The great concern about the use of hazardous additives in food packaging materials has shown the way to new bio-based materials, such as nanoclays incorporating bioactive essential oils (EO). One of the still unresolved issues is the proper incorporation of these materials into a polymeric matrix. The in situ polymerization seems to be a promising technique, not requiring high temperatures or toxic solvents. Therefore, in this study, the bulk radical polymerization of styrene was investigated in the presence of sodium montmorillonite (NaMMT) and organo-modified montmorillonite (orgMMT) including thyme (TO), oregano (OO), and basil (BO) essential oil. It was found that the hydroxyl groups present in the main ingredients of TO and OO may participate in side retardation reactions leading to lower polymerization rates (measured gravimetrically by the variation of monomer conversion with time) accompanied by higher polymer average molecular weight (measured via GPC). The use of BO did not seem to affect significantly the polymerization kinetics and polymer MWD. These results were verified from independent experiments using model compounds, thymol, carvacrol and estragol instead of the clays. Partially intercalated structures were revealed from XRD scans. The glass transition temperature (from DSC) and the thermal stability (from TGA) of the nanocomposites formed were slightly increased from 95 to 98 °C and from 435 to 445 °C, respectively. Finally, better dispersion was observed when orgMMT was added instead of NaMMT.

Environmental pollution by arsenic (As) and hexavalent chromium (Cr(VI)) has been one of the most serious environmental problems in recent years around the world. Their presence in water is a result of both natural and anthropogenic activities, and poses serious risks to human health due to their high toxicity. Adsorption is a leading method used to remove arsenic and chromium, with biochar, a carbonaceous pyrolytic product made from various types of biomass, under low oxygen conditions, being one of the most common adsorbents due to its high surface area. Although biochar’s ability to immobilize and remove As and Cr(VI) is high, in order to increase the adsorption capacity and nutrient release potential of rice husk biochar, it is essential to select an appropriate pyrolysis and biochar modification technique. Physical or biological activation, steam/gas activation, UV irradiation, magnetization, alkali/acid treatment, and nano-modification are the main modification methods that will be discussed in this review. These modifications have led to multi-fold enhancement in adsorption/reduction capacity of As and Cr(VI), compared with plain biochar. This review provides a recent literature overview of the different biochar modification methods, as well as the factors that influence their capacity to successfully remove As and Cr(VI), along with regeneration potentials.