Degradation of Dyes Using Zinc Oxide as the Photocatalyst

In this study, ZnO was synthesized via precipitation method. The resulting ZnO catalyst was characterised by X-ray Diffraction (XRD), Fourier Transform Infrared (FT-IR), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Particle Size Analysis (PSA) and surface area measurement (BET method). XRD analysis showed that hydrozincite (Zn5(CO3)2(OH)6) was formed during precipitation process and the decomposition of hydrozincite was completed at temperature ~ 400 °C after 2 hours calcination in air. The ZnO produced was spherical in shape (morphology), has a surface area of 25.8 m2g-1and particle size of 255 ± 2 nm with hexagonal crystal structure. The ZnO produced was tested for photodegradation of Methyl Orange (MO), Methylene Blue (MB), and Reactive Orange 16 (RO 16) under the illumination of ultraviolet (UV, λmax = 365 nm) light. Various parameters affecting the degradation performance such as catalyst loading, initial dye concentrations, initial pH, light intensity, different light sources and addition of oxidants was examined. The removal percentage of dyes increased with increasing mass of ZnO up to an optimum mass but decreased with increasing initial concentrations of the dye. Enhanced colour removal for MO, MB and RO 16 was observed when the UV lamp used was changed from 6 to 100 watts. In addition, the highest removal was achieved at pH 11 and addition of H2O2 and K2S2O8 led to an enhancement in the removal of all the three dyes. The photocatalytic degradation of mixed dyes solution (consists of a mixture of MO, MB and RO 16) was conducted and 64.90 % removal was observed. The photodegradation of dyes followed first-order kinetics

Synthesis and characterization of zinc oxide/maghemite nanocomposite: influence of heat treatment on photocatalytic degradation of 2,4-dichlorophenoxyacetic acid

In the current study, ultraviolet-active zinc oxide/maghemite (ZnO/γ-Fe2O3) nanocomposite catalysts were prepared and applied to the photodecomposition of 2,4-dichlorophenoxyacetic acid (2,4-D). 2,4-D is a herbicide that is widely used in agriculture and landscape turf management. The ZnO/γ-Fe2O3 nanocomposite catalyst was prepared using a simple and efficient precipitation–thermal decomposition method. Comprehensive experimental studies and characterizations such as X-ray diffraction (XRD), TEM, Brunauer–Emmett–Teller (BET) and UV–vis diffuse reflectance spectrum (UV-DRS) analyses were conducted to optimize the photoactivity of the nanoparticles. Interestingly, the synthesized ZnO/γ-Fe2O3 nanocomposite catalyst exhibited a hexagonal phase with wurtzite structure, and their active surface area decreased with increasing calcination temperature. Based on the TEM micrographs, the appearance of the ZnO/γ-Fe2O3 nanocomposite catalyst is nearly spherically shaped with a mean particle size in the range of 13–35 nm. The nano-ZnO/γ-Fe2O3 that underwent heat treatment at 450 °C exhibited better photodecomposition of 2,4-D, which was primarily due to the highest specific surface area and the smallest particle size among the synthesized samples

Experimental and numerical studies of acoustical and ventilation performances of glass louver window

The noise attenuation and ventilation performances of the glass louver window were investigated using experimental and numerical methods in order to improve the understanding of this common feature in noise mitigation issue. Sound pressure levels (SPLs) data were measured for frequencies ranging from 100 Hz to 6000 Hz for a room fitted with a louver window. It was found that the louver window was able to attenuate 1.4 %, 5.5 % and 12.0 % of the noise when the panels were partially and fully closed at 30°, 60° and 90°, respectively. For frequencies below 3000 Hz, the best attenuation occurred around 1700 Hz to 2000 Hz for all panel angles. The insertion loss (IL) is similar for frequencies ranging from 3000 Hz to 6000 Hz when the louver window was fully closed at 90°. The velocity magnitude of the air passed through the louver panels increased with increased panel angle. The reduction of the mass flow rate for air passed through the louver window when the panels were partially closed at 30° and 60° are 7.7 % and 46.2 %, respectively

Experimental and numerical studies on the design of a sonic crystal window

Four sets of numerical models were created to study the effects of shapes, staggering patterns, Helmholtz resonators and array configurations on the acoustical performance of sonic crystals (SCs) in order to design an efficient SC window to mitigate the traffic noise level at a room in a student hostel of NUS. Rectangular SCs consistently obtained highest transmission loss for frequencies ranging from 300 Hz to 3000 Hz compared to diamond and semi-circle SCs. Fully staggered pattern performed better than non-staggered and 50 % staggered patterns for frequencies below 1700 Hz. Helmholtz resonators were useful for enhancing low frequency noise mitigation. The prototype of the final designed SC window was fabricated and tested in order to validate the simulation result. Generally, numerical and experimental results were in similar trends. Maximum transmission loss of the SC window was found to be occurred at 900 Hz which was about 18 dB

Mechanism and Kinetics Study for Photocatalytic Oxidation Degradation: A Case Study for Phenoxyacetic Acid Organic Pollutant

Photocatalysis is a rapidly expanding technology for wastewater treatment, including a wide range of organic pollutants. Thus, understanding the kinetics and mechanism of the photocatalytic oxidation (PCO) for degradation of phenoxyacetic acid (PAA) is an indispensable component of risk assessment. In this study, we demonstrated that the central composite design (CCD) coupled with response surface methodology (RSM) was successfully employed to probe the kinetics and mechanism of PCO degradation for PAA using an efficient zinc oxide (ZnO) photocatalyst. In our current case study, four independent factors such as ZnO dosage, initial concentration of PAA, solution pH, and reaction time on the PCO degradation for PAA were examined in detail. Based on our results obtained from RSM analyses, an efficient pathway leading to the high degradation rate (>90%) was applying 0.4 g/L of ZnO dosage with 16 mg/L of concentration of PAA at pH 6.73 for 40 minutes. The experimental results were fitted well with the derived response model with R2 = 0.9922. This study offers a cost-effective way for probing our global environmental water pollution issue

Photodegradation of chlorophenoxyacetic acids by ZnO/y-Fe2O3 nanocatalysts : a comparative study

ZnO/γ-Fe2O3 nanocomposite was synthesized via simple precipitation. The synthesized nanocatalysts underwent heat treatment at 450oC for an hour. The characteristics of the nanocomposite were investigated by XRD, TEM, and BET surface area measurement. Zeta potential analysis was used to examine the surface charge properties of the nanocatalysts. The synthesized nanocomposite has an average particle size of 11 nm and a surface area of 20 m2 g-1. The potential of ZnO/γ-Fe2O3 as a photocatalyst was evaluated by photodegrading chlorophenoxyacetic acids (PAA, 2,4-D, 2,4,5-T and 4CA). The decomposition of chlorophenoxyacetic acids by ZnO/γ-Fe2O3 followed 4CA > 2,4,5-T ≈ 2,4-D > PAA. The result indicates the applicability of ZnO/γ-Fe2O3 nanocomposite as a photocatalyst in removing organic pollutants in wastewater

Study Protocol for a Randomized Controlled Trial of Choral Singing Intervention to Prevent Cognitive Decline in At-Risk Older Adults Living in the Community

Introduction: This study is a parallel-arm randomized controlled trial evaluating choral singing’s efficacy and underlying mechanisms in preventing cognitive decline in at-risk older participants.Methods: Three-hundred and sixty community-dwelling, non-demented older participants are recruited for a 2-year intervention. Inclusion criteria are self-reported cognitive complaints, early cognitive impairment based on neuropsychological test scores or multiple risk factors of dementia. Participants are randomized to either weekly choral singing sessions or general health education. The primary outcome is cognitive performance, measured by a composite cognitive test score (CCTS). Secondary outcomes include depression, anxiety and neuropsychiatric symptoms; perceived stress; sleep quality and severity of dementia symptoms. Underlying mechanisms are examined using blood- and urine-based biomarkers and neuroimaging.Results: Screening began in July 2016. The first group of participants (n = 93) have been recruited. Intervention and control treatments are ongoing and will end in December 2019.Discussion: An evidence-based singing intervention for dementia prevention holds potential for healthcare savings and societal welfare.Trial Registration: NCT02919748, IRB Approval Number: NUS 2508

Synthesis of zinc oxide and zinc oxide / iron oxide catalysts and their photocatalytic activity in degrading herbicides

In this study, ZnO and ZnO/Fe2O3 catalysts were synthesized via precipitation method. The effect of Fe addition, calcination temperature and duration on the characteristics of the resulting catalyst were investigated by performing Thermogravimetric Analysis (TGA), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), surface area measurement (BET method), Diffuse Reflectance Spectroscopy (DRS) and Inductively-coupled plasma atomic emission spectroscopy (ICP-AES). XRD analysis showed that the addition of Fe resulted in the formation of hexagonal structure of ZnO and cubic structure of γ-Fe2O3 by calcining the sample at 450 °C for one hour. The catalysts produced were spherical in shape. The increase in the calcination temperature and duration does not change the morphology and band gap energy of the resulting catalysts. However, the surface area of the catalyst decreased and hence leads to an increment in its particle size as the calcination temperature and duration increased. ICP-AES results revealed that the iron content in ZnO/γ-Fe2O3 is in good agreement with the calculated values. The efficiency of the synthesized ZnO/γ-Fe2O3 as photocatalysts was evaluated by photodegrading herbicides 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), phenoxyacetic acid (PAA) and 4-chlorophenoxyacetic acid (4-CPA) under the irradiation of ultraviolet (UV, λmax = 365 nm) light. Various parameters affecting the degradation performance such as catalyst dosage, initial concentration of herbicides and initial pH were examined. The removal percentage of chlorophenoxyacetic acids increased with increasing mass of ZnO/γ-Fe2O3 up to an optimum loading (0.4 g L-1 for 2,4-D and 2,4,5-T with 66.07 and 68.16 %, respectively and 0.5 g L-1 for PAA and 4-CPA with 60.90 and 74.38 %, respectively) but decreased with increasing initial concentration (from 10 - 50 mg L-1) of the herbicides. The removal of chlorophenoxyacetic acids is highest at pH 7. The photodegradation of chlorophenoxyacetic acids followed first-order kinetic scheme. The intermediates detected by UPLC for 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), phenoxyacetic acid (PAA) and 4-chlorophenoxyacetic acid (4-CPA) are 2,4-dichlorophenol, 2,4,5-trichlorophenol, phenol and 4-chlorophenol, respectively. Experimental design methodology was applied using response surface methodology (RSM) to optimise the degradation percentage of chlorophenoxyacetic acids. The multivariate experimental design was employed to develop a quadratic model as a functional relationship between the degradation percentage of chlorophenoxyacetic acids and catalyst dosage, initial concentration of herbicides and initial pH. The degradation percentage of 2,4-D approached 99.26 % under optimised conditions of 0.50 g ZnO/γ-Fe2O3, 10.00 mg L-1 2,4-D and at a pH of 7.49 whereas 2,4,5-T achieved 83.58 % under optimised conditions of 0.41 g ZnO/γ-Fe2O3, 10.60 mg L-1 2,4,5-T and at pH 7.11. The maximum removal percentage of PAA approached 76.43 % under optimised conditions of 0.51 g ZnO/γ-Fe2O3, 10.20 mg L-1 PAA and at pH 6.63. Further, 4-CPA showed maximum removal of 91.87 % under optimised conditions of 0.49 g ZnO/γ-Fe2O3, 10.10 mg L-1 4-CPA and at pH 7.25. In addition, the experimental data showed good agreement with the predicted results obtained from statistical analysis which indicates response surface methodology is applicable in optimising the degradation percentage of chlorophenoxyacetic acids

Synthesis and photocatalysis of ZnO/γ-Fe2O3 nanocomposite in degrading herbicide 2,4-dichlorophenoxyacetic acid

ZnO/γ-Fe2O3 catalysts were fabricated via a simple precipitation route using zinc acetate and iron acetate as the precursors and ammonia as the precipitant. The resulted nanocatalysts were subjected to heat treatment at 450°C for 2 h. The characteristics of the nanocomposite were investigated by various characterization techniques. The synthesized nanocomposite has an average particle size of 13 nm and a surface area of 17 m2/g. The photocatalytic activity of ZnO/γ-Fe2O3 nanocomposite was evaluated by photodegrading 2,4-dichlorophenoxyacetic acid (2,4-D) under UV irradiation. The results showed that ZnO/γ-Fe2O3 nanocomposite exhibited enhanced photoactivity compared to pure ZnO with almost 20% increment within 4 h of reaction time. The result indicated the applicability of ZnO/γ-Fe2O3 nanocomposite to be used as photocatalyst in removing organic pollutants in wastewater

Simple Response Surface Methodology: Investigation on Advance Photocatalytic Oxidation of 4-Chlorophenoxyacetic Acid Using UV-Active ZnO Photocatalyst

The performance of advance photocatalytic degradation of 4-chlorophenoxyacetic acid (4-CPA) strongly depends on photocatalyst dosage, initial concentration and initial pH. In the present study, a simple response surface methodology (RSM) was applied to investigate the interaction between these three independent factors. Thus, the photocatalytic degradation of 4-CPA in aqueous medium assisted by ultraviolet-active ZnO photocatalyst was systematically investigated. This study aims to determine the optimum processing parameters to maximize 4-CPA degradation. Based on the results obtained, it was found that a maximum of 91% of 4-CPA was successfully degraded under optimal conditions (0.02 g ZnO dosage, 20.00 mg/L of 4-CPA and pH 7.71). All the experimental data showed good agreement with the predicted results obtained from statistical analysis