Carbon nanotube production from greenhouse gases during syngas synthesis

The impact of climate change around the world has led governments, institutions and industries to increase their efforts to combat it by seeking new and innovative technologies. Carbon dioxide (CO2) is believed to be the primary reason for global warming. Therefore, the capture and transformation of some of the billions of tons of CO2 produced annually by burning fossil fuels into useful products such as carbon nanotubes (CNTs) and carbon nanofibers (CNFs) is one of the methods being pursed in current research activities. The conversion of two major greenhouse gases, CO2 and methane (CH4), into CNTs and synthesis gas, which is a mixture of carbon monoxide (CO) and hydrogen (H2) has been studied experimentally by passing a CO2/CH4 mixture through a vertically orientated Chemical Vapour Deposition (CVD) reactor at temperatures ranging from 650°C to 950°C . Two different catalysts were used, a lanthanum nickel alloy (LaNi5) and a mischmetal nickel alloy. Transmission electron microscopy (low and high magnification), Raman spectroscopy and gas chromatography were used to analyze the products from the experiment. The apparent activation energy for CH4 and CO2 consumption, and H2 and CO production were estimated to be 41.7, 47.5, 54.5 and 47.5 kJ/ mol, respectively in the temperature range 1023 – 1123K. The CO2 and CH4 were decomposed, forming CNFs and CNTs as shown by the transmission electron microscope images. The findings showed that as the temperature increased the CNFs and CNTs became, less defined and fewer in number. The mischmetal nickel alloy had a smaller amount of amorphous carbon deposit compared to the lanthanum nickel alloy

Removal of Heavy Metals Using Bentonite Clay and Inorganic Coagulants

Heavy metals have always been defined as elements with a density higher than 5 g/cm3. They are regarded as serious wastewater contaminants with detrimental effect to human and environment. Their removal from wastewater poses a serious challenge as they require cost-effective reagent and treatment technique. About 200 mL solution of acid mine drainage (AMD) collected from the Western decant in Krugersdorp, South Africa was poured into five 500 mL glass beakers. Three different sets of experiments (employing mixing, shaking and no mixing) were conducted using a jar test and a shaker with 1.5 g bentonite clay, 20–60 mL of 0.043 M FeCl3 and Al2(SO4)3 and a flocculent of bentonite clay and FeCl3 dosage, respectively. The experiments were conducted without pH adjustment. The samples settled for 1 hour after which the pH, conductivity and turbidity were measured. The results show that a combination of bentonite clay and FeCl3 exhibits a better turbidity removal efficiency compared to the samples with bentonite clay, FeCl3 and AlCl3 respectively. The variation of the turbidity removal in the samples with mixing shaking and without mixing is insignificant, showing that destabilization-hydrolysis depends upon the strength of the reagent and the physicochemical properties of the solution. The results also show that hydrolysis occurs at low pH, indicating that it plays an insignificant role in destabilization. The SEM micrographs show that turbidity removal is a physical phenomenon

Adsorptive removal of BTEX compounds from wastewater using activated carbon derived from macadamia nut shells

In this study, adsorptive removal of benzene, toluene, ethylbenzene and xylenes (BTEX) from synthetic water using activated carbon adsorbent derived from macadamia nut shells was investigated. The surface  functional groups of the synthesized adsorbents were assessed by Fourier transform infrared spectra. The specific surface area, pore size and pore volume at 77 K nitrogen adsorption, surface morphology, and the crystalline structure of the adsorbents were determined using Brunauer-Emmett-Teller, scanning electron microscopy and x-ray diffraction, respectively. Batch adsorption mode was used to evaluate the performance of the activated carbon. The stock solutions of synthetic wastewater were prepared by dissolving 100 mg/L of each of the BTEX compound into distilled water in a 250 mL volumetric flask. Effect of initial concentration of BTEX compounds, contact time, and mass of adsorbent on the removal of BTEX compounds from the synthetic wastewater was investigated. The macadamia nut shell–derived activated carbon (MAC) proved to be an effective adsorbent for BTEX compounds, with a large surface area of 405.56 m2/g. The exposure time to reach equilibrium for maximum removal of BTEX was observed to be 20 min. The adsorption capacity of the BTEX compounds by MAC followed the following adsorption order: benzene > toluene > ethylbenzene > xylene.&nbsp

DNA hybridisation sensors for product authentication and tracing : state of the art and challenges

Abstract: The wide use of biotechnology applications in bioprocesses such as the food and beverages industry, pharmaceuticals, and medical diagnostics has led to not only the invention of innovative products but also resulted in consumer and environmental concerns over the safety of biotechnology-derived products. Controlling and monitoring the quality and reliability of biotechnology-derived products is a challenge. Current tracking and tracing systems such as barcode labels and radio frequency identification systems track the location of products from primary manufactures and/or producers throughout globalised distribution channels. However, when it comes to product authentication and tracing, simply knowing the location of the product in the supply chain is not sufficient. DNA hybridisation sensors allows for a holistic approach into product authentication and tracing in that they enable the attribution of active ingredients in biotechnology-derived products to their source. In this article, the state-of-the-art of DNA hybridisation sensors, with a focus on the application of graphene as the backbone, for product authentication and tracing is reviewed. Candidate DNA biocompatible materials, properties and transduction schemes that enable detection of DNA are covered in the discussion. Limitations and challenges of the use of DNA biosensing technologies in real-life environmental, biomedical and industrial fields as opposed to clean-cut laboratory conditions are also enumerated. By considering experimental research versus reality, this article outlines and highlights research needed to overcome commercialisation barriers faced by DNA biosensing technologies. In addition, the content is thought-provoking to facilitate development of cutting edge research activities in the field

Recent advancements in the use of plastics as a carbon source for carbon nanotubes synthesis - a review

DATA AVAILABILITY STATEMENT : Data will be available on request.Plastics, which majorly consist of polypropylene (PP), polyethylene (linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE) and high-density polyethylene (HDPE)), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), etc., are the most abundant municipal solid wastes (MSW). They have been utilized as a cheap carbon feedstock in the synthesis of carbon nanotubes (CNTs) because of their high hydrocarbon content, mainly carbon and hydrogen, especially for the polyolefins. In this review, the detailed progress made so far in the use of plastics (both waste and virgin) as cheap carbon feedstock in the synthesis of CNTs (only) over the years is studied. The primary aim of this work is to provide an expansive landscape made so far, especially in the areas of catalysts, catalyst supports, and the methods employed in their preparations and other operational growth conditions, as well as already explored applications of plastic-derived CNTs. This is to enable researchers to easily access, understand, and summarise previous works done in this area, forging ahead towards improving the yield and quality of plastic-derived CNTs, which could extend their market and use in other purity-sensitive applications.The University of Johannesburg (UJ), South Africa, under the Global Excellence Stature (GES) Fellowship 4.0.https://www.cell.com/heliyonhj2024Chemical EngineeringSDG-11:Sustainable cities and communitiesSDG-12:Responsible consumption and productio

Corn cob char as catalyst support for developing carbon nanotubes from waste polypropylene plastics : comparison of activation techniques

The future and continuity of nanomaterials are heavily dependent on their availability and affordability. This could be achieved when cheap materials are actively employed as starting materials for nanomaterials synthesis. In this study, waste corn cob char was used as support during the preparation of the NiMo catalyst, and the effect of different char-activating techniques on the microstructure, yield and quality of carbon nanotubes (CNTs) obtained from waste polypropylene (PP) plastics using the chemical vapor deposition (CVD) technique was investigated. Properties of the catalysts and obtained nanomaterials were evaluated by XRD, SEM, N2 physisorption experiment, FTIR, Raman spectroscopy and TEM. Results showed improved surface properties of the NiMo catalyst supported on chemically (NiMo/ACX) and physically activated char (NiMo/ACT) compared to the NiMo catalyst supported on non-activated char (NiMo/AC0 ). High-quality CNTs were deposited over NiMo/ACT compared to NiMo/ACX and NiMo/AC0 . It was also observed that different activation methods resulted in the formation of CNTs of different microstructures and yield. Optimum yield (470.0 mg CNTs/g catalyst) was obtained with NiMo/AC0 , while NiMo/ACT gave the least product yield (70.0 mg CNTs/g catalyst) of the as-produced nanomaterials. Based on the results of the analysis, it was concluded that utilizing a cheap pyrogenic product of waste corn cob as a catalyst support in a bimetallic NiMo catalyst could offer a promising approach to mass producing CNTs and as a low-cost alternative in CNTs production from waste plastics.The University of Johannesburg, South Africa, under the Global Excellence Stature Fourth Industrial Revolution (GES 4IR) Scholarship.https://www.mdpi.com/journal/polymersdm2022Chemical Engineerin

Catalytic performance of calcium titanate for catalytic decomposition of waste polypropylene to carbon nanotubes in a single-stage CVD reactor

Abstract: Please refer to full text to view abstract

Effect of different catalyst supports on the quality, yield and morphology of carbon nanotubes produced from waste polypropylene plastics

The role of the effect of the support on the reactivity of heterogeneous catalysts cannot be over-emphasized. Therefore, the study documented in this article investigated the effect of different metal oxide supports (MgO, CaO and TiO2 ) and mixed oxide supports (CaTiO3 ) on the performance of a bimetallic NiMo catalyst prepared via the sol–gel method during the catalytic growth of carbon nanotubes (CNTs) from waste polypropylene (PP). Waste PP was pyrolyzed at 700 ◦C in a single-stage chemical vapor deposition reactor and off-gas was utilized in-situ as a cheap carbon feedstock for the growth of CNTs under similar conditions for all the prepared NiMo catalysts (supported and unsupported). The structures of the prepared catalysts and deposited carbon were extensively characterized using X-ray diffraction (XRD), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), etc. The catalytic performance of NiMo supported and unsupported catalysts was evaluated in terms of the yield, purity, and morphology of synthesized CNTs. The results revealed that the stabilizing role of supports is fundamental in preventing nanoparticle agglomeration and aggregation, thereby resulting in improved yield and quality of CNTs. Supported NiMo catalysts produced better aligned graphitic and high-quality CNTs. The NiMo/CaTiO3 catalyst produced the highest carbon of 40.0%, while unsupported NiMo produced low-quality CNTs with the lowest carbon yield of 18.4%. Therefore, the type of catalyst support and overall stability of catalytic materials play significant roles in the yield and quality of CNTs produced from waste PP.http://www.mdpi.com/journal/catalystspm2021Chemical Engineerin

Artificial neural network for predicting the performance of waste polypropylene plastic-derived carbon nanotubes

DATA AVAILABILITY : Data/Code is available for sharing.In this study, an artificial neural network model using function fitting neural networks was developed to describe the yield and quality of multi-walled carbon nanotubes deposited over NiMo/CaTiO3 catalyst using waste polypropylene plastics as cheap hydrocarbon feedstock using a single-stage chemical vapour deposition technique. The experimental dataset was developed using a user-specific design with four numeric factors (input variable): synthesis temperature, furnace heating rate, residence time, and carrier gas (nitrogen) flow rate to control the performance (yield and quality) of produced carbon nanotubes. Levenberg–Marquardt algorithm was utilized in training, validating, and testing the experimental dataset. The predicted model gave a considerable correlation coefficient (R) value close to 1. The presented model would be of remarkable benefit to successfully describe and predict the performance of polypropylene-derived carbon nanotubes and show how the predictive variables could affect the response variables (quality and yield) of carbon nanotubes.The University of Johannesburg (UJ), South Africa, under the Global Excellence Stature (GES) Fellowship 4.0. Open access funding provided by University of Johannesburg.https://link.springer.com/journal/13762hj2024Chemical EngineeringSDG-09: Industry, innovation and infrastructureSDG-12:Responsible consumption and productio

Parametric optimization of the production of cellulose nanocrystals (CNCs) from South African corncobs via an empirical modelling approach

In this study, cellulose nanocrystals (CNCs) were obtained from South African corncobs using an acid hydrolysis process. The delignification of corncobs was carried out by using alkali and bleaching pretreatment. Furthermore, the Box-Behnken Design (BBD) was used as a design of experiment (DOE) for statistical experimentations that will result in logical data to develop a model that explains the effect of variables on the response (CNCs yield). The effects (main and interactive) of the treatment variables (time, temperature, and acid concentration) were investigated via the response methodology approach and the obtained model was used in optimizing the CNCs yield. Surface morphology, surface chemistry, and the crystallinity of the synthesized CNC were checked using scanning electron microscopy (SEM), a Fourier Transform Infra-red spectroscopy (FTIR), and an X-ray diffraction (XRD) analysis, respectively. The SEM image of the raw corncobs revealed a smooth and compact surface morphology. Results also revealed that CNCs have higher crystallinity (79.11%) than South African waste corncobs (57.67%). An optimum yield of 80.53% CNCs was obtained at a temperature of 30.18 °C, 30.13 min reaction time, and 46 wt% sulfuric acid concentration. These optimized conditions have been validated to confirm the precision. Hence, the synthesized CNCs may be suitable as filler in membranes for different applications.Global Excellence Status (GES), University of Johannesburg.http://www.nature.com/scientificreportsam2023Chemical Engineerin