Fabrication and optimization of curcumin-multiwalled carbon nanotube (C-MWCNT) conjugate reinforced electrospun polyacrylonitrile membrane for water treatment applications

In the recent times, one of the most crucial tasks related to water resources is the treatment of polluted water. This study reports the development of a functionalized nanofibrous membrane with enhanced filtration performance, heavy metal removal, and photocatalytic dye degradation for the effective treatment of contaminated water. The nanofibrous mats were developed by the process of electrospinning using a polymeric solution of polyacrylonitrile (PAN) reinforced with curcumin-multiwalled carbon nanotube (C-MWCNT) conjugate. The experimental trials for membrane fabrication were adapted based on the design of experiments (DoE) approach by making use of the Box-Behnken design (BBD) for a three-variable system, a component of response surface methodology (RSM). The three variable parameters selected for optimization of the electrospinning process were the dopant concentration (in weight percentage), the flow rate (in millilitre per hour), and the spinning time (in hours), respectively, and a total of 15 fibrous membranes were fabricated. The SEM analysis of the fabricated membranes revealed alterations in the surface morphology of the fibrous mats with variations in the electrospinning parameters. The infrared spectrum of the fibrous mats, validated the incorporation C-MWCNT conjugate in PAN, thereby confirming the formation of PAN/C-MWNCNT membrane. The mean flow pore size and breaking force of the PAN/C-MWCNT membranes was also obtained using a universal testing machine (UTM) and porometer, respectively. To choose the best membrane for efficient filtration experiments, the performance of each of the prepared membranes was assessed in terms of solute rejection percentage (SR%), permeate flux (PF), and pure water flux (PWF). The statistical analysis of the assessed parameters in accordance with the membranes prepared was done using the MINITAB software, and the three-dimensional (3D) surface plots were constructed using the STATISTICA software to visualize and validate the relation between each of the electrospinning parameters and the corresponding membrane performance characteristics. Similarly, the potential of the electrospun membranes for efficient heavy metal ion removal and photocatalysis were also tested independently and the optimal electrospinning parameters were determined for the same. Based on the results, it was observed that the PAN/C-MWCNT membranes could serve as potential candidates for the treatment of polluted water.

Tailoring Vanadium-Based Magnetic Catalyst by In Situ Encapsulation of Tungsten Disulfide and Applications in Abatement of Multiple Pollutants

A magnetic nanocomposite of tungsten and vanadium was employed as a catalyst for the mitigation of water contaminants, including a carcinogenic dye (Congo red, CR), a widely used pesticide (glyphosate), and the bacterial strain Escherichia coli. Additionally, it was subjected to several characterization techniques. X-ray diffraction spectroscopy examination validated the synthesized nanoparticles' crystalline nature, and scanning electron microscopy and energy-dispersive X-ray analysis were employed to examine the morphology and elemental composition of the catalyst. The use of thermogravimetric analysis enabled the elaboration of the thermal behavior of tungsten sulfide-vanadium decorated with Fe2O3 nanoparticles. The experiments were conducted under visible light conditions. The highest levels of photodegradation of 96.24 ± 2.5% for CR and 98 ± 1.8% for glyphosate were observed following a 180 min exposure to visible light at pH values of 6 and 8, respectively. The quantum yields for CR and Gly were calculated to be 9.2 × 10-3 and 4.9 × 10-4 molecules photon-1, respectively. The findings from the scavenger analysis suggest the involvement of hydroxyl radicals in the degradation mechanism. The study evaluated the inhibition of E. coli growth when exposed to a concentration of 0.1 g/10 mL of the photocatalyst, utilizing a 1 mL sample of the bacterial strain. The successful elimination of CR and glyphosate from water-based solutions, along with the subsequent antibacterial experiments, has substantiated the efficacy of the photocatalyst in the field of environmental remediation.

Chitosan-Based Polymer Nanocomposites for Environmental Remediation of Mercury Pollution

Mercury is a well-known heavy metal pollutant of global importance, typically found in effluents (lakes, oceans, and sewage) and released into the atmosphere. It is highly toxic to humans, animals and plants. Therefore, the current challenge is to develop efficient materials and techniques that can be used to remediate mercury pollution in water and the atmosphere, even in low concentrations. The paper aims to review the chitosan-based polymer nanocomposite materials that have been used for the environmental remediation of mercury pollution since they possess multifunctional properties, beneficial for the adsorption of various kinds of pollutants from wastewater and the atmosphere. In addition, these chitosan-based polymer nanocomposites are made of non-toxic materials that are environmentally friendly, highly porous, biocompatible, biodegradable, and recyclable; they have a high number of surface active sites, are earth-abundant, have minimal surface defects, and are metal-free. Advances in the modification of the chitosan, mainly with nanomaterials such as multi-walled carbon nanotube and nanoparticles (Ag, TiO₂, S, and ZnO), and its use for mercury uptake by batch adsorption and passive sampler methods are discussed.

Multipollutant Abatement through Visible Photocatalytic System

Water pollution damages the aquatic environment due to the presence of organic contaminants, which in turn is distressing to the ecosystem. Photocatalytic activity is a greener and promising method to degrade these organic contaminants. In this research, we present the degradation of diverse water pollutants through zinc/iron oxide nanoparticles serving as photocatalysts. The photocatalyst was studied for its efficiency to photodegrade congo red, brilliant green and para nitro phenol. Moreover, it also presented an antibacterial activity against the bacterium E. coli. Photocatalyst was characterized via X-ray diffraction, scanning electron microscopy-energy dispersive X-ray spectroscopy, and fourier-transform infrared spectroscopy. Tauc plot was used to measure the optical band gap (1.84 eV). The effect of various parameters such as catalyst dose, contact time, dye dose/concentration and pH were also investigated to determine the optimum point of maximum degradation through response surface methodology. A face-centered composite design was used, and a quadratic model was followed by congo red, brilliant green dyes and para nitrophenol. The maximum photodegradation efficiencies were 99%, 94.3%, and 78.5% for congo red, brilliant green and phenol, respectively. Quantum yield for congo red, brilliant green and para-nitrophenol were 9.62 × 10−8, 1.17 × 10−7 and 4.11 × 10−7 molecules/photons, while the reaction rates were 27.1 µmolg−1h−1, 29.61 µmolg−1h−1 and 231 µmolg−1h−1, respectively.

Multifunctional ZnO-Co3O4 @ polymer hybrid nanocoatings with controlled adsorption, photocatalytic and anti-microbial functions for polluted water systems

Triple action pollutant responsive multi-layer hybrid nanocoatings of architecture PEI(PAA/ZnO-Co3O4)n were constructed through ZnO-Co3O4 binary oxide co-precipitation followed by its inclusion in multi-layer polymeric thin films using Layer-by-Layer (LbL) deposition. Characterization of the designed architecture was carried out via FTIR, XRD, UV-Vis, and Raman spectroscopic studies to evaluate the chemical nature, bonding, and crystallographic behavior of ZnO-Co3O4. Peaks of ZnO-Co3O4 were recorded at 586.38, 486.08, and 443.64 cm-1 while pronounced shifting of ZnO characteristic E2 (high) peak ~ 450 cm-1 and appearance of modes around 495, 530, 630, and 719 cm-1 indexed via Raman studies validated Co3O4 impregnation into ZnO structure. XRD patterns of ZnO-Co3O4 compared to their previously reported pristine structures also justified the formation of binary oxide as unit composite. SEM micrographs confirmed homogenous multi-layered depositions while EDX analysis confirmed their uniform elemental distribution in the unit structure. Sequential multi-layer buildup up to 48 layer pairs was monitored using ellipsometry with maximum film thickness ~ 89 nm and by UV-Vis at 376 nm. The prepared thin films exhibited significant photodegradation of methylene blue ~ 91% and Cu (II) adsorption capacity ~ 89% within first 90 min of contact, along with prominent bactericidal efficiency against E. coli within 24 h of reaction time. FAAS, ICP-OES, and UV-Vis spectroscopy analyses make these multifunctional hybrid nanocoatings promising for industrial wastewater as well as drinking water purification setups. Furthermore, protuberant recycling and regenerative capacity make these hybrid nanocoatings an eco-friendly system for hydro-remediation.

Graphitic carbon nitride/NH2-MIL-101(Fe) composite for environmental remediation: Visible-light-assisted photocatalytic degradation of acetaminophen and reduction of hexavalent chromium

Herein, an efficient photocatalyst composed of graphitic carbon nitrate and iron-based metal-organic framework (g-C₃N₄/NH₂-MIL-101(Fe)) composite was fabricated by a solvothermal method for the degradation of acetaminophen (AAP) and reduction of Cr(VI) under sunlight illumination. The composite was confirmed by X-ray diffraction. UV-visible spectra showed that the bare g-C₃N₄, pure Fe-MOF, and composite harvest solar light effectively. The photocatalytic experiment indicated that the composite exhibited superior reduction efficiency of Cr(VI) (66%) compared to the bare g-C₃N₄ (35%) and pure Fe-MOF (51%) at pH 7. As the pH decreases from 9 to 2, the reduction efficiency increased. The highest Cr(VI) reduction (91%) was observed at pH 2. On the other hand, the catalyst degraded 94% of AAP at pH 7 compared to the bare g-C₃N₄ (42%) and pure Fe-MOF (60%) in the presence of hydrogen peroxide. A radical scavenger experiment endorsed that the generation of superoxide radicals was the main reason for the AAP degradation. The cyclic stability test indicated that there was no substantial decrease in the degradation efficiency of AAP after ten repeated cycles. The kinetic studies showed that the photodegradation of AAP and reduction Cr(VI) was well-fitted to the first-order kinetics. Gas chromatography-mass spectrometry analysis showed that hydroquinone, aliphatic carboxylic acids, monohydroxy, and dihydroxy paracetamol were the main products formed as a result of such degradation process. Therefore, the iron-based MOF and their composites can be used as effective photocatalysts for pollutants degradation.

Synthesis of high-performance conjugated microporous polymer/TiO2 photocatalytic antibacterial nanocomposites

High-performance conjugated microporous polymer (CMP)/TiO₂ photocatalytic antibacterial nanocomposites were successfully synthesized by in situ Sonogashira polymerization. TiO₂ was uniformly dispersed onto the surface and within the CMP which show the microporous nature with narrow pore size distribution. The high crystallinity and thermal stability of the CMP/TiO₂ nanocomposites are attractive for use as antibacterial materials. The composites we prepared showed excellent photocatalytic antibacterial properties for the inactivation of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) under visible light irradiation. The photocatalytic antibacterial rates of nanocomposites against E. coli and S. aureus after 120 min of visible light irradiation were 98.14% and 100%, respectively. The superoxide anion (O₂^-) was confirmed to be an important substance in the antibacterial process above. The cytocompatibility of the antibacterial agents was studied in terms of cytotoxicity against NIH 3T3 fibroblasts. More than 95% of the cells were still alive in the presence of the nanocomposites, both without and with light irradiation, indicating the good cytocompatibility of the nanocomposites. Judging from the excellent photocatalytic antibacterial properties and ultralow toxicity of nanocomposites, these materials can be used in many fields such as medical treatment, transportation and construction.

Microwave photo-oxidation with diverse oxidants for Congo red degradation: effect of oxidants, degradation pathway and economic analysis

The present study investigated the efficacy of microwave photo-oxidation (MWPO) process with two oxidants i.e. persulphate (PS) and hydrogen peroxide (H₂O₂) for degradation of Congo red (CR). The result indicated a CR degradation efficiency of 98% and 96.8% with PS and H₂O₂, respectively, in 30 min of reaction with corresponding PS dosage of 50 mg/L and H₂O₂ dosage of 180 mg/L. The COD removal efficiency with the two oxidants were 97.7% and 94.9%, respectively. Higher dosages of oxidant and CR reduced the efficiency of the process in both the cases due to self-quenching. Effect of pH and initial CR concentration on CR removal efficiency also has been studied. Degradation of CR followed pseudo-first-order kinetics with a removal rate constant of 0.12/min and 0.09/min, respectively, with PS and H₂O₂. The main mechanism of CR degradation was cleavage of the benzene-benzene bond, cleavage of benzene-N bond and hydroxylation. Economic analysis of the MWPO process indicated an energy consumption of 18.3 kWh/g of CR removal and 18.4 kWh/g of COD removal. The process was effective in the rapid degradation and mineralization of high concentration of CR within 30 min.

Chitosan nanocomposites for water treatment by fixed-bed continuous flow column adsorption: A review

Nowadays, access to clean water sources worldwide and particularly in Southern Africa is inadequate because of its pollution by organic, inorganic, and microorganism contaminants. A range of conventional water treatment techniques has been used to resolve the problem. However, these methods are currently facing the confronts posed by new emerging contaminants. Therefore, there is a need to develop simple and lower cost-effective water purification methods that use recyclable bio-based natural polymers such as chitosan modified with nanomaterials. These novel functional chitosan-based nanomaterials have been proven to effectively eliminate the different environmental pollutants from wastewater to acceptable levels. This paper aims to present a review of the recent development of functional chitosan modified with carbon nanostructured and inorganic nanoparticles. Their application as biosorbents in fixed-bed continuous flow column adsorption for water purification is also discussed.

Morphology engineering of ZnO nanorod arrays to hierarchical nanoflowers for enhanced photocatalytic activity and antibacterial action against Escherichia coli

A facile, efficient hydrothermal synthesis of ZnO nanoflowers followed by post-synthetic annealing and their photocatalytic and antibacterial properties are reported.

Alkyl-capped copper oxide nanospheres and nanoprolates for sustainability: water treatment and improved lubricating performance

Metal oxide nanoparticles of different nature have been used in different fields such as therapeutics, biomarkers, tribology or environmental remediation, among others. Besides, the surface modification of such nanoparticles is of particular interest to bring designed functions. In this paper we describe the synthesis of CuO nanoparticles with two different geometries (spherical and prolate) and decorated with long alkyl chains in order to use as dye removers by adsorption and/or photo-degradation of a persistent model dye (Congo Red) and as lubricant additives to improve the tribological performance of base lubricant oils. Alkyl-functionalized CuO nanoparticles demonstrated a high stability in oily suspensions and an improvement in the friction reducing the CoF ca. 26%; the alkyl-decorated nanoparticles showed also higher adsorption kinetics for Congo Red than the neat ones following a pseudo-second-order trend, although with lower adsorption efficiency. The synthesis, surface modification and physic-chemical characterization of spherical and prolate CuO nanoparticles are described as well as their applications as lubricant additives and Congo Red photocatalytic removal.