Degradation of bisphenol-a and 2-Nitrophenol by combined advanced oxidation technologies

Philosophiae Doctor - PhDEmerging micropollutants such as bisphenol-A and 2-nitrophenol present a great threat in drinking water due to their adverse effects. Most conventional technologies in water and wastewater treatment are not designed to eliminate these xenobiotics; instead pollutants are merely transferred from one phase to another. Advanced oxidation technologies (AOTs) however, have been identified as suitable routes for the degradation of these potential damaging substances based on free radical mechanisms and use of less expensive chemicals. Moreover, due to the structural complexity of wastewater and the existence of pollutants as mixtures, no single advanced oxidation technology can convincingly remove all forms of contaminants and then most often than not, a combination of treatment processes is required for an effective purification process. Besides, the problem of adequate degradation of emerging contaminants in the environment, when AOT(s) are used individually, they present inherent problems. For instance, powder TiO₂ photocatalysts obstruct light penetration, thus prevent effective interaction of UV light with the target pollutants, and particulates present problems of post-filtration and recovery of catalyst particles after treatment. Additionally, TiO₂ has a high band gap energy, high electron-hole recombination rate, and is prone to aggregation of the suspended particles. Similarly, the dielectric barrier discharge (DBD) system produces ultra violet light and hydrogen peroxide within the plasma zone which is not fully maximised for the mineralization of persistent organic pollutants. Rapid oxidation and aggregation of nano zero valent iron particles in photo-Fentons process reduce the particles mobility and affect its performance. In the same vein, the jet loop reactor (JLR) system is characterised by low impingement yield, which is responsible for low mineralization rate. In light of this background, this research investigated the degradation of bisphenol-A and 2- nitrophenol in aqueous solution using the following combined advanced oxidation methods: DBD/supported TiO₂ or Ag doped TiO₂ photocatalysts, DBD/photo-Fenton induced process and JLR/UV/H₂O₂. The target was to assess the performance of each single system and then identify the best combined AOTs capable of significantly mineralizing the target compounds. Firstly, two materials were developed namely supported TiO₂ and stabilized nano zero valent Fe. The TiO₂ photocatalyst supported on a stainless steel mesh was synthesised using sol-gel solution of 8 % PAN/DMF/TiCl₄. The influence of calcination temperature and holding time on the formation of nanocrystals was investigated. Afterwards, various amounts of metallic silver were deposited on the (optimum) supported TiO₂ photocatalyst using thermal evaporation. The catalysts were characterized by several analytical methods; HRSEM, HRTEM, EDS, SAED, FTIR, TGA-DSC, UV-vis/diffuse reflectance spectroscopy, XRD, BET, and XPS. The photocatalytic activity of the prepared catalysts was determined using methylene blue as a model pollutant under ultra-violet light irradiation. Secondly, the TiO2 photocatalyst and 2.4 % Ag doped TiO₂ nanocomposites obtained as optimums (in section 1) were combined with the DBD to decompose BPA or 2-NP in aqueous solution. Moreover, the photo-Fenton process was applied for degradation of the model pollutants, and different dosages of stabilized nZVI (in the range of 0.02 -1.00 g) were added to the DBD system to induce the photo-Fenton process and improve BPA or 2-NP degradation efficiency. Finally, a jet loop reactor (JLR) presenting advanced mixing by the “impinging effect” was explored to decompose BPA or 2-NP in aqueous solution as a function of inlet applied pressure, solution pH, and initial concentration of BPA or 2-NP. Subsequently, different concentrations of hydrogen peroxide (H₂O₂) were added to the JLR to enhance the mineralization process. Furthermore, a combination of JLR with in-line UV light and H₂O₂ were further utilised to decompose BPA or 2-NP in aqueous solution. The residual concentration of the model compounds and intermediates were analysed using high performance liquid chromatography (HPLC) and liquid chromatography mass spectrometry (LCMS). The concentration of the ozone, hydrogen peroxide and hydroxyl radicals generated by the DBD in the presence or absence of a catalyst was monitored using Ultraviolet-visible spectroscopy and Photoluminescence spectroscopy. The results revealed that the optimal thermal conditions to obtain well supported uniformly grown, highly active crystalline TiO₂ catalysts with high specific surface area was 350 ºC at a 3 h holding time in N2 atmosphere with a flow rate of 20 mL/min. Pyrolysis temperature and holding time played an important role on the crystalline nature and photocatalytic activity of the catalyst. Moreover, 2.4 % Ag doped TiO₂ nanocomposites exhibited higher photocatalytic activity for methylene blue degradation than the undoped supported TiO₂ nanocrystals. The results indicated that combining DBD with 2.4 % Ag doped TiO₂ nanocomposites achieved 89 % and 81 % removal efficiency for BPA or 2-NP compared to 67.22 % or 56.8 % obtain when using the DBD system alone. The 2.4 % Ag doped TiO₂ nanocomposites demonstrated excellent activity and offered photochemical stability after four repeated applications.In the case of the photo-Fenton induced process, nano zero valent iron particles (nZVI) stabilized with polyethylene glycol were synthesised using a modified borohydride reduction method. The HRSEM, BET, XRD, and XPS analysis confirmed the formation of filamentous, high surface area iron nanoparticles in the zero valent state. Unlike combined DBD/Ag doped TiO2 nanocomposites, 100 % or complete removal of BPA or 2-NP in aqueous solution was achieved with DBD/nZVI system within 30 minutes compared to 67.9 % (BPA) or 56.8 % (2-NP) with DBD alone after 80 minutes. The removal efficiency was attributable to the production of an increased concentration of OH radicals as well as existence of a synergetic effect in the combined DBD/nZVI system. Five new transformation products namely: 4-nitrophenol (C₆H₅NO₃), 4-nitrosophenolate (C₆H₄NO₂), 4-(prop-1-en-2-yl) cyclohexa-3,5-diene-1,2-dione, (C₉H₈O₂), 4-(2- hydroxylpropan-2-yl)cyclohexane-3,5-diene-1,2-dione (C₉H₁₀O₃), and 1,2-dimethyl-4-(2- nitropropan-2-yl)benzene (C₉H₁₀NO₄) were identified during the degradation of BPA. While, three aromatic intermediate compounds such as 2-nitro-1,3,5-benzenetriolate (C₆H₂NO₅), 2- nitro-1,4-benzoquinone (C₆H₃NO₄), and 2,5-dihydroxyl-1,4-benzoquinone (C₆H₄O₄) respectively were identified during the degradation of 2-NP for the first time in the DBD with JT14 or JT17 using LC-MS. These intermediate compounds have never been reported in the literature, thereby expanding the number of BPA or 2-NP intermediates in the data base in the DBD/JT14 or DBD/nZVI system. BPA degradation proceeded via ozonation, hydroxylation, dimerization, and decarboxylation and nitration step, while 2-NP proceeded via hydroxylation, nitration and denitration respectively. Furthermore, maximum removal efficiency of BPA or 2-NP in aqueous solution using JLR alone under the optimum solution pH (3), inlet pressure (4 bar), flow rate (0.0007 m3/s) was 14.0 % and 13.2 % respectively after 80 minutes. A removal efficiency of 34.9 % was recorded for BPA while 33.2 % was achieved for 2-NP using combined JLR/UV under the same conditions as JLR alone. For the combined JLR/H₂O₂ under optimum conditions of inlet pressure (4 bar), solution pH (3) and peroxide dosage (0.34 g/L), a 51.3 % and 50.1 % removal efficiency was achieved for BPA and 2-NP respectively under same conditions relative to JLR alone. Combination of JLR/UV/H₂O₂ achieved 77.7 % (BPA) or 76.6 % (2- NP) removal efficiency under the same conditions. The combined JLR/UV/H₂O₂ process was found to be most effective combination under the optimized operating parameters due to existence of a synergetic index value of 6.42 or 6.84. This implies that JLR should be coupled with UV and H₂O₂ to achieve greater mineralization efficiency instead of using the system individually. The obtained experimental data of these combined treatment processes fitted the pseudo-first order kinetic models. The combination of the JLR/UV/H₂O₂ was found to be energy efficient and could effectively degrade BPA or 2-NP in aqueous solution to a greater extent than the JLR, JLR/UV or JLR/H₂O₂ system. However, the total organic carbon (TOC) reduction value by all combined DBD and JLR system recorded was not completely achieved due to the formation of recalcitrant intermediate compounds under the applied conditions. In conclusion, this study is reporting for the first time a combination of supported 2.4 % Ag doped TiO₂ nanocomposites with dielectric barrier discharge system for BPA/2-NP degradation in aqueous solution; a combination jet loop reactor based on impingement with in-line UV lamp and H2O2 for successfully decomposing BPA or 2-NP in aqueous solution; as well as a combination of dielectric barrier discharge system and stabilised nano zero valent iron particles, which induced a photo-Fenton process for highly effective removal of BPA or 2-NP in aqueous solution. This study conclusively supports the hypothesis that combined advanced oxidation technologies offer a sustainable and highly efficient means of achieving partial or complete removal of BPA or 2-NP in aqueous solutions. Considering all the combinations of AOTs investigated in this study, the novel DBD/photo-Fenton-induced process under optimised operating parameters was found to be the most efficient in the elimination of BPA or 2-NP in aqueous solutions. The combination of DBD with photo- Fenton like process offers a promising advanced waste water purification technology in the immediate future. Based on these findings, it is recommended that DBD should be redesigned to prevent loss of ozone and JLR system reconfigured to increase impingement and cavitational yield in order to have an effective combination treatment strategy for waste water purification especially in large scale waste water management.National Research Foundation (NRF) and Water Research Commission, South Afric

Hypoglycaemic activity of biosynthesized copper oxide nanoparticles in alloxan-induced diabetic Wister rats

Diabetes mellitus (DM) is a metabolic disorder that affects the body's ability to produce or use insulin. This study evaluated the hypoglycaemic activity of biosynthesized copper oxide nanoparticles (CuO-NPs) in alloxan-induced diabetic Wister rats. CuO-NPs were synthesized via the green route and characterized using different analytical tools. Diabetes was induced intraperitoneally using 90 mg/kg body weight of alloxan monohydrate in albino rats. Thirty (30) rats were randomly divided into 5 groups of 6 rats each and orally treated for 21 days. Groups I and II were treated with 300 mg/kg bwt Cereus hildmannianus extract and CuO-NPs, respectively. Groups III and IV received 5 mg/kg bwt of Glibenclamide and 2 mL of normal saline, respectively, while Group V was left untreated as the diabetic control. Blood glucose (BG) levels and body weight changes were monitored at 3- and 7- day intervals, respectively, throughout 21-day treatment period. Lipid profiles, enzyme assays and histopathological studies of the liver were also carried out

Entrapped chemically synthesized gold nanoparticles combined with polyethylene glycol and chloroquine diphosphate as an improved antimalarial drug

Objective(s): Drug delivery is an engineering technology to control the release and delivery of therapeutic agents to target organs, tissues, and cells. Metallic nanoparticles, such as gold nanoparticles (AuNPs) have exceptional properties which enable efficient drug transport into different cell types with reduced side effects and cytotoxicity to other tissues.Materials and Methods: AuNPs were synthesized by adopting the Turkevich method to reduce tetra chloroauric (III) acid (HAuCl4) solution with sodium citrate. A factorial design of 24 was used to investigate the influence of temperature, stirring speed, and the volume of citrate and gold salt on the size of AuNPs synthesis. The produced chemical-AuNPs (CN-AuNPs) were characterized using ultraviolet-visible spectroscopy and dynamic light scattering (DLS) which was conjugated with polyethylene glycol (PEG) loaded with chloroquine diphosphate. The latter were characterized with transmission electron microscopy (TEM), Energy dispersive x-ray spectroscopy (EDS), selected area electron diffraction (SAED) patterns and Fourier transmission infrared spectroscopy. The antimalarial activities of the three formulations were tested on Plasmodium-infected mice. Moreover, the evaluation of curative potentials of the formulations was carried out via parasite counts. The anemic and pathological conditions of nano-encapsulation were investigated for their cytotoxicity level. Results: The CN-AuNPs show surface plasmon resonance absorption ranging from 526 to 529 nm with smaller particle size at the lower citrate volume. The TEM image of CN-AuNPs with polyethylene glycol (PEG) and CN-AuNPs-PEG encapsulated with chloroquine diphosphate revealed spherical shape with EDS showing the appearance of gold (Au) at 2.0, 2.1, and 9.9 KeV. The SAED also revealed that the AuNPs were crystalline in nature. The in vitro time-dependent encapsulation release showed an extension of time release, compared to CN-AuNPs-PEG with parasitemia clearance at the same level of cytotoxicity. Conclusion: Therefore, although improved activity of the CN-AuNPs-PEG encapsulating was achieved but its cytotoxicity still is a limitation

Treatment of persistent organic pollutants in wastewater using hydrodynamic cavitation in synergy with advanced oxidation process

Persistent organic pollutants (POPs) are very tenacious wastewater contaminants. The consequences of their existence have been acknowledged for negatively affecting the ecosystem with specific impact upon endocrine disruption and hormonal diseases in humans. Their recalcitrance and circumvention of nearly all the known wastewater treatment procedures are also well documented. The reported successes of POPs treatment using various advanced technologies are not without setbacks such as low degradation efficiency, generation of toxic intermediates, massive sludge production, and high energy expenditure and operational cost. However, advanced oxidation processes (AOPs) have recently recorded successes in the treatment of POPs in wastewater. AOPs are technologies which involve the generation of OH radicals for the purpose of oxidising recalcitrant organic contaminants to their inert end products. This review provides information on the existence of POPs and their effects on humans. Besides, the merits and demerits of various advanced treatment technologies as well as the synergistic efficiency of combined AOPs in the treatment of wastewater containing POPs was reported. A concise review of recently published studies on successful treatment of POPs in wastewater using hydrodynamic cavitation technology in combination with other advanced oxidation processes is presented with the highlight of direction for future research focus

Effective removal of malachite green from local dyeing wastewater using zinc-tungstate based materials

The frequent use of an industrial dye such as malachite green (MG) has caused major water body deterioration and is one of the most pressing global challenges, demanding effective treatment techniques. To solve these issues, a simplistic method was developed to synthesize zinc-tungstate (ZnWO4) nanoparticles and also dope the surface matrix of the ZnWO4 nanoparticles using nonmetals of boron (B), carbon (C), and nitrogen (N) at different ratios for enhanced MG removal from wastewater. The prepared nanomaterials were characterized by different methods for crystal structure composition, surface properties, surface morphology, microstructures, functional groups, and elemental oxidation states. The BET analysis revealed a mesoporous structure with surface areas of 30.740 m2/g for ZnWO4, 38.513 m2/g for ZnWO4@BCN, 37.368 m2/g for ZnWO4@BCN/B, 39.325 m2/g for ZnWO4@BCN/C, and 45.436 m2/g for ZnWO4@BCN/N nanocomposites. The best removal of MG was accomplished at pH (8), contact period (50 min), nanoadsorbent dose (0.8 g/L), initial MG concentration (20 mg/L), and temperature (303 K). The maximum adsorption capacities of ZnWO4 and ZnWO4@BCN/N towards MG were 218.645 and 251.758 mg/g, respectively. At equilibrium, the Freundlich isotherm and pseudo-second-order kinetic models were the best fits for the experimental data of MG adsorption on both nanoadsorbents. After eight cycles of adsorption and desorption, both ZnWO4 and ZnWO4@BCN/N were found to be good at removing MG, with efficiencies of 71.00 and 74.20%, respectively. Thermodynamic investigations further validated the spontaneity and endothermic nature of the adsorption process. All study findings confirm the nanoadsorbents exceptional capability and economic feasibility for removing MG dye

Hypoglycaemic activity of biosynthesized copper oxide nanoparticles in alloxan‐induced diabetic Wister rats

Abstract Background Diabetes mellitus (DM) is a metabolic disorder that affects the body's ability to produce or use insulin. This study evaluated the hypoglycaemic activity of biosynthesized copper oxide nanoparticles (CuO‐NPs) in alloxan‐induced diabetic Wister rats. Methods CuO‐NPs were synthesized via the green route and characterized using different analytical tools. Diabetes was induced intraperitoneally using 90 mg/kg body weight of alloxan monohydrate in albino rats. Thirty (30) rats were randomly divided into 5 groups of 6 rats each and orally treated for 21 days. Groups I and II were treated with 300 mg/kg bwt Cereus hildmannianus extract and CuO‐NPs, respectively. Groups III and IV received 5 mg/kg bwt of Glibenclamide and 2 mL of normal saline, respectively, while Group V was left untreated as the diabetic control. Blood glucose (BG) levels and body weight changes were monitored at 3‐ and 7‐day intervals, respectively, throughout 21‐day treatment period. Lipid profiles, enzyme assays and histopathological studies of the liver were also carried out. Results Spheroidal tenorite phase of CuO‐NPs with a crystallite size of 62.57 nm, surface area (20.64 m2/g) and a UV‐maximum absorption at 214.27 nm was formed. The diabetic rats treated with 300 mg/kg bwt CuO‐NPs had the highest BG lowering ability (from 482.75 ± 27.70 to 124.50 ± 2.50 mg/dL). A significant difference (p < 0.05) in weight gain and serum enzymes was also observed in the CuO‐NPs treated group compared with other groups. The CuO‐NPs‐treated group had a significant increase (p < 0.05) in HDL‐cholesterol and a decrease in total cholesterol, triglycerides, LDL‐cholesterol and VLDL‐cholesterol compared with other groups. Conclusion The green synthesized CuO‐NPs nanoparticles significantly reduced (p < 0.05) blood glucose levels in rats and other associated indices and could serve as drug lead in the treatment of diabetes

Taguchi optimization design of diameter-controlled synthesis of multi walled carbon nanotubes for the adsorption of Pb(II) and Ni(II) from chemical industry wastewater

Herein, Taguchi L9 orthogonal array was used for the first time to optimize synthesis of diameter-controlled multi walled carbon nanotubes (MWCNTs). The nanoadsorbents, MWCNTs5-15 nm and MWCNTs16-25 nm were applied for Pb(II) and Ni(II) ion removal from paint, battery and electroplating wastewater. The results indicated successful synthesis of MWCNTs with diameter distribution ranges of 5-15 nm and 16-25 nm. The synthetized smaller diameter MWCNTs5-15 nm revealed higher Brunauer-Emett-Teller (BET) surface area of 1306 ± 5 m2/g compared to larger diameter MWCNTs16-25 nmwith the surface area of 1245 ± 4 m2/g. They demonstrated excellent adsorption of Pb(II) and Ni(II) ions within the permissible concentration proposed by WHO at pH, contact time, adsorbent dosage and temperature of 5, 60 min, 30 mg/L and 50 °C, respectively. Particularly, MWCNTs5-15 nm possessed high adsorption capacity of 215.38 ± 0.03 mg/g for Pb(II) and 230.78 ± 0.01 mg/g for Ni(II). Again, the maximum adsorption capacity of 201.35 ± 0.02 and 206.40 ± 0.02 mg/g was achieved for Pb(II) and Ni(II) using MWCNTs16-25 nm. All in all, the adsorption capacity of the nanoadsorbents at the investigated diameter range showed higher efficiency compared to other materials for heavy metals elimination from chemical industrial wastewater.Ministry of National Development (MND)National Environmental Agency (NEA)National Research Foundation (NRF)This research was made possible through the financial support of the Petroleum Technology Development Fund, Nigeria (grant number PTDF/ED/LSS/PhD/TCE/123/17). SCARCE is supported by the National Research Foundation, Prime Minister’s Office, Singapore, the Ministry of National Development, Singapore, and National Environment Agency, Ministry of Sustainability and the Environment, Singapore under the Closing the Waste Loop R&D Initiative as part of the Urban Solutions & Sustainability e Integration Fund (Award No. USS-IF-2018-4)

TiO2 assisted photocatalysts for degradation of emerging organic pollutants in water and wastewater

International audienc