Electrospun Silica-Polyacrylonitrile Nanohybrids for Water Treatments.

In this work, the removal of NOM (natural organic matter) as represented by humic acid by means of electrospun nanofiber adsorptive membranes (ENAMs) is described. Polyacrylonitrile (PAN) was used for the preparation of ENAMs incorporating silica nanoparticles as adsorbents. The addition of silica to the polymer left visible changes on the structural morphology and fibers' properties of the membrane. The membrane samples were characterized by pure water permeability, contact angle measurement, SEM, XPS, and XRD. This study assesses the preliminary performance of PAN-Si membranes for the removal of natural organic matter (NOM). The membrane rejected the humic acid, a surrogate of NOM, from 69.57% to 87.5%.

Catalyst- and Stabilizer-Free Rational Synthesis of Ionic Polymer Nanoparticles in One Step for Oil/Water Separation Membranes.

Ionic polymer nanoparticles (IPNs) were synthesized in one pot by quaternization precipitation polymerization (QPP) as a novel polymerization technique. QPP eliminated the usage of high-cost ionic monomers and reduced the number of steps for the preparation of IPN. The monomers 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 4-vinylbenzyl chloride (VBC) polymerized in the presence of azobisisobutyronitrile (AIBN) and underwent quaternization simultaneously, which yielded ionic poly(DMAEMA-co-VBC) nanoparticles in one step with the size of 50-80 nm without any stabilizer and catalyst. Similarly, 4-vinylpyridine (VP) and VBC polymerized in the presence of AIBN and underwent quaternization simultaneously, which yielded ionic poly(VP-co-VBC) nanoparticles in one step with the size of 70-90 nm without any stabilizer and catalyst. The as-synthesized IPN was further utilized for the fabrication of hydrophilic nanocomposite ultrafiltration membranes for oil/water separation. Fabricated hybrid membranes were characterized and studied for oil rejection properties. It exhibited an oil rejection of >96% with a pure water permeability of 219 L/m2 h bar.

Role of persistent free radicals and lewis acid sites in visible-light-driven wet peroxide activation by solid acid biochar catalysts - A mechanistic study.

We report the synthesis of H2SO4-modified biochars (SBCs) as solid-acid catalysts to activate H2O2 at circumneutral pH under visible light radiation. Spent coffee grinds were pyrolyzed with TiO2 at 300, 500 and 600 °C followed by steeping in 5 M H2SO4 and were used for the Fenton-like degradation of methyl orange (MO). The catalytic activity of SBC depended on the pyrolysis temperature and correlated well with the surface acidity and persistent free radical (PFR) concentration. Results showed that a complete MO removal and a TOC reduction of 70.2% can be achieved with SBC500 under photo-Fenton conditions. However, poisoning of the Lewis acid sites on SBC by PO43- led to a dramatic decrease in the removal of MO with inhibition effects more pronounced than with radical scavengers, suggesting the key role played by acid-sites on the activation of H2O2. Finally, electron paramagnetic resonance (EPR) studies identified •OH as the key transient in the degradation followed by •O2- and 1O2. These findings suggest that H2O2 was likely adsorbed on the surface oxygenated functional groups before being decomposed by accepting electrons from the PFRs on the SBC surface.

Generalized Kubelka's theory for light transmission in multilayer materials and its application for UV light penetration in filtering facepiece respirators.

The spread of SARS-CoV-2 has resulted in the shortage of filtering facepiece respirators (FFRs). As a result, the use of ultraviolet (UV) irradiation for disinfection and reuse of FFRs has been the topic of much investigation. In this article, a mathematical model is developed based on Kubelka's theory to determine light transmission in multilayer materials, such as N95 masks. Using this model, the predicted UV transmittance and absorbance of a N95 mask layers were found to be in close agreement with the experimental values. In addition, when the mask was exposed to UV equally from both surfaces, the estimated minimum UV irradiance inside the N95 mask was 14.5% of the incident irradiance, suggesting a significant degree of light penetration. The proposed model provides a simple and practical methodology for the design and use of UV decontamination equipment for FFRs and other multilayer materials.

Superhydrophobic modification of electrospun nanofibrous Si@PVDF membranes for desalination application in vacuum membrane distillation.

Superhydrophobic nanofibers have received prominent attention owing to their exceptional properties and researchers are focused on developing high-performing MD membranes. Herein, we fabricate superhydrophobic electrospun nanofibrous membranes using polyvinylidene fluoride (PVDF) solutions with silica nanoparticles (0 wt% to 6 wt%) to create multiscale (or hierarchical) surface roughness. For superhydrophobicity, the composite membranes (Si@PVDF) were subjected to a two-step modification that included acid pre-treatment and silanization with fluoroalkylsilane (FAS) compound of low surface energy. The acid pre-treatment enhances the hydroxyl group of SiO2 nanoparticles and create active sites in abundance for silanization. The modified membranes (FAS-Si@PVDF-A) having 6 wt% SiO2 showed excellent wetting resistance with water contact angle (WCA) up to 154.6 ± 2.2°, smaller average pore size of 0.27 ± 0.3 µm, and high liquid entry pressure (LEP) of 143 ± 4 kPa. It was observed, increasing silica content decreased the fiber diameter and average pore size and increased WCA and LEP of modified membranes. The modified superhydrophobic membranes gave stable permeate flux, exhibited strong wetting resistance and excellent salt rejection in vacuum membrane distillation (VMD) test. The optimal FAS-Si@PVDF-A membrane (6 wt% SiO2) of thickness 98 ± 5 µm produced a stable permeate flux of more than 11.5 kg m-2 h-1 and salt rejection as high as 99.9% after 22 h of continuous operation using NaCl solution (3.5 wt%) as feed. Therefore, this modification provided superhydrophobic membranes possessing robust anti-wetting properties with significant permeability and has encouraging application in membrane distillation for desalination.

Kinetics and Monte Carlo simulation of UV disinfection of B. subtilis spores and SARS-CoV-2 in dried saliva droplets.

Surfaces can be contaminated by droplets produced through coughing or sneezing. In this exploratory work, the UV disinfection results of Bacillus subtilis spores in dried saliva droplets were fitted to a three-parameter kinetic model (R2 ≥ 0.97). This model has a disinfection rate constant for single organisms and a smaller one for aggregates found in droplets. The fraction of organisms found in aggregates (ß) could account for the effects of different-sized droplets in the experimental work. Since a wide spectrum of droplet sizes can be produced, and some of the rate constants were uncertain, Monte Carlo simulation was used to estimate the UV inactivation performance in dried saliva droplets in a variety of conditions. Using conservative distribution for ß, the model was applied to the UV disinfection of SARS-CoV-2 in dried saliva droplets. It was shown that a one-log reduction of SARS-CoV-2 was very likely (p>99.9%) and a two-log reduction was probable (p=75%) at a dose of 60 mJ/cm2. Aggregates tend to be variable and limit the log reductions that can be achieved at high UV doses.

One-step synthesis of zwitterionic graphene oxide nanohybrid: Application to polysulfone tight ultrafiltration hollow fiber membrane.

In this paper, novel zwitterionic graphene oxide (GO) nanohybrid was synthesized using monomers [2-(Methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA) and N,N'-methylenebis(acrylamide) (MBAAm) (GO@poly(SBMA-co-MBAAm), and incorporated into polysulfone (PSF) hollow fiber membrane for the effectual rejection of dye from the wastewater. The synthesized nanohybrid was characterized using FT-IR, PXRD, TGA, EDX, TEM and zeta potential analysis. The occurrence of nanohybrid on the membrane matrix and the elemental composition were analyzed by XPS. The as-prepared tight ultrafiltration hollow fiber membrane exhibited high rejection of reactive black 5 (RB-5, 99%) and reactive orange 16 (RO-16, 74%) at a dye concentration of 10 ppm and pure water flux (PWF) of 49.6 L/m2h. Fabricated nanocomposite membranes were also studied for their efficacy in the removal of both monovalent (NaCl) and divalent salts (Na2SO4). The results revealed that the membrane possesses complete permeation to NaCl with less rejection of Na2SO4 (<5%). In addition, the nanocomposite membrane revealed outstanding antifouling performance with the flux recovery ratio (FRR) of 73% towards bovine serum albumin (BSA). Therefore, the in-house prepared novel nanocomposite membrane is a good candidate for the effective decolorization of wastewater containing dye.

Thermally stable, enhanced water barrier, high strength starch bio-composite reinforced with lignin containing cellulose nanofibrils.

Lignin containing cellulose nanofibrils (LCNF) were obtained by mechanically fibrillating unbleached tree bark after alkaline extraction and used as a reinforcement in thermoplastic starch (TPS) to develop novel biodegradable composite films. With the addition of 15 wt % LCNF, the tensile strength and modulus of the composites increased by 319 % and 800 % compared to neat TPS films, respectively. The crystalline property of cellulose and the high interaction between TPS and LCNF improved the mechanical property of the composite films. The composite film Tonset and Tmax were 263.1 °C and 316.5 °C, respectively, compared to 250.5 °C and 297.3 °C for neat TPS. The composite films also showed higher water barrier property. Experimental results showed that LCNF features a high lignin content. Lignin, a natural polymer, contains hydrophobic and aromatic groups and, thus, can increase the water barrier property and thermal stability of TPS/LCNF composite films.

Photocatalytic production of dihydroxyacetone from glycerol on TiO2 in acetonitrile.

In this paper, photocatalytic production of dihydroxyacetone (DHA) from glycerol in acetonitrile on TiO2 was investigated. HPLC-MS analysis showed that glycerol was converted to DHA, glyceraldehyde (GAD), glyceric acid and several other chemicals. Using acetonitrile as the reaction medium instead of water not only provided a more selective process for production of DHA but also increased the glycerol conversion. After 300 min, with 1 g L-1 catalyst loading and 4 mM initial glycerol concentration, glycerol conversion and DHA selectivity were 96.8% and 17.8% in acetonitrile compared to 36.1% and 14.7% in water, respectively. The half-life of glycerol decreased by a factor of 6.2, from 467 min to 75 min, by changing the solvent from water to acetonitrile. Experiments using biodiesel-derived crude glycerol verified the effectiveness of the proposed process for the photocatalytic production of DHA from crude glycerol. A mechanism was proposed to explain the higher selectivity towards DHA over GAD in this process.

Corn-derived dendrimer-like carbohydrate phytoglycogen nanoparticles as selective fluorescent sensor for silver ions.

A dendrimer-like carbohydrate phytoglycogen (PG) extracted from corn was modified as a fluorescent nanocarrier via a simple method. Fluorescein was successfully linked to PG by covalent bonds through APTES as the bridge. NMR, XPS, UV, fluorescence and confocal microscopy validated the high feasibility and efficiency of the preparation of fluorescent phytoglycogen (F-PG). The morphology of F-PG was investigated by TEM and XRD analysis which showed amorphous nature and spherical or cauliflower-like shape with highly branched structures inside. The fluorescent carbohydrate nanoparticles inherited the high stability and excellent dispersibility in water, which was proved by DLS measurements. Furthermore, ratiometric response towards silver ions could be obtained from fluorescence spectroscopy in aqueous media without the need of adding organic solvents, with good linearity (R2 = 0.993) and high selectivity, indicating a great potential of applying this renewable biopolymer as a sensor for silver ions in aqueous solution.

Effects of total suspended solids, particle size, and effluent temperature on the kinetics of peracetic acid decomposition in municipal wastewater.

In this study, the influence of total suspended solids (TSS) and particle size as well as effluent temperature on peracetic acid (PAA) decomposition kinetics in municipal wastewater was investigated. PAA decomposition was best described following second order kinetics in primary effluent (PE) and first order kinetics in secondary effluent (SE) samples. For synthetic samples prepared by varying TSS levels, PAA demand increased on average by about 0.042 mg/L in PE and 0.034 mg/L in SE for every 10 mg/L increase in TSS. Similarly, the PAA decay rate constant in these samples increased at a rate of 0.0014 L/mg.min and 0.00039 min-1, respectively, per 10 mg/L TSS. To examine the effect of particle size, synthetic samples with narrow size fractions (20-45, 45-75, and 75-90 µm) were prepared. It was found that samples with smaller particle size fractions had a greater PAA demand and decay rate constant. Effluent temperature also enhanced the PAA decomposition rate with the calculated activation energies for PE and SE samples being 29,980 J/mol and 34,860 J/mol, respectively.

Recent advances in polysaccharide bio-based flocculants.

Natural polysaccharides, derived from biomass feedstocks, marine resources, and microorganisms, have been attracting considerable attention as benign and environmentally friendly substitutes for synthetic polymeric products. Besides many other applications, these biopolymers are rapidly emerging as viable alternatives to harmful synthetic flocculating agents for the removal of contaminants from water and wastewater. In recent years, a great deal of effort has been devoted to improve the production and performance of polysaccharide bio-based flocculants. In this review, current trends in preparation and chemical modification of polysaccharide bio-based flocculants and their flocculation performance are discussed. Aspects including mechanisms of flocculation, biosynthesis, classification, purification and characterization, chemical modification, the effect of physicochemical factors on flocculating activity, and recent applications of polysaccharide bio-based flocculants are summarized and presented.

Tailing propensity in the ultraviolet disinfection of trickling filter and activated sludge wastewater treatment processes.

In this paper, the effect of suspended flocs on the tailing of ultraviolet (UV) disinfection kinetics of secondary effluents was examined. To achieve this goal, final effluents produced in two processes for treating wastewater; namely, a trickling filter system and an activated sludge system, were collected and their UV disinfection were compared. Tailing of the UV dose response curve was controlled by the fraction of flocs that are both culturable and UV-resistant, referred to as the 'tailing propensity'. Using this parameter, the contribution of various floc size fractions in reducing the UV disinfection efficiency of wastewater samples was quantified. Activated sludge flocs larger than 125 µm exhibited as much as 35 times greater tailing propensity than smaller flocs in the range of 20-25 µm. Within a fixed size range, the tailing propensity of flocs generated in the trickling filter system was 3 to 8 times higher than that of activated sludge flocs, and this difference increased with the floc size. A mathematical model was developed to predict the UV disinfection of secondary effluents from suspended particle size distribution data. The model showed good agreement with experimental results.

Cellulose fibre networks reinforced with carboxymethyl cellulose/chitosan complex layer-by-layer.

An eco-friendly and full-polysaccharide polyelectrolyte complex system was developed to enhance the wet and dry tensile strength of cellulose fibre networks. Cellulose fibres were treated by carboxymethyl cellulose (CMC) in pulp suspension. Paper sheets made from CMC-treated fibres were further modified via the layer-by-layer (LbL) deposition of CMC/chitosan (CS) complex. The effect of number of CMC/CS layers on the strength properties of cellulose fibre networks (both under wet and dry conditions) was studied and sample structure was investigated by scanning electron microscopy (SEM). Water vapour transmission rate (WVTR) of CMC/CS-treated samples was also examined. The observed changes in the strength properties of treated samples were explained based on the competition between the rate of diffusion of CS to the fibre-fibre bond areas and the rate of disassociation of fibre-fibre interactions during the LbL deposition process.

Mechanical behavior of transparent nanofibrillar cellulose-chitosan nanocomposite films in dry and wet conditions.

Transparent, biocompatible and biodegradable chitosan (CS) nanocomposite films reinforced with nanofibrillar cellulose (NFC) were prepared by solution casting. The effects of NFC content on the mechanical properties in dry and wet conditions were investigated. The incorporation of NFC significantly enhanced the mechanical properties, especially in wet conditions. The ultimate tensile strength and Young׳s modulus of chitosan were improved by 12 times and 30 times, respectively, for the nanocomposite containing 32wt% of NFC in wet conditions. The mechanism of the remarkable reinforcements was studied by analyzing the swelling behavior of NFC-CS nanocomposites. The mechanical properties of wet NFC-CS nanocomposite films matched well with those of human skin, which demonstrate potential for uses as artificial skin and wound dressings.

Paper microfluidics goes digital.

The first example of so-called "digital microfluidics" (DMF) implemented on paper by inkjet printing is reported. A sandwich enzyme-linked immunosorbent assay (ELISA) is demonstrated as an example of a complex, multistep protocol that would be difficult to achieve with capillary-driven paper microfluidics. Furthermore, it is shown that paper-based DMF devices have comparable performance to traditional photolithographically patterned DMF devices at a fraction of the cost.

Preparation of multiwalled carbon nanotube-supported nickel catalysts using incipient wetness method.

In this paper, a systematic study on preparation of multiwalled carbon nanotube (MWCNT)-supported nickel catalyst is pursued. Functional groups are introduced on the surface of MWCNTs using nitric acid, sulfuric acid, and partial oxidation in air. Nickel oxide nanoparticles are formed on the surface of functionalized multiwalled carbon nanotubes by incipient wetness impregnation of nickel nitrate, followed by calcination in air. The effects of acid type and concentration, acid treatment time, partial oxidation, nickel loading, precursor solvent, and calcination temperature on the size of the nickel nanoparticles and homogeneity of the composite material are evaluated. Characteristics of the Ni/MWCNT catalysts were examined using BET, scanning transmission electron microscopy, X-ray diffraction, thermogravimetric analysis in air and nitrogen, temperature-programmed reduction, X-ray photoelectron spectroscopy, acid-base titration, and zeta-potential analyzer. Results of this work are useful for formulating CNT-supported nickel catalysts for a wide range of different applications, such as reforming of hydrocarbons, catalytic hydrothermal gasification of biomass, and energy storage.

Effects of ultrasound on suspended particles in municipal wastewater.

The objective of this research is to explore the fundamental characteristics of how particles in wastewater respond to ultrasound, with an aim to improve wastewater disinfection. Particles of a predetermined size fraction and concentration were treated with varying doses of ultrasound at 20.3 kHz. Ultrasonic power transfer to the fluid was measured using calorimetry or acoustical measurements. Image analysis particle counting was used to measure the size distribution of particles before and after ultrasound treatment. The influence of three parameters: particle origin (raw wastewater or from the aeration basin of the activated sludge process), particle concentration, and particle size on the percentage of particle breakage after ultrasound treatment was compared. It was found that raw wastewater and aeration basin particles of the same size fraction (90-106 microm) responded to ultrasound in a similar way. Particle breakage was not affected by changes in particle concentration from 100 to 400 particles per mL. Larger wastewater particles (90-250 microm) were more susceptible to breakage than smaller ones (38-63 microm diameter). The percentage of particle breakage increased linearly with a logarithmic increase in the ultrasound energy density, that is the ultrasound energy delivered per unit volume of the sample (R(2)=0.48-0.91). An expression that predicts the percent of particles broken as a function of ultrasound energy density is provided.