Green synthesis of copper oxide nanoparticles using extracts of Solanum macrocarpon fruit and their redox responses on SPAu electrode

Abstract: Please refer to full text to view abstrac

Harnessing Project-Based Learning to Enhance STEM Students’ Critical Thinking Skills Using Water Treatment Activity

Water treatment processes are designed to ensure that any pollutant’s adverse effects on the environment are reduced to the minimum allowable discharge limit. Water-literate individuals ought to effectively and constantly think about novel hydrologic concepts to improve the quality and sufficiency of water. Socio-hydrological issues remain the main source of water pollution and insufficiency in society. Therefore, effective water management and treatment require societal understanding. The complexity of water issues requires equipping STEM education students with the necessary knowledge to acquire water solution reasoning skills. However, STEM students need meaningful challenges with everyday connections to capture their interest to apply intuitive understanding in project-based learning. Water-related issues such as high turbidity are ubiquitous problems facing communities. This study specifically explored how project-based learning can be harnessed to enhance STEM students’ critical thinking skills using water treatment activities. The water treatment activity involved the development of novel products using agricultural wastes for efficient water treatment. The social issues associated with agricultural wastes, especially orange and banana peels in the environment, are too obvious to be overlooked; hence, they were chosen as base materials to develop water treatment products. The study adopted an action research design and involved 12 purposively selected third-year Bachelor of Science students majoring in Chemistry at a South African university. The students were divided into two groups consisting of six participants. The researchers implemented team teaching and invoked students’ knowledge of Earth Science, Physics, Chemistry, and Technology to develop and implement laboratory experimental activities and class-based lesson plans. The empirical investigation was underpinned by the Five Steps of Project-Based Learning as the underlying theoretical framework. The chemistry of the processed peels such as particle size and functional groups provided insight into the mechanism responsible for water turbidity reduction. Laboratory experimental results revealed that the turbidity reduction obtained from the use of processed banana peels was higher than the processed orange peels coagulant. However, the performance of both coagulants in turbidity reduction complied with the South African National Standard (SANS241) for drinking water quality

Ce2O3/BiVO4 Embedded in rGO as Photocatalyst for the Degradation of Methyl Orange under Visible Light Irradiation

A p–n heterojunction semiconductor structure composed of Ce3O4 and BiVO4 has been synthesized and then incorporated into reduced graphene oxide (rGO) by the hydrothermal method. The ternary composites were characterized by X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron diffraction spectroscopy (EDS), and UV–vis spectroscopy. The efficiency of the composites as photocatalysts was determined by studying the oxidative degradation of methyl orange in aqueous solution under visible light irradiation. The effect of parameters such as pH, catalyst loading, and concentration of the dye solution was examined in order to determine their influence on the photocatalytic activity of the composites. The composite incorporated into reduced graphene oxide presented the highest percentage (above 90%) in 2 h time, attributed to the effect of the increased surface area. The process of the enhanced photocatalytic activity has been discussed based on the energy band positions of the nanoparticles within the composite

Photocatalytic Reduction of Hexavalent Chromium Using Cu_3.21Bi_4.79S₉/g-C₃N₄ Nanocomposite

The photocatalytic reduction of hexavalent chromium, Cr(VI), to the trivalent species, Cr(III), has continued to inspire the synthesis of novel photocatalysts that are capable of achieving the task of converting Cr(VI) to the less toxic and more useful species. In this study, a novel functionalized graphitic carbon nitride (Cu3.21Bi4.79S9/gC3N4) was synthesized and characterized by using X-ray diffraction (XRD), thermogravimetry analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), and scanning electron microscope (SEM). The composite was used for the photocatalytic reduction of hexavalent chromium, Cr(VI), under visible light irradiation. A 92.77% efficiency of the reduction was achieved at pH 2, using about 10 mg of the photocatalyst and 10 mg/L of the Cr(VI) solution. A pseudo-first-order kinetic study indicated 0.0076 min−1, 0.0286 min−1, and 0.0393 min−1 rate constants for the nanoparticles, pristine gC3N4, and the nanocomposite, respectively. This indicated an enhancement in the rate of reduction by the functionalized gC3N4 by 1.37- and 5.17-fold compared to the pristine gC3N4 and Cu3.21Bi4.79S9, respectively. A study of how the presence of other contaminants including dye (bisphenol A) and heavy-metal ions (Ag(I) and Pb(II)) in the system affects the photocatalytic process showed a reduction in the rate from 0.0393 min−1 to 0.0019 min−1 and 0.0039 min−1, respectively. Finally, the radical scavenging experiments showed that the main active species for the photocatalytic reduction of Cr(VI) are electrons (e−), hydroxyl radicals (·OH−), and superoxide (·O2−). This study shows the potential of functionalized gC3N4 as sustainable materials in the removal of hexavalent Cr from an aqueous solution

Photocatalytic Reduction of Hexavalent Chromium Using Cu3.21Bi4.79S9/g-C3N4 Nanocomposite

The photocatalytic reduction of hexavalent chromium, Cr(VI), to the trivalent species, Cr(III), has continued to inspire the synthesis of novel photocatalysts that are capable of achieving the task of converting Cr(VI) to the less toxic and more useful species. In this study, a novel functionalized graphitic carbon nitride (Cu3.21Bi4.79S9/gC3N4) was synthesized and characterized by using X-ray diffraction (XRD), thermogravimetry analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), and scanning electron microscope (SEM). The composite was used for the photocatalytic reduction of hexavalent chromium, Cr(VI), under visible light irradiation. A 92.77% efficiency of the reduction was achieved at pH 2, using about 10 mg of the photocatalyst and 10 mg/L of the Cr(VI) solution. A pseudo-first-order kinetic study indicated 0.0076 min−1, 0.0286 min−1, and 0.0393 min−1 rate constants for the nanoparticles, pristine gC3N4, and the nanocomposite, respectively. This indicated an enhancement in the rate of reduction by the functionalized gC3N4 by 1.37- and 5.17-fold compared to the pristine gC3N4 and Cu3.21Bi4.79S9, respectively. A study of how the presence of other contaminants including dye (bisphenol A) and heavy-metal ions (Ag(I) and Pb(II)) in the system affects the photocatalytic process showed a reduction in the rate from 0.0393 min−1 to 0.0019 min−1 and 0.0039 min−1, respectively. Finally, the radical scavenging experiments showed that the main active species for the photocatalytic reduction of Cr(VI) are electrons (e−), hydroxyl radicals (·OH−), and superoxide (·O2−). This study shows the potential of functionalized gC3N4 as sustainable materials in the removal of hexavalent Cr from an aqueous solution

Photocatalytic reduction of hexavalent chromium using Zn2SnO4–ZnO modified g-C3N4 composite

In this study, a novel hierarchical g-C3N4/Zn2SnO4–ZnO heterojunction system was reported as an efficient photocatalyst for the reduction of Cr(VI). The fabrication of the composite involved the synthesis of the complex metal oxide (Zn2SnO4–ZnO), followed by the in-situ integration into graphitic carbon nitride. The structure, morphology, and optical properties of the as-prepared tertiary composite were determined using various analytical techniques. The results indicated the improvement in surface area and the electronic structure of the semiconductor heterostructures. Photocatalytic measurement showed the efficiency of the ternary composite to cause a reduction of the band gap energy, delayed charge recombination process and enhancement of the visible light absorption. Reaction parameters including the solution pH, photocatalyst (g-C3N4/ZTO-ZnO) dosage, and the initial concentration of Cr(VI) on the degradation efficiency of the photocatalyst were evaluated. The solution pH was varied from 2 to 8, and pH 2 displayed the highest removal of Cr(VI) with 99.2 % removal efficiency for the g-C3N4/ZTO-ZnO, while the ZTO-ZnO exhibited 72 % efficiency. Finally, the kinetic study of the photocatalytic reaction showed an increase in the overall rate constant k with the increase in initial concentration of Cr(VI). The outstanding performance of the ternary composite compared to the bare complex metal oxide makes the innovative g-C3N4/Zn2SnO4–ZnO composite a promising material for the removal of Cr(VI) from aquatic environment

Photocatalytic reduction of Cr(VI) using star-shaped Bi2S3 obtained from microwave irradiation of bismuth complex

The reduction of hexavalent chromium specie, Cr(VI), to trivalent chromium, Cr(III), in aqueous solutions using star-shaped nanostructured Bi2S3, prepared via a facile microwave irradiation of bismuth dithiocarbamate complex is reported. The bismuth sulphide were characterized using X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectrometer (EDX). The study showed that Cr(VI) reduction was dependent on its initial concentration, the pH value of the solution, and the Bi2S3 dosage. Almost all the Cr(VI) in a concentration of 2 ppm and at pH 2 was reduced within 90 min by the addition of 100 mg L-1 of the Bi2S3. The reduction capacity of the nanostructure was attributed to photocatalytic-induced reduction process as well as the high specific surface area. Pseudo-first order kinetics model parameters well described the Cr(VI) reduction experimental data with high correlation factor of 0.998. This study demonstrates that microwave irradiation of precursor complex could offer a quick and facile route to nanostructured photocatalyst, which are good candidate material for the removal of trace chromium in surface water

Adsorptive and Coagulative Removal of Trace Metals from Water Using Surface Modified Sawdust-Based Cellulose Nanocrystals

The presence of toxic metals in surface and natural waters, even at trace levels, poses a great danger to humans and the ecosystem. Although the combination of adsorption and coagulation techniques has the potential to eradicate this problem, the use of inappropriate media remains a major drawback. This study reports on the application of NaNO2/NaHCO3 modified sawdust-based cellulose nanocrystals (MCNC) as both coagulant and adsorbent for the removal of Cu, Fe and Pb from aqueous solution. The surface modified coagulants, prepared by electrostatic interactions, were characterized using Fourier transform infrared, X-ray diffraction (XRD), and scanning electron microscopy/energy-dispersive spectrometry (SEM/EDS). The amount of coagulated/adsorbed trace metals was then analysed using inductively coupled plasma atomic emission spectroscopy (ICP-AES). SEM analysis revealed the patchy and distributed floccules on Fe-flocs, which was an indication of multiple mechanisms responsible for Fe removal onto MCNC. A shift in the peak position attributed to C2H192N64O16 from 2θ = 30 to 24.5° occurred in the XRD pattern of both Pb- and Cu-flocs. Different process variables, including initial metal ions concentration (10–200 mg/L), solution pH (2–10), and temperature (25–45 °C) were studied in order to investigate how they affect the reaction process. Both Cu and Pb adsorption followed the Langmuir isotherm with a maximum adsorption capacity of 111.1 and 2.82 mg/g, respectively, whereas the adsorption of Fe was suggestive of a multilayer adsorption process; however, Fe Langmuir maximum adsorption capacity was found to be 81.96 mg/g. The sequence of trace metals removal followed the order: Cu > Fe > Pb. The utilization of this product in different water matrices is an effective way to establish their robustness

Photocatalytic Degradation of Tetracycline in Aqueous Solution Using Copper Sulfide Nanoparticles

In this paper, spherical-shaped pure phase djurleite (Cu31S16) and roxbyite (Cu7S4) nanoparticles were prepared by a solvothermal decomposition of copper(II) dithiocarbamate complex in dodecanthiol (DDT). The reaction temperature was used to control the phases of the samples, which were represented as Cu31S16 (120 °C), Cu31S16 (150 °C), Cu7S4 (220 °C), and Cu7S4 (250 °C) and were characterized by using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and absorption spectroscopy. The samples were used as photocatalysts for the degradation of tetracycline (TC) under visible light irradiation. The results of the study showed that Cu7S4 (250 °C) exhibited the best activity in the reaction system with the TC degradation rate of up to 99% within 120 min of light exposure, while the Cu31S16 (120 °C) system was only 46.5% at the same reaction condition. In general, roxbyite Cu7S4 (250 °C) could be considered as a potential catalyst for the degradation of TC in solution

Application of coal fly ash based ceramic membranes in wastewater treatment: A sustainable alternative to commercial materials

The continued increase in the global population has resulted in increased water demand for domestic, agricultural, and industrial purposes. These activities have led to the generation of high volumes of wastewater, which has an impact on water quality. Consequently, more practical solutions are needed to improve the current wastewater treatment systems. The use of improved ceramic membranes for wastewater treatment holds significant prospects for advancement in water treatment and sanitation. Hence, different studies have employed ceramic membranes in wastewater treatment and the search for low-cost and environmentally friendly starting materials has continued to engender research interests. This review focuses on the application of coal fly ash in membrane technology for wastewater treatment. The processes of membrane fabrication and the various limitations of the material. Several factors that influence the properties and performance of coal fly ash ceramic membranes in wastewater treatment are also presented. Some possible solutions to the limitations are also proposed, while cost analysis of coal fly ash-based membranes is explored to evaluate its potential for large-scale applications