Carbon nanotubes (CNTs) have been recognised as a promising material in a wide range of applications, from safety to energy-related devices.

Graphene is a single-atom-thick sheet of sp2 hybridized carbon atoms that are packed in a hexagonal honeycomb crystalline structure. This promising structure has endowed graphene with advantages in electrical, thermal, and mechanical properties such as room-temperature quantum Hall effect, long-range ballistic transport with around 10 times higher electron mobility than in Si and thermal conductivity in the order of 5,000 W/mK, and high electron mobility at room temperature (250,000 cm2/V s). Another promising characteristic of graphene is large surface area (2,630 m2/g) which has emerged so far with its utilization as novel electronic devices especially for ultrasensitive chemical sensor and reinforcement for the structural component applications. The application of graphene is challenged by concerns of synthesis techniques, and the modifications involved to improve the usability of graphene have attracted extensive attention. Therefore, in this review, the research progress conducted in the previous decades with graphene and its derivatives for chemical detection and the novelty in performance enhancement of the chemical sensor towards the specific gases and their mechanism have been reviewed. The challenges faced by the current graphene-based sensors along with some of the probable solutions and their future improvements are also being included.

This paper focused on thermal conductivity and viscosity of deionised water and ethylene glycol-based nanofluids at three different temperatures (6C, 25C and 40C). For the preparation of nanofluids, a two-step method, comprised of homogenisation and sonication, was used on a mixture of MWCNT-OH, PVP and the base fluid. The results revealed that thermal conductivity was enhanced by about 8.86% for 0.8 wt% deionised water-based MWCNT-OH nanofluid, and by 5.37% for 0.2 wt% ethylene glycol-based MWCNT-OH nanofluid. Meanwhile, in viscosity test, the highest temperature of 40C exhibited lowest viscosity. This phenomenon happened only with ethylene glycol-based nanofluid, whilst the data on the viscosity of deionised water-based nanofluid was inconsistent at certain nanofluid concentrations . In conclusion, addition of MWCNT-OH into base fluid enhanced base fluid performance , giving it the potential to be used in cooling system applications.

Monitoring environmental hazards and pollution control is vital for the detection of harmful toxic gases from industrial activities and natural processes in the environment, such as nitrogen dioxide (NO2), ammonia (NH3), hydrogen (H2), hydrogen sulfide (H2S), carbon dioxide (CO2), and sulfur dioxide (SO2). This is to ensure the preservation of public health and promote workplace safety. Graphene and its derivatives, especially reduced graphene oxide (rGO), have been designated as ideal materials in gas-sensing devices as their electronic properties highly influence the potential to adsorb specified toxic gas molecules. Despite its exceptional sensitivity at low gas concentrations, the sensor selectivity of pristine graphene is relatively weak, which limits its utility in many practical gas sensor applications. In view of this, the hybridization technique through heterojunction configurations of rGO with metal oxides has been explored, which showed promising improvement and a synergistic effect on the gas-sensing capacity, particularly at room temperature sensitivity and selectivity, even at low concentrations of the target gas. The unique features of graphene as a preferential gas sensor material are first highlighted, followed by a brief discussion on the basic working mechanism, fabrication, and performance of hybridized rGO/metal oxide-based gas sensors for various toxic gases, including NO2, NH3, H2, H2S, CO2, and SO2. The challenges and prospects of the graphene/metal oxide-based based gas sensors are presented at the end of the review.

A major problem being faced by existing coolants is the limited amount of heat that can be absorbed by the fluids. An innovative way to overcome this limitation is by utilizing a nano-coolant as a heat transfer medium in a cooling application. This paper was aimed at formulating an efficient nanofluid from Pyrograf III HHT24 carbon nanofibers (CNF) in a base fluid consisting of deionized water (DI) and ethylene glycol (EG) with polyvinylpyrrolidone (PVP) as the dispersant. The experiment was conducted by setting the variable weight percentage of CNF from 0.1 wt% to 1.0 wt%, with the base fluid ratio of 90:10 (DI:EG) weight percent. Then, the thermal properties of the formulated nanofluids were investigated. The test on the thermal conductivity of the nanofluids showed that the highest thermal conductivity of 0.642 W/m.K in this experiment was produced when the concentration of nanofluid is 0.5 wt% at a temperature of 40°C. Experimental investigations into the forced convective heat transfer performance of the CNF-based nanofluid in a laminar flow through a mini heat transfer test rig showed that the presence of nanoparticles enhanced the heat transfer coefficient as opposed to the original base fluid. The highest heat transfer coefficient was reported using nanofluid with a concentration of 0.6 wt% at 40°C. The enhancement of the heat transfer coefficient was due to the higher thermal conductivity value. The Nusselt number was also calculated and presented in this paper. This study showed that the CNF-based nanofluids have a huge potential to replace existing coolants in electronic cooling applications. Thus, in order to commercialize nanofluids in practice, more fundamental studies are needed to understand the crucial parameters that affect their thermal characteristics.

Non-covalent functionalisation of the carbon nanotube (CNT) sidewall through polymer wrapping is the key strategy for improving well-dispersed CNTs without persistent alteration of their electronic properties. In this work, the effect of reaction time on regioregular poly (3-hexylthiophene-2,5-diyl) (P3HT)-wrapped hydroxylated multi-walled CNT (MWCNT-OH) nanocomposites was investigated. Five different reaction times (24, 48, 72, 96, and 120 h) were conducted at room temperature in order to clearly determine the factors that influenced the quality of wrapped MWCNT-OH. Morphological analysis using Field Emission Scanning Electron Microscopic (FESEM) and High-Resolution Transmission Electron Microscope (HRTEM) analysis showed that P3HT successfully wrapped the MWCNT-OH sidewall, evidenced by the changes in the mean diameter size of the nanocomposites. Results obtained from Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS) as well as Thermogravimetric Analysis (TGA) showed a significant effect of the wrapped polymer on the CNT sidewall as the reaction time increased. Overall, the method used during the preparation of P3HT-wrapped MWCNT-OH and the presented results significantly provided a bottom-up approach to determine the effect of different reaction times on polymer wrapping to further expand this material for novel applications, especially chemical sensors.

In this study, multi-walled carbon nanotubes (MWCNTs) were chemically modified using three acid treatment methods to introduce the surface oxygen functional group (SOFG). The presence of SOFG on the MWCNTs has been characterized by Fourier Transform Infrared (FTIR) spectroscopy. Morphology, structural and thermal properties were performed using Field Emission Scanning Electron Microscopy (FESEM), Raman spectroscopy, and Thermogravimetric analysis (TGA), respectively. The result shows that the modification with acid treatment significantly affects the degree of defects and surface group functionality of surface oxidized MWCNTs from method B. The preparation of nanofluids using MWCNTs produced from method B (MWCNT-MB) was prepared using two different parameters: with and without polyvinylpyrrolidone (PVP) as surfactant. The experiment was conducted by setting variable carbon particle concentration from 0.1 wt.% to 1.0 wt.%, and the amount of PVP is 10% of carbon particles at different temperatures (6 °C, 25 °C, 40 °C). Based on visual observation, the dispersion of carbon particles was enhanced by the presence of PVP as the stabilizing agent. The thermal conductivity performance of nanofluids revealed that the surface oxidized MWCNTs with PVP show enhanced thermal conductivity compared to the nanofluid containing MWCNTs without PVP. The improvement contributes to this in terms of stability and homogenization of nanoparticles. Hence the improved distribution of MWCNTs in water-based media improves thermal conductivity. These promising properties of MWCNTs in water-based fluids would enable the nanofluids to be used in heat transfer fluid and cooling applications.

Oxidation by acid treatment is one of the chemical methods used to introduce surface oxygen functional group (SOFG) and defects on the surface of carbon nanofibers (CNFs). Therefore, many researchers used this method to improve the dispersion ability of CNFs in aqueous media. However, only few researchers used combination of chemical and mechanical method for oxidation of CNFs. In this work, as-received CNFs were treated using chemical method with an addition of mechanical method. On the first experiment (Method A) concentrated sulphuric acid and nitric acid were used and followed by combinations of mechanical method using ultrasonication water bath under reflux. The addition mechanical method through reflux was eliminated and different times of ultrasonication were used in method B and method C. Outer diameter of each CNFs samples were determined from FESEM images and were found to be in range of 50 nm–190 nm. Whereas, Raman spectroscopy was used to analyse any structural defects of CNFs samples during each treatment methods. From the findings, acid treatment of CNFs with addition of mechanical method using ultrasonication showed remarkably effect on the CNFs morphology.