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| dc.contributor.supervisor | Muiva, Cosmas mulwa | |
| dc.contributor.supervisor | Kuvarega, Alex | |
| dc.contributor.author | Sebuso, Dineo Pono | |
| dc.date.accessioned | 2023-02-01T13:23:09Z | |
| dc.date.available | 2023-02-01T13:23:09Z | |
| dc.date.issued | 2021-12 | |
| dc.identifier.citation | Sebuso,D (2022) Green synthesis of multilayer graphene/zno nanocomposite for photocatalytic application, Master's thesis, Botswana International University of Science and Technology: Palapye | en_US |
| dc.identifier.uri | http://repository.biust.ac.bw/handle/123456789/520 | |
| dc.description.abstract | Green nanotechnology is an innovative research field with emphasis on the development of methods that minimize the use of health hazardous substances for environmental remediation. This study reports on the biosynthesis of nanostructured multilayer graphene (MLG) and zinc oxide (ZnO) from natural extracts for environmental applications. ZnO nanoparticles are fabricated for the first-time using Ageratum Houstonianum leaf extract as an effective chelating agent. Besides this, a green chemistry route involving the utilization of waste biomass was used for fabrication of multilayer graphene. This route was chosen because it offers good control of size, morphology and does not involve use of toxic reducing agents or surfactants thus contributing towards green nanotechnology. MLG was synthesized from corn husk via alkali-acid treatment. This entails extraction of cellulose followed by carbonization of the nanomaterial and activation of the carbon material. The separately synthesized nanostructures were used to synthesize MLG/ZnO nanocomposites of different ratios of MLG/ZnO (1:1, 1:2, 1:3) through ex-situ casting of the two materials (MLG/ZnO_1, MLG/ZnO_2, MLG/ZnO_3). The X-ray diffraction (XRD) profiles and Raman spectra exhibited predominant features of MLG and confirmed a hexagonal wurtzite phase of ZnO in the composite verifying the formation of MLG/ZnO nanocomposite. The UV-Vis absorbance spectra analysis revealed that incorporation of MLG to ZnO narrowed the band gap of ZnO nanoparticles, and consequently improved the light absorption of the semiconductor in the visible range. From Scanning electron microscopy (SEM) and High-Resolution TEM (HRTEM) analysis, short hexagonal nanorods were observed for ZnO while sheet-like structures with ripples and crinkles were observed for MLG. Energy dispersive spectroscopy (EDS) confirmed the purity of the samples and successful incorporation of MLG and ZnO with presence of only C, O and Zn in the composites. Brunauer-Emmett-Teller (BET) analysis revealed less surface area of 0.42 m2 /g for bare ZnO and increased surface area of 148.74 m2 /g in the composite (MLG/ZnO_3). Brilliant black (BB), congo red (CR) and rhodamine B (RhB) were chosen as model pollutants in this study, because they are among the many water pollutants from textiles and industries which are found to be stable with complex structures hence making them environmentally problematic. The nanocomposites were initially applied for xv photodegradation of BB under direct sunlight irradiation to determine the best performing nanocomposite. It is worth to note that MLG/ZnO_3 nanocomposite showed the best photocatalytic performance of 93% degradation compared to pristine ZnO, MLG/ZnO_1 and MLG/ZnO_2, which showed lower photocatalytic activity. The best performing nanocomposite was further used to degrade CR and RhB and gave degradation efficiencies of 86 and 100%, respectively while pure ZnO showed degradations of 71% and 85% for CR and RhB, respectively. The obtained results showed high photocatalytic activity for the optimized MLG/ZnO nanocomposite in RhB and CR under natural sunlight irradiation. The nanocomposite further demonstrated 95% degradation for doxycycline (DOX) under UV light. The photodegradation mechanism was proposed and discussed in light of scavenging experiments using the optimum composite for all the four pollutants. It was revealed that holes play a major role in photodegradation of BB while the main reactive species in the photodecomposition of CR, RhB and DOX were found to be superoxide radicals. This work provides an insight for cheap, sustainable and eco-friendly methods for the fabrication of nanomaterials for environmental remediation and better ways of recycling waste biomass to fabricate valuable materials to solve society problems. | en_US |
| dc.language.iso | en | en_US |
| dc.publisher | Botswana International University of Science and Technology (BIUST) | en_US |
| dc.subject | Nanotechnology | en_US |
| dc.subject | Nanostructured multilayer graphene | en_US |
| dc.subject | Zinc oxide | en_US |
| dc.subject | Ageratum Houstonianum | en_US |
| dc.subject | Chelating agent. | en_US |
| dc.title | Green synthesis of multilayer graphene/zno nanocomposite for photocatalytic application | en_US |
| dc.description.level | msc | en_US |
| dc.dc.description | Thesis (MSc of Science in Physics--Botswana International University of Science and Technology, 2021 | |
| dc.description.accessibility | unrestricted | en_US |
| dc.description.department | paa | en_US |
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