Surface modification via wet chemical etching of single-crystalline silicon for photovoltaic application

The potential of solar cells have not been fully tapped due to the lack of energy conversion efficiency. There are three important mechanisms in producing high efficiency cells to harvest solar energy; reduction of light reflectance, enhancement of light trapping in the cell and increment of light absorption. The current work represent studies conducted in surface modification of single-crystalline silicon solar cells using wet chemical etching techniques. Two etching types are applied; alkaline etching (KOH:IPA:DI) and acidic etching (HF:HNO₃:DI). The alkaline solution resulted in anisotropic profile that leads to the formation of inverted pyramids. While acidic solution formed circular craters along the front surface of silicon wafer. This surface modification will leads to the reduction of light reflectance via texturizing the surface and thereby increases the short circuit current and conversion rate of the solar cells.     

Atrovirisidone B, a new prenylated depsidone with cytotoxic property from the roots of Garcinia atroviridis

A new prenylated depsidone, atrovirisidone B (2), together with naringenin (3) and 3,8"-binaringenin (4) were isolated from the roots of Garcinia atroviridis. Their structures were determined on the basis of spectral data interpretation. Compound 2 showed cytotoxic activity against human breast (MCF-7), human prostate (DU-145) and human lung (H-460) cancer cells.     

The compartmentation of ethylene in developing cotyledons of Phaseolus vulgaris L.

Isolated cotyledons of Phaseolus vulgaris L. cv. Canadian Wonder accumulated ¹⁴C₂H₄ (0.7–1 l l^-1) from air to give partition coefficients of 1 to 4, which greatly exceeded the value obtained with steam killed cotyledons (0.05) and with water (0.11). After ¹⁴C₂H₄ treatment, 98% of the ¹⁴C in the tissue remained as ¹⁴C₂H₄. The labelled ethylene accumulated by cotyledons was released only slowly (1–10% h^-1) either in an air stream or into toluene. Heating to 60°C for 2 h, but not freezing and thawing, caused the immediate release of ¹⁴C₂H₄ from the tissue. Propylene and vinyl chloride competitively inhibited the accumulation of ¹⁴C₂H₄.Cotyledons emanated endogenous ethylene at a very low rate but after heating (although not freezing and thawing) 13 nl of ethylene per g fresh mass were released within minutes. It was concluded that french bean cotyledons hold ethylene in a compartmented form in sufficient amount to account for at least 200 h of emanation.Abbreviation PPO diphenyloxazole     

Anthraquinones from Hedyotis capitellata

Four new furanoanthraquinones, 2-hydroxymethyl-3,4-[2'-(1-hydroxy-1-methylethyl)-dihydrofurano]-8-hydroxyanthraquinone, 2-hydroxymethyl-3,4-[1'-hydroxy-2'-(1-hydroxy-1-methylethyl)-dihydrofurano]-8-hydroxyanthraquinone, 2-hydroxymethyl-3,4-[2'-1-hydroxy-1-methylethyl)-dihydrofurano]anthraquinone and 2-methyl-3,4-[2'-(1-hydroxy-1-methylethyl)-dihydrofurano] anthraquinone or capitellataquinone A-D and four known anthraquinones, rubiadin, anthragallol 2-methyl ether, alizarin 1-methyl ether and digiferruginol, together with scopoletin were isolated from the stems of Hedyotis capitellata Wall (Rubiaceae). Lucidin-3-O-beta-glucoside was isolated from the roots of the plant. Characterization of the new compounds was carried out by extensive NMR studies using FGCOSY, FGHMQC, FGHMBC and DEPT-135 in addition to other spectroscopic methods.     

Optimisation of the Photonic Efficiency of TiO2 Decorated on MWCNTs for Methylene Blue Photodegradation

MWCNTs/TiO₂ nanocomposite was prepared by oxidising MWCNT in H₂SO₄/HNO₃ then decorating it with TiO₂-p25 nanopowder. The composites were characterised using XRD, TEM, FT-IR PL and UV−vis spectroscopy. The TEM images have shown TiO₂ nanoparticles immobilised onto the sidewalls of the MWCNTs. The UV-vis spectrum confirms that the nanocomposites can significantly absorb more light in the visible regions compared with the commercial TiO₂ (P25). The catalytic activity of these nanocomposites was determined by photooxidation of MB aqueous solution in the presence of visible light. The MWCNTs/TiO₂ (1:3) mass ratio showed maximum degradation efficiency. However, its activity was more favourable in alkaline and a neutral pH than an acidic medium.     

A Facile Thermal-Treatment Route to Synthesize ZnO Nanosheets and Effect of Calcination Temperature

A facile thermal-treatment route was successfully used to synthesize ZnO nanosheets. Morphological, structural, and optical properties of obtained nanoparticles at different calcination temperatures were studied using various techniques. The FTIR, XRD, EDX, SEM and TEM images confirmed the formation of ZnO nanosheets through calcination in the temperature between 500 to 650°C. The SEM images showed a morphological structure of ZnO nanosheets, which inclined to crumble at higher calcination temperatures. The XRD and FTIR spectra revealed that the samples were amorphous at 30°C but transformed into a crystalline structure during calcination process. The average particle size and degree of crystallinity increased with increasing calcination temperature. The estimated average particle sizes from TEM images were about 23 and 38 nm for the lowest and highest calcination temperature i.e. 500 and 650°C, respectively. The optical properties were determined by UV–Vis reflection spectrophotometer and showed a decrease in the band gap with increasing calcination temperature.     

Novel sesquiterpene and copyrine alkaloids from Anaxagorea javanica Blume

A novel sesquiterpene, nordine (or 2,2,9-trimethyl-5-methylene-12-oxa-bicyclo[6.3.1]dodecane-4,9-diol) (1) and two new copyrine alkaloids of eupolauridine skeleton, viz., 4,11-dimethoxyeupolauridine (2) and 2-methoxy-3-hydroxyeupolauridine (3), along with five alkaloidal (4–8) and nine non-alkaloidal compounds (9–17), have been isolated from the bark and roots of Anaxagorea javanica Blume. The structures of the new constituents were deduced by NMR spectral data. Compounds 6 and 7 displayed moderate inhibition of NO production with IC₅₀ values of 18.2 and 32.3 μg/ml respectively.     

Antioxidant, radical-scavenging, anti-inflammatory, cytotoxic and antibacterial activities of methanolic extracts of some Hedyotis species

The antioxidant, radical-scavenging, anti-inflammatory, cytotoxic and antibacterial activities of methanolic extracts of seven Hedyotisspecies were investigated. The antioxidant activity was evaluated by the ferric thiocyanate (FTC) and thiobarbituric acid (TBA) methods while the radical scavenging activity was measured by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) method. The anti-inflammatory activity related to NO inhibition of the plant extracts was measured by the Griess assay while cytotoxicity were measured by the MTT assay against CEM-SS cell line. The antibacterial bioassay (against 4 bacteria, i.e. Bacillus subtilis B28 (mutant), Bacillus subtilis B29 (wild-type), Pseudomonas aeruginosa UI 60690 and methicillin resistant Staphylococcus aureus, (MRSA) was also carried out using the disc-diffusion method. All tested extracts exhibited very strong antioxidant properties when compared to Vitamin E (alpha-tocopherol) with percent inhibition of 89-98% in the FTC and 60-95% in the TBA assays. In the DPPH method, H. herbacea exhibited the strongest radical scavenging activity with an IC50 value of 32 microg/ml. The results from the Griess assay showed that the tested extracts are weak inhibitors of NO synthase. However, all tested extracts exhibited moderate cytotoxic properties against CEM-SS cell line giving CD50 values in the range of 21-41 microg/ml. In the antibacterial bioassay, the stems and the roots of H. capitellata showed moderate activity against the 4 tested bacteria while the leaves showed moderate activity towards B. subtilis B28, MRSA and P. aeruginosa only. The roots of H. dichotoma showed strong antibacterial activity against all 4 bacteria. All other extracts did not exhibit any antibacterial activity.