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Background Authentication of food and agricultural products is important to trace out the right product and ensure the customer’s preference and their health. Sesame (Sesamum indicum L.) is one of the most important crops used for food and medicine in Ethiopia and different varieties and cultivars are produced in different regions of the country. This study was undertaken to determine the total flavonoid content, total phenolic content, antioxidant activity, and fatty acids profile of black and white sesame seed varieties. Samples were obtained from three major sesame seed-producing districts of Ethiopia. Results The total phenolic content (TPC), total flavonoid content (TFC), and the half-maximal inhibitory concentration (IC50) were ranged from 2.95 to 6.95 mgGAE/g, 2.13–4.99 mgCE/g and 8.3–16.8 AAE/g of the sample, respectively. In general, white sesame seed samples showed the highest TPC, TFC, and antioxidant activity than the black variety. Location wise, samples collected from the Metema district were found to contain a relatively higher concentration of the phytochemicals. The white seed variety was characterized by significantly higher content of oil (53.2–58.2% by mass of the sample) than the back variety (47.6–51.4%).The oil content of the seeds was found to contain nine identifiable fatty acids (FAs). The total unsaturated fatty acids constituted more than 82% of the total FAs, while the saturated FAs were lower than 18% of the total FAs. Among the unsaturated FAs, linoleic acid (C18:2, omega-6 FAs) was the dominant FA (42.5–44.3%) followed by oleic acids (37.2–38.9%). On the other hand, palmitic acids (9.35–11.2%) and stearic acid (5.78–6.52%) were the dominant FAs among the saturated FAs. Conclusions The studied samples had higher concentration of linoleic acid (omega-6 FA) than oleic acid, as opposed to other reported accessions of sesame seeds. Furthermore, white sesame seeds were richer in oil content than the black variety. The high concentration of unsaturated FAs, omega-6 FA, and phenolic compounds make sesame seeds nutritionally and medicinally important for the human diet. Unlike the fatty acids profiles, the level of phenolic compounds in sesame seeds was highly dependent on the geographical region and varietal type of the seeds.

Low-cost, non-noble-metal electrocatalysts are required for direct methanol fuel cells, but their development has been hindered by limited activity, high onset potential, low conductivity, and poor durability. A surface electronic structure tuning strategy is presented, which involves doping of a foreign oxophilic post-transition metal onto transition metal aerogels to achieve a non-noble-metal aerogel Ni97 Bi3 with unprecedented electrocatalytic activity and durability in methanol oxidation. Trace amounts of Bi are atomically dispersed on the surface of the Ni97 Bi3 aerogel, which leads to an optimum shift of the d-band center of Ni, large compressive strain of Bi, and greatly increased conductivity of the aerogel. The electrocatalyst is endowed with abundant active sites, efficient electron and mass transfer, resistance to CO poisoning, and outstanding performance in methanol oxidation. This work sheds light on the design of high-performance non-noble-metal electrocatalysts.

Because of their good mechanical flexibility and large exposed surfaces, two-dimensional (2D) nanostructures have attracted tremendous attention in the fields of renewable energy storage and conver...

Developing a low cost but efficient photocatalyst with maximum utilization of sunlight, minimum charge carrier recombination and improved stability is very crucial and challenging. Triphenylphosphine modification of HKUST-1 followed by controlled calcination resulted in a phosphorus doped carbon/Cu2O composite (HKUST-1-P-300). The structure and band properties were fully studied, and phenol degradation and H2 evolution were employed to evaluate the photocatalytic activity. Under visible light irradiation, HKUST-1-P-300 showed superior photocatalytic activity and stability. A phenol degradation efficiency of up to 99.8% was achieved within 90 minutes, and also a remarkable H2 evolution rate of 1208 μmol was achieved. The external quantum efficiency of solar hydrogen evolution over this photocatalyst, without noble metal loading, reaches 48.6% at 425 nm. More auspiciously, the photocatalytic reaction continued for more than 12 h without performance degradation. To get further evidence for the origin of the improved photocatalytic activity of the HKUST-1-P-300, a series of characterization studies have been carried out. To the best of our knowledge, this work represents the first example of using P-doped carbon/Cu2O both for phenol degradation and H2 production. Mechanistic studies were carried out to give insights into the photodegradation process, and the superior photocatalytic activity of HKUST-1-P-300 can be ascribed to enhanced visible light absorption efficiency, higher surface area, efficient separation of photogenerated charge carriers, reduced aggregation of Cu2O and the synergistic effect of the P-doped carbon/Cu2O structures. This work demonstrates a facile and promising approach for designing low cost, highly stable and efficient heterostructured photocatalysts that can be applicable for energy and environmental applications.

Insufficient catalytic activity and stability, and high cost are the key barriers for Pt-based electrocatalysts in wide practical applications. Herein, a hierarchically porous PtNi nanoframe/N-doped graphene aerogel (PtNiNF-NGA) electrocatalyst with outstanding performance toward methanol oxidation reaction (MOR) in acid electrolyte has been developed via a facile tert-butanol-assisted structure reconfiguration strategy. The ensemble of the high-alloying-degree-modulated electronic structure and correspondingly the optimum MOR reaction pathway, the structure superiorities of hierarchical porosity, thin edges, Pt-rich corners, and the anchoring effect of the NGA, endow the PtNiNF-NGA with both prominent electrocatalytic activity and stability. The mass and specific activity (1647 mA/mgPt , 3.8 mA/cm2 ) of the PtNiNF-NGA are 5.8 and 7.8 times higher than those of commercial Pt/C, respectively. Especially, it exhibits exceptional stability under a 5-hour chronoamperometry test and 2200-cycle cyclic voltammetry scanning. This work is of high inspiration for the design of Pt-based electrocatalysts with both high activity and stability.

Additional file 1: Figure (S1). GC–MS chromatogram of the fatty acid methyl esters of white sesame seed variety collected from Metema district. "IS" refers to the internal standard (undecanoic acid methyl ester). Figure (S2). GC–MS chromatogramof methyl esters of fatty acids present in Black sesame seed collected from Metema district. Figure (S3). GC–MS chromatogram of methyl esters of fatty acids present in white sesame seed collected from West Armachiho district. Figure (S4). GC–MS chromatogram of methyl esters of fatty acids present in Black sesame seed collected from West Armachiho district. Figure (S5). GC–MS chromatogram of methyl esters of fatty acids present in white sesame seed collected from Amuru district. Figure (S6). GC–MS chromatogram of methyl esters of fatty acids present in black sesame seed collected from Amuru district.

Photoelectrochemical (PEC) water splitting is a promising technology for solar hydrogen production to build a sustainable, renewable and clean energy economy. Hematite (α-Fe2O3) based photoanodes offer promise for such applications, due to their high chemical stability, great abundance and low cost. Despite these promising properties, progress towards the manufacture of practical water splitting devices has been limited. This review is intended to highlight recent advancements and the limitations that still hamper the full utilization of hematite electrodes in PEC water splitting systems. We review recent progress in manipulating hematite for PEC water splitting through various approaches, focused on e.g. enhancing light absorption, water oxidation kinetics, and charge carrier collection efficiency. As the morphology affects various properties, progress in morphological characterization from thicker planar films to recent ultrathin nanophotonic morphologies is also examined. Special emphasis has been given to various ultrathin films and nanophotonic structures which have not been given much attention in previous review articles.

Leaf samples ofUrtica simensiscollected from different locations of Ethiopia were analyzed for their proximate compositions, total phenolic and flavonoid contents, antioxidant activities, and fatty acid profiles. The proximate analysis results revealed the presence of ash in the range 17.2–24.3%, crude fat 3.19–3.50%, crude protein 3.42–6.38%, crude fiber 9.37–14.0%, and carbohydrate 56.7–63.7%. The determined total polyphenols, flavonoids, and antioxidant activities ranged 2.18–4.84 mg gallic acid, 1.35–4.46 mg catechin, and 1.58–3.36 mg ascorbic acid, respectively, equivalents per gram of dry sample. High variability was observed for polyphenol and flavonoid contents while only random variation was observed for crude fat and carbohydrate among samples from different locations. In addition, the fatty acid profiles of the leaves were analyzed by using gas chromatography coupled with mass spectrometry. A total of 16 different fatty acids were detected in the samples. Linolenic, palmitic, and linoleic acids were the major fatty acids with average compositions of 36.6, 20.7, and 15.5%, respectively, of the total fatty acid. The result of this study revealed that the carbohydrate and ash contents of leaves ofUrtica simensisare exceptionally high to make the leaves a significant source of the dietary important chemicals. Additionally, the lipid fraction of the leaves was found to be rich in essential fatty acids (α-linolenic and linoleic acids) that are critically required in the human diet.

Metal-organic framework (MOF) assisted hydrothermal pretreatment and co-catalysis strategy based on UiO-66 MOF is developed for the first time. The Planetree exfoliating bark was pretreated with or without UiO-66 assisted hydrothermal method at a temperature ranging from 160 to 240 °C for 1–3 h residence. With the rise of pretreatment severity, the total reducing sugar (TRS) was increased till reached maximum, 180 mg g−1, in the presence of UiO-66. The fitting models validate the optimal hydrothermal condition was at 180 °C and 1 h, which was characterized with high TRS and very low yield of furfural and HMF. The TRS from enzymatic hydrolysis reaches maximum, 391 mg g−1, in the presence of MOF co-catalysis and the maximum ethanol yield achieved was 73%. Altered morphology, higher surface area and porosity are noticed after MOF assisted hydrothermal pretreatment. This study insights the MOFs’ application in lignocellulose biomass processing.

Hydrogen production from photocatalytic water splitting by non-noble-metal photocatalysts is considered to be the most promising solution to the world energy crisis issues. Herein, a chrysanthemum-like crystalline C@Cu2O/CuO composite with remarkable photochemical water reduction activity has been successfully fabricated via conditioned calcinations of the Cu(II) based MOF. Under visible light irradiation, Cu2O/CuO/C-350 gives a remarkable H2 evolution rate of 26.7 mmol g−1h−1 with high external quantum efficiency of 52.4% at 425 nm. The unique morphology, significantly improved charge carrier separation and synergistic effects of the composite system should be responsible for the excellent photocatalytic activity. To get further evidence about the origin of the improved photoactivity of the Cu2O/CuO/C-350, a series of characterization has been carried out. These findings propose a new unexplored avenue for the fabrication of highly active and low cost photocatalyst for practical H2 generation via photochemical water reduction.

A Cu2O/CuO heterostructure modified with CuS is proposed as a highly promising and stable photocathode for solar hydrogen production. The Cu2O/CuO/CuS heterostructure was synthesized by in situ growth of Cu2O/CuO via simple electrodeposition of Cu film followed by annealing in air, and then the surfaces of the heterostructure were sequentially modified by loading CuS via a successive ion layer adsorption and reaction (SILAR) approach. Experimental evidence, including Raman, XANES/EXAFS and XPS spectra, is presented for the interfacial reaction between CuS and Cu2O/CuO. The optimized Cu2O/CuO/CuS photocathode provides a remarkably enhanced photocurrent density of −5.4 mA cm−2 (i.e. >2.5 times than that of bare Cu2O/CuO) at 0 V vs. RHE under standard AM 1.5 light illumination. Due to the bicatalytic effects in suppressing electron–hole recombination, a further increase in photocurrent density to −5.7 mA cm−2 was noticed after decorating the Cu2O/CuO surface with both CuS and Pt. To the best of our knowledge, this is the highest performance yet reported for a cocatalyst modified Cu2O/CuO photoelectrode for solar water splitting. More importantly, the Cu2O/CuO heterostructure modified with optimum CuS afforded an impressive solar conversion efficiency of ABPE% = 3.6%, which is a greater than fourfold increase compared to the bare Cu2O/CuO. The stability of the bare Cu2O/CuO photocathode showed about a 44% decrease in initial photocurrent density within 1 h, whereas 85% and 92% of the initial photocurrent was maintained after 1 h when the photocathode was modified with CuS and with both CuS and Pt, respectively. This highly enhanced photoelectrochemical property is attributed to the fast transfer of photogenerated electrons resulting in suppressed electron–hole recombination and the synergistic effect of a heterojunction in light absorption and charge separation. This work demonstrates a facile strategy and potential use of low cost CuS as an efficient cocatalyst for solar hydrogen production that can be applicable in the general field of energy conversion.

Developing a new cellulase-MOF composite system with enhanced stability and reusability for cellulose hydrolysis was aimed. Physical adsorption strategy was employed to fabricate two cellulase composites, and the activity of composite was characterized by hydrolysis of carboxymethyl cellulose. The NH2 functionalized UiO-66-NH2 MOF exhibited higher protein loading than the precursor UiO-66, due to the extra anchor sites of NH2 groups. The immobilized cellulase showed enhanced thermostability, pH tolerance and lifetime. The maximum activity attained at 55 °C could be kept 85% when used at 80 °C, and the residual activities were 72% after ten cycles and 65% after 30 days storage. The abundant NH2 and COOH groups of MOF adsorb cellulase and enhance its stability, and the resulted heterogeneity offered the opportunity of recovering composite via mild centrifuge. The findings suggest the promising future of developing cellulase-MOF composite with ultrahigh activities and stabilities for practical application.

Herein, we present a highly photoactive photoanode for solar water oxidation using three dimensional (3D) urchin-like hematite (α-Fe2O3) nanostructures modified with ultra-thin reduced graphene oxide (rGO). rGO acts as both electron conducting scaffold and surface passivation layer. By virtue of these combined effects, the composite photoanode exhibits 1.47 times higher photocurrent density (1.06 mA cm−2, at 1.23 V vs. reversible hydrogen electrode (RHE)) and two-fold enhancement in the photoconversion efficiency than that of pristine α-Fe2O3. The dual effect of rGO as both electron conducting scaffold and surface passivation layer is further evidenced from the 1.82 and 1.67 fold enhancements in charge separation and charge injection efficiencies at 1.23 and 1 V vs. RHE respectively. To get further evidence about the origin of the improved photoactivity of the rGO modified photoanode, a series of electrochemical, photoelectrochemical and impedance spectroscopy measurements were carried out. Our results demonstrate the benefits of a noble metal free highly promising photoanode for photoelectrochemical water oxidation.

One of the major challenges in photoelectrochemical water splitting is to develop an efficient photoanode that can oxidize water at low applied potential. Herein, a codoped (Sn, Zr) α-Fe2O3 photoanode modified with a stable and earth abundant nickel oxyhydroxide (NiOOH) co-catalyst that can split water at low applied potential is reported. First, an unintentional gradient monodoped (Sn) α-Fe2O3 photoanode was synthesized at controlled annealing temperature that achieved a photocurrent density of 0.86 mA cm−2 at 1.23 V vs. RHE. Further doping with an optimized amount of Zr outperformed the monodoped (Sn) α-Fe2O3 photoanode providing significantly much higher photocurrent density (1.34 mA cm−2). The remarkably improved electrical conductivity and more than three times higher charge carrier density (as evidenced from electrochemical impedance spectroscopy measurements and Mott–Schottky analysis) of the codoped (Sn, Zr) α-Fe2O3 photoanode highlight the importance of codoping. The synergetic effect of codoping (Sn, Zr) led to 1.6-fold enhancement in charge separation efficiency at 1.23 V compared to the monodoped (Sn) α-Fe2O3 photoanode. The NiOOH modified codoped (Sn, Zr) α-Fe2O3 photoanode exhibited drastically lower onset potential (0.58 V) and a photocurrent density of 1.64 mA cm−2 at 1.23 V. Interestingly a 160 mV cathodic shift in photocurrent onset potential was also observed. Concomitant with this, the NiOOH modified codoped (Sn, Zr) α-Fe2O3 photoanode exhibited 1.6 to 9.5-fold enhancement in charge injection efficiency (ηinj) at the kinetic control region of 0.7 to 0.9 V compared to the unmodified codoped photoanode. Gas evolution measurements also showed that the NiOOH modified codoped α-Fe2O3 photoanode achieved an average Faradaic efficiency of 93%.

Here we report the design, synthesis and characterization of a novel Cu2O/CuO heterojunction decorated with a nickel cocatalyst as a highly efficient photocathode for solar hydrogen production. The heterojunction structure was shown and examined by X-ray absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Tip-enhanced Raman spectroscopy (TERS). Due to the synergistic effect, the Cu2O/CuO heterojunction gave a remarkably improved photocurrent density (−2.1 mA cm−2), i.e. 3.1 times higher than a Cu2O photoelectrode. Additionally, the Cu2O/CuO heterojunction, when decorated with the nickel cocatalyst, showed six-fold and two-fold increases in photocurrent density (−4.3 mA cm−2) respectively when compared to Cu2O and the bare Cu2O/CuO at 0 V vs. RHE under AM 1.5 illumination (100 mW cm−2). Interestingly, the Ni decorated Cu2O/CuO photocathode showed an impressive solar conversion efficiency of 2.71% at −0.4 V vs. Pt, i.e. 467% higher compared to the bare Cu2O/CuO. After 20 minutes of standard solar illumination, 87.7% of the initial photocurrent density was retained for the nickel decorated Cu2O/CuO heterojunction. This is more than 1.5 times that of the bare Cu2O/CuO (53.6%), suggesting that surface modification with Ni not only effectively promotes water splitting but also stabilizes the photoelectrode. The enhanced photoelectrochemical performance is attributable to the efficient charge transfer and protective role of Ni, the improved crystallinity and the synergistic effect of the heterojunction in light absorption and charge separation. This inexpensive photocathode with increased photocurrent density and photostability offers a higher promise for solar hydrogen production.

Hematite (α-Fe2O3) is a suitable candidate for photoelectrochemical water splitting due to its well-suited band structure, stability, and availability. However, water splitting using a low external potential is the major challenge that limits the practical application of hematite. Here, we achieve a very low onset potential using a sequential surface treatment approach to overcome two fundamental limiting factors, sluggish hole transfer, and interfacial recombination, independently. First, a heavily doped Fe2-xSnxO3 surface passivation layer was created by Sn4+ surface treatment which can robustly inhibit interfacial recombination. Then, an NiOOH catalyst layer was deposited that greatly enhances the charge transfer process across the passivated electrode/electrolyte interface. By exploiting this approach, the optimized sequentially treated photoanode (Fe2O3/Fe2-xSnxO3/NiOOH) exhibits a low photocurrent onset potential of 0.49 V vs. RHE and a saturated photocurrent density of 2.4 mA cm-2 V at 1.5 V vs. RHE. Transient photocurrent and impedance spectroscopy measurements further reveal that the combined Fe2-xSnxO3/NiOOH layers reduce interfacial recombination and enhance charge transfer across the electrode/electrolyte interface. The results provide convincing evidence that it is possible to address the problems of surface trap recombination and sluggish catalysis independently by employing surface passivation layers first and catalysts later sequentially.

A one dimensional (1D) Cu2O straddled with graphene is proposed as a highly promising and stable photocathode for solar hydrogen production. The Cu2O nanowire arrays modified with an optimized concentration of graphene provide much higher improved photocurrent density −4.8 mA cm−2, (which is two times that of bare 1D Cu2O, −2.3 mA cm−2), at 0 V vs. RHE under AM 1.5 illumination (100 mW cm−2) and solar conversion efficiency reaching 3.3% at an applied potential of −0.55 V vs. the Pt counter electrode. Surprisingly, 1D Cu2O with an optimum graphene concentration exhibits an inspiring photocurrent density from 2.1 to 1.1 mA cm−2 at a higher positive potential range of 0.2–0.4 V vs. RHE, which is 300–550% higher compared with that of bare 1D Cu2O. This is the highest value ever reported for a Cu2O-based photocathode at such a positive potential. After 20 minutes of standard solar irradiation, 83% of the initial photocurrent density was retained for the nanocomposite which is more than five times compared to the bare Cu2O (14.5%). A Faradic efficiency of 74% was obtained for the evolved H2 gas measurement. To get evidence for the photostability of the graphene modified photocathode, detailed characterization was carried out. The high PEC performance of the graphene/Cu2O nanocomposite is attributed to the improved crystallinity and the synergetic effect of graphene in absorbing visible light, suppressing the charge recombination and photocorrosion of the photoelectrode by preventing direct contact with the electrolyte. This inexpensive photocathode prepared free of noble metals, showed enhanced high photocurrent density with good stability and is a highly promising photocathode for solar hydrogen production.

The levels of essential metals (Ca, Mg, Fe, Mn, Zn, Cu, Co, Cr, Ni) and toxic metals (Cd, Pb) were determined in the leaves of Croton macrostachyus (traditional medicinal plant) collected from four different regions of Ethiopia (Akaki, Abomsa, Bonga and Dilla) and also in the infusions of leaves collected from Akaki using flame atomic absorption spectrometry. An optimized digestion procedure took 2.5 h for the digestion of 0.5 g of powdered sample with 2 mL of HNO 3 and 2 mL of HClO 4 at 270 o C while 2 h were needed to digest 25 mL infusion with 4 mL of HNO 3 and 1 mL HClO 4 . The recoveries of metals were in the range 92–103% for the leaves powder and 94–105% for the infusion samples. The mean concentration ranges (mg/g) were Ca (5,823–12,040), Mg (1,971–4,961), Fe (192–581), Mn (157–1,770), Zn (19.5–60.5), Cu (6.31–18.6), Co (1.97–3.45), Cr (2.13–8.75), Ni (2.15–3.80), Cd (0.75–1.08) and Pb (1.05–2.19) for the leave powders and Ca (716–1,776), Mg (16.7–80.9), Fe (1.39–3.34), Mn (2.17–3.40), Zn (0.674–7.88), Cu (1.94–2.31), Co (0.157–0.224), Cr (0.144–1.23), Ni (0.203–0.267), Cd (0.05–0.098) and Pb (0.0148–0.185) for the infusion samples. Among the quantified metals in the infusion samples, Ca showed the highest leaching rate (61.5%) in the 24 h infusion while Fe exhibit the lowest (1%) leaching rate in the 3 h infusion. KEY WORDS : Traditional medicinal plant, Croton macrostachyus , Croton leaves powder, Croton leaves infusion, Major metals, Trace metals, Ethiopia Bull. Chem. Soc. Ethiop. 2015 , 29(1), 11-26 DOI: http://dx.doi.org/10.4314/bcse.v29i1.2