The viscosity of dilute carbon nanotube (1D) and graphene oxide (2D) nanofluids

An ultra-sensitive ammonia sensor based on a quartz crystal microbalance using nanofibers overlaid with carboxylic group-functionalized MWCNTs

Detecting ammonia at low concentrations is crucial in various fields, including environmental monitoring, industrial processes, and healthcare. This study explores the development and performance of an ultra-sensitive ammonia sensor using carboxylic group-functionalized multi-walled carbon nanotubes (f-MWCNTs) overlaid on polyvinyl acetate nanofibers coated on a quartz crystal microbalance (QCM). The sensor demonstrates high responsiveness, with a frequency shift response of over 120 Hz when exposed to 1.5 ppm ammonia, a sensitivity of 23.3 Hz ppm-1 over a concentration range of 1.5-7.5 ppm, and a detection limit of 50 ppb. Additionally, the sensor exhibits a rapid response time of only 14 s, excellent selectivity against other gases, such as acetic acid, formaldehyde, methanol, ethanol, propanol, benzene, toluene, and xylene, and good stability in daily use. These characteristics make the sensor a promising tool for real-time ammonia detection in diverse applications.

Decisive role of electrostatic interaction in rheological evolution of graphene oxide under ultrasonic fragmentation

The aqueous dispersibility and processability of graphene oxide (GO) are pivotal for various applications, including the fluid assembly of macroscopic materials and nanofluidic systems. Despite the widespread utilization of ultrasonic treatment to achieve homogeneous dispersions, the rheological changes of GO during sonication have remained relatively unexplored, leading to conflicting research findings. In this study, we demonstrate that the viscoelastic evolution of GO can significantly differ under ultrasonic fragmentation depending on the balance between repulsion force and attraction force at the initial state before fragmentation. When electrostatic repulsion is in delicate equilibrium with attractive forces, gelation occurs under ultrasonic fragmentation, leading to increased viscosity under sonication. Conversely, when electrostatic repulsion predominates, viscosity decreases during sonication. This study reconciles conflicting observations on the rheological evolution of GO dispersions under ultrasonic fragmentation and provides valuable guidance and insights for the rheological engineering of GO colloidal systems.

Study of molar properties of GO after doping with transition metals for photodegradation of fluorescent dyes

We synthesized graphene oxide (GO) doped with transition metal ions and characterized it using XPS, FT-IR, TGA/DTG, XRD, SEM, AFM, ICP-OES, UV/vis, and Raman spectroscopy. An intrinsic viscosity [η] of 0.002-0.012 g% @ 0.002 aq-GO was determined for viscosity average molecular weight (M _v) of GO at 288.15, 298.15, and 308.15 K. Mark-Houwink (M-H) constants k (cm³ g^-1) and a (cm³ mol g^-2) were calculated for 5-15 mg/100 mL polyvinylpyrrolidone (PVP), using 29, 40, 55 kg mol^-1 as markers for calculating M _v by fitting the [η] to the Mark-Houwink-Sakurada equation (MHSE). We obtained 48 134.19 g mol^-1 M _v at 298.15 K, and the apparent molar (V _{ϕ m} , cm³ mol^-1), limiting molar volumes (V ⁰ _GO)_GO⃑0, enthalpy (ΔH _m, J mol^-1), entropy (ΔS _m, J mol^-1 K^-1), viscosity (η _m, mPa s mol^-1), surface tension (γ _m, mN m^-1 mol^-1), friccohesity (σ _m, scm^-1 mol^-1), fractional volume (ϕ _m, cm³ mol^-1), isentropic compressibility (K _sϕ,m, 10^-4 cm s² g^-1 mol), infer GO molar consistency throughout the chemical processes. Molar properties (MPs) infer a GO monodispersion producing negative electrons (e^-) and positive holes (h⁺) under sunlight. The transition metal ions (Fe²⁺, Mn²⁺, Ni²⁺, Cr³⁺, TMI) doped onto GO (TMI-GO), can photodegrade methylene blue (MB) in 60 min compared with 120 min using GO alone. The 4011 C atoms, 688 hexagonal sheets, 222 π-conjugations, and 4011 FE were calculated from the 48 134.19 g mol^-1. The functional edges are the negative and positive holes generating centres of the GO 2D sheets.

The adsorption of NO2, SO2, and O3 molecules on the Al-doped stanene nanotube: a DFT study

Adsorption of pollutant gas molecules (NO₂, SO₂, and O₃) on the surface of the Al-doped stanene nanotube was investigated within the first principle calculations of density functional theory (DFT). Adsorption mechanisms were studied by analyzing optimized structures, band structures, projected density of states (PDOS), charge density difference (CDD), molecular orbitals, and band theory. Investigation of charge transfer by Mulliken population showed that NO₂ accumulated while SO₂ and O₃ depleted charge density on the Al-doped nanotube. The differences in band structures before and after adsorption implied that the electronic characteristics of Al-doped nanotube changed dramatically in case of NO₂ adsorption, which converted Al-doped nanotube to a semiconductor material. High adsorption energy and the significant overlap between PDOS spectra indicated that the adsorption process was chemisorption for NO₂, SO₂, and O₃ on the doped nanotube with the obtained order of O₃ > SO₂ > NO₂. The results showed that the adsorption of NO₂, SO₂, and O₃ occurred on the Al-doped stanene nanotube, and that all the three gas molecules could be detected by Al-doped stanene nanotube with various detection strengths.

Graphene-Based Nanofluids: Production Parameter Effects on Thermophysical Properties and Dispersion Stability

In this study, the thermophysical properties and dispersion stability of graphene-based nanofluids were investigated. This was conducted to determine the influence of fabrication temperature, nanomaterial concentration, and surfactant ratio on the suspension effective properties and stability condition. First, the nanopowder was characterized in terms of crystalline structure and size, morphology, and elemental content. Next, the suspensions were produced at 10 °C to 70 °C using different concentrations of surfactants and nanomaterials. Then, the thermophysical properties and physical stability of the nanofluids were determined. The density of the prepared nanofluids was found to be higher than their base fluid, but this property showed a decrease with the increase in fabrication temperature. Moreover, the specific heat capacity showed very high sensitivity toward the graphene and surfactant concentrations, where 28.12% reduction in the property was achieved. Furthermore, the preparation temperature was shown to be the primary parameter that effects the nanofluid viscosity and thermal conductivity, causing a maximum reduction of ~4.9% in viscosity and ~125.72% increase in thermal conductivity. As for the surfactant, using low concentration demonstrated a short-term stabilization capability, whereas a 1:1 weight ratio of graphene to surfactant and higher caused the dispersion to be physically stable for 45 consecutive days. The findings of this work are believed to be beneficial for further research investigations on thermal applications of moderate temperatures.

Carbon-Based Nanofluids and Their Advances towards Heat Transfer Applications-A Review

Nanofluids have opened the doors towards the enhancement of many of today's existing thermal applications performance. This is because these advanced working fluids exhibit exceptional thermophysical properties, and thus making them excellent candidates for replacing conventional working fluids. On the other hand, nanomaterials of carbon-base were proven throughout the literature to have the highest thermal conductivity among all other types of nanoscaled materials. Therefore, when these materials are homogeneously dispersed in a base fluid, the resulting suspension will theoretically attain orders of magnitude higher effective thermal conductivity than its counterpart. Despite this fact, there are still some challenges that are associated with these types of fluids. The main obstacle is the dispersion stability of the nanomaterials, which can lead the attractive properties of the nanofluid to degrade with time, up to the point where they lose their effectiveness. For such reason, this work has been devoted towards providing a systematic review on nanofluids of carbon-base, precisely; carbon nanotubes, graphene, and nanodiamonds, and their employment in thermal systems commonly used in the energy sectors. Firstly, this work reviews the synthesis approaches of the carbon-based feedstock. Then, it explains the different nanofluids fabrication methods. The dispersion stability is also discussed in terms of measuring techniques, enhancement methods, and its effect on the suspension thermophysical properties. The study summarizes the development in the correlations used to predict the thermophysical properties of the dispersion. Furthermore, it assesses the influence of these advanced working fluids on parabolic trough solar collectors, nuclear reactor systems, and air conditioning and refrigeration systems. Lastly, the current gap in scientific knowledge is provided to set up future research directions.

Porous Graphene Composite Polymer Fibres

Since the isolation of graphene, there have been boundless pursuits to exploit the many superior properties that this material possesses; nearing the two-decade mark, progress has been made, but more is yet to be done for it to be truly exploited at a commercial scale. Porous graphene (PG) has recently been explored as a promising membrane material for polymer composite fibres. However, controlling the incorporation of high surface area PG into polymer fibres remain largely unexplored. Additionally, most polymer-graphene composites suffer from low production rates and yields. In this paper, graphene-loaded microfibres, which can be produced at a very high rate and yield have been formed with a carrier polymer, polycaprolactone. For the first time, PG has been incorporated into polymer matrices produced by a high-output manufacturing process and analysed via multiple techniques; scanning electron microscopy (SEM), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Raman spectra showed that single layer graphene structures were achieved, evidence for which was also backed up by the other techniques. Fibres with an average diameter ranging from 3-8 μm were produced with 3-5 wt% PG. Here, we show how PG can be easily processed into polymeric fibres, allowing for widespread use in electrical and ultrafiltration systems.

Carbon Nanotube Film Electrodes with Acrylic Additives: Blocking Electrochemical Charge Transfer Reactions

Carbon nanotubes (CNTs) processed into conductive films by liquid phase deposition technologies reveal increasing interest as electrode components in electrochemical device platforms for sensing and energy storage applications. In this work we show that the addition of acrylic latex to water-based CNT inks not only favors the fabrication of stable and robust flexible electrodes on plastic substrates but, moreover, sensitively enables the control of their electrical and electrochemical transport properties. Importantly, within a given concentration range, the acrylic additive in the films, being used as working electrodes, effectively blocks undesired faradaic transfer reactions across the electrode-electrolyte interface while maintaining their capacitance response as probed in a three-electrode electrochemical device configuration. Our results suggest a valuable strategy to enhance the chemical stability of CNT film electrodes and to suppress non-specific parasitic electrochemical reactions of relevance to electroanalytical and energy storage applications.