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Summary: Recently, the assimilation of pH‐sensitive natural pigments into biopolymers has shown promising prospects for pH‐reactive based smart packaging material. Unlike synthetic pigments, which have potential safety problems due to migration, natural pigments have negligible toxicity levels both to humans and the environment and some even possess nutritional and pharmacological properties. To complement the advantages of natural pigments, natural biopolymers have proven to be ideal candidates for the development of smart packaging because of their biocompatibility, availability, biodegradability, stability, minimum toxicity and good film‐forming capability. Smart packaging gives consumers real‐time signals on the quality of packaged food via food deterioration indicators like pH alteration. This review will consider the recent progress in the development of pH‐responsive smart packaging based on natural pH‐sensitive pigments and natural biopolymers from 2013 to the present. It will further discuss the challenges and opportunities of colorimetric smart packaging. [ABSTRACT FROM AUTHOR]

Summary: This work developed an active selenium nanoparticles‐based potato starch film. The incorporation of selenium nanoparticles (SeNPs) improved the microstructure, physical and biological properties of the nanocomposite film. Scanning electron microscopy (SEM) showed a slight increase in surface roughness and heterogeneity of nanocomposite film. Addition of SeNPs resulted in an improvement in film thickness and density from 0.02 ± 0.01 to 0.04 ± 0.00 mm and 1.01 ± 0.12 to 1.31 ± 0.03 g cm−3, respectively, while water content, film solubility, swelling degree as well as water vapour transmission rate decreased. Integration of SeNPs into potato starch film caused a significant change (P < 0.05) of colour to red (a*) and yellow (b*). The tensile strength also improved with addition of SeNPs from 3.42 to 9.86 MPa. The presence of SeNPs in the potato starch film enhanced its antioxidant and antimicrobial activity. The overall migration and specific migration were within acceptable levels as stipulated in the EU regulations. The findings of this study present an alternative biodegradable biopolymer material that can be used as active food packaging material in replacement of nonbiodegradable synthetic polymer material. [ABSTRACT FROM AUTHOR]

Summary: The past decade has seen nanotechnology progressively being adopted by the food industry. Its wide application in food packaging has redefined conservative food packaging with active and intelligent packaging. Nanomaterials do not only influence food quality and safety but also offer health‐related benefits. Selenium nanoparticles (SeNPs) have been preferred in recent years because of their high biological activity. However, they are generally synthesised using physicochemical methods which are associated with toxicity. In the past decade, efforts have been directed towards advancement of green synthesis of SeNPs to minimise hazardous by‐products. The antioxidant and biocidal effects of SeNPs are generally investigated by direct contact between the oxidisable matter and/or test organisms. Lately, there is focus on the effect SeNPs incorporated into packaging films. This paper will review developments on SeNPs synthesised via plant extracts from the year 2010 to present and their potential application in active food packaging. [ABSTRACT FROM AUTHOR]

• A rapid solvothermal method was developed using Moringa oleifera leaf extract. • Selenium nanoparticles were amorphous and exhibited a polygonal-like nanostructure. • Energy Dispersive Spectroscopy mapping showed uniform distribution of selenium. • Selenium nanoparticles exhibited antibacterial activity against three food pathogens. In this study, a rapid solvothermal method was developed using Moringa oleifera leaf extract as a reducing agent. Synthesized selenium nanoparticles were amorphous and exhibited a polygonal-like nanostructure with an average size of 82.86 ± 19.42 nm. Energy Dispersive Spectroscopy mapping showed uniform distribution of selenium as a dorminant element. The nanoparticles exhibited antibacterial activity against Escherichia coli , Salmonella typhimurium as well as Bacillus cereus. Therefore, this demonstrates its potential application in the development of active food packaging. [ABSTRACT FROM AUTHOR]

Tungsten trioxide (WO3) is a photocatalyst that has gained interest amongst researchers because of its non-toxicity, narrow band gap and superior charge transport. Due to its fast charge recombination, modification is vital to counteract this limitation. In this paper, we report on the fabrication of Mn-doped WO3/SnS2 nanoparticles, which were synthesised with the aim of minimising the recombination rates of the photogenerated species. The nanomaterials were characterised using spectroscopic techniques (UV-Vis-diffuse reflectance spectroscopy (DRS), Raman, XRD, photoluminescence (PL) and electrochemical impedance spectroscopy (EIS)) together with microscopic techniques (FESEM-EDS and high resolution transmission electron microscopy selected area electron diffraction (HRTEM-SAED)) to confirm the successful formation of Mn-WO3/SnS2 nanoparticles. The Mn-doped WO3/SnS2 composite was a mixture of monoclinic and hexagonal phases, confirmed by XRD and Raman analysis. The Mn-WO3/SnS2 heterojunction showed enhanced optical properties compared to those of the un-doped WO3/SnS2 nanoparticles, which confirms the successful charge separation. The Brunauer–Emmett–Teller (BET) analysis indicated that the nanoparticles were mesoporous as they exhibited a Type IV isotherm. These nanomaterials appeared as a mixture of rectangular rods and sheet-like shapes with an increased surface area (77.14 m2/g) and pore volume (0.0641 cm3/g). The electrochemical measurements indicated a high current density (0.030 mA/cm2) and low charge transfer resistance (157.16 Ω) of the Mn-WO3/SnS2 heterojunction, which infers a high charge separation, also complemented by photoluminescence with low emission peak intensity. The Mott–Schottky (M-S) plot indicated a positive slope characteristic of an n–n heterojunction semiconductor, indicating that electrons are the major charge carriers. Thus, the efficiency of Mn-WO3/SnS2 heterojunction photocatalyst was monitored for the degradation of chlorpyrifos. The effects of pH (3–9), catalyst loading (0.1–2 g) and initial chlorpyrifos concentration (100 ppb–20 ppm) were studied. It was observed that the degradation was purely due to photocatalysis, as no loss of chlorpyrifos was observed within 30 min in the dark. Chlorpyrifos removal using Mn-WO3/SnS2 was performed at the optimum conditions of pH = 7, catalyst loading = 1 g and chlorpyrifos concentration = 1000 ppb in 90 min. The complete degradation of chlorpyrifos and its major degradation by-product 3,5,6-trichloropyridin-2-ol (TCP) was achieved. Kinetic studies deduced a second order reaction at 209 × 10−3 M−1s−1. [ABSTRACT FROM AUTHOR]

Chitosan-based nanofibres were synthesized using a fibre electrospinning technique and tested for the removal of 3-methyl- 4-nitrophenol from aqueous solutions. The downside of chitosan-based materials is swelling. In this study, it was found that the addition of polyisoprene not only improved the electrospinning ability of chitosan but also reduced the swelling of the nanofibres by 50%. The adsorption studies of 3-methyl-4-nitrophenol on the chitosan-based nanofibres were conducted in a batch process. The nanofibres were found to remove up to 90% of 3-methyl-4-nitrophenol with an adsorption reduction capacity of 12% at each cycle of reusability test. The reduction capacity was associated with the chemical interaction of the adsorbate and the adsorbent. This indicated that the nanofibres can effectively remove 3-methyl-4-nitrophenol from water for at least 3 cycles. The adsorption efficiency improved as the degree of cross-linking was reduced and the adsorption mechanism followed the Freundlich isotherm suggesting that the adsorption of 3-methyl-4-nitrophenol occurred in different layers on the surface of the nanofibres. The degree of crosslinking of the electrospun nanofibres with glutaraldehyde was found to affect the adsorption capacity. Nanofibres with different degrees of crosslinking were used to study the effect of pH, adsorbent dose, and initial concentration. [ABSTRACT FROM AUTHOR]

This work describes the synthesis of Fe-Ag/functionalized-multiwalled carbon nanotube (f-MWCNT)/polyethersulphone (PES) nanostructured-hybrid membranes via a modified phase inversion method and its permeability properties. As-synthesized MWCNTs were first treated with acid and then Fe and Ag nanoparticles (Fe-Ag NPs) were uniformly dispersed on the surface of the f-MWCNTs using a microwave-assisted polyol method prior to addition to the PES polymer matrix. The addition of Fe-Ag/f-MWCNTs into the PES polymer increased the surface roughness of PES membranes and resulted to a higher hydrophilicity. Thermal stability and crystallinity properties of PES were significantly improved. The Fe-Ag/f-MWCNTs enhanced the surface charge density of the PES membranes and were found not to leach from PES. Performance evaluation studies revealed that the addition of Fe-Ag/f-MWCNTs into the PES polymer matrix increased water flux from 26.5 to 36.9 L/m 2 h and improved the rejection of Cr 6+ ions (up to 94%) in a cross-flow system. Furthermore, the addition of Fe-Ag/f-MWCNTs improved fouling resistance of PES membranes. The improved properties of these hybrid membranes make the ideal for use as either point-of-use or end-of-use water purification system for production of potable water. [ABSTRACT FROM AUTHOR]

Novel chitosan (CTs) nanocomposite beads containing alumina (Al 2 O 3 , denoted as Al in the nanocomposites) and functionalized multiwalled carbon nanotubes (f-MWCNTs) (CTsAl/f-MWCNTs) were prepared using an environmentally benign phase inversion method and subsequently used for the removal of nitrates (NO 3 − ) in water. The ellipsoidal beads with an average size of 3 mm were readily formed at room temperature and contained a small amount of Al (20 wt%) and f-MWCNTs (5%). The beads were found to adsorb nitrates effectively over a wide range of pH (pH 2 – pH 6) and showed maximum nitrates removal of 96.8% from a 50 mg/L nitrate water solution. Pure CTs beads on the other hand removed only 23% at pH 4. Kinetic studies suggested that the particle diffusion was rate controlling step for the adsorption of nitrates on CTsAl/f-MWCNT nanocomposite beads. Langmuir-Freundlich isotherms revealed that the adsorption of nitrates was on the heterogeneous surface of CTsAl/f-MWCNT beads. The Dubinin–Radushkevich (D-R) isotherm further revealed that the adsorption of nitrates was by electrostatic interaction. Thermodynamic studies suggested that the adsorption was spontaneous and exothermic. More than 70% recovery was achieved for 5 cycles of desorption-degeneration studies. Al and f-MWCNTs have shown to improve swelling and solubility of CTs. [ABSTRACT FROM AUTHOR]

This study was conducted to determine the presence and levels of toxic metals on selected water sources in a rural community in Lochiel, South Africa. Collection of water samples from identified drinking water sources (open wells, community tanks, water treatment works and boreholes) was done in all seasons of the year (winter, spring, summer and autumn) between 2014 and 2015. The concentrations of identified toxic metals (cobalt, chromium, copper, lead, zinc, manganese and iron) were measured using ICP-OES. Some water sources were found to contain concentrations of toxic metals at levels slightly higher than USEPA, WHO and SANS241 set limits ( e.g. manganese and cobalt), while others were found to be within the acceptable limits. This suggested that the residents residing in locations that have water sources containing toxic metals at the concentrations above the set limits are at risk and susceptible to suffer diseases caused by these toxic metals. The side effects of the metals may not be acute; however prolonged exposure to the toxic metals may result in detrimental effects since they are known to bioaccumulate in the body. [ABSTRACT FROM AUTHOR]

This work reports on the synthesis of multi-walled carbon nanotubes (MWCNTs) and their use in branched polyethyleneimine-multiwalled carbon nanotube (PEI-MWCNT) polymeric nanocomposite adsorbents for the removal of Cr 6+ from contaminated water. The nanostructured materials were characterized using TEM, Raman, FTIR, BET surface area and zeta potential measurements. TEM confirmed the average diameter of the MWCNTs to be 25 nm. The point of zero-charge of PEI was at pH 8 and that of PEI-MWCNTs was at pH 7.7. FTIR analysis confirmed the formation of a new bond (–C O at 1716 cm −1 ) between the functional groups on the MWCNTs and PEI. Batch adsorption and kinetic studies showed that the PEI-MWCNT nanocomposite materials were more efficient in the removal of Cr 6+ solution from water samples. The optimum conditions for adsorption were pH ≤ 4, contact time of 60 min. When the PEI-MWCNT dosage was increased the adsorption capacity increased. The kinetic adsorption data obtained for Cr 6+ solution followed pseudo-second order model. The adsorption of Cr 6+ solution reached equilibrium within 60 min of contact time with a removal of 99%. The adsorbents were effective even after 5 cycles of use. [ABSTRACT FROM AUTHOR]

Electrospun cyclodextrin (CD)-based nanofibers with capabilities to remove pollutants from water have been synthesized and characterized. The high-quality nanofibers presented here were synthesized in two simple steps that involvedin-situelectrospinning of the nanofibers and all nanocomponents, followed by the reduction of silver (Ag+) and iron (Fe3+) ions to nanoparticles using an environmentally benign process that involved irradiation of the electrospun fibers using a tailor-made UV-equipped furnace at low temperatures. In the previously reported study it was observed that Ag and Fe nanoparticles effectively removed a range of different strains of Gram-negative and Gram-positive bacteria from water. As such, this study focused on improving the thermal and mechanical properties of the nanofibers prepared from polymer blends of β-CDs with cellulose acetate (CA) and small additions (2 wt%) of functionalized multiwalled carbon nanotubes (f-MWCNTs). The electrospinning parameters were varied to determine the optimum conditions for preparation of uniform non-beaded nanofibers. Bead-free and uniform nanofibers were obtained at a polymer concentration of 32% at the ratio of 1:1 β-CDs:CA, syringe injection flow rate of 0.7 mL h−1, 15 cm between the tip of the spinneret and the collector, and a voltage of 16 kV. The addition of f-MWCNTs was found to improve the tensile strength of the nanofibers by twofold, relative to nanofibers with no f-MWCNTs. The thermal degradation of the nanofibers was improved by a magnitude of 50°C. The study has shown that adding small amounts of f-MWCNTs improved the thermal stability and mechanical strength of the CD/CA nanofibers significantly. [ABSTRACT FROM PUBLISHER]

Over the past two decades, phenol oxidases, particularly laccases and tyrosinases, have been extensively used for the removal of numerous pollutants in wastewaters due to their broad substrate specificity and their ability to use readily accessible molecular oxygen as the essential cofactor. As for other enzymes, immobilisation of laccases and tyrosinases has been shown to improve the performance and efficiency of the biocatalysts in solution. Several reviews have addressed the enzyme immobilisation techniques and the application of phenol oxidases to decontaminate wastewaters. This paper offers an overview of the recent publications, mainly from 2012 onwards, on the various immobilisation techniques applied to laccases and tyrosinases to induce and/or increase the performance of the biocatalysts. In this paper, the emphasis is on the efficiencies achieved, in terms of structural modifications, stability and resistance to extreme conditions (pH, temperature, inhibitors, etc.), reactivity, reusability, and broad substrate specificity, particularly for application in bioremediation processes. The advantages and disadvantages of several enzyme immobilisation techniques are also discussed. The relevance and effectiveness of the immobilisation techniques with respect to wastewater decontamination are critically assessed. A perspective on the future directions for large-scale application of the phenol oxidases in immobilised forms is provided. [ABSTRACT FROM AUTHOR]

In this study, a series of Ag-loaded hyperbranched polyethyleneimine/polyethersulfone (HPEI/PES) nanofibrous membranes were prepared via electrospinning. Hyperbranched polyethyleneimine was used as a dispersant and capping agent by the chelation of Ag ions by its internal imine groups and due to its highly branched structure. The nanofibrous membranes were characterised using scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), pure water flux and contact angle measurements. The SEM images revealed smooth, dense and uniform nanofibres with average diameters ranging from 107.8 ± 46.2 to 145.9 ± 49.9 nm. Spherical AgNPs with an average diameter of 6.4 ± 2.3 nm were observed. Characterisation using XRD coupled with selected area electron diffraction (SAED) confirmed that the AgNPs were crystalline with a peak corresponding to the (111) crystal lattice. The modified nanofibrous membranes displayed a high pure water flux of up to 630.14 ± 10.25 L/m2.h. The modified nanofibrous membranes displayed excellent antibacterial properties against Escherichia coli , Staphylococcus aureus and Pseudomonas aeruginosa achieving an inhibition of growth rate (I R) ≥ 99%. It was also found that the modified nanofibrous membranes prevented the attachment and colonisation of the three bacterial species. The antifouling characteristics of the nanofibrous membranes were assessed by filtration of bovine serum albumin (BSA), a model foulant. An increased flux recovery ratio for the modified nanofibrous membranes (68.43–86.71%) was observed as compared to that of the pristine PES membrane (51.8%), showing that fouling resistance and bacterial growth inhibition could be improved simultaneously by integrating antifouling and antibacterial properties. • Ag-HPEI/PES nanofibrous membranes were prepared via electrospinning on a commercial PES membrane. • The membranes were used for the inactivation o f E. coli , S. aureus and P. aeruginosa in water. • SEM- mapping and TEM confirmed the uniform dispersion of nano-sized AgNPs within the membrane fibres. • Antibacterial studies confirmed the bactericidal nature of Ag-HPEI/PES. [ABSTRACT FROM AUTHOR]

A photocatalytically active membrane was synthesized through the embedding of HPEI/TiO2 nanocomposite in PES membrane for the removal of methyl orange (MO) dye from water. Membranes were characterized using scanning electron microscopy coupled with energy dispersive X-ray, atomic force microscopy, water contact angle measurements and water flux analysis. PES/HPEI/TiO2 membranes showed improved hydrophilicity and were effective in the photodegradation of MO. The reaction rate for MO degradation was 11.6 x 10-3 min-1, and the degradation was accompanied by the generation of sulphate ions as degradation by-products. [ABSTRACT FROM AUTHOR]

Chitosan (CS)-based nanocomposite materials are highly prone to swelling when in contact with water. It is therefore essential to modify them to enhance their resistance to swelling, in order to be applicable in water treatment. In this study, the CS-based nanofibres were prepared using the electrospinning technique. The nanofibres were prepared from a polymer blend of CS, and other polymers (polyacrylamide (PAA) and polyethylene glycol (PEG)) added in small optimized quantities to enhance the ability to electrospun CS. Elastic polyisoprene (PIP) and functionalized multi-walled carbon nanotubes (f-MWCNTs) were incorporated in the electrospinnable solution blend of CS, PAA and PEG to reduce the swelling behaviour of the CS-based nanofibres and to improve their mechanical strength and thermal properties. PIP did not only improve the morphology of the resulting nanofibres but also reduced their swelling behaviour by twofold. The addition of f-MWCNTs was found to improve the tensile strength of the nanofibres by twofold, relative to nanofibres with no f-MWCNTs. The thermal degradation of the nanofibres was improved by a magnitude of 50°C. Antibacterial silver (Ag) and iron (Fe) nanoparticles (NPs) were embedded on the nanofibres for their possible use in disinfection processes. These NPs have demonstrated a potential to kill bacteria in water and, therefore, the prepared nanofibres can be used in disinfection water treatment processes with reduced swelling capacity. [ABSTRACT FROM AUTHOR]

Templated synthesis of nanoparticles has been shown to result in uniform sized and well dispersed particles. Titanium dioxide (TiO 2 ) nanoparticles were prepared through a modified sol–gel method using hyperbranched polyethyleneimine (HPEI) as a template to reduce their agglomeration. The synthesised HPEI/TiO 2 nanocomposites were characterised by techniques such as Transmission Electron microscopy (TEM), Fourier Transform Infrared spectroscopy (FTIR), Powder-X-ray Diffraction spectroscopy (XRD) and Thermo-gravimetric analysis (TGA). TEM micrographs illustrated formation of small and well dispersed TiO 2 nanoparticles. The use of HPEI therefore had a huge impact on the size, shape and dispersion of theTiO 2 nanoparticles. [ABSTRACT FROM AUTHOR]