Nonjabulo P. Gule

Advances in biofouling mitigation: A review

ABSTRACT The attachment of microbial biomass on solid surfaces is a universal phenomenon that occurs in natural and engineering systems and is responsible for various types of biofouling. Biological fouling, also referred to as biofouling, remains one of the most critical problems toward the durable application of materials. The eradication of this problem using sustainable and environmentally friendly techniques is still of critical importance and is therefore receiving significant interest from researchers worldwide. The authors start with a definition of processes that lead to biofouling and their relevance to various industrial applications. The most relevant findings from past research are presented and particular emphasis is focused on present research, where recent developments in surface modification receive specific attention.

Furanone-containing poly(vinyl alcohol) nanofibers for cell-adhesion inhibition.

The 3(2H) furanone derivative 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF) was investigated for its antimicrobial and cell-adhesion inhibition properties against Klebsiella pneumoniae Xen 39, Staphylococcus aureus Xen 36, Escherichia coli Xen 14, Pseudomonas aeruginosa Xen 5 and Salmonella typhimurium Xen 26. Nanofibers electrospun from solution blends of DMHF and poly(vinyl alcohol) (PVA) were tested for their ability to inhibit surface-attachment of bacteria. Antimicrobial and adhesion inhibition activity was determined via the plate counting technique. To quantify viable but non-culturable cells and to validate the plate counting results, bioluminescence and fluorescence studies were carried out. Nanofiber production was upscaled using the bubble electrospinning technique. To ascertain that no DMHF leached into filtered water, samples of water filtered through the nanofibrous mats were analyzed using gas chromatography coupled with mass spectrometry (GC-MS). Scanning electron microscopy (SEM) and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) were used to characterize the electrospun nanofibers.

Immobilized furanone derivatives as inhibitors for adhesion of bacteria on modified poly(styrene-co-maleic) anhydride)

The ability of brominated furanones and other furanone compounds with 2(3H) and 2(5H) cores to inhibit bacterial adhesion of surfaces as well deactivate (destroy) them has been previously reported. The furanone derivatives 4-(2-(2-aminoethoxy)-2,5-dimethyl-3(2H)-furanone and 5-(2-(2-aminoethoxy)-ethoxy)methyl)-2(5H)-furanone were synthesized in our laboratory. These furanone derivatives were then covalently immobilized onto poly(styrene-co-maleic anhydride) (SMA) and electrospun to fabricate nonwoven nanofibrous mats with antimicrobial and cell-adhesion inhibition properties. The electrospun nanofibrous mats were tested for their ability to inhibit cell attachment by strains of bacteria commonly found in water ( Klebsiella pneumoniae Xen 39, Staphylococcus aureus Xen 36, Escherichia coli Xen 14, Pseudomonas aeruginosa Xen 5, and Salmonella tymphimurium Xen 26). Proton nuclear magnetic resonance spectroscopy ((1)H NMR), electrospray mass spectroscopy (ES-MS), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were used to confirm the structures of the synthesized furanones as well as their successful immobilization on SMA. To ascertain that the immobilized furanone compounds do not leach into filtered water, samples of water, filtered through the nanofibrous mats were analyzed using gas chromatography coupled with mass spectroscopy (GC-MS). The morphology of the electrospun nanofibers was characterized using scanning electron microscopy (SEM).

Laccase-immobilized dendritic nanofibrous membranes as a novel approach towards the removal of bisphenol A

ABSTRACT Laccase enzymes from Rhus vernificera were covalently bound on hyperbranched polyethyleneimine/polyethersulfone (HPEI/PES) electrospun nanofibrous membranes and used for the removal of bisphenol A (BPA) from water. The laccase enzyme was anchored on the dendritic membranes through the abundant peripheral amine groups on the HPEI using glutaraldehyde as a crosslinker. The membranes were characterized with attenuated total reflectance-Fourier transform infrared spectroscopy, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) and ultraviolet–visible spectroscopy and correlative light and electron microscopy (CLEM). Furthermore, contact-angle analyses, pure water flux measurements and rejection analyses were carried out. CLEM showed that the enzymes were uniformly dispersed on the nanofibres while SEM analysis revealed that the nanofibres had an average diameter of 354 ± 37 nm. EDS showed the presence of Cu, which is the active entity in laccase enzymes. The laccase-modified membranes were hydrophilic (50°–53° contact angle) and exhibited high BPA rejection of 89.6% as compared to the 52.4% demonstrated by pristine PES. The laccase-modified membranes also maintained a constant permeate flux (7.07 ± 5.54 L/m2 h) throughout the filtration process. Recyclability studies indicated that the membranes still maintained a high BPA removal of up to 79% even after four filtration cycles.

Smart block copolymers of PVP and an alkylated PVP derivative: synthesis, characterization, thermoresponsive behaviour and self-assembly

Stimuli responsive block copolymers of biocompatible poly(3-ethyl-N-vinylpyrrolidone) and poly(N-vinylpyrrolidone), i.e. EPVP–PVP, were readily synthesized via RAFT-mediated polymerization. The thermoresponsive behaviour and temperature induced self-assembly, in aqueous solutions, was studied using various spectroscopic and microscopy techniques. We obtained different morphologies, i.e. spherical and cylindrical micelles, and vesicles, via temperature induced self-assembly, of aqueous solutions of a single diblock copolymer by simply adjusting the solution concentration. This study establishes the biocompatible EPVP/PVP combination as a versatile stimuli responsive block copolymer system suitable for applications in drug delivery.

Recent Applications of Laccase Modified Membranes in the Removal of Bisphenol A and Other Organic Pollutants

Bisphenol A (BPA) has been found to be the most rapidly generated endocrine disrupting compound (EDC) with an annual production of over 10 million tons. This synthetic compound has been used extensively in the production of polycarbonate plastics, epoxy resins and thermal papers. It has been detected at elevated levels in industrial wastewater effluents, natural waters and drinking water. Recent studies have shown that BPA affects the proper functioning of the endocrine system in human beings and animals. Exposure to BPA has been associated with immunotoxic, mutagenic and carcinogenic effects at very low levels (ng/L to μg/L). It has also been proven that BPA increases chances of having diabetes, obesity and cancer. Thus, the removal of BPA from water has become a major concern in water research. Enzymatic degradation of BPA has proven to be an efficient and environmentally friendly approach and the use of laccase modified membranes has been reported in many studies. This article provides an in-depth review on the removal of BPA and other toxic organic micro-contaminants from water by laccase modified membrane systems.