Destruction of pentachlorobiphenyl in soil by supercritical CO(2) extraction coupled with polymer-stabilized palladium nanoparticles

Supercritical carbon dioxide extraction of plant phytochemicals for biological and environmental applications - A review

Recently, supercritical fluid CO₂ extraction (SFE) has emerged as a promising and pervasive technology over conventional extraction techniques for various applications, especially for bioactive compounds extraction and environmental pollutants removal. In this context, temperature and pressure regulate the solvent density and thereby effects the yield, selectivity, and biological/therapeutic properties of the extracted components. However, the nature of plant matrices primarily determines the extraction mechanism based on either density or vapor pressure. The present review aims to cover the recent research and developments of SFE technique in the extraction of bioactive plant phytochemicals with high antioxidant, antibacterial, antimalarial, and anti-inflammatory activities, influencing parameters, process conditions, the investigations for improving the yield and selectivity. In another portion of this review focuses on the ecotoxicology and toxic metal recovery applications. Nonpolar properties of Sc-CO₂ create strong solvent strength via distinct intermolecular interaction forces with micro-pollutants and toxic metal complexes. This results in efficient removal of these contaminants and makes SFE technology as a superior alternative for conventional solvent-based treatment methods. Moreover, a compelling assessment on the therapeutic, functional, and solvent properties of SFE is rarely focused, and hence this review would add significant value to the SFE based research studies. Furthermore, we mention the limitations and potential of future perspectives related to SFE applications.

Degradation of lindane and hexachlorobenzene in supercritical carbon dioxide using palladium nanoparticles stabilized in microcellular high-density polyethylene

Palladium nanoparticles stabilized in microcellular high-density polyethylene prepared through supercritical foaming, supercritical impregnation, and H2 reduction are used for the hydrodechlorination of lindane and hexachlorobenzene in supercritical carbon dioxide below 100 °C. Both lindane and hexachlorobenzene can be almost 100% transformed to cyclohexane in 1 h. Reaction intermediates, such as lower chlorinated products or benzene, are not observed or exist in trace amount indicating that most of them may undergo reactions without leaving the metal surface.

Decontaminating soil organic pollutants with manufactured nanoparticles

Organic pollutants in soils might threaten the environmental and human health. Manufactured nanoparticles are capable to reduce this risk efficiently due to their relatively large capacity of sorption and degradation of organic pollutants. Stability, mobility, and reactivity of nanoparticles are prerequisites for their efficacy in soil remediation. On the basis of a brief introduction of these issues, this review provides a comprehensive summary of the application and effectiveness of various types of manufactured nanoparticles for removing organic pollutants from soil. The main categories of nanoparticles include iron (oxides), titanium dioxide, carbonaceous, palladium, and amphiphilic polymeric nanoparticles. Their advantages (e.g., unique properties and high sorption capacity) and disadvantages (e.g., high cost and low recovery) for soil remediation are discussed with respect to the characteristics of organic pollutants. The factors that influence the decontamination effects, such as properties, surfactants, solution chemistry, and soil organic matter, are addressed.

Overview of in situ and ex situ remediation technologies for PCB-contaminated soils and sediments and obstacles for full-scale application

Polychlorinated biphenyls (PCB) are persistent organic pollutants used worldwide between the 1930s and 1980s. Although their use has been heavily restricted, PCB can be found in contaminated soils and sediments. The most frequent remediation solutions adopted are "dig and dump" and "dig and incinerate", but there are currently new methods that could be more sustainable alternatives. This paper takes a look into the remediation options available for PCB-contaminated soils and sediments, differentiating between biological, chemical, physical and thermal methods. The use of combined technologies was also reviewed. Most of them are still in an initial development stage and further research in different implementation issues is needed. There is no single technology that is the solution for PCB contamination problem. The successful remediation of a site will depend on proper selection, design and adjustment of the technology or combined technologies to the site characteristics.

Reductive dechlorination for remediation of polychlorinated biphenyls

Technologies such as thermal, oxidative, reductive, and microbial methods for the remediation of polychlorinated biphenyls (PCBs) have previously been reviewed. Based on energy consumption, formation of PCDD/F, and remediation efficiency, reductive methods have emerged as being advantageous for remediation of PCBs. However, many new developments in this field have not been systematically reviewed. Therefore, reductive technologies published in the last decade related to remediation of PCBs will be reviewed here. Three categories, including catalytic hydrodechlorination with H(2), Fe-based reductive dechlorination, and other reductive dechlorination methods (e.g., hydrogen-transfer dechlorination, base-catalyzed dechlorination, and sodium dispersion) are specifically reviewed. In addition, the advantages of each remediation technology are discussed. In this review, 108 articles are referenced.

Fabrication of a form- and size-variable microcellular-polymer-stabilized metal nanocomposite using supercritical foaming and impregnation for catalytic hydrogenation

This article presents the fabrication of size-controllable and shape-flexible microcellular high-density polyethylene-stabilized palladium nanoparticles (Pd/m-HDPE) using supercritical foaming, followed by supercritical impregnation. These nanomaterials are investigated for use as heterogeneous hydrogenation catalysts of biphenyls in supercritical carbon dioxide with no significant surface and inner mass transfer resistance. The morphology of the Pd/m-HDPE is examined using scanning electron microscopy images of the pores inside Pd/m-HDPE catalysts and transmission electron microscopy images of the Pd particles confined in an HDPE structure. This nanocomposite simplifies industrial design and operation. These Pd/m-HDPE catalysts can be recycled easily and reused without complex recovery and cleaning procedures.