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Due to complex structure and surface functionalities, photoluminescence mechanisms of Carbon Dots are unknown, and it is challenging to synthesize Carbon Dots to achieve the desired optical properties. Herein, Carbon Dots simultaneously exhibiting high-color-purity (FWHM~24 nm) long wavelength one-photon fluorescence emission at 620 nm and NIR induced two-photon fluorescence emission at 630 and 680 nm are prepared by edge amino protonation treatment. Systematic analysis reveals that the protonation of 2,3-diaminophenazine changes the molecular state of Carbon Dots, decreases the photon transition band gap, and triggers red fluorescence emission with the dramatically narrowed peak width. As the oxidation products of reactant o-phenylendiamine, the emergence of 2,3-diaminophenazine as a photoluminescence determiner suggests that fluorophore products of precursor conversion are viable determinants of the desired luminescence properties of Carbon Dots. This work shows a new way for predicting and controlling photoluminescence properties of Carbon Dots, and may guide the development of tunable Carbon Dots for a broad range of applications. Carbon dots have garnered great interest due to their optical properties, however, engineering of the optical properties remains a challenge. Here, Zhang et al. produce carbon dots with a high color purity, providing a useful approach for engineering the optical properties of carbon dots.

Electrocatalytic CO 2 reduction is a typical reaction involving two reactants (CO 2 and H 2 O). However, the role of H 2 O dissociation, which provides active *H species to multiple protonation steps, is usually overlooked. Herein, we construct a dual-active sites catalyst comprising atomic Cu sites and Cu nanoparticles supported on N-doped carbon matrix. Efficient electrosynthesis of multi-carbon products is achieved with Faradaic efficiency approaching 75.4% with a partial current density of 289.2 mA cm −2 at −0.6 V. Experimental and theoretical studies reveal that Cu nanoparticles facilitate the C-C coupling step through *CHO dimerization, while the atomic Cu sites boost H 2 O dissociation to form *H. The generated *H migrate to Cu nanoparticles and modulate the *H coverage on Cu NPs, and thus promote *CO-to-*CHO. The dual-active sites effect of Cu single-sites and Cu nanoparticles gives rise to the catalytic performance. A dual-site catalyst consisting of Cu nanoparticles (NPs) and atomic Cu sites is designed. The atomic Cu boosts H2O dissociation for modulating the *H coverage on Cu NPs, improving the efficiency of CO2 electroreduction to multi-carbon products.

Although diatomic nitrogen is famously inert, a variety of transition metals can bind to it through a process termed backbonding. As the nitrogen weakly shares its own electrons, some electrons from the metal reach back out to it. Nonmetals would not seem to have the capacity for this type of bonding, but now Légaré et al. show that conventionally electron-deficient boron can be coaxed into it (see the Perspective by Broere and Holland). The authors treated boron-based precursors with potassium under a nitrogen atmosphere to produce several compounds with sandwiched dinitrogen between two boron centers in reduced motifs reminiscent of metal complexes. Science , this issue p. 896 ; see also p. 871 A boron compound reduced by potassium can bind N 2 in a motif reminiscent of transition metal complexes. Currently, the only compounds known to support fixation and functionalization of dinitrogen (N 2 ) under nonmatrix conditions are based on metals. Here we present the observation of N 2 binding and reduction by a nonmetal, specifically a dicoordinate borylene. Depending on the reaction conditions under which potassium graphite is introduced as a reductant, N 2 binding to two borylene units results in either neutral (B 2 N 2 ) or dianionic ([B 2 N 2 ] 2– ) products that can be interconverted by respective exposure to further reductant or to air. The 15 N isotopologues of the neutral and dianionic molecules were prepared with 15 N-labeled dinitrogen, allowing observation of the nitrogen nuclei by 15 N nuclear magnetic resonance spectroscopy. Protonation of the dianionic compound with distilled water furnishes a diradical product with a central hydrazido B 2 N 2 H 2 unit. All three products were characterized spectroscopically and crystallographically.

Highly effective electrocatalysts promoting CO 2 reduction reaction (CO 2 RR) is extremely desirable to produce value-added chemicals/fuels while addressing current environmental challenges. Herein, we develop a layer-stacked, bimetallic two-dimensional conjugated metal-organic framework (2D c -MOF) with copper-phthalocyanine as ligand (CuN 4 ) and zinc-bis(dihydroxy) complex (ZnO 4 ) as linkage (PcCu-O 8 -Zn). The PcCu-O 8 -Zn exhibits high CO selectivity of 88%, turnover frequency of 0.39 s −1 and long-term durability (>10 h), surpassing thus by far reported MOF-based electrocatalysts. The molar H 2 /CO ratio (1:7 to 4:1) can be tuned by varying metal centers and applied potential, making 2D c -MOFs highly relevant for syngas industry applications. The contrast experiments combined with operando spectroelectrochemistry and theoretical calculation unveil a synergistic catalytic mechanism; ZnO 4 complexes act as CO 2 RR catalytic sites while CuN 4 centers promote the protonation of adsorbed CO 2 during CO 2 RR. This work offers a strategy on developing bimetallic MOF electrocatalysts for synergistically catalyzing CO 2 RR toward syngas synthesis. Effective electrocatalyst is crucial in promoting CO 2 reduction to address current energy/environmental issue. Here, the authors develop bimetallic layered two-dimensional conjugated metal-organic framework to synergistically and efficiently electro-catalyze CO 2 to CO toward syngas synthesis.

ERp44 retrieves some endoplasmic reticulum (ER)-resident enzymes and immature oligomers of secretory proteins from the Golgi. Association of ERp44 with its clients is regulated by pH-dependent mechanisms, but the molecular details are not fully understood. Here we report high-resolution crystal structures of human ERp44 at neutral and weakly acidic pH. These structures reveal key regions in the C-terminal tail (C tail) missing in the original crystal structure, including a regulatory histidine-rich region and a subsequent extended loop. The former region forms a short α-helix (α16), generating a histidine-clustered site (His cluster). At low pH, the three Trx-like domains of ERp44 (“a,” “b,” and “b′”) undergo significant rearrangements, likely induced by protonation of His157 located at the interface between the a and b domains. The α16-helix is partially unwound and the extended loop is disordered in weakly acidic conditions, probably due to electrostatic repulsion between the protonated histidines in the His cluster. Molecular dynamics simulations indicated that helix unwinding enhances the flexibility of the C tail, disrupting its normal hydrogen-bonding pattern. The observed pH-dependent conformational changes significantly enlarge the positively charged regions around the client-binding site of ERp44 at low pH. Mutational analyses showed that ERp44 forms mixed disulfides with specific cysteines residing on negatively charged loop regions of Ero1α. We propose that the protonation states of the essential histidines regulate the ERp44–client interaction by altering the C-tail dynamics and surface electrostatic potential of ERp44.

Materials capable of extracting gold from complex sources, especially electronic waste (e-waste), are needed for gold resource sustainability and effective e-waste recycling. However, it remains challenging to achieve high extraction capacity and precise selectivity if only a trace amount of gold is present along with other metallic elements . Here we report an approach based on reduced graphene oxide (rGO) which provides an ultrahigh capacity and selective extraction of gold ions present in ppm concentrations (>1000 mg of gold per gram of rGO at 1 ppm). The excellent gold extraction performance is accounted to the graphene areas and oxidized regions of rGO. The graphene areas spontaneously reduce gold ions to metallic gold, and the oxidized regions allow good dispersibility of the rGO material so that efficient adsorption and reduction of gold ions at the graphene areas can be realized. By controlling the protonation of the oxidized regions of rGO, gold can be extracted exclusively, without contamination by the other 14 co-existing elements typically present in e-waste. These findings are further exploited to demonstrate recycling gold from real-world e-waste with good scalability and economic viability, as exemplified by using rGO membranes in a continuous flow-through process. High extraction capacity with precise selectivity to trace amounts of gold over a wide range of co-existing elements remains a challenge for effective e-waste recycling. Here, authors demonstrate the excellent performance of rGO for gold extraction from e-waste leachate, even at minute concentrations.

Converting CO 2 emissions, powered by renewable electricity, to produce fuels and chemicals provides an elegant route towards a carbon-neutral energy cycle. Progress in the understanding and synthesis of Cu catalysts has spurred the explosive development of electrochemical CO 2 reduction (CO 2 RR) technology to produce hydrocarbons and oxygenates; however, Cu, as the predominant catalyst, often exhibits limited selectivity and activity towards a specific product, leading to low productivity and substantial post-reaction purification. Here, we present a single-atom Pb-alloyed Cu catalyst (Pb 1 Cu) that can exclusively (~96% Faradaic efficiency) convert CO 2 into formate with high activity in excess of 1 A cm –2 . The Pb 1 Cu electrocatalyst converts CO 2 into formate on the modulated Cu sites rather than on the isolated Pb. In situ spectroscopic evidence and theoretical calculations revealed that the activated Cu sites of the Pb 1 Cu catalyst regulate the first protonation step of the CO 2 RR and divert the CO 2 RR towards a HCOO* path rather than a COOH* path, thus thwarting the possibility of other products. We further showcase the continuous production of a pure formic acid solution at 100 mA cm –2 over 180 h using a solid electrolyte reactor and Pb 1 Cu. Alloying copper with isolated heteroatoms enables the C protonation of CO 2 to HCOO* on activated copper sites, resulting in exclusive electrochemical CO 2 -to-HCOOH conversion with considerably high activity.

Electrochemical CO 2 conversion to methane, powered by intermittent renewable electricity, provides an entrancing opportunity to both store renewable electric energy and utilize emitted CO 2 . Copper-based single atom catalysts are promising candidates to restrain C-C coupling, suggesting feasibility in further protonation of CO* to CHO* for methane production. In theoretical studies herein, we find that introducing boron atoms into the first coordination layer of Cu-N 4 motif facilitates the binding of CO* and CHO* intermediates, which favors the generation of methane. Accordingly, we employ a co-doping strategy to fabricate B-doped Cu-N x atomic configuration (Cu-N x B y ), where Cu-N 2 B 2 is resolved to be the dominant site. Compared with Cu-N 4 motifs, as-synthesized B-doped Cu-N x structure exhibits a superior performance towards methane production, showing a peak methane Faradaic efficiency of 73% at −1.46 V vs . RHE and a maximum methane partial current density of −462 mA cm −2 at −1.94 V vs . RHE. Extensional calculations utilizing two-dimensional reaction phase diagram analysis together with barrier calculation help to gain more insights into the reaction mechanism of Cu-N 2 B 2 coordination structure. Developing efficient electrocatalysts for selective CO2 conversion is of high interest. Here the authors investigate B doped Cu single atom catalysts with Cu-N2B2 coordination for enhanced CO2 to CH4 conversion.

Aerogels with regularly porous structure and uniformly distributed conductive networks have received extensive attention in wearable electronic sensors, electromagnetic shielding, and so on. However, the poor mechanical properties of the emerging nanofibers-based aerogels are limited in practical applications. In this work, we developed a synchronous deprotonation-protonation method in the KOH/dimethyl sulfoxide (DMSO) system at room temperature for achieving chitin cross-linked aramid nanofibers (CANFs) rather than chitin nanofibers (ChNFs) and aramid nanofibers (ANFs) separately by using chitin and aramid pulp as raw materials. After freeze-drying process, the cross-linked chitin/aramid nanofibers (CA) aerogel exhibited the synergetic properties of ChNF and ANF by the dual-nanofiber compensation strategy. The mechanical stress of CA aerogel was 170 kPa at 80% compressive strain, increased by 750% compared with pure ChNF aerogel. Similarly, the compressibility of CA aerogel was somewhat improved compared to ANF aerogel. The enhancement verified that the crosslinking reaction between ANF and ChNF during the synchronous deprotonation process was formed. Afterwards, the conductive aerogels with uniform porous structure (CA-M) were successfully obtained by vacuum impregnating CA aerogels in Ti 3 C 2 T x MXene solution, displaying low thermal conductivity (0.01 W/(m·K)), high electromagnetic interference (EMI) shielding effectiveness (SE) (75 dB), flame retardant, and heat insulation. Meanwhile, the as-obtained CA-M aerogels were also applied as a pressure sensor with excellent compression cycle stability and superior human motion monitoring capabilities. As a result, the dual-nanofiber based conductive aerogels have great potentials in flexible/wearable electronics, EMI shielding, flame retardant, and heat insulation.

The control of charge transfer between radical anions and cations is a promising way for decoding the emission mechanism in electrochemiluminescence (ECL) systems. Herein, a type of donor-acceptor (D-A) covalent organic framework (COF) with triphenylamine and triazine units is designed as a highly efficient ECL emitter with tunable intrareticular charge transfer (IRCT). The D-A COF demonstrates 123 folds enhancement in ECL intensity compared with its benzene-based COF with small D-A contrast. Further, the COF’s crystallinity- and protonation-modulated ECL behaviors confirm ECL dependence on intrareticular charge transfer between donor and acceptor units, which is rationalized by density functional theory. Significantly, dual-peaked ECL patterns of COFs are achieved through an IRCT mediated competitive oxidation mechanism: the coreactant-mediated oxidation at lower potential and the direct oxidation at higher potential. This work provides a new fundamental and approach to improve the ECL efficiency for designing next-generation ECL devices. Controlling the charge transfer between radical anions and cations is a promising way to tune the emission mechanism in electrochemiluminescence (ECL) systems. Here, the authors report a donor-acceptor based covalent organic framework, using triphenylamine and triazine building units, and demonstrate efficient ECL based on an adjustable intrareticular charge transfer.