Photoelectrochemical Properties of WO3 Thin Films Prepared by Electrodeposition

AbstractTungsten trioxide (WO3) thin films were synthesised by electrodeposition using peroxotungtic acid as the precursor electrolyte solution for use as photoanodes in a photoelectrochemical cell for solar hydrogen applications. The films were coated at deposition potentials varying from 0.30 to 0.90V versus Ag/AgCl in order to study the effect of the potential on the mineralogical, morphological, optical, and photoelectrochemical properties of the nanoparticulate films. The films were composed of monoclinic WO3, the degree of crystallinity and preferred orientation of the orthogonal planes of which increased with deposition potential and associated film thickness. In contract, increasing the deposition potential had a minimal impact on the particle sizes, which were in the range ∼80-90nm. While films deposited at the potential range of 0.30 to 0.60V showed controlled nanostructures with thicknesses in the range 168-431nm, increasing the deposition potential from 0.70 to 0.90V resulted in rapid increase in film, which led to cracking from drying stress. Linear voltammetry data suggested that the optimal potential for the deposition of stable films was in the range 0.37 to 0.60V. However, the data for the film deposited at a potential of 0.30V indicated a film of high quality. Further, the data for the film deposited at a potential of 0.60V indicated a film of a low quality and so this voltage represents a transition point for stable-unstable film growth and unstressed-stressed nanostructure from drying. The trends in the optical transmission properties showed that the photocatalytic activity of the films could be expected to decrease with increasing potential, thickness, and crystallinity. That is, the band gap and projected absorption edge exhibited a red shift. This was attributed to the relative effects of the surface and volume band gaps, in which the latter would increase relative to the former with increasing thickness. The photocurrent densities reflected the effects of increasing solid volume and decreasing band gap with increasing film thickness. The exception was the reduced performance of the film deposited at the potential of 0.60 V. This outcome was attributed to the competition between the photogeneration and recombination of electron-hole pairs, where the potential of 0.60V represents the transition point described above

Comparison of Simultaneous Nitrification and Denitrification for Three Different Reactors

Discharge of high NH 4 -N containing wastewater into water bodies has become a critical and serious issue due to its negative impact on water and environmental quality. In this research, the performance of three different reactors was assessed and compared with regard to the removal of NH 4 -N from wastewater. The highest nitrogen removal efficiency of 98.3% was found when the entrapped sludge reactor (ESR), in which the sludge was entrapped in polyethylene glycol polymer, was used. Under intermittent aeration, nitrification and denitrification occurred simultaneously in the aerobic and anaerobic periods. Moreover, internal carbon was consumed efficiently for denitrification. On the other hand, internal carbon consumption was not found to occur in the suspended sludge reactor (SSR) and the mixed sludge reactor (MSR) and this resulted in nitrogen removal efficiencies of SSR and MSR being 64.7 and 45.1%, respectively. Nitrification and denitrification were the main nitrogen removal processes in the aerobic and anaerobic periods, respectively. However, due to the absence of sufficient organic carbon, denitrification was uncompleted resulting in high NO 3 -N contents in the effluent

Iron Doped Titania Thin Films Prepared by Spin Coating

Thin films of titania (TiO2) doped with 1–5 wt-%Fe were spin coated on glass slides and then annealed at 500°C for 2 h. Results revealed that all of the films were ∼500 nm in thickness and consisted of anatase. Increasing the dopant levels revealed the following trends: the major (101) anatase peak shifted to larger lattice spacing [the peaks were normalised using the principal (210) chromium coating peak as an in situ standard]; the microstructures showed increasing shrinkage cracking, a phenomenon that has not been reported previously; the optical transmittance generally decreased; the amplitude of the transmittance curves generally decreased; and the optical indirect band gap decreased from 3.40 to 3.18 eV, possibly due to silicon contamination, residual thermal stress and/or the formation of midgap states from Fe-doping

Comparison of Simultaneous Nitrification and Denitrification for Three Different Reactors

Discharge of high NH4-N containing wastewater into water bodies has become a critical and serious issue due to its negative impact on water and environmental quality. In this research, the performance of three different reactors was assessed and compared with regard to the removal of NH4-N from wastewater. The highest nitrogen removal efficiency of 98.3% was found when the entrapped sludge reactor (ESR), in which the sludge was entrapped in polyethylene glycol polymer, was used. Under intermittent aeration, nitrification and denitrification occurred simultaneously in the aerobic and anaerobic periods. Moreover, internal carbon was consumed efficiently for denitrification. On the other hand, internal carbon consumption was not found to occur in the suspended sludge reactor (SSR) and the mixed sludge reactor (MSR) and this resulted in nitrogen removal efficiencies of SSR and MSR being 64.7 and 45.1%, respectively. Nitrification and denitrification were the main nitrogen removal processes in the aerobic and anaerobic periods, respectively. However, due to the absence of sufficient organic carbon, denitrification was uncompleted resulting in high NO3-N contents in the effluent

Thin Solid Films

Optimisation of particle sizes of WO3 films is important for photoelectrochemical applications. However, most of the developed size-controlled synthesis techniques involve complicated instruments or vacuum systems. The present work presents an alternative method using carboxylic acid-assisted electrodeposition where WO3 thin films were deposited from peroxotungstic acid (PTA) solution containing different carboxylic acids (formic, oxalic, citric). The effects of carboxylic acids on the electrodeposition and the resultant morphological, mineralogical, optical, and photoelectrochemical properties of the WO3 films were investigated. The analysis showed that the films consisted of equiaxed nanoparticulate monoclinic WO3. The deposition thicknesses and the average grain (individual particle and agglomerate) sizes of the films were dependent on the amount of hydronium ions and the molecular weight and associated sizes of the conjugate bases released upon the dissociation of carboxylic acids in the PTA solutions, which result in hydrogen bond formation and molecular dispersion. The photocurrent densities of the films deposited with carboxylic acids were greater than that of the film deposited from pure PTA. These differences were attributed to improvements in (1) grain size, which controls photogenerated electron-hole transport, and (2) effective grain boundary area, which controls the numbers of active reaction sites and electron-hole recombination sites

Heterotrophic nitrification and aerobic denitrification using pure-culture bacteria for wastewater treatment

Due to the high water demand and unsustainable water resource, wastewater reclamation and wastewater treatment prior to discharge have become current important issues. Various treatment technologies, such as biological processes, have been improved as alternatives. In this study, the biological nitrogen removal system using pure-culture Bacillus licheniformis was developed and used as an internal treatment unit in an aquarium to improve the effluent quality for water reuse. The efficiencies for NH4-N and total nitrogen (TN) removal and the quality of treated water verified the occurrence of heterotrophic nitrification and aerobic denitrification; the nitrification rate was 0.84 mg/L-h and the denitrification rate was 0.62 mg/L-h. The maximal NH4-N and TN removal efficiencies were approximately 73% at the influent NH4-N of 30 mg/L. However, the other competitive heterotroph of Pseudomonas sp. was observed, which resulted in dramatically decreasing efficiencies and an enlarged ratio of carbon consumption and nitrogen removal. Although the overall performance of the B. licheniformis system was lower than the system using mixed-culture nitrifying and heterotrophic denitrifying microorganisms, the advantages of the B. licheniformis system were ease of operation and the fact that it is a land-limited treatment system. The research is ongoing to enhance performance and maintain excellent efficiency in a long-term operation

Electrocoagulation for spent coolant from machinery industry

Spent coolant is considered as one of the most polluting industrial wastes and causes environmental problems. It mostly contains high non-biodegradable organic carbon and oil contents; the biodegradability index was very low at 0.04, which is difficult to be effectively treated by common treatment systems. Electrocoagulation (EC) was proposed for a pre-treatment of coolant. The laboratory-scale of EC reactor was developed with Al electrodes and 10 mm of interelectrodes. The efficiency of the EC reactor on chemical oxygen demand (COD) removal was investigated at various current densities and electrolysis times. The highest current density of 50 mA/cm2 induced a short electrolysis time of 10 min to reach the steady state of approximately 65% COD removal. When lower current densities of 20–40 mA/cm2 were supplied to the EC reactor, COD removal efficiency of 65% can be achieved at longer electrolysis times. According to the specific energy consumption and sludge production, the optimal condition for spent coolant treatment was the current density of 20 mA/cm2 and electrolysis time of 30 min in which a COD removal of efficiency of 68% was obtained, 0.88 kWh/kg-COD of the specific energy consumption and 0.04 kg/kg-COD of the sludge production