Application of membrane filters in determination of the adsorption of tetracycline hydrochloride on graphene oxide

This paper shows the use of membrane filters in adsorption of solution of tetracycline hydrochloride on graphene materials. The adsorption process was monitored at different wavelengths, different pH values ​​at certain time intervals.

The absorbances of the solutions were measured by UV-Vis spectrophotometry at two wavelengths (275 nm and 356 nm), and three pH values (pH 4, pH 7 and pH 10) every 90 minutes for 6 hours of monitoring, with constant stirring in an ultrasonic bath.

The results showed decrease in absorbance at both wavelength and in all three pH values which proved the adsorption of tetracycline hydrochloride on GO and rGO. The largest decrease in absorbance was 98.1%. The most suitable pH value for adsorption was pH 4.

This paper used a unique approach to filtration through membrane filters, which in the future could lead to the development of membrane filters based on graphene materials.

Boosting Supercapacitor Performance of Graphene by Coupling with Nitrogen-Doped Hollow Carbon Frameworks

Graphene as a suitable electrode has been extensively used for electrochemical double-layer capacitors based on its excellent properties, including high electrical conductivity and large specific surface area. However, one of the drawbacks is the unavoidable stacking tendency between the graphene nanosheets, resulting in limited electrochemically specific surface area. Herein, novel graphene nanosheets supported by hollow nitrogen-doped carbon frameworks derived from ZIF-8 (GPNC) were fabricated through a simple polyethyleneimine (PEI)-assisted pyrolysis strategy, to boost capacitance performance. Benefiting from the unique scaffold/support role of hollow nitrogen-doped carbon frameworks within the graphene interlayer, the GPNC with a large specific surface area, along with ample micropore/mesopore channels and high nitrogen content, is capable of facilitating electron and electrolyte ion migration kinetics and enhancing intrinsic electrochemical activity. Thus, the GPNC exhibits the highest charge storage of 218 F g^-1 and superior rate capability of 74 % when the current density increased from 0.5 to 20 Ag^-1 in comparison to pristine graphene and common ZIF-derived carbon/graphene electrodes. The assembled GPNC//GPNC two-electrode system further delivers a maximum power of 9080 Wkg^-1 with outstanding electrochemical retention of 84 % over 10 000 cycles.

Performance-Enhanced Activated Carbon Electrodes for Supercapacitors Combining Both Graphene-Modified Current Collectors and Graphene Conductive Additive

Graphene has been widely used in the active material, conductive agent, binder or current collector for supercapacitors, due to its large specific surface area, high conductivity, and electron mobility. However, works simultaneously employing graphene as conductive agent and current collector were rarely reported. Here, we report improved activated carbon (AC) electrodes (AC@G@NiF/G) simultaneously combining chemical vapor deposition (CVD) graphene-modified nickel foams (NiF/Gs) current collectors and high quality few-layer graphene conductive additive instead of carbon black (CB). The synergistic effect of NiF/Gs and graphene additive makes the performances of AC@G@NiF/G electrodes superior to those of electrodes with CB or with nickel foam current collectors. The performances of AC@G@NiF/G electrodes show that for the few-layer graphene addition exists an optimum value around 5 wt %, rather than a larger addition of graphene, works out better. A symmetric supercapacitor assembled by AC@G@NiF/G electrodes exhibits excellent cycling stability. We attribute improved performances to graphene-enhanced conductivity of electrode materials and NiF/Gs with 3D graphene conductive network and lower oxidation, largely improving the electrical contact between active materials and current collectors.

Chemically Activated Covalent Triazine Frameworks with Enhanced Textural Properties for High Capacity Gas Storage

Chemical activation of porous/nonporous materials to achieve high surface area sorbents with enhanced textural properties is a very promising strategy. The chemical activation using KOH, however, could lead to broad distribution of pores originating from the simultaneous pore deepening and widening pathways. Accordingly, establishing correlation between the chemical/textural properties of starting porous/nonporous materials and various pore formation mechanisms is quite critical to realize superior porosity and gas uptake properties. Here, we show that the chemical and textural properties of starting porous organic polymers, that is, covalent triazine frameworks (CTF), have profound effect on the resulting porosity of the frameworks. The chemical activation of microporous CTF-1 using KOH at 700 °C enabled the preparation of chemically activated CTF-1, caCTF-1-700, which predominantly showed pore deepening, leading to an increased surface area of 2367 m² g^-1 and significantly enhanced gas adsorption properties with CO₂ uptake capacities up to 6.0 mmol g^-1 at 1 bar and 1.45 mmol g^-1 at 0.15 bar and 273 K along with a isosteric heats of adsorption (Q_st) of 30.6 kJ mol^-1. In addition, a remarkable H₂ uptake capacity of 2.46 and 1.66 wt % at 77 and 87 K, 1 bar along with the Q_st value of 10.95 kJ mol^-1 at zero coverage was also observed for the caCTF-1-700. Notably, the activation of mesoporous CTF-2 under the same conditions was accompanied by a decrease in its surface area and also in the conversion of mesopores into the micropores, thus leading to a pore deepening/narrowing rather than widening. We attributed this result to the presence of reactive weak spots, triazine moieties, for the chemical activation reaction within the CTF backbone. These results collectively suggest the critical role of chemical and pore characteristics of porous organic polymers in chemical activation to realize solid-sorbents for high capacity gas storage applications.

Chlorine-doped reduced graphene oxide nanosheets as an efficient and stable electrode for supercapacitor in acidic medium

We demonstrate the efficient doping of reduced graphene oxide (RGO) by Chlorine and its capacitive performance was calculated by cyclic voltammetry and charge-discharge cycling in 1M H2SO4 solution. In this regard, we are prepared RGO nanosheets through a simple, eco-friendly and efficient electrochemical method, with selectively functionalized edges by chlorine which involves added the RGO to the halogen-containing acid solution and dispersed by ultrasonic. After synthesis, Cl-RGO is characterized using X-ray diffraction, Raman spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, Energy-dispersive X-ray (EDX) spectroscopy and tunneling electron microscopy. FTIR spectra show the chlorine-containing functional groups. Energy-dispersive X-ray spectroscopy analysis confirmed the presence of doped chlorine in RGO. Raman spectroscopy shows a high density of defects in the RGO layer. Electrochemical characteristics of Cl-RGO are characterized by cyclic voltammetery, galvanostatic charge/discharge and electrochemical impedance spectroscopy. According to the galvanostatic charge/discharge analysis, Cl-RGO represents specific capacitance (Cs) of 178.4Fg(-1) at current density of 1Ag(-1), which is higher than that of RGO (100.5Fg(-1)) in H2SO4 solution.

Facile one-pot synthesis and application of nitrogen and sulfur-doped activated graphene in simultaneous electrochemical determination of hydroquinone and catechol

A high sensitivity sensor for detection of hydroquinone and catechol was constructed based on nitrogen and sulfur co-doped activated graphene.

Doped graphene supercapacitors

Heteroatom-doped graphitic frameworks have received great attention in energy research, since doping endows graphitic structures with a wide spectrum of properties, especially critical for electrochemical supercapacitors, which tend to complement or compete with the current lithium-ion battery technology/devices. This article reviews the latest developments in the chemical modification/doping strategies of graphene and highlights the versatility of such heteroatom-doped graphitic structures. Their role as supercapacitor electrodes is discussed in detail. This review is specifically focused on the concept of material synthesis, techniques for electrode fabrication and metrics of performance, predominantly covering the last four years. Challenges and insights into the future research and perspectives on the development of novel electrode architectures for electrochemical supercapacitors based on doped graphene are also discussed.

Nitrogen-Doped Carbon Nanotube Spherical Particles for Supercapacitor Applications: Emulsion-Assisted Compact Packing and Capacitance Enhancement

The combination of the control of CNT assembly density and the control of intrinsic carbon properties by doping can synergistically improve the supercapacitor performance of CNT-based electrodes. We prepared a dense-packed CNT spherical assembly via emulsion-assisted evaporation and subsequently conducted nitrogen (N) doping to make CNT-based supercapacitors. The assembly of CNT spherical particles is applied as the supercapacitor electrode. We control the N doping content and obtain a specific capacity of 215 F/g at a current density of 0.2 A/g, which is 3.1 times higher than that of the untreated sample. The enhancement stems from high pseudocapacitance and high electrical conductivity that result from the N doping of the CNT assembly. In a comparison of the specific capacitance of N-CNT spherical particles with that of the CNT films prepared by conventional solution-coating, we found that N-CNT samples display a capacitance that is 1.8 times higher, thus confirming the morphological advantage provided by the CNT packing and the hierarchical porous structure in the CNT particle assembly. Our approach allows a facile and high throughput production of high performance electrodes based on CNTs that are commercially available. Moreover, our approach can be extended to produce spherical particles consisting of other nanostructured carbon materials and their composites.