluorine terminations in MXene enable an enriched local magnesium‐ion concentration and a durable magnesium fluoride‐rich solid electrolyte interphase on the Ti3C2Tx film surface. Meanwhile, Ti3C2Tx MXene exhibits a high lattice geometrical fit with Mg (≈96%) to guide the horizontal electrodeposition of Mg. Consequently, the developed Ti3C2Tx film achieves reversible Mg plating/stripping with high Coulombic efficiencies (>99.4%) at high‐current‐density (5.0 mA cm−2) and high‐Mg‐utilization (50%) conditions. When this Ti3C2Tx film is coupled with a pre‐magnesized Mo6S8 cathode, the anode‐free Mg‐metal full‐cell prototype exhibits a volumetric energy density five times higher than its standard Mg‐metal counterpart. This work provides insights into the rational design of anode current collectors to guide horizontal Mg electrodeposition for anode‐free Mg metal batteries. [ABSTRACT FROM AUTHOR]

Magnesium metal batteries are promising candidates for next‐generation high‐energy‐density and low‐cost energy storage systems. Their application, however, is precluded by infinite relative volume changes and inevitable side reactions of Mg metal anodes. These issues become more pronounced at large areal capacities that are required for practical batteries. Herein, for the first time, double‐transition‐metal MXene films are developed to promote deeply rechargeable magnesium metal batteries using Mo2Ti2C3 as a representative example. The freestanding Mo2Ti2C3 films, which are prepared using a simple vacuum filtration method, possess good electronic conductivity, unique surface chemistry, and high mechanical modulus. These superior electro‐chemo‐mechanical merits of Mo2Ti2C3 films help to accelerate electrons/ions transfer, suppress electrolyte decomposition and dead Mg formation, as well as maintain electrode structural integrity during long‐term and large‐capacity operation. As a result, the as‐developed Mo2Ti2C3 films exhibit reversible Mg plating/stripping with high Coulombic efficiency of 99.3% at a record‐high capacity of 15 mAh cm−2. This work not only sheds innovative insights into current collector design for deeply cyclable Mg metal anodes, but also paves the way for the application of double‐transition‐metal MXene materials in other alkali and alkaline earth metal batteries. [ABSTRACT FROM AUTHOR]

Selenium, a metalloid, commonly known for its essentiality has emerged out as a water pollutant of concern for environmentalist due to its presence in natural water resources above the permissible limit. The high level of selenium in the environment poses severe health and ecosystem threats, therefore, its monitoring in water is of paramount concern. The present contribution summarizes and critically analyzes the field promising techniques, in particular, voltammetry and optical approach, for selenium quantification in water. The role of sensor material (organic fluorophores, colorimetric dyes and quantum dots), electrode surface modifiers (Hg, Bi, polymers, nanomaterials, etc.), chelators, etc., to overcome various challenges and achieve better sensor performance in terms of detection limit, range, reproducibility, stability, selectivity, sensitivity, and so forth are critically discussed. To end with, the possible future developments are discussed towards the realization of a cost-effective & field deployable monitoring device for on-site selenium analysis. [ABSTRACT FROM AUTHOR]

Herein, we report an environmental friendly, facile, and completely green synthetic method for producing carbon quantum dots (CQDs) from whey, a major dairy waste. The as-prepared monodispersed diameter CQDs exhibit blue luminescence with noteworthy quantum yield (~11.4%) and excitation dependent emission behaviour. Nuclear magnetic resonance (NMR) analysis reveals the presence of aromatized carbon peaks, leading to polymerized CQDs diameter architecture during whey pyrolysis. The X-ray and selected area electron diffraction patterns confirm their amorphous nature. Further, we demonstrate, these CQDs as an effective sensor probe for selective selenite monitoring in water upon functionalization with appropriate ligand. The functionalized GCQDs probe is shown to detect selenite with high sensitivity in 10–1000 ppb detection range. Further it is selective for selenite over other relevant ions (such as Cu 2+ , As 3+ , As 5+ , Pb 2+ , Ni 2+ , Se 6+ , Cl - , Br - , NO 3 − , NO 2 − and F − ) and displays a sub-ppb detection limit at 1.1% relative standard deviation. [ABSTRACT FROM AUTHOR]

Hydrogen production from water using photocatalysts under sunlight still remains a huge challenge. The search for a suitable photocatalyst combines an ability to dissociate water molecules with a band gap that absorbs light in the visible range and also water stability. In this regard, our present study represents a facile method for fabricating carbon quantum dots (CQDs) and Au@CQDs, which are useful for photocatalytic hydrogen generation from water. The optical properties revealed a band gap energy (eV) for CQDs (2.78) and Au@CQDs (2.68); additionally, photoluminescence analysis of CQDs showed maximum emission at 460 nm while also exhibiting a red shift when excited at longer wavelengths. Spherical shaped CQDs, with an average size of 7 nm (d spacing of 0.22 nm), and core shell Au@CQDs, with a shell thickness of 6 nm, were observed by HRTEM analysis. Comparatively, both CQDs (260 μmol) and Au@CQDs (280 μmol) displayed a higher rate of hydrogen production under sunlight irradiation than other carbon materials reported in earlier literature. In photoelectrochemical analysis, current densities associated with Au@CQDs and CQDs photoelectrodes (PEs) were found to be 16 mA cm−2 and 6 mA cm−2, respectively at a very low bias of 0.16 V. Moreover, frequency response analysis (FRA) associated with Randel's equivalent circuit showed that polarization/charge transfer resistance for Au@CQDs was very low (2.74 Ohm) over that of CQDs PEs (88.8 Ohm), which was 12.9 kOhm for bare TiO2 PEs. All these observations indicate that both CQDs and Au@CQDs are ample for preventing an electron–hole recombination processes, which ultimately leads to superior photocatalytic water splitting. [ABSTRACT FROM AUTHOR]

Carbon quantum dots (CQDs) have emerged out as promising fluorescent probes for hazardous heavy metals detection in recent past. In this study, water soluble CQDs were synthesized by facile microwave pyrolysis of citric acid & cysteamine, and functionalized with ditheritheritol to impart thiol functionalities at surface for selective detection of toxic arsenite in water. Microscopic analysis reveals that the synthesized CQDs are of uniform size (diameter ∼5 nm) and confirmed to have surface SH groups by FT-IR. The functionalized probe is then demonstrated for arsenite detection in water by “Turn-On” read out mechanism, which reduces the possibility of false positive signals associated with “turn off’ probes reported earlier. The blue luminescent functionalized CQDs exhibit increase in fluorescence intensity on arsenite addition in 5–100 ppb wide detection range. The probe can be used for sensitive detection of arsenite in environmental water to a theoretical detection limit (3s) of 0.086 ppb (R 2 = 0.9547) with good reproducibility at 2.6% relative standard deviation. The presented reliable, sensitive, rapid fCQDs probe demonstrated to exhibit high selectivity towards arsenite and exemplified for real water samples as well. The analytical performance of the presented probe is comparable to existing organic & semiconductor based optical probes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Covalent conjugation of GQDs with L-glutaminase enzyme has been performed. • The prepared bioconjugate was tested for electrochemical and PL-based sensing of Gln. • Electrochemical analysis revealed LOD and LOQ values of 360 µM and 1,100 µM, respectively. • PL approach yielded K sv , LOD, and LOQ values of 2.2 × 103 M−1, 9.42 µM, and 28.6 µM, respectively. This research describes the synthesis of a covalent bioconjugate of graphene quantum dots (GQDs) and glutaminase (10 units·mg−1) for electrochemical and photoluminescent (PL) detection of L-glutamine (Gln). As synthesized GQDs exhibited uniform size distribution, (average diameter ~5–10 nm, and discrete blue emission characteristics (λ ex = 391 ± 2 nm and λ em = 480 ± 2 nm)). Accordingly, the immobilization of glutaminase over the surface of the GQDs was confirmed by the characteristic Fourier-transform infrared (FTIR) spectroscopy peaks of the amide bond at 1,703 and 1,390 cm−1. The conjugate was used to detect Gln using electrochemical and PL approaches on a parallel basis over a concentration range of 100–1,000 µM. Electrochemical analysis of Gln using cyclic voltammetry revealed a limit of detection (LOD) and limit of quantification (LOQ) values of 360.4 µM and 1,100 µM, respectively. In comparison, quantification of Gln based on the PL approach yielded a Stern-Volmer quenching constant, LOD, and LOQ values of 2.2 × 103 M−1, 9.42 µM, and 28.57 µM, respectively. As such, the PL spectroscopy-based analysis was seen to have better sensitivity for Gln quantification than the electrochemical analysis. The PL-based approach is a more recommendable option for Gln quantification with high sensitivity and rapidity. [ABSTRACT FROM AUTHOR]

In this research, a facile and economical route is introduced for the transformation of pharmaceutical waste (i.e., expired medicines) into value-added fluorescent carbon quantum dots (pharmaceutically derived CQDs abbreviated as 'P-CQDs'). The synthesized P-CQDs were identified to have surface functionalities of –OH, C=O, and C=C with an average size of ~2–3 nm and a high quantum yield of 35.3%. The photoluminescence of P-CQDs recorded a maximum optical emission intensity at 2.8 eV (425 nm). The binding of Cu (II) ions by -COOH functionalities on the surface of P-CQDs led to its fluorescence quenching (turn-off) over a wide Cu (II) concentration range of 0.25–50 ppm. The P-CQDs exhibited the detection limit of 0.66 ppm (well below the WHO permissible limit of 2 ppm). The fluorescence intensity of the P-CQDs-Cu (II) complex was recovered from NaHCO 3. Hence, their "off-on" behavior was also explored for security ink applications for information encryption and decryption. Moreover, the rich oxygenated groups on the surface of the P-CQDs were utilized for green synthesis of plasmonic Ag@P-CQDs nanostructures, which were also demonstrated to have enhanced potential as bactericidal materials (e.g., against both E. coli and S. aureus). The overall results of this study are demonstrated to help create new and diverse routes for converting expired drugs into value-added nanostructures. Unlabelled Image • Luminescent carbon quantum dots (QY 35.3%) are synthesized from expired drugs. • CQDs were utilized to obtain plasmonic nanostructures Ag@PCQDs. • Process was optimized for upscaled use of expired drugs and their management. • CQDs and Ag@PCQDs are useful as chemosensor and security ink material, respectively. • Ag@PCQDs showed antibactericidal activity against Gram positive and negative bacteria. [ABSTRACT FROM AUTHOR]