Vulcanized rubber, due to its superior mechanical properties, has long been used in various industries, especially automotive. The rubber industry has evolved and expanded over the years to meet the increasing global demands for tires. Today tires consist of about 19% natural rubber and 24% synthetic rubber, while plastic polymer and metal, filler and additives make up the rest. Over 1.6 billion new tires are produced annually and around 1 billion waste tires are generated. Tires are extensively designed with several complex processes to make them virtually indestructible. Since tire rubber does not decompose easily, their disposal at the end of service life creates a monumental environmental impact. However, waste tire rubber (WTR) consist of valuable rubber hydrocarbon, making its recovery or regeneration highly desirable. The conventional recovery method of WTR tends to produce undesirable products due to the destruction of the polymeric chain and exponentially degenerates the vulcanizates' physical properties. Since then, multiple devulcanization processes were introduced to effectively and selectively cleave vulcanizate's crosslinks while retaining the polymeric networks. Different devulcanization methods such as chemical, mechanical, irradiation, biological and their combinations that have been explored until now are reviewed here. Besides, an overview of the latest development of devulcanization by ionic liquids and deep eutectic solvents are also described. While such devulcanization technique provides new sustainability pathway(s) for WTR, the generated devulcanizate also possesses comparable physical properties to that of virgin products. This further opens the possibility of novel circular economic opportunities worldwide.
COVID'19 pandemic has devastated several industries and solar energy is no exception. In its economic relief package, Malaysia has announced approximately US$ 2.9 billion in expenditure for the installation of new grids, LED street lights and rooftop solar panels. The Government will also open the tender for a 1400 MW solar power project in the year 2020, which is expected to generate 5 billion ringgit (US$1.1 billion) in investments. As these measures are intended to sustain the existing growth of solar energy potential in the country, it is vital to assess its status quo. Hence, this paper aims to review the current status of renewable energy in Malaysia as well as the initiatives taken before the pandemic to promote solar photovoltaic (PV) technology to meet the energy demands through the low-carbon pathway.
Contamination of water sources with various organic and inorganic non-biodegradable pollutants is becoming a growing concern due to industrialization, urbanization, and the inefficiency of traditional wastewater treatment processes. Transition Metal Carbides/Nitrides (MXenes) are emerging as advanced nanomaterials of choice for treating contaminated water owing to their excellent conductivity, mechanical flexibility, high specific surface area, scalable production, rich surface functionalities, and layered morphology. MXenes have demonstrated enhanced ability to adsorb various organic and inorganic contaminants depending upon their surface terminal groups (-OH, -F, and -O) and interlayer spacing. Titanium carbide (Ti3C2Tx) is most researched to date due to its ease of processing and stability. Ti3C2Tx has shown excellent performance in absorbing heavy metal ions and radioactive heavy metals. This review summarizes state-of-the-art Ti3C2Tx synthesis, including selective etching techniques, optimization of the desired adsorption features (controlling surface functional groups, intercalation, sonication, and functionalization), and regeneration and adsorption mechanism to remove contaminants. Furthermore, the review also compares the adsorption performance of Ti3C2Tx with other commercial adsorbents (including chitosan, cellulose, biomass, and zeolites). Ti3C2Tx has been found to have an adsorption efficiency of more than 90% in most studies due to its layered structure, which makes the functional groups easily accessible, unique and novel compared to other conventional nanomaterials and adsorbents. The challenges, potential solutions, and prospects associated with the commercial development of Ti3C2Tx as adsorbents are also discussed. The review establishes a framework for future wastewater treatment research using MXenes to address the global problem of water scarcity.
The effect of electron beam radiation on ethylene-propylene diene terpolymer/polypropylene blends is studied as an attempt to develop radiation sterilizable polypropylene/ethylene-propylene diene terpolymer blends suitable for medical devices. The polypropylene/ethylene-propylene diene terpolymer blends with mixing ratios of 80/20, 50/50, 20/80 were prepared in an internal mixer at 165°C and a rotor speed of 50 rpm/min followed by compression molding. The blends and the individual components were radiated using 3.0 MeV electron beam accelerator at doses ranging from 0 to 100 kGy in air and room temperature. All the samples were tested for tensile strength, elongation at break, hardness, impact strength, and morphological properties. After exposing to 25 and 100 kGy radiation doses, 50% PP blend was selected for in vivo studies. Results revealed that radiation-induced crosslinking is dominating in EPDM dominant blends, while radiation-induced degradation is prevailing in PP dominant blends. The 20% PP blend was found to be most compatible for 20-60 kGy radiation sterilization. The retention in impact strength with enhanced tensile strength of 20% PP blend at 20-60 kGy believed to be associated with increased compatibility between PP and EPDM along with the radiation-induced crosslinking. The scanning electron micrographs of the fracture surfaces of the PP/EPDM blends showed evidences consistent with the above contentation. The in vivo studies provide an instinct that the radiated blends are safe to be used for healthcare devices.
This research explores the potential of microwave-synthesized MoS2-graphene nanohybrid as additives to enhance the tribological properties of diesel-based engine oil. The synthesis method offers significant advantages, reducing both synthesis time and energy consumption by 90-98% compared to conventional approaches. The synthesized nanohybrids are characterized through FESEM, EDX, XRD, and Raman spectroscopy to understand their morphology and functional group interactions. These nanohybrids are incorporated into 20W40 engine oil following synthesis, and a comprehensive assessment of their properties is conducted. This evaluation covers critical parameters like viscosity index, stability, volatility, as well as tribological properties, oxidation resistance, and thermal conductivity of the oil-nanohybrid system. Results demonstrate that adding just 0.05 wt% of MoS2-graphene nanohybrid leads to a remarkable 58.82% reduction in friction coefficient and a significant 36.26% decrease in the average wear scar diameter. Additionally, oxidation resistance improves by 19.21%, while thermal conductivity increases notably by 19.83% (at 100 °C). The study demonstrates the synergistic effects of these nanohybrids in reducing friction and wear, enhancing oxidation resistance, and improving thermal conductivity. In conclusion, this research highlights the potential of microwave-synthesized MoS2-graphene nanohybrid as promising tribological additives for diesel engine oils. Their successful integration could significantly enhance the performance and durability of critical mechanical components in diesel engines, representing a significant advancement in lubrication technology.
Bones are nanocomposites consisting of a collagenous fibre network, embedded with calcium phosphates mainly hydroxyapatite (HA) nanocrystallites. As bones are subjected to continuous loading and unloading process every day, they often tend to become prone to fatigue and breakdown. Therefore, this review addresses the use of nanocomposites particularly polymers reinforced with nanoceramics that can be used as load bearing bone implants. Further, nanocomposite preparation and dispersion modification techniques have been highlighted along with thorough discussion on the influence that various nanofillers have on the physico-mechanical properties of nanocomposites in relation to that of natural bone properties. This review updates the nanocomposites that meet the physico-mechanical properties (strength and elasticity) as well as biocompatibility requirement of a load bearing bone implant and also attempts to highlight the gaps in the reported studies to address the fatigue and creep properties of the nanocomposites.
Strain sensors in the form of buckypaper (BP) infiltrated with various polymers are considered a viable option for strain sensor applications such as structural health monitoring and human motion detection. Graphene has outstanding properties in terms of strength, heat and current conduction, optics, and many more. However, graphene in the form of BP has not been considered earlier for strain sensing applications. In this work, graphene-based BP infiltrated with polyvinyl alcohol (PVA) was synthesized by vacuum filtration technique and polymer intercalation. First, Graphene oxide (GO) was prepared via treatment with sulphuric acid and nitric acid. Whereas, to obtain high-quality BP, GO was sonicated in ethanol for 20 min with sonication intensity of 60%. FTIR studies confirmed the oxygenated groups on the surface of GO while the dispersion characteristics were validated using zeta potential analysis. The nanocomposite was synthesized by varying BP and PVA concentrations. Mechanical and electrical properties were measured using a computerized tensile testing machine, two probe method, and hall effect, respectively. The electrical conducting properties of the nanocomposites decreased with increasing PVA content; likewise, electron mobility also decreased while electrical resistance increased. The optimization study reports the highest mechanical properties such as tensile strength, Young's Modulus, and elongation at break of 200.55 MPa, 6.59 GPa, and 6.79%, respectively. Finally, electrochemical testing in a strain range of ε ~ 4% also testifies superior strain sensing properties of 60 wt% graphene BP/PVA with a demonstration of repeatability, accuracy, and preciseness for five loading and unloading cycles with a gauge factor of 1.33. Thus, results prove the usefulness of the nanocomposite for commercial and industrial applications.
With the rapid urbanisation happening around the world followed by the massive demand for clean energy resources, green cities play a pivotal role in building a sustainable future for the people. The continuing depletion of natural resources has led to the development of renewable energy with algae as the promising source. The high growth rate of microalgae and their strong bio-fixation ability to convert CO2 into O2 have been gaining attention globally and intensive research has been conducted regarding the microalgae benefits. The focus on potential of microalgae in contributing to the development of green cities is rising. The advantage of microalgae is their ability to gather energy from sunlight and carbon dioxide, followed by transforming the nutrients into biomass and oxygen. This leads to the creation of green cities through algae cultivation as waste and renewable materials can be put to good use. The challenges that arise when using algae and the future prospect in terms of SDGs and economy will also be covered in this review. The future of green cities can be enhanced with the adaptation of algae as the source of renewable plants to create a better outlook of an algae green city.
We studied the reinforcing effects of treated and untreated nanohydroxyapatite (NHA) on poly-lactic acid (PLA). The NHA surface was treated with three different types of chemicals; 3-aminopropyl triethoxysilane (APTES), sodium n-dodecyl sulfate (SDS) and polyethylenimine (PEI). The nanocomposite samples were prepared using melt mixing techniques by blending 5 wt% untreated NHA and 5 wt% surface-treated NHA (mNHA). Based on the FESEM images, the interfacial adhesion between the mNHA filler and PLA matrix was improved upon surface treatment in the order of mNHA (APTES) > mNHA (SDS) > mNHA (PEI). As a result, the PLA-5wt%mNHA (APTES) nanocomposite showed increased viscoelastic properties such as storage modulus, damping parameter, and creep permanent deformation compared to pure PLA. Similarly, PLA-5wt%mNHA (APTES) thermal properties improved, attaining higher Tc and Tm than pure PLA, reflecting the enhanced nucleating effect of the mNHA (APTES) filler.
The continuous deterioration of the environment due to extensive industrialization and urbanization has raised the requirement to devise high-performance environmental remediation technologies. Membrane technologies, primarily based on conventional polymers, are the most commercialized air, water, solid, and radiation-based environmental remediation strategies. Low stability at high temperatures, swelling in organic contaminants, and poor selectivity are the fundamental issues associated with polymeric membranes restricting their scalable viability. Polymer-metal-carbides and nitrides (MXenes) hybrid membranes possess remarkable physicochemical attributes, including strong mechanical endurance, high mechanical flexibility, superior adsorptive behavior, and selective permeability, due to multi-interactions between polymers and MXene's surface functionalities. This review articulates the state-of-the-art MXene-polymer hybrid membranes, emphasizing its fabrication routes, enhanced physicochemical properties, and improved adsorptive behavior. It comprehensively summarizes the utilization of MXene-polymer hybrid membranes for environmental remediation applications, including water purification, desalination, ion-separation, gas separation and detection, containment adsorption, and electromagnetic and nuclear radiation shielding. Furthermore, the review highlights the associated bottlenecks of MXene-Polymer hybrid-membranes and its possible alternate solutions to meet industrial requirements. Discussed are opportunities and prospects related to MXene-polymer membrane to devise intelligent and next-generation environmental remediation strategies with the integration of modern age technologies of internet-of-things, artificial intelligence, machine-learning, 5G-communication and cloud-computing are elucidated.
Two superior adsorbents, namely bentonite and graphene oxide (GO), were hybridised to study the removal of copper and nickel ions from synthetic and industrial wastewater. The as-synthesised GO, bentonite/GO and bentonite were characterised by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and N2 adsorption-desorption analysis. The factors influencing the adsorption behaviours including contact time, initial solution pH, ionic strength, initial concentration of metal ions, temperature and adsorbent dosage were systematically investigated by batch equilibrium method. The adsorption equilibrium for copper and nickel onto bentonite was attained in 90 min while equilibrium was reached in 60 min on bentonite/GO. The adsorption of copper and nickel was pH-dependent in the range from pH 2 to pH 7 and from pH 2 to pH 8. Pseudo-first-order kinetic model excellently described the adsorption of copper and nickel onto bentonite and bentonite/GO. The equilibrium adsorption data was well described by the Langmuir isotherm model and the maximum adsorption capacity was 248.9 mg/g, 558.4 mg/g, 215.8 mg/g and 402.5 mg/g for bentonite-copper, bentonite/GO-copper, bentonite-nickel and bentonite/GO-nickel adsorption systems, respectively. The bentonite/GO composite exhibited a higher adsorption capacity of both cations from synthetic wastewater than pure bentonite owning to the synergistic effect between bentonite and GO. In all adsorption studies, copper was more efficiently removed than nickel due to its higher tendency to form bond with adsorbent surfaces. The adsorption of copper and nickel on bentonite/GO was mainly due to cation exchange, intermolecular and electrostatic interactions and physisorption dominated the adsorption processes. The practical application of bentonite/GO on adsorption of copper was investigated using real wastewater and its removal efficiency was beyond 98%. The excellent adsorption performances of composites for the copper and nickel removal from wastewater demonstrated its significant potential for pollution mitigations.
The pollution of water resources due to the disposal of industrial wastes that have organic material like phenol is causing worldwide concern because of their toxicity towards aquatic life, human beings and the environment. Phenol causes nervous system damage, renal kidney disease, mental retardation, cancer and anaemia. In this study, magnetic palm kernel biochar is used for removal of phenol from wastewater. The effect of parameters such as pH, agitation speed, contact time and magnetic biochar dosage are validated using design of experiments. The statistical analysis reveals that the optimum conditions for the highest removal (93.39%) of phenol are obtained at pH of 8, magnetic biochar dosage of 0.6 g, agitation speed at 180 rpm and time of 60 min with the initial concentration of 10 mg/L. The maximum adsorption capacities of phenol were found to be 10.84 mg/g and Langmuir and Freundlich isotherm models match the experimental data very well and adsorption kinetic obeys a pseudo-second order. Hence, magnetic palm kernel can be a potential candidate for phenol removal from wastewater.
In this study, MoS2-hBN hybrid nanoparticles were synthesized using an advanced microwave platform for new nanolubricant formulations. The synthesized nanoparticles were characterized by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy. The hybrid nanoparticles were then introduced into a 20W40 diesel-based engine oil to produce a nanolubricant. The physical and chemical properties of the nanolubricant were investigated, including the viscosity index, stability, volatility, tribological properties, oxidation properties, and thermal conductivity. The results showed that the inclusion of 0.05 wt% MoS2-hBN hybrid nanoparticles in the oil significantly reduced the coefficient of friction and wear scar diameter by 68.48% and 35.54%, respectively. Moreover, it exhibited substantial oxidation and thermal conductivity improvement of 38.76% and 28.30%, respectively, at 100 °C. These findings demonstrate the potential of MoS2-hBN hybrid nanoparticles as an effective additive to enhance the properties of nanolubricant significantly. Furthermore, this study offers valuable insights into the underlying mechanisms responsible for the observed enhancements. The promising outcomes of this investigation contribute to the advancement of nanotechnology-based lubricants, showcasing their potential for improving engine efficiency and prolonging the lifespan of machinery.
The increasing demand for high-performance lithium-ion batteries (LIBs) has emphasized the need for affordable and sustainable materials, prompting the exploration of waste upcycling to address global sustainability challenges. In this study, we efficiently converted polypropylene (PP) plastic waste from used centrifuge tubes into activated polypropylene carbon (APC) using microwave-assisted pyrolysis. The synthesis of APC was optimized using response surface methodology/central composite design (RSM/CCD). Based on the RSM results, the optimal conditions for PP plastic conversion into carbon were determined as follows: HNO3 concentration of 3.5 M, microwave temperature of 230 °C, and holding time of 25 min. Under these conditions, the obtained intensity ratio of Id/Ig in PP carbon was 0.681 ± 0.013, with an error of 6.81 ± 0.013 % between predicted and actual values. The physicochemical studies, including FESEM-EDX, XRD, and Raman spectroscopy, confirmed the successful synthesis of APC samples. The APC 800 material exhibited a well-organized three-dimensional structure characterized by large pores and mesopores, enabling fast ion transport in the electrode. As a result, the APC 800 electrode demonstrated an initial discharge capacity of 381.0 mAh/g, an improved initial coulombic efficiency of 85.1%, and excellent cycling stability after 100 cycles. Notably, the APC 800 electrode displayed remarkable rate performance, showing a reversible capacity of 355.1 mAh/g when the current density was reset to 0.2 A/g, highlighting its high electrochemical reversibility. The outstanding characteristics of APC 800 as an anode electrode material for high-performance lithium-ion batteries suggest a promising future for its application in the field.
This study presents the adsorption of methylene blue (MB) dye using latex char derived from pyrolysis of latex gloves. The adsorption process was investigated systematically using Response Surface Methodology (RSM) with a Central Composite Design (CCD). The effects of four key variables, namely pH, time, temperature, and adsorbent dosage, were studied using a factorial design enriched with center points and axial points. Experimental data were analyzed using a second-order polynomial regression model to construct a response surface model, which elucidated the relationship between the variables and MB removal efficiency. The study found that the char obtained at 800°C exhibited the highest adsorption capacity due to its increased carbonization, expanded surface area, and diverse pore structure. Analysis of Variance (ANOVA) confirmed the significance of the quadratic model, with remarkable agreement between predicted and experimental outcomes. Diagnostic plots validated the model's reliability, while 3D contour graphs illustrated the combined effects of variables on MB removal efficiency. Optimization using DoE software identified optimal conditions resulting in a 99% removal efficiency, which closely matched experimental results. Additionally, adsorption isotherms revealed that the Freundlich model best described the adsorption behavior, indicating heterogeneous surface adsorption with multilayer adsorption. This comprehensive study provides valuable insights into the adsorption process of MB dye using latex char, with implications for wastewater treatment and environmental remediation.
Industrial effluents contain several organic and inorganic contaminants. Among others, dyes and heavy metals introduce a serious threat to drinking waterbodies. These pollutants can be noxious or carcinogenic in nature, and harmful to humans and different aquatic species. Therefore, it is of high importance to remove heavy metals and dyes to reduce their environmental toxicity. This has led to an extensive research for the development of novel materials and techniques for the removal of heavy metals and dyes. One route to the removal of these pollutants is the utilization of magnetic carbon nanotubes (CNT) as adsorbents. Magnetic carbon nanotubes hold remarkable properties such as surface-volume ratio, higher surface area, convenient separation methods, etc. The suitable characteristics of magnetic carbon nanotubes have led them to an extensive search for their utilization in water purification. Along with magnetic carbon nanotubes, the buckypaper (BP) membranes are also favorable due to their unique strength, high porosity, and adsorption capability. However, BP membranes are mostly used for salt removal from the aqueous phase and limited literature shows their applications for removal of heavy metals and dyes. This study focuses on the existence of heavy metal ions and dyes in the aquatic environment, and methods for their removal. Various fabrication approaches for the development of magnetic-CNTs and CNT-based BP membranes are also discussed. With the remarkable separation performance and ultra-high-water flux, magnetic-CNTs, and CNT-based BP membranes have a great potential to be the leading technologies for water treatment in future.
Modified multi-walled carbon nanotubes (f-MWCNTs) and hydroxyapatite nanorods (n-HA) were reinforced into polypropylene (PP) with the support of a melt compounding approach. Varying composition of f-MWCNTs (0.1-0.3 wt.%) and nHA (15-20 wt.%) were reinforced into PP, to obtain biocomposites of different compositions. The morphology, thermal and mechanical characteristics of PP/n-HA/f-MWCNTs were observed. Tensile studies reflected that the addition of f-MWCNTs is advantageous in improving the tensile strength of PP/n-HA nanocomposites but decreases its Young's modulus significantly. Based on the thermal study, the f-MWCNTs and n-HA were known to be adequate to enhance PP's thermal and dimensional stability. Furthermore, MTT studies proved that PP/n-HA/f-MWCNTs are biocompatible. Consequently, f-MWCNTs and n-HA reinforced into PP may be a promising nanocomposite in orthopedics industry applications such as the human subchondral bone i.e. patella and cartilage and fabricating certain light-loaded implants.
Substantial discharge of hazardous substances, especially dyes and heavy metal ions to the environment, has become a global concern due to many industries neglecting the environmental protocols in waste management. A massive discharge of contaminantsfrom different anthropogenic activities, can pose alarming threats to living species and adverse effect to the ecosystem stability. In the process of treating the polluted water, various methods and materials are used. Hybrid nanocomposites have attained numerous interest due to the combination of remarkable features of the organic and inorganic elements in a single material. In this regards, carbon and polymer based nanocomposites have gained particular interest because of their tremendous magnetic properties and stability. These nanocomposites can be fabricated using several approaches that include filling, template, hydrothermal, pulsed-laser irradiation, electro-spinning, detonation induced reaction, pyrolysis, ball milling, melt-blending, and many more. Moreover, carbon-based and polymer-based magnetic nanocomposites have been utilized for an extensive number of applications such as removal of heavy metal and dye adsorbents, magnetic resonance imaging, and drug delivery. This review emphasized mainly on the production of magnetic carbon and polymer nanocomposites employing various approaches and their applications in water and wastewater treatment. Furthermore, the future opportunities and challenges in applying magnetic nanocomposites for heavy metal ion and dye removal from water and wastewater treatment plant.
Due to the rapid growth in the heavy metal-based industries, their effluent and local dumping have created significant environmental issues. In the past, typically, removal of heavy metals was handled by reverse osmosis and ion exchange techniques, but these methods have many disadvantages. Therefore, extensive work into the development of improved techniques has increased, especially for heavy metal removal. Many countries are currently researching new materials and techniques based on nanotechnology for various applications that involve extracting heavy metals from different water sources such as wastewater, groundwater, drinking water and surface water. Nanotechnology provides the possibility of enhancing existing techniques to tackle problems more efficiently. The development in nanotechnology has led to the discovery of many new materials such as magnetic nanoparticles. These nanoparticles demonstrate excellent properties such as surface-volume ratio, higher surface area, low toxicity and easy separation. Besides, magnetic nanoparticles can be easily and efficiently recovered after adsorption compared with other typical adsorbents. This review mainly emphasises on the efficiency of heavy metal removal using magnetic nanoadsorbent from aqueous solution. In addition, an in-depth analysis of the synthesis, characterisation and modification approaches of magnetic nanoparticles is systematically presented. Furthermore, future opportunities and challenges of using magnetic particles as an adsorbent for the removal of heavy metals are also discussed.
Adsorption capacity and percentage removal efficiency of Cu(II) and Ni(II) ions were studied and compared between raw kaolinite and acid-activated kaolinite. Acid-activated kaolin was prepared by refluxing raw kaolinite with concentrated sulphuric acid followed by calcination to enhance its surface properties and adsorption ability. Both raw and acid-activated kaolinite samples were characterized by Fourier transform infrared spectroscopy, energy dispersive X-ray, scanning electron micrograph and zeta potential analysis. Upon acid treatment, acid-activated kaolinite was discovered to have altered chemical composition and larger BET surface area as compared with raw kaolinite. The batch adsorption studies on aqueous solution were performed under different factors such as contact time, pH condition, adsorbent dosage, initial metal ion concentration and temperature. The optimum condition was selected for each factor including a contact time of 60 min, pH of 7.0, adsorbent dosage of 0.1 g, initial metal ion concentration of 100 mg/L and temperature of 25 °C. Then, the adsorption studies on wastewater samples were carried out at the selected optimum conditions. Acid-activated kaolinite always had better adsorption capacity and percentage removal efficiency than raw kaolinite due to the increasing amount of negative charges on the adsorbent surface and the number of metal ion binding sites upon acid treatment. The adsorption kinetic obtained was well described by the pseudo-second-order model, whereas the adsorption isotherms obtained were well described by either the Freundlich or the Langmuir adsorption model. The results showed that acid-activated kaolinite adsorbent is a better option as a favourable and feasible commercial low-cost adsorbent for wastewater treatment.