Effect Of Microwave Power Research Articles

Visible light photoreforming of greenhouse gases by nano Cu-Al LDH intercalated with urea-derived anions.

The accumulation of anthropogenic greenhouse gases (GHGs) in the atmosphere causes global warming. Global efforts are carried out to prevent temperature overshooting and limit the increase in the Earth's surface temperature to 1.5 °C. Carbon dioxide and methane are the largest contributors to global warming. We have synthesized copper-aluminium layered double hydroxide (Cu-Al LDH) catalysts by urea hydrolysis under microwave (MW) irradiation. The effect of MW power, urea concentration, and MII/MIII ratios was studied. The physicochemical properties of the prepared LDH catalysts were characterized by several analysis techniques. The results confirmed the formation of the layered structure with the intercalation of urea-derived anions. The urea-derived anions enhanced the optical and photocatalytic properties of the nano Cu-Al LDH in the visible-light region. The photocatalytic activity of the prepared Cu-Al LDH catalysts was tested for greenhouse gas conversion (CH4, CO2, and H2O) under visible light. The dynamic gas mixture flow can pass through the reactor at room temperature under atmospheric pressure. The results show a high conversion percentage for both CO2 and CH4. The highest converted amounts were 7.48 and 1.02 mmol mL-1 g-1 for CH4 and CO2, respectively, under the reaction conditions. The main product was formaldehyde with high selectivity (>99%). The results also show the stability of the catalysts over several cycles. The current work represents a green chemistry approach for efficient photocatalyst synthesis, visible light utilization, and GHGs' conversion into a valuable product.

Kinetic studies for microwave-assisted drying of Oraby date slices

This study was conducted to evaluate the effects of microwave (MW) output power on the drying kinetics and quality of ascorbic acid pretreated and untreated Oraby date slices (2, 4 and 6 mm in thickness and 24 ± 2 mm in diameter) at the end of khalal stage. The initial moisture content was 1.7397 d.b. The drying experiments were carried out using three levels of MW output power 160, 320 and 480 W. The obtained experimental data were fitted with three empirical models. The effect of MW power on drying time and drying rate were determined. Effect of drying on sugars, total phenols, tannins contents and color measurements were studied. Because of occurrence of some charring (burning) when MW drying of 4- and 6-mm slices goes beyond moisture content of 0.3678 kg[H2O].kg-1dry matter, thereafter MW drying was stopped, then drying was completed using a conventional oven at 60°C to avoid sample discoloration or burning. MW drying of 2 mm slices was completed without showing such burning. The Midilli et al. model was the best fit for the data of MW drying as well as the following convention oven drying. All sensory attributes for the dried Oraby date slices were acceptable by the panelists, however, the 2 mm slices received the highest panelists’ scores. MW shortened the time needed for drying.

Microwave-Assisted Extraction of Andrographolide, 14-Deoxy-11,12- didehydroandrographolide and Neoandrographolide from Andrographis paniculata: An Optimisation Study

Background: Andrographis paniculata is often used as functional foods owing to its broad range of pharmaceutical activities due to the presence of main terpene compounds such as andrographolide, 14-deoxy-11,12-didehydroandrographolide and neoandrographolide. The aforementioned compounds must be extracted from the plant material before it can be routinely used as a functional food ingredient. Objective: This work presents an optimisation study of microwave-assisted extraction (MAE) of terpene from Andrographis paniculata. In this study, two factors at three-level central composite face centred design was employed to optimise the process variables, including the effect of microwave power (75-175 W) and ethanol concentration (20-85%) on extraction of terpene from Andrographis paniculata. Methods: The experimental design was set based on initial screening on the effect of mesh size and solid solvent ratio. The present work was performed at fixed mesh size and solid solvent ratio, which corresponds to the highest yield established experimentally. Two most significant factors, i.e. microwave power and ethanol concentration was chosen and further studied for optimisation using a response surface methodology. The three-level, two-factor central composite design (CCD) has been employed to determine the effect of microwave power (15, 25 and 35 W/mL) and ethanol concentration (20, 52.5 and 85%) on the yield of terpene extraction. Identification and quantification of the terpene were performed via Ultra-Performance Liquid Chromatography- Photodiode Array (UPLCPDA). Results: The regression analysis showed good fit of the experimental data to the quadratic equation with coefficient of determination (R2) value of 0.997. The optimum condition was found at microwave power of 140 W with 85% ethanol concentration, produced the highest yield of andrographolide (10.926 ± 0.053 mg/g DW), 14-deoxy-11,12-didehydroandrographolide (4.336 ± 0.215 mg/g DW) and neoandrographolide (5.698 ± 0.252 mg/g DW). The model developed through response surface modelling has a desirability of 97.5% and the error between the experiment and the model predictions ranged from 2.4 to 5.2%. Conclusion: A successful optimisation of terpene extraction from A. paniculata via MAE was achieved at microwave power of 140 W and 85% ethanol. The model developed from the regression analysis is sufficiently accurate and can be used to predict the yield of terpene extraction from A. paniculata.

Performance of a microwave radiation induced persulfate-hydrogen peroxide binary-oxidant process in treating dinitrodiazophenol wastewater

A persulfate-hydrogen peroxide (PS-H2O2) binary-oxidant system activated by microwave (MW) radiation was used to treat dinitrodiazophenol (DDNP) industrial wastewater. While evaluating the treatment efficacy of the MW-PS-H2O2 process, the effects of MW power, PS dosage, n(PS)/n(H2O2) ratio, and initial pH on chemical oxygen demand (COD) removal and reaction kinetics (kobs) were investigated. The transformation of organics was also examined. The best treatment efficacy (COD removal = 73.92% and kobs = 0.1996 mg/(L min)) after a reaction time of 16 min was achieved using optimized operation parameters (initial pH = 3.0, PS dosage = 3.70 mmol/L, H2O2 dosage = 2.45 mmol/L, MW power = 450 W). Increasing MW power and PS dosage within certain ranges and an acidic environment improved treatment efficacy, but too high MW power and too low H2O2 dosage (indicated by too high n(PS)/n(H2O2) ratio) significantly inhibited treatment efficacy. The benzene-ring structure, nitro group, and diazo group of organics in the wastewater were greatly degraded. The radicals SO4·- and ⋅OH were major contributors to organics degradation, and the major reactive oxygen species differed under different operation parameters. The MW-PS-H2O2 process improved the biodegradability of the wastewater 10-fold (to 0.606) and required approximately half as much electrical power as comparative processes (MW-PS and MW-H2O2). Therefore, the MW-PS-H2O2 binary-oxidant process is an effective and promising DDNP industrial wastewater pre-treatment method, and shows superior treatment efficacy compared to single-oxidant processes while also consuming less electrical power.

Microwave assisted synthesis of Guar-g-polyacrylamide

Microwave (MW) assisted synthesis of guar-g-polyacrylamide (G-g-PAA), a co-polymer of wide applications is being reported in the present communication. Graft co-polymerization of the guar gum (GG) with acrylamide (AA) under the influence of MW in absence of any radical initiators and catalyst resulted in grafting yields comparable to redox (potassium persulphate/Ascorbic acid) initiated conventional heating graft co-polymerization in very short reaction times. The grafting efficiency up to 20% was further increased when initiators and catalyst were used with MW heating. The effect of MW power and exposure time on the grafting yields, both in presence and in absence of redox initiator and catalyst were studied. Maximum grafting efficiency achieved under MW was 66.66% in 0.22 min in comparison to 49.12% in 90 min by the conventional method. A representative MW grafted copolymer was characterized using IR, 1H NMR, XRD and TGA.

Microwave assisted oxidation of polyethylene under solid-state conditions with potassium permanganate

The surface oxidation of polyethylene (PE) under solid-state conditions with potassium permanganate has been investigated. This oxidation was also performed under solid-state conditions with potassium permanganate by using a domestic microwave (MW) oven at a different time intervals of 0, 20, 30, 50, and 60 s of MW irradiation. In order to see the effect of MW power on the surface oxidation of PE, the oxidation was carried out at different power of MW irradiation. The oxidation was also performed at different molar ratio of repeating unit of PE/KMnO 4 and at constant MW irradiation time and power. According to the data which was obtained from FT-IR spectroscopy, the vinylic and hydroxy groups are observed on the polymer surface. It is noteworthy that no hydroperoxy group have been formed during this oxidation process. Furthermore, PE and oxidized PE have similar TGA and DTG thermograms.