Heterojunctions of rGO/metal oxide nanocomposites as promising gas-sensing materials—A review

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

Effect of reaction time on the structure and optical properties of P3HT/MWCNT-OH nanocomposites

In the present study, regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) coated hydroxylated multi-walled carbon nanotubes (MWCNT-OH) nanocomposites were prepared over different reaction times of non-covalent functionalization. The reaction time was set as 24, 48, 72, 96, and 120 hours. The structure and optical characteristics of nanocomposites were analyzed using Fourier-transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectroscopy, respectively. Reaction time affected prepared nanocomposites by decreasing the intensity of the P3HT/MWCNT-OH peaks gradually with increasing of the reaction time. Comparing with the pure P3HT and MWCNT-OH, the calculated energy band gap and the Urbach energy of the nanocomposites were reduced proportionally as the reaction time reached 120 hours and achieved 2.60 and 0.329 eV, respectively

Carbon Nanotubes: Functionalisation And Their Application In Chemical Sensors

Carbon nanotubes (CNTs) have been recognised as a promising material in a wide range of applications, from safety to energy-related devices. However, poor solubility in aqueous and organic solvents has hindered the utilisation and applications of carbon nanotubes. As studies progressed, the methodology for CNTs dispersion was established. The current state of research in CNTs either single wall or multiwall/polymer nanocomposites has been reviewed in context with the various types of functionalisation presently employed. Functionalised CNTs have been playing an increasingly central role in the research, development, and application of carbon nanotube-based nanomaterials and systems. The extremely high surface-to-volume ratio, geometry, and hollow structure of nanomaterials are ideal for the adsorption of gas molecules. This offers great potential applications, such as in gas sensor devices working at room temperature. Particularly, the advent of CNTs has fuelled the invention of CNTbased gas sensors which are very sensitive to the surrounding environment. The presence of O2, NH3, NO2 gases and many other chemicals and molecules can either donate or accept electrons, resulting in an alteration of the overall conductivity. Such properties make CNTs ideal for nano-scale gas-sensing materials. Conductive-based devices have already been demonstrated as gas sensors. However, CNTs still have certain limitations for gas sensor application, such as a long recovery time, limited gas detection, and weakness to humidity and other gases. Therefore, the nanocomposites of interest consisting of polymer and CNTs have received a great deal of attention for gas-sensing application due to higher sensitivity over a wide range of gas concentrations at room temperature compared to only using CNTs and the polymer of interest separatel

Thermo-electrical and mechanical studies on polymer-organically modified montmorillonite composites / Norhana Abdul Halim

The field of polymer-nanoclay composite has attracted a lot of attention in materials studies due to the dramatic improvement on polymers characteristics. For example mechanical and thermal properties, chemical resistance as well as the reduced gas permeability. However, structural changes and the mechanisms that may contribute to these improvements are not fully understood. In this work, the study on polymer nanoclay composite concentrates on the effects of OMON inclusion within different polymer matrix systems. The matrixes are a series of natural rubbers (Standard Malaysia Rubber – Latex grade (SMRL); Deproteinized Natural Rubber (DPNR) and Epoxidized Natural Rubber (ENR-50)), plasticized Polyvinyl chloride (pPVC) and Polyethylene (PE). OMON is a renewed Montmorillonite (Mon) clay mineral, where chemical modifications carried out had changed the organophobic property of this mineral into organophylic. XRD analyses demonstrate the intercalation of polymeric chains, showing the increase in OMON basal spacing d001 from 1.840 nm to 3.864 nm. From the FTIR spectra of polymer-OMON composites, matrix-OMON silicates interaction is shown with the appearance of (Si-O-R) band and the changes in SiH (SiH and SiH) vibrations. Investigation on the improved matrix-OMON interactions within polymer-OMON composites concentrates on their thermo-electrical and mechanical responses. TSC measurement is chosen to carry out the thermo-electrical studies, which involves instrumentation of TSC system. The high sensitivity of TSC technique is capable to detect various dipoles and space charges relaxations, as shown with the emergence of , and peaks. Observations and analyses on and OMON peaks reveal the effects of matrix-alkyl and matrix-silicate interactions on methylene groups (CH2) and alkyl chains (CH2)n within OMON gallery in the composites. Decomposition on TSC peaks confirm the involvement of various distributed relaxation processes. It also reveals the existence of molecular-ion deep traps with high activation energy E (> 4eV). Analyses on pre-exponential factor n from N-fitting method distinguish a range of dipole relaxations. It gives characteristic relaxation time n that suggest the occurances of dipole (10-10 s to 10-13 s), dipole-segmental (10-14 s to 10-17 s) and segmental (10-18 s to 10-28 s) relaxation modes. Several n (10+1 s to 10-4 s) from experimental TSC peaks also confirm the cooperative relaxation around the glass transition temperature Tg. Abstract Analyses and observations on some basic mechanical properties generated from tensile test demonstrate structural effects on the entire composite system. Various matrix-alkyl chains and matrix-silicate interactions induce interfacial adhesion, interparticle bridging flocculated and stacking layer structure, which influence the elasticity modulus Young Y, Tensile strength max and Maximum elongation max. Polar matrix-silicate interactions within CENR-50 (30%) composite had improved the interfacial adhesion, which contributed to the significant increase in modulus Y (15420 %) compares to that of pristine ENR-50. Similarly, CpPVC (30%) that is a pPVC composite with the improved OMON stacked structure (N 21 layers) also demonstrates the increased modulus Y (2323 %). Polymers intercalation into OMON gallery can promote certain chemical reactions, which affect the inner structure of a composite. For example, chains crosslinking within OMON gallery that creates the interparticle bridging flocculated structure also promotes more slippage on the matrix chain during stress loading. As a result, it improves the Maximum elongation max with the increase of OMON content as shown by the CSMRL (30%) (max 70 %) and CDPNR (30%) (max 125 %) composites

Dasar dan Perundangan Pengajian Pekerja Asing di Malaysia: Melestari Matlamat Pembangunan Mampan No. 8

Dalam memastikan kelastarian pembagunan ekonomi Malaysia pemintaaan pekerja asing meningkat saban tahun dalam sektor 3 D (Dangerous, Dirty, Difficult ataupun Bahaya, Kotor dan Susah). Pekerjaan Baik dan Kemajuan Ekonomi (SDG 8) merupakankan salah satu daripada 17 Matlamat Pembangunan Mampan yang berkait rapat dengan pekerja asing. Objektif utama kertas kerja ini adalah menganalisa dasar dan peruntukan undang-undang serta agensi berkaitan pekerja asing dalam konteks SDG 8 dengan mengunakan pendekataan kaedah kualitatif. Matlamat Pembangunan Mampan No. 8, merupakan titik kesimbangan sosial dan perkembangan ekonomi negara sangat diperlukan. Hak pekerja asing di Malaysia turut dilindungi dan tertakluk kepada pemakaian dasar dan perundangan sediaada. Namun kegitu kebanjiran migran dari pelbagai benua perlu dikawal supaya Malaysia tidak menjadi tempat ·pusat himpunan' pelbagai kerakyatan serta boleh mengundang pelbagai masalah seperti jenayah dan sosial dikalangan masyarakat setempat

Colour analysis of organic synthetic dye coating paint films consisting 4-hydroxycoumarin derivatives after exposed to UV-A

This work investigates the visible optical stability of coating paint film consisting organic synthetic dye, 4-hydroxycoumarin derivatives to the exposure to ultraviolet A (UV-A) light. An azo dye was synthesized by coupling diazonium salt of aniline derivative (obtained by diazonation of 4-chloroaniline in presence of sodium nitrite and hydrochloric acid) with 4-hydroxycoumarin in the presence of sodium hydroxide. The azo dye was mixed with xylene before using it as a pigment in the coating composition. The mixture of poly(methyl methacrylate) (PMMA) and acrylic polyol was used as the coating binder. The synthesized dye and binder were then mixed at specific ratio to form a complete coating solution. Two coating solutions with PMMA having different molecular weights (Mw: 350,000 gmol-1 and Mw: 996,000 gmol-1) were used in this study. Each of them was labelled as 350 K and 996 K indicating its molecular weight. Both mixtures were applied as coating paint films on glass substrates were exposed to UV-A for fast photo-degradation process. The visible optical stability of the coating paint films was measured and recorded at an interval of eight-hours exposure for 35 days using the Commission Internationale de l'Eclairage (CIE) L∗a∗b∗ colour coordinate system. The obtained datas were analysed using standard deviation (STD). In this study, both coating samples showed low standard deviation for hue angle, namely 0.206 for 996 K and 0.258 for 350 K which indicates a high colour stability. However, the 350 K possesses a smaller colour difference (ΔE) of 0.798 compared to 1.418 for 996 K. © 2019 IOP Publishing Ltd

Wpływ czasu reakcji na strukturę i właściwości optyczne nanokompozytów P3HT/MWCNT-OH

In the present study, regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) coated hydroxylated multi-walled carbon nanotubes (MWCNT-OH) nanocomposites were prepared over different reaction times of non-covalent functionalization. The reaction time was set as 24, 48, 72, 96, and 120 hours. The structure and optical characteristics of nanocomposites were analyzed using Fourier-transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectroscopy, respectively. Reaction time affected prepared nanocomposites by decreasing the intensity of the P3HT/MWCNT-OH peaks gradually with increasing of the reaction time. Comparing with the pure P3HT and MWCNT-OH, the calculated energy band gap and the Urbach energy of the nanocomposites were reduced proportionally as the reaction time reached 120 hours and achieved 2.60 and 0.329 eV, respectively.Syntetyzowano hydroksylowane wielościenne nanorurki węglowe (MWCNT-OH) pokryte stereoregularnym poli(3-heksylotiofen-2,5-diylu) (P3HT) oraz zbadano wpływ czasu reakcji niekowalencyjnej funkcjonalizacji na strukturę i właściwości optyczne otrzymanego nanokompozytu. Czas reakcji wynosił 24, 48, 72, 96 i 120 godzin. W badaniach wykorzystano spektroskopię w podczerwieni z transformacją Fouriera (FTIR) oraz ultrafioletową UV-Vis. Wraz ze wzrostem czasu reakcji następowało stopniowe zmniejszenie intensywności pików P3HT/MWCNT-OH. W porównaniu z P3HT i MWCNT-OH obliczona przerwa energetyczna i energia Urbacha zmniejszały się wraz z wydłużeniem czasu reakcji i osiągnęły odpowiednio 2,60 i 0,329 eV przy czasie reakcji 120 godzin

EDLC performance of ammonium salt-green polymer electrolyte sandwiched in metal-free electrodes

AbstractMicroplastic and metal waste from electronic industries are becoming a major threat to the environment and marine ecosystem. Green processing and employing natural derived materials are solutions to this issue. In this work, an electrical double-layer capacitor (EDLC) fabricated from green polymer electrolyte (GPE) sandwiched in between two microbial cellulose-based electrodes is characterized. The eco-friendly electrode films of interconnected cellulose and multiwalled carbon nanotube (MWCNT) are obtained via harmless, inexpensive, and simple procedure. The GPE consists of methylcellulose-potato starch blend as polymer blend and ammonium iodide (NH4I) is chosen as ion provider. Glycerol serves as plasticization agent for alternative pathways enabling ionic migration. The most optimum GPE possesses good ionic conductivity of ∼ 10−3 S/cm. Ions are the dominant charge carrier in the GPE as ion transference number shown to be close to unity. Linear sweep voltammetry (LSV) analysis illustrated that the GPE is electrochemically stable up to 2.4 V. The green EDLC stores energy through non-Faradaic mechanism and the specific capacitance from charge-discharge, Ccd is influenced by the sweep rates. The EDLC can be charged and discharged up to 2 V with a stable 1000 cyclability performance. This work implied the potential of microbial cellulose-based EDLC as ideal green-based energy storage device for low voltage applications such as smart electronic textiles

Wpływ wstępnej obróbki na strukturę celulozy bakteryjnej z Nata de Coco (Acetobacter xylinum)

This paper presents a structural analysis of various methods to produce bacterial cellulose (BC) from Nata de Coco (Acetobacter xylinum). BC sheet, BC chem and BC mech powders were successfully prepared using oven drying, chemical and mechanical treatment. The X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and field emission scanning electron microscopy (FESEM) were used to analyze the structure of prepared BC. The structure of bacterial cellulose was compared with the structure of commercial microcrystalline cellulose (MCC) and cotton fabric. The XRD results showed that the BC sheet sample had the highest degree of crystallinity (81.76%) compared to cotton cellulose (75.73%). The crystallite size of cotton was larger than the BC sheet, with the value of 6.83 ηm and 4.55 ηm, respectively. The peaks in the FTIR spectra of all BC were comparable to the commercial MCC and cotton fabrics. FESEM images showed that the prepared BC sheet, BC mech, and BC chem had an almost similar structure like commercial MCC and cotton fabric. It was concluded that simple preparation of BC could be implemented and used for further BC preparation as reinforcement in polymer composites, especially in food packaging.Niniejszy artykuł zawiera analizę struktury celulozy bakteryjnej (BC) wytworzonej z Nata de Coco (Acetobacter xylinum) różnymi metodami. Folia BC i proszki BC chem oraz BC mech zo -stały wytworzone poprzez suszenie w piecu, obróbkę chemiczną i mechaniczną. Do oceny struktury celulozy bakteryjnej stosowano dyfrakcję rentgenowską (XRD), spektroskopię Fouriera w podczerwieni (FTIR) i skaningową mikroskopię elektronową z emisją polową (FESEM). Strukturę celulozy bakteryjnej porównano ze strukturą handlowej celulozy mikrokrystalicznej (MCC) i tkaniny bawełnianej. Wyniki XRD wykazały, że najwyższy stopień krystaliczności miała próbka arkusza BC (81,76%) w porównaniu z celulozą bawełnianą (75,73%). Wielkość krystalitów bawełny była większa niż folii BC i wynosiła, odpowiednio, 6,83 ηm oraz 4,55 ηm. Piki widm FTIR wszystkich otrzymanych form celulozy bakteryjnej były porównywalne z komercyjnymi tkaninami bawełnianymi i z celulozy mikrokrystalicznej. Zdjęcia FESEM folii BC oraz proszków BC mech i BC chem również były podobne do komercyjnej MCC i tkaniny bawełnianej. Stwierdzono, że z wykorzystaniem prostych technik można otrzymać BC, która może być stosowana jako wzmocnienie w kompozytach polimerowych, w szczególności w opakowaniach do żywności

Microbial phosphotriesterase: structure, function, and biotechnological applications

The role of phosphotriesterase as an enzyme which is able to hydrolyze organophosphate compounds cannot be disputed. Contamination by organophosphate (OP) compounds in the environment is alarming, and even more worrying is the toxicity of this compound, which affects the nervous system. Thus, it is important to find a safer way to detoxify, detect and recuperate from the toxicity effects of this compound. Phosphotriesterases (PTEs) are mostly isolated from soil bacteria and are classified as metalloenzymes or metal-dependent enzymes that contain bimetals at the active site. There are three separate pockets to accommodate the substrate into the active site of each PTE. This enzyme generally shows a high catalytic activity towards phosphotriesters. These microbial enzymes are robust and easy to manipulate. Currently, PTEs are widely studied for the detection, detoxification, and enzyme therapies for OP compound poisoning incidents. The discovery and understanding of PTEs would pave ways for greener approaches in biotechnological applications and to solve environmental issues relating to OP contamination