Multi-functional magnesium hydroxide coating for iron nanoparticles towards prolonged reactivity in Cr(VI) removal from aqueous solutions

In this study, the reactive performance of magnesium hydroxide-coated iron nanoparticles (Fe @Mg(OH)2) was investigated for the removal of hexavalent chromium (Cr(VI)) from aqueous solutions. Short-and long-term progressive-release of Fe @Mg(OH)2 reactivity was evaluated through several batch tests. The Multi-functional effect of the environmentally-friendly Mg(OH)2 coating shell was represented by the progressive shell-dissolution in water and preventing the rapid corrosion of Fe-core, which resulted in a controlled release of Fe reactivity towards Cr(VI). Fe @Mg(OH)2 showed good performance in preserving Fe long-term reactivity within a wide range of pH (3.0-9.0) and temperature (15-55 oC). The long-term investigation of Fe @Mg(OH)2 performance towards Cr(VI) removal confirmed the progressive and maintained reactivity, represented by the continuous release of Fe electrons, to achieve 100% removal efficiency of 40 mg/L initial Cr(VI) concentration over 50 days reaction time, to be reported for the first time in the literature. Fe @Mg(OH)2 showed high regeneration abilities up to 5 cycles with 1.36 times average enhancement in Cr(VI) removal efficiency compared to that of Fe. Moreover, Fe @Mg(OH)2 achieved an increase in the shelf-live longevity performance up to 30 days without any storing solution with 90% final Cr(VI) removal efficiency after 180 min reaction time

Behavior of dental composite materials in sterilized and non-sterilized landfill leachate

Treatment of used and unused dental resin based composites resulting from the activities of dental industries and clinics is challenging. Disposal to landfill site is commonly utilized to manage this waste. We investigated the release of monomers from dental composites in landfill leachate and the chemical changes of sterilized and non-sterilized leachate in the existence of dental composites. Solid phase micro-extraction (SPME) coupled with high performance liquid chromatography (HPLC) was used to extract and quantify the released monomers. Chemical characterization of leachate was carried out using pH meter, gas chromatography (GC), ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS). The HPLC results, revealed that Bis-GMA, TEGDMA, UDMA, HEMA and BPA monomers were released from dental composites. According to the results of pH, GC, IC and ICP-MS, the presence of dental composites has no significant effect in the chemistry of leachate except increasing the production of CH4 and CO_2. However, autoclaving increased pH values and decreased calcium concentration in sterilized samples. Furthermore, Mn^concentration increased and Fe^ concentration decreased in non-sterilized samples due to microbial activities