Tautomerism alters the structure and properties of materials, which can be exploited to control their chemical and biological activities. The role of pH-induced tautomerism of polyvinylpyrrolidone (PVP) was determined by measuring the size, stability, and antioxidant and antibacterial properties of microwave synthesized-silver nanoparticles (AgNPs). TEM and XRD analyses confirmed the formation of face-centered cubic silver nanoparticles. PVP stabilized the AgNPs by interaction with the carbonyl or hydroxyl groups depending on the tautomerization under different pH conditions. At pH 4, PVP was stable in the keto tautomer, stabilizing Ag through electron donation of oxygen atoms in the carbonyl group, producing smaller AgNPs with a higher zeta potential. At pH 7 and 9, the enol tautomer PVP stabilized the AgNPs via oxygen atoms in the hydroxyl group, forming large nanoparticles. The keto form of PVP improved the stability and antioxidant and antibacterial properties of AgNPs compared with the enol form. This study also excluded the antioxidant contribution of PVP via hydrogen donation to free radicals. A facile method for controlling the size of AgNPs by adapting the pH-induced tautomerism of PVP that affects their stability and antioxidant and antibacterial activities is thus reported.

To consider silver nanoparticles (AgNPs) as a colorimetric sensor for H₂O₂ we require investigation of the effects of the homogeneity of the nanoparticle size and morphology on the sensor parameters.

Alumina extraction from red mud has been investigated by magnetic separation with three-step treatment. First, the addition of red mud with Na2CO3 (12 wt%) and heated at 110 °C for 4 h. The second step was carbon reduction using coal with mass ratio of (red mud+Na2CO3) : coal was 1:3 then roasted at temperature of 850, 950, and 1050 °C for 1, 2, and 3 h. The third step was magnetic separation. The magnetic separation was carried out in order to remove magnetite produced during roasting process. Magnetic and non-magnetic phases obtained were characterized by XRD and SEM-EDX techniques. The non-magnetic phase obtained was leached using HCl 6 M, and then aluminum content was determined by Inductively Coupled Plasma (ICP). The result revealed that the highest aluminum oxide extracted from the red mud was 20.66 wt% obtained by roasting at temperature of 1050 °C for 2 h.