Rational Design of Nanoporous MoS2/VS2 Heteroarchitecture for Ultrahigh Performance Ammonia SensorsZhang, Shuaihua; Wang, Jiayu; Torad, Nagy L.; Xia, Wei; Aslam, Muhammad Aamir; Kaneti, Yusuf Valentino; Hou, Zhufeng; Ding, Zejun; Da, Bo; Fatehmulla, Amanullah; Aldhafiri, Abdullah M.; Farooq, Wazirzada Aslam; Tang, Jing; Bando, Yoshio; Yamauchi, Yusuke
doi: 10.1002/smll.201901718pmid: 31515944
2D transition metal dichalcogenides (TMDs) have received widespread interest by virtue of their excellent electrical, optical, and electrochemical characteristics. Recent studies on TMDs have revealed their versatile utilization as electrocatalysts, supercapacitors, battery materials, and sensors, etc. In this study, MoS2 nanosheets are successfully assembled on the porous VS2 (P‐VS2) scaffold to form a MoS2/VS2 heterostructure. Their gas‐sensing features, such as sensitivity and selectivity, are investigated by using a quartz crystal microbalance (QCM) technique. The QCM results and density functional theory (DFT) calculations reveal the impressive affinity of the MoS2/VS2 heterostructure sensor toward ammonia with a higher adsorption uptake than the pristine MoS2 or P‐VS2 sensor. Furthermore, the adsorption kinetics of the MoS2/VS2 heterostructure sensor toward ammonia follow the pseudo‐first‐order kinetics model. The excellent sensing features of the MoS2/VS2 heterostructure render it attractive for high‐performance ammonia sensors in diverse applications.
Thermodynamically Stable Mesoporous C3N7 and C3N6 with Ordered Structure and Their Excellent Performance for Oxygen Reduction ReactionKim, In Young; Kim, Sungho; Premkumar, Selvarajan; Yang, Jae‐Hun; Umapathy, Siva; Vinu, Ajayan
doi: 10.1002/smll.201903572pmid: 31782908
Carbon nitrides with a high N/C atomic ratio (>2) are expected to offer superior basicity and unique electronic properties. However, the synthesis of these nanostructures is highly challenging since many parts of the CN frameworks in the carbon nitride should be replaced with thermodynamically less stable NN frameworks as the nitrogen content increases. Thermodynamically stable C3N7 and C3N6 with an ordered mesoporous structure are synthesized at 250 and 300 °C respectively via a pyrolysis process of 5‐amino‐1H‐tetrazole (5‐ATTZ). Polymerization of the precursor to the ordered mesoporous C3N7 and C3N6 is clearly proved by X‐ray and electron diffraction analyses. A combined analysis including diverse spectroscopy and FDMNES and density functional theory (DFT) calculations demonstrates that the NN bonds are stabilized in the form of tetrazine and/or triazole moieties in the C3N7 and C3N6. The ordered mesoporous C3N7 represents the better oxygen reduction reaction (ORR) performances (onset potential: 0.81 V vs reversible hydrogen electrode (RHE), electron transfer number: 3.9 at 0.5 V vs RHE) than graphitic carbon nitride (g‐C3N4) and the ordered mesoporous C3N6. The study on the mechanism of ORR suggests that nitrogen atoms in the tetrazine moiety of the ordered mesoporous C3N7 act as active sites for its improved ORR activity.
Predictions of Pattern Formation in Amino Acid Adlayers at the In Vacuo Graphene Interface: Influence of Termination StateAwuah, Joel B.; Walsh, Tiffany R.
doi: 10.1002/smll.201903403pmid: 31663292
Controlled self‐assembly of biomolecules on graphene offers a pathway for realizing its full potential in biological applications. Microscopy has revealed the self‐assembly of amino acid adlayers into dimer rows on nonreactive substrates. However, neither the spontaneous formation of these patterns, nor the influence of amino acid termination state on the formation of patterns has been directly resolved to date. Molecular dynamics simulations, with the ability to reveal atomic level details and exert full control over the termination state, are used here to model initially disordered adlayers of neutral, zwitterionic, and neutral–zwitterionic mixtures for two types of amino acids, tryptophan and methionine, adsorbed on graphene in vacuo. The simulations of the zwitterion‐containing adlayers exhibit the spontaneous emergence of dimer row ordering, mediated by charge‐driven intermolecular interactions. In contrast, adlayers containing only neutral species do not assemble into ordered patterns. It is also found that the presence of trace amounts of water reduces the interamino acid interactions in the adlayers, but does not induce or disrupt pattern formation. Overall, the findings reveal the balance between the lateral interamino acid interactions and amino acid–graphene interactions, providing foundational insights for ultimately realizing the predictable pattern formation of biomolecules adsorbed on unreactive surfaces.
Amine Functionalized Metal–Organic Framework Coordinated with Transition Metal Ions: d–d Transition Enhanced Optical Absorption and Role of Transition Metal Sites on Solar Light Driven H2 ProductionKarthik, P.; Shaheer, A. R. Mahammed; Vinu, Ajayan; Neppolian, Bernaurdshaw
doi: 10.1002/smll.201902990pmid: 31724829
Design and development of efficient photocatalysts for H2 production from water and sunlight have gained significant attention as the solar assisted approach is considered to be a promising approach for the generation of clean fuel. However, the poor charge carrier separation and light harvesting ability of existing photocatalysts limits the efficiency of photoconversion of water. In this work, the synthesis of transition metal ions (M2+ = Co2+, Cu2+, and Ni2+) coordinated with Ti‐metal organic frameworks (Ti‐MOFs) through a simple post‐synthetic coordination method for efficient solar light‐driven H2 production is reported. Notably, coordination of M2+ ions with Ti‐MOF significantly improves the optical absorption by d–d transitions and the multimetal sites facilitate the fast charge carrier separation, thereby enhancing the solar light‐driven H2 production activity. Very interestingly, the rate of solar light‐driven H2 production is varied with respect to different metal ions coordination due to the position of d–d bands absorption in the solar spectrum, and the complexing tendency of M2+ ions with sacrificial electron donors. A maximum solar H2 production rate of 1583.55 µmol h−1 g−1 is achieved with a Cu2+ coordinated Ti‐MOF, which is ≈13 fold higher than that of the pristine Ti‐MOF.
Tungsten Nitride, Well‐Dispersed on Porous Carbon: Remarkable Catalyst, Produced without Addition of Ammonia, for the Oxidative Desulfurization of Liquid FuelKhan, Nazmul Abedin; Bhadra, Biswa Nath; Park, Suk Woo; Han, Yong‐Su; Jhung, Sung Hwa
doi: 10.1002/smll.201901564pmid: 31166653
Polyanilines (pANIs), loaded with phosphotungstic acid (PTA), are pyrolyzed to get WO3 or W2N (≈6 and ≈7 nm, respectively), which is well‐dispersed on pANI‐derived porous carbons (pDCs). Depending on the pyrolysis temperature, WO3/pDC, W2N/pDC, or W2N‐W/pDCs could be obtained selectively. pANI acts as both the precursor of pDC and the nitrogen source for the nitridation of WO3 into W2N during the pyrolysis. Importantly, W2N could be obtained from the pyrolysis without ammonia feeding. The obtained W2N/pDC is applied as a heterogeneous catalyst for the oxidative desulfurization (ODS) of liquid fuel for the first time, and the results are compared with WO3/pDC and WO3/ZrO2. The W2N/pDC is very efficient in ODS with remarkable performance compared with WO3/pDC or WO3/ZrO2, which is applied as a representative ODS catalyst. For example, W2N/pDC shows around 3.4 and 2.7 times of kinetic constant and turnover frequency (based on 5 min of reaction), respectively, compared to that of WO3/ZrO2. Moreover, the catalysts could be regenerated in a facile way. Therefore, W2N/pDC could be produced facilely from pyrolysis (without ammonia feeding) of PTA/pANI, and W2N, well‐dispersed on pDC, can be suggested as a very efficient oxidation catalyst for the desulfurization of liquid fuel.
ROS‐Sensitive Degradable PEG–PCL–PEG Micellar ThermogelLee, Hyun Jung; Jeong, Byeongmoon
doi: 10.1002/smll.201903045pmid: 31523921
A reactive oxygen species (ROS)‐sensitive degradable polymer would be a promising material in designing a disease‐responsive system or accelerating degradation of polymers with slow hydrolysis kinetics. Here, a thermogelling poly(ethylene glycol)–polycaprolactone–poly(ethylene glycol) (PEG–PCL–PEG or EG12–CL20–EG12) triblock copolymer with an oxalate group at the middle of the polymer is reported. The polymers form micelles with an average size of 100 nm in water. Thermogelation is observed in a concentration range of 8.0−37.0 wt%. In particular, the aqueous PEG–PCL–PEG triblock copolymer solutions are in a gel state at 37 °C in a concentration range of 25.0–37.0 wt%, whereas the aqueous PEG–PCL diblock copolymer solutions are in a sol state in the same concentration range at 37 °C. Thus, the gel depot could dissolve out once degradation of the triblock copolymers occurs at the oxalate group as confirmed by the in vitro experiment. In vivo gel formation is confirmed by injecting an aqueous PEG–PCL–PEG solution (36.0 wt%) into the subcutaneous layer of rats. The gel completely disappears in 21 d. A model polypeptide drug (cyclosporine A) is released over 21 d from the in situ formed gel. The micelle‐based thermogel of PEG–PCL–PEG with ROS‐triggering degradability is a promising injectable material for biomedical applications.
Synergistic Control of Structural Disorder and Surface Bonding Nature to Optimize the Functionality of Manganese Oxide as an Electrocatalyst and a Cathode for Li–O2 BatteriesJin, Xiaoyan; Park, Mihui; Shin, Seung‐Jae; Jo, Yujin; Kim, Min Gyu; Kim, Hyungjun; Kang, Yong‐Mook; Hwang, Seong‐Ju
doi: 10.1002/smll.201903265pmid: 31490620
An efficient way to improve the electrocatalyst and Li–O2 battery performances of metal oxide is developed by an exquisite synergistic control over structural disorder and surface bonding nature. The effects of amorphous nature and surface chemical environment on the functionalities of metal oxide are systematically investigated with well‐crystalline and amorphous MnO2 nanocrystals with/without surface anchoring of highly oxidized iodate clusters. The amorphous MnO2 nanocrystal containing anchored iodate clusters shows much better performance as an oxygen evolution electrocatalyst and cathode catalyst for Li–O2 batteries than both iodate‐free amorphous and well‐crystalline homologues, underscoring the remarkable advantage of simultaneous enhancement of structural disorder and surface electron density. In situ X‐ray absorption spectroscopic analysis demonstrates the promoted formation of double (MnO) bond, a critical step of oxygen evolution reaction, upon amorphization caused by the poor orbital overlap inside highly disordered crystallites. The beneficial effects of iodate anchoring and amorphization on electrocatalyst functionality are attributable to the alteration of surface bonding character, stabilization of Jahn–Teller active Mn3+ species, and enhanced charge transfer of interfaces. The present study underscores that fine‐tuning of structural disorder and surface bonding nature provides an effective methodology to explore efficient metal oxide‐based electrocatalysts.