Effect of carbon precursor and initial pH on cobalt-doped carbon xerogel for oxygen reduction

In this study, cobalt-doped carbon xerogel (Co-CX) was synthesised via sol-gel polymerisation of phenolic compounds (i.e., resorcinol, phenol and m-cresol) and formaldehyde, and this polymerisation was catalysed by cobalt nitrate and followed by a carbonisation process. The effect of the initial pH value (5.5, 6.5 and 7.5) as well as the type of carbon precursors on the structural properties of Co-CX was investigated via field emission scanning electron microscope (FESEM), Brunauer-Emmett-Teller (BET) and X-ray diffractometry (XRD). The catalytic activity of Co-CX for the oxygen reduction reaction (ORR) in 0.1 M KOH was studied using a rotating ring-disk electrode (RRDE) technique. The structural properties and ORR activities were affected by different initial pH values as well as the type of carbon precursor. A carbon precursor consisting of resorcinol-formaldehyde with an initial pH value of 7.5 exhibited the best catalytic activity. The initial pH plays an important role in promoting micro/mesopores. The FESEM and BET results revealed that Co doping promotes the formation of additional pores. The RRDE result indicated that Co-CX exhibited good catalytic activity that tends to favour a four-electron pathway.     

Mechanochemical solid state synthesis and optical properties of Cd0.5Zn0.5Se nanocrystals

High-quality Cd_0.5Zn_0.5Se nanoparticles with diameters ranging from 2.6 to 4.3 nm were synthesized via intensive mechanical milling for up to 20 h. The full width at half maximum (FWHM) and broadening of the diffraction peaks increased with increasing ball milling process and later decreased. XRD pattern confirmed a dominant zinc blende phase at (x = 0.5) composition. The optical spectra of the nanoparticles exhibited an onset absorption peak at 349 nm, with maximum absorption at 290 nm. The luminescence properties of the nanoparticles at room temperature were analyzed via photoluminescence spectroscopy, revealing band-edge emission at 354 nm. Photoluminescence (PL) spectra exhibit broad emission band at the range of (380–508) nm photon energy. The PL spectrum has two distinctive shoulders at 403 and 450 nm. Band emissions of 1.74, 1.54 and 1.4 eV at longer wavelengths that were associated with the surface state were also observed. High-transmission electron microscopy (HRTEM) revealed the successful annihilation of such defects with continuous milling.     

Nanocellulose-based fibres derived from palm oil by-products and their in vitro biocompatibility analysis

Abstract

Fibres with nanocellulose isolated from oil palm empty fruit bunches (OPEFBs) were produced. Nanocellulose and PVA-nanocellulose fibres were prepared by wet spinning in an acetone coagulation bath without drawing. The addition of nanocellulose was varied from 10% to 30%, to reveal the beneficial effects of nanocellulose content on the properties of produced spun-fibres. Higher concentration of nanocellulose increased the stiffness of spun-fibres. PVA and PVA-bacterial cellulose fibres were also produced as a control and for comparison, respectively. The nanocellulose fibre formed a compact structure, while PVA fibres had hollow structures. The effect of the produced spun-fibres on the biocompatibility of calf pulmonary artery endothelial cells was assayed by an MTT test. Based on the MTT assay the addition of nanocellulose increased the percentage of cell viability of the obtained spun-fibres slightly. These results point towards the use of sustainable sources of nanocellulose as a beneficial and biocompatible fibre material.     

Effect of front air attack angles on heat transfer coefficient of the cross‐flow of four flat tube

Heat transfer coefficients are studied experimentally for airflow over a four‐flat‐tube configuration with different inlet attack angles. The range of Re numbers was from 1668 to 3782. The heat fluxes are 13.2, 38.5, and 99.8 W/m². In this paper, 45 samples of a flat tube with inlet airflow angles (30°, 45°, and 90°) are set up to investigate its thermal performance. The design of experimental approach was used to conduct the heat transfer parametric study by designing 45 experiments, analyzing the empirical model, and optimizing heat transfer. The response was modeled using a general factorial design model based on experimental data. From analysis of variance (ANOVA), we obtained significant coefficients by performing the 5% test of level of significance. The results indicated that both the Nu and Re numbers increase for all heat flux cases and these decrease with increasing the air attack. Also shown are that the Colburn j‐factor decreases with increase of air velocity. It was found that the ANOVA results are appropriate to the collected experimental data, as the R² and R²‐adjusted statistics are found to be 92.61% and 90.97%, respectively, for Nu number. In a similar manner, for Colburn j‐factor, the R² and R²‐adjusted statistic are 96.97% and 96.29%, respectively.     

Cathodic electrodeposition of SnS in the presence of EDTA in aqueous media

Cathodic electrodeposition in the presence of EDTA in aqueous solution was found to offer some noteworthy improvements in our attempt to synthesise an SnS thin film. EDTA has shown its capacity for improving the longevity of the deposition bath as well as the adhesion of the deposited film on a titanium substrate. Photoelectrochemical analysis reveals outstanding photoactivity of the electrodeposited thin film, while an optical study shows an energy gap of approximately 1.1 eV. The effects of chelating agent were extracted from the results of cyclic voltammetry, photoelectrochemical test, scanning electron microscopy and X-ray diffraction spectroscopy. The latter which displays better defined signals reaffirms the appreciable improvement in the polycrystallinity of the thin film. Analysis of peak locations, coincidentally, confirms that SnS of Herzenbergite form has been obtained.     

Cathodic electrodeposition of Cu2S thin film for solar energy conversion

Cathodic electrodeposition in the presence of EDTA in aqueous solution was used to prepare Cu₂S thin film deposited on Ti substrate. The effect of deposition potential, concentration and deposition time was studied to determine the optimum condition for electro-deposition process. Cyclic voltammetry was performed to elucidate the electrodic processes that occur while potentials for electrodeposition were applied to determine the optimum potential for electrodeposition. The thin films are characterised by X-ray diffractometry. The photoactivity of the deposited films and their conduction types were evaluated using photoelectrochemical technique. The band gap energy and type of optical transitions were determined from optical absorbance data.