Jingxia Qiu

Low cost and green preparation process for α-Fe2O3@gum arabic electrode for high performance sodium ion batteries

Conventional electrode manufacturing processes for lithium ion batteries involve the use of toxic organic solvents (such as N-methyl-2-pyrrolidone, NMP). A low cost and green preparation process for high performance electrodes for sodium ion batteries (SIBs) is important to address simultaneously the environmental and health risks of production processes and the shortage of lithium metal. Herein, gum arabic (GA), which is a non-toxic biodegradable biopolymer, is used as a water soluble binder to design a water-based electrode preparation process to fabricate α-Fe2O3 electrodes (i.e., α-Fe2O3@GA electrode). The α-Fe2O3@GA electrode demonstrates better mechanical properties and binding capability than that of the α-Fe2O3 electrode with poly(vinylidene fluoride) (PVDF) as the binder (α-Fe2O3@PVDF electrode). Due to these merits, a higher rate and cycling performance of the α-Fe2O3@GA electrode are achieved compared with the α-Fe2O3@PVDF electrode when both electrodes are used for SIBs application. The α-Fe2O3@GA electrode demonstrates high initial discharge and charge capacities of 2437 and 1102 mA h g−1 at the current density of 0.2 A g−1. The α-Fe2O3@GA electrode maintains a high reversible discharge capacity of 492 mA h g−1 at the current density of 5 A g−1 after 500 cycles with a fading rate of 0.08% per cycle after the first cycle, which indicates a superior cycling performance. The outstanding performance of the resultant SIBs suggests that the green fabrication process of the α-Fe2O3@GA electrode would play a critical role in the future battery industry.

Graphitic carbon nitride/BiOCl composites for sensitive photoelectrochemical detection of ciprofloxacin

Ciprofloxacin, as a second generation of fluoroquinolone antibiotics, has been proved to cause environmental harm and exhibits toxic effects on the wastewater and surface water even at low concentrations due to their continuous input and persistence. Despite tremendous efforts, developing ciprofloxacin detection method with accuracy and sensitivity at low-cost remains a great challenge. Herein, graphitic carbon nitride/BiOCl composite (g-CN/BiOCl) has been designed for a facile and sensitive photoelectrochemical (PEC) monitoring platform of ciprofloxacin at first time. BiOCl can be modified with the g-CN nanosheets which are obtained via solvothermal process at low-temperature conditions. The use of g-CN is shown to strongly enhance the PEC response of BiOCl due to the formation of heterojunctions. The photocurrent generated at the g-CN/BiOCl-modified ITO (with 13wt%g-CN content) is much higher and more stable than that of a BiOCl-modified ITO. Based on these findings, the g-CN/BiOCl-modified ITO was used to design a PEC assay for the antibiotic ciprofloxacin. Furthermore, the limit of detection of the ciprofloxacin PEC sensor has been significantly lowered to 0.2ngmL(-1). In addition, the PEC sensor can detect ciprofloxacin in the wide range of 0.5-1840ngmL(-1).

Photoelectrochemical sensing of 4-chlorophenol based on Au/BiOCl nanocomposites.

The Au/BiOCl composites have been prepared by a facile one-pot ethylene glycol (EG) assisted solvothermal reaction in the presence of ionic liquid 1-hexadecyl-3-methylimidazolium chloride ([C16mim]Cl). During the synthesis procedure, the [C16mim]Cl has been used as Cl source, solvent of this system, and dispersing agent to effectively disperse Au on the surface of BiOCl. The as-prepared samples have been systematically characterized by multiple instruments to investigate the structure, morphology, and photoelectrochemical properties. According to the photoelectrochemical data, the Au/BiOCl composites exhibit better photoelectrochemical performance toward the detection of 4-chlorophenol than that of the pure BiOCl. The photocurrent response of Au/BiOCl modified electrode is high and stable under light irradiation. The proposed Au/BiOCl modified electrode shows a wide linear response ranging from 0.16 to 20mgL(-1) with detection limit of 0.05mgL(-1). It indicates a dramatically promising application of bismuth oxyhalides in photoelectrochemical detection. It will be expected that the present study may be lightly extended to the monitor of other organic pollutants by photoelectrochemical detection of the Au/BiOCl composites.

Photoelectrochemical sensing of bisphenol a based on graphitic carbon nitride/bismuth oxyiodine composites

Graphitic carbon nitride/bismuth oxyiodine (g-CN/BiOI) composites with excellent photoelectrochemical (PEC) performance have been designed for a facile and sensitive PEC monitoring platform of bisphenol A (BPA) for the first time. The g-CN/BiOI composites were synthesized by a facile microwave method with 1-butyl-3-methylimidazolium iodine ([Bmim]I) as precursor. The heterojunction comprising g-CN and BiOI has been fabricated. The internal electric field formed at the interface of the heterojunction contributed to the separation of photogenerated electron–hole pairs. Consequently, the g-CN/BiOI composites achieved a greatly improved photocurrent density (∼2-fold) compared to the pure BiOI. In addition, the photocurrent of g-CN/BiOI composites can be further enhanced by introducing BPA into the aqueous solution. The increased photocurrent was applied as the PEC detection signal to trace the concentration of BPA sensitively and effectively. The self-constructed BPA PEC sensor displayed a satisfactory sensing performance with a rapid response, a wide linear range (80–3200 ng mL−1) and a low detection limitation (26 ng mL−1, S/N = 3). Moreover, the BPA PEC sensor exhibited an agreeable anti-interference capacity and outstanding stability, and provided a promising analytical method to detect BPA in the environment.

Hexamethylenetetramine-assisted hydrothermal synthesis of octahedral nickel ferrite oxide nanocrystallines with excellent supercapacitive performance

Octahedral nickel ferrite oxide (NiFe2O4) nanocrystals with average sizes of 81, 69, 63 and 46xa0nm were fabricated using hexamethylenetetramine as adscititious alkali via a facile hydrothermal route at various temperatures. The formation mechanism of octahedral nickel ferrite oxide nanocrystals was discussed in detail. Interestingly, the nanocrystalline size decreased with the increase in the hydrothermal reaction temperature. We studied the influence of hydrothermal temperatures on the evolution of the nanocrystalline and analyzed the relationship between the sizes of the nanocrystalline and their capacitive properties. Compared to the large-sized counterpart (81, 69 and 63xa0nm), the small-sized nanocrystals (46xa0nm) presented a maximum specific capacitance (562.1xa0Fxa0g−1) and remarkable cycling stability (80.3% capacity retention after 1500 cycles) at 4xa0Axa0g−1. The excellent performance of the NiFe2O4 nanocrystals (46xa0nm) was mainly attributed to the unique octahedral nanostructures with a small size (fully exposing more electroactive sites and providing more sufficient expressways for rapid charge transfer) and their compositional advantages of nickel and cobalt (multiple oxidation states for redox reactions and relatively desirable electroconductivity). More remarkably, an asymmetric supercapacitor composed of NiFe2O4 (as the positive electrode) and activated carbon (as the negative electrode) displayed an ultrahigh energy density (34.91xa0Whxa0kg−1 at 1100xa0Wxa0kg−1) and an advanced cycling stability (84.5% capacity retention after 1000 cycles), which suggested that the decreased crystal size played a pivotal role in size-dependent capacitive performance enhancement.

Low-crystalline mesoporous CoFe2O4/C composite with oxygen vacancies for high energy density asymmetric supercapacitors

Recently, nano/micro-scale Fe-based ferrites with high electrochemical performances have attracted extensive attention. However, almost all the mixed Fe-based oxide research paid close attention to the crystalline phase, despite the low-crystalline or amorphous phase possessing excellent electrochemical performance. Herein, a low-crystalline mesoporous cobalt ferrite and carbon composite (L-CoFe2O4/C) material with high surface area and superior electrical conductivity was prepared via a simple citric acid assisted sol–gel approach and calcination process. The L-CoFe2O4/C electrode exhibits an unprecedented specific capacitance (600 F g−1 at 1 A g−1), which precedes some of the reported mixed Fe-based ferrite electrodes and their crystalline counterparts. The excellent electrochemical performance can mainly be attributed to the sufficient diffusion and reaction of electrolyte ions, more surface defects (e.g. oxygen vacancies) for redox reactions, and the predominant electro-conductivity of the composite during the charging/discharging process. Moreover, an L-CoFe2O4/C-based asymmetric supercapacitor exhibited high energy density and power density, and outperformed most of the reported mixed Fe-based symmetric and asymmetric supercapacitors. These findings promote new opportunities for low-crystalline Fe-based metal oxides as high performance energy storage devices.

Pseudocapacitive performance of binder-free nanostructured TT-Nb2O5/FTO electrode in aqueous electrolyte

TT-Nb2O5 nanoparticles grown on electrically conducting fluorine-doped tin oxide (FTO) glass were successfully synthesized by a facile one-pot hydrothermal method at low temperature. The as-prepared nanostructured TT-Nb2O5/FTO was directly used as the working electrode to investigate its pseudocapacitive performance without any binder or conductive agent, which exhibited a high specific capacitance of 322 F g-1 at a current density of 3.68 A g-1, excellent rate capability (258.1 F g-1 at a high scan rate of 100 mV s-1 is about 91.6% of that at 5 mV s-1), and good cycling stability (the capacitance retention is 74.3% after 3000 cycles). More importantly, it is the first time electrochemical measurements for Nb2O5 electrode in aqueous electrolyte, which are low-cost and easy to operate, have been carried out.

Interfacial self-assembly of monolayer Mg-doped NiO honeycomb structured thin film with enhanced performance for gas sensing

The relatively low sensitivity, slow response and complicated or energy consuming preparation processes of NiO-based sensors greatly restrict their further application. In this work, monolayer Mg-doped NiO thin film was fabricated via an interfacial self-assemble strategy and a subsequent annealing process. Polystyrene spheres with diameters of about 700xa0nm were used as templates. The as-prepared monolayer Mg-doped NiO thin film presents a honeycomb structure. The film formation process and possible sensing mechanism of the honeycomb structured Mg-doped NiO thin film are also discussed. Moreover, the film-based gas sensor presents a high selectivity to ethanol gas against other gases. The response ratio of the Mg-doped NiO film sensor to 100xa0ppm ethanol is 10.4 at 325xa0°C. This ratio is also much better than some of the previously reported values in literatures. Furthermore, the Mg-doped NiO sensor also shows a significantly enhanced sensing properties in terms of higher selectivity, faster response and recovery time than our honeycomb structured pure NiO thin film. The remarkable properties may be attributed to the honeycomb structure and the Mg doping, which produce more active sites for the gas reaction and adsorption on the surface of the sensing materials. This facile fabrication strategy can be further utilized to prepare other monolayer metal oxide film-based devices.