## Current Issue 2020, Volume 33,  Issue 3

column
2020, 33(3): i-iv.
2020, 33(3): v-vi.
Microbial electrolysis cells (MECs) present an attractive route for energy-saving hydrogen (H2) production along with treatment of various wastewaters, which can convert organic matter into H2 with the assistance of microbial electrocatalysis. However, the development of such renewable technologies for H2 production still faces considerable challenges regarding how to enhance the H2 production rate and to lower the energy and the system cost. In this review, we will focus on the recent research progress of MEC for H2 production. First, we present a brief introduction of MEC technology and the operating mechanism for H2 production. Then, the electrode materials including some typical electrocatalysts for hydrogen production are summarized and discussed. We also highlight how various substrates used in MEC affect the associated performance of hydrogen generation. Finally we presents several key scientific challenges and our perspectives on how to enhance the electrochemical performance.
Metallophilic interaction is a unique type of weak intermolecular interaction, where the electronic configuration of two metal atoms is closed shell. Despite its significance in multidisciplinary fields, the nature of metallophilic interaction is still not well understood. In this work, we investigated the electronic structures and bonding characteristic of bimetallic Au$_{2}$@Cu$_{6}$ nanocluster through density functional theory method, which was reported in experiments recently [Angew. Chem. Int. Ed. 55 , 3611 (2016)]. In general thinking, interaction between two moieties of (CuSH)$_{6}$ ring and (Au$_{2}$PH$_{3}$)$_{2}$ in the Au$_{2}$@Cu$_{6}$ nanocluster can be viewed as a d$^{10}$-$\sigma$ closed-shell interaction. However, chemical bonding analysis shows that there is a ten center-two electron (10c-2e) multicenter bonding between two moieties. Further comparative studies on other bimetallic nanocluster M$_{2}$@Cu$_{6}$ (M = Ag, Cu, Zn, Cd, Hg) also revealed that multicenter bonding is the origin of electronic stability of the complexes besides the d$^{10}$-$\sigma$ closed-shell interaction. This will provide valuable insights into the understanding of closed-shell interactions.
The dielectric properties between in-particle/water interface and bulk solution are significantly different, which are ignored in the theories of surface potential estimation. The analytical expressions of surface potential considering the dielectric saturation were derived in mixed electrolytes based on the nonlinear Poisson-Boltzmann equation. The surface potentials calculated from the approximate analytical and exact numerical solutions agreed with each other for a wide range of surface charge densities and ion concentrations. The effects of dielectric saturation became important for surface charge densities larger than 0.30 C/m$^2$. The analytical models of surface potential in different mixed electrolytes were valid based on original Poisson-Boltzmann equation for surface charge densities smaller than 0.30 C/m$^2$. The analytical model of surface potential considering the dielectric saturation for low surface charge density can return to the result of classical Poisson-Boltzmann theory. The obtained surface potential in this study can correctly predict the adsorption selectivity between monovalent and bivalent counterions.
A superamphiphobic (SAP) surface was fabricated by electrodepositing Cu-Ni micro-nano particles on aluminum substrate and modifying via 1H, 1H, 2H, 2H-perfluorodecyltrimethoxysilane. Scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy were employed to investigate the morphology and chemical composition. The results showed that the SAP surface had three-dimensional micro-nano structures and exhibited a maximum water contact angle of 160.0$^{\circ}$, oil contact angle of 151.6$^{\circ}$, a minimum water slide angle of 0$^{\circ}$ and oil slide angle of 9$^{\circ}$. The mechanical strength and chemical stability of the SAP surface were tested further. The experimental results showed that the SAP surface presented excellent resistance to wear, prominent acid-resistance and alkali-resistance, self-cleaning and anti-fouling properties.
In view of the high activity of Pt single atoms in the low-temperature oxidation of CO, we investigate the adsorption behavior of Pt single atoms on reduced rutile TiO$_2$(110) surface and their interaction with CO and O$_2$ molecules using scanning tunneling microscopy and density function theory calculations. Pt single atoms were prepared on the TiO$_2$(110) surface at 80 K, showing their preferred adsorption sites at the oxygen vacancies. We characterized the adsorption configurations of CO and O$_2$ molecules separately to the TiO$_2$-supported Pt single atom samples at 80 K. It is found that the Pt single atoms tend to capture one CO to form Pt-CO complexes, with the CO molecule bonding to the fivefold coordinated Ti (Ti$_{5 \rm{c}}$) atom at the next nearest neighbor site. After annealing the sample from 80 K to 100 K, CO molecules may diffuse, forming another type of complexes, Pt-(CO)$_2$. For O$_2$ adsorption, each Pt single atom may also capture one O$_2$ molecule, forming Pt-O$_2$ complexes with O$_2$ molecule bonding to either the nearest or the next nearest neighboring Ti$_{5 \rm{c}}$ sites. Our study provides the single-molecule-level knowledge of the interaction of CO and O$_2$ with Pt single atoms, which represent the important initial states of the reaction between CO and O$_2$.
Polydiacetylene (PDA) is one kind of the conjugated polymer with layered structure, which can serve as a host to accommodate the guest components through intercalation. In these intercalated PDAs, some of them were reported to have a nearly perfect organized structure and perform completely reversible thermochromism. Till now, these reported intercalated PDAs were made by only introducing a single component for intercalation. Here, we chose 10, 12-pentacosadiynoic acid (PCDA) as the monomer, of which the carboxyl-terminal groups can interact with either Tb$^{3+}$ ions or melamines (MAs). When the feeding molar ratio of PCDA, MA, and Tb$^{3+}$ ion was 3:267:1, only Tb$^{3+}$ ions were intercalated though excess MAs existed. Such Tb$^{3+}$-intercalated poly-PCDA exhibited completely reversible thermochromism, where almost all the carboxyl groups interacted with Tb$^{3+}$ ions to form the nearly perfect structure. When the feeding molar ratio of PCDA, MA, and Tb$^{3+}$ ion was 3:267:0.6, both Tb$^{3+}$ ions and MAs were intercalated. There existed some defects in the imperfect MA-intercalated domains and at the domain boundaries. The MA/Tb$^{3+}$-intercalated poly-PCDA exhibits partially reversible thermochromism, where the backbones near the defects are hard to return the initial conformation, while the rest, those at nearly perfect organized domains, are still able to restore the initial conformation.
In recent years, flexible pressure sensors have attracted much attention owing to their potential applications in motion detection and wearable electronics. As a result, important innovations have been reported in both conductive materials and the underlying substrates, which are the two crucial components of a pressure sensor. 1D materials like nanowires are being widely used as the conductive materials in flexible pressure sensors, but such sensors usually exhibit low performances mainly due to the lack of strong interfacial interactions between the substrates and 1D materials. In this paper, we report the use of graphene/graphene scrolls hybrid multilayers films as the conductive material and a micro-structured polydimethylsiloxane substrate using Epipremnum aureum leaf as the template to fabricate highly sensitive pressure sensors. The 2D structure of graphene allows to strongly anchor the scrolls to ensure the improved adhesion between the highly conductive hybrid films and the patterned substrate. We attribute the increased sensitivity (3.5 kPa$^{-1}$), fast response time ($<$50 ms), and the good reproducibility during 1000 loading-unloading cycles of the pressure sensor to the synergistic effect between the 1D scrolls and 2D graphene films. Test results demonstrate that these sensors are promising for electronic skins and motion detection applications.
One simple and environmental friendly synthesis strategy for preparing low-cost magnetic Fe$_3$C@C materials has been facilely developed using a modified sol-gel approach, wherein natural magnetite acted as the iron source. A chelating polycarboxylic acid such as citric acid (CA) was employed as the carbon source, and it dissolved Fe very effectively, Fe$_3$O$_4$ and natural magnetite to composite an iron-citrate complex with the assistance of ammonium hydroxide. The core-shell structure of the as-prepared nanocomposites was formed directly by high-temperature pyrolysis. The Fe$_3$C@C materials exhibited superparamagnetic properties (38.09 emu/mg), suggesting potential applications in biomedicine, environment, absorption, catalysis, etc.
Smart nanoparticles that respond to pathophysiological parameters, such as pH, GSH, and H$_2$O$_2$, have been developed with the huge and urgent demand for the high-efficient drug delivery systems (DDS) for cancer therapy. Herein, cubic poly(ethylene glycol) (PEG)-modified mesoporous amorphous iron oxide (AFe) nanoparticles (AFe-PEG) have been successfully prepared as pH-stimulated drug carriers, which can combine doxorubicin (DOX) with a high loading capacity of 948 mg/g, forming a novel multifunctional AFe-PEG/DOX nanoparticulate DDS. In an acidic microenvironment, the AFe-PEG/DOX nanoparticles will not only release DOX efficiently, but also release Fe ions to catalyze the transformation of H$_2$O$_2$ to $\cdot$OH, acting as fenton reagents. In vitro experimental results proved that the AFe-PEG/DOX nanoparticles can achieve combination of chemotherapeutic (CTT) and chemodynamic therapeutic (CDT) effects on Hela tumor cells. Furthermore, the intrinsic magnetism of AFe-PEG/DOX makes its cellular internalization efficiency be improved under an external magnetic field. Therefore, this work develops a new and promising magnetically targeted delivery and dual CTT/CDT therapeutic nano-medicine platform based on amorphous iron oxide.