Abstract
Virus infections such as Ebola, HIV, Aids, and Influenza have spread throughout the world over the years, with Covid 19 being the most recent and concerning viral infection. Since the 18th century, antiviral drugs have been used as a first line of defense against these viral infections to suppress the activity of the virus in the body and prevent transmission. In addition, Covid-19 many antiviral drugs such as nevirapine, oseltamivir, and efivaraz have been used as clinical trial drug for Covid-19 patients and it was found not to be effective because their enzymes did not bind with Covid-19 infection. However, the oversupply and extensive use of antiviral drugs has come at a price as these drugs are detected in the environment, especially water bodies contributing to the depletion of the water quality. The wastewater treatment plants (WWTPs) are not efficient in degrading and removing these antiviral drugs (ARVs) with their conventional processes, as a result, these ARVs get discharged with the effluent in surface and groundwater, affecting the quality of water. According to the Green Drop Report released in 2022, over 50 % of South African wastewater treatment plants are operating in a poor state and only less than 10 % are operating efficiently. Moreover, this threatens the quality of life for all organisms and humans as they rely highly on the sustainability of water for survival. And the continuous release of these organic pollutants from WWTPs continues to cause disruption in the environment as animals and humans drink the contaminated water. Hence, it causes health concerns such as antiviral drug resistance, defects on unborn babies, etc. The removal and breakdown of these emerging organic pollutants have been difficult, limiting access to clean and safe drinking water.
To address the limitations of WWTPs in removing these ARVs, new technologies for degrading and removing ARVs in water have been developed. There may be a need to develop effective techniques to remove organic pollutants in wastewater treatment plants before the effluent is deposited in rivers, dams, and lakes, thereby purifying water. The use of nanomaterials in heterogeneous photocatalysis has
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emerged as one of the promising technologies that can be incorporated into WWTPs to improve the efficiency of removing organic pollutants.
Hence, this work presents the use of a supramolecular β-cyclodextrin linked into a 2D/2D formed heterostructure of tungsten trioxide with titanium carbide MXene through hexamethylene diisocynate (HMDI) bifunctional linker (WO3-Ti3C3@β-CD nanocomposite) for the degradation of oseltamivir in wastewater. Oseltamivir is an ARV drug used mostly to treat influenza infections. It has been found frequently in bodies of water in many countries including South Africa.
The experimental data reported in this work highlights steps that were followed to develop the nanocomposite. In brief, tungsten trioxide (WO3) nanoparticles were synthesized through a hydrothermal method.Titanium carbide (Ti3C2) MXene was synthesized by etching out an aluminum layer from titanium aluminium carbide (Ti3AlC2) MAX phase, followed by delaminating the layers using dimethyl sulfoxide (DMSO). The WO3-Ti3C2 heterostructure was synthesized in a similar method as WO3, using hydrothermal. The WO3-Ti3C2@β-CD was synthesized by linking the formed WO3-Ti3C2 with β-cyclodextrin through HMDI as a bifunctional linker. Successful linking was monitored with FTIR, with the disappearance of the isocyanate peak.
Furthermore, the polymorphic nature, structural fingerprint, crystallinity, morphology, surface area, and elemental composition of the synthesized nanocomposite and pristine WO3 nanoparticles and Ti3C2 MXene were determined using microscopic and spectroscopic techniques. The data obtained from these tools confirmed the formation of the WO3-Ti3C2 heterostructure and the successful linkage of the heterostructure to a β-cyclodextrin through an HMDI bifunctional linker.
UV-vis DRS, PL, EIS, and photocurrent response were used to conduct optical and electrochemical studies on the synthesized nanomaterials. These techniques revealed that the WO3-Ti3C2@β-CD nanocomposite exhibited excellent light absorption response and low recombination of photoinduced charges compared to pristine WO3 and WO3-Ti3C2. The enhanced visible light response may be caused by the presence of Ti3C2 MXene with excellent conductivity and electrical properties, as well as the larger surface area of the nanocomposite which provides active sites on the surface.
The oseltamivir pollutant was first degraded using bacteria in the biological system, and the highest degradation efficiency achieved was 65.6 % when degrading 5 mg/L oseltamivir. Combining the biological and photocatalytic systems improved degradation efficiency. After optimizing the degradation environment, it was discovered that oseltamivir degrades better in a solution of 5 mg/L, with a catalyst loading of 25 mg and a working pH of 3. The nanocomposite showed improved photo efficiency as compared to pristine WO3 and WO3-Ti3C2 with the highest degradation efficiency of 85 % while pristine WO3 and WO3-Ti3C2 reached 50.4 % and 60.5 %, respectively. High-resolution mass spectrometry was used to assess the degree of photo efficiency that was attained from the nanocomposite. The efficacy of this photocatalytic method was demonstrated by the fact that the hydroxycarboxylic group was the smallest detected fragment. This group can be further broken down into alcohol, a less toxic and harmless by-product than oseltamivir.