Synthesis and characterization of pristine and lanthanum modified wo3 nanoparticles for the photocatalytic degradation of organic dyes

Abstract : South Africa is rich in naturally occurring resources including water, coal, oil, land. Individuals and industries use these resources as raw material inputs on a daily basis. However, they create significant amounts of pollution such as persistent organic pollutants (POPs). Such pollutants can be classified as inorganic, microbial and organic. Organic pollutants such as organic dyes are found in textile effluents that escape to the environment. They are designed to have a high degree of stability to fading upon sunlight exposures, chemicals and microbial attack leading to the ineffectiveness of current conventional wastewater treatment methods. Conventional wastewater treatment methods have been reported to be ineffective in the degradation of textile dyes because of their chemical stability. These methods have low effectiveness, with limited flexibility, they require specialized equipment and further handling of the generated waste. These methods are reported to have the ability to effectively remove colour, but for but lack the ability to completely degrade the dye molecules. Developed methods such as advanced oxidation processes (AOPs) use of photocatalytic semiconductors. These semiconductors have been researched and reported to have the characteristics to effectively treat wastewater by completely degrading a diversity of organic pollutants. A widely used semiconductor is monoclinic tungsten trioxide (WO3). It is viewed as an ideal candidate for photocatalytic applications. It is a photocatalyst that is responsive in the visible region, it absorbs light in the region up to 480 nm. WO3 has small band-gap energy which has been reported to range from 2.4−2.8 eV and high oxidation power of valence band (VB) holes and thus displays enhanced photoabsorption in visible-light irradiation. This gives WO3 the advantage to be used as an indoor pollutant treatment as well as outdoor applications. Hence, this project aims to utilize lanthanum-doped WO3 for the photodegradation of refractory vi organic dyes. Lanthanides as dopants are reported to improve the photocatalytic activity of the catalyst by increasing the adsorption capacity for pollutants, as well as, reducing the electron-hole recombination rates. In this study, pristine tungsten trioxide (WO3) nanoparticles were synthesized using the impregnation method with tungstic acid (H2WO4) and nitric acid as precursors, Lanthanum nitrate hydrate was used as a source of lanthanum (La) dopant. The as-synthesized nanoparticles were annealed at 450ºC for 3 hrs. The nanoparticles were characterized using X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), coupled with energy dispersive X-ray (EDX), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, zeta potential, UV-visible spectroscopy (UV-vis), X-Ray photoelectron spectroscopy (XPS) and Ion chromatography (IC). Spectroscopic instruments such as XRD, Raman and FTIR confirmed the nanoparticles were composed of monoclinic polymorphs. The spherical morphology was confirmed by TEM and SEM, with EDX confirming the presence of tungsten, oxygen and lanthanum in the samples. The band gap energy obtained from the DRS measurements were found to be 2.45, 2.42 and 2.57 eV for m-WO3, 1-La-WO3, and 5-La-WO3 nanoparticles respectively. XPS was used to determine the valence band maximum (VBM) which was used to calculate the conduction band and estimate the band edge position. XPS band edge positions were in agreement with the UV-vis band edge positions. Zeta potential confirmed the point of zero charge for the nanoparticles to be at pH 3.8. Ion chromatography confirmed the evolution of the chlorides and sulphate ions from the degradation of Methylene blue and Congo red respectively.M.Tech. (Chemistry

Exposure assessment of engineered nanomaterials released from commercially available nano-enabled products into water systems

Abstract: Please refer to full text to view abstract.Ph.D. (Chemistry

Assessment of Nanopollution from Commercial Products in Water Environments

The use of nano-enabled products (NEPs) can release engineered nanomaterials (ENMs) into water resources, and the increasing commercialisation of NEPs raises the environmental exposure potential. The current study investigated the release of ENMs and their characteristics from six commercial products (sunscreens, body creams, sanitiser, and socks) containing nTiO2, nAg, and nZnO. ENMs were released in aqueous media from all investigated NEPs and were associated with ions (Ag+ and Zn2+) and coating agents (Si and Al). NEPs generally released elongated (7–9 × 66–70 nm) and angular (21–80 × 25–79 nm) nTiO2, near-spherical (12–49 nm) and angular nAg (21–76 × 29–77 nm), and angular nZnO (32–36 × 32–40 nm). NEPs released varying ENMs’ total concentrations (ca 0.4–95%) of total Ti, Ag, Ag+, Zn, and Zn2+ relative to the initial amount of ENMs added in NEPs, influenced by the nature of the product and recipient water quality. The findings confirmed the use of the examined NEPs as sources of nanopollution in water resources, and the physicochemical properties of the nanopollutants were determined. Exposure assessment data from real-life sources are highly valuable for enriching the robust environmental risk assessment of nanotechnology

The role of men in determining fertility among the Banyankore of Southwestern Uganda - By JAMES P. N. NTOZI.

This work is the third in a monograph series based on surveys on the determinants of fertility in Ankole, Uganda. As stated in the foreword, this study is significant, in view of the gaps in the existing body of research: the dearth of research on men’s role in determining fertility and the sideline attention devoted to cultural factors which increasingly prove very central to fertility behaviour

Improved electro-oxidation of triclosan at nano-zinc oxide-multiwalled carbon nanotube modified glassy carbon eiectrode

An electrochemical sensor for oxidation of triclosan at a nano-zinc oxide-multiwalled carbon nanotube (nZnO–MWCNT) composite modified glassy carbon (GC) electrode was examined by cyclic voltammetry (CV), differential pulse voltammetry (DPV), chronoamperometry and square wave voltammetry (SWV) in a pH 7.0 phosphate buffer. By combining the benefits of nZnO–MWCNT composite and GC electrode, the resulting modified electrode exhibited outstanding electrocatalytic behavior towards oxidation of triclosan by giving higher currents and lower oxidation peak potential compared to the bare GC electrode, nZnO and MWCNT modified electrodes. The effects of various parameters on the voltammetric response of triclosan were investigated. Under optimized conditions, the resulting sensor offered an excellent response for triclosan in the concentration range from 1.5 μg L−1 to 2.0 mg L−1 with detection limit of 1.3 μg L−1 and a coefficient of determination (R2) of 0.9931. The diffusion coefficient of triclosan was determined to be 1.65 × 10−6 cm2 s−1. The electrochemical sensor showed satisfactory stability, selectivity and reproducibility when stored under room conditions

Characterisation of Engineered Nanomaterials in Nano-Enabled Products Exhibiting Priority Environmental Exposure

Analytical limitations have constrained the determination of nanopollution character from real-world sources such as nano-enabled products (NEPs), thus hindering the development of environmental safety guidelines for engineered nanomaterials (ENMs). This study examined the properties of ENMs in 18 commercial products: sunscreens, personal care products, clothing, and paints—products exhibiting medium to a high potential for environmental nanopollution. It was found that 17 of the products contained ENMs; 9, 3, 3, and 2 were incorporated with nTiO2, nAg, binaries of nZnO + nTiO2, and nTiO2 + nAg, respectively. Commonly, the nTiO2 were elongated or angular, whereas nAg and nZnO were near-spherical and angular in morphology, respectively. The size ranges (width × length) were 7–48 × 14–200, 34–35 × 37–38, and 18–28 nm for nTiO2, nZnO, and nAg respectively. All ENMs were negatively charged. The total concentration of Ti, Zn, and Ag in the NEPs were 2.3 × 10−4–4.3%, 3.4–4.3%, and 1.0 × 10−4–11.3 × 10−3%, respectively. The study determined some key ENM characteristics required for environmental risk assessment; however, challenges persist regarding the accurate determination of the concentration in NEPs. Overall, the study confirmed NEPs as actual sources of nanopollution; hence, scenario-specific efforts are recommended to quantify their loads into water resources

Characterisation of Engineered Nanomaterials in Nano-Enabled Products Exhibiting Priority Environmental Exposure

Analytical limitations have constrained the determination of nanopollution character from real-world sources such as nano-enabled products (NEPs), thus hindering the development of environmental safety guidelines for engineered nanomaterials (ENMs). This study examined the properties of ENMs in 18 commercial products: sunscreens, personal care products, clothing, and paints—products exhibiting medium to a high potential for environmental nanopollution. It was found that 17 of the products contained ENMs; 9, 3, 3, and 2 were incorporated with nTiO2, nAg, binaries of nZnO + nTiO2, and nTiO2 + nAg, respectively. Commonly, the nTiO2 were elongated or angular, whereas nAg and nZnO were near-spherical and angular in morphology, respectively. The size ranges (width × length) were 7–48 × 14–200, 34–35 × 37–38, and 18–28 nm for nTiO2, nZnO, and nAg respectively. All ENMs were negatively charged. The total concentration of Ti, Zn, and Ag in the NEPs were 2.3 × 10−4–4.3%, 3.4–4.3%, and 1.0 × 10−4–11.3 × 10−3%, respectively. The study determined some key ENM characteristics required for environmental risk assessment; however, challenges persist regarding the accurate determination of the concentration in NEPs. Overall, the study confirmed NEPs as actual sources of nanopollution; hence, scenario-specific efforts are recommended to quantify their loads into water resources

Occurrence and environmental levels of triclosan and triclocarban in selected wastewater treatment plants in Gauteng Province, South Africa

Triclosan and triclocarban are industrial chemicals that are frequently added into consumer and personal care products. Information on the levels on these compounds in water systems in the African continent is still very scarce. In the present study, the occurrence, seasonal variation, and estimated removal of TCS and TCC in six different wastewater treatment plants in Gauteng Province, South Africa, were investigated over a period of two years, together with effluent receiving river water. The instrumental analysis was carried out using Shimadzu LCMS/MS 8030, employing negative electrospray ionization. Both target compounds were ubiquitously detected with influent and raw sludge having elevated concentrations. Generally, TCS concentrations were higher than those of TCC. The concentrations obtained for TCS were (influent, 2.01–17.6 μg/L; effluent, 0.990–13.0 μg/L; river, 0.880–8.72 μg/L; raw sludge, 3.65–15.0 μg/kg; treated sludge, 2.08–7.81 μg/kg and biosolids, 2.16–13.5 μg/kg); while TCC levels were obtained to be (influent, 0.0860–2.84 μg/L; effluent, <LOD - 1.89 μg/L; river, nd - 0.360 μg/L; raw sludge, 3.65–11.8 μg/kg; treated sludge, 1.21–9.19 μg/kg; biosolids, 2.59–8.23 μg/kg). Occurrence of TCS in wastewater was found to be influenced by temporal changes. This was not the case for occurrence of TCS and TCC in sludge samples. Similar to their environmental occurrence, the estimated treatment efficiencies also varied across the wastewater treatments plants, with the highest elimination rates of 63% and 97% for TCS and TCC, respectively

Environmental Dissemination of Selected Antibiotics from Hospital Wastewater to the Aquatic Environment

The environmental dissemination of selected antibiotics from hospital wastewater into municipal wastewater and lastly to a receiving water body was investigated. Selected antibiotics (azithromycin (AZM), ciprofloxacin (CIP), clindamycin (CDM), doxycycline (DXC) and sulfamethoxazole (SMZ)) present in effluents of academic hospital wastewater, influents, sewage sludge, and effluents of municipal wastewater, receiving water, and its benthic sediment samples were quantified using the Acquity® Waters Ultra-Performance Liquid Chromatography System hyphenated with a Waters Synapt G2 coupled to a quadrupole time-of-flight mass spectrometer. The overall results showed that all assessed antibiotics were found in all matrices. For solid matrices, river sediment samples had elevated concentrations with mean concentrations of 34,834, 35,623, 50,913, 55,263, and 41,781 ng/g for AZM, CIP, CDM, DXC, and SMZ, respectively, whereas for liquid samples, hospital wastewater and influent of wastewater had the highest concentrations. The lowest concentrations were observed in river water, with mean concentrations of 11, 97, 15, and 123 ng/L, except for CDM, which was 18 ng/L in the effluent of wastewater. The results showed that the highest percentages of antibiotics removed was SMZ with 90%, followed by DXC, AZM and CIP with a removal efficiency of 85%, 83%, and 83%, respectively. The antibiotic that showed the lowest removal percentage was CDM with 66%. However, the calculated environmental dissemination analysis through the use of mass load calculations revealed daily release of 15,486, 14,934, 1526, 922, and 680 mg/d for SMZ, CIP, AZM, DXC, and CDM, respectively, indicating a substantial release of selected antibiotics from wastewater to the river system, where they are possibly adsorbed in the river sediment. Further research into the efficient removal of antibiotics from wastewater and the identification of antibiotic sources in river sediment is needed

Aquatic Environment Exposure and Toxicity of Engineered Nanomaterials Released from Nano-Enabled Products: Current Status and Data Needs

Rapid commercialisation of nano-enabled products (NEPs) elevates the potential environmental release of engineered nanomaterials (ENMs) along the product life cycle. The current review examined the state of the art literature on aquatic environment exposure and ecotoxicity of product released (PR) engineered nanomaterials (PR–ENMs). Additionally, the data obtained were applied to estimate the risk posed by PR–ENMs to various trophic levels of aquatic biota as a means of identifying priority NEPs cases that may require attention with regards to examining environmental implications. Overall, the PR–ENMs are predominantly associated with the matrix of the respective NEPs, a factor that often hinders proper isolation of nano-driven toxicity effects. Nevertheless, some studies have attributed the toxicity basis of observed adverse effects to a combination of the released ions, ENMs and other components of NEPs. Notwithstanding the limitation of current ecotoxicology data limitations, the risk estimated herein points to an elevated risk towards fish arising from fabrics’ PR–nAg, and the considerable potential effects from sunscreens’ PR–nZnO and PR–nTiO2 to algae, echinoderms, and crustaceans (PR–nZnO), whereas PR–nTiO2 poses no significant risk to echinoderms. Considering that the current data limitations will not be overcome immediately, we recommend the careful application of similar risk estimation to isolate/prioritise cases of NEPs for detailed characterisation of ENMs’ release and effects in aquatic environments