Zih-Yu Shih

Synthesis and analytical applications of photoluminescent carbon nanodots

We have developed a simple approach for the preparation of carbon nanodots (C-dots) from coffee grounds. As-prepared C-dots have an average diameter of 5 ± 2 nm, of which quantum yield is 3.8%. We have validated the practicality of C-dots for cell imaging and surface-assisted laser desorption/ionization-mass spectrometry (SALDI-MS) of angiotensin I and insulin.

Porous palladium copper nanoparticles for the electrocatalytic oxidation of methanol in direct methanol fuel cells

A facile method has been demonstrated for the preparation of PdCu nanoparticles (NPs) with various morphologies from Pd2+ and Cu2+ reduced by ascorbate in the presence of dodecyltrimethylammonium chloride (DTAC) at 95 °C. We have found that DTAC is important to assist the growth of PdCu with high-energy surfaces through the etching and capping of certain surfaces of Pd and PdCu seeds. By varying the Pd2+/Cu2+ molar ratio, different morphologies of PdCu NPs have been prepared. Cubic PdCu NPs have a dominant Pd3Cu composition when prepared at a high Pd2+/Cu2+ molar ratio (20/1), while porous PdCu NPs have a dominant PdCu3 composition when prepared at a low Pd2+/Cu2+ molar ratio (1/10). The copper content not only controls the morphology, but also affects the catalytic activity toward the methanol oxidation reaction (MOR) in alkaline media. Upon increasing the copper content, the catalytic activity toward the MOR increases, mainly due to the advantages of the electroactive surface area, more direct cathodic oxide reduction (lower onset potential for the formation of Pd–OH), and synergistic effects. Porous PdCu NP-modified electrodes provide a higher catalytic activity (363 A g−1) toward the MOR at a more negative onset potential (−0.62 V vs. Ag/AgCl) on the porous PdCu electrodes than commercial Pd/C-modified ones do (180 A g−1) at −0.52 V. To the best of our knowledge, this is the first example using porous PdCu NP-modified electrodes as anodes under alkaline conditions in direct methanol fuel cells (DMFCs). With the advantages of high electrochemical activity, stability, and cost effectiveness, the porous PdCu NPs have great potential as anode catalysts for DMFCs.

Gold/Platinum nanosponges for electrocatalytic oxidation of methanol

We have prepared Aun/Pt nanosponges that are highly electroactive for the oxidation of MeOH, from Pt nanosponges and AuCl4− ions through galvanic reactions at ambient temperature and pressure. At AuCl4− concentrations of 0, 0.1, 0.3, 0.5, 1.0, and 2.0 mM and a constant content of Pt nanosponges, we obtained Aun/Pt nanosponges having values of n of 0, 0.1, 0.2, 0.3, 0.5, and 0.8, respectively. The average size of the Au nanoparticles deposited on the surfaces of the Pt nanosponges increased upon increasing the AuCl4− concentration (at a constant Pt nanosponge content). We used UV–Vis absorption spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, inductively coupled plasma mass spectrometry, and transmission electron microscopy to characterize the as-prepared Aun/Pt nanosponges. These techniques revealed that the Aun/Pt nanosponges comprised spherical Au nanoparticles (diameter: 6–17 nm) and assemblies of Pt nanorods (width: 3 nm; length: 17 nm). Cyclic voltammetry indicated that the electrocatalytic oxidation of MeOH was dependent on the content of Au nanoparticles on the surfaces of the Pt nanosponges. The Au0.5/Pt nanosponges provided the highest electrocatalytic efficiency—indeed, it was superior to those of commercial Pt nanoparticles and other previously reported Pt nanosponges. The Au0.5/Pt nanosponges exhibited a mass activity of 231 mA mg−1 and a forward-to-reverse anodic peak current ratio of 2.2—i.e., excellent electrocatalytic activity for the oxidation of MeOH.

Palladium copper nanosponges for electrocatalytic reduction of oxygen and glucose detection

A facile and one-pot wet chemical approach has been applied for the preparation of palladium copper (PdCu) nanosponges (NSs) through the reduction of Pd2+ and Cu2+ ions with L-ascorbic acid in the presence of sodium dodecyl sulfate (SDS) at 95 °C. The PdCu NSs prepared in the presence of 12.5, 25, and 37.5 mM SDS have sizes of 46.0 ± 4.3, 36.8 ± 4.5, and 37.2 ± 2.6 nm, respectively. Relative to a Pd NP electrode (0.33 mA cm−2), Cu NP electrode (0.31 mA cm−2), commercial Pd/C electrode (0.34 mA cm−2) and Pt/C electrode (0.66 mA cm−2), PdCu NS-modified electrodes provide a high current density for the oxygen reduction reaction (1.93 mA cm−2) under alkaline conditions. In addition, the PdCu NS-modified electrodes provide high catalytic activity for glucose oxidation at −0.01 V vs. Ag/AgCl and are stable even after sweeping for 43 200 s in 0.1 M NaOH containing 0.1 M glucose. The higher catalytic activity of the PdCu NSs is mainly due to their greater electroactive surface area (EASA) and the synergistic effect caused by the intimate contact between Pd and Cu. The PdCu NS-modified electrodes exhibit high sensitivity (1560 μA mM−1 cm−2), good selectivity, and fast response to glucose over a linear range of 0–30 μM (R2 = 0.997), with a limit of detection (LOD) of 4.1 μM. With the advantages of good stability, excellent electrocatalytic activity, and cost effectiveness, PdCu NSs hold great potential for use in fuel cells using methanol or ethanol as fuel and for the fabrication of electrochemical sensors for the detection of glucose in blood samples.

Synthesis of Cu9S8/carbon nanotube nanocomposites with high electrocatalytic activity for the oxygen reduction reaction

We have synthesized Cu9S8/carbon nanotube (CNT) nanocomposites (NCs) with high electrocatalytic activity for direct methanol fuel cells (DMFCs). Cu9S8/CNT NCs are prepared from Cu(NO3)2, CNTs, and thioacetamide in the presence of poly(vinylpyrrolidone) under alkaline conditions. There are Cu9S8 nanoparticles (diameter: 50 ± 6 nm) and aggregates on the surfaces of CNTs. The as-prepared Cu9S8/CNT NC modified electrodes provide a four-electron pathway for the oxygen reduction reaction (ORR) in alkaline media. Three representative Cu9S8/CNT electrodes (mass loading: 1.63 mg cm−2) provide a mean limiting current density of 3.43 ± 0.03 mA cm−2 (each with three measurements) at a constant scan rate of 1 mV s−1 and a rotation rate of 3600 rpm. At a constant potential of −0.5 V, the kinetic rate constant for the Cu9S8/CNT is 2.82 × 10−2 cm s−1, revealing higher activity of the Cu9S8/CNT electrodes in the ORR. The Cu9S8/CNT relative to Pt/C electrodes is more tolerant against methanol and carbon monoxide poisoning. These low-cost, stable, and highly active Cu9S8/CNT electrodes have great potential for use in DMFCs.

Preparation of Photocatalytic Au–Ag2Te Nanomaterials

A facile approach has been developed for the preparation of various morphologies of Au-Ag(2)Te nanomaterials (NMs) that exhibit strong photocatalytic activity. Te NMs (nanowires, nanopencils, and nanorice) were prepared from TeO(2) in the presence of various concentrations (16, 8, and 4 M) of a reducing agent (N(2)H(4)) at different temperatures (25 and 60 °C). These three Te NMs were then used to prepare Au-Ag(2)Te NMs by spontaneous redox reactions with Au(3+) and Ag(+) ions sequentially. The Au-Ag(2)Te nanopencils exhibit the highest activity toward degradation of methylene blue and formation of active hydroxyl radicals on solar irradiation, mainly because they absorb light in the visible region most strongly. All three differently shaped Au-Ag(2)Te NMs (10 μg mL(-1)) provide a death rate of Escherichia coli greater than 80% within 60 min, which is higher than that of 51% for commercial TiO(2) nanoparticles (100 μg mL(-1)). Under light irradiation, the Au NPs in Au-Ag(2)Te NMs enhance the overall photo-oxidation ability of Ag(2)Te NMs through faster charge separation because of good contact between Ag(2)Te and Au segments. With high antibacterial activity and low toxicity toward normal cells, the Au-Ag(2)Te NMs hold great potential for use as efficient antibacterial agents.