Preparation and characterization of carbon based adsorbents and their application for the removal of selected inorganic and organic pollutants

Ph.D. (Chemistry)Abstract: Environmental pollution is one of the major challenges worldwide. This is because of the increase in contamination of water, soil and air by trace metals and organic based contaminants arising from different activities. These activities include mining operations, agricultural runoffs and paint industries, among others. The prevalence of inorganic and organic pollutants in the environment calls for urgent intervention to try and mitigate the challenges that are due to pollutants that cause water to be scarce. The existence of pollutants in the environmental matrices encourages the development of methods that are effective and efficient in the extraction, separation and preconcentration of trace metals and pharmaceutical drugs. Therefore, the main aim of this study was to prepare the pollution-cleaning and multipurpose adsorbents from waste material. The pollutants investigated in this study include toxic trace elements and refractory metals such as arsenic (As), lead (Pb), cadmium (Cd), thallium (Tl), antimony (Sb) and tellurium (Te), among others. In addition, antibiotics such as sulfamethoxazole (SMX), ciprofloxacin (CIPRO), danofloxacin (DANO) and enrofloxacin (ENRO) were also investigated. Activated carbon derived from waste tyres was used as adsorbent or as a main component in composite and nanofibers materials. The idea behind the use of the waste tyre was inspired by the fact that research on reuse and recycling of waste tyres are an actual and challenging subject. On the other hand, the production of activated carbon from waste tyres and its use as the pollution-cleaning adsorbents was considered a doubly effective solution for environmental pollution. In this thesis, two comprehensive reviews and various sample preparation methods for removal, extraction and preconcentration of selected trace metals and antibiotics prior to spectrophotometric, spectrometric and chromatographic detection. The developed sample preparation methods were applied to environmental samples. These methodologies include solid phase extraction (SPE), dispersive solid phase extraction (DSPE), ultrasound assisted dispersive solid phase extraction (UA-DSPE), microwave assisted solid phase extraction (MASPE) and ultrasound assisted solid phase microextraction (UA-DSPME. The summary of the work presented are listed below: 1. A comprehensive review detailing the application of myriad carbonaceous materials for the removal of toxic trace elements in the environment is presented. The adsorptive removal of heavy metals such Tl, Te, Hg, Cd and Pb using carbon based adsorbents such..

Application of activated carbon-decorated polyacrylonitrile nanofibers as an adsorbent in dispersive solid-phase extraction of fluoroquinolones from wastewater

A cheap and simple sample preparation method, consisting of a dispersive solid-phase method and an adsorbent, activated carbon decorated PAN nanofibers, was employed and used for the extraction of antibiotics (ciprofloxacin, danofloxacin, and enrofloxacin) in wastewater. Electrospun PAN nanofibers that were decorated with activated carbon produced from waste tires were used as the solid phase and the antibiotics analyzed by using high-performance liquid chromatography. Parameters such as pH, mass of adsorbent (MA), extraction volume (EV), and extraction time (ET) were optimized owing to their potential effect on the extraction of antibiotics from water. The recovery of all antibiotics was satisfactory, in the range of 90%–99%. The limits of detection and quantification were 0.05, 0.11, 0.20, and 0.53, 1.21, 2.17 µg/L, respectively. The precision was determined from the repeatability and reproducibility and expressed as the intra-day (n = 20) and inter-day (n = 5) precision. The intra-day and inter-day precision was reported in terms of the percentage relative standard deviation, which was 3% and 4%, respectively. The adsorption capacity of the activated carbon-decorated PAN nanofibers was satisfactory, and the reusability of the adsorbent was impressive when reused ten times. The accuracy of the dispersive solid phase extraction (DSPE) was validated by spike recovery tests; the results proved the reliability and efficiency of adsorbing antibiotics from wastewater. Finally, the proposed method was applied to wastewater samples collected from a wastewater treatment plant, which included influent, secondary, and effluent wastewater. Keywords: Wastewater, Nanofibers, Activated carbon, Antibiotics, Polyacrylonitril

Application of waste tyre-based activated carbon for the removal of heavy metals in wastewater

This study presents the preparation and characterization of chemically activated carbonaceous materials obtained from waste tyres and the prepared adsorbent was applied for the adsorptive removal of Cd(II) and Pb(II) in the domestic wastewater samples. The activation efficiency of phosphoric acid (H3PO4) and hydrogen peroxide (H2O2) were evaluated and H2O2 was chosen as the appropriate activating agent as compared to phosphoric acid. The developed adsorbent was characterized using the scanning electron microscope (SEM), Brunnuer Emmet Teller (BET) which helped to decide which adsorbent material is best in terms of the surface area and Fourier transform infrared spectroscopy (FT-IR). Two-level fractional factorial design was used for the optimization of parameters affecting the adsorptive removal of Cd(II) and Pb(II). The optimum conditions were found to be 6.5, 0.2 g, 32.5 min and 55 mg L−1, for sample pH, mass of adsorbent, contact time and initial concentration, respectively. Amongst every adsorption isotherms that were used, Langmuir model was preferred due to the highest value of the correlation coefficient (r2). Therefore, the adsorption capacities of Cd(II) and Pb(II) were 201 and 196 mg g−1, respectively. The regeneration studies were performed and the adsorbent was capable of been used ten times and the material was stable with only a slight decrease in the removal efficiency of Cd(II) and Pb(II). Furthermore, the prepared adsorbent prepared was successfully applied for the removal of Cd(II) and Pb(II) in real environmental samples and the inductively coupled plasma optical emission spectroscopy was used for the analysis