Yaoyu Feng

Core/Shell Colloidal Quantum Dot Exciplex States for the Development of Highly Efficient Quantum-Dot-Sensitized Solar Cells

Searching suitable panchromatic QD sensitizers for expanding the light-harvesting range, accelerating charge separation, and retarding charge recombination is an effective way to improve power conversion efficiency (PCE) of quantum-dot-sensitized solar cells (QDSCs). One possible way to obtain a wide absorption range is to use the exciplex state of a type-II core/shell-structured QDs. In addition, this system could also provide a fast charge separation and low charge-recombination rate. Herein, we report on using a CdTe/CdSe type-II core/shell QD sensitizer with an absorption range extending into the infrared region because of its exciplex state, which is covalently linked to TiO2 mesoporous electrodes by dropping a bifunctional linker molecule mercaptopropionic acid (MPA)-capped QD aqueous solution onto the film electrode. High loading and a uniform distribution of QD sensitizer throughout the film electrode thickness have been confirmed by energy dispersive X-ray (EDX) elemental mapping. The accelerated electron injection and retarded charge-recombination pathway in the built CdTe/CdSe QD cells in comparison with reference CdSe QD-based cells have been confirmed by impedance spectroscopy, fluorescence decay, and intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) analysis. With the combination of the high QD loading and intrinsically superior optoelectronic properties of type-II core/shell QD (wide absorption range, fast charge separation, and slow charge recombination), the resulting CdTe/CdSe QD-based regenerative sandwich solar cells exhibit a record PCE of 6.76% (J(sc) = 19.59 mA cm(-2), V(oc) = 0.606 V, and FF = 0.569) with a mask around the active film under a full 1 sun illumination (simulated AM 1.5), which is the highest reported to date for liquid-junction QDSCs.

Near Infrared Absorption of CdSexTe1–x Alloyed Quantum Dot Sensitized Solar Cells with More than 6% Efficiency and High Stability

CdSe0.45Te0.55 alloyed quantum dots (QDs) with excitonic absorption onset at 800 nm and particle size of 5.2 nm were prepared via a noninjection high-temperature pyrolysis route and used as a sensitizer in solar cells. A postsynthesis assembly approach with use of bifunctional linker molecule mercaptopropionic acid (MPA) capped water-soluble QDs, obtained via ex situ ligand exchange from the initial oil-dispersible QDs, was adopted for tethering QDs onto mesoporous TiO2 film. With the combination of high loading of the QD sensitizer and intrinsic superior optoelectronic properties (wide absorption range, high conduction band edge, high chemical stability, etc., relative to their constituents CdSe and CdTe) of the adopted CdSe0.45Te0.55 QD sensitizer, the resulting CdSexTe1-x alloyed QD-based solar cells exhibit a record conversion efficiency of 6.36% (Jsc = 19.35 mA/cm(2), Voc = 0.571 V, FF = 0.575) under full 1 sun illumination, which is remarkably better than that of the reference CdSe and CdTe QD based ones. Furthermore, the solar cells with Cu2S counter electrodes based on eletrodeposition of Cu on conductive glass show long-term (more than 500 h) stability.

Effects of pH and temperature on the survival of coliphages MS2 and Qβ

The RNA F-specific coliphages, MS2 and Qβ, have been used as virus indicators in water and wastewater studies. It is therefore useful to have a good understanding concerning the effects of environmental factors on their survival in order to choose an appropriate candidate for assessing microbial safety in relation to water quality management. The effects of pH and temperature on the survival of these two coliphages were investigated. MS2 survived better in acidic conditions than in an alkaline environment. In contrast, Qβ had a better survival rate in alkaline conditions than in an acidic environment. The inactivation rates of both coliphages were lowest within the pH range 6–8 and the temperature range 5–35°C. The inactivation rates of both coliphages increased when the pH was decreased to below 6 or increased to above 8. The inactivation rates of both coliphages increased with increasing temperature. Qβ behaved peculiarly in extreme pH buffers, i.e. it was inactivated very rapidly initially when subjected to an extreme pH environment, although the inactivation rate subsequently decreased. In general, MS2 was a better indicator than Qβ. However, within the pH range 6–9 and at temperatures not above 25°C, either MS2 or Qβ could be used as a viral indicator.

Use of Semiconductor Quantum Dots for Photostable Immunofluorescence Labeling of Cryptosporidium parvum

ABSTRACT Cryptosporidium parvum is a waterborne pathogen that poses potential risk to drinking water consumers. The detection of Cryptosporidium oocysts, its transmissive stage, is used in the latest U.S. Environmental Protection Agency method 1622, which utilizes organic fluorophores such as fluorescein isothiocyanate (FITC) to label the oocysts by conjugation with anti-Cryptosporidium sp. monoclonal antibody (MAb). However, FITC exhibits low resistance to photodegradation. This property will inevitably limit the detection accuracy after a short period of continuous illumination. In view of this, the use of inorganic fluorophores, such as quantum dot (QD), which has a high photobleaching threshold, in place of the organic fluorophores could potentially enhance oocyst detection. In this study, QD605-streptavidin together with biotinylated MAb was used for C. parvum oocyst detection. The C. parvum oocyst detection sensitivity increased when the QD605-streptavidin concentration was increased from 5 to 15 nM and eventually leveled off at a saturation concentration of 20 nM and above. The minimum QD605-streptavidin saturation concentration for detecting up to 4,495 ± 501 oocysts (mean ± standard deviation) was determined to be 20 nM. The difference in the enumeration between 20 nM QD605-streptavidin with biotinylated MAb and FITC-MAb was insignificant (P > 0.126) when various C. parvum oocyst concentrations were used. The QD605 was highly photostable while the FITC intensity decreased to 19.5% ± 5.6% of its initial intensity after 5 min of continuous illumination. The QD605-based technique was also shown to be sensitive for oocyst detection in reservoir water. This observation showed that the QD method developed in this study was able to provide a sensitive technique for detecting C. parvum oocysts with the advantage of having a high photobleaching threshold.

Effect of particles on the recovery of Cryptosporidium oocysts from source water samples of various turbidities

ABSTRACT Cryptosporidium parvum can be found in both source and drinking water and has been reported to cause serious waterborne outbreaks which threaten public health safety. The U.S. Environmental Protection Agency has developed method 1622 for detection of Cryptosporidium oocysts present in water. Method 1622 involves four key processing steps: filtration, immunomagnetic separation (IMS), fluorescent-antibody (FA) staining, and microscopic evaluation. The individual performance of each of these four steps was evaluated in this study. We found that the levels of recovery of C. parvum oocysts at the IMS-FA and FA staining stages were high, averaging more than 95%. In contrast, the level of recovery declined significantly, to 14.4%, when the filtration step was incorporated with tap water as a spiking medium. This observation suggested that a significant fraction of C. parvum oocysts was lost during the filtration step. When C. parvum oocysts were spiked into reclaimed water, tap water, microfiltration filtrate, and reservoir water, the highest mean level of recovery of (85.0% ± 5.2% [mean ± standard deviation]) was obtained for the relatively turbid reservoir water. Further studies indicated that it was the suspended particles present in the reservoir water that contributed to the enhanced C. parvum oocyst recovery. The levels of C. parvum oocyst recovery from spiked reservoir water with different turbidities indicated that particle size and concentration could affect oocyst recovery. Similar observations were also made when silica particles of different sizes and masses were added to seeded tap water. The optimal particle size was determined to be in the range from 5 to 40 μm, and the corresponding optimal concentration of suspended particles was 1.42 g for 10 liters of tap water.

Investigation into biofilms in a local drinking water distribution system

Biofilm growth within a water distribution system could lead to operational problems such as pipe corrosion, water quality deterioration and other undesirable impacts in water distribution systems. With the high ambient temperatures experienced in Singapore, the operating environment in water distribution systems is expected to be more conducive to biofilm development. We have recently conducted a survey on biofilms potentially present in a local water distribution system. The survey results indicated that residual chlorine (+− standard deviation) decreased from 1.49 +− 0.61 mg/l (water plant outlets) to 0.82 +− 0.21 mg/l (block pipes) or 0.18 +− 0.06 mg/l (unit pipes), respectively. Consumed chlorine, instead of residual chlorine, was found to be correlated with biofilm bacterial population. Assimilable organic carbon (AOC) level was 160 +− 66 μg acetate C/l, and AOC : PO4-P : NO3-N was about 8 : 13 : 1. Carbon source seemed to be the limiting nutrient for bacterial growth. The concentration of iron increased from <0.04 mg/l (water plant outlets) to 0.22 +− 0.10 mg/l (all sites). All samples showed negative results in a coliform test. The average heterotrophic plate count (HPC) for the suspended bacteria was 20 colony-forming units (c.f.u.)/ml (2 days, 35 ◦C) or 290 c.f.u./ml (8 days, 35 ◦C). The average HPC for the biofilm bacteria was 6500 c.f.u./cm (2 days, 35 ◦C) or 29 000 c.f.u./cm (8 days, 35 ◦C). High HPC values in samples B2a, B2b and B3a (representing biofilm samples at site 2 from block/unit pipes and biofilm samples at site 3 from block pipes, respectively) illustrated that the relevant sample sites had a higher probaboility of biofilm growth. * Corresponding author: Dr J. Y. Hu Center for Water Research Department of Civil Engineering Faculty of Engineering National University of Singapore 10 Kent Ridge Crescent Singapore 119260 T 65 6874 4540 F 65 6779 1635 E cvehujy@nus.edu.sg 1 Center for Water Research, Department of Civil Engineering, Faculty of Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260 2 Water Department, Public Utility Board, 111 Somerset Road, #15-01, Singapore 238164

Kinetics of β-mannanase fermentation by Bacillus licheniformis

Bacterial growth, konjac powder utilization and β-mannanase production by Bacillus licheniformis NK-27 in batch fermentation were used to develop a model of the process. The optimal set of parameters was estimated by fitting the model to experimental data. The results predicted by the model were in good agreement with the experimental data.

Strong optical limiting capability of a triosmium cluster bonded indium porphyrin complex [(TPP)InOs3(μ-H)2(CO)9(μ-η2-C5H4N)]

The metal-metal bonded indium porphyrin-osmium cluster complex [(TPP)InOs3(mu-H)2(CO)9(mu-eta2-C5H4N)] was first synthesized and characterized using the indium porphyrin hydride as the precursor. The complex has very good optical limiting performance with determined optical limiting threshold of 0.4 J cm(-2).

Synthesis and characterization of [Ga(TPP)H] (TPP=tetraphenylporphyrinato)

Abstract The synthesis, spectroscopic and structural characterization of the stable gallium hydride compound [Ga(TPP)H] (TPP=5,10,15,20-tetraphenylporphyrinato) have been reported. The hydride compound was synthesized in high yield (85%) by reducing [Ga(TPP)Cl] with sodium borohydride in N , N -dimethylformamide. The title compound was fully characterized by spectroscopic methods (IR, UV–Vis, and 1 H NMR spectroscopy) and its molecular structure was established by X-ray crystallography. The Ga–H IR stretch occurs at 1864 cm −1 , and the hydride 1 H NMR resonance locates at −6.47 ppm. The gallium–hydrogen distance is 1.48(4) A, whereas the gallium atom lies 0.46(1) A from the perfect porphyrin plane.

Tetra­aqua­bis­[5-(4-pyridyl N-oxide)­tetrazolato-κN2]­cadmium: the intermediate in the synthesis of a tetrazole from a nitrile and an azide

The intermediate [Cd(4-PTZ)(2)(H(2)O)(4)] [4-PTZ is 5-(4-pyridyl N-oxide)tetrazolate, C(6)H(4)N(5)O], (I), in the synthesis of 4-HPTZ, (II), from the cycloaddition reaction of 4-cyanopyridine N-oxide with NaN(3) in water using CdCl(2) as catalyst, was structurally characterized. The unique Cd atom lies on a twofold axis and the coordination geometry of the Cd atom is that of a slightly distorted octahedron, involving four water molecules and two tetrazolate ligands. The catalytic role of the Cd(2+) ion in the tetrazole generation reaction stems from the formation of (I). In acidic solution, (I) can be disassociated and the free ligand, (II), can be released.