Current Chinese Science - Volume 1, Issue 1, 2021

Gas sensing materials essentially dominate the performances of the gas sensors which are widely applied in environmental monitoring, industrial production and medical diagnosis. However, most of the traditional gas sensing materials show excellent performances only at high operating temperatures, which are high energy consumptive and have potential issues in terms of reliability and safety of the sensors. Therefore, the development of Room Temperature (RT) gas sensing materials becomes a research hotspot in this field. In recent years, graphene-based materials have been studied as a class of promising RT gas sensing materials because graphene has a unique twodimensional (2D) structure with high electron mobility and superior feasibility of assembling with other “guest components” (mainly small organic molecules, macromolecules and nanoparticles). More interestingly, its electrical properties become even more sensitive toward gas molecules at RT after surface modification. In this review, we have summarized the recently reported graphenebased RT gas sensing materials for the detection of NO2, H2S, NH3, CO2, CO, SO2, Volatile Organic Compounds (VOCs) (i.e. formaldehyde, acetone, toluene, ethanol), as well as Liquefied Petroleum Gas (LPG) and highlighted the latest researches with respect to supramolecular modification of graphene for gas sensing. The corresponding structural features and gas sensing mechanisms of the graphene-based gas sensors have also been generalized.

For decades, the over-exploitation of fossil fuel has made it urgent to develop alternative energy. Photoelectrochemical (PEC) water splitting is a promising approach to generate hydrogen, which is referred to as the fuel of the future due to its high enthalpy of combustion and zero pollution. Though impressive progress has been made over the years, PEC water splitting efficiency is still far from volume production of hydrogen, and more efforts are required to reduce the overpotential, inhibit the yield of hydrogen peroxide by-product, improve the PEC current density, improve light-harvesting capability, and develop low-cost earth-abundant catalysts. Recently, chirality has shown to play a pivotal role in addressing the issues of PEC water splitting via the effect of chiralinduced spin controlling and chiral-enhanced light harvesting. It is high time to pay attention to the art of chirality in promoting water splitting efficiency. Herein, recent progress in this field is reviewed, the approaches to introducing chirality into photo/electronic catalysts for PEC water splitting are summarized, characterization techniques applied in this research field are summed up, the challenges of chirality-enhanced PEC water splitting are discussed, and based on the present achievements, its bright future is anticipated.

Background: Essential Balm (EB) is a commonly used medicine with high volatility and short shelf-life during storage. Objective: Slowing down the volatilization rate of EB and exploring the effect of fiber on the volatilization rate of EB. Methods: In this study, electrospinning technology was used to convert the liquid EB into solid EB in order to improve the balm’s storage and longevity. Results: Specifically, core-sheath nanofibers coated with EB were prepared by traditional coaxial electrospinning technology, in which polyvinylpyrrolidone K90 was used as polymer sheath to reduce the volatilization of EB in the core layer. Scanning electron microscopy images showed that the core-sheath flow rate ratio is proportional to the sizes and number of spindles. EB was successfully placed into the fibers and showed good compatibility with the carriers. Infrared spectroscopy indicated the presence of a hydrogen bond between them. Volatility tests showed that all prepared composites could delay the volatility of EB and improve its physical stability. Conclusion: This methodology can be applied toward increasing the shelf-life of liquid drugs by using core-sheath nanofibers. The core-sheath fibers with good morphology are more propitious to delay the volatilization rate of EB.

Background: Noble-metal nanocrystals have been extensively studied over the past decades because of their unique optical properties. The polyol process is considered an effective method for silver (Ag) nanocrystals’ synthesis in solution even though the reproducibility of its shape controlling is still a challenge. Here, Ag nanowires and nanocubes were synthesized by the polyol process, in which the Ag+ ions are directly reduced by ethylene glycol with a certain amount of Cl− ions added. We present the relationship between the final morphology of the Ag nanostructures with the parameters of reaction, including temperature, growth time, injection rate, and the amount of sodium chloride. The as-synthesized nanowires and nanocubes were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The uniformly distributed nanocubes with a mean edge length of 140 nm were obtained. The localized surface plasmon resonance of Ag nanocubes was characterized by laser scanning fluorescence confocal microscopy. The photoluminescence enhancement was observed on the perovskite film coupled with Ag nanocubes. Objective: We aimed to synthesize uniform and controllable silver nanocubes and nanowires through the polyol process and explore the interaction between CsPbBr3 perovskite film and Ag nanocubes antennas. Methods: We synthesized silver nanocubes and nanowires through the polyol process where the silver nitrate (AgNO3) was reduced by Ethylene Glycol (EG) in the presence of a blocking agent polyvinylpyrrolidone (PVP). Results: We successfully synthesized Ag nanocubes with an average edge length of 140 nm and Ag nanowires with a uniform distribution in terms of both shape and size through a polyol process with sodium chloride (NaCl) as the additive. In addition, the local photoluminescence (PL) enhancement was observed in a perovskite film by combining Ag nanocubes, which is attributed to the antennas plasmonic effect of the Ag nanocubes. Conclusions: In summary we studied the parameters in the polyol process such as reaction temperature, growth time, injection rate, kind of halide ion and NaCl amount for the synthesis of Ag nanowires and nanocubes. Our results suggest that the concentration of Cl- and the growth time have the main influence on Ag nanowires and nanocubes formation. The optimum growth time was found to be 60 min and 120 min for the formation of Ag nanowires and nanocubes, respectively. In addition, we revealed that the opportune reaction temperature of Ag nanowires was 140 °C. The injection rate of precursors was also found to play an important role in the final morphology of Ag nanowires and nanocubes. In addition, for the generation of Ag nanocubes, the presence of Cl− ion in the reaction is critical, which can eliminate most of the byproducts. We obtained the Ag nanowires with a uniform distribution in terms of both shape and size, and nanocubes with average lengths of 140 nm by the polyol process with the optimal parameters. Plasmon-coupled emission induced by noble-metal nanocrystals has attracted more attention in recent years. In this work, the PL of a perovskite film was enhanced by the coupling of Ag nanocubes due to the surface plasmonic effect.

Three polymers containing different numbers of thiophene groups were constructed. Degradation experiments on the aqueous solutions of tetracycline and norfloxacin revealed that the polymer with three thiophene groups in the monomer indicated the best degradation efficiency of 73.7% for tetracycline and 56.9% for norfloxacin. Moreover, this polymer had a relatively stronger ability to separate and transport photocharging carriers under visible light. Therefore, the photocatalytic performance of conjugated polymers could be regulated by changing the number of characteristic groups. Background: Antibiotic residues in the environment are considered as one of the most serious sources of environmental pollution. Although catalyst photodegradation is regarded as the most promising strategy to solve environmental pollution-related problems, it still requires new and advanced photocatalysts. Objective: To design new organic conjugated material structures. Materials and Methods: Three polymers (ThME-1, ThME-2, and ThME-3) were prepared by the condensation of melamine with 2, 5-thiophenedicarboxaldehyde, thieno[3, 2-b]thiophene-2, 5-dicarbaldehyde, and dithieno[3, 2-b:2’, 3’-d]thiophene-2, 6-dicarbaldehyde. The photocatalytic performance of these polymers was investigated by testing their diffused light absorption capacity, photocurrent response, AC impedance, specific surface area, fluorescence, and thermal stability. Results: ThME-3, containing three thiophene groups in the monomer, manifested the best degradation efficiency of 73.7% for tetracycline and 56.9% for norfloxacin. Conclusion: The photocatalytic performance of conjugated polymers could be regulated by changing the number of characteristic groups.

Background: As an advanced design technique, topology optimization has received much attention over the past three decades. Topology optimization aims at finding an optimal material distribution in order to maximize the structural performance while satisfying certain constraints. It is a useful tool for the conceptional design. At the same time, additive manufacturing technologies have provided unprecedented opportunities to fabricate intricate shapes generated by topology optimization. Objective: To design a highly efficient structure using topology optimization and to fabricate it using additive manufacturing. Method: The bi-directional evolutionary structural optimization (BESO) technique provides the conceptional design, and the topology-optimized result is post-processed to obtain smooth structural boundaries. Results: We have achieved a highly efficient and elegant structural design which won the first prize in a national competition in China on design optimization and additive manufacturing. Conclusion: In this paper, we present an effective topology optimization approach to maximize the structural load-bearing capacity and establish a procedure to achieve efficient and elegant structural designs. In the loading test of the final competition, our design carried the highest loading and won the first prize in the competition, which demonstrates the capability of BESO in engineering applications.

Background: The corrosion of steel bar leads to the deterioration of structural behaviors, high cost maintenance, shortened service life. The bridge deck structures constructed by Fiber Reinforced Polymer (FRP) bars and High-Volume Fly Ash-Self-Compacting Concrete (HVFA-SCC) can achieve low energy consumption, sustainable construction and high durability. However, the structural behaviors of this bridge deck are still unclear. Objective: The aim of this paper is to study the structural behaviors, including ultimate loads, failure mode, cracking behavior, deflection and strain of one-way HVFA-SCC slabs reinforced with Glass- FRP (GFRP). Experimental: Eleven full-scale HVFA-SCC slabs, varying in reinforcement diameter, reinforcement ratio, shear-span ratio, the type of reinforcing materials and concrete matrix materials, were tested by using a four-point bending load. Methods: The test results of tested specimens were compared with existing theoretical models, such as crack load, ultimate bearing capacity, maximum crack width, maximum crack space and deflection predicted model. Results: The GFRP reinforced HVFA-SCC slab exhibits similar structural behaviors to the GFRP reinforced NC slab. The maximum crack width of HVFA-SCC slab is significantly increased by using GFRP bars with a diameter of 19 mm. Conclusion: It is concluded that it is feasible to use HVFA-SCC instead of NC combined with GFRP bars in bridge deck structures. The stress limit of concrete materials (0.45fc) is the main governing factor for the service limit state (SLS) of GFRP reinforced HVFA-SCC slabs. The maximum crack width of GFRP reinforced HVFA-SCC slabs can be predicted by using EHE-08 and GB 50608-2010 models.