Extraction of the Volatile Oils of Dictyopteris membranacea Batters 1902 by Focused Microwave-assisted Hydrodistillation and Supercritical Carbon Dioxide: Empirical Kinetic Modelling Approach, Apparent Solubility and Rate Constants

Supercritical carbon dioxide extraction (SCCO2) and focused microwave-assisted hydrodistillation (FMAHD) were used comparatively to isolate the volatile oils of the brown alga Dictyopteris membranacea from the crude ether extract. The volatiles fractions were analysed by GC/MS, the major compounds were: dictyopterene A, 6-butyl-1,4-cycloheptadiene, 1-undecen-3-one, 1,4-undecadien-3-one, (3-oxoundec-4-enyl) sulphur, tetradecanoic acid, hexadecanoic acid, 3-hexyl-4,5-dithiacycloheptanone, and albicanol. A kinetics study of the extraction of the volatile fractions obtained by the two processes was carried out, an external calibration allowed to quantify the content of the main metabolites. Empirical models were applied to adjust the experimental kinetics values but also to determine the values of apparent solubilities for SCCO2 and the rate constants for FMAHD. The results obtained revealed that the SCCO2 process was characterized by the coexistence of three distinct phases. For FMAHD, the extraction mechanism included two steps. This work is licensed under a Creative Commons Attribution 4.0 International License

Hypericum sp.: essential oil composition and biological activities

Phytochemical composition of Hypericum genus has been investigated for many years. In the recent past, studies on the essential oils (EO) of this genus have been progressing and many of them have reported interesting biological activities. Variations in the EO composition of Hypericum species influenced by seasonal variation, geographic distribution, phenological cycle and type of the organ in which EO are produced and/or accumulated have also been reported. Although many reviews attributed to the characterization as well as biological activities of H. perforatum crude extracts have been published, no review has been published on the EO composition and biological activities of Hypericum species until recently (Crockett in Nat Prod Commun 5(9):1493–1506, 2010; Bertoli et al. in Global Sci Books 5:29–47, 2011). In this article, we summarize and update information regarding the composition and biological activities of Hypericum species EO. Based on experimental work carried out in our laboratory we also mention possible biotechnology approaches envisaging EO improvement of some species of the genus.Fundação para a Ciência e a Tecnologia (FCT) - project PTDC/AGR AAM/70418/2006, SFRH/BD/ 13283/2003

A Review on Recent Development of Cooling Technologies for Photovoltaic Modules

When converting solar energy to electricity, a big proportion of energy is not converted for electricity but for heating PV cells, resulting in increased cell temperature and reduced electrical efficiency. Many cooling technologies have been developed and used for PV modules to lower cell temperature and boost electric energy yield. However, little crucial review work was proposed to comment cooling technologies for PV modules. Therefore, this paper has provided a thorough review of the up-to-date development of existing cooling technologies for PV modules, and given appropriate comments, comparisons and discussions. According to the ways or principles of cooling, existing cooling technologies have been classified as fluid medium cooling (air cooling, water cooling and nanofluids cooling), optimizing structural configuration cooling and phase change materials cooling. Potential influential factors and sub-methods were collected from the review work, and their contributions and impact have been discussed to guide future studies. Although most cooling technologies reviewed in this paper are matured, there are still problems need to be solved, such as the choice of cooling fluid and its usability for specific regions, the fouling accumulation and cleaning of enhanced heat exchangers with complex structures, the balance between cooling cost and net efficiency of PV modules, the cooling of circulating water in tropical areas and the freezing of circulating water in cold areas. To be advocated, due to efficient heat transfer and spectral filter characters, nanofluids can promote the effective matching of solar energy at both spectral and spatial scales to achieve orderly energy utilization