Structural and performance properties of UV-assisted TiO2 deposited nano-composite PVDF/SPES membranes

In this research, the surface of poly (vinylidene fluoride) (PVDF)/sulfonated polyethersulfone (SPES) blend membrane prepared via immersion precipitation was modified by depositing of TiO₂ nano-particles followed by UV irradiation to activate their photocatalytic property. The membranes were characterized by FTIR, SEM, AFM, contact angle, dead end filtration (pure water flux and BSA solution flux), antifouling analysis and antibacterial activity. The FTIR spectrum confirmed the presence of OH functional groups on the PVDF/SPES membrane structure, which was the key factor for deposition, and self-assembly of TiO₂ nanoparticles on the membrane surface. The SEM and AFM images indicated that the TiO₂ nanoparticles were deposited on the PVDF/SPES membrane. The contact angle measurements showed that the hydrophilicity of PVDF/SPES membrane was strongly improved by TiO₂ deposition and UV irradiation. The filtration results indicated that the initial flux of TiO₂ deposited PVDF/SPES membranes was lower than the initial flux of neat PVDF/SPES membrane. However, the former membranes showed lower flux decline compared to the neat PVDF/SPES membrane. The BSA rejection of modified membranes was improved. The fouling analysis demonstrated that the TiO₂ deposited PVDF/SPES membranes showed the fewer tendencies to fouling. The results of antibacterial study showed that the UV irradiated TiO₂ deposited PVDF/SPES membranes possess high antibacterial property.     

A novel current-mode four-quadrant CMOS analog multiplier/divider

This paper presents, a new current mode four-quadrant CMOS analog multiplier/divider based on dual translinear loops. Compared with the previous works this circuit has a simpler structure resulting in lower power consumption and higher frequency response. Simulation results, performed using HSPICE with 0.25 μm technology, confirm performance of the proposed circuit.     

Fate of toxic cyanobacterial cells and disinfection by-products formation after chlorination

Drinking water sources in many regions are subject to proliferation of toxic cyanobacteria (CB). Chlorination of source water containing toxic cyanobacterial cells for diverse treatment purposes might cause cell damage, toxin release and disinfection by-products (DBP) formation. There is limited information available on chlorination of different toxic CB cells and DBP formation potentials. This work: (1) determines the extent of lysis and toxins/taste and odor compound release in chlorinated natural water from CB cells (Anabaena circinalis, Microcystis aeruginosa, Cylindrospermopsis raciborskii, and Aphanizomenon issatsckenka) from laboratory cultures and natural blooms; (2) assesses the rates of oxidation of toxins by free chlorine under environmental conditions; (3) studies the DBP formation associated with the chlorination of CB cell suspensions. With chlorine exposure (CT) value of <4.0 mg min/L >60% cells lost viability causing toxin release. Cell membrane damage occurred faster than oxidation of released toxins. Kinetic analysis of the oxidation of toxins in natural water revealed significant differences in their susceptibility to chlorine, saxitoxins being the easiest to oxidize, followed by cylindrospermopsin and microcystin-LR. Furthermore, concentrations of trihalomethanes and haloacetic acids (<40 μg/L) and N-nitrosodimethylamine (<10 ng/L) as chlorination by-products were lower than the guideline values even at the highest CT value (220 mg min/L). However, the DBP concentrations in environmental bloom conditions with very high cell numbers were over the guideline values.     

Sustained release of CIP from TiO2-PVDF/starch nanocomposite mats with potential application in wound dressing

Electrospinning is an economical and alluring method to fabricate wound dressing mats from a variety of natural and synthetic materials. In this study, polyvinylidene fluoride (PVDF) and starch composite mats containing ciprofloxacin (CIP) loaded on titanium dioxide nanoparticles (TiO₂) were prepared. Fourier Transform Infrared spectra of CIP, synthesized TiO₂ NPs, TiO₂/CIP, and PVDF/starch composite mats are analyzed. Scanning electron microscopy images revealed that the fiber diameter of PVDF nanofibers thickens by increasing starch, which varies between 180 nm and 550 nm. Strain at break of PVDF, starch, PVDF/starch (2:1 w:w; P2S1), PVDF/starch (1:1 w:w; P1S1), PVDF/starch (1:2 w:w; P1S2), and nanofibers were 103 ± 11, 3 ± 0.6, 27 ± 4, 52 ± 5.2, 7.7 ± 1%, respectively. Based on strain at break and young modulus, P2S1 was selected as a suitable candidate for wound dressing to which load TiO₂/CIP as a bioactive agent. The release rate of CIP showed that about 40% of the drug is released in the first 2 days. Furthermore, the antibacterial activity of dressings was investigated using Escherichia coli and Staphylococcus aureus microorganisms and zones of clearance were obvious around the specimen on the agar plate. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48916.     

褐煤干燥提质和无粘结剂成型技术的研究现状及进展

论述了褐煤中水分的存在形式,即褐煤中的水分主要由外在水分、内在水分和结晶水组成,其中外在水分较易脱除。介绍了国内外褐煤干燥提质技术、针对高水分褐煤干燥研发的新技术及与褐煤干燥相关的其他提质技术的研究进展,其中,新研发的褐煤干燥技术中,过热蒸汽流化床褐煤干燥技术(WTA)具有效率高、能耗低、安全等特点,在单位能耗方面具有明显优势。通过对褐煤无粘结剂型煤的成型工艺及型煤耐水性能的试验研究,说明褐煤无粘结剂成型技术制备的型煤样品质量良好,吸收水分的速率大大降低,热解与燃烧活性也有所下降。最后分析了褐煤无粘结剂成型机理,即主要有沥青假说、腐植酸假说、毛细孔假说、胶体假说和分子粘合假说5种。     

Influence of polyethyleneimine layer and zinc nitrate on morphology and structure of PES-based membranes with highly selective properties

In this paper, nanofiltration (NF) polymer membranes based on polyestersulphone (PES) were prepared by the phase inversion method. Polyethyleneimine (PEI) and zinc nitrate (Zn(NO₃)₂) as a surface modifier and glutealdehyde (GA) as cross-linker was used. Fourier transform infrared spectroscopy analysis (FTIR) was used to confirm the chemical composition on the membrane surface. Membranes were also characterized using field emission scanning electron microscopy (FESEM) and 3D surface images. Water contact angle, average pore size and porosity measurements, water flux, salt rejection, and membrane anti-fouling ability were discussed. Modified membranes showed a smoother surface than the original membrane. The amount of pure water flux decreased with increasing the concentration of modifiers at the surface, but the yield of Na₂SO₄ salt increased, 53% in virgin membrane and 83% in M3 membrane. Modified membranes had better anti-fouling and hydrophilicity properties than primary membranes. The lowest contact angle value was 26.2° for M4. Also, the best anti-clogging comparable properties were for the M3 membrane with FRR = 63.37%, R_r = 10.69%, R_ir = 36.6%, and R_t = 47.3%. By increasing the concentration of modifiers, the removal of CuNO₃⁻ and CuSO₄ improved that the M1 membrane (97.59%) had the highest Cu(NO₃)₂ separation and the M4 membrane (87.5%) had the most increased CuSO₄ separation.     

Comprehensive kinetic study for Fischer–Tropsch reaction over KMoFe/CNTs nano-structured catalyst

The kinetics of the Fischer–Tropsch (FT) reaction was evaluated through detailed experimentation with a KMo bimetallic promoted Fe catalyst supported on carbon nanotubes (CNTs). The kinetic tests were conducted in a fixed-bed reactor under operating conditions of P = 6.9–41.3 bar, T = 543–563 K, H₂/CO = 1, gas hourly specific velocity (GHSV) = 2000 h⁻¹. This study aimed to investigate the mechanism prevailing in CO activation and the rate equation for CO consumption during FT reactions over a 0.5K5Mo10Fe/CNTs catalyst. To evaluate the synergistic effects of Fe, Mo, and K phases on the catalyst activity, both fresh and spent catalysts were thoroughly characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy and energy-dispersive spectroscopy (SEM-EDS), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) to ascertain the different phases (active sites) present and relevant interactions. Based on the adsorption of carbon monoxide and hydrogen, 22 possible mechanisms for monomer formation were proposed for FT synthesis in accordance with the Langmuir–Hinshelwood–Hougen–Watson (LHHW) and Eley–Rideal (ER) adsorption theories. The best fit kinetic model was identified through a multi-variable non-linear regression analysis. The selected mechanistic model was based on carbide formation approach, where H₂-assisted adsorption of CO was considered for the derivation. Kinetic parameters such as activation energy, adsorption enthalpies of H₂, and CO were estimated to be 65.0, −13.0, and −54.0 kJ/mol, respectively. Considering the developed kinetic model, the effects of reaction temperature and pressure were assessed on Fischer–Tropsch synthesis (FTS) product distribution. Additionally, the kinetic model was compared with the typical Anderson–Schulz–Flory model, suggesting the effects of water-gas-shift and the existence of additional formation pathway such as secondary re-adsorption of olefins for heavier hydrocarbons.     

The Effect of Viscoelasticity of Polymeric Adhesives on Shear Stress Distribution in a Single-Lap Joint

In this paper, the effect of viscoelasticity of adhesives on shear stress distribution in the adhesive layer of a single-lap joint under shear load is studied. The joint comprises two elastic single isotropic adherend layers joined by a viscoelastic adhesive polymer. A three-parameter viscoelastic solid model is used to deduce the governing differential equation in the Laplace domain, which is solved using residue theorem. Results show that for an impulse load of 100 N, the maximum shear stress in the adhesive layer is reduced to 39% of its initial value. Also, the ratio of viscous modulus of the adhesive to its shear modulus has an adverse effect on the peak shear stress. An increase in the thickness of the adhesive layer reduced the induced peak shear stress in the joint. Moreover, the shear strain in the adhesive layer reached its steady value after 1000 seconds.     

Identification of nonlinear boundary effects using nonlinear normal modes

Local nonlinear effects due to micro-slip/slap introduced in boundaries of structures have dominant influence on their lower modal model. This paper studies these effects by experimentally observing the behavior of a clamped–free beam structure with local nonlinearities due to micro-slip at the clamped end. The structure is excited near one of its resonance frequencies and recorded responses are employed to identify the nonlinear effects at the boundary. The nonlinear response of structure is defined using an amplitude-dependent nonlinear normal mode identified from measured responses. A new method for reconstructing nonlinear normal mode is represented in this paper by relating the nonlinear normal mode to the clamped end displacement-dependent stiffness parameters using an eigensensitivity analysis. Solution of obtained equations results equivalent stiffness models at different vibration amplitudes and the corresponding nonlinear normal mode is identified. The approach results nonlinear modes with efficient capabilities in predicting dynamical behavior of the structure at different loading conditions. To evaluate the efficiency of the identified model, the structure is excited at higher excitation load levels than those employed in identification procedures and the observed responses are compared with the predictions of the model at the corresponding input force levels. The predictions are in good agreement with the observed behavior indicating success of identification procedure in capturing the physical merits involve in the boundary local nonlinearities.     

Diffusion model for charge transfer from a photosynthetic reaction center to an electrode in a photovoltaic device

In spite of a high quantum efficiency in the bacterial photosynthetic reaction center (RC) the overall efficiency in a RC-based photovoltaic device is very poor partly because of an inefficient collection of charges by electrodes. To explain charge transport between the RC and an electrode a diffusion model is proposed. The numerical solution of the diffusion process describes the measured photocurrent well. An approximation of the initial condition is also made to obtain analytical expressions for the photocurrent. The model suggests that the slow transient response of the photocurrent is due to the diffusion in a biological photovoltaic device.