Tailor‐Made Hole‐Conducting Coadsorbents for Highly Efficient Organic Dye‐Sensitized Solar Cells

The Y‐shaped, low molecular mass, hole‐conductor (HC), acidic coadsorbents 4‐{3,7‐bis[4‐(2‐ethylhexyloxy)phenyl]‐10H‐phenothiazin‐10‐yl}benzoic acid ( PTZ1 ) and 4‐{3,7‐bis[4‐(2‐ethylhexyloxy)phenyl]‐10H‐phenothiazin‐10‐yl}biphenyl‐4‐carboxylic acid ( PTZ2 ) were developed. Owing to their tuned and negative‐shifted HOMO levels (vs. NHE), they were used as HC coadsorbents in dye‐sensitized solar cells (DSSCs) to improve cell performance through desired cascade‐type hole‐transfer processes. Their detailed functions as HC coadsorbents in DSSCs were investigated to obtain evidence for the desired cascade‐type hole‐transfer processes. They have multiple functions, such as preventing π–π stacking of dye molecules, harvesting light of shorter wavelengths, and faster dye regeneration. By using PTZ2 as the tailor‐made HC coadsorbent on the TiO₂ surface with the organic dye NKX2677, an extremely high conversion efficiency of 8.95 % was achieved under 100 mW cm^?2 AM 1.5G simulated light (short‐circuit current J_SC=16.56 mA cm^?2, open‐circuit voltage V_OC=740 mV, and fill factor of 73 %). Moreover, J_SC was increased by 13 %, V_OC by 27 % and power‐conversion efficiency by 49 % in comparison to an NKX2677‐based DSSC without an HC coadsorbent. This is due to the HC coadsorbent having a HOMO energy level well matched to that of the NKX‐2677 dye to induce the desired cascade‐type hole‐transfer processes, which are associated with a slower charge recombination, fast dye regeneration, effective screening of liquid electrolytes, and an induced negative shift of the quasi‐Fermi level of the electrode. Thus, this new class of Y‐shaped, low molecular weight, organic, HC coadsorbents based on phenothiazine carboxylic acid derivatives hold promise for highly efficient organic DSSCs.     

Effect of solution pH on the stability of mixed silica -alumina suspension in the presence of polyacrylic acid (PAA) with different molecular weights

The influence of solution pH (in the range 3–9) on mixed silica-alumina suspension in the absence and presence of polyacrylic acid (PAA) was studied. The composition of the adsorbent was SiO₂ (97%) and Al₂O₃ (3%). The turbidimetry method was applied to record changes in the stability of the investigated systems as a function of time. It was shown that the suspension without the polymer is less stable at pH 3, whereas at pH 6 and 9, the systems were stable. PAA with molecular weights 100 000 and 240 000 at pH 3 (improvement of system stability conditions) and PAA 2 000 at pH 6 (deterioration of suspension stability) have a great effect on the silica-alumina suspension stability. The stabilization-flocculation properties of polyacrylic acid are a result of a specific conformation of its chains on the solid surface where it depends on the solution pH and the polymer molecular weight.     

Utilization of Makgeolli Sludge Filtrate (MSF) as Low-Cost Substrate for Bacterial Cellulose Production by Gluconacetobacter xylinus

Search for efficient low-cost substrate/additives are gaining significant impetus in bacterial cellulose (BC) production. Makgeolli sludge (a traditional Korean wine distillery waste) is enriched with organic acid, alcohol, and sugar. Using makgeolli sludge filtrate (MSF) and Hestrin–Schramm (HS) medium (g/l of distilled water: glucose, 10.0; peptone, 5.0; yeast extract, 5.0; disodium phosphate, 2.7; citric acid, 1.15; pH 5.0), two different media—namely the modified HS media (ingredients of HS media except glucose dissolved in MSF) and mixed modified HS media (equal volume mixture of original and modified HS media)—were formulated. BC production with Gluconacetobacter xylinus was studied using the two above referred medium. Keeping HS medium as reference, effect of initial pH, glucose, ethanol, and organic acid concentration on BC production was also studied. It suggests that increasing initial glucose (up to 25 g/l) though improves BC production but results in poor BC yield above 15 g/l of glucose. However, addition of alcohol (up to 1%v/v) or citric acid (up to 20 mM) escalate productivity up to four and two times, respectively. In both modified HS media and mixed modified HS medium, BC production was four to five times higher than that of original HS medium. Even MSF alone surpassed HS medium in BC production. Scanning electron microscopy showed that BC microfibrils from MSF based media were several micrometers long and about 25–60 nm widths. X-ray diffraction patterns suggested the produced BC were of cellulose I polymorph.     

Dual Role of Silver Moieties Coupled with Ordered Mesoporous Cobalt Oxide towards Electrocatalytic Oxygen Evolution Reaction

Herein, we show that the performance of mesostructured cobalt oxide electrocatalyst for oxygen evolution reaction (OER) can be significantly enhanced by coupling of silver species. Various analysis techniques including pair distribution function and Rietveld refinement, X‐ray absorption spectroscopy at synchrotron as well as advanced electron microscopy revealed that silver exists as metallic Ag particles and well‐dispersed Ag₂O nanoclusters within the mesostructure. The benefits of this synergy are twofold for OER: highly conductive metallic Ag improves the charge transfer ability of the electrocatalysts while ultra‐small Ag₂O clusters provide the centers that can uptake Fe impurities from KOH electrolyte and boost the catalytic efficiency of Co–Ag oxides. The current density of mesostructured Co₃O₄ at 1.7 V_RHE is increased from 102 to 211 mA cm^?2 with incorporation of silver spices. This work presents the dual role of silver moieties and demonstrates a simple method to increase the OER activity of Co₃O₄.     

A FOURIER SPECTRAL SCHEME FOR SOLVING NONLINEAR KLEIN-GORDON EQUATION

A Fourier spectral scheme is proposed for solving the periodic problem of nonlinear Klein-Gordon equation. Its stability and convergence are investigated. Numerical results are also presented.     

A Dipolar Anthracene Dye: Synthesis,Optical Properties and Two‐photon Tissue Imaging

Two‐photon microscopy is a powerful tool for studying biological systems. In search of novel two‐photon absorbing dyes for bioimaging, we synthesized a new anthracene‐based dipolar dye (anthradan) and evaluated its two‐photon absorbing and imaging properties. The new anthradan, 9,10‐bis(o‐dimethoxy‐phenyl)‐anthradan, absorbs and emits at longer wavelengths than acedan, a well‐known two‐photon absorbing dye. It is also stable under two‐photon excitation conditions and biocompatible, and thus used for two‐photon imaging of mouse organ tissues to show bright, near‐red fluorescence along with negligible autofluorescence. Such an anthradan thus holds promise as a new class of two‐photon absorbing dyes for the development of fluorescent probes and tags for biological systems.     

Detection of Iprobenfos and Edifenphos using a new Multi-aptasensor

The sensitive detection of iprobenfos (IBF) and edifenphos (EDI) was successfully conducted by using a new aptamer-based colorimetric multi-aptasensor. The dissociation constants of this multi-target aptamer to both iprobenfos and edifenphos were found to be 1.67 μM and 38 nM, respectively, according to the isothermal calorimetry assay. The aptamer EIA2 was selective to only IBF and EDI, confirmed by AuNP assays. By using this multi-aptasensor, both pesticides IBF and EDI can be eventually detected in a range from 10 nM to 5 nM, respectively. This multi-aptasensor was successfully implemented in spiked rice samples and the accuracies of this AuNP-based multi-aptasensor were around 80 and 90% in spiked paddy and polished rice samples, respectively. This aptamer EIA2 could be applied not only for the detection of pesticides from real samples in agriculture field as POC, but also can be used as a bioreceptor for other types of aptasensors.