Biostabilised icosahedral gold nanoparticles: synthesis, cyclic voltammetric studies and catalytic activity towards 4-nitrophenol reduction

A green and cost-effective biosynthetic approach for the preparation of icosahedral gold nanoparticles (AuNPs) using an aqueous leaf extract of Polygonum minus as reducing and stabilising factor is described. The reduction of Au3+ ions to elemental Au rapidly occurred and is completed within 20 minutes at room temperature. The size of the nanoparticles is highly sensitive to the AuCl4 −/leaf extract concentration ratio and pH. Transmission electron microscopy and X-ray diffraction data indicated that the nanoparticles were in a crystalline shape (face-centred cubic), mostly icosahedral and nearly monodispersed with an average size of 23 nm. Cyclic voltammetric studies suggested that flavonoids, such as quercetin and myricetin present in the leaf extract had a tendency to donate electrons to Au3+ ions and the formation of elemental Au was possible due to the transfer of electrons from these flavonoids to Au3+ ions. Infrared absorption of the AuNPs and the leaf extract revealed that the oxidised (quinone) form of quercetin and myricetin were presumably the main stabilising agents in the formation of stable nanoparticles. The present biosynthesis of AuNPs was simple, rapid, cost-effective and environmentally friendly. The newly prepared biostabilised icosahedral AuNPs show good catalytic activity in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP)

Strength and morphological characteristics of organic soil stabilized with magnesium chloride

Organic soil causes major problems in infrastructure development. It has high compressibility and low shear strength, and requires chemical stabilization if it is to be a sustainable geomaterial. This research investigated the strength and microstructural properties of organic soil stabilized with magnesium chloride (MgCl2). Unconfined compressive strength tests were undertaken to assess shear strength properties, and microstructural changes were monitored via field-emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectrometry (EDAX). The results confirm that MgCl2 improves the compressive strength of organic soil. The strength of MgCl2-stabilized organic soil is increased to around 3 - 5 times that of untreated soil during the first 7 days of curing. FESEM results show that the porosity of organic soil is filled by a new cementitious compound, identified as magnesium silicate hydrate (M-S-H)

Development of sustainable masonry units from flood mud soil: Strength and morphology investigations

In the aftermath of the mega flood 2014–2015 event on the East Coast of the Peninsular Malaysia high piles of debris and mud were found deposited on the affected area. The cost of cleaning and removal of the debris and mud was extremely high. Utilisation of the flood mud soil as an aggregate to develop sustainable masonry units could be possible through chemical stabilisation to increase the strength of the soil. Biomass silica (BS) stabiliser was used to enhance the engineering properties of the flood mud. The flood mud soil sample was taken from Kuala Krai, Kelantan, after the flood event, which occurred during December 2014 and January 2015. The Unconfined Compressive Strength (UCS) of unstabilised samples and samples stabilised using 3%, 5% and 10% stabiliser, was measured after three and seven days of curing. The stabiliser could increase the soil strength up to 10-fold (1330 kPa) of the unstabilised strength but was still lower than the strength requirement specified by British Standard Institute. An addition of 2% of cooking salt at 105 °C curing could significantly improve the UCS. Microstructural analyses via Energy-Dispersive X-ray spectrometry (EDX) and Field-Emission Scanning Electron Microscopy (FESEM) tests were undertaken to examine the influence of BS stabiliser, cooking salt and heat curing on UCS development. The additional cooking salt with heat curing caused the aggregation and enhanced the chemical reaction of the BS stabilised soil. The formation of Calcium Silicate Hydrate (CSH) and Calcium Aluminate Hydrate (CAH), as shown by white-coloured lumps, filled the pore spaces of the biomass silica stabilised soils. The aggregation and CSH and CAH products resulted in a dense and strong soil structure and subsequent strength development. This research indicates that the mixture of BS stabiliser and cooking salt can be used to manufacture mud-based masonry units as a sustainable construction and building material