Proton Reservoir Research Articles

Dynamic Creation of a Local Acid-like Environment for Hydrogen Evolution Reaction in Natural Seawater.

Electrolysis of natural seawater driven by renewable energy is practically attractive for green hydrogen production. However, because precipitation initiated by an increase in local pH near to the cathode deactivates catalysts or blocks electrolyzer channels, limited catalysts are capable of operating with untreated, natural seawater (viz., pH 8.2 to 8.3 and ca. 35 g salts L-1); most are used in strongly alkaline or acidic seawater. Here, we report a new natural seawater electrolysis cathode with precipitation-suppression via a Pt/WO2 catalyst to create a dynamically local acid-like environment. The in situ formed hydrogen tungsten bronze (HxWOy) phase via continuous hydrogen insertion from water acts as a proton reservoir. As a result, dynamically stored protons create a local acid-like environment near the Pt active sites. We evidence that this tailored acid-like environment boosts the hydrogen evolution reaction in natural seawater splitting and neutralizes generated OH- species to restrict precipitation formations. Consequently, a long-term stability of >500 h at 100 mA cm-2 was exhibited in direct seawater electrolysis.

Sulfonate-Functionalized Metal-Organic Framework as a Porous "Proton Reservoir" for Boosting Electrochemical Reduction of Nitrate to Ammonia.

The electrochemical reduction reaction of nitrate (NO3RR) is an attractive route to produce ammonia at ambient conditions, but the conversion from nitrate to ammonia, which requires nine protons, has to compete with both the two-proton process of nitrite formation and the hydrogen evolution reaction. Extensive research efforts have thus been made in recent studies to develop electrocatalysts for the NO3RR facilitating the production of ammonia. Rather than designing another better electrocatalyst, herein, we synthesize an electrochemically inactive, porous, and chemically robust zirconium-based metal-organic framework (MOF) with enriched intraframework sulfonate groups, SO3-MOF-808, as a coating deposited on top of the catalytically active copper-based electrode. Although both the overall reaction rate and electrochemically active surface area of the electrode are barely affected by the MOF coating, with negatively charged sulfonate groups capable of enriching more protons near the electrode surface, the MOF coating significantly promotes the selectivity of the NO3RR toward the production of ammonia. In contrast, the use of MOF coating with positively charged trimethylammonium groups to repulse protons strongly facilitates the conversion of nitrate to nitrite, with selectivity of more than 90% at all potentials. Under the optimal operating conditions, the copper electrocatalyst with SO3-MOF-808 coating can achieve a Faradaic efficiency of 87.5% for ammonia production, a nitrate-to-ammonia selectivity of 95.6%, and an ammonia production rate of 97 μmol/cm2 h, outperforming all of those achieved by both the pristine copper (75.0%; 93.9%; 87 μmol/cm2 h) and copper with optimized Nafion coating (83.3%; 86.9%; 64 μmol/cm2 h). Findings here suggest the function of MOF as an advanced alternative to the commercially available Nafion to enrich protons near the surface of electrocatalyst for NO3RR, and shed light on the potential of utilizing such electrochemically inactive MOF coatings in a range of proton-coupled electrocatalytic reactions.

Imidazolium-based ionic liquids as proton reservoir for stable polyaniline cathode in zinc-iodine batteries

Aqueous zinc (Zn)-iodine (I2) batteries (ZIBs) are promising large-scale energy storage systems with high safety and low cost. However, the practical application of ZIBs is hindered by the dissolution of I3- ions, which leads to the shuttle effect and the loss of active iodine. Herein, we adopt an electrolyte modification strategy using two imidazolium-based ionic liquids (1-butyl-3-methylimidazolium iodide ([BMIM]I) and 1-ethyl-3-methylimidazolium iodide ([EMIM]I)) as electrolyte additives to restrain the dissolution of I3- ions and enhance the performance of ZIBs. To be specific, the imidazole rings in [BMIM]+ and [EMIM]+ can be used as the proton sources, promoting the conversion of imine to protonated amines –NH+= in the polyaniline and subsequent adsorption of I3- ions. Therefore, the dissolution of I3- ions and shuttle effect are prevented, facilitating the reaction kinetics of cathode. As a proof of concept, the ZIB using [BMIM]I and [EMIM]I as electrolyte additives demonstrates remarkable cycling performance (72.2 % capacity retention after 1000 cycles) at a high current density of 20 mA cm−2

Capacitive behaviors for surface-sulfonated polyaniline nanofibers in different acidic electrolytes

Abstract Unique surface-sulfonated polyaniline nanofibers (PANI-S) were fabricated through one-pot polymerization to evaluate the feasibility of their applications as electrode materials for high-performance supercapacitors that can be operated in relatively weak acidic electrolytes. Benefiting from the self-doping effect and improved dispersion in aqueous solution for the nanofibers, as well as the effective buffering function of the electrolyte, the PANI-S exhibits excellent capacitive performance across a broad pH value range in acidic electrolytes. More clearly, the specific capacitance of the PANI-S remains remarkably stable, ranging from 752.4 to 754.4 F g−1 at a scan rate of 5 mV s−1 and from 575.4 to 536.8 F g−1 at a current density of 1 A g−1, as the pH value of the electrolyte varies from 0 to 6. However, the capacity retention rate of PANI-S gradually decreases from 79.2% to 37.2% as the current density increases from 1 A g−1 to 20 A g−1, with the pH of the buffered solution increasing from 0 to 6. The excellent electrochemical activity in low acidic electrolytes for PANI nanofibers can be attributed to the compensation effects of the self-doped local proton reservoir.

Sensitivity Enhancement of Ultra-Wideline NMR by Progressive Saturation of the Proton Reservoir Under Magic-Angle Spinning.

Solid-state NMR of low-γ nuclides is often characterized by low sensitivity and by significant spectral broadenings induced by the quadrupolar and the chemical-shift anisotropy interactions. Herein, we introduce an indirect acquisition method, termed PROgressive Saturation of the Proton Reservoir Under Spinning (PROSPRUS), which could facilitate the acquisition of ultra-wideline NMR spectra under magic-angle spinning (MAS), in systems with a sufficiently long dipolar relaxation time, T1D. PROSPRUS NMR relies on the generation of so-called second-order dipolar order among abundant protons undergoing MAS, and on the subsequent depletion of this dipolar order by a series of looped cross-polarization events, transferring the proton order into polarization of the low-γ I-nuclei as a function of the latter's offsets. While the spin dynamics of the ensuing experiment is complex, particularly when dealing with narrow I spectral lines, it is shown that PROSPRUS can lead to faithful lineshapes for ultra-wideline spin-1/2 and spin-1 species, providing high sensitivity with extremely low RF power requirements. It is also shown that the ensuing 1H-detected PROSPRUS experiments can efficiently characterize I-spin lineshapes in excess of 1 MHz without having to retune electronics, while providing improvements in sensitivity per unit time over current broadband direct-detection methods by up to a factor of four.

Sulfonated polyaniline/MXene composite electrode with high cycling stability for anti-freezing flexible supercapacitor

Polyaniline (PANi) is widely used in supercapacitors owing to its unique structural flexibility and redox behavior. However, due to the limitations of the inherent molecular structure, the expansion and contraction of the PANi skeleton will be triggered during the charging and discharging process, leading to decreased stability and rapid degradation. For this reason, we design a novel sulfonated polyaniline structure of aniline copolymerized with 2-aminobenzenesulfonic acid, thus immobilizing the sulfonic acid group (−SO3H) side chain onto the PANi main chain. The −SO3H acts as a proton reservoir to provide protons for PANi, accelerating the occurrence of redox reactions and providing pseudocapacitance, effectively suppressing the deprotonation phenomenon. Then SPANi is grown in-situ on the interlayers of MXene, which induces the disordered polymer to be ordered on the MXene substrate, forming a 3D interconnected network composite with both high specific capacitance and excellent stability. SPANi/MXene composite has an outstanding specific capacitance of 512.45 F g−1 at 1 A/g and retains up to 92.16 % of the initial capacitance after 10,000 cycles. Assembled with PHEAA-PAA-MXene double-crosslinked organogel electrolyte to form an anti-freezing device with a specific capacitance of 158.63 F g−1, it retains a high specific capacitance of 118.26 F g−1 even under the extreme conditions of −40 °C. The capacitance retention after 10,000 cycles is 95.2 % (20 °C) and 81.82 % (−40 °C), respectively. This work provides simple and effective methods to fabricate high-performance PANi-based electrodes and anti-freezing supercapacitors.

Redox-active “Structural Pillar” molecular doping strategy towards High-Performance polyaniline-based flexible supercapacitors

To coordinate flexibility to electrodes without sacrificing their electrochemical properties is critical for the development of wearable supercapacitors (SCs). Polyaniline (PANI) is well-known pseudocapacitive electrode material due to its high conductivity and different oxidation states upon switchable structures. However, its rigid conjugated backbone and structural instability caused by repeated doping/de-doping during cycling severely impede its utilization in flexible SCs. Herein, we deploy a directional freezing and redox-active “structural pillar” molecular doping strategy to boost PANI-based flexible SCs with high performance. The directional freezing strategy constructs an interconnected 3D honeycomb hydrogel structure with PANI nanofibers, which guarantees fast ion diffusion and electron transport and meanwhile exposes abundant active sites. The large-sized dopant 2-amino-4-bromoanthraquinone-2-sulfonic acid sodium (AQNS) is used as the structural pillar to alleviate the structural instability of PANI during cycling and provides additional pseudocapacitance arising from its redox active quinone groups. Moreover, the negatively charged −SO3− on AQNS can further interact with H+ in the electrolyte to act as an internal proton reservoir, assisting the protonation of –NH- and −N = in PANI to facilitate its charge storage process. Consequently, the PANI-AQNS electrode achieves a high specific capacitance of 578 F g−1 at 1 A g−1 and its symmetric SCs exhibit a specific capacitance of 199 F g−1 at 0.5 A g−1 with an energy density of 13.61 W h kg−1 at a power density of 175 W kg−1. Upon 2000 cycles of dynamic deformations, the SCs can still maintain above 90 % of the initial capacitance, verifying their excellent flexibility-relevant property.

Periodic Adjacent Pd‐Fe Pair Sites for Enhanced Nitrate Electroreduction to Ammonia via Accelerating Proton Relay

AbstractRecently, bimetallic nanoparticles (NPs) are promising for driving nitrate (NO3 −) reduction reaction (NO3RR) to produce ammonia (NH3) due to their multiple active sites and electron redistribution via strong metal–metal interaction. However, the quantitatively determining the atomic configuration of the active sites and revealing their respective roles in NO3RR process are still challenged. Herein, the configuration of atomically ordered PdFe3 L12 intermetallic NPs into mesoporous carbon nanofibers (O‐PdFe3‐mCNFs) is reported as an efficient NO3RR catalyst for NH3 synthesis. Compared to the face‐centered cubic one, the O‐PdFe3‐mCNFs demonstrate a high NO3− removal of 98.3% within 270 min with a large NH3 yield rate of 1014.2 µmol h−1 cm−2. The detailed in situ and theoretical analysis reveals that the high performance of O‐PdFe3‐mCNFs is attributed to the synergetic effect from the periodic adjacent Pd‐Fe pair sites at the ordered (110) facet via accelerating proton relay, where the Fe sites show preferable stabilization of nitrogen−oxygen (*NO) intermediates while Pd sites serve as proton reservoir for *NO hydrogenation. Moreover, the strong d‐d orbital hybridization tunes d‐band center of the alloy NPs and effectively modulates the adsorption energy of *NO3− and *NO. This synergetic electrocatalyst design offers a new avenue for developing highly efficient multifunctional NO3RR catalysts.

Green proton reservoirs of PANI for disposable high-performance zinc-ion batteries

Rechargeable batteries are widely used to power various electronic devices. However, their toxic components cause serious environmental pollution when discarded. To date, the toxicity characteristics of rechargeable batteries do not meet the requirements for implantable medical devices. Herein, we report an organic cathode using tannin-protonated polyaniline (Tannin-PANI). As “green proton reservoirs”, plant-derived tannins continuously supply H+ to maintain high electrochemical activity and excellent reversibility of Tannin-PANI. Hence, the Tannin-PANI-based cathode exhibited a capacity of 92.8 mAh g−1 after 1500 cycles at 10.0 A g−1. Moreover, it demonstrated long-term stability for more than 10,000 cycles in bacterial cellulose-based gel electrolyte. Further, the Tannin-PANI-based cathode showed excellent in vitro biocompatibility, and a pouch cell composed of the Tannin-PANI electrode had no significant impact on plant growth. This study provides further insights into the design of implantable batteries with high stability, excellent biocompatibility, and high environmental compatibility.

Dual Channel H2O2 Photosynthesis in Pure Water over S-Scheme Heterojunction Cs3PMo12/CC Boosted by Proton and Electron Reservoirs.

Dual channel photo-driven H2O2 production in pure water on small-scale on-site setups is a promising strategy to provide low-concentrated H2O2 whenever needed. This process suffers, however, strongly from the fast recombination of photo-generated charge carriers and the sluggish oxidation process. Here, insoluble Keggin-type cesium phosphomolybdate Cs3PMo12O40 (abbreviated to Cs3PMo12) is introduced to carbonized cellulose (CC) to construct S-scheme heterojunction Cs3PMo12/CC. Dual channel H2O2 photosynthesis from both H2O oxidation and O2 reduction in pure water has been thus achieved with the production rate of 20.1mmolL-1gcat. -1h-1, apparent quantum yield (AQY) of 2.1% and solar-to-chemical conversion (SCC) efficiency of 0.050%. H2O2 accumulative concentration reaches 4.9mmol L-1. This high photocatalytic activity is guaranteed by unique features of Cs3PMo12/CC, namely, S-scheme heterojunction, electron reservoir, and proton reservoir. The former two enhance the separation of photo-generated charge carriers, while the latter speeds up the torpid oxidation process. In situ experiments reveal that H2O2 is formed via successive single-electron transfer in both channels. In real practice, exposing the reaction system under natural sunlight outdoors successfully results in 0.24mmol L-1 H2O2. This work provides a key practical strategy for designing photocatalysts in modulating redox half-reactions in photosynthesis.

Novel sulfonated polyaniline/graphene oxide electrode with high cycling stability for all-solid-state flexible supercapacitors

Polyaniline (PANi) has high theoretical specific capacitance by storing energy through redox reactions and thus is widely used in supercapacitors. However, the skeleton of PANi expands and contracts during the process of ion inhalation and exfoliation, which leads to a decrease in electrochemical performance. To solve this problem, we graft the sulfonic acid group onto the PANi backbone via a borate ester bond, which serves as a proton reservoir to provide protons for PANi to undergo redox reactions and provide pseudocapacitance. SPANi is then polymerized in situ on graphene oxide (GO), and its comprehensive performance of the electrode is further enhanced by designing ordered structures and synergistic interactions. The SPANi5/GO5 composite that are created in-situ have a fantastic specific capacitance of 460.56 F g−1 at 1 A g−1 and maintained 85.19% of the primary capacitance after 10,000 cycles. The device is assembled with PAAM/H2SO4/GO as the gel electrolyte, which achieves a specific capacitance of 137.75 F g−1, and the capacitance is retains at 90.74% after 10,000 cycles. The supercapacitor exhibits a large energy density of 13.76 Wh kg−1 when the power density is 200.27 W kg−1. The present study presents a novel and efficient approach for the fabrication of high-performance supercapacitor electrodes.

Value‐Added Cascade Synthesis Mediated by Paired‐Electrolysis Using an Ultrathin Microenvironment‐Inbuilt Metalized Covalent Organic Framework Heterojunction

AbstractEnergy‐saving and value‐added management in advanced catalysis is highly desirable but is challenged by the limitations of multifunctional catalysts and catalytic modules. Herein, an azo‐linked phthalocyanine‐porphyrin covalent organic framework (COF) with the ultrathin layered nanostructure grown on carbon nanotubes (NiPc‐azo‐H2Pp@CNTs) has been designed and synthesized, which can serve as a highly active and stable bifunctional heterojunction electrocatalyst for selective paired‐electrosynthesis through coupling anodic iodide oxidation reaction and cathodic CO2 conversion. Particularly, the inbuilt local microenvironment conferred by the dihydroporphyrin moieties in COF can act as a proton reservoir to promote the proton relay at the heterojunction interface during the electrocatalytic process. Moreover, through the cascade construction of dual electrocatalytic/organocatalytic modules, the cathode‐generated CO can be further converted to dimethyl carbonate with a yield of 6.21 mmol L−1 h−1, while the anode‐produced iodine can be derived into iodoform on the hundred‐milligram scale. It is worth noting that the value‐added cascade synthesis mediated by paired‐electrolysis using the distinctive and high‐powered electrocatalysts will help advance the sustainable development of industrial intelligent manufacturing.

Participation of electrochemically inserted protons in the hydrogen evolution reaction on tungsten oxides.

Understanding the mechanisms by which electrodes undergo the hydrogen evolution reaction (HER) is necessary to design better materials for aqueous energy storage and conversion. Here, we investigate the HER mechanism on tungsten oxide electrodes, which are stable in acidic electrolytes and can undergo proton-insertion coupled electron transfer concomitant with the HER. Electrochemical characterization showed that anhydrous and hydrated tungsten oxides undergo changes in HER activity coincident with changes in proton composition, with activity in the order HxWO3·H2O > HxWO3 > HxWO3·2H2O. We used operando X-ray diffraction and density functional theory to understand the structural and electronic changes in the materials at high states of proton insertion, when the oxides are most active towards the HER. H0.69WO3·H2O and H0.65WO3 have similar proton composition, structural symmetry, and electronic properties at the onset of the HER, yet exhibit different activity. We hypothesize that the electrochemically inserted protons can diffuse in hydrogen bronzes and participate in the HER. This would render the oxide volume, and not just the surface, as a proton and electron reservoir at high overpotentials. HER activity is highest in HxWO3·H2O, which optimizes both the degree of proton insertion and solid-state proton transport kinetics. Our results highlight the interplay between the HER and proton insertion-coupled electron transfer on transition metal oxides, many of which are non-blocking electrodes towards protons.

Controllable proton-reservoir ordered gel towards reversible switching and reliable electromagnetic interference shielding.

Smart and dynamic electromagnetic interference (EMI) shielding materials possess a remarkable capacity to modify their EMI shielding abilities, rendering them invaluable in various civil and military applications. However, the present response mechanism of switch-type EMI shielding materials is slightly restricted, as it primarily depends on continuous pressure induction, thereby resulting in concerns regarding their durability and reliability. Herein, for the first time, we demonstrate a novel method for achieving solvent-responsive, reversible switching, and robust EMI shielding capabilities using a controlled proton-reservoir ordered gel. The gel contains polyaniline (PANI) and sodium alginate (SA). Initially, SA acts as a proton reservoir for PANI in an aqueous system, enhancing the doping level of PANI and improving its electrical conductivity. Additionally, PANI and SA chains respond to diverse polar solvents, such as water, acetonitrile, ethanol, n-hexane, and air, inducing distinct conformations that affect the degree of PANI conjugation and electron migration along the chains. This process is reversible and non-destructive to the polymer chain, ensuring the effective and uncompromised performance of the EMI shielding switch. We can achieve precise and reversible tuning (on/off) of EMI shielding with different effectiveness levels by manipulating the solvents within the framework. This work opens a new solvent-stimuli avenue for the development of EMI shielding materials with reliable and intelligent on/off switching capabilities.

Enhanced the zinc ion storage performance of PANI in ZnSO4 aqueous electrolyte by doping with sulfonated graphene quantum dots

Polyaniline (PANI) is a kind of low-cost and sustainable electrode material for large-scale aqueous zinc ion batteries. However, PANI always shows poor cycling performance because of deprotonation in cheap weakly acidic electrolytes. In this work, we find that sulfonated graphene quantum dots (SGQDs) dopant can alleviate the above-mentioned problem effectively because the -SO3−groups on the SGQDs can act as a local proton reservoir and increase the protonation of PANI. When tested as zinc ion cells in ZnSO4 aqueous electrolyte, the SGQDs doped PANI electrodes exhibit excellent rate performance (115 mA h/g at 1 A/g and 105 mA h/g at 5 A/g) and good cycling stability (retain 81% after 1500 cycles), which are much better than that of pure PANI. Furthermore, the chemical oxidation method used to prepare powdered PANI is easy to scale up. This work provides a potential strategy for enhancing the Zn-ion storage performance of PANI in cheap weakly acidic electrolytes by versatile carbon quantum dots materials.

Long-life P-type co-doped polyaniline cathodes for ultrahigh-energy-density aqueous zinc-ion batteries

Conductive polyaniline (PANI) is considered as a promising cathode material for aqueous zinc-ion batteries (AZIBs) due to its reversible redox properties. In this study, we prepared a binder-free PANI (βPG-PANI-6) cathode co-doped with β-naphthalene sulfonic acid (β-NSA), HClO4, and graphitic acid (GA) via a layer-by-layer self-assembled electro-polymerization method. As a soft template, β-NSA micelles can be doped with HClO4 into PANI nanoparticles to prevent the tight accumulation of PANI chains. Moreover, β-NSA and GA adsorbed on the surface of PANI nanoparticles through layer-by-layer self-assembly contain abundant weak acid groups, which can act as internal proton reservoirs to offer protons to guarantee high redox activity. During the electro-polymerization process, the flexible GA matrix which forms NO bond closely with PANI can alleviate the volume expansion effect of PANI. As a result, the βPG-PANI-6 cathode can obtain superior discharge specific capacity (560.5 mAh/g, 0.2 A/g), excellent rate performance (251.3 mAh/g, 10 A/g). It is commendable that the AZIBs assembled by βPG-PANI-6 cathode deliver ultra-high energy density and power density (535.31 Wh/kg @ 187.16 W/kg, 184.45 Wh/kg @ 7378.01 W/kg). This study expands the doping chemistry of PANI and advances the development of conducting polymer for AZIBs to a new level.

Continuum Modeling of Gas and Ions Transport in a High-Surface-Area Carbon (HSC) Nanopore

PEM fuel cell (PEMFC) is one of the promising energy conversion devices for emission-free transportation applications. It is beneficial in faster charging and better scalability compared to battery-powered vehicles, making PEMFC a viable option for heavy-duty vehicles which require higher efficiency and longer lifetimes. To economically compete with the combustion engine and improve commercialization, the PEMFC cathode desires optimization in enhancing the utilization of the expensive Pt catalyst. Integration of high-surface-area carbon (HSC) has shown to increase accessible Pt surface by diminishing ionomer poisoning as Pt particles can be loaded inside the nanoscale micropores (<5 nm) that ionomer cannot penetrate due to size restriction. However, separating Pt catalysts from ionomers requires a water pathway to deliver the proton to the interior catalyst surface, leading to RH-dependent electrochemical surface area (ECSA). In this work, we develop a steady-state, isothermal continuum model to study the gas and ions transport within HSC nanopores. The pore is represented as a straight cylindrical channel filled with water with an ionomer domain at the pore mouth serving as a proton reservoir. The ionomer phase contains H+, OH-, and background stationary SO3 - while the water phase only includes H+ and OH-. The Poisson-Nernst-Plank equations describe the flux of ions, and O2 transport is described by Fick’s law. Non-ideal behaviors including nanoconfinement effects and dielectric saturation are considered in the pore water phase, reflected by corrections in ion chemical potentials, diffusion coefficients of transport species, and dielectric constant. The electrical double layer (EDL) at the water-electrode interface is depicted as discrete finite domains applying the Gouy-Chapman-Stern (GCS) theory, with the oxygen reduction reaction (ORR) occurring at a finite reaction plane at the outer Helmholtz plane (OHP) through both acidic and alkaline reaction pathways. Donnan potential drop is solved at the ionomer-pore water interface and governs potential distribution in the pore water phase, further determining ionic concentrations at the catalyst surface and thus the kinetic region of polarization curves. The strong-adsorbed water adlayers due to nanoconfinement effects create a transport barrier for O2 approaching the catalyst surface, leading to higher mass transport resistance. A comparison between a flooded pore scenario (only a water phase exists in the pore) and a wetted pore scenario (the pore wall is covered by a water film while a gas phase also exists in the pore) shows that mass transport is hindered in the flooding pore as O2 dissolves in the pore water through a limited pore-ionomer interfacial area, while pore gas phase in the wetted pore serves as an extra O2 resource. This suggests that the management of HSC water uptake needs to avoid pore flooding while ensuring enough wettability to allow proton transport. The model is expected to couple with HSC pore size distribution measured from experiments and upscale to a cell-level model in future work.

Single-Nanoparticle-Level Understanding of Oxidase-like Activity of Au Nanoparticles on Polymer Nanobrush-Based Proton Reservoirs.

Enzyme-mimicking nanoparticles play a key role in important catalytic processes, from biosensing to energy conversion. Therefore, understanding and tuning their performance is crucial for making further progress in biological applications. We developed an efficient and sensitive electrochemical method for the real-time monitoring of the glucose oxidase (GOD)-like activity of single nanoparticle through collision events. Using brush-like sulfonate (-SO3-)-doped polyaniline (PANI) decorated on TiO2 nanotube arrays (TiNTs-SPANI) as the electrode, we fabricated a proton reservoir with excellent response and high proton-storage capacity for evaluating the oxidase-like activity of individual Au nanoparticles (AuNPs) via instantaneous collision processes. Using glucose electrocatalysis as a model reaction system, the GOD-like activity of individual AuNPs could be directly monitored via electrochemical tests through the nanoparticle collision-induced proton generation. Furthermore, based on the perturbation of the electrical double layer of SPANI induced by proton injection, we investigated the relationship between the measured GOD-like activities of the plasmonic nanoparticles (NPs) and the localized surface plasmon resonance (LSPR) as well as the environment temperature. This work introduces an efficient platform for understanding and characterizing the catalytic activities of nanozymes at the single-nanoparticle level.

Engineering sulfuric acid-pretreated biochar supporting MnO2 for efficient toxic organic pollutants removal from aqueous solution in a wide pH range

Manganese dioxides (MnO2) and biochar materials are both desirable candidates for environmental remediation of toxic organic pollutants (TOPs) in water due to wide availability and environmental-friendly. In practical application, however, MnO2 suffers from low redox activity owing to deprotonation, while biochar is subject to limited removal capacity. Herein, a difunctional engineering sulfuric acid-pretreated biochar supporting MnO2 composite (MBC-A) was firstly synthesized and optimized to remove various TOPs from aqueous solution. Specifically, sulfuric acid not only served as an active agent to improve the specific surface area of biochar for improvement of adsorption capacity and more MnO2 loading, but also facilitated the introduction of sulfonic acid groups (-SO3H) as an internal proton reservoir to inhibit inactivation of MnO2 due to deprotonation in alkaline. Thanks to adsorption and oxidation, MBC-A showed excellent removal capacity (214.9 mg/g) and fast reaction kinetics (360 min) for tetracycline (TC), exceeding precursor and other materials reported in literature. Importantly, the effective operation pH range of MBC-A was broadened to 1–13 with the help of buffering capacity of –SO3H groups. The dominant driving force of adsorption were π-π interaction and hydrogen bond; while reactive oxidative species were mainly ascribed to singlet oxygen (1O2), hydroxyl radical (·OH) and reactive Mn3+. The possible reactive sites and pathway were investigated by combining experimental results with density functional theory (DFT) calculation. Further, the results of multiple cyclic runs, removal in real river water and toxicity assessment demonstrated well reusability, high environmental security, and excellent practical applicability of MBC-A.

Indirectly detected satellite-transition quadrupolar NMR via progressive saturation of the proton reservoir

Static satellite-transitions (ST) NMR line shapes from half-integer quadrupolar nuclei could be very informative: they can deliver insight about local motions over a wide range of timescales, and can report on small changes in the local electronic environments as reflected by variations in the quadrupolar parameters. Satellite transitions, however, are typically “invisible” for half-integer quadrupolar nuclei due to their sheer breadth, leading to low signal-to-noise ratio –especially for unreceptive low-gamma or dilute quadrupolar nuclei. Very recently we have introduced a method for enhancing the NMR sensitivity of unreceptive X nuclei in static solids dubbed PROgressive Saturation of the Proton Reservoir (PROSPR), which opens the possibility of magnifying the signals from such spins by repeatedly imprinting frequency-selective X-driven depolarizations on the much more sensitive 1H NMR signal. Here, we show that PROSPR's efficacy is high enough for enabling the detection of static ST NMR for challenging species like 35Cl, 33S and even 17O –all at natural-abundance. The ensuing ST-PROSPR NMR experiment thus opens new approaches to probe ultra-wideline (6–8 MHz wide) spectra. These highly pronounced anisotropies can in turn deliver new vistas about dynamic changes in solids, as here illustrated by tracking ST line shapes as a function of temperature during thermally-driven events.