Bentonite clay reinforced alginate grafted composite hydrogel with remarkable sorptive performance toward removal of methylene green.

The rapid industrial progress in today's world has led to an alarming increase in water pollution caused by various contaminants such as synthetic dyes. To address this issue, a new hydrogel sorbent, BC-r-Na-Alg-g-p(NIPAm-co-AAc), was developed by combining bentonite clay, sodium alginate, and poly(N-isopropyl acrylamide-co-acrylic acid) through one-pot free radical polymerization at 60 °C. The developed sorbent was characterized using several analytical techniques including SEM, FTIR, TGA, UTM, and swelling studies. The swelling capacity of the sorbent was observed to increase remarkably with an increase in pH, reaching a maximum of 9664 % at pH 11. In batch mode sorption experiments, the sorbent's performance toward methylene green (MG) was investigated by analysing the effects of contact time, pH, temperature, and concentration. The experimental data were fitted to pseudo-second-order kinetic and Langmuir isotherm models, indicating chemisorption as the dominant interaction mode between the anionic sorbent and cationic MG. However, physisorption may also occur to a lesser extent, indicated by the significant R2 of the pseudo-first-order kinetic and Freundlich isotherm models. Additionally, the sorbent exhibited very little decrease (approximately 5 %) in sorptive performance for six sorption-desorption cycles. Overall, the facile fabrication, excellent swelling (9664 %), promising sorption performance (2573 mg.g-1), and good recyclability (6 cycles) make the developed sorbent a potential candidate for various industrial applications.

Paper-based colorimetric sensor using a single-atom nanozyme for the ultrasensitive detection of Cr(VI) in short-necked clams.

Single-atom nanozymes (SAzymes) as a class of highly active nanozymes with the advantages of high atom utilization, high catalytic activity and stability have attracted great attention. In this work, Fe-N-C SAzymes with exceptional oxidase (OXD)-like activity were achieved utilizing polyvinylpyrrolidone (PVP) as a template. The Fe-N-C SAzymes with remarkable OXD-like activity could oxidize TMB to blue oxTMB, but 8-hydroxyquinoline (8-HQ) as a metal chelator is capable of discoloring oxTMB. Thus, the addition of 8-HQ decolorized the solution. However, upon the introduction of Cr(VI) ions, 8-HQ preferentially chelated with the Cr(VI) ions, reversing the inhibition of the color reaction and restoring the blue color. Based on this phenomenon, we constructed a novel paper-based analytical device (PAD) that exhibited a linear range of 5-1000 µM and an LOD of 1.2 µM. Importantly, the PAD used in this study shows the merits of simplicity, low preparation costs, and rapid reaction times. When combined with smartphone RGB analysis, it enables the simultaneous analysis of eight different Cr(VI) concentrations without the need for large-scale instrumentation. Moreover, the proposed PAD displays high selectivity, accuracy and utility in testing actual short-necked clam samples. This work not only provides a simple and cost-effective method to detect Cr(VI) but also makes a contribution to rapid food testing.

Smartphone-assisted colorimetric sensor arrays based on nanozymes for high throughput identification of heavy metal ions in salmon.

The rapid, precise, and high-throughput identification of multiple heavy metals ions holds immense importance in ensuring food safety and promoting public health. This study presents a novel smartphone-assisted colorimetric sensor array for the rapid and precise detection of multiple heavy metals ions. The sensor array is based on three signal recognition elements (AuPt@Fe-N-C, AuPt@N-C, and Fe-N-C) and the presence of different heavy metal ions affects the nanozymes-chromogenic substrate (TMB) catalytic color production, enabling the differentiation and quantification of various heavy metal ions. Combined with a smartphone-based RGB mode, the colorimetric sensor array can successfully identify five different heavy metal ions (Hg2+, Pb2+, Co2+, Cr6+, and Fe3+) as low as 0.5 µM and different ratios of binary and ternary mixed heavy metal ions in just 5 min. The sensor array successfully tested seawater and salmon samples with a total heavy metal content of 10 µM in the South China Sea (Haikou and Wenchang). Overall, this study highlights the potential of smartphone-assisted colorimetric sensor arrays for the rapid and precise detection of multiple heavy metal ions, which could significantly contribute to food safety and public health monitoring.

Ultrathin ternary PtNiRu nanowires for enhanced oxygen reduction and methanol oxidation catalysis via d-band center regulation.

Direct methanol fuel cells rely on the efficiency of their anode/cathode electrocatalysts to facilitate the methanol oxidation reaction and oxygen reduction reaction, respectively. Platinum-based nanocatalysts are at the forefront due to their superior catalytic properties. However, the high-cost, scarcity, and low CO tolerance of platinum pose challenges for the scalable application of DMFCs. Herein, we report novel ultrathin ternary PtNiRu alloy nanowires to improve Pt utilization and CO tolerance. These novel electrocatalysts incorporate the oxophilic metal Ru into ultrathin PtNi nanowires, aiming to enhance the intrinsic activity of platinum while leveraging the long-term durability and high utilization efficiency provided by the bimetallic synergistic effect. The PtNiRu NWs significantly enhance both mass activity and specific activity for ORR, performing about 6.9 times and 3.9 times better than commercial Pt/C, respectively. After a rigorous durability test of 10,000 cycles, the PtNiRu NWs only exhibited a 25.2 % loss in mass activity. Additionally, for MOR, the MA and SA of PtNiRu NWs exceed that of Pt/C catalyst by 4.30 and 2.72 times, respectively, and exhibit exceptional resistance to CO poisoning. Theoretical insights from density functional theory calculations suggest that the introduction of Ru modulates the d-band center of the surface Pt atoms, which contributes to decreased binding strength of oxygenated species and an elevated dissolution potential, substantiating the enhanced performance metrics, and the durability enhancement stems from the stronger PtM bonds than those in PtNiRu NWs resulted from PtRu covalent interactions. These findings not only provide a new perspective on platinum-based nanocatalysts but also significantly advance the quest for more efficient and durable electrocatalysts for DMFCs, representing a substantial stride in fuel cell technology.

The Identification of Oral Cariogenic Bacteria through Colorimetric Sensor Array Based on Single-Atom Nanozymes.

Effective identification of multiple cariogenic bacteria in saliva samples is important for oral disease prevention and treatment. Here, a simple colorimetric sensor array is developed for the identification of cariogenic bacteria using single-atom nanozymes (SANs) assisted by machine learning. Interestingly, cariogenic bacteria can increase oxidase-like activity of iron (Fe)─nitrogen (N)─carbon (C) SANs by accelerating electron transfer, and inversely reduce the activity of Fe─N─C further reconstruction with urea. Through machine-learning-assisted sensor array, colorimetric responses are developed as "fingerprints" of cariogenic bacteria. Multiple cariogenic bacteria can be well distinguished by linear discriminant analysis and bacteria at different genera can also be distinguished by hierarchical cluster analysis. Furthermore, colorimetric sensor array has demonstrated excellent performance for the identification of mixed cariogenic bacteria in artificial saliva samples. In view of convenience, precise, and high-throughput discrimination, the developed colorimetric sensor array based on SANs assisted by machine learning, has great potential for the identification of oral cariogenic bacteria so as to serve for oral disease prevention and treatment.

Fluorine-Like BH4-Doped Li6PS5Cl with Improved Ionic Conductivity and Electrochemical Stability.

Sulfide-based solid electrolytes with high ionic conductivity have attracted a lot of attention. However, the incompatibility and interfacial instability of sulfides with the lithium metal anode have emerged as pivotal constraints on their development. To address this challenge, we proposed and successfully synthesized the BH4- doped argyrodite-type electrolyte Li6PS5Cl0.9(BH4)0.1 by mechanical ball milling and annealing. This electrolyte not only exhibits an exceptionally high ionic conductivity of 2.83 × 10-3 S cm-1 at 25 °C but also demonstrates outstanding electrochemical stability. The Li/Li6PS5Cl0.9(BH4)0.1/Li symmetric cell can stably run for more than 400 h at a current density of 0.2 mA cm-2. In sharp contrast, although the F- doped sample, Li6PS5Cl0.3F0.7, can highly improve Li6PS5Cl's electrochemical stability, the ionic conductivity will reduce dramatically to 6.63 × 10-4 S cm-1. The stepwise current method reveals a critical current density of 3.5 mA cm-2 for Li6PS5Cl0.9(BH4)0.1, which makes it a competitive sulfide-based solid electrolyte. This research offers valuable insights for designing new borohydride-containing solid electrolytes.

Construction and Application of Nanozyme Sensor Arrays.

Compared with traditional "lock-key mode" biosensors, a sensor array consists of a series of sensing elements based on intermolecular interactions (typically hydrogen bonds, van der Waals forces, and electrostatic interactions). At the same time, sensor arrays also have the advantages of fast response, high sensitivity, low energy consumption, low cost, rich output signals, and imageability, which have attracted widespread attention from researchers. Nanozymes are nanomaterials which own enzyme-like properties. Because of the adjustable activity, high stability, and cost effectiveness of nanozymes, they are potential candidates for construction of sensor arrays to output different signals from analytes through the chemoresponse of colorants, which solves the shortcomings of traditional sensors that they cannot support multiple detection and lack universality. Recently, a sensor array based on nanozymes as nonspecific recognition receptors has attracted much more attention from researchers and has been applied to precise recognition of proteins, bacteria, and heavy metals. In this perspective, attention is given to nanozymes and the regulation of their enzyme-like activity. Particularly, the building principles and methods for sensor arrays based on nanozymes are analyzed, and the applications are summarized. Finally, the approaches to overcome the challenges and perspectives are also presented and analyzed for facilitating further research and development of nanozyme sensor arrays. This perspective should be helpful for gaining insight into research ideas within the field of nanozyme sensor arrays.

Elevating sensing capability via dual-atom catalysts boosted luminol cathodic electrochemiluminescence.

BACKGROUND: The advancement of highly sensitive electrochemiluminescence (ECL) biosensors has garnered escalating interest over time. Owing to the distinctive physicochemical attributes, the signal amplification strategy facilitated by functional nanomaterials has achieved notable milestones. Single-atom catalysts (SACs), featuring atomically dispersed metal active sites, have garnered significant attention. SACs offer unprecedented control over active sites and surface structures at the atomic level. However, to fully harness their potential, ongoing efforts focus on strategies to enhance the catalytic performance of SACs, profoundly influencing both the sensitivity and selectivity of SACs-based sensing platforms. RESULTS: In this study, we focused on the synthesis and application of Fe-Co-PNC dual-atom catalysts (DACs) with the incorporation of phosphorus, aiming to enhance catalytic efficiency, particularly in the context of the oxygen reduction reaction (ORR) correlated cathodic luminol ECL. The synergistic effects arising from the combination of Fe and Co in DACs were explored by ECL emission. Comparative studies with Fe-PNC SACs highlighted the superior catalytic performance of Fe-Co-PNC DACs. The ECL sensing platform exhibited excellent sensitivity, which provided a fast detection of Trolox with a wide linear range (0.1 µM-1.0 mM) and a low detection limit (LOD) of 0.03 µM. The platform demonstrated remarkable reproducibility and long-term stability, showcasing its potential for practical biosensing applications. SIGNIFICANCE: This study introduced the novel concept of Fe-Co-PNC DACs. The demonstrated synergistic effects and enhanced catalytic efficiency of DACs offer new avenues for the rational design of advanced catalysts. The successful application in the sensitive detection of Trolox emphasizes their potential significance in biosensing. It not only expands our understanding of SACs but also opens doors for the development of efficient and stable catalysts with broader applications.

Electrogenerated Chemiluminescence Imaging of Single-Atom Nanocatalysts.

Single-atom catalysts (SACs), distinguished by their maximum atom efficiency and precise control over the coordination and electronic properties of individual atoms, show great promise in electrocatalysis. Gaining a comprehensive understanding of the electrochemical performance of SACs requires the screening of electron transfer process at micro/nano scale. This research pioneers the use of electrogenerated chemiluminescence microscopy (ECLM) to observe the electrocatalytic reactions at individual SACs. It boasts sensitivity at the single photon level and temporal resolution down to 100 ms, enabling real-time capture of the electrochemical behavior of individual SACs during potential sweeping. Leveraging the direct correlation between ECL emission and heterogeneous electron transfer processes, we introduced photon flux density for quantitative analysis, unveiling the electrocatalytic efficiency of individual SACs. This approach systematically reveals the relationship between SACs based on different metal atoms and their peroxidase (POD)-like activity. The outcomes contribute to a fundamental understanding of SACs and pave the way for designing SACs with diverse technological and industrial applications.

Nonmetal catalyst boosting amplification of both colorimetric and electrochemical signal for multi-mode nitrite sensing.

Recently, nanozymes as an outstanding alternative to natural enzymes has attracted wide attention because of its high stability performance. In this study, PNC nonmetal nanozymes with high oxidase-like activity was synthesized can specifically catalyze colorless 3,3,5,5-tetramethyl-benzidine(TMB) to form blue oxidized TMB (TMBox). In the presence of nitrite, it further oxidizes TMBox to obtain yellow derivative products attributed to nitrite inducing diazotization reaction in TMBox. Based on this principle, a colorimetric and electrochemical sensing system was developed, and the ultra-sensitive multi-mode detection of nitrite was realized by combining RGB mode of smart phone, UV-Vis spectrum and electrochemical method. Compared with single signal detection, the multi-mode sensing system can realize self-validation to achieve more reliable detection results. What's more, the developed multi-mode sensing could quickly and sensitively detect nitrite in real sample, especially RGB mode of smart phone meeting the equipment limited areas, suggesting a broad application prospects in food safety.

Perspectives for the Role of Single-Atom Nanozymes in Assisting Food Safety Inspection and Food Nutrition Evaluation.

Single-atom nanozymes (SAzymes) have been greatly developed for rapid detection, owing to their rich active sites and excellent catalytic activity. Although several excellent reviews concentrating on SAzymes have been reported, they mainly focused on advanced synthesis, sensing mechanisms, and biomedical applications. To date, few reviews elaborate on the promising applications of SAzymes in food safety inspection and food nutrition evaluation. In this paper, we systematically reviewed the enzyme-like activity of SAzymes and the catalytic mechanism, in addition to recent research advances of SAzymes in the domain of food safety inspection and food nutrition evaluation in the past few years. Furthermore, current challenges hampering practical applications of SAzymes in food assay are summarized and analyzed, and possible research areas focusing on SAzyme-based sensors in rapid food testing are also proposed.

Cascade Reaction Regulated Electrochemiluminescence via Dual-Atomic-Site Catalysts.

Single-atom catalysts (SACs), a novel kind of electrocatalysts with full metal utilization, have been developed as unique signal amplifiers in several sensing platforms. Herein, based on theoretical prediction of the oxygen reduction reaction (ORR) mechanism on different atom sites, we constructed dual-atomic-site catalysts (DACs), Fe/Mn-N-C, to catalyze luminol-dissolved oxygen electrochemiluminescence (ECL). Computational simulation indicated that the weak adsorption of OH* on a single Fe site was overcome by introducing Mn as the secondary metallic active site, resulting in a synergic dual-site cascade mechanism. The superior catalytic activity of Fe/Mn-N-C DACs for the ORR was proven by the highly efficient cathodic luminol ECL, surpassing the performance of single-site catalysts (SACs), Fe-N-C and Mn-N-C. Furthermore, the ECL system, enhanced by a cascade reaction, exhibited remarkable sensitivity to ascorbic acid, with a detection limit of 0.02 nM. This research opens up opportunities for enhancing both the ECL efficiency and sensing performance by employing a rational atomic-scale design for DACs.

Unraveling the Dominance of Structural Vacancies in Sodium Ion Conductivity in Na3SO4F.

Solid electrolytes are important materials for energy storage and conversion applications, and the coexistence of the paddle-wheel effect and vacancy diffusion mechanism is commonly observed in many solid electrolytes. However, the mechanism that significantly contributes to this remains unknown. To address this issue, we assess the phase stability and conduction properties of Na3SO4F (NSOF) and magnesium-doped NSOF (Na2.98Mg0.01SO4F, NMSOF). Our results reveal that incorporating Na vacancies in NSOF (i.e., NMSOF) leads to a significant increase in ionic conductivity, with a 2 order of magnitude difference compared to NSOF. The phase transition temperature of NMSOF is also significantly lower than that of NSOF, demonstrating the role of vacancies in enhancing the mobility of Na cations. Furthermore, Raman spectroscopy confirms that the polyanion SO42- rotation has a minor effect on the sodium conduction mechanism. Our study provides a fundamental understanding of the sodium conduction mechanism of polyanion-based sodium superionic conductors, including the impact of vacancies on Na conductivity.

Partially selenized FeCo layered double hydroxide as bifunctional electrocatalyst for efficient and stable alkaline (sea)water splitting.

Seawater electrolysis to produce hydrogen is a clean and sustainable strategy for the development of clean and sustainable energy storage systems. However, the erosion and destruction of electrocatalysts of the devices by Cl- in seawater during splitting process make it very difficult to realize. In this work, a partially selenized FeCo layered double hydroxide (Se-FeCo-LDH) catalyst is successfully synthesized, which shows good electrocatalytic performance in seawater during water splitting due to both its excellent conductivity and large surface area. Moreover, an anion aggregation layer around the electrode during the catalytic process can be formed to avoid electrode erosion and destruction by Cl- as well as the competitive reaction of chloride oxidation with the oxygen evolution reaction (OER), which not only improves the catalytic efficiency but also the durability of the catalyst. As a result, the overpotential is only 229 mV at a current density of 100 mA cm-2 for OER in 1 M KOH. Only 1.446 V and 1.491 V voltages are required to reach a current density of 10 mA cm-2 in overall alkaline water and seawater splitting, respectively. Besides, this Se-FeCo-LDH catalyst also achieves long-term stability up to 245 h in overall alkaline seawater splitting. The development of Se-FeCo-LDH catalyst should have an enlightening effect in the field of hydrogen production by (sea)water electrolysis.

Research Progress in Iron-Based Nanozymes: Catalytic Mechanisms, Classification, and Biomedical Applications.

Natural enzymes are crucial in biological systems and widely used in biology and medicine, but their disadvantages, such as insufficient stability and high-cost, have limited their wide application. Since Fe3O4 nanoparticles were found to show peroxidase-like activity, researchers have designed and developed a growing number of nanozymes that mimic the activity of natural enzymes. Nanozymes can compensate for the defects of natural enzymes and show higher stability with lower cost. Iron, a nontoxic and low-cost transition metal, has been used to synthesize a variety of iron-based nanozymes with unique structural and physicochemical properties to obtain different enzymes mimicking catalytic properties. In this perspective, catalytic mechanisms, activity modulation, and their recent research progress in sensing, tumor therapy, and antibacterial and anti-inflammatory applications are systematically presented. The challenges and perspectives on the development of iron-based nanozymes are also analyzed and discussed.

Dual recognition elements for selective determination of progesterone based on molecularly imprinted electrochemical aptasensor.

A novel molecularly imprinted electrochemical aptasensor (MIEAS) was constructed for selective progesterone (P4) detection based on SnO2-graphene (SnO2-Gr) nanomaterial and gold nanoparticles (AuNPs). SnO2-Gr with a large specific area and excellent conductivity improved the adsorption capacity of P4. Aptamer, as biocompatible monomer, was captured by AuNPs on modified electrode through Au-S bond. An electropolymerized molecularly imprinted polymer (MIP) film consisted of p-aminothiophenol as chemical functional monomer and P4 as template molecule. Due to the synergetic effect of MIP and aptamer towards P4, this MIEAS exhibited better selectivity than the sensor with MIP or aptamer as single recognition element. The prepared sensor had a low detection limit of 1.73 × 10-15 M in a wide linear range from 10-14 M to 10-5 M. Satisfactory recovery obtained in tap water and milk samples proved that this sensor had great potential in environmental and food analysis.

Chevrel Phase Mo6 S8 Nanosheets Featuring Reversible Electrochemical Li-Ion Intercalation as Effective Dynamic-Phase Promoter for Advanced Lithium-Sulfur Batteries.

Modifying sulfur cathodes with lithium polysulfides (LiPSs) adsorptive and electrocatalytic host materials is regarded as one of the most effective approaches to address the challenging problems in lithium-sulfur (Li-S) batteries. However, because of the high operating voltage window of Li-S batteries from 1.7 to 2.8 V, most of the host materials cannot participate in the sulfur redox reactions within the same potential region, which exhibit fixed or single functional property, hardly fulfilling the requirement of the complex and multiphase process. Herein, Chevrel phase Mo6 S8 nanosheets with high electronic conductivity, fast ion transport capability, and strong polysulfide affinity are introduced to sulfur cathode. Unlike most previous inactive hosts with a fixed affinity or catalytic ability toward LiPSs, the reaction involving Mo6 S8 is intercalative and the adsorbability for LiPSs as well as the ionic conductivity can be dynamically enhanced via reversible electrochemical lithiation of Mo6 S8 to Li-ion intercalated Lix Mo6 S8 , thereby suppressing the shuttling effect and accelerating the conversion kinetics. Consequently, the Mo6 S8 nanosheets act as an effective dynamic-phase promoter in Li-S batteries and exhibit superior cycling stability, high-rate capability, and low-temperature performance. This study opens a new avenue for the development of advanced hosts with dynamic regulation activity for high performance Li-S batteries.

Single-atom boosted electrochemiluminescence via phosphorus doping of Fe-N/P-C catalysts.

Single-atom catalyst (SAC), one of the most attractive catalysts in the field of energy conversion and storage, was proven as efficient accelerator for luminol-dissolved oxygen electrochemiluminescence (ECL) via the catalysis of oxygen reduction reaction (ORR). In this work, we synthesized heteroatom doping SACs of Fe-N/P-C for the catalysis of cathodic luminol ECL. The doping of P could lower the reaction energy barrier of the OH* reduction, and promote catalytic efficiency toward ORR. The formation of reactive oxygen species (ROS) during ORR triggered cathodic luminol ECL. Greatly enhanced ECL emission catalyzed by SACs proved that Fe-N/P-C exhibited higher catalytic activity to ORR compared with Fe-N-C. Since the system was highly dependent on oxygen, an ultra-sensitive detection of a typical antioxidant, ascorbic acid, was achieved with detection limit of 0.03 nM. This study provides possibility to greatly enhance the performance of ECL platform through rational tailoring of SACs via heteroatom doping.

Coupling heterostructured CoP-NiCoP nanopin arrays with MXene (Ti3C2Tx) as an efficient bifunctional electrocatalyst for overall water splitting.

Developing a highly effective bifunctional electrocatalyst for alkaline-condition electrochemical water splitting is both essential and challenging. The work presented here successfully synthesizes and employs a heterostructured CoP-NiCoP ultra-long nanopin array in situ growing on MXene (Ti3C2Tx) as a stable bifunctional electrocatalyst for electrochemical water-splitting. The heterogeneous structure formed by CoP nanoparticles and NiCoP nanopins provides extra active sites for water-splitting. Also, Ti3C2Tx works as a support substrate during electrochemical operations, accelerating mass transfer, ion transport, and rapid gas product diffusion. Meanwhile, throughout the catalytic process, the dense nanopin arrays shield Ti3C2Tx from further oxidation. At a result, the CoP-NiCoP-Ti3C2Tx (denoted as CP-NCP-T) demonstrated excellent catalytic activity, with overpotentials of just 46 mV for hydrogen evolution at 10 mA cm-2 and 281 mV for oxygen evolution at 50 mA cm-2. Furthermore, in 1.0 M KOH solution, the outstanding bifunctional electrode (CP-NCP-T || CP-NCP-T) exhibits efficient electrochemical water splitting activity (1.54 V@10 mA cm-2) and outperforms the comparable device Pt/C || IrO2 (1.62 V@10 mA cm-2).

Electrochemically Stable Li3-xIn1-xHfxCl6 Halide Solid Electrolytes for All-Solid-State Batteries.

Halide solid electrolytes (SEs) stand out among the many different types of SEs owing to their high ionic conductivity and excellent oxidative stability. Aliovalent substitution is a common strategy to enhance the ionic conductivity of halide electrolytes, but this strategy significantly decreases their electrochemical stability. Herein, we report Hf-substituted Li3InCl6 (Li3-xIn1-xHfxCl6, 0 ≤ x ≤ 0.7) SEs, in which a low concentration (0.1 ≤ x ≤ 0.5) of Hf enhances the ionic conductivity without affecting the electrochemical stability. Among them, Li2.7In0.7Hf0.3Cl6 exhibits a high ionic conductivity of 1.28 mS cm-1 and a wide electrochemical stability window of 2.68-4.22 V. All-solid-state batteries fabricated using Li2.7In0.7Hf0.3Cl6 SE present high discharge capacity and good cycling stability at 25 °C. Furthermore, we summarize the methods of crystal structure regulation by which aliovalent substitution of halide SEs is achieved and discuss potential research directions in the design of novel halide SEs with high ionic conductivity and electrochemical stability.