Volume Ratio Of H2O Research Articles

In-Situ Fabrication of a Self-Aligned Selective Emitter Silicon Solar Cell Using the Gold Top Contacts To Facilitate the Synthesis of a Nanostructured Black Silicon Antireflective Layer Instead of an External Metal Nanoparticle Catalyst.

Silicon solar cells with nanopore-type black silicon (b-Si) antireflection (AR) layers and self-aligned selective emitter (SE) are reported in which the b-Si structure is prepared without the traditional addition of a nanoparticle (NP) catalyst. The contact-assisted chemical etching (CACE) method is reported here for the first time, in which the metal top contacts on silicon solar cell surfaces function as the catalysts for b-Si fabrication and the whole etching process can be done in minutes at room temperature. The CACE method is based on the metal-assisted chemical etching (MACE) solution but without or metal precursor in the Si etchant (HF:H2O2:H2O), and the Au top contacts, or catalysts, are not removed from the solar cell surface after the etching. The effects of etching time, HF and H2O2 concentration, and the HF:H2O2 ratio on the b-Si morphology, surface reflectivity, and solar cell efficiency have been investigated. Higher [HF] and [H2O2] with longer etching time cause collapse of the b-Si nanoporous structure and penetration of the p-n junctions, which are detrimental to the solar cell efficiency. The b-Si solar cell fabricated with the HF:H2O2:H2O volume ratio of 3:3:20 and a 3 min etch time shows the highest efficiency 8.99% along with a decrease of reflectivity from 36.1% to 12.6% compared to that of the nonetched Si solar cell.

Ni/TiO2: A promising low-cost photocatalytic system for solar H2 production from ethanol–water mixtures

Low-cost semiconductor photocatalysts that can efficiently harvest solar energy and generate H2 from water or biofuels will be critical to future hydrogen economies. Here, we evaluate the performance of low-cost Ni/TiO2 photocatalysts (Ni loadings 0–4wt.%) for H2 production from ethanol–water mixtures (0–100vol.% EtOH) under UV excitation. Ni(II) was deposited on P25 TiO2 by the complex precipitation method, followed by H2 reduction at 500°C for 2h to obtain Ni/TiO2 photocatalysts. TGA, TEM, XRD, Ni 2p XPS, Ni L-edge NEXAFS, Ni K-edge EXAFS, UV–Vis and photoluminescence measurements confirmed that Ni0 was the dominant nickel species on the surface of the Ni/TiO2 photocatalysts, with the Ni particle size ∼1–2nm. The photocatalytic activity of Ni/TiO2 photocatalysts was highly dependent on the Ni loading, with the optimal Ni loading being 0.5wt.%, which afforded a H2 production rate of 11.6mmolg−1h−1 (or 0.258mmolm−2h−1) at an EtOH:H2O volume ratio of 10:90 and a UV flux comparable to that in sunlight. High H2 production rates were achieved over a wide range of EtOH:H2O concentrations, with a 95:5 volume ratio affording the highest rate (24.3mmolg−1h−1). The 0.5wt.% Ni/TiO2 photocatalyst displayed superior photocatalytic activity to a 2wt.% Au/TiO2 reference photocatalyst at low ethanol concentrations (1–15vol.%), which is attributed to the high co-catalyst dispersion achieved in the Ni/TiO2 system. Results suggest that Ni/TiO2 photocatalysts are promising alternatives to M/TiO2 (M=Pd, Pt or Au) photocatalysts for solar H2 production from biofuels.

Anti-reflection layers fabricated by a one-step copper-assisted chemical etching with inverted pyramidal structures intermediate between texturing and nanopore-type black silicon

A new one-step copper-assisted chemical etching technique is reported to more economically prepare nanopore-type anti-reflective layers, which can effectively suppress reflection of Si wafer surfaces for solar cell applications. In contrast to the Au and Ag processes, phosphorous acid (rather than hydrogen peroxide) is utilized as a reducing agent to reduce Cu2+ to Cu0 nanoparticles. The Cu nanoparticles catalyse the oxidization of Si in the vicinity of the nanoparticles to SiO2, which is then etched by HF to form nanopores. The effects of the HF and H3PO3 concentrations, the HF : H2O volume ratio, and the etching time on the black silicon morphology with the corresponding Si surface reflectivity have been systematically investigated. The size and shape of the pores are controlled by [Cu2+] and the subsequent size of the NPs as controlled by [H3PO3], while the depth of the pores are limited by [HF] and the etch time. With [Cu2+] = 500 μM and [H3PO3] = 10 mM, the fabricated black silicon possesses the lowest relative effective reflectivity, 0.96%, and the shortest nanopore length (590 nm).

Hydrothermal synthesis and luminescence properties of 3D walnut-like CaMoO4:Eu3+ red phosphors

Tetragonal CaMoO4:Eu3+ red phosphors with walnut-like 3D microsphere ere synthesized via an ethylene glycol (EG)-mediated hydrothermal method in the presence of urea. The as-synthesized products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL). It was found that the volume ratio of H2O to EG, reaction time and urea concentration played critical roles in the morphology of Eu3+-doped calcium molybdate microstructures. The results showed that the Eu3+-doped CaMoO4 microwalnuts were well-crystallized and assembled by many nanosheets. The walnut-like CaMoO4:Eu3+ microspheres can display a red emission under ultraviolet (394nm) and Eu3+ concentration has great effect on the luminescence intensity in 5D0→7F2 transition.

Preparation and properties of organic-inorganic modified SiO2 thin films

Polydimethylsiloxane (PDMS), tetraethoxysilane (TEOS), ethyl alcohol (EtOH) and deionized water were main raw materials to prepare silicone-modified hybrid thin films using sol-gel method. The effect of the contents of H2O and PDMS on thin films was studied. When the volume ratio of H2O to TEOS is 0.5, the optimum quality of thin films is obtained. And the gelation time is affected slightly by H2O content. Uniform thin films are obtained when the volume ratio of PDMS to TEOS is 0.2. Yet, the sol would be inactive in 6 d. Various properties of thin films were studied, including hardness, adhesive quality, hydrophobic property, corrosion protection property, and abrasion resistance. Test results show that the pencil hardness is generally 3–6 H, and adhesive quality achieves the highest standard of 0. When the sintering temperature is below 400 °C, the contact angle is about 95° and hydrophobic films are obtained. The abrasion resistance of thin films is better than that of aluminum alloy when the sintering temperature is higher than 300 °C. And the excellent corrosion protective effect is obtained by single-layer coating when the sintering temperature is higher than 400 °C.

Facile tailoring of titanate nanostructures at low alkaline concentration by a solvothermal route

Nanostructured titanates with different morphologies such as nanoflakes, nanotubes, and nanofibers have been selectively synthesized by a simple solvothermal treatment of commercial anatase TiO2 using the mixed water–ethanol cosolvent at low alkaline concentration. The effects of solvothermal temperature, volume ratio of H2O to C2H5OH, amount of NaOH and solvents on the formation of titanate nanostructures have been systematically studied through X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). At low concentration of NaOH solution (the actual concentration of OH− in the solution is only 0.58 M), different titanate nanostructures are achieved by simply changing the volume ratio of H2O to C2H5OH at 180 °C and titanate nanotubes can be synthesized between 100 and 180 °C. A probable formation mechanism is proposed based on XRD, SEM and TEM analysis. The influence of cosolvent on the transformation from anatase TiO2 to titanate is also investigated.

Large-scale controllable synthesis of dumbbell-like BiVO4 photocatalysts with enhanced visible-light photocatalytic activity

The controllable synthesis of novel dumbbell-like BiVO4 hierarchical nanostructures has been successfully obtained via a simple hydrothermal route. The as-synthesized products were studied by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and UV–vis absorption spectroscopy. The results showed that the nucleation and growth of the nanodumbbells were governed by an oriented aggregation growth mechanism. It is noteworthy that the concentration of poly(vinyl pyrrolidone) and the volume ratio of H2O to CH3COOH were crucial to the growth of the final nanoarchitectures. Control experiments were also carried out to investigate the factors which impact on the morphology of the products. Furthermore, the as-prepared BiVO4 hierarchical nanostructures demonstrated the superior visible-light-driven photocatalytic efficiency, which is helpful for the separation and recycle considering their promising applications in harmful pollutants disposal.

A Convenient Method for Synthesis of Nano-Titania Thin Films from Aqueous TiO<sub>2</sub> Precursor Sols

Anatase TiO2 thin films were prepared on glass substrates by dip-coating method with TiCl4 as the Ti precursor hydrolysis in a mixed solvent of alcohol and water. The effects of preparation parameters such as the alcohol species, the alcohol/water (A/W) ratio, and the dosage of TiCl4 (the volume ratio of TiCl4 and mixed solution) were investigated. The best preparation condition was optimized that with the isopropanol / H2O volume ratio of 65:35, the dosage of TiCl4 at 3%. XRD, SEM, TEM and UV–Vis photospectroscopy were used to analyze the characteristics of the solution and films. The films have a high hydrophilicity after illuminating with ultraviolet light, it have a good adherence and can be used as an efficient photocatalyst.

Study on Treatment of Acetylspiramycin Pharmaceutical Wastewater by the Photo-Fenton Oxidation Process

Acetylspiramycin pharmaceutical wastewater is a kind of biorefractory organic wastewater. It is meaningful academically and actually that the Photo-Fenton method is used in the oxidation and degradation of the effluent water. After pretreatment of the wastewater with COD 6169mg/L, the oxidation reactions were proceeded which the oxidation effects were evaluated by the changes of COD and BOD5. Orthogonal experiment was applied based on the single factor experiment, the optimal process conditions were determined as follows, the volume ratio of H2O¬2: FeSO4•7H2O 1:1, the dosage of FeSO4•7H2O 7.8mmol/L, the pH value 3.0 and on the solar ray radiation respectively. Under the said conditions, the ratio of BOD5/COD went from 0.15 to 0.24 indicating that biodegradability had improved. Meanwhile COD reduced largely. The removal rate of COD calculated on this stage reached 78.9%. Added to the former pretreatment process, the total removal rate of COD was up to 88.6%. It was higher than other disposal technologies of antibiotic pharmaceutical wastewater and displayed a promising future.

CdS with Various Novel Hierarchical Nanostructures by Nanobelts/Nanowires Self-Assembly: Controllable Preparation and Their Optical Properties

Many fascinating CdS hierarchical nanostructures, including nanobelt networks, flower/sphere networks by nanobelts/wires self-assembly, and nanowires, have been successfully prepared in high yields and purities by a novel dithizone (DTZ) and tetraethylenepentamine (TEPA)-synergistically directed method. A detailed study of the effect of experimental parameters on the morphology is presented. Results and analyses demonstrated that the Cd(Ac)2/dithizone (DTZ) molar ratio and the volume ratio of H2O and TEPA have an immense function in the subtle morphology control of CdS products. A possible growth process of DTZ and TEPA-synergistic-assisted gradual crystallization and subsequent self-assembling is proposed as a plausible mechanistic interpretation for the formation of those novel nanostructures. More importantly, this is the first time to synthesize wurtzite CdS ultrathin nanobelts in solution. The photoluminescence properties of various CdS hierarchical structures are also investigated.

Tetraethylenepentamine‐Directed Controllable Synthesis of Wurtzite ZnSe Nanostructures with Tunable Morphology

A novel tetraethylenepentamine (TEPA)-directed method has been successfully developed for the controlled synthesis of ZnSe particles with distinctive morphologies, including nanobelts, nanowires, and hierarchically solid/hollow spheres. These structures, self-assembled from nanobelts and nanorods, have been synthesized by adjusting the reaction parameters, such as the solvent composition, reaction temperature, and the aging time. Results reveal that the volume ratio of H2O and TEPA plays a crucial role in the final morphology of ZnSe products. The mechanisms of phase formation and morphology control of ZnSe particles are proposed and discussed in detail. The products have been characterized by means of X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy (TEM), selected area electron diffraction, high-resolution TEM, Raman spectra and luminescence spectroscopy. The as-prepared ZnSe nanoparticles display shape- and size-dependent photoluminescent optical properties. This is the first time to report preparation of complex hollow structures of ZnSe crystals with hierarchy through a simple solution-based route. This synthetic route is designed to exploit a new H2O/TEPA/N2H4H2O system possibly for the preparation of other semiconductor nanomaterials.

Low-Temperature Synthesis of Nanometer-Sized Crystalline TiO2 Particles and Their Photoinduced Decomposition of Formic Acid

Anatase TiO2 particles with an average size of 2.7 nm in an as-grown state were obtained below 373 K from an H2O–EtOH mixed solution of TiOSO4 by a facile liquid phase method. The volume ratio of H2O to EtOH was revealed to be the key for crystallinity of the particles. The as-grown particles prepared from the H2O–EtOH solution (H2O/EtOH (mL/mL) = 150/100) showed a high photoreactivity in the TiO2 photoinduced decarboxylation of HCOOH under a deaerated condition. In contrast, under an aerated condition, the rate of the reaction increased with an increase in calcining temperature (Tc) due to the improvement of anatase crystallinity, going through a maximum at Tc = 873 K.